Myostatin deficiency is associated with lipidomic abnormalities in skeletal muscles

Exerkines and redox homeostasis

Exercise physiology has gained increasing interest due to its wide effects to promote health. Recent years have seen a growth in this research field also due to the finding of several circulating factors that mediate the effects of exercise. These factors, termed exerkines, are metabolites, growth factors, and cytokines secreted by main metabolic organs during exercise to regulate exercise systemic and tissue-specific effects. The metabolic effects of exerkines have been broadly explored and entail a promising target to modulate beneficial effects of exercise in health and disease. However, exerkines also have broad effects to modulate redox signaling and homeostasis in several cellular processes to improve stress response. Since redox biology is central to exercise physiology, this review summarizes current evidence for the cross-talk between redox biology and exerkines actions. The role of exerkines in redox biology entails a response to oxidative stress-induced pathological cues to improve health outcomes and to modulate exercise adaptations that integrate redox signaling.

Myostatin: a potential therapeutic target for metabolic syndrome

Metabolic syndrome is a complex metabolic disorder, its main clinical manifestations are obesity, hyperglycemia, hypertension and hyperlipidemia. Although metabolic syndrome has been the focus of research in recent decades, it has been proposed that the occurrence and development of metabolic syndrome is related to pathophysiological processes such as insulin resistance, adipose tissue dysfunction and chronic inflammation, but there is still a lack of favorable clinical prevention and treatment measures for metabolic syndrome. Multiple studies have shown that myostatin (MSTN), a member of the TGF-β family, is involved in the development and development of obesity, hyperlipidemia, diabetes, and hypertension (clinical manifestations of metabolic syndrome), and thus may be a potential therapeutic target for metabolic syndrome. In this review, we describe the transcriptional regulation and receptor binding pathway of MSTN, then introduce the role of MSTN in regulating mitochondrial function and autophagy, review the research progress of MSTN in metabolic syndrome. Finally summarize some MSTN inhibitors under clinical trial and proposed the use of MSTN inhibitor as a potential target for the treatment of metabolic syndrome.

Effects of a myostatin mutation in Japanese quail (Coturnix japonica) on the physicochemical and histochemical characteristics of the pectoralis major muscle

The aim of this study was to compare the carcass, meat quality, and histochemical characteristics of pectoralis major (PM) muscle between wild type (WT) and myostatin (Mstn) homozygous mutant (HO) quail lines. The HO quail line exhibited significantly heavier body weight (HO vs. WT, 115.7 g vs. 106.2 g, approximately 110%) and PM muscle weight (HO vs. WT, 18.0 g vs. 15.2 g, approximately 120%) compared to the WT (p < 0.001). However, the two groups had similar traits (pH, redness, yellowness, and drip loss) for meat quality, although slightly higher lightness and cooking loss were observed in the mutant quail (103% and 141%, respectively, p < 0.05). For histochemical traits of PM muscle, Mstn mutant quail exhibited lower type IIA and higher type IIB percentage in the deep region than WT quail (p < 0.05), indicating a fiber conversion from the type IIA to IIB. However, the two quail lines had comparable histochemical traits in the superficial region (p > 0.05). These data suggest that Mstn mutation greatly increases muscle mass without significantly affecting meat quality.

Myostatin Knockout Affects Mitochondrial Function by Inhibiting the AMPK/SIRT1/PGC1α Pathway in Skeletal Muscle

