Macrophage Notch1 signaling modulates regulatory T cells via the TGFB axis in early MASLD

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Background & aimsHepatic immune imbalance is critical in driving metabolic dysfunction-associated steatotic liver disease (MASLD) progression. The role of hepatic regulatory T cells (Tregs) in MASLD initiation and the mechanisms responsible for their change are not completely understood. MethodsA mouse model subjected to a short-term high-fat diet (HFD) to mimic early steatosis, along with liver biopsy samples from patients with simple steatosis and macrophage-specific Notch1 knockout mice (Notch1M-KO)， was used to investigate the role of Tregs in early MASLD and the effect of hepatic macrophage Notch1 signaling on Treg frequency. Using Exos-miRNA-sequencing, we analyzed the miRNA correlated with Treg differentiation. ResultsHere we showed that a decrease in Tregs contributed to HFD-induced hepatic steatosis and insulin resistance (n=5/group/time point, p<0.001). Remarkably, the frequency of Tregs exhibited a negative correlation with Notch1 activation in hepatic macrophages during hepatic steatosis (n=38/group, r=-0.735, p<0.001). Furthermore, we found that Notch1 deficiency attenuated hepatic lipid deposition and reversed Treg levels (n=5 per group, p<0.01, p<0.05). Moreover, Treg depletion in Notch1M-KO mice greatly diminished the ameliorative effect of macrophagic Notch1 deletion on hepatic steatosis. Mechanistically, macrophage Notch1 activation increased its exosomal miR-142a-3p level (1-2-fold), impairing Treg differentiation by targeting TGFBR1 on T cells. Consistently, HFD-fed Notch1M-KO mice exhibited reduced miR-142a-3p levels, elevated TGFBR1 expression on T cells, and increased Tregs frequency in the liver. ConclusionsThese findings highlight the critical role of hepatic Tregs in the early stage of MASLD and add a novel, non-negligible pathway for macrophage involvement in hepatic steatosis. We identify a previously unrecognized molecular mechanism of macrophage Notch1/exosomal miR-142a-3p/TGFBR1 pathway in regulating Treg differentiation, providing the rationale for refined therapeutic strategies for MASLD. Impact and implicationsThe immune mechanisms driving MASLD progression, particularly in the early stages, are not fully understood, which limits the development of effective interventions. This study elucidated a novel mechanism by which hepatic macrophage Notch1 signaling modulated Tregs through the exosomal miR-142a-3p/TGFBR1 axis, contributing to the progression of MASLD. These findings provide a rationale for a potential immunological approach to treat MASLD in the future.