Regulation Of Protein Metabolism Research Articles

Moderate-Intensity Strength Exercise to Exhaustion Results in More Pronounced Signaling Changes in Skeletal Muscles of Strength-Trained Compared With Untrained Individuals.

Lysenko, EA, Popov, DV, Vepkhvadze, TF, Sharova, AP, and Vinogradova, OL. Moderate-intensity strength exercise to exhaustion results in more pronounced signaling changes in skeletal muscles of strength-trained compared with untrained individuals. J Strength Cond Res 34(4): 1103-1112, 2020-The aim of our investigation was to compare the response pattern of signaling proteins and genes regulating protein synthesis and degradation in skeletal muscle after strength exercise sessions performed to volitional fatigue in strength-trained and untrained males. Eight healthy recreationally active males and 8 power-lifting athletes performed 4 sets of unilateral leg presses to exhaustion (65% 1 repetition maximum). Biopsy samples of m. vastus lateralis were obtained before, 1 and 5 hours after cessation of exercise. Phosphorylation of p70S6k, 4EBP1, and ACC increased, whereas phosphorylation of eEF2 and FOXO1 decreased only in the trained group after exercise. Expression of DDIT4, MURF1, and FOXO1 mRNAs increased and expression of MSTN mRNA decreased also only in the trained group after exercise. In conclusion, moderate-intensity strength exercise performed to volitional fatigue changed the phosphorylation status of mTORC1 downstream signaling molecules and markers of ubiquitin-proteasome system activation in trained individuals, suggesting activation of protein synthesis and degradation. In contrast to the trained group, signaling responses in the untrained group were considerably less pronounced. It can be assumed that the slowdown in muscle mass gain as the athletes increase in qualification cannot be associated with a decrease in the sensitivity of systems regulating protein metabolism, but possibly with inadequate intake or assimilation of nutrients necessary for anabolism. Perhaps, the intake of highly digestible protein or protein-carbohydrate dietary supplements could contribute to the increase in muscle mass in strength athletes.

МЕТАБОЛИЗМ БЕЛКОВ В ОРГАНИЗМЕ РАСТУЩИХ БОРОВКОВ ПРИ ДОБАВЛЕНИИ В РАЦИОН 20-ГИДРОКСИЭКДИЗОНА

One of the approaches to the creation of biologically active additives in pig nutrition can be the use of phytopreparations, in par-ticular, 20-hydroxyecdysone (20-GE), which regulates protein metabolism in piglets. The aim of this work is to assess the effect of 20-GE on the metabolism of proteins in the body and to measure their turnover in grow-ing boars. The experiment was carried out on boars (♂ Danish Yorkshire × ♀ Danish Landrace) from 60 to 120 days of age. At the age of 60 days, boars were divided into 2 groups: control and experimental, fed with feed with a content (g / kg) of crude protein 158.7, lysine 7.7, threonine 4.8, methionine 4.6, exchange energy (EE) 12.7 MJ / kg. The ratio of the first limiting amino acid lysine to EE was 61%. The boars of the experimental group were injected with 20-GE at a dose of 1.6 mg / kg of body weight. In boars of the experimental group, compared with the con-trol, there was a decrease in urinary nitrogen excretion (by 26.8%, P≤0.05). Nitrogen re-tention was higher in boars of the experi-mental group by 19.0% (P≤0.001) compared to the control. The results of studies on pro-tein turnover obtained using a stable isotope indicate that the anabolic effect of 20-GE isdetermined by an increase in the rate of pro-tein synthesis at the same rates of their deg-radation, nitrogen flow against the back-ground of a decrease in its endogenous loss-es. 20-GE by activating a signal through protein kinase B provides an increase in bio-synthetic processes at the stage of transla-tion. It was concluded that the use of 20-GE in boars cultivation increases the efficiency of using amino acids for the synthesis and deposition of proteins in the body.

