Quantitative genetic analysis of glucose transporter 4 mRNA levels in baboon adipose

Apolipoprotein J protects cardiomyocytes from lipid-mediated inflammation and cytotoxicity induced by the epicardial adipose tissue of diabetic patients

Diabetic patients present increased volume and functional alterations in epicardial adipose tissue (EAT). We aimed to analyze EAT from type 2 diabetic patients and the inflammatory and cytotoxic effects induced on cardiomyocytes. Furthermore, we analyzed the cardioprotective role of apolipoprotein J (apoJ). EAT explants were obtained from nondiabetic patients (ND), diabetic patients without coronary disease (DM), and DM patients with coronary disease (DM-C) after heart surgery. Morphological characteristics and gene expression were evaluated. Explants were cultured for 24 h and the content of nonesterified fatty acids (NEFA) and sphingolipid species in secretomes was evaluated by lipidomic analysis. Afterwards, secretomes were added to AC16 human cardiomyocytes for 24 h in the presence or absence of cardioprotective molecules (apoJ and HDL). Cytokine release and apoptosis/necrosis were assessed by ELISA and flow cytometry. The EAT from the diabetic samples showed altered expression of genes related to lipid accumulation, insulin resistance, and inflammation. The secretomes from the DM samples presented an increased ratio of pro/antiatherogenic ceramide (Cer) species, while those from DM-C contained the highest concentration of saturated NEFA. DM and DM-C secretomes promoted inflammation and cytotoxicity on AC16 cardiomyocytes. Exogenous Cer16:0, Cer24:1, and palmitic acid reproduced deleterious effects in AC16 cells. These effects were attenuated by exogenous apoJ. Diabetic secretomes promoted inflammation and cytotoxicity in cardiomyocytes. This effect was exacerbated in the secretomes of the DM-C samples. The increased content of specific NEFA and ceramide species seems to play a key role in inducing such deleterious effects, which are attenuated by apoJ.

Effect of magnesium sulfate administration to improve insulin resistance in type 2 diabetes animal model: using the hyperinsulinemic-euglycemic clamp technique

This study attempted to elucidate the possible mechanism of magnesium sulfate (MgSO₄ ) administration on reducing insulin resistance in type 2 diabetic rats. Fifty Wistar rats were divided into five groups: NDC was fed the normal diet, CD received high-fat diet with 35 mg/kg of streptozotocin, CD-Mg animals received MgSO₄ via drinking water, CD-Ins1, and CD-Ins2 animals treated with low or high dose of insulin. Body weight and blood glucose levels were measured weekly. Intraperitoneal glucose tolerance test (IPGTT), insulin tolerance test, and metabolic cage assessment were performed monthly. After 12 weeks, the hyperinsulinemic-euglycemic clamp was performed for all animals and blood sample was taken to measure glycated hemoglobin (HbA1c), plasma insulin, glucagon, calcium, and magnesium levels. Liver and gastrocnemius muscle were isolated to measure glucagon receptor (GR), Glucose 6 phosphatase (G6Pase), Phosphoenolpyruvate carboxykinase (Pepck) and Glucose transporter 4 (Glut4) genes expression and GLUT4 protein translocation into the cell membrane. Consuming of high-fat diet generated insulin-resistant rats. Magnesium or insulin therapy altered insulin resistance, blood glucose, IPGTT, gluconeogenesis pathway, GR, body weight, the percentage of body fat, and HbA1C in diabetic rats. Administrations of MgSO₄ or insulin in Type 2 diabetes mellitus animals increase GLUT4 gene and protein expression. Mg could improve glucose tolerance via stimulation of Glut4 gene expression and translocation and also suppression of the gluconeogenesis pathway and GR gene expression. Mg also increased glucose infusion rate and displayed beneficial effects in the treatment of glucose metabolism and improved insulin resistance.

