Long noncoding RNAs and Diabetic Retinopathy: Current Understanding, Future Directions and Challenges

Diabetic retinopathy remains as the leading cause of preventable blindness in working-aged people. The pathophysiology of this sight-threatening disease is complex and involves intricate interactions among metabolic, hemodynamic and epigenetic pathways, leading to molecular, structural, functional and genomic abnormalities in retinal vascular and nonvascular cells. Diabetes also results in differential expressions of several noncoding RNAs, including micro RNAs (miRNAs) and long noncoding RNAs (LncRNAs). Compared to about 2000 miRNA identified in human genome thus far, more than 30,000 LncRNA transcripts have been already identified, but the function and mechanisms of action of most of the LncRNAs is still not fully characterized, and there remains a possibility that some LncRNAs could have diverse functions under different contexts. LncRNAs do not code for proteins, but they have many regulatory functions, and regulate gene expression by interacting with DNA, RNA and protein. Aberrant expressions of several LncRNAs including MALAT1, MEG3, HOTAIR, MIAT1 and H19, is associated with metabolic abnormalities implicated in the pathogenesis of diabetic retinopathy. LncRNAs are also released into circulation and show high organ and cell specificity, and greater disease-associated differences compared to disease-associated mRNAs. Furthermore, LncRNAs maintain stable expression in the plasma and can be isolated from total RNA present in biological samples including blood, which makes them promising and reliable candidates for diagnostic or prognostic markers and therapeutic targets for various diseases. With continued improvement in innovative RNA modifications and delivery modalities, use of LncRNAs as possible biomarkers, and of LncRNA-based therapeutics, for diabetic retinopathy appears promising.