PEPCK-M expression in mouse liver potentiates, not replaces, PEPCK-C mediated gluconeogenesis

The structural characteristics, beneficial effects and biological mechanisms of food and medicinal plant polysaccharides on exercise-induced fatigue: A review

Exercise-induced fatigue is a common non-pathological condition as a result of excessive or exhaustive sport exercise, and its effective alleviation is essential for optimal sport performance. The use of polysaccharides extracted from food and medicinal plants has been increasingly recognized for their efficacy in relieving exercise-induced fatigue, owing to their remarkable effects and lack of side effects as supplements. Through a comprehensive analysis of nearly two decades of research, we have identified that polysaccharides derived from food and medicinal plants exhibit anti-fatigue properties primarily through antioxidant mechanisms, modulation of immune responses, regulation of gut microbiota, and the regulation of metabolic processes-often involving a combination of these factors. Importantly, the anti-fatigue effects and mechanisms of action are strongly dependent on their molecular composition structural characteristics, molecular weight, and other physiochemical properties. This article aims to provide an up-to-date and systematic review of the beneficial effects and underlying biological mechanisms for alleviation of exercise-induced fatigue and the molecular properties of dietary and medicinal plant polysaccharides. The ultimate goal is to establish a more robust theoretical foundation and identify the potential structural modifications of food and medicinal plant polysaccharides in mitigating exercise-induced fatigue.

The neglected PCK1/glucagon (inter)action in nutrient homeostasis beyond gluconeogenesis: Disease pathogenesis and treatment

BACKGROUND

Glucagon plays a central role in hepatic adaptation during fasting, with the upregulation of hepatic phosphoenolpyruvate carboxykinase 1 (PCK1) traditionally associated with increased gluconeogenesis. However, recent experimental models and clinical studies have challenged this view, suggesting a more complex interplay between PCK1 and glucagon, which extends beyond gluconeogenesis and has broader implications for metabolic regulation in health and disease.

SCOPE OF REVIEW

This review provides a comprehensive overview of the current evidence on the multifaceted roles of PCK1 in glucagon-dependent hepatic adaptation during fasting, which is crucial for maintaining systemic homeostasis not only of glucose, but also of lipids and amino acids. We explore the relationship between PCK1 deficiency and glucagon resistance in metabolic disorders, including inherited PCK1 deficiency and metabolic dysfunction-associated steatotic liver disease (MASLD), and compare findings from experimental animal models with whole-body or tissue-specific ablation of PCK1 or the glucagon receptor. We propose new research platforms to advance the therapeutic potential of targeting PCK1 in metabolic diseases.

MAJOR CONCLUSIONS

We propose that hepatic PCK1 deficiency might be an acquired metabolic disorder linking alterations in lipid metabolism with impaired glucagon signaling. Our findings highlight interesting links between glycerol, PCK1 deficiency, elevated plasma alanine levels and glucagon resistance. We conclude that the roles of PCK1 and glucagon in metabolic regulation are more complex than previously assumed. In this (un)expected scenario, hepatic PCK1 deficiency and glucagon resistance appear to exert limited control over glycemia, but have broader metabolic effects related to lipid and amino acid dysregulation. Given the shift in glucagon research from receptor inhibition to activation, we propose that a similar paradigm shift is needed in the study of hepatic PCK1. Understanding PCK1 expression and activity in the glucagon-dependent hepatic adaptation to fasting might provide new perspectives and therapeutic opportunities for metabolic diseases.

Cytosolic PEPCK deficiency caused by a novel homozygous frame-shift variant presenting as resolved hypoglycemia and acute liver failure at birth

Cytosolic phosphoenolpyruvate carboxykinase (PEPCK) is an enzyme encoded by the PCK1 gene and plays a rate limiting step in gluconeogenesis occurring mainly in the liver during prolonged fasting. Biallelic deficiency of this enzyme results in a rare inborn error of metabolism disorder (OMIM # 261680). The main clinical and laboratory manifestations include fasting hypoglycemia and lactic acidosis with urinary excretion of Tricarboxylic Acid (TCA) cycles metabolites, particularly fumarate. The initial presentation varies between individuals in terms of age at initial presentation and clinical manifestations, however clinical information is lacking as it was diagnosed so far in less than 30 patients with a total of 6 different mutations which are all either missense or splice variants. We describe the first homozygous frame-shift mutation in the PCK1 gene, leading to cytosolic PEPCK deficiency. This resulted in transient hypoglycemia and acute liver failure with extreme hyperferritinemia (>40,000 ng/ml) during the first days of life. This severe very early-onset presentation that was not described earlier expands our clinical and genetic spectrum of this rare metabolic disorder.

Integration of metabolomic and transcriptomic analyses reveals regulatory functions of the ChREBP transcription factor in energy metabolism

The transcription factor carbohydrate response element binding protein (ChREBP) activates genes of glucose, fructose, and lipid metabolism in response to carbohydrate feeding. Integrated transcriptomic and metabolomic analyses in rats with GalNac-siRNA-mediated suppression of ChREBP expression in liver reveal other ChREBP functions. GalNac-siChREBP treatment reduces expression of genes involved in coenzyme A (CoA) biosynthesis, with lowering of CoA and short-chain acyl-CoA levels. Despite suppression of pyruvate kinase, pyruvate levels are maintained, possibly via increased expression of pyruvate and amino acid transporters. In addition, expression of multiple anaplerotic enzymes is decreased by GalNac-siChREBP treatment, affecting TCA cycle intermediates. Finally, GalNAc-siChREBP treatment suppresses late steps in purine and NAD synthesis, with increases in precursors and lowering of end products in both pathways. In sum, our study reveals functions of ChREBP beyond its canonical roles in carbohydrate and lipid metabolism to include regulation of substrate transport, mitochondrial function, and energy balance.

Porcine reproductive and respiratory syndrome virus activates lipid synthesis through a ROS-dependent AKT/PCK1/INSIG/SREBPs axis

The porcine reproductive and respiratory syndrome virus (PRRSV) is a highly contagious pathogen in pigs. This study aimed to investigate the impact of PRRSV infection on cellular metabolism, particularly focusing on lipid metabolism to understand its role in promoting viral replication. We conducted a metabolic analysis on MARC-145 cells before and after PRRSV infection. Our results demonstrated that the most significant alterations in cellular metabolism, accounting for 40.8 % of total changes, were related to lipid metabolism. These changes were primarily driven by the activation of sterol regulatory-element binding proteins (SREBPs), critical regulators of lipid biosynthesis. To understand the mechanisms behind SREBPs activation by PRRSV, we investigated the involvement of upstream effectors, specifically protein kinase B (AKT) and phosphoenolpyruvate carboxykinase 1 (PCK1). Our findings indicated that PRRSV infection triggered AKT activation, leading to the subsequent activation of PCK1. Activated PCK1 then phosphorylated insulin-induced genes (INSIGs), resulting in their degradation. This degradation facilitated the translocation of SREBPs from the endoplasmic reticulum to the nucleus. Additionally, we observed that PRRSV infection stimulated the production of reactive oxygen species (ROS), which played a critical role in activating AKT. Collectively, our findings demonstrate that PRRSV enhances lipid synthesis through a ROS-dependent AKT/PCK1/INSIG/SREBPs signaling axis, which provides new insights into the metabolic strategies employed by PRRSV.

Distinct metabolic responses to thermal stress between invasive freshwater turtle Trachemys scripta elegans and native freshwater turtles in China

Different responses or tolerance to thermal stress between invasive and native species can affect the outcome of interactions between climate change and biological invasion. However, knowledge about the physiological mechanisms that modulate the interspecific differences in thermal tolerance is limited. The present study analyzes the metabolic responses to thermal stress by the globally invasive turtle, Trachemys scripta elegans, as compared with two co-occurring native turtle species in China, Pelodiscus sinensis and Mauremys reevesii. Changes in metabolite contents and the expression or enzyme activities of genes involved in energy sensing, glucose metabolism, lipid metabolism, and tricarboxylic acid (TCA) cycle after exposure to gradient temperatures were assessed in turtle juveniles. Invasive and native turtles showed distinct metabolic responses to thermal stress. T. scripta elegans showed greater transcriptional regulation of energy sensors than the native turtles. Enhanced anaerobic metabolism was needed by all three species under extreme heat conditions, but phosphoenolpyruvate carboxykinase and lactate dehydrogenase in the invader showed stronger upregulation or stable responses than the native species, which showed inhibition by high temperatures. These contrasts were pronounced in the muscles of the three species. Regulation of lipid metabolism was observed in both T. scripta elegans and P. sinensis but not in M. reevesii under thermal stress. Thermal stress did not inhibit the TCA cycle in turtles. Different metabolic responses to thermal stress may contribute to interspecific differences in thermal tolerance. Overall, our study further suggested the potential role of physiological differences in mediating interactions between climate change and biological invasion.

