Unveiling the Role of <i>Sdc4</i>⁺ Monocytes in NASH: A Single-Cell RNA Sequencing Study

Nonalcoholic steatohepatitis (NASH) involves liver inflammation and fibrosis. Monocytes, key immune cells differentiating into macrophages and dendritic cells, are understudied in NASH using single-cell RNA sequencing (scRNA-seq). Liver nonparenchymal cells from NASH and control mice underwent scRNA-seq to identify monocyte subsets and transcriptional profiles. Findings were validated via transfection, coculture, immunofluorescence, and qPCR. scRNA-seq analysis revealed that Ly6c^hi monocytes in Cluster 0 appeared to be converted into macrophages in the liver, potentially contributing to the progression of NASH inflammation. Similarly, Ly6c^lo monocytes in Cluster 1 seemed to differentiate into dendritic cells, possibly mediating T-cell immune responses in NASH. Notably, Sdc4 was uniquely abundant in Cluster 0. Sdc4⁺ monocytes were elevated in NASH patients and mice versus controls. Under lipotoxic conditions, Sdc4-deficient (sh-Sdc4) monocytes exhibited upregulated expression of CD206 (an M2 marker) and IL-10. When cocultured with sh-Sdc4 monocytes under palmitic acid stimulation, HepG2 cells accumulated fewer lipid droplets and produced less TNF-α protein, along with increased IL-10 genes, compared to controls. Our study elucidates the heterogeneity and functional transformation of two major monocyte subsets in NASH. We foundSdc4+ monocytes may exacerbate NASH through pro-inflammatory mechanisms.