Identification of altered gene expression in skeletal muscles from Duchenne muscular dystrophy patients

Synaptopodin-2 Isoforms Have Specific Binding Partners and Display Distinct, Muscle Cell Type-Specific Expression Patterns

Synaptopodin-2 (SYNPO2) is a protein associated with the Z-disc in striated muscle cells. It interacts with α-actinin and filamin C, playing a role in Z-disc maintenance under stress by chaperone-assisted selective autophagy (CASA). In smooth muscle cells, SYNPO2 is a component of dense bodies. Furthermore, it has been proposed to play a role in tumor cell proliferation and metastasis in many different kinds of cancers. Alternative transcription start sites and alternative splicing predict the expression of six putative SYNPO2 isoforms differing by extended amino- and/or carboxy-termini. Our analyses at mRNA and protein levels revealed differential expression of SYNPO2 isoforms in cardiac, skeletal and smooth muscle cells. We identified synemin, an intermediate filament protein, as a novel binding partner of the PDZ-domain in the amino-terminal extension of the isoforms mainly expressed in cardiac and smooth muscle cells, and demonstrated colocalization of SYNPO2 and synemin in both cell types. A carboxy-terminal extension, mainly expressed in smooth muscle cells, is sufficient for association with dense bodies and interacts with α-actinin. SYNPO2 therefore represents an additional and novel link between intermediate filaments and the Z-discs in cardiomyocytes and dense bodies in smooth muscle cells, respectively. In pathological skeletal muscle samples, we identified SYNPO2 in the central and intermediate zones of target fibers of patients with neurogenic muscular atrophy, and in nemaline bodies. Our findings help to understand distinct functions of individual SYNPO2 isoforms in different muscle tissues, but also in tumor pathology.

CMYA5 is a novel interaction partner of FHL2 in cardiac myocytes

Four-and-a-half LIM domains protein 2 (FHL2) is an anti-hypertrophic adaptor protein that regulates cardiac myocyte signalling and function. Herein, we identified cardiomyopathy-associated 5 (CMYA5) as a novel FHL2 interaction partner in cardiac myocytes. In vitro pull-down assays demonstrated interaction between FHL2 and the N- and C-terminal regions of CMYA5. The interaction was verified in adult cardiac myocytes by proximity ligation assays. Immunofluorescence and confocal microscopy demonstrated co-localisation in the same subcellular compartment. The binding interface between FHL2 and CMYA5 was mapped by peptide arrays. Exposure of neonatal rat ventricular myocytes to a CMYA5 peptide covering one of the FHL2 interaction sites led to an increase in cell area at baseline, but a blunted response to chronic phenylephrine treatment. In contrast to wild-type hearts, loss or reduced FHL2 expression in Fhl2-targeted knockout mouse hearts or in a humanised mouse model of hypertrophic cardiomyopathy led to redistribution of CMYA5 into the perinuclear and intercalated disc region. Taken together, our results indicate a direct interaction of the two adaptor proteins FHL2 and CMYA5 in cardiac myocytes, which might impact subcellular compartmentation of CMYA5.

Titin M-line insertion sequence 7 is required for proper cardiac function in mice

Titin is a giant sarcomeric protein that is involved in a large number of functions, with a primary role in skeletal and cardiac sarcomere organization and stiffness. The titin gene (TTN) is subject to various alternative splicing events, but in the region that is present at the M-line, the only exon that can be spliced out is Mex5, which encodes for the insertion sequence 7 (is7). Interestingly, in the heart, the majority of titin isoforms are Mex5+, suggesting a cardiac role for is7. Here, we performed comprehensive functional, histological, transcriptomic, microscopic and molecular analyses of a mouse model lacking the Ttn Mex5 exon (ΔMex5), and revealed that the absence of the is7 is causative for dilated cardiomyopathy. ΔMex5 mice showed altered cardiac function accompanied by increased fibrosis and ultrastructural alterations. Abnormal expression of excitation-contraction coupling proteins was also observed. The results reported here confirm the importance of the C-terminal region of titin in cardiac function and are the first to suggest a possible relationship between the is7 and excitation-contraction coupling. Finally, these findings give important insights for the identification of new targets in the treatment of titinopathies.

A pig BodyMap transcriptome reveals diverse tissue physiologies and evolutionary dynamics of transcription

A comprehensive transcriptomic survey of pigs can provide a mechanistic understanding of tissue specialization processes underlying economically valuable traits and accelerate their use as a biomedical model. Here we characterize four transcript types (lncRNAs, TUCPs, miRNAs, and circRNAs) and protein-coding genes in 31 adult pig tissues and two cell lines. We uncover the transcriptomic variability among 47 skeletal muscles, and six adipose depots linked to their different origins, metabolism, cell composition, physical activity, and mitochondrial pathways. We perform comparative analysis of the transcriptomes of seven tissues from pigs and nine other vertebrates to reveal that evolutionary divergence in transcription potentially contributes to lineage-specific biology. Long-range promoter–enhancer interaction analysis in subcutaneous adipose tissues across species suggests evolutionarily stable transcription patterns likely attributable to redundant enhancers buffering gene expression patterns against perturbations, thereby conferring robustness during speciation. This study can facilitate adoption of the pig as a biomedical model for human biology and disease and uncovers the molecular bases of valuable traits.

A comprehensive transcriptomic survey of the pig could enable mechanistic understanding of tissue specialization and accelerate its use as a biomedical model. Here the authors characterize four distinct transcript types in 31 adult pig tissues to dissect their distinct structural and transcriptional features and uncover transcriptomic variability related to tissue physiology.

Myospryn deficiency leads to impaired cardiac structure and function and schizophrenia-associated symptoms

The desmin-associated protein myospryn, encoded by the cardiomyopathy-associated gene 5 (CMYA5), is a TRIM-like protein associated to the BLOC-1 (Biogenesis of Lysosomes Related Organelles Complex 1) protein dysbindin. Human myospryn mutations are linked to both cardiomyopathy and schizophrenia; however, there is no evidence of a direct causative link of myospryn to these diseases. Therefore, we sought to unveil the role of myospryn in heart and brain. We have genetically inactivated the myospryn gene by homologous recombination and demonstrated that myospryn null hearts have dilated phenotype and compromised cardiac function. Ultrastructural analyses revealed that the sarcomere organization is not obviously affected; however, intercalated disk (ID) integrity is impaired, along with mislocalization of ID and sarcoplasmic reticulum (SR) protein components. Importantly, cardiac and skeletal muscles of myospryn null mice have severe mitochondrial defects with abnormal internal vacuoles and extensive cristolysis. In addition, swollen SR and T-tubules often accompany the mitochondrial defects, strongly implying a potential link of myospryn together with desmin to SR- mitochondrial physical and functional cross-talk. Furthermore, given the reported link of human myospryn mutations to schizophrenia, we performed behavioral studies, which demonstrated that myospryn-deficient male mice display disrupted startle reactivity and prepulse inhibition, asocial behavior, decreased exploratory behavior, and anhedonia. Brain neurochemical and ultrastructural analyses revealed prefrontal-striatal monoaminergic neurotransmitter defects and ultrastructural degenerative aberrations in cerebellar cytoarchitecture, respectively, in myospryn-deficient mice. In conclusion, myospryn is essential for both cardiac and brain structure and function and its deficiency leads to cardiomyopathy and schizophrenia-associated symptoms.

