Analysis of gene expression differences between utrophin/dystrophin-deficient vs mdx skeletal muscles reveals a specific upregulation of slow muscle genes in limb muscles.

Dystrophin deficiency leads to the progressive muscle wasting disease Duchenne muscular dystrophy (DMD). Dystrophin-deficient mdx mice are characterized by skeletal muscle weakness and degeneration but they appear outwardly normal in contrast to DMD patients. Mice lacking both dystrophin and the dystrophin homolog utrophin [double knockout (dko)] have muscle degeneration similar to mdx mice, but they display clinical features similar to DMD patients.

Temporal and spatial mRNA expression patterns of TGF-beta1, 2, 3 and TbetaRI, II, III in skeletal muscles of mdx mice.

To address potential regulatory roles of TGF-beta1 in muscle inflammation and fibrosis associated with dystrophin deficiency, we performed quantitative RT-PCR and in situ hybridization to characterize the temporal and spatial mRNA expression patterns of TGF-beta1 and other TGF-beta subfamily members, TGF-beta2 and TGF-beta3, as well as their receptors, in quadriceps and diaphragm muscles of mdx mice. TGF-beta1 mRNA was markedly upregulated in the endomysial inflammatory cells and regenerating fibers of mdx quadriceps and diaphragm, with the mRNA levels correlated with the degree of endomysial inflammation. Upregulation of TGF-beta2, beta3, and their receptors was also appreciated but to a much lesser degree.

Distinctive morphological and gene/protein expression signatures during myogenesis in novel cell lines from extraocular and hindlimb muscle.

Skeletal muscles are not created equal. The underutilized concept of muscle allotypes defines distinct muscle groups that differ in their intrinsic capacity to express novel traits when exposed to a facilitating extrinsic environment. Allotype-specific traits may have significance as determinants of the preferential involvement or sparing of muscle groups that is observed in a variety of neuromuscular diseases.

Claudin-5 localizes to the lateral membranes of cardiomyocytes and is altered in utrophin/dystrophin-deficient cardiomyopathic mice.

Remodeling of adherens junction, gap junction, and desmosomal proteins at the intercalated discs of cardiomyocytes in heart characterizes several animal models of cardiomyopathy, especially dilated cardiac myopathy (DCM). In this study, we show that the tight junction protein, claudin-5, is present in cardiac muscle and localizes to the lateral membranes of cardiomyocytes in normal mice. We further examined claudin-5 in utrophin/dystrophin-deficient (double knockout, dko) mice, a mouse model of muscular dystrophy with cardiomyopathy, and found that claudin-5 mRNA and protein levels are decreased in dko hearts as compared with normal.

Conserved and muscle-group-specific gene expression patterns shape postnatal development of the novel extraocular muscle phenotype.

Current models in skeletal muscle biology do not fully account for the breadth, causes, and consequences of phenotypic variation among skeletal muscle groups. The muscle allotype concept arose to explain frank differences between limb, masticatory, and extraocular (EOM) muscles, but there is little understanding of the developmental regulation of the skeletal muscle phenotypic range. Here, we used morphological and DNA microarray analyses to generate a comprehensive temporal profile for rat EOM development.

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.

Postnatal suppression of myomesin, muscle creatine kinase and the M-line in rat extraocular muscle.

The M-line and its associated creatine kinase (CK) M-isoform (CK-M) are ubiquitous features of skeletal and cardiac muscle. The M-line maintains myosin myofilaments in register, links the contractile apparatus to the cytoskeleton for external force transfer and localizes CK-based energy storage and transfer to the site of highest ATP demand. We establish here that the muscle group responsible for movements of the eye, extraocular muscle (EOM), is divergent from other striated muscles in lacking both an M-line and its associated CK-M.

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).

Comprehensive expression profiling by muscle tissue class and identification of the molecular niche of extraocular muscle.

Muscle tissue is an elegant model for biologic integration of structure with function and is frequently affected by a variety of inherited diseases. Traditional muscle classes--skeletal, cardiac, and smooth--share basic aspects of contractile and energetics mechanisms but also have distinctive role-specific adaptations. We used large-scale oligonucleotide microarrays to broaden knowledge of the adaptive expression patterns underlying muscle tissue differences and to identify transcript subsets that are most likely to represent candidate disease genes.

Paradoxical absence of M lines and downregulation of creatine kinase in mouse extraocular muscle.

The M lines are structural landmarks in striated muscles, necessary for sarcomeric stability and as anchoring sites for the M isoform of creatine kinase (CK-M). These structures, especially prominent in fast skeletal muscles, are missing in rodent extraocular muscle, a particularly fast and active muscle group. In this study, we tested the hypotheses that 1).

Constitutive properties, not molecular adaptations, mediate extraocular muscle sparing in dystrophic mdx mice.

Extraocular muscle (EOM) is spared in Duchenne muscular dystrophy. Here, we tested putative EOM sparing mechanisms predicted from existing dystrophinopathy models. Data show that mdx mouse EOM contains dystrophin-glycoprotein complex (DGC)-competent and DGC-deficient myofibers distributed in a fiber type-specific pattern.

Persistent over-expression of specific CC class chemokines correlates with macrophage and T-cell recruitment in mdx skeletal muscle.

Prior studies and the efficacy of immunotherapies provide evidence that inflammation is mechanistic in pathogenesis of Duchenne muscular dystrophy. To identify putative pro-inflammatory mechanisms, we evaluated chemokine gene/protein expression patterns in skeletal muscle of mdx mice. By DNA microarray, reverse transcription-polymerase chain reaction, quantitative polymerase chain reaction, and immunoblotting, convergent evidence established the induction of six distinct CC class chemokine ligands in adult MDX: CCL2/MCP-1, CCL5/RANTES, CCL6/mu C10, CCL7/MCP-3, CCL8/MCP-2, and CCL9/MIP-1gamma.

A chronic inflammatory response dominates the skeletal muscle molecular signature in dystrophin-deficient mdx mice.

Mutations in dystrophin cause Duchenne muscular dystrophy (DMD), but absent dystrophin does not invariably cause necrosis in all muscles, life stages and species. Using DNA microarray, we established a molecular signature of dystrophinopathy in the mdx mouse, with evidence that secondary mechanisms are key contributors to pathogenesis. We used variability controls, adequate replicates and stringent analytic tools, including significance analysis of microarrays to estimate and manage false positive rates.