miRNA-221 and -222 Increase Upon Loss of Insulin-like Growth Factor 1 Receptor in Type 2 Diabetes

Bradford, AB and Woods, TC

Department of Physiology, Dr. T. Cooper Woods Laboratory

Tulane University School of Medicine

Type 2 diabetes is associated with a 2 to 4 times increased risk of heart attack and stroke, due to an increase in vascular inflammation. An increase in two miRNAs, miR-221 and -222, occurs in type 2 diabetic patients and leads to the acceleration of vascular inflammation. miR-221/222 act by down regulating cyclin-dependent kinase inhibitor, p27Kip1, in vascular smooth muscle cells (VSMCs) and exosome-mediated pro-inflammatory effects on endothelial cells and macrophages. When there are changes in insulin receptor (IR) and insulin-like growth factor receptor (IGFR) signaling, the expression of these miRNAs changes, as well. We hypothesize that the loss of IGFR, coupled with physiological insulin stimulation, promotes an increase in the expression of miR-221/-222. Correspondingly, there is an increase in miR-221/222 content in VSMC-derived exosomes and a decrease in the expression of p27Kip1 in VSMCs.

In response to physiological insulin stimulation, murine VSMCs lacking IGFR (VIGFRKO) exhibited a dose-dependent increase in miR-221 (1.62 +/- 0.30, p<0.05) and in miR-222 (2.30 +/- 0.58, p<0.05) expression. P27KIP1 expression (0.78 +/- 0.10, p<0.05) in VIGFRKOs was significantly decreased when compared to wild type, following stimulation with insulin. There was also a significant increase in the miR-221 (2.34 +/-0.24, p<0.05) and miR-222 (2.86 +/- 0.53, p<0.05) content of exosomes derived from insulin-stimulated VIGFRKOs. An ELISA performed for exosomal marker CD63 demonstrated insignificant difference between wild-type and knockout-derived exosomes. We conclude that loss of IGFR alters insulin signaling, likely through an increase in IR holoreceptors, promoting increased vascular miR-221/222 in both smooth muscle cells and their exosomes. This miR increase leads to downregulation of p27KIP1. These changes in insulin signaling will lead to an increase in vascular inflammation, and this suggests that the loss of vascular IGFR in type 2 diabetes contributes to the cardiovascular complications of diabetes.