Massive muscle cell degeneration in the early stage of merosin-deficient congenital muscular dystrophy

Characteristics of nuclear architectural abnormalities of myotubes differentiated from LmnaH222P/H222P skeletal muscle cells

The presence of nuclear architectural abnormalities is a hallmark of the nuclear envelopathies, which are a group of diseases caused by mutations in genes encoding nuclear envelope proteins. Mutations in the lamin A/C gene cause several diseases, named laminopathies, including muscular dystrophies, progeria syndromes, and lipodystrophy. A mouse model carrying with the LmnaH222P/H222P mutation (H222P) was shown to develop severe cardiomyopathy but only mild skeletal myopathy, although abnormal nuclei were observed in their striated muscle. In this report, we analyzed the abnormal-shaped nuclei in myoblasts and myotubes isolated from skeletal muscle of H222P mice, and evaluated the expression of nuclear envelope proteins in these abnormal myonuclei. Primary skeletal muscle cells from H222P mice proliferated and efficiently differentiated into myotubes in vitro, similarly to those from wild-type mice. During cell proliferation, few abnormal-shaped nuclei were detected; however, numerous markedly abnormal myonuclei were observed in myotubes from H222P mice on days 5 and 7 of differentiation. Time-lapse observation demonstrated that myonuclei with a normal shape maintained their normal shape, whereas abnormal-shaped myonuclei remained abnormal for at least 48 h during differentiation. Among the abnormal-shaped myonuclei, 65% had a bleb with a string structure, and 35% were severely deformed. The area and nuclear contents of the nuclear blebs were relatively stable, whereas the myocytes with nuclear blebs were actively fused within primary myotubes. Although myonuclei were markedly deformed, the deposition of DNA damage marker (γH2AX) or apoptotic marker staining was rarely observed. Localizations of lamin A/C and emerin were maintained within the blebs, strings, and severely deformed regions of myonuclei; however, lamin B1, nesprin-1, and a nuclear pore complex protein were absent in these abnormal regions. These results demonstrate that nuclear membranes from H222P skeletal muscle cells do not rupture and are resistant to DNA damage, despite these marked morphological changes.

Phase 1 Open-Label Study of Omigapil in Patients With LAMA2- or COL6-Related Dystrophy

Background and Objectives

Omigapil is a small molecule which inhibits the GAPDH-Siah1-mediated apoptosis pathway. Apoptosis is a pathomechanism underlying the congenital muscular dystrophy subtypes LAMA2-related dystrophy (LAMA2-RD) and COL6-related dystrophy (COL6-RD). Studies of omigapil in the (dyw/dyw) LAMA2-RD mouse model demonstrated improved survival, and studies in the (dy2J/dy2J) LAMA2-RD mouse model and the (Col6a1-/-) COL6-RD mouse model demonstrated decreased apoptosis.

Methods

A phase 1 open-label, sequential group, ascending oral dose, cohort study of omigapil in patients with LAMA2-RD or COL6-RD ages 5-16 years was performed (1) to establish the pharmacokinetic (PK) profile of omigapil at a range of doses, (2) to evaluate the safety and tolerability of omigapil at a range of doses, and (3) to establish the feasibility of conducting disease-relevant clinical assessments. Patients were enrolled in cohorts of size 4, with each patient receiving 4 weeks of vehicle run-in and 12 weeks of study drug (at daily doses ranging from 0.02 to 0.08 mg/kg). PK data from each cohort were analyzed before each subsequent dosing cohort was enrolled. A novel, adaptive dose-finding method (stochastic approximation with virtual observation recursion) was used to allow for dose escalation/reduction between cohorts based on PK data.

Results

Twenty patients were enrolled at the NIH (LAMA2-RD: N = 10; COL6-RD: N = 10). Slightly greater than dose-proportional increases in systemic exposure to omigapil were seen at doses 0.02-0.08 mg/kg/d. The dose which achieved patient exposure within the pre-established target area under the plasma concentration-vs-time curve (AUC0-24h) range was 0.06 mg/kg/d. In general, omigapil was safe and well tolerated. No consistent changes were seen in the disease-relevant clinical assessments during the duration of the study.

Discussion

This study represents the thus far only clinical trial of a therapeutic small molecule for LAMA2-RD and COL6-RD, completed with an adaptive trial design to arrive at dose adjustments. The trial met its primary end point and established that the PK profile of omigapil is suitable for further development in pediatric patients with LAMA2-RD or COL6-RD, the most common forms of congenital muscular dystrophy. While within the short duration of the study disease-relevant clinical assessments did not demonstrate significant changes, this study establishes the feasibility of performing interventional clinical trials in these rare disease patient populations.

Classification of Evidence

This study provides Class IV evidence of omigapil in a dose-finding phase 1 study.

Trial Registration Information

Clinical Trials NCT01805024.

Lama1 upregulation prolongs the lifespan of the dyH/dyH mouse model of LAMA2-related congenital muscular dystrophy

LAMA2-related congenital muscular dystrophy (LAMA2-CMD), characterized by laminin-α2 deficiency, is debilitating and ultimately fatal. To date, no effective therapy has been clinically available. Laminin-α1, which shares significant similarities with laminin-α2, has been proven as a viable compensatory modifier. To evaluate its clinical applicability, we establish a Lama2 exon-3 deletion mouse model (dyH/dyH). The dyH/dyH mice exhibit early lethality and typical LAMA2-CMD phenotypes, allowing the evaluation of various endpoints. In dyH/dyH mice treated with synergistic activation mediator-based CRISPRa-mediated Lama1 upregulation, a nearly doubled median survival is observed, as well as improvements in weight and grip. Significant therapeutical effects are revealed by MRI, serum biochemical indices, and muscle pathology studies. Treating LAMA2-CMD with LAMA1 upregulation is feasible and that early intervention can alleviate symptoms and extend lifespan. Additionally, we reveal limitations of LAMA1 upregulation, including high-dose mortality and non-sustained expression, which require further optimization in future studies.

Novel Homozygous Pathogenic Mutations of LAMA 2 Gene in Patients with Congen ital Muscular Dystrophy

The laminin α2 subunit is a protein encoded by the laminin α2 gene(LAMA2) which has the role of adhesion (attachment of cells to one another). Genetics consideration showed that mutation in LAMA2 caused a collection of muscle-wasting conditions called muscular dystrophy. This disorder causes disconnection of muscular cells and degeneration of the musculoskeletal system. In this study, we defined the molecular consideration of three patients with laminin α2 deficiency by clinical presentations of congenital muscular dystrophy. In this regard, 65 exons of the LAMA2 gene were amplified by polymerase chain reaction. Moreover, multiple ligation-dependent probe amplification and next generation sequencing (NGS) were carried out for all the patients. Because of NGS negativity, gene sequencing was performed. Results of searching for rearrangements of the LAMA2 gene enabled us to recognize homozygous pathogenic mutations c.2049_c.2050del, c.7156-2A>G, and c,1303C>T. These mutations produce an out-of-frame transcript that will be degraded by nonsense mediated decay. Therefore, we think these changes are pathogenic ones.

A Family of Laminin α2 Chain-Deficient Mouse Mutants: Advancing the Research on LAMA2-CMD

The research on laminin α2 chain-deficient congenital muscular dystrophy (LAMA2-CMD) advanced rapidly in the last few decades, largely due to availability of good mouse models for the disease and a strong interest in preclinical studies from scientists all over the world. These mouse models continue to provide a solid platform for understanding the LAMA2-CMD pathology. In addition, they enable researchers to test laborious, necessary routines, but also the most creative scientific approaches in order to design therapy for this devastating disorder. In this review we present animals belonging to the laminin α2 chain-deficient “dy/dy” mouse family (dy/dy, dy^2J/dy^2J, dy^3K/dy^3K, dy^W/dy^W, et al.) and a summary of the scientific progress they facilitated. We also raise a few questions that need to be addressed in order to maximize the usefulness of laminin α2 murine mutants and to further advance the LAMA2-CMD studies. We believe that research opportunities offered by the mouse models for LAMA2-CMD will continuously support our efforts to find a treatment for the disease.

Antioxidants Reduce Muscular Dystrophy in the dy2J/dy2J Mouse Model of Laminin α2 Chain-Deficient Muscular Dystrophy

Congenital muscular dystrophy with laminin α2 chain-deficiency (LAMA2-CMD) is a severe neuromuscular disorder without a cure. Using transcriptome and proteome profiling as well as functional assays, we previously demonstrated significant metabolic impairment in skeletal muscle from LAMA2-CMD patients and mouse models. Reactive oxygen species (ROS) increase when oxygen homeostasis is not maintained and, here, we investigate whether oxidative stress indeed is involved in the pathogenesis of LAMA2-CMD. We also analyze the effects of two antioxidant molecules, N-acetyl-L-cysteine (NAC) and vitamin E, on disease progression in the dy^2J/dy^2J mouse model of LAMA2-CMD. We demonstrate increased ROS levels in LAMA2-CMD mouse and patient skeletal muscle. Furthermore, NAC treatment (150 mg/kg IP for 6 days/week for 3 weeks) led to muscle force loss prevention, reduced central nucleation and decreased the occurrence of apoptosis, inflammation, fibrosis and oxidative stress in LAMA2-CMD muscle. In addition, vitamin E (40 mg/kg oral gavage for 6 days/week for 2 weeks) improved morphological features and reduced inflammation and ROS levels in dy^2J/dy^2J skeletal muscle. We suggest that NAC and to some extent vitamin E might be potential future supportive treatments for LAMA2-CMD as they improve numerous pathological hallmarks of LAMA2-CMD.

A novel de novo variant of LAMA2 contributes to merosin deficient congenital muscular dystrophy type 1A: Case report

Merosin deficient congenital muscular dystrophy type 1A (MDC1A) is caused by defects in the LAMA2 gene. Patients with MDC1A exhibit severe symptoms, including congenital hypotonia, delayed motor development and contractures. The present case report describes a Vietnamese male child with clinical manifestations of delayed motor development, limb-girdle muscular dystrophy, severe scoliosis and white matter abnormality in the brain. Whole exome sequencing (WES) was performed with subsequent validation using Sanger sequencing, and a de novo missense variant (NM_000426.3:c.1964T>C, p.Leu655Pro) and a splice site variant (NG_008678.1:c.3556-13T>A) in the LAMA2 gene of the proband was detected. The missense variant located in exon 14 and has not been reported previously, to the best of our knowledge; whereas the splice site variant has been previously reported to cause premature termination of transcription in patients with MDC1A. In silico tools predicted that the missense variant was damaging. Phenotype-genotype analysis suggested that this proband was associated with classical early onset MDC1A. The co-existence of a de novo and a heterozygous variant in the LAMA2 gene suggested that the de novo variant contributed to the autosomal recessive manner of the disease. Careful consideration of this event by clinical confirmation of parental carrier status may help to accurately determine the risk of occurrence of this disease in future offspring. Additionally, WES is recommended as a powerful tool to assist in identifying potentially causative variants for heterogeneous diseases such as MDC1A.

Immunobiology of Inherited Muscular Dystrophies

The immune response to acute muscle damage is important for normal repair. However, in chronic diseases such as many muscular dystrophies, the immune response can amplify pathology and play a major role in determining disease severity. Muscular dystrophies are inheritable diseases that vary tremendously in severity, but share the progressive loss of muscle mass and function that can be debilitating and lethal. Mutations in diverse genes cause muscular dystrophy, including genes that encode proteins that maintain membrane strength, participate in membrane repair, or are components of the extracellular matrix or the nuclear envelope. In this article, we explore the hypothesis that an important feature of many muscular dystrophies is an immune response adapted to acute, infrequent muscle damage that is misapplied in the context of chronic injury. We discuss the involvement of the immune system in the most common muscular dystrophy, Duchenne muscular dystrophy, and show that the immune system influences muscle death and fibrosis as disease progresses. We then present information on immune cell function in other muscular dystrophies and show that for many muscular dystrophies, release of cytosolic proteins into the extracellular space may provide an initial signal, leading to an immune response that is typically dominated by macrophages, neutrophils, helper T-lymphocytes, and cytotoxic T-lymphocytes. Although those features are similar in many muscular dystrophies, each muscular dystrophy shows distinguishing features in the magnitude and type of inflammatory response. These differences indicate that there are disease-specific immunomodulatory molecules that determine response to muscle cell damage caused by diverse genetic mutations. © 2018 American Physiological Society. Compr Physiol 8:1313-1356, 2018.

Extracellular matrix-driven congenital muscular dystrophies

Skeletal muscle function relies on the myofibrillar apparatus inside myofibers as well as an intact extracellular matrix surrounding each myofiber. Muscle extracellular matrix (ECM) plays several roles including but not limited to force transmission, regulation of growth factors and inflammatory responses, and influencing muscle stem cell (i.e. satellite cell) proliferation and differentiation. In most myopathies, muscle ECM undergoes remodeling and fibrotic changes that may be maladaptive for normal muscle function and recovery. In addition, mutations in skeletal muscle ECM and basement proteins can cause muscle disease. In this review, we summarize the clinical features of two of the most common congenital muscular dystrophies, COL6-related dystrophies and LAMA2-related dystrophies, which are caused by mutations in muscle ECM and basement membrane proteins. The study of clinical features of these diseases has helped to inform basic research and understanding of the biology of muscle ECM. In return, basic studies of muscle ECM have provided the conceptual framework to develop therapeutic interventions for these and other similar disorders of muscle.

Tackling muscle fibrosis: From molecular mechanisms to next generation engineered models to predict drug delivery

Muscle fibrosis represents the end stage consequence of different diseases, among which muscular dystrophies, leading to severe impairment of muscle functions. Muscle fibrosis involves the production of several growth factors, cytokines and proteolytic enzymes and is strictly associated to inflammatory processes. Moreover, fibrosis causes profound changes in tissue properties, including increased stiffness and density, lower pH and oxygenation. Up to now, there is no therapeutic approach able to counteract the fibrotic process and treatments directed against muscle pathologies are severely impaired by the harsh conditions of the fibrotic environment. The design of new therapeutics thus need innovative tools mimicking the obstacles posed by the fibrotic environment to their delivery. This review will critically discuss the role of in vivo and 3D in vitro models in this context and the characteristics that an ideal model should possess to help the translation from bench to bedside of new candidate anti-fibrotic agents.

A novel early onset phenotype in a zebrafish model of merosin deficient congenital muscular dystrophy

Merosin deficient congenital muscular dystrophy (MDC1A) is a severe neuromuscular disorder with onset in infancy that is associated with severe morbidities (particularly wheelchair dependence) and early mortality. It is caused by recessive mutations in the LAMA2 gene that encodes a subunit of the extracellular matrix protein laminin 211. At present, there are no treatments for this disabling disease. The zebrafish has emerged as a powerful model system for the identification of novel therapies. However, drug discovery in the zebrafish is largely dependent on the identification of phenotypes suitable for chemical screening. Our goal in this study was to elucidate novel, early onset abnormalities in the candyfloss (caf) zebrafish, a model of MDC1A. We uncovered and characterize abnormalities in spontaneous coiling, the earliest motor movement in the zebrafish, as a fully penetrant change specific to caf mutants that is ideal for future drug testing.

