Regulation of messenger ribonucleic acid expression for gluconeogenic enzymes during glucagon infusions into lactating cows

Effects of Rumen-Protected Creatine Pyruvate on Meat Quality, Hepatic Gluconeogenesis, and Muscle Energy Metabolism of Long-Distance Transported Beef Cattle

Pre-slaughter long-distance transport resulted in a rapid depletion of muscle glycogen and led to a higher rate of dark, firm and dry (DFD) meat. Therefore, enhancing muscle glycogen reserves is critical for beef cattle prior to transportation. Creatine pyruvate (CrPyr) can provide simultaneous pyruvate and creatine and both are proven to promote the glycogen reserves. This study aimed to investigate the effects of transport treatment and dietary supplementation of rumen-protected (RP)-CrPyr on the meat quality, muscle energy metabolism, and hepatic gluconeogenesis of beef cattle. Twenty 18 month-old male Simmental crossbred cattle (659 ± 16 kg) were allotted 4 treatments based on a 2 × 2 factorial arrangement with two RP-CrPyr levels (140 g/d or 0 g/d) and two transport treatments (12 h or 5 min): ST_CrPyr0, ST_CrPyr140, LT_CrPyr0 and LT_CrPyr140. Three cattle per group were slaughtered after 30 days of feeding. The interaction of transport and RP-CrPyr had a significant effect on the muscle pH45 min, redness, glycogen content, GP, and AMP level (P < 0.05). Compared with short-distance transport, long-distance transport increased the muscle pH45 min value, redness, yellowness, drip loss, creatine level (P < 0.05), decreased muscle glycogen content, glycolytic potential (GP), and liver glucose amount (P < 0.05). Supplementation of RP-CrPyr decreased the activities of creatine kinase and lactate dehydrogenase in serum, muscle pH24 h value, redness, yellowness, lactate content, AMP level, and AMP/ATP (P < 0.05), increased the muscle glycogen content, GP, hexokinase activity, ATP and ADP levels, and ATP/ADP, liver pyruvate and glucose contents, activity of pyruvate carboxylase in the liver of cattle than those in the nonsupplemented treatments (P < 0.05). These results indicated that dietary RP-CrPyr supplementation might be favorable to improve meat quality and regulatory capacity of energy metabolism of beef cattle suffering long-distance transport followed with recovery treatment by increasing muscle glycogen storage, energy supply, and hepatic gluconeogenesis.

Energy substrate metabolism in skeletal muscle and liver when consuming diets of different energy levels: comparison between Tibetan and Small-tailed Han sheep

The energy intake of Tibetan sheep on the harsh Qinghai-Tibetan Plateau (QTP) varies greatly with seasonal forage fluctuations and is often below maintenance requirements, especially during the long, cold winter. The liver plays a crucial role in gluconeogenesis and skeletal muscle is the primary tissue of energy expenditure in mammals. Both play important roles in energy substrate metabolism and regulating energy metabolism homeostasis of the body. This study aimed to gain insight into how skeletal muscle and liver of Tibetan sheep regulate energy substrate metabolism to cope with low energy intake under the harsh environment of the QTP. Tibetan sheep (n = 24; 48.5 ± 1.89 kg BW) were compared with Small-tailed Han sheep (n = 24; 49.2 ± 2.21 kg BW), which were allocated randomly into one of four groups that differed in dietary digestible energy densities: 8.21, 9.33, 10.45 and 11.57 MJ /kg DM. The sheep were slaughtered after a 49-d feeding period, skeletal muscle and liver tissues were collected and measurements were made of the activities of the key enzymes of energy substrate metabolism and the expressions of genes related to energy homeostasis regulation. Compared with Small-tailed Han sheep, Tibetan sheep exhibited higher capacities of propionate to glucose conversion and fatty acid oxidation and ketogenesis in the liver, higher glucose utilization efficiency in both skeletal muscle and liver, but lower activities of fatty acid oxidation and protein mobilization in skeletal muscle, especially when in negative energy balance. However, the Small-tailed Han sheep exhibited higher capacities to convert amino acids and lactate to glucose and higher levels of glycolysis and lipogenesis in the liver than Tibetan sheep. These differences in gluconeogenesis and energy substrate metabolism conferred the Tibetan sheep an advantage over Small-tailed Han sheep to cope with low energy intake and regulate whole-body energy homeostasis under the harsh environment of the QTP.

