A role for ATP-citrate lyase, malic enzyme, and pyruvate/citrate cycling in glucose-induced insulin secretion

Mitochondrial complex I inhibition triggers NAD+-independent glucose oxidation via successive NADPH formation, "futile" fatty acid cycling, and FADH2 oxidation

Inhibition of mitochondrial complex I (NADH dehydrogenase) is the primary mechanism of the antidiabetic drug metformin and various unrelated natural toxins. Complex I inhibition can also be induced by antidiabetic PPAR agonists, and it is elicited by methionine restriction, a nutritional intervention causing resistance to diabetes and obesity. Still, a comprehensible explanation to why complex I inhibition exerts antidiabetic properties and engenders metabolic inefficiency is missing. To evaluate this issue, we have systematically reanalyzed published transcriptomic datasets from MPP-treated neurons, metformin-treated hepatocytes, and methionine-restricted rats. We found that pathways leading to NADPH formation were widely induced, together with anabolic fatty acid biosynthesis, the latter appearing highly paradoxical in a state of mitochondrial impairment. However, concomitant induction of catabolic fatty acid oxidation indicated that complex I inhibition created a "futile" cycle of fatty acid synthesis and degradation, which was anatomically distributed between adipose tissue and liver in vivo. Cofactor balance analysis unveiled that such cycling would indeed be energetically futile (-3 ATP per acetyl-CoA), though it would not be redox-futile, as it would convert NADPH into respirable FADH2 without any net production of NADH. We conclude that inhibition of NADH dehydrogenase leads to a metabolic shift from glycolysis and the citric acid cycle (both generating NADH) towards the pentose phosphate pathway, whose product NADPH is translated 1:1 into FADH2 by fatty acid cycling. The diabetes-resistant phenotype following hepatic and intestinal complex I inhibition is attributed to FGF21- and GDF15-dependent fat hunger signaling, which remodels adipose tissue into a glucose-metabolizing organ.

Compilations and updates on residual feed intake in sheep

The increasing global demand for food and the strong effect of climate change have forced animal science to advance regarding new methods of selection in search of more efficient animals in production systems. Feed consumption represents more than 70% of the costs of sheep farms, and more efficient animals can increase the farmers' profitability. One of the main measures of feed efficiency is estimated residual feed intake (RFI), created in 1963 by Robert Koch for estimation in cattle and later adapted for sheep. Animals with negative RFI values (RFI-) are more efficient than animals with positive values (RFI+), with influence on the variables of performance, carcass quality and production of enteric gases. The RFI is the most common and accepted metric of the feed efficiency trait for genetic selection, since it is independent of growth traits, unlike the feed conversion ratio. The purpose of this review article was to present updated literature information on the relationship of RFI estimates with performance measures, molecular markers, greenhouse gas production and feed efficiency, the technical aspects and physiological basis of metabolic in sheep.

PTPN2 Regulates Metabolic Flux to Affect β-Cell Susceptibility to Inflammatory Stress

Protein tyrosine phosphatase N2 (PTPN2) is a type 1 diabetes (T1D) candidate gene identified from human genome-wide association studies. PTPN2 is highly expressed in human and murine islets and becomes elevated upon inflammation and models of T1D, suggesting that PTPN2 may be important for β-cell survival in the context of T1D. To test whether PTPN2 contributed to β-cell dysfunction in an inflammatory environment, we generated a β-cell-specific deletion of Ptpn2 in mice (PTPN2-β knockout [βKO]). Whereas unstressed animals exhibited normal metabolic profiles, low- and high-dose streptozotocin-treated PTPN2-βKO mice displayed hyperglycemia and accelerated death, respectively. Furthermore, cytokine-treated Ptpn2-KO islets resulted in impaired glucose-stimulated insulin secretion, mitochondrial defects, and reduced glucose-induced metabolic flux, suggesting β-cells lacking Ptpn2 are more susceptible to inflammatory stress associated with T1D due to maladaptive metabolic fitness. Consistent with the phenotype, proteomic analysis identified an important metabolic enzyme, ATP-citrate lyase, as a novel PTPN2 substrate.

ARTICLE HIGHLIGHTS

Histone Acyl Code in Precision Oncology: Mechanistic Insights from Dietary and Metabolic Factors

Cancer etiology involves complex interactions between genetic and non-genetic factors, with epigenetic mechanisms serving as key regulators at multiple stages of pathogenesis. Poor dietary habits contribute to cancer predisposition by impacting DNA methylation patterns, non-coding RNA expression, and histone epigenetic landscapes. Histone post-translational modifications (PTMs), including acyl marks, act as a molecular code and play a crucial role in translating changes in cellular metabolism into enduring patterns of gene expression. As cancer cells undergo metabolic reprogramming to support rapid growth and proliferation, nuanced roles have emerged for dietary- and metabolism-derived histone acylation changes in cancer progression. Specific types and mechanisms of histone acylation, beyond the standard acetylation marks, shed light on how dietary metabolites reshape the gut microbiome, influencing the dynamics of histone acyl repertoires. Given the reversible nature of histone PTMs, the corresponding acyl readers, writers, and erasers are discussed in this review in the context of cancer prevention and treatment. The evolving 'acyl code' provides for improved biomarker assessment and clinical validation in cancer diagnosis and prognosis.

Metabolic and Molecular Amplification of Insulin Secretion

The pancreatic β cells are at the hub of myriad signals to regulate the secretion of an adequate amount of insulin needed to re-establish postprandial euglycemia. The β cell possesses sophisticated metabolic enzymes and a variety of extracellular receptors and channels that amplify insulin secretion in response to autocrine, paracrine, and neurohormonal signals. Considerable research has been undertaken to decipher the mechanisms regulating insulin secretion. While the triggering pathway induced by glucose is needed to initiate the exocytosis process, multiple other stimuli modulate the insulin secretion response. This chapter will discuss the recent advances in understanding the role of the diverse glucose- and fatty acid-metabolic coupling factors in amplifying insulin secretion. It will also highlight the intracellular events linking the extracellular receptors and channels to insulin secretion amplification. Understanding these mechanisms provides new insights into learning more about the etiology of β-cell failure and paves the way for developing new therapeutic strategies for type 2 diabetes.

Cydonia oblonga Miller fruit extract exerts an anti-obesity effect in 3T3-L1 adipocytes by activating the AMPK signaling pathway

BACKGROUND/OBJECTIVES

The fruit of Cydonia oblonga Miller (COM) is used traditionally in Mediterranean region medicine to prevent or treat obesity, but its mechanism of action is still unclear. Beyond a demonstrated anti-obesity effect, the fruit was tested for the mechanism of adipogenesis in 3T3-L1 preadipocytes.

MATERIALS/METHODS

3T3-L1 preadipocytes were cultured for 8 days with COM fruit extract (COME) at different concentrations (0-600 µg/mL) with adipocyte differentiation medium. The cell viability was measured using an MTT assay; triglyceride (TG) was stained with Oil Red O. The expression levels of the adipogenesis-related genes and protein expression were analyzed by reverse transcription polymerase chain reaction and Western blotting, respectively.

RESULTS

COME inhibited intracellular TG accumulation during adipogenesis. A COME treatment in 3T3-L1 cells induced upregulation of the adenosine monophosphate-activated protein kinase (AMPK)α phosphorylation and downregulation of the adipogenic transcription factors, such as sterol regulatory element-binding protein 1c, peroxisome proliferator-activated receptor γ, and CCAAT/enhancer binding protein α. The COME treatment reduced the mRNA expression of fatty acyl synthetase, adenosine triphosphate-citrate lyase, adipocyte protein 2, and lipoprotein lipase. It increased the mRNA expression of hormone-sensitive lipase and carnitine palmitoyltransferase I in 3T3-L1 cells.

