Serum proteomic profiling reveals fragments of MYOM3 as potential biomarkers for monitoring the outcome of therapeutic interventions in muscular dystrophies

DIA-Based Proteomic Analysis Reveals MYOZ2 as a Key Protein Affecting Muscle Growth and Development in Hybrid Sheep

Hybridization of livestock can be used to improve varieties, and different hybrid combinations produce unique breeding effects. In this study, male Southdown and Suffolk sheep were selected to hybridize with female Hu sheep to explore the effects of male parentage on muscle growth and the development of offspring. Using data-independent acquisition technology, we identified 119, 187, and 26 differentially abundant proteins (DAPs) between Hu × Hu (HH) versus Southdown × Hu (NH), HH versus Suffolk × Hu (SH), and NH versus SH crosses. Two DAPs, MYOZ2 and MYOM3, were common to the three hybrid groups and were mainly enriched in muscle growth and development-related pathways. At the myoblast proliferation stage, MYOZ2 expression decreased cell viability and inhibited proliferation. At the myoblast differentiation stage, MYOZ2 expression promoted myoblast fusion and enhanced the level of cell fusion. These findings provide new insights into the key proteins and metabolic pathways involved in the effect of male parentage on muscle growth and the development of hybrid offspring in sheep.

N-terminal titin fragment: a non-invasive, pharmacodynamic biomarker for microdystrophin efficacy

BACKGROUND

Multiple clinical trials to assess the efficacy of AAV-directed gene transfer in participants with Duchenne muscular dystrophy (DMD) are ongoing. The success of these trials currently relies on standard functional outcome measures that may exhibit variability within and between participants, rendering their use as sole measures of drug efficacy challenging. Given this, supportive objective biomarkers may be useful in enhancing observed clinical results. Creatine kinase (CK) is traditionally used as a diagnostic biomarker of DMD, but its potential as a robust pharmacodynamic (PD) biomarker is difficult due to the wide variability seen within the same participant over time. Thus, there is a need for the discovery and validation of novel PD biomarkers to further support and bolster traditional outcome measures of efficacy in DMD.

METHOD

Potential PD biomarkers in DMD participant urine were examined using a proteomic approach on the Somalogic platform. Findings were confirmed in both mdx mice and Golden Retriever muscular dystrophy (GRMD) dog plasma samples.

RESULTS

Changes in the N-terminal fragment of titin, a well-known, previously characterized biomarker of DMD, were correlated with the expression of microdystrophin protein in mice, dogs, and humans. Further, titin levels were sensitive to lower levels of expressed microdystrophin when compared to CK.

CONCLUSION

The measurement of objective PD biomarkers such as titin may provide additional confidence in the assessment of the mechanism of action and efficacy in gene therapy clinical trials of DMD.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03368742.

A functional mini-GDE transgene corrects impairment in models of glycogen storage disease type III

Glycogen storage disease type III (GSDIII) is a rare inborn error of metabolism affecting liver, skeletal muscle, and heart due to mutations of the AGL gene encoding for the glycogen debranching enzyme (GDE). No curative treatment exists for GSDIII. The 4.6 kb GDE cDNA represents the major technical challenge toward the development of a single recombinant adeno-associated virus-derived (rAAV-derived) vector gene therapy strategy. Using information on GDE structure and molecular modeling, we generated multiple truncated GDEs. Among them, an N-terminal-truncated mutant, ΔNter2-GDE, had a similar efficacy in vivo compared with the full-size enzyme. A rAAV vector expressing ΔNter2-GDE allowed significant glycogen reduction in heart and muscle of Agl-/- mice 3 months after i.v. injection, as well as normalization of histology features and restoration of muscle strength. Similarly, glycogen accumulation and histological features were corrected in a recently generated Agl-/- rat model. Finally, transduction with rAAV vectors encoding ΔNter2-GDE corrected glycogen accumulation in an in vitro human skeletal muscle cellular model of GSDIII. In conclusion, our results demonstrated the ability of a single rAAV vector expressing a functional mini-GDE transgene to correct the muscle and heart phenotype in multiple models of GSDIII, supporting its clinical translation to patients with GSDIII.

How Can Proteomics Help to Elucidate the Pathophysiological Crosstalk in Muscular Dystrophy and Associated Multi-System Dysfunction?

This perspective article is concerned with the question of how proteomics, which is a core technique of systems biology that is deeply embedded in the multi-omics field of modern bioresearch, can help us better understand the molecular pathogenesis of complex diseases. As an illustrative example of a monogenetic disorder that primarily affects the neuromuscular system but is characterized by a plethora of multi-system pathophysiological alterations, the muscle-wasting disease Duchenne muscular dystrophy was examined. Recent achievements in the field of dystrophinopathy research are described with special reference to the proteome-wide complexity of neuromuscular changes and body-wide alterations/adaptations. Based on a description of the current applications of top-down versus bottom-up proteomic approaches and their technical challenges, future systems biological approaches are outlined. The envisaged holistic and integromic bioanalysis would encompass the integration of diverse omics-type studies including inter- and intra-proteomics as the core disciplines for systematic protein evaluations, with sophisticated biomolecular analyses, including physiology, molecular biology, biochemistry and histochemistry. Integrated proteomic findings promise to be instrumental in improving our detailed knowledge of pathogenic mechanisms and multi-system dysfunction, widening the available biomarker signature of dystrophinopathy for improved diagnostic/prognostic procedures, and advancing the identification of novel therapeutic targets to treat Duchenne muscular dystrophy.

The Profiling of 179 miRNA Expression in Serum from Limb Girdle Muscular Dystrophy Patients and Healthy Controls

Limb girdle muscular dystrophies (LGMDs) are a group of genetically inherited neuromuscular diseases with a very variable clinical presentation and overlapping traits. Over the last few years there has been an increasing interest in the use of non-invasive circulating biomarkers to monitor disease progression and to evaluate the efficacy of therapeutic approaches. Our aim was to identify the miRNA signature with potential value for LGMD patient screening and stratification. Using miRCURY LNA miRNA qPCR Serum/Plasma Panel, we analyzed 179 miRNAs from 16 patients, divided in four pools based on their genetic diagnosis, and from healthy controls. The miRNAs analysis showed a total of 107 dysregulated miRNAs in LGMD patients when compared to the healthy controls. After filtering via skeletal tissue expression and gene/pathways target analysis, the number of dysregulated miRNAs drastically reduced. Six selected miRNAs-let-7f-5p (in LGMDR1), miR-20a-5p (in LGMDR2), miR-130b-5p, miR-378a-5p (both in LGMDR3), miR-376c-3p and miR-382-5p (both in LGMDR4)-whose expression was significantly lower compared to controls in the different LGMD pools, were further investigated. The bioinformatic analysis of the target genes in each selected miRNA revealed ECM-receptor interaction and TGF-beta signaling as the most involved pathways. The correlation analysis showed a good correlation of let-7f-5p with fibrosis and with the cross sectional area of type I and type II fibers, while miR-130b-5p showed a good correlation with the age of onset of the disease. The receiver operating characteristic curves showed how single miRNAs were able to discriminate a specific group of LGMD patients and how the combination of six miRNAs was able to discriminate LGMD patients from controls.

