The novel Chromogranin A-derived serpinin and pyroglutaminated serpinin peptides are positive cardiac beta-adrenergic-like inotropes

Three forms of serpinin peptides, serpinin (Ala26Leu), pyroglutaminated (pGlu)-serpinin (pGlu23Leu) and serpinin-Arg-Arg-Gly (Ala29Gly), are derived from cleavage at pairs of basic residues in the highly conserved C terminus of Chromogranin A (CgA). Serpinin induces PN-1 expression in (neuro)endocrine cells to up-regulate granule biogenesis via a cAMP-protein kinase A-Sp1 pathway, while pGlu-serpinin inhibits cell death. The aim of this study was to test the hypothesis that serpinin peptides are produced in the heart and act as novel β-adrenergic-like cardiac modulators. We detected serpinin peptides in the rat heart by HPLC and ELISA methods. The peptides included predominantly Ala29Gly and pGlu-serpinin and a small amount of serpinin. Using the Langendorff perfused rat heart to evaluate the hemodynamic changes, we found that serpinin and pGlu-serpinin exert dose-dependent positive inotropic and lusitropic effects at 11-165 nM, within the first 5 min after administration. The pGlu-serpinin-induced contractility is more potent than that of serpinin, starting from 1 nM. Using the isolated rat papillary muscle preparation to measure contractility in terms of tension development and muscle length, we further corroborated the pGlu-serpinin-induced positive inotropism. Ala29Gly was unable to affect myocardial performance. Both pGlu-serpinin and serpinin act through a β1-Adrenergic Receptor/Adenylate Cyclase/cAMP/PKA pathway, indicating that, contrary to the β-blocking profile of the other CgA-derived cardiosuppressive peptides, vasostatin-1 and catestatin, these two C-terminal peptides act as β-adrenergic-like agonists. In cardiac tissue extracts, pGlu-serpinin increased intracellular cAMP levels and phosphorylation of Phospholamban(PNL)ser16, ERK1/2 and GSK-3β. Serpinin and pGlu-serpinin peptides emerge as novel β-adrenergic inotropic and lusitropic modulators, suggesting that CgA and the other derived cardioactive peptides can play a key role on how the myocardium orchestrates its complex response to sympatho-chromaffin stimulations.