Inhibition of MSTN signal pathway may participate in LIPUS preventing bone loss in ovariectomized rats

Mechanism and physical activities in bone-skeletal muscle crosstalk

Bone and skeletal muscle work in coordination to maintain the function of the musculoskeletal system, in which skeletal muscle contraction drives the movement of the bone lever system while bone provides insert sites for skeletal muscle through the bone-muscle junction. Existing evidence suggests that factors secreted by skeletal muscle and bone mediate the interaction between the two tissues. Herein, we focused on the relationship between skeletal muscle and bone and the underlying mechanism of the interaction. Exercise can promote bone strength and secrete osteocalcin and insulin-like growth factor I into the blood, thus improving muscle quality. In addition, exercise can also promote myostatin, interleukin-6, Irisin, and apelin in muscles to enter the blood so that they can act on bones to maintain the balance between bone absorption and bone formation. There is a special regulatory axis interleukin-6/osteocalcin between myokines and osteokines, which is mainly influenced by exercise. Therefore, we pay attention to the important factors in the bone-muscle intersection that are affected by exercise, which were found or their functions were expanded, which strengthened the connection between organs of the whole body, highlighting the importance of exercise and contributing to the diagnosis, prevention, and treatment of osteoporosis and sarcopenia in the clinic.

Exercise ameliorates anxious behavior and promotes neuroprotection through osteocalcin in VCD-induced menopausal mice

AIMS

As the ovaries age and women transition to menopause and postmenopause, reduced estradiol levels are associated with anxiety and depression. Exercise contributes to alleviate anxiety and depression and the bone-derived hormone osteocalcin has been reported to be necessary to prevent anxiety-like behaviors. The aim of this study was to investigate the effects of exercise on anxiety behaviors in climacteric mice and whether it was related to osteocalcin.

METHODS

Menopausal mouse model was induced by intraperitoneal injection of 4-vinylcyclohexene diepoxide (VCD). Open field, elevated plus maze, and light-dark tests were used to detect anxious behavior in mice. The content of serum osteocalcin was measured and its correlation with anxiety behavior was analyzed. BRDU and NEUN co-localization cells were detected with immunofluorescence. Western blot was applied to obtain apoptosis-related proteins.

RESULTS

The VCD mice showed obvious anxiety-like behaviors and 10 weeks of treadmill exercise significantly ameliorated the anxiety and increased circulating osteocalcin in VCD mice. Exercise increased the number of BRDU and NEUN co-localization cells in hippocampal dentate gyrus, reduced the number of impaired hippocampal neurons, inhibited the expression of BAX, cleaved Caspase3, and cleaved PARP, promoted the expression of BCL-2. Importantly, circulating osteocalcin levels were positively associated with the improvements of anxiety, the number of BRDU and NEUN co-localization cells in hippocampal dentate gyrus and negatively related to impaired hippocampal neurons.

CONCLUSION

Exercise ameliorates anxiety behavior, promotes hippocampal dentate gyrus neurogenesis, and inhibits hippocampal cell apoptosis in VCD-induced menopausal mice. They are related to circulating osteocalcin, which are increased by exercise.

Low-intensity pulsed ultrasound enhances the positive effects of high-intensity treadmill exercise on bone in rats

INTRODUCTION

Moderate exercise benefits bone health, but excessive loading leads to bone fatigue and a decline in mechanical properties. Low-intensity pulsed ultrasound (LIPUS) can stimulate bone formation. The purpose of this study was to explore whether LIPUS could augment the skeletal benefits of high-intensity exercise.

MATERIALS AND METHODS

MC3T3-E1 osteoblasts were treated with LIPUS at 80 mW/cm2 or 30 mW/cm2 for 20 min/day. Forty rats were divided into sham treatment normal control (Sham-NC), sham treatment high-intensity exercise (Sham-HIE), 80 mW/cm2 LIPUS (LIPUS80), and high-intensity exercise combined with 80 mW/cm2 LIPUS (LIPUS80-HIE). The rats in HIE group were subjected to 30 m/min slope treadmill exercise for 90 min/day, 6 days/week for 12 weeks. The LIPUS80-HIE rats were irradiated with LIPUS (1 MHz, 80 mW/cm2) for 20 min/day at bilateral hind limb after exercise.