A schizophrenia associated CMYA5 allele displays differential binding with desmin

CMYA5 is a candidate gene for schizophrenia because of the genetic association of variant rs10043986 (C > T) to this severe mental disorder. Studies of CMYA5 and its gene product, myospryn, in the brain and neuronal cells have not been previously reported. The SNP rs10043986 changes the 4,063rd amino acid from Pro to Leu, which is likely to alter protein function. To understand its potential role in the brain, we examined the neuronal expression of myospryn and its binding partner, desmin, an intermediate filament (IF) protein, and investigated how the two alleles of myospryn affect its binding to desmin. Myospryn and desmin are shown to be expressed in the brain and myospryn is shown to localize to the cytoplasm and nucleus of myoblast, neuroblastoma, and glioblastoma cell lines. Peripherin and vimentin, known brain IF proteins, have high protein similarity to desmin but were found not to interact with myospryn using yeast two-hybrid (Y2H). Using a quantitative Y2H assay and surface plasmon resonance, the T allele (Leu) of rs10043986 was found to have stronger binding to desmin than the C allele (Pro). Based on findings described in this report, we hypothesize that the interaction between myospryn to IF provides structural support and efficient rearrangement of the cytoskeleton network during early neuritogenesis.

Associations of sex hormone-binding globulin and testosterone with genome-wide DNA methylation

Background

Levels of sex hormone-binding globulin (SHBG) and the androgen testosterone have been associated with risk of diseases throughout the lifecourse. Although both SHBG and testosterone have been shown to be highly heritable, only a fraction of that heritability has been explained by genetic studies. Epigenetic modifications such as DNA methylation may explain some of the missing heritability and could potentially inform biological knowledge of endocrine disease mechanisms involved in development of later life disease. Using data from the Avon Longitudinal Study of Parents and Children (ALSPAC), we explored cross-sectional associations of SHBG, total testosterone and bioavailable testosterone in childhood (males only) and adolescence (both males and females) with genome-wide DNA methylation. We also report associations of a SHBG polymorphism (rs12150660) with DNA methylation, which leads to differential levels of SHBG in carriers, as a genetic proxy of circulating SHBG levels.

Results

We identified several novel sites and genomic regions where levels of SHBG, total testosterone, and bioavailable testosterone were associated with DNA methylation, including one region associated with total testosterone in males (annotated to the KLHL31 gene) in both childhood and adolescence and a second region associated with bioavailable testosterone (annotated to the CMYA5 gene) at both time-points. We also identified one region where both SHBG and bioavailable testosterone in males in childhood (annotated to the ZNF718 gene) was associated with DNA methylation.

Conclusion

Our findings have important implications in the understanding of the biological processes of SHBG and testosterone, with the potential for future work to determine the molecular mechanisms that could underpin these associations.

Electronic supplementary material

The online version of this article (10.1186/s12863-018-0703-y) contains supplementary material, which is available to authorized users.

Ryanodine receptors are part of the myospryn complex in cardiac muscle

The Cardiomyopathy-associated gene 5 (Cmya5) encodes myospryn, a large tripartite motif (TRIM)-related protein found predominantly in cardiac and skeletal muscle. Cmya5 is an expression biomarker for a number of diseases affecting striated muscle and may also be a schizophrenia risk gene. To further understand the function of myospryn in striated muscle, we searched for additional myospryn paralogs. Here we identify a novel muscle-expressed TRIM-related protein minispryn, encoded by Fsd2, that has extensive sequence similarity with the C-terminus of myospryn. Cmya5 and Fsd2 appear to have originated by a chromosomal duplication and are found within evolutionarily-conserved gene clusters on different chromosomes. Using immunoaffinity purification and mass spectrometry we show that minispryn co-purifies with myospryn and the major cardiac ryanodine receptor (RyR2) from heart. Accordingly, myospryn, minispryn and RyR2 co-localise at the junctional sarcoplasmic reticulum of isolated cardiomyocytes. Myospryn redistributes RyR2 into clusters when co-expressed in heterologous cells whereas minispryn lacks this activity. Together these data suggest a novel role for the myospryn complex in the assembly of ryanodine receptor clusters in striated muscle.

Multi-level omics analysis in a murine model of dystrophin loss and therapeutic restoration

Duchenne muscular dystrophy (DMD) is a classical monogenic disorder, a model disease for genomic studies and a priority candidate for regenerative medicine and gene therapy. Although the genetic cause of DMD is well known, the molecular pathogenesis of disease and the response to therapy are incompletely understood. Here, we describe analyses of protein, mRNA and microRNA expression in the tibialis anterior of the mdx mouse model of DMD. Notably, 3272 proteins were quantifiable and 525 identified as differentially expressed in mdx muscle (P < 0.01). Therapeutic restoration of dystrophin by exon skipping induced widespread shifts in protein and mRNA expression towards wild-type expression levels, whereas the miRNome was largely unaffected. Comparison analyses between datasets showed that protein and mRNA ratios were only weakly correlated (r = 0.405), and identified a multitude of differentially affected cellular pathways, upstream regulators and predicted miRNA-target interactions. This study provides fundamental new insights into gene expression and regulation in dystrophic muscle.

The CMYA5 gene confers risk for both schizophrenia and major depressive disorder in the Han Chinese population

OBJECTIVES

A recent genome-wide association study (GWAS) of the European population implicated the CMYA5 gene in schizophrenia. Previous functional studies showed that the CMYA5 protein can interact with DTNBP1 and PKA, providing further support for a role of CMYA5 in the pathogenesis of schizophrenia. However, this association requires additional validation in independent populations.

METHODS

To validate the association between CMYA5 and schizophrenia and major depressive disorder, we genotyped 16 SNPs within the CMYA5 gene and performed case-control studies in 1330 schizophrenia patients, 1045 patients with major depressive disorder, and 1235 normal controls. All patients were of Han Chinese origin.

RESULTS

rs6883197 and rs259127 were significantly associated with schizophrenia, and rs12514461, rs259127, and rs7343 were associated with major depressive disorder. Additionally, one risk haplotype of rs16877109-rs3828611 (G-G) was associated with both schizophrenia (P = 0.0000784, after correction) and major depressive disorder (P = 0.00230, after correction).

CONCLUSIONS

Our findings support the idea that specific alleles and haplotype in the CMYA5 confer genetic risk for both schizophrenia and major depressive disorder in the Han Chinese population.

