Margaret J. Morris

Chronic high-fat diet in fathers programs β-cell dysfunction in female rat offspring

The global prevalence of obesity is increasing across most ages in both sexes. This is contributing to the early emergence of type 2 diabetes and its related epidemic. Having either parent obese is an independent risk factor for childhood obesity. Although the detrimental impacts of diet-induced maternal obesity on adiposity and metabolism in offspring are well established, the extent of any contribution of obese fathers is unclear, particularly the role of non-genetic factors in the causal pathway. Here we show that paternal high-fat-diet (HFD) exposure programs β-cell ‘dysfunction’ in rat F1 female offspring. Chronic HFD consumption in Sprague–Dawley fathers induced increased body weight, adiposity, impaired glucose tolerance and insulin sensitivity. Relative to controls, their female offspring had an early onset of impaired insulin secretion and glucose tolerance that worsened with time, and normal adiposity. Paternal HFD altered the expression of 642 pancreatic islet genes in adult female offspring (P < 0.01); genes belonged to 13 functional clusters, including cation and ATP binding, cytoskeleton and intracellular transport. Broader pathway analysis of 2,492 genes differentially expressed (P < 0.05) demonstrated involvement of calcium-, MAPK- and Wnt-signalling pathways, apoptosis and the cell cycle. Hypomethylation of the Il13ra2 gene, which showed the highest fold difference in expression (1.76-fold increase), was demonstrated. This is the first report in mammals of non-genetic, intergenerational transmission of metabolic sequelae of a HFD from father to offspring.

Neurochemical evidence of cardiac sympathetic activation and increased central nervous system norepinephrine turnover in severe congestive heart failure.

OBJECTIVES The aim of this study was to characterize cardiac sympathetic nervous function in patients with severe heart failure and to investigate the influence of the cause of heart failure, hemodynamic variables and central nervous system catecholamine release on cardiac sympathetic tone. BACKGROUND Although heart failure is generally accompanied by sympathoexcitation, the integrity of cardiac sympathetic nerve function in heart failure remains controversial, particularly in relation to nerve firing activity and to the capacity of sympathetic nerves to recapture norepinephrine. Additionally, the location of the afferent and central neural pathways implicated in heart failure-induced sympathoexcitation remains unclear. METHODS Radiotracer techniques were applied in 41 patients with severe heart failure and 15 healthy control subjects to study the biochemical aspects of whole body and cardiac sympathetic activity. Hemodynamic indexes of cardiac performance were measured in the heart failure group, and their association with sympathetic activity was studied. Jugular venous catechol spillover was measured to study the central noradrenergic control of sympathetic outflow. RESULTS Sympathoexcitation was evident in the heart failure group, reflected by a 62% increase (p < 0.001) in total body and a 277% increase (p < 0.001) in cardiac norepinephrine spillover rates. These changes were accompanied by significant increases in the cardiac spillover of the norepinephrine precursor dihydroxyphenylalanine, the sympathetic cotransmitter neuropeptide Y and the extraneuronal metabolite 3-methoxy-4-hydroxyphenylglycol. The level of cardiac sympathetic activity was significantly correlated (r = 0.59, p < 0.001) with the mean pulmonary artery pressure. An increase in the spillover of dihydroxyphenylalanine and 3-methoxy-4-hydroxyphenylglycol from the brain was present, suggesting activation of central noradrenergic neurons. CONCLUSIONS Cardiac sympathetic activation is present in severe heart failure, bearing a close relation with pulmonary artery pressures, independent of heart failure etiology. Activation of noradrenergic neurons in the brain is also present and may be the underlying central nervous mechanism of the sympathoexcitation observed in heart failure.

Maternal and Postnatal Overnutrition Differentially Impact Appetite Regulators and Fuel Metabolism

Maternal obesity is increasing, and it is known that the intrauterine experience programs fetal and newborn metabolism. However, the relative contributions of pre- or postnatal factors are unknown. We hypothesized that maternal overnutrition caused by long-term maternal obesity would exert a stronger detrimental impact than postnatal overnutrition on offspring metabolic homeostasis, with additional postnatal overnutrition exaggerating these alterations. Female Sprague Dawley rats were exposed to chow or high-fat cafeteria diet for 5 wk before mating and throughout gestation and lactation. On postnatal d 1, litters were adjusted to three per litter to induce postnatal overnutrition (vs. 12 in control). Hypothalamic appetite regulators neuropeptide Y and proopiomelanocortin, glucose transporter 4, and lipid metabolic markers were measured. At postnatal d 20, male pups born of obese dams, or those overnourished postnatally, were 42% heavier than controls; combining both interventions led to 80% greater body weight. Maternal obesity increased pup adiposity and led to glucose intolerance in offspring; these were exaggerated by additional postnatal overnutrition during lactation. Maternal obesity was also linked to hyperlipidemia in offspring and reduced hypothalamic neuropeptide Y and increased proopiomelanocortin mRNA expression. Postnatal overnutrition of offspring from obese dams amplified these hypothalamic changes. Both maternal and postnatal overnutrition reduced muscle glucose transporter 4. Adipose carnitine palmitoyl-transferase-1 and adipose triglyceride lipase mRNA was up-regulated only by postnatal overnutrition. Maternal overnutrition appears to alter central appetite circuits and promotes early-onset obesity; postnatal overnutrition interacted to cause peripheral lipid and glucose metabolic disorders, supporting the critical message to reduce early-life adverse nutritional impact.

Estrogen deficiency causes central leptin insensitivity and increased hypothalamic neuropeptide Y.

OBJECTIVE: Altered fat distribution is a consequence of menopause, but the mechanisms responsible are unknown. Estrogen insufficiency in humans can be modeled using ovariectomized rats. We have shown that increased adiposity in these rats is due to reduced physical activity and transient hyperphagia, and can be reversed with 17β-estradiol treatment. The aims of this study were to examine whether this altered energy balance is associated with circulating leptin insufficiency, central leptin insensitivity, decreased hypothalamic leptin receptor (Ob-Rb) expression, and/or increased hypothalamic neuropeptide Y (NPY).METHODS: Plasma leptin levels, adipose tissue ob gene expression, energy balance responses to i.c.v. leptin, hypothalamic Ob-Rb expression and NPY concentration in five separate hypothalamic regions were measured in adult female rats after either ovariectomy or sham operations.RESULTS: Obesity was not associated with hypoleptinemia or decreased ob gene expression in ovariectomized rats; however, it was associated with insensitivity to central leptin administration. Food intake was less suppressed and spontaneous physical activity was less stimulated by leptin. This was not due to decreased hypothalamic Ob-Rb expression. NPY concentration in the paraventricular nucleus of the hypothalamus was elevated in the ovariectomized rats, consistent with leptin insensitivity; however this effect was transient and disappeared as body fat and leptin levels increased further and hyperphagia normalized.CONCLUSION: Impaired central leptin sensitivity and overproduction of NPY may contribute to excess fat accumulation caused by estrogen deficiency.

Increases in plasma neuropeptide Y concentrations during sympathetic activation in man.

Neuropeptide Y (NPY) coexists with noradrenaline in postganglionic sympathetic neurons. In order to test the hypothesis that NPY may be released along with catecholamines by activation of the sympathoadrenal system we measured plasma NPY-like immunoreactivity (NPY-LI) concentrations during cold pressor test, head up tilt and bicycle exercise in healthy volunteers. All 3 manoeuvres resulted in elevation of blood pressure, heart rate and plasma noradrenaline and adrenaline concentrations. These were accompanied by increases in plasma NPY-LI concentrations on cold pressor test and exercise, but not with head up tilt. The increases in both NPY-LI and catecholamines were greatest with exercise. These findings suggest that NPY is released at the same time as noradrenaline when sympathetic noradrenergic nerves are activated.

Hypothalamic Neuroendocrine Circuitry is Programmed by Maternal Obesity: Interaction with Postnatal Nutritional Environment

Objective Early life nutrition is critical for the development of hypothalamic neurons involved in energy homeostasis. We previously showed that intrauterine and early postnatal overnutrition programmed hypothalamic neurons expressing the appetite stimulator neuropeptide Y (NPY) and suppressor proopiomelanocortin (POMC) in offspring at weaning. However, the long-term effects of such programming and its interactions with post-weaning high-fat-diet (HFD) consumption are unclear. Research Design and Methods Female Sprague Dawley rats were exposed to chow or HFD for 5 weeks before mating, throughout gestation and lactation. On postnatal day 1, litters were adjusted to 3/litter to induce postnatal overnutrition (vs. 12 in control). At postnatal day 20, half of the rats from each maternal group were weaned onto chow or HFD for 15 weeks. Hypothalamic appetite regulators, and fuel (glucose and lipid) metabolic markers were measured. Results Offspring from obese dams gained more weight than those from lean dams independent of post-weaning diet. Maternal obesity interacted with post-weaning HFD consumption to cause greater levels of hyperphagia, adiposity, hyperlipidemia, and glucose intolerance in offspring. This was linked to increased hypothalamic NPY signaling and leptin resistance in adult offspring. Litter size reduction had a detrimental impact on insulin and adiponectin, while hypothalamic NPY and POMC mRNA expression were suppressed in the face of normal energy intake and weight gain. Conclusions Maternal obesity, postnatal litter size reduction and post-weaning HFD consumption caused obesity via different neuroendocrine mechanims. There were strong additive effects of maternal obesity and post-weaning HFD consumption to increase the metabolic disorders in offspring.

Elevated anxiety and depressive-like behavior in a rat model of genetic generalized epilepsy suggesting common causation.

The explanation for the increased prevalence of neuropsychiatric disorders in epilepsy patients is uncertain, with both biological and psychosocial factors proposed. Increasing evidence supports the idea of shared neurobiological processes leading both to seizures and to behavioral, emotional and cognitive disturbance. This study addresses this using Genetic Absence Epilepsy Rats from Strasbourg (GAERS), a model of human generalized epilepsy. We subjected GAERS (n=47) and Non-Epileptic Control rats (NEC; n=73) to behavioral measures of depression and anxiety at 7 and 13 weeks of age, ages prior to and after seizure onset. We employed the Sucrose-Preference Test (SPT), the Elevated Plus Maze (EPM), and the Open Field Arena (OFA). GAERS exhibited significantly greater levels of both depression- and anxiety-like behaviors on all measures, including reduced consumption of sucrose solution in the SPT; lower percentage of time in the open arms of the EPM; and reduced exploratory activity and less time spent in the inner area of the OFA. These differences were evident at both 7 and 13 weeks of age, before and after the onset of epilepsy. Increased anxiety- and depressive-like behaviors are observed in GAERS. These behavioral differences exist before the onset of seizures indicating that they are not secondary consequences of seizures, and suggest shared factors in the biological diathesis underlying the two kinds of disorder. Studying affective disturbance in animal models of epilepsy may illuminate the pathogenesis of affective disorder more generally, as well as modeling psychiatric comorbidities common in epilepsy patients.

Effect of short-term cigarette smoke exposure on body weight, appetite and brain neuropeptide Y in mice

Although nicotinic receptors have been demonstrated in hypothalamic appetite-regulating areas and nicotine administration alters food intake and body weight in both animals and humans, the mechanisms underlying the effects of smoking on appetite circuits remain unclear. Conflicting effects of nicotine on the major orexigenic peptide, neuropeptide Y (NPY), have been observed in the brain, but the effects of smoking are unknown. Thus, we aimed to investigate how cigarette smoking affects body weight, food intake, plasma leptin concentration, hypothalamic NPY peptide, adipose mass and mRNA expression of uncoupling proteins (UCP), and tumor necrosis factor (TNF) α. Balb/C mice (8 weeks) were exposed to cigarette smoke (three cigarettes, three times a day for 4 consecutive days) or sham exposed. Body weight and food intake were recorded. Plasma leptin and brain NPY were measured by radioimmunoassay. UCPs and TNF α mRNA were measured by real-time PCR. Food intake dropped significantly from the first day of smoking, and weight loss became evident within 2 days. Brown fat and retroperitoneal white fat masses were significantly reduced, and plasma leptin concentration was decreased by 34%, in line with the decreased fat mass. NPY concentrations in hypothalamic subregions were similar between two groups. UCP1 mRNA was decreased in white fat and UCP3 mRNA increased in brown fat in smoking group. Short-term cigarette smoke exposure led to reduced body weight, food intake, and fat mass. The reduction in plasma leptin concentration may have been too modest to increase NPY production; alternatively, change in NPY or its function might have been offset by nicotine or other elements in cigarette smoke.

Established maternal obesity in the rat reprograms hypothalamic appetite regulators and leptin signaling at birth

Objective:Key appetite regulators and their receptors are already present in the fetal hypothalamus, and may respond to hormones such as leptin. Intrauterine food restriction or hyperglycemia can reprogram these circuits, possibly predisposing individuals to adverse health outcomes in adulthood. Given the global obesity epidemic, maternal overweight and obesity is becoming more prevalent. Earlier, we observed rapid growth of pups from obese dams during the suckling period. However, it is unclear whether this is because of alterations in leptin and hypothalamic appetite regulators at birth.Design:Female Sprague–Dawley rats were fed palatable high-fat diet (HFD) or chow for 5 weeks to induce obesity before mating. The same diet continued during gestation. At day 1, after birth, plasma and hypothalamus were collected from male and female pups.Measurements:Body weight and organ mass were recorded. Leptin and insulin levels were measured in the plasma by radioimmunoassay. Hypothalamic mRNA expression of neuropeptide-Y (NPY), pro-opiomelanocortin, leptin receptor and its downstream signal, STAT3 (signal transducer and activator of transcription 3), were measured using real-time PCR.Results:Body and organ weights of pups from obese dams were similar to those from lean dams, across both genders. However, plasma leptin levels were significantly lower in offspring from obese dams (male: 0.53±0.13 vs 1.05±0.21 ng ml−1; female: 0.33±0.09 vs 2.12±0.57 ng ml−1, respectively; both P<0.05). Hypothalamic mRNA expression of NPY, pro-opiomelanocortin, leptin receptor and STAT3 were also significantly lower in pups from obese dams.Conclusion:Long-term maternal obesity, together with lower leptin levels in pups from obese dams may contribute to the lower expression of key appetite regulators on day 1 of life, suggesting altered intrauterine neuron development in response to intrauterine overnutrition, which may contribute to eating disorders later in life.

Changes in gut microbiota in rats fed a high fat diet correlate with obesity-associated metabolic parameters.

The gut microbiota is emerging as a new factor in the development of obesity. Many studies have described changes in microbiota composition in response to obesity and high fat diet (HFD) at the phylum level. In this study we used 16s RNA high throughput sequencing on faecal samples from rats chronically fed HFD or control chow (n = 10 per group, 16 weeks) to investigate changes in gut microbiota composition at the species level. 53.17% dissimilarity between groups was observed at the species level. Lactobacillus intestinalis dominated the microbiota in rats under the chow diet. However this species was considerably less abundant in rats fed HFD (P<0.0001), this being compensated by an increase in abundance of propionate/acetate producing species. To further understand the influence of these species on the development of the obese phenotype, we correlated their abundance with metabolic parameters associated with obesity. Of the taxa contributing the most to dissimilarity between groups, 10 presented significant correlations with at least one of the tested parameters, three of them correlated positively with all metabolic parameters: Phascolarctobacterium, Proteus mirabilis and Veillonellaceae, all propionate/acetate producers. Lactobacillus intestinalis was the only species whose abundance was negatively correlated with change in body weight and fat mass. This species decreased drastically in response to HFD, favouring propionate/acetate producing bacterial species whose abundance was strongly correlated with adiposity and deterioration of metabolic factors. Our observations suggest that these species may play a key role in the development of obesity in response to a HFD.