RESULTS

LIPUS significantly accelerated the proliferation, differentiation, mineralization, and migration of MC3T3-E1 cells. Compared to 30 mW/cm2 LIPUS, 80 mW/cm2 LIPUS got better promotion effect. 12 weeks of high-intensity exercise significantly reduced the muscle force, which was significantly reversed by LIPUS. Compared with the Sham-NC group, Sham-HIE group significantly optimized bone microstructure and enhanced mechanical properties of femur, and LIPUS80-HIE further enhanced the improvement effect on bone. The mechanisms may be related to activate Wnt/β-catenin signal pathway and then up-regulate the protein expression of Runx2 and VEGF, the key factors of osteogenesis and angiogenesis.

CONCLUSION

LIPUS could augment the skeletal benefits of high-intensity exercise through Wnt/β-catenin signal pathway.

Low-intensity pulsed ultrasound in obstetrics and gynecology: advances in clinical application and research progress

In the past decade, research on ultrasound therapy in obstetrics and gynecology has rapidly developed. Currently, high-intensity ultrasound has been widely used in clinical practice, while low-intensity ultrasound has gradually emerged as a new trend of transitioning from pre-clinical research to clinical applications. Low-intensity pulsed ultrasound (LIPUS), characterized by a non-invasive low-intensity pulse wave stimulation method, employs its non-thermal effects to achieve safe, economical, and convenient therapeutic outcomes. LIPUS converts into biochemical signals within cells through pathways such as cavitation, acoustic flow, and mechanical stimulation, regulating molecular biological mechanisms and exerting various biological effects. The molecular biology mechanisms underlying the application of LIPUS in obstetrics and gynecology mainly include signaling pathways, key gene expression, angiogenesis, inflammation inhibition, and stem cell differentiation. LIPUS plays a positive role in promoting soft tissue regeneration, bone regeneration, nerve regulation, and changes in cell membrane permeability. LIPUS can improve the treatment benefit of premature ovarian failure, pelvic floor dysfunction, nerve damage caused by intrauterine growth restriction, ovariectomized osteoporosis, and incomplete uterine involution through the above biological effects, and it also has application value in the adjuvant treatment of malignant tumors such as ovarian cancer and cervical cancer. This study outlines the biological mechanisms and applications of LIPUS in treating various obstetric and gynecologic diseases, aiming to promote its precise application and provide a theoretical basis for its use in the field.

Molecular basis and therapeutic potential of myostatin on bone formation and metabolism in orthopedic disease

Myostatin, a member of the transforming growth factor-β (TGF-β) superfamily, is a key autocrine/paracrine inhibitor of skeletal muscle growth. Recently, researchers have postulated that myostatin is a negative regulator of bone formation and metabolism. Reportedly, myostatin is highly expressed in the fracture area, affecting the endochondral ossification process during the early stages of fracture healing. Furthermore, myostatin is highly expressed in the synovium of patients with rheumatoid arthritis (RA) and is an effective therapeutic target for interfering with osteoclast formation and joint destruction in RA. Thus, myostatin is a potent anti-osteogenic factor and a direct modulator of osteoclast differentiation. Evaluation of the molecular pathway revealed that myostatin can activate SMAD and mitogen-activated protein kinase signaling pathways, inhibiting the Wnt/β-catenin pathway to synergistically regulate muscle and bone growth and metabolism. In summary, inhibition of myostatin or the myostatin signaling pathway has therapeutic potential in the treatment of orthopedic diseases. This review focused on the effects of myostatin on bone formation and metabolism and discussed the potential therapeutic effects of inhibiting myostatin and its pathways in related orthopedic diseases.

