Tuesday, December 10, 2013

How Staphylococcus Aureus Evades and Undermines the Immune Response

Staphylococcus aureus is a bacterial pathogen that is largely responsible for human infections that impact the skin and soft tissue.   These kinds of infections can be serious enough to lead to life threatening conditions such as sepsis (blood poisoning as a result of microorganisms or the toxins they produce), endocarditis (inflammation of the interior lining of the chambers of the heart) and bacteremia (bacteria in the blood).  A distinctive characteristic of a staphylococcal infection is the formation of abscesses that are comprised of bacterial colonies surrounded by fibrin – a structural protein.  The severity of infections with this organism has been attributed to its ability to evade and undermine the immune response.   It is, therefore, essential to understand the nature of its mechanism of action in regard to defending itself from the immune system.

Human immunity can be delineated into two distinct responses.  The first if referred to as the “innate” response and the second as the “adaptive” response.  The former is designed to respond immediately to an invasion by deleterious organisms such as bacteria.   The adaptive response is typically secondary and engages the T and B lymphocyte populations that are in constant circulation within the blood and lymph systems.  This response affords more enduring and long term immunity to the insulting microorganism(s).
As part of the innate response to Staphylococcus aureus infection, neutrophils – white blood cells that move to the site of infection – release their DNA in the a form that is referred to as neutrophil extracellular traps (NETs).   The intrinsic purpose of these NETs is to immobilize the pathogen and enhance the activity of peptides – small proteins – that possess anti-bacterial activity.  However, Staphylococcus aureus effectively undermines this immune response.

The mechanism of action that the pathogen employs to counteract the role of neutrophils has been characterized through the efforts of Dr. Vilasack Thammavongsa and his colleagues at the Department of Microbiology of the University of Chicago.   As a result of their research efforts, they discovered that staphylococcus aureus sidesteps the innate immune response by effectively converting NETs to deoxyadenosine.   This modification is a product of two enzymes – nuclease and adenosine synthase – secreted by the pathogen.  This action triggers the destruction of immune cells and also prevents macrophages – white cells whose role is to ingest invading organisms - from entering the staphylococcal abscesses.


This finding is of great value; for, it helps elucidates the mechanism through which staphylococcus successfully evades the human immune system.

Tuesday, November 19, 2013

A Comparison of the Deleterious Impact of Human Exposure to Methylmercury and PCBs

In a scientific paper entitled, Neurobehavioral toxicity of methylmercury and PCBs Effects-profiles and sensitive populations authored by Dr. Christopher Newland from the Department of Psychology, Auburn University that appeared in the Journal of Environmental Toxicology and Pharmacology, the investigator compares the toxicology of methylmercury and polychlorinated biphenyls (PCBs) in human populations.
Both methylmercury and PCBs are known to be potent neurotoxic agents that have deleterious consequences in terms of the sensory, motor and cognitive abilities of those who have suffered sufficient exposure.

PCBs represent a class of compounds in which over 200 separate substances are members.  There appears to be a wide range of varying toxic effects among these substances depending upon their precise molecular structure.  However, they all bind to the aryl hydrocarbon receptor (ahr) found on the surface of mammalian cells.  Disruption of the usual binding to the Ah receptor can play havoc with the healthy functioning of the nervous system and can account for the wide-ranging toxic effects of PCBs.

Methylmercury is the toxic form of mercury that human populations are usually exposed to.  When ingested it is rapidly absorbed by the gut into the bloodstream and can penetrate the blood-brain barrier by two routes.  It can passively pass through this barrier due to its lipid solubility.  Secondarily, it can actively combine with the amino acid cystein that is one of the 20 amino acids that are the building blocks for the synthesis of proteins.  Once bound it readily penetrates the blood-brain barrier carried by a methionine transporter. The blood-brain barrier is the physiological barrier that usually protects the brain from any foreign and potentially harmful substances that may be circulating in the bloodstream.  Once within the brain the methyl group is enzymatically removed leaving the highly toxic mercury that can persist for a prolonged period of time.
  
According to the author, “methylmercury exposure affects the visual, auditory, and somatosensory systems.”
In addition, “Methylmercury exposure during adulthood produces a progressive and irreversible constriction of the visual field a pattern of toxicity not associated with developmental exposures. Methylmercury exposure during gestation or lactation affects higher-order visual function.”  Motor damage including nystagmus – rapid involuntary movement of the eyes -  that suggests damage to the cerebellum and cerebral palsy that suggests damage to the cerebral cortex have been shown in victims of the Minamata exposure in Japan as previously described.

Since PCBs and methylmercury contaminants are both found in fish and since seafood is the usual route of exposure of these dangerous chemicals for humans, it would be efficacious, from a public health standpoint, to examine the synergistic effects of these compounds on human health.   

Wednesday, November 13, 2013

The Legacy of Mercury Poisoning in Japan

It has been almost sixty years since medical investigators first pinpointed the nature of an apparently new illness that struck the residents of Minamata, Japan.  This disease came to be referred to as Minamata Disease.   It all seemed to have begun during the spring and summer of 1956 with the appearance of what was referred to at the time as a strange disease that impacted fishing families living in villages in and around Minamata Bay. 

The symptoms that the victims of this ailment presented were numb hands and feet, sudden difficulty in walking and a definitive impairment in speech.  Extreme cases resulted in convulsions and death.  Of the 54 cases that presented with this disease in 1956, 31% died.   This was a disturbing statistic.  This galaxy of symptoms suggested a neurological basis for the disease.

By the year’s end researches at Kumamoto University had identified the etiology of the illness as being heavy metal poisoning from the ingestion of contaminated local fish and shellfish.   This diagnosis was consistent with the evidence; heavy metals are known to play havoc with the nervous system as exemplified by lead poisoning.  It remained to discover the origin of the contamination and the offending metal.
  
Investigators focused on the Shin Nippon Chisso Hiryo chemical plant facility that had been known to discharge its untreated waste directed into the local waterways.   The plant owners managed to delay a thorough investigation for a number of years.  Ultimately the chemical culprit was discovered – methyl mercury, a highly toxic substance.

It was not until May of 1968 that the plant halted production of acetaldehyde that employed a mercury catalyst in its chemical synthesis.  This overdue decision finally halted its use of mercury.  Furthermore, even though it was shown that there existed a persistent contamination of  methylmercury  on the seafloor,  Minamata Bay was not closed for fishing until 1975.


To this day, the research continues regarding the long term effects of the ingestion of low levels of methyl mercury from contaminated seafood.  The controversy has not subsided regarding who has been victimized and who is liable for the costly toll on individual lives.

Friday, November 1, 2013

Viral-and Bacterial Co-infection

An unfortunate side effect of infection with the flu virus is a secondary bacterial pneumonia often called a co-infection.  This complication can prove to be very deleterious especially among at-risk populations such as the elderly.  The actual cause of this apparent increased susceptibility has not been well defined.
There are two disparate routes through which the immune system can exert its effect.  The more readily understood strategy is referred to as resistance in which the immune system is mobilized to detect the offending pathogen and eliminate it.  There is, however, another route that the immune system can take and that is tolerance in which the immune system adapts to a certain level of tissue damage inflicted by the offending organism.  Interestingly enough, the deleterious impact of infectious disease can be the result of either failed resistance or failed tolerance.

