M. Mirza1, M. Cottam1, A. Naveed1, K. Idrees1 1Vanderbilt University Medical Center, Nashville, TN, USA
Introduction: The role of Tumor-associated Macrophages (TAMs) in metastatic Colorectal Cancer (mCRC) remains largely unexplored. This study employs single-cell RNA sequencing (scRNAseq) to unravel the functional diversity of TAMs in mCRC, and elucidates their potential role as a molecular driver of Epithelial-Mesenchymal Transition (EMT) in colorectal peritoneal metasatsis (CPM).
Methods: scRNAseq was conducted on 25 tumor samples from 19 mCRC patients, and bulk RNAseq on 72 samples from 17 patients. TAM sub-clusters were identified and validated. Kaplan-Meier survival analysis estimated overall survival using The Cancer Genome Atlas Colon Cancer dataset.
Results: Utilizing scRNAseq, we identified six unique sub-populations of TAMs in mCRC which were differentially distributed within mCRC. (Figure 1a). CPM was enriched with TAMs expressing SPP1, MARCO, and TGF-B, which were associated with immunosuppressive and pro-tumorigenic pathways, including induction of EMT. Notably, we identified several paired ligand-receptor interactions between TAMs and cancer cells, including TGF-β/TGF-βR and SPP1/CD44, which drive EMT in cancer cells. Intriguingly, our analysis of cancer cells revealed EMT as a prominent co-expressed gene module enriched in CPM (Figure 1b). We validated the enrichment of unique TAM sub-populations and the EMT gene signature in an independent cohort of mCRC. Survival analysis indicated that TAMs and EMT, correlated with poor survival in CRC patients. In-vitro experiments confirmed these findings.
Conclusions: Single-cell resolution analysis of CRC metastasis reveals TAMs' functional heterogeneity and their role in promoting EMT and tumor progression. These insights partially explain the aggressive tumor biology and potential benefits of therapies targeting TAMs in mCRC.
