The effects of different intensities of exercise and active vitamin D on mouse bone mass and bone strength

Effects of acute- and long-term aerobic exercises at different intensities on bone in mice

INTRODUCTION

Exercise intensity determines the benefits of aerobic exercise. Our objectives were, in aerobic exercise at different intensities, to determine (1) changes in bone metabolism-related genes after acute exercise and (2) changes in bone mass, strength, remodeling, and bone formation-related proteins after long-term exercise.

MATERIALS AND METHODS

Total 36 male C57BL/6J mice were divided into a control group and exercise groups at 3 different intensities: low, moderate, or high group. Each exercise group was assigned to acute- or long-term exercise groups. Tibias after acute exercise were evaluated by real-time PCR analysis. Furthermore, hindlimbs of long-term exercise were assessed by micro-CT, biomechanical, histological, and immunohistochemical analyses.

RESULTS

Acute moderate-intensity exercise decreased RANKL level as bone resorption marker, whereas low- and high-intensity exercise did not alter it. Additionally, only long-term exercise at moderate intensity increased bone mass and strength. Moderate-intensity exercise promoted osteoblast activity and suppressed osteoclast activity. After low- and high-intensity exercise, osteoblast and osteoclast activity were unchanged. An increase in the number of β-catenin-positive cells and a decrease in sclerostin-positive cells were observed in the only moderate group.

CONCLUSION

These results showed that moderate-intensity exercise can inhibit bone resorption earlier, and long-term exercise can increase bone mass and strength through promoted bone formation via the Wnt/β-catenin activation. High-intensity exercise, traditionally considered better for bone, may fail to stimulate bone remodeling, leading to no change in bone mass and strength. Our findings suggest that moderate-intensity exercise, neither too low nor high, can maintain bone health.

Moderate intensity aerobic training reduces the signs of peripheral sensitization in a mouse model of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a global health problem for many reasons including the comorbidities, such as diabetic neuropathy (DPN), which is the most common. It has been suggested that aerobic training can improve metabolic health in individuals with T2DM. Still, the effect of aerobic training on DPN signs and its relationship with serum levels of tumor necrosis tumor alpha (TNF-α), an essential molecule in T2DM development, is unknown. We evaluated the effect of two intensities of aerobic training in adult male C57BL/6 mice divided into six groups: sedentary control (CTRL), control with low-intensity training (CTRL-LI), control with moderate-intensity training (CTRL-MI), T2DM sedentary (T2DM), T2DM with low-intensity training (T2DM-LI), and T2DM with moderate-intensity training (T2DM-MI). We induced the T2DM model by combining a hypercaloric diet and low doses of streptozotocin. We measured serum TNF-α levels and correlated them with peripheral sensitization and the cardinal signs of T2DM in mice. Moderate intensity aerobic training decreased the symptoms of DPN and improved metabolic health in T2DM. Interestingly, decreased TNF-α serum levels correlated with reduced peripheral thermal sensitivity and mechanical sensitivity by aerobic training. Moderate intensity aerobic training counteracts the development and symptoms of DPN and improve metabolic health in T2DM. Decreased TNF-α correlates with reduced peripheral thermal sensitivity and mechanical sensitivity by aerobic training.

Effects of exercise on the expression of long non-coding RNAs in the bone of mice with osteoporosis

