Reduced satellite cell number in situ in muscular contractures from children with cerebral palsy

Muscle satellite cells and fibro-adipogenic progenitors from muscle contractures of children with cerebral palsy have impaired regenerative capacity

AIM

To evaluate the mechanosensitivity of muscle satellite cells (MuSCs) and fibro-adipogenic progenitors (FAPs) in cerebral palsy (CP) and the efficacy of the drug verteporfin in restoring cells' regenerative capacity.

METHOD

Muscle biopsies were collected from six children with CP and six typically developing children. MuSCs and FAPs were isolated and plated on collagen-coated polyacrylamide gels at stiffnesses of 0.2 kPa, 8 kPa, and 25 kPa. Cells were treated with verteporfin to block mechanosensing or with dimethyl sulfoxide as a negative control. MuSC differentiation and FAP activation into myofibroblasts were measured using immunofluorescence staining.

RESULTS

Surprisingly, MuSC differentiation was not affected by stiffness; however, stiff substrates resulted in large myonuclear clustering. Across all stiffnesses, MuSCs from children with CP had less differentiation than those of their typically developing counterparts. FAP activation into myofibroblasts was significantly higher in children with CP than their typically developing peers, but was not affected by stiffness. Verteporfin did not affect differentiation or activation in either cell population, but slightly decreased myonuclear clustering on stiff substrates.

INTERPRETATION

Cells from children with CP were less regenerative and more fibrotic compared to those of their typically developing counterparts, with MuSCs being sensitive to increases in stiffness. Therefore, the mechanosensitivity of MuSCs and FAPs may represent a new target to improve differentiation and activation in CP muscle.

Muscle type-specific effects of bilateral abobotulinumtoxinA injection on muscle growth and contractile function in spastic mice

Intramuscular injection of botulinum neurotoxin type A (BoNT-A) is commonly used to improve or maintain the joint range of motion in young children with spasticity. However, the effectiveness of BoNT-A treatment is variable and movement limitations are recurrent. Here we show long-term effects of a single, bilateral abobotulinumtoxinA (aboBoNT-A) injection in the gastrocnemius medialis and soleus muscles of wild-type and spastic (B6.Cg-Glrbspa/J with a mutation in the glycine receptor) mice at a young age (6-7 days). Specifically, we evaluated the impact of aboBoNT-A-A on gait, physical performance, and spontaneous physical behavior, as well as on contractile force characteristics, morphology, and histological phenotype of soleus and gastrocnemius muscles by comparing their results to those of saline-injected controls up to 9 weeks after the injection. The detailed time course of the study specifies the timing of the aboBoNT-A injection at 1 week, the period of behavioral studies from 4-9 weeks, and the age of the mice (10 weeks) at the time of contractile force characteristics and histology assessments. In spastic mice, aboBoNT-A injection had a minor and very specific effect on physical performance, by only modestly increasing stride length as a function of age. aboBoNT-A injection caused a reduction in the force-generating capacity and a slightly smaller physiological cross-sectional area in gastrocnemius medialis, but not in soleus. Reduced physiological cross-sectional area in aboBoNT-A-injected muscles was due to a lower number of muscle fibers, rather than reduced muscle fiber cross-sectional area. The percentage of slow-type muscle fibers and mitochondrial succinate dehydrogenase activity were increased, which was associated with an improved muscle endurance capacity. In conclusion, aboBoNT-A injection reduced the number of muscle fibers, causing muscle hypertrophy in remaining fibers and a shift towards more oxidative fibers, resulting in an improved endurance capacity and gait. This study proposed potential cellular mechanisms for the therapeutic efficacy of aboBoNT-A in spasticity.

Serious Game with Electromyography Feedback and Physical Therapy in Young Children with Unilateral Spastic Cerebral Palsy and Equinus Gait: A Prospective Open-Label Study

The clinical effects of a serious game with electromyography feedback (EMGs_SG) and physical therapy (PT) was investigated prospectively in children with unilateral spastic cerebral palsy (USCP). An additional aim was to better understand the influence of muscle shortening on function. Thirty children with USCP (age 7.6 ± 2.1 years) received four weeks of EMGs_SG sessions 2×/week including repetitive, active alternating training of dorsi- and plantar flexors in a seated position. In addition, each child received usual PT treatment ≤ 2×/week, involving plantar flexor stretching and command strengthening on dorsi- and plantar flexors. Five-Step Assessment parameters, including preferred gait velocity (normalized by height); plantar flexor extensibility (XV1); angle of catch (XV3); maximal active ankle dorsiflexion (XA); and derived coefficients of shortening, spasticity, and weakness for both soleus and gastrosoleus complex (GSC) were compared pre and post treatment (t-tests). Correlations were explored between the various coefficients and gait velocities at baseline. After four weeks of EMGs_SG + PT, there was an increase in normalized gait velocity from 0.72 ± 0.13 to 0.77 ± 0.13 m/s (p = 0.025, d = 0.43), a decrease in coefficients of shortening (soleus, 0.10 ± 0.07 pre vs. 0.07 ± 0.08 post, p = 0.004, d = 0.57; GSC 0.16 ± 0.08 vs. 0.13 ± 0.08, p = 0.003, d = 0.58), spasticity (soleus 0.14 ± 0.06 vs. 0.12 ± 0.07, p = 0.02, d = 0.46), and weakness (soleus 0.14 ± 0.07 vs. 0.11 ± 0.07, p = 0.005, d = 0.55). At baseline, normalized gait velocity correlated with the coefficient of GSC shortening (R = -0.43, p = 0.02). Four weeks of EMGs_SG and PT were associated with improved gait velocity and decreased plantar flexor shortening. A randomized controlled trial comparing EMGs_SG and conventional PT is needed.

Histological analysis of the gastrocnemius muscle in preschool and school age children with cerebral palsy compared with age-matched typically developing children

Inconsistent alterations in skeletal muscle histology have been reported in adolescents with cerebral palsy (CP) and whether alterations are present in young children and differ from older children is not yet known. This study aimed to define histological alterations in the medial gastrocnemius (MG) of ambulant CP (gross-motor classification system, GMFCS I-III) stratified in two age groups (preschool children, PS: 2-5 and school age children, SA: 6-9-yr old) compared with age-matched typically developing (TD) children. We hypothesized that alterations in muscle microscopic properties are already present in PS-CP and are GMFCS level specific. Ultrasound guided percutaneous microbiopsies were collected in 46 CP (24-PS) and 45 TD (13-PS) children. Sections were stained to determine fiber cross-sectional area (fCSA) and proportion, capillary, and satellite cell amount. Average absolute and normalized fCSA were similar in CP and TD, but a greater percentage of smaller fibers was found in CP. Coefficient of variation (CV) was significantly larger in PS-CP-GMFCS I-II and for type I fiber. In SA-CP, all fiber types contributed to the higher CV. Type IIx proportion was higher and type I was lower in PS-CP-GMFCS-III and for all SA-CP. Reduced capillary-to-fiber ratio was present in PS-CP-GMFCS II-III and in all SA-CP. Capillary fiber density was lower in SA-CP. Capillary domain was enhanced in all CP, but capillary spatial distribution was maintained as was satellite cell content. We concluded that MG histological alterations are already present in very young CP but are only partly specific for GMFCS level and age.NEW & NOTEWORTHY Inconsistent histological alterations have been reported in children with cerebral palsy (CP) but whether they are present in very young and ambulant CP children and differ from those reported in old CP children is not known. This study highlighted for the first time that enhanced muscle fiber size variability and loss of capillaries are already present in very young CP children, even in the most ambulant ones, and these alterations seem to extend with age.

