Keeping the home fires burning: AMP-activated protein kinase

Perturbations in mitochondrial metabolism associated with defective cardiolipin biosynthesis: An in-organello real-time NMR study

Mitochondria are central to cellular metabolism; hence, their dysfunction contributes to a wide array of human diseases. Cardiolipin, the signature phospholipid of the mitochondrion, affects proper cristae morphology, bioenergetic functions, and metabolic reactions carried out in mitochondrial membranes. To match tissue-specific metabolic demands, cardiolipin typically undergoes an acyl tail remodeling process with the final step carried out by the phospholipid-lysophospholipid transacylase tafazzin. Mutations in tafazzin are the primary cause of Barth syndrome. Here, we investigated how defects in cardiolipin biosynthesis and remodeling impacts metabolic flux through the TCA cycle and associated yeast pathways. Nuclear magnetic resonance was used to monitor in real-time the metabolic fate of 13C3-pyruvate in isolated mitochondria from three isogenic yeast strains. We compared mitochondria from a WT strain to mitochondria from a Δtaz1 strain that lacks tafazzin and contains lower amounts of unremodeled cardiolipin and mitochondria from a Δcrd1 strain that lacks cardiolipin synthase and cannot synthesize cardiolipin. We found that the 13C-label from the pyruvate substrate was distributed through twelve metabolites. Several of the metabolites were specific to yeast pathways including branched chain amino acids and fusel alcohol synthesis. While most metabolites showed similar kinetics among the different strains, mevalonate concentrations were significantly increased in Δtaz1 mitochondria. Additionally, the kinetic profiles of α-ketoglutarate, as well as NAD+ and NADH measured in separate experiments, displayed significantly lower concentrations for Δtaz1 and Δcrd1 mitochondria at most time points. Taken together, the results show how cardiolipin remodeling influences pyruvate metabolism, tricarboxylic acid cycle flux, and the levels of mitochondrial nucleotides.

AMPK and glucose deprivation exert an isoform-specific effect on the expression of Na+,K+-ATPase subunits in cultured myotubes

In skeletal muscle, Na+,K+-ATPase (NKA), a heterodimeric (α/β) P-type ATPase, has an essential role in maintenance of Na+ and K+ homeostasis, excitability, and contractility. AMP-activated protein kinase (AMPK), an energy sensor, increases the membrane abundance and activity of NKA in L6 myotubes, but its potential role in regulation of NKA content in skeletal muscle, which determines maximum capacity for Na+ and K+ transport, has not been clearly delineated. We examined whether energy stress and/or AMPK affect expression of NKA subunits in rat L6 and primary human myotubes. Energy stress, induced by glucose deprivation, increased protein content of NKAα1 and NKAα2 in L6 myotubes, while decreasing the content of NKAα1 in human myotubes. Pharmacological AMPK activators (AICAR, A-769662, and diflunisal) modulated expression of NKA subunits, but their effects only partially mimicked those that occurred in response to glucose deprivation, indicating that AMPK does not mediate all effects of energy stress on NKA expression. Gene silencing of AMPKα1/α2 increased protein levels of NKAα1 in L6 myotubes and NKAα1 mRNA levels in human myotubes, while decreasing NKAα2 protein levels in L6 myotubes. Collectively, our results suggest a role for energy stress and AMPK in modulation of NKA expression in skeletal muscle. However, their modulatory effects were not conserved between L6 myotubes and primary human myotubes, which suggests that coupling between energy stress, AMPK, and regulation of NKA expression in vitro depends on skeletal muscle cell model.

How mass spectrometry can be exploited to study AMPK

AMP-activated protein kinase (AMPK) is a key regulator of metabolism and a recognised target for the treatment of metabolic diseases such as Type 2 diabetes (T2D). Here, we review how mass spectrometry (MS) can be used to study short-term control by AMPK via protein phosphorylation and long-term control due to changes in protein expression. We discuss how MS can quantify AMPK subunit levels in tissues from different species. We propose hydrogen-deuterium exchange (HDX)-MS to investigate molecular mechanisms of AMPK activation and thermoproteomic profiling (TPP) to assess off-target effects of pharmacological AMPK activators/inhibitors. Lastly, because large MS data sets are generated, we consider different approaches that can be used for their interpretation.

Will AMPK be a potential therapeutic target for hepatocellular carcinoma?

Cancer is the disease that poses the greatest threat to human health today. Among them, hepatocellular carcinoma (HCC) is particularly prominent due to its high recurrence rate and extremely low five-year postoperative survival rate. In addition to surgical treatment, radiotherapy, chemotherapy, and immunotherapy are the main methods for treating HCC. Due to the natural drug resistance of chemoradiotherapy and targeted drugs, satisfactory results have not been achieved in terms of therapeutic efficacy and cost. AMP-Activated Protein Kinase (AMPK) is a serine/threonine protein kinase. It mainly coordinates the metabolism and transformation of energy between cells, which maintaining a balance between energy supply and demand. The processes of cell growth, proliferation, autophagy, and survival all involve various reaction of cells to energy changes. The regulatory role of AMPK in cellular energy metabolism plays an important role in the occurrence, development, treatment, and prognosis of HCC. Here, we reviewed the latest progress on the regulatory role of AMPK in the occurrence and development of HCC. Firstly, the molecular structure and activation mechanism of AMPK were introduced. Secondly, the emerging regulator related to AMPK and tumors were elaborated. Next, the multitasking roles of AMPK in the occurrence and development mechanism of HCC were discussed separately. Finally, the translational implications and the challenges of AMPK-targeted therapies for HCC treatment were elaborated. In summary, these pieces of information suggest that AMPK can serve as a promising specific therapeutic target for the treatment of HCC.

No energy, no autophagy-Mechanisms and therapeutic implications of autophagic response energy requirements

Autophagy is a lysosome-mediated self-degradation process of central importance for cellular quality control. It also provides macromolecule building blocks and substrates for energy metabolism during nutrient or energy deficiency, which are the main stimuli for autophagy induction. However, like most biological processes, autophagy itself requires ATP, and there is an energy threshold for its initiation and execution. We here present the first comprehensive review of this often-overlooked aspect of autophagy research. The studies in which ATP deficiency suppressed autophagy in vitro and in vivo were classified according to the energy pathway involved (oxidative phosphorylation or glycolysis). A mechanistic insight was provided by pinpointing the critical ATP-consuming autophagic events, including transcription/translation/interaction of autophagy-related molecules, autophagosome formation/elongation, autophagosome fusion with the lysosome, and lysosome acidification. The significance of energy-dependent fine-tuning of autophagic response for preserving the cell homeostasis, and potential implications for the therapy of cancer, autoimmunity, metabolic disorders, and neurodegeneration are discussed.

Perturbations in mitochondrial metabolism associated with defective cardiolipin biosynthesis: An in-organello real-time NMR study

Mitochondria are central to cellular metabolism; hence, their dysfunction contributes to a wide array of human diseases including cancer, cardiopathy, neurodegeneration, and heritable pathologies such as Barth syndrome. Cardiolipin, the signature phospholipid of the mitochondrion promotes proper cristae morphology, bioenergetic functions, and directly affects metabolic reactions carried out in mitochondrial membranes. To match tissue-specific metabolic demands, cardiolipin typically undergoes an acyl tail remodeling process with the final step carried out by the phospholipid-lysophospholipid transacylase tafazzin. Mutations in the tafazzin gene are the primary cause of Barth syndrome. Here, we investigated how defects in cardiolipin biosynthesis and remodeling impact metabolic flux through the tricarboxylic acid cycle and associated pathways in yeast. Nuclear magnetic resonance was used to monitor in real-time the metabolic fate of 13C3-pyruvate in isolated mitochondria from three isogenic yeast strains. We compared mitochondria from a wild-type strain to mitochondria from a Δtaz1 strain that lacks tafazzin and contains lower amounts of unremodeled cardiolipin, and mitochondria from a Δcrd1 strain that lacks cardiolipin synthase and cannot synthesize cardiolipin. We found that the 13C-label from the pyruvate substrate was distributed through about twelve metabolites. Several of the identified metabolites were specific to yeast pathways, including branched chain amino acids and fusel alcohol synthesis. Most metabolites showed similar kinetics amongst the different strains but mevalonate and α-ketoglutarate, as well as the NAD+/NADH couple measured in separate nuclear magnetic resonance experiments, showed pronounced differences. Taken together, the results show that cardiolipin remodeling influences pyruvate metabolism, tricarboxylic acid cycle flux, and the levels of mitochondrial nucleotides.

