THBS1+ macrophages fuel pathogenic inflammation in alcohol-associated liver disease.

BACKGROUND: Alcohol-associated liver disease (ALD) is one of the most common chronic liver diseases worldwide, with a pathological spectrum ranging from simple steatosis to steatohepatitis and, ultimately, cirrhosis. Severe alcohol-associated hepatitis (sAH) arises acutely within this continuum as a rapidly developing inflammatory condition associated with high mortality and poor prognosis. METHODS: To investigate important cellular subpopulations, we integrated single-cell RNA sequencing (scRNA-seq) data from the peripheral blood and liver tissues of healthy individuals and patients with ALD (including those with alcoholic cirrhosis and sAH). A murine metabolic dysfunction-associated steatotic liver disease and alcohol-associated liver disease (MetALD)-like model was established by combining a metabolic dysfunction-associated steatohepatitis-inducing diet with controlled ethanol exposure. The model was used for histopathological analyses, and CD45+ cells from peripheral blood and liver tissues were isolated for scRNA-seq. Analyses included cell composition profiling, differential expression, pathway enrichment, pseudotime trajectory inference, transcriptional regulatory network reconstruction, and cell-cell communication analysis. In parallel, we generated THBS1‑KO and IL15‑KO immortalized bone marrow-derived macrophages cell lines in vitro and conducted functional assays to validate their roles. RESULTS: ScRNA-seq data revealed significant enrichment of IL15+ monocytes and THBS1+​​​​ monocyte-derived macrophages (moMFs) in patients with sAH, both exhibiting highly proinflammatory characteristics. Pseudotime analysis indicated that circulating IL15+ monocytes could dynamically differentiate into hepatic THBS1+ moMFs. Pathological staining and scRNA-seq data from the MetALD mouse model yielded similar results, further confirming the dynamic evolution of IL15+​​​​ monocytes into THBS1+​​​​ moMFs. In vitro cellular experiments also substantiated the proinflammatory roles of THBS1 and IL15. CONCLUSIONS: Our study reveals that circulating IL15+​​​​ monocytes dynamically differentiate into hepatic THBS1+​​​​ moMFs, and the combined proinflammatory action of these subsets accelerates the progression of ALD.