Myostatin (Mstn) is a major negative regulator of skeletal muscle mass and initiates multiple metabolic changes. The deletion of the Mstn gene in mice leads to reduced mitochondrial functions. However, the underlying regulatory mechanisms remain unclear. In this study, we used CRISPR/Cas9 to generate myostatin-knockout (Mstn-KO) mice via pronuclear microinjection. Mstn-KO mice exhibited significantly larger skeletal muscles. Meanwhile, Mstn knockout regulated the organ weights of mice. Moreover, we found that Mstn knockout reduced the basal metabolic rate, muscle adenosine triphosphate (ATP) synthesis, activities of mitochondrial respiration chain complexes, tricarboxylic acid cycle (TCA) cycle, and thermogenesis. Mechanistically, expressions of silent information regulator 1 (SIRT1) and phosphorylated adenosine monophosphate-activated protein kinase (pAMPK) were down-regulated, while peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) acetylation modification increased in the Mstn-KO mice. Skeletal muscle cells from Mstn-KO and WT were treated with AMPK activator 5-aminoimidazole-4-carboxamide riboside (AICAR), and the AMPK inhibitor Compound C, respectively. Compared with the wild-type (WT) group, Compound C treatment further down-regulated the expression or activity of pAMPK, SIRT1, citrate synthase (CS), isocitrate dehydrogenase (ICDHm), and α-ketoglutarate acid dehydrogenase (α-KGDH) in Mstn-KO mice, while Mstn knockout inhibited the AICAR activation effect. Therefore, Mstn knockout affects mitochondrial function by inhibiting the AMPK/SIRT1/PGC1α signaling pathway. The present study reveals a new mechanism for Mstn knockout in regulating energy homeostasis.

Role of fatty acid transport protein 4 in metabolic tissues: insights into obesity and fatty liver disease

Fatty acid (FA) metabolism is a series of processes that provide structural substances, signalling molecules and energy. Ample evidence has shown that FA uptake is mediated by plasma membrane transporters including FA transport proteins (FATPs), caveolin-1, fatty-acid translocase (FAT)/CD36, and fatty-acid binding proteins. Unlike other FA transporters, the functions of FATPs have been controversial because they contain both motifs of FA transport and fatty acyl-CoA synthetase (ACS). The widely distributed FATP4 is not a direct FA transporter but plays a predominant function as an ACS. FATP4 deficiency causes ichthyosis premature syndrome in mice and humans associated with suppression of polar lipids but an increase in neutral lipids including triglycerides (TGs). Such a shift has been extensively characterized in enterocyte-, hepatocyte-, and adipocyte-specific Fatp4-deficient mice. The mutants under obese and non-obese fatty livers induced by different diets persistently show an increase in blood non-esterified free fatty acids and glycerol indicating the lipolysis of TGs. This review also focuses on FATP4 role on regulatory networks and factors that modulate FATP4 expression in metabolic tissues including intestine, liver, muscle, and adipose tissues. Metabolic disorders especially regarding blood lipids by FATP4 deficiency in different cell types are herein discussed. Our results may be applicable to not only patients with FATP4 mutations but also represent a model of dysregulated lipid homeostasis, thus providing mechanistic insights into obesity and development of fatty liver disease.

Myostatin Knockout Regulates Bile Acid Metabolism by Promoting Bile Acid Synthesis in Cattle

Myostatin (MSTN) is a major negative regulator of skeletal muscle mass and causes a variety of metabolic changes. However, the effect of MSTN knockout on bile acid metabolism has rarely been reported. In this study, the physiological and biochemical alterations of serum in MSTN^+/- and wild type (WT) cattle were investigated. There were no significant changes in liver and kidney biochemical indexes. However, compared with the WT cattle, lactate dehydrogenase, total bile acid (TBA), cholesterol, and high-density lipoprotein (HDL) in the MSTN^+/- cattle were significantly increased, and glucose, low-density lipoprotein (LDL), and triglycerides (TG) were significantly decreased, indicating that MSTN knockout affected glucose and lipid metabolism and total bile acids content. Targeted metabolomic analysis of the bile acids and their derivatives was performed on serum samples and found that bile acids were significantly increased in the MSTN^+/- cattle compared with the WT cattle. As the only bile acid synthesis organ in the body, we performed metabolomic analysis on the liver to study the effect of MSTN knockout on hepatic metabolism. Metabolic pathway enrichment analysis of differential metabolites showed significant enrichment of the primary bile acid biosynthesis and bile secretion pathway in the MSTN^+/- cattle. Targeted metabolomics data further showed that MSTN knockout significantly increased bile acid content in the liver, which may have resulted from enhanced bile acid synthesis due to the expression of bile acid synthesis genes, cholesterol 7 alpha-hydroxylase (CYP7A1) and sterol 27-hydroxylase (CYP27A1), and upregulation in the liver of the MSTN^+/- cattle. These results indicate that MSTN knockout does not adversely affect bovine fitness but regulates bile acid metabolism via enhanced bile acid synthesis. This further suggests a role of MSTN in regulating metabolism.

