Obestatin controls the ubiquitin–proteasome and autophagy–lysosome systems in glucocorticoid‐induced muscle cell atrophy

BackgroundRepetition of the onset of aspiration pneumonia in aged patients is common and causes chronic inflammation. The inflammation induces proinflammatory cytokine production and atrophy in the muscles. The proinflammatory cytokines induce muscle proteolysis by activating calpains and caspase‐3, followed by further degradation by the ubiquitin‐proteasome system. Autophagy is another pathway of muscle atrophy. However, little is known about the relationship between aspiration pneumonia and muscle. For swallowing muscles, it is not clear whether they produce cytokines. The main objective of this study was to determine whether aspiration pneumonia induces muscle atrophy in the respiratory (the diaphragm), skeletal (the tibialis anterior, TA), and swallowing (the tongue) systems, and their possible mechanisms.MethodsWe employed a mouse aspiration pneumonia model and computed tomography (CT) scans of aged pneumonia patients. To induce aspiration pneumonia, mice were inoculated with low dose pepsin and lipopolysaccharide solution intra‐nasally 5 days a week. The diaphragm, TA, and tongue were isolated, and total RNA, proteins, and frozen sections were stored. Quantitative real‐time polymerase chain reaction determined the expression levels of proinflammatory cytokines, muscle E3 ubiquitin ligases, and autophagy related genes. Western blot analysis determined the activation of the muscle proteolysis pathway. Frozen sections determined the presence of muscle atrophy. CT scans were used to evaluate the muscle atrophy in aged aspiration pneumonia patients.ResultsThe aspiration challenge enhanced the expression levels of proinflammatory cytokines in the diaphragm, TA, and tongue. Among muscle proteolysis pathways, the aspiration challenge activated caspase‐3 in all the three muscles examined, whereas calpains were activated in the diaphragm and the TA but not in the tongue. Activation of the ubiquitin‐proteasome system was detected in all the three muscles examined. The aspiration challenge activated autophagy in the TA and the tongue, whereas weak or little activation was detected in the diaphragm. The aspiration challenge resulted in a greater proportion of smaller myofibers than in controls in the diaphragm, TA, and tongue, suggesting muscle atrophy. CT scans clearly showed that aspiration pneumonia was followed by muscle atrophy in aged patients.ConclusionsAspiration pneumonia induced muscle atrophy in the respiratory, skeletal, and swallowing systems in a preclinical animal model and in human patients. Diaphragmatic atrophy may weaken the force of cough to expectorate sputum or mis‐swallowed contents. Skeletal muscle atrophy may cause secondary sarcopenia. The atrophy of swallowing muscles may weaken the swallowing function. Thus, muscle atrophy could become a new therapeutic target of aspiration pneumonia.

Section: Discussionmentioning

confidence: 95%

Aspiration pneumonia induces muscle atrophy in the respiratory, skeletal, and swallowing systems

Komatsu

Okazaki

Ebihara

et al. 2018

“…The GC‐induced loss of muscle mass is mainly because of decreased protein synthesis and increased protein degradation, which results in reduction of muscle fibre area and density . Myofibrillar protein degradation depends on ubiquitin proteasome machinery and autophagy‐lysosome machinery, which plays a major role in the catabolic action of GCs . The ubiquitin proteasome system is activated under GCs treatment .…”

Section: Introductionmentioning

confidence: 99%

Myricanol rescues dexamethasone‐induced muscle dysfunction via a sirtuin 1‐dependent mechanism

Shen

Liao

Liu

et al. 2019

Background Muscle atrophy and weakness are adverse effects of high dose or the sustained usage of glucocorticoids. Loss of mitochondria and degradation of protein are highly correlated with muscle dysfunction. The deacetylase sirtuin 1 (SIRT1) plays a vital role in muscle remodelling. The current study was designed to identify myricanol as a SIRT1 activator, which could protect skeletal muscle against dexamethasone‐induced wasting. Methods The dexamethasone‐induced atrophy in C2C12 myotubes was evaluated by expression of myosin heavy chain, muscle atrophy F‐box (atrogin‐1), and muscle ring finger 1 (MuRF1), using western blots. The mitochondrial content and oxygen consumption were assessed by MitoTracker staining and extracellular flux analysis, respectively. Muscle dysfunction was established in male C57BL/6 mice (8–10 weeks old, n = 6) treated with a relatively high dose of dexamethasone (25 mg/kg body weight, i.p., 10 days). Body weight, grip strength, forced swimming capacity, muscle weight, and muscle histology were assessed. The expression of proteolysis‐related, autophagy‐related, apoptosis‐related, and mitochondria‐related proteins was analysed by western blots or immunoprecipitation. Results Myricanol (10 μM) was found to rescue dexamethasone‐induced muscle atrophy and dysfunction in C2C12 myotubes, indicated by increased expression of myosin heavy chain (0.33 ± 0.14 vs. 0.89 ± 0.21, * P < 0.05), decreased expression of atrogin‐1 (2.31 ± 0.67 vs. 1.53 ± 0.25, * P < 0.05) and MuRF1 (1.55 ± 0.08 vs. 0.99 ± 0.12, ** P < 0.01), and elevated ATP production (3.83 ± 0.46 vs. 5.84 ± 0.79 nM/mg protein, ** P < 0.01), mitochondrial content (68.12 ± 10.07% vs. 116.38 ± 5.12%, * P < 0.05), and mitochondrial oxygen consumption (166.59 ± 22.89 vs. 223.77 ± 22.59 pmol/min, ** P < 0.01). Myricanol directly binds and activates SIRT1, with binding energy of −5.87 kcal/mol. Through activating SIRT1 deacetylation, myricanol inhibits forkhead box O 3a transcriptional activity to reduce protein degradation, induces autophagy to enhance degraded protein clearance, and increases peroxisome proliferator‐activated receptor γ coactivator‐1α activity to promote mitochondrial biogenesis. In dexamethasone‐induced muscle wasting C57BL/6 mice, 5 mg/kg myricanol treatment reduces the loss of muscle mass; the percentages of quadriceps and gastrocnemius muscle in myricanol‐treated mice are 1.36 ± 0.02% and 0.87 ± 0.08%, respectively (cf. 1.18 ± 0.06% and 0.78 ± 0.05% in dexamethasone‐treated mice, respectively). Myricanol also rescues dexamethasone‐induced muscle weakness, indicated by improved grip strength (70.90 ± 4.59 vs. 120.58 ± 7.93 g, ** P < 0.01) and prolonged swimming exhaustive time (48.80 ± 11.43 vs. 83.75 ± 15.19 s, **...

