关键词: 非酒精性脂肪性肝病, 非酒精性脂肪性肝炎, 脂肪酸结合蛋白4

Abstract: Objective To investigate the role of fatty acid binding protein 4 (FABP4) in the progression of non-alcoholic steatohepatitis (NASH) in mice. Methods Male C57BL/6J mice, aged 8-10 weeks and weighing about 20 g, were randomly divided into three groups with six mice in each group: normal control diet plus intraperitoneal injection of corn oil (ND+Oil), western diet plus intraperitoneal injection of corn oil (WD+Oil), and western diet plus intraperitoneal injection of carbon tetrachloride (WD+CCl4). The mice were raised for 12 weeks to construct the NASH model. Hematoxylin-eosin (H&E) staining, Sirius red staining, liver tissue biochemistry and real-time fluorescence quantitative PCR (qRT-PCR) were used to detect the degree of fat deposition, inflammatory reaction and fibrosis in the mouse liver; the expression of FABP4 was detected by qRT-PCR and Western blotting (WB). Then, FABP4 knockout (FABP4 KO) mice and littermate C57BL/6J wild-type mice (8-week-old male mice, weighing about 20 g) were used to construct the NASH model with a western diet plus intraperitoneal injection of CCl₄. After 12 weeks, the degree of fat deposition, inflammatory reaction and fibrosis in the mouse liver were detected. The expression profiling sequencing of the mice liver tissues were performed and related signaling pathways were verified. Results Compared with the ND+Oil group, elevated serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in the WD+Oil group were observed. Lipid droplet accumulation, triglycerides (TG) level,and positive areas of Sirius red were elevated in the mice liver tissue. The mRNA expression of lipid synthesis genes (Acc, Fasn), the inflammatory factors (Tnf-a, Il-6, and Il-1β), and the fibrosis-associated factors (Col1a1, α-Sma) in the liver tissues were upregulated in the WD+Oil group (all P<0.05); while there was no statistical significance for Acc and Col1a1. Compared with the WD+Oil group, the levels of serum AST and ALT in the WD+CCl₄ group were increased (all P<0.05). Significant increase of lipid droplet and fibrotic areas, and elevated TG level in liver tissue were observed. The mRNA expression of Acc, Fasn, Tnf-α, Il-6, Il-1β, Col1a1 and α-Sma was upregulated (all P<0.05). However, there was no statistical significance for Acc and Il-6. Furthermore, we found the mRNA and protein expression of FABP4 in the mice liver were elevated in the WD+Oil group and WD+CCl₄ group when comparing with the respective control group. In the NASH model, compared with WT mice, FABP4 KO mice showed a significant reduction in hepatic lipid droplets. The positive areas of F4/80, Col1a1, and α-Sma in liver tissue were significantly decreased by immunohistochemical (IHC) detection, and the mRNA expression levels of hepatic Acc, Fasn, Tnf-α, Il-6, α-Sma, and Col1a1 were significantly reduced (all P<0.05). The protein levels of TNF-α, IL-1β, α-SMA, COL1A1, and TGF-β1 were also downregulated. Mechanistically, deficiency of FABP4 reduces hepatic steatosis, inflammatory changes, and fibrosis in NASH mice by regulating the PPAR γ and TGF-β1/Smad2/3 signaling pathways. Conclusion FABP4 is highly expressed in liver tissues of NASH mice. Deficiency of FABP4 improves the progression of NASH in mice by partially reducing lipogenesis, enhancing lipolysis and inhibiting the phosphorylation level of Smad2/3, which suggests that FABP4 may be a therapeutic target for improving NASH.

Key words: Non-alcoholic fatty liver disease, Non-alcoholic steatohepatitis, Fatty acid binding protein 4