Role of AMP-activated protein kinase in metabolic depression in animals

SARM1 deficiency induced depressive-like behavior via AMPKα/p-eEF2 axis to synapse dysfunction

Sterile Alpha and TIR Motif Containing 1 (SARM1) are proteins implicated in various neurological processes; however, their role in depression remains unexplored. This study investigated the contribution of SARM1 to depressive-like behaviors in a chronic stress-induced depression model and SARM1 knockout (KO) mice. Depressive-like behaviors were assessed using a battery of behavioral tests, including the Open Field Test (OFT), the Forced Swim Test (FST), the Sucrose Preference Test (SPT), and the Tail Suspension Test (TST). Mitochondrial energy metabolism alteration, cytokine level changes, and other related molecular signaling protein expression were evaluated using ELISA and western blotting techniques to investigate the underlying mechanisms. Behavioral assessments (OFT, FST, SPT, TST) revealed depressive-like phenotypes in SARM1 KO mice, accompanied by altered mitochondrial energy metabolism (NAD+, ATP) in the cortex. Intriguingly, SARM1 depletion led to peripheral inflammation, as evidenced by elevated cytokine levels in plasma but not in brain regions (cortex). In addition, we found dysregulated energy metabolism, AMPK signaling, and synaptic plasticity in the cortex of SARM1 KO mice. Notably, AICAR (Acadesine), an AMPK activator, ameliorated depressive-like behaviors and synaptic dysfunction, while Compound C, an AMPK inhibitor, reversed these effects. Additionally, NH125, an eEF2 kinase inhibitor, improved depressive-like behaviors in SARM1 KO mice. These findings demonstrate that SARM1 is critical in regulating depressive-like behaviours through the AMPKα/p-eEF2 signaling pathway. Targeting AMPK signaling and synaptic function may offer novel therapeutic avenues for depression.

Cancer stem cells: advances in the glucose, lipid and amino acid metabolism

Cancer stem cells (CSCs) are a class of cells with self-renewal and multi-directional differentiation potential, which are present in most tumors, particularly in aggressive tumors, and perform a pivotal role in recurrence and metastasis and are expected to be one of the important targets for tumor therapy. Studies of tumor metabolism in recent years have found that the metabolic characteristics of CSCs are distinct from those of differentiated tumor cells, which are unique to CSCs and contribute to the maintenance of the stemness characteristics of CSCs. Moreover, these altered metabolic profiles can drive the transformation between CSCs and non-CSCs, implying that these metabolic alterations are important markers for CSCs to play their biological roles. The identification of metabolic changes in CSCs and their metabolic plasticity mechanisms may provide some new opportunities for tumor therapy. In this paper, we review the metabolism-related mechanisms of CSCs in order to provide a theoretical basis for their potential application in tumor therapy.

Sloth metabolism may make survival untenable under climate change scenarios

Although climate change is predicted to have a substantial effect on the energetic requirements of organisms, the longer-term implications are often unclear. Sloths are limited by the rate at which they can acquire energy and are unable to regulate core body temperature (Tb) to the extent seen in most mammals. Therefore, the metabolic impacts of climate change on sloths are expected to be profound. Here we use indirect calorimetry to measure the oxygen consumption (VO2) and Tb of highland and lowland two-fingered sloths (Choloepus hoffmanni) when exposed to a range of different ambient temperatures (Ta) (18 °C -34 °C), and additionally record changes in Tb and posture over several days in response to natural fluctuations in Ta. We use the resultant data to predict the impact of future climate change on the metabolic rate and Tb of the different sloth populations. The metabolic responses of sloths originating from the two sites differed at high Ta's, with lowland sloths invoking metabolic depression as temperatures rose above their apparent 'thermally-active zone' (TAZ), whereas highland sloths showed increased RMR. Based on climate change estimates for the year 2100, we predict that high-altitude sloths are likely to experience a substantial increase in metabolic rate which, due to their intrinsic energy processing limitations and restricted geographical plasticity, may make their survival untenable in a warming climate.

Phosphoproteomic changes in response to anoxia are tissue-specific in the anoxia-tolerant crucian carp (Carassius carassius)

Crucian carp (Carassius carassius), a freshwater fish, can survive chronic anoxia for several months at low temperatures. Consequently, anoxia-related physiological and biochemical adaptations in this species have been studied for more than half a century. Still, despite for the well-known role of protein phosphorylation in regulating cellular processes, no studies have comprehensively characterized the phosphoproteome in crucian carp. In this study, we report the global phosphoproteome in crucian carp brain and liver during anoxia and reoxygenation. By applying a bottom-up proteomic approach on enriched phosphopeptides we found that the brain phosphoproteome shows surprisingly few changes during anoxia-reoxygenation exposure with only 109 out of 4200 phosphopeptides being differentially changed compared to normoxic controls. By contrast, in the liver 395 out of 1287 phosphopeptides changed. Although most changes occurred in the liver phosphoproteome, the pattern of changes indicated metabolic depression and decreased translation in both brain and liver. We also found changes in phosphoproteins involved in apoptotic regulation and reactive oxygen species handling in both tissues. In the brain, some of the most changed phosphopeptides belonged to proteins involved in central nervous system development and neuronal activity at the synaptic cleft. Changed phosphoproteins specific for liver tissue were related to glucose metabolism, such as glycolytic flux and glycogenolysis. In conclusion, protein phosphorylation in response to anoxia and reoxygenation showed both common and tissue-specific changes related to the functional differences between brain and liver.

