Lack of Nogo-B expression ameliorates PPARγ deficiency-aggravated liver fibrosis by regulating TLR4-NF-κB-TNF-α axis and macrophage polarization

Abstract

Liver fibrosis is an important pathologic process in response to chronic or repetitive liver injury. It can advance to liver cirrhosis. Both peroxisome proliferator-activated receptor gamma (PPARγ) and Nogo-B play critical roles in fibrogenesis, while PPARγ is essential for the development. However, the effect of Nogo-B deficiency on the development of liver fibrosis in cell-specific PPARγ deficient mice remains unknown. In this study, hepatocyte or macrophage PPARγ deficient (hPPARγ KO or mPPARγ KO) mice, Nogo-B deficient mice, and cell-specific PPARγ plus Nogo-B double deficient (hPPARγ/Nogo-B DKO or mPPARγ/Nogo-B DKO) mice were induced liver fibrosis by CCl₄ injection. We found hPPARγ KO mice showed enhanced liver fibrotic signatures compared to mPPARγ KO mice after CCl₄ administration. Hepatocyte or macrophage PPARγ deficiency further enhanced CCl₄-induced severe inflammation infiltration, apoptosis and M1 macrophage polarization in the liver. In contrast, Nogo-B deficiency effectively ameliorated PPARγ deficiency-aggravated liver injury and fibrosis. It ameliorated PPARγ deficiency-aggravated liver inflammation and fibrosis by suppressing hepatic stellate cell activation, TLR4-NF-κB/TNF-α signaling and M1 macrophage polarization. In conclusion, our study demonstrates that PPARγ deficiency increases susceptibility of mice to develop CCl₄-induced liver injury/fibrosis, which is potently reduced by Nogo-B deficiency, indicating Nogo-B inhibition might be a therapeutic approach for liver fibrosis treatment.

Keywords: Inflammation; Liver fibrosis; Macrophage polarization; Nogo-B; PPARγ.