Conditions Of Energy Deprivation Research Articles

Evaluating the effects of sodium metabisulfite on the cognitive and motor function in Drosophila melanogaster.

Sodium metabisulfite is widely used as a preservative in many food and beverage products, yet its potential effects on cognitive and motor functions at low concentrations remain poorly understood. Evaluating learning, short-term memory, and motor activity is essential, as these functions are critical indicators of neurological health and could be impacted by low-level exposure to sodium metabisulfite. The aim of this study was to investigate the effects of sublethal concentrations of sodium metabisulfite on cognitive and motor functions using Drosophila melanogaster (fruit flies) as the model organism. Different levels of sodium metabisulfite were administered to male and female fruit flies, and their learning and short-term memory were observed. Additionally, their climbing activity with and without stressors (heat shock, ultraviolet A exposure, or energy deprivation) was examined. Our findings indicated that sodium metabisulfite did not impair learning, short-term memory, or motor activity. Furthermore, sodium metabisulfite did not affect the motor activity of fruit flies under heat, ultraviolet A, and energy-deprived conditions. In conclusion, our results suggested that the sublethal concentration of sodium metabisulfite did not harm cognitive and motor functions and did not exacerbate the effects of environmental stressors.

Cyanidin-3-glucoside Enhances Longevity and Heat Stress Resilience in Drosophila melanogaster

AbstractBackground:Anthocyanins have gained significant attention in recent years due to their diverse physiological benefits, which include antioxidant and anti-inflammatory properties. However, research on the impact of pure anthocyanin compounds on lifespan under different stress conditions, remains a relatively unexplored area. This study aimed to investigate the influence of cyanidin-3-glucoside (C3G), a pure anthocyanin compound found in common plants, on the lifespan ofDrosophila melanogaster(fruit flies) subjected to stress (i.e. energy deprivation and heat stress) and nonstress conditions.Methods:Flies were exposed to various concentrations of C3G from the time of hatching until natural death for the lifespan assay. For stress assays, a separate cohort of male and female flies was subjected to daily heat stress or food deprivation, and their survival was monitored.Results:We found out that C3G prolonged the lifespan of fruit flies in the presence or absence of heat stress. Interestingly, under energy-deprived conditions, lifespan extension was not evident, and a high dose of C3G even led to a shorter lifespan. Moreover, we observed that the sex of the flies did not significantly influence the lifespan modulation by C3G, regardless of whether they were subjected to stress or nonstress conditions.Conclusion:Overall, these findings suggest that C3G may offer promising benefits in enhancing lifespan under certain conditions, while caution should be exercised in dosage selection, especially in energy-deprived scenarios. Further investigations are required to elucidate the underlying mechanisms responsible for the multifaceted effects of C3G on lifespan, thereby exploring its potential applications in promoting longevity and mitigating stress-related challenges.

ADP enhances the allosteric activation of eukaryotic elongation factor 2 kinase by calmodulin

Protein translation, one of the most energy-consumptive processes in a eukaryotic cell, requires robust regulation, especially under energy-deprived conditions. A critical component of this regulation is the suppression of translational elongation through reduced ribosome association of the GTPase eukaryotic elongation factor 2 (eEF-2) resulting from its specific phosphorylation by the calmodulin (CaM)-activated α-kinase eEF-2 kinase (eEF-2K). It has been suggested that the eEF-2K response to reduced cellular energy levels is indirect and mediated by the universal energy sensor AMP-activated protein kinase (AMPK) through direct stimulatory phosphorylation and/or downregulation of the eEF-2K-inhibitory nutrient-sensing mTOR pathway. Here, we provide structural, biochemical, and cell-biological evidence of a direct energy-sensing role of eEF-2K through its stimulation by ADP. A crystal structure of the nucleotide-bound complex between CaM and the functional core of eEF-2K phosphorylated at its primary stimulatory site (T348) reveals ADP bound at a unique pocket located on the face opposite that housing the kinase active site. Within this basic pocket (BP), created at the CaM/eEF-2K interface upon complex formation, ADP is stabilized through numerous interactions with both interacting partners. Biochemical analyses using wild-type eEF-2K and specific BP mutants indicate that ADP stabilizes CaM within the active complex, increasing the sensitivity of the kinase to CaM. Induction of energy stress through glycolysis inhibition results in significantly reduced enhancement of phosphorylated eEF-2 levels in cells expressing ADP-binding compromised BP mutants compared to cells expressing wild-type eEF-2K. These results suggest a direct energy-sensing role for eEF-2K through its cooperative interaction with CaM and ADP.

