X-linked myopathy with excessive autophagy: a new hereditary muscle disease

Identification of a Novel Intronic Mutation in VMA21 Associated with a Classical Form of X-Linked Myopathy with Autophagy

Introduction   VMA21 -related myopathy is one of the rare forms of slowly progressive myopathy observed in males. Till now, there have been only a handful of reports, mainly from Europe and America, and two reports from India. Method  Here, we describe a case of genetically confirmed VMA21 -associated myopathy with clinical, histopathological, and imaging features with a list of known VMA21 mutations. Results  A 29-year-old man had the onset of symptoms at 18 years of age with features of proximal lower limb weakness. Muscle magnetic resonance imaging showed the preferential involvement of vasti and adductor magnus. A biopsy of the left quadriceps femoris showed features of autophagic vacuolar myopathy with vacuoles containing granular eosinophilic materials. In targeted next-generation sequencing, hemizygous mutation in the 3' splice site of intron 2 of the VMA21 gene (c.164-7 T > A) was identified and confirmed the diagnosis of X-linked myopathy with excessive autophagy. Conclusion  This report expands the phenotypic and genotypic profile of VMA21 -related myopathy, with a yet unreported mutation in India.

Phenotype variability and natural history of X-linked myopathy with excessive autophagy

OBJECTIVE

X-linked myopathy with excessive autophagy (XMEA) linked to the VMA21 gene leads to autophagy failure with progressive vacuolation and atrophy of skeletal muscles. Current knowledge of this rare disease is limited. Our objective was to define the clinical, radiological, and natural history of XMEA.

METHODS

We conducted a retrospective study collecting clinical, genetic, muscle imaging, and biopsy data of XMEA patients followed in France and reviewed the literature for additional cases.

RESULTS

Eighteen males had genetically confirmed XMEA in France, carrying four different VMA21 variants. Mean age at disease onset was 9.4 ± 9.9 (range 1-40) years. In 14/18 patients (77.8%), onset occurred during childhood (< 15 years); however in four patients, the disease started in adulthood. Patients had anterior and medial compartment thigh muscle weakness, distal contractures (56.3%), elevated CK levels (1287.9 ± 757.8 U/l) and autophagic vacuoles with sarcolemmal features on muscle histopathology. Muscle MRI (n = 10) showed a characteristic pattern of lower limb muscle involvement. In 11 patients, outcome measures were available for an average follow-up period of 10.6 ± 9.8 years and six of them show disease progression. Mean change of functional outcomes was 0.5 ± 1.2 points for Brooke and 2.2 ± 2.5 points for Vignos score, 7/16 patients (43.8%) needed a walking aid and 3/16 (18.8%) were wheelchair-bound (median age of 40 years old, range 39-48). The variant c.164-7 T > G was associated with a later onset of symptoms. Respiratory insufficiency was common (57.1%) but cardiac involvement rare (12.5%).

INTERPRETATION

XMEA has variable age of onset, but a characteristic clinical, histopathological, and muscle imaging presentation, guiding the diagnosis. Although slowly, motor disability progresses with time, and relevant genotype-phenotype correlations will help design future clinical trials.

Severe congenital X-linked myopathy with excessive autophagy secondary to an apparently synonymous but pathogenic novel variant

X-linked myopathy with excessive autophagy is a rare inherited disease characterized by aberrant accumulation of autophagic vacuoles in skeletal muscle. Affected males usually show a slow progression and the heart is characteristically spared. We present four male patients from the same family with an extremely aggressive form of this disease, requiring permanent mechanical ventilation from birth. Ambulation was never achieved. Three died, one in the first hour of life, one at 7 years and one at 17 years, the last death being a consequence of heart failure. Muscle biopsy showed pathognomonic features of the disease in the 4 affected males. Genetic study found a novel synonymous variant in VMA21, c.294C>T (Gly98=). Genotyping was consistent with co-segregation with the phenotype in an X-linked recessive manner. An alteration of the normal splice pattern was confirmed by transcriptome analysis, proving that the apparently synonymous variant was the cause of this extremely severe phenotype.

Novel Intronic Mutation in VMA21 Causing Severe Phenotype of X-Linked Myopathy with Excessive Autophagy-Case Report

X-linked Myopathy with Excessive Autophagy (XMEA) is a rare autophagic vacuolar myopathy caused by mutations in the Vacuolar ATPase assembly factor VMA21 gene; onset usually occurs during childhood and rarely occurs during adulthood. We described a 22-year-old patient with XMEA, whose onset was declared at 11 through gait disorder. He had severe four-limb proximal weakness and amyotrophy, and his proximal muscle MRC score was between 2 and 3/5 in four limbs; creatine kinase levels were elevated (1385 IU/L), and electroneuromyography and muscle MRI were suggestive of myopathy. Muscle biopsy showed abnormalities typical of autophagic vacuolar myopathy. We detected a hemizygous, unreported, intronic, single-nucleotide substitution c.164-20T>A (NM_001017980.4) in intron 2 of the VMA21 gene. Fibroblasts derived from this patient displayed a reduced level of VMA21 transcripts (at 40% of normal) and protein, suggesting a pathogenicity related to an alteration of the splicing efficiency associated with an intron retention. This patient with XMEA displayed a severe phenotype (rapid weakness of upper and lower limbs) due to a new intronic variant of VMA21, related to an alteration in the splicing efficiency associated with intron retention, suggesting that phenotype severity is closely related to the residual expression of the VMA21 protein.

X-linked Myopathy with Excessive Autophagy - A Rare Cause of Vacuolar Myopathy in Children

X-linked myopathy with excessive autophagy (XMEA) is a rare, recently characterized type of autophagic vacuolar myopathy caused by mutations in the VMA21 gene. It is characterized by slowly progressive weakness restricted to proximal limb muscles and generally has a favorable outcome. The characteristic histological and ultrastructural features distinguish this entity from other mimics, notably Danon disease. XMEA is an under recognized disease and should be considered in the differentials of slowly progressive myopathy in children. Awareness of this rare entity is also important for the pathologists in order to distinguish it from other causes of vacuolar myopathy in view of its favourable prognosis. We report the first genetically confirmed case of XMEA from India in an 8-year-old boy which was diagnosed based on the characteristic light microscopic and ultrastructural findings on muscle biopsy and subsequently confirmed by mutation analysis. The differential diagnostic considerations are also discussed.

Role of autophagy in muscle disease

Beside inherited muscle diseases many catabolic conditions such as insulin resistance, malnutrition, cancer growth, aging, infections, chronic inflammatory status, inactivity, obesity are characterized by loss of muscle mass, strength and function. The decrease of muscle quality and quantity increases morbidity, mortality and has a major impact on the quality of life. One of the pathogenetic mechanisms of muscle wasting is the dysregulation of the main protein and organelles quality control system of the cell: the autophagy-lysosome. This review will focus on the role of the autophagy-lysosome system in the different conditions of muscle loss. We will also dissect the signalling pathways that are involved in excessive or defective autophagy regulation. Finally, the state of the art of autophagy modulators that have been used in preclinical or clinical studies to ameliorate muscle mass will be also described.

X-linked myopathy with excessive autophagy: First report of an Israeli family presenting with late onset lower limb girdle weakness

X-linked myopathy with excessive autophagy (XMEA) is a rare disorder characterized by slow progressive muscle weakness and distinctive pathology of excessive autophagic vacuoles on muscle biopsy. Here we report on five patients, in a single family, with proximal lower limb weakness. The proband, a 25-year-old man, presented with 5 years of progressive lower limbs proximal muscle weakness. His maternal grandfather and three of his maternal male cousins had similar clinical findings and were initially suspected to have Becker muscular dystrophy. Muscle biopsy in two affected family members demonstrated autophagic myopathy, and guided the genetic investigations to the identification of a pathogenic mutation, c.272G > C in the VMA21 gene, known to cause XMEA [1]. To the best of our knowledge this is the first identified Israeli Jewish family afflicted by XMEA.

The Role of Autophagy in Skeletal Muscle Diseases

Skeletal muscle is the most abundant type of tissue in human body, being involved in diverse activities and maintaining a finely tuned metabolic balance. Autophagy, characterized by the autophagosome–lysosome system with the involvement of evolutionarily conserved autophagy-related genes, is an important catabolic process and plays an essential role in energy generation and consumption, as well as substance turnover processes in skeletal muscles. Autophagy in skeletal muscles is finely tuned under the tight regulation of diverse signaling pathways, and the autophagy pathway has cross-talk with other pathways to form feedback loops under physiological conditions and metabolic stress. Altered autophagy activity characterized by either increased formation of autophagosomes or inhibition of lysosome-autophagosome fusion can lead to pathological cascades, and mutations in autophagy genes and deregulation of autophagy pathways have been identified as one of the major causes for a variety of skeleton muscle disorders. The advancement of multi-omics techniques enables further understanding of the molecular and biochemical mechanisms underlying the role of autophagy in skeletal muscle disorders, which may yield novel therapeutic targets for these disorders.

Altered in vitro muscle differentiation in X-linked myopathy with excessive autophagy

X-linked myopathy with excessive autophagy (XMEA) is a genetic disease associated with weakness of the proximal muscles. It is caused by mutations in the VMA21 gene, coding for a chaperone that functions in the vacuolar ATPase (v-ATPase) assembly. Mutations associated with lower content of assembled v-ATPases lead to an increase in lysosomal pH, culminating in partial blockage of macroautophagy, with accumulation of vacuoles of undigested content. Here, we studied a 5-year-old boy affected by XMEA, caused by a small indel in the VMA21 gene. Detection of sarcoplasmic Lc3 (also known as MAP1LC3B)-positive vacuoles in his muscle biopsy confirmed an autophagy defect. To understand how autophagy is regulated in XMEA myogenesis, we used patient-derived muscle cells to evaluate autophagy during in vitro muscle differentiation. An increase in lysosomal pH was observed in the patient's cells, compatible with predicted functional defect of his mutation. Additionally, there was an increase in autophagic flux in XMEA myotubes. Interestingly, we observed that differentiation of XMEA myoblasts was altered, with increased myotube formation observed through a higher fusion index, which was not dependent on lysosomal acidification. Moreover, no variation in the expression of myogenic factors nor the presence of regenerating fibers in the patient's muscle were observed. Myoblast fusion is a tightly regulated process; therefore, the uncontrolled fusion of XMEA myoblasts might generate cells that are not as functional as normal muscle cells. Our data provide new evidence on the reason for predominant muscle involvement in the context of the XMEA phenotype.