Use and Importance of Nonhuman Primates in Metabolic Disease Research: Current State of the Field

Obesity and its multiple metabolic sequelae, including type 2 diabetes, cardiovascular disease, and fatty liver disease, are becoming increasingly widespread in both the developed and developing world. There is an urgent need to identify new approaches for the prevention and treatment of these costly and prevalent metabolic conditions. Accomplishing this will require the use of appropriate animal models for preclinical and translational investigations in metabolic disease research. Although studies in rodent models are often useful for target/pathway identification and testing hypotheses, there are important differences in metabolic physiology between rodents and primates, and experimental findings in rodent models have often failed to be successfully translated into new, clinically useful therapeutic modalities in humans. Nonhuman primates represent a valuable and physiologically relevant model that serve as a critical translational bridge between basic studies performed in rodent models and clinical studies in humans. The purpose of this review is to evaluate the evidence, including a number of specific examples, in support of the use of nonhuman primate models in metabolic disease research, as well as some of the disadvantages and limitations involved in the use of nonhuman primates. The evidence taken as a whole indicates that nonhuman primates are and will remain an indispensable resource for evaluating the efficacy and safety of novel therapeutic strategies targeting clinically important metabolic diseases, including dyslipidemia and atherosclerosis, type 2 diabetes, hepatic steatosis, steatohepatitis, and hepatic fibrosis, and potentially the cognitive decline and dementia associated with metabolic dysfunction, prior to taking these therapies into clinical trials in humans.

Baboons as a model to study genetics and epigenetics of human disease

A major challenge for understanding susceptibility to common human diseases is determining genetic and environmental factors that influence mechanisms underlying variation in disease-related traits. The most common diseases afflicting the US population are complex diseases that develop as a result of defects in multiple genetically controlled systems in response to environmental challenges. Unraveling the etiology of these diseases is exceedingly difficult because of the many genetic and environmental factors involved. Studies of complex disease genetics in humans are challenging because it is not possible to control pedigree structure and often not practical to control environmental conditions over an extended period of time. Furthermore, access to tissues relevant to many diseases from healthy individuals is quite limited. The baboon is a well-established research model for the study of a wide array of common complex diseases, including dyslipidemia, hypertension, obesity, and osteoporosis. It is possible to acquire tissues from healthy, genetically characterized baboons that have been exposed to defined environmental stimuli. In this review, we describe the genetic and physiologic similarity of baboons with humans, the ability and usefulness of controlling environment and breeding, and current genetic and genomic resources. We discuss studies on genetics of heart disease, obesity, diabetes, metabolic syndrome, hypertension, osteoporosis, osteoarthritis, and intrauterine growth restriction using the baboon as a model for human disease. We also summarize new studies and resources under development, providing examples of potential translational studies for targeted interventions and therapies for human disease.

Modulation of GLUT4 expression by oral administration of Mg(2+) to control sugar levels in STZ-induced diabetic rats

It has been previously shown that oral magnesium administration decreases the levels of glucose in the plasma. However, the mechanisms are not fully understood. The aim of this study was to determine the potential role of GLUT4 on plasma glucose levels by orally administering magnesium sulfate to diabetic rats. Animals were distributed among 4 groups (n = 10 rats per group): one group served as the non-diabetic control, while the other groups had diabetes induced by streptozotocin (intraperitoneal (i.p.) injection). The diabetic rats were either given insulin by i.p. injection (2.5 U·(kg body mass)(-1)·day(-1)), or magnesium sulfate in their drinking water (10 g·L(-1)). After 8 weeks of treatment, we conducted an i.p. glucose tolerance test (IPGTT), measured blood glucose and plasma magnesium levels, and performed in-vitro and in-vivo insulin level measurements by radioimmunoassay. Gastrocnemius (leg) muscles were isolated for the measurement of GLU4 mRNA expression using real-time PCR. Administration of magnesium sulfate improved IPGTT and lowered blood glucose levels almost to the normal range. However, the insulin levels were not changed in either of the in-vitro or in-vivo studies. The expression of GLU4 mRNA increased 23% and 10% in diabetic magnesium-treated and insulin-treated groups, respectively. Our findings suggest that magnesium lowers blood glucose levels via increased GLU4 mRNA expression, independent to insulin secretion.

