Regulation of eukaryotic initiation factor eIF2B: glycogen synthase kinase-3 phosphorylates a conserved serine which undergoes dephosphorylation in response to insulin

Mechanical and signaling responses of unloaded rat soleus muscle to chronically elevated β-myosin activity

It has been reported that muscle functional unloading is accompanied by an increase in motoneuronal excitability despite the elimination of afferent input. Thus, we hypothesized that pharmacological potentiation of spontaneous contractile soleus muscle activity during hindlimb unloading could activate anabolic signaling pathways and prevent the loss of muscle mass and strength. To investigate these aspects and underlying molecular mechanisms, we used β-myosin allosteric effector Omecamtiv Mekarbil (OM). We found that OM partially prevented the loss of isometric strength and intrinsic stiffness of the soleus muscle after two weeks of disuse. Notably, OM was able to attenuate the unloading-induced decrease in the rate of muscle protein synthesis (MPS). At the same time, the use of drug neither prevented the reduction in the markers of translational capacity (18S and 28S rRNA) nor activation of the ubiquitin-proteosomal system, which is evidenced by a decrease in the cross-sectional area of fast and slow muscle fibers. These results suggest that chemically-induced increase in low-intensity spontaneous contractions of the soleus muscle during functional unloading creates prerequisites for protein synthesis. At the same time, it should be assumed that the use of OM is advisable with pharmacological drugs that inhibit the expression of ubiquitin ligases.

Lithium: effects in animal models of vanishing white matter are not promising

Vanishing white matter (VWM) is a devastating autosomal recessive leukodystrophy, resulting in neurological deterioration and premature death, and without curative treatment. Pathogenic hypomorphic variants in subunits of the eukaryotic initiation factor 2B (eIF2B) cause VWM. eIF2B is required for regulating the integrated stress response (ISR), a physiological response to cellular stress. In patients' central nervous system, reduced eIF2B activity causes deregulation of the ISR. In VWM mouse models, the extent of ISR deregulation correlates with disease severity. One approach to restoring eIF2B activity is by inhibition of GSK3β, a kinase that phosphorylates eIF2B and reduces its activity. Lithium, an inhibitor of GSK3β, is thus expected to stimulate eIF2B activity and ameliorate VWM symptoms. The effects of lithium were tested in zebrafish and mouse VWM models. Lithium improved motor behavior in homozygous eif2b5 mutant zebrafish. In lithium-treated 2b4he2b5ho mutant mice, a paradoxical increase in some ISR transcripts was found. Furthermore, at the dosage tested, lithium induced significant polydipsia in both healthy controls and 2b4he2b5ho mutant mice and did not increase the expression of other markers of lithium efficacy. In conclusion, lithium is not a drug of choice for further development in VWM based on the limited or lack of efficacy and significant side-effect profile.

Signaling plasticity in the integrated stress response

The Integrated Stress Response (ISR) is an essential homeostatic signaling network that controls the cell's biosynthetic capacity. Four ISR sensor kinases detect multiple stressors and relay this information to downstream effectors by phosphorylating a common node: the alpha subunit of the eukaryotic initiation factor eIF2. As a result, general protein synthesis is repressed while select transcripts are preferentially translated, thus remodeling the proteome and transcriptome. Mounting evidence supports a view of the ISR as a dynamic signaling network with multiple modulators and feedback regulatory features that vary across cell and tissue types. Here, we discuss updated views on ISR sensor kinase mechanisms, how the subcellular localization of ISR components impacts signaling, and highlight ISR signaling differences across cells and tissues. Finally, we consider crosstalk between the ISR and other signaling pathways as a determinant of cell health.

Control of Selective mRNA Translation in Neuronal Subcellular Compartments in Health and Disease

In multiple cell types, mRNAs are transported to subcellular compartments, where local translation enables rapid, spatially localized, and specific responses to external stimuli. Mounting evidence has uncovered important roles played by local translation in vivo in axon survival, axon regeneration, and neural wiring, as well as strong links between dysregulation of local translation and neurologic disorders. Omic studies have revealed that >1000 mRNAs are present and can be selectively locally translated in the presynaptic and postsynaptic compartments from development to adulthood in vivo A large proportion of the locally translated mRNAs is specifically upregulated or downregulated in response to distinct extracellular signals. Given that the local translatome is large, selectively translated, and cue-specifically remodeled, a fundamental question concerns how selective translation is achieved locally. Here, we review the emerging regulatory mechanisms of local selective translation in neuronal subcellular compartments, their mRNA targets, and their orchestration. We discuss mechanisms of local selective translation that remain unexplored. Finally, we describe clinical implications and potential therapeutic strategies in light of the latest advances in gene therapy.

Insulin signaling in skeletal muscle during inflammation and/or immobilisation

BACKGROUND

The decline in the downstream signal transduction pathway of anabolic hormone, insulin, could play a key role in the muscle atrophy and insulin resistance observed in patients with intensive care unit acquired weakness (ICUAW). This study investigated the impact of immobilisation via surgical knee and ankle fixation and inflammation via Corynebacterium parvum injection, alone and in combination, as risk factors for altering insulin transduction and, therefore, their role in ICUAW.

RESULTS

Muscle weight was significantly decreased due to immobilisation [estimated effect size (95% CI) - 0.10 g (- 0.12 to - 0.08); p < 0.001] or inflammation [estimated effect size (95% CI) - 0.11 g (- 0.13 to - 0.09); p < 0.001] with an additive effect of both combined (p = 0.024). pAkt was only detectable after insulin stimulation [estimated effect size (95% CI) 85.1-fold (76.2 to 94.0); p < 0.001] irrespective of the group and phosphorylation was not impaired by the different perturbations. Nevertheless, the phosphorylation of GSK3 observed in the control group after insulin stimulation was decreased in the immobilisation [estimated effect size (95% CI) - 40.2 (- 45.6 to - 34.8)] and inflammation [estimated effect size (95% CI) - 55.0 (- 60.4 to - 49.5)] groups. The expression of phosphorylated GS (pGS) was decreased after insulin stimulation in the control group and significantly increased in the immobilisation [estimated effect size (95% CI) 70.6-fold (58.8 to 82.4)] and inflammation [estimated effect size (95% CI) 96.7 (85.0 to 108.5)] groups.

CONCLUSIONS

Both immobilisation and inflammation significantly induce insulin resistance, i.e., impair the insulin signaling pathway downstream of Akt causing insufficient GSK phosphorylation and, therefore, its activation which caused increased glycogen synthase phosphorylation, which could contribute to muscle atrophy of immobilisation and inflammation.

Airway smooth muscle function in asthma

Known to have affected around 340 million people across the world in 2018, asthma is a prevalent chronic inflammatory disease of the airways. The symptoms such as wheezing, dyspnea, chest tightness, and cough reflect episodes of reversible airway obstruction. Asthma is a heterogeneous disease that varies in clinical presentation, severity, and pathobiology, but consistently features airway hyperresponsiveness (AHR)—excessive airway narrowing due to an exaggerated response of the airways to various stimuli. Airway smooth muscle (ASM) is the major effector of exaggerated airway narrowing and AHR and many factors may contribute to its altered function in asthma. These include genetic predispositions, early life exposure to viruses, pollutants and allergens that lead to chronic exposure to inflammatory cells and mediators, altered innervation, airway structural cell remodeling, and airway mechanical stress. Early studies aiming to address the dysfunctional nature of ASM in the etiology and pathogenesis of asthma have been inconclusive due to the methodological limitations in assessing the intrapulmonary airways, the site of asthma. The study of the trachealis, although convenient, has been misleading as it has shown no alterations in asthma and it is not as exposed to inflammatory cells as intrapulmonary ASM. Furthermore, the cartilage rings offer protection against stress and strain of repeated contractions. More recent strategies that allow for the isolation of viable intrapulmonary ASM tissue reveal significant mechanical differences between asthmatic and non-asthmatic tissues. This review will thus summarize the latest techniques used to study ASM mechanics within its environment and in isolation, identify the potential causes of the discrepancy between the ASM of the extra- and intrapulmonary airways, and address future directions that may lead to an improved understanding of ASM hypercontractility in asthma.

