USP18 mediates high glucose‐induced cardiomyocyte injury by regulating the JAK/STAT signaling pathway through stabilizing FOXC2 expression

ABSTRACT Background Cardiomyopathy is one of the complications of diabetes, among which myocardial fibrosis is the most typical feature. Ubiquitin‐specific peptidase 18 (USP18) is a deubiquitinating enzyme. Multiple studies suggest that it may have the potential to protect against myocardial injury under diabetes, but the specific mechanism remains unclear. Methods The high glucose (HG) was used to treat neonatal mouse ventricular myocytes (NMVMs) to induce diabetic myocardial injury models, and gene expression was detected by quantitative reverse transcription polymerase chain reaction (RT‐qPCR) and Western blot. The phenotypes of NMVMs were measured using cell counting kit‐8 (CCK‐8), the corresponding kits, flow cytometry, enzyme‐linked immunosorbent assay (ELISA), and DCFH‐DA probe. Besides, cell fibrosis was reflected by immunofluorescence (IF) and Western blot assay. Ubiquitination analysis and Cycloheximide (CHX) experiment were applied to assess protein ubiquitination and degradation, respectively. Results USP18 was downregulated in HG‐induced NMVMs, and USP18 overexpression promoted viability and inhibited apoptosis of NMVMs exposed to HG. Meanwhile, the inflammation, oxidative stress, and fibrosis of NMVMs impelled by HG were reversed after USP18 upregulation. Mechanically, USP18 stabilized forkhead box C2 (FOXC2) expression by reducing its ubiquitination to participate in regulating NMVM viability, apoptosis, inflammation, oxidative stress, and fibrosis via the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. Conclusions USP18 inhibits the ubiquitination of FOXC2 to stabilize its expression, thereby mediating HG‐induced myocardial injury through the JAK/STAT pathway.