AK2 is an AMP-sensing negative regulator of BRAF in tumorigenesis

The RAS–BRAF signaling is a major pathway of cell proliferation and their mutations are frequently found in human cancers. Adenylate kinase 2 (AK2), which modulates balance of adenine nucleotide pool, has been implicated in cell death and cell proliferation independently of its enzyme activity. Recently, the role of AK2 in tumorigenesis was in part elucidated in some cancer types including lung adenocarcinoma and breast cancer, but the underlying mechanism is not clear. Here, we show that AK2 is a BRAF-suppressor. In in vitro assays and cell model, AK2 interacted with BRAF and inhibited BRAF activity and downstream ERK phosphorylation. Energy-deprived conditions in cell model and the addition of AMP to cell lysates strengthened the AK2-BRAF interaction, suggesting that AK2 is involved in the regulation of BRAF activity in response to cell metabolic state. AMP facilitated the AK2–BRAF complex formation through binding to AK2. In a panel of HCC cell lines, AK2 expression was inversely correlated with ERK/MAPK activation, and AK2-knockdown or -knockout increased BRAF activity and promoted cell proliferation. Tumors from HCC patients showed low-AK2 protein expression and increased ERK activation compared to non-tumor tissues and the downregulation of AK2 was also verified by two microarray datasets (TCGA-LIHC and GSE14520). Moreover, AK2/BRAF interaction was abrogated by RAS activation in in vitro assay and cell model and in a mouse model of HRASG12V-driven HCC, and AK2 ablation promoted tumor growth and BRAF activity. AK2 also bound to BRAF inhibitor-insensitive BRAF mutants and attenuated their activities. These findings indicate that AK2 monitoring cellular AMP levels is indeed a negative regulator of BRAF, linking the metabolic status to tumor growth.

Heterogeneity of Starved Yeast Cells in IF1 Levels Suggests the Role of This Protein in vivo.

In mitochondria, a small protein IF1 suppresses the hydrolytic activity of ATP synthase and presumably prevents excessive ATP hydrolysis under conditions of energy deprivation. In yeast Saccharomyces cerevisiae, IF1 homologs are encoded by two paralogous genes: INH1 and STF1. INH1 expression is known to aggravate the deleterious effects of mitochondrial DNA (mtDNA) depletion. Surprisingly, no beneficial effects of INH1 and STF1 were documented for yeast so far, and the functions of INH1 and STF1 in wild type cells are unclear. Here, we put forward a hypothesis that INH1 and STF1 bring advantage during the fast start of proliferation after reentry into exponential growth from post-diauxic or stationary phases. We found that yeast cells increase the concentration of both proteins in the post-diauxic phase. Post-diauxic phase yeast cells formed two subpopulations distinct in Inh1p and Stf1p concentrations. Upon exit from the post-diauxic phase cells with high level of Inh1-GFP started growing earlier than cells devoid of Inh1-GFP. However, double deletion of INH1 and STF1 did not increase the lag period necessary for stationary phase yeast cells to start growing after reinoculation into the fresh medium. These results point to a redundancy of the mechanisms preventing uncontrolled ATP hydrolysis during energy deprivation.

Regulation and Role of AMP-Activated Protein Kinase at the Cellular Level and Relevance to Diabetes Mellitus

Adenosine Mono phosphate -activated protein kinase (AMPK) is a metabolic master switch that senses the cellular AMP levels. However, it is now also regarded as a nutrient-sensing enzyme due to its ability to detect glucose deprivation inside the cell. Under conditions of energy deprivation, AMPK is activated, which in turn switches on all the energy-producing metabolic pathways, while switching off energy-consuming metabolic pathways and cellular processes. There is a growing interest in AMPK due to its role in a wide array of pathological processes including diabetes mellitus. It is the therapeutic target of one of the most commonly prescribed classes of antidiabetic drugs, namely the biguanides such as metformin. The current article presents a review of AMPK structure, triggers, and mechanisms of its activation as well as its role in cell metabolism, mitochondrial homeostasis, autophagy, and cell proliferation. It also briefly addresses the relevance of AMPK to pathogenesis and management of diabetes mellitus.

Regulation of GH and GH Signaling by Nutrients.

