Sarcolemmal Organization in Skeletal Muscle Lacking Desmin: Evidence for Cytokeratins Associated with the Membrane Skeleton at Costameres

Abstract

The sarcolemma of fast-twitch muscle is organized into "costameres," structures that are oriented transversely, over the Z and M lines of nearby myofibrils, and longitudinally, to form a rectilinear lattice. Here we examine the role of desmin, the major intermediate filament protein of muscle in organizing costameres. In control mouse muscle, desmin is enriched at the sarcolemmal domains that lie over nearby Z lines and that also contain ␤-spectrin. In tibialis anterior muscle from mice lacking desmin due to homologous recombination, most costameres are lost. In myofibers from desmin Ϫ/Ϫ quadriceps, by contrast, most costameric structures are stable. Alternatively, Z line domains may be lost, whereas domains oriented longitudinally or lying over M lines are retained. Experiments with pan-specific antibodies to intermediate filament proteins and to cytokeratins suggest that control and desmin Ϫ/Ϫ muscles express similar levels of cytokeratins. Cytokeratins concentrate at the sarcolemma at all three domains of costameres when the latter are retained in desmin Ϫ/Ϫ muscle and redistribute with ␤-spectrin at the sarcolemma when costameres are lost. Our results suggest that desmin associates with and selectively stabilizes the Z line domains of costameres, but that cytokeratins associate with all three domains of costameres, even in the absence of desmin. INTRODUCTIONDuchenne Muscular Dystrophy and related muscular dystrophies are caused by the mutation or loss of dystrophin and dystrophin-associated proteins (Campbell, 1995;Bonnemann et al., 1996;Straub and Campbell, 1997;Ozawa et al., 1998), respectively, but the functions of these proteins in healthy skeletal muscle are still poorly understood. Dystrophin, which is a member of the spectrin superfamily of membrane skeletal proteins (Davison and Critchley, 1988;Koenig et al., 1988;Dhermy, 1991;Ahn and Kunkel, 1993), accumulates in healthy muscle on the cytoplasmic face of the sarcolemma in linear structures that are oriented both longitudinally and transversely (Masuda et al., 1992;Minetti et al., 1992;Porter et al., 1992;Straub et al., 1992;Williams and Bloch, 1999b). The transverse structures, which lie at the sarcolemma over the Z and M lines of nearby myofibrils, are organized in a rib-like pattern and so are referred to as "costameres" (Pardo et al., 1983a). We also use this term to include the longitudinal elements, which, with the transverse domains, form a lattice-like network that underlies most of the skeletal muscle sarcolemma. All three costameric domains are enriched in dystrophin (Porter et al., 1992). We have found that, in the absence of dystrophin, the longitudinal and M line domains of costameres are more susceptible to disruption in Duchenne muscle and in muscle from the mdx mouse (Porter et al., 1992;Williams and Bloch, 1999b; see also Ehmer et al., 1997), suggesting that dystrophin functions more to stabilize these sarcolemmal domains than the domains that overlie Z lines. These studies also suggest that other structures associated with the sarco...

Specific Interaction of the Actin-binding Domain of Dystrophin with Intermediate Filaments Containing Keratin 19

“…The fact that actin is linked primarily to the Z-disks of striated muscle suggests that it is unlikely to mediate all the connections between the contractile apparatus and costameres, (Lazarides, 1980;Thornell, 1992;Capetanaki and Milner, 1998). Ultrastructural evidence, as well as studies of mice lacking desmin due to homologous recombination, suggest that desmin-based intermediate filaments are important in linking the Z-disks of superficial myofibrils to costameres at the sarcolemma (Granger and Lazarides, 1979;Pierobon-Bormioli, 1981;Street, 1983;Shear and Bloch, 1985;O'Neill et al, 2002), perhaps through a plectin cross-linker (Hijikata et al, 2003). Consistent with this, two desminassociated proteins, syncoilin and desmuslin or synemin, have been shown to bind dystrobrevin, a ligand of dystrophin (Mizuno et al, 2001;Newey et al, 2001).…”

“…We recently reported that some fast twitch muscle fibers in the desmin-null mouse retained normal costameres, suggesting that desmin is not necessary to align costameres with the underlying contractile apparatus (O'Neill et al, 2002). Because cytokeratins are expressed in developing muscle and in muscle tumors (Langbein et al, 1989;Miettinen and Rapola, 1989;Kosmehl et al, 1990), and reverse transcription-PCR procedures suggested that mRNAs encoding cytokeratins were present in muscle extracts (Ursitti et al, 2004), we looked for cytokeratins in adult skeletal muscle and found them concentrated near the sarcolemma at costameres (O'Neill et al, 2002).…”

“…Because cytokeratins are expressed in developing muscle and in muscle tumors (Langbein et al, 1989;Miettinen and Rapola, 1989;Kosmehl et al, 1990), and reverse transcription-PCR procedures suggested that mRNAs encoding cytokeratins were present in muscle extracts (Ursitti et al, 2004), we looked for cytokeratins in adult skeletal muscle and found them concentrated near the sarcolemma at costameres (O'Neill et al, 2002). Cytokeratins are present at all costameric domains and not simply those overlying Z-disks (O'Neill et al, 2002), suggesting that they may play a more widespread role at the sarcolemma than desmin or actin. We cloned and sequenced K8 and K19 from striated muscle and localized these cytokeratins at the costameres of cardiac muscle (Ursitti et al, 2004).…”

“…In addition, synemin, which copolymerizes with desmin (Granger et al, 1982;Bellin et al, 1999;Hirako et al, 2003), binds vinculin (Bellin et al, 2001), the quintessential costameric protein, and may concentrate at costameres (Mizuno et al, 2004). Like actin filaments, however, desmin-based intermediate filaments are concentrated near the Z-disks of each sarcomere and between the Z-disks and the sarcolemma (Granger and Lazarides, 1978;Lazarides, 1978;Granger and Lazarides, 1979;Richardson et al, 1981;Capetanaki and Milner, 1998;O'Neill et al, 2002), making them unlikely candidates to mediate connections between the contractile apparatus and the domains of costameres overlying M-lines or oriented longitudinally along the sarcolemma.We recently reported that some fast twitch muscle fibers in the desmin-null mouse retained normal costameres, suggesting that desmin is not necessary to align costameres with the underlying contractile apparatus (O'Neill et al, 2002). Because cytokeratins are expressed in developing muscle and in muscle tumors (Langbein et al, 1989;Miettinen and Rapola, 1989;Kosmehl et al, 1990), and reverse transcription-PCR procedures suggested that mRNAs encoding cytokeratins were present in muscle extracts (Ursitti et al, 2004), we looked for cytokeratins in adult skeletal muscle and found them concentrated near the sarcolemma at costameres (O'Neill et al, 2002).…”

“…Like actin filaments, however, desmin-based intermediate filaments are concentrated near the Z-disks of each sarcomere and between the Z-disks and the sarcolemma (Granger and Lazarides, 1978;Lazarides, 1978;Granger and Lazarides, 1979;Richardson et al, 1981;Capetanaki and Milner, 1998;O'Neill et al, 2002), making them unlikely candidates to mediate connections between the contractile apparatus and the domains of costameres overlying M-lines or oriented longitudinally along the sarcolemma.…”