Skeletal Muscle Transcription Research Articles

AMPK-mediated regulation of transcription in skeletal muscle

Skeletal muscle phenotype plays a critical role in human performance and health, and skeletal muscle oxidative capacity is a key determinant of exercise tolerance. More recently, defective muscle oxidative metabolism has been implicated in a number of conditions associated with the metabolic syndrome, cardiovascular disease and muscle-wasting disorders. AMPK (AMP-activated protein kinase) is a critical regulator of cellular and organismal energy balance. AMPK has also emerged as a key regulator of skeletal muscle oxidative function, including metabolic enzyme expression, mitochondrial biogenesis and angiogenesis. AMPK mediates these processes primarily through alterations in gene expression. The present review examines the role of AMPK in skeletal muscle transcription and provides an overview of the known transcriptional substrates mediating the effects of AMPK on skeletal muscle phenotype.

Acute Inhibition of Fatty Acid Import Inhibits GLUT4 Transcription in Adipose Tissue, but Not Skeletal or Cardiac Muscle Tissue, Partly Through Liver X Receptor (LXR) Signaling

OBJECTIVEInsulin-mediated glucose uptake is highly sensitive to the levels of the facilitative GLUT protein GLUT4. Transcription of the GLUT4 gene is repressed in states of insulin deficiency and insulin resistance and can be induced by states of enhanced energy output, such as exercise. The cellular signals that regulate GLUT4 transcription are not well understood. We hypothesized that changes in energy substrate flux regulate GLUT4 transcription.RESEARCH DESIGN AND METHODSTo test this hypothesis, we used transgenic mice in which expression of the chloramphenicol acetyltransferase (CAT) gene is driven by a functional 895-bp fragment of the human GLUT4 promoter, thereby acting as a reporter for transcriptional activity. Mice were treated with a single dose of etomoxir, which inhibits the transport of long-chain fatty acids into mitochondria and increases basal, but not insulin-mediated, glucose flux. GLUT4 and transgenic CAT mRNA were measured.RESULTSEtomoxir treatment significantly reduced CAT and GLUT4 mRNA transcription in adipose tissue, but did not change transcription in heart and skeletal muscle. Downregulation of GLUT4 transcription was cell autonomous, since etomoxir treatment of 3T3-L1 adipocytes resulted in a similar downregulation of GLUT4 mRNA. GLUT4 transcriptional downregulation required the putative liver X receptor (LXR) binding site in the human GLUT4 gene promoter in adipose tissue and 3T3-L1 adipocytes. Treatment of 3T3-L1 adipocytes with the LXR agonist, TO901317, partially restored GLUT4 expression in etomoxir-treated cells.CONCLUSIONSOur data suggest that long-chain fatty acid import into mitochondria in adipose tissue may produce ligands that regulate expression of metabolic genes.

Calcineurin activates interleukin-6 transcription in mouse skeletal muscle in vivo and in C2C12 myotubes in vitro.

Expression of the cytokine interleukin-6 (IL-6) by skeletal muscle is hugely increased in response to a single bout of endurance exercise, and this appears to be mediated by increases in intracellular calcium. We examined the effects of endurance exercise on IL-6 mRNA levels and promoter activity in skeletal muscle in vivo, and the role of the calcium-activated calcineurin signaling pathway on muscle IL-6 expression in vivo and in vitro. IL-6 mRNA levels in the mouse tibialis anterior (TA) were increased 2-10-fold by a single bout of treadmill exercise or by 3 days of voluntary wheel running. Moreover, an IL-6 promoter-driven luciferase transgene was activated in TA by both treadmill and wheel-running exercise and by injection with a calcineurin plasmid. Exercise also increased muscle mRNA expression of the calcineurin regulatory gene MCIP1, as did treatment of C(2)C(12) myotubes with the calcium ionophore A23187. Cotransfection of C(2)C(12) myotubes with a constitutively active calcineurin construct significantly increased while cotransfection with the calcineurin inhibitor CAIN inhibited activity of a mouse IL-6 promoter-reporter construct. Cotransfection with a myocyte enhancer-factor-2 (MEF-2) expression construct increased basal IL-6 promoter activity and augmented the effects of calcineurin cotransfection, while cotransfection with the MEF-2 antagonist MITR repressed calcineurin-activated IL-6 promoter activity in vitro. Surprisingly, cotransfection with a dominant-negative form of another calcineurin-activated transcription factor, nuclear factor activator of T cells (NFAT), greatly potentiated both basal and calcineurin-stimulated IL-6 promoter activity in C(2)C(12) myotubes. Mutation of the MEF-2 DNA binding sites attenuated, while mutation of the NFAT DNA binding sites potentiated basal and calcineurin-activated IL-6 promoter activity. Finally, CREB and C/EBP were necessary for basal IL-6 promoter activity and sufficient to increase IL-6 promoter activity but had minimal roles in calcineurin-activated IL-6 promoter activity. Together, these results suggest that IL-6 transcription in skeletal muscle cells can be activated by a calcineurin-MEF-2 axis which is antagonized by NFAT.

