Interleukin-34 as a fibroblast-derived marker of liver fibrosis in patients with non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a common cause of chronic non-viral liver disease. Activation of macrophages and hepatic stellate cells is a critical step that promotes liver fibrosis. We aimed to explore the feasibility of interleukin-34 (IL-34), a key regulator of macrophages, as a fibrosis marker in patients with NAFLD. We enrolled 197 liver biopsy-proven NAFLD patients. We evaluated the serum levels of IL-34, macrophage-colony stimulating factor (M-CSF), soluble CD163 (sCD163), 40 cytokines/chemokines, hyaluronic acid, type IV collagen 7s, and clinically-approved fibrosis scores. IL-34 increased with the progression of fibrosis and was an independent marker for liver fibrosis. Immunostaining experiments, using resected liver specimens from NAFLD patients, revealed that IL-34 was mainly expressed on liver fibroblasts. IL-34 based fibrosis score (0.0387*IL-34 (pg/ml) + 0.3623*type IV collagen 7s (ng/ml) + 0.0184*age (year)-1.1850) was a practical predictive model of liver fibrosis. Using receiver-operating characteristic analyses, the area under the curve, sensitivity, and specificity of IL-34 based fibrosis score were superior or comparable to the other fibrosis biomarkers and scores. In conclusion, the IL-34 based fibrosis score, including serum IL-34, type IV collagen 7s and age, is a feasible diagnostic marker of liver fibrosis in NAFLD patients.