Activation of ubiquitin-proteasome pathway is involved in skeletal muscle wasting in a rat model with biliary cirrhosis: potential role of TNF-alpha

Ursodeoxycholic acid induces sarcopenia associated with decreased protein synthesis and autophagic flux

BACKGROUND

Skeletal muscle generates force and movements and maintains posture. Under pathological conditions, muscle fibers suffer an imbalance in protein synthesis/degradation. This event causes muscle mass loss and decreased strength and muscle function, a syndrome known as sarcopenia. Recently, our laboratory described secondary sarcopenia in a chronic cholestatic liver disease (CCLD) mouse model. Interestingly, the administration of ursodeoxycholic acid (UDCA), a hydrophilic bile acid, is an effective therapy for cholestatic hepatic alterations. However, the effect of UDCA on skeletal muscle mass and functionality has never been evaluated, nor the possible involved mechanisms.

METHODS

We assessed the ability of UDCA to generate sarcopenia in C57BL6 mice and develop a sarcopenic-like phenotype in C₂C₁₂ myotubes and isolated muscle fibers. In mice, we measured muscle strength by a grip strength test, muscle mass by bioimpedance and mass for specific muscles, and physical function by a treadmill test. We also detected the fiber's diameter and content of sarcomeric proteins. In C₂C₁₂ myotubes and/or isolated muscle fibers, we determined the diameter and troponin I level to validate the cellular effect. Moreover, to evaluate possible mechanisms, we detected puromycin incorporation, p70S6K, and 4EBP1 to evaluate protein synthesis and ULK1, LC3 I, and II protein levels to determine autophagic flux. The mitophagosome-like structures were detected by transmission electron microscopy.

RESULTS

UDCA induced sarcopenia in healthy mice, evidenced by decreased strength, muscle mass, and physical function, with a decline in the fiber's diameter and the troponin I protein levels. In the C₂C₁₂ myotubes, we observed that UDCA caused a reduction in the diameter and content of MHC, troponin I, puromycin incorporation, and phosphorylated forms of p70S6K and 4EBP1. Further, we detected increased levels of phosphorylated ULK1, the LC3II/LC3I ratio, and the number of mitophagosome-like structures. These data suggest that UDCA induces a sarcopenic-like phenotype with decreased protein synthesis and autophagic flux.

CONCLUSIONS

Our results indicate that UDCA induces sarcopenia in mice and sarcopenic-like features in C₂C₁₂ myotubes and/or isolated muscle fibers concomitantly with decreased protein synthesis and alterations in autophagic flux.

Evaluation of Prolonged Endometrial Inflammation Associated with the Periparturient Metabolic State in Dairy Cows

The objectives of this study were to assess the sequential dynamics of the endometrial polymorphonuclear cells (PMN) after calving by endometrial cytology, and clarify the factors that cause prolonged endometrial inflammation in lactating dairy cows. A total of 33 lactating Holstein dairy cows were used from -4 to 8 wk relative to calving (0 wk: the calving week). Endometrial samples were obtained sequentially from 2 to 8 wk. Body condition score and backfat thickness were obtained weekly from -4 to 8 wk. Blood samples collected from -4 to 8 wk were analyzed for indicators of energy status, hepatic function, systemic inflammation, and calcium. Blood amino acids were measured at 2 wk. Daily milk production was determined between 5 and 65 d postpartum. Based on the sequential cytological analysis, the endometrial inflammation threshold was set at ≥5.0% PMN, and the median wk of PMN% lower than 5.0% was 4.5 wk in this study; therefore, we classified the cows into the early group (cows with endometrial inflammation converged within 4 wk: n = 17) and the late group (cows with endometrial inflammation converged at or after 5 wk: n = 16). There were no differences in daily milk production, energy status, hepatic function, blood calcium concentration, and systemic inflammatory response. The late group had lower body condition scores and backfat thickness during the experimental period, and a higher blood concentration of 3-methyl histidine, indicating muscle breakdown, was observed in the late group at 2 wk. Our findings indicated that the lack of body fat reservation during the peripartum period and the increased muscle breakdown after calving were risk factors for prolonged endometrial inflammation.

A Nanocurcumin and Pyrroloquinoline Quinone Formulation Prevents Hypobaric Hypoxia-Induced Skeletal Muscle Atrophy by Modulating NF-κB Signaling Pathway

Kushwaha, Asha D., and Deepika Saraswat. A nanocurcumin and pyrroloquinoline quinone formulation prevents hypobaric hypoxia-induced skeletal muscle atrophy by modulating NF-κB signaling pathway. High Alt Med Biol 00:000-000, 2022. Background: Hypobaric hypoxia (HH)-induced deleterious skeletal muscle damage depends on exposure time and availability of oxygen at cellular level, which eventually can limit human work performance at high altitude (HA). Despite the advancements made in pharmacological (performance enhancer, antioxidants) and nonpharmacological therapeutics (acclimatization strategies), only partial success has been achieved in improving physical performance at HA. A distinctive combination of nanocurcumin (NC) and pyrroloquinoline quinone (PQQ) has been formulated (named NCF [nanocurcumin formulation], Indian patent No. 302877) in our laboratory, and has proven very promising in improving cardiomyocyte adaptation to chronic HH. We hypothesized that NCF might improve skeletal muscle adaptation and could be a performance enhancer at HA. Material and Methods: Adult Sprague-Dawley rats (220 ± 10 g) were divided into five groups (n = 6/group): normoxia vehicle control, hypoxia vehicle control, hypoxia NCF, hypoxia NC, and hypoxia PQQ. All the animals (except those in normoxia) were exposed to simulated HH in a chamber at temperature 22°C ± 2°C, humidity 50% ± 5%, altitude 25,000 ft for 1, 3, or 7 days. After completion of the stipulated exposure time, gastrocnemius and soleus muscles were excised from animals for further analysis. Results: Greater lengths of hypoxic exposure caused progressively increased muscle ring finger-1 (MuRF-1; p < 0.01) expression and calpain activation (0.56 ± 0.05 vs. 0.13 ± 0.02 and 0.44 ± 0.03 vs. 0.12 ± 0.021) by day 7, respectively in the gastrocnemius and soleus muscles. Myosin heavy chain type I (slow oxidative) fibers significantly (p > 0.01) decreased in gastrocnemius (>50%) and soleus (>46%) muscles by the seventh day of exposure. NCF supplementation showed (p ≤ 0.05) tremendous improvement in skeletal muscle acclimatization through effective alleviation of oxidative damage, and changes in calpain activity and atrophic markers at HA compared with hypoxia control or treatment alone with NC/PQQ. Conclusion: Thus, NCF-mediated anti-oxidative, anti-inflammatory effects lead to decreased proteolysis resulting in mitigated skeletal muscle atrophy under HH.

Magnesium Lithospermate B Attenuates High-Fat Diet-Induced Muscle Atrophy in C57BL/6J Mice

Magnesium lithospermate B (MLB) is a primary hydrophilic component of Danshen, the dried root of Salvia miltiorrhiza used in traditional medicine, and its beneficial effects on obesity-associated metabolic abnormalities were reported in our previous study. The present study investigated the anti-muscle atrophy potential of MLB in mice with high-fat diet (HFD)-induced obesity. In addition to metabolic abnormalities, the HFD mice had a net loss of skeletal muscle weight and muscle fibers and high levels of muscle-specific ubiquitin E3 ligases, namely the muscle atrophy F-box (MAFbx) and muscle RING finger protein 1 (MuRF-1). MLB supplementation alleviated those health concerns. Parallel changes were revealed in high circulating tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), skeletal TNF receptor I (TNFRI), nuclear factor-kappa light chain enhancer of activated B cells (NF-κB), p65 phosphorylation, and Forkhead box protein O1 (FoxO1) as well as low skeletal phosphoinositide 3-kinase (PI3K) and protein kinase B (Akt) phosphorylation. The study revealed that MLB prevented obesity-associated skeletal muscle atrophy, likely through the inhibition of MAFbx/MuRF-1-mediated muscular degradation. The activation of the PI3K-Akt-FoxO1 pathway and inhibition of the TNF-α/TNFRI/NF-κB pathway were assumed to be beneficial effects of MLB.