CONCLUSIONS

COME inhibits adipogenesis via the AMPK signaling pathways. COME may be used to prevent and treat obesity.

Targets for pollutants in rat and human pancreatic beta-cells: The effect of prolonged exposure to sub-lethal concentrations of hexachlorocyclohexane isomers on the expression of function- and survival-related proteins

Decades after most countries banned hexachlorocyclohexane, HCH isomers still pollute the environment. Many studies described HCH as a pro-diabetic factor; nevertheless, the effect of HCH isomers on pancreatic beta-cells remains unexplored. This study investigated the effects of a one-month exposure to α-HCH, β-HCH, and γ-HCH on protein expression in human (NES2Y) and rat (INS1E) pancreatic beta-cell lines. α-HCH and γ-HCH increased proinsulin and insulin levels in INS1E cells, while β-HCH showed the opposite trend. α-HCH altered the expression of PKA, ATF3, and PLIN2. β-HCH affected the expression of GLUT1, GLUT2, PKA, ATF3, p-eIF2α, ATP-CL, and PLIN2. γ-HCH altered the expression of PKA, ATF3, PLIN2, PLIN5, and IDH1. From the tested proteins, PKA, ATF3, and PLIN-2 were the most sensitive to HCH exposure and have the potential to be used as biomarkers.

Nrf2: Therapeutic target of islet function protection in diabetes and islet transplantation

Nuclear factor-erythroid 2-related factor 2 (Nrf2) has been reported as a major intracellular regulator of antioxidant stress, notably in islet β cells with low antioxidant enzyme content. Nrf2 is capable of regulating antioxidant function, while it can also regulate insulin secretion, proliferation, and differentiation of β cells, ER stress, as well as mitochondrial function. Thus, Nrf2 pharmacological activators have been employed in the laboratory for the treatment of diabetic mice. Islet cells are exposed to oxidative environment when islet is being transplanted. Accordingly, less than 50% of islet cells are well transplanted, and their normal function is maintained. The pharmacological activation of Nrf2 has been confirmed to protect islet cells at different stages of transplantation stages during experiments for islet transplantation.

Wild-Type Isocitrate Dehydrogenase-Dependent Oxidative Decarboxylation and Reductive Carboxylation in Cancer and Their Clinical Significance

The human isocitrate dehydrogenase (IDH) gene encodes for the isoenzymes IDH1, 2, and 3, which catalyze the conversion of isocitrate and α-ketoglutarate (α-KG) and are required for normal mammalian metabolism. Isocitrate dehydrogenase 1 and 2 catalyze the reversible conversion of isocitrate to α-KG. Isocitrate dehydrogenase 3 is the key enzyme that mediates the production of α-KG from isocitrate in the tricarboxylic acid (TCA) cycle. In the TCA cycle, the decarboxylation reaction catalyzed by isocitrate dehydrogenase mediates the conversion of isocitrate to α-KG accompanied by dehydrogenation, a process commonly known as oxidative decarboxylation. The formation of 6-C isocitrate from α-KG and CO₂ catalyzed by IDH is termed reductive carboxylation. This IDH-mediated reversible reaction is of great importance in tumor cells. We outline the role of the various isocitrate dehydrogenase isoforms in cancer, discuss the metabolic implications of interference with IDH, summarize therapeutic interventions targeting changes in IDH expression, and highlight areas for future research.

Antipsychotics impair regulation of glucose metabolism by central glucose

Hypothalamic detection of elevated circulating glucose triggers suppression of endogenous glucose production (EGP) to maintain glucose homeostasis. Antipsychotics alleviate symptoms associated with schizophrenia but also increase the risk for impaired glucose metabolism. In the current study, we examined whether two acutely administered antipsychotics from different drug classes, haloperidol (first generation antipsychotic) and olanzapine (second generation antipsychotic), affect the ability of intracerebroventricular (ICV) glucose infusion approximating postprandial levels to suppress EGP. The experimental protocol consisted of a pancreatic euglycemic clamp, followed by kinomic and RNA-seq analyses of hypothalamic samples to determine changes in serine/threonine kinase activity and gene expression, respectively. Both antipsychotics inhibited ICV glucose-mediated increases in glucose infusion rate during the clamp, a measure of whole-body glucose metabolism. Similarly, olanzapine and haloperidol blocked central glucose-induced suppression of EGP. ICV glucose stimulated the vascular endothelial growth factor (VEGF) pathway, phosphatidylinositol 3-kinase (PI3K) pathway, and kinases capable of activating K_ATP channels in the hypothalamus. These effects were inhibited by both antipsychotics. In conclusion, olanzapine and haloperidol impair central glucose sensing. Although results of hypothalamic analyses in our study do not prove causality, they are novel and provide the basis for a multitude of future studies.

Kinetic and data-driven modeling of pancreatic β-cell central carbon metabolism and insulin secretion

Pancreatic β-cells respond to increased extracellular glucose levels by initiating a metabolic shift. That change in metabolism is part of the process of glucose-stimulated insulin secretion and is of particular interest in the context of diabetes. However, we do not fully understand how the coordinated changes in metabolic pathways and metabolite products influence insulin secretion. In this work, we apply systems biology approaches to develop a detailed kinetic model of the intracellular central carbon metabolic pathways in pancreatic β-cells upon stimulation with high levels of glucose. The model is calibrated to published metabolomics datasets for the INS1 823/13 cell line, accurately capturing the measured metabolite fold-changes. We first employed the calibrated mechanistic model to estimate the stimulated cell's fluxome. We then used the predicted network fluxes in a data-driven approach to build a partial least squares regression model. By developing the combined kinetic and data-driven modeling framework, we gain insights into the link between β-cell metabolism and glucose-stimulated insulin secretion. The combined modeling framework was used to predict the effects of common anti-diabetic pharmacological interventions on metabolite levels, flux through the metabolic network, and insulin secretion. Our simulations reveal targets that can be modulated to enhance insulin secretion. The model is a promising tool to contextualize and extend the usefulness of metabolomics data and to predict dynamics and metabolite levels that are difficult to measure in vitro. In addition, the modeling framework can be applied to identify, explain, and assess novel and clinically-relevant interventions that may be particularly valuable in diabetes treatment.

Discovery and characterization of novel ATP citrate lyase inhibitors from natural products by a luminescence-based assay

ATP citrate lyase (ACLY) is a key enzyme in glucolipid metabolism with therapeutic prospect for treating hyperlipidemia and various cancers. Much effort has been put into discovering ACLY inhibitors. However, current screening approaches have limitations in sensitivity, portability and high-throughput. To develop a general screening assay, we investigated series of conditions affecting the enzymatic reaction based on the ADP-Glo luminescence assay. Bovine serum albumin (0.001%) added triggered strong and stable fluorescence signal. The optimized assay was validated and applied to screen our natural product library. Two novel inhibitors were identified with IC₅₀ values of 3.86 ± 0.62 μM (2) and 15.48 ± 2.51 μM (4). Their aggregations and target specificities were also examined. 2 was characterized as a noncompetitive inhibitor of ACLY, while 4 was a competitive inhibitor of CoA, which was also elucidated by docking studies. In anticancer activity evaluation, 2 with higher inhibition potency did not exhibit anticancer effect, probably owing to its insufficient cell-permeability. 4 showed moderate inhibition in the proliferation of A549 and PC3 cells. This study not only developed a general approach for ACLY inhibitor discovery, but also identified a new scaffold ACLY inhibitor, which could be served as a hit compound in drug design.

