RNA-Binding Protein MBNL2 Drives Cardiac Hypertrophy and Dysfunction by Facilitating TPM3 Splicing

Cardiac hypertrophy is a major contributor to heart failure development, making its prevention and treatment critical for reducing heart failure-associated mortality. Although alternative splicing is recognized as a key regulatory mechanism in myocardial hypertrophy, the precise pathways involved remain incompletely defined.

To investigate the role of MBNL2 (muscleblind-like protein 2) in the heart, we overexpressed MBNL2 in cardiomyocytes via adeno-associated virus serotype 9 delivery. In addition, cardiomyocyte-specific MBNL2 knockout mice were generated, and transverse aortic constriction surgery or isoproterenol injection was performed to induce cardiac hypertrophy and dysfunction in mice. The underlying mechanisms were further investigated using RNA sequencing, alternative splicing analysis, and RNA immunoprecipitation.

MBNL2 expression was significantly increased in the heart tissues from patients with ischemic cardiomyopathy and in mice with cardiac hypertrophy. Cardiac-specific overexpression of MBNL2 induced cardiac hypertrophy and dysfunction. Mechanistically, MBNL2 promoted exon 9 skipping of TPM3 (tropomyosin 3), generating the TPM3 isoform lacking exon 9 (TPM3-Δe9). In neonatal mouse cardiomyocytes, TPM3-Δe9 knockdown partially reduced oxidative stress and mitigated mitochondrial damage induced by MBNL2 overexpression. Adeno-associated virus serotype 9-mediated knockdown of TPM3-Δe9 partially attenuated cardiac hypertrophy in MBNL2-overexpressing mice. Notably, cardiac-specific MBNL2 knockout or TPM3-Δe9 knockdown in mice attenuated cardiac dysfunction induced by transverse aortic constriction. Further, we found that elevated TPM3-Δe9 was associated with RNF20 (ring finger protein 20) and was accompanied by reduced RNF20 interaction with NCoR1 (nuclear receptor corepressor 1), increased NCoR1 expression, and decreased PPARα (peroxisome proliferator-activated receptor alpha) signaling. The protective effects of MBNL2 or TPM3-Δe9 knockdown in hypertrophic cardiomyocytes were partially reversed by treatment with the PPARα inhibitor GW6471.

This study uncovers a novel, critical role for MBNL2 in pathological cardiac hypertrophy through regulation of TPM3 alternative splicing and mitochondrial function, highlighting MBNL2 as a potential therapeutic target for cardiac hypertrophy and dysfunction.