SEARCH

SEARCH BY CITATION

Abstract

Hepatic ischemia/reperfusion (I/R) leads to liver injury and dysfunction through the initiation of a biphasic inflammatory response that is regulated by the transcription factor nuclear factor κB (NF-κB). We have previously shown that there is an age-dependent difference in the injury response to hepatic I/R in mice that correlates with divergent activation of NF-κB such that young mice have greater NF-κB activation, but less injury than old mice. In this study, we investigated the mechanism by which age alters the activation of NF-κB in the liver during I/R. Young (4-5 weeks) and old (12-14 months) mice underwent partial hepatic I/R. Livers were obtained for RNA microarray analysis and protein expression assays. Using microarray analysis, we identified age-dependent differences in the expression of genes related to protein ubiquitinylation and the proteasome. In old mice, genes that are involved in the ubiquitin-proteasome pathway were significantly down-regulated during I/R. Consistent with these findings, expression of a critical proteasome subunit, non-adenosine triphosphatase 4 (PSMD4), was reduced in old mice. Expression of the NF-κB inhibitory protein, IκBα, was increased in old mice and was greatly phosphorylated and ubiquitinylated. The data provide strong evidence that the age-related defect in hepatic NF-κB signaling during I/R is a result of decreased expression of PSMD4, a proteasome subunit responsible for recognition and recruitment of ubiquitinylated substrates to the proteasome. It appears that decreased PSMD4 expression prevents recruitment of phosphorylated and ubiquitinylated IκBα to the proteasome, resulting in a defect in NF-κB activation. (HEPATOLOGY 2009.)