miR-146a mediates inflammatory changes and fibrosis in the heart in diabetes

Hyperglycemia induced endothelial injury is a key pathogenetic factor in diabetic cardiomyopathy. In diabetes, changes in pro-inflammatory cytokines are a key mechanism leading to cardiac fibrosis. We have previously demonstrated alteration of miR-146a in chronic diabetic complications. Here, we investigated the role of endothelial miR-146a in mediating inflammation and fibrosis in diabetic cardiomyopathy. To examine the effects of miR-146a on the inflammatory mediators, an endothelial specific miR-146a overexpressing transgenic mice (TG) using tie-2 promoter, was generated. We examined these mice and wild type littermate controls with or without STZ induced diabetes. Transthoracic echocardiography was performed. Cardiac tissues were examined for inflammatory cytokine mRNAs and proteins by real time RT-PCR or ELISA. Cardiac fibrosis was examined by histology staining. Human cardiac microvascular endothelial cells (HCMECs) and primary endothelial cells isolated from mice were used following incubation with various levels of glucose with or without miR-146a mimics or antagomir transfection. In hearts of wild type mice with diabetes, increased expression of inflammatory markers and extracellular matrix proteins (IL6, TNFα, IL-1β, MCP-1, NF-κB, Col1α1, Col4α1) were seen compared to wild type controls. These changes were prevented in the diabetic TG mice. In addition, WT diabetic mice showed cardiac functional abnormalities, which were improved in the diabetic TG mice. In vitro studies showed glucose induced increase the expressions of the above inflammatory cytokines and specific NF-κB regulators (IRAK1 &TRAF6). Such changes were corrected in the HCMECs following miR-146a mimic transfection. These data indicate that in diabetes, increased inflammatory cytokine and extracellular matrix protein productions and associated cardiac functional alterations are regulated by endothelial miR-146a. Identification of such mechanisms may potentially lead to the development of novel RNA based therapeutics.