Inhaled ozone (O3)-induces changes in serum metabolomic and liver transcriptomic profiles in rats.
ABSTRACT: Air pollution has been linked to increased incidence of diabetes. Recently, we showed that ozone (O3) induces glucose intolerance, and increases serum leptin and epinephrine in Brown Norway rats. In this study, we hypothesized that O3 exposure will cause systemic changes in metabolic homeostasis and that serum metabolomic and liver transcriptomic profiling will provide mechanistic insights. In the first experiment, male Wistar Kyoto (WKY) rats were exposed to filtered air (FA) or O3 at 0.25, 0.50, or 1.0ppm, 6h/day for two days to establish concentration-related effects on glucose tolerance and lung injury. In a second experiment, rats were exposed to FA or 1.0ppm O3, 6h/day for either one or two consecutive days, and systemic metabolic responses were determined immediately after or 18h post-exposure. O3 increased serum glucose and leptin on day 1. Glucose intolerance persisted through two days of exposure but reversed 18h-post second exposure. O3 increased circulating metabolites of glycolysis, long-chain free fatty acids, branched-chain amino acids and cholesterol, while 1,5-anhydroglucitol, bile acids and metabolites of TCA cycle were decreased, indicating impaired glycemic control, proteolysis and lipolysis. Liver gene expression increased for markers of glycolysis, TCA cycle and gluconeogenesis, and decreased for markers of steroid and fat biosynthesis. Genes involved in apoptosis and mitochondrial function were also impacted by O3. In conclusion, short-term O3 exposure induces global metabolic derangement involving glucose, lipid, and amino acid metabolism, typical of a stress-response. It remains to be examined if these alterations contribute to insulin resistance upon chronic exposure.
Project description:Long-term exposure to particulate air pollutants has been linked to increased incidence of Type 2 Diabetes (T2DM). Recently, we showed that the gaseous pollutant, O3, induced glucose intolerance, and increased serum leptin and epinephrine in Brown Norway rats. In this study, we hypothesized that O3 exposure will cause broad scale changes in metabolic homeostasis involving liver, muscle and adipose tissues, and that serum metabolomic and liver transcriptomic profiling will provide mechanistic insights into pollutant-induced metabolic alterations. In the first experiment, male Wistar Kyoto (WKY) rats were exposed to filtered air (FA) or O3 at 0.25, 0.50, or 1.00 ppm, 6h/day for two consecutive days to establish concentration-related effects on glucose tolerance and lung injury. In a second experiment, rats were exposed to FA or 1.0 ppm O3, 6h/day for either one day or two consecutive days and systemic metabolic responses were determined immediately after each exposure or after an 18h recovery period. In WKY rats, O3 increased serum fasting glucose and leptin on day 1. Glucose intolerance persisted through two days of exposure but reversed 18h post second exposure. O3 exposure increased circulating metabolites of glycolysis, long-chain free fatty acids, branched chain amino acids (BCAA) and cholesterol while 1,5- anhydroglucitol, bile acids and metabolites of TCA cycle were decreased, indicating impaired glycemic control, muscle proteolysis and adipose lipolysis. Liver gene expression profile after O3 exposure reflected a response to the serum metabolite changes, as evidenced by increased expression of genes for glycolysis, TCA cycle and gluconeogenesis, and decreased expression of genes involved in steroid and fat biosynthesis. In conclusion, short-term O3 exposure induced hormonal changes and global metabolic disorder reflective of changes in peripheral glucose, lipid, and amino acid metabolism, representative of a stress-response. It remains to be examined if these metabolic alterations contribute to insulin resistance upon chronic exposure. Rats were exposed to filtered air (FA) or Ozone at 1 ppm, 6h/day for two consecutive days to establish ozone-exposure related effects on transcriptomic profiles. Samples were taken at three time points: 1 day (1day0hrs) - at the end of the 6 hour exposure period, 2 days (2day0hrs) - at the end of the of the second day 6 hour exposure period) and 2 days 18 hours (2day18hrs) - 18 hours after the 6 hour exposure period on the second day. Total liver RNA was isolated from ~20 mg tissue with a commercially available RNeasy mini kit (Qiagen, Valencia, CA) using silica gel membrane purification. Liver RNA was resuspended in 30μl of RNAse- free water. RNAse inhibitor was added and RNA yield was determined spectrophotometrically on a NanoDrop 1000 (Thermo Scientific, Wilmington, DE). RNA integrity was assessed by the RNA 6000 LabChip® kit using a 2100 Bioanalyzer (Agilent Technologies, Palo Alto, CA). We examined global gene expression changes using the Affymetrix platform (RG- 230 PM Array strip). Biotin-labeled cRNA was produced from total RNA using an Affymetrix “IVT-express labeling kit “(cat# 901229).
