RNA sequencing reveals a slow to fast muscle fiber type transition after olanzapine infusion in rats

Combined sulforaphane and β-sitosterol mitigate olanzapine-induced metabolic disorders in rats: Insights on FOXO, PI3K/AKT, JAK/STAT3, and MAPK signaling pathways

One of the best antipsychotics for treating schizophrenia and bipolar disorders is olanzapine (OLA). However, its use is restricted owing to unfavorable adverse effects as liver damage, dyslipidemia, and weight gain. The primary objective of the present investigation was to examine the signaling mechanisms that underlie the metabolic disruption generated by OLA. Besides, the potential protective effect of sulforaphane (SFN) and β-sitosterol (βSS) against obesity and metabolic toxicity induced by OLA were inspected as well. A total of five groups of male Wistar rats were established, including the control, OLA, SFN+OLA, βSS+OLA, and the combination + OLA groups. Hepatic histopathology, biochemical analyses, ultimate body weights, liver function, oxidative stress, and pro-inflammatory cytokines were evaluated. In addition to the relative expression of FOXO, the signaling pathways for PI3K/AKT, JAK/STAT3, and MAPK were assessed as well. All biochemical and hepatic histopathological abnormalities caused by OLA were alleviated by SFN and/or βSS. A substantial decrease in systolic blood pressure (SBP), proinflammatory cytokines, serum lipid profile parameters, hepatic MDA, TBIL, AST, and ALT were reduced through SFN or/and βSS. To sum up, the detrimental effects of OLA are mediated by alterations in the Akt/FOXO3a/ATG12, Ras/SOS2/Raf-1/MEK/ERK1/2, and Smad3,4/TGF-β signaling pathways. The administration of SFN and/or βSS has the potential to mitigate the metabolic deficit, biochemical imbalances, hepatic histological abnormalities, and the overall unfavorable consequences induced by OLA by modulating the abovementioned signaling pathways.

Respiratory SARS-CoV-2 Infection Causes Skeletal Muscle Atrophy and Long-Lasting Energy Metabolism Suppression

Muscle fatigue represents the most prevalent symptom of long-term COVID, with elusive pathogenic mechanisms. We performed a longitudinal study to characterize histopathological and transcriptional changes in skeletal muscle in a hamster model of respiratory SARS-CoV-2 infection and compared them with influenza A virus (IAV) and mock infections. Histopathological and bulk RNA sequencing analyses of leg muscles derived from infected animals at days 3, 30, and 60 post-infection showed no direct viral invasion but myofiber atrophy in the SARS-CoV-2 group, which was accompanied by persistent downregulation of the genes related to myofibers, ribosomal proteins, fatty acid β-oxidation, tricarboxylic acid cycle, and mitochondrial oxidative phosphorylation complexes. While both SARS-CoV-2 and IAV infections induced acute and transient type I and II interferon responses in muscle, only the SARS-CoV-2 infection upregulated TNF-α/NF-κB but not IL-6 signaling in muscle. Treatment of C2C12 myotubes, a skeletal muscle cell line, with combined IFN-γ and TNF-α but not with IFN-γ or TNF-α alone markedly impaired mitochondrial function. We conclude that a respiratory SARS-CoV-2 infection can cause myofiber atrophy and persistent energy metabolism suppression without direct viral invasion. The effects may be induced by the combined systemic interferon and TNF-α responses at the acute phase and may contribute to post-COVID-19 persistent muscle fatigue.

Discovery of a second citric acid cycle complex

Together, Nobel Prize honoured work, mathematics, physics and the laws of nature have drawn a concept of clockwise cycling carboxylic acids in Krebs' Citric Acid Cycle. A Citric Acid Cycle complex is defined by specific substrate, product and regulation. Recently, the Citric Acid Cycle 1.1 complex was introduced as an NAD⁺-regulated cycle with the substrate, lactic acid and the product, malic acid. Here, we introduce the concept of the Citric Acid Cycle 2.1 complex as an FAD-regulated cycle with the substrate, malic acid and the products, succinic acid or citric acid. The function of the Citric Acid Cycle 2.1 complex is to balance stress situations within the cell. We propose that the biological function of Citric Acid Cycle 2.1 in muscles is to accelerate recovery of ATP; whereas in white tissue adipocytes our testing of the theoretical concept led to the storage of energy as lipids.

