The role of mitochondrial-mediated apoptosis in a myelodysplastic syndrome secondary to congenital deletion of the short arm of chromosome 4.
OBJECTIVE
Myelodysplastic syndromes (MDS) are characterized by peripheral cytopenia and ineffective hematopoiesis. In adult-onset MDS and in certain inherited marrow failure syndromes, apoptosis is increased and is mediated mainly through activation of the Fas pathway. It is unclear whether the various myelodysplastic disorders share the same apoptosis pathways. I investigated apoptosis pathways in a patient with refractory cytopenia with ring sideroblasts associated with congenital 4p deletion to determine the mechanism for bone marrow failure.


METHODS
Marrow cells and lymphoblast cell lines generated from peripheral blood were analyzed for apoptosis and protein expression by flow cytometry, Western blot, and confocal microscopy, either directly or after gamma irradiation (15 G). Cell viability after treatment with inhibitors of specific apoptosis pathways was also determined.


RESULTS
Compared to controls, the patient's marrow and lymphoblastoid cells showed significantly higher apoptosis rates and activation of caspase-3. Investigation of the mitochondrial apoptosis pathway showed a consistent pro-apoptosis profile, namely, upregulation of Bax, Bax-alpha, cytochrome c, and Apaf1, and low bcl-2. Differences between the patient's and the normal cells were further accentuated after irradiation; p53 expression was strikingly higher in the patient only after irradiation. In contrast, Fas and FADD expression on the patient's and the control's cells were comparable. Addition of caspase 3 or caspase 9 inhibitors markedly increased patient cell viablity, but blocking anti-Fas antibody did not.


CONCLUSIONS
The ineffective hematopoiesis in this case is explained by increased apoptosis and is linked to hyperactivation of the mitochondrial cell death machinery and not to the Fas pathway, which might be secondary to an intramitochondrial defect. This information is crucial because the development of anti-apoptotic agents for the treatment of MDS may not be universally efficacious and should target the specific derangement.
Dror
Yigal
Y
The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada. yigal.dror@sickkids.ca
D000293:Adolescent; D000328:Adult; D017209:Apoptosis / Q000528:radiation effects; D016022:Case-Control Studies; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D002872:Chromosome Deletion; D002894:Chromosomes, Human, Pair 4; D005260:Female; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000528:radiation effects / Q000648:ultrastructure; D008928:Mitochondria / Q000201:enzymology / Q000502:physiology*; D024101:Mitochondrial Proteins / Q000096:biosynthesis / Q000378:metabolism / Q000528:radiation effects; D009190:Myelodysplastic Syndromes / Q000209:etiology / Q000235:genetics / Q000473:pathology*; D010198:Pancytopenia; D015854:Up-Regulation / Q000528:radiation effects
D024101:Mitochondrial Proteins; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases