LEISHMANIA METABOLISM: NEW THERAPEUTIC APPROACH TO INFECTION UNCOVERED

         Scientists from the Bio21 Institute at the University of Melbourne have come up with a novel technique for understanding infectious parasites and bacteria using labeled carbon atoms (¹³C). In a paper published in the Journal of Biological Chemistry, they followed the intracellular and secretion metabolites of the labeled carbon atoms using gas chromatography mass spectrometry and ¹³C NMR. Specifically, the scientists investigated the metabolic mechanism of Leishmania parasites as they “proliferate within nutritionally complex niches in their sandfly vector and mammalian hosts”. Leishmania parasites possess the ability to infect many animals and therefore treatment and vaccine development has been made difficult.

         Leishmania results in a wide spectrum of diseases in humans that range from “self-limiting cutaneous infections to disseminating infections that can lead to severe morbidity and death,” infecting more than 12 million people with 50,000 deaths annually.  The study lead by Dr. Malcolm McConville attempts to narrow the gaps in understanding the carbon metabolism of Leishmania, with the eventual intention to develop insight into possible new therapeutic pathways.

         The glycosome is an important localization point for many enzymes involved in the glycolytic pathway of Leishmania. Specifically, glycosomal succinate fermentation was responsible for the regeneration of ATP and NAD+ that was consumed in the upper glycolytic pathway, which is facilitated by enzymes sequestered within glycosomes. The tricarboxylic acid cycle (TCA cycle) was found to catabolize most of the C4 dicarboxylic acids generated during succinate fermentation. TCA cycle anaplerosis (intermediate reactions) was thus needed to sustain glutamate production in Leishmania.

         These results encouraged researchers to experimentally inhibit mitochondrial metabolic pathways within Leishmania, keeping in mind the implications as a potential avenue for therapy. Using Sodium fluoroacetate they were able to inhibit mitochondrial aconitase and they witnessed the rapid depletion of intracellular glutamate pools and growth arrest. Exogenous application of a high concentration of glutamate was found to alleviate the witnessed growth arrest. They concluded a tight coupling between glycosomal and mitochondrial metabolism pathway in Leishmania promastigotes. Furthermore, they suggest that somewhat surprisingly, the TCA cycle in Leishmania has crucial anabolic functions not witnessed in some other trypanosomatid parasites. The carbon labeling technique for understanding carbon metabolic pathways in parasites may have valuable potential in drug development and the discovery of unexpected parasitic metabolic processes.

REFERENCE: McConville et al. Isotopomer Profiling of Leishmania mexicana Promastigotes Reveals Important Roles for Succinate Fermentation and Aspartate Uptake in Tricarboxylic Acid Cycle (TCA) Anaplerosis, Glutamate Synthesis, and Growth. Journal of Biological Chemistry. 2011: 31(286) 27706-27717.

WHY MEN SEEK STATUS: THE BATTLE FOR SUCCESS

By René A. Azeez, Honours BSc. Developmental Biology, University of Toronto. July 30, 2011.

         Researchers from the University of California and the University of New Mexico have combined efforts in an attempt to delineate the reason for dominance seeking behavior in men. The paper entitled “Why do men seek status? Fitness payoffs to dominance and prestige” was published in the July edition of Proceedings of the Royal Society B: Biological Sciences.

         Previous studies have demonstrated that men considered to be wealthier have more offspring. Moreover, cross societal interpretations of status, e.g. wealth, hunting skills, and warriorship, have been shown to have a correlation to reproduction success. Modern industrial societies have also been shown to often reflect the same.

         In this study, researchers began by defining social status as “relative access to contested resources within a social group.” They went on to test several predictions with the Tsimane foragers of Bolivia serving as the test population. The test population came specifically from two of the more acculturated villages called Ton’tumsi and Jinac. The Tsimane were described as being semi-sedentary and living in communities from 30 to 500 individuals. Using different data analysis techniques, including correlation tests and OLS regression models, they were able to determine the feasibility of their predictions.

         Firstly, they were able to determine that men of higher social status had higher offspring survivorship. They also showed that men of higher social status were found to have had more extra-marital affairs within the prior 5 years, albeit owing more to community-wide influence than to dyadic physical confrontation. The number of serial marriages also correlated to winning physical confrontations and community-wide influence and the wives of influential men gave birth at earlier ages. The wives were more likely to spend more time interacting with offspring if the husband is more prone to winning physical confrontations, but this behavior does not seemingly undergo modification owing to community-wide influence. The study also went on to describe greater kinship relationships for those men prone to winning physical confrontations, greater generosity from influential men, more deference being afforded by dominant and prestigious men, and overall complex fitness gain mechanisms.

