Redox Homeostasis in Ocular Tissues: Circadian Regulation of Glutathione in the Lens?

An ultraviolet-driven rescue pathway for oxidative stress to eye lens protein human gamma-D crystallin

Human gamma-D crystallin (HGD) is a major constituent of the eye lens. Aggregation of HGD contributes to cataract formation, the leading cause of blindness worldwide. It is unique in its longevity, maintaining its folded and soluble state for 50-60 years. One outstanding question is the structural basis of this longevity despite oxidative aging and environmental stressors including ultraviolet radiation (UV). Here we present crystallographic structures evidencing a UV-induced crystallin redox switch mechanism. The room-temperature serial synchrotron crystallographic (SSX) structure of freshly prepared crystallin mutant (R36S) shows no post-translational modifications. After aging for nine months in the absence of light, a thiol-adduct (dithiothreitol) modifying surface cysteines is observed by low-dose SSX. This is shown to be UV-labile in an acutely light-exposed structure. This suggests a mechanism by which a major source of crystallin damage, UV, may also act as a rescuing factor in a finely balanced redox system.

CircSTRBP contributes to H2O2-induced lens epithelium cell dysfunction through increasing NOX4 mRNA stability by recruiting IGF2BP1

Previous studies have shown that the development of age-related cataract (ARC) is involved in lens epithelium dysfunction, which is associated with abnormally expressed circular RNAs (circRNAs). The current work aims to probe the role of circSTRBP (hsa_circ_0088,427) in hydrogen peroxide (H2O2)-induced lens epitheliums. Lens epithelium tissues were harvested from ARC or normal subjects (n = 23). CircSTRBP, spermatid perinuclear RNA binding protein (STRBP), and nicotinamide adenine dinucleotide phosphate oxidase subunit 4 (NOX4) levels were measured using quantitative reverse transcription polymerase chain reaction (qRT-PCR). Cell proliferation, cycle progression, and apoptosis were assessed using 5-ethynyl-2'-deoxyuridine (EdU), Cell Counting Kit-8 (CCK-8), and flow cytometry assays. Caspase 3 activity, reactive oxygen species (ROS), malondialdehyde (MDA), and Glutathione peroxidases (GSH-PX) levels were detected using corresponding kits. NOX4 protein level was determined using Western blot. The interaction between insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) and circSTRBP or NOX4 was assessed through RNA immunoprecipitation (RIP). CircSTRBP and NOX4 abundances were increased in lens epithelium samples from ARC patients and H2O2-treated SRA01/04 cells. CircSTRBP knockdown might abolish H2O2-triggered SRA01/04 cell proliferation repression and apoptosis and oxidative stress promotion. In mechanism, circSTRBP is bound with IGF2BP1 and improves the stability and expression of NOX4 mRNA in SRA01/04 cells. CircSTRBP facilitated H2O2-induced SRA01/04 cell apoptosis and oxidative stress through by enhancing NOX4 mRNA stability via recruiting IGF2BP1, providing novel insights for ARC progression and treatment.

Swimming exercise reverses transcriptomic changes in aging mouse lens

BACKGROUND

The benefits of physical activity for the overall well-being of elderly individuals are well-established, the precise mechanisms through which exercise improves pathological changes in the aging lens have yet to be fully understood.

METHODS

3-month-old C57BL/6J mice comprised young sedentary (YS) group, while aging mice (18-month-old) were divided into aging sedentary (AS) group and aging exercising (AE) group. Mice in AE groups underwent sequential stages of swimming exercise. H&E staining was employed to observe alterations in lens morphology. RNA-seq analysis was utilized to examine transcriptomic changes. Furthermore, qPCR and immunohistochemistry were employed for validation of the results.

RESULTS

AE group showed alleviation of histopathological aging changes in AS group. By GSEA analysis of the transcriptomic changes, swimming exercise significantly downregulated approximately half of the pathways that underwent alterations upon aging, where notable improvements were 'calcium signaling pathway', 'neuroactive ligand receptor interaction' and 'cell adhesion molecules'. Furthermore, we revealed a total of 92 differentially expressed genes between the YS and AS groups, of which 10 genes were observed to be mitigated by swimming exercise. The result of qPCR was in consistent with the transcriptome data. We conducted immunohistochemical analysis on Ciart, which was of particular interest due to its dual association as a common aging gene and its significant responsiveness to exercise. The Protein-protein Interaction network of Ciart showed the involvement of the regulation of Rorb and Sptbn5 during the process.

CONCLUSION

The known benefits of exercise could extend to the aging lens and support further investigation into the specific roles of Ciart-related pathways in aging lens.

Understanding mechanisms of antioxidant action in health and disease

Several different reactive oxygen species (ROS) are generated in vivo. They have roles in the development of certain human diseases whilst also performing physiological functions. ROS are counterbalanced by an antioxidant defence network, which functions to modulate ROS levels to allow their physiological roles whilst minimizing the oxidative damage they cause that can contribute to disease development. This Review describes the mechanisms of action of antioxidants synthesized in vivo, antioxidants derived from the human diet and synthetic antioxidants developed as therapeutic agents, with a focus on the gaps in our current knowledge and the approaches needed to close them. The Review also explores the reasons behind the successes and failures of antioxidants in treating or preventing human disease. Antioxidants may have special roles in the gastrointestinal tract, and many lifestyle features known to promote health (especially diet, exercise and the control of blood glucose and cholesterol levels) may be acting, at least in part, by antioxidant mechanisms. Certain reactive sulfur species may be important antioxidants but more accurate determinations of their concentrations in vivo are needed to help assess their contributions.