Unveiling the degradative route of the V247M α-sarcoglycan mutant responsible for LGMD-2D

ELK1 inhibition alleviates amyloid pathology and memory decline by promoting the SYVN1-mediated ubiquitination and degradation of PS1 in Alzheimer's disease

ELK1 is a member of the E-twenty-six transcription factor family and is usually activated by phosphorylation at Ser383 and Ser389 by extracellular signal-regulated kinase 1/2 (ERK1/2). Dysregulation of ERK1/2 is involved in Alzheimer's disease (AD)-related neuropathogenesis and cognitive impairments. However, the role of ELK1 in AD pathogenesis remains unclear. Here we report that the expression of ELK1 was significantly increased in the brain tissues of patients with AD and AD model mice. The genetic knockdown of ELK1 or inhibition of its phosphorylation by an interfering peptide (TAT-DEF-ELK1 (TDE)) reduced amyloidogenic processing of APP by targeting PS1, consequently inhibiting Aβ generation and alleviating synaptic and memory impairments in APP23/PS45 double-transgenic AD model mice. In addition, we further found that ELK1 regulated the expression of PS1 by competitively inhibiting the interaction between PS1 and its E3 ubiquitin ligase synoviolin (SYVN1), thereby inhibiting the SYVN1-mediated ubiquitination and degradation of PS1. Our results demonstrate that ELK1 aberrantly increases in AD and genetic or pharmacological inhibition of ELK1 can alleviate AD-related pathology and memory impairments by enhancing the SYVN1-mediated PS1 ubiquitination and degradation, indicating that ELK1 may be a novel target for AD treatment.

The novel use of the CFTR corrector C17 in muscular dystrophy: pharmacological profile and in vivo efficacy

Sarcoglycanopathies are rare forms of severe muscular dystrophies currently without a therapy. Mutations in sarcoglycan (SG) genes cause the reduction or absence of the SG-complex, a tetramer located in the sarcolemma that plays a protective role during muscle contraction. Missense mutations in SGCA, which cause α-sarcoglycanopathy, otherwise known as LGMD2D/R3, lead to folding defective forms of α-SG that are discarded by the cell quality control. Recently, we demonstrated how a small molecule called C17, initially identified as a CFTR corrector, can be re-used to ameliorate the dystrophic phenotype of a mouse model of α-sarcoglycanopathy. Here, we have examined the pharmacological profile of C17 by performing ADME (absorption, distribution, metabolism, and elimination) studies. Our data show that C17 is well-distributed to relevant organs like heart and skeletal muscle, and likely metabolized in the small intestine into hydrophilic and hydrophobic derivatives. Elimination occurs through faeces (unmodified and modified C17) and urine (modified forms). Interestingly, we detected a quantifiable amount of C17 in treated muscles 48 h after an acute parenteral administration. This led to design a regimen of chronic treatment with a reduced dosing frequency. The result was the recovery of muscle strength, thanks to the rescue of the SG-complex, despite containing a mutated subunit, at the level of the sarcolemma. Thus, we can conclude that CFTR corrector C17 has a reasonable pharmacological profile and great potential to become a valuable therapeutic option for LGMD2D/R3 and other forms of muscular dystrophy caused by folding defective but potentially functional proteins.

Efficacy of Cystic Fibrosis Transmembrane Regulator Corrector C17 in Beta-Sarcoglycanopathy-Assessment of Patient's Primary Myotubes

Limb-girdle muscular dystrophy type 2E/R4 (LGMD2E/R4) is a rare disease that currently has no cure. It is caused by defects in the SGCB gene, mainly missense mutations, which cause the impairment of the sarcoglycan complex, membrane fragility, and progressive muscle degeneration. Here, we studied the fate of some β-sarcoglycan (β-SG) missense mutants, confirming that, like α-SG missense mutants, they are targeted for degradation through the ubiquitin-proteasome system. These data, collected using HEK-293 cells expressing either the I119F- or Y184C mutants of β-SG, were subsequently confirmed in primary myotubes derived from an LGMD2E/R4 patient carrying a homozygous I92T mutation. The knowledge that β-SG with an amino acid substitution shares a pathway of degradation with α-SG mutants, allowed us to explore the pharmacological approach successfully tested in LGMD2D/R3. Several CFTR correctors, particularly corrector C17, preserved β-SG mutants from degradation and promoted localization at the sarcolemma of the entire SG complex. The presence of the complex, despite containing a mutated subunit, improved sarcolemma integrity, as evidenced by the reduced creatine kinase release from myotubes under hypoosmotic stress. These results suggest that β-SG missense mutants undergo proteasomal degradation as α-SG mutants, and that CFTR correctors, particularly C17, may be used as a potential therapeutic option for recovering and stabilizing the SG complex in patients with sarcoglycanopathies.

UPS-dependent strategies of protein quality control degradation

The degradation of damaged proteins is critical for tissue integrity and organismal health because damaged proteins have a high propensity to form aggregates. E3 ubiquitin ligases are key regulators of protein quality control (PQC) and mediate the selective degradation of damaged proteins, a process termed 'PQC degradation' (PQCD). The degradation signals (degrons) that trigger PQCD are based on hydrophobic sites that are normally buried within the native protein structure. However, an open question is how PQCD-specialized E3 ligases distinguish between transiently misfolded proteins, which can be efficiently refolded, and permanently damaged proteins, which must be degraded. While significant progress has been made in characterizing degradation determinants, understanding the key regulatory signals of cellular and organismal PQCD pathways remains a challenge.

