Department of Surgery, Experimental Surgery and Regenerative Medicine, University of Munich (LMU), Nußbaumstr. 20, D-80336 Munich, Germany.
Biochem Biophys Res Commun. 2013 Nov 1;440(4):617-22. doi: 10.1016/j.bbrc.2013.09.114. Epub 2013 Oct 5.
Osteoporotic fractures show reduced callus formation and delayed bone healing. Cellular sources of fracture healing are mesenchymal stem cells (MSC) that differentiate into osteoblasts by stimulation with osteoinductive cytokines, such as BMP-2. We hypothesized that impaired signal transduction and reduced osteogenic differentiation capacity in response to BMP-2 may underlie the delayed fracture healing. Therefore, MSC were isolated from femoral heads of healthy and osteoporotic patients. Grouping was carried out by bone mineral densitometry in an age-matched manner. MSC were stimulated with BMP-2. Signal transduction was assessed by western blotting of pSMAD1/5/8 and pERK1/2 as well as by quantitative RT-PCR of Runx-2, Dlx5, and Osteocalcin. Osteogenic differentiation was assessed by quantifying Alizarin Red staining. Osteoporotic MSC featured an accurate phosphorylation pattern of SMAD1/5/8 but a significantly reduced activation of ERK1/2 by BMP-2 stimulation. Furthermore, osteoporotic MSC showed significantly reduced basal expression levels of Runx-2 and Dlx5. However, Runx-2, Dlx5, and Osteocalcin expression showed adequate up-regulation due to BMP-2 stimulation. The global osteogenic differentiation in standard osteogenic differentiation media was reduced in osteoporotic MSC. Nevertheless, osteoporotic MSC were shown to feature an adequate induction of osteogenic differentiation due to BMP-2 stimulation. Taken together, we here demonstrate osteoporosis associated alterations in BMP-2 signaling but sustained specific osteogenic differentiation capacity in response to BMP-2. Therefore, BMP-2 may represent a promising therapeutic agent for the treatment of fractures in osteoporotic patients.
骨质疏松性骨折表现出减少的骨痂形成和延迟的骨愈合。骨折愈合的细胞来源是间充质干细胞（MSC），它们通过刺激成骨细胞分化成成骨细胞，例如 BMP-2。我们假设，对 BMP-2的信号转导受损和成骨分化能力降低可能是骨折愈合延迟的原因。因此，从健康和骨质疏松患者的股骨头中分离出 MSC。通过骨矿物质密度测定以年龄匹配的方式进行分组。用 BMP-2 刺激 MSC。通过 Western blot 检测 pSMAD1/5/8 和 pERK1/2 的磷酸化以及定量 RT-PCR 检测 Runx-2、Dlx5 和 Osteocalcin 来评估信号转导。通过定量分析茜素红染色来评估成骨分化。骨质疏松性 MSC 具有准确的 SMAD1/5/8 磷酸化模式，但 BMP-2 刺激时 ERK1/2 的激活显著降低。此外，骨质疏松性 MSC 的 Runx-2 和 Dlx5 的基础表达水平明显降低。然而，由于 BMP-2 的刺激，Runx-2、Dlx5 和 Osteocalcin 的表达显示出足够的上调。在标准成骨分化培养基中，骨质疏松性 MSC 的整体成骨分化减少。然而，由于 BMP-2 的刺激，骨质疏松性 MSC 显示出足够的成骨分化诱导。总之，我们在这里证明了与骨质疏松症相关的 BMP-2 信号转导改变，但对 BMP-2 有持续的特定成骨分化能力。因此，BMP-2 可能是治疗骨质疏松症患者骨折的有前途的治疗剂。
