Independent variability of microtubule perturbations associated with dystrophinopathy

Abstract

Absence of the protein dystrophin causes Duchenne muscular dystrophy. Dystrophin directly binds to microtubules in vitro, and its absence in vivo correlates with disorganization of the subsarcolemmal microtubule lattice, increased detyrosination of α-tubulin, and altered redox signaling. We previously demonstrated that the dystrophin homologue utrophin neither binds microtubules in vitro nor rescues microtubule lattice organization when overexpressed in muscles of dystrophin-deficient mdx mice. Here, we fine-mapped the dystrophin domain necessary for microtubule binding to spectrin-like repeats 20–22. We show that transgenic mdx mice expressing a full-length dystrophin/utrophin chimera completely lacking microtubule binding activity are surprisingly rescued for all measured dystrophic phenotypes, including full restoration of microtubule lattice organization. Conversely, despite the presence of dystrophin at the sarcolemma, β-sarcoglycan-deficient skeletal muscle presents with a disorganized and densified microtubule lattice. Finally, we show that the levels of α-tubulin detyrosination remain significantly elevated to that of mdx levels in transgenic mdx mice expressing nearly full-length dystrophin. Our results demonstrate that the microtubule-associated perturbations of mdx muscle are distinct, separable, and can vary independently from other parameters previously ascribed to dystrophin deficiency.

Integrative effects of dystrophin loss on metabolic function of the mdx mouse

“…To explore the mechanism by which the absence of dystrophin may result in metabolic changes leading to alterations in body composition, a transgenic mdx mouse with skeletal muscle specific expression of a C-terminally truncated dystrophin was used. This transgenic mouse has fully corrected skeletal muscle pathology and has been extensively backcrossed onto the mdx genetic background 23 , 24 . These mice demonstrated the same lean body composition, similar to the mdx mouse, regardless of the presence of the transgene (Fig.…”

“…The transgenic mice used in this study have been extensively backcrossed (>10 generations) on to the C57BL/10 background strain 23 , yet these mice, regardless of genotype retain a lean phenotype. These mice, which have largely corrected the dystrophic process in skeletal muscle, suggest that the lean phenotype is not dependent on the presence of muscle pathology.…”

Variable cytoplasmic actin expression impacts the sensitivity of different dystrophin‐deficient mdx skeletal muscles to eccentric contraction

“…Each ECC was separated by 3 min of rest to prevent fatigue. The corresponding force drop associated with this protocol for mdx EDL muscle is 85–90% but variations in mechanical parameters across other laboratories can cause force drop from 39% to 90% . The force measured at each ECC was expressed as a percentage of the force produced during the first (“initial”) contraction.…”

Tubulin acetylation increases cytoskeletal stiffness to regulate mechanotransduction in striated muscle

“…The abundance of tubulin acetylation is governed by the equilibrium balance of cytosolic deacetylases (including HDAC6) and the acetyltransferase (αTAT1 in mice) 7 with increased α TAT1 activity mediating the increased α-tubulin acetylation during acute cell stress 24 . As an orthogonal approach to tubacin treatment we used the genetic overexpression of α TAT in mouse FDB muscle in order to induce an increase tubulin acetylation via acetyltransferase mechanism.…”

“…Microtubule binding to actin, intermediate filaments and protein cytolinkers regulates cytoskeletal mechanics and mechanotransduction [1][2][3][4] . This occurs in striated muscle where there is evidence that disease-altered microtubules contribute to the pathological increase in cytoskeletal mechanics [3][4][5][6][7][8] and mechanotransduction 3,4,8 . This pathologic excess of microtubule dependent mechanotransduction manifested in increased susceptibility to contraction induced injury in skeletal muscle and a predisposition to arrhythmic events in the heart 8 .…”