Single-cell and spatial analyses reveal the association between gene expression of glutamine synthetase with the immunosuppressive phenotype of APOE+CTSZ+TAM in cancers

The heterogeneity of tumour-associated macrophages contributes to the clinical outcomes and indications for immune checkpoint blockade in colorectal cancer patients

Tumor-associated macrophages (TAMs), one of the major immune cell types in colorectal cancer (CRC) tumor microenvironment (TME), play indispensable roles in immune responses against tumor progression. In this study, we aimed to know whether the extensive inter and intra heterogeneity of TAMs contributes to the clinical outcomes and indications for immune checkpoint blockade (ICB) in CRC. We used single-cell RNA sequencing (scRNA-Seq) data from 60 CRC patients and charactrized TAMs based on anatomic locations, tumor regions, stages, grades, metastatic status, MSS/MSI classification and pseudotemporal differentiation status. We then defined a catalog of 21 gene modules that determine macrophage status, and identified 7 of them as relevant to clinical outcomes and 11 as indications for ICB therapy. On this basis, we constructed a unique TAM subgroup profile, aiming to find features that may be highly responsive to immunotherapy for the CRC with poor prognosis under conventional treatment. This TAM subpopulation is enriched in tumors and is associated with poor prognosis, but exhibits a high immunotherapy response signature (HIM TAM). Further spatial transcriptome analysis and ligand-receptor interaction analysis confirmed that HIM TAM is involved in shaping TIME, especially the regulation of T cells. Our study provides insights into different TAM subtypes, highlights the importance of TAM heterogeneity in relation to patient prognosis and immunotherapy response, and reveals potential immunotherapy strategies based on TAM characteristics for CRC that does not respond well to conventional therapy.

Macrophage heterogeneity and its interactions with stromal cells in tumour microenvironment

Macrophages and tumour stroma cells account for the main cellular components in the tumour microenvironment (TME). Current advancements in single-cell analysis have revolutionized our understanding of macrophage diversity and macrophage-stroma interactions. Accordingly, this review describes new insight into tumour-associated macrophage (TAM) heterogeneity in terms of tumour type, phenotype, metabolism, and spatial distribution and presents the association between these factors and TAM functional states. Meanwhile, we focus on the immunomodulatory feature of TAMs and highlight the tumour-promoting effect of macrophage-tumour stroma interactions in the immunosuppressive TME. Finally, we summarize recent studies investigating macrophage-targeted therapy and discuss their therapeutic potential in improving immunotherapy by alleviating immunosuppression.

Novel tumor-associated macrophage populations and subpopulations by single cell RNA sequencing

Tumor-associated macrophages (TAMs) are present in almost all solid tumor tissues. 16They play critical roles in immune regulation, tumor angiogenesis, tumor stem cell activation, tumor invasion and metastasis, and resistance to therapy. However, it is unclear how TAMs perform these functions. With the application of single-cell RNA sequencing (scRNA-seq), it has become possible to identify TAM subpopulations associated with distinct functions. In this review, we discuss four novel TAM subpopulations in distinct solid tumors based on core gene signatures by scRNA-seq, including FCN1 +, SPP1 +, C1Q + and CCL18 + TAMs. Functional enrichment and gene expression in scRNA-seq data from different solid tumor tissues found that FCN1 + TAMs may induce inflammation; SPP1 + TAMs are potentially involved in metastasis, angiogenesis, and cancer cell stem cell activation, whereas C1Q + TAMs participate in immune regulation and suppression; And CCL18 + cells are terminal immunosuppressive macrophages that not only have a stronger immunosuppressive function but also enhance tumor metastasis. SPP1 + and C1Q + TAM subpopulations can be further divided into distinct populations with different functions. Meanwhile, we will also present emerging evidence highlighting the separating macrophage subpopulations associated with distinct functions. However, there exist the potential disconnects between cell types and subpopulations identified by scRNA-seq and their actual function.

Glutamine synthetase and hepatocellular carcinoma

Glutamine synthetase (GS) is an enzyme that converts ammonia and glutamate to glutamine using adenosine triphosphate. GS is expressed in the brain, kidney, and liver tissues under normal physiological conditions. GS is involved in abnormal lipid metabolism of the liver by catalyzing de novo synthesis of glutamine, thereby inducing liver inflammation. Metabolic dysfunction-associated steatotic liver diseases (MASLD), such as Metabolic Associated Fatty Liver Disease and Metabolic Associated Steato Hepatitis, are considered risk factors for HCC. GS may also be involved in the development and progression of hepatocellular carcinoma (HCC) through other signaling pathways, including the rapamycin (mTOR) and Wnt/β-catenin signaling pathways. Furthermore, the correct combination of HSP70, GPC3, and GS can improve the accuracy and precision of HCC diagnosis. However, the prognostic value of GS in different HCC populations remains controversial. The expression of GS affects the sensitivity of HCC cells to radiotherapy and chemotherapy. In addition, immunotherapy has been approved for the treatment of advanced HCC. This article delves into the development and application of GS in HCC, laying a theoretical foundation for the subsequent exploration of GS as a potential target for treating HCC.

Intercellular Molecular Crosstalk Networks within Invasive and Immunosuppressive Tumor Microenvironment Subtypes Associated with Clinical Outcomes in Four Cancer Types

Heterogeneity is a critical basis for understanding how the tumor microenvironment (TME) contributes to tumor progression. However, an understanding of the specific characteristics and functions of TME subtypes (subTMEs) in the progression of cancer is required for further investigations into single-cell resolutions. Here, we analyzed single-cell RNA sequencing data of 250 clinical samples with more than 200,000 cells analyzed in each cancer datum. Based on the construction of an intercellular infiltration model and unsupervised clustering analysis, four, three, three, and four subTMEs were revealed in breast, colorectal, esophageal, and pancreatic cancer, respectively. Among the subTMEs, the immune-suppressive subTME (subTME-IS) and matrix remodeling with malignant cells subTME (subTME-MRM) were highly enriched in tumors, whereas the immune cell infiltration subTME (subTME-ICI) and precancerous state of epithelial cells subTME (subTME-PSE) were less in tumors, compared with paracancerous tissues. We detected and compared genes encoding cytokines, chemokines, cytotoxic mediators, PD1, and PD-L1. The results showed that these genes were specifically overexpressed in different cell types, and, compared with normal tissues, they were upregulated in tumor-derived cells. In addition, compared with other subTMEs, the expression levels of PDCD1 and TGFB1 were higher in subTME-IS. The Cox proportional risk regression model was further constructed to identify possible prognostic markers in each subTME across four cancer types. Cell-cell interaction analysis revealed the distinguishing features in molecular pairs among different subTMEs. Notably, ligand-receptor gene pairs, including COL1A1-SDC1, COL6A2-SDC1, COL6A3-SDC1, and COL4A1-ITGA2 between stromal and tumor cells, associated with tumor invasion phenotypes, poor patient prognoses, and tumor advanced progression, were revealed in subTME-MRM. C5AR1-RPS19, LGALS9-HAVCR2, and SPP1-PTGER4 between macrophages and CD8+ T cells, associated with CD8+ T-cell dysfunction, immunosuppressive status, and tumor advanced progression, were revealed in subTME-IS. The spatial co-location information of cellular and molecular interactions was further verified by spatial transcriptome data from colorectal cancer clinical samples. Overall, our study revealed the heterogeneity within the TME, highlighting the potential pro-invasion and pro-immunosuppressive functions and cellular infiltration characteristics of specific subTMEs, and also identified the key cellular and molecular interactions that might be associated with the survival, invasion, immune escape, and classification of cancer patients across four cancer types.