Magnetic Resonance Imaging Is Sensitive to Pathological Amelioration in a Model for Laminin-Deficient Congenital Muscular Dystrophy (MDC1A)

Purpose

To elucidate the reliability of MRI as a non-invasive tool for assessing in vivo muscle health and pathological amelioration in response to Losartan (Angiotensin II Type 1 receptor blocker) in DyW mice (mouse model for Laminin-deficient Congenital Muscular Dystrophy Type 1A).

Methods

Multiparametric MR quantifications along with histological/biochemical analyses were utilized to measure muscle volume and composition in untreated and Losartan-treated 7-week old DyW mice.

Results

MRI shows that DyW mice have significantly less hind limb muscle volume and areas of hyperintensity that are absent in WT muscle. DyW mice also have significantly elevated muscle levels (suggestive of inflammation and edema). Muscle T₂ returned to WT levels in response to Losartan treatment. When considering only muscle pixels without T₂ elevation, DyW T₂ levels are significantly lower than WT (suggestive of fibrosis) whereas Losartan-treated animals do not demonstrate this decrease in muscle T₂. MRI measurements suggestive of elevated inflammation and fibrosis corroborate with increased Mac-1 positive cells as well as increased Picrosirius red staining/COL1a gene expression that is returned to WT levels in response to Losartan.

Conclusions

MRI is sensitive to and tightly corresponds with pathological changes in DyW mice and thus is a viable and effective non-invasive tool for assessing pathological changes.

Laminin-α2 Chain-Deficient Congenital Muscular Dystrophy: Pathophysiology and Development of Treatment

Laminin-211 is a major constituent of the skeletal muscle basement membrane. It stabilizes skeletal muscle and influences signal transduction events from the myomatrix to the muscle cell. Mutations in the gene encoding the α2 chain of laminin-211 lead to congenital muscular dystrophy type 1A (MDC1A), a life-threatening disease characterized by severe hypotonia, progressive muscle weakness, and joint contractures. Common complications include severely impaired motor ability, respiratory failure, and feeding difficulties. Several adequate animal models for laminin-α2 chain deficiency exist and analyses of different MDC1A mouse models have led to a significant improvement in our understanding of MDC1A pathogenesis. Importantly, the animal models have been indispensable tools for the preclinical development of new therapeutic approaches for laminin-α2 chain deficiency, highlighting a number of important disease driving mechanisms that can be targeted by pharmacological approaches. In this chapter, I will describe laminin-211 and discuss the cellular and molecular pathophysiology of MDC1A as well as progression toward development of treatment.

Dysregulation of matricellular proteins is an early signature of pathology in laminin-deficient muscular dystrophy

Background

MDC1A is a congenital neuromuscular disorder with developmentally complex and progressive pathologies that results from a deficiency in the protein laminin α₂. MDC1A is associated with a multitude of pathologies, including increased apoptosis, inflammation and fibrosis. In order to assess and treat a complicated disease such as MDC1A, we must understand the natural history of the disease so that we can identify early disease drivers and pinpoint critical time periods for implementing potential therapies.

Results

We found that DyW mice show significantly impaired myogenesis and high levels of apoptosis as early as postnatal week 1. We also saw a surge of inflammatory response at the first week, marked by high levels of infiltrating macrophages, nuclear factor κB activation, osteopontin expression and overexpression of inflammatory cytokines. Fibrosis markers and related pathways were also observed to be elevated throughout early postnatal development in these mice, including periostin, collagen and fibronectin gene expression, as well as transforming growth factor β signaling. Interestingly, fibronectin was found to be the predominant fibrous protein of the extracellular matrix in early postnatal development. Lastly, we observed upregulation in various genes related to angiotensin signaling.

Methods

We sought out to examine the dysregulation of various pathways throughout early development (postnatal weeks 1-4) in the DyW mouse, the most commonly used mouse model of laminin-deficient muscular dystrophy. Muscle function tests (stand-ups and retractions) as well as gene (qRT-PCR) and protein levels (western blot, ELISA), histology (H&E, picrosirius red staining) and immunohistochemistry (fibronectin, TUNEL assay) were used to assess dysregulation of matricelluar protieins.

Conclusions

Our results implicate the involvement of multiple signaling pathways in driving the earliest stages of pathology in DyW mice. As opposed to classical dystrophies, such as Duchenne muscular dystrophy, the dysregulation of various matricellular proteins appears to be a distinct feature of the early progression of DyW pathology. On the basis of our results, we believe that therapies that may reduce apoptosis and stabilize the homeostasis of extracellular matrix proteins may have increased efficacy if started at a very early age.

Bortezomib partially improves laminin α2 chain-deficient muscular dystrophy

Congenital muscular dystrophy, caused by mutations in LAMA2 (the gene encoding laminin α2 chain), is a severe and incapacitating disease for which no therapy is yet available. We have recently demonstrated that proteasome activity is increased in laminin α2 chain-deficient muscle and that treatment with the nonpharmaceutical proteasome inhibitor MG-132 reduces muscle pathology in laminin α2 chain-deficient dy(3K)/dy(3K) mice. Here, we explore the use of the selective and therapeutic proteasome inhibitor bortezomib (currently used for treatment of relapsed multiple myeloma and mantle cell lymphoma) in dy(3K)/dy(3K) mice and in congenital muscular dystrophy type 1A muscle cells. Outcome measures included quantitative muscle morphology, gene and miRNA expression analyses, proteasome activity, motor activity, and survival. Bortezomib improved several histological hallmarks of disease, partially normalized miRNA expression (miR-1 and miR-133a), and enhanced body weight, locomotion, and survival of dy(3K)/dy(3K) mice. In addition, bortezomib reduced proteasome activity in congenital muscular dystrophy type 1A myoblasts and myotubes. These findings provide evidence that the proteasome inhibitor bortezomib partially reduces laminin α2 chain-deficient muscular dystrophy. Investigation of the clinical efficacy of bortezomib administration in congenital muscular dystrophy type 1A clinical trials may be warranted.

Roles of nonmyogenic mesenchymal progenitors in pathogenesis and regeneration of skeletal muscle

Adult skeletal muscle possesses a remarkable regenerative ability that is dependent on satellite cells. However, skeletal muscle is replaced by fatty and fibrous connective tissue in several pathological conditions. Fatty and fibrous connective tissue becomes a major cause of muscle weakness and leads to further impairment of muscle function. Because the occurrence of fatty and fibrous connective tissue is usually associated with severe destruction of muscle, the idea that dysregulation of the fate switch in satellite cells may underlie this pathological change has emerged. However, recent studies identified nonmyogenic mesenchymal progenitors in skeletal muscle and revealed that fatty and fibrous connective tissue originates from these progenitors. Later, these progenitors were also demonstrated to be the major contributor to heterotopic ossification in skeletal muscle. Because nonmyogenic mesenchymal progenitors represent a distinct cell population from satellite cells, targeting these progenitors could be an ideal therapeutic strategy that specifically prevents pathological changes of skeletal muscle, while preserving satellite cell-dependent regeneration. In addition to their roles in pathogenesis of skeletal muscle, nonmyogenic mesenchymal progenitors may play a vital role in muscle regeneration by regulating satellite cell behavior. Conversely, muscle cells appear to regulate behavior of nonmyogenic mesenchymal progenitors. Thus, these cells regulate each other reciprocally and a proper balance between them is a key determinant of muscle integrity. Furthermore, nonmyogenic mesenchymal progenitors have been shown to maintain muscle mass in a steady homeostatic condition. Understanding the nature of nonmyogenic mesenchymal progenitors will provide valuable insight into the pathophysiology of skeletal muscle. In this review, we focus on nonmyogenic mesenchymal progenitors and discuss their roles in muscle pathogenesis, regeneration, and homeostasis.

