Hepatic <i>Mettl14</i> Knockout Disrupts Bile Acid Homeostasis and Alters Fecal Microbiota Composition

Bile acids are multifunctional signaling molecules that play significant roles in maintaining microbial homeostasis. N6-methyladenine (m⁶A), the most abundant epitranscriptomic modification, mediates various biological processes by modulating RNA metabolism. However, the precise regulatory mechanisms of m⁶A methylation in bile acid metabolism, and its downstream effects on microbiota remain unclear. In this study, liver-specific Mettl14 knockout (Mettl14-LKO) reshaped bile acid profile and expression levels of proteins related to bile acid metabolism, namely CYP7A1, FXR, and BSEP. M⁶A-seq data revealed m⁶A methylated peaks on Cyp7a1. Mettl14-LKO significantly elevated expression of m⁶A "reader" IGF2BP3. Knockdown of IGF2BP3 inhibited CYP7A1 expression by decreasing mRNA stability. Mechanistically, Mettl14-LKO promoted bile acid synthesis by upregulating CYP7A1 expression in an m⁶A-IGF2BP3-dependent manner. Interestingly, Mettl14-LKO reduced bile acid content in the ileum due to decreased BSEP levels in the liver. Noteworthy, we discovered for the first time that Mettl14 knockout in the liver altered fecal microbiota composition. Specifically, it changed the abundance of Cyanobacteria and Patescibacteria at the phylum level, and Lachnochostridium, Candidatus-Saccharimonas, and Roseburia at the genera level. Remarkably, Roseburia was negatively correlated with bile acid levels and CYP7A1 expression. Our findings provide new insights into the role of METTL14 in regulating bile acid homeostasis and its impact on fecal microbiota. Roseburia emerges as a potential target for addressing metabolic diseases linked to disrupted METTL14 signaling.