Preosteoblasts

Once stem cells are committed to the osteoblast lineage, proliferating osteoprogenitors become preosteoblasts, cell growth declines, and there is a progressive expression of differentiation markers by osteoblasts (Stein et al. 1996). Osteoblastic differentiation is characterized by the sequential expression of alkaline phosphatase (ALP), an early marker of osteoblastic phenotype, followed by the synthesis and deposition of collagen type I, bone matrix proteins, and glycosaminoglycans and an increased expression of os-... 

Li W, Duncan RL, Karin NJ, Farach-Carson MC. 1997. 1,25 (OH)2D3 enhances PTH-induced Ca2+ transients in preosteoblasts by activating L-type Ca2+ channels. Am J Physiol. 273 E599-605. 

Another interesting approach is to use nanofiber scaffolds as a crystallization matrix to mimic biological composites. Xia and coworkers were able to produce meshes with a gradient of calcium phosphate content to mimic the tendon-to-bone insertion site [206], The variation in composition led to an interesting spatial gradient in stiffness of the scaffold. This was also reflected in an activity gradient of seeded mouse preosteoblast cells. 

Other applications use self-assembling fibers to coat materials. For example, preassembled peptide amphiphiles have been covalently immobilized on titanium implant surfaces via a silane layer (Sargeant et al., 2008). Primary bovine artery endothelial cells or mouse calvarial preosteoblastic cells spread on these coated surface and proliferated to a far greater extent than on samples where the peptide amphiphiles had been drop cast onto the metal surface. This study therefore suggests that covalent attachment is required in order to prevent fibers lifting from the coated surface and to encourage maximal cell growth. 

The application of tensile stresses to osteoblasts appears to cause induction of the BMP-4 gene in preosteoblastic cells and adjacent spindle-shaped fibroblasts suggesting that BMP-4 may play a pivotal role by acting as an autocrine and a paracrine factor for recruiting osteoblasts in tensile stress-induced osteogenesis. Intermittent hydrostatic pressure (IHC) up-regulates osteopontin (OPN) mRNA expression in osteoblast cell cultures. In both... 

Bone resorption in response to continuous mechanical deformation appears to be regulated by cells of osteoblast lineage such as preosteoblasts, osteoblasts, bone lining cells and osteocytes, and stretch-enhanced, osteoclastlike cell formation involves prostaglandins, but not PGE2 (Soma et al., 1996). Stretch-induced increases in osteopontin and osteonectin were inhibited by addition of the calcium channel antagonist nifedipine suggesting an important role for L-type calcium channels in early mechanical strain transduction pathways in osteoblasts. 

Fig. 17 Images of 3D nanofibrous structure produced by wet-spinning metliod (a). Preosteoblast proliferation on TCP and 3D scaffold (b). ALP activity of preosteoblasts on TCP and 3D scaffolds [147]...

Rodan, S.B., Wesolowski, G., Hilton, D.J., Nicola, N.A. and Rodan, G.A. (1990) Leukemia inhibitory factor binds with high affinity to preosteoblastic RCT-1 cells and potentiates the retinoic acid induction of alkaline phosphatase. Endocrinology 127 1602-1608. 

The resorption phase is followed by ingress of preosteoblasts into the base of the resorption cavity. These cells become osteoblasts and elaborate new bone matrix constituents that help form the osteoid. Once the osteoid reaches a thickness of -15-20 pm, mineralization begins. A complete remodeling cycle normally requires about 3-6 months. 

The low temperature of formation and inherent porosity also permits the addition of antibiotics (Bohner et al. 1997, Takechi et al. 1998) or growth factors that stimulate the differentiation of preosteoblastic cells (Blom et al. 2000). However, the enhanced capability of the cement is somewhat offset by a longer hardening time (Ginebra et al. 2001). 

Strontium ranelate is an orally active agent that can be classified as both an antiresorptive agent and a bone-forming agent (42,43). It is able not only to stimulate replication of preosteoblastic cells to promote bone formation but also is able to decrease osteoclastic activity to prevent bone resorption. Biochemical markers for bone formation (e g., bone-specific alkaline phosphatase), which normally decrease in the presence of antiresorptive therapy, are elevated in the presence of strontium ranelate (44). Lumbar spine BMD increased 11.4% in patients treated with this new agent. 

MC3T3E1 preosteoblasts were cultured to test in vitro cytotoxicity for the GEMOSIL coated on the 35 mm culture dishes. The proliferation of the MC3T3-E1 cells on the coated dishes was conducted using MTS assay. The MTS absorbance of each group was measured on day 1,3, 5,... 

When testing the viability of pulp cells in the presence of the new cement, the preosteoblast culture showed that GEMOSIL increased cell growth 25% from day 1 to day 5 but decreased cell growth 25% after the day 5. It was not clear by what mechanisms the material affects cell cycles and whether the cells in the preosteoblast ceU culture underwent apoptosis in... 

Misra RDK, et al. Cellular response of preosteoblasts to nanograined/ultrafine-grained stmctures. Acta Biomater 2009 5(5) 1455—67. 

FIGURE 2.9 Effect of chitosan on adhesion, proliferation and viability of MC3T3-E1 subclone 4 mouse preosteoblasts cells, (a) Cells readily attach to all of the nanocomposites surface and exhibit protruding arms due to focal adhesion. The addition of chitosan results in enhanced (b) cell adhesion and (c) spreading on the nanocomposites surface as quantified using Image (NIH). (d) All the nanocomposites support cell proliferation, (e) Viability of cells remains high. Reproduced with permission from Ref. [85] American Chemical Society. 

S.-W. Choi, Y. Zhang, S. Thomopoulos, Y. Xia. In vitro mineralization by preosteoblasts in poly(DL-lactide-co-glycolide) inverse opal scaffolds reinforced with hydroxyapatite nanoparticles. Langmuir 26(14), 12126-12131,2010. 

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