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.

Ex vivo adult stem cell characterization from multiple muscles in ambulatory children with cerebral palsy during early development of contractures

Cerebral palsy (CP) is one of the most common conditions leading to lifelong childhood physical disability. Literature reported previously altered muscle properties such as lower number of satellite cells (SCs), with altered fusion capacity. However, these observations highly vary among studies, possibly due to heterogeneity in patient population, lack of appropriate control data, methodology and different assessed muscle. In this study we aimed to strengthen previous observations and to understand the heterogeneity of CP muscle pathology. Myogenic differentiation of SCs from the Medial Gastrocnemius (MG) muscle of patients with CP (n = 16, 3-9 years old) showed higher fusion capacity compared to age-matched typically developing children (TD, n = 13). Furthermore, we uniquely assessed cells of two different lower limb muscles and showed a decreased myogenic potency in cells from the Semitendinosus (ST) compared to the MG (TD: n = 3, CP: n = 6). Longitudinal assessments, one year after the first botulinum toxin treatment, showed slightly reduced SC representations and lower fusion capacity (n = 4). Finally, we proved the robustness of our data, by assessing in parallel the myogenic capacity of two samples from the same TD muscle. In conclusion, these data confirmed previous findings of increased SC fusion capacity from MG muscle of young patients with CP compared to age-matched TD. Further elaboration is reported on potential factors contributing to heterogeneity, such as assessed muscle, CP progression and reliability of primary outcome parameters.

Lifelong Fitness in Ambulatory Children and Adolescents with Cerebral Palsy I: Key Ingredients for Bone and Muscle Health

Physical activity of a sufficient amount and intensity is essential to health and the prevention of a sedentary lifestyle in all children as they transition into adolescence and adulthood. While fostering a fit lifestyle in all children can be challenging, it may be even more so for those with cerebral palsy (CP). Evidence suggests that bone and muscle health can improve with targeted exercise programs for children with CP. Yet, it is not clear how musculoskeletal improvements are sustained into adulthood. In this perspective, we introduce key ingredients and guidelines to promote bone and muscle health in ambulatory children with CP (GMFCS I-III), which could lay the foundation for sustained fitness and musculoskeletal health as they transition from childhood to adolescence and adulthood. First, one must consider crucial characteristics of the skeletal and muscular systems as well as key factors to augment bone and muscle integrity. Second, to build a better foundation, we must consider critical time periods and essential ingredients for programming. Finally, to foster the sustainability of a fit lifestyle, we must encourage commitment and self-initiated action while ensuring the attainment of skill acquisition and function. Thus, the overall objective of this perspective paper is to guide exercise programming and community implementation to truly alter lifelong fitness in persons with CP.

Resident muscle stem cell myogenic characteristics in postnatal muscle growth impairments in children with cerebral palsy

Children with cerebral palsy (CP), a perinatal brain alteration, have impaired postnatal muscle growth, with some muscles developing contractures. Functionally, children are either able to walk or primarily use wheelchairs. Satellite cells are muscle stem cells (MuSCs) required for postnatal development and source of myonuclei. Only MuSC abundance has been previously reported in contractured muscles, with myogenic characteristics assessed only in vitro. We investigated whether MuSC myogenic, myonuclear, and myofiber characteristics in situ differ between contractured and noncontractured muscles, across functional levels, and compared with typically developing (TD) children with musculoskeletal injury. Open muscle biopsies were obtained from 36 children (30 CP, 6 TD) during surgery; contracture correction for adductors or gastrocnemius, or from vastus lateralis [bony surgery in CP, anterior cruciate ligament (ACL) repair in TD]. Muscle cross sections were immunohistochemically labeled for MuSC abundance, activation, proliferation, nuclei, myofiber borders, type-1 fibers, and collagen content in serial sections. Although MuSC abundance was greater in contractured muscles, primarily in type-1 fibers, their myogenic characteristics (activation, proliferation) were lower compared with noncontractured muscles. Overall, MuSC abundance, activation, and proliferation appear to be associated with collagen content. Myonuclear number was similar between all muscles, but only in contractured muscles were there associations between myonuclear number, MuSC abundance, and fiber cross-sectional area. Puzzlingly, MuSC characteristics were similar between ambulatory and nonambulatory children. Noncontractured muscles in children with CP had a lower MuSC abundance compared with TD-ACL injured children, but similar myogenic characteristics. Contractured muscles may have an intrinsic deficiency in developmental progression for postnatal MuSC pool establishment, needed for lifelong efficient growth and repair.

DNA Methylation Analysis Reveals Distinct Patterns in Satellite Cell-Derived Myogenic Progenitor Cells of Subjects with Spastic Cerebral Palsy

Spastic type cerebral palsy (CP) is a complex neuromuscular disorder that involves altered skeletal muscle microanatomy and growth, but little is known about the mechanisms contributing to muscle pathophysiology and dysfunction. Traditional genomic approaches have provided limited insight regarding disease onset and severity, but recent epigenomic studies indicate that DNA methylation patterns can be altered in CP. Here, we examined whether a diagnosis of spastic CP is associated with intrinsic DNA methylation differences in myoblasts and myotubes derived from muscle resident stem cell populations (satellite cells; SCs). Twelve subjects were enrolled (6 CP; 6 control) with informed consent/assent. Skeletal muscle biopsies were obtained during orthopedic surgeries, and SCs were isolated and cultured to establish patient-specific myoblast cell lines capable of proliferation and differentiation in culture. DNA methylation analyses indicated significant differences at 525 individual CpG sites in proliferating SC-derived myoblasts (MB) and 1774 CpG sites in differentiating SC-derived myotubes (MT). Of these, 79 CpG sites were common in both culture types. The distribution of differentially methylated 1 Mbp chromosomal segments indicated distinct regional hypo- and hyper-methylation patterns, and significant enrichment of differentially methylated sites on chromosomes 12, 13, 14, 15, 18, and 20. Average methylation load across 2000 bp regions flanking transcriptional start sites was significantly different in 3 genes in MBs, and 10 genes in MTs. SC derived MBs isolated from study participants with spastic CP exhibited fundamental differences in DNA methylation compared to controls at multiple levels of organization that may reveal new targets for studies of mechanisms contributing to muscle dysregulation in spastic CP.

Myonuclear permanence in skeletal muscle memory: a systematic review and meta-analysis of human and animal studies

