Tibialis Anterior Research Articles

A Portable Passive Ankle-Foot Orthosis for Walking Propulsion and Drop-Foot Prevention

Abstract Individuals with a drop-foot generally have issues of foot-slap and toe-drag, and ankle-foot orthoses (AFOs) have been developed for them to address the drop-foot gait. However, the currently available active AFOs usually have heavier mass, larger volume, and additional power sources, and almost all of the passive AFOs can achieve dorsiflexion assistance at the cost of making plantarflexion more difficult, which increases the wearer's metabolic cost of walking. This paper illustrates the development and validation of a passive AFO for walking propulsion and drop-foot prevention of individuals with a drop-foot gait. The AFO is primarily composed of a propulsion module, a drop-foot prevention module, and a support module. The propulsion module can detect the wearer's gait stages, and it can control the energy storage and release of an energy storage spring-A by switching the state of a clutch-A mechanism. The drop-foot prevention module is designed to correct the abnormal gait of individuals with a drop-foot gait during the swing phase. Experiments are conducted to evaluate the performance of the developed AFO. The experimental results demonstrate that during a gait cycle, reductions of 7.74%, 6.72%, and 16.36% of the average muscle activities of the gastrocnemius, soleus, and tibialis anterior are observed, respectively. The significance of this study is the development of a portable passive AFO that has the potential to provide plantarflexion assistance and dorsiflexion assistance for the wearers during the late stance phase and swing phase, respectively.

Direct extrusion of multifascicle prevascularized human skeletal muscle for volumetric muscle loss surgery

Skeletal muscle is composed of multiple fascicles, which are parallel bundles of muscle fibers surrounded by connective tissues that contain blood vessels and nerves. Here, we fabricated multifascicle human skeletal muscle scaffolds that mimic the natural structure of human skeletal muscle bundles using a seven-barrel nozzle. For the core material to form the fascicle structure, human skeletal myoblasts were encapsulated in Matrigel with calcium chloride. Meanwhile, the shell that plays a role as the connective tissue, human fibroblasts and human umbilical vein endothelial cells within a mixture of porcine muscle decellularized extracellular matrix and sodium alginate at a 95:5 ratio was used. We assessed four types of extruded scaffolds monolithic-monoculture (Mo-M), monolithic-coculture (Mo–C), multifascicle-monoculture (Mu-M), and multifascicle-coculture (Mu-C) to determine the structural effect of muscle mimicking scaffold. The Mu-C scaffold outperformed other scaffolds in cell proliferation, differentiation, vascularization, mechanical properties, and functionality. In an in vivo mouse model of volumetric muscle loss, the Mu-C scaffold effectively regenerated the tibialis anterior muscle defect, demonstrating its potential for volumetric muscle transplantation. Our nozzle will be further used to produce other volumetric functional tissues, such as tendons and peripheral nerves.

Adipogenic-Myogenic Signaling in Engineered Human Muscle Grafts used to Treat Volumetric Muscle Loss.

Tissue-engineered muscle grafts (TEMGs) are a promising treatment for volumetric muscle loss (VML). In this study, human myogenic progenitors (hMPs) cultured on electrospun fibrin microfiber bundles and evaluated the therapeutic potential of engineered hMP TEMGs in the treatment of murine tibialis anterior (TA) VML injuries is employed. In vitro, the hMP TEMGs express mature muscle markers by 21 days. Upon implantation into VML injuries, the hMP TEMGs enable remarkable regeneration. To further promote wound healing and myogenesis, human adipose-derived stem/stromal cells (hASCs) as fibroadipogenic progenitor (FAP)-like cells with the potential to secrete pro-regenerative cytokines are incorporated. The impact of dose and timing of seeding the hASCs on in vitro myogenesis and VML recovery using hMP-hASC TEMGs are investigated. The hASCs increase myogenesis of hMPs when co-cultured at 5% hASCs: 95% hMPs and with delayed seeding. Upon implantation into immunocompromised mice, hMP-hASC TEMGs increase cell survival, collagen IV deposition, and pro-regenerative macrophage recruitment, but result in excessive adipose tissue growth after 28 days. These data demonstrate the interactions of hASCs and hMPs enhance myogenesis in vitro but there remains a need to optimize treatments to minimize adipogenesis and promote full therapeutic recovery following VML treatment.

Biosponge-Encased Placental Stem Cells for Volumetric Muscle Loss Repair.

