Muscle Protein Degradation Research Articles

Codonopsis lanceolata ameliorates sarcopenic obesity via recovering PI3K/Akt pathway and lipid metabolism in skeletal muscle

BackgroundThe incidence of sarcopenic obesity, muscle atrophy induced by obesity, has steadily increased and is emerging as a health problem. Although the anti-obesity effect of Codonopsis lanceolata (CL) is known, its efficacy against sarcopenic obesity has not been studied. PurposeWe aimed to investigate the effect of CL on sarcopenic obesity and the changes in the related mechanisms to confirm the potential of CL as an effective natural therapeutic agent for sarcopenic obesity. MethodsC57BL/6 mice were fed a high-fat diet (HFD) for 9 weeks, and CL was administered for 6 weeks with HFD feeding. Body weight and grip strength were measured twice a week. After sacrifice, muscle fiber histological analysis, blood lipid analysis, muscle triglyceride extraction, western blot, and real-time PCR were performed. High-performance liquid chromatography (HPLC)-electrospray ionization (ESI)-mass spectrometry (MS) analysis and in vitro experiments using C2C12 cells were performed to verify the main and active compounds of CL. Confluent C2C12 cells were differentiated for 4 days, and then the main compound of CL was co-treated with palmitic acid for 24 h. ResultsCL reduced body weight, mass of three fat tissues (epididymal fat, mesenteric fat, and perirenal fat), adipocyte cross-sectional area (CSA), and improved insulin signaling. Simultaneously, CL improved grip strength, mass of three muscle tissues (quadriceps, gastrocnemius, and soleus), and muscle fiber CSA. These results were due to the recovery of both the phosphatidylinositol-3-kinase (PI3K)/ protein kinase B (Akt) signaling pathway and lipid metabolisms in skeletal muscle. Lipids accumulated in skeletal muscle interrupt the PI3K/Akt pathway, but CL reduced intramyocellular triglyceride concentration by restoring gene expression of factors related to triglyceride synthesis and fatty acid oxidation. Therefore, the activated PI3K/Akt pathway enhanced muscle protein synthesis by increasing phosphorylation of ribosomal protein S6 kinase 1 and eIF4E-binding protein 1 and suppressed muscle protein degradation by decreasing expression of muscle ring finger-1 and muscle atrophy F-box protein. In addition, tangshenoside I (TS) was verified as the main compound of CL by HPLC-ESI-MS analysis, and its efficacy of inhibiting myotube atrophy and lipid accumulation in myotubes was confirmed, verifying that TS is an active compound. ConclusionCL is an effective natural material for sarcopenic obesity that suppresses muscle atrophy by inhibiting the accumulation of lipids in skeletal muscle through restoration of impaired PI3K/Akt pathway and lipid metabolism.

Pea Proteins Have Anabolic Effects Comparable to Milk Proteins on Whole Body Protein Retention and Muscle Protein Metabolism in Old Rats.

Plant proteins are attracting rising interest due to their pro-health benefits and environmental sustainability. However, little is known about the nutritional value of pea proteins when consumed by older people. Herein, we evaluated the digestibility and nutritional efficiency of pea proteins compared to casein and whey proteins in old rats. Thirty 20-month-old male Wistar rats were assigned to an isoproteic and isocaloric diet containing either casein (CAS), soluble milk protein (WHEY) or Pisane™ pea protein isolate for 16 weeks. The three proteins had a similar effect on nitrogen balance, true digestibility and net protein utilization in old rats, which means that different protein sources did not alter body composition, tissue weight, skeletal muscle protein synthesis or degradation. Muscle mitochondrial activity, inflammation status and insulin resistance were similar between the three groups. In conclusion, old rats used pea protein with the same efficiency as casein or whey proteins, due to its high digestibility and amino acid composition. Using these plant-based proteins could help older people diversify their protein sources and more easily achieve nutritional intake recommendations.

Lysosomal Function Impacts the Skeletal Muscle Extracellular Matrix.

