Energetic Stress Research Articles

Reliability of resting metabolic rate between and within day measurements using the Vyntus CPX system and comparison against predictive formulas.

Background: To detect longitudinal changes of resting metabolic rate (RMR) resulting from the effects of energetic stress, reliable RMR measurements are crucial. The Vyntus CPX is a new automated indirect calorimetry system for which RMR reliability has not been determined. Additionally, its agreement with common predictive RMR formulas is unknown. Aim: To determine the within and between-day reliability of RMR measurements using the Vyntus CPX system and its agreement with predictive RMR formulas. Methods: Young (31 ± 7 years) healthy participants (n = 26, 12 females, 14 males) completed three measurements of RMR, two consecutive measures on the same day, one the day before/after, all under standardised conditions. Reliability was assessed with pairwise comparisons of between-day at the same time (BDST), within day consecutive measurements (WDCM) and between-day different time (BDDT), for parameters of reliability (mean change (MC), intraclass correlation (ICC) and typical error of measurement (TEM)). Measured RMR values (kcal/day) were compared against predictive values of 4 common formulas. Results: Parameters of reliability (mean, (95% confidence interval)) were: -BDST: MC, 0.2(-2.3-2.7)% (p = 0.67); ICC, 0.92(0.84-0.97); TEM, 4.5(3.5-6.2)%. -WDCM: MC, -2.5(-6.2-1.3)% (p = 0.21); ICC, 0.88(0.74-0.88); TEM, 7.0(5.4-9.8)%. -BDDT: MC, -1.5(-4.8-1.9)% (p = 0.57); ICC, 0.90(0.76-0.95); TEM, 6.1(4.8-8.5)%. RMRratios (measured/predicted) were: 1.04 ± 0.14 (Nelson, p = 0.13), 1.03 ± 0.10 (Mifflin, p = 0.21), 0.98 ± 0.09 (Harris-benedict, p = 0.30), 0.95 ± 0.11 (Cunningham1980, p = 0.01), 1.00 ± 0.12 (Cunningham1991, p = 0.90) and 0.96 ± 0.13 (DXA, p = 0.03). Conclusions: The Vyntus CPX is reliable and measured RMR values agreed with four predictive formulas but are lower than Cunningham1980 and DXA RMR estimates for this population.

Targeting Mitochondrial Protein Expression as a Future Approach for Cancer Therapy.

Extensive metabolic remodeling is a fundamental feature of cancer cells. Although early reports attributed such remodeling to a loss of mitochondrial functions, it is now clear that mitochondria play central roles in cancer development and progression, from energy production to synthesis of macromolecules, from redox modulation to regulation of cell death. Biosynthetic pathways are also heavily affected by the metabolic rewiring, with protein synthesis dysregulation at the hearth of cellular transformation. Accumulating evidence in multiple organisms shows that the metabolic functions of mitochondria are tightly connected to protein synthesis, being assembly and activity of respiratory complexes highly dependent on de novo synthesis of their components. In turn, protein synthesis within the organelle is tightly connected with the cytosolic process. This implies an entire network of interactions and fine-tuned regulations that build up a completely under-estimated level of complexity. We are now only preliminarily beginning to reconstitute such regulatory level in human cells, and to perceive its role in diseases. Indeed, disruption or alterations of these connections trigger conditions of proteotoxic and energetic stress that could be potentially exploited for therapeutic purposes. In this review, we summarize the available literature on the coordinated regulation of mitochondrial and cytosolic mRNA translation, and their effects on the integrity of the mitochondrial proteome and functions. Finally, we highlight the potential held by this topic for future research directions and for the development of innovative therapeutic approaches.

Costs of territoriality: a review of hypotheses, meta-analysis, and field study.

