Sex differences in high-fat diet-induced obesity, metabolic alterations and learning, and synaptic plasticity deficits in mice

Thidoredxin-2 overexpression fails to rescue chronic high calorie diet induced hippocampal dysfunction

A high calorie diet (HCD) can impair hippocampal synaptic plasticity and cognitive function in animal models. Mitochondrial thioredoxin 2 (TRX-2) is critical for maintaining intracellular redox status, but whether it can protect against HCD-induced impairment of synaptic plasticity is unknown. We found that levels of TRX-2 are reduced in the hippocampus of wild type mice maintained for 8 months on a HCD, and that the mice on the HCD exhibit impaired hippocampal synaptic plasticity (long-term potentiation at CA1 synapses) and cognitive function (novel object recognition). Transgenic mice overexpressing human TRX-2 (hTRX-2) exhibit increased resistance to diquat-induced oxidative stress in peripheral tissues. However, neither the HCD nor hTRX-2 overexpression affected levels of lipid peroxidation products (F2 isoprostanes) in the hippocampus, and hTRX-2 transgenic mice were not protected against the adverse effects of the HCD on hippocampal synaptic plasticity and cognitive function. Our findings indicate that TRX-2 overexpression does not mitigate adverse effects of a HCD on synaptic plasticity, and also suggest that oxidative stress may not be a pivotal factor in the impairment of synaptic plasticity and cognitive function caused by HCDs.

Menopause, obesity and inflammation: interactive risk factors for Alzheimer's disease

Alzheimer’s disease (AD) is a multifactorial neurodegenerative disorder, the development of which is regulated by several environmental and genetic risk factors. Two factors theorized to contribute to the initiation and/or progression of AD pathogenesis are age-related increases in inflammation and obesity. These factors may be particularly problematic in women. The onset of menopause in mid-life elevates the vulnerability of women to AD, an increased risk that is likely associated with the depletion of estrogens. Menopause is also linked with an abundance of additional changes, including increased central adiposity and inflammation. Here, we review the current literature to explore the interactions between obesity, inflammation, menopause and AD.

Role of neuroinflammation in the emotional and cognitive alterations displayed by animal models of obesity

Obesity is associated with a high prevalence of mood disorders and cognitive dysfunctions in addition to being a significant risk factor for important health complications such as cardiovascular diseases and type 2 diabetes. Identifying the pathophysiological mechanisms underlying these health issues is a major public health challenge. Based on recent findings, from studies conducted on animal models of obesity, it has been proposed that inflammatory processes may participate in both the peripheral and brain disorders associated with the obesity condition including the development of emotional and cognitive alterations. This is supported by the fact that obesity is characterized by peripheral low-grade inflammation, originating from increased adipose tissue mass and/or dysbiosis (changes in gut microbiota environment), both of which contribute to increased susceptibility to immune-mediated diseases. In this review, we provide converging evidence showing that obesity is associated with exacerbated neuroinflammation leading to dysfunction in vulnerable brain regions associated with mood regulation, learning, and memory such as the hippocampus. These findings give new insights to the pathophysiological mechanisms contributing to the development of brain disorders in the context of obesity and provide valuable data for introducing new therapeutic strategies for the treatment of neuropsychiatric complications often reported in obese patients.

Estrogens protect male mice from obesity complications and influence glucocorticoid metabolism

BACKGROUND

Although the prevalence of obesity is higher among women than men, they are somewhat protected from the associated cardiometabolic consequences. The increase in cardiovascular disease risk seen after the menopause suggests a role for estrogens. There is also growing evidence for the importance of estrogen on body fat and metabolism in males. We hypothesized that that estrogen administration would ameliorate the adverse effects of obesity on metabolic parameters in males.

METHODS

Male and female C57Bl/6 mice were fed control or obesogenic (DIO) diets from 5 weeks of age until adulthood. Glucose tolerance testing was performed at 13 weeks of age. Mice were killed at 15 weeks of age and liver and adipose tissue were collected for analysis of gene expression. A second cohort of male mice underwent the same experimental design with the addition of estradiol pellet implantation or sham surgery at 6 weeks.

RESULTS

DIO males had greater mesenteric adipose deposition and more severe increases in plasma glucose, insulin and lipids than females. Treatment of males with estradiol from 6 weeks of age prevented DIO-induced increases in adipose tissue mass and alterations in glucose-insulin homeostasis. We also identified sex differences in the transcript levels and activity of hepatic and adipose glucocorticoid metabolizing enzymes. Estrogen treatment feminized the pattern of DIO-induced changes in glucocorticoid metabolism, rendering males similar to females.

CONCLUSIONS

Thus, DIO induces sex-specific changes in glucose-insulin homeostasis, which are ameliorated in males treated with estrogen, highlighting the importance of sex steroids in metabolism. Given that altered peripheral glucocorticoid metabolism has been observed in rodent and human obesity, our results also suggest that sexually dimorphic expression and activity of glucocorticoid metabolizing enzymes may have a role in the differential metabolic responses to obesity in males and females.

High-fat diet induces hepatic insulin resistance and impairment of synaptic plasticity

High-fat diet (HFD)-induced obesity is associated with insulin resistance, which may affect brain synaptic plasticity through impairment of insulin-sensitive processes underlying neuronal survival, learning, and memory. The experimental model consisted of 3 month-old C57BL/6J mice fed either a normal chow diet (control group) or a HFD (60% of calorie from fat; HFD group) for 12 weeks. This model was characterized as a function of time in terms of body weight, fasting blood glucose and insulin levels, HOMA-IR values, and plasma triglycerides. IRS-1/Akt pathway was assessed in primary hepatocytes and brain homogenates. The effect of HFD in brain was assessed by electrophysiology, input/output responses and long-term potentiation. HFD-fed mice exhibited a significant increase in body weight, higher fasting glucose- and insulin levels in plasma, lower glucose tolerance, and higher HOMA-IR values. In liver, HFD elicited (a) a significant decrease of insulin receptor substrate (IRS-1) phosphorylation on Tyr608 and increase of Ser307 phosphorylation, indicative of IRS-1 inactivation; (b) these changes were accompanied by inflammatory responses in terms of increases in the expression of NFκB and iNOS and activation of the MAP kinases p38 and JNK; (c) primary hepatocytes from mice fed a HFD showed decreased cellular oxygen consumption rates (indicative of mitochondrial functional impairment); this can be ascribed partly to a decreased expression of PGC1α and mitochondrial biogenesis. In brain, HFD feeding elicited (a) an inactivation of the IRS-1 and, consequentially, (b) a decreased expression and plasma membrane localization of the insulin-sensitive neuronal glucose transporters GLUT3/GLUT4; (c) a suppression of the ERK/CREB pathway, and (d) a substantial decrease in long-term potentiation in the CA1 region of hippocampus (indicative of impaired synaptic plasticity). It may be surmised that 12 weeks fed with HFD induce a systemic insulin resistance that impacts profoundly on brain activity, i.e., synaptic plasticity.

Juvenile obesity enhances emotional memory and amygdala plasticity through glucocorticoids

In addition to metabolic and cardiovascular disorders, obesity is associated with adverse cognitive and emotional outcomes. Its growing prevalence during adolescence is particularly alarming since recent evidence indicates that obesity can affect hippocampal function during this developmental period. Adolescence is a decisive period for maturation of the amygdala and the hypothalamic-pituitary-adrenal (HPA) stress axis, both required for lifelong cognitive and emotional processing. However, little data are available on the impact of obesity during adolescence on amygdala function. Herein, we therefore evaluate in rats whether juvenile high-fat diet (HFD)-induced obesity alters amygdala-dependent emotional memory and whether it depends on HPA axis deregulation. Exposure to HFD from weaning to adulthood, i.e., covering adolescence, enhances long-term emotional memories as assessed by odor-malaise and tone-shock associations. Juvenile HFD also enhances emotion-induced neuronal activation of the basolateral complex of the amygdala (BLA), which correlates with protracted plasma corticosterone release. HFD exposure restricted to adulthood does not modify all these parameters, indicating adolescence is a vulnerable period to the effects of HFD-induced obesity. Finally, exaggerated emotional memory and BLA synaptic plasticity after juvenile HFD are alleviated by a glucocorticoid receptor antagonist. Altogether, our results demonstrate that juvenile HFD alters HPA axis reactivity leading to an enhancement of amygdala-dependent synaptic and memory processes. Adolescence represents a period of increased susceptibility to the effects of diet-induced obesity on amygdala function.

