Low-Level Vibrations Retain Bone Marrow's Osteogenic Potential and Augment Recovery of Trabecular Bone during Reambulation

Judex S (2010) Low-Level Vibrations Retain Bone Marrow's Osteogenic Potential and Augment Recovery of Trabecular Bone during Reambulation. PLoS ONE 5(6): e11178. doi:10.1371/journal.pone.0011178 Low-Level Vibrations Retain Bone Marrow's Osteogenic Potential and Augment Recovery of Trabecular Bone during Reambulation Engin Ozcivici 0 Yen K. Luu 0 Clinton T. Rubin 0 Stefan Judex 0 Sudha Agarwal, Ohio State University, United States of America 0 Department of Biomedical Engineering, Stony Brook University , Stony Brook, New York , United States of America Mechanical disuse will bias bone marrow stromal cells towards adipogenesis, ultimately compromising the regenerative capacity of the stem cell pool and impeding the rapid and full recovery of bone morphology. Here, it was tested whether brief daily exposure to high-frequency, low-magnitude vibrations can preserve the marrow environment during disuse and enhance the initiation of tissue recovery upon reambulation. Male C57BL/6J mice were subjected to hindlimb unloading (HU, n = 24), HU interrupted by weight-bearing for 15 min/d (HU+SHAM, n = 24), HU interrupted by low-level whole body vibrations (0.2 g, 90 Hz) for 15 min/d (HU+VIB, n = 24), or served as age-matched controls (AC, n = 24). Following 3 w of disuse, half of the mice in each group were released for 3 w of reambulation (RA), while the others were sacrificed. RA+VIB mice continued to receive vibrations for 15 min/d while RA+SHAM continued to receive sham loading. After disuse, HU+VIB mice had a 30% greater osteogenic marrow stromal cell population, 30% smaller osteoclast surface, 76% greater osteoblast surface but similar trabecular bone volume fraction compared to HU. After 3 w of reambulation, trabecular bone of RA+VIB mice had a 30% greater bone volume fraction, 51% greater marrow osteoprogenitor population, 83% greater osteoblast surfaces, 59% greater bone formation rates, and a 235% greater ratio of bone lining osteoblasts to marrow adipocytes than RA mice. A subsequent experiment indicated that receiving the mechanical intervention only during disuse, rather than only during reambulation, was more effective in altering trabecular morphology. These data indicate that the osteogenic potential of bone marrow cells is retained by low-magnitude vibrations during disuse, an attribute which may have contributed to an enhanced recovery of bone morphology during reambulation. - Funding: This research was kindly funded by NASA and the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: SJ, YKL and CTR have submitted a series of patents to the US Patent and Trademark Office regarding the method and application of the mechanical signal. All PLoS ONE policies on sharing data and materials will be adhered to. CTR is the scientific founder of Marodyne Medical, LLC and both he and the company may benefit from the results of this research. The removal of weight-bearing from the skeleton as a consequence of spaceflight, bedrest, paraplegia, or aging adversely affects the mass and architecture of trabecular bone [1,2]. Unfortunately, full recovery of skeletal tissues upon reambulation may not be possible [3], increasing the risk of traumatic and atraumatic fractures and, ultimately, compromising quality of life [4]. Failure of the bone structure to recover on reambulation may in part be caused by the collapse of the osteogenic potential of bone marrow cell populations during disuse. Without relevant mechanical signals, marrow stromal cells with the potential to become bone cells may instead die or commit to other cell lineages such as adipocytes [57]. As a consequence, a reduced or distracted niche of osteogenic cells may not be capable to effectively rebuild the intricate skeletal morphology upon the reintroduction of regulatory signals associated with load-bearing [8]. Consistent with the importance of mechanical signals to maintain the osteogenic potential of bone marrow cells, superposition of exogenous mechanical signals onto normal daily activities can enhance bone at both the cellular and tissue levels [911] with exercise promoting osteoblastogenesis and inhibiting adipogenesis [12]. Despite the various benefits that exercise provides, many exercise-based interventions have been ineffective in stemming tissue deterioration during disuse [1,13,14] or to fully recapture bone mass upon reambulation [1,15]. Exercise typically imposes a limited number of loading cycles at relatively high magnitudes (.1200 microstrain) and low (,10 Hz) loading frequencies [16,17]. Functional daily activities, however, subject the skeleton to a much greater spectrum of loading magnitudes, frequencies and cycles, including high-frequency signals induced by quasi-isometric muscle activity [18,19]. As bone can sense and respond to high-frequency mechanical signals, even if applied at extremely low magnitudes [20,21], it is conceivable that that these mechanical signal components are critical to the retention of cellular and tissue homeostasis. Consistent with this hypothesis, the decline in trabecular bone formation rates during disuse can be rescued by brief applications of low-magnitude whole body vibration, but not by similar periods of normal weight bearing [22]. These physical signals retain their osteogenic influence even when the mode of application virtually eliminates extracellular matrix deformations [23,24]. It is therefore possible that high-frequency mechanical stimuli are sensed directly by cells within the bone marrow to initiate a cascade of events promoting the population of mesenchymal cells and biasing their differentiation towards osteoblastogenesis. In the healthy, physically active skeleton, low-magnitude whole body vibrations can potentiate bones anabolic responsiveness by biasing the differentiation and proliferation of mesenchymal stem cells in the marrow towards a musculoskeletal lineage [25]. The importance of these mechanical signals in preserving the viability of stromal cells in the bone marrow environment during disuse is unknown. Here, we tested whether specific bone marrow cell populations as well as trabecular bone morphology can benefit from the application of low-level whole body vibrations during disuse and reambulation. In the second phase of this study, it was investigated whether trabecular bone recovery during reambulation can be augmented more effectively by applying mechanical signals only during disuse or only during reambulation. Materials and Methods Experimental design All procedures were reviewed and approved by the Institutional Animal Care and Use Committee (IACUC). Seven-week old male C57BL/6J (B6) mice were used for all phases of the study (n = 108 total). At this age, trabecular bone mass has peaked in this specific inbred mouse strain [26] even though the (...truncated)