Mitochondrial Genome-Encoded Long Noncoding RNA (Lnc) and Mitochondrial Ribonucleases in Diabetic Retinopathy.

Aim: Hyperglycemia damages mitochondria and downregulates transcription of mtDNA-encoded genes and the long noncoding RNA Lnc, causing mitochondrial genomic instability. The genes encoded by mtDNA are transcribed as large polycistronic transcripts, and the 5' ends of precursor tRNAs are processed by mitochondrial-targeted ribonuclease P (MRPPs). Our aim was to investigate the role of MRPP1 in the downregulation of Lnc in diabetic retinopathy.

Methods: Using human retinal endothelial cells incubated in 20 mM D-glucose for 96 h, the gene expression and mitochondrial localization (immunofluorescence) of MRPP1 and the interaction between MRPP1 and Lnc (determined by RNA-FISH and RNA immunoprecipitation) were quantified. The results were confirmed in retinal microvessels from streptozotocin-induced diabetic mice and from human donors with documented diabetic retinopathy.

Results: Compared to normal glucose, high glucose decreased mRNA and mitochondrial localization of MRPP1 and its interaction with Lnc. While MRPP1 overexpression prevented glucose-induced decrease in MRPP1-Lnc interaction, Lnc expression and mitochondrial damage (reduction in protective nucleoids in mtDNA), MRPP1-siRNA further worsened them. Similar results were obtained from retinal microvessels from diabetic mice and from human donors with diabetic retinopathy.

Conclusions: Downregulation of MRPP1 in diabetes suppresses Lnc transcription, resulting in mitochondrial functional and genomic instability, ultimately leading to the development of diabetic retinopathy. Thus, preventing MRPP1 downregulation has the potential to inhibit retinopathy and prevent the fear of vision loss in diabetic patients.