Molecular therapy for genetic muscle diseases--status 1999

A Critical Review of Electroporation as A Plasmid Delivery System in Mouse Skeletal Muscle

The gene delivery to skeletal muscles is a promising strategy for the treatment of both muscular disorders (by silencing or overexpression of specific gene) and systemic secretion of therapeutic proteins. The use of a physical method like electroporation with plate or needle electrodes facilitates long-lasting gene silencing in situ. It has been reported that electroporation enhances the expression of the naked DNA gene in the skeletal muscle up to 100 times and decreases the changeability of the intramuscular expression. Coelectransfer of reporter genes such as green fluorescent protein (GFP), luciferase or beta-galactosidase allows the observation of correctly performed silencing in the muscles. Appropriate selection of plasmid injection volume and concentration, as well as electrotransfer parameters, such as the voltage, the length and the number of electrical pulses do not cause long-term damage to myocytes. In this review, we summarized the electroporation methodology as well as the procedure of electrotransfer to the gastrocnemius, tibialis, soleus and foot muscles and compare their advantages and disadvantages.

Recent Progress toward Engineering HIV-1-Specific Neutralizing Monoclonal Antibodies

The recent discoveries of broadly potent neutralizing human monoclonal antibodies represent a new generation of antiretrovirals for the treatment and prophylaxis. Antibodies are generally considered more effective and safer and have been proved to provide passive protection against mucosal challenge in humanized mice and macaques. Several neutralizing Abs could protect animals against HIV-1 but are not effective when used in an established infected model for therapy. In order to overcome the limitation of antiviral activities, multiple antibody-engineering technologies have been explored to generate "the better" neutralizing antibodies against HIV-1 since bNAbs attack viral entry by various mechanisms. Thus, a promising direction of research is to discover and exploit rational antibody combination or engineered antibodies (eAbs) as potential candidate therapeutics against HIV-1. It has been reported that inclusion of fusion-neutralizing antibodies in a set of bNAbs could improve their overall activities and neutralizing spectrum. Here, we review several routes for engineering bNAbs, such as design and generation of bispecific antibodies, specific glycosylation of antibodies to enhance antiviral activity, and variable region-specific modification guided by structure and computer, as well as reviewing antibody-delivery technologies by non-viral vector, viral vector, and human hematopoietic stem/progenitor cells transduced with a lentiviral construct. We also discuss the optimized antiviral activities and benefits of these strategy and potential mechanisms.

Factors influencing the efficacy, longevity, and safety of electroporation-assisted plasmid-based gene transfer into mouse muscles

Intramuscular injection of plasmid is a potential alternative to viral vectors for the transfer of therapeutic genes into skeletal muscle fibers. The low efficiency of plasmid-based gene transfer can be enhanced by electroporation (EP) coupled with the intramuscular application of hyaluronidase. We have investigated several factors that can influence the efficiency of plasmid-based gene transfer. These factors include electrical parameters of EP, optimal use of hyaluronidase, age and strain of the host, and plasmid size. Muscles of very young and mature normal, mdx, and immunodeficient mice were injected with plasmids expressing beta-galactosidase, microdystrophin, full-length dystrophin, or full-length utrophin. Transfection efficiency, muscle fiber damage, and duration of transgene expression were analyzed. The best transfection level with the least collateral damage was attained at 175-200 V/cm. Pretreatment with hyaluronidase markedly increased transfection, which was also influenced by the plasmid size and the strain and the age of the mice. Even in immunodeficient mice, there was a significant late decline in transgene expression and plasmid DNA copies, although both still remained relatively high after 1 year. Thus, properly optimized EP-assisted plasmid-based gene transfer is a feasible, efficient, and safe method of gene replacement therapy for dystrophin deficiency of muscle but readministration may be necessary.

The molecular era of myology

This review covers, in general terms, the salient features and impact of molecular myology under the following headings: its role in providing clues for the understanding of molecular etiology and pathogenesis of genetic myopathies, its contribution to the modernization and rationalization of the classification of muscle diseases, providing means of precise diagnosis and prevention of myopathies, development of radically new cell and gene therapies, and determination of future research directions. Myology appears to be among the medical disciplines that have benefited a great deal from molecular science. This remarkable progress will hopefully translate into effective treatment capabilities in the near future.

Transfer of full-length Dmd to the diaphragm muscle of Dmd(mdx/mdx) mice through systemic administration of plasmid DNA

Mutations in the gene encoding dystrophin, a large cytoskeletal protein in muscle, lead to Duchenne muscular dystrophy (DMD). Affected individuals often die of respiratory failure resulting primarily from diaphragm muscle degeneration. Here we report a new procedure to transfer the full-length dystrophin cDNA into the diaphragm muscle of Dmd(mdx/mdx) mice, which carry a mutation in the dystrophin gene (Dmd). Significant gene transfer was found after intravenous injection of naked plasmid DNA followed by a brief (eight second) occlusion of blood flow at the vena cava. This is the first demonstration of gene transfer into the diaphragm muscle through systemic administration of naked plasmid DNA. The approach has potential application for treatment of DMD.