Muscle development and homeostasis are critical for normal muscle function. A key aspect of muscle physiology during development, growth, and homeostasis is modulation of protein turnover, the balance between synthesis and degradation of muscle proteins. Protein degradation depends upon lysosomal pH, generated and maintained by proton pumps. Sphingolipid transporter 1 (spns1), a highly conserved gene encoding a putative late endosome/lysosome carbohydrate/H+ symporter, plays a pivotal role in maintaining optimal lysosomal pH and spns1−/− mutants undergo premature senescence. However, the impact of dysregulated lysosomal pH on muscle development and homeostasis is not well understood. We found that muscle development proceeds normally in spns1−/− mutants prior to the onset of muscle degeneration. Dysregulation of the extracellular matrix (ECM) at the myotendinous junction (MTJ) coincided with the onset of muscle degeneration in spns1−/− mutants. Expression of the ECM proteins laminin 111 and MMP-9 was upregulated. Upregulation of laminin 111 mitigated the severity of muscle degeneration, as inhibition of adhesion to laminin 111 exacerbated muscle degeneration in spns1−/− mutants. MMP-9 upregulation was induced by tnfsf12 signaling, but abrogation of MMP-9 did not impact muscle degeneration in spns1−/− mutants. Taken together, these data indicate that dysregulated lysosomal pH impacts expression of ECM proteins at the myotendinous junction.

Leucine-Rich Diet Improved Muscle Function in Cachectic Walker 256 Tumour-Bearing Wistar Rats.

Skeletal muscle atrophy occurs in several pathological conditions, such as cancer, especially during cancer-induced cachexia. This condition is associated with increased morbidity and poor treatment response, decreased quality of life, and increased mortality in cancer patients. A leucine-rich diet could be used as a coadjutant therapy to prevent muscle atrophy in patients suffering from cancer cachexia. Besides muscle atrophy, muscle function loss is even more important to patient quality of life. Therefore, this study aimed to investigate the potential beneficial effects of leucine supplementation on whole-body functional/movement properties, as well as some markers of muscle breakdown and inflammatory status. Adult Wistar rats were randomly distributed into four experimental groups. Two groups were fed with a control diet (18% protein): Control (C) and Walker 256 tumour-bearing (W), and two other groups were fed with a leucine-rich diet (18% protein + 3% leucine): Leucine Control (L) and Leucine Walker 256 tumour-bearing (LW). A functional analysis (walking, behaviour, and strength tests) was performed before and after tumour inoculation. Cachexia parameters such as body weight loss, muscle and fat mass, pro-inflammatory cytokine profile, and molecular and morphological aspects of skeletal muscle were also determined. As expected, Walker 256 tumour growth led to muscle function decline, cachexia manifestation symptoms, muscle fibre cross-section area reduction, and classical muscle protein degradation pathway activation, with upregulation of FoxO1, MuRF-1, and 20S proteins. On the other hand, despite having no effect on the walking test, inflammation status or muscle oxidative capacity, the leucine-rich diet improved muscle strength and behaviour performance, maintained body weight, fat and muscle mass and decreased some protein degradation markers in Walker 256 tumour-bearing rats. Indeed, a leucine-rich diet alone could not completely revert cachexia but could potentially diminish muscle protein degradation, leading to better muscle functional performance in cancer cachexia.

Synbiotics Alleviate Hepatic Damage, Intestinal Injury and Muscular Beclin-1 Elevation in Rats after Chronic Ethanol Administration.

The purpose of this study was to investigate the beneficial effects of synbiotics on liver damage, intestinal health, and muscle loss, and their relevance in rats with chronic ethanol feeding. Thirty Wistar rats fed with a control liquid diet were divided into control and synbiotics groups, which were respectively provided with water or synbiotics solution (1.5 g/kg body weight/day) for 2 weeks. From the 3rd to 8th week, the control group was divided into a C group (control liquid diet + water) and an E group (ethanol liquid diet + water). The synbiotics group was separated in to three groups, SC, ASE, and PSE. The SC group was given a control liquid diet with synbiotics solution; the ASE group was given ethanol liquid diet with synbiotics solution, and the PSE group was given ethanol liquid diet and water. As the results, the E group exhibited liver damage, including increased AST and ALT activities, hepatic fatty changes, and higher CYP2E1 expression. Intestinal mRNA expressions of occludin and claudin-1 were significantly decreased and the plasma endotoxin level was significantly higher in the E group. In muscles, beclin-1 was significantly increased in the E group. Compared to the E group, the PSE and ASE groups had lower plasma ALT activities, hepatic fatty changes, and CYP2E1 expression. The PSE and ASE groups had significantly higher intestinal occludin and claudin-1 mRNA expressions and lower muscular beclin-1 expression when compared to the E group. In conclusion, synbiotics supplementation might reduce protein expression of muscle protein degradation biomarkers such as beclin-1 in rats with chronic ethanol feeding, which is speculated to be linked to the improvement of intestinal tight junction and the reduction of liver damage.