Objective: Volumetric muscle loss (VML) leads to permanent muscle mass and functional impairments. While mesenchymal stromal cells (MSCs) and their secreted factors can aid muscle regeneration, MSCs exhibit limited persistence in injured tissue post-transplantation. Human placental-derived stem cells (hPDSCs), sharing surface markers with MSCs, demonstrate superior regenerative potential due to their fetal origin. Previously, a biosponge (BS) scaffold was shown to augment muscle regeneration post-VML. This study aims to coapply BS therapy and hPDSCs to further enhance muscle recovery following VML. Approach: A VML defect was created by removing ∼20% of the tibialis anterior muscle mass in male Lewis rats. Injured muscles were either left untreated or treated with BS or BS-encapsulated hPDSCs cultured under normoxic or hypoxic conditions. On day 28 postinjury, peak isometric torque was measured, and the muscle was harvested for analysis. Results: BS encapsulated hPDSCs subjected to hypoxic preconditioning persisted in larger quantities and enhanced muscle mass at day 28 postinjury. BS encapsulated hPDSCs cultured under normoxic or hypoxic conditions increased small myofibers (<500 µm2) percentage, MyoD protein expression, and both pro- and anti-inflammatory macrophage marker expression. BS encapsulated hPDSCs also reduced fibrosis and BS remodeling rate. Innovation: This study is the first to examine the therapeutic effects of hPDSCs in a rat VML model. A BS carrier and hypoxic preconditioning were investigated to mitigate low cell survival postimplantation. Conclusion: hPDSCs augment the regenerative effect of BS. Combining hPDSCs and BS emerges as a promising strategy worthy of further investigation.

Abstract B006: The role of tumor specific IGFBP-3 in the onset and progression of skeletal muscle wasting in a murine model of pancreatic cancer

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer- related death and is highly associated with skeletal muscle wasting (SMW) that leads to treatment intolerance and reduced survival. Research substantiates the role of increased levels of Insulin-like Growth Factor Binding Protein-3 (IGFBP-3) in PDAC-related SMW. Canonically, supraphysiological levels of IGFBP-3 block insulin-like growth factor-1 (IGF-1) binding, thus downregulating the activation of its downstream targets Akt and mTOR. Non-canonical signaling via TGF-βRI results in aberrant FoxO1 signaling, which upregulates the ubiquitin proteasome pathway (UPP) and induces autophagy. Dysregulated UPP and autophagy activation have been shown to promote muscle degradation. Recent findings from our lab implicate canonical and non-canonical signaling of tumor associated IGFBP-3 in increased protein catabolism and decreased anabolism, resulting in SMW in a syngeneic murine model of PDAC. We tested the hypothesis that genetic ablation of IGFBP-3 in PDAC tumor cells attenuates SMW via regulation of Akt and FoxO1, leading to decreases in UPP and autophagy in skeletal muscle.Methods: C57BL/6J female mice (6-8 weeks) were randomized to one of three groups: 1) no tumor control (NTC) (n=10), 2) KCKO-Luc parental cells (PDAC) (n=14), or 3) IGFBP-3-/- KCKO-Luc (n=14). Tumor cells were injected orthotopically. Tumor and lean mass were assessed longitudinally via dual energy x-ray absorptiometry (DEXA). At sacrifice, quadriceps muscles were collected for protein and transcriptional analysis, Tibialis Anterior (TA) muscles for histology and serum for ELISA. TA frozen sections were stained with Oil Red O (ORO) to highlight intramuscular adipogenesis.Results: PDAC mice experience significantly reduced survival (T1/2=56 days) compared to IGFBP-3-/- mice that maintained 100% survival at day 100 (p&amp;lt;0.0001). IGFBP-3-/- mice lost significantly less lean mass from baseline to day 56 compared to PDAC mice (p&amp;lt;0.0001). PDAC mice exhibited 3-fold elevated serum levels of IGFBP-3 compared to NTC and IGFBP-3-/- mice (p&amp;lt;0.01). Transcriptionally, PDAC mice displayed increased expression of igfbp3, tgfbr1, and UPP associated genes fbxo32, and trim63 compared to NTC and IGFBP-3-/- mice. Further, the ratio of pAkt (Ser473), pS6 (Ser235/236), and pFoxO1 (Ser253) to total protein levels were significantly reduced in PDAC mice (p&amp;lt;0.05 vs NTC and IGFBP-3-/-). Additionally, protein levels of ULK1 and the ratio of LC3bII over LC3bI, markers of autophagy, are elevated in PDAC mice compared to NTC and IGFBP-3-/- mice (p&amp;lt;0.05). Lastly, there is a significant increase in ORO positive staining in PDAC mice compared to NTC and IGFBP-3-/- mice (p&amp;lt;0.0001).Conclusion: These findings suggest that PDAC-related SMW is driven by tumor derived IGFBP-3, which acts as an endocrine factor on skeletal muscle cells to inhibit protein synthesis and activate FoxO1 signaling to upregulate the UPP and autophagy. Lastly, we identify skeletal muscle adipogenesis as a biomarker for autophagy upregulation and SMW. Citation Format: Zachary R Sechrist, Calvin L Cole. The role of tumor specific IGFBP-3 in the onset and progression of skeletal muscle wasting in a murine model of pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B006.