A Flavonoid Concentrate from Moringa Oleifera Lam. Leaves Extends Exhaustive Swimming Time by Improving Energy Metabolism and Antioxidant Capacity in Mice

Moringa oleifera Lam. leaves contain various nutrients and bioactive compounds. The present study aimed to assess the anti-fatigue capacity of a flavonoids concentrate purified from M. oleifera Lam. leaves. The total flavonoids in the purified extract were analyzed by ultra-performance liquid chromatography electrospray ionization tandem mass spectrometry (UPLC-MS/MS). The mice were supplemented with purified M. oleifera Lam. leaf flavonoid-rich extract (MLFE) for 14 days. The weight-loaded forced swimming test was used for evaluating exercise endurance. The 90-min non-weight-bearing swimming test was carried out to assess biochemical biomarkers correlated to fatigue and energy metabolism. UPLC-MS/MS analysis identified 83 flavonoids from MLFE. MLFE significantly increased the swimming time by 60%. Serum lactate (9.9 ± 0.9 vs. 8.9 ± 0.7), blood urea nitrogen (BUN) (8.8 ± 0.8 vs. 7.2 ± 0.5), and nonesterified fatty acid (NEFA) (2.4 ± 0.2 vs. 1.7 ± 0.3) were significantly elevated; phosphoenolpyruvate carboxykinase (PEPCK), glucokinase (GCK), and nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA expression were significantly downregulated; and heme oxygenase 1 mRNA expression was significantly upregulated in muscle after swimming. MLFE supplement significantly decreased serum lactate (8.0 ± 1.0 vs. 9.9 ± 0.9), BUN (8.6 ± 0.4 vs. 8.9 ± 0.8), and NEFA (2.3 ± 0.4 vs. 2.4 ± 0.2) and increased the protein and mRNA expression of GCK, PEPCK, and Nrf2. The enhancement of glucose metabolism and antioxidant function by MLFE contributes partly to its anti-fatigue action.

Mitochondrial heterogeneity and adaptations to cellular needs

Although it is well described that mitochondria are at the epicentre of the energy demands of a cell, it is becoming important to consider how each cell tailors its mitochondrial composition and functions to suit its particular needs beyond ATP production. Here we provide insight into mitochondrial heterogeneity throughout development as well as in tissues with specific energy demands and discuss how mitochondrial malleability contributes to cell fate determination and tissue remodelling.

Effect of chronic noise exposure on glucose and lipid metabolism in mice via modulating gut microbiota and regulating CREB/CRTC2 and SREBP1/SCD pathway

Chronic noise exposure is correlated with gut microbiota dysbiosis and glucose and lipid metabolism disorders. However, evidence on the mechanisms underlying of gut microbiota alterations in chronic noise induced glucose and lipid metabolism disorders is limited, and the potential aftereffects of chronic noise exposure on metabolic disorders remain unclear. In present study, we established chronic daytime and nighttime noise exposure mice models to explore the effects and underlying mechanism of gut microbiota on chronic noise-induced glucose and lipid metabolism disorders. The results showed that exposure to chronic daytime or nighttime noise significantly increased the fasting blood glucose, serum and liver TG levels, impaired glucose tolerance, and decreased serum HDL-C levels and liver TC levels in mice. However, after 4 weeks of recovery, only serum TG of mice in nighttime noise recovery group remained elevated. Besides, exposure to chronic noise reduced the intestinal tight junction protein levels and increased intestinal permeability, while this effect did not completely dissipate even after the recovery period. Moreover, chronic noise exposure changed the gut microbiota and significantly regulated metabolites and metabolic pathways, and further activate hepatic gluconeogenesis CRTC2/CREB-PCK1 signaling pathway and lipid synthesis SREBP1/SCD signaling pathway through intestinal hepatic axis. Together, our findings demonstrated that chronic daytime and nighttime noise exposure could cause the glucose and lipid metabolism disorder by modulating the gut microbiota and serum metabolites, and activating hepatic gluconeogenic CREB/CRTC2-PCK1 signaling and lipid synthesis SREBP1/SCD signaling pathway. The potential aftereffects of noise exposure during wakefulness on metabolic disorders are more significant than that of noise exposure during sleep.

An integrative view on glucagon function and putative role in the progression of pancreatic neuroendocrine tumours (pNETs) and hepatocellular carcinomas (HCC)

Cancer metabolism research area evolved greatly, however, is still unknown the impact of systemic metabolism control and diet on cancer. It makes sense that systemic regulators of metabolism can act directly on cancer cells and activate signalling, prompting metabolic remodelling needed to sustain cancer cell survival, tumour growth and disease progression. In the present review, we describe the main glucagon functions in the control of glycaemia and of metabolic pathways overall. Furthermore, an integrative view on how glucagon and related signalling pathways can contribute for pancreatic neuroendocrine tumours (pNETs) and hepatocellular carcinomas (HCC) progression, since pancreas and liver are the major organs exposed to higher levels of glucagon, pancreas as a producer and liver as a scavenger. The main objective is to bring to discussion some glucagon-dependent mechanisms by presenting an integrative view on microenvironmental and systemic aspects in pNETs and HCC biology.

Interactions between innate immunity and insulin signaling affect resistance to infection in insects

An active immune response is energetically demanding and requires reallocation of nutrients to support resistance to and tolerance of infection. Insulin signaling is a critical global regulator of metabolism and whole-body homeostasis in response to nutrient availability and energetic needs, including those required for mobilization of energy in support of the immune system. In this review, we share findings that demonstrate interactions between innate immune activity and insulin signaling primarily in the insect model Drosophila melanogaster as well as other insects like Bombyx mori and Anopheles mosquitos. These studies indicate that insulin signaling and innate immune activation have reciprocal effects on each other, but that those effects vary depending on the type of pathogen, route of infection, and nutritional status of the host. Future research will be required to further understand the detailed mechanisms by which innate immunity and insulin signaling activity impact each other.

Measurement of gluconeogenesis by 2H2O labeling and mass isotopomer distribution analysis

The gluconeogenesis pathway, which converts nonsugar molecules into glucose, is critical for maintaining glucose homeostasis. Techniques that measure flux through this pathway are invaluable for studying metabolic diseases such as diabetes that are associated with dysregulation of this pathway. We introduce a new method that measures fractional gluconeogenesis by heavy water labeling and gas chromatographic-mass spectrometric analysis. This technique circumvents cumbersome benchwork or inference of positionality from mass spectra. The enrichment and pattern of deuterium label on glucose is quantified by use of mass isotopomer distribution analysis, which informs on how much of glucose-6-phosphate-derived glucose comes from the gluconeogenesis (GNG) pathway. We use an in vivo model of the GNG pathway that is based on previously published models but offers a new approach to calculating GNG pathway and subpathway contributions using combinatorial probabilities. We demonstrated that this method accurately quantifies fractional GNG through experiments that perturb flux through the pathway and by probing analytical sensitivity. While this method was developed in mice, the results suggest that it is translatable to humans in a clinical setting.

Integrated Transcriptomic and Metabolomic Analyses Reveal Low-Temperature Tolerance Mechanism in Giant Freshwater Prawn Macrobrachium rosenbergii

Water temperature, as an important environmental factor, affects the growth and metabolism of aquatic animals and even their survival. The giant freshwater prawn (GFP) Macrobrachium rosenbergii is a kind of warm-water species, and its survival temperature ranges from 18 °C to 34 °C. In this study, we performed transcriptomic and metabolomic analyses to clarify the potential molecular mechanism of responding to low-temperature stress in adult GFP. The treatments with low-temperature stress showed that the lowest lethal temperature of the GFP was 12.3 °C. KEGG enrichment analyses revealed that the differentially expressed genes and metabolites were both enriched in lipid and energy metabolism pathways. Some key genes, such as phosphoenolpyruvate carboxykinase and fatty acid synthase, as well as the content of the metabolites dodecanoic acid and alpha-linolenic acid, were altered under low-temperature stress. Importantly, the levels of unsaturated fatty acids were decreased in LS (low-temperature sensitive group) vs. Con (control group). In LT (low-temperature tolerant group) vs. Con, the genes related to fatty acid synthesis and degradation were upregulated to cope with low-temperature stress. It suggested that the genes and metabolites associated with lipid metabolism and energy metabolism play vital roles in responding to low-temperature stress. This study provided a molecular basis for the selection of a low-temperature tolerant strain.

