[Molecular mechanisms of mitochondrial dysfunction mediated by the MAPK axis in diabetic cataract]

Objective To explore molecular mechanisms of mitochondrial dysfunction mediated by p38 mitogen-activated protein kinase (p38 MAPK) in diabetic cataract (DC). Methods Lens epithelial cells (LECs) from cell line SRA01/04 were divided into the following six treatment groups: blank group (Con), osmotic control group, high glucose group (HG), HG+sh-p38 MAPK group, HG+sh-p38 MAPK+oe-NC group and HG+sh-p38 MAPK+oe-Pink1 group. The Con group was exposed to normal glucose concentration (5.5 mmol/L) for 48 hours; the osmotic control group was exposed to 5.5 mmol/L glucose and 49.5 mmol/L mannitol for 48 hours; the other groups were exposed to 55 mmol/L glucose for 48 hours to induce a DC model in vitro. 36 Sprague-Dawley rats were divided into a control group, a DC group and a DC+SB203580 group, with 12 rats in each group. At the 12th week, the lens of each group were analyzed histologically. Oxidative stress indicators like malondialdehyde (MDA), reactive oxygen species (ROS), superoxide dismutase (SOD), ATP synthase activity, mitochondrial membrane potential analysis, and mitochondrial DNA (mtDNA) copy number were measured using commercial kits. The protein expression was analyzed using Western blot. Results Compared with the Con group, the HG group showed significantly increased levels of MDA and ROS, but significantly decreased levels of SOD, ATP synthase activity, mtDNA copy number and the JC-1 red/green (aggregate/monomer) ratio in LECs. Compared with the HG group, the HG+sh-p38 MAPK group exhibited significantly decreased levels of MDA and ROS, but significantly increased levels of SOD, ATP synthase activity, mtDNA copy number and the JC-1 red/green (aggregate/monomer) ratio in LECs. Compared with the HG+sh-p38 MAPK group, the HG+sh-p38 MAPK+oe-Pink1 group showed significantly decreased ATP synthase activity, mtDNA copy number and JC-1 red/green ratio in LECs. In LECs of HG+sh-p38 MAPK+oe-Pink1 group, the protein levels of PTEN-induced kinase 1 (Pink1), Parkin, microtubule-associated protein 1 light chain 3 (LC3) II/LC3 I, cleaved caspase-3 (c-caspase-3) and Cytochrome C (Cyt-C) were higher than those of HG+sh-p38 MAPK group, while the protein levels of p62 and B cell lymphoma 2 (Bcl2) were lower. The expression of p-p38 MAPK in LECs of rats in DC+SB203580 group was lower than that in DC group. Compared with the control group, the DC group exhibited significantly increased levels of ROS and MDA and the expression levels of mitochondrial autophagy-related proteins (including Parkin, Pink1, LC3-II/LC3-I ratio, c-caspase-3 and Cyt-C), but significantly decreased levels of SOD, p62 and Bcl2 proteins. SB203580 treatment showed the opposite regulatory effect. Conclusions In both in vitro and in vivo DC models, inhibition of p38 MAPK signaling down-regulates the Pink1/Parkin pathway, thereby reducing the oxidative stress caused by LEC mitochondrial dysfunction and attenuating the histopathological changes in the lens of DC rats.