Skeletal muscle atrophy is commonly associated with immobilization, ageing, and catabolic diseases such as diabetes and cancer cachexia. Epigenetic regulation of gene expression resulting from ...chromatin remodeling through histone acetylation has been implicated in muscle disuse. The present work was designed to test the hypothesis that treatment with trichostatin A (TSA), a histone deacetylase inhibitor, would partly counteract unloading-induced muscle atrophy. Soleus muscle atrophy (-38%) induced by 14 days of rat hindlimb suspension was reduced to only 25% under TSA treatment. TSA partly prevented the loss of type I and IIa fiber size and reversed the transitions of slow-twitch to fast-twitch fibers in soleus muscle. Unloading or TSA treatment did not affect myostatin gene expression and follistatin protein. Soleus protein carbonyl content remained unchanged, whereas the decrease in glutathione vs. glutathione disulfide ratio and the increase in catalase activity (biomarkers of oxidative stress) observed after unloading were abolished by TSA treatment. The autophagy-lysosome pathway (Bnip3 and microtubule-associated protein 1 light chain 3 proteins, Atg5, Gabarapl1, Ulk1, and cathepsin B and L mRNA) was not activated by unloading or TSA treatment. However, TSA suppressed the rise in muscle-specific RING finger protein 1 (MuRF1) caused by unloading without affecting the forkhead box (Foxo3) transcription factor. Prevention of muscle atrophy by TSA might be due to the regulation of the skeletal muscle atrophy-related MuRF1 gene. Our findings suggest that TSA may provide a novel avenue to treat unloaded-induced muscle atrophy.
Although several lines of evidence link muscle-derived oxidants and inflammation to skeletal muscle wasting via regulation of apoptosis and proteolysis, little information is currently available on ...muscle repair. The present work was designed to study oxidative stress response, inflammatory cytokines, apoptotic, or proteolytic pathways during the early (1 and 5 days) and later (14 days) stages of the regrowth process subsequent to 14 days of hindlimb unloading. During the early stages of reloading, muscle mass recovery (day 5) was facilitated by transcriptional downregulation (day 1) of pathways involved in muscle proteolysis mu-calpain, atrogin-1/muscle atrophy F-box (MAFbx), and muscle RING finger-1/(MuRF1) mRNA and upregulation of an autophagy-related protein Beclin-1 (day 5). At the same time, oxidative stress (glutathione vs. glutathione disulfide ratio, superoxide dismutase, catalase activities) remained still enhanced, whereas the increased uncoupling protein 3 gene expression recovered. Increased caspase-9 (mitochondrial-driven apoptosis) and decreased caspase-12 (sarcoplasmic reticulum-mediated apoptosis) activation was also normalized at early stages (day 5). Conversely, the receptor-mediated apoptotic pathway initiated by ligand-induced (tumor necrosis factor-alpha, TNF-alpha) binding and promoting the activation of caspase-8 remained elevated until 14 days. Our data suggest that at early stages, muscle repair is mediated via the modulation of mitochondrial-driven apoptosis and muscle proteolysis. Despite full muscle mass recovery, oxidative stress and TNF-alpha-mediated apoptotic pathway are still activated till later stages of muscle remodeling.
Purpose
We explored whether altered expression of factors tuning mitochondrial metabolism contributes to muscular adaptations with endurance training in the condition of lowered ambient oxygen ...concentration (hypoxia) and whether these adaptations relate to oxygen transfer as reflected by subsarcolemmal mitochondria and oxygen metabolism in muscle.
Methods
Male volunteers completed 30 bicycle exercise sessions in normoxia or normobaric hypoxia (4,000 m above sea level) at 65 % of the respective peak aerobic power output. Myoglobin content, basal oxygen consumption, and re-oxygenation rates upon reperfusion after 8 min of arterial occlusion were measured in
vastus
muscles by magnetic resonance spectroscopy. Biopsies from
vastus lateralis
muscle, collected pre and post a single exercise bout, and training, were assessed for levels of transcripts and proteins being associated with mitochondrial metabolism.
Results
Hypoxia specifically lowered the training-induced expression of markers of respiratory complex II and IV (i.e. SDHA and isoform 1 of COX-4; COX4I1) and preserved fibre cross-sectional area. Concomitantly, trends (
p
< 0.10) were found for a hypoxia-specific reduction in the basal oxygen consumption rate, and improvements in oxygen repletion, and aerobic performance in hypoxia. Repeated exercise in hypoxia promoted the biogenesis of subsarcolemmal mitochondria and this was co-related to expression of isoform 2 of COX-4 with higher oxygen affinity after single exercise, de-oxygenation time and myoglobin content (
r
≥ 0.75). Conversely, expression in COX4I1 with training correlated negatively with changes of subsarcolemmal mitochondria (
r
< −0.82).
Conclusion
Hypoxia-modulated adjustments of aerobic performance with repeated muscle work are reflected by expressional adaptations within the respiratory chain and modified muscle oxygen metabolism.
