Actions of Short-Term Fasting on Human Skeletal Muscle Myogenic and Atrogenic Gene Expression

A comparison of interferential current efficacy in elderly intervertebral disc degeneration patients with or without sarcopenia: a retrospective study

BACKGROUND

Intervertebral disc degeneration and sarcopenia are both age-related diseases without effective treatments. Their comorbidities may worsen the prognosis, and further studies on interaction and therapy are needed. The purpose of the study was to investigate the prevalence of sarcopenia in intervertebral disc degeneration, and to compare the characteristics of intervertebral disc degeneration with and without sarcopenia and effects of interferential current.

METHODS

One hundred twenty disc degeneration patients were included from 2021 to 2022 in a single institute. Medical records, examination results and radiological reports were reviewed. Patients with sarcopenia were screened and grouped according to Asian Working Group for Sarcopenia 2019. VAS, ODI, SARC-F, SMI, gait speed (GS), grip strength, disc Pfirrmann grading, standard cross-sectional area (SCSA), degree of fatty infiltration (DFF), and nerve conduction velocity (NCV) were assessed before and after treatment.

RESULTS

The prevalence of sarcopenia in intervertebral disc degeneration was 28.3%. The difference of VAS, ODI, disc Pfirrmann grading, SCSA, DFF and NCV between two groups were significant before intervention (P < 0.05), SCSA and DFF were related to the degree of disc degeneration. The improvement of SMI, GS, grip strength, VAS, SARC-F and ODI in intervertebral disc degeneration with sarcopenia group was significant after intervention, as well as SMI, GS, grip strength, VAS and ODI in those without sarcopenia (P < 0.05). The improvement of grip strength, GS, ODI and SARC-F in intervertebral disc degeneration with sarcopenia group were greater than the one without sarcopenia (P < 0.05), whereas there was no significance in improvement degree of other indicators between the two groups (P > 0.05).

CONCLUSION

The prevalence of sarcopenia was high in intervertebral disc degeneration, and paravertebral muscles degeneration correlated with the degree of disc degeneration. Compared to those without sarcopenia, intervertebral disc degeneration patients with sarcopenia have more severe pain, poorer mobility and neurological function. Interferential current is effective in intervertebral disc degeneration patients and sarcopenia patients.

Temporal Expression of Myogenic Regulatory Genes in Different Chicken Breeds during Embryonic Development

The basic units of skeletal muscle in all vertebrates are multinucleate myofibers, which are formed from the fusion of mononuclear myoblasts during the embryonic period. In order to understand the regulation of embryonic muscle development, we selected four chicken breeds, namely, Cornish (CN), White Plymouth Rock (WPR), White Leghorn (WL), and Beijing-You Chicken (BYC), for evaluation of their temporal expression patterns of known key regulatory genes (Myomaker, MYOD, and MSTN) during pectoral muscle (PM) and thigh muscle (TM) development. The highest expression level of Myomaker occurred from embryonic days E13 to E15 for all breeds, indicating that it was the crucial stage of myoblast fusion. Interestingly, the fast-growing CN showed the highest gene expression level of Myomaker during the crucial stage. The MYOD gene expression at D1 was much higher, implying that MYOD might have an important role after hatching. Histomorphology of PM and TM suggested that the myofibers was largely complete at E17, which was speculated to have occurred because of the expression increase in MSTN and the expression decrease in Myomaker. Our research contributes to lay a foundation for the study of myofiber development during the embryonic period in different chicken breeds.

Markers of muscle atrophy and impact of treatment with pergolide in horses with pituitary pars intermedia dysfunction and muscle atrophy