Advanced therapeutic approaches in sarcoglycanopathies

Sarcoglycanopathies are rare autosomal recessive diseases belonging to the family of limb-girdle muscular dystrophies. They are caused by mutations in the genes coding for α-, β-, γ-, and δ-sarcoglycan. The mutations impair the assembly of a key structural complex, which normally protects the sarcolemma of striated muscle from contraction-derived stress. Although heterogeneous, sarcoglycanopathies are characterized by progressive muscle degeneration, increased serum creatine kinase levels, loss of ambulation often during adolescence, and variable cardio-respiratory impairment. Genetic defects can impair sarcoglycan synthesis or produce a protein that is defective in folding. There is currently no effective treatment available; however, both gene replacement strategy and small molecule-based approaches show great promise and have entered or are starting to enter clinical trials.

The missense mutation C667F in murine β-dystroglycan causes embryonic lethality, myopathy and blood-brain barrier destabilization

Dystroglycan (DG) is an extracellular matrix receptor consisting of an α- and a β-DG subunit encoded by the DAG1 gene. The homozygous mutation (c.2006G>T, p.Cys669Phe) in β-DG causes muscle-eye-brain disease with multicystic leukodystrophy in humans. In a mouse model of this primary dystroglycanopathy, approximately two-thirds of homozygous embryos fail to develop to term. Mutant mice that are born undergo a normal postnatal development but show a late-onset myopathy with partially penetrant histopathological changes and an impaired performance on an activity wheel. Their brains and eyes are structurally normal, but the localization of mutant β-DG is altered in the glial perivascular end-feet, resulting in a perturbed protein composition of the blood-brain and blood-retina barrier. In addition, α- and β-DG protein levels are significantly reduced in muscle and brain of mutant mice. Owing to the partially penetrant developmental phenotype of the C669F β-DG mice, they represent a novel and highly valuable mouse model with which to study the molecular effects of β-DG functional alterations both during embryogenesis and in mature muscle, brain and eye, and to gain insight into the pathogenesis of primary dystroglycanopathies.

An evolutionarily conserved ubiquitin ligase drives infection and transmission of flaviviruses

Mosquito-borne flaviviruses such as dengue (DENV) and Zika (ZIKV) cause hundreds of millions of infections annually. The single-stranded RNA genome of flaviviruses is translated into a polyprotein, which is cleaved equally into individual functional proteins. While structural proteins are packaged into progeny virions and released, most of the nonstructural proteins remain intracellular and could become cytotoxic if accumulated over time. However, the mechanism by which nonstructural proteins are maintained at the levels optimal for cellular fitness and viral replication remains unknown. Here, we identified that the ubiquitin E3 ligase HRD1 is essential for flaviviruses infections in both mammalian hosts and mosquitoes. HRD1 directly interacts with flavivirus NS4A and ubiquitylates a conserved lysine residue for ER-associated degradation. This mechanism avoids excessive accumulation of NS4A, which otherwise interrupts the expression of processed flavivirus proteins in the ER. Furthermore, a small-molecule inhibitor of HRD1 named LS-102 effectively interrupts DENV2 infection in both mice and Aedes aegypti mosquitoes, and significantly disturbs DENV transmission from the infected hosts to mosquitoes owing to reduced viremia. Taken together, this study demonstrates that flaviviruses have evolved a sophisticated mechanism to exploit the ubiquitination system to balance the homeostasis of viral proteins for their own advantage and provides a potential therapeutic target to interrupt flavivirus infection and transmission.

Modeling Sarcoglycanopathy in Danio rerio

Sarcoglycanopathies, also known as limb girdle muscular dystrophy 3-6, are rare muscular dystrophies characterized, although heterogeneous, by high disability, with patients often wheelchair-bound by late adolescence and frequently developing respiratory and cardiac problems. These diseases are currently incurable, emphasizing the importance of effective treatment strategies and the necessity of animal models for drug screening and therapeutic verification. Using the CRISPR/Cas9 genome editing technique, we generated and characterized δ-sarcoglycan and β-sarcoglycan knockout zebrafish lines, which presented a progressive disease phenotype that worsened from a mild larval stage to distinct myopathic features in adulthood. By subjecting the knockout larvae to a viscous swimming medium, we were able to anticipate disease onset. The δ-SG knockout line was further exploited to demonstrate that a δ-SG missense mutant is a substrate for endoplasmic reticulum-associated degradation (ERAD), indicating premature degradation due to protein folding defects. In conclusion, our study underscores the utility of zebrafish in modeling sarcoglycanopathies through either gene knockout or future knock-in techniques. These novel zebrafish lines will not only enhance our understanding of the disease's pathogenic mechanisms, but will also serve as powerful tools for phenotype-based drug screening, ultimately contributing to the development of a cure for sarcoglycanopathies.

Synthesis and Evaluation of Bithiazole Derivatives As Potential α-Sarcoglycan Correctors

4'-Methyl-4,5'-bithiazoles were previously identified as cystic fibrosis transmembrane regulator (CFTR) correctors, thus being able to correct folding defective mutants of the channel regulating chloride transport through the membrane. Additionally, bithiazole derivative C17 was reported to recover α-sarcoglycan in vitro and in vivo. We report here the synthesis of two new derivatives of C17, in which the two sides of the bithiazole scaffold were modified. The synthesized compounds and the corresponding precursors were tested in myogenic cells to evaluate the expression of α-sarcoglycan. The results highlighted that both substitutions of the bithiazole scaffold are important to achieve the maximum recovery of the α-sarcoglycan mutant. Nonetheless, partial preservation of the activity was observed. Accordingly, this paves the way to further derivatizations/optimization and target fishing studies, which were preliminarily performed in this study as a proof of concept, allowing the investigation of the molecular mechanisms leading to the α-sarcoglycan correction.

