Akt regulates skeletal development through GSK3, mTOR, and FoxOs.
Although Akt plays key roles in various cellular processes, the functions of Akt and Akt downstream signaling pathways in the cellular processes of skeletal development remain to be clarified. By analyzing transgenic embryos that expressed constitutively active Akt (myrAkt) or dominant-negative Akt in chondrocytes, we found that Akt positively regulated the four processes of chondrocyte maturation, chondrocyte proliferation, cartilage matrix production, and cell growth in skeletal development. As phosphorylation of GSK3beta, S6K, and FoxO3a was enhanced in the growth plates of myrAkt transgenic mice, we examined the Akt downstream signaling pathways by organ culture. The Akt-mTOR pathway was responsible for positive regulation of the four cellular processes. The Akt-FoxO pathway enhanced chondrocyte proliferation but inhibited chondrocyte maturation and cartilage matrix production, while the Akt-GSK3 pathway negatively regulated three of the cellular processes in limb skeletons but not in vertebrae due to less GSK3 expression in vertebrae. These findings indicate that Akt positively regulates the cellular processes of skeletal growth and endochondral ossification, that the Akt-mTOR, Akt-FoxO, and Akt-GSK3 pathways positively or negatively regulate the cellular processes, and that Akt exerts its function in skeletal development by tuning the three pathways in a manner dependent on the skeletal part.
Rokutanda
Satoshi
S
Department of Cell Biology, Unit of Basic Medical Sciences, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki 852-8588, Japan.
Fujita
Takashi
T
Kanatani
Naoko
N
Yoshida
Carolina A
CA
Komori
Hisato
H
Liu
Wenguang
W
Mizuno
Akio
A
Komori
Toshihisa
T
D000818:Animals; D001846:Bone Development; D018929:Cell Culture Techniques; D004622:Embryo, Mammalian; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D017930:Genes, Reporter; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007150:Immunohistochemistry; D049410:Luciferases, Renilla / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D009924:Organ Culture Techniques; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases
D051858:Forkhead Transcription Factors; D049452:Green Fluorescent Proteins; D049410:Luciferases, Renilla; D011494:Protein Kinases; C546843:mTOR protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D038362:Glycogen Synthase Kinase 3