Abstract PO-029: Pancreatic cancer-associated cachexia as a 3-stage systemic disease with changes in body composition, tissue-specific wasting across time and alterations in glucose metabolism

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease that rapidly deteriorates the organism resulting in <10% 5-years survival in humans. Cancer-associated cachexia (CAC) is a multi-organ complex syndrome that accompanies PDAC in 85% of the cases. CAC is often characterized by the loss of body weight, including loss of muscle and fat tissues. Chronic inflammation, myokines and adipokines (released from muscle and fat, respectively), together with few recent tumor-derived factors, have been shown to collectively induce some of the metabolic changes in peripheral tissues that lead to wasting. Those include the synthesis of acute phase proteins in the liver, lipolysis and browning of the white adipose tissues (WAT), and protein degradation in the skeletal muscle. However, how these changes affect systemic metabolism, such as amino-acid utilization for liver gluconeogenesis, the systemic consequences of increased free fatty acids from lipolysis and their final destination for b-oxidation, or the rewiring of glucose metabolism, are processes not fully understood during cachexia. Here we established a 3-stage model of cachexia progression, including pre-, early- and late-CAC stages, in a doxycycline inducible murine model of PDAC (p48(Cre/+);tetKRAS(LSL/+);p53(fl/fl)), in both genders. We have monitored body weight loss, changes in body composition using DEXA scan, food intake and survival, across time since the start of doxycycline administration (i.e. tumor initiation). We have submitted these mice to metabolic cages aiming to distinguish in which of the 3 stages fat consumption starts, as well as monitored the weight of 8 tissue types (pancreas, liver, iWAT, eWAT, brown adipose tissue, quadriceps, gastrocnemius and soleus) over time. Overall, we have defined pre-CAC as “weight-gaining stage, before body weight peaks”, early-CAC as <10% and late-CAC as >10% of body weight loss, together with specific changes in body composition in each stage, food intake only happening at the very end stage, while all non-tumoral tissues present significant reduced weight at early stages. We have performed metabolomics and lipidomics in all peripheral tissues, aiming to identify changes that occur not only at early- but also at the pre-CAC stages, when pancreatic tumors already weighed more than double of the normal pancreas. In addition, glucose tolerance test analyses showed that tumor-bearing mice cleared the glucose more rapidly than control mice, even at pre-CAC stages, opening new avenues to continue studying glucose metabolism in the periphery such as increased liver gluconeogenesis and peripheral insulin resistance. Together, these results allowed us to establish a murine model to study cachexia in 3 stages, similar to what happens in humans. Furthermore, metabolomic data from the peripheral tissues, tumor interstitial fluid (TIF) and plasma, will allow us to identify the metabolic landscape of the entire organism throughout the progression of the disease, and potentially propose new therapeutic windows to target or prevent wasting in cancer. Citation Format: Blanca Majem, Insia Naqvi, Courtney Dennis, Lucas Dailey, Clary B. Clish, Nada Kalaany. Pancreatic cancer-associated cachexia as a 3-stage systemic disease with changes in body composition, tissue-specific wasting across time and alterations in glucose metabolism [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2021 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2021;81(22 Suppl):Abstract nr PO-029.

Pathophysiological mechanisms leading to muscle loss in chronic kidney disease.

Loss of muscle proteins is a deleterious consequence of chronic kidney disease (CKD) that causes a decrease in muscle strength and function, and can lead to a reduction in quality of life and increased risk of morbidity and mortality. The effectiveness of current treatment strategies in preventing or reversing muscle protein losses is limited. The limitations largely stem from the systemic nature of diseases such as CKD, which stimulate skeletal muscle protein degradation pathways while simultaneously activating mechanisms that impair muscle protein synthesis and repair. Stimuli that initiate muscle protein loss include metabolic acidosis, insulin and IGF1 resistance, changes in hormones, cytokines, inflammatory processes and decreased appetite. A growing body of evidence suggests that signalling molecules secreted from muscle can enter the circulation and subsequently interact with recipient organs, including the kidneys, while conversely, pathological events in the kidney can adversely influence protein metabolism in skeletal muscle, demonstrating the existence of crosstalk between kidney and muscle. Together, these signals, whether direct or indirect, induce changes in the levels of regulatory and effector proteins via alterations in mRNAs, microRNAs and chromatin epigenetic responses. Advances in our understanding of the signals and processes that mediate muscle loss in CKD and other muscle wasting conditions will support the future development of therapeutic strategies to reduce muscle loss.