Aberrant Adenosine Triphosphate Release and Impairment of P2Y2-Mediated Signaling in Sarcoglycanopathies

Sarcoglycanopathies, limb-girdle muscular dystrophies (LGMD) caused by genetic loss-of-function of the membrane proteins sarcoglycans (SGs), are characterized by progressive degeneration of skeletal muscle. In these disorders, muscle necrosis is associated with immune-mediated damage, whose triggering and perpetuating molecular mechanisms are not fully elucidated yet. Extracellular adenosine triphosphate (eATP) seems to represent a crucial factor, with eATP activating purinergic receptors. Indeed, in vivo blockade of the eATP/P2X7 purinergic pathway ameliorated muscle disease progression. P2X7 inhibition improved the dystrophic process by restraining the activity of P2X7 receptors on immune cells. Whether P2X7 blockade can display a direct action on muscle cells is not known yet. In this study, we investigated eATP effects in primary cultures of myoblasts isolated from patients with LGMDR3 (α-sarcoglycanopathy) and in immortalized cells isolated from a patient with LGMDR5 (γ-sarcoglycanopathy). Our results demonstrated that, owing to a reduced ecto-ATPase activity and/or an enhanced release of ATP, patient cells are exposed to increased juxtamembrane concentrations of eATP and display a higher susceptivity to eATP signals. The purinoceptor P2Y2, which proved to be overexpressed in patient cells, was identified as a pivotal receptor responsible for the enhanced ATP-induced or UTP-induced Ca²⁺ increase in affected myoblasts. Moreover, P2Y2 stimulation in LDMDR3 muscle cells induced chemotaxis of immune cells and release of interleukin-8. In conclusion, a higher eATP concentration and sensitivity in primary human muscle cells carrying different α-SG or γ-SG loss-of-function mutations indicate that eATP/P2Y2 is an enhanced signaling axis in cells from patients with α-/γ-sarcoglycanopathy. Understanding the basis of the innate immune-mediated damage associated with the dystrophic process may be critical in overcoming the immunologic hurdles associated with emerging gene therapies for these disorders.

Genotype-phenotype correlations in alpha-sarcoglycanopathy: a systematic review

BACKGROUND

Mutations in the alpha-sarcoglycan gene cause limb-girdle muscular dystrophy 2D, an autosomal recessive muscle wasting disorder primarily affecting the muscles of the shoulder and pelvic girdles. To date, no previous study has collated all known mutations in alpha-sarcoglycan and mapped these to the associated phenotypes.

AIMS

To examine for correlations between mutation locations, or mutation type, and the phenotype caused in all reported mutations in alpha-sarcoglycan.

METHODS

We present a systematic literature review examining correlations between mutation locations, or mutation type, and the phenotype caused in all reported cases of limb-girdle muscular dystrophy 2D.

RESULTS

From 134 unique genotypes collated, a strong prevalence of missense mutations (64% of all unique mutations) was found in this gene. Mutation hotspots were noted in exon three and the extracellular domain, with mutation densities varying significantly between both exons and protein domains (p ≤ 0.01). All compound heterozygous limb-girdle muscular dystrophy 2D patients with cardiac involvement contained at least one mutation in exon three, a novel finding. All non-sense mutations in alpha-sarcoglycan give a severe phenotype, as do genotypes involving a combination of exons four and five. This study confirms on a large, diverse cohort the extremely high prevalence of the c.229C > T mutation.

CONCLUSIONS

This study demonstrates the vast variation in disease severity seen between patients possessing the same mutation, highlighting the difficulty identifying genotype-phenotype correlations in this condition. Novel findings including the involvement of exon three in all compound heterozygous patients who suffered from cardiomyopathy, and the severity of mutations involving exons four and five may help to guide investigations and therapeutic decisions in an era of personalised medicine.

CFTR corrector C17 is effective in muscular dystrophy, in vivo proof of concept in LGMDR3

Limb-girdle muscular dystrophy R3 (LGMDR3) is caused by mutations in the SGCA gene coding for α-sarcoglycan (SG). Together with β- γ- and δ-SG, α-SG forms a tetramer embedded in the dystrophin associated protein complex crucial for protecting the sarcolemma from mechanical stresses elicited by muscle contraction. Most LGMDR3 cases are due to missense mutations, which result in non-properly folded, even though potentially functional α-SG. These mutants are prematurely discarded by the cell quality control. Lacking one subunit, the SG-complex is disrupted. The resulting loss of function leads to sarcolemma instability, muscle fiber damage and progressive limb muscle weakness. LGMDR3 is severely disabling and, unfortunately, still incurable. Here, we propose the use of small molecules, belonging to the class of cystic fibrosis transmembrane regulator (CFTR) correctors, for recovering mutants of α-SG defective in folding and trafficking. Specifically, CFTR corrector C17 successfully rerouted the SG-complex containing the human R98H-α-SG to the sarcolemma of hind-limb muscles of a novel LGMDR3 murine model. Notably, the muscle force of the treated model animals was fully recovered. To our knowledge, this is the first time that a compound designated for cystic fibrosis is successfully tested in a muscular dystrophy and may represent a novel paradigm of treatment for LGMDR3 as well as different other indications in which a potentially functional protein is prematurely discarded as folding-defective. Furthermore, the use of small molecules for recovering the endogenous mutated SG has an evident advantage over complex procedures such as gene or cell transfer.

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

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

New genotype-phenotype correlations in a large European cohort of patients with sarcoglycanopathy