Serum inflammatory cytokines as disease biomarkers in the DE50-MD dog model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a fatal muscle-wasting disease, caused by mutations in the dystrophin gene, characterised by cycles of muscle degeneration, inflammation and regeneration. Recently, there has been renewed interest specifically in drugs that ameliorate muscle inflammation in DMD patients. The DE50-MD dog is a model of DMD that closely mimics the human DMD phenotype. We quantified inflammatory proteins in serum from wild-type (WT) and DE50-MD dogs aged 3-18 months to identify biomarkers for future pre-clinical trials. Significantly higher concentrations of C-C motif chemokine ligand 2 (CCL2), granulocyte-macrophage colony-stimulating factor (GM-CSF or CSF2), keratinocyte chemotactic-like (KC-like, homologous to mouse CXCL1), TNFα (or TNF), and interleukins IL2, IL6, IL7, IL8 (CXCL8), IL10, IL15 and IL18 were detected in DE50-MD serum compared to WT serum. Of these, CCL2 best differentiated the two genotypes. The relative level of CCL2 mRNA was greater in the vastus lateralis muscle of DE50-MD dogs than in that of WT dogs, and CCL2 was expressed both within and at the periphery of damaged myofibres. Serum CCL2 concentration was significantly associated with acid phosphatase staining in vastus lateralis biopsy samples in DE50-MD dogs. In conclusion, the serum cytokine profile suggests that inflammation is a feature of the DE50-MD phenotype. Quantification of serum CCL2 in particular is a useful non-invasive biomarker of the DE50-MD phenotype.

Histone deacetylase inhibitors improve antisense-mediated exon-skipping efficacy in mdx mice

Antisense-mediated exon skipping is one of the most promising therapeutic strategies for Duchenne muscular dystrophy (DMD), and some antisense oligonucleotide (ASO) drugs have already been approved by the US FDA despite their low efficacy. The potential of this therapy is still limited by several challenges, including the reduced expression of the dystrophin transcript and the strong 5'-3' imbalance in mutated transcripts. We therefore hypothesize that increasing histone acetylation using histone deacetylase inhibitors (HDACi) could correct the transcript imbalance, offering more available pre-mRNA target and ultimately increasing dystrophin rescue. Here, we evaluated the impact of such a combined therapy on the Dmd transcript imbalance phenomenon and on dystrophin restoration levels in mdx mice. Analysis of the Dmd transcript levels at different exon-exon junctions revealed a tendency to correct the 5'-3' imbalance phenomenon following treatment with HDACi. Significantly higher levels of dystrophin restoration (up to 74% increase) were obtained with givinostat and valproic acid compared with mice treated with ASO alone. Additionally, we demonstrate an increase in H3K9 acetylation in human myocytes after treatment with valproic acid. These findings indicate that HDACi can improve the therapeutic potential of exon-skipping approaches, offering promising perspectives for the treatment of DMD.

Longitudinal assessment of blood-borne musculoskeletal disease biomarkers in the DE50-MD dog model of Duchenne muscular dystrophy

Background: Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease caused by mutations in the dystrophin gene. Due to their phenotypic similarity to human patients, large animal models are invaluable tools for pre-clinical trials. The DE50-MD dog is a relatively new model of DMD, and carries a therapeutically-tractable mutation lying within the hotspot for human patients, making it especially valuable. Prior to conducting therapeutic trials using this novel animal model, it is essential to establish a panel of viable biomarkers. Methods: We evaluated a panel of blood-borne biomarkers of musculoskeletal disease in the DE50-MD dog. Venous blood samples were obtained monthly throughout an 18-month study period in DE50-MD (N=18) and wild-type (WT) control (N=14) dogs. A panel of potential plasma/serum biomarkers of DMD was measured and their theoretical utility in future clinical trials determined using sample size calculations. Results: Compared to WT dogs, DE50-MD dogs had substantially higher circulating creatine kinase (CK) activities, myomesin-3 (MYOM3), and the dystromiRs miR-1, miR-133a and miR-206, but significantly lower serum myostatin concentrations. An age-associated pattern, similar to that observed in DMD patients, was seen for CK and MYOM3. Sample size calculations suggested that low cohort sizes (N≤3) could be used to detect up to a 50% improvement in DE50-MD results towards WT levels for each biomarker or a combination thereof (via principal component analysis); as few as N=3 animals should enable detection of a 25% improvement using a combined biomarker approach (alpha 0.05, power 0.8). Conclusions: We have established a panel of blood-borne biomarkers that could be used to monitor musculoskeletal disease or response to a therapeutic intervention in the DE50-MD dog using low numbers of animals. The blood biomarker profile closely mimics that of DMD patients, supporting the hypothesis that this DMD model would be suitable for use in pre-clinical trials.

Longitudinal assessment of blood-borne musculoskeletal disease biomarkers in the DE50-MD dog model of Duchenne muscular dystrophy

Background: Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease caused by mutations in the dystrophin gene. Due to their phenotypic similarity to human patients, large animal models are invaluable tools for pre-clinical trials. The DE50-MD dog is a relatively new model of DMD, and carries a therapeutically-tractable mutation lying within the hotspot for human patients, making it especially valuable. Prior to conducting therapeutic trials using this novel animal model, it is essential to establish a panel of viable biomarkers. Methods: We evaluated a panel of blood-borne biomarkers of musculoskeletal disease in the DE50-MD dog. Venous blood samples were obtained monthly throughout an 18-month study period in DE50-MD (N=18) and wild-type (WT) control (N=14) dogs. A panel of potential plasma/serum biomarkers of DMD was measured and their theoretical utility in future clinical trials determined using sample size calculations. Results: Compared to WT dogs, DE50-MD dogs had substantially higher circulating creatine kinase (CK) activities, myomesin-3 (MYOM3), and the dystromiRs miR-1, miR-133a and miR-206, but significantly lower serum myostatin concentrations. An age-associated pattern, similar to that observed in DMD patients, was seen for CK and MYOM3. Sample size calculations suggested that low cohort sizes (N≤3) could be used to detect up to a 50% improvement in DE50-MD results towards WT levels for each biomarker or a combination thereof (via principal component analysis); as few as N=3 animals should enable detection of a 25% improvement using a combined biomarker approach (alpha 0.05, power 0.8). Conclusions: We have established a panel of blood-borne biomarkers that could be used to monitor musculoskeletal disease or response to a therapeutic intervention in the DE50-MD dog using low numbers of animals. The blood biomarker profile closely mimics that of DMD patients, supporting the hypothesis that this DMD model would be suitable for use in pre-clinical trials.