One aspect of skeletal muscle memory is the ability of a previously trained muscle to hypertrophy more rapidly following a period of detraining. Although the molecular basis of muscle memory remains to be fully elucidated, one potential mechanism thought to mediate muscle memory is the permanent retention of myonuclei acquired during the initial phase of hypertrophic growth. However, myonuclear permanence is debated and would benefit from a meta-analysis to clarify the current state of the field for this important aspect of skeletal muscle plasticity. The objective of this study was to perform a meta-analysis to assess the permanence of myonuclei associated with changes in physical activity and ageing. When available, the abundance of satellite cells (SCs) was also considered given their potential influence on changes in myonuclear abundance. One hundred forty-seven peer-reviewed articles were identified for inclusion across five separate meta-analyses; (1-2) human and rodent studies assessed muscle response to hypertrophy; (3-4) human and rodent studies assessed muscle response to atrophy; and (5) human studies assessed muscle response with ageing. Skeletal muscle hypertrophy was associated with higher myonuclear content that was retained in rodents, but not humans, with atrophy (SMD = -0.60, 95% CI -1.71 to 0.51, P = 0.29, and MD = 83.46, 95% CI -649.41 to 816.32, P = 0.82; respectively). Myonuclear and SC content were both lower following atrophy in humans (MD = -11, 95% CI -0.19 to -0.03, P = 0.005, and SMD = -0.49, 95% CI -0.77 to -0.22, P = 0.0005; respectively), although the response in rodents was affected by the type of muscle under consideration and the mode of atrophy. Whereas rodent myonuclei were found to be more permanent regardless of the mode of atrophy, atrophy of ≥30% was associated with a reduction in myonuclear content (SMD = -1.02, 95% CI -1.53 to -0.51, P = 0.0001). In humans, sarcopenia was accompanied by a lower myonuclear and SC content (MD = 0.47, 95% CI 0.09 to 0.85, P = 0.02, and SMD = 0.78, 95% CI 0.37-1.19, P = 0.0002; respectively). The major finding from the present meta-analysis is that myonuclei are not permanent but are lost during periods of atrophy and with ageing. These findings do not support the concept of skeletal muscle memory based on the permanence of myonuclei and suggest other mechanisms, such as epigenetics, may have a more important role in mediating this aspect of skeletal muscle plasticity.

The Short-Term Impact of Botulinum Neurotoxin-A on Muscle Morphology and Gait in Children with Spastic Cerebral Palsy

Children with spastic cerebral palsy (SCP) are often treated with intramuscular Botulinum Neurotoxin type-A (BoNT-A). Recent studies demonstrated BoNT-A-induced muscle atrophy and variable effects on gait pathology. This group-matched controlled study in children with SCP compared changes in muscle morphology 8-10 weeks post-BoNT-A treatment (n = 25, median age 6.4 years, GMFCS level I/II/III (14/9/2)) to morphological changes of an untreated control group (n = 20, median age 7.6 years, GMFCS level I/II/III (14/5/1)). Additionally, the effects on gait and spasticity were assessed in all treated children and a subgroup (n = 14), respectively. BoNT-A treatment was applied following an established integrated approach. Gastrocnemius and semitendinosus volume and echogenicity intensity were assessed by 3D-freehand ultrasound, spasticity was quantified through electromyography during passive muscle stretches at different velocities. Ankle and knee kinematics were evaluated by 3D-gait analysis. Medial gastrocnemius (p = 0.018, -5.2%) and semitendinosus muscle volume (p = 0.030, -16.2%) reduced post-BoNT-A, but not in the untreated control group, while echogenicity intensity did not change. Spasticity reduced and ankle gait kinematics significantly improved, combined with limited effects on knee kinematics. This study demonstrated that BoNT-A reduces spasticity and partly improves pathological gait but reduces muscle volume 8-10 weeks post-injections. Close post-BoNT-A follow-up and well-considered treatment selection is advised before BoNT-A application in SCP.

The Myotube Analyzer: how to assess myogenic features in muscle stem cells

BACKGROUND

The analysis of in vitro cultures of human adult muscle stem cells obtained from biopsies delineates the potential of skeletal muscles and may help to understand altered muscle morphology in patients. In these analyses, the fusion index is a commonly used quantitative metric to assess the myogenic potency of the muscle stem cells. Since the fusion index only partly describes myogenic potency, we developed the Myotube Analyzer tool, which combines the definition of the fusion index with extra features of myonuclei and myotubes obtained from satellite cell cultures.

RESULTS

The software contains image adjustment and mask editing functions for preprocessing and semi-automatic segmentation, while other functions can be used to determine the features of nuclei and myotubes. The fusion index and a set of five novel parameters were tested for reliability and validity in a comparison between satellite cell cultures from children with cerebral palsy and typically developing children. These novel parameters quantified extra nucleus and myotube properties and can be used to describe nucleus clustering and myotube shape. Two analyzers who were trained in cell culture defined all parameters using the Myotube Analyzer app. Out of the six parameters, five had good reliability reflected by good intra-class correlation coefficients (> 0.75). Children with cerebral palsy were significantly different from the typically developing children (p < 0.05) for five parameters, and for three of the six parameters, these differences exceeded the minimal detectable differences.

CONCLUSIONS

The Myotube Analyzer can be used for the analysis of fixed differentiated myoblast cultures with nuclear and MyHC staining. The app can calculate the fusion index, an already existing parameter, but also provides multiple new parameters to comprehensively describe myogenic potential in its output. The raw data used to determine these parameters are also available in the output. The parameters calculated by the tool can be used to detect differences between cultures from children with cerebral palsy and typically developing children. Since the program is open source, users can customize it to fit their own analysis requirements.

Insights into muscle stem cell dynamics during postnatal development

During development, resident stem cell populations contribute to the growth and maturation of tissue and organs. In skeletal muscle, muscle stem cells, or satellite cells (SCs), are responsible for the maturation of postnatal myofibers. However, the role SCs play in later stages of postnatal growth, and thus, when they enter a mature quiescent state is controversial. Here, we discuss the current literature regarding the role SCs play in all stages of postnatal growth, from birth to puberty onset to young adulthood. We additionally highlight the implications of SC loss or dysfunction during developmental stages, both in the context of experimental paradigms and disease settings.

Understanding skeletal muscle in cerebral palsy: a path to personalized medicine?

Until recently, there has been little interest in understanding the intrinsic features associated with the pathomorphology of skeletal muscle in cerebral palsy (CP). Coupled with emerging evidence that challenges the role of spasticity as a determinant of gross motor function and in the development of fixed muscle contractures, it has become increasingly important to further elucidate the underlying mechanisms responsible for muscle alterations in CP. This knowledge can help clinicians to understand and apply treatment modalities that take these aspects into account. Thus, the inherent heterogeneity of the CP phenotype allows for the potential of personalized medicine through the understanding of muscle pathomorphology on an individual basis and tailoring treatment approaches accordingly. This review aims to summarize recent developments in the understanding of CP muscle and their relationship to musculoskeletal manifestations, in addition to proposing a treatment paradigm that incorporates this new knowledge.

Glycine receptor subunit-ß -deficiency in a mouse model of spasticity results in attenuated physical performance, growth and muscle strength

Spasticity is the most common neurological disorder associated with increased muscle contraction causing impaired movement and gait. The aim of this study was to characterize the physical performance, skeletal muscle function, and phenotype of mice with a hereditary spastic mutation (B6.Cg-Glrb^spa/J). Motor function, gait, and physical activity of juvenile and adult spastic mice and the morphological, histological, and mechanical characteristics of their soleus and gastrocnemius medialis muscles were compared with those of their wild-type (WT) littermates. Spastic mice showed attenuated growth, impaired motor function, and low physical activity. Gait of spastic mice was characterized by a typical hopping pattern. Spastic mice showed lower muscle forces, which were related to the smaller physiological cross-sectional area of spastic muscles. The muscle-tendon complex length-force relationship of adult gastrocnemius medialis was shifted toward shorter lengths, which was explained by attenuated longitudinal tibia growth. Spastic gastrocnemius medialis was more fatigue resistant than WT gastrocnemius medialis. This was largely explained by a higher mitochondrial content in muscle fibers and relatively higher percentage of slow-type muscle fibers. Muscles of juvenile spastic mice showed similar differences compared with WT juvenile mice, but these were less pronounced than between adult mice. This study shows that in spastic mice, disturbed motor function and gait is likely to be the result of hyperactivity of skeletal muscle and impaired skeletal muscle growth, which progress with age.