Metabolic cycles and signals for insulin secretion

In this review, we focus on recent developments in our understanding of nutrient-induced insulin secretion that challenge a key aspect of the "canonical" model, in which an oxidative phosphorylation-driven rise in ATP production closes KATP channels. We discuss the importance of intrinsic β cell metabolic oscillations; the phasic alignment of relevant metabolic cycles, shuttles, and shunts; and how their temporal and compartmental relationships align with the triggering phase or the secretory phase of pulsatile insulin secretion. Metabolic signaling components are assigned regulatory, effectory, and/or homeostatic roles vis-à-vis their contribution to glucose sensing, signal transmission, and resetting the system. Taken together, these functions provide a framework for understanding how allostery, anaplerosis, and oxidative metabolism are integrated into the oscillatory behavior of the secretory pathway. By incorporating these temporal as well as newly discovered spatial aspects of β cell metabolism, we propose a much-refined MitoCat-MitoOx model of the signaling process for the field to evaluate.

Maturation of beta cells: lessons from in vivo and in vitro models

The ability to maintain normoglycaemia, through glucose-sensitive insulin release, is a key aspect of postnatal beta cell function. However, terminally differentiated beta cell identity does not necessarily imply functional maturity. Beta cell maturation is therefore a continuation of beta cell development, albeit a process that occurs postnatally in mammals. Although many important features have been identified in the study of beta cell maturation, as of yet no unified mechanistic model of beta cell functional maturity exists. Here, we review recent findings about the underlying mechanisms of beta cell functional maturation. These findings include systemic hormonal and nutritional triggers that operate through energy-sensing machinery shifts within beta cells, resulting in primed metabolic states that allow for appropriate glucose trafficking and, ultimately, insulin release. We also draw attention to the expansive synergistic nature of these pathways and emphasise that beta cell maturation is dependent on overlapping regulatory and metabolic networks.

Contribution of Mitochondria to Insulin Secretion by Various Secretagogues

Significance: Mitochondria determine glucose-stimulated insulin secretion (GSIS) in pancreatic β-cells by elevating ATP synthesis. As the metabolic and redox hub, mitochondria provide numerous links to the plasma membrane channels, insulin granule vesicles (IGVs), cell redox, NADH, NADPH, and Ca²⁺ homeostasis, all affecting insulin secretion. Recent Advances: Mitochondrial redox signaling was implicated in several modes of insulin secretion (branched-chain ketoacid [BCKA]-, fatty acid [FA]-stimulated). Mitochondrial Ca²⁺ influx was found to enhance GSIS, reflecting cytosolic Ca²⁺ oscillations induced by action potential spikes (intermittent opening of voltage-dependent Ca²⁺ and K⁺ channels) or the superimposed Ca²⁺ release from the endoplasmic reticulum (ER). The ATPase inhibitory factor 1 (IF1) was reported to tune the glucose sensitivity range for GSIS. Mitochondrial protein kinase A was implicated in preventing the IF1-mediated inhibition of the ATP synthase. Critical Issues: It is unknown how the redox signal spreads up to the plasma membrane and what its targets are, what the differences in metabolic, redox, NADH/NADPH, and Ca²⁺ signaling, and homeostasis are between the first and second GSIS phase, and whether mitochondria can replace ER in the amplification of IGV exocytosis. Future Directions: Metabolomics studies performed to distinguish between the mitochondrial matrix and cytosolic metabolites will elucidate further details. Identifying the targets of cell signaling into mitochondria and of mitochondrial retrograde metabolic and redox signals to the cell will uncover further molecular mechanisms for insulin secretion stimulated by glucose, BCKAs, and FAs, and the amplification of secretion by glucagon-like peptide (GLP-1) and metabotropic receptors. They will identify the distinction between the hub β-cells and their followers in intact and diabetic states. Antioxid. Redox Signal. 36, 920-952.

A Comparison of Mother’s Milk and the Neonatal Urine Metabolome: A Unique Fingerprinting for Different Nutritional Phenotypes

The ability of metabolomics to provide a snapshot of an individual’s metabolic state makes it a very useful technique in neonatology for investigating the complex relationship between nutrition and the state of health of the newborn. Through an ¹H-NMR metabolomics analysis, we aimed to investigate the metabolic profile of newborns by analyzing both urine and milk samples in relation to the birth weight of neonates classified as AGA (adequate for the gestational age, n = 51), IUGR (intrauterine growth restriction, n = 14), and LGA (large for gestational age, n = 15). Samples were collected at 7 ± 2 days after delivery. Of these infants, 42 were exclusively breastfed, while 38 received mixed feeding with a variable amount of commercial infant formula (less than 40%) in addition to breast milk. We observed a urinary spectral pattern for oligosaccharides very close to that of the corresponding mother’s milk in the case of exclusively breastfed infants, thus mirroring the maternal phenotype. The absence of this good match between the infant urine and human milk spectra in the case of mixed-fed infants could be reasonably ascribed to the use of a variable amount of commercial infant formulas (under 40%) added to breast milk. Furthermore, our findings did not evidence any significant differences in the spectral profiles in terms of the neonatal customize centile, i.e., AGA (adequate for gestational age), LGA (large for gestational age), or IGUR (intrauterine growth restriction). It is reasonable to assume that maternal human milk oligosaccharide (HMO) production is not or is only minimally influenced by the fetal growth conditions for unknown reasons. This hypothesis may be supported by our metabolomics-based results, confirming once again the importance of this approach in the neonatal field.

Effects of ingested nanocellulose and nanochitosan materials on carbohydrate digestion and absorption in an in vitro small intestinal epithelium model

Nanoscale materials derived from natural biopolymers like cellulose and chitosan have many potentially useful agri-food and oral drug delivery applications. Because of their large and potentially bioactive surface areas and other unique physico-chemical properties, it is essential when evaluating their toxicological impact to assess potential effects on the digestion and absorption of co-ingested nutrients. Here, the effects of cellulose nanofibers (CNF), cellulose nanocrystals (CNC), and chitosan nanoparticles (Chnp) on the digestion and absorption of carbohydrates were studied. Starch digestion was assessed by measuring maltose released during simulated digestion of starch solutions. Glucose absorption was assessed by measuring translocation from the resulting digestas across an in vitro transwell tri-culture model of the small intestinal epithelium and calculating the area under the curve increase in absorbed glucose, analogous to the glycemic index. At 1% w/w, CNF and Chnp had small but significant effects (11% decrease and 14% increase, respectively) and CNC had no effect on starch hydrolysis during simulated digestion of a 1% w/w rice starch solution. In addition, at 2% w/w CNC had no effect on amylolysis in 1% solutions of either rice, corn, or wheat starch. Similarly, absorption of glucose from digestas of starch solutions (i.e., from maltose), was unaffected by 1% w/w CNF or CNC, but was slightly increased (10%, p<0.05) by 1% Chnp, possibly due to the slightly higher maltose concentration in the Chnp-containing digestas. In contrast, all of the test materials caused sharp increases (~1.2, 1.5, and 1.6 fold for CNC, CNF, and Chnp, respectively) in absorption of glucose from starch-free digestas spiked with free glucose at a concentration corresponding to complete hydrolysis of 1% w/w starch. The potential for ingested cellulose and chitosan nanomaterials to increase glucose absorption could have important health implications. Further studies are needed to elucidate the mechanisms underlying the observed increases and to evaluate the potential glycemic effects in an intact in vivo system.