This article has an associated First Person interview with the first author of the paper.

Summary: Here, we show that in X-linked myopathy with excessive autophagy there is increased fusion of myoblasts, which is not caused by the primary lysosomal acidification defect.

X-Linked Myopathy with Excessive Autophagy; A Case Report

X-linked myopathy with excessive autophagy (XMEA) is a rare, slowly progressive muscle disease characterized by membrane-bound sarcoplasmic vacuoles distinct from other forms of myopathies with vacuoles. We report this rare condition in a 5-year-old boy with proximal muscle weakness and morphological evidence of autophagic vacuoles.

Autophagy Defects in Skeletal Myopathies

Autophagy is an evolutionarily conserved catabolic process that targets different types of cytoplasmic cargo (such as bulk cytoplasm, damaged cellular organelles, and misfolded protein aggregates) for lysosomal degradation. Autophagy is activated in response to biological stress and also plays a critical role in the maintenance of normal cellular homeostasis; the latter function is particularly important for the integrity of postmitotic, metabolically active tissues, such as skeletal muscle. Through impairment of muscle homeostasis, autophagy dysfunction contributes to the pathogenesis of many different skeletal myopathies; the observed autophagy defects differ from disease to disease but have been shown to involve all steps of the autophagic cascade (from induction to lysosomal cargo degradation) and to impair both bulk and selective autophagy. To highlight the molecular and cellular mechanisms that are shared among different myopathies with deficient autophagy, these disorders are discussed based on the nature of the underlying autophagic defect rather than etiology or clinical presentation.

Inflachromene inhibits autophagy through modulation of Beclin 1 activity

Autophagy is a central intracellular catabolic mechanism that mediates the degradation of cytoplasmic proteins and organelles, and regulation of autophagy is essential for homeostasis. HMGB1 is an important sepsis mediator when secreted and also functions as an inducer of autophagy by binding to Beclin 1. In this study, we studied the effect of inflachromene (ICM), a novel HMGB1 secretion inhibitor, on autophagy. ICM inhibited autophagy by inhibiting nucleocytoplasmic translocation of HMGB1 and by increasing Beclin 1 ubiquitination for degradation by enhancing the interaction between Beclin 1 and E3 ubiquitin ligase RNF216. These data suggest that ICM could be used as a potential autophagy suppressor.

Nanoparticles restore lysosomal acidification defects: Implications for Parkinson and other lysosomal-related diseases

Lysosomal impairment causes lysosomal storage disorders (LSD) and is involved in pathogenesis of neurodegenerative diseases, notably Parkinson disease (PD). Strategies enhancing or restoring lysosomal-mediated degradation thus appear as tantalizing disease-modifying therapeutics. Here we demonstrate that poly(DL-lactide-co-glycolide) (PLGA) acidic nanoparticles (aNP) restore impaired lysosomal function in a series of toxin and genetic cellular models of PD, i.e. ATP13A2-mutant or depleted cells or glucocerebrosidase (GBA)-mutant cells, as well as in a genetic model of lysosomal-related myopathy. We show that PLGA-aNP are transported to the lysosome within 24 h, lower lysosomal pH and rescue chloroquine (CQ)-induced toxicity. Re-acidification of defective lysosomes following PLGA-aNP treatment restores lysosomal function in different pathological contexts. Finally, our results show that PLGA-aNP may be detected after intracerebral injection in neurons and attenuate PD-related neurodegeneration in vivo by mechanisms involving a rescue of compromised lysosomes.

[Finland: an ideally valued genetic heritage]

Si la Finlande est souvent assimilée à une « petite » nation du fait de la taille restreinte de sa population, elle n’en est pas moins un géant en matière de myologie. Sa contribution, très originale, à la découverte de nombreuses myopathies et neuropathies héréditaires est là pour le prouver. Rarement pays aura valorisé son patrimoine génétique autant que la patrie de Sibelius. Particulière par les origines de sa population et fière de sa langue non-indo-européenne, la Finlande cultive pourtant une ouverture d’esprit et une volonté de collaboration sans pareilles. Deux qualités très utiles et très appréciées dans le concert international des équipes travaillant dans le domaine neuromusculaire.

Muscle magnetic resonance imaging abnormalities in X-linked myopathy with excessive autophagy

INTRODUCTION

X-linked myopathy with excessive autophagy (XMEA) is an X-linked recessive myopathy due to recently reported mutations in the VMA21 gene.

METHODS

Four men from 2 separate families were studied. The clinical presentation, genetic data, muscle biopsy, and muscle MRI were analyzed.

RESULTS

A known VMA21 mutation, c.163+4A>G, and a new mutation, c.163+3A>G, respectively, were found in the 2 families. The clinical course was characterized by onset in childhood and progressive muscle weakness with a limb-girdle pattern. Muscle biopsy revealed a mild myopathy with an increased number of giant autophagic vacuoles. Whole-body muscle MRI showed that pelvic girdle and proximal thighs were the most and earliest affected territories, with sparing of rectus femoris muscles. Muscle changes essentially consisted of degenerative fatty replacement.

