Sarcospan-Deficient Mice Maintain Normal Muscle Function

ABSTRACT Sarcospan is an integral membrane component of the dystrophin-glycoprotein complex (DGC) found at the sarcolemma of striated and smooth muscle. The DGC plays important roles in muscle function and viability as evidenced by defects in components of the DGC, which cause muscular dystrophy. Sarcospan is unique among the components of the complex in that it contains four transmembrane domains with intracellular N- and C-terminal domains and is a member of the tetraspan superfamily of proteins. Sarcospan is tightly linked to the sarcoglycans, and together these proteins form a subcomplex within the DGC. Stable expression of sarcospan at the sarcolemma is dependent upon expression of the sarcoglycans. Here we describe the generation and analysis of mice carrying a null mutation in the Sspngene. Surprisingly, the Sspn-deficient muscle maintains expression of other components of the DGC at the sarcolemma, and no gross histological abnormalities of muscle from the mice are observed. The Sspn-deficient muscle maintains sarcolemmal integrity as determined by serum creatine kinase and Evans blue uptake assays, and the Sspn-deficient muscle maintains normal force and power generation capabilities. These data suggest either that sarcospan is not required for normal DGC function or that theSspn-deficient muscle is compensating for the absence of sarcospan, perhaps by utilizing another protein to carry out its function.

Download Full-text

Impact of sarcoglycan complex on mechanical signal transduction in murine skeletal muscle

AJP Cell Physiology ◽

10.1152/ajpcell.00192.2005 ◽

2006 ◽

Vol 290 (2) ◽

pp. C411-C419 ◽

Cited By ~ 52

Author(s):

Elisabeth R. Barton

Keyword(s):

Skeletal Muscle ◽

Mechanical Load ◽

Eccentric Contraction ◽

Eccentric Contractions ◽

Normal Muscle ◽

Glycoprotein Complex ◽

Dystrophin Glycoprotein Complex ◽

Severe Pathology ◽

Murine Skeletal Muscle ◽

Dystrophin Glycoprotein

Loss of the dystrophin glycoprotein complex (DGC) or a subset of its components can lead to muscular dystrophy. However, the patterns of symptoms differ depending on which proteins are affected. Absence of dystrophin leads to loss of the entire DGC and is associated with susceptibility to contractile injury. In contrast, muscles lacking γ-sarcoglycan (γ-SG) display little mechanical fragility and still develop severe pathology. Animals lacking dystrophin or γ-SG were used to identify DGC components critical for sensing dynamic mechanical load. Extensor digitorum longus muscles from 7-wk-old normal (C57), dystrophin- null ( mdx), and γ-SG-null ( gsg−/−) mice were subjected to a series of eccentric contractions, after which ERK1/2 phosphorylation levels were determined. At rest, both dystrophic strains had significantly higher ERK1 phosphorylation, and gsg−/− muscle also had heightened ERK2 phosphorylation compared with wild-type controls. Eccentric contractions produced a significant and transient increase in ERK1/2 phosphorylation in normal muscle, whereas the mdx strain displayed no significant proportional change of ERK1/2 phosphorylation after eccentric contraction. Muscles from gsg−/− mice had no significant increase in ERK1 phosphorylation; however, ERK2 phosphorylation was more robust than in C57 controls. The reduction in mechanically induced ERK1 phosphorylation in gsg−/− muscle was not dependent on age or severity of phenotype, because muscle from both young and old (age 20 wk) animals exhibited a reduced response. Immunoprecipitation experiments revealed that γ-SG was phosphorylated in normal muscle after eccentric contractions, indicating that members of the DGC are modified in response to mechanical perturbation. This study provides evidence that the SGs are involved in the transduction of mechanical information in skeletal muscle, potentially unique from the entire DGC.

Download Full-text

Mitochondrial dysfunction in skeletal muscle of fukutin deficient mice is resistant to exercise- and AICAR-induced rescue

10.1101/2020.05.27.118844 ◽

2020 ◽

Author(s):

W. Michael Southern ◽

Anna S. Nichenko ◽

Anita E. Qualls ◽

Kensey Portman ◽

Ariel Gidon ◽

...