Analysis of potential TAK1/Map3k7 phosphorylation targets in hypertrophy and cachexia models of skeletal muscle.

TGFβ-activated kinase-1 (TAK1) is phosphorylated during both muscle growth and muscle wasting. To understand how this can lead to such opposite effects, we first performed multiplex kinase array of mouse embryonic stem cells with and without stimulation of TAK1 to determine its potential downstream targets. The phosphorylation of these targets was then compared in three different models: hypertrophic longissimus muscle of Texel sheep, tibialis anterior muscle of mice with cancer-induced cachexia and C2C12-derived myofibers, with and without blockade of TAK1 phosphorylation. In both Texel sheep and in cancer-induced cachexia, phosphorylation of both TAK1 and p38 was increased. Whereas p90RSK was increased in Texel sheep but not cachexia and the phosphorylation of HSP27 and total Jnk were increased in cachexia but not Texel. To understand this further, we examined the expression of these proteins in C2C12 cells as they differentiated into myotubes, with and without blockade of TAK1 phosphorylation. In C2C12 cells, decreased phosphorylation of TAK1 leads to reduced phosphorylation of p38, JNK, and HSP27 after 16 h and muscle fiber hypertrophy after 3 days. However, continuous blockade of this pathway leads to muscle fiber failure, suggesting that the timing of TAK1 activation controls the expression of context-dependent targets.

Age-related histone H3.3 accumulation associates with a repressive chromatin in mouse tibialis anterior muscle

The present study aimed to investigate age-related changes in histone variant H3.3 and its role in the aging process of mouse tibialis anterior muscle. H3.3 level significantly increased with age and correlated with H3K27me3 level. Acute exercise successfully upregulated the target gene expression in 8-wk-old mice, whereas no upregulation was noted in 53-wk-old mice. H3K27me3 level was increased at these loci in response to acute exercise in 8-wk-old mice. However, in 53-wk-old mice, H3.3 and H3K27me3 levels were increased at rest and were not affected by acute exercise. Furthermore, forced H3.3 expression in the skeletal muscle of 8-wk-old mice led to a gradual improvement in motor function. The results suggest that age-related H3.3 accumulation induces the formation of repressive chromatin in the mouse tibialis anterior muscle. However, H3.3 accumulation also appears to play a positive role in enhancing skeletal muscle function.

Melatonin protects against sarcopenia in middle-aged mice.

Sarcopenia is a common age-related disease. Melatonin (MEL) is an age-related endocrine hormone, which displays a crucial role in resisting oxidative stress during aging. Importantly, the antioxidant properties of MEL can be mediated by mitochondria. Therefore, we wondered whether MEL could mitigate oxidative stress caused by mitochondria in sarcopenia. The middle-aged mice were administered 5 mg/kg/d and 10 mg/kg/d of MEL for 2 months. Young mice were used as the control group. After treatment with MEL, the grip strength of the fore/hind limbs, running time, and distance were elevated, and the weights of the gastrocnemius (GA), tibialis anterior (TA), extensor digitorum longus (EDL), and soleus (SOL) were enhanced in middle-aged mice. Additionally, MEL was observed to alleviate histological damage and increase the cross-sectional area of muscle fibers in GA tissues of middle-aged mice. Furthermore, following MEL treatment, there was an increase in the percentage and size of normal mitochondria as well as mtDNA copy number but a reduction in the levels of malondialdehyde (MDA), protein carbonyl, and reactive oxygen species (ROS) in the GA tissues of middle-aged mice. At the molecular level, MEL repressed the levels of ATROGIN-1, muscle RING-finger protein-1 (MURF-1), and the ratio of p-P38/P38, but elevated the expression of cytochrome c oxidase subunit 4 (COX4), cystatin C (CYTC), nuclear respiratory factor 1 (NRF-1), mitochondrial transcription factor A (TFAM), and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) in the GA tissues of middle-aged mice. Importantly, 10 mg/kg MEL was more efficacious in the treatment of sarcopenia than 5 mg/kg MEL. MEL attenuates sarcopenia in middle-aged mice, and the mechanism may relate to mitochondria-induced oxidative stress and the PGC-1α/TFAM pathway.