Regulatory Role and Potential Importance of GDF-8 in Ovarian Reproductive Activity

Growth differentiation factor-8 (GDF-8) is a member of the transforming growth factor-beta superfamily. Studies in vitro and in vivo have shown GDF-8 to be involved in the physiology and pathology of ovarian reproductive functions. In vitro experiments using a granulosa-cell model have demonstrated steroidogenesis, gonadotrophin responsiveness, glucose metabolism, cell proliferation as well as expression of lysyl oxidase and pentraxin 3 to be regulated by GDF-8 via the mothers against decapentaplegic homolog signaling pathway. Clinical data have shown that GDF-8 is expressed widely in the human ovary and has high expression in serum of obese women with polycystic ovary syndrome. GDF-8 expression in serum changes dynamically in patients undergoing controlled ovarian hyperstimulation. GDF-8 expression in serum and follicular fluid is correlated with the ovarian response and pregnancy outcome during in vitro fertilization. Blocking the GDF-8 signaling pathway is a potential therapeutic for ovarian hyperstimulation syndrome and ovulation disorders in polycystic ovary syndrome. GDF-8 has a regulatory role and potential importance in ovarian reproductive activity and may be involved in folliculogenesis, ovulation, and early embryo implantation.

Electric pulse stimulation inhibited lipid accumulation on C2C12 myotubes incubated with oleic acid and palmitic acid

OBJECTIVE

To investigate the effect of electrical pulse stimulation (EPS) on lipid accumulation and alteration of fatty acid-related enzymes in C2C12 myotubes incubated with fatty acids.

METHODS

Mouse C2C12 myotubes were incubated with oleic acid and palmitic acid, and differentiated C2C12 myotubes were treated with EPS, oil-red O (ORO), BODIPY staining and triglyceride (TG) content were examined. Total RNA was isolated, and real-time polymerase chain reaction analysis was performed.

RESULTS

(1) EPS decreased TG content (p < .01). (2) EPS significantly induced the mRNA expression of FAD/CD36 (p < .05), FATP4 (p < .001), FABP1 (p < .01) and FABP5 (p < .01). (3) EPS significantly inhibited the mRNA expression of fatty acid synthase (p < .01). (4) Adipose triglyceride lipase and hormone-sensitive lipase expression were significantly elevated (p < .001), and induced the mRNA expression of CPT1 (p < .01), ACOX1 (p < .05), UCP3 (p < .05) and PPARα (p < .001) after EPS.

CONCLUSION

EPS reduced lipid droplet accumulation; enhanced CD36, FATP4, FABP1 and FABP5 expression; inhibited C2C12 myotube fatty acid re-esterification; and promoted fatty acid oxidation in C2C12 myotubes.

Myostatin Deficiency Protects C2C12 Cells from Oxidative Stress by Inhibiting Intrinsic Activation of Apoptosis

Ischemia reperfusion (IR) injury remains an important topic in clinical medicine. While a multitude of prophylactic and therapeutic strategies have been proposed, recent studies have illuminated protective effects of myostatin inhibition. This study aims to elaborate on the intracellular pathways involved in myostatin signaling and to explore key proteins that convey protective effects in IR injury. We used CRISPR/Cas9 gene editing to introduce a myostatin (Mstn) deletion into a C2C12 cell line. In subsequent experiments, we evaluated overall cell death, activation of apoptotic pathways, ROS generation, lipid peroxidation, intracellular signaling via mitogen-activated protein kinases (MAPKs), cell migration, and cell proliferation under hypoxic conditions followed by reoxygenation to simulate an IR situation in vitro (hypoxia reoxygenation). It was found that mitogen-activated protein kinase kinase 3/6, also known as MAPK/ERK Kinase 3/6 (MEK3/6), and subsequent p38 MAPK activation were blunted in C2C12-Mstn^−/− cells in response to hypoxia reoxygenation (HR). Similarly, c-Jun N-terminal kinase (JNK) activation was negated. We also found the intrinsic activation of apoptosis to be more important in comparison with the extrinsic activation. Additionally, intercepting myostatin signaling mitigated apoptosis activation. Ultimately, this research validated protective effects of myostatin inhibition in HR and identified potential mediators worth further investigation. Intercepting myostatin signaling did not inhibit ROS generation overall but mitigated cellular injury. In particular, intrinsic activation of apoptosis origination from mitochondria was alleviated. This was presumably mediated by decreased activation of p38 caused by the diminished kinase activity increase of MEK3/6. Overall, this work provides important insights into HR signaling in C2C12-Mstn^−/− cells and could serve as basis for further research.