Integrated Application of Low-Intensity Pulsed Ultrasound in Diagnosis and Treatment of Atrophied Skeletal Muscle Induced in Tail-Suspended Rats

Long-term exposure to microgravity leads to muscle atrophy, which is primarily characterized by a loss of muscle mass and strength and reduces one′s functional capability. A weightlessness-induced muscle atrophy model was established using the tail suspension test to evaluate the intervention or therapeutic effect of low-intensity pulsed ultrasound (LIPUS) on muscle atrophy. The rats were divided into five groups at random: the model group (B), the normal control group (NC), the sham-ultrasound control group (SUC), the LIPUS of 50 mW/cm2 radiation group (50 UR), and the LIPUS of 150 mW/cm2 radiation group (150 UR). Body weight, gastrocnemius weight, muscle force, and B-ultrasound images were used to evaluate muscle atrophy status. Results showed that the body weight, gastrocnemius weight, and image entropy of the tail suspension group were significantly lower than those of the control group (p < 0.01), confirming the presence of muscle atrophy. Although the results show that the muscle force and two weights of the rats stimulated by LIPUS are still much smaller than those of the NC group, they are significantly different from those of the pure tail suspension B group (p < 0.01). On day 14, the gastrocnemius forces of the rats exposed to 50 mW/cm2 and 150 mW/cm2 LIPUS were 150% and 165% of those in the B group. The gastrocnemius weights were both 135% of those in the B group. This suggests that ultrasound can, to a certain extent, prevent muscular atrophy.

Regulation of Myostatin on the Growth and Development of Skeletal Muscle

Myostatin (MSTN), a member of the transforming growth factor-β superfamily, can negatively regulate the growth and development of skeletal muscle by autocrine or paracrine signaling. Mutation of the myostatin gene under artificial or natural conditions can lead to a significant increase in muscle quality and produce a double-muscle phenotype. Here, we review the similarities and differences between myostatin and other members of the transforming growth factor-β superfamily and the mechanisms of myostatin self-regulation. In addition, we focus extensively on the regulation of myostatin functions involved in myogenic differentiation, myofiber type conversion, and skeletal muscle protein synthesis and degradation. Also, we summarize the induction of reactive oxygen species generation and oxidative stress by myostatin in skeletal muscle. This review of recent insights into the function of myostatin will provide reference information for future studies of myostatin-regulated skeletal muscle formation and may have relevance to agricultural fields of study.

Low-Intensity Pulsed Ultrasound Alleviates Osteoarthritis Condition Through Focal Adhesion Kinase-Mediated Chondrocyte Proliferation and Differentiation

OBJECTIVE

Osteoarthritis (OA) is a prevalent chronic multifactorial degenerative disease characterized by joint tissue inflammation, osteophyte formation, subchondral bone sclerosis, and articular cartilage degradation. Low-intensity pulsed ultrasound (LIPUS), a noninvasive ultrasound technique, is widely used to attenuate diseases. The aim of this study was to investigate whether LIPUS can ameliorate OA, and to explore its underlying molecular mechanism.

DESIGN

The OA model was established in a C57BL/6 mouse by the anterior cruciate ligament transaction method. OA was assessed using arthritis scoring and weightbearing parameters. Chondrocyte proliferation was detected by a CCK-8 assay. The levels of interleukin-6 (IL-6), IL-8 and tumor necrosis factor-α (TNF-α) in synovial fluid of the mice were measured by enzyme-linked immunosorbent assay.

RESULTS

In OA mice, the arthritis score and weightbearing abilities were dramatically improved by LIPUS treatment. LIPUS also remarkably declined the levels of inflammatory cytokines IL-6, IL-8, and TNF-α in synovial fluid of OA mice. Moreover, LIPUS promoted chondrocyte proliferation and differentiation by activating focal adhesion kinase (FAK) signaling. Inhibition of FAK significantly blocked LIPUS-mediated cell proliferation and differentiation in vitro, as well as inflammation condition in OA mice.

CONCLUSION

LIPUS alleviates OA through promoting chondrocytes proliferation and differentiation by activating FAK, which could act as an intervening target for OA treatment.

