TLR2 inhibition ameliorates the amplification effect of LPS on lipid accumulation and lipotoxicity in hepatic cells

Liting Zhang; Zehui Xie; Hongmiao Yu; Haoxuan Du; Xuqiao Wang; Jiazheng Cai; Yingfei Qiu; Rui Chen; Xiaofeng Jiang; Zelin Liu; Yi Li; Tuo Chen

doi:10.21037/atm-21-4012

TLR2 inhibition ameliorates the amplification effect of LPS on lipid accumulation and lipotoxicity in hepatic cells

Ann Transl Med. 2021 Sep;9(18):1429. doi: 10.21037/atm-21-4012.

Authors

Liting Zhang^{1

2

3}, Zehui Xie⁴, Hongmiao Yu⁵, Haoxuan Du⁶, Xuqiao Wang⁷, Jiazheng Cai⁷, Yingfei Qiu⁷, Rui Chen⁷, Xiaofeng Jiang⁷, Zelin Liu⁷, Yi Li^{1

7}, Tuo Chen^{1

2}

Affiliations

¹ State Key Laboratory of Cryospheric Science, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, China.
² University of Chinese Academy of Sciences, Beijing, China.
³ Department of Infectious Diseases, The First Hospital of Lanzhou University, Lanzhou, China.
⁴ The First School of Clinical Medicine, Lanzhou University, Lanzhou, China.
⁵ Children's Hospital and Institute of Biomedical Sciences, Fudan University, Shanghai, China.
⁶ The First Clinical Medical College of Lanzhou University, Lanzhou, China.
⁷ School/Hospital of Stomatology, Lanzhou University, Lanzhou, China.

Abstract

Background: Gut microbiome dysbiosis is related to the pathogenesis of nonalcoholic fatty liver disease (NAFLD), and the role of toll-like receptor 2 (TLR2) in its molecular mechanism is controversial. Here, we investigated the effects and mechanisms of Escherichia coli-derived lipopolysaccharide (LPS) on lipid accumulation and lipotoxicity in palmitic acid (PA)-treated L02 cell as an NAFLD cell model, and the role of TLR2 in this process.

Methods: Oil red O staining assay and free fatty acid (FFA) content test were performed to determine the effects of LPS on lipid accumulation in a PA-induced NAFLD cell model with or without TLR2 inhibition. The levels of IL-6 and TNF-α were measured to investigate inflammation conditions. Hoechst 33342 staining assay and Caspase-3 activity assay were used to test cell apoptosis, and the expression levels of proteins in the IRS1/PI3K/AKT signaling pathway, TLR2/MyD88/IKKα/NF-κB signaling pathway, and mitochondrion-dependent apoptotic signaling pathway were detected using Western blot.

Results: Lipid accumulation, pro-inflammatory cytokine release, and cell apoptosis with high levels were observed in the PA-induced NAFLD cell model, and LPS aggravated these processes. Whereas TLR2 inhibition could significantly ameliorate PA-induced and LPS-amplified lipid accumulation, inflammatory, and cell apoptosis, it had no significant effect on L02 cells treated with LPS alone.

Conclusions: These results were confirmed by activation or inhibition of the IRS1/PI3K/AKT signaling pathway, TLR2/MyD88/IKKα/NF-κB signaling pathway, and mitochondrion-dependent apoptotic signaling pathway, and were reflected by changes on their proteins expression. TLR2 is involved in PA-induced lipid accumulation and lipotoxicity in L02 cells, which could be aggravated by LPS, although LPS-induced amplification might not be through direct interaction with TLR2.

Keywords: Toll-like receptor 2; inflammation; lipid accumulation; lipopolysaccharide (LPS); nonalcoholic fatty liver disease (NAFLD).