Nitish R. Mahapatra
Other affiliations: Indian Institute of Chemical Biology, University of California, Berkeley, Veterans Health Administration ...read more
Bio: Nitish R. Mahapatra is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Chromogranin A & CREB. The author has an hindex of 27, co-authored 73 publications receiving 1905 citations. Previous affiliations of Nitish R. Mahapatra include Indian Institute of Chemical Biology & University of California, Berkeley.
Papers published on a yearly basis
TL;DR: Loss of the physiological "brake" catestatin in Chga mice coupled with dysregulation of transmitter storage and release may act in concert to alter autonomic control of the circulation in vivo, eventuating in hypertension.
Abstract: The secretory prohormone chromogranin A (CHGA) is overexpressed in essential hypertension, a complex trait with genetic predisposition, while its catecholamine release–inhibitory fragment catestatin is diminished, and low catestatin predicts augmented adrenergic pressor responses. These findings from studies on humans suggest a mechanism whereby diminished catestatin might increase the risk for hypertension. We generated Chga–/– and humanized mice through transgenic insertion of a human CHGA haplotype in order to probe CHGA and catestatin in vivo. Chga–/– mice displayed extreme phenotypic changes, including: (a) decreased chromaffin granule size and number; (b) elevated BP; (c) loss of diurnal BP variation; (d) increased left ventricular mass and cavity dimensions; (e) decreased adrenal catecholamine, neuropeptide Y (Npy), and ATP contents; (f) increased catecholamine/ATP ratio in the chromaffin granule; and (g) increased plasma catecholamine and Npy levels. Rescue of elevated BP to normalcy was achieved by either exogenous catestatin replacement or humanization of Chga–/– mice. Loss of the physiological “brake” catestatin in Chga–/– mice coupled with dysregulation of transmitter storage and release may act in concert to alter autonomic control of the circulation in vivo, eventuating in hypertension.
TL;DR: A surprising pattern of CHGA variants is shown that alter the expression and function of this gene, both in vivo and in vitro, including rare alleles that qualitatively change the encoded product to alter the signaling potency ofCHGA-derived catecholamine release-inhibitory catestatin peptides.
Abstract: The chromogranin/secretogranin proteins are costored and coreleased with catecholamines from secretory vesicles in chromaffin cells and noradrenergic neurons. Chromogranin A (CHGA) regulates catecholamine storage and release through intracellular (vesiculogenic) and extracellular (catecholamine release–inhibitory) mechanisms. CHGA is a candidate gene for autonomic dysfunction syndromes, including intermediate phenotypes that contribute to human hypertension. Here, we show a surprising pattern of CHGA variants that alter the expression and function of this gene, both in vivo and in vitro. Functional variants include both common alleles that quantitatively alter gene expression and rare alleles that qualitatively change the encoded product to alter the signaling potency of CHGA-derived catecholamine release–inhibitory catestatin peptides.
TL;DR: Rank order of variant inhibitory potency for all four nicotinic processes was identical, suggesting mediation by similar combinations of receptor α/β subunits and that crucial catestatin residues are likely to be identical across the four processes.
Abstract: The catestatin fragment of chromogranin A is an endogenous inhibitor of nicotinic cholinergic transmission, functioning in negative feedback control of catecholamine secretion. We explored naturally occurring polymorphisms in the amino acid sequence of catestatin. Three human variants were identified: Gly364Ser, Pro370Leu, and Arg374Gln. Variants were tested for ability to inhibit four nicotinic processes. The rank order of potency for inhibition of catecholamine secretion was Pro370Leu wild type Gly364Ser Arg374Gln. Decrease in potency was paralleled by decline in Hill slope, suggesting that negative cooperativity at ascending dose might underlie loss of potency. Several lines of evidence indicated that each variant acted as a nicotinic antagonist: potency to inhibit secretion paralleled inhibition of agonist-triggered 22 Na uptake (r 0.986); variants inhibited secretion with similar potency when triggered by several nicotinic agonists, though not by agents using other secretory pathways or bypassing the nicotinic receptor; and blockade of secretion was noncompetitive with agonist. Variants also inhibited desensitization of secretion after prior agonist exposure and stimulation of secretory protein biosynthesis by agonist. Rank order of variant inhibitory potency for all four nicotinic processes was identical (Pro370Leu wild type Gly364Ser Arg374Gln), suggesting mediation by similar combinations of receptor / subunits and that crucial catestatin residues are likely to be identical across the four processes. When catestatin variants were mixed in likely heterozygotic (1:1 M ratio) combinations, the inhibitory curve was left-shifted onto that of the more potent variant in the combination, suggesting phenotypic dominance. The results have quantitative implications for interindividual variations in human nicotinic signaling.
