Mitochondrial dysfunction is associated with hypertrophic cardiomyopathy in Pompe disease-specific induced pluripotent stem cell-derived cardiomyocytes

Pompe disease (PD) is a rare autosomal recessive disorder that presents with progressive hypertrophic cardiomyopathy. However, the detailed mechanism remains clarified. Herein, PD patient-specific induced pluripotent stem cells were differentiated into cardiomyocytes (PD-iCMs) that exhibited cardiomyopathic features of PD, including decreased acid alpha-glucosidase activity, lysosomal glycogen accumulation and hypertrophy. The defective mitochondria were involved in the cardiac pathology as shown by the significantly decreased number of mitochondria and impaired respiratory function and ATP production in PD-iCMs, which was partially due to elevated levels of intracellular reactive oxygen species produced from depolarized mitochondria. Further analysis showed that impaired fusion and autophagy of mitochondria and declined expression of mitochondrial complexes underlies the mechanism of dysfunctional mitochondria. This was alleviated by supplementation with recombinant human acid alpha-glucosidase that improved the mitochondrial function and concomitantly mitigated the cardiac pathology. Therefore, this study suggests that defective mitochondria underlie the pathogenesis of cardiomyopathy in patients with PD.

CRISPR-mediated generation and characterization of a Gaa homozygous c.1935C>A (p.D645E) Pompe disease knock-in mouse model recapitulating human infantile onset-Pompe disease

Pompe disease, an autosomal recessive disorder caused by deficient lysosomal acid α-glucosidase (GAA), is characterized by accumulation of intra-lysosomal glycogen in skeletal and oftentimes cardiac muscle. The c.1935C>A (p.Asp645Glu) variant, the most frequent GAA pathogenic mutation in people of Southern Han Chinese ancestry, causes infantile-onset Pompe disease (IOPD), presenting neonatally with severe hypertrophic cardiomyopathy, profound muscle hypotonia, respiratory failure, and infantile mortality. We applied CRISPR-Cas9 homology-directed repair (HDR) using a novel dual sgRNA approach flanking the target site to generate a Gaaem1935C>A knock-in mouse model and a myoblast cell line carrying the Gaa c.1935C>A mutation. Herein we describe the molecular, biochemical, histological, physiological, and behavioral characterization of 3-month-old homozygous Gaaem1935C>A mice. Homozygous Gaaem1935C>A knock-in mice exhibited normal Gaa mRNA expression levels relative to wild-type mice, had near-abolished GAA enzymatic activity, markedly increased tissue glycogen storage, and concomitantly impaired autophagy. Three-month-old mice demonstrated skeletal muscle weakness and hypertrophic cardiomyopathy but no premature mortality. The Gaaem1935C>A knock-in mouse model recapitulates multiple salient aspects of human IOPD caused by the GAA c.1935C>A pathogenic variant. It is an ideal model to assess innovative therapies to treat IOPD, including personalized therapeutic strategies that correct pathogenic variants, restore GAA activity and produce functional phenotypes.

Chemogenetic activation of hypoglossal motoneurons in a mouse model of Pompe disease

Pompe disease is a lysosomal storage disease resulting from absence or deficiency of acid α-glucosidase (GAA). Tongue-related disorders including dysarthria, dysphagia, and obstructive sleep apnea are common in Pompe disease. Our purpose was to determine if designer receptors exclusively activated by designer drugs (DREADDs) could be used to stimulate tongue motor output in a mouse model of Pompe disease. An adeno-associated virus serotype 9 (AAV9) encoding an excitatory DREADD (AAV9-hSyn-hM3D(Gq)-mCherry, 2.44 × 1010 vg) was administered to the posterior tongue of 5-7-wk-old Gaa null (Gaa-/-) mice. Lingual EMG responses to intraperitoneal injection of saline or a DREADD ligand (JHU37160-dihydrochloride, J60) were assessed 12 wk later during spontaneous breathing. Saline injection produced no consistent changes in lingual EMG. Following the DREADD ligand, there were statistically significant (P < 0.05) increases in both tonic and phasic inspiratory EMG activity recorded from the posterior tongue. Brainstem histology confirmed mCherry expression in hypoglossal (XII) motoneurons in all mice, thus verifying retrograde movement of the AAV9 vector. Morphologically, Gaa-/- XII motoneurons showed histological characteristics that are typical of Pompe disease, including an enlarged soma and vacuolization. We conclude that lingual delivery of AAV9 can be used to drive functional expression of DREADD in XII motoneurons in a mouse model of Pompe disease.NEW & NOTEWORTHY In a mouse model of Pompe disease, lingual injection of adeno-associated virus (AAV) serotype 9 encoding DREADD was histologically verified to produce transgene expression in hypoglossal motoneurons. Subsequent intraperitoneal delivery of a DREADD ligand stimulated tonic and phase tongue motor output.In a mouse model of Pompe disease, lingual injection of adeno-associated virus (AAV) serotype 9 encoding DREADD was histologically verified to produce transgene expression in hypoglossal motoneurons. Subsequent intravenous delivery of a DREADD ligand stimulated tonic and phase tongue motor output.

Efficacious Androgen Hormone Administration in Combination with Adeno-Associated Virus Vector-Mediated Gene Therapy in Female Mice with Pompe Disease

Pompe disease is an autosomal recessive lysosomal storage disorder caused by deficiency of acid α-glucosidase (GAA), resulting in skeletal muscle weakness and cardiomyopathy that progresses despite currently available therapy in some patients. The development of gene therapy with adeno-associated virus (AAV) vectors revealed a sex-dependent decrease in efficacy in female mice with Pompe disease. This study evaluated the effect of testosterone on gene therapy with an AAV2/8 vector containing a liver-specific promoter to drive expression of GAA (AAV2/8-LSPhGAA) in female GAA-knockout (KO) mice that were implanted with pellets containing testosterone propionate before vector administration. Six weeks after treatment, neuromuscular function and muscle strength were improved as demonstrated by increased Rotarod and wirehang latency for female mice treated with testosterone and vector, in comparison with vector alone. Biochemical correction improved after the addition of testosterone as demonstrated by increased GAA activity and decreased glycogen content in the skeletal muscles of female mice treated with testosterone and vector, in comparison with vector alone. An alternative androgen, oxandrolone, was evaluated similarly to reveal increased GAA in the diaphragm and extensor digitorum longus of female GAA-KO mice after oxandrolone administration; however, glycogen content was unchanged by oxandrolone treatment. The efficacy of androgen hormone treatment in females correlated with increased mannose-6-phosphate receptor in skeletal muscle. These data confirmed the benefits of brief treatment with an androgen hormone in mice with Pompe disease during gene therapy.

Complex Transposon Insertion as a Novel Cause of Pompe Disease

Pompe disease (OMIM#232300) is an autosomal recessive lysosomal storage disorder caused by mutations in the GAA gene. According to public mutation databases, more than 679 pathogenic variants have been described in GAA, none of which are associated with mobile genetic elements. In this article, we report a novel molecular genetic cause of Pompe disease, which could be hardly detected using routine molecular genetic analysis. Whole genome sequencing followed by comprehensive functional analysis allowed us to discover and characterize a complex mobile genetic element insertion deep in the intron 15 of the GAA gene in a patient with infantile onset Pompe disease.

Protein structural features predict responsiveness to pharmacological chaperone treatment for three lysosomal storage disorders

Three-dimensional structures of proteins can provide important clues into the efficacy of personalized treatment. We perform a structural analysis of variants within three inherited lysosomal storage disorders, comparing variants responsive to pharmacological chaperone treatment to those unresponsive to such treatment. We find that predicted ΔΔG of mutation is higher on average for variants unresponsive to treatment, in the case of datasets for both Fabry disease and Pompe disease, in line with previous findings. Using both a single decision tree and an advanced machine learning approach based on the larger Fabry dataset, we correctly predict responsiveness of three Gaucher disease variants, and we provide predictions for untested variants. Many variants are predicted to be responsive to treatment, suggesting that drug-based treatments may be effective for a number of variants in Gaucher disease. In our analysis, we observe dependence on a topological feature reporting on contact arrangements which is likely connected to the order of folding of protein residues, and we provide a potential justification for this observation based on steady-state cellular kinetics.

