Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Bone. 2013 Apr;53(2):575-86. doi: 10.1016/j.bone.2012.12.013. Epub 2012 Dec 27.
Long bone is an anatomically complicated tissue with trabecular-rich metaphyses at two ends and cortical-rich diaphysis at the center. The traditional flushing method isolates only mesenchymal progenitor cells from the central region of long bones and these cells are distant from the bone surface. We propose that mesenchymal progenitors residing in endosteal bone marrow that is close to the sites of bone formation, such as trabecular bone and endosteum, behave differently from those in the central bone marrow. In this report, we separately isolated endosteal bone marrow using a unique enzymatic digestion approach and demonstrated that it contained a much higher frequency of mesenchymal progenitors than the central bone marrow. Endosteal mesenchymal progenitors express common mesenchymal stem cell markers and are capable of multi-lineage differentiation. However, we found that mesenchymal progenitors isolated from different anatomical regions of the marrow did exhibit important functional differences. Compared with their central marrow counterparts, endosteal mesenchymal progenitors have superior proliferative ability with reduced expression of cell cycle inhibitors. They showed greater immunosuppressive activity in culture and in a mouse model of inflammatory bowel disease. Aging is a major contributing factor for trabecular bone loss. We found that old mice have a dramatically decreased number of endosteal mesenchymal progenitors compared with young mice. Parathyroid hormone (PTH) treatment potently stimulates bone formation. A single PTH injection greatly increased the number of endosteal mesenchymal progenitors, particularly those located at the metaphyseal bone, but had no effect on their central counterparts. In summary, endosteal mesenchymal progenitors are more metabolically active and relevant to physiological bone formation than central mesenchymal progenitors. Hence, they represent a biologically important target for future mesenchymal stem cell studies.
长骨是一种解剖结构复杂的组织，其两端富含小梁的骺端和中心富含皮质的骨干。传统的冲洗方法只能从长骨的中心区域分离出间充质祖细胞，而这些细胞远离骨表面。我们提出，位于靠近骨形成部位（如小梁骨和骨内膜）的骨内膜骨髓中的间充质祖细胞与中心骨髓中的祖细胞行为不同。在本报告中，我们使用独特的酶消化方法分别分离出骨内膜骨髓，并证明其含有比中心骨髓更高频率的间充质祖细胞。骨内膜间充质祖细胞表达常见的间充质干细胞标志物，并具有多谱系分化能力。然而，我们发现从骨髓不同解剖区域分离的间充质祖细胞确实表现出重要的功能差异。与中心骨髓对应物相比，骨内膜间充质祖细胞具有更高的增殖能力，细胞周期抑制剂的表达降低。它们在培养中和炎症性肠病的小鼠模型中表现出更强的免疫抑制活性。衰老是小梁骨丢失的一个主要促成因素。我们发现，与年轻小鼠相比，老年小鼠的骨内膜间充质祖细胞数量明显减少。甲状旁腺激素（PTH）治疗可强力刺激骨形成。单次 PTH 注射可显著增加骨内膜间充质祖细胞的数量，特别是骺端骨的间充质祖细胞，但对其中心对应物没有影响。总之，骨内膜间充质祖细胞比中心间充质祖细胞更具代谢活性，与生理骨形成相关。因此，它们代表了未来间充质干细胞研究的一个重要生物学目标。