TL;DR: Nicotinic cholinergic stimulus-transcription coupling occurs in vivo and can be provoked either directly or indirectly (by vesicular transmitter depletion).
Abstract: Stimulation of chromaffin cell secretion in vitro triggers not only secretion but also resynthesis of just released catecholamines and chromogranin A, the precursor of the catecholamine release-inhibitory, nicotinic cholinergic antagonist peptide catestatin. Does stimulus-transcription coupling occur in vivo? And does catestatin antagonize secretion and transcription in vivo? To answer these questions, we employed a novel mouse strain harboring a chromogranin A promoter/firefly luciferase reporter transgene. Tissue-specific expression of the reporter was established by both luminescence and reverse transcription-PCR. Secretion and transcription in vivo were triggered by either direct nicotinic stimulation or vesicular transmitter depletion. Nicotinic blockade in vivo was attempted with either the classical antagonist chlorisondamine or the novel antagonist catestatin. Luciferase reporter expression was exquisitely sensitive over a large dynamic range, was specific for the transgenic animals, and paralleled typical neuroendocrine distribution of endogenous chromogranin A. Adrenal ontogeny revealed a rise of embryonic transgene expression until embryonal day 18, with an abrupt postnatal decline. Direct nicotinic stimulation of chromaffin cells caused catecholamine release and transgene transcription, each of which was nearly completely blocked by chlorisondamine. Similar adrenal results were obtained during vesicular catecholamine depletion. Both secretion and transcription were substantially blocked in the adrenal gland by catestatin. In brain and sympathetic nerve, stimulation of transcription was more modest, and reserpine responses were only incompletely blocked by chlorisondamine or catestatin, perhaps because of limited blood-brain barrier penetration by these cationic antagonists. Thus, nicotinic cholinergic stimulus-transcription coupling occurs in vivo and can be provoked either directly or indirectly (by vesicular transmitter depletion). Such coupling triggers the biosynthesis of chromogranin A, the precursor of catestatin. Catestatin itself blocks stimulation of both secretion and transcription in vivo. Thus, chromogranin A and its catestatin fragment may lie at the nexus of nicotinic cholinergic signaling in vivo.
TL;DR: It is established that a CgA-GFP fusion protein expressed in neuroendocrine PC12 cells is trafficked to the dense core secretory granule and thereby sorted to the regulated pathway for exocytosis and the data reveal for the first time that the CGA77-115 domain of the mature protein may be necessary (though perhaps not sufficient) for trafficking C gA into the regulated pathways of secretion.
Abstract: Chromogranin A (CgA) is the index member of the chromogranin/secretogranin (or 'granin') family of regulated secretory proteins that are ubiquitously distributed in amine- and peptide-containing secretory granules of endocrine, neuroendocrine and neuronal cells. Because of their abundance and such widespread occurrence, granins have often been used as prototype proteins to elucidate mechanisms of protein targeting into dense-core secretory granules. In this study, we used a series of full-length, point mutant or truncated CgA-green fluorescent protein (GFP) chimeras to explore routing of CgA in neuroendocrine PC12 cells. Using sucrose gradient fractionation and 3D deconvolution microscopy to determine the subcellular localization of the GFP chimeras, as well as secretagogue-stimulated release, the present study establishes that a CgA-GFP fusion protein expressed in neuroendocrine PC12 cells is trafficked to the dense core secretory granule and thereby sorted to the regulated pathway for exocytosis. We show that information necessary for such trafficking is contained within the N-terminal but not the C-terminal region of CgA. We find that CgA's conserved N-terminal hydrophobic Cys(17)-Cys(38) loop structure may not be sufficient for sorting of CgA into dense-core secretory granules, nor is its stabilization by a disulfide bond necessary for such sorting. Moreover, our data reveal for the first time that the CgA(77-115) domain of the mature protein may be necessary (though perhaps not sufficient) for trafficking CgA into the regulated pathway of secretion.