Gene Expression Profile of Human Skeletal Muscle and Adipose Tissue of Chinese Han Patients with Type 2 Diabetes Mellitus

To study the differential patterns of gene expression in skeletal muscle and adipose tissue between type 2 diabetes mellitus (T2DM) patients and healthy subjects using DNA microarray analysis. T2DM patiens were divided into female group, young male group and old male group. DNA microarray analysis and quantitative real-time PCR were carried out to analyze the relation between gene expressions and T2DM. The mRNA expression of 298, 578, and 350 genes was changed in the skeletal muscle of diabetes mellitus patients compared with control subjects. The 1320, 1143, and 2847 genes were modified in adipose tissue of the three groups. Among the genes surveyed, the change of 25 and 39 gene transcripts in skeletal muscle and adipose tissue was > or = 2 folds. These differentially expressed genes were classified into 15 categories according to their functions. New genes are found and T2DM can be prevented or cured.

Expression profiling of skeletal muscle following acute and chronic β2-adrenergic stimulation: implications for hypertrophy, metabolism and circadian rhythm

BackgroundSystemic administration of β-adrenoceptor (β-AR) agonists has been found to induce skeletal muscle hypertrophy and significant metabolic changes. In the context of energy homeostasis, the importance of β-AR signaling has been highlighted by the inability of β1-3-AR-deficient mice to regulate energy expenditure and susceptibility to diet induced obesity. However, the molecular pathways and gene expression changes that initiate and maintain these phenotypic modulations are poorly understood. Therefore, the aim of this study was to identify differential changes in gene expression in murine skeletal muscle associated with systemic (acute and chronic) administration of the β2-AR agonist formoterol.ResultsSkeletal muscle gene expression (from murine tibialis anterior) was profiled at both 1 and 4 hours following systemic administration of the β2-AR agonist formoterol, using Illumina 46K mouse BeadArrays. Illumina expression profiling revealed significant expression changes in genes associated with skeletal muscle hypertrophy, myoblast differentiation, metabolism, circadian rhythm, transcription, histones, and oxidative stress. Differentially expressed genes relevant to the regulation of muscle mass and metabolism (in the context of the hypertrophic phenotype) were further validated by quantitative RT-PCR to examine gene expression in response to both acute (1-24 h) and chronic administration (1-28 days) of formoterol at multiple timepoints. In terms of skeletal muscle hypertrophy, attenuation of myostatin signaling (including differential expression of myostatin, activin receptor IIB, phospho-Smad3 etc) was observed following acute and chronic administration of formoterol. Acute (but not chronic) administration of formoterol also significantly induced the expression of genes involved in oxidative metabolism, including hexokinase 2, sorbin and SH3 domain containing 1, and uncoupling protein 3. Interestingly, formoterol administration also appeared to influence some genes associated with the peripheral regulation of circadian rhythm (including nuclear factor interleukin 3 regulated, D site albumin promoter binding protein, and cryptochrome 2).ConclusionThis is the first study to utilize gene expression profiling to examine global gene expression in response to acute β2-AR agonist treatment of skeletal muscle. In summary, systemic administration of a β2-AR agonist had a profound effect on global gene expression in skeletal muscle. In terms of hypertrophy, β2-AR agonist treatment altered the expression of several genes associated with myostatin signaling, a previously unreported effect of β-AR signaling in skeletal muscle. This study also demonstrates a β2-AR agonist regulation of circadian rhythm genes, indicating crosstalk between β-AR signaling and circadian cycling in skeletal muscle. Gene expression alterations discovered in this study provides insight into many of the underlying changes in gene expression that mediate β-AR induced skeletal muscle hypertrophy and altered metabolism.