Profiling the Skeletal Muscle Proteome in Patients on Atypical Antipsychotics and Mood Stabilizers

Atypical antipsychotics (AAP) are used in the treatment of severe mental illness. They are associated with several metabolic side effects including insulin resistance. The skeletal muscle is the primary tissue responsible for insulin-stimulated glucose uptake. Dysfunction of protein regulation within the skeletal muscle following treatment with AAPs may play a role in the associated metabolic side effects. The objective of this study was to measure protein abundance in the skeletal muscle of patients on long-term AAP or mood stabilizer treatment. Cross-sectional muscle biopsies were obtained from patients with bipolar disorder and global protein abundance was measured using stable isotope labeling by amino acid (SILAC) combined with high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). Sixteen patients completed muscle biopsies and were included in the proteomic analyses. A total of 40 proteins were significantly different between the AAP group and the mood stabilizer group. In-silico pathway analysis identified significant enrichment in several pathways including glucose metabolism, cell cycle, apoptosis, and folate metabolism. Proteome abundance changes also differed based on protein biological processes and function. In summary, significant differences in proteomic profiles were identified in the skeletal muscle between patients on AAPs and mood stabilizers. Future work is needed to validate these findings in prospectively sampled populations.

Advanced Fiber Type-Specific Protein Profiles Derived from Adult Murine Skeletal Muscle

Skeletal muscle is a heterogeneous tissue consisting of blood vessels, connective tissue, and muscle fibers. The last are highly adaptive and can change their molecular composition depending on external and internal factors, such as exercise, age, and disease. Thus, examination of the skeletal muscles at the fiber type level is essential to detect potential alterations. Therefore, we established a protocol in which myosin heavy chain isoform immunolabeled muscle fibers were laser microdissected and separately investigated by mass spectrometry to develop advanced proteomic profiles of all murine skeletal muscle fiber types. All data are available via ProteomeXchange with the identifier PXD025359. Our in-depth mass spectrometric analysis revealed unique fiber type protein profiles, confirming fiber type-specific metabolic properties and revealing a more versatile function of type IIx fibers. Furthermore, we found that multiple myopathy-associated proteins were enriched in type I and IIa fibers. To further optimize the assignment of fiber types based on the protein profile, we developed a hypothesis-free machine-learning approach, identified a discriminative peptide panel, and confirmed our panel using a public data set.

The protein kinase D1-mediated inflammatory pathway is involved in olanzapine-induced impairment of skeletal muscle insulin signaling in rats

AIMS

Skeletal muscle insulin resistance (SMIR) contributes to the metabolic syndrome. Mounting evidence has demonstrated that the second generation antipsychotic olanzapine causes SMIR. The present study sought to investigate the molecular mechanisms underlying olanzapine-induced SMIR.

MAIN METHODS

Male rats were given olanzapine (5 mg/kg, by a gavage method) for consecutive eight weeks. Plasma glucose and insulin concentrations were determined enzymatically or by ELISA. Gene/protein expression was analyzed by Real-Time PCR, Western blot and/or immunohistochemistry.

KEY FINDINGS

Olanzapine increased fasting plasma insulin concentration, and decreased glucose clearance during insulin tolerance test in rats. In skeletal muscle, it decreased protein expression of membrane glucose transporter (GLUT) 4, the ratio of membrane to total GLUT4, and total insulin receptor substrate 1 (IRS1). However, it increased protein phosphorylation of Ser³⁰⁷ in IRS1, Y⁶⁰⁷ in phosphoinositide 3-kinase p85α and Ser³⁰⁷ in AKT. These results indicate olanzapine-induced impairment of skeletal muscle insulin signaling. Mechanistically, olanzapine upregulated mRNA expression of TNFα, IL6 and IL1β, and protein phosphorylation of both IκB kinase (IKK)α/β and nuclear factor (NF)κB p65. Furthermore, it increased protein phosphorylation of Ser^485/491 in AMPKα2, whereas it decreased AMPKα2 activity. More importantly, both Western blot and immunohistochemical analyses revealed that olanzapine increased protein phosphorylation of Ser^744/748 in protein kinase D1 (PKD1).

