Impairment of the mitochondrial respiratory enzyme activity triggers sequential activation of apoptosis-inducing factor-dependent and caspase-dependent signaling pathways to induce apoptosis after spinal cord injury.
The mitochondrion participates in caspase-independent or caspase-dependent apoptotic pathways through the release of apoptosis-inducing factor or cytochrome c. Whether both mitochondrial apoptotic cascades are triggered in the injured spinal cord remains unknown. Here, we demonstrated that neurons, astrocytes and microglia in spinal segments proximal to a complete spinal cord transection underwent two phases of apoptotic cell death. The early phase of high-molecular weight (HMW) DNA fragmentation was associated with nuclear translocation of apoptosis-inducing factor, reduction in mitochondrial respiratory chain enzyme activity and decrease in cellular ATP concentration. The delayed phase of low-molecular weight (LMW) DNA fragmentation was accompanied by cytosolic release of cytochrome c, activation of caspases 9 and 3, and resumption of mitochondrial respiratory functions and ATP contents. Microinfusion of coenzyme Q(10), an electron carrier in mitochondrial respiratory chain, into the epicenter of the transected spinal cord attenuated both phases of induced apoptosis, and reversed the elicited mitochondrial dysfunction, bioenergetic failure, and activation of apoptosis-inducing factor, cytochrome c, or caspases 9 and 3. We conclude that mitochondrial dysfunction after spinal cord transection represents the initiating cellular events that trigger the sequential activation of apoptosis-inducing factor-dependent and caspase-dependent signaling cascades, leading to apoptotic cell death in the injured spinal cord.
Wu
Kay L H
KL
Graduate Institute of Medicine, Kaohsiung Medical University, and Department of Medical Edcuation and Research, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan.
Hsu
Chin
C
Chan
Julie Y H
JY
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051033:Apoptosis Inducing Factor / Q000502:physiology*; D053148:Caspase 3 / Q000502:physiology; D053453:Caspase 9 / Q000502:physiology; D003067:Coenzymes / Q000494:pharmacology; D045304:Cytochromes c / Q000502:physiology; D053938:DNA Fragmentation; D004579:Electron Transport / Q000502:physiology*; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors; D008297:Male; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D009245:NADH Dehydrogenase / Q000037:antagonists & inhibitors; D021381:Protein Transport; D051381:Rats; D017207:Rats, Sprague-Dawley; D013047:Specific Pathogen-Free Organisms; D013116:Spinal Cord / Q000201:enzymology; D013119:Spinal Cord Injuries / Q000503:physiopathology*; D014451:Ubiquinone / Q000031:analogs & derivatives / Q000494:pharmacology
D051033:Apoptosis Inducing Factor; D003067:Coenzymes; D014451:Ubiquinone; D000255:Adenosine Triphosphate; D045304:Cytochromes c; D009245:NADH Dehydrogenase; D003576:Electron Transport Complex IV; C505410:Casp3 protein, rat; C506435:Casp9 protein, rat; D053148:Caspase 3; D053453:Caspase 9; C024989:coenzyme Q10