Microtubules Underlie Dysfunction in Duchenne Muscular Dystrophy

Abstract

Duchenne muscular dystrophy (DMD) is a fatal X-linked degenerative muscle disease caused by the absence of the microtubule-associated protein dystrophin, which results in a disorganized and denser microtubule cytoskeleton. In addition, mechanotransduction-dependent activation of calcium (Ca2+) and reactive oxygen species (ROS) signaling underpins muscle degeneration in DMD. We show that in muscle from adult mdx mice, a model of DMD, a brief physiologic stretch elicited microtubule-dependent activation of NADPH (reduced-form nicotinamide adenine dinucleotide phosphate) oxidase–dependent production of ROS, termed X-ROS. Further, X-ROS amplified Ca2+ influx through stretch-activated channels in mdx muscle. Consistent with the importance of the microtubules to the dysfunction in mdx muscle, muscle cells with dense microtubule structure, such as those from adult mdx mice or from young wild-type mice treated with Taxol, showed increased X-ROS production and Ca2+ influx, whereas cells with a less dense microtubule network, such as young mdx or adult mdx muscle treated with colchicine or nocodazole, showed little ROS production or Ca2+ influx. In vivo treatments that disrupted the microtubule network or inhibited NADPH oxidase 2 reduced contraction-induced injury in adult mdx mice. Furthermore, transcriptome analysis identified increased expression of X-ROS–related genes in human DMD skeletal muscle. Together, these data show that microtubules are the proximate element responsible for the dysfunction in Ca2+ and ROS signaling in DMD and could be effective therapeutic targets for intervention.

Microtubule binding distinguishes dystrophin from utrophin

“…In the absence of dystrophin, the subsarcolemmal microtubule lattice becomes disorganized (19,20,35,44), and this disorganization contributes to the dystrophic phenotype of the mdx mouse (43,58). Like dystrophin, utrophin couples membranebound dystrophin-associated proteins with costameric actin filaments, suggesting that up-regulation of utrophin could compensate for the loss of dystrophin (28)(29)(30)(31).…”

Single Mechanosensitive and Ca2+-Sensitive Channel Currents Recorded from Mouse and Human Embryonic Stem Cells

“…In the case of mESCs, stretch-induced generation of reactive oxygen species (ROS) and integrin-mediated PI3K-Akt signaling appears to promote differentiation (Schmelter et al, 2006;Heo et al, 2011). Since it is also known that ROS generation is stimulated by MscCa activity via Ca 2+ influx (Amma et al, 2005) and MscCa activity is itself stimulated by ROS generation (Khairallah et al, 2012), the stretch response of mouse ESCs may reflect a relatively exaggerated stretch-induced Ca 2+ influx due to higher MscCa expression. Future tests for this idea may be provided by suppression and up-regulation of MscCa expression, in mESCs and hESCs, respectively, and testing the responses of these cells to cyclic strain protocols.…”

“…We will focus here mainly on MscCa because of the recent intense interest in the role of mechanosensitive 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 signaling pathways in regulating ESC biology (Discher et al, 2009;Cohen & Cho, 2008;Keung et al, 2010;D'Angelo et al, 2011;Lee et al, 2011;Sun et al, 2012 …”

“…To date, most attention has focused on the role of soluble growth factors, cytokines and receptor-operated signaling pathways (Dreesen & Brivanlou, 2007;Pera & Tam, 2010). However, there is growing evidence that mechanical signals also play significant roles in ESC fate decisions (For reviews see Discher et al, 2009;Cohen & Cho, 2008;Keung et al, 2010;D'Angelo et al, 2011;Lee et al, 2011;Sun et al, 2012). In particular, several studies have shown that applying cyclic strain/stretch to mouse and human ESCs grown on elastic substrates can modify fate decisions in different directions (Saha et al, 2006;Schmelter et al, 2006;Gwak et al, 2008;Shimizu et al, 2008;Heo & Lee, 2011;Wan et al, 2011;Horiuchi et al, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2012; Teramura et al, 2012).…”

Utrophin suppresses low frequency oscillations and coupled gating of mechanosensitive ion channels in dystrophic skeletal muscle

“…There is now strong evidence showing mechanosensitive (MS) ion channels contribute to pathological Ca 2C entry in dystrophic skeletal muscle. [14][15][16][17][18][19][20][21][22][23] Recent work suggests MS channels in skeletal muscle are formed from TRPV4 proteins, although the precise subunit composition remains to be determined. 24 The mechanisms by which MS channels transduce mechanical forces in skeletal muscle are only beginning to be understood.…”