Dynamic restoration of dystrophin to dystrophin-deficient myotubes

Dystrophin domains are observed in myoblast transplantation experiments and in muscle fibers after somatic reversion in human Duchenne and mdx mouse muscular dystrophy. However, the formation and evolution of dystrophin-positive domains are not well established. Using a muscle satellite cell coculture system, we examined the dynamic restoration of dystrophin expression in dystrophin-deficient myotubes. The dystrophin-positive domains around source nuclei were clearly identified in hybrid myotubes. The occurrence of dystrophin domains was higher in myotubes differentiated from cocultures with a low concentration of normal wild-type satellite cells in relation to dystrophin-deficient satellite cells. At higher seeding ratios, the domain feature of dystrophin expression was more transitory and decreased as myotubes differentiated over time in culture. The average domain size initially increased with the addition of new nuclei by fusion early after differentiation of cocultures. However, separating dystrophin-positive domains according to their number of dystrophin-expressing contributory nuclei showed that diffusion of dystrophin contributed to domain elongation, even in early myotubes and later without fusion of additional nuclei. Diffusion occurred for all domains of one to six wild-type nuclei, and the diffusion rate was higher in domains with larger numbers of nuclei. This dynamic domain feature of dystrophin expression was also related to restoring the organization of dystrophin-associated proteins and acetylcholine receptors to hybrid myotubes. Factors regulating domain formation and diffusion therefore are important considerations in the design of strategies for both myoblast transplantation and gene therapy of Duchenne muscular dystrophy.

Clinical and molecular studies in a unique family with autosomal dominant limb-girdle muscular dystrophy and Paget disease of bone

PURPOSE

To characterize the clinical features and perform linkage analysis of candidate loci in a large Illinois family with autosomal dominant limb-girdle muscular dystrophy (LGMD) and Paget disease of bone (PDB).

METHODS

The family includes 11 affected individuals (8 M, 3 F). Clinical, biochemical and radiologic evaluations were performed to delineate clinical features of the disorder. Linkage analysis with polymorphic markers was performed for previously identified LGMD, PDB and cardiomyopathy loci.

RESULTS

Onset of PDB is early, at a mean age of 35 y, with classic distribution involving the spine, pelvis, and skull. Muscle weakness and atrophy is progressive with mildly elevated to normal creatine phosphokinase levels. Muscle biopsy in the oldest male revealed vacuolated fibers, however, in others revealed nonspecific myopathy. Affected individuals die from progressive muscle weakness, and respiratory and cardiac failure in their 40s-60s. Linkage analysis excluded autosomal dominant and recessive LGMD, PDB, and cardiomyopathy loci.

CONCLUSION

Autosomal dominant LGMD associated with PDB is an unusual disorder. Linkage analysis indicates a unique locus in this family.

Therapies in muscular dystrophy: current concepts and future prospects

In the fast moving field of muscular dystrophy, therapeutic matters are now high on the agenda. Despite little progress made in the understanding of the exact pathogenesis, hopes have been raised with the advent of molecular medicine applied to such disorders. A constellation of techniques or therapeutic solutions are now available, but very few have reached the clinical stage. Gene therapy, cell therapy and pharmacological therapy look more promising, but their clinical application may still take years. We review the various alternatives and suggest that some of them might be used in combination.

Reprogramming the male gamete genome: a window to successful gene therapy

Hematopoiesis and spermatogenesis both initiate from a stem cell capable of renewal and differentiation. Each pathway reflects the expression of unique combinations of facultative, i.e. tissue-specific and constitutive, i.e. housekeeping, genes in each cell type. In spermatogenesis, as in hematopoiesis, commitment is mediated by the mechanism of potentiation whereby specific chromatin domains are selectively opened along each chromosome. Within each open chromatin domain, a unique battery of gene(s) is availed to tissue-specific and ubiquitous transacting factors that are necessary to initiate transcription. In the absence of an open domain, trans-factor access is denied, and the initiation of transcription cannot proceed. Cell-fate is thus ultimately defined by the unique series of open-potentiated cell-specific chromatin domains. Defining the mechanism that opens chromatin domains is fundamental in understanding how differentiation from stem cells is controlled and whether cell-fate can be modified. A recent examination of the mammalian spermatogenic pathway [Kramer, J.A., McCarrey, J.M, Djakiew, D., Krawetz, S.A., 1998. Differentiation: the selective potentiation of chromatin domains. Development 125, 4749-4755] supports the view that cell fate is mediated by global changes in chromatin conformation. This stride underscores the possibility of moderating differentiation through chromatin conformation. It is likely that gene therapeutics capable of selectively potentiating individual genic domains in populations of differentiating and/or replicating cells that modify cellular phenotype will be developed in the next millennium.