Phosphoproteomics changes due to allograft-induced stress responses of Pinctada fucata martensii

Protein phosphorylation modifications are post-translational modifications (PTMs) that play important roles in signal transduction and immune regulation. Implanting a spherical nucleus into a recipient shellfish is critical in marine pearl aquaculture. Protein phosphorylation may be important in the immune responses of Pinctada fucata martensii after nucleus implantation, but their involvement in regulation remains unclear. Here, phosphoproteomics of P. f. martensii gill tissues was conducted 12 h after nuclear implantation using label-free data-independent acquisition (DIA) with LC-MS/MS. Among the 4024 phosphorylated peptides with quantitative information, 181 were up-regulated and 148 were down-regulated. Functional enrichment analysis of these differentially expressed phosphorylated proteins (DEPPs) revealed significant enrichment in functions related to membrane trafficking, exosomes, cytoskeleton, and signal transduction mechanisms. Further, 16 conserved motifs were identified among the DEPPs, including the RSphP, SphP, RSphA, RSphE, PTphP, and ATphP motifs that were significantly conserved, and which may be related to specific kinase recognition. Parallel response monitoring (PRM) analysis validated the abundances of 12 DEPPs from the proteomics, indicating that the phosphoproteomics analyses were robust. 12 DEPPs were selected from the proteomics results through Quantitative real-time PCR (qPCR) technology, and verification analysis was conducted at the gene level. The study suggests that kinases such as MAPKs, Akt, and CK2 may regulate the phosphorylation of related proteins following nuclear implantation. Furthermore, the important signaling pathways of Rap 1, IL-17A, and NF-κB, which are influenced by phosphorylated or dephosphorylated proteins, are found to be involved in this response. Overall, this study revealed the protein phosphorylation responses after nucleus implantation in P. f. martensii, helping to elucidate the characteristics and mechanisms of immune regulation responses in P. f. martensii, in addition to promoting a further understanding of protein phosphorylation modification functions in P. f. martensii.

Combined effects of temperature and emersion-immersion cycles on metabolism and bioenergetics of the Pacific oyster Crassostrea (Magallana) gigas

Life on tidal coasts presents physiological major challenges for sessile species. Fluctuations in oxygen and temperature can affect bioenergetics and modulate metabolism and redox balance, but their combined effects are not well understood. We investigated the effects of intermittent hypoxia (12h/12h) in combination with different temperature regimes (normal (15 °C), elevated (30 °C) and fluctuating (15 °C water/30 °C air)) on the Pacific oyster Crassostrea (Magallana) gigas. Fluctuating temperature led to energetic costly metabolic rearrangements and accumulation of proteins in oyster tissues. Elevated temperature led to high (60%) mortality and oxidative damage in survivors. Normal temperature had no major negative effects but caused metabolic shifts. Our study shows high plasticity of oyster metabolism in response to oxygen and temperature fluctuations and indicates that metabolic adjustments to oxygen deficiency are strongly modulated by the ambient temperature. Co-exposure to constant elevated temperature and intermittent hypoxia demonstrates the limits of this adaptive metabolic plasticity.

Protective Role of AMPK against PINK1B9 Flies' Neurodegeneration with Improved Mitochondrial Function

Adenosine 5'-monophosphate-activated protein kinase (AMPK)'s effect in PTEN-induced kinase 1 (PINK1) mutant Parkinson's disease (PD) transgenic flies and the related mechanism is seldom studied. The classic MHC-Gal4/UAS PD transgenic flies was utilized to generate the disease characteristics specifically expressed in flies' muscles, and Western blot (WB) was used to measure the expression of the activated form of AMPK to investigate whether activated AMPK alters in PINK1B9 PD flies. MHC-Gal4 was used to drive AMPK overexpression in PINK1B9 flies to demonstrate the crucial role of AMPK in PD pathogenesis. The abnormal wing posture and climbing ability of PINK1B9 PD transgenic flies were recorded. Mitochondrial morphology via transmission electron microscopy (TEM) and ATP and NADH: ubiquinone oxidoreductase core subunit S3 (NDUFS3) protein levels were tested to evaluate the alteration of the mitochondrial function in PINK1B9 PD flies. Phosphorylated AMPKα dropped significantly in PINK1B9 flies compared to controls, and AMPK overexpression rescued PINKB9 flies' abnormal wing posture rate. The elevated dopaminergic neuron number in PPL1 via immunofluorescent staining was observed. Mitochondrial dysfunction in PINK1B9 flies has been ameliorated with increased ATP level, restored mitochondrial morphology in muscle, and increased NDUFS3 protein expression. Conclusively, AMPK overexpression could partially rescue the PD flies via improving PINK1B9 flies' mitochondrial function.

