Small intestinal morphology and sugar transporters expression when consuming diets of different energy levels: comparison between Tibetan and small-tailed Han sheep

Some non-structural carbohydrates, especially starch, escape ruminal fermentation, are converted into glucose, and are absorbed from the small intestine. This glucose provides an important source of energy, and its usage is more efficient than glucose from carbohydrates which are fermented as short chain fatty acids in the rumen and, subsequently, undergo hepatic gluconeogenesis. Tibetan sheep graze on the harsh Qinghai-Tibetan Plateau (QTP) all year round and their carbohydrate and energy intakes fluctuate greatly with seasonal forage availability. Consequently, a high capacity to absorb glucose from the small intestine would be particularly beneficial for Tibetan sheep to allow them to cope with the inconsistent dietary intakes. This study examined how the small intestinal morphology and sugar transporters’ expression of Tibetan and Small-tailed Han (Han) sheep respond to fluctuating energy intakes under the harsh conditions of the QTP. Han sheep graze on the QTP only in summer and are generally raised in feedlots. Twenty-four Tibetan sheep and 24 Han sheep, all wethers, were assigned randomly to four groups (n = 6 per breed/group), with each group offered a diet differing in digestible energy content: 8.21, 9.33, 10.45 and 11.57 MJ/kg DM. After 49 d, all sheep were slaughtered, tissues of the small intestine were collected, and measurements were made of the morphology and glucose transporters and the related regulation gene expressions. At intakes of low energy levels, Tibetan sheep had a greater villus surface area in the duodenum, jejunum and ileum and higher mRNA expression of sodium-dependent glucose transporter 1 in the duodenum and ileum (P < 0.05) than Han sheep. In the glucose transporter 2 (GLUT2) mediated glucose absorption pathway, Tibetan sheep had higher GLUT2 and taste receptor family 1 member 2 and 3 mRNA expressions than Han sheep in the duodenum, jejunum and ileum (P < 0.05). We concluded that the differences between breeds indicated a greater glucose absorption capacity in the small intestine of Tibetan than Han sheep, which would confer an advantage to Tibetan over Han sheep to an inconsistent energy intake on the harsh QTP. These findings suggested that ruminants raised under harsh environmental conditions with highly fluctuating dietary intakes, as is often the case in grazing ruminants worldwide, are able to absorb glucose from the small intestine to a greater extent than ruminants raised under more moderate conditions.     

D-Pinitol and myo-Inositol Stimulate Translocation of Glucose Transporter 4 in Skeletal Muscle of C57BL/6 Mice

Diabetes mellitus is a complex disease that is characterized by the defection of insulin sensitivity in such peripheral tissues as skeletal muscle, adipose tissue and liver. We have previously demonstrated that certain inositol derivatives stimulated glucose uptake accompanied by the translocation of glucose transporter 4 (GLUT4) to the plasma membrane in L6 myotubes. We investigated in this present study whether an oral intake of D-pinitol (PI) and myo-inositol (MI) would affect GLUT4 translocation in the skeletal muscle of mice. PI or MI at 1 g/kg BW administered orally to mice 30 min before a post-oral injection of glucose at 2 g/kg BW resulted in both PI and MI increasing GLUT4 translocation in the skeletal muscle and lowering the plasma glucose and insulin levels. PI and MI, therefore, have the potential to prevent diabetes mellitus by reducing the postprandial blood glucose level and stimulating GLUT4 translocation in the skeletal muscle.     

Genetic diversity of three Chinese native sheep breeds

The sheep (Ovis aries L.) has been an important farm animal species since its domestication. A wide array of indigenous sheep breeds with abundant phenotypic diversity exists for domestication and selection. Therefore, assessing the genetic diversity of a local sheep resource using a multi-molecular system is helpful for maintaining and conserving those breeds. This study aimed to investigate the genetic diversity of three native Chinese sheep breeds (Tibetan sheep, Sishui Fur sheep, and Small-tailed Han sheep) using 15 microsatellite markers and the second exon of the DRA gene. In regards to the microsatellites, on average, 19 alleles per loci were observed among all individuals. Across loci, the HO within the population was 0.652 ± 0.022 in Tibetan sheep, 0.603 ± 0.023 in Small-tailed Han sheep and 0.635 ± 0.022 in SFS, and for most populations, the H _E and H _O were inconsistent. In addition, affluent private alleles within the breed indicated that the breeds have different domestication histories or sites. In regards to the 2 exon of the DRA gene, three haplotypes were constructed by seven single-nucleotide polymorphisms (SNPs), which were identified in the second DRA exon and inferred the potential for phenotypic variety in these Chinese native sheep. In summary, the current study reveals the importance of implementing effective conservation strategies for these three native Chinese sheep.     

