Partial-thickness rotator cuff tears frequently enlarge due to increased local strain and often p... more Partial-thickness rotator cuff tears frequently enlarge due to increased local strain and often progress to full-thickness tears. Studies suggest the addition of new tendinous tissue to injured cuff tendons would significantly decrease peak strain, possibly protecting against tear progression. The aim of this study was to assess the ability of a highly-porous collagen implant to induce new tissue formation and limit tear progression when placed on the bursal surface of partial-thickness cuff tears. Methods: Following arthroscopic subacromial decompression, the implant was attached to the bursal surface of the supraspinatus tendon in a prospective series of 13 patients with intermediate-(3-6 mm) to high-grade (>6 mm) partial-thickness cuff tears (5 articular, 3 bursal, 5 intra-substance). Tendon thickness, defect size, and tendon quality were evaluated using magnetic resonance imaging (MRI) preoperatively and at 3, 6, 12, and 24 months postoperatively. Clinical outcomes were assessed using the Constant and American Shoulder and Elbow Society scores at the same preoperative and follow-up times. Results: The implant induced significant new tissue formation in all patients by 3 months (mean increase in tendon thickness 2.2 AE 0.26 mm). This tissue matured over time and became radiologically indistinguishable from the underlying tendon. The partial-thickness cuff tears showed consistent filling of the defects, with complete healing in 7 patients at 12 months, and a progressive improvement in tendon quality in the remaining patients. No tear progression was observed by MRI in any of the patients at 24 months. All clinical scores improved significantly over time. At 24 months, 12 of 13 patients (92%) had satisfactory or better results. Conclusion: The results of this clinical study demonstrated the ability of a highly-porous collagen implant to induce new tendon-like tissue formation and create an environment conductive to the healing of partial-thickness cuff tears.
A healthy skeletal muscle mass is essential in attenuating the complications of obesity. Importan... more A healthy skeletal muscle mass is essential in attenuating the complications of obesity. Importantly, healthy muscle function is maintained through adequate repair following overuse and injury. The purpose of this study was to investigate the impact of diet-induced obesity (DIO) on skeletal muscle repair and the functionality of the muscle satellite cell (SC) population. Male C57BL/6J mice were fed a standard chow or high-fat diet (60% kcal fat; DIO) for 8 weeks. Muscles from DIO mice subjected to cardiotoxin injury displayed attenuated muscle regeneration, as indicated by prolonged necrosis, delayed expression of MyoD and Myogenin, elevated collagen content, and persistent embryonic myosin heavy chain expression. While no significant differences in SC content were observed, SCs from DIO muscles did not activate normally nor did they respond to exogenous hepatocyte growth factor (HGF) despite similar receptor (cMet) density. Furthermore, HGF release from crushed muscle was significa...
Journal of science in sport and exercise, May 13, 2022
Purpose The purpose of this study was to examine the response of myokines to blood-flow restricte... more Purpose The purpose of this study was to examine the response of myokines to blood-flow restricted resistance-exercise (BFR-RE) in younger and older males before and after completing a 12-week resistance-training program. Methods There were 8 younger (24.8 ± 3.9 yrs) and 7 older (68.3 ± 5.0 yrs) untrained male participants completed this study. Anthropometric and maximal strength (1RM) measurements were collected before and after a 12-week, supervised, progressive full-body resistance-training program. As well, an acute bout of full-body BFR-RE was performed with venipuncture blood samples collected before and immediately following the BFR-RE, followed by sampling at 3, 6, 24 and 48 h. Results The 12-week training program stimulated a 32.2% increase in average strength and 30% increase in strength per kg of fat free mass. The response of particular myokines to the acute bout of BFR-RE was influenced training status (IL-4, untrained = 78.1 ± 133.2 pg/mL vs. trained = 59.8 ± 121.6 pg/mL, P = 0.019; IL-7, untrained = 3.46 ± 1.8 pg/mL vs. trained = 2.66 ± 1.3 pg/mL, P = 0.047) or both training and age (irisin, P = 0.04; leukemia inhibitory factor, P < 0.001). As well, changes in strength per kg of fat free mass were correlated with area under the curve for IL-4 (r = 0.537; P = 0.039), IL-6 (r = 0. 525; P = 0.044) and LIF (r = − 0.548; P = 0.035) in the untrained condition. Conclusion This study identified that both age and training status influence the myokine response to an acute bout of BFR-RE with the release of IL-4, IL-6 and LIF in the untrained state being associated with changes in strength per kg of fat free mass.
Journal of science in sport and exercise, May 13, 2022
Purpose The purpose of this study was to examine the response of myokines to blood-flow restricte... more Purpose The purpose of this study was to examine the response of myokines to blood-flow restricted resistance-exercise (BFR-RE) in younger and older males before and after completing a 12-week resistance-training program. Methods There were 8 younger (24.8 ± 3.9 yrs) and 7 older (68.3 ± 5.0 yrs) untrained male participants completed this study. Anthropometric and maximal strength (1RM) measurements were collected before and after a 12-week, supervised, progressive full-body resistance-training program. As well, an acute bout of full-body BFR-RE was performed with venipuncture blood samples collected before and immediately following the BFR-RE, followed by sampling at 3, 6, 24 and 48 h. Results The 12-week training program stimulated a 32.2% increase in average strength and 30% increase in strength per kg of fat free mass. The response of particular myokines to the acute bout of BFR-RE was influenced training status (IL-4, untrained = 78.1 ± 133.2 pg/mL vs. trained = 59.8 ± 121.6 pg/mL, P = 0.019; IL-7, untrained = 3.46 ± 1.8 pg/mL vs. trained = 2.66 ± 1.3 pg/mL, P = 0.047) or both training and age (irisin, P = 0.04; leukemia inhibitory factor, P < 0.001). As well, changes in strength per kg of fat free mass were correlated with area under the curve for IL-4 (r = 0.537; P = 0.039), IL-6 (r = 0. 525; P = 0.044) and LIF (r = − 0.548; P = 0.035) in the untrained condition. Conclusion This study identified that both age and training status influence the myokine response to an acute bout of BFR-RE with the release of IL-4, IL-6 and LIF in the untrained state being associated with changes in strength per kg of fat free mass.
