Transgenic overexpression of ADAM12 suppresses muscle regeneration and aggravates dystrophy in aged mdx mice

Muscular dystrophies are characterized by insufficient restoration and gradual replacement of the skeletal muscle by fat and connective tissue. ADAM12 has previously been shown to alleviate the pathology of young dystrophin-deficient mdx mice, a model for Duchenne muscular dystrophy. The observed effect of ADAM12 was suggested to be mediated via a membrane-stabilizing up-regulation of utrophin, alpha7B integrin, and dystroglycans. Ectopic ADAM12 expression in normal mouse skeletal muscle also improved regeneration after freeze injury, presumably by the same mechanism. Hence, it was suggested that ADAM12 could be a candidate for nonreplacement gene therapy of Duchenne muscular dystrophy. We therefore evaluated the long-term effect of ADAM12 overexpression in muscle. Surprisingly, we observed loss of skeletal muscle and accelerated fibrosis and adipogenesis in 1-year-old mdx mice transgenically overexpressing ADAM12 (ADAM12(+)/mdx mice), even though their utrophin levels were mildly elevated compared with age-matched controls. Thus, membrane stabilization was not sufficient to provide protection during prolonged disease. Consequently, we reinvestigated skeletal muscle regeneration in ADAM12 transgenic mice (ADAM12(+)) after a knife cut lesion and observed that the regeneration process was significantly impaired. ADAM12 seemed to inhibit the satellite cell response and delay myoblast differentiation. These results discourage long-term therapeutic use of ADAM12. They also point to impaired regeneration as a possible factor in development of muscular dystrophy.     

A dystroglycan mutation associated with limb-girdle muscular dystrophy

Dystroglycan, which serves as a major extracellular matrix receptor in muscle and the central nervous system, requires extensive O-glycosylation to function. We identified a dystroglycan missense mutation (Thr192→Met) in a woman with limb-girdle muscular dystrophy and cognitive impairment. A mouse model harboring this mutation recapitulates the immunohistochemical and neuromuscular abnormalities observed in the patient. In vitro and in vivo studies showed that the mutation impairs the receptor function of dystroglycan in skeletal muscle and brain by inhibiting the post-translational modification, mediated by the glycosyltransferase LARGE, of the phosphorylated O-mannosyl glycans on α-dystroglycan that is required for high-affinity binding to laminin.     

Elimination of myostatin does not combat muscular dystrophy in dy mice but increases postnatal lethality

Myostatin is a TGF-beta family member and a negative regulator of skeletal muscle growth. It has been proposed that reduction or elimination of myostatin could be a treatment for degenerative muscle diseases such as muscular dystrophy. Laminin-deficient congenital muscular dystrophy is one of the most severe forms of muscular dystrophy. To test the possibility of ameliorating the dystrophic phenotype in laminin deficiency by eliminating myostatin, we crossed dy(W) laminin alpha2-deficient and myostatin null mice. The resulting double-deficient dy(W)/dy(W);Mstn(-/-) mice had a severe clinical phenotype similar to that of dy(W)/dy(W) mice, even though muscle regeneration was increased. Degeneration and inflammation of muscle were not alleviated. The pre-weaning mortality of dy(W)/dy(W);Mstn(-/-) mice was increased compared to dy(W)/dy(W), most likely due to significantly less brown and white fat in the absence of myostatin, and postweaning mortality was not significantly improved. These results show that eliminating myostatin in laminin-deficiency promotes muscle formation, but at the expense of fat formation, and does not reduce muscle pathology. Any future therapy based on myostatin may have undesirable side effects.     

RNAi-mediated knockdown of dystrophin expression in adult mice does not lead to overt muscular dystrophy pathology

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. The peak of the pathology attributed to dystrophin deficiency happens between 3 and 8 weeks of age in mdx mice, the animal model of DMD. Accordingly, we hypothesized that the pathology observed with dystrophin deficiency may be developmentally regulated. Initially, we demonstrated that profound small interfering RNA-mediated dystrophin knockdown could be achieved in mouse primary muscle cultures. The use of adeno-associated virus vectors to express short-hairpin RNAs targeting dystrophin in skeletal muscle in vivo yielded a potent and specific dystrophin knockdown, but only after approximately 5 months, indicating the very long half-life of dystrophin. Interestingly, and in contrast to what is observed in congenital dystrophin deficiency, long-term ( approximately 1 year) dystrophin knockdown in adult mice did not result, per se, in overt dystrophic pathology or upregulation of utrophin. This supports our hypothesis and suggests new pathophysiology of the disease. Furthermore, taking into account the rather long half-life of dystrophin, and the notion that the development of pathology is age-dependent, it indicates that a single gene therapy approach before the onset of pathology might convey a long-term cure for DMD.     