Physical activity or exercise are known to promote bone formation and decrease bone resorption to maintain skeletal and bone health both in animal models and in humans with osteoporosis. Previous studies have indicated that long non-coding RNAs (lncRNAs) are able to regulate bone metabolism. Therefore, the present study aimed to evaluate whether lncRNAs responded to exercise by regulating the balance of bone metabolism in order to prevent osteoporosis. To meet this end, ovariectomized mice were used in the present study to establish an osteoporosis model. The exercise treatment groups were subjected to 9 weeks of treadmill running exercise in 4 weeks of the operation was performed Femurs were collected to measure bone mineral density, bone mass, bone formation and resorption. The expression levels of lncRNAs were subsequently measured using microarray and gene function analyses. The pairwise comparison results [ovariectomy (OVX) vs. OVX + exercise (EX); OVX vs. SHAM; SHAM vs. SHAM + EX; OVX + EX vs. SHAM + EX] of the gene microarray analysis revealed that the expression of 2,424 lncRNAs (1718 upregulated and 706 downregulated) were significantly altered in the mouse femurs following treadmill running. Gene Ontology (GO) analysis, incorporating the GO annotations ‘biological processes’, ‘molecular function’ and ‘cellular components’, of osteoporosis revealed that the VEGF, mTOR and NF-κB signaling pathways were potential targets of the lncRNAs. Moreover, it was possible to predict the target microRNAs (miRNAs) of six lncRNAs (LOC105246953, LOC102637959, NONMMUT014677, NONMMUT027251, ri|D130079K21|PX00187K16|1491 and NONMMUT006626), which suggested that the underlying mechanism by which lncRNAs respond to exercise involved bone regulation via lncRNA-miRNA sponge adsorption. Overall, these results suggested that the treadmill running exercise did regulate lncRNA expression in the bone, and that this was involved in the prevention of osteoporosis.

Multiple Applications of Different Exercise Modalities with Rodents

A large proportion of chronic diseases can be derived from a sedentary lifestyle. Raising physical activity awareness is indispensable, as lack of exercise is the fourth most common cause of death worldwide. Animal models in different research fields serve as important tools in the study of acute or chronic noncommunicable disorders. With the help of animal-based exercise research, exercise-mediated complex antioxidant and inflammatory pathways can be explored, which knowledge can be transferred to human studies. Whereas sustained physical activity has an enormous number of beneficial effects on many organ systems, these animal models are easily applicable in several research areas. This review is aimed at providing an overall picture of scientific research studies using animal models with a focus on different training modalities. Without wishing to be exhaustive, the most commonly used forms of exercise are presented.

CCL2 is a critical mechano-responsive mediator in crosstalk between osteoblasts and bone mesenchymal stromal cells

It has been known that moderate mechanical loading, like that caused by exercise, promotes bone formation. However, its underlying mechanisms remain elusive. Here we showed that moderate running dramatically improved trabecular bone in mice tibias with an increase in bone volume fraction and trabecular number and a decrease in trabecular pattern factor. Results of immunohistochemical and histochemical staining revealed that moderate running mainly increased the number of osteoblasts but had no effect on osteoclasts. In addition, we observed a dramatic increase in the number of colony forming unit-fibroblast in endosteal bone marrow and the percentage of CD45^- Leptin receptor⁺ (CD45^- LepR⁺ ) endosteal mesenchymal progenitors. Bioinformatics analysis of the transcriptional data from gene expression omnibus (GEO) database identified chemokine c-c-motif ligands (CCL2) as a critical candidate induced by mechanical loading. Interestingly, we found that CCL2 was up-regulated mainly in osteoblastic cells in the tibia of mice after moderate running. Further, we found that mechanical loading up-regulated the expression of CCL2 by activating ERK1/2 pathway, thereby stimulating migration of endosteal progenitors. Finally, neutralizing CCL2 abolished the recruitment of endosteal progenitors and the increased bone formation in mice after 4 weeks running. These results therefore uncover an unknown connection between osteoblasts and endosteal progenitors recruited in the increased bone formation induced by mechanical loading.

