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1.  Collagen type I hydrogel allows migration, proliferation and osteogenic differentiation of rat bone marrow stromal cells 
Hydrogels are potentially useful for many purposes in regenerative medicine including drug and growth factor delivery, as single scaffold for bone repair or as a filler of pores of another biomaterial in which host mesenchymal progenitor cells can migrate in and differentiate into matrix-producing osteoblasts. Collagen type I is of special interest as it is a very important and abundant natural matrix component. The purpose of this study was to investigate whether rat bone marrow stromal cells (rBMSCs) are able to adhere to, to survive, to proliferate and to migrate in collagen type I hydrogels and whether they can adopt an osteoblastic fate. rBMSCs were obtained from rat femora and plated on collagen type I hydrogels. Prior to harvest by day 7, 14, and 21, hydrogels were fluorescently labeled, cryo-cut and analyzed by fluorescent-based and laser scanning confocal microscopy to determine cell proliferation, migration, and viability. Osteogenic differentiation was determined by alkaline phosphatase activity. Collagen type I hydrogels allowed the attachment of rBMSCs to the hydrogel, their proliferation, and migration towards the inner part of the gel. rBMSCs started to differentiate into osteoblasts as determined by an increase in alkaline phosphatase activity after two weeks in culture. This study therefore suggests that collagen type I hydrogels could be useful for musculoskeletal regenerative therapies.
doi:10.1002/jbm.a.32696
PMCID: PMC2891839  PMID: 20186733
Collagen type I hydrogel; bone marrow stromal cells; cell migration; osteogenic differentiation; bone regeneration
2.  Characterization of Circulating Osteoblast Lineage Cells in Humans 
Bone  2007;40(5):1370-1377.
We recently identified circulating osteoblastic cells using antibodies to osteocalcin (OCN) or alkaline phosphatase (AP). We now provide a more detailed characterization of these cells. Specifically, we demonstrate that 46% of OCN positive (OCNpos) cells express AP, and 37% also express the hematopoietic/endothelial marker, CD34. Using two different anti-OCN antibodies and forward/side light scatter characteristics by flow cytometry, we find that OCNpos cells consist of two distinct populations: one population exhibits low forward/side scatter, consistent with a small cell phenotype with low granularity, and a second population has higher forward/side scatter (larger and more granular cell). The smaller, low granularity population also co-expresses CD34, whereas the larger, more granular cells are CD34 negative. Using samples from 26 male subjects aged 28 to 68 years, we demonstrate that the concentration of circulating OCNpos cells increases as a function of age (R = 0.59, P = 0.002). By contrast, CD34pos cells tend to decrease with age (R = −0.31, P = 0.18); as a consequence, the ratio of OCNpos:CD34pos cells also increases significantly with age (R = 0.54, P = 0.022). These findings suggest significant overlap between circulating cells expressing OCN and those expressing the hematopoietic/endothelial marker, CD34. Further studies are needed to define the precise role of circulating OCNpos cells not only in bone remodeling but rather also potentially in the response to vascular injury.
doi:10.1016/j.bone.2006.12.064
PMCID: PMC1920541  PMID: 17320497
Circulating; mesenchymal; osteocalcin; immunophenotyping

Results 1-2 (2)