Application of multi-omics combined with bioinformatics techniques to assess salinity stress response and tolerance mechanisms of Pacific oyster (Crassostrea gigas) during depuration

Depuration is a vital stage to ensure the safety of oyster consumption, and salinity had a great impact on the environmental adaptability of oysters, but the underlying molecular mechanism was poorly understood during depuration stage. Here, Crassostrea gigas was depurated for 72 h at different salinity (26, 29, 32, 35, 38 g/L, corresponding to ±20%, ±10% salinity fluctuation away from oyster's production area) and then analyzed by using transcriptome, proteome, and metabolome combined with bioinformatics techniques. The transcriptome showed that the salinity stress led to 3185 differentially expressed genes and mainly enriched in amino acid metabolism, carbohydrate metabolism, lipid metabolism, etc. A total of 464 differentially expressed proteins were screened by the proteome, and the number of up-regulated expression proteins was less than the down-regulated, indicating that the salinity stress would affect the regulation of metabolism and immunity in oysters. 248 metabolites significantly changed in response to depuration salinity stress in oysters, including phosphate organic acids and their derivatives, lipids, etc. The results of integrated omics analysis indicated that the depuration salinity stress induced abnormal metabolism of the citrate cycle (TCA cycle), lipid metabolism, glycolysis, nucleotide metabolism, ribosome, ATP-binding cassette (ABC) transport pathway, etc. By contrast with Pro-depuration, more radical responses were observed in the S38 group. Based on the results, we suggested that the 10% salinity fluctuation was suitable for oyster depuration and the combination of multi-omics analysis could provide a new perspective for the analysis of the mechanism changes.

The ancient CgPEPCK-1, not CgPECK-2, evolved into a multifunctional molecule as an intracellular enzyme and extracellular PRR

Phosphoenolpyruvate carboxykinase (PEPCK) is a well-known lyase involved in gluconeogenesis, while their evolution and function differentiation have not been fully understood. In this study, by constructing a phylogenetic tree to examine PEPCKs throughout the evolution from poriferans to vertebrates, Mollusk was highlighted as the only phylum to exhibit two distinct lineages, Mollusca_PEPCK-1 and Mollusca_PEPCK-2. Further study of two representative members from Crassostrea gigas (CgPEPCK-1 and CgPEPCK-2) showed that they both shared conserved sequences and structural characteristics of the catalytic enzyme, while CgPEPCK-2 displayed a higher expression level than CgPEPCK-1 in all tested tissues, and CgPEPCK-1 was specifically implicated in the immune defense against LPS stimulation and Vibrio splendidus infection. Functional analysis revealed that CgPEPCK-2 had stronger enzymatic activity than CgPEPCK-1, while CgPEPCK-1 exhibited stronger binding activity with various PAMPs, and only the protein of CgPEPCK-1 increased significantly in hemolymph during immune stimulation. All results supported that distinct sequence and function differentiations of the PEPCK gene family should have occurred since Mollusk. The more advanced evolutionary branch Mollusca_PEPCK-2 should preserve its essential function as a catalytic enzyme to be more specialized and efficient, while the ancient branch Mollusca_PEPCK-1 probably contained some members, such as CgPEPCK-1, that should be integrated into the immune system as an extracellular immune recognition receptor.

Deficiency of gluconeogenic enzyme PCK1 promotes metabolic-associated fatty liver disease through PI3K/AKT/PDGF axis activation in male mice

Metabolic associated fatty liver disease (MAFLD) encompasses a broad spectrum of hepatic disorders, including steatosis, nonalcoholic steatohepatitis (NASH) and fibrosis. We demonstrated that phosphoenolpyruvate carboxykinase 1 (PCK1) plays a central role in MAFLD progression. Male mice with liver Pck1 deficiency fed a normal diet displayed hepatic lipid disorder and liver injury, whereas fibrosis and inflammation were aggravated in mice fed a high-fat diet with drinking water containing fructose and glucose (HFCD-HF/G). Forced expression of hepatic PCK1 by adeno-associated virus ameliorated MAFLD in male mice. PCK1 deficiency stimulated lipogenic gene expression and lipid synthesis. Moreover, loss of hepatic PCK1 activated the RhoA/PI3K/AKT pathway by increasing intracellular GTP levels, increasing secretion of platelet-derived growth factor-AA (PDGF-AA), and promoting hepatic stellate cell activation. Treatment with RhoA and AKT inhibitors or gene silencing of RhoA or AKT1 alleviated MAFLD progression in vivo. Hepatic PCK1 deficiency may be important in hepatic steatosis and fibrosis development through paracrine secretion of PDGF-AA in male mice, highlighting a potential therapeutic strategy for MAFLD.

Changes in life history parameters and transcriptome profile of Serangium japonicum associated with feeding on natural prey (Bemisia tabaci) and alternate host (Corcyra cephalonica eggs)

BACKGROUND

The mass production of natural predators with prolonged shelf life is a prerequisite for their field application as pest control agents. The traditional methods used for the mass production of Serangium japonicum rely heavily on the consistent supply of natural prey. This study explains the effects of B. tabaci (natural prey) and C. cephalonica eggs (alternative food) on life history and transcriptome profile of S. japanicum.

METHODS

This study compares the effects of B. tabaci (natural prey) and C. cephalonica eggs (alternative food) on biology, reproduction, and predatory efficacy, and transcriptome profile of S. japanicum.

RESULTS

This study revealed that S. japonicum was able to successfully complete its life cycle while feeding on B. tabaci (natural prey) and C. cephalonica eggs (alternative food). The C. cephalonica eggs fed S. japonicum individuals had longer developmental period and lower fecundity as compared to those feeding on whitefly but the survival rates (3rd instar nymphs, 4th instar nymphs and pupae) and predatory efficacy of C. cephalonica eggs fed S. japonicum individuals were significantly similar to to those feeding on whitefly.Transcriptome analysis showed that when faced with dietary changes, S. japanicum could successfully feed on C. cephalonica eggs by regulating genes related to nutrient transport, metabolism, and detoxification. Moreover, S. japanicum degraded excess cellular components through ribosomal autophagy and apoptosis, which provided sufficient materials and energy for survival and basic metabolism.

CONCLUSION

Corcyra cephalonica eggs can be used as an alternate host for the predator, Serangium japonicum, as the survival rates and predatory efficacy of the predator are similar to those feeding on the natural host (B.tabaci). When faced with dietary changes, S. japanicum could successfully feed on C. cephalonica eggs as revealed by upregulation of genes related to nutrient transport, metabolism, and detoxification. These findings are of great significance for studying the functional evolution of S. japonicum in response to dietary changes.

The SLC25A47 locus controls gluconeogenesis and energy expenditure

Mitochondria provide essential metabolites and adenosine triphosphate (ATP) for the regulation of energy homeostasis. For instance, liver mitochondria are a vital source of gluconeogenic precursors under a fasted state. However, the regulatory mechanisms at the level of mitochondrial membrane transport are not fully understood. Here, we report that a liver-specific mitochondrial inner-membrane carrier SLC25A47 is required for hepatic gluconeogenesis and energy homeostasis. Genome-wide association studies found significant associations between SLC25A47 and fasting glucose, HbA1c, and cholesterol levels in humans. In mice, we demonstrated that liver-specific depletion of SLC25A47 impaired hepatic gluconeogenesis selectively from lactate, while significantly enhancing whole-body energy expenditure and the hepatic expression of FGF21. These metabolic changes were not a consequence of general liver dysfunction because acute SLC25A47 depletion in adult mice was sufficient to enhance hepatic FGF21 production, pyruvate tolerance, and insulin tolerance independent of liver damage and mitochondrial dysfunction. Mechanistically, SLC25A47 depletion leads to impaired hepatic pyruvate flux and malate accumulation in the mitochondria, thereby restricting hepatic gluconeogenesis. Together, the present study identified a crucial node in the liver mitochondria that regulates fasting-induced gluconeogenesis and energy homeostasis.

Metformin can mitigate skeletal dysplasia caused by Pck2 deficiency

As an important enzyme for gluconeogenesis, mitochondrial phosphoenolpyruvate carboxykinase (PCK2) has further complex functions beyond regulation of glucose metabolism. Here, we report that conditional knockout of Pck2 in osteoblasts results in a pathological phenotype manifested as craniofacial malformation, long bone loss, and marrow adipocyte accumulation. Ablation of Pck2 alters the metabolic pathways of developing bone, particularly fatty acid metabolism. However, metformin treatment can mitigate skeletal dysplasia of embryonic and postnatal heterozygous knockout mice, at least partly via the AMPK signaling pathway. Collectively, these data illustrate that PCK2 is pivotal for bone development and metabolic homeostasis, and suggest that regulation of metformin-mediated signaling could provide a novel and practical strategy for treating metabolic skeletal dysfunction.