Usually, a deadly outcome of a microbial infection is relegated to either high virulence or decidedly poor resistance on the part of the host immune system.  However, there is another possible explanation.   The damage produced by an invading pathogen can be directly related to the toxins it produces, or to the inflammatory response precipitated by the immune system that can lead to tissue damage.  This latter effect is referred to as “extrinsic virulence.”  Insufficient tissue protection and subsequent repair of damaged tissue can also contribute to the lethality of the infectious process.
   
Dr. Amanda Jamieson and her colleagues at the Howard Hughes Medical Institute and Department of Immunobiology at the Yale University School of Medicine chose to study the co-infection of the influenza virus with Legionella pneumophila using a mouse model as a way of determining whether it is resistance or tolerance on the part of the host immune system that determines lethality.

Through their detailed studies, they found that susceptibility to co-infection occurred even when the bacterial infection was controlled by the immune system.  From this, they were able to conclude that the failure of host defenses was directly related to a diminished capacity to tolerate tissue damage.
 

This is a very interesting finding that may have practical implications regarding the clinical approach to patients whose health is seriously impacted by co-infection.

Tuesday, October 8, 2013

Behavioral Disturbances as a Result of Inner Ear Defects

Inner ear defects in children can lead to a severe hearing loss.  A subset (20 – 95%) of these children also experience vestibular dysfunction pertaining to balance.  This latter condition is related to the fact that within the inner ear resides an anatomical structure referred to as the cochlea.  The cochlea serves both auditory and balance functions.

Interestingly enough, among these cases, there also exists a high incidence of behavioral issues including hyperactivity.  It has been proposed that socio-environmental factors could be risk factors that would help explain this relationship.  Another possibility is that the associated inner ear defect might directly modify brain structure and thereby result in behavioral dysfunction.

To test this hypothesis, Dr. Michelle W. Antoine and her colleagues - from the Department of Neuroscience at the Albert Einstein College of Medicine, Bronx, New York - using the mouse animal model and applying the tools available in Molecular Biology have uncovered a link between inner ear defects and discreet molecular changes within the brain.

In the genetic mouse model that was studied, the same correlation exists between inner ear defect and increased levels of hyperactivity as was found in humans.  It seems that a gene referred to as Slc12a2 is responsible for a protein product that functions as a sodium-potassium-chloride co-transporter that is expressed in many tissues including the inner ear and the central nervous system (CNS).  It is precisely this gene that is mutated in the mouse model studied.  This mutated gene is rendered non-functional.  It is therefore quite plausible that the loss of this gene could result in both inner ear defect and the behavioral disorder characterized by hyperactivity.

In attempt to further elucidate the mechanism by which motor activity is heightened in the effected mice, the investigators found that within the nucleus accumbens – an area of the mammalian brain that plays a role in fear, aggression of impulsivity – the levels of key mediators of neuronal activity were increased.  These mediators include pCREB and pERK.  In addition, hyperactivity was alleviated upon the administration of the pERK inhibitor, SL327.


These findings are of great importance; for they demonstrate that, “sensory impairment, such as inner ear dysfunction, can induce specific molecular changes in the brain that cause maladaptive behaviors, such as hyperactivity, that have been traditionally considered exclusively of cerebral origin.”

Friday, September 27, 2013

Mimicking Morphogenesis in the Lab

Morphogenesis is the name given to the intricate process through which complex organs and tissues are created during the development of the fetus in-utero.  With the stunning and rapid advances made in the areas of biochemistry, molecular biology and genetics especially in regard to stem cells – stem cells are the pluripotent cells that have the inherent capacity to differentiate into a wide variety of specialized tissue cells -, a significant amount of information has been accumulated regarding the molecular mechanisms behind this process. 
   
In fact, there have been many recent examples of stem cells that have been induced to initiate morphogenesis in a laboratory setting (in vitro).  These studies have been outlined in a review article by Drs. Toshiro Sato and Hans Clevers from the Department of Gastroenterology at the Keio University School of Medicine in Tokyo, Japan that appeared in the journal Science, Vol. 340. June, 2013.  The example the reviewers cite came directly from their own efforts.  In their studies, they have successfully initiated morphogenesis in the laboratory in three-dimensional human cell cultures that resulted in the elaboration of what they refer to as, “Mini-Guts.”

One of the reasons they chose the small intestine as their in vitro model is because this organ has a higher self-renewal rate than any other mammalian tissue.  In fact, all the cells within the small intestine are renewed within five days.  The reason for this remarkable rate is due to the activity of a particular stem cell.  This stem cell type possesses a unique protein receptor on its surface, Lgr5, that binds preferentially with R-spondins a type of protein essential to the process of morphogenesis.  These Lgr5+ cells differentiate into a host of cell types that constitute a healthy and functional small intestine.  In addition, these Lgr5+ cells persist throughout the entire life of the organism.

To accomplish the successful in vitro production of mini-guts- epithelial organoids - that retain the identity and properties of the original tissue, the investigators used  Matrigel that is, in fact, a laminin and collagen-rich matrix that simulates the structural components of the basal lamina of the small intestine.  Additional factors and components that represent the minimal requirements for stem cell growth were also added to this matrix.


This impressive accomplishment has profound implications for the study of disease processes.  For example, it is now feasible to use this same methodology to produce mini-guts from cells derived from patients with adenomas and colorectal cancers.  These organoids could then be studied alongside of organoids derived from normal tissue.   Such studies could prove invaluable in understanding and delineating the etiology of these illnesses. 

Tuesday, September 17, 2013

The Fate of Incorrectly Folded Proteins

Cellular proteins play many diverse and essential roles in the living cell.  The roles of these proteins range from providing structural integrity and function in muscle, as an example, to assisting in the many chemical reactions that are essential to ordinary metabolism.  They also play a fundamental role in maintaining homeostasis throughout the entire organism.  Each cell contains a rich population of diverse proteins numbering literally in the thousands.  Given this reality, it is essential that these proteins function normally.

Ribosomes are the organelles – the term literally means little organs -that function as the site for protein manufacture within the cell.  The blueprint for the structure of each unique protein is specified by the cell’s DNA.  Once the newly formed protein is complete, it is released from the ribosome and enters the cellular cytoplasm.  Upon release from the ribosomal surface, the nascent protein must fold into a precise configuration in order to attain full functionality.  This folding process is spontaneous.  However, the many diverse macromolecules that fill the cytoplasmic intracellular environment can impose a serious impediment to this folding process.
 
To meet this challenge, a sophisticated “chaperone” system is designed to reduce unfavorable interactions with the cytoplasmic environment in order to enhance the likelihood of successful folding.  It does this through a repetitious series of binding and release.  If these repeated attempts fail, evidence from scientific investigations has shown that the folding process is ultimately terminated for it may pose a threat to cellular energy resources and increase the abundance of toxic reactive oxygen species.

The nature of this termination mechanism – using growing yeast cells as the model organism – has been studied in detail by Dr. Chenchao Xu and his colleagues from the Temasek Life Sciences Laboratory at the National University of Singapore.  From their studies, they have shown that the folding process is terminated by a specialized pathway that utilizes the modification of the unfolded protein by an enzyme-mediated chemical reaction known as  o-mannosylation involving  the transfer of mannose – a sugar – to the serine – an amino acid – residue of the protein.   This modification was shown to disable folding entirely.
 
