PEPCK Activity Research Articles

Effects of Short-Term Temperature Stress on Metabolic and Digestive Enzymes Activities of Procambarus clarkii

To investigate the effects of temperature stress on metabolic and digestive enzyme activities of Procambarus clarkii, the test species was transferred from 20°C (control group) to 10°C and 30°C, and samples were collected at 0, 3, 6, 12, 24, and 48h. The activities of pyruvate kinase (PK), hexokinase (HK) and hosphoenolpyruvate carboxykinase (PEPCK) in muscle and hepatopancreas of Procambarus clarkii was determined. The changes in α-amylase (α-AMY) and lipase (LPS) activity in intestinal and hepatopancreas were also examined. The results showed that the activities of digestive and metabolic enzymes in Procambarus clarkii were significantly affected by extreme water temperature (P<0.05). During the whole experimentation period, PK, HK, and PEPCK activities in the low-temperature group (10°C) were lower than those in the control group (20°C) (P < 0.05). Meanwhile, LPS and α-AMY activities in the low-temperature group (10°C) were also significantly lower than those in the control group (20°C) (P < 0.05). In the high-temperature group (30°C), the activities of PK, HK, and PEPCK metabolic enzymes in muscle and hepatopancreas decreased first. Then they increased, and their activity levels were significantly lower than those in the control group (P<0.05). At the same time, the activities of LPS and α-AMY digestive enzymes in the intestines and hepatopancreas were significantly lower than those in the control group(P<0.05). In summary, this study examined the impact of temperature stress on the metabolic and digestive enzyme activities in Procambarus clarkii, shedding light on its self-regulation mechanisms in response to temperature fluctuations. The findings provide a scientific foundation for understanding the species’ adaptation to environmental changes.

The Molecular Mechanism of Farnesoid X Receptor Alleviating Glucose Intolerance in Turbot (Scophthalmus maximus)

To explore the molecular targets for regulating glucose metabolism in carnivorous fish, the turbot (Scophthalmus maximus) was selected as the research object to study. Farnesoid X receptor (FXR; NR1H4), as a ligand-activated transcription factor, plays an important role in glucose metabolism in mammals. However, the mechanisms controlling glucose metabolism mediated by FXR in fish are not understood. It was first found that the protein levels of FXR and its target gene, small heterodimer partner (SHP), were significantly decreased in the high-glucose group (50 mM, HG) compared with those in the normal glucose group (15 mM, CON) in primary hepatocytes of turbot. By further exploring the function of FXR in turbot, the full length of FXR in turbot was cloned, and its nuclear localization function was characterized by subcellular localization. The results revealed that the FXR had the highest expression in the liver, and its capability to activate SHP expression through heterodimer formation with retinoid X receptor (RXR) was proved, which proved RXR could bind to 15 binding sites of FXR by forming hydrogen bonds. Activation of FXR in both the CON and HG groups significantly increased the expression of glucokinase (gk) and pyruvate kinase (pk), while it decreased the expression of cytosolic phosphoenolpyruvate carboxykinase (cpepck), mitochondrial phosphoenolpyruvate carboxykinase (mpepck), glucose-6-phosphatase 1 (g6pase1) and glucose-6-phosphatase 2 (g6pase2), and caused no significant different in glycogen synthetase (gs). ELISA experiments further demonstrated that under the condition of high glucose with activated FXR, it could significantly decrease the activity of PEPCK and G6PASE in hepatocytes. In a dual-luciferase reporter assay, the FXR could significantly inhibit the activity of G6PASE2 and cPEPCK promoters by binding to the binding site ‘ATGACCT’. Knockdown of SHP after activation of FXR reduced the inhibitory effect on gluconeogenesis. In summary, FXR can bind to the mpepck and g6pase2 promoters to inhibit their expression, thereby directly inhibiting the gluconeogenesis pathway. FXR can also indirectly inhibit the gluconeogenesis pathway by activating shp. These findings suggest the possibility of FXR as a molecular target to regulate glucose homeostasis in turbot.