The evolution of territoriality reflects the balance between the benefit and cost of monopolising a resource. While the benefit of territoriality is generally intuitive (improved access to resources), our understanding of its cost is less clear. This paper combines: 1. a review of hypotheses and meta-analytic benchmarking of costs across diverse taxa; and 2. a new empirical test of hypotheses using a longitudinal study of free-living male territorial lizards. The cost of territoriality was best described as a culmination of multiple factors, but especially costs resulting from the time required to maintain a territory (identified by the meta-analysis) or those exacerbated by a territory that is large in size (identified by the empirical test). The meta-analysis showed that physiological costs such as energetic expenditure or stress were largely negligible in impact on territory holders. Species that used territories to monopolise access to mates appeared to incur the greatest costs, whereas those defending food resources experienced the least. The single largest gap in our current understanding revealed by the literature review is the potential cost associated with increased predation. There is also a clear need for multiple costs to be evaluated concurrently in a single species. The empirical component of this study showcases a powerful analytical framework for evaluating a range of hypotheses using correlational data obtained in the field. More broadly, this paper highlights key factors that should be considered in any investigation that attempts to account for the evolutionary origin or ecological variation in territorial behaviour within and between species.

Enhanced Vulnerability of LKB1-Deficient NSCLC to Disruption of ATP Pools and Redox Homeostasis by 8-Cl-Ado.

Loss-of-function somatic mutations of STK11, a tumor suppressor gene encoding LKB1 that contributes to the altered metabolic phenotype of cancer cells, is the second most common event in lung adenocarcinomas and often co-occurs with activating KRAS mutations. Tumor cells lacking LKB1 display an aggressive phenotype, with uncontrolled cell growth and higher energetic and redox stress due to its failure to balance ATP and NADPH levels in response to cellular stimulus. The identification of effective therapeutic regimens for patients with LKB1-deficient non-small cell lung cancer (NSCLC) remains a major clinical need. Here, we report that LKB1-deficient NSCLC tumor cells displayed reduced basal levels of ATP and to a lesser extent other nucleotides, and markedly enhanced sensitivity to 8-Cl-adenosine (8-Cl-Ado), an energy-depleting nucleoside analog. Treatment with 8-Cl-Ado depleted intracellular ATP levels, raised redox stress, and induced cell death leading to a compensatory suppression of mTOR signaling in LKB1-intact, but not LKB1-deficient, cells. Proteomic analysis revealed that the MAPK/MEK/ERK and PI3K/AKT pathways were activated in response to 8-Cl-Ado treatment and targeting these pathways enhanced the antitumor efficacy of 8-Cl-Ado. IMPLICATIONS: Together, our findings demonstrate that LKB1-deficient tumor cells are selectively sensitive to 8-Cl-Ado and suggest that therapeutic approaches targeting vulnerable energy stores combined with signaling pathway inhibitors merit further investigation for this patient population.

Neurochemical abnormalities in chronic fatigue syndrome: a pilot magnetic resonance spectroscopy study at 7 Tesla

RationaleChronic fatigue syndrome (CFS) is a common and burdensome illness with a poorly understood pathophysiology, though many of the characteristic symptoms are likely to be of brain origin. The use of high-field proton magnetic resonance spectroscopy (MRS) enables the detection of a range of brain neurochemicals relevant to aetiological processes that have been linked to CFS, for example, oxidative stress and mitochondrial dysfunction.MethodsWe studied 22 CFS patients and 13 healthy controls who underwent MRS scanning at 7 T with a voxel placed in the anterior cingulate cortex. Neurometabolite concentrations were calculated using the unsuppressed water signal as a reference.ResultsCompared to controls, CFS patients had lowered levels of glutathione, total creatine and myo-inositol in anterior cingulate cortex. However, when using N-acetylaspartate as a reference metabolite, only myo-inositol levels continued to be significantly lower in CFS participants.ConclusionsThe changes in glutathione and creatine are consistent with the presence of oxidative and energetic stress in CFS patients and are potentially remediable by nutritional intervention. A reduction in myo-inositol would be consistent with glial dysfunction. However, the relationship of the neurochemical abnormalities to the causation of CFS remains to be established, and the current findings require prospective replication in a larger sample.

Ulk1, Not Ulk2, Is Required for Exercise Training-Induced Improvement of Insulin Response in Skeletal Muscle.

