The impact of glutaredoxin 1 and glutaredoxin 2 double knockout on lens epithelial cell function.

Glutaredoxins (Grx1 and Grx2) are thiol-repair antioxidant enzymes that play vital roles in cellular redox homeostasis and various cellular processes. This study aims to evaluate the functions of the glutaredoxin (Grx) system, including glutaredoxin 1 (Grx1) and glutaredoxin 2 (Grx2), using Grx1/Grx2 double knockout (DKO) mice as a model. We isolated primary lens epithelial cells (LECs) from wild-type (WT) and DKO mice for a series of in vitro analyses. Our results revealed that Grx1/Grx2 DKO LECs exhibited slower growth rates, reduced proliferation, and aberrant cell cycle distribution compared to WT cells. Elevated levels of ß-galactosidase activity were observed in DKO cells, along with a lack of caspase 3 activation, suggesting that these cells may be undergoing senescence. Additionally, DKO LECs displayed compromised mitochondrial function, characterized by decreased ATP production, reduced expression levels of oxidative phosphorylation (OXPHOS) complexes III and IV, and increased proton leak. A compensatory metabolic shift towards glycolysis was observed in DKO cells, indicating an adaptive response to Grx1/Grx2 deficiency. Furthermore, loss of Grx1/Grx2 affected cellular structure, leading to increased polymerized tubulin, stress fiber formation, and vimentin expression in LECs. In conclusion, our study demonstrates that Grx1/Grx2 double deletion in LECs results in impaired cell proliferation, aberrant cell cycle progression, disrupted apoptosis, compromised mitochondrial function, and altered cytoskeletal organization. These findings underscore the importance of Grx1 and Grx2 in maintaining cellular redox homeostasis and the consequences of their deficiency on cellular structure and function. Further research is needed to elucidate the precise molecular mechanisms underlying these observations and to investigate potential therapeutic strategies targeting Grx1 and Grx2 for various physiological processes and oxidative-stress related diseases such as cataract.

Antioxidant System and Endoplasmic Reticulum Stress in Cataracts.

The primary underlying contributor for cataract, a leading cause of vision impairment and blindness worldwide, is oxidative stress. Oxidative stress triggers protein damage, cell apoptosis, and subsequent cataract formation. The nuclear factor-erythroid 2-related factor 2 (Nrf2) serves as a principal redox transcriptional factor in the lens, offering a line of defense against oxidative stress. In response to oxidative challenges, Nrf2 dissociates from its inhibitor, Kelch-like ECH-associated protein 1 (Keap1), moves to the nucleus, and binds to the antioxidant response element (ARE) to activate the Nrf2-dependent antioxidant system. In parallel, oxidative stress also induces endoplasmic reticulum stress (ERS). Reactive oxygen species (ROS), generated during oxidative stress, can directly damage proteins, causing them to misfold. Initially, the unfolded protein response (UPR) activates to mitigate excessive misfolded proteins. Yet, under persistent or severe stress, the failure to rectify protein misfolding leads to an accumulation of these aberrant proteins, pushing the UPR towards an apoptotic pathway, further contributing to cataractogenesis. Importantly, there is a dynamic interaction between the Nrf2 antioxidant system and the ERS/UPR mechanism in the lens. This interplay, where ERS/UPR can modulate Nrf2 expression and vice versa, holds potential therapeutic implications for cataract prevention and treatment. This review explores the intricate crosstalk between these systems, aiming to illuminate strategies for future advancements in cataract prevention and intervention. The Nrf2-dependent antioxidant system communicates and cross-talks with the ERS/UPR pathway. Both mechanisms are proposed to play pivotal roles in the onset of cataract formation.