It is well known that certain connective tissue cells (viz., dermal fibroblasts) can express the gene for a muscle actin--alpha-smooth muscle actin--and can contract. This process contributes to skin wound closure and is responsible for Dupuytren's contracture. The objective of this study was to determine if human osteoblasts can also express the gene for alpha-smooth muscle actin. Immunohistochemistry using a monoclonal antibody for alpha-smooth muscle actin was performed on human cancellous bone samples obtained from 20 individuals at the time of total joint arthroplasty. The percentages of resting and active osteoblasts on the bone surfaces containing this muscle actin isoform were evaluated. Explants of human bone were also studied for the expression of alpha-smooth muscle actin in the tissue and in the outgrowing cells with time in culture. Western blot analysis was performed to quantify the alpha-smooth muscle actin content of the outgrowing cells relative to smooth muscle cell controls. Nine +/- 2% (mean +/- SEM; n = 20) of the cells classified as inactive osteoblasts and 69 +/- 3% (n = 19) of the cells identified as active osteoblasts on the bone surface contained alpha-smooth muscle actin. This difference was highly statistically significant (Student's t test, p < 0.0001). Similar profiles of alpha-smooth muscle actin-expressing cells were found in explants cultured for up to 12 weeks. Cells forming a layer on the surface of the explants and growing out from them in monolayer also contained alpha-smooth muscle actin by immunohistochemistry and Western blot analysis. Human osteoblasts can express the gene for alpha-smooth muscle actin. This expression should be considered a phenotypic characteristic of this cell type, conferred by its progenitor cells: bone marrow stromal-derived stem cells, and perhaps pericytes and smooth muscle cells.
"Of note, under certain conditions such as inflammation, cells associated with vessels (e.g. pericytes, endothelial cells and smooth muscle cells) or their precursors are capable of differentiating into osteoblast-like cells (Schor et al. 1995; Reilly et al. 1998; Kinner and Spector 2002) suggesting that the forming microvasculature is a potential source for osteogenic cells. "
[Show abstract][Hide abstract] ABSTRACT: Thrombin-related peptide 508 (TP508) accelerates bone regeneration during distraction osteogenesis (DO). We have examined the effect of TP508 on bone regeneration during DO by immunolocalization of Runx2 protein, a marker of osteoblast differentiation, and of osteopontin (OPN) and bone sialoprotein (BSP), two late markers of the osteoblast lineage. Distraction was performed in tibiae of rabbits over a period of 6 days. TP508 (30 or 300 microg) or vehicle was injected into the distraction gap at the beginning and end of the distraction period. Two weeks after active distraction, tissue samples were harvested and processed for immunohistochemical analysis. We also tested the in vitro effect of TP508 on Runx2 mRNA expression in osteoblast-like (MC3T3-E1) cells by polymerase chain reaction analysis. Runx2 and OPN protein were observed in preosteoblasts, osteoblasts, osteocytes of newly formed bone, blood vessel cells and many fibroblast-like cells of the soft connective tissue. Immunostaining for BSP was more restricted to osteoblasts and osteocytes. Significantly more Runx2- and OPN-expressing cells were seen in the group treated with 300 microg TP508 than in the control group injected with saline or with 30 microg TP508. However, TP508 failed to increase Runx2 mRNA levels significantly in MC3T3-E1 cells after 2-3 days of exposure. Our data suggest that TP508 enhances bone regeneration during DO by increasing the proportion of cells of the osteoblastic lineage. Clinically, TP508 may shorten the healing time during DO; this might be of benefit when bone regeneration is slow.
Cell and Tissue Research 11/2007; 330(1):35-44. DOI:10.1007/s00441-007-0448-9 · 3.57 Impact Factor
"The CNC culture was maintained for an additional 3 to 7 days and then examined for the presence of calcified nodules (Fig. 4E), alkaline phosphatase (ALPase) activity, and/or Runx2 expression (Fig. 4F,G), which validated the differentiation of CNC cells into osteoblasts. A fairly high percentage of osteoblast progenitor cells in the bone marrow express α-SMA (Bianco et al., 2001; Kinner and Spector, 2002). Given the fact that a large number of postmigratory CNC cells expresses α-SMA (Fig. 2F) but only a small percentage of them will become smooth muscle cells in adult, we decided to test whether some of the α-SMA positive cells may differentiate into osteoprogenitors. "
[Show abstract][Hide abstract] ABSTRACT: The cranial neural crest (CNC) is a transient cell population that originates at the crest of the neural fold and gives rise to multiple cell types during craniofacial development. Traditionally, researchers have used tissue explants, such as the neural tube, to obtain primary neural crest cells for their studies. However, this approach has inevitably resulted in simultaneous isolation of neural and non-neural crest cells as both of these cells migrate away from tissue explants. Using the Wnt1-Cre/R26R mouse model, we have obtained a pure population of neural crest cells and established a primary CNC cell culture system in which the cell culture medium best supports the proliferation of E10.5 first branchial arch CNC cells and maintains these cells in their undifferentiated state. Differentiation of CNC cells can be initiated by switching to a differentiation medium. In this model, cultured CNC cells can give rise to neurons, glial cells, osteoblasts, and other cell types, faithfully mimicking the differentiation process of the post-migratory CNC cells in vivo. Taken together, our study shows that the Wnt1-Cre/R26R mouse first branchial arch provides an excellent model for obtaining post-migratory neural crest cells free of any mesodermal contaminants. The cultured neural crest cells are under sustained proliferative, undifferentiated, or lineage-enhanced conditions, hence, serving as a tool for the investigation of the regulatory mechanism of CNC cell fate determination in normal and abnormal craniofacial development.
"Recent studies have identified a contractile muscle actin isoform, a-smooth muscle actin (SMA), in osteoblasts   as well as in a number of other musculoskeletal connective tissue cells . Associated studies demonstrated the ability of SMA-expressing osteoblastic cells to contract a collagen-glycosaminoglycan analog of extracellular matrix in vitro  . It was proposed that SMA-enabled contraction might be responsible for the retraction of osteoblasts on the bone surface at the initiation of the remodeling cycle. "
[Show abstract][Hide abstract] ABSTRACT: Distraction osteogenesis has proven to be of great value for the treatment of a variety of musculoskeletal problems. Little is still known, however, about the phenotypic changes in the cells participating in the bone formation process, induced by the procedure. Recent findings of the expression of a contractile muscle actin isoform, alpha-smooth muscle actin (SMA), in musculoskeletal connective tissue cells prompted this immunohistochemical study of the expression of SMA in cells participating in distraction osteogenesis in a rat model. The tissues within and adjacent to the distraction site could be distinguished histologically on the basis of cell morphology, density, and extracellular matrix make-up. The percentage of SMA-containing cells within each tissue zone was graded from 0 to 4. The majority of the cells in each of the zones stained positive for SMA within five days of the distraction period. The SMA-containing cells included those with elongated morphology in the center of the distraction site and the active osteoblasts on the surfaces of the newly forming bone. These finding warrant further investigation of the role of this contractile actin isoform in distraction osteogenesis and investigation of the effects of modulation of this actin isoform on the procedure.
Journal of Orthopaedic Research 02/2003; 21(1):20-7. DOI:10.1016/S0736-0266(02)00088-8 · 2.99 Impact Factor
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