A Dietary Fat Excess Alters Metabolic and Neuroendocrine Responses Before the Onset of Metabolic Diseases

Early changes in neuroendocrine pathways are essential in the development of metabolic pathologies. Thus, it is important to have a better understanding of the signals involved in their initiation. Long-term consumption of high-fat diets induces insulin resistance, obesity, diabetes. Here, we have investigated early neural and endocrine events in the hypothalamus and hippocampus induced by a short-term high fat, low carbohydrate diet in adult male Wistar rats. The release of serotonin, which is closely associated with the actions of insulin and leptin, was measured, by electrochemical detection following reverse-phase liquid chromatography (HPLC), in the extracellular space of the medial hypothalamus and the dorsal hippocampus in samples obtained from non-anesthetized animals, by microdialysis. The high-fat diet had a specific effect on the hypothalamus. Serotonin release induced by food intake was reduced after 1 week, and effectively ceased after 6 weeks of the diet. After 1 week, there was an increased gene expression of the insulin receptor and the insulin receptor substrates IRS1 and IRS2, as measured by real-time PCR. After 6 weeks of diet, insulin gene expression increased. Leptinemia increased in all cases. This new data support the concept that high-fat diets, in addition to have peripheral effects, cause a rapid alteration in specific central mechanisms involved in energy and glucose homeostasis. The changes in the gene expression of insulin and signaling elements represent possible adaptations aimed at counterbalancing the reduced responsiveness of the serotonergic system to nutritional signals and maintaining homeostasis. Sophie M. Banas and Claude Rouch have contributed equally to this work.     

Role of adipogenic and thermogenic genes in susceptibility or resistance to develop diet-induced obesity in rats

The aim of the present work was to assess whether changes in adipose tissue gene expression related with adipogenesis and/or thermogenesis could be involved in the mechanism conferring susceptibility or resistance to develop obesity in high-fat fed outbreed rats. For this purpose, male Wistar rats were fed with standard laboratory diet (control group) or high fat diet. After 15 days, two groups of rats with significant differences on body weight gain in response to the high fat diet were characterized and identified as diet-induced obesity (DIO) and diet resistant (DR) rats. A significant increase in visceral white adipose tissue (WAT) PPARgamma and aP2 (p < 0.05) mRNA levels associated to a decrease in RARgamma expression (p < 0.05) was observed in DIO rats, suggesting an increase of adipogenesis. Furthermore, our data showed a marked increase in brown adipose tissue (BAT) of UCP1 mRNA in DIO animals (p < 0.01) (without affecting PGC-1alpha gene expression), whereas no changes were found in WAT UCP2 gene expression. All these data suggest that the variations found in the expression pattern of PPARgamma, aP2 and RARgamma by high-fat diet could be involved, at least in part, in the differences in body weight gain and adiposity observed between DR and DIO animals. The compensatory adaptations through the increase in energy expenditure by changes on the expression levels of UCP1 seem not to be enough to avoid the obesity onset in the DIO group.     

Modulation of lipid homeostasis in response to continuous or intermittent high-fat diet in pigs

A high-fat diet is known to induce atherosclerosis in animal models. Dietary factors and timing of atherogenic food delivery may affect plasma lipoprotein content composition and its potential atherogenic effect. Increasingly often, humans spend periods/days eating in a completely unregulated way, ingesting excessive amounts of food rich in oils and fats, alternating with periods/days when food intake is more or less correct. We investigate the effect on lipid homeostasis of a high-fat diet administered either continuously or intermittently. We investigated control pigs receiving standard diet (C, n=7), pigs receiving a high-fat diet every day for 10 weeks (CHF, n=5), and pigs receiving a high-fat diet every other week for 10 weeks (IHF, n=7). IHF animals were shown to have a different lipid profile compared with CHF animals, with a significant increase in high-density lipoproteins (HDL) levels with respect to C and CHF groups. CHF also showed significantly higher values of TC/HDL cholesterol compared with C and IHF. Hepatic expression analysis of genes involved in lipid homeostasis showed an increasing trend of nuclear receptor LXRα along with its target genes in the CHF group and in the IHF group, whereas SREBP2 and LDLr were significantly inhibited. A significant correlation was found between ABCA1 expression and circulating levels of HDL-C. Periodic withdrawals of a high-fat atherogenic diet compared with a regular administration results in a different adaptive response of lipoprotein metabolism, which leads to a significantly higher plasma level of HDL-C and lower TC/HDL-C.     

