Membrane lipid rafts are disturbed in the response of rat skeletal muscle to short-term disuse

Abstract

Marked loss of skeletal muscle mass occurs under various conditions of disuse, but the molecular and cellular mechanisms leading to atrophy are not completely understood. We investigate early molecular events that might play a role in skeletal muscle remodeling during mechanical unloading (disuse). The effects of acute (6-12 h) hindlimb suspension on the soleus muscles from adult rats were examined. The integrity of plasma membrane lipid rafts was tested utilizing cholera toxin B subunit or fluorescent sterols. In addition, resting intracellular Ca level was analyzed. Acute disuse disturbed the plasma membrane lipid-ordered phase throughout the sarcolemma and was more pronounced in junctional membrane regions. Ouabain (1 µM), which specifically inhibits the Na-K-ATPase α2 isozyme in rodent skeletal muscles, produced similar lipid raft changes in control muscles but was ineffective in suspended muscles, which showed an initial loss of α2 Na-K-ATPase activity. Lipid rafts were able to recover with cholesterol supplementation, suggesting that disturbance results from cholesterol loss. Repetitive nerve stimulation also restores lipid rafts, specifically in the junctional sarcolemma region. Disuse locally lowered the resting intracellular Ca concentration only near the neuromuscular junction of muscle fibers. Our results provide evidence to suggest that the ordering of lipid rafts strongly depends on motor nerve input and may involve interactions with the α2 Na-K-ATPase. Lipid raft disturbance, accompanied by intracellular Ca dysregulation, is among the earliest remodeling events induced by skeletal muscle disuse.

Loss of melusin is a novel, neuronal NO synthase/FoxO3‐independent master switch of unloading‐induced muscle atrophy

“…Although both nNOS and melusin are costamere proteins, unloading‐induced, mitochondrial‐derived oxidative stress initiates nNOS redistribution in the sarcoplasm, whereas it does not appear involved in melusin protein decrease. A short unloading bout induces also disorganization in the lipid‐ordered phase of sarcolemma, detachment of cytoskeletal components, such as the non‐muscle α‐actinin isoform 4, and loss of function of α 2 Na‐K‐ATPase pump . It remains to be determined whether any of these unloading‐induced perturbations would act upstream or downstream melusin loss from costameres and catabolism.…”

Sarcolemmal loss of active nNOS (Nos1) is an oxidative stress‐dependent, early event driving disuse atrophy

“…Although mitochondrial dysfunction characterizes some types of muscle disuse , it still remains unknown what induces it and through which mechanism(s) it dysregulates nNOS distribution and activity. The finding that a 6–12 h unloading bout, through reduced motor nerve activity, induces disruption of the sarcolemma lipid‐ordered phase and dysfunction of the α 2 Na‐K‐ATPase pump , concomitantly with the redistribution of the non‐muscle α‐actinin isoform 4 from the subsarcolemmal compartment to the cytosolic one , suggests alternative hypothetical primary mechanisms. Whether primarily or secondarily released, ROS are recognized positive modulators of nNOS phosphorylation , which variably affects the enzyme activity depending on the S‐residue involved [1,53,54].…”

Early endplate remodeling and skeletal muscle signaling events following rat hindlimb suspension

“…Moreover, it is established that the α2 Na,K‐ATPase isozyme is enriched in endplate membrane where it co‐localizes and functionally and molecularly interacts with the nAChRs (Chibalin et al, ; Heiny et al, ; Matchkov & Krivoi, ). The loss of α2 Na,K‐ATPase activity accompanied by disturbances in lipid rafts are observed even after 6–12 hr of hindlimb suspension (Kravtsova et al, ; Petrov et al, ) suggesting the possibility of corresponding changes in the nAChRs distribution. Notably, in skeletal muscle, Na,K‐ATPase activation depends on adenosine monophosphate‐activated protein kinase (AMPK) (Benziane et al, ), a key regulator of glucose, lipid, and protein metabolism (Hardie, Schaffer, & Brunet, ).…”

“…These signaling events are of a special interest, highly debated and needs multiple time points of study to discover the molecular mechanisms that trigger disuse-induced functional alterations (Baehr et al, 2017;Baldwin et al, 2013;Vilchinskaya et al, 2017). Endplates specifically contribute to maintenance of the safety factor for neuromuscular transmission (Ruff, 2011;Wood & Slater, 2001) and endplate lipid raft disturbance is among the earliest remodeling events induced by skeletal muscle disuse (Petrov et al, 2017). Cholesterol and lipid rafts serve as a signaling platform for nicotinic acetylcholine receptors (nAChRs) clustering (Willmann et al, 2006;Zhu, Xiong, & Mei, 2006).…”