Pituitary pars intermedia dysfunction (PPID) is a common endocrine disorder of aged horses, with muscle atrophy as one of the clinical signs. We sought to compare muscle mass and regulation of skeletal muscle proteolysis between horses with PPID and muscle atrophy to older horses without PPID, and to assess the impact of treatment with pergolide (dopaminergic agonist) on PPID horses. We hypothesized that PPID-associated muscle atrophy is a result of increased proteolysis, and that markers of muscle atrophy and proteolysis would improve over time with pergolide treatment. Markers of muscle atrophy, adiposity, insulin regulation, skeletal muscle composition, and proteolysis (muscle atrophy F- box/atrogin 1 [MAFbx1], muscle RING finger 1 [MuRF1], Bcl2/adenovirus EIV 19kD interacting protein 3 [Bnip3], and microtubule-associated light chain 3 [LC3]) were compared between PPID and control horses. PPID horses were treated for 12 weeks with either pergolide or placebo. Dose of pergolide was adjusted based upon monthly measurement of adrenocorticotropin, and markers of muscle atrophy, adiposity, insulin regulation, skeletal muscle composition, and proteolysis were compared after 12 weeks of treatment. Horses with PPID exhibited increased transcript abundance of MuRF1 (P= 0.04) compared to control. However, no difference was observed in transcript abundance of markers of proteolysis with treatment (P ≥ 0.25). Pergolide treated horses lost weight (P = 0.02) and improved fasting insulin (P = 0.02), while placebo treated horses gained weight and rump fat thickness (P = 0.02). Findings from this study suggest that treatment with pergolide may promote weight loss and improve insulin regulation in horses with PPID, but does not impact muscle mass or markers of muscle proteolysis.

Genome-Wide Transcriptome Analysis Reveals Intermittent Fasting-Induced Metabolic Rewiring in the Liver

Scope: Intermittent fasting (IF) has been extensively reported to promote improved energy homeostasis and metabolic switching. While IF may be a plausible strategy to ameliorate the epidemiological burden of disease in many societies, our understanding of the underlying molecular mechanisms behind such effects is still lacking. The present study has sought to investigate the relationship between IF and changes in gene expression. We focused on the liver, which is highly sensitive to metabolic changes due to energy status. Mice were randomly assigned to ad libitum feeding or IF for 16 hours per day or for 24 hours on alternate days for 3 months, after which genome-wide transcriptome analysis of the liver was performed using RNA sequencing. Our findings revealed that IF caused robust transcriptomic changes in the liver that led to a complex array of metabolic changes. We also observed that the IF regimen produced distinct profiles of transcriptomic changes, highlighting the significance of temporally different periods of energy restriction. Our results suggest that IF can regulate metabolism via transcriptomic mechanisms and provide insight into how genetic interactions within the liver might lead to the numerous metabolic benefits of IF.

Effect of skeletal muscle phenotype and gender on fasting-induced myokine expression in mice

Skeletal muscle secretes myokines, which are involved in metabolism and muscle function regulation. The role of fasting on myokine expression in skeletal muscle is largely unknown. In this study, we used gastrocnemius skeletal muscle RNA sequencing data from fasting male mice in the Gene Expression Omnibus (GEO) database. Adopted male and female C57BL/6J mice that fasted for 24 h were included to examine the effect of fasting on myokine expression in slow-twitch soleus and fast-twitch tiabialis anterior (TA) skeletal muscle. We found that fasting significantly affected many myokines in muscle. Fasting reduced Fndc5 and Igf1 gene expression in soleus and TA muscles in both male and female mice without muscle phenotype or gender differences, but Il6, Mstn and Erfe expression was influenced by fasting with fibre type- and gender-dependent effects. Fasting also induced muscle atrophy marker genes Murf1 and Fbxo32 and reduced myogenesis factor Mef2 expression without muscle fibre or gender differences. We further found that the expression of transcription factors Pgc1α, Pparα, Pparγ and Pparδ had muscle fibre type-dependent effects, and the expression of Pgc1α and Pparα had gender-dependent effects. The sophisticated expression pattern of myokines would partially explain the complicated cross-talk between skeletal muscle and other organs in different genders and muscles phenotypes, and it is worth further investigation.

Intermittent bolus feeding promotes greater lean growth than continuous feeding in a neonatal piglet model

Background

Orogastric tube feeding is indicated in neonates with an impaired ability to ingest food normally and can be administered with an intermittent bolus or continuous feeding schedule.

Objectives

The objectives were to 1) compare the long-term effect of continuous with intermittent feeding on growth using the newborn pig as a model, 2) determine whether feeding frequency alters lean tissue and fat mass gain, and 3) identify the signaling mechanisms by which protein deposition is controlled in skeletal muscle in response to feeding frequency.

