Low magnitude and high frequency mechanical loading prevents decreased bone formation responses of 2T3 preosteoblasts

Abstract

Bone loss due to osteoporosis or disuse such as in paraplegia or microgravity is a significant health problem. As a treatment for osteoporosis, brief exposure of intact animals or humans to low magnitude and high frequency (LMHF) mechanical loading has been shown to normalize and prevent bone loss. However, the underlying molecular changes and the target cells by which LMHF mechanical loading alleviate bone loss are not known. Here, we hypothesized that direct application of LMHF mechanical loading to osteoblasts alters their cell responses, preventing decreased bone formation induced by disuse or microgravity conditions. To test our hypothesis, preosteoblast 2T3 cells were exposed to a disuse condition using the Random Positioning Machine (RPM) and intervened with an LMHF mechanical load (0.1-0.4g at 30Hz for 10-60 min/day). Exposure of 2T3 cells to the RPM decreased bone formation responses as determined by alkaline phosphatase (ALP) activity and mineralization even in the presence of a submaximal dose of BMP4 (20ng/ml). However, LMHF mechanical loading prevented the RPM-induced decrease in ALP activity and mineralization. Mineralization induced by LMHF mechanical loading was enhanced by treatment with bone morphogenic protein 4 (BMP4) and blocked by the BMP antagonist noggin, suggesting a role for BMPs in this response. In addition, LMHF mechanical loading rescued the RPM-induced decrease in gene expression of ALP, runx2, osteomodulin, parathyroid hormone receptor 1, and osteoglycin. These findings suggest that preosteoblasts may directly respond to LMHF mechanical loading to induce differentiation responses. The mechanosensitive genes identified here provide potential targets for pharmaceutical treatments that may be used in combination with low level mechanical loading to better treat osteoporosis or disuse-induced bone loss.

Simulation of Microgravity by Magnetic Levitation and Random Positioning: Effect on Human A431 Cell Morphology

“…Recently, the RPM is used as a simulator for microgravity in various studies investigating responses in animal cells (for example Grimm et al 2002;Uva et al 2002;Infanger et al 2006;Pardo et al 2005;Patel et al 2009;Meloni et al 2006). However, the mode of operation of the RPM that was used in these studies varies.…”

Gene Expression Microarrays in Microgravity Research: Toward the Identification of Major Space Genes

“…They again found that ALP, Runx2, PthR1 were down-regulated in simulated microgravity. They also found that low magnitude and high frequency (LMHF) mechanical loading (0.1 ~ 0.4 g at 30 Hz for 10 ~ 60 min/day) prevented a decrease in ALP, Runx2, PthR1, but static conditions had no effect (Patel et al, 2009). …”

Osteogenic differentiation of bone marrow-derived mesenchymal stromal cells on bone-derived scaffolds: effect of microvibration and role of ERK1/2 activation

“…This may suggest that ERK1/2 is an essential pathway in the mechanotransduction process. We therefore hypothesized that ERK1/2 activation may also play an essential role in LMHF vibration mediated-BMSC osteodifferentiation.Here, it is relevant to note that the in vitro data presented in two studies by Lau et al (2010) and Patel et al (2009) to provide an explanation for the anabolic and anti-resorptive role of LMHF vibration observed in vivo, are obtained from bone cells in two dimensional (2D) cultures. However, investigating the role of LMHF vibration on osteogenic cells in 3D cultures might mimic in vivo conditions.…”

“…Interestingly, microvibration can enhance the peak levels of these genes and intensify the pattern occurred in osteogenic differentiation. The observation could thus prove that microvibration is benefi cial for osteogenesis.3D culture has been demonstrated to promote cell osteogenic differentiation and mineralisation (Kinoshita et al, 1999;Rattner et al, 2000). To test the advantage of 3D culture on osteogenic differentiation in response to LMHF vibration, ALP activity was measured on day 14.…”