Immortalized myogenic cells from congenital muscular dystrophy type1A patients recapitulate aberrant caspase activation in pathogenesis: a new tool for MDC1A research

Background

Congenital muscular dystrophy Type 1A (MDC1A) is a severe, recessive disease of childhood onset that is caused by mutations in the LAMA2 gene encoding laminin-α2. Studies with both mouse models and primary cultures of human MDC1A myogenic cells suggest that aberrant activation of cell death is a significant contributor to pathogenesis in laminin-α2-deficiency.

Methods

To overcome the limited population doublings of primary cultures, we generated immortalized, clonal lines of human MDC1A myogenic cells via overexpression of both CDK4 and the telomerase catalytic component (human telomerase reverse transcriptase (hTERT)).

Results

The immortalized MDC1A myogenic cells proliferated indefinitely when cultured at low density in high serum growth medium, but retained the capacity to form multinucleate myotubes and express muscle-specific proteins when switched to low serum medium. When cultured in the absence of laminin, myotubes formed from immortalized MDC1A myoblasts, but not those formed from immortalized healthy or disease control human myoblasts, showed significantly increased activation of caspase-3. This pattern of aberrant caspase-3 activation in the immortalized cultures was similar to that found previously in primary MDC1A cultures and laminin-α2-deficient mice.

Conclusions

Immortalized MDC1A myogenic cells provide a new resource for studies of pathogenetic mechanisms and for screening possible therapeutic approaches in laminin-α2-deficiency.

Triggering regeneration and tackling apoptosis: a combinatorial approach to treating congenital muscular dystrophy type 1 A

Merosin-deficient congenital muscular dystrophy type 1A (MDC1A) is an autosomal recessive disorder caused by mutations in the laminin-α2 gene (OMIM: 607855). Currently, no treatment other than palliative care exists for this disease. In our previous work, genetic interventions in the Lama2(Dy-w) mouse model for MDC1A demonstrated that limited regeneration and uncontrolled apoptosis are important drivers of this disease. However, targeting one of these disease drivers without addressing the other results in only partial rescue of the phenotype. The present study was designed to determine whether utilizing a combinatorial treatment approach can lead to a more profound amelioration of the disease pathology. To accomplish this task, we generated Bax-null Lama2(Dy-w)mice that overexpressed muscle-specific IGF-1 (Lama2(Dy-w)Bax(-/-)+IGF-1tg). Further to test the translational potential of IGF-1 administration in combination with Bax inhibition, we treated Lama2(Dy-w)Bax(-/-) mice postnatally with systemic recombinant human IGF-1 (IPLEX™). These two combinatorial treatments lead to similar, promising outcomes. In addition to increased body and muscle weights, both transgenic overexpression and systemic administration of IGF-1 combined with Bax-inhibition resulted in improved muscle phenotype and locomotory function that were nearly indistinguishable from wild-type mice. These results provide a fundamental proof of concept that justifies the use of a combination therapy as an effective treatment for MDC1A and highlights a compelling argument toward shifting the paradigm in treating multifaceted neuromuscular diseases.

Omigapil treatment decreases fibrosis and improves respiratory rate in dy(2J) mouse model of congenital muscular dystrophy

Introduction

Congenital muscular dystrophy is a distinct group of diseases presenting with weakness in infancy or childhood and no current therapy. One form, MDC1A, is the result of laminin alpha-2 deficiency and results in significant weakness, respiratory insufficiency and early death. Modification of apoptosis is one potential pathway for therapy in these patients.

Methods

dy^2J mice were treated with vehicle, 0.1 mg/kg or 1 mg/kg of omigapil daily via oral gavage over 17.5 weeks. Untreated age matched BL6 mice were used as controls. Functional, behavioral and histological measurements were collected.

Results

dy^2J mice treated with omigapil showed improved respiratory rates compared to vehicle treated dy^2J mice (396 to 402 vs. 371 breaths per minute, p<0.03) and similar to control mice. There were no statistical differences in normalized forelimb grip strength between dy^2J and controls at baseline or after 17.5 weeks and no significant differences seen among the dy^2J treatment groups. At 30–33 weeks of age, dy^2J mice treated with 0.1 mg/kg omigapil showed significantly more movement time and less rest time compared to vehicle treated. dy^2J mice showed normal cardiac systolic function throughout the trial. dy^2J mice had significantly lower hindlimb maximal (p<0.001) and specific force (p<0.002) compared to the control group at the end of the trial. There were no statistically significant differences in maximal or specific force among treatments. dy^2J mice treated with 0.1 mg/kg/day omigapil showed decreased percent fibrosis in both gastrocnemius (p<0.03) and diaphragm (p<0.001) compared to vehicle, and in diaphragm (p<0.013) when compared to 1 mg/kg/day omigapil treated mice. Omigapil treated dy^2J mice demonstrated decreased apoptosis.

Conclusion

Omigapil therapy (0.1 mg/kg) improved respiratory rate and decreased skeletal and respiratory muscle fibrosis in dy^2J mice. These results support a putative role for the use of omigapil in laminin deficient congenital muscular dystrophy patients.

Laminin-211 in skeletal muscle function

A chain is no stronger than its weakest link is an old idiom that holds true for muscle biology. As the name implies, skeletal muscle's main function is to move the bones. However, for a muscle to transmit force and withstand the stress that contractions give rise to, it relies on a chain of proteins attaching the cytoskeleton of the muscle fiber to the surrounding extracellular matrix. The importance of this attachment is illustrated by a large number of muscular dystrophies caused by interruption of the cytoskeletal-extracellular matrix interaction. One of the major components of the extracellular matrix is laminin, a heterotrimeric glycoprotein and a major constituent of the basement membrane. It has become increasingly apparent that laminins are involved in a multitude of biological functions, including cell adhesion, differentiation, proliferation, migration and survival. This review will focus on the importance of laminin-211 for normal skeletal muscle function.

A splice site mutation in laminin-α2 results in a severe muscular dystrophy and growth abnormalities in zebrafish

Congenital muscular dystrophy (CMD) is a clinically and genetically heterogeneous group of inherited muscle disorders. In patients, muscle weakness is usually present at or shortly after birth and is progressive in nature. Merosin deficient congenital muscular dystrophy (MDC1A) is a form of CMD caused by a defect in the laminin-α2 gene (LAMA2). Laminin-α2 is an extracellular matrix protein that interacts with the dystrophin-dystroglycan (DGC) complex in membranes providing stability to muscle fibers. In an N-ethyl-N-nitrosourea mutagenesis screen to develop zebrafish models of neuromuscular diseases, we identified a mutant fish that exhibits severe muscular dystrophy early in development. Genetic mapping identified a splice site mutation in the lama2 gene. This splice site is highly conserved in humans and this mutation results in mis-splicing of RNA and a loss of protein function. Homozygous lama2 mutant zebrafish, designated lama2^cl501/cl501, exhibited reduced motor function and progressive degeneration of skeletal muscles and died at 8–15 days post fertilization. The skeletal muscles exhibited damaged myosepta and detachment of myofibers in the affected fish. Laminin-α2 deficiency also resulted in growth defects in the brain and eye of the mutant fish. This laminin-α2 deficient mutant fish represents a novel disease model to develop therapies for modulating splicing defects in congenital muscular dystrophies and to restore the muscle function in human patients with CMD.