Neurochemical and electrophysiological deficits in the ventral hippocampus and selective behavioral alterations caused by high-fat diet in female C57BL/6 mice

Mounting experimental evidence, predominantly from male rodents, demonstrates that high-fat diet (HFD) consumption and ensuing obesity are detrimental to the brain. To shed additional light on the neurological consequences of HFD consumption in female rodents and to determine the relatively early impact of HFD in the likely continuum of neurological dysfunction in the context of chronic HFD intake, this study investigated effects of HFD feeding for up to 12weeks on selected behavioral, neurochemical, and electrophysiological parameters in adult female C57BL/6 mice; particular focus was placed on the ventral hippocampus (vHIP). Selected locomotor, emotional and cognitive functions were evaluated using behavioral tests after 5weeks on HFD or control (low-fat diet) diets. One week later, mice were sacrificed and brain regional neurochemical (monoamine) analysis was performed. Behaviorally naïve mice were maintained on their respective diets for an additional 5-6weeks at which time synaptic plasticity was determined in ex vivo slices from the vHIP. HFD-fed female mice exhibited increased: (i) locomotor activity in the open field testing, (ii) mean turn time on the pole test, (iii) swimming time in the forced swim test, and (iv) number of marbles buried in the marble burying test. In contrast, the novel object recognition memory was unaffected. Mice on HFD also had decreased norepinephrine and dopamine turnover, respectively, in the prefrontal cortex and the vHIP. HFD consumption for a total of 11-12weeks altered vHIP synaptic plasticity, evidenced by significant reductions in the paired-pulse ratio and long-term potentiation (LTP) magnitude. In summary, in female mice, HFD intake for several weeks induced multiple behavioral alterations of mainly anxiety-like nature and impaired monoamine pathways in a brain region-specific manner, suggesting that in the female, certain behavioral domains (anxiety) and associated brain regions, i.e., the vHIP, are preferentially targeted by HFD.

Sex differences in feeding behavior in rats: the relationship with neuronal activation in the hypothalamus

There is general agreement that the central nervous system in rodents differs between sexes due to the presence of gonadal steroid hormone during differentiation. Sex differences in feeding seem to occur among species, and responses to fasting (i.e., starvation), gonadal steroids (i.e., testosterone and estradiol), and diet (i.e., western-style diet) vary significantly between sexes. The hypothalamus is the center for controlling feeding behavior. We examined the activation of feeding-related peptides in neurons in the hypothalamus. Phosphorylation of cyclic AMP response element-binding protein (CREB) is a good marker for neural activation, as is the Fos antigen. Therefore, we predicted that sex differences in the activity of melanin-concentrating hormone (MCH) neurons would be associated with feeding behavior. We determined the response of MCH neurons to glucose in the lateral hypothalamic area (LHA) and our results suggested MCH neurons play an important role in sex differences in feeding behavior. In addition, fasting increased the number of orexin neurons harboring phosphorylated CREB in female rats (regardless of the estrous day), but not male rats. Glucose injection decreased the number of these neurons with phosphorylated CREB in fasted female rats. Finally, under normal spontaneous food intake, MCH neurons, but not orexin neurons, expressed phosphorylated CREB. These sex differences in response to fasting and glucose, as well as under normal conditions, suggest a vulnerability to metabolic challenges in females.

Adipocyte SIRT1 knockout promotes PPARγ activity, adipogenesis and insulin sensitivity in chronic-HFD and obesity

OBJECTIVE

Adipose tissue is the primary site for lipid deposition that protects the organisms in cases of nutrient excess during obesogenic diets. The histone deacetylase Sirtuin 1 (SIRT1) inhibits adipocyte differentiation by targeting the transcription factor peroxisome proliferator activated-receptor gamma (PPARγ).

METHODS

To assess the specific role of SIRT1 in adipocytes, we generated Sirt1 adipocyte-specific knockout mice (ATKO) driven by aP2 promoter onto C57BL/6 background. Sirt1 (flx/flx) aP2Cre (+) (ATKO) and Sirt1 (flx/flx) aP2Cre (-) (WT) mice were fed high-fat diet for 5 weeks (short-term) or 15 weeks (chronic-term). Metabolic studies were combined with gene expression analysis and phosphorylation/acetylation patterns in adipose tissue.

RESULTS

On standard chow, ATKO mice exhibit low-grade chronic inflammation in adipose tissue, along with glucose intolerance and insulin resistance compared with control fed mice. On short-term HFD, ATKO mice become more glucose intolerant, hyperinsulinemic, insulin resistant and display increased inflammation. During chronic HFD, WT mice developed a metabolic dysfunction, higher than ATKO mice, and thereby, knockout mice are more glucose tolerant, insulin sensitive and less inflamed relative to control mice. SIRT1 attenuates adipogenesis through PPARγ repressive acetylation and, in the ATKO mice adipocyte PPARγ was hyperacetylated. This high acetylation was associated with a decrease in Ser273-PPARγ phosphorylation. Dephosphorylated PPARγ is constitutively active and results in higher expression of genes associated with increased insulin sensitivity.

CONCLUSION

Together, these data establish that SIRT1 downregulation in adipose tissue plays a previously unknown role in long-term inflammation resolution mediated by PPARγ activation. Therefore, in the context of obesity, the development of new therapeutics that activate PPARγ by targeting SIRT1 may provide novel approaches to the treatment of T2DM.

Growth hormone receptor antagonist transgenic mice are protected from hyperinsulinemia and glucose intolerance despite obesity when placed on a HF diet

Reduced GH levels have been associated with improved glucose metabolism and increased longevity despite obesity in multiple mouse lines. However, one mouse line, the GH receptor antagonist (GHA) transgenic mouse, defies this trend because it has reduced GH action and increased adiposity, but glucose metabolism and life span are similar to controls. Slight differences in glucose metabolism and adiposity profiles can become exaggerated on a high-fat (HF) diet. Thus, in this study, male and female GHA and wild-type (WT) mice in a C57BL/6 background were placed on HF and low-fat (LF) diets for 11 weeks, starting at 10 weeks of age, to assess how GHA mice respond to additional metabolic stress of HF feeding. On a HF diet, all mice showed significant weight gain, although GHA gained weight more dramatically than WT mice, with males gaining more than females. Most of this weight gain was due to an increase in fat mass with WT mice increasing primarily in the white adipose tissue perigonadal depots, whereas GHA mice gained in both the sc and perigonadal white adipose tissue regions. Notably, GHA mice were somewhat protected from detrimental glucose metabolism changes on a HF diet because they had only modest increases in serum glucose levels, remained glucose tolerant, and did not develop hyperinsulinemia. Sex differences were observed in many measures with males reacting more dramatically to both a reduction in GH action and HF diet. In conclusion, our findings show that GHA mice, which are already obese, are susceptible to further adipose tissue expansion with HF feeding while remaining resilient to alterations in glucose homeostasis.