Dopamine neuron activity evoked by sucrose and sucrose-predictive cues is augmented by peripheral and central manipulations of glucose availability

Food deprivation drives eating through multiple signals and circuits. Decreased glucose availability (i.e., cytoglucopenia) drives eating and also increases the value of sucrose. Ventral tegmental area (VTA) dopamine neurons (DANs) contribute to the evaluation of taste stimuli, but their role in integrating glucoprivic signals remains unknown. We monitored VTA DAN activity via Cre-dependent expression of a calcium indicator with in vivo fibre photometry. In ad libitum fed rats, intraoral sucrose evoked a phasic increase in DAN activity. To manipulate glucose availability, we administered (intraperitoneal, lateral or fourth ventricular) the antiglycolytic agent 5-thio-D-glucose (5TG), which significantly augmented the phasic DAN activity to sucrose. 5TG failed to alter DAN activity to water or saccharin, suggesting the response was selective for caloric stimuli. 5TG enhancement of sucrose-evoked DAN activity was stronger after fourth ventricular administration, suggesting a critical node of action within the hindbrain. As 5TG also increases blood glucose, in a separate study, we used peripheral insulin, which stimulates eating, to decrease blood glucose-which was associated with increased DAN activity to intraoral sucrose. DAN activity developed to a cue predictive of intraoral sucrose. While 5TG augmented cue-evoked DAN activity, its action was most potent when delivered to the lateral ventricle. Together, the studies point to central glucose availability as a key modulator of phasic DAN activity to food and food-cues. As glucose sensing neurons are known to populate the hypothalamus and brainstem, results suggest differential modulation of cue-evoked and sucrose-evoked DAN activity.

Machine Learning-Based Analysis Reveals Triterpene Saponins and Their Aglycones in Cimicifuga racemosa as Critical Mediators of AMPK Activation

Cimicifuga racemosa (CR) extracts contain diverse constituents such as saponins. These saponins, which act as a defense against herbivores and pathogens also show promise in treating human conditions such as heart failure, pain, hypercholesterolemia, cancer, and inflammation. Some of these effects are mediated by activating AMP-dependent protein kinase (AMPK). Therefore, comprehensive screening for activating constituents in a CR extract is highly desirable. Employing machine learning (ML) techniques such as Deep Neural Networks (DNN), Logistic Regression Classification (LRC), and Random Forest Classification (RFC) with molecular fingerprint MACCS descriptors, 95 CR constituents were classified. Calibration involved 50 randomly chosen positive and negative controls. LRC achieved the highest overall test accuracy (90.2%), but DNN and RFC surpassed it in precision, sensitivity, specificity, and ROC AUC. All CR constituents were predicted as activators, except for three non-triterpene compounds. The validity of these classifications was supported by good calibration, with misclassifications ranging from 3% to 17% across the various models. High sensitivity (84.5-87.2%) and specificity (84.1-91.4%) suggest suitability for screening. The results demonstrate the potential of triterpene saponins and aglycones in activating AMP-dependent protein kinase (AMPK), providing the rationale for further clinical exploration of CR extracts in metabolic pathway-related conditions.

Melatonin Improves Glucose Homeostasis and Insulin Sensitivity by Mitigating Inflammation and Activating AMPK Signaling in a Mouse Model of Sleep Fragmentation

Sleep fragmentation (SF) can increase inflammation and production of reactive oxygen species (ROS), leading to metabolic dysfunction. SF is associated with inflammation of adipose tissue and insulin resistance. Several studies have suggested that melatonin may have beneficial metabolic effects due to activating AMP-activated protein kinase (AMPK). However, it is unclear whether melatonin affects the AMPK signaling pathway in SF-induced metabolic dysfunction. Therefore, we hypothesize that SF induces metabolic impairment and inflammation in white adipose tissue (WAT), as well as altered intracellular homeostasis. We further hypothesize that these conditions could be improved by melatonin treatment. We conducted an experiment using adult male C57BL/6 mice, which were divided into three groups: control, SF, and SF with melatonin treatment (SF+Mel). The SF mice were housed in SF chambers, while the SF+Mel mice received daily oral melatonin. After 12 weeks, glucose tolerance tests, insulin tolerance tests, adipose tissue inflammation tests, and AMPK assessments were performed. The SF mice showed increased weight gain, impaired glucose regulation, inflammation, and decreased AMPK in WAT compared to the controls. Melatonin significantly improved these outcomes by mitigating SF-induced metabolic dysfunction, inflammation, and AMPK downregulation in adipose tissue. The therapeutic efficacy of melatonin against cardiometabolic impairments in SF may be due to its ability to restore adipose tissue homeostatic pathways.

The Killer's Web: Interconnection between Inflammation, Epigenetics and Nutrition in Cancer

Inflammation is a key contributor to both the initiation and progression of tumors, and it can be triggered by genetic instability within tumors, as well as by lifestyle and dietary factors. The inflammatory response plays a critical role in the genetic and epigenetic reprogramming of tumor cells, as well as in the cells that comprise the tumor microenvironment. Cells in the microenvironment acquire a phenotype that promotes immune evasion, progression, and metastasis. We will review the mechanisms and pathways involved in the interaction between tumors, inflammation, and nutrition, the limitations of current therapies, and discuss potential future therapeutic approaches.

Steady Laminar Flow Decreases Endothelial Glycolytic Flux While Enhancing Proteoglycan Synthesis and Antioxidant Pathways

Endothelial cells in steady laminar flow assume a healthy, quiescent phenotype, while endothelial cells in oscillating disturbed flow become dysfunctional. Since endothelial dysfunction leads to atherosclerosis and cardiovascular disease, it is important to understand the mechanisms by which endothelial cells change their function in varied flow environments. Endothelial metabolism has recently been proven a powerful tool to regulate vascular function. Endothelial cells generate most of their energy from glycolysis, and steady laminar flow may reduce endothelial glycolytic flux. We hypothesized that steady laminar but not oscillating disturbed flow would reduce glycolytic flux and alter glycolytic side branch pathways. In this study, we exposed human umbilical vein endothelial cells to static culture, steady laminar flow (20 dynes/cm2 shear stress), or oscillating disturbed flow (4 ± 6 dynes/cm2 shear stress) for 24 h using a cone-and-plate device. We then measured glucose and lactate uptake and secretion, respectively, and glycolytic metabolites. Finally, we explored changes in the expression and protein levels of endothelial glycolytic enzymes. Our data show that endothelial cells in steady laminar flow had decreased glucose uptake and 13C labeling of glycolytic metabolites while cells in oscillating disturbed flow did not. Steady laminar flow did not significantly change glycolytic enzyme gene or protein expression, suggesting that glycolysis may be altered through enzyme activity. Flow also modulated glycolytic side branch pathways involved in proteoglycan and glycosaminoglycan synthesis, as well as oxidative stress. These flow-induced changes in endothelial glucose metabolism may impact the atheroprone endothelial phenotype in oscillating disturbed flow.

