1 Department of Orthopaedics, Erasmus MC, University Medical Centre , Rotterdam, The Netherlands .
Tissue Eng Part A. 2014 Jan;20(1-2):23-33. doi: 10.1089/ten.TEA.2013.0080. Epub 2013 Oct 2.
In articular cartilage repair, cells that will be responsible for the formation of repair tissue are often exposed to an osteochondral environment. To study cartilage repair mechanisms in vitro, we have recently developed a bovine osteochondral biopsy culture model in which cartilage defects can be simulated reproducibly. Using this model, we now aimed at studying the chondrogenic potential of human bone marrow-derived mesenchymal stem cells (hBMSCs) in an osteochondral environment. In contrast to standard in vitro chondrogenesis, it was found that supplementing transforming growth factor beta (TGFβ) to culture medium was not required to induce chondrogenesis of hBMSCs in an osteochondral environment. hBMSC culture in defects created in osteochondral biopsies or in bone-only biopsies resulted in comparable levels of cartilage-related gene expression, whereas culture in cartilage-only biopsies did not induce chondrogenesis. Subcutaneous implantation in nude mice of osteochondral biopsies containing hBMSCs in osteochondral defects resulted in the formation of more cartilaginous tissue than hBMSCs in chondral defects. The subchondral bone secreted TGFβ; however, the observed results could not be attributed to TGFβ, as either capturing TGFβ with an antibody or blocking the canonical TGFβ signaling pathway did not result in significant changes in cartilage-related gene expression of hBMSCs in the osteochondral culture model. Inhibition of BMP signaling did not prevent chondrogenesis. In conclusion, we demonstrate that chondrogenesis of hBMSCs is induced by factors secreted from the bone. We have strong indications that this is not solely mediated by members of the TGFβ family but other, yet unknown, factors originating from the subchondral bone appeared to play a key role.
在关节软骨修复中，负责形成修复组织的细胞通常会暴露在一个骨软骨环境中。为了在体外研究软骨修复机制，我们最近开发了一种牛骨软骨活检培养模型，可在其中重复模拟软骨缺陷。使用这种模型，我们现在旨在研究人骨髓间充质干细胞（hBMSCs）在骨软骨环境中的软骨形成潜力。与标准的体外软骨发生相比，发现在骨软骨环境中诱导 hBMSC 软骨发生不需要补充转化生长因子β（TGFβ）到培养基中。在骨软骨活检或仅骨活检中创建的缺陷中培养 hBMSC 会导致软骨相关基因表达的可比水平，而在仅软骨活检中培养则不会诱导软骨发生。将含有 hBMSC 的骨软骨缺损的骨软骨活检植入裸鼠皮下，导致形成的软骨组织多于软骨缺损中的 hBMSC。软骨下骨分泌 TGFβ；然而，观察到的结果不能归因于 TGFβ，因为用抗体捕获 TGFβ或阻断经典的 TGFβ信号通路不会导致骨软骨培养模型中 hBMSC 的软骨相关基因表达发生显著变化。BMP 信号的抑制并不能阻止软骨发生。总之，我们证明 hBMSC 的软骨发生是由骨分泌的因子诱导的。我们有强烈的迹象表明，这不仅仅是由 TGFβ 家族成员介导的，而是来自软骨下骨的其他未知因素似乎发挥了关键作用。