CONCLUSIONS

This study highlights a distinctive MRI pattern of muscle involvement, which can be helpful for diagnosis of XMEA, even before muscle biopsy or genetic analysis.

No cardiomyopathy in X-linked myopathy with excessive autophagy

In X-linked myopathy with excessive autophagy (XMEA) progressive sarcoplasmic accumulation of autolysosomes filled with undegraded debris leads to atrophy and weakness of skeletal muscles. XMEA is caused by compromised acidification of lysosomes resulting from hypofunction of the proton pump vacuolar ATPase (V-ATPase), due to hypomorphic mutations in VMA21, whose protein product assembles V-ATPase. To what extent the cardiac muscle is affected is unknown. Therefore we performed a comprehensive cardiac evaluation in four male XMEA patients, and also examined pathology of one deceased patient's cardiac and skeletal muscle. None of the symptomatic men (aged 25-48 years) had history or symptoms of cardiomyopathy. Resting electrocardiograms and echocardiographies were normal. MRI showed normal left ventricle ejection fraction and myocardial mass. Myocardial late-gadolinium enhancement was not detected. The deceased patient's skeletal but not cardiac muscle showed characteristic accumulation of autophagic vacuoles. In conclusion, in classic XMEA the myocardium is structurally, electrically and clinically spared.

X-linked myopathy with excessive autophagy: a failure of self-eating

Autophagic vacuolar myopathies (AVMs) are a group of disorders united by shared histopathological features on muscle biopsy that include the aberrant accumulation of autophagic vacuoles. The classic conditions that compose the AVMs include Pompe Disease, Danon Disease and X-linked myopathy with excessive autophagy (XMEA). Other disorders, including acquired myopathies like chloroquine toxicity, also have features of an autophagic myopathy. This review is focused on XMEA, a myopathy with onset of slowly progressive proximal weakness and elevated serum creatine kinase (2× to 20× normal) typically in the first decade of life. However, both late-adult onset and severe, sometimes lethal, neonatal cases also occur. Skeletal muscle pathology is characterized by numerous cytoplasmic autophagic vacuoles, complex muscle fiber splitting with internalization of capillaries, and complement C5b-9 deposition within vacuoles and along the sarcolemma. The autophagic vacuoles have sarcolemmal features. Mutations in the VMA21 gene at Xq28 cause XMEA by reducing the activity of lysosomal hydrolases. The VMA21 protein regulates the assembly of the V-ATPase required to acidify the lysosome. Increased lysosomal pH and poor degradation of cellular debris may secondarily induce autophagy, the net effect being accumulation of autophagolysosomes. The relationship of XMEA to other lysosomal disorders of muscle and potential therapeutic interventions for XMEA are discussed.

Late adult-onset of X-linked myopathy with excessive autophagy

INTRODUCTION

X-linked myopathy with excessive autophagy (XMEA) is characterized by autophagic vacuoles with sarcolemmal features. Mutations in VMA21 result in insufficient lysosome acidification, causing progressive proximal weakness with onset before age 20 years and loss of ambulation by middle age.

METHODS

We describe a patient with onset of slowly progressive proximal weakness of the lower limbs after age 50, who maintains ambulation with the assistance of a cane at age 71.

RESULTS

Muscle biopsy at age 66 showed complex muscle fiber splitting, internalized capillaries, and vacuolar changes characteristic of autophagic vacuolar myopathy. Vacuoles stained positive for sarcolemmal proteins, LAMP2, and complement C5b-9. Ultrastructural evaluation further revealed basal lamina reduplication and extensive autophagosome extrusion. Sanger sequencing identified a known pathologic splice site mutation in VMA21 (c.164-7T>G).

CONCLUSIONS

This case expands the clinical phenotype of XMEA and suggests VMA21 sequencing be considered in evaluating men with LAMP2-positive autophagic vacuolar myopathy.

Molecular regulation of autophagy and its implications for metabolic diseases

PURPOSE OF REVIEW

Autophagy is an evolutionarily conserved cellular programme for the turnover of organelles, proteins, and other macromolecules, involving the lysosomal degradation pathway. Emerging evidence suggests that autophagy can play a central role in human metabolism as well as impact diverse cellular processes including organelle homeostasis, cell death and proliferation, lipid and glycogen metabolism, and the regulation of inflammation and immune responses. The purpose of this review is to examine recent evidence for the role of autophagy in cellular metabolism, and its relevance to select human diseases that involve disorders of metabolism.

RECENT FINDINGS

Recent studies suggest that autophagy may play multiple roles in metabolic diseases, including diabetes and its complications, metabolic syndrome and obesity, myopathies and other inborn errors of metabolism, as well as other diseases that may involve altered mitochondrial function.

SUMMARY

Strategies aimed at modulating autophagy may lead to therapies for diseases in which altered cellular and tissue metabolism play a key role.

