Nitish R Mahapatra

Chromogranin A (CHGA) is ubiquitously expressed in secretory cells of the endocrine, neuroendocrine, and neuronal tissues. Although this protein has long been known as a marker for neuroendocrine tumors, its role in cardiovascular disease states including essential hypertension (EH) has only recently been recognized. It acts as a prohormone giving rise to bioactive peptides such as vasostatin-I (human CHGA1-76) and catestatin (human CHGA352-372) that exhibit several cardiovascular regulatory functions. CHGA is over-expressed but catestatin is diminished in EH. Moreover, genetic variants in the promoter, catestatin, and 3'-untranslated regions of the human CHGA gene alter autonomic activity and blood pressure. Consistent with these findings, targeted ablation of this gene causes severe arterial hypertension and ventricular hypertrophy in mice. Transgenic expression of the human CHGA gene or exogenous administration of catestatin restores blood pressure in these mice. Thus, the accumulated evidence establishes CHGA as a novel susceptibility gene for EH.

Catestatin is a 21-amino acid residue, cationic and hydrophobic peptide that is formed endogenously by proteolytic cleavage of its precursor chromogranin A, a major protein co-stored and co-released with catecholamines from the storage vesicles in adrenal chromaffin cells and adrenergic neurons. This peptide exhibits potent catecholamine release-inhibitory activity by acting on the neuronal nicotinic acetylcholine receptor. It also stimulates histamine release from mast cells via heterotrimeric G-proteins in a receptor-independent manner. Plasma levels of catestatin are diminished not only in hypertensive patients but also in their still-normotensive offspring, indicating its role in the pathogenesis of hypertension. Consistently, exogenous catestatin rescues hypertension in chromogranin A knockout mice and diminishes blood pressure responses to activation of sympathetic outflow in rats. These hypotensive actions of catestatin may be caused directly by autocrine inhibition of catecholamine release from the sympathoadrenal system and indirectly by paracrine stimulation of the potent vasodilator histamine release from mast cells. Recently, three human variants of catestatin displaying differential potencies for inhibition of catecholamine secretion have been identified. One of these variants (Gly364Ser) causes increased baroreceptor sensitivity, increased cardiac parasympathetic activity, and decreased cardiac sympathetic activity, and it seems to alter the risk for hypertension. These cardiovascular effects may have resulted by action of this peptide in the baroreceptor centre of the nucleus tractus solitarius. Thus, accumulating evidence documents the endogenous peptide catestatin as a novel regulator of cardiac function and blood pressure. © The Author 2008.

Catestatin (CST) is a catecholamine release-inhibitory peptide secreted from the adrenergic neurons and the adrenal glands. It regulates the cardiovascular functions and it is associated with cardiovascular diseases. Though its mechanisms of actions are not known, there are evidences of cross-talk between the adrenergic and CST signaling. We hypothesized that CST moderates the adrenergic overdrive and studied its effects on norepinephrine-mediated hypertrophic responses in H9c2 cardiac myoblasts. CST alone regulated the expression of a number of fetal genes that are induced during hypertrophy. When cells were pre-treated CST, it blunted the modulation of those genes by norepinephrine. Norepinephrine (2 µM) treatment also increased cell size and enhanced the level of Troponin T in the sarcomere. These effects were attenuated by the treatment with CST. CST attenuated the immediate generation of ROS and the increase in glutathione peroxidase activity induced by norepinephrine treatment. Expression of fosB and AP-1 promoter–reporter constructs was used as the endpoint readout for the interaction between the CST and adrenergic signals at the gene level. It showed that CST largely attenuates the stimulatory effects of norepinephrine and other mitogenic signals through the modulation of the gene regulatory modules in a characteristic manner. Depending upon the dose, the signaling by CST appears to be disparate, and at 10–25 nM doses, it primarily moderated the signaling by the β1/2-adrenoceptors. This study, for the first time, provides insights into the modulation of adrenergic signaling in the heart by CST.