Ameliorating cancer cachexia by inhibiting cancer cell release of Hsp70 and Hsp90 with omeprazole.

BackgroundCancer cachexia, characterized by muscle and fat tissue wasting, is a major determinant of cancer‐related mortality without established treatment. Recent animal data revealed that cancer cells induce muscle wasting by releasing Hsp70 and Hsp90 as surface proteins on extracellular vesicles (EVs). Here, we test a therapeutic strategy for ameliorating cancer cachexia by inhibiting the release of Hsp70 and Hsp90 using proton pump inhibitor omeprazole.MethodsOmeprazole effect on Hsp70/90 release through EVs by Lewis lung carcinoma (LLC) cells in vitro, serum levels of Hsp70/90 and Hsp70/90‐carrying EVs in LLC tumour‐bearing mice, and LLC‐induced muscle protein degradation pathways in C2C12 myotubes and mice were determined. Omeprazole effect on endolysosomal pH and Rab27b expression in LLC cells were analysed.ResultsOmeprazole treatment of LLC cells inhibited Hsp70/90 and Hsp70/90‐carrying EV release in a dose‐dependent manner (1 to 10 μM) and attenuated the catabolic activity of LLC cell‐conditioned medium on C2C12 myotubes. Systemic omeprazole administration to LLC tumour‐bearing mice (5 mg/kg/day subcutaneously) for 2 weeks blocked elevation of serum Hsp70, Hsp90, and Hsp70/90‐carrying EVs, abrogated skeletal muscle catabolism, and prevented loss of muscle function as well as muscle and epididymal fat mass without altering tumour growth. Consequently, median survival increased by 23.3%. Mechanistically, omeprazole increased cancer cell endolysosomal pH level dose‐dependently (0.1 to 1 μM) by inhibiting vacuolar H+‐ATPase. Further, omeprazole suppressed the highly elevated expression of Rab27b, a key regulator of EV release, in LLC cells.ConclusionsOmeprazole ameliorates cancer cachexia by inhibiting cancer cell release of Hsp70 and Hsp90.

Naringenin alleviates cisplatin induced muscle atrophy by regulating RIPK1/AMPK/NF-κB pathway

Cisplatin (DDP) is a commonly used chemotherapy drug, but DDP can cause skeletal muscle atrophy and cachexia. This study combined the DDP-induced C2C12 myotube atrophy model and the LLC tumour-bearing mouse cachexia model under DDP treatment to explore the effect and mechanism of naringenin (NAR) in alleviating skeletal muscle atrophy and cachexia. NAR alleviated the decreases in body weight, food intake, muscle, adipose tissue and kidney weight and forelimb grip strength in LLC tumour-bearing mice under DDP treatment and reduced the serum level of TNF-α. High dose NAR also enhanced the antitumour effect of DDP. NAR can prevent the cross-sectional area reduction of skeletal muscle fibres and prevent the change in fibre type ratio induced by DDP. NAR intervention inhibits the RIPK1/AMPK/NF-κB pathway in skeletal muscle, downregulates the expression of Atrogin1 and MuRF1, and inhibits the degradation of skeletal muscle protein. In C2C12 myotubes treated with DDP, NAR inhibited the RIPK1/AMPK/NF-κB pathway to reduce myotube cell atrophy, and the overexpression of RIPK1 reversed the therapeutic effect of NAR. These results indicate that NAR downregulates the expression of Atrogin1 and MuRF1 by regulating the RIPK1/AMPK/NF-κB pathway and alleviates DDP-induced skeletal muscle atrophy.

Inhibitory Effect of the Glycerophosphate Moiety of Lipoteichoic Acid from Lactic Acid Bacteria on Dexamethasone-Induced Atrogin-1 Expression in C2C12 Myotubes.