Mitigating or exacerbating effects of maternal-fetal programming of female mice through the food choice environment

Humans live, eat, and become overweight/obese in complex surroundings where there are many available food choices. Prenatal exposure to poor food choices predisposes offspring to increased negative health risks, including obesity. Many animal experiments have analyzed intergenerational body weight parameters in an environment without food choices, which may not be directly translatable to the human food environment. In this study, offspring from mothers with a defined high-fat diet (HFD) or low-fat diet (LFD) were arbitrarily assigned to either an exclusively LFD or HFD or to a diet where they have a choice between LFD and HFD (choice diet). Offspring displayed negative outcomes of increased body weight, body fat, serum leptin, and blood glucose levels when given the choice diet compared with offspring on the LFD. Conversely, improved energy expenditure was found for offspring given the choice diet compared with offspring from HFD dams given LFD. In addition, maternal diet-specific influences on offspring metabolic parameters were identified, especially in offspring from HFD dams, including positive outcomes of reduced leptin in LFD offspring, reduced corticosterone and cholesterol levels in HFD offspring, and increased exercise levels in choice offspring, as well as the negative outcome of increased calorie intake in LFD offspring from HFD dams. This defined model can now be used as the basis for future studies to characterize the cycle of inter- and intragenerational obesity and whether more realistic diet environments, especially those including choice, can mitigate phenotype.

Epigenetic and developmental influences on the risk of obesity, diabetes, and metabolic syndrome

Metabolic syndrome is a growing cause of morbidity and mortality worldwide. Metabolic syndrome is characterized by the presence of a variety of metabolic disturbances including obesity, hyperlipidemia, hypertension, and elevated fasting blood sugar. Although the risk for metabolic syndrome has largely been attributed to adult lifestyle factors such as poor nutrition, lack of exercise, and smoking, there is now strong evidence suggesting that predisposition to the development of metabolic syndrome begins in utero. First posited by Hales and Barker in 1992, the "thrifty phenotype" hypothesis proposes that susceptibility to adult chronic diseases can occur in response to exposures in the prenatal and perinatal periods. This hypothesis has been continually supported by epidemiologic studies and studies involving animal models. In this review, we describe the structural, metabolic and epigenetic changes that occur in response to adverse intrauterine environments including prenatal and postnatal diet, maternal obesity, and pregnancy complications. Given the increasing prevalence of metabolic syndrome in both the developed and developing worlds, a greater understanding and appreciation for the role of the intrauterine environment in adult chronic disease etiology is imperative.

Prenatal metformin exposure in a maternal high fat diet mouse model alters the transcriptome and modifies the metabolic responses of the offspring

AIMS

Despite the wide use of metformin in metabolically challenged pregnancies, the long-term effects on the metabolism of the offspring are not known. We studied the long-term effects of prenatal metformin exposure during metabolically challenged pregnancy in mice.

MATERIALS AND METHODS

Female mice were on a high fat diet (HFD) prior to and during the gestation. Metformin was administered during gestation from E0.5 to E17.5. Male and female offspring were weaned to a regular diet (RD) and subjected to HFD at adulthood (10-11 weeks). Body weight and several metabolic parameters (e.g. body composition and glucose tolerance) were measured during the study. Microarray and subsequent pathway analyses on the liver and subcutaneous adipose tissue of the male offspring were performed at postnatal day 4 in a separate experiment.

RESULTS

Prenatal metformin exposure changed the offspring's response to HFD. Metformin exposed offspring gained less body weight and adipose tissue during the HFD phase. Additionally, prenatal metformin exposure prevented HFD-induced impairment in glucose tolerance. Microarray and annotation analyses revealed metformin-induced changes in several metabolic pathways from which electron transport chain (ETC) was prominently affected both in the neonatal liver and adipose tissue.

CONCLUSION

This study shows the beneficial effects of prenatal metformin exposure on the offspring's glucose tolerance and fat mass accumulation during HFD. The transcriptome data obtained at neonatal age indicates major effects on the genes involved in mitochondrial ATP production and adipocyte differentiation suggesting the mechanistic routes to improved metabolic phenotype at adulthood.

Diet-induced obesity attenuates endotoxin-induced cognitive deficits

Activation of the immune system can impair cognitive function, particularly on hippocampus dependent tasks. Several factors such as normal aging and prenatal experiences can modify the severity of these cognitive deficits. One additional factor that may modulate the behavioral response to immune activation is obesity. Prior work has shown that obesity alters the activity of the immune system. Whether diet-induced obesity (DIO) influences the cognitive deficits associated with inflammation is currently unknown. The present study explored whether DIO alters the behavioral response to the bacterial endotoxin, lipopolysaccharide (LPS). Female C57BL/6J mice were fed a high-fat (60% fat) or control diet (10% fat) for a total of five months. After consuming their respective diets for four months, mice received an LPS or saline injection and were assessed for alterations in spatial learning. One month later, mice received a second injection of LPS or saline and tissue samples were collected to assess the inflammatory response within the periphery and central nervous system. Results showed that LPS administration impaired spatial learning in the control diet mice, but had no effect in DIO mice. This lack of a cognitive deficit in the DIO female mice is likely due to a blunted inflammatory response within the brain. While cytokine production within the periphery (i.e., plasma, adipose, and spleen) was similar between the DIO and control mice, the DIO mice failed to show an increase in IL-6 and CD74 in the brain following LPS administration. Collectively, these data indicate that DIO can reduce aspects of the neuroinflammatory response as well as blunt the behavioral reaction to an immune challenge.

High-fat diet consumption disrupts memory and primes elevations in hippocampal IL-1β, an effect that can be prevented with dietary reversal or IL-1 receptor antagonism

High-fat diet (HFD)-induced obesity is reaching worldwide proportions. In addition to causing obesity, HFDs also induce a variety of health disorders, which includes cognitive decline. Hippocampal function may be particularly vulnerable to the negative consequences of HFD, and it is suspected that 'primed' neuroinflammatory processes may mediate this response. To examine the link between diet, hippocampal function and neuroinflammation, male Wistar rats were fed a medium or HFD. Hippocampal memory function was measured using contextual pre-exposure fear conditioning (CPE-FC). Rats fed a HFD demonstrated impaired memory, an effect that was augmented with longer duration of HFD consumption. HFD-induced memory impairments were linked to potentiated levels of interleukin-1 beta (IL-1β) protein in the hippocampus 2h after the foot-shock that occurs during CPE-FC. Central IL-1 receptor antagonism, with intracisterna magna (ICM) administration of hIL-1RA prior to the foot-shock prevented the diet-induced memory disruption, suggesting a critical role for IL-1β in this phenomenon. Additionally, obese animals whose diet regimen was reversed from HFD back to standard chow recovered memory function and did not demonstrate a foot-shock-induced hippocampal IL-1β increase. Interestingly, dietary reversal neutralized the negative impact of HFD on memory and IL-1β, yet animals maintained physiological evidence of obesity (increased body mass and serum leptin), indicating that dietary components, not body mass, may mediate the negative effects on memory.

Altered motivation masks appetitive learning potential of obese mice

Eating depends strongly on learning processes which, in turn, depend on motivation. Conditioned learning, where individuals associate environmental cues with receipt of a reward, forms an important part of hedonic mechanisms; the latter contribute to the development of human overweight and obesity by driving excessive eating in what may become a vicious cycle. Although mice are commonly used to explore the regulation of human appetite, it is not known whether their conditioned learning of food rewards varies as a function of body mass. To address this, groups of adult male mice of differing body weights were tested two appetitive conditioning paradigms (pavlovian and operant) as well as in food retrieval and hedonic preference tests in an attempt to dissect the respective roles of learning/motivation and energy state in the regulation of feeding behavior. We found that (i) the rate of pavlovian conditioning to an appetitive reward develops as an inverse function of body weight; (ii) higher body weight associates with increased latency to collect food reward; and (iii) mice with lower body weights are more motivated to work for a food reward, as compared to animals with higher body weights. Interestingly, as compared to controls, overweight and obese mice consumed smaller amounts of palatable foods (isocaloric milk or sucrose, in either the presence or absence of their respective maintenance diets: standard, low fat-high carbohydrate or high fat-high carbohydrate). Notably, however, all groups adjusted their consumption of the different food types, such that their body weight-corrected daily intake of calories remained constant. Thus, overeating in mice does not reflect a reward deficiency syndrome and, in contrast to humans, mice regulate their caloric intake according to metabolic status rather than to the hedonic properties of a particular food. Together, these observations demonstrate that excess weight masks the capacity for appetitive learning in the mouse.

