CMTM4 promotes PD-L1-mediated macrophage apoptosis by enhancing STAT2 phosphorylation in sepsis

Abstract

Background

Macrophage apoptosis is a key contributor to the elimination of immune cells and increased susceptibility during sepsis. CKLF like MARVEL transmembrane domain containing 4 (CMTM4) is a membrane protein with four transmembrane domains. It has recently been implicated in the regulation of immune cell biological functions. However, its role in regulating macrophage apoptosis during sepsis has not been extensively studied.

Methods

Clinical samples were analyzed to determine CMTM4 expression levels and their correlation with clinical examination results. An in vitro model was developed using C57BL/6 mice and the THP-1 cell line. An immunofluorescence analysis was used to assess protein expression levels, apoptosis, and protein co-localization. Western blotting (WB) was used to measure protein expression levels, while flow cytometry was used to detect cell apoptosis. Transcriptomic sequencing was conducted to identify differentially expressed genes and to perform a functional enrichment analysis. Transcription factors were screened using databases. Chromatin immunoprecipitation, followed by quantitative PCR (ChIP-qPCR), was conducted to analyze protein–DNA interactions, and co-immunoprecipitation (Co-IP) was used to examine protein–protein interactions.

Results

CMTM4 expression in macrophages was upregulated in sepsis. The inhibition of CMTM4 expression reduced macrophage apoptosis. PD-L1 was identified as a key molecule regulated by CMTM4 in macrophage apoptosis. CMTM4 regulates PD-L1 by promoting the phosphorylation of its transcription factor, STAT2, rather than directly binding to PD-L1.

Conclusion

In sepsis, CMTM4 facilitates PD-L1-dependent macrophage apoptosis by enhancing STAT2 phosphorylation. This discovery offers new insights for the diagnosis and treatment of sepsis.