Unc51 like autophagy activating kinase 1 (Ulk1), the primary autophagy regulator, has been linked to metabolic adaptation in skeletal muscle to exercise training. Here we compared the roles of Ulk1 and homologous Ulk2 in skeletal muscle insulin action following exercise training to gain more mechanistic insights. Inducible, skeletal muscle-specific Ulk1 knock-out (Ulk1-iMKO) mice and global Ulk2 knock-out (Ulk2–/–) mice were subjected to voluntary wheel running for 6 weeks followed by assessment of exercise capacity, glucose tolerance, and insulin signaling in skeletal muscle after a bolus injection of insulin. Both Ulk1-iMKO and Ulk2–/– mice had improved endurance exercise capacity post-exercise. Ulk1-iMKO did not improve glucose clearance during glucose tolerance test, while Ulk2–/– had only marginal improvement. However, exercise training-induced improvement of insulin action in skeletal muscle, indicated by Akt-S473 phosphorylation, was only impaired in Ulk1-iMKO. These data suggest that Ulk1, but not Ulk2, is required for exercise training-induced improvement of insulin action in skeletal muscle, implicating crosstalk between catabolic and anabolic signaling as integral to metabolic adaptation to energetic stress.

The pathological effects of a Nosema ceranae infection in the giant honey bee, Apis dorsata Fabricius, 1793

Nosema ceranae is an intracellular microsporidian pathogen that lives in the midgut ventricular cells of all known honey bee Apis species. We suspect that N. ceranae may also cause energetic stress in the giant honey bee because this parasite is known to disrupt nutrient absorption resulting in energetic stress in the honey bee species Apis mellifera. To understand how N. ceranae impacts the energetic stress of the giant honey bee, A. dorsata, we measured the hemolymph trehalose levels of experimentally infected giant honey bees on days three, five, seven, and fourteen post infection (p.i.). We also measured the hypopharyngeal gland protein content, the total midgut proteolytic enzyme activity, honey bee survival, infection ratio, and spore loads comparing infected and uninfected honey bees across the same time frame. Nosema ceranae-infected honey bees had significantly lowered survival, trehalose levels, hypopharyngeal gland protein content, and midgut proteolytic enzyme activity. We found an increasing level of parasitic loads and infection ratio of N. ceranae-infected bees after inoculation. Collectively, our results suggest that the giant honey bee suffers from energetic stress and limited nutrient absorption from a N. ceranae infection, which results in lowered survival in comparison to uninfected honey bees. Our findings highlight that other honey bee species besides A. mellifera are susceptible to microsporidian pathogens that they harbor, which results in negative effects on health and survival. Therefore, these pathogens might be transmitted at a community level, in the natural environment, resulting in negative health effects of multiple honey bee species.

Comprehensive Interrogation of Metabolic and Bioenergetic Responses of Early-Staged Zebrafish (Danio rerio) to a Commercial Copper Hydroxide Nanopesticide.

The use of copper hydroxide nanopesticide can pose exposure risks to aquatic organisms. In this study, the toxicity of a copper hydroxide nanopesticide, compared to conventional copper sulfate at environmentally relevant doses, was evaluated using metabolomics and bioenergetic assays in embryonic zebrafish. At a copper concentration of 100 μg/L, the nanopesticide caused higher mortality and deformity compared to copper ions alone; despite higher copper accumulation, increased metallothionein and elevated ATP-binding cassette (ABC) transporter activity in zebrafish exposed to copper ions were observed. Both nanopesticide and copper ions reduced the abundance of metabolites of glycolysis and induced energetic stress in zebrafish. The nanopesticide also increased concentrations of several organic acids involved in the tricarboxylic acid (TCA) cycle and elevated the activity of isocitrate dehydrogenase and α-ketoglutarate dehydrogenase, suggesting enhanced TCA cycle activity. Nanopesticide exposure depleted both glutamate and glutamine parallel to the upregulation of the TCA cycle. In addition, zebrafish exposed to the nanopesticide appeared to shift metabolism toward amino acid catabolism and lipid accumulation based upon altered expression profiles of glutaminase, glutamate dehydrogenase, fatty acid synthase, and acetyl-CoA carboxylase. Lastly, the ability of the ions to increase oxidative phosphorylation to alleviate energetic stress was reduced in the case of the nanopesticide. We hypothesize that, unlike copper ions alone, the nanopesticide induces higher toxicity to zebrafish because of increased protein catabolism. This study provides a comprehensive understanding of the risks of copper hydroxide nanopesticide exposure in relation to metabolic activity and mitochondrial function.