High-value utilization of the waste hydrolysate of Dioscorea zingiberensis for docosahexaenoic acid production in Schizochytrium sp

The starch saccharification liquid of Dioscorea zingiberensis tubers (SSLD) is a glucose-rich agro-industrial waste. Herein, SSLD was used as a novel potential carbon source for the biosynthesis of docosahexaenoic acid (DHA) in Schizochytrium sp. to achieve waste recycling and high-value utilization. Component analysis showed that SSLD contains abundant nutrients, such as glucose, amino acids, phenolics and flavonoids. When the total sugar concentration in SSLD was optimized to 90 g/L, the biomass and DHA yield reached 44.85 and 6.60 g/L, respectively, which were 32.1% and 36.92% higher than that at pure glucose culture condition. Fermentation characteristics and gene expression analysis showed that SSLD could remarkably improve cell antioxidant capacity, which is beneficial to scavenge intracellular reactive oxygen species and increase the gene expression of antioxidant enzymes in Schizochytrium sp. Hence, SSLD is an effective and economic carbon source for DHA production in Schizochytrium sp.

Malic enzyme 2 promotes the progression of hepatocellular carcinoma via increasing triglyceride production

The incidence and mortality of hepatocellular carcinoma (HCC) are gradually increasing during the past years. Recently, some studies have reported that malic enzyme (ME) plays an important role in cancer development, while the involvement of ME2 in HCC remains still undetermined. Here, we demonstrated that ME2 played an oncogenic role in HCC. ME2 was overexpressed in HCC tissues. TCGA database showed that the ME2 transcript level was inversely associated with the survival of HCC patients. Loss‐of‐function and gain‐of‐function assays showed that ME2 promoted HCC cell growth and migration. Furthermore, the xenografted tumorigenesis of MHCC97H cells was retarded by ME2 knockdown. ME2 silencing also suppressed the cell cycle process and induced apoptosis. Mechanistically, ME2 potentiated triglyceride synthesis, inhibition of which suppressed the proliferation and migration. We propose that ME2 promotes HCC progression by increasing triglyceride production.

Dietary citrate acutely induces insulin resistance and markers of liver inflammation in mice

Citrate is widely used as a food additive being part of virtually all processed foods. Although considered inert by most of the regulatory agencies in the world, plasma citrate has been proposed to play immunometabolic functions in multiple tissues through altering a plethora of cellular pathways. Here, we used a short-term alimentary intervention (24 hours) with standard chow supplemented with citrate in amount corresponding to that found in processed foods to evaluate its effects on glucose homeostasis and liver physiology in C57BL/6J mice. Animals supplemented with dietary citrate showed glucose intolerance and insulin resistance as revealed by glucose and insulin tolerance tests. Moreover, animals supplemented with citrate in their food displayed fed and fasted hyperinsulinemia and enhanced insulin secretion during an oral glucose tolerance test. Citrate treatment also amplified glucose-induced insulin secretion in vitro in INS1-E cells. Citrate supplemented animals had increased liver PKCα activity and altered phosphorylation at serine or threonine residues of components of insulin signaling including IRS-1, Akt, GSK-3 and FoxO1. Furthermore, citrate supplementation enhanced the hepatic expression of lipogenic genes suggesting increased de novo lipogenesis, a finding that was reproduced after citrate treatment of hepatic FAO cells. Finally, liver inflammation markers were higher in citrate supplemented animals. Overall, the results demonstrate that dietary citrate supplementation in mice causes hyperinsulinemia and insulin resistance both in vivo and in vitro, and therefore call for a note of caution on the use of citrate as a food additive given its potential role in metabolic dysregulation.

Meta-Analysis of Heifer Traits Identified Reproductive Pathways in Bos indicus Cattle

Fertility traits measured early in life define the reproductive potential of heifers. Knowledge of genetics and biology can help devise genomic selection methods to improve heifer fertility. In this study, we used ~2400 Brahman cattle to perform GWAS and multi-trait meta-analysis to determine genomic regions associated with heifer fertility. Heifer traits measured were pregnancy at first mating opportunity (PREG1, a binary trait), first conception score (FCS, score 1 to 3) and rebreeding score (REB, score 1 to 3.5). The heritability estimates were 0.17 (0.03) for PREG1, 0.11 (0.05) for FCS and 0.28 (0.05) for REB. The three traits were highly genetically correlated (0.75-0.83) as expected. Meta-analysis was performed using SNP effects estimated for each of the three traits, adjusted for standard error. We identified 1359 significant SNPs (p-value < 9.9 × 10-6 at FDR < 0.0001) in the multi-trait meta-analysis. Genomic regions of 0.5 Mb around each significant SNP from the meta-analysis were annotated to create a list of 2560 positional candidate genes. The most significant SNP was in the vicinity of a genomic region on chromosome 8, encompassing the genes SLC44A1, FSD1L, FKTN, TAL2 and TMEM38B. The genomic region in humans that contains homologs of these genes is associated with age at puberty in girls. Top significant SNPs pointed to additional fertility-related genes, again within a 0.5 Mb region, including ESR2, ITPR1, GNG2, RGS9BP, ANKRD27, TDRD12, GRM1, MTHFD1, PTGDR and NTNG1. Functional pathway enrichment analysis resulted in many positional candidate genes relating to known fertility pathways, including GnRH signaling, estrogen signaling, progesterone mediated oocyte maturation, cAMP signaling, calcium signaling, glutamatergic signaling, focal adhesion, PI3K-AKT signaling and ovarian steroidogenesis pathway. The comparison of results from this study with previous transcriptomics and proteomics studies on puberty of the same cattle breed (Brahman) but in a different population identified 392 genes in common from which some genes-BRAF, GABRA2, GABR1B, GAD1, FSHR, CNGA3, PDE10A, SNAP25, ESR2, GRIA2, ORAI1, EGFR, CHRNA5, VDAC2, ACVR2B, ORAI3, CYP11A1, GRIN2A, ATP2B3, CAMK2A, PLA2G, CAMK2D and MAPK3-are also part of the above-mentioned pathways. The biological functions of the positional candidate genes and their annotation to known pathways allowed integrating the results into a bigger picture of molecular mechanisms related to puberty in the hypothalamus-pituitary-ovarian axis. A reasonable number of genes, common between previous puberty studies and this study on early reproductive traits, corroborates the proposed molecular mechanisms. This study identified the polymorphism associated with early reproductive traits, and candidate genes that provided a visualization of the proposed mechanisms, coordinating the hypothalamic, pituitary, and ovarian functions for reproductive performance in Brahman cattle.

Metabolic Reprogramming by Reduced Calorie Intake or Pharmacological Caloric Restriction Mimetics for Improved Cancer Immunotherapy

Caloric restriction and fasting have been known for a long time for their health- and life-span promoting effects, with coherent observations in multiple model organisms as well as epidemiological and clinical studies. This holds particularly true for cancer. The health-promoting effects of caloric restriction and fasting are mediated at least partly through their cellular effects-chiefly autophagy induction-rather than reduced calorie intake per se. Interestingly, caloric restriction has a differential impact on cancer and healthy cells, due to the atypical metabolic profile of malignant tumors. Caloric restriction mimetics are non-toxic compounds able to mimic the biochemical and physiological effects of caloric restriction including autophagy induction. Caloric restriction and its mimetics induce autophagy to improve the efficacy of some cancer treatments that induce immunogenic cell death (ICD), a type of cellular demise that eventually elicits adaptive antitumor immunity. Caloric restriction and its mimetics also enhance the therapeutic efficacy of chemo-immunotherapies combining ICD-inducing agents with immune checkpoint inhibitors targeting PD-1. Collectively, preclinical data encourage the application of caloric restriction and its mimetics as an adjuvant to immunotherapies. This recommendation is subject to confirmation in additional experimental settings and in clinical trials. In this work, we review the preclinical and clinical evidence in favor of such therapeutic interventions before listing ongoing clinical trials that will shed some light on this subject.