The extensive transgenerational transcriptomic effects of ocean acidification on the olfactory epithelium of a marine fish are associated with a better viral resistance

Background

Progressive CO₂-induced ocean acidification (OA) impacts marine life in ways that are difficult to predict but are likely to become exacerbated over generations. Although marine fishes can balance acid–base homeostasis efficiently, indirect ionic regulation that alter neurosensory systems can result in behavioural abnormalities. In marine invertebrates, OA can also affect immune system function, but whether this is the case in marine fishes is not fully understood. Farmed fish are highly susceptible to disease outbreak, yet strategies for overcoming such threats in the wake of OA are wanting. Here, we exposed two generations of the European sea bass (Dicentrarchus labrax) to end-of-century predicted pH levels (IPCC RCP8.5), with parents (F1) being exposed for four years and their offspring (F2) for 18 months. Our design included a transcriptomic analysis of the olfactory rosette (collected from the F2) and a viral challenge (exposing F2 to betanodavirus) where we assessed survival rates.

Results

We discovered transcriptomic trade-offs in both sensory and immune systems after long-term transgenerational exposure to OA. Specifically, RNA-Seq analysis of the olfactory rosette, the peripheral olfactory organ, from 18-months-old F2 revealed extensive regulation in genes involved in ion transport and neuronal signalling, including GABAergic signalling. We also detected OA-induced up-regulation of genes associated with odour transduction, synaptic plasticity, neuron excitability and wiring and down-regulation of genes involved in energy metabolism. Furthermore, OA-exposure induced up-regulation of genes involved in innate antiviral immunity (pathogen recognition receptors and interferon-stimulated genes) in combination with down-regulation of the protein biosynthetic machinery. Consistently, OA-exposed F2 challenged with betanodavirus, which causes damage to the nervous system of marine fish, had acquired improved resistance.

Conclusion

F2 exposed to long-term transgenerational OA acclimation showed superior viral resistance, though as their metabolic and odour transduction programs were altered, odour-mediated behaviours might be consequently impacted. Although it is difficult to unveil how long-term OA impacts propagated between generations, our results reveal that, across generations, trade-offs in plastic responses is a core feature of the olfactory epithelium transcriptome in OA-exposed F2 offspring, and will have important consequences for how cultured and wild fish interacts with its environment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08647-w.

Midkine noncanonically suppresses AMPK activation through disrupting the LKB1-STRAD-Mo25 complex

Midkine (MDK), a secreted growth factor, regulates signal transduction and cancer progression by interacting with receptors, and it can be internalized into the cytoplasm by endocytosis. However, its intracellular function and signaling regulation remain unclear. Here, we show that intracellular MDK interacts with LKB1 and STRAD to disrupt the LKB1-STRAD-Mo25 complex. Consequently, MDK decreases the activity of LKB1 to dampen both the basal and stress-induced activation of AMPK by glucose starvation or treatment of 2-DG. We also found that MDK accelerates cancer cell proliferation by inhibiting the activation of the LKB1-AMPK axis. In human cancers, compared to other well-known growth factors, MDK expression is most significantly upregulated in cancers, especially in liver, kidney and breast cancers, correlating with clinical outcomes and inversely correlating with phosphorylated AMPK levels. Our study elucidates an inhibitory mechanism for AMPK activation, which is mediated by the intracellular MDK through disrupting the LKB1-STRAD-Mo25 complex.

Activation of the Hippo Pathway in Rana sylvatica: Yapping Stops in Response to Anoxia

Wood frogs (Rana sylvatica) display well-developed anoxia tolerance as one component of their capacity to endure prolonged whole-body freezing during the winter months. Under anoxic conditions, multiple cellular responses are triggered to efficiently cope with stress by suppressing gene transcription and promoting activation of mechanisms that support cell survival. Activation of the Hippo signaling pathway initiates a cascade of protein kinase reactions that end with phosphorylation of YAP protein. Multiple pathway components of the Hippo pathway were analyzed via immunoblotting, qPCR or DNA-binding ELISAs to assess the effects of 24 h anoxia and 4 h aerobic recovery, compared with controls, on liver and heart metabolism of wood frogs. Immunoblot results showed significant increases in the relative levels of multiple proteins of the Hippo pathway representing an overall activation of the pathway in both organs under anoxia stress. Upregulation of transcript levels further confirmed this. A decrease in YAP and TEAD protein levels in the nuclear fraction also indicated reduced translocation of these proteins. Decreased DNA-binding activity of TEAD at the promoter region also suggested repression of gene transcription of its downstream targets such as SOX2 and OCT4. Furthermore, changes in the protein levels of two downstream targets of TEAD, OCT4 and SOX2, established regulated transcriptional activity and could possibly be associated with the activation of the Hippo pathway. Increased levels of TAZ in anoxic hearts also suggested its involvement in the repair mechanism for damage caused to cardiac muscles during anoxia. In summary, this study provides the first insights into the role of the Hippo pathway in maintaining cellular homeostasis in response to anoxia in amphibians.