Calcium-dependent signalling pathways are believed to play an important role in skeletal muscle atrophy, but whether intracellular Ca
2+
homeostasis is affected in that situation remains obscure. We ...show here that there is a 20% atrophy of the fast-type
flexor digitorum brevis
(FDB) muscle in rats hind limb unloaded (HU) for 2 weeks, with no change in fibre type distribution. In voltage-clamp experiments, the amplitude of the slow Ca
2+
current was found similar in fibres from control and HU animals. In fibres loaded with the Ca
2+
dye indo-1, the value for the rate of Ca
2+
decay after the end of 5–100-ms-long voltage-clamp depolarisations from −80 to +10 mV was found to be 30–50% lower in fibres from HU animals. This effect was consistent with a reduced contribution of both saturable and non-saturable components of myoplasmic Ca
2+
removal. However, there was no change in the relative amount of parvalbumin, and type 1 sarco-endoplasmic reticulum Ca
2+
-ATPase was increased by a factor of three in the atrophied muscles. Confocal imaging of mitochondrial membrane potential showed that atrophied FDB fibres had significantly depolarized mitochondria as compared to control fibres. Depolarization of mitochondria in control fibres with carbonyl cyanide-p-trifluoromethoxyphenylhydrazone induced a slowing of the decay of Ca
2+
transients accompanied by an increase in resting Ca
2+
and a reduction of the peak amplitude of the transients. Overall results provide the first functional evidence for severely altered intracellular Ca
2+
removal capabilities in atrophied fast-type muscle fibres and highlight the possible contribution of reduced mitochondrial polarisation.
Calcium-dependent signalling pathways are believed to play an important role in skeletal muscle atrophy, but whether intracellular Ca(2+) homeostasis is affected in that situation remains obscure. We ...show here that there is a 20% atrophy of the fast-type flexor digitorum brevis (FDB) muscle in rats hind limb unloaded (HU) for 2 weeks, with no change in fibre type distribution. In voltage-clamp experiments, the amplitude of the slow Ca(2+) current was found similar in fibres from control and HU animals. In fibres loaded with the Ca(2+) dye indo-1, the value for the rate of Ca(2+) decay after the end of 5-100-ms-long voltage-clamp depolarisations from -80 to +10 mV was found to be 30-50% lower in fibres from HU animals. This effect was consistent with a reduced contribution of both saturable and non-saturable components of myoplasmic Ca(2+) removal. However, there was no change in the relative amount of parvalbumin, and type 1 sarco-endoplasmic reticulum Ca(2+)-ATPase was increased by a factor of three in the atrophied muscles. Confocal imaging of mitochondrial membrane potential showed that atrophied FDB fibres had significantly depolarized mitochondria as compared to control fibres. Depolarization of mitochondria in control fibres with carbonyl cyanide-p-trifluoromethoxyphenylhydrazone induced a slowing of the decay of Ca(2+) transients accompanied by an increase in resting Ca(2+) and a reduction of the peak amplitude of the transients. Overall results provide the first functional evidence for severely altered intracellular Ca(2+) removal capabilities in atrophied fast-type muscle fibres and highlight the possible contribution of reduced mitochondrial polarisation.
1 Université Claude Bernard Lyon I, Laboratoire
de Physiologie des Eléments Excitables, Unité Mixte de
Recherche 5123 Centre National de la Recherche Scientifique, 69622 Villeurbanne, France; 2 ... Institut National de la Santé et
de la Recherche Médicale, U 418, Hôpital Debrousse, 69322 Lyon, France
ACTH has been shown to depolarize bovine
adrenal zona fasciculata cells by inhibiting a K + current.
The effects of this hormone on such cells have been reexamined using
perforated and standard patch recording methods. In current clamp
experiments, ACTH (10 nM) induced a membrane depolarization to
36 ± 1 mV ( n = 56), which was mimicked by
forskolin (10 µM) or by 8-(4-chlorophenylthio)-cAMP (8 mM).
ACTH-induced membrane depolarizations were associated in the majority
of cells with an increase in membrane conductance. In the other cells, these membrane responses could occur without change or could be correlated with a transient or with a continuous
Cs + -sensitive decrease in membrane conductance. The
depolarizations associated with an increase in membrane conductance
were depressed by Cl current inhibitors
diphenylamine-2-carboxylic acid (DPC; 1 mM), anthracene-9-carboxylic
acid (9-AC; 1 mM), DIDS (400 µM), verapamil (100 µM), and
glibenclamide (20 µM). In voltage-clamped Cs + -loaded
cells, ACTH activated a time-independent current that displayed an
outward rectification and reversed at 21.5 mV ± 2 ( n = 6). This current, observed in the presence of
internal EGTA (5 mM), was depressed in low Cl external
solution and was inhibited by DPC, 9-AC, DIDS,
5-nitro-2-(3-phenylpropylamino)benzoic acid, verapamil, and
glibenclamide. ACTH-stimulated cortisol secretion was blocked by
Cl channel inhibitors DIDS (400 µM) and DPC (1 mM). The
present results reveal that, in addition to inhibiting a K +
current, ACTH activates in bovine zona fasciculata cells a
Ca 2+ -insensitive, cAMP-dependent Cl current.
This Cl current is involved in the ACTH-induced membrane
depolarization, which seems to be a crucial step in stimulating steroidogenesis.
adrenocorticotropic hormone; calf adrenal zona fasciculata cells; whole cell recording; membrane potential; membrane current; chloride
current inhibitors
ACTH has been shown to depolarize bovine adrenal zona fasciculata cells by inhibiting a K+ current. The effects of this hormone on such cells have been reexamined using perforated and standard patch ...recording methods.
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