Atrogin-1, which is an important regulator of ubiquitin-mediated protein degradation in skeletal muscle, is a major marker of muscle loss and disuse muscle atrophy. To investigate which components of lactic acid bacteria (LAB) suppress dexamethasone (DEX)-induced atrogin-1 expression, mouse skeletal muscle C2C12 myotubes were treated with DEX in the presence or absence of components of LAB. Heat-killed cells and lipoteichoic acid (LTA) derived from five LAB strains significantly suppressed DEX-induced atrogin-1 expression. The glycerophosphate (GroP) fraction prepared from chemically-degraded LTA and sn-glycerol-1-phosphate suppressed DEX-induced atrogin-1 expression, whereas the glycolipid anchor fraction of LTA did not. Heat-killed cells obtained by culturing under low-Mn2+ conditions, which generated fewer poly-GroP polymers in LTA, displayed significantly lower inhibitory activity compared to heat-killed cells grown under normal conditions. These results suggested that LTA of LAB contributed to suppressing atrogin-1 expression and that the GroP moiety of LTA was responsible for its inhibitory activity.

Alcalase Potato Protein Hydrolysate-PPH902 Enhances Myogenic Differentiation and Enhances Skeletal Muscle Protein Synthesis under High Glucose Condition in C2C12 Cells.

Sarcopenia is an aging associated disorder involving skeletal muscle atrophy and a reduction in muscle strength, and there are no pharmaceutical interventions available thus far. Moreover, conditions such as hyperglycaemia are known to further intensify muscle degradation. Therefore, novel strategies to attenuate skeletal muscle loss are essential to enhance muscle function and thereby improve the quality of life in diabetic individuals. In this study, we have investigated the efficiency of a potato peptide hydrolysate PPH902 for its cytoprotective effects in skeletal muscle cells. PPH902 treatment in C2C12 cells showed the dose-dependent activation of the Akt/mTOR signalling pathway that is involved in skeletal myogenesis. According to Western blotting analysis, PPH902 induced the phosphorylation of Akt, mTOR proteins and induced the myogenic differentiation of C2C12 myoblasts in a differentiation medium. The phosphorylation myogenic transcription factor Foxo3A was also found to be increased in the cells treated with PPH902. In addition, treatment with PPH902 ameliorated the high glucose induced reduction in cell viability in a dose-dependent manner. Moreover, the number of myotubes in a differentiation medium reduced upon high glucose challenge, but treatment with PPH902 increased the number of differentiated myotubes. Further, the phosphorylations of AMPK and mitochondrial-related transcription factors such as PGC-1α were suppressed upon high glucose challenge but PPH902 treatment restored the protein levels. We demonstrate, for the first time, that a specific potato peptide has a therapeutic effect against sarcopenia. In addition, PPH902 improved the myogenic differentiation and their mitochondrial biogenesis and further improved myogenic protein and inhibited muscle protein degradation in C2C12 cells challenged under a high glucose condition.

Efficacy of passive repetitive stretching of skeletal muscle on myofiber hypertrophy and genetic suppression on MAFbx, MuRF1, and myostatin.

Skeletal muscles undergo adaptations in response to mechanical stimuli such as stretching. However, there is limited evidence regarding the hypertrophic effects of passive repetitive stretching in vivo. We examined the effect of passive repetitive stretching on skeletal muscle myofiber morphology, satellite cell content, and messenger RNA expression of myogenic regulatory factors and signaling molecules involved in muscle protein synthesis and degradation. The gastrocnemius muscles of mice were stretched 15 times/min by manual ankle dorsiflexion for 15min, 5days a week for 2weeks. We found that passive repetitive stretching significantly increased myofiber cross-sectional area. In stretched gastrocnemius muscles, the messenger RNA expression of p70S6K and myogenin was upregulated, whereas MuRF1, MAFbx, myostatin, and 4E-BP1 were downregulated. The phosphorylation level of p70S6K was significantly increased in stretched muscles. The number of Pax7+ cells was unaffected. Passive repetitive stretching induces muscle hypertrophy by regulating signaling pathways involved in muscle protein turnover. These findings are applicable to clinical muscle strengthening and for the maintenance of skeletal muscle mass and function in patients who are unconscious or paralyzed.