Inactivation of the dual Bmp/Wnt inhibitor Sostdc1 enhances pancreatic islet function

Current endeavors in the type 2 diabetes (T2D) field include gaining a better understanding of extracellular signaling pathways that regulate pancreatic islet function. Recent data suggest that both Bmp and Wnt pathways are operative in pancreatic islets and play a positive role in insulin secretion and glucose homeostasis. Our laboratory found the dual Bmp and Wnt antagonist Sostdc1 to be upregulated in a mouse model of islet dysmorphogenesis and nonimmune-mediated lean diabetes. Because Bmp signaling has been proposed to enhance β-cell function, we evaluated the role of Sostdc1 in adult islet function using animals in which Sostdc1 was globally deleted. While Sostdc1-null animals exhibited no pancreas development phenotype, a subset of mutants exhibited enhanced insulin secretion and improved glucose homeostasis compared with control animals after 12-wk exposure to high-fat diet. Loss of Sostdc1 in the setting of metabolic stress results in altered expression of Bmp-responsive genes in islets but did not affect expression of Wnt target genes, suggesting that Sostdc1 primarily regulates the Bmp pathway in the murine pancreas. Furthermore, our data indicate that removal of Sostdc1 enhances the downregulation of the closely related Bmp inhibitors Ctgf and Gremlin in islets after 8-wk exposure to high-fat diet. These data imply that Sostdc1 regulates expression of these inhibitors and provide a means by which Sostdc1-null animals show enhanced insulin secretion and glucose homeostasis. Our studies provide insights into Bmp pathway regulation in the endocrine pancreas and reveal new avenues for improving β-cell function under metabolic stress.     

Adropin deficiency is associated with increased adiposity and insulin resistance

Adropin is a secreted peptide that improves hepatic steatosis and glucose homeostasis when administered to diet-induced obese mice. It is not clear if adropin is a peptide hormone regulated by signals of metabolic state. Moreover, the significance of a decline in adropin expression with obesity with respect to metabolic disease is also not clear. We investigated the regulation of serum adropin by metabolic status and diet. Serum adropin levels were high in chow-fed conditions and were suppressed by fasting and diet-induced obesity (DIO). High adropin levels were observed in mice fed a high-fat low carbohydrate diet, whereas lower levels were observed in mice fed a low-fat high carbohydrate diet. To investigate the role of adropin deficiency in metabolic homeostasis, we generated adropin knockout mice (AdrKO) on the C57BL/6J background. AdrKO displayed a 50%-increase in increase in adiposity, although food intake and energy expenditure were normal. AdrKO also exhibited dyslipidemia and impaired suppression of endogenous glucose production (EndoR(a)) in hyperinsulinemic-euglycemic clamp conditions, suggesting insulin resistance. While homo- and heterozygous carriers of the null adropin allele exhibited normal DIO relative to controls, impaired glucose tolerance associated with weight gain was more severe in both groups. In summary, adropin is a peptide hormone regulated by fasting and feeding. In fed conditions, adropin levels are regulated dietary macronutrients, and increase with dietary fat content. Adropin is not required for regulating food intake, however, its functions impact on adiposity and are involved in preventing insulin resistance, dyslipidemia, and impaired glucose tolerance.     

Gut microflora is a key player in host energy homeostasis

Gut microflora is now considered as a key organ involved in host energy homeostasis. Recent data suggest that the alterations of the gut bacteria ecosystem could contribute to the development of metabolic disorders such as type 2 diabetes and obesity. First, gut microflora may increase energy efficiency of non digested food via the fermentation, thus providing more energy to the host. Secondly, fatty acids flux and storage in the adipose tissue is under the control of the fasting-induced adipocyte factor FIAF, which expression depends on gut microflora. Third, high-fat diet feeding changes gut bacteria profile, leading to a drop in bifidobacteria content, which correlates with a higher LPS plasma levels, thereby participating to the onset of inflammation, insulin resistance and type 2 diabetes associated with obesity. Changing gut microflora composition could be a useful tool to prevent or to treat high-fat/low fibres diet-induced metabolic syndrome. double dagger.     

The hypothalamic POMC mRNA expression is upregulated in prenatally undernourished male rat offspring under high-fat diet