Bold Behavior Is Associated with Genes That Regulate Energy Use but Does Not Covary with Body Condition in Food-Restricted Snails

AbstractTheoretical models about the relationship between food restriction and individual differences in risk-taking behavior (i.e., boldness) have led to conflicting predictions: some models predict that food restriction increases boldness, while other models predict that food restriction decreases boldness. This discrepancy may be partially attributable to an underappreciation for animals' complex physiological responses to food restriction. To understand the proximate mechanisms mediating state-dependent boldness, we used freshwater snails (Helisoma trivolvis) to examine the relationships among food availability, body condition, boldness (latency to reemerge from shell and exploration), and mRNA expression of three genes (adenosine monophosphate-activated protein kinase [AMPK], molluscan insulin-like peptide [MIP], and serotonin receptor [5-HT]) involved in maintaining energy homeostasis during periods of moderate food restriction. Latency to reemerge and exploratory behavior decreased over time, but fed snails were bolder than fasted snails, suggesting that food restriction reduces bold behavior. Although food restriction decreased body condition, there was not a relationship between body condition and latency to reemerge from shell. However, expression of MIP was positively correlated with latency to reemerge from shell. Furthermore, AMPK was positively correlated with MIP and negatively correlated with body condition and 5-HT. Therefore, individual differences in physiological responses to food restriction, not overall body condition per se, appear to be more closely associated with state-dependent bold behavior. Finally, snails that experienced a novel assay environment returned to their initial "shy" behavior, suggesting that habituation to the assay environment may contribute to snails expressing bolder behavior over time.

MicroRNA-mediated inhibition of AMPK coordinates tissue-specific downregulation of skeletal muscle metabolism in hypoxic naked mole-rats

Naked mole-rats reduce their metabolic requirements to tolerate severe hypoxia. However, the regulatory mechanisms that underpin this metabolic suppression have yet to be elucidated. 5'-AMP-activated protein kinase (AMPK) is the cellular 'master' energy effector and we hypothesized that alterations in the AMPK pathway contribute to metabolic reorganization in hypoxic naked mole-rat skeletal muscle. To test this hypothesis, we exposed naked mole-rats to 4 h of normoxia (21% O2) or severe hypoxia (3% O2), while indirectly measuring whole-animal metabolic rate and fuel preference. We then isolated skeletal muscle and assessed protein expression and post-translational modification of AMPK, and downstream changes in key glucose and fatty acid metabolic proteins mediated by AMPK, including acetyl-CoA carboxylase (ACC1), glycogen synthase (GS) and glucose transporters (GLUTs) 1 and 4. We found that in hypoxic naked mole-rats (1) metabolic rate decreased ∼80% and fuel use switched to carbohydrates, and that (2) levels of activated phosphorylated AMPK and GS, and GLUT4 expression were downregulated in skeletal muscle, while ACC1 was unchanged. To explore the regulatory mechanism underlying this hypometabolic state, we used RT-qPCR to examine 55 AMPK-associated microRNAs (miRNAs), which are short non-coding RNA post-transcriptional silencers. We identified changes in 10 miRNAs (three upregulated and seven downregulated) implicated in AMPK downregulation. Our results suggest that miRNAs and post-translational mechanisms coordinately reduce AMPK activity and downregulate metabolism in naked mole-rat skeletal muscle during severe hypoxia. This novel mechanism may support tissue-specific prioritization of energy for more essential organs in hypoxia.

Update on the adverse effects of microcystins on the liver

Microcystins (MCs) are the most common cyanobacteria toxins in eutrophic water, which have strong hepatotoxicity. In the past decade, epidemiological and toxicological studies on liver damage caused by MCs have proliferated, and new mechanisms of hepatotoxicity induced by MCs have also been discovered and confirmed. However, there has not been a comprehensive and systematic review of these new findings. Therefore, this paper summarizes the latest advances in studies on the hepatotoxicity of MCs to reveal the effects and mechanisms of hepatotoxicity induced by MCs. Current epidemiological studies have confirmed that symptoms or signs of liver damage appear after human exposure to MCs, and a long time of exposure can even lead to liver cancer. Toxicological studies have shown that MCs can affect the expression of oncogenes by activating cell proliferation pathways such as MAPK and Akt, thereby promoting the occurrence and development of cancer. The latest evidence shows that epigenetic modifications may play an important role in MCs-induced liver cancer. MCs can cause damage to the liver by inducing hepatocyte death, mainly manifested as apoptosis and necrosis. The imbalance of liver metabolic homeostasis may be involved in hepatotoxicity induced by MCs. In addition, the combined toxicity of MCs and other toxins are also discussed in this article. This detailed information will be a valuable reference for further exploring of MCs-induced hepatotoxicity.

Bioenergetics in environmental adaptation and stress tolerance of aquatic ectotherms: linking physiology and ecology in a multi-stressor landscape

Energy metabolism (encompassing energy assimilation, conversion and utilization) plays a central role in all life processes and serves as a link between the organismal physiology, behavior and ecology. Metabolic rates define the physiological and life-history performance of an organism, have direct implications for Darwinian fitness, and affect ecologically relevant traits such as the trophic relationships, productivity and ecosystem engineering functions. Natural environmental variability and anthropogenic changes expose aquatic ectotherms to multiple stressors that can strongly affect their energy metabolism and thereby modify the energy fluxes within an organism and in the ecosystem. This Review focuses on the role of bioenergetic disturbances and metabolic adjustments in responses to multiple stressors (especially the general cellular stress response), provides examples of the effects of multiple stressors on energy intake, assimilation, conversion and expenditure, and discusses the conceptual and quantitative approaches to identify and mechanistically explain the energy trade-offs in multiple stressor scenarios, and link the cellular and organismal bioenergetics with fitness, productivity and/or ecological functions of aquatic ectotherms.

