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 <i>Ly6c</i>^hi monocytes in Cluster 0 appeared to be converted into macrophages in the liver, potentially contributing to the progression of NASH inflammation. Similarly, <i>Ly6c</i>^lo monocytes in Cluster 1 seemed to differentiate into dendritic cells, possibly mediating T-cell immune responses in NASH. Notably, <i>Sdc4</i> was uniquely abundant in Cluster 0. <i>Sdc4</i>⁺ monocytes were elevated in NASH patients and mice versus controls. Under lipotoxic conditions, <i>Sdc4</i>-deficient (sh-<i>Sdc4</i>) monocytes exhibited upregulated expression of <i>CD206</i> (an M2 marker) and <i>IL-10</i>. When cocultured with sh-<i>Sdc4</i> monocytes under palmitic acid stimulation, HepG2 cells accumulated fewer lipid droplets and produced less TNF-α protein, along with increased <i>IL-10</i> 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.