A systematic integrative approach reveals novel microRNAs in diabetic nephropathy.

Background:Despite huge efforts, the underlying molecular mechanisms of diabetic nephropathy (DN) are yet elusive, and holistic views have rarely been generated. Considering the complexity of DN pathogenesis, the integration of datasets from different molecular types to construct a multilayer map of DN can provide a comprehensive insight toward the disease mechanisms and also can generate new knowledge. Here, we have re-analyzed two mRNA microarray datasets related to glomerular and tubulointerstitial compartments of human diabetic kidneys.Materials and Methods:The quality of the datasets was confirmed by unsupervised hierarchical clustering and principal component analysis. For each dataset, differentially expressed (DE) genes were identified, and transcription factors (TFs) regulating these genes and kinases phosphorylating the TFs were enriched. Furthermore, microRNAs (miRNAs) targeting the DE genes, TFs, and kinases were detected. Based on the harvested genes for glomeruli and tubulointerstitium, key signaling pathways and biological processes involved in diseases pathogenesis were recognized. In addition, the interaction of different elements in each kidney compartment was depicted in multilayer networks, and topology analysis was performed to identify key nodes. Central miRNAs whose target genes were most likely to be related to DN were selected, and their expressions were quantitatively measured in a streptozotocin-induced DN mouse model.Results:Among the examined miRNAs, miR-208a-3p and miR-496a-3p are, for the first time, found to be significantly overexpressed in the cortex of diabetic kidneys compared to controls.Conclusion:We predict that miR-208 is involved in oxygen metabolism and regulation of cellular energy balance. Furthermore, miR-496 potentially regulates protein metabolism and ion transport. However, their exact functions remain to be investigated in future studies. Taken together, starting from transcriptomics data, we have generated multilayer interaction networks and introduced novel players in DN.

Effects of dietary 20-hydroxyecdysone supplementation on whole-body protein turnover in growing pigs

One of the approaches to creating biologically active additives for use in pig breeding can be the use of 20-hydroxyecdysone regulating protein metabolism in piglets. The purpose of the work is to assess the effect of 20-hydroxyecdysone on turnover of protein in piglets. The experiment was carried out on barrows (♂ Danish Yorkshire × ♀ Danish landrace) to achieve a live weight of 53-62 kg. At the age of 60 days, 2 groups of piglets were formed: control and experimental. Piglets of the experimental group were injected with 20-hydroxyecdysone at a dose of 1.6 mg / kg body weight. In piglets of the experimental group, in comparison with the control, a decrease in the excretion of nitrogen in the urine was noted (by 26.8%, P <0.05). Nitrogen deposition was higher in piglets of the experimental group by 19.0% (P <0.001) compared with the control. 20-hydroxyecdysone contributed to increased protein deposition in the body of piglets due to protein synthesizing activity. Thus, the use of 20-hydroxyecdysone in pigs increases the efficiency of using amino acids for the synthesis and deposition of proteins in the body.

Increased Adenine Nucleotide Degradation in Skeletal Muscle Atrophy.

Adenine nucleotides (AdNs: ATP, ADP, AMP) are essential biological compounds that facilitate many necessary cellular processes by providing chemical energy, mediating intracellular signaling, and regulating protein metabolism and solubilization. A dramatic reduction in total AdNs is observed in atrophic skeletal muscle across numerous disease states and conditions, such as cancer, diabetes, chronic kidney disease, heart failure, COPD, sepsis, muscular dystrophy, denervation, disuse, and sarcopenia. The reduced AdNs in atrophic skeletal muscle are accompanied by increased expression/activities of AdN degrading enzymes and the accumulation of degradation products (IMP, hypoxanthine, xanthine, uric acid), suggesting that the lower AdN content is largely the result of increased nucleotide degradation. Furthermore, this characteristic decrease of AdNs suggests that increased nucleotide degradation contributes to the general pathophysiology of skeletal muscle atrophy. In view of the numerous energetic, and non-energetic, roles of AdNs in skeletal muscle, investigations into the physiological consequences of AdN degradation may provide valuable insight into the mechanisms of muscle atrophy.