Pharmacological chaperones are small molecule drugs that bind to proteins to help stabilize the folded state. One set of diseases for which this treatment has been effective is the lysosomal storage disorders, which are caused by defective lysosomal enzymes. However, not all genotypes are equally responsive to treatment. For instance, missense mutants that are particularly destabilized relative to WT are less likely to respond. The availability of datasets containing responsiveness data for large numbers of mutants, along with crystal structures of the protein involved in each disease, make machine learning methods incorporating sequence-based and structural data feasible. We hypothesize that data from two diseases, Fabry and Pompe disease, may be useful for predicting responsiveness of variants in the related Gaucher disease. Results suggest that many rare variants in Gaucher disease could be amenable to existing drugs. Results also suggest that drug responsiveness depends on protein topology in such a way that mutations in early-to-fold residues are more likely to be non-responsive to pharmacological chaperone treatment, which is consistent with a simple kinetic model of stability rescue. This study provides an example of how machine learning can be used to inform further studies towards personalized treatment in medicine.

Endolysosomal N-glycan processing is critical to attain the most active form of the enzyme acid alpha-glucosidase

Acid alpha-glucosidase (GAA) is a lysosomal glycogen-catabolizing enzyme, the deficiency of which leads to Pompe disease. Pompe disease can be treated with systemic recombinant human GAA (rhGAA) enzyme replacement therapy (ERT), but the current standard of care exhibits poor uptake in skeletal muscles, limiting its clinical efficacy. Furthermore, it is unclear how the specific cellular processing steps of GAA after delivery to lysosomes impact its efficacy. GAA undergoes both proteolytic cleavage and glycan trimming within the endolysosomal pathway, yielding an enzyme that is more efficient in hydrolyzing its natural substrate, glycogen. Here, we developed a tool kit of modified rhGAAs that allowed us to dissect the individual contributions of glycan trimming and proteolysis on maturation-associated increases in glycogen hydrolysis using in vitro and in cellulo enzyme processing, glycopeptide analysis by MS, and high-pH anion-exchange chromatography with pulsed amperometric detection for enzyme kinetics. Chemical modifications of terminal sialic acids on N-glycans blocked sialidase activity in vitro and in cellulo, thereby preventing downstream glycan trimming without affecting proteolysis. This sialidase-resistant rhGAA displayed only partial activation after endolysosomal processing, as evidenced by reduced catalytic efficiency. We also generated enzymatically deglycosylated rhGAA that was shown to be partially activated despite not undergoing proteolytic processing. Taken together, these data suggest that an optimal rhGAA ERT would require both N-glycan and proteolytic processing to attain the most efficient enzyme for glycogen hydrolysis and treatment of Pompe disease. Future studies should examine the amenability of next-generation ERTs to both types of cellular processing.

Three-dimensional tissue-engineered human skeletal muscle model of Pompe disease

In Pompe disease, the deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA) causes skeletal and cardiac muscle weakness, respiratory failure, and premature death. While enzyme replacement therapy using recombinant human GAA (rhGAA) can significantly improve patient outcomes, detailed disease mechanisms and incomplete therapeutic effects require further studies. Here we report a three-dimensional primary human skeletal muscle ("myobundle") model of infantile-onset Pompe disease (IOPD) that recapitulates hallmark pathological features including reduced GAA enzyme activity, elevated glycogen content and lysosome abundance, and increased sensitivity of muscle contractile function to metabolic stress. In vitro treatment of IOPD myobundles with rhGAA or adeno-associated virus (AAV)-mediated hGAA expression yields increased GAA activity and robust glycogen clearance, but no improvements in stress-induced functional deficits. We also apply RNA sequencing analysis to the quadriceps of untreated and AAV-treated GAA-/- mice and wild-type controls to establish a Pompe disease-specific transcriptional signature and reveal novel disease pathways. The mouse-derived signature is enriched in the transcriptomic profile of IOPD vs. healthy myobundles and partially reversed by in vitro rhGAA treatment, further confirming the utility of the human myobundle model for studies of Pompe disease and therapy.

Combined proteomic and lipidomic studies in Pompe disease allow a better disease mechanism understanding

Pompe disease (PD) is caused by deficiency of the enzyme acid α-glucosidase resulting in glycogen accumulation in lysosomes. Clinical symptoms include skeletal myopathy, respiratory failure, and cardiac hypertrophy. We studied plasma proteomic and lipidomic profiles in 12 PD patients compared to age-matched controls. The proteomic profiles were analyzed by nLC-MS/MS SWATH method. Wide-targeted lipidomic analysis was performed by LC-IMS/MS, allowing to quantify >1100 lipid species, spanning 13 classes. Significant differences were found for 16 proteins, with four showing the most relevant changes (GPLD1, PON1, LDHB, PKM). Lipidomic analysis showed elevated levels of three phosphatidylcholines and of the free fatty acid 22:4, and reduced levels of six lysophosphatidylcholines. Up-regulated glycolytic enzymes (LDHB and PKM) are involved in autophagy and glycogen metabolism, while down-regulated PON1 and GPLD1 combined with lipidomic data indicate an abnormal phospholipid metabolism. Reduced GPLD1 and dysregulation of lipids with acyl-chains characteristic of GPI-anchor structure suggest the potential involvement of GPI-anchor system in PD. Results of proteomic analysis displayed the involvement of multiple cellular functions affecting inflammatory, immune and antioxidant responses, autophagy, Ca²⁺ -homeostasis, and cell adhesion. The combined multi-omic approach revealed new biosignatures in PD, providing novel insights in disease pathophysiology with potential future clinical application.

A generic assay for the identification of splicing variants that induce nonsense-mediated decay in Pompe disease

DNA variants affecting mRNA expression and processing in genetic diseases are often missed or poorly characterized. We previously reported a generic assay to identify variants that affect mRNA expression and splicing in Pompe disease, a monogenic disorder caused by deficiency of acid α-glucosidase (GAA). However, this assay could miss mRNA that is subjected to degradation. Here, we inhibited mRNA degradation using cycloheximide and performed unbiased splicing analysis of all GAA exons using exon flanking RT-PCR and exon internal RT-qPCR. In four patients that were suspected of harboring splicing variants but for which aberrant splicing could not be detected in normally growing cells, we detected a total of 10 novel splicing events in cells treated with cycloheximide. In addition, we found that sequences of GAA introns 6 and 12 were naturally included in a subset of transcripts from patients and healthy controls, indicating inefficient canonical splicing. Identification of aberrant splicing caused by the common Asian variant c.546G>T allowed the development of an antisense oligonucleotide that promoted canonical GAA pre-mRNA splicing and elevated GAA enzymatic activity. Our results indicate that this extended generic splicing assay allows the detection of aberrant splicing in cases of mRNA degradation to enable functional analysis of unknown splicing variants and the development of targeted treatment options.

The Release of a Soluble Glycosylated Protein from Glycogen by Recombinant Lysosomal α-Glucosidase (rhGAA) In Vitro and Its Presence in Serum In Vivo

In studies on the degradation of glycogen by rhGAA, a glycosylated protein core material was found which consists of about 5-6% of the total starting glycogen. There was an additional 25% of the glycogen unaccounted for based on glucose released. After incubation of glycogen with rhGAA until no more glucose was released, no other carbohydrate was detected on HPAEC-PAD. Several oligosaccharides are then detectable if the medium is first boiled in 0.1 N HCl or incubated with trypsin. It is present in serum either in an HCl extract or in a trypsin digest. The characteristics of the in vivo serum material are identical to the material in the in vitro incubation medium. One oligosaccharide cannot be further degraded by rhGAA, from the incubation medium as well as from serum co-elute on HPAEC-PAD. Several masked oligosaccharides in serum contain m-inositol, e-inositol, and sorbitol as the major carbohydrates. The presence of this glycosylated protein in serum is a fraction of glycogen that is degraded outside the lysosome and the cell. The glycosylated protein in the serum is not present in the serum of Pompe mice not on ERT, but it is present in the serum of Pompe disease patients who are on ERT, so it is a biomarker of GAA degradation of lysosomal glycogen.