Multiple signalling pathways redundantly control glucose transporter GLUT4 gene transcription in skeletal muscle

Increased glucose transporter GLUT4 expression in skeletal muscle is an important benefit of regular exercise, resulting in improved insulin sensitivity and glucose tolerance. The Ca(2+)-calmodulin-dependent kinase II (CaMKII), calcineurin and AMPK pathways have been implicated in GLUT4 gene regulation based on pharmacological evidence. Here, we have used a more specific genetic approach to establish the relative role of the three pathways in fast and slow muscles. Plasmids coding for protein inhibitors of CaMKII or calcineurin were co-transfected in vivo with a GLUT4 enhancer-reporter construct either in normal mice or in mice expressing a kinase dead (KD) AMPK mutant. GLUT4 reporter activity was not inhibited in the slow soleus muscle by blocking either CaMKII or calcineurin alone, but was inhibited by blocking both pathways. GLUT4 reporter activity was likewise unchanged in the soleus of KD-AMPK mice, but was significantly reduced by incapacitation of either CaMKII or calcineurin in these mice. On the other hand, in the fast tibialis anterior (TA) muscle, calcineurin appears to exert a prominent role in the control of GLUT4 reporter activity, independent of CaMKII and AMPK. The results point to a muscle type-specific and redundant regulation of GLUT4 enhancer based on the interplay of multiple signalling pathways, all of which are known to affect myocyte enhancing factor 2 (MEF2) transcriptional activity, a point of convergence of different pathways on muscle gene regulation.

Exercise capacity in chronic heart failure patients is related to active gene transcription in skeletal muscle and not apoptosis

Muscle wasting partly explains exercise intolerance in chronic heart failure (CHF) patients. Skeletal muscle loss may result from apoptosis, and exercise training has been suggested to halt this process. The terminal deoxynucleotidyl transferase end-labeling (TUNEL) technique is frequently used to show apoptosis, but lacks specificity. Before and after 4 months exercise training, skeletal muscle biopsies of 16 CHF patients (59.4+/-2.2 years, 11 men, 50% ischemic etiology, ejection fraction 28.8+/-2.7%, 66.3+/-3.6% of predicted oxygen uptake) and eight sedentary controls were analyzed for apoptosis (TUNEL, including the stringent variant without proteinase K digestion, immunohistochemical analyses using antibodies against cleaved caspase-3 and cleaved poly(ADP-ribose) polymerase, PARP, and active gene transcription (anti-splicing factor SC-35). The number of TUNEL-positive nuclei in CHF patients was comparable with controls (3.2+/-0.7 vs. 3.1+/-1.7/mm(2), P=0.2) and was not related to exercise parameters. With the stringent TUNEL and both immunostaining techniques, apoptosis was not detected. Co-occurrence of TUNEL and of SC-35 splicing factor suggests that at least part of TUNEL-positive nuclei is undergoing active gene transcription and therefore is not apoptotic. The SC-35-positive area correlated with % of predicted oxygen uptake (r=0.6, P=0.02), Wattmax (r=0.7, P=0.005) and VE/VCO2 slope (r=-0.6, P=0.03). At baseline, SC-35 immunoreactive area was significantly larger than in controls (P=0.001), but after exercise training, the difference was minimized (P=0.07). Skeletal muscle apoptosis in CHF patients could not be confirmed. Active gene transcription might stain false positive for apoptotic nuclei with TUNEL. The level of active gene transcription/splicing was related to exercise performance.

Exercise, PGC-1α, and metabolic adaptation in skeletal muscleThis paper article is one of a selection of papers published in this Special Issue, entitled 14th International Biochemistry of Exercise Conference – Muscles as Molecular and Metabolic Machines, and has undergone the Journal’s usual peer review process.

