Fine-needle percutaneous muscle microbiopsy technique as a feasible tool to address histological analysis in young children with cerebral palsy and age-matched typically developing children.

Cerebral palsy (CP) is a heterogeneous group of motor disorders attributed to a non-progressive lesion in the developing brain. Knowledge on skeletal muscle properties is important to understand the impact of CP and treatment but data at the microscopic levels are limited and inconsistent. Currently, muscle biopsies are collected during surgery and are restricted to CP eligible for such treatment or they may refer to another muscle or older children in typically developing (TD) biopsies. A minimally invasive technique to collect (repeated) muscle biopsies in young CP and TD children is needed to provide insights into the early muscle microscopic alterations and their evolution in CP. This paper describes the protocol used to 1) collect microbiopsies of the medial gastrocnemius (MG) and semitendinosus (ST) in CP children and age-matched TD children, 2) handle the biopsies for histology, 3) stain the biopsies to address muscle structure (Hematoxylin & Eosin), fiber size and proportion (myosin heavy chain), counting of the satellite cells (Pax7) and capillaries (CD31). Technique feasibility and safety as well as staining feasibility and measure accuracy were evaluated. Two microbiopsies per muscle were collected in 56 CP (5.8±1.1 yr) and 32 TD (6±1.1 yr) children using ultrasound-guided percutaneous microbiopsy technique. The biopsy procedure was safe (absence of complications) and well tolerated (Score pain using Wong-Baker faces). Cross-sectionally orientated fibers were found in 86% (CP) and 92% (TD) of the biopsies with 60% (CP) and 85% (TD) containing more than 150 fibers. Fiber staining was successful in all MG biopsies but failed in 30% (CP) and 16% (TD) of the ST biopsies. Satellite cell staining was successful in 89% (CP) and 85% (TD) for MG and in 70% (CP) and 90% (TD) for ST biopsies, while capillary staining was successful in 88% (CP) and 100% (TD) of the MG and in 86% (CP) and 90% (TD) for the ST biopsies. Intraclass coefficient correlation showed reliable and reproducible measures of all outcomes. This study shows that the percutaneous microbiopsy technique is a safe and feasible tool to collect (repeated) muscle biopsies in young CP and TD children for histological analysis and it provides sufficient muscle tissue of good quality for reliable quantification.

Observations of nemaline bodies in muscle biopsies of critically ill patients infected with SARS-CoV-2.

Patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) who have been admitted to the intensive care unit (ICU) often face months of physical disability after discharge. To optimize recovery, it is important to understand the role of musculoskeletal alterations in critically ill patients infected with SARS-CoV-2. The main aim of the present study was to describe the presence and morphology of nemaline bodies found in the skeletal muscle tissue from critically ill patients infected with SARS-CoV-2. In n = 7 patients infected with SARS-CoV-2, ultrastructural characteristics of vastus lateralis muscle obtained on days 1-3 and days 5-8 following ICU admission were investigated in more detail with electron microscopy. Those muscle biopsies consistently showed variable degrees of myofiber necrosis and myofibrillar disorganization. In 4/7 (57%) patients on days 5-8, the Z-line material accumulated into nemaline bodies with a typical lattice-like appearance at higher magnification, similar to that found in nemaline myopathy. This study is the first to describe the disintegration of myofibrils and the accumulation of Z-line material into nemaline bodies in the skeletal muscle tissue obtained from critically ill coronavirus disease-19 patients following ICU admission, which should be interpreted primarily as a non-specific pathological response of extreme myofibrillar disintegration associated with myofiber necrosis.

The Role of Skeletal Muscle Mitochondria in Colorectal Cancer Related Cachexia: Friends or Foes?

Up to 60% of colorectal cancer (CRC) patients develop cachexia. The presence of CRC related cachexia is associated with more adverse events during systemic therapy, leading to a high mortality rate. The main manifestation in CRC related cachexia is the loss of skeletal muscle mass, resulting from an imbalance between skeletal muscle protein synthesis and protein degradation. In CRC related cachexia, systemic inflammation, oxidative stress, and proteolytic systems lead to mitochondrial dysfunction, resulting in an imbalanced skeletal muscle metabolism. Mitochondria fulfill an important function in muscle maintenance. Thus, preservation of the skeletal muscle mitochondrial homeostasis may contribute to prevent the loss of muscle mass. However, it remains elusive whether mitochondria play a benign or malignant role in the development of cancer cachexia. This review summarizes current (mostly preclinical) evidence about the role of skeletal muscle mitochondria in the development of CRC related cachexia. Future human research is necessary to determine the physiological role of skeletal muscle mitochondria in the development of human CRC related cachexia.