SIGNIFICANCE

The present results suggest that the PKD1-mediated inflammatory pathway is involved in olanzapine-induced impairment of skeletal muscle insulin signaling in rats. Our findings may go new insight into the mechanisms underlying olanzapine-induced SMIR.

Rethinking the Citric Acid Cycle: Connecting Pyruvate Carboxylase and Citrate Synthase to the Flow of Energy and Material

In 1937, Sir H. A Krebs first published the Citric Acid Cycle, a unidirectional cycle with carboxylic acids. The original concept of the Citric Acid Cycle from Krebs’ 1953 Nobel Prize lecture illustrates the unidirectional degradation of lactic acid to water, carbon dioxide and hydrogen. Here, we add the heart lactate dehydrogenase•proton-linked monocarboxylate transporter 1 complex, connecting the original Citric Acid Cycle to the flow of energy and material. The heart lactate dehydrogenase•proton-linked monocarboxylate transporter 1 complex catalyses the first reaction of the Citric Acid Cycle, the oxidation of lactate to pyruvate, and thus secures the provision of pyruvic acid. In addition, we modify Krebs’ original concept by feeding the cycle with oxaloacetic acid. Our concept enables the integration of anabolic processes and allows adaption of the organism to recover ATP faster.

The two-cell model of glucose metabolism: a hypothesis of schizophrenia

Schizophrenia is a chronic and severe mental disorder that affects over 20 million people worldwide. Common symptoms include distortions in thinking, perception, emotions, language, and self awareness. Different hypotheses have been proposed to explain the development of schizophrenia, however, there are no unifying features between the proposed hypotheses. Schizophrenic patients have perturbed levels of glucose in their cerebrospinal fluid, indicating a disturbance in glucose metabolism. We have explored the possibility that disturbances in glucose metabolism can be a general mechanism for predisposition and manifestation of the disease. We discuss glucose metabolism as a network of signaling pathways. Glucose and glucose metabolites can have diverse actions as signaling molecules, such as regulation of transcription factors, hormone and cytokine secretion and activation of neuronal cells, such as microglia. The presented model challenges well-established concepts in enzyme kinetics and glucose metabolism. We have developed a 'two-cell' model of glucose metabolism, which can explain the effects of electroconvulsive therapy and the beneficial and side effects of olanzapine treatment. Arrangement of glycolytic enzymes into metabolic signaling complexes within the 'two hit' hypothesis, allows schizophrenia to be formulated in two steps. The 'first hit' is the dysregulation of the glucose signaling pathway. This dysregulation of glucose metabolism primes the central nervous system for a pathological response to a 'second hit' via the astrocytic glycogenolysis signaling pathway.

Cell autonomous requirement of neurofibromin (Nf1) for postnatal muscle hypertrophic growth and metabolic homeostasis

BACKGROUND

Neurofibromatosis type 1 (NF1) is a multi-organ disease caused by mutations in neurofibromin 1 (NF1). Amongst other features, NF1 patients frequently show reduced muscle mass and strength, impairing patients' mobility and increasing the risk of fall. The role of Nf1 in muscle and the cause for the NF1-associated myopathy are mostly unknown.

METHODS

To dissect the function of Nf1 in muscle, we created muscle-specific knockout mouse models for NF1, inactivating Nf1 in the prenatal myogenic lineage either under the Lbx1 promoter or under the Myf5 promoter. Mice were analysed during prenatal and postnatal myogenesis and muscle growth.

RESULTS

Nf1^Lbx1 and Nf1^Myf5 animals showed only mild defects in prenatal myogenesis. Nf1^Lbx1 animals were perinatally lethal, while Nf1^Myf5 animals survived only up to approximately 25 weeks. A comprehensive phenotypic characterization of Nf1^Myf5 animals showed decreased postnatal growth, reduced muscle size, and fast fibre atrophy. Proteome and transcriptome analyses of muscle tissue indicated decreased protein synthesis and increased proteasomal degradation, and decreased glycolytic and increased oxidative activity in muscle tissue. High-resolution respirometry confirmed enhanced oxidative metabolism in Nf1^Myf5 muscles, which was concomitant to a fibre type shift from type 2B to type 2A and type 1. Moreover, Nf1^Myf5 muscles showed hallmarks of decreased activation of mTORC1 and increased expression of atrogenes. Remarkably, loss of Nf1 promoted a robust activation of AMPK with a gene expression profile indicative of increased fatty acid catabolism. Additionally, we observed a strong induction of genes encoding catabolic cytokines in muscle Nf1^Myf5 animals, in line with a drastic reduction of white, but not brown adipose tissue.

