The chromogranin A fragment catestatin: specificity, potency and mechanism to inhibit exocytotic secretion of multiple catecholamine storage vesicle co-transmitters

Background Secretory granules of chromaffin cells and neurons co-store and release, by exocytosis, the acidic soluble protein chromogranin A (human, CHGA; rodent, Chga) along with catecholamines, neuropepticles and adenosine triphosphate (ATP). CHGA serves as a proprotein and upon proteolytic cleavage it generates active peptides, including catestatin (human CHGA(352-372)), first discovered in adrenal medullary chrornaffin granules. Studies in our laboratory demonstrated that catestatin acts at the nicotinic acetylcholine receptor to inhibit catecholamine secretion. However, the specificity of catestatin to exert nicotinic - cholinergic antagonism among its co-transmitters is not clearly known, nor is the potential effect of catestatin on multiple vesicle co-transmitters understood. Aim Here we probed the specificity of catestatin's actions among its co-transmitters: catecholamines, ATP, and neuropeptide Y (NIPY). Methods We studied the effects of each transmitter on exocytotic secretion of its co-transmitters from PC12 chromaffin cells, stimulating secretion by triggering physiological pathways at multiple sites. Results We observed that, among chrornaffin granule co-transmitters, only catestatin and NPY inhibited catecholamine release induced by nicotinic-cholinergic stimulation; catestatin was more than tenfold more potent than NPY in this setting. We also stimulated norepinephrine secretion by other chromaffin cell agonists: catestatin blocked norepinephrine release induced by nicotine, but not by other agents (such as membrane depolarization) acting at later stages in the secretory pathway, nor by agents acting on other receptor classes. By contrast, NPY acted less specifically, blocking norepinephrine release triggered by either nicotine or membrane depolarization. Catestatin inhibited nicotinic - cholinergic co-release of all classes of chromaffin granule co-transmitters: catecholamines, chromogranins, neuropepticles, and ATP. Naturally occurring variants of human catestatin (Gly364Ser and Pro370Leu) exhibited parallel changes in potency to inhibit secretion of catecholamines and ATP. Conclusion We conclude that, among the chromaffin granule co-transmitters, catestatin acts as the most specific and potent inhibitor of physiological pathway (nicotinic-cholinergic) stimulated secretion. Furthermore, catestatin generally inhibits nicotinically triggered exocytotic release of multiple co-transmitters from chromaffin granules. The results have physiological and pharmacological implications for co-transmission in the sympathochromaffin system.