AMPK as a direct sensor of long-chain fatty acyl-CoA esters

A mitochondrial NADPH-cholesterol axis regulates extracellular vesicle biogenesis to support hematopoietic stem cell fate

Mitochondrial fatty acid oxidation (FAO) is essential for hematopoietic stem cell (HSC) self-renewal; however, the mechanism by which mitochondrial metabolism controls HSC fate remains unknown. Here, we show that within the hematopoietic lineage, HSCs have the largest mitochondrial NADPH pools, which are required for proper HSC cell fate and homeostasis. Bioinformatic analysis of the HSC transcriptome, biochemical assays, and genetic inactivation of FAO all indicate that FAO-generated NADPH fuels cholesterol synthesis in HSCs. Interference with FAO disturbs the segregation of mitochondrial NADPH toward corresponding daughter cells upon single HSC division. Importantly, we have found that the FAO-NADPH-cholesterol axis drives extracellular vesicle (EV) biogenesis and release in HSCs, while inhibition of EV signaling impairs HSC self-renewal. These data reveal the existence of a mitochondrial NADPH-cholesterol axis for EV biogenesis that is required for hematopoietic homeostasis and highlight the non-stochastic nature of HSC fate determination.

Differences in Leukocyte Transcriptomes of Morbidly Obese Patients With High Output Heart Failure: A Pilot Study

Background and Objectives

Heart failure is characterized by alterations of gene expression that provide insight into the underlying pathophysiologic mechanisms. However, obesity-related high output heart failure (HOHF) is a specific phenotype of heart failure that has not been studied using gene expression. Our aim in this study was to examine the variances in leukocyte transcriptomes of morbidly obese patients with HOHF.

Methods

In this cross-sectional study, we applied stranded total RNA-sequencing to six patients with morbid obesity and HOHF and 6 patients with morbid obesity and non-HOHF. Differential gene expression was calculated, and Ingenuity Pathway Analysis software was used to interpret the canonical pathways, functional changes, upstream regulators, and networks in these patients.

Results

We found in patients with HOHF that there were 116 differentially expressed genes with upregulation of 114 genes and downregulation of 2 genes. The differentially expressed genes were involved with cell proliferation, mitochondrial function, erythropoiesis, erythrocyte stability, and apoptosis. The top upregulated canonical pathways associated with differentially expressed genes were autophagy, adenosine monophosphate-activated protein kinase signaling, and senescence pathways. We identified GATA binding protein 1 as an upstream regulator and nuclear factor kappa-light-chain-enhancer of activated B cells associated network.

Conclusions

We are the first to report the differential gene expression in patients with obesity-related HOHF and reveal the various pathophysiologic mechanisms underlying the disease. Further research is needed to determine the role of cellular function and maintenance, inflammation, and iron homeostasis in obesity-related HOHF.

Endothelial NOX5 Expression Modulates Thermogenesis and Lipolysis in Mice Fed with a High-Fat Diet and 3T3-L1 Adipocytes through an Interleukin-6 Dependent Mechanism

Obesity is a global health issue associated with the development of metabolic syndrome, which correlates with insulin resistance, altered lipid homeostasis, and other pathologies. One of the mechanisms involved in the development of these pathologies is the increased production of reactive oxygen species (ROS). One of the main producers of ROS is the family of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, among which NOX5 is the most recently discovered member. The aim of the present work is to describe the effect of endothelial NOX5 expression on neighboring adipose tissue in obesity conditions by using two systems. An in vivo model based on NOX5 conditional knock-in mice fed with a high-fat diet and an in vitro model developed with 3T3-L1 adipocytes cultured with conditioned media of endothelial NOX5-expressing bEnd.3 cells, previously treated with glucose and palmitic acid. Endothelial NOX5 expression promoted the expression and activation of specific markers of thermogenesis and lipolysis in the mesenteric and epididymal fat of those mice fed with a high-fat diet. Additionally, the activation of these processes was derived from an increase in IL-6 production as a result of NOX5 activity. Accordingly, 3T3-L1 adipocytes treated with conditioned media of endothelial NOX5-expressing cells, presented higher expression of thermogenic and lipolytic genes. Moreover, endothelial NOX5-expressing bEnd.3 cells previously treated with glucose and palmitic acid also showed interleukin (IL-6) production. Finally, it seems that the increase in IL-6 stimulated the activation of markers of thermogenesis and lipolysis through phosphorylation of STAT3 and AMPK, respectively. In conclusion, in response to obesogenic conditions, endothelial NOX5 activity could promote thermogenesis and lipolysis in the adipose tissue by regulating IL-6 production.

AMPK Activity: A Primary Target for Diabetes Prevention with Therapeutic Phytochemicals

Diabetes is a metabolic syndrome characterized by inadequate blood glucose control and is associated with reduced quality of life and various complications, significantly shortening life expectancy. Natural phytochemicals found in plants have been traditionally used as medicines for the prevention of chronic diseases including diabetes in East Asia since ancient times. Many of these phytochemicals have been characterized as having few side effects, and scientific research into the mechanisms of action responsible has accumulated mounting evidence for their efficacy. These compounds, which may help to prevent metabolic syndrome disorders including diabetes, act through relevant intracellular signaling pathways. In this review, we examine the anti-diabetic efficacy of several compounds and extracts derived from medicinal plants, with a focus on AMP-activated protein kinase (AMPK) activity.

