Gut mycobiota-associated tryptophan catabolites protect against metabolic dysfunction-associated steatotic liver disease

However, the beneficial role of commensal mycobiota in MASLD progression remains poorly understood. Comparing the gut microbiome differences, we demonstrated that the deficiency of Caspase Recruitment Domain-containing protein 9 (CARD9), an adaptor protein for a microbiota recognition receptor, exacerbated HFD-induced MASLD in a gut fungi-dependent manner.

CARD9 deficiency reduced the abundance of Saccharomyces cerevisiae (S. cerevisiae), which was a probiotic alleviating MASLD progression. S.cerevisiae promoted a significantly greater abundance of 5-hydroxyindoleacetic acid (5-HIAA) in intestine through TLR1, which then alleviated MASLD phenotypes via “gut-liver” axis. Particularly, 5-HIAA directly bond to aryl-hydrocarbon receptor (AhR) and stimulated its nuclear translocation, subsequently inducing fatty acid oxidation via carnitine palmitoyl transferase 1A (CPT1A) and acyl-CoA oxidase 1 (ACOX1) transactivation.