Platelets contribute to the reduction of liver fibrosis in mice

Several recent studies have reported that liver cirrhosis (LC) can be ameliorated, but few adequate strategies are available against liver fibrosis. Although LC clinically shows thrombocytopenia and hypersplenism, the correlation with liver fibrosis and platelets remains unclear. The aim of the present study was to investigate the effect of platelets on liver fibrosis in mouse models.To induce liver fibrosis, C57BL6 female mice were injected i.p. with 1 mL/kg carbon tetrachloride (CCl(4)) twice a week for 8 weeks. Thrombocytosis was achieved by giving thrombopoietin or splenectomy in addition to CCl(4) intoxication. At 8 weeks, whole blood and liver specimens were obtained for studies as follows: peripheral platelet counts, histopathological examination, hydroxyproline assay, immunostaining, quantification of mRNA expression, and microarray analysis.Thrombocytosis significantly reduced liver fibrosis and hydroxyproline content of liver tissues compared to mice with CCl(4) administration alone. Platelets suppressed increments in mRNA expression for transforming growth factor-beta, and increased matrix metalloproteinase-9 expression in the liver. Microarray analysis of the liver revealed that platelets upregulated gene expressions involved in cell proliferation compared to expression in mice with CCl(4) intoxication alone. Platelets also increased liver volume, proliferative cell nuclear antigen labeling index, and mitotic index in fibrotic mice.These results clearly show that platelets reduce liver fibrosis and promote liver regeneration, even under cirrhotic conditions. We, therefore, propose that platelets could offer a potent tool in the treatment of liver cirrhosis.