High glucose down-regulates microRNA-181a-5p to increase pro-fibrotic gene expression by targeting early growth response factor 1 in HK-2 cells

Tubulointerstitial fibrosis (TIF) plays an important role in the progression of renal fibrosis in diabetic nephropathy (DN). Accumulating evidence supports a crucial effect of early growth response factor 1 (Egr1) on renal fibrosis in DN, but the underlying mechanisms are not entirely clear. Here, we explored the aggravating role of Egr1 and identified microRNA-181a-5p (miR-181a-5p) as an upstream regulator of Egr1 in TIF of DN. We demonstrated that overexpression of Egr1 enhanced, whereas small interfering RNA targeting Egr1 decreased the expressions of transforming growth factor β1 (TGF-β1) and fibrosis-related genes including fibronectin and collagen I in human proximal tubule cell line (HK-2) cells. We then found that miR-181a-5p expression was down-regulated, accompanied by the corresponding up-regulation of Egr1, TGF-β1, fibronectin and collagen I in renal tissues of type 2 diabetic Otsuka-Long-Evans-Tokushima-Fatty rats with DN, and that the expression of miR-181a-5p was negatively correlated with the level of Egr1 in HK-2 cells treated with high glucose. Furthermore, we identified that miR-181a-5p directly suppressed Egr1 to decrease the expressions of TGF-β1, fibronectin and collagen I in HK-2 cells through targeting the 3′ untranslated region of Egr1. The functional relevance of miR-181a-5p-induced Egr1 decrease was supported by inhibition and overexpression of miR-181a-5p in HK-2 cells. Thus, we concluded that aberrant Egr1 expression, which can be suppressed by miR-181a-5p directly, plays a crucial role in the progression of renal TIF in DN. This study indicates that targeting miR-181a-5p may be a novel therapeutic approach of DN.