Endurance exercise promotes skeletal muscle adaptation, and exercise-induced peroxisome proliferator-activated receptor gamma coactivator-1alpha (Pgc-1alpha) gene expression may play a pivotal role in the adaptive processes. Recent applications of mouse genetic models and in vivo imaging in exercise studies have started to delineate the signaling-transcription pathways that are involved in the regulation of the Pgc-1alpha gene. These studies revealed the importance of p38 mitogen-activated protein kinase/activating transcription factor 2 and protein kinase D/histone deacetylase 5 signaling transcription axes in exercise-induced Pgc-1alpha transcription and metabolic adaptation in skeletal muscle. The signaling-transcription network that is responsible for exercise-induced skeletal muscle adaption remains to be fully elucidated.

Transcription of the human uncoupling protein 3 gene is governed by a complex interplay between the promoter and intronic sequences

Uncoupling protein (UCP) 3 is an inner mitochondrial membrane transporter mainly produced in skeletal muscle in humans. UCP3 plays a role in fatty acid metabolism and energy homeostasis and modulates insulin sensitivity. In humans, UCP3 content is higher in fast-twitch glycolytic muscle than in slow-twitch oxidative muscle and is dysregulated in type 2 diabetes. Here, we studied the molecular mechanisms determining human UCP3 levels in skeletal muscle and their regulation by fasting in transgenic mice. We produced a series of transgenic lines with constructs bearing different putative regulatory regions of the human UCP3 gene, including promoter and intron sequences. UCP3 mRNA and reporter gene expression and activity were measured in different skeletal muscles and tissues. The profile of expression and the response to fasting and thyroid hormone of human UCP3 mRNA in transgenic mice with 16 kb of the human UCP3 gene were similar to that of the endogenous human gene. Various parts of the UCP3 promoter did not confer expression in transgenic lines. Inclusion of intron 1 resulted in an expression profile in skeletal muscle that was identical to that of human UCP3 mRNA. Further dissection of intron 1 revealed that distinct regions were involved in skeletal muscle expression, distribution among fibre types and response to fasting. The control of human UCP3 transcription in skeletal muscle is not solely conferred by the promoter, but depends on several cis-acting elements in intron 1, suggesting a complex interplay between the promoter and intronic sequences.

Resistance Exercise Produces A Metabolic Gene Expression Signature Similar To Endurance Exercise

Resistance training (RT) has been proposed as a beneficial intervention modality for patients with metabolic syndrome and type II diabetes because of increasing evidence that similar metabolic benefits may be achieved with RT as with endurance training. Much of the improvements resulted from exercise training are associated with transient modifications in skeletal muscle induced by an acute bout of exercise. PURPOSE: to examine the transcriptional regulation of metabolic genes in skeletal muscle induced by an acute bout of resistance exercise (RE). METHODS: Subjects (11 female and 12 male, 18 to 40 y) trained the non-dominant elbow flexors for 12 weeks resulting in a 14.2 +/- 6.2 % increase in muscle volume and a 59.7 +/- 20.4% increase in 1RM strength. Six days after the last exercise session, an acute bout of RE was performed and bilateral biopsies were taken 4 hr post-exercise from both the trained and the untrained arms. RNA was extracted and prepared for expression profiling using the Affymetrix Human Genome U133 Plus 2 chips. Absolute expression values were calculated using MAS.5 and dChip and analysis was carried out using Gene Spring. RESULTS: RE induced augmented mRNA levels of regulators implicated in 1) mitochondrial biogenesis including PGC1-a (↑2.88, p=0.0015), SIRT1(↑1.25, p=0.0152) and PRKAG2 (↑4.80, p=0.0009); 2) insulin signaling including IRS2 (↑3.42, p=0.0010), RRAD (↑5.01, p=0.0007) and NR4A1 (↑4.48, p=0.0020); and 3) capillary biogenesis including VEGF (↑1.85, p=0.0027), HIF1A (↑1.67, p=0.0004) and CYR61 (↑3.02, p=0.0045). Transcriptional modification of key lipid metabolism genes favored fatty acid repartitioning towards esterification with mRNA levels for LPL and CPT1B being decreased (LPL, ↓1.71 fold, p=0.0001; CPT1B, ↓1.42 fold, p=0.0246), and for FABPs being increased (FABP4, ↑1.56 fold, p=0.0003; FABP5, ↑1.50, p=0.0065). CONCLUSION: Similar to endurance exercise, acute RE exhibits favorable regulation of metabolic gene transcription in skeletal muscle, implying, in part, an explanation for the beneficial role of resistance training in treating metabolic disturbances.

