Trbp inhibits cardiac fibrosis through TGF-β pathway-mediated cross-talk between cardiomyocytes and fibroblasts.

Cardiac remodeling in response to disease or tissue damage severely impairs heart function. Therefore, the description of the molecular mechanisms responsible is essential for the development of effective therapies. Trbp (Tarbp2) is a multifunctional RNA-binding protein that is essential during heart development, but its role in the adult heart and cardiac remodeling remains unknown. We generated inducible conditional knockout mice to delete Trbp from cardiomyocytes in young adults (Trbp-cKOs). While Trbp-cKO mice did not display a detectable phenotype, under stress conditions induced by transverse aortic constriction pressure overload, they rapidly developed severe heart failure; this was associated with maladaptive cardiac remodeling and increased interstitial fibrosis. RNA-sequencing revealed the induction of a fibrotic gene expression network and the TGF-β signaling pathway in Trbp-cKO hearts. In cultured neonatal rat ventricle cardiomyocytes (NRCMs), inhibition of Trbp resulted in an induction of the expression of both Tgfβ2 and Ltbp2; in contrast, Trbp overexpression repressed Tgfβ2 expression. Knockdown of Trbp in NRCMs that were co-cultured with neonatal rat cardiac fibroblasts (NRCFs) resulted in an increase in fibrotic gene expression. However, knockdown of Trbp in NRCMs combined with knockdown of Tgfβ2 in NRCFs using the same co-culture system failed to induce the same change in fibrotic gene expression. These data provide evidence for a critical role for Trbp in regulating cardiac fibrosis during cardiac remodeling mediated by cross-talk between cardiomyocytes and fibroblasts. The link to TGF-β signaling also highlights its importance and reveals a novel approach to intervention by targeting of Trbp.