Human dystrophin expression corrects the myopathic phenotype in transgenic mdx mice

Abstract

Duchenne and the less severe Becker form of muscular dystrophy (DMD,BMD) result from genetic deficiency in the level and/or activity of the protein dystrophin. The recent availability of cDNA based minigenes encoding recombinant dystrophin polypeptides has raised the possibility of somatic gene transfer as a therapeutic approach to treat dystrophin deficiency. In this respect, the mdx mouse provides a useful model of DMD exhibiting features characteristic of both the early myopathic and later fibrotic phases of the human disease. Using a mutated human cDNA, compatible in size with virus-based somatic gene transfer vectors, the pathophysiological consequences of restoring dystrophin expression have been examined in transgenic mdx mice. Transgene expression was correlated with a marked reduction of the skeletal myofibre necrosis and regeneration which is a major feature of the dystrophin-deficient phenotype in young mdx mice. The cDNA construct which is based on a very mild BMD phenotype thus encodes a highly functional dystrophin molecule whose reduced size renders it an attractive candidate for development as a therapeutic gene transfer reagent.

Preservation of Muscle Force in Mdx3cv Mice Correlates with Low-Level Expression of a Near Full-Length Dystrophin Protein

“…6 Investigators have also studied the effect of varying dystrophin levels in mdx mice, a mouse model for DMD. [11][12][13] Uniform expression of full-length dystrophin or minidystrophin at 20% or higher levels results in remarkable improvement in muscle pathology and strength in transgenic mdx mice. 12,13 Muscle degeneration/regeneration, sarcolemma leakage, and muscle-specific force are all normalized.…”

“…Few studies have evaluated the effect of low level (Ͻ20%) dystrophin expression in animal models of DMD. Wells and colleagues 11 reported partial amelioration of muscle disease in transgenic mdx mice that express a minidystrophin gene at ϳ17% of the normal level. They observed a significant reduction in muscle degeneration but the serum creatine kinase (CK) level remained high.…”

Function of the Myogenin Gene Promoter in the Muscular Dystrophic Transgenic dy/dy Mouse.

“…It is uncertain as to whether or not LacZ gene expression affects cell growth and development. 2) 9.1 ± 2.8 2.3 ± 0.7** 8.7 ± 2.4 Number of cells 3) 106.2 ± 25.5 55.0 ± 11.9* 96.6 ± 20.2 Average area (µm 2 ) 4) 8568 ± 596 4818 ± 560** 9006 ± 110 Area of 50 cells (µm 2 ) 5) 9700 ± 210 5350 ± 550* 8070 ± 590…”

“…The implantation of muscle precursor cells from normal mice into dystrophindeficient mdx mice has proven to be a useful technique in demonstrating biochemical rescue. The rate of replacement of the missing gene can be verified either quantitatively or histologically by immunostaining [2][3][4]. A second verification method involves direct intramuscular injection of recombinant plasmids that express dystrophin [15], without displaying severe progressive myopathy.…”

“…It is also difficult to determine whether this biochemical rescue results in any improvement in the structure or the functioning of the treated muscle, because the vigorous regeneration of mdx muscle more than compensates for the degeneration. Although Mdx mice do not suffer from severe progressive myopathy, they exhibit biochemical and histological defects similar to those seen in patients with DMD [4]. Few studies however, have actually used the dy/dy transgenic mouse as a model.…”