Blueberry‐Enriched Diets Reduce Metabolic Syndrome and Insulin Resistance in Rats

Several studies suggest that anthocyanin intake could modify risk factors for metabolic syndrome. Blueberries are a rich, whole‐food source of anthocyanins. We tested the effect of a semi‐purified diet with added whole blueberry powder (2% w:w) or a carbohydrate‐matched control diet on factors of metabolic syndrome in the obesity‐prone Zucker Fatty rat, fed either a low fat (10% fat) diet or a high fat (45% fat) diet. After 90 days, both the low fat blueberry (LFB) and high fat blueberry (HFB) groups had reduced abdominal fat compared to controls, and the LFB group had reduced body weight and % fat mass. Both LFB and HFB groups had significantly reduced triglycerides, total cholesterol, fasting insulin, and fasting glucose. LFB and HFB also had improved glucose clearance, as measured by a glucose tolerance test. Given the improved glucose control, we then measured mRNA transcripts in skeletal muscle and retroperitoneal fat related to glucose and lipid uptake and metabolism by PCR Array. The results suggest that regular intake of blueberry reduced several key risk factors for cardiovascular disease and metabolic syndrome. Furthermore, these benefits were augmented when fed a low fat diet. Finally, blueberry diet conferred tissue changes in several genes related to lipid and glucose metabolism, which could support the in vivo results of greater insulin sensitivity and reduced fat accumulation.

Reprogramming to a muscle fate by fusion recapitulates differentiation

Fusion of mammalian cells to form stable, non-dividing heterokaryons results in nuclear reprogramming without the exchange of genetic material. In this report, we show that reprogramming in somatic cell heterokaryons involves activation of the canonical skeletal muscle transcription factors as well as contraction-excitation genes. Thus, the effect of heterokaryon formation on gene expression is to induce a recapitulation of differentiation. Heterokaryons formed with a relatively refractory cell type, the hepatocyte cell line HepG2, revealed the importance of both MyoD expression and other unidentified cytoplasmic components, neither of which are sufficient for efficient muscle gene activation, but are synergistic. We provide evidence that de-repression by transient histone deacetylase inhibition can induce MyoD expression and increase the extent and efficiency of muscle gene transcription. Taken together, the results suggest that understanding the mechanistic basis, using a combination of approaches, and taking into account cell history, will facilitate an increase in the efficiency and fidelity of conversion from one differentiated phenotype to another desired cell type. Inherent advantages of the heterokaryon system merit further investigation in the pursuit of directed cloning.

Identification and characterisation of human dysferlin transcript variants: implications for dysferlin mutational screening and isoforms

In conducting dysferlin mutational screening using blood mRNA instead of genomic DNA, we identified the occurrence of alternative splicing involving novel dysferlin exons, i.e. exons 5a and 40a, in addition to previously reported alternative splicing of exon 17. Further study employing long range RT-PCR and subcloning revealed a total of fourteen dysferlin transcripts with maintained dysferlin reading frame. The study also characterised the differences in relative frequencies of the dysferlin transcripts in skeletal muscle and blood. The findings have potential implications for molecular diagnosis of dysferlinopathy and the identification of dysferlin isoforms.

Age and diet affect gene expression profile in canine skeletal muscle.

We evaluated gene transcription in canine skeletal muscle (biceps femoris) using microarray analysis to identify effects of age and diet on gene expression. Twelve female beagles were used (six 1-year olds and six 12-year olds) and they were fed one of two experimental diets for 12 months. One diet contained primarily plant-based protein sources (PPB), whereas the second diet contained primarily animal-based protein sources (APB). Affymetrix GeneChip Canine Genome Arrays were used to hybridize extracted RNA. Age had the greatest effect on gene transcription (262 differentially expressed genes), whereas the effect of diet was relatively small (22 differentially expressed genes). Effects of age (regardless of diet) were most notable on genes related to metabolism, cell cycle and cell development, and transcription function. All these genes were predominantly down-regulated in geriatric dogs. Age-affected genes that were differentially expressed on only one of two diets were primarily noted in the PPB diet group (144/165 genes). Again, genes related to cell cycle (22/35) and metabolism (15/19) had predominantly decreased transcription in geriatric dogs, but 6/8 genes related to muscle development had increased expression. Effects of diet on muscle gene expression were mostly noted in geriatric dogs, but no consistent patterns in transcription were observed. The insight these data provide into gene expression profiles of canine skeletal muscle as affected by age, could serve as a foundation for future research pertaining to age-related muscle diseases.

