# Hepatocyte Mettl3 Deficiency Drives Primary Sclerosing Cholangitis and Liver Fibrosis via Cholangiocyte‐Macrophage Crosstalk

## TL;DR

This study shows that a deficiency in the Mettl3 gene in liver cells causes a liver disease called primary sclerosing cholangitis and suggests that restoring Mettl3 could be a potential treatment.

## Contribution

The study identifies hepatocyte Mettl3 deficiency as a novel driver of PSC and demonstrates its therapeutic reversal through Mettl3 restoration.

## Key findings

- Hepatocyte-specific Mettl3 deletion induces PSC-like pathology with biliary inflammation and fibrosis.
- Restoring Mettl3 via genetic or viral methods significantly reduces PSC progression and liver fibrosis.
- Mettl3 deficiency increases cytokine secretion, promoting macrophage infiltration and cholangiocyte activation.

## Abstract

Effective therapies for primary sclerosing cholangitis (PSC), a progressive cholestatic liver disease characterized by biliary inflammation and fibrotic damage, remain limited due to an incomplete elucidation of its underlying molecular mechanisms. Although N6‐methyladenosine (m6A) RNA methylation has been implicated in hepatic pathophysiology, its role in PSC remains undefined. Here, we demonstrate that hepatocyte‐specific deletion of Mettl3, a critical m6A methyltransferase, induces spontaneous PSC‐like pathology characterized by ductular reaction and peribiliary fibrosis. Therapeutic restoration of Mettl3 through genetic knock‐in or AAV8‐mediated hepatocyte‐specific overexpression significantly attenuated 3,5‐diethoxycarbonyl‐1,4‐dihydrocollidine (DDC)‐induced PSC progression. Integrated single‐cell and bulk transcriptomic profiles revealed an expansion of Trem2+ macrophages that interact with Spp1high cholangiocytes via the Cd44‐Spp1 axis. Genetic ablation of Trem2 or cholangiocyte‐specific deletion of Spp1 significantly suppressed DDC‐induced biliary injury. Mechanistically, Mettl3‐deficient hepatocytes secreted higher levels of macrophage‐recruiting cytokines (such as Mif and Csf1), facilitating the recruitment of Trem2+ macrophage, which subsequently activated cholangiocytes through Cd44‐Spp1 signaling, exacerbated biliary inflammation and fibrosis. Notably, pharmacological activation of Mettl3 in adult hepatocytes substantially mitigated PSC progression and liver fibrosis. Collectively, our findings establish hepatocyte Mettl3 deficiency as a pivotal driver of PSC pathogenesis and highlight the therapeutic potential of targeting the m6A epitranscriptome in cholestatic liver diseases.

Schematic illustration demonstrating that hepatic Mettl3 depletion significantly elevates the secretion of Mif and Csf1. This elevation facilitates Trem2+ macrophage infiltration and triggers cholangiocyte remodeling through the Spp1‐Cd44 interaction, resulting in spontaneous PSC development in vivo. This pathogenic cascade is reversed by hepatic Mettl3 knock‐in, AAV8‐mediated Mettl3 overexpression, and pharmacological Mettl3 activation (MA3).