Sarcoglycanopathies comprise four subtypes of autosomal recessive limb-girdle muscular dystrophies (LGMDR3, LGMDR4, LGMDR5 and LGMDR6) that are caused, respectively, by mutations in the SGCA, SGCB, SGCG and SGCD genes. In 2016, several clinicians involved in the diagnosis, management and care of patients with LGMDR3-6 created a European Sarcoglycanopathy Consortium. The aim of the present study was to determine the clinical and genetic spectrum of a large cohort of patients with sarcoglycanopathy in Europe. This was an observational retrospective study. A total of 33 neuromuscular centres from 13 different European countries collected data of the genetically confirmed patients with sarcoglycanopathy followed-up at their centres. Demographic, genetic and clinical data were collected for this study. Data from 439 patients from 13 different countries were collected. Forty-three patients were not included in the analysis because of insufficient clinical information available. A total of 159 patients had a confirmed diagnosis of LGMDR3, 73 of LGMDR4, 157 of LGMDR5 and seven of LGMDR6. Patients with LGMDR3 had a later onset and slower progression of the disease. Cardiac involvement was most frequent in LGMDR4. Sixty per cent of LGMDR3 patients carried one of the following mutations, either in a homozygous or heterozygous state: c.229C>T, c.739G>A or c.850C>T. Similarly, the most common mutations in LMGDR5 patients were c.525delT or c.848G>A. In LGMDR4 patients the most frequent mutation was c.341C>T. We identified onset of symptoms before 10 years of age and residual protein expression lower than 30% as independent risk factors for losing ambulation before 18 years of age, in LGMDR3, LGMDR4 and LGMDR5 patients. This study reports clinical, genetic and protein data of a large European cohort of patients with sarcoglycanopathy. Improving our knowledge about these extremely rare autosomal recessive forms of LGMD was helped by a collaborative effort of neuromuscular centres across Europe. Our study provides important data on the genotype-phenotype correlation that is relevant for the design of natural history studies and upcoming interventional trials in sarcoglycanopathies.

[Sarcoglycanopathies: state of the art and therapeutic perspectives]

Sarcoglycanopathies are the third most common cause of autosomal recessive limb girdle muscular dystrophies (LGMD). They are the result of a deficiency in one of the sarcoglycans a, b, g, or d. The usual clinical presentation is that of a symmetrical involvement of the muscles of the pelvic and scapular girdles as well as of the trunk, associated with more or less severe cardio-respiratory impairment and a marked increase of serum CK levels. The first symptoms appear during the first decade, the loss of ambulation occurring often during the second decade. Lesions observed on the muscle biopsy are dystrophic. This is associated with a decrease or an absence of immunostaining of the sarcoglycan corresponding to the mutated gene and, to a lesser degree, of the other three sarcoglycans. Many mutations have been reported in the four incriminated genes and some of them are prevalent in certain populations. To date, there is no curative treatment, which does not prevent the development of many clinical trials, especially in gene therapy.

Genetic cause of heterogeneous inherited myopathies in a cohort of Greek patients

Inherited muscle disorders are caused by pathogenic changes in numerous genes. Herein, we aimed to investigate the etiology of muscle disease in 24 consecutive Greek patients with myopathy suspected to be genetic in origin, based on clinical presentation and laboratory and electrophysiological findings and absence of known acquired causes of myopathy. Of these, 16 patients (8 females, median 24 years-old, range 7 to 67 years-old) were diagnosed by Whole Exome Sequencing as suffering from a specific type of inherited muscle disorder. Specifically, we have identified causative variants in 6 limb-girdle muscular dystrophy genes (6 patients; ANO5, CAPN3, DYSF, ISPD, LAMA2, SGCA), 3 metabolic myopathy genes (4 patients; CPT2, ETFDH, GAA), 1 congenital myotonia gene (1 patient; CLCN1), 1 mitochondrial myopathy gene (1 patient; MT-TE) and 3 other myopathy-associated genes (4 patients; CAV3, LMNA, MYOT). In 6 additional family members affected by myopathy, we reached genetic diagnosis following identification of a causative variant in an index patient. In our patients, genetic diagnosis ended a lengthy diagnostic process and, in the case of Multiple acyl-CoA dehydrogenase deficiency and Pompe's disease, it enabled specific treatment to be initiated. These results further expand the genotypic and phenotypic spectrum of inherited myopathies.

Proteostasis Regulation in the Endoplasmic Reticulum: An Emerging Theme in the Molecular Pathology and Therapeutic Management of Familial Hypercholesterolemia

Familial hypercholesterolemia (FH) is an autosomal genetic disease characterized by high serum low-density lipoprotein (LDL) content leading to premature coronary artery disease. The main genetic and molecular causes of FH are mutations in low-density lipoprotein receptor gene (LDLR) resulting in the non-clearance of LDL from the blood by hepatocytes and consequently the formation of plaques. LDLR is synthesized and glycosylated in the endoplasmic reticulum (ER) and then transported to the plasma membrane via Golgi. It is estimated that more than 50% of reported FH-causing mutations in LDLR result in misfolded proteins that are transport-defective and hence retained in ER. ER accumulation of misfolded proteins causes ER-stress and activates unfolded protein response (UPR). UPR aids protein folding, blocks further protein synthesis, and eliminates misfolded proteins via ER-associated degradation (ERAD) to alleviate ER stress. Various studies demonstrated that ER-retained LDLR mutants are subjected to ERAD. Interestingly, chemical chaperones and genetic or pharmacological inhibition of ERAD have been reported to rescue the transport defective mutant LDLR alleles from ERAD and restore their ER-Golgi transport resulting in the expression of functional plasma membrane LDLR. This suggests the possibility of pharmacological modulation of proteostasis in the ER as a therapeutic strategy for FH. In this review, we picture a detailed analysis of UPR and the ERAD processes activated by ER-retained LDLR mutants associated with FH. In addition, we discuss and critically evaluate the potential role of chemical chaperones and ERAD modulators in the therapeutic management of FH.

Combined Use of CFTR Correctors in LGMD2D Myotubes Improves Sarcoglycan Complex Recovery

Sarcoglycanopathies are rare limb girdle muscular dystrophies, still incurable, even though symptomatic treatments may slow down the disease progression. Most of the disease-causing defects are missense mutations leading to a folding defective protein, promptly removed by the cell’s quality control, even if possibly functional. Recently, we repurposed small molecules screened for cystic fibrosis as potential therapeutics in sarcoglycanopathy. Indeed, cystic fibrosis transmembrane regulator (CFTR) correctors successfully recovered the defective sarcoglycan-complex in vitro. Our aim was to test the combined administration of some CFTR correctors with C17, the most effective on sarcoglycans identified so far, and evaluate the stability of the rescued sarcoglycan-complex. We treated differentiated myogenic cells from both sarcoglycanopathy and healthy donors, evaluating the global rescue and the sarcolemma localization of the mutated protein, by biotinylation assays and western blot analyses. We observed the additive/synergistic action of some compounds, gathering the first ideas on possible mechanism/s of action. Our data also suggest that a defective α-sarcoglycan is competent for assembly into the complex that, if helped in cell traffic, can successfully reach the sarcolemma. In conclusion, our results strengthen the idea that CFTR correctors, acting probably as proteostasis modulators, have the potential to progress as therapeutics for sarcoglycanopathies caused by missense mutations.

