C-type natriuretic peptide plays a fundamental role in cardiac function

S. M. Chu, A. J. Moyes, A. J. Hobbs. William Harvey Research Institute, Barts and The London, Queen Mary University of London, London, United Kingdom.

Introduction: C-type natriuretic peptide (CNP) is synthesised and released by the endothelium and plays a vital role in the maintenance of vascular homeostasis (Moyes et al. 2014. J. Clin. Invest. 124:4039). However, a similar regulatory role of endogenous CNP in the heart has yet to be elucidated. Therefore, we generated two unique mouse strains (C57BLK6 background) with endothelium (Tie²-Cre) and cardiomyocyte (αMHC-Cre)-restricted deletion of CNP to investigate if the peptide modulates coronary vascular reactivity and cardiac function.

Method: Langendorff isolated hearts were used to investigate the effect of CNP deletion on coronary vascular reactivity in response to the endothelium-dependent vasodilators bradykinin (10nmol), acetylcholine (0.1-1nmol), and reactive hyperaemia (80s flow cessation). Ischaemia-reperfusion (I/R) injury (35mins ischaemia followed by 60mins reperfusion) was also investigated in cell-specific knockout animals. Pressure overload-induced heart failure (abdominal aortic constriction [AAC]; 6 weeks) was used to study the effect of CNP deletion during cardiac stress. Echocardiography was performed before and after AAC and fibrosis determined by picrosirius red staining. A subset of experiments were repeated in mice with global deletion of natriuretic peptide receptor-C (NPR-C) to delineate the signalling pathway triggered by CNP. Data are presented as mean±SEM and statistical analyses were performed using unpaired Student’s t-test, or one- or two-way ANOVA with Bonferroni post-hoc tests.

Results: Coronary endothelial reactivity was reduced in endothelial CNP knockout (ecCNP KO) mice compared to wildtype (WT) in response to bradykinin (21.14±2.89% vs 31.68±2.68%; P<0.05; n=7-9), acetylcholine (23.62±6.08% vs 39.84±5.36%; P<0.05; n=7-9) and reactive hyperaemia (1493±280.8a.u vs 2804±456.6a.u; P<0.05; n=6-8). These observations were paralleled in NPR-C KO animals. ecCNP KO did not exacerbate I/R injury, whilst mice with cardiomyocyte-restricted deletion of CNP (cmCNP KO) and NPR-C KO animals exhibited a larger infarct size compared to WT (cmCNP KO 35.89±3.64% vs 13.02±1.70%; P<0.0005; n=8-12; NPR-C KO 35.21±4.46% vs 18.20±4.35%; P<0.05; n=7-8). cmCNP KO mice also displayed greater cardiac dysfunction and fibrosis after AAC compared to WT (ejection fraction (EF), 50.35±2.32% vs 64.72±0.81%; fibrosis, 4.14±0.35% vs 2.94±0.35%; both P<0.05; n=9-10); similar results were observed in NPR-C KO animals. Infusion of CNP (0.2mg/kg/day; osmotic minipump, s.c.) in WT, but not NPR-C KO, animals rescued the decline in cardiac function.

Conclusions: Endothelial and cardiomyocyte-derived CNP have distinct, complementary roles in the heart, modulating cardiac function by influencing coronary vascular tone and protecting against heart failure and I/R injury. These protective effects of CNP are mediated, at least in part, via NPR-C.