Cyclin-dependent kinase inhibitors p21 and p27 function as critical regulators of liver regeneration following 90% hepatectomy in the rat

BACKGROUND Liver reduction is the main curative treatment for primary liver cancer, but its use remains limited as liver regeneration requires a minimum of 30% functional parenchyma. AIM To study the dynamics of the liver regeneration process and consequent behavior of cell cycle regulators in rats after extended hepatectomy (90%) and postoperative glucose infusions. METHODS Post-hepatectomy liver failure was triggered in 84 Wistar rats by reducing their liver mass by 90%. The animals received a post-operative glucose infusion and were randomly assigned to two groups: One to investigate the survival rate and the other for biochemical analyses. Animals that underwent laparotomy or 70% hepatectomy were used as controls. Blood and liver samples were collected on postoperative days 1 to 7. Liver morphology, function, and regeneration were studied with histology, immunohistochemistry, and western blotting. RESULTS Postoperative mortality after major resection reached 20% and 55% in the first 24 h and 48 h, respectively, with an overall total of 70% 7 d after surgery. No apparent signs of apoptotic cell death were detected in the extended hepatectomy rat livers, but hepatocytes displaying a clear cytoplasm and an accumulation of hyaline material testified to changes affecting their functional activities. Liver regeneration started properly, as early events initiating cell proliferation occurred within the first 3 h, and the G1 to S transition was detected in less than 12 h. However, a rise in p27 (Kip1) followed by p21 (Waf1/Cip1) cell cycle inhibitor levels led to a delayed S phase progression and mitosis. Overall, liver regeneration in rats with a 90% hepatectomy was delayed by 24 h and associated with a delayed onset and lower peak magnitude of hepatocellular deoxyribonucleic acid synthesis. CONCLUSION This work highlights the critical importance of the cyclin/cyclin-dependent kinase inhibitors of the Cip/Kip family in regulating the liver regeneration timeline following extended hepatectomy.