Myostatin negatively regulates the expression of the steroid receptor co-factor ARA70

NCOA4 is regulated by HIF and mediates mobilization of murine hepatic iron stores after blood loss

The mechanisms by which phlebotomy promotes the mobilization of hepatic iron stores are not well understood. NCOA4 (nuclear receptor coactivator 4) is a widely expressed intracellular protein previously shown to mediate the autophagic degradation of ferritin. Here, we investigate a local requirement for NCOA4 in the regulation of hepatic iron stores and examine mechanisms of NCOA4 regulation. Hepatocyte-targeted Ncoa4 knockdown in nonphlebotomized mice had only modest effects on hepatic ferritin subunit levels and nonheme iron concentration. After phlebotomy, mice with hepatocyte-targeted Ncoa4 knockdown exhibited anemia and hypoferremia similar to control mice with intact Ncoa4 regulation but showed a markedly impaired ability to lower hepatic ferritin subunit levels and hepatic nonheme iron concentration. This impaired hepatic response was observed even when dietary iron was limited. In both human and murine hepatoma cell lines, treatment with chemicals that stabilize hypoxia inducible factor (HIF), including desferrioxamine, cobalt chloride, and dimethyloxalylglycine, raised NCOA4 messenger RNA. This NCOA4 messenger RNA induction occurred within 3 hours, preceded a rise in NCOA4 protein, and was attenuated in the setting of dual HIF-1α and HIF-2α knockdown. In summary, we show for the first time that NCOA4 plays a local role in facilitating iron mobilization from the liver after blood loss and that HIF regulates NCOA4 expression in cells of hepatic origin. Because the prolyl hydroxylases that regulate HIF stability are oxygen- and iron-dependent enzymes, our findings suggest a novel mechanism by which hypoxia and iron deficiency may modulate NCOA4 expression to impact iron homeostasis.

Crosstalk Between Autophagy and Ferroptosis and Its Putative Role in Ischemic Stroke

Autophagy is a conserved process to maintains homeostasis via the degradation of toxic cell contents, which can either promote cell survival or accelerate cellular demise. Ferroptosis is a recently discovered iron-dependent cell death pathway associated with the accumulation of lethal reactive lipid species. In the past few years, an increasing number of studies have suggested the crosstalk between autophagy and ferroptosis. Ischemic stroke is a complex brain disease regulated by several cell death pathways, including autophagy and ferroptosis. However, the potential links between autophagy and ferroptosis in ischemic stroke have not yet been explored. In this review, we briefly overview the mechanisms of ferroptosis and autophagy, as well as their possible connections in ischemic stroke. The elucidation of crosstalk between different cell death pathways may provide insight into new future ischemic stroke therapies.

Low-Intensity Exercise Suppresses CCAAT/Enhancer-Binding Protein δ/Myostatin Pathway Through Androgen Receptor in Muscle Cells

BACKGROUND

Androgen production following exercise has been suggested to contribute anabolic actions of muscle. However, the underlying mechanisms of the androgen receptor (AR) in androgen's action are still unclear.

OBJECTIVE

In the present study, we examined androgen/AR-mediated action in exercise, especially for the suppression of myostatin, a potent negative regulator of muscle mass.

METHODS

To examine the effects of exercise, we employed low-intensity exercise in mice and electric pulse stimulation (EPS) in C2C12 myotubes. Androgen production by C2C12 myotubes was measured by enzyme-linked immunosorbent assay. To block the action of AR, we pretreated C2C12 myotubes with flutamide. Quantitative real-time polymerase chain reaction was used to determine the expression levels of proteolytic genes including CCAAT/enhancer-binding protein delta (C/EBPδ), myostatin and muscle E3 ubiquitin ligases, as well as myogenic genes such as myogenin and PGC1α. The activation of 5'-adenosine-activated protein kinase and STAT3 was determined by Western blot analysis.