Variations in body weight, food intake and body composition after long-term high-fat diet feeding in C57BL/6J mice

OBJECTIVE

To investigate the variations in body weight, food intake, and body composition of both male and female C57BL/6J mice during a diet-induced obesity model with high-fat diet (HFD) feeding.

METHODS

Mice were individually housed and fed ad libitum either a low-fat diet (LFD, 10% calories from fat; n = 15 male, n = 15 female) or HFD (45% calories from fat; n = 277 male, n = 278 female) from 8 to 43 weeks of age. Body weight, food intake, and body composition were routinely measured.

RESULTS

Body weight was significantly increased with HFD (vs. LFD) in males from week 14 (P = 0.0221) and in females from week 27 (P = 0.0076). Fat mass and fat-free mass of all groups were significantly increased over time (all P < 0.0001), with a large variation observed in fat mass. Baseline fat mass, fat-free mass, and daily energy intake were significant predictors of future body weight for both sexes (P < 0.0001). Baseline fat mass was a significant predictor of future body fat (P < 0.0001).

CONCLUSIONS

Both males and females have large variations in fat mass, and this variability increases over time, while that of fat-free mass remains relatively stable. Sex differences exist in HFD responses and multivariate predicting models of body weight.

Estrogen restores brain insulin sensitivity in ovariectomized non-obese rats, but not in ovariectomized obese rats

OBJECTIVE

We previously demonstrated that obesity caused the reduction of peripheral and brain insulin sensitivity and that estrogen therapy improved these defects. However, the beneficial effect of estrogen on brain insulin sensitivity and oxidative stress in either ovariectomy alone or ovariectomy with obesity models has not been determined. We hypothesized that ovariectomy alone or ovariectomy with obesity reduces brain insulin sensitivity and increases brain oxidative stress, which are reversed by estrogen treatment.

MATERIALS/METHODS

Thirty female rats were assigned as either sham-operated or ovariectomized. After the surgery, each group was fed either a normal diet or high-fat diet for 12 weeks. At week 13, rats in each group received either the vehicle or estradiol for 30 days. At week 16, blood and brain were collected for determining the peripheral and brain insulin sensitivity as well as brain oxidative stress.

RESULTS

We found that ovariectomized rats and high-fat diet fed rats incurred obesity, reduced peripheral and brain insulin sensitivity, and increased brain oxidative stress. Estrogen ameliorated peripheral insulin sensitivity in these rats. However, the beneficial effect of estrogen on brain insulin sensitivity and brain oxidative stress was observed only in ovariectomized normal diet-fed rats, but not in ovariectomized high fat diet-fed rats.

CONCLUSIONS

Our results suggested that reduced brain insulin sensitivity and increased brain oxidative stress occurred after either ovariectomy or obesity. However, the reduced brain insulin sensitivity and the increased brain oxidative stress in ovariectomy with obesity could not be ameliorated by estrogen treatment.

High fat diet produces brain insulin resistance, synaptodendritic abnormalities and altered behavior in mice

Insulin resistance and other features of the metabolic syndrome are increasingly recognized for their effects on cognitive health. To ascertain mechanisms by which this occurs, we fed mice a very high fat diet (60% kcal by fat) for 17days or a moderate high fat diet (HFD, 45% kcal by fat) for 8weeks and examined changes in brain insulin signaling responses, hippocampal synaptodendritic protein expression, and spatial working memory. Compared to normal control diet mice, cerebral cortex tissues of HFD mice were insulin-resistant as evidenced by failed activation of Akt, S6 and GSK3β with ex-vivo insulin stimulation. Importantly, we found that expression of brain IPMK, which is necessary for mTOR/Akt signaling, remained decreased in HFD mice upon activation of AMPK. HFD mouse hippocampus exhibited increased expression of serine-phosphorylated insulin receptor substrate 1 (IRS1-pS(616)), a marker of insulin resistance, as well as decreased expression of PSD-95, a scaffolding protein enriched in post-synaptic densities, and synaptopodin, an actin-associated protein enriched in spine apparatuses. Spatial working memory was impaired as assessed by decreased spontaneous alternation in a T-maze. These findings indicate that HFD is associated with telencephalic insulin resistance and deleterious effects on synaptic integrity and cognitive behaviors.

The selective orexin receptor 1 antagonist ACT-335827 in a rat model of diet-induced obesity associated with metabolic syndrome

The orexin system regulates feeding, nutrient metabolism and energy homeostasis. Acute pharmacological blockade of orexin receptor 1 (OXR-1) in rodents induces satiety and reduces normal and palatable food intake. Genetic OXR-1 deletion in mice improves hyperglycemia under high-fat (HF) diet conditions. Here we investigated the effects of chronic treatment with the novel selective OXR-1 antagonist ACT-335827 in a rat model of diet-induced obesity (DIO) associated with metabolic syndrome (MetS). Rats were fed either standard chow (SC) or a cafeteria (CAF) diet comprised of intermittent human snacks and a constant free choice between a HF/sweet (HF/S) diet and SC for 13 weeks. Thereafter the SC group was treated with vehicle (for 4 weeks) and the CAF group was divided into a vehicle and an ACT-335827 treatment group. Energy and water intake, food preference, and indicators of MetS (abdominal obesity, glucose homeostasis, plasma lipids, and blood pressure) were monitored. Hippocampus-dependent memory, which can be impaired by DIO, was assessed. CAF diet fed rats treated with ACT-335827 consumed less of the HF/S diet and more of the SC, but did not change their snack or total kcal intake compared to vehicle-treated rats. ACT-335827 increased water intake and the high-density lipoprotein associated cholesterol proportion of total circulating cholesterol. ACT-335827 slightly increased body weight gain (4% vs. controls) and feed efficiency in the absence of hyperphagia. These effects were not associated with significant changes in the elevated fasting glucose and triglyceride (TG) plasma levels, glucose intolerance, elevated blood pressure, and adiposity due to CAF diet consumption. Neither CAF diet consumption alone nor ACT-335827 affected memory. In conclusion, the main metabolic characteristics associated with DIO and MetS in rats remained unaffected by chronic ACT-335827 treatment, suggesting that pharmacological OXR-1 blockade has minimal impact in this model.

Effect of insulin on excitatory synaptic transmission onto dopamine neurons of the ventral tegmental area in a mouse model of hyperinsulinemia

Obesity has drastically increased over the last few decades. Obesity is associated with elevated insulin levels, which can gain access to the brain, including into dopamine neurons of the ventral tegmental area (VTA), a brain region critical for mediating reward-seeking behavior. Synaptic plasticity of VTA dopamine neurons is associated with altered motivation to obtain reinforcing substances such as food and drugs of abuse. Under physiological circumstances, insulin in the VTA can suppress excitatory synaptic transmission onto VTA dopamine neurons and reduce aspects of palatable feeding behavior. However, it is unknown how insulin modulates excitatory synaptic transmission in pathological circumstances such as hyperinsulinemia. Using patch-clamp electrophysiology, we demonstrate that, in a hyperinsulinemic mouse model, insulin has reduced capacity to cause a synaptic depression of VTA dopamine neurons, although both low-frequency stimulation-induced long-term depression and cannabinoid-induced depression were normal. These results suggest that insulin action in the VTA during pathological hyperinsulinemia is disrupted and may lead to increased feeding behavior.

