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Astronauts experience severe musculoskeletal degradation in space. After returning to earth, bone loss recovery did not parallel muscle recovery. Fascia may play an important role as a considerable part of muscle force is transmitted to bone through fascia. However, little is known about how fascia changes in microgravity and its effect on the development of musculoskeletal degeneration. In this study, a rat hindlimb unloading model was used to simulate microgravity (21 days of tail suspension) and then reloading for 7 days, 14 days and 21 days. After different periods, bone mineral density (BMD) and microstructure of the tibia were analyzed by μCT, the mechanical properties of the tibia were determined by the three-point bending test and the mechanical properties of fascia were explored by tensile test. The results show that, after tail suspension, collagen Ⅰ in myofascia was significantly increased (p < 0.05), the myofascial elastic modulus was significantly decreased (p < 0.05), BMD of the tibia was significantly decreased (p < 0.05) and the microstructure of the tibia had deteriorated. After 21 days of reloading, there was no significant improvement in the myofascial elastic modulus as well as in the tibial maximum load. Correlation analysis results showed that the myofascial elastic modulus was significantly correlated with the tibial maximum load. In summary, the deterioration of mechanical property of myofascia induced by tail suspension did not recover when the time of reloading was the same as the time of unloading. This indicates that the delayed bone recovery after being exposed to microgravity was associated with deterioration of myofascia. • Myofascia was significantly changed in simulated microgravity and couldn't recover. • There was a significant correlation between myofascia and bone. • The delayed bone recovery after simulated microgravity was associated with myofascia. [ABSTRACT FROM AUTHOR]

Exercise training has been reported to prevent bone loss in ovariectomized (OVX) rats and postmenopausal women. We hypothesized that treadmill training inhibited adipogenesis and enhanced osteogenesis through the regulation of adipocyte differentiation factor peroxisome proliferators-activated receptor gamma (PPARγ) and the osteogenic factor runt-related transcription factor 2 (Runx2) in a model of OVX-induced osteoporosis. To test this hypothesis, 3-month-old female Sprague-Dawley rats were divided randomly into the following groups: Sham, OVX, OVX exercised (EX), and OVX estrogen replacement (E(2)). At the end of the experiment, the bone mineral density (BMD) was detected using DEXA and the morphology change of bone tissues and uterus was observed by HE staining. The protein expression for PPARγ and Runx2 were measured by immunohistochemistry and western blot and the bone triacylglycerol (TG) was extracted by methanol/chloroform. OVX dramatically increased the number of fat vacuoles, protein levels for PPARγ and Runx2 as well as the TG level in tibiae and lumbar vertebrate. In contrast, the serum level of E(2), the lumbar vertebrate BMD as well as the proximal and distal femur BMD was significantly decreased in the OVX group. All changes induced by OVX were significantly reversed by exercise treatment except for the protein expression level of Runx2. Moreover, exercise treatment produced no estrogenic effects on uterus as evidenced by the uterus wet weight and histology. Treadmill training could prevent bone loss induced by OVX through the inhibition of adipocyte differentiation factor PPARγ rather than promoting osteogenic factor Runx2. [ABSTRACT FROM AUTHOR]

It is well known that the bone loss which may lead to bone fracture risk occurs under microgravity and disuse. Besides bone mineral density (BMD), the role of collagen as the main component of bone in the mechanism has unknown. In addition, myofascia, which is also mainly composed of collagen, plays an important role in the force transmission in musculoskeletal system. In this study, the collagen alternations of hindlimb tibia and myofascia in tail-suspension rats, which hindlimb unloading as a model to simulate microgravity and/or disuse, were investigated and further the correlations with the mechanical properties were analyzed. The collagen fiber orientations were observed by second-harmonic generation (SHG) microscopy and quantitatively analyzed in MATLAB. Bone mechanical properties were measured by three-point-bending test and nanoindentation. Myofascial mechanical properties were explored by tensile test. The results showed: 1) the collagen fibers orientation both in bone and myofascia were dispersed, as standard deviation of collagen fiber orientation increased.2) the mechanical properties of tibia were decreased by unloading both at macro level (maximum load, breaking load and stiffness, etc.) and micro level (hardness). In myofascia, the yield strain and ultimate strain were significantly decreased. 3) correlation analysis showed bone collagen orientation was related to bone hardness/elastic modulus, and myofascial collagen orientation was related to myofascial elastic modulus and yield limit. Additionally, myofascial mechanical properties were related to bone mechanical properties. These suggested disordered collagen orientation may be related to the deterioration of mechanical properties in both bone and myofascia under simulated microgravity. The alternation of myofascial mechanical property may have a certain impact on the deterioration of bone mechanical properties through affecting the force transmission from muscle to bone. • The collagen fibers orientation both in bone and myofascia were dispersed under microgravity • The bone collagen orientation was related to bone hardness and elastic modulus • The myofascial collagen orientation was related to myofascial elastic modulus and yield limit • The myofascial mechanical properties were related to bone mechanical properties • The alternation of myofascial mechanical property may have a certain impact on the deterioration of bone mechanical properties through affecting the force transmission from muscle to bone [ABSTRACT FROM AUTHOR]

Conventional exercises could not prevent the deterioration of astronaut's bone and muscle effectively during space flight. On the ground, stretching is widely used to improve the joint range of motion (ROM) and muscle performance. However, study on how stretching affected bone mass and bone quality was rarely reported and the animal stretching modes were not ideal. Therefore, the aim of this study was to develop a device that stretching the hindlimb of rats to study the effects of stretching on bone in hindlimb unloading rats. The ankle joint angel of conscious rat was kept at 30° for periodical stretching by this device. 32 Sprague Dawley rats were randomly divided into 4 groups (n = 8, each): control group (CON); CON plus stretching group (CONS); tail-suspension group (TS); TS plus stretching group (TSS). On the 29th day of the experiment, the bone mineral density (BMD) and trabecular microstructure were analyzed by μCT, the mechanical properties of tibia were determined by three-point bending test and the muscle performance was measured by multi-channel physiological signal tester. The data showed that the muscle strength and wet weight in TSS group were significantly higher than TS group. After stretching, the BMD, trabecular microstructure and mechanical properties of tibia in TSS group were also significantly better than TS group. In addition, these results of bone showed no significant difference between TSS group and CON group. This device we developed could quantitatively stretch the hindlimb of rat and prevent the bone and muscle degeneration induced by tail-suspension. Our results suggested that stretching could be a useful exercise mode to keep bone and muscle healthy for astronauts or people who could not do conventional exercise. • The effect of conventional exercise on countering the degeneration of musculoskeletal system in space was limited. • Designing a rat stretching device which is more suitable for practical application. • Periodic stretching can maintain bone quality in hindlimb unloading rat. [ABSTRACT FROM AUTHOR]