Abstract 20413: Microrna-195 Promotes Apoptosis in Cardiomyocytes by Down-Regulating Sirt1
Background: Saturated free fatty acids induce apoptosis in cardiomyocytes, which is implicated in diabetic cardiomyopathy. However, the underlying mechanisms remain not fully understood. MiRNAs are a class of short RNA molecules and they repress their target gene expression and/or protein translation. MiRNAs have been involved in cardiac pathophysiology. This study was to examine whether miR-195 regulates palmitate-induced cardiomyocyte apoptosis by targeting Sirt1, a member of the silent information regulator (Sir2) family.
Methods and Results: In cultured neonatal mouse cardiomyocytes, incubation with palmitate up-regulated miR-195 expression, increased reactive oxygen species (ROS) production and induced apoptosis as determined by up-regulation of caspase-3 activity and DNA fragmentation as well as reduction of Bcl-2. Knockdown of miR-195 by its antagomir decreased ROS production and apoptosis in palmitate-stimulated cardiomyocytes. In contrast, miR-195 mimic enhanced palmitate-induced ROS production and apoptosis. The induction of miR-195 paralleled a reduction of Sirt1, a known anti-apoptotic protein, in palmitate-stimulated cardiomyocytes. We further showed that miR-195 targeted the Sirt1 protein through the conserved target site located in the 3′ un-translational region of Sirt1 mRNA. In concordance, knockdown of miR-195 increased whereas transfection of miR-195 mimic reduced endogenous Sirt1 protein levels in cardiomyocytes. Furthermore, activation of Sirt1 by resveratrol inhibited palmitate-induced apoptosis. On the other hand, knockdown of Sirt1 by siRNA or inhibition of Sirt1 with nicotinamide enhanced apoptosis. The inhibitory effect of Sirt1 on apoptosis was associated with a reduction of ROS in palmitate-stimulated cardiomyocytes.
Conclusions: This study for the first time demonstrates an important pro-apoptotic role of miR-195 in cardiomyocytes and identifies Sirt1 as a direct target of miR-195. The effect of miR-195 on apoptosis is mediated through down-regulation of Sirt1 and elevation of ROS production. Thus, these findings provide a novel signalling mechanism by which palmitate induces apoptosis via miR-195/Sirt1/ROS pathways in cardiomyocytes.
- © 2010 by American Heart Association, Inc.