Epigenetic Modifications Induced by Nutrients in Early Life Phases: Gender Differences in Metabolic Alteration in Adulthood.

Metabolic chronic diseases, also named noncommunicable diseases (NCDs), are considered multifactorial pathologies, which are dramatically increased during the last decades. Noncommunicable diseases such as cardiovascular diseases, obesity, diabetes mellitus, cancers, and chronic respiratory diseases markedly increase morbidity, mortality, and socioeconomic costs. Moreover, NCDs induce several and complex clinical manifestations that lead to a gradual deterioration of health status and quality of life of affected individuals. Multiple factors are involved in the development and progression of these diseases such as sedentary behavior, smoking, pollution, and unhealthy diet. Indeed, nutrition has a pivotal role in maintaining health, and dietary imbalances represent major determinants favoring chronic diseases through metabolic homeostasis alterations. In particular, it appears that specific nutrients and adequate nutrition are important in all periods of life, but they are essential during specific times in early life such as prenatal and postnatal phases. Indeed, epidemiologic and experimental studies report the deleterious effects of an incorrect nutrition on health status several decades later in life. During the last decade, a growing interest on the possible role of epigenetic mechanisms as link between nutritional imbalances and NCDs development has been observed. Finally, because of the pivotal role of the hormones in fat, carbohydrate, and protein metabolism regulation throughout life, it is expected that any hormonal modification of these processes can imbalance metabolism and fat storage. Therefore, a particular interest to several chemicals able to act as endocrine disruptors has been recently developed. In this review, we will provide an overview and discuss the epigenetic role of some specific nutrients and chemicals in the modulation of physiological and pathological mechanisms.

HEMATOLOGICAL PROFILE IN THE YAKUT BREED HORSES AND PRILENSKOYE

The morpho-physiological indicators of the peripheral blood of the Yakut and Prilensk horses were studied depending on their habitat in different climatic zones of Yakutia. Studies were conducted in the farms of Ust-Aldan, Nyurbinsky and Khangalassky districts of the Republic of Sakha (Yakutia). In each selected farm, research groups were selected from among clinically healthy horses with 50 heads each at the age of 5-6 years based on the principle of analogues. The studies were covered two seasons of the year: in winter and spring, under usual conditions of horses. As a result of the research, was found a significant difference in the hemoglobin level in the blood of horses within the Yakut breed depending on their territorial affiliation P (M1-M2) <0.05 (123.0 ± 0.25 g / l; 114 ± 0.38 g / l). A higher level of erythrocyte counts in peripheral blood was observed in Yakut breed horses in the Nyurbinsky district (7.02 ± 0.72 million / μl.), and the lowest - in horses of the same breed in the Ust-Aldan region (6.2 ± 0.31 million mcl). There is no significant difference between horse breeds.The results of morphophysiological studies of peripheral blood indicate the specificity of the adaptive response of the body of the Yakut and Prilensk horse breeds to extremely low temperatures, poor nutrition in the winter, lack of food in the spring are characterized by seasonal regulation of protein metabolism.

Leucine Supplementation Improves Effort Tolerance of Rats With Hyperthyroidism.

