Human recombinant chromogranin A-derived vasostatin-1 mimics preconditioning via an adenosine/nitric oxide signaling mechanism

Abstract

The acidic protein chromogranin A (CgA) is the precursor of several regulatory peptides generated by specific proteolytic processes. Human recombinant CgA NH2-terminal fragment STA-CgA1-78 (hrSTA-CgA1-78), containing vasostatin-1 (CgA1-76) domain, exerts a negative inotropic effect and counteracts the β-adrenergic positive inotropic effect on the rat heart. We hypothesized an involvement of nitric oxide (NO)-dependent pathway in both cardiodepression and cardioprotection by hrSTA-CgA1-78. We also hypothesized an involvement of adenosine A1 receptor and protein kinase C (PKC) in cardioprotection by hrSTA-CgA1-78. Therefore, we evaluated whether 1) the cardioinhibition mediated by hrSTA-CgA1-78 involves the Gi/o proteins/NO-dependent signal transduction cascade, 2) hrSTA-CgA1-78 induces ischemic preconditioning-like protective effects on the myocardium, and 3) inhibition of NO synthase (NOS), adenosine A1 receptor, or PKC affects hrSTA-CgA1-78 protection. Using the isolated rat heart, we found that the reduction of left ventricular pressure (LVP), rate-pressure product, and maximal values of the first derivative of LVP elicited by hrSTA-CgA1-78 at 33 nM is abolished by blocking Gi/o proteins with pertussis toxin, scavenging NO with hemoglobin, and blocking NOS activity with NG-monomethyl-l-arginine or N5-(iminoethyl)-l-ornithine, soluble guanylate cyclase with 1 H-[1,2,4]oxadiazole-[4,4-a]quinoxalin-1-one, and protein kinase (PKG) with KT5823. Data suggest the involvement of the Gi/o proteins/NO-cGMP-PKG pathway in the hrSTA-CgA1-78-dependent cardioinhibition. When given before 30 min of ischemia, hrSTA-CgA1-78 significantly reduced the size of the infarct from 64 ± 4 to 32 ± 3% of the left ventricular mass. This protective effect was abolished by either NOS inhibition or PKC blockade and was attenuated, but not suppressed, by the blockade of A1 receptors. These results suggest that hrSTA-CgA1-78 activity triggers two different pathways: one of these pathways is mediated by A1 receptors, and the other is mediated by NO release. As with repeated brief preconditioning ischemia, hrSTA-CgA1-78 may be considered a stimulus strong enough to trigger both pathways, which may converge on PKC.