Exercise is perhaps the single "intervention" recognized as a deterrent to both osteoporosis and obesity, yet the manner in which mechanical signals inhibit their pathogenesis remains unknown. Brief daily periods of high frequency (30-90 Hz), low magnitude (<0.4g) mechanical signals (LMMS) are anabolic to both bone and muscle. In an unexpected finding, these signals also suppress adipogenesis, with 29% less total visceral abdominal fat in mice subject to 12w of LMMS. The starkly distinct response of these tissues (?bone &muscle;?fat) to LMMS suggests that these signals influence the differentiation pathway of mesenchymal stem cells (MSCs). Translated to the human, this would help explain why a sedentary lifestyle is permissive to both osteoporosis and obesity, seemingly distinct diseases, and could suggest that LMMS reduce adipogenesis and strengthen the musculoskeletal system as much by defining the fate of MSCs as influencing the resident cell population within bone, muscle, or fat. We hypothesize that LMMS drive MSCs towards a bone and muscle phenotype, simultaneously suppressing a path towards adiposity.
Three specific aims are designed to better understand the means by which LMMS influences the body composition of the growing, aging, obese and diseased animal: 1. To identify those genes involved in the tissue response to LMMS, young male B6 mice will be subject to daily LMMS, and early through late (4d, 6 &12w) expression levels of 96 candidate genes in marrow, fat and bone, representing those involved in regulating these tissues, will be correlated to alterations in bone and fat mass, and compared to baseline and age matched control. 2. The long-term phenotypic impact of LMMS, and their ability to influence dietary and genetic models of obesity, will be defined at 3 &6 months in healthy male B6 mice fed a normal or high-fat diet (Diet Induced Obesity), as well as a transgenic strain of mice prone to adiposity (leptin-deficient ob/ob). The status of marrow, fat and bone, and level of triglycerides and free fatty acid in the serum, liver, muscle and adipose tissue, will be quantified and compared to controls. 3. To determine if LMMS influences the differentiation pathway of MSCs, irradiated C57BL/6J mice (B6) transplanted with marrow from GFP+ donors will be subject to LMMS, and following 6 &12w, the number of GFP+ cells in fat, marrow and bone will be compared to age matched recipient GFP+ controls. To establish if MSCs can be independently influenced by LMMS, the ability of these signals to suppress adipogenesis and promote osteoblastogenesis will be evaluated in MSC cultures (C3H10T1/2) using an in vitro system used to deliver LMMS. Together, these studies will help define how the musculoskeletal, adipose and stem cell systems respond to subtle changes in their mechanical environment, and represents a step in establishing a non-drug means of inhibiting osteoporosis and obesity.
Augmentation of Trabecular Bone by Low Magnitude Strain This work will investigate the mechanisms behind the anabolic potential of extremely low- magnitude mechanical signals, and how they strengthen both bone and muscle. Research over the last period of funding has also shown that these signals markedly suppress adiposity, by influencing the differentiation pathway of mesenchymal stem cells rather than elevating the animal's metabolism, indicating a previously unrecognized mechanical means of the regulating fat and bone production. This research will provide the foundation to translate this work to the clinic as a safe, non-pharmacologic, intervention for the control of osteoporosis and obesity.
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