Diurnal Regulation of Peripheral Glucose Metabolism: Potential Effects of Exercise Timing

Diurnal oscillations in energy metabolism are linked to the activity of biological clocks and contribute to whole‐body glucose homeostasis. Postprandially, skeletal muscle takes up approximately 80% of circulatory glucose and hence is a key organ in maintenance of glucose homeostasis. Dysregulation of molecular clock components in skeletal muscle disrupts whole‐body glucose homeostasis. Next to light‐dark cycles, nonphotic cues such as nutrient intake and physical activity are also potent cues to (re)set (dys)regulated clocks. Physical exercise is one of the most potent ways to improve myocellular insulin sensitivity. Given the role of the biological clock in glucose homeostasis and the power of exercise to improve insulin sensitivity, one can hypothesize that there might be an optimal time for exercise to maximally improve insulin sensitivity and glucose homeostasis. In this review, we aim to summarize the available information related to the interaction of diurnal rhythm, glucose homeostasis, and physical exercise as a nonphotic cue to correct dysregulation of human glucose metabolism.     

Phylogenetic Relationships of Sheep Populations from Coastal Areas in East Asia

Using the method of random sampling in typical colonies of the central area of the habitat and several electrophoresis techniques, the variations of 12 structural loci encoding blood protein of 60 Small-tailed Han sheep were examined and compared with those of four other sheep populations from coastal areas in East Asia to explore their phylogenetic relationships. Average heterozygosity of the five populations was: Kharkhorin sheep 0.3447, Ulaanbaatar sheep 0.3285, Small-tailed Han sheep 0.3157, Hu sheep 0.3884, and Cham Tribe sheep 0.2300. The earlier researchers' conclusion through documentary research, indicating that Small-tailed Han sheep and Hu sheep both evolved from Mongolian sheep, was further verified by the results of this study. Hu sheep, Small-tailed Han sheep, and Cham Tribe sheep were decreasingly affected by the bloodline of Mongolian sheep. A partial founder population, i.e., Mongolian sheep forming current Small-tailed Han sheep, possibly made a contribution to the bloodline of Cham Tribe sheep.     

Diacylglycerol kinase ε deficiency preserves glucose tolerance and modulates lipid metabolism in obese mice

Diacylglycerol kinases (DGKs) catalyze the phosphorylation and conversion of diacylglycerol (DAG) into phosphatidic acid. DGK isozymes have unique primary structures, expression patterns, subcellular localizations, regulatory mechanisms, and DAG preferences. DGKε has a hydrophobic segment that promotes its attachment to membranes and shows substrate specificity for DAG with an arachidonoyl acyl chain in the sn-2 position of the substrate. We determined the role of DGKε in the regulation of energy and glucose homeostasis in relation to diet-induced insulin resistance and obesity using DGKε-KO and wild-type mice. Lipidomic analysis revealed elevated unsaturated and saturated DAG species in skeletal muscle of DGKε KO mice, which was paradoxically associated with increased glucose tolerance. Although skeletal muscle insulin sensitivity was unaltered, whole-body respiratory exchange ratio was reduced, and abundance of mitochondrial markers was increased, indicating a greater reliance on fat oxidation and intracellular lipid metabolism in DGKε KO mice. Thus, the increased intracellular lipids in skeletal muscle from DGKε KO mice may undergo rapid turnover because of increased mitochondrial function and lipid oxidation, rather than storage, which in turn may preserve insulin sensitivity. In conclusion, DGKε plays a role in glucose and energy homeostasis by modulating lipid metabolism in skeletal muscle.     