Comparing the efficacy of exercise therapy on adult flexible flatfoot individuals through a network meta-analysis of randomized controlled trials

The aim of this study is to compare the efficacy of different exercise interventions for adult flexible flatfoot. Nine databases (PubMed, EMBASE, Web of Science, the Cochrane Central Register of Controlled Trials (CENTRAL), SCOPUS, PRDro, Google Scholar, China National Knowledge Infrastructure(CNKI) and Wanfang data) were systematically searched from their inception until February 2024. The search resulted in 2112 records, with 11 studies included. All networks revealed low heterogeneity and non-significant inconsistency (I2 ≤ 25.0%). Three network plots were formed for navicular drop. Firstly, compared with the control group, strengthening the posterior tibial muscle + stretching the iliopsoas muscle + TCE (MD: 3.32, 95% CI: 1.78, 4.89), PNF (MD: 1.81, 95%CI: -0.05, 3.70), SFE (MD: 1.23, 95%CI: 1.02, 1.44) all showed better effects. And strengthening the posterior tibial muscle + stretching the iliopsoas muscle + TCE exercise is considered to be the most effective intervention, with SUCRA of 0.97. Secondly, compared with the control group, hip-focused neuromuscular exercise (MD: 6.22, 95% CI: -1.69, 14.12), SFE with EMG biofeedback (MD: -0.81, 95%CI: -1.59, 3.21) all showed better effects. And hip-focused neuromuscular exercise is considered to be the most effective intervention, with SUCRA of 0.92. Thirdly, the internal foot muscle training combined with gluteus muscle strengthening is significantly better than the other two groups, with SUCRA of 0.99. For the foot posture index, comprehensive reinforcement (MD: 1.95, 95% CI − 0.19, 4.03) showed better effects compared with the control group. In the probability ranking table, comprehensive reinforcement is significantly better than the other two groups, with SUCRA of 0.98. For the foot function index, orthoses wear + stretching + eccentric progressive resistive exercise of tibialis posterior is significantly better than the other two groups, with SUCRA of 0.92. In conclusion, various exercise therapies improve the arch shape and function of patients with flexible flatfoot, particularly hip muscle and lower limb overall muscle training.

Analysis of Wavelet Coherence in Calf Agonist-Antagonist Muscles during Dynamic Fatigue.

Dynamic muscle fatigue during repetitive movements can lead to changes in communication between the central nervous system and peripheral muscles. This study investigated these changes by examining electromyogram (EMG) characteristics from agonist and antagonist muscles during a fatiguing task. Twenty-two healthy male university students (age: 22.92 ± 2.19 years) performed heel raises until fatigue. EMG signals from lateral gastrocnemius (GL) and tibialis anterior (TA) muscles were processed using synchrosqueezed wavelet transform (SST). Root mean square (RMS), mean frequency (MF), power across frequency ranges, wavelet coherence, and co-activation ratio were computed. During the initial 80% of the task, RMS and EMG power increased for both muscles, while MF declined. In the final 20%, GL parameters stabilized, but TA showed significant decreases. Beta and gamma intermuscular coherence increased upon reaching 60% of the task. Alpha coherence and co-activation ratio remained constant. Results suggest that the central nervous system adopts a differentiated control strategy for agonist and antagonist muscles during fatigue progression. Initially, a coordinated "common drive" mechanism enhances both muscle groups' activity. Later, despite continued increases in muscle activity, neural-muscular coupling remains stable. This asynchronous, differentiated control mechanism enhances our understanding of neuromuscular adaptations during fatigue, potentially contributing to the development of more targeted fatigue assessment and management strategies.