Prostate cancer cell migration induced by myopodin isoforms is associated with formation of morphologically and biochemically distinct actin networks

Myopodin is an actin-binding protein that promotes cancer cell migration in response to serum stimulation and is associated with invasive tumor development. To determine whether enhanced migration reflects changes in actin cytoskeleton remodeling, fluorescence confocal microscopy was used to examine the composition and morphology of filamentous actin structures in mock-transduced cells vs. stably transduced PC3 cells expressing human myopodin isoforms, and the chemokinetic response of cells was quantified using transwell assays. The same approaches were used to analyze the effects of external migration stimuli, actin polymerization inhibitors or deletion of the isoform-specific amino- and/or carboxy termini on cell migration and actin bundle formation. Results indicate that the termini of the myopodin isoforms differentially alter the formation of morphologically distinct F-actin networks that also differ in their myosin and myopodin staining patterns. Furthermore, enhanced cell migration was reduced by >50% when actin bundle formation was impaired by myopodin-truncation, low concentrations of an actin polymerization inhibitor, or in the absence of an external migration stimulus. Human myopodin isoforms are therefore potent regulators of stress fiber formation, inducing the formation of biochemically and morphologically distinct F-actin networks in the cell body whose presence directly correlates with increased cell migration.

Μyospryn: a multifunctional desmin-associated protein

Desmin, the muscle-specific intermediate filament protein, forms a 3D scaffold that links the contractile apparatus to the costameres of plasma membrane, intercalated disks, the nucleus, and also other membranous organelles. The cellular scaffold formed by desmin and its binding partners might be implicated in signaling and trafficking processes, vital mechanisms for the survival of the mammalian cell. One novel desmin-associated protein is the tripartite motif-like protein myospryn. Myospryn was initially identified as an associated partner to the biogenesis of lysosome-related organelles complex 1 protein dysbindin, implicating its potential involvement in vesicle trafficking and organelle biogenesis and/or positioning. Myospryn is also an A kinase anchoring protein, raising the possibility that together with desmin and other cytoskeletal and signaling proteins, it could participate in the subcellular targeting of protein kinase A activity in striated muscle. As with desmin, different members of this scaffold might play a crucial role in the pathogenesis of muscle disease, since any disturbance in these highly coordinated signaling pathways is expected to compromise efficient maintenance of structure-function integrity of muscle and lead to different cardiac and skeletal myopathies.

Proteomic assessment of the acute phase of dystrophin deficiency in mdx mice

Duchenne muscular dystrophy (DMD) is caused by the absence of a functional dystrophin protein and is modeled by the mdx mouse. The mdx mouse suffers an early necrotic bout in the hind limb muscles lasting from approximately 4 to 7 weeks. The purpose of this investigation was to determine the extent to which dystrophin deficiency changed the proteome very early in the disease process. In order to accomplish this, proteins from gastrocnemius from 6-week-old C57 (n = 6) and mdx (n = 6) mice were labeled with fluorescent dye and subjected to two-dimensional differential in-gel electrophoresis (2D-DIGE). Resulting differentially expressed spots were excised and protein identity determined via MALDI-TOF followed by database searching using MASCOT. Proteins of the immediate energy system and glycolysis were generally down-regulated in mdx mice compared to C57 mice. Conversely, expression of proteins involved in the Kreb's cycle and electron transport chain were increased in dystrophin-deficient muscle compared to control. Expression of cytoskeletal components, including tubulins, vimentin, and collagen, were increased in mdx mice compared to C57 mice. Importantly, these changes are occurring at only 6 weeks of age and are caused by acute dystrophin deficiency rather than more chronic injury. These data may provide insight regarding early pathologic changes occurring in dystrophin-deficient skeletal muscle.

The molecular characterization and associations of porcine cardiomyopathy asssociated 5 (CMYA5) gene with carcass trait and meat quality

The cardiomyopathy associated 5 (CMYA5) gene was also called TRIM76, which was belonged to the tripartite motif super family of proteins (TRIM). It was a direct transcriptional target for MEF2A and it played an important role in myofibrillogenesis. In the present study, a 12056 bp cDNA sequence of the porcine CMYA5 gene was obtained by RT-PCR. The sequence encoded a large protein consisting of 4003 amino acids and the carboxyl terminus of the predicted CMYA5 protein comprised of a B-box coiled-coil, two fibronectin type III (FN3) repeats, and SPRY domains. The porcine CMYA5 gene was assigned to chromosome 2q21-24 by using the radiation hybrid (IMpRH) panel, and it was significantly linked to microsatellite Sw1602 with LOD scores of 6.74. Semi-quantitative RT-PCR revealed that the porcine CMYA5 gene was broadly expressed in all seven tissues(heart, liver, spleen, lung, kidney, skeletal muscle and adipose)harvested from different developmental stages(new born, five weeks and adult tongcheng pigs), with a high level in heart and skeletal muscle. One SNP (A7189C), leading to the amino acid alteration from the Ile residue to the Leu residue, was found and detected by BspTI PCR-restriction fragment length polymorphism. The association analysis revealed that the substitution of A7189C had significant associations with the percentage of ham (p < 0.05), water loss (p < 0.01) and intramuscular fat (p < 0.05). These results provide the evidence that the porcine CMYA5 gene can act as a potential candidate gene affecting pig meat quality.

Interactions with M-band titin and calpain 3 link myospryn (CMYA5) to tibial and limb-girdle muscular dystrophies

Mutations in the C terminus of titin, situated at the M-band of the striated muscle sarcomere, cause tibial muscular dystrophy (TMD) and limb-girdle muscular dystrophy (LGMD) type 2J. Mutations in the protease calpain 3 (CAPN3), in turn, lead to LGMD2A, and secondary CAPN3 deficiency in LGMD2J suggests that the pathomechanisms of the diseases are linked. Yeast two-hybrid screens carried out to elucidate the molecular pathways of TMD/LGMD2J and LGMD2A resulted in the identification of myospryn (CMYA5, cardiomyopathy-associated 5) as a binding partner for both M-band titin and CAPN3. Additional yeast two-hybrid and coimmunoprecipitation studies confirmed both interactions. The interaction of myospryn and M-band titin was supported by localization of endogenous and transfected myospryn at the M-band level. Coexpression studies showed that myospryn is a proteolytic substrate for CAPN3 and suggested that myospryn may protect CAPN3 from autolysis. Myospryn is a muscle-specific protein of the tripartite motif superfamily, reported to function in vesicular trafficking and protein kinase A signaling and implicated in the pathogenesis of Duchenne muscular dystrophy. The novel interactions indicate a role for myospryn in the sarcomeric M-band and may be relevant for the molecular pathomechanisms of TMD/LGMD2J and LGMD2A.

Transcriptomic analysis of dystrophin RNAi knockdown reveals a central role for dystrophin in muscle differentiation and contractile apparatus organization

BACKGROUND

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disorder caused by mutations in the dystrophin gene. DMD has a complex and as yet incompletely defined molecular pathophysiology hindering development of effective ameliorative approaches. Transcriptomic studies so far conducted on dystrophic cells and tissues suffer from non-specific changes and background noise due to heterogeneous comparisons and secondary pathologies. A study design in which a perfectly matched control cell population is used as reference for transcriptomic studies will give a much more specific insight into the effects of dystrophin deficiency and DMD pathophysiology.