Exogenous mitochondrial transfer and endogenous mitochondrial fission facilitate AML resistance to OxPhos inhibition

Acute myeloid leukemia (AML) cells are highly dependent on oxidative phosphorylation (OxPhos) for survival, and they continually adapt to fluctuations in nutrient and oxygen availability in the bone marrow (BM) microenvironment. We investigated how the BM microenvironment affects the response to OxPhos inhibition in AML by using a novel complex I OxPhos inhibitor, IACS-010759. Cellular adhesion, growth, and apoptosis assays, along with measurements of expression of mitochondrial DNA and generation of mitochondrial reactive oxygen species indicated that direct interactions with BM stromal cells triggered compensatory activation of mitochondrial respiration and resistance to OxPhos inhibition in AML cells. Mechanistically, inhibition of OxPhos induced transfer of mitochondria derived from mesenchymal stem cells (MSCs) to AML cells via tunneling nanotubes under direct-contact coculture conditions. Inhibition of OxPhos also induced mitochondrial fission and increased functional mitochondria and mitophagy in AML cells. Mitochondrial fission is known to enhance cell migration, so we used electron microscopy to observe mitochondrial transport to the leading edge of protrusions of AML cells migrating toward MSCs. We further demonstrated that cytarabine, a commonly used antileukemia agent, increased mitochondrial transfer of MSCs to AML cells triggered by OxPhos inhibition. Our findings indicate an important role of exogenous mitochondrial trafficking from BM stromal cells to AML cells as well as endogenous mitochondrial fission and mitophagy in the compensatory adaptation of leukemia cells to energetic stress in the BM microenvironment.

Mitochondria-localized AMPK responds to local energetics and contributes to exercise and energetic stress-induced mitophagy.

Mitochondria form a complex, interconnected reticulum that is maintained through coordination among biogenesis, dynamic fission, and fusion and mitophagy, which are initiated in response to various cues to maintain energetic homeostasis. These cellular events, which make up mitochondrial quality control, act with remarkable spatial precision, but what governs such spatial specificity is poorly understood. Herein, we demonstrate that specific isoforms of the cellular bioenergetic sensor, 5' AMP-activated protein kinase (AMPKα1/α2/β2/γ1), are localized on the outer mitochondrial membrane, referred to as mitoAMPK, in various tissues in mice and humans. Activation of mitoAMPK varies across the reticulum in response to energetic stress, and inhibition of mitoAMPK activity attenuates exercise-induced mitophagy in skeletal muscle in vivo. Discovery of a mitochondrial pool of AMPK and its local importance for mitochondrial quality control underscores the complexity of sensing cellular energetics in vivo that has implications for targeting mitochondrial energetics for disease treatment.

