Effects of ZASP mutations on Z-disc proteins associated with myofibrillar myopathy in skeletal muscle

Myofibrillar myopathies (MFM) are caused by mutations in at least 6 Z-disc associated proteins, including ZASP, myotilin, desmin, BAG3, αβ-crystallin, and filamin C. MFM are characterized by early and prominent disruption of the Z-disc with focal dissolution of myofibrils and ectopic accumulation of myofibrillar proteins. Similar morphological changes in skeletal muscle in MFM suggest a shared cellular and molecular disease mechanism. ZASP interacts with myotilin, and knock down of ZASP in mice results in alterations in the amounts of other MFM gene products. We hypothesize that ZASP associations with other MFM gene products play a role in the disease mechanism in zaspopathy. To examine the effects of ZASP mutations on the other MFM gene products in skeletal muscle, WT and mutant (A147T and A165V) ZASP-GFP proteins were expressed by electroporation in the tibialis anterior muscles of opposite limbs in wild type mice (n = 18). Muscle tissues were harvested at 1, 2, and 4 weeks after the electroporation. The amount and distribution of MFM gene products, F-actin, and α-actinin-2 were examined in the electroporated mouse muscle fibers and in skeletal muscle fibers of patients with zaspopathy. Wild type and mutant ZASP interactions with other MFM gene products were examined by co-IP and pulldown assays. Preliminary data suggests that wild type and mutant ZASP associate with myotilin, desmin, and BAG3. The effects of ZASP mutations on the other MFM gene products and the effects of the other MFM gene defects on ZASP will provide insight into shared disease mechanisms in this group of degenerative myopathies.