Metabolic stress, hepatic lipid accumulation, and macrophage-associated sterile inflammation are closely involved in the development of metabolic dysfunction-associated steatotic liver disease (MASLD). Tirzepatide improves metabolic outcomes, but its effects on macrophage inflammatory signaling in MASLD remain unclear. This study investigated the protective effects of tirzepatide against high-fat, high-fructose diet (HFHFD)-induced MASLD and examined the potential involvement of macrophage Dectin-1/spleen tyrosine kinase (Syk)/nuclear factor-κB (NF-κB) signaling. After 7 weeks of HFHFD feeding to establish the MASLD model, male C57BL/6J mice received tirzepatide (10 nmol/kg, subcutaneously, every 3 days) for an additional 7 weeks. Biochemical assays, histology, hepatic RNA sequencing (RNA-seq), RT-qPCR, Western blotting, and immunofluorescence were performed. Palmitic acid (PA)-stimulated RAW264.7 cells, siRNA-mediated Dectin-1 knockdown, and a RAW264.7 cell-derived conditioned medium-based macrophage-hepatocyte indirect interaction model were used for mechanistic validation. Tirzepatide treatment improved HFHFD-induced metabolic dysfunction, liver injury, hepatic steatosis, and inflammatory responses in mice. RNA-seq revealed enrichment of C-type lectin receptor and NF-κB signaling pathways, while HFHFD-induced Clec7a upregulation was reversed by tirzepatide. Tirzepatide reduced hepatic macrophage accumulation, Dectin-1 expression, and Syk/p65 phosphorylation. In PA-stimulated RAW264.7 cells, tirzepatide suppressed pro-inflammatory cytokine expression and secretion and inhibited Dectin-1/Syk/NF-κB activation. Conditioned medium from tirzepatide-treated RAW264.7 cells attenuated lipid accumulation and abnormalities in lipid metabolism- and inflammation-related gene expression in HepG2 cells. Dectin-1 knockdown itself attenuated PA-induced inflammatory responses and was associated with a reduced additional response to tirzepatide. These findings suggest that tirzepatide alleviates HFHFD-induced MASLD, with suppression of macrophage Dectin-1/Syk/NF-κB signaling potentially contributing to these effects.