Finally, the authors of this study propose that the function of this mechanism designed to thwart repeated folding attempts is to end apparently futile chaperone-directed folding.  As mentioned previously, repeated and unsuccessful cycles of folding can seriously impinge upon cellular energy reserves.  The fate of unfolded proteins is their ultimate degradation.


This kind of study helps to elucidate complex cellular mechanisms and highlights the importance of maintaining homeostasis within the cellular environment.

Thursday, August 29, 2013

A Loss of Function of a Key Protein Associated with Severe Early-Onset Mammalian Obesity

There has been a growing body of evidence to suggest an association between early-onset and severe human obesity with a protein and therefore genetic dysfunction. The actual molecular mechanism responsible for this malady has remained somewhat elusive. However, Dr. Masato Asai and his colleagues from the Division of Endocrinology, Department of Medicine at Boston Children’s Hospital at Harvard Medical School, Boston MA have helped to further clarify the biological origin for this serious condition.

One of the pivotal roles of the cell membrane in living cells is providing the medium through which individual cells communicate with their external environment. For complex organisms such as mammals this is especially critical in order for cells to successfully respond to all the chemical signals that are generated in order to maintain and sustain a state of homeostasis – the regulation of an organism’s internal environment to maintain constancy and stability – so vital for survival.

To fulfill this purpose there is a particular class of membrane-bound proteins referred to as G protein-coupled receptors (GPCRs) that modulate cellular responses to a whole host of stimuli. A sub-category of this class of proteins is represented by the melanocortin receptors (MCRs).  Within this group there exists a subset of receptors tied to specific functions as the following table demonstrates –

Receptor Type      Associated Function
MC1R                     Skin Pigmentation
MC2R                     Hypothalamic-Adrenal-Pituitary Axis – responsive to stress in the external environment MC3R, MC4R         Energy Homeostasis
MC5R                      Exocrine Function

Previous studies have implicated MCR4 in connection with mammalian obesity. Furthermore, it has been shown that there are so-called accessory proteins that play an important role in the function of the MCRs that have been described above. One of these accessory proteins, MRAP2, is associated with MCR4. Given these data, MRAP2, produced in the mammalian brain, would make an excellent candidate for further study. Dr. Asai together with his colleagues genetically modified mice to produce an organism with a dysfunctional MRAP2 protein. These animals developed severe obesity at a young age.

Finally, a study of humans with severe early-onset obesity revealed four rare and possibly pathogenic genetically-derived modifications in MRAP2 further suggesting that this protein may be the causative link to this disease. These represent very important findings in regards to this kind of severe obesity in humans. This may prove to have therapeutic value in the future.

Monday, August 19, 2013

The Surprising effect of Gastric Bypass Surgery on Diabetes

Roux-en-Y gastric bypass (RYGB) is a radical surgical intervention that is used for those individuals who suffer from intractable and severe obesity and want desperately to reduce their weight.  Surprisingly, it has been shown that this is also the best approach for the treatment of obesity-related diabetes (Type 2).  It is so effective in this regard that those patients who have successfully undergone this procedure are often able to dispense with their anti-diabetic medication entirely.  It is currently not fully understood how this particular surgical procedure produces this encouraging result.

In RYGB the following surgical modifications are performed –
  • The stomach is divided producing a small gastric pouch (GP) that can only accommodate a small amount of food.
  • A portion of the small intestine is transected – made into two branches – and one arm of the transection is connected to the GP and is referred to as the Roux limb (RL)
  • Both of these branches meet at the so-called “common limb” (CL) and all contents of the GP then proceed through the rest of the digestive tract.

 As a result of these modifications, food entering the esophagus travels to the GP and then to the RL bypassing the remaining part of the stomach – the so-called “distal stomach” (DS) -, the duodenum and part of the jejunum – these areas represent the upper portion of the small intestine.  The RL is thereby exposed to undigested nutrients.  This change may be implicated in the positive effect that this procedure exerts on diabetes. 

In order to further elucidate the mechanism for this change, Dr. Nima Saeidi at the Center for Basic and Translational Obesity Research, Division of Endocrinology at Boston’s Children’s Hospital studied RYGB using the rat as the animal model.   The results of their studies proved very interesting.  They found that within the cells of the tissues of the RL there is a definitive reprogramming of the intestinal metabolism of glucose.  It is important to remember that a key feature of diabetes is the failure of certain body cells to take up glucose from the circulation  and that the serious symptoms  associated with long-term diabetic patients  are directly related to the chronically high levels of glucose in the blood.  This shift in glucose metabolism associated with RYGB was found to include the increased cellular production of an important enzyme involved in glucose metabolism – glucose transporter-1, an increase in glucose uptake, an enhancement of aerobic glycolysis – the metabolic pathway involved in breaking down glucose and a shift in metabolism towards supporting tissue growth.  Furthermore Dr. Saeidi and his team were able to show that this shift in metabolism is directly related to the fact that the RL is exposed to undigested nutrients.


This is an important finding in support of the efficacy of RYGB in dealing with not only obesity but also obesity-related diabetes.  Furthermore, through a further elucidation of the mechanism by which this anti-diabetic effect operates, a clearer picture is generated in regards to an overall understanding of glucose metabolism.

Thursday, August 8, 2013

The Biology of Longevity

Most everyone aspires to living a long and healthy life.  There are certain populations of human and individuals who have had the good fortune to enjoy the benefits of longevity.  This reality has raised the inevitable question – how is this possible?  Recently, scientists engaged in basic research in an attempt to answer this question have come to have a greater understanding of the molecular mechanisms that may help account for longevity in animals and especially in humans.

Surprisingly, the animal model that has been used for this work is the tiny invertebrate worm – Caenorhabditis elegans (C. elegans); this organism grows to an adult size of ~ 1 mm and has a natural lifespan of about 20 days.  C. elegans has a rather complex lifecycle in which it goes through three separate larval stages before it reaches adulthood.  The obvious question that comes to mind is – how can using a simple invertebrate such as C. elegans as an animal can ever hope to shed light on human longevity?   Interestingly, the significant metabolic pathways that are implicated in longevity – as we shall describe shortly – are highly conserved in nature and have direct application to the human system.  The advantage of using an animal model with such a short generation span makes it ideal for studying longevity in a controlled laboratory setting.  In addition, there is mutated form of C. elegans that has a lifespan of up to 10 times the normal, or ~ 200 days.  Use of this variant has helped immeasurably in uncovering the molecular mechanisms for this state.

Dr. R. Shmookler Reiss and his associates at Departments of Geriatrics and Biochemistry and Molecular
Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas have devoted a great deal of time and effort in the pursuit of discovering biomarkers that account for this remarkably increased longevity in C. elegans.   In the painstaking process they have used such techniques as introducing so-called interfering RNA (iRNA) to knockout certain areas of the organism’s genome, adding transgenes and gene mapping.  In casting a wide net they have incorporated proteomics – the analysis of cellular protein products, transcriptomics – the analysis of all RNAs within the cell and metabolomics – an analysis of cellular metabolic pathways- in their studies.

As a result of this exhaustive analysis, they have discovered that the organisms within this high longevity mutant population lack the enzyme PI3 kinase catalytic subunit (PI3Kcs) This enzyme catalyzes the phosphorylation of Phosphatidylinositol 4, 5-bisphosphate (PIP2) to Phosphatidylinositol 3, 4, 5-triphosphate (PIP3) PIP3 resides within the cell membrane and plays a critical role in cell division.  This lack of such a key enzyme is a result of the introduction of a so-called “stop gene” within the gene responsible for the production of PIP3.  As a result of this mutation, the organism produces immature oocytes and is effectively sterile.

