Differential Association of 4E-BP2-Interacting Proteins Is Related to Selective Delayed Neuronal Death after Ischemia

Cerebral ischemia induces an inhibition of protein synthesis and causes cell death and neuronal deficits. These deleterious effects do not occur in resilient areas of the brain, where protein synthesis is restored. In cellular stress conditions, as brain ischemia, translational repressors named eukaryotic initiation factor (eIF) 4E-binding proteins (4E-BPs) specifically bind to eIF4E and are critical in the translational control. We previously described that 4E-BP2 protein, highly expressed in brain, can be a molecular target for the control of cell death or survival in the reperfusion after ischemia in an animal model of transient cerebral ischemia. Since these previous studies showed that phosphorylation would not be the regulation that controls the binding of 4E-BP2 to eIF4E under ischemic stress, we decided to investigate the differential detection of 4E-BP2-interacting proteins in two brain regions with different vulnerability to ischemia-reperfusion (IR) in this animal model, to discover new potential 4E-BP2 modulators and biomarkers of cerebral ischemia. For this purpose, 4E-BP2 immunoprecipitates from the resistant cortical region and the vulnerable hippocampal cornu ammonis 1 (CA1) region were analyzed by two-dimensional (2-D) fluorescence difference in gel electrophoresis (DIGE), and after a biological variation analysis, 4E-BP2-interacting proteins were identified by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry. Interestingly, among the 4E-BP2-interacting proteins identified, heat shock 70 kDa protein-8 (HSC70), dihydropyrimidinase-related protein-2 (DRP2), enolase-1, ubiquitin carboxyl-terminal hydrolase isozyme-L1 (UCHL1), adenylate kinase isoenzyme-1 (ADK1), nucleoside diphosphate kinase-A (NDKA), and Rho GDP-dissociation inhibitor-1 (Rho-GDI), were of notable interest, showing significant differences in their association with 4E-BP2 between resistant and vulnerable regions to ischemic stress. Our data contributes to the first characterization of the 4E-BP2 interactome, increasing the knowledge in the molecular basis of the protection and vulnerability of the ischemic regions and opens the way to detect new biomarkers and therapeutic targets for diagnosis and treatment of cerebral ischemia.

Hypoxic Treatment of Zebrafish Embryos and Larvae

Zebrafish has emerged as an informative animal model to study the biological impact and molecular mechanisms of hypoxia. Here we describe a simple method to induce hypoxia in zebrafish embryos and larvae. This protocol is easy and reproducible and does not require expensive equipment or specialized devices. It can be adapted in large, medium, and small scales. This protocol is also well-suited for experiments requiring chemical drug treatment and can be applied to other fish and amphibian species.

In vitro supplementation with the porcine plasma product, betaGRO®, stimulates activity of porcine fetal myoblasts and neonatal satellite cells in a divergent manner

Two separate experiments were conducted to evaluate the effect of betaGRO® supplementation on in vitro porcine fetal myoblasts (PFM) and porcine satellite cells (PSC) proliferation, fusion and myotube thickness. The PFM and PSC were isolated from the m. longissimus dorsi of day 60 of gestation fetuses and piglets within 24 h of birth, respectively. Proliferation assays were conducted as 4×3 factorial arrangements with time of culture (24, 48, 72, 96 h) and media treatment (standard porcine media supplemented with 10% (vol/vol) fetal bovine serum (HS); HS without 10% fetal bovine serum (LS); and LS supplemented with 10 mg/ml betaGRO® (BG)) as main effects. Fusion and myotube growth assays were conducted as 2×2 factorial designs with serum concentration (HS or LS), and betaGRO® inclusion (0 or 10 mg/ml) as main effects. There was a treatment×time interaction and betaGRO®×serum interactions for proliferation, fusion and myotube thickness of PFM (P<0.01). At all-time points, HS and BG-PFM had greater proliferation rates compared LS (P<0.01). The HS treatment had greater proliferation rates than BG (P<0.02) except at 72 h of culture (P=0.44). When betaGRO® was added to LS media, fusion percentage and myotube thickness decreased (P<0.01), while fusion percentage increased (P<0.01) and myotube thickness was unaffected (P=0.63) when betaGRO® was added to HS media. There were treatment×time and betaGRO®×serum interactions for proliferation rate and fusion rate of PSC, respectively (P<0.01). At all-time points, HS had greater proliferation rates than LS and BG (P<0.01), and LS had greater proliferation rates than BG (P<0.02). When betaGRO® was added to LS and HS media, fusion percentage increased for both media types (P<0.01). There was no betaGRO®×serum interaction (P=0.63) for PSC myotube thickness; however, betaGRO® supplemented myotubes were thicker (P<0.01) than non-betaGRO® supplemented myotubes. These two experiments indicate in vitro betaGRO® supplementation stimulates divergent responses based on the age of cell examined.

