GPER modulates microbial liver gut axis and suppresses hepatocellular carcinoma

Background: Metabolic dysfunction-associated steatotic liver disease (MASLD) affects nearly one-third of U.S. adults and can progress to MASH, cirrhosis, and HCC. High obesity and diabetes rates accelerate disease progression. Emerging evidence highlights the liver-gut axis and microbiota-derived metabolites as key regulators of liver metabolism and tumorigenesis. This study shows that G protein coupled estrogen receptor (GPER) is central to this axis, regulating lipid metabolism, gut-liver barrier integrity, and microbial colonization. We identified a protective microbial consortium (BIOM) enriched in MASLD but lost in advanced disease, inversely correlating with dyslipidemia, and GPER enhances their engraftment. Methods: GPER expression was assessed by immunohistochemistry, RT qPCR, and Western blot. Barrier integrity was measured with TEER and FITC dextran assays. Microbial colonization and metabolite production were quantified via 16S rRNA sequencing and LC-MS/MS. Functional assays included MTT proliferation, wound-healing, colony formation, and spheroid growth. DNA damage was evaluated by immunofluorescence and proteomics. KEAP1/NRF2 signaling, autophagy, and bile acid transporter expression (FXR, FGF19, BSEP, OSTbeta, NTCP) were analyzed by RT PCR and Western blot. Statistical analyses involved multigroup comparisons and microbial-metabolic correlations. Results: Our preliminary data demonstrate that GPER expression is highest in MASLD and progressively declines in MASH, cirrhosis, and HCC, with high GPER levels correlating with the presence of the protective BIOM microbial consortium in MASLD but their loss in advanced disease. Activation of GPER in liver cancer cells enhances microbial proliferation, biofilm formation, and metabolite production, whereas GPER knockdown diminishes these effects. Functionally, GPER activation suppresses HCC cell proliferation, migration, and colony formation, reduces intracellular lipid accumulation. For the first time, we identified ergothioneine as a pharmacologic activator of GPER, which expands BIOM species, promotes probiotic biofilm engraftment, and prolongs biofilm viability; these effects are abolished with GPER knockdown. GPER signaling further strengthens membrane integrity, upregulates bile acid transporters, activates KEAP1/NRF2 antioxidant pathways. Collectively, these findings establish GPER as a critical regulator linking host receptor signaling to microbiome-mediated metabolic homeostasis and liver tumor suppression, highlighting its potential as a therapeutic target to prevent MASLD progression. Conclusions: GPER functions as a pivotal regulator of the liver-gut axis, connecting host signaling to microbial and metabolic homeostasis. These findings establish GPER as a prime therapeutic target to prevent MASLD progression to MASH, cirrhosis, and HCC, providing a mechanistic framework for microbiome and metabolite based interventions in metabolic liver cancer.