Epidemiological studies demonstrated that adverse environmental factors leading to intrauterine growth retardation (IUGR) and low birth weight may predispose individuals to increased risk of metabolic syndrome. In rats, we previously demonstrated that adult male IUGR offspring from prenatal 70% food-restricted dams throughout gestation (FR30) were predisposed to energy balance dysfunctions such as impaired glucose intolerance, hyperleptinemia, hyperphagia and adiposity. We investigated whether postweaning moderate high-fat (HF) diet would amplify the phenotype focusing on the hypothalamus gene expression profile. Prenatally undernourished rat offspring were HF-fed from weaning until adulthood while body weight and food intake were measured. Tissue weights, glucose tolerance and plasma endocrine parameters levels were determined in 4-month-old rats. Hypothalamic gene expression profiling of adult FR30 rat was performed using Illumina microarray analysis and the RatRef-12 Expression BeadChip that contains 21,792 rat genes. Under HF diet, contrary to C animals, FR30 rats displayed increased body weight. However, most of the endocrine disorders observed in chow diet-fed adult FR30 were alleviated. We also observed very few gene expression changes in hypothalamus of FR30 rat. Amongst factors involved in hypothalamic energy homeostasis programming system, only the POMC and transthyretin mRNA expression levels were preferentially increased under HF diet. Both elevated gene expression levels may be seen as adaptive mechanisms counteracting against deleterious effects of HF feeding in FR30 animals. This study shows that the POMC gene expression is a key target of long-term developmental programming in prenatally undernourished male rat offspring, specifically within an obesogenic environment.     

GRK5 deficiency decreases diet-induced obesity and adipogenesis

Identification of the protein factors that regulate the adipogenesis and lipid metabolism of adipose tissue is critical for the understanding of the physiology and pathology of obesity and energy homeostasis. In this study, we found that G protein coupled receptor (GPCR) kinase 5 (GRK5) was expressed at a relatively high level in the white adipose tissue. When fed on a high-fat diet, GRK5(-/-) mice gained significantly less weight and had decreased WAT mass than their wild type littermates, which could not be attributed to alterations in food consumption or energy expenditure. However, GRK5(-/-) mice showed a 30-70% decreased expression of lipid metabolism and adipogenic genes in WAT. Moreover, GRK5(-/-) embryonic fibroblasts and preadipocytes exhibited 40-70% decreased expression of adipogenic genes and impaired adipocyte differentiation when induced in vitro. Taken together, these results suggest that GRK5 is an important regulator of adipogenesis and is crucial for the development of diet-induced obesity.     

Decreased resistin expression in mice with different sensitivities to a high-fat diet.

The regulation of resistin, a new adipose-derived circulating factor, is the subject of controversy. In particular, the question of its modulation in obesity led to opposite results reported by two different groups. In the current study, we assayed adipocyte resistin mRNA using fluorescent real-time RT-PCR. We studied the expression of resistin in mice which are differently sensitive to diet-induced obesity: the FVB/n strain, which poorly responds to high-fat diet and transgenic mice that express human alpha 2A-AR in adipose tissue in the absence of beta 3-adrenergic receptor (AR) under the FVB genetic background which are highly sensitive to high-fat diet and develop hyperplastic obesity. We observed that FVB mice, which have no significant increased body weight after an 8-week high-fat diet period, exhibited no alteration of resistin expression. In contrast, the transgenic mice developing high-fat diet-induced obesity exhibited markedly downregulated adipocyte resistin mRNA. We also showed that obesity induced by gold thioglucose injection in FVB/n mice reduces the expression of resistin in isolated adipocytes. This argues for decreased expression of resistin as a hallmark of obesity. Moreover, our data show that feeding a high-fat diet is not a primary determinant of resistin regulation.     

The Orphan G Protein-Coupled Receptor Gene GPR178 Is Evolutionary Conserved and Altered in Response to Acute Changes in Food Intake

G protein-coupled receptors (GPCRs) are a class of integral membrane proteins mediating physiological functions fundamental for survival, including energy homeostasis. A few years ago, an amino acid sequence of a novel GPCR gene was identified and named GPR178. In this study, we provide new insights regarding the biological significance of Gpr178 protein, investigating its evolutionary history and tissue distribution as well as examining the relationship between its expression level and feeding status. Our phylogenetic analysis indicated that GPR178 is highly conserved among all animal species investigated, and that GPR178 is not a member of a protein family. Real-time PCR and in situ hybridization revealed wide expression of Gpr178 mRNA in both the brain and periphery, with high expression density in the hypothalamus and brainstem, areas involved in the regulation of food intake. Hence, changes in receptor expression were assessed following several feeding paradigms including starvation and overfeeding. Short-term starvation (12–48h) or food restriction resulted in upregulation of Gpr178 mRNA expression in the brainstem, hypothalamus and prefrontal cortex. Conversely, short-term (48h) exposure to sucrose or Intralipid solutions downregulated Gpr178 mRNA in the brainstem; long-term exposure (10 days) to a palatable high-fat and high-sugar diet resulted in a downregulation of Gpr178 in the amygdala but not in the hypothalamus. Our results indicate that hypothalamic Gpr178 gene expression is altered during acute exposure to starvation or acute exposure to palatable food. Changes in gene expression following palatable diet consumption suggest a possible involvement of Gpr178 in the complex mechanisms of feeding reward.     

