A- and B-utrophin have different expression patterns and are differentially up-regulated in mdx muscle

Dystrophins, utrophins, and associated scaffolding complexes: role in mammalian brain and implications for therapeutic strategies

Two decades of molecular, cellular, and functional studies considerably increased our understanding of dystrophins function and unveiled the complex etiology of the cognitive deficits in Duchenne muscular dystrophy (DMD), which involves altered expression of several dystrophin-gene products in brain. Dystrophins are normally part of critical cytoskeleton-associated membrane-bound molecular scaffolds involved in the clustering of receptors, ion channels, and signaling proteins that contribute to synapse physiology and blood-brain barrier function. The utrophin gene also drives brain expression of several paralogs proteins, which cellular expression and biological roles remain to be elucidated. Here we review the structural and functional properties of dystrophins and utrophins in brain, the consequences of dystrophins loss-of-function as revealed by numerous studies in mouse models of DMD, and we discuss future challenges and putative therapeutic strategies that may compensate for the cognitive impairment in DMD based on experimental manipulation of dystrophins and/or utrophins brain expression.

Effect of dystrophin deficiency on selected intrinsic laryngeal muscles of the mdx mouse

BACKGROUND

Intrinsic laryngeal muscles (ILM) show biological differences from the broader class of skeletal muscles. Yet most research regarding ILM specialization has been completed on a few muscles, most notably the thyroarytenoid and posterior cricoarytenoid. Little information exists regarding the biology of other ILM. Early evidence suggests that the interarytenoid (IA) and cricothyroid (CT) may be more similar to classic skeletal muscle than their associated laryngeal muscles. Knowledge of the IA and CT's similarity or dissimilarity to typical skeletal muscle may hold implications for the treatment of dysphonia.

PURPOSE

The purpose of this study was to further define IA and CT biology by examining their response to the biological challenge of dystrophin deficiency.

METHOD

Control and dystrophin-deficient superior cricoarytenoid (SCA; mouse counterpart of IA) and CT muscles were examined for fiber morphology, sarcolemmal integrity, and immunohistochemical detection of dystrophin.

RESULTS

Despite the absence of dystrophin, experimental muscles did not show disease markers.

CONCLUSIONS

The SCA and the CT appear spared in dystrophin-deficient mouse models. These laryngeal muscles possess specializations that separate them from typical skeletal muscle. Considered in light of previous research, the CT and IA may represent transitional form of muscle, evidencing properties of typical and specialized skeletal muscle.

Chronic administration of membrane sealant prevents severe cardiac injury and ventricular dilatation in dystrophic dogs

Duchenne muscular dystrophy (DMD) is a fatal disease of striated muscle deterioration caused by lack of the cytoskeletal protein dystrophin. Dystrophin deficiency causes muscle membrane instability, skeletal muscle wasting, cardiomyopathy, and heart failure. Advances in palliative respiratory care have increased the incidence of heart disease in DMD patients, for which there is no cure or effective therapy. Here we have shown that chronic infusion of membrane-sealing poloxamer to severely affected dystrophic dogs reduced myocardial fibrosis, blocked increased serum cardiac troponin I (cTnI) and brain type natriuretic peptide (BNP), and fully prevented left-ventricular remodeling. Mechanistically, we observed a markedly greater primary defect of reduced cell compliance in dystrophic canine myocytes than in the mildly affected mdx mouse myocytes, and this was associated with a lack of utrophin upregulation in the dystrophic canine cardiac myocytes. Interestingly, after chronic poloxamer treatment, the poor compliance of isolated canine myocytes remained evident, but this could be restored to normal upon direct application of poloxamer. Collectively, these findings indicate that dystrophin and utrophin are critical to membrane stability-dependent cardiac myocyte mechanical compliance and that poloxamer confers a highly effective membrane-stabilizing chemical surrogate in dystrophin/utrophin deficiency. We propose that membrane sealant therapy is a potential treatment modality for DMD heart disease and possibly other disorders with membrane defect etiologies.

The utrophin A 5'-UTR drives cap-independent translation exclusively in skeletal muscles of transgenic mice and interacts with eEF1A2

The molecular mechanisms regulating expression of utrophin A are of therapeutic interest since upregulating its expression at the sarcolemma can compensate for the lack of dystrophin in animal models of Duchenne Muscular Dystrophy (DMD). The 5'-UTR of utrophin A has been previously shown to drive cap-independent internal ribosome entry site (IRES)-mediated translation in response to muscle regeneration and glucocorticoid treatment. To determine whether the utrophin A IRES displays tissue specific activity, we generated transgenic mice harboring control (CMV/betaGAL/CAT) or utrophin A 5'-UTR (CMV/betaGAL/UtrA/CAT) bicistronic reporter transgenes. Examination of multiple tissues from two CMV/betaGAL/UtrA/CAT lines revealed that the utrophin A 5'-UTR drives cap-independent translation of the reporter gene exclusively in skeletal muscles and no other examined tissues. This expression pattern suggested that skeletal muscle-specific factors are involved in IRES-mediated translation of utrophin A. We performed RNA-affinity chromatography experiments combined with mass spectrometry to identify trans-factors that bind the utrophin A 5'-UTR and identified eukaryotic elongation factor 1A2 (eEF1A2). UV-crosslinking experiments confirmed the specificity of this interaction. Regions of the utrophin A 5'-UTR that bound eEF1A2 also mediated cap-independent translation in C2C12 muscle cells. Cultured cells lacking eEF1A2 had reduced IRES activity compared with cells overexpressing eEF1A2. Together, these results suggest an important role for eEF1A2 in driving cap-independent translation of utrophin A in skeletal muscle. The trans-factors and signaling pathways driving skeletal-muscle specific IRES-mediated translation of utrophin A could provide unique targets for developing pharmacological-based DMD therapies.

The roles of the dystrophin-associated glycoprotein complex at the synapse

Duchenne muscular dystrophy is caused by mutations in the dystrophin gene and is characterized by progressive muscle wasting. A number of Duchenne patients also present with mental retardation. The dystrophin protein is part of the highly conserved dystrophin-associated glycoprotein complex (DGC) which accumulates at the neuromuscular junction (NMJ) and at a variety of synapses in the peripheral and central nervous systems. Many years of research into the roles of the DGC in muscle have revealed its structural function in stabilizing the sarcolemma. In addition, the DGC also acts as a scaffold for various signaling pathways. Here, we discuss recent advances in understanding DGC roles in the nervous system, gained from studies in both vertebrate and invertebrate model systems. From these studies, it has become clear that the DGC is important for the maturation of neurotransmitter receptor complexes and for the regulation of neurotransmitter release at the NMJ and central synapses. Furthermore, roles for the DGC have been established in consolidation of long-term spatial and recognition memory. The challenges ahead include the integration of the behavioral and mechanistic studies and the use of this information to identify therapeutic targets.