Effects of metformin supplementation in high-carbohydrate diets on growth performance, glucose metabolism, intestinal flora, and PI3K/AKT signaling pathway of hybrid grouper (Epinephelus fuscoguttatus♀×Epinephelus lanceolatu♂)

Metformin, or 1,1-dimethylbiguanide, is a hypoglycemic drug that lowers blood glucose by reducing glycogen synthesis and increasing glucose uptake in peripheral tissues. Six diets with iso-nitrogenous and iso-lipid compositions were prepared, including a positive control (20 % carbohydrate, PC) and a negative control (30 % carbohydrate, T0). The experimental diets contained 0.2 % (T2), 0.4 % (T4), 0.6 % (T6), and 0.8 % (T8) metformin based on the negative control diet. A total of 540 hybrid groupers, with consistent size and health conditions, were randomly assigned to six groups. Each group contained 30 fish, with three replicates per group, and they were fed for eight weeks. The high-carbohydrate diet reduced weight gain, digestive enzyme activities and specific growth rates (P>0.05), while significantly increasing hepatosomatic indices (P<0.05). Metformin supplementation reduced both hepatosomatic and viscerosomatic indices (P<0.05). The high-carbohydrate diet led to increased levels of glucose, triglycerides, low-density lipoprotein, hepatic fructose 1,6-bisphosphatase, and glucose-6-phosphatase in the serum (P<0.05). In contrast, metformin supplementation significantly lowered glucose, insulin, triglycerides, and low-density lipoprotein levels (P<0.05), while enhancing the activities of hepatic glucokinase, phosphofructokinase-1, and pyruvate kinase (P<0.05). It significantly reduced the activities of PEPCK and G6Pase and downregulated the expression of ir, pi3k, pdk, ampkα1, and gs in fish on high-carbohydrate diets, while metformin supplementation upregulated the expression of ir, pi3k, pdk, ampkα1, and gs genes compared to the T0 group (P<0.05). In terms of microbiota, a high-carbohydrate diet increased pathogenic bacteria like Proteobacteria and Photobacterium, while metformin boosted beneficial bacteria such as Firmicutes and Brevibacillus. Overall, the high-carbohydrate diet impaired growth and insulin sensitivity, while metformin improved glucose metabolism, promoted beneficial bacteria, and supported intestinal health.

Fibroblast growth factor 1 (FGF1) improves glucose homeostasis, modulates gut microbial composition, and reduces inflammatory responses in rainbow trout (Oncorhynchus mykiss) fed a high-fat diet

High-fat diets (HFDs) are widely used in aquaculture due to their lipid and protein-conserving effects, thereby reducing feed costs. However, prolonged feeding of HFD often leads to metabolic disorders in fish, such as disruption of hepatic lipid homeostasis, liver injury, and disruption of glucose homeostasis. Fibroblast growth factor 1 (FGF1) plays an essential role in controlling glucose levels in the body and dampening immune reactions. However, its impact on teleosts remains poorly researched. The therapeutic potential of recombinant FGF1 (rFGF1) was examined in a 6-week culture experiment involving rainbow trout (Oncorhynchus mykiss) that were fed an HFD. The results revealed that rFGF1 significantly reduced serum glucose levels and hepatic PEPCK and G6PC activities, but improved hepatic glycogen (P < 0.05), compared to the HFD + PBS group. Further experiments indicated that the inhibitory effect of rFGF1 on hepatic gluconeogenesis was mediated by the cAMP signaling pathway and was dependent on the high expression of PDE4D. In addition, rFGF1 increased hepatic glycogen content, which involves the AKT-GSK3β axis. Despite this increase, rFGF1 did not lead to glycogen storage disease, as shown by reduced hepatic inflammation as a result of decreased GOT (glutamic oxaloacetic transaminase), GPT (glutamic pyruvic transaminase), and elevated SOD (superoxide dismutase) in the rFGF1-treated group, accompanied by decreased il-1β, il-6, and xbp-1, and elevated nrf2 and number of hepatocyte autophagosomes. Alterations in gut microbes and short-chain fatty acids (SCFAs) were noted, indicating that rFGF1 caused a notable rise in intestinal Lactobacillus, acetic acid, and butyric acid levels. This study investigated the molecular mechanisms of rFGF1 on glucose metabolism and inflammatory responses in an HFD-fed rainbow trout model, providing new insights to improve the regulation of glucose metabolism in carnivorous fish.

Study on the Mechanism of GABA-Rich Adzuki Bean Regulating Blood Glucose Based on the IRS/PI3K/AKT Pathway.