The impact of exome sequencing on the diagnostic yield of muscular dystrophies in consanguineous families

Muscular dystrophies (MDs) are a heterogeneous group of inherited disorders that are characterized by progressive skeletal muscle weakness and dystrophic changes on muscle biopsy. The broad genetic and clinical heterogeneity of MDs make the accurate diagnosis difficult via conventional approaches. This study investigated 23 patients from eight unrelated consanguineous families with MDs. Previous clinical assessments did not accurately clarify the type of their MD and/or misdiagnose them with another disease. Exome sequencing (ES) is an efficient, time-saving, and cost-effective tool, enabling disease-causing variant (DCV) detection in affected individuals. We investigated the use of ES to diagnose MD and discover the underlying genetic etiology. We achieved a remarkable diagnostic success rate of 87.5% (7 out of 8 families) which is the highest rate reported thus far compared to previous studies. We identified two novel pathogenic variants in DYSF gene (c.4179delG, c.1149+3G > C). The latter variant impacts the splicing machinery of DYSF mRNA. Moreover, we further assessed the pathogenicity of four recurrent variants ((DYSF, c.4076T > C), (GMPPB, c.458C > T), (SGCA, c.739G > A) (TTN, c.7331G > A), designated their neurological impact and added new phenotypes in patients with these variants. To our knowledge, this is the first study applying an ES-based comprehensive molecular diagnosis to Jordanian cohort with MDs. Our findings confirmed that ES is a powerful approach for the diagnosis of MD patients. This efficient method of molecular diagnosis is crucial for guiding patient clinical care, genetic counseling, and most importantly, paving the way for gene therapy which is currently in clinical trials.

Identification of thiostrepton as a pharmacological approach to rescue misfolded alpha-sarcoglycan mutant proteins from degradation

Limb-girdle muscular dystrophy type 2D (LGMD2D) is characterized by a progressive proximal muscle weakness. LGMD2D is caused by mutations in the gene encoding α-sarcoglycan (α-SG), a dystrophin-associated glycoprotein that plays a key role in the maintenance of sarcolemma integrity in striated muscles. We report here on the development of a new in vitro high-throughput screening assay that allows the monitoring of the proper localization of the most prevalent mutant form of α-SG (R77C substitution). Using this assay, we screened a library of 2560 FDA-approved drugs and bioactive compounds and identified thiostrepton, a cyclic antibiotic, as a potential drug to repurpose for LGMD2D treatment. Characterization of the thiostrepton effect revealed a positive impact on R77C-α-SG and other missense mutant protein localization (R34H, I124T, V247M) in fibroblasts overexpressing these proteins. Finally, further investigations of the molecular mechanisms of action of the compound revealed an inhibition of the chymotrypsin-like activity of the proteasome 24 h after thiostrepton treatment and a synergistic effect with bortezomib, an FDA-approved proteasome inhibitor. This study reports on the first in vitro model for LGMD2D that is compatible with high-throughput screening and proposes a new therapeutic option for LGMD2D caused by missense mutations of α-SG.

A molecular overview of the primary dystroglycanopathies

Dystroglycan is a major non-integrin adhesion complex that connects the cytoskeleton to the surrounding basement membranes, thus providing stability to skeletal muscle. In Vertebrates, hypoglycosylation of α-dystroglycan has been strongly linked to muscular dystrophy phenotypes, some of which also show variable degrees of cognitive impairments, collectively termed dystroglycanopathies. Only a small number of mutations in the dystroglycan gene, leading to the so called primary dystroglycanopathies, has been described so far, as opposed to the ever-growing number of identified secondary or tertiary dystroglycanopathies (caused by genetic abnormalities in glycosyltransferases or in enzymes involved in the synthesis of the carbohydrate building blocks). The few mutations found within the autonomous N-terminal domain of α-dystroglycan seem to destabilise it to different degrees, without influencing the overall folding and targeting of the dystroglycan complex. On the contrary other mutations, some located at the α/β interface of the dystroglycan complex, seem to be able to interfere with its maturation, thus compromising its stability and eventually leading to the intracellular engulfment and/or partial or even total degradation of the dystroglycan uncleaved precursor.

Repairing folding-defective α-sarcoglycan mutants by CFTR correctors, a potential therapy for limb-girdle muscular dystrophy 2D

Limb-girdle muscular dystrophy type 2D (LGMD2D) is a rare autosomal-recessive disease, affecting striated muscle, due to mutation of SGCA, the gene coding for α-sarcoglycan. Nowadays, more than 50 different SGCA missense mutations have been reported. They are supposed to impact folding and trafficking of α-sarcoglycan because the defective polypeptide, although potentially functional, is recognized and disposed of by the quality control of the cell. The secondary reduction of α-sarcoglycan partners, β-, γ- and δ-sarcoglycan, disrupts a key membrane complex that, associated to dystrophin, contributes to assure sarcolemma stability during muscle contraction. The complex deficiency is responsible for muscle wasting and the development of a severe form of dystrophy. Here, we show that the application of small molecules developed to rescue ΔF508-CFTR trafficking, and known as CFTR correctors, also improved the maturation of several α-sarcoglycan mutants that were consequently rescued at the plasma membrane. Remarkably, in myotubes from a patient with LGMD2D, treatment with CFTR correctors induced the proper re-localization of the whole sarcoglycan complex, with a consequent reduction of sarcolemma fragility. Although the mechanism of action of CFTR correctors on defective α-sarcoglycan needs further investigation, this is the first report showing a quantitative and functional recovery of the sarcoglycan-complex in human pathologic samples, upon small molecule treatment. It represents the proof of principle of a pharmacological strategy that acts on the sarcoglycan maturation process and we believe it has a great potential to develop as a cure for most of the patients with LGMD2D.

