Overexpression of 15-lipoxygenase in the vascular endothelium is associated with increased thymic apoptosis in LDL receptor-deficient mice.
BACKGROUND
15-Lipoxygenase (15-LO) is a nonheme iron-containing enzyme that catalyzes the peroxidation of fatty acids. Herein, we studied the effect of 15-LO overexpression in the vascular endothelium on thymocyte apoptosis by evaluating thymuses from low-density lipoprotein receptor-deficient (LDL-RD) mice and LDL-RD/15-LO mice. Thymuses were evaluated by immunohistochemistry and by TUNEL whereas in vitro studies were carried out by employing freshly isolated thymocytes from the respective mice and evaluation of apoptosis by propidium iodide and annexin V cytometry.


RESULTS
The apoptotic index in LDL-RD/15-LO mice was significantly higher than in the LDL-RD mice. In the thymic medulla the difference was smaller, although still significant. Freshly isolated thymus cells from LDL-RD/15-LO mice exhibited a higher rate of spontaneous cell death than controls. Incubation of thymus cells in the presence of the cell-permeable caspase-3 inhibitor DEVD-CMK resulted in a decrease in the frequency of apoptotic cells in LDL-RD/15-LO thymocytes, whereas no effect was evident in control thymocytes. The antioxidant N-acetylcysteine causes the increase in apoptosis in both groups.


CONCLUSIONS
LDL-RD/15-LO mice exhibit increased thymocyte apoptosis both in vivo and in vitro. These findings may suggest a role for 15-LO in the natural selection of thymocytes.
Afek
A
A
Institute of Pathology, Sheba Medical Center, Tel Hashomer, Israel.
Zurgil
N
N
Bar-Dayan
Y
Y
Polak-Charcon
S
S
Goldberg
I
I
Deutsch
M
M
Kopolovich
J
J
Keren
G
G
Harats
D
D
George
J
J
D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis; D001093:Arachidonate 15-Lipoxygenase / Q000235:genetics / Q000502:physiology*; D053148:Caspase 3; D061945:Caspase Inhibitors; D002478:Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D017637:Clonal Deletion / Q000502:physiology*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009842:Oligopeptides / Q000494:pharmacology; D011973:Receptors, LDL / Q000172:deficiency / Q000235:genetics; D013601:T-Lymphocytes / Q000166:cytology*; D013950:Thymus Gland / Q000098:blood supply / Q000166:cytology*
D000975:Antioxidants; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D009842:Oligopeptides; D011973:Receptors, LDL; C120992:benzyloxycarbonyl aspartyl-glutamyl-valyl-aspartyl-chloromethyl ketone; D001093:Arachidonate 15-Lipoxygenase; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D000111:Acetylcysteine