Characterization of aging-associated up-regulation of constitutive nuclear factor-κB binding activity

Changes occur in gene expression during aging in vivo and in replicative senescence in vitro, suggesting that aging can affect gene regulation. We have recently observed age-related changes in ubiquitously expressed, oxidative stress-responsive nuclear factor-kappaB (NF-kappaB) pathway during aging. Here we report a significant age-related increase in nuclear NF-kappaB binding activity together with increased protein levels of p52 and p65 components in rat liver. An additional, higher molecular weight protein band seen in their western blots suggests that their post-translational modification (but not phosphorylation) occurs in liver, which might affect their nuclear localization and binding activity during aging. However, aging did not affect the protein levels of the main IkappaB inhibitors (IkappaBalpha and IkappaBbeta) or IkappaB kinase (IKK)-complex subunits (IKKalpha, -beta, and -gamma) involved in NF-kappaB activation. In addition, the level of Ser(32)-phosphorylated IkappaBalpha was unaffected by age, suggesting that neither the IKK complex nor altered level of the main inhibitors is involved in the observed up-regulation of NF-kappaB binding activity. Furthermore, the expression of NF-kappaB mRNAs (p50, p52, p65, and c-rel) and the mRNAs of their inhibitors (IkappaBalpha and IkappaBbeta) did not show any statistically significant age-related changes. These results indicate that the expression level of NF-kappaB genes is not significantly affected by aging. The up-regulation of constitutive nuclear NF-kappaB binding activity and increased levels of nuclear p52 and p65 proteins might affect the expression of some NF-kappaB target genes in the aging liver.