Effects of heat treatments on texture of abalone muscles and its mechanism

The objective of this study was to develop suitable heating conditions and reveal the mechanism of texture changes in abalone muscles. The milder heat treatments (60 °C-10 min and 70 °C-10 min) increased shear force and hardness of abalone muscles. However, with increased heating time or temperature (70 °C-30 min, 80 °C-10 min and 100 °C-10 min), shear force and hardness significantly decreased in abalone muscles. Decreases in the extraction rate and solubility of myofibrillar proteins (MPs), and increase in myofibrillar fragmentation index were observed in cooked abalone muscles, indicating denaturation of MPs induced by heat treatment. Heat treatment also led to protein degradation in abalone muscles as increases in dissolution rate of protein, trichloroacetic acid-soluble peptides content, soluble collagen content, and dissolution rate of hydroxyproline and glycosaminoglycan were observed. In addition, changes in miscrostructure, water content and water holding capatity (WHC) were noted in cooked abalone muscles. Correlation analysis showed that protein denaturation/degradation was responsible for changes in microstructure and WHC, which ultimately affected the textural properties of cooked abalone muscles.

Impaired Muscle Mitochondrial Function in Familial Partial Lipodystrophy.

Familial partial lipodystrophy (FPL), Dunnigan variety is characterized by skeletal muscle hypertrophy and insulin resistance besides fat loss from the extremities. The cause for the muscle hypertrophy and its functional consequences is not known. To compare muscle strength and endurance, besides muscle protein synthesis rate between subjects with FPL and matched controls (n = 6 in each group). In addition, we studied skeletal muscle mitochondrial function and gene expression pattern to help understand the mechanisms for the observed differences. Body composition by dual-energy X-ray absorptiometry, insulin sensitivity by minimal modelling, assessment of peak muscle strength and fatigue, skeletal muscle biopsy and calculation of muscle protein synthesis rate, mitochondrial respirometry, skeletal muscle transcriptome, proteome, and gene set enrichment analysis. Despite increased muscularity, FPL subjects did not demonstrate increased muscle strength but had earlier fatigue on chest press exercise. Decreased mitochondrial state 3 respiration in the presence of fatty acid substrate was noted, concurrent to elevated muscle lactate and decreased long-chain acylcarnitine. Based on gene transcriptome, there was significant downregulation of many critical metabolic pathways involved in mitochondrial biogenesis and function. Moreover, the overall pattern of gene expression was indicative of accelerated aging in FPL subjects. A lower muscle protein synthesis and downregulation of gene transcripts involved in muscle protein catabolism was observed. Increased muscularity in FPL is not due to increased muscle protein synthesis and is likely due to reduced muscle protein degradation. Impaired mitochondrial function and altered gene expression likely explain the metabolic abnormalities and skeletal muscle dysfunction in FPL subjects.

Beneficial Effects of Resveratrol in Mouse Gastrocnemius: A Hint to Muscle Phenotype and Proteolysis.

We hypothesized that the phenolic compound resveratrol mitigates muscle protein degradation and loss and improves muscle fiber cross-sectional area (CSA) in gastrocnemius of mice exposed to unloading (7dI). In gastrocnemius of mice (female C57BL/6J, 10 weeks) exposed to a seven-day period of hindlimb immobilization with/without resveratrol treatment, markers of muscle proteolysis (tyrosine release, systemic troponin-I), atrophy signaling pathways, and muscle phenotypic features and function were analyzed. In gastrocnemius of unloaded mice treated with resveratrol, body and muscle weight and function were attenuated, whereas muscle proteolysis (tyrosine release), proteolytic and apoptotic markers, atrophy signaling pathways, and myofiber CSA significantly improved. Resveratrol treatment of mice exposed to a seven-day period of unloading prevented body and muscle weight and limb strength loss, while an improvement in muscle proteolysis, proteolytic markers, atrophy signaling pathways, apoptosis, and muscle fiber CSA was observed in the gastrocnemius muscle. These findings may have potential therapeutic implications in the management of disuse muscle atrophy in clinical settings.

Out of Control: The Role of the Ubiquitin Proteasome System in Skeletal Muscle during Inflammation.

