Bone loss recovery in mice following microgravity with concurrent bone-compartment-specific osteocyte characteristics

Space missions provide the opportunity to investigate the influence of gravity on the dynamic remodelling processes in bone. Mice were examined following space flight and subsequent recovery to determine the effects on bone compartment-specific microstructure and composition. The resulting bone loss following microgravity recovered only in trabecular bone, while in cortical bone the tissue mineral density was restored after only one week on Earth. Detection of TRAP-positive bone surface cells in the trabecular compartment indicated increased resorption following space flight. In cortical bone, a persistent reduced viability of osteocytes suggested an impaired sensitivity to mechanical stresses. A compartment-dependent structural recovery from microgravity-induced bone loss was shown, with a direct osteocytic contribution to persistent low bone volume in the cortical region even after a recovery period. Trabecular recovery was not accompanied by changes in osteocyte characteristics. These post-space-flight findings will contribute to the understanding of compositional changes that compromise bone quality caused by unloading, immobilisation, or disuse.

Differences in fracture healing between female and male C57BL/6J mice

Background: Mice are increasingly used in fracture healing research because of the opportunity to use transgenic animals. While both, male and female mice are employed, there is no consensus in the literature whether fracture healing differs between both sexes. Therefore, the aim of the present study was to analyse diaphyseal fracture healing in female and male C57BL/6J mice, a commonly used mouse strain in bone research. Methods: For that purpose, 12-week-old female (17–20 g) and male mice (22–26 g) received a standardised femur midshaft osteotomy stabilised by an external fixator. Mice were euthanized 10 and 21 days after fracture and bone healing was analysed by biomechanical testing, µCT, histology, immunohistochemistry and qPCR. Results: Ten days after fracture, male mice displayed significantly more cartilage but less fibrous tissue in the fracture callus compared to female mice, whereas the amount of bone did not differ. At day 21, male mice showed a significantly larger fracture callus compared to female mice. The relative amount of bone in the fracture callus did not significantly differ between both sexes, whereas its tissue mineral density was significantly higher in male mice on day 21, indicating more mature bone and slightly more rapid fracture healing. These results were confirmed by a significantly greater absolute bending stiffness of the fractured femurs of male mice on day 21. On the molecular level, male mice displayed increased active β-catenin expression in the fracture callus, whereas oestrogen receptor α (ERα) expression was lower. Conclusions: These results suggest that male mice display more rapid fracture healing with more prominent cartilaginous callus formation. This might be due to the higher weight of male mice, resulting in increased mechanical loading of the fracture. Furthermore, male mice displayed significantly greater activation of osteoanabolic Wnt/β-catenin signalling, which might also contribute to more rapid bone regeneration.

Features of the structural and functional state of bone tissue in patients with generalized periodontitis who live in different anthropogenically loaded areas

Introduction. A research was conducted of the features of the structural and functional state of bone tissue in patients with generalized periodontitis with rheumatoid arthritis who live in different anthropogenically loaded areas. Aim. The aim of the research is to assess the bone tissue mineral density according to the indicators of densitometric researches and the level of a marker of bone metabolism in generalized periodontitis of I and II degree of severity. Material and methods. We examined 105 patients with GP of the I and II degree of severity, among whom were patients with rheumatoid arthritis who live in environmentally favorable and unfavorable areas. Peculiarities of the structural and functional state of bone tissue were assessed using an ultrasonic densitometer Sunlight Mini Omni TM and the level of a marker of bone tissue resorption of deoxypyridinoline in urine. Results. Patients with generalized periodontitis with rheumatoid arthritis who live in environmentally unfavorable areas, found the largest number of people with signs of osteopenia, osteoporosis and elevated levels of deoxypyridinoline. In particular, in generalized periodontitis of the II degree of severity with osteopenia – 14 people (48.27%), with osteoporosis – 9 people (31%), the level of deoxypyridinoline determined in women was 12.03 ± 0.16 n/mol, which in 2.2 times significantly higher than the group of healthy (p < 0.001). Conclusions. According to densitometric parameters and the level of deoxypyridinoline in the urine, the acceleration of bone tissue resorption in patients with generalized periodontitis of the II degree of severity with rheumatoid arthritis who live in environmentally unfavorable areas was established.