Enhanced expression of lipogenic genes may contribute to hyperglycemia and alterations in plasma lipids in response to dietary iron deficiency

Iron deficiency (ID) remains a public health concern affecting ~25% of the world’s population. Metabolic consequences of ID include elevated plasma glucose concentrations consistent with increased reliance on glucose as a metabolic substrate, though the mechanisms controlling these responses remain unclear. To further characterize the metabolic response to ID, weanling male Sprague–Dawley rats were fed either a control (C; 40 mg Fe/kg diet) or iron-deficient (ID; 3 mg Fe/kg diet) diet or were pair-fed (PF) the C diet to the level of intake of the ID group for 21 days. In addition to reductions in hemoglobin, hematocrit, and plasma iron, the ID group also exhibited higher percent body fat and plasma triglycerides compared to the PF group. Steady-state levels of both plasma glucose and insulin increased 40 and 45%, respectively, in the ID group compared to the PF group. Plasma cortisol levels were decreased 67% in the ID group compared to the PF diet group. The systematic evaluation of the expression of genes involved in insulin signaling, glucose metabolism, and fatty acid metabolism in the liver and skeletal muscle revealed significant alterations in the expression of 48 and 52 genes in these tissues, respectively. A significant concurrent increase in lipogenic gene expression and decrease in gene expression related to β-oxidation in both the liver and skeletal muscle, in combination with differential tissue expression of genes involved in glucose metabolism, provides novel insight into the adaptive metabolic response in rodent models of severe iron deficiency anemia.     

Nitrogen utilisation,energy utilisation and methane emissions of sheep grazing in two types of pasture

Livestock grazing plays a significant role in maintaining grasslands and promoting animal production globally. To understand the livestock performance in sown pasture (SP) vs native pasture (NP) is important to ensure more effective grassland-livestock interactions with minimal environmental impact. A 2 (treatment) * 2 (period) Latin Square design experiment was conducted with 10 growing Hu sheep ♂ × thin-tailed Han sheep ♀ rams grazed perennially SP vs NP in an inland arid region of China. The objectives were to evaluate the effects of grazing management on nutrient digestibility, nitrogen (N) and energy utilisation and methane (CH₄) emission. The N intake, N retained and energy intake (gross energy (GE), and digestible and metabolisable energy) of sheep grazing in SP were significantly increased compared with those grazing in NP. There were significant linear relationships between DM intake (DMI) (g/kg BW or g/kg BW^0.75) or CH₄ (g/kg BW or g/kg BW^0.75) emissions and forage nutrient and GE concentrations within each grassland type. The linear regression analysis indicated that forage CP or ether extract concentration was a good predictor for DMI (g/kg BW or g/kg BW^0.75) (R² = 0.756 or 0.752), and CH₄ emission could be predicted using forage nutrient and GE concentrations (R² = 0.381–0.503). These results suggest that DMI and CH₄ emissions per unit metabolic BW were accurately predicted by multiple-factor combinations of forage nutrients, including ether extract and CP paired with GE. The present output could provide useful information for the development of sustainable sheep grazing systems in the inland arid regions of the world.     

藏羚羊骨骼肌肌红蛋白含量及乳酸脱氢酶、苹果酸脱氢酶活力的研究

目的:探讨藏羚羊骨骼肌对低氧环境的适应机制。方法:以生活在同海拔高度(4 300 m)的藏绵羊和低海拔绵羊(1 800 m)为对照,用分光光度法测定三种动物骨骼肌中肌红蛋白(Mb)含量、乳酸(LA)含量,酶活力法测定三种动物骨骼肌中乳酸脱氢酶(LDH)和苹果酸脱氢酶(MDH)活力。结果:藏羚羊骨骼肌中Mb含量明显高于藏绵羊和低海拔绵羊(P<0.05),而藏绵羊和低海拔绵羊间无明显差异。LA含量和LDH活力明显低于藏绵羊和低海拔绵羊(P<0.05),而MDH活力及MDH/LDH比值显著高于藏绵羊和低海拔绵羊(P<0.05),藏绵羊和低海拔绵羊间无明显差异。结论:藏羚羊可能通过增加骨骼肌中Mb的含量,提高其在低氧环境获取氧的能力,且藏羚羊骨骼肌组织中有氧代谢比例高,这可能与肌肉中Mb含量较高有关,推测藏羚羊较高的Mb含量可能是其适应高原缺氧条件的分子基础之一。     

Dissociation of obesity and insulin resistance in transgenic mice with skeletal muscle expression of uncoupling protein 1.

