The constitutive androstane receptor protects against metabolic dysfunction-associated steatotic liver disease through sex specific interactions with the gut microbiota

ABSTRACT Background The gut-liver axis is involved in Metabolic dysfunction-Associated Steatotic Liver Disease (MASLD), but the host molecular actors involved in such dialogue have not yet been fully characterized. Objective We investigated the sex-dependent role of the Constitutive Androstane Receptor (CAR) as a hepatic sensor of microbial signals in MASLD pathophysiology. Design Male and female Car+/+ and Car-/- mice were fed a western diet (WD) for 4, 14 or 35 weeks. We performed plasma biochemistry, liver histology, bile acid and cholesterol quantification, untargeted multi-omics approach combining liver RNA-sequencing and 16S rRNA sequencing, together with co-housing, fecal microbiota transplantation and analysis of publicly available transcriptomics data in human cohorts. Results Short-term WD revealed CAR-dependent protection against steatosis, together with perturbations in the transcriptional signatures of multiple transcription factors involved in hepatocyte identity in males. After 14 weeks, CAR deletion increased WD-induced liver damage, inflammation and fibrosis, and disrupted bile acid, cholesterol and gut microbiota homeostasis, in males only. Co-housing and fecal microbiota transplantations revealed that a Car+/+ gut microbiota protected against WD-induced liver damage, while a Car-/- microbiota was reshaped by a Car+/+ host. No CAR-dependent phenotype was observed in females. Finally, in human cohorts, hepatic CAR expression decreased in advanced clinical stages of MASLD. Conclusion CAR is a sex-dependent protective nuclear receptor against MASLD progression, acting both as a transcriptional regulator of hepatocyte identity and as a mediator of the host-microbiota crosstalk. KEY MESSAGES What is already known on this topic The gut-liver axis contributes to Metabolic dysfunction-Associated Steatotic Liver Disease (MASLD) progression. CAR is a liver enriched nuclear receptor with sex-dependent activity, recognizing a broad range of xenobiotic and endobiotic metabolites and regulating xenobiotic, glucose, lipid, bile acid and cholesterol metabolism. New studies have also unveiled its ability to recognize bacterial-derived metabolites under physiological conditions. However, its role in MASLD remains controversial. The only FDA-approved drug for advanced MASLD targets a liver nuclear receptor (thyroid hormone receptor-β) but is effective in fewer than a third of patients. What this study adds CAR is required for the adaptive transcriptional response of hepatocytes to a western diet, acting as an upstream regulator of multiple transcription factors during early MASLD. CAR protects against MASLD in a sex-dependent manner through a causal, bidirectional crosstalk with the gut microbiota, as demonstrated by co-housing and fecal microbiota transplantation experiments In patient cohorts, hepatic CAR mRNA expression decreases at advanced MASLD clinical stages. How this study might affect research, practice or policy Nuclear receptor mechanisms in metabolic disease should be systematically assessed for sex dimorphism, as protective pathways identified in one sex may not generalise to the other. These findings suggest that both the gut microbiota and CAR itself could be targeted, in a sex-informed manner, as therapeutic strategies for MASLD. VISUAL ABSTRACT