Postpartum supplementation with fermented ammoniated condensed whey altered nutrient partitioning to support hepatic metabolism

Our previously published paper demonstrated that fermented ammoniated condensed whey (FACW) supplementation improved feed efficiency and metabolic profile in postpartum dairy cows. The objective of this study was to further explore the effects of FACW supplementation on liver triglyceride content, hepatic gene expression and protein abundance, and plasma biomarkers related to liver function, inflammation, and damage. Individually fed multiparous Holstein cows were blocked by calving date and randomly assigned to postpartum (1 to 45 d in milk, DIM) isonitrogenous treatments: control diet (n = 20) or diet supplemented with FACW (2.9% dry matter of diet as GlucoBoost; Fermented Nutrition, Luxemburg, WI, replacing soybean meal; n = 19). Liver biopsies were performed at 14 and 28 DIM for analysis of mRNA expression, protein abundance, and liver triglyceride content. There was marginal evidence for a reduction in liver triglyceride content at 14 DIM in FACW-supplemented cows compared with the control group. Cows supplemented with FACW had greater mRNA expression of glucose-6-phosphatase at 14 DIM relative to control. Supplementation with FACW increased mRNA expression of pyruvate carboxylase (PC), but did not alter cytosolic phosphoenolpyruvate carboxykinase (PCK1), resulting in a 2.4-fold greater PC:PCK1 ratio for FACW-supplemented cows compared with control. There was no evidence for a FACW effect on mRNA expression of propionyl-CoA carboxylase nor on mRNA expression or protein abundance of lactate dehydrogenase A or B. Cows supplemented with FACW had lower plasma urea nitrogen compared with control. Plasma l-lactate was greater for FACW-supplemented cows compared with control at 2 h before feeding time at 21 DIM. There was no evidence for altered expression of IL1B or IL10, or blood biomarkers related to liver function and damage. Greater glucose-6-phosphatase and PC gene expression, together with greater blood glucose and similar milk lactose output, suggests that FACW increased the supply of glucose precursors, resulting in greater gluconeogenesis between 3 and 14 DIM. Greater hepatic PC:PCK1 ratio, together with previously reported decreased plasma β-hydroxybutyrate and the marginal evidence for lower liver triglyceride content at 14 DIM, suggests greater hepatic capacity for complete oxidation of fatty acids in FACW-supplemented cows compared with control. Overall, improvements in metabolite profile and feed efficiency observed with postpartum supplementation of FACW may be attributed to increased gluconeogenic and anaplerotic precursors, most likely propionate, due to modulated rumen fermentation.

Effect of sorghum grain supplementation on glucose metabolism in cattle and sheep fed temperate pasture

The aim of this work was to evaluate the effect of sorghum grain supplementation on plasma glucose, insulin and glucagon concentrations, and hepatic mRNA concentrations of insulin receptor (INSR), pyruvate carboxylase (PC), and phosphoenolpyruvate carboxykinase (PCK1) mRNA and their association with nutrient intake, digestion and rumen volatile fatty acids (VFA) in cattle and sheep fed a fresh temperate pasture. Twelve Hereford × Aberdeen Angus heifers and 12 Corriedale × Milchschaf wethers in positive energy balance were assigned within each species to one of two treatments (n = 6 per treatment within specie): non-supplemented or supplemented with sorghum grain at 15 g/kg of their body weight (BW). Supplemented cattle had greater plasma glucose concentrations, decreased plasma glucagon concentrations and tended to have greater plasma insulin and insulin-to-glucagon ratio than non-supplemented ones. Hepatic expression of INSR and PC mRNA did not differ between treatments but PCK1 mRNA was less in supplemented than non-supplemented cattle. Supplemented sheep tended to have greater plasma glucagon concentrations than non-supplemented ones. Plasma glucose, insulin, insulin-to-glucagon ratio, and hepatic expression of INSR and PC mRNA did not differ between treatments, but PCK1 mRNA was less in supplemented than non-supplemented sheep. The inclusion of sorghum grain in the diet decreased PCK1 mRNA but did not affect PC mRNA in both species; these effects were associated with changes in glucose and endocrine profiles in cattle but not in sheep. Results would suggest that sorghum grain supplementation of animals in positive energy balance (cattle and sheep) fed a fresh temperate pasture would modify hepatic metabolism to prioritize the use of propionate as a gluconeogenic precursor.