Clinical impact of sarcopenia assessment in patients with liver cirrhosis

Introduction: Sarcopenia is defined as loss of skeletal muscle mass, strength, and function, and it is associated with increased morbidity and mortality in patients with chronic liver disease.Areas covered: The aim of this review is to provide a detailed report on the pathophysiological mechanisms underlying sarcopenia in cirrhotic patients, the several imaging methods available for the assessment of sarcopenia and the clinical studies evaluating the prognostic role of sarcopenia presence in cirrhotic patients.Expert opinion: Sarcopenia pathogenesis is complex and multifaceted, as chronic catabolic conditions, increased energy expenditure, reduced appetite, side effects of multiple therapies, alterations in circulating levels of hormones, low protein synthesis, presence of ascites or portosystemic shunts are all factors contributing to muscle atrophy in cirrhotic patients. Computed tomography scan is the most validated method to evaluate muscle mass and quality. Sarcopenia is associated with a higher rate waitlist mortality, hepatic encephalopathy, and lower quality of life in patients with liver cirrhosis. Future studies should make an effort to unify and validate liver disease-specific cutoffs for the definition of sarcopenia.

Molecular Mechanism Contributing to Malnutrition and Sarcopenia in Patients with Liver Cirrhosis

Liver cirrhosis is frequently accompanied by disease-related malnutrition (DRM) and sarcopenia, defined as loss of skeletal muscle mass and function. DRM and sarcopenia often coexist in cirrhotic patients and are associated with increased morbidity and mortality. The clinical manifestation of both comorbidities are triggered by multifactorial mechanisms including reduced nutrient and energy intake caused by dietary restrictions, anorexia, neuroendocrine deregulation, olfactory and gustatory deficits. Maldigestion and malabsorption due to small intestinal bacterial overgrowth, pancreatic insufficiency or cholestasis may also contribute to DRM and sarcopenia. Decreased protein synthesis and increased protein degradation is the cornerstone mechanism to muscle loss, among others mediated by disease- and inflammation-mediated metabolic changes, hyperammonemia, increased myostatin and reduced human growth hormone. The concise pathophysiological mechanisms and interactions of DRM and sarcopenia in liver cirrhosis are not completely understood. Furthermore, most knowledge in this field are based on experimental models, but only few data in humans exist. This review summarizes known and proposed molecular mechanisms contributing to malnutrition and sarcopenia in liver cirrhosis and highlights remaining knowledge gaps. Since, in the prevention and treatment of DRM and sarcopenia in cirrhotic patients, more research is needed to identify potential biomarkers for diagnosis and development of targeted therapeutic strategies.

Liver Cirrhosis and Sarcopenia from the Viewpoint of Dysbiosis

Sarcopenia in patients with liver cirrhosis (LC) has been attracting much attention these days because of the close linkage to adverse outcomes. LC can be related to secondary sarcopenia due to protein metabolic disorders and energy metabolic disorders. LC is associated with profound alterations in gut microbiota and injuries at the different levels of defensive mechanisms of the intestinal barrier. Dysbiosis refers to a state in which the diversity of gut microbiota is decreased by decreasing the bacterial species and the number of bacteria that compose the gut microbiota. The severe disturbance of intestinal barrier in LC can result in dysbiosis, several bacterial infections, LC-related complications, and sarcopenia. Here in this review, we will summarize the current knowledge of the relationship between sarcopenia and dysbiosis in patients with LC.

Skeletal muscle volume loss among liver cirrhosis patients receiving levocarnitine predicts poor prognosis

Sarcopenia has a negative impact on the prognosis of patients with liver cirrhosis (LC). We investigated the significance of skeletal muscle volume and its changes in LC patients taking levocarnitine (L-carnitine).We retrospectively analyzed 51 LC patients taking L-carnitine from December 2012 to March 2019. Skeletal mass index was calculated as the left-right sum of the major × minor axis of psoas muscle at the third lumbar vertebra, divided by height squared (psoas muscle index [PMI]). Patients were classified into 2 groups (low and normal PMI) depending on PMI < 6.0 and < 3.4 cm/m for men and women, respectively. Changes in PMI per month during L-carnitine administration (ΔPMI/m) were calculated, and we classified the patients into 2 groups (severe and mild muscle atrophy) depending on ΔPMI/m below the lower quartile. We assessed overall survival (OS).At the start of L-carnitine administration, there were no significant differences in OS between groups with low and normal PMI. Multivariate analysis showed that ΔPMI/m (hazard ratio [HR], 0.007; P = .005) and L-carnitine administration period (HR, 0.956; P = .021) were significantly associated with OS. Patients with severe muscle atrophy had a significantly lower OS than those with mild muscle atrophy. There was the positive correlation relationship between ΔPMI/m and L-carnitine administration period.Among LC patients taking L-carnitine, progressive muscle volume loss was a predictor of poor prognosis. L-carnitine administration for longer may be able to prevent muscle volume loss and lead to a better prognosis in LC patients.

Preclinical insights into the gut-skeletal muscle axis in chronic gastrointestinal diseases

Muscle wasting represents a constant pathological feature of common chronic gastrointestinal diseases, including liver cirrhosis (LC), inflammatory bowel diseases (IBD), chronic pancreatitis (CP) and pancreatic cancer (PC), and is associated with increased morbidity and mortality. Recent clinical and experimental studies point to the existence of a gut‐skeletal muscle axis that is constituted by specific gut‐derived mediators which activate pro‐ and anti‐sarcopenic signalling pathways in skeletal muscle cells. A pathophysiological link between both organs is also provided by low‐grade systemic inflammation. Animal models of LC, IBD, CP and PC represent an important resource for mechanistic and preclinical studies on disease‐associated muscle wasting. They are also required to test and validate specific anti‐sarcopenic therapies prior to clinical application. In this article, we review frequently used rodent models of muscle wasting in the context of chronic gastrointestinal diseases, survey their specific advantages and limitations and discuss possibilities for further research activities in the field. We conclude that animal models of LC‐, IBD‐ and PC‐associated sarcopenia are an essential supplement to clinical studies because they may provide additional mechanistic insights and help to identify molecular targets for therapeutic interventions in humans.

Controversies in Diagnosing Sarcopenia in Cirrhosis-Moving from Research to Clinical Practice

Sarcopenia, defined as loss of muscle mass and function, is increasingly recognized as a common consequence of advanced cirrhosis that is associated with adverse clinical outcomes. Despite the recent proliferation in publications pertaining to sarcopenia in end-stage liver disease, there remains no single 'best method' for its diagnosis. The inability to identify a gold standard is common to other specialties, including geriatrics from which many diagnostic tools are derived. Controversies in diagnosis have implications for the accuracy and reproducibility of cohort studies in the field, largely prohibit the introduction of sarcopenia measurement into routine patient care and impede the development of clinical trials to identify appropriate therapies. Difficulties in diagnosis are partly driven by our ongoing limited understanding of the pathophysiology of sarcopenia in cirrhosis, the mechanisms by which it impacts on patient outcomes, the heterogeneity of patient populations, and the accuracy, availability and cost of assessments of muscle mass and function. This review discusses the currently studied diagnostic methods for sarcopenia in cirrhosis, and outlines why reaching a consensus on sarcopenia diagnosis is important and suggests potential ways to improve diagnostic criteria to allow us to translate sarcopenia research into improvements in clinical care.

Sarcopenia in cirrhosis: from pathogenesis to interventions

Sarcopenia (severe muscle depletion) is a prevalent muscle abnormality in patients with cirrhosis that confers poor prognosis both pre- and post-liver transplantation. The pathogenesis of sarcopenia is multifactorial and results from an imbalance between protein synthesis and breakdown. Nutritional, metabolic, and biochemical abnormalities seen in chronic liver disease alter whole body protein homeostasis. Hyperammonemia, increased autophagy, proteasomal activity, lower protein synthesis, and impaired mitochondrial function play an important role in muscle depletion in cirrhosis. Factors including cellular energy status, availability of metabolic substrates (e.g., branched-chain amino acids), alterations in the endocrine system (insulin resistance, circulating levels of insulin, insulin-like growth factor-1, corticosteroids, and testosterone), cytokines, myostatin, and exercise are involved in regulating muscle mass. A favored atrophy of type II fast-twitch glycolytic fibers seems to occur in patients with cirrhosis and sarcopenia. Identification of muscle biological abnormalities and underlying mechanisms is required to plan clinical trials to reverse sarcopenia through modulation of specific mechanisms. Accordingly, a combination of nutritional, physical, and pharmacological interventions might be necessary to reverse sarcopenia in cirrhosis. Moderate exercise should be combined with appropriate energy and protein intake, in accordance with clinical guidelines. Interventions with branched chain amino acids, testosterone, carnitine, or ammonia-lowering therapies should be considered individually. Various factors such as dose, type, duration of supplementations, etiology of cirrhosis, amount of dietary protein intake, and compliance with supplementation and exercise should be the focus of future large randomized controlled trials investigating both prevention and treatment of sarcopenia in this patient population.

