Bulk and Single-Cell Transcriptome Analyses Revealed That the Pyroptosis of Glioma-Associated Macrophages Participates in Tumor Progression and Immunosuppression

Abstract

Glioma is the most common of all central nervous system (CNS) malignancies and is associated with a poor prognosis. Pyroptosis has been proven to be associated with the progression of multiple tumors and CNS diseases. However, the relationships between pyroptosis and clinical prognosis and immune cell infiltration are unclear in glioma. In this study, we conducted a comprehensive exploration of pyroptosis in glioma. First, prognosis-related genes were screened at each key regulatory locus in the pyroptosis pathway, and the prognostic ability and coexpression relationships of GSDMD and its upstream pathway genes NLRC4/CASP1/CASP4 were identified and well validated in multiple datasets. Tissue microarray-based immunohistochemistry results showed higher levels of NLRC4 and N-terminal GSDMD in high-grade gliomas, providing conclusive evidence of pyroptosis in gliomas. The robustness of the prognostic model based on these four genes was well validated in TCGA and CGGA cohorts. Bulk RNA-seq-based analysis showed that the group defined as the high-risk group according to the model showed activation of multiple inflammatory response pathways and impaired synaptic gene expression and had a higher infiltration of bone marrow-derived macrophages (BMDMs) and a hypersuppressed immune microenvironment. More importantly, three independent single-cell RNA-seq (scRNA-seq) datasets demonstrated that tumor-infiltrating macrophages, particularly BMDMs but not tissue-resident microglia, showed significant coexpression of the GSDMD and CASP genes, and BMDMs from high-grade gliomas accounted for a higher proportion of immune infiltrating cells and had higher expression of pyroptosis genes. Finally, we revealed the activation of pathways in response to LPS/bacteria and oxidative stress during BMDM development toward the pyroptosis cell fate by pseudotime trajectory analysis, suggesting potential BMDM pyroptosis initiators. The above results provide not only novel insights into the pathological mechanisms of glioma but also novel therapeutic targets for glioma, suggesting the potential application of pyroptosis inhibitors (e.g., disulfiram).

The dance of macrophage death: the interplay between the inevitable and the microenvironment

“…Some studies demonstrate that either cancer cells or tumor-derived molecules can act as DAMPs causing inflammasome activation and pyroptosis in macrophages ( 211 , 212 , 214 , 215 , 225 ). Interestingly, it was also reported that pyroptosis and/or inflammasome activation in TAMs can arise as a side effect of various anticancer therapies ( 214 , 215 , 225 , 226 ) or may be triggered by factors other than DAMPs ( 216 , 227 ). In this section, we take a closer look at all this evidence.…”

“…Since macrophage pyroptosis can be induced by a range of factors, DAMPs may not be the exclusive initiators of this process in TME. A recent study on the correlation between the occurrence of TAMs pyroptosis and cancer progression utilizing single-cell RNA-sequencing analysis demonstrated that human glioma-infiltrating macrophages, MDMs in particular, had significant co-expression of caspase-1 and GSDMD genes ( 216 ). Moreover, MDMs from high-grade gliomas showed increased transcripts of pyroptotic genes and their elevated infiltration was a characteristic of the high-risk group.…”

“…Moreover, MDMs from high-grade gliomas showed increased transcripts of pyroptotic genes and their elevated infiltration was a characteristic of the high-risk group. Authors proposed LPS/bacteria and oxidative stress as potential initiators of MDMs pyroptosis since the signaling pathways responding to such factors were activated during macrophages’ progression toward the pyroptosis fate ( 216 ). It is particularly intriguing, considering evidence of the presence of bacteria and LPS in human gliomas ( 229 ).…”

Gasdermins: a dual role in pyroptosis and tumor immunity

“…Pyroptosis induced by GSDMD and NLRC4 in high-grade gliomas can promote the progression of gliomas and enhance the sensitivity of these tumors to immune checkpoint therapy by recruiting immune cells ( 127 ). The inflammatory immune microenvironment induced by pyroptosis can promote the invasion and proliferation of glioma stem cells and is also related to the infiltration of M2 pheno-type bone marrow-derived macrophages (BMDMs) ( 72 , 128 ). In the future, it is necessary to construct a GSDMD-deficient mouse model to probe the effects of pyroptosis as a drug target on gliogenesis and the tumor immune microenvironment ( 72 , 127 ).…”