The adzuki bean is a mature seed of the red bean leguminous plant, and people like to eat it because of its nutritious properties and moderate proportion of amino acids. Adzuki bean germination and the enrichment of GABA greatly improve the health effects of the adzuki bean. The effects of the GABA-rich adzuki bean on the expression of insulin-pathway-related genes and proteins in the liver of T2DM mice were studied via Western blotting and qPCR. The results showed that a GABA-rich adzuki bean diet could promote glycogen synthesis in the liver of T2DM mice, inhibit the activities of PEPCK and G-6-Pase, and significantly down-regulate the gene expression levels of PEPCK, G6PC and FOXO1 (p < 0.05) and the phosphorylation levels of FOXO1 and GSK3β. In addition, it can also up-regulate the expression of the AMPKα gene and down-regulate the expression of the SREBP1c gene to inhibit the synthesis of triglycerides and cholesterol in T2DM mice. Lipid accumulation in mice can alleviate glucose and lipid metabolism disorders and play an effective role in regulating blood glucose at liver tissue targets. This study suggested that the GABA-rich adzuki bean can improve hyperglycemia in type 2 diabetic mice by activating the IRS/PI3K/AKT signaling pathway in the liver.

Marine thermal fluctuation induced gluconeogenesis by the transcriptional regulation of CgCREBL2 in Pacific oysters

Marine thermal fluctuation profoundly influences energy metabolism, physiology, and survival of marine life. In the present study, short-term and long-term high-temperature stresses were found to affect gluconeogenesis by inhibiting PEPCK activity in the Pacific oyster (Crassostrea gigas), which is a globally distributed species that encounters significant marine thermal fluctuations in intertidal zones worldwide. CgCREBL2, a key molecule in the regulation of gluconeogenesis, plays a critical role in the transcriptional regulation of PEPCK in gluconeogenesis against high-temperature stress. CgCREBL2 was able to increase the transcription of CgPEPCK by either binding the promoter of CgPEPCK gene or activating CgPGC-1α and CgHNF-4α after short-term (6 h) high-temperature stress, while only by binding CgPEPCK after long-term (60 h) high-temperature stress. These findings will further our understanding of the effect of marine thermal fluctuation on energy metabolism on marine organisms.

Changes of glycolysis and gluconeogenesis key enzymes in the muscle of the shrimp Penaeus vannamei in response to hypoxia and reoxygenation

Although the shrimp Penaeus vannamei can tolerate oxygen-limited conditions, the organisms may suffer detrimental effects in several processes, including growth, reproduction, immune responses, and others. During hypoxia, the shrimp makes metabolic adjustments in energy use and glucose homeostasis. Glucose is hydrolyzed during glycolysis and synthesized from non-glycosidic metabolites in gluconeogenesis. Although these pathways share many enzymes, the processes are not exactly the reverse of each other. We studied the first and last irreversible steps of glycolysis and gluconeogenesis catalyzed by hexokinase/glucose-6-phosphatase (HK/G6Pase) and pyruvate kinase/pyruvate carboxylase/phosphoenolpyruvate carboxykinase (PK/PC/PEPCK), respectively, in muscle under hypoxia and hypoxia followed by reoxygenation to gain insights about the coordinated metabolic responses that maintain glucose balance during oxygen stress. For the first group, HK gene expression was induced in hypoxia while G6Pase was reduced in hypoxia and reoxygenation, whereas for enzymes activity, HK was maintained and G6Pase was only detected in reoxygenation. For the second group, gene expression increased in PK in hypoxia, in PC in reoxygenation and in both cases, the enzymatic activities were maintained. Mitochondrial PEPCK expression increased during hypoxia and cytosolic PEPCK decreased, while total PEPCK activity was maintained. Intracellular lactate decreased during hypoxia while glucose levels were maintained. Altogether the results show that in limited oxygen, the expression of glycolytic enzymes-genes are induced, the gluconeogenic counterparts are active, although with more varied responses to oxygen limited conditions, and intracellular glucose levels are maintained.

The operation of PEPCK increases light harvesting plasticity in C4 NAD-ME and NADP-ME photosynthetic subtypes: A theoretical study.