Cardioprotective O-GlcNAc signaling is elevated in murine female hearts via enhanced O-GlcNAc transferase activity

The post-translational modification of intracellular proteins by O-linked β-GlcNAc (O-GlcNAc) has emerged as a critical regulator of cardiac function. Enhanced O-GlcNAcylation activates cytoprotective pathways in cardiac models of ischemia-reperfusion (I/R) injury; however, the mechanisms underpinning O-GlcNAc cycling in response to I/R injury have not been comprehensively assessed. The cycling of O-GlcNAc is regulated by the collective efforts of two enzymes: O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which catalyze the addition and hydrolysis of O-GlcNAc, respectively. It has previously been shown that baseline heart physiology and pathophysiology are impacted by sex. Here, we hypothesized that sex differences in molecular signaling may target protein O-GlcNAcylation both basally and in ischemic hearts. To address this question, we subjected male and female WT murine hearts to ex vivo ischemia or I/R injury. We assessed hearts for protein O-GlcNAcylation, abundance of OGT, OGA, and glutamine:fructose-6-phosphate aminotransferase (GFAT2), activity of OGT and OGA, and UDP-GlcNAc levels. Our data demonstrate elevated O-GlcNAcylation in female hearts both basally and during ischemia. We show that OGT activity was enhanced in female hearts in all treatments, suggesting a mechanism for these observations. Furthermore, we found that ischemia led to reduced O-GlcNAcylation and OGT-specific activity. Our findings provide a foundation for understanding molecular mechanisms that regulate O-GlcNAcylation in the heart and highlight the importance of sex as a significant factor when assessing key regulatory events that control O-GlcNAc cycling. These data suggest the intriguing possibility that elevated O-GlcNAcylation in females contributes to reduced ischemic susceptibility.

Metabolic control by AMPK in white adipose tissue

White adipose tissue (WAT) plays an important role in the integration of whole-body metabolism by storing fat and mobilizing triacylglycerol when needed. The released free fatty acids can then be oxidized by other tissues to provide ATP. AMP-activated protein kinase (AMPK) is a key regulator of metabolic pathways, and can be targeted by a new generation of direct, small-molecule activators. AMPK activation in WAT inhibits insulin-stimulated lipogenesis and in some situations also inhibits insulin-stimulated glucose uptake, but AMPK-induced inhibition of β-adrenergic agonist-stimulated lipolysis might need to be re-evaluated in vivo. The lack of dramatic effects of AMPK activation on basal metabolism in WAT could be advantageous when treating type 2 diabetes with pharmacological pan-AMPK activators.

Mitigation of aircraft noise-induced vascular dysfunction and oxidative stress by exercise, fasting, and pharmacological α1AMPK activation: molecular proof of a protective key role of endothelial α1AMPK against environmental noise exposure

AIMS

Environmental stressors such as traffic noise represent a global threat, accounting for 1.6 million healthy life years lost annually in Western Europe. Therefore, the noise-associated health side effects must be effectively prevented or mitigated. Non-pharmacological interventions such as physical activity or a balanced healthy diet are effective due to the activation of the adenosine monophosphate-activated protein kinase (α1AMPK). Here, we investigated for the first time in a murine model of aircraft noise-induced vascular dysfunction the potential protective role of α1AMPK activated via exercise, intermittent fasting, and pharmacological treatment.

METHODS AND RESULTS

Wild-type (B6.Cg-Tg(Cdh5-cre)7Mlia/J) mice were exposed to aircraft noise [maximum sound pressure level of 85 dB(A), average sound pressure level of 72 dB(A)] for the last 4 days. The α1AMPK was stimulated by different protocols, including 5-aminoimidazole-4-carboxamide riboside application, voluntary exercise, and intermittent fasting. Four days of aircraft noise exposure produced significant endothelial dysfunction in wild-type mice aorta, mesenteric arteries, and retinal arterioles. This was associated with increased vascular oxidative stress and asymmetric dimethylarginine formation. The α1AMPK activation with all three approaches prevented endothelial dysfunction and vascular oxidative stress development, which was supported by RNA sequencing data. Endothelium-specific α1AMPK knockout markedly aggravated noise-induced vascular damage and caused a loss of mitigation effects by exercise or intermittent fasting.

CONCLUSION

Our results demonstrate that endothelial-specific α1AMPK activation by pharmacological stimulation, exercise, and intermittent fasting effectively mitigates noise-induced cardiovascular damage. Future population-based studies need to clinically prove the concept of exercise/fasting-mediated mitigation of transportation noise-associated disease.

Effect of Metformin on the Functional and Electrophysiological Recovery of Crush Injury-Induced Facial Nerve Paralysis in Diabetic Rats

The impact of metformin on the rat facial nerve following crush injury has only occasionally been documented to date. The purpose of the current investigation was to use functional and electrophysiological evaluations to investigate the effects of metformin administration on recovery following crush injury to the rat facial nerve. The rats were randomly divided into four groups: the nonDM/PBS group (n = 4), the nonDM/metformin group (n = 4), the DM/PBS group (n = 4), and the DM/metformin group (n = 4). Diabetes was generated by an intraperitoneal injection of streptozotocin. Facial nerve paralysis was induced by a crush injury 7 days after diabetes induction. The blood glucose levels of the DM/PBS and DM/metformin groups were maintained at over 300 mg/dL, whereas the blood glucose levels of the nonDM/PBS and nonDM/metformin groups were maintained at less than 150 mg/dL. There was no significant difference between the two nonDM groups. In comparison to the PBS group, the metformin group's recurrence of vibrissa fibrillation occurred noticeably sooner over time. The nonDM/metformin group showed the highest recovery rate in the second, third, and fourth weeks post-crush, respectively. The threshold of action potential 4 weeks after crush injury showed that the nonDM/metformin group had a significantly lower mean threshold of MAP compared to other groups. The short-term effect of metformin on the recovery of facial nerve blood flow (FNBF) was significantly increased compared to the DM/PBS group. However, there was no significant difference in FNBF between the nonDM/metformin and nonDM/PBS groups. A diabetic condition promoted a delay in FN regeneration. Metformin is able to accelerate functional recovery in diabetic or nondiabetic FN-injured rats. Further studies using a morphometric or molecular approach are planned to understand the pharmacologic mechanism of metformin.

The emerging roles of MAPK-AMPK in ferroptosis regulatory network

Ferroptosis, a newform of programmed cell death, driven by peroxidative damages of polyunsaturated-fatty-acid-containing phospholipids in cellular membranes and is extremely dependent on iron ions, which is differs characteristics from traditional cell death has attracted greater attention. Based on the curiosity of this new form of regulated cell death, there has a tremendous progress in the field of mechanistic understanding of ferroptosis recent years. Ferroptosis is closely associated with the development of many diseases and involved in many diseases related signaling pathways. Not only a variety of oncoproteins and tumor suppressors can regulate ferroptosis, but multiple oncogenic signaling pathways can also have a regulatory effect on ferroptosis. Ferroptosis results in the accumulation of large amounts of lipid peroxides thus involving the onset of oxidative stress and energy stress responses. The MAPK pathway plays a critical role in oxidative stress and AMPK acts as a sensor of cellular energy and is involved in the regulation of the energy stress response. Moreover, activation of AMPK can induce the occurrence of autophagy-dependent ferroptosis and p53-activated ferroptosis. In recent years, there have been new advances in the study of molecular mechanisms related to the regulation of ferroptosis by both pathways. In this review, we will summarize the molecular mechanisms by which the MAPK-AMPK signaling pathway regulates ferroptosis. Meanwhile, we sorted out the mysterious relationship between MAPK and AMPK, described the crosstalk among ferroptosis and MAPK-AMPK signaling pathways, and summarized the relevant ferroptosis inducers targeting this regulatory network. This will provide a new field for future research on ferroptosis mechanisms and provide a new vision for cancer treatment strategies. Video Abstract.

Sexual Dimorphism in Cardiometabolic Diseases: The Role of AMPK

Cardiovascular diseases (CVDs) are the leading cause of mortality and disability among both males and females. The risk of cardiovascular diseases is heightened by the presence of a risk factor cluster of metabolic syndrome, covering obesity and obesity-related cardiometabolic risk factors such as hypertension, glucose, and lipid metabolism dysregulation primarily. Sex hormones contribute to metabolic regulation and make women and men susceptible to obesity development in a different manner, which necessitates sex-specific management. Identifying crucial factors that protect the cardiovascular system is essential to enhance primary and secondary prevention of cardiovascular diseases and should be explicitly studied from the perspective of sex differences. It seems that AMP-dependent protein kinase (AMPK) may be such a factor since it has the protective role of AMPK in the cardiovascular system, has anti-diabetic properties, and is regulated by sex hormones. Those findings highlight the potential cardiometabolic benefits of AMPK, making it an essential factor to consider. Here, we review information about the cross-talk between AMPK and sex hormones as a critical point in cardiometabolic disease development and progression and a target for therapeutic intervention in human disease.

