Résumé :
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The primary muscle fiber injury in DMD is due to total absence of dystrophin. With evolution of the disease, an increasing extent of myofibrosis, the precise mechanisms of which remain to be fully determined, likely accelerates myofiber death. Ischaemia has long been considered a possible factor of myoinjury. It is currently attributed to functional vascular alterations resulting from smooth muscle cell dystrophin deficiency and from ectopic sarcoplasmic nNOS location impeding paracrine NO release that normally regulates vasoconstrictive responses to exercise. We examined here the possible relationships between fibrosis and myofiber ischaemia on an anatomical basis. Frozen transversal sections from 15 DMD patients (6–10 years) and normal age-matched controls, immunostained for endothelial (CD31) and smooth muscle (alpha-SMA) cells, were used to set-up large scale reconstructions containing hundreds of microvessels. Vessels, myofiber sections and endomysium were segmented out of the images, and the following parameters measured: 1) arteriolarization index (percentage of arteriolar to total vascular area), 2) number of capillaries/mm2, 3) distance separating capillaries from their nearest neighbors, 4) size/size variation of capillary domains defined as part of the muscle section closer to one capillary than to any other, 5) capillary tortuosity (length of capillaries) and individual myofiber vascularization indices: (i) the individual capillary-to-fiber ratio which takes into account the sharing factor, (ii) capillary-to-fiber perimeter exchange index, (iii) capillary-to-fiber distance. On the one hand DMD muscle showed conspicuous arteriolization and marked increase of the capillary-to-fiber distance with intersposed collagen deposits, forming. two major obstacles to gas exchanges. On the other hand, there was marked increase of both capillary tortuosity and capillary-to-fiber perimeter exchange index, suggesting an adaptative neoangiogenic phenomenon associated with injury and/or hypoxia-induced myofiber regeneration (see Christov et al, Mol Biol Cell 2007). Apparently, microvascular hyperplasia is likely to precede capillary depletion seen in the terminal stages of the disease.
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