Efficacy of 12 weeks oral beta-alanine supplementation in patients with chronic obstructive pulmonary disease: a double-blind, randomized, placebo-controlled trial.

BACKGROUND: Beta-alanine (BA) supplementation increases muscle carnosine, an abundant endogenous antioxidant and pH buffer in skeletal muscle. Carnosine loading promotes exercise capacity in healthy older adults. As patients with chronic obstructive pulmonary disease (COPD) suffer from elevated exercise-induced muscle oxidative/carbonyl stress and acidosis, and from reduced muscle carnosine stores, it was investigated whether BA supplementation augments muscle carnosine and induces beneficial changes in exercise capacity, quadriceps function, and muscle oxidative/carbonyl stress in patients with COPD. METHODS: In this double-blind, randomized, placebo (PL)-controlled trial (clinicaltrials.gov identifier: NCT02770417), 40 patients (75% male) with COPD (mean ± standard deviation: age 65 ± 6 years; FEV1 % predicted 55 ± 14%) were assigned to 12 weeks oral BA or PL supplementation (3.2 g/day). The primary outcome, i.e. muscle carnosine, was quantified from m. vastus lateralis biopsies obtained before and after intervention. Co-primary outcomes, i.e. incremental and constant work rate cycle capacity, were also assessed. Linear mixed model analyses were performed. Compliance with and side effects of supplement intake and secondary outcomes (quadriceps strength and endurance, and muscle oxidative/carbonyl stress) were also assessed. RESULTS: Beta-alanine supplementation increased muscle carnosine in comparison with PL in patients with COPD (mean difference [95% confidence interval]; +2.82 [1.49-4.14] mmol/kg wet weight; P < 0.001). Maximal incremental cycling capacity (VO2 peak: +0.5 [-0.7 to 1.7] mL/kg/min; P = 0.384, Wpeak: +5 [-1 to 11] W; P = 0.103) and time to exhaustion on the constant work rate cycle test (+28 [-179 to 236] s; P = 0.782) did not change significantly. Compliance with supplement intake was similar in BA (median (quartile 1-quartile 3); 100 (98-100)%) and PL (98 (96-100)%) (P = 0.294) groups, and patients did not report side effects possibly related to supplement intake. No change was observed in secondary outcomes. CONCLUSIONS: Beta-alanine supplementation is efficacious in augmenting muscle carnosine (+54% from mean baseline value) without side effects in patients with COPD in comparison with PL. However, accompanied beneficial changes in exercise capacity, quadriceps function, and muscle oxidative/carbonyl stress were not observed.

Extra-Articular Impingement at the Anterior Inferior Iliac Spine: A Cause of Refractory Periarticular Pain After Total Hip Arthroplasty.

BACKGROUND: Periarticular pain after total hip arthroplasty (THA) can significantly impair the postoperative functionality. Extra-articular impingement between the greater trochanter and the anterior inferior iliac spine is presented as a cause of refractive pain after THA. METHODS: Twenty patients were treated for refractive periarticular pain and limited internal rotation between January 2014 and April 2016. All patients underwent a positive chair rise test, pelvic inclination test, and Marcainisation test. Patients were treated with bone resection of the anterior part of the greater trochanter with or without component revision. RESULTS: At a mean follow-up of 20 months, all functional outcomes had improved significantly. All patients were willing to undergo the surgery again. Sixteen (80%) indicated the result as very good, 3 (15%) as good, and one (5%) as poor. Two patients developed a postoperative heterotopic ossification that required resection. CONCLUSIONS: Extra-articular impingement should be considered as a possible cause of refractive groin pain after THA. Bony resection through the Hueter interval provides immediate pain relief with improved functional outcomes 1 year after surgery.

Gluteus Maximus Transfer as an Augmentation Technique for Patients With Severe Abductor Deficiency of the Hip.