Exploring the Role of ATP-Citrate Lyase in the Immune System

Studies over the past decade have revealed that metabolism profoundly influences immune responses. In particular, metabolism causes epigenetic regulation of gene expression, as a growing number of metabolic intermediates are substrates for histone post-translational modifications altering chromatin structure. One of these substrates is acetyl-coenzyme A (CoA), which donates an acetyl group for histone acetylation. Cytosolic acetyl-CoA is also a critical substrate for de novo synthesis of fatty acids and sterols necessary for rapid cellular growth. One of the main enzymes catalyzing cytosolic acetyl-CoA formation is ATP-citrate lyase (ACLY). In addition to its classical function in the provision of acetyl-CoA for de novo lipogenesis, ACLY contributes to epigenetic regulation through histone acetylation, which is increasingly appreciated. In this review we explore the current knowledge of ACLY and acetyl-CoA in mediating innate and adaptive immune responses. We focus on the role of ACLY in supporting de novo lipogenesis in immune cells as well as on its impact on epigenetic alterations. Moreover, we summarize alternative sources of acetyl-CoA and their contribution to metabolic and epigenetic regulation in cells of the immune system.

Polymorphisms in ovine ME1 and CA1 genes and their association with feed efficiency in Hu sheep

Improving feed efficiency would increase profitability for producers. The objective of this study was to detect the expression levels of ME1 and CA1 and the polymorphisms of ME1 and CA1 associated with the feed conversion ratio (FCR) and residual feed intake (RFI) of Hu sheep by using qRT-PCR, pooled DNA sequencing and KASPar assay. The qRT-PCR results indicated that the expression levels of ME1 and CA1 were significantly higher in the liver tissues of low-RFI sheep than in those of the high-RFI sheep (p <.01). Association analysis demonstrated that the polymorphism ME1 g.453 C > T was significantly associated with FCR and RFI (p <.05). The polymorphism CA1 g.199 C > T had a significantly associated with FCR (p <.05) and no association with RFI (p >.05). Significant differences were observed between the combined genotypes and FCR and RFI at different measurement periods (p <.05). Thus, we propose the use of these two polymorphisms as new candidate molecular markers for improving feed efficiency in sheep populations.

The Pancreatic β-Cell: The Perfect Redox System

Pancreatic β-cell insulin secretion, which responds to various secretagogues and hormonal regulations, is reviewed here, emphasizing the fundamental redox signaling by NADPH oxidase 4- (NOX4-) mediated H₂O₂ production for glucose-stimulated insulin secretion (GSIS). There is a logical summation that integrates both metabolic plus redox homeostasis because the ATP-sensitive K⁺ channel (K_ATP) can only be closed when both ATP and H₂O₂ are elevated. Otherwise ATP would block K_ATP, while H₂O₂ would activate any of the redox-sensitive nonspecific calcium channels (NSCCs), such as TRPM2. Notably, a 100%-closed K_ATP ensemble is insufficient to reach the -50 mV threshold plasma membrane depolarization required for the activation of voltage-dependent Ca²⁺ channels. Open synergic NSCCs or Cl^- channels have to act simultaneously to reach this threshold. The resulting intermittent cytosolic Ca²⁺-increases lead to the pulsatile exocytosis of insulin granule vesicles (IGVs). The incretin (e.g., GLP-1) amplification of GSIS stems from receptor signaling leading to activating the phosphorylation of TRPM channels and effects on other channels to intensify integral Ca²⁺-influx (fortified by endoplasmic reticulum Ca²⁺). ATP plus H₂O₂ are also required for branched-chain ketoacids (BCKAs); and partly for fatty acids (FAs) to secrete insulin, while BCKA or FA β-oxidation provide redox signaling from mitochondria, which proceeds by H₂O₂ diffusion or hypothetical SH relay via peroxiredoxin "redox kiss" to target proteins.

Mechanisms controlling pancreatic islet cell function in insulin secretion

Metabolic homeostasis in mammals is tightly regulated by the complementary actions of insulin and glucagon. The secretion of these hormones from pancreatic β-cells and α-cells, respectively, is controlled by metabolic, endocrine, and paracrine regulatory mechanisms and is essential for the control of blood levels of glucose. The deregulation of these mechanisms leads to various pathologies, most notably type 2 diabetes, which is driven by the combined lesions of impaired insulin action and a loss of the normal insulin secretion response to glucose. Glucose stimulates insulin secretion from β-cells in a bi-modal fashion, and new insights about the underlying mechanisms, particularly relating to the second or amplifying phase of this secretory response, have been recently gained. Other recent work highlights the importance of α-cell-produced proglucagon-derived peptides, incretin hormones from the gastrointestinal tract and other dietary components, including certain amino acids and fatty acids, in priming and potentiation of the β-cell glucose response. These advances provide a new perspective for the understanding of the β-cell failure that triggers type 2 diabetes.

Nrf2: The Master and Captain of Beta Cell Fate

Prolonged hyperglycemia is toxic to pancreatic β cells, generating excessive reactive oxygen species, defective glucose-stimulated insulin secretion, decreased insulin production, and eventually β cell death and diabetes. Nrf2 is a master regulator of cellular responses to counteract dangerous levels of oxidative stress. Maintenance of β cell mass depends on Nrf2 to promote the survival, function, and proliferation of β cells. Indeed, Nrf2 activation decreases inflammation, increases insulin sensitivity, reduces body weight, and preserves β cell mass. Therefore, numerous pharmacological activators of Nrf2 are being tested in clinical trials for the treatment of diabetes and diabetic complications. Modulating Nrf2 activity in β cells is a promising therapeutic approach for the treatment of diabetes.

NAD+ metabolism: pathophysiologic mechanisms and therapeutic potential

Nicotinamide adenine dinucleotide (NAD+) and its metabolites function as critical regulators to maintain physiologic processes, enabling the plastic cells to adapt to environmental changes including nutrient perturbation, genotoxic factors, circadian disorder, infection, inflammation and xenobiotics. These effects are mainly achieved by the driving effect of NAD+ on metabolic pathways as enzyme cofactors transferring hydrogen in oxidation-reduction reactions. Besides, multiple NAD+-dependent enzymes are involved in physiology either by post-synthesis chemical modification of DNA, RNA and proteins, or releasing second messenger cyclic ADP-ribose (cADPR) and NAADP+. Prolonged disequilibrium of NAD+ metabolism disturbs the physiological functions, resulting in diseases including metabolic diseases, cancer, aging and neurodegeneration disorder. In this review, we summarize recent advances in our understanding of the molecular mechanisms of NAD+-regulated physiological responses to stresses, the contribution of NAD+ deficiency to various diseases via manipulating cellular communication networks and the potential new avenues for therapeutic intervention.

