Serum amyloid A1 exacerbates hepatic steatosis via TLR4-mediated NF-κB signaling pathway

• Main Authors: Bin Jiang (Author), Dongdong Wang (Author), Yunfu Hu (Author), Wenxuan Li (Author), Fengjiang Liu (Author), Xudong Zhu (Author), Xiaoyu Li (Author), Hanwen Zhang (Author), Hui Bai (Author), Qing Yang (Author), Xiuna Yang (Author), Jingjing Ben (Author), Qi Chen (Author)
• Format: Book
• Published: Elsevier, 2022-05-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.
• Notes: 2212-8778; 10.1016/j.molmet.2022.101462
• Keywords: Hepatic steatosis; Non-alcoholic fatty liver disease; NF-κB signaling pathway; Obesity; Serum amyloid A1; Toll-like receptor; Internal medicine; RC31-1245
• Source: Molecular Metabolism, Vol 59, Iss , Pp 101462- (2022)

Objective: Chronic inflammatory response plays a prominent role in obesity-related nonalcoholic fatty liver disease (NAFLD). However, the intrahepatic triggering mechanism of inflammation remains obscure. This study aimed to elucidate the role of serum amyloid A1 (SAA1), an acute-phase response protein, in the obesity-induced hepatic inflammation and NAFLD. Methods: Male mice were fed a high fat diet (HFD) for 16 weeks, and insulin resistance, hepatic steatosis, and inflammation in mice were monitored. Murine SAA1/2 was genetically manipulated to investigate the role of SAA1 in NAFLD. Results: We found that SAA1 was increased in the NAFLD liver in both humans and mice. Knockout of SAA1/2 or knockdown of hepatic SAA1/2 promoted energy expenditure and alleviated HFD-induced metabolic disorder, hepatic steatosis, and inflammation. Endogenous overexpression of SAA1 in hepatocytes by adeno-associated virus 8 (AAV8) transfection aggravated overnutrition-associated gain of body weight, insulin resistance, hepatic lipid accumulation, and liver injury, which were markedly alleviated by knockout of murine toll-like receptor 4 (TLR4). Mechanistically, SAA1 directly bound with TLR4/myeloid differentiation 2 (MD2) to induce TLR4 internalization, leading to the activation of nuclear factor (NF)-κB signaling and production of both SAA1 and other inflammatory cytokines, including interleukin (IL)-6 and C-C chemokine ligand (CCL2) in hepatocytes. Administration of HFD mice with an AAV8-shRNA-SAA1/2 showed a therapeutic effect on hepatic inflammation and NAFLD progression. Conclusions: These results demonstrate that SAA1 triggers hepatic steatosis and intrahepatic inflammatory response by forming a SAA1/TLR4/NF-κB/SAA1 feedforward regulatory circuit, which, in turn, leads to NAFLD progression. SAA1 may act as a potential target for the disease intervention.