The hormonal milieu of the testis was examined in streptozocin-induced diabetic (STZ-D) adult mal... more The hormonal milieu of the testis was examined in streptozocin-induced diabetic (STZ-D) adult male Wistar and Long-Evans rats. Serum testosterone, creatinine, and urea nitrogen (BUN) levels and blood glucose concentrations were determined in diabetic and control Wistar rats (experiment 1). These parameters plus luteinizing hormone (LH) and folliclestimulating hormone (FSH) levels were studied in experiments 2 and 3 with Long-Evans rats in untreated diabetic, control, insulin-treated diabetic, nondiabetic STZ-injected, and semistarved groups. Wistar diabetic rats had significantly decreased serum testosterone and increased blood glucose, BUN, and serum creatinine compared with controls. Several findings in Long-Evans rats suggested the existence of a primary Leydig cell defect in steroidogenesis during untreated diabetes that was completely or partially compensated for by increased pituitary gonadotropin secretion. Serum LH and FSH levels increased in Long-Evans diabetic rats. Serum testosterone was significantly reduced only in experiment 2. These hormonal alterations from control levels were not seen in insulin-treated diabetic animals. Semistarved animals, weight matched to the diabetic group in experiment 2, had significantly decreased serum testosterone and increased FSH levels. In addition, Long-Evans diabetic rat BUN and serum creatinine levels increased much less or were unchanged from control values compared with the increase noted in diabetic Wistar rats. In light of the hypogonadism that complicates clinical uremia, these findings suggest the more apt use of the Long-Evans strain rather than the Wistar strain in the study of STZ-D hypogonadal function. Indices to evaluate
Background: Knee osteoarthritis (OA) is the most prevalent medical condition in individuals over ... more Background: Knee osteoarthritis (OA) is the most prevalent medical condition in individuals over the age of 65 years, and is a progressive joint degenerative condition with no known cure. Research suggests that there is a strong relationship between knee pain and loss of physical function. The resulting lifestyle modifications negatively impact not only disease onset and progression but also overall health, work productivity, and quality of life of the affected individual. Purpose: The goal of this investigation was to examine the feasibility of using an emerging technology called lower body positive pressure (LBPP) to simulate weight loss and reduce acute knee pain during treadmill walking exercise in overweight individuals with radiographically confirmed symptomatic knee OA. Design: Prospective case series. Methods: Twenty-two overweight individuals with knee OA completed two 20-minute treadmill walking sessions (one full weight bearing and one LBPP supported) at a speed of 3.1 mph, 0% incline. Acute knee pain was assessed using a visual analog scale, and the percentage of LBPP support required to minimize knee pain was evaluated every 5 minutes. Knee Osteoarthritis Outcome Scores were used to quantify knee pain and functional status between walking sessions. The order of testing was randomized, with sessions occurring a minimum of 1 week apart. Results: A mean LBPP of 12.4% of body weight provided participants with significant pain relief during walking, and prevented exacerbation of acute knee pain over the duration of the 20-minute exercise session. Patients felt safe and confident walking with LBPP support on the treadmill, and demonstrated no change in Knee Osteoarthritis Outcome Scores over the duration of the investigation. Conclusion: Results suggest that LBPP technology can be used safely and effectively to simulate weight loss and reduce acute knee pain during weight-bearing exercise in an overweight knee OA patient population. These results could have important implications for the development of future treatment strategies used in the management of at-risk patients with progressive knee OA.
Terminal Schwann cells (TSCs) help regulate the formation, maintenance, function, and repair of n... more Terminal Schwann cells (TSCs) help regulate the formation, maintenance, function, and repair of neuromuscular junctions (NMJs) and axon guidance after muscle injury. Premature activation of muscle satellite cells (SCs), induced by isosorbide dinitrate (ISDN) before injury, accelerates myogenic regeneration, disrupts NMJ remodeling and maturation, decreases Sema3A protein-induced neuro-repulsion, and is accompanied by time-dependent changes in S100B protein levels. Here, to study the effects of premature SC activation on TSCs and SCs, both expressing P75 nerve growth-factor receptor, in situ hybridization was used to identify transcripts of S100B and Sema3A, and the number, intensity, and diameter of expression sites were analyzed. The number of sites/fields expressing S100B and Sema3A increased with regeneration time (both p < 0.001). Expression-site intensity (S100B) and diameter (S100B and Sema3A) decreased during regeneration (p = 0.005; p < 0.05, p = 0.006, respectively). ...
International Journal of Sports Physical Therapy, 2021
Background Adolescent females are at significant risk for sustaining an ACL injury. The Y-Balance... more Background Adolescent females are at significant risk for sustaining an ACL injury. The Y-Balance Test (YBT) is frequently used to evaluate neuromuscular control and lower extremity function. However, few studies have quantified 2D lower extremity kinematics during performance of the YBT, and there is an absence of kinematic data specific to at-risk adolescent females. Purpose To examine lower extremity joint kinematics during execution of the YBT by healthy and ACL-injured adolescent females. Study Design Prospective cohort. Methods Twenty-five healthy and ten ACL-injured (mean time from injury 143 days) adolescent females were assessed using the YBT. Sagittal and frontal plane knee and ankle motion was video recorded during execution of the YBT anterior reach movement. Ankle dorsi-flexion, knee flexion, and knee valgus angles were quantified via kinematic analysis. ANOVAs with a post hoc Bonferroni correction were used to compare YBT scoring (%LL) and kinematic data between groups...
Journal of pharmacy & pharmaceutical sciences : a publication of the Canadian Society for Pharmaceutical Sciences, Societe canadienne des sciences pharmaceutiques, 2018
MyoNovin is a novel skeletal muscle-regenerating compound developed through synthesis of two nitr... more MyoNovin is a novel skeletal muscle-regenerating compound developed through synthesis of two nitro groups onto a guaifenesin backbone to deliver nitric oxide to skeletal muscle with a potential to treat muscle atrophy. The purpose of this study was to utilize in silico, in vitro, and in vivo approaches to characterize MyoNovin and examine its safety, biodistribution, and feasibility for drug delivery. In silico software packages were used to predict the physicochemical and biopharmaceutical properties of MyoNovin. In vitro cardiotoxicity was assessed using human cardiomyocytes (RL-14) while effects on CYP3A4 metabolic enzyme and antioxidant activity were examined using commercial kits. A novel HPLC assay was developed to measure MyoNovin concentration in serum, and delineate initial pharmacokinetic and acute toxicity after intravenous administration (20 mg/kg) to male Sprague-Dawley rats. MyoNovin showed relatively high lipophilicity with a LogP value of 3.49, a 20-fold higher skin ...
Deflazacort slows the progress of Duchenne muscular dystrophy (DMD) with fewer side effects than ... more Deflazacort slows the progress of Duchenne muscular dystrophy (DMD) with fewer side effects than prednisone. In mdx mice, deflazacort treatment augments repair and growth of new muscle fibers. We tested the hypothesis that deflazacort improves muscle function and promotes repair by increasing myogenic cell proliferation and fiber differentiation. mdx mice (3.5 weeks old) were treated with deflazacort (1.2 mg/kg) or vehicle for 4 weeks. Forelimb grip strength was measured. After 4 weeks, the right tibialis anterior muscle (TA) was crush injured to induce synchronous regeneration. DNA was labeled using different markers 24 and 2 h before collecting tissues 4 days after injury. The expression of creatine kinase (CK) isoforms, laminin-2 (merosin) mRNA and protein, and proliferation by myogenic cells were measured and satellite cells were identified by immunolocalization of c-met receptor. Peak grip strength increased 15% within 10 days of treatment, and was maintained up to 6 weeks afte...