Growth hormone (GH) and insulin-like growth factor-1 (IGF-I) are pleiotropic hormones with important roles in lifespan. They promote growth, anabolic actions, and body maintenance, and in conditions of energy deprivation, favor catabolic feedback mechanisms switching from carbohydrate oxidation to lipolysis, with the aim to preserve protein storages and survival. IGF-I/insulin signaling was also the first one identified in the regulation of lifespan in relation to the nutrient-sensing. Indeed, nutrients are crucial modifiers of the GH/IGF-I axis, and these hormones also regulate the complex orchestration of utilization of nutrients in cell and tissues. The aim of this review is to summarize current knowledge on the reciprocal feedback among the GH/IGF-I axis, macro and micronutrients, and dietary regimens, including caloric restriction. Expanding the depth of information on this topic could open perspectives in nutrition management, prevention, and treatment of GH/IGF-I deficiency or excess during life.

The role of AMPK in regulation of Na+,K+-ATPase in skeletal muscle: does the gauge always plug the sink?

AMP-activated protein kinase (AMPK) is a cellular energy gauge and a major regulator of cellular energy homeostasis. Once activated, AMPK stimulates nutrient uptake and the ATP-producing catabolic pathways, while it suppresses the ATP-consuming anabolic pathways, thus helping to maintain the cellular energy balance under energy-deprived conditions. As much as ~ 20-25% of the whole-body ATP consumption occurs due to a reaction catalysed by Na+,K+-ATPase (NKA). Being the single most important sink of energy, NKA might seem to be an essential target of the AMPK-mediated energy saving measures, yet NKA is vital for maintenance of transmembrane Na+ and K+ gradients, water homeostasis, cellular excitability, and the Na+-coupled transport of nutrients and ions. Consistent with the model that AMPK regulates ATP consumption by NKA, activation of AMPK in the lung alveolar cells stimulates endocytosis of NKA, thus suppressing the transepithelial ion transport and the absorption of the alveolar fluid. In skeletal muscles, contractions activate NKA, which opposes a rundown of transmembrane ion gradients, as well as AMPK, which plays an important role in adaptations to exercise. Inhibition of NKA in contracting skeletal muscle accentuates perturbations in ion concentrations and accelerates development of fatigue. However, different models suggest that AMPK does not inhibit or even stimulates NKA in skeletal muscle, which appears to contradict the idea that AMPK maintains the cellular energy balance by always suppressing ATP-consuming processes. In this short review, we examine the role of AMPK in regulation of NKA in skeletal muscle and discuss the apparent paradox of AMPK-stimulated ATP consumption.

AMP-activated protein kinase activation primes cytoplasmic translocation and autophagic degradation of the BCR-ABL protein in CML cells.

Chronic myeloid leukemia is driven by the BCR‐ABL oncoprotein, a constitutively active protein tyrosine kinase. Although tyrosine kinase inhibitors (TKIs) have greatly improved the prognosis of CML patients, the emergence of TKI resistance is an important clinical problem, which deserves additional treatment options based on unique biological properties to CML cells. In this study, we show that metabolic homeostasis is critical for survival of CML cells, especially when the disease is in advanced stages. The BCR‐ABL protein activates AMP‐activated protein kinase (AMPK) for ATP production and the mTOR pathway to suppress autophagy. BCR‐ABL is detected in the nuclei of advanced‐stage CML cells, in which ATP is sufficiently supplied by enhanced glucose metabolism. AMP‐activated protein kinase is further activated under energy‐deprived conditions and triggers autophagy through ULK1 phosphorylation and mTOR inhibition. In addition, AMPK phosphorylates 14‐3‐3 and Beclin 1 to facilitate cytoplasmic translocation of nuclear BCR‐ABL in a BCR‐ABL/14‐3‐3τ/Beclin1/XPO1 complex. Cytoplasmic BCR‐ABL protein undergoes autophagic degradation when intracellular ATP is exhausted by disruption of the energy balance or forced autophagy flux with AMP mimetics, mTOR inhibitors, or arsenic trioxide, leading to apoptotic cell death. This pathway represents a novel therapeutic vulnerability that could be useful for treating TKI‐resistant CML.