Pikachurin interaction with dystroglycan is diminished by defective O-mannosyl glycosylation in congenital muscular dystrophy models and rescued by LARGE overexpression

Visuo-tactile integration occurs in a privileged way in peripersonal space, namely when visual and tactile stimuli are in spatial proximity. Here, we investigated whether crossmodal spatial effects (i.e. stronger crossmodal interactions for spatially congruent compared to incongruent visual and tactile stimuli) are also present when visual stimuli presented near the body are indirectly viewed in a mirror, thus appearing in far space. Participants had to attend to one of their hands throughout a block of stimuli in order to detect infrequent tactile target stimuli at that hand while ignoring tactile targets at the unattended hand, all tactile non-target stimuli, and any visual stimuli. Visual stimuli were presented simultaneously with tactile stimuli, in the same (congruent) or opposite (incongruent) hemispace with respect to the tactile stimuli. In one group of participants the visual stimuli were delivered near the participants' hands and were observed as indirect mirror reflections ('mirror' condition), while in the other group these were presented at a distance from the hands ('far' condition). The main finding was that crossmodal spatial modulations of ERPs recorded over and close to somatosensory cortex were present in the 'mirror' condition but not the 'far' condition. That is, ERPs were enhanced in response to tactile stimuli coupled with spatially congruent versus incongruent visual stimuli when the latter were viewed through a mirror. These effects emerged around 190 ms after stimuli onset, and were modulated by the focus of spatial attention. These results provide evidence that visual stimuli observed in far space via a mirror are coded as near-the-body stimuli according to their known rather than to their perceived location. This suggests that crossmodal interactions between vision and touch may be modulated by previous knowledge of reflecting surfaces (i.e. top-down processing).     

Pikachurin interaction with dystroglycan is diminished by defective O-mannosyl glycosylation in congenital muscular dystrophy models and rescued by LARGE overexpression

Congenital muscular dystrophies (CMD) such as muscle–eye–brain disease caused by defective glycosylation of α-dystroglycan (α-DG) exhibit defective photoreceptor synaptic function. Mouse knockouts of dystroglycan and its extracellular matrix binding partner pikachurin recapitulate this phenotype. In this study, pikachurin–α-dystroglycan interactions in several mouse models of CMD were examined by pikachurin overlay experiments. The results show that hypoglycosylation of α-dystroglycan resulted in markedly reduced pikachurin–α-dystroglycan interactions. Expression of pikachurin is abolished at the outer plexiform layer of two mouse models, protein O-mannose N-acetylglucosaminyl transferase 1 (POMGnT1) knockout and Large^myd mice. Overexpressing LARGE restored this interaction in POMGnT1 knockout cells. These results indicate that pikachurin interactions with α-dystroglycan and its localization at the photoreceptor ribbon synapse require normal glycosylation of α-dystroglycan.     

Evaluation of the gastrointestinal tract in mdx mice: an experimental model of Duchenne muscular dystrophy

This study describes the functional and morphological alterations in the intestines of mdx mice (n = 4) compared with the intestinal features of C57BL/10 mice (n = 7) at 2 months of age. The whole gut transit time (carmine red) and the upper gut transit time (activated charcoal) were measured, and light microscopy was utilized to view stained sections (H&E and picrosirius red) for histological analysis. No significant difference in mean evacuation time for the whole gut was observed between the two groups, but a significant delay in activated charcoal passage was observed in the mdx mice. Visually, a higher concentration of collagen fibers in the submucosal region was apparent in the mdx mice. The concentration of collagen fibers in the stomach and small intestine suggests a direct relationship with the decrease in motility of the upper gastrointestinal tract in the mdx mice. Further experimental studies should be conducted to develop therapeutic alternatives to collagen inhibition to control these manifestations.     

Monosomy of distal 4q does not cause facioscapulohumeral muscular dystrophy.

