ALKBH5-Modified HMGB1-STING Activation Contributes to Radiation Induced Liver Disease via Innate Immune Response

Purpose: Radiation therapy, which is vital for the treatment of primary liver cancer, comes with unavoidable liver injury, which limits its implementation. N6-methyladenosine (m6A) methylation is involved in many molecular functions. However, its role in radiation-induced liver diseases (RILD) remains unknown. Herein, we investigate the role of m6A methylation in RILD. Methods and Materials: Methylated RNA-immunoprecipitation sequencing and RNA transcriptome sequencing were used to reveal the methylation pattern of human hepatic stellate cells (HSCs) exposed to irradiation. C3H/HeN mice and stimulator of interferon genes (STING)-deficient mice underwent x-ray irradiation of 24 Gy in 3 fractions. The m6A methylation of the high-mobility group box 1 (HMGB1) transcript was validated using methylated RNA immunoprecipitation, RNA immuno-precipitation, luciferase assays, and a messenger RNA decay assay. Results: Human hepatic stellate cells showed significant differences in methylation patterns after 8 Gy of x-ray irradiation. Irradiation recruited AlkB homolog 5 (ALKBH5) to demethylate m6A residues in the 3' untranslated region of HMGB1, which resulted in the activation of STING-interferon regulatory factor 3 signaling. Changes in the transcription of the 3' untranslated region of HMGB1 occurred after the knockdown of ALKBH5, which were eliminated after m6A residue muta-tion. Strikingly, ALKBH5 deficiency or HMGB1 silencing both attenuated type I interferon production and decreased hepato-cyte apoptosis. In vivo depletion of ALKBH5 abolished the upregulation of HMGB1-mediated STING signaling and decreased liver inflammation, which was consistent with STING(-/-) mice treated with irradiation. Notably, YTHDF2 (m6A reader protein) directly bound to HMGB1 m6A-modified sites and promoted its degradation. Conclusions: ALKBH5-dependent HMGB1 expression mediates STING-interferon regulatory factor 3 innate immune response in RILD. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

The study revealed the important role of m6A methylation in regulating the STING-interferon regulatory factor 3 signaling in radiation-induced liver diseases, with ALKBH5 and HMGB1 playing crucial roles. These findings contribute to a better understanding of the mechanisms of liver injury caused by radiation therapy.