Lactylation-regulated METTL3-mediated cholesterol metabolic reprogramming via FDFT1 facilitates macrophage polarization in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) exhibits limited clinical response to immunotherapy, highlighting the pressing need for novel strategies targeting its immunosuppressive microenvironment. While metabolic reprogramming and epigenetic alterations contribute to malignancy, the role of lactate-driven protein lactylation in remodeling the tumor microenvironment remains elusive. This study aimed to investigate the role of histone and non-histone lactylation in HCC, focusing on its regulatory impact on cholesterol metabolism and anti-tumor immune responses. To elucidate novel epigenetic mechanisms driven by lactate-induced histone and non-histone lactylation, global lactylome profiling was implemented in this study. Additionally, customized site-specific antibodies, RNA sequencing, lipidomics, and single-cell RNA-seq (scRNA-seq) validation were employed to systematically investigate the underlying regulatory network. Next, spontaneous orthotopic HCC mouse models, humanized orthotopic HCC models, and flow cytometry were utilized to explore the functional characteristics of METTL3-K27 lactylation. Mechanistically, H3K18 lactylation upregulated METTL3 expression, while site-specific METTL3 K27 lactylation facilitated m⁶A modification of FDFT1 transcripts. Moreover, IGF2BP2 recognized these epitranscriptomic marks to promote FDFT1 translation, thereby enhancing cholesterol biosynthesis and efflux. Then, this metabolite-driven reprogramming polarized tumor-associated macrophages toward an immunosuppressive M2 phenotype. These findings highlighted the pivotal role of the H3K18la/METTL3-K27la/FDFT1 axis in reprogramming the TME. Consequently, targeting this pathway may alleviate immunosuppression in HCC, establishing a novel therapeutic strategy that interconnects histone lactylation, non-histone lactylation, cholesterol metabolic reprogramming, and immune modulation.