Palmitic acid conjugation enhances potency of tricyclo-DNA splice switching oligonucleotides

Tricyclo-DNA (tcDNA) is a conformationally constrained oligonucleotide analog that has demonstrated great therapeutic potential as antisense oligonucleotide (ASO) for several diseases. Like most ASOs in clinical development, tcDNA were modified with phosphorothioate (PS) backbone for therapeutic purposes in order to improve their biodistribution by enhancing association with plasma and cell protein. Despite the advantageous protein binding properties, systemic delivery of PS-ASO remains limited and PS modifications can result in dose limiting toxicities in the clinic. Improving extra-hepatic delivery of ASO is highly desirable for the treatment of a variety of diseases including neuromuscular disorders such as Duchenne muscular dystrophy. We hypothesized that conjugation of palmitic acid to tcDNA could facilitate the delivery of the ASO from the bloodstream to the interstitium of the muscle tissues. We demonstrate here that palmitic acid conjugation enhances the potency of tcDNA-ASO in skeletal and cardiac muscles, leading to functional improvement in dystrophic mice with significantly reduced dose of administered ASO. Interestingly, palmitic acid-conjugated tcDNA with a full phosphodiester backbone proved effective with a particularly encouraging safety profile, offering new perspectives for the clinical development of PS-free tcDNA-ASO for neuromuscular diseases.

Multiomic Approaches to Uncover the Complexities of Dystrophin-Associated Cardiomyopathy

Despite major progress in treating skeletal muscle disease associated with dystrophinopathies, cardiomyopathy is emerging as a major cause of death in people carrying dystrophin gene mutations that remain without a targeted cure even with new treatment directions and advances in modelling abilities. The reasons for the stunted progress in ameliorating dystrophin-associated cardiomyopathy (DAC) can be explained by the difficulties in detecting pathophysiological mechanisms which can also be efficiently targeted within the heart in the widest patient population. New perspectives are clearly required to effectively address the unanswered questions concerning the identification of authentic and effectual readouts of DAC occurrence and severity. A potential way forward to achieve further therapy breakthroughs lies in combining multiomic analysis with advanced preclinical precision models. This review presents the fundamental discoveries made using relevant models of DAC and how omics approaches have been incorporated to date.

Analysis of long intergenic non-coding RNAs transcriptomic profiling in skeletal muscle growth during porcine embryonic development

Skeletal muscle growth plays a critical role during porcine muscle development stages. Genome-wide transcriptome analysis reveals that long intergenic non-coding RNAs (lincRNAs) are implicated as crucial regulator involving in epigenetic regulation. However, comprehensive analysis of lincRNAs in embryonic muscle development stages remain still elusive. Here, we investigated the transcriptome profiles of Duroc embryonic muscle tissues from days 33, 65, and 90 of gestation using RNA-seq, and 228 putative lincRNAs were identified. Moreover, these lincRNAs exhibit the characteristics of shorter transcripts length, longer exons, less exon numbers and lower expression level compared with protein-coding transcripts. Expression profile analysis showed that a total of 120 lincRNAs and 2638 mRNAs were differentially expressed. In addition, we also performed quantitative trait locus (QTL) mapping analysis for differentially expressed lincRNAs (DE lincRNAs), 113 of 120 DE lincRNAs were localized on 2200 QTLs, we observed many QTLs involved in growth and meat quality traits. Furthermore, we predicted potential target genes of DE lincRNAs in cis or trans regulation. Gene ontology and pathway analysis reveals that potential targets of DE lincRNAs mostly were enriched in the processes and pathways related to tissue development, MAPK signaling pathway, Wnt signaling pathway, TGF-beta signaling pathway and insulin signaling pathway, which involved in skeletal muscle physiological functions. Based on cluster analysis, co-expression network analysis of DE lincRNAs and their potential target genes indicated that DE lincRNAs highly regulated protein-coding genes associated with skeletal muscle development. In this study, many of the DE lincRNAs may play essential roles in pig muscle growth and muscle mass. Our study provides crucial information for further exploring the molecular mechanisms of lincRNAs during skeletal muscle development.

Plasma lipidomic analysis shows a disease progression signature in mdx mice

Duchenne muscular dystrophy (DMD) is a rare genetic disorder affecting paediatric patients. The disease course is characterized by loss of muscle mass, which is rapidly substituted by fibrotic and adipose tissue. Clinical and preclinical models have clarified the processes leading to muscle damage and myofiber degeneration. Analysis of the fat component is however emerging as more evidence shows how muscle fat fraction is associated with patient performance and prognosis. In this article we aimed to study whether alterations exist in the composition of lipids in plasma samples obtained from mouse models. Analysis of plasma samples was performed in 4 mouse models of DMD and wild-type mice by LC–MS. Longitudinal samplings of individual mice covering an observational period of 7 months were obtained to cover the different phases of the disease. We report clear elevation of glycerolipids and glycerophospholipids families in dystrophic mice compared to healthy mice. Triacylglycerols were the strongest contributors to the signatures in mice. Annotation of individual lipids confirmed the elevation of lipids belonging to these families as strongest discriminants between healthy and dystrophic mice. A few sphingolipids (such as ganglioside GM2, sphingomyelin and ceramide), sterol lipids (such as cholesteryl oleate and cholesteryl arachidonate) and a fatty acyl (stearic acid) were also found to be affected in dystrophic mice. Analysis of serum and plasma samples show how several lipids are affected in dystrophic mice affected by muscular dystrophy. This study sets the basis to further investigations to understand how the lipid signature relates to the disease biology and muscle performance.

Proteins associated with quality deterioration of prepared chicken breast based on differential proteomics during refrigerated storage

BACKGROUND

Prepared chicken breast deterioration is a complex biochemical process, of which protein change is one of the main features. The present research focuses on the analysis of proteins related to the deterioration in quality of prepared chicken breast through differential proteomics analysis.

RESULTS

The physicochemical indexes of prepared chicken breast showed that quality gradually decreased at the second week of refrigerated storage, while the deterioration of chicken breast meat was obvious at the third week. Three key time points of quality change were determined to be at 0th, 2th and 5th week, respectively. In addition, 39 differential proteins were successfully identified using two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Most of the identified proteins showed significant differences in expression at the three key points of storage, of which actin, myosin, α-1,4-glucan phosphorylase, phosphoglucomutase 1, heat shock protein β-1, tubulin β-7 chain and skeletal muscle type tropomodulin (fragment) were closely related to the quality deterioration of prepared chicken breast, and thus potential indicator proteins to evaluate the quality of chicken breast.

CONCLUSION

The current study indicated that the physicochemical quality of prepared breast notably changed during refrigerated storage. Three key time points of quality change in the storage process of prepared chicken breast were determined. Furthermore, differential proteomics identified the key proteins related to freshness, which provides a theoretical basis for exploring the mechanism of chicken breast deterioration. © 2020 Society of Chemical Industry.