Kisspeptin-52 partially rescues the activity of the hypothalamus-pituitary-gonadal axis in underweight male rats dosed with an anti-obesity compound

Energy metabolism and reproduction are closely linked and reciprocally regulated. The detrimental effect of underweight on reproduction complicates the safety evaluation of anti-obesity drugs, making it challenging to distinguish pathological changes mediated through the intended drug-induced weight loss from direct drug effects on reproductive organs. Four-weeks dosing of normal weight Sprague Dawley rats with a glucagon-like peptide 1 (GLP-1)/glucagon receptor co-agonist induced a robust weight loss, accompanied by histological findings in prostate, seminal vesicles, mammary glands, uterus/cervix and vagina. Characterization of the hypothalamus-pituitary-gonadal (HPG) axis in male rats revealed reduced hypothalamic Kiss1 mRNA levels and decreased serum luteinizing hormone (LH) and testosterone concentrations following co-agonist dosing. These alterations resemble hypogonadotropic hypogonadism typically seen in adverse energy deprived conditions, like chronic food restriction. Concomitant daily administration of kisspeptin-52 from day 21 to the end of the four-week co-agonist dosing period evoked LH and testosterone responses without normalizing histological findings. This incomplete rescue by kisspeptin-52 may be due to the rather short kisspeptin-52 treatment period combined with a desensitization observed on testosterone responses. Concomitant leptin treatment from day 21 did not reverse co-agonist induced changes in HPG axis activity. Furthermore, a single co-agonist injection in male rats slightly elevated LH levels but left testosterone unperturbed, thereby excluding a direct acute inhibitory effect on the HPG axis. Our data suggest that the reproductive phenotype after repeated co-agonist administration was driven by the intended weight loss, however, we cannot exclude a direct organ related effect in chronically treated rats.

Abstract TP471: Oxygen-Glucose Deprivation and Denser Extracellular Matrix Cause Cerebral Capillary Endothelial Cells to Lose Elasticity

Objective: Cerebral ischemia affects the mechano-response of vasculature and the remodeling of extracellular matrix (ECM) components. The present study investigates how oxygen-glucose deprivation (OGD) affects the brain endothelial cell (BEC) stiffness. We further aim to study whether ECM components affect the cellular stiffness in normal and energy deprived conditions. Methods: Primary human BECs received a 16h OGD followed by the reperfusion with normal culture media. Young’s Modulus (YM) and topography in the BEC surface were determined by atomic force microscopy (AFM). To test the effect of ECM composition on the BEC stiffness, various concentrations (5-500 uM) of collagen type IV were used for culture dish coating. BECs on the coating beds underwent 16h OGD and served for YM measurements. Per dish, 10-20 single BECs were measured. Results: BECs under OGD conditions became significantly stiffer (2.1-fold, *P<0.05) than the normoxic control, and the increased stiffness sustained even after the reperfusion for 24h, indicating energy deprivation is a primary factor for the increased stiffness under acute stress conditions. AFM topography confirmed that OGD induced rough and filamentous plasma membrane surface in BECs, suggesting a cytoskeletal change was induced by OGD. BECs grown on a 10x denser collagen type IV (500 uM) layer showed a significant increase (2.3-fold, ***P<0.001) in cellular stiffness, compared with the conventional concentration of 50 uM, suggesting that denser extracellular matrix makes BEC stiffer. Also, in BECs cultured on a denser ECM layer, OGD response was absent in terms of cellular stiffness. Conclusion: The present study found that OGD increased BEC stiffness. In addition, increasing the density of the ECM alone was enough to generate stiffer BECs. These mechanical properties of BECs may be a physical factor mediating endothelial responses after stroke.

Solution Structure of the Carboxy-Terminal Tandem Repeat Domain of Eukaryotic Elongation Factor 2 Kinase and Its Role in Substrate Recognition

Eukaryotic elongation factor 2 kinase (eEF-2K), an atypical calmodulin-activated protein kinase, regulates translational elongation by phosphorylating its substrate, eukaryotic elongation factor 2 (eEF-2), thereby reducing its affinity for the ribosome. The activation and activity of eEF-2K are critical for survival under energy-deprived conditions and is implicated in a variety of essential physiological processes. Previous biochemical experiments have indicated that the binding site for the substrate eEF-2 is located in the C-terminal domain of eEF-2K, a region predicted to harbor several α-helical repeats. Here, using NMR methodology, we have determined the solution structure of a C-terminal fragment of eEF-2K, eEF-2K562–725 that encodes two α-helical repeats. The structure of eEF-2K562–725 shows signatures characteristic of TPR domains and of their SEL1-like sub-family. Furthermore, using the analyses of NMR spectral perturbations and ITC measurements, we have localized the eEF-2 binding site on eEF-2K562–725. We find that eEF-2K562–725 engages eEF-2 with an affinity comparable to that of the full-length enzyme. Furthermore, eEF-2K562–725 is able to inhibit the phosphorylation of eEF-2 by full-length eEF-2K in trans. Our present studies establish that eEF-2K562–725 encodes the major elements necessary to enable the eEF-2K/eEF-2 interactions.

