Elevation of ISG15 promotes diabetic kidney disease by modulating renal tubular epithelial cell pyroptosis

Fibrosis and inflammation in the renal tubular epithelial cells (TECs) are key contributors to the pathology of diabetic kidney disease (DKD). Nevertheless, the precise triggers of these processes remain unclear. This study aimed to explore the role of interferon-stimulated gene 15 (ISG15) in the injury of TECs induced by high glucose (HG) conditions and its implications for the development of DKD. ISG15 knockout (ISG15 KO) mice injected with streptozotocin-treated mice on a high-fat diet were used to investigate its role in DKD. Cellular models with ISG15 knockdown were exposed to HG conditions to assess the effects of ISG15 on cellular responses. Subsequently, we evaluated the impact of ISG15 on pyroptosis, a form of programmed cell death, to understand its potential role in DKD pathology. Furthermore, RNA sequencing (RNA-seq) and molecular biology techniques were employed to explore the signalling pathways potentially regulated by ISG15. We first confirmed an up-regulation of ISG15 within the renal tubule in DKD. The deletion of ISG15 alleviated renal functional damage, fibrosis and inflammation, which correlated with reduced ISGylation levels. Mechanistic investigation revealed that HG stimulation in TECs disrupted the mtDNA-cGAS-STING signalling, which exacerbates the DKD through the NLRP3-CASP1-GSDMD axis. Furthermore, we uncovered a bidirectional regulatory loop between STING and ISG15, with STING enhancing ISG15 expression upstream and ISG15 modulating STING expression through ISGylation. ISG15-mtDNA-STING emerges as a critical hub that integrates the processes of pyroptosis, fibrosis and inflammation. Therapeutic interventions that target this signalling network at various levels may pave the way for innovative treatments for DKD. ISG15 is highly expressed in both DKD mice and renal tubular epithelial cell cultured in HG condition. ISG15 promotes DKD pyroptosis via NLRP3-CASP1-GSDMD axis. ISG15-mtDNA-STING emerges as a critical hub that integrates the processes of pyroptosis.