CONCLUSIONS

Our results demonstrate a cell autonomous role for Nf1 in myogenic cells during postnatal muscle growth required for metabolic and proteostatic homeostasis. Furthermore, Nf1 deficiency in muscle drives cross-tissue communication and mobilization of lipid reserves.

Gene Expression Profile in Similar Tissues Using Transcriptome Sequencing Data of Whole-Body Horse Skeletal Muscle

Horses have been studied for exercise function rather than food production, unlike most livestock. Therefore, the role and characteristics of tissue landscapes are critically understudied, except for certain muscles used in exercise-related studies. In the present study, we compared RNA-Seq data from 18 Jeju horse skeletal muscles to identify differentially expressed genes (DEGs) between tissues that have similar functions and to characterize these differences. We identified DEGs between different muscles using pairwise differential expression (DE) analyses of tissue transcriptome expression data and classified the samples using the expression values of those genes. Each tissue was largely classified into two groups and their subgroups by k-means clustering, and the DEGs identified in comparison between each group were analyzed by functional/pathway level using gene set enrichment analysis and gene level, confirming the expression of significant genes. As a result of the analysis, the differences in metabolic properties like glycolysis, oxidative phosphorylation, and exercise adaptation of the groups were detected. The results demonstrated that the biochemical and anatomical features of a wide range of muscle tissues in horses could be determined through transcriptome expression analysis, and provided proof-of-concept data demonstrating that RNA-Seq analysis can be used to classify and study in-depth differences between tissues with similar properties.

Astrocytes and neurons communicate via a monocarboxylic acid shuttle

Since formulation of the Astrocyte-Neuron Lactate Shuttle (ANLS) hypothesis in 1994, the hypothesis has provoked criticism and debate. Our review does not criticise, but rather integrates experimental data characterizing proton-linked monocarboxylate transporters (MCTs) into the ANLS. MCTs have wide substrate specificity and are discussed to be in protein complex with a proton donor (PD). We particularly focus on the proton-driven transfer of l-lactic acid (l-lacH) and pyruvic acid (pyrH), were PDs link MCTs to a flow of energy. The precise nature of the PD predicts the activity and catalytic direction of MCTs. By doing so, we postulate that the MCT4·phosphoglycerate kinase complex exports and at the same time in the same astrocyte, MCT1·carbonic anhydrase II complex imports monocarboxylic acids. Similarly, neuronal MCT2 preferentially imports pyrH. The repertoire of MCTs in astrocytes and neurons allows them to communicate via monocarboxylic acids. A change in imported pyrH/l-lacH ratio in favour of l-lacH encodes signals stabilizing the transit of glucose from astrocytes to neurons. The presented astrocyte neuron communication hypothesis has the potential to unite the community by suggesting that the exchange of monocarboxylic acids paves the path of glucose provision.

Second-Generation Antipsychotics and Dysregulation of Glucose Metabolism: Beyond Weight Gain

Second-generation antipsychotics (SGAs) are the cornerstone of treatment for schizophrenia because of their high clinical efficacy. However, SGA treatment is associated with severe metabolic alterations and body weight gain, which can increase the risk of type 2 diabetes and cardiovascular disease, and greatly accelerate mortality. Several underlying mechanisms have been proposed for antipsychotic-induced weight gain (AIWG), but some studies suggest that metabolic changes in insulin-sensitive tissues can be triggered before the onset of AIWG. In this review, we give an outlook on current research about the metabolic disturbances provoked by SGAs, with a particular focus on whole-body glucose homeostasis disturbances induced independently of AIWG, lipid dysregulation or adipose tissue disturbances. Specifically, we discuss the mechanistic insights gleamed from cellular and preclinical animal studies that have reported on the impact of SGAs on insulin signaling, endogenous glucose production, glucose uptake and insulin secretion in the liver, skeletal muscle and the endocrine pancreas. Finally, we discuss some of the genetic and epigenetic changes that might explain the different susceptibilities of SGA-treated patients to the metabolic side-effects of antipsychotics.

