Unrestrained erythroblast development in Nix-/- mice reveals a mechanism for apoptotic modulation of erythropoiesis.
Normal production of RBCs requires that the antiapoptotic protein Bcl-xl be induced at end stages of differentiation in response to erythropoietin (Epo) signaling. The critical proapoptotic pathways inhibited by Bcl-xl in erythroblasts are unknown. We used gene targeting in the mouse to evaluate the BH3-only factor Nix, which is transcriptionally up-regulated during Epo-stimulated in vitro erythrocyte differentiation. Nix null mice are viable and fertile. Peripheral blood counts revealed a profound reticulocytosis and thrombocytosis despite normal serum Epo levels and blood oxygen tension. Nix null mice exhibited massive splenomegaly, with splenic and bone marrow erythroblastosis and reduced apoptosis in vivo during erythrocyte maturation. Hematopoietic progenitor populations were unaffected. Cultured Nix null erythroid cells were hypersensitive to Epo and resistant to apoptosis stimulated by cytokine deprivation and calcium ionophore. Transcriptional profiling of Nix null spleens revealed increased expression of cell cycle and erythroid genes, including Bcl-xl, and diminished expression of cell death and B cell-related genes. Thus, cell-autonomous Nix-mediated apoptosis in opposition to the Epo-induced erythroblast survival pathway appears indispensable for regulation of erythrocyte production and maintenance of hematological homeostasis. These results suggest that physiological codependence and coordinated regulation of pro- and antiapoptotic Bcl2 family members may represent a general regulatory paradigm in hematopoiesis.
Diwan
Abhinav
A
Center for Molecular Cardiovascular Research and Department of Pediatrics, Children's Hospital Medical Center, University of Cincinnati, Cincinnati, OH 45267, USA.
Koesters
Andrew G
AG
Odley
Amy M
AM
Pushkaran
Suvarnamala
S
Baines
Christopher P
CP
Spike
Benjamin T
BT
Daria
Diedre
D
Jegga
Anil G
AG
Geiger
Hartmut
H
Aronow
Bruce J
BJ
Molkentin
Jeffery D
JD
Macleod
Kay F
KF
Kalfa
Theodosia A
TA
Dorn
Gerald W
GW
D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D051017:Apoptosis Regulatory Proteins / Q000172:deficiency* / Q000235:genetics* / Q000502:physiology; D002470:Cell Survival / Q000235:genetics; D002478:Cells, Cultured; D004900:Erythroblasts / Q000378:metabolism / Q000473:pathology*; D004913:Erythrocytes, Abnormal / Q000378:metabolism / Q000473:pathology*; D004920:Erythropoiesis / Q000235:genetics*; D004921:Erythropoietin / Q000502:physiology; D007425:Intracellular Membranes / Q000378:metabolism / Q000473:pathology; D008565:Membrane Proteins / Q000172:deficiency* / Q000235:genetics* / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008930:Mitochondria, Liver / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D024101:Mitochondrial Proteins / Q000172:deficiency* / Q000235:genetics* / Q000502:physiology; D010539:Permeability; D015398:Signal Transduction / Q000235:genetics
D051017:Apoptosis Regulatory Proteins; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; C501741:Nix protein, mouse; D004921:Erythropoietin