Leucine is a regulator of protein metabolism in vivo and information on its action on effort tolerance of both animals and humans with hyperthyroidism is scarce. The objective of the present study was to verify the influence of leucine supplementation on the effort tolerance of Wistar rats with experimental hyperthyroidism. 40 animals were divided into four groups of ten: control (C), hormone (H), leucine (L), and hormone + leucine (HL). Hyperthyroidism was induced by daily administration of 20 μ⋅g100 g-1 of levothyroxine sodium in aqueous suspension by gavage. Leucine was supplemented by adding 5% of the amino acid to the conventional feed. The animals’ blood was collected by cardiac puncture to analyze TSH, T4, and T3 levels. The effort tolerance was determined by the swimming test with a 7% load attached to animals’ tails. Statistical analysis was performed using the Shapiro-Wilk normality test, followed by the analysis of variance (ANOVA) of repeated measures of two factors (treatment × time) and Tukey post hoc, with a significance level of p < 0.05. Administering thyroid hormone increased the swimming performance of rats after 14 and 21 days, but with a drop in performance at 28 days. The HL group, on the other hand, had a significantly higher swimming performance compared to the other groups after 28 days of treatment. Leucine supplementation associated with the experimental model of hyperthyroidism improved the performance of rats in a swimming test after 28 days of treatment.

Cinnamaldehyde regulates H2 O 2 -induced skeletal muscle atrophy by ameliorating the proteolytic and antioxidant defense systems.

Skeletal muscle atrophy/wasting is associated with impaired protein metabolism in diverse physiological and pathophysiological conditions. Elevated levels of reactive oxygen species (ROS), disturbed redox status, and weakened antioxidant defense system are the major contributing factors toward atrophy. Regulation of protein metabolism by controlling ROS levels and its associated catabolic pathways may help in treating atrophy and related clinical conditions. Although cinnamaldehyde (CNA) enjoys the established status of antioxidant and its role in ROS management is reported, impact of CNA on skeletal muscle atrophy and related pathways is still unexplored. In the current study, the impact of CNA on C2C12 myotubes and the possible protection of cultured cells from H 2 O 2 -induced atrophy is examined. Myotubes were treated with H 2 O 2 in the presence and absence of CNA and the changes in the antioxidative, proteolytic systems, and mitochondrial functions were scored. Morphological analysis showed significant protective effects of CNA on length, diameter, and nuclei fusion index of myotubes. The evaluation of biochemical markers of atrophy; creatine kinase, lactate dehydrogenase, succinate dehydrogenase along with the study of muscle-specific structural protein (i.e., myosin heavy chain-fast [MHCf] type) showed significant protection of proteins by CNA. CNA pretreatment not only checked the activation of proteolytic systems (ubiquitin-proteasome E3-ligases [MuRF1/Atrogin1]), autophagy [Beclin1/LC3B], cathepsin L, calpain, caspase), but also prevented any alteration in the activities of antioxidative defense enzymes (catalase, glutathione- S-transferase, glutathione-peroxidase, superoxide dismutase, glutathione reductase). The results suggest that CNA protects myotubes from H 2 O 2 -induced atrophy by inhibiting/resisting the amendments in proteolytic systems and maintains cellular redox-balance.

PO-076 High and moderate intensity strength exercises to exhaustion activate different signaling cascades regulating protein metabolism in trained skeletal muscle

Objective The aim of the study was to evaluate the activation of signaling cascades regulating protein synthesis and degradation after strength exercise sessions of high and moderate intensity in the muscles of athletes adapted to strength training.&#x0D; Methods Eight strength-trained men were recruited for the experiment. The volunteers performed 4 sets of leg press to volitional fatigue with moderate intensity (65% 1RM) for one leg and 4 sets of leg press to volitional fatigue with high intensity (85% of 1RM) for contralateral leg. The sets for both legs were performed in turn with rest intervals of 2 min. Biopsy from m. vastus lateralis was performed before, 1, 5 and 10 hours after cessation of exercise. Content of signaling proteins was evaluated using Western blot.&#x0D; Results Total work performed by the leg during moderate intensity strength exercise was 32% (P˂0,001) higher in comparison with contralateral leg performing high intensity exercise. The phosphorylation levels of p70S6kThr389 and 4E-BP1Thr37 / 46 increased only after the exercise of moderate intensity (P˂0.05). On the contrary, the phosphorylation level of ERK1 / 2Thr202 / Tyr204 increased only after the exercise of high intensity (P˂0.05). The level of phosphorylation of eEF2Thr56 significantly decreased after 1 (P˂0.001), 5 (P˂0.01) and 10 (P˂0.01) hours after the exercise of high intensity. The phosphorylation level of ACCSer79, an AMPK activation marker, was significantly increased 1 hour after the exercise of moderate intensity (P˂0.01). The phosphorylation level of FOXO1Ser256 significantly decreased after the exercises of both intensities (5 hours after the exercise of moderate intensity, P˂0.001; 1 hour after the exercise of high intensity, P˂0.05).&#x0D; Conclusions Strength exercises of high and moderate intensity, performed to volitional fatigue, may cause activation of different signaling cascades. Herewith, activation of mTORC1 after strength exercise is more dependent on the total work, whereas the ERK1 / 2 and eEF2 activation on the exercise intensity.&#x0D; The work was supported by RFBR grant №17-04-00878.