“…Interestingly, the obestatin action is not due to an effect on the FoxO3, which appears to be phosphorylated or inactivated under basal conditions. Recent data have shown that Akt/mTOR activation combined with PKD/CAMKII/AMPK inactivation by the obestatin signalling is required to inhibit FoxO‐dependent atrogenes in catabolic processes provoked by glucocorticoids . This is consistent with the activation of S6K1 and by eIF4E availability, through phosphorylation of 4E‐BP1, key regulators of protein synthesis, which shift the balance from protein degradation to protein synthesis in obestatin‐treated mice.…”

Section: Discussionmentioning

confidence: 60%

“…In terms of protein degradation, obestatin treatment led to a 43.6% ± 7.6% and 42.8% ± 14.0% decrease in the expression of the ubiquitin E3‐ligases MuRF1 and MAFbx, respectively ( Figure A). One mechanism by which obestatin reduces the expression of the ubiquitin E3 ligases is the phosphorylation and subsequent nuclear exclusion of FoxO family members . As shown in Figure B, obestatin‐treated mice showed a striking increase in FoxO1 phosphorylation at T24 [pFoxO1 (T24); 130.4% ± 18.0%] and FoxO4 phosphorylation at T28 [pFoxO4 (T28); 378.6% ± 59.5%] related to control mice but did not change basal FoxO3a phosphorylation at T32 [pFoxO3 (T32)].…”

Section: Resultsmentioning

confidence: 96%

See 1 more Smart Citation

Improvement of Duchenne muscular dystrophy phenotype following obestatin treatment

González‐Sánchez

Sánchez‐Temprano

Cid‐Díaz

et al. 2018

Self Cite

BackgroundThis study was performed to test the therapeutic potential of obestatin, an autocrine anabolic factor regulating skeletal muscle repair, to ameliorate the Duchenne muscular dystrophy (DMD) phenotype.Methods and resultsUsing a multidisciplinary approach, we characterized the ageing‐related preproghrelin/GPR39 expression patterns in tibialis anterior (TA) muscles of 4‐, 8‐, and 18‐week‐old mdx mice (n = 3/group) and established the effects of obestatin administration at this level in 8‐week‐old mdx mice (n = 5/group). The findings were extended to in vitro effects on human immortalized DMD myotubes. An analysis of TAs revealed an age‐related loss of preproghrelin expression, as precursor of obestatin, in mdx mice. Administration of obestatin resulted in a significant increase in tetanic specific force (33.0% ± 1.5%, P < 0.05), compared with control mdx mice. Obestatin‐treated TAs were characterized by reduction of fibres with centrally located nuclei (10.0% ± 1.2%, P < 0.05) together with an increase in the number of type I fibres (25.2% ± 1.7%, P < 0.05) associated to histone deacetylases/myocyte enhancer factor‐2 and peroxisome proliferator‐activated receptor‐gamma coactivator 1α axis, and down‐regulation of ubiquitin E3‐ligases by inactivation of FoxO1/4, indexes of muscle atrophy. Obestatin reduced the level of contractile damage and tissue fibrosis. These observations correlated with decline in serum creatine kinase (58.8 ± 15.2, P < 0.05). Obestatin led to stabilization of the sarcolemma by up‐regulation of utrophin, α‐syntrophin, β‐dystroglycan, and α7β1‐integrin proteins. These pathways were also operative in human DMD myotubes.ConclusionsThese results highlight the potential of obestatin as a peptide therapeutic for preserving muscle integrity in DMD, thus allowing a better efficiency of gene or cell therapy in a combined therapeutic approach.