The majority of critically ill intensive care unit (ICU) patients with severe sepsis develop ICU-acquired weakness (ICUAW) characterized by loss of muscle mass, reduction in myofiber size and decreased muscle strength leading to persisting physical impairment. This phenotype results from a dysregulated protein homeostasis with increased protein degradation and decreased protein synthesis, eventually causing a decrease in muscle structural proteins. The ubiquitin proteasome system (UPS) is the predominant protein-degrading system in muscle that is activated during diverse muscle atrophy conditions, e.g., inflammation. The specificity of UPS-mediated protein degradation is assured by E3 ubiquitin ligases, such as atrogin-1 and MuRF1, which target structural and contractile proteins, proteins involved in energy metabolism and transcription factors for UPS-dependent degradation. Although the regulation of activity and function of E3 ubiquitin ligases in inflammation-induced muscle atrophy is well perceived, the contribution of the proteasome to muscle atrophy during inflammation is still elusive. During inflammation, a shift from standard- to immunoproteasome was described; however, to which extent this contributes to muscle wasting and whether this changes targeting of specific muscular proteins is not well described. This review summarizes the function of the main proinflammatory cytokines and acute phase response proteins and their signaling pathways in inflammation-induced muscle atrophy with a focus on UPS-mediated protein degradation in muscle during sepsis. The regulation and target-specificity of the main E3 ubiquitin ligases in muscle atrophy and their mode of action on myofibrillar proteins will be reported. The function of the standard- and immunoproteasome in inflammation-induced muscle atrophy will be described and the effects of proteasome-inhibitors as treatment strategies will be discussed.

The Prophylactic Effects of Glutamine on Muscle Protein Synthesis and Degradation in Rats with Ethanol-Induced Liver Damage.

The purpose of this research was to investigate the prophylactic effects of glutamine on muscle protein synthesis and degradation in rats with ethanol-induced liver injury. For the first 2 weeks, Wistar rats were divided into two groups and fed a control (n = 16) or glutamine-containing diet (n = 24). For the following 6 weeks, rats fed the control diet were further divided into two groups (n = 8 per group) according to whether their diet contained no ethanol (CC) or did contain ethanol (CE). Rats fed the glutamine-containing diet were also further divided into three groups (n = 8 per group), including a GG group (glutamine-containing diet without ethanol), GE group (control diet with ethanol), and GEG group (glutamine-containing diet with ethanol). After 6 weeks, results showed that hepatic fatty change, inflammation, altered liver function, and hyperammonemia had occurred in the CE group, but these were attenuated in the GE and GEG groups. Elevated intestinal permeability and a higher plasma endotoxin level were observed in the CE group, but both were lower in the GE and GEG groups. The level of a protein synthesis marker (p70S6K) was reduced in the CE group but was higher in both the GE and GEG groups. In conclusion, glutamine supplementation might elevate muscle protein synthesis by improving intestinal health and ameliorating liver damage in rats with chronic ethanol intake.

Bcaa Alleviates Rats Skeletal Muscle Protein Degradation After Eccentric Exercise By Reducing KLF15 Expression

PURPOSE: Exercise-induced muscle damage after high-intensity eccentric exercise can lead to degradation of skeletal muscle protein, thereby affecting the training effect. The purpose of this study is to explore the effect of branched-chain amino acid (BCAA) supplementation on muscle damage caused by one-time eccentric exercise, and the regulation of KLF15-mediated proteolytic pathways in the process. METHODS: 64 male SD rats were randomly divided into eight groups: placebo + control group (PC, n = 8), placebo + immediately after exercise group (PE, n = 8), placebo +6 h after exercise group (PE6, n = 8), placebo +12 h after exercise group (PE12, n = 8), BCAA + control group (BC, n = 8), BCAA + immediately after exercise group (BE, n = 8), BCAA +6 h after exercise group (BE6, n = 8), BCAA +12 h after exercise group (BE12, n = 8). Rats in BCAA groups were supplied BCAA (1 g/kg/day) 3 times before exercise. The placebo groups were supplied the same volume of distilled water. Rats in exercise groups underwent a bout of 2 h eccentric exercise on treadmill (-16° slope, a speed of 16 m/min). Blood and gastrocnemius were collected immediately after exercise in PE and BE, 6 h after exercise in PE6 and BE6, and 12 h after exercise in PE12 and BE12. The expression of 3-MH in blood was detected by ELISA. RT-qPCR was used to measure the mRNA expression of KLF15, Atrogin-1, MuRF-1 and MHC-II in gastrocnemius. RESULTS: The mRNA expression of MHC-II (P < 0.05), KLF15 (P < 0.05), Atrogin-1 (P < 0.05), MuRF-1 (P < 0.01) in PE were higher than those in PC, MHC-II (P < 0.05) in PE6 and Atrogin-1 (P < 0.05) in PE12 were higher than in PC. MHC-II (P < 0.05) was higher in BE6 than in BE. Compared with PE, the mRNA expression of KLF15 (P < 0.01), Atrogin-1(P < 0.05), MuRF-1 (P < 0.01) in BE were significantly lower, Atrogin-1 (P < 0.05) in BE12 was lower than that in PE12. 3-MH (P < 0.05) content was higher in PE12 than in PC, 3-MH (P < 0.01) content was lower in BE and BE6 than in BC, 3-MH (P < 0.01) content was higher in BC than in PC. CONCLUSIONS: BCAA may reduce skeletal muscle proteolysis by lowering the level of gene transcription in the KLF15-related protein degradation pathway, which occurs immediately after exercise.