The effects of locomotion on bone marrow mesenchymal stem cell fate: insight into mechanical regulation and bone formation

Bone marrow mesenchymal stem cells (BMSCs) refer to a heterogeneous population of cells with the capacity for self-renewal. BMSCs have multi-directional differentiation potential and can differentiate into chondrocytes, osteoblasts, and adipocytes under specific microenvironment or mechanical regulation. The activities of BMSCs are closely related to bone quality. Previous studies have shown that BMSCs and their lineage-differentiated progeny (for example, osteoblasts), and osteocytes are mechanosensitive in bone. Thus, a goal of this review is to discuss how these ubiquious signals arising from mechanical stimulation are perceived by BMSCs and then how the cells respond to them. Studies in recent years reported a significant effect of locomotion on the migration, proliferation and differentiation of BMSCs, thus, contributing to our bone mass. This regulation is realized by the various intersecting signaling pathways including RhoA/Rock, IFG, BMP and Wnt signalling. The mechanoresponse of BMSCs also provides guidance for maintaining bone health by taking appropriate exercises. This review will summarize the regulatory effects of locomotion/mechanical loading on BMSCs activities. Besides, a number of signalling pathways govern MSC fate towards osteogenic or adipocytic differentiation will be discussed. The understanding of mechanoresponse of BMSCs makes the foundation for translational medicine.

Effects of high-intensity interval training in more or less active mice on biomechanical, biophysical and biochemical bone parameters

High-intensity interval training (HIIT) is of scientific interest due its role in improving physical fitness, but the effects of HIIT on bone health need be carefully explored. Further, it is necessary to know whether HIIT effects on bone health are dependent on the physical activity levels. This may be experimentally tested since we have built a large cage (LC) that allows animals to move freely, promoting an increase of spontaneous physical activity (SPA) in comparison to a small cage (SC). Thus, we examined the effects of HIIT on biophysical, biomechanical and biochemical parameters of bone tissue of C57BL/6J mice living in cages of two different sizes: small (SC) or large (LC) cages with 1320 cm² and 4800 cm² floor space, respectively. Male mice were subdivided into two groups within each housing type: Control (C) and Trained (T). At the end of the interventions, all mice were euthanized to extract the femur bone for biophysical, biomechanical and biochemical analyses. Based a significant interaction from two-way ANOVA, trained mice kept in large cage (but not for trained mice housed in SC) exhibited a reduction of tenacity and displacement at failure in bone. This suggests that long-term HIIT program, in addition with a more active lifestyle correlates with exerts negative effects on the bone of healthy mice. A caution must also be raised about the excessive adoption of physical training, at least regarding bone tissue. On the other hand, increased calcium was found in femur of mice housed in LC. In line with this, LC-C mice were more active (i.e. SPA) than other groups. This implies that an active lifestyle without long-term high intensity physical training seems to play a role in promoting benefits to bone tissue. Our data provides new insights for treatment of osteo-health related disorders.

Effect of regular resistance exercise, vitamin D, and calcium supplements on the bone mineral content and density in postmenopausal model of rats: An experimental study

Background

Postmenopausal osteoporosis progressively occurs due to alteration in the estrogen level during the menopause period, and subsequently elevates the risk of fractures.

Objective

To evaluate the effect of regular resistance exercise, vitamin D, and calcium supplements on bone mineral content and density, postmenopausal rats used.

Materials and Methods

In this experimental study, 72 female Sprague-Dawley rats (8-10 wk: 250 ± 15 gr) were ovariectomized and randomly divided into nine groups (n = 8/each): control, placebo, exercise (EX), exercise with vitamin D supplement (EX + D), exercise with calcium (EX + Ca), exercise with calcium and vitamin D (EX + Ca + D), vitamin D administration (D), calcium administration (Ca), and calcium and vitamin D (Ca + D) groups. Finally, the tail, hip, and lumbar bone mineral content, bone mineral density, bone thickness, and bone cells were evaluated in each group.

Results

The tail, hip, and lumbar bone mineral density was increased significantly in the EX + Vit D group compared to the control group (p = 0.004, p = 0.007, p = 0.003, respectively). However, there were no significant changes in the bone mineral content of the hips and lumbar among the groups. Besides, bone thickness in the Ex + Vit D group was more than the other groups (p = 0.02). The number of osteoclast cells were decreased in the Ca + Vit D, Ex + Ca, Ex + Vit D, and Ex + Vit D + Ca groups compared to the control group. Osteocyte numbers were increased only in the Ex + Vit D group.