An Emerging Role for Epigenetics in Cerebral Palsy

Cerebral palsy is a set of common, severe, motor disabilities categorized by a static, nondegenerative encephalopathy arising in the developing brain and associated with deficits in movement, posture, and activity. Spastic CP, which is the most common type, involves high muscle tone and is associated with altered muscle function including poor muscle growth and contracture, increased extracellular matrix deposition, microanatomic disruption, musculoskeletal deformities, weakness, and difficult movement control. These muscle-related manifestations of CP are major causes of progressive debilitation and frequently require intensive surgical and therapeutic intervention to control. Current clinical approaches involve sophisticated consideration of biomechanics, radiologic assessments, and movement analyses, but outcomes remain difficult to predict. There is a need for more precise and personalized approaches involving omics technologies, data science, and advanced analytics. An improved understanding of muscle involvement in spastic CP is needed. Unfortunately, the fundamental mechanisms and molecular pathways contributing to altered muscle function in spastic CP are only partially understood. In this review, we outline evidence supporting the emerging hypothesis that epigenetic phenomena play significant roles in musculoskeletal manifestations of CP.

Transcriptional analysis of muscle tissue and isolated satellite cells in spastic cerebral palsy

AIM

To analyze transcriptomes from muscle tissue and cells to improve our understanding of differences in gene expression and molecular function in cerebral palsy (CP) muscle.

METHOD

In this case-control study, eight participants with CP (five males, three females; mean [SD] age 14y 2mo [1y 8mo]) and 11 comparison individuals (eight males, three females; mean [SD] age 14y 0mo [2y 6mo]) were enrolled after informed consent/assent and skeletal muscle was obtained during surgery. RNA was extracted from tissue and from primary satellite cells grown to form myotubes in vitro. RNA sequencing data were analyzed using validated informatics pipelines.

RESULTS

Analysis identified expression of 6308 genes in the tissue samples and 7459 in the cultured cells. Significant differential expression between CP and control was identified in 87 genes in the tissue and 90 genes in isolated satellite cell-derived myotube cultures.

INTERPRETATION

Both tissue and cell analyses identified differential expression of genes associated with muscle development and multiple pathways of interest. What this paper adds Expression differences were found in muscle tissue and in isolated muscle cells. There was low variability in expression among cells isolated from different muscles. Expression differences suggest complex functional alterations in spastic cerebral palsy.

Differential DNA methylation and transcriptional signatures characterize impairment of muscle stem cells in pediatric human muscle contractures after brain injury

Limb contractures are a debilitating and progressive consequence of a wide range of upper motor neuron injuries that affect skeletal muscle function. One type of perinatal brain injury causes cerebral palsy (CP), which affects a child's ability to move and is often painful. While several rehabilitation therapies are used to treat contractures, their long-term effectiveness is marginal since such therapies do not change muscle biological properties. Therefore, new therapies based on a biological understanding of contracture development are needed. Here, we show that myoblast progenitors from contractured muscle in children with CP are hyperproliferative. This phenotype is associated with DNA hypermethylation and specific gene expression patterns that favor cell proliferation over quiescence. Treatment of CP myoblasts with 5-azacytidine, a DNA hypomethylating agent, reduced this epigenetic imprint to TD levels, promoting exit from mitosis and molecular mechanisms of cellular quiescence. Together with previous studies demonstrating reduction in myoblast differentiation, this suggests a mechanism of contracture formation that is due to epigenetic modifications that alter the myogenic program of muscle-generating stem cells. We suggest that normalization of DNA methylation levels could rescue myogenesis and promote regulated muscle growth in muscle contracture and thus may represent a new nonsurgical approach to treating this devastating neuromuscular condition.

Muscle-tendon unit in children with cerebral palsy

Muscle-tendon unit surgery for correction of deformities and movement dysfunction in children with cerebral palsy (CP) is fairly complicated. An understanding of basic muscle-tendon unit properties and their adaptation to both CP and surgery are important to develop advances in this field. In this review, we provide information to therapists, surgeons, and scientists regarding the short- and long-term adaptations of the muscle-tendon unit. Surgical releases, lengthening, and transpositions are discussed, as are some of the tissue, cellular, and molecular adaptations. What this paper adds Muscle strength, tone, and control must be considered in surgical interventions for cerebral palsy (CP). Muscle-tendon unit lengthening causes significant and lasting weakness requiring prolonged rehabilitation. Sarcomere length increases in CP muscle may be one of the underlying causes of muscle weakness. Muscle satellite cells are decreased and epigenetically modified in a way that may limit muscle growth in CP.

Stretch-induced satellite cell deformation incontracturedmuscles in children with cerebral palsy

Satellite cells (SCs) are quiescent, adult skeletal muscle stem cells responsible for postnatal muscle growth and repair. Children with cerebral palsy (CP) have muscle contractures with reduced SC abundance, extracellular matrix abnormalities and reduced serial sarcomere number resulting in greatly increased in vivo sarcomere length, perhaps due to impaired sarcomere addition, compared to children with typical development (TD). Stretch is a strong activator of SCs that leads to addition of sarcomeres during bone-muscle growth. Mechanical loading and subsequent deformation of intracellular structures can lead to activation and proliferation, perhaps by cytoskeletal transmissions of extracellular mechanical signals to the nuclei. The primary aim of this study was to determine the effect of ex vivo stretch-induced sarcomere length change on SC deformation in children with CP and TD. Muscle biopsies were obtained from twelve children (7 CP, 5 TD) during surgery. Fiber bundles were labeled with fluorescent antibodies for Pax7 (SC), DRAQ5 (nuclei), and alpha-actinin (sarcomere protein). Fibers were stretched using a custom jig and imaged using confocal microscopy. SC nuclear length, height and aspect ratio underwent increased deformation with increasing sarcomere length (p < 0.05) in both groups. Slopes of association for SC nuclear length, aspect ratio and sarcomere lengths were similar between CP and TD. Our results indicate that SC in children with CP undergo similar deformation as TD across sarcomere lengths.

Contribution of extracellular matrix components to the stiffness of skeletal muscle contractures in patients with cerebral palsy

Purpose: Joint contractures in children with cerebral palsy contain muscle tissue that is mechanically stiffer with higher collagen content than typically developing children. Interestingly, the correlation between collagen content and stiffness is weak. To date, no data are available on collagen types or other extracellular matrix proteins in these muscles, nor any information regarding their function. Thus, our purpose was to measure specific extracellular protein composition in cerebral palsy and typically developing human muscles along with structural aspects of extracellular matrix architecture to determine the extent to which these explain mechanical properties. Materials and Methods: Biopsies were collected from children with cerebral palsy undergoing muscle lengthening procedures and typically developing children undergoing anterior cruciate ligament reconstruction. Tissue was prepared for the determination of collagen types I, III, IV, and VI, proteoglycan, biglycan, decorin, hyaluronic acid/uronic acid and collagen crosslinking. Results: All collagen types increased in cerebral palsy along with pyridinoline crosslinks, total proteoglycan, and uronic acid. In all cases, type I or total collagen and total proteoglycan were positive predictors, while biglycan was a negative predictor of stiffness. Together these parameters accounted for a greater degree of variance within groups than across groups, demonstrating an altered relationship between extracellular matrix and stiffness with cerebral palsy. Further, stereological analysis revealed a significant increase in collagen fibrils organized in cables and an increased volume fraction of fibroblasts in CP muscle. Conclusions: These data demonstrate a novel adaptation of muscle extracellular matrix in children with cerebral palsy that includes alterations in extracellular matrix protein composition and structure related to mechanical function.