The Failed Clinical Story of Myostatin Inhibitors against Duchenne Muscular Dystrophy: Exploring the Biology behind the Battle

Myostatin inhibition therapy has held much promise for the treatment of muscle wasting disorders. This is particularly true for the fatal myopathy, Duchenne Muscular Dystrophy (DMD). Following on from promising pre-clinical data in dystrophin-deficient mice and dogs, several clinical trials were initiated in DMD patients using different modality myostatin inhibition therapies. All failed to show modification of disease course as dictated by the primary and secondary outcome measures selected: the myostatin inhibition story, thus far, is a failed clinical story. These trials have recently been extensively reviewed and reasons why pre-clinical data collected in animal models have failed to translate into clinical benefit to patients have been purported. However, the biological mechanisms underlying translational failure need to be examined to ensure future myostatin inhibitor development endeavors do not meet with the same fate. Here, we explore the biology which could explain the failed translation of myostatin inhibitors in the treatment of DMD.

Reproduction traits of heterozygous myostatin knockout sows crossbred with homozygous myostatin knockout boars

Few studies exist on homozygous myostatin gene mutant (MSTN^-/- ) pigs, especially on their reproductive ability. We have previously shown that semen quality of homozygous MSTN^-/- boars is comparable to that of wild type (WT). However, no data exist on the reproductive ability of heterozygous MSTN gene mutant (MSTN^{+/ -} ) sows. The present study highlights showed that the heterozygous MSTN^{+/ -} sows have delayed pubertal age than WT sows (255.80 ± 6.79 versus 191.10 ± 3.42, respectively). The number of services per pregnancy of heterozygous MSTN^{+/ -} sows is significantly higher than that of WT sows (3.33 ± 0.43 versus 1.60 ± 0.25, respectively). Moreover, although heterozygous MSTN^{+/ -} sows have natural reproduction ability, their litter size was significantly lower than that of WT sows (7.75 ± 0.44 versus 14.25 ± 0.60, respectively). Offsprings generated from heterozygous MSTN^{+/ -} sow and homozygous MSTN^-/- boar were genotyped with the PCR and sequencing method to detect myostatin mutation and to identify whether the piglets are homozygous MSTN^-/- or heterozygous MSTN^{+/ -} . The proportion of homozygous MSTN^-/- piglets was significantly lower than that of heterozygous MSTN^{+/ -} piglets (2.50 ± 0.35 versus 5.25 ± 0.60, respectively). Furthermore, none of the sows presented dystocia, and the phenotype of heterozygous MSTN^{+/ -} piglets was normal. However, 10% homozygous MSTN^-/- piglets died of dyspnoea within 2 hr after birth, 60% of homozygous MSTN^-/- piglets showed large tongues, and 50% had umbilical hernias. In summary, this study for the first time reports the reproduction traits of heterozygous MSTN^{+/ -} sows crossbred with homozygous MSTN^-/- boars. This study will pave the way in a new direction for the breeding and development of super lean meat varieties in the future.