Myotendinous junction defects and reduced force transmission in mice that lack alpha7 integrin and utrophin

The alpha7beta1 integrin, dystrophin, and utrophin glycoprotein complexes are the major laminin receptors in skeletal muscle. Loss of dystrophin causes Duchenne muscular dystrophy, a lethal muscle wasting disease. Duchenne muscular dystrophy-affected muscle exhibits increased expression of alpha7beta1 integrin and utrophin, which suggests that these laminin binding complexes may act as surrogates in the absence of dystrophin. Indeed, mice that lack dystrophin and alpha7 integrin (mdx/alpha7(-/-)), or dystrophin and utrophin (mdx/utr(-/-)), exhibit severe muscle pathology and die prematurely. To explore the contribution of the alpha7beta1 integrin and utrophin to muscle integrity and function, we generated mice lacking both alpha7 integrin and utrophin. Surprisingly, mice that lack both alpha7 integrin and utrophin (alpha7/utr(-/-)) were viable and fertile. However, these mice had partial embryonic lethality and mild muscle pathology, similar to alpha7 integrin-deficient mice. Dystrophin levels were increased 1.4-fold in alpha7/utr(-/-) skeletal muscle and were enriched at neuromuscular junctions. Ultrastructural analysis revealed abnormal myotendinous junctions, and functional tests showed a ninefold reduction in endurance and 1.6-fold decrease in muscle strength in these mice. The alpha7/utr(-/-) mouse, therefore, demonstrates the critical roles of alpha7 integrin and utrophin in maintaining myotendinous junction structure and enabling force transmission during muscle contraction. Together, these results indicate that the alpha7beta1 integrin, dystrophin, and utrophin complexes act in a concerted manner to maintain the structural and functional integrity of skeletal muscle.

Dysregulated intracellular signaling and inflammatory gene expression during initial disease onset in Duchenne muscular dystrophy

Duchenne muscular dystrophy is a debilitating genetic disorder characterized by severe muscle wasting and early death in affected boys. The primary cause of this disease is mutations in the dystrophin gene that result in the absence of the protein dystrophin and the associated dystrophin-glycoprotein complex in the plasma membrane of muscle fibers. In normal muscle, this complex forms a link between the extracellular matrix and the cytoskeleton that is thought to protect muscle fibers from contraction-induced membrane lesions and to regulate cell signaling cascades. Although the primary defect is known, the mechanisms that initiate disease onset have not been characterized. Data collected during early maturation suggest that inflammatory and immune responses are key contributors to disease pathogenesis and may be initiated by aberrant signaling in dystrophic muscle. However, detailed time course studies of the inflammatory and immune processes are incomplete and need to be characterized further to understand the disease progression. The purposes of this review are to examine the possibility that initial disease onset in dystrophin-deficient muscle results from aberrant inflammatory signaling pathways and to highlight the potential clinical relevance of targeting these pathways to treat Duchenne muscular dystrophy.

Differential expression of utrophin-A and -B promoters in the central nervous system (CNS) of normal and dystrophic mdx mice

Utrophin (Utrn) is the autosomal homolog of dystrophin, the Duchene Muscular Dystrophy (DMD) locus product and of therapeutic interest, as its overexpression can compensate dystrophin's absence. Utrn is transcribed by Utrn-A and -B promoters with mRNAs differing at their 5' ends. However, previous central nervous system (CNS) studies used C-terminal antibodies recognizing both isoforms. As this distinction may impact upregulation strategies, we generated Utrn-A and -B promoter-specific antibodies, Taqman Polymerase chain reaction (PCR)-based absolute copy number assays, and luciferase-reporter constructs to study CNS of normal and dystrophic mdx mice. Differential expression of Utrn-A and -B was noted in microdissected and capillary-enriched fractions. At the protein level, Utrn-B was predominantly expressed in vasculature and ependymal lining, whereas Utrn-A was expressed in neurons, astrocytes, choroid plexus and pia mater. mRNA quantification demonstrated matching patterns of differential expression; however, transcription-translation mismatch was noted for Utrn-B in caudal brain regions. Utrn-A and Utrn-B proteins were significantly upregulated in olfactory bulb and cerebellum of mdx brain. Differential promoter activity, mRNA and protein expressions were studied in cultured C2C12, bEnd3, neurons and astrocytes. Promoter activity ranking for Utrn-A and -B was neurons > astrocytes > C2C12 > bEnd3 and bEnd3 > astrocytes > neurons > C2C12, respectively. Our results identify promoter usage patterns for therapeutic targeting and define promoter-specific differential distribution of Utrn isoforms in normal and dystrophic CNS.

The value of mammalian models for duchenne muscular dystrophy in developing therapeutic strategies

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy. There is no effective treatment and patients typically die in approximately the third decade. DMD is an X-linked recessive disease caused by mutations in the dystrophin gene. There are three mammalian models of DMD that have been used to understand better the pathogenesis of disease and develop therapeutic strategies. The mdx mouse is the most widely used model of DMD that displays some features of muscle degeneration, but the pathogenesis of disease is comparatively mild. The severity of disease in mice lacking both dystrophin and utrophin is similar to DMD, but one has to account for the discrete functions of utrophin. Canine X-linked muscular dystrophy (cxmd) is the best representation of DMD, but the phenotype of the most widely used golden retriever (GRMD) model is variable, making functional endpoints difficult to ascertain. Although each mammalian model has its limitations, together they have been essential for the development of several treatment strategies for DMD that target dystrophin replacement, disease progression, and muscle regeneration.

Targeting artificial transcription factors to the utrophin A promoter: effects on dystrophic pathology and muscle function

Duchenne muscular dystrophy is caused by a genetic defect in the dystrophin gene. The absence of dystrophin results in muscle fiber necrosis and regeneration, leading to progressive muscle fiber loss. Utrophin is a close analogue of dystrophin. A substantial, ectopic expression of utrophin in the extrasynaptic sarcolemma of dystrophin-deficient muscle fibers can prevent deleterious effects of dystrophin deficiency. An alternative approach for the extrasynaptic up-regulation of utrophin involves the augmentation of utrophin transcription via the endogenous utrophin A promoter using custom-designed transcriptional activator proteins with zinc finger (ZFP) motifs. We tested a panel of custom-designed ZFP for their ability to activate the utrophin A promoter. Expression of one such ZFP efficiently increased, in a time-dependent manner, utrophin transcript and protein levels both in vitro and in vivo. In dystrophic mouse (mdx) muscles, administration of adenoviral vectors expressing this ZFP led to significant enhancement of muscle function with decreased necrosis, restoration of the dystrophin-associated proteins, and improved resistance to eccentric contractions. These studies provide evidence that specifically designed ZFPs can act as strong transcriptional activators of the utrophin A promoter. These may thus serve as attractive therapeutic agents for dystrophin deficiency states such as Duchenne muscular dystrophy.

Downstream utrophin enhancer is required for expression of utrophin in skeletal muscle

BACKGROUND

Duchenne muscular dystrophy is caused by the absence of the muscle cytoskeletal protein dystrophin. Utrophin is an autosomal homologue of dystrophin, and overexpression of utrophin is expected to compensate for the dystrophin deficit. We previously reported that the 5.4-kb 5'-flanking region of the utrophin gene containing the A-utrophin core promoter did not drive transgene expression in heart and skeletal muscle. To clarify the regulatory mechanism of utrophin expression, we generated a nuclear localization signal-tagged LacZ transgenic (Tg) mouse, in which the LacZ gene was driven by the 129-bp downstream utrophin enhancer (DUE) and the 5.4-kb 5'-flanking region of the utrophin promoter.