         The group of researchers was able to conclude that the Tsimane and other small scale societies have demonstrated the male social status as being significantly influential on fitness determination.

REFERENCE:

Von Ruden C., Gurven M., and Kaplan H. Why do men seek status? Fitness payoffs to dominance and prestige. Proceedings of the Royal Society B: Biological Sciences. 2011: 2223-2232.

DECODING AUTOPHAGOSOMES: A CLUE TO PARKINSON'S, HUNTINGTON'S, DEMENTIA

By René A. Azeez, Honours BSc. Developmental Biology, University of Toronto. July 27, 2011.

         A paper centered on autophagy, the catabolic process by which a cell degrades its intercytoplasmic components transported in double-membraned autophagosomes by the action of its lysosomal machinery, may have implications in understanding the development of many neurodegenerative diseases, including Huntington’s disease, Parkinson’s disease, and dementia. Research from the Rubinsztein lab at the Cambridge Institute for Medical Research had previously demonstrated autophagy as an important regulator of the levels of proteins and pathogens prone to aggregation which in turn play a role in the development of these and potentially other diseases. In fact, apart from regulation of numerous physiological and pathological processes, and innate and acquired immunity, it is hypothesized that autophagosome function may play a role in cancer, infectious diseases, and ageing.

         Preautophagosomal structures stemming from the plasma membrane and other cellular sites form phagophores which in turn elongate and undergo fusion to become autophagosomes. However, the mechanism which governs the maturation of preautophagosomes to fully formed autophagosomes is largely unknown. A recent study from the same group at the Cambridge Institute for Medical Research entitled “Autophagosome Precursor Maturation Requires Homotypic Fusion” attempted to shed some light on the mechanism. More than 30 autophagy related proteins (Atg) have been previously shown to play some role in regulating autophagy. In this study, researchers were able to reveal that Atg16L1 precursors underwent homotypic fusion in order to form mature autophagosomes. This increases the size of the vesicles which appears to enhance acquisition of LC3, a key autophagosome protein, and maturation into autophagosomes. Furthermore, they were able to determine through a combination of colocalization analysis, knockdown experiments, live cell imaging, in vitro fusion assay, HCS and Image J methods etc., that the homotypic fusion of Atg16L1 precursors is dependant on the SNARE protein VAMP7 together with partner SNARE proteins including syntaxin 7, syntaxin 8, and Vti1b.

         By understanding new steps in the formation of autophagosomes, researchers have given insight and possible new therapeutic direction to the management of the many diseases and conditions for which autophagy plays a role.

REFERENCE:

Moreau K., Ravikumar B., Renna M., Puri C, and Rubinsztein D. C. Autophagosome precursor maturation requires homotypic fusion. 2011. Cell (146): 303-317.

ANXIETY: POSSIBLE TARGET FOR TREATMENT IDENTIFIED

By René A. Azeez, Honours BSc. Developmental Biology, University of Toronto. July 25, 2011.

 British Baptist preacher Charles Haddon Spurgeon said of anxiety, “Anxiety does not empty tomorrow of its sorrows, but only empties today of its strengths.” Fear, which can be defined as an emotional response to a perceived treat, differs from anxiety in that anxiety can often occur without an identifiable triggering stimulus.          Anxiety is defined as having both psychological and physiological constituents and is characterized by “somatic, emotional, cognitive, and behavioral components.” Researchers from Queen’s University, Kingston, Ontario, have come one step closer in identifying a new method for regulating anxiety.

         Prior to the study, it was understood that neuropeptide Y (NPY) is one of the most abundant chemicals in the mammalian brain and that NPY counteracts the responses to acute threat in animal models. It was also known that intracerebroventricular (i.c.v) administration of NPY is anxiolytic (anxiety reducing). However, less had been known about the particular contributions of the area of the brain known as the lateral septum as relates to NPY-regulated anxiety reduction. NPY-like-immunoreactivity is highly expressed in the lateral septum.

         The study lead by Dr. Natalie L. Trent, of the Queen’s University’s Centre for Neuroscience Studies, was designed to investigate the effects of NPY infusions into the lateral septum across a range of anxiety related behaviors and to examine the effects of antagonizing NPY Y1 receptors on anxiety responses. 

         Rats were tested in three paradigms. The first is called the plus-maze test, in which it was found that NPY infusion into the lateral septum had no effects on the anxiety equitable behaviors as determined by the test. Furthermore, introduction of both NPY and Y1 antagonist (BIBO 3304) yielded the same result. A second test called the novelty-induced suppression of feeding test, found that rats were significantly quicker in initiating snack consumption following their first infusion of NPY, indicating a reduction in anxiety. This anxiolysis was attenuated when NPY and Y1 antagonist were co-infused into the lateral septum. The third test, called the shock-probe burying test showed that rats spent less time burying an electrified probe, a marker of reduced anxiety, after being infused with NPY. However, in this case, the Y1 antagonist did not attenuate anxiolysis. The results were enough to conclude that activation of NPY receptors in the lateral septum reduced anxiety-related responses, albeit in a test specific manner. This observation makes investigating the potential role of other NPY receptors (Y2 and/or Y5) in anxiolysis of particular interest.

