MDM2-mediated ubiquitination of LKB1 contributes to the development of diabetic cataract

Diabetic cataract (DC) is a common complication of diabetes mellitus. The epithelial-mesenchymal transition (EMT) of lens epithelial cells (LECs) is a crucial event in the development of DC. Murine double minute 2 (MDM2) is an E3 ubiquitin ligase that promotes EMT by regulating diverse targets. However, little is known about how MDM2 is involved in the pathogenesis of DC. We found the mRNA and protein levels of MDM2 were up-regulated in the lens of DC patients and rats. Thus, high glucose (HG)-induced human lens epithelial cells (HLECs) were constructed for further investigation. The results showed that the level of MDM2 was increased in HG-cultured HLECs, and the MDM2 knockdown alleviated HG-induced abnormal migration, EMT, and oxidative stress damage. Moreover, co-immunoprecipitation and ubiquitination assays demonstrated that MDM2 down-regulated LKB1 expression by ubiquitination degradation. LKB1 was found to be lower expressed in human and rat DC lenses, and HG-stimulated HLECs. Also, LKB1 overexpression mitigated HG-induced dysfunction of HLECs. Finally, our data showed that the changes related to EMT and oxidative stress induced by MDM2 knockdown were restored by down-regulation of LKB1. Together, MDM2 may involve in the pathogenesis of DC through down-regulating LKB1. MDM2 might be an effective therapeutical target of DC.