Cholesterol metabolism is a potential therapeutic target in Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is a lethal muscle disease detected in approximately 1:5000 male births. DMD is caused by mutations in the DMD gene, encoding a critical protein that links the cytoskeleton and the extracellular matrix in skeletal and cardiac muscles. The primary consequence of the disrupted link between the extracellular matrix and the myofibre actin cytoskeleton is thought to involve sarcolemma destabilization, perturbation of Ca2+ homeostasis, activation of proteases, mitochondrial damage, and tissue degeneration. A recently emphasized secondary aspect of the dystrophic process is a progressive metabolic change of the dystrophic tissue; however, the mechanism and nature of the metabolic dysregulation are yet poorly understood. In this study, we characterized a molecular mechanism of metabolic perturbation in DMD.

METHODS

We sequenced plasma miRNA in a DMD cohort, comprising 54 DMD patients treated or not by glucocorticoid, compared with 27 healthy controls, in three groups of the ages of 4-8, 8-12, and 12-20 years. We developed an original approach for the biological interpretation of miRNA dysregulation and produced a novel hypothesis concerning metabolic perturbation in DMD. We used the mdx mouse model for DMD for the investigation of this hypothesis.

RESULTS

We identified 96 dysregulated miRNAs (adjusted P-value <0.1), of which 74 were up-regulated and 22 were down-regulated in DMD. We confirmed the dysregulation in DMD of Dystro-miRs, Cardio-miRs, and a large number of the DLK1-DIO3 miRNAs. We also identified numerous dysregulated miRNAs yet unreported in DMD. Bioinformatics analysis of both target and host genes for dysregulated miRNAs predicted that lipid metabolism might be a critical metabolic perturbation in DMD. Investigation of skeletal muscles of the mdx mouse uncovered dysregulation of transcription factors of cholesterol and fatty acid metabolism (SREBP-1 and SREBP-2), perturbation of the mevalonate pathway, and the accumulation of cholesterol in the dystrophic muscles. Elevated cholesterol level was also found in muscle biopsies of DMD patients. Treatment of mdx mice with Simvastatin, a cholesterol-reducing agent, normalized these perturbations and partially restored the dystrophic parameters.

CONCLUSIONS

This investigation supports that cholesterol metabolism and the mevalonate pathway are potential therapeutic targets in DMD.

Knockout of MYOM1 in human cardiomyocytes leads to myocardial atrophy via impairing calcium homeostasis

Myomesin-1 (encoded by MYOM1 gene) is expressed in almost all cross-striated muscles, whose family (together with myomesin-2 and myomesin-3) helps to cross-link adjacent myosin to form the M-line in myofibrils. However, little is known about its biological function, causal relationship and mechanisms underlying the MYOM1-related myopathies (especially in the heart). Regrettably, there is no MYMO1 knockout model for its study so far. A better and further understanding of MYOM1 biology is urgently needed. Here, we used CRISPR/Cas9 gene-editing technology to establish an MYOM1 knockout human embryonic stem cell line (MYOM1-/- hESC), which was then differentiated into myomesin-1 deficient cardiomyocytes (MYOM1-/- hESC-CMs) in vitro. We found that myomesin-1 plays an important role in sarcomere assembly, contractility regulation and cardiomyocytes development. Moreover, myomesin-1-deficient hESC-CMs can recapitulate myocardial atrophy phenotype in vitro. Based on this model, not only the biological function of MYOM1, but also the aetiology, pathogenesis, and potential treatments of myocardial atrophy caused by myomesin-1 deficiency can be studied.

An acute eccentric exercise increases circulating myomesin 3 fragments

Discovery of blood biomarkers to evaluate exercise-induced muscle damage have attracted many researchers and coaches. This study aimed to determine changes in circulating myomesin 3 fragments as a novel biomarker for exercise-induced muscle damage. Nine healthy males performed 10 sets of 40 repetitions of one-leg calf-raise exercise by the load corresponding to the half of their body weight. Muscle symptoms were evaluated by a visual analog scale (VAS). Blood samples were collected before and 2, 4, 24, 48, 72, and 96 h post-exercise. Plasma myomesin 3 fragments levels were significantly increased at 96 h after the eccentric exercise. The myomesin 3 fragments levels were correlated with other biomarkers of muscle damage and the muscle symptoms. These results suggest that the circulating myomesin 3 fragments levels are potential biomarkers reflecting eccentric exercise-induced muscle damage.

Novel free-circulating and extracellular vesicle-derived miRNAs dysregulated in Duchenne muscular dystrophy

Aim: To perform cross-sectional and longitudinal miRNA profiling in plasma from Duchenne muscular dystrophy (DMD) subjects and find non-invasive biomarkers in DMD. Subjects/materials & methods: Plasma was collected from 14 age and sex matched controls and 46 DMD subjects. Free-circulating and extracellular vesicle (EV)-derived miRNA expression was measured by RT-qPCR. Results: Free-circulating and EVs derived miR-29c-3p and miR-133a-3p are dysregulated in DMD subjects. Free-circulating and EV-derived miR-29c-3p are reduced in DMD subjects undergoing daily corticosteroid treatment. Free-circulating miR-1-3p and miR-122-5p are longitudinally upregulated in ambulant DMD subjects. Conclusion: We detected novel free-circulating and EV-derived dysregulated miRNAs in plasma from DMD subjects and characterized the longitudinal profile of free-circulating miRNA on plasma from DMD subjects.

Changes in Urinary Titin Fragment in Response to Different Types of Dynamic Eccentric Exercises

The urinary level of the titin fragment has been considered a non-invasive and sensitive biomarker for muscle damage in clinical cases. However, there is little evidence regarding changes in the urinary titin fragment in response to exercise-induced muscle damage. In this study, we aimed to investigate whether the urinary titin fragment reflects the magnitude of muscle damage induced by two lower-limb eccentric exercises. In this study, healthy young male subjects performed drop jump (n=9) and eccentric ergometer exercise (n=9). Blood and urine samples were collected at various time points before and after the exercises. Although perceived muscle soreness assessed by sit-to-stand tasks was increased at 24 h and 48 h after both drop jump and the eccentric ergometer exercise groups, the pressure pain threshold was not changed. Changes of the urinary titin fragment, plasma myomesin 3 fragments, creatine kinase (CK), and myoglobin (Mb) after the eccentric exercises were increased but not statistically significant. Meanwhile, we found that the changes in the urinary titin fragment levels in response to both drop jump and the eccentric ergometer exercise were correlated with those of plasma CK and Mb levels. These results provide evidence that the urinary titin fragment level is a non-invasive biomarker reflecting the magnitude of eccentric exercise-induced muscle damage.