A comprehensive transcriptomic analysis of differentiating embryonic stem cells in response to the overexpression of Mesogenin 1

The mutation of somitogenesis protein Mesogenin 1 (Msgn1) has been widely used to study the direct link between somitogenesis and the development of an embryo. Several studies have used gene expression profiling of somitogenesis to identify the key genes in the process, but few have focused on the pathways involved and the coexpression patterns of associated pathways. Here we employed time-course microarray datasets of differentiating embryonic stem cells by overexpressing the transcription factor Msgn1 from the public database library of Gene Expression Omnibus (GEO). Then we applied gene set enrichment analysis (GSEA) to the datasets and performed candidate transcription factors selection. As a result, several significantly regulated pathways and transcription factors (TFs), as well as some of the specific signaling pathways, were identified during somitogenesis under Msgn1 overexpression, most of which had not been reported previously. Finally, significant core genes such as Hes1 and Notch1 as well as some of the TFs such as PPARs and FOXs were identified to construct coexpression networks of related pathways, the expression patterns of which had been validated by our following quantitative real-time PCR (qRT-PCR). The results of our study may help us better understand the molecular mechanisms of somitogenesis in mice at the genome-wide level.

Regulation of myogenesis and skeletal muscle regeneration: effects of oxygen levels on satellite cell activity

Reduced oxygen (O₂) levels (hypoxia) are present during embryogenesis and exposure to altitude and in pathologic conditions. During embryogenesis, myogenic progenitor cells reside in a hypoxic microenvironment, which may regulate their activity. Satellite cells are myogenic progenitor cells localized in a local environment, suggesting that the O₂ level could affect their activity during muscle regeneration. In this review, we present the idea that O₂ levels regulate myogenesis and muscle regeneration, we elucidate the molecular mechanisms underlying myogenesis and muscle regeneration in hypoxia and depict therapeutic strategies using changes in O₂ levels to promote muscle regeneration. Severe hypoxia (≤1% O₂) appears detrimental for myogenic differentiation in vitro, whereas a 3-6% O₂ level could promote myogenesis. Hypoxia impairs the regenerative capacity of injured muscles. Although it remains to be explored, hypoxia may contribute to the muscle damage observed in patients with pathologies associated with hypoxia (chronic obstructive pulmonary disease, and peripheral arterial disease). Hypoxia affects satellite cell activity and myogenesis through mechanisms dependent and independent of hypoxia-inducible factor-1α. Finally, hyperbaric oxygen therapy and transplantation of hypoxia-conditioned myoblasts are beneficial procedures to enhance muscle regeneration in animals. These therapies may be clinically relevant to treatment of patients with severe muscle damage.-Chaillou, T. Lanner, J. T. Regulation of myogenesis and skeletal muscle regeneration: effects of oxygen levels on satellite cell activity.

Regulation of myogenesis by environmental hypoxia

In aerobic organisms, oxygen is a critical factor for tissue and organ morphogenesis from embryonic development throughout the adult life. It regulates various intracellular pathways involved in cellular metabolism, proliferation, cell survival and fate. Organisms or tissues rapidly respond to changes in oxygen availability by activating complex signalling networks, which culminate in the control of mRNA translation and/or gene expression. This Commentary presents the effects of hypoxia during embryonic development, myoblasts and satellite cell proliferation and differentiation in vertebrates. We also outline the relationship between Notch, Wnt and growth factor signalling pathways, as well as the post-transcriptional regulation of myogenesis under conditions of hypoxia.