Herbal tea, a novel adjuvant therapy for treating type 2 diabetes mellitus: A review

Type 2 diabetes mellitus (T2DM) is a metabolic, endocrine disease characterized by persistent hyperglycemia. Several studies have shown that herbal tea improves glucose metabolism disorders in patients with T2DM. This study summarizes the published randomized controlled trials (RCTs) on herbal tea as a adjuvant therapy for treating T2DM and found that herbal teas have potential add-on effects in lowering blood glucose levels. In addition, we discussed the polyphenol contents in common herbal teas and their possible adverse effects. To better guide the application of herbal teas, we further summarized the hypoglycemic mechanisms of common herbal teas, which mainly involve: 1) improving insulin resistance, 2) protecting islet β-cells, 3) anti-inflammation and anti-oxidation, 4) inhibition of glucose absorption, and 5) suppression of gluconeogenesis. In conclusion, herbal tea, as a novel adjuvant therapy for treating T2DM, has the potential for further in-depth research and product development.

Simulation of the crosstalk between glucose and acetaminophen metabolism in a liver zonation model

The liver metabolizes a variety of substances that sometimes interact and regulate each other. The modeling of a single cell or a single metabolic pathway does not represent the complexity of the organ, including metabolic zonation (heterogeneity of functions) along with liver sinusoids. Here, we integrated multiple metabolic pathways into a single numerical liver zonation model, including drug and glucose metabolism. The model simulated the time-course of metabolite concentrations by the combination of dynamic simulation and metabolic flux analysis and successfully reproduced metabolic zonation and localized hepatotoxicity induced by acetaminophen (APAP). Drug metabolism was affected by nutritional status as the glucuronidation reaction rate changed. Moreover, sensitivity analysis suggested that the reported metabolic characteristics of obese adults and healthy infants in glucose metabolism could be associated with the metabolic features of those in drug metabolism. High activities of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphate phosphatase in obese adults led to increased APAP oxidation by cytochrome P450 2E1. In contrast, the high activity of glycogen synthase and low activities of PEPCK and glycogen phosphorylase in healthy infants led to low glucuronidation and high sulfation rates of APAP. In summary, this model showed the effects of glucose metabolism on drug metabolism by integrating multiple pathways into a single liver metabolic zonation model.

Glycosylation defects, offset by PEPCK-M, drive entosis in breast carcinoma cells

On glucose restriction, epithelial cells can undergo entosis, a cell-in-cell cannibalistic process, to allow considerable withstanding to this metabolic stress. Thus, we hypothesized that reduced protein glycosylation might participate in the activation of this cell survival pathway. Glucose deprivation promoted entosis in an MCF7 breast carcinoma model, as evaluated by direct inspection under the microscope, or revealed by a shift to apoptosis + necrosis in cells undergoing entosis treated with a Rho-GTPase kinase inhibitor (ROCKi). In this context, curbing protein glycosylation defects with N-acetyl-glucosamine partially rescued entosis, whereas limiting glycosylation in the presence of glucose with tunicamycin or NGI-1, but not with other unrelated ER-stress inducers such as thapsigargin or amino-acid limitation, stimulated entosis. Mitochondrial phosphoenolpyruvate carboxykinase (PEPCK-M; PCK2) is upregulated by glucose deprivation, thereby enhancing cell survival. Therefore, we presumed that PEPCK-M could play a role in this process by offsetting key metabolites into glycosyl moieties using alternative substrates. PEPCK-M inhibition using iPEPCK-2 promoted entosis in the absence of glucose, whereas its overexpression inhibited entosis. PEPCK-M inhibition had a direct role on total protein glycosylation as determined by Concanavalin A binding, and the specific ratio of fully glycosylated LAMP1 or E-cadherin. The content of metabolites, and the fluxes from ¹³C-glutamine label into glycolytic intermediates up to glucose-6-phosphate, and ribose- and ribulose-5-phosphate, was dependent on PEPCK-M content as measured by GC/MS. All in all, we demonstrate for the first time that protein glycosylation defects precede and initiate the entosis process and implicates PEPCK-M in this survival program to dampen the consequences of glucose deprivation. These results have broad implications to our understanding of tumor metabolism and treatment strategies.

Vitamin C deficiency induces hypoglycemia and cognitive disorder through S-nitrosylation-mediated activation of glycogen synthase kinase 3β

Vitamin C (VC, l-ascorbic acid) is an essential nutrient that plays a key role in metabolism and functions as a potent antioxidant in regulating the S-nitrosylation and denitrosylation of target proteins. The precise function of VC deprivation in glucose homeostasis is still unknown. In the absence of L-gulono-1,4-lactone oxidoreductase, an essential enzyme for the last step of VC synthesis, VC deprivation resulted in persistent hypoglycemia and subsequent impairment of cognitive functions in female but not male mouse pups. The cognitive disorders caused by VC deprivation were largely reversed when these female pups were given glucose. VC deprivation-induced S-nitrosylation of glycogen synthase kinase 3β (GSK3β) at Cys14, which activated GSK3β and inactivated glycogen synthase to decrease glycogen synthesis and storage under the feeding condition, while VC deprivation inactivated glycogen phosphorylase to decrease glycogenolysis under the fasting condition, ultimately leading to hypoglycemia and cognitive disorders. Treatment with Nω-Nitro-l-arginine methyl ester (l-NAME), a specific inhibitor of nitric oxide synthase, on the other hand, effectively prevented S-nitrosylation and activation of GSK3β in female pups in response to the VC deprivation and reversed hypoglycemia and cognitive disorders. Overall, this research identifies S-nitrosylation of GSK3β and subsequent GSK3β activation as a previously unknown mechanism controlling glucose homeostasis in female pups in response to VC deprivation, implying that VC supplementation in the prevention of hypoglycemia and cognitive disorders should be considered in the certain groups of people, particularly young females.

Mitochondrial phosphoenolpyruvate carboxykinase promotes tumor growth in estrogen receptor-positive breast cancer via regulation of the mTOR pathway

BACKGROUND

Tumor cells may aberrantly express metabolic enzymes to adapt to their environment for survival and growth. Targeting cancer-specific metabolic enzymes is a potential therapeutic strategy. Phosphoenolpyruvate carboxykinase (PEPCK) catalyzes the conversion of oxaloacetate to phosphoenolpyruvate and links the tricarboxylic acid cycle and glycolysis/gluconeogenesis. Mitochondrial PEPCK (PEPCK-M), encoded by PCK2, is an isozyme of PEPCK and is distributed in mitochondria. Overexpression of PCK2 has been identified in many human cancers and demonstrated to be important for the survival program initiated upon metabolic stress in cancer cells. We evaluated the expression status of PEPCK-M and investigated the function of PEPCK-M in breast cancer.

METHODS

We checked the expression status of PEPCK-M in breast cancer samples by immunohistochemical staining. We knocked down or overexpressed PCK2 in breast cancer cell lines to investigate the function of PEPCK-M in breast cancer.

RESULTS

PEPCK-M was highly expressed in estrogen receptor-positive (ER⁺ ) breast cancers. Decreased cell proliferation and G₀ /G₁ arrest were induced in ER⁺ breast cancer cell lines by knockdown of PCK2. PEPCK-M promoted the activation of mTORC1 downstream signaling molecules and the E2F1 pathways in ER⁺ breast cancer. In addition, glucose uptake, intracellular glutamine levels, and mTORC1 pathways activation by glucose and glutamine in ER⁺ breast cancer were attenuated by PCK2 knockdown.

CONCLUSION

PEPCK-M promotes proliferation and cell cycle progression in ER⁺ breast cancer via upregulation of the mTORC1 and E2F1 pathways. PCK2 also regulates nutrient status-dependent mTORC1 pathway activation in ER⁺ breast cancer. Further studies are warranted to understand whether PEPCK-M is a potential therapeutic target for ER⁺ breast cancer.