Circulating Biomarkers in Muscular Dystrophies: Disease and Therapy Monitoring

Muscular dystrophies are a group of inherited disorders that primarily affect the muscle tissues. Across the muscular dystrophies, symptoms commonly compromise the quality of life in all areas of functioning. It is well noted that muscular dystrophies need reliable and measurable biomarkers that will monitor the progress of the disease and evaluate the potential therapeutic approaches. In this review, we analyze the current findings regarding the development of blood-based circulating biomarkers for different types of muscular dystrophies. We emphasize those muscular dystrophies that gained particular interest for the development of biomarkers, including Duchenne muscular dystrophy, Becker muscular dystrophy, myotonic dystrophy types 1 and 2, Ullrich congenital muscular dystrophy, congenital muscular dystrophy type 1A, Facioscapulohumeral muscular dystrophy, and limb-girdle muscular dystrophy types 2A, 2B, 2C, and 2D, recently renamed as limb-girdle muscular dystrophy R1 calpain3-related, R2 dysferlin-related, R5 γ-sarcoglycan-related, and R3 α-sarcoglycan-related. This review highlights the up-to-date progress in the development of biomarkers at the level of proteins, lipids, and metabolites, as well as microRNAs (miRNAs) that currently are the main potential biomarker candidates in muscular dystrophies.

Duchenne Muscular Dystrophy: recent advances in protein biomarkers and the clinical application

INTRODUCTION

Early biomarker discovery studies have praised the value of their emerging results, predicting an unprecedented impact on health care. Biomarkers are expected to provide tests with increased specificity and sensitivity compared to existing measures, improve the decision-making process, and accelerate the development of therapies. For rare disorders, like Duchenne Muscular Dystrophy (DMD) such biomarkers can assist the development of therapies, therefore also helping to find a cure for the disease.

AREA COVERED

State-of-the-art technologies have been used to identify blood biomarkers for DMD and efforts have been coordinated to develop and promote translation of biomarkers for clinical practice. Biomarker translation to clinical practice is however, adjoined by challenges related to the complexity of the disease, involving numerous biological processes, and the limited sample resources. This review highlights the current progress on the development of biomarkers, describing the proteomics technologies used, the most promising findings and the challenges encountered.

EXPERT OPINION

Strategies for effective use of samples combined with orthogonal proteomics methods for protein quantification are essential for translating biomarkers to the patient's bed side. Progress is achieved only if strong evidence is provided that the biomarker constitutes a reliable indicator of the patient's health status for a specific context of use.

Long-Term Efficacy of AAV9-U7snRNA-Mediated Exon 51 Skipping in mdx52 Mice

Gene therapy and antisense approaches hold promise for the treatment of Duchenne muscular dystrophy (DMD). The advantages of both therapeutic strategies can be combined by vectorizing antisense sequences into an adeno-associated virus (AAV) vector. We previously reported the efficacy of AAV-U7 small nuclear RNA (U7snRNA)-mediated exon skipping in the mdx mouse, the dys⁻/utr⁻ mouse, and the golden retriever muscular dystrophy (GRMD) dog model. In this study, we examined the therapeutic potential of an AAV-U7snRNA targeting the human DMD exon 51, which could be applicable to 13% of DMD patients. A single injection of AAV9-U7 exon 51 (U7ex51) induces widespread and sustained levels of exon 51 skipping, leading to significant restoration of dystrophin and improvement of the dystrophic phenotype in the mdx52 mouse. However, levels of dystrophin re-expression are lower than the skipping levels, in contrast with previously reported results in the mdx mouse, suggesting that efficacy of exon skipping may vary depending on the targeted exon. Additionally, while low levels of exon skipping were measured in the brain, the dystrophin protein could not be detected, in line with a lack of improvement of their abnormal behavioral fear response. These results thus confirm the high therapeutic potential of the AAV-mediated exon-skipping approach, yet the apparent discrepancies between exon skipping and protein restoration levels suggest some limitations of this experimental model.

Longitudinal serum biomarker screening identifies malate dehydrogenase 2 as candidate prognostic biomarker for Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD) is a fatal disease for which no cure is available. Clinical trials have shown to be largely underpowered due to inter-individual variability and noisy outcome measures. The availability of biomarkers able to anticipate clinical benefit is highly needed to improve clinical trial design and facilitate drug development.

METHODS

In this study, we aimed to appraise the value of protein biomarkers to predict prognosis and monitor disease progression or treatment outcome in patients affected by DMD. We collected clinical data and 303 blood samples from 157 DMD patients in three clinical centres; 78 patients contributed multiple blood samples over time, with a median follow-up time of 2 years. We employed linear mixed models to identify biomarkers that are associated with disease progression, wheelchair dependency, and treatment with corticosteroids and performed survival analysis to find biomarkers whose levels are associated with time to loss of ambulation.

RESULTS

Our analysis led to the identification of 21 proteins whose levels significantly decrease with age and nine proteins whose levels significantly increase. Seven of these proteins are also differentially expressed in non-ambulant patients, and three proteins are differentially expressed in patients treated with glucocorticosteroids. Treatment with corticosteroids was found to partly counteract the effect of disease progression on two biomarkers, namely, malate dehydrogenase 2 (MDH2, P = 0.0003) and ankyrin repeat domain 2 (P = 0.0005); however, patients treated with corticosteroids experienced a further reduction on collagen 1 serum levels (P = 0.0003), especially following administration of deflazacort. A time to event analysis allowed to further support the use of MDH2 as a prognostic biomarker as it was associated with an increased risk of wheelchair dependence (P = 0.0003). The obtained data support the prospective evaluation of the identified biomarkers in natural history and clinical trials as exploratory biomarkers.

CONCLUSIONS

We identified a number of serum biomarkers associated with disease progression, loss of ambulation, and treatment with corticosteroids. The identified biomarkers are promising candidate prognostic and surrogate biomarkers, which may support drug developers if confirmed in prospective studies. The serum levels of MDH2 are of particular interest, as they correlate with disease stage and response to treatment with corticosteroids, and are also associated with the risk of wheelchair dependency and pulmonary function.

The M-band: The underestimated part of the sarcomere

The sarcomere is the basic unit of the myofibrils, which mediate skeletal and cardiac Muscle contraction. Two transverse structures, the Z-disc and the M-band, anchor the thin (actin and associated proteins) and thick (myosin and associated proteins) filaments to the elastic filament system composed of titin. A plethora of proteins are known to be integral or associated proteins of the Z-disc and its structural and signalling role in muscle is better understood, while the molecular constituents of the M-band and its function are less well defined. Evidence discussed here suggests that the M-band is important for managing force imbalances during active muscle contraction. Its molecular composition is fine-tuned, especially as far as the structural linkers encoded by members of the myomesin family are concerned and depends on the specific mechanical characteristics of each particular muscle fibre type. Muscle activity signals from the M-band to the nucleus and affects transcription of sarcomeric genes, especially via serum response factor (SRF). Due to its important role as shock absorber in contracting muscle, the M-band is also more and more recognised as a contributor to muscle disease.