Myocardial insulin signaling and glucose transport are up-regulated in Goto-Kakizaki type 2 diabetic rats after ileal transposition

BACKGROUND

Ileal transposition (IT) as one of the effective treatments for non-obese type 2 diabetes mellitus has been widely investigated. However, the mechanisms underlying profound improvements in glucose homeostasis are still uncertain. Our objective was to explore the myocardial insulin signal transduction and glucose disposal in non-obese type 2 diabetes mellitus rats after IT surgery.

METHODS

Adult male Goto-Kakizaki (GK) rats or Sprague-Dawley (SD) rats were randomly assigned to diabetic IT, diabetic sham-IT, and non-diabetic control SD groups. Food intake, body weight, fasting plasma glucose, insulin tolerance, and serum glucagon-like peptide-1 (GLP-1) were measured. Subsequently, the myocardial glucose uptake and the protein levels of insulin receptor-beta (IR-β), phosphorylated IR-β, insulin receptor substrate 1 (IRS-1), phosphorylated IRS-1, and IRS-1-associated phosphatidylinositol-3 kinase (PI3K) from myocardial cell lysates were evaluated. We also assessed the expression of glucose transporter 4 (GLUT4) in both skeletal muscle and myocardial cell lysates.

RESULTS

Compared to sham operations within 6 months, IT surgery for GK rats did (1) result in less food intake and reduced body weight gain over time, (2) improve plasma glucose homeostasis with increased serum GLP-1 secretion and myocardial glucose uptake, (3) increase protein expression of insulin signaling pathway, including IR-β, IRS-1 and their phosphorylation levels, and IRS-1-associated PI3K in the myocardium, and (4) enhance the protein levels of membrane GLUT4 in skeletal muscle and myocardium.

CONCLUSIONS

IT surgery ameliorates glucose disorder in GK type 2 diabetic rats. Meanwhile, IT surgery is effective in up-regulating both myocardial insulin signaling and glucose disposal within 6 months.

Coronary artery disease is associated with higher epicardial retinol-binding protein 4 (RBP4) and lower glucose transporter (GLUT) 4 levels in epicardial and subcutaneous adipose tissue

OBJECTIVE

Retinol-binding protein 4 (RBP4), produced by adipocytes and hepatocytes, contributes to an unfavourable lipid profile and insulin resistance, which can contribute to the development of coronary artery disease (CAD). Recently, several studies have shown that epicardial adipose tissue (EAT) differs from subcutaneous adipose tissue (SAT) and plays a role on the physiopathology of CAD because of its proximity to the coronary arteries. We aimed to study the expression and secretion levels of RBP4 in both fat tissues and explore its possible association with CAD.

RESEARCH DESIGN AND METHODS

Fifty-eight patients undergoing heart surgery were included in the study. We analysed RBP4 mRNA expression by real-time PCR, protein expression by Western blot and immunohistochemistry, and secretion of EAT and SAT explants from CAD and non-CAD patients by Enzyme Immunoassay.

RESULTS

Retinol-binding protein 4 is expressed at similar levels in EAT and SAT, mainly from adipocytes. Protein levels were higher in EAT from CAD than non-CAD patients (0·63 ± 0·09 arbitrary units (a.u).; n = 10) vs (0·41 ± 0·04 a.u.; n = 13, P = 0·039). In contrast, GLUT4 mRNA levels were lower in EAT from CAD than non-CAD patients (6·55 ± 0·16 a.u.; n = 13) vs (7·21 ± 0·18 a.u.; n = 14, P = 0·012). We also found differential expression in SAT between samples from CAD and non-CAD patients [(6·63 ± 0·16 a.u.; n = 14) vs (7·21 ± 0·14 a.u.; n = 14, P = 0·009)]. Besides, EAT releases higher RBP4 levels than SAT after 3, 6, 24 and 48 h of culture. These levels were independent of CAD but significantly higher in diabetic than nondiabetic patients.

