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). However, a similar regulatory role of endogenous CNP in the heart has yet to be elucidated. Therefore, I have used three unique mouse strains with endothelium (Tie2-Cre), cardiomyocyte (αMHC-Cre) and fibroblast (Col1α2-Cre)-restricted deletion of CNP to investigate if the peptide modulates coronary vascular reactivity and cardiac function. Methods: 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) and acetylcholine (0.1-1nmol). Vasodilatation associated with reperfusion was investigated by transient cessation of flow (20-80 seconds). Ischaemia reperfusion (IR) injury (35 minutes ischaemia followed by 60 minutes reperfusion) was also investigated in cell-specific knockout (KO) animals. Isoprenaline (ISO; 20mg/kg/day, 7days)- and pressure overload (abdominal aortic constriction [AAC]; 6 weeks)-induced heart failure were used to study the effect of CNP deletion during cardiac stress, with cardiac function assessed by echocardiography. Cardiac fibrosis and hypertrophy were determined by picro-sirius red and wheat-germ agglutinin fluorescence staining, respectively. A subset of experiments was repeated in mice with global deletion of natriuretic peptide receptor-C (NPR-C) to delineate the signalling pathway triggered by CNP. Real time qPCR was used to determine hypertrophic and fibrotic gene expression in left ventricles isolated from mice subjected to AAC or sham. Neonatal cardiomyocytes were isolated to investigate angiotensin (Ang)II-induced hypertrophy. Results: Coronary endothelial reactivity was reduced in endothelial CNP (ecCNP) KO mice compared to wild type (WT) in response to bradykinin, acetylcholine and reperfusion-induced vasodilatation. These observations were paralleled in NPR-C KO animals. ecCNP KO did not exacerbate IR 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 mice also displayed greater cardiac dysfunction and fibrosis after ISO infusion or AAC compared to WT; similar results were observed in fbCNP KO and NPR-C KO animals. Infusion of CNP (0.2mg/kg/day; osmotic mini-pump, s.c.) in WT, but not NPR-C KO, animals rescued the decline in cardiac function. CNP (1μM) administration in isolated cardiomyocyte also blunted Ang II-induced hypertrophy. Pro-hypertrophic and pro-fibrotic gene expression (ANP, β-MHC and MMP-2) was augmented in cmCNP KO and NPR-C KO mice compared to littermate controls following AAC. Conclusions: Endothelial, cardiomyocyte and fibroblast-derived CNP have distinct, complementary roles in the heart, modulating cardiac function by influencing coronary vascular tone and protecting against heart failure and IR injury. These protective effects of CNP are mediated, at least in part, via NPR-C activation. Developing CNP mimetics or selective NPR-C agonists could be a novel therapeutic intervention in cardiovascular disease.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:766256 |
| Date | January 2018 |
| Creators | Chu, Sandy Min Yin |
| Publisher | Queen Mary, University of London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://qmro.qmul.ac.uk/xmlui/handle/123456789/54048 |
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