Cholesterol Depletion Uncouples �-dystroglycans from Discrete Sarcolemmal Domains, Reducing the Mechanical Activity of Skeletal Muscle

Abstract

Background/Aims: β-Dystroglycan (β-DG) is a transmembrane glycoprotein that links the intracellular cytoskeleton to the extracellular matrix and is crucial for the molecular pathway of lateral force transmission in muscle. We aimed to investigate the effect of decreasing sarcolemmal cholesterol on the distribution of β-DG, its interaction with dystrophin and the impact on the contraction efficiency of muscle. Methods: Isolated rat extensor digitorum longus muscles were incubated with methyl β-cyclodextrin (MβCD) to deplete cholesterol and with MβCD-cholesterol to restore cholesterol. Electric stimulation protocols were used to determine muscle force and fatigue. Detergent-resistant membranes (lipid rafts) were separated from isolated skeletal muscle sarcolemma. The distribution and interactions of β-DG, caveolin-3 and dystrophin were determined by an immunoreactivity analysis. Results: Cholesterol depletion in muscle results in a weakened force of contraction, which recovers after cholesterol restoration. The rate of fatigue is unaffected, but fatigue recovery is dependent upon cholesterol restoration. MβCD modifies the structures of lipid rafts obtained from MβCD-treated muscles by, displacing the membrane proteins β-DG and caveolin-3 f from the lipid raft, thus reducing the interaction of β-DG with dystrophin. Conclusion: Cholesterol depletion weakens the muscle contractile force by disturbing the sarcolemmal distribution of β-dystroglycan and its interaction with dystrophin, two key proteins in the alignment of lateral force transmission pathway.

Cholesterol depletion impairs contractile machinery in neonatal rat cardiomyocytes

“…In non-muscle cells, cholesterol regulates actin cytoskeleton architecture and cortical mechanical properties2345 whereas in smooth and skeletal muscle cells, cholesterol is important for modulating the contraction of these cells67856. However, less is known about how cholesterol affects cardiomyocyte physiology and how its depletion affects cell contractility.…”

“…Cholesterol-depleted endothelial cells3 and fibroblasts4 also show an increase in cell stiffness due to actin remodeling and that is probably due to an enhancement in membrane-cytoskeleton adhesion energy5. In skeletal muscle cells, cholesterol depletion impairs contraction, causes vacuolization and morphological abnormalities and uncouples a transmembrane glycoprotein, β-dystroglycan that connects the extracellular matrix to the cytoskeleton of those cells678. However, less is known about how cholesterol depletion might affect cardiomyocyte physiology and contraction dynamics.…”

Gestational Undernourishment Modifies the Composition of Skeletal Muscle Transverse Tubule Membranes and the Mechanical Properties of Muscles in Newborn Rats

“…These proteins are known to be located almost exclusively in the TT membranes. In contrast, β-Dystroglycan is known to be a protein marker of the sarcolemma, distributed in a costameric arrangement close to the opening of the TT membrane system [29]. …”

“…Muscle force in Newtons (N) was determined using a mass calibration curve. The fatigue protocol was performed at 50% and 30% with continuous stimulation of 75 Hz given for 1 s at 100 V every 0.3 s, as previously described [29]. To evaluate fatigue, muscle contractile recovery was performed after 10 min of the completion of the fatigue protocol, as follows: five tetanic stimulations of 1 s, 75 Hz at 100 V every 5 min.…”

“…However, it is unknown whether PMCA is expressed in new-born SM. In terms of lipid composition, the TT membrane from normal adult SM is enriched in cholesterol and sphingolipids, with a phospholipid/cholesterol ratio between 0.5 and 0.9 in different species [24,28,29]. However, no data are available on the lipid content of TT membranes from new-born SM.…”