Molecular and Metabolic Mechanism of Low-Intensity Pulsed Ultrasound Improving Muscle Atrophy in Hindlimb Unloading Rats

Low-intensity pulsed ultrasound (LIPUS) has been proved to promote the proliferation of myoblast C2C12. However, whether LIPUS can effectively prevent muscle atrophy has not been clarified, and if so, what is the possible mechanism. The aim of this study is to evaluate the effects of LIPUS on muscle atrophy in hindlimb unloading rats, and explore the mechanisms. The rats were randomly divided into four groups: normal control group (NC), hindlimb unloading group (UL), hindlimb unloading plus 30 mW/cm² LIPUS irradiation group (UL + 30 mW/cm²), hindlimb unloading plus 80 mW/cm² LIPUS irradiation group (UL + 80 mW/cm²). The tails of rats in hindlimb unloading group were suspended for 28 days. The rats in the LIPUS treated group were simultaneously irradiated with LIPUS on gastrocnemius muscle in both lower legs at the sound intensity of 30 mW/cm² or 80 mW/cm² for 20 min/d for 28 days. C2C12 cells were exposed to LIPUS at 30 or 80 mW/cm² for 5 days. The results showed that LIPUS significantly promoted the proliferation and differentiation of myoblast C2C12, and prevented the decrease of cross-sectional area of muscle fiber and gastrocnemius mass in hindlimb unloading rats. LIPUS also significantly down regulated the expression of MSTN and its receptors ActRIIB, and up-regulated the expression of Akt and mTOR in gastrocnemius muscle of hindlimb unloading rats. In addition, three metabolic pathways (phenylalanine, tyrosine and tryptophan biosynthesis; alanine, aspartate and glutamate metabolism; glycine, serine and threonine metabolism) were selected as important metabolic pathways for hindlimb unloading effect. However, LIPUS promoted the stability of alanine, aspartate and glutamate metabolism pathway. These results suggest that the key mechanism of LIPUS in preventing muscle atrophy induced by hindlimb unloading may be related to promoting protein synthesis through MSTN/Akt/mTOR signaling pathway and stabilizing alanine, aspartate and glutamate metabolism.

MSTN is an important myokine for weight-bearing training to attenuate bone loss in ovariectomized rats

Weight-bearing training, as one of resistance exercises, is beneficial to bone health. Myostatin (MSTN) is a negative regulator of skeletal muscle growth and development. Animals lacking MSTN show increased bone mineral density (BMD). The aim of this study was to investigate the preventive effect of weight-bearing training on bone loss in ovariectomized rats and whether it was related to MSTN. In this study, the rats were randomly assigned to three group: Sham-ovariectomized (Sham), ovariectomized (OVX), ovariectomized and weight-bearing training (OWT). The rats in the OWT group ran at 20-m/min bearing with 35% of their body weight for 6 days/week. After 10 weeks, compared with the OVX group, weight-bearing training increased the BMD of total femur and trabecular bone by 8.13% and 57.44%, respectively. The OVX-induced destruction of bone microarchitecture including the thickness and number of trabeculae and bone volume fraction was all significantly improved (9.26%, 47.68%, 63.03%) in the OWT group. The OVX-induced degradation of bone mechanical properties was significantly enhanced in the OWT group (maximum load increased by 35.46%, stiffness increased by 89.19%, energy absorption increased by 53.4%; elastic modulus increased by 26.3%). Ten-week weight-bearing training also significantly upregulated the mRNA and protein expression of Wnt1 and β-catenin, which is crucial in bone development. Compared with the Sham group, MSTN in serum and muscle increased in the OVX group, but it decreased in the OWT group compared with the OVX group. Its receptor ActRIIB and downstream molecules Smad2/3 in the OVX group were downregulated in bone by weight-bearing training. The results indicated that MSTN is an important myokine for weight-bearing training to attenuate bone loss in ovariectomized rats.

[Research progress on mechanism of myokines regulating bone tissue cells]

Objective

To review the effects and mechanisms of various myokines secreted by skeletal muscle on various bone tissue cells.

Methods

Literature related to myokines and their regulation of bone tissue cells was reviewed and analyzed comprehensively in recent years.