A proton-inhibited DEG/ENaC ion channel maintains neuronal ionstasis and promotes neuronal survival under stress

The nervous system participates in the initiation and modulation of systemic stress. Ionstasis is of utmost importance for neuronal function. Imbalance in neuronal sodium homeostasis is associated with pathologies of the nervous system. However, the effects of stress on neuronal Na⁺ homeostasis, excitability, and survival remain unclear. We report that the DEG/ENaC family member DEL-4 assembles into a proton-inactivated sodium channel. DEL-4 operates at the neuronal membrane and synapse to modulate Caenorhabditis elegans locomotion. Heat stress and starvation alter DEL-4 expression, which in turn alters the expression and activity of key stress-response transcription factors and triggers appropriate motor adaptations. Similar to heat stress and starvation, DEL-4 deficiency causes hyperpolarization of dopaminergic neurons and affects neurotransmission. Using humanized models of neurodegenerative diseases in C. elegans, we showed that DEL-4 promotes neuronal survival. Our findings provide insights into the molecular mechanisms by which sodium channels promote neuronal function and adaptation under stress.

Neurotrophic effects of intermittent fasting, calorie restriction and exercise: a review and annotated bibliography

In the last decades, important progress has been achieved in the understanding of the neurotrophic effects of intermittent fasting (IF), calorie restriction (CR) and exercise. Improved neuroprotection, synaptic plasticity and adult neurogenesis (NSPAN) are essential examples of these neurotrophic effects. The importance in this respect of the metabolic switch from glucose to ketone bodies as cellular fuel has been highlighted. More recently, calorie restriction mimetics (CRMs; resveratrol and other polyphenols in particular) have been investigated thoroughly in relation to NSPAN. In the narrative review sections of this manuscript, recent findings on these essential functions are synthesized and the most important molecules involved are presented. The most researched signaling pathways (PI3K, Akt, mTOR, AMPK, GSK3β, ULK, MAPK, PGC-1α, NF-κB, sirtuins, Notch, Sonic hedgehog and Wnt) and processes (e.g., anti-inflammation, autophagy, apoptosis) that support or thwart neuroprotection, synaptic plasticity and neurogenesis are then briefly presented. This provides an accessible entry point to the literature. In the annotated bibliography section of this contribution, brief summaries are provided of about 30 literature reviews relating to the neurotrophic effects of interest in relation to IF, CR, CRMs and exercise. Most of the selected reviews address these essential functions from the perspective of healthier aging (sometimes discussing epigenetic factors) and the reduction of the risk for neurodegenerative diseases (Alzheimer's disease, Huntington's disease, Parkinson's disease) and depression or the improvement of cognitive function.

AMP-activated protein kinase: An energy sensor and survival mechanism in the reinstatement of metabolic homeostasis

Cells are programmed to favorably respond towards the nutrient availability by adapting their metabolism to meet energy demands. AMP-activated protein kinase (AMPK) is a highly conserved serine/threonine energy-sensing kinase. It gets activated upon a decrease in the cellular energy status as reflected by an increased AMP/ATP ratio, ADP, and also during the conditions of glucose starvation without change in the adenine nucelotide ratio. AMPK functions as a centralized regulator of metabolism, acting at cellular and physiological levels to circumvent the metabolic stress by restoring energy balance. This review intricately highlights the integrated signaling pathways by which AMPK gets activated allosterically or by multiple non-canonical upstream kinases. AMPK activates the ATP generating processes (e.g., fatty acid oxidation) and inhibits the ATP consuming processes that are non-critical for survival (e.g., cell proliferation, protein and triglyceride synthesis). An integrated signaling network with AMPK as the central effector regulates all the aspects of enhanced stress resistance, qualified cellular housekeeping, and energy metabolic homeostasis. Importantly, the AMPK mediated amelioration of cellular stress and inflammatory responses are mediated by stimulation of transcription factors such as Nrf2, SIRT1, FoxO and inhibition of NF-κB serving as main downstream effectors. Moreover, many lines of evidence have demonstrated that AMPK controls autophagy through mTOR and ULK1 signaling to fine-tune the metabolic pathways in response to different cellular signals. This review also highlights the critical involvement of AMPK in promoting mitochondrial health, and homeostasis, including mitophagy. Loss of AMPK or ULK1 activity leads to aberrant accumulation of autophagy-related proteins and defective mitophagy thus, connecting cellular energy sensing to autophagy and mitophagy.

Induction of lysosomal and mitochondrial biogenesis by AMPK phosphorylation of FNIP1

Cells respond to mitochondrial poisons with rapid activation of the adenosine monophosphate-activated protein kinase (AMPK), causing acute metabolic changes through phosphorylation and prolonged adaptation of metabolism through transcriptional effects. Transcription factor EB (TFEB) is a major effector of AMPK that increases expression of lysosome genes in response to energetic stress, but how AMPK activates TFEB remains unresolved. We demonstrate that AMPK directly phosphorylates five conserved serine residues in folliculin-interacting protein 1 (FNIP1), suppressing the function of the folliculin (FLCN)-FNIP1 complex. FNIP1 phosphorylation is required for AMPK to induce nuclear translocation of TFEB and TFEB-dependent increases of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) and estrogen-related receptor alpha (ERRα) messenger RNAs. Thus, mitochondrial damage triggers AMPK-FNIP1-dependent nuclear translocation of TFEB, inducing sequential waves of lysosomal and mitochondrial biogenesis.

Fetal lung hypoxia and energetic cell failure in the nitrofen-induced congenital diaphragmatic hernia rat model

PURPOSE

Congenital diaphragmatic hernia (CDH) pathogenesis is poorly understood. We hypothesize that fetal CDH lungs are chronically hypoxic because of lung hypoplasia and tissue compression, affecting the cell bioenergetics as a possible explanation for abnormal lung development.

METHODS

To investigate this theory, we conducted a study using the rat nitrofen model of CDH. We evaluated the bioenergetics status using H1 Nuclear magnetic resonance and studied the expression of enzymes involved in energy production, the hypoxia-inducible factor 1α, and the glucose transporter 1.

RESULTS

The nitrofen-exposed lungs have increased levels of hypoxia-inducible factor 1α and the main fetal glucose transporter, more evident in the CDH lungs. We also found imbalanced AMP:ATP and ADP:ATP ratios, and a depleted energy cellular charge. Subsequent transcription levels and protein expression of the enzymes involved in bioenergetics confirm the attempt to prevent the energy collapse with the increase in lactate dehydrogenase C, pyruvate dehydrogenase kinase 1 and 2, adenosine monophosphate deaminase, AMP-activated protein kinase, calcium/calmodulin-dependent protein kinase 2, and liver kinase B1, while decreasing ATP synthase.

CONCLUSION

Our study suggests that changes in energy production could play a role in CDH pathogenesis. If confirmed in other animal models and humans, this could lead to the development of novel therapies targeting the mitochondria to improve outcomes.

Metformin Pre-Treatment as a Means of Mitigating Disuse-Induced Rat Soleus Muscle Wasting

Currently, no ideal treatment exists to combat skeletal muscle disuse-induced atrophy and loss of strength. Because the activity of AMP-activated protein kinase (AMPK) in rat soleus muscle is suppressed at the early stages of disuse, we hypothesized that pre-treatment of rats with metformin (an AMPK activator) would exert beneficial effects on skeletal muscle during disuse. Muscle disuse was performed via hindlimb suspension (HS). Wistar rats were divided into four groups: (1) control (C), (2) control + metformin for 10 days (C+Met), (3) HS for 7 days (HS), (4) metformin treatment for 7 days before HS and during the first 3 days of 1-week HS (HS+Met). Anabolic and catabolic markers were assessed using WB and RT-PCR. Treatment with metformin partly prevented an HS-induced decrease in rat soleus weight and size of slow-twitch fibers. Metformin prevented HS-related slow-to-fast fiber transformation. Absolute soleus muscle force in the HS+Met group was increased vs. the HS group. GSK-3β (Ser9) phosphorylation was significantly increased in the HS+Met group vs. the HS group. Metformin pre-treatment partly prevented HS-induced decrease in 18S+28S rRNA content and attenuated upregulation of calpain-1 and ubiquitin. Thus, pre-treatment of rats with metformin can ameliorate disuse-induced reductions in soleus muscle weight, the diameter of slow-type fibers, and absolute muscle strength.