The question that immediately arises from this data – how can the loss of such a critical enzyme result in enhanced longevity?  The answer seems to lie in the fact that PI3K is a key component in the Insulin – IGF-1 signaling pathway that is involved in many functions that are necessary for metabolism, growth, and fertility in animal models like C. elegans and also within humans.  The disruption of the insulin -IGF-1 signaling pathway in the C. elegans longevity mutant apparently increases lifespan significantly.  One apparent explanation for this seeming paradox is that the price the organism pays for reproductive success is a diminishment of lifespan.  While this relationship between longevity and the insulin -IGF-1 signaling pathway is evidenced in C. elegans, mammals with an analogous defect are, in fact, at risk for age-related diseases and increased mortality.  This difference in effect probably relates to the more complex metabolic machinery resident in a mammal versus a small invertebrate such as C. elegans.

However, within humans and other animal models, increased longevity has been associated with the nutritional state of the organism – over nutrition apparently shifts cellular metabolism in such a way as to lead to the over production of free radicals and other metabolic byproducts that are toxic to cells and a nutritional state that meets but does not exceed the individual’s nutritional requirements enhances longevity.


Although these studies focus on very specific aspects of the longevity of organisms, they do make important inroads into the overall understanding of the biological mechanisms involved in prolonging lifespan.

Friday, July 26, 2013

Neurogenesis in the Human Brain

It was once believed that the growth of new neurons – those specialized cells in the human central and peripheral nervous systems that allow for the transmission of nerve impulses – did not occur in the adult brain.  This has been shown to be substantially incorrect.  How the growth of new neurons – through a process referred to as neurogenesis – in the adult human brain was discovered is quite interesting.

Indirect evidence for neurogenesis was derived some fifteen years ago though an ingenious approach.  This study focused on the hippocampal region of the brain that is known to be involved in the storage and processing of memories.  This area of the brain would obviously be an excellent candidate for studying neurogenesis.  The result of this investigation was that neurogenesis was detected in five individuals up to 75 years of age.  To accomplish this, the investigators injected the human subjects with a label that binds permanently with the host’s DNA.  The compound used was bromoedeoxyuridine (BrdU).  Once BrdU is incorporated in the DNA, it can be detected using antibodies that specifically react with the modified DNA.  This specific binding can then be visualized by the experimenter with the proviso that the patients so injected were willing to donate their brains following death.  This type of study was eventually curtailed due to problems associated with its safety.

Recent studies conducted by Dr. Kirtsy L. Spalding and colleagues from the Department of Cell and Molecular Biology Karolinska Institutet in Stockholm, Sweden were based on more direct evidence derived from an unusual source.  It seems that during the era of extensive above-ground testing of nuclear warheads between 1945 and 1963, a considerable amount of the radioactive isotope of Carbon (C14 ) was released into the atmosphere.  The amount of C14 in the air has steadily declined since the Limited Test Ban Treaty of 1963 effectively banned above-ground testing.
 
Since dividing cells require carbon and since the source of that carbon is from the atmosphere, C14 becomes incorporated into the cellular DNA.  Furthermore, the amount of incorporated C14 directly corresponds to the amount of C14 in the atmosphere at the time of cell division.  Therefore ,to calculate the age of the cell, the investigator simply has to measure the amount of this isotope that was incorporated into its DNA.
From the analysis of the data, Spalding and his investigative group were able to show that human adult-brain neurogenesis is, in fact, confined to the hippocampus and some subpopulations actively divide while others do not.  From this data, it has been estimated that one-third of adult hippocampal neurons are actively dividing.  This activity within the hippocampus makes sense given the role of this region of the brain in creating and managing memories throughout the lifetime of the individual.


This is an important and elegant study for it answers the question whether or not the adult human brain undergoes neurogenesis unambiguously and is also able to provide a quantitative as well as a qualitative answer.

Friday, July 19, 2013

How the Malaria Parasite Hides Itself from the Mosquito’s Defenses

Malaria remains a potent killer to the human inhabitants of the tropical regions in the so-called “undeveloped world.”  This disease results in approximately one million deaths a year in Africa, alone.  An insect vector, the female Anopheles mosquito that requires blood to mature its eggs, is responsible for its transmission to humans.  There are a host of human maladies caused by such diverse organisms as viruses, protozoans and even worms that infect humans and that are carried by mosquitoes and other insects.

The causative agent for human malaria is a parasite referred to as Plasmodium falciparum.  The life cycle of P. falciparum is quite complex and intriguing.  When it is first inadvertently ingested by the mosquito from an infected host, the parasite undergoes a progression of transformations.  The specialized sexual precursor cells – male and female - are rapidly activated to form complete and functional sex cells – gametes.  Male and female gamete pairs subsequently fuse to from the incipient new organism called the zygote.  Within 18 – 24 hours, this zygote develops into a motile organism called the ookinete that is infectious to the mosquito.  This ookinete rapidly enters the insect’s midgut and forms an oocyst.  Within the oocyst more than 10,000 sporozoites are created within ten days.  Once this oocyst ruptures, these sporozoites navigate to the mosquito’s salivary glands where they are transferred to the next human host upon the mosquito’s bite.

Given this information, the questions that comes to mind are the following –
  • What are the mosquito’s natural defenses against this parasite?
  • How does the P. falciparum successfully elude these defenses?

The investigations of Dr. Alvaro Molina-Cruz and colleagues at the Laboratory of Malaria and Vector Research at the National Institute of Allergy and Infectious Diseases at the National Institute of Health in Rockville Maryland helped elucidate the mechanism by which the parasite escapes the immune defenses of its host.

It has been well established that insects have a first line of immune defense, as do vertebrates, referred to as the innate immune system (IIR).  IIR utilizes both humoral (chemical) and cellular defense mechanisms; it is quite sophisticated.  In spite of this ability to fend off foreign invaders, P. falciparum manages to survive and propagate in this hostile environment.

Molina-Cruz and the team of collaborators were able to identify a gene product from the parasite that enables the invading organism to infect its host mosquito without activating the innate immune system described earlier.  The gene responsible for producing this product was identified as Pfs47.  In fact when this gene was disrupted from its normal functionality, the parasite’s survival within the host was greatly reduced.

This finding is significant, for it establishes the fact that the Pfs47 gene contained within P. falciparum is essential for the efficient transmission of the parasite responsible for malaria from the vector to its human host.

Thursday, July 4, 2013

The CCR5 Receptor and HIV/AIDS

The recently reported news that an AIDS patient has been successfully cured of his disease is a very exciting development in regards to global public health.  The methodology used to affect this outcome is directly related to the manner in which the human immunodeficiency virus (HIV) gains entry into its host cell.  HIV enters and ultimately kills the so-called,” T-Helper” cell that plays a critical role in adaptive human immunity.  Once a significant portion of these cells are destroyed, the patient displays the classic symptoms of AIDS – the inability to successfully fight off infections by invading micro-organisms.