Keyword(s):

Skeletal Muscle ◽

Muscle Function ◽

Ampk Signaling ◽

Beneficial Effects ◽

Glycoprotein Complex ◽

Metabolic Defects ◽

Dystrophin Glycoprotein Complex ◽

Mitochondrial Defects ◽

Primary Basis ◽

Dystrophin Glycoprotein

AbstractDisruptions in the dystrophin-glycoprotein complex (DGC) are clearly the primary basis underlying various forms of muscular dystrophies and dystroglycanopathies, but the cellular consequences of DGC disruption are still being investigated. Mitochondrial abnormalities are becoming an apparent consequence and contributor to dystrophy disease pathology. Herein, we demonstrate that muscle-specific deletion of the fukutin gene [Myf5/fktn-KO mice (KO)], a model of secondary dystroglycanopathy, results in ~30% lower muscle strength (P<0.001) and 16% lower mitochondrial function (P=0.002) compared to healthy littermate controls (LM). We also observed ~80% lower PGC-1α signaling (P=0.004), a primary transcription factor for mitochondrial biogenesis, in KO mice that likely contributes to the mitochondrial defects. PGC-1α is post-translationally regulated via phosphorylation by AMPK. Treatment with the AMPK agonist AICAR (5-aminoimidazole-4-carboxamide ribonucleotide) failed to rescue mitochondrial deficits in KO mice (P=0.458) but did have beneficial (~30% greater) effects on recovery of muscle contractility following injury in both LM and KO mice compared to saline treatment (P=0.006). The beneficial effects of AMPK stimulation via AICAR on muscle function may be partially explained by AMPK’s other role of regulating skeletal muscle autophagy, a cellular process critical for clearance of damaged and/or dysfunctional organelles. Two primary conclusions can be drawn from this data, 1) fukutin deletion produces intrinsic muscular metabolic defects that likely contribute to dystroglycanopathy disease pathology, and 2) AICAR treatment accelerates recovery of muscle function following injury suggesting AMPK signaling as a possible target for therapeutic strategies.

Download Full-text

Direct interaction of β-dystroglycan with F-actin

Biochemical Journal ◽

10.1042/bj20030808 ◽

2003 ◽

Vol 375 (2) ◽

pp. 329-337 ◽

Cited By ~ 46

Author(s):

Yun-Ju CHEN ◽

Heather J. SPENCE ◽

Jacqueline M. CAMERON ◽

Thomas JESS ◽

Jane L. ILSLEY ◽

...

Keyword(s):

Muscular Dystrophy ◽

Direct Interaction ◽

Cytoplasmic Tail ◽

Yeast Two Hybrid ◽

Glycoprotein Complex ◽

Biological Studies ◽

Dystrophin Glycoprotein Complex ◽

Dystrophin Glycoprotein ◽

Two Hybrid ◽

Sarcolemmal Integrity

Dystroglycans are essential transmembrane adhesion receptors for laminin. α-Dystroglycan is a highly glycosylated extracellular protein that interacts with laminin in the extracellular matrix and the transmembrane region of β-dystroglycan. β-Dystroglycan, via its cytoplasmic tail, interacts with dystrophin and utrophin and also with the actin cytoskeleton. As a part of the dystrophin–glycoprotein complex of muscles, dystroglycan is also important in maintaining sarcolemmal integrity. Mutations in dystrophin that lead to Duchenne muscular dystrophy also lead to a loss of dystroglycan from the sarcolemma, and chimaeric mice lacking muscle dystroglycan exhibit a severe muscular dystrophy phenotype. Using yeast two-hybrid analysis and biochemical and cell biological studies, we show, in the present study, that the cytoplasmic tail of β-dystroglycan interacts directly with F-actin and, furthermore, that it bundles actin filaments and induces an aberrant actin phenotype when overexpressed in cells.