Translational research on Myology and Mobility Medicine: 2021 semi-virtual PDM3 from Thermae of Euganean Hills, May 26 - 29, 2021

On 19-21 November 2020, the meeting of the 30 years of the Padova Muscle Days was virtually held while the SARS-CoV-2 epidemic was hitting the world after a seemingly quiet summer. During the 2020-2021 winter, the epidemic is still active, despite the start of vaccinations. The organizers hope to hold the 2021 Padua Days on Myology and Mobility Medicine in a semi-virtual form (2021 S-V PDM3) from May 26 to May 29 at the Thermae of Euganean Hills, Padova, Italy. Here the program and the Collection of Abstracts are presented. Despite numerous world problems, the number of submitted/selected presentations (lectures and oral presentations) has increased, prompting the organizers to extend the program to four dense days.

Skeletal Muscle in Cerebral Palsy: From Belly to Myofibril

This review will provide a comprehensive, up-to-date review of the current knowledge regarding the pathophysiology of muscle contractures in cerebral palsy. Although much has been known about the clinical manifestations of both dynamic and static muscle contractures, until recently, little was known about the underlying mechanisms for the development of such contractures. In particular, recent basic science and imaging studies have reported an upregulation of collagen content associated with muscle stiffness. Paradoxically, contractile elements such as myofibrils have been found to be highly elastic, possibly an adaptation to a muscle that is under significant in vivo tension. Sarcomeres have also been reported to be excessively long, likely responsible for the poor force generating capacity and underlying weakness seen in children with cerebral palsy (CP). Overall muscle volume and length have been found to be decreased in CP, likely secondary to abnormalities in sarcomerogenesis. Recent animal and clinical work has suggested that the use of botulinum toxin for spasticity management has been shown to increase muscle atrophy and fibrofatty content in the CP muscle. Given that the CP muscle is short and small already, this calls into question the use of such agents for spasticity management given the functional and histological cost of such interventions. Recent theories involving muscle homeostasis, epigenetic mechanisms, and inflammatory mediators of regulation have added to our emerging understanding of this complicated area.

Muscle Microbiopsy to Delineate Stem Cell Involvement in Young Patients: A Novel Approach for Children With Cerebral Palsy

Cerebral palsy (CP), the single largest cause of childhood physical disability, is characterized firstly by a lesion in the immature brain, and secondly by musculoskeletal problems that progress with age. Previous research reported altered muscle properties, such as reduced volume and satellite cell (SC) numbers and hypertrophic extracellular matrix compared to typically developing (TD) children (>10 years). Unfortunately, data on younger CP patients are scarce and studies on SCs and other muscle stem cells in CP are insufficient or lacking. Therefore, it remains difficult to understand the early onset and trajectory of altered muscle properties in growing CP children. Because muscle stem cells are responsible for postnatal growth, repair and remodeling, multiple adult stem cell populations from young CP children could play a role in altered muscle development. To this end, new methods for studying muscle samples of young children, valid to delineate the features and to elucidate the regenerative potential of muscle tissue, are necessary. Using minimal invasive muscle microbiopsy, which was applied in young subjects under general anaesthesia for the first time, we aimed to isolate and characterize muscle stem cell-derived progenitors of TD children and patients with CP. Data of 15 CP patients, 3–9 years old, and 5 aged-matched TD children were reported. The muscle microbiopsy technique was tolerated well in all participants. Through the explant technique, we provided muscle stem cell-derived progenitors from the Medial Gastrocnemius. Via fluorescent activated cell sorting, using surface markers CD56, ALP, and PDGFRa, we obtained SC-derived progenitors, mesoangioblasts and fibro-adipogenic progenitors, respectively. Adipogenic, skeletal, and smooth muscle differentiation assays confirmed the cell identity and ability to give rise to different cell types after appropriate stimuli. Myogenic differentiation in CP SC-derived progenitors showed enhanced fusion index and altered myotube formation based on MYOSIN HEAVY CHAIN expression, as well as disorganization of nuclear spreading, which were not observed in TD myotubes. In conclusion, the microbiopsy technique allows more focused muscle research in young CP patients. Current results show altered differentiation abilities of muscle stem cell-derived progenitors and support the hypothesis of their involvement in CP-altered muscle growth.

Joint and Muscle Assessments of the Separate Effects of Botulinum NeuroToxin-A and Lower-Leg Casting in Children With Cerebral Palsy

Botulinum NeuroToxin-A (BoNT-A) injections to the medial gastrocnemius (MG) and lower-leg casts are commonly combined to treat ankle equinus in children with spastic cerebral palsy (CP). However, the decomposed treatment effects on muscle or tendon structure, stretch reflexes, and joint are unknown. In this study, BoNT-A injections to the MG and casting of the lower legs were applied separately to gain insight into the working mechanisms of the isolated treatments on joint, muscle, and tendon levels. Thirty-one children with spastic CP (GMFCS I-III, age 7.4 ± 2.6 years) received either two weeks of lower-leg casts or MG BoNT-A injections. During full range of motion slow and fast passive ankle rotations, joint resistance and MG stretch reflexes were measured. MG muscle and tendon lengths were assessed at resting and at maximum dorsiflexion ankle angles using 3D-freehand ultrasound. Treatment effects were compared using non-parametric statistics. Associations between the effects on joint and muscle or tendon levels were performed using Spearman correlation coefficients (p < 0.05). Increased joint resistance, measured during slow ankle rotations, was not significantly reduced after either treatment. Additional joint resistance assessed during fast rotations only reduced in the BoNT-A group (-37.6%, p = 0.013, effect size = 0.47), accompanied by a reduction in MG stretch reflexes (-70.7%, p = 0.003, effect size = 0.56). BoNT-A increased the muscle length measured at the resting ankle angle (6.9%, p = 0.013, effect size = 0.53). Joint angles shifted toward greater dorsiflexion after casting (32.4%, p = 0.004, effect size = 0.56), accompanied by increases in tendon length (5.7%, p = 0.039, effect size = 0.57; r = 0.40). No associations between the changes in muscle or tendon lengths and the changes in the stretch reflexes were found. We conclude that intramuscular BoNT-A injections reduced stretch reflexes in the MG accompanied by an increase in resting muscle belly length, whereas casting resulted in increased dorsiflexion without any changes to the muscle length. This supports the need for further investigation on the effect of the combined treatments and the development of treatments that more effectively lengthen the muscle.

Does a Reduced Number of Muscle Stem Cells Impair the Addition of Sarcomeres and Recovery from a Skeletal Muscle Contracture? A Transgenic Mouse Model

BACKGROUND

Children with cerebral palsy have impaired muscle growth and muscular contractures that limit their ROM. Contractures have a decreased number of serial sarcomeres and overstretched lengths, suggesting an association with a reduced ability to add the serial sarcomeres required for normal postnatal growth. Contractures also show a markedly reduced number of satellite cells-the muscle stem cells that are indispensable for postnatal muscle growth, repair, and regeneration. The potential role of the reduced number of muscle stem cells in impaired sarcomere addition leading to contractures must be evaluated.

QUESTIONS/PURPOSES

(1) Does a reduced satellite cell number impair the addition of serial sarcomeres during recovery from an immobilization-induced contracture? (2) Is the severity of contracture due to the decreased number of serial sarcomeres or increased collagen content?