METHODS

Two Tg lines were established. The levels of transgene mRNA expression in several tissues were examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative RT-PCR. Cryosections of several tissues were stained with haematoxylin and eosin and X-gal.

RESULTS

The transgene expression patterns were consistent with endogenous utrophin in several tissues including heart and skeletal muscle. Transgene expression was also up-regulated more in regenerating muscle than in nonregenerating muscle. Moreover, utrophin expression was augmented in the skeletal muscle of DUE Tg/dystrophin-deficient mdx mice through cross-breeding experiments. We finally established cultures of primary myogenic cells from this Tg mouse and found that utrophin up-regulation during muscle differentiation depends on the DUE motif.

CONCLUSIONS

Our results showed that DUE is indispensable for utrophin expression in skeletal muscle and heart, and primary myogenic cells from this Tg mice provide a high through-put screening system for drugs that up-regulate utrophin expression.

IRES-mediated translation of utrophin A is enhanced by glucocorticoid treatment in skeletal muscle cells

Glucocorticoids are currently the only drug treatment recognized to benefit Duchenne muscular dystrophy (DMD) patients. The nature of the mechanisms underlying the beneficial effects remains incompletely understood but may involve an increase in the expression of utrophin. Here, we show that treatment of myotubes with 6α−methylprednisolone-21 sodium succinate (PDN) results in enhanced expression of utrophin A without concomitant increases in mRNA levels thereby suggesting that translational regulation contributes to the increase. In agreement with this, we show that PDN treatment of cells transfected with monocistronic reporter constructs harbouring the utrophin A 5′UTR, causes an increase in reporter protein expression while leaving levels of reporter mRNAs unchanged. Using bicistronic reporter assays, we further demonstrate that PDN enhances activity of an Internal Ribosome Entry Site (IRES) located within the utrophin A 5′UTR. Analysis of polysomes demonstrate that PDN causes an overall reduction in polysome-associated mRNAs indicating that global translation rates are depressed under these conditions. Importantly, PDN causes an increase in the polysome association of endogenous utrophin A mRNAs and reporter mRNAs harbouring the utrophin A 5′UTR. Additional experiments identified a distinct region within the utrophin A 5′UTR that contains the inducible IRES activity. Together, these studies demonstrate that a translational regulatory mechanism involving increased IRES activation mediates, at least partially, the enhanced expression of utrophin A in muscle cells treated with glucocorticoids. Targeting the utrophin A IRES may thus offer an important and novel therapeutic avenue for developing drugs appropriate for DMD patients.

Combined deficiency of dystrophin and beta1 integrin in the cardiac myocyte causes myocardial dysfunction, fibrosis and calcification

The dystrophin-glycoprotein complex is a large complex of membrane-associated proteins linking the cytoskeleton to the extracellular matrix in muscle. Transmembrane heterodimeric (alphabeta) integrins serve also as cellular adhesion molecules and mechanotransducers. In the animal model for Duchenne muscular dystrophy, the mdx mouse, loss of dystrophin causes more severe abnormalities in skeletal than in cardiac muscle. We hypothesized that ablation of cardiac myocyte integrins in the mdx background would lead to a severe cardiomyopathic phenotype. Mdx mice were crossed to ones with cardiac myocyte-specific deletion of beta1 integrin (beta1KO) to generate beta1KOmdx. Unstressed beta1KOmdx mice were viable and had normal cardiac function; however, high mortality was seen in peri- and postpartum females by 6 months of age, when severe myocardial necrosis and fibrosis and extensive dystrophic calcification was seen. Decreased ventricular function and blunted adrenergic responsiveness was found in the beta1KOmdx mice compared with control (Lox/Lox, no Cre), beta1KO, and mdx. Similarly, adult beta1KOmdx males were more prone to isoproterenol-induced heart failure and death compared with control groups. Given the extensive calcification, we analyzed transcript levels of genes linked to fibrosis and calcification and found matrix gamma-carboxyglutamic acid protein, decorin, periostin, and the osteoblast transcription factor Runx2/Cbfa1 significantly increased in beta1KOmdx cardiac muscle. Our data show that combined deficiency of dystrophin and integrins in murine cardiac myocytes results in more severe cardiomyopathic changes in the stressed myocardium than reduction of either dystrophin or integrins alone and predisposes to myocardial calcification.

MicroRNA-206: the skeletal muscle-specific myomiR

MicroRNAs (miRNAs) are a class of non-coding RNAs involved in post-transcriptional gene silencing. A small number of striated muscle-specific miRNAs have been identified and shown to have an important role in myogenesis, embryonic muscle growth and cardiac function and hypertrophy. One of these myomiRs (myo=muscle+miR=miRNA), miR-206, is unique in that it is only expressed in skeletal muscle. The purpose of this review is to discuss what is currently known about miR-206 and its function in myogenesis as well as propose potential new roles for miR-206 in skeletal muscle biology. The review is also intended to serve as a comprehensive resource for miR-206 with the hope of encouraging further research on the role of miR-206 in skeletal muscle.

Subcutaneous injection, from birth, of epigallocatechin-3-gallate, a component of green tea, limits the onset of muscular dystrophy in mdx mice: a quantitative histological, immunohistochemical and electrophysiological study

Dystrophic muscles suffer from enhanced oxidative stress. We have investigated whether administration of an antioxidant, epigallocatechin-3-gallate (EGCG), a component of green tea, reduces their oxidative stress and pathophysiology in mdx mice, a mild phenotype model of human Duchenne-type muscular dystrophy. EGCG (5 mg/kg body weight in saline) was injected subcutaneously 4x a week into the backs of C57 normal and dystrophin-deficient mdx mice for 8 weeks after birth. Saline was injected into normal and mdx controls. EGCG had almost no observable effects on normal mice or on the body weights of mdx mice. In contrast, it produced the following improvements in the blood chemistry, muscle histology, and electrophysiology of the treated mdx mice. First, the activities of serum creatine kinase were reduced to normal levels. Second, the numbers of fluorescent lipofuscin granules per unit volume of soleus and diaphragm muscles were significantly decreased by about 50% compared to the numbers in the corresponding saline-treated controls. Third, in sections of diaphragm and soleus muscles, the relative area occupied by histologically normal muscle fibres increased significantly 1.5- to 2-fold whereas the relative areas of connective tissue and necrotic muscle fibres were substantially reduced. Fourth, the times for the maximum tetanic force of soleus muscles to fall by a half increased to almost normal values. Fifth, the amount of utrophin in diaphragm muscles increased significantly by 17%, partially compensating for the lack of dystrophin expression.

Modulation of utrophin A mRNA stability in fast versus slow muscles via an AU-rich element and calcineurin signaling

We examined the role of post-transcriptional mechanisms in controlling utrophin A mRNA expression in slow versus fast skeletal muscles. First, we determined that the half-life of utrophin A mRNA is significantly shorter in the presence of proteins isolated from fast muscles. Direct plasmid injection experiments using reporter constructs containing the full-length or truncated variants of the utrophin 3'UTR into slow soleus and fast extensor digitorum longus muscles revealed that a region of 265 nucleotides is sufficient to confer lower levels of reporter mRNA in fast muscles. Further analysis of this region uncovered a conserved AU-rich element (ARE) that suppresses expression of reporter mRNAs in cultured muscle cells. Moreover, stability of reporter mRNAs fused to the utrophin full-length 3'UTR was lower in the presence of fast muscle protein extracts. This destabilization effect seen in vivo was lost upon deletion of the conserved ARE. Finally, we observed that calcineurin signaling affects utrophin A mRNA stability through the conserved ARE. These results indicate that ARE-mediated mRNA decay is a key mechanism that regulates expression of utrophin A mRNA in slow muscle fibers. This is the first demonstration of ARE-mediated mRNA decay regulating the expression of a gene associated with the slow myogenic program.