Muscle Atrophy and mRNA-miRNA Network Analysis of Vascular Endothelial Growth Factor (VEGF) in a Mouse Model of Denervation-Induced Disuse.

Skeletal muscle atrophy is frequently caused by the disuse of muscles.It impacts quality of life, especially in aging populations and those with chronic diseases. Understanding the molecular mechanisms underlying muscle atrophy is crucial for developing effective therapies. To investigate the roles of vascular endothelial growth factor (VEGF) and various microRNAs (miRNAs) in muscle atrophy using a mouse model of denervation (DEN)-induced disuse, and to elucidate their interactions and regulatory functions through comprehensive network analysis. The right sciatic nerve of C57BL/6J mice (n=6) was excised to simulate DEN, with the left serving as a sham surgery control (Sham). Following a two-week period, wet muscle weight was measured. Total RNA was extracted from the tibialis anterior muscle for microarray analysis. Significant expression changes were analyzed via Kyoto Encyclopedia of Genes and Genomes (KEGG)pathway analysis and miRNet for miRNAs. Denervated limbs showed a significant reduction in muscle weight. Over 1,000 genes displayed increased expression, while 527 showed reductions to less than half of control levels. VEGF, along with specific miRNAs such as miR-106a-5p, miR-mir20a-5p, mir93-5p and mir17-5p, occupied central regulatory nodes within the gene network. Functional analysis revealed that these molecules are involved in key biological processes including regulation of cell migration, vasculature development, and regulation of endothelial cell proliferation. The increased miRNAswere subjected to further network analysis that revealed significant regulatory interactions with target mRNAs. VEGF and miRNAs play crucial roles in the progression of skeletal muscle atrophy, offering potential targets for therapeutic interventions aimed at reducing atrophy and enhancing muscle regeneration.

GSDMD KNOCKOUT ALLEVIATES SEPSIS-ASSOCIATED SKELETAL MUSCLE ATROPHY BY INHIBITING IL18/AMPK SIGNALING.

Background: Sepsis commonly leads to skeletal muscle atrophy, characterized by substantial muscle weakness and degeneration, ultimately contributing to an adverse prognosis. Studies have shown that programmed cell death is an important factor in the progression of muscle loss in sepsis. However, the precise role and mechanism of pyroptosis in skeletal muscle atrophy are not yet fully comprehended. Therefore, we aimed to examine the role and mechanism of action of the pyroptosis effector protein GSDMD in recognized cellular and mouse models of sepsis. Methods: The levels of GSDMD and N-GSDMD in skeletal muscle were evaluated 2, 4, and 8 days after cecal ligation and puncture. Sepsis was produced in mice that lacked the Gsdmd gene (Gsdmd knockout) and in mice with the normal Gsdmd gene (wild-type) using a procedure called cecal ligation and puncture. The degree of muscular atrophy in the gastrocnemius and tibialis anterior muscles was assessed 72 h after surgery in the septic mouse model. In addition, the architecture of skeletal muscles, protein expression, and markers associated with pathways leading to muscle atrophy were examined in mice from various groups 72 h after surgery. The in vitro investigations entailed the use of siRNA to suppress Gsdmd expression in C2C12 cells, followed by stimulation of these cells with lipopolysaccharide to evaluate the impact of Gsdmd downregulation on muscle atrophy and the related signaling cascades. Results: This study has demonstrated that the GSDMD protein, known as the "executive" protein of pyroptosis, plays a crucial role in the advancement of skeletal muscle atrophy in septic mice. The expression of N-GSDMD in the skeletal muscle of septic mice was markedly higher compared with the control group. The Gsdmd knockout mice exhibited notable enhancements in survival, muscle strength, and body weight compared with the septic mice. Deletion of the Gsdmd gene reduced muscular wasting in the gastrocnemius and tibialis anterior muscles caused by sepsis. Studies conducted in living organisms ( in vivo ) and in laboratory conditions ( in vitro ) have shown that the absence of the Gsdmd gene decreases indicators of muscle loss associated with sepsis by blocking the IL18/AMPK signaling pathway. Conclusion: The results of this study demonstrate that the lack of Gsdmd has a beneficial effect on septic skeletal muscle atrophy by reducing the activation of IL18/AMPK and inhibiting the ubiquitin-proteasome system and autophagy pathways. Therefore, our research provides vital insights into the role of pyroptosis in sepsis-related skeletal muscle wasting, which could potentially lead to the development of therapeutic and interventional approaches for preventing septic skeletal muscle atrophy.