Download Full-text

Membrane Targeting and Stabilization of Sarcospan Is Mediated by the Sarcoglycan Subcomplex

The Journal of Cell Biology ◽

10.1083/jcb.145.1.153 ◽

1999 ◽

Vol 145 (1) ◽

pp. 153-165 ◽

Cited By ~ 95

Author(s):

Rachelle H. Crosbie ◽

Connie S. Lebakken ◽

Kathleen H. Holt ◽

David P. Venzke ◽

Volker Straub ◽

...

Keyword(s):

Plasma Membrane ◽

Muscular Dystrophy ◽

Genetic Mutations ◽

Myotendinous Junction ◽

Normal Muscle ◽

Glycoprotein Complex ◽

Muscle Plasma Membrane ◽

Dystrophin Glycoprotein Complex ◽

And Function ◽

Dystrophin Glycoprotein

The dystrophin–glycoprotein complex (DGC) is a multisubunit complex that spans the muscle plasma membrane and forms a link between the F-actin cytoskeleton and the extracellular matrix. The proteins of the DGC are structurally organized into distinct subcomplexes, and genetic mutations in many individual components are manifested as muscular dystrophy. We recently identified a unique tetraspan-like dystrophin-associated protein, which we have named sarcospan (SPN) for its multiple sarcolemma spanning domains (Crosbie, R.H., J. Heighway, D.P. Venzke, J.C. Lee, and K.P. Campbell. 1997. J. Biol. Chem. 272:31221–31224). To probe molecular associations of SPN within the DGC, we investigated SPN expression in normal muscle as a baseline for comparison to SPN's expression in animal models of muscular dystrophy. We show that, in addition to its sarcolemma localization, SPN is enriched at the myotendinous junction (MTJ) and neuromuscular junction (NMJ), where it is a component of both the dystrophin– and utrophin–glycoprotein complexes. We demonstrate that SPN is preferentially associated with the sarcoglycan (SG) subcomplex, and this interaction is critical for stable localization of SPN to the sarcolemma, NMJ, and MTJ. Our experiments indicate that assembly of the SG subcomplex is a prerequisite for targeting SPN to the sarcolemma. In addition, the SG– SPN subcomplex functions to stabilize α-dystroglycan to the muscle plasma membrane. Taken together, our data provide important information about assembly and function of the SG–SPN subcomplex.

Download Full-text

Role of dystrophin and utrophin for assembly and function of the dystrophin glycoprotein complex in non-muscle tissue

Cellular and Molecular Life Sciences ◽

10.1007/s00018-005-5461-0 ◽

2006 ◽

Vol 63 (14) ◽

pp. 1614-1631 ◽

Cited By ~ 103

Author(s):

T. Haenggi ◽

J. -M. Fritschy

Keyword(s):

Muscle Tissue ◽

Glycoprotein Complex ◽

Dystrophin Glycoprotein Complex ◽

And Function ◽

Dystrophin Glycoprotein

Download Full-text

Contraction-Induced Loss of Plasmalemmal Electrophysiological Function Is Dependent on the Dystrophin Glycoprotein Complex

Frontiers in Physiology ◽

10.3389/fphys.2021.757121 ◽

2021 ◽

Vol 12 ◽

Author(s):

Cory W. Baumann ◽

Angus Lindsay ◽

Sylvia R. Sidky ◽

James M. Ervasti ◽

Gordon L. Warren ◽

...

Keyword(s):