Chitosan decorated essential oil nanoemulsions for enhanced antibacterial activity using a microfluidic device and response surface methodology

In this work, the antibacterial activity of Satureja Khuzestanica essential oil nanoemulsions improved by employing chitosan (ch/SKEO NE) against E. coli bacterium. The optimum ch/SKEO NE with mean droplet size of 68 nm was attained at 1.97, 1.23, and 0.10%w/w of surfactant, essential oil and chitosan, using Response Surface Methodology (RSM). Applying microfluidic platform, the ch/SKEO NE resulted in improved antibacterial activity owing to the modification of surface properties. The nanoemulsion samples showed a significant rupturing effect on the E. coli bacterial cell membrane which resulted in a rapid release of cellular contents. This action was remarkably intensified by executing microfluidic chip in parallel to the conventional method. Having treated the bacteria in the microfluidic chip for 5 min with a 8 μg/mL concentration of ch/SKEO NE, the bacterial integrity disrupted quickly, and the activity was totally lost in a 10-min period at 37 μg/mL, while it took 5 h for a complete inhibition in the conventional method using the same concentration of ch/SKEO NE. It can be concluded that nanoemulsification of EOs using chitosan coating can intensify the interaction of nanodroplets with the bacterial membrane, especially within the microfluidic chips which provides high contact surface area.

The mammalian purine salvage pathway as an exploitable route for cerebral bioenergetic support after brain injury

Purine-based molecules play ancient, fundamental, and evolutionarily-conserved roles across life on Earth, ranging from DNA and RNA, to the universal energy currency, ATP. In mammals, the two primary routes for the synthesis of the adenine nucleotides ATP, ADP and AMP, and, as a consequence, the major bioactive metabolite adenosine, are the de novo purine biosynthesis (DNPB) pathway, and the purine salvage pathway (PSP). Of the two, the PSP dominates in both the mammalian brain and heart. This is because the PSP utilizes the breakdown products of ATP, occasioned by the high energy demands of these organs, to rapidly regenerate adenine nucleotides. This resynthesis route, while efficient and energetically favourable, leaves these organs vulnerable to loss of salvageable metabolites, with the potential for protracted depletion of the means to synthesize ATP, and the ability to deploy neuro- and cardioprotective adenosine. Having previously shown that hippocampal cellular ATP and adenosine release can be increased by supplying substrates for the PSP (d-ribose and adenine), we now explore the expression of DNPB and PSP enzymes in hippocampal neurons and astrocytes based on available transcriptomic data. We find that key enzymes of the PSP are expressed at higher levels than those in the DNPB pathway, and that PSP enzymes are expressed at higher levels in neurons than in astrocytes. These data reflect the importance of the PSP in the mammalian brain and imply that pharmacological targeting of the PSP may be particularly beneficial to neurons at times of metabolic stress. This article is part of the Special Issue on 'Purinergic Signaling: 50 years'.

Current Understanding on the Role of Lipids in Macrophages and Associated Diseases

Lipid metabolism is the major intracellular mechanism driving a variety of cellular functions such as energy storage, hormone regulation and cell division. Lipids, being a primary component of the cell membrane, play a pivotal role in the survival of macrophages. Lipids are crucial for a variety of macrophage functions including phagocytosis, energy balance and ageing. However, functions of lipids in macrophages vary based on the site the macrophages are residing at. Lipid-loaded macrophages have recently been emerging as a hallmark for several diseases. This review discusses the significance of lipids in adipose tissue macrophages, tumor-associated macrophages, microglia and peritoneal macrophages. Accumulation of macrophages with impaired lipid metabolism is often characteristically observed in several metabolic disorders. Stress signals differentially regulate lipid metabolism. While conditions such as hypoxia result in accumulation of lipids in macrophages, stress signals such as nutrient deprivation initiate lipolysis and clearance of lipids. Understanding the biology of lipid accumulation in macrophages requires the development of potentially active modulators of lipid metabolism.

Current insights in molecular characterization of non-alcoholic fatty liver disease and treatment

There is a continuously rising incidence of non-alcoholic fatty liver disease (NAFLD) around the world, which parallels the increasing incidence of metabolic diseases. NAFLD is a range of liver conditions that contains simple non-alcoholic fatty liver and advanced non-alcoholic steatohepatitis. In serious cases, NAFLD may develop into cirrhosis or even liver cancer. NAFLD has an intense relationship with metabolic syndrome, type 2 diabetes mellitus. It is known that gut microbiota, and functional molecules such as adenosine monophosphate-activated protein kinase JNK, and peroxisome proliferator-activated receptors (PPARs) in progressing and treating NAFLD. Traditionally, the conventional and effective therapeutic strategy is lifestyle intervention. Nowadays, new medicines targeting specific molecules, such as farnesoid X receptor, PPARs, and GLP-1 receptor, have been discovered and shown beneficial effects on patients with NAFLD. In this article, we focus on the molecular mechanisms and therapeutic approaches to NAFLD.

Does oxidative DNA damage trigger histotoxic hypoxia via PARP1/AMP-driven mitochondrial ADP depletion-induced ATP synthase inhibition in Alzheimer's disease?

The low cerebral metabolic rate of oxygen despite the relatively preserved perfusion in Alzheimer's disease (AD) patients' medial temporal lobes suggest histotoxic hypoxia due to mitochondrial dysfunction that is independent of, but could precede, insulin resistance. Neuropathological, metabolomic, and preclinical evidence are consistent with the notion that this mitochondrial dysfunction may be contributed to by oxidative stress and DNA damage, leading to poly-(ADP-ribose)-polymerase-1 (PARP1) activation and consequent AMP accumulation, clogging of mitochondrial adenine nucleotide transporters (ANTs), matrix ADP deprivation, and ATP synthase inhibition. Complementary mechanisms may include mitochondrial-protein poly-ADP-ribosylation and mitochondrial-biogenesis suppression via PARPs outcompeting Sirtuin-1 (SIRT1) for nicotinamide-adenine-dinucleotide (NAD⁺).

IKCa channels control breast cancer metabolism including AMPK-driven autophagy

Ca²⁺-activated K⁺ channels of intermediate conductance (IK) are frequently overexpressed in breast cancer (BC) cells, while IK channel depletion reduces BC cell proliferation and tumorigenesis. This raises the question, of whether and mechanistically how IK activity interferes with the metabolic activity and energy consumption rates, which are fundamental for rapidly growing cells. Using BC cells obtained from MMTV-PyMT tumor-bearing mice, we show that both, glycolysis and mitochondrial ATP-production are reduced in cells derived from IK-deficient breast tumors. Loss of IK altered the sub-/cellular K⁺- and Ca²⁺- homeostasis and mitochondrial membrane potential, ultimately resulting in reduced ATP-production and metabolic activity. Consequently, we find that BC cells lacking IK upregulate AMP-activated protein kinase activity to induce autophagy compensating the glycolytic and mitochondrial energy shortage. Our results emphasize that IK by modulating cellular Ca²⁺- and K⁺-dynamics contributes to the remodeling of metabolic pathways in cancer. Thus, targeting IK channel might disturb the metabolic activity of BC cells and reduce malignancy.