PNPLA3 variant M148 causes resistance to starvation-mediated lipid droplet autophagy in human hepatocytes.

The mechanism of how patatin-like phospholipase domain-containing protein 3 (PNPLA3) variant M148 is associated with increased risk of development of hepatic steatosis is still debated. Here, we propose a novel role of PNPLA3 as a key player during autophagosome formation in the process of lipophagy. A human hepatocyte cell line, HepG2 cells, expressing recombinant I148 or 148M, was used to study lipophagy under energy deprived conditions, and lipid droplet morphology was investigated using florescence microscopy, image analysis and biochemical assays. Autophagic flux was studied using the golden-standard of LC3-II turnover in combination with the well characterized GFP-RFP-LC3 vector. To discriminate between, perturbed autophagic initiation and lysosome functionality, lysosomes were characterized by Lysotracker staining and LAMP1 protein levels as well as activity and activation of cathepsin B. For validation, human liver biopsies genotyped for I148 and 148M were analyzed for the presence of LC3-II and PNPLA3 on lipid droplets. We show that the M148-PNPLA3 variant is associated with lipid droplets that are resistant to starvation-mediated degradation. M148 expressing hepatocytes reveal decreased autophagic flux and reduced lipophagy. Both I148-PNPLA3 and M148-PNPLA3 colocalize and interact with LC3-II, but the M148-PNPLA3 variant has lower ability to bind LC3-II. Together, our data indicate that PNPLA3 might play an essential role in lipophagy in hepatocytes and furthermore that the M148-PNPLA3 variant appears to display a loss in this activity, leading to decreased lipophagy.

PARK2 Depletion Connects Energy and Oxidative Stress to PI3K/Akt Activation via PTEN S-Nitrosylation

SummaryPARK2 is a gene implicated in disease states with opposing responses in cell fate determination, yet its contribution in pro-survival signaling is largely unknown. Here we show that PARK2 is altered in over a third of all human cancers, and its depletion results in enhanced phosphatidylinositol 3-kinase/Akt (PI3K/Akt) activation and increased vulnerability to PI3K/Akt/mTOR inhibitors. PARK2 depletion contributes to AMPK-mediated activation of endothelial nitric oxide synthase (eNOS), enhanced levels of reactive oxygen species, and a concomitant increase in oxidized nitric oxide levels, thereby promoting the inhibition of PTEN by S-nitrosylation and ubiquitination. Notably, AMPK activation alone is sufficient to induce PTEN S-nitrosylation in the absence of PARK2 depletion. Park2 loss and Pten loss also display striking cooperativity to promote tumorigenesis in vivo. Together, our findings reveal an important missing mechanism that might account for PTEN suppression in PARK2-deficient tumors, and they highlight the importance of PTEN S-nitrosylation in supporting cell survival and proliferation under conditions of energy deprivation.

The Arabidopsis bZIP11 transcription factor links low-energy signalling to auxin-mediated control of primary root growth.

Plants have to tightly control their energy homeostasis to ensure survival and fitness under constantly changing environmental conditions. Thus, it is stringently required that energy-consuming stress-adaptation and growth-related processes are dynamically tuned according to the prevailing energy availability. The evolutionary conserved SUCROSE NON-FERMENTING1 RELATED KINASES1 (SnRK1) and the downstream group C/S1 basic leucine zipper (bZIP) transcription factors (TFs) are well-characterised central players in plants’ low-energy management. Nevertheless, mechanistic insights into plant growth control under energy deprived conditions remains largely elusive. In this work, we disclose the novel function of the low-energy activated group S1 bZIP11-related TFs as regulators of auxin-mediated primary root growth. Whereas transgenic gain-of-function approaches of these bZIPs interfere with the activity of the root apical meristem and result in root growth repression, root growth of loss-of-function plants show a pronounced insensitivity to low-energy conditions. Based on ensuing molecular and biochemical analyses, we propose a mechanistic model, in which bZIP11-related TFs gain control over the root meristem by directly activating IAA3/SHY2 transcription. IAA3/SHY2 is a pivotal negative regulator of root growth, which has been demonstrated to efficiently repress transcription of major auxin transport facilitators of the PIN-FORMED (PIN) gene family, thereby restricting polar auxin transport to the root tip and in consequence auxin-driven primary root growth. Taken together, our results disclose the central low-energy activated SnRK1-C/S1-bZIP signalling module as gateway to integrate information on the plant’s energy status into root meristem control, thereby balancing plant growth and cellular energy resources.