Gluconeogenesis in dairy cows: the secret of making sweet milk from sour dough

Gluconeogenesis is a crucial process to support glucose homeostasis when nutritional supply with glucose is insufficient. Because ingested carbohydrates are efficiently fermented to short-chain fatty acids in the rumen, ruminants are required to meet the largest part of their glucose demand by de novo genesis after weaning. The qualitative difference to nonruminant species is that propionate originating from ruminal metabolism is the major substrate for gluconeogenesis. Disposal of propionate into gluconeogenesis via propionyl-CoA carboxylase, methylmalonyl-CoA mutase, and the cytosolic form of phosphoenolpyruvate carboxykinase (PEPCK) has a high metabolic priority and continues even if glucose is exogenously supplied. Gluconeogenesis is regulated at the transcriptional and several posttranscriptional levels and is under hormonal control (primarily insulin, glucagon, and growth hormone). Transcriptional regulation is relevant for regulating precursor entry into gluconeogenesis (propionate, alanine and other amino acids, lactate, and glycerol). Promoters of the bovine pyruvate carboxylase (PC) and PEPCK genes are directly controlled by metabolic products. The final steps decisive for glucose release (fructose 1,6-bisphosphatase and glucose 6-phosphatase) appear to be highly dependent on posttranscriptional regulation according to actual glucose status. Glucogenic precursor entry, together with hepatic glycogen dynamics, is mostly sufficient to meet the needs for hepatic glucose output except in high-producing dairy cows during the transition from the dry period to peak lactation. Lactating cows adapt to the increased glucose requirement for lactose production by mobilization of endogenous glucogenic substrates and increased hepatic PC expression. If these adaptations fail, lipid metabolism may be altered leading to fatty liver and ketosis. Increasing feed intake and provision of glucogenic precursors from the diet are important to ameliorate these disturbances. An improved understanding of the complex mechanisms underlying gluconeogenesis may further improve our options to enhance the postpartum health status of dairy cows.

Identification of the cyclic AMP responsive element (CRE) that mediates transcriptional regulation of the pyruvate carboxylase gene in HepG2 cells

Pyruvate carboxylase (PC) catalyzes the first committed step in gluconeogenesis. Here we investigated the effect of various hormones including cAMP, dexamethasone and insulin on the abundance of PC mRNA in the human hepatocyte cell line, HepG2. Treatment of HepG2 cells with 1 microM of glucagon increased the expression of PC mRNA threefold within 72 h. Treatment with 1mM 8-Br-cAMP caused the abundance of PC mRNA to increase by 2-3-fold by 48 h, peak at fourfold at 72 h, and remain unchanged to 96 h. This is in contrast to phosphoenolpyruvate carboxykinase (PEPCK) for which expression was decreased after 72 h, suggesting a distinct difference in the control of these two enzymes in the long term. Dexamethasone or insulin alone did not affect the abundance of PC mRNA whereas treatment of HepG2 cells with the combination of 1mM 8-Br-cAMP and 0.5 microM dexamethasone further increased the abundance of PC mRNA, suggesting the predominant role of 8-Br-cAMP over dexamethasone. Transient transfection of the luciferase reporter construct driven by a 1.95 kbp 5'-flanking sequence of the mouse PC gene and a plasmid encoding the human cAMP-responsive element binding protein increased luciferase reporter activity to 7-fold similar to that observed with a PEPCK promoter-luciferase reporter construct. Deletion of the 5'-flanking region of the PC gene to 781 bp resulted in the complete loss of CREB-mediated induction of reporter gene, suggesting the presence of the cAMP-responsive unit is located between 1.95 kbp and 781 bp upstream of the mouse PC gene. Electrophoretic mobility shifted and chromatin immunoprecipitation assays demonstrated that CREB bind to -1639/-1631 CRE of mouse PC gene in vitro and in vivo, respectively.