L-Carnitine Suppresses Loss of Skeletal Muscle Mass in Patients With Liver Cirrhosis

Liver cirrhosis (LC) is a major cause of secondary sarcopenia. Sarcopenia makes the prognosis worse; thus, novel therapeutic options for sarcopenia in patients with LC are urgently required as they are currently limited. In this retrospective study, 158 patients with LC were screened, and 35 of those patients who were treated with L‐carnitine for more than 6 months and for whom skeletal muscle mass changes could be evaluated by computer tomography were enrolled. Of the 158 patients, 79 patients who did not receive L‐carnitine supplementation served as controls. Cases and controls were propensity score matched for age, sex, presence of hepatocellular carcinoma, and branched chain amino acid administration, and changes in skeletal muscle mass and clinical data were compared. The 35 patients who received L‐carnitine supplementation and 35 propensity score‐matched patients who did not receive carnitine supplementation comprised the final enrollment. Compared with control patients, patients who received L‐carnitine had significantly worse liver function, which is associated with rapid progress of skeletal muscle depletion. However, loss of skeletal muscle mass was significantly suppressed in patients receiving L‐carnitine, and a significant effect was observed in patient subgroups stratified by age, sex, presence of hepatocellular carcinoma, and branched chain amino acid administration. The change ratios of most laboratory data, including vitamin D and insulin‐like growth factor 1 levels, were similar in the two groups, but ammonia levels were significantly less in those receiving L‐carnitine. However, even in patients receiving L‐carnitine but not showing an ammonia decrease, loss of skeletal muscle was significantly suppressed. Conclusion: L‐carnitine suppresses loss of skeletal muscle mass and may therefore be a novel therapeutic option for sarcopenia in patients with LC. (Hepatology Communications 2018; 00:000‐000)

Skeletal muscle myopenia in mice model of bile duct ligation and carbon tetrachloride-induced liver cirrhosis

Skeletal muscle myopathy is universal in cirrhotic patients, however, little is known about the main mechanisms involved. The study aims to investigate skeletal muscle morphological, histological, and functional modifications in experimental models of cirrhosis and the principal molecular pathways responsible for skeletal muscle myopathy. Cirrhosis was induced by bile duct ligation (BDL) and carbon tetrachloride (CCl4) administration in mice. Control animals (CTR) underwent bile duct exposure or vehicle administration only. At sacrifice, peripheral muscles were dissected and weighed. Contractile properties of extensor digitorum longus (EDL) were studied in vitro. Muscle samples were used for histological and molecular analysis. Quadriceps muscle histology revealed a significant reduction in cross-sectional area of muscle and muscle fibers in cirrhotic mice with respect to CTR. Kinetic properties of EDL in both BDL and CCl4 were reduced with respect to CTR; BDL mice also showed a reduction in muscle force and a decrease in the resistance to fatigue. Increase in myostatin expression associated with a decrease in AKT-mTOR expressions was observed in BDL mice, together with an increase in LC3 protein levels. Upregulation of the proinflammatory citochines TNF-a and IL6 and an increased expression of NF-kB and MuRF-1 were observed in CCl4 mice. In conclusion, skeletal muscle myopenia was present in experimental models of BDL and CCl4-induced cirrhosis. Moreover, reduction in protein synthesis and activation of protein degradation were the main mechanisms responsible for myopenia in BDL mice, while activation of ubiquitin-pathway through inflammatory cytokines seems to be the main potential mechanism involved in CCl4 mice.

Down-regulation of common NFκB-iNOS pathway by chronic Thalidomide treatment improves Hepatopulmonary Syndrome and Muscle Wasting in rats with Biliary Cirrhosis

Thalidomide can modulate the TNFα-NFκB and iNOS pathway, which involve in the pathogenesis of hepatopulmonary syndrome (HPS) and muscle wasting in cirrhosis. In bile duct ligated-cirrhotic rats, the increased circulating CD16⁺ (inflammatory) monocytes and its intracellular TNFα, NFκB, monocyte chemotactic protein (MCP-1) and iNOS levels were associated with increased circulating MCP-1/soluable intercellular cell adehesion molecule-1 (sICAM-1), pulmonary TNFα/NOx, up-regulated M1 polarization, exacerbated angiogenesis and hypoxemia (increased AaPO₂) in bronchoalveolar lavage (BAL) fluid and pulmonary homogenates. Meanwhile, a significant correlation was noted between circulating CD16⁺ monocyte/M1 (%) macrophages in BAL; M1 (%) macrophages in BAL/pulmonary iNOS mRNA expression; pulmonary iNOS mRNA expression/relative pulmonary MVD; pulmonary NOx level/AaPO₂; circulating CD16⁺ monocyte/M1 (%) macrophages in muscle homogenates; 3-nitrotyrosine (representative of peroxynitrite) concentration/M1 (%) macrophages in muscle homogenates. The in vitro data demonstrated an iNOS-dependent inhibition of thalidomide on the TNFα-stimulated angiogenesis and myogenesis in human pulmonary artery endothelial cells (HPAECs) and C2C12 myoblasts. Significantly, the co-culture of CD16⁺ monocyte from different rats with HPAECs, or co-culture of supernatant of above mixed cultures with HPAECs or C2C12 myoblasts stimulated angiogenesis, migration and myogenesis. Our findings demonstrate that TNFα inhibitor thalidomide markedly diminishes the severity of experimental HPS and muscle wasting by down-regulation of common peripheral and local NFκB-iNOS pathway.

What is new about diet in hepatic encephalopathy

There is a relationship between hepatic encephalopathy (HE) protein malnutrition and muscle wasting. Muscle may play an alternative role in ammonia detoxification. Molecular mechanisms responsible for muscle depletion are under investigation. Specific nutrients may interact to reverse the molecular pathways involved in muscle wasting at an early stage. Training exercises have also been proposed to improve skeletal muscle mass. However, these data refer to small groups of patients. The amelioration of muscle mass may potentially help to prevent HE. The pathogenesis of HE is associated with modifications of the gut microbiota and diet is emerging to play a relevant role in the modulation of the gut milieu. Vegetarian and fibre-rich diets have been shown to induce beneficial changes on gut microbiota in healthy people, with reduction of Bacteroides spp., Enterobacteriaceae, and Clostridium cluster XIVa bacteria. By way of contrast, it has been suggested that a high-fat or protein diet may increase Firmicutes and reduce Bacteroidetes phylum. Milk-lysozyme and milk-oligosaccharides have also been proposed to induce a "healthy" microbiota. At present, no studies have been published describing the modification of the gut microbiota in cirrhotic patients with HE as a response to specific diets. New research is needed to evaluate the potentiality of foods in the modulation of gut microbiota in liver disease and HE.

Testosterone therapy increases muscle mass in men with cirrhosis and low testosterone: A randomised controlled trial

BACKGROUND & AIMS

Low testosterone and sarcopenia are common in men with cirrhosis and both are associated with increased mortality. Whether testosterone therapy in cirrhosis improves muscle mass and other outcomes is unknown.

METHODS

We conducted a 12-month, double-blinded, placebo-controlled trial of intramuscular testosterone undecanoate in 101 men with established cirrhosis and low serum testosterone (total testosterone <12nmol/L or free testosterone <230pmol/L) in a single tertiary centre. Body composition was assessed using dual-energy X-ray absorptiometry at baseline, 6 and 12months.

RESULTS

At study completion, appendicular lean mass was significant higher in testosterone-treated subjects, with a mean adjusted difference (MAD) of +1.69kg, (CI +0.40; +2.97kg, p=0.021). Secondary outcomes included a substantially higher total lean mass in the active group (MAD +4.74kg, CI +1.75; +7.74kg, p=0.008), matched by reduced fat mass (MAD -4.34kg, CI -6.65; -2.04, p<0.001). Total bone mass increased (MAD +0.08kg, CI +0.01; +0.15kg, p=0.009) as did bone mineral density at the femoral neck (MAD +0.287points, CI +0.140; +0.434, p<0.001). Haemoglobin was higher with testosterone therapy (MAD +10.2g/L, CI +1.50; +18.9g/L, p=0.041) and percentage glycosylated haemoglobin (HbA1c) lower (MAD -0.35%, CI -0.05; -0.54, p=0.028). Mortality was non-significantly lower in testosterone-treated patients (16% vs. 25.5%, p=0.352). There was no increase in adverse events in testosterone-treated subjects.