Lipoic acid administration prevents nonalcoholic steatosis linked to long-term high-fat feeding by modulating mitochondrial function

Nonalcoholic steatosis is an important hepatic complication of obesity linked to mitochondrial dysfunction and insulin resistance. Furthermore, lipoic acid has been reported to have beneficial effects on mitochondrial function. In this study, we analyzed the potential protective effect of lipoic acid supplementation against the development of nonalcoholic steatosis associated with a long-term high-fat diet feeding and the potential mechanism of this effect. Wistar rats were fed on a standard diet (n=10), a high-fat diet (n=10) and a high-fat diet supplemented with lipoic acid (n=10). A group pair-fed to the latter group (n=6) was also included. Lipoic acid prevented hepatic triglyceride accumulation and liver damage in rats fed a high-fat diet (?68%±11.3% vs. obese group) through the modulation of genes involved in lipogenesis and mitochondrial β-oxidation and by improving insulin sensitivity. Moreover, this molecule showed an inhibitory action on electron transport chain complexes activities (P<.01–P<.001) and adenosine triphosphate synthesis (P<.05), and reduced significantly energy efficiency. By contrast, lipoic acid induced an increase in mitochondrial copy number and in Ucp2 gene expression (P<.001 vs. obese). In summary, this investigation demonstrated the ability of lipoic acid to prevent nonalcoholic steatosis induced by a high-fat intake. Finally, the novelty and importance of this study are the finding of how lipoic acid modulates some of the mitochondrial processes involved in energy homeostasis. The reduction in mitochondrial energy efficiency could also explain, at least in part, the beneficial effects of lipoic acid not only in fatty liver but also in preventing excessive body weight gain.     

Upregulation of bone morphogenetic protein GDF-3/Vgr-2 expression in adipose tissue of FABP4/aP2 null mice

High-fat-fed C57Bl/6J FABP4/aP2 null mice develop obesity but not the related hyperglycemia or hyperinsulinemia characteristic of type II diabetes. FABP4/aP2 protein's function to bind fatty acids in the adipocytes may promote total body energy homeostasis by linking energy depots to the ability to express signaling molecules similar to leptin. To test this hypothesis, proteomic analysis of serum proteins from high-fat-fed wild-type and FABP4/aP2 null mice revealed that the GDF-3/Vgr-2 protein, a bone morphogenetic protein, was upregulated in C57Bl/6J FABP4/aP2 null mice. The increase in serum GDF-3/Vgr-2 protein was correlated with a 27-fold increase in adipose GDF-3/Vgr-2 mRNA. In contrast, leptin expression was unaltered between FABP4/aP2 null and wild-type animals. The expression of GDF-3/Vgr-2 mRNA was not substantially different in adipose tissue of db/db and tb/tb mice compared to wild-type controls. The expression of GDF-3/Vgr-2 mRNA was dependent upon the age and diet of the animals, declining as a function of age in high-fat-fed wild-type animals while increasing in the FABP4/aP2 null strain. These results identify GDF-3/Vgr-2 as an age- and fat-regulated, adipose-derived cytokine suggesting a linkage between adipocyte fatty acid metabolism and the expression of the bone morphogenetic family of differentiation regulators.     

Maternal prenatal undernutrition programs adipose tissue gene expression in adult male rat offspring under high-fat diet

Several studies have shown that maternal undernutrition leading to low birth weight predisposes offspring to the development of metabolic pathologies such as obesity. Using a model of prenatal maternal 70% food restriction diet (FR30) in rat, we evaluated whether postweaning high-fat (HF) diet would amplify the phenotype observed under standard diet. We investigated biological parameters as well as gene expression profile focusing on white adipose tissues (WAT) of adult offspring. FR30 procedure does not worsen the metabolic syndrome features induced by HF diet. However, FR30HF rats displayed catch-up growth to match the body weight of adult control HF animals, suggesting an increase of adiposity while showing hyperleptinemia and a blunted increase of corticosterone. Using quantitative RT-PCR array, we demonstrated that FR30HF rats exhibited leptin and Ob-Rb as well as many peptide precursor and receptor gene expression variations in WAT. We also showed that the expression of genes involved in adipogenesis was modified in FR30HF animals in a depot-specific manner. We observed an opposite variation of STAT3 phosphorylation levels, suggesting that leptin sensitivity is modified in WAT adult FR30 offspring. We demonstrated that 11β-HSD1, 11β-HSD2, GR, and MR genes are coexpressed in WAT and that FR30 procedure modifies gene expression levels, especially under HF diet. In particular, level variation of 11β-HSD2, whose protein expression was detected by Western blotting, may represent a novel mechanism that may affect WAT glucocorticoid sensitivity. Data suggest that maternal undernutrition differently programs the adult offspring WAT gene expression profile that may predispose for altered fat deposition.     