         The researchers hope that the finding will lead to more selective treatment options for anxiety disorders.

REFERENCE:

Trent N. L., Menard J. L. Infusions of neuropeptide Y into the lateral septum reduce anxiety-related behaviors in the rat. Pharmacology, Biochemistry, and Behavior. 2011 (99): 580-590.

WHERE NO BONE HAS GONE BEFORE: SUBSTANCE P MEDIATES HETEROTROPIC OSSIFICATION

By René A. Azeez, Honours BSc. Developmental Biology, University of Toronto. July 23, 2011.

            In the field of Developmental Biology one of the most fundamental principles is that of contextual determination, i.e. a cell goes along it’s particular lineage to become what it is destined to become based on a number of complex contextual factors. A condition known as Heterotopic Ossification (HO) in which patients have incurred soft tissue damage leading to the formation of extraskeletal bone is a common and serious reflection of the contextual principle. Although researchers have had advances in understanding the genetics of HO, the cellular and molecular triggers of HO have long remained unclear. That is, until recently when researchers from Northwestern University Feinberg School of Medicine and the Perelman School of Medicine at the University of Pennsylvania have managed to shed some light on the molecular mechanism of HO.

            In a previous study researchers were able to conclude that all forms of HO had something in common; the requirement of an inflammatory trigger. However, acknowledging that inflammation triggers are regulated by multiple cytokines (small cell signaling molecules that are secreted by the glial cells of the nervous system) and multiple complex neuro-endocrine controls, they conceded that identifying specific regulatory loci (specific gene or DNA sequences) that control these inflammatory triggers was difficult. Researchers were able to deduce that a pro-inflammatory neuropeptide known as Substance P (SP) was present in active areas of bone regeneration following a fracture.  Moreover, the receptor for SP had been found on cells and tissues associated with bone tissue formation and degradation. SP had also been shown to mediate immune modulation and injury-induced mobilization of CD29⁺, a cell involved in HO formation.

In this study, researchers lead by Lixin Kan studied the role of SP in patients with multiple forms of HO including sporadic, post-traumatic, neurologically associated HO, and fibrodysplasia ossificans progressiva or FOP (the genetic form of HO). They were able to show that SP expression intensified in early sporadic HO and FOP lesions. Moreover they were able to show that blocking SP prevented HO in these cases. Additionally, they were able to determine that cells that robustly express the SP receptor are required to mediate BMP-dependant (bone morphogenic protein) HO.

These results allowed researchers to determine that SP is seemingly critical in HO induction, and they go on to suggest that blocking SP or SP mediated HO pathways can be a potentially viable therapeutic approach in preventing HO.

REFERENCE: Lixin Kan, Vitali Y Lounev, Robert J Pignolo, Lishu Duan, Yijie Liu, Stuart R Stock, Tammy L McGuire, Bao Lu, Norma P Gerard, Eileen M Shore, Frederick S Kaplan, and John A Kessler. Substance P signaling mediates BMP dependent heterotopic ossification. Journal of Cellular Biochemistry, 2011.

NEW LUNG CANCER GENE: THE POWER OF MOUSE MODELS IN UNDERSTANDING HUMAN DISEASE

By René A. Azeez, Honours BSc. Developmental Biology, University of Toronto. July 20, 2011.

                Cancer research faces many obstacles, the least of which is the sheer number of mechanisms by which cancer can arise and proliferate. Because of this and other factors, including the argument that cancer is evolutionarily conserved, it is hard to say with absolute certainty that a singular “cure for cancer” is a feasible goal. However, intuitively it seems that having an understanding of individual cancers and specific targets for treatment would be a more realistic and beneficial outlook. Alison Dooley of the David H. Koch Institute for Cancer Research at MIT is the lead author of a paper entitled “Nuclear Factor I/B is an oncogene in small cell lung cancer” that was published in the July 15 edition of Genes and Development. In the paper it is revealed that researchers have pinpointed a gene which apparently drives the progression of small cell lung cancer (SCLC).

            SCLC is an aggressive cancer accounting for about 15% of lung cancer cases and is often only diagnosed after it has metastasized. SCLC kills over 90% of patients within half a decade of being diagnosed. Previously, SCLC had been poorly characterized at the genomic level. Dr. Dooley and her team used a previously designed mouse model in which the tumor suppressor genes, Trp53 and Rb1, were conditionally deleted to identify genetic alterations that occur during SCLC progression.