Impaired abductor function of the hip following severe abductor deficiencies can be devastating for functionality and quality of life. Recently, gluteus maximus transfer has been proposed as a solution to these difficult problems. However, outcome results are sparse. The aim of this study was to evaluate the effects of gluteus maximus transfer on improvement of pain, disability, and quality of life in patients with severe hip abductor deficiencies. Gluteus maximus transfer was performed in 16 patients with severe disruption of the abductor muscles of the hip. Data were collected preoperatively and at 6 weeks, 3 and 6 months, and 1 to 2 years after surgery. The measurements pertained to complications, healing of the flap based on magnetic resonance imaging (MRI) findings (in 10 patients), evaluation of Trendelenburg gait and sign, and patient-reported outcome measures of pain, disability, and quality of life. Preoperatively, all patients had a positive Trendelenburg sign and reported severe pain at the level of the greater trochanter. At a mean follow-up of 20 months, the Trendelenburg sign was negative in 7 patients and the Trendelenburg gait had disappeared in 7 patients. There was an improvement in patient-reported outcome measures but not to a significant level except for the pain subscores. Two patients had a postoperative seroma that resulted in a visible bump on the lateral side. Seven of 10 repairs with MRI follow-up showed perfect ingrowth on MRI without signs of rerupture. Gluteus maximus transfer for abductor deficiency of the hip may be effective for pain relief and functional improvements. Most patients showed an improved quality of life but were not completely pain free. [Orthopedics. 2020;43(4):e299-e305.].

The effect of anti-gravity training after meniscal or chondral injury in the knee. A systematic review.

Reduced impact loading or anti-gravity training has recently been introduced as a new tool in the rehabilitation of orthopaedic conditions that require restricted weight bearing. The purpose of this strategy is to speed up the functional rehabilitation while at the same time protect the healing structures from harmful effects associated with impact loading. Anti- gravity treadmills (AlterG ® ) and harness suspension devices seem to be the two most promising techniques. It is however today unclear how effective these devices are. The purpose of our study was therefore to perform a systematic literature review on the actual technology available and its effect on impact load reduction, as well as its effectiveness in accelerating functional recovery after meniscal and chondral injury to the knee. The results from our work demonstrate that only a limited number of studies are available, usually of moderate quality. The data suggest a variable effect on cartilage regeneration, and a potential for accelerated functional recovery in gait and running dynamics both with anti-gravity treadmill as well as suspension harness systems.

Biopsy samples from the erector spinae of persons with nonspecific chronic low back pain display a decrease in glycolytic muscle fibers.

BACKGROUND CONTEXT: Low back pain (LBP) in Western Europe was classified as having the highest disability and overall burden among 291 studied conditions. For an extensive period of time, evidence related to morphological changes (eg, atrophy and fat infiltration) of the paraspinal muscles in persons with LBP has accumulated. Despite this evidence, there is limited knowledge on muscle fiber type composition of these muscles, and their relation to LBP. PURPOSE: The aim of the study is to investigate differences in muscle fiber type composition between persons with nonspecific chronic low back pain (NSCLBP) and healthy controls for the lumbar erector spinae (ES) and multifidus (MF) muscle. STUDY DESIGN AND SETTING: A cross-sectional study took place in the REVAL Rehabilitation Research Center, Hasselt University, Diepenbeek, Belgium. PATIENT SAMPLE: Twenty persons with NSCLBP (age: 44.5±7.42) and 18 healthy controls (age: 39.89±7.90) participated in this study. OUTCOME MEASURES: The primary outcome measure was paraspinal muscle fiber type composition. Secondary outcomes consisted of physiologic measures (maximal aerobic capacity and back muscle strength) and functional measures (activity level). METHODS: Biopsy samples were taken from the lumbar ES and MF muscle at the L4 spinal level. These samples were stained using immunofluorescent antibodies against myosin heavy chains. In each sample, number and size (CSA) of type I, I/IIa, IIa, IIa/x, and IIx muscle fibers were quantified. From these data the relative cross-sectional fiber areas (RCSA) were calculated. To analyze differences in fiber type composition between healthy persons and persons with NSCLBP, a repeated measurements analysis of variance was used. Secondary outcome measures were analyzed using a Student's t test, and Wilcoxon test. This study was supported by the research fund of Hasselt University without potential conflict of interest. RESULTS: There were no significant differences between both groups regarding anthropometric data. There were no significant between group differences for CSA in the ES. Persons with NSCLBP displayed a nonsignificant (p=.0978) increase in the number of type I muscle fibers, and a significant decrease (p=.0019) in the number of type IIx muscle fibers in the ES muscle. Persons with NSCLBP also displayed a trend toward a higher (p=.0596) RCSA for type I fibers and a significantly lower RCSA for type IIx fibers (p=.0411). There were no significant between group differences within the MF. Regarding the secondary outcome measures, there was a significant between group difference in activity level (p=.0004) and isokinetic back muscle strength (p=.0342). CONCLUSIONS: This is the first study to examine muscle fiber type characteristics in both the ES and MF muscle of persons with NSCLBP. Based on muscle fiber characteristics, the paraspinal muscles of persons with NSCLBP seems to display a larger oxidative potential based on an increase of the number type I fibers at the expense of type IIx glycolytic fibers.

