Targeting squalene epoxidase restores anti-PD-1 efficacy in metabolic dysfunction-associated steatohepatitis-induced hepatocellular carcinoma.

Abstract

Squalene epoxidase (SQLE) promotes metabolic dysfunction-associated steatohepatitis-associated hepatocellular carcinoma (MASH-HCC), but its role in modulating the tumour immune microenvironment in MASH-HCC remains unclear. We established hepatocyte-specific <i>Sqle</i> transgenic (tg) and knockout mice, which were subjected to a choline-deficient high-fat diet plus diethylnitrosamine to induce MASH-HCC. SQLE function was also determined in orthotopic and humanised mice. Immune landscape alterations of MASH-HCC mediated by SQLE were profiled by single-cell RNA sequencing and flow cytometry. Hepatocyte-specific <i>Sqle</i> tg mice exhibited a marked increase in MASH-HCC burden compared with wild-type littermates, together with decreased tumour-infiltrating functional IFN-γ⁺ and Granzyme B⁺ CD8⁺ T cells while enriching Arg-1⁺ myeloid-derived suppressor cells (MDSCs). Conversely, hepatocyte-specific <i>Sqle</i> knockout suppressed tumour growth with increased cytotoxic CD8⁺ T cells and reduced Arg-1⁺ MDSCs, inferring that SQLE promotes immunosuppression in MASH-HCC. Mechanistically, SQLE-driven cholesterol accumulation in tumour microenvironment underlies its effect on CD8⁺ T cells and MDSCs. SQLE and its metabolite, cholesterol, impaired CD8⁺ T cell activity by inducing mitochondrial dysfunction. Cholesterol depletion in vitro abolished the effect of SQLE-overexpressing MASH-HCC cell supernatant on CD8⁺ T cell suppression and MDSC activation, whereas cholesterol supplementation had contrasting functions on CD8⁺ T cells and MDSCs treated with SQLE-knockout supernatant. Targeting SQLE with genetic ablation or pharmacological inhibitor, terbinafine, rescued the efficacy of anti-PD-1 treatment in MASH-HCC models. SQLE induces an impaired antitumour response in MASH-HCC via attenuating CD8⁺ T cell function and augmenting immunosuppressive MDSCs. SQLE is a promising target in boosting anti-PD-1 immunotherapy for MASH-HCC.