Facioscapulohumeral muscular dystrophy (FSHD) is a hereditary neuromuscular disorder transmitted in an autosomal dominant fashion. FSHD has been located by linkage analysis in the most distal part of chromosome 4q. The disease is associated with deletions within a 3.2 kb tandem repeat sequence, D4Z4. We have studied a family in which an abnormal chromosome 4 segregates through three generations in phenotypically normal subjects. This chromosome is the derivative of a (4;D or G) (q35;p12) translocation. Molecular analysis of the region 4q35 showed the absence of the segment ranging from the telomere to locus D4F104S1. Probe p13E-11 (D4F104S1), which detects polymorphic EcoRI fragments containing D4Z4, in Southern blot analysis showed only one allele in the carriers of the abnormal chromosome 4. Probe p13E-11 EcoRI fragments are contained in the subtelomeric region of 4q and their rearrangements associated with FSHD suggested that the gene responsible for the muscular dystrophy could be subject to a position effect variegation (PEV) because of its proximity to subtelomeric heterochromatin. The absence of the 4q telomeric region in our phenotypically normal cases indicates that haploinsufficiency of the region containing D4Z4 does not cause FSHD.     

Dissociation of the dystroglycan complex in caveolin-3-deficient limb girdle muscular dystrophy

Limb girdle muscular dystrophy is a group of clinically and genetically heterogeneous disorders inherited in an autosomal recessive or dominant mode. Caveolin-3, the muscle-specific member of the caveolin gene family, is implicated in the pathogenesis of autosomal dominant limb girdle muscular dystrophy 1C. Here we report on a 4-year-old girl presenting with myalgia and muscle cramps due to a caveolin-3 deficiency in her dystrophic skeletal muscle as a result of a heterozygous 136G-->A substitution in the caveolin-3 gene. The novel sporadic missense mutation in the caveolin signature sequence of the caveolin-3 gene changes an alanine to a threonine (A46T) and prevents the localization of caveolin-3 to the plasma membrane in a dominant negative fashion. Caveolin-3 has been suggested to interact with the dystrophin-glycoprotein complex, which in striated muscle fibers links the cytoskeleton to the extracellular matrix and with neuronal nitric oxide synthase. Similar to dystrophin-deficient Duchenne muscular dystrophy, a secondary decrease in neuronal nitric oxide synthase and alpha-dystroglycan expression was detected in the caveolin-3-deficient patient. These results implicate an important function of the caveolin signature sequence and common mechanisms in the pathogenesis of dystrophin-glycoprotein complex-associated muscular dystrophies with caveolin-3-deficient limb girdle muscular dystrophy.     

Comparative evolution of muscular dystrophy in diaphragm,gastrocnemius and masseter muscles from old male mdx mice

X chromosome-linked muscular dystrophic mdx mouse lacks the sarcolemmal protein dystrophin and represents a genetic homologue of human Duchenne muscular dystrophy (DMD). The present study analysed some aspects of pathological processes such as fibrosis, frequency of centralized nuclei, presence of degenerative or regenerative fibres, expression of utrophin and associated protein complexes, and myosin heavy chain isoforms in three muscles [diaphragm (DIA), gastrocnemius (GTC) and masseter (MAS)] from old male mdx mice. All parameters investigated comparatively in these pathological muscles provided evidence that the MAS mdx muscle presents a slight deterioration pattern in comparison to that of DIA and GTC muscles. Utrophin and associated proteins are present in many cell clusters with continuous membrane labelling in MAS muscle. Respective proportions of myosin heavy chain isoforms, measured by electrophoresis/densitometry, showed only slight change in GTC muscle, significant evolution in DIA muscle but drastic isoform conversions in MAS muscle. These results highlighted the difference in deterioration susceptibility of various muscles to muscular dystrophy. The reason why this occurs in MAS muscles is still obscure and discussed in terms of the comparative developmental origins of these muscles.     

Calcium-binding proteins in skeletal muscles of the mdx mice: potential role in the pathogenesis of Duchenne muscular dystrophy

Duchenne muscular dystrophy is one of the most common hereditary diseases. Abnormal ion handling renders dystrophic muscle fibers more susceptible to necrosis and a rise in intracellular calcium is an important initiating event in dystrophic muscle pathogenesis. In the mdx mice, muscles are affected with different intensities and some muscles are spared. We investigated the levels of the calcium-binding proteins calsequestrin and calmodulin in the non-spared axial (sternomastoid and diaphragm), limb (tibialis anterior and soleus), cardiac and in the spared extraocular muscles (EOM) of control and mdx mice. Immunoblotting analysis showed a significant increase of the proteins in the spared mdx EOM and a significant decrease in the most affected diaphragm. Both proteins were comparable to the cardiac muscle controls. In limb and sternomastoid muscles, calmodulin and calsequestrin were affected differently. These results suggest that differential levels of the calcium-handling proteins may be involved in the pathogenesis of myonecrosis in mdx muscles. Understanding the signaling mechanisms involving Ca²⁺-calmodulin activation and calsequestrin expression may be a valuable way to develop new therapeutic approaches to the dystrophinopaties.     