The roles of growth regulation and appendage patterning genes in the morphogenesis of treehopper pronota

Treehoppers of the insect family Membracidae have evolved enlarged and elaborate pronotal structures, which is hypothesized to involve co-opted expression of genes that are shared with the wings. Here, we investigate the similarity between the pronotum and wings in relation to growth. Our study reveals that the ontogenetic allometry of the pronotum is similar to that of wings in Membracidae, but not the outgroup. Using transcriptomics, we identify genes related to translation and protein synthesis, which are mutually upregulated. These genes are implicated in the eIF2, eIF4/p70S6K and mTOR pathways, and have known roles in regulating cell growth and proliferation. We find that species-specific differential growth patterning of the pronotum begins as early as the third instar, which suggests that expression of appendage patterning genes occurs long before the metamorphic molt. We propose that a network related to growth and size determination is the more likely mechanism shared with wings. However, regulators upstream of the shared genes in pronotum and wings need to be elucidated to substantiate whether co-option has occurred. Finally, we believe it will be helpful to distinguish the mechanisms leading to pronotal size from those regulating pronotal shape as we make sense of this spectacular evolutionary innovation.

The role of eIF2 phosphorylation in cell and organismal physiology: new roles for well-known actors

Control of protein synthesis (mRNA translation) plays key roles in shaping the proteome and in many physiological, including homeostatic, responses. One long-known translational control mechanism involves phosphorylation of initiation factor, eIF2, which is catalysed by any one of four protein kinases, which are generally activated in response to stresses. They form a key arm of the integrated stress response (ISR). Phosphorylated eIF2 inhibits eIF2B (the protein that promotes exchange of eIF2-bound GDP for GTP) and thus impairs general protein synthesis. However, this mechanism actually promotes translation of certain mRNAs by virtue of specific features they possess. Recent work has uncovered many previously unknown features of this regulatory system. Several studies have yielded crucial insights into the structure and control of eIF2, including that eIF2B is regulated by several metabolites. Recent studies also reveal that control of eIF2 and the ISR helps determine organismal lifespan and surprising roles in sensing mitochondrial stresses and in controlling the mammalian target of rapamycin (mTOR). The latter effect involves an unexpected role for one of the eIF2 kinases, HRI. Phosphoproteomic analysis identified new substrates for another eIF2 kinase, Gcn2, which senses the availability of amino acids. Several genetic disorders arise from mutations in genes for eIF2α kinases or eIF2B (i.e. vanishing white matter disease, VWM and microcephaly, epileptic seizures, microcephaly, hypogenitalism, diabetes and obesity, MEHMO). Furthermore, the eIF2-mediated ISR plays roles in cognitive decline associated with Alzheimer's disease. New findings suggest potential therapeutic value in interfering with the ISR in certain settings, including VWM, for example by using compounds that promote eIF2B activity.

Regulation and function of elF2B in neurological and metabolic disorders

Eukaryotic initiation factor 2B, eIF2B is a guanine nucleotide exchange, factor with a central role in coordinating the initiation of translation. During stress and disease, the activity of eIF2B is inhibited via the phosphorylation of its substrate eIF2 (p-eIF2α). A number of different kinases respond to various stresses leading to the phosphorylation of the alpha subunit of eIF2, and collectively this regulation is known as the integrated stress response, ISR. This targeting of eIF2B allows the cell to regulate protein synthesis and reprogramme gene expression to restore homeostasis. Advances within structural biology have furthered our understanding of how eIF2B interacts with eIF2 in both the productive GEF active form and the non-productive eIF2α phosphorylated form. Here, current knowledge of the role of eIF2B in the ISR is discussed within the context of normal and disease states focusing particularly on diseases such as vanishing white matter disease (VWMD) and permanent neonatal diabetes mellitus (PNDM), which are directly linked to mutations in eIF2B. The role of eIF2B in synaptic plasticity and memory formation is also discussed. In addition, the cellular localisation of eIF2B is reviewed and considered along with the role of additional in vivo eIF2B binding factors and protein modifications that may play a role in modulating eIF2B activity during health and disease.

Therapy Trial Design in Vanishing White Matter: An Expert Consortium Opinion

Vanishing white matter (VWM) is a leukodystrophy caused by recessive variants in the genes EIF2B1-EIF2B5. It is characterized by chronic neurologic deterioration with superimposed stress-provoked episodes of rapid decline. Disease onset spans from the antenatal period through senescence. Age at onset predicts disease evolution for patients with early onset, whereas disease evolution is unpredictable for later onset; patients with infantile and early childhood onset consistently have severe disease with rapid neurologic decline and often early death, whereas patients with later onset have highly variable disease. VWM is rare, but likely underdiagnosed, particularly in adults. Apart from measures to prevent stressors that could provoke acute deteriorations, only symptomatic care is currently offered. With increased insight into VWM disease mechanisms, opportunities for treatment have emerged. EIF2B1-EIF2B5 encode the 5-subunit eukaryotic initiation factor 2B complex, which is essential for translation of mRNAs into proteins and is a principal regulator of the integrated stress response (ISR). ISR deregulation is central to VWM pathology. Targeting components of the ISR has proven beneficial in mutant VWM mouse models, and several drugs are now in clinical development. However, clinical trials in VWM pose considerable challenges: low numbers of known patients with VWM, unpredictable disease course for patients with onset after early childhood, absence of intermediate biomarkers, and novel first-in-human molecular targets. Given these challenges and considering the critical need to offer therapies, we have formulated recommendations for enhanced diagnosis, drug trial setup, and patient selection, based on our expert evaluation of molecular, laboratory, and clinical data.

Effects of Various Muscle Disuse States and Countermeasures on Muscle Molecular Signaling

Skeletal muscle is capable of changing its structural parameters, metabolic rate and functional characteristics within a wide range when adapting to various loading regimens and states of the organism. Prolonged muscle inactivation leads to serious negative consequences that affect the quality of life and work capacity of people. This review examines various conditions that lead to decreased levels of muscle loading and activity and describes the key molecular mechanisms of muscle responses to these conditions. It also details the theoretical foundations of various methods preventing adverse muscle changes caused by decreased motor activity and describes these methods. A number of recent studies presented in this review make it possible to determine the molecular basis of the countermeasure methods used in rehabilitation and space medicine for many years, as well as to identify promising new approaches to rehabilitation and to form a holistic understanding of the mechanisms of gravity force control over the muscular system.

Shared and distinct mechanisms of skeletal muscle atrophy: A narrative review

Maintenance of skeletal muscle mass and function is an incredibly nuanced balance of anabolism and catabolism that can become distorted within different pathological conditions. In this paper we intend to discuss the distinct intracellular signaling events that regulate muscle protein atrophy for a given clinical occurrence. Aside from the common outcome of muscle deterioration, several conditions have at least one or more distinct mechanisms that creates unique intracellular environments that facilitate muscle loss. The subtle individuality to each of these given pathologies can provide both researchers and clinicians with specific targets of interest to further identify and increase the efficacy of medical treatments and interventions.