The repeated emergence of NADP-malic enzyme (ME), NAD-ME and phosphoenolpyruvatecarboxykinase (PEPCK) subtypes of C4 photosynthesis are iconic examples of convergent evolution, which suggests that these biochemistries do not randomly assemble, but are instead specific adaptations resulting from unknown evolutionary drivers. Theoretical studies that are based on the classic biochemical understanding have repeatedly proposed light-use efficiency as a possible benefit of the PEPCK subtype. However, quantum yield measurements do not support this idea. We explore this inconsistency here via an analytical model that features explicit descriptions across a seamless gradient between C4 biochemistries to analyse light harvesting and dark photosynthetic metabolism. Our simulations show that the NADP-ME subtype, operated by the most productive crops, is the most efficient. The NAD-ME subtype has lower efficiency, but has greater light harvesting plasticity (the capacity to assimilate CO2 in the broadest combination of light intensity and spectral qualities). In both NADP-ME and NAD-ME backgrounds, increasing PEPCK activity corresponds to greater light harvesting plasticity but likely imposed a reduction in photosynthetic efficiency. We draw the first mechanistic links between light harvesting and C4 subtypes, providing the theoretical basis for future investigation.

Fish oil minimises feed intake and improves insulin sensitivity in Zucker fa/fa rats.

Long-chain n-3 PUFA (LC n-3 PUFA) prevent, in rodents, insulin resistance (IR) induced by a high-fat and/or fructose diet but not IR induced by glucocorticoids. In humans, contrasting effects have also been reported. We investigated their effects on insulin sensitivity, feed intake (FI) and body weight gain in genetically insulin resistant male obese (fa/fa) Zucker (ZO) rats during the development of obesity. ZO rats were fed a diet supplemented with 7 % fish oil (FO) + 1 % corn oil (CO) (wt/wt) (ZOFO), while the control group was fed a diet containing 8 % fat from CO (wt/wt) (ZOCO). Male lean Zucker (ZL) rats fed either FO (ZLFO) or CO (ZLCO) diet were used as controls. FO was a marine-derived TAG oil containing EPA 90 mg/g + DHA 430 mg/g. During an oral glucose tolerance test, glucose tolerance remained unaltered by FO while insulin response was reduced in ZOFO only. Liver insulin sensitivity (euglycaemic-hyperinsulinaemic clamp + 2 deoxyglucose) was improved in ZOFO rats, linked to changes in phosphoenolpyruvate carboxykinase expression, activity and glucose-6-phosphatase activity. FI in response to intra-carotid insulin/glucose infusion was decreased similarly in ZOFO and ZOCO. Hypothalamic ceramides levels were lower in ZOFO than in ZOCO. Our study demonstrates that LC n-3 PUFA can minimise weight gain, possibly by alleviating hypothalamic lipotoxicity, and liver IR in genetically obese Zucker rats.

COVID-19-related hyperglycemia is associated with infection of hepatocytes and stimulation of gluconeogenesis

Occurrence of hyperglycemia upon infection is associated with worse clinical outcome in COVID-19 patients. However, it is still unknown whether SARS-CoV-2 directly triggers hyperglycemia. Herein, we interrogated whether and how SARS-CoV-2 causes hyperglycemia by infecting hepatocytes and increasing glucose production. We performed a retrospective cohort study including patients that were admitted at a hospital with suspicion of COVID-19. Clinical and laboratory data were collected from the chart records and daily blood glucose values were analyzed to test the hypothesis on whether COVID-19 was independently associated with hyperglycemia. Blood glucose was collected from a subgroup of nondiabetic patients to assess pancreatic hormones. Postmortem liver biopsies were collected to assess the presence of SARS-CoV-2 and its transporters in hepatocytes. In human hepatocytes, we studied the mechanistic bases of SARS-CoV-2 entrance and its gluconeogenic effect. SARS-CoV-2 infection was independently associated with hyperglycemia, regardless of diabetic history and beta cell function. We detected replicating viruses in human hepatocytes from postmortem liver biopsies and in primary hepatocytes. We found that SARS-CoV-2 variants infected human hepatocytesin vitrowith different susceptibility. SARS-CoV-2 infection in hepatocytes yields the release of new infectious viral particles, though not causing cell damage. We showed that infected hepatocytes increase glucose production and this is associated with induction of PEPCK activity. Furthermore, our results demonstrate that SARS-CoV-2 entry in hepatocytes occurs partially through ACE2- and GRP78-dependent mechanisms. SARS-CoV-2 infects and replicates in hepatocytes and exerts a PEPCK-dependent gluconeogenic effect in these cells that potentially is a key cause of hyperglycemia in infected patients.

