The Role of Akt1 in Terminal Stages of Endochondral Bone Formation: Angiogenesis and Ossification

Bone. 2009 Dec;45(6):1133-45. doi: 10.1016/j.bone.2009.08.003. Epub 2009 Aug 11.

Abstract

Longitudinal bone growth is the result of endochondral bone formation which takes place in the growth plate. The rate of chondrocyte proliferation and hypertrophy, vascular invasion with the formation of primary ossification centers and cartilage replacement by bone tissue are all important processes required for normal growth. We have shown a role for the PI3K signaling pathway in chondrocyte hypertrophy and bone growth in tibia explant cultures. In this current study, we aimed to investigate the role of Akt1, an important target of PI3K, in endochondral ossification. Akt1 KO mice showed reduced size compared to their littermates throughout life, but the largest difference in body size was observed around 1 week of age. Focusing on this specific developmental stage, we discovered delayed secondary ossification in the long bones of Akt1 KO mice. A delay in formation of a structure resembling a secondary ossification center was also seen in tibia organ cultures treated with the PI3K inhibitor LY294002. The expression of matrix metalloproteinase-14 (MMP-14), the main protease responsible for development of secondary ossification centers, was decreased in the epiphysis of Akt1 KO mice, possibly explaining the delay in secondary ossification centers seen in the Akt1 KO mice. Bone mineral density (BMD) and bone mineral content (BMC) measured in the proximal tibia of 1-year-old mice were decreased in Akt1 KO mice, suggesting that the original delay in ossification might affect bone quality in older animals.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acid Phosphatase / metabolism
  • Animals
  • Body Size / drug effects
  • Bone Density / drug effects
  • Bone Density / physiology
  • Chondrogenesis / drug effects
  • Chondrogenesis / physiology*
  • Chromones / pharmacology
  • Isoenzymes / metabolism
  • Matrix Metalloproteinase 14 / metabolism
  • Matrix Metalloproteinase 9 / metabolism
  • Mice
  • Mice, Knockout
  • Morpholines / pharmacology
  • Neovascularization, Physiologic* / drug effects
  • Organ Culture Techniques
  • Osteogenesis / drug effects
  • Osteogenesis / physiology*
  • Proto-Oncogene Proteins c-akt / deficiency
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Radiography
  • Tartrate-Resistant Acid Phosphatase
  • Tibia / anatomy & histology
  • Tibia / diagnostic imaging
  • Tibia / enzymology
  • Tibia / physiology
  • Vascular Endothelial Growth Factor A / metabolism

Substances

  • Chromones
  • Isoenzymes
  • Morpholines
  • Vascular Endothelial Growth Factor A
  • 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
  • Proto-Oncogene Proteins c-akt
  • Acid Phosphatase
  • Tartrate-Resistant Acid Phosphatase
  • Matrix Metalloproteinase 9
  • Matrix Metalloproteinase 14