Impaired retinoic acid signaling mediated Rbm20 downregulation induces aberrant splicing of CaV1.2 calcium channel: implications in myocardial hypertrophy.

AIMS: Myocardial hypertrophy, a pathological adaptation to chronic stress, predisposes to heart failure through dysregulated calcium handling. Alternative splicing (AS) of CaV1.2 calcium channel participates in myocardial hypertrophy, and RNA-binding motif protein 20 (Rbm20) regulates CaV1.2 AS. Moreover, impaired retinoic acid receptor β (RARβ) is implicated in cardiac pathologies, but its roles in handling cardiac intracellular calcium during myocardial hypertrophy remain unknown. Here, we explore whether impaired RARβ exacerbates cardiac pathological remodeling by disrupting Rbm20-mediated CaV1.2 AS.

METHODS AND RESULTS: Transverse aortic constriction (TAC) and isoproterenol (ISO)-induced murine hypertrophic hearts showed increased CaV1.2 alternative exon 9* (CaV1.2E9*), accompanied with reduced Rbm20 expression. Rbm20 downregulated CaV1.2 exon 9* in cardiomyocytes. Bioinformatic analysis of human hypertrophic cardiomyopathy datasets revealed impaired RA signaling, marked by RARβ downregulation, which was confirmed in TAC hearts and ISO-treated neonatal rat ventricular myocytes (NRVMs). RARβ knockdown increased the proportion of CaV1.2E9* channels and K+-triggered intracellular Ca2+ concentration ([Ca2+]i) in NRVMs. Chromatin immunoprecipitation and dual-luciferase assays identified that RARβ directly binds to Rbm20 promoter region, and adapalene (ADP), a selective RARβ agonist, increased their binding affinity. For clinical relevance, ADP restored Rbm20 expression, normalized CaV1.2E9* splicing, decreased K+-triggered [Ca2+]i, and attenuated cardiomyocyte hypertrophy. In vivo, ADP administration alleviated myocardial hypertrophy in TAC mice.

CONCLUSION: Our findings reveal impaired RARβ drives CaV1.2 aberrant splicing by downregulating Rbm20, establishing a feedforward loop of intracellular calcium imbalances and hypertrophic remodeling. Significantly, ADP restores CaV1.2 AS and intracellular calcium homeostasis by activating RARβ in cardiomyocytes, highlighting a novel therapeutic approach for myocardial hypertrophy.