SLC31A1 exon 1 methylation reduces intracellular copper ion and promotes diabetic cardiac fibrosis

BACKGROUND: Metal homeostasis is linked to cellular organelles modification. Dynamic lipid droplet (LD)-mitochondria interactions contribute to diabetes-related complications. However, little is known about whether and how copper regulates LD-mitochondria contacts in diabetic cardiac fibrosis (CF). METHODS: Leptin receptor-deficient (db/db) mice were used to induce diabetic CF. To investigate target gene function in vivo, AAV9 vectors carrying the cardiac fibroblast-specific POSTN promoter-driven small hairpin RNAs were administered. SLC31A1 overexpression was achieved via AAV9 plasmid specifically targeting cardiac fibroblasts to assess its rescue effect on diabetic CF. In vitro, neonatal mouse primary cardiac fibroblasts were stimulated with high glucose/high fatty acids (HG/HF) to mimic diabetic CF. RESULTS: Lower copper concentrations were accompanied by SLC31A1 downregulation and increased LD-mitochondria contacts in diabetic CF and HG/HF-induced cardiac fibroblasts. Fibroblast-specific SLC31A1 deficiency enhanced the LD-mitochondria contacts, fibroblast proliferation, and diabetic CF. Mechanistically, intracellular copper deficiency inhibited the specific binding of H3K27me3 to the PLIN5 promoter and promoted transcription. Furthermore, enhanced DNMT3A expression increases the DNA methylation level in the exon 1 region of SLC31A1. Increased methylated CpGs recruited MeCP2, suppressing SLC31A1 expression. Conversely, epigenetic repression rescued SLC31A1 expression, resulting in a certain degree of inhibition of diabetic CF. Human diabetic cardiomyopathy (DCM) heart tissue analyses validated our findings. CONCLUSIONS: This study demonstrates the critical role of SLC31A1 exon 1 methylation-mediated copper depletion in promoting diabetic CF, identifying cardiac fibroblast-specific rescue of copper depletion as a potential therapeutic approach for diabetic CF.