Chondroid metaplasia of paraspinal connective tissue in the degenerative spine.

A 51-year-old male was routinely biopsied during a paraspinal muscle study. The biopsy sample was taken from the right erector spinae muscle at the fourth lumbar vertebra. The patient had no history of (diagnosed) major back trauma. The obtained sample was histologically analyzed (hematoxylin and eosin, safranin O), and complementary magnetic resonance imaging was performed. The biopsied sample contained chondroid tissue. Based on its location, the biopsy sample was appointed as chondroid metaplasia. Although chondroid metaplasia is not uncommon in humans, this is the first report of chondroid metaplasia within the paraspinal connective tissue. We propose a novel mechanism to explain the paraspinal chrondrogenic changes, related to spinal degeneration.

Feasibility, accuracy and safety of a percutaneous fine-needle biopsy technique to obtain qualitative muscle samples of the lumbar multifidus and erector spinae muscle in persons with low back pain.

The lumbar muscular system, in particular the lumbar multifidus muscle (LM) and the erector spinae muscle (ES), plays an important role in stabilizing and mobilizing the lumbar spine. Based on the topography, the lumbar paraspinal muscles can be classified into local and global muscles. LM is part of the local system, whereas ES is part of the global system. Therefore, it is interesting to investigate the muscle fibre type composition in both muscles. There is accumulating evidence that nonspecific chronic low back pain is associated with lumbar muscle dysfunction. To further elucidate this lumbar paraspinal muscle dysfunction, it is important to understand the structural characteristics of individual muscle fibres of LM and ES. Muscle fibre type composition can be investigated in muscle tissue samples. So far, muscle samples are taken by using invasive procedures that are not well tolerated. The aim of this article was to evaluate the feasibility, accuracy and safety of a percutaneous fine-needle biopsy technique to obtain muscle samples from LM and ES in persons with nonspecific chronic low back pain and to evaluate the feasibility of performing immunofluorescence analysis of myosin heavy chain isoform expression to investigate muscle fibre type composition. Preliminary investigations in cadavers were performed to determine the optimal vertebral level and puncture site to obtain muscle samples of LM and ES through a single skin puncture. In 15 persons with nonspecific chronic low back pain, muscle samples of LM and ES were taken under local anaesthesia with the percutaneous fine-needle biopsy technique, preceded by determination of the puncture site with ultrasonography. Muscle fibre type composition was investigated using immunofluorescence analysis of myosin heavy chain expression. The subjects reported little or no pain and were willing to repeat the procedure. The obtained muscle tissue contained transverse-sectioned muscle fibres in which muscle fibre contractile characteristics of the paraspinal muscles could be evaluated with immunofluorescence analysis of the myosin heavy chains. We can conclude that percutaneous microbiopsy appears to be feasible and accurate, and safe to use to obtain muscle tissue from the paraspinal muscles. The use of ultrasonography to determine the puncture site is necessary to ensure biopsy of the correct muscles and to ensure the safety of the procedure.

High Intensity Aerobic and Resistance Exercise Can Improve Glucose Tolerance in Persons With Multiple Sclerosis: A Randomized Controlled Trial.