RESULTS

Using RNA interference (RNAi) to knock down dystrophin in myotubes from C57BL10 mice, we created a homogenous model to study the transcriptome of dystrophin-deficient myotubes. We noted significant differences in the global gene expression pattern between these myotubes and their matched control cultures. In particular, categorical analyses of the dysregulated genes demonstrated significant enrichment of molecules associated with the components of muscle cell contractile unit, ion channels, metabolic pathways and kinases. Additionally, some of the dysregulated genes could potentially explain conditions and endophenotypes associated with dystrophin deficiency, such as dysregulation of calcium homeostasis (Pvalb and Casq1), or cardiomyopathy (Obscurin, Tcap). In addition to be validated by qPCR, our data gains another level of validity by affirmatively reproducing several independent studies conducted previously at genes and/or protein levels in vivo and in vitro.

CONCLUSION

Our results suggest that in striated muscles, dystrophin is involved in orchestrating proper development and organization of myofibers as contractile units, depicting a novel pathophysiology for DMD where the absence of dystrophin results in maldeveloped myofibers prone to physical stress and damage. Therefore, it becomes apparent that any gene therapy approaches for DMD should target early stages in muscle development to attain a maximum clinical benefit. With a clear and specific definition of the transcriptome of dystrophin deficiency, manipulation of identified dysregulated molecules downstream of dystrophin may lead to novel ameliorative approaches for DMD.

The sarcomeric Z-disc component myopodin is a multiadapter protein that interacts with filamin and alpha-actinin

Here we introduce myopodin as a novel filamin C binding partner. Corroborative yeast two-hybrid and biochemical analyses indicate that the central part of myopodin that shows high homology to the closely related protein synaptopodin and that is common to all its currently known or predicted variants interacts with filamin C immunoglobulin-like domains 20-21. A detailed characterization of the previously described interaction between myopodin and alpha-actinin demonstrates for the first time that myopodin contains three independent alpha-actinin-binding sites. Newly developed myopodin-specific antibodies reveal expression at the earliest stages of in vitro differentiation of human skeletal muscle cells preceding the expression of sarcomeric alpha-actinin. Myopodin colocalizes with filamin and alpha-actinin during all stages of muscle development. By contrast, colocalization with its previously identified binding partner zyxin is restricted to early developmental stages. Genetic and cellular analyses of skeletal muscle provided direct evidence for an alternative transcriptional start site in exon three, corroborating the expression of a myopodin variant lacking the PDZ domain encoded by exons 1 and 2 in skeletal muscle. We conclude that myopodin is a multiadapter protein of the sarcomeric Z-disc that links nascent myofibrils to the sarcolemma via zyxin, and might play a role in early assembly and stabilization of the Z-disc. Mutations in FLNC, ACTN2 and several other genes encoding Z-disc-related proteins cause myopathy and cardiomyopathy. Its localization and its association with the myopathy-associated proteins filamin C and alpha-actinin make myopodin an interesting candidate for a muscle disease gene.

Loss of positive allosteric interactions between neuronal nitric oxide synthase and phosphofructokinase contributes to defects in glycolysis and increased fatigability in muscular dystrophy

Duchenne muscular dystrophy (DMD) involves a complex pathophysiology that is not easily explained by the loss of the protein dystrophin, the primary defect in DMD. Instead, many features of the pathology are attributable to the secondary loss of neuronal nitric oxide synthase (nNOS) from dystrophin-deficient muscle. In this investigation, we tested whether the loss of nNOS contributes to the increased fatigability of mdx mice, a model of DMD. Our findings show that the expression of a muscle-specific, nNOS transgene increases the endurance of mdx mice and enhances glycogen metabolism during treadmill-running, but did not affect vascular perfusion of muscles. We also find that the specific activity of phosphofructokinase (PFK; the rate limiting enzyme in glycolysis) is positively affected by nNOS in muscle; PFK-specific activity is significantly reduced in mdx muscles and the muscles of nNOS null mutants, but significantly increased in nNOS transgenic muscles and muscles from mdx mice that express the nNOS transgene. PFK activity measured under allosteric conditions was significantly increased by nNOS, but unaffected by endothelial NOS or inducible NOS. The specific domain of nNOS that positively regulates PFK activity was assayed by cloning and expressing different domains of nNOS and assaying their effects on PFK activity. This approach yielded a polypeptide that included the flavin adenine dinucleotide (FAD)-binding domain of nNOS as the region of the molecule that promotes PFK activity. Smaller peptides in this domain were then synthesized and used in activity assays that showed a 36-amino acid peptide in the FAD-binding domain in which most of the positive allosteric activity of nNOS for PFK resides. Mapping this peptide onto the structure of nNOS shows that the peptide is exposed on the surface, readily available for binding. Collectively, these findings indicate that defects in glycolytic metabolism and increased fatigability in dystrophic muscle may be caused in part by the loss of positive allosteric interactions between nNOS and PFK.

Biology of myospryn: what's known?

Myospryn (CMYA5, cardiomyopathy-associated 5) is a muscle-specific member of the TRIM superfamily, discovered a few years ago. Properties and functions of the little-studied protein remain largely enigmatic, but identified interactions have suggested that myospryn is involved in two seemingly distinct processes, protein kinase A signalling and vesicular trafficking. Recent findings have implicated myospryn in Duchenne muscular dystrophy and cardiac disease, making it an exciting new player in the field of muscle biology and pathology.

In vitro characterization of native mammalian smooth-muscle protein synaptopodin 2

An analysis of the primary structure of the actin-binding protein fesselin revealed it to be the avian homologue of mammalian synaptopodin 2 [Schroeter, Beall, Heid, and Chalovich (2008) Biochem. Biophys. Res. Commun. 371, 582-586]. We isolated two synaptopodin 2 isoforms from rabbit stomach that corresponded to known types of human synaptopodin 2. The purification scheme used was that developed for avian fesselin. These synaptopodin 2 forms shared several key functions with fesselin. Both avian fesselin and mammalian synaptopodin 2 bound to Ca(2+)-calmodulin, alpha-actinin and smooth-muscle myosin. In addition, both proteins stimulated the polymerization of actin in a Ca(2+)-calmodulin-dependent manner. Synaptopodin 2 has never before been shown to polymerize actin in the absence of alpha-actinin, to polymerize actin in a Ca(2+)-calmodulin-dependent manner, or to bind to Ca(2+)-calmodulin or myosin. These properties are consistent with the proposed function of synaptopodin 2 in organizing the cytoskeleton.

