In VitroMicrodistraction of Preosteoblasts: Distraction Promotes Proliferation and Oscillation Promotes Differentiation

Abstract

Osteoblast biology is influenced in vivo by a 3-dimensional (3D) extracellular matrix that mediates their adhesion and interaction and by a constant state of compressive and tensile forces. To study the role of mechanical stress on osteoblasts in vitro, these parameters must be addressed. Therefore, this study describes the use of a novel, in vitro system that subjects cells to distractive and compressive forces in a 3D environment. This system, termed a microdistractor system, was used to apply linear forces to 3D collagen type I gels containing preosteoblasts. Gels were induced for up to 16 days in osteogenic medium and subjected to either constant linear distraction (distraction gels) or to repeating cycles of distraction and compression (oscillation gels). The effect of these stresses was evaluated over time by measuring proliferation rates, protein synthesis (i.e., cellular activity), and osteogenic differentiation levels. While linear forces in general appeared to increase protein synthesis, force-specific effects on proliferation and differentiation were observed. Specifically, distraction forces appeared to enhance MC3T3 proliferation while distraction/compressive forces appeared to accelerate their osteogenic differentiation program. Therefore, these results suggest that the microdistraction system may be an appropriate in vitro system for the study of mechanobiology in osteoblast phenotype.

Compressive forces induce osteogenic gene expression in calvarial osteoblasts

“…OC/ BGLAP, the most abundant protein in bone, is a mature osteoblastic marker and its expression correlates with bone formation (Bilezikian et al, 2002;Ferna´ndez-TresguerresHerna´ndez-Gil et al, 2006;Hall, 2005). Up-regulation of OC/Bglap expression has been reported under cyclic tensile strain after 9 days (Mikuni-Takagaki et al, 1996) and upregulation of Akp2 and OC/Bglap was shown under periodic distraction and compression of collagen type I gels after 8 days (Gabbay et al, 2006). However, OC/Bglap expression has not been shown to be up-regulated by mechanical strain in other studies (Kaspar et al, 2000;Koike et al, 2005).…”

“…Furthermore, studies used 3-D culture systems to observe the effects of biomechanical forces on osteoblastic cells (Cartmell et al, 2003;Duty et al, 2007;Gabbay et al, 2006;Tanaka et al, 2005). Other studies observed cell growth in 3-D cultures in the absence of any mechanical stimuli (Cao et al, 2003;Ishaug et al, 1997).…”

“…Studies have shown that 3-D scaffolds can support osteoblast differentiation and mineralization (Cao et al, 2003; Ishaug et al, 1997). Furthermore, long term compressive forces induced mineralization while oscillation accelerated differentiation of osteoblastic cells (Gabbay et al, 2006;Visconti et al, 2004). Such studies are highly instructive and point out the need to investigate welldefined applied compressive forces that allow deliberate, systematic application of mechanical stresses to aid in tissue remodeling.…”

Tissue Engineering in Cleft Palate and Other Congenital Malformations

“…Loboa et al found that regions exposed to tensile strains of 13% or less corresponded to bone regeneration, whereas low periosteal hydrostatic pressures were associated with cartilaginous differentiation. In efforts to further dissect the influence of mechanical forces on osteogenesis at a cellular level in vitro, Gabbay et al used a microdistraction device capable of applying linear forces in a three-dimensional environment (39). MC3T3 preosteoblasts were suspended in three-dimensional collagen gels and exposed to either continuous distraction, or cyclical distraction and compression.…”

Experimental and Computational Investigation of the Role of Stress Fiber Contractility in the Resistance of Osteoblasts to Compression

“…The response of osteoblasts to mechanical signaling is attributed to deformation of the cell and surrounding matrix [2] [3]. Previous studies have shown that compressive loading induces mineralization of osteoblastic cells [4] and is an effective up-regulator of osteogenesis [5]. Furthermore, static and dynamic compression of chondrocytes has been shown to effect the regulation of type II collagen and aggrecan gene expression [6].…”