Net protein balance correlates with expression of autophagy, mitochondrial biogenesis, and fat metabolism-related genes in skeletal muscle from older adults

The mechanisms leading to sarcopenia, the main cause for frailty in older adults, are still unclear. Autophagy and the ubiquitin-proteasome system (UPS) may play a role in mediating muscle protein breakdown related to sarcopenia. In addition to loss of muscle mass, compromised muscle performance observed in sarcopenic patients has been linked to muscle mitochondria dysfunction. Increased fat deposition and fat cell infiltration in muscle frequently seen in skeletal muscle of older adults may play an additional role for the pathogenesis of sarcopenia. Therefore, the first objective of this study was to understand differences in expression of genes related to autophagy, UPS, mitochondrial biogenesis, and fat metabolism in skeletal muscle of older adults compared with young adults. Our second objective was to determine the correlation between whole body protein kinetics (WBPK) and gene expression with age. Real-time quantitative PCR was used to determine the relative expression of targeted genes, and hierarchical regression analysis was used to determine if age had a moderating effect on the correlation between expression of targeted genes and WBPK. Increases in the expression of autophagy-related genes and fat metabolism-related genes were observed in muscle of older adults compared with young adults. In addition, age enhanced the negative correlations between mitochondrial biogenesis genes and net protein balance. These results suggest that dysregulated gene expression of mitochondrial biogenesis could play a role in muscle loss in older adults.

A comparison of the mitochondrial proteome and lipidome in the mouse and long-lived Pipistrelle bats

It is accepted that smaller mammals with higher metabolic rates have shorter lifespans. The very few species that do not follow these rules can give insights into interesting differences. The recorded maximum lifespans of bats are exceptional - over 40 years, compared with the laboratory mouse of 4 years. We investigated the differences in the biochemical composition of mitochondria between bat and mouse species. We used proteomics and ultra-high-performance liquid chromatography coupled with high resolution mass spectrometry lipidomics, to interrogate mitochondrial fractions prepared from Mus musculus and Pipistrellus pipistrellus brain and skeletal muscle. Fatty acid binding protein 3 was found at different levels in mouse and bat muscle mitochondria and its orthologues were investigated in Caenorhabditis elegans knock-downs for LBP 4, 5 and 6. In the bat, high levels of free fatty acids and N-acylethanolamine lipid species together with a significantly greater abundance of fatty acid binding protein 3 in muscle (1.8-fold, p=0.037) were found. Manipulation of fatty acid binding protein orthologues in C. elegans suggest these proteins and their role in lipid regulation are important for mitochondrial function.

New evidence of exercise training benefits in myostatin-deficient mice: Effect on lipidomic abnormalities

Myostatin (Mstn) inactivation or inhibition is considered as a promising treatment for various muscle-wasting disorders because it promotes muscle growth. However, myostatin-deficient hypertrophic muscles show strong fatigability associated with abnormal mitochondria and lipid metabolism. Here, we investigated whether endurance training could improve lipid metabolism and mitochondrial membrane lipid composition in mice where the Mstn gene was genetically ablated (Mstn^-/- mice). In Mstn^-/- mice, 4 weeks of daily running exercise sessions (65-70% of the maximal aerobic speed for 1 h) improved significantly aerobic performance, particularly the endurance capacity (up to +280% compared with untrained Mstn^-/- mice), to levels comparable to those of trained wild type (WT) littermates. The expression of oxidative and lipid metabolism markers also was increased, as indicated by the upregulation of the Cpt1, Ppar-δ and Fasn genes. Moreover, endurance training also increased, but far less than WT, citrate synthase level and mitochondrial protein content. Interestingly endurance training normalized the cardiolipin fraction in the mitochondrial membrane of Mstn^-/- muscle compared with WT. These results suggest that the combination of myostatin inhibition and endurance training could increase the muscle mass while preserving the physical performance with specific effects on cardiolipin and lipid-related pathways.

Predictive value of serum myostatin for the severity and clinical outcome of heart failure

BACKGROUND

The exact relationship between serum myostatin and the severity and prognosis of chronic heart failure (CHF) is unclear. In this study, we investigated the association between serum myostatin and the severity and prognosis in patients with CHF.