METHODS

The hindlimbs of satellite cell-specific Cre-inducible mice (Pax7; Rosa26; n = 10) were maintained in plantarflexion with plaster casts for 2 weeks so that the soleus was chronically shortened and the number of its serial sarcomeres was reduced by approximately 20%. Subsequently, mice were treated with either tamoxifen to reduce the number of satellite cells or a vehicle (an injection and handling control). The transgenic mouse model with satellite cell ablation combined with a casting model to reduce serial sarcomere number recreates two features observed in muscular contractures in children with cerebral palsy. After 30 days, the casts were removed, the mice ankles were in plantarflexion, and the mice's ability to recover its ankle ROM by cage remobilization for 30 days were evaluated. We quantified the number of serial sarcomeres, myofiber area, and collagen content of the soleus muscle as well as maximal ankle dorsiflexion at the end of the recovery period.

RESULTS

Mice with reduced satellite cell numbers did not regain normal ankle ROM in dorsiflexion; that is, the muscles remained in plantarflexion contracture (-16° ± 13° versus 31° ± 39° for the control group, -47 [95% confidence interval -89 to -5]; p = 0.03). Serial sarcomere number of the soleus was lower on the casted side than the contralateral side of the mice with a reduced number of satellite cells (2214 ± 333 versus 2543 ± 206, -329 [95% CI -650 to -9]; p = 0.04) but not different in the control group (2644 ± 194 versus 2729 ± 249, -85 [95% CI -406 to 236]; p = 0.97). The degree of contracture was strongly associated with the number of sarcomeres and myofiber area (r =0.80; P < 0.01) rather than collagen content. No differences were seen between groups in terms of collagen content and the fraction of muscle area.

CONCLUSIONS

We found that a reduced number of muscle stem cells in a transgenic mouse model impaired the muscle's ability to add sarcomeres in series and thus to recover from an immobilization-induced contracture.

CLINICAL RELEVANCE

The results of our study in transgenic mouse muscle suggests there may be a mechanistic relationship between a reduced number of satellite cells and a reduced number of serial sarcomeres. Contracture development, secondary to impaired sarcomere addition in muscles in children with cerebral palsy may be due to a reduced number of muscle stem cells.

Conference report on contractures in musculoskeletal and neurological conditions

Limb contractures are debilitating complications associated with various muscle and nervous system disorders. This report summarizes presentations at a conference at the Shirley Ryan AbilityLab in Chicago, Illinois, on April 19-20, 2018, involving researchers and physicians from diverse disciplines who convened to discuss current clinical and preclinical understanding of contractures in Duchenne muscular dystrophy, stroke, cerebral palsy, and other conditions. Presenters described changes in muscle architecture, activation, extracellular matrix, satellite cells, and muscle fiber sarcomeric structure that accompany or predispose muscles to contracture. Participants identified ongoing and future research directions that may lead to understanding of the intersecting factors that trigger contractures. These include additional studies of changes in muscle, tendon, joint, and neuronal tissues during contracture development with imaging, molecular, and physiologic approaches. Participants identified the requirement for improved biomarkers and outcome measures to identify patients likely to develop contractures and to accurately measure efficacy of treatments currently available and under development.

Recent advances in understanding resistance exercise training-induced skeletal muscle hypertrophy in humans

Skeletal muscle plays a pivotal role in the maintenance of physical and metabolic health and, critically, mobility. Accordingly, strategies focused on increasing the quality and quantity of skeletal muscle are relevant, and resistance exercise is foundational to the process of functional hypertrophy. Much of our current understanding of skeletal muscle hypertrophy can be attributed to the development and utilization of stable isotopically labeled tracers. We know that resistance exercise and sufficient protein intake act synergistically and provide the most effective stimuli to enhance skeletal muscle mass; however, the molecular intricacies that underpin the tremendous response variability to resistance exercise-induced hypertrophy are complex. The purpose of this review is to discuss recent studies with the aim of shedding light on key regulatory mechanisms that dictate hypertrophic gains in skeletal muscle mass. We also aim to provide a brief up-to-date summary of the recent advances in our understanding of skeletal muscle hypertrophy in response to resistance training in humans.

Epigenetic Marks at the Ribosomal DNA Promoter in Skeletal Muscle Are Negatively Associated With Degree of Impairment in Cerebral Palsy

Introduction: Cerebral palsy (CP) is the most common motor impairment in children. Skeletal muscles in individuals with CP are typically weak, thin, and stiff. Whether epigenetic changes at the ribosomal DNA (rDNA) promoter are involved in this dysregulation remains unknown. Methods: Skeletal muscle samples were collected from 19 children with CP and 10 typically developed (TD) control children. Methylation of the rDNA promoter was analyzed using the Agena Epityper Mass array and gene expression by qRT-PCR. Results: Biceps brachii muscle ribosome biogenesis was suppressed in CP as compared to TD. Average methylation of the rDNA promoter was not different between CP and TD but negatively correlated to elbow flexor contracture in the CP group. Discussions: We observed a negative correlation between rDNA promoter methylation and degree of muscle contracture in the CP group. Children with CP with more severe motor impairment had less methylation of the rDNA promoter compared to less affected children. This finding suggests the importance of neural input and voluntary muscle movements for promoter methylation to occur in the biceps muscle.

Proteasome inhibition preserves longitudinal growth of denervated muscle and prevents neonatal neuromuscular contractures

Muscle contractures are a prominent and disabling feature of many neuromuscular disorders, including the 2 most common forms of childhood neurologic dysfunction: neonatal brachial plexus injury (NBPI) and cerebral palsy. There are currently no treatment strategies to directly alter the contracture pathology, as the pathogenesis of these contractures is unknown. We previously showed in a mouse model of NBPI that contractures result from impaired longitudinal muscle growth. Current presumed explanations for growth impairment in contractures focus on the dysregulation of muscle stem cells, which differentiate and fuse to existing myofibers during growth, as this process has classically been thought to control muscle growth during the neonatal period. Here, we demonstrate in a mouse model of NBPI that denervation does not prevent myonuclear accretion and that reduction in myonuclear number has no effect on functional muscle length or contracture development, providing definitive evidence that altered myonuclear accretion is not a driver of neuromuscular contractures. In contrast, we observed elevated levels of protein degradation in NBPI muscle, and we demonstrate that contractures can be pharmacologically prevented with the proteasome inhibitor bortezomib. These studies provide what we believe is the first strategy to prevent neuromuscular contractures by correcting the underlying deficit in longitudinal muscle growth.

From movement to action: a new framework for cerebral palsy

The interpretation of cerebral palsy (CP) is closely linked to points of view that are no longer acceptable: 1) the idea that it is primarily a motor problem (posture and movement disorder); 2) the idea that it is only a central (cerebral) pathology; 3) the idea that it is a non-progressive disease (fixed encephalopathy). Actually, the problems that contribute to producing the CP clinical picture are several and complex. First of all, building of the action, starting from subject motivation, through motor imagery and subsequent project elaboration. Sequentially, executive planning, disorder often hidden under the most remarkable alteration of motor patterns and muscle tone. Finally, realization, conditioned by the idea that the locomotor apparatus is only and always the victim of an incapable central nervous system. Little known and very neglected perceptive components can contribute to compromising subject motor control. The influences that primitive changes of musculoskeletal system, often depending on site, nature, size and time of the lesion, exert on the possible choices of the central nervous system are often overlooked. Peripheral structures can in fact modify considerably the expression of palsy (understood as the form of adaptive functions) primitively. At least six different sources of error can be identified in the cerebral palsied child. For a rehabilitative intervention with greater possibilities of effectiveness, it is necessary to recognize and evaluate each of them. Especially as regards the prevention of secondary deformities, the responsibility attributed to physiotherapy must be re-evaluated.