            Using multiple techniques to identify genetic alterations in SCLC tumors and metastases, researchers were able to show that although the majority of the genome was surprisingly unaltered from normal cells, there were several high-level focal amplifications and deletions in tumor specimens. Nuclear factor I/B (NFIB) was found to represent a newly identified amplified gene in SCLC tumor cell expression profiles. Researchers were then able to confirm that NFIB amplifications were also seen in human SCLC.

            Knocking out NFIB in human SCLC tumors, researchers were also able to demonstrate that “NFIB is integral to human SCLC cell line viability and/or proliferation, likely depending on the NFIB levels or the cellular context of each individual tumor.” Researchers went further to demonstrate through analyses (transformations, arrays, gene set enrichment analysis) that NFIB seems to have oncogenic (cancer causing) properties.

            Dr. Dooley and her team point out that using a mouse model allowed for tumors to be initiated by defined genetic events and the disease progresses in the absence of smoking induced passenger mutations that could occur in studying the cancer type in humans. They also point out that a wealth of tumor and metastasis samples could be collected from mouse models at different stages giving more insight into the dynamic properties of genetic expression as relates to SCLC. They suggest that future efforts to identify point mutations in mouse SCLC models in conjunction with cross-species analyses would serve to prioritize the daunting number of meaningful mutations being expressed in human SCLC. It is conceivable that this approach would be beneficial in other types of cancers as well.

REFERENCE:

Dooley A. et al. Nuclear Factor I/B is an oncogene in small cell lung cancer. Genes and Development, 2011: (25) 1470-1475.

AUTOIMMUNE DISEASES AND PEANUT ALLERGIES: BORROWED APPROACH

By René A. Azeez, Honours BSc. Developmental Biology, University of Toronto. July 18, 2011.

Arguably the man most synonymous with intelligence in the western world, Albert Einstein, said “The process of scientific discovery is, in effect, a continual flight from wonder”. In the process of inquisition scientists revisit questions, integrating novel approaches and fresh perspectives. In an article published in the journal Current Allergy and Asthma Reports entitled ‘Immunological Similarities between Selected Autoimmune Diseases and Peanut Allergy: Possible New Therapeutics Approach’, authors Michael A. Matucci and Stephen C. Dreskin decided to look at peanut allergies from the vantage point that tolerance to foods represents the normal state just as tolerance to self-proteins represents a normal state. Using this idea as the foundation to explore peanut allergies, they compared similar immunological abnormalities arising from both peanut allergies and several autoimmune diseases and suggest that understanding these similarities may lead to new therapeutic approaches for the treatment of several food allergies.

The authors stated that four ideas stimulated the article. The first idea is that patients who carry the peanut allergy exhibit elevated IgG; a type of antibody; levels compared to non-allergic control patients. This is also seen in patients with some autoimmune diseases. The second idea is that published works point to the fact that several links between autoimmunity and allergies. The third idea comes from the fact that research in both allergy and autoimmunity is focused on the regulation of T and B cells; the major cells of the adaptive immune response; by regulatory T cells. For the final inspirational idea the authors suggest that the “you are what you eat” proposal points to a greater similarity between food allergy and autoimmunity than is currently understood.

The authors used the example of autoimmune thyroidosis to highlight the similarity. Elevated IgG comparable to what is seen in patients with peanut allergies were seen in patients with autoimmune thyroidosis. It is currently thought that the disease is caused by abnormal suppressor T Cell function. The authors point out that while production of IgE; another immunoglobulin; is an absolute necessity in allergic diseases, IgG’s role is underappreciated.

Noticing the similarities, the authors decided to ask themselves whether current methods of treating autoimmune diseases, specifically immunomodulatory approaches, could be applicable to the treatment of peanut and ultimately other food allergies. They singled out Rituximab, an antibody initially developed to treat follicular lymphoma by targeting certain B-cells, as having potential for application to the treatment of food allergies. The drug has been shown useful in the treatment of several autoimmune diseases including rheumatoid arthritis, autoimmune hemolytic anemia, and systemic lupus erythematosus. In their conclusion they stated that plasma cell directed therapies may become greater targeted and clinically more viable in the future. They expect that a role for B-cell targeted therapies may someday be used alone or in concert with other approaches for the treatment of severe food allergies.

REFERENCE:                                                                                                                                          

Martucci M. A., and Dreskin S. C. Immuno Immunological Similarities between Selected Autoimmune Diseases and Peanut Allergy: Possible New Therapeutics Approach.  . Current allergy Asthma Reports, 2011, 11: 334-339.