NF-κB/Apaf1/caspase-9 Axis Suppresses Autophagy to Drive Tubular Inflammation and Apoptosis in Septic Acute Kidney Injury

Septic acute kidney injury (AKI) is a life-threatening complication of systemic infection, characterized by rapid loss of renal function and high mortality. Despite its clinical significance, the underlying molecular mechanisms remain incompletely elucidated. In this study, we identify the NF-κB/ apoptotic protease-activating factor 1(Apaf1)/caspase-9 signaling axis as a central regulator of tubular apoptosis and inflammation through suppression of autophagy. Using proximal tubule-specific Apaf1 knockout mice, we demonstrate that Apaf1 deficiency significantly mitigates LPS-induced renal dysfunction, reduces histopathological injury, and decreases tubular apoptosis, as evidenced by TUNEL staining and cleaved-caspase-3 expression. Correspondingly, renal inflammatory cytokines, including Il6, Tnfa, and Mcp1, are markedly downregulated. In vitro, Apaf1 knockdown in LPS-treated BUMPT (The Boston University mouse proximal tubular cell line) cells similarly reduces apoptosis and inflammation, whereas Apaf1 overexpression exacerbates these pathological responses, confirming its pivotal role in tubular injury. Mechanistic studies reveal that Apaf1 mediates activation of caspase-9, which subsequently suppresses autophagic flux, as indicated by altered LC3 and p62 expression. Pharmacologic inhibition of caspase-9 using Z-LEHD-FMK restores autophagy, attenuates tubular apoptosis, and dampens inflammatory cytokine production in both cell culture and murine models, highlighting caspase-9 as a critical downstream effector. Furthermore, NF-κB functions as an upstream transcriptional activator of Apaf1, linking inflammatory signaling to autophagy suppression and tubular injury. Collectively, our findings delineate a sequential NF-κB/Apaf1/caspase-9/autophagy pathway that amplifies tubular inflammation and apoptosis in septic AKI. Targeting this axis may provide a novel therapeutic strategy to preserve tubular integrity, limit inflammation, and improve renal outcomes in patients with septic AKI.