METHODS

Two hundred and eighty-eight CHF patients and 62 healthy controls were studied. Cardiac ultrasound and serum myostatin, N-terminal pro-B-type natriuretic peptide (NT-proBNP) and other parameters were detected. CHF patients were divided into 3 groups according to tertiles of NT-proBNP or myostatin levels respectively.

RESULTS

Serum myostatin levels were higher in CHF patients than in controls. New York Heart Association (NYHA) class IV patients had the highest levels of serum myostatin among the four NYHA classes. Compared with the low tertile NT-proBNP group, serum myostatin levels were significantly higher in the moderate and high tertile groups (15.47 ± 4.25 vs. 14.18 ± 3.69 ng/mL, p = .026; 16.28 ± 5.34 vs. 14.18 ± 3.69 ng/mL, p = .002). During 51-months follow-up, of 173 patients there were 36 deaths. Compared to survivors, nonsurvivors had significantly higher serum myostatin (18.11 ± 4.52 vs. 14.85 ± 5.11 ng/mL, p < .01). Patients in the high tertile myostatin group had lower survival rate (73.95% vs. 93.75%; p < .05) and larger number of CHF rehospitalization than those in the low tertile group. Cox regression analysis showed that serum myostatin was an independent predictor of mortality.

CONCLUSIONS

Serum myostatin levels can reflect the severity of CHF and be a predictor of adverse prognosis in CHF patients.

Inefficient ATP synthesis by inhibiting mitochondrial respiration causes lipids to decrease in MSTN-lacking muscles of loach Misgurnus anguillicaudatus

Myostatin (MSTN) lacking could lead to enhanced muscle growth and lipid metabolism disorder in animals. Plenty of researches have been performed to warrant a better understanding of the mechanisms underlying the enhanced muscle growth; however, mechanisms for lipid metabolic changes are poorly understood. In this study, MSTN-depletion loaches Misgurnus anguillicaudatus (MU for short) were firstly generated by CRISPR/Cas9 technique. Based on histological observation, we found that skeletal muscle fat accumulation in MU sharply reduced compared with wild-type loaches (WT for short). To further investigate the fat change, muscle lipidomic analysis was performed. There were no significant differences in three membrane phospholipid contents between WT and MU. The contents of six other major lipid species in MU muscles were all significantly lower than those in WT muscles, indicating that MSTN deficiency could obviously decrease muscle lipid production in the loach. Meanwhile, it was also supported by results of three lipogenesis-related genes' expressions. And then combined with muscle ATP determination and gene expression profiles of the five mitochondrial respiration chain complexes, we speculated that MSTN lacking may cause the weak of mitochondrial respiration functions in the loach muscles, leading to ATP synthesis decreasing and finally reducing the production of lipids.

Vascular endothelial growth factor B inhibits lipid accumulation in C2C12 myotubes incubated with fatty acids

To investigate (1) the effect of vascular endothelial growth factor B (VEGFB) on lipid accumulation and the alteration of fatty acids and fatty acid-related enzymes in C2C12 myotubes incubated with fatty acids and (2) the regulatory effect of VEGFB on skeletal muscle lipid metabolism. Mouse C2C12 myotubes were incubated with oleic acid (OA) and palmitic acid (PA), and differentiated mature C2C12 myotubes were treated with VEGFB. Oil-red O staining, BODIPY staining and cell triglycerides (TG) content were examined. Total RNA was isolated, and real-time PCR analysis was performed. Treatment with 100 μM OA and 50 μM PA induced lipid droplet accumulation and increased TG content (p < .01), and 100 ng/mL VEGFB reduced lipid droplet accumulation and decreased TG content (p < .01). Treatment with 100 ng/mL VEGFB significantly induced the mRNA expression of fatty acid transport protein 1 (FATP1) (p < .01) and FATP4 (p < .01). Treatment with 100 ng/mL VEGFB significantly induced the mRNA expression of adipose TG lipase and hormone-sensitive lipase (p < .01) as well as carnitine palmitoyltransferase I (p < .01), peroxisome proliferator-activated receptor-γ coactivator-1α (p < .01), acyl-coa dehydrogenase very long chain (p < .05), acyl-coa synthetase long-chain family member 1 (p < .01), peroxisomal acyl-coenzyme A oxidase 1 (p < .05), and mitochondrial uncoupling protein 3 (p < .01). VEGFB enhanced FATP1and FATP4 expression, promoted C2C12 myotube fatty acid oxidation and TG decomposition, and inhibited C2C12 myotube fatty acid re-esterification, thus inhibiting lipid accumulation in C2C12 myotubes incubated with fatty acids.

