Mir452 protects against septic acute kidney injury by targeting Apaf1 to relieve CASP9-mediated suppression of autophagy.

Abstract

Septic acute kidney injury (AKI) is associated with high mortality and currently lacks effective therapeutics. Mir452 (microRNA 452) is a newly identified, highly sensitive biomarker for septic AKI, but the biological function of Mir452 was unknown. Here we report that Mir452 protects kidney tubular cells in septic AKI by repressing APAF1 (apoptotic peptidase activating factor 1) and associated caspase activation to preserve macroautophagy/autophagy. Using mouse and cell models of septic AKI induced by lipopolysaccharide (LPS), we found that inhibition of Mir452 exacerbated renal dysfunction, tubular apoptosis, and inflammatory responses, whereas Mir452 mimics significantly attenuated kidney injury. Mechanistically, Mir452 was shown to directly bind to the 3 untranslated region (3UTR) of Apaf1 mRNA, repressing APAF1 expression and thereby inhibiting apoptosome-mediated CASP9 activation. This repression further alleviated caspase-mediated cleavage of autophagy-related proteins like BECN1 and ATG5, leading to the preservation of autophagic flux, which in turn limits inflammasome activation and inflammation. Notably, tubule-specific deletion of Apaf1 recapitulated the protective effects of Mir452, whereas forced Apaf1 expression aggravated injury, an effect reversed by CASP9 knockdown. Furthermore, Mir452 significantly promotes protective autophagy in septic AKI by suppressing the APAF1-CASP9 axis, as evidenced by upregulated ATG5 and BECN1 expression, enhanced LC3-II accumulation and autophagosome-lysosome fusion, along with reduced SQSTM1/p62 levels. Functional rescue experiments demonstrated that Mir452's anti-inflammatory effects depend entirely on activated autophagy, as overexpression fails when autophagy is inhibited. Together, the results unveil the Mir452-APAF1-CASP9-autophagy signaling axis that provides an intrinsic anti-inflammation and anti-apoptosis mechanism, suggesting new therapeutic targets for septic AKI.