circNfix attenuates acute kidney injury by driving m6A-dependent degradation of YTHDF2 to stabilize DAPK2 mRNA.

Abstract

Although circular RNAs (circRNAs) have been implicated in acute kidney injury (AKI), their functional mechanisms beyond acting as miRNA sponges remain poorly understood, and the role of N6-methyladenosine (m6A) modification in circRNA-mediated regulation in AKI is yet to be explored. Here, we identify a novel mechanism by which the m6A-modified circRNA circNfix contributes to the regulation of septic AKI (SAKI). In tubular epithelial cells (TECs), downregulation of RBM47 reduces circNfix expression during SAKI. m6A-modified circNfix scaffolds the E3 ligase HECTD1 to induce K48-linked polyubiquitination and proteasomal degradation of the m6A reader YTHDF2. This stabilizes DAPK2 mRNA, a key target of YTHDF2, inhibiting NF-κB activation, thereby reducing TEC apoptosis and inflammation. In mouse models of SAKI and ischemia-reperfusion injury-AKI, AAV-mediated circNfix delivery lowered YTHDF2, suppressed inflammation, improved renal function, and attenuated damage. In septic AKI patients, circNfix levels in plasma and urine were significantly decreased, negatively correlated with serum creatinine. Urinary and plasma circNfix showed diagnostic potential. Our study reveals a mechanism where an m6A-modified circRNA contributes to AKI progression by degrading its reader protein, suggesting that circNfix may represent a potential therapeutic target and non-invasive biomarker.