Aqueous Extract of Guava (Psidium guajava L.) Leaf Ameliorates Hyperglycemia by Promoting Hepatic Glycogen Synthesis and Modulating Gut Microbiota

Type 2 diabetes mellitus (T2DM) is a major global health concern. Psidium guajava L. (guava) is widely used for food as well as a folk medicine. Previous studies have shown its anti-diabetic and anti-inflammatory properties. However, the underlying mechanisms remains to be elusive. In this study, we assessed the potential therapeutic effects of aqueous extract of guava leaves (GvAEx) on T2DM and explored their potential mechanisms in vivo and in vitro. GvAEx was gavage administered for 12 weeks in diabetic db/db mice. Our results have demonstrated that GvAEx significantly lowered fasting plasma glucose levels (p < 0.01) and improved glucose tolerance and insulin sensitivity (p < 0.01, p < 0.05, respectively). Additionally, GvAEx increased hepatic glycogen accumulation, glucose uptake and decreased the mRNA expression levels of gluconeogenic genes. Furthermore, GvAEx-treatment caused higher glucose transporter 2 (GLUT2) expression in the membrane in hepatocytes. Notably, for the first time, we have elaborated the possible mechanism of the hypoglycemic effect of GvAEx from the perspective of intestinal microbiota. GvAEx has significantly changed the composition of microbiota and increased short chain fatty acid (SCFA) -producing Lachnospiraceae family and Akkermansia genus in the gut. Taken together, GvAEx could alleviate hyperglycemia and insulin resistance of T2DM by regulating glucose metabolism in the liver and restoring the gut microbiota. Thus, GvAEx has the potential for drug development against T2DM.

METTL3 Regulated the Meat Quality of Rex Rabbits by Controlling PCK2 Expression via a YTHDF2–N6-Methyladenosine Axis

N6-methyladenosine (m⁶A) is the most prevalent internal mRNA modification in eukaryotes. The M⁶A modification plays an important role in transcription and cell function. The mechanism by which m⁶A modification regulates meat quality remains elusive. In this study, gene knockout and overexpression were used to explore m⁶A-modified regulation of meat quality. The content of PCK2 in blood increased significantly with the increase of Rex rabbits’ age. PCK2 expression levels in the longissimus lumborum and liver also increased significantly with the increase of Rex rabbits’ age. However, the expression level of PCK2 showed no significant difference in adipose tissue. In cell experiments, we found that METTL3 inhibited adipocyte differentiation by targeting the PCK2 gene via the recognition function of YTHDF2. Finally, the results of correlation analysis showed that PCK2 expression was positively correlated with intramuscular fat, whereas PCK2 expression was negatively correlated with total water loss rate at three different stages. In addition, PCK2 expression was also negatively correlated with reduced pH value at 75 and 165 days. Intramuscular fat content, pH and muscle water holding capacity are the main factors affecting the taste and flavor of muscle. Therefore, N6-methyladenosine regulated muscle quality by targeting the PCK2 gene.

Ameliorative Effect of Oxytocin on FBN1 and PEPCK Gene Expression, and Behavioral Patterns in Rats' Obesity-Induced Diabetes

Amelioration of hyperinsulinemia and insulin resistance associated with obesity is a cardinal target for therapeutics. Therefore, we investigated the relation of Fibrilln-1 (FBN1) mRNA expression and hepatic phosphoenolpyruvate caboxykinase (PEPCK) enzyme to the ameliorative impact of oxytocin on obesity-induced diabetes, suggesting glycogenolysis markers in diabetic models. Four groups of forty male Wistar rats were formed (n = 10): a control group fed basal diet and intraperitoneal injections of saline; an oxytocin-injected group; a diet-induced obese group fed a high-fat/high-sugar diet and injected with saline; a diet-induced obese group injected with oxytocin. Depending on blood glucose levels, obese groups were further sub-grouped into prediabetic, and diabetic rats, with 5 rats each, at the ninth and the 16th week of the feeding period, respectively. FBN1 expression and PEPCK activity were determined using the qPCR technique and some biochemical parameters (glycemic, lipid profile, kidney, and liver functions) were determined using kits. Obese groups showed an elevation of brain FBN1 expression, high serum lipid profile, high glucose level, and a deleterious impact on liver and kidney functions. Obese groups showed the stimulator effect of the PEPCK enzyme and time-dependent pathological changes in renal and hepatic tissues. The motor activities were negatively correlated with FBN1 gene expression in prediabetic and diabetic rats. In addition to our previous review of the crucial role of asprosin, here we showed that oxytocin could ameliorate obesity-induced diabetes and decrease FBN1 gene expression centrally to block appetite. Oxytocin caused decreases in PEPCK enzyme activity as well as glycogenolysis in the liver. Therefore, oxytocin has a potential effect on FBN1 expression and PEPCK enzyme activity in the obesity-induced diabetic-rat model.

Deoxynivalenol triggers porcine intestinal tight junction disorder through hijacking SLC5A1 and PGC1α-mediated mitochondrial function

Deoxynivalenol (DON) is a mycotoxin frequently occurring in human and animal food worldwide, which raises increasing public health concerns. Growing evidence suggests that mitochondria is a pivotal molecular target for DON. However, the contribution of mitochondrial dysfunction to the pathogenesis of DON-induced gut epithelial barrier disruption remains poorly understood. In an animal experiment, piglets exposed to 2.89 mg DON/kg feed for 4 weeks showed altered metabolomic profiling in the serum and compromised transcriptome in the jejunum. DON exposure also impaired mitochondrial structure in the jejunal mucosa, corresponding with dysfunction of the tight junctions. In IPEC-J2 cells, metabolomic and transcriptomic analyses revealed that DON exposure perturbed biological processes occurring in the mitochondria and disordered the expression of genes involved in mitochondrial energy metabolism. Fuel utilization from glucose was affected by DON exposure, as were mitochondrial morphological dynamics leading to increased fragmentation. A marked loss of Na⁺/glucose cotransporter (SLC5A1) and peroxisome proliferator activated receptor-γ co-activator 1α (PGC1α) was observed in DON-treated cells. Taken together, our data highlight the critical role of impaired mitochondrial energy metabolism and mitochondrial biogenesis in abnormal intestinal tight junction upon DON exposure, and provide a potential mitochondrial target for intestinal mucosal restoration following DON exposure.

Lentinan Impairs the Early Development of Zebrafish Embryos, Possibly by Disrupting Glucose and Lipid Metabolism

LNT is the major biologically active substance extracted from Lentinus edodes (L. edodes). Although functional and pharmacological studies have demonstrated that LNT has multiple benefits for animals and humans, the safety assessment is far from sufficient. To evaluate the potential safety risk, larval zebrafish were continuously exposed to varying concentrations of LNT for 120 h. The 96 h LC50 of LNT was determined to be 1228 μg/mL, and morphological defects including short body length, reduced eye and swim bladder sizes and yolk sac edema were observed. In addition, LNT exposure significantly reduced the blood flow velocity and locomotor activity of larval zebrafish. The biochemical parameters were also affected, showing reduced glucose, triglyceride and cholesterol levels in zebrafish larvae after being exposed to LNT. Correspondingly, the genes involved in glucose and lipid metabolism were disrupted. In conclusion, the present study demonstrates the adverse potential of high concentrations of LNT on the development of zebrafish larvae in the early life stage.

GABA administration improves liver function and insulin resistance in offspring of type 2 diabetic rats

This study investigated the role of GABA in attenuating liver insulin resistance (IR) in type 2 diabetes parents and reducing its risk in their descendants' liver. Both sexes' rats were divided into four groups of non-diabetic control, diabetic control (DC), GABA-treated (GABA), and insulin-treated (Ins). The study duration lasted for six months and the young animals followed for four months. Consequently, hyperinsulinemic-euglycemic clamp was performed for all animals. Apart from insulin tolerance test (ITT), serum and liver lipid profile were measured in all groups. Glycogen levels, expression of Foxo1, Irs2, Akt2, and Pepck genes in the liver were assessed for all groups. Overall, GABA improved ITT, increased liver glycogen levels and decreased lipid profile, blood glucose level, and HbA1c in parents and their offspring in compared to the DC group. GIR also increased in both parents and their offspring by GABA. Moreover, the expression of Foxo1, Irs2, Akt2, and Pepck genes improved in GABA-treated parents and their descendants in compared to DC group. Results indicated that GABA reduced liver IR in both parents and their offspring via affecting their liver insulin signaling and gluconeogenesis pathways.