RESULTS

Both mRNA and protein levels of AR significantly increased in skeletal muscle of low-intensity exercised mice and C2C12 myotubes exposed to EPS. Production of testosterone and dihydrotestosterone from EPS-treated C2C12 myotubes was markedly increased. Of interest, we found that myostatin was clearly inhibited by EPS, and its inhibition was significantly abrogated when AR was blocked by flutamide. To test how AR suppresses myostatin, we examined the effects of EPS on C/EBPδ because the promoter region of myostatin has several C/EBP recognition sites. C/EBPδ expression was decreased by EPS, and this decrease was negated by flutamide. IL-6 and phospho-STAT3 (pSTAT3) expression, the downstream pathway of myostatin, were decreased by EPS and this was also reversed by flutamide. Similar downregulation of C/EBPδ, myostatin, and IL-6 was seen in skeletal muscle of low-intensity exercised mice.

CONCLUSIONS

Muscle AR expression and androgen production were increased by exercise and EPS treatment. As a mechanistical insight, it is suggested that AR inhibited myostatin expression transcriptionally by C/EBPδ suppression, which negatively influences IL-6/pSTAT3 expression and consequently contributes to the prevention of muscle proteolysis during exercise.

Regional Variation in Androgen Receptor Expression and Biomechanical Properties May Contribute to Cryptorchidism Susceptibility in the LE/orl Rat

Background: The process of testicular descent requires androgen and insulin-like 3, hormones secreted by fetal Leydig cells. Knowledge concerning distinct and common functions of these hormones in regulating development of the fetal gubernaculum remains limited and/or conflicting. The current studies were designed to better define characteristics of androgen receptor (AR) expression, function and regulation, as well as the biomechanical properties of normal and cryptorchid gubernaculum during fetal development. Methods: We studied fetal gubernacula from Long Evans outbred (LE/wt) rats and an inbred (LE/orl) strain with an inherited form of cryptorchidism associated with an AR signaling defect. Gubernacular cells or whole organs obtained from LE/wt and LE/orl fetal gubernacula underwent AR immunostaining and quantitative image analysis. The effects of dihydrotestosterone (DHT) on AR expression, muscle fiber morphology, hyaluronan (HA) levels and glycosaminoglycan (GAG) content were measured in LE/wt gubernacula. Finally, the spatial mechanics of freshly harvested LE/wt and LE/orl fetal gubernacula were compared using micropipette aspiration. Results: AR is expressed in the nucleus of mesenchymal core, tip and cord cells of the embryonic (E) day 17 and 21 fetal gubernaculum, and is enhanced by DHT in primary cultures of gubernacular mesenchymal cells. Enhanced AR expression at the tip was observed in LE/wt but not LE/orl gubernacula. In in vitro studies of whole mount fetal gubernaculum, DHT did not alter muscle fiber morphology, HA content or GAG production. Progressive swelling with reduced cellular density of the LE/wt gubernaculum at E19-21 was associated with increased central stiffness in LE/wt but not in LE/orl fetuses. Conclusions: These data confirm nuclear AR expression in gubernacular mesenchyme with distal enhancement at the tip/cord region in LE/wt but not LE/orl rat fetuses. DHT enhanced cellular AR expression but had no major effects on muscle morphology or matrix composition in the rat fetal gubernaculum in vitro. Regional increased stiffness and decreased cell density between E19 and E21 were observed in LE/wt but not LE/orl fetal gubernacula. Developmental differences in cell-specific AR expression in LE/orl fetal gubernacula may contribute to the dysmorphism and aberrant function that underlies cryptorchidism susceptibility in this strain.

Polygenic inheritance of cryptorchidism susceptibility in the LE/orl rat

STUDY HYPOTHESIS

Susceptibility to inherited cryptorchidism in the LE/orl rat may be associated with genetic loci that influence developmental patterning of the gubernaculum by the fetal testis.

STUDY FINDING

Cryptorchidism in the LE/orl rat is associated with a unique combination of homozygous minor alleles at multiple loci, and the encoded proteins are co-localized with androgen receptor (AR) and Leydig cells in fetal gubernaculum and testis, respectively.