FaGAPC2/FaPKc2.2 and FaPEPCK reveal differential citric acid metabolism regulation in late development of strawberry fruit.

Citric acid is the primary organic acid that affects the taste of strawberry fruit. Glycolysis supplies key substrates for the tricarboxylic acid cycle (TCA cycle). However, little is known about the regulatory mechanisms of glycolytic genes on citric acid metabolism in strawberry fruits. In this study, the citric acid content of strawberry fruit displayed a trend of rising and decreasing from the initial red stage to the full red stage and then dark red stage. Thus, a difference in citric acid metabolic regulation was suspected during strawberry fruit development. In addition, overexpression of either cytoplasm glyceraldehyde-3-phosphate dehydrogenase (FxaC_14g13400, namely FaGAPC2) or pyruvate kinase (FxaC_15g00080, namely FaPKc2.2) inhibited strawberry fruit ripening and the accumulation of citric acid, leading to a range of maturity stages from partial red to full red stage. The combined transcriptome and metabolome analysis revealed that overexpression of FaGAPC2 and FaPKc2.2 significantly suppressed the expression of phosphoenolpyruvate carboxykinase (FxaC_1g21491, namely FaPEPCK) but enhanced the content of glutamine and aspartic acid. Meanwhile, the activities of PEPCK and glutamate decarboxylase (GAD) were inhibited, but the activities of glutamine synthase (GS) were increased in FaGAPC2/FaPKc2.2-overexpressed fruit. Further, functional verification demonstrated that overexpression of FaPEPCK can promote strawberry fruit ripening, resulting in a range of maturity stage from full red to dark red stage, while the citric acid synthase (CS) activities and citric acid content were significantly decreased. Overall, this study revealed that FaGAPC2/FaPKc2.2 and FaPEPCK perform an important role in reducing citric acid content in strawberry fruit, and FaGAPC2/FaPKc2.2 mainly by promoting the GS degradation pathway and FaPEPCK mainly by inhibiting the CS synthesis pathway.

Responses to aluminum and cadmium of a RNAi sorghum line with decreased levels of phosphoenolpyruvate carboxylase 3 (PPC3)

Phosphoenolpyruvate carboxylase (PEPC) is an enzyme family with central roles in carbon and nitrogen metabolisms. In order to obtain knowledge about the function of specific PEPC isoenzymes, we have characterized RNAi sorghum lines with decreased level of PPC3 (Ppc3 lines). PPC3 is the main root PEPC, and participates in responses to salinity and ammonium stress. This prompted us to study the responses of Ppc3 lines to Al and Cd stress. Both Al and Cd treatments decreased germination rate, growth rate, and shoot and root biomass production. These detrimental effects were higher in Ppc3 lines than in Wt. Root PPC3 expression and PEPC activity was increased by Al and Cd in Wt, but not in Ppc3 lines. The treatments also increased PPC2 and PPCK gene expression, and PEPCk activity, but these changes did not substitute the lack of PPC3. The production and secretion of exudates by plant roots play an important role in plant tolerance to Al and Cd toxicity. Al (2 days of treatment) caused a 40-fold increase of the citrate content of root exudates, without differences between Wt and Ppc3 lines. On the contrary, Cd (7 days of treatment) caused a 400-fold increase of citrate in Wt exudates, but only a 30-fold increase in Ppc3 lines. These results indicate that although PPC3 is not necessary for early production of organic acids in root exudates, it is crucial for maintaining high level of synthesis and accumulation of citrate, and that PPC3 is the main PEPC isoenzyme responsible for this response to heavy metal stress.

Hepatic metabolite responses to 4-day complete fasting and subsequent refeeding in rats.

