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Akt activation is required for TGF-?1-induced osteoblast differentiation of MC3T3-E1 pre-osteoblasts.

ABSTRACT:

Background

We have previously reported that repeated treatment of human periodontal ligament cells and murine pre-osteoblast MC3T3-E1 cells with transforming growth factor-beta 1 (TGF-?1) inhibited their osteoblastic differentiation because of decreased insulin-like growth factor-1 (IGF-1) secretion. We also found that IGF-1/PI3K signaling plays an important role in osteoblast differentiation induced by TGF-?1 treatment; however, the downstream signaling controlling this remains unknown. The aim of this current study is to investigate whether Akt activation is required for osteoblast differentiation.

Methodology/principal findings

MC3T3-E1 cells were cultured in osteoblast differentiation medium (OBM) with or without 0.1 ng/mL TGF-?1. OBM containing TGF-?1 was changed every 12 h to provide repeated TGF-?1 administration. MC3T3-E1 cells were infected with retroviral vectors expressing constitutively active (CA) or dominant-negative (DN)-Akt. Alkaline phosphatase (ALP) activity and osteoblastic marker mRNA levels were substantially decreased by repeated TGF-?1 treatment compared with a single TGF-?1 treatment. However, expression of CA-Akt restored ALP activity following TGF-?1 treatment. Surprisingly, ALP activity increased following multiple TGF-?1 treatments as the number of administrations of TGF-?1 increased. Activation of Akt significantly enhanced expression of osteocalcin, but TGF-?1 treatment inhibited this. Mineralization of MC3T3-E1 cells was markedly enhanced by CA-Akt expression under all medium conditions. Exogenous IGF-1 restored the down-regulation of osteoblast-related gene expression by repeated TGF-?1 administration. However, in cells expressing DN-Akt, these levels remained inhibited regardless of IGF-1 treatment. These findings indicate that Akt activation is required for the early phase of osteoblast differentiation of MC3T3-E1 cells induced by TGF-?1. However, Akt activation is insufficient to reverse the inhibitory effects of TGF-?1 in the late stages of osteoblast differentiation.

Conclusions

TGF-?1 could be an inducer or an inhibitor of osteoblastic differentiation of MC3T3-E1 cells depending on the state of Akt phosphorylation. Our results indicate that Akt is the molecular switch for TGF-?1-induced osteoblastic differentiation of MC3T3-E1 cells.

SUBMITTER: Suzuki E

PROVIDER: S-EPMC4254279 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Akt activation is required for TGF-β1-induced osteoblast differentiation of MC3T3-E1 pre-osteoblasts.

Suzuki Eiichi E Ochiai-Shino Hiromi H Aoki Hideto H Onodera Shoko S Saito Akiko A Saito Atsushi A Azuma Toshifumi T

PloS one 20141203 12

<h4>Background</h4>We have previously reported that repeated treatment of human periodontal ligament cells and murine pre-osteoblast MC3T3-E1 cells with transforming growth factor-beta 1 (TGF-β1) inhibited their osteoblastic differentiation because of decreased insulin-like growth factor-1 (IGF-1) secretion. We also found that IGF-1/PI3K signaling plays an important role in osteoblast differentiation induced by TGF-β1 treatment; however, the downstream signaling controlling this remains unknown. ...[more]

PMID: 25470129

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