OsNOA1 functions in a threshold-dependent manner to regulate chloroplast proteins in rice at lower temperatures

BackgroundAlthough decreased protein expressions have been observed in NOA1 (Nitric Oxide Associated protein 1) deficient plants, the molecular mechanisms of how NOA1 regulates protein metabolism remain poorly understood. In this study, we have used a global comparative proteomic approach for both OsNOA1 suppression and overexpression transgenic lines under two different temperatures, in combination with physiological and biochemical analyses to explore the regulatory mechanisms of OsNOA1 in rice.ResultsIn OsNOA1-silenced or highly overexpressed rice, considerably different expression patterns of both chlorophyll and Rubisco as well as distinct phenotypes were observed between the growth temperatures at 22 °C and 30 °C. These observations led us to hypothesize there appears a narrow abundance threshold for OsNOA1 to function properly at lower temperatures, while higher temperatures seem to partially compensate for the changes of OsNOA1 abundance. Quantitative proteomic analyses revealed higher temperatures could restore 90% of the suppressed proteins to normal levels, whereas almost all of the remaining suppressed proteins were chloroplast ribosomal proteins. Additionally, our data showed 90% of the suppressed proteins in both types of transgenic plants at lower temperatures were located in the chloroplast, suggesting a primary effect of OsNOA1 on chloroplast proteins. Transcript analyses, along with in vitro pull-down experiments further demonstrated OsNOA1 is associated with the function of chloroplast ribosomes.ConclusionsOur results suggest OsNOA1 functions in a threshold-dependent manner for regulation of chloroplast proteins at lower temperatures, which may be mediated by interactions between OsNOA1 and chloroplast ribosomes.

Association of genes of different functional classes with type 1 diabetes

The genetic structure of susceptibility to type 1 diabetes (T1D) in the population of Tomsk was studied. We had a group of T1D patients (N = 285) and a population sample (N = 300) and we studied 58 SNPs localized in the 47 genes which products are involved in various metabolic pathways and processes as fibrogenesis, endothelial dysfunction, and inflammation. Genotyping was performed by mass spectrometry using the Sequenom MassARRAY system (United States). We compared the group of T1D patients and the population sample and found an association with the predisposition to disease for seven markers: rs3765124 of the ADAMDEC1 gene, genotype AA (p = 0.004), allele A (p = 0.033); rs1007856 of the ITGB5 gene, genotype TT (p = 0.015), allele T (p = 0.036); rs20579 of the LIG1 gene, genotype CC (p = 0.004), allele C (p = 0.002); rs12980602 of the IFNL2 gene, allele C (p = 0.029); rs4986819 of the PARP4 gene, allele C (p = 0.044); rs1143674 of the ITGA4 gene genotype GG (p = 0.002); rs679620 of the MMP3 gene, genotype AA (p = 0.008). Thus, the products of genes associated with T1D belong to different molecular classes: metalloproteases (ADAMDEC1, MMP3), cytokines (IL28A), cell surface receptors (ITGA4), adhesion molecules (ITGB5), DNA ligases (LIG1), and ribosyltransferase enzymes (PARP4). The ADAMDEC1, ITGA4, and ITGB5 genes belong to two biological processes: cell communication and signal transduction. The LIG1 and PARP4 genes regulate the metabolism of nucleic acids, MMP3 is involved in the regulation of protein metabolism, and the IFNL2 is involved in the immune response.