Abstract MP211: NAD Redox Imbalance Exacerbates Diabetic Cardiomyopathy

Diabetes and heart failure are linked to NAD redox imbalance, whose role in diabetic cardiomyopathy has not been directly tested. Streptozotocin-induced diabetes in WT mice for 16 weeks promoted declines in systolic and diastolic function, which associated with lowered cardiac NAD/NADH ratio (NAD redox imbalance). To test the hypothesis that , we employed mouse models with cardiac-specific manipulations of NAD redox states. Cardiac-specific Ndufs4-KO mice (cKO) exhibit lowered cardiac NAD/NADH ratio with normal baseline function, geometry and energetics. Control and cKO mice were challenged with 8-week diabetic stress. Metabolomic analyses of plasma collected after the diabetic stress showed similar hyperglycemia and dyslipidemia stresses in diabetic control and diabetic cKO mice. Chronic diabetic stress promoted systolic and diastolic dysfunctions in control mice, which were further exacerbated in diabetic cKO mice in both male and female cohorts. Collagen levels and transcript analyses of fibrosis and extracellular matrix-dependent pathways showed no change in diabetic cKO hearts, suggesting that cardiomyocyte dysfunction is a likely culprit for the exacerbated dysfunction. Increased protein acetylation, including SOD2-K68Ac, was observed in diabetic cKO hearts. Inhibited antioxidant function by SOD2-K68Ac promoted protein oxidation in diabetic cKO hearts, suggesting oxidative stress as a pathogenic mechanism. We next examined phosphorylation status of myofilament proteins in these diabetic hearts. MyBPC-S282Pi levels are suppressed in failing hearts and remained unchanged in diabetic cKO hearts. TnI-S150Pi increases myofilament calcium sensitivity and prolongs calcium dissociation, while TnI-S23/24Pi imposes the opposite effects. TnI-S150Pi levels were elevated in diabetic cKO hearts, while TnI-S23/24Pi levels unchanged. Therefore, exacerbated diastolic dysfunction in diabetic cKO hearts is due to the selective phosphorylation at TnI-S150. AMPK is activated by energetic stress and phosphorylates TnI-S150. ATP levels decreased, and AMP/ATP ratio increased in diabetic cKO hearts, implicating impaired energetics to promote TnI-S150Pi and dysfunction. Elevation of NAD levels normalized cardiac NAD redox balance in diabetic cKO hearts. Elevated levels of SOD2-K68Ac and TnI-S150Pi, exacerbated systolic and diastolic dysfunction in diabetic cKO hearts were all reversed by elevation of NAD levels. Dysfunction in diabetic control hearts was also ameliorated by elevation of NAD levels. These data collectively conclude that NAD redox imbalance is a positive mediator of the progression of diabetic cardiomyopathy.

Асоціація активності 5’АМФ-активованої протеїнкінази з тривалістю захворювання та вмістом HbA1c у лейкоцитах пацієнтів із цукровим діабетом

Актуальність. 5’АМФ­активована протеїнкіназа (АМФК) — фермент, який керує енергетичним балансом клітини. При енергетичному напруженні в клітині й збільшенні концентрації АМФ ATФ замінюється в обмінних центрах АМФ, що призводить до алостеричної активації АМФК фосфорилюванням треоніну­172 α­субодиницею LKB1­комплексу у відповідь на зміни в клітинній енергії або CAMKKβ, який активізує внутрішньоклітинний Ca2+. Мета дослідження — вивчити діяльність головного сенсора енергії клітини — АМФК у лейкоцитах пацієнтів, які отримують препарати інсуліну, метформін чи інші цукрознижувальні лікарські засоби залежно від тривалості хвороби й концентрації глікованого гемоглобіну (HbA1c). Матеріали та методи. Пацієнти з цукровим діабетом, які отримували моно­ або комбіновану терапію інсуліном і його аналогами, метформіном, дапагліфлозином і похідними сульфонілсечовини, були розділені на 5 груп: перша — із рівнем HbA1c, близьким до норми, 6,9–7,6 %; друга — 7,6–9,0 %; третя — > 9 %; четверта — > 10 %; п’ята — > 11 %. Для визначення кількості фосфо­АМФК використали ІФА­набори. Результати. Встановлено, що зі збільшенням умісту HbA1c в крові рівень активностi АМФК у лейкоцитах поступово знижується. Активність АМФК у лейкоцитах пацієнтів із тривалістю захворювання ~ 20 років була втричі нижчою, ніж у хворих із 10­річним стажем. Збільшення цитозолей у відновленій формі відіграє центральну роль в управлінні аденозинмонофосфат­активованою протеїнкіназою. Високі умови харчування, такі як діабетичне середовище, збільшують співвідношення відновлених форм до окислених через каскади, включаючи поліольний шлях. Ця зміна окислювально­відновного потенціалу пов’язана з резистентністю до інсуліну й розвитком діабетичних ускладнень. Висновки. Таким чином, активність АМФК у лейкоцитах може бути індикатором діабетичної компенсації в пацієнтів із цукровим діабетом.

