Squalene epoxidase induces nonalcoholic steatohepatitis via binding to carbonic anhydrase 3 and is a therapeutic target

ABSTRACT Backgrounds & Aims Squalene epoxidase (SQLE) is the rate-limiting enzyme for cholesterol biosynthesis. We elucidated the functional significance, molecular mechanisms and clinical impact of SQLE in non-alcoholic steatohepatitis (NASH). Methods We performed studies with hepatocyte specific Sqle overexpression transgenic (Sqle tg) mice and mice given high fat high cholesterol (HFHC) or methionine-and choline-deficient (MCD) diet to induce NASH. SQLE downstream target carbonic anhydrase 3 (CA3) was identified by co-immunoprecipitation and Western Blot. Some mice were given SQLE inhibitor (terbinafine) and CA3 inhibitor (acetazolamide) to study the therapeutic effects in NASH. Human samples (n=217) including 65 steatoses, 80 NASH and 72 healthy controls were analyzed for SQLE levels in liver tissue and in serum. Results SQLE is highly up-regulated in human NASH and mouse models of NASH. Sqle tg mice triggered spontaneous insulin resistance, hepatic steatosis, liver injury and accelerated HFHC or MCD diet-induced NASH development. Mechanistically, SQLE tg mice caused hepatic cholesterol accumulation, thereby triggering pro-inflammatory NF-κB signaling and steatohepatitis. SQLE directly bound to CA3, which induced SREBP1C activation, ACC, FASN and SCD1 expression and de novo hepatic lipogenesis. Combined targeting SQLE (terbinafine) and CA3 (acetazolamide) synergistically ameliorated NASH in mice with superior efficacy to either drug alone. Serum SQLE with CA3 could distinguish patients with NASH from steatosis and healthy controls (AUROC 0.815; 95% CI: 0.758–0.871). Conclusions SQLE drivers the initiation and progression of NASH through inducing cholesterol biosynthesis, and SQLE/CA3 axis-mediated lipogenesis. Combined targeting of SQLE and CA3 confers therapeutic benefit in NASH. Serum SQLE and CA3 are novel biomarkers for the non-invasive diagnosis of patient with NASH.