Adenosine monophosphate activated protein kinase contributes to skeletal muscle health through the control of mitochondrial function

Skeletal muscle is one of the largest organs in the body and the largest protein repository. Mitochondria are the main energy-producing organelles in cells and play an important role in skeletal muscle health and function. They participate in several biological processes related to skeletal muscle metabolism, growth, and regeneration. Adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor and regulator of systemic energy balance. AMPK is involved in the control of energy metabolism by regulating many downstream targets. In this review, we propose that AMPK directly controls several facets of mitochondrial function, which in turn controls skeletal muscle metabolism and health. This review is divided into four parts. First, we summarize the properties of AMPK signal transduction and its upstream activators. Second, we discuss the role of mitochondria in myogenesis, muscle atrophy, regeneration post-injury of skeletal muscle cells. Third, we elaborate the effects of AMPK on mitochondrial biogenesis, fusion, fission and mitochondrial autophagy, and discuss how AMPK regulates the metabolism of skeletal muscle by regulating mitochondrial function. Finally, we discuss the effects of AMPK activators on muscle disease status. This review thus represents a foundation for understanding this biological process of mitochondrial dynamics regulated by AMPK in the metabolism of skeletal muscle. A better understanding of the role of AMPK on mitochondrial dynamic is essential to improve mitochondrial function, and hence promote skeletal muscle health and function.

Interaction of a natural compound nanoemulsion with Gram negative and Gram positive bacterial membrane; a mechanism based study using a microfluidic chip and DESI technique

The antibacterial activity of a nanoemulsion prepared from Satureja Khusitanica essential oil against a Gram-negative (Escherichia coli) and a Gram-positive (Bacillus atrophaeus) bacteria evaluated using microfluidic and conventional techniques. The effect of different residence time and concentrations on the antibacterial activity of nanoemulsion was studied by measuring the release of protein, nucleic acids, potassium, and also recording the MIC, MBC and time killing assays. Remarkable intensification was observed by employing microfluidic chip regarding a high-contact surface area between nanodroplets and bacterial membrane. The MIC and MBC values for E. coli and B. atrophaeus in conventional method were 400 and 1600 µg mL^-1, respectively, whereas these values reduced to 11 to 50 µg mL^-1 using microfluidic system. B. atrophaeus seemed to be more resistant than E. coli to the nanoemulsion treatment, perhaps due to different cell wall structures. Bacterial cell wall changes were examined using a desorption electrospray ionization (DESI) technique. It was found that the structural changes were more imminent in Gram negative E. coli by detecting a number of released lipids including phosphatidyl glycerol and phosphatidyl ethanolamines. The DESI spectra of B. atrophaeus revealed no M/Z related lipid release. These findings may help providing novel nano based natural antibacterials.

Obesity: a perfect storm for carcinogenesis

Obesity-related cancers account for 40% of the cancer cases observed in the USA and obesity is overtaking smoking as the most widespread modifiable risk factor for carcinogenesis. Here, we use the hallmarks of cancer framework to delineate how obesity might influence the carcinogenic hallmarks in somatic cells. We discuss the effects of obesity on (a) sustaining proliferative signaling; (b) evading growth suppressors; (c) resisting cell death; (d) enabling replicative immortality; (e) inducing angiogenesis; (f) activating invasion and metastasis; (g) reprogramming energy metabolism; and (h) avoiding immune destruction, together with its effects on genome instability and tumour-promoting inflammation. We present the current understanding and controversies in this evolving field, and highlight some areas in need of further cross-disciplinary focus. For instance, the relative importance of the many potentially causative obesity-related factors is unclear for each type of malignancy. Even within a single tumour type, it is currently unknown whether one obesity-related factor consistently plays a predominant role, or if this varies between patients or, even in a single patient with time. Clarifying how the hallmarks are affected by obesity may lead to novel prevention and treatment strategies for the increasingly obese population.

Function and regulation of ULK1: From physiology to pathology

The expression of ULK1, a core protein of autophagy, is closely related to autophagic activity. Numerous studies have shown that pathological abnormal expression of ULK1 is associated with various human diseases such as neurological disorders, infections, cardiovascular diseases, liver diseases and cancers. In addition, new advances in the regulation of ULK1 have been identified. Furthermore, targeting ULK1 as a therapeutic strategy for diseases is gaining attention as new corresponding activators or inhibitors are being developed. In this review, we describe the structure and regulation of ULK1 as well as the current targeted activators and inhibitors. Moreover, we highlight the pathological disorders of ULK1 expression and its critical role in human diseases.

Targeted Proteomic Approaches for Proteome-Wide Characterizations of the AMP-Binding Capacities of Kinases

Kinases play important roles in cell signaling, and adenosine monophosphate (AMP) is known to modulate cellular energy homeostasis through AMP-activated protein kinase (AMPK). Here, we explored novel AMP-binding kinases by employing a desthiobiotin-conjugated AMP acyl-phosphate probe to enrich efficiently AMP-binding proteins. Together with a parallel-reaction monitoring-based targeted proteomic approach, we uncovered 195 candidate AMP-binding kinases. We also enriched desthiobiotin-labeled peptides from adenine nucleotide-binding sites of kinases and analyzed them using LC-MS/MS in the multiple-reaction monitoring mode, which resulted in the identification of 44 peptides derived from 43 kinases displaying comparable or better binding affinities toward AMP relative to adenosine triphosphate (ATP). Moreover, our proteomic data revealed a potential involvement of AMP in the MAPK pathway through binding directly to the relevant kinases, especially MEK2 and MEK3. Together, we revealed the AMP-binding capacities of a large number of kinases, and our work built a strong foundation for understanding how AMP functions as a second messenger to modulate cell signaling.

Balancing energy and protein homeostasis at ER-mitochondria contact sites

The endoplasmic reticulum (ER) is the largest organelle of the cell and participates in multiple essential functions, including the production of secretory proteins, lipid synthesis, and calcium storage. Sustaining proteostasis requires an intimate coupling with energy production. Mitochondrial respiration evolved to be functionally connected to ER physiology through a physical interface between both organelles known as mitochondria-associated membranes. This quasi-synaptic structure acts as a signaling hub that tunes the function of both organelles in a bidirectional manner and controls proteostasis, cell death pathways, and mitochondrial bioenergetics. Here, we discuss the main signaling mechanisms governing interorganellar communication and their putative role in diseases including cancer and neurodegeneration.

Perisciatic Nerve Dexmedetomidine Alleviates Spinal Oxidative Stress and Improves Peripheral Mitochondrial Dynamic Equilibrium in a Neuropathic Pain Mouse Model in an AMPK-Dependent Manner

Neuropathic pain (NPP) is a debilitating clinical condition that presently has few effective treatments. NPP is caused by uncontrolled central oxidative stress and inflammation. Preliminary studies indicate that dexmedetomidine (DEX), an agonist of the alpha-2 adrenergic receptor, is beneficial for treating NPP. In this paper, the effects of administering DEX around injured nerves in a chronic constriction injury- (CCI-) induced neuropathic pain mouse model are investigated. According to the results, the perineural DEX significantly reversed the decline in the mechanical threshold and thermal latency in CCI mice ( $p<0.001$ ). In the peripherally affected ischiadic nerve, the perineuronal DEX upregulated the expressions of pAMPK, OPA1, and SNPH but not Drp1 or KIF5B. The aforementioned effects of administering DEX can be partially reversed by compound C, a selective and reversible inhibitor of AMP-activated protein kinase (AMPK). Furthermore, it was found that perineural DEX significantly inhibited the CCI-induced upregulation of the immediate early gene c-Fos, overexpression of the inflammatory factors tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), attenuation of the NADH dehydrogenase complexes I, II, III, and IV, and the repression of ATP, SOD, and GSH in the dorsal horn of the spinal cord (DHSC) ( $p<0.01$ ). These findings indicate that perineuronal DEX protected the injured ischiadic nerves and attenuated neuropathic pain via AMPK activation to improve energy supply in the peripheral injured nerves, alleviate the inflammatory factor release, and inhibit oxidative stress in the DHSC.