GAA gene mutation detection following clinical evaluation and enzyme activity analysis in Azeri Turkish patients with Pompe disease

Pompe disease (PD) is a rare autosomal recessive multi-systemic lysosomal storage disorder, caused by mutations in the acid alpha-glucosidase (GAA) gene located on 17q25.2-q25.3. It is one of about 50 rare genetic diseases categorized as lysosomal storage disorders. This disease is characterized by a range of different symptoms related to acid alpha-glucosidase deficiency. Mutation recognition in the GAA gene can be very significant for purposes such as therapeutic interference, early diagnosis and genotype-phenotype relationship. In the current study, peripheral blood samples were gathered from patients with PD and healthy members of three families. Enzymatic activity of GAA was checked. Then, mutation detection was performed by polymerase chain reaction followed by direct sequencing of all exons in samples with decreased enzyme activity. The identified mutations were investigated using bioinformatics tools to predict possible effects on the protein product and also to compare the mutated sequence with near species. Three novel mutations (c.1966-1968delGAG, c.2011-2012delAT and c.1475-1481dupACCCCAC) were identified in the GAA gene. Assessment of the effects of these mutations on protein structure and function showed the possibility of harmful effects and their significant alterations in the protein structure. The three novel GAA gene mutations detected in this study expand the information about the molecular genetics of PD and can be used to helpdiagnosis and genetic counseling of affected families.

Moss-Derived Human Recombinant GAA Provides an Optimized Enzyme Uptake in Differentiated Human Muscle Cells of Pompe Disease

Pompe disease is an autosomal recessive lysosomal storage disorder (LSD) caused by deficiency of lysosomal acid alpha-glucosidase (GAA). The result of the GAA deficiency is a ubiquitous lysosomal and non-lysosomal accumulation of glycogen. The most affected tissues are heart, skeletal muscle, liver, and the nervous system. Replacement therapy with the currently approved enzyme relies on M6P-mediated endocytosis. However, therapeutic outcomes still leave room for improvement, especially with regard to skeletal muscles. We tested the uptake, activity, and effect on glucose metabolism of a non-phosphorylated recombinant human GAA produced in moss (moss-GAA). Three variants of moss-GAA differing in glycosylation pattern have been analyzed: two with terminal mannose residues in a paucimannosidic (Man3) or high-mannose (Man 5) configuration and one with terminal N-acetylglucosamine residues (GnGn). Compared to alglucosidase alfa the moss-GAA GnGn variant showed increased uptake in differentiated myotubes. Moreover, incubation of immortalized muscle cells of Gaa^-/- mice with moss-GAA GnGn led to similarly efficient clearance of accumulated glycogen as with alglucosidase alfa. These initial data suggest that M6P-residues might not always be necessary for the cellular uptake in enzyme replacement therapy (ERT) and indicate the potential of moss-GAA GnGn as novel alternative drug for targeting skeletal muscle in Pompe patients.

Muscle glycogen concentrations and response to diet and exercise regimes in Warmblood horses with type 2 Polysaccharide Storage Myopathy

Type 1 polysaccharide storage myopathy (PSSM1) is a glycogen storage disorder of known cause whereas the basis for type 2 PSSM (PSSM2) is unknown. The same diet and exercise regime prescribed for PSSM1 is recommended for PSSM2; however, the benefit of these recommendations for PSSM2 is undocumented. The objectives of this study were to determine traits of PSSM2 Warmblood horses (WB), determine the changes in exercise responses that occur with a recommended low-starch/fat-supplemented diet and exercise regime, and determine if glycogen concentrations correspond to the severity of signs. Owners of PSSM2 WB (2008-2016), completed a retrospective questionnaire regarding their horse. Glycogen concentrations were analyzed in skeletal muscle of PSSM2 WB (n = 36) obtained prior to recommendations and in control WB with no evident myopathy (n = 23). Chi-square, Fisher's exact, McNemar's tests with Bonferroni correction and Mann Whitney testing were utilized. Abnormal exercise responses reported by owners, began at approximately 6 years of age and included a decline in performance, a reluctance to collect and reluctance to go forward in over 50% of horses. With the recommended diet and exercise regime, 80% of PSSM2 WB owners reported an overall improvement with significant decreases in the proportion of horses showing a decline in performance and rhabdomyolysis. However, 53% of PSSM2 WB were still not advancing as expected with reluctance to go forward and collect persisting in approximately one third of horses. Median muscle glycogen concentrations did not differ between PSSM2 WB and WB with no evident myopathy. PSSM2 WB with the highest glycogen concentrations were significantly more likely to show a decline in performance than those with lower glycogen concentrations. In conclusion, diet and exercise recommendations ideal for PSSM1 improve but do not eliminate the decline in performance and reluctance to go forward under saddle characteristic of PSSM2.

Lipidic Nanoparticles Comprising Phosphatidylinositol Mitigate Immunogenicity and Improve Efficacy of Recombinant Human Acid Alpha-Glucosidase in a Murine Model of Pompe Disease

Enzyme replacement therapy with recombinant human acid α-glucosidase (rhGAA) is complicated by the formation of anti-rhGAA antibodies, a short circulating half-life, instability in the plasma, and limited uptake into target tissue. Previously, we have demonstrated that phosphatidylinositol (PI) containing liposomes can reduce the immunogenicity and extend plasma survival of factor VIII (FVIII) in a mouse model of hemophilia A. In this article, we investigate the ability of PI liposomes to be used as a delivery vehicle to overcome the issues that complicate therapy with rhGAA. In a murine model of Pompe disease, administration of PI-rhGAA mitigated the immunogenicity of rhGAA, resulting in a significantly lower formation of anti-rhGAA antibodies. PI-rhGAA also showed minimal improvements to the pharmacokinetic parameters and efficacy measures compared to free rhGAA. Overall, these data suggest that PI-rhGAA may have the potential to be a useful therapeutic option for improving the treatment of Pompe disease.

Differential diagnosis of vacuolar muscle biopsies: use of p62, LC3 and LAMP2 immunohistochemistry

Intrafibral vacuoles are the morphological hallmark in a wide variety of human skeletal muscle disorders with different etiology. In most cases, differential diagnosis is feasible with a routine histochemical work up of muscle biopsy. Ultrastructural analysis is an important confirmatory tool, but it is not widely available. Immunohistochemical stainings for p62, LAMP2 and LC3 are commonly available as tissutal marker for autophagy. We compared the immunohistochemical patterns for autophagic markers p62, LC3 and LAMP2 with routine histochemical markers in 39 biopsies from patients with definite diagnoses of glycogen storage disease type 2 (LOPD or Pompe disease, PD), sporadic inclusion body myositis (sIBM), oculo-pharyngeal muscular dystrophy (OPMD) and necrotizing myopathy (NM). Moreover, we also analyzed muscles of 10 normal controls. In PD group, LC3 and LAMP2 showed an higher percentage of positive fibers, whereas p62 was limited to a minority of fibers, thus paralleling the results of histochemical stainings; in NM group, LAMP2 and LC-3 were diffusely and unspecifically expressed in necrotic fibers, with p62 significantly expressed only in two cases. OPMD biopsies did not reveal any significant positivity. The most interesting results were observed in sIBM group, where p62 was expressed in all cases, even in fibers without other markers positivity. There results, although limited to a small number of cases, suggest that the contemporary use of p62, LAMP2 and LC-3 staining may have an adjunctive role in characterizing muscle fiber vacuoles, revealing autophagic pathway activation and providing further clues for the understanding of pathogenetic mechanisms.s.

Late-onset Pompe disease in a 54 year-old sportsman with an episode of syncope: a case report

Pompe disease is an extra-rare metabolic storage disease with deficiency of acid-alpha-glucosidase (GAA) enzyme activity, which leads to the pathologic accumulation of glycogen in target tissues (skeletal muscles, heart, brain). Clinical features and severity vary by the age of onset, rate of extent of organ involvement. In the late-onset Pompe disease (LOPD) form, essential cardiomyopathy seems to be uncommon. Muscles weakness and respiratory failure are the main symptoms of adult patient with Pompe disease. In presented case LOPD coupled with patient's regular sporting activity and healthy diet, which may explain the low intensity of the symptoms and the slow progress of the disease, lack of skeletal muscles weakness and lack of brain manifestation. Myocardial storage deposits are the only abnormalities found.

