Leptin-specific mechanisms for impaired liver regeneration in ob/ob mice after toxic injury

Background & Aims: Profound impairment of liver regeneration in rodents with dysfunctional leptin signaling has been attributed to non-alcohol-induced fatty liver disorders (NAFLD). Our aim was to establish whether defective liver regeneration in ob/ob mice is a direct consequence of leptin-dependent, intracellular signaling mechanisms controlling cell-cycle regulation in hepatocytes. Methods: After exposure to a single hepatotoxic dose of (CCl4), the regenerative response to hepatic injury was studied in leptin-deficient ob/ob and control mice. The effects of leptin supplementation (100 mug . kg(-1) . day(-1)) were examined. We assessed entry into and progression through the cell cycle and activation of key signaling intermediates and transcriptional regulators. Results: CCl4-induced liver injury was equally severe in ob/ob and control mice. In leptin-deficient mice, it was associated with exaggerated activation of NF-kappaB and STAT3 during the priming phase, abrogation of tumor necrosis factor (TNF) and interleukin (IL)-6 release at the time of G1/S transition, and failure of hepatocyte induction of cyclin D1 and cell cycle entry. Leptin replacement corrected these defects in ob/ob mice by restoring TNF and IL-6 release and inducing cyclin D1. Hepatocytes entered S phase and progressed, as in wild-type mice, to vigorous mitosis and normal hepatic regenerative response. In ob/ob mice, low doses of TNF before CCl4 also were associated with restitution of TNF release and proliferative capabilities. Conclusions: Impaired liver regeneration in ob/ob mice is caused by leptin deficiency. We propose that altered cytokine production in ob/ob mice is part of the mechanisms responsible for impaired proliferation in response to hepatic injury.