Conclusion

Resistance exercise in combination with vitamin D and calcium have a positive effect on the bone mineral density and bone mineral content and might be able to prevent or delay the osteoporosis among elderly women. However, additional researches are needed to assess the molecular pathways of this process.

Medium-Intensity Treadmill Exercise Exerts Beneficial Effects on Bone Modeling Through Bone Marrow Mesenchymal Stromal Cells

As a type of multipotential cells, bone marrow mesenchymal stromal cells (BMMSCs) can differentiate into chondrocytes, osteoblasts, and adipocytes under different loading condition or specific microenvironment. Previous studies have shown that BMMSCs and their lineage-differentiated progeny (for example, osteoblasts), and osteocytes are mechanosensitive in bone. The appropriate physical activity and exercise could help attenuate bone loss, effectively stimulate bone formation, increase bone mineral density (BMD), prevent the progression of osteoporosis, and reduce the risk of bone fractures. Bone morphogenetic protein (BMP) is originally discovered as a protein with heterotopic bone-inducing activity in the bone matrix that exerts a critical role in multiple stages of bone metabolism. In the present study, the medium-intensity treadmill exercise enhanced bone formation and increased osteocalcin (OCN) and osteopontin (OPN) mRNA expression as well as activation of the BMP-Smad signaling pathway in vivo. In order to investigate the effect of a BMP-Smad signaling pathway, we injected mice with activated enzyme inhibitors (LDN-193189HCL) and subjected the mice to treadmill exercise intervention. LDN-193189HCL attenuated the BMD and bone mass mediated by medium-intensity exercise and BMP-Smad signaling pathway.

Mitochondrial dysfunction impairs osteogenesis, increases osteoclast activity, and accelerates age related bone loss

The pathogenesis of declining bone mineral density, a universal feature of ageing, is not fully understood. Somatic mitochondrial DNA (mtDNA) mutations accumulate with age in human tissues and mounting evidence suggests that they may be integral to the ageing process. To explore the potential effects of mtDNA mutations on bone biology, we compared bone microarchitecture and turnover in an ageing series of wild type mice with that of the PolgA^mut/mut mitochondrial DNA ‘mutator’ mouse. In vivo analyses showed an age-related loss of bone in both groups of mice; however, it was significantly accelerated in the PolgA^mut/mut mice. This accelerated rate of bone loss is associated with significantly reduced bone formation rate, reduced osteoblast population densities, increased osteoclast population densities, and mitochondrial respiratory chain deficiency in osteoblasts and osteoclasts in PolgA^mut/mut mice compared with wild-type mice. In vitro assays demonstrated severely impaired mineralised matrix formation and increased osteoclast resorption by PolgA^mut/mut cells. Finally, application of an exercise intervention to a subset of PolgA^mut/mut mice showed no effect on bone mass or mineralised matrix formation in vitro. Our data demonstrate that mitochondrial dysfunction, a universal feature of human ageing, impairs osteogenesis and is associated with accelerated bone loss.

Impacts of exercise interventions on different diseases and organ functions in mice

Background

In recent years, much evidence has emerged to indicate that exercise can benefit people when performed properly. This review summarizes the exercise interventions used in studies involving mice as they are related to special diseases or physiological status. To further understand the effects of exercise interventions in treating or preventing diseases, it is important to establish a template for exercise interventions that can be used in future exercise-related studies.

Methods

PubMed was used as the data resource for articles. To identify studies related to the effectiveness of exercise interventions for treating various diseases and organ functions in mice, we used the following search language: (exercise [Title] OR training [Title] OR physical activity [Title]) AND (mice [title/abstract] OR mouse [title/abstract] OR mus [title/abstract]). To limit the range of search results, we included 2 filters: one that limited publication dates to "in 10 years" and one that sorted the results as "best match". Then we grouped the commonly used exercise methods according to their similarities and differences. We then evaluated the effectiveness of the exercise interventions for their impact on diseases and organ functions in 8 different systems.