Design

Neonatal pigs were fed the same amount of a balanced formula by orogastric tube either as an intermittent bolus meal every 4 h (INT) or as a continuous infusion (CON). Body composition was assessed at the start and end of the study by dual-energy X-ray absorptiometry, and hormone and substrate profiles, muscle mass, protein synthesis, and indexes of nutrient and insulin signaling were measured after 21 d.

Results

Body weight, lean mass, spine length, and skeletal muscle mass were greater in the INT group than in the CON group. Skeletal muscle fractional protein synthesis rates were greater in the INT group after a meal than in the CON group and were associated with higher circulating branched-chain amino acid and insulin concentrations. Skeletal muscle protein kinase B (PKB) and ribosomal protein S6 kinase phosphorylation and eukaryotic initiation factor (eIF) 4E-eIF4G complex formation were higher, whereas eIF2α phosphorylation was lower in the INT group than in the CON group, indicating enhanced activation of insulin and amino acid signaling to translation initiation.

Conclusions

These results suggest that when neonates are fed the same amounts of nutrients as intermittent meals rather than continuously there is greater lean growth. This response can be ascribed, in part, to the pulsatile pattern of amino acids, insulin, or both induced by INT, which enables the responsiveness of anabolic pathways to feeding to be sustained chronically in skeletal muscle.

Postoperative inflammation and insulin resistance in relation to body composition, adiposity and carbohydrate treatment: A randomised controlled study

Background & aims

The aims of this study were to identify whether differences in distribution of adipose tissue and skeletal muscle in obese and non-obese individuals contribute to the magnitude of the postoperative inflammatory response and insulin resistance, with and without preoperative treatment with carbohydrate drinks.

Methods

Thirty-two adults (16 obese/16 non-obese) undergoing elective major open abdominal surgery participated in this 2 × 2 factorial, randomised, double-blind, placebo-controlled study. Participants received Nutricia preOp^® or placebo (800 ml on the night before surgery/400 ml 2–3 h preoperatively) after stratifying for obesity. Insulin sensitivity was measured using the hyperinsulinaemic-euglycaemic clamp preoperatively and on the 1st postoperative day. Vastus lateralis, omental and subcutaneous fat biopsies were taken pre- and postoperatively and analysed after RNA extraction. The primary endpoint was within subject differences in insulin sensitivity.

Results

Major abdominal surgery was associated with a 42% reduction in insulin sensitivity from mean(SD) M value of 37.3(11.8) μmol kg⁻¹ fat free mass (FFM) to 21.7(7.4) μmol kg⁻¹ FFM, but this was not influenced by obesity or preoperative carbohydrate treatment. Activation of the triggering receptor expressed on myeloid cells (TREM1) pathway was seen in response to surgery in omental fat samples. In postoperative muscle samples, gene expression differences indicated activation of the peroxisome proliferator-activated receptor (PPAR-α)/retinoid X-receptor (RXR-α) pathway in obese but not in non-obese participants. There were no significant changes in gene expression pathways associated with carbohydrate treatment.

Conclusion

The reduction in insulin sensitivity associated with major abdominal surgery was confirmed but there were no differences associated with preoperative carbohydrates or obesity.

The role of E3 ubiquitin-ligases MuRF-1 and MAFbx in loss of skeletal muscle mass

The ubiquitin-proteasome system (UPS) is the main regulatory mechanism of protein degradation in skeletal muscle. The ubiquitin-ligase enzymes (E3s) have a central role in determining the selectivity and specificity of the UPS. Since their identification in 2001, the muscle specific E3s, muscle RING finger-1 (MuRF-1) and muscle atrophy F-box (MAFbx), have been shown to be implicated in the regulation of skeletal muscle atrophy in various pathological and physiological conditions. This review aims to explore the involvement of MuRF-1 and MAFbx in catabolism of skeletal muscle during various pathologies, such as cancer cachexia, sarcopenia of aging, chronic kidney disease (CKD), diabetes, and chronic obstructive pulmonary disease (COPD). In addition, the effects of various lifestyle and modifiable factors (e.g. nutrition, exercise, cigarette smoking, and alcohol) on MuRF-1 and MAFbx regulation will be discussed. Finally, evidence of potential strategies to protect against skeletal muscle wasting through inhibition of MuRF-1 and MAFbx expression will be explored.