To Explore the Mechanism and Equivalent Molecular Group of Radix Astragali and Semen Lepidii in Treating Heart Failure Based on Network Pharmacology

Radix Astragali and Semen Lepidii (HQ-TLZ) is a commonly used herbal medicine combination for treatment of heart failure, which has a good clinical effect. However, its active components and mechanism of action are not clear, which limits its clinical application and development. In this study, we explored the mechanism of action of HQ-TLZ in the treatment of heart failure based on network pharmacology. We obtained 11 active ingredients and 109 targets from the TCMSP database and SwissTargetPrediction database. Next, we constructed the action network and carried out enrichment analysis. The results showed that HQ-TLZ treatment of heart failure is primarily achieved by regulating the insulin resistance, erbB signaling pathway, PI3K-Akt signaling pathway, and VEGF signaling pathway. After inverse targeting, molecular docking, and literature search, we determined that the equivalent molecular groups of HQ-TLZ in the treatment of heart failure were quercetin and kaempferol. Based on network pharmacology, we reveal the mechanism of action of HQ-TLZ in the treatment of heart failure to a certain extent. At the same time, we determined the composition of the equivalent molecular group. This provides a bridge for the consistency evaluation of natural herbs and molecular compounds, which is beneficial to the development of novel drugs and further research.

Amino Acid Trafficking and Skeletal Muscle Protein Synthesis: A Case of Supply and Demand

Skeletal muscle protein synthesis is a highly complex process, influenced by nutritional status, mechanical stimuli, repair programs, hormones, and growth factors. The molecular aspects of protein synthesis are centered around the mTORC1 complex. However, the intricacies of mTORC1 regulation, both up and downstream, have expanded overtime. Moreover, the plastic nature of skeletal muscle makes it a unique tissue, having to coordinate between temporal changes in myofiber metabolism and hypertrophy/atrophy stimuli within a tissue with considerable protein content. Skeletal muscle manages the push and pull between anabolic and catabolic pathways through key regulatory proteins to promote energy production in times of nutrient deprivation or activate anabolic pathways in times of nutrient availability and anabolic stimuli. Branched-chain amino acids (BCAAs) can be used for both energy production and signaling to induce protein synthesis. The metabolism of BCAAs occur in tandem with energetic and anabolic processes, converging at several points along their respective pathways. The fate of intramuscular BCAAs adds another layer of regulation, which has consequences to promote or inhibit muscle fiber protein anabolism. This review will outline the general mechanisms of muscle protein synthesis and describe how metabolic pathways can regulate this process. Lastly, we will discuss how BCAA availability and demand coordinate with synthesis mechanisms and identify key factors involved in intramuscular BCAA trafficking.

The role of GSK3 in metabolic pathway perturbations in cancer

Malignant transformation and tumor progression are accompanied by significant perturbations in metabolic programs. As such, cancer cells support high ATP turnover to construct the building blocks needed to fuel neoplastic growth. The coordination of metabolic networks in malignant cells is dependent on the collaboration with cellular signaling pathways. Glycogen synthase kinase 3 (GSK3) lies at the convergence of several signaling axes, including the PI3K/AKT/mTOR, AMPK, and Wnt pathways, which influence cancer initiation, progression and therapeutic responses. Accordingly, GSK3 modulates metabolic processes, including protein and lipid synthesis, glucose and mitochondrial metabolism, as well as autophagy. In this review, we highlight current knowledge of the role of GSK3 in metabolic perturbations in cancer.

The Role of GSK-3β in the Regulation of Protein Turnover, Myosin Phenotype, and Oxidative Capacity in Skeletal Muscle under Disuse Conditions

Skeletal muscles, being one of the most abundant tissues in the body, are involved in many vital processes, such as locomotion, posture maintenance, respiration, glucose homeostasis, etc. Hence, the maintenance of skeletal muscle mass is crucial for overall health, prevention of various diseases, and contributes to an individual’s quality of life. Prolonged muscle inactivity/disuse (due to limb immobilization, mechanical ventilation, bedrest, spaceflight) represents one of the typical causes, leading to the loss of muscle mass and function. This disuse-induced muscle loss primarily results from repressed protein synthesis and increased proteolysis. Further, prolonged disuse results in slow-to-fast fiber-type transition, mitochondrial dysfunction and reduced oxidative capacity. Glycogen synthase kinase 3β (GSK-3β) is a key enzyme standing at the crossroads of various signaling pathways regulating a wide range of cellular processes. This review discusses various important roles of GSK-3β in the regulation of protein turnover, myosin phenotype, and oxidative capacity in skeletal muscles under disuse/unloading conditions and subsequent recovery. According to its vital functions, GSK-3β may represent a perspective therapeutic target in the treatment of muscle wasting induced by chronic disuse, aging, and a number of diseases.

Hepatic DNAJB9 Drives Anabolic Biasing to Reduce Steatosis and Obesity

Nutrients stimulate the anabolic synthesis of proteins and lipids, but selective insulin resistance in obesity biases the anabolic program toward lipogenesis. Here, we report the identification of a DNAJB9-driven program that favors protein synthesis and energy production over lipid accumulation. We show there are two pools of DNAJB9 cochaperone. DNAJB9 in the ER lumen promotes the degradation of the lipogenic transcription factor SREBP1c through ERAD, whereas its counterpart on the ER membrane promotes the assembly of mTORC2 in the cytosol and stimulates the synthesis of proteins and ATP. The expression of Dnajb9 is induced by nutrients and downregulated in the obese mouse liver. Restoration of hepatic DNAJB9 expression effectively improves insulin sensitivity, restores protein synthesis, and suppresses food intake, accompanied by reduced hepatic steatosis and adiposity in multiple mouse models of obesity. Therefore, targeting the anabolic balance may provide a unique opportunity to tackle obesity and diabetes.

Regulation of eukaryotic translation initiation factor 6 dynamics through multisite phosphorylation by GSK3

Eukaryotic translation initiation factor 6 (eIF6) is essential for the synthesis of 60S ribosomal subunits and for regulating the association of 60S and 40S subunits. A mechanistic understanding of how eIF6 modulates translation in response to stress, specifically starvation-induced stress, is lacking. We here show a novel mode of eIF6 regulation by glycogen synthase kinase 3 (GSK3) that is predominantly active in response to serum starvation. Both GSK3α and GSK3β phosphorylate human eIF6. Multiple residues in the C terminus of eIF6 are phosphorylated by GSK3 in a sequential manner. In response to serum starvation, eIF6 accumulates in the cytoplasm, and this altered localization depends on phosphorylation by GSK3. Disruption of eIF6 phosphorylation exacerbates the translation inhibitory response to serum starvation and stalls cell growth. These results suggest that eIF6 regulation by GSK3 contributes to the attenuation of global protein synthesis that is critical for adaptation to starvation-induced stress.

Cellular and molecular features of neurogenic skeletal muscle atrophy

Neurogenic atrophy refers to the loss of muscle mass and function that results directly from injury or disease of the peripheral nervous system. Individuals with neurogenic atrophy may experience reduced functional status and quality of life and, in some circumstances, reduced survival. Distinct pathological findings on muscle histology can aid in diagnosis of a neurogenic cause for muscle dysfunction, and provide indicators for the chronicity of denervation. Denervation induces pleiotypic responses in skeletal muscle, and the molecular mechanisms underlying neurogenic muscle atrophy appear to share common features with other causes of muscle atrophy, including activation of FOXO transcription factors and corresponding induction of ubiquitin-proteasomal and lysosomal degradation. In this review, we provide an overview of histologic features of neurogenic atrophy and a summary of current understanding of underlying mechanisms.

Curcumin ameliorates CKD-induced mitochondrial dysfunction and oxidative stress through inhibiting GSK-3β activity

Curcumin has been reported to attenuate muscle atrophy. However, the underling mechanism remains unclear. The aim of this study was to investigate whether curcumin could improve chronic kidney disease (CKD)-induced muscle atrophy and mitochondrial dysfunction by inhibiting glycogen synthase kinase-3β (GSK-3β) activity. The sham and CKD mice were fed either a control diet or an identical diet containing 0.04% curcumin for 12 weeks. The C2C12 myotubes were treated with H₂O₂ in the presence or absence of curcumin. In addition, wild-type and muscle-specific GSK-3β knockout (KO) CKD model mice were made by 5/6 nephrectomy, and the sham was regarded as control. Curcumin could exert beneficial effects, including weight maintenance and improved muscle function, increased mitochondrial biogenesis, alleviated mitochondrial dysfunction by increasing adenosine triphosphate levels, activities of mitochondrial electron transport chain complexes and basal mitochondrial respiration and suppressing mitochondrial membrane potential. In addition, curcumin modulated redox homeostasis by increasing antioxidant activity and suppressed mitochondrial oxidative stress. Moreover, the protective effects of curcumin had been found to be mediated via inhibiting GSK-3β activity in vitro and in vivo. Importantly, GSK-3β KO contributed to improved mitochondrial function, attenuated mitochondrial oxidative damage and augmented mitochondrial biogenesis in muscle of CKD. Overall, this study suggested that curcumin alleviated CKD-induced mitochondrial oxidative damage and mitochondrial dysfunction via inhibiting GSK-3β activity in skeletal muscle.

