IGF-I secreted by osteoblasts acts as a potent chemotactic factor for osteoblasts.
Osteoblast recruitment to the site of future bone formation is essential for skeletal development, bone remodeling and fracture healing. A number of factors associated with bone tissue have been reported to induce directional migration of osteoblasts but the mechanism remains to be clarified. In this study, to explore a major chemotactic factor(s) for osteoblasts, we examined the serum-free medium conditioned by MC3T3-E1 osteoblast-like cells for its ability to induce osteoblast migration. Employing sequential chromatography and tandem mass spectrometry analysis, we purified and identified IGF-I as a potent chemotactic factor from the conditioned medium. IGF-I induced cell migration of both MC3T3-E1 cells and primary mouse osteoblasts, and checkerboard analysis revealed that IGF-I markedly induced directional migration (chemotaxis) of osteoblasts. Neutralization of mouse IGF-I with monoclonal antibodies resulted in delayed osteoblast monolayer wound healing and cellular polarization but addition of human IGF-I reversed these effects. IGF-I also promoted cell spreading on fibronectin in an integrin beta1-dependent manner. IGF-I induced Akt and Rac activation and localized accumulation of phosphatidylinositol 3,4,5-triphosphate (PtdIns (3,4,5)P3) at the membrane in osteoblasts. The phosphatidyl inositol 3 kinase (PI3K) inhibitor LY294002 inhibited IGF-I-induced cell migration and wound healing. Together, the results suggest that IGF-I secreted from osteoblasts in the bone tissue is a potent chemotactic factor that may play a major role in recruitment of osteoblasts during bone formation.
Nakasaki
Manando
M
Department of Biology, Osaka Medical Center for Cancer and Cardiovascular Diseases, 1-3-2 Nakamichi, Higashinari-ku, Osaka 537-8511, Japan. man-and@umin.ac.jp
Yoshioka
Kiyoko
K
Miyamoto
Yasuhide
Y
Sasaki
Takehiko
T
Yoshikawa
Hideki
H
Itoh
Kazuyuki
K
D016475:3T3 Cells; D000818:Animals; D002630:Chemotactic Factors / Q000378:metabolism*; D002633:Chemotaxis / Q000502:physiology*; D017077:Culture Media, Conditioned; D016895:Culture Media, Serum-Free; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
D002630:Chemotactic Factors; D017077:Culture Media, Conditioned; D016895:Culture Media, Serum-Free; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020930:MAP Kinase Kinase Kinases