Metabolic Reprogramming is a Hallmark of Metabolism Itself

The reprogramming of metabolism has been identified as one of the hallmarks of cancer. It is becoming more and more frequent to connect other diseases with metabolic reprogramming. This article aims to argue that metabolic reprogramming is not driven by disease but instead is the main hallmark of metabolism, based on its dynamic behavior that allows it to continuously adapt to changes in the internal and external conditions.

Insight on Transcriptional Regulation of the Energy Sensing AMPK and Biosynthetic mTOR Pathway Genes

The Adenosine Monophosphate-activated Protein Kinase (AMPK) and the Mechanistic Target of Rapamycin (mTOR) are two evolutionarily conserved kinases that together regulate nearly every aspect of cellular and systemic metabolism. These two kinases sense cellular energy and nutrient levels that in turn are determined by environmental nutrient availability. Because AMPK and mTOR are kinases, the large majority of studies remained focused on downstream substrate phosphorylation by these two proteins, and how AMPK and mTOR regulate signaling and metabolism in normal and disease physiology through phosphorylation of their substrates. Compared to the wealth of information known about the signaling and metabolic pathways modulated by these two kinases, much less is known about how the transcription of AMPK and mTOR pathway genes themselves are regulated, and the extent to which AMPK and mTOR regulate gene expression to cause durable changes in phenotype. Acute modification of cellular systems can be achieved through phosphorylation, however, induction of chronic changes requires modulation of gene expression. In this review we will assemble evidence from published studies on transcriptional regulation by AMPK and mTOR and discuss about the putative transcription factors that regulate expression of AMPK and mTOR complex genes.

Biomarker-based assessment of the muscle maintenance and energy status of anurans from an extremely seasonal semi-arid environment, the Brazilian Caatinga

Strongly seasonal environments pose challenges for performance and survival of animals, especially when resource abundance seasonally fluctuates. We investigated the seasonal variation of key metabolic biomarkers in the muscles of males from three species (Rhinella jimi, R. granulosa and Pleurodema diplolister) of anurans from the drastically seasonal Brazilian semi-arid area, Caatinga. We examined the expression of proteins regulating energy turnover (AMP-activated protein kinase [AMPK] and protein kinase B [AKT]), protein synthesis and homeostasis (total and phosphorylated eukaryotic initiation factor 2α [eIF2α and p-eIF2α] and chaperone proteins [HSP 60, 70, and 90]) in muscles predominantly related to reproduction and locomotion. Cytochrome c oxidase (COX) activity was also assessed as an index of the muscle aerobic capacity. The expression pattern of metabolic biomarkers indicates that the maintenance of muscular function is regulated in a species-specific manner during the drastic seasonal variation. Rhinella jimi and R. granulosa that remain active during the drought appear to maintain muscles through more energy expensive pathways including elevated protein synthesis, while the aestivating P. diplolister employs energy conservation strategy suppressing protein synthesis, decreasing chaperone expression and increasing expression of AMPK. Two (P. diplolister and R. granulosa) of the three studied species activate cell survival pathways during the drought likely to prevent muscle atrophy, and all three studied species maintain the muscle aerobic capacity throughout the year, despite the resource limitation. These strategies are important considering the unpredictability of the reproductive event and high demand on muscular activity during the reproductive season in these amphibians. SUMMARY STATEMENT: We studied seasonal variation of key metabolic biomarkers in the muscles of anurans that experience drastic variation in environmental conditions and differ in seasonal activity patterns.

Transcriptional and post-translational activation of AMPKα by oxidative, heat, and cold stresses in the red flour beetle, Tribolium castaneum

The AMP-activated protein kinase (AMPK) has important roles in the regulation of energy metabolism, and AMPK activity and its regulation have been the focus of relevant investigations. However, functional characterization of AMPK is still limited in insects. In this study, the full-length cDNA coding AMPKα (TcAMPKα) was isolated from the red flour beetle, Tribolium castaneum. The TcAMPKα gene contains an ORF of 1581 bp encoding a protein of 526 amino acid residues, which shared conserved domain structure with Drosophila melanogaster and mammalian orthologs. Exposure of female adults to oxidative, heat, and cold stresses caused an increase in TcAMPKα mRNA expression levels and phosphorylation of Thr-173 in the activation loop. The RNAi-mediated knockdown of TcAMPKα resulted in the increased sensitivity of T. castaneum to oxidative, heat, and cold stresses. These results suggest that stress signals regulate TcAMPKα activity, and TcAMPKα plays an important role in enabling protective mechanisms and processes that confer resistance to environmental stress.