High-resolution Light Microscopy (HRLM) and Digital Analysis of Pompe Disease Pathology

Pompe disease is an autosomal recessive lysosomal storage disorder caused by a deficiency of the lysosomal enzyme acid α-glucosidase, responsible for the degradation of lysosomal glycogen. Absent or low levels of the enzyme leads to lysosomal glycogen accumulation in cardiac and skeletal muscle cells, resulting in progressive muscle weakness and death from cardiac or respiratory failure. Recombinant enzyme replacement and gene therapy are now being investigated as treatment modalities for this disease. A knockout mouse model for Pompe disease, induced by the disruption of exon 6 within the acid α-glucosidase gene, mimics the human disease and has been used to evaluate the efficacy of treatment modalities for clearing glycogen. However, for accurate histopathological assessment of glycogen clearance, maximal preservation of in situ lysosomal glycogen is essential. To improve retention of glycogen in Pompe tissues, several fixation and embedding regimens were evaluated. The best glycogen preservation was obtained when tissues fixed with 3% glutaraldehyde and postfixed with 1% osmium tetroxide were processed into epon-araldite. Preservation was confirmed by staining with the Periodic acid-Schiff's reaction and by electron microscopy. This methodology resulted in high-resolution light microscopy (HRLM) sections suitable for digital quantification of glycogen content in heart and skeletal muscle. Combining this method of tissue fixation with computer-assisted histomorphometry has provided us with what we believe is the most objective and reproducible means of evaluating histological glycogen load in Pompe disease.

Neuropathology in respiratory-related motoneurons in young Pompe (Gaa(-/-)) mice

Respiratory and/or lingual dysfunction are among the first motor symptoms in Pompe disease, a disorder resulting from absence or dysfunction of the lysosomal enzyme acid α-glucosidase (GAA). Here, we histologically evaluated the medulla, cervical and thoracic spinal cords in 6 weeks old asymptomatic Pompe (Gaa(-/-)) mice to determine if neuropathology in respiratory motor regions has an early onset. Periodic acid-Schiff (PAS) staining indicated glycogen accumulation was exclusively occurring in Gaa(-/-) hypoglossal, mid-cervical and upper thoracic motoneurons. Markers of DNA damage (Tunel) and ongoing apoptosis (Cleaved Caspase 3) did not co-localize with PAS staining, but were prominent in a medullary region which included the nucleus tractus solitarius, and also in the thoracic spinal dorsal horn. We conclude that respiratory-related motoneurons are particularly susceptible to GAA deficiency and that neuronal glycogen accumulation and neurodegeneration may occur independently in early stage disease. The data support early therapeutic intervention in Pompe disease.

Intracranial arterial abnormalities in patients with late onset Pompe disease (LOPD)

BACKGROUND AND OBJECTIVES

Pompe disease is a rare metabolic disorder due to lysosomal alpha-glucosidase (GAA) deficiency. It is considered as a multi-systemic disease since, although glycogen accumulation is largely prominent in heart, skeletal and respiratory muscles, other organs can also be affected. As regards the vascular system, few reports have documented cerebrovascular malformations in Pompe patients. The aim of this study was to define the presence and type of intracranial arterial abnormalities in a cohort of late onset Pompe disease (LOPD) patients.

METHODS

We have studied 21 LOPD patients with cerebral CT angiography (CTA), using maximum intensity projection and volume rendering technique for 3D-image reconstruction.

RESULTS

We found intracranial arterial abnormalities in 13/21 patients (62 %), of whom: 2/21 patients (9.5 %) showed an unruptured intracranial aneurysm (respectively 2 and 4 mm), 10/21 (47 %) had a vertebrobasilar dolichoectasia (VBD) and 1/21 a basilar artery fenestration. Signs of lacunar encephalopathy (insular, capsular and frontal subcortical lesions) were detected in 13/21 patients (62 %) and this correlated with the presence of respiratory impairment (p = 0.017).

CONCLUSIONS

These findings differ from what has been previously observed in healthy, aged-matched populations and confirm that cerebral arteries abnormalities, mainly involving the posterior circle, are not so rare in LOPD patients and are often accompanied by a lacunar encephalopathy that might represent a hypoxic-ischemic origin. A CTA or an MRA is recommended, in LOPD patients, for early detection of cerebrovascular malformations as they could lead to life-threatening events such as sub-arachnoid haemorrhage or brainstem compression.

Salmeterol enhances the cardiac response to gene therapy in Pompe disease

Enzyme replacement therapy (ERT) with recombinant human (rh) acid α-glucosidase (GAA) has prolonged the survival of patients. However, the paucity of cation-independent mannose-6-phosphate receptor (CI-MPR) in skeletal muscle, where it is needed to take up rhGAA, correlated with a poor response to ERT by muscle in Pompe disease. Clenbuterol, a selective β2 receptor agonist, enhanced the CI-MPR expression in striated muscle through Igf-1 mediated muscle hypertrophy, which correlated with increased CI-MPR (also the Igf-2 receptor) expression. In this study we have evaluated 4 new drugs in GAA knockout (KO) mice in combination with an adeno-associated virus (AAV) vector encoding human GAA, 3 alternative β2 agonists and dehydroepiandrosterone (DHEA). Mice were injected with AAV2/9-CBhGAA (1E+11 vector particles) at a dose that was not effective at clearing glycogen storage from the heart. Heart GAA activity was significantly increased by either salmeterol (p<0.01) or DHEA (p<0.05), in comparison with untreated mice. Furthermore, glycogen content was reduced in the heart by treatment with DHEA (p<0.001), salmeterol (p<0.05), formoterol (p<0.01), or clenbuterol (p<0.01) in combination with the AAV vector, in comparison with untreated GAA-KO mice. Wirehang testing revealed that salmeterol and the AAV vector significantly increased performance, in comparison with the AAV vector alone (p<0.001). Similarly, salmeterol with the vector increased performance significantly more than any of the other drugs. The most effective individual drugs had no significant effect in absence of vector, in comparison with untreated mice. Thus, salmeterol should be further developed as adjunctive therapy in combination with either ERT or gene therapy for Pompe disease.

Response of 33 UK patients with infantile-onset Pompe disease to enzyme replacement therapy

BACKGROUND

Enzyme replacement therapy (ERT) for infantile-onset Pompe disease has been commercially available for almost 10 years. We report the experience of its use in a cohort treated at three specialist lysosomal treatment centres in the UK.

METHODS

A retrospective case-note review was performed, with additional data being gathered from two national audits on all such patients treated with ERT. The impact on the outcome of various characteristics, measured just prior to the initiation of ERT (baseline), was evaluated using logistic regression.

RESULTS

Thirty-three patients were identified; 13/29 (45%) were cross-reactive immunological material (CRIM) negative, and nine were immunomodulated. At baseline assessment, 79% were in heart failure, 66% had failure to thrive and 70% had radiological signs of focal pulmonary collapse. The overall survival rate was 60%, ventilation-free survival was 40% and 30% of patients were ambulatory. Median follow-up of survivors was 4 years, 1.5 months (range 6 months to 13.5 years). As with previous studies, the CRIM status impacted on all outcome measures. However, in this cohort, baseline failure to thrive was related to death and lack of ambulation, and left ventricular dilatation was a risk factor for non-ventilator-free survival.

CONCLUSION

The outcome of treated patients remains heterogeneous despite attempts at immunomodulation. Failure to thrive at baseline and left ventricular dilation appear to be associated with poorer outcomes.

Defects in calcium homeostasis and mitochondria can be reversed in Pompe disease

Mitochondria-induced oxidative stress and flawed autophagy are common features of neurodegenerative and lysosomal storage diseases (LSDs). Although defective autophagy is particularly prominent in Pompe disease, mitochondrial function has escaped examination in this typical LSD. We have found multiple mitochondrial defects in mouse and human models of Pompe disease, a life-threatening cardiac and skeletal muscle myopathy: a profound dysregulation of Ca(2+) homeostasis, mitochondrial Ca(2+) overload, an increase in reactive oxygen species, a decrease in mitochondrial membrane potential, an increase in caspase-independent apoptosis, as well as a decreased oxygen consumption and ATP production of mitochondria. In addition, gene expression studies revealed a striking upregulation of the β 1 subunit of L-type Ca(2+) channel in Pompe muscle cells. This study provides strong evidence that disturbance of Ca(2+) homeostasis and mitochondrial abnormalities in Pompe disease represent early changes in a complex pathogenetic cascade leading from a deficiency of a single lysosomal enzyme to severe and hard-to-treat autophagic myopathy. Remarkably, L-type Ca(2+)channel blockers, commonly used to treat other maladies, reversed these defects, indicating that a similar approach can be beneficial to the plethora of lysosomal and neurodegenerative disorders.