Comprehensive investigation of selectivity landscape of glycogen synthase kinase-3 inhibitors

Interaction signatures of drug candidates are characteristic to off-target (neutral) and antitarget (negative) effects, inferring reduced efficiency, side-effects and high attrition rate. Today's retroactive scaled-down virtual screening (VS) experiments relying on benchmarking datasets are extensively involved to assess ligand enrichment in the real-world problem. In recent years, unbiased benchmarking sets turned into a tremendous need to assist virtual screening methodologies for emerging drug targets. To date, the benchmarking datasets are quite limited, whereas glycogen synthase kinase-3 (GSK-3) is not included into directories of benchmarking datasets such as DUD-e, MUV, etc. Herein we introduced our in-house algorithm to build an unbiased benchmarking dataset, including highly selective, moderately selective and nonselective inhibitors for a significant therapeutic target - GSK-3, suitable for both ligand-based and structure-based VS approaches. These datasets are unbiased in terms of physico-chemical properties and topological descriptors, as resulted from mean(ROC-AUC) leave-one-out cross-validation (LOO CV). and additional 2 D similarity search. Moreover, we investigated the gradual selectivity dataset by application of multiple 2 D similarity coefficients and distances, 3 D similarity and docking. Besides the resulted links between the enrichment of selective GSK-3 inhibitors and their chemical structures, a database of compounds and their 3 D similarity signatures including cut-off thresholds for enhanced selectivity was generated. 2 D similarity space analysis revealed that selectivity problem cannot be evaluated appropriately with 2 D similarity searching alone. The current analysis provided useful, comprehensive insights, which may facilitate the knowledge-based identification of novel selective GSK-3 inhibitors.Communicated by Ramaswamy H. Sarma.

Partial Least Squares Discriminant Analysis and 3D Similarity Perspective Applied to Analyze Comprehensively the Selectivity of Glycogen Synthase Kinase 3 Inhibitors

The current work was conducted to investigate the effectiveness of two conceptually distinct in silico ligand-based tools: Partial Least Squares Discriminant Analysis (PLS-DA) and 3D similarity, including shape, physico-chemical and electrostatics to classify target-specific pharmacophores with enrichment power for selective GSK-3 inhibitors against the phylogenetically related CDK-2, CDK-4, CDK-5 and PKC. All virtual screens were performed on four data sets of targets matched pairwise, including selective and nonselective inhibitors for GSK-3. The classification method PLS-DA results revealed that all obtained models are statistically robust according to the cross-validation and response permutation tests. Regarding selective GSK-3 inhibitors differentiation in terms of selectivity (Se), specificity (Sp), and accuracy (ACC), the PLS-DA models for CDK-4/GSK-3, and PKC/GSK-3 datasets are highly efficient discriminative. 3D similarity searches for CDK-4/GSK-3, PKC/GSK-3, and CDK-2/GSK-3 datasets using the most selective reference molecules lead to highest enrichments of selective GSK-3 inhibitors. EON yields excellent early and overall enrichments for ET_ST and ET_combo for most selective query for CDK-4/GSK-3. CDK-5/GSK-3 dataset didn't show consistent statistically significant enrichments for 3D similarity virtual screening. The current methodology is reliable and could be used as a powerful tool for the detection of potentially selective molecules targeting GSK-3.

Cardiac Contractility Modulation Attenuates Chronic Heart Failure in a Rabbit Model via the PI3K/AKT Pathway

The Akt plays an important role in regulating cardiac growth, myocardial angiogenesis, and cell death in cardiac myocytes. However, there are few studies to focus on the responses of the Akt pathway to cardiac contractility modulation (CCM) in a chronic heart failure (HF) model. In this study, the effects of CCM on the treatment of HF in a rabbit model were investigated. Thirty six-month-old rabbits were randomly separated into control, HF, and CCM groups. The rabbits in HF and CCM groups were pressure uploaded, which can cause an aortic constriction. Then, CCM was gradually injected to the myocardium of rabbits in the CCM group, and this process lasted for four weeks with six hours per day. Rabbit body weight, heart weight, and heart beating rates were recorded during the experiment. To assess the CCM impacts, rabbit myocardial histology was examined as well. Additionally, western blot analysis was employed to measure the protein levels of Akt, FOXO3, Beclin, Pi3k, mTOR, GSK-3β, and TORC2 in the myocardial histology of rabbits. Results showed that the body and heart weight of rabbits decreased significantly after suffering HF when compared with those in the control group. However, they gradually recovered after CCM application. The CCM significantly decreased collagen volume fraction in myocardial histology of HF rabbits, indicating that CCM therapy attenuated myocardial fibrosis and collagen deposition. The levels of Akt, FOXO3, Beclin, mTOR, GSK-3β, and TORC2 were significantly downregulated, but Pi3k concentration was greatly upregulated after CCM utilization. Based on these findings, it was concluded that CCM could elicit positive effects on HF therapy, which was potentially due to the variation in the Pi3k/Akt signaling pathway.

Resveratrol modulates the Akt/GSK-3β signaling pathway in a middle cerebral artery occlusion animal model

Cerebral ischemia is a major cause of neurodegenerative disease. It induces neuronal vulnerability and susceptibility, and leads to neuronal cell death. Resveratrol is a polyphenolic compound that acts as an anti-oxidant. It exerts a neuroprotective effect against focal cerebral ischemic injury. Akt signaling pathway is accepted as a representative cell survival pathway, including proliferation, growth, and glycogen synthesis. This study investigated whether resveratrol regulates Akt/glycogen synthase kinase-3β (GSK-3β) pathway in a middle cerebral artery occlusion (MCAO)-induced ischemic brain injury. Adult male rats were intraperitoneally injected with vehicle or resveratrol (30 mg/kg) and cerebral cortices were isolated 24 h after MCAO. Neurological behavior test, corner test, brain edema measurment, and 2,3,5-triphenyltetrazolium chloride staining were performed to elucidate the neuroprotective effects of resveratrol. Phospho-Akt and phospho-GSK-3β expression levels were measured using Western blot analysis. MCAO injury led to severe neurobehavioral deficit, infraction, and histopathological changes in cerebral cortex. However, resveratrol treatment alleviated these changes caused by MCAO injury. Moreover, MCAO injury induced decreases in phospho-Akt and phospho-GSK-3β protein levels, whereas resveratrol attenuated these decreases. Phosphorylations of Akt and GSK-3β act as a critical role for the suppression of apoptotic cell death. Thus, our finding suggests that resveratrol attenuates neuronal cell death in MCAO-induced cerebral ischemia and Akt/GSK-3β signaling pathway contributes to the neuroprotective effect of resveratrol.