Lysosomal-mediated waste clearance in retinal pigment epithelial cells is regulated by CRYBA1/βA3/A1-crystallin via V-ATPase-MTORC1 signaling

In phagocytic cells, including the retinal pigment epithelium (RPE), acidic compartments of the endolysosomal system are regulators of both phagocytosis and autophagy, thereby helping to maintain cellular homeostasis. The acidification of the endolysosomal system is modulated by a proton pump, the V-ATPase, but the mechanisms that direct the activity of the V-ATPase remain elusive. We found that in RPE cells, CRYBA1/βA3/A1-crystallin, a lens protein also expressed in RPE, is localized to lysosomes, where it regulates endolysosomal acidification by modulating the V-ATPase, thereby controlling both phagocytosis and autophagy. We demonstrated that CRYBA1 coimmunoprecipitates with the ATP6V0A1/V₀-ATPase a1 subunit. Interestingly, in mice when Cryba1 (the gene encoding both the βA3- and βA1-crystallin forms) is knocked out specifically in RPE, V-ATPase activity is decreased and lysosomal pH is elevated, while cathepsin D (CTSD) activity is decreased. Fundus photographs of these Cryba1 conditional knockout (cKO) mice showed scattered lesions by 4 months of age that increased in older mice, with accumulation of lipid-droplets as determined by immunohistochemistry. Transmission electron microscopy (TEM) of cryba1 cKO mice revealed vacuole-like structures with partially degraded cellular organelles, undigested photoreceptor outer segments and accumulation of autophagosomes. Further, following autophagy induction both in vivo and in vitro, phospho-AKT and phospho-RPTOR/Raptor decrease, while pMTOR increases in RPE cells, inhibiting autophagy and AKT-MTORC1 signaling. Impaired lysosomal clearance in the RPE of the cryba1 cKO mice also resulted in abnormalities in retinal function that increased with age, as demonstrated by electroretinography. Our findings suggest that loss of CRYBA1 causes lysosomal dysregulation leading to the impairment of both autophagy and phagocytosis.

VMA21 deficiency prevents vacuolar ATPase assembly and causes autophagic vacuolar myopathy

X-linked Myopathy with Excessive Autophagy (XMEA) is a childhood onset disease characterized by progressive vacuolation and atrophy of skeletal muscle. We show that XMEA is caused by hypomorphic alleles of the VMA21 gene, that VMA21 is the diverged human ortholog of the yeast Vma21p protein, and that like Vma21p, VMA21 is an essential assembly chaperone of the vacuolar ATPase (V-ATPase), the principal mammalian proton pump complex. Decreased VMA21 raises lysosomal pH which reduces lysosomal degradative ability and blocks autophagy. This reduces cellular free amino acids which leads to downregulation of the mTORC1 pathway, and consequent increased macroautophagy resulting in proliferation of large and ineffective autolysosomes that engulf sections of cytoplasm, merge, and vacuolate the cell. Our results uncover a novel mechanism of disease, namely macroautophagic overcompensation leading to cell vacuolation and tissue atrophy.

Autophagy Mechanism, Regulation, Functions, and Disorders

Autophagy is a self-digesting mechanism responsible for removal of damaged organelles, malformed proteins during biosynthesis, and nonfunctional long-lived proteins by lysosome. Autophagy has been divided into three general types depending on the mechanism by which intracellular materials are delivered into lysosome for degradation that is, microautophagy, chaperone-mediated autophagy (CMA), and macroautophagy. In microautophagy cytoplasm material is sequestered through direct invagination to the lysosomal membrane. Whereas in CMA proteins flagged with pentapeptide motif (KFERQ) were selectively degraded through direct translocation into lysosome. Macroautophagy involves the formation of subcellular double-membrane-bound structures called autophagosomes that contain degradable contents of cytoplasm materials and deliver them into lysosomes for breakdown by lysosomal enzymes. The molecular mechanism of autophagy involves several conserved Atg (autophagy-related) proteins. Systems produce modified complexes Atg8-PE and Atg5-Atg12-Atg16 as autophagy regulators. Autophagy is activated in response to diverse stress and physiological conditions. For example, food deprivation, hyperthermia, and hypoxia are mediated by factors like insulin/IGF-1, m-TOR signaling, FOXO transcription factors, and chaperones. The perturbance in autophagy may lead to several types of cancers, myopathies, and neuromuscular disorders. Several autophagy inducers and inhibitors like 3-methyladenine (3-MA), bafilomycin A1, LY294002 (LY), and Velcade have been used to treat disease is an intense field of study.

The role of autophagy in the pathogenesis of glycogen storage disease type II (GSDII)

Regulated removal of proteins and organelles by autophagy-lysosome system is critical for muscle homeostasis. Excessive activation of autophagy-dependent degradation contributes to muscle atrophy and cachexia. Conversely, inhibition of autophagy causes accumulation of protein aggregates and abnormal organelles, leading to myofiber degeneration and myopathy. Defects in lysosomal function result in severe muscle disorders such as Pompe (glycogen storage disease type II (GSDII)) disease, characterized by an accumulation of autophagosomes. However, whether autophagy is detrimental or not in muscle function of Pompe patients is unclear. We studied infantile and late-onset GSDII patients and correlated impairment of autophagy with muscle wasting. We also monitored autophagy in patients who received recombinant α-glucosidase. Our data show that infantile and late-onset patients have different levels of autophagic flux, accumulation of p62-positive protein aggregates and expression of atrophy-related genes. Although the infantile patients show impaired autophagic function, the late-onset patients display an interesting correlation among autophagy impairment, atrophy and disease progression. Moreover, reactivation of autophagy in vitro contributes to acid α-glucosidase maturation in both healthy and diseased myotubes. Together, our data suggest that autophagy protects myofibers from disease progression and atrophy in late-onset patients.