Myomesin is part of an integrity pathway that responds to sarcomere damage and disease

The structure and function of the sarcomere of striated muscle is well studied but the steps of sarcomere assembly and maintenance remain under-characterized. With the aid of chaperones and factors of the protein quality control system, muscle proteins can be folded and assembled into the contractile apparatus of the sarcomere. When sarcomere assembly is incomplete or the sarcomere becomes damaged, suites of chaperones and maintenance factors respond to repair the sarcomere. Here we show evidence of the importance of the M-line proteins, specifically myomesin, in the monitoring of sarcomere assembly and integrity in previously characterized zebrafish muscle mutants. We show that myomesin is one of the last proteins to be incorporated into the assembling sarcomere, and that in skeletal muscle, its incorporation requires connections with both titin and myosin. In diseased zebrafish sarcomeres, myomesin1a shows an early increase of gene expression, hours before chaperones respond to damaged muscle. We found that myomesin expression is also more specific to sarcomere damage than muscle creatine kinase, and our results and others support the use of myomesin assays as an early, specific, method of detecting muscle damage.

Disease-specific and glucocorticoid-responsive serum biomarkers for Duchenne Muscular Dystrophy

Extensive biomarker discoveries for DMD have occurred in the past 7 years, and a vast array of these biomarkers were confirmed in independent cohorts and across different laboratories. In these previous studies, glucocorticoids and age were two major confounding variables. In this new study, using SomaScan technology and focusing on a subset of young DMD patients who were not yet treated with glucocorticoids, we identified 108 elevated and 70 decreased proteins in DMD relative to age matched healthy controls (p value < 0.05 after adjusting for multiple testing). The majority of the elevated proteins were muscle centric followed by cell adhesion, extracellular matrix proteins and a few pro-inflammatory proteins. The majority of decreased proteins were of cell adhesion, however, some had to do with cell differentiation and growth factors. Subsequent treatment of this group of DMD patients with glucocorticoids affected two major groups of pharmacodynamic biomarkers. The first group consisted of 80 serum proteins that were not associated with DMD and either decreased or increased following treatment with glucocorticoids, and therefore were reflective of a broader effect of glucocorticoids. The second group consisted of 17 serum proteins that were associated with DMD and these tended to normalize under treatment, thus reflecting physiologic effects of glucocorticoid treatment in DMD. In summary, we have identified a variety of circulating protein biomarkers that reflect the complex nature of DMD pathogenesis and response to glucocorticoids.

Emerging proteomic biomarkers of X-linked muscular dystrophy

Introduction: Progressive skeletal muscle wasting is the manifesting symptom of Duchenne muscular dystrophy, an X-linked inherited disorder triggered by primary abnormalities in the DMD gene. The almost complete loss of dystrophin isoform Dp427 causes a multi-system pathology that features in addition to skeletal muscle weakness also late-onset cardio-respiratory deficiencies, impaired metabolism and abnormalities in the central nervous system. Areas covered: This review focuses on the mass spectrometry-based proteomic characterization of X-linked muscular dystrophy with special emphasis on the identification of novel biomarker candidates in skeletal muscle tissues, as well as non-muscle tissues and various biofluids. Individual sections focus on molecular and cellular aspects of the pathogenic changes in dystrophinopathy, proteomic workflows used in biomarker research, the proteomics of the dystrophin-glycoprotein complex and the potential usefulness of newly identified protein markers involved in fibre degeneration, fibrosis and inflammation. Expert opinion: The systematic application of large-scale proteomic surveys has identified a distinct cohort of both tissue- and biofluid-associated protein species with considerable potential for improving diagnostic, prognostic and therapy-monitoring procedures. Novel proteomic markers include components involved in fibre contraction, cellular signalling, ion homeostasis, cellular stress response, energy metabolism and the immune response, as well as maintenance of the cytoskeletal and extracellular matrix.

AAV-8 and AAV-9 Vectors Cooperate with Serum Proteins Differently Than AAV-1 and AAV-6

Under intravenous delivery, recombinant adeno-associated vectors (rAAVs) interact with blood-borne components in ways that can critically alter their therapeutic efficiencies. We have previously shown that interaction with human galectin 3 binding protein dramatically reduces rAAV-6 efficacy, whereas binding of mouse C-reactive protein improves rAAV-1 and rAAV-6 transduction effectiveness. Herein we have assessed, through qualitative and quantitative studies, the proteins from mouse and human sera that bind with rAAV-8 and rAAV-9, two vectors that are being considered for clinical trials for patients with neuromuscular disorders. We show that, in contrast to rAAV-1 and rAAV-6, there was a substantial similarity in protein binding patterns between mouse and human sera for these vector serotypes. To establish an in vivo role for the vector binding of these sera proteins, we chose to study platelet factor 4 (PF4), which interacts with both vectors in both mouse and human sera. Experiments using PF4-knockout mice showed that a complete lack of PF4 did not alter skeletal muscle transduction for these vectors, whereas heart transduction was moderately improved. Our results strongly support our position that the impact of serum proteins on the transduction properties of rAAV-8 and rAAV-9, already observed in mouse models, should be similar in human preclinical trials.

Tracking disease progression non-invasively in Duchenne and Becker muscular dystrophies

BACKGROUND

Analysis of muscle biopsies allowed to characterize the pathophysiological changes of Duchenne and Becker muscular dystrophies (D/BMD) leading to the clinical phenotype. Muscle tissue is often investigated during interventional dose finding studies to show in situ proof of concept and pharmacodynamics effect of the tested drug. Less invasive readouts are needed to objectively monitor patients' health status, muscle quality, and response to treatment. The identification of serum biomarkers correlating with clinical function and able to anticipate functional scales is particularly needed for personalized patient management and to support drug development programs.

METHODS

A large-scale proteomic approach was used to identify serum biomarkers describing pathophysiological changes (e.g. loss of muscle mass), association with clinical function, prediction of disease milestones, association with in vivo ³¹ P magnetic resonance spectroscopy data and dystrophin levels in muscles. Cross-sectional comparisons were performed to compare DMD patients, BMD patients, and healthy controls. A group of DMD patients was followed up for a median of 4.4 years to allow monitoring of individual disease trajectories based on yearly visits.

RESULTS

Cross-sectional comparison enabled to identify 10 proteins discriminating between healthy controls, DMD and BMD patients. Several proteins (285) were able to separate DMD from healthy, while 121 proteins differentiated between BMD and DMD; only 13 proteins separated BMD and healthy individuals. The concentration of specific proteins in serum was significantly associated with patients' performance (e.g. BMP6 serum levels and elbow flexion) or dystrophin levels (e.g. TIMP2) in BMD patients. Analysis of longitudinal trajectories allowed to identify 427 proteins affected over time indicating loss of muscle mass, replacement of muscle by adipose tissue, and cardiac involvement. Over-representation analysis of longitudinal data allowed to highlight proteins that could be used as pharmacodynamic biomarkers for drugs currently in clinical development.