Effects of Plantar Mechanical Stimulation on Anabolic and Catabolic Signaling in Rat Postural Muscle Under Short-Term Simulated Gravitational Unloading

It is known that plantar mechanical stimulation (PMS) is able to attenuate unloading-induced skeletal muscle atrophy and impaired muscle function. However, molecular mechanisms underlying the effect of PMS on skeletal muscle during unloading remain undefined. The aim of the study was to evaluate the effects of PMS on anabolic and catabolic signaling pathways in rat soleus at the early stages of mechanical unloading. Wistar rats were randomly assigned to ambulatory control, hindlimb suspension (HS) for 1 or 3 days, and HS for 1 or 3 days with PMS. The key anabolic and catabolic markers were assessed by western blotting and RT-PCR. Protein synthesis (PS) rate was estimated using SUnSET technique. PMS attenuated a 1-day HS-induced decrease in 4E-BP1, GSK-3β, and AMPK phosphorylation. PMS also partially prevented a decrease in PS, phosphorylation of GSK-3β, nNOS, and an increase in eEF2 phosphorylation after 3-day HS. PMS during 1- and 3-day HS prevented MuRF-1, but not MAFbx, upregulation but did not affect markers of ribosome biogenesis (18S + 28S rRNA, c-myc) as well as AKT phosphorylation. Thus, PMS during 3-day HS partially prevented a decrease in the global rate of PS in rat soleus muscle, which was accompanied by attenuation of MuRF-1 mRNA expression as well as changes in GSK-3β, nNOS, and eEF2 phosphorylation.

An expanding GSK3 network: implications for aging research

The last few decades of longevity research have been very exciting. We now know that longevity and healthspan can be manipulated across species, from unicellular eukaryotes to nonhuman primates, and that while aging itself is inevitable, how we age is malleable. Numerous dietary, genetic, and pharmacological studies now point to links between metabolism and growth regulation as a central aspect in determining longevity and, perhaps more importantly, health with advancing age. Here, we focus on a relatively new player in aging studies GSK3, glycogen synthase kinase, a key factor in growth and metabolism whose name fails to convey the extensive breadth of its role in cellular adaptation. First, we provide a brief overview of GSK3, touching on those aspects that are likely relevant to aging. Then, we outline the role of GSK3 in cellular functions including growth signaling, cell fate, and metabolism. Next, we describe evidence demonstrating a direct role for GSK3 in a range of age-related diseases, despite the fact that they differ considerably in their etiology and pathology. Finally, we discuss the role that GSK3 may play in normative aging and how GSK3 might be a suitable target to oppose age-related disease vulnerability.

Phosphorylation and Signal Transduction Pathways in Translational Control

Protein synthesis, including the translation of specific messenger RNAs (mRNAs), is regulated by extracellular stimuli such as hormones and by the levels of certain nutrients within cells. This control involves several well-understood signaling pathways and protein kinases, which regulate the phosphorylation of proteins that control the translational machinery. These pathways include the mechanistic target of rapamycin complex 1 (mTORC1), its downstream effectors, and the mitogen-activated protein (MAP) kinase (extracellular ligand-regulated kinase [ERK]) signaling pathway. This review describes the regulatory mechanisms that control translation initiation and elongation factors, in particular the effects of phosphorylation on their interactions or activities. It also discusses current knowledge concerning the impact of these control systems on the translation of specific mRNAs or subsets of mRNAs, both in physiological processes and in diseases such as cancer.

IMP2 Increases Mouse Skeletal Muscle Mass and Voluntary Activity by Enhancing Autocrine Insulin-Like Growth Factor 2 Production and Optimizing Muscle Metabolism

Insulin-like growth factor 2 (IGF2) mRNA binding protein 2 (IMP2) was selectively deleted from adult mouse muscle; two phenotypes were observed: decreased accrual of skeletal muscle mass after weaning and reduced wheel-running activity but normal forced treadmill performance. Reduced wheel running occurs when mice are fed a high-fat diet but is normalized when mice consume standard chow. The two phenotypes are due to altered output from different IMP2 client mRNAs. The reduced fiber size of IMP2-deficient muscle is attributable, in part, to diminished autocrine Igf2 production; basal tyrosine phosphorylation of the insulin and IGF1 receptors is diminished, and Akt1 activation is selectively reduced. Gsk3α is disinhibited, and S536-phosphorylated ε subunit of eukaryotic initiation factor 2B [eIF2Bε(S536)] is hyperphosphorylated. Protein synthesis is reduced despite unaltered mTOR complex 1 activity. The diet-dependent reduction in voluntary exercise is likely due to altered muscle metabolism, as contractile function is normal. IMP2-deficient muscle exhibits reduced fatty acid oxidation, due to a reduced abundance of mRNA of peroxisome proliferator-activated receptor α (PPARα), an IMP2 client, and PPARα protein. IMP2-deficient muscle fibers treated with a mitochondrial uncoupler to increase electron flux, as occurs with exercise, exhibit reduced oxygen consumption from fatty acids, with higher oxygen consumption from glucose. The greater dependence on muscle glucose metabolism during increased oxygen demand may promote central fatigue and thereby diminish voluntary activity.

Noncanonical Modulation of the eIF2 Pathway Controls an Increase in Local Translation during Neural Wiring

Local translation is rapidly regulated by extrinsic signals during neural wiring, but its control mechanisms remain elusive. Here we show that the extracellular cue Sema3A induces an initial burst in local translation that precisely controls phosphorylation of the translation initiation factor eIF2α via the unfolded protein response (UPR) kinase PERK. Strikingly, in contrast to canonical UPR signaling, Sema3A-induced eIF2α phosphorylation bypasses global translational repression and underlies an increase in local translation through differential activity of eIF2B mediated by protein phosphatase 1. Ultrasensitive proteomics analysis of axons reveals 75 proteins translationally controlled via the Sema3A-p-eIF2α pathway. These include proteostasis- and actin cytoskeleton-related proteins but not canonical stress markers. Finally, we show that PERK signaling is needed for directional axon migration and visual pathway development in vivo. Thus, our findings reveal a noncanonical eIF2 signaling pathway that controls selective changes in axon translation and is required for neural wiring.

Prospective Views for Whey Protein and/or Resistance Training Against Age-related Sarcopenia

Skeletal muscle aging is characterized by decline in skeletal muscle mass and function along with growing age, which consequently leads to age-related sarcopenia, if without any preventive timely treatment. Moreover, age-related sarcopenia in elder people would contribute to falls and fractures, disability, poor quality of life, increased use of hospital services and even mortality. Whey protein (WP) and/or resistance training (RT) has shown promise in preventing and treating age-related sarcopenia. It seems that sex hormones could be potential contributors for gender differences in skeletal muscle and age-related sarcopenia. In addition, skeletal muscle and the development of sarcopenia are influenced by gut microbiota, which in turn is affected by WP or RT. Gut microbiota may be a key factor for WP and/or RT against age-related sarcopenia. Therefore, focusing on sex hormones and gut microbiota may do great help for preventing, treating and better understanding age-related sarcopenia.

Acute recovery from disuse atrophy: the role of stretch-activated ion channels in the activation of anabolic signaling in skeletal muscle

The aim of the study was to 1) measure time-course alternations in the rate of protein synthesis (PS) and phosphorylation status of the key anabolic markers, and 2) find out the role of stretch-activated ion channels (SACs) in the activation of anabolic signaling in the rat soleus during an acute reloading following disuse atrophy. Wistar rats were subjected to 14-day hindlimb suspension (HS) followed by 6, 12, and 24 h of reloading. To examine the role of SAC in the reloading-induced activation of anabolic signaling, the rats were treated with gadolinium (Gd³⁺), a SAC blocker. The content of signaling proteins was determined by Western blot. c-Myc mRNA expression was assessed by RT-PCR. After 24-h reloading, the PS rate was elevated by 44% versus control. After 6-h reloading, the p-70-kDa ribosomal protein S6 kinase (p70S6k) and translation initiation factor 4E-binding protein 1 (4E-BP1) did not differ from control; however, 12-h reloading resulted in an upregulation of both p70s6k and 4E-BP1 phosphorylation versus control. The phosphorylation of AKT (Ser473) and glycogen synthase kinase-3β (Ser9) was reduced after HS and then completely restored by 12-h reloading. c-Myc was significantly upregulated during the entire reloading. Gd³⁺ treatment during reloading (12 h) prevented a full phosphorylation of p70S6k, rpS6, 4E-BP1, as well as PS activation. The results of the study suggest that 1) enhanced PS during the acute recovery from HS may be associated with the activation of ribosome biogenesis as well as mammalian target of rapamycin complex 1 (mTORC1)-dependent signaling pathways, and 2) functional SACs are necessary for complete activation of mTORC1 signaling in rat soleus during acute recovery from HS.