In order to successfully invade its target cell, HIV must bind to specific proteins found on the surface of T-Helper cells.  One of these cell surface proteins is referred to CCR5 (CD195) – a member of the chemokine receptor family – and the protein product of the CCR-5 gene.  Chemokines are factors that are used to attract T cells to particular tissue or organ targets when battling infection.  If this protein is absent or the product of a mutated gene, HIV will fail to bind and therefore be unable to infect the target cell.  It is important to remember that viruses have an absolute requirement for access into a living cell in order to produce an infection; for, they need to exploit the intracellular processes of a living cell in order to make copies of themselves.  The molecular biology of HIV has been studied extensively and, as a consequence, this mechanism of action is well understood.

In addition, there is a percentage of the human population that is innately resistant to HIV infection even upon exposure to the virus.  This apparent insensitivity to HIV infection is readily explained by the fact that these individuals possess defective variants of the CCR-5 gene.
Thanks to the ingenuity and inventiveness of Drs. Gero Hutter, Eckard Thiel and colleagues from the Charite Hospital in Berlin Germany, an approach to a potential cure of AIDS was recognized that involves the widely used procedure of bone marrow transplantation – the first successful human bone marrow transplantation was accomplished in 1975 in Seattle pioneered by Dr. Donnall Thomas who won a Nobel Prize in Medicine for his efforts.
 
In this particular case, the patient presented with acute myelogenous leukemia (AML) as well as AIDS.  The protocol that was developed involved the destruction of the AIDS patient’s immune system followed by recovery using bone marrow from a suitable donor who was also immune to HIV infection on account of a defect in the CCR-5 gene as described above.  As a result of this approach, the patient became asymptomatic and free of HIV.  This is possible because all the immuno-competent cells in the human immune system repertoire are derived from progenitors found in the bone marrow and once the patient’s own immune cells were successfully replaced by the donor’s, then he became HIV resistant.

Since bone marrow transplantation has inherent risks, it is not the recommended approach for AIDS patients; unless, they also suffer from leukemia.  However, there is considerable hope in developing methodologies to use gene modification techniques to modify an AIDS patient’s own immune cells so that they would exhibit the CCR-5 gene variant and render them HIV resistant.

Thursday, June 27, 2013

Autism and Genetic Mutations

Autism spectrum disorders (ASD) is a general term that encompasses a group of disorders that have as their point of origin anomalies in the development of the human brain.  The neurological symptoms that have been associated with ASD include: impairment of normal social development, difficulties with verbal and nonverbal communication and marked repetitive behaviors.  In terms of the latter symptom, anomalies in the brain circuits that are also implicated in obsessive compulsive disorder (OCD) have been identified.  The syndromes that fall within the general definition of ASD include autistic disorder, Rett syndrome, childhood disintegrative disorder, pervasive developmental disorder-not otherwise specified (PDD-NOS) and Asperger syndrome. Paradoxically, certain individuals sometimes display uncanny abilities in visual skills, music, math and art.

In general, the disease is discovered in young children, usually between 2 and 3 years old.  ASD has been diagnosed in over 2 million individuals in the U.S. and many millions throughout the world.  Evidence obtained through the statistics compiled by the Center for Disease Control (CDC) indicates that the incidents of ASD are increasing.  The reasons for this are unclear.

What has been ascertained is that there is strong genetic component in this disease.  What makes ASD particularly refractory to the development of a definitive cure is that the molecular biology is quite complex and involves a multiplicity of genes.  In this report, the findings of Dr. Brian J O’Roak and his colleagues, from the Department of Genome Studies at the University of Washington in Seattle and other collaborating institutions, will be examined.

Autism spectrum disorders (ASD) is a general term that encompasses a group of disorders that have as their point of origin anomalies in the development of the human brain.  The neurological symptoms that have been associated with ASD include: impairment of normal social development, difficulties with verbal and nonverbal communication and marked repetitive behaviors.  In terms of the latter symptom, anomalies in the brain circuits that are also implicated in obsessive compulsive disorder (OCD) have been identified.  The syndromes that fall within the general definition of ASD include autistic disorder, Rett syndrome, childhood disintegrative disorder, pervasive developmental disorder-not otherwise specified (PDD-NOS) and Asperger syndrome. Paradoxically, certain individuals sometimes display uncanny abilities in visual skills, music, math and art.

In general, the disease is discovered in young children, usually between 2 and 3 years old.  ASD has been diagnosed in over 2 million individuals in the U.S. and many millions throughout the world.  Evidence obtained through the statistics compiled by the Center for Disease Control (CDC) indicates that the incidents of ASD are increasing.  The reasons for this are unclear.

What has been ascertained is that there is strong genetic component in this disease.  What makes ASD particularly refractory to the development of a definitive cure is that the molecular biology is quite complex and involves a multiplicity of genes.  In this report, the findings of Dr. Brian J O’Roak and his colleagues, from the Department of Genome Studies at the University of Washington in Seattle and other collaborating institutions, will be examined.

In this exhaustive study, samples from 2446 ASD patients were used.  Of the 192 candidate genes, 44 genes were selected.  This selection was based on the determination to look at disruptive mutations, known associations with ADS-related symptoms, overlap with genes known to be involved in neurodevelopment and gene copy number variation (CNV).

A summary of the results of this work follows –
  • Discovery of 27 de-novo genetic mutation events in 16 genes
  • 59% of these mutations predicted to either shorten the protein gene products or disrupt the splicing that is required to yield functional protein products
  • Recurrent disruptive mutations in six genes – CHD8, DYRK1A, GRIN2B, TBR1, PTEN AND TBL1XR1.  Five of these genes are contained within the catenin-chromatin-remodeling network.

This data confirms associations with specific genes and particular phenotypic expressions of ASD – CHD8 has been linked to macrocephaly and DYRK1A with microcephaly.  In addition, these results confirm the possible role of the catenin-chromatin-remodeling network - a critical network of genes and gene products involved in embryonic development.  However, these data do not establish an unambiguous causal relationship between these genetic anomalies and ASD.  This work represents an important contribution in the search for such direct causal link that may eventually lead to therapeutic relief for individuals with ASD.

Monday, June 17, 2013

Alternative Genetic Splicing – What is its Significance?

There exists a seeming paradox among the many species that constitute vertebrates – animals with backbones.  The fact is that although so many of these species share similar families of protein-coding genes, they are very distinct in terms of their physical characteristics – their phenotypes.  There is no clear explanation of how this phenomenon can be defined on the molecular level.

What has been well established is the fact that over the evolutionary time scale for these various species – approximately 350 million years – significant changes have occurred in their respective transciptomes.  A transcriptome represents the entire set of all RNA molecules within a cell including Messenger RNA (mRNA), Ribosomal RNA (rRNA) and Transfer RNA (tRNA) and the so-called “non-coding” RNA.  It can either be used to represent the complete set of transcripts for an entire organism or for a particular cell type – for a particular organ, for example.  The transcriptome, in essence, is a quantitative measure of the genes that are actually being expressed at any given time and as such can very dependent upon the particular set of environmental conditions that the organism is subjected to.

From the accumulated data, it seems unlikely that changes in gene expression can account for the diversity of characteristics found among members of the vertebrate family.  It seems more likely that changes in alternative splicing (AS) may be responsible for the species-specific differences found in nature.  AS is a process in which a single gene can, in fact, result in the production of more than one protein.  This is a regulated process that determines what exons – that portion of a gene that that has coding information for the final protein product - will be included or excluded in the final m-RNA.  It is this mechanism that accounts for the fact that far more proteins are produced from the ~ 20,000 protein-coding genes found in the human genome than would ordinarily be expected.