Samidorphan mitigates olanzapine-induced weight gain and metabolic dysfunction in rats and non-human primates

BACKGROUND

Olanzapine, regarded as one of the most efficacious antipsychotic medications for the treatment of schizophrenia, is associated with a high risk of weight gain and metabolic dysfunction. ALKS 3831, a clinical candidate for treatment of schizophrenia, is a combination of olanzapine and samidorphan, an opioid receptor antagonist. The addition of samidorphan is intended to mitigate weight gain and the metabolic dysregulation associated with the use of olanzapine.

METHODS

Non-clinical studies were conducted to assess the metabolic effects of olanzapine and samidorphan alone and in combination at clinically relevant exposure levels.

RESULTS

Chronic olanzapine administration in male and female rats shifted body composition by increasing adipose mass, which was accompanied by an increase in the rate of weight gain in female rats. Co-administration of samidorphan normalized body composition in both sexes and attenuated weight gain in female rats. In hyperinsulinemic euglycemic clamp experiments conducted prior to measurable changes in weight and/or body composition, olanzapine decreased hepatic insulin sensitivity and glucose uptake in muscle while increasing uptake in adipose tissue. Samidorphan appeared to normalize glucose utilization in both tissues, but did not restore hepatic insulin sensitivity. In subsequent studies, samidorphan normalized olanzapine-induced decreases in whole-body glucose clearance following bolus insulin administration. Results from experiments in female monkeys paralleled the effects in rats.

CONCLUSIONS

Olanzapine administration increased weight gain and adiposity, both of which were attenuated by samidorphan. Furthermore, the combination of olanzapine and samidorphan prevented olanzapine-induced insulin insensitivity. Collectively, these data indicate that samidorphan mitigates several metabolic abnormalities associated with olanzapine in both the presence and the absence of weight gain.

Mitochondrial Adaptations in Elderly and Young Men Skeletal Muscle Following 2 Weeks of Bed Rest and Rehabilitation

The aim of the study was to evaluate the expression levels of proteins related to mitochondrial biogenesis regulation and bioenergetics in vastus lateralis muscle biopsies from 16 elderly and 7 young people subjected to 14 days of bed-rest, causing atrophy, and subsequent 14 days of exercise training. Based on quantitative immunoblot analyses, in both groups a reduction of two key regulators of mitochondrial biogenesis/remodeling and activity, namely PGC-1α and Sirt3, was revealed during bed-rest, with a subsequent up-regulation after rehabilitation, indicating an involvement of PGC-1α-Sirt3 axis in response to the treatments. A difference was observed comparing the young and elderly subjects as, for both proteins, the abundance in the elderly was more affected by immobility and less responsive to exercise. The expression levels of TOM20 and Citrate Synthase, assayed as markers of outer mitochondrial membrane and mitochondrial mass, showed a noticeable sensitivity in the elderly group, where they were affected by bed-rest and rehabilitation recalling the pattern of PGC-1α. TOM20 and CS remained unchanged in young subjects. Single OXPHOS complexes showed peculiar patterns, which were in some cases dissimilar from PGC-1α, and suggest different influences on protein biogenesis and degradation. Overall, exercise was capable to counteract the effect of immobility, when present, except for complex V, which was markedly downregulated by bed-rest, but remained unaffected after rehabilitation, maybe as result of greater extent of degradation processes over biogenesis. Phosphorylation extent of AMPK, and its upstream activator LKB1, did not change after bed-rest and rehabilitation in either young or elderly subjects, suggesting that the activation of energy-sensing LKB1-AMPK signaling pathway was “missed” due to its transient nature, or was not triggered under our conditions. Our study demonstrates that, as far as the expression of various proteins related to mitochondrial biogenesis/remodeling, adaptations to bed-rest and rehabilitation in the two populations were different. The impact of bed-rest was greater in the elderly subjects, where the pattern (decrease after bed rest and recovery following rehabilitation) was accompanied by changes of mitochondrial mass. Modifications of protein abundance were matched with data obtained from gene expression analyses of four public human datasets focusing on related genes.

WWOX somatic ablation in skeletal muscles alters glucose metabolism

OBJECTIVE

WWOX, a well-established tumor suppressor, is frequently lost in cancer and plays important roles in DNA damage response and cellular metabolism.