Interacting Effects of Density‐Dependent and Density‐Independent Factors on Growth Rates in Southwestern Cutthroat Trout Populations

AbstractDensity‐dependent (DD) and density‐independent (DI) effects play an important role in shaping fish growth rates, an attribute that correlates with many life history traits in fishes. Consequently, understanding the extent to which DD and DI effects influence growth rates is valuable for fisheries assessments because it can inform managers about how populations may respond as environmental conditions continue to change (e.g., threats from climate change). We used a Rio Grande Cutthroat Trout Oncorhynchus clarkii virginalis (RGCT) capture–mark–recapture data set collected over 2 years along a temperature and density gradient in northern New Mexico streams to test the extent to which DD and DI effects interact to influence specific growth rates. We found that temperature (DI) and density (DD) interacted with RGCT life stage (i.e., immature or mature) to affect growth rates. We only detected evidence of a negative DD effect on RGCT growth for the immature fraction of a population when exposed to the warmest stream temperatures. Our results suggest that competition most strongly affected the immature portion of RGCT populations, and this effect was only detectable when temperatures were warmest and energetic stress was likely at its highest. The quadratic relationship between temperature and growth rates also demonstrated that stream temperatures were below as well as above optimal growth temperatures for RGCT. Growth rates in our RGCT populations were influenced by complex interactions of DD and DI effects, and our results suggest that the negative consequences of warming trends associated with climate change on RGCT populations may be exacerbated by DD effects.

AML-108: Exogenous Mitochondrial Transfer and Endogenous Mitochondrial Fission Facilitate Resistance to OxPhos Inhibition in AML

<h3>Context:</h3> Oxidative phosphorylation (OxPhos) inhibition induces mitochondrial trafficking from BM stromal cells to AML and is accompanied by mitochondrial fission and mitophagy. The mitochondrial coupling and crosstalk with BM stromal cells facilitate the development of resistance to OxPhos inhibition in AML cells. <h3>Objective:</h3> Acute myeloid leukemia (AML) cells are highly dependent on OxPhos for survival and continually adapt to fluctuations in nutrient and oxygen availability in the environment. We investigated how the BM microenvironment affects the response to OxPhos inhibition in AML by using a novel complex I OxPhos inhibitor, IACS-010759. <h3>Design:</h3> Primary AML cells from 26 patients, primary normal MSCs, and AML cell lines were utilized and treated with the OxPhos inhibitor IACS-0107598 and/or cytarabine. Cap analysis of gene expression transcriptome analyses for AML PDXs, primary samples, and AML cell lines has been performed. We performed an extracellular flux assay to measure the oxygen consumption rate. To visualize mitochondria, AML cell lines and MSCs were stably transfected with mitochondria-targeted PDHA1-GFP and -dsRed, respectively. Electron microscopy and immunoelectron microscopy analysis have been performed. <h3>Results:</h3> Cellular adhesion, growth, and apoptosis assays, along with measurements of mtDNA expression and mitochondrial reactive oxygen species generation, indicated that direct interactions with BM stromal cells triggered the compensatory activation of mitochondrial respiration and resistance to OxPhos inhibition in AML cells. Mechanistically, OxPhos inhibition induced (1) transfer of mesenchymal stem cell (MSC)-derived mitochondria to AML cells via tunneling nanotubes under direct-contact co-culture conditions and (2) mitochondrial fission with an increase in functional mitochondria and mitophagy in AML cells. Mitochondrial fission is known to enhance cell migration, and we observed mitochondrial transport to the leading edge of protrusions of migrating AML cells toward MSCs by electron microscopy analysis. We further demonstrated that cytarabine, a commonly used antileukemia agent, increased IACS-010759-triggered mitochondrial transfer from MSCs to AML cells. <h3>Conclusions:</h3> Our findings indicate an important role of exogenous mitochondrial trafficking from BM stromal cells to AML cells and of endogenous mitochondrial fission and mitophagy in the compensatory adaptation of leukemia cells to energetic stress in the BM microenvironment.

