Our previous study revealed that 3T3-L1 preadipocytes can differentiate to either osteoblasts or adipocytes in response to bone morphogenic protein 9 (BMP9). In the present study, we try to further investigate whether the Wnt/β-catenin signaling plays a crucial role in this process. It was found that BMP9 effectively activated the Wnt/β-catenin signaling, and induced the expression levels of certain canonical Wnt ligands and their receptors in preadipocytes. Exogenous expression of β-catenin, Wnt1, Wnt3a, and Wnt10b potentiated BMP9-induced alkaline phosphatase (ALP) activity, while β-catenin knockdown or Dickkopf 1 (Dkk1) diminished BMP9-induced ALP activity. Moreover, it was demonstrated that β-catenin overexpression promoted BMP9-induced mineralization, and increased the expression levels of late osteogenic markers osteopontin and osteocalcin. Furthermore, β-catenin inhibited BMP9-induced lipid accumulation and the adipogenic marker adipocyte fatty acid binding protein (aP2). The cell-implantation assay results identified that β-catenin not only augmented BMP9-induced ectopic bone formation, but also blocked adipogenesis in vivo. Mechanistically, it was found that β-catenin and BMP9 synergistically stimulated the osteogenic transcription factors runt-related transcription factor 2 (Runx2) and Osterix (OSX). However, BMP9-induced adipogenic transcription factors, peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT enhancer-binding protein α (C/EBPα), were inhibited by β-catenin. Therefore, these findings suggested that the Wnt/β-catenin signaling, potentially via the modulation of osteogenic and adipogenic transcriptional factors, exerts an opposite effect on BMP9-induced osteogenic and adipogenic differentiation in preadipocytes.

中文翻译：

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Wnt/β-连环蛋白信号转导在 BMP9 诱导的 3T3-L1 前脂肪细胞的成骨和脂肪形成分化中的相反作用。

我们之前的研究表明，3T3-L1 前脂肪细胞可以分化为成骨细胞或脂肪细胞，以响应骨形态发生蛋白 9 (BMP9)。在本研究中，我们试图进一步研究 Wnt/β-catenin 信号是否在这一过程中起着至关重要的作用。结果发现，BMP9 可有效激活 Wnt/β-连环蛋白信号，并诱导前脂肪细胞中某些经典 Wnt 配体及其受体的表达水平。β-连环蛋白、Wnt1、Wnt3a 和 Wnt10b 的外源表达增强了 BMP9 诱导的碱性磷酸酶 (ALP) 活性，而 β-连环蛋白敲低或 Dickkopf 1 (Dkk1) 减少了 BMP9 诱导的 ALP 活性。此外，已证明β-连环蛋白过表达促进了 BMP9 诱导的矿化，并增加了晚期成骨标志物骨桥蛋白和骨钙素的表达水平。此外，β-连环蛋白抑制 BMP9 诱导的脂质积累和脂肪生成标志物脂肪细胞脂肪酸结合蛋白 (aP2)。细胞植入试验结果表明，β-连环蛋白不仅增强了 BMP9 诱导的异位骨形成，而且还阻断了体内脂肪生成。从机制上讲，发现 β-连环蛋白和 BMP9 协同刺激成骨转录因子 runt 相关转录因子 2 (Runx2) 和 Osterix (OSX)。然而，BMP9 诱导的脂肪形成转录因子、过氧化物酶体增殖物激活受体 γ (PPARγ) 和 CCAAT 增强子结合蛋白 α (C/EBPα) 被 β-连环蛋白抑制。因此，这些发现表明 Wnt/β-连环蛋白信号可能通过调节成骨和脂肪形成转录因子，