We evaluated the effect of skeletal muscle mitochondrial uncoupling on energy and glucose metabolism under different diets. For 3 mo, transgenic HSA-mUCP1 mice with ectopic expression of uncoupling protein 1 in skeletal muscle and wild-type littermates were fed semisynthetic diets with varying macronutrient ratios (energy % carbohydrate-protein-fat): HCLF (41:42:17), HCHF (41:16:43); LCHF (11:45:44). Body composition, energy metabolism, and insulin resistance were assessed by NMR, indirect calorimetry, and insulin tolerance test, respectively. Gene expression in different organs was determined by real-time PCR. In wild type, both high-fat diets led to an increase in body weight and fat. HSA-mUCP1 mice considerably increased body fat on HCHF but stayed lean on the other diets. Irrespective of differences in body fat content, HSA-mUCP1 mice showed higher insulin sensitivity and decreased plasma insulin and liver triglycerides. Respiratory quotient and gene expression indicated overall increased carbohydrate oxidation of HSA-mUCP1 but a preferential channeling of fatty acids into muscle rather than liver with high-fat diets. Evidence for increased lipogenesis in white fat of HSA-mUCP1 mice suggests increased energy dissipating substrate cycling. Retinol binding protein 4 expression in white fat was increased in HSA-mUCP1 mice despite increased insulin sensitivity, excluding a causal role in the development of insulin resistance. We conclude that skeletal muscle mitochondrial uncoupling does not protect from the development of obesity in all circumstances. Rather it can lead to a "healthy" obese phenotype by preserving insulin sensitivity and a high metabolic flexibility, thus protecting from the development of obesity associated disturbances of glucose homeostasis.     

Programming of glucose-insulin metabolism in adult sheep after maternal undernutrition

The present study examines the effects of late vs. early gestation undernutrition on adult glucose-insulin homeostasis in sheep and investigates whether the lower birth weight of twins alters glucose-insulin handling in adult life. Pregnant sheep were fed to requirement (100% intake) from day 0 of gestation to term [ approximately 147 days of gestation (dGA), control singles (CS) n = 5; control twins (CT) n = 5] or to 50% requirement from days 0-30 dGA [nutrient restricted during early gestation (NRE); n = 5] or day 110-term [NR during late nutrition (NRL); n = 4]. At all other times, NR sheep received 100% intake. All sheep lambed naturally; offspring were weaned at 10 wk and were reared on pasture until 1 yr of age. At this time, indwelling catheters were inserted, and 2-4 days later, basal metabolic and endocrine status and responses to an intravenous glucose tolerance test (IVGTT) and feeding were assessed. Adipose and skeletal muscle were then sampled after humane euthanasia and were analyzed for expression of insulin-signaling proteins and GLUT4. Between groups, birth weight of singletons was similar and increased relative to twins. At 1 yr of age, weights were similar between groups. The areas under the curve for glucose and insulin during the IVGTT were greater in NRL vs. other groups, indicating glucose intolerance. This was associated with reduced adipose, but not muscle, GLUT4, and increased adipose tissue mass. Adult glucose-insulin homeostasis in sheep was unaffected by fetal number. In conclusion, prenatal undernutrition, specifically during late gestation, affects adult offspring intermediary metabolism, and, in particular, glucose-insulin homeostasis.     

