76th ENMC International Workshop: pathophysiology and therapy in the mdx mouse 21-23 January 2000, Naarden, The Netherlands

Enhancing translation: guidelines for standard pre-clinical experiments in mdx mice

Duchenne Muscular Dystrophy is an X-linked disorder that affects boys and leads to muscle wasting and death due to cardiac involvement and respiratory complications. The cause is the absence of dystrophin, a large structural protein indispensable for muscle cell function and viability. The mdx mouse has become the standard animal model for pre-clinical evaluation of potential therapeutic treatments. Recent years have seen a rapid increase in the number of experimental compounds being evaluated in the mdx mouse. There is, however, much variability in the design of these pre-clinical experimental studies. This has made it difficult to interpret and compare published data from different laboratories and to evaluate the potential of a treatment for application to patients. The authors therefore propose the introduction of a standard study design for the mdx mouse model. Several aspects, including animal care, sampling times and choice of tissues, as well as recommended endpoints and methodologies are addressed and, for each aspect, a standard procedure is proposed. Testing of all new molecules/drugs using a widely accepted and agreed upon standard experimental protocol would greatly improve the power of pre-clinical experimentations and help identifying promising therapies for the translation into clinical trials for boys with Duchenne Muscular Dystrophy.

Transient receptor potential cation channels in normal and dystrophic mdx muscle

To investigate the defective calcium regulation of dystrophin-deficient muscle fibres we studied gene expression and localization of non-voltage gated cation channels in normal and mdx mouse skeletal muscle. We found TRPC3, TRPC6, TRPV4, TRPM4 and TRPM7 to be the most abundant isoforms. Immunofluorescent staining of muscle cross-sections with antibodies against TRP proteins showed sarcolemmal localization of TRPC6 and TRPM7, both, for mdx and control. TRPV4 was found only in a fraction of fibres at the sarcolemma and around myonuclei, while TRPC3 staining revealed intracellular patches, preferentially in mdx muscle. Transcripts of low abundance coding for TRPC5, TRPA1 and TRPM1 channels were increased in mdx skeletal muscle at certain stages. The increased Ca(2+)-influx into dystrophin-deficient mdx fibres cannot be explained by increased gene expression of major TRP channels. However, a constant TRP channel expression in combination with the well described weaker Ca(2+)-handling system of mdx fibres may indicate an imbalance between Ca(2+)-influx and cellular Ca(2+)-control.

Sarcolemmal ion channels in dystrophin-deficient skeletal muscle fibres

Duchenne muscular dystrophy (DMD) is a genetic disease caused by mutations in the dystrophin gene and characterized by progressive skeletal muscle degeneration. A current hypothesis suggests that degeneration of dystrophin-deficient skeletal muscle results from a chronic intracellular Ca2+ overload. Ca2+ handling in skeletal muscle is tightly controlled by the membrane potential which is set by sarcolemmal ion channels activity. Also, with regard to the subsarcolemmal localization of dystrophin, it is reasonable to enquire if the distribution and function of ion channels might be affected by the absence of dystrophin. This paper briefly summarizes the current knowledge of the properties of sarcolemmal ion channels in fully differentiated dystrophin-deficient skeletal muscle fibres.

Histological parameters for the quantitative assessment of muscular dystrophy in the mdx-mouse

Duchenne muscular dystrophy is a severe X-linked hereditary disease caused by the absence of functional dystrophin. The dystrophin-deficient mdx-mouse strain is a widely used animal model for dystrophin-deficiency. Several therapeutic approaches for muscular dystrophy have been proposed by different laboratories. In order to compare the efficacy of these therapies in the mdx-mouse, it is essential to implement standardized protocols for the assessment of functional and histological parameters in this mouse model. Here, we determine that the minimal 'Feret's diameter' is a geometrical parameter that allows for reliable measure of muscle fiber cross-sectional size. Using this geometrical parameter we calculate variance coefficients of the muscle fiber size and provide reference values for the quantitative assessment of dystrophic symptoms in frequently investigated muscles of wild-type and mdx-mouse. In addition, we compare the variance coefficients of the muscle fiber size with the percentage of muscle fibers with centralized nuclei; another histological hallmark of muscular dystrophy.