Adipose reduction in the activity of the repressor ICER is responsible for insulin resistance elicited by the transcriptional factors CREB in obesity

BACKGROUND AND AIMS: Sustained adipose activation of the transcriptional activators cAMP response binding proteins (CREB) in obesity leads to impaired expression of the glucose transporter GLUT4 and adiponectin (adipoq) in mice model of obesity. Diminution of GLUT4 and adipoq caused by CREB is indirect and relies on the increased repressive activity of the CREB target gene activating transcription factor 3 (ATF3). Specific inactivation of CREB in adipocytes decreases ATF3 production and improves whole-body insulin sensitivity of mice in the context of diet-induced obesity. Thus, elevation of CREB activity is a key mechanism responsible for adipocyte dysfunction and systemic insulin resistance. The inducible cAMP early repressor (ICER) is a negative regulator of the CREB activity. In fact, ICER antagonizes the CREB factor by competing for the regulation of similar target genes. The goal of the study was to investigate whether loss of ICER expression in adipocytes could be responsible for increased CREB activity in obesity. MATERIALS AND METHODS: Mice C57bl6 were fed with a high fat diet (HFD) for 12 weeks to increase body weight and generate insulin resistance. Biopsies of visceral adipose tissues (VAT) were prepared from human lean (BMI=24}0.5 Kg/m2) or obese subjects (BMI>35 Kg/m2). Total RNA and protein were prepared from white adipose tissues (WAT) of chow- or HFD-fed mice and VAT of lean and obese subjects. Activities of CREBs and ICER were monitored by electromobility shift assays (EMSA). The role of ICER on CREB activity was confirmed in 3T3-L1 adipocytes cells. Briefly after differentiation, the cells were electroporated with the plasmid coding for ICER cDNA. Gene expression was quantified by quantitative real-time PCR and western Blotting experiments. RESULTS: The expression of ICER is reduced in WAT of HFD-induced obese mice when compared to chow mice as measured by real-time PCR and EMSA. Similar result was found in human tissues. Reduction in ICER expression was associated with increased ATF3 expression and decreased adipoq and GLUT4 contents. Diminution in ICER levels was observed in adipocytes fraction whereas its expression was unchanged in stroma vascular fraction of WAT. Overexpression of ICER in 3T3-L1 adipocytes silenced the expression of ATF3, confirming the regulation of the factor by ICER. The expression of ICER is regulated by histone deacetylases activity (HDAC). Inhibition of HDACs in 3T3-L1 adipocytes cells using trichostatin inhibited the production of ICER. The whole activity of HDAC was reduced in WAT and VAT of obese mice and human obese subjects. CONCLUSION: Impaired adipose expression of ICER is responsible of increased CREB activity in adipocytes in obesity. This mechanism relies on reduction of the HDAC activity.

Arginase II Promotes Macrophage Inflammatory Responses Through Mitochondrial Reactive Oxygen Species, Contributing to Insulin Resistance and Atherogenesis.

BACKGROUND: Macrophage-mediated chronic inflammation is mechanistically linked to insulin resistance and atherosclerosis. Although arginase I is considered antiinflammatory, the role of arginase II (Arg-II) in macrophage function remains elusive. This study characterizes the role of Arg-II in macrophage inflammatory responses and its impact on obesity-linked type II diabetes mellitus and atherosclerosis. METHODS AND RESULTS: In human monocytes, silencing Arg-II decreases the monocytes' adhesion to endothelial cells and their production of proinflammatory mediators stimulated by oxidized low-density lipoprotein or lipopolysaccharides, as evaluated by real-time quantitative reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. Macrophages differentiated from bone marrow cells of Arg-II-deficient (Arg-II(-/-)) mice express lower levels of lipopolysaccharide-induced proinflammatory mediators than do macrophages of wild-type mice. Importantly, reintroducing Arg-II cDNA into Arg-II(-/-) macrophages restores the inflammatory responses, with concomitant enhancement of mitochondrial reactive oxygen species. Scavenging of reactive oxygen species by N-acetylcysteine prevents the Arg-II-mediated inflammatory responses. Moreover, high-fat diet-induced infiltration of macrophages in various organs and expression of proinflammatory cytokines in adipose tissue are blunted in Arg-II(-/-) mice. Accordingly, Arg-II(-/-) mice reveal lower fasting blood glucose and improved glucose tolerance and insulin sensitivity. Furthermore, apolipoprotein E (ApoE)-deficient mice with Arg-II deficiency (ApoE(-/-)Arg-II(-/-)) display reduced lesion size with characteristics of stable plaques, such as decreased macrophage inflammation and necrotic core. In vivo adoptive transfer experiments reveal that fewer donor ApoE(-/-)Arg-II(-/-) than ApoE(-/-)Arg-II(+/+) monocytes infiltrate into the plaque of ApoE(-/-)Arg-II(+/+) mice. Conversely, recipient ApoE(-/-)Arg-II(-/-) mice accumulate fewer donor monocytes than do recipient ApoE(-/-)Arg-II(+/+) animals. CONCLUSIONS: Arg-II promotes macrophage proinflammatory responses through mitochondrial reactive oxygen species, contributing to insulin resistance and atherogenesis. Targeting Arg-II represents a potential therapeutic strategy in type II diabetes mellitus and atherosclerosis. (J Am Heart Assoc. 2012;1:e000992 doi: 10.1161/JAHA.112.000992.).