Tocotrienol-rich fraction supplementation reduces hyperglycemia-induced skeletal muscle damage through regulation of insulin signaling and oxidative stress in type 2 diabetic mice

Chronic hyperglycemia induces impairment of muscle growth and development of diabetes mellitus (DM). Since skeletal muscle is the major site for disposal of ingested glucose, impaired glucose metabolism causes imbalance between protein synthesis and degradation which adversely affects physical mobility.In this study, we investigated the effect of tocotrienol-rich fraction (TRF) supplementation on skeletal muscle damage in diabetic mice. Diabetes was induced by a high-fat diet with streptozotocin (STZ) injection (100 mg/kg) in male C57BL/6J mice. After diabetes was induced (fasting blood glucose levels≥250 mg/dl), normal control (CON) and diabetic control (DMC) groups were administrated with olive oil, while TRF treatment groups were administrated with TRF (dissolved in olive oil) at low dose (100 mg/kg BW, LT) or high dose (300 mg/kg BW, HT) by oral gavage for 12 weeks.TRF supplementation ameliorated muscle atrophy, plasma insulin concentration and homeostatic model assessment estimated insulin resistance in diabetic mice. Moreover, TRF treatment up-regulated IRS-1 and Akt levels accompanied by increased translocation of GLUT4. Furthermore, TRF increased mitochondrial biogenesis by activating SIRT1, SIRT3 and AMPK in diabetic skeletal muscle. These changes were in part mechanistically explained by reduced levels of skeletal muscle proteins related to oxidative stress (4-hydroxynonenal, protein carbonyls, Nrf2 and HO-1), inflammation (NFkB, MCP-1, IL-6 and TNF-α), and apoptosis (Bax, Bcl₂ and caspase-3) in diabetic mice. Taken together, these results suggest that TRF might be useful as a beneficial nutraceutical to prevent skeletal muscle atrophy associated with diabetes by regulating insulin signaling via AMPK/SIRT1/PGC1α pathways in type 2 diabetic mice.     

Muscle-specific loss of apoptosis-inducing factor leads to mitochondrial dysfunction, skeletal muscle atrophy, and dilated cardiomyopathy

Cardiac and skeletal muscle critically depend on mitochondrial energy metabolism for their normal function. Recently, we showed that apoptosis-inducing factor (AIF), a mitochondrial protein implicated in programmed cell death, plays a role in mitochondrial respiration. However, the in vivo consequences of AIF-regulated mitochondrial respiration resulting from a loss-of-function mutation in Aif are not known. Here, we report tissue-specific deletion of Aif in the mouse. Mice in which Aif has been inactivated specifically in cardiac and skeletal muscle exhibit impaired activity and protein expression of respiratory chain complex I. Mutant animals develop severe dilated cardiomyopathy, heart failure, and skeletal muscle atrophy accompanied by lactic acidemia consistent with defects in the mitochondrial respiratory chain. Isolated hearts from mutant animals exhibit poor contractile performance in response to a respiratory chain-dependent energy substrate, but not in response to glucose, supporting the notion that impaired heart function in mutant animals results from defective mitochondrial energy metabolism. These data provide genetic proof that the previously defined cell death promoter AIF has a second essential function in mitochondrial respiration and aerobic energy metabolism required for normal heart function and skeletal muscle homeostasis.     

Excess Thyroid Hormone and Carbohydrate Metabolism

ObjectiveTo review the pertinent basic and clinical research describing the complex effects of excess thyroid hormone on carbohydrate metabolism.MethodsWe performed a MEDLINE search of the English-language literature using a combination of words (ie, “thyrotoxicosis and diabetes,” “diabetic ketoacidosis and thyroid storm,” “carbohydrate metabolism and hyperthyroid,” “glucose homeostasis and thyrotoxicosis”) to identify key articles addressing various aspects of the thyroid’s influence on carbohydrate metabolism.ResultsThyroid hormone affects glucose homeostasis via its actions on a variety of organs including increased hepatic glucose output, increased futile cycling of glucose degradation products between the skeletal muscle and the liver, decreased glycogen stores in the liver and skeletal muscle, altered oxidative and nonoxidative glucose metabolism, decreased active insulin output from the pancreas, and increased renal insulin clearance. Thyroid hormone also affects adipokines and adipose tissue, further predisposing the patient to ketosis.ConclusionsThyrotoxicosis can alter carbohydrate metabolism in a type 2 diabetic patient to such an extent that diabetic ketoacidosis develops if untreated. Based on the current understanding of this relationship, all diabetic patients should be screened for thyroid dysfunction because correcting hyperthyroidism can profoundly affect glucose homeostasis. Similarly, patients presenting in diabetic ketoacidosis should undergo a thyroid function assessment. (Endocr Pract. 2009;15:254-262)     