CONCLUSION

Testosterone therapy in men with cirrhosis and low serum testosterone safely increases muscle mass, bone mass and haemoglobin, and reduces fat mass and HbA1c. This is the first evidence-based therapy for sarcopenia in cirrhosis and thus requires larger-scale investigation into its potential impact on mortality.

LAY SUMMARY

Both low testosterone and muscle wasting are associated with increased risk of death in men with severe liver disease. Administering testosterone to men with liver disease who have low testosterone levels significantly increases their muscle mass. In addition, testosterone has non-muscle beneficial effects which may be able to increase survival in this population.

CLINICAL TRIAL NUMBER

Australian New Zealand Clinical Trials Registry trial number ACTRN 12614000526673.

Japan Society of Hepatology guidelines for sarcopenia in liver disease (1st edition): Recommendation from the working group for creation of sarcopenia assessment criteria

Sarcopenia is defined by muscle loss and muscle dysfunction. Sarcopenia is classified into primary and secondary types, based on the cause. Primary sarcopenia is mainly aging-related sarcopenia, whereas secondary sarcopenia is the reduced muscle mass and strength that accompanies an underlying disease. Given the essential role of the liver in metabolism, secondary sarcopenia due to nutritional disorders or other factors can frequently occur in liver disease. In 2015, the Japan Society of Hepatology (JSH) decided to establish its own assessment criteria for sarcopenia in liver disease because the number of liver disease patients with sarcopenia is expected to increase and there is cumulative evidence to indicate sarcopenic patients have poor clinical outcomes. A working group to create assessment criteria for sarcopenia has thus been established by the JSH. In this article, we summarize the current knowledge with regard to sarcopenia and present the assessment criteria for sarcopenia in liver disease proposed by the JSH (1st edition). To the best of our knowledge, this is globally the first proposed assessment criteria for sarcopenia specializing in liver disease.

UBE2D2 is not involved in MuRF1-dependent muscle wasting during hindlimb suspension

The Ubiquitin Proteasome System (UPS) is mainly responsible for the increased protein breakdown observed in muscle wasting. The E3 ligase MuRF1 is so far the only enzyme known to direct the main contractile proteins for degradation (i.e. troponin I, myosin heavy chains and actin). However, MuRF1 does not possess any catalytic activity and thus depends on the presence of a dedicated E2 for catalyzing the covalent binding of polyubiquitin (polyUb) chains on the substrates. The E2 enzymes belonging to the UBE2D family are commonly used for in vitro ubiquitination assays but no experimental data suggesting their physiological role as bona fide MuRF1-interacting E2 enzymes are available. In this work, we first found that the mRNA levels of critical E3 enzymes implicated in the atrophying program (MuRF1, MAFbx, Nedd4 and to a lesser extent Mdm2) are tightly and rapidly controlled during the atrophy (up regulation) and recovery (down regulation) phases in the soleus muscle from hindlimb suspended rats. By contrast, E3 ligases (Ozz, ASB2β and E4b) implicated in other processes (muscle development or regeneration) poorly responded to atrophy and recovery. UBE2B, an E2 enzyme systematically up regulated in various catabolic situations, was controlled at the mRNA levels like the E3s implicated in the atrophying process. By contrast, UBE2D2 was progressively repressed during atrophy and recovery, which makes it a poor candidate for a role during muscle atrophy. In addition, UBE2D2 did not exhibit any affinity with MuRF1 using either yeast two-hybrid or Surface Plasmon Resonance (SPR) approaches. Finally, UBE2D2 was unable to promote the degradation of the MuRF1 substrate α-actin in HEK293T cells, suggesting that no functional interaction exists between these enzymes within a cellular context. Altogether, our data strongly suggest that UBE2D2 is not the cognate ubiquitinating enzyme for MuRF1 and that peculiar properties of UBE2D enzymes may have biased in vitro ubiquitination assays.

UBE2B is implicated in myofibrillar protein loss in catabolic C2C12 myotubes

BACKGROUND

Skeletal muscle protein loss is an adaptive response to various patho-physiological situations, and the ubiquitin proteasome system (UPS) is responsible for the degradation of the bulk of muscle proteins. The role of E2 ubiquitin-conjugating enzymes is still poorly understood in skeletal muscle.

METHODS

We screened for E2s expression levels in C2C12 myotubes submitted to the catabolic glucocorticoid dexamethasone (Dex).

RESULTS

One micromolar Dex induced an accumulation of proteasome substrates (polyUb conjugates) and an overexpression of the muscle-specific E3 ligase MuRF1 and of six E2 enzymes, UBE2A, UBE2B, UBE2D1, UBE2D2, UBE2G1, and UBE2J1. However, only MuRF1 and UBE2B were sensitive to mild catabolic conditions (0.16 μM Dex). UBE2B knockdown induced a sharp decrease of total (-18%) and K48 (-28%) Ub conjugates, that is, proteasome substrates, indicating an important role of UBE2B in the overall protein breakdown in catabolic myotubes.

CONCLUSIONS

Interestingly, these results indicate an important role of UBE2B on muscle protein homeostasis during catabolic conditions.

Skeletal muscle proteolysis is associated with sympathetic activation and TNF-α-ubiquitin-proteasome pathway in liver cirrhotic rats

BACKGROUND AND AIM

This study examined the effects of adrenergic blockade on muscle wasting and expression of the ubiquitin-proteasome system, tumor necrosis factor-α (TNF-α) and its signaling pathways in skeletal muscles of cirrhotic rats.

METHODS

Cirrhosis was induced by bile duct ligation in adult male Sprague-Dawley rats for 5 weeks. Oral administration of propranolol (75 mg/kg per day) and intraperitoneal administration of TNF-α receptor antagonist (100 µg/kg per day) were delivered for the last 7 and 14 days experimental periods, respectively.

RESULTS

Bile duct ligation caused a reduction of myosin heavy chain protein and muscle wasting. The release of free tyrosine and 3-methylhistidine, MAFbx and MuRF-1 ubiquitin ligase expression, myosin heavy chain protein ubiquitination, and 20S proteasome activity were higher in skeletal muscles of cirrhotic rats than in sham controls. In addition, circulating norepinephrine, protein levels of muscle TNF-α, TNF-α receptor-1, and TNF receptor-associated factor-2, phosphorylation of IKK-α/β, IκB-α, and p65, and NF-κB activity were also increased. Administration of propranolol and TNF-α receptor antagonist led to reduction of post-receptor actions of TNF-α and ubiquitin-proteasome activity in cirrhotic rats.

CONCLUSIONS

Our findings suggest a potential role of the sympathetic system, in association with pro-inflammatory responses, in the pathogenesis of muscle wasting in liver cirrhosis.

Review article: sarcopenia in cirrhosis--aetiology, implications and potential therapeutic interventions

BACKGROUND

Sarcopenia (loss of muscle mass) is common in cirrhosis and is associated with poor outcomes. Current teaching recommends the use of protein supplementation and exercise, however, this fails to address many other factors which contribute to muscle loss in this setting.

AIMS

To summarise existing knowledge regarding the aetiology of sarcopenia in cirrhosis, diagnostic modalities and the clinical significance of this condition. In addition to discuss recent research findings that may allow the development of more effective treatments.

METHODS

We conducted a Medline and PubMed search using the search terms 'sarcopenia', 'muscle', 'body composition', 'cirrhosis', 'liver' and 'malnutrition' from inception to October 2015.

RESULTS

Cirrhotic patients with sarcopenia have reduced survival, experience increased rates of infection and have worse outcomes following liver transplantation. The aetiology of this condition is more complex than simple protein and calorie malnutrition. Cirrhosis also results in depleted glycogen stores and metabolic alterations that cause excessive protein catabolism, increased activation of the ubiquitin-proteasome pathway and inappropriate muscle autophagy. Satellite cell differentiation and proliferation is also reduced due to a combination of elevated myostatin levels, reduced IGF-1 and hypogonadism. Although there is some evidence supporting the use of late evening snacks, branched chain amino acid supplementation and high protein/high calorie diets, well designed clinical trials addressing the effects of treatment on body composition in cirrhosis are lacking.