WHAT IS KNOWN ALREADY

Prior studies have shown aberrant perinatal gubernacular migration, muscle patterning defects and reduced fetal testicular testosterone in the LE/orl strain. In addition, altered expression of androgen-responsive, cytoskeletal and muscle-related transcripts in the LE/orl fetal gubernaculum suggest a role for defective AR signaling in cryptorchidism susceptibility.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

The long-term LE/orl colony and short-term colonies of outbred Crl:LE and Crl:SD, and inbred WKY/Ncrl rats were maintained for studies. Animals were intercrossed (LE/orl X WKY/Ncrl), and obligate heterozygotes were reciprocally backcrossed to LE/orl rats to generate 54 F2 males used for genotyping and/or linkage analysis. At least five fetuses per gestational time point from two or more litters were used for quantitative real-time RT-PCR (qRT-PCR) and freshly harvested embryonic (E) day 17 gubernaculum was used to generate conditionally immortalized cell lines. We completed genotyping and gene expression analyses using genome-wide microsatellite markers and single nucleotide polymorphism (SNP) arrays, PCR amplification, direct sequencing, restriction enzyme digest with fragment analysis, whole genome sequencing (WGS), and qRT-PCR. Linkage analysis was performed in Haploview with multiple testing correction, and qRT-PCR data were analyzed using ANOVA after log transformation. Imaging was performed using custom and commercial antibodies directed at candidate proteins in gubernaculum and testis tissues, and gubernaculum cell lines.

MAIN RESULTS AND THE ROLE OF CHANCE

LE/orl rats showed reduced fertility and fecundity, and higher risk of perinatal death as compared with Crl:LE rats, but there were no differences in breeding outcomes between normal and unilaterally cryptorchid males. Linkage analysis identified multiple peaks, and with selective breeding of outbred Crl:LE and Crl:SD strains for alleles within two of the most significant (P < 0.003) peaks on chromosomes 6 and 16, we were able to generate a non-LE/orl cryptorchid rat. Associated loci contain potentially functional minor alleles (0.25-0.36 in tested rat strains) including an exonic deletion in Syne2, a large intronic insertion in Ncoa4 (an AR coactivator) and potentially deleterious variants in Solh/Capn15, Ankrd28, and Hsd17b2. Existing WGS data indicate that homozygosity for these combined alleles does not occur in any other sequenced rat strain. We observed a modifying effect of the Syne2(del) allele on expression of other candidate genes, particularly Ncoa4, and for muscle and hormone-responsive transcripts. The selected candidate genes/proteins are highly expressed, androgen-responsive and/or co-localized with developing muscle and AR in fetal gubernaculum, and co-localized with Leydig cells in fetal testis.

LIMITATIONS, REASONS FOR CAUTION

The present study identified multiple cryptorchidism-associated linkage peaks in the LE/orl rat, containing potentially causal alleles. These are strong candidate susceptibility loci, but further studies are needed to demonstrate functional relevance to the phenotype.

WIDER IMPLICATIONS OF THE FINDINGS

Association data from both human and rat models of spontaneous, nonsyndromic cryptorchidism support a polygenic etiology of the disease. Both the present study and a human genome-wide association study suggest that common variants with weak effects contribute to susceptibility, and may exist in genes encoding proteins that participate in AR signaling in the developing gubernaculum. These findings have potential implications for the gene-environment interaction in the etiology of cryptorchidism.

LARGE SCALE DATA

Sequences were deposited in the Rat Genome Database (RGD, http://rgd.mcw.edu/).

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by: R01HD060769 from the Eunice Kennedy Shriver National Institute for Child Health and Human Development (NICHD), 2P20GM103446 and P20GM103464 from the National Institute of General Medical Sciences (NIGMS), and Nemours Biomedical Research. The authors have no competing interests to declare.

Iron and Neurodegeneration: Is Ferritinophagy the Link?

