Intracellullar cholesterol accumulation caused by HBV induces ATF6-mediated endoplasmic reticulum stress to trigger endoplasmic reticulophagy

Backgroud: Hepatitis B virus (HBV) Infection can cause Cholesterol accumulation, induce endoplasmic reticulum stress (ERS) and enhance Autophagy in hepatocytes. However, the mechanisms underlying these interactions remain unclear, as well as the potential benefit of cholesterol-lowering treatment in patients with chronic hepatitis B (CHB). Therefore, the effects of of Cholesterol accumulation caused by HBV on ERS and Autophagy were explored in this study, aiming to identify the key molecules mediating the crosstalk between ERS and endoplasmic reticulophagy (ER-phagy).

Methods: Bioinformatics, immunohistochemistry (IHC), proteomics, western blot, and transmission electron microscopy (TEM) were used to analyse clinical specimens, HBV transgenic animal and cell models.

Results: Analysis of Gene Expression Omnibus (GEO) database demonstrated that the transcription levels of LDLR, SREBF2/SREBP2, ATF6, MAP1LC3B/LC3B and SQSTM1/p62 in CHB tissues were higher than those in normal liver tissues. The IHC results showed that the expressions of LDLR, SREBP2, GRP78, ATF6, LC3B, p62 and FAM134B in CHB tissues were higher than those in normal liver tissues. The free Cholesterol content, the expression of GRP78, ATF6, LC3B II, p62 and FAM134B were higher in the livers of HBV transgenic mice and HepG2.2.15 cells compared with their control groups. TEM showed endoplasmic reticulum (ER) expansion and degranulation, as well as ER-phagy, in the livers of HBV transgenic mice and HepG2.2.15 cells. Furthermore, melatonin administration, an ATF6 inhibitor, attenuated hepatic inflammation, alleviated ERS, downregulated ATF6 expression, and inhibited ER-phagy in HBV transgenic mice and HepG2.2.15 cells. Fatostatin administration, a Cholesterol synthesis inhibitor, attenuated hepatic inflammation, decreased the free Cholesterol content, alleviated ERS, downregulated GRP78 and ATF6 expression, and inhibited ER-phagy in HBV transgenic mice and HepG2.2.15 cells CONCLUSION: HBV Infection leads to Cholesterol accumulation in hepatocytes, which promotes ATF6-mediated ERS and FAM134B-mediated ER-phagy. Reducing intracellular Cholesterol accumulation alleviates ATF6-mediated ERS, inhibits FAM134B-mediated ER-phagy, and attenuates hepatic inflammation. ATF6 may represent a promising therapeutic target for an Adjuvant treatment of CHB. Our study provides experimental evidence for the use of statin as an Adjuvant treatment of CHB.

Activating transcription factor 6; Cholesterol metabolism; Endoplasmic reticulophagy; Endoplasmic reticulum stress; Hepatitis B virus.