CONCLUSION

Retinol-binding protein 4 levels behave differently in EAT and SAT with respect to CAD. However, both adipose tissues have lower GLUT4 levels in patients with CAD. These findings suggest a differential regulation of RBP4 production in EAT and SAT that may be influenced by local factors.

Development of structural MR brain imaging protocols to study genetics and maturation

Structural imaging research offers excellent translational benefits when non-human primate (NHP) models are employed. In this paper, we will discuss the development of anatomical MR imaging protocols for two important applications of structural imaging in NHPs: studies of genetic variability in brain morphology and longitudinal imaging of fetal brain maturation trends. In contrast with imaging studies of adult humans, structural imaging in the NHPs is challenging due to a comparatively small brain size (2- to 200-fold smaller volume, depending on the species). This difference in size is further accentuated in NHP studies of brain development in which fetal brain volumes are 10-50% of their adult size. The sizes of cortical gyri and sulci scale allometrically with brain size. Thus, achieving spatial sampling that is comparable to that of high-quality human studies (approximately 1.0 mm(3)) requires a brain-size-adjusted reduction in the sampling volumes of from 500-to-150 microm(3). Imaging at this spatial resolution while maintaining sufficient contrast and signal to noise ratio necessitates the development of specialized MRI protocols. Here we discuss our strategy to optimize the protocol parameters for two commonly available structural imaging sequences: MPRAGE and TrueFisp. In addition, computational tools developed for the analysis of human structural images were applied to the NHP studies. These included removal of non-brain tissues, correction for RF inhomogeneity, spatial normalization, building of optimized target brain and analysis of cerebral gyrification and individual cortical variability. Finally, recent findings in the genetics of cerebral gyrification and tracking of maturation trends in the fetal, newborn and adult brain are described.

Characterization of ghrelin in pedigreed baboons: evidence for heritability and pleiotropy

BACKGROUND

Ghrelin is an orexigenic hormone that is produced primarily in the stomach, and stimulates food intake via its receptors situated in the hypothalamus.

OBJECTIVE

The purpose of this study was to characterize baboon ghrelin cDNA and investigate the genetic influence on the variation in plasma ghrelin levels in baboons.

METHODS AND PROCEDURES

The sample consisted of 376 baboons (263 females, 113 males) from a pedigreed colony at the Southwest Foundation for Biomedical Research, San Antonio, Texas. Ghrelin cDNA was cloned by reverse-transcription polymerase chain reaction (RT-PCR) and sequenced. Real-time RT-PCR was performed to quantify mRNA from the collected tissues. Genetic contribution to plasma ghrelin was estimated using a variance components method implemented in SOLAR.

RESULTS

The baboon coding region and predicted amino acid sequence for ghrelin showed 97 and 96% sequence identity with humans, respectively. Maximum expression of ghrelin mRNA was detected in hypothalamus and stomach. Mean +/- s.e. plasma levels of ghrelin were 3,406 +/- 99 pg/ml. A significant heritability was observed for plasma ghrelin (h(2)= 0.25, P < 0.001). A genome-wide scan revealed the evidence of suggestive linkage for a locus affecting plasma ghrelin on chromosome 9q22 (between markers D9S910 and D9S261, logarithm of the odds (LOD) score = 2.3). Significant genetic correlations (P < 0.001) among ghrelin, body weight, and leptin were observed.

DISCUSSION

These results indicate a significant genetic component in the variation of plasma ghrelin in baboons and reveal a high degree of similarity between baboon and human ghrelin with respect to its cDNA and its correlation with other obesity traits.

Genome-wide scan of plasma cholecystokinin in baboons shows linkage to human chromosome 17

OBJECTIVE

Cholecystokinin (CCK) is known to inhibit food intake and is an important signal for controlling meal volume, indicating a possible role in weight regulation. Our objective was to investigate genetic influences on plasma CCK in baboons.