Project description:Leptin is thought to exert its actions on energy homeostasis through the long form of the leptin receptor (OB-Rb), which is present in the hypothalamus and in certain peripheral organs, including adipose tissue. In this study, we examined whether leptin has direct effects on the function of brown and white adipose tissue (BAT and WAT, respectively) at the metabolic and molecular levels. The chronic peripheral intravenous administration of leptin in vivo for 4 d resulted in a 1.6-fold increase in the in vivo glucose utilization index of BAT, whereas no significant change was found after intracerebroventricular administration compared with pair-fed control rats, compatible with a direct effect of leptin on BAT. The effect of leptin on WAT fat pads from lean Zucker Fa/ fa rats was assessed ex vivo, where a 9- and 16-fold increase in the rate of lipolysis was observed after 2 h of exposure to 0.1 and 10 nM leptin, respectively. In contrast, no increase in lipolysis was observed in the fat pads from obese fa/fa rats, which harbor an inactivating mutation in the OB-Rb. At the level of gene expression, leptin treatment for 24 h increased malic enzyme and lipoprotein lipase RNA 1.8+/-0.17 and 1.9+/-0.14-fold, respectively, while aP2 mRNA levels were unaltered in primary cultures of brown adipocytes from lean Fa/fa rats. Importantly, however, no significant effect of leptin was observed on these genes in brown adipocytes from obese fa/fa animals. The presence of OB-Rb receptors in adipose tissue was substantiated by the detection of its transcripts by RT-PCR, and leptin treatment in vivo and in vitro activated the specific STATs implicated in the signaling pathway of the OB-Rb. Taken together, our data strongly suggest that leptin has direct effects on BAT and WAT, resulting in the activation of the Jak/STAT pathway and the increased expression of certain target genes, which may partially account for the observed increase in glucose utilization and lipolysis in leptin-treated adipose tissue.
Project description:Air pollutants have been associated with increased diabetes in humans. We hypothesized that ozone would impair glucose homeostasis by altering insulin signaling and/or endoplasmic reticular (ER) stress in young and aged rats. One, 4, 12, and 24 month old Brown Norway (BN) rats were exposed to air or ozone, 0.25 or 1.0 ppm, 6 h/day for 2 days (acute) or 2 d/week for 13 weeks (subchronic). Additionally, 4 month old rats were exposed to air or 1.0 ppm ozone, 6 h/day for 1 or 2 days (time-course). Glucose tolerance tests (GTT) were performed immediately after exposure. Serum and tissue biomarkers were analyzed 18 h after final ozone for acute and subchronic studies, and immediately after each day of exposure in the time-course study. Age-related glucose intolerance and increases in metabolic biomarkers were apparent at baseline. Acute ozone caused hyperglycemia and glucose intolerance in rats of all ages. Ozone-induced glucose intolerance was reduced in rats exposed for 13 weeks. Acute, but not subchronic ozone increased ?2-macroglobulin, adiponectin and osteopontin. Time-course analysis indicated glucose intolerance at days 1 and 2 (2>1), and a recovery 18 h post ozone. Leptin increased day 1 and epinephrine at all times after ozone. Ozone tended to decrease phosphorylated insulin receptor substrate-1 in liver and adipose tissues. ER stress appeared to be the consequence of ozone induced acute metabolic impairment since transcriptional markers of ER stress increased only after 2 days of ozone. In conclusion, acute ozone exposure induces marked systemic metabolic impairments in BN rats of all ages, likely through sympathetic stimulation.