Acute high-caffeine exposure increases autophagic flux and reduces protein synthesis in C2C12 skeletal myotubes.

Caffeine is a highly catabolic dietary stimulant. High caffeine concentrations (1-10mM) have previously been shown to inhibit protein synthesis and increase protein degradation in various mammalian cell lines. The purpose of this study was to examine the effect of short-term caffeine exposure on cell signaling pathways that regulate protein metabolism in mammalian skeletal muscle cells. Fully differentiated C2C12 skeletal myotubes either received vehicle (DMSO) or 5mM caffeine for 6h. Our analysis revealed that caffeine promoted a 40% increase in autolysosome formation and a 25% increase in autophagic flux. In contrast, caffeine treatment did not significantly increase the expression of the skeletal muscle specific ubiquitin ligases MAFbx and MuRF1 or 20S proteasome activity. Caffeine treatment significantly reduced mTORC1 signaling, total protein synthesis and myotube diameter in a CaMKKβ/AMPK-dependent manner. Further, caffeine promoted a CaMKII-dependent increase in myostatin mRNA expression that did not significantly contribute to the caffeine-dependent reduction in protein synthesis. Our results indicate that short-term caffeine exposure significantly reduced skeletal myotube diameter by increasing autophagic flux and promoting a CaMKKβ/AMPK-dependent reduction in protein synthesis.

Muscle-specific deletion of BDK amplifies loss of myofibrillar protein during protein undernutrition

Branched-chain amino acids (BCAAs) are essential amino acids for mammals and play key roles in the regulation of protein metabolism. However, the effect of BCAA deficiency on protein metabolism in skeletal muscle in vivo remains unclear. Here we generated mice with lower BCAA concentrations by specifically accelerating BCAA catabolism in skeletal muscle and heart (BDK-mKO mice). The mice appeared to be healthy without any obvious defects when fed a protein-rich diet; however, bolus ingestion of BCAAs showed that mTORC1 sensitivity in skeletal muscle was enhanced in BDK-mKO mice compared to the corresponding control mice. When these mice were fed a low protein diet, the concentration of myofibrillar protein was significantly decreased (but not soluble protein) and mTORC1 activity was reduced without significant change in autophagy. BCAA supplementation in drinking water attenuated the decreases in myofibrillar protein levels and mTORC1 activity. These results suggest that BCAAs are essential for maintaining myofibrillar proteins during protein undernutrition by keeping mTORC1 activity rather than by inhibiting autophagy and translation. This is the first report to reveal the importance of BCAAs for protein metabolism of skeletal muscle in vivo.

IP3R-mediated Ca2+ release regulates protein metabolism in Drosophila neuroendocrine cells: implications for development under nutrient stress.

Successful completion of animal development is fundamentally reliant on nutritional cues. Surviving periods of nutritional insufficiency requires adaptations that are coordinated, in part, by neural circuits. As neuropeptides secreted by neuroendocrine (NE) cells modulate neural circuits, we investigated NE cell function during development under nutrient stress. Starved Drosophila larvae exhibited reduced pupariation if either insulin signaling or IP3/Ca2+ signaling were downregulated in NE cells. Moreover, an IP3R (inositol 1,4,5-trisphosphate receptor) loss-of-function mutant displayed reduced protein synthesis, which was rescued by overexpression of either InR (insulin receptor) or IP3R in NE cells of the mutant, suggesting that the two signaling pathways might be functionally compensatory. Furthermore, cultured IP3R mutant NE cells, but not neurons, exhibited reduced protein translation. Thus cell-specific regulation of protein synthesis by IP3R in NE cells influences protein metabolism. We propose that this regulation helps developing animals survive in poor nutritional conditions.

