MicroRNA-21 Implicated in Down-Regulation of PPAR-α in Diabetic Retinopath

Abstract

Purpose : Peroxisome proliferator-activated receptor-alpha (PPAR-α) is an important transcription factor regulating expression of numerous genes implicated in lipid metabolism, glucose metabolism and insulin resistance. Two longitudinal clinical studies reported that fenofibrate, a specific PPARα agonist, showed beneficial effects on diabetic retinopathy (DR) in type 2 diabetes patients. Our recent studies showed that PPAR-α possesses anti-inflammatory and anti-apoptotic functions, and down-regulation of PPAR-α in diabetic retina is associated with pathogenic features of DR, although its mechanism was not well-understood. MiRNAs are small non-coding RNA molecules, widely present in the body and regulate a variety of developmental, physiological and pathological processes. It was reported that dysregulation of some miRNAs expression was implicated in the development and progression of diabetes. The purpose of this study was to elucidate the role of miRNAs in the down-regulation of PPAR-α in DR.

Methods : MiRNA expression changes in the retina of 6 month-old db/db mice were examined by microarray and, further validated the changes by quantitative reverse transcription-PCR (qRT-PCR). The expression levels of PPAR-α and selected miRNAs as well as diabetic markers in both in vitro and in vivo models were examined by qRT-PCR, Western blot and histochemical analyses.

Results : The miRNA microarray and qRT-PCR results showed that expression of miR-21, known as a PPAR-α targeting miRNA, was significantly up-regulated in the retina of db/db mice. Expression levels of PPAR-α were significantly down-regulated in db/db mouse retinas, whereas significantly up-regulated in the retina of miR-21 knockout mice. Similarly, human retinal capillary endothelial cells (HRCEC) treated with diabetic stressors significantly up-regulated miR-21 and down-regulated PPAR-α. Furthermore, transfection of miR-21 mimic in HRCEC resulted in significant down-regulation of PPAR-α, whereas miR-21 inhibitor significantly up-regulated the expression of PPAR-α.

Conclusions : The present study showed that the up-regulation of miR-21 in the retina of diabetic mice is responsible, at least in part, to the down-regulation of PPAR-α, which plays an important role in DR. Our studies also suggest that knock-down of miR-21 in the retina offers a therapeutic benefit to reduce inflammatory responses, oxidative stress and neuronal apoptosis in DR.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.