Undernutrition regulates the expression of a novel splice variant of myostatin and insulin-like growth factor 1 in ovine skeletal muscle

Undernutrition suppresses the growth of skeletal muscles and alters the expression of insulin-like growth factor 1 (IGF1), a key mitogen, and myostatin, a potent inhibitor of myogenesis. These changes can explain, at least in part, the reduced growth of skeletal muscles in underfed lambs. We have recently identified a myostatin splice variant (MSV) that binds to and antagonizes the canonical signaling of myostatin. In the present study, we hypothesized that the expression of MSV would be reduced in conjunction with myostatin and IGF1 in response to underfeeding in skeletal muscles of sheep. Young growing ewes were fed either ad libitum or an energy-restricted diet (30% of maintenance requirements) for 28 d. This regime of underfeeding resulted in a 24% reduction in body mass (P < 0.001) and a 36% reduction in the mass of the semitendinosus muscles relative to controls (P < 0.001) by day 28. The concentrations of MSV and IGF1 messenger RNA (mRNA) were reduced (both P < 0.001), but myostatin mRNA was not altered in semitendinosus muscles. Unlike the reduced expression of mRNA, the abundance of MSV protein was increased (P < 0.05) and there was no change in the abundance of myostatin protein. Our results suggest that undernutrition for 28 d decreases the signaling of myostatin by increasing the abundance of MSV protein. Although this action may reduce the growth inhibitory activity of myostatin, it cannot prevent the loss of growth of skeletal muscles during undernutrition.

The Effect of Rate of Weight Reduction on Serum Myostatin and Follistatin Concentrations in Competitive Wrestlers

Purpose:

To evaluate anthropometric measures and serum markers of myostatin-pathway activity after different weight-reduction protocols in wrestlers.

Methods:

Subjects were randomly assigned to a gradual-weight-reduction (GWR) or rapid-weight-reduction (RWR) group. Food logs were collected for the duration of the study. Anthropometric measurements and serum samples were collected after an 8-h fast at baseline and after the weight-reduction intervention. Subjects reduced body mass by 4%. The GWR group restricted calories over 12 d, while the RWR group restricted calories over 2 d. A series of 2 × 5 repeated-measures (RM) ANOVAs was conducted to examine differences in nutrient consumption, while separate 2 × 2 RM ANOVAs were conducted to examine differences in anthropometric measures and serum markers. When applicable, Tukey post hoc comparisons were conducted. Significance for all tests was set at P < .05.

Results:

There were no between-groups differences for any anthropometric measure (P > .05). Subjects in both groups experienced a significant reduction in body mass, fat mass, lean mass, and percent body fat (P < .05). There were no between-groups differences in serum markers of myostatin-pathway activity (P > .05), but subjects in the RWR condition experienced a significant increase in serum myostatin (P < .01), a decrease in follistatin (P < .01), and an increase in myostatin-to-follistatin ratio (P < .001).

Conclusion:

Although there were no between-groups differences for any outcome variables, the serum myostatin-to-follistatin ratio was significantly increased in the RWR group, possibly signaling the early stages of skeletal-muscle catabolism.

Fasting increases human skeletal muscle net phenylalanine release and this is associated with decreased mTOR signaling

Aim

Fasting is characterised by profound changes in energy metabolism including progressive loss of body proteins. The underlying mechanisms are however unknown and we therefore determined the effects of a 72-hour-fast on human skeletal muscle protein metabolism and activation of mammalian target of rapamycin (mTOR), a key regulator of cell growth.

Methods

Eight healthy male volunteers were studied twice: in the postabsorptive state and following 72 hours of fasting. Regional muscle amino acid kinetics was measured in the forearm using amino acid tracers. Signaling to protein synthesis and breakdown were assessed in skeletal muscle biopsies obtained during non-insulin and insulin stimulated conditions on both examination days.

Results

Fasting significantly increased forearm net phenylalanine release and tended to decrease phenylalanine rate of disappearance. mTOR phosphorylation was decreased by ∼50% following fasting, together with reduced downstream phosphorylation of 4EBP1, ULK1 and rpS6. In addition, the insulin stimulated increase in mTOR and rpS6 phosphorylation was significantly reduced after fasting indicating insulin resistance in this part of the signaling pathway. Autophagy initiation is in part regulated by mTOR through ULK1 and fasting increased expression of the autophagic marker LC3B-II by ∼30%. p62 is degraded during autophagy but was increased by ∼10% during fasting making interpretation of autophagic flux problematic. MAFbx and MURF1 ubiquitin ligases remained unaltered after fasting indicating no change in protesomal protein degradation.