CL316,243, a β3-adrenergic receptor agonist, induces muscle hypertrophy and increased strength.

Studies in vitro have demonstrated that β3-adrenergic receptors (β3-ARs) regulate protein metabolism in skeletal muscle by promoting protein synthesis and inhibiting protein degradation. In this study, we evaluated whether activation of β3-ARs by the selective agonist CL316,243 modifies the functional and structural properties of skeletal muscles of healthy mice. Daily injections of CL316,243 for 15 days resulted in a significant improvement in muscle force production, assessed by grip strength and weight tests, and an increased myofiber cross-sectional area, indicative of muscle hypertrophy. In addition, atomic force microscopy revealed a significant effect of CL316,243 on the transversal stiffness of isolated muscle fibers. Interestingly, the expression level of mammalian target of rapamycin (mTOR) downstream targets and neuronal nitric oxide synthase (NOS) was also found to be enhanced in tibialis anterior and soleus muscles of CL316,243 treated mice, in accordance with previous data linking β3-ARs to mTOR and NOS signaling pathways. In conclusion, our data suggest that CL316,243 systemic administration might be a novel therapeutic strategy worthy of further investigations in conditions of muscle wasting and weakness associated with aging and muscular diseases.

Adjustments of Protein Metabolism in Fasting Arctic Charr, Salvelinus alpinus

Protein metabolism, including the interrelated processes of synthesis and degradation, mediates the growth of an animal. In ectothermic animals, protein metabolism is responsive to changes in both biotic and abiotic conditions. This study aimed to characterise responses of protein metabolism to food deprivation that occur in the coldwater salmonid, Arctic charr, Salvelinus alpinus. We compared two groups of Arctic charr: one fed continuously and the other deprived of food for 36 days. We measured the fractional rate of protein synthesis (KS) in individuals from the fed and fasted groups using a flooding dose technique modified for the use of deuterium-labelled phenylalanine. The enzyme activities of the three major protein degradation pathways (ubiquitin proteasome, lysosomal cathepsins and the calpain systems) were measured in the same fish. This study is the first to measure both KS and the enzymatic activity of protein degradation in the same fish, allowing us to examine the apparent contribution of different protein degradation pathways to protein turnover in various tissues (red and white muscle, liver, heart and gills). KS was lower in the white muscle and in liver of the fasted fish compared to the fed fish. There were no observable effects of food deprivation on the protease activities in any of the tissues with the exception of liver, where the ubiquitin proteasome pathway seemed to be activated during fasting conditions. Lysosomal proteolysis appears to be the primary degradation pathway for muscle protein, while the ubiquitin proteasome pathway seems to predominate in the liver. We speculate that Arctic charr regulate protein metabolism during food deprivation to conserve proteins.

Action of leucine in heart hypertrophy induced by thyroid hormone in rats

Leucine is a regulator of protein metabolism in vivo, but there is little information regarding its effect on hyperthyroidism-induced cardiac hypertrophy. This study aimed to verify the action of leucine in heart hypertrophy using an experimental model of hyperthyroidism in rats. A total of 40 Wistar rats were used and allocated randomly into four groups: control (C), hormone (H), leucine (L) and hormone plus leucine (HL). Hyperthyroidism was induced by administering daily by gavage 20 μg of levothyroxine sodium in aqueous suspension per 100 g of body weight, and leucine was supplemented by adding 5% of the amino acid to conventional food. After 28 days, the heart was removed and weighed; the left ventricle was separated along with the interventricular septum and weighed. Histological slides were made from the left ventricle and stained with hematoxylin-eosin to measure the transverse diameter of cardiomyocytes. Two-way analysis of variance (ANOVA) and Tukey post-test were used and significance level set at 5%. There was a significant increase in the absolute heart weight, the left ventricular weight and cardiomyocyte diameter in rats of the H group compared to the other groups. The addition of leucine inhibited heart hypertrophy. Levothyroxine sodium-induced cardiac hypertrophy in Wistar rats is inhibited by leucine.