Metabolism within the tumor microenvironment and its implication on cancer progression: An ongoing therapeutic target

Since reprogramming energy metabolism is considered a new hallmark of cancer, tumor metabolism is again in the spotlight of cancer research. Many studies have been carried out and many possible therapies have been developed in the last years. However, tumor cells are not alone. A series of extracellular components and stromal cells, such as endothelial cells, cancer-associated fibroblasts, tumor-associated macrophages, and tumor-infiltrating T cells, surround tumor cells in the so-called tumor microenvironment (TME). Metabolic features of these cells are being studied in deep in order to find relationships between metabolism within the TME and tumor progression. Moreover, it cannot be forgotten that tumor growth is able to modulate host metabolism and homeostasis, so that TME is not the whole story. Importantly, the metabolic switch in cancer is just a consequence of the flexibility and adaptability of metabolism and should not be surprising. Treatments of cancer patients with combined therapies including antitumor agents with those targeting stromal cell metabolism, antiangiogenic drugs, and/or immunotherapy are being developed as promising therapeutics.

The metabolic response of the Bradypus sloth to temperature

Poikilotherms and homeotherms have different, well-defined metabolic responses to ambient temperature (T a ), but both groups have high power costs at high temperatures. Sloths (Bradypus) are critically limited by rates of energy acquisition and it has previously been suggested that their unusual departure from homeothermy mitigates the associated costs. No studies, however, have examined how sloth body temperature and metabolic rate vary with T a . Here we measured the oxygen consumption (VO2) of eight brown-throated sloths (B. variegatus) at variable T a 's and found that VO2 indeed varied in an unusual manner with what appeared to be a reversal of the standard homeotherm pattern. Sloth VO2 increased with T a , peaking in a metabolic plateau (nominal 'thermally-active zone' (TAZ)) before decreasing again at higher T a values. We suggest that this pattern enables sloths to minimise energy expenditure over a wide range of conditions, which is likely to be crucial for survival in an animal that operates under severe energetic constraints. To our knowledge, this is the first evidence of a mammal provisionally invoking metabolic depression in response to increasing T a 's, without entering into a state of torpor, aestivation or hibernation.

Mitochondrial Dysfunction and Infection Generate Immunity-Fecundity Tradeoffs in Drosophila

Physiological responses to short-term environmental stressors, such as infection, can have long-term consequences for fitness, particularly if the responses are inappropriate or nutrient resources are limited. Genetic variation affecting energy acquisition, storage, and usage can limit cellular energy availability and may influence resource-allocation tradeoffs even when environmental nutrients are plentiful. Here, we utilized Drosophila mitochondrial-nuclear genotypes to test whether disrupted mitochondrial function interferes with nutrient-sensing pathways, and whether this disruption has consequences for tradeoffs between immunity and fecundity. We found that an energetically-compromised genotype was relatively resistant to rapamycin-a drug that targets nutrient-sensing pathways and mimics resource limitation. Dietary resource limitation decreased survival of energetically-compromised flies. Furthermore, survival of infection with a natural pathogen was decreased in this genotype, and females of this genotype experienced immunity-fecundity tradeoffs that were not evident in genotypic controls with normal energy metabolism. Together, these results suggest that this genotype may have little excess energetic capacity and fewer cellular nutrients, even when environmental nutrients are not limiting. Genetic variation in energy metabolism may therefore act to limit the resources available for allocation to life-history traits in ways that generate tradeoffs even when environmental resources are not limiting.

Effect of pre-slaughter shackling and wing flapping on plasma parameters, postmortem metabolism, AMPK, and meat quality of broilers

The objective of this study was to determine the effects of shackling and wing flapping on stress, postmortem metabolism, AMP-activated protein kinase (AMPK), and quality of broiler pectoralis major. Before slaughter, a total of 80 Arbor Acres broilers was randomly categorized into 2 replicate pens (40 broilers per pen) and each pen randomly divided into 2 groups (shackling, T; control, C). Corticosterone, creatine kinase, and lactate dehydrogenase were determined on blood plasma parameters. Pectoralis major were removed after evisceration and used for determination of energy metabolism, meat quality, and AMPK phosphorylation. In this study, shackling and wing flapping increased (P < 0.05) plasma corticosterone level, creatine kinase activity, and lactate dehydrogenase activity. Shackling and wing flapping increased (P < 0.05) AMPKα(Thr172) and acetyl-CoA carboxylase (ACC) phosphorylation, followed by rapid glycolysis and accumulation of lactic acid, and leading to a fast pH decline in the initial postmortem meat. Shackling and wing flapping have an adverse effect on final meat quality, which increased (P < 0.05) muscle lightness, drip loss, and cooking loss. The results indicate that antemortem shackling and wing flapping increased stress and AMPKα(Thr172) phosphorylation, which may accelerate glycolysis and lead to a low water-holding capacity of broiler meat.

Effects of detraining and retraining on muscle energy-sensing network and meteorin-like levels in obese mice

Background

Increased intramuscular peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) with exercise directly or indirectly affects other tissues, but the effector pathway of PGC-1α has not been clearly elucidated. The purpose of this study was to investigate the effect of exercise and/or dietary change on the protein levels of the soleus muscle energy-sensing network and meteorin-like (Metrnl), and additionally to analyze the detraining and retraining effects in high-fat diet (HFD)-induced obese mice.