INTRODUCTION: The prevalence of impaired glucose tolerance (IGT) is higher in persons with multiple sclerosis (MS) compared to healthy controls, indicating metabolic deficits that may increase comorbidity. In other populations, IGT can, at least partly, be reversed by intense physical exercise, but this is never investigated before in MS. AIM: To investigate the effect of high intensity aerobic and resistance training on glucose tolerance and skeletal muscle GLUT4 content in MS. METHODS: Thirty-four persons with MS (aged 45 ± 3 years, EDSS 2.5 ± 1.07) were randomized into three groups, including a (1) sedentary control group (SED, n = 11), (2) 12-week high intensity interval plus resistance training group (HITR, n = 12), or (3) 12-week high intensity continuous aerobic training plus resistance training group (HCTR, n = 11). Before and after 12 weeks, glucose tolerance and skeletal muscle GLUT4 content were determined by an oral glucose tolerance test and analysis of a m.vastus lateralis biopsy, respectively. RESULTS: There were no significant changes for subjects of SED. From pre- to post-intervention, total area under the glucose curve (tAUC) decreased significantly in both HITR (-6.9 ± 6.2%) and HCTR (-11.0 ± 7.7%) (P < 0.05). Insulin tAUC decreased (-12.3 ± 14.7%) within HCTR and muscle GLUT4 content increased (+6.6 ± 4.5%) in HITR. CONCLUSION: Twelve weeks of high intensity aerobic exercise in combination with resistance training improved glucose tolerance in persons with MS.

Altered signaling for mitochondrial and myofibrillar biogenesis in skeletal muscles of patients with multiple sclerosis.

Patients with multiple sclerosis (pwMS) experience muscle weakness and lowered muscle oxidative capacity. To explore the etiology for the development of such muscle phenotype we studied skeletal muscle adenosine monophosphate (AMP)-activated protein kinase phosphorylation (phospho-AMPKα, governing mitochondrial biogenesis) and mammalian target of rapamycin phosphorylation (phospho-mTOR, governing myofibrillar biogenesis) in pwMS. After assessment of body composition, muscle strength, exercise tolerance, and muscle fiber type, muscle phospho-AMPKα and phospho-mTOR were assessed in 14 pwMS and 10 healthy controls (part 1). Next, an endurance exercise bout was executed by 9 pwMS and 7 healthy subjects, with assessment of changes in muscle phospho-AMPKα and phospho-mTOR (part 2). Increased basal muscle phospho-AMPKα and phospho-mTOR were present in MS (P < 0.01) and independently related to MS. Correlations between muscle phospho-AMPKα or phospho-mTOR and whole-body fat mass, peak oxygen uptake, and expanded disability status scale (P < 0.05) were found. After endurance exercise muscle phospho-AMPKα and phospho-mTOR remained increased in pwMS (P < 0.01). Muscle signaling cascades for mitochondrial and myofibrillar biogenesis are altered in MS and related to the impairment and disability level. These findings indicate a link between muscle signaling cascades and the level of disability and impairment, and thus may open a new area for the development of novel therapies for peripheral muscle impairment in MS.

Multiple sclerosis affects skeletal muscle characteristics.

BACKGROUND: The impact of multiple sclerosis (MS) on skeletal muscle characteristics, such as muscle fiber cross sectional area (CSA), fiber type proportion, muscle strength and whole muscle mass, remains conflicting. METHODS: In this cross sectional study, body composition and muscle strength of the quadriceps were assessed in 34 MS (EDSS: 2.5±0.19) patients and 18 matched healthy controls (HC). Hereafter a muscle biopsy (m.vastus lateralis) was taken. RESULTS: Compared to HC, mean muscle fiber CSA of all fibers, as well as CSA of type I, II and IIa fibers were smaller and muscle strength of the quadriceps was lower in MS patients. Whole body composition was comparable between groups. However, compared to HC, the biopsied leg tended to have a higher fat percentage (p = 0.1) and a lower lean mass (p = 0.06) in MS patients. CONCLUSION: MS seems to negatively influence skeletal muscle fiber CSA, muscle strength and muscle mass of the lower limbs of mildly affected MS patients. This emphasises the need for rehabilitation programs focusing on muscle preservation of the lower limb. TRIAL REGISTRATION: ClinicalTrials.gov NCT01845896.

A primary culture of mouse proximal tubular cells, established on collagen-coated membranes.