Sex-specific effects of high fat diet on indices of metabolic syndrome in 3xTg-AD mice: implications for Alzheimer's disease

Multiple factors of metabolic syndrome have been implicated in the pathogenesis of Alzheimer's disease (AD), including abdominal obesity, insulin resistance, endocrine dysfunction and dyslipidemia. High fat diet, a common experimental model of obesity and metabolic syndrome, has been shown to accelerate cognitive decline and AD-related neuropathology in animal models. However, sex interacts with the metabolic outcomes of high fat diet and, therefore, may alter neuropathological consequences of dietary manipulations. This study examines the effects of sex and high fat diet on metabolic and AD-related neuropathological outcomes in 3xTg-AD mice. Three month-old male and female 3xTg-AD mice were fed either standard or high fat diets for 4 months. Obesity was observed in all high fat fed mice; however, ectopic fat accumulation, hyperglycemia and hyperinsulinemia were observed only in males. Interestingly, despite the different metabolic outcomes of high fat diet, the neuropathological consequences were similar: both male and female mice maintained under high fat diet exhibited significant worsening in behavioral performance and hippocampal accumulation of β-amyloid protein. Because high fat diet resulted in obesity and increased AD-like pathology in both sexes, these data support a role of obesity-related factors in promoting AD pathogenesis.

Role of standardized grape polyphenol preparation as a novel treatment to improve synaptic plasticity through attenuation of features of metabolic syndrome in a mouse model

SCOPE

Metabolic syndrome has become an epidemic and poses tremendous burden on the health system. People with metabolic syndrome are more likely to experience cognitive decline. As obesity and sedentary lifestyles become more common, the development of early prevention strategies is critical. In this study, we explore the potential beneficial effects of a combinatory polyphenol preparation composed of grape seed extract, Concord purple grape juice extract, and resveratrol, referred to as standardized grape polyphenol preparation (SGP), on peripheral as well as brain dysfunction induced by metabolic syndrome.

METHODS AND RESULTS

We found dietary fat content had minimal effect on absorption of metabolites of major polyphenols derived from SGP. Using a diet-induced animal model of metabolic syndrome (DIM), we found that brain functional connectivity and synaptic plasticity are compromised in the DIM mice. Treatment with SGP not only prevented peripheral metabolic abnormality but also improved brain synaptic plasticity.

CONCLUSION

Our study demonstrated that SGP, comprised of multiple bioavailable and bioactive components targeting a wide range of metabolic syndrome related pathological features, provides greater global protection against peripheral and central nervous system dysfunctions and can be potentially developed as a novel prevention/treatment for improving brain connectivity and synaptic plasticity important for learning and memory.

Ghrelin, neuropeptide Y, and other feeding-regulatory peptides active in the hippocampus: role in learning and memory

The hippocampus is a brain region of primary importance for neurogenesis, which occurs during early developmental states as well as during adulthood. Increases in neuronal proliferation and in neuronal death with age have been associated with drastic changes in memory and learning. Numerous neurotransmitters are involved in these processes, and some neuropeptides that mediate neurogenesis also modulate feeding behavior. Concomitantly, feeding peptides, which act primarily in the hypothalamus, are also present in the hippocampus. This review aims to ascertain the role of several important feeding peptides in cognitive functions, either through their local synthesis in the hippocampus or through their actions via specific receptors in the hippocampus. A link between neurogenesis and the orexigenic or anorexigenic properties of feeding peptides is discussed.

Male mice that lack the G-protein-coupled receptor GPR41 have low energy expenditure and increased body fat content

SCFA are produced in the gut by bacterial fermentation of undigested carbohydrates. Activation of the Gαi-protein-coupled receptor GPR41 by SCFA in β-cells and sympathetic ganglia inhibits insulin secretion and increases sympathetic outflow, respectively. A possible role in stimulating leptin secretion by adipocytes is disputed. In the present study, we investigated energy balance and glucose homoeostasis in GPR41 knockout mice fed on a standard low-fat or a high-fat diet. When fed on the low-fat diet, body fat mass was raised and glucose tolerance was impaired in male but not female knockout mice compared to wild-type mice. Soleus muscle and heart weights were reduced in the male mice, but total body lean mass was unchanged. When fed on the high-fat diet, body fat mass was raised in male but not female GPR41 knockout mice, but by no more in the males than when they were fed on the low-fat diet. Body lean mass and energy expenditure were reduced in male mice but not in female knockout mice. These results suggest that the absence of GPR41 increases body fat content in male mice. Gut-derived SCFA may raise energy expenditure and help to protect against obesity by activating GPR41.

Sexual dimorphic regulation of body weight dynamics and adipose tissue lipolysis

Background

Successful reduction of body weight (BW) is often followed by recidivism to obesity. BW-changes including BW-loss and -regain is associated with marked alterations in energy expenditure (EE) and adipose tissue (AT) metabolism. Since these processes are sex-specifically controlled, we investigated sexual dimorphisms in metabolic processes during BW-dynamics (gain-loss-regain).

Research Design

Obesity was induced in C57BL/6J male (m) and female (f) mice by 15 weeks high-fat diet (HFD) feeding. Subsequently BW was reduced (-20%) by caloric restriction (CR) followed by adaptive feeding, and a regain-phase. Measurement of EE, body composition, blood/organ sampling were performed after each feeding period. Lipolysis was analyzed ex-vivo in gonadal AT.

Results

Male mice exhibited accelerated BW-gain compared to females (relative BW-gain m:140.5±3.2%; f:103.7±6.5%; p<0.001). In consonance, lean mass-specific EE was significantly higher in females compared to males during BW-gain. Under CR female mice reached their target-BW significantly faster than male mice (m:12.2 days; f:7.6 days; p<0.001) accompanied by a sustained sex-difference in EE. In addition, female mice predominantly downsized gonadal AT whereas the relation between gonadal and total body fat was not altered in males. Accordingly, only females exhibited an increased rate of forskolin-stimulated lipolysis in AT associated with significantly higher glycerol concentrations, lower RER-values, and increased AT expression of adipose triglyceride lipase (ATGL) and hormone sensitive lipase (HSL). Analysis of AT lipolysis in estrogen receptor alpha (ERα)–deficient mice revealed a reduced lipolytic rate in the absence of ERα exclusively in females. Finally, re-feeding caused BW-regain faster in males than in females.

Conclusion

The present study shows sex-specific dynamics during BW-gain-loss-regain. Female mice responded to CR with an increase in lipolytic activity, and augmented lipid-oxidation leading to more efficient weight loss. These processes likely involve ERα-dependent signaling in AT and sexual dimorphic regulation of genes involved in lipid metabolism.

Adult mice maintained on a high-fat diet exhibit object location memory deficits and reduced hippocampal SIRT1 gene expression

Mounting evidence has established that diet-induced obesity (DIO) is associated with deficits in hippocampus-dependent memory. The bulk of research studies dealing with this topic have utilized rats fed a high-fat diet as an experimental model. To date, there has been a paucity of research studies that have established whether the memory deficits exhibited in DIO rats can be recapitulated in mice. Moreover, the majority of experiments that have evaluated memory performance in rodent models of DIO have utilized memory tests that are essentially aversive in nature (i.e., Morris water maze). The current study sought to fill an empirical void by determining if mice maintained on a high-fat diet exhibit deficits in two non-aversive memory paradigms: novel object recognition (NOR) and object location memory (OLM). Here we report that mice fed a high-fat diet over 23 weeks exhibit intact NOR, albeit a marked impairment in hippocampus-dependent OLM. We also determined the existence of corresponding aberrations in gene expression within the hippocampus of DIO mice. DIO mice exhibited significant reductions in both SIRT1 and PP1 mRNA within the hippocampus. Our data suggest that mice maintained on a high-fat diet present with impaired hippocampus-dependent spatial memory and a corresponding alteration in the expression of genes that have been implicated in memory consolidation.