Anti-fatigue effect of quercetin on enhancing muscle function and antioxidant capacity

The aim of this study was to evaluate the anti-fatigue effect of quercetin in mice. Three-week-old male BALB/c mice, fed with/without 0.005% quercetin for 6 weeks, were randomly divided into two experimental sets (loaded swimming and non-loading swimming tests). Our data indicated that dietary quercetin supplementation prolonged the exhaustive swimming time. In addition, lactic acid (LD) and blood urea nitrogen (BUN) levels, lactate dehydrogenase (LDH) and creatine kinase (CK) activities in serum were significantly decreased, while the levels of non-esterified free fatty acids (NEFA) in serum and the content of liver glycogen and muscle glycogen were significantly enhanced in dietary quercetin supplementation group. Furthermore, dietary quercetin supplementation significantly enhanced the glutathione peroxidase (GPx) and catalase (CAT) activities in serum, liver and gastrocnemius muscle and enhanced the total superoxide dismutase (T-SOD) activity in gastrocnemius muscle, but decreased the malondialdehyde (MDA) content and reactive oxygen species (ROS) level. Meanwhile, dietary quercetin supplementation affected the mRNA expression of regulators factors involved in muscle damage and inflammation, glucose metabolism and gluconeogenesis, muscle mitochondrial fatty acid β-oxidation and antioxidant related genes. Together, our data confirm that dietary quercetin supplementation can promote anti-fatigue capacity by promoting the antioxidant capacity and glycogen storage, as well as enhancing muscle function. PRACTICAL APPLICATIONS: Quercetin is a natural polyphenolic flavonoid substance. Here we confirm that quercetin has anti-fatigue activity. Our study indicates that quercetin may be used as natural anti-fatigue functional food or drugs.

Physiological responses and molecular strategies in heart of silver carp (Hypophthalmichthys molitrix) under hypoxia and reoxygenation

A sufficient oxygen concentration is essential for fish growth, reproduction, and metabolism. Silver carp (Hypophthalmichthys molitrix) is sometimes challenged by hypoxia during intensive aquaculture or because of environmental changes. However, the response to hypoxic stress in the heart of silver carp remains relatively unknown. In the present study, we reported the effects of hypoxia on histological structures, enzyme activities, and gene expression in the heart of silver carp. Hematoxylin and eosin (H&E) staining of heart sections showed that the myocardial fibers gradually became disordered, swollen, and even ruptured during hypoxic treatment. These phenotypes were also supported by increased activities of injury-related enzymes. Moreover, the transcriptome was analyzed to determine the molecular strategies of hypoxia adaptation in the heart. PI3K-Akt signaling pathway, FoxO signaling pathway, and JAK-STAT signaling pathway were the most prominent pathways activated by hypoxia. Twenty significantly differentially expressed genes were selected to create a network diagram related to cell proliferation, carbohydrate metabolism, oxidative stress, and angiogenesis. Additionally, reoxygenation could ameliorate cardiac injury and eliminate the effects of hypoxia on gene expression. This was the first comparative transcriptomic study to explore the molecular mechanism of the response to hypoxia and reoxygenation in the heart of silver carp. Our results provide a theoretical basis for cultivating hypoxia-tolerant carp varieties in the future.

Ins and Outs of the TCA Cycle: The Central Role of Anaplerosis

The reactions of the tricarboxylic acid (TCA) cycle allow the controlled combustion of fat and carbohydrate. In principle, TCA cycle intermediates are regenerated on every turn and can facilitate the oxidation of an infinite number of nutrient molecules. However, TCA cycle intermediates can be lost to cataplerotic pathways that provide precursors for biosynthesis, and they must be replaced by anaplerotic pathways that regenerate these intermediates. Together, anaplerosis and cataplerosis help regulate rates of biosynthesis by dictating precursor supply, and they play underappreciated roles in catabolism and cellular energy status. They facilitate recycling pathways and nitrogen trafficking necessary for catabolism, and they influence redox state and oxidative capacity by altering TCA cycle intermediate concentrations. These functions vary widely by tissue and play emerging roles in disease. This article reviews the roles of anaplerosis and cataplerosis in various tissues and discusses how they alter carbon transitions, and highlights their contribution to mechanisms of disease. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Multitissue 2H/13C flux analysis reveals reciprocal upregulation of renal gluconeogenesis in hepatic PEPCK-C-knockout mice

The liver is the major source of glucose production during fasting under normal physiological conditions. However, the kidney may also contribute to maintaining glucose homeostasis in certain circumstances. To test the ability of the kidney to compensate for impaired hepatic glucose production in vivo, we developed a stable isotope approach to simultaneously quantify gluconeogenic and oxidative metabolic fluxes in the liver and kidney. Hepatic gluconeogenesis from phosphoenolpyruvate was disrupted via liver-specific knockout of cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C; KO). 2H/13C isotopes were infused in fasted KO and WT littermate mice, and fluxes were estimated from isotopic measurements of tissue and plasma metabolites using a multicompartment metabolic model. Hepatic gluconeogenesis and glucose production were reduced in KO mice, yet whole-body glucose production and arterial glucose were unaffected. Glucose homeostasis was maintained by a compensatory rise in renal glucose production and gluconeogenesis. Renal oxidative metabolic fluxes of KO mice increased to sustain the energetic and metabolic demands of elevated gluconeogenesis. These results show the reciprocity of the liver and kidney in maintaining glucose homeostasis by coordinated regulation of gluconeogenic flux through PEPCK-C. Combining stable isotopes with mathematical modeling provides a versatile platform to assess multitissue metabolism in various genetic, pathophysiological, physiological, and pharmacological settings.

Differential expression of PEPCK isoforms is correlated to Aedes aegypti oogenesis and embryogenesis

The mosquito Aedes aegypti undertakes a shift in carbohydrate metabolism during embryogenesis, including an increase in the activity of phosphoenolpyruvate carboxykinase (PEPCK), a key gluconeogenic enzyme, at critical steps of embryo development. All eukaryotes studied to date present two PEPCK isoforms, namely PEPCK-M (mitochondrial) and PEPCK-C (cytosolic). In A. aegypti, however, these proteins are so far uncharacterized. In the present work we describe two A. aegypti PEPCK isoforms by sequence alignment, protein modeling, and transcription analysis in different tissues, as well as PEPCK enzymatic activity assays in mitochondrial and cytoplasmic compartments during oogenesis and embryogenesis. First, we characterized the protein sequences compared to other organisms, and identified conserved sites and key amino acids. We also performed structure modeling for AePEPCK(M) and AePEPCK(C), identifying highly conserved structural sites, as well as a signal peptide in AePEPCK(M) localized in a very hydrophobic region. Moreover, after blood meal and during mosquito oogenesis and embryogenesis, both PEPCKs isoforms showed different transcriptional profiles, suggesting that mRNA for the cytosolic form is transmitted maternally, whereas the mitochondrial form is synthesized by the zygote. Collectively, these results improve our understanding of mosquito physiology and may yield putative targets for developing new methods for A. aegypti control.

Puerarin suppresses the hepatic gluconeogenesis via activation of PI3K/Akt signaling pathway in diabetic rats and HepG2 cells

Pueraria, a Chinese herbal medicine, plays an important role in many classic prescriptions for the treatment of diabetes. Puerarin is the main component of pueraria. The current in vivo and in vitro research mainly focus on exploring the potential mechanism of puerarin in inhibiting hepatic gluconeogenesis. The type 2 diabetic rats were established by a combination of small dosage of streptozotocin (STZ) injection with high-fat diet. After the administration of puerarin 4 weeks, the parameters of the glucose and lipid metabolism were determined. HepG2 cells were treated by palmitic acid (PA) to induce the insulin resistance in vitro model. After the treatment of puerarin, the glucose consumption and cell viability were examined. Then, the protein expression of PI3K, Akt, pAkt, pFOXO1, FOXO1, PEPCK and G6pase in liver tissue and HepG2 cells were evaluated by western blot. RT-PCR was used to measure the content of PEPCK, G6pase mRNA in liver tissue. The results showed that puerarin administration significantly decrease the level of FBG, HbA1C and triglycerides in diabetic rats. Mechanistic research showed that puerarin activating PI3K/Akt is puerarin-mediated beneficial effects and can be reversed by inhibitor of PI3K or Akt. In conclusion, puerarin inhibits hepatic gluconeogenesis by activating PI3K/Akt signaling pathway.

PEPCK-M recoups tumor cell anabolic potential in a PKC-ζ-dependent manner

Background

Mitochondrial phosphoenolpyruvate carboxykinase (PEPCK-M; PCK2) is expressed in all cancer types examined and in neuroprogenitor cells. The gene is upregulated by amino acid limitation and ER-stress in an ATF4-dependent manner, and its activity modulates the PEP/Ca²⁺ signaling axis, providing clear arguments for a functional relationship with metabolic adaptations for cell survival. Despite its potential relevance to cancer metabolism, the mechanisms responsible for its pro-survival activity have not been completely elucidated.

Methods

[U-¹³C]glutamine and [U-¹³C]glucose labeling of glycolytic and TCA cycle intermediates and their anabolic end-products was evaluated quantitatively using LC/MS and GC/MS in conditions of abundant glucose and glucose limitation in loss-of-function (shRNA) and gain-of-function (lentiviral constitutive overexpression) HeLa cervix carcinoma cell models. Cell viability was assessed in conjunction with various glucose concentrations and in xenografts in vivo.

