Abstract 13392: Deficiency of Microrna-378 Contributes to the Development of Cardiac Fibrosis Involving a Tgfβ1-dependent Paracrine Mechanism

Abstract

Understanding the regulation of cardiac fibrosis is critical for controlling adverse cardiac remodeling during the development of heart failure. Previous studies implicated that microRNA-378 is primarily expressed in cardiomyocytes, and it is down-regulated during heart failure. To understand the consequence of miR-378 depletion during cardiac remodeling, the present study employed a LNA-modified-antimiR to target miR-378 in vivo. Results showed that loss of miR-378 function in mouse hearts led to the development of cardiomyocyte hypertrophy and fibrosis. Upon evaluation of the mechanism of profibrotic response of miR-378 inhibition, we found that antimiR treatment induced TGFβ1 expression in mouse hearts as well as in cultured cardiomyocytes, whereas its expression in cardiomyocytes abolished AngII-stimulated induction of TGFβ1 mRNA. Among various secreted cytokines, only TGFβ1 levels were found to be increased in the conditioned-media of miR-378 depleted cardiomyocytes. Treatment of cardiac fibroblasts with the conditioned-media of miR-378 depleted myocytes activated pSMAD2/3, a critical step in TGFβ-signaling, and induced fibrotic gene expression. This effect of miR-378 depletion was counteracted by including a TGFβ1-neutralizing antibody in the conditioned-medium. In cardiomyocytes, antimiR-mediated stimulation of TGFβ1 mRNA was correlated with the increased expression of c-fos and c-jun. Adenovirus expressing dominant negative N-Ras or c-Jun prevented antimiR-mediated induction of TGFβ1 mRNA, documenting the importance of Ras and AP-1 signaling in this response. These results demonstrate that reduction in miR-378 levels during pathological conditions participate in the process of cardiac remodeling through paracrine release of a profibrotic cytokine, TGFβ1, from cardiomyocytes. Our data imply that the presence of miR-378 in cardiomyocytes plays a critical role in the protection of neighboring fibroblasts from activation by pro-fibrotic stimuli.