Sandip Kumar Nandi

The amino groups of lysine and arginine residues in proteins react with reducing sugars and carbonyl compounds to form advanced glycation endproducts (AGEs). Several AGEs have been detected in human lenses, and their levels have been shown to increase with age and cataract formation. AGEs can lead to structural changes, yellow pigmentation, and cross‐linking of lens proteins. Studies have shown a positive correlation between AGEs levels and lens age, stiffness, and cataracts. Recent research suggests that DJ‐1 can inhibit the accumulation of AGEs in cellular proteins by reversing the early glycation steps. Our study found that DJ‐1 is present in epithelial cells and the outer cortex of the human lens. DJ‐1 is catalytically active in human lenses, and its ability to metabolize methylglyoxal (MGO) into D‐lactate diminishes as the lens ages. The formation of MGH‐1 from MGO was promoted in lens proteins treated with the DJ‐1 inhibitor. Recombinant DJ‐1 prevents α‐dicarbonyl‐mediated cross‐linking and AGE accumulation in human αB‐crystallin. DJ‐1 prevents glyoxal‐mediated cell death and AGE accumulation in human lens epithelial cells. Taken together, our results suggest that DJ‐1 in the human lens hinders AGE accumulation. Enhancing its activity using pharmacological agents can potentially delay or prevent the onset of presbyopia and cataracts.

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Axonal degeneration and death of retinal ganglion cells (RGCs) are the primary causes of vision loss in glaucoma. In this study, we evaluated the efficacy of a peptide (peptain-1) that exhibits robust chaperone and anti-apoptotic activities against RGC loss in two rodent models and in cultured RGCs. In cultures of rat primary RGCs and in rat retinal explants peptain-1 significantly decreased hypoxia-induced RGC loss when compared to a scrambled peptide. Intraperitoneally (i.p.) injected peptain-1 (conjugated to a Cy7 fluorophore) was detected in the retina indicative of its ability to cross the blood-retinal barrier. Peptain-1 treatment inhibited RGC loss in the retina of mice subjected to ischemia/reperfusion (I/R) injury. A reduction in anterograde axonal transport was also ameliorated by peptain-1 treatment in the retina of I/R injured mice. Furthermore, i.p. injections of peptain-1 significantly reduced RGC death and axonal loss and partially restored retinal mitochondrial cytochrome c oxidase subunit 6b2 (COX 6b2) levels in rats subjected to five weeks of elevated intraocular pressure. We conclude that i.p. injected peptain-1 gains access to the retina and protects both RGC somas and axons against the injury caused by I/R and ocular hypertension. Based on these findings, peptain-1 has the potential to be developed as an efficacious neuroprotective agent for the treatment of glaucoma.

Acylation of lysine residues is a common post-translational modification of cellular proteins. Here, we show that lysine succinylation, a type of acylation, occurs in human lens proteins. All of the major crystallins exhibited N^ε-succinyllysine (SuccK) residues. Quantification of SuccK in human lens proteins (from donors between the ages of 20 and 73 years) by LC–MS/MS showed a range between 1.2 and 14.3 pmol/mg lens protein. The total SuccK levels were slightly reduced in aged lenses (age > 60 years) relative to young lenses (age < 30 years). Immunohistochemical analyses revealed that SuccK was present in epithelium and fiber cells. Western blotting and immunoprecipitation experiments revealed that SuccK is particularly prominent in αB-crystallin, and succinylation in vitro revealed that αB-crystallin is more prone to succinylation than αA-crystallin. Mass spectrometric analyses showed succinylation at K72, K90, K92, K166, K175, and potentially K174 in human lens αB-crystallin. We detected succinylation at K72, K82, K90, K92, K103, K121, K150, K166, K175, and potentially K174 by mass spectrometry in mildly succinylated αB-crystallin. Mild succinylation improved the chaperone activity of αB-crystallin along with minor perturbation in tertiary and quaternary structure of the protein. These observations imply that succinylation is beneficial to αB-crystallin by improving its chaperone activity with only mild conformational alterations.