Freeze-dried porous collagen scaffolds for the repair of volumetric muscle loss injuries.

Volumetric muscle loss (VML) injuries are characterized by the traumatic loss of skeletal muscle resulting in permanent damage to both tissue architecture and electrical excitability. To address this challenge, we previously developed a 3D aligned collagen-glycosaminoglycan (CG) scaffold platform that supported in vitro myotube alignment and maturation. In this work, we assessed the ability of CG scaffolds to facilitate functional muscle recovery in a rat tibialis anterior (TA) model of VML. Functional muscle recovery was assessed following implantation of either non-conductive CG or electrically conductive CG-polypyrrole (PPy) scaffolds at 4, 8, and 12 weeks post-injury by in vivo electrical stimulation of the peroneal nerve. After 12 weeks, scaffold-treated muscles produced maximum isometric torque that was significantly greater than non-treated tissues. Histological analysis further supported these reparative outcomes with evidence of regenerating muscle fibers at the material-tissue interface in scaffold-treated tissues that was not observed in non-repaired muscles. Scaffold-treated muscles possessed higher numbers of M1 and M2 macrophages at the injury while conductive CG-PPy scaffold-treated muscles showed significantly higher levels of neovascularization as indicated by the presence of pericytes and endothelial cells, suggesting a persistent wound repair response not observed in non-treated tissues. Finally, only tissues treated with non-conductive CG scaffolds displayed neurofilament staining similar to native muscle, further corroborating isometric contraction data. Together, these findings show that CG scaffolds can facilitate improved skeletal muscle function and endogenous cellular repair, highlighting their potential use as therapeutics for VML injuries.

Influence of foot strike pattern on co-contraction around the ankle and oxygen uptake during running at 19 km/h.

This study investigated the coactivation of plantar flexor and dorsiflexor muscles and oxygen uptake during running with forefoot and rearfoot strikes at 15 and 19 km/h. We included 16 male runners in this study. The participants ran each foot strike pattern for 5 min at 15 and 19 km/h on a treadmill. During the running, respiratory gas exchange data and surface electromyographic (EMG) activity of the medial gastrocnemius (MG), lateral gastrocnemius (LG), soleus, and tibialis anterior muscles of the right lower limb were continuously recorded. The indices of oxygen uptake, energy expenditure (EE), and muscle activation were calculated during the last 2 min in each condition. During the stance phase of running at 15 and 19 km/h, activation of the tibialis anterior and MG muscles was lower and higher, respectively, with forefoot strike than with rearfoot strike. The foot strike pattern did not influence the oxygen uptake. These results suggest that the foot strike pattern has no clear effect on the oxygen uptake when running at 15 and 19 km/h. However, forefoot strike leads to plantar flexion dominance during co-contraction of the tibialis anterior and MG muscles, which are an antagonist and agonist for plantar flexion, respectively, during the stance phase.

Functional study of the ST6GAL2 gene regulating skeletal muscle growth and development

ST6GAL2, a member of the sialoglycosyltransferase family, primarily localizes within the cellular Golgi apparatus. However, the role of the ST6GAL2 gene in skeletal muscle growth and development remains elusive. In this study, the impact of the ST6GAL2 gene on the proliferation, differentiation, and apoptosis of primary chicken myoblasts at the cellular level was investigated. Quantitative fluorescent PCR was used to measure the expression levels of genes. Subsequently, using gene knockout mice, we assessed its effects on skeletal muscle growth and development in vivo. Our findings reveal that the ST6GAL2 gene promotes the expression of cell cycle and proliferation-related genes, including CCNB2 and PCNA, and apoptosis-related genes, such as Fas and Caspase-9. At the individual level, double knockout of ST6GAL2 inhibited the formation of both fast and slow muscle fibers in the quadriceps, extensor digitorum longus, and tibial anterior muscle, while promoting their formation in the gastrocnemius and soleus. These results collectively demonstrate that the ST6GAL2 gene facilitates the proliferation, apoptosis, and fusion processes of primary chicken myoblasts. Additionally, it promotes the enlargement of cross-sectional muscle fiber areas and regulates the formation of fast and slow muscle fibers at the individual level, albeit inhibiting muscle fusion. This study provides valuable insights into the role of the ST6GAL2 gene in promoting proliferation of skeletal muscle.