CONCLUSION

Sarcopenia in cirrhosis has a complex pathogenesis and simple dietary interventions are insufficient. Improved understanding of the multiple mechanisms involved should allow the development of more effective therapies, which target the specific underlying metabolic derangements.

Six-week anaerobic training improves proteolytic profile of diabetic rats

OBJECTIVE

To evaluate the effect of six-week anaerobic training on the mRNA expression of genes related to proteolysis Ubb (Ubiquitin), E2-14kDa, Trim63 (MuRF1 protein) and Nfkb1 in the skeletal muscle of diabetic rats.

MATERIALS AND METHODS

Four groups were established: DE (DiabetesExercised), DS (Diabetes Sedentary), CE (Control Exercised) and CS (Control Sedentary). The training consisted of 3 sets of 12 jumps in the liquid mean with load equivalent to 50% of BW for 6 weeks. Euthanasia occurred under ip anesthesia, and blood, adipose tissue and skeletal muscles were collected. Gene expression was quantified by RT-PCR in the gastrocnemius muscle. ANOVA one-way was used for comparison among groups, with post-hoc (Tukey) when necessary, considering p < 0.05.

RESULTS

We observed reduction in the body weight and adipose tissue in the diabetic groups. The muscle mass was reduced in DS, which could be reversed by training (DE). Although DS and DE have presented similar body weight, the training protocol in DE promoted reduction in the adipose tissue, and increase of muscle mass. Anaerobic training was efficient to reduce glycaemia only in the diabetic animals until 6 hours after the end of training. The Trim63 gene expression was increased in DS; decreased Ubb gene level was observed in trained rats (CE and DE) compared to sedentary (CS and DS), and DE presented the lowest level of E2-14kDa gene expression.

CONCLUSION

Six-week anaerobic training promoted muscle mass gain, improved glycemic control, and exerted inhibitory effect on the proteolysis of gastrocnemius muscle of diabetic rats.

Protein kinetics in human endotoxaemia and their temporal relation to metabolic, endocrine and proinflammatory cytokine responses

BACKGROUND

Sepsis is associated with profound alterations in protein metabolism. The unpredictable time course of sepsis and the multiplicity of confounding factors prevent studies of temporal relations between the onset of endocrine and proinflammatory cytokine responses and the onset of protein catabolism. This study aimed to determine the time course of whole-body protein catabolism, and relate it to the endocrine, metabolic and cytokine responses in a human endotoxaemia model of early sepsis.

METHODS

Six healthy male volunteers were studied twice in random order, before and for 600 min after administration of either an intravenous bolus of Escherichia coli lipopolysaccharide (LPS) or sterile saline. Whole-body protein synthesis, breakdown and net protein breakdown were measured by amino acid tracer infusion, and related to changes in plasma levels of growth hormone, glucagon, cortisol, insulin-like growth factor (IGF) 1, tumour necrosis factor (TNF) α and interleukin (IL) 6.

RESULTS

Protein synthesis, breakdown and net protein breakdown increased and peaked 120 min after LPS administration (P < 0·001), the alterations persisting for up to 480 min. These peaks coincided with peaks in plasma growth hormone, TNF-α and IL-6 concentrations (P = 0·049, P < 0·001 and P < 0·001 for LPS versus saline), whereas plasma cortisol concentration peaked later. No alterations in plasma insulin or glucagon concentrations, or in the IGF axis were observed during the period of abnormalities of protein metabolism.

CONCLUSION

LPS administration induced an early protein catabolic response in young men and this coincided with changes in plasma growth hormone, TNF-α and IL-6 concentrations, rather than changes in cortisol, glucagon, insulin or the IGF axis. Surgical relevance Sepsis in surgical patients is common and remains associated with substantial mortality. Although sepsis is a heterogeneous condition and its pathophysiology therefore difficult to study, a universal and profound clinical problem is protein catabolism not responsive to nutritional support. Human experimental endotoxaemia is a promising model of clinical sepsis that can be used to elucidate underlying pathophysiology and explore novel therapeutic approaches. This study demonstrates that human experimental endotoxaemia replicates the changes in whole-body protein turnover seen in clinical sepsis. Frequent measurements allowed identification of tumour necrosis factor (TNF) α, interleukin (IL) 6 and growth hormone as putative mediators. Human experimental endotoxaemia is a valid model for further study of mechanisms and putative therapies of catabolism associated with sepsis. In particular, effects of TNF-α and IL-6 blockade should be evaluated.

The Sick and the Weak: Neuropathies/Myopathies in the Critically Ill

Critical illness polyneuropathies (CIP) and myopathies (CIM) are common complications of critical illness. Several weakness syndromes are summarized under the term intensive care unit-acquired weakness (ICUAW). We propose a classification of different ICUAW forms (CIM, CIP, sepsis-induced, steroid-denervation myopathy) and pathophysiological mechanisms from clinical and animal model data. Triggers include sepsis, mechanical ventilation, muscle unloading, steroid treatment, or denervation. Some ICUAW forms require stringent diagnostic features; CIM is marked by membrane hypoexcitability, severe atrophy, preferential myosin loss, ultrastructural alterations, and inadequate autophagy activation while myopathies in pure sepsis do not reproduce marked myosin loss. Reduced membrane excitability results from depolarization and ion channel dysfunction. Mitochondrial dysfunction contributes to energy-dependent processes. Ubiquitin proteasome and calpain activation trigger muscle proteolysis and atrophy while protein synthesis is impaired. Myosin loss is more pronounced than actin loss in CIM. Protein quality control is altered by inadequate autophagy. Ca(2+) dysregulation is present through altered Ca(2+) homeostasis. We highlight clinical hallmarks, trigger factors, and potential mechanisms from human studies and animal models that allow separation of risk factors that may trigger distinct mechanisms contributing to weakness. During critical illness, altered inflammatory (cytokines) and metabolic pathways deteriorate muscle function. ICUAW prevention/treatment is limited, e.g., tight glycemic control, delaying nutrition, and early mobilization. Future challenges include identification of primary/secondary events during the time course of critical illness, the interplay between membrane excitability, bioenergetic failure and differential proteolysis, and finding new therapeutic targets by help of tailored animal models.

Role of E2-Ub-conjugating enzymes during skeletal muscle atrophy

The Ubiquitin Proteasome System (UPS) is a major actor of muscle wasting during various physio-pathological situations. In the past 15 years, increasing amounts of data have depicted a picture, although incomplete, of the mechanisms implicated in myofibrillar protein degradation, from the discovery of muscle-specific E3 ligases to the identification of the signaling pathways involved. The targeting specificity of the UPS relies on the capacity of the system to first recognize and then label the proteins to be degraded with a poly-ubiquitin (Ub) chain. It is fairly assumed that the recognition of the substrate is accomplished by the numerous E3 ligases present in mammalian cells. However, most E3s do not possess any catalytic activity and E2 enzymes may be more than simple Ub-providers for E3s since they are probably important actors in the ubiquitination machinery. Surprisingly, most authors have tried to characterize E3 substrates, but the exact role of E2s in muscle protein degradation is largely unknown. A very limited number of the 35 E2s described in humans have been studied in muscle protein breakdown experiments and the vast majority of studies were only descriptive. We review here the role of E2 enzymes in skeletal muscle and the difficulties linked to their study and provide future directions for the identification of muscle E2s responsible for the ubiquitination of contractile proteins.

Changes in nutritional status after liver transplantation

Chronic liver disease has an important effect on nutritional status, and malnourishment is almost universally present in patients with end-stage liver disease who undergo liver transplantation. During recent decades, a trend has been reported that shows an increase in number of patients with end-stage liver disease and obesity in developed countries. The importance of carefully assessing the nutritional status during the work-up of patients who are candidates for liver replacement is widely recognised. Cirrhotic patients with depleted lean body mass (sarcopenia) and fat deposits have an increased surgical risk; malnutrition may further impact morbidity, mortality and costs in the post-transplantation setting. After transplantation and liver function is restored, many metabolic alterations are corrected, dietary intake is progressively normalised, and lifestyle changes may improve physical activity. Few studies have examined the modifications in body composition that occur in liver recipients. During the first 12 mo, the fat mass progressively increases in those patients who had previously depleted body mass, and the muscle mass recovery is subtle and non-significant by the end of the first year. In some patients, unregulated weight gain may lead to obesity and may promote metabolic disorders in the long term. Careful monitoring of nutritional changes will help identify the patients who are at risk for malnutrition or over-weight after liver transplantation. Physical and nutritional interventions must be investigated to evaluate their potential beneficial effect on body composition and muscle function after liver transplantation.