Oxygen changes drive non-uniform scaling in Drosophila melanogaster embryogenesis

We previously demonstrated that, while changes in temperature produce dramatic shifts in the time elapsed during Drosophila melanogaster embryogenesis, the relative timing of events within embryogenesis does not change. However, it was unclear if this uniform scaling is an intrinsic property of developing embryos, or if it is specific to thermal fluctuations. To investigate this, here we characterize the embryonic response to changes in oxygen concentration, which also impact developmental rate, using time-lapse imaging, and find it fundamentally different from the temperature response. Most notably, changes in oxygen levels drive developmental heterochrony, with the timing of several morphological processes showing distinct scaling behaviors. Gut formation is severely slowed by decreases in oxygen, while head involution and syncytial development are less impacted than the rest of development, and the order of several developmental landmarks is inverted at different oxygen levels. These data reveal that the uniform scaling seen with changes in temperature is not a trivial consequence of adjusting developmental rate. The developmental rate changes produced by changing oxygen concentrations dwarf those induced by temperature, and greatly impact survival. While extreme temperatures increase early embryo mortality, mild hypoxia increases arrest and death during mid-embryogenesis and mild hyperoxia increases survival over normoxia.

Direct effects of hypoxia and nitric oxide on ecdysone secretion by insect prothoracic glands

Insect molting and metamorphosis are controlled by the molt stimulating hormone ecdysone. A recent study suggests that reduced tissue oxygenation correlates with the size-sensing mechanism responsible for triggering molting. When reared in hypoxia, larvae of Manduca sexta and Drosophila melanogaster initiate molting at lower weights than do larvae reared in normoxia. Furthermore, in Drosophila, the signaling gas nitric oxide (NO) appears to be required for normal developmental timing. As observed in Drosophila, NO signaling targets the nuclear hormone receptor beta fushi tarazu transcription factor 1 (βFTZ-F1) through activation of Drosophila hormone receptor 3 (DHR3), two key regulators of ecdysone production and metamorphic tissue progression. We set out to directly examine the effects of hypoxia and NO on ecdysone secretion using prothoracic glands from feeding fifth (last) larval stage M. sexta. Our results indicate that in vitro treatment of prothoracic glands with hypoxia (2% oxygen) or the NO donor DETA-NONOate significantly inhibit ecdysone secretion. Protein markers of glandular activity were also in keeping with an initial inhibition, measured a decrease in phosphorylated ERK (extracellular signal regulated kinase) and an increase in non-phosphorylated 4EBP (eukaryotic initiation factor 4E binding protein). Additionally, gene expression levels of Manduca hormone receptor 3 (mhr3), βftz-f1, nitric oxide synthase (nos), and the PTTH receptor torso, were quantified using real-time PCR. NO treatment increased mhr3 expression and decreased nos expression. Hypoxia increased mhr3 transcription after 2 hr, but decreased transcription after 12 hr, with no effect on nos expression. Both NO and hypoxia had small effects on βftz-f1 expression, yet strongly increased torso transcription. Our results demonstrate that, in isolated prothoracic glands, hypoxia and NO signaling directly inhibit ecdysteroid secretion, but at the same time alter aspects of prothoracic gland function that may enhance secretory response.

Metabolic suppression during protracted exposure to hypoxia in the jumbo squid, Dosidicus gigas, living in an oxygen minimum zone

The jumbo squid, Dosidicus gigas, can survive extended forays into the oxygen minimum zone (OMZ) of the Eastern Pacific Ocean. Previous studies have demonstrated reduced oxygen consumption and a limited anaerobic contribution to ATP production, suggesting the capacity for substantial metabolic suppression during hypoxic exposure. Here we provide a more complete description of energy metabolism and explore the expression of proteins indicative of transcriptional and translational arrest that may contribute to metabolic suppression. We demonstrate a suppression of total ATP demand under hypoxic conditions (1% oxygen, PO2 = 0.8 kPa) in both juveniles (52%) and adults (35%) of the jumbo squid. Oxygen consumption rates are reduced to 20% under hypoxia relative to air-saturated controls. Concentrations of Arg-P and ATP declined initially, reaching a new steady state (~30% of controls) after the first hour of hypoxic exposure. Octopine began accumulating after the first hour of hypoxic exposure, once Arg-P breakdown resulted in sufficient free arginine for substrate. Octopine reached levels near 30 mmoles g-1 after 3.4 h of hypoxic exposure. Succinate did increase through hypoxia but contributed minimally to total ATP production. Glycogenolysis in mantle muscle presumably serves to maintain muscle functionality and balance energetics during hypoxia. We provide evidence that post-translational modifications on histone proteins and translation factors serve as a primary means of energy conservation and that select components of the stress response are altered in hypoxic squids. Reduced ATP consumption under hypoxia serves to maintain ATP levels, prolong fuel store use and minimize the accumulation of acidic intermediates of anaerobic ATP generating pathways during prolonged diel forays into the OMZ. Metabolic suppression likely limits active, daytime foraging at depth in the core of the OMZ, but confers an energetic advantage over competitors that must remain in warm, oxygenated surface waters. Moreover, capacity for metabolic suppression provides habitat flexibility as oxygen minimum zones expand due to climate change.