M Wave ◽

Glycoprotein Complex ◽

Dystrophic Mouse ◽

Dystrophin Deficiency ◽

Torque Loss ◽

Dystrophin Glycoprotein Complex ◽

The Many ◽

Dystrophin Glycoprotein ◽

Mouse Lines

Weakness and atrophy are key features of Duchenne muscular dystrophy (DMD). Dystrophin is one of the many proteins within the dystrophin glycoprotein complex (DGC) that maintains plasmalemmal integrity and cellular homeostasis. The dystrophin-deficient mdx mouse is also predisposed to weakness, particularly when subjected to eccentric (ECC) contractions due to electrophysiological dysfunction of the plasmalemma. Here, we determined if maintenance of plasmalemmal excitability during and after a bout of ECC contractions is dependent on intact and functional DGCs rather than, solely, dystrophin expression. Wild-type (WT) and dystrophic mice (mdx, mL172H and Sgcb−/− mimicking Duchenne, Becker and Limb-girdle Type 2E muscular dystrophies, respectively) with varying levels of dystrophin and DGC functionality performed 50 maximal ECC contractions with simultaneous torque and electromyographic measurements (M-wave root-mean-square, M-wave RMS). ECC contractions caused all mouse lines to lose torque (p<0.001); however, deficits were greater in dystrophic mouse lines compared to WT mice (p<0.001). Loss of ECC torque did not correspond to a reduction in M-wave RMS in WT mice (p=0.080), while deficits in M-wave RMS exceeded 50% in all dystrophic mouse lines (p≤0.007). Moreover, reductions in ECC torque and M-wave RMS were greater in mdx mice compared to mL172H mice (p≤0.042). No differences were observed between mdx and Sgcb−/− mice (p≥0.337). Regression analysis revealed ≥98% of the variance in ECC torque loss could be explained by the variance in M-wave RMS in dystrophic mouse lines (p<0.001) but not within WT mice (R2=0.211; p=0.155). By comparing mouse lines that had varying amounts and functionality of dystrophin and other DGC proteins, we observed that (1) when all DGCs are intact, plasmalemmal action potential generation and conduction is maintained, (2) deficiency of the DGC protein β-sarcoglycan is as disruptive to plasmalemmal excitability as is dystrophin deficiency and, (3) some functionally intact DGCs are better than none. Our results highlight the significant role of the DGC plays in maintaining plasmalemmal excitability and that a collective synergism (via each DGC protein) is required for this complex to function properly during ECC contractions.

Download Full-text

Abstract 15657: Regulation of Cardiac Regeneration by Hippo Pathway and Dystrophin Glycoprotein Complex

Circulation ◽

10.1161/circ.130.suppl_2.15657 ◽

2014 ◽

Vol 130 (suppl_2) ◽

Author(s):

Yuka Morikawa ◽

James F Martin

Keyword(s):

Hippo Pathway ◽

Myocardial Damage ◽

Cardiac Regeneration ◽

Myocardial Cell ◽

Damage Area ◽

Glycoprotein Complex ◽

Dystrophin Glycoprotein Complex ◽

Heart Size ◽

The Hippo Pathway ◽

Dystrophin Glycoprotein

Regeneration of the mammalian heart is limited in adults. In rodents, endogenous regenerative capacity exists during development and in neonate but is rapidly repressed after birth. We are elucidating the mechanisms responsible for regenerative repression and applying this knowledge to reactivate cardiac regeneration in adult hearts. We have previously shown that the Hippo pathway is responsive for regenerative repression, however, the molecular and cellular mechanism responsible remain unclear. The Hippo pathway controls heart size by repressing myocardial cell proliferation during development. By deleting Salv, a modulator of Hippo pathway, we found myocardial damage in the postnatal and adult heart was repaired anatomically and functionally. This heart repair occurred primarily through proliferation of preexisting cardiomyocyte. We observed that cardiomyocytes in border the zone protrude and fill the damage area during Hippo-mediated cardiac regeneration and thus preventing formation of fibrotic scars. The molecular analysis identified components of dystrophin glycoprotein complex (DGC) as downstream targets of Hippo pathway. The DGC anchors the cytoskeleton and extracellular matrix and is involved in cell migration. The studies using the muscular dystrophy mouse model, mdx, reveals that DGC is required for endogenous cardiac regeneration and cardiomyocyte protrusion. Taken together, we show that cardiomyocyte protrusion is an essential process for cardiac regeneration and the Hippo pathway regulates it through regulating DGC. Our studies provide insights into the mechanisms leading to repair of damaged hearts from endogenous cardiomyocytes and novel information into DGC function.

Download Full-text