Project description:Leptin receptor, which is encoded by the diabetes (db) gene and is highly expressed in the choroid plexus, regulatesenergy homeostasis, the balance between food intake and energy expenditure, fertility and bone mass. Here, using CRISPR/Cas9 technology, we created the leptin receptor knockout rat. Homozygous leptin receptor null rats are characterized by obesity, hyperphagia, hyperglycemia, glucose intolerance, hyperinsulinemia and dyslipidemia. Due to long-term poor glycemic control, the leptin receptor knockout rats also develop some diabetic complications such as pancreatic, hepatic and renal lesions. In addition, the leptin receptor knockout rats show a significant decrease in bone volume and bone mineral density of the femur compared with their wild-type littermates. Our model has rescued some deficiency of the existing rodent models, such as the transient hyperglycemia of db/db mice in the C57BL/6J genetic background and the delayed onset of glucose intolerance in the Zucker rats, and it is proven to be a useful animal model for biomedical and pharmacological research on obesity and diabetes.
Project description:Genistein, a natural food compound mainly present in soybeans, is considered a potent antioxidant and to improve glucose homeostasis. However, its mechanism of action remains poorly understood. Here, we analyzed whether genistein could antagonize the progression of the hyperinsulinemic normoglycemic state (pre-diabetes) toward full-blown T2DM in Zucker Diabetic Fatty (ZDF) rats by decreasing mitochondrial oxidative stress and improving skeletal muscle oxidative capacity. Rats were assigned to three groups: (1) lean control (CNTL), (2) fa/fa CNTL, and (3) fa/fa genistein (GEN). GEN animals were subjected to a 0.02% (w/w) genistein-enriched diet for 8 weeks, whereas CNTL rats received a standard diet. We show that genistein did not affect the overall response to a glucose challenge in ZDF rats. In fact, genistein may exacerbate glucose intolerance as fasting glucose levels were significantly higher in fa/fa GEN (17.6 ± 0.7 mM) compared with fa/fa CNTL animals (14.9 ± 1.4 mM). Oxidative stress, established by electron spin resonance (ESR) spectroscopy, carbonylated protein content and UCP3 levels, remained unchanged upon dietary genistein supplementation. Furthermore, respirometry measurements revealed no effects of genistein on mitochondrial function. In conclusion, dietary genistein supplementation did not improve glucose homeostasis, alleviate oxidative stress, or augment skeletal muscle metabolism in ZDF rats.
Project description:In the obese state, enlarged adipose cells display an altered gene-expression profile and metabolic capacity. The aim of this study was to gain insight into their secretory function, by assessing two secreted proteins, leptin and angiotensinogen, in adipose cells of obese (fa/fa) Zucker rats. A marked and co-ordinate increase in leptin mRNA, gene transcription and promoter activity was observed in obese compared with lean (Fa/fa) rat adipose cells, and this resulted in increased leptin release in culture. Two sets of observations suggest that this effect is due to the fa mutation. First, adipose-cell leptin release was higher in heterozygous (Fa/fa) than in homozygous (Fa/Fa) lean rats. Second, leptin release was not enhanced in enlarged adipose cells of FalFa rats fed a high-fat diet for 15 days. At variance with leptin, angiotensinogen production was not significantly increased in the obese cells. Dexamethasone stimulated both leptin and angiotensinogen release in lean and obese rat adipose cells. The magnitude of leptin stimulation was higher in fa/fa than in Fa/fa rats, whereas angiotensinogen release was increased to the same extent in both genotypes. These observations suggest that leptin production is specifically enhanced in enlarged adipose cells of obese Zucker rats and that cell hypertrophy is not the sole determinant of this feature. Increased leptin production might be related to disruption of leptin signalling by the fa mutation.
Project description:Effectors of the phosphoinositide 3-kinase (PI3K) signal transduction pathway contribute to the hypothalamic regulation of energy and glucose homeostasis in divergent ways. Here we show that central nervous system (CNS) action of the PI3K signaling intermediate atypical protein kinase C (aPKC) constrains food intake, weight gain, and glucose intolerance in both rats and mice. Pharmacological inhibition of CNS aPKC activity acutely increases food intake and worsens glucose tolerance in chow-fed rodents and causes excess weight gain during high-fat diet (HFD) feeding. Similarly, selective deletion of the aPKC isoform Pkc-? in proopiomelanocortin (POMC) neurons disrupts leptin action, reduces melanocortin content in the paraventricular nucleus, and markedly increases susceptibility to obesity, glucose intolerance, and insulin resistance specifically in HFD-fed male mice. These data implicate aPKC as a novel regulator of energy and glucose homeostasis downstream of the leptin-PI3K pathway in POMC neurons.