Results

Bone and skeletal muscle are important members of the motor system, and they are closely related in anatomy, genetics, and physiopathology. In recent years, it has been found that skeletal muscle can secrete a variety of myokines to regulate bone marrow mesenchymal stem cells, osteoblasts, osteoclasts, and bone cells; these factors mutual crosstalk between myoskeletal unit, contact each other and influence each other, forming a complex myoskeletal micro-environment, and to some extent, it has a positive impact on bone repair and reconstruction.

Conclusion

Myokines are potential targets for the dynamic balance of bone tissue cells. In-depth study of its mechanism is helpful to the prevention and treatment of myoskeletal diseases.

Longitudinal effects of low-intensity pulsed ultrasound on osteoporosis and osteoporotic bone defect in ovariectomized rats

Low-intensity pulsed ultrasound (LIPUS) with an intensity (spatial average temporal average, I_SATA) of 30 mW/cm² has been widely proved to be effective on impaired bone healing, but showing little effectiveness in the treatment of osteoporosis. We hypothesized that the intensity of LIPUS may be a key factor in explaining this difference, thus two intensity levels, the widely used 30 mW/cm² and a higher 150 mW/cm², were used to simultaneously treat osteoporosis and osteoporotic bone defect in ovariectomized (OVX) rats with a 1-mm drill hole on their left femurs.Results showed that 150 mW/cm² LIPUS augmented the healing rate of the drill hole than 30 mW/cm² after 3-week LIPUS treatment, although did not further enhance the healing rate after 6-week LIPUS treatment. For ameliorating osteoporosis, 150 mW/cm² LIPUS achieved more advantages over 30 mW/cm² in improving bone density, microstructure and biomechanics 6 weeks after LIPUS intervention. In conclusion, LIPUS with an intensity of 30 mW/cm² was sufficient to facilitate bone defect healing, but a higher intensity can be considered as a rapid trigger for osteoporotic bone repair. In addition, improving the intensity of LIPUS may be a potentially effective consideration for alleviation of osteoporosis, and the LIPUS regimen in the treatment of osteoporosis remains to be optimized.

Deciphering Myostatin's Regulatory, Metabolic, and Developmental Influence in Skeletal Diseases

Current research findings in humans and other mammalian and non-mammalian species support the potent regulatory role of myostatin in the morphology and function of muscle as well as cellular differentiation and metabolism, with real-life implications in agricultural meat production and human disease. Myostatin null mice (mstn^−/−) exhibit skeletal muscle fiber hyperplasia and hypertrophy whereas myostatin deficiency in larger mammals like sheep and pigs engender muscle fiber hyperplasia. Myostatin’s impact extends beyond muscles, with alterations in myostatin present in the pathophysiology of myocardial infarctions, inflammation, insulin resistance, diabetes, aging, cancer cachexia, and musculoskeletal disease. In this review, we explore myostatin’s role in skeletal integrity and bone cell biology either due to direct biochemical signaling or indirect mechanisms of mechanotransduction. In vitro, myostatin inhibits osteoblast differentiation and stimulates osteoclast activity in a dose-dependent manner. Mice deficient in myostatin also have decreased osteoclast numbers, increased cortical thickness, cortical tissue mineral density in the tibia, and increased vertebral bone mineral density. Further, we explore the implications of these biochemical and biomechanical influences of myostatin signaling in the pathophysiology of human disorders that involve musculoskeletal degeneration. The pharmacological inhibition of myostatin directly or via decoy receptors has revealed improvements in muscle and bone properties in mouse models of osteogenesis imperfecta, osteoporosis, osteoarthritis, Duchenne muscular dystrophy, and diabetes. However, recent disappointing clinical trial outcomes of induced myostatin inhibition in diseases with significant neuromuscular wasting and atrophy reiterate complexity and further need for exploration of the translational application of myostatin inhibition in humans.

