Catalase post-translational modifications as key targets in the control of erythrocyte redox homeostasis in children with obesity and insulin resistance

Abstract

Insulin resistance (IR) is the most common metabolic disturbance in children with obesity. Children with obesity and insulin resistance (ObIR+) display a detriment in erythroid antioxidant defenses, caused by an impaired catalase activity and the increase in oxidative and pro-inflammatory markers. Therefore, erythrocytes from ObRI+ are more vulnerable to any oxidative stress elicitor. Since catalase is one of the erythrocytes' first antioxidant defenses, we intended to delve into the mechanisms underlying catalase's impaired activity. Given the lack of cellular organelles in erythrocytes, which prevents protein synthesis, we aimed study catalase post-translational modifications (PTMs) as targets of pro-inflammatory and pro-oxidant status of these cells in children with obesity and IR. Catalase levels of O- glycosylation, tyrosine nitration and S-glutathionylation were analyzed by Western blotting (WB) using immunoprecipitated catalase (IP-CAT) from erythrocyte lysates. Furthermore, Catalase was also identified by LC-MS/MS after isolation and enrichment of erythrocyte nitrosated proteins with a biotin switch approach. The results obtained suggest that catalase inhibition seen in children with obesity is partly due to the increase in the S-nitrosation of the enzyme. Indeed, exogenous administration of nitric oxide (NO) to cultured erythrocytes resulted in a decrease in catalase activity in all groups. Signals of other PTMs (O-glycosylation, Tyr -nitration and S-glutathionylation) were also detected in the erythrocyte catalase in every groups, although levels of catalase O-glycosylation and S-gluta-thionylation decreased in ObIR+. No evidence of differences in Tyr-nitration of catalase levels were found among groups. The study again highlights the role of erythrocytes as sensors of the inflammatory and pro-oxidant response to which these cells are subjected in children with obesity and insulin resistance.