RESEARCH METHODS AND PROCEDURES

Subjects were 376 baboons (males = 113, females = 263) from the Southwest National Primate Research Center, housed at the Southwest Foundation for Biomedical Research, San Antonio, Texas. Anthropometric and biochemical parameters were analyzed. Genetic effects on plasma CCK were estimated by the maximum likelihood-based variance components method implemented in the software program SOLAR (Sequential Oligogenic Linkage Analysis Routines).

RESULTS

Male baboons (32.7 +/- 6 kg) were much heavier than females (20.2 +/- 4 kg). Similarly, mean (+/- standard deviation) plasma CCK values were also higher in male baboons (13.8 +/- 6 pM) than female baboons (12.5 +/- 4 pM). Significant heritabilities were observed for plasma CCK (0.14 +/- 0.1, p < 0.05), body weight (h2 = 0.62 +/- 0.15, p < 10(-8)), and glucose (h2 = 0.68 +/- 0.17, p < 10(-7)). A genome-wide scan of plasma CCK detected a strong signal for a quantitative trait locus (QTL) on chromosome 17p12-13 [logarithm of the odds (LOD) = 3.1] near marker D17S804. Suggestive evidence of a second QTL was observed on chromosome 4q34-35 (LOD = 2.3) near marker D4S2374.

DISCUSSION

A substantial contribution of additive genetic effects to the variation in plasma levels of CCK was demonstrated in baboons. The identification of a QTL for plasma CCK on chromosome 17p is significant, as several obesity-related traits such as BMI, leptin, adiponectin, and acylation stimulating protein have already been mapped to this region.

A second-generation genetic linkage map of the baboon (Papio hamadryas) genome

Construction of genetic linkage maps for nonhuman primate species provides information and tools that are useful for comparative analysis of chromosome structure and evolution and facilitates comparative analysis of meiotic recombination mechanisms. Most importantly, nonhuman primate genome linkage maps provide the means to conduct whole genome linkage screens for localization and identification of quantitative trait loci that influence phenotypic variation in primate models of common complex human diseases such as atherosclerosis, hypertension, and diabetes. In this study we improved a previously published baboon whole genome linkage map by adding more loci. New loci were added in chromosomal regions that did not have sufficient marker density in the initial map. Relatively low heterozygosity loci from the original map were replaced with higher heterozygosity loci. We report in detail on baboon chromosomes 5, 12, and 18 for which the linkage maps are now substantially improved due to addition of new informative markers.

Quantitative genetic analysis of the metabolic syndrome in Hispanic children

Childhood obesity is associated with a constellation of metabolic derangements including glucose intolerance, hypertension, and dyslipidemia, referred to as metabolic syndrome. The purpose of this study was to investigate genetic and environmental factors contributing to the metabolic syndrome in Hispanic children. Metabolic syndrome, defined as having three or more metabolic risk components, was determined in 1030 Hispanic children, ages 4-19 y, from 319 families enrolled in the VIVA LA FAMILIA study. Anthropometry, body composition by dual energy x-ray absorptiometry, clinical signs, and serum biochemistries were measured using standard techniques. Risk factor analysis and quantitative genetic analysis were performed. Of the overweight children, 20%, or 28% if abnormal liver function is included in the definition, presented with the metabolic syndrome. Odds ratios for the metabolic syndrome were significantly increased by body mass index z-score and fasting serum insulin; independent effects of sex, age, puberty, and body composition were not seen. Heritabilities +/- SE for waist circumference, triglycerides (TG), HDL, systolic blood pressure (SBP), glucose, and alanine aminotransferase (ALT) were highly significant. Pleiotropy (a common set of genes affecting two traits) detected between SBP and waist circumference, SBP and glucose, HDL and waist circumference, ALT and waist circumference, and TG and ALT may underlie the clustering of the components of the metabolic syndrome. Significant heritabilities and pleiotropy seen for the components of the metabolic syndrome indicate a strong genetic contribution to the metabolic syndrome in overweight Hispanic children.