Omi/HtrA2 Regulates a Mitochondria-Dependent Apoptotic Pathway in a Murine Model of Septic Encephalopathy

Abstract Background/Aims: the pathogenesis of sepsis-associated encephalopathy (SAE) is multifactorial, involving neurotransmitter alterations, inflammatory cytokines, oxidative damage, mitochondrial dysfunction, apoptosis, and other factors. Mitochondria are major producers of reactive oxygen species, resulting in cellular injury. Omi/HtrA2 is a proapoptotic mitochondrial serine protease involved in caspase-dependent cell death; it is translocated from mitochondria to the cytosol after an apoptotic insult. We previously found that UCF-101, a specific inhibitor of Omi/HtrA2, has neuroprotective effects on cerebral oxidative injury and cognitive impairment in septic rats. In this study, the mechanisms and molecular pathways underlying these effects were investigated. Methods: Male Sprague–Dawley rats were subjected to cecal ligation and puncture (CLP) or sham-operated laparotomy and were administered vehicle or UCF-101 (10 µmol/kg). The hippocampus was isolated for subsequent analysis. Omi/HtrA2 expression in the mitochondria or cytosol was evaluated by immunofluorescence or western blotting. Terminal deoxynucleotidyl transferase dUTP nick end labeling staining was utilized to evaluate levels of apoptosis, and western blotting was used to evaluate apoptosis-related proteins, such as cleaved caspase-3, caspase-9, and poly (ADP-ribose) polymerase (PARP). Tight junction expression was assessed by immunofluorescence and western blotting. Mitochondrial function, inflammatory cytokines, and oxidative stress were also assayed. In addition, a wet/dry method was used to evaluate brain edema and Evans blue extravasation was used to evaluate blood–brain barrier (BBB) integrity. Results: After CLP treatment, the hippocampus exhibited a mild increase in Omi/HtrA2 expression; cytosolic Omi/HtrA2 expression increased significantly, whereas mitochondrial Omi/HtrA2 expression was reduced, indicating that CLP-induced oxidative stress resulted in the translocation of Omi/HtrA2 from mitochondria to the cytosol. Hippocampal cleaved caspase-3, caspase-9, and PARP levels were significantly higher in animals treated with CLP than in sham-operated animals, while XIAP expression was lower. Treatment with UCF-101 prevented the mobilization of Omi/HtrA2 from mitochondria to the cytosol, attenuated XIAP degradation, and decreased cleaved caspase-3, caspase-9, and PARP expression as well as apoptosis. UCF-101 also reversed the decreased mitochondrial complex I, II, and III respiration a