Interleukin (IL)-20 is a proinflammatory cytokine of the IL-10 family and involved in rheumatoid arthritis, atherosclerosis, stroke, and osteoporosis. However, the pathophysiological roles of IL-20 in liver injury have not been extensively studied. We explored the involvement of IL-20 in liver injury and the therapeutic potential of IL-20 antagonists for treating liver fibrosis. Compared with normal liver tissue from healthy individuals, the amount of IL-20 was much higher in hepatocytes and hepatic stellate cells in liver biopsies from patients with fibrosis, cirrhosis, and hepatocellular carcinoma. Carbon tetrachloride (CCl4) treatment induced IL-20 that further up-regulated the expression of transforming growth factor (TGF)-β1 and p21WAF1 and resulted in cell cycle arrest in the Clone-9 rat hepatocyte cell line. IL-20 activated quiescent rat hepatic stellate cells (HSCs) and up-regulated TGF-β1 expression. IL-20 also increased TGF-β1, tumor necrosis factor (TNF)-α, and type I collagen (Col-I) expression, and promoted the proliferation and migration of activated HSCs. Serum IL-20 was significantly elevated in mice with short-term and long-term CCl4-induced liver injury. In mice with short-term liver injury, anti-IL-20 monoclonal antibody (7E) and anti-IL-20 receptor (IL-20R1) monoclonal antibody (51D) attenuated hepatocyte damage caused by CCl4, TGF-β1, and chemokine production. In mice with long-term liver injury, 7E and 51D inhibited CCl4-induced cell damage, TGF-β1 production, liver fibrosis, HSC activation, and extracellular matrix accumulation, which was caused by the reduced expression of tissue inhibitors of metalloproteinases as well as increased metalloproteinase expression and Col-I production. IL-20R1-deficient mice were protected from short-term and long-term liver injury. Conclusion: We identified a pivotal role of IL-20 in liver injury and showed that 7E and 51D may be therapeutic for liver fibrosis.
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