Résumé :
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Golden Retriever Muscular Dystrophy (GRMD) is a very suitable animal model related to dystrophin deficiency. The phenotype of dogs is very close to the disease pattern in humans. Innovative therapies are thus being tested on dogs before a transfer towards humans and proper outcome measures must be developed to test their effects. Since an innovative gene therapy needed to be assessed on the forelimb of GRMD dogs, a unique and dedicated dynamometer was designed to assess strength around the wrist joint. The device is built around interchangeable torquemeters with a nominal scale of either 2 Nm or 20 Nm, depending on the function tested and the weakness of the dogs. Both torquemeters precision is 0.2% of the full scale. The system is made of three articulated arms. The first one supports the torquemeter which axis is precisely aligned with the wrist axis of the dog by means of a 3D high precision positioning plateform, on which the hand is firmly maintained. The second arm supports cradles for tightly maintaining both arm and forearm. The third articulated arm holds the stimulation needles which depth under the skin surface can be finely adjusted.During the experiments, the dogs were anaesthetised and closely monitored for both respiratory and cardiac functions. The stimulation of carpal flexors and extensors was performed by direct nerve stimulation using two thin insulated needles (28G). The flexion and extension torques were measured during the stimulation of either the median and ulnar common nerve branches or the radial nerve. Stimulation trains were generated during 500 ms at supramaximal intensity and various stimulation frequencies (5, 10, 20, 25, 50, 100, 133 and 200 Hz, see figure). Thirty-second rest periods were respected between contractions.Several healthy and GRMD dogs were evaluated at various ages. At the age of 3 months, GRMD dogs already presented a decrease in strength of about 20% for both carpal flexion and extension. The reproducibility of the techniques was assessed during repeated measurements over the same anaesthesia. On the poster, we will present some data on the measurement principle, the choice of the stimulation parameters and some preliminary results for both carpal flexion and extension. Our final goal is to assess the strength in GRMD dogs injected in a forelimb with a recombinant Adeno-Associated Virus serotype 8 (rAAV8) expressing a optimized U7 snRNA specific for the correction by exon skipping of the GRMD dystrophin transcript.This project is supported by AFM (Association Franse contre les Myopathies) and by ADNA (Advanced Diagnostics for New Therapeutic Approaches), a program dedicated to personalized medicine, coordinated by Institut Meux and supported by research and innovation aid from the French public agency, OSEO.
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