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 (Egrl) on renal fibrosis in DN, but the underlying mechanisms are not entirely clear. Here, we explored the aggravating role of Egrl and identified microRNA-181a-5p (miR-181a-5p) as an upstream regulator of Egrl in TIF of DN. We demonstrated that overexpression of Egrl enhanced, whereas small interfering RNA targeting Egrl decreased the expressions of transforming growth factor beta 1 (TGF-(beta 1) 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 Egrl, TGF-beta 1, 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 Egrl in HK-2 cells treated with high glucose. Furthermore, we identified that miR-181a-5p directly suppressed Egrl to decrease the expressions of TGF-beta 1, fibronectin and collagen I in HK-2 cells through targeting the 3' untranslated region of Egrl. The functional relevance of miR-181a-5p-induced Egrl 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. (C) 2017 Published by Elsevier Inc.