In addition to OPN, osteocytes produce various factors such as osteoblast/osteocyte factor 45 (OF45) [37], sclerostin [38], dentin matrix acidic phosphoprotein (DMP)-1 [39], β-catenin [40] and receptor activator of nuclear factor-kappaB ligand (RANKL) [41]. These factors regulate the onset of both bone formation and resorption, and play pivotal roles Selleck INCB018424 in maintaining bone homeostasis and remodeling in response to mechanical stimuli. During loading, osteocytes may experience various forms of mechanical stimuli, such as fluid flow shear stress, hydrostatic pressure, and direct cellular deformation by substrate strain, among

others [42], [43] and [44]. These various forms of loading induce biological changes in osteocytes in a complex manner. Although there are an increasing number of studies assessing primary osteocytes and the osteocyte-like cell line, MLO-Y4 [45] responses to fluid shear stress [46] and [47], there is little research concerning the responses of osteocytes to compressive forces, particularly studies learn more focusing on primary osteocytes in culture. The MLO-Y4 cell line has thick actin bundles (stress fibers) in the cell bodies, similar to that observed in primary osteoblasts [48] and [49], and they appear to be more sensitive to fluid shear stress than osteoblast-like cell lines, such as MC3T3-E1 cells, in calcium response [50]. In comparison, in primary osteocytes, the actin cytoskeleton is localized to the cell

processes and is diffusely distributed throughout the cell body [51], with a reduced calcium-dependent response to fluid flow shear stress than that observed with primary osteoblasts [46]. This differential response to fluid shear stress between primary osteocytes and MLO-Y4 cells may stem from the distribution of Inositol monophosphatase 1 the actin cytoskeleton. As such, it might be necessary to investigate physiological loading responses with primary osteocytes. For this reason, we previously used primary chicken osteocytes to test compressive strain

using our newly established culture system [52]. This system provides mechanical strain as a single, quantified degree of compressive force in the culture substrate in the range from 1.2 to 2.9% strain (submitted). This degree of strain is conventionally thought to be within the hyperphysiological range of loading. However, the surrounding bone matrix is heterogeneous, resulting in magnified local tissue strain at the level of the osteocytes [53] and [54]. Recently, ultra high-voltage electron microscopes were used to analyze the microstructure of osteocyte cell processes and the surrounding bone matrix [55]. The findings suggested that osteocytes might have mechanical signal amplification systems that are mediated via their processes. In fact, in studies of direct cellular deformation, the degree of strain sensed by the osteocytes was determined to be larger than that withstood during daily activity [56]. Moreover, Jacobs et al.