While abundant skeletal (ask-actin) and cardiac (aca-actin) actin isoforms are famous for their essential role in striated muscle contraction, low abundance non-muscle ?cytoplasmic? actin isoforms (bcyto- and gcyto-actin) are also emerging as important in the maintenance of specialized structures (and functions) in normal and diseased skeletal muscle. During this project, we generated and characterized muscle-specific mouse lines either lacking or overexpressing bcyto-actin or gcyto-actin to understand their endogenous functions and role(s) in dystrophin-deficient muscular dystrophy. Interestingly, each bcyto-actin or gcyto-actin single knockout develops a qualitatively similar phenotype characterized by a progressive myopathy with significant myofiber degeneration/regeneration and muscle weakness. We have shown that skeletal muscle-specific overexpression of bcyto-actin or gcyto-actin in dystrophin-deficient mdx mice affords significant protection from eccentric contraction-induced force drop while overexpression of a C272A mutant of gcyto-actin affords no protection. These and other data suggest that eccentric contraction drives a rapidly-reversible, reactive oxygen species (ROS)-mediated inhibition of sarcomeric contractility that may function to protect dystrophic muscles from damage caused by repeated, high force contractions. Our new preliminary data show that muscle-specific ablation of bcyto-actin or gcyto-actin from wildtype muscle results in eccentric contraction-induced force drop that is reversed by the nonspecific antioxidant N-acetylcysteine. Finally, we have obtained new data suggesting that gcyto-actin is important for repair of membrane damage. Going forward, we will make use of our unique animal models, isoform-specific reagents, and biochemical and physiological methodologies to address new fundamental questions about cytoplasmic actins in normal skeletal muscle function and in dystrophin-deficient muscular dystrophy.
In aim 1, we will identify the sources of ROS contributing to eccentric contraction-induced force drop in dystrophic mdx skeletal muscle as well as the downstream targets of ROS that ultimately inhibit force production.
In aim 2, we will investigate the role of oxidative stress in driving the myopathy and eccentric contraction-induced force drop associated with genetic ablation of bcyto- or gcyto-actin in skeletal muscle.
In aim 3, the interplay between cytoplasmic actin isoforms and ROS in membrane repair will be investigated using state-of-the-art imaging approaches to analyze muscles from the same mouse lines used in aims 1 and 2. The results of the proposed studies will further delineate the unique and important contributions of cytoplasmic actin isoforms to the function of normal and dystrophic skeletal muscle.
We have established several unique lines of mice that enable us to elucidate the important functions of low abundance cytoplasmic actins in normal and diseased skeletal muscle. Of greatest immediate relevance to public health, we propose experiments that will mechanistically explain the dramatic, but reversible muscle weakness in dystrophic muscle exposed to lengthening, or eccentric contractions. While protection from eccentric contractions is well accepted as proof-of-concept for new therapies to treat muscular dystrophies, the cause of weakness is poorly understood. We are proposing to elucidate the mechanisms through which each type of actin contributes to muscle cell maintenance to provide the foundation for therapy development.
| Patrinostro, Xiaobai; Roy, Pallabi; Lindsay, Angus et al. (2018) Essential nucleotide- and protein-dependent functions of Actb/?-actin. Proc Natl Acad Sci U S A 115:7973-7978 |
| Lindsay, Angus; Schmiechen, Alexandra; Chamberlain, Christopher M et al. (2018) Neopterin/7,8-dihydroneopterin is elevated in Duchenne muscular dystrophy patients and protects mdx skeletal muscle function. Exp Physiol 103:995-1009 |
| O'Rourke, Allison R; Lindsay, Angus; Tarpey, Michael D et al. (2018) Impaired muscle relaxation and mitochondrial fission associated with genetic ablation of cytoplasmic actin isoforms. FEBS J 285:481-500 |
| Patrinostro, Xiaobai; O'Rourke, Allison R; Chamberlain, Christopher M et al. (2017) Relative importance of ?cyto- and ?cyto-actin in primary mouse embryonic fibroblasts. Mol Biol Cell 28:771-782 |
| Wu, Xin-Sheng; Lee, Sung Hoon; Sheng, Jiansong et al. (2016) Actin Is Crucial for All Kinetically Distinguishable Forms of Endocytosis at Synapses. Neuron 92:1020-1035 |
| Dandapat, Abhijit; Perrin, Benjamin J; Cabelka, Christine et al. (2016) High Frequency Hearing Loss and Hyperactivity in DUX4 Transgenic Mice. PLoS One 11:e0151467 |
| Simionescu-Bankston, Adriana; Pichavant, Christophe; Canner, James P et al. (2015) Creatine kinase B is necessary to limit myoblast fusion during myogenesis. Am J Physiol Cell Physiol 308:C919-31 |
| Narayanan, Praveena; Chatterton, Paul; Ikeda, Akihiro et al. (2015) Length regulation of mechanosensitive stereocilia depends on very slow actin dynamics and filament-severing proteins. Nat Commun 6:6855 |
| Cheever, Thomas R; Ervasti, James M (2013) Actin isoforms in neuronal development and function. Int Rev Cell Mol Biol 301:157-213 |
| Perrin, Benjamin J; Strandjord, Dana M; Narayanan, Praveena et al. (2013) ýý-Actin and fascin-2 cooperate to maintain stereocilia length. J Neurosci 33:8114-21 |
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