Cell-matrix interactions in muscle disease

The extracellular matrix (ECM) provides a solid scaffold and signals to cells through ECM receptors. The cell-matrix interactions are crucial for normal biological processes and when disrupted they may lead to pathological processes. In particular, the biological importance of ECM-cell membrane-cytoskeleton interactions in skeletal muscle is accentuated by the number of inherited muscle diseases caused by mutations in proteins conferring these interactions. In this review we introduce laminins, collagens, dystroglycan, integrins, dystrophin and sarcoglycans. Mutations in corresponding genes cause various forms of muscular dystrophy. The muscle disorders are presented as well as advances toward the development of treatment.

Autophagy is increased in laminin α2 chain-deficient muscle and its inhibition improves muscle morphology in a mouse model of MDC1A

Congenital muscular dystrophy caused by laminin α2 chain deficiency (also known as MDC1A) is a severe and incapacitating disease, characterized by massive muscle wasting. The ubiquitin-proteasome system plays a major role in muscle wasting and we recently demonstrated that increased proteasomal activity is a feature of MDC1A. The autophagy-lysosome pathway is the other major system involved in degradation of proteins and organelles within the muscle cell. However, it remains to be determined if the autophagy-lysosome pathway is dysregulated in muscular dystrophies, including MDC1A. Using the dy(3K)/dy(3K) mouse model of laminin α2 chain deficiency and MDC1A patient muscle, we show here that expression of autophagy-related genes is upregulated in laminin α2 chain-deficient muscle. Moreover, we found that autophagy inhibition significantly improves the dystrophic dy(3K)/dy(3K) phenotype. In particular, we show that systemic injection of 3-methyladenine (3-MA) reduces muscle fibrosis, atrophy, apoptosis and increases muscle regeneration and muscle mass. Importantly, lifespan and locomotive behavior were also greatly improved. These findings indicate that enhanced autophagic activity is pathogenic and that autophagy inhibition holds a promising therapeutic potential in the treatment of MDC1A.

Bcl-2 inhibits the innate immune response during early pathogenesis of murine congenital muscular dystrophy

Laminin α2 (LAMA2)-deficient congenital muscular dystrophy is a severe, early-onset disease caused by abnormal levels of laminin 211 in the basal lamina leading to muscle weakness, transient inflammation, muscle degeneration and impaired mobility. In a Lama2-deficient mouse model for this disease, animal survival is improved by muscle-specific expression of the apoptosis inhibitor Bcl-2, conferred by a MyoD-hBcl-2 transgene. Here we investigated early disease stages in this model to determine initial pathological events and effects of Bcl-2 on their progression. Using quantitative immunohistological and mRNA analyses we show that inflammation occurs very early in Lama2-deficient muscle, some aspects of which are reduced or delayed by the MyoD-hBcl-2 transgene. mRNAs for innate immune response regulators, including multiple Toll-like receptors (TLRs) and the inflammasome component NLRP3, are elevated in diseased muscle compared with age-matched controls expressing Lama2. MyoD-hBcl-2 inhibits induction of TLR4, TLR6, TLR7, TLR8 and TLR9 in Lama2-deficient muscle compared with non-transgenic controls, and leads to reduced infiltration of eosinophils, which are key death effector cells. This congenital disease model provides a new paradigm for investigating cell death mechanisms during early stages of pathogenesis, demonstrating that interactions exist between Bcl-2, a multifunctional regulator of cell survival, and the innate immune response.

The collagen VI-related myopathies: muscle meets its matrix

The collagen VI-related myopathy known as Ullrich congenital muscular dystrophy is an early-onset disease that combines substantial muscle weakness with striking joint laxity and progressive contractures. Patients might learn to walk in early childhood; however, this ability is subsequently lost, concomitant with the development of frequent nocturnal respiratory failure. Patients with intermediate phenotypes of collagen VI-related myopathy display a lesser degree of weakness and a longer period of ambulation than do individuals with Ullrich congenital muscular dystrophy, and the spectrum of disease finally encompasses mild Bethlem myopathy, in which ambulation persists into adulthood. Dominant and recessive autosomal mutations in the three major collagen VI genes-COL6A1, COL6A2, and COL6A3-can underlie this entire clinical spectrum, and result in deficient or dysfunctional microfibrillar collagen VI in the extracellular matrix of muscle and other connective tissues, such as skin and tendons. The potential effects on muscle include progressive dystrophic changes, fibrosis and evidence for increased apoptosis, which potentially open avenues for pharmacological intervention. Optimized respiratory management, including noninvasive nocturnal ventilation together with careful orthopedic management, are the current mainstays of treatment and have already led to a considerable improvement in life expectancy for children with Ullrich congenital muscular dystrophy.

Apoptosis inhibitors and mini-agrin have additive benefits in congenital muscular dystrophy mice

Mutations in LAMA2 cause a severe form of congenital muscular dystrophy, called MDC1A. Studies in mouse models have shown that transgenic expression of a designed, miniaturized form of the extracellular matrix molecule agrin (‘mini-agrin’) or apoptosis inhibition by either overexpression of Bcl2 or application of the pharmacological substance omigapil can ameliorate the disease. Here, we tested whether mini-agrin and anti-apoptotic agents act on different pathways and thus exert additive benefits in MDC1A mouse models. By combining mini-agrin with either transgenic Bcl2 expression or oral omigapil application, we show that the ameliorating effect of mini-agrin, which acts by restoring the mechanical stability of muscle fibres and, thereby, reduces muscle fibre breakdown and concomitant fibrosis, is complemented by apoptosis inhibitors, which prevent the loss of muscle fibres. Treatment of mice with both agents results in improved muscle regeneration and increased force. Our results show that the combination of mini-agrin and anti-apoptosis treatment has beneficial effects that are significantly bigger than the individual treatments and suggest that such a strategy might also be applicable to MDC1A patients.

Proinflammatory signals and the loss of lymphatic vessel hyaluronan receptor-1 (LYVE-1) in the early pathogenesis of laminin alpha2-deficient skeletal muscle

Congenital muscular dystrophy type 1A, a severe neuromuscular disease characterized by early-onset muscle weakness and degeneration, is caused by insufficient levels of laminin α2 (LAMA2) in the basal lamina surrounding muscle fibers and other cells. A better understanding of the molecular mechanisms leading to muscle loss is needed to develop therapeutic interventions for this disease. Here, the authors show that inflammation is an early feature of pathogenesis in Lama2-deficient mouse muscle, indicated by elevated expression of tenascin C in the endomysium around muscle fibers, infiltration of macrophages, and induction of the inflammatory cytokines tumor necrosis factor α (TNFα) and IL-1β. In addition, the expression of lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1), a specific marker for lymphatic vessel endothelial cells, is dramatically reduced early in Lama2-deficient muscle pathogenesis. LYVE-1 expression, which is inhibited by TNFα, is also decreased in muscles undergoing degeneration due to dystrophin deficiency and cardiotoxin damage. LYVE-1 expression thus provides a useful biomarker to monitor the onset of muscle pathogenesis, likely serving as an indicator of inflammatory signals present in muscles. Together, the data show that inflammatory pathways are activated in the earliest stages of Lama2-deficient disease progression and could play a role in early muscle degeneration.