Physiological and genetic convergence supports hypoxia resistance in high-altitude songbirds

Skeletal muscle plays a central role in regulating glucose uptake and body metabolism; however, highland hypoxia is a severe challenge to aerobic metabolism in small endotherms. Therefore, understanding the physiological and genetic convergence of muscle hypoxia tolerance has a potential broad range of medical implications. Here we report and experimentally validate a common physiological mechanism across multiple high-altitude songbirds that improvement in insulin sensitivity contributes to glucose homeostasis, low oxygen consumption, and relative activity, and thus increases body weight. By contrast, low-altitude songbirds exhibit muscle loss, glucose intolerance, and increase energy expenditures under hypoxia. This adaptive mechanism is attributable to convergent missense mutations in the BNIP3L gene, and METTL8 gene that activates MEF2C expression in highlanders, which in turn increases hypoxia tolerance. Together, our findings from wild high-altitude songbirds suggest convergent physiological and genetic mechanisms of skeletal muscle in hypoxia resistance, which highlights the potentially medical implications of hypoxia-related metabolic diseases.     

The role of protein translocation in the regulation of glycogen metabolism

Early biochemical analyses of metabolic pathways assumed that the free diffusion of substrates and enzymes in an evenly mixed cellular space provided the interactions that enabled reactions to proceed. Metabolic complexes have since been shown to assemble and disassemble in response to changes in cellular conditions, and in turn, to channel metabolic intermediates within discreet cellular compartments, allowing for the efficient use or storage of energy. A fundamental component to the formation of metabolic complexes and the channeling of metabolites is the translocation of enzymes in response to specific extra- and intracellular signals. These generalities play an important role in the metabolism of glucose to glycogen within skeletal muscle and liver. In this review, the similarities and differences in skeletal muscle and liver glucose metabolism with regards to glucose transport and intracellular processing will be addressed during the fasted to fed transition. More specifically, the importance of isoform expression and protein translocation in the tissue specific control of glucose homeostasis will be covered.     

Myostatin regulates glucose metabolism via the AMP-activated protein kinase pathway in skeletal muscle cells

Myostatin (Mstn) is a secreted growth factor predominately expressed in skeletal muscle that negatively regulates skeletal muscle mass. Recent studies have indicated that loss function of myostatin not only increases muscle mass but also improves insulin sensitivity in vivo. In the present report, we demonstrated that myostatin regulates glucose metabolism by promoting glucose consumption and glucose uptake, increasing glycolysis, and inhibiting glycogen synthesis in skeletal muscle cells. Microarray analysis revealed that myostatin upregulates several genes involved in regulating glucose metabolism such as Glut1, Glut4, Hk2, and IL-6. Further investigation of the molecular basis of these phenomena revealed that AMP-activated protein kinase (AMPK), a key component for maintaining energy homeostasis, was activated by myostatin for promotion of glycolysis. Taken together, these findings provide the first experimental evidence that myostatin regulates glucose metabolism through the AMPK signal pathway in muscle cells. Importantly, our findings highlight that continued investigation of the metabolic function of myostatin is necessary for a comprehensive understanding of its active role in the regulation of skeletal muscle energy metabolism.     

Insulin Sensitivity in Adipose and Skeletal Muscle Tissue of Dairy Cows in Response to Dietary Energy Level and 2,4-Thiazolidinedione (TZD)