MicroRNA-206 is overexpressed in the diaphragm but not the hindlimb muscle of mdx mouse

MicroRNAs are highly conserved, noncoding RNAs involved in posttranscriptional gene silencing. MicroRNAs have been shown to be involved in a range of biological processes, including myogenesis and muscle regeneration. The objective of this study was to test the hypothesis that microRNA expression is altered in dystrophic muscle, with the greatest change occurring, of the muscles examined, in the diaphragm. The expression of the muscle-enriched microRNAs was determined in the soleus, plantaris, and diaphragm muscles of control and dystrophin-deficient ( mdx) mice by semiquantitative PCR. In the soleus and plantaris, expression of the mature microRNA 133a (miR-133a) and miR-206, respectively, was decreased by ∼25%, whereas in the diaphragm, miR-206 expression increased by 4.5-fold relative to control. The increased expression of miR-206 in the mdx diaphragm was paralleled by a 4.4-fold increase in primary miRNA-206 (pri-miRNA-206) transcript level. Expression of Myod1 was elevated 2.7-fold only in the mdx diaphragm, consistent with an earlier finding demonstrating Myod1 can activate pri-miRNA-206 transcription. Transcript levels of Drosha and Dicer, major components of microRNA biogenesis pathway, were unchanged in mdx muscle, suggesting the pathway is not altered under dystrophic conditions. Previous in vitro analysis found miR-206 was capable of repressing utrophin expression; however, under dystrophic conditions, both utrophin transcript and protein levels were significantly increased by 69% and 3.9-fold, respectively, a finding inconsistent with microRNA regulation. These results are the first to report alterations in expression of muscle-enriched microRNAs in skeletal muscle of the mdx mouse, suggesting microRNAs may have a role in the pathophysiology of muscular dystrophy.

Ets-2 repressor factor silences extrasynaptic utrophin by N-box mediated repression in skeletal muscle

Utrophin is the autosomal homologue of dystrophin, the protein product of the Duchenne's muscular dystrophy (DMD) locus. Utrophin expression is temporally and spatially regulated being developmentally down-regulated perinatally and enriched at neuromuscular junctions (NMJs) in adult muscle. Synaptic localization of utrophin occurs in part by heregulin-mediated extracellular signal-regulated kinase (ERK)-phosphorylation, leading to binding of GABPalpha/beta to the N-box/EBS and activation of the major utrophin promoter-A expressed in myofibers. However, molecular mechanisms contributing to concurrent extrasynaptic silencing that must occur to achieve NMJ localization are unknown. We demonstrate that the Ets-2 repressor factor (ERF) represses extrasynaptic utrophin-A in muscle. Gel shift and chromatin immunoprecipitation studies demonstrated physical association of ERF with the utrophin-A promoter N-box/EBS site. ERF overexpression repressed utrophin-A promoter activity; conversely, small interfering RNA-mediated ERF knockdown enhanced promoter activity as well as endogenous utrophin mRNA levels in cultured muscle cells in vitro. Laser-capture microscopy of tibialis anterior NMJ and extrasynaptic transcriptomes and gene transfer studies provide spatial and direct evidence, respectively, for ERF-mediated utrophin repression in vivo. Together, these studies suggest "repressing repressors" as a potential strategy for achieving utrophin up-regulation in DMD, and they provide a model for utrophin-A regulation in muscle.

Comparative in silico analysis of two vaccine candidates for group A streptococcus predicts that they both may have similar safety profiles

BACKGROUND

Concerns of immune cross-reactivity, between epitopes of the group A streptococcal (GAS) M-proteins and host proteins have hindered the progress of an effective GAS vaccine. An ideal M-protein based subunit vaccine should not elicit heart tissue cross-reactive antibody responses and should not activate M-protein specific CD4+ T-cells. In the current study we used a bioinformatic and immunoinformatic approach to assess the safety of J8 and J14, chimeric vaccine constructs containing a GAS derived M-protein epitope embedded in flanking GCN4 region. We demonstrate that at the primary amino acid level J8 and J14 show very little homology to human proteins. ProPred, RANKPEP and HLABIND algorithms failed to predict significant binding between the M-protein specific regions of J8 and J14 and class II binding alleles. A single peptide was predicted to bind to HLA class I allele B_2705. This data was supported by cellular proliferation assays demonstrating few peripheral blood mononuclear cells (PBMCs) from donors respond to J8 and J14. Reassuringly, there was no correlation between proliferation to these peptides, and proliferation to host proteins. This data suggests that J8 and J14 are unlikely to induce cross-reactive immune responses, and will be safe for use in humans.

Dissecting the signaling and mechanical functions of the dystrophin-glycoprotein complex

Duchenne muscular dystrophy is a severe disorder caused by mutations in the dystrophin gene. Dystrophin is required for assembly of the dystrophin-glycoprotein complex and provides a mechanically strong link between the cytoskeleton and the extracellular matrix. Several proteins in the complex also participate in signaling cascades, but the relationship between these signaling and mechanical functions in the development of muscular dystrophy is unclear. To explore the mechanisms of myofiber necrosis in dystrophin-deficient muscle, we tested the hypothesis that restoration of this complex without a link to the cytoskeleton ameliorates dystrophic pathology. Transgenic mice were generated that express Dp116, a non-muscle isoform of dystrophin that assembles the dystrophin-glycoprotein complex, in muscles of dystrophin-deficient mdx4cv mice. However, the phenotype of these mice was more severe than in controls. Displacement of utrophin by Dp116 correlated with the severity of dystrophy in different muscle groups. Comparison with other transgenic lines demonstrated that parts of the dystrophin central rod domain were required to localize neuronal nitric oxide synthase to the sarcolemma, but this was not correlated with presence or extent of dystrophy. Our results suggest that mechanical destabilization, rather than signaling dysfunction, is the primary cause of myofiber necrosis in dystrophin-deficient muscle.

Pathological pattern of Mdx mice diaphragm correlates with gradual expression of the short utrophin isoform Up71

Utrophin gene is transcribed in a large mRNA of 13 kb that codes for a protein of 395 kDa. It shows amino acid identity with dystrophin of up to 73% and is widely expressed in muscle and non-muscle tissues. Up71 is a short utrophin product of the utrophin gene with the same cysteine-rich and C-terminal domains as full-length utrophin (Up395). Using RT-PCR, Western blots analysis, we demonstrated that Up71 is overexpressed in the mdx diaphragm, the most pathological muscle in dystrophin-deficient mdx mice, compared to wild-type C57BL/10 or other mdx skeletal muscles. Subsequently, we demonstrated that this isoform displayed an increased expression level up to 12 months, whereas full-length utrophin (Up395) decreased. In addition, beta-dystroglycan, the transmembrane glycoprotein that anchors the cytoplasmic C-terminal domain of utrophin, showed similar increase expression in mdx diaphragm, as opposed to other components of the dystrophin-associated protein complex (DAPC) such as alpha-dystrobrevin1 and alpha-sarcoglycan. We demonstrated that Up71 and beta-dystroglycan were progressively accumulated along the extrasynaptic region of regenerating clusters in mdx diaphragm. Our data provide novel functional insights into the pathological role of the Up71 isoform in dystrophinopathies.