Collection of the Abstracts of the 2019Sp PMD: Translational Myology and Mobility Medicine

The Interdepartmental Research Centre of Myology (CIR-Myo), Department of Biomedical Sciences, University of Padova, Italy and the A&C M-C Foundation for Translational Myology, Padova, Italy organized with the scientific support of Helmut Kern, Jonathan C. Jarvis, Viviana Moresi, Marco Narici, Feliciano Protasi, Marco Sandri and Ugo Carraro, the 2019SpringPaduaMuscleDays: Translational Myology and Mobility Medicine, an International Conference held March 28-30, 2019 in Euganei Hills and Padova (Italy). Presentations and discussions of the Three Physiology Lectures and of the seven Sessions (I: Spinal Cord Neuromodulation and h-bFES in SC; II: Muscle epigenetics in aging and myopathies; III: Experimental approaches in animal models; IV: Face and Voice Rejuvenation; V: Muscle Imaging; VI: Official Meeting of the EU Center of Active Aging; VII: Early Rehabilitation after knee and hip replacement) were at very high levels. This was true in the past and will be true in future events thanks to researchers and clinicians who were and are eager to attend the PaduaMuscleDays.

Identification of the inhibitory activity of walnut extract on the E3 ligase Syvn1

Synoviolin (Syvn1), an E3 ubiquitin ligase in endoplasmic reticulum‑associated protein degradation, is involved in rheumatoid arthritis, fibrosis, liver cirrhosis and obesity. We previously demonstrated that Syvn1 negatively regulates the function of peroxisome proliferator‑activated receptor gamma coactivator‑1β (PGC‑1β). In addition, treatment with a Syvn1 inhibitor suppressed weight gain in a mouse model of obesity by activating PGC‑1β via Syvn1 inhibition. It has been suggested that the Syvn1 inhibitors may have therapeutic benefits in obese patients. The present study tested the inhibitory activity of walnut extract, a natural product, on Syvn1 activity. Walnut extract inhibited the effect of Syvn1 on the cell proliferation of rheumatoid synovial cells and repressed the interaction between PGC‑1β and Syvn1 in an in vitro binding assay. Polyubiquitination of PGC‑1β by Syvn1 was suppressed by walnut extract in a concentration‑dependent manner, but walnut extract did not have an inhibitory effect on the autoubiquitination of Syvn1. Treatment with walnut extract in mouse embryonic fibroblasts increased the number of mitochondria, suggesting that exposure to the extract recovered PGC‑1β function. These results demonstrated that constituents of walnut extract may serve as lead compounds in drug development efforts aiming to produce drugs to treat patients with obesity and obesity‑associated metabolic diseases.

The NRF2‑PGC‑1β pathway activates kynurenine aminotransferase 4 via attenuation of an E3 ubiquitin ligase, synoviolin, in a cecal ligation/perforation‑induced septic mouse model

Sepsis‑associated encephalopathy (SAE) is a systemic inflammatory response syndrome of which the precise associated mechanisms remain unclear. Synoviolin (Syvn1) is an E3 ubiquitin ligase involved in conditions associated with chronic inflammation, including rheumatoid arthritis, obesity, fibrosis and liver cirrhosis. However, the role of Syvn1 in acute inflammation is not clear. The aim of the present study was to investigate the role of Syvn1 in a septic mouse model induced by cecal ligation/perforation (CLP). Metabolome analysis revealed that kynurenine (KYN), a key factor for the development of neuroinflammation, was increased in CLP‑induced septic mice. Notably, KYN was not detected in CLP‑induced septic Syvn1‑deficient mice. KYN is converted to kynurenic acid (KYNA) by kynurenine aminotransferases (KATs), which has a neuroprotective effect. The expression of KAT4 was significantly increased in Syvn1‑deficient mice compared to that in wild‑type mice. Promoter analysis demonstrated that Syvn1 knockdown induced the KAT4 promoter activity, as assessed by luciferase reporter activity, whereas Syvn1 overexpression repressed this activity in a dose‑dependent manner. Furthermore, the KAT4 promoter was significantly activated by the transcriptional factors, NF‑E2‑related factor 2 and peroxisome proliferator‑activated receptor coactivator 1β, which are targets of Syvn1‑induced degradation. In conclusion, the results of the current study demonstrates that the repression of Syvn1 expression induces the conversion of neurotoxic KYN to neuroprotective KYNA in a CLP‑induced mouse model of sepsis, and that Syvn1 is a potential novel target for the treatment of SAE.

Exciting perspectives for Translational Myology in the Abstracts of the 2018Spring PaduaMuscleDays: Giovanni Salviati Memorial - Chapter III - Abstracts of March 16, 2018

