The microenvironment, or niche, regulates stem cell fate and improves differentiation efficiency. Human umbilical cord mesenchymal stem cells (hUC-MSCs) are ideal cell source for bone tissue engineering. However, the role of the microenvironments in hUC-MSC-based bone regeneration is not yet fully understood. This study is aimed at investigating the effects of the in vitro culture microenvironment (hUC-MSCs, nano-hydroxyapatite/collagen/poly (L-lactide) (nHAC/PLA), osteogenic media (OMD), and recombinant human bone morphogenetic protein-7 (rhBMP-7)) and the in vivo transplanted microenvironment (ectopic and orthotopic) on bone regeneration ability of hUC-MSCs. The isolated hUC-MSCs showed self-renewal potential and MSCs’ characteristics. In the in vitro two-dimensional culture microenvironment, OMD or OMD with rhBMP-7 significantly enhanced hUC-MSCs’ osteocalcin immunofluorescence staining, alkaline phosphatase, and Alizarin red staining; OMD with rhBMP-7 exhibited the highest ALP secretion and mineralized matrix formation. In the in vitro three-dimensional culture microenvironment, nHAC/PLA supported hUC-MSCs’ adhesion, proliferation, and differentiation; the microenvironment containing OMD or OMD and rhBMP-7 shortened cell proliferation progression and made osteogenic differentiation progression advance; rhBMP-7 significantly attenuated the inhibiting effect of OMD on hUC-MSCs’ proliferation and significantly enhanced the promoting effect of OMD on gene expression and protein secretion of osteogenic differentiation markers, calcium and phosphorous concentration, and mineralized matrix formation. The in vitro three-dimensional culture microenvironment containing OMD and rhBMP-7 induced hUC-MSCs to form the most new bones in ectopic or orthotopic microenvironment as proved by microcomputed tomography and hematoxylin and eosin staining, but bone formation in orthotopic microenvironment was significantly higher than that in ectopic microenvironment. The results indicated that the combination of in vitro hUC-MSCs+nHAC/PLA+OMD+rhBMP-7 microenvironment and in vivo orthotopic microenvironment provided a more optimized niche for bone regeneration of hUC-MSCs. This study elucidates that hUC-MSCs and their local microenvironment, or niche, play an important role in hUC-MSC-based bone regeneration. The endogenously produced BMP may serve an important regulatory role in the process.

中文翻译：

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微环境对人脐带间充质干细胞骨再生的影响

微环境或生态位调节干细胞命运并提高分化效率。人脐带间充质干细胞 (hUC-MSCs) 是骨组织工程的理想细胞来源。然而，微环境在基于 hUC-MSC 的骨再生中的作用尚未完全了解。本研究旨在研究体外培养微环境（hUC-MSCs、纳米羟基磷灰石/胶原蛋白/聚（L-丙交酯）（nHAC/PLA）、成骨培养基（OMD）和重组人骨形态发生蛋白- 7 (rhBMP-7)) 和体内移植微环境（异位和原位）对 hUC-MSCs 骨再生能力的影响。分离的 hUC-MSCs 显示出自我更新的潜力和 MSCs 的特征。在体外二维培养微环境，OMD或OMD与rhBMP-7显着增强hUC-MSCs的骨钙素免疫荧光染色、碱性磷酸酶和茜素红染色；带有rhBMP-7 的OMD 表现出最高的ALP 分泌和矿化基质形成。在体外三维培养微环境，nHAC/PLA支持hUC-MSCs的粘附、增殖和分化；含有OMD或OMD和rhBMP-7的微环境缩短了细胞增殖进程，促进了成骨分化进程；rhBMP-7显着减弱OMD对hUC-MSCs增殖的抑制作用，显着增强OMD对成骨分化标志物基因表达和蛋白分泌、钙磷浓度、矿化基质形成的促进作用。在体外微计算机断层扫描和苏木精伊红染色证明，含有OMD和rhBMP-7的三维培养微环境诱导hUC-MSCs在异位或原位微环境中形成最多的新骨，但原位微环境中的骨形成明显高于异位微环境。微环境。结果表明，体外hUC-MSCs+nHAC/PLA+OMD+rhBMP-7微环境和体内原位微环境的结合为hUC-MSCs的骨再生提供了更优化的生态位。该研究阐明了 hUC-MSC 及其局部微环境或生态位，在基于 hUC-MSC 的骨再生中发挥重要作用。内源性 BMP 可能在该过程中发挥重要的调节作用。