LAUSR

A nonsense mutation in codon Glu180 of TNNT1 gene encoding the slow skeletal muscle isoform of troponin T (ssTnT) causes a recessively inherited severe nemaline myopathy (Amish nemaline myopathy, ANM). Muscle biopsies of ANM patients showed a total loss of ssTnT. The present study developed and characterized mice with the E180 nonsense mutation knocked-in the Tnnt1 gene (ssTnT-KI). Homozygotes of ssTnT-KI mice survived to adulthood. Histology studies revealed significant increases of centralized nuclei in the soleus muscle of ssTnT-KI when compared with age matched wild type controls. Immunohistochemistry staining showed atrophic slow type 1 fibers in ssTnT-KI mouse soleus muscle with severe inflammatory cells infiltration. Western blots confirmed the absence of full length ssTnT with no ssTnT fragments detectable, mimicking that seen in the muscle of ANM patients. Contractile properties of ssTnT-KI mouse soleus muscle measured in situ demonstrated a decreased fatigue resistance. Significant expression of cardiac TnT is detected in soleus muscle of ssTnT-KI mice, consistent with the presence of active muscle regeneration. Decrease of slow type isoforms and increase of fast type isoforms of other myofilament proteins with a significant hypertrophy of fast fibers in ssTnT-KI mouse soleus muscle indicate a potentially compensatory adaptation to the loss of slow fiber functions. The ssTnT-KI mouse line provides a model of ANM for pathogenesis, pathophysiology and therapeutic studies.