Liver Regeneration After Ischemia Reperfusion Injury in High-Fat-Diet Induced Hepatic Microsteatosis and Macrosteatosis.

Abstract

Fatty livers have low tolerance to IRI and high risks of organ failure after transplantation. Impaired liver regeneration, often attributed to fatty livers, is a frequent feature in acute liver failure. The present study unveils mechanisms of hepatic regeneration in clinically relevant models of lean and steatotic hepatic IRI. Methods and Results: C57BL6 mice were fed with standard or high-fat (HF; 60% of total kilocalories) diets for up to 8 weeks. Mice fed with a standard diet had virtually no liver fat inclusions, whereas HF-diet-fed mice with about 29-33g and 40-45g of body weight were characterized by prevalence of liver microsteatosis (MiS) and macrosteatosis (MaS), respectively (assessed by H&E, Oil-red O staining, and triglyceride levels). Mice were submitted to partial warm ischemia for 60- or 90-min ischemia followed by reperfusion. In 60-min IRI, all lean, MiS, and MaS mice survived post-reperfusion. MaS mice had significantly higher serum AST (11632±3238 vs. 2123±1424 vs. 380±269) levels (U/L) compared with MiS (p<0.05) and lean (p<0.05) mice, respectively, at 24h after IRI. Cyclin D1 is one of the key regulatory proteins of the cell cycle; its expression is required for transition from the G1 into the S phase. The relatively well-preserved lean livers showed significantly increased Cyclin D1 expression (1.18±0.26 vs. 0.24±0.13 vs. 0.04±0.01), but reduced PCNA levels (0.03±0.003 vs. 0.86±0.14 vs. 0.29±0.03), compared with MiSand MaS livers (respectively, p<0.05) at 48h post-IRI. In 90-min IRI, all lean and MiS mice survived surgery, despite significant liver damage, while only 40% of the MaS mice were alive after the first two postoperative days. Here, lean mice showed significantly higher expression levels of both Cyclin D1 (0.47±0.01vs. 0.31±0.02 vs. 0.10±0.02) and PCNA (0.40±0.05 vs. 0.23±0.05 vs. 0.13±0.04), compared with MiS and MaS mice (respectively, p<0.05) at 48h post-IRI. PCNA protein expression levels correlated with the hepatocyte proliferation index in all evaluated tissues. Conclusion: This thorough study demonstrates distinct expression patterns of cell-cycle regulators in macrosteatotic, microsteatotic and lean livers after IRI. Moreover, it suggests that while Cyclin D1 levels reflect the capability of livers to regenerate post-reperfusion, PCNA levels represent their regenerative activity.