Chromogranin A (CgA) is a prohormone and a granulogenic factor that regulates secretory pathways in neuroendocrine tissues. In β-cells of the endocrine pancreas, CgA is a major cargo in insulin secretory vesicles. The impact of CgA deficiency on the formation and exocytosis of insulin vesicles is yet to be investigated. In addition, no literature exists on the impact of CgA on mitochondrial function in β-cells. Using three different antibodies, we demonstrate that CgA is processed to vasostatin- and catestatin-containing fragments in pancreatic islet cells. CgA deficiency in Chga-KO islets leads to compensatory overexpression of chromogranin B, secretogranin II, SNARE proteins and insulin genes, as well as increased insulin protein content. Ultrastructural studies of pancreatic islets revealed that Chga-KO β-cells contain fewer immature secretory granules than wild-type (WT) control but increased numbers of mature secretory granules and plasma membrane-docked vesicles. Compared to WT control, CgA-deficient β-cells exhibited increases in mitochondrial volume, numerical densities and fusion, as well as increased expression of nuclear encoded genes (Ndufa9, Ndufs8, Cyc1 and Atp5o). These changes in secretory vesicles and the mitochondria likely contribute to the increased glucose-stimulated insulin secretion observed in Chga-KO mice. We conclude that CgA is an important regulator for coordination of mitochondrial dynamics, secretory vesicular quanta and GSIS for optimal secretory functioning of β-cells, suggesting a strong, CgA-dependent positive link between mitochondrial fusion and GSIS.

Chromogranin A (CHGA) is a major protein in the secretory granules of chromaffin cells. CHGA also gives rise to cardiovascular/metabolism regulatory peptides, such as catestatin (CST) and pancreastatin (PST). While CST is a potent inhibitor of catecholamine secretion, PST is a potent physiological inhibitor of glucose-induced insulin secretion. Recently, several SNPs were identified in the CST and PST domains of CHGA locus in different populations. Among the discovered SNPs, CST variant allele Ser-364 was associated with blood pressure alteration and PST variant allele Ser-297 was associated with significantly higher plasma glucose level. In this study, we examined whether these CST and PST variant alleles exist and influence cardiovascular and metabolic phenotypes in Japanese population. Our study comprised of 343 Japanese subjects aged 45-85 years (143 men and 200 women, mean age 66 ± 8 years). We determined the genotypes of CST and PST by PCR-direct sequencing method and carried out genotype-phenotype association analysis. In 343 participants, the minor allele frequency of CST variant Ser-364 was 6.10%. On the other hand, we did not detect the PST variant Ser-297 in this entire study population. The presence of Ser-364 allele was associated with increased in baPWV (an index of systemic arterial stiffness) that suggests an initiation and/or progression atherogenesis and hypertension. The Ser- 364 allele was also associated with elevated systolic blood pressure and pulse pressure, consistent with increased baPWV. In conclusion, the CST Ser-364 allele may increase the risk for cardiovascular diseases in Japanese population.

Catestatin (CST), a chromogranin-A-derived peptide, is a potent endogenous inhibitor of the neuronal nicotinic acetylcholine receptor (nAChR). It exerts an anti-hypertensive effect by acting as a 'physiological brake' on transmitter release into the circulation. However, the mechanism of interaction of CST with nAChR is only partially understood. To unravel molecular interactions of the wild-type human CST (CST-WT) as well as its naturally occurring variants (CST-364S and CST-370L, which have Gly→Ser and Pro→Leu substitutions, respectively) with the human α 3β4 nAChR, we generated a homology-modeled human α3β4 nAChR structure and solution structures of CST peptides. Docking and molecular dynamics simulations showed that ~90% of interacting residues were within 15 N-terminal residues of CST peptides. The rank order of binding affinity of these peptides with nAChR was: CST-370L>CSTWT>CST-364S; the extent of occlusion of the receptor pore by these peptides was also in the same order. In corroboration with computational predictions, circular dichroism analysis revealed significant differences in global structures of CST peptides (e.g. the order of α-helical content was: CST-370L>CST-WT>CST-364S). Consistently, CST peptides blocked various stages of nAChR signal transduction, such as nicotine- or acetylcholine-evoked inward current, rise in intracellular Ca2+ and catecholamine secretion in or from neuron-differentiated PC12 cells, in the same rank order. Taken together, this study shows molecular interactions between human CST peptides and human α3β4 nAChR, and demonstrates that alterations in the CST secondary structure lead to the gain of potency for CST-370L and loss of potency for CST-364S. These findings have implications for understanding the nicotinic cholinergic signaling in humans. © 2012.