de Castro Luis Fernandez, Sworder Brian J, Mui Byron, Futrega Kathryn, Berendsen Agnes, Phillips Matthew D, Burbach Nathan J, Cherman Natasha, Kuznetsov Sergei, Gabet Yankel, Holmbeck Kenn, Robey Pamela G
Skeletal Biology Section, National Institute of Dental and Craniofacial Research, National Institutes of Health, Department of Health and Human Services, National Institutes of Health, Bethesda, MD, USA.
Department of Molecular Medicine, Boston University, Boston, MA, USA.
Bone Res. 2021 Dec 2;9(1):49. doi: 10.1038/s41413-021-00169-7.
In a previous transcriptomic study of human bone marrow stromal cells (BMSCs, also known as bone marrow-derived "mesenchymal stem cells"), SFRP2 was highly over-represented in a subset of multipotent BMSCs (skeletal stem cells, SSCs), which recreate a bone/marrow organ in an in vivo ectopic bone formation assay. SFRPs modulate WNT signaling, which is essential to maintain skeletal homeostasis, but the specific role of SFRP2 in BMSCs/SSCs is unclear. Here, we evaluated Sfrp2 deficiency on BMSC/SSC function in models of skeletal organogenesis and regeneration. The skeleton of Sfrp2-deficient (KO) mice is overtly normal; but their BMSCs/SSCs exhibit reduced colony-forming efficiency, reflecting low SSC self-renewal/abundancy. Sfrp2 KO BMSCs/SSCs formed less trabecular bone than those from WT littermates in the ectopic bone formation assay. Moreover, regeneration of a cortical drilled hole defect was dramatically impaired in Sfrp2 KO mice. Sfrp2-deficient BMSCs/SSCs exhibited poor in vitro osteogenic differentiation as measured by Runx2 and Osterix expression and calcium accumulation. Interestingly, activation of the Wnt co-receptor, Lrp6, and expression of Wnt target genes, Axin2, C-myc and Cyclin D1, were reduced in Sfrp2-deficient BMSCs/SSCs. Addition of recombinant Sfrp2 restored most of these activities, suggesting that Sfrp2 acts as a Wnt agonist. We demonstrate that Sfrp2 plays a role in self-renewal of SSCs and in the recruitment and differentiation of adult SSCs during bone healing. SFRP2 is also a useful marker of BMSC/SSC multipotency, and a factor to potentially improve the quality of ex vivo expanded BMSC/SSC products.
在先前一项关于人骨髓基质细胞（BMSC，也称为骨髓来源的“间充质干细胞”）的转录组学研究中，分泌型卷曲相关蛋白2（SFRP2）在多能BMSC（骨骼干细胞，SSC）亚群中高度富集，该亚群在体内异位骨形成试验中可重建骨/骨髓器官。SFRP家族蛋白调节WNT信号通路，而WNT信号通路对维持骨骼稳态至关重要，但SFRP2在BMSC/SSC中的具体作用尚不清楚。在此，我们在骨骼器官发生和再生模型中评估了Sfrp2基因缺失对BMSC/SSC功能的影响。Sfrp2基因缺失（KO）小鼠的骨骼外观正常；但其BMSC/SSC的集落形成效率降低，反映出SSC自我更新/丰度较低。在异位骨形成试验中，Sfrp2基因敲除的BMSC/SSC形成的小梁骨比野生型同窝小鼠的少。此外，Sfrp2基因敲除小鼠皮质钻孔缺损的再生明显受损。通过Runx2和Osterix表达以及钙积累测定，Sfrp2基因缺失的BMSC/SSC在体外的成骨分化较差。有趣的是，在Sfrp2基因缺失的BMSC/SSC中，Wnt共受体Lrp6的激活以及Wnt靶基因Axin2、C-myc和细胞周期蛋白D1的表达均降低。添加重组Sfrp2可恢复大部分这些活性，表明Sfrp2作为Wnt激动剂发挥作用。我们证明Sfrp2在SSC的自我更新以及骨愈合过程中成年SSC的募集和分化中发挥作用。SFRP2也是BMSC/SSC多能性的有用标志物，以及潜在改善体外扩增的BMSC/SSC产品质量的一个因素。