Muscle-specific expression of insulin-like growth factor 1 improves outcome in Lama2Dy-w mice, a model for congenital muscular dystrophy type 1A

MDC1A, the second most prevalent form of congenital muscular dystrophy, results from laminin-α2 chain deficiency. This disease is characterized by extensive muscle wasting that results in extremely weak skeletal muscles. A large percentage of children with MDC1A are faced with respiratory as well as ambulatory difficulties. We investigated the effects of overexpressing insulin-like growth factor-1 (IGF-1) as a potential therapeutic target for the disease in the Lama2(Dy-w) mouse, a model that closely resembles human MDC1A. IGF-1 transgenic Lama2(Dy-w) mice showed increased survivability, body weight and muscle weight. In addition, these mice showed better ability to stand up on their hind limbs: a typical exploratory behavior seen in healthy mice. Histology and immunohistochemistry analyses revealed increased regenerative capacity and proliferation in IGF-1 transgenic Lama2(Dy-w) muscles. Western blot analysis showed increased phosphorylation of Akt and ERK1/2, both known to enhance myogenesis. Additionally, we saw increases in the expression of the regeneration markers MyoD, myogenin and embryonic myosin (myosin heavy chain 3, MYH3). We conclude that overexpression of IGF-1 in Lama2(Dy-w) mice increases lifespan and improves their overall wellbeing mainly through the restoration of impaired muscle regeneration, as fibrosis or inflammation was not impacted by IGF-1 in this disease model. Our results demonstrate that IGF-1 has a promising therapeutic potential in the treatment of MDC1A.

Skeletal muscle laminin and MDC1A: pathogenesis and treatment strategies

Laminin-211 is a cell-adhesion molecule that is strongly expressed in the basement membrane of skeletal muscle. By binding to the cell surface receptors dystroglycan and integrin α7β1, laminin-211 is believed to protect the muscle fiber from damage under the constant stress of contractions, and to influence signal transmission events. The importance of laminin-211 in skeletal muscle is evident from merosin-deficient congenital muscular dystrophy type 1A (MDC1A), in which absence of the α2 chain of laminin-211 leads to skeletal muscle dysfunction. MDC1A is the commonest form of congenital muscular dystrophy in the European population. Severe hypotonia, progressive muscle weakness and wasting, joint contractures and consequent impeded motion characterize this incurable disorder, which causes great difficulty in daily life and often leads to premature death. Mice with laminin α2 chain deficiency have analogous phenotypes, and are reliable models for studies of disease mechanisms and potential therapeutic approaches. In this review, we introduce laminin-211 and describe its structure, expression pattern in developing and adult muscle and its receptor interactions. We will also discuss the molecular pathogenesis of MDC1A and advances toward the development of treatment.

Proteasome inhibition improves the muscle of laminin α2 chain-deficient mice

Muscle atrophy, a significant characteristic of congenital muscular dystrophy with laminin α2 chain deficiency (also known as MDC1A), occurs by a change in the normal balance between protein synthesis and protein degradation. The ubiquitin-proteasome system (UPS) plays a key role in protein degradation in skeletal muscle cells. In order to identify new targets for drug therapy against MDC1A, we have investigated whether increased proteasomal degradation is a feature of MDC1A. Using the generated dy(3K)/dy(3K) mutant mouse model of MDC1A, we studied the expression of members of the ubiquitin-proteasome pathway in laminin α2 chain-deficient muscle, and we treated dy(3K)/dy(3K) mice with the proteasome inhibitor MG-132. We show that members of the UPS are upregulated and that the global ubiquitination of proteins is raised in dystrophic limb muscles. Also, phosphorylation of Akt is diminished in diseased muscles. Importantly, proteasome inhibition significantly improves the dystrophic dy(3K)/dy(3K) phenotype. Specifically, treatment with MG-132 increases lifespan, enhances locomotive activity, enlarges muscle fiber diameter, reduces fibrosis, restores Akt phosphorylation and decreases apoptosis. These studies promote better understanding of the disease process in mice and could lead to a drug therapy for MDC1A patients.

Distinct roles for laminin globular domains in laminin alpha1 chain mediated rescue of murine laminin alpha2 chain deficiency

Background

Laminin α2 chain mutations cause congenital muscular dystrophy with dysmyelination neuropathy (MDC1A). Previously, we demonstrated that laminin α1 chain ameliorates the disease in mice. Dystroglycan and integrins are major laminin receptors. Unlike laminin α2 chain, α1 chain binds the receptors by separate domains; laminin globular (LG) domains 4 and LG1-3, respectively. Thus, the laminin α1 chain is an excellent tool to distinguish between the roles of dystroglycan and integrins in the neuromuscular system.

Methodology/Principal Findings

Here, we provide insights into the functions of laminin α1LG domains and the division of their roles in MDC1A pathogenesis and rescue. Overexpression of laminin α1 chain that lacks the dystroglycan binding LG4-5 domains in α2 chain deficient mice resulted in prolonged lifespan and improved health. Importantly, diaphragm and heart muscles were corrected, whereas limb muscles were dystrophic, indicating that different muscles have different requirements for LG4-5 domains. Furthermore, the regenerative capacity of the skeletal muscle did not depend on laminin α1LG4-5. However, this domain was crucial for preventing apoptosis in limb muscles, essential for myelination in peripheral nerve and important for basement membrane assembly.

Conclusions/Significance

These results show that laminin α1LG domains and consequently their receptors have disparate functions in the neuromuscular system. Understanding these interactions could contribute to design and optimization of future medical treatment for MDC1A patients.

Pathology is alleviated by doxycycline in a laminin-alpha2-null model of congenital muscular dystrophy

OBJECTIVE

Congenital muscular dystrophy type 1A is an autosomal recessive disease that is caused by loss-of-function mutations in the laminin-alpha2 gene, and results in motor nerve and skeletal muscle dysfunction. In a previous study, we used genetic modifications to show that inappropriate induction of apoptosis was a significant contributor to pathogenesis in a laminin-alpha2-deficient mouse model of congenital muscular dystrophy type 1A. To identify a possible pharmacological therapy for laminin-alpha2 deficiency, we designed this study to determine whether treatment with minocycline or doxycycline, which are tetracycline derivatives reported to have antiapoptotic effects in mammals, would significantly increase lifespan and improve neuromuscular function in laminin-alpha2-deficient mice.

METHODS

Mice that were homozygous for a targeted, inactivating mutation of the laminin-alpha2 gene were placed into control, minocycline-treated, or doxycycline-treated groups. Drug treatment began within 2 weeks of birth, and the progression of disease was followed over time using behavioral, growth, histological, and molecular assays.

RESULTS

We found that treatment with either minocycline or doxycycline increased the median lifespan of laminin-alpha2-null mice from approximately 32 days to approximately 70 days. Furthermore, doxycycline improved postnatal growth rate and delayed the onset of hind-limb paralysis. Doxycycline-treated laminin-alpha2-deficient muscles had increased Akt phosphorylation, decreased inflammation, and decreased levels of Bax protein, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling-positive myonuclei, and activated caspase-3.

INTERPRETATION

Doxycycline or other drugs with similar functional profiles may be a possible route to improving neuromuscular dysfunction caused by laminin-alpha2-deficiency.