Quantifying Effect of Onabotulinum Toxin A on Passive Muscle Stiffness in Children with Cerebral Palsy Using Ultrasound Shear Wave Elastography

OBJECTIVE

A pilot study was conducted to longitudinally quantify effect of onabotulinum toxin A (BoNT-A) on passive muscle properties in children with cerebral palsy using ultrasound shear wave elastography.

DESIGN

This was a prospective longitudinal cohort study.

RESULTS

Between 1 and 3 mos post-BoNT-A, a significant improvement in the shear modulus of the lateral gastrocnemius was found at 10-degrees plantar flexion (PF) (-7.57 [-10.98, -5.07], P = 0.02) and 0-degrees PF (-14.74 [-18.21, -9.38], P = 0.03). There was a notable, but nonsignificant, difference in shear modulus at 20-degrees PF, 10-degrees PF, and 0-degrees PF between pre-BoNT-A and 1 mo post-BoNT-A. Pre-BoNT-A shear modulus was not significantly different from 3 mos post-BoNT-A at all foot positions. No significant differences in ankle passive range of motion or spasticity were found.

CONCLUSION

Despite no significant change in ankle range of motion or spasticity, shear wave elastography was able to detect a difference in lateral gastrocnemius passive muscle properties in children with cerebral palsy after BoNT-A injections. The difference in passive muscle properties resolved by 3 mos post-BoNT-A.

Muscle contracture and passive mechanics in cerebral palsy

Skeletal muscle contractures represent the permanent shortening of a muscle-tendon unit, resulting in loss of elasticity and, in extreme cases, joint deformation. They may result from cerebral palsy, spinal cord injury, stroke, muscular dystrophy, and other neuromuscular disorders. Contractures are the prototypic and most severe clinical presentation of increased passive mechanical muscle force in humans, often requiring surgical correction. Intraoperative experiments demonstrate that high muscle passive force is associated with sarcomeres that are abnormally stretched, although otherwise normal, with fewer sarcomeres in series. Furthermore, changes in the amount and arrangement of collagen in the extracellular matrix also increase muscle stiffness. Structural light and electron microscopy studies demonstrate that large bundles of collagen, referred to as perimysial cables, may be responsible for this increased stiffness and are regulated by interaction of a number of cell types within the extracellular matrix. Loss of muscle satellite cells may be related to changes in both sarcomeres and extracellular matrix. Future studies are required to determine the underlying mechanism for changes in muscle satellite cells and their relationship (if any) to contracture. A more complete understanding of this mechanism may lead to effective nonsurgical treatments to relieve and even prevent muscle contractures.

Combining muscle morphology and neuromotor symptoms to explain abnormal gait at the ankle joint level in cerebral palsy

BACKGROUND

Individuals with spastic cerebral palsy (CP) have neuromotor symptoms contributing towards their gait patterns. However, the role of altered muscle morphology alongside these symptoms is yet to be fully investigated.

RESEARCH QUESTION

To what extent can medial gastrocnemius and tibialis anterior volume and echo-intensity, plantar/dorsiflexion strength and selective motor control, plantarflexion spasticity and passive ankle dorsiflexion explain abnormal ankle gait.

METHOD

In thirty children and adolescents with spastic CP (8.6 ± 3.4 y/mo) and ten typically developing peers (9.9 ± 2.4 y/mo), normalised muscle volume and echo-intensity were estimated. Both cohorts also underwent three-dimensional gait analysis, whilst for participants with spastic CP, plantar/dorsi-flexion strength and selective motor control, plantarflexion spasticity and maximum ankle dorsiflexion were also measured. The combined contribution of these parameters towards five clinically meaningful features of gait were evaluated, using backwards multiple regression analyses.

RESULTS

With respect to the typically developing cohort, the participants with spastic CP had deficits in normalised medial gastrocnemius and tibialis anterior volume of 40% and 33%, and increased echo-intensity values of 19% and 16%, respectively. The backwards multiple regression analyses revealed that the combination of reduced ankle dorsiflexion, muscle volume, plantarflexion strength and dorsiflexion selective motor control could account for 12-62% of the variance in the chosen features of gait.

SIGNIFICANCE

The combination of altered muscle morphology and neuromotor symptoms partly explained abnormal gait at the ankle in children with spastic CP. Both should be considered as important measures for informed treatment decision-making, but further work is required to better unravel the complex pathophysiology.

Spinal Hyper-Excitability and Altered Muscle Structure Contribute to Muscle Hypertonia in Newborns After Antenatal Hypoxia-Ischemia in a Rabbit Cerebral Palsy Model

Rabbit kits after global antenatal hypoxic-ischemic injury exhibit motor deficits similar to humans with cerebral palsy. We tested several mechanisms previously implicated in spinal hyper-excitability after perinatal brain injury that may explain muscle hypertonia in newborns. Stiffness of hind limb muscles during passive stretch, electromyogram, and spinal excitability by Hoffman reflex, were assessed in rabbit kits with muscle hypertonia after global hypoxic-ischemic brain injury and naïve controls. Affected muscle architecture, motoneuron morphology, primary afferents density, gliosis, and KCC2 expression transporter in the spinal cord were also examined. Decrease knee stiffness after anesthetic administration was larger, but residual stiffness was higher in hypertonic kits compared to controls. Hypertonic kits exhibited muscle shortening and atrophy, in both agonists and antagonists. Sarcomere length was longer in tibialis anterior in hypertonic kits than in controls. Hypertonic kits had decreased rate dependent depression and increased H_max/M_max in H-reflex. Motor neuron soma sizes, primary afferent density were not different between controls and hypertonic kits. Length of dendritic tree and ramification index were lower in hypertonic group. Gene expression of KCC2 was lower in hypertonic kits, but protein content was not different between the groups. In conclusion, while we found evidence of decreased supraspinal inhibitory control and increased excitability by H-reflex that may contribute to neuronal component in hypertonia, increased joint resistance to stretch was explained predominantly by changes in passive properties of muscles and joints. We did not find structural evidence of increased sensory afferent input or morphological changes in motoneurons that might explain increased excitability. Gliosis, observed in spinal gray matter, may contribute to muscle hypertonia.

Resistance Training Combined With Stretching Increases Tendon Stiffness and Is More Effective Than Stretching Alone in Children With Cerebral Palsy: A Randomized Controlled Trial

Aim: Stretching is often used to increase/maintain muscle length and improve joint range of motion (ROM) in children with cerebral palsy (CP). However, outcomes at the muscle (remodeling) and resulting function appear to be highly variable and often unsatisfactory. During passive joint rotation, the Achilles tendon lengthens more than the in-series medial gastrocnemius muscle in children with CP, which might explain the limited effectiveness of stretching interventions. We aimed to ascertain whether increasing tendon stiffness, by performing resistance training, improves the effectiveness of passive stretching, indicated by an increase in medial gastrocnemius fascicle length. Methods: Sixteen children with CP (Age median [IQR]: 9.6 [8.6, 10.5]) completed the study. Children were randomly assigned to a combined intervention of stretching and strengthening of the calf muscles (n = 9) or a control (stretching-only) group (n = 7). Medial gastrocnemius fascicle length at a resting ankle angle, lengthening during passive joint rotations, and tendon stiffness were assessed by combining dynamometry and ultrasound imaging. The study was registered on clinicaltrials.gov (NCT02766491). Results: Resting fascicle length and tendon stiffness increased more in the intervention group compared to the control group (median [95% CI] increase fascicle length: 2.2 [1.3, 4.3] mm; stiffness: 13.6 [9.9, 17.7] N/mm) Maximum dorsiflexion angle increased equally in both groups. Conclusion: This study provides proof of principle that a combined resistance and stretching intervention can increase tendon stiffness and muscle fascicle length in children with CP. This demonstrates that remodeling of muscle structure is possible with non-invasive interventions in spastic CP.

