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

[Advances of low-intensity pulsed ultrasound for treatment of musculoskeletal disorders in the past decade]

Musculoskeletal disorders (MSDs) are characterized by extensive pathological involvement and high prevalence and cause a significant disease burden. Long-term drug administration often causes by adverse effects with poor therapeutic efficacy. Low-intensity pulsed ultrasound (LIPUS), as a specialized therapeutic modality, delivers acoustic energy at a low intensity in a pulsed wave mode, thus ensuring stable energy transmission to the target tissues while minimizing thermal effects. This non-invasive approach has demonstrated significant potential for MSD treatment by delivering effective physical stimulations. Extensive animal and clinical studies have demonstrated the efficacy of LIPUS for accelerating the healing process of fresh fractures and nonunions, promoting soft tissue regeneration and suppressing inflammatory responses. Emerging evidence suggests promising applications of LIPUS in skeletal muscle injury treatment and promoting tissue regeneration and repair. This review outlines the recent advancements and mechanistic studies of LIPUS for treatment of common MSDs including fractures, nonunions, muscle injuries, and osteoarthritis, addressing also the technical parameters of commercially available LIPUS devices, current therapeutic approaches, the existing challenges, and future research directions.

Traditional pediatric massage enhanced the skeletal muscle mass in OVA-exposed adolescent rats via regulating SCFAs-FFAR2-IGF-1/AKT pathway

Objective

This study aimed to investigate the potential relation between the retarded growth of skeletal muscle (SM) and dysbiosis of gut microbiota (GM) in children with asthma, and to explore the potential action mechanisms of traditional pediatric massage (TPM) from the perspective of regulating GM and short-chain fatty acids (SCFAs) production by using an adolescent rat model of asthma.

Methods

Male Sprague-Dawley rats aged 3weeks were divided randomly into the 5 groups (n=6~7) of control, ovalbumin (OVA), OVA + TPM, OVA + methylprednisolone sodium succinate (MP) and OVA + SCFAs. Pulmonary function (PF) was detected by whole body plethysmograph, including enhanced pause and minute ventilation. Airway allergic inflammation (AAI) status was assessed by concentrations of OVA-specific immunoglobulin E in plasma, interleukin (IL)-4 and IL-1β in bronchoalveolar lavage fluid via ELISA assay. SM mass was assessed by using cross-sectional areas of diaphragm muscle and gastrocnemius via hematoxylin and eosin staining. GM and SCFAs production were detected by 16S rDNA sequencing and GC-MS, respectively. The protein and gene expressions of free fatty acid receptor 2 in SM were detected by using immunohistochemical staining and qRT-PCR, respectively. qRT-PCR was used to detect other relative gene expressions that were closely related with SM mass. The activity of insulin-like growth factor-1 (IGF-1)/protein kinase B (PKB/AKT) pathway in SM was detected by western blotting test.

Results

OVA exposure caused obvious AAI and poor PF in adolescent rats. OVA-exposed adolescent rats had a retarded growth of SM mass and inhibited activity of IGF-1/AKT pathway, which was related with GM dysbiosis, reduced SCFAs production and FFAR2 expressions in SM. TPM efficiently enhanced the SM mass, along with alleviating AAI and improving PF. TPM activated IGF-1/AKT pathway in SM, which was closely related with correcting GM dysbiosis, enhanced SCFAs production and FFAR2 expressions.

Conclusion

The retarded growth of SM mass and inhibition of IGF-1/AKT pathway existed in OVA-exposed adolescent rats, which was related with GM dysbiosis, reduced SCFAs production and FFAR2 expressions in SM. TPM efficiently enhanced the SM mass, at least, partially via regulating GM, enhancing SCFAs production and activating FFAR2-IGF-1/AKT pathway.

Effect of traction therapy on muscle satellite cell proliferation and differentiation in a rat model of knee stiffness

BACKGROUND

In the rat knee stiffness model, the duration of traction treatment is mostly 20-40 min; however, relatively few studies have been conducted on longer traction treatment of extended knee stiffness in rats. Therefore, the aim of this study was to explore the efficacy of prolonged traction and its mechanism of action in extended knee stiffness in rats.

METHODS

The model of extended knee joint stiffness was established in rats and treated with powered flexion position traction. On the 10th and 20th days respectively, passive range of motion (PROM) assessments and musculoskeletal ultrasound were conducted. Rectus femoris muscle tissues were taken for Western blotting (WB) to detect the expression of muscle satellite cells proliferation and differentiation signaling factors. Histopathological staining was used to evaluate the degree of muscle atrophy and muscle fibrosis in the rectus femoris muscle, and immunofluorescence double staining was used to detect proliferation of muscle satellite cells number. The results from these analyses were used to assess the therapeutic outcomes of the traction treatment.