Cellular response and extracellular matrix breakdown in rotator cuff tendon rupture

PURPOSE

The aim of this study was to investigate the relationship between the disruption of ECM and cellular events including autophagic cell death, apoptosis and cell differentiation into myofibroblasts in the degenerative rotator cuff tendon.

METHODS

Tendon samples were collected from 30 patients undergoing surgery for rotator cuff tears. Apoptosis, autophagic cell death and myofibroblasts of the tendon cells in the ruptured rotator cuff tendon were detected by immunohistochemical staining. The distribution of autophagic cell death, apoptosis, myofibroblasts and cell density were assessed and correlated with the disruption of ECM which was graded 0-3 points using a customized scoring system.

RESULTS

The highest percentage of autophagic cell death (51.9 ± 1.5%) was observed in grade 2 matrix, significantly different from that in matrix graded 0, 1 and 3 (P2Vs0 < 0.001; P2Vs1 < 0.001; P2Vs3 = 0.008, respectively). The highest apoptosis (34.8 ± 1.6%) was found in grade 3 matrix (P3Vs0 < 0.001; P3Vs1 < 0.001; P3Vs2 = 0.044, respectively). The percentage of myofibroblasts significantly increased as the ECM degenerated, with the highest percentage in grade 3 matrix (19.8 ± 1.3%) (P3Vs0 < 0.001; P3Vs11 < 0.001; P3Vs2 = 0.044, respectively). The total cell density varied with the grade of ECM, with maximum cell density in the matrix that was graded 1 (674 ± 27) and minimum cell density in matrix 3 area (395 ± 17) (P1Vs3 < 0.001).

CONCLUSION

This study indicates that autophagic cell death, apoptosis and myofibroblast cell differentiation occur in ruptured rotator cuff tissue. These cellular events are closely related to the extent of damage to the ECM structure.

[Eludication of pathomechanism of and development of therapy for autophagic vacuolar myopathies]

Autophagic vacuolar myopathy (AVM) is an entity defined by the presence of autophagic vacuoles on muscle pathology. There are two emerging categories in AVM in addition to the best characterized Pompe disease. One is Danon disease and its related disorders, which are characterized by autophagic vacuoles with unique sarcolemmal features (AVSF). AVSF express virtually all sarcolemmal proteins, in addition to acetylcholinesterase, on their vacuolar membranes. Danon disease is caused by primary deficiency of a lysosomal membrane protein, LAMP-2. Interestingly, in this disease, the number of AVSF increases as the patients age. Other AVSF myopathies include X-linked myopathy with excessive autophagy which is now known to be caused by VMA21 mutations. The other AVM is typified by the presence of rimmed vacuoles, which are actually clusters of autophagic vacuoles on electron microscopy. One of the well known diseases in this group is distal myopathy with rimmed vacuoles (DMRV), also called hereditary inclusion body myopathy (HIBM). DMRV is caused by mutations in GNE gene that encode a rate-limiting enzyme in the sialic acid biosynthetic pathway. Interestingly, in DMRV model mice, sialic acid supplementation almost completely precluded the disease phenotype, indicating that decreased sialic acid is the cause of myopathic phenotype and sialic acid supplementation can prevent the disease process. Interestingly, both genetically diagnosable AVSF myopathies are primarily due to lysosomal dysfunctions. In contrast, rimmed vacuoles are secondarily caused by extra-lysosomal defects, such as hyposialylation in DMRV/HIBM, and are formed at later stages of the disease.

VMA21 deficiency: a case of myocyte indigestion

The Vma21p protein in yeast is an essential assembly chaperone for the vacuolar ATPase, the major proton pump of cellular membranes. In this issue, Ramachandran et al. (2009) report that mutations in the gene encoding the human homolog VMA21 cause the disease X-linked myopathy with excessive autophagy through an unexpected mechanism.

Congenital myopathies--a comprehensive update of recent advancements

The congenital myopathies are relatively newly discovered compared with other categories of muscle diseases. Current research continues to clarify and classify the congenital myopathies. These pose a diagnostic problem and cannot be diagnosed by routine hematoxylin and eosin stain. A lot of special techniques are required to diagnose them correctly and it's various subtypes. The disease specific structural changes seen in the muscle are detected by enzyme histochemistry, immunohistochemistry and electron microscopy. Through this review we provide an up-to-date analysis of congenital myopathies including clinical and pathologic aspects.