Loss of myogenic potential and fusion capacity of muscle stem cells isolated from contractured muscle in children with cerebral palsy

Cerebral palsy (CP) is the most common cause of pediatric neurodevelopmental and physical disability in the United States. It is defined as a group of motor disorders caused by a nonprogressive perinatal insult to the brain. Although the brain lesion is nonprogressive, there is a progressive, lifelong impact on skeletal muscles, which are shorter, spastic, and may develop debilitating contractures. Satellite cells are resident muscle stem cells that are indispensable for postnatal growth and regeneration of skeletal muscles. Here we measured the myogenic potential of satellite cells isolated from contractured muscles in children with CP. When compared with typically developing (TD) children, satellite cell-derived myoblasts from CP differentiated more slowly (slope: 0.013 (SD 0.013) CP vs. 0.091 (SD 0.024) TD over 24 h, P < 0.001) and fused less (fusion index: 21.3 (SD 8.6) CP vs. 81.3 (SD 7.7) TD after 48 h, P < 0.001) after exposure to low-serum conditions that stimulated myotube formation. This impairment was associated with downregulation of several markers important for myoblast fusion and myotube formation, including DNA methylation-dependent inhibition of promyogenic integrin-β 1D (ITGB1D) protein expression levels (-50% at 42 h), and ~25% loss of integrin-mediated focal adhesion kinase phosphorylation. The cytidine analog 5-Azacytidine (5-AZA), a demethylating agent, restored ITGB1D levels and promoted myogenesis in CP cultures. Our data demonstrate that muscle contractures in CP are associated with loss of satellite cell myogenic potential that is dependent on DNA methylation patterns affecting expression of genetic programs associated with muscle stem cell differentiation and muscle fiber formation.

Development of a transendothelial shuttle by macrophage modification

One of the limiting factors in tissue regeneration, particularly in the context of chronic disease such as myodystrophy, motor neuron disease, sarcopenia, and cardiovascular disease, is limited availability of stem cells. We propose employing autologous macrophages to deliver stem cells, thereby facilitating tissue regeneration, by a novel and relatively non-invasive therapeutic intervention. Circulatory monocytic cells of M1 phenotype have capacity for transendothelial migration to infiltrate damaged tissue, making them ideal delivery vehicles. However, in order to deliver viable stem cells, these macrophages must undergo phagosome maturation arrest. Our aim was to induce phagosome maturation arrest in prepolarised M1 macrophages, whilst maintaining capacity for phagocytic engulfment (including phagosome formation) and transendothelial migration. Primary human M1 macrophages were treated with a wortmannin-concanamycin A-chloroquine cocktail to induce arrest. Modified cells were allowed to ingest 4.5 μm protein-coated fluorescent latex beads (simulated stem cells), before migratory capacity in response to MCP-1 was assessed over a 2-hr period in a Transwell co-culture system. Data indicate that phagosome acidification (as indicated by pHrodo®) was prevented in treated cells, effectively limiting digestion of ingested "cargo" (1.23 ± 0.26% vs. 7.52 ± 0.98% in controls; p < .0001). Neither phagocytic engulfment capacity (68.67 ± 3.51% vs. 61.19 ± 4.68%) nor migratory capacity (70.14 ± 12.6 vs. 72.86 ± 16.0 migrated cells per well) was compromised. We conclude that macrophages were successfully modified into transendothelial delivery vehicles, without compromising required functionality. This delivery system can be exploited to develop a novel method for focussed stem cell and/or drug delivery.

Reduced skeletal muscle satellite cell number alters muscle morphology after chronic stretch but allows limited serial sarcomere addition

INTRODUCTION

Muscles add sarcomeres in response to stretch, presumably to maintain optimal sarcomere length. Clinical evidence from patients with cerebral palsy, who have both decreased serial sarcomere number and reduced satellite cells (SCs), suggests a hypothesis that SCs may be involved in sarcomere addition.

METHODS

A transgenic Pax7-DTA mouse model underwent conditional SC depletion, and their soleii were then stretch-immobilized to assess the capacity for sarcomere addition. Muscle architecture, morphology, and extracellular matrix (ECM) changes were also evaluated.

RESULTS

Mice in the SC-reduced group achieved normal serial sarcomere addition in response to stretch. However, muscle fiber cross-sectional area was significantly smaller and was associated with hypertrophic ECM changes, consistent with fibrosis.

CONCLUSIONS

While a reduced SC population does not hinder serial sarcomere addition, SCs play a role in muscle adaptation to chronic stretch that involves maintenance of both fiber cross-sectional area and ECM structure. Muscle Nerve 55: 384-392, 2017.

Skeletal muscle fiber-type specific succinate dehydrogenase activity in cerebral palsy

INTRODUCTION

Children with cerebral palsy (CP) exhibit increased energy expenditure during movement, but whether this is due in part to decrements in skeletal muscle mitochondrial oxidative capacity is unknown. Accordingly, we compared fiber-type specific succinate dehydrogenase (SDH) activity in children with CP with typically developing (TD) children.

METHODS

SDH activity and myofiber areas of type 1 and 2A fibers were measured in semitendinosus biopsies of both groups (n = 5/group).

RESULTS

SDH activity was ∼35% higher in type 1 compared with type 2A fibers, but there were no differences between groups. Average myofiber area was 45% smaller in CP versus TD (P < 0.05), and type 2A fibers were 32% larger than type 1 fibers (P < 0.05) only in TD children.

CONCLUSIONS

Fiber-type specific SDH activity is similar between TD children and children with CP. This suggests that increased energy expenditure in children with CP is not related to impaired mitochondrial oxidative capacity. Muscle Nerve, 2016 Muscle Nerve 55: 122-124, 2017.

Gastrocnemius muscle-tendon interaction during walking in typically-developing adults and children, and in children with spastic cerebral palsy

BACKGROUND

Our understanding of the interaction of muscle bellies and their tendons in individuals with muscle pathology is limited. Knowledge of these interactions may inform us of the effects of musculoskeletal pathologies on muscle-tendon dynamics and the subsequent neurological control strategies used in gait. Here, we investigate gastrocnemius muscle-tendon interaction in typically-developing (TD) adults and children, and in children with spastic cerebral palsy (SCP).

METHODS

We recruited six TD adults (4 female; mean age: 34 yrs. (24-54)), eight TD children (5 female; mean age: 10 yrs. (6-12)) and eight independently ambulant children with SCP (5 female; mean age 9 yrs. (6-12); 3 unilaterally-affected). A combination of 3D motion capture and 2D real-time ultrasound imaging were used to compute the gastrocnemius musculo-tendinous unit (MTU) length and estimate muscle belly and tendon lengths during walking. For the TD subjects, the measurements were made for heel-toe walking and voluntary toe-walking.

RESULTS

The gastrocnemius muscle bellies of children with SCP lengthened during single support (p = 0.003). In contrast, the muscle bellies of TD subjects did not demonstrate an increase in length over the period of single support under heel-toe or toe-walking conditions.

CONCLUSION

We observed lengthening of the gastrocnemius muscle bellies in children with SCP during single support, a phase of the gait cycle in which the muscle is reported consistently to be active. Repeated lengthening of muscle bellies while they are active may lead to muscle damage and have implications for the natural history of gait in this group.