Dystrophin glycoprotein complex-associated Gbetagamma subunits activate phosphatidylinositol-3-kinase/Akt signaling in skeletal muscle in a laminin-dependent manner

Previously, we showed that laminin-binding to the dystrophin glycoprotein complex (DGC) of skeletal muscle causes a heterotrimeric G-protein (Galphabetagamma) to bind, changing the activation state of the Gsalpha subunit. Others have shown that laminin-binding to the DGC also leads to Akt activation. Gbetagamma, released when Gsalpha is activated, is known to bind phosphatidylinositol-3-kinase (PI3K), which activates Akt in other cells. Here, we investigate whether muscle Akt activation results from Gbetagamma, using immunoprecipitation and immunoblotting, and purified Gbetagamma. In the presence of laminin, PI3K-binding to the DGC increases and Akt becomes phosphorylated and activated (pAkt), and glycogen synthase kinase is phosphorylated. Antibodies, which specifically block laminin-binding to alpha-dystroglycan, prevent PI3K-binding to the DGC. Purified bovine brain Gbetagamma also caused PI3K and Akt activation. These results show that DGC-Gbetagamma is binding PI3K and activating pAkt in a laminin-dependent manner. Mdx mice, which have greatly diminished amounts of DGC proteins, display elevated pAkt signaling and increased expression of integrin beta1 compared to normal muscle. This integrin binds laminin, Gbetagamma, and PI3K. Collectively, these suggest that PI3K is an important target for the Gbetagamma, which normally binds to DGC syntrophin, and activates PI3K/Akt signaling. Disruption of the DGC in mdx mouse is causing dis-regulation of the laminin-DGC-Gbetagamma-PI3K-Akt signaling and is likely to be important to the pathogenesis of muscular dystrophy. Upregulating integrin beta1 expression and activating the PI3K/Akt pathway in muscular dystrophy may partially compensate for the loss of the DGC. The results suggest new therapeutic approaches to muscle disease.

Laminin-111 restores regenerative capacity in a mouse model for alpha7 integrin congenital myopathy

Mutations in the alpha7 integrin gene cause congenital myopathy characterized by delayed developmental milestones and impaired mobility. Previous studies in dystrophic mice suggest the alpha7beta1 integrin may be critical for muscle repair. To investigate the role that alpha7beta1 integrin plays in muscle regeneration, cardiotoxin was used to induce damage in the tibialis anterior muscle of alpha7 integrin-null mice. Unlike wild-type muscle, which responded rapidly to repair damaged myofibers, alpha7 integrin-deficient muscle exhibited defective regeneration. Analysis of Pax7 and MyoD expression revealed a profound delay in satellite cell activation after cardiotoxin treatment in alpha7 integrin-null animals when compared with wild type. We have recently demonstrated that the muscle of alpha7 integrin-null mice exhibits reduced laminin-alpha2 expression. To test the hypothesis that loss of laminin contributes to the defective muscle regeneration phenotype observed in alpha7 integrin-null mice, mouse laminin-111 (alpha1, beta1, gamma1) protein was injected into the tibialis anterior muscle 3 days before cardiotoxin-induced injury. The injected laminin-111 protein infiltrated the entire muscle and restored myogenic repair and muscle regeneration in alpha7 integrin-null muscle to wild-type levels. Our data demonstrate a critical role for a laminin-rich microenvironment in muscle repair and suggest laminin- 111 protein may serve as an unexpected and novel therapeutic agent for patients with congenital myopathies.

The genetic and molecular basis of muscular dystrophy: roles of cell-matrix linkage in the pathogenesis

Muscular dystrophies are a heterogeneous group of genetic disorders. In addition to genetic information, a combination of various approaches such as the use of genetic animal models, muscle cell biology, and biochemistry has contributed to improving the understanding of the molecular basis of muscular dystrophy's etiology. Several lines of evidence confirm that the structural linkage between the muscle extracellular matrix and the cytoskeleton is crucial to prevent the progression of muscular dystrophy. The dystrophin-glycoprotein complex links the extracellular matrix to the cytoskeleton, and mutations in the component of this complex cause Duchenne-type or limb-girdle-type muscular dystrophy. Mutations in laminin or collagen VI, muscle matrix proteins, are known to cause a congenital type of muscular dystrophy. Moreover, it is not only the primary genetic defects in the structural or matrix proteins, but also the primary mutations of enzymes involved in the protein glycosylation pathway that are now recognized to disrupt the matrix-cell interaction in a certain group of muscular dystrophies. This group of diseases is caused by the secondary functional defects of dystroglycan, a transmembrane matrix receptor. This review considers recent advances in understanding the molecular pathogenesis of muscular dystrophies that can be caused by the disruption of the cell-matrix linkage.

The role of apoptosis in neuromuscular diseases and prospects for anti-apoptosis therapy

Although genetic mutations that are responsible for most of the inherited neuromuscular diseases have been identified, the molecular and cellular mechanisms that cause muscle and nerve depletion are not well understood and therapies are lacking. Histological studies of many neuromuscular diseases indicated that loss of motor-nerve and/or skeletal-muscle function might be due to excessive cell death by apoptosis. Recent studies have confirmed this possibility by showing that pathology in mouse models of amyotrophic lateral sclerosis, congenital muscular dystrophy, oculopharyngeal muscular dystrophy and collagen-VI deficiency, but not Duchenne muscular dystrophy, is significantly ameliorated by genetic or pharmacological interventions that have been designed to inhibit apoptosis. Thus, apoptosis greatly contributes to pathology in mouse models of several neuromuscular diseases, and appropriate anti-apoptosis therapy might therefore be beneficial for the corresponding human diseases.

Diagnostic significance of membrane attack complex and vitronectin in childhood dermatomyositis

In the current study, whether particular histologic distributions of membrane attack complex and vitronectin are correlated to clinical characteristics of patients with childhood dermatomyositis was investigated. The specimens from 11 patients with childhood dermatomyositis were examined immunocytochemically and compared with those taken from 6 adult dermatomyositis and 5 childhood polymyositis patients. Four out of five membrane attack complex-positive specimens were derived from patients who were within 1 to 3 months from the onset of childhood dermatomyositis and were not treated with prednisone. There were two patients at early stages of childhood dermatomyositis without pathologic characteristics of the disease. However, marked deposits of membrane attack complex on capillaries were seen in one of them. The immunoreactivity of vitronectin was detected at locations similar to those of membrane attack complex. Our results suggest that the detection of membrane attack complex and vitronectin in muscle capillaries will help us diagnose childhood dermatomyositis at an early stage.

Diseased muscles that lack dystrophin or laminin-alpha2 have altered compositions and proliferation of mononuclear cell populations

Background

Multiple types of mononucleate cells reside among the multinucleate myofibers in skeletal muscles and these mononucleate cells function in muscle maintenance and repair. How neuromuscular disease might affect different types of muscle mononucleate cells had not been determined. In this study, therefore, we examined how two neuromuscular diseases, dystrophin-deficiency and laminin-α2-deficiency, altered the proliferation and composition of different subsets of muscle-derived mononucleate cells.

Methods

We used fluorescence-activated cell sorting combined with bromodeoxyuridine labeling to examine proliferation rates and compositions of mononuclear cells in diseased and healthy mouse skeletal muscle. We prepared mononucleate cells from muscles of mdx (dystrophin-deficient) or Lama2^-/- (laminin-α2-deficient) mice and compared them to cells from healthy control muscles. We enumerated subsets of resident muscle cells based on Sca-1 and CD45 expression patterns and determined the proliferation of each cell subset in vivo by BrdU incorporation.

