Kupffer Cell-Derived Interleukin-6 Aggravates Radiation-Induced Liver Disease by Activating Hepatocyte STAT3 to Promote Ccng1 Transcription.

BACKGROUND: Radiation-induced liver disease (RILD) is a serious complication of radiation therapy for upper abdominal tumors, the cellular and molecular basis of which remain mostly unclear. METHODS AND MATERIALS: Single-cell RNA sequencing (scRNA-seq) analysis of rat liver tissues was conducted to identify the key cytokines regulating RILD. Critical downstream target genes of RILD were determined using a chromatin immunoprecipitation (ChIP) assay. The BRL-3A cell line was selected for in vitro experiments. RESULTS: Pathological damage and immune cell infiltration were most severe at 2 weeks after irradiation (IR). ScRNA-seq analysis revealed that Kupffer cells represented the highest proportion of cells after IR (42.4%) and characteristically expressed Il6. Anti-interleukin (IL)-6 could alleviate liver damage and hepatocyte apoptosis after IR, whereas sgp130Fc could not. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the JAK‒STAT signaling pathway in hepatocytes significantly changed after IR. In hepatocytes, STAT3 was significantly activated after IR. ChIP assays indicated that p-STAT3 bound to the promoter of the Ccng1 gene. Flow cytometry revealed that simple addition of exogenous IL-6 significantly aggravated radiation-induced cell apoptosis and cell cycle arrest in BRL-3A cells, and additional Ccng1 knockdown alleviated this damage. Ccng1 knockdown accelerated γH2AX degradation in BRL-3A cells after IR. In cells cultured in IL-6, Ccng1 knockdown upregulated TP53. CONCLUSIONS: Paracrine secretion of IL-6 by Kuppfer cells activates STAT3 in hepatocytes through classical signaling. Activated STAT3 increases Ccng1 transcription. CCNG1 protein may promote TP53 degradation. When TP53 is downregulated, hepatocyte apoptosis increases significantly, resulting in atypical RILD.