The cellular and molecular mechanisms for neutropenia in Barth syndrome.
Barth syndrome (BTHS), a rare, X-linked, recessive disease, is characterized by neutropenia and cardiomyopathy. BTHS is caused by loss-of-function mutations of the tafazzin (TAZ) gene. We developed a model of BTHS by transfecting human HL60 myeloid progenitor cells with TAZ-specific shRNAs. Results demonstrate a significant downregulation in TAZ expression, mimicking the effects of naturally occurring truncation mutations in TAZ. Flow cytometry analyses of cells with TAZ-specific, but not scrambled, shRNAs demonstrate nearly twofold increase in the proportion of annexin V-positive cells and significantly increased dissipation of mitochondrial membrane potential as determined by DIOC6 staining. Transfection of TAZ-specific shRNA had similar effects in U937 myeloid cells but not in lymphoid cell lines. Further studies in HL60 myeloid progenitor cells revealed aberrant release of cytochrome c from mitochondria and significantly elevated levels of activated caspase-3 in response to TAZ knockdown. Treatment with caspase-specific inhibitor zVAD-fmk resulted in substantially reduced apoptosis to near-normal levels. These data suggest that neutropenia in BTHS is attributable to increased dissipation of mitochondrial membrane potential, aberrant release of cytochrome c, activation of caspase-3, and accelerated apoptosis of myeloid progenitor cells, and that this defect can be partially restored in vitro by treatment with caspase-specific inhibitors.
Department of Medicine, University of Washington, Seattle, WA, USA.
Vahagn
V
Makaryan
Willem
W
Kulik
Frederic M
FM
Vaz
Christopher
C
Allen
Yigal
Y
Dror
David C
DC
Dale
Andrew A
AA
Aprikyan
D000217:Acyltransferases; D017209:Apoptosis / Q000235:genetics; D056889:Barth Syndrome / Q000150:complications*; D002308:Cardiolipins / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics; D005786:Gene Expression Regulation; D020868:Gene Silencing; D018922:HL-60 Cells; D006801:Humans; D019169:Jurkat Cells; D053078:Membrane Potential, Mitochondrial / Q000235:genetics; D023461:Myeloid Progenitor Cells / Q000378:metabolism; D009503:Neutropenia / Q000209:etiology* / Q000378:metabolism*; D054504:Precursor Cells, T-Lymphoid / Q000378:metabolism; D034741:RNA, Small Interfering; D014157:Transcription Factors / Q000235:genetics; D020298:U937 Cells
D002308:Cardiolipins; D034741:RNA, Small Interfering; D014157:Transcription Factors; D000217:Acyltransferases; C108675:TAFAZZIN protein, human