Results

A total of 331 articles were included in the analysis procedure. The articles were then segmented into 8 systems for which the exercise interventions were used in targeting and treating disorders: motor system (60 studies), metabolic system (45 studies), cardio-cerebral vascular system (58 studies), nervous system (74 studies), immune system (32 studies), respiratory system (7 studies), digestive system (1 study), and the system related to the development of cancer (54 studies). The methods of exercise interventions mainly involved the use of treadmills, voluntary wheel-running, forced wheel-running, swimming, and resistance training. It was found that regardless of the specific exercise method used, most of them demonstrated positive effects on various systemic diseases and organ functions. Most diseases were remitted with exercise regardless of the exercise method used, although some diseases showed the best remission effects when a specific method was used.

Conclusion

Our review strongly suggests that exercise intervention is a cornerstone in disease prevention and treatment in mice. Because exercise interventions in humans typically focus on chronic diseases, national fitness, and body weight loss, and typically have low intervention compliance rates, it is important to use mice models to investigate the molecular mechanisms underlying the health benefits from exercise interventions in humans.

Use of adult mesenchymal stromal cells in tissue repair: impact of physical exercise

Physical exercise (PE) has unquestionable beneficial effects on health, which likely extend into several organ-to-cell physiological processes. At the cell scale, endogenous mesenchymal stromal cells (MSCs) contribute to tissue repair, although their repair capacities may be insufficient in paucicellular or severely damaged tissues. For this reason, MSC transplantation holds great promise for tissue repair. With the goals of understanding if PE has beneficial effects on MSC biology and if PE potentiates their role in tissue repair, we reviewed literature reports regarding the effects of PE on MSC properties (specifically, proliferation, differentiation, and homing) and of a combination of PE and MSC transplantation on tissue repair (specifically neural, cartilage, and muscular tissues). Contradictory results have been reported; interpretation is complicated because various and different species, cell sources, and experimental protocols, specifically exercise programs, have been used. On the basis of these data, the effects of exercise on MSC proliferation and differentiation depend on exercise characteristics (type, intensity, duration, etc.) and on the characteristics of the tissue from which the MSCs were collected. For the in vitro studies, the level of strain (and other details of the mechanical stimulus), the time elapsed between the end of exposure to strain and MSC collection, the age of the donors, as well as the passage number at which the MSCs are evaluated also play a role. The combination of PE and MSC engraftment improves neural, cartilage, and muscular tissue recovery, but it is not clear whether the effects of MSCs and exercise are additive or synergistic.

The effect of testosterone itself and in combination with letrozole on bone mineral density in male rats

Testosterone is an essential hormone to maintain bone integrity; however, the effect of aromatase enzyme in androgen-induced bone maintenance remains somewhat unclear. The present study evaluated the effect of testosterone itself and combined with letrozole, an aromatase inhibitor, on bone mineral density of male rats. Total of 48 male rats were divided into 4 equal groups (n = 12/group); sham group, O: orchiectomy, O + T: orchiectomized rats treated with testosterone, O + T + L: orchiectomized rats treated with combination of testosterone and letrozole. Bone density (BMD), bone markers, and vitamin D metabolism parameters were checked in all groups before and after the study. There was no significant difference in baseline values of these parameters, but at the end of the study there was a significant decrease in delta BMD at both lumbar and femor in orchiectomized rats in comparison with the sham group (p < 0.001, p < 0.001, respectively). Both testosterone and its combination with letrozole increased lumbar and femoral BMD of orchiectomized rats, with a higher increase in lumbar BMD in O + T group. CTX were higher in O group rats. The present study showed a major role for testosterone on BMD maintenance in male rats. However, testosterone has a potent effect on lumbar BMD, by the aromatization to estradiol.

