Mechanical Loading Stimulates Differentiation of Periodontal Osteoblasts in a Mouse Osteoinduction Model: Effect on Type I Collagen and Alkaline Phosphatase Genes

Abstract

The effects of mechanical loading on the osteoblast phenotype remain unclear because of many variables inherent to the current experimental models. This study reports on utilization of a mouse tooth movement model and a semiquantitative video image analysis of in situ hybridization to determine the effect of mechanical loading on cell-specific expression of type I collagen (collagen I) and alkaline phosphatase (ALP) genes in periodontal osteoblasts, using nonosseous cells as an internal standard. The histomorphometric analysis showed intense osteoid deposition after 3 days of treatment, confirming the osteoinductive nature of the mechanical signal. The results of in situ hybridization showed that in control periodontal sites both collagen I and ALP mRNAs were expressed uniformly across the periodontium. Treatment for 24 hours enhanced the ALP mRNA level about twofold over controls and maintained that level of stimulation after 6 days. In contrast, collagen I mRNA level was not affected after 24 hours of treatment, but it was stimulated 2.8-fold at day 6. This increase reflected enhanced gene expression in individual osteoblasts, since the increase in osteoblast number was small. These results indicate that (1) the mouse model and a semiquantitative video image analysis are suitable for detecting osteoblast-specific gene regulation by mechanical loading; (2) osteogenic mechanical stress induces deposition of bone matrix primarily by stimulating differentiation of osteoblasts, and, to a lesser extent, by an increase in number of these cells; (3) ALP is an early marker of mechanically-induced differentiation of osteoblasts. (4) osteogenic mechanical stimulation in vivo produces a cell-specific 2.8-fold increase in collagen gene expression in mature, matrix-depositing osteoblasts located on the bone surface and within the osteoid layer.

Influence of low-level laser on bone remodeling during induced tooth movement in rats

“…After the seventh day, the laser activated the osteoclasts less intensively, allowing time for the non-irradiated group to achieve a bone resorption degree similar to that of the irradiated group. Considering that the number of osteoblasts during the 7-and 14-day periods of movement is relatively the same according to the literature 19 and that the osteoclasts are stimulated only at the first period of experiment in irradiated group, a statistically significant difference is present only among the 7-day subgroups.…”

Bone ingrowth on the surface of endosseous implants. Part 1: Mathematical model

“…This phase can be enhanced by the presence of growth factors (Linkhart et al, 1996) and is also influenced by the mechanical state of the tissue. Actually, moderate mechanical stimulation of cells can enhance osseointegration (Rubin and McLeod, 1994) by promoting differentiation of osteogenic cells into osteoblasts and increasing the secretion of growth factors (Pavlin et al, 2000;Pavlin and Gluhak-Heinrich, 2001), but excessive levels of tensile or deviatoric stresses can also induce the formation of a not desirable fibrous tissue around the implant (Jones et al, 1995;Jasty et al, 1997). The global importance of this phase, sometimes referred to as osteoconduction, is crucial and has been highlighted in Davies (2003).…”

Effect of Mechanical Loading On Periodontal Cells

“…A recently developed tooth movement model in wild-type and transgenic mice (Pavlin et al, 2000a(Pavlin et al, ,b, 2001a allows for the study of genetic responses in individual cell populations within the periodontal ligament and the alveolar bone perturbed by mechanical stress in a non-invasive manner. This paper reviews the approaches for studying mechanical responses in synthetic cells of mineralized tissue, with a focus on animal periodontal models, and recent advances in the application of molecular and transgenic techniques for studying mechanically induced regulation of osteoblast marker genes.…”