Methods

One hundred male C57BL/6 mice were divided into normal-diet + sedentary (CO, n = 20) and HFD + sedentary (HF, n = 80) groups, and obesity was induced in the HF group through consumption of a 45% HFD for 6 weeks. The HF group was subdivided into HF only (n = 20), HF + training (HFT, n = 20), dietary change + sedentary (HFND, n = 20), and HFND + training (HFNDT, n = 20) groups, and the mice in the training groups underwent a treadmill training for 8 weeks, 5 times per week, 40 min per day. The HFT and HFNDT groups underwent 8-week training, 8-week detraining, and 4-week retraining.

Results

An 8-week training was effective in increasing the protein levels of soleus muscle AMP-activated protein kinase (AMPK), PGC-1α, and plasma Metrnl in the obese mice (P < 0.05). Moreover, exercise in obesity reduced body weight (P < 0.05), and exercise with dietary conversion was effective in reducing body weight (P < 0.05) and fat mass (P < 0.05) after 8-week training. 8-week detraining restored the increased protein level to the pre-exercise state, but, the previous exercise effect in body weight and fat mass (P < 0.05) of the HFNDT group remained until the end of 4-week detraining. 4-week retraining was effective in increasing the protein levels of soleus muscle AMPK, PGC-1α, blood Metrnl (P < 0.05), and reducing in body weight (P < 0.05) and fat mass (P < 0.05), when retraining with dietary change.

Conclusions

The results of this study suggest that regular exercise is indispensable to reduce body weight and fat mass through upregulation of the muscle energy-sensing network and Metrnl protein levels, and retraining with dietary change is necessary to obtain the retraining effects more quickly.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0751-3) contains supplementary material, which is available to authorized users.

Thermal acclimation mitigates cold-induced paracellular leak from the Drosophila gut

Chill susceptible insects suffer tissue damage and die at low temperatures. The mechanisms that cause chilling injury are not well understood but a growing body of evidence suggests that a cold-induced loss of ion and water homeostasis leads to hemolymph hyperkalemia that depolarizes cells, leading to cell death. The apparent root of this cascade is the net leak of osmolytes down their concentration gradients in the cold. Many insects, however, are capable of adjusting their thermal physiology, and cold-acclimated Drosophila can maintain homeostasis and avoid injury better than warm-acclimated flies. Here, we test whether chilling causes a loss of epithelial barrier function in female adult Drosophila, and provide the first evidence of cold-induced epithelial barrier failure in an invertebrate. Flies had increased rates of paracellular leak through the gut epithelia at 0 °C, but cold acclimation reduced paracellular permeability and improved cold tolerance. Improved barrier function was associated with changes in the abundance of select septate junction proteins and the appearance of a tortuous ultrastructure in subapical intercellular regions of contact between adjacent midgut epithelial cells. Thus, cold causes paracellular leak in a chill susceptible insect and cold acclimation can mitigate this effect through changes in the composition and structure of transepithelial barriers.

Changes in the phosphoproteome of brown adipose tissue during hibernation in the ground squirrel, Ictidomys tridecemlineatus

Mammalian hibernation is characterized by metabolic rate depression and a strong decrease in core body temperature that together create energy savings such that most species do not have to eat over the winter months. Brown adipose tissue (BAT), a thermogenic tissue that uses uncoupled mitochondrial respiration to generate heat instead of ATP, plays a major role in rewarming from deep torpor. In the present study we developed a label-free liquid chromatography mass spectrometry (LC-MS) strategy to investigate both differential protein expression and protein phosphorylation in BAT extracts from euthermic vs. hibernating ground squirrels (Ictidomys tridecemlineatus). In particular, we incorporated the filter-assisted sample preparation protocol, which provides a more in-depth analysis compared with gel-based and other LC-MS proteomics approaches. Surprisingly, mitochondrial membrane and matrix protein expression in BAT was largely constant between active euthermic squirrels and their hibernating counterparts. Validation by immunoblotting confirmed that the protein levels of mitochondrial respiratory chain complexes were largely unchanged in hibernating vs. euthermic animals. On the other hand, phosphoproteomics revealed that pyruvate dehydrogenase (PDH) phosphorylation increased during squirrel hibernation, confirmed by immunoblotting with phospho-specific antibodies. PDH phosphorylation leads to its inactivation, which suggests that BAT carbohydrate oxidation is inhibited during hibernation. Phosphorylation of hormone-sensitive lipase (HSL) was also found to increase during hibernation, suggesting that HSL would be active in BAT to produce the fatty acids that are likely the primary fuel for thermogenesis upon arousal. Increased perilipin phosphorylation along with that of a number of other proteins was also revealed, emphasizing the importance of protein phosphorylation as a regulatory mechanism during mammalian hibernation.

Direct and indirect activation of eukaryotic elongation factor 2 kinase by AMP-activated protein kinase

BACKGROUND

Eukaryotic elongation factor 2 (eEF2) kinase (eEF2K) is a key regulator of protein synthesis in mammalian cells. It phosphorylates and inhibits eEF2, the translation factor necessary for peptide translocation during the elongation phase of protein synthesis. When cellular energy demand outweighs energy supply, AMP-activated protein kinase (AMPK) and eEF2K become activated, leading to eEF2 phosphorylation, which reduces the rate of protein synthesis, a process that consumes a large proportion of cellular energy under optimal conditions.

