Single-Cell Profiling Identifies a CCR2(+) Neutrophil-like Population Associated with Colorectal Cancer Liver Metastasis in a Murine Model.

Colorectal liver metastases (CRLMs) are a major contributor to recurrence and mortality in colorectal cancer (CRC), with approximately a quarter of patients developing liver metastases over the course of the disease. Bone-marrow-derived myeloid lineages are sent into the circulatory system and colonize pre-metastatic niches, yet the transcriptional programs by which they establish a pro-metastatic microenvironment remain incompletely defined. Using an MC38 splenic-injection CRLM mouse model, we generated single-cell RNA sequencing (scRNA-seq) profiles of FACS-sorted CD11b+Gr1+ bone marrow myeloid cells, together with bulk RNA sequencing profiles of bone marrow and peripheral blood. Downstream analyses were performed in silico, including clustering and annotation, trajectory inference, cell-cell communication analysis, weighted gene co-expression network analysis (WGCNA), and pathway enrichment, with subset specificity examined against a public dataset of E. coli (Escherichia coli)-infected mice.

Within the CD11b+Gr1+ compartment, a CCR2+ neutrophil-like population (Ly6g+S100a8/9+) emerging during terminal differentiation was identified, which was enriched in CRLM mice but nearly absent in controls. Communication inference revealed an FN1-CD44 interaction involving mature neutrophils, which was associated with an epithelial-mesenchymal transition signature and upregulation of Tgfb1 and Il1b. This subpopulation was not recovered in the infection dataset, suggesting relative specificity to CRLMs. Within the constraints of a splenectomized hepatic colonization model, integrated transcriptomic analysis highlighted a CCR2+ bone marrow neutrophil-like population as a candidate contributor to CRLM, challenging the view that CCR2+ pro-metastatic myeloid cells are exclusively monocytic and suggesting candidate biomarkers and therapeutic targets for further study.