Role of Osmotic Response Element-Binding Protein in High Glucose-Induced Cataractogenesis: Involvement of ERK and p38 MAPK Pathways

Abstract

Osmotic Response Element-binding Protein (OREBP) is a key regulator in cellular responses to osmotic stress. However, its specific role in cataractogenesis remains unclear. This study aimed to investigate the mechanisms regulating OREBP expression in high-glucose environments and examine the associated signaling pathways. Human Lens Epithelial Cells (HLEpiCs) were cultured and treated with normal (25 mmol/L) and high (300 mmol/L) concentrations of D-glucose. To assess the cellular response, western blot analysis was performed to detect the activation of ERK/p38MAPKs in HLEpiCs. The mRNA and protein expression levels of OREBP were measured using RT-PCR and western blot techniques, respectively. Specific inhibitors for ERK (U0126) and p38 MAPK (SB239063) were applied to assess their roles in OREBP expression. Additionally, OREBP expression was examined in the lens subcapsular epithelium of diabetic patients and rats using RT-PCR and immunofluorescence techniques. Following exposure to varying glucose concentrations, OREBP mRNA levels in HLEpiCs peaked at 4 hours with 300 mM glucose, showing significant upregulation at 2 and 4 hours (Fig. 1A, Fig. B). Western blot analysis revealed a corresponding increase in OREBP protein levels after 24 hours of high glucose exposure. Morphologically, HLEpiCs exhibited compact growth and increased apoptosis under high glucose conditions, contrasting with their initial polygonal morphology. OREBP expression was markedly elevated in the lens subcapsular epithelium of diabetic patients and rats, correlating with high glucose stress. Furthermore, phosphorylation of ERK and p38 MAPK proteins was significantly induced within 45 minutes of exposure to 300 mM glucose. Inhibition experiments using ERK inhibitor U0126 and p38 MAPK inhibitor SB239063 demonstrated substantial downregulation of OREBP mRNA expression. Combination treatment with both inhibitors consistently suppressed OREBP protein expression after 24 hours of high glucose exposure. In summary, our study reveals that OREBP is upregulated in response to high glucose levels through the activation of ERK and p38 MAPK pathways. These findings provide valuable insights into the molecular mechanisms of cellular responses to osmotic stress in high-glucose environments, offering potential therapeutic targets for diabetic cataracts. Future research should explore the specific functions of OREBP in cataractogenesis and its potential as a therapeutic target.