Chronic intermittent hypoxia affects the cytosolic phospholipase A2α/cyclooxygenase 2 pathway via β2-adrenoceptor-mediated ERK/p38 stimulation.

Cardiac resistance against acute ischemia/reperfusion (I/R) injury can be enhanced by adaptation to chronic intermittent hypoxia (CIH), but the changes at the molecular level associated with this adaptation are still not fully explored. Phospholipase A2 (PLA2) plays an important role in phospholipid metabolism and may contribute to membrane destruction under conditions of energy deprivation during I/R. The aim of this study was to determine the effect of CIH (7000m, 8h/day, 5weeks) on the expression of cytosolic PLA2α (cPLA2α) and its phosphorylated form (p-cPLA2α), as well as other related signaling proteins in the left ventricular myocardium of adult male Wistar rats. Adaptation to CIH increased the total content of cPLA2α by 14% in myocardial homogenate, and enhanced the association of p-cPLA2α with the nuclear membrane by 85%. The total number of β-adrenoceptors (β-ARs) did not change but the β2/β1 ratio markedly increased due to the elevation of β2-ARs and drop in β1-ARs. In parallel, the amount of adenylyl cyclase decreased by 49% and Giα proteins increased by about 50%. Besides that, cyclooxygenase 2 (COX-2) and prostaglandin E2 (PGE2) increased by 36 and 84%, respectively. In parallel, we detected increased phosphorylation of protein kinase Cα, ERK1/2 and p38 (by 12, 48 and 19%, respectively). These data suggest that adaptive changes induced in the myocardium by CIH may include activation of cPLA2α and COX-2 via β2-AR/Gi-mediated stimulation of the ERK/p38 pathway.

Permanent dynamic transporter-mediated turnover of glutamate across the plasma membrane of presynaptic nerve terminals: arguments in favor and against.

Mechanisms for maintenance of the extracellular level of glutamate in brain tissue and its regulation still remain almost unclear, and criticism of the current paradigm of glutamate transport and homeostasis has recently appeared. The main premise for this study is the existence of a definite and non-negligible concentration of ambient glutamate between the episodes of exocytotic release in our experiments with rat brain nerve terminals (synaptosomes), despite the existence of a very potent Na+-dependent glutamate uptake. Glutamate transporter reversal is considered as the main mechanisms of glutamate release under special conditions of energy deprivation, hypoxia, hypoglycemia, brain trauma, and stroke, underlying an increase in the ambient glutamate concentration and development of excitotoxicity. In the present study, a new vision on transporter-mediated release of glutamate as one of the main mechanisms involved in the maintenance of definite concentration of ambient glutamate under normal energetical status of nerve terminals is forwarded. It has been suggested that glutamate transporters act effectively in outward direction in a non-pathological manner, and this process is thermodynamically synchronized with uptake and provides effective outward glutamate current, thereby establishing and maintaining permanent and dynamic glutamatein/glutamate(out) gradient and turnover across the plasma membrane. In this context, non-transporter tonic glutamate release by diffusion, spontaneous exocytosis, cystine-glutamate exchanger, and leakage through anion channels can be considered as a permanently added 'new' exogenous substrate using two-substrate kinetic model calculations. Permanent glutamate turnover is of value for tonic activation of post/presynaptic glutamate receptors, long-term potentiation, memory formation, etc. Counterarguments against this mechanism are also considered.