Factors Influencing Mitochondrial Function as a Key Mediator of Glucose-Induced Insulin Release: Highlighting Nicotinamide Nucleotide Transhydrogenase

Pancreatic β-cells recognize blood glucose changes and release insulin that is a peptide hormone responsible for stable glycemia. Diabetes, a chronic disorder of insulin insufficiency, leads to disturbed glucose homeostasis and multi-organ problems. Glucose and insulin are key markers in the follow-up and control of this disease. Mitochondrial metabolism of pancreatic beta cells is a crucial part of glucose-stimulated cascade of insulin secretion. Effective factors on β-cells mitochondrial function in production of compounds such as tricarboxylic acid intermediates, glutamate, nicotinamide adenine dinucleotide phosphate, and reactive oxygen species can have great effects on the secretion of insulin under diabetes. This review enhances our knowledge of factors influencing mitochondrial function as a key mediator of glucose-induced insulin release that accordingly will be helpful to further our understanding of the mechanisms implicated in the progressive beta cell failure that results in diabetes.

Maternal Resveratrol Treatment Re-Programs and Maternal High-Fat Diet-Induced Retroperitoneal Adiposity in Male Offspring

Obesity during pregnancy increases the risk of cardiovascular problems, diabetes, asthma, and cognitive impairments, affecting the offspring. It is important to reduce the negative effects of obesity and high-fat (HF) diet during pregnancy. We employed a rat model of maternal HF diet to evaluate the possible de-programming effects of resveratrol in rodent male offspring with maternal HF diet/obesity. Male rat offspring were randomized into four groups: maternal control diet/postnatal control diet, maternal HF diet/postnatal control diet, maternal control diet plus maternal resveratrol treatment/postnatal control diet, and maternal HF diet plus maternal resveratrol treatment/postnatal control diet. Maternal HF diet during pregnancy plus lactation resulted in retroperitoneal adiposity in the male offspring. Maternal resveratrol treatment re-programmed maternal HF exposure-induced visceral adiposity. Offspring that received prenatal HF diet showed higher leptin/soluble leptin receptor (sOB-R) ratio than offspring that received prenatal control diet. Maternal resveratrol treatment ameliorated maternal HF exposure-induced increase in leptin/sOB-R ratio and altered the expression of genes for crucial fatty acid synthesis enzymes in the offspring. Thus, maternal resveratrol administration reduces retroperitoneal adiposity in rat offspring exposed to prenatal HF diet/obesity and could be used to ameliorate negative effects of maternal HF diet in the offspring.

Lipid-associated metabolic signalling networks in pancreatic beta cell function

Significant advances have been made in deciphering the mechanisms underlying fuel-stimulated insulin secretion by pancreatic beta cells. The contribution of the triggering/ATP-sensitive potassium (K_ATP)-dependent Ca²⁺ signalling and K_ATP-independent amplification pathways, that include anaplerosis and lipid signalling of glucose-stimulated insulin secretion (GSIS), are well established. A proposed model included a key role for a metabolic partitioning 'switch', the acetyl-CoA carboxylase (ACC)/malonyl-CoA/carnitine palmitoyltransferase-1 (CPT-1) axis, in beta cell glucose and fatty acid signalling for insulin secretion. This model has gained overwhelming support from a number of studies in recent years and is now refined through its link to the glycerolipid/NEFA cycle that provides lipid signals through its lipolysis arm. Furthermore, acetyl-CoA carboxylase may also control beta cell growth. Here we review the evidence supporting a role for the ACC/malonyl-CoA/CPT-1 axis in the control of GSIS and its particular importance under conditions of elevated fatty acids (e.g. fasting, excess nutrients, hyperlipidaemia and diabetes). We also document how it is linked to a more global lipid signalling system that includes the glycerolipid/NEFA cycle.

TCA Cycle Rewiring as Emerging Metabolic Signature of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a common malignancy. Despite progress in treatment, HCC is still one of the most lethal cancers. Therefore, deepening molecular mechanisms underlying HCC pathogenesis and development is required to uncover new therapeutic strategies. Metabolic reprogramming is emerging as a critical player in promoting tumor survival and proliferation to sustain increased metabolic needs of cancer cells. Among the metabolic pathways, the tricarboxylic acid (TCA) cycle is a primary route for bioenergetic, biosynthetic, and redox balance requirements of cells. In recent years, a large amount of evidence has highlighted the relevance of the TCA cycle rewiring in a variety of cancers. Indeed, aberrant gene expression of several key enzymes and changes in levels of critical metabolites have been observed in many solid human tumors. In this review, we summarize the role of the TCA cycle rewiring in HCC by reporting gene expression and activity dysregulation of enzymes relating not only to the TCA cycle but also to glutamine metabolism, malate/aspartate, and citrate/pyruvate shuttles. Regarding the transcriptional regulation, we focus on the link between NF-κB-HIF1 transcriptional factors and TCA cycle reprogramming. Finally, the potential of metabolic targets for new HCC treatments has been explored.

Mitochondrial Citrate Transport System in the Fungus Mucor circinelloides: Identification, Phylogenetic Analysis, and Expression Profiling During Growth and Lipid Accumulation

The mitochondrial citrate transport system, composed of citrate and malate transporters (MTs), can regulate the citrate efflux from mitochondria to cytosol, and then citrate is cleaved into OAA and acetyl-CoA which can be used for fatty acid (FA) biosynthesis. However, in the fungus Mucor circinelloides the molecular mechanism of citrate efflux from the mitochondria by this system and its role in FA synthesis is unclear. In the present study, we have analyzed the genome of high lipid-producing strain WJ11 and the low lipid-producing strain CBS 277.49 to find the potential genes involving in this system. Five potential genes are present in the genome of WJ11. These genes encode one citrate transport protein (CT), one tricarboxylate carrier (TCT), one MT, and two 2-oxoglutarate:malate antiporters (SoDIT-a and SoDIT-b). However, the genome of CBS 277.49 contains the same set of genes, except for the presence of just one SoDIT. The proteins from WJ11 had similar properties as their counterparts in CBS 277.49. Moreover, phylogenetic analyses revealed the evolutionary relationship of these proteins and illuminated their typical motifs related to potential functions. Additionally, the expression of these genes was analyzed to predict the possible functions in lipid metabolism in M. circinelloides. This is the first study to report the in silico analysis of structures and functions of the mitochondrial citrate transport system in M. circinelloides. This work showed a new strategy for research for the selection of candidate genes for further detailed functional investigation of the mitochondrial citrate transport system in lipid accumulation.

Integrated In Vivo Quantitative Proteomics and Nutrient Tracing Reveals Age-Related Metabolic Rewiring of Pancreatic β Cell Function

Pancreatic β cell physiology changes substantially throughout life, yet the mechanisms that drive these changes are poorly understood. Here, we performed comprehensive in vivo quantitative proteomic profiling of pancreatic islets from juvenile and 1-year-old mice. The analysis revealed striking differences in abundance of enzymes controlling glucose metabolism. We show that these changes in protein abundance are associated with higher activities of glucose metabolic enzymes involved in coupling factor generation as well as increased activity of the coupling factor-dependent amplifying pathway of insulin secretion. Nutrient tracing and targeted metabolomics demonstrated accelerated accumulation of glucose-derived metabolites and coupling factors in islets from 1-year-old mice, indicating that age-related changes in glucose metabolism contribute to improved glucose-stimulated insulin secretion with age. Together, our study provides an in-depth characterization of age-related changes in the islet proteome and establishes metabolic rewiring as an important mechanism for age-associated changes in β cell function.

Organismal age impacts fundamental aspects of β cell physiology. Wortham et al. apply proteomics and targeted metabolomics to islets from juvenile and adult mice, revealing age-related changes in metabolic enzyme abundance and production of coupling factors that enhance insulin secretion. This work provides insight into age-associated changes to the β cell.

Proteomics Recapitulates Ovarian Proteins Relevant to Puberty and Fertility in Brahman Heifers (Bos indicus L.)