RESULTS

The findings indicated that chronic persistent traction significantly improved joint mobility, notably enhanced the proliferation of muscle satellite cells, and inhibited their differentiation. Furthermore, the treatment facilitated the repair and regeneration of damaged tissues, reduced muscular atrophy and fibrosis in the rectus femoris muscle, and alleviated knee stiffness.

CONCLUSION

Chronic persistent traction can effectively relieve knee joint stiffness, and its mechanism is related to the activation and proliferation of the rectus femoris muscle satellite cells, thereby promoting the repair and regeneration of damaged skeletal muscle.

Mechanistic study of the effect of flexible fixation and load-bearing stress environment on fracture healing and shaping

BACKGROUND

The biomechanical environment created by suture-button fixation Latarjet is conducive to the healing and shaping of the transplanted coracoid, but its mechanism remains unclear. The latest research has found that the absence of stem cell chemokine (CXCL12) impeded bone regeneration in Sonic Hedgehog (SHH)-deficient animals. However, whether the biomechanical environment affects SHH and CXCL12 function has not been studied.

METHODS

Rat fracture models were constructed to simulate stress environments under non-load-bearing and load-bearing conditions. The fracture healing and shaping, as well as the expression levels of SHH and CXCL12, were assessed through gross viewing, micro-computed tomography (micro-CT), and histochemical staining.

RESULTS

Under flexible fixation, the relative bone volume (BV/TV) of rats exposed to the load-bearing stress environment was significantly higher than that of rats under a non-load-bearing stress environment (p ≤ 0.05). Adverse bone shaping was not observed in rats subjected to flexible fixation. The levels of SHH and CXCL12 in load-bearing rats exhibited significant elevation (p ≤ 0.05). Under a load-bearing stress environment, no significant difference was observed in the BV/TV between the flexible fixation group and the rigid fixation group (p ≥ 0.05), but there was excessive hyperplasia of the fracture callus in the rigid fixation group. The levels of SHH and CXCL12 in rats subjected to rigid fixation were significantly elevated (p ≤ 0.05).

CONCLUSIONS

Flexible fixation and load-bearing stress environment may contribute to bone healing and shaping by influencing the levels of SHH and CXCL12, suggested that this mechanism may be relevant to the healing and shaping of the transplanted coracoid after suture-button fixation Latarjet.

Low-intensity pulsed ultrasound (LIPUS) promotes skeletal muscle regeneration by regulating PGC-1α/AMPK/GLUT4 pathways in satellite cells/myoblasts

Low-Intensity Pulsed Ultrasound (LIPUS) holds therapeutic potential in promoting skeletal muscle regeneration, a biological process mediated by satellite cells and myoblasts. Despite their central roles in regeneration, the detailed mechanistic of LIPUS influence on satellite cells and myoblasts are not fully underexplored. In the current investigation, we administrated LIPUS treatment to injured skeletal muscles and C2C12 myoblasts over five consecutive days. Muscle samples were collected on days 6 and 30 post-injury for an in-depth histological and molecular assessment, both in vivo and in vitro with immunofluorescence analysis. During the acute injury phase, LIPUS treatment significantly augmented the satellite cell population, concurrently enhancing the number and size of newly formed myofibers whilst reducing fibrosis levels. At 30 days post-injury, the LIPUS-treated group demonstrated a more robust satellite cell pool and a higher myofiber count, suggesting that early LIPUS intervention facilitates satellite cell proliferation and differentiation, thereby promoting long-term recovery. Additionally, LIPUS markedly accelerated C2C12 myoblast differentiation, with observed increases in AMPK phosphorylation in myoblasts, leading to elevated expression of Glut4 and PGC-1α, and subsequent glucose uptake and mitochondrial biogenesis. These findings imply that LIPUS-induced modulation of myoblasts may culminate in enhanced cellular energy availability, laying a theoretical groundwork for employing LIPUS in ameliorating skeletal muscle regeneration post-injury. NEW & NOTEWORTHY: Utilizing the cardiotoxin (CTX) muscle injury model, we investigated the influence of LIPUS on satellite cell homeostasis and skeletal muscle regeneration. Our findings indicate that LIPUS promotes satellite cell proliferation and differentiation, thereby facilitating skeletal muscle repair. Additionally, in vitro investigations lend credence to the hypothesis that the regulatory effect of LIPUS on satellite cells may be attributed to its capability to enhance cellular energy metabolism.