METHODS

We re-analyzed several genome-wide association studies (GWAS) using the Type 2 Diabetes Knowledge Portal website to uncover WWOX's association with metabolic syndrome (MetS). Using several engineered mouse models, we studied the effect of somatic WWOX loss on glucose homeostasis.

RESULTS

Several WWOX variants were found to be strongly associated with MetS disorders. In mouse models, somatic ablation of Wwox in skeletal muscle (WwoxΔSKM) results in weight gain, glucose intolerance, and insulin resistance. Furthermore, WwoxΔSKM mice display reduced amounts of slow-twitch fibers, decreased mitochondrial quantity and activity, and lower glucose oxidation levels. Mechanistically, we found that WWOX physically interacts with the cellular energy sensor AMP-activated protein kinase (AMPK) and that its loss is associated with impaired activation of AMPK, and with significant accumulation of the hypoxia inducible factor 1 alpha (HIF1α) in SKM.

CONCLUSIONS

Our studies uncover an unforeseen role of the tumor suppressor WWOX in whole-body glucose homeostasis and highlight the intimate relationship between cancer progression and metabolic disorders, particularly obesity and type-2 diabetes.

SUBJECT AREAS

Genetics, Metabolic Syndrome, Diabetes.

TFAM overexpression diminishes skeletal muscle atrophy after hindlimb suspension in mice

The present study aims to investigate if overexpressing the mitochondrial transcription factor A (TFAM) gene in a transgenic mouse model diminishes soleus and gastrocnemius atrophy occurring during hindlimb suspension (HLS). Additionally, we aim to observe if combining exercise training in TFAM transgenic mice prior to HLS has a synergistic effect in preventing skeletal muscle atrophy. Male C57BL/6J-based transgenic mice (12-14 weeks old) overexpressing TFAM were assigned to a control (T-Control), 7-day HLS (T-HLS), and 2-week exercise training prior to 7-day HLS (T-Ex + HLS) groups. These groups were compared to male C57BL/6J wild-type (WT) mice (12-14 weeks old) assigned to Control, 7-day HLS (HLS), 2-week exercise training prior to 7-day HLS (Ex + HLS), and 2-week exercise training (Ex). Overexpressing TFAM results in a decrease of 8.3% in soleus and 2.6% in gastrocnemius muscle weight to bodyweight ratio after only HLS compared to wild-type mice incurring a loss of 27.1% in soleus and 21.5% in gastrocnemius muscle after HLS. Our data indicates TFAM may play a critical role in protecting skeletal muscle from disuse atrophy and is correlated with increased expression of antioxidants (SOD-2) and potential redox balance. TFAM may be an attractive molecule of interest for potential, future therapeutic development. NEW AND NOTEWORTHY: To the best of our knowledge, this is the first time a TFAM overexpression transgenic mouse model is being used in the analysis of disuse-induced skeletal muscle atrophy. Here we provide evidence of a potential role for TFAM in diminishing skeletal muscle atrophy.

Duplication of a Single myhz1.1 Gene Facilitated the Ability of Goldfish (Carassius auratus) to Alter Fast Muscle Contractile Properties With Seasonal Temperature Change

Seasonal temperature changes markedly effect the swimming performance of some cyprinid fish acutely tested at different temperatures, involving a restructuring of skeletal muscle phenotype including changes in contractile properties and myosin heavy chain expression. We analyzed the transcriptome of fast myotomal muscle from goldfish (Carassius auratus L.) acclimated to either 8 or 25°C for 4 weeks (12 h light: 12 h dark) and identified 10 myosin heavy chains (myh) and 13 myosin light chain (myl) transcripts. Goldfish orthologs were classified based on zebrafish nomenclature as myhz1.1α, myhz1.1β, myhz1.1γ, myha, myhb, embryo_myh1, myh9b, smyh2, symh3, and myh11 (myosin heavy chains) and myl1a, myl1b, myl2, myl9a, myl9b, myl3, myl13, myl6, myl12.1a, myl12.1b, myl12.2a, myl12.2b, and myl10 (myosin light chains). The most abundantly expressed transcripts myhz1.1α, myhz1.1β, myhz1.1γ, myha, myl1a, myl1b, myl2, and myl3) were further investigated in fast skeletal muscle of goldfish acclimated to either 4, 8, 15, or 30°C for 12 weeks (12 h light:12 h dark). Total copy number for the myosin heavy chains showed a distinct optimum at 15°C (P < 0.01). Together myhz1.1α and myhz1.1β comprised 90 to 97% of myhc transcripts below 15°C, but only 62% at 30°C. Whereas myhz1.1α and myhz1.1β were equally abundant at 4 and 8°C, myhz1.1β transcripts were 17 and 12 times higher than myhz1.1α at 15 and 30°C, respectively, (P < 0.01). Myhz1.1γ expression was at least nine-fold higher at 30°C than at cooler temperatures (P < 0.01). In contrast, the expression of myha and myosin light chains showed no consistent pattern with acclimation temperature. A phylogenetic analysis indicated that the previously reported ability of goldfish and common carp to alter contractile properties and myofibrillar ATPase activity with temperature acclimation was related to the duplication of a single myhz1.1 fast muscle myosin heavy chain found in basal cyprinids such as the zebrafish (Danio rerio).