BackgroundFasting has been widely used to improve various metabolic diseases in humans. Adaptive fasting is necessary for metabolic adaptation during prolonged fasting, which could overcome the great advantages of short-term fasting. The liver is the main organ responsible for energy metabolism and metabolic homeostasis. To date, we lack literature that describes the physiologically relevant adaptations of the liver during prolonged fasting and refeeding. For that reason, this study aims to evaluate the response of the liver of Sprague-Dawley (SD) rats to prolonged fasting and refeeding.MethodsSixty-six male SD rats were divided into the fasting groups, which were fasted for 0, 4, 8, 12, 24, 48, 72, or 96 h, and the refeeding groups, which were refed for 1, 3, or 6 days after 96 h of fasting. Serum glucose, TG, FFA, β-hydroxybutyrate, insulin, glucagon, leptin, adiponectin and FGF21 levels were assessed. The glucose content, PEPCK activity, TG concentration and FFA content were measured in liver tissue, and the expression of genes involved in gluconeogenesis (PEPCK and G6Pase), ketogenesis (PPARα, CPT-1a and HMGCS2) and the protein expression of nutrient-sensing signaling molecules (AMPK, mTOR and SIRT1) were determined by RT-qPCR and western blotting, respectively.ResultsFasting significantly decreased the body weight, which was totally recovered to baseline after 3 days of refeeding. A 4-day fast triggered an energy metabolic substrate shift from glucose to ketones and caused serum hormone changes and changes in the protein expression levels of nutrient-sensing signaling molecules. Glycogenolysis served as the primary fuel source during the first 24 h of fasting, while gluconeogenesis supplied the most glucose thereafter. Serum FFA concentrations increased significantly with 48 h of fasting. Serum FFAs partly caused high serum β-hydroxybutyrate levels, which became an important energy source with the prolongation of the fasting duration. One day of refeeding quickly reversed the energy substrate switch. Nutrient-sensing signaling molecules (AMPK and SIRT1 but not mTOR signaling) were highly expressed at the beginning of fasting (in the first 4 h). Serum insulin and leptin decreased with fasting initiation, and serum glucagon increased, but adiponectin and FGF21 showed no significant changes. Herein, we depicted in detail the timing of the metabolic response and adaptation of the liver to a 4-day water-only fast and subsequent refeeding in rats, which provides helpful support for the design of safe prolonged and intermittent fasting regimens.

Irisin Regulates Hepatic Glucose Metabolism via AMPK and PI3K/Akt Activation

Irisin plays a crucial role in the glucose metabolism of mammals and fish. However, the mechanism by which irisin regulates hepatic glucose metabolism is not entirely known. To clarify irisin’s function and underlying mechanisms in common carp glucose metabolism, the FNDC5 expression patterns were detected after insulin/glucagon injection, long-term high-glucose, and high-fat diet feeding. In vivo, the activity of PFK and the synthesis of liver glycogen were significantly increased, while the enzyme activity of PEPCK was reduced after intraperitoneal injection with irisin. In contrast, irisin siRNA attenuated the brain and liver FNDC5a and FNDC5b expression, and the serum glucose was increased. Glut2, gs, hk, and pfk were considerably downregulated in the brain and liver, while pygl, pepck, and g6pase were remarkably upregulated after siRNA treatment. In vitro, irisin activates the phosphorylation level of AMPK and PI3K/Akt in primary hepatocytes. Compound C and wortmannin inhibit AMPK and PI3K/Akt, reversing irisin-induced expression of g6pase, fbpase, pepck, gk, gs, pfk, hk, and gsk3b. At the same time, compound C attenuated irisin-induced expression of pi3k and akt. Our research reveals the mechanisms of irisinA and irisinB as glucose metabolism regulators in teleost for the first time.

The Role of Palmitoleic Acid in Regulating Hepatic Gluconeogenesis through SIRT3 in Obese Mice

Hepatic gluconeogenesis is a crucial process to maintain glucose level during starvation. However, unabated glucose production in diabetic patients is a major contributor to hyperglycemia. Palmitoleic acid is a monounsaturated fatty acid (16:1n7) that is available from dietary sources. Palmitoleic acid exhibits health beneficial effects on diabetes, insulin resistance, inflammation, and metabolic syndrome. However, the mechanism by which palmitoleate reduces blood glucose is still unclear. SIRT3 is a key metabolism-regulating NAD+-dependent protein deacetylase. It is known that fasting elevates the expression of SIRT3 in the liver and it regulates many aspects of liver’s response to nutrient deprivation, such as fatty acid oxidation and ketone body formation. However, it is unknown whether SIRT3 also regulates gluconeogenesis. Our study revealed that palmitoleic acid reduced hepatic gluconeogenesis and the expression of SIRT3 under high-fat diet conditions. Overexpression of SIRT3 in the liver and hepatocytes enhanced gluconeogenesis. Further study revealed that SIRT3 played a role in enhancing the activities of gluconeogenic enzymes, such as PEPCK, PC, and MDH2. Therefore, our study indicated that under a high-fat diet, palmitoleic acid decreased gluconeogenesis by reducing enzymatic activities of PEPCK, PC, and MDH2 by down-regulating the expression of SIRT3.