AIM

The goal of the present study was to elucidate the mechanisms by which AMPK activation leads to increased eEF2 phosphorylation to decrease protein synthesis.

METHODS

Using genetically modified mouse embryo fibroblasts (MEFs), effects of treatments with commonly used AMPK activators to increase eEF2 phosphorylation were compared with that of the novel compound 991. Bacterially expressed recombinant eEF2K was phosphorylated in vitro by recombinant activated AMPK for phosphorylation site-identification by mass spectrometry followed by site-directed mutagenesis of the identified sites to alanine residues to study effects on the kinetic properties of eEF2K. Wild-type eEF2K and a Ser491/Ser492 mutant were retrovirally re-introduced in eEF2K-deficient MEFs and effects of 991 treatment on eEF2 phosphorylation and protein synthesis rates were studied in these cells.

RESULTS & CONCLUSIONS

AMPK activation leads to increased eEF2 phosphorylation in MEFs mainly by direct activation of eEF2K and partly by inhibition of mammalian target of rapamycin complex 1 (mTORC1) signaling. Treatment of MEFs with AMPK activators can also lead to eEF2K activation independently of AMPK probably via a rise in intracellular Ca²⁺. AMPK activates eEF2K by multi-site phosphorylation and the newly identified Ser491/Ser492 is important for activation, leading to mTOR-independent inhibition of protein synthesis. Our study provides new insights into the control of eEF2K by AMPK, with implications for linking metabolic stress to decreased protein synthesis to conserve energy reserves, a pathway that is of major importance in cancer cell survival.

The Modulating Effects of Cardiac Resynchronization Therapy on Myocardial Metabolism in Heart Failure

Heart failure (HF) is associated with changes in cardiac substrate utilization and energy metabolism, including a decline in high-energy phosphate content, mitochondrial dysfunction, and phosphotransfer enzyme deficiency. A shift toward glucose metabolism was noted in the end stage of HF in animals, although HF in humans may not be associated with a shift toward predominant glucose utilization. Deficiencies of micronutrients are well-established causes of cardiomyopathy. Correction of these deficits can improve heart function. The genes governing the energy metabolism were predominantly underexpressed in nonischemic cardiomyopathy and hypertrophic cardiomyopathy but were overexpressed in ischemic cardiomyopathy. Cardiac resynchronization therapy (CRT) has been proven to increase cardiac efficiency without increasing myocardial oxygen consumption. Altered myocardial metabolism is normalized by CRT to improve ventricular function.

The physiology of lipid storage and use in reptiles

Lipid metabolism is central to understanding whole-animal energetics. Reptiles store most excess energy in lipid form, mobilise those lipids when needed to meet energetic demands, and invest lipids in eggs to provide the primary source of energy to developing embryos. Here, I review the mechanisms by which non-avian reptiles store, transport, and use lipids. Many aspects of lipid absorption, transport, and storage appear to be similar to birds, including the hepatic synthesis of lipids from glucose substrates, the transport of triglycerides in lipoproteins, and the storage of lipids in adipose tissue, although adipose tissue in non-avian reptiles is usually concentrated in abdominal fat bodies or the tail. Seasonal changes in fat stores suggest that lipid storage is primarily for reproduction in most species, rather than for maintenance during aphagic periods. The effects of fasting on plasma lipid metabolites can differ from mammals and birds due to the ability of non-avian reptiles to reduce their metabolism drastically during extended fasts. The effect of fasting on levels of plasma ketones is species specific: β-hydroxybutyrate concentration may rise or fall during fasting. I also describe the process by which the bulk of lipids are deposited into oocytes during vitellogenesis. Although this process is sometimes ascribed to vitellogenin-based transport in reptiles, the majority of lipid deposition occurs via triglycerides packaged in very-low-density lipoproteins (VLDLs), based on physiological, histological, biochemical, comparative, and genomic evidence. I also discuss the evidence for non-avian reptiles using 'yolk-targeted' VLDLs during vitellogenesis. The major physiological states - feeding, fasting, and vitellogenesis - have different effects on plasma lipid metabolites, and I discuss the possibilities and potential problems of using plasma metabolites to diagnose feeding condition in non-avian reptiles.

Evolving Lessons on the Complex Role of AMPK in Normal Physiology and Cancer

AMP kinase (AMPK) is an evolutionarily conserved enzyme required for adaptive responses to various physiological and pathological conditions. AMPK executes numerous cellular functions, some of which are often perceived at odds with each other. While AMPK is essential for embryonic growth and development, its full impact in adult tissues is revealed under stressful situations that organisms face in the real world. Conflicting reports about its cellular functions, particularly in cancer, are intriguing and a growing number of AMPK activators are being developed to treat human diseases such as cancer and diabetes. Whether these drugs will have only context-specific benefits or detrimental effects in the treatment of human cancer will be a subject of intense research. Here we review the current state of AMPK research with an emphasis on cancer and discuss the yet unresolved context-dependent functions of AMPK in human cancer.