Tannic acid facilitates expression of the polypyrimidine tract binding protein and alleviates deleterious inclusion of CHRNA1 exon P3A due to an hnRNP H-disrupting mutation in congenital myasthenic syndrome

We recently reported that the intronic splice-site mutation IVS3-8G>A of CHRNA1 that encodes the muscle nicotinic acetylcholine receptor α subunit disrupts binding of a splicing repressor, hnRNP H. This, in turn, results in exclusive inclusion of the downstream exon P3A. The P3A(+) transcript encodes a non-functional α subunit that comprises 50% of the transcripts in normal human skeletal muscle, but its functional significance remains undetermined. In an effort to search for a potential therapy, we screened off-label effects of 960 bioactive chemical compounds and found that tannic acid ameliorates the aberrant splicing due to IVS3-8G>A but without altering the expression of hnRNP H. Therefore, we searched for another splicing trans-factor. We found that the polypyrimidine tract binding protein (PTB) binds close to the 3′ end of CHRNA1 intron 3, that PTB induces skipping of exon P3A and that tannic acid increases the expression of PTB in a dose-dependent manner. Deletion assays of the PTB promoter region revealed that the tannic acid-responsive element is between positions −232 and −74 from the translation initiation site. These observations open the door to the discovery of novel therapies based on PTB overexpression and to detecting possible untoward effects of the overexpression.

Interactions between ROS and AMP kinase activity in the regulation of PGC-1α transcription in skeletal muscle cells

Reactive oxygen species (ROS) play an important role in cellular function via the activation of signaling cascades. ROS have been shown to affect mitochondrial biogenesis, morphology, and function. Their beneficial effects are likely mediated via the upregulation of transcriptional regulators such as peroxisome proliferator-activated receptor-gamma coactivator-1 protein-alpha (PGC-1alpha). However, the ROS signals that regulate PGC-1alpha transcription in skeletal muscle are not understood. Here we examined the effect of H2O2 on the regulation of PGC-1alpha expression, and its relationship to AMPK activation. We demonstrate that 24 h of exogenous H2O2 treatment increased PGC-1alpha promoter activity and mRNA expression. Both effects were blocked with the addition of N-acetylcysteine, a ROS scavenger. These effects were mediated, in part, via upstream stimulatory factor-1/Ebox DNA binding and involved 1) interactions with downstream sequences and 2) the activation of AMPK. Elevated ROS led to the activation of AMPK, likely via a decline in ATP levels. The activation of AMPK using 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside increased PGC-1alpha promoter activity and mRNA levels but reduced ROS production. Thus the net effect of AMPK activation on PGC-1alpha expression was a result of increased transcriptional activation, counterbalanced by reduced ROS production. The effects of H2O2 on PGC-1alpha expression differed depending on the level of ROS within the cell. Low levels of ROS result in reduced PGC-1alpha mRNA in the absence of an effect on PGC-1alpha promoter activation. In contrast, elevated levels of H2O2 induce PGC-1alpha transcription indirectly, via AMPK activation. These data identify unique interactions between ROS and AMPK activation on the expression of PGC-1alpha in muscle cells.

Abstract 485: Follistatin-Like 1 is a Novel Secreted Muscle Protein that Confers Cardiovascular Protection