Regulatory effect of diosgenin on lipogenic genes expression in high-fat diet-induced obesity in mice

Obesity is one of the most serious health problems in the world, increasing the risk of other chronic diseases. Alterations in fatty acid synthesis related genes are crucially involved in obesity progression. Diosgenin (DG) was one of the phytosterols compounds with vital activity against lipid disorders. Therefore, this study was intended to evaluate the protective effect of DG on lipogenesis in the high-fat diet (HFD)-induced obesity in mice, via investigating the expression of two of the fatty acid synthesis–involved genes; sterol regulatory element-binding protein (SREBP-1c) and fatty acid synthase (FASN) genes. Thirty adult male mice were divided into 3 groups. Control group, fed with normal diet; HFD group, mice fed with a high-fat diet and HFD + DG group, mice fed with a high-fat diet and supplemented in parallel with DG for 6 consecutive weeks. The effect of DG on Body weights, liver enzymes, lipid profile, were evaluated. Histopathological fatty changes as well as SREBP-1c and FASN gene expression were also investigated. DG significantly alleviated body weight gain, adjusted liver enzymes, and improved lipid profile. Additionally, DG ameliorated the histopathological changes by reducing the lipid vacuoles and hence the hepatosteatosis. Accordingly, DG significantly downregulated the two-fold increase in the SREBP-1c and FASN gene expression observed in the HFD group. In conclusion, DG possesses a beneficial impact against diet-induced obesity in mice, which makes it a good candidate for NAFLD and obesity prevention.     

Effects of lipoic acid on apelin in 3T3-L1 adipocytes and in high-fat fed rats

Lipoic acid (LA) is an antioxidant with therapeutic properties on several diseases like diabetes and obesity. Apelin is a novel adipokine with potential beneficial actions on glucose metabolism and insulin resistance. The aim of this study was to examine in 3T3-L1 adipocytes the effects of LA on apelin gene expression and secretion, as well as elucidate the signaling pathways involved. We also tested the regulation of adipose apelin gene expression by LA supplementation in a model of high-fat diet-induced obesity. LA increased apelin secretion but not apelin gene expression in 3T3-L1 adipocytes. The AMPK inhibitor Compound C induced an increase in LA-stimulated apelin production, and, on the contrary, the AMPK activator AICAR completely reversed the LA stimulatory effects on apelin secretion, also inducing a significant reduction in apelin mRNA levels in this in vitro model. Apelin mRNA levels were increased in those animals fed with the high-fat diet, while the caloric restriction decreased apelin mRNA to control levels. However, apelin gene expression was not significantly modified in rats treated with LA compared with the obese group. The current data suggest the ability of LA to modulate apelin secretion by adipocytes. However the insulin-sensitizing effect of LA in vivo is not related to changes in apelin gene expression in our model of diet-induced obesity.     

Different functional responsibility of the small intestine to high-fat/high-energy diet determined the expression of obesity-prone and obesity-resistant phenotypes in rats

The objective of the present experiment was to assess the involvement of small intestine in expression of susceptibility or resistance to the high-fat/high-energy diet. The investigation was carried out in adult male Sprague-Dawley rats fed either standard laboratory diet (3.2 kcal/g, 9.5 % fat) or high-fat (HF) diet (4.04 kcal/g, 30 % fat) for 4 weeks as well as in HF rats that were retrospectively designated on the bases of their higher or lower weight gain as sensitive (DIO) or resistant (DR) to obesity. Our results revealed in HF group significant increase in energy intake, food efficiency, weight gain and Lee s index of obesity. Moreover, in comparison with controls, a significantly increased duodenal and jejunal alkaline phosphatase (AP) and alpha-glucosidase activity as well as hypertrophy of jejunal mucosa (increased protein/DNA ratio) were observed in HF fed rats. In contrast, intestinal function was inversely related to energy intake or to the development of adiposity in DIO vs. DR rats. The DR rats had significantly greater AP and alpha-glucosidase activity and more pronounced suppression of energy intake than obese DIO rats. It indicates that the increase of enzyme activities and the lowered effectiveness of nutrient absorption might be a significant factor preventing the expression of obesity proneness. This information contributes to a better understanding of a complex interaction between HF diet feeding and small intestinal adaptability, which determines the energy homeostasis and predict the ability to resist or develop obesity in these phenotypes.