Conclusions

Our results show that during fasting increased net phenylalanine release in skeletal muscle is associated to reduced mTOR activation and concomitant decreased downstream signaling to cell growth.

Increased expression of atrogenes and TWEAK family members after severe burn injury in nonburned human skeletal muscle

Severe burn induces rapid skeletal muscle proteolysis after the injury, which persists for up to 1 year and results in skeletal muscle atrophy despite dietary and rehabilitative interventions. The purpose of this research was to determine acute changes in gene expression of skeletal muscle mass regulators postburn injury. Specimens were obtained for biopsy from the vastus lateralis of a nonburned leg of eight burned subjects (6M, 2F: 34.8 ± 2.7 years: 29.9 ± 3.1% TBSA burn) at 5.1 ± 1.1 days postburn injury and from matched controls. mRNA expression of cytokines and receptors in the tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) families, and the ubiquitin proteasome E3 ligases, atrogin-1 and MuRF-1, was determined. TNF receptor 1A was over 3.5-fold higher in burn. Expression of TNF-like weak inducer of apoptosis and its receptor were over 1.6 and 6.0-fold higher in burn. IL-6, IL-6 receptor, and glycoprotein 130 were elevated in burned subjects with IL-6 receptor over 13-fold higher. The level of suppressor of cytokine signaling-3 was also increased nearly 6-fold in burn. Atrogin-1 and MuRF-1 were more than 4- and 3-fold higher in burn. These results demonstrate for the first time that severe burn in humans has a remarkable impact on gene expression in skeletal muscle of a nonburned limb of genes that promote inflammation and proteolysis. Because these changes likely contribute to the acute skeletal muscle atrophy in areas not directly affected by the burn, in the future it will be important to determine the responsible systemic cues.

Regulation of protein degradation pathways by amino acids and insulin in skeletal muscle of neonatal pigs

BACKGROUND

The rapid gain in lean mass in neonates requires greater rates of protein synthesis than degradation. We previously delineated the molecular mechanisms by which insulin and amino acids, especially leucine, modulate skeletal muscle protein synthesis and how this changes with development. In the current study, we identified mechanisms involved in protein degradation regulation. In experiment 1, 6- and 26-d-old pigs were studied during 1) euinsulinemic-euglycemic-euaminoacidemic, 2) euinsulinemic-euglycemic-hyperaminoacidemic, and 3) hyperinsulinemic-euglycemic-euaminoacidemic clamps for 2 h. In experiment 2, 5-d-old pigs were studied during 1) euinsulinemic-euglycemic-euaminoacidemic-euleucinemic, 2) euinsulinemic-euglycemic-hypoaminoacidemic-hyperleucinemic, and 3) euinsulinemic-euglycemic-euaminoacidemic-hyperleucinemic clamps for 24 h. We determined in muscle indices of ubiquitin-proteasome, i.e., atrogin-1 (MAFbx) and muscle RING-finger protein-1 (MuRF1) and autophagy-lysosome systems, i.e., unc51-like kinase 1 (UKL1), microtubule-associated protein light chain 3 (LC3), and lysosomal-associated membrane protein 2 (Lamp-2). For comparison, we measured ribosomal protein S6 (rpS6) and eukaryotic initiation factor 4E (eIF4E) activation, components of translation initiation.

RESULTS

Abundance of atrogin-1, but not MuRF1, was greater in 26- than 6-d-old pigs and was not affected by insulin, amino acids, or leucine. Abundance of ULK1 and LC3 was higher in younger pigs and not affected by treatment. The LC3-II/LC3-I ratio was reduced and ULK1 phosphorylation increased by insulin, amino acids, and leucine. These responses were more profound in younger pigs. Abundance of Lamp-2 was not affected by treatment or development. Abundance of eIF4E, but not rpS6, was higher in 6- than 26-d-old-pigs but unaffected by treatment. Phosphorylation of eIF4E was not affected by treatment, however, insulin, amino acids, and leucine stimulated rpS6 phosphorylation, and the responses decreased with development.