Lysosomal myopathies: an excessive build-up in autophagosomes is too much to handle

Lysosomes are membrane-bound acidic organelles that contain hydrolases used for intracellular digestion of various macromolecules in a process generally referred to as autophagy. In normal skeletal and cardiac muscles, lysosomes usually appear morphologically unremarkable and thus are not readily visible on light microscopy. In distinct neuromuscular disorders, however, lysosomes have been shown to be structurally abnormal and functionally impaired, leading to the accumulation of autophagic vacuoles in myofibers. More specifically, there are myopathies in which buildup of these autophagic vacuoles seem to predominate the pathological picture. In such conditions, autophagy is considered not merely a secondary event, but a phenomenon that actually contributes to disease pathomechanism and/or progression. At present, there are two disorders in the muscle which are associated with primary defect in lysosomal proteins, namely Danon disease and Pompe disease. Other myopathies which have prominent autophagy in the skeletal muscle include X-linked myopathy with excessive autophagy (XMEA). In this review, these disorders are briefly characterized, and the role of autophagy in the context of the pathomechanism of these disorders is highlighted.

Danon disease with typical early-onset cardiomyopathy in a male: focus on a novel LAMP-2 mutation

We report a case of a 16-yr-old male with Danon disease caused by a novel mutation in the LAMP-2 gene. Mutations in the LAMP-2 gene result in the absence of LAMP-2 on immunohistochemical staining of muscle tissue, thus defining Danon disease, a rare X-linked myopathy. It is characterized clinically by HCM or left ventricular hypertrophy, a WPW pattern on ECG, variable degrees of muscular weakness (skeletal myopathy), mental retardation, and retinal changes. The patient presented with severe skeletal muscular weakness and respiratory failure. He also had a history of two OHTs, the first one for severe HCM and the second for allograft rejection. The patient's myopathy was initially presumed to be exclusively related to steroid-induced "critical care myopathy." However, further evaluation with a thigh muscle biopsy revealed autophagic vacuoles with sarcolemnal features suggestive of a lysosomal storage disorder. DNA analysis ultimately identified a previously unreported hemizygous IVS6+3_+6delGAGT splice site deletion mutation in the LAMP-2 gene located within the 5' splice site of intron 6, consistent with Danon disease.

An X-linked myopathy with postural muscle atrophy and generalized hypertrophy, termed XMPMA, is caused by mutations in FHL1

We have identified a large multigenerational Austrian family displaying a novel form of X-linked recessive myopathy. Affected individuals develop an adult-onset scapulo-axio-peroneal myopathy with bent-spine syndrome characterized by specific atrophy of postural muscles along with pseudoathleticism or hypertrophy and cardiac involvement. Known X-linked myopathies were excluded by simple-tandem-repeat polymorphism (STRP) and single-nucleotide polymorphism (SNP) analysis, direct gene sequencing, and immunohistochemical analysis. STRP analysis revealed significant linkage at Xq25-q27.1. Haplotype analysis based on SNP microarray data from selected family members confirmed this linkage region on the distal arm of the X chromosome, thereby narrowing down the critical interval to 12 Mb. Sequencing of functional candidate genes led to the identification of a missense mutation within the four and a half LIM domain 1 gene (FHL1), which putatively disrupts the fourth LIM domain of the protein. Mutation screening of FHL1 in a myopathy family from the UK exhibiting an almost identical phenotype revealed a 3 bp insertion mutation within the second LIM domain. FHL1 on Xq26.3 is highly expressed in skeletal and cardiac muscles. Western-blot analysis of muscle biopsies showed a marked decrease in protein expression of FHL1 in patients, in concordance with the genetic data. In summary, we have to our knowledge characterized a new disorder, X-linked myopathy with postural muscle atrophy (XMPMA), and identified FHL1 as the causative gene. This is the first FHL protein to be identified in conjunction with a human genetic disorder and further supports the role of FHL proteins in the development and maintenance of muscle tissue. Mutation screening of FHL1 should be considered for patients with uncharacterized myopathies and cardiomyopathies.

Danon disease as a cause of autophagic vacuolar myopathy

Danon disease, an extremely rare X-linked dominant disorder, is characterized clinically by hypertrophic cardiomyopathy (HCM), skeletal myopathy, and variable degree of mental retardation with autophagic vacuoles in skeletal and cardiac muscle. Reportedly, Danon disease is caused by a primary deficiency of a major lysosomal membrane glycoprotein, LAMP2 (lysosome-associated membrane protein 2). Here we review the clinical features, molecular genetics, related animal model, and differential diagnosis of Danon disease.

LAMP-2 positive vacuolar myopathy with dilated cardiomyopathy

We report a 46-year-old male patient with late-onset vacuolar myopathy and dilated cardiomyopathy. Acid maltase activity of the muscle was normal, but the biopsied muscle specimen stained for lysosome-associated membrane protein-2 (LAMP-2), which has recently been reported to be deficient in muscles of patients with Danon disease. The clinical features of the patient are distinct from X-linked myopathy with excessive autophagy, infantile autophagic vacuolar myopathy and autophagic vacuolar myopathy with late-onset and multiorgan involvement (Kaneda).