Project description:High ambient levels of ozone (O3) and fine particulate matter (PM2.5) are associated with cardiovascular morbidity and mortality, especially in people with preexisting cardiopulmonary diseases. Enhanced susceptibility to the toxicity of air pollutants may include individuals with metabolic syndrome (MetS).We tested the hypothesis that cardiovascular responses to O3 and PM2.5 will be enhanced in rats with diet-induced MetS.Male Sprague-Dawley rats were fed a high-fructose diet (HFrD) to induce MetS and then exposed to O3, concentrated ambient PM2.5, or the combination of O3 plus PM2.5 for 9 days. Data related to heart rate (HR), HR variability (HRV), and blood pressure (BP) were collected.Consistent with MetS, HFrD rats were hypertensive and insulin resistant, and had elevated fasting levels of blood glucose and triglycerides. Decreases in HR and BP, which were found in all exposure groups, were greater and more persistent in HFrD rats compared with those fed a normal diet (ND). Coexposure to O3 plus PM2.5 induced acute drops in HR and BP in all rats, but only ND rats adapted after 2 days. HFrD rats had little exposure-related changes in HRV, whereas ND rats had increased HRV during O3 exposure, modest decreases with PM2.5, and dramatic decreases during O3 plus PM2.5 coexposures.Cardiovascular depression in O3- and PM2.5-exposed rats was enhanced and prolonged in rats with HFrD-induced MetS. These results in rodents suggest that people with MetS may be prone to similar exaggerated BP and HR responses to inhaled air pollutants.
Project description:1. The effect of insulin (0.5, 10 and 50 munits/ml of perfusate) on glucose uptake and disposal in skeletal muscle was studied in the isolated perfused hindquarter of obese (fa/fa) and lean (Fa/Fa) Zucker rats and Osborne-Mendel rats. 2. A concentration of 0.5 munit of insulin/ml induced a significant increase in glucose uptake (approx. 2.5 mumol/min per 30 g of muscle) in lean Zucker rats and in Osborne-Mendel rats, and 10 munits of insulin/ml caused a further increase to approx. 6 mumol/min per 30 g of muscle; but 50 munits of insulin/ml had no additional stimulatory effect. In contrast, in obese Zucker rats only 10 and 50 munits of insulin/ml had a stimulatory effect on glucose uptake, the magnitude of which was decreased by 50-70% when compared with either lean control group. Since under no experimental condition tested was an accumulation of free glucose in muscle-cell water observed, the data suggest an impairment of insulin-stimulated glucose transport across the muscle-cell membrane in obese Zucker rats. 3. The intracellular disposal of glucose in skeletal muscle of obese Zucker rats was also insulin-insensitive: even at insulin concentrations that clearly stimulated glucose uptake, no effect of insulin on lactate oxidation (nor an inhibitory effect on alanine release) was observed; [14C]glucose incorporation into skeletal-muscle lipids was stimulated by 50 munits of insulin/ml, but the rate was still only 10% of that observed in lean Zucker rats. 4. The data indicate that the skeletal muscle of obese Zucker rats is insulin-resistant with respect to both glucose-transport mechanisms and intracellular pathways of glucose metabolism, such as lactate oxidation. The excessive degree of insulin-insensitivity in skeletal muscle of obese Zucker rats may represent a causal factor in the development of the glucose intolerance in this species.
Project description:The Zucker fatty (ZF) rat harboring a missense mutation (fatty, fa) in the leptin receptor gene (Lepr) develops obesity without diabetes; Zucker diabetic fatty (ZDF) rats derived from the ZF strain exhibit obesity with diabetes and are widely used for research on type 2 diabetes (T2D). Here we establish a novel diabetic strain derived from normoglycemic ZF rats. In our ZF rat colony, we incidentally found fa/fa homozygous male rats having reproductive ability, which is generally absent in these animals. During maintenance of this strain by mating fa/fa males and fa/+ heterozygous females, we further identified fa/fa male rats exhibiting diabetes. We then performed selective breeding using the fa/fa male rats that exhibited relatively high blood glucose levels at 10 weeks of age, resulting in establishment of a diabetic strain that we designated Hos:ZFDM-Lepr(fa) (ZFDM). These fa/fa male rats developed diabetes as early as 10 weeks of age, reaching 100% incidence by 21 weeks of age, while none of the fa/+ male rats developed diabetes. The phenotypic characteristics of this diabetic strain are distinct from those of normoglycemic ZF rats. ZFDM rat strain having high reproductive efficiency should serve as a more useful animal model of T2D.