PPARβ/δ attenuates palmitate-induced endoplasmic reticulum stress and induces autophagic markers in human cardiac cells.

BACKGROUND: Chronic endoplasmic reticulum (ER) stress contributes to the apoptotic cell death in the myocardium, thereby playing a critical role in the development of cardiomyopathy. ER stress has been reported to be induced after high-fat diet feeding in mice and also after saturated fatty acid treatment in vitro. Therefore, since several studies have shown that peroxisome proliferator-activated receptor (PPAR)β/δ inhibits ER stress, the main goal of this study consisted in investigating whether activation of this nuclear receptor was able to prevent lipid-induced ER stress in cardiac cells. METHODS AND RESULTS: Wild-type and transgenic mice with reduced PPARβ/δ expression were fed a standard diet or a high-fat diet for two months. For in vitro studies, a cardiomyocyte cell line of human origin, AC16, was treated with palmitate and the PPARβ/δ agonist GW501516. Our results demonstrate that palmitate induced ER stress in AC16 cells, a fact which was prevented after PPARβ/δ activation with GW501516. Interestingly, the effect of GW501516 on ER stress occurred in an AMPK-independent manner. The most striking result of this study is that GW501516 treatment also upregulated the protein levels of beclin 1 and LC3II, two well-known markers of autophagy. In accordance with this, feeding on a high-fat diet or suppression of PPARβ/δ in knockout mice induced ER stress in the heart. Moreover, PPARβ/δ knockout mice also displayed a reduction in autophagic markers. CONCLUSION: Our data indicate that PPARβ/δ activation might be useful to prevent the harmful effects of ER stress induced by saturated fatty acids in the heart by inducing autophagy.

Nutritional influences on lipogenesis and thermogenesis after a carbohydrate meal.

In vivo lipogenesis and thermogenesis were studied for 24 h after ingestion of 500 g of carbohydrate (CHO) in subjects who had consumed either a high-fat, a mixed, or a high-CHO diet during the 3-6 days preceding the test. CHO oxidation and conversion to fat was significantly less in the high-fat diet group (222 +/- 5 g) than in the mixed (300 +/- 13 g) or high-CHO diet (331 +/- 7 g) groups, resulting in a greater glycogen storage in the high-fat (278 +/- 6 g) than in the other two groups (197 +/- 11 and 170 +/- 2 g). Net lipogenesis occurred sooner and lasted longer in the high-CHO group, amounting to 0.8 +/- 0.5, 3.4 +/- 0.6, and 9 +/- 1 g of lipid synthesized in the high-fat, mixed, and high-CHO groups, respectively. The thermic effect of the CHO load was 5.2 +/- 0.5% on the high-fat, 6.5 +/- 0.4% on the mixed diet, and 8.6 +/- 0.4% on the high-CHO diet. Significant relationships were demonstrated between the postabsorptive nonprotein respiratory quotient and net lipogenesis after the CHO load (r = 0.82) and between net lipogenesis and the increase in energy expenditure (r = 0.71). It is concluded that the antecedent diet influences the amount of net lipogenesis and the magnitude of thermogenesis after a large CHO test meal. However, lipogenesis remains too limited even after such large CHO intakes to cause an increase in the body's fat content.

Urate-induced acute renal failure and chronic inflammation in liver-specific Glut9 knockout mice.

Plasma urate levels are higher in humans than rodents (240-360 vs. â^¼30 μM) because humans lack the liver enzyme uricase. High uricemia in humans may protect against oxidative stress, but hyperuricemia also associates with the metabolic syndrome, and urate and uric acid can crystallize to cause gout and renal dysfunctions. Thus, hyperuricemic animal models to study urate-induced pathologies are needed. We recently generated mice with liver-specific ablation of Glut9, a urate transporter providing access of urate to uricase (LG9KO mice). LG9KO mice had moderately high uricemia (â^¼120 μM). To further increase their uricemia, here we gavaged LG9KO mice for 3 days with inosine, a urate precursor; this treatment was applied in both chow- and high-fat-fed mice. In chow-fed LG9KO mice, uricemia peaked at 300 μM 2 h after the first gavage and normalized 24 h after the last gavage. In contrast, in high-fat-fed LG9KO mice, uricemia further rose to 500 μM. Plasma creatinine strongly increased, indicating acute renal failure. Kidneys showed tubule dilation, macrophage infiltration, and urate and uric acid crystals, associated with a more acidic urine. Six weeks after inosine gavage, plasma urate and creatinine had normalized. However, renal inflammation, fibrosis, and organ remodeling had developed despite the disappearance of urate and uric acid crystals. Thus, hyperuricemia and high-fat diet feeding combined to induce acute renal failure. Furthermore, a sterile inflammation caused by the initial crystal-induced lesions developed despite the disappearance of urate and uric acid crystals.