Structure, mechanism and regulation of pyruvate carboxylase

PC (pyruvate carboxylase) is a biotin-containing enzyme that catalyses the HCO(3)(-)- and MgATP-dependent carboxylation of pyruvate to form oxaloacetate. This is a very important anaplerotic reaction, replenishing oxaloacetate withdrawn from the tricarboxylic acid cycle for various pivotal biochemical pathways. PC is therefore considered as an enzyme that is crucial for intermediary metabolism, controlling fuel partitioning toward gluconeogenesis or lipogenesis and in insulin secretion. The enzyme was discovered in 1959 and over the last decade there has been much progress in understanding its structure and function. PC from most organisms is a tetrameric protein that is allosterically regulated by acetyl-CoA and aspartate. High-resolution crystal structures of the holoenzyme with various ligands bound have recently been determined, and have revealed details of the binding sites and the relative positions of the biotin carboxylase, carboxyltransferase and biotin carboxyl carrier domains, and also a unique allosteric effector domain. In the presence of the allosteric effector, acetyl-CoA, the biotin moiety transfers the carboxy group between the biotin carboxylase domain active site on one polypeptide chain and the carboxyltransferase active site on the adjacent antiparallel polypeptide chain. In addition, the bona fide role of PC in the non-gluconeogenic tissues has been studied using a combination of classical biochemistry and genetic approaches. The first cloning of the promoter of the PC gene in mammals and subsequent transcriptional studies reveal some key cognate transcription factors regulating tissue-specific expression. The present review summarizes these advances and also offers some prospects in terms of future directions for the study of this important enzyme.

Expression of pyruvate carboxylase mRNA variants in liver of dairy cattle at calving

Background

Bovine liver expresses six pyruvate carboxylase (PC) transcript variants, bPC5′A, bPC5′B, bPC5′C, bPC5′D, bPC5′E, and bPC5′F, which only differ at the 5′ untranslated region (UTR) and contain a common coding region. The objective of this experiment was to determine the profile and abundance of PC transcripts in bovine liver at calving.

Methodology/Principal Findings

A ribonuclease protection assay (RPA) protocol was developed to simplify analysis of these variants and investigate the changes in abundance of each 5′ UTR transcript relative to total PC mRNA. Liver biopsy samples collected from seven cows on +1 d relative to calving were analyzed by RPA to determine the profile in PC 5′ UTR variants. Results show that all six bovine PC 5′ UTR variants are detected at calving. Data indicate that bovine PC 5′ UTR variant A is the most abundant, variants C and E are least abundant and expression of variants B, D and F is intermediate at calving.

Conclusions

This manuscript describes a simplified RPA method that quantifies the abundance of six PC transcripts by using two riboprobes. The lack of uniformity in the pattern of PC 5′ UTR variants at calving suggests an additional complexity for control of bovine PC mRNA expression at calving that may be the result of transcriptional controls, variation in mRNA processing, or a combination of these processes.