Empagliflozin Inhibits Hepatic Gluconeogenesis and Increases Glycogen Synthesis by AMPK/CREB/GSK3β Signalling Pathway.

Increases in glucose production and decreases in hepatic glycogen storage induce glucose metabolic abnormalities in type 2 diabetes (T2DM). Empagliflozin, a sodium-dependent glucose transporter 2 (SGLT2) inhibitor, is an effective hypoglycemic drug; however, the effects of empagliflozin on hepatic gluconeogenesis and glycogenesis are still unclear. In this study, we investigated the effects and mechanisms of empagliflozin on hepatic gluconeogenesis and glycogenesis in vivo and in vitro. Empagliflozin was administered via gavage to db/db mice for 8 weeks, and human hepatocyte HL7702 cells were treated with empagliflozin after palmitic acid (PA) stimulation. Compared with the control db/db mice, empagliflozin-treated mice showed a significant reduction in urine glucose levels, blood glucose levels, body weight and intraperitoneal glucose tolerance test (IPGTT) blood glucose levels. Moreover, the expression levels and activities of key gluconeogenesis enzymes PEPCK and G6Pase were dramatically reduced in the empagliflozin-treated mice, and the protein expression levels of AMPK/CREB/GSK3β signalling pathway-related molecules were significantly changed. In HL7702 cells, empagliflozin ameliorated glucose production and PEPCK and G6Pase expression and activity. Empagliflozin could also prevent the decreases in glycogen content and regulate the protein expression levels of AMPK/CREB/GSK3β signalling pathway-related molecules. Then, we selected the AMPK agonist AICAR and inhibitor compound C to further verify the effects of the AMPK signalling pathway on hepatic gluconeogenesis and glycogen synthesis. The results of the 5-Aminoimidazole-4-carboxamide1-β-D-ribofuranoside (AIACR) intervention in HL7702 cells were consistent with those of empagliflozin treatment, and the effects of empagliflozin were abolished by compound C. In summary, empagliflozin could maintain glucose homoeostasis by reducing gluconeogenesis and increasing glycogenesis through the AMPK/CREB/GSK3β signalling pathway.

The effect of coffee consumption on glucose homeostasis and redox-inflammatory responses in high-fat diet-induced obese rats

Coffee effects on glucose homeostasis in obesity remain controversial. We investigated whether coffee mitigates the negative effects on glucose metabolism induced by a high-fat diet and the interrelationships with redox-inflammatory responses. Rats were treated with: control (CT-); coffee (CT+) 3.9 g of freeze-dried coffee/kg of diet; high-fat (HF-); or high-fat + coffee 3.9 g of freeze-dried coffee/kg of diet (HF+) diet. The high-fat diet increased weight gain, feed efficiency, HOMA β, muscle and hepatic glycogen, intestinal CAT and SOD activity, hepatic protein (CARB) and lipid oxidation (MDA), muscle Prkaa1 mRNA and IL6 levels, and decreased food intake, hepatic GR, GPX and SOD activities, intestinal CARB, intestinal Slc2a2 and Slc5a1 and hepatic Prkaa1 and Prkaa2 mRNA levels, hepatic glucose-6-phosphatase and muscle hexokinase (HK) activities, compared to the control diet. The high-fat diet with coffee increased hepatic GST activity and TNF and decreased IL6 and intestinal glucosidase activity compared with the high-fat diet. The coffee diet increased muscle glycogen, hepatic CARB and PEPCK activity, and decreased hepatic GR and SOD activities and intestinal CARB, compared with the control diet. Coffee increased insulin levels, HOMA IR/β, FRAP, muscle Prkaa1 mRNA levels and hepatic and muscle phosphofructokinase-1, and it decreased intestinal CAT, hepatic Slc2a2 mRNA levels and muscle HK activity, regardless of the diet type. In conclusion, chronic coffee consumption improves antioxidant and anti-inflammatory responses, but does not ameliorate glucose homeostasis in a high-fat diet-induced obesity model. In addition, coffee consumption increases insulin secretion and promotes muscle glycogen synthesis in rats maintained on a control diet.