Myologists working in Padua (Italy) were able to continue a half-century tradition of studies of skeletal muscles, that started with a research on fever, specifically if and how skeletal muscle contribute to it by burning bacterial toxin. Beside main publications in high-impact-factor journals by Padua myologists, I hope to convince readers (and myself) of the relevance of the editing Basic and Applied Myology (BAM), retitled from 2010 European Journal of Translational Myology (EJTM), of the institution of the Interdepartmental Research Center of Myology of the University of Padova (CIR-Myo), and of a long series of International Conferences organized in Euganei Hills and Padova, that is, the PaduaMuscleDays. The 2018Spring PaduaMuscleDays (2018SpPMD), were held in Euganei Hills and Padua (Italy), in March 14-17, and were dedicated to Giovanni Salviati. The main event of the “Giovanni Salviati Memorial”, was held in the Aula Guariento, Accademia Galileiana di Scienze, Lettere ed Arti of Padua to honor a beloved friend and excellent scientist 20 years after his premature passing. Using the words of Prof. Nicola Rizzuto, we all share his believe that Giovanni “will be remembered not only for his talent and originality as a biochemist, but also for his unassuming and humanistic personality, a rare quality in highly successful people like Giovanni. The best way to remember such a person is to gather pupils and colleagues, who shared with him the same scientific interests and ask them to discuss recent advances in their own fields, just as Giovanni have liked to do”. Since Giovanni’s friends sent many abstracts still influenced by their previous collaboration with him, all the Sessions of the 2018SpPMD reflect both to the research aims of Giovanni Salviati and the traditional topics of the PaduaMuscleDays, that is, basics and applications of physical, molecular and cellular strategies to maintain or recover functions of skeletal muscles. The translational researches summarized in the 2018SpPMD Abstracts are at the appropriate high level to attract approval of Ethical Committees, the interest of International Granting Agencies and approval for publication in top quality, international journals. The abstracts of the March 16, 2018 Padua Muscle Day are listed in this chapter III. All 2018SpPMD Abstracts are indexed at the end of the Chapter IV.

Degradation routes of trafficking-defective VLDLR mutants associated with Dysequilibrium syndrome

Low density lipoprotein receptor (LDLR) family members are involved in signaling in the developing brain. Previously we have reported that missense mutations in the Very Low Density Lipoprotein Receptor gene (VLDLR), causing Dysequilibrium syndrome (DES), disrupt ligand-binding, due to endoplasmic reticulum (ER) retention of the mutants. We explored the degradation routes of these VLDLR mutants in cultured cells. Our results indicate that VLDLR mutants are retained in the ER for prolonged periods which could be facilitated by association with the ER-resident chaperone calnexin. The mutants were prone to aggregation and capable of eliciting ER stress. The VLDLR mutants were found to be degraded predominantly by the proteasomal pathway, since ubiquitinated VLDLR was found to accumulate in response to proteasomal inhibition. Further, the mutants were found to interact with the ER degradation adaptor protein SEL1L. The degradation of VLDLR wild type and mutant were delayed in CRISPR/Cas9 edited SEL1L knock-out cells which was reversed by exogenous expression of SEL1L. In summary, ER retention of pathogenic VLDLR mutants involves binding to calnexin, elevated ER stress, and delayed degradation which is dependent on SEL1L. Since core LDLR family members share common structural domains, common mechanisms may be involved in their ER processing.

A dystroglycan mutation (p.Cys667Phe) associated to muscle-eye-brain disease with multicystic leucodystrophy results in ER-retention of the mutant protein

Dystroglycan (DG) is a cell adhesion complex composed by two subunits, the highly glycosylated α-DG and the transmembrane β-DG. In skeletal muscle, DG is involved in dystroglycanopathies, a group of heterogeneous muscular dystrophies characterized by a reduced glycosylation of α-DG. The genes mutated in secondary dystroglycanopathies are involved in the synthesis of O-mannosyl glycans and in the O-mannosylation pathway of α-DG. Mutations in the DG gene (DAG1), causing primary dystroglycanopathies, destabilize the α-DG core protein influencing its binding to modifying enzymes. Recently, a homozygous mutation (p.Cys699Phe) hitting the β-DG ectodomain has been identified in a patient affected by muscle-eye-brain disease with multicystic leucodystrophy, suggesting that other mechanisms than hypoglycosylation of α-DG could be implicated in dystroglycanopathies. Herein, we have characterized the DG murine mutant counterpart by transfection in cellular systems and high-resolution microscopy. We observed that the mutation alters the DG processing leading to retention of its uncleaved precursor in the endoplasmic reticulum. Accordingly, small-angle X-ray scattering data, corroborated by biochemical and biophysical experiments, revealed that the mutation provokes an alteration in the β-DG ectodomain overall folding, resulting in disulfide-associated oligomerization. Our data provide the first evidence of a novel intracellular mechanism, featuring an anomalous endoplasmic reticulum-retention, underlying dystroglycanopathy.

Myoclonus dystonia and muscular dystrophy: ɛ-sarcoglycan is part of the dystrophin-associated protein complex in brain

Background

Myoclonus‐dystonia is a neurogenic movement disorder caused by mutations in the gene encoding ɛ‐sarcoglycan. By contrast, mutations in the α‐, β‐, γ‐, and δ‐sarcoglycan genes cause limb girdle muscular dystrophies. The sarcoglycans are part of the dystrophin‐associated protein complex in muscle that is disrupted in several types of muscular dystrophy. Intriguingly, patients with myoclonus‐dystonia have no muscle pathology; conversely, limb‐girdle muscular dystrophy patients have not been reported to have dystonia‐associated features. To gain further insight into the molecular mechanisms underlying these differences, we searched for evidence of a sarcoglycan complex in the brain.

Methods

Immunoaffinity chromatography and mass spectrometry were used to purify ubiquitous and brain‐specific ɛ‐sarcoglycan directly from tissue. Cell models were used to determine the effect of mutations on the trafficking and assembly of the brain sarcoglycan complex.

Results

Ubiquitous and brain‐specific ɛ‐sarcoglycan isoforms copurify with β‐, δ‐, and ζ‐sarcoglycan, β‐dystroglycan, and dystrophin Dp71 from brain. Incorporation of a muscular dystrophy‐associated β‐sarcoglycan mutant into the brain sarcoglycan complex impairs the formation of the βδ‐sarcoglycan core but fails to abrogate the association and membrane trafficking of ɛ‐ and ζ‐sarcoglycan.