Promoting brain remodelling and plasticity for stroke recovery: therapeutic promise and potential pitfalls of clinical translation

Recent laboratory findings suggest that it might be possible to promote cerebral plasticity and neurological recovery after stroke by use of exogenous pharmacological or cell-based treatments. Brain microvasculature and glial cells respond in concert to ischaemic stressors and treatment, creating an environment in which successful recovery can ensue. Neurons remote from and adjacent to the ischaemic lesion are enabled to sprout, and neural precursor cells that accumulate with cerebral microvessels in the perilesional tissue further stimulate brain plasticity and neurological recovery. These factors interact in a highly dynamic way, facilitating temporally and spatially orchestrated responses of brain networks. In view of the complexity of the systems involved, stroke treatments that stimulate and amplify these endogenous restorative mechanisms might also provoke unwanted side-effects. In experimental studies, adverse effects have been identified when neurorestorative treatments were administered to animals with severe associated illnesses, after thrombolysis with alteplase, and when therapies were initiated outside appropriate time windows. Balancing the opportunities and possible risks, we provide suggestions for the translation of restorative therapies from the laboratory to the clinic.

Blood-borne metabolic factors in obesity exacerbate injury-induced gliosis

Reactive gliosis, a sign of neuroinflammation, has been observed in mice with adult-onset obesity as well as CNS injury. The hypothesis that obesity-derived metabolic factors exacerbate reactive gliosis in response to mechanical injury was tested here on cultured primary glial cells subjected to a well-established model of scratch wound injury. Cells treated with serum from mice with diet-induced obesity (DIO) showed higher immunoreactivity of CD11b (marker for microglia) and GFAP (marker for astrocytes), with morphological changes at both the injury border and areas away from the injury. The effect of DIO serum was greater than that of scratch injury alone. Leptin was almost as effective as DIO serum in inducing microgliosis and astrogliosis in a dose-response manner. By contrast, C-reactive protein (CRP) mainly induced microgliosis in noninjured cells; injury-induced factors appeared to attenuate this effect. The effect of CRP also differed from the effect of the antibiotic minocycline. Minocycline attenuated the microgliosis and to a lesser extent astrogliosis, particularly in CRP-treated cells, thus serving as a negative control. We conclude that blood-borne proinflammatory metabolic factors in obesity increase reactive gliosis and probably exacerbate CNS injury.

High-fat diets induce changes in hippocampal glutamate metabolism and neurotransmission

Obesity and high-fat (HF) diets have a deleterious impact on hippocampal function and lead to impaired synaptic plasticity and learning deficits. Because all of these processes need an adequate glutamatergic transmission, we have hypothesized that nutritional imbalance triggered by these diets might eventually concern glutamate (Glu) neural pathways within the hippocampus. Glu is withdrawn from excitatory synapses by specific uptake mechanisms involving neuronal (EAAT-3) and glial (GLT-1, GLAST) transporters, which regulate the time that synaptically released Glu remains in the extracellular space and, consequently, the duration and location of postsynaptic receptor activation. The goal of the present study was to evaluate in mouse hippocampus the effect of a short-term high-fat dietary treatment on 1) Glu uptake kinetics, 2) the density of Glu carriers and Glu-degrading enzymes, 3) the density of Glu receptor subunits, and 4) synaptic transmission and plasticity. Here, we show that HF diet triggers a 50% decrease of the Michaelis-Menten constant together with a 300% increase of the maximal velocity of the uptake process. Glial Glu carriers GLT-1 and GLAST were upregulated in HF mice (32 and 27%, respectively), whereas Glu-degrading enzymes glutamine synthase and GABA-decarboxilase appeared to be downregulated in these animals. In addition, HF diet hippocampus displayed diminished basal synaptic transmission and hindered NMDA-induced long-term depression (NMDA-LTD). This was coincident with a reduced density of the NR2B subunit of NMDA receptors. All of these results are compatible with the development of leptin resistance within the hippocampus. Our data show that HF diets upregulate mechanisms involved in Glu clearance and simultaneously impair Glu metabolism. Neurochemical changes occur concomitantly with impaired basal synaptic transmission and reduced NMDA-LTD. Taken together, our results suggest that HF diets trigger neurochemical changes, leading to a desensitization of NMDA receptors within the hippocampus, which might account for cognitive deficits.

Histone deacetylases 1 and 2 regulate autophagy flux and skeletal muscle homeostasis in mice

Maintenance of skeletal muscle structure and function requires efficient and precise metabolic control. Autophagy plays a key role in metabolic homeostasis of diverse tissues by recycling cellular constituents, particularly under conditions of caloric restriction, thereby normalizing cellular metabolism. Here we show that histone deacetylases (HDACs) 1 and 2 control skeletal muscle homeostasis and autophagy flux in mice. Skeletal muscle-specific deletion of both HDAC1 and HDAC2 results in perinatal lethality of a subset of mice, accompanied by mitochondrial abnormalities and sarcomere degeneration. Mutant mice that survive the first day of life develop a progressive myopathy characterized by muscle degeneration and regeneration, and abnormal metabolism resulting from a blockade to autophagy. HDAC1 and HDAC2 regulate skeletal muscle autophagy by mediating the induction of autophagic gene expression and the formation of autophagosomes, such that myofibers of mice lacking these HDACs accumulate toxic autophagic intermediates. Strikingly, feeding HDAC1/2 mutant mice a high-fat diet from the weaning age releases the block in autophagy and prevents myopathy in adult mice. These findings reveal an unprecedented and essential role for HDAC1 and HDAC2 in maintenance of skeletal muscle structure and function and show that, at least in some pathological conditions, myopathy may be mitigated by dietary modifications.

Sex-dimorphism in cardiac nutrigenomics: effect of trans fat and/or monosodium glutamate consumption

BACKGROUND

A paucity of information on biological sex-specific differences in cardiac gene expression in response to diet has prompted this present nutrigenomics investigation. Sexual dimorphism exists in the physiological and transcriptional response to diet, particularly in response to high-fat feeding. Consumption of Trans-fatty acids (TFA) has been linked to substantially increased risk of heart disease, in which sexual dimorphism is apparent, with males suffering a higher disease rate. Impairment of the cardiovascular system has been noted in animals exposed to Monosodium Glutamate (MSG) during the neonatal period, and sexual dimorphism in the growth axis of MSG-treated animals has previously been noted. Processed foods may contain both TFA and MSG.

METHODS

We examined physiological differences and changes in gene expression in response to TFA and/or MSG consumption compared to a control diet, in male and female C57BL/6J mice.

RESULTS

Heart and % body weight increases were greater in TFA-fed mice, who also exhibited dyslipidemia (P < 0.05). Hearts from MSG-fed females weighed less than males (P < 0.05). 2-factor ANOVA indicated that the TFA diet induced over twice as many cardiac differentially expressed genes (DEGs) in males compared to females (P < 0.001); and 4 times as many male DEGs were downregulated including Gata4, Mef2d and Srebf2. Enrichment of functional Gene Ontology (GO) categories were related to transcription, phosphorylation and anatomic structure (P < 0.01). A number of genes were upregulated in males and downregulated in females, including pro-apoptotic histone deacetylase-2 (HDAC2). Sexual dimorphism was also observed in cardiac transcription from MSG-fed animals, with both sexes upregulating approximately 100 DEGs exhibiting sex-specific differences in GO categories. A comparison of cardiac gene expression between all diet combinations together identified a subset of 111 DEGs significant only in males, 64 DEGs significant in females only, and 74 transcripts identified as differentially expressed in response to dietary manipulation in both sexes.

CONCLUSION

Our model identified major changes in the cardiac transcriptional profile of TFA and/or MSG-fed mice compared to controls, which was reflected by significant differences in the physiological profile within the 4 diet groups. Identification of sexual dimorphism in cardiac transcription may provide the basis for sex-specific medicine in the future.