Given these assumptions arrived at from well-supported evidence, Dr. Nuno L. Barbosa-Morais and colleagues, from the Banting and Best Department at the Donnelly Centre of Medical Research at the University of Toronto, Canada, conducted a genome-wide investigation of AS differences among equivalent organs from vertebrate organisms encompassing all vertebrates higher on the evolutionary scale than fishes – tetrapods.  The organs that they used for the investigation were whole brain, forebrain cortex, cerebellum, heart, skeletal muscle, liver, kidney, and testis.  This approach engendered a significant amount of precise and demanding work

From this exhaustive study, they found significant differences in the complexity of AS between the various lineages studied with the highest complexity found within primates.  The species examined spanned ~ 350 million years in the evolutionary time scale.  Furthermore, within 6 million years the splicing patterns of the individual organs studied diverged to the extent that they were more closely correlated with the identity of the species than to the organ type.

These results add significantly to the understanding of the underlying genetic mechanisms that account for the diversity of characteristics found within the vertebrate family of organisms.


Wednesday, June 5, 2013

The Relationship between Obesity and Insulin Resistance

Metabolism – the sum of all the chemical reactions in the body necessary for sustaining life - and immunity – the ability of the organism to defend against threats posed by the invasion of microorganisms such as bacteria and viruses – are intimately linked in the biology of mammals. It is this relationship that allows the organism to adapt to changes in both the internal and external environments. However, within the modern western diet and lifestyle that promotes the development of obesity, this close association of metabolism and immunity can have deleterious consequences. Through the evolutionary history of the human species, humanity has had to survive in the face of the possibility of death as a result of starvation, infection and predation. It is only relatively recently in human societal development that such threats have been significantly lessened due to the introduction of agriculture to meet the nutritional needs of human populations and significant progress in technology and medicine. These age-old threats have been supplanted, however, by new concerns regarding individual mortality posed by cardiovascular disease, diabetes and cancer. The evidence now strongly indicates that obesity is an essential component of these troubling diseases. Between 1980 and 2008, the total number of obese individuals has essentially doubled worldwide to .5 billion individuals and the global death rate attributed to obesity is currently at ~ 3 million people per year. Drs. Justin Odegaard and Ajay Chawla from the Cardiovascular Research Institute at the University of California at San Francisco have examined the “cellular and molecular connections between chronic low-grade inflammation, insulin resistance and obesity-induced metabolic disease.” The focus for this report will be on the relationship between obesity and insulin resistance. Within this context, obesity can be defined as an imbalance between caloric intake and energy expenditure – calories in/calories out. This state of imbalance leads to the storage of excess nutrients in white adipose tissue (WAT). For lean individuals this imbalance is readily compensated by metabolic adjustments in WAT, liver and skeletal muscles. However, in a state of chronic over-nutrition, these pathways are overwhelmed leading to wide-ranging intracellular and extracellular dysfunction. Although these deleterious effects are the result of complex metabolic processes, the end product of these disturbances leads to the inhibition of insulin signaling – insulin resistance - through the modification of the insulin receptor substrate resulting in diabetes. In addition, the metabolic stress responses that are a product of chronic obesity, leads to the triggering of the innate immune receptors resulting in inflammation. This is, indeed, troubling data especially in regards to global public health. It appears that chronic over-nutrition is a cause for concern since the health ramifications that result from obesity have a major impact on individual quality of life and mortality.

Tuesday, May 21, 2013

Genetic Mutations Associated with Human Melanoma


As we have described in previous articles, there is a strong association between cancer and genetic mutations that disrupt the normal constraints placed upon cell growth and division.  In this article, evidence will be presented that links a particular set of unusual genetic mutations with human melanoma. 

Melanoma is a particularly deadly cancer of the skin.  The cells that become cancerous in melanoma are the so-called melanocytes that elaborate melanin – the pigment responsible for skin color.  The precise etiology of melanoma is not known; however, exposure to ultraviolet (UV) radiation either from natural sunlight or derived artificially from tanning beds increases the risk of developing this cancer.  The particular danger inherent in melanoma is the propensity of cancerous cells to travel from the initial site of development to other tissues of the body – a process referred to as metastasis.  It is therefore important to detect the presence of the cancerous mass before it has the opportunity to spread.

The research to date has revealed that most genetic mutations associated with various cancers seem to reside within the protein-coding regions of genes or at the splice junctions.  However Dr. Franklin W. Huang and his colleagues at the Broad Institute of Harvard and MIT, Cambridge MA were interested in determining whether any mutations consistent with tumor production appeared outside of the protein-coding regions.

To arrive at an answer to this question, the investigators performed an exhaustive analysis of whole-genome sequencing data from 70 individual cancerous melanomas.  From this analysis they discovered two independent mutations that reside within the promoter region – the promoter region of the genome lies outside of the protein coding region of the genes and is responsible for the initiation of gene transcription – for that region of the genome responsible for the production of the telemorase reverse transcriptase enzyme (TERT).  These mutations were found in 71% of the melanomas examined – this represents a remarkably high association.    In addition, they found an elevated frequency of these mutations in human bladder and liver cancer cells grown in culture.  TERT is of particular significance because this enzyme is responsible for lengthening telomeres in DNA strands and promoting cells to grow out of control.  It would, therefore, be a reasonable candidate for the mechanism of tumorigenesis. 

Friday, May 3, 2013

Single Nucleotide Polymorphisms and Intestinal Cancer


The complete sequencing of the human genome has revolutionized the study of human biology especially in relation to the understanding of the etiology of cancer.  This has been made possible by the fact that data can be accumulated from the DNA of cancer patients and studied to determine if there are any underlying patterns in regards to genetic anomalies that correlate with the different types of cancers.  Cancer results from a particular cell type growing out of control of the usual biological restraints placed upon such growth.  Cancer can arise from any tissue in the human body. 

For many years it has been known that there are certain genes that correlate with cancer development; these genes are referred to as oncogenes.  One such oncogene is referred to as myc found on human chromosome 8 (there are 23 chromosome pairs that make up the human genome – 22 pairs are so-called somatic chromosomes and 1 pair is the sex chromosomes).  It has been clearly shown that the activated product of the deregulated myc oncogene interferes with controlled cell growth and apoptosis – programmed cell death.  The net effect of these actions is uncontrolled cell growth and ultimately carcinogenesis.  Furthermore, single nucleotide polymorphisms (SNPs) – SNPs are alterations in genetic structure that represent a change in a single nucleotide – have been found upstream from the myc gene that strongly correlate with increased incidences  of different types of human cancer, including cancers of the breast, bladder and prostate.

The hypothetical causal relationship of the existence of myc-related SNPs to cancer has been extremely difficult to unambiguously confirm.  For this reason, Dr. Inderpreet Kaur Sur and his colleagues at the Science for Life Center at the Department of Biosciences and Nutrition, Karolinska Institutet in Stockholm, Sweden studied in detail the relationship between SNPs associated with the myc oncogene and intestinal tumors using the mouse model.  For the purposes of this study, the team generated mice deficient in a myc regulatory element called rs6983267.  This element is, in fact, a known SNP that is associated with more human cancer-related deaths than any other studied genetic mutation.