Activation of hepatic inflammatory pathways by catecholamines is associated with hepatic insulin resistance in male ischemic stroke rats

Patients who experience acute ischemic stroke may develop hyperglycemia, even in the absence of diabetes. In the current study we determined the effects of acute stroke on hepatic insulin signaling, TNF-α expression, endoplasmic reticulum (ER) stress, the activities of c-Jun N-terminal kinase (JNK), inhibitor κB kinase β (IKK-β), and nuclear factor-κB (NF-κB) pathways. Rats with cerebral ischemia developed higher blood glucose, and insulin levels, and insulin resistance index, as well as hepatic gluconeogenic enzyme expression compared with the sham-treated group. The hepatic TNF-α mRNA and protein levels were elevated in stroke rats in association with increased ER stress, phosphorylation of JNK1/2 and IKK-β proteins, IκB/NF-κB signaling, and phosphorylation of insulin receptor-1 (IRS-1) at serine residue. The basal and insulin-stimulated tyrosine phosphorylation of IRS-1 and AKT proteins was reduced. In addition, acute stroke increased circulating catecholamines in association with hepatic adrenergic signaling activation. After administration of a nonselective β-adrenergic receptor blocker (propranolol) before induction of cerebral ischemic injury, hepatic adrenergic transduction, TNF-α expression, ER stress, and the activation of the JNK1/2, IKK-β, and NF-κB pathways, and serine phosphorylation of IRS-1 were all attenuated. In contrast, the phosphorylated IRS-1 at tyrosine site and AKT levels were partially restored with improved poststroke hyperglycemia and insulin resistance index. These results suggest that acute ischemic stroke can activate proinflammatory pathways in the liver by the catecholamines and is associated with the development of hepatic insulin resistance.

Resveratrol prevents TNF-α-induced muscle atrophy via regulation of Akt/mTOR/FoxO1 signaling in C2C12 myotubes

Muscle atrophy poses a serious concern to patients inflicted with inflammatory diseases. There is now increasing evidence which suggests a vital role for tumor necrosis factor alpha (TNF-α) in muscle pathology associated with impairment of differentiation and muscle wasting. Resveratrol has been an ascribed inhibitory effect on glucocorticoid-induced muscle atrophy in vitro, but the influence of resveratrol on the growth of C2C12 myotubes exposed to TNF-α remains unclear. The present study aimed to investigate the involvement of TNF-α in the regulation of skeletal muscle hypertrophy and atrophy, and the possibility to interfere with such modulations by means of resveratrol supplementation. For this purpose, C2C12 myotubes were treated with TNF-α in the presence or absence of resveratrol. Myotube treatment with TNF-α contributes to both hyperexpression of the muscle-specific ubiquitin ligase MAFbx and MuRF1, and these alterations are linked to a decrease of anabolic targets (Akt, mTOR, p70S6k and 4E-BP1) and an increase of catabolic targets (FoxO1, FoxO3a, MAFbx and MuRF1). Resveratrol supplementation effectively counteracts TNF-α induced muscle protein loss and reverses declining expression of Akt, mTOR, p70S6K, 4E-BP1and FoxO1, but exerts no influence of FoxO3a expression. Our study demonstrates that resveratrol can reverse the muscle cell atrophy caused by TNF-α through regulation of the Akt/mTOR/FoxO1 signaling pathways, followed by inhibition of the atrophy-related ubiquitin ligase. Our findings suggested that resveratrol could represent a possible strategy to improve muscle mass.

Type VI collagen turnover-related peptides-novel serological biomarkers of muscle mass and anabolic response to loading in young men

BACKGROUND

Immobilization-induced loss of muscle mass is a complex phenomenon with several parallels to sarcopenic and cachectic muscle loss. Muscle is a large organ with a protein turnover that is orders of magnitude larger than most other tissues. Thus, we hypothesize that muscle loss and regain is reflected by peptide biomarkers derived from type VI collagen processing released in the circulation.

METHODS

In order to test this hypothesis, we set out to develop an ELISA assay against an type VI collagen N-terminal globular domain epitope (IC6) and measured the levels of IC6 and an MMP-generated degradation fragment of collagen 6, (C6M) in a human immobilization-remobilization study setup with young (n = 11) and old (n = 9) men. They were subjected to 2 weeks of unilateral lower limb immobilization followed by 4 weeks of remobilization including thrice weekly resistance training, using the contralateral leg as internal controls. Subjects were sampled for strength, quadriceps muscle volume and blood at baseline (PRE), post-immobilization (2W), and post-remobilization (4W). Blood were subsequently analyzed for levels of the C6M and IC6 biomarkers. We subsequently tested if there was any correlation between C6M, IC6, or the C6M/IC6 ratio and muscle mass or strength at baseline. We also tested whether there was any relation between these biomarkers and changes in muscle mass or strength with immobilization or remobilization.

RESULTS

The model produced significant loss of muscle mass and strength in the immobilized leg. This loss was bigger in young subjects than in elderly, but whereas the young recovered almost fully, the elderly had limited regrowth of muscle. We found a significant correlation between IC6 and muscle mass at baseline in young subjects (R (2) = 0.6563, p = 0.0045), but none in the elderly. We also found a significant correlation between C6M measured at the 4W time point and the change in muscle mass during remobilization, again only manifesting in the young men(R (2) = 0.6523, p = 0.0085). This discrepancy between the young and the elderly may be caused in part by much smaller changes in muscle mass in the elderly and partly by the relative small sample size.

CONCLUSION

While we cannot rule out the possibility that these biomarkers in part stem from other tissues, our results strongly indicate that these markers represent novel biomarkers of muscle mass or change in muscle mass in young men.

Posttransplant sarcopenia: an underrecognized early consequence of liver transplantation

Liver transplantation is believed to reverse the clinical and metabolic abnormalities of cirrhosis. Reduced skeletal muscle mass or sarcopenia contributes to increased mortality and adverse consequences of cirrhosis. Failure of reversal of sarcopenia of cirrhosis after liver transplantation is not well recognized. Six temporally, geographically, and methodologically distinct follow-up studies in 304 cirrhotics reported conflicting data on changes in indirect measures of skeletal muscle mass after transplantation. Distinct measures of body composition but not skeletal muscle mass were used and did not focus on the clinical consequences of sarcopenia after transplantation. A number of studies reported an initial rapid postoperative loss of lean mass followed by incomplete recovery with a maximum follow-up of 2 years. Posttransplant sarcopenia may be responsible for metabolic syndrome and impaired quality of life after liver transplantation. Potential reasons for failure to reverse sarcopenia after liver transplantation include use of immunosuppressive agents [mammalian target of rapamycin (mTOR) and calcineurin inhibitors] that impair skeletal muscle growth and protein accretion. Repeated hospitalizations, posttransplant infections, and renal failure also contribute to posttransplant sarcopenia. Finally, recovery from muscle deconditioning is limited by lack of systematic nutritional and physical-activity-based interventions to improve muscle mass. Despite the compelling data on sarcopenia before liver transplantation, the impact of posttransplant sarcopenia on clinical outcomes is not known. There is a compelling need for studies to examine the mechanisms and consequences of sarcopenia post liver transplantation to permit development of therapies to prevent and reverse this disorder.

Resistin mediates the hepatic stellate cell phenotype

AIM: To describe the role of resistin in liver fibrosis.

METHODS: For the in vivo animal study, Sprague Dawley rats were subjected to bile duct ligation (BDL) for 4 wk. Rat liver, adipose tissue (epididymal fat) and serum were analyzed for resistin expression. For the in vitro experiment, rat primary hepatic stellate cells (HSCs) and Kupffer cells (KCs) were used. HSCs were exposed to recombinant resistin, and collagen I, transforming growth factor β1, α smooth muscle actin, tissue inhibitor of metalloproteinase 1 and connective tissue growth factor expression were analyzed. Resistin gene and protein expression was quantified as was the expression of pro-inflammatory cytokines including tumor necrosis factor α (TNFα), interleukin (IL)-1, IL-6, IL-8 and monocyte chemotactic protein-1 (MCP-1). The effects of resistin on HSC proliferation, migration and apoptosis were determined. The effects of resistin on KCs were also investigated.