Deregulated protein kinase A signaling and myospryn expression in muscular dystrophy

Alterations in signaling pathway activity have been implicated in the pathogenesis of Duchenne muscular dystrophy, a degenerative muscle disease caused by a deficiency in the costameric protein dystrophin. Accordingly, the notion of the dystrophin-glycoprotein complex, and by extension the costamere, as harboring signaling components has received increased attention in recent years. The localization of most, if not all, signaling enzymes to this subcellular region relies on interactions with scaffolding proteins directly or indirectly associated with the dystrophin-glycoprotein complex. One of these scaffolds is myospryn, a large, muscle-specific protein kinase A (PKA) anchoring protein or AKAP. Previous studies have demonstrated a dysregulation of myospryn expression in human Duchenne muscular dystrophy, suggesting a connection to the pathophysiology of the disorder. Here we report that dystrophic muscle exhibits reduced PKA activity resulting, in part, from severely mislocalized myospryn and the type II regulatory subunit (RIIalpha) of PKA. Furthermore, we show that myospryn and dystrophin coimmunoprecipitate in native muscle extracts and directly interact in vitro. Our findings reveal for the first time abnormalities in the PKA signal transduction pathway and myospryn regulation in dystrophin deficiency.

Angiotensin II type 1 receptor blockade attenuates TGF-beta-induced failure of muscle regeneration in multiple myopathic states

Skeletal muscle has the ability to achieve rapid repair in response to injury or disease. Many individuals with Marfan syndrome (MFS), caused by a deficiency of extracellular fibrillin-1, exhibit myopathy and often are unable to increase muscle mass despite physical exercise. Evidence suggests that selected manifestations of MFS reflect excessive signaling by transforming growth factor (TGF)-beta (refs. 2,3). TGF-beta is a known inhibitor of terminal differentiation of cultured myoblasts; however, the functional contribution of TGF-beta signaling to disease pathogenesis in various inherited myopathic states in vivo remains unknown. Here we show that increased TGF-beta activity leads to failed muscle regeneration in fibrillin-1-deficient mice. Systemic antagonism of TGF-beta through administration of TGF-beta-neutralizing antibody or the angiotensin II type 1 receptor blocker losartan normalizes muscle architecture, repair and function in vivo. Moreover, we show TGF-beta-induced failure of muscle regeneration and a similar therapeutic response in a dystrophin-deficient mouse model of Duchenne muscular dystrophy.

Fibre type-specific increase in passive muscle tension in spinal cord-injured subjects with spasticity

Patients with spasticity typically present with an increased muscle tone that is at least partly caused by an exaggerated stretch reflex. However, intrinsic changes in the skeletal muscles, such as altered mechanical properties of the extracellular matrix or the cytoskeleton, have been reported in response to spasticity and could contribute to hypertonia, although the underlying mechanisms are poorly understood. Here we examined the vastus lateralis muscles from spinal cord-injured patients with spasticity (n = 7) for their passive mechanical properties at three different levels of structural organization, in comparison to healthy controls (n = 7). We also assessed spasticity-related alterations in muscle protein expression and muscle ultrastructure. At the whole-muscle level in vivo, we observed increased passive tension (PT) in some spasticity patients particularly at long muscle lengths, unrelated to stretch reflex activation. At the single-fibre level, elevated PT was found in cells expressing fast myosin heavy chain (MyHC) isoforms, especially MyHC-IIx, but not in those expressing slow MyHC. Type IIx fibres were present in higher than normal proportions in spastic muscles, whereas type I fibres were proportionately reduced. At the level of the isolated myofibril, however, there were no differences in PT between patients and controls. The molecular size of the giant protein titin, a main contributor to PT, was unchanged in spasticity, as was the titin : MyHC ratio and the relative desmin content. Electron microscopy revealed extensive ultrastructural changes in spastic muscles, especially expanded connective tissue, but also decreased mitochondrial volume fraction and appearance of intracellular amorphous material. Results strongly suggest that the global passive muscle stiffening in spasticity patients is caused to some degree by elevated PT of the skeletal muscles themselves. We conclude that this increased PT component arises not only from extracellular matrix remodelling, but also from structural and functional adaptations inside the muscle cells, which alter their passive mechanical properties in response to spasticity in a fibre type-dependent manner.

A new technique for the quantitative assessment of 8-oxoguanine in nuclear DNA as a marker of oxidative stress. Application to dystrophin-deficient DMD skeletal muscles

This is the first report on the development of an immunohistochemical technique, combined with quantitative image analysis, for the assessment of oxidative stress quantitatively in nuclear DNA in situ, and its application to measure DNA damage in Duchenne muscular dystrophic (DMD) muscles. Three sequential staining procedures for cell nuclei, a cell marker, and a product of oxidative DNA damage, 8-oxoguanine (8-oxoG), were performed. First, the nuclei in muscle sections were stained with Neutral Red followed by the capture of their images with an image analysis system used for absorbance measurements. Second, the same sections were then immunostained for laminin in basement membranes as the cell marker. Next, the sections were treated with 2 N HCl to remove the bound Neutral Red and to denature tissue DNA. Third, the sections were immunostained for 8-oxoG in DNA, using diaminobenzidine (DAB) to reveal the antibody complex. This was followed by capture of the images of the immunostained sections as previously. The absorbances at 451.2 nm of bound Neutral Red and DAB polymer oxides, the final product of 8-oxoG immunostaining, were measured in the same myonuclei in the sections. Analysis of these absorbances permitted indices of the 8-oxoG content, independent of the nuclear densities, to be determined in nuclear DNA in single myofibres and myosatellite cells surrounded by basement membranes. We found that the mean index for the myonuclei in biceps brachii muscles of 2- to 7-year-old patients was 14% higher than that in age-matched normal controls. This finding of the increased oxidative stress in the myonuclei in young DMD muscles agrees with the previous reports of increased oxidative stress in the cytoplasm in the DMD myofibres and myosatellite cells. The present technique for the quantitative assessment of oxidative stress in nuclear DNA in situ is applicable not only in biomedical research but also in the development of effective drugs for degenerative diseases related to oxidative stress.

Parents' perspectives on coping with Duchenne muscular dystrophy

BACKGROUND

The author, who has a grown son with Duchenne Muscular Dystrophy (DMD), has personally experienced a lack of available information for parents about coping with DMD. Therefore, as a longtime personal goal, she developed this study to address that lack of information.

METHODS

Fifteen semi-structured interviews were conducted with 23 parents (n = 7 with both parents; n = 1 with two sisters; n = 6 with mothers only; n = 1 with father only). The purpose of the interviews was to examine the strategies parents use to cope when their sons have DMD. The interviews were conducted in 12 states, taped and transcribed.

RESULTS

Grounded theory analysis of the interview data indicated the willingness of these parents to share information to empower others like themselves.

CONCLUSIONS

Parents want to be heard and valued as experts on DMD by medical and other professionals who interact with their sons. In addition, they want to proactively participate in their sons' lives and to encourage other parents to do the same.

