FABP7 in Hepatic Macrophages Promotes Fibroblast Activation and CD4+ T-Cell Migration by Regulating M2 Polarization During Liver Fibrosis.

Hepatic macrophages respond to various microenvironmental signals and play a central role in maintaining hepatic homeostasis, dysregulation of which leads to various liver diseases. Fatty acid-binding protein 7 (FABP7), an intracellular lipid chaperone for polyunsaturated fatty acids (PUFAs), is highly expressed in liver macrophages. However, the mechanisms by which FABP7 regulates hepatic macrophage activation remain unclear. Therefore, we aimed to elucidate the mechanisms underlying the effects of FABP7 on the functions of hepatic macrophages in metabolic dysfunction-associated steatohepatitis (MASH) and liver fibrosis models. In this study, we found that FABP7-deficient macrophages exhibited impaired M2 polarization, which reduced the fibrotic response of myofibroblasts and CD4⁺ T-cell infiltration into the liver tissues in a carbon tetrachloride (CCl₄)-induced hepatic fibrosis model. In vitro, FABP7-deficient macrophages exhibited decreased levels of peroxisome proliferator-activated receptor (PPAR)-γ and its target genes, including C-C motif chemokine ligand (CCL)-17 and transforming growth factor-β (TGF-β), compared to the wild-type (WT) macrophages post-interleukin (IL)-4 stimulation. However, these effects were inhibited by a PPARγ inhibitor. IL-4-stimulated WT macrophages also promoted CD4⁺ T-cell migration and hepatic fibroblast (TWNT-1 hepatic stellate cell [HSC]) activation, indicated by increased mRNA levels of actin alpha 2, smooth muscle (ACTA2), and collagen type I alpha 1 (COL1A1); however, these effects were inhibited in FABP7-deficient macrophages. Overall, FABP7 in hepatic macrophages modulated the crosstalk between hepatic fibroblasts and T cells by regulating M2 polarization. Therefore, regulation of hepatic macrophage function by FABP7 is a potential therapeutic target for liver fibrosis.