Molecular mechanism involved in cyclophosphamide-induced cardiotoxicity: Old drug with a new vision

Cyclophosphamide (CP) is an important anticancer drug which belongs to the class of alkylating agent. Cyclophosphamide is mostly used in bone marrow transplantation, rheumatoid arthritis, lupus erythematosus, multiple sclerosis, neuroblastoma and other types of cancer. Dose-related cardiotoxicity is a limiting factor for its use. CP-induced cardiotoxicity ranges from 7 to 28% and mortality ranges from 11 to 43% at the therapeutic dose of 170-180 mg/kg, i.v. CP undergoes hepatic metabolism that results in the production of aldophosphamide. Aldophosphamide decomposes into phosphoramide mustard & acrolein. Phosphoramide is an active neoplastic agent, and acrolein is a toxic metabolite which acts on the myocardium and endothelial cells. This is the first review article that talks about cyclophosphamide-induced cardiotoxicity and the different signaling pathways involved in its pathogenicity. Based on the available literature, CP is accountable for cardiomyocytes energy pool alteration by affecting the heart fatty acid binding proteins (H-FABP). CP has been found associated with cardiomyocytes apoptosis, inflammation, endothelial dysfunction, calcium dysregulation, endoplasmic reticulum damage, and mitochondrial damage. Molecular mechanism of cardiotoxicity has been discussed in detail through crosstalk of Nrf2/ARE, Akt/GSK-3β/NFAT/calcineurin, p53/p38MAPK, NF-kB/TLR-4, and Phospholamban/SERCA-2a signaling pathway. Based on the available literature we support the fact that metabolites of CP are responsible for cardiotoxicity due to depletion of antioxidants/ATP level, altered contractility, damaged endothelium and enhanced pro-inflammatory/pro-apoptotic activities resulting into cardiomyopathy, myocardial infarction, and heart failure. Dose adjustment, elimination/excretion of acrolein and maintenance of endogenous antioxidant pool could be the therapeutic approach to mitigate the toxicities.

Regulation of Protein Synthesis in Inactivated Skeletal Muscle: Signal Inputs, Protein Kinase Cascades, and Ribosome Biogenesis

Disuse atrophy of skeletal muscles is characterized by a significant decrease in the mass and size of muscle fibers. Disuse atrophy develops as a result of prolonged reduction in the muscle functional activity caused by bed rest, limb immobilization, and real or simulated microgravity. Disuse atrophy is associated with the downregulation of protein biosynthesis and simultaneous activation of protein degradation. This review is focused on the key molecular mechanisms regulating the rate of protein synthesis in mammalian skeletal muscles during functional unloading.

Dysregulated Translation in Neurodevelopmental Disorders: An Overview of Autism-Risk Genes Involved in Translation

Regulated local translation-whereby specific mRNAs are transported and localized in subcellular domains where they are translated in response to regional signals-allows for remote control of gene expression to concentrate proteins in subcellular compartments. Neurons are highly polarized cells with unique features favoring local control for axonal pathfinding and synaptic plasticity, which are key processes involved in constructing functional circuits in the developing brain. Neurodevelopmental disorders are caused by genetic or environmental factors that disturb the nervous system's development during prenatal and early childhood periods. The growing list of genetic mutations that affect mRNA translation raises the question of whether aberrant translatomes in individuals with neurodevelopmental disorders share common molecular features underlying their stereotypical phenotypes and, vice versa, cause a certain degree of phenotypic heterogeneity. Here, we briefly give an overview of the role of local translation during neuronal development. We take the autism-risk gene list and discuss the molecules that (perhaps) are involved in mRNA transport and translation. Both exaggerated and suppressed translation caused by mutations in those genes have been identified or suggested. Finally, we discuss some proof-of-principle regimens for use in autism mouse models to correct dysregulated translation.

Molecular Mechanisms of Lithium Action: Switching the Light on Multiple Targets for Dementia Using Animal Models

Lithium has long been used for the treatment of psychiatric disorders, due to its robust beneficial effect as a mood stabilizing drug. Lithium’s effectiveness for improving neurological function is therefore well-described, stimulating the investigation of its potential use in several neurodegenerative conditions including Alzheimer’s (AD), Parkinson’s (PD) and Huntington’s (HD) diseases. A narrow therapeutic window for these effects, however, has led to concerted efforts to understand the molecular mechanisms of lithium action in the brain, in order to develop more selective treatments that harness its neuroprotective potential whilst limiting contraindications. Animal models have proven pivotal in these studies, with lithium displaying advantageous effects on behavior across species, including worms (C. elegans), zebrafish (Danio rerio), fruit flies (Drosophila melanogaster) and rodents. Due to their susceptibility to genetic manipulation, functional genomic analyses in these model organisms have provided evidence for the main molecular determinants of lithium action, including inhibition of inositol monophosphatase (IMPA) and glycogen synthase kinase-3 (GSK-3). Accumulating pre-clinical evidence has indeed provided a basis for research into the therapeutic use of lithium for the treatment of dementia, an area of medical priority due to its increasing global impact and lack of disease-modifying drugs. Although lithium has been extensively described to prevent AD-associated amyloid and tau pathologies, this review article will focus on generic mechanisms by which lithium preserves neuronal function and improves memory in animal models of dementia. Of these, evidence from worms, flies and mice points to GSK-3 as the most robust mediator of lithium’s neuro-protective effect, but it’s interaction with downstream pathways, including Wnt/β-catenin, CREB/brain-derived neurotrophic factor (BDNF), nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and toll-like receptor 4 (TLR4)/nuclear factor-κB (NFκB), have identified multiple targets for development of drugs which harness lithium’s neurogenic, cytoprotective, synaptic maintenance, anti-oxidant, anti-inflammatory and protein homeostasis properties, in addition to more potent and selective GSK-3 inhibitors. Lithium, therefore, has advantages as a multi-functional therapy to combat the complex molecular pathology of dementia. Animal studies will be vital, however, for comparative analyses to determine which of these defense mechanisms are most required to slow-down cognitive decline in dementia, and whether combination therapies can synergize systems to exploit lithium’s neuro-protective power while avoiding deleterious toxicity.

Regulation of translation initiation factor eIF2B at the hub of the integrated stress response

Phosphorylation of the translation initiation factor eIF2 is one of the most widely used and well-studied mechanisms cells use to respond to diverse cellular stresses. Known as the integrated stress response (ISR), the control pathway uses modulation of protein synthesis to reprogram gene expression and restore homeostasis. Here the current knowledge of the molecular mechanisms of eIF2 activation and its control by phosphorylation at a single-conserved phosphorylation site, serine 51 are discussed with a major focus on the regulatory roles of eIF2B and eIF5 where a current molecular view of ISR control of eIF2B activity is presented. How genetic disorders affect eIF2 or eIF2B is discussed, as are syndromes where excess signaling through the ISR is a component. Finally, studies into the action of recently identified compounds that modulate the ISR in experimental systems are discussed; these suggest that eIF2B is a potential therapeutic target for a wide range of conditions. This article is categorized under: Translation > Translation Regulation.