High fertility and early puberty in Bos indicus heifers are desirable and genetically correlated traits in beef production. The hypothalamus-pituitary-ovarian (HPO) axis synthesizes steroid hormones, which contribute to the shift from the pre-pubertal state into the post-pubertal state and influence subsequent fertility. Understanding variations in abundance of proteins that govern steroid synthesis and ovarian signaling pathways remains crucial to understanding puberty and fertility. We used whole ovaries of six pre-pubertal and six post-pubertal Brahman heifers to conduct differential abundance analyses of protein profiles between the two physiological states. Extracted proteins were digested into peptides followed by identification and quantification with massspectrometry (MS) by sequential window acquisition of all instances of theoretical fragment ion mass spectrometry (SWATH-MS). MS and statistical analysis identified 566 significantly differentially abundant (DA) proteins (adjusted p < 0.05), which were then analyzed for gene ontology and pathway enrichment. Our data indicated an up-regulation of steroidogenic proteins contributing to progesterone synthesis at luteal phase post-puberty. Proteins related to progesterone signaling, TGF-β, retinoic acid, extracellular matrix, cytoskeleton, and pleiotrophin signaling were DA in this study. The DA proteins probably relate to the formation and function of the corpus luteum, which is only present after ovulation, post-puberty. Some DA proteins might also be related to granulosa cells signaling, which regulates oocyte maturation or arrest in ovaries prior to ovulation. Ten DA proteins were coded by genes previously associated with reproductive traits according to the animal quantitative trait loci (QTL) database. In conclusion, the DA proteins and their pathways were related to ovarian activity in Bos indicus cattle. The genes that code for these proteins may explain some known QTLs and could be targeted in future genetic studies.

Cyanidin-3-O-galactoside-enriched Aronia melanocarpa extract attenuates weight gain and adipogenic pathways in high-fat diet-induced obese C57BL/6 mice

Aronia melanocarpa are a rich source of anthocyanins that have received considerable interest for their relations to human health. In this study, the anti-adipogenic effect of cyanidin-3-O-galactoside-enriched Aronia melanocarpa extract (AM-Ex) and its underlying mechanisms were investigated in an in vivo system. Five-week-old male C57BL/6N mice were randomly divided into five groups for 8-week feeding with a control diet (CD), a high-fat diet (HFD), or a HFD with 50 (AM-Ex 50), 100 (AM-Ex 100), or 200 AM-Ex (AM-Ex 200) mg/kg body weight/day. HFD-fed mice showed a significant increase in body weight compared to the CD group, and AM-Ex dose-dependently inhibited this weight gain. AM-Ex significantly reduced the food intake and the weight of white fat tissue, including epididymal fat, retroperitoneal fat, mesenteric fat, and inguinal fat. Treatment with AM-Ex (50 to 200 mg/kg) reduced serum levels of leptin, insulin, triglyceride, total cholesterol, and low density lipoprotein (LDL)-cholesterol. Real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that AM-Ex suppressed adipogenesis by decreasing CCAAT/enhancer binding protein α, peroxisome proliferator-activated receptor γ, sterol regulatory element-binding protein-1c, peroxisome proliferator-activated receptor gamma coactivator-1α, acetyl-CoA carboxylase 1, ATP-citrate lyase, fatty acid synthase, and adipocyte protein 2 messenger RNA (mRNA) expressions. These results suggest that AM-Ex is potentially beneficial for the suppression of HFD-induced obesity by modulating multiple pathways associated with adipogenesis and food intake.

The pivotal role of protein acetylation in linking glucose and fatty acid metabolism to β-cell function

Protein acetylation has a crucial role in energy metabolism. Here we performed the first large-scale profiling of acetylome in rat islets, showing that almost all enzymes in core metabolic pathways related to insulin secretion were acetylated. Label-free quantitative acetylome of islets in response to high glucose revealed hyperacetylation of enzymes involved in fatty acid β-oxidation (FAO), including trifunctional enzyme subunit alpha (ECHA). Acetylation decreased the protein stability of ECHA and its ability to promote FAO. The overexpression of SIRT3, a major mitochondrial deacetylase, prevented the degradation of ECHA via decreasing its acetylation level in β-cells. SIRT3 expression was upregulated in rat islets upon exposure to low glucose or fasting. SIRT3 overexpression in islets markedly decreased palmitate-potentiated insulin secretion, whereas islets from SIRT3 knockout mice secreted more insulin, with an opposite action on FAO. ECHA overexpression partially reversed SIRT3 deficiency-elicited insulin hypersecretion. Our study highlights the potential role of protein acetylation in insulin secretion.

Postprandial metabolomics: GC-MS analysis reveals differences in organic acid profiles of impaired fasting glucose individuals in response to highland barley loads

The HB load producing low postprandial glucose and insulin responses brings about several alterations in organic acids.

Effects of a High-Fat Diet on Adipose Tissue CD8+ T Cells in Young vs. Adult Mice

T cells are involved in chronic inflammation of adipose tissue in obese conditions. However, the impact of age on the adipose T cells remains unknown. In this study, we investigated T cells in the white adipose tissue of young and adult mice. Obesity was induced in the mice using a high-fat diet (HFD) for 14 weeks. The young mice were fed an HFD at 3 weeks old, and adult mice were fed the HFD at 12 weeks old. Relative to adult mice, the young mice gained less fat and exhibited better glucose tolerance. Their adipose tissue contained more CD8+ T cells and higher levels of pro-inflammatory cytokines. Young mice showed a larger increase in CD4+ T cells. The young and adult mice showed similar insulin tolerance. HFD reduced the colon muscle layer, which was more obvious in the young mice. These data suggested that young and adult mice exhibit different responses to an HFD in terms of adipose tissue, glucose tolerance, and the colon muscle layer. The increase in CD8+ T cells and CD4+ T cells, together with higher levels of pro-inflammatory cytokines, suggested elevated inflammation in the presence of less fat gain in the young mice, which was unexpected. The significance of this inflammation remains unknown. We propose that inflammation might inhibit energy storage in the adipose tissue to provide more energy to the lean body mass in favor of growth in the young mice. The present study provides another example of the beneficial effect of inflammation in physiological conditions.

Integrated analysis of the gene expression profile and DNA methylation profile of obese patients with type 2 diabetes

In order to better understand the etiology of obese type 2 diabetes (T2D) at the molecular level, the present study investigated the gene expression and DNA methylation profiles associated with T2D via systemic analysis. Gene expression (GSE64998) and DNA methylation profiles (GSE65057) from liver tissues of healthy controls and obese patients with T2D were downloaded from the Gene Expression Omnibus database. Differentially-expressed genes (DEGs) and differentially-methylated genes (DMGs) were identified using the Limma package, and their overlapping genes were additionally determined. Enrichment analysis was performed using the BioCloud platform on the DEGs and the overlapping genes. Using Cytoscape software, protein-protein interaction (PPI), transcription factor target networks and microRNA (miRNA) target networks were then constructed in order to determine associated hub genes. In addition, a further GSE15653 dataset was utilized in order to validate the DEGs identified in the GSE64998 dataset analyses. A total of 251 DEGs, including 124 upregulated and 127 downregulated genes, were detected, and a total of 9,698 genes were demonstrated to be differentially methylated in obese patients with T2D compared with non-obese healthy controls. A total of 103 overlapping genes between the two datasets were revealed, including 47 upregulated genes and 56 downregulated genes. The identified overlapping genes were revealed to be strongly associated with fatty acid and glucose metabolic pathways, in addition to oxidation/reduction. The overlapping genes cyclin D1 (CCND1), PPARG coactivator α (PPARGC1A), fatty acid synthase (FASN), glucokinase (GCK), steraroyl-coA desaturase (SCD) and tyrosine aminotransferase (TAT) had higher degrees in the PPI, transcription target networks and miRNA target networks. In addition, among the 251 DEGs, a total of 35 DEGs were validated to be being shared genes between the datasets, which included a number of key genes in the PPI network, including CCND1, FASN and TAT. Abnormal gene expression and DNA methylation patterns that were implicated in fatty acid and glucose metabolic pathways and oxidation/reduction reactions were detected in obese patients with T2D. Furthermore, the CCND1, PPARGC1A, FANS, GCK, SCD and TAT genes may serve a role in the development of obesity-associated T2D.

