Densitometry of adiponectin bands from 3 separate experiments in series is shown on right side. refractory period was incorporated. Mechanical suppression of adipogenesis with LIV involved inhibition of GSK3 with subsequent activation of -catenin as has been shown for HMS. These data indicate that mechanical biasing of MSC lineage selection is more dependent on event scheduling than on load magnitude or duration. As such, a full day of rest should not be required to reset the mechanical MC-976 responsiveness of MSCs, and suggests that incorporating several brief mechanical challenges within a 24 hour period may improve salutary endpoints in vivo. That two diverse mechanical inputs are enhanced by repetition after a refractory period suggests that rapid cellular adaptation can be targeted. Keywords:Mechanotransduction, Adipogenesis, Obesity, Osteoblastogenesis, -catenin == 1. INTRODUCTION == Exercise influences a range of physiologic systems, and is part of both prevention and treatment strategies for diseases including obesity and osteoporosis. Often examined within the context of the musculoskeletal and adipose systems, exercise in general – and mechanical signals in particular – are recognized to be anabolic to bone and muscle and inhibitory to formation of fat. Mechanically mediated influences on musculoskeletal and fat phenotypes are achieved not only through the resident cell population (osteocytes, adipocytes, myocytes), but also by biasing the differentiation of their common progenitor, the mesenchymal stem cell (MSC) (Krishnan et al., 2006;David et al., 2007;Menuki et al., 2008). Studies using high magnitude mechanical loading, a regimen that assumes that benefits of exercise respond to increasing intensity and duration, and that a single daily session is sufficient to maximize any beneficial response (Egan et al., 2010), show that mechanical signals are recognized directly by the MSC population, and serve to promote osteoblastogenesis and inhibit adipogenesis even under environmental conditions inducing fat formation (Sen et al., 2008). If we allow that assumptions about intensity, duration and daily repetition are incorrect, however, we may be able to improve design of mechanical regimens. The sensitivity of MSC to mechanical signals allows study of a single target where comparisons can be made between diverse types of mechanical input generated during loading, including both high and low intensity strain. That non-strenuous loading such as standing or walking can impact aging and disuse provides evidence that neither magnitude nor duration is essential to mechanical challenge (Rubin and Rubin 2010). Even brief exposure to high frequency, small accelerations (30Hz/0.3g/20 min/day) can stimulate bone formation and inhibit adiposity (Rubin et al., 2001;Garman et al., 2007;Rubin et al., 2007;Humphries et al., 2009;Slatkovska et al., 2010;Wenger et al., 2010). MC-976 Refining mechanical regimens to control MSC commitment MC-976 should be an important goal to harness this non-pharmacologic strategy. Mechanical biasing of MSC lineage emphasizes the reciprocal relationship between bone and fat formation: decreased adipogenesis due to PPAR haploinsufficiency results in enhanced bone acquisition (Akune et al., 2004). This osteoblast/adipocyte relationship relies on -catenin, which modulates adipogenesis through attenuation of PPAR expression (Ross et al., 2000). Further, -catenin is critical to mechanical restraint of adipocyte differentiation; mechanical inhibition of adipogenesis is prevented by -catenin knockdown (Sen et al., 2009). Mechanical phosphorylation and inhibition of GSK3 serves to preserve -catenin (Armstrong et al., 2007;Sen et al., 2008) and also prolongs NFATc1 activation resulting in upregulation of COX2, which in turn promotes MSC commitment towards an osteochondroprogenitor lineage (Sen et al., 2009). It is important to understand the types of mechanical signals recognized by MSC. We here investigate whether brief periods of Low Intensity Vibration (LIV, low strain/high frequency) can influence MSC commitment in a manner similar to High Magnitude Strain (HMS, high strain/low frequency), and if these mechanical MC-976 effects could be enhanced by incorporating a refractory period between loading events. == 2. MATERIALS AND METHODS == == Experimental Design == MSC grown under media conditions which promote adipogenesis by 58 days were exposed to two distinct mechanical regimens. High magnitude strain (HMS) delivered as a 6h daily protocol was used as a starting point (Sen et al., 2008) for comparison with effects of low intensity vibration (LIV) to inhibit adipogenesis. To determine if modifications in delivery of mechanical regimens could Rabbit Polyclonal to PKC zeta (phospho-Thr410) influence efficacy, the duration and number of daily applications were altered, and further separated by a refractory period. Molecular pathways involved in the cellular response were compared between HMS and LIV. == Reagents == Fetal bovine serum was from Atlanta Biologicals (Atlanta, GA). Culture media, trypsin-EDTA reagent, antibiotics, Lipofectamine 2000, reverse transcriptase,Taqpolymerase and siRNA were from Invitrogen. Insulin and SB415286 were from Sigma-Aldrich. DKK-1 was from R & D Systems (Minneapolis, MN). RNA isolation kit was.