Chromaffin Cell physiology: Novel molecular approaches

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DESCRIPTION (provided by applicant): Chromogranin A (CHGA) is a 48 kDa acidic proprotein giving rise to biologically active peptides including a novel fragment (bovine CHGA344-364; human CHGA352-372) which we have discovered and called "catestatin," that acts as a potent (IC50 about200-400 nM) and specific inhibitor of nicotine-induced catecholamine (CA) secretion and agonist desensitization. We have recently generated CHGA knockout (Chga-/-) mice that displayed higher systolic (SBP) and diastolic blood pressure (DBF), and non-dipping. We also identified 3 naturally occurring human catestatin variants (Gly364Ser, Pro370Leu, Arg374Gln). We found that Gly364Ser variant causes profound alteration in human autonomic activity. This proposal explores the mechanism of development of hypertension in Chga-/- mice, modulation by nicotine, mechanism of action of catestatin variants in su perfused rat adrenal gland and generation of catestatin variants through 4 specific aims: Aim I. Explore the mechanism of development of higher SBP and DBP in Chga-/- mice and nicotinic modulation of BP phenotype. "Rescue" the elevated BP phenotype in Chga-/- mice by introduction of a bacterial artificial chromosome (BAG) containing the human CHGA gene (CHGA +) into the germline of Chga-/- mice. Aim II. Generation of mice with conditional Chga-/- in phenylethanolamine N-methyl transferase (Chga-Pnmt-/-) producing cells, to determine whether ablation of Chga restricted to adrenergic cells is sufficient to cause hypertension and its associated nicotinic response alterations. Aim III. Determine the effects of human catestatin variants (Gly364Ser, Pro370Leu, Arg374Gln) on nicotine-evoked CA secretion from superfused rat adrenal gland and desensitization. Aim IV. Proteolytic processing of human CHGA to generation of human catestatin variants. These studies, utilizing unique knockout, transgenic, and human variants of catestatin, are likely to establish novel catestatin mechanisms in the development of hypertension and its modulation through nicotinic-cholinergic receptors.