gms | German Medical Science

Background: Duchenne Muscular Dystrophy (DMD) and its murine model, mdx, are characterized by Ca2+ induced muscle damage, fibrosis and muscle weakness. Furthermore, DMD patients have distorted dentofacial morphology which could be a result of changed masticatory mechanics due to muscular dysfunction.

Aim: To determine potential changes in masticatory mechanics we searched for morphological abnormalities including nuclei localisation, fibre diameters and collagen expression and examined the expression of myosin heavy chain (MHC)-isoforms in control and mdx mice.

Methods: The mRNA and protein levels of the MHC-isoforms were studied using quantitative RT-PCR, western blot analyses and histochemistry in Musculus masseter, temporalis, soleus and tongue of both mouse strains.

Results: Dystrophin-deficient masticatory muscles contained 11–75% fibres with centralized nuclei, numerous inflammatory foci and an accumulation of collagen except tongue. Furthermore, a significant increased mean fibre diameter was observed all tested mdx muscles. In contrast to soleus muscle the MHC type I isoform was not detectable in masticatory muscle tissues of control and mdx mice. In mdx masticatory muscles and tongue MHC type IIb and IIx were significantly down regulated.

Conclusion: These observations suggest that mdx masticatory muscles are differentially affected by the disease process. However, the observed down regulation of the MHC IIx and IIb isoforms may be responsible for the functional misbalance of masticatory muscles in DMD and could be causing morphological changes which are observed in this disorder.