Single-Cell RNA Sequencing Revealing that MMP12+ Macrophages are Associated with Cancer Liver Metastasis.

ABSTRACT

AIM: We aimed to explore the MMP12+ macrophages function in liver metastasis of Colorectal cancer [CRC]. BACKGROUND: CRC has a high incidence, and a great many patients develop liver metastases. Some studies have found that macrophages may participate in the liver metastasis of CRC. OBJECTIVE: This study aimed to determine the factors and major signaling pathways of MMP12+ macrophages affecting liver metastasis of CRC. METHODS: The single-cell RNA sequencing [scRNA-seq] data of CRC and bulk transcriptome data were downloaded. After filtering scRNA-seq data, dimensionality reduction and clustering were performed to identify different cell subgroups. The FindAll- Markers function was used to calculate the differentially expressed genes in each cell subgroup, and the genes in the promising set were uploaded to the DAVID database to analyze the biological processes to which these genes were enriched. Differentially expressed genes among macrophage subgroups were selected by the AverageExpression function. Then, the CIBERSORT algorithm was used to compute the proportion of each macrophage subgroup in each bulk tissue and determine the most significant macrophage subgroup. The dynamic changes of gene expression in macrophage subgroup were computed by Pseudotime. Finally, CellChat was applied to investigate the effect of the macrophage subgroup on epithelial cells and the ligand-receptor effect of B cells and T cells. RESULTS: Clustering scRNA-seq data showed a larger proportion of macrophages in liver metastases. The proportion of MMP12+ macrophage subtypes increased gradually among normal, tumor, and liver metastasis groups, and MMP12+ macrophages were associated with angiogenesis, cell migration, and inhibited T cell proliferation. The Pseudotime showed higher expression levels of genes related to angiogenesis and enhanced TGF-ß signaling pathway and the negative regulation of T cell proliferation with the occurrence of liver metastasis in MMP12+ macrophages. MMP12+ macrophages can promote the proliferation of epithelial cells and inhibit the activation of T cells and B cells. CONCLUSION: MMP12+ macrophages promoted liver metastasis of CRC by influencing angiogenesis, TGF-ß signaling pathway expression, and regulation of T cells and B cells.