Autophagic vacuolar myopathy

Autophagic vacuoles are a frequent feature in numerous neuromuscular disorders. However, they are also pathognomonic morphologic hallmarks in a slowly emerging new group of conditions called autophagic vacuolar myopathies (AVMs), of which Danon disease, originally called "lysosomal glycogen storage disease with normal acid maltase," is the best known entity. Other such conditions, often although not always described from Japan, are X-linked myopathy with excessive authophagy, infantile autophagic vacuolar myopathy, adult-onset autophagic vacuolar myopathy with multiorgan involvement, and X-linked congenital autophagic vacuolar myopathy. Although only 1 protein, the transmembranous lysosomal protein LAMP-2, has been found mutated in Danon disease, the remaining AVMs are genetically still incompletely identified. Several of these conditions not only share autophagic vacuoles, but such autophagic vacuoles also have morphologic properties of the sarcolemma, thus rendering them autophagic vacuoles with sarcolemmal features, an almost pathognomonic phenomenon of this group of disorders.

Autophagic vacuolar myopathy in twin girls

Hereditary autophagic vacuolar myopathy (AVM) may occur in several diseases including the rimmed vacuolar myopathies, acid maltase deficiency, Danon disease, infantile autophagic vacuolar myopathy and X-linked myopathy with excessive autophagy (XMEA). In the latter three conditions the vacuoles are lined by membranes with sarcolemmal features. We present two unusual cases of autophagic vacuolar myopathy in twin girls born at term with no family history of neurological disease. After initial normal developmental milestones they developed progressive leg weakness and wasting with contractures from the age of 12 years. Investigations showed raised CK, normal female karyotype, normal acid maltase activity, normal nerve conduction and myopathic EMG features. Frozen sections of skeletal muscle were stained using routine tinctorial and histochemical methods. Immunohistochemical staining for spectrin, merosin, dystrophin, complement membrane attack complex and sarcoglycans was performed and ultrastructural examination undertaken. Direct sequence analysis of the lamp-2 gene using genomic DNA extracted from lymphocytes was performed. Histological analysis of the muscle biopsies demonstrated myofibres with vacuoles lacking glycogen and lipid many of which were delineated using immunohistochemistry for merosin, dystrophin and sarcoglycans. Ultrastructural examination showed duplication of the myofibre basal lamina with associated autophagic material. Vacuoles within myofibres were either membrane bound containing autophagic material or lined by plasma membrane and basal lamina. Intermyofibrillar glycogen was increased. Sequence analysis of the coding region and intron/exon boundaries of the lamp-2 gene was normal. This is the first report of female cases of AVM with sarcolemmal features. We suggest that these patients may represent manifesting carriers of XMEA, or alternatively, a new form of disease with a similar phenotype having autosomal recessive inheritance.

Congenital myopathies

Most congenital myopathies have been defined on account of the morphological findings in enzyme histochemical preparations. In effect, the diagnosis of this group of diseases continues to be made on the histological pattern of muscle biopsies. However, progress has been made in elucidating the molecular genetic background of several of the congenital myopathies. In this updated review we address those congenital myopathies for which gene defects and mutant proteins have been found (central core disease, nemaline myopathies, desminopathy, actinopathy, certain vacuolar myopathies, and myotubular myopathy) and the other disease with central nuclei (centronuclear myopathy).

Electron microscopy in neuromuscular disorders

Electron microscopy has a strategic position in the diagnosis of neuromuscular disorders. In muscular fibers, the main abnormalities include vacuoles, inclusion bodies, and myofibrillar disorganization with or without abnormal inclusion material. Vacuolar changes include lipidic and glycogenic storage vacuoles, rimmed vacuoles, and lysosomal and autophagic vacuoles. Accumulation of abnormal inclusion material is found in nemaline myopathy, actinopathies, and hyaline body myopathy. Myofibrillar disorganization involves cores, multiminicores, and myosin chain depletion. Myofibrillar myopathies associate a pathologic pattern of myofibrillar dissolution and ectopic protein expression. They can be divided into two groups: myofibrillar myopathies with multiple expression proteins and myofibrillar myopathies with desmin and alphaB-crystallin expression only. In these two conditions, electron microscopy shows accumulation of a granulofilamentous material immunoreactive for desmin. At least three genes are implicated: desmin, alphaB-crystallin, and myotilin. Lastly, electron microscopy serves to identify changes, pathogenic or not, which are not shown up by light microscopy. Moreover, electron microscopy gives insight on pathophysiological mechanisms and can guide molecular genetics analysis.

Autophagy

Autophagy is a major intracellular pathway for the degradation and recycling of long-lived proteins and cytoplasmic organelles. Like apoptotic programmed cell death, autophagy is an essential part of growth regulation and maintenance of homeostasis in multicellular organisms. Autophagic vacuole formation is also activated as an adaptive response to a variety of extracellular and intracellular stimuli, including nutrient deprivation, hormonal or therapeutic treatment, bacterial infection, aggregated and misfolded proteins and damaged organelles. Mediators of class I and class III PI3 kinase signaling pathways and trimeric G proteins play major roles in regulating autophagosome formation during the stress response. Defective autophagy is the underlying cause of a number of pathological conditions, including vacuolar myopathies, neurodegenerative diseases, liver disease, and some forms of cancer. This chapter provides an overview of the morphology and molecular basis of autophagosome formation and offers a glimpse into the role of autophagy in normal growth and development, while discussing the pathological implications of its deregulation.