TL;DR: It is suggested that the natural selection against large insertion/deletion is so weak that a large amount of variation is maintained in a population.
Abstract: The relationship between the two estimates of genetic variation at the DNA level, namely the number of segregating sites and the average number of nucleotide differences estimated from pairwise comparison, is investigated. It is found that the correlation between these two estimates is large when the sample size is small, and decreases slowly as the sample size increases. Using the relationship obtained, a statistical method for testing the neutral mutation hypothesis is developed. This method needs only the data of DNA polymorphism, namely the genetic variation within population at the DNA level. A simple method of computer simulation, that was used in order to obtain the distribution of a new statistic developed, is also presented. Applying this statistical method to the five regions of DNA sequences in Drosophila melanogaster, it is found that large insertion/deletion (greater than 100 bp) is deleterious. It is suggested that the natural selection against large insertion/deletion is so weak that a large amount of variation is maintained in a population.
TL;DR: For the next few weeks the course is going to be exploring a field that’s actually older than classical population genetics, although the approach it’ll be taking to it involves the use of population genetic machinery.
Abstract: So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to
TL;DR: It is essential that the medical profession play a central role in critically evaluating the evidence related to drugs, devices, and procedures for the detection, management, or prevention of disease.
Abstract: It is essential that the medical profession play a central role in critically evaluating the evidence related to drugs, devices, and procedures for the detection, management, or prevention of disease. Properly applied, rigorous, expert analysis of the available data documenting absolute and relative benefits and risks of these therapies and procedures can improve the effectiveness of care, optimize patient outcomes, and favorably affect the cost of care by focusing resources on the most effective strategies. One important use of such data is the production of clinical practice guidelines that, in turn, can provide a foundation for a variety of other applications, such as performance measures, appropriate use criteria, clinical decision support tools, and quality improvement tools. The American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA) have jointly engaged in the production of guidelines in the area of cardiovascular disease since 1980. The ACCF/AHA Task Force on Practice Guidelines (Task Force) is charged with developing, updating, and revising practice guidelines for cardiovascular diseases and procedures, and the Task Force directs and oversees this effort. Writing committees are charged with assessing the evidence as an independent group of authors to develop, update, or revise recommendations for clinical practice. Experts in the subject under consideration have been selected from both organizations to examine subject-specific data and write guidelines in partnership with representatives from other medical practitioner and specialty groups. Writing committees are specifically charged to perform a formal literature review; weigh the strength of evidence for or against particular tests, treatments, or procedures; and include estimates of expected health outcomes where data exist. Patient-specific modifiers, comorbidities, and issues of patient preference that may influence the choice of tests or therapies are considered. When available, information from studies on cost is considered, but data on efficacy and clinical outcomes constitute …
TL;DR: A. Alice K. Jacobs, MD, FACC, FAHA, Chair, 2009-2011 as discussed by the authors, and Sidney C. Smith, Jr., MD, FAACC, Immediate Past Chair, 2006-2008 
Abstract: Alice K. Jacobs, MD, FACC, FAHA, Chair, 2009–2011 Sidney C. Smith, Jr, MD, FACC, FAHA, Immediate Past Chair, 2006–2008 [⁎⁎⁎] Jeffrey L. Anderson, MD, FACC, FAHA, Chair-Elect Nancy Albert, PhD, CCNS, CCRN Christopher E. Buller, MD, FACC[⁎⁎⁎] Mark A. Creager, MD, FACC,
01 Jan 2011