Hereditary muscular dystrophy in mdx mice as a homologous model for introduction of cell technologies in the treatment of progressive muscular dystrophies in humans

Life-time monitoring of the main clinical and laboratory manifestations of hereditary muscular dystrophy in mdx mice confirmed the presence of mutation in exon 23 of dystrophin gene and the absence of this protein in skeletal muscles of mutant animals. Muscular dystrophy in mice was similar to human progressive muscle disorder, which allows the use of this model for the development of cell technologies for the treatment of hereditary muscular diseases in humans.Translated from Byulleten Eksperimentalnoi Biologii i Meditsiny, Vol. 138, No. 10, pp. 477–480, October, 2004     

Axonal sprouting in mdx mice and its relevance to cell and gene mediated therapies for Duchenne muscular dystrophy

We investigated whether pre-terminal axons and motor terminals retained their ability to sprout in the murine X-linked muscular dystrophy (mdx). Immunofluorescence confocal microscopy observation of nerve terminals and acetylcholine receptors in mdx muscles with crushed and non-crushed nerves showed that most of the junctions had intraterminal sprouting and that the number of junctions with extraterminal sprouting increased after the nerve crush lesion. Since new dystrophin-positive muscle fibers generated by cell-mediated therapies need to be innervated to proceed with their maturation and dystrophin production, these results suggest that the use of inducing factors to increase the sprouting capacity of nerve terminals could be an additional tool in the success of cell-mediated therapies.     

Expression of human full-length and minidystrophin in transgenic mdx mice: implications for gene therapy of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a lethal X-linked recessivedisorder with a high spontaneous mutation rate and no effectivetreatment, hence development of genetic based therapies is animportant goal. We report that expression of a recombinant humanminidystrophin cDNA, compatible with current viral vectors,can significantly reduce the myopathic phenotype in transgenicmdx mice, even when expressed at only 20–30% of endogenousdystrophin levels at the sarcolemma. To the extent that dataobtained in mouse studies are applicable to DMD, the virtualelimination of morphological and biochemical abnormalities inthe mdx mouse supports the use of this cDNA in somatic genetherapy protocols for DMD.     

AMPK activation stimulates autophagy and ameliorates muscular dystrophy in the mdx mouse diaphragm

Duchenne muscular dystrophy (DMD) is characterized by myofiber death from apoptosis or necrosis, leading in many patients to fatal respiratory muscle weakness. Among other pathological features, DMD muscles show severely deranged metabolic gene regulation and mitochondrial dysfunction. Defective mitochondria not only cause energetic deficiency, but also play roles in promoting myofiber atrophy and injury via opening of the mitochondrial permeability transition pore. Autophagy is a bulk degradative mechanism that serves to augment energy production and eliminate defective mitochondria (mitophagy). We hypothesized that pharmacological activation of AMP-activated protein kinase (AMPK), a master metabolic sensor in cells and on-switch for the autophagy-mitophagy pathway, would be beneficial in the mdx mouse model of DMD. Treatment of mdx mice for 4 weeks with an established AMPK agonist, AICAR (5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside), potently triggered autophagy in the mdx diaphragm without inducing muscle fiber atrophy. In AICAR-treated mdx mice, the exaggerated sensitivity of mdx diaphragm mitochondria to calcium-induced permeability transition pore opening was restored to normal levels. There were associated improvements in mdx diaphragm histopathology and in maximal force-generating capacity, which were not linked to increased mitochondrial biogenesis or up-regulated utrophin expression. These findings suggest that agonists of AMPK and other inducers of the autophagy-mitophagy pathway can help to promote the elimination of defective mitochondria and may thus serve as useful therapeutic agents in DMD.     