Prednisolone‐induced changes in dystrophic skeletal muscle

Although glucocorticoids delay the progression of Duchenne muscular dystrophy (DMD) their mechanism of action is unknown. Skeletal muscle gene expression profiles of mdx mice, an animal model of DMD, treated with prednisolone were compared with control mice at 1 and 6 wk. Of the 89 early differentially regulated genes and ESTs, delta-sarcoglycan, myosin Va, FK506-binding protein 51 (FKBP51), the potassium channel regulator potassium inwardly-rectifying channel Isk-like (IRK2) and ADAM 10 were overexpressed, whereas growth hormone-releasing hormone receptor (GHRHR) and Homer-2 were underexpressed. The 58 late differentially overexpressed genes included kallikreins (13, 16, and 26), FKBP51, PI3K alpha regulatory subunit, and IGFBP6, while underexpressed genes included NeuroD and nicotinic cholinergic receptor gamma. At both time points, overexpression of a cohort of genes relating to metabolism and proteolysis was apparent, alongside the differential expression of genes relating to calcium metabolism. Treatment did not increase muscle regeneration, reduce the number of infiltrating macrophages, or alter utrophin expression or localization. However, in the treated mdx soleus muscle, the percentage of slow fibers was significantly lower compared with untreated controls after 6 wk of treatment. These results show that glucocorticoids confer their benefit to dystrophic muscle in a complex fashion, culminating in a switch to a more normal muscle fiber type.

The topoisomerase 1-interacting protein BTBD1 is essential for muscle cell differentiation

DNA topoisomerase I (Topo1) contributes to vital biological functions, but its regulation is not clearly understood. The BTBD1 protein was recently cloned on the basis of its interaction with the core domain of Topo1 and is expressed particularly in skeletal muscle. To determine BTBD1 functions in this tissue, the in vitro model used was the C2C12 mouse muscle cell line, which expresses BTBD1 mainly after myotube differentiation. We studied the effects of a stably overexpressed BTBD1 protein truncated of the 108 N-terminal amino-acid residues and harbouring a C-terminal FLAG tag (Delta-BTBD1). The proliferation speed of Delta-BTBD1 C2C12 cells was significantly decreased and no myogenic differentiation was observed, although these cells maintained their capacity to enter adipocyte differentiation. These alterations could be related to Topo1 deregulation. This hypothesis is further supported by the decrease in nuclear Topo1 content in Delta-BTBTD1 proliferative C2C12 cells and the switch from the main peripheral nuclear localization of Topo1 to a mainly nuclear diffuse localization in Delta-BTBTD1 C2C12 cells. Finally, this study demonstrated that BTBD1 is essential for myogenic differentiation.

Altered activity of signaling pathways in diaphragm and tibialis anterior muscle of dystrophic mice

Duchenne muscular dystrophy is a musculoskeletal disease caused by mutations in the dystrophin gene. The purpose of this study was to use the mouse model of muscular dystrophy (mdx) to determine if the progression of the dystrophic phenotype in the diaphragm (costal) versus limb skeletal muscle (tibialis anterior) is associated with specific changes in extracellular regulated kinase (ERK1/2), p70 S6 kinase (p70(S6k)), or p38 signaling pathways. The studies detected that consistent with an earlier dystrophic phenotype, phosphorylation of p70(S6k) is elevated by 40% in the diaphragm with no change in limb muscle. In addition, phosphorylation of p38 kinase was decreased by 33% in the mdx diaphragm muscle. Levels of ERK1/2 as well as phosphorylation states were elevated in the diaphragm and limb muscle of mdx mice compared with age-matched control muscles. These results indicate that distinct signaling pathways are differentially activated in skeletal muscle of mdx mice. The specificity of these responses, particularly in the diaphragm, provides insight for potential targets for blunting the progression of the muscular dystrophy phenotype.

Myospryn Is a Novel Binding Partner for Dysbindin in Muscle

Dysbindin is a coiled-coil-containing protein that was initially identified in a screen for dystrobrevin-interacting proteins. Recently, dysbindin has been shown to be involved in the biogenesis of lysosome-related organelles and is also a major schizophrenia susceptibility factor. Although dysbindin has been implicated in a number of different cellular processes, little is known about its function. To determine the function of dysbindin in muscle, we performed a yeast two-hybrid screen to identify potential interacting proteins. Here we show that dysbindin binds to a novel 413-kDa protein, myospryn, which is expressed in cardiac and skeletal muscle. The transcript encoding myospryn encompasses genethonin-3, a transcript that is down-regulated in muscle from Duchenne muscular dystrophy patients and stretch-responsive protein 553, which is up-regulated in experimental muscle hypertrophy. The C terminus of myospryn contains BBC, FN3, and SPRY domains in a configuration reminiscent of the tripartite motif protein family, as well as the dysbindin-binding site and a region mediating self-association. Dysbindin and myospryn co-immunoprecipitate from muscle extracts and are extensively co-localized. These data demonstrate for the first time that there are tissue-specific ligands for dysbindin that may play important roles in the different disease states involving this protein.

Multiple types of skeletal muscle atrophy involve a common program of changes in gene expression

Skeletal muscle atrophy is a debilitating response to starvation and many systemic diseases including diabetes, cancer, and renal failure. We had proposed that a common set of transcriptional adaptations underlie the loss of muscle mass in these different states. To test this hypothesis, we used cDNA microarrays to compare the changes in content of specific mRNAs in muscles atrophying from different causes. We compared muscles from fasted mice, from rats with cancer cachexia, streptozotocin-induced diabetes mellitus, uremia induced by subtotal nephrectomy, and from pair-fed control rats. Although the content of >90% of mRNAs did not change, including those for the myofibrillar apparatus, we found a common set of genes (termed atrogins) that were induced or suppressed in muscles in these four catabolic states. Among the strongly induced genes were many involved in protein degradation, including polyubiquitins, Ub fusion proteins, the Ub ligases atrogin-1/MAFbx and MuRF-1, multiple but not all subunits of the 20S proteasome and its 19S regulator, and cathepsin L. Many genes required for ATP production and late steps in glycolysis were down-regulated, as were many transcripts for extracellular matrix proteins. Some genes not previously implicated in muscle atrophy were dramatically up-regulated (lipin, metallothionein, AMP deaminase, RNA helicase-related protein, TG interacting factor) and several growth-related mRNAs were down-regulated (P311, JUN, IGF-1-BP5). Thus, different types of muscle atrophy share a common transcriptional program that is activated in many systemic diseases.

Temporal gene expression profiling of dystrophin-deficient (mdx) mouse diaphragm identifies conserved and muscle group-specific mechanisms in the pathogenesis of muscular dystrophy

Mutations in dystrophin are the proximate cause of Duchenne muscular dystrophy (DMD), but pathogenic mechanisms linking the absence of dystrophin from the sarcolemma to myofiber necrosis are not fully known. The muscular dystrophies also have properties not accounted for by current disease models, including the temporal delay to disease onset, broad species differences in severity, and diversity of skeletal muscle responses. To address the mechanisms underlying the differential targeting of muscular dystrophy, we characterized temporal expression profiles of the diaphragm in dystrophin-deficient (mdx) mice between postnatal days 7 and 112 using oligonucleotide microarrays and contrasted these data with published hindlimb muscle data. Although the diaphragm and hindlimb muscle groups differ in severity of response to dystrophin deficiency, and exhibited substantial divergence in some transcript categories including inflammation and muscle-specific genes, our data show that the general mechanisms operative in muscular dystrophy are highly conserved. The two muscle groups principally differed in expression levels of differentially regulated genes, as opposed to the non-conserved induced/repressed transcripts defining fundamentally distinct mechanisms. We also identified a postnatal divergence of the two wild-type muscle group expression profiles that temporally correlated with the onset and progression of the dystrophic process. These findings support the hypothesis that conserved disease mechanisms interacting with baseline differences in muscle group-specific transcriptomes underlie their differential responses to DMD. We further suggest that muscle group-specific transcriptional profiles contribute toward the muscle targeting and sparing patterns observed for a variety of metabolic and neuromuscular diseases.