Mounting evidence indicates that the lysosome-autophagy pathway plays a critical role in iron release from ferritin, the main iron storage cellular protein, hence in the distribution of iron to the cells. The recent identification of nuclear receptor co-activator 4 as the receptor for ferritin delivery to selective autophagy sheds further light on the understanding of the mechanisms underlying this pathway. The emerging view is that iron release from ferritin through the lysosomes is a general mechanism in normal and tumour cells of different tissue origins, but it has not yet been investigated in brain cells. Defects in the lysosome-autophagy pathway are often involved in the pathogenesis of neurodegenerative disorders, and brain iron homeostasis disruption is a hallmark of many of these diseases. However, in most cases, it has not been established whether iron dysregulation is directly involved in the pathogenesis of the diseases or if it is a secondary effect derived from other pathogenic mechanisms. The recent evidence of the crucial involvement of autophagy in cellular iron handling offers new perspectives about the role of iron in neurodegeneration, suggesting that autophagy dysregulation could cause iron dyshomeostasis. In this review, we recapitulate our current knowledge on the routes through which iron is released from ferritin, focusing on the most recent advances. We summarise the current evidence concerning lysosome-autophagy pathway dysfunctions and those of iron metabolism and discuss their potential interconnections in several neurodegenerative disorders, such as Alzheimer's, Parkinson's and Huntington's diseases; amyotrophic lateral sclerosis; and frontotemporal lobar dementia.

Deep RNA sequencing of the skeletal muscle transcriptome in swimming fish

Deep RNA sequencing (RNA-seq) was performed to provide an in-depth view of the transcriptome of red and white skeletal muscle of exercised and non-exercised rainbow trout (Oncorhynchus mykiss) with the specific objective to identify expressed genes and quantify the transcriptomic effects of swimming-induced exercise. Pubertal autumn-spawning seawater-raised female rainbow trout were rested (n = 10) or swum (n = 10) for 1176 km at 0.75 body-lengths per second in a 6,000-L swim-flume under reproductive conditions for 40 days. Red and white muscle RNA of exercised and non-exercised fish (4 lanes) was sequenced and resulted in 15–17 million reads per lane that, after de novo assembly, yielded 149,159 red and 118,572 white muscle contigs. Most contigs were annotated using an iterative homology search strategy against salmonid ESTs, the zebrafish Danio rerio genome and general Metazoan genes. When selecting for large contigs (>500 nucleotides), a number of novel rainbow trout gene sequences were identified in this study: 1,085 and 1,228 novel gene sequences for red and white muscle, respectively, which included a number of important molecules for skeletal muscle function. Transcriptomic analysis revealed that sustained swimming increased transcriptional activity in skeletal muscle and specifically an up-regulation of genes involved in muscle growth and developmental processes in white muscle. The unique collection of transcripts will contribute to our understanding of red and white muscle physiology, specifically during the long-term reproductive migration of salmonids.

Expression and function of nuclear receptor co-activator 4: evidence of a potential role independent of co-activator activity

Nuclear receptor coactivator 4 (NcoA4), also known as androgen receptor-associated protein 70 (ARA70), was initially discovered as a component of Ret-Fused Gene expressed in a subset of papillary thyroid carcinomas. Subsequent studies have established NcoA4 as a coactivator for a variety of nuclear receptors, including peroxisome proliferator activated receptors α and γ, and receptors for steroid hormones, vitamins D and A, thyroid hormone, and aryl hydrocarbons. While human NcoA4 has both LXXLL and FXXLF motifs that mediate p160 coactivator nuclear receptor interactions, this ubiquitously expressed protein lacks clearly defined functional domains. Several studies indicate that NcoA4 localizes predominantly to the cytoplasm and affects ligand-binding specificity of the androgen receptor, which has important implications for androgen-independent prostate cancer. Two NcoA4 variants, which may exert differential activities, have been identified in humans. Recent studies suggest that NcoA4 may play a role in development, carcinogenesis, inflammation, erythrogenesis, and cell cycle progression that may be independent of its role as a receptor coactivator. This review summarizes what is currently known of the structure, expression, regulation, and potential functions of this unique protein in cancerous and non-cancerous pathologies.