Targeted inhibition of Ca2+/calmodulin signaling exacerbates the dystrophic phenotype in mdx mouse muscle

In this study, we crossbred mdx mice with transgenic mice expressing a small peptide inhibitor for calmodulin (CaM), known as the CaM-binding protein (CaMBP), driven by the slow fiber-specific troponin I slow promoter. This strategy allowed us to determine the impact of interfering with Ca(2+)/CaM-based signaling in dystrophin-deficient slow myofibers. Consistent with impairments in the Ca(2+)/CaM-regulated enzymes calcineurin and Ca(2+)/CaM-dependent kinase, the nuclear accumulation of nuclear factor of activated T-cell c1 and myocyte enhancer factor 2C was reduced in slow fibers from mdx/CaMBP mice. We also detected significant reductions in the levels of peroxisome proliferator gamma co-activator 1alpha and GA-binding protein alpha mRNAs in slow fiber-rich soleus muscles of mdx/CaMBP mice. In parallel, we observed significantly lower expression of myosin heavy chain I mRNA in mdx/CaMBP soleus muscles. This correlated with fiber-type shifts towards a faster phenotype. Examination of mdx/CaMBP slow muscle fibers revealed significant reductions in A-utrophin, a therapeutically relevant protein that can compensate for the lack of dystrophin in skeletal muscle. In accordance with lower levels of A-utrophin, we noted a clear exacerbation of the dystrophic phenotype in mdx/CaMBP slow fibers as exemplified by several pathological indices. These results firmly establish Ca(2+)/CaM-based signaling as key to regulating expression of A-utrophin in muscle. Furthermore, this study illustrates the therapeutic potential of using targets of Ca(2+)/CaM-based signaling as a strategy for treating Duchenne muscular dystrophy (DMD). Finally, our results further support the concept that strategies aimed at promoting the slow oxidative myofiber program in muscle may be effective in altering the relentless progression of DMD.

Utrophin upregulation for treating Duchenne or Becker muscular dystrophy: how close are we?

Duchenne muscular dystrophy (DMD) is a severe muscle-wasting disorder for which there is currently no effective treatment. This disorder is caused by mutations or deletions in the gene encoding dystrophin that prevent expression of dystrophin at the sarcolemma. A promising pharmacological treatment for DMD aims to increase levels of utrophin, a homolog of dystrophin, in muscle fibers of affected patients to compensate for the absence of dystrophin. Here, we review recent developments in our understanding of the regulatory pathways that govern utrophin expression, and highlight studies that have used activators of these pathways to alleviate the dystrophic symptoms in DMD animal models. The results of these preclinical studies are promising and bring us closer to implementing appropriate utrophin-based drug therapies for DMD patients.

Absence of alpha 7 integrin in dystrophin-deficient mice causes a myopathy similar to Duchenne muscular dystrophy

Both the dystrophin-glycoprotein complex and alpha7beta1 integrin have critical roles in the maintenance of muscle integrity via the provision of mechanical links between muscle fibres and the basement membrane. Absence of either dystrophin or alpha7 integrin results in a muscular dystrophy. To clarify the role of alpha7 integrin and dystrophin in muscle development and function, we generated integrin alpha7/dystrophin double-mutant knockout (DKO) mice. Surprisingly, DKO mice survived post-natally and were indistinguishable from wild-type, integrin alpha7-deficient and mdx mice at birth, but died within 24-28 days. Histological analysis revealed a severe muscular dystrophy in DKO mice with endomysial fibrosis and ectopic calcification. Weight loss was correlated with the loss of muscle fibres, indicating that progressive muscle wasting in the double mutant was most likely due to inadequate muscle regeneration. The data further support that premature death of DKO mice is due to cardiac and/or respiratory failure. The integrin alpha7/dystrophin-deficient mouse model, therefore, resembles the pathological changes seen in Duchenne muscular dystrophy and suggests that the different clinical severity of dystrophin deficiency in human and mouse may be due to a fine-tuned difference in expression of dystrophin and integrin alpha7 in both species. Together, these findings indicate an essential role for integrin alpha7 in the maintenance of dystrophin-deficient muscles.

The GTPase RhoA increases utrophin expression and stability, as well as its localization at the plasma membrane

The Rho family of small GTPases are signalling molecules involved in cytoskeleton remodelling and gene transcription. Their activities are important for many cellular processes, including myogenesis. In particular, RhoA positively regulates skeletal-muscle differentiation. We report in the present study that the active form of RhoA increases the expression of utrophin, the autosomal homologue of dystrophin in the mouse C2C12 and rat L8 myoblastic cell lines. Even though this RhoA-dependent utrophin increase is higher in proliferating myoblasts, it is maintained during myogenic differentiation. This occurs via two mechanisms: (i) transcriptional activation of the utrophin promoter A and (ii) post-translational stabilization of utrophin. In addition, RhoA increases plasma-membrane localization of utrophin. Thus RhoA activation up-regulates utrophin levels and enhances its localization at the plasma membrane.

Increased matrix-metalloproteinase-2 and matrix-metalloproteinase-9 expression in the brain of dystrophic mdx mouse

Brain edema and severe alterations of the glial and endothelial cells have recently been demonstrated in the dystrophin-deficient mdx mouse, an experimental model of Duchenne muscular dystrophy, and an increase in microvessel density in patients affected by Duchenne muscular dystrophy has also been shown. In order to further elucidate the mechanisms underlying the angiogenetic processes occurring in Duchenne muscular dystrophy, in this study we analyzed matrix-metalloproteinase-2 and -9 expression in the brain of 20-month-old mdx and control mice by means of immunohistochemistry, in situ hybridization, immunoblotting and gelatin zymography. Moreover, we studied vascular endothelial growth factor expression by means of Western blot and immunohistochemistry, and by dual immunofluorescence using anti-vascular endothelial growth factor and anti matrix-metalloproteinase-2 and-9 antibodies. Ultrastructural features of the brain choroidal plexuses were evaluated by electron microscopy. Spatial relationships between endothelium and astrocyte processes were studied by confocal laser microscopy, using an anti-CD31 antibody as a marker of endothelial cells, and anti-glial fibrillary acidic protein (GFAP) as a marker of glial cells. The results demonstrate that high expression of matrix-metalloproteinase-2 and matrix-metalloproteinase-9 protein content occurs in mdx brain and in choroidal plexuses where, by in situ hybridization, matrix-metalloproteinase-2 and matrix-metalloproteinase-9 mRNA was localized in the epithelial cells. Moreover, matrix-metalloproteinase-2 mRNA was found in both mdx perivascular astrocytes and blood vessels, while matrix-metalloproteinase-9 mRNA was localized in mdx vessels. Through zymography, increased expression of matrix-metalloproteinase-2 and matrix-metalloproteinase-9 was found in mdx brain compared with the controls. These enhanced matrix-metalloproteinase levels in mdx mice were found to be associated with increased vascular endothelial growth factor expression, as determined by immunoblotting and immunocytochemistry and with ultrastructural alterations of the mdx choroidal epithelial cells and brain vessels, as previously reported [Nico B, Frigeri A, Nicchia GP, Corsi P, Ribatti D, Quondamatteo F, Herken R, Girolamo F, Marzullo A, Svelto M, Roncali L (2003) Severe alterations of endothelial and glial cells in the blood-brain barrier of dystrophic mdx mice. Glia 42:235-251]. Indeed, in the mdx epithelial cells of the plexuses, the apical microvilli were located on the lateral membranes, whereas in the controls they were uniformly distributed over the free ventricular surface. Moreover, by dual immunofluorescence, a colocalization of vascular endothelial growth factor and matrix-metalloproteinase-2 and matrix-metalloproteinase-9 was found in the ependymal and epithelial cells of plexuses in mdx mice and, under confocal laser microscopy, mdx CD-31 positive vessels were enveloped by less GFAP-positive astrocyte processes than the controls. Overall, these data point to a specific pathogenetic role of matrix-metalloproteinase-2 and matrix-metalloproteinase-9 in neurological dysfunctions associated with Duchenne muscular dystrophy.