Conclusions

ɛ‐Sarcoglycan is part of the dystrophin‐associated protein complex in brain. Partial preservation of ɛ‐ and ζ‐sarcoglycan in brain may explain the absence of myoclonus dystonia‐like features in muscular dystrophy patients. © 2016 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

The ubiquitin ligase tripartite-motif-protein 32 is induced in Duchenne muscular dystrophy

Activation of the proteasome pathway is one of the secondary processes of cell damage, which ultimately lead to muscle degeneration and necrosis in Duchenne muscular dystrophy (DMD). In mdx mice, the proteasome inhibitor bortezomib up-regulates the membrane expression of members of the dystrophin complex and reduces the inflammatory reaction. However, chronic inhibition of the 26S proteasome may be toxic, as indicated by the systemic side-effects caused by this drug. Therefore, we sought to determine the components of the ubiquitin-proteasome pathway that are specifically activated in human dystrophin-deficient muscles. The analysis of a cohort of patients with genetically determined DMD or Becker muscular dystrophy (BMD) unveiled a selective up-regulation of the ubiquitin ligase tripartite motif-containing protein 32 (TRIM32). The induction of TRIM32 was due to a transcriptional effect and it correlated with disease severity in BMD patients. In contrast, atrogin1 and muscle RING-finger protein-1 (MuRF-1), which are strongly increased in distinct types of muscular atrophy, were not affected by the DMD dystrophic process. Knock-out models showed that TRIM32 is involved in ubiquitination of muscle cytoskeletal proteins as well as of protein inhibitor of activated STAT protein gamma (Piasγ) and N-myc downstream-regulated gene, two inhibitors of satellite cell proliferation and differentiation. Accordingly, we showed that in DMD/BMD muscle tissue, TRIM32 induction was more pronounced in regenerating myofibers rather than in necrotic muscle cells, thus pointing out a role of this protein in the regulation of human myoblast cell fate. This finding highlights TRIM32 as a possible therapeutic target to favor skeletal muscle regeneration in DMD patients.

Mitochondrial ubiquitin ligase activator of NF-κB regulates NF-κB signaling in cells subjected to ER stress

The nuclear factor-κB (NF-κB) transcription factor family members control various biological processes, such as apoptosis and proliferation. The endoplasmic reticulum (ER) has emerged as a major site of cellular homeostasis regulation. The accumulation of misfolded protein in the ER causes stress and ER stress-induced NF-κB activation to protect cells from apoptosis. In this study, we found a putative ER stress-response element (ERSE) on the promoter of mitochondrial ubiquitin ligase activator of NF-κB (MULAN), and that MULAN expression was upregulated by ER stress. MULAN specifically activated NF-κB dependent gene expression in an E3 ligase activity-dependent manner. The ectopic expression of MULAN induced the nuclear translocation of endogenous p65 and the degradation of IκB. Binding assay revealed that MULAN was associated with transforming growth factor β-activated kinase (TAK1). The knockdown of MULAN using siRNA inhibited the activation of NF-κB in the cells subjected to ER stress. The findings of our study indicate that MULAN is an E3 ligase that regulates NF-κB activation to protect cells from ER stress-induced apoptosis.

The E3 ligase synoviolin controls body weight and mitochondrial biogenesis through negative regulation of PGC-1β

Obesity is a major global public health problem, and understanding its pathogenesis is critical for identifying a cure. In this study, a gene knockout strategy was used in post-neonatal mice to delete synoviolin (Syvn)1/Hrd1/Der3, an ER-resident E3 ubiquitin ligase with known roles in homeostasis maintenance. Syvn1 deficiency resulted in weight loss and lower accumulation of white adipose tissue in otherwise wild-type animals as well as in genetically obese (ob/ob and db/db) and adipose tissue-specific knockout mice as compared to control animals. SYVN1 interacted with and ubiquitinated the thermogenic coactivator peroxisome proliferator-activated receptor coactivator (PGC)-1β, and Syvn1 mutants showed upregulation of PGC-1β target genes and increase in mitochondrion number, respiration, and basal energy expenditure in adipose tissue relative to control animals. Moreover, the selective SYVN1 inhibitor LS-102 abolished the negative regulation of PGC-1β by SYVN1 and prevented weight gain in mice. Thus, SYVN1 is a novel post-translational regulator of PGC-1β and a potential therapeutic target in obesity treatment.

Spectrum of muscular dystrophies associated with sarcolemmal-protein genetic defects

Muscular dystrophies are heterogeneous genetic disorders that share progressive muscle wasting. This may generate partial impairment of motility as well as a dramatic and fatal course. Less than 30 years ago, the identification of the genetic basis of Duchenne muscular dystrophy opened a new era. An explosion of new information on the mechanisms of disease was witnessed, with many thousands of publications and the characterization of dozens of other genetic forms. Genes mutated in muscular dystrophies encode proteins of the plasma membrane and extracellular matrix, several of which are part of the dystrophin-associated complex. Other gene products localize at the sarcomere and Z band, or are nuclear membrane components. In the present review, we focus on muscular dystrophies caused by defects that affect the sarcolemmal and sub-sarcolemmal proteins. We summarize the nature of each disease, the genetic cause, and the pathogenic pathways that may suggest future treatment options. We examine X-linked Duchenne and Becker muscular dystrophies and the autosomal recessive limb-girdle muscular dystrophies caused by mutations in genes encoding sarcolemmal proteins. The mechanism of muscle damage is reviewed starting from disarray of the shock-absorbing dystrophin-associated complex at the sarcolemma and activation of inflammatory response up to the final stages of fibrosis. We trace only a part of the biochemical, physiopathological and clinical aspects of muscular dystrophy to avoid a lengthy list of different and conflicting observations. We attempt to provide a critical synthesis of what we consider important aspects to better understand the disease. In our opinion, it is becoming ever more important to go back to the bedside to validate and then translate each proposed mechanism. This article is part of a Special Issue entitled: Neuromuscular Diseases: Pathology and Molecular Pathogenesis.