Prevention of fatty liver in transition dairy cows by subcutaneous injections of glucagon

The main objective of this study was to test the extent to which injecting glucagon subcutaneously for 14 d beginning at d 2 postpartum would prevent fatty liver development in transition dairy cows. Twenty-four multiparous Holstein cows were fed 6 kg of cracked corn in addition to their standard diet during the last 30 d of a dry period to induce postpartum development of fatty liver. Glucagon at either 7.5 or 15 mg/d or saline (control) was injected subcutaneously 3 times daily for 14 d beginning at d 2 postpartum. Glucagon at 15 mg/ d prevented liver triacylglycerol accumulation in postpartum dairy cows. Glucagon at 7.5 mg/d showed potential for fatty liver prevention. Glucagon increased concentration of plasma glucose and insulin and decreased plasma nonesterified fatty acid concentrations. No effects of glucagon were detected on plasma beta-hydroxybutyrate concentrations. Glucagon affected neither feed intake nor milk production. Moreover, milk composition was not altered by glucagon. Milk urea N concentrations decreased, and plasma urea N concentrations tended to decrease during glucagon administration, indicating that glucagon may improve protein use. Liver glycogen concentrations were not affected by glucagon. No significant differences in body condition scores were detected among treatments throughout the study. These results indicate that subcutaneous glucagon injections can prevent fatty liver in transition dairy cows without causing major production and metabolite disturbances.

Effects of Short-Term Glucagon Administration on Gluconeogenic Enzymes in the Liver of Midlactation Dairy Cows

During lactation, the dairy cow experiences an increased demand for glucose to support milk production. Increased glucose demand can be met through increased capacity for gluconeogenesis, increased supply of glucose precursors, or a combination of both processes. Glucagon, a key hormone in glucose homeostasis, acts to promote gluconeogenesis and increase glucose output from liver. The objective of this study was to determine the effect of short-term administration of glucagon on expression of gluconeogenic enzymes in lactating dairy cattle. Sixteen multiparous Holstein cows were selected from the Purdue University Animal Sciences Dairy Research Center herd. Cows were stratified on the basis of milk production and days in milk and randomly assigned to either a saline or glucagon injection group (n = 8 per group). Cows were injected subcutaneously at -21, -14, -7, and 0 h relative to final glucagon and saline injections with either 3.75 mg of lyophilized bovine glucagon (15 mg/d) dissolved in 60 mL of 0.15 M NaCl (pH 10.25) or 60 mL of 0.15 M NaCl. Liver biopsy samples were obtained 1 wk before injection to establish baseline values and at 3 h after cows received final glucagon and saline injections. Biopsy samples were analyzed for mRNA abundance, enzyme activity, protein abundance, and in vitro measures of gluconeogenesis. Glucagon did not alter pyruvate carboxylase or cytosolic phosphoenolpyruvate carboxykinase (PEPCK) mRNA abundance, enzyme activity, or protein abundance, although there was a tendency for greater mRNA expression with the glucagon treatment (4.69 vs. 6.78, arbitrary units). Glucagon injections did not change mitochondrial PEPCK mRNA expression. Gluconeogenesis from 2.5 mM [2-(14)C]propionate and 2.0 mM [U-(14)C]lactate was similar in liver biopsy samples from glucagon-treated and control cows. There was no effect of glucagon on dry matter intake and milk production. Glucose, nonesterified fatty acids, beta-hydroxybutyrate acid, and insulin were not altered by glucagon. Blood glucagon was elevated, 76.09 vs. 96.14 pg/mL, for cows receiving glucagon injections. The data indicate that 24-h administration of glucagon does not alter cytosolic PEPCK mRNA expression or result in immediate alterations in total PEPCK enzyme activity and gluconeogenic capacity.