Gonadotropin-regulated testicular RNA helicase (GRTH/DDX25) gene: cell-specific expression and transcriptional regulation by androgen in transgenic mouse testis

Gonadotropin-regulated testicular RNA helicase is a multifunctional enzyme present in both Leydig and germ cells that is essential for the progress of spermatogenesis. GRTH gene expression is transcriptionally upregulated by human chorionic gonadotropin (hCG) via second messenger (cAMP) and androgen in Leydig cells. The regulatory region(s) in the GRTH gene that is/are required for its cell-specific expression in the testis and hCG/androgen dependent expression were investigated in transgenic mice carrying sequential deletions of 5' flanking sequences of the GRTH gene. GFP-reporter gene expression directed by the GRTH 5' flanking sequences extending to -3.6 kb was specifically located in Leydig cells and the 205 bp minimal promoter domain was sufficient for this cell-specific expression. The 1 kb (5' to the ATG codon) transgene-directed expression was markedly increased by in vivo hCG treatment. Administration of the androgen receptor inhibitor Flutamide blocked the basal and hCG stimulated GFP expression in Leydig cells. We conclude that the expression of GRTH in testicular cells is differentially regulated by its 5' flanking sequence and that the 1 kb fragment of GRTH gene contains sequences for androgen regulation of its expression in Leydig cells.

Effect of kinin B2 receptor ablation on skeletal muscle development and myostatin gene expression

Bradykinin (BK) is an active peptide that binds to the kinin B(2) receptor and induces biological events during the development and adult life. In this study we aimed to investigate the effect of kinin B(2) receptor ablation in the postnatal skeletal muscle development and body composition in adult life. For studies of skeletal muscle development, control (C57Bl6 - WT) and B(2) receptor knockout mice (B(2)(-/-)) were sacrificed at 15, 30 and 90days after birth, the gastrocnemius skeletal muscle was weighed and myostatin gene expression evaluated by real time PCR. For energy balance determination, data from control and B(2)(-/-) at 90 and 120days were collected by calorimetric method. Body composition at 120days was determined by chloroform-methanol (total body fat) and Lowry-modified method (total body protein). The results show that B(2)(-/-) have significantly increased total body weight at 15, 30 and 90days of life, when compared to WT. The weight of the gastrocnemius skeletal muscle was also significantly increased at 30 and 90days of life. Body composition analyses revealed that B(2)(-/-) mice exhibit more total corporal protein and less total corporal fat. Energy balance revealed that B(2)(-/-) have increased metabolizable energy intake and energy expenditure when compared to control mice, resulting in a lower energy gain. Interestingly, myostatin mRNA expression was significantly decreased in 15 and 30days old B(2)(-/-) mice and after icatibant treatment of WT adult mice for 5days. In conclusion, together our results show that kinin B(2) receptor deletion increases lean mass, reduces fat mass and improves metabolism efficiency in mice. The mechanism involved in this phenotype could be related to the reduction of myostatin gene expression during postnatal life.

Variable expression of nuclear receptor coactivator 4 (NcoA4) during mouse embryonic development

Human nuclear receptor coactivator 4 (NcoA4) amplifies the activity of several ligand-activated nuclear transcription factors, including the aryl hydrocarbon receptor (AhR) and androgen receptor (AR). Because these receptors exert important regulatory effects during development, with AhR ubiquitously expressed after embryonic day 9.5 (E9.5) and AR expressed from E12 onward, we examined NcoA4 expression in mouse embryos from E9.5 to E17.5. Full-length NcoA4 transcript was detected by RT-PCR at all embryonic stages and in all adult mouse tissues examined, although a novel splice variant was also detected. Western blot analysis indicated the expression of full-length NcoA4 protein, which was more highly expressed at later (E15.5-E17.5) embryonic stages. NcoA4 protein was also present at varying levels in all adult mouse tissues examined. A dynamic expression profile for NcoA4 during early development was indicated by immunohistochemistry in cardiac, hepatic, and lung tissue. Unlike human NcoA4, murine NcoA4 lacks an LXXLL motif, which has been implicated in the interaction with AR. Overexpression of murine NcoA4 augmented the transcriptional activity of AhR by 5-fold and AR by only 1.5-fold in COS cells. These studies demonstrate ubiquitous NcoA4 expression throughout development and suggest that this coactivator may play a role in modulating nuclear receptor activity, particularly that of the AhR, during development.

