Transcriptome heterogeneity of monocytes and its contribution to formation of immune microenvironment in prostate cancer

Our current knowledge on transcriptomic characteristics of monocytic populations in prostate cancer remains very limited. This is due to complexity of studying heterogeneous circulating immune cells, due to variability of cell phenotypes and antigen expression in malignant tumors. The use of single-cell sequencing provides an opportunity to study the transcriptional profile of monocytes, which may resolve many questions related to the role of different monocyte subpopulations in formation of the tumor immune microenvironment in patients with prostate cancer. The aim of our study was to characterize the contribution of transcriptional features of monocyte subpopulations to the formation of the immune microenvironment in prostate cancer. The study included 3 patients with acinar adenocarcinoma of the prostate and one patient with small acinar prostatic adenocarcinoma. The transcriptomic profile of peripheral blood monocyte cells was obtained using single-cell RNA sequencing (scRNA-seq). Counting matrices were obtained using Cell Ranger and analyzed in R/Seurat, taking into account duplicates (scDblFinder) and filtering low-quality cells. After normalization (SCTransform), integration (Harmony), and clustering (UMAP, PCA, FindClusters), clusters were annotated in Azimuth, and ligand–receptor interactions were explored using CellChat. Transcriptome profiling of monocytic cells using single-cell RNA sequencing (scRNA-seq) revealed that among the highly expressed genes of classical monocytes, there is a network aimed at increasing the pro-inflammatory background of the immune environment (S100A8, S100A9, IL-6). Non-classical monocytes were characterized by increased expression of TRPC6, NO/cGMP signaling components (GUCY1A1/B1), and Sema3A, which are associated with angiogenesis, monocyte recruitment, and their polarization into immunosuppressive phenotypes. Intermediate monocytes demonstrated activation of regulatory-migratory programs (ETS1, CCL5) along with elements of T cell interaction (CD3E, CD247, SKAP1) and IL signaling. The signaling profiles of monocyte subpopulations in prostate cancer show diversity in both outgoing and incoming pathways, reflecting their functional heterogeneity. Features associated with activation of TGFβ -, galectin-, and TRAIL-signaling are noted, thus suggesting involvement of different monocyte subtypes into arising intercellular interactions within tumor microenvironment. Hence, the performed analysis emphasizes an important role of transcriptional features of monocyte subpopulations in development of intercellular interactions and formation of the immune microenvironment in prostate cancer.