Targeting ATP-Citrate Lyase in Hyperlipidemia and Metabolic Disorders

Chronic overnutrition and a sedentary lifestyle promote imbalances in metabolism, often manifesting as risk factors for life-threating diseases such as atherosclerotic cardiovascular disease (ASCVD) and nonalcoholic fatty liver disease (NAFLD). Nucleocytosolic acetyl-coenzyme A (CoA) has emerged as a central signaling node used to coordinate metabolic adaptations in response to a changing nutritional status. ATP-citrate lyase (ACL) is the enzyme primarily responsible for the production of extramitochondrial acetyl-CoA and is thus strategically positioned at the intersection of nutrient catabolism and lipid biosynthesis. Here, we discuss recent findings from preclinical studies, as well as Mendelian and clinical randomized trials, demonstrating the importance of ACL activity in metabolism, and supporting its inhibition as a potential therapeutic approach to treating ASCVD, NAFLD, and other metabolic disorders.

Protein malnutrition blunts the increment of taurine transporter expression by a high-fat diet and impairs taurine reestablishment of insulin secretion

Taurine (Tau) restores β-cell function in obesity; however, its action is lost in malnourished obese rodents. Here, we investigated the mechanisms involved in the lack of effects of Tau in this model. C57BL/6 mice were fed a control diet (CD) (14% protein) or a protein-restricted diet (RD) (6% protein) for 6 wk. Afterward, mice received a high-fat diet (HFD) for 8 wk [CD + HFD (CH) and RD + HFD (RH)] with or without 5% Tau supplementation after weaning on their drinking water [CH + Tau (CHT) and RH + Tau (RHT)]. The HFD increased insulin secretion through mitochondrial metabolism in CH and RH. Tau prevented all those alterations in CHT only. The expression of the taurine transporter (Tau-T), as well as Tau content in pancreatic islets, was increased in CH but had no effect on RH. Protein malnutrition programs β cells and impairs Tau-induced restoration of mitochondrial metabolism and biogenesis. This may be associated with modulation of the expression of Tau-T in pancreatic islets, which may be responsible for the absence of effect of Tau in protein-malnourished obese mice.-Branco, R. C. S., Camargo, R. L., Batista, T. M., Vettorazzi, J. F., Borck, P. C., dos Santos-Silva, J. C. R., Boschero, A. C., Zoppi, C. C., Carneiro, E. M. Protein malnutrition blunts the increment of taurine transporter expression by a high-fat diet and impairs taurine reestablishment of insulin secretion.

The Pancreatic β-Cell: A Bioenergetic Perspective

The pancreatic β-cell secretes insulin in response to elevated plasma glucose. This review applies an external bioenergetic critique to the central processes of glucose-stimulated insulin secretion, including glycolytic and mitochondrial metabolism, the cytosolic adenine nucleotide pool, and its interaction with plasma membrane ion channels. The control mechanisms responsible for the unique responsiveness of the cell to glucose availability are discussed from bioenergetic and metabolic control standpoints. The concept of coupling factor facilitation of secretion is critiqued, and an attempt is made to unravel the bioenergetic basis of the oscillatory mechanisms controlling secretion. The need to consider the physiological constraints operating in the intact cell is emphasized throughout. The aim is to provide a coherent pathway through an extensive, complex, and sometimes bewildering literature, particularly for those unfamiliar with the field.

ATP-citrate lyase: genetics, molecular biology and therapeutic target for dyslipidemia

PURPOSE OF REVIEW

ATP-citrate lyase (ACLY) has re-emerged as a drug target for LDL cholesterol (LDL-C) lowering. We review ACLY as a therapeutic strategy, its genetics, its molecular and cellular biology, and also its inhibition.

RECENT FINDINGS

ACLY is a critical enzyme linking glucose catabolism to lipogenesis by providing acetyl-CoA from mitochondrial citrate for fatty acid and cholesterol biosynthesis. Human genetic variants have been associated with enhanced growth and survival of several cancers, and with attenuated plasma triglyceride responses to dietary fish oil. In mice, liver-specific Acly deficiency protects from hepatic steatosis and dyslipidemia, whereas adipose tissue-specific Acly deletion has no phenotype, supporting therapeutic inhibition of ACLY. A lipid-regulating compound, bempedoic acid, was discovered to potently inhibit ACLY, and in animal models, it prevents dyslipidemia and attenuates atherosclerosis. Phase 2 clinical trials revealed that bempedoic acid effectively lowers LDL-C as monotherapy, combined with ezetimibe, added to statin therapy and in statin-intolerant hypercholesterolemic patients.

SUMMARY

The efficacy of bempedoic acid as an LDL-C-lowering agent has validated ACLY inhibition as a therapeutic strategy. Positive results of phase 3 patient studies, together with long-term cardiovascular disease outcome trials, are required to establish ACLY as a major new target in cardiovascular medicine.

STAT3 Undergoes Acetylation-dependent Mitochondrial Translocation to Regulate Pyruvate Metabolism

Cytoplasmic STAT3, after activation by growth factors, translocates to different subcellular compartments, including nuclei and mitochondria, where it carries out different biological functions. However, the precise mechanism by which STAT3 undergoes mitochondrial translocation and subsequently regulates the tricarboxylic acid (TCA) cycle-electron transport chain (ETC) remains poorly understood. Here, we clarify this process by visualizing STAT3 acetylation in starved cells after serum reintroduction or insulin stimulation. CBP-acetylated STAT3 undergoes mitochondrial translocation in response to serum introduction or insulin stimulation. In mitochondria, STAT3 associates with the pyruvate dehydrogenase complex E1 (PDC-E1) and subsequently accelerates the conversion of pyruvate to acetyl-CoA, elevates the mitochondrial membrane potential, and promotes ATP synthesis. SIRT5 deacetylates STAT3, thereby inhibiting its function in mitochondrial pyruvate metabolism. In the A549 lung cancer cell line, constitutively acetylated STAT3 localizes to mitochondria, where it maintains the mitochondrial membrane potential and ATP synthesis in an active state.

Toward Connecting Metabolism to the Exocytotic Site

Within cells the regulated exocytosis of secretory granules controls multiple physiological functions, including endocrine hormone secretion. Release of the glucose-regulating hormone insulin from pancreatic islet β cells is critical for whole-body metabolic homeostasis. Impaired insulin secretion appears early in the progression to type 2 diabetes (T2D). Key mechanisms that control the β-cell exocytotic response, mediating the long-known but little understood metabolic amplification of insulin secretion, are becoming clearer. Recent insights indicate a convergence of metabolism-driven signals, such as lipid-derived messengers and redox-dependent deSUMOylation, at the plasma membrane to augment Ca²⁺-dependent insulin exocytosis. These pathways have important implications for the metabolic control of hormone secretion, for the functional compensation that occurs in obesity, and for impaired insulin secretion in diabetes.