G.P.5 Over expression of the LARGE transgene exacerbates muscle pathology in the mdx mouse

Duchenne muscle dystrophy is an X-linked muscle wasting disorder caused by mutations in the DMD gene preventing the production of a functional dystrophin protein. The lack of dystrophin de-stabilises the dystrophin associated protein complex (DAPC) and consequently DMD muscles are more susceptible to exercised induced muscle damage. We hypothesised stabilising the DAPC at the sarcolemma in mdx mice may reduce muscle susceptibility to exercise induced damage and consequently ameliorate muscle pathology. To evaluate this we crossed mice over-expressing the putative glycotransferase, LARGE, which facilitates the binding of alpha dystroglycan to laminin in the extracellular matrix, with mdx mice. The presence of the LARGE transgene in the LV5/mdx mice was established through genotyping and expression was confirmed through immunostaining. Pathological findings characterised by myofibre size variation, increased central nucleation, presence of inflammatory cells and calcium deposits was more serve in 8-week old LV5/mdx mice quadriceps and diaphragm muscles compared to mdx littermate controls. To determine if the over-expression of the LARGE transgene initiated muscle pathology early we analysed 3-week old quadriceps muscles. Stark degeneration was observed in LV5/mdx vastus muscles, in contrast to the rectus femoris which was well preserved. Few pathological findings were observed in the age matched mdx littermate controls. We also assessed the effect of over-expression of LARGE on muscle function using a standardised in vivo exercise test on the tibialis anterior muscle in situ. A significant drop in maximum force produced following eccentric contractions was observed in 22-week old LV5/mdx mice compared to littermate controls. Overall we show the over-expression of LARGE exacerbates DMD pathology in the mdx mice. Further work to establish an underlining mechanism for the deleterious effect of over-expressing LARGE in mdx mice is currently ongoing.