Recently, we found that resident myogenic stem satellite cells upregulate a multi-functional secr... more Recently, we found that resident myogenic stem satellite cells upregulate a multi-functional secreted protein, semaphorin 3A (Sema3A), exclusively at the early-differentiation phase in response to muscle injury; however, its physiological significance is still unknown. Here we show that Sema3A impacts slow-twitch fiber generation through a signaling pathway, cell-membrane receptor (neuropilin2-plexinA3) → myogenin-myocyte enhancer factor 2D → slow myosin heavy chain. This novel axis was found by small interfering RNA-transfection experiments in myoblast cultures, which also revealed an additional element that Sema3A-neuropilin1/plexinA1, A2 may enhance slow-fiber formation by activating signals that inhibit fast-myosin expression. Importantly, satellite cell-specific Sema3A conditional-knockout adult mice (Pax7CreER(T2) -Sema3A(fl) °(x) activated by tamoxifen-i.p. injection) provided direct in vivo evidence for the Sema3A-driven program, by showing that slow-fiber generation and mus...
Regenerative mechanisms that regulate intramuscular motor innervation are thought to reside in th... more Regenerative mechanisms that regulate intramuscular motor innervation are thought to reside in the spatiotemporal expression of axon-guidance molecules. Our previous studies proposed an unexplored role of resident myogenic stem cell (satellite cell)-derived myoblasts as a key presenter of a secreted neural chemorepellent semaphorin 3A (Sema3A); hepatocyte growth factor (HGF) and basic fibroblast growth factor (FGF2) triggered its expression exclusively at the early differentiation phase. In order to advance this concept, the present study described that transmembrane heparan/chondroitin sulfate proteoglycans syndecan-2, 4 may be the plausible receptor candidates for HGF and FGF2 to signal Sema3A expression. Results showed that mRNA expression of syndecan-2, 4 was abundant (two magnitudes higher than syndecan-1, 3) in early-differentiated myoblasts and their in vitro knockdown diminished the HGF/FGF2-induced expression of Sema3A down to a baseline level. Pretreatment with heparitinas...
This study coupled proton magnetic resonance spectroscopy (1 H-NMR) and in situ hybridization plu... more This study coupled proton magnetic resonance spectroscopy (1 H-NMR) and in situ hybridization plus autoradiography in a novel examination of different phenotypes of adult myogenesis that arise from genetic disruptions in mice. Study of muscle extracts from normal and dystrophin-deficient mdx limb and diaphragm muscles confirmed our previous findings linking taurine and muscle regeneration at the peak of damage and repair. 1 H-NMR distinguished biochemical differences in regenerating muscles that were consistent with the extent of repair in three strains: mdx dystrophic mice; MyoD(-/-) mice that lack expression of the early myogenic regulatory gene MyoD; and a double-mutant mdx:MyoD(-/-) strain lacking expression of both MyoD and dystrophin. We tested the hypothesis that differences in spectra according to genotype and the regeneration phenotype are related specifically to proliferation by committed myogenic precursor cells. 1 H-NMR distinguished the three mutant strains: Taurine was highest in mdx muscles, with the phenotype of most effective regeneration; lowest in MyoD(-/-) muscles, with the least effective formation of new muscle in repair, as reported previously; and intermediate in double-mutant muscles, now reported to show an intermediate repair phenotype. The early and late muscle precursors (mpcs) expressing myf5 and myogenin were examined for proliferation. Eighteen percent of mdx myf5-positive mpcs were proliferative, whereas myf5-positive mpcs did not proliferate in regenerating muscles that lacked MyoD expression. By contrast, whereas 30% of myogenin-positive mpcs were proliferative in mdx muscles, almost none were proliferative in MyoD(-/-) muscles, and 12% were proliferative in double-mutant muscles. Therefore, the extent of accumulated structural regeneration, taurine levels, and proliferation of late mpc (expressing myogenin) were congruent across genotypes. Proliferation by early mpc (expressing myf5) was inhibited by the lack of MyoD expression during muscle regeneration. These studies indicate the potential for 1 H-NMR monitoring of muscle status in disease, regenera
Application of mechanical stretch to cultured adult rat muscle satellite cells results in release... more Application of mechanical stretch to cultured adult rat muscle satellite cells results in release of hepatocyte growth factor (HGF) and accelerated entry into the cell cycle. Stretch activation of cultured rat muscle satellite cells was observed only when medium pH was between 7.1 and 7.5, even though activation of satellite cells was accelerated by exogenous HGF over a pH range from 6.9 to 7.8. Furthermore, HGF was only released in stretched cultures when the pH of the medium was between 7.1 and 7.4. Conditioned medium from stretched satellite cell cultures stimulated activation of unstretched satellite cells, and the addition of anti-HGF neutralizing antibodies to stretch-conditioned medium inhibited the stretch activation response. Conditioned medium from satellite cells that were stretched in the presence of nitric-oxide synthase (NOS) inhibitorNω-nitro-l-arginine methyl ester hydrochloride did not accelerate activation of unstretched control satellite cells, and HGF was not rel...