Increasing evidence indicates that skeletal muscle secretes factors, referred to as myokines, that affect the behavior of neighboring or remote organs. Myogenic Akt signaling confers vascular protection during normal tissue growth. We focused on the identification of novel factors secreted from Akt1-activated skeletal muscle that have protective effects on the cardiovascular systems through paracrine mechanisms. Transgenic Akt1 overexpression in skeletal muscle led to myofiber growth that was coupled to an increase in muscle capillary density. Follistatin-like 1 (Fstl1) was selected as a potential myokine after a screening of upregulated transcripts in skeletal muscle of inducible Akt1 transgenic mice by microarray analysis. Myogenic Akt activation led to an induction of Fstl1 by muscle and increased circulating levels of Fstl1. Ischemic hindlimb surgery also induced Fstl1 expression by muscle and increased Fstl1 levels in serum. Intramuscular administration of an adenoviral vector expressing Fstl1 (Ad-Fstl1) accelerated flow recovery and increased capillary density in the ischemic hindlimbs of wild-type mice. These stimulatory effects were dependent on the upregulation of Akt-endothelial nitric oxide synthase (eNOS) signaling axes within endothelial cells. In cultured human umbilical vein endothelium cells, Ad-Fstl1 stimulated migration and differentiation into network structures, and inhibited apoptosis under conditions of serum deprivation. The pro-angiogenic actions of Fstl1 were mediated through its ability to activate Akt-eNOS signaling pathways. Furthermore, Ad-Fstl1 protected neonatal rat ventricular myocytes from hypoxia/reoxygenation-induced apoptosis and this protective effect was dependent on Akt activation. The intravenous administration of Ad-Fstl1 to wild-type mice resulted in a marked reduction in myocardial infarct size following ischemia-reperfusion injury that was accompanied by a significant reduction in apoptosis in the heart. These data indicate that Fstl1 is a novel Akt1-regulated myokine that can function to promote the new blood vessel growth in response to ischemia and protect against myocardial ischemia-reperfusion injury through its ability to activate Akt signaling in remote tissues.

Dramatic Reversal of Derangements in Muscle Metabolism and Left Ventricular Function After Bariatric Surgery

Objective The study objective was to define muscle metabolic and cardiovascular changes after surgical intervention in clinically severe obese patients. Methods Obesity is a state of metabolic dysregulation that can lead to maladaptive changes in heart and skeletal muscle, including insulin resistance and heart failure. In a prospective longitudinal study, 43 consecutive patients underwent metabolic profiling, skeletal muscle biopsies, and resting echocardiograms at baseline and 3 and 9 months after bariatric surgery. Results Body mass index decreased (mean changes, 95% confidence interval [CI]): 7.7 kg/m 2 (95% CI, 6.70-8.89) at 3 months and 5.6 kg/m 2 (95% CI, 4.45-6.80; P < .0001) at 9 months after surgery, with restoration of insulin sensitivity and decreases in plasma leptin at the same time points. Concurrent with these changes were dramatic decreases in skeletal muscle transcript levels of stearoyl coenzyme-A desaturase and pyruvate dehydrogenase kinase-4 at 3 and 9 months ( P < .0001, for both) and a significant decrease in peroxisome proliferation activated receptor-α–regulated genes at 9 months. Left ventricular relaxation impairment, assessed by tissue Doppler imaging, normalized 9 months after surgery. Conclusion Weight loss results in the reversal of systemic and muscle metabolic derangements and is accompanied by a normalization of left ventricular diastolic function.

The “rejuvenatory” impact of lipoic acid on mitochondrial function in aging rats may reflect induction and activation of PPAR-γ coactivator-1α

In aging rats, lipoic acid exerts a "rejuvenative" impact on mitochondria in various tissues, boosting mitochondrial membrane potential and oxygen consumption, while decreasing mitochondrial production of oxidants. A likely explanation for this phenomenon is that the mitochondria in aging rodents are structurally and functionally impaired by excessive oxidant stress - and that lipoic acid reverses this damage by amplifying key antioxidant mechanisms that protect mitochondria. A likely mediator of this effect is PPARgamma coactivator-1alpha (PGC-1alpha), which recently has been shown to promote transcription of the manganese-dependent superoxide dismutase, uncoupling protein-2, and an array of other proteins which provide antioxidant protection to mitochondria. Lipoic acid has been reported to activate both p38 MAP kinase and AMP-activated kinase (AMPK); p38 MAP kinase can boost the transcription, half-life, and coactivational activity of PGC-1alpha, and AMPK is known to promote its transcription in skeletal muscle and endothelial cells. Thus, it is intriguing to speculate that the remarkable antioxidant effects of lipoic acid therapy reflect not only induction of phase 2 antioxidants (e.g. glutathione and heme oxygenase-1), but also induction of various proteins that function expressly to protect mitochondria from self-generated oxidant stress. Further research is required to evaluate this model.

Apoptosis versus active gene transcription in skeletal muscle of chronic heart failure patients. The effect of exercise training

Apoptosis versus active gene transcription in skeletal muscle of chronic heart failure patients. The effect of exercise training