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Abstract

Despite advances in modern medicine, heart failure (HF) is one of the leading causes of death in developed countries. HF is a progressive condition that gradually affects the heart. It is a common end point for all heart diseases. There is no definite treatment currently available. Therapeutic approaches focus on slowing the progress of the disease but do not treat the underlining molecular changes in the heart. Therefore, a novel approach is needed to effectively treat the underlining molecular causes of HF. Relaxin (RLN) and its cognate receptor, RXFP1, have recently gained recognition in the setting of cardiovascular disease because of their beneficial vasodilator, anti-fibrotic, anti-apoptotic, and other properties. Furthermore, studies have shown that activation of RXFP1 by RLN induces positive inotropic effects from both failing and non-failing atrial myocardium. Interestingly, ventricular cardiomyocytes do not respond to RLN treatment due to a distinct RXFP1 expression pattern between atria and ventricles. Thus, the aim of this study was to investigate the effects of a combined RXFP1 gene transfer with RLN stimulation in the setting of a murine HF model. A trans-aortic constriction (TAC) operation was performed on mice to induce HF. Adeno-associated virus (AAV) was used for gene transfer followed by chronic RLN administration via osmotic pumps. Further investigation of the RXFP1 signaling pathway was also performed in an in vitro setting to support the findings from the in vivo model. AAV transduction achieved a stable overexpression of RXFP1 in the ventricle. No adverse effect from the viral treatment was detected in either healthy or HF animals. RXFP1 gene therapy with chronic RLN administration was able to rescue TAC induced HF, while RXFP1 gene therapy alone only protected the animals from the development of severe HF. RXFP1 activation significantly affected cAMP accumulation and phosphorylation of phospholamban (PLB) at serine 16 leading to an increase in sarcoplasmic reticulum (SR) Ca2+ content which might explain the observed positive inotropy. Prolonged RXFP1 activation did not result in detrimental Ca2+ mishandling like other inotropic stimuli. Finally, the RXFP1-RLN signaling pathway resembled that of other β-adrenergic signaling pathways but with a significant reduction in initial activation strength, which seemed to be pivotal for prolonged inotropic effects and favorable molecular changes. In conclusion, gene therapy treatment consisting of RXFP1 overexpression and chronic RLN administration could rescue HF by artificially inducing inotropic responses in the ventricle through ectopic expression of RXFP1 with RLN administration.