eIF4EBP3L acts as a gatekeeper of TORC1 in activity-dependent muscle growth by specifically regulating Mef2ca translational initiation

Muscle activity promotes muscle growth through the TOR-4EBP pathway by controlling the translation of specific mRNAs, including Mef2ca, a muscle transcription factor required for normal growth.

Muscle fiber size is activity-dependent and clinically important in ageing, bed-rest, and cachexia, where muscle weakening leads to disability, prolonged recovery times, and increased costs. Inactivity causes muscle wasting by triggering protein degradation and may simultaneously prevent protein synthesis. During development, muscle tissue grows by several mechanisms, including hypertrophy of existing fibers. As in other tissues, the TOR pathway plays a key role in promoting muscle protein synthesis by inhibition of eIF4EBPs (eukaryotic Initiation Factor 4E Binding Proteins), regulators of the translational initiation. Here, we tested the role of TOR-eIF4EBP in a novel zebrafish muscle inactivity model. Inactivity triggered up-regulation of eIF4EBP3L (a zebrafish homolog of eIF4EBP3) and diminished myosin and actin content, myofibrilogenesis, and fiber growth. The changes were accompanied by preferential reduction of the muscle transcription factor Mef2c, relative to Myod and Vinculin. Polysomal fractionation showed that Mef2c decrease was due to reduced translation of mef2ca mRNA. Loss of Mef2ca function reduced normal muscle growth and diminished the reduction in growth caused by inactivity. We identify eIF4EBP3L as a key regulator of Mef2c translation and protein level following inactivity; blocking eIF4EBP3L function increased Mef2ca translation. Such blockade also prevented the decline in mef2ca translation and level of Mef2c and slow myosin heavy chain proteins caused by inactivity. Conversely, overexpression of active eIF4EBP3L mimicked inactivity by decreasing the proportion of mef2ca mRNA in polysomes, the levels of Mef2c and slow myosin heavy chain, and myofibril content. Inhibiting the TOR pathway without the increase in eIF4EBP3L had a lesser effect on myofibrilogenesis and muscle size. These findings identify eIF4EBP3L as a key TOR-dependent regulator of muscle fiber size in response to activity. We suggest that by selectively inhibiting translational initiation of mef2ca and other mRNAs, eIF4EBP3L reprograms the translational profile of muscle, enabling it to adjust to new environmental conditions.

Most genes are transcribed into mRNA and then translated into proteins that function in various cellular processes. Initiation of mRNA translation is thus a fundamental control point in gene expression. Working in a zebrafish model, we have found that muscle activity (or inactivity) can differentially regulate the translation of specific mRNAs and thereby control the growth of skeletal muscle. Emerging evidence suggests that control of translational initiation of particular mRNAs by an intracellular signaling pathway acting through TORC1 is a major regulator of cell growth and function. We show here that muscle activity both activates the TORC1 pathway and suppresses the expression of a downstream TORC1 target—the translational inhibitor eIF4EBP3L. This removes a brake on translation of certain mRNAs. Conversely, we show that muscle inactivity can up-regulate this translational inhibitor, thereby causing reduced translation of these mRNAs. One of the mRNAs targeted in this manner by eIF4EBP3L is Mef2ca, which encodes a transcription factor that promotes assembly of muscle contractile apparatus. Our work thus reveals a mechanism by which muscle growth can be differentially influenced depending on the context of muscle activity (or lack thereof). If this pathway operates in people, it may help explain how exercise regulates muscle growth and performance.