CONCLUSIONS

The rapid growth of neonatal muscle is in part due to the positive balance between the activation of protein synthesis and degradation signaling. Insulin, amino acids, and, particularly, leucine, act as signals to modulate muscle protein synthesis and degradation in neonates.

The central role of myostatin in skeletal muscle and whole body homeostasis

Myostatin is a powerful negative regulator of skeletal muscle mass in mammalian species. It plays a key role in skeletal muscle homeostasis and has now been well described since its discovery. Myostatin is capable of inducing muscle atrophy via its inhibition of myoblast proliferation, increasing ubiquitin-proteasomal activity and downregulating activity of the IGF-Akt pathway. These well-recognized effects are seen in multiple atrophy causing situations, including injury, diseases such as cachexia, disuse and space flight, demonstrating the importance of the myostatin signalling mechanism. Based on this central role, significant work has been pursued to inhibit myostatin's actions in vivo. Importantly, several new studies have uncovered roles for myostatin distinct from skeletal muscle size. Myostatin has been suggested to play a role in cardiomyocyte homeostasis, glucose metabolism and adipocyte proliferation, all of which are examined in detail below. Based on these effects, myostatin inhibition has potential to be widely utilized in many Western diseases such as chronic obstructive pulmonary disease, type II diabetes and obesity. However, if myostatin inhibitors are to successfully translate from bench-top to bedside in the near future, awareness must be raised on these non-traditional effects of myostatin away from skeletal muscle. Indeed, further research into these novel areas is required.

Anabolic signaling and protein deposition are enhanced by intermittent compared with continuous feeding in skeletal muscle of neonates

Orogastric tube feeding is indicated for neonates with impaired ability to ingest and can be administered by intermittent bolus or continuous schedule. Our aim was to determine whether feeding modalities affect muscle protein deposition and to identify mechanisms involved. Neonatal pigs were overnight fasted (FAS) or fed the same amount of food continuously (CON) or intermittently (INT; 7 × 4 h meals) for 29 h. For 8 h, between hours 20 and 28, pigs were infused with [(2)H(5)]phenylalanine and [(2)H(2)]tyrosine, and amino acid (AA) net balances were measured across the hindquarters. Insulin, branched-chain AA, phenylalanine, and tyrosine arterial concentrations and whole body phenylalanine and tyrosine fluxes were greater for INT after the meal than for CON or FAS. The activation of signaling proteins leading to initiation of mRNA translation, including eukaryotic initiation factor (eIF)4E·eIF4G complex formation in muscle, was enhanced by INT compared with CON feeding or FAS. Signaling proteins of protein degradation were not affected by feeding modalities except for microtubule-associated protein light chain 3-II, which was highest in the FAS. Across the hindquarters, AA net removal increased for INT but not for CON or FAS, with protein deposition greater for INT. This was because protein synthesis increased following feeding for INT but remained unchanged for CON and FAS, whereas there was no change in protein degradation across any dietary treatment. These results suggest that muscle protein accretion in neonates is enhanced with intermittent bolus to a greater extent than continuous feeding, mainly by increased protein synthesis.

Late evening snack: exploiting a period of anabolic opportunity in cirrhosis

BACKGROUND AND AIM

Cirrhosis is a state of accelerated starvation with impaired protein synthesis. Increased rate of gluconeogenesis and alterations in skeletal muscle signaling pathways result in anabolic resistance and consequent loss of muscle mass or sarcopenia in cirrhosis. Late evening snack (LES) is an intervention to reduce the postabsorptive (fasting) phase with the potential to improve substrate utilization and reverse sarcopenia. Published reports were evaluated to examine the effect of LES on regulation of substrate utilization (short-term studies) and nutritional outcomes (long-term studies).

METHODS

PubMed, EMBASE, Google scholar and OVID databases were searched. All studies published on LES in cirrhosis were included. Studies that included few (n < 3) subjects and patients with hepatocellular carcinoma were excluded.