Mice generated by in vitro fertilization exhibit vascular dysfunction and shortened life span.

Children conceived by assisted reproductive technologies (ART) display a level of vascular dysfunction similar to that seen in children of mothers with preeclamspia. The long-term consequences of ART-associated vascular disorders are unknown and difficult to investigate in healthy children. Here, we found that vasculature from mice generated by ART display endothelial dysfunction and increased stiffness, which translated into arterial hypertension in vivo. Progeny of male ART mice also exhibited vascular dysfunction, suggesting underlying epigenetic modifications. ART mice had altered methylation at the promoter of the gene encoding eNOS in the aorta, which correlated with decreased vascular eNOS expression and NO synthesis. Administration of a deacetylase inhibitor to ART mice normalized vascular gene methylation and function and resulted in progeny without vascular dysfunction. The induction of ART-associated vascular and epigenetic alterations appeared to be related to the embryo environment; these alterations were possibly facilitated by the hormonally stimulated ovulation accompanying ART. Finally, ART mice challenged with a high-fat diet had roughly a 25% shorter life span compared with control animals. This study highlights the potential of ART to induce vascular dysfunction and shorten life span and suggests that epigenetic alterations contribute to these problems.

The Lin28/let-7 axis regulates glucose metabolism.

The let-7 tumor suppressor microRNAs are known for their regulation of oncogenes, while the RNA-binding proteins Lin28a/b promote malignancy by inhibiting let-7 biogenesis. We have uncovered unexpected roles for the Lin28/let-7 pathway in regulating metabolism. When overexpressed in mice, both Lin28a and LIN28B promote an insulin-sensitized state that resists high-fat-diet induced diabetes. Conversely, muscle-specific loss of Lin28a or overexpression of let-7 results in insulin resistance and impaired glucose tolerance. These phenomena occur, in part, through the let-7-mediated repression of multiple components of the insulin-PI3K-mTOR pathway, including IGF1R, INSR, and IRS2. In addition, the mTOR inhibitor, rapamycin, abrogates Lin28a-mediated insulin sensitivity and enhanced glucose uptake. Moreover, let-7 targets are enriched for genes containing SNPs associated with type 2 diabetes and control of fasting glucose in human genome-wide association studies. These data establish the Lin28/let-7 pathway as a central regulator of mammalian glucose metabolism.

Autocrine Action of IGF2 Regulates Adult β-Cell Mass and Function.

Insulin-like growth factor 2 (IGF2), produced and secreted by adult β-cells, functions as an autocrine activator of the β-cell insulin-like growth factor 1 receptor signaling pathway. Whether this autocrine activity of IGF2 plays a physiological role in β-cell and whole-body physiology is not known. Here, we studied mice with β-cell-specific inactivation of Igf2 (βIGF2KO mice) and assessed β-cell mass and function in aging, pregnancy, and acute induction of insulin resistance. We showed that glucose-stimulated insulin secretion (GSIS) was markedly reduced in old female βIGF2KO mice; glucose tolerance was, however, normal because of increased insulin sensitivity. While on a high-fat diet, both male and female βIGF2KO mice displayed lower GSIS compared with control mice, but reduced β-cell mass was observed only in female βIGF2KO mice. During pregnancy, there was no increase in β-cell proliferation and mass in βIGF2KO mice. Finally, β-cell mass expansion in response to acute induction of insulin resistance was lower in βIGF2KO mice than in control mice. Thus, the autocrine action of IGF2 regulates adult β-cell mass and function to preserve in vivo GSIS in aging and to adapt β-cell mass in response to metabolic stress, pregnancy hormones, and acute induction of insulin resistance.

Characterization of a MAF1 knockout mouse model

L'ARN polymérase 3 transcrit un petit groupe de gènes fortement exprimés et impliqués dans plusieurs mécanismes moléculaires. Les ARNs de transfert ou ARNt représentent plus ou moins la moitié du transcriptome de l'ARN polymérase 3. Ils sont directement impliqués dans la traduction des protéines en agissant comme transporteurs d'acides aminés qui sont incorporés à la chaîne naissante de polypeptides. Chez des levures cultivées dans un milieu jusqu'à épuisement des nutriments, Maf1 réprime la transcription par l'ARN polymérase 3, favorisant ainsi l'économie énergétique cellulaire. Dans