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

PURPOSE: 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 biological function can be modulated by multiple epigenetic RNA modifications, including N6-methyladenosine (m6A) methylation. However, the mechanism for m6A methylation in KC-induced inflammatory response in RILD remains unclear. The present study investigated the function of m6A modification in KCs contributing to RILD.

METHODS AND MATERIALS: Methylated RNA-immunoprecipitation sequencing (MeRIP-seq) 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 polymerase chain reaction were used to evaluate gene expression. DNA pull-down and CHIP assays were performed to verify target gene binding and identify binding site.

RESULTS: MeRIP-seq revealed a significantly increased m6A modification level 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 and protected against RILD in addition to suppressing inflammatory cytokines and hepatocyte apoptosis. Moreover, clinically collected human normal liver tissue samples post-irradiation showed increased expression of STING and IL-1β in KCs compared to the non-irradiation group. Notably, STING pharmacological inhibition alleviated irradiation-induced liver injury in mice, indicating its potential therapeutic role in RILD.

CONCLUSIONS: The results of our study reveal that TEAD1-STING-NLRP3 signaling activation contributes to RILD via METTL3-dependent m6A modification.