Effect of low-intensity focused ultrasound therapy on postpartum uterine involution in puerperal women: A randomized controlled trial

BACKGROUND

Short-term poor uterine involution manifests as uterine contraction weakness. This is one of the important causes of postpartum hemorrhage, posing a serious threat to the mother's life and safety. The study aims to investigate whether low-intensity focused ultrasound (LIFUS) can effectively shorten lochia duration, alleviate postpartum complications, and accelerate uterine involution compared with the sham treatment.

METHODS

A multicenter, concealed, randomized, blinded, and sham-controlled clinical trial was conducted across three medical centers involving 176 subjects, utilizing a parallel group design. Enrollment occurred between October 2019 and September 2020, with a 42-day follow-up period. Participants meeting the inclusion and exclusion criteria based on normal prenatal examinations were randomly divided into the LIFUS group or the sham operation group via computer-generated randomization. Patients in the LIFUS group received usual care with the LIFUS protocol, wherein a LIFUS signal was transmitted to the uterine site through coupling gel, or sham treatment, where no low-intensity ultrasound signal output was emitted. The primary outcome, lochia duration, was assessed via weekly telephonic follow-ups post-discharge. The involution of the uterus, measured by uterine fundus height, served as the secondary outcome.

RESULTS

Among the 256 subjects screened for eligibility, 176 subjects were enrolled and randomly assigned to either the LIFUS group (n = 88) or the Sham group (n = 88). Data on the height of the uterine fundus were obtained from all the patients, with 696 out of 704 measurements (99%) successfully recorded. Overall, a statistically significant difference was noted in time to lochia termination (hazard ratio: 2.65; 95% confidence interval [CI]: 1.82-3.85; P < 0.001). The decline in fundal height exhibited notable discrepancies between the two groups following the second treatment session (mean difference: -1.74; 95% CI: -1.23 to -2.25; P < 0.001) and the third treatment session (mean difference: -3.26; 95% CI: -2.74 to -3.78; P < 0.001) after delivery. None of the subjects had any adverse reactions, such as skin damage or allergies during the treatment.

CONCLUSIONS

This study found that LIFUS treatment can promote uterine involution and abbreviate the duration of postpartum lochia. Ultrasound emerges as a safe and effective intervention, poised to address further clinical inquiries in the domain of postpartum rehabilitation.

Integrated Omics Approach: Revealing the Mechanism of Auxenochlorella pyrenoidosa Protein Extract Replacing Fetal Bovine Serum for Fish Muscle Cell Culture

The process of producing cell-cultured meat involves utilizing a significant amount of culture medium, including fetal bovine serum (FBS), which represents a considerable portion of production expense while also raising environmental and safety concerns. This study demonstrated that supplementation with Auxenochlorella pyrenoidosa protein extract (APE) under low-serum conditions substantially increased Carassius auratus muscle (CAM) cell proliferation and heightened the expression of Myf5 compared to the absence of APE. An integrated intracellular metabolomics and proteomics analysis revealed a total of 13 and 67 differentially expressed metabolites and proteins, respectively, after supplementation with APE in the medium containing 5%FBS, modulating specific metabolism and signaling pathways, which explained the application of APE for passage cell culture under low-serum conditions. Further analysis revealed that the bioactive factors in the APE were protein components. Moreover, CAM cells cultured in reconstructed serum-free media containing APE, l-ascorbic acid, insulin, transferrin, selenium, and ethanolamine exhibited significantly accelerated growth in a scale-up culture. These findings suggest a promising alternative to FBS for fish muscle cell culture that can help reduce production costs and environmental impact in the production of cultured meat.