Results

We found that the proliferation and composition of the mononucleate cells in dystrophin-deficient and laminin-α2-deficient diseased muscles are different than in healthy muscle. The mdx and Lama2^-/- muscles showed similar significant increases in CD45⁺ cells compared to healthy muscle. Changes in proliferation, however, differed between the two diseases with proliferation increased in mdx and decreased in Lama2^-/- muscles compared to healthy muscles. In particular, the most abundant Sca-1^-/CD45^- subset, which contains muscle precursor cells, had increased proliferation in mdx muscle but decreased proliferation in Lama2^-/- muscles.

Conclusion

The similar increases in CD45⁺ cells, but opposite changes in proliferation of muscle precursor cells, may underlie aspects of the distinct pathologies in the two diseases.

Muscle-specific BCL2 expression ameliorates muscle disease in laminin {alpha}2-deficient, but not in dystrophin-deficient, mice

To examine the role of apoptosis in neuromuscular disease progression, we have determined whether pathogenesis in dystrophin-deficient (mdx) and laminin alpha2-deficient (Lama2-null) mice is ameliorated by overexpression of the anti-apoptosis protein BCL2 in diseased muscles. The mdx mice are a model for the human disease, Duchenne muscular dystrophy (DMD), and the Lama2-null mice are a model for human congenital muscular dystrophy type 1A (MDC1A). For these studies, we generated transgenic mice that overexpressed human BCL2 under control of muscle-specific MyoD or MRF4 promoter fragments. We then used cross-breeding to introduce the transgenes into diseased mdx or Lama2-null mice. In mdx mice, we found that overexpression of BCL2 failed to produce any significant differences in muscle pathology. In contrast, in the Lama2-null mice, we found that muscle-specific expression of BCL2 led to a several-fold increase in lifespan and an increased growth rate. Thus, BCL2-mediated apoptosis appears to play a significant role in pathogenesis of laminin alpha2 deficiency, but not of dystrophin deficiency, suggesting that therapies designed to ameliorate disease by inhibition of apoptosis are more likely to succeed in MDC1A than in DMD.

Inhibition of apoptosis improves outcome in a model of congenital muscular dystrophy

The most common form of human congenital muscular dystrophy (CMD) is caused by mutations in the laminin-alpha2 gene. Loss of laminin-alpha2 function in this autosomal recessive type 1A form of CMD results in neuromuscular dysfunction and, often, early death. Laminin-alpha2-deficient skeletal muscles in both humans and mice show signs of muscle cell death by apoptosis. To examine the significance of apoptosis in CMD1A pathogenesis, we determined whether pathogenesis in laminin-alpha2-deficient (Lama2(-/-)) mice could be ameliorated by inhibiting apoptosis through either (a) inactivation of the proapoptosis protein Bax or (b) overexpression of the antiapoptosis protein Bcl-2 from a muscle-specific transgene. We found that both of these genetic interventions produced a several-fold increase in the lifespan of Lama2(-/-) mice. Bax inactivation also improved postnatal growth rate and myofiber histology and decreased fixed contractures of Lama2(-/-) mice. Thus, Bcl-2 family-mediated apoptosis contributes significantly to pathogenesis in the mouse model of CMD1A, and antiapoptosis therapy may be a possible route to amelioration of neuromuscular dysfunction due to laminin-alpha2 deficiency in humans.

Muscle-fiber apoptosis in neuromuscular diseases

Muscle-fiber loss is a characteristic of many progressive neuromuscular disorders. Over the past decade, identification of a growing number of apoptosis-associated factors and events in pathological skeletal muscle provided increasing evidence that apoptotic cell-death mechanisms account significantly for muscle-fiber atrophy and loss in a wide spectrum of neuromuscular disorders. It became obvious that there is not one specific pathway for muscle fibers to undergo apoptotic degradation. In contrast, certain neuromuscular diseases seem to involve characteristic expression patterns of apoptosis-related factors and pathways. Furthermore, there are some characteristics of muscle-fiber apoptosis that rely on the muscle fiber itself as an extremely specified cell type. Multinucleated muscle fibers with successive muscle-fiber segments controlled by individual nuclei display some specifics different from apoptosis of mononucleated cells. This review focuses on the expression patterns of apoptosis-associated factors in different primary and secondary neuromuscular disorders and gives a synopsis of current knowledge.

The zebrafish as a model for muscular dystrophy and congenital myopathy

The muscular dystrophies and congenital myopathies are inherited diseases of the skeletal muscle, which lead to a loss of muscle function and are often fatal. While many of the loci involved are already known, these conditions remain incurable, and genetic models are being developed in an effort to understand the pathological mechanisms involved. Recently several papers have shown that the zebrafish, which is now widely used in developmental genetic studies, will provide a useful addition to our toolkit in this regard. Here we describe these studies, including a zebrafish model of what is potentially the novel pathological mechanism of muscle attachment failure in Duchenne and other muscular dystrophies.

Clarifying the boundaries between the inflammatory and dystrophic myopathies: insights from molecular diagnostics and microarrays

Clinical and histopathologic overlaps between the muscular dystrophies and inflammatory myopathies are being increasingly recognized. Most patients with a muscular dystrophy show improvement with prednisone treatment, although they will not be cured; many patients with idiopathic inflammatory myopathies are cured. Dysferlin-deficiency was recently recognized as a cause of late-onset dystrophy with substantial inflammation in muscle. Corticosteroid usage by these patients may result in nonrecoverable loss of strength. Therefore, it is important to rule out dysferlin-deficiency before initiating a course of corticosteroids. Newly emerging, genome-wide transcriptional profiling technology allows the identification of the interacting pathways that are active in the muscle of patients with inflammatory myopathies or dystrophies. There are several, complex molecular pathways; however, the comparison of expression profiles in patients with different muscle disorders permits the delineation of disease-specific patterns. It is hoped that novel approaches for treating the inflammatory myopathies and dystrophies can be derived from intimate knowledge of the pathways involved in each disease, and the key molecules that provide cross-talk between pathways.

Complement 3 deficiency and oral prednisolone improve strength and prolong survival of laminin alpha2-deficient mice

Complement deposition and macrophages are common in biopsies of children with muscular dystrophy. While the presumed roles of complement and macrophages have been those of scavenger to remove and clear necrotic fibers, there is some evidence that they play a primary role in the pathogenesis of these diseases. Here, we explore the role of complement in the pathogenesis of the most severe animal model of congenital dystrophy, the dy-/- mouse, which is laminin alpha2-deficient. We generated animals deficient in both C3 and laminin alpha2. C3 is the third component of the complement cascade and is required for activation of either the classical or alternative pathways. Thirty-three percent of the dy-/-:C3+ mice (n=59) died before 24 weeks while only 14% of the dy-/-:C3-/- (n=29) mice died (p=0.04). Absolute forepaw strength was 25-30% greater for the dy-/-:C3-/- mice up to 20 weeks of age (p<0.05 compared to complement-sufficient). Forepaw strength adjusted for weight also showed significant differences with C3-/- mice being stronger up to 20 weeks (p<0.05). However, by 24 weeks, the two groups did not differ for strength. Next, we treated 20 mice with twice weekly oral prednisolone. Survival at 24 weeks for the prednisolone treated dy-/- mice (C3-/- or C3+) was 90% (p=0.04). This work shows that complement insufficiency and weekly prednisone prolong survival and improve strength of the laminin alpha2-deficient mouse. This work suggests that the complement system may contribute directly to the pathogenesis of this form of dystrophy. Because complement activity may be modified pharmacologically, this work may have implications for treatment of children with congenital muscular dystrophy secondary to laminin alpha2 deficiency.