A and B utrophin in human muscle and sarcolemmal A-utrophin associated with tumours

Utrophin is an autosomal homologue of dystrophin, abnormal expression of which is responsible for X-linked Duchenne and Becker muscular dystrophy. In normal mature muscle utrophin is confined to blood vessels, nerves and myotendinous and neuromuscular junctions. When dystrophin is absent utrophin is abundant on the sarcolemma. This has raised the possibility that up-regulation of utrophin may be of therapeutic benefit. Two full-length transcripts of utrophin, A and B, have been identified, which are regulated by alternatively spliced 5' promoters. In dystrophic mouse muscle, the A isoform is present on the sarcolemma, whereas the B form is confined to blood vessels. We show here using immunohistochemistry and human isoform-specific antibodies that A- and B-utrophin localisation is the same in human muscle. The A isoform is present on the sarcolemma of foetal human muscle fibres, regenerating fibres, fibres deficient in dystrophin and on blood vessels and neuromuscular junctions. B-utrophin is only detected on blood vessels. We also show that muscle adjacent to some soft tissue tumours shows increased sarcolemmal utrophin-A, showing that utrophin and dystrophin can simultaneously localise to the sarcolemma and raising the possibility that factor(s) from the tumour cells or accompanying inflammatory cells may have a role in regulating utrophin.

The utrophin A 5'-untranslated region confers internal ribosome entry site-mediated translational control during regeneration of skeletal muscle fibers

Utrophin up-regulation in muscle fibers of Duchenne muscular dystrophy patients represents a potential therapeutic strategy. It is thus important to delineate the regulatory events presiding over utrophin in muscle in attempts to develop pharmacological interventions aimed at increasing utrophin expression. A number of studies have now shown that under several experimental conditions, the abundance of utrophin is increased without a corresponding elevation in its mRNA. Here, we examine whether utrophin expression is regulated at the translational level in regenerating muscle fibers. Treatment of mouse tibialis anterior muscles with cardiotoxin to induce muscle degeneration/regeneration led to a large (approximately 14-fold) increase in the levels of utrophin A with a modest change in expression of its transcript (40%). Isolation of the mouse utrophin A 5'-untranslated region (UTR) revealed that it is relatively long with a predicted high degree of secondary structure. In control muscles, the 5'-UTR of utrophin A caused an inhibition upon translation of a reporter protein. Strikingly, this inhibition was removed during regeneration, indicating that expression of utrophin A in regenerating muscles is translationally regulated via its 5'-UTR. Using bicistronic reporter vectors, we observed that this translational effect involves an internal ribosome entry site in the utrophin A 5'-UTR. Thus, internal ribosome entry site-mediated translation of utrophin A can, at least partially, account for the discordant expression of utrophin A protein and transcript in regenerating muscle. These findings provide a novel target for up-regulating levels of utrophin A in Duchenne muscular dystrophy muscle fibers via pharmacological interventions.

A 1.3 kb promoter fragment confers spatial and temporal expression of utrophin A mRNA in mouse skeletal muscle fibers

Upregulation of utrophin in muscle is currently being examined as a potential therapy for Duchenne muscular dystrophy patients. In this context, we generated transgenic mice harboring a 1.3 kb human utrophin A promoter fragment driving expression of the lacZ gene. Characterization of reporter expression during postnatal muscle development revealed that the levels and localization of beta-galactosidase parallel expression of utrophin A transcripts. Moreover, we noted that the utrophin A promoter is more active in slow soleus muscles. Additionally, expression of the reporter gene was regulated during muscle regeneration in a manner similar to utrophin A transcripts. Together, these results show that the utrophin A promoter-lacZ construct mirrors expression of utrophin A mRNAs indicating that this utrophin A promoter fragment confers temporal and spatial patterns of expression in skeletal muscle. This transgenic mouse will be valuable as an in vivo model for developing and testing molecules aimed at increasing utrophin A expression.

Satellite cells and utrophin are not directly correlated with the degree of skeletal muscle damage inmdxmice

To determine whether muscle satellite cells and utrophin are correlated with the degree of damage in mdx skeletal muscles, we measured the area of the degenerative region as an indicator of myofiber degeneration in the masseter, gastrocnemius, soleus, and diaphragm muscles of mdx mice. Furthermore, we analyzed the expression levels of the paired box homeotic gene 7 ( pax7), m-cadherin (the makers of muscle satellite cells), and utrophin mRNA. We also investigated the immunolocalization of m-cadherin and utrophin proteins in the muscles of normal C57BL/10J (B10) and mdx mice. The expression level of pax7 mRNA and the percentage of m-cadherin-positive cells among the total number of cell nuclei in the muscle tissues in all four muscles studied were greater in the mdx mice than in the B10 mice. However, there was no significant correlation between muscle damage and expression level for pax7 mRNA ( R = −0.140), nor was there a correlation between muscle damage and the percentage of satellite cells among the total number of cell nuclei ( R = −0.411) in the mdx mice. The expression level of utrophin mRNA and the intensity of immunostaining for utrophin in all four muscles studied were greater in the mdx mice than in the B10 mice. However, there also was not a significant correlation between muscle damage and expression level of utrophin mRNA ( R = 0.231) in the mdx mice, although upregulated utrophin was incorporated into the sarcolemma. These results suggest that satellite cells and utrophin are not directly correlated with the degree of skeletal muscle damage in mdx mice.

The utrophin promoter A drives high expression of the transgenic LacZ gene in liver, testis, colon, submandibular gland, and small intestine

BACKGROUND

Duchenne muscular dystrophy (DMD) is caused by the absence of the muscle cytoskeletal protein dystrophin. Utrophin is an autosomal homologue of dystrophin, and overexpression of the protein is expected to compensate for the defect of dystrophin. The utrophin gene has two promoters, A and B, and promoter A of the utrophin gene is a possible target of pharmacological interventions for DMD because A-utrophin is up-regulated in dystrophin-deficient mdx skeletal and cardiac muscles. To investigate the utrophin promoter A activity in vivo, we generated nuclear localization signal-tagged LacZ transgenic mice, where the LacZ gene was driven by the 5-kb flanking region of the A-utrophin gene.