RESULTS: Following BDL, rat epididymal fat and serum rather than liver showed higher resistin expression compared to control rats. In liver, resistin was expressed in quiescent HSCs and KCs. Resistin treatment resulted in enhancement of TNFα, IL-6, IL-8 and MCP-1 gene expression and increased IL-6 and MCP-1 protein in HSCs. Resistin activated HSC phospho-MAPK/p38, and p38 inhibition diminished IL-6 and MCP-1 expression. Furthermore, resistin facilitated HSC proliferation and migration, but decreased apoptosis which was via an IL-6 and MCP-1 mechanism. Finally, resistin-induced transforming growth factor β1 from KCs enhanced HSC collagen Iexpression.

CONCLUSION: Resistin directly and indirectly modulates HSC behavior towards a more pro-fibrogenic phenotype.

Muscle wasting in animal models of severe illness

Muscle wasting is a serious complication of various clinical conditions that significantly worsens the prognosis of the illnesses. Clinically relevant models of muscle wasting are essential for understanding its pathogenesis and for selective preclinical testing of potential therapeutic agents. The data presented here indicate that muscle wasting has been well characterized in rat models of sepsis (endotoxaemia, and caecal ligation and puncture), in rat models of chronic renal failure (partial nephrectomy), in animal models of intensive care unit patients (corticosteroid treatment combined with peripheral denervation or with administration of neuromuscular blocking drugs) and in murine and rat models of cancer (tumour cell transplantation). There is a need to explore genetically engineered mouse models of cancer. The degree of protein degradation in skeletal muscle is not well characterized in animal models of liver cirrhosis, chronic heart failure and chronic obstructive pulmonary disease. The major difficulties with all models are standardization and high variation in disease progression and a lack of reflection of clinical reality in some of the models. The translation of the information obtained by using these models to clinical practice may be problematic.

Structure of the proteasome

The ubiquitin-proteasomal system is an essential element of the protein quality control machinery in cells. The central part of this system is the 20S proteasome. The proteasome is a barrel-shaped multienzyme complex, containing several active centers hidden at the inner surface of the hollow cylinder. So, the regulation of the substrate entry toward the inner proteasomal surface is a key control mechanism of the activity of this protease. This chapter outlines the knowledge on the structure of the subunits of the 20S proteasome, the binding and structure of some proteasomal regulators and inducible proteasomal subunits. Therefore, this chapter imparts the knowledge on proteasomal structure which is required for the understanding of the following chapters.

Cachexia and protein-energy wasting in children with chronic kidney disease

Children with chronic kidney disease (CKD) are at risk for "cachexia" or "protein-energy wasting" (PEW). These terms describe a pathophysiologic process resulting in the loss of muscle, with or without loss of fat, and involving maladaptive responses, including anorexia and elevated metabolic rate. PEW has been defined specifically in relation to CKD. We review the diagnostic criteria for cachexia and PEW in CKD and consider the limitations and applicability of these criteria to children with CKD. In addition, we present an overview of the manifestations and mechanisms of cachexia and PEW. A host of pathogenetic factors are considered, including systemic inflammation, endocrine perturbations, and abnormal neuropeptide signaling, as well as poor nutritional intake. Mortality risk, which is 100- to 200-fold higher in patients with end-stage renal disease than in the general population, is strongly correlated with the components of cachexia/PEW. Further research into the causes and consequences of wasting and growth retardation is needed in order to improve the survival and quality of life for children with CKD.

Insulin alleviates degradation of skeletal muscle protein by inhibiting the ubiquitin-proteasome system in septic rats

Hypercatabolism is common under septic conditions. Skeletal muscle is the main target organ for hypercatabolism, and this phenomenon is a vital factor in the deterioration of recovery in septic patients. In skeletal muscle, activation of the ubiquitin-proteasome system plays an important role in hypercatabolism under septic status. Insulin is a vital anticatabolic hormone and previous evidence suggests that insulin administration inhibits various steps in the ubiquitin-proteasome system. However, whether insulin can alleviate the degradation of skeletal muscle protein by inhibiting the ubiquitin-proteasome system under septic condition is unclear. This paper confirmed that mRNA and protein levels of the ubiquitin-proteasome system were upregulated and molecular markers of skeletal muscle proteolysis (tyrosine and 3-methylhistidine) simultaneously increased in the skeletal muscle of septic rats. Septic rats were infused with insulin at a constant rate of 2.4 mU.kg^-1.min^-1 for 8 hours. Concentrations of mRNA and proteins of the ubiquitin-proteasome system and molecular markers of skeletal muscle proteolysis were mildly affected. When the insulin infusion dose increased to 4.8 mU.kg^-1.min^-1, mRNA for ubiquitin, E2-14 KDa, and the C2 subunit were all sharply downregulated. At the same time, the levels of ubiquitinated proteins, E2-14KDa, and the C2 subunit protein were significantly reduced. Tyrosine and 3-methylhistidine decreased significantly. We concluded that the ubiquitin-proteasome system is important skeletal muscle hypercatabolism in septic rats. Infusion of insulin can reverse the detrimental metabolism of skeletal muscle by inhibiting the ubiquitin-proteasome system, and the effect is proportional to the insulin infusion dose.

Models of accelerated sarcopenia: critical pieces for solving the puzzle of age-related muscle atrophy

Sarcopenia, the age-related loss of skeletal muscle mass, is a significant public health concern that continues to grow in relevance as the population ages. Certain conditions have the strong potential to coincide with sarcopenia to accelerate the progression of muscle atrophy in older adults. Among these conditions are co-morbid diseases common to older individuals such as cancer, kidney disease, diabetes, and peripheral artery disease. Furthermore, behaviors such as poor nutrition and physical inactivity are well-known to contribute to sarcopenia development. However, we argue that these behaviors are not inherent to the development of sarcopenia but rather accelerate its progression. In the present review, we discuss how these factors affect systemic and cellular mechanisms that contribute to skeletal muscle atrophy. In addition, we describe gaps in the literature concerning the role of these factors in accelerating sarcopenia progression. Elucidating biochemical pathways related to accelerated muscle atrophy may allow for improved discovery of therapeutic treatments related to sarcopenia.

Protein nitration is associated with increased proteolysis in skeletal muscle of bile duct ligation-induced cirrhotic rats

Cirrhosis is characterized by skeletal muscle wasting. In this study, the effects of nitric oxide production on skeletal muscle protein nitration and degradation in cirrhosis were investigated. Cirrhosis was induced by bile duct ligation (BDL) in Sprague-Dawley rats for 4 weeks. The BDL-induced cirrhotic rats and sham-operated rats were then injected daily with either saline or N(G)-l-nitro-arginine methyl ester (l-NAME) for 7 days from week 4 to week 5, after which nitrite/nitrate, glutathione reduction, as well as protein nitration, ubiquitination, and degradation were assessed in skeletal muscle. Elevated muscular nitrite/nitrate concentrations, protein nitration, total ubiquitin conjugates, and degradation fragments of myosin heavy chain as well as diminished glutathione reduction levels were observed in BDL-induced cirrhotic rats as compared with controls. Administration of l-NAME for 1 week led to reduction of nitrite/nitrate levels; protein nitration was also decreased in the skeletal muscle. In addition, ubiquitination of muscular proteins and degradation of myosin heavy chain were significantly diminished after treatment of l-NAME. In conclusion, nitrosative stress occurred in the skeletal muscle of BDL-induced cirrhotic rats and may lead to increased proteolysis of muscle-specific structural proteins.

Skeletal muscle contractile properties and proinflammatory cytokine gene expression in human endotoxaemia

Background

Muscle dysfunction associated with sepsis contributes to morbidity and mortality but the underlying mechanisms are unclear. This study examined whether muscle weakness relates to an intrinsic defect in contraction, or to central mechanisms associated with acute illness, and whether systemic endotoxaemia induces changes in gene expression for proinflammatory cytokines within human muscle in vivo.

Methods

In this experimental study, 12 healthy men received intravenous Escherichia coli lipopolysaccharide (LPS, 4 ng/kg) or saline (control). Voluntary and electrically stimulated quadriceps contraction, and tumour necrosis factor (TNF) α mRNA expression in quadriceps muscle biopsies were studied before and after the infusion.

Results

Endotoxaemia induced transient weakness of voluntary quadriceps contraction, equivalent to a 7·8 (95 per cent confidence interval 2·1 to 13·5) per cent reduction in contractile force at 180 min (P = 0·027) and a 9·0 (5·2 to 12·8) per cent reduction at 300 min (P = 0·008). Electrically stimulated contraction was unaffected. LPS administration resulted in an apparent fibre-specific induction of TNF-α mRNA.

