HuR-mediated posttranscriptional modification of Cx40 and coronary microvascular dysfunction in type 2 diabetes

Abstract Background Diabetic patients with coronary microvascular disease (CMD) exhibit higher cardiac mortality than patients without CMD. However, the molecular mechanism by which diabetes promotes CMD is poorly understood. RNA-binding protein HuR is a key regulator of mRNA stability and translation of many genes, and there is growing evidence showing the potential role of HuR in cardiovascular disease. In this study, we investigated the role of HuR and its target genes in the development of CMD in type 2 diabetic mice. Methods Type 2 diabetes was induced in male mice by a high-fat diet combined with a single injection of low-dose streptozotocin. We assessed coronary flow velocity reserve (CFVR, a determinant of coronary microvascular function) in vivo and isolated cardiac endothelial cells (CECs) from those mice for in vitro experiment. Coronary endothelial function was evaluated in the 3rd order of coronary arteries using a wire myograph. Human CECs from 4 control subjects and 4 diabetic patients were purchased from the company. Results Diabetic mice exhibited decreases in CFVR and capillary density in the left ventricle (LV). HuR protein levels in CECs were significantly lower in diabetic mice and diabetic patients than in the controls. Endothelial-specific HuR-KO mice also displayed significant reductions in CFVR and capillary density. By examining mRNA levels of 92 genes associated with endothelial function, we found that HuR, Cx40, and Nox4 levels were decreased in CECs from diabetic and HuR-KO mice in comparison to control mice. Cx40 protein level and HuR binding to Cx40 mRNA were downregulated in CECs from diabetic mice, and Cx40-KO mice exhibited decreased CFVR, attenuated endothelium-dependent relaxation, and reduced capillary density in the LV. Furthermore, endothelium-specific Cx40 overexpression ameliorated endothelial functions by augmenting endothelium-dependent relaxation and increasing capillary density in the LV, and resulted in the improvement of CFVR in diabetic mice. Conclusions These data suggest that decreased HuR, a specific mRNA binding protein that downregulates gap junction protein Cx40 in CECs, plays an important role in the development of coronary microvascular disease in diabetes. Restoration of Cx40 expression and function is potentially a novel therapeutic strategy for diabetic cardiovascular complications.