[Expression of FoxO1 mRNA in muscle tissue of Bamei, Landrace and Landrace x Bamei]

Total RNA was extracted from soleus muscle, gastrocnemius muscle and extensor digitorum longus in hind leg of the 6-month-old male Bamei, Landrace, and the crossbred pigs (LandracexBamei). The primers of pig FoxO1 were designed and synthesized according to its homologous sequences of human, chimpanzee and rat. The optimal reaction condition and system of PCR was sieved to clone pig FoxO1 gene. Subsequently, the differential expression of FoxO1 mRNA was investigated in different types of skeletal muscle from Bamei, Landrace, and the crossbred pigs by SQ RT-PCR. The expression level of beta-actin was determined as a loading control. The results showed that the expression level of FoxO1 was different in various economic pig breeds and skeletal muscle types. The expression of FoxO1 in skeletal muscle of Bamei and the crossbred pigs was significantly higher than that of Landrace (Plt;0.01). Moreover, the expression of FoxO1 was lowest in soleus muscle, which mainly contains typemuscle fiber, and most abundant in extensor digitorum longus, which mainly contains typeb muscle fiber. This suggests that FoxO1 expression level has the negative correlation with the con-tent of typemuscle fiber. Skeletal muscle development of different economic types of pig breeds may be closely related to the regulation of FoxO1 gene.

Mighty is a novel promyogenic factor in skeletal myogenesis

Genetic analysis has revealed an important function in myogenesis for Myostatin, a member of the TGF-beta superfamily. However, the cascade of genes that responds to Myostatin signalling to regulate myogenesis is not well understood. Thus, a suppressive subtraction hybridization to identify such genes was undertaken and here we report the cloning and characterization of a novel gene, Mighty. Mighty is expressed in a variety of different tissues but appears to be specifically regulated by Myostatin in skeletal muscle. Overexpression of Mighty in C2C12 cells results in early withdrawal of myoblasts from the cell cycle, enhanced and accelerated differentiation and hypertrophy of myotubes. Most importantly, Mighty overexpression leads to increased and earlier expression of MyoD and increased secretion of another known differentiation inducing factor, IGF-II. Furthermore, viral expression of Mighty in mdx mice resulted in an increase in the number of larger healthy muscle fibers. Given its role in myogenesis, we propose that Mighty is a critical promyogenic factor which plays a key role in the signalling pathway downstream of Myostatin.

Androgens negatively regulate myostatin expression in an androgen-dependent skeletal muscle

Myostatin is an important negative regulator of skeletal muscle growth, while androgens are strong positive effectors. In order to investigate the possible interaction between myostatin and androgen pathways, we followed myostatin expression in the androgen-dependent levator ani (LA) muscle of the rat as a function of androgen status. By testosterone deprivation (castration), we induced LA growth arrest in young male rats, whilst atrophy in adult ones, however, both processes could be reversed by testosterone supplementation. After castration, a significant up-regulation of active myostatin protein (and its propeptide) was found, whereas the subsequent testosterone treatment reduced myostatin protein levels to normal values in both young and adult rats. Similarly, a testosterone-induced suppression of myostatin mRNA levels was observed in castrated adult but not in young animals. Altogether, androgens seem to have strong negative impact on myostatin expression, which might be a key factor in the weight regulation of LA muscle.

Myostatin regulates cardiomyocyte growth through modulation of Akt signaling

Myostatin is a highly conserved, potent negative regulator of skeletal muscle hypertrophy in many species, from rodents to humans, although its mechanisms of action are incompletely understood. Transcript profiling of hearts from a genetic model of cardiac hypertrophy revealed dramatic upregulation of myostatin, not previously recognized to play a role in the heart. Here we show that myostatin abrogates the cardiomyocyte growth response to phenylephrine in vitro through inhibition of p38 and the serine-threonine kinase Akt, a critical determinant of cell size in many species from drosophila to mammals. Evaluation of male myostatin-null mice revealed that their cardiomyocytes and hearts overall were slightly smaller at baseline than littermate controls but exhibited more exuberant growth in response to chronic phenylephrine infusion. The increased cardiac growth in myostatin-null mice corresponded with increased p38 phosphorylation and Akt activation in vivo after phenylephrine treatment. Together, these data demonstrate that myostatin is dynamically regulated in the heart and acts more broadly than previously appreciated to regulate growth of multiple types of striated muscle.