Signaling Pathways Involved in the Regulation of mRNA Translation

Translation is a key step in the regulation of gene expression and one of the most energy-consuming processes in the cell. In response to various stimuli, multiple signaling pathways converge on the translational machinery to regulate its function. To date, the roles of phosphoinositide 3-kinase (PI3K)/AKT and the mitogen-activated protein kinase (MAPK) pathways in the regulation of translation are among the best understood. Both pathways engage the mechanistic target of rapamycin (mTOR) to regulate a variety of components of the translational machinery. While these pathways regulate protein synthesis in homeostasis, their dysregulation results in aberrant translation leading to human diseases, including diabetes, neurological disorders, and cancer. Here we review the roles of the PI3K/AKT and MAPK pathways in the regulation of mRNA translation. We also highlight additional signaling mechanisms that have recently emerged as regulators of the translational apparatus.

Muscle Atrophy Induced by Mechanical Unloading: Mechanisms and Potential Countermeasures

Prolonged periods of skeletal muscle inactivity or mechanical unloading (bed rest, hindlimb unloading, immobilization, spaceflight and reduced step) can result in a significant loss of musculoskeletal mass, size and strength which ultimately lead to muscle atrophy. With advancement in understanding of the molecular and cellular mechanisms involved in disuse skeletal muscle atrophy, several different signaling pathways have been studied to understand their regulatory role in this process. However, substantial gaps exist in our understanding of the regulatory mechanisms involved, as well as their functional significance. This review aims to update the current state of knowledge and the underlying cellular mechanisms related to skeletal muscle loss during a variety of unloading conditions, both in humans and animals. Recent advancements in understanding of cellular and molecular mechanisms, including IGF1-Akt-mTOR, MuRF1/MAFbx, FOXO, and potential triggers of disuse atrophy, such as calcium overload and ROS overproduction, as well as their role in skeletal muscle protein adaptation to disuse is emphasized. We have also elaborated potential therapeutic countermeasures that have shown promising results in preventing and restoring disuse-induced muscle loss. Finally, identified are the key challenges in this field as well as some future prospectives.

Inhibition mechanism of CDK-2 and GSK-3β by a sulfamoylphenyl derivative of indoline-a molecular dynamics study

A good understanding of the inhibition mechanism of enzymes exhibiting high levels of similarity is the first step to the discovery of new drugs with selective potential. Examples of such proteins include glycogen synthase kinase-3 (GSK-3β) and cyclin-dependent kinase 2 (CDK-2). This article reports the mechanism of such enzyme inhibition as analyzed by an indoline sulfamylophenyl derivative (CHEMBL410072). Previous work has shown that such compounds exhibit selective properties towards their biological targets. This study used a combined procedure involving docking and molecular dynamics simulations, which allowed identification of interactions responsible for stabilization of complexes, and analysis of the dynamic stability of the systems obtained. The initial data obtained during the molecular docking stage show that the ligand molecule exhibits a similar affinity towards both active sites, which was confirmed by quantification of identified interactions and energy values. However, the data do not cover dynamic aspects of the considered systems. Molecular dynamics simulations realized for both complexes indicate significant dissimilarities in dynamics properties of both side chains of the considered ligands, especially in the case of the part containing the sulfamide group. Such increased mobility of the analyzed systems disrupts the stability of binding in the stabilized complex with GSK-3β protein, which finally affects also the binding affinity of the ligand molecule towards this enzyme.

Ligand-induced rapid skeletal muscle atrophy in HSA-Fv2E-PERK transgenic mice

Background

Formation of 43S and 48S preinitiation complexes plays an important role in muscle protein synthesis. There is no muscle-wasting mouse model caused by a repressed 43S preinitiation complex assembly.

Objective

The aim of the present study was to develop a convenient mouse model of skeletal muscle wasting with repressed 43S preinitiation complex assembly.

Material and methods

A ligand-activatable PERK derivative Fv2E-PERK causes the phosphorylation of eukaryotic initiation factor 2α (eIF2α), which inhibits 43S preinitiation complex assembly. Thus, muscle atrophic phenotypes, intracellular signaling pathways, and intracellular free amino acid profiles were investigated in human skeletal muscle α-actin (HSA) promoter-driven Fv2E-PERK transgenic (Tg) mice.

Results

HSA-Fv2E-PERK Tg mice treated with the artificial dimerizer AP20187 phosphorylates eIF2α in skeletal muscles and leads to severe muscle atrophy within a few days of ligand injection. Muscle atrophy was accompanied by a counter regulatory activation of mTORC1 signaling. Moreover, intracellular free amino acid levels were distinctively altered in the skeletal muscles of HSA-Fv2E-PERK Tg mice.

Conclusions

As a novel model of muscle wasting, HSA-Fv2E-PERK Tg mice provide a convenient tool for studying the pathogenesis of muscle loss and for assessing putative therapeutics.

Inhibition of ERK1/2 Restores GSK3β Activity and Protein Synthesis Levels in a Model of Tuberous Sclerosis

Tuberous sclerosis (TS) is a multi-organ autosomal dominant disorder that is best characterized by neurodevelopmental deficits and the presence of benign tumors. TS pathology is caused by mutations in tuberous sclerosis complex (TSC) genes and is associated with insulin resistance, decreased glycogen synthase kinase 3β (GSK3β) activity, activation of the mammalian target of rapamycin complex 1 (mTORC1), and subsequent increase in protein synthesis. Here, we show that extracellular signal–regulated kinases (ERK1/2) respond to insulin stimulation and integrate insulin signaling to phosphorylate and thus inactivate GSK3β, resulting in increased protein synthesis that is independent of Akt/mTORC1 activity. Inhibition of ERK1/2 in Tsc2^−/− cells—a model of TS—rescues GSK3β activity and protein synthesis levels, thus highlighting ERK1/2 as a potential therapeutic target for the treatment of TS.

Cardiomyocyte specific overexpression of a 37 amino acid domain of regulator of G protein signalling 2 inhibits cardiac hypertrophy and improves function in response to pressure overload in mice

Regulator of G protein signalling 2 (RGS2) is known to play a protective role in maladaptive cardiac hypertrophy and heart failure via its ability to inhibit G_q- and G_s- mediated GPCR signalling. We previously demonstrated that RGS2 can also inhibit protein translation and can thereby attenuate cell growth. This G protein-independent inhibitory effect has been mapped to a 37 amino acid domain (RGS2^eb) within RGS2 that binds to eukaryotic initiation factor 2B (eIF2B). When expressed in neonatal rat cardiomyocytes, RGS2^eb attenuates both protein synthesis and hypertrophy induced by G_q- and G_s- activating agents. In the current study, we investigated the potential cardioprotective role of RGS2^eb by determining whether RGS2^eb transgenic (RGS2^eb TG) mice with cardiomyocyte specific overexpression of RGS2^eb show resistance to the development of hypertrophy in comparison to wild-type (WT) controls. Using transverse aortic constriction (TAC) in a pressure-overload hypertrophy model, we demonstrated that cardiac hypertrophy was inhibited in RGS2^eb TG mice compared to WT controls following four weeks of TAC. Expression of the hypertrophic markers atrial natriuretic peptide (ANP) and β-myosin heavy chain (MHC-β) was also reduced in RGS2^eb TG compared to WT TAC animals. Furthermore, cardiac function in RGS2^eb TG TAC mice was significantly improved compared to WT TAC mice. Notably, cardiomyocyte cell size was significantly decreased in TG compared to WT TAC mice. These results suggest that RGS2 may limit pathological cardiac hypertrophy at least in part via the function of its eIF2B-binding domain.

IL-18-dependent NKG2D ligand upregulation on accessory cells is mediated by the PI3K/GSK-3 pathway

NK cells are critical for the control of viral infections. Studies have shown that efficient NK cell activation in response to infection with VV in vivo requires multiple pathways, including the NKG2D pathway. We have recently shown that IL-18 is necessary for the activation of NK cells through upregulation of the NKG2D ligand Rae-1 on DCs upon VV infection. However, how IL-18R signaling on the accessory cells contributes to Rae-1 up-regulation remains to be defined. In this study, we found IL-18-mediated Rae-1 up-regulation in accessory cells, including macrophages and DCs, to be dependent on the MyD88-PI3K pathway. We further found that IL-18 signaling through PI3K led to inhibition of GSK-3, which we found to be a negative regulator of Rae-1. Finally, we demonstrated that in vivo inhibition of GSK-3 could restore Rae-1 up-regulation on IL18R-/- DCs and partially rescue NK-cell activation against VV, leading to improved viral control in IL-18R-/- mice. Our results showed that IL18-dependent Rae-1 up-regulation on accessory cells is mediated by the MyD88-PI3K-GSK3 pathway. These observations may provide important insights into the design of effective NK cell-based immunotherapies.