AMPK and the Challenge of Treating Hypoxic Pulmonary Hypertension

Hypoxic pulmonary hypertension (HPH) is characterized by sustained elevation of pulmonary artery pressure produced by vasoconstriction and hyperproliferative remodeling of the pulmonary artery and subsequent right ventricular hypertrophy (RVH). The search for therapeutic targets for cardiovascular pathophysiology has extended in many directions. However, studies focused on mitigating high-altitude pulmonary hypertension (HAPH) have been rare. Because AMP-activated protein kinase (AMPK) is involved in cardiovascular and metabolic pathology, AMPK is often studied as a potential therapeutic target. AMPK is best characterized as a sensor of cellular energy that can also restore cellular metabolic homeostasis. However, AMPK has been implicated in other pathways with vasculoprotective effects. Notably, cellular metabolic stress increases the intracellular ADP/ATP or AMP/ATP ratio, and AMPK activation restores ATP levels by activating energy-producing catabolic pathways and inhibiting energy-consuming anabolic pathways, such as cell growth and proliferation pathways, promoting cardiovascular protection. Thus, AMPK activation plays an important role in antiproliferative, antihypertrophic and antioxidant pathways in the pulmonary artery in HPH. However, AMPK plays contradictory roles in promoting HPH development. This review describes the main findings related to AMPK participation in HPH and its potential as a therapeutic target. It also extrapolates known AMPK functions to discuss the less-studied HAPH context.

The physiological control of eating: signals, neurons, and networks

During the past 30 yr, investigating the physiology of eating behaviors has generated a truly vast literature. This is fueled in part by a dramatic increase in obesity and its comorbidities that has coincided with an ever increasing sophistication of genetically based manipulations. These techniques have produced results with a remarkable degree of cell specificity, particularly at the cell signaling level, and have played a lead role in advancing the field. However, putting these findings into a brain-wide context that connects physiological signals and neurons to behavior and somatic physiology requires a thorough consideration of neuronal connections: a field that has also seen an extraordinary technological revolution. Our goal is to present a comprehensive and balanced assessment of how physiological signals associated with energy homeostasis interact at many brain levels to control eating behaviors. A major theme is that these signals engage sets of interacting neural networks throughout the brain that are defined by specific neural connections. We begin by discussing some fundamental concepts, including ones that still engender vigorous debate, that provide the necessary frameworks for understanding how the brain controls meal initiation and termination. These include key word definitions, ATP availability as the pivotal regulated variable in energy homeostasis, neuropeptide signaling, homeostatic and hedonic eating, and meal structure. Within this context, we discuss network models of how key regions in the endbrain (or telencephalon), hypothalamus, hindbrain, medulla, vagus nerve, and spinal cord work together with the gastrointestinal tract to enable the complex motor events that permit animals to eat in diverse situations.

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.

Hepatic microRNA modulation might be an early event to non-alcoholic fatty liver disease development driven by high-fat diet in male mice

INTRODUCTION

Metabolic alterations caused by an imbalance of macronutrient consumption are often related to the modulation of microRNAs (miRNAs), which could alter mRNAs expression profile and accelerate the development of non-alcoholic fatty liver disease (NAFLD).

AIMS

This study aimed to investigate the contribution of miRNAs in modulating early stages of NAFLD in mice submitted to a high-fat diet (HFD).

METHODS AND RESULTS

Male Swiss mice, fed either a control diet or an HFD for 1, 3, 7, 15, 30, 56 days, were assessed for metabolic alterations, gene expression and NAFLD markers. A hepatocyte cell line was used to investigate the effects of miR-370 modulation on enzymes involved in β-oxidation. Body weight and adiposity were higher after 7 days of HFD. Fasting glucose and insulin increased after 3 and 7 days of HFD, respectively. While hepatic lipid content increased from the first day on, hepatic glycogen had a decrease after 3 days of HFD consumption. miR-370 and Let-7 expression increased with acute and chronic exposure to HFD, accompanied by carnitine palmitoyltransferase 1A (Cpt1a), acyl-CoA dehydrogenase very long chain (Acadvl) and protein kinase AMP-activated Catalytic Subunit 2 (Prkaa2) downregulation, while decreased miR-122 expression was accompanied by 1-acylglycerol-3-phosphate-O-acyltransferase (Agpat) upregulation after 56 days of HFD consumption, some of them confirmed by in vitro experiments. Despite fluctuations in TNFa and IL6 mRNA levels, molecular modulation was consistent with hepatic TG and NAFLD development.

CONCLUSION

Hepatic miR-370-122-Let7 miRNA modulation could be the first insult to NAFLD development, preceding changes in glycemic homeostasis and adiposity.

Deciphering the mechanism by which the yeast Phaffia rhodozyma responds adaptively to environmental, nutritional, and genetic cues

Phaffia rhodozyma is a basidiomycetous yeast that synthesizes astaxanthin (ASX), which is a powerful and highly valuable antioxidant carotenoid pigment. P. rhodozyma cells accrue ASX and gain an intense red-pink coloration when faced with stressful conditions such as nutrient limitations (e.g., nitrogen or copper), the presence of toxic substances (e.g., antimycin A), or are affected by mutations in the genes that are involved in nitrogen metabolism or respiration. Since cellular accrual of ASX occurs under a wide variety of conditions, this yeast represents a valuable model for studying the growth conditions that entail oxidative stress for yeast cells. Recently, we proposed that ASX synthesis can be largely induced by conditions that lead to reduction-oxidation (redox) imbalances, particularly the state of the NADH/NAD+ couple together with an oxidative environment. In this work, we review the multiple known conditions that elicit ASX synthesis expanding on the data that we formerly examined. When considered alongside the Mitchell's chemiosmotic hypothesis, the study served to rationalize the induction of ASX synthesis and other adaptive cellular processes under a much broader set of conditions. Our aim was to propose an underlying mechanism that explains how a broad range of divergent conditions converge to induce ASX synthesis in P. rhodozyma. The mechanism that links the induction of ASX synthesis with the occurrence of NADH/NAD+ imbalances may help in understanding how other organisms detect any of a broad array of stimuli or gene mutations, and then adaptively respond to activate numerous compensatory cellular processes.

Integrated or Independent Actions of Metformin in Target Tissues Underlying Its Current Use and New Possible Applications in the Endocrine and Metabolic Disorder Area

Metformin is considered the first-choice drug for type 2 diabetes treatment. Actually, pleiotropic effects of metformin have been recognized, and there is evidence that this drug may have a favorable impact on health beyond its glucose-lowering activity. In summary, despite its long history, metformin is still an attractive research opportunity in the field of endocrine and metabolic diseases, age-related diseases, and cancer. To this end, its mode of action in distinct cell types is still in dispute. The aim of this work was to review the current knowledge and recent findings on the molecular mechanisms underlying the pharmacological effects of metformin in the field of metabolic and endocrine pathologies, including some endocrine tumors. Metformin is believed to act through multiple pathways that can be interconnected or work independently. Moreover, metformin effects on target tissues may be either direct or indirect, which means secondary to the actions on other tissues and consequent alterations at systemic level. Finally, as to the direct actions of metformin at cellular level, the intracellular milieu cooperates to cause differential responses to the drug between distinct cell types, despite the primary molecular targets may be the same within cells. Cellular bioenergetics can be regarded as the primary target of metformin action. Metformin can perturb the cytosolic and mitochondrial NAD/NADH ratio and the ATP/AMP ratio within cells, thus affecting enzymatic activities and metabolic and signaling pathways which depend on redox- and energy balance. In this context, the possible link between pyruvate metabolism and metformin actions is extensively discussed.

Phosphorylation of Na+,K+-ATPase at Tyr10 of the α1-Subunit is Suppressed by AMPK and Enhanced by Ouabain in Cultured Kidney Cells

Na⁺,K⁺-ATPase (NKA) is essential for maintenance of cellular and whole-body water and ion homeostasis. In the kidney, a major site of ion transport, NKA consumes ~ 50% of ATP, indicating a tight coordination of NKA and energy metabolism. AMP-activated protein kinase (AMPK), a cellular energy sensor, regulates NKA by modulating serine phosphorylation of the α1-subunit, but whether it modulates other important regulatory phosphosites, such as Tyr10, is unknown. Using human kidney (HK-2) cells, we determined that the phosphorylation of Tyr10 was stimulated by the epidermal growth factor (EGF), which was opposed by inhibitors of Src kinases (PP2), tyrosine kinases (genistein), and EGF receptor (EGFR, gefitinib). AMPK activators AICAR and A-769662 suppressed the EGF-stimulated phosphorylation of EGFR (Tyr1173) and NKAα1 at Tyr10. The phosphorylation of Src (Tyr416) was unaltered by AICAR and increased by A-769662. Conversely, ouabain (100 nM), a pharmacological NKA inhibitor and a putative adrenocortical hormone, enhanced the EGF-stimulated Tyr10 phosphorylation without altering the phosphorylation of EGFR (Tyr1173) or Src (Tyr416). Ouabain (100–1000 nM) increased the ADP:ATP ratio, while it suppressed the lactate production and the oxygen consumption rate in a dose-dependent manner. Treatment with ouabain or gene silencing of NKAα1 or NKAα3 subunit did not activate AMPK. In summary, AMPK activators and ouabain had antagonistic effects on the phosphorylation of NKAα1 at Tyr10 in cultured HK-2 cells, which implicates a role for Tyr10 in coordinated regulation of NKA-mediated ion transport and energy metabolism.