Prenatal stress induces long-term effects in cell turnover in the hippocampus-hypothalamus-pituitary axis in adult male rats

Subchronic gestational stress leads to permanent modifications in the hippocampus-hypothalamus-pituitary-adrenal axis of offspring probably due to the increase in circulating glucocorticoids known to affect prenatal programming. The aim of this study was to investigate whether cell turnover is affected in the hippocampus-hypothalamus-pituitary axis by subchronic prenatal stress and the intracellular mechanisms involved. Restraint stress was performed in pregnant rats during the last week of gestation (45 minutes; 3 times/day). Only male offspring were used for this study and were sacrificed at 6 months of age. In prenatally stressed adults a decrease in markers of cell death and proliferation was observed in the hippocampus, hypothalamus and pituitary. This was associated with an increase in insulin-like growth factor-I mRNA levels, phosphorylation of CREB and calpastatin levels and inhibition of calpain -2 and caspase -8 activation. Levels of the anti-apoptotic protein Bcl-2 were increased and levels of the pro-apoptotic factor p53 were reduced. In conclusion, prenatal restraint stress induces a long-term decrease in cell turnover in the hippocampus-hypothalamus-pituitary axis that might be at least partly mediated by an autocrine-paracrine IGF-I effect. These changes could condition the response of this axis to future physiological and pathophysiological situations.

Metabolic stress-induced inflammation plays a major role in the development of osteoarthritis in mice

OBJECTIVE

Obesity is associated with systemic inflammation and is a risk factor for osteoarthritis (OA) development. We undertook this study to test the hypothesis that metabolic stress-induced inflammation, and not mechanical overload, is responsible for the development of high-fat diet-induced OA in mice.

METHODS

Human C-reactive protein (CRP)-transgenic mice received a high-fat diet without or with 0.005% (weight/weight) rosuvastatin or 0.018% (w/w) rosiglitazone, 2 different drugs with antiinflammatory properties. Mice fed chow were included as controls. After 42 weeks, mice were killed and histologic OA grading of the knees was performed. To monitor the overall inflammation state, systemic human CRP levels were determined.

RESULTS

Male mice on a high-fat diet had significantly higher OA grades than mice on chow and showed no correlation between OA severity and body weight. In male mice, high-fat diet-induced OA was significantly inhibited by rosuvastatin or rosiglitazone to OA grades observed in control mice. Both treatments resulted in reduced human CRP levels. Furthermore, a positive correlation was found between the relative individual induction of human CRP evoked by a high-fat diet on day 3 and OA grade at end point.

CONCLUSION

High-fat diet-induced OA in mice is due to low-grade inflammation and not to mechanical overload, since no relationship between body weight and OA grade was observed. Moreover, the OA process was inhibited to a great extent by treatment with 2 drugs with antiinflammatory properties. The inflammatory response to a metabolic high-fat challenge may predict individual susceptibility to developing OA later in life. The use of statins or peroxisome proliferator-activated receptor γ agonists (e.g., rosiglitazone) could be a strategy for interfering with the progression of OA.

Effects of current exercise and diet on late-life cognitive health of former college football players

OBJECTIVE

To determine the relative influence of current exercise and diet on the late-life cognitive health of former Division I collision-sport collegiate athletes (ie, football players) compared with noncollision-sport athletes and non-athletes.

METHODS

Graduates (n = 400) of a Midwestern university (average age, 64.09 years; standard deviation, 13.32) completed a self-report survey to assess current demographics/physical characteristics, exercise, diet, cognitive difficulties, and physical and mental health.

RESULTS

Former football players reported more cognitive difficulties, as well as worse physical and mental health than controls. Among former football players, greater intake of total and saturated fat and cholesterol and lower overall diet quality were significantly correlated with cognitive difficulties; current dietary intake was not associated with cognitive health for the noncollision-sport athletes or nonathletes. Hierarchical regressions predicting cognitive difficulties indicated that income was positively associated with fewer cognitive difficulties and predicted 8% of the variance; status as a former football player predicted an additional 2% of the variance; and the interaction between being a football player and total dietary fat intake significantly predicted an additional 6% of the total variance (total model predicted 16% of variance). Greater intake of dietary fat was associated with increased cognitive difficulties, but only in the former football players, and not in the controls. Prior participation in football was associated with worse physical and mental health, while more frequent vigorous exercise was associated with higher physical and mental health ratings.

CONCLUSION

Former football players reported more late-life cognitive difficulties and worse physical and mental health than former noncollision-sport athletes and nonathletes. A novel finding of the present study is that current dietary fat was associated with more cognitive difficulties, but only in the former football players. These results suggest the need for educational interventions to encourage healthy dietary habits to promote the long-term cognitive health of collision-sport athletes.

High fat diet intake during pre and periadolescence impairs learning of a conditioned place preference in adulthood

BACKGROUND

Brain regions that mediate learning of a conditioned place preference (CPP) undergo significant development in pre and periadolescence. Consuming a high fat (HF) diet during this developmental period and into adulthood can lead to learning impairments in rodents. The present study tested whether HF diet intake, consumed only in pre and periadolescence, would be sufficient to cause impairments using a CPP procedure.

METHODS

Rats were randomly assigned to consume a HF or a low fat (LF) diet during postnatal days (PD) 21-40 and were then placed back on a standard lab chow diet. A 20-day CPP procedure, using HF Cheetos® as the unconditioned stimulus (US), began either the next day (PD 41) or 40 days later (PD 81). A separate group of adult rats were given the HF diet for 20 days beginning on PD 61, and then immediately underwent the 20-day CPP procedure beginning on PD 81.

RESULTS

Pre and periadolescent exposure to a LF diet or adult exposure to a HF diet did not interfere with the development of a HF food-induced CPP, as these groups exhibited robust preferences for the HF Cheetos® food-paired compartment. However, pre and periadolescent exposure to the HF diet impaired the development of a HF food-induced CPP regardless of whether it was assessed immediately or 40 days after the exposure to the HF diet, and despite showing increased consumption of the HF Cheetos® in conditioning.

CONCLUSIONS

Intake of a HF diet, consumed only in pre and periadolescence, has long-lasting effects on learning that persist into adulthood.

A high fructose diet does not affect amphetamine self-administration or spatial water maze learning and memory in female rats

High energy diets can have a detrimental effect on brain plasticity. For example, a high fructose diet impairs spatial memory in male rats. The aim of the present study was to determine whether a high fructose diet impairs another form of learning and memory: drug reinforcement learning. Female Sprague-Dawley rats were fed a high fructose diet (60%) from weaning at postnatal day (PND) 21, then allowed to acquire lever-pressing maintained by intravenous (i.v.) amphetamine at PND 68, 109, or 165. Acquisition was tested on a fixed ratio one (FR1) schedule of reinforcement (0.025 mg/kg/infusion, 1h daily sessions, 10 sessions over 14 days), followed by testing for reinforcing efficacy on a progressive ratio (PR) schedule (0.025, 0.01, and 0.1mg/kg/infusion), 14 days of abstinence, and within-session extinction and reinstatement tests. Subsequently, water maze acquisition and retention were tested in these subjects as well as a separate cohort tested in the water maze only. The diet had no effect on acquisition, reinforcing efficacy, extinction, or reinstatement of amphetamine seeking. Nor did the diet alter any measures of spatial memory. The high fructose diet did decrease body mass and increase relative liver and spleen mass, but did not affect plasma triglyceride concentrations consistently. Together with prior research on males, these results suggest that the metabolism of fructose and the effects of a high fructose diet on learning and memory may be sex-dependent.

Impaired adaptive cellular responses to oxidative stress and the pathogenesis of Alzheimer's disease

As is generally true with other age-related diseases, Alzheimer's disease (AD) involves oxidative damage to cellular components in the affected tissue, in this case the brain. The causes and consequences of oxidative stress in neurons in AD are not fully understood, but considerable evidence points to important roles for accumulation of amyloid β-peptide upstream of oxidative stress and perturbed cellular Ca(2+) homeostasis and energy metabolism downstream of oxidative stress. The identification of mutations in the β-amyloid precursor protein and presenilin-1 as causes of some cases of early onset inherited AD, and the development of cell culture and animal models based on these mutations has greatly enhanced our understanding of the AD process, and has greatly expanded opportunities for preclinical testing of potential therapeutic interventions. In this regard, and of particular interest to us, is the elucidation of adaptive cellular stress response pathways (ACSRP) that can counteract multiple steps in the AD neurodegenerative cascades, thereby limiting oxidative damage and preserving cognitive function. ACSRP can be activated by factors ranging from exercise and dietary energy restriction, to drugs and phytochemicals. In this article we provide an overview of oxidative stress and AD, with a focus on ACSRP and their potential for preventing and treating AD.

