Muscle wasting during sepsis reflects increased expression and activity of the ubiquitin-proteasome proteolytic pathway and is at least in part mediated by glucocorticoids. The ubiquitination of proteins destined to be degraded by the proteasome is regulated by multiple enzymes, including ubiquitin ligases. We tested the hypothesis that sepsis upregulates the gene expression of the newly described ubiquitin ligases, MuRF1 and atrogin-1/MAFbx. Sepsis was induced in rats by cecal ligation and puncture. Control rats were sham-operated. In some experiments, rats were treated with the glucocorticoid receptor antagonist RU 38486 before induction of sepsis. At various time points after induction of sepsis, mRNA levels for MuRF1 and atrogin-1/MAFbx were determined in extensor digitorum longus muscles by real-time PCR. Sepsis resulted in a 10-16-fold increase in gene expression of the ubiquitin ligases studied here. These changes were much greater than those observed previously for another ubiquitin ligase, E3alpha, in muscle during sepsis. Treatment of rats with RU 38486 prevented the sepsis-induced increase in mRNA levels for MuRF1 and atrogin-1/MAFbx, suggesting that glucocorticoids participate in the upregulation of these genes in muscle during sepsis. The present results lend further support to the concept that the ubiquitin-proteasome pathway plays an important role in sepsis-induced muscle proteolysis and suggest that multiple ubiquitin ligases may participate in the development of muscle wasting during sepsis.
"The ubiquitin–proteasome pathway increases protein breakdown during skeletal muscle atrophy. Two ubiquitin ligases, Muscle Ring Finger1 (MuRF1) and Muscle Atrophy F-box (MAFbx) also called Atrogin-1  , serve as markers of skeletal muscle atrophy under a multitude of catabolic perturbations, such as fasting, diabetes , cancer, renal failure, and experimental sepsis   . "
[Show abstract][Hide abstract] ABSTRACT: Androgens regulate body composition and skeletal muscle mass in males, but the molecular mechanisms are not fully understood. Recently, we demonstrated that trenbolone (a potent synthetic testosterone analogue that is not a substrate for 5-alpha reductase or for aromatase) induces myotrophic effects in skeletal muscle without causing prostate enlargement, which is in contrast to the known prostate enlarging effects of testosterone. These previous results suggest that the 5α-reduction of testosterone is not required for myotrophic action. We now report differential gene expression in response to testosterone versus trenbolone in the highly androgen-sensitive levator ani/bulbocavernosus (LABC) muscle complex of the adult rat after 6 weeks of orchiectomy (ORX), using real time PCR. The ORX-induced expression of atrogenes (Muscle RING-finger protein-1 [MuRF1] and atrogin-1) was suppressed by both androgens, with trenbolone producing a greater suppression of atrogin-1 mRNA compared to testosterone. Both androgens elevated expression of anabolic genes (insulin-like growth factor-1 and mechano-growth factor) after ORX. ORX-induced increases in expression of glucocorticoid receptor (GR) mRNA were suppressed by trenbolone treatment, but not testosterone. In ORX animals, testosterone promoted WNT1-inducible-signaling pathway protein 2 (WISP-2) gene expression while trenbolone did not. Testosterone and trenbolone equally enhanced muscle regeneration as shown by increases in LABC mass and in protein expression of embryonic myosin by Western blotting. In addition, testosterone increased WISP-2 protein levels. Together, these findings identify specific mechanisms by which testosterone and trenbolone may regulate skeletal muscle maintenance and growth.
"High concentrations of glucocorticoids can induce muscle atrophy, in part by upregulation of MuRF1 and MAFbx (Wray et al., 2003; Stitt et al., 2004). It was shown that glucocorticoids synergize with FOXO1 in inducing transcription of the MuRF1 gene (David et al., 2008; Zhao et al., 2009). "
[Show abstract][Hide abstract] ABSTRACT: Abstract The molecular mechanisms underlying skeletal muscle maintenance involve interplay between multiple signaling pathways. Under normal physiological conditions, a network of interconnected signals serves to control and coordinate hypertrophic and atrophic messages, culminating in a delicate balance between muscle protein synthesis and proteolysis. Loss of skeletal muscle mass, termed "atrophy", is a diagnostic feature of cachexia seen in settings of cancer, heart disease, chronic obstructive pulmonary disease, kidney disease, and burns. Cachexia increases the likelihood of death from these already serious diseases. Recent studies have further defined the pathways leading to gain and loss of skeletal muscle as well as the signaling events that induce differentiation and post-injury regeneration, which are also essential for the maintenance of skeletal muscle mass. In this review, we summarize and discuss the relevant recent literature demonstrating these previously undiscovered mediators governing anabolism and catabolism of skeletal muscle.
Critical Reviews in Biochemistry and Molecular Biology 11/2013; 49(1). DOI:10.3109/10409238.2013.857291 · 7.71 Impact Factor
"In this study, pulmonary inflammation was associated with increases in plasma cortisol levels, providing indirect evidence to support the notion that systemic inflammation might have occurred in this model. Previously, IT-LPS instillation was reported to increase the plasma concentration of corticosterone; the endogenous GC in mice , and in other models of inflammation -or GC-associated muscle atrophy administration of GR-receptor antagonists prevented or attenuated muscle atrophy [62,63]. "
[Show abstract][Hide abstract] ABSTRACT: Chronic obstructive pulmonary disease (COPD) is accompanied by pulmonary inflammation and associated with extra-pulmonary manifestations, including skeletal muscle atrophy. Glycogen synthase kinase-3 (GSK-3) has been implicated in the regulation of muscle protein- and myonuclear turnover; two crucial processes that determine muscle mass. In the present study we investigated the effect of the selective GSK-3 inhibitor SB216763 on muscle mass in a guinea pig model of lipopolysaccharide (LPS)-induced pulmonary inflammation-associated muscle atrophy.
Guinea pigs were pretreated with either intranasally instilled SB216763 or corresponding vehicle prior to each LPS/saline challenge twice weekly. Pulmonary inflammation was confirmed and indices of muscle mass were determined after 12 weeks. Additionally, cultured skeletal muscle cells were incubated with tumor necrosis factor α (TNF-α) or glucocorticoids (GCs) to model the systemic effects of pulmonary inflammation on myogenesis, in the presence or absence of GSK-3 inhibitors.
Repeated LPS instillation induced muscle atrophy based on muscle weight and muscle fiber cross sectional area. Intriguingly, GSK-3 inhibition using SB216763 prevented the LPS-induced muscle mass decreases and myofiber atrophy. Indices of protein turnover signaling were unaltered in guinea pig muscle. Interestingly, inhibition of myogenesis of cultured muscle cells by TNF-α or synthetic GCs was prevented by GSK-3 inhibitors.
In a guinea pig model of LPS-induced pulmonary inflammation, GSK-3 inhibition prevents skeletal muscle atrophy without affecting pulmonary inflammation. Resistance to inflammation- or GC-induced impairment of myogenic differentiation, imposed by GSK-3 inhibition, suggests that sustained myogenesis may contribute to muscle mass maintenance despite persistent pulmonary inflammation. Collectively, these results warrant further exploration of GSK-3 as a potential novel drug target to prevent or reverse muscle wasting in COPD.
Respiratory research 11/2013; 14(1):117. DOI:10.1186/1465-9921-14-117 · 3.09 Impact Factor
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