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Insights into the Role of Choline Kinase in Endochondral Bone Formation and Human Osteoblasts Function Open Access

Descriptions

Other title
Subject/Keyword
chondrocyte
osteoblast
endochondral bone formation
phosphocholine
radius and ulna
choline kinase
growth plate
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Li, Zhuo
Supervisor and department
Vance, Dennis (Biochemistry)
Examining committee member and department
Berry, Fred (Medical Genetics)
Doschak, Michael (Pharmaceutcal Sciences)
Stern, Paula (Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School)
Joseph, Casey (Biochemistry)
Department
Department of Biochemistry
Specialization

Date accepted
2014-03-24T13:52:20Z
Graduation date
2014-06
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
Choline kinase (CK) phosphorylates choline to phosphocholine (PCho) and is the first enzyme in the CDP-choline pathway that generates phosphatidylcholine (PC). CK has three isoforms (CKα1, CKα2 and CKβ) that are encoded by two genes, Chkα and Chkb. Inactivation of Chkα results in embryonic lethality, whereas Chkb-/- mice display neonatal forelimb bone deformations. To understand the mechanisms underlying the bone deformations, we compared the biology and biochemistry of bone formation from embryonic to neonatal Chkb-/- and Chkb+/+ mice. The deformations are specific to the radius and ulna and occur during the late embryonic stage. The radius and ulna of Chkb-/- mice display expanded hypertrophic zones, unorganized proliferative columns in their growth plates, and delayed formation of primary ossification centers. The differentiation of chondrocytes in the radius and ulna of Chkb-/- mice was impaired, as was chondrocyte proliferation and expression of matrix metalloproteinases 9 and 13. In chondrocytes from Chkb-/- mice, PC was slightly lower than in wild-type mice whereas the amount of PCho was decreased by approximately 75%. In addition, the radius and ulna from Chkb-/- mice contained fewer osteoclasts along the cartilage/bone interface. These data indicate that CKβ plays an important role in endochondral bone formation by modulating growth plate physiology. There is limited knowledge about PC biosynthesis in bone formation. Thus, we characterized PC metabolism in both primary human osteoblasts (HOB) and human osteosarcoma MG-63 cells. Our results show that the CDP-choline pathway is the only de novo route for PC biosynthesis in both HOB and MG-63 cells. Both CK activity and CKα expression in MG-63 cells were significantly higher than in HOB cells. Silencing of CKα in MG-63 cells had no significant effect on PC concentration but decreased the amount of PCho by approximately 80%. Silencing of CKα also reduced cell proliferation. Moreover, pharmacological inhibition of CK activity impaired the mineralization capacity of MG-63 cells. These data suggest that CK and its product PCho are required for the normal growth and mineralization of MG-63 cells. In summary, these studies outline the physiological importance of CKβ in murine endochondral bone formation and CKα in human osteoblasts function.
Language
English
DOI
doi:10.7939/R3HM52T3N
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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File title: Zhuo Li
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