Synergetic effect of soluble whey protein hydrolysate and Panax ginseng berry extract on muscle atrophy in hindlimb-immobilized C57BL/6 mice

BackgroundSarcopenia, defined as loss of muscle mass and strength with age, becomes a public health concern as the elderly population increases. This study aimed to determine whether the mixture of soluble whey protein hydrolysate (WPH) and Panax ginseng berry extract (GBE) has a synergetic effect on sarcopenia and, if so, to identify the relevant mechanisms and optimal mixing ratio. MethodsIn the first experiment, C57BL/6 mice were hindlimb immobilized for one-week and then administered WPH 800 mg/kg, GBE 100 mg/kg, WPH 800 mg/kg+ GBE 100 mg/kg mixture, and Fructus Schisandrae extract (SFE) 200 mg/kg for two weeks. In the second experiment, experimental design was same, but mice were administered three different doses of WPH and GBE mixture (WPH 800 mg/kg+ GBE 100 mg/kg, WPH 800 mg/kg+ GBE 90 mg/kg, WPH 1000 mg/kg+ GBE 75 mg/kg). ResultsIn the first experiment, we confirmed the synergetic effect of WPH and GBE on muscle mass and identified that GBE was more effective on the protein synthesis side, and WPH tended to be slightly more effective for protein degradation. In the second experiment, among three different ratios, the WPH 800 mg/kg+ GBE 100 mg/kg was most effective for muscle mass and strength. The mixtures activated muscle protein synthesis via PI3K/Akt/mTORc1 pathway and inhibited muscle protein degradation via suppressing ubiquitin-proteasome system (UPS) and autophagy-lysosome system (ALS), and these effects were more GBE dose-dependent than WPH. ConclusionThe WPH and GBE mixture having a synergetic effect is a potential agent to prevent sarcopenia.

Pathophysiology and mechanisms of primary sarcopenia (Review).

Aging causes skeletal muscle atrophy, and myofiber loss can be a critical component of this process. In 1989, Rosenberg emphasized the importance of the loss of skeletal muscle mass that occurs with aging and coined the term 'sarcopenia'. Since then, sarcopenia has attracted considerable attention due to the aging population in developed countries. The presence of sarcopenia is closely related to staggering, falls and even frailty in the elderly, which in turn leads to the need for nursing care. Sarcopenia is often associated with a poor prognosis in the elderly. Therefore, it is crucial to investigate the causes and pathogenesis of sarcopenia, and to develop and introduce interventional strategies in line with these causes and pathogenesis. Sarcopenia can be a primary component of physical frailty. The association between sarcopenia, frailty and locomotive syndrome is complex; however, sarcopenia is a muscle‑specific concept that is relatively easy to approach in research. In the elderly, a lack of exercise, malnutrition and hormonal changes lead to neuromuscular junction insufficiency, impaired capillary blood flow, reduced repair and regeneration capacity due to a decrease in the number of muscle satellite cells, the infiltration of inflammatory cells and oxidative stress, resulting in muscle protein degradation exceeding synthesis. In addition, mitochondrial dysfunction causes metabolic abnormalities, such as insulin resistance, which may lead to quantitative and qualitative abnormalities in skeletal muscle, resulting in sarcopenia. The present review article focuses on age‑related primary sarcopenia and outlines its pathogenesis and mechanisms.