Single-Cell RNA Sequencing Dissect The Landscape Of Gastric Cancer Tumor Microenvironment

As the fifth most common tumor in the world,gastric cancer has the third highest mortality.Due to the lack of effective treatment,the prognosis of patients with advanced gastric cancer is poor,and the survival time is only about one year.Finding new targets is the key to further improve the therapeutic effect and prolong the survival time of patients with advanced gastric cancer.Tumor microenvironment is an important factor affecting tumor progression,metastasis and drug resistance.Targeting tumor microenvironment has become a new strategy and method for tumor therapy.Although the heterogeneity and related molecular mechanisms of gastric cancer microenvironment have been revealed,the specific functions of cell subsets in the tumor microenvironment and the interactions between cell subsets are still lacking.Therefore,improving our understanding of the cell subsets in the gastric cancer microenvironment is essential for the development of more effective drugs.To elucidate the landscape of the tumor microenvironment in gastric cancer and further explore the functional roles of key cell subsets,the tumor microenvironment of gastric cancer was dissected at the single-cell level in this study.Meanwhile,the characteristics and potential molecular mechanisms of different cell types in tumor samples and adjacent-mucosa samples were compared.Then,this paper focused on cancerassociated fibroblasts(CAFs)to explore the heterogeneity of CAFs and its role in the progression of gastric cancer.Additionally,the specific functions of extracellular-matrix remodeling related eCAFs and the potential mechanism of their activation in tumor microenvironment were explored.In this study,single-cell transcriptome sequencing was performed on tumor samples and adjacent-mucosa(AM)samples from eight patients with gastric cancer,and transcriptome data of 36,897 cells were obtained and analyzed.We found seven cell types in gastric cancer microenvironment,including epithelial cells,endothelial cells,fibroblasts,T cells,B cells,macrophages and mast cells.Each cell type presented heterogeneity in the gastric cancer microenvironment,that is,each cell type was composed of multiple cell subsets.By comparing the tumor-derived cells and the AM-derived cells,we found that the tumor-derived cells showed a specific expression profile compared with the AMderived cells,and the number of infiltrating cell subsets in the two samples also showed a significant difference.Notably,we found several cell subsets play vital roles in gastric cancer progression:Firstly,we found that an endothelial cell subset expressed both endothelial and fibroblast marker genes,suggesting that this is a group of endothelial cells undergoing the EndMT(Endothelial-to-mesenchymal transition)process.Then,we found an exhausted T-cell subset in the gastric cancer microenvironment,and the infiltration of this subset was significantly higher in diffuse patients than in intestinal patients.Finally,we found that there were four CAF subgroups in gastric cancer microenvironment,which were myofibroblasts,pericytes,inflammatory CAFs(iCAFs)and extracellular matrix CAFs(eCAFs).These four CAF subgroups presented different molecular characteristics and various functions in gastric cancer microenvironment.Additionally,two CAF subsets,inflammatory CAFs(iCAFs)and extracellular matrix CAFs(eCAFs),communicated with adjacent immune cell subsets in the GC TME.iCAFs interacted with T cells by secreting interleukin(IL)-6 and C-X-C motif chemokine ligand 12(CXCL12),while eCAFs correlated with M2 macrophages via the expression of periostin(POSTN).eCAFs,which function as a pro-invasive CAF subset,decreased the overall survival time of patients with GC.We also showed that the activation of eCAFs may be related to TGFβ signaling pathway.In conclusion,the single-cell transcriptome map of the gastric cancer microenvironment was analyzed in this paper,identifying several key cell subsets.The important functions of eCAFs and the potential molecular mechanism of its activation were discussed,providing a scientific basis for the development of related drugs targeting the tumor microenvironment in gastric cancer.