The pharmacological chaperone AT2220 increases the specific activity and lysosomal delivery of mutant acid alpha-glucosidase, and promotes glycogen reduction in a transgenic mouse model of Pompe disease

Pompe disease is an inherited lysosomal storage disorder that results from a deficiency in acid α-glucosidase (GAA) activity due to mutations in the GAA gene. Pompe disease is characterized by accumulation of lysosomal glycogen primarily in heart and skeletal muscles, which leads to progressive muscle weakness. We have shown previously that the small molecule pharmacological chaperone AT2220 (1-deoxynojirimycin hydrochloride, duvoglustat hydrochloride) binds and stabilizes wild-type as well as multiple mutant forms of GAA, and can lead to higher cellular levels of GAA. In this study, we examined the effect of AT2220 on mutant GAA, in vitro and in vivo, with a primary focus on the endoplasmic reticulum (ER)-retained P545L mutant form of human GAA (P545L GAA). AT2220 increased the specific activity of P545L GAA toward both natural (glycogen) and artificial substrates in vitro. Incubation with AT2220 also increased the ER export, lysosomal delivery, proteolytic processing, and stability of P545L GAA. In a new transgenic mouse model of Pompe disease that expresses human P545L on a Gaa knockout background (Tg/KO) and is characterized by reduced GAA activity and elevated glycogen levels in disease-relevant tissues, daily oral administration of AT2220 for 4 weeks resulted in significant and dose-dependent increases in mature lysosomal GAA isoforms and GAA activity in heart and skeletal muscles. Importantly, oral administration of AT2220 also resulted in significant glycogen reduction in disease-relevant tissues. Compared to daily administration, less-frequent AT2220 administration, including repeated cycles of 4 or 5 days with AT2220 followed by 3 or 2 days without drug, respectively, resulted in even greater glycogen reductions. Collectively, these data indicate that AT2220 increases the specific activity, trafficking, and lysosomal stability of P545L GAA, leads to increased levels of mature GAA in lysosomes, and promotes glycogen reduction in situ. As such, AT2220 may warrant further evaluation as a treatment for Pompe disease.

Pain in adult patients with Pompe disease: a cross-sectional survey

BACKGROUND

Pompe disease is a rare hereditary metabolic myopathy caused by a deficiency of acid-α-glucosidase. We investigated the presence and severity of pain and its interference with daily activities in a large group of adults with Pompe disease, who we compared with an age-matched control group.

METHODS

Data were collected in a cross-sectional survey in Germany and The Netherlands. Pain was assessed using the short-form brief pain inventory (BPI). Patients also completed the Short Form-36 item (SF-36v2), the Hospital Anxiety and Depression Scale (HADS) and the Rotterdam Handicap Scale (RHS).

RESULTS

Forty-five percent of the 124 adult Pompe patients reported having had pain in the previous 24h, against 27% of the 111 controls (p=0.004). The median pain severity score in Pompe patients reporting pain was 3.1 (on a scale from 0 to 10), indicating mild pain; against 2.6 amongst controls (p=0.06). The median score of pain interference with daily activities in patients who reported pain was 3.3, against 1.3 in controls (p=0.001). Relative to patients without pain, those with pain had lower RHS scores (p=0.02), lower SF-36 Physical and Mental component summary scores (p<0.001 and p=0.049), and higher levels of depression and anxiety (p=0.005 and p=0.003).

CONCLUSIONS

To date, this is one of the largest studies on pain in a specific neuromuscular disorder. Nearly one in two Pompe patients had experienced pain in the previous 24h. Although pain severity and its interference with daily life were mild, pain was related to a reduced quality of life, less participation in daily life, and greater depression and anxiety. Its management should therefore be seen as part of clinical practice involving Pompe patients.

Stbd1 is highly elevated in skeletal muscle of Pompe disease mice but suppression of its expression does not affect lysosomal glycogen accumulation

Previous studies strongly suggest that starch binding domain containing protein 1 (Stbd1) plays an important role in intracellular glycogen trafficking into lysosomes. We report here that Stbd1 expression is markedly increased in skeletal muscles but not in heart and liver of GAA-KO mice. An AAV2/9 vector expressing a Stbd1-specific shRNA effectively suppressed Stbd1 expression but did not alter lysosomal glycogen accumulation in the affected tissues of GAA-KO mice. Our results indicate that inhibition of Stbd1 does not appear to be an effective therapeutic approach for Pompe disease.

Dysregulation of multiple facets of glycogen metabolism in a murine model of Pompe disease

Pompe disease, also known as glycogen storage disease (GSD) type II, is caused by deficiency of lysosomal acid α-glucosidase (GAA). The resulting glycogen accumulation causes a spectrum of disease severity ranging from a rapidly progressive course that is typically fatal by 1 to 2 years of age to a slower progressive course that causes significant morbidity and early mortality in children and adults. The aim of this study is to better understand the biochemical consequences of glycogen accumulation in the Pompe mouse. We evaluated glycogen metabolism in heart, triceps, quadriceps, and liver from wild type and several strains of GAA^−/− mice. Unexpectedly, we observed that lysosomal glycogen storage correlated with a robust increase in factors that normally promote glycogen biosynthesis. The GAA^−/− mouse strains were found to have elevated glycogen synthase (GS), glycogenin, hexokinase, and glucose-6-phosphate (G-6-P, the allosteric activator of GS). Treating GAA^−/− mice with recombinant human GAA (rhGAA) led to a dramatic reduction in the levels of glycogen, GS, glycogenin, and G-6-P. Lysosomal glycogen storage also correlated with a dysregulation of phosphorylase, which normally breaks down cytoplasmic glycogen. Analysis of phosphorylase activity confirmed a previous report that, although phosphorylase protein levels are identical in muscle lysates from wild type and GAA^−/− mice, phosphorylase activity is suppressed in the GAA^−/− mice in the absence of AMP. This reduction in phosphorylase activity likely exacerbates lysosomal glycogen accumulation. If the dysregulation in glycogen metabolism observed in the mouse model of Pompe disease also occurs in Pompe patients, it may contribute to the observed broad spectrum of disease severity.

Auditory system involvement in late onset Pompe disease: a study of 20 Italian patients

Glycogen storage disease type II (GSD II), also known as Pompe disease, is an autosomal recessive inherited disorder caused by a reduced activity of acid alpha glucosidase (GAA). Two different clinical entities have been described: rapidly fatal infantile and late onset forms. Hearing loss has been described in classic infantile Pompe patients but rarely in late onset cases. The main purpose of this study was to investigate the involvement of the auditory system in a cohort of Italian patients with late onset GSD II. We have enrolled 20 patients, 12 males and 8 females. The auditory system assessment included speech and pure tone audiometry, impedance audiometry and auditory brainstem responses (ABR). A combined interpretation of those tests allowed us to define the origin of the hearing impairment (sensorineural, conductive or mixed). Clinically, all patients but one denied subjective hearing disturbances. On the other hand, audiological evaluation revealed that 21/40 patient ears (52.5%) had a hearing impairment: 57% had a sensorineural deficit, 33% showed a conductive hearing loss whereas 10% presented with a mixed pattern. Our study revealed that, in this group of GSDII late onset patients, the auditory system impairment was more frequently present than thought with a prominent cochlear involvement. Our results emphasize the importance of a routinely auditory function evaluation in all forms of Pompe disease.