The effect of Bu Zhong Yi Qi decoction on simulated weightlessness‑induced muscle atrophy and its mechanisms

Microgravity has been previously demonstrated to induce skeletal muscle atrophy, loss of muscle force and disorders in myogenesis and metabolism. Current pharmacological strategies exhibit poor efficacy. Bu Zhong Yi Qi decoction (BZ) is a well-known traditional Chinese medicine decoction used for myasthenia gravis. In the present study, its effect on unloading induced muscle atrophy was investigated. The mousetail suspension model was used to simulate weightlessness induced muscle atrophy. The results indicated that BZ could significantly protect muscles from simulated weightlessness-induced atrophy. To elucidate the underlying mechanisms, drugCIPHER-CS methods were introduced to predict its potential targets, significantly enriched pathways and biological processes. The results demonstrated that the calcium signaling pathway, citrate cycle, biosynthetic and lipid metabolic process are affected by BZ. Among the targets, nuclear receptor corepressor 1 (NCoR1) is one of the most important proteins involved in myogenesis and metabolism. The results indicated that BZ significantly downregulated NCoR 1 expression, and further induced muscle differentiation and metabolism by regulating NCoR1-associated gene expression in vivo and in vitro. In summary, the present study indicated that may be effective in combating weightlessness-induced muscle atrophy. Combined with bioinformatics, the underlying mechanism for this decoction was investigated, which provided an improved understanding of this decoction.

Global deletion of BCATm increases expression of skeletal muscle genes associated with protein turnover

Consumption of a protein-containing meal by a fasted animal promotes protein accretion in skeletal muscle, in part through leucine stimulation of protein synthesis and indirectly through repression of protein degradation mediated by its metabolite, α-ketoisocaproate. Mice lacking the mitochondrial branched-chain aminotransferase (BCATm/Bcat2), which interconverts leucine and α-ketoisocaproate, exhibit elevated protein turnover. Here, the transcriptomes of gastrocnemius muscle from BCATm knockout (KO) and wild-type mice were compared by next-generation RNA sequencing (RNA-Seq) to identify potential adaptations associated with their persistently altered nutrient signaling. Statistically significant changes in the abundance of 1,486/∼39,010 genes were identified. Bioinformatics analysis of the RNA-Seq data indicated that pathways involved in protein synthesis [eukaryotic initiation factor (eIF)-2, mammalian target of rapamycin, eIF4, and p70S6K pathways including 40S and 60S ribosomal proteins], protein breakdown (e.g., ubiquitin mediated), and muscle degeneration (apoptosis, atrophy, myopathy, and cell death) were upregulated. Also in agreement with our previous observations, the abundance of mRNAs associated with reduced body size, glycemia, plasma insulin, and lipid signaling pathways was altered in BCATm KO mice. Consistently, genes encoding anaerobic and/or oxidative metabolism of carbohydrate, fatty acids, and branched chain amino acids were modestly but systematically reduced. Although there was no indication that muscle fiber type was different between KO and wild-type mice, a difference in the abundance of mRNAs associated with a muscular dystrophy phenotype was observed, consistent with the published exercise intolerance of these mice. The results suggest transcriptional adaptations occur in BCATm KO mice that along with altered nutrient signaling may contribute to their previously reported protein turnover, metabolic and exercise phenotypes.