Conclusion

Endotoxaemia results in a reduction in voluntary muscle contractile force without an apparent defect in stimulated muscle contraction. Loss of volition may be a more important factor than intrinsic dysfunction in acute sepsis-associated human muscle weakness.

Cachexia in the non-obese diabetic mouse is associated with CD4+ T-cell lymphopenia

One of the long-term consequences of Type I diabetes is weight loss with muscle atrophy, the hallmark phenotype of cachexia. A number of disorders that result in cachexia are associated with immune deficiency. However, whether immune deficiency is a cause or an effect of cachexia is not known. This study examines the non-obese diabetic mouse, the mouse model for spontaneous Type I diabetes, as a potential model to study lymphopenia in cachexia, and to determine whether lymphopenia plays a role in the development of cachexia. The muscle atrophy seen in patients with Type I diabetes involves active protein degradation by activation of the ubiquitin-proteasome pathway, indicating cachexia. Evidence of cachexia in the non-obese diabetic mouse was determined by measuring skeletal muscle atrophy, activation of the ubiquitin-proteasome pathway, and apoptosis, a state also described in some models of cachexia. CD4+ T-cell subset lymphopenia was measured in wasting and non-wasting diabetic mice. Our data show that the mechanism of wasting in diabetic mice involves muscle atrophy, a significant increase in ubiquitin conjugation, and upregulation of the ubiquitin ligases, muscle RING finger 1 (MuRF1) and muscle atrophy F box/atrogin-1 (MAFbx), indicating cachexia. Moreover, fragmentation of DNA isolated from atrophied muscle tissue indicates apoptosis. While CD4+ T-cell lymphopenia is evident in all diabetic mice, CD4+ T cells that express a very low density of CD44 were significantly lost in wasting, but not non-wasting, diabetic mice. These data suggest that CD4+ T-cell subsets are not equally susceptible to cachexia-associated lymphopenia in diabetic mice.

Roles and potential therapeutic targets of the ubiquitin proteasome system in muscle wasting

Muscle wasting, characterized by the loss of protein mass in myofibers, is in most cases largely due to the activation of intracellular protein degradation by the ubiquitin proteasome system (UPS). During the last decade, mechanisms contributing to this activation have been unraveled and key mediators of this process identified. Even though much remains to be understood, the available information already suggests screens for new compounds inhibiting these mechanisms and highlights the potential for pharmaceutical drugs able to treat muscle wasting when it becomes deleterious. This review presents an overview of the main pathways contributing to UPS activation in muscle and describes the present state of efforts made to develop new strategies aimed at blocking or slowing muscle wasting.

Publication history: Republished from Current BioData's Targeted Proteins database (TPdb; ).

Molecular characterization of the encoding regions and tissue expression analyses for three novel porcine genes--HNRPA1, YIPF5 and UB2D2

The complete encoding regions of three porcine genes--heterogeneous nuclear ribonucleoprotein A1 (HNRPA1), YIP1 family member 5 (YIPF5) and ubiquitin-conjugating enzyme E2 D2 (UB2D2) were amplified using the reverse transcriptase polymerase chain reaction (RT-PCR) based on the conserved encoding region information of the mouse or other mammals and the referenced highly homologous pig ESTs of these conserved encoding regions. These three novel porcine genes were assigned to GeneID: 768103, 768112, and 780418. The phylogenetic tree analysis revealed that the swine HNRPA1 has closer genetic relationships with the HNRPA1 of mouse and rhesus monkey, but the swine YIPF5 has a closer genetic relationship with the YIPF5 of cattle and the swine UB2D2 shows an evolutional model different with the UB2D2 of other five species. The tissue expression analysis indicated that the swine HNRPA1 gene was moderately expressed in fat, spleen and kidney, weakly expressed in muscle and lung, and hardly expressed in small intestine, large intestine and liver. The swine YIPF5 gene was moderately expressed in fat and spleen, and hardly expressed in small intestine, large intestine, liver, lung, muscle and kidney. The swine UB2D2 gene was weakly expressed in lung, and hardly expressed in small intestine, large intestine, liver, muscle, fat, spleen and kidney. Our experiment established the primary foundation for further research on these three swine genes.

Pentoxifylline inhibits Ca2+-dependent and ATP proteasome-dependent proteolysis in skeletal muscle from acutely diabetic rats

Previous studies from this laboratory have shown that catecholamines exert an inhibitory effect on muscle protein degradation through a pathway involving the cAMP cascade. The present work investigated the systemic effect of pentoxifylline (PTX; cAMP-phosphodiesterase inhibitor) treatment on the rate of overall proteolysis, the activity of proteolytic systems, and the process of protein synthesis in extensor digitorum longus muscles from normal and acutely diabetic rats. The direct in vitro effect of this drug on the rates of muscle protein degradation was also investigated. Muscles from diabetic rats treated with PTX showed an increase (22%) in the cAMP content and reduction in total rates of protein breakdown and in activity of Ca2+-dependent (47%) and ATP proteasome-dependent (23%) proteolytic pathways. The high content of m-calpain observed in muscles from diabetic rats was abolished by PTX treatment. The addition of PTX (10(-3) M) to the incubation medium increased the cAMP content in muscles from normal (22%) and diabetic (51%) rats and induced a reduction in the rates of overall proteolysis that was accompanied by decreased activity of the Ca2+-dependent and ATP proteasome-dependent proteolytic systems, in both groups. The in vitro addition of H-89, an inhibitor of protein kinase A (PKA), completely blocked the effect of PTX on the reduction of proteolysis in muscles from normal and diabetic rats. The present data suggest that PTX exerts a direct inhibitory effect on protein degradative systems in muscles from acutely diabetic rats, probably involving the participation of cAMP intracellular pathways and activation of PKA, independently of tumor necrosis factor-alpha inhibition.

NF-kappa B-mediated MyoD decay during muscle wasting requires nitric oxide synthase mRNA stabilization, HuR protein, and nitric oxide release

Muscle wasting (cachexia) is a consequence of chronic diseases, such as cancer, and is associated with degradation of muscle proteins such as MyoD. The cytokines tumor necrosis factor alpha and gamma interferon induce muscle degeneration by activating the transcription factor NF-kappaB and its target genes. Here, we show that a downstream target of NF-kappaB is the nitric oxide (NO) synthase gene (iNos) and suggest that NO production stimulates MyoD mRNA loss. In fact, although cytokine treatment of iNos(-/-) mice activated NF-kappaB, it did not trigger MyoD mRNA degeneration, demonstrating that NF-kappaB-mediated muscle wasting requires an active iNOS-NO pathway. The induced expression of iNOS by cytokines relies on both transcriptional activation via NF-kappaB and increased mRNA stability via the RNA-binding protein HuR. Moreover, we show that HuR regulates iNOS expression in an AMP-activated protein kinase (AMPK)-dependent manner. Furthermore, AMPK activation results in HuR nuclear sequestration, inhibition of iNOS synthesis, and reduction in cytokine-induced MyoD loss. These results define iNOS and HuR as critical players in cytokine-induced cachexia, establishing them as potential therapeutic targets.

Stimulated resistin expression in white adipose of rats with bile duct ligation-induced liver cirrhosis: relationship to cirrhotic hyperinsulinemia and increased tumor necrosis factor-alpha

Resistin, an adipose-derived polypeptide hormone, is proposed as a candidate of insulin resistance, although its roles in inhibiting adipogenesis and in inflammation have also been suggested. Liver cirrhosis is characterized by elevated circulating proinflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha), hyperinsulinemia and insulin resistance. The study aimed to examine resistin expression and its association with insulin and TNF-alpha in a cirrhotic rat model using bile duct ligation (BDL). The BDL-induced cirrhotic rats showed significantly lower fat mass, insulin sensitivity and elevated plasma insulin and TNF-alpha compared to sham animals. In addition, epididymal TNF-alpha and resistin mRNA and protein levels were higher in cirrhotic rats. In normal control rats, in vivo insulin infusion and ex vivo administration of TNF-alpha to cultured fat pads increased resistin gene expression significantly. These results implied that hyperinsulinemia and increased TNF-alpha levels might upregulate adipose resistin gene in BDL-induced liver cirrhosis. Further study is necessary to document the role of resistin in metabolic abnormalities of liver cirrhosis.