Effect of age and oxidative stress on tyrosine phosphorylation of ZAP-70

Oxidative stress is believed to be one of the leading contributors to the aging process and loss Of Cellular function with aging. Although. several age-associated phenomena have been correlated with reactive oxygen species, the role of oxidative stress ill the age-related decline of T-cell activity is not yet clear. The Present study was carried out to determine the effect of reactive oxygen species on tyrosine phosphorylation of ZAP-70, a key enzyme in the T-cell signal transduction pathway. Our previous as well Lis present studies have demonstrated an age-related down-regulation of tyrosine phosphorylation of ZAP-70 following activation of freshly isolated T cells with various stimulating agents. Currently, we observe that under mild and chronic oxidative stress, tyrosine phosphorylation of ZAP-70 is impaired following stimulation of the T cells with anti-CD3 antibody. Interesting, in contrast to our observation using freshly isolated T cells, there is no age-associated impairment of tyrosilic phosphorylation of ZAP-70 when T cells, cultured for 2 days in a scrum-Free medium in the presence or in the absence of oxidative stress, are stimulated with anti-CD3 antibody. The current observation suggests that the age-associated down-regulation of tyrosine phosphorylation of ZAP-70 is not an intrinsic defect inherent or the T cells due to aging and is reversible. We also observed that under oxidative stress in vitro. there as no significant difference in inhibition of tyrosine phosphorylation OF ZAP-70 in T cells isolated from elderly and young donors. Finally, it was also noted that the down-regulation of tyrosine phosphorylation of ZAP-70 under oxidative stress in young and elderly donors was not due to impairment in the net expression of ZAP-70 under oxidative stress thereby suggesting that dysregulation in the balance of kinase-phosphatase activities under oxidative stress might have been implicated in the observed phenomenon. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.