Bax and Bak do not exhibit functional redundancy in mediating radiation-induced endothelial apoptosis in the intestinal mucosa.
OBJECTIVE
To address in vivo the issue of whether Bax and Bak are functionally redundant in signaling apoptosis, capable of substituting for each other.


METHODS
Mice were exposed to whole-body radiation, and endothelial cell apoptosis was quantified using double immunostaining with TUNEL and anti-CD31 antibody. Crypt survival was determined at 3.5 days after whole-body radiation by the microcolony survival assay. Actuarial animal survival was calculated by the product-limit Kaplan-Meier method, and autopsies were performed to establish cause of death.


RESULTS
Radiation exposure of Bax- and Bak-deficient mice, both expressing a wild-type acid sphingomyelinase (ASMase) phenotype, indicated that Bax and Bak are both mandatory, though mutually independent, for the intestinal endothelial apoptotic response. However, neither affected epithelial apoptosis at crypt positions 4-5, indicating specificity toward endothelium. Furthermore, Bax deficiency and Bak deficiency each individually mimicked ASMase deficiency in inhibiting crypt lethality in the microcolony assay and in rescuing mice from the lethal gastrointestinal syndrome.


CONCLUSIONS
The data indicate that Bax and Bak have nonredundant functional roles in the apoptotic response of the irradiated intestinal endothelium. The observation that Bax deficiency and Bak deficiency also protect crypts in the microcolony assay provides strong evidence that the microvascular apoptotic component is germane to the mechanism of radiation-induced damage to mouse intestines, regulating reproductive cell death of crypt stem cell clonogens.
Rotolo
Jimmy A
JA
Laboratory of Signal Transduction, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Maj
Jerzy G
JG
Feldman
Regina
R
Ren
Decheng
D
Haimovitz-Friedman
Adriana
A
Cordon-Cardo
Carlos
C
Cheng
Emily H-Y
EH
Kolesnick
Richard
R
Fuks
Zvi
Z
D000818:Animals; D017209:Apoptosis; D015415:Biomarkers / Q000378:metabolism; D003114:Colony-Forming Units Assay; D042783:Endothelial Cells / Q000166:cytology / Q000528:radiation effects*; D004730:Endothelium, Vascular / Q000166:cytology / Q000528:radiation effects; D005260:Female; D020287:In Situ Nick-End Labeling; D007413:Intestinal Mucosa / Q000166:cytology / Q000528:radiation effects*; D007421:Intestine, Small / Q000166:cytology / Q000528:radiation effects*; D007583:Jejunum / Q000166:cytology / Q000528:radiation effects; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000378:metabolism; D011832:Radiation Injuries / Q000209:etiology / Q000473:pathology; D013108:Sphingomyelin Phosphodiesterase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D014916:Whole-Body Irradiation; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000172:deficiency / Q000502:physiology*; D051028:bcl-2-Associated X Protein / Q000172:deficiency / Q000502:physiology*
D015415:Biomarkers; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; C112980:acid sphingomyelinase-1; D013108:Sphingomyelin Phosphodiesterase