METTL3-Mediated STING Upregulation and Activation in Kupffer Cells Contribute to Radiation-Induced Liver Disease via Pyroptosis.

Abstract

Radiation therapy is a vital adjuvant treatment for liver cancer, although the challenge of radiation-induced liver diseases (RILDs) limits its implementation. Kupffer cells (KCs) are a crucial cell population of the hepatic immune system, and their biologic function can be modulated by multiple epigenetic RNA modifications, including N⁶-methyladenosine (m⁶A) methylation. However, the mechanism for m⁶A methylation in KC-induced inflammatory responses in RILD remains unclear. The present study investigated the function of m⁶A modification in KCs contributing to RILD. Methylated RNA-immunoprecipitation sequencing and RNA transcriptome sequencing were used to explore the m⁶A methylation profile of primary KCs isolated from mice after irradiation with 3 × 8 Gy. Western blotting and quantitative real-time PCR were used to evaluate gene expression. DNA pulldown and chromatin immunoprecipitation assays were performed to verify target gene binding and identify binding sites. Methylated RNA-immunoprecipitation sequencing revealed significantly increased m⁶A modification levels in human KCs after irradiation, suggesting the potential role of upregulated m⁶A in RILD. In addition, the study results corroborated that methyltransferase-like 3 (METTL3) acts as a main modulator to promote the methylation and gene expression of TEAD1, leading to STING-NLRP3 signaling activation. Importantly, it was shown that IGF2BP2 functions as an m⁶A "reader" to recognize methylated TEAD1 mRNA and promote its stability. METTL3/TEAD1 knockdown abolished the activation of STING-NLRP3 signaling, protected against RILD, and suppressed inflammatory cytokines and hepatocyte apoptosis. Moreover, clinical human normal liver tissue samples collected after irradiation showed increased expression of STING and interleukin-1β in KCs compared with nonirradiated samples. Notably, STING pharmacologic inhibition alleviated irradiation-induced liver injury in mice, indicating its potential therapeutic role in RILD. The results of our study reveal that TEAD1-STING-NLRP3 signaling activation contributes to RILD via METTL3-dependent m⁶A modification.