Phenotypes of mouse diabetes and rat fatty due to mutations in the OB (leptin) receptor

Pharmacological evaluation of a β-hydroxyphosphonate analogue of l-carnitine in obese Zucker fa/fa rats

In this study, we evaluated the effect of an analogue of l-carnitine on parameters involved with Metabolic Syndrome in obese Zucker rats. Twenty-four rats were treated for 5 weeks with l-carnitine (300 mg/kg) and its analogue at two concentrations (100 and 250 mg/kg) to assess their impact on glucose, triglycerides and cholesterol in liver and blood samples, as well as the amount of liver glycogen. Liver slices were also analysed. The analogue reduced the levels of glucose, triglycerides and cholesterol in liver and the level of triglycerides in serum. At 100 mg/kg, the analogue proved more effective than l-carnitine in improving the biochemical alterations present in liver. The amount of liver glycogen content was higher in obese animals treated with both l-carnitine and the analogue. No changes on insulin and leptin were observed in animals treated. l-carnitine and its analogue reduced the microvesicular fatty infiltration in liver. This study demonstrated that the analogue tested is more potent and efficient than l-carnitine and improves the pharmacological profile of l-carnitine.

Overview of animal models of obesity

The focus of this overview is on the animal models of obesity most commonly utilized in research. The models include monogenic models in the leptin pathway, polygenic diet-dependent models, and, in particular for their historical perspective, surgical and chemical models of obesity. However, there are far too many models to consider all of them comprehensively, especially those caused by selective molecular genetic approaches modifying one or more genes in specific populations of cells. Further, the generation and use of inducible transgenic animals (induced knock-out or knock-in) is not covered, even though they often carry significant advantages compared to traditional transgenic animals, e.g., influences of the genetic modification during the development of the animals can be minimized. The number of these animal models is simply too large to be covered in this unit.

Energy metabolism and the skeleton: Reciprocal interplay

The relation between bone remodelling and energy expenditure is an intriguing, and yet unexplained, challenge of the past ten years. In fact, it was only in the last few years that the skeleton was found to function, not only in its obvious roles of body support and protection, but also as an important part of the endocrine system. In particular, bone produces different hormones, like osteocalcin (OC), which influences energy expenditure in humans. The undercarboxylated form of OC has a reduced affinity for hydroxyapatite; hence it enters the systemic circulation more easily and exerts its metabolic functions for the proliferation of pancreatic β-cells, insulin secretion, sensitivity, and glucose tolerance. Leptin, a hormone synthesized by adipocytes, also has an effect on both bone remodelling and energy expenditure; in fact it inhibits appetite through hypothalamic influence and, in bone, stimulates osteoblastic differentiation and inhibits apoptosis. Leptin and serotonin exert opposite influences on bone mass accrual, but several features suggest that they might operate in the same pathway through a sympathetic tone. Serotonin, in fact, acts via two opposite pathways in controlling bone remodelling: central and peripheral. Serotonin product by the gastrointestinal tract (95%) augments bone formation by osteoblast, whereas brain-derived serotonin influences low bone mineral density and its decrease leads to an increase in bone resorption parameters. Finally, amylin (AMY) acts as a hormone that alters physiological responses related to feeding, and plays a role as a growth factor in bone. In vitro AMY stimulates the proliferation of osteoblasts, and osteoclast differentiation. Here we summarize the evidence that links energy expenditure and bone remodelling, with particular regard to humans.

Testosterone interacts with the feedback mechanisms engaged by Tyr985 of the leptin receptor and diet-induced obesity

Inhibitory signaling through Tyr985 of the leptin receptor contributes to the attenuation of anorectic leptin action in obese animals. Leptin receptor (LEPR-B) Tyr985Leu homozygote mutant mice (termed l/l) were previously generated to study Tyr985's contributions to inhibition of LEPR-B signaling; young female l/l mice display a lean, leptin-sensitive phenotype, while young male l/l are not significantly different from wild-type. We report here that testosterone (but not estrogen) determines the sex-specificity of the l/l phenotype. This provides additional insight into the cellular mechanism by which gonadal hormones determine central sensitivity to leptin, and may help elucidate the long-noted sex differences in leptin sensitivity. Additionally, we observed that Tyr985 signaling protects against a diet-dependent switch that exacerbates obesity with high fat feeding, such that the enhanced leptin sensitivity of l/l mice on a normal diet leads to increased adiposity in the face of chronic high-fat diet.

Anorexic effects of intra-VTA leptin are similar in low-fat and high-fat-fed rats but attenuated in a subgroup of high-fat-fed obese rats

Leptin is an adiposity hormone that plays an important role in regulating food intake and energy homeostasis. This study investigated the effects of a high-fat (HF) and a low-fat, high-carbohydrate/sugar (LF) diet on leptin sensitivity in the ventral tegmental area (VTA) in rats. The animals were exposed to a HF or LF diet for 16 weeks. Then the effects of intra-VTA leptin (150 and 500 ng/side, unilateral dose) on food intake and body weights were investigated while the animals were maintained on the HF or LF diet. Long-term exposure to the HF or LF diet led to similar body weight gain in these groups. The HF-fed animals consumed a smaller amount of food by weight than the LF-fed animals but both groups consumed the same amount of calories. The bilateral administration of leptin into the VTA decreased food intake (72 h) and body weights (48 h) to a similar degree in the HF and LF-fed animals. When the HF-fed animals were ranked by body weight gain it was shown that the diet-induced obese rats (HF-fed DIO, upper quartile for weight gain) were less sensitive to the effects of leptin on food intake and body weights than the diet-resistant rats (HF-fed DR, lower quartile for weight gain). A control experiment with fluorescent Cy3-labeled leptin showed that leptin did not spread beyond the borders of the VTA. This study indicates that leptin sensitivity in the VTA is the same in animals that are exposed to a HF or LF diet. However, HF-fed DIO rats are less sensitive to the effects of leptin in the VTA than HF-fed DR rats. Leptin resistance in the VTA might contribute to overeating and weight gain when exposed to a HF diet.

Stem cell transplantation increases antioxidant effects in diabetic mice

Intra bone marrow-bone marrow transplantation (IBM- BMT) + thymus transplantation (TT) has been shown to reduce the incidence of graft versus host disease (GVHD) and restore donor-derived T cell function. In addition, an increase in insulin sensitivity occurred in db/db mice after IBM-BMT+TT treatment. Heme oxygenase (HO)-1 is a stress inducible enzyme which exert antioxidant, antiapoptotic, and immune-modulating properties. We examined whether IBM-BMT+TT could modulate the expression of HO-1 in the kidneys of db/db mice. Six-week-old db/db mice with blood glucose levels higher than 250 mg/dl were treated with IBM-BMT+TT. Six weeks later, the db/db mice showed decreased body weight, blood glucose levels and insulin, and increased plasma adiponectin levels. The upregulation of HO-1 was associated with significantly (p<0.05) increased levels of peNOS and pAKT, but decreased levels of iNOS in the kidneys of db/db mice. Plasma creatinine levels also decreased (p<0.05), and the expression of type IV collagen was improved. Thus IBM-BMT+TT unregulated the expression of HO-1, peNOS and pAKT, while decreasing iNOS levels in the kidney of db/db mice. This was associated with an improvement in renal function.

Susceptibility variants for waist size in relation to abdominal, visceral, and hepatic adiposity in postmenopausal women

Genome-wide association studies have identified common genetic variants that can contribute specifically to the risk of abdominal adiposity, as measured by waist circumference or waist-to-hip ratio. However, it is unknown whether these genetic risk factors affect relative body fat distribution in the abdominal visceral and subcutaneous compartments. The association between imaging-based abdominal fat mass and waist-size risk variants in the FTO, LEPR, LYPLAL1, MSRA, NRXN3, and TFAP2B genes was investigated. A cross-sectional sample of 60 women was selected among study participants of The Multiethnic Cohort, who were aged 60 to 65 years, of European or Japanese descent, and with a body mass index (calculated as kg/m(2)) between 18.5 and 40. Dual-energy x-ray absorptiometry and abdominal magnetic resonance imaging scans were used to measure adiposity. After adjustments for age, ethnicity, and total fat mass, the FTO variants showed an association with less abdominal subcutaneous fat and a higher visceral-to-subcutaneous abdominal fat ratio, with the variant rs9941349 showing significant associations most consistently (P=0.003 and 0.03, respectively). Similarly, the LEPR rs1137101 variant was associated with less subcutaneous fat (P=0.01) and a greater visceral-to-subcutaneous fat ratio (P=0.03) and percent liver fat (P=0.007). MSRA rs545854 variant carriers had a lower percent of leg fat. Our findings provide initial evidence that some of the genetic risk factors identified for larger waist size might also contribute to disproportionately greater intra-abdominal and liver fat distribution in postmenopausal women. If replicated, these genetic variants can be incorporated with other biomarkers to predict high-risk body fat distribution.

Expression of ghrelin receptor (GHSR-1a) in rat epididymal spermatozoa and the effects of its activation

In this study we demonstrated the expression of the ghrelin receptor GHSR-1a in rat spermatids and epididymal spermatozoa, as well as some effects of ghrelin on the spermatozoa in vitro. For the demonstration of GHSR-1a the immunocytochemical, immunofluorescence and Western blotting techniques were applied using three different types of antibodies. The response of spermatozoa to ghrelin was tested in a series of in vitro experiments and their effects were evaluated using confocal microscopy and flow cytometry. GHSR-1a protein was found as expressed in the Golgi and acrosomes of spermatids and acrosome regions or the head cell membrane of epididymal spermatozoa. The GHSR-1a expression in spermatozoa was also confirmed by Western blot. No differences were found in percentage of spermatozoa showing annexin-V binding and expression of active form caspase-3 between control and ghrelin-treated spermatozoa. This result may indicate no pro-apoptotic effects of ghrelin neither at 10(-9) nor 10(-6)mol/L concentration. Ghrelin (10(-6)mol/L) increased free intracellular calcium ion concentration in the rat spermatozoa. Moreover, stimulation with 10(-6)mol/L ghrelin increased, while 10(-4)mol/L ghrelin decreased the number of spermatozoa showing progressive motility. In conclusion, the expression of the GHSR-1a receptor in spermatozoa, as well as ghrelin influences on sperm motility and intracellular calcium ion concentration suggest that such biological effects of ghrelin may be produced under in vivo conditions.

Nutrition-induced differences in body composition, compensatory growth and endocrine status in growing pigs

In this experiment, we assessed the effect of amino acid (AA) intake restriction in entire male Yorkshire pigs between 15 and 38 kg BW (restriction phase) on BW gain, body composition and plasma levels of blood urea nitrogen (BUN), cortisol, insulin-like growth factor I (IGF-I), growth hormone (GH) and leptin during the subsequent re-alimentation phase. During the restriction phase, 36 pigs were allotted to one of two dietary treatments: adequate AA intake (control) or AA-limiting diets (AA-30%). Thereafter, pigs were fed common non-limiting diets up to 110 kg BW. Throughout the experiment, pigs were scale-fed at 90% of the estimated voluntary daily digestible energy intake. At the end of the restriction phase, pigs on AA-30% had lesser BW gain (650 v. 784 g/day; P < 0.001), loin area (LA; 12.2 v. 14.2 cm2; P < 0.001), BUN (4.6 v. 6.3 mg/dl; P < 0.02), lesser plasma levels of IGF-I (440 v. 640 ng/m; P < 0.001) and cortisol (8.2 v. 19.2 μg/dl; P < 0.001), greater backfat thickness (BF; 7.56 v. 6.56 mm; P < 0.02), and greater plasma levels of leptin (2.7 v. 1.8 ng/ml; P = 0.027) and GH (3.3 v. 2.0 ng/ml; P = 0.05) than pigs on control. During the re-alimentation phase, previously restricted pigs showed full compensatory growth (CG) in terms of BW gain (1170 v. 1077 g/day; P < 0.002), whole-body protein deposition (Pd) (179 v. 163 g/day; P < 0.001) as well as physical and chemical body composition (whole-body lipid to body protein mass ratio, LB/PB; 1.14 v. 1.15; P > 0.10). Besides GH at 45 kg BW (4.2 v. 2.4 ng/ml; P = 0.066), there were no effects of previous AA intake restriction on leptin, IGF-I and BUN during the re-alimentation phase (P > 0.10). Plasma cortisol and IGF-I levels may act as an indicator of AA-induced restriction in Pd in growing pigs. Plasma BUN level does not appear as a sensitive indicator for compensatory Pd. Plasma leptin and GH levels allow for the involvement of the brain in controlling chemical body composition. Full CG was observed during the energy-dependent phase of Pd in growing pigs and might be driven by a target LB/PB, possibly mediated via plasma leptin, IGF-I and GH levels.

Hypercytolipidemia-induced nuclear lipoapoptosis: cytochemical analysis and integrated review of hypogonadal, diabetes-obesity syndrome-induced female reproductive axis disruption

Expression of the diabetes (db/db) mutation (i.e., leptin receptor defect) in C57BL/KsJ mice results in the functional suppression of the female pituitary-gonadal axis accompanied by premature utero-ovarian lipocytoatrophy. The current studies define the cytostructural, metabolic and endocrine disturbances associated with hypercytolipidemia and coincident nuclear lipoapoptosis following expression of the db/db-mutation. Adult, female C57BL/KsJ control (+/+ and +/? genotypes) and db/db mutant littermates were monitored for systemic alterations in blood glucose, insulin, luteinizing hormone (LH) and 17-B-estradiol (E2) concentrations associated with db/db-enhanced cytolipid depositions and TUNEL-labeled 3'-DNA fragmentation indexed nuclear lipoapoptosis. Obesity, hyperglycemia and hyperinsulinemia, in addition to depressed LH and E2 concentrations, characterized all db/db-mutants relative to control indices. Structural and cytochemical analysis of basophilic gonadotroph cells, ovarian follicular granulosa cells and uterine endometrial epithelial layers indicated that db/db mutants demonstrated prominent hypercytolipidemia relative to control cytoarchitecture profiles. Vasolipidemia and interstitial cytoadiposity were prominent in all db/db tissue compartments. In each affected cell type within the db/db pituitary-reproductive tract axis, hypercytolipidemia was localized with pronounced nuclear lipo-infiltration and 3'-DNA TUNEL-labeled fragmentation. These data indicate that coincident cytostructural, endocrine and metabolic disturbances associated with hypogonadal pituitary-reproductive tract hypercytolipidemia are functional manifestations of the expressed diabetes-obesity syndrome in db/db-mutants. The progressive vaso-, interstitial-, and cyto-lipidemic alterations in cytoarchitecture correlated with the coincident nuclear lipoapoptotic dissolution and pronounced organo-involution, alterations which contributed to the functional disruption of the pituitary-hypogonadal axis in C57BL/KsJ-db/db mice.

Adiponectin and leptin in human severe insulin resistance - diagnostic utility and biological insights

There is an intimate interplay between systemic insulin action and the actions of the adipocyte-derived proteins leptin and adiponectin. Concordant findings in humans and rodents demonstrate that leptin gates critical physiological functions to the prevailing nutritional state, however the physiological functions of adiponectin are less convincingly established. Murine evidence suggests that adiponectin can exert insulin-sensitising effects, plasma concentrations of adiponectin in humans correlate in most populations with insulin sensitivity, and increasingly strong evidence suggests an association between common genetic variation around the adiponectin gene and diabetes. However rare and severe genetic variants lowering adiponectin levels have not been convincingly associated with insulin resistance, and the discordant and sometimes extreme hyperadiponectinaemia seen in patients with severe insulin resistance due to loss of insulin receptor function poses a challenge to the widely held view that low adiponectin in humans plays a role in causing prevalent insulin resistance. The mechanism underlying this phenomenon remains to be elucidated, but the best available evidence implicates increased production of adiponectin in states of insulin receptor dysfunction, attributable at least in part to increased transcription of the ADIPOQ gene. Further investigation of the cellular basis of insulin receptoropathy-related hyperadiponectinaemia may shine further light on the human pathobiology of this most abundant and enigmatic product of adipose tissue.

Anti-inflammatory and cardioprotective effects of tadalafil in diabetic mice

Background

Insulin resistance impairs nitric oxide (NO) bioavailability and obesity promotes a state of chronic inflammation and damages the vascular endothelium. Phosphodiesterase-5 inhibitors restore NO signaling and may reduce circulating inflammatory markers, and improve metabolic parameters through a number of mechanisms. We hypothesized that daily administration of the PDE-5 inhibitor, tadalafil (TAD) will attenuate inflammation, improve fasting plasma glucose and triglyceride levels, body weight, and reduce infarct size after ischemia/reperfusion injury in obese, diabetic mice.

Methods

Twenty leptin receptor null (db/db) mice underwent treatment with TAD (1 mg/Kg) or 10% DMSO for 28 days. Body weight and fasting plasma glucose levels were determined weekly. Upon completion, hearts were isolated and subjected to 30 min global ischemia followed by 60 min reperfusion in a Langendorff model. Plasma samples were taken for cytokine analysis and fasting triglyceride levels. Infarct size was measured using computer morphometry of tetrazolium stained sections. Additionally, ventricular cardiomyocytes were isolated and subjected to 40 min of simulated ischemia and reoxygenation. Necrosis was determined using trypan blue exclusion and LDH release assay and apoptosis was assessed by TUNEL assay after 1 h or 18 h of reoxygenation, respectively.

Results

Treatment with TAD caused a reduction in infarct size in the diabetic heart (23.2±1.5 vs. 47.8±3.7%, p<0.01, n = 6/group), reduced fasting glucose levels (292±31.8 vs. 511±19.3 mg/dL, p<0.001) and fasting triglycerides (43.3±21 vs. 129.7±29 mg/dL, p<0.05) as compared to DMSO, however body weight was not significantly reduced. Circulating tumor necrosis factor-α and interleukin-1β were reduced after treatment compared to control (257±16.51 vs. 402.3±17.26 and 150.8±12.55 vs. 264±31.85 pg/mL, respectively; P<0.001) Isolated cardiomyocytes from TAD-treated mice showed reduced apoptosis and necrosis.

Conclusion

We have provided the first evidence that TAD therapy ameliorates circulating inflammatory cytokines and chemokines in a diabetic animal model while improving fasting glucose levels and reducing infarct size following ischemia-reperfusion injury in the heart.

The receptive function of hypothalamic and brainstem centres to hormonal and nutrient signals affecting energy balance

The hypothalamic arcuate nucleus (ARC) and the area postrema (AP) represent targets for hormonal and metabolic signals involved in energy homoeostasis, e.g. glucose, amylin, insulin, leptin, peptide YY (PYY), glucagon-like peptide 1 (GLP-1) and ghrelin. Orexigenic neuropeptide Y expressing ARC neurons are activated by food deprivation and inhibited by feeding in a nutrient-dependent manner. PYY and leptin also reverse or prevent fasting-induced activation of the ARC. Interestingly, hypothalamic responses to fasting are blunted in different models of obesity (e.g. diet-induced obesity (DIO) or late-onset obesity). The AP also responds to feeding-related signals. The pancreatic hormone amylin acts via the AP to control energy intake. Amylin-sensitive AP neurons are also glucose-responsive. Furthermore, diet-derived protein attenuates amylin responsiveness suggesting a modulation of AP sensitivity by macronutrient supply. This review gives an overview of the receptive function of the ARC and the AP to hormonal and nutritional stimuli involved in the control of energy balance and the possible implications in the context of obesity. Collectively, there is consistency between the neurophysiological actions of these stimuli and their effects on energy homoeostasis under experimental conditions. However, surprisingly little progress has been made in the development of effective pharmacological approaches against obesity. A promising way to improve effectiveness involves combination treatments (e.g. amylin/leptin agonists). Hormonal alterations (e.g. GLP-1 and PYY) are also considered to mediate body weight loss observed in obese patients receiving bariatric surgery. The effects of hormonal and nutritional signals and their interactions might hold the potential to develop poly-mechanistic therapeutic strategies against obesity.

Leptin signaling and circuits in puberty and fertility

Leptin is an adipocyte-derived hormone involved in a myriad of physiological process, including the control of energy balance and several neuroendocrine axes. Leptin-deficient mice and humans are obese, diabetic, and display a series of neuroendocrine and autonomic abnormalities. These individuals are infertile due to a lack of appropriate pubertal development and inadequate synthesis and secretion of gonadotropins and gonadal steroids. Leptin receptors are expressed in many organs and tissues, including those related to the control of reproductive physiology (e.g., the hypothalamus, pituitary gland, and gonads). In the last decade, it has become clear that leptin receptors located in the brain are major players in most leptin actions, including reproduction. Moreover, the recent development of molecular techniques for brain mapping and the use of genetically modified mouse models have generated crucial new findings for understanding leptin physiology and the metabolic influences on reproductive health. In the present review, we will highlight the new advances in the field, discuss the apparent contradictions, and underline the relevance of this complex physiological system to human health. We will focus our review on the hypothalamic circuitry and potential signaling pathways relevant to leptin’s effects in reproductive control, which have been identified with the use of cutting-edge technologies of molecular mapping and conditional knockouts.

Central nervous system endoplasmic reticulum stress in a murine model of type 2 diabetes

AIMS/HYPOTHESIS

Type 2 diabetes is associated with complications in the central nervous system (CNS), including learning and memory, and an increased risk for neurodegenerative diseases. The mechanism underlying this association is not understood. The aim of this study was to gain greater insight into the possible mechanisms of diabetes-induced cognitive decline.

METHODS

We used microarray technology to identify and examine changes in gene expression in the hippocampus of a murine model of type 2 diabetes, the db/db mouse. Bioinformatics approaches were then used to investigate the biological significance of these genes. To validate the biological significance we evaluated mRNA and protein levels.

RESULTS

At 8 and 24 weeks, 256 and 822 genes, respectively, were differentially expressed in the db/db mice. The most significantly enriched biological functions were related to mitochondria, heat shock proteins, or the endoplasmic reticulum (ER), the majority of which were downregulated. The ER-enriched cluster was one of the clusters that contained the highest number of differentially expressed genes. Several of the downregulated genes that were differentially expressed at 24 but not at 8 weeks are directly involved in the unfolded protein response (UPR) pathway and include two heat shock proteins (encoded by Hspa5 and Hsp90b1), a transcriptional factor (x-box binding protein 1, encoded by Xbp1), and an apoptotic mediator (DNA-damage inducible transcript 3, encoded by Ddit3).

CONCLUSIONS/INTERPRETATION

The changes that we observed in the UPR pathway due to ER stress may play a role in the pathogenesis of CNS complications in diabetes. The results of this study are a foundation for the development of pharmacological targets to reduce ER stress in diabetic hippocampi.

Rhodiola crenulata root ameliorates derangements of glucose and lipid metabolism in a rat model of the metabolic syndrome and type 2 diabetes

ETHNOPHARMACOLOGICAL RELEVANCE

Rhodiola species are traditionally used as tonics and stimulants to treat asthenia, suggesting their possible regulatory effect on energy metabolism. Clinical trials have demonstrated their glucose-lowering effect in type 2 diabetes.

AIM OF THE STUDY

To examine the effects of Rhodiola on glucose and lipid metabolism in the metabolic syndrome and type 2 diabetes.

MATERIALS AND METHODS

Zucker diabetic fatty (ZDF) rats were treated with Rhodiola crenulata root (RCR) powder (100 and 500 mg/kg, by gavage, once daily for 4 weeks). In addition, the effects of RCR on sucrose-induced acute hyperglycemia in mice and olive oil-induced hypertriglyceridemia in rats were also examined. Biochemical variables were determined enzymatically or by ELISA.

RESULTS

In ZDF rats, RCR treatment decreased the increased plasma insulin and triglyceride concentrations at baseline, the index of the homeostasis model assessment of insulin resistance (HOMA-IR) and excessive hepatic triglyceride accumulation. This treatment also inhibited abnormal increases in plasma glucose and insulin concentrations during oral glucose tolerance test. Furthermore, RCR reversed the increased adipose insulin resistance index, and accelerated the decline of plasma concentrations of non-esterified fatty acids after exogenous glucose stimulation. However, RCR minimally affected sucrose-induced acute hyperglycemia in mice and olive oil-induced acute hypertriglyceridemia in rats.

CONCLUSIONS

The present results demonstrate that RCR treatment improves metabolic derangements in animal model of the metabolic syndrome and type 2 diabetes. Our findings may provide new pharmacological basis of therapeutics for the adaptogenic plants to treat metabolic derangements-associated disorders, such as asthenia.

Leptin action via LepR-b Tyr1077 contributes to the control of energy balance and female reproduction

Leptin action in the brain signals the repletion of adipose energy stores, suppressing feeding and permitting energy expenditure on a variety of processes, including reproduction. Leptin binding to its receptor (LepR-b) promotes the tyrosine phosphorylation of three sites on LepR-b, each of which mediates distinct downstream signals. While the signals mediated by LepR-b Tyr1138 and Tyr985 control important aspects of energy homeostasis and LepR-b signal attenuation, respectively, the role of the remaining LepR-b phosphorylation site (Tyr1077) in leptin action has not been studied. To examine the function of Tyr1077, we generated a "knock-in" mouse model expressing LepR-b (F1077), which is mutant for LepR-b Tyr1077. Mice expressing LepR-b (F1077) demonstrate modestly increased body weight and adiposity. Furthermore, females display impairments in estrous cycling. Our results suggest that signaling by LepR-b Tyr1077 plays a modest role in the control of metabolism by leptin, and is an important link between body adiposity and the reproductive axis.

Cigarette smoking and brain regulation of energy homeostasis

Cigarette smoking is an addictive behavior, and is the primary cause of cardiovascular and pulmonary disease, and cancer (among other diseases). Cigarette smoke contains thousands of components that may affect caloric intake and energy expenditure, although nicotine is the major addictive substance present, and has the best described actions. Nicotine exposure from cigarette smoke can change brain feeding regulation to reduce appetite via both energy homeostatic and reward mechanisms, causing a negative energy state which is characterized by reduced energy intake and increased energy expenditure that are linked to low body weight. These findings have led to the public perception that smoking is associated with weight loss. However, its effects at reducing abdominal fat mass (a predisposing factor for glucose intolerance and insulin resistance) are marginal, and its promotion of lean body mass loss in animal studies suggests a limited potential for treatment in obesity. Smoking during pregnancy puts pressure on the mother's metabolic system and is a significant contributor to adverse pregnancy outcomes. Smoking is a predictor of future risk for respiratory dysfunction, social behavioral problems, cardiovascular disease, obesity, and type-2 diabetes. Catch-up growth is normally observed in children exposed to intrauterine smoke, which has been linked to subsequent childhood obesity. Nicotine can have a profound impact on the developing fetal brain, via its ability to rapidly and fully pass the placenta. In animal studies this has been linked with abnormal hypothalamic gene expression of appetite regulators such as downregulation of NPY and POMC in the arcuate nucleus of the hypothalamus. Maternal smoking or nicotine replacement leads to unhealthy eating habits (such as junk food addiction) and other behavioral disorders in the offspring.

Upregulation of astrocytic leptin receptor in mice with experimental autoimmune encephalomyelitis

The detrimental role of leptin in experimental autoimmune encephalomyelitis (EAE) is opposite to its neuroprotective role in other neuropathologies. We hypothesize that a shifted cellular distribution of leptin receptors underlies the differential effects of leptin. A robust increase of ObR immunoreactivity was seen along glial fibrillary acidic protein (GFAP)(+) intermediate filaments in reactive astrocytes in the hippocampus and hypothalamus of mice with EAE. Although astrocyte-specific GFAP mRNA and protein were both increased, ObRa mRNA was elevated only after resolution of EAE symptoms, and ObRb mRNA was even decreased at the peak time of symptoms of EAE. A cell type-specific action of leptin may underlie its differential effects.

Characteristics of glucocorticoid synthesis-related factors in the adrenals of obese Zucker rats (short communication)

To understand the molecular mechanism of hyperglucocorticoidism in obese Zucker rats, this study investigated glucocorticoid synthesis-related factors and their transcription factors in the adrenals. glucocorticoid synthesis-related factors and their transcription factors in the adrenals. The serum corticosterone level after foot shock stress was higher in obese Zucker rats than in lean Zucker rats. after foot shock stress was higher in obese Zucker rats than in lean Zucker rats. In the adrenals from obese Zucker rats, the mRNA and protein levels of steroidogenic acute regulatory protein were higher than those from lean Zucker rats. rats. However, the mRNA level of steroidogenic factor-1(SF-1), an important transcription factor for these glucocorticoid synthesis-related factors, did not differ between lean and obese Zucker rats. glucocorticoid synthesis-related factors, did not differ between lean and obese Zucker rats. Focusing on leptin signal transduction, Akt phosphorylation, which was known to inhibit glucocorticoid secretion, decreased in the adrenals from obese Zucker rats. from obese Zucker rats. We found that the stress-induced glucocorticoid secretion and the glucocorticoid synthesis related factors in the adrenals were increased in obese Zucker rats. factors in the adrenals were increased in obese Zucker rats. The decrease of Akt phosphorylation in the adrenals might induce these increases in obese Zucker rats.adrenals might induce these increases in obese Zucker rats.

Integrative role of the histaminergic system in feeding and taste perception

Feeding behavior is regulated by a complex interplay of many endogenous substances, such as peptides and neurotransmitters in the central nervous system. Histamine is a neurotransmitter which expresses an anorectic effect on food intake via histamine H(1) receptors. The histaminergic system exists downstream of leptin, a satiety factor secreted from white adipose tissue. Because direct stimulation of the histaminergic system by histamine H(3)-inverse agonists or antagonists can normalize the obese phenotype in which animal models with exogenous leptin resistance, which resembles human obesity, the potential roles of histamine H(3) receptors as a therapeutic target now draw attention. Histaminergic activity is enhanced during feeding, and an oral somatic sensation is thought to affect histaminergic activity while blood glucose levels do not. In addition, gustatory information can modulate histaminergic activity by two mechanisms: by physiological excitation of the chorda tympani nerve, one of the taste nerves and by emotions elicited by taste perception, i.e., taste palatability. Particularly, aversive and hazardous taste stimuli tonically facilitate histaminergic activity, suggesting that the histaminergic system is involved in the response to harmful stimuli. Together with recent findings, it is postulated that the histaminergic system responds to both mechanical and chemical sensory input from the oral cavity during feeding and is exerted as a part of the danger response system.

Gastric stimulation for weight loss

The prevalence of obesity is growing to epidemic proportions, and there is clearly a need for minimally invasive therapies with few adverse effects that allow for sustained weight loss. Behavior and lifestyle therapy are safe treatments for obesity in the short term, but the durability of the weight loss is limited. Although promising obesity drugs are in development, the currently available drugs lack efficacy or have unacceptable side effects. Surgery leads to long-term weight loss, but it is associated with morbidity and mortality. Gastric electrical stimulation (GES) has received increasing attention as a potential tool for treating obesity and gastrointestinal dysmotility disorders. GES is a promising, minimally invasive, safe, and effective method for treating obesity. External gastric pacing is aimed at alteration of the motility of the gastrointestinal tract in a way that will alter absorption due to alteration of transit time. In addition, data from animal models and preliminary data from human trials suggest a role for the gut-brain axis in the mechanism of GES. This may involve alteration of secretion of hormones associated with hunger or satiety. Patient selection for gastric stimulation therapy seems to be an important determinant of the treatment’s outcome. Here, we review the current status, potential mechanisms of action, and possible future applications of gastric stimulation for obesity.

Genetic control of ATGL-mediated lipolysis modulates adipose triglyceride stores in leptin-deficient mice

Dissecting the genetics of complex traits such as obesity allows the identification of causal genes for disease. Here, we show that the BALB/c mouse strain carries genetic variants that confer resistance to obesity induced by leptin-deficiency or a high-fat diet (HFD). We set out to identify the physiological and genetic bases underlying this phenotype. When compared with C57BL6/J ob/ob mice (B6), BALB/c ob/ob mice exhibited decreased food intake, increased thermogenic capacity, and improved fat catabolism, each of which can potentially modify obesity. Interestingly, analysis of F1 ob/ob (progeny of B6 ob/+ × BALB/c ob+) mice revealed that obesity resistance in BALB/c ob/ob mice principally relied upon improved fat mobilization. This was mechanistically explained by increased adipose triglyceride lipase (ATGL) content in adipocytes, along with increased lipolysis and fatty acid oxidation. We conducted a genome-wide scan and defined a quantitative trait locus (QTL) on chromosome 2. BALB/c alleles on chromosome 2 not only associated with the obesity resistance phenotype but also supported increased ATGL content in adipose tissue. In summary, our study provides evidence that leptin-independent control of adipocyte lipolysis rates directly modifies the balance of macronutrient handling and is sufficient to regulate fat mass in the absence of alterations in food intake and energy expenditure.-Marcelin, G., S-M. Liu, X. Li, G. J. Schwartz, and S. Chua.

Rosiglitazone treatment reversed depression- but not psychosis-like behavior of db/db diabetic mice

The objective of the present study was to examine the effect of long-term management of insulin resistance and hyperglycemia on neurobehavioral deficits in db/db mice. In this study, 5-week-old db/db and lean control mice were fed with rosiglitazone (20 mg/kg/day) mixed or standard chow for a duration of 5 weeks. Mice were monitored weekly for blood glucose concentration. Five weeks after the onset of treatment, they were subjected to the forced swim test (FST), pre-pulse inhibition (PPI), open field test (OFT) and fear-potentiated startle (FPS) test to examine for depression, psychosis-like behavior, locomotor activity and emotional learning, respectively. Rosiglitazone normalized hyperglycemia and improved glucose tolerance. Rosiglitazone significantly reduced immobility time in the FST in db/db mice, suggesting an antidepressant-like effect. However, rosiglitazone failed to reverse disruption of PPI in db/db mice, indicating its ineffectiveness against psychosis-like behavior. In the OFT, rosiglitazone did not affect the activity of db/db mice, suggesting its antidepressant-like effect was independent of changes in locomotor activity. In the FPS test, db/db mice showed impaired emotional learning and rosiglitazone failed to correct it. In conclusion, long-term blood glucose management in type-2 diabetics may help to limit the co-occurrence of depression but not the psychotic symptoms and ability to cope with stress.

Dietary soy protein induces hepatic lipogenic enzyme gene expression while suppressing hepatosteatosis in obese female Zucker rats bearing DMBA-initiated mammary tumors

Fatty liver is associated with obesity and breast cancer. We used an obese rat model of mammary cancer to examine whether hepatosteatosis is modifiable by diet and associated with altered expression of hepatic lipogenic enzyme genes, thyroid hormone system genes and cholesterol metabolism-related genes. Beginning at the age of 5 weeks, lean and obese female Zucker rats were fed high-isoflavone soy protein- or casein (control protein)-containing diets. Rats were euthanized at 200 days of age [corresponding to 147 days after administration of carcinogen to induce mammary tumors; (Hakkak et al. in, Oncol Lett 2:29-36, 2011)]. Obese rats had a greater degree of liver steatosis than lean rats. Obese casein-fed rats had marked steatosis with small foci of mononuclear infiltration, whereas obese soy protein-fed rats had a significantly lower steatosis index. Comparisons between lean and obese casein-fed rats showed that obesity was associated with significant reductions in hepatic mRNA abundance for Glucose 6-Phosphate Dehydrogenase (G6PD), 6-Phosphogluconate Dehydrogenase (6PGD), Thyroid Receptor Alpha 1 (TRα1), Thyroid Receptor Beta 1 (TRβ1) and Iodothyronine Deiodinase 1 (DIO1). The soy protein diet was associated with increased expression of Fatty Acid Synthase (FASN), Malic Enzyme 1 (ME1), 6PGD, Sterol Regulatory Element Binding Protein-1c (SREBP-1c) and SREBP-2 genes in the livers of obese but not lean rats. Western blot analysis showed a significant induction of ME1 protein expression in the livers of obese, soy protein-fed rats, which paralleled the increased serum insulin level in this group. Long-term soy protein consumption can counter hepatic steatosis while coincidently promoting hepatic lipogenic gene expression, the latter likely a consequence of elevated serum insulin. We suggest that elevations in serum insulin, hepatic lipogenesis and cholesterol synthesis all contributed to the increased tumorigenesis previously observed for the obese, soy protein-fed rats.

Protein-tyrosine phosphatases are involved in interferon resistance associated with insulin resistance in HepG2 cells and obese mice

Insulin resistance is a risk factor for non-response to interferon/ribavirin therapy in patients with chronic hepatitis C. The aim of this study was to determine the role played by protein-tyrosine phosphatases (PTPs) in the absence of interferon-α (IFNα) response associated with insulin resistance. We induced insulin resistance by silencing IRS-2 or by treating HepG2 cells with tumor necrosis factor-α (TNFα) and analyzed insulin response by evaluating Akt phosphorylation and IFNα response by measuring Stat-1 tyrosine phosphorylation and 2',5'-oligoadenylate synthase and myxovirus resistance gene expression. The response to IFNα was also measured in insulin-resistant obese mice (high fat diet and ob/ob mice) untreated and treated with metformin. Silencing IRS-2 mRNA induces insulin resistance and inhibits IFNα response. Likewise, TNFα suppresses insulin and IFNα response. Treatment of cells with pervanadate and knocking down PTP-1B restores insulin and IFNα response. Both silencing IRS-2 and TNFα treatment increase PTP and PTP-1B activity. Metformin inhibits PTP and improves IFNα response in insulin-resistant cells. Insulin-resistant ob/ob mice have increased PTP-1B gene expression and activity in the liver and do not respond to IFNα administration. Treatment with metformin improves this response. In HepG2 cells, insulin resistance provokes IFNα resistance, which is associated with an increased PTP-1B activity in the liver. Inhibition of PTP-1B activity with pervanadate and metformin or knocking down PTP-1B reestablishes IFNα response. Likewise, metformin decreases PTP-1B activity and improves response to IFNα in insulin-resistant obese mice. The use of PTP-1B inhibitors may improve the response to IFNα/ribavirin therapy.

Dendritically targeted Bdnf mRNA is essential for energy balance and response to leptin

Mutations in the Bdnf gene, which produces transcripts with either short or long 3' untranslated regions (3' UTRs), cause human obesity; however, the precise role of brain-derived neurotrophic factor (BDNF) in the regulation of energy balance is unknown. Here we show the relationship between Bdnf mRNA with a long 3' UTR (long 3' UTR Bdnf mRNA), leptin, neuronal activation and body weight. We found that long 3' UTR Bdnf mRNA was enriched in the dendrites of hypothalamic neurons and that insulin and leptin could stimulate its translation in dendrites. Furthermore, mice harboring a truncated long Bdnf 3' UTR developed severe hyperphagic obesity, which was completely reversed by viral expression of long 3' UTR Bdnf mRNA in the hypothalamus. In these mice, the ability of leptin to activate hypothalamic neurons and inhibit food intake was compromised despite normal activation of leptin receptors. These results reveal a novel mechanism linking leptin action to BDNF expression during hypothalamic-mediated regulation of body weight, while also implicating dendritic protein synthesis in this process.

Accelerated wound closure in a diabetic mouse model after exposure to phenanthrenequinone

BACKGROUND

Reactive oxygen species (ROS) have been shown to be important in wound healing by promoting angiogenesis (also mentioned by Ushio-Fukai and Nakamura). Likewise ROS have been implicated by toxicological studies as a primary mechanism of air pollution-associated morbidity. We sought to determine how exposure to a reactive diesel exhaust chemical (phenanthrenequinone [PQ]), which promotes formation of ROS and is considered an air pollutant, would affect wound healing. Since wound healing is compromised in diabetic (db) individuals, we examined the effects of PQ on wound healing in a db mouse model.

METHODS

db mice consumed PQ-containing chow for a short period (2 weeks) before wounding and through generations. Wound closure rates and wound vascularization were evaluated 10 days after wounding. The effects of PQ on endothelial cell proliferation and ROS generation in vitro were also measured.

RESULTS

db mice exposed to short-term PQ and PQ-exposed first-generation db mice demonstrated the highest closure rates, significantly better than control db mice (P < 0.05). Furthermore, a higher concentration of PQ in sera of db mice coincides with the higher rate of closure. PQ was also shown to produce ROS in cell culture and stimulate endothelial cell proliferation at nanomolar concentrations. Second- and third-generation db mice exposed to PQ did not show improved wound healing.

CONCLUSIONS

This study suggests that the free radical-generating air pollutant PQ enhances wound closure in the db mouse model possibly by stimulating angiogenesis, as suggested by in vitro results. We speculate that PQ may increase oxidation levels systemically and therefore help modulate inflammation at the wound site. Alternatively, antioxidant mechanisms recruited for wound healing may interfere with PQ metabolism and elimination as it accumulates in sera. Generational resistance to improve wound healing in PQ-exposed db mice could also be due to disturbances in metabolism caused by continuous exposure. In either case, these results introduce a new perspective on the effects of air pollution on wound healing.

Effects of Chronic Social Stress on Obesity

The prevalence of overweight and obesity has markedly increased during the past few decades. Stress has been suggested as one environmental factor that may contribute to the development of obesity. In this review, we discuss the role that exposure to chronic stress may play in the development of obesity, with particular attention to the effects of chronic psychosocial stress. Of particular importance is the effect that social stress has on dietary preference, food consumption, and regional distribution of adipose tissue. We present evidence from human and animal studies that links sympathetic nervous system and hypothalamic-pituitary-adrenal axis hyperactivity with visceral obesity, and that stress tends to alter the pattern of food consumption, and promotes craving of nutrient-dense "comfort foods." Lastly, we discuss the visible burrow system, a model of chronic social stress used in our laboratory to assess the effects of social subordination on behavioral and metabolic profile.

Glucose enhances leptin signaling through modulation of AMPK activity

Leptin exerts its action by binding to and activating the long form of leptin receptors (LEPRb). LEPRb activates JAK2 that subsequently phosphorylates and activates STAT3. The JAK2/STAT3 pathway is required for leptin control of energy balance and body weight. Defects in leptin signaling lead to leptin resistance, a primary risk factor for obesity. Body weight is also regulated by nutrients, including glucose. Defects in glucose sensing also contribute to obesity. Here we report crosstalk between leptin and glucose. Glucose starvation blocked the ability of leptin to stimulate tyrosyl phosphorylation and activation of JAK2 and STAT3 in a variety of cell types. Glucose dose-dependently enhanced leptin signaling. In contrast, glucose did not enhance growth hormone-stimulated phosphorylation of JAK2 and STAT5. Glucose starvation or 2-deoxyglucose-induced inhibition of glycolysis activated AMPK and inhibited leptin signaling; pharmacological inhibition of AMPK restored the ability of leptin to stimulate STAT3 phosphorylation. Conversely, pharmacological activation of AMPK was sufficient to inhibit leptin signaling and to block the ability of glucose to enhance leptin signaling. These results suggest that glucose and/or its metabolites play a permissive role in leptin signaling, and that glucose enhances leptin sensitivity at least in part by attenuating the ability of AMPK to inhibit leptin signaling.

Functional heterogeneity of arcuate nucleus pro-opiomelanocortin neurons: implications for diverging melanocortin pathways

Arcuate nucleus (ARC) pro-opiomelanocortin (POMC) neurons are essential regulators of food intake, energy expenditure, and glucose homeostasis. POMC neurons integrate several key metabolic signals that include neurotransmitters and hormones. The change in activity of POMC neurons is relayed to melanocortin receptors in distinct regions of the central nervous system. This review will summarize the role of leptin and serotonin receptors in regulating the activity of POMC neurons and provide a model in which different melanocortin pathways regulate energy and glucose homeostasis.

High susceptibility to zymbal gland and intestinal carcinogenesis in diabetic Otsuka long-evans Tokushima Fatty rats

Diabetes mellitus (DM) and obesity are believed to be risk factors for colorectal cancer in humans. In experiment 1, male nondiabetic Long-Evans Tokushima Otsuka (LETO) rats and Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model animal of type 2 DM, were whole-body X-irradiated (4 Gy) at 6 and 8 weeks of age and euthanized at 78 weeks of age (n=15, respectively). The incidences of small intestine adenocarcinoma in LETO and OLETF rats were 0% and 30%, respectively. In experiment 2, male LETO and OLETF rats (n=24, respectively) were given s.c. injections of 15 mg/kg azoxymethane (AOM) once weekly for 3 weeks and euthanized at 36 weeks of age. The incidences of Zymbal gland tumors in LETO and OLETF rats were 0% and 67%, respectively (P<0.001), whereas those of small intestine adenocarcinoma were 0% and 43% (P<0.001) and those of cecum/colon adenocarcinoma were 46% and 79% (P<0.05), respectively. Fatty change of hepatocytes was common in OLETF rats (63%) but not in LETO rats. Serum triglyceride and free fatty acid levels in OLETF rats were significantly higher than in LETO rats at sacrifice, whereas serum insulin levels in OLETF rats were very diverse. These data suggest that hyperlipidemia plays a significant role in high susceptibility to lower intestinal tract carcinogenesis in OLETF rats; this strain is susceptible to AOM-induced Zymbal gland carcinogenesis.

Challenges and opportunities of defining clinical leptin resistance

The widespread use of the inadequately defined term "leptin resistance" led the National Institutes of Health to convene a workshop aimed at developing a quantitative definition of this term that would facilitate mechanistic research into leptin's actions in human health and disease. Although leptin-responsive conditions are recognized, the field is limited by a lack of robust, easily quantifiable behavioral or metabolic biomarkers of the hormone's action. Further advances require biomarkers that can be used to identify patients who may benefit from leptin therapy and that are useful for understanding the determinants of clinical leptin responsiveness.

New experimental models of diabetic nephropathy in mice models of type 2 diabetes: efforts to replicate human nephropathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. The use of experimental models of DN has provided valuable information regarding many aspects of DN, including pathophysiology, progression, implicated genes, and new therapeutic strategies. A large number of mouse models of diabetes have been identified and their kidney disease was characterized to various degrees. Most experimental models of type 2 DN are helpful in studying early stages of DN, but these models have not been able to reproduce the characteristic features of more advanced DN in humans such as nodules in the glomerular tuft or glomerulosclerosis. The generation of new experimental models of DN created by crossing, knockdown, or knockin of genes continues to provide improved tools for studying DN. These models provide an opportunity to search for new mechanisms involving the development of DN, but their shortcomings should be recognized as well. Moreover, it is important to recognize that the genetic background has a substantial effect on the susceptibility to diabetes and kidney disease development in the various models of diabetes.

Ischemia-reperfusion injury in rat steatotic liver is dependent on NFκB P65 activation

BACKGROUND

Steatotic liver grafts tolerate ischemia-reperfusion (I/R) injury poorly, contributing to increased primary graft nonfunction following transplantation. Activation of nuclear factor kappa-B (NFκB) following I/R injury plays a crucial role in activation of pro-inflammatory responses leading to injury.

METHODS

We evaluated the role of NFκB in steatotic liver injury by using an orthotopic liver transplant (OLT) model in Zucker rats (lean to lean or obese to lean) to define the mechanisms of steatotic liver injury. Obese donors were treated with bortezomib to assess the role of NF-κB in steatotic liver I/R injury. Hepatic levels of NF-κB and pro-inflammatory cytokines were analyzed by ELISA. Serum transaminase levels and histopathological analysis were performed to assess associated graft injury.

RESULTS

I/R injury in steatotic liver results in significant increases in activation of NF-κB (40%, p<0.003), specifically the p65 subunit following transplantation. Steatotic donor pretreatment with proteasome inhibitor bortezomib (0.1mg/kg) resulted in significant reduction in levels of activated NF-κB (0.58±0.18 vs. 1.37±0.06O.D./min/10 μg protein, p<0.003). Bortezomib treatment also reduced expression of pro-inflammatory cytokines MIP-2 compared with control treated steatotic and lean liver transplants respectively (106±17.5 vs. 443.3±49.9 vs. 176±10.6 pg/mL, p=0.02), TNF-α (223.8±29.9 vs. 518.5±66.5 vs. 264.5±30.1 pg/2 μg protein, p=0.003) and IL-1β (6.0±0.91 vs. 19.8±5.2 vs. 5±1.7 pg/10 μg protein, p=0.02) along with a significant reduction in ALT levels (715±71 vs. 3712.5±437.5 vs. 606±286 U/L, p=0.01).

CONCLUSION

These results suggest that I/R injury in steatotic liver transplantation are associated with exaggerated activation of NFκB subunit p65, leading to an inflammatory mechanism of reperfusion injury and necrosis. Proteasome inhibition in steatotic liver donor reduces NFκB p65 activation and inflammatory I/R injury, improving transplant outcomes of steatotic grafts in a rat model.

Sleep and obesity: a focus on animal models

The rapid rise in obesity prevalence in the modern world parallels a significant reduction in restorative sleep (Agras et al., 2004; Dixon et al., 2007, 2001; Gangwisch and Heymsfield, 2004; Gupta et al., 2002; Sekine et al., 2002; Vioque et al., 2000; Wolk et al., 2003). Reduced sleep time and quality increases the risk for obesity, but the underlying mechanisms remain unclear (Gangwisch et al., 2005; Hicks et al., 1986; Imaki et al., 2002; Jennings et al., 2007; Moreno et al., 2006). A majority of the theories linking human sleep disturbances and obesity rely on self-reported sleep. However, studies with objective measurements of sleep/wake parameters suggest a U-shaped relationship between sleep and obesity. Studies in animal models are needed to improve our understanding of the association between sleep disturbances and obesity. Genetic and experimenter-induced models mimicking characteristics of human obesity are now available and these animal models will be useful in understanding whether sleep disturbances determine propensity for obesity, or result from obesity. These models exhibit weight gain profiles consistently different from control animals. Thus a careful evaluation of animal models will provide insight into the relationship between sleep disturbances and obesity in humans. In this review we first briefly consider the fundamentals of sleep and key sleep disturbances, such as sleep fragmentation and excessive daytime sleepiness (EDS), observed in obese individuals. Then we consider sleep deprivation studies and the role of circadian alterations in obesity. We describe sleep/wake changes in various rodent models of obesity and obesity resistance. Finally, we discuss possible mechanisms linking sleep disturbances with obesity.

Leptin receptors

The hormone leptin, secreted predominantly from adipose tissue, plays a crucial role in the regulation of numerous neuroendocrine functions, from energy homeostasis to reproduction. Genetic deficiency as a consequence of leptin or leptin receptor mutations, although rare in humans, leads to early onset of chronic hyperphagia and massive obesity. In most human obesity, however, leptin levels are chronically elevated. Under these conditions of persistent hyperleptinaemia, and particularly when obesity is associated with a high-fat diet, leptin resistance develops, and signalling through the leptin receptor is curtailed, fuelling further weight gain. Here, we review the role of leptin receptors in the regulation of feeding and obesity development. Leptin receptors are found in each of the major components of the CNS "feeding" circuitry-the brainstem, hypothalamus and distributed reward centres. Through these receptors, leptin exerts influences on signalling and integration within these circuits to alter feeding behaviours. Although some progress is now being made with peptide analogues, the leptin receptor has not proved to be amenable to small molecule pharmacological intervention to date. Where clinical benefit from recombinant leptin administration has been achieved, this has been under circumstances of complete endogenous leptin deficiency or relative hypoleptinaemia such as in lipodystrophy.

An overview of mongenic and syndromic obesities in humans

Obesity is increasing in prevalence in the United States with over 65% of adults considered overweight and 16% of children with BMI > 95 percentile. The heritability of obesity is estimated between 40% and 70%, but the genetics of obesity for most individuals are complex and involve the interaction of multiple genes and environment. There are however several syndromic and non-syndromic forms of obesity that are monogenic and oligogenic that provide insight into the underlying molecular control of food intake and the neural networks that control ingestive behavior and satiety to regulate body weight and which may interact with treatment exposures to produce or exacerbate obesity in childhood cancer survivors.

Leptin in early life: a key factor for the development of the adult metabolic profile

Leptin levels during the perinatal period are important for the development of metabolic systems involved in energy homeostasis. In rodents, there is a postnatal leptin surge, with circulating leptin levels increasing around postnatal day (PND) 5 and peaking between PND 9 and PND 10. At this time circulating leptin acts as an important trophic factor for the development of hypothalamic circuits that control energy homeostasis and food seeking and reward behaviors. Blunting the postnatal leptin surge results in long-term leptin insensitivity and increased susceptibility to diet-induced obesity during adulthood. Pharmacologically increased leptin levels in the postnatal period also have long-term effects on metabolism. Nevertheless, this effect is controversial as postnatal hyperleptinemia is reported to both increase and decrease the predisposition to obesity in adulthood. The different effects reported in the literature could be explained by the different moments at which this hormone was administered, suggesting that modifications of the neonatal leptin surge at specific time points could selectively affect the development of central and peripheral systems that are undergoing modifications at this moment resulting in different metabolic and behavioral outcomes. In addition, maternal nutrition and the hormonal environment during pregnancy and lactation may also modulate the offspring's response to postnatal modifications in leptin levels. This review highlights the importance of leptin levels during the perinatal period in the development of metabolic systems that control energy homeostasis and how modifications of these levels may induce long-lasting and potentially irreversible effects on metabolism.

Positional cloning of a type 2 diabetes quantitative trait locus; tomosyn-2, a negative regulator of insulin secretion

We previously mapped a type 2 diabetes (T2D) locus on chromosome 16 (Chr 16) in an F2 intercross from the BTBR T (+) tf (BTBR) Lep^ob/ob and C57BL/6 (B6) Lep^ob/ob mouse strains. Introgression of BTBR Chr 16 into B6 mice resulted in a consomic mouse with reduced fasting plasma insulin and elevated glucose levels. We derived a panel of sub-congenic mice and narrowed the diabetes susceptibility locus to a 1.6 Mb region. Introgression of this 1.6 Mb fragment of the BTBR Chr 16 into lean B6 mice (B6.16^BT36–38) replicated the phenotypes of the consomic mice. Pancreatic islets from the B6.16^BT36–38 mice were defective in the second phase of the insulin secretion, suggesting that the 1.6 Mb region encodes a regulator of insulin secretion. Within this region, syntaxin-binding protein 5-like (Stxbp5l) or tomosyn-2 was the only gene with an expression difference and a non-synonymous coding single nucleotide polymorphism (SNP) between the B6 and BTBR alleles. Overexpression of the b-tomosyn-2 isoform in the pancreatic β-cell line, INS1 (832/13), resulted in an inhibition of insulin secretion in response to 3 mM 8-bromo cAMP at 7 mM glucose. In vitro binding experiments showed that tomosyn-2 binds recombinant syntaxin-1A and syntaxin-4, key proteins that are involved in insulin secretion via formation of the SNARE complex. The B6 form of tomosyn-2 is more susceptible to proteasomal degradation than the BTBR form, establishing a functional role for the coding SNP in tomosyn-2. We conclude that tomosyn-2 is the major gene responsible for the T2D Chr 16 quantitative trait locus (QTL) we mapped in our mouse cross. Our findings suggest that tomosyn-2 is a key negative regulator of insulin secretion.

Humans carry many genetic variants that confer small effects on metabolic traits relevant to type 2 diabetes. These effects are amplified by environmental stressors like obesity. We used morbid obesity as a sensitizer to identify genes that contribute to the diabetes susceptibility of the BTBR mouse strain. Using mapping and breeding strategies, we were able to narrow a genetic region to one containing just 13 genes. One of these genes, tomosyn-2, emerged as a prime candidate. Our functional studies showed that tomosyn-2 is an inhibitor of insulin secretion, and it binds to the proteins involved in the fusion of insulin containing granules with the plasma membrane. We found a coding mutation and demonstrated that this mutation affects the stability of the protein product. Our work with Tomosyn-2 provides new insights into the regulation of insulin secretion and emphasizes that negative regulation is critical for avoiding insulin-induced hypoglycemia.

Adipose triglyceride lipase expression and fasting regulation are differently affected by cold exposure in adipose tissues of lean and obese Zucker rats

Adipose triglyceride lipase (ATGL) hydrolyzes triacylglycerols to diacylglycerols in the first step of lipolysis, providing substrates for hormone-sensitive lipase (HSL). Here we studied whether ATGL messenger RNA (mRNA) and protein levels were affected by 24-h cold exposure in different white adipose tissue depots and in interscapular brown adipose tissue of lean and obese Zucker rats submitted to feeding and 14-h fasting conditions. HSL mRNA expression was also studied in selected depots. In both lean and obese rats, as a general trend, cold exposure increased ATGL mRNA and protein levels in the different adipose depots, except in the brown adipose tissue of lean animals, where a decrease was observed. In lean rats, cold exposure strongly improved fasting up-regulation of ATGL expression in all the adipose depots. Moreover, in response to fasting, in cold-exposed lean rats, there was a stronger positive correlation between circulating nonesterified fatty acids (NEFA) and ATGL mRNA levels in the adipose depots and a higher percentage increase of circulating NEFA in comparison with control animals not exposed to cold. In obese rats, fasting-induced up-regulation of ATGL was impaired and was not improved by cold. The effects of obesity and cold exposure on HSL mRNA expression were similar to those observed for ATGL, suggesting common regulatory mechanisms for both proteins. Thus, cold exposure increases ATGL expression and improves its fasting-up-regulation in adipose tissue of lean rats. In obese rats, cold exposure also increases ATGL expression but fails to improve its regulation by fasting, which could contribute to the increased difficulty for mobilizing lipids in these animals.

Ablation of LMO4 in glutamatergic neurons impairs leptin control of fat metabolism

The LIM domain only 4 (LMO4) protein is expressed in the hypothalamus, but its function there is not known. Using mice with LMO4 ablated in postnatal glutamatergic neurons, including most neurons of the paraventricular (PVN) and ventromedial (VMH) hypothalamic nuclei where LMO4 is expressed, we asked whether LMO4 is required for metabolic homeostasis. LMO4 mutant mice exhibited early onset adiposity. These mice had reduced energy expenditure and impaired thermogenesis together with reduced sympathetic outflow to adipose tissues. The peptide hormone leptin, produced from adipocytes, activates Jak/Stat3 signaling at the hypothalamus to control food intake, energy expenditure, and fat metabolism. Intracerebroventricular infusion of leptin suppressed feeding similarly in LMO4 mutant and control mice. However, leptin-induced fat loss was impaired and activation of Stat3 in the VMH was blunted in these mice. Thus, our study identifies LMO4 as a novel modulator of leptin function in selective hypothalamic nuclei to regulate fat metabolism.

Progression of pancreatitis prior to diabetes onset in WBN/Kob-Lepr(fa) rats

We established the WBN/Kob-Lepr(fa) rat as a new congenic strain for the fa allele of the leptin receptor gene (Lepr). Homozygous (fa/fa) WBN/Kob-Lepr(fa) rats provide a model of non-insulin-dependent diabetes, although its onset is secondary to pancreatitis. In the present study, we compared histopathological observations of pancreatitis in each genotype of this rat, to examine its suitability as a model of pancreatitis. The histopathological findings of the pancreatitis revealed intense changes dependent on age, such as hemorrhage or hemosiderin deposition. The pancreatitis in homozygous (fa/fa) WBN/Kob-Lepr(fa) rats were more severe than those of WBN/Kob rats.

Analysis of time-dependent adaptations in whole-body energy balance in obesity induced by high-fat diet in rats

Background

High-fat (HF) diet has been extensively used as a model to study metabolic disorders of human obesity in rodents. However, the adaptive whole-body metabolic responses that drive the development of obesity with chronically feeding a HF diet are not fully understood. Therefore, this study investigated the physiological mechanisms by which whole-body energy balance and substrate partitioning are adjusted in the course of HF diet-induced obesity.

Methods

Male Wistar rats were fed ad libitum either a standard or a HF diet for 8 weeks. Food intake (FI) and body weight were monitored daily, while oxygen consumption, respiratory exchange ratio, physical activity, and energy expenditure (EE) were assessed weekly. At week 8, fat mass and lean body mass (LBM), fatty acid oxidation and uncoupling protein-1 (UCP-1) content in brown adipose tissue (BAT), as well as acetyl-CoA carboxylase (ACC) content in liver and epidydimal fat were measured.

Results

Within 1 week of ad libitum HF diet, rats were able to spontaneously reduce FI to precisely match energy intake of control rats, indicating that alterations in dietary energy density were rapidly detected and FI was self-regulated accordingly. Oxygen consumption was higher in HF than controls throughout the study as whole-body fat oxidation also progressively increased. In HF rats, EE initially increased, but then reduced as dark cycle ambulatory activity reached values ~38% lower than controls. No differences in LBM were detected; however, epidydimal, inguinal, and retroperitoneal fat pads were 1.85-, 1.89-, and 2.54-fold larger in HF-fed than control rats, respectively. Plasma leptin was higher in HF rats than controls throughout the study, indicating the induction of leptin resistance by HF diet. At week 8, UCP-1 content and palmitate oxidation in BAT were 3.1- and 1.5-fold higher in HF rats than controls, respectively, while ACC content in liver and epididymal fat was markedly reduced.

Conclusion

The thermogenic response induced by the HF diet was offset by increased energy efficiency and time-dependent reduction in physical activity, favoring fat accumulation. These adaptations were mainly driven by the nutrient composition of the diet, since control and HF animals spontaneously elicited isoenergetic intake.

Sixteen years and counting: an update on leptin in energy balance

Cloned in 1994, the ob gene encodes the protein hormone leptin, which is produced and secreted by white adipose tissue. Since its discovery, leptin has been found to have profound effects on behavior, metabolic rate, endocrine axes, and glucose fluxes. Leptin deficiency in mice and humans causes morbid obesity, diabetes, and various neuroendocrine anomalies, and replacement leads to decreased food intake, normalized glucose homeostasis, and increased energy expenditure. Here, we provide an update on the most current understanding of leptin-sensitive neural pathways in terms of both anatomical organization and physiological roles.

Effects of insulin and leptin in the ventral tegmental area and arcuate hypothalamic nucleus on food intake and brain reward function in female rats

There is evidence for a role of insulin and leptin in food intake, but the effects of these adiposity signals on the brain reward system are not well understood. Furthermore, the effects of insulin and leptin on food intake in females are underinvestigated. These studies investigated the role of insulin and leptin in the ventral tegmental area (VTA) and the arcuate hypothalamic nucleus (Arc) on food intake and brain reward function in female rats. The intracranial self-stimulation procedure was used to assess the effects of insulin and leptin on the reward system. Elevations in brain reward thresholds are indicative of a decrease in brain reward function. The bilateral administration of leptin into the VTA (15-500 ng/side) or Arc (15-150 ng/side) decreased food intake for 72 h. The infusion of leptin into the VTA or Arc resulted in weight loss during the first 48 (VTA) or 24 h (Arc) after the infusions. The administration of insulin (0.005-5 mU/side) into the VTA or Arc decreased food intake for 24 h but did not affect body weights. The bilateral administration of low, but not high, doses of leptin (15 ng/side) or insulin (0.005 mU/side) into the VTA elevated brain reward thresholds. Neither insulin nor leptin in the Arc affected brain reward thresholds. These studies suggest that a small increase in leptin or insulin levels in the VTA leads to a decrease in brain reward function. A relatively large increase in insulin or leptin levels in the VTA or Arc decreases food intake.