Fat and carbohydrate metabolism during exercise in late-onset Pompe disease

Pompe disease is caused by absence of the lysosomal enzyme acid alpha-glucosidase. It is generally assumed that intra-lysosomal hydrolysis of glycogen does not contribute to skeletal muscle energy production during exercise. However, this hypothesis has never been tested in vivo during exercise. We examined the metabolic response to exercise in patients with late-onset Pompe disease, in order to determine if a defect in energy metabolism may play a role in the pathogenesis of Pompe disease. We studied six adult patients with Pompe disease and 10 healthy subjects. The participants underwent ischemic forearm exercise testing, and peak work capacity was determined. Fat and carbohydrate metabolism during cycle exercise was examined with a combination of indirect calorimetry and stable isotope methodology. Finally, the effects of an IV glucose infusion on heart rate, ratings of perceived exertion, and work capacity during exercise were determined. We found that peak oxidative capacity was reduced in the patients to 17.6 vs. 38.8 ml kg(-1) min(-1) in healthy subjects (p = 0.002). There were no differences in the rate of appearance and rate of oxidation of palmitate, or total fat and carbohydrate oxidation, between the patients and the healthy subjects. None of the subjects improved exercise tolerance by IV glucose infusion. In conclusion, peak oxidative capacity is reduced in Pompe disease. However, skeletal muscle fat and carbohydrate use during exercise was normal. The results indicate that a reduced exercise capacity is caused by muscle weakness and wasting, rather than by an impaired skeletal muscle glycogenolytic capacity. Thus, it appears that acid alpha-glucosidase does not play a significant role in the production of energy in skeletal muscle during exercise.

36 months observational clinical study of 38 adult Pompe disease patients under alglucosidase alfa enzyme replacement therapy

OBJECTIVES

Glycogen storage disease type 2(GSD2)/Pompe disease is characterized by respiratory and skeletal muscle weakness and atrophy, resulting in functional disability and reduced life span.

METHODS

We present an open-label, investigator-initiated observational study of alglucosidase alfa enzyme replacement therapy (ERT) in 38 adult-onset GSD2 patients (20 female, 18 male) with a mean age at disease onset of 36.2 ± 10.5 years. Mean delay between symptom onset and start of ERT was 14.5 ± 7.2 years. Assessments included serial Walton Gardner Medwin scale, arm function tests, timed 10-meter walk tests, 4- stair climb tests, modified Gowers' maneuvers, 6-minute walk test (6MWT), MRC sum score, forced vital capacities (FVC), creatine kinase (CK) levels, and SF-36 selfreporting questionnaires. All tests were performed at baseline and every 12 months for 36 months of ERT.

RESULTS

In the 6MWT we found 21 patients able to walk at baseline a mean distance of 312 ± 165.5 m, improving to 344 ± 165.8 m after 12 months (p=0.006), remaining at 356.4 ± 155.9 m at 24 months (p=0.033), and declining to 325.6 ± 174.8 m after 36 months of ERT (p=0.49, n.s.). The mean FVC in 28 patients was 80.27 ± 14.08% of predicted normal at baseline, after 12 months 79.19 ± 13.09%, at 24 months 78.62 ± 16.55%, and 77.19 ± 18.05%after 36 months. Only mean CK levels were significantly decreased by 8.8% (p=0.041). All other tests were statistically nonsignificant changed.

CONCLUSION

Our data denote a rather variable course of neuromuscular deficits in chronic adult-onset Pompe patients during 36 months of alglucosidase alfa ERT.

The impact of antibodies in late-onset Pompe disease: a case series and literature review

Pompe disease (glycogen storage disease type II, GSD II) is an autosomal recessive disease caused by a deficiency of acid α-glucosidase (GAA), leading to lysosomal glycogen accumulation in various tissues, most notably cardiac, skeletal and smooth muscle. While both infantile and late-onset patients have benefited greatly from alglucosidase alfa (Myozyme®) enzyme replacement therapy (ERT), a subgroup of patients does not demonstrate as pronounced a response as others. Various factors have been identified which may help predict the response to ERT in infantile Pompe disease patients. High, sustained antibody titers (HSAT) have been correlated with poor response to ERT in infantile Pompe cases. However, the literature on the role of antibodies in the late-onset Pompe disease (LOPD) population is limited. Our literature review highlights the need for studies to explore the potential impact of antibodies in LOPD. Further supporting the importance of this issue, our retrospective chart review of sixty LOPD patients revealed that six of these sixty (10%) LOPD patients developed HSAT of ≥1:51,200 on two or more occasions at or beyond 6 months on ERT. Here, we present a series of three of these six LOPD patients for whom detailed antibody data and clinical data were available for greater than 1 year on ERT. These three patients developed HSAT corresponding with clinical decline as demonstrated by pulmonary function, quality of life, and motor function testing, affirming the development of HSAT in a subset of patients with LOPD, and its potentially negative impact on clinical response to ERT. The findings of our study and literature review lead us to conclude that there is a strong indication for systematic studies to accurately delineate the potential impact of antibodies in LOPD.

Algorithm for Pompe disease newborn screening: results from the Taiwan screening program

BACKGROUND

Pompe disease is caused by a deficiency in acid α-glucosidase (GAA) and results in progressive, debilitating, and often life-threatening symptoms. Newborn screening has led to the early diagnosis of Pompe disease, but the best algorithm for screening has not yet been established.

MATERIALS AND METHODS

GAA and neutral α-glucosidase (NAG) activities in dried blood spots (DBSs) were assayed using 4-methylumbelliferyl-β-d-glucopyranoside as the substrate. We also measure α-galactosidase A (GLA) activity in DBSs for comparison. A total of 473,738 newborns were screened for Pompe disease, and the data were analyzed retrospectively to determine the best screening algorithm.

RESULTS

The fluorescence assay used in the screening possessed good reproducibility, but the NAG/GAA ratio was superior in separating the true-positive from the false-positive cases. An NAG/GAA cutoff ratio≥60 produces a positive predictive value (PPV) of 63.4%, and in our sample, only two cases of later-onset Pompe disease would have been missed. The GLA/GAA ratio is not as effective as the NAG/GAA ratio.

CONCLUSION

A suitable control enzyme can improve the performance of newborn screening. Newborn screening for Pompe disease can be performed using the NAG/GAA ratio as a cutoff even in the presence of GAA partial deficiency.

Transcriptional response to GAA deficiency (Pompe disease) in infantile-onset patients

Pompe disease is a genetic disorder resulting from a deficiency of lysosomal acid alpha-glucosidase (GAA) that manifests as a clinical spectrum with regard to symptom severity and rate of progression. In this study, we used microarrays to examine gene expression from the muscle of two cohorts of infantile-onset Pompe patients to identify transcriptional differences that may contribute to the disease phenotype. We found strong similarities among the gene expression profiles generated from biceps and quadriceps, and identified a number of signaling pathways altered in both cohorts. We also found that infantile-onset Pompe patient muscle had a gene expression pattern characteristic of immature or regenerating muscle, and exhibited many transcriptional markers of inflammation, despite having few overt signs of inflammatory infiltrate. Further, we identified genes exhibiting correlation between expression at baseline and response to therapy. This combined dataset can serve as a foundation for biological discovery and biomarker development to improve the treatment of Pompe disease.

Functional analysis of variant lysosomal acid glycosidases of Anderson-Fabry and Pompe disease in a human embryonic kidney epithelial cell line (HEK 293 T)

The functional significance of missense mutations in genes encoding acid glycosidases of lysosomal storage disorders (LSDs) is not always clear. Here we describe a method of investigating functional properties of variant enzymes in vitro using a human embryonic kidney epithelial cell line. Site-directed mutagenesis was performed on the parental plasmids containing cDNA encoding for alpha-galactosidase A (α-Gal A) and acid maltase (α-Glu) to prepare plasmids encoding relevant point mutations. Mutant plasmids were transfected into HEK 293 T cells, and transient over-expression of variant enzymes was measured after 3 days. We have illustrated the method by examining enzymatic activities of four unknown α-Gal A and one α-Glu variants identified in our patients with Anderson-Fabry disease and Pompe diseases respectively. Comparison with control variants known to be either pathogenic or non-pathogenic together with over-expression of wild-type enzyme allowed determination of the pathogenicity of the mutation. One leader sequence novel variant of α-Gal A (p.A15T) was shown not to significantly reduce enzyme activity, whereas three other novel α-Gal A variants (p.D93Y, p.L372P and p.T410I) were shown to be pathogenic as they resulted in significant reduction of enzyme activity. A novel α-Glu variant (p.L72R) was shown to be pathogenic as this significantly reduced enzyme activity. Certain acid glycosidase variants that have been described in association with late-onset LSDs and which are known to have variable residual plasma and leukocyte enzyme activity in patients appear to show intermediate to low enzyme activity (p.N215S and p.Q279E α-Gal A respectively) in the over-expression system.