MSTN is a key mediator for low-intensity pulsed ultrasound preventing bone loss in hindlimb-suspended rats

Low-intensity pulsed ultrasound (LIPUS) has been used to accelerate bone fracture healing. However, the issue whether LIPUS is effective in preventing osteoporosis has not been clarified, and if so, what possible mechanisms might be responsible. Myostatin (MSTN) is a negative regulator of muscle growth, and its absence will trigger a positive response to bone. In this study, we examined the effects of LIPUS on bone micro-structure, mechanical properties and damage healing of hindlimb-suspended rats, and investigated whether the inhibition of MSTN plays a role in this process. The rats were randomly divided into four groups: Normal control group (NC), Hind limb suspension group (HLS), Hind limb suspension and 80 mW/cm² LIPUS irradiation group (HLS+ 80 mW/cm²), Hind limb suspension and 30 mW/cm² LIPUS irradiation group (HLS+ 30 mW/cm²). The HLS+ 80 mW/cm² rats were treated with LIPUS (1 MHz, 80 mW/cm²) and the HLS+ 30 mW/cm² rats were treated with LIPUS (1 MHz, 30 mW/cm²) on the femur for 20 min/day for 28 days. MC3T3-E1 cells were respectively cultured with the serum of wild type mouse and MSTN knockout mouse at 1% concentration for 7 days. After 28 days, LIPUS effectively prevented the destruction of bone microstructure and the decline of mechanical properties, and promoted bone defect healing in the tail-suspended rats. In addition, LIPUS effectively reduced the MSTN content in the quadriceps and serum of the tail-suspended rats, inhibited its receptor and downstream signaling molecules and activated the Wnt signaling pathway in femurs. Growth of MC-3T3-E1 cell cultured with the serum of MSTN knockout mice was superior to that with wild mice serum on day 7. These results indicate that MSTN is a key mediator in LIPUS preventing bone loss caused by hindlimb-suspension.

Dual Role of Caveolin-1 in β-Catenin Signaling During Fracture Healing Induced by Low-Intensity Pulsed Ultrasound in Rabbits

We did this research to observe the effect of LIPUS on long bone fracture repair and caveolin-1, β-catenin signaling expression in the radius defects of rabbits, to explore its possible molecular mechanisms. 24 male New Zealand rabbits with bilateral radial bone defects were divided into 4 groups randomly, n = 6. The right side had daily LIPUS exposure for 20 minutes, while the left received sham treatment. After 7, 14, 21, 28 days, respectively, fracture healing was observed by X-ray imaging and Dual Energy X-ray Absorptiometry (DXA) scan, specimens were harvested for histology, immunohistochemistry, and gene expression analysis. We found that LIPUS brought forward endochondral ossification, increased the bone callus size without changes in Bone Mineral Density (BMD). The caveolin-1 expression increased first then decreased, while the β-catenin kept growing during the process. These demonstrated that caveolin-1 participated in fracture healing accelerated by LIPUS, which was speculated to play a dual role in β-catenin signaling expression.

Precise editing of myostatin signal peptide by CRISPR/Cas9 increases the muscle mass of Liang Guang Small Spotted pigs

Myostatin (MSTN), a member of the transforming growth factor-β superfamily, is a negative regulator of muscle growth and development. Disruption of the MSTN gene in various mammalian species markedly promotes muscle growth. Previous studies have mainly focused on the disruption of the MSTN peptide coding region in pigs but not on the modification of the signal peptide region. In this study, the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) system was used to successfully introduce two mutations (PVD20H and GP19del) in the MSTN signal peptide region of the indigenous Chinese pig breed, Liang Guang Small Spotted pig. Both mutations in signal peptide increased the muscle mass without inhibiting the production of mature MSTN peptide in the cells. Histological analysis revealed that the enhanced muscle mass in MSTN^+/PVD20H pig was mainly due to an increase in the number of muscle fibers. The expression of MSTN in the longissimus dorsi muscle of MSTN^+/PVD20H and MSTN^KO/PVD20H pigs was significantly downregulated, whereas that of myogenic regulatory factors, including MyoD, Myogenin, and Myf-5, was significantly upregulated when compared to those in the longissimus dorsi muscle of wild-type pigs. Meanwhile, the mutations also activated the PI3K/Akt pathway. The results of this study indicated that precise editing of the MSTN signal peptide can enhance porcine muscle development without markedly affecting the expression of mature MSTN peptide, which could exert other beneficial biological functions in the edited pigs.