Blood Flow Restriction Training Improves Muscular Outcomes in Patients With Chronic Ankle Instability: A Critically Appraised Topic

Clinical Scenario: The high recurrence of lateral ankle sprains progresses to chronic ankle instability (CAI) and can affect many athletes in all sports. CAI is often associated with a decrease in muscle strength, an increase in pain, a decrease in the range of motion, and a decrease in balance or neuromuscular control. The use of blood flow restriction (BFR) with CAI can increase muscular outcomes and be used as a rehabilitation tool. Clinical Question: Is there evidence to suggest that BFR improves strength, muscle activation, and/or cross-sectional area of the lower leg musculature in those with CAI? Clinical Bottom Line: There is moderate evidence to support therapeutic exercise with low-intensity BFR in patients with CAI. The evidence concluded a significant improvement in BFR to increase muscle activation of the fibularis longus, anterior tibialis, vastus lateralis, and soleus. There is moderate evidence suggesting BFR can induce strength gains in the muscles of the lower extremity in patients with CAI. Strength of Recommendation: The comprehensive evidence is a Strength of Recommendation Taxonomy (SORT) Grade B, with a level of evidence of 2, according to the Centre for Evidence-Based Medicine (CEBM) for the studies included.

Eccentric contraction increases hydrogen peroxide levels and alters gene expression through Nox2 in skeletal muscle of male mice.

Hydrogen peroxide (H2O2) is one of the key signaling factors regulating skeletal muscle adaptation to muscle contractions. Eccentric (ECC) and concentric (CONC) contractions drive different muscle adaptations with ECC resulting in greater changes. The present investigation tested the hypothesis that ECC produces higher cytosolic and mitochondrial H2O2 concentrations [H2O2] and alters gene expression more than CONC. Cytosolic and mitochondrial H2O2-sensitive fluorescent proteins, HyPer7 and MLS-HyPer7, were expressed in the anterior tibialis muscle of C57BL6J male mice. Before and for 60 min after either CONC or ECC (100 Hz, 50 contractions), [H2O2]cyto and [H2O2]mito were measured by in vivo fluorescence microscopy. RNA sequencing was performed in control (noncontracted), CONC, and ECC muscles to identify genes impacted by the contractions. [H2O2]cyto immediately after ECC was greater than after CONC (CONC: +6%, ECC: +11% vs. rest, P < 0.05) and remained higher for at least 60 min into recovery. In contrast, the elevation of [H2O2]mito was independent of the contraction modes (time; P < 0.0042, contraction mode; P = 0.4965). The impact of ECC on [H2O2]cyto was abolished by NADPH oxidase 2 (Nox2) inhibition (GSK2795039). Differentially expressed genes were not present after CONC or ECC + GSK but were found after ECC and were enriched for vascular development and apoptosis-related genes, among others. In conclusion, in mouse anterior tibialis, ECC, but not CONC, evokes a pronounced cytosolic H2O2 response, caused by Nox2, that is mechanistically linked to gene expression modifications.NEW & NOTEWORTHY This in vivo model successfully characterized the effects of eccentric (ECC) and concentric (CONC) contractions on cytosolic and mitochondrial [H2O2] in mouse skeletal muscle. Compared with CONC, ECC induced higher and more sustained [H2O2]cyto-an effect that was abolished by Nox2 inhibition. ECC-induced [H2O2]cyto elevations were requisite for altered gene expression.

Allogenic Vertebral Body Adherent Mesenchymal Stromal Cells Promote Muscle Recovery in Diabetic Mouse Model of Limb Ischemia