METHODS

Four transgenic lines were established by mating four independent founders with C57BL/6J mice. The levels of mRNA for beta-galactosidase in several tissues were examined by RT-PCR. Cryosections from several tissues were stained with hematoxylin and eosin (H&E) and with 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal).

RESULTS

The 5-kb upstream region of the A-utrophin gene showed high transcriptional activity in liver, testis, colon, submandibular gland, and small intestine, consistent with the endogenous expression of utrophin protein. Surprisingly, the levels of both beta-gal protein and mRNA for the transgene in cardiac and skeletal muscles were extremely low, even in nuclei near the neuromuscular junctions. These results indicate that the regulation of the utrophin gene in striated muscle is different from that in non-muscle tissues.

CONCLUSIONS

Our results clearly showed that the utrophin A promoter is not sufficient to drive expression in muscle, but other regulatory elements are required.

Molecular, cellular, and pharmacological therapies for Duchenne/Becker muscular dystrophies

Although the molecular defect causing Duchenne/Becker muscular dystrophy (DMD/BMD) was identified nearly 20 years ago, the development of effective therapeutic strategies has nonetheless remained a daunting challenge. Over the years, a variety of different approaches have been explored in an effort to compensate for the lack of the DMD gene product called dystrophin. This review not only presents some of the most promising molecular, cellular, and pharmacological strategies but also highlights some issues that need to be addressed before considering their implementation. Specifically, we describe current strategies being developed to exogenously deliver healthy copies of the dystrophin gene to dystrophic muscles. We present the findings of several studies that have focused on repairing the mutant dystrophin gene using various approaches. We include a discussion of cell-based therapies that capitalize on the use of myoblast or stem cell transfer. Finally, we summarize the results of several studies that may eventually lead to the development of appropriate drug-based therapies. In this context, we review our current knowledge of the mechanisms regulating expression of utrophin, the autosomal homologue of dystrophin. Given the complexity associated with the dystrophic phenotype, it appears likely that a combinatorial approach involving different therapeutic strategies will be necessary for the appropriate management and eventual treatment of this devastating neuromuscular disease.

Factors Associated with Induced Chronic Inflammation in mdx Skeletal Muscle Cause Posttranslational Stabilization and Augmentation of Extrasynaptic Sarcolemmal Utrophin

Chronic inflammation in tibialis anterior muscles of mdx mice was produced by a single injection of a recombinant adenovirus vector (AV) expressing an immunogenic beta-galactosidase (beta-gal). In regions of intense beta-gal staining, mononuclear infiltrates abounded, and muscle fibers showed strong extrasynaptic utrophin immunostaining, restoration of dystrophin-associated protein complex, and a marked reduction of the prevalence of centronucleation. Immunoblot analysis confirmed an increase of endogenous utrophin without an increase of the mRNA of the major muscle isoform utrA. Significantly better maximal tetanic force values were demonstrated in the inflammatory versus control mdx muscles. The resistance to lengthening contraction- induced damage was also significantly increased in the former. In muscles of mice lacking TNF-alpha gene, AV vector did not induce inflammation and extrajunctional utrophin increase did not occur. In the inflammatory mdx muscles, proteolytic activity of calcium-activated calpain was reduced, and in mdx myotubes in vitro, incubation with NO donors also reduced calpain-mediated utrophin proteolysis. Since utrophin was shown to be a natural substrate of calpain and known inhibitors of calpain in cultured mdx myotubes increased utrophin levels, the above results were consistent with the following conclusions: (1) extrasynaptic utrophin increase is mainly responsible for the antidystrophic effect; (2) extrasynaptic utrophin increase is a result of posttranscriptional mechanism(s) related to proinflammatory factors; and (3) reduction of endogenous muscle calpain activity by inflammatory cytokines has an important role in the stabilization and increase of the extrasynaptic utrophin.

Expression Analysis of the SG-SSPN Complex in Smooth Muscle and Endothelial Cells of Human Umbilical Cord Vessels

Recently, participation of the sarcoglycan (SG)-sarcospan (SSPN) complex in the development of cardiomyopathy in patients with limb-girdle muscular dystrophy has been shown, and presence of the complex in smooth muscle may be important for the contraction/dilation process of vessels. However, there are few studies determining the SG-SSPN complex in vascular smooth muscle and endothelial cells of vessels. In this study, we analyzed by reverse transcriptase-polymerase chain reaction and immunofluorescence the expression of different components of the complex in vein/artery smooth muscle and endothelial cells of the human umbilical cord. By RNA analysis, we observed expression of alpha-, beta-, gamma-, delta-, epsilon-SG, and SSPN in smooth muscle cells. In endothelial cells, RNA expression was restricted to beta-, delta-, epsilon-SG, and SSPN. At protein level, we observed in smooth muscle the presence of beta-, delta-, epsilon-SG, and SSPN. In endothelial cells, immunostaining only evidenced the presence of epsilon-SG and SSPN. However, colocalization of SGs and SSPN with dystrophin and utrophin was noted. These results, interestingly, suggest that the SG-SSPN complex may either form with dystrophin or utrophin in smooth muscle cells, and with utrophin in endothelial cells. Additionally, we also observed in some smooth muscle regions the colocalization of the SG-SSPN complex with caveolin, with colocalization being more pronounced between epsilon-SG-SSPN and caveolin in endothelial cells.

Dystrophin- and MLP-deficient mouse hearts: marked differences in morphology and function, but similar accumulation of cytoskeletal proteins

In humans, cytoskeletal dystrophin and muscle LIM protein (MLP) gene mutations can cause dilated cardiomyopathy, yet these mutations may have different effects in mice, owing to increased accumulation of other, compensatory cytoskeletal proteins. Consequently, we characterized left-ventricular (LV) morphology and function in vivo using high-resolution cine-magnetic resonance imaging (MRI) in 2- to 3-month old dystrophin-deficient (mdx) and MLP-null mice, and their respective controls. LV passive stiffness was assessed in isolated, perfused hearts, and cytoskeletal protein levels were determined using Western blot analyses. In mdx mouse hearts, LV-to-body weight ratio, cavity volume, ejection fraction, stroke volume, and cardiac output were normal. However, MLP-null mouse hearts had 1.2-fold higher LV-to-body weight ratios (P<0.01), 1.5-fold higher end-diastolic volumes (P<0.01), and decreased ejection fraction compared with controls (25% vs. 66%, respectively, P<0.01), indicating dilated cardiomyopathy and heart failure. In both models, isolated, perfused heart end-diastolic pressure-volume relationships and passive left-ventricular stiffness were normal. Hearts from both models accumulated desmin and beta-tubulin, mdx mouse hearts accumulated utrophin and MLP, and MLP-null mouse hearts accumulated dystrophin and syncoilin. Although the increase in MLP and utrophin in the mdx mouse heart was able to compensate for the loss of dystrophin, accumulation of desmin, syncoilin and dystrophin were unable to compensate for the loss of MLP, resulting in heart failure.

