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.