In addition, the investigators discovered that myc transcripts – mRNAs generated from the myc gene locus - were expressed in the intestinal crypts indicating that the myc gene was active in these genetically modified mice but at lower levels.  Most importantly, these mice proved to be remarkably resistant to the expression of intestinal tumors even when they were crossed with mice possessing the APCmin mutation – a mutation known to cause spontaneous intestinal tumors.

These results are extremely important.  They confirm the relationship between a particular SNP associated with the myc oncogene and tumorigenesis.  Although these results were obtained using the mouse as the model organism, for obvious reasons, the SNP studied has been well-established in human cancers.  Furthermore, these results show the immense benefits now being realized from the exhaustive study of the human genome; for, the etiology of cancer has been strongly linked to genetic anomalies.

Tuesday, April 23, 2013

The Role of Platelets in Defense against Malaria

Platelets are normal constituents of the blood.  They play a fundamental role in blood clotting, but have been shown to play other more diverse functions.  For example, it has been well established that platelets impede the growth of the malaria parasite, Plasmodium falciparum.  The malaria parasite enters the bloodstream following the bite of its carrier, the female anopheles mosquito.  Once circulating in the bloodstream, the parasite preferentially invades circulating red blood cells.  Platelets bind to parasitized cells and kill the parasites within.  This has been amply demonstrated in studies with mice – normally resistant to infection – that have been purposefully depleted of platelets.  These mice invariably die of infection.  It has also been shown, that this property of platelets is independent of species – platelets derived from mice or humans exert the same effect in either host.  In addition, platelets seemed to bind to both infected and non-infected cells, but have a marked preference for infected red cells. 

Although this capability of platelets has been well established, the actual molecular mechanism underlying this function has not been fully demonstrated.  Dr. Brendan J. McMorran and his colleagues from the Australian School of Advanced Medicine in Macquarie University, Sydney Australia and the Menzies Research Institute Tasmania University, Hobart, Australia have made a significant contribution to the understanding of the mechanism involved.

From their work, they have shown that platelet factor 4 (PF4) together with the Duffy-antigen receptor (Fy) are necessary for the platelet-mediated eradication of the Plasmodium falciparum parasite.  Furthermore, they have shown that upon the binding of platelets to the parasitized red blood cell, PF4 is released and that it is this protein that is responsible for the killing of the parasites residing within the infected red blood cells.  In order for PF4 to exert its effect, Fy needs to be present; it is Fy that selectively binds to PF4.  It has also been shown that those individuals that have a genetic anomaly that undermines the expression of Fy are devoid of the protection against the parasite provided by platelets.

These findings help to elucidate the role that platelets play in the defense against parasitic infections.  Uncovering the underlying mechanism for such a defense may prove to be invaluable in combating malaria - a disease that has a devastating impact on a significant portion of the world’s population.    

Friday, April 5, 2013

DNA Supercoils


The structure of DNA is ordinarily represented as a double helix.  In fact, functional DNA found within cells has an additional level of complexity – the double helix also twists upon itself resulting in “extended intertwined loops” called plectonemes.  Since it is well established that there is close and necessary relationship between structure and function in the biological realm, it is of immense scientific interest to understand the dynamics of this supercoiling property.

DNA, of course, possesses the blueprint upon which life is based – it contains the information that is used to construct the structural and enzymatic proteins that are essential for life.  In order to fulfill its role successfully, the genomic processes depend upon exquisite and precise mechanisms to control the expression of genes.  Furthermore, since the complex structure of DNA involving supercoils plays a pivotal role in these control mechanisms, it would be of interest to understand the dynamics of the individual plectonemes.

Current understanding of supercoiling suggests that this phenomenon is caused by the movement of proteins along the path of the DNA molecule.  This movement produces perturbations in the DNA structure causing the DNA to twist or writhe- the coiling of the DNA around itself.  The overall impact of these conformational changes induces both local and global effects.

A locally-derived distortion or destabilization of the DNA can alter transcription – the process by which the information contained in genes is transcribed to messenger RNA (m-RNA) – or induce binding to the DNA.  A global change in the overall conformation of DNA can bring distant sections of the DNA together resulting in genetic recombination.

Heretofore, it has proved to be an immense technological problem to study the actual dynamics of supercoiling since analysis has relied, almost exclusively, upon static imaging.  Dr. M.T.J. van Loenhout and his colleagues from the Delft University of Technology, Department of Bionanoscience, Kavti Institute of Nanoscience in Delft Netherlands have overcome this obstacle by designing what they refer to as, “single-molecule magnetic tweezers.”  With this new analytical tool, they have been able to study the real-time dynamics of individual plectonemes.

Van Loenhout and his co-workers have found that plectonemes move along the DNA by simple diffusion or what they refer to as, “fast hopping” that enables long range plectoneme displacement.  These conclusions as to the nature of the supercoiling of DNA are extremely important for they help elucidate the dynamics of a process that is fundamental to the nature of DNA within living cells. 

Tuesday, March 26, 2013

Chronic Myeloid Leukemia (CML) and a Remarkable Drug to Treat It.


Chronic Myeloid Leukemia impacts approximately 5000 people a year.  It is characterized by the uncontrolled growth of a subset of circulating white blood cells (WBC).  The onset of this disease correlates with a particular genetic abnormality that has been well categorized.  The change in the genetic material is demonstrated by the appearance of the so-called “Philadelphia” chromosome.  This chromosome results from the anomalous exchange of genes between chromosome 9 and chromosome 22 – the human genome possesses 23 pairs of chromosomes one pair of which contains the genes that determine human gender XX (female) and XY (male).  This genetic rearrangement results in the juxtaposition of two genes namely, BCR and ABL.  The resulting gene combination, BCR-ABL is responsible for the production of a novel gene product that contributes to uncontrolled cell growth i.e. CML.

The realization of this mechanism opened the possibility that if the activity of the deleterious protein product could be curtailed, a cure of CML could be envisioned.  This particular approach is known as molecular targeting, for it targets a particular molecular substance known to play a critical role in the development of disease – in this case, CML.

When it became clear that the “offending” protein was a member of a class of proteins referred to as kinase enzymes, Drs. Zimmerman and Buchdunger tested a plethora of possible drug candidates to see what compound could precisely target this enzyme without adversely affecting any other cellular processes.  Their work proved rewarding; they ultimately discovered the efficacy of a drug given the name, Gleevec (imatinib).

The results have been very impressive.  As reported in the Journal of the National Cancer Institute (JNCI), CML patients who have been treated with Gleevec have gone into complete remission after two years of treatment and have been shown to have survival rates similar to the general population.  According to a statement released by the journal, “This study offers the first evidence that a disseminated cancer, not amenable to surgery, can be controlled to the point of giving patients a normal life expectancy.”

These results are extraordinary, yet they point to the efficacy of the molecular targeting approach.  This methodology may prove applicable to other heretofore treatment-resistant diseases. 

Friday, March 15, 2013

Stimulants, Opiates and the Human Brain

Chemical stimulants such as cocaine and opiates such as morphine profoundly influence behavior through their interaction with and alteration of brain chemistry.  Members of the opiate family of compounds are known to markedly reduce the experience of pain.  Of particular interest in this regard is the neurotrophic factor, BDNF – a direct product of brain chemistry.  BDNF plays a very important role in maintaining so-called “neural plasticity.”  This plasticity represents an intrinsic ability of the human brain to alter neuronal pathways and synapses – the junctions between nerve cells that allow the passage of electrical signals through the nervous system – in response to changes in behavior and the environment especially in regard to bodily injury.  This is a highly adaptive function of the brain that is often seen in the victims of stroke – allowing individuals to compensate for brain damage.