A simple method is described to establish primary cultures of kidney proximal tubule cells (PTC) on membranes. The permeable membranes represent a unique culture surface, allowing a high degree of differentiation since both apical and basolateral membranes are accessible for medium. Proximal tubule (PT) segments from collagenase-digested mouse renal cortices were grown for 7 days, by which time cells were organized as a confluent monolayer. Electron microscopic evaluation revealed structurally polarized epithelial cells with numerous microvilli, basolateral invaginations, and apical tight junctions. Immunoblotting for markers of distinct parts of the nephron demonstrated that these primary cultures only expressed PT-specific proteins. Moreover immunodetection of distinct components of the receptor-mediated endocytic pathway and uptake of FITC-albumin indicated that these cells expressed a functional endocytotic apparatus. In addition, primary cultures possessed the PT brush-border enzymes, alkaline phosphatase, and gamma-glutamyl-transferase, and a phloridzin-sensitive sodium-dependent glucose transport at their apical side. Electrophysiological measurements show that the primary cultured cells have a low transepithelial resistance and high short-circuit current that was completely carried by Na(+) similar to a leaky epithelium like proximal tubule cells. This novel method established well-differentiated PTC cultures.

Leukemia inhibitory factor is produced by myelin-reactive T cells from multiple sclerosis patients and protects against tumor necrosis factor-alpha-induced oligodendrocyte apoptosis.

In multiple sclerosis (MS), damage to oligodendrocytes is believed to be caused by an aberrant immune response initiated by autoreactive T cells. Increasing evidence indicates that these T cells are not exclusively detrimental but might also exert protective effects. We report for the first time that myelin-reactive T-cell clones from eight MS patients (6/19) and five healthy controls (4/11) produce leukemia inhibitory factor (LIF), a member of the neuropoietic family of neurotrophins. In addition, T-cell clones specific for tetanus toxoid, CD4(+) and CD8(+) T cells, and monocytes, but not B cells, secreted LIF. LIF-producing T lymphocytes and macrophages were also identified immunohistochemically in both active and chronic-active MS lesions. We further demonstrated dose-dependent protective effects of LIF on tumor necrosis factor-alpha-induced apoptosis of oligodendrocytes. In conclusion, our data demonstrate that peripheral and CNS-infiltrating T cells from MS patients produce LIF, a protective factor for oligodendrocytes. This study emphasizes that secretion of LIF may contribute to the neuroprotective effects of autoreactive T cells.

Cytokine-induced cell death in human oligodendroglial cell lines: I. Synergistic effects of IFN-gamma and TNF-alpha on apoptosis.

Multiple sclerosis is a chronic inflammatory disease of the central nervous system. Myelin and oligodendrocytes are considered the major targets of injury caused by a cell-mediated immune response. There is circumstantial evidence that proinflammatory cytokines like tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) could have disease-promoting roles in multiple sclerosis (MS). In the present study, the cytotoxic effects of IFN-gamma and TNF-alpha on the human oligodendroglial cell lines human oligodendroglioma (HOG) and MO3.13 were analyzed. When the oligodendroglial cell lines were cultured in the presence of IFN-gamma or TNF-alpha, apoptotic cell death was observed in both cell lines after >24 hr incubation. Apoptosis was evidenced by a decrease in cell viability, apoptotic changes in cell and nucleus morphology, and disruption of the membrane asymmetry. Our data show that TNF-alpha and IFN-gamma induce apoptosis in a dose-dependent fashion in both oligodendroglial cell lines and that their synergistic effect results in enhanced cell death. Understanding the regulation of cell death pathways in oligodendrocytes is critical for protecting myelin-producing cells and their associated axons during injury in patients with MS.

Skeletal muscle repair by adult human mesenchymal stem cells from synovial membrane.

We have demonstrated previously that adult human synovial membrane-derived mesenchymal stem cells (hSM-MSCs) have myogenic potential in vitro (De Bari, C., F. Dell'Accio, P. Tylzanowski, and F.P. Luyten. 2001. Arthritis Rheum. 44:1928-1942). In the present study, we have characterized their myogenic differentiation in a nude mouse model of skeletal muscle regeneration and provide proof of principle of their potential use for muscle repair in the mdx mouse model of Duchenne muscular dystrophy. When implanted into regenerating nude mouse muscle, hSM-MSCs contributed to myofibers and to long term persisting functional satellite cells. No nuclear fusion hybrids were observed between donor human cells and host mouse muscle cells. Myogenic differentiation proceeded through a molecular cascade resembling embryonic muscle development. Differentiation was sensitive to environmental cues, since hSM-MSCs injected into the bloodstream engrafted in several tissues, but acquired the muscle phenotype only within skeletal muscle. When administered into dystrophic muscles of immunosuppressed mdx mice, hSM-MSCs restored sarcolemmal expression of dystrophin, reduced central nucleation, and rescued the expression of mouse mechano growth factor.