Placental Origins of Chronic Disease

Epidemiological evidence links an individual's susceptibility to chronic disease in adult life to events during their intrauterine phase of development. Biologically this should not be unexpected, for organ systems are at their most plastic when progenitor cells are proliferating and differentiating. Influences operating at this time can permanently affect their structure and functional capacity, and the activity of enzyme systems and endocrine axes. It is now appreciated that such effects lay the foundations for a diverse array of diseases that become manifest many years later, often in response to secondary environmental stressors. Fetal development is underpinned by the placenta, the organ that forms the interface between the fetus and its mother. All nutrients and oxygen reaching the fetus must pass through this organ. The placenta also has major endocrine functions, orchestrating maternal adaptations to pregnancy and mobilizing resources for fetal use. In addition, it acts as a selective barrier, creating a protective milieu by minimizing exposure of the fetus to maternal hormones, such as glucocorticoids, xenobiotics, pathogens, and parasites. The placenta shows a remarkable capacity to adapt to adverse environmental cues and lessen their impact on the fetus. However, if placental function is impaired, or its capacity to adapt is exceeded, then fetal development may be compromised. Here, we explore the complex relationships between the placental phenotype and developmental programming of chronic disease in the offspring. Ensuring optimal placentation offers a new approach to the prevention of disorders such as cardiovascular disease, diabetes, and obesity, which are reaching epidemic proportions.

Lipid modulation of skeletal muscle mass and function

Loss of skeletal muscle mass is a characteristic feature of various pathologies including cancer, diabetes, and obesity, as well as being a general feature of ageing. However, the processes underlying its pathogenesis are not fully understood and may involve multiple factors. Importantly, there is growing evidence which supports a role for fatty acids and their derived lipid intermediates in the regulation of skeletal muscle mass and function. In this review, we discuss evidence pertaining to those pathways which are involved in the reduction, increase and/or preservation of skeletal muscle mass by such lipids under various pathological conditions, and highlight studies investigating how these processes may be influenced by dietary supplementation as well as genetic and/or pharmacological intervention.

Pharmacophore-based screening and drug repurposing exemplified on glycogen synthase kinase-3 inhibitors

The current study was conducted to elaborate a novel pharmacophore model to accurately map selective glycogen synthase kinase-3 (GSK-3) inhibitors, and perform virtual screening and drug repurposing. Pharmacophore modeling was developed using PHASE on a data set of 203 maleimides. Two benchmarking validation data sets with focus on selectivity were assembled using ChEMBL and PubChem GSK-3 confirmatory assays. A drug repurposing experiment linking pharmacophore matching with drug information originating from multiple data sources was performed. A five-point pharmacophore model was built consisting of a hydrogen bond acceptor (A), hydrogen bond donor (D), hydrophobic (H), and two rings (RR). An atom-based 3D quantitative structure-activity relationship (QSAR) model showed good correlative and satisfactory predictive abilities (training set [Formula: see text]; test set: [Formula: see text]; whole data set: stability [Formula: see text]). Virtual screening experiments revealed that selective GSK-3 inhibitors are ranked preferentially by Hypo-1, but fail to retrieve nonselective compounds. The pharmacophore and 3D QSAR models can provide assistance to design novel, potential GSK-3 inhibitors with high potency and selectivity pattern, with potential application for the treatment of GSK-3-driven diseases. A class of purine nucleoside antileukemic drugs was identified as potential inhibitor of GSK-3, suggesting the reassessment of the target range of these drugs.

GSK-3β/NFAT Signaling Is Involved in Testosterone-Induced Cardiac Myocyte Hypertrophy

Testosterone induces cardiac hypertrophy through a mechanism that involves a concerted crosstalk between cytosolic and nuclear signaling pathways. Nuclear factor of activated T-cells (NFAT) is associated with the promotion of cardiac hypertrophy, glycogen synthase kinase-3β (GSK-3β) is considered to function as a negative regulator, mainly by modulating NFAT activity. However, the role played by calcineurin-NFAT and GSK-3β signaling in testosterone-induced cardiac hypertrophy has remained unknown. Here, we determined that testosterone stimulates cardiac myocyte hypertrophy through NFAT activation and GSK-3β inhibition. Testosterone increased the activity of NFAT-luciferase (NFAT-Luc) in a time- and dose-dependent manner, with the activity peaking after 24 h of stimulation with 100 nM testosterone. NFAT-Luc activity induced by testosterone was blocked by the calcineurin inhibitors FK506 and cyclosporine A and by 11R-VIVIT, a specific peptide inhibitor of NFAT. Conversely, testosterone inhibited GSK-3β activity as determined by increased GSK-3β phosphorylation at Ser9 and β-catenin protein accumulation, and also by reduction in β-catenin phosphorylation at residues Ser33, Ser37, and Thr41. GSK-3β inhibition with 1-azakenpaullone or a GSK-3β-targeting siRNA increased NFAT-Luc activity, whereas overexpression of a constitutively active GSK-3β mutant (GSK-3βS9A) inhibited NFAT-Luc activation mediated by testosterone. Testosterone-induced cardiac myocyte hypertrophy was established by increased cardiac myocyte size and [³H]-leucine incorporation (as a measurement of cellular protein synthesis). Calcineurin-NFAT inhibition abolished and GSK-3β inhibition promoted the hypertrophy stimulated by testosterone. GSK-3β activation by GSK-3βS9A blocked the increase of hypertrophic markers induced by testosterone. Moreover, inhibition of intracellular androgen receptor prevented testosterone-induced NFAT-Luc activation. Collectively, these results suggest that cardiac myocyte hypertrophy induced by testosterone involves a cooperative mechanism that links androgen signaling with the recruitment of NFAT through calcineurin activation and GSK-3β inhibition.

eIF2B: recent structural and functional insights into a key regulator of translation

The eukaryotic translation initiation factor (eIF) eIF2B is a key regulator of mRNA translation, being the guanine nt exchange factor (GEF) responsible for the recycling of the heterotrimeric G-protein, eIF2, which is required to allow translation initiation to occur. Unusually for a GEF, eIF2B is a multi-subunit protein, comprising five different subunits termed α through ε in order of increasing size. eIF2B is subject to tight regulation in the cell and may also serve additional functions. Here we review recent insights into the subunit organization of the mammalian eIF2B complex, gained both from structural studies of the complex and from studies of mutations of eIF2B that result in the neurological disorder leukoencephalopathy with vanishing white matter (VWM). We will also discuss recent data from yeast demonstrating a novel function of the eIF2B complex key for translational regulation.

The Molecular Mechanisms of Calpains Action on Skeletal Muscle Atrophy

Skeletal muscle atrophy is associated with a loss of muscle protein which may result from both increased proteolysis and decreased protein synthesis. Investigations on cell signaling pathways that regulate muscle atrophy have promoted our understanding of this complicated process. Emerging evidence implicates that calpains play key roles in dysregulation of proteolysis seen in muscle atrophy. Moreover, studies have also shown that abnormally activated calpain results muscle atrophy via its downstream effects on ubiquitin-proteasome pathway (UPP) and Akt phosphorylation. This review will discuss the role of calpains in regulation of skeletal muscle atrophy mainly focusing on its collaboration with either UPP or Akt in atrophy conditions in hope to stimulate the interest in development of novel therapeutic interventions for skeletal muscle atrophy.