Satellite cells from adult rat muscle coexpress proliferating cell nuclear antigen and MyoD upon ... more Satellite cells from adult rat muscle coexpress proliferating cell nuclear antigen and MyoD upon entry into the cell cycle, suggesting that MyoD plays a role during the recruitment of satellite cells. Moreover, the finding that muscle regeneration is compromised in MyoD−/− mice, has provided evidence for the role of MyoD during myogenesis in adult muscle. In order to gain further insight into the role of MyoD during myogenesis in the adult, we compared satellite cells from MyoD−/− and wildtype mice as they progress through myogenesis in single-myofiber cultures and in tissuedissociated cell cultures (primary cultures). Satellite cells undergoing proliferation and differentiation were traced immunohistochemically using antibodies against various regulatory proteins. In addition, an antibody against the mitogen-activated protein kinases ERK1 and ERK2 was used to localize the cytoplasm of the fiber-associated satellite cells regardless of their ability to express specific myogenic regulatory factor proteins. We show that during the initial days in culture the myofibers isolated from both the MyoD−/− and the wildtype mice contain the same number of proliferating, ERK+ satellite cells. However, the MyoD−/− satellite cells continue to proliferate and only a very small number of cells transit into the myogenin+ state, whereas the wildtype cells exit the proliferative compartment and enter the myogenin+ stage. Analyzing tissuedissociated cultures of MyoD−/− satellite cells, we identified numerous cells whose nuclei were positive for the Myf5 protein. In contrast, quantification of Myf5+ cells in the wildtype cultures was difficult due to the low level of Myf5 protein present. The Myf5+ cells in the MyoD−/− cultures were often positive for desmin, similar to the MyoD+ cells in the wildtype cultures. Myogenin+ cells were identified in the MyoD−/− primary cultures, but their appearance was delayed compared to the wildtype cells. These "delayed" myogenin+ cells can express other differentiation markers such as MEF2A and cyclin D3 and fuse into myotubes. Taken together, our studies suggest that the presence of MyoD is critical for the normal progression of satellite cells
American Journal of Physiology-Cell Physiology, 2011
Successful regeneration and remodeling of the intramuscular motoneuron network and neuromuscular ... more Successful regeneration and remodeling of the intramuscular motoneuron network and neuromuscular connections are critical for restoring skeletal muscle function and physiological properties. The regulatory signals of such coordination remain unclear, although axon-guidance molecules may be involved. Recently, satellite cells, resident myogenic stem cells positioned beneath the basal lamina and at high density at the myoneural junction regions of mature fibers, were shown to upregulate a secreted neural chemorepellent semaphorin 3A (Sema3A) in response to in vivo muscle-crush injury. The initial report on that expression centered on the observation that hepatocyte growth factor (HGF), an essential cue in muscle fiber growth and regeneration, remarkably upregulates Sema3A expression in early differentiated satellite cells in vitro [Tatsumi et al., Am J Physiol Cell Physiol 297: C238–C252, 2009]. Here, we address regulatory effects of basic fibroblast growth factor (FGF2) and transform...
American Journal of Physiology-Cell Physiology, 2009
Regenerative coordination and remodeling of the intramuscular motoneuron network and neuromuscula... more Regenerative coordination and remodeling of the intramuscular motoneuron network and neuromuscular connections are critical for restoring skeletal muscle function and physiological properties. The regulatory mechanisms of such coordination remain unclear, although both attractive and repulsive axon guidance molecules may be involved in the signaling pathway. Here we show that expression of a neural secreted chemorepellent semaphorin 3A (Sema3A) is remarkably upregulated in satellite cells of resident myogenic stem cells that are positioned beneath the basal lamina of mature muscle fibers, when treated with hepatocyte growth factor (HGF), established as an essential cue in muscle fiber growth and regeneration. When satellite cells were treated with HGF in primary cultures of cells or muscle fibers, Sema3A message and protein were upregulated as revealed by reverse transcription-polymerase chain reaction and immunochemical studies. Other growth factors had no inductive effect except f...
Although an increase in nitric oxide (NO) in muscle is reported to improve the outcome of deflaza... more Although an increase in nitric oxide (NO) in muscle is reported to improve the outcome of deflazacort treatment for mdx mouse muscular dystrophy, the genetic homologue of Duchenne muscular dystrophy (DMD), the impact such treatment on the functional outcomes of the disease, including fiber susceptibility to exercise-induced injury, is not established. Experiments were designed to test whether treatment with deflazacort and L-arginine (a substrate for NO synthase, NOS) would change the extent of fiber injury induced by 24 h of voluntary exercise. The impact of exercise-related injury to induce a secondary regenerative response by muscle was also examined as corroborating evidence of muscle damage. Dystrophic mdx mice were treated for 3 wk with placebo, deflazacort, or deflazacort plus either L-arginine or N G-nitro-L-arginine methyl ester (a NOS inhibitor). Deflazacort, especially combined with L-arginine, spared quadriceps muscle from injury-induced regeneration (myf5 expression) compared with placebo treatment, despite an increase in membrane permeability immediately after exercise (assessed by Evans blue dye infiltration). Deflazacort alone prevented the typical progressive loss of function (measured as voluntary distance run over 24 h) that was observed 3 months later in placebotreated mice. Therefore, combined deflazacort plus L-arginine treatment spared mdx dystrophic limb muscle from exercise-induced damage and the need for regeneration and induced a persistent functional improvement in distance run. Results suggest a potential new treatment option for improving the quality of life for boys with DMD. Key words: nitric oxide • myf5 • exercise • utrophin • muscle regeneration he absence of dystrophin from skeletal muscle increases the susceptibility to exerciseinduced fiber damage (1-6). This susceptibility is one of the hallmark signs of dysfunction in muscular dystrophy in mdx mice, the genetic homologue of human Duchenne muscular dystrophy (DMD). Despite significant capacity for muscle regeneration in the mdx mouse, dystrophin deficiency leads to fiber weakness, muscle fiber loss, muscle fibrosis, and early death in both mice and humans (7-9). Although much less severe than DMD, parallels between mdx mouse and human muscular dystrophies demonstrate that the mouse is a strong model for investigating the pathophysiology of dystrophy and the structure-function relationship of the dystrophin-associated dystroglycan complex (DGC). The model is also effective in T
Satellite cells, muscle precursor cells in skeletal muscle, are normally quiescent and become act... more Satellite cells, muscle precursor cells in skeletal muscle, are normally quiescent and become activated by disease or injury. A lack of dystrophin and changes in the expression or activity of neuronal nitric oxide synthase (NOS-I) affect the timing of activation in vivo. Nitric oxide synthase inhibition delays muscle repair in normal mice, and worsens muscular dystrophy in the mdx mouse, a genetic homologue of Duchenne muscular dystrophy. However, the potential role of activation and repair events mediated by nitric oxide in determining the outcome of steroid or other treatments for muscular dystrophy is not clear. We tested the hypothesis that the extent of repair in dystrophic muscles of mdx mice is partly dependent on NOS-Im expression and activity. Myotube formation in regenerating muscle was promoted by deflazacort treatment of mdx dystrophic mice (P , 0:05), and improved by combination with the nitric oxide synthase substrate, L-arginine, especially in the diaphragm. NOS-Im mRNA expression and activity were present in satellite cells and very new myotubes of regenerating and dystrophic muscle. Deflazacort treatment resulted in increased NOS-Im expression in regenerating muscles in a strong and specific correlation with myf5 expression (r ¼ 0:95, P , 0:01), a marker for muscle repair. Nitric oxide synthase inhibition prevented the deflazacort-induced rise in NOS-Im and myf5 expression in the diaphragm without affecting the diameter of non-regenerating fibres. These in vivo studies suggest that gains in NOS-Im expression and nitric oxide synthase activity in satellite cells can increase the extent and speed of repair, even in the absence of dystrophin in muscle fibres. NOS-Im may be a useful therapeutic target to augment the effects of steroidal or other treatments of muscular dystrophy.
Partial-thickness rotator cuff tears frequently enlarge due to increased local strain and often p... more Partial-thickness rotator cuff tears frequently enlarge due to increased local strain and often progress to full-thickness tears. Studies suggest the addition of new tendinous tissue to injured cuff tendons would significantly decrease peak strain, possibly protecting against tear progression. The aim of this study was to assess the ability of a highly-porous collagen implant to induce new tissue formation and limit tear progression when placed on the bursal surface of partial-thickness cuff tears. Methods: Following arthroscopic subacromial decompression, the implant was attached to the bursal surface of the supraspinatus tendon in a prospective series of 13 patients with intermediate-(3-6 mm) to high-grade (>6 mm) partial-thickness cuff tears (5 articular, 3 bursal, 5 intra-substance). Tendon thickness, defect size, and tendon quality were evaluated using magnetic resonance imaging (MRI) preoperatively and at 3, 6, 12, and 24 months postoperatively. Clinical outcomes were assessed using the Constant and American Shoulder and Elbow Society scores at the same preoperative and follow-up times. Results: The implant induced significant new tissue formation in all patients by 3 months (mean increase in tendon thickness 2.2 AE 0.26 mm). This tissue matured over time and became radiologically indistinguishable from the underlying tendon. The partial-thickness cuff tears showed consistent filling of the defects, with complete healing in 7 patients at 12 months, and a progressive improvement in tendon quality in the remaining patients. No tear progression was observed by MRI in any of the patients at 24 months. All clinical scores improved significantly over time. At 24 months, 12 of 13 patients (92%) had satisfactory or better results. Conclusion: The results of this clinical study demonstrated the ability of a highly-porous collagen implant to induce new tendon-like tissue formation and create an environment conductive to the healing of partial-thickness cuff tears.
A healthy skeletal muscle mass is essential in attenuating the complications of obesity. Importan... more A healthy skeletal muscle mass is essential in attenuating the complications of obesity. Importantly, healthy muscle function is maintained through adequate repair following overuse and injury. The purpose of this study was to investigate the impact of diet-induced obesity (DIO) on skeletal muscle repair and the functionality of the muscle satellite cell (SC) population. Male C57BL/6J mice were fed a standard chow or high-fat diet (60% kcal fat; DIO) for 8 weeks. Muscles from DIO mice subjected to cardiotoxin injury displayed attenuated muscle regeneration, as indicated by prolonged necrosis, delayed expression of MyoD and Myogenin, elevated collagen content, and persistent embryonic myosin heavy chain expression. While no significant differences in SC content were observed, SCs from DIO muscles did not activate normally nor did they respond to exogenous hepatocyte growth factor (HGF) despite similar receptor (cMet) density. Furthermore, HGF release from crushed muscle was significa...
Journal of science in sport and exercise, May 13, 2022
Purpose The purpose of this study was to examine the response of myokines to blood-flow restricte... more Purpose The purpose of this study was to examine the response of myokines to blood-flow restricted resistance-exercise (BFR-RE) in younger and older males before and after completing a 12-week resistance-training program. Methods There were 8 younger (24.8 ± 3.9 yrs) and 7 older (68.3 ± 5.0 yrs) untrained male participants completed this study. Anthropometric and maximal strength (1RM) measurements were collected before and after a 12-week, supervised, progressive full-body resistance-training program. As well, an acute bout of full-body BFR-RE was performed with venipuncture blood samples collected before and immediately following the BFR-RE, followed by sampling at 3, 6, 24 and 48 h. Results The 12-week training program stimulated a 32.2% increase in average strength and 30% increase in strength per kg of fat free mass. The response of particular myokines to the acute bout of BFR-RE was influenced training status (IL-4, untrained = 78.1 ± 133.2 pg/mL vs. trained = 59.8 ± 121.6 pg/mL, P = 0.019; IL-7, untrained = 3.46 ± 1.8 pg/mL vs. trained = 2.66 ± 1.3 pg/mL, P = 0.047) or both training and age (irisin, P = 0.04; leukemia inhibitory factor, P < 0.001). As well, changes in strength per kg of fat free mass were correlated with area under the curve for IL-4 (r = 0.537; P = 0.039), IL-6 (r = 0. 525; P = 0.044) and LIF (r = − 0.548; P = 0.035) in the untrained condition. Conclusion This study identified that both age and training status influence the myokine response to an acute bout of BFR-RE with the release of IL-4, IL-6 and LIF in the untrained state being associated with changes in strength per kg of fat free mass.
Journal of science in sport and exercise, May 13, 2022
Purpose The purpose of this study was to examine the response of myokines to blood-flow restricte... more Purpose The purpose of this study was to examine the response of myokines to blood-flow restricted resistance-exercise (BFR-RE) in younger and older males before and after completing a 12-week resistance-training program. Methods There were 8 younger (24.8 ± 3.9 yrs) and 7 older (68.3 ± 5.0 yrs) untrained male participants completed this study. Anthropometric and maximal strength (1RM) measurements were collected before and after a 12-week, supervised, progressive full-body resistance-training program. As well, an acute bout of full-body BFR-RE was performed with venipuncture blood samples collected before and immediately following the BFR-RE, followed by sampling at 3, 6, 24 and 48 h. Results The 12-week training program stimulated a 32.2% increase in average strength and 30% increase in strength per kg of fat free mass. The response of particular myokines to the acute bout of BFR-RE was influenced training status (IL-4, untrained = 78.1 ± 133.2 pg/mL vs. trained = 59.8 ± 121.6 pg/mL, P = 0.019; IL-7, untrained = 3.46 ± 1.8 pg/mL vs. trained = 2.66 ± 1.3 pg/mL, P = 0.047) or both training and age (irisin, P = 0.04; leukemia inhibitory factor, P < 0.001). As well, changes in strength per kg of fat free mass were correlated with area under the curve for IL-4 (r = 0.537; P = 0.039), IL-6 (r = 0. 525; P = 0.044) and LIF (r = − 0.548; P = 0.035) in the untrained condition. Conclusion This study identified that both age and training status influence the myokine response to an acute bout of BFR-RE with the release of IL-4, IL-6 and LIF in the untrained state being associated with changes in strength per kg of fat free mass.
The hormonal milieu of the testis was examined in streptozocin-induced diabetic (STZ-D) adult mal... more The hormonal milieu of the testis was examined in streptozocin-induced diabetic (STZ-D) adult male Wistar and Long-Evans rats. Serum testosterone, creatinine, and urea nitrogen (BUN) levels and blood glucose concentrations were determined in diabetic and control Wistar rats (experiment 1). These parameters plus luteinizing hormone (LH) and folliclestimulating hormone (FSH) levels were studied in experiments 2 and 3 with Long-Evans rats in untreated diabetic, control, insulin-treated diabetic, nondiabetic STZ-injected, and semistarved groups. Wistar diabetic rats had significantly decreased serum testosterone and increased blood glucose, BUN, and serum creatinine compared with controls. Several findings in Long-Evans rats suggested the existence of a primary Leydig cell defect in steroidogenesis during untreated diabetes that was completely or partially compensated for by increased pituitary gonadotropin secretion. Serum LH and FSH levels increased in Long-Evans diabetic rats. Serum testosterone was significantly reduced only in experiment 2. These hormonal alterations from control levels were not seen in insulin-treated diabetic animals. Semistarved animals, weight matched to the diabetic group in experiment 2, had significantly decreased serum testosterone and increased FSH levels. In addition, Long-Evans diabetic rat BUN and serum creatinine levels increased much less or were unchanged from control values compared with the increase noted in diabetic Wistar rats. In light of the hypogonadism that complicates clinical uremia, these findings suggest the more apt use of the Long-Evans strain rather than the Wistar strain in the study of STZ-D hypogonadal function. Indices to evaluate
Background: Knee osteoarthritis (OA) is the most prevalent medical condition in individuals over ... more Background: Knee osteoarthritis (OA) is the most prevalent medical condition in individuals over the age of 65 years, and is a progressive joint degenerative condition with no known cure. Research suggests that there is a strong relationship between knee pain and loss of physical function. The resulting lifestyle modifications negatively impact not only disease onset and progression but also overall health, work productivity, and quality of life of the affected individual. Purpose: The goal of this investigation was to examine the feasibility of using an emerging technology called lower body positive pressure (LBPP) to simulate weight loss and reduce acute knee pain during treadmill walking exercise in overweight individuals with radiographically confirmed symptomatic knee OA. Design: Prospective case series. Methods: Twenty-two overweight individuals with knee OA completed two 20-minute treadmill walking sessions (one full weight bearing and one LBPP supported) at a speed of 3.1 mph, 0% incline. Acute knee pain was assessed using a visual analog scale, and the percentage of LBPP support required to minimize knee pain was evaluated every 5 minutes. Knee Osteoarthritis Outcome Scores were used to quantify knee pain and functional status between walking sessions. The order of testing was randomized, with sessions occurring a minimum of 1 week apart. Results: A mean LBPP of 12.4% of body weight provided participants with significant pain relief during walking, and prevented exacerbation of acute knee pain over the duration of the 20-minute exercise session. Patients felt safe and confident walking with LBPP support on the treadmill, and demonstrated no change in Knee Osteoarthritis Outcome Scores over the duration of the investigation. Conclusion: Results suggest that LBPP technology can be used safely and effectively to simulate weight loss and reduce acute knee pain during weight-bearing exercise in an overweight knee OA patient population. These results could have important implications for the development of future treatment strategies used in the management of at-risk patients with progressive knee OA.
Terminal Schwann cells (TSCs) help regulate the formation, maintenance, function, and repair of n... more Terminal Schwann cells (TSCs) help regulate the formation, maintenance, function, and repair of neuromuscular junctions (NMJs) and axon guidance after muscle injury. Premature activation of muscle satellite cells (SCs), induced by isosorbide dinitrate (ISDN) before injury, accelerates myogenic regeneration, disrupts NMJ remodeling and maturation, decreases Sema3A protein-induced neuro-repulsion, and is accompanied by time-dependent changes in S100B protein levels. Here, to study the effects of premature SC activation on TSCs and SCs, both expressing P75 nerve growth-factor receptor, in situ hybridization was used to identify transcripts of S100B and Sema3A, and the number, intensity, and diameter of expression sites were analyzed. The number of sites/fields expressing S100B and Sema3A increased with regeneration time (both p < 0.001). Expression-site intensity (S100B) and diameter (S100B and Sema3A) decreased during regeneration (p = 0.005; p < 0.05, p = 0.006, respectively). ...
International Journal of Sports Physical Therapy, 2021
Background Adolescent females are at significant risk for sustaining an ACL injury. The Y-Balance... more Background Adolescent females are at significant risk for sustaining an ACL injury. The Y-Balance Test (YBT) is frequently used to evaluate neuromuscular control and lower extremity function. However, few studies have quantified 2D lower extremity kinematics during performance of the YBT, and there is an absence of kinematic data specific to at-risk adolescent females. Purpose To examine lower extremity joint kinematics during execution of the YBT by healthy and ACL-injured adolescent females. Study Design Prospective cohort. Methods Twenty-five healthy and ten ACL-injured (mean time from injury 143 days) adolescent females were assessed using the YBT. Sagittal and frontal plane knee and ankle motion was video recorded during execution of the YBT anterior reach movement. Ankle dorsi-flexion, knee flexion, and knee valgus angles were quantified via kinematic analysis. ANOVAs with a post hoc Bonferroni correction were used to compare YBT scoring (%LL) and kinematic data between groups...
Journal of pharmacy & pharmaceutical sciences : a publication of the Canadian Society for Pharmaceutical Sciences, Societe canadienne des sciences pharmaceutiques, 2018
MyoNovin is a novel skeletal muscle-regenerating compound developed through synthesis of two nitr... more MyoNovin is a novel skeletal muscle-regenerating compound developed through synthesis of two nitro groups onto a guaifenesin backbone to deliver nitric oxide to skeletal muscle with a potential to treat muscle atrophy. The purpose of this study was to utilize in silico, in vitro, and in vivo approaches to characterize MyoNovin and examine its safety, biodistribution, and feasibility for drug delivery. In silico software packages were used to predict the physicochemical and biopharmaceutical properties of MyoNovin. In vitro cardiotoxicity was assessed using human cardiomyocytes (RL-14) while effects on CYP3A4 metabolic enzyme and antioxidant activity were examined using commercial kits. A novel HPLC assay was developed to measure MyoNovin concentration in serum, and delineate initial pharmacokinetic and acute toxicity after intravenous administration (20 mg/kg) to male Sprague-Dawley rats. MyoNovin showed relatively high lipophilicity with a LogP value of 3.49, a 20-fold higher skin ...
Deflazacort slows the progress of Duchenne muscular dystrophy (DMD) with fewer side effects than ... more Deflazacort slows the progress of Duchenne muscular dystrophy (DMD) with fewer side effects than prednisone. In mdx mice, deflazacort treatment augments repair and growth of new muscle fibers. We tested the hypothesis that deflazacort improves muscle function and promotes repair by increasing myogenic cell proliferation and fiber differentiation. mdx mice (3.5 weeks old) were treated with deflazacort (1.2 mg/kg) or vehicle for 4 weeks. Forelimb grip strength was measured. After 4 weeks, the right tibialis anterior muscle (TA) was crush injured to induce synchronous regeneration. DNA was labeled using different markers 24 and 2 h before collecting tissues 4 days after injury. The expression of creatine kinase (CK) isoforms, laminin-2 (merosin) mRNA and protein, and proliferation by myogenic cells were measured and satellite cells were identified by immunolocalization of c-met receptor. Peak grip strength increased 15% within 10 days of treatment, and was maintained up to 6 weeks afte...
