Oxidant-mediated mitochondrial injury in eosinophil apoptosis: enhancement by glucocorticoids and inhibition by granulocyte-macrophage colony-stimulating factor.
The mainstay of asthma therapy, glucocorticosteroids (GCs) have among their therapeutic effects the inhibition of inflammatory cytokine production and induction of eosinophil apoptosis. In the absence of prosurvival cytokines (e.g., GM-CSF), eosinophils appear to be short-lived, undergoing apoptosis over 96 h in vitro. In a dose-dependent manner, GC further enhances apoptosis, while prosurvival cytokines inhibit apoptosis and antagonize the effect of GC. The mechanisms of eosinophil apoptosis, its enhancement by GC, and antagonism of GC by GM-CSF are not well-understood. As demonstrated in this study, baseline apoptosis of eosinophils resulted from oxidant-mediated mitochondrial injury that was significantly enhanced by GC. Mitochondrial injury was detected by early and progressive loss of mitochondrial membrane potential and the antioxidant protein, Mn superoxide dismutase (SOD). Also observed was the activation/translocation of the proapoptotic protein, Bax, to mitochondria. Underscoring the role of oxidants was the inhibition of mitochondrial changes and apoptosis with culture in hypoxia, or pretreatment with a flavoprotein inhibitor or a SOD mimic. GCs demonstrated early (40 min) and late (16 h) activation of proapoptotic c-Jun NH2-terminal kinase (JNK) and decreased the antiapoptotic protein X-linked inhibitor of apoptosis, a recently demonstrated inhibitor of JNK activation. Similarly, inhibition of JNK prevented GC-enhanced mitochondrial injury and apoptosis. Importantly, GM-CSF prevented GC-induced loss of X-linked inhibitor of apoptosis protein, late activation of JNK, and mitochondrial injury even in the face of unchanged oxidant production, loss of MnSOD, and early JNK activation. These data demonstrate that oxidant-induced mitochondrial injury is pivotal in eosinophil apoptosis, and is enhanced by GC-induced prolonged JNK activation that is in turn inhibited by GM-CSF.
Gardai
Shyra J
SJ
Department of Pediatrics, National Jewish Medical and Research Center, Denver, CO 80206, USA.
Hoontrakoon
Raweewan
R
Goddard
Cally D
CD
Day
Brian J
BJ
Chang
Ling Yi
LY
Henson
Peter M
PM
Bratton
Donna L
DL
D000276:Adjuvants, Immunologic / Q000494:pharmacology* / Q000502:physiology; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002478:Cells, Cultured; D003907:Dexamethasone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D004306:Dose-Response Relationship, Immunologic; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004804:Eosinophils / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology*; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology; D016877:Oxidants / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000502:physiology*; D010539:Permeability / Q000187:drug effects; D014176:Protein Biosynthesis; D011506:Proteins; D013482:Superoxide Dismutase / Q000037:antagonists & inhibitors / Q000378:metabolism; D051636:X-Linked Inhibitor of Apoptosis Protein
D000276:Adjuvants, Immunologic; D000975:Antioxidants; D016877:Oxidants; D011506:Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D003907:Dexamethasone; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D013482:Superoxide Dismutase; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases