Increased deposition of extracellular matrix components in the thymus gland of MDX mouse: correlation with the muscular lesion.

The present work describes the expression of extracellular proteins in the thymus and skeletal muscle of the X-linked dystrophic MDX mouse which corresponds to an experimental model for the human disease Duchenne muscular dystrophy. MDX dystrophic mice showed marked alterations in the thymic cytoarchitecture including cortical atrophy that was paralleled by denser epithelial cell network with intense immunolabelling for cytokeratins pair 8/18 and increased vascularization assessed with monoclonal antibody anti-desmin. Consistent augmentation of intrathymic extracellular matrix components (ECM) was observed especially at weaning and by the onset of disease. Interestingly, the amount of ECM elements in the gastrocnemius muscle of MDX wild-type dystrophic mice also showed a prominent difference as compared to age-matched non-dystrophic BALB/cAn animals. A marked but uneven overdeposition of reticulin and collagen fibres (type I, type IV), laminin and fibronectin were often present in the skeletal muscle of dystrophic mice, mostly around lesioned fibres. Alterations in both organs positively correlated with the degree of dystrophy thus suggesting that similar stimuli may be enhancing ECM production in both thymus and skeletal muscle. Although the thymus gland might not be directly involved in the development of the murine X-linked muscular dystrophy, it should be considered as a further target in this disease.