Chronic limb threatening ischemia (CLTI) carries a significant risk for amputation especially in diabetic patients with poor options for revascularization. Phase I trials have demonstrated efficacy of allogeneic mesenchymal stromal cells (MSC) in treating diabetic CLTI. Vertebral bone adherent mesenchymal stromal cells (vBA-MSC) are derived from vertebral bodies of deceased organ donors which offer the distinct advantage of providing a 1,000x greater yield compared to that of living donor bone aspiration. This study describes the effects of intramuscular injection of allogenic vBA-MSC in promoting limb perfusion and muscle recovery in a diabetic CLTI mouse model. A CLTI mouse model was created through unilateral ligation of the femoral artery in male polygenic diabetic TALLYHO mice. Treated mice were injected with vBA-MSC into the gracilis muscle of the ischemic limb 7 days post ligation. Gastrocnemius or tibialis muscle was assessed post-mortem for fibrosis by collagen staining, capillary density via immunohistochemistry, and mRNA by quantitative real time PCR. Laser Doppler perfusion imaging and plantar flexion muscle testing were performed to quantify changes in limb perfusion and muscle function. Compared to vehicle control, treated mice demonstrated indicators of muscle recovery including decreased fibrosis, increased perfusion, muscle torque, and angiogenesis. PCR analysis of muscle obtained 7- and 30-days post vBA-MSC injection showed an upregulation in expression of MyoD1 (p = 0.03) and MyH3 (p = 0.008) mRNA representing muscle regeneration, VEGF-A (p = 0.002 ; p = 0.004) signifying angiogenesis as well as IL-10 (p < 0.001), T regulatory cell marker Foxp3 (p = 0.04), and M2-biased macrophage marker Mrc1 (CD206) (p = 0.02). These findings indicate human allogeneic vBA-MSC ameliorate ischemic muscle damage and rescue muscle function. These results in a murine model will enable further studies to develop potential therapies for diabetic CLTI patients.

Osteopathic Approach to Proximal Hamstring Tendinopathy-related Sciatic Nerve Entrapment (PHTrSNE): Case Report

Abstract Proximal Hamstring Tendinopathy (PHT) provides a challenging diagnosis for clinicians due to limited evidence-based research. Presenting as chronic pain originating at the ischial tuberosity, PHT can progress to entrap the sciatic nerve, resulting in proximal hamstring tendinopathy-related sciatic nerve entrapment (PHTrSNE). This case expands the understanding of PHT by describing the osteopathic assessment and treatment of a runner with PHTrSNE. A 24-year-old female marathoner presented to the neurology clinic with a unique running gait: a left leg circumduction, or “leg whip,” that presented only when running. She also reported constantly dull hamstring pain, which occasionally elicited a sharp, shooting pain from her lower gluteal muscles to mid-hamstrings. Activities such as prolonged sitting and intense running exacerbated the sharp pain. On examination, the patient displayed ischial tuberosity tenderness and positive tests for hamstring tendinopathy. Evaluation with EMG/NCS showed mild chronic denervation of the left tibialis anterior muscle. A treatment plan for the patient’s PHTrSNE was created based on the principles of the neurological model of osteopathic medicine. Patients presenting with chronic hamstring discomfort accompanied by sharp, shooting pain may benefit from the diagnostic and therapeutic approach outlined in this study.

Neuromuscular adaptations to perturbation-based balance training using treadmill belt accelerations do not transfer to an obstacle trip in older people: A cross-over randomised controlled trial

BackgroundThis study examined (i) adaptations in muscle activity following perturbation-based balance training (PBT) using treadmill belt-accelerations or PBT using walkway trips and (ii) whether adaptations during treadmill PBT transfer to a walkway trip. MethodsThirty-eight older people (65+ years) undertook two PBT sessions, including 11 treadmill belt-accelerations and 11 walkway trips. Surface electromyography (EMG) was measured bilaterally on the rectus femoris (RF), tibialis anterior (TA), semitendinosus (ST) and gastrocnemius medial head (GM) during the first (T1) and eleventh (T11) perturbations. Adaptations (within-subjects - 1st vs 11th perturbations for treadmill and walkway PBT) and their transfer (between-subjects – 1st walkway trip after treadmill PBT vs 1st walkway trip with no prior training) effects were examined for the EMG parameters. ResultsTreadmill PBT reduced post-perturbation peak muscle activation magnitude (left RF, TA, ST, right RF, ST, GM), onset latency (right TA), time to peak (right RF) and co-contraction index (knee muscles) (P < 0.05). Walkway PBT reduced post-trip onset latencies (right TA, ST), peak magnitude (left ST, right GM), time to peak (right RF, ST) and pre-perturbation muscle activity (right TA) (P < 0.05). Those who undertook treadmill PBT were not different to those without prior training during the first walkway trip (P > 0.05). ConclusionsBoth treadmill and walkway PBT induced earlier initiation and peak activation of right limb muscles responsible for the first recovery step. Treadmill PBT also reduced co-contraction of the knee muscles. Adaptations in muscle activity following treadmill PBT did not transfer to a walkway trip.