Liver regeneration is impaired in macrophage colony stimulating factor deficient mice after partial hepatectomy: the role of M-CSF-induced macrophages.

Macrophage colony stimulating factor (M-CSF), which induces maturation of macrophages, is notably expressed in the liver. Thus, the specific purpose of this study was to investigate the role of M-CSF in liver regeneration after partial hepatectomy (PH). Osteopetrotic (op/op) mice, genetically lacking functional M-CSF, or their littermate mice underwent 70% PH. Animals were sacrificed at the designated time points after PH, and remnant liver tissues were harvested for further investigations. Proliferation of hepatocytes was evaluated by the expression of BrdU and the liver-body weight ratio. The mRNA expression levels of TNF-α and IL-6 and protein expression levels of phosphorylated (p) STAT3 were measured. The number of Kupffer cells (KCs) was determined by immunohistochemistry. Furthermore, KCs were isolated from op/op mice or littermate mice, and mRNA expression levels of TNF- α and IL-6 were assessed after stimulation with LPS. In littermate mice, steady liver regeneration was observed. The number of KCs reduced markedly by about 60% in the op/op mice compared with littermates as reported previously. Furthermore, these cells were morphologically small and immature. In littermate mice, the peak expression levels of TNF-α and IL-6 in the liver was observed 1h after PH, which was consistent with data in previous reports. In contrast, in op/op mice, the peak expression levels were observed 3 h after PH and were significantly lower compared with littermate mice. As a result, the proliferation of hepatocytes was significantly impaired in op/op mice. The mRNA expression level of IL-6, but not TNF-α,was significantly reduced in isolated KCs from op/op mice compared with the littermates after stimulation with LPS, suggesting that the function of KCs is different between op/op mice and littermate mice. To clarify the role of M-CSF in liver regeneration, op/op mice received intraperitoneally, mouse recombinant M-CSF 2 d before PH, and liver regeneration was also assessed. As a result, the numbers of Kupffer cells and liver regeneration were recovered in the op/op mice treated with M-CSF to a similar extent to those in their littermates. Thus, M-CSF-induced hepatic macrophages play an important role in liver regeneration after PH.