Okadaic acid augments utrophin in myogenic cells

Duchenne muscular dystrophy is a fatal childhood disease caused by mutations that abolish the expression of dystrophin in muscle. Utrophin is a paralogue of dystrophin and can functionally replace it in skeletal muscle. A potential therapeutic approach is to increase utrophin levels in muscle. One way to achieve this aim is to increase the expression of the utrophin gene at a transcriptional level via promoter activation. In this study, we have shown that utrophin A mRNA levels can be induced by okadaic acid in murine myogenic C2C12 cells. We have found that a utrophin A promoter reporter can be induced by Sp1 in C2C12 myoblasts, but not in myotubes. This activation can be enhanced by okadaic acid treatment. Our data suggest that this induction is due to Sp1 phosphorylation during myogenesis and thus, utrophin expression in muscle could be regulated by treatment with phosphatase inhibitors. Control of utrophin promoter activation could then be used to increase the expression of utrophin, and thus ameliorate the symptoms of Duchenne muscular dystrophy.

A-utrophin up-regulation in mdx skeletal muscle is independent of regeneration

Duchenne muscular dystrophy is a fatal childhood disease caused by mutations that abolish the expression of dystrophin in muscle. Utrophin is a paralogue of dystrophin and can functionally replace it in skeletal muscle. A method to induce utrophin up-regulation in muscle should therefore be therapeutically useful in Duchenne muscular dystrophy. The search for such a method needs to be informed by an understanding of the mechanisms controlling utrophin expression in muscle. Two full length utrophin isoforms are expressed: A and B. A-utrophin is up-regulated in dystrophin deficient skeletal muscle and we sought to test the hypothesis that this up-regulation occurs as a consequence of ongoing regeneration. We measured utrophin expression by immunohistochemistry and immunoblotting in the oesophageal outer muscular layer and in gamma-irradiated limb muscle from mdx mice. Skeletal muscle in these tissues is dystrophin deficient but not regenerating; we found that A-utrophin up-regulation still occurred. We conclude that utrophin up-regulation in skeletal muscle does not depend on regeneration. An alternative hypothesis involving competition for binding sites between utrophin and dystrophin is discussed. These results have important implications for future studies aiming to effect therapeutic utrophin up-regulation in Duchenne muscular dystrophy patients.

Advances in Duchenne muscular dystrophy gene therapy

Since the initial characterization of the genetic defect for Duchenne muscular dystrophy, much effort has been expended in attempts to develop a therapy for this devastating childhood disease. Gene therapy was the obvious answer but, initially, the dystrophin gene and its product seemed too large and complex for this approach. However, our increasing knowledge of the organization of the gene and the role of dystrophin in muscle function has indicated ways to manipulate them both. Gene therapy for Duchenne muscular dystrophy now seems to be in reach.

Autosomal dominant progressive nephropathy with deafness: linkage to a new locus on chromosome 11q24

Focal segmental glomerulosclerosis (FSGS) and Alport syndrome (AS) are two major causes of end-stage renal disease (ESRD). A few families with autosomal dominant FSGS have been reported with linkage to chromosome 19q13 or 11q22, while AS is usually linked to mutations in type IV collagen (COL4) subunit genes. A phenotype resembling AS may also be seen with myosin heavy chain-9 (MYH9) gene mutations. This study ascertained a multigeneration family (CHP-177) with clinical aspects of both FSGS and AS where we identified a new locus for the trait. A genome-wide scan was performed with 400 markers, and fine mapping was performed for chromosome 11 markers. Data were analyzed by GENEHUNTER and VITESSE under various models. CHP-177 is a 39-member kindred residing near New Delhi, India, with seven affecteds and showed male-to-male transmission. Two members had ESRD. Renal biopsies showed both FSGS lesions and thin glomerular basement membranes. Five of the affecteds also had sensorineural deafness, which involved both low and high frequency in some members. The AS loci, i.e., COL4A3/COL4A4 and MYH9 (LOD scores: -6.1 and -4.3, respectively) and FSGS loci, on 19q13 and 11q22, were excluded from linkage. A significant evidence of linkage was observed for 11q24 region, with a multipoint LOD (z-score) of 3.2 for marker D11S4464 at theta = 0. The z-1 confidence interval for the linked region spans a genetic distance of 7 cM. This study thus reports an autosomal dominant nephropathy with features of both FSGS and AS in which linkage to currently known loci for such phenotypes was excluded and a new locus on 11q24 was identified. The findings suggest further locus heterogeneity for the autosomal dominant nephropathy phenotype.

Expression of utrophin A mRNA correlates with the oxidative capacity of skeletal muscle fiber types and is regulated by calcineurin/NFAT signaling

Utrophin levels have recently been shown to be more abundant in slow vs. fast muscles, but the nature of the molecular events underlying this difference remains to be fully elucidated. Here, we determined whether this difference is due to the expression of utrophin A or B, and examined whether transcriptional regulatory mechanisms are also involved. Immunofluorescence experiments revealed that slower fibers contain significantly more utrophin A in extrasynaptic regions as compared with fast fibers. Single-fiber RT-PCR analysis demonstrated that expression of utrophin A transcripts correlates with the oxidative capacity of muscle fibers, with cells expressing myosin heavy chain I and IIa demonstrating the highest levels. Functional muscle overload, which stimulates expression of a slower, more oxidative phenotype, induced a significant increase in utrophin A mRNA levels. Because calcineurin has been implicated in controlling this slower, high oxidative myofiber program, we examined expression of utrophin A transcripts in muscles having altered calcineurin activity. Calcineurin inhibition resulted in an 80% decrease in utrophin A mRNA levels. Conversely, muscles from transgenic mice expressing an active form of calcineurin displayed higher levels of utrophin A transcripts. Electrophoretic mobility shift and supershift assays revealed the presence of a nuclear factor of activated T cells (NFAT) binding site in the utrophin A promoter. Transfection and direct gene transfer studies showed that active forms of calcineurin or nuclear NFATc1 transactivate the utrophin A promoter. Together, these results indicate that expression of utrophin A is related to the oxidative capacity of muscle fibers, and implicate calcineurin and its effector NFAT in this mechanism.

Pharmacological strategies for muscular dystrophy

Duchenne muscular dystrophy (DMD) is a fatal, genetic disorder whose relentless progression underscores the urgency for developing a cure. Although Duchenne initiated clinical trials roughly 150 years ago, therapies for DMD remain supportive rather than curative. A paradigm shift towards developing rational therapeutic strategies occurred with identification of the DMD gene. Gene- and cell-based therapies designed to replace the missing gene and/or dystrophin protein have achieved varying degrees of success. However, pharmacological strategies not designed to replace dystrophin per se appear promising, and can circumvent many hurdles hampering gene- and cell-based therapy. Here, we will review present pharmacological strategies, in particular those dealing with functional substitution of dystrophin by utrophin and enhancing muscle progenitor commitment by myostatin blockade, with a view toward facilitating drug discovery for DMD.

Ets, Ap-1 and GATA factor families regulate the utrophin B promoter: potential regulatory mechanisms for endothelial-specific expression

Duchenne muscular dystrophy is caused by dystrophin deficiency, which can be prevented in the mdx mouse model by over-expression of an autosomal homologue, utrophin. Utrophin has two characterised full-length promoters, A and B. No data are available on the transcriptional regulation of B utrophin, which has been recently localised to the endothelium. Similar to characterised endothelial promoters, Ets and Ap-1 individually trans-activate the human B core promoter. Synergistic activation by GATA-2 and c-jun to the order of 20-fold was observed.