Flk-1+ adipose-derived mesenchymal stem cells differentiate into skeletal muscle satellite cells and ameliorate muscular dystrophy in mdx mice

Duchenne muscular dystrophy (DMD) is a severe hereditary disease characterized by the absence of dystrophin on the sarcolemma of muscle fiber. This absence results in widespread muscle damage and satellite cell activation. After depletion of the satellite cell pool, skeletal muscle is then invariably replaced by connective tissue, leading to progressive muscle weakness. Herein, we isolated Flk-1(+) mesenchymal stem cells (MSCs) from adult adipose tissue and induced them to differentiate into skeletal muscle cells in culture. Within mdx mice, an animal model of DMD, adipose tissue-derived Flk-1(+) MSCs (AD-MSCs) homed to and differentiated into cells that repaired injured muscle tissue. This repair correlated with reconstitution of dystrophin expression on the damaged fibers. Flk-1(+) AD-MSCs also differentiated into muscle satellite cells. This differentiation may have accounted for long-term reconstitution. These cells also differentiated into endothelial cells, thereby possibly improving fiber regeneration as a result of the induced angiogenesis. Therefore, Flk-1(+) AD-MSC transplants may repair muscular dystrophy.     

Limb girdle muscular dystrophy in Manitoba Hutterites does not map to any of the known LGMD loci

Limb girdle muscular dystrophy (LGMD) is a heterogeneous group of disorders affecting primarily the shoulder and pelvic girdles. Autosomal dominant and recessive forms have been identified; 8 have been mapped and 1 more has been postulated on the basis of exclusion of linkage. An autosomal recessive muscular dystrophy was first described in 1976 in the Hutterite Brethren, a North American genetic and religious isolate [Shokeir and Kobrinsky, 1976; Clin Genet 9:197–202]. In this report, we discuss the results of linkage analysis in 4 related Manitoba Hutterite sibships with 21 patients affected with a mild autosomal recessive form of LGMD. Because of the difficulties in assigning a phenotype in some asymptomatic individuals, stringent criteria for the affected phenotype were employed. As a result, 7 asymptomatic relatives with only mildly elevated CK levels were assigned an unknown phenotype to prevent their possible misclassification. Two-point linkage analysis of the disease locus against markers linked to 7 of the known LGMD loci and 3 other candidate genes yielded lod scores of ≤−2 at θ=0.01 in all cases and in most cases at θ=0.05. This suggests that there is at least 1 additional locus for LGMD. Am. J. Med. Genet. 72:363–368, 1997. © 1997 Wiley-Liss, Inc.     

Transgenic overexpression of human Bcl-2 in islet beta cells inhibits apoptosis but does not prevent autoimmune destruction

Insulin-dependent diabetes mellitus results when > 90% ofthe insulin-producing ß cells in the pancreatic isletsare killed as a result of autoimmune attack by T cells. Duringthe progression to diabetes, islet ß cells die as a resultof different insults from the immune system. Agents such asperforin and granzymes, CD95 ligand and tumor necrosis factor-,or cytokines and free-radicals have all been shown to causeß cell apoptosis. The anti-apoptotic protein, Bcl-2, mightprotect against some of these stimuli. We have therefore generatedtransgenic mice expressing human Bcl-2 in their islet ßcells. Although Bcl-2 was able to prevent apoptosis inducedby cytotoxic agents against ß cells in vitro, Bcl-2 alonecould not prevent or ameliorate cytotoxic or autoimmune ßcell damage in vivo.     

Abolishing Trp53-dependent apoptosis does not benefit spinal muscular atrophy model mice

Spinal muscular atrophy (SMA) is the most common genetic motoneuron degenerative disorder, but the mechanism(s) of motoneuron death is unclear. Previously, a direct interaction between tumor-suppressive TP53 protein and the SMA determinant gene product, survival motor neuron protein, was identified and therefore it has been suggested that a mechanism of TP53-dependent apoptosis plays an important role in motoneuron degeneration in SMA. We used our SMA model mice, generated by a combination of knockout and transgenic techniques, to decipher the role of TP53 protein in the motoneuron degeneration in SMA. We detected a significant increase of Trp53 expression in the spinal cord of SMA-like mice compared to their normal littermates. After crossing SMA-like mice with Trp53 knockout mice, the progeny Trp53-deficient SMA-like mice did not show milder disease severity or longer lifespan compared to SMA littermates with wild-type Trp53 genes. Our studies provide in vivo evidence indicating that Trp53-dependent apoptosis does not play a crucial role in motoneuron degeneration in SMA-like mice. European Journal of Human Genetics (2006) 14, 372-375. doi:10.1038/sj.ejhg.5201556; published online 4 January 2006.