CONCLUSIONS

Serum proteomic analysis allowed to not only discriminate among DMD, BMD, and healthy subjects, but it enabled to detect significant associations with clinical function, dystrophin levels, and disease progression.

Downregulation of miRNA-29, -23 and -21 in urine of Duchenne muscular dystrophy patients

AIM

To study the signature of 87 urinary miRNAs in Duchenne muscular dystrophy (DMD) patients, select the most dysregulated and determine statistically significant differences in their expression between controls, ambulant (A) and nonambulant (NA) DMD patients, and patients on different corticosteroid regimens. Patients/materials & methods: Urine was collected from control (n = 20), A (n = 31) and NA (n = 23) DMD patients. miRNA expression was measured by reverse transcription-quantitative PCR.

RESULTS

miR-29c-3p was significantly downregulated in A DMD patients while miR-23b-3p and miR-21-5p were significantly downregulated in NA DMD patients compared with age-matched controls.

CONCLUSION

miR-29c-3p, miR-23b-3p and miR-21-5p are promising novel noninvasive biomarkers for DMD, and miR-29c-3p levels are differentially affected by different steroid regimens, supporting the antifibrotic effect of steroid therapy.

High urinary ferritin reflects myoglobin iron evacuation in DMD patients

Duchenne muscular dystrophy (DMD) is an X-linked disease caused by mutations in the dystrophin gene leading to the absence of the normal dystrophin protein. The efforts of many laboratories brought new treatments of DMD to the reality, but ongoing and forthcoming clinical trials suffer from absence of valuable biomarkers permitting to follow the outcome of the treatment day by day and to adjust the treatment if needed. In the present study the levels of 128 urinary proteins including growth factors, cytokines and chemokines were compared in urine of DMD patients and age related control subjects by antibody array approach. Surprisingly, statistically significant difference was observed only for urinary ferritin whose level was 50 times higher in young DMD patients. To explain the observed high urinary ferritin content we analysed the levels of iron, iron containing proteins and proteins involved in regulation of iron metabolism in serum and urine of DMD patients and their age-matched healthy controls. Obtained data strongly suggest that elevated level of urinary ferritin is functionally linked to the renal management of myoglobin iron derived from leaky muscles of DMD patients. This first observation of the high level of ferritin in urine of DMD patients permits to consider this protein as a new urinary biomarker in muscular dystrophies and sheds light on the mechanisms of iron metabolism and kidney functioning in DMD.

Cross-sectional serum metabolomic study of multiple forms of muscular dystrophy

Muscular dystrophies are characterized by a progressive loss of muscle tissue and/or muscle function. While metabolic alterations have been described in patients’‐derived muscle biopsies, non‐invasive readouts able to describe these alterations are needed in order to objectively monitor muscle condition and response to treatment targeting metabolic abnormalities. We used a metabolomic approach to study metabolites concentration in serum of patients affected by multiple forms of muscular dystrophy such as Duchenne and Becker muscular dystrophies, limb‐girdle muscular dystrophies type 2A and 2B, myotonic dystrophy type 1 and facioscapulohumeral muscular dystrophy. We show that 15 metabolites involved in energy production, amino acid metabolism, testosterone metabolism and response to treatment with glucocorticoids were differentially expressed between healthy controls and Duchenne patients. Five metabolites were also able to discriminate other forms of muscular dystrophy. In particular, creatinine and the creatine/creatinine ratio were significantly associated with Duchenne patients performance as assessed by the 6‐minute walk test and north star ambulatory assessment. The obtained results provide evidence that metabolomics analysis of serum samples can provide useful information regarding muscle condition and response to treatment, such as to glucocorticoids treatment.

Proteomic profiling of mdx-4cv serum reveals highly elevated levels of the inflammation-induced plasma marker haptoglobin in muscular dystrophy

X-linked muscular dystrophy is caused by primary abnormalities in the Dmd gene and is characterized by the almost complete loss of the membrane cytoskeletal protein dystrophin, which triggers sarcolemmal instability, abnormal calcium homeostasis, increased proteolysis and impaired excitation-contraction coupling. In addition to progressive necrosis, crucial secondary pathologies are represented by myofibrosis and the invasion of immune cells in damaged muscle fibres. In order to determine whether these substantial changes within the skeletal musculature are reflected by an altered rate of protein release into the circulatory system or other plasma fluctuations, we used label-free mass spectrometry to characterize serum from the mdx-4cv model of Duchenne muscular dystrophy. Comparative proteomics revealed a large number of increased vs. decreased protein species in mdx-4cv serum. A serum component with greatly elevated levels was identified as the inflammation-inducible plasma marker haptoglobin. This acute phase response protein is usually secreted in relation to tissue damage and sterile inflammation. Both immunoblot analyses and enzyme-linked immunosorbent assays confirmed the increased concentration of haptoglobin in crude mdx-4cv serum. This suggests that haptoglobin, in conjunction with other altered serum proteins, represents a novel diagnostic, prognostic and/or therapy-monitoring biomarker candidate to evaluate the inflammatory response in the mdx-4cv animal model of dystrophinopathy.

Identification of serum protein biomarkers for utrophin based DMD therapy

Despite promising therapeutic avenues, there is currently no effective treatment for Duchenne muscular dystrophy (DMD), a lethal monogenic disorder caused by the loss of the large cytoskeletal protein, dystrophin. A highly promising approach to therapy, applicable to all DMD patients irrespective to their genetic defect, is to modulate utrophin, a functional paralogue of dystrophin, able to compensate for the primary defects of DMD restoring sarcolemmal stability. One of the major difficulties in assessing the effectiveness of therapeutic strategies is to define appropriate outcome measures. In the present study, we utilised an aptamer based proteomics approach to profile 1,310 proteins in plasma of wild-type, mdx and Fiona (mdx overexpressing utrophin) mice. Comparison of the C57 and mdx sera revealed 83 proteins with statistically significant >2 fold changes in dystrophic serum abundance. A large majority of previously described biomarkers (ANP32B, THBS4, CAMK2A/B/D, CYCS, CAPNI) were normalised towards wild-type levels in Fiona animals. This work also identified potential mdx markers specific to increased utrophin (DUS3, TPI1) and highlights novel mdx biomarkers (GITR, MYBPC1, HSP60, SIRT2, SMAD3, CNTN1). We define a panel of putative protein mdx biomarkers to evaluate utrophin based strategies which may help to accelerate their translation to the clinic.