Results

PEPCK-M levels linearly correlated with [U-¹³C]glutamine label abundance in most glycolytic and TCA cycle intermediate pools under nutritional stress. In particular, serine, glycine, and proline metabolism, and the anabolic potential of the cell, were sensitive to PEPCK-M activity. Therefore, cell viability defects could be rescued by supplementing with an excess of those amino acids. PEPCK-M silenced or inhibited cells in the presence of abundant glucose showed limited growth secondary to TCA cycle blockade and increased ROS.

In limiting glucose conditions, downregulation of PKC-ζ tumor suppressor has been shown to enhance survival. Consistently, HeLa cells also sustained a survival advantage when PKC-ζ tumor suppressor was downregulated using shRNA, but this advantage was abolished in the absence of PEPCK-M, as its inhibition restores cell growth to control levels. The relationship between these two pathways is also highlighted by the anti-correlation observed between PEPCK-M and PKC-ζ protein levels in all clones tested, suggesting co-regulation in the absence of glucose. Finally, PEPCK-M loss negatively impacted on anchorage-independent colony formation and xenograft growth in vivo.

Conclusions

All in all, our data suggest that PEPCK-M might participate in the mechanisms to regulate proteostasis in the anabolic and stalling phases of tumor growth. We provide molecular clues into the clinical relevance of PEPCK-M as a mechanism of evasion of cancer cells in conditions of nutrient stress.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40170-020-00236-3.

Restoring the epigenetically silenced PCK2 suppresses renal cell carcinoma progression and increases sensitivity to sunitinib by promoting endoplasmic reticulum stress

Rationale: Tumors have significant abnormalities in various biological properties. In renal cell carcinoma (RCC), metabolic abnormalities are characteristic biological dysfunction that cannot be ignored. Despite this, many aspects of this dysfunction have not been fully explained. The purpose of this study was to reveal a new mechanism of metabolic and energy-related biological abnormalities in RCC.

Methods: Molecular screening and bioinformatics analysis were performed in RCC based on data from The Cancer Genome Atlas (TCGA) database. Regulated pathways were investigated by qRT-PCR, immunoblot analysis and immunohistochemistry. A series of functional analyses was performed in cell lines and xenograft models.

Results: By screening the biological abnormality core dataset-mitochondria-related dataset and the metabolic abnormality core dataset-energy metabolism-related dataset in public RCC databases, PCK2 was found to be differentially expressed in RCC compared with normal tissue. Further analysis by the TCGA database showed that PCK2 was significantly downregulated in RCC and predicted a poor prognosis. Through additional studies, it was found that a low expression of PCK2 in RCC was caused by methylation of its promoter region. Restoration of PCK2 expression in RCC cells repressed tumor progression and increased their sensitivity to sunitinib. Finally, mechanistic investigations indicated that PCK2 mediated the above processes by promoting endoplasmic reticulum stress.

Conclusions: Collectively, our results identify a specific mechanism by which PCK2 suppresses the progression of renal cell carcinoma (RCC) and increases sensitivity to sunitinib by promoting endoplasmic reticulum stress. This finding provides a new biomarker for RCC as well as novel targets and strategies for the treatment of RCC.

Novel missense variants in PCK1 gene cause cytosolic PEPCK deficiency with growth failure from inadequate caloric intake

Cytosolic PEPCK deficiency (PCKDC) is a rare autosomal recessive inborn error of metabolism, which can present with hypoglycemia, lactic acidosis, and liver failure. It is caused by biallelic pathogenic variants in the PCK1 gene. Only four PCK1 variants have been previously reported in seven patients with PCKDC, and their clinical course of this condition has not been well characterized. Here, we report a Hispanic male with novel biallelic PCK1 variants, p.(Gly430Asp) and p.(His496Gln), who had a unique clinical presentation. He presented with a new onset of growth failure, elevated blood lactate, transaminitis, and abnormal urine metabolites profile, but he has not had documented hypoglycemia. Growth restriction happened due to insufficient caloric intake, and it was improved with nutritional intervention. PCKDC is a manageable disorder and therefore appropriate nutritional and clinical suspicion from typical lab abnormalities which lead to molecular confirmation tests are essential to prevent poor clinical outcomes.

Intricate Regulation of Phosphoenolpyruvate Carboxykinase (PEPCK) Isoforms in Normal Physiology and Disease

BACKGROUND

The phosphoenolpyruvate carboxykinase (PEPCK) isoforms are considered as rate-limiting enzymes for gluconeogenesis and glyceroneogenesis pathways. PEPCK exhibits several interesting features such as a) organelle-specific isoforms (cytosolic and a mitochondrial) in vertebrate clade, b) tissue-specific expression of isoforms and c) organism-specific requirement of ATP or GTP as a cofactor. In higher organisms, PEPCK isoforms are intricately regulated and activated through several physiological and pathological stimuli such as corticoids, hormones, nutrient starvation and hypoxia. Isoform-specific transcriptional/translational regulation and their interplay in maintaining glucose homeostasis remain to be fully understood. Mounting evidence indicates the significant involvement of PEPCK isoforms in physiological processes (development and longevity) and in the progression of a variety of diseases (metabolic disorders, cancer, Smith-Magenis syndrome).

OBJECTIVE

The present systematic review aimed to assimilate existing knowledge of transcriptional and translational regulation of PEPCK isoforms derived from cell, animal and clinical models.

CONCLUSION

Based on current knowledge and extensive bioinformatics analysis, in this review we have provided a comparative (epi)genetic understanding of PCK1 and PCK2 genes encompassing regulatory elements, disease-associated polymorphisms, copy number variations, regulatory miRNAs and CpG densities. We have also discussed various exogenous and endogenous modulators of PEPCK isoforms and their signaling mechanisms. A comprehensive review of existing knowledge of PEPCK regulation and function may enable identification of the underlying gaps to design new pharmacological strategies and interventions for the diseases associated with gluconeogenesis.

Integrative analysis of proteomic and metabonomics data for identification of pathways related to Rhizoma Paridis-induced hepatotoxicity

Clinical reports on hepatotoxicity that arise from Rhizoma Paridis have recently received widespread attention. Because the hepatotoxicity mechanism is little understood, this research strived to investigate the hepatotoxicity mechanism of Rhizoma Paridis extracts based on iTRAQ quantitative proteomics and metabonomics. The extraction solutions were administrated to rats for 7 days by gavage, and the hepatotoxicity was assessed through quantification of biochemical indexes and Oil red O staining. Additionally, the mechanism of hepatotoxicity was investigated by metabonomics based upon GC-MS and iTRAQ quantitative proteomics. The biochemical and histopathological analysis stood out that Rhizoma Paridis extract could induce liver injury, which was proved by the formation of fat droplets, the changes of mitochondrial structure, and biochemical parameters. The iTRAQ proteomics and metabonomics revealed that Rhizoma Paridis-induced hepatotoxicity was chiefly connected with the abnormal activity of mitochondrion function, which brought about oxidative stress injuries and inflammation, finally causing cell apoptosis. Collectively, we have provided previously uncharacterized hepatotoxic mechanism induced by Rhizoma Paridis and a reference to ensure its safe use in the future.

Propionate enhances the expression of key genes involved in the gluconeogenic pathway in bovine intestinal epithelial cells

Approximately 15 to 50% of short-chain fatty acids (SCFA) reach the ruminant small intestine. Previous research suggests that activation of small intestinal gluconeogenesis induced by propionate has beneficial effects on energy homeostasis. However, the regulatory effect of propionate on key gluconeogenic genes in enterocytes of the bovine small intestine remains less known. Therefore, the purpose of this study was to establish the long-term cultures of bovine intestinal epithelial cells (BIEC) from bovine jejunum tissue using SV40T (1:200; Santa Cruz, Shanghai, China) and investigate the regulatory effect of propionate on the key gluconeogenic genes in BIEC. Our study showed that long-term BIEC cultures were established by SV40T-induced immortalization. Immortal BIEC were distinguished by the expression of cytokeratin 18, villin, fatty acid binding protein 2, and small intestine peptidase. The mRNA expression of genes involved in the SCFA transporters, monocarboxylate transporter 4, and Na⁺/H⁺ exchanger isoforms 1 were significantly elevated with 20 mM SCFA compared with untreated controls. In addition, BIEC exhibited significant uptake of propionate and butyrate from the culture medium. Remarkably, 3 mM propionate induced profound changes in mRNA level of key genes involved in gluconeogenesis, including phosphoenolpyruvate carboxykinase 2, pyruvate carboxylase, fructose-1,6-bisphosphatase 1, and peroxisome proliferator-activated receptor-γ coactivator 1α. Additionally, 3 mM propionate enhanced the expression of PGC1A mRNA at 3, 6, 12, and 24 h of incubation. These findings suggest that propionate controls the mRNA expression of genes involved in key enzymes for gluconeogenesis in the enterocytes of bovines.