Overexpression of constitutively active PKG-I protects female, but not male mice from diet-induced obesity

Cyclic guanosine monophosphate (cGMP)-dependent protein kinase I (PKG-I) is a multifunctional protein. The direct effects of PKG-I activation on energy homeostasis and obesity development are not well understood. Herein, we generated transgenic mice with expression of the constitutively active PKG-I in adipose tissue as well as in other tissues. Male and female PKG-I overexpressing mice were fed a low-fat (LF) or high-fat (HF) diet for 16 weeks. HF-fed female PKG-I transgenic mice had decreased body weight gain, lower percentage of body fat, and improved glucose tolerance compared to HF-fed wild-type (WT) controls. In contrast, male transgenic PKG-I mice were not resistant to the development of HF-diet-induced obesity, and exhibited similar levels of adiposity and glucose intolerance as HF-fed WT controls. Furthermore, we found that HF-fed female transgenic PKG-I mice had increased energy expenditure and cold-induced adaptive thermogenesis compared to HF-fed WT controls, which was associated with increased expression of uncoupling protein-1 (UCP1) in brown adipose tissue (BAT). In addition, the rates of lipolysis in white adipose tissue (WAT) were also increased in female transgenic PKG-I mice compared to WT controls due to increased phosphorylation of hormone-sensitive lipase (HSL). However, in male mice, adaptive thermogenesis or WAT lipolysis was similar between transgenic PKG-I mice and WT controls. Together, these data demonstrate sex differences in effects of PKG-I activation on the regulation of adipose tissue function and its contribution to diet induced obesity.

Obesity/hyperleptinemic phenotype impairs structural and functional plasticity in the rat hippocampus

Epidemiological studies estimate that greater than 60% of the adult US population may be categorized as either overweight or obese, and there is a growing appreciation that the complications of obesity extend to the central nervous system (CNS). While the vast majority of these studies have focused on the hypothalamus, more recent studies suggest that the complications of obesity may also affect the structural and functional integrity of the hippocampus. A potential contributor to obesity-related CNS abnormalities is the adipocyte-derived hormone leptin. In this regard, decreases in CNS leptin activity may contribute to deficits in hippocampal synaptic plasticity and suggest that leptin resistance, a well-described phenomenon in the hypothalamus, may also be observed in the hippocampus. Unfortunately, the myriad of metabolic and endocrine abnormalities in diabetes/obesity phenotypes makes it challenging to assess the role of leptin in hippocampal neuroplasticity deficits associated with obesity models. To address this question, we examined hippocampal morphological and behavioral plasticity following lentivirus-mediated downregulation of hypothalamic insulin receptors (hypo-IRAS). Hypo-IRAS rats exhibit increases in body weight, adiposity, plasma leptin and triglyceride levels. As such, hypo-IRAS rats develop a phenotype that is consistent with features of the metabolic syndrome. In addition, hippocampal morphological plasticity and performance of hippocampal-dependent tasks are adversely affected in hypo-IRAS rats. Leptin-mediated signaling is also decreased in hypo-IRAS rats. We will discuss these findings in the context of how hyperleptinemia and hypertriglyceridemia may represent mechanistic mediators of the neurological consequences of impaired hippocampal synaptic plasticity in obesity.

Obesity/hyperleptinemic phenotype adversely affects hippocampal plasticity: effects of dietary restriction

Epidemiological studies estimate that greater than 60% of the adult US population may be categorized as either overweight or obese and there is a growing appreciation that obesity affects the functional integrity of the central nervous system (CNS). We recently developed a lentivirus (LV) vector that produces an insulin receptor (IR) antisense RNA sequence (IRAS) that when injected into the hypothalamus selectively decreases IR signaling in hypothalamus, resulting in increased body weight, peripheral adiposity and plasma leptin levels. To test the hypothesis that this obesity/hyperleptinemic phenotype would impair hippocampal synaptic transmission, we examined short term potentiation (STP) and long term potentiation (LTP) in the hippocampus of rats that received the LV-IRAS construct or the LV-Control construct in the hypothalamus (hypo-IRAS and hypo-Con, respectively). Stimulation of the Schaffer collaterals elicits STP that develops into LTP in the CA1 region of hypo-Con rats; conversely, hypo-IRAS rats exhibit STP that fails to develop into LTP. To more closely examine the potential role of hyperleptinemia in these electrophysiological deficits, hypo-IRAS were subjected to mild food restriction paradigms that would either: 1) prevent the development of the obesity phenotype; or 2) reverse an established obesity phenotype in hypo-IRAS rats. Both of these paradigms restored LTP in the CA1 region and reversed the decreases in the phosphorylated/total ratio of GluA1 Ser845 AMPA receptor subunit expression observed in the hippocampus of hypo-IRAS rats. Collectively, these data support the hypothesis that obesity impairs hippocampal synaptic transmission and support the hypothesis that these deficits are mediated through the impairment of hippocampal leptin activity.

Postnatal Sim1 deficiency causes hyperphagic obesity and reduced Mc4r and oxytocin expression

Single-minded 1 (SIM1) mutations are one of the few known causes of nonsyndromic monogenic obesity in both humans and mice. Although the role of Sim1 in the formation of the hypothalamus has been described, its postdevelopmental, physiological functions have not been well established. Here we demonstrate that postnatal CNS deficiency of Sim1 is sufficient to cause hyperphagic obesity. We conditionally deleted Sim1 after birth using CaMKII-Cre (alpha-calcium/calmodulin-dependent protein kinase II-Cre) lines to recombine a floxed Sim1 allele. Conditional Sim1 heterozygotes phenocopied germ line Sim1 heterozygotes, displaying hyperphagic obesity and increased length. We also generated viable conditional Sim1 homozygotes, demonstrating that adult Sim1 expression is not essential for mouse or neuron survival and revealing a dosage-dependent effect of Sim1 on obesity. Using stereological cell counting, we showed that the phenotype of both germ line heterozygotes and conditional Sim1 homozygotes was not attributable to global hypocellularity of the paraventricular nucleus (PVN) of the hypothalamus. We also used retrograde tract tracing to demonstrate that the PVN of germ line heterozygous mice projects normally to the dorsal vagal complex and the median eminence. Finally, we showed that conditional Sim1 homozygotes and germ line Sim1 heterozygotes exhibit a remarkable decrease in hypothalamic oxytocin (Oxt) and PVN melanocortin 4 receptor (Mc4r) mRNA. These results demonstrate that the role of Sim1 in feeding regulation is not limited to formation of the PVN or its projections and that the hyperphagic obesity in Sim1-deficient mice may be attributable to changes in the leptin-melanocortin-oxytocin pathway.

The impact of dietary energy intake on cognitive aging

Rodents that are insulin resistant and obese as the result of genetic factors, overeating and/or a sedentary lifestyle, exhibit cognitive deficits that worsen with advancing age compared to their more svelte counterparts. Data from epidemiological and clinical studies suggest similar adverse effects of excessive dietary energy intake and insulin resistance on cognition in humans. Our findings from studies of animal models suggest that dietary energy restriction can enhance neural plasticity and reduce the vulnerability of the brain to age-related dysfunction and disease. Dietary energy restriction may exert beneficial effects on the brain by engaging adaptive cellular stress response pathways resulting in the up-regulation of genes that encode proteins that promote neural plasticity and cell survival (e.g., neurotrophic factors, protein chaperones and redox enzymes). Two energy state-sensitive factors that are proving particularly important in regulating energy balance and improving/preserving cognitive function are brain-derived neurotrophic factor and glucagon-like peptide 1. Alternate day calorie restriction, novel insulin-sensitizing and neuroprotective agents, and drugs that activate adaptive stress response pathways, are examples of approaches for preserving cognitive function that show promise in preclinical studies.