Recently, we found that resident myogenic stem satellite cells upregulate a multi-functional secr... more Recently, we found that resident myogenic stem satellite cells upregulate a multi-functional secreted protein, semaphorin 3A (Sema3A), exclusively at the early-differentiation phase in response to muscle injury; however, its physiological significance is still unknown. Here we show that Sema3A impacts slow-twitch fiber generation through a signaling pathway, cell-membrane receptor (neuropilin2-plexinA3) → myogenin-myocyte enhancer factor 2D → slow myosin heavy chain. This novel axis was found by small interfering RNA-transfection experiments in myoblast cultures, which also revealed an additional element that Sema3A-neuropilin1/plexinA1, A2 may enhance slow-fiber formation by activating signals that inhibit fast-myosin expression. Importantly, satellite cell-specific Sema3A conditional-knockout adult mice (Pax7CreER(T2) -Sema3A(fl) °(x) activated by tamoxifen-i.p. injection) provided direct in vivo evidence for the Sema3A-driven program, by showing that slow-fiber generation and mus...
Regenerative mechanisms that regulate intramuscular motor innervation are thought to reside in th... more Regenerative mechanisms that regulate intramuscular motor innervation are thought to reside in the spatiotemporal expression of axon-guidance molecules. Our previous studies proposed an unexplored role of resident myogenic stem cell (satellite cell)-derived myoblasts as a key presenter of a secreted neural chemorepellent semaphorin 3A (Sema3A); hepatocyte growth factor (HGF) and basic fibroblast growth factor (FGF2) triggered its expression exclusively at the early differentiation phase. In order to advance this concept, the present study described that transmembrane heparan/chondroitin sulfate proteoglycans syndecan-2, 4 may be the plausible receptor candidates for HGF and FGF2 to signal Sema3A expression. Results showed that mRNA expression of syndecan-2, 4 was abundant (two magnitudes higher than syndecan-1, 3) in early-differentiated myoblasts and their in vitro knockdown diminished the HGF/FGF2-induced expression of Sema3A down to a baseline level. Pretreatment with heparitinas...
This study coupled proton magnetic resonance spectroscopy (1 H-NMR) and in situ hybridization plu... more This study coupled proton magnetic resonance spectroscopy (1 H-NMR) and in situ hybridization plus autoradiography in a novel examination of different phenotypes of adult myogenesis that arise from genetic disruptions in mice. Study of muscle extracts from normal and dystrophin-deficient mdx limb and diaphragm muscles confirmed our previous findings linking taurine and muscle regeneration at the peak of damage and repair. 1 H-NMR distinguished biochemical differences in regenerating muscles that were consistent with the extent of repair in three strains: mdx dystrophic mice; MyoD(-/-) mice that lack expression of the early myogenic regulatory gene MyoD; and a double-mutant mdx:MyoD(-/-) strain lacking expression of both MyoD and dystrophin. We tested the hypothesis that differences in spectra according to genotype and the regeneration phenotype are related specifically to proliferation by committed myogenic precursor cells. 1 H-NMR distinguished the three mutant strains: Taurine was highest in mdx muscles, with the phenotype of most effective regeneration; lowest in MyoD(-/-) muscles, with the least effective formation of new muscle in repair, as reported previously; and intermediate in double-mutant muscles, now reported to show an intermediate repair phenotype. The early and late muscle precursors (mpcs) expressing myf5 and myogenin were examined for proliferation. Eighteen percent of mdx myf5-positive mpcs were proliferative, whereas myf5-positive mpcs did not proliferate in regenerating muscles that lacked MyoD expression. By contrast, whereas 30% of myogenin-positive mpcs were proliferative in mdx muscles, almost none were proliferative in MyoD(-/-) muscles, and 12% were proliferative in double-mutant muscles. Therefore, the extent of accumulated structural regeneration, taurine levels, and proliferation of late mpc (expressing myogenin) were congruent across genotypes. Proliferation by early mpc (expressing myf5) was inhibited by the lack of MyoD expression during muscle regeneration. These studies indicate the potential for 1 H-NMR monitoring of muscle status in disease, regenera
Application of mechanical stretch to cultured adult rat muscle satellite cells results in release... more Application of mechanical stretch to cultured adult rat muscle satellite cells results in release of hepatocyte growth factor (HGF) and accelerated entry into the cell cycle. Stretch activation of cultured rat muscle satellite cells was observed only when medium pH was between 7.1 and 7.5, even though activation of satellite cells was accelerated by exogenous HGF over a pH range from 6.9 to 7.8. Furthermore, HGF was only released in stretched cultures when the pH of the medium was between 7.1 and 7.4. Conditioned medium from stretched satellite cell cultures stimulated activation of unstretched satellite cells, and the addition of anti-HGF neutralizing antibodies to stretch-conditioned medium inhibited the stretch activation response. Conditioned medium from satellite cells that were stretched in the presence of nitric-oxide synthase (NOS) inhibitorNω-nitro-l-arginine methyl ester hydrochloride did not accelerate activation of unstretched control satellite cells, and HGF was not rel...