Activation of AMP-activated protein kinase induce expression of FoxO1, FoxO3a, and myostatin after exercise-induced muscle damage

AMP-activated protein kinase (AMPK) has been shown to regulate protein metabolism in skeletal muscle. We previously found that levels of Forkhead box proteins, FoxO1 and FoxO3a, and myostatin in rat gastrocnemius increased after exercise-induced muscle damage (EIMD). Eccentric muscle contractions (ECs), defined as elongation of muscle under tension, were used for inducing EIMD. The objective of this study was to clarify whether AMPK participates in activation and expression of FoxO proteins and myostatin in rat gastrocnemius muscle after EIMD. Wistar rats were randomly assigned into the following three groups; CON (n = 6), 180ECs group (ankle angular velocity, 180°/s; n = 6), and 30ECs group (ankle angular velocity, 30°/s; n = 6). 20 ECs were conducted with percutaneous electrical stimulation of gastrocnemius and simultaneous forced dorsiflexion of ankle joint (from 0° to 45°). To evaluate activation of AMPK, we measured the phosphorylated states of AMPK and acetyl CoA carboxylase. For evaluation of the direct relationships of AMPK and other proteins, we also examined contents of FoxOs and myostatin with stimulation of L6 myotube with AMPK agonist, 5 –aminoimidazole -4 –carboxamide -1-β-d-ribofuranoside (AICAR) (0.1, 0.5, 1, 1.5, and 2 mM). Western blotting was employed for protein analysis. Significant torque deficit was only observed in the 180ECs, suggesting EIMD. We also observed that phosphorylated AMPKα was induced in response to 180ECs (p < 0.01 vs. CON). Additionally, the level of phosphorylated acetyl CoA carboxylase was significantly higher in response to 180ECs and 30ECs. The phosphorylated states of FoxO1, FoxO3a, and myostatin expression were increased significantly in response to 180ECs. Furthermore, treatment of L6 myotubes with AICAR showed similar tendencies to that observed in in vivo gastrocnemius muscle treated with 180ECs. Therefore, we conclude that activation of AMPK plays a key role in increasing the level of FoxO1, FoxO3a, and myostatin in gastrocnemius after EIMD.

Altered signaling pathway governing protein metabolism in skeletal muscle of the Japanese black bear during hibernation

Hibernating mammals experience prolonged periods of torpor and starvation during winter survival. While continued physical inactivity and malnutrition lead to profound loss of skeletal muscle in most mammals, hibernating animals show limited muscle atrophy and can successfully maintain physical function following hibernation. Since net balance between protein synthesis and degradation determines total mass of skeletal muscle, we hypothesized that hibernating animals uniquely alter the regulatory mechanisms governing protein metabolism to prevent muscle atrophy during hibernation. In this study, alteration of signaling pathways regulating protein metabolism was examined in skeletal muscle of the Japanese black bear (Ursus thibetanus japonicus). Sartorius muscle samples were collected from bear leg on late November and early April (pre/post‐hibernation). Ubiquitin‐proteasome pathway (as assessed by increased expression of Atrogin1 and MuRF1 mRNA) was significantly activated in skeletal muscle following hibernation. In contrast, as indicated by a significant increase in S6K1 phosphorylation, activation state of mTOR signaling which functions as a central regulator of protein synthesis was increased following hibernation. Additionally, gene expression of myostatin, a negative regulator of muscle mass, was significantly decreased on post‐hibernation. These observations suggest that protein synthesis rate may be enhanced in skeletal muscle of hibernating bear, which then lead to limited loss of muscle mass and maintenance of physical performance. This work was supported by JSPS KAKENHI Grant Number 25702041 and 26560369.