Establishment of a highly sensitive sandwich ELISA for the N-terminal fragment of titin in urine

Muscle damage and loss of muscle mass are triggered by immobilization, loss of appetite, dystrophies and chronic wasting diseases. In addition, physical exercise causes muscle damage. In damaged muscle, the N-terminal and C-terminal regions of titin, a giant sarcomere protein, are cleaved by calpain-3, and the resulting fragments are excreted into the urine via glomerular filtration. Therefore, we considered titin fragments as promising candidates for reliable and non-invasive biomarkers of muscle injury. Here, we established a sandwich ELISA that can measure the titin N-terminal fragment over a biologically relevant range of concentrations, including those in urine samples from older, non-ambulatory Duchenne muscular dystrophy patients and from healthy donors under everyday life conditions and after exercise. Our results indicate that the established ELISA could be a useful tool for the screening of muscular dystrophies and also for monitoring the progression of muscle disease, evaluating the efficacy of therapeutic approaches, and investigating exercise-related sarcomeric disruption and repair processes.

Selective release of muscle-specific, extracellular microRNAs during myogenic differentiation

MyomiRs are muscle-specific microRNAs (miRNAs) that regulate myoblast proliferation and differentiation. Extracellular myomiRs (ex-myomiRs) are highly enriched in the serum of Duchenne Muscular Dystrophy (DMD) patients and dystrophic mouse models and consequently have potential as disease biomarkers. The biological significance of miRNAs present in the extracellular space is not currently well understood. Here we demonstrate that ex-myomiR levels are elevated in perinatal muscle development, during the regenerative phase that follows exercise-induced myoinjury, and concomitant with myoblast differentiation in culture. Whereas ex-myomiRs are progressively and specifically released by differentiating human primary myoblasts and C2C12 cultures, chemical induction of apoptosis in C2C12 cells results in indiscriminate miRNA release. The selective release of myomiRs as a consequence of cellular differentiation argues against the idea that they are solely waste products of muscle breakdown, and suggests they may serve a biological function in specific physiological contexts. Ex-myomiRs in culture supernatant and serum are predominantly non-vesicular, and their release is independent of ceramide-mediated vesicle secretion. Furthermore, ex-myomiRs levels are reduced in aged dystrophic mice, likely as a consequence of chronic muscle wasting. In conclusion, we show that myomiR release accompanies periods of myogenic differentiation in cell culture and in vivo. Serum myomiR abundance is therefore a function of the regenerative/degenerative status of the muscle, overall muscle mass, and tissue expression levels. These findings have implications for the use of ex-myomiRs as biomarkers for DMD disease progression and monitoring response to therapy.

Neo-epitope Peptides as Biomarkers of Disease Progression for Muscular Dystrophies and Other Myopathies

For several decades, serological biomarkers of neuromuscular diseases as dystrophies, myopathies and myositis have been limited to routine clinical biochemistry panels. Gauging the pathological progression is a prerequisite for proper treatment and therefore identifying accessible, easy to monitor biomarkers that can predict the disease progression would be an important advancement. Most muscle diseases involve accelerated muscle fiber degradation, inflammation, fatty tissue substitution and/or fibrosis. All these pathological traits have been shown to give rise to serological peptide biomarkers in other tissues, underlining the potential application of existing biomarkers of such traits in muscle disorders. A significant quantity of tissue is involved in these pathological mechanisms alongside with qualitative changes in protein turnover in myofibrillar, extra-cellular matrix and immunological cell protein fractions accompanied by alterations in body fluids. We propose that protein and peptides can leak out of the afflicted muscles and can be of use in diagnosis, prediction of pathology trajectory and treatment efficacy. Proteolytic cleavage systems are especially modulated during a range of muscle pathologies, thereby giving rise to peptides that are differentially released during disease manifestation. Therefore, we believe that pathology-specific post-translational modifications like cleavages can give rise to neoepitope peptides that may represent a promising class of peptides for discovery of biomarkers pertaining to neuromuscular diseases.

Circulating miRNAs are generic and versatile therapeutic monitoring biomarkers in muscular dystrophies

The development of medical approaches requires preclinical and clinical trials for assessment of therapeutic efficacy. Such evaluation entails the use of biomarkers, which provide information on the response to the therapeutic intervention. One newly-proposed class of biomarkers is the microRNA (miRNA) molecules. In muscular dystrophies (MD), the dysregulation of miRNAs was initially observed in muscle biopsy and later extended to plasma samples, suggesting that they may be of interest as biomarkers. First, we demonstrated that dystromiRs dysregulation occurs in MD with either preserved or disrupted expression of the dystrophin-associated glycoprotein complex, supporting the utilization of dystromiRs as generic biomarkers in MD. Then, we aimed at evaluation of the capacity of miRNAs as monitoring biomarkers for experimental therapeutic approach in MD. To this end, we took advantage of our previously characterized gene therapy approach in a mouse model for α-sarcoglycanopathy. We identified a dose-response correlation between the expression of miRNAs on both muscle tissue and blood serum and the therapeutic benefit as evaluated by a set of new and classically-used evaluation methods. This study supports the utility of profiling circulating miRNAs for the evaluation of therapeutic outcome in medical approaches for MD.

Clinical utility of serum biomarkers in Duchenne muscular dystrophy

Assessments of disease progression and response to therapies in Duchenne muscular dystrophy (DMD) patients remain challenging. Current DMD patient assessments include complex physical tests and invasive procedures such as muscle biopsies, which are not suitable for young children. Defining alternative, less invasive and objective outcome measures to assess disease progression and response to therapy will aid drug development and clinical trials in DMD. In this review we highlight advances in development of non-invasive blood circulating biomarkers as a means to assess disease progression and response to therapies in DMD.

Identification of novel, therapy-responsive protein biomarkers in a mouse model of Duchenne muscular dystrophy by aptamer-based serum proteomics

There is currently an urgent need for biomarkers that can be used to monitor the efficacy of experimental therapies for Duchenne Muscular Dystrophy (DMD) in clinical trials. Identification of novel protein biomarkers has been limited due to the massive complexity of the serum proteome and the presence of a small number of very highly abundant proteins. Here we have utilised an aptamer-based proteomics approach to profile 1,129 proteins in the serum of wild-type and mdx (dystrophin deficient) mice. The serum levels of 96 proteins were found to be significantly altered (P < 0.001, q < 0.01) in mdx mice. Additionally, systemic treatment with a peptide-antisense oligonucleotide conjugate designed to induce Dmd exon skipping and recover dystrophin protein expression caused many of the differentially abundant serum proteins to be restored towards wild-type levels. Results for five leading candidate protein biomarkers (Pgam1, Tnni3, Camk2b, Cycs and Adamts5) were validated by ELISA in the mouse samples. Furthermore, ADAMTS5 was found to be significantly elevated in human DMD patient serum. This study has identified multiple novel, therapy-responsive protein biomarkers in the serum of the mdx mouse with potential utility in DMD patients.