The effects of dietary energy level and 2,4-thiazolidinedione (TZD) injection on feed intake, body fatness, blood biomarkers and TZD concentrations, genes related to insulin sensitivity in adipose tissue (AT) and skeletal muscle, and peroxisome proliferator-activated receptor gamma (PPARG) protein in subcutaneous AT (SAT) were evaluated in Holstein cows. Fourteen nonpregnant nonlactating cows were fed a control low-energy (CON, 1.30 Mcal/kg) diet to meet 100% of estimated nutrient requirements for 3 weeks, after which half of the cows were assigned to a higher-energy diet (OVE, 1.60 Mcal/kg) and half of the cows continued on CON for 6 weeks. All cows received an intravenous injection of TZD starting 2 weeks after initiation of dietary treatments and for an additional 2 weeks, which served as the washout period. Cows fed OVE had greater energy intake and body mass than CON, and TZD had no effect during the administration period. The OVE cows had greater TZD clearance rate than CON cows. The lower concentration of nonesterified fatty acids (NEFA) and greater concentration of insulin in blood of OVE cows before TZD injection indicated positive energy balance and higher insulin sensitivity. Administration of TZD increased blood concentrations of glucose, insulin, and beta-hydroxybutyrate (BHBA) at 2 to 4 weeks after diet initiation, while the concentration of NEFA and adiponectin (ADIPOQ) remained unchanged during TZD. The TZD upregulated the mRNA expression of PPARG and its targets FASN and SREBF1 in SAT, but also SUMO1 and UBC9 which encode sumoylation proteins known to down-regulate PPARG expression and curtail adipogenesis. Therefore, a post-translational response to control PPARG gene expression in SAT could be a counteregulatory mechanism to restrain adipogenesis. The OVE cows had greater expression of the insulin sensitivity-related genes IRS1, SLC2A4, INSR, SCD, INSIG1, DGAT2, and ADIPOQ in SAT. In skeletal muscle, where PPARA and its targets orchestrate carbohydrate metabolism and fatty acid oxidation, the OVE cows had greater glyceroneogenesis (higher mRNA expression of PC and PCK1), whereas CON cows had greater glucose transport (SLC2A4). Administration of TZD increased triacylglycerol concentration and altered expression of carbohydrate- and fatty acid oxidation-related genes in skeletal muscle. Results indicate that overfeeding did not affect insulin sensitivity in nonpregnant, nonlactating dairy cows. The bovine PPARG receptor appears TZD-responsive, with its activation potentially leading to greater adipogenesis and lipogenesis in SAT, while differentially regulating glucose homeostasis and fatty acid oxidation in skeletal muscle. Targeting PPARG via dietary nutraceuticals while avoiding excessive fat deposition might improve insulin sensitivity in dairy cows during times such as the peripartal period when the onset of lactation naturally decreases systemic insulin release and sensitivity in tissues such as AT.     

Diabetes-Related Ankyrin Repeat Protein (DARP/Ankrd23) Modifies Glucose Homeostasis by Modulating AMPK Activity in Skeletal Muscle

Skeletal muscle is the major site for glucose disposal, the impairment of which closely associates with the glucose intolerance in diabetic patients. Diabetes-related ankyrin repeat protein (DARP/Ankrd23) is a member of muscle ankyrin repeat proteins, whose expression is enhanced in the skeletal muscle under diabetic conditions; however, its role in energy metabolism remains poorly understood. Here we report a novel role of DARP in the regulation of glucose homeostasis through modulating AMP-activated protein kinase (AMPK) activity. DARP is highly preferentially expressed in skeletal muscle, and its expression was substantially upregulated during myotube differentiation of C2C12 myoblasts. Interestingly, DARP-/- mice demonstrated better glucose tolerance despite similar body weight, while their insulin sensitivity did not differ from that in wildtype mice. We found that phosphorylation of AMPK, which mediates insulin-independent glucose uptake, in skeletal muscle was significantly enhanced in DARP-/- mice compared to that in wildtype mice. Gene silencing of DARP in C2C12 myotubes enhanced AMPK phosphorylation, whereas overexpression of DARP in C2C12 myoblasts reduced it. Moreover, DARP-silencing increased glucose uptake and oxidation in myotubes, which was abrogated by the treatment with AICAR, an AMPK activator. Of note, improved glucose tolerance in DARP-/- mice was abolished when mice were treated with AICAR. Mechanistically, gene silencing of DARP enhanced protein expression of LKB1 that is a major upstream kinase for AMPK in myotubes in vitro and the skeletal muscle in vivo. Together with the altered expression under diabetic conditions, our data strongly suggest that DARP plays an important role in the regulation of glucose homeostasis under physiological and pathological conditions, and thus DARP is a new therapeutic target for the treatment of diabetes mellitus.