Endoplasmic reticulum stress induces autophagy through activation of p38 MAPK in fibroblasts from Pompe disease patients carrying c.546G>T mutation

Pompe disease (glycogen storage disease type II) is an autosomal recessive myopathic disorder arising from the deficiency of lysosomal acid α-glucosidase (GAA). Activation of autophagy is a key pathophysiological feature in skeletal muscle fibers and fibroblasts from patients with Pompe disease. The accumulation of autophagic vacuoles has been shown to interfere with the efficacy of enzyme replacement therapy with recombinant human GAA. However, the induction mechanism of autophagy in Pompe disease is still unclear. In this study, we show that misfolded GAA-induced endoplasmic reticulum (ER) stress triggers autophagy in a manner regulated by p38 MAPK signaling pathways in fibroblasts from late-onset patients with Pompe disease. By studying normal fibroblasts and patient fibroblasts carrying a c.546G>T mutation, we uncovered that mutant GAA was rapidly degraded by proteasome. In addition, we found both activation of ER stress response and autophagy in these patient fibroblasts. Treatment with N-butyl-deoxynojirimycin (NB-DNJ), which acts as a pharmacological chaperone for certain mutant forms of GAA, led to attenuation of not only ER stress, but also autophagy in patient fibroblasts. Levels of phosphorylated p38 MAPK observed in patient fibroblasts were decreased after treatment with NB-DNJ. The autophagic response in patient fibroblasts was also negatively regulated by treatment with the p38 MAPK inhibitor SB203580. These findings define a critical role for ER stress in the activation of autophagy due to GAA mutation, and provide evidence that chaperone therapy may be a useful treatment for alleviation of autophagy in Pompe disease patients carrying a chaperon-responsive mutation.

Fiber type conversion by PGC-1α activates lysosomal and autophagosomal biogenesis in both unaffected and Pompe skeletal muscle

PGC-1α is a transcriptional co-activator that plays a central role in the regulation of energy metabolism. Our interest in this protein was driven by its ability to promote muscle remodeling. Conversion from fast glycolytic to slow oxidative fibers seemed a promising therapeutic approach in Pompe disease, a severe myopathy caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA) which is responsible for the degradation of glycogen. The recently approved enzyme replacement therapy (ERT) has only a partial effect in skeletal muscle. In our Pompe mouse model (KO), the poor muscle response is seen in fast but not in slow muscle and is associated with massive accumulation of autophagic debris and ineffective autophagy. In an attempt to turn the therapy-resistant fibers into fibers amenable to therapy, we made transgenic KO mice expressing PGC-1α in muscle (tgKO). The successful switch from fast to slow fibers prevented the formation of autophagic buildup in the converted fibers, but PGC-1α failed to improve the clearance of glycogen by ERT. This outcome is likely explained by an unexpected dramatic increase in muscle glycogen load to levels much closer to those observed in patients, in particular infants, with the disease. We have also found a remarkable rise in the number of lysosomes and autophagosomes in the tgKO compared to the KO. These data point to the role of PGC-1α in muscle glucose metabolism and its possible role as a master regulator for organelle biogenesis - not only for mitochondria but also for lysosomes and autophagosomes. These findings may have implications for therapy of lysosomal diseases and other disorders with altered autophagy.

Low bone mass in Pompe disease: muscular strength as a predictor of bone mineral density

Pompe disease is an inherited metabolic myopathy caused by deficiency of acid alpha-glucosidase. The introduction of enzyme replacement therapy as treatment for the disease may change prospects for patients and may require that more attention be paid to co-morbidities such as osteoporosis.

METHODS

Bone mineral status was assessed in children and adults with Pompe disease and compared with reference values by means of dual energy X-ray absorptiometry (DXA) technology (GE Lunar DPX, GE Health Care). Bone mineral density (BMD) of the total body and the lumbar spine (L2-L4) was measured in adults and children; BMD of the femoral neck was measured in adults only. Exclusion criteria were: age<4 years, severe contractures, and inability to transfer the patient.

RESULTS

46 patients were enrolled in the study; 36 adults and 10 children. The BMD was significantly lower in Pompe patients than in healthy individuals. Sixty-seven percent of patients had a BMD Z-score below -1, 26% were classified as osteoporosis/low bone mass for chronological age (T-score<-2.5 in adults or Z-score<-2 in children), 66% had a BMD Z-score below -1 of the femoral neck, and 34% had a BMD Z-score below -1 for the lumbar spine. Osteoporosis/low bone mass for chronological age was more frequent in patients who were wheelchair-bound, but was also observed in ambulant patients. We found a significant correlation between proximal muscle strength and total body BMD. Of the 10 children, 8 (all four patients with the classic infantile form) had a low BMD.

CONCLUSION

Low BMD is a frequent finding in patients with Pompe disease and may be causally related to decreased proximal muscle strength. BMD should be monitored at regular intervals. Children deserve specific attention.

Glycoengineered acid alpha-glucosidase with improved efficacy at correcting the metabolic aberrations and motor function deficits in a mouse model of Pompe disease

Improving the delivery of therapeutics to disease-affected tissues can increase their efficacy and safety. Here, we show that chemical conjugation of a synthetic oligosaccharide harboring mannose 6-phosphate (M6P) residues onto recombinant human acid alpha-glucosidase (rhGAA) via oxime chemistry significantly improved its affinity for the cation-independent mannose 6-phosphate receptor (CI-MPR) and subsequent uptake by muscle cells. Administration of the carbohydrate-remodeled enzyme (oxime-neo-rhGAA) into Pompe mice resulted in an approximately fivefold higher clearance of lysosomal glycogen in muscles when compared to the unmodified counterpart. Importantly, treatment of immunotolerized Pompe mice with oxime-neo-rhGAA translated to greater improvements in muscle function and strength. Treating older, symptomatic Pompe mice also reduced tissue glycogen levels but provided only modest improvements in motor function. Examination of the muscle pathology suggested that the poor response in the older animals might have been due to a reduced regenerative capacity of the skeletal muscles. These findings lend support to early therapeutic intervention with a targeted enzyme as important considerations in the management of Pompe disease.

Visual hallucinations in a patient with adult onset acid maltase deficiency disorder

A 66-year-old male presented with visual hallucinations. He had chronically elevated serum creatine kinase (CK) levels without muscle weakness. His hospital course was complicated by hypercapnic respiratory failure requiring mechanical ventilation. His hallucinations completely subsided on mechanical ventilation. Elevated CK levels prompted a muscle biopsy, which showed myopathy consistent with acid maltase deficiency disorder (AMDD). This is the first reported case of adult onset AMDD presenting with psychiatric symptoms. Our objective in reporting this case is to encourage early recognition of neuromuscular respiratory failure in AMDD and to reinforce that respiratory failure may develop without associated extremity muscle weakness.

Biochemical and pharmacological characterization of different recombinant acid alpha-glucosidase preparations evaluated for the treatment of Pompe disease

Pompe disease results in the accumulation of lysosomal glycogen in multiple tissues due to a deficiency of acid alpha-glucosidase (GAA). Enzyme replacement therapy for Pompe disease was recently approved in Europe, the U.S., Canada, and Japan using a recombinant human GAA (Myozyme, alglucosidase alfa) produced in CHO cells (CHO-GAA). During the development of alglucosidase alfa, we examined the in vitro and in vivo properties of CHO cell-derived rhGAA, an rhGAA purified from the milk of transgenic rabbits, as well as an experimental version of rhGAA containing additional mannose-6-phosphate intended to facilitate muscle targeting. Biochemical analyses identified differences in rhGAA N-termini, glycosylation types and binding properties to several carbohydrate receptors. In a mouse model of Pompe disease, glycogen was more efficiently removed from the heart than from skeletal muscle for all enzymes, and overall, the CHO cell-derived rhGAA reduced glycogen to a greater extent than that observed with the other enzymes. The results of these preclinical studies, combined with biochemical characterization data for the three molecules described within, led to the selection of the CHO-GAA for clinical development and registration as the first approved therapy for Pompe disease.