Dissection of temporal gene expression signatures of affected and spared muscle groups in dystrophin-deficient (mdx) mice

Although dystrophin mutations are the proximate cause of Duchenne muscular dystrophy (DMD), interactions among heterogeneous downstream mechanisms may be key phenotypic determinants. Temporal gene expression profiling was used to identify and correlate diverse transcriptional patterns to one another and to the disease course, for both affected and spared muscle groups, in postnatal day 7-112 dystrophin-deficient (mdx) mice. While 719 transcripts were differentially expressed at one or more ages in leg muscle, only 56 genes were altered in the spared extraocular muscles (EOM). Contrasting molecular signatures of affected versus spared muscles provide compelling evidence that the absence of dystrophin alone is necessary but not sufficient to cause the patterned fibrosis, inflammation and failure of muscle regeneration characteristic of dystrophinopathy. Dystrophic and adaptive changes in the microarray profiles were further quantified using an aggregate disease load index (DLI) to measure stage-dependent transcriptional impact in both muscles. DLI analysis highlighted the divergent responses of EOM and leg muscle groups. Cellular process-specific DLIs in leg muscle identified positively correlated temporal expression profiles for some gene classes, and the independence of others, that are linked to major disease components. Data also showed a previously unrecognized transient and selective developmental delay in pre-necrotic mdx skeletal muscle that was confirmed by qPCR. Taken together, validation and targeting of signaling pathways responsible for the coordination of the fibrotic, proteolytic and inflammatory mechanisms shown here for mdx muscle may yield new therapeutic means of mitigating the devastating consequences of DMD.

Gene expression profiling of Duchenne muscular dystrophy skeletal muscle

The primary cause of Duchenne muscular dystrophy (DMD) is a mutation in the dystrophin gene, leading to absence of the corresponding protein, disruption of the dystrophin-associated protein complex, and substantial changes in skeletal muscle pathology. Although the primary defect is known and the histological pathology well documented, the underlying molecular pathways remain in question. To clarify these pathways, we used expression microarrays to compare individual gene expression profiles for skeletal muscle biopsies from DMD patients and unaffected controls. We have previously published expression data for the 12,500 known genes and full-length expressed sequence tags (ESTs) on the Affymetrix HG-U95Av2 chips. Here we present comparative expression analysis of the 50,000 EST clusters represented on the remainder of the Affymetrix HG-U95 set. Individual expression profiles were generated for biopsies from 10 DMD patients and 10 unaffected control patients. Two methods of statistical analysis were used to interpret the resulting data (t-test analysis to determine the statistical significance of differential expression and geometric fold change analysis to determine the extent of differential expression). These analyses identified 183 probe sets (59 of which represent known genes) that differ significantly in expression level between unaffected and disease muscle. This study adds to our knowledge of the molecular pathways that are altered in the dystrophic state. In particular, it suggests that signaling pathways might be substantially involved in the disease process. It also highlights a large number of unknown genes whose expression is altered and whose identity therefore becomes important in understanding the pathogenesis of muscular dystrophy.

Striated muscle cytoarchitecture: an intricate web of form and function

Striated muscle is an intricate, efficient, and precise machine that contains complex interconnected cytoskeletal networks critical for its contractile activity. The individual units of the sarcomere, the basic contractile unit of myofibrils, include the thin, thick, titin, and nebulin filaments. These filament systems have been investigated intensely for some time, but the details of their functions, as well as how they are connected to other cytoskeletal elements, are just beginning to be elucidated. These investigations have advanced significantly in recent years through the identification of novel sarcomeric and sarcomeric-associated proteins and their subsequent functional analyses in model systems. Mutations in these cytoskeletal components account for a large percentage of human myopathies, and thus insight into the normal functions of these proteins has provided a much needed mechanistic understanding of these disorders. In this review, we highlight the components of striated muscle cytoarchitecture with respect to their interactions, dynamics, links to signaling pathways, and functions. The exciting conclusion is that the striated muscle cytoskeleton, an exquisitely tuned, dynamic molecular machine, is capable of responding to subtle changes in cellular physiology.

Gene expression comparison of biopsies from Duchenne muscular dystrophy (DMD) and normal skeletal muscle

The primary cause of Duchenne muscular dystrophy (DMD) is a mutation in the dystrophin gene leading to the absence of the corresponding RNA transcript and protein. Absence of dystrophin leads to disruption of the dystrophin-associated protein complex and substantial changes in skeletal muscle pathology. Although the histological pathology of dystrophic tissue has been well documented, the underlying molecular pathways remain poorly understood. To examine the pathogenic pathways and identify new or modifying factors involved in muscular dystrophy, expression microarrays were used to compare individual gene expression profiles of skeletal muscle biopsies from 12 DMD patients and 12 unaffected control patients. Two separate statistical analysis methods were used to interpret the resulting data: t test analysis to determine the statistical significance of differential expression and geometric fold change analysis to determine the extent of differential expression. These analyses identified 105 genes that differ significantly in expression level between unaffected and DMD muscle. Many of the differentially expressed genes reflect changes in histological pathology. For instance, immune response signals and extracellular matrix genes are overexpressed in DMD muscle, an indication of the infiltration of inflammatory cells and connective tissue. Significantly more genes are overexpressed than are underexpressed in dystrophic muscle, with dystrophin underexpressed, whereas other genes encoding muscle structure and regeneration processes are overexpressed, reflecting the regenerative nature of the disease.

Patterns of gene expression in atrophying skeletal muscles: response to food deprivation

During fasting and many systemic diseases, muscle undergoes rapid loss of protein and functional capacity. To define the transcriptional changes triggering muscle atrophy and energy conservation in fasting, we used cDNA microarrays to compare mRNAs from muscles of control and food-deprived mice. Expression of >94% of genes did not change, but interesting patterns emerged among genes that were differentially expressed: 1) mRNAs encoding polyubiquitin, ubiquitin extension proteins, and many (but not all) proteasome subunits increased, which presumably contributes to accelerated protein breakdown; 2) a dramatic increase in mRNA for the ubiquitin ligase, atrogin-1, but not most E3s; 3) a significant suppression of mRNA for myosin binding protein H (but not other myofibrillar proteins) and IGF binding protein 5, which may favor cell protein loss; 4) decreases in mRNAs for several glycolytic enzymes and phosphorylase kinase subunits, and dramatic increases in mRNAs for pyruvate dehydrogenase kinase 4 and glutamine synthase, which should promote glucose sparing and gluconeogenesis. During fasting, metallothionein mRNA increased dramatically, mRNAs for extracellular matrix components fell, and mRNAs that may favor cap-independent mRNA translation rose. Significant changes occurred in mRNAs for many growth-related proteins and transcriptional regulators. These transcriptional changes indicate a complex adaptive program that should favor protein degradation and suppress glucose oxidation in muscle. Similar analysis of muscles atrophying for other causes is allowing us to identify a set of atrophy-specific changes in gene expression.