Combined intermittent fasting and ERK inhibition enhance the anti-tumor effects of chemotherapy via the GSK3\u03b2-SIRT7 axis

Dietary interventions such as intermittent fasting (IF) have emerged as an attractive strategy for cancer therapies; therefore, understanding the underlying molecular mechanisms is pivotal. Here, we find SIRT7 decline markedly attenuates the anti-tumor effect of IF. Mechanistically, AMP-activated protein kinase (AMPK) phosphorylating SIRT7 at T263 triggers further phosphorylation at T255/S259 by glycogen synthase kinase 3β (GSK3β), which stabilizes SIRT7 by decoupling E3 ligase UBR5. SIRT7 hyperphosphorylation achieves anti-tumor activity by disrupting the SKP2-SCF E3 ligase, thus preventing SKP2-mediated K63-linked AKT polyubiquitination and subsequent activation. In contrast, GSK3β-SIRT7 axis is inhibited by EGF/ERK2 signaling, with ERK2 inactivating GSK3β, thus accelerating SIRT7 degradation. Unfavorably, glucose deprivation or chemotherapy hijacks the GSK3β-SIRT7 axis via ERK2, thus activating AKT and ensuring survival. Notably, Trametinib, an FDA-approved MEK inhibitor, enhances the efficacy of combination therapy with doxorubicin and IF. Overall, we have revealed the GSK3β-SIRT7 axis that must be fine-tuned in the face of the energetic and oncogenic stresses in malignancy.

Evaluating adaptive hypotheses for female-led infanticide in wild chimpanzees

Although rare among group-living primates, infanticide by females has been reported in several chimpanzee, Pan troglodytes, populations. We examined 13 infanticidal attacks over 47 years at Gombe National Park, Tanzania to evaluate three adaptive hypotheses. (1) Exploitation of the infant as a food resource – by eating a vulnerable neonate, attackers gain calories that may be important during periods of food scarcity or energetic stress. (2) Resource competition – Gombe females concentrate their foraging in overlapping core areas and dominance rank influences foraging success. By killing the infant of a female with high core area overlap, the perpetrator removes a current and future competitor, improving her access to food. (3) Low cost – female chimpanzees mature and reproduce slowly, and longevity increases reproductive success. Physical aggression causes risk of severe injury or death, so females will only mount attacks when risks to the perpetrator are low. In support of hypothesis 1, females usually consumed the carcass. However, attacks were not more likely in times of resource or energy scarcity. In support of hypothesis 2, females attacked others with whom they shared core areas, but attacks did not cause shifts in ranging patterns. In support of hypothesis 3, one or more attackers always outranked the victim, the attacks often involved coalitions and victims usually lacked kin support. Attacks were more likely to be successful when attackers were not hindered by clinging infants and victims could not retreat. Our results provide further evidence for female competition and the adaptive value of female-led infanticide in this species.

Extracellular vesicle-based interorgan transport of mitochondria from energetically stressed adipocytes

Adipocytes undergo intense energetic stress in obesity resulting in loss of mitochondrial mass and function. We have found that adipocytes respond to mitochondrial stress by rapidly and robustly releasing small extracellular vesicles (sEVs). These sEVs contain respiration-competent, but oxidatively damaged mitochondrial particles, which enter circulation and are taken up by cardiomyocytes, where they trigger a burst of ROS. The result is compensatory antioxidant signaling in the heart that protects cardiomyocytes from acute oxidative stress, consistent with a preconditioning paradigm. As such, a single injection of sEVs from energetically stressed adipocytes limits cardiac ischemia/reperfusion injury in mice. This study provides the first description of functional mitochondrial transfer between tissues and the first vertebrate example of "inter-organ mitohormesis." Thus, these seemingly toxic adipocyte sEVs may provide a physiological avenue of potent cardio-protection against the inevitable lipotoxic or ischemic stresses elicited by obesity.

Alkaline intracellular pH (pHi) activates AMPK–mTORC2 signaling to promote cell survival during growth factor limitation

