Senp1 O-GlcNAcylation Promotes Mitochondrial Fragmentation by Regulating Fis1 SUMO1-ylation Underlying Diabetic Cataract.

PURPOSE: Cataract is a major cause of blindness among patients with diabetes mellitus. The pathology underlying diabetic cataract (DC) is complex because of changes in biological processes caused by chronic hyperglycemia. O-GlcNAcylation is highly dependent on glucose availability and regulates mitochondrial functions. Dysregulation of O-GlcNAcylation has been reported in DC. Mitochondria in lens epithelial cells are key organelles for energy supply and redox homeostasis of the lens. Mitochondrial dysfunction is a hallmark of DC. However, whether O-GlcNAcylation regulates mitochondrial function underlying DC has not been fully studied.

METHODS

An animal model of DC was established in Sprague-Dawley male rats by feeding a 60% high-fat diet and injecting streptozotocin. Mitochondria were visualized using confocal laser scanning microscope and transmission electron microscope. O-GlcNAcylated proteins were verified using liquid chromatography tandem mass spectrometry and immunoprecipitation assays. Lentivirus-encapsulated plasmids were constructed to generate stable transfected cell lines. The histomorphology of the lens was assessed by hematoxylin and eosin staining.

RESULTS

High glucose levels promoted mitochondrial fission by upregulating Senp1 O-GlcNAcylation at the S137 site. Senp1 S137 O-GlcNAcylation inhibited Fis1 deSUMO1-ylation. Fis1 SUMO1-ylation decreased its interaction with Mfn2, which reduced the contact between mitochondria-associated ER membranes (MAMs), thereby promoting mitochondrial fragmentation. Site-specific mutation of Senp1 S137A released the inhibitory effect on Fis1 deSUMOylation and mitigated high-glucose induced mitochondrial fragmentation.

CONCLUSIONS

Senp1 S137 O-GlcNAcylation regulates mitochondrial fragmentation in lens epithelial cells underlying DC. Senp1 O-GlcNAcylation increase mediates mitochondrial fragmentation by upregulating Fis1 SUMO1-ylation, which in turn reduces the contact of mitochondria-associated endoplasmic reticulum membranes and promotes mitochondrial fragmentation.