The Role of AMPK Signaling in Brown Adipose Tissue Activation

Obesity is becoming a pandemic, and its prevalence is still increasing. Considering that obesity increases the risk of developing cardiometabolic diseases, research efforts are focusing on new ways to combat obesity. Brown adipose tissue (BAT) has emerged as a possible target to achieve this for its functional role in energy expenditure by means of increasing thermogenesis. An important metabolic sensor and regulator of whole-body energy balance is AMP-activated protein kinase (AMPK), and its role in energy metabolism is evident. This review highlights the mechanisms of BAT activation and investigates how AMPK can be used as a target for BAT activation. We review compounds and other factors that are able to activate AMPK and further discuss the therapeutic use of AMPK in BAT activation. Extensive research shows that AMPK can be activated by a number of different kinases, such as LKB1, CaMKK, but also small molecules, hormones, and metabolic stresses. AMPK is able to activate BAT by inducing adipogenesis, maintaining mitochondrial homeostasis and inducing browning in white adipose tissue. We conclude that, despite encouraging results, many uncertainties should be clarified before AMPK can be posed as a target for anti-obesity treatment via BAT activation.

Tangeretin boosts the anticancer activity of metformin in breast cancer cells via curbing the energy production

BACKGROUND

Breast cancer is the first leading cause of women cancer-related deaths worldwide. While there are many proposed treatments for breast cancer, low efficacy, toxicity, and resistance are still major therapeutic obstacles. Thus, there is a need for safer and more effective therapeutic approaches. Because of the direct link between obesity and carcinogenesis, energy restriction mimetic agents (ERMAs) such as the antidiabetic agent, metformin was proposed as a novel antiproliferative agent. However, the anticancer dose of metformin alone is relatively high and impractical to be implemented safely in patients. The current work aimed to sensitize resistant breast cancer cells to metformin's antiproliferative effect using the natural potential anticancer agent, tangeretin.

METHODS

The possible synergistic combination between metformin and tangeretin was initially evaluated using MTT cell viability assay in different breast cancer cell lines (MCF-7, MDA-MB-231, and their resistant phenotype). The possible mechanisms of synergy were investigated via Western blotting analysis, reactive oxygen species (ROS) measurement, annexin/PI assay, cell cycle analysis, and wound healing assay.

RESULTS

The results indicated the ability of tangeretin to improve the anticancer activity of metformin. Interestingly, the improved activity was almost equally observed in both parental and resistant cancer cells, which underlines the importance of this combination in cases of the emergence of resistance. The synergy was mediated through the enhanced activation of AMPK and ROS generation in addition to the improved inhibition of cell migration, induction of cell cycle arrest, and apoptosis in cancer cells.

CONCLUSION

The current work underscores the importance of metformin as an ERMA in tackling breast cancer and as a novel approach to boost its anticancer activity via a synergistic combination with tangeretin.

Regulation of Autophagy Enzymes by Nutrient Signaling

Autophagy is the primary catabolic program of the cell that promotes survival in response to metabolic stress. It is tightly regulated by a suite of kinases responsive to nutrient status, including mammalian target of rapamycin complex 1 (mTORC1), AMP-activated protein kinase (AMPK), protein kinase C-α (PKCα), MAPK-activated protein kinases 2/3 (MAPKAPK2/3), Rho kinase 1 (ROCK1), c-Jun N-terminal kinase 1 (JNK), and Casein kinase 2 (CSNK2). Here, we highlight recently uncovered mechanisms linking amino acid, glucose, and oxygen levels to autophagy regulation through mTORC1 and AMPK. In addition, we describe new pathways governing the autophagic machinery, including the Unc-51-like (ULK1), vacuolar protein sorting 34 (VPS34), and autophagy related 16 like 1 (ATG16L1) enzyme complexes. Novel downstream targets of ULK1 protein kinase are also discussed, such as the ATG16L1 subunit of the microtubule-associated protein 1 light chain 3 (LC3)-lipidating enzyme and the ATG14 subunit of the VPS34 complex. Collectively, we describe the complexities of the autophagy pathway and its role in maintaining cellular nutrient homeostasis during times of starvation.

Butyrate Protects Porcine Colon Epithelium from Hypoxia-Induced Damage on a Functional Level

The large intestinal epithelium is confronted with the necessity to adapt quickly to varying levels of oxygenation. In contrast to other tissues, it meets this requirement successfully and remains unharmed during (limited) hypoxic periods. The large intestine is also the site of bacterial fermentation producing short-chain fatty acids (SCFA). Amongst these SCFA, butyrate has been reported to ameliorate many pathological conditions. Thus, we hypothesized that butyrate protects the colonocytes from hypoxic damage. We used isolated porcine colon epithelium mounted in Ussing chambers, incubated it with or without butyrate and simulated hypoxia by changing the gassing regime to test this hypothesis. We found an increase in transepithelial conductance and a decrease in short-circuit current across the epithelia when simulating hypoxia for more than 30 min. Incubation with 50 mM butyrate significantly ameliorated these changes to the epithelial integrity. In order to characterize the protective mechanism, we compared the effects of butyrate to those of iso-butyrate and propionate. These two SCFAs exerted similar effects to butyrate. Therefore, we propose that the protective effect of butyrate on colon epithelium under hypoxia is not (only) based on its nutritive function, but rather on the intracellular signaling effects of SCFA.

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

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