Myeloid-specific FATP4 deficiency induces a sex-dimorphic susceptibility for NASH in mice fed with high-fat/high-cholesterol diet.

Newborns with FATP4 mutations exhibit ichthyosis prematurity syndrome (IPS), and adult patients show skin hyperkeratosis, allergies, and eosinophilia. We have previously shown that the polarization of macrophages is altered by FATP4 deficiency, however, the role of myeloid FATP4 in the pathogenesis of non-alcoholic steatohepatitis (NASH) is not known. We herein phenotyped myeloid-specific Fatp4-deficient (Fatp4M-/ - ) mice under chow and high-fat/high-cholesterol (HFHC) diet. Bone-marrow-derived macrophages (BMDMs) from Fatp4M-/- mice showed significant reduction in cellular sphingolipids in males and females, and additionally cellular phospholipids in females. BMDMs and Kupffer cells from Fatp4M-/- mice exhibited increased LPS-dependent activation of pro-inflammatory cytokines and transcription factors PPARγ, CEBPα, and p-FoxO1. Correspondingly, these mutants under chow diet displayed thrombocytopenia, splenomegaly, and elevated liver enzymes. After HFHC feeding, Fatp4M-/- mice showed increased MCP-1 expression in liver and subcutaneous fat. Plasma MCP-1, IL4, and IL13 levels were elevated in male mutants, and those of IL5 and IL6 were additionally elevated in female mutants. After HFHC feeding, male mutants showed an increase in hepatic steatosis and inflammation, while female mutants showed a greater severity in hepatic fibrosis associated with immune cell infiltration. Thus, myeloid-FATP4 deficiency led to steatotic and inflammatory NASH in males and females, respectively. Our work offers some implications for patients with FATP4 mutations, and also highlights considerations in the design of sex-targeted therapies for NASH treatment.