The mechanistic target of rapamycin (mTOR) complex 2 (mTORC2) signaling controls cell metabolism, promotes cell survival, and contributes to tumorigenesis, yet its upstream regulation remains poorly defined. Although considerable evidence supports the prevailing view that amino acids activate mTOR complex 1 but not mTORC2, several studies reported paradoxical activation of mTORC2 signaling by amino acids. We noted that after amino acid starvation of cells in culture, addition of an amino acid solution increased mTORC2 signaling. Interestingly, we found the pH of the amino acid solution to be alkaline, ∼pH 10. These observations led us to discover and demonstrate here that alkaline intracellular pH (pHi) represents a previously unknown activator of mTORC2. Using a fluorescent pH-sensitive dye (cSNARF1-AM) coupled with live-cell imaging, we demonstrate that culturing cells in media at an alkaline pH induces a rapid rise in the pHi, which increases mTORC2 catalytic activity and downstream signaling to the pro-growth and pro-survival kinase Akt. Alkaline pHi also activates AMPK, a canonical sensor of energetic stress. Functionally, alkaline pHi activates AMPK-mTOR signaling, which attenuates apoptosis caused by growth factor withdrawal. Collectively, these findings reveal that alkaline pHi increases mTORC2- and AMPK-mediated signaling to promote cell survival during conditions of growth factor limitation, analogous to the demonstrated ability of energetic stress to activate AMPK–mTORC2 and promote cell survival. As an elevated pHi represents an underappreciated hallmark of cancer cells, we propose that the alkaline pHi stress sensing by AMPK–mTORC2 may contribute to tumorigenesis by enabling cancer cells at the core of a growing tumor to evade apoptosis and survive.

AMPK-deficiency forces metformin-challenged cancer cells to switch from carbohydrate metabolism to ketogenesis to support energy metabolism.

Epidemiologic studies in diabetic patients as well as research in model organisms have indicated the potential of metformin as a drug candidate for the treatment of various types of cancer, including breast cancer. To date most of the anti-cancer properties of metformin have, in large part, been attributed either to the inhibition of mitochondrial NADH oxidase complex (Complex I in the electron transport chain) or the activation of AMP-activated kinase (AMPK). However, it is becoming increasingly clear that AMPK activation may be critical to alleviate metabolic and energetic stresses associated with tumor progression suggesting that it may, in fact, attenuate the toxicity of metformin instead of promoting it. Here, we demonstrate that AMPK opposes the detrimental effects of mitochondrial complex I inhibition by enhancing glycolysis at the expense of, and in a manner dependent on, pyruvate availability. We also found that metformin forces cells to rewire their metabolic grid in a manner that depends on AMPK, with AMPK-competent cells upregulating glycolysis and AMPK-deficient cell resorting to ketogenesis. In fact, while the killing effects of metformin were largely rescued by pyruvate in AMPKcompetent cells, AMPK-deficient cells required instead acetoacetate, a product of fatty acid catabolism indicating a switch from sugar to fatty acid metabolism as a central resource for ATP production in these cells. In summary, our results indicate that AMPK activation is not responsible for metformin anticancer activity and may instead alleviate energetic stress by activating glycolysis.

Methylmalonic Acid Compromises Respiration and Reduces the Expression of Differentiation Markers of SH-SY5Y Human Neuroblastoma Cells.

Methylmalonic acidemia is a rare metabolic disorder caused by the deficient activity of l-methylmalonyl-CoA mutase or its cofactor 5-deoxyadenosylcobalamin and is characterized by accumulation of methylmalonic acid (MMA) and alternative metabolites. The brain is one of the most affected tissues and neurologic symptoms, characterized by seizures, mental retardation, psychomotor abnormalities, and coma, commonly appear in newborns. The molecular mechanisms of neuropathogenesis in methylmalonic acidemia are still poorly understood, specifically regarding the impairments in neuronal development, maturation, and differentiation. In this study, we investigated the effects of MMA in both undifferentiated and differentiated phenotypes of SH-SY5Y human neuroblastoma cells. We observed an increase in glucose consumption and reduction in respiratory parameters of both undifferentiated and differentiated cells after exposition to MMA, suggesting that differentiated cells are slightly more prone to perturbations in respiratory parameters by MMA than undifferentiated cells. Next, we performed qPCR of mature neuronal-specific gene markers and measured mitochondrial functioning to evaluate the role of MMA during differentiation. Our results showed that MMA impairs the respiratory parameters only at the late stage of differentiation and downregulates the transcriptional gene profile of mature neuronal markers neuron-specific enolase (ENO2) and synaptophysin (SYP). Altogether, our findings point out important changes observed during neuronal maturation and energetic stress vulnerability that can play a role in the neurological clinical symptoms at the newborn period and reveal important molecular mechanisms that could help the screening of targets to new approaches in the therapies of this disease.