Inhibition of chylomicron assembly leads to dissociation of hepatic steatosis from inflammation and fibrosis

Abstract

Regulating dietary fat absorption may impact progression of nonalcoholic fatty liver disease (NAFLD). Here, we asked if inducible inhibition of chylomicron assembly, as observed in intestine-specific microsomal triglyceride (TG) transfer protein knockout mice (Mttp-IKO), could retard NAFLD progression and/or reverse established fibrosis in two dietary models. Mttp-IKO mice fed a methionine/choline-deficient (MCD) diet exhibited reduced hepatic TGs, inflammation, and fibrosis, associated with reduced oxidative stress and downstream activation of c-Jun N-terminal kinase and nuclear factor kappa B signaling pathways. However, when Mttpflox mice were fed an MCD for 5 weeks and then administered tamoxifen to induce Mttp-IKO, hepatic TG was reduced, but inflammation and fibrosis were increased after 10 days of reversal along with adaptive changes in hepatic lipogenic mRNAs. Extending the reversal time, following 5 weeks of MCD feeding to 30 days led to sustained reductions in hepatic TG, but neither inflammation nor fibrosis was decreased, and both intestinal permeability and hepatic lipogenesis were increased. In a second model, similar reductions in hepatic TG were observed when mice were fed a high-fat/high-fructose/high-cholesterol (HFFC) diet for 10 weeks, then switched to chow ± tamoxifen (HFFC → chow) or (HFFC → Mttp-IKO chow), but again neither inflammation nor fibrosis was affected. In conclusion, we found that blocking chylomicron assembly attenuates MCD-induced NAFLD progression by reducing steatosis, oxidative stress, and inflammation. In contrast, blocking chylomicron assembly in the setting of established hepatic steatosis and fibrosis caused increased intestinal permeability and compensatory shifts in hepatic lipogenesis that mitigate resolution of inflammation and fibrogenic signaling despite 50–90-fold reductions in hepatic TG.