The role of circulating miRNA a potential biomarker for diabetic retinopathy.

Abstract

Purpose: To explore the extent to which circulating miRNAs serve as diagnostic biomarkers of Type II diabetes mellitus and to validate circulating miRNAs as prognostic biomarkers in diabetes-induced retinopathy.

Methods: Circulating miRNAs were extracted from freshly isolated plasma samples of two groups of patients, aged 30 to 65: (1) non-diabetic, healthy controls and (2) diabetic patients, without microvascular complications. The expression levels of various miRNA were identified using a PCR-based microarray. The list of candidate miRNA were validated with total RNA fraction (using PAXgene technology) from whole blood of a larger cohort of diabetic patients with and without T2D representing multiple stages of DR (non-proliferatory, NPDR and proliferatory PDR). We then validated our findings by cell culture studies using Muller cells in different conditions, and by in vivo studies using high fat diet mouse model.

Results: We report that miR-15a is upregulated in patients with DR, with noted increases as the severity of DR increases. miR-15a significantly increases oxidative stress by targeting Akt3, as demonstrated by overexpressing miR-15a in Müller cells (MIO-M1). We found pancreatic β-cells (INS-1) under high glucose and hypoxic stress produce significantly higher levels of miR-15a. We validated our findings in mouse model, where we observed significantly higher miR-15a expression in both blood-derived exosomes and in the retina.

Conclusions: This study not only emphasizes the role of miR-15a in the pathogenesis of DR, but also suggests that miR-15a could serve as a potential candidate for a diagnostic, prognostic, and predictive biomarker for DR. To our knowledge, this is the first evidence demonstrating that as t2D progress, pancreatic β-cells activate the transcription of miR-15a in order to meet an increased insulin demand. This excess miR-15a enters into the blood stream via exosomes, which transport miR-15a into the retina. This unique observation not only highlights the exciting potential for miRNAs as diagnostic biomarkers for t2D complications, but also may prove to be a new target for therapeutic intervention to prevent DR.