Relaxin independent cardio protection by cardiomyocyte-specific RXFP1-overexpression

J. Wingert (Heidelberg)¹, E. Meinhardt (Heidelberg)¹, N. Sasipong (Heidelberg)¹, M. Pott (Heidelberg)¹, P. Most (Heidelberg)², H. A. Katus (Heidelberg)¹, N. Frey (Heidelberg)¹, P. Raake (Augsburg)³, P. Schlegel (Heidelberg)^1
1Universitätsklinikum Heidelberg Klinik für Innere Med. III, Kardiologie, Angiologie u. Pneumologie Heidelberg, Deutschland; ²Universitätsklinikum Heidelberg Innere Medizin III, Inst. für Molekulare und Translationale Kardiologie Heidelberg, Deutschland; ³Universitätsklinikum Augsburg I. Medizinische Klinik Augsburg, Deutschland

Objective:
Cardiomyocyte (CM)-specific overexpression of Relaxin-receptor 1 (RXFP1), along with additional Relaxin (RLN) supplementation, significantly attenuates heart failure (HF) in a pressure-overload model induced by transverse aortic constriction (TAC).
Transgenic mice with high levels of CM-specific overexpression of human RXFP1 (hRXFP1tg) exhibit protection from TAC-induced HF even in the absence of exogenous RLN supplementation. This finding suggests a potential RXFP1 receptor activity that occurs even without its cognate ligand. To further investigate this hypothesis, a RLN knockout model was employed to examine the role of endogenous RLN in receptor activation and its effects on heart failure progression.

Methods and results:
Transgenic mice with a systemic RLN-knockout (RLNko) were generated. hRXFP1tg were cross bred with RLNko to generate transgenics with a CM-specific overexpression of human RXFP1 in the absence of systemic RLN (hRXtg/RLNko).
To evaluate cardioprotective RXFP1 effects in the absence of endogenous RLN, hRXtg/RLNko and RLNko controls were subjected to TAC. CM-specific RXFP1 overexpression protects from TAC-induced pressure overload even in the absence of systemic RLN, with TAC/hRXtg/RLNko presenting not only less decline in systolic left ventricular (LV) function but also abrogated LV dilation and cardiac hypertrophy compared to TAC/RLNko mice. Molecularly, TAC/hRXtg/RLNko hearts showed attenuated activation of the fetal gene program as well as less CM hypertrophy in histological sections compared to TAC/RLNko hearts.
Additionally, we observed attenuated activation of fetal genes in hRXtg/RLNko compared to RLNko. This aligns with previous findings that RLNko induces cardiac fibrosis, supporting the notion that the absence of endogenous RLN serves as a pathological stimulus that could be mitigated by hRXFP1 overexpression.

Conclusion:
CM-specific RXFP1 overexpression protects from TAC-induced HF even in the absence of systemic RLN, suggesting an alternative mechanism of receptor activation through intrinsic activity, alternative endogenous ligands or crosstalk with other receptors.