Activation of peroxisome proliferator-activated receptor-gamma during hepatic ischemia is age-dependent

Abstract

Hepatic ischemia/reperfusion injury is a complication of liver surgery, transplantation, and shock and is known to be age-dependent. Our laboratory has recently shown that peroxisome proliferator-activated receptor-gamma (PPARgamma) is down-regulated during hepatic ischemia and that this exacerbates injury. Here we examined whether activation of PPARgamma during ischemia was age-dependent. Male mice of different ages (young: 4-5 weeks; adult: 10-12 weeks; old: 10-12 months) were subjected to up to 90 min of hepatic ischemia. PPARgamma activation occurred throughout ischemia in young mice, whereas activation in adult and old mice was lost after 30 min. No significant differences were noted in PPARgamma ligand expression among the age groups. However, in young mice we observed a predominance of PPARgamma1 in the nucleus, whereas in old mice this isoform remained largely in the cytoplasm. Finally, the degree of PPARgamma activation was associated with autophagy in the liver, a mechanism of self-preservation. PPARgamma activation is prolonged in young mice as compared to older mice. This appears to be mediated by a selective retention of PPARgamma1 in the nucleus and is associated with increased autophagy. The data suggest that PPARgamma activation is an important component of the age-dependent response to hepatic ischemia/reperfusion injury.

Figure 1

Hepatic activation of PPARγ during ischemia in different age groups of mice. Liver nuclear extracts were analyzed by EMSA. Y, young mice (4–5 weeks of age); A, adult mice (10–12 weeks of age); O, old mice (10–12 months of age). Results are representative of 4 sets of experiments.

Figure 2

Hepatic expression of endogenous ligands (left) and potential ligands (right) for PPARγ. 15d-PGJ₂ was measured in liver extracts by ELISA. Fatty acids were determined by gas chromatography at the Mouse Metabolic Phenotyping Center at the University of Cincinnati. Data are means ± SEM with n=4 per group. *P<0.05 compared with sham-operated mice.

Figure 3

Expression of PPARγ isoforms in liver cytoplasmic and nuclear extracts during hepatic ischemia. PPARγ1 and PPARγ2 expression were determined by Western blot. Y, young mice (4–5 weeks of age); A, adult mice (10–12 weeks of age); O, old mice (10–12 months of age). Results are representative of 3 sets of experiments.

Figure 4

Autophagy in the liver during hepatic ischemia. Liver lysates were analyzed for autophagy activity by Western blot for LC3B. Conversion of LC3B-I to LC3B-II is an indicator of autophagy. Y, young mice (4–5 weeks of age); A, adult mice (10–12 weeks of age); O, old mice (10–12 months of age). Results are representative of 4 sets of experiments.

Figure 5

Effect of rosiglitazone on hepatic autophagy during ischemia in adult mice. Mice were treated orally with methylcellulose (veh) or 10 mg/kg rosiglitazone (rosi) dissolved in methylcellulose 30 minutes prior to the induction of ischemia. Liver lysates were analyzed for autophagy activity by Western blot for LC3B. Results are representative of 2 sets of experiments.