RESULTS

Late evening snack decreased lipid oxidation and improved nitrogen balance, irrespective of the composition or type of formulation used. Daytime isocaloric isonitrogenous snacks did not have the metabolic or clinical benefit of LES. LES decreased skeletal muscle proteolysis. No studies have examined its effect on muscle protein synthesis. There was inconsistent translation into an increase in lean body or skeletal muscle mass. Improved quality of life occurs but decreased mortality or need for transplantation has not been reported. The optimal composition of LES has not been defined, but based on mechanistic considerations, a branched chain supplemented LES holds most promise.

CONCLUSIONS

Late evening snack holds the most promise as an intervention to reverse anabolic resistance and sarcopenia of cirrhosis with improved quality of life in patients with cirrhosis. Long term benefit and improved survival need critical evaluation.

Sepsis downregulates myostatin mRNA levels without altering myostatin protein levels in skeletal muscle

Myostatin is a negative regulator of muscle mass and has been reported to be upregulated in several conditions characterized by muscle atrophy. The influence of sepsis on myostatin expression and activity is poorly understood. Here, we tested the hypothesis that sepsis upregulates the expression and downstream signaling of myostatin in skeletal muscle. Because sepsis-induced muscle wasting is at least in part regulated by glucocorticoids, we also determined the influence of glucocorticoids on myostatin expression. Sepsis was induced in rats by cecal ligation and puncture and control rats were sham-operated. In other experiments, rats were injected intraperitoneally with dexamethasone (10 mg/kg) or corresponding volume of vehicle. Surprisingly, myostatin mRNA levels were reduced and myostatin protein levels were unchanged in muscles from septic rats. Muscle levels of activin A, follistatin, and total and phosphorylated Smad2 (p-Smad2) were not influenced by sepsis, suggesting that myostatin downstream signaling was not altered during sepsis. Interestingly, total and p-Smad3 levels were increased in septic muscle, possibly reflecting altered signaling through pathways other than myostatin. Similar to sepsis, treatment of rats with dexamethasone reduced myostatin mRNA levels and did not alter myostatin protein levels. Fasting, an additional condition characterized by muscle wasting, reduced myostatin mRNA and activin A protein levels, increased myostatin protein, and did not influence follistatin and p-Smad2 levels. Of note, total and p-Smad3 levels were reduced in muscle during fasting. The results suggest that sepsis and glucocorticoids do not upregulate the expression and activity of myostatin in skeletal muscle. The role of myostatin may vary between different conditions characterized by muscle wasting. Downstream signaling through Smad2 and 3 is probably regulated not only by myostatin but by other mechanisms as well.

Myostatin expression is increased by food deprivation in a muscle-specific manner and contributes to muscle atrophy during prolonged food deprivation in mice

During food deprivation (FD), skeletal muscle protein is broken down to produce amino acids for hepatic gluconeogenesis to maintain blood glucose levels. However, it is unclear what role, if any, the secreted antigrowth factor myostatin (MSTN) plays in the muscle atrophy induced by FD. We therefore examined expression and function of MSTN in FD in mice. Two days of FD significantly decreased muscle mass and protein content and increased mRNA levels of ubiquitin ligases MuRF-1 and atrogin-1 in fast-twitch tibialis anterior (TA) muscle but not slow-twitch soleus (Sol) muscle, while 2 days of refeeding returned these to fed values in TA. MSTN mRNA levels were significantly increased approximately threefold by 2 days, but not 1 day, of FD and returned to fed levels with 2 days of refeeding in TA but were not significantly affected by FD or refeeding in Sol. TA mass decreased to a similar amount after 1 day of FD in wild-type mice and mice null for the MSTN gene but was decreased to a greater amount in wild-type than MSTN-null mice by 2 days of FD. In addition, blood glucose levels decreased and corticosterone levels increased to a greater extent in MSTN-null mice after 2 days of FD, but surprisingly muscle MuRF-1 and atrogin-1 mRNA levels were not affected by the lack of MSTN during FD. Similarly, changes in hepatic enzyme expression in response to FD were identical between wild-type and MSTN-null mice. Our data are consistent with the hypothesis that MSTN is dispensable for the initial atrophy occurring in response to FD but attenuates the decrease in fast-twitch muscle mass during prolonged FD.