Satellite cells from adult rat muscle coexpress proliferating cell nuclear antigen and MyoD upon ... more Satellite cells from adult rat muscle coexpress proliferating cell nuclear antigen and MyoD upon entry into the cell cycle, suggesting that MyoD plays a role during the recruitment of satellite cells. Moreover, the finding that muscle regeneration is compromised in MyoD−/− mice, has provided evidence for the role of MyoD during myogenesis in adult muscle. In order to gain further insight into the role of MyoD during myogenesis in the adult, we compared satellite cells from MyoD−/− and wildtype mice as they progress through myogenesis in single-myofiber cultures and in tissuedissociated cell cultures (primary cultures). Satellite cells undergoing proliferation and differentiation were traced immunohistochemically using antibodies against various regulatory proteins. In addition, an antibody against the mitogen-activated protein kinases ERK1 and ERK2 was used to localize the cytoplasm of the fiber-associated satellite cells regardless of their ability to express specific myogenic regulatory factor proteins. We show that during the initial days in culture the myofibers isolated from both the MyoD−/− and the wildtype mice contain the same number of proliferating, ERK+ satellite cells. However, the MyoD−/− satellite cells continue to proliferate and only a very small number of cells transit into the myogenin+ state, whereas the wildtype cells exit the proliferative compartment and enter the myogenin+ stage. Analyzing tissuedissociated cultures of MyoD−/− satellite cells, we identified numerous cells whose nuclei were positive for the Myf5 protein. In contrast, quantification of Myf5+ cells in the wildtype cultures was difficult due to the low level of Myf5 protein present. The Myf5+ cells in the MyoD−/− cultures were often positive for desmin, similar to the MyoD+ cells in the wildtype cultures. Myogenin+ cells were identified in the MyoD−/− primary cultures, but their appearance was delayed compared to the wildtype cells. These "delayed" myogenin+ cells can express other differentiation markers such as MEF2A and cyclin D3 and fuse into myotubes. Taken together, our studies suggest that the presence of MyoD is critical for the normal progression of satellite cells
American Journal of Physiology-Cell Physiology, 2011
Successful regeneration and remodeling of the intramuscular motoneuron network and neuromuscular ... more Successful regeneration and remodeling of the intramuscular motoneuron network and neuromuscular connections are critical for restoring skeletal muscle function and physiological properties. The regulatory signals of such coordination remain unclear, although axon-guidance molecules may be involved. Recently, satellite cells, resident myogenic stem cells positioned beneath the basal lamina and at high density at the myoneural junction regions of mature fibers, were shown to upregulate a secreted neural chemorepellent semaphorin 3A (Sema3A) in response to in vivo muscle-crush injury. The initial report on that expression centered on the observation that hepatocyte growth factor (HGF), an essential cue in muscle fiber growth and regeneration, remarkably upregulates Sema3A expression in early differentiated satellite cells in vitro [Tatsumi et al., Am J Physiol Cell Physiol 297: C238–C252, 2009]. Here, we address regulatory effects of basic fibroblast growth factor (FGF2) and transform...
American Journal of Physiology-Cell Physiology, 2009
Regenerative coordination and remodeling of the intramuscular motoneuron network and neuromuscula... more Regenerative coordination and remodeling of the intramuscular motoneuron network and neuromuscular connections are critical for restoring skeletal muscle function and physiological properties. The regulatory mechanisms of such coordination remain unclear, although both attractive and repulsive axon guidance molecules may be involved in the signaling pathway. Here we show that expression of a neural secreted chemorepellent semaphorin 3A (Sema3A) is remarkably upregulated in satellite cells of resident myogenic stem cells that are positioned beneath the basal lamina of mature muscle fibers, when treated with hepatocyte growth factor (HGF), established as an essential cue in muscle fiber growth and regeneration. When satellite cells were treated with HGF in primary cultures of cells or muscle fibers, Sema3A message and protein were upregulated as revealed by reverse transcription-polymerase chain reaction and immunochemical studies. Other growth factors had no inductive effect except f...
Although an increase in nitric oxide (NO) in muscle is reported to improve the outcome of deflaza... more Although an increase in nitric oxide (NO) in muscle is reported to improve the outcome of deflazacort treatment for mdx mouse muscular dystrophy, the genetic homologue of Duchenne muscular dystrophy (DMD), the impact such treatment on the functional outcomes of the disease, including fiber susceptibility to exercise-induced injury, is not established. Experiments were designed to test whether treatment with deflazacort and L-arginine (a substrate for NO synthase, NOS) would change the extent of fiber injury induced by 24 h of voluntary exercise. The impact of exercise-related injury to induce a secondary regenerative response by muscle was also examined as corroborating evidence of muscle damage. Dystrophic mdx mice were treated for 3 wk with placebo, deflazacort, or deflazacort plus either L-arginine or N G-nitro-L-arginine methyl ester (a NOS inhibitor). Deflazacort, especially combined with L-arginine, spared quadriceps muscle from injury-induced regeneration (myf5 expression) compared with placebo treatment, despite an increase in membrane permeability immediately after exercise (assessed by Evans blue dye infiltration). Deflazacort alone prevented the typical progressive loss of function (measured as voluntary distance run over 24 h) that was observed 3 months later in placebotreated mice. Therefore, combined deflazacort plus L-arginine treatment spared mdx dystrophic limb muscle from exercise-induced damage and the need for regeneration and induced a persistent functional improvement in distance run. Results suggest a potential new treatment option for improving the quality of life for boys with DMD. Key words: nitric oxide • myf5 • exercise • utrophin • muscle regeneration he absence of dystrophin from skeletal muscle increases the susceptibility to exerciseinduced fiber damage (1-6). This susceptibility is one of the hallmark signs of dysfunction in muscular dystrophy in mdx mice, the genetic homologue of human Duchenne muscular dystrophy (DMD). Despite significant capacity for muscle regeneration in the mdx mouse, dystrophin deficiency leads to fiber weakness, muscle fiber loss, muscle fibrosis, and early death in both mice and humans (7-9). Although much less severe than DMD, parallels between mdx mouse and human muscular dystrophies demonstrate that the mouse is a strong model for investigating the pathophysiology of dystrophy and the structure-function relationship of the dystrophin-associated dystroglycan complex (DGC). The model is also effective in T
Satellite cells, muscle precursor cells in skeletal muscle, are normally quiescent and become act... more Satellite cells, muscle precursor cells in skeletal muscle, are normally quiescent and become activated by disease or injury. A lack of dystrophin and changes in the expression or activity of neuronal nitric oxide synthase (NOS-I) affect the timing of activation in vivo. Nitric oxide synthase inhibition delays muscle repair in normal mice, and worsens muscular dystrophy in the mdx mouse, a genetic homologue of Duchenne muscular dystrophy. However, the potential role of activation and repair events mediated by nitric oxide in determining the outcome of steroid or other treatments for muscular dystrophy is not clear. We tested the hypothesis that the extent of repair in dystrophic muscles of mdx mice is partly dependent on NOS-Im expression and activity. Myotube formation in regenerating muscle was promoted by deflazacort treatment of mdx dystrophic mice (P , 0:05), and improved by combination with the nitric oxide synthase substrate, L-arginine, especially in the diaphragm. NOS-Im mRNA expression and activity were present in satellite cells and very new myotubes of regenerating and dystrophic muscle. Deflazacort treatment resulted in increased NOS-Im expression in regenerating muscles in a strong and specific correlation with myf5 expression (r ¼ 0:95, P , 0:01), a marker for muscle repair. Nitric oxide synthase inhibition prevented the deflazacort-induced rise in NOS-Im and myf5 expression in the diaphragm without affecting the diameter of non-regenerating fibres. These in vivo studies suggest that gains in NOS-Im expression and nitric oxide synthase activity in satellite cells can increase the extent and speed of repair, even in the absence of dystrophin in muscle fibres. NOS-Im may be a useful therapeutic target to augment the effects of steroidal or other treatments of muscular dystrophy.
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