Pharmacological control of cellular calcium handling in dystrophic skeletal muscle

Duchenne muscular dystrophy arises due to the lack of the cytoskeletal protein dystrophin. In Duchenne muscular dystrophy muscle, the lack of dystrophin is accompanied by alterations in the dystrophin-glycoprotein complex. We and others have found that the absence of dystrophin in cells of the Duchenne muscular dystrophy animal model, the mdx mouse, leads to elevated Ca(2+) influx and cytosolic Ca(2+) concentrations when exposed to stress. We have also shown that alpha-methylprednisolone, the only drug used successfully in the therapy of Duchenne muscular dystrophy, and creatine lowered cytosolic Ca(2+) levels in mdx myotubes. It is likely that chronic elevation of [Ca(2+)] in the cytosol in response to stress is an initiating event for apoptosis and/or necrosis in Duchenne muscular dystrophy or mdx muscle and that alterations in mitochondrial function and metabolism are involved. Other cellular signalling pathways (e.g. nitric oxide) might also be affected.

Steroids in Duchenne muscular dystrophy: from clinical trials to genomic research

Steroids represent the only pharmacological palliative treatment for Duchenne muscular dystrophy. However, they do have side effects and despite a large number of published studies showing their efficacy, they are still not universally used. This is largely due to the lack of functional outcome and quality of life measures in most of the published studies and suggests that further trials might be required to answer some of the still unclear aspects of their role. Another important aspect of steroid therapy in Duchenne dystrophy is that we do not know how they work in dystrophic muscle. We have initiated a collaborative study on gene profiling using microarray in steroid-treated mdx mice. cDNA microarray studies were performed to examine the levels of skeletal muscle gene expression in a pool of mdx mice treated with prednisolone for 1 and 6 weeks. Interesting preliminary data on untreated mdx mice suggest that the gene profiling of young (7 weeks) versus older (12 weeks) mice is very significantly different. Furthermore, a large number of genes showed significant changes in expression at the mRNA level on treatment with prednisolone. These included structural protein genes; signalling genes and genes involved in immune response. Hopefully, analysis of this pattern of steroid-induced gene expression will provide some insight into understanding how glucocorticoids improve strength in Duchenne dystrophy, and may help in developing more effective and less toxic therapeutic approaches.

Global/temporal gene expression in diaphragm and hindlimb muscles of dystrophin-deficient (mdx) mice

The mdx mouse is a model for human Duchenne muscular dystrophy (DMD), an X-linked degenerative disease of skeletal muscle tissue characterized by the absence of the dystrophin protein. The mdx mice display a much milder phenotype than DMD patients. After the first week of life when all mdx muscles evolve like muscles of young DMD patients, mdx hindlimb muscles substantially compensate for the lack of dystrophin, whereas mdx diaphragm muscle becomes progressively affected by the disease. We used cDNA microarrays to compare the expression profile of 1,082 genes, previously selected by a subtractive method, in control and mdx hindlimb and diaphragm muscles at 12 time points over the first year of the mouse life. We determined that 1) the dystrophin gene defect induced marked expression remodeling of 112 genes encoding proteins implicated in diverse muscle cell functions and 2) two-thirds of the observed transcriptomal anomalies differed between adult mdx hindlimb and diaphragm muscles. Our results showed that neither mdx diaphram muscle nor mdx hindlimb muscles evolve entirely like the human DMD muscles. This finding should be taken under consideration for the interpretation of future experiments using mdx mice as a model for therapeutic assays.

Microarray analysis of normal and dystrophic skeletal muscle

The development and increasingly common use of DNA microarrays for comprehensive RNA expression analysis has had a substantial impact on the study of molecular pathology. DNA microarrays are orderly, high-density arrangements of nucleic acid spots that can be used as substrates for global gene expression analysis. Prior to their development, technical limitations necessitated that the molecular mechanisms underlying biological processes be broken down into their component parts and each gene or protein studied individually. This approach, focused as it is on a single aspect of a scientific phenomenon, does not allow appreciation or understanding of the fact that biological pathways do not exist in isolation, but are influenced by numerous factors. Enormous technological advances have been made over the past decade and now high-density DNA microarrays can provide rapid measurement of thousands of distinct transcripts simultaneously. These experiments raise the exciting opportunity to examine biological pathways in all their complexity and to compare the hypotheses deduced from the study of histological pathology with the findings of molecular pathology. This review focuses on how microarray technology has been used to interrogate muscular gene expression and, in particular, on how data generated from differential expression analysis of dystrophic and normal skeletal muscle has contributed to understanding the molecular pathophysiological pathways of muscular dystrophy.

Muscular dystrophy into the new millennium

Since the identification of the gene for Duchenne muscular dystrophy and its protein product some 15 years ago, the basic defects in all the commoner forms of dystrophy have now been identified. It is thus possible, on the basis of this information, to make a precise diagnosis in an affected individual and to offer accurate genetic counselling and prenatal diagnosis. Now newer technologies are being applied to the investigation of these disorders. These include studies of single nucleotide polymorphisms, microarray analysis and expression profiling, the yeast two-hybrid assay, and proteomics. A great deal of new information is emerging in this way which will hopefully help us to understand the causes of inter-familial and intra-familial variation and particularly pathogenesis, a detailed understanding of which could be the first step in finding effective treatments.

Function and genetics of dystrophin and dystrophin-related proteins in muscle

The X-linked muscle-wasting disease Duchenne muscular dystrophy is caused by mutations in the gene encoding dystrophin. There is currently no effective treatment for the disease; however, the complex molecular pathology of this disorder is now being unravelled. Dystrophin is located at the muscle sarcolemma in a membrane-spanning protein complex that connects the cytoskeleton to the basal lamina. Mutations in many components of the dystrophin protein complex cause other forms of autosomally inherited muscular dystrophy, indicating the importance of this complex in normal muscle function. Although the precise function of dystrophin is unknown, the lack of protein causes membrane destabilization and the activation of multiple pathophysiological processes, many of which converge on alterations in intracellular calcium handling. Dystrophin is also the prototype of a family of dystrophin-related proteins, many of which are found in muscle. This family includes utrophin and alpha-dystrobrevin, which are involved in the maintenance of the neuromuscular junction architecture and in muscle homeostasis. New insights into the pathophysiology of dystrophic muscle, the identification of compensating proteins, and the discovery of new binding partners are paving the way for novel therapeutic strategies to treat this fatal muscle disease. This review discusses the role of the dystrophin complex and protein family in muscle and describes the physiological processes that are affected in Duchenne muscular dystrophy.