Integrated metabolomics and proteomics analysis to understand muscle atrophy resistance in hibernating Spermophilus dauricus

Hibernating Spermophilus dauricus experiences minor muscle atrophy, which is an attractive anti-disuse muscle atrophy model. Integrated metabolomics and proteomics analysis was performed on the hibernating S. dauricus during the pre-hibernation (PRE) stage, torpor (TOR) stage, interbout arousal (IBA) stage, and post-hibernation (POST) stage. Time course stage transition-based (TOR vs. PRE, IBA vs. TOR, POST vs. IBA) differential expression analysis was performed based on the R limma package. A total of 14 co-differential metabolites were detected. Among these, l-cystathionine, l-proline, ketoleucine, serine, and 1-Hydroxy-3,6,7-Trimethoxy-2, 8-Diprenylxanthone demonstrated the highest levels in the TOR stage; Beta-Nicotinamide adenine dinucleotide, Dihydrozeatin, Pannaric acid, and Propionylcarnitine demonstrated the highest levels in the IBA stage; Adrenosterone, PS (18:0/14,15-EpETE), S-Carboxymethylcysteine, TxB2, and 3-Phenoxybenzylalcohol demonstrated the highest levels in the POST stage. Kyoto Encyclopedia of Genes and Genomes pathways annotation analysis indicated that biosynthesis of amino acids, ATP-binding cassette transporters, and cysteine and methionine metabolism were co-differential metabolism pathways during the different stages of hibernation. The stage-specific metabolism processes and integrated enzyme-centered metabolism networks in the different stages were also deciphered. Overall, our findings suggest that (1) the periodic change of proline, ketoleucine, and serine contributes to the hindlimb lean tissue preservation; and (2) key metabolites related to the biosynthesis of amino acids, ATP-binding cassette transporters, and cysteine and methionine metabolism may be associated with muscle atrophy resistance. In conclusion, our co-differential metabolites, co-differential metabolism pathways, stage-specific metabolism pathways, and integrated enzyme-centered metabolism networks are informative for biologists to generate hypotheses for functional analyses to perturb disuse-induced muscle atrophy.

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.

Low-intensity pulsed ultrasound and parathyroid hormone improve muscle atrophy in estrogen deficiency mice

Due to aging and long-term estrogen deficiency, postmenopausal women suffer muscle atrophy (MA), which is characterized by decreased muscle mass and muscle quality. Low-intensity pulsed ultrasound (LIPUS) is an acoustic wave inducing biological effects mainly by the mechanical stimulation and used as a non-invasive physical therapy for muscle repair. Parathyroid hormone (PTH) is an 84-amino-acid polypeptide, and its bioactive fragment [PTH (1-34)] has potential application in the treatment of MA. We speculate that the combination of physical therapy (i.e., the LIPUS) and regulatory hormone (i.e., the PTH) would be more effective in the treatment of MA. The objective of this study was to evaluate the individual and combined effects of LIPUS and PTH therapy on MA in estrogen deficiency mice. Seventy 8-week-old female C57BL/6J mice were used in this study and the MA model was induced by an intraperitoneal injection of 4-vinylcyclohexene diepoxide (VCD) for 20 consecutive days. The VCD-induced MA mice were randomly divided into MA, LIPUS, PTH and LIPUS + PTH (Combined) groups (n = 10/group). In the LIPUS group, the mice were treated by LIPUS in bilateral quadriceps muscles for 20 min, five times a week for 6 weeks. In the PTH group, the mice received subcutaneous injection of PTH (1-34) (80 ug/kg/d) five times a week, for 6 weeks. In the Combined group, the PTH was administrated 30 min before each LIPUS session. Hematoxylin-eosin (H&E) staining, serum biochemical analysis and quantitative real-time polymerase chain reaction (qRT-PCR) were applied to evaluate the therapeutic effects of related treatments. The results showed that the MA mice had a disordered estrus cycle, significantly decreased muscle mass and myofibers cross-sectional area (CSA). After treatments, LIPUS, PTH and Combined groups had a significantly increased CSA, compared with the MA mice without treatment. In addition, Combined group had a significantly increased mRNA expression of Pax7, MyoD and MyoG, compared with LIPUS and PTH monotherapy groups. Our findings indicated that the combination of LIPUS and PTH treatment improves muscle regeneration ability, which might have potential for treating MA in postmenopausal women.

The therapeutic effects of low-intensity pulsed ultrasound in musculoskeletal soft tissue injuries: Focusing on the molecular mechanism

Musculoskeletal soft tissue injuries are very common and usually occur during both sporting and everyday activities. The intervention of adjuvant therapies to promote tissue regeneration is of great importance to improving people's quality of life and extending their productive lives. Though many studies have focused on the positive results and effectiveness of the LIPUS on soft tissue, the molecular mechanisms standing behind LIPUS effects are much less explored and reported, especially the intracellular signaling pathways. We incorporated all research on LIPUS in soft tissue diseases since 2005 and summarized studies that uncovered the intracellular molecular mechanism. This review will also provide the latest evidence-based research progress in this field and suggest research directions for future experiments.

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.