Metabolic dysregulation in the Atp7b-/- Wilson's disease mouse model

Inactivating mutations in the copper transporter Atp7b result in Wilson's disease. The Atp7b-/- mouse develops hallmarks of Wilson's disease. The activity of several nuclear receptors decreased in Atp7b-/- mice, and nuclear receptors are critical for maintaining metabolic homeostasis. Therefore, we anticipated that Atp7b-/- mice would exhibit altered progression of diet-induced obesity, fatty liver, and insulin resistance. Following 10 wk on a chow or Western-type diet (40% kcal fat), parameters of glucose and lipid homeostasis were measured. Hepatic metabolites were measured by liquid chromatography-mass spectrometry and correlated with transcriptomic data. Atp7b-/- mice fed a chow diet presented with blunted body-weight gain over time, had lower fat mass, and were more glucose tolerant than wild type (WT) littermate controls. On the Western diet, Atp7b-/- mice exhibited reduced body weight, adiposity, and hepatic steatosis compared with WT controls. Atp7b-/- mice fed either diet were more insulin sensitive than WT controls; however, fasted Atp7b-/- mice exhibited hypoglycemia after administration of insulin due to an impaired glucose counterregulatory response, as evidenced by reduced hepatic glucose production. Coupling gene expression with metabolomic analyses, we observed striking changes in hepatic metabolic profiles in Atp7b-/- mice, including increases in glycolytic intermediates and components of the tricarboxylic acid cycle. In addition, the active phosphorylated form of AMP kinase was significantly increased in Atp7b-/- mice relative to WT controls. Alterations in hepatic metabolic profiles and nuclear receptor signaling were associated with improved glucose tolerance and insulin sensitivity as well as with impaired fasting glucose production in Atp7b-/- mice.

Transcriptomic profiling sheds light on the blue-light and red-light response of oyster mushroom (Pleurotus ostreatus)

Blue light is an important environmental factor that induces mushroom primordium differentiation and fruiting body development. Although blue-light treatment has been applied for the production of oyster mushroom (Pleurotus ostreatus), the blue-light response mechanisms of P. ostreatus still remain unclear. In the present study, we exposed the primordium of P. ostreatus to blue-light, red-light, and dark conditions for 7 days. Subsequently, comparative transcriptomics analysis of the stipe, pileus, and gill under the three light conditions was performed to reveal the gene expression response mechanism of P. ostreatus to blue light and red light. The results showed that blue light enhanced the growth and development of all the three organs of P. ostreatus, especially the pileus. In contrast, red light slightly (non-significantly) inhibited pileus growth. When compared with red-light and dark treatments, blue-light treatment significantly upregulated gene expression involved in glycolysis/gluconeogenesis, the pentose phosphate pathway and the peroxisome in the pileus, but not in the gill or stipe. Most of the glycolysis and pentose phosphate pathway genes were upregulated in the pileus by blue light. When compared with dark treatment, red-light treatment downregulated the expression of many respiration metabolism genes in the pileus. These results revealed that blue light enhanced the activation of glycolysis and the pentose phosphate pathway, whereas red light weakened glycolysis and pentose phosphate pathway activation. The conclusion can be drawn that blue light improved P. ostreatus fruiting body (particularly, the pileus) growth rate via enhancement of glycolysis and the pentose phosphate pathway.

Phosphoenolpyruvate from Glycolysis and PEPCK Regulate Cancer Cell Fate by Altering Cytosolic Ca2

Changes in phosphoenolpyruvate (PEP) concentrations secondary to variations in glucose availability can regulate calcium signaling in T cells as this metabolite potently inhibits the sarcoplasmic reticulum Ca2+/ATPase pump (SERCA). This regulation is critical to assert immune activation in the tumor as T cells and cancer cells compete for available nutrients. We examined here whether cytosolic calcium and the activation of downstream effector pathways important for tumor biology are influenced by the presence of glucose and/or cataplerosis through the phosphoenolpyruvate carboxykinase (PEPCK) pathway, as both are hypothesized to feed the PEP pool. Our data demonstrate that cellular PEP parallels extracellular glucose in two human colon carcinoma cell lines, HCT-116 and SW480. PEP correlated with cytosolic calcium and NFAT activity, together with transcriptional up-regulation of canonical targets PTGS2 and IL6 that was fully prevented by CsA pre-treatment. Similarly, loading the metabolite directly into the cell increased cytosolic calcium and NFAT activity. PEP-stirred cytosolic calcium was also responsible for the calmodulin (CaM) dependent phosphorylation of c-Myc at Ser62, resulting in increased activity, probably through enhanced stabilization of the protein. Protein expression of several c-Myc targets also correlated with PEP levels. Finally, the participation of PEPCK in this axis was interrogated as it should directly contribute to PEP through cataplerosis from TCA cycle intermediates, especially in glucose starvation conditions. Inhibition of PEPCK activity showed the expected regulation of PEP and calcium levels and consequential downstream modulation of NFAT and c-Myc activities. Collectively, these results suggest that glucose and PEPCK can regulate NFAT and c-Myc activities through their influence on the PEP/Ca2+ axis, advancing a role for PEP as a second messenger communicating metabolism, calcium cell signaling, and tumor biology.

Glucagon regulation of carbohydrate metabolism in rainbow trout: in vivo glucose fluxes and gene expression

Glucagon increases fish glycaemia, but how it affects glucose fluxes in vivo has never been characterized. The goal of this study was to test the hypothesis that glucagon stimulates hepatic glucose production (rate of appearance, R _a) and inhibits disposal (rate of disposal, R _d) in rainbow trout. Changes in the mRNA abundance of key proteins involved in glycolysis, gluconeogenesis and glycogen breakdown were also monitored. The results show that glucagon increases glycaemia (+38%) by causing a temporary mismatch between R _a and R _d before the two fluxes converge below baseline (-17%). A novel aspect of the regulation of trout gluconeogenesis is also demonstrated: the completely different effects of glucagon on the expression of three Pepck isoforms (stimulation of pck1, inhibition of pck2a and no response of pck2b). Glycogen phosphorylase was modulated differently among tissues, and muscle upregulated pygb and downregulated pygm Glucagon failed to activate the cAMP-dependent protein kinase or FoxO1 signalling cascades. We conclude that trout hyperglycaemia results from the combination of two responses: (i) an increase in R _a glucose induced by the stimulation of gluconeogenesis through transcriptional activation of pck1 (and possibly glycogen phosphorylase), and (ii) a decrease in R _d glucose via inhibition of glycogen synthase and glycolysis. The observed decrease in glucose fluxes after 4 h of glucagon administration may be caused by a counter-regulatory response of insulin, potentially linked to the decrease in pygm transcript abundance. Overall, however, these integrated effects of glucagon only lead to modest changes in glucose fluxes that partly explain why trout seem to be unable to control glycaemia very tightly.

Pharmacology and preclinical validation of a novel anticancer compound targeting PEPCK-M

BACKGROUND

Phosphoenolpyruvate carboxykinase (PEPCK) catalyzes the decarboxylation of oxaloacetate to phosphoenolpyruvate. The mitochondrial isozyme, PEPCK-M is highly expressed in cancer cells, where it plays a role in nutrient stress response. To date, pharmacological strategies to target this pathway have not been pursued.

METHODS

A compound embodying a 3-alkyl-1,8-dibenzylxanthine nucleus (iPEPCK-2), was synthesized and successfully probed in silico on a PEPCK-M structural model. Potency and target engagement in vitro and in vivo were evaluated by kinetic and cellular thermal shift assays (CETSA). The compound and its target were validated in tumor growth models in vitro and in murine xenografts.

RESULTS

Cross-inhibitory capacity and increased potency as compared to 3-MPA were confirmed in vitro and in vivo. Treatment with iPEPCK-2 inhibited cell growth and survival, especially in poor-nutrient environment, consistent with an impact on colony formation in soft agar. Finally, daily administration of the PEPCK-M inhibitor successfully inhibited tumor growth in two murine xenograft models as compared to vehicle, without weight loss, or any sign of apparent toxicity.

CONCLUSION

We conclude that iPEPCK-2 is a compelling anticancer drug targeting PEPCK-M, a hallmark gene product involved in metabolic adaptations of the tumor.