MiR-378a-3p Participates in Metformin's Mechanism of Action on C2C12 Cells under Hyperglycemia.

Metformin is the most used biguanide drug for the treatment of type 2 diabetes mellitus. Despite being mostly known for its hepatic anti-gluconeogenic effect, it is also known to modulate microRNAs (miRNAs, miRs) associated with metabolic diseases. The latter mechanism could be relevant for better understanding metformin’s mechanisms underlying its biological effects. In the current work, we found that metformin increases miR-378a-3p expression (p < 0.002) in C2C12 myoblasts previously exposed to hyperglycemic conditions. While the inhibition of miR-378a-3p was shown to impair metformin’s effect in ATP production, PEPCK activity and the expression of Tfam. Finally, mitophagy, an autophagic process responsible for the selective degradation of mitochondria, was found to be induced by miR-378a-3p (p < 0.04). miR-378a-3p stimulated mitophagy through a process independent of sestrin-2 (SESN2), a stress-responsible protein that has been recently demonstrated to positively modulate mitophagy. Our findings provide novel insights into an alternative mechanism of action of metformin involving miR-378a-3, which can be used in the future for the development of improved therapeutic strategies against metabolic diseases.

Effects of calcium treatment on malate metabolism and γ-aminobutyric acid (GABA) pathway in postharvest apple fruit

Calcium treatment effects on malate metabolism and the GABA pathway in ‘Cripps Pink’ apple fruit during storage were investigated. Postharvest apple fruit treated with 1% and 4% calcium chloride solutions were stored at 25 ± 1 °C. The 4% calcium treatment suppressed declines in titratable acidity and malate content and increased succinate and oxalate concentrations. Calcium treatment also reduced the respiration rate and decreased ethylene production peak during storage. Moreover, 4% calcium treatment significantly enhanced cyNAD-MDH and PEPC activities and upregulated MdMDH1, MdMDH2, MdPEPC1 and MdPEPC2 expression while inhibiting cyNADP-ME and PEPCK activities and downregulating MdME1, MdME4 and MdPEPCK2 expression. Surprisingly, calcium treatment changed the content of some free amino acids (GABA, proline, alanine, aspartic acid and glutamate), two of which (glutamate and GABA) are primary metabolites of the GABA pathway. Furthermore, calcium application enhanced GABA pathway activity by increasing MdGAD1, MdGAD2, MdGABA-T1/2 and MdSSADH transcript levels.

Kinetic and structural analysis of Escherichia coli phosphoenolpyruvate carboxykinase mutants

BackgroundPhosphoenolpyruvate carboxykinase (PEPCK) is a metabolic enzyme in the gluconeogenesis pathway, where it catalyzes the reversible conversion of oxaloacetate (OAA) to phosphoenolpyruvate (PEP) and CO2. The substrates for Escherichia coli PEPCK are OAA and MgATP, with Mn2+ acting as a cofactor. Analysis of PEPCK structures have revealed amino acid residues involved in substrate/cofactor coordination during catalysis. MethodsKey residues involved in coordinating the different substrates and cofactor bound to E. coli PEPCK were mutated. Purified mutant enzymes were used for kinetic assays. The structure of some mutant enzymes were determined using X-ray crystallography. ResultsMutation of residues D269 and H232, which comprise part of the coordination sphere of Mn2+, reduced kcat by 14-fold, and significantly increased the Km values for Mn2+ and OAA. Mutation of K254 a key residue in the P-loop motif that interacts with MgATP, significantly elevated the Km value for MgATP and reduced kcat. R65 and R333 are key residues that interacts with OAA. The R65Q and R333Q mutations significantly increased the Km value for OAA and reduced kcat respectively. ConclusionsOur results show that mutation of residues involved in coordinating OAA, MgATP and Mn2+ significantly reduce PEPCK activity. K254 plays an important role in phosphoryl transfer, while R333 is involved in both OAA decarboxylation and phosphoryl transfer by E. coli PEPCK. General significanceIn higher organisms including humans, PEPCK helps to regulate blood glucose levels, hence PEPCK is a potential drug target for patients with non-insulin dependent diabetes mellitus.