Genomic Analysis To Identify Signatures of Artificial Selection and Loci Associated with Important Economic Traits in Duroc Pigs

Identifying genetic basis of domestication and improvement in livestock contributes to our understanding of the role of artificial selection in shaping the genome. Here we used whole-genome sequencing and the genotyping by sequencing approach to detect artificial selection signatures and identify the associated SNPs of two economic traits in Duroc pigs. A total of 38 candidate selection regions were detected by combining the fixation index and the Composite Likelihood Ratio methods. Further genome-wide association study revealed seven associated SNPs that were related with intramuscular fat content and feed conversion ratio traits, respectively. Enrichment analysis suggested that the artificial selection regions harbored genes, such as MSTN, SOD2, MC5R and CD83, which are responsible for economic traits including lean muscle mass, fertility and immunization. Overall, this study found a series of candidate genes putatively associated with the breeding improvement of Duroc pigs and the polygenic basis of adaptive evolution, which can provide important references and fundamental information for future breeding programs.

Transcriptomic analyses reveal rhythmic and CLOCK-driven pathways in human skeletal muscle

Circadian regulation of transcriptional processes has a broad impact on cell metabolism. Here, we compared the diurnal transcriptome of human skeletal muscle conducted on serial muscle biopsies in vivo with profiles of human skeletal myotubes synchronized in vitro. More extensive rhythmic transcription was observed in human skeletal muscle compared to in vitro cell culture as a large part of the in vivo mRNA rhythmicity was lost in vitro. siRNA-mediated clock disruption in primary myotubes significantly affected the expression of ~8% of all genes, with impact on glucose homeostasis and lipid metabolism. Genes involved in GLUT4 expression, translocation and recycling were negatively affected, whereas lipid metabolic genes were altered to promote activation of lipid utilization. Moreover, basal and insulin-stimulated glucose uptake were significantly reduced upon CLOCK depletion. Our findings suggest an essential role for the circadian coordination of skeletal muscle glucose homeostasis and lipid metabolism in humans.

Skeletal muscle expression of p43, a truncated thyroid hormone receptor α, affects lipid composition and metabolism

Thyroid hormone is a major regulator of metabolism and mitochondrial function. Thyroid hormone also affects reactions in almost all pathways of lipids metabolism and as such is considered as the main hormonal regulator of lipid biogenesis. The aim of this study was to explore the possible involvement of p43, a 43 Kda truncated form of the nuclear thyroid hormone receptor TRα1 which stimulates mitochondrial activity. Therefore, using mouse models overexpressing p43 in skeletal muscle (p43-Tg) or lacking p43 (p43-/-), we have investigated the lipid composition in quadriceps muscle and in mitochondria. Here, we reported in the quadriceps muscle of p43-/- mice, a fall in triglycerides, an inhibition of monounsaturated fatty acids (MUFA) synthesis, an increase in elongase index and an decrease in desaturase index. However, in mitochondria from p43-/- mice, fatty acid profile was barely modified. In the quadriceps muscle of p43-Tg mice, MUFA content was decreased whereas the unsaturation index was increased. In addition, in quadriceps mitochondria of p43-Tg mice, we found an increase of linoleic acid level and unsaturation index. Last, we showed that cardiolipin content, a key phospholipid for mitochondrial function, remained unchanged both in quadriceps muscle and in its mitochondria whatever the mice genotype. In conclusion, this study shows that muscle lipid content and fatty acid profile are strongly affected in skeletal muscle by p43 levels. We also demonstrate that regulation of cardiolipin biosynthesis by the thyroid hormone does not imply p43.