title: Inhibition of insulin-like growth factor-1 (IGF-1) expression by prolonged transforming growth factor-β1 (TGF-β1) administration suppresses osteoblast differentiation.
abstract: TGF-β1 can regulate osteoblast differentiation not only positively but also negatively. However, the mechanisms of negative regulation are not well understood. We previously established the reproducible model for studying the suppression of osteoblast differentiation by repeated or high dose treatment with TGF-β1, although single low dose TGF-β1 strongly induced osteoblast differentiation. The mRNA expression and protein level of insulin-like growth factor-1 (IGF-1) were remarkably decreased by repeated TGF-β1 administration in human periodontal ligament cells, human mesenchymal stem cells, and murine preosteoblast MC3T3-E1 cells. Repeated TGF-β1 administration subsequently decreased alkaline phosphatase (ALP) activity and mRNA expression of osteoblast differentiation marker genes, such as RUNX2, ALP, and bone sialoprotein (BSP). Additionally, repeated administration significantly reduced the downstream signaling pathway of IGF-1, such as Akt phosphorylation in these cells. Surprisingly, exogenous and overexpressed IGF-1 recovered ALP activity and mRNA expression of osteoblast differentiation marker genes even with repeated TGF-β1 administration. These facts indicate that the key mechanism of inhibition of osteoblast differentiation induced by repeated TGF-β1 treatment is simply due to the down-regulation of IGF-1 expression. Inhibition of IGF-1 signaling using small interfering RNA (siRNA) against insulin receptor substrate-1 (IRS-1) suppressed mRNA expression of RUNX2, ALP, BSP, and IGF-1 even with single TGF-β1 administration. This study showed that persistence of TGF-β1 inhibited osteoblast differentiation via suppression of IGF-1 expression and subsequent down-regulation of the PI3K/Akt pathway. We think this fact could open the way to use IGF-1 as a treatment tool for bone regeneration in prolonged inflammatory disease.
authors.affiliation: Oral Health Science Center, Tokyo Dental College, 261-8502 Chiba, Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Ochiai
authors.forename: Shoko
authors.initials: S
authors.lastname: Okada
authors.forename: Akiko
authors.initials: A
authors.lastname: Saito
authors.forename: Kazuto
authors.initials: K
authors.lastname: Hoshi
authors.forename: Haruto
authors.initials: H
authors.lastname: Yamashita
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Takato
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Azuma
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D001847:Bone Diseases / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D006801:Humans; D055504:Insulin Receptor Substrate Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology*; D010513:Periodontal Ligament / Q000166:cytology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D053773:Transforming Growth Factor beta1 / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D015415:Biomarkers; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D034741:RNA, Small Interfering; D053773:Transforming Growth Factor beta1; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; C494918:AKT1 protein, human; D051057:Proto-Oncogene Proteins c-akt