Multiscale experimental study on the effects of different weight-bearing levels during moderate treadmill exercise on bone quality in growing female rats

Background

Bone tissue displays a hierarchical organization. Mechanical environments influence bone mass and structure. This study aimed to explore the effects of different mechanical stimuli on growing bone properties at macro–micro–nano scales.

Methods

Sixty five-week-old female Wistar rats were treadmill exercised at moderate intensity with the speed of 12 m/min, and then randomly divided into five groups according to weight-bearing level. After 8 weeks of experiment, femurs were harvested to perform multiscale tests.

Results

Bone formation was significantly increased by weight-bearing exercise, whereas bone resorption was not significantly inhibited. Trabecular and cortical bone mineral densities showed no significant increase by weight-bearing exercise. The microstructure of trabecular bone was significantly improved by 12% weight-bearing exercise. However, similar positive effects were not observed with further increase in weight-bearing levels. The nanomechanical properties of trabecular bone were not significantly changed by weight-bearing exercise. The macrostrength of whole femur and the nanomechanical properties of cortical bone significantly decreased in the 19% and 26% weight-bearing exercise groups.

Conclusion

When rats ran on the treadmill at moderate intensity during growth period, additional 12% weight-bearing level could significantly increase bone formation, improve microstructure of trabecular bone, as well as maintain the structure and mechanical properties of cortical bone. Excessive weight-bearing level caused no positive effects on the trabecular bone microstructure and properties of cortical bone at all scales. In addition, increased weight-bearing level exerted no significant influence on trabecular and cortical bone mineral densities.

Reduced PDGF-AA in subchondral bone leads to articular cartilage degeneration after strenuous running

To identify the effects of running on articular cartilage and subchondral bone remodeling, C57BL/6 mice were randomly divided into three groups: control, moderate-, and strenuous running. Magnetic resonance imaging showed bone marrow lesions in the knee subchondral bone in the strenuous-running group in contrast with the other two groups. The microcomputed tomography analysis showed promoted bone formation in the subchondral bone in mice subjected to strenuous running. Histological and immunohistochemistry results indicated that terminal differentiation of chondrocytes and degeneration of articular cartilage were enhanced but, synthesis of platelet-derived growth factor-AA (PDGF-AA) in the subchondral bone was suppressed after strenuous running. In vitro, excessive mechanical treatments suppressed the expression of PDGF-AA in osteoblasts, and the condition medium from mechanical-treated osteoblasts stimulated maturation and terminal differentiation of chondrocytes. These results indicate that strenuous running suppresses the synthesis of PDGF-AA in subchondral bone, leading to downregulated PDGF/Akt signal in articular cartilage and thus cartilage degeneration.

Mathematical modeling of bone in-growth into undegradable porous periodic scaffolds under mechanical stimulus

Undegradable scaffolds, as a key element in bone tissue engineering, prevail in the present clinical applications, and the bone in-growth into such scaffolds under mechanical stimulus is an important issue to evaluate the bone-repair effect. This work aims to develop a mathematical framework to investigate the effect of mechanical stimulus on the bone in-growth into undegradable scaffolds. First, the osteoclast and osteoblast activities were coupled by their autocrine and paracrine effects. Second, the mechanical stimulus was empirically incorporated into the coupling cell activities on the basis of experimental observations. Third, the effect of mechanical stimulus including intensity and duration on the bone in-growth process was numerically studied; moreover, the homeostasis of scaffold–bone system under the mechanical stimulus was also treated. The results showed that the numbers of osteoblasts and osteoclasts in the scaffold–bone system tended to constants representing the system homeostasis. Both the mechanical intensity and duration optimized the final bone formation. The numerical results of the bone formation were comparable to the experimental results in rats. The findings from this modeling study could be used to explain many physiological phenomena and clinical observations. The developed model integrates both cell and tissue scales, which can be used as a platform to investigate bone remodeling under mechanical stimulus.