ABAD ACTIVITY IN ALZHEIMER'S DISEASE

Changes in glucose metabolism have been observed in the brains of Alzheimer's disease sufferers. This suggests that neurons require an alternative energy source that can bypass glycolysis in order to produce energy. The oxidation of fatty acids is crucial at this point as the products of this catabolism can feed into the second stage of the respiratory cycle. ABAD is a key enzyme in the production of ketone bodies and sex steroid homeostasis in the brain and has been found to be up-regulated in AD (He et al., 1999, He et al., 2001, Lustbader et al., 2004). Additionally, ABAD is up-regulated under conditions of energy deprivation and increased ketogenesis (Du Yan et al., 2000, Yao et al., 2011). The abundance of Aβ present in the mitochondria in AD binds to ABAD and acts to either inhibit or alter the catalytic function of ABAD (Lustbader et al., 2004, Muirhead et al., 2010a). The effect of Aβ binding to ABAD could result in an energy deficit in the brain. -ABAD Activity Assay - using the fluorogenic probe cyclohexenyl amino naphthalene alcohol ((-)-CHANA), which when oxidized by ABAD produces cyclohexenyl amino naphthalene ketone (CHANK), which emits fluorescence at 520nm (Froemming and Sames, 2007, Muirhead et al., 2010b)-Mitochondrial integrity assays -Mass Spectrometry -Lipidomic and Fatty Acid Analysis Investigations into ABAD activity using (-)-CHANA activity assay suggest ABAD activity increases when glucose levels were decreased in mouse primary cortical neurons. This increase in activity is potentially controlled by posttranslational modifications of ABAD. Further effects downstream in lipid metabolism have also been observed upon changes in glucose levels. The increase of ABAD activity suggests that the cells are relying on the production of ketone bodies as an alternative energy source. Downstream effects of altering ABAD activity include changes in lipid content suggesting that the β -oxidation of fatty acids is altered. In AD, lipid changes have previously been noted along with a decline in cerebral metabolic glucose rate. The up-regulation of ABAD could be a protective mechanism and by increasing its activity the toxic effects of A β could be reversed.

The REGγ Proteasome Regulates Hepatic Lipid Metabolism through Inhibition of Autophagy

The ubiquitin-proteasome and autophagy-lysosome systems are major proteolytic pathways, whereas function of the Ub-independent proteasome pathway is yet to be clarified. Here, we investigated roles of the Ub-independent REGγ-proteasome proteolytic system in regulating metabolism. We demonstrate that mice deficient for the proteasome activator REGγ exhibit dramatic autophagy induction and are protected against high-fat diet (HFD)-induced liver steatosis through autophagy. Molecularly, prevention of steatosis in the absence of REGγ entails elevated SirT1, a deacetylase regulating autophagy and metabolism. REGγ physically binds to SirT1, promotes its Ub-independent degradation, and inhibits its activity to deacetylate autophagy-related proteins, thereby inhibiting autophagy under normal conditions. Moreover, REGγ and SirT1 dissociate from each other through a phosphorylation-dependent mechanism under energy-deprived conditions, unleashing SirT1 to stimulate autophagy. These observations provide a function of the REGγ proteasome in autophagy and hepatosteatosis, underscoring mechanistically a crosstalk between the proteasome and autophagy degradation system in the regulation of lipid homeostasis.

Shuttling glucose across brain microvessels, with a little help from GLUT1 and AMP kinase. Focus on “AMP kinase regulation of sugar transport in brain capillary endothelial cells during acute metabolic stress”

The Blood-Brain Barrier: a Gatekeeper of Brain “Individuality” The blood-brain barrier (BBB) maintains the individuality of brain fluid, while allowing it to selectively import nutrients and process toxic products. Its major constituent is a single layer of continuous, nonfenestrated endothelium lining the microvessels, whose unique features account in large part for the integrity of the barrier. The endothelial cell monolayer is the major determinant, but other cells in the central nervous system (e.g., pericytes and astrocytes) contribute to the integrity of the BBB. The interendothelial tight junctions of the BBB are one of its signature elements that greatly restrict paracellular permeability to solutes, fluid, and transmigrating cells. This is markedly distinct from the leakier, discontinuous, and fenestrated endothelium of liver microvessels (sinusoids). For example, the tight junctions of the cerebral endothelium (pial vessels) confer an electrical resistance (1,300 ·cm 2 ) far higher than other endothelia (6). Therefore, communication between blood and the brain interstitial fluid requires individually tailored molecular mechanisms. Transcytosis is the movement of molecules through a cellular barrier. Whereas proteins can traverse through vesicular carrier processes that could carry solutes through fluid phase endocytosis, the brain microvasculature is uniquely poor in plasmalemmal and cytoplasmic caveolae (1). Instead, bidirectional passage of small molecules across the BBB is stringently regulated by numerous transporters and receptors. These typically work in tandem across the luminal and abluminal membranes of the endothelial cell.