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.

Deconstructing Pompe disease by analyzing single muscle fibers: to see a world in a grain of sand

Autophagy is a major pathway for delivery of proteins and organelles to lysosomes where they are degraded and recycled. We have previously shown excessive autophagy in a mouse model of Pompe disease (glycogen storage disease type II), a devastating myopathy caused by a deficiency of the glycogen-degrading lysosomal enzyme acid alpha-glucosidase. The autophagic buildup constituted a major pathological component in skeletal muscle and interfered with delivery of the therapeutic enzyme. To assess the role of autophagy in the pathogenesis of the human disease, we have analyzed vesicles of the lysosomal-degradative pathway in isolated single muscle fibers from Pompe patients. Human myofibers showed abundant autophagosome formation and areas of autophagic buildup of a wide range of sizes. In patients, as in the mouse model, the enormous autophagic buildup causes greater skeletal muscle damage than the enlarged, glycogenfilled lysosomes outside the autophagic regions. Clearing or preventing autophagic buildup seems, therefore, a necessary target of Pompe disease therapy.

Adult-onset glycogen storage disease type 2: clinico-pathological phenotype revisited

The need for clinical awareness and diagnostic precision of glycogen storage disease type 2 (GSD2) has increased, as enzyme replacement therapy has become available. So far, only small series have reported the muscle pathology of late-onset GSD2. We reassessed 43 muscle biopsies of 38 GSD2 patients. In all patients the diagnosis of GSD2 has been established by biochemistry and/or mutational analysis of the GAA gene. Additionally to the expected morphological features, ultrastructural analysis revealed a high incidence of autophagic vacuoles, lipofuscin debris, structural Z-line disorganization and histological neurogenic-like pattern that were not thoroughly appreciated, previously. Comparing age at onset and morphology, excessive vacuolar and autophagic myopathy and mitochondrial disorganization of virtually all fibres is common in infants. At juvenile onset, a more moderate vacuolization without significant differences in overall morphology is notable. At late-onset, the spectrum of vacuolar myopathy is more divergent, ranging from almost normal to severe. Here pronounced secondary alterations are observed that include lipofuscin debris, autophagic vacuoles with residual lysosomal bodies and granular inclusions, structural mitochondrial and Z-line texture alterations. Moreover, there is a high incidence of subtle neurogenic-like alteration in all subtypes. Nineteen patients were genetically tested; in 15 patients the common leaky splicing mutation c.-45T>G (or IVS1-13T>G) in intron1 of the GAA gene was found on at least one allele, facilitating genetic screening. In our patients, GAA genotype appears not to be associated with secondary alterations such as autophagic vacuoles, structural alterations or neurogenic-like changes. These findings may have implications for our understanding of the pathogenesis of GSD2 and for assessing therapeutic success of enzyme replacement therapy.

Hyaluronidase increases the biodistribution of acid alpha-1,4 glucosidase in the muscle of Pompe disease mice: an approach to enhance the efficacy of enzyme replacement therapy

Pompe disease (glycogen storage disease type II) is a glycogen storage disease caused by a deficiency of the lysosomal enzyme, acid maltase/acid alpha-1,4 glucosidase (GAA). Deficiency of the enzyme leads primarily to intra-lysosomal glycogen accumulation, primarily in cardiac and skeletal muscles, due to the inability of converting glycogen into glucose. Enzyme replacement therapy (ERT) has been applied to replace the deficient enzyme and to restore the lost function. However, enhancing the enzyme activity to the muscle following ERT is relatively insufficient. In order to enhance GAA activity into the muscle in Pompe disease, efficacy of hyaluronidase (hyase) was examined in the heart, quadriceps, diaphragm, kidney, and brain of mouse model of Pompe disease. Administration of hyase 3000 U/mouse (intravenous) i.v. or i.p. (intraperitoneal) and 10 min later recombinant human GAA (rhGAA) 20 mg/kg i.v. showed more GAA activity in hyase i.p. injected mice compared to those mice injected with hyase via i.v. Injection of low dose of hyase (3000 U/mouse) or high dose of hyase (10,000 U/mouse) i.p. and 20 min or 60 min later 20 mg/kg rhGAA i.v. increased GAA activity into the heart, diaphragm, kidney, and quadriceps compared to hyase untreated mice. These studies suggest that hyase enhances penetration of enzyme into the tissues including muscle during ERT and therefore hyase pretreatment may be important in treating Pompe disease.

Autophagy and mistargeting of therapeutic enzyme in skeletal muscle in Pompe disease

Enzyme replacement therapy (ERT) became a reality for patients with Pompe disease, a fatal cardiomyopathy and skeletal muscle myopathy caused by a deficiency of glycogen-degrading lysosomal enzyme acid alpha-glucosidase (GAA). The therapy, which relies on receptor-mediated endocytosis of recombinant human GAA (rhGAA), appears to be effective in cardiac muscle, but less so in skeletal muscle. We have previously shown a profound disturbance of the lysosomal degradative pathway (autophagy) in therapy-resistant muscle of GAA knockout mice (KO). Our findings here demonstrate a progressive age-dependent autophagic buildup in addition to enlargement of glycogen-filled lysosomes in multiple muscle groups in the KO. Trafficking and processing of the therapeutic enzyme along the endocytic pathway appear to be affected by the autophagy. Confocal microscopy of live single muscle fibers exposed to fluorescently labeled rhGAA indicates that a significant portion of the endocytosed enzyme in the KO was trapped as a partially processed form in the autophagic areas instead of reaching its target--the lysosomes. A fluid-phase endocytic marker was similarly mistargeted and accumulated in vesicular structures within the autophagic areas. These findings may explain why ERT often falls short of reversing the disease process and point toward new avenues for the development of pharmacological intervention.

Anaplerotic diet therapy in inherited metabolic disease: therapeutic potential

Beginning with phenylketonuria, dietary therapy for inborn errors has focused primarily on the restriction of the precursor to an affected catabolic pathway in an attempt to limit the production of potential toxins. Anaplerotic therapy is based on the concept that there may exist an energy deficit in these diseases that might be improved by providing alternative substrate for both the citric acid cycle (CAC) and the electron transport chain for enhanced ATP production. This article focuses on this basic problem, as it may relate to most catabolic disorders, and provides our current experience involving inherited diseases of mitochondrial fat oxidation, glycogen storage, and pyruvate metabolism using the anaplerotic compound triheptanoin. The observations have led to a realization that 'inter-organ' signalling and 'nutrient sensors' such as adenylate monophosphate mediated-protein kinase (AMPK) and mTOR (mammalian target of rapamycin) appear to play a significant role in the intermediary metabolism of these diseases. Activated AMPK turns on catabolic pathways to augment ATP production while turning off synthetic pathways that consume ATP. Information is provided regarding the inter-organ requirements for more normal metabolic function during crisis and how anaplerotic therapy using triheptanoin, as a direct source of substrate to the CAC for energy production, appears to be a more successful approach to an improved quality of life for these patients.

The effect of L-alanine therapy in a patient with adult onset glycogen storage disease type II

Adult-onset glycogen storage disease type II (GSD II) (McKusick 232300) is a progressive disabling myopathy. At present there is no treatment of proven clinical efficacy. Enzyme replacement therapy may in the future provide benefit but it will be costly and is not yet freely available. L-Alanine, a simple and relatively cheap therapy, has been shown to reduce protein degradation in GSD II patients but has not previously been assessed for clinical benefit in a controlled study. In this study L-alanine was assessed in a double blind, placebo-controlled, crossover n = 1 study. Assessments consisted of spirometry, cardiopulmonary exercise testing, quality of life measurements, biochemical markers and assessment by the criterion 4-component model of body composition. Alanine therapy was associated with a 15% gain in total body protein. However, the patient showed no functional improvement and reported feeling worse after treatment. Further controlled studies in a small group may be warranted, but not widespread use of this therapy.