Ultrastructural and immunocytochemical study of skeletal muscles in a murine model of Down syndrome

Down syndrome (DS) is a genetically-based disease which, in humans, affects about 1 over 700 newborns and is due to the presence of all or part of an extra chromosome 21. Among their several pathological traits, DS subjects suffer from an altered motor coordination but, although these difficulties in motility represent a serious problem in daily life, scarce data exist in the literature on skeletal muscles in DS. This is likely due to the obvious difficulties in obtaining bioptic material from patients with DS; however, this limitation may be partly overcome using suitable animal models. The Ts65Dn mouse bearing a trisomy for a segment of chromosome 16 (i.e. the homologue of human chromosome 21) is the most extensively studied murine model of DS since displays a remarkable number of phenotypic traits expressed in the human condition, including motor dysfunctions. By combining morphometry and immunocytochemistry at transmission electron microscopy, we examined the fine structure of skeletal myofibres, with particular attention to myonuclei, in adult and late adult Ts65Dn mice and their age-matched euploid controls, with the aim to evaluate the combined effect of DS and age on skeletal muscle. Our observations demonstrated in Ts65Dn mice an irregular arrangement of myofibrils and structural alterations of mitochondria, which often occurred in large clusters instead of being lined between myofibrils. In addition, myonuclei showed morphological modifications and changes in the amount of factors involved in RNA processing.