TAK1: A Molecular Link Between Liver Inflammation, Fibrosis, Steatosis, and Carcinogenesis

Chronic insult and persistent injury can cause liver inflammation, fibrosis, and carcinogenesis; it can also be associated with metabolic disorders. Identification of critical molecules that link the process of inflammation and carcinogenesis will provide prospective therapeutic targets for liver diseases. Rapid advancements in gene engineering technology have allowed the elucidation of the underlying mechanism of transformation, from inflammation and metabolic disorders to carcinogenesis. Transforming growth factor-β-activated kinase 1 (TAK1) is an upstream intracellular protein kinase of nuclear factor kappa-B (NF-κB) and c-Jun N-terminal kinases, which are activated by numerous cytokines, growth factors, and microbial products. In this study, we highlighted the functional roles of TAK1 and its interaction with transforming growth factor-β, WNT, AMP-activated protein kinase, and NF-κB signaling pathways in liver inflammation, steatosis, fibrosis, and carcinogenesis based on previously published articles.

Advance toward isolation, extraction, metabolism and health benefits of kaempferol, a major dietary flavonoid with future perspectives

As a major ubiquitous secondary metabolite, flavonoids are widely distributed in planta. Among flavonoids, kaempferol is a typical natural flavonol in diets and medicinal plants with myriad bioactivities, such as anti-inflammatory activity, anti-cancer activity, antioxidant activity, and anti-diabetic activity. However, the natural sources, absorption and metabolism as well as the bioactivities of kaempferol have not been reviewed comprehensively and systematically. This review highlights the latest research progress and the effect of kaempferol in the prevention and treatment of various chronic diseases, as well as its protective health effects, and provides a theoretical basis for future research to be used in nutraceuticals. Further, comparison of the different extraction and analytical methods are presented to highlight the most optimum for PG recovery and its detection in plasma and body fluids. Such review aims at improving the value-added applications of this unique dietary bioactive flavonoids at commercial scale and to provide a reference for its needed further development.

SNF1-related protein kinase 1: the many-faced signaling hub regulating developmental plasticity in plants

The Snf1-related protein kinase 1 (SnRK1) is the plant homolog of the heterotrimeric AMP-activated protein kinase/sucrose non-fermenting 1 (AMPK/Snf1), which works as a major regulator of growth under nutrient-limiting conditions in eukaryotes. Along with its conserved role as a master regulator of sugar starvation responses, SnRK1 is involved in controlling the developmental plasticity and resilience under diverse environmental conditions in plants. In this review, through mining and analyzing the interactome and phosphoproteome data of SnRK1, we are highlighting its role in fundamental cellular processes such as gene regulation, protein synthesis, primary metabolism, protein trafficking, nutrient homeostasis, and autophagy. Along with the well-characterized molecular interaction in SnRK1 signaling, our analysis highlights several unchartered regions of SnRK1 signaling in plants such as its possible communication with chromatin remodelers, histone modifiers, and inositol phosphate signaling. We also discuss potential reciprocal interactions of SnRK1 signaling with other signaling pathways and cellular processes, which could be involved in maintaining flexibility and homeostasis under different environmental conditions. Overall, this review provides a comprehensive overview of the SnRK1 signaling network in plants and suggests many novel directions for future research.

AMPK: a key regulator of energy stress and calcium-induced autophagy

Autophagy is a well-known cell-survival strategy orchestrated by a conserved set of proteins. It equips the cells with mechanisms to attain homeostasis during unfavorable conditions such as stress by breaking down the cellular components and reusing them for energy as well as for building new components required for survival. A basal level of autophagy is required for achieving homeostasis under normal conditions through regular turnover of macromolecules and organelles. Initiation of autophagy is regulated by two key components of the nutrient/energy sensor pathways; mammalian target of rapamycin 1 (mTORC1) and AMP-activated kinase (AMPK). Under energy-deprived conditions, AMPK is activated triggering autophagy, whereas, in nutrient-rich conditions, the growth-promoting kinase mTORC1 is activated inhibiting autophagy. Thus, the reciprocal regulation of autophagy by AMPK and mTORC1 defines a fundamental mechanism by which cells respond to nutrient availability. Interestingly, cytoplasmic calcium is also found to be an activator of AMPK and autophagy through a calmodulin/CaMKKβ pathway. However, the physiological significance of the regulation of autophagy by cytoplasmic calcium is currently unclear. This review focuses on the current understanding of the mechanism of autophagy and its regulation by AMPK.

Alanine alters the carbohydrate metabolism of rainbow trout: glucose flux and cell signaling

In rainbow trout, dietary carbohydrates are poorly metabolized compared with other macronutrients. One prevalent hypothesis suggests that high dietary amino acid levels could contribute to the poor utilization of carbohydrates in trout. In mammals, alanine is considered an important gluconeogenic precursor, but has recently been found to stimulate AMP-activated protein kinase (AMPK) to reduce glucose levels. In trout, the effect of alanine on glucose flux is unknown. The goal of this study was to determine the effects of 4 h exogenous alanine infusion on glucose metabolism in rainbow trout. Glucose flux, and the rate of glucose appearance (Ra) and disposal (Rd) were measured in vivo. Key glycolytic and gluconeogenic enzyme expression and activity, and cell signaling molecules relevant to glucose metabolism were assessed in the liver and muscle. The results show that alanine inhibits glucose Ra (from 13.2±2.5 to 7.3±1.6 μmol kg-1 min-1) and Rd (from 13.2±2.5 to 7.4±1.5 μmol kg-1 min-1) and the slight mismatch between Ra and Rd caused a reduction in glycemia, similar to the effects of insulin in trout. The reduction in glucose Rd can be partially explained by a reduction in glut4b expression in red muscle. In contrast to mammals, trout alanine-dependent glucose-lowering effects did not involve hepatic AMPK activation, suggesting a different mechanistic basis. Interestingly, protein kinase B (AKT) activation increased only in muscle, similar to effects observed in insulin-infused trout. We speculate that alanine-dependent effects were probably mediated through stimulation of insulin secretion, which could indirectly promote alanine oxidation to provide the needed energy.

Dietary Control of Inflammation and Resolution

The healing of any injury requires a dynamic balance of initiation and resolution of inflammation. This hypothesis-generating review presents an overview of the various nutrients that can act as signaling agents to modify the metabolic responses essential for the optimal healing of injury-induced inflammation. In this hypothesis-generating review, we describe a defined nutritional program consisting of an integrated interaction of a calorie-restricted anti-inflammatory diet coupled with adequate levels of omega-3 fatty acids and sufficient levels of dietary polyphenols that can be used in clinical trials to treat conditions associated with insulin resistance. Each dietary intervention works in an orchestrated systems-based approach to reduce, resolve, and repair the tissue damage caused by any inflammation-inducing injury. The orchestration of these specific nutrients and their signaling metabolites to facilitate healing is termed the Resolution Response. The final stage of the Resolution Response is the activation of intracellular 5' adenosine monophosphate-activated protein kinase (AMPK), which is necessary to repair tissue damaged by the initial injury-induced inflammation. The dietary optimization of the Resolution Response can be personalized to the individual by using standard blood markers. Once each of those markers is in their appropriate ranges, activation of intracellular AMPK will be facilitated. Finally, we outline how the resulting activation of AMPK will affect a diverse number of other intercellular signaling systems leading to an extended healthspan.