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

• Author / Creator

  Li, Zhuo

• 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.

• Subjects / Keywords

  • Growth plate
  • Choline kinase
  • Radius and ulna
  • Chondrocyte
  • Osteoblast
  • Phosphocholine
  • Endochondral bone formation

• Graduation date

  Spring 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3HM52T3N

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.