Proteomic signature of muscle atrophy in rainbow trout

Muscle deterioration arises as a physiological response to elevated energetic demands of fish during sexual maturation and spawning. Previously, we used this model to characterize the transcriptomic mechanisms associated with fish muscle degradation and identified potential biological markers of muscle growth and quality. However, transcriptional measurements do not necessarily reflect changes in active mature proteins. Here we report the characterization of proteomic profile in degenerating muscle of rainbow trout in relation to the female reproductive cycle using a LC/MS-based label-free protein quantification method. A total of 146 significantly changed proteins in atrophying muscles (FDR <5%) was identified. Proteins were clustered according to their gene ontology identifiers. Muscle atrophy was associated with decreased abundance in proteins of anaerobic respiration, protein biosynthesis, monooxygenases, follistatins, and myogenin, as well as growth hormone, interleukin-1 and estrogen receptors. In contrast, proteins of MAPK/ERK kinase, glutamine synthetase, transcription factors, Stat3, JunB, Id2, and NFkappaB inhibitor, were greater in atrophying muscle. These changes are discussed in light of the mammalian muscle atrophy paradigm and proposed fish-specific mechanisms of muscle degradation. These data will help identify genes associated with muscle degeneration and superior flesh quality in rainbow trout, facilitating identification of genetic markers for muscle growth and quality.

Chronic resistance training decreases MuRF-1 and Atrogin-1 gene expression but does not modify Akt, GSK-3beta and p70S6K levels in rats

Long-term adaptation to resistance training is probably due to the cumulative molecular effects of each exercise session. Therefore, we studied in female Wistar rats the molecular effects of a chronic resistance training regimen (3 months) leading to skeletal muscle hypertrophy in the plantaris muscle. Our results demonstrated that muscle proteolytic genes MuRF-1 and Atrogin-1 were significantly decreased in the exercised group measured 24 h after the last resistance exercise session (41.64 and 61.19%, respectively; P < 0.05). Nonetheless, when measured at the same time point, 4EBP-1, GSK-3beta and eIF2Bepsilon mRNA levels and Akt, GSK-3beta and p70S6K protein levels (regulators of translation initiation) were not modified. Such data suggests that if gene transcription constitutes a control point in the protein synthesis pathway this regulation probably occurs in early adaptation periods or during extreme situations leading to skeletal muscle remodeling. However, proteolytic gene expression is modified even after a prolonged resistance training regimen leading to moderate skeletal muscle hypertrophy.

Influence of preexercise muscle glycogen content on transcriptional activity of metabolic and myogenic genes in well-trained humans

To determine whether preexercise muscle glycogen content influences the transcription of several early-response genes involved in the regulation of muscle growth, seven male strength-trained subjects performed one-legged cycling exercise to exhaustion to lower muscle glycogen levels (Low) in one leg compared with the leg with normal muscle glycogen (Norm) and then the following day completed a unilateral bout of resistance training (RT). Muscle biopsies from both legs were taken at rest, immediately after RT, and after 3 h of recovery. Resting glycogen content was higher in the control leg (Norm leg) than in the Low leg (435 +/- 87 vs. 193 +/- 29 mmol/kg dry wt; P < 0.01). RT decreased glycogen content in both legs (P < 0.05), but postexercise values remained significantly higher in the Norm than the Low leg (312 +/- 129 vs. 102 +/- 34 mmol/kg dry wt; P < 0.01). GLUT4 (3-fold; P < 0.01) and glycogenin mRNA abundance (2.5-fold; not significant) were elevated at rest in the Norm leg, but such differences were abolished after exercise. Preexercise mRNA abundance of atrogenes was also higher in the Norm compared with the Low leg [atrogin: approximately 14-fold, P < 0.01; RING (really interesting novel gene) finger: approximately 3-fold, P < 0.05] but decreased for atrogin in Norm following RT (P < 0.05). There were no differences in the mRNA abundance of myogenic regulatory factors and IGF-I in the Norm compared with the Low leg. Our results demonstrate that 1) low muscle glycogen content has variable effects on the basal transcription of select metabolic and myogenic genes at rest, and 2) any differences in basal transcription are completely abolished after a single bout of heavy resistance training. We conclude that commencing resistance exercise with low muscle glycogen does not enhance the activity of genes implicated in promoting hypertrophy.