The Interaction Between Autophagy and Epithelial-Mesenchymal Transition via NICD/ULK1 is Involved in the Formation of Diabetic Cataracts

Abstract BackgroundCataracts are the leading cause of blindness and a common ocular complication of diabetes. Epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs) and altered autophagic activity occur during the development of diabetic cataracts. The disturbed interaction of autophagy with EMT in LECs stimulated by high glucose may participate in cataract formation.MethodsWe employed a diabetic rat model induced by streptozotocin (STZ) and human lens epithelial HLE-B3 cells stimulated with high glucose to observe the interaction of autophagy and EMT. Lens opacification was observed by slit-lamp bio-microscope, and the histological changes of lenses were detected under light microscope through paraffin section staining with hematoxylin-eosin. The autophagosomes in lens epithelial cells in vivo and in vitro were quantified under a transmission electron microscopy. The expression of EMT and autophagy markers were measured by Western blotting and immunofluorescence staining. Cell migration was determined by transwell and scratch wound assays. Co-immunoprecipitation (Co-IP) was performed to verify protein-protein interactions. Overexpression of proteins were induced by cell transfection. ResultsIn LECs, high glucose induces EMT by activating Jagged1/Notch1/NICD/Snail and inhibits autophagy through the AKT/mTOR/ULK1 signaling pathways in vivo and in vitro, resulting in diabetic cataracts. Enhanced autophagic activity by rapamycin, an mTOR inhibitor, suppressed EMT by degrading Notch1 through SQSTM1/p62 and LC3 in LECs, while inhibition of the Notch signaling pathway by DAPT, an inhibitor of γ-secretase, not only prevented EMT but also activated autophagy by downregulating the expression of NICD, which binds to ULK1, phosphorylates it, and then inhibits autophagic initiation.ConclusionsWe demonstrated a new interaction of autophagy and EMT involving NICD/ULK1, which mediates crosstalk between these two important events in the formation of diabetic cataracts. Activating autophagy and suppressing EMT mutually promote each other, identifying a potential target and strategy for the prevention of diabetic cataracts.