BDNF has been shown to play a key role in the kind of neural and behavioral plasticity that is induced by the use of cocaine and other stimulants.  Furthermore, it has been demonstrated that the mode of action of BDNF in this regard is intimately connected with the mesolimbic dopamine (DA) system that represents a key reward circuit in the brain.  Dopamine is one of major neurotransmitters in the brain that is involved in many diverse brain functions.  It is the irreversible loss of dopamine-producing cells that results in the symptoms associated with Parkinson’s disease.  The net result of the interaction of BDNF with DA system is the promotion of further actions of stimulant drugs.

Dr. Ja Wook Koo and his colleagues at the Fishberg Department of Neuroscience and Friedman Brain Institute at the Mount Sinai School of Medicine in New York have implicated BDNF in the mode of action of the opiate drug, morphine and have helped elucidate the mechanism through which it works.  In contrast to stimulants, opiates exert their effect on the brain through the promotion of DA signaling by the inhibition of ϒ-aminobutyric acid (GABA) – an important neurotransmitter in the brain that plays a role in regulating neuronal excitability through an inhibitory pathway.  The investigators have clearly shown that BDNF is, in fact, a negative modulator of morphine action.

This is an important finding in that is helps elucidate the mechanisms involved  with  brain-associated adaptations within the reward circuitry that occur with the use of morphine – a drug that is widely used to treat severe chronic pain especially at the end of life. 

Thursday, February 28, 2013

How the Paramyxovirus Evades Human Innate Immunity

Paramyxoviruses represent a class of single-stranded RNA viruses that include the measles, parainfluenza, Sendai and Nipah viruses.  The resulting infections associated with these viruses involve respiratory ailments, and ubiquitous childhood diseases.   Paramyxoviruses – associated diseases represent a significant public health concern especially among children and the elderly.   The major route for disease transmission is via respiration.   Although measles has decreased dramatically in the developed world due mainly to extensive vaccination programs, it continues to be problematic in Africa and Central and South America.
The human immune system is equipped with two tiers of defense against viral infections – the innate and adaptive systems.  The innate system represents the first line of defense.  Within this line of defense, the retinoic acid – inducible gene 1 (RIG -1) – like melanoma differentiation – associated protein 5 (MDA5) senses a broad spectrum of viruses in the form of their cytoplasmic viral RNAs and subsequently activates antiviral innate immunity.
 
Through the process of biological evolution, viruses have developed diverse mechanisms to evade the innate immune system.  It has been shown that Paramyxovirus, manages to effectively subvert this immunological defense mechanism.  How this is accomplished is poorly understood.  Dr. Carina Motz and colleagues at the Department of Biochemistry and Gene Center at Ludwig – Maximilians University in Munich, Germany have labored painstakingly to elucidate the mechanism of this evasion.

They were able to demonstrate that this class of viruses elaborates a protein product – Paramyxovirus V Protein – that is able to alter the configuration of the host MDA5 protein in such a way as to effectively inhibit its antiviral signaling function.  The end result of this interaction is a compromised first line of defense.

Such studies add significantly to the body of information that helps explain how certain types of virus infections lead to disease in spite of host defense mechanisms.  This information may prove to be invaluable in regards to potential cures and treatments of intractable ailments. 


Wednesday, February 13, 2013

How Did the Earth Get its Moon?

We, as inhabitants of planet Earth, take the presence of the Moon in the night sky for granted.  Yet, the evidence tells us that at one time in the Earth's 4 and ½ billion year history there was no satellite in Earth orbit.  The generally accepted explanation among astronomers and cosmologists is that at a time early in the Earth's history there was a collision between Earth and another large planet resulting in the ejection of massive amounts of material into Earth orbit forming a disk of debris.  It is further postulated that from this disk, the Moon was formed in a process not unlike the formation of the planets of our solar system around the sun.  This is referred to as the giant impact theory.

According to this paradigm, a low-velocity impact of a planetary body (impactor) roughly the size of Mars could produce an iron-poor debris disk with sufficient total mass and energy in the form of angular momentum – a measure of the rotation of a body that is the product of its inertia and angular velocity - to produce an iron-poor Moon.  In addition, this model also predicts that the debris disk would contain material primarily from the impactor's mantle.   This data is where the inconsistency lies; for, the Earth and Moon, in fact, share many similarities in regards to composition, including the isotopes of oxygen, chromium and titanium.  It is unlikely that any postulated impactor would share these similarities.


Dr. Robin M Canup from the Planetary Science Directorate at the Southwest Research Institute in Boulder, Colorado has proposed a solution to this apparent dilemma.  Canup has postulated through the use of sophisticated and computer-assisted simulations that if a larger-sized impactor than the one proposed in the giant impact theory was involved, then the resulting collision with Earth would produce a disk with the same composition as the Earth's mantle.  The actual size of the impactor used in these simulations was comparable in mass to the Earth.


This proposed scenario demonstrates just how chaotic and disruptive the environment of our solar system was during the early stages of its evolution.  The cosmos is, in fact, ever-changing in its past, its present and for the foreseeable future. 

Thursday, February 7, 2013

Insights into the Mode of Action of the Human Cytomegalovirus

There is form of the human cytomegalovirus that is responsible for herpes – this virus is referred to as the herpesvirus human cytomegalovirus (HCMV).  This virus can have severe repercussions for infants and those individuals who are immune-compromised such as AIDS patients.  The entire HCMV genome was completely sequenced twenty years ago.  In spite of this accomplishment, the understanding of the complete array of proteins that are produced by this virus has not been fully elucidated.  This is because of the fact that although the genome is quite small – 240 kilobases (kb) – it has been estimated that there are between 165 and 252 open reading frames (ORFs).  An ORF is the part of a reading frame in the genome that contains no stop codons – stop codons terminate transcription.

A gene is defined as that part of the genome (DNA) that contains the information for the production of a protein product.  Transcription is the first step in the process that converts the information contained within the reading frame into what is referred to as messenger RNA (m-RNA).  It is the m-RNA that migrates to the highly specialized cell organelles, the ribosomes, where proteins are ultimately produced.  This phase is called translation.  It seems that the translation products of HCMV are far more complex than previously believed.

To help unravel this apparent mystery, Dr. Noam Stern-Ginossar and colleagues at the Department of Cellular and Molecular Pharmacology at Howard Hughes Medical Institute of California at San Francisco infected human foreskin fibroblasts (HFFs) with a clinical strain of HCMV.  They subsequently harvested cells 5, 24 and 72 hours post infection and analyzed the full range of translation protein products. 
As a result of this very intensive analysis, they were able to identify 751 translated ORFs - hundreds of which had not been identified before.  The explanation that best fits the results is that transcription involves the use of alternative start sites with the net effect being the production of multiple and distinct protein products.  This result was not anticipated by the investigators and demonstrates a level of complexity that far exceeded expectations.

This kind of work is significant in that it provides important insights into the full scope of the functional and antigenic – a measure of the capacity to produce an immune response – potential of HCMV.