Single-cell analysis reveals crosstalk between TREM1-positive myeloid cells and cancer-associated fibroblasts in colorectal cancer progression

Abstract Background The limited efficacy of immunotherapy in colorectal cancer (CRC) underscores the need to better define immunosuppressive mechanisms within the tumor microenvironment (TME). We applied single-cell RNA sequencing (scRNA-seq) to characterize stromal–immune interactions shaping the CRC TME. Methods Paired tumor and adjacent normal mucosa samples from eight patients with CRC were analyzed by scRNA-seq. Integrated bioinformatic approaches, including trajectory inference, transcriptional regulon analysis, and cell–cell communication modeling, were used to define cellular differentiation and intercellular signaling. Key findings were validated using The Cancer Genome Atlas datasets, multiplex immunofluorescence staining, and in vitro functional assays. Results Trajectory analysis demonstrated a progressive increase in triggering receptor expressed on myeloid cells 1 (TREM1) expression during tumor-associated myeloid differentiation. TREM1-positive myeloid cells exhibited enriched M2-like signatures and were preferentially associated with consensus molecular subtype 4 tumors, characterized by stromal activation and poor clinical outcomes. Stromal profiling identified an α-smooth muscle actin (ACTA2)-positive population associated with CRC progression. Spatial analyses revealed close localization of TREM1-positive myeloid cells and ACTA2-positive cancer-associated fibroblasts (CAFs) in tumor tissues. Mechanistically, integrated bioinformatic analyses indicated that TREM1-positive myeloid cells engage CAFs primarily through secreted phosphoprotein 1 (SPP1) signaling, while CAFs reinforce immunosuppressive myeloid phenotypes via TGF-β-associated extracellular matrix pathways. Functional assays showed that TREM1 inhibition reduced SPP1 expression and attenuated M2 macrophage polarization. Conclusions These findings identify a bidirectional interaction between TREM1-positive myeloid cells and CAFs that contributes to a profibrotic and immunosuppressive CRC microenvironment, highlighting the TREM1–SPP1 axis as a pathway of potential translational relevance.