Acute Experimental Mastitis Is Not Causal Toward the Development of Energy-Related Metabolic Disorders in Early Postpartum Dairy Cows

Twenty Holstein cows in early lactation (7 d in milk) were administered 100 microg of Escherichia coli lipopolysaccharide (LPS) dissolved in 10 mL of sterile 0.9% NaCl saline (treatment; TRT) or 10 mL of sterile saline (control) into both right mammary quarters to test the hypothesis that acute experimental mastitis would have negative impacts on aspects of energy metabolism that might lead to the development of metabolic disorders. A primed continuous intravenous infusion (14-micromol/kg of BW priming dose; 11.5-micromol/kg of BW per h continuous infusion) of 6,6-dideuterated glucose was used to determine pre- and posttreatment glucose kinetics using steady-state tracer methodologies. The LPS-treated cows displayed productive, clinical, and physiological signs of moderate to severe inflammation; control cows displayed no signs of immune activation. Pretreatment glucose rates of appearance (Ra) into plasma were similar (715 and 662 +/- 33 mmol/h for TRT and control, respectively) between treatment groups. Intramammary LPS infusion into TRT cows resulted in increased glucose Ra relative to control cows (mean glucose Ra from 150 through 270 min after intramammary infusion were 815 and 674 +/- 21 mmol/h for TRT and control cows, respectively). Furthermore, plasma concentrations of glucose increased, whereas plasma nonesterified fatty acids, glycerol, and beta-hydroxybutyrate concentrations decreased, in TRT relative to control cows. Interestingly, plasma insulin concentration increased dramatically in TRT cows and occurred prior to the small increase in plasma glucose concentration. Although these results only represent the early stages of inflammation, they are not consistent with a causal relationship between mastitis and energy-related metabolic disorders and instead suggest a coordinated protective effect by the immune system on metabolism during the early stages of mammary insult.

Phlorizin administration increases hepatic gluconeogenic enzyme mRNA abundance but not feed intake in late-lactation dairy cows

Gluconeogenic capacity may be an important factor regulating dry matter intake (DMI) in lactating dairy cows. To determine whether increased glucose demand affects feed intake and hepatic gene expression, lactating Holstein cows were treated with phlorizin or vehicle (propylene glycol) for 7 d. Multiparous cows (n = 12; 269 +/- 65 d in milk, mean +/- SD) were randomly assigned to treatment sequence in a crossover design and were adapted to a common diet for 7 d before the beginning of the experiment. Phlorizin injected s.c. at 4 g/d caused glucose excretion in urine at the rate of 474 g/d. Although phlorizin decreased lactose synthesis and milk production (both P < 0.01), DMI and 3.5% fat-corrected milk production were not altered by treatment. A net deficit of 383 g glucose/d in milk and urine for phlorizin (relative to control) was likely replaced partially through increased gluconeogenesis. The molar insulin:glucagon ratio was decreased 17% by phlorizin (P < 0.001) and hepatic phosphoenolpyruvate carboxykinase, glucose-6-phosphatase, and pyruvate carboxylase mRNA abundance increased (all P < 0.05). Late-lactation dairy cows adapted quickly to an increase in peripheral glucose demand; adaptation mechanisms likely included enhanced gluconeogenic capacity, whereas DMI was not altered.

Cloning and characterization of bovine cytosolic and mitochondrial PEPCK during transition to lactation

The cytosolic (C) and mitochondrial (M) forms of phosphoenolpyruvate carboxykinase (PEPCK; EC 4.1.1.32) are encoded by two different nuclear genes in mouse, human, and chicken. Our objective was to clone the two forms of PEPCK for bovine and determine their expression during the immediate periparturient interval in dairy cows. Bovine PEPCK-C cDNA contains 2,592 nucleotides and contains 84% similarity to the coding sequence of human PEPCK-C cDNA. A 449-nt partial clone of the 3' end of PEPCK-M is 76% similar to the corresponding sequence of human PEPCK-M. The coding sequence of bovine PEPCK-C and coding sequence of the partial PEPCK-M clone were 58% similar but the similarities in the 3'-untranslated regions were negligible. Northern blot analysis revealed single transcripts of 2.85 and 2.35 kb for PEPCK-C and PEPCK-M, respectively. The transition to lactation did not alter PEPCK-M transcript expression, but expression of PEPCK-C mRNA was transiently increased during early lactation, indicating that enhanced hepatic gluconeogenesis during this period may be tied to enhanced capacity for cytosolic rather than mitochondrial formation of phosphoenolpyruvate.