C5b-9 terminal complement complex protects oligodendrocytes from death by regulating Bad through phosphatidylinositol 3-kinase/Akt pathway.
Apoptosis of oligodendrocytes is induced by serum growth factor deprivation. We showed that oligodendrocytes and progenitor cells respond to serum withdrawal by a rapid decline of Bcl-2 mRNA expression and caspase-3-dependent apoptotic death. Sublytic assembly of membrane-inserted terminal complement complexes consisting of C5b, C6, C7, C8, and C9 proteins (C5b-9) inhibits caspase-3 activation and apoptotic death of oligodendrocytes. In this study, we examined an involvement of the mitochondria in oligodendrocyte apoptosis and the role of C5b-9 on this process. Decreased phosphatidylinositol 3-kinase and Akt activities occurred in association with cytochrome c release and caspase-9 activation when cells were placed in defined medium. C5b-9 inhibited the mitochondrial pathway of apoptosis in oligodendrocytes, as shown by decreased cytochrome c release and inhibition of caspase-9 activation. Phosphatidylinositol 3-phosphate kinase and Akt activities were also induced by C5b-9, and the phosphatidylinositol 3-phosphate kinase inhibitor LY294002 reversed the protective effect of C5b-9. Phosphatidylinositol 3-phosphate kinase activity was also responsible for the phosphorylation of Bad at Ser112 and Ser136. This phosphorylation resulted in dissociation of Bad from the Bad/Bcl-xL complex in a G(i)alpha-dependent manner. The mitochondrial pathway of oligodendrocyte apoptosis is, therefore, inhibited by C5b-9 through post-translational regulation of Bad. This mechanism may be involved in the promotion of oligodendrocyte survival in inflammatory demyelinating disorders affecting the CNS.
Soane
L
L
Department of Pathology, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
Cho
H J
HJ
Niculescu
F
F
Rus
H
H
Shin
M L
ML
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology*; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D015938:Complement Membrane Attack Complex / Q000502:physiology*; D003574:Cytochrome c Group / Q000037:antagonists & inhibitors / Q000378:metabolism; D004306:Dose-Response Relationship, Immunologic; D015536:Down-Regulation / Q000276:immunology; D004789:Enzyme Activation / Q000276:immunology; D006801:Humans; D009025:Morpholines / Q000494:pharmacology; D009836:Oligodendroglia / Q000166:cytology / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology*; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein
D002352:Carrier Proteins; D053453:Caspase 9; D020169:Caspases; D002867:Chromones; D015938:Complement Membrane Attack Complex; D003574:Cytochrome c Group; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D012694:Serine; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein; C494819:BAD protein, human; C494811:BCL2L1 protein, human; C494821:Bad protein, rat; C494813:Bcl2l1 protein, rat; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494918:AKT1 protein, human; C494920:Akt1 protein, rat; C506433:CASP9 protein, human; C506435:Casp9 protein, rat