Pyroptosis, a new form of programmed cell death, was associated with inflammation, immunity, and the development of tumor through activation of inflammasome, including multiple myeloma15, lung cancer16, gastric cancer17, cervical cancer18 and colorectal cancer19. Ding et al. demonstrated that pyroptosis inducers exhibited antitumor immunity activity by inhibiting tumor growth and metastasis20. However, the fundamental role of pyroptosis in the pathogenesis, development and treatment of AML remains to be revealed. Here, we revealed that the transcriptional level of pyroptosis-related genes was altered in AML by bioinformatic analysis. In addition, AML patients were clustered into two subtypes according to the expression level of 40 pyroptosis-related genes. Interestingly, the ES of immune gene sets between two AML subtypes was significantly different and four of them were related with AML prognosis. Finally, nine hub genes from the four prognostic gene sets were predicted to be associated with the prognosis of AML.
Pyroptosis-related genes were abnormally expressed in AML and were related to the survival outcome of patients. In our analysis, pyroptosis-related factor IL18 were elevated in the peripheral blood samples of 132 AML patients from TCGA database, which were consistent with the research of Jia et al6. We found that CASP3 were protective factors for AML patients through univariate cox regression analysis. In addition, Yang et al. established the heteroplastic AML mouse model using THP-1 cells and demonstrated that vitamin B6 triggered the lysis of GSDME by activating CASP3, induced noncanonical pyroptosis of leukemic THP-1 cells in mice, and could also induce pyroptosis of primary AML cells in vitro, exerting anti-AML activity. Similarly, another study confirmed that ardisianone induced pyroptosis of HL60 cells through activation of CASP3 and CASP1 and promoted the differentiation of leukemic cells into monocytes and macrophages21. All of the above confirmed the protective role of CASP3 in AML. In contrast to our findings that CASP1 was a risky factor for AML patients, Johnson et al. demonstrated that DPP8/9 inhibitor induced death of AML cells through CASP1-dependent pyroptosis22. GSDMD, an important protein mediating the lysis of cytomembrane in pyroptosis, were found to be down-regulated in AML in our bioinformatic study. However, Ahn et al. showed that arsenic inhibited the formation of Asc pyroptosome and cleavage of GSDMD, and reduced expression of PML-RARA in acute promyelocytic leukemia (APL), indicating that GSDMD may promoted the development of APL23. GZMB was found to be a risk factor for AML and its hypermethylation was associated with inferior overall survival24. The expression level of GZMA was positively correlated with GZMB, but its role in AML has not been reported. In conclusion, pyroptosis was closely associated with the progress of AML. However, the specific role of pyroptosis in the occurrence, development and treatment of AML needs to be further investigated.
The concise classification method is conducive to the target treatment of AML. According to the genome-wide methylation profiles of cancer samples, Gao et al. developed three AML subtypes with different outcomes and identified their marker genes25. In addition, metabolism-related genes, ferroptosis-related genes, immune-related genes and DNA repair genes could become potential prognostic biomarkers for AML26–28. Here, based on the activity changes of pyroptosis-related genes in AML samples, we stratified AML into two subtypes. Interestingly, AML patients of subtype 1 with lower level of pyroptosis tended to have better prognosis. By comparing the two pyroptosis clusters with cytogenetic risk categories and Fab classifications, we found that pyroptosis was negatively with the prognosis in AML patients with poor karyotypes, which demonstrated that the classification of two distinct pyroptosis patterns was reasonable.
Pyroptosis is closely related to immunity, and both play important roles in the genesis and development of AML. First, single cell transcriptomic data demonstrated that three pyroptosis-related genes CASP1, ELANE and ZBP1 were differently expressed in immune microenvironment of the healthy and AML patients. CASP1, an important molecule of classical cell pyroptosis pathway, was mainly expressed in monocytes. Guo et al. reported that inflammatory monocytes could be activated by abnormal IL-36 production in AML, which in turn blocked CD8 T cell-mediated leukemia clearance and promoted leukemic progenitor cell growth29. Therefore, we inferred that CASP1 may be involved in the development of AML by influencing the function of monocytes. Another important pyroptosis-related gene ELANE was mostly expressed in granulocyte macrophage progenitors (GMPs). Disruption of GMP formation by deleting the lineage-restricted transcription factor C/EBPa inhibited normal granulocyte formation and prevented initiation of AML30. Second, we found that 311 immune gene sets were commonly enriched in “high pyroptosis group” subtype 2, indicating the close relationship between pyroptosis and immunity in AML, which have ever been reported in colon cancer and cervical cancer 31, 32. 4 of 311 immunity-related gene sets associated with IL10, helper T cell (Th), progenitor and MDSCs were found to be related with poor prognosis in AML patients. High level IL10 released by regulatory T cells could elevated the stemness of AML cells by activating the PI3K/AKT signal pathway and helped AML cells evade immune surveillance33. Th17 cells secreted signature cytokine IL-17A and induced proliferation of IL-17 receptor (IL-17R) positive AML cells. AML patients with a high proportion of Th17 cells had a poor prognosis, while patients with a high proportion of Th1 cells had longer survival34. MDSCs activated by pyroptosis-related genes might creat an immunosuppressive microenvironment and promote AML development35, 36. Third, we conducted enrichment analysis of all the genes from the 4 immunity-related prognostic gene sets and found that they were related to ribonucleoside binding, nucleoside binding, purine necleoside binding and so on, which might worsen the prognosis by disturbing DNA synthesis and damage repair in AML. Finally, nine hub genes from the four immunity-related prognostic gene sets were identified and two of them, including OAS1 and ISG15, have been shown to be associated with the prognosis of AML37, 38. In addition, ISG15 and IFIH1, as the stimulators of interferon signaling, may promote the development of AML by activating pyroptosis-related genes 36, 39–41.