The chromogranin A fragment reveals how a single change in the protein sequence exerts strong cardioregulatory effects by engaging neuropilin-1.

Aim: Chromogranin A (CgA), a 439-residue long protein, is an important cardiovascular regulator and a precursor of various bioactive fragments. Under stressful/pathological conditions, CgA cleavage generates the CgA proangiogenic fragment. The present work investigated the possibility that human CgA influences the mammalian cardiac performance, evaluating the role of its C-terminal sequence.

Methods: Haemodynamic assessment was performed on an ex vivo Langendorff rat heart model, while mechanistic studies were performed using perfused hearts, H9c2 cardiomyocytes and in silico.

Results: On the ex vivo heart, CgA elicited direct dose-dependent negative inotropism and vasodilation, while CgA , a fragment lacking the C-terminal R residue, was ineffective. Antibodies against the PGPQLR C-terminal sequence abrogated the CgA -dependent cardiac and coronary modulation. Ex vivo studies showed that CgA -dependent effects were mediated by endothelium, neuropilin-1 (NRP1) receptor, Akt/NO/Erk1,2 pathways, nitric oxide (NO) production and S-nitrosylation. In vitro experiments on H9c2 cardiomyocytes indicated that CgA also induced eNOS activation directly on the cardiomyocyte component by NRP1 targeting and NO involvement and provided beneficial action against isoproterenol-induced hypertrophy, by reducing the increase in cell surface area and brain natriuretic peptide (BNP) release. Molecular docking and all-atom molecular dynamics simulations strongly supported the hypothesis that the C-terminal R residue of CgA directly interacts with NRP1.

Conclusion: These results suggest that CgA is a new cardioregulatory hormone and that the removal of R represents a critical switch for turning "off" its cardioregulatory activity.