Akt activation is required for TGF-β1-induced osteoblast differentiation of MC3T3-E1 pre-osteoblasts.
Akt activation is required for TGF-β1-induced osteoblast differentiation of MC3T3-E1 pre-osteoblasts.
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DOI：
10.1371/journal.pone.0112566
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发表时间：
2014
期刊：
影响因子：
3.7
通讯作者：
Azuma T
中科院分区：
文献类型：
--
作者：
Suzuki E;Ochiai-Shino H;Aoki H;Onodera S;Saito A;Saito A;Azuma T
我们以前曾报道过，用转化生长因子-β 1（TGF-β1）反复处理人牙周膜细胞和小鼠前成骨细胞MC 3 T3-E1细胞，由于胰岛素样生长因子-1（IGF-1）分泌减少，抑制了它们的成骨分化。我们还发现IGF-1/PI 3 K信号在TGF-β1诱导的成骨细胞分化中起重要作用;然而，控制这一过程的下游信号仍然未知。本研究的目的是探讨成骨细胞分化是否需要Akt激活。将MC 3 T3-E1细胞在含有或不含0.1 ng/mL TGF-β1的成骨细胞分化培养基（OBM）中培养。每12小时更换含TGF-β1的OBM，以提供重复的TGF-β1给药。用表达组成型活性（CA）或显性阴性（DN）-Akt的逆转录病毒载体感染MC 3 T3-E1细胞。与单次TGF-β 1处理相比，反复TGF-β1处理显著降低碱性磷酸酶（ALP）活性和成骨细胞标志物mRNA水平。然而，在TGF-β1处理后，CA-Akt的表达恢复ALP活性。令人惊讶的是，随着TGF-β1给药次数的增加，多次TGF-β 1治疗后ALP活性增加。Akt的激活显著增强了骨钙素的表达，但TGF-β1处理抑制了这种表达。在所有培养基条件下，CA-Akt表达均显著增强MC 3 T3-E1细胞的矿化。外源性IGF-1可恢复TGF-β1对成骨细胞相关基因表达的下调。然而，在表达DN-Akt的细胞中，无论IGF-1处理如何，这些水平仍然受到抑制。这些结果表明，Akt活化是TGF-β1诱导MC 3 T3-E1细胞向成骨细胞分化的早期阶段所必需的。然而，Akt激活不足以逆转TGF-β1在成骨细胞分化后期的抑制作用。TGF-β1对MC 3 T3-E1细胞的成骨分化有诱导或抑制作用，其作用与Akt磷酸化状态有关。我们的结果表明Akt是TGF-β1诱导MC 3 T3-E1细胞向成骨细胞分化的分子开关。
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. The aim of this current study is to investigate whether Akt activation is required for osteoblast differentiation. MC3T3-E1 cells were cultured in osteoblast differentiation medium (OBM) with or without 0.1 ng/mL TGF-β1. OBM containing TGF-β1 was changed every 12 h to provide repeated TGF-β1 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-β1 treatment compared with a single TGF-β1 treatment. However, expression of CA-Akt restored ALP activity following TGF-β1 treatment. Surprisingly, ALP activity increased following multiple TGF-β1 treatments as the number of administrations of TGF-β1 increased. Activation of Akt significantly enhanced expression of osteocalcin, but TGF-β1 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-β1 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-β1. However, Akt activation is insufficient to reverse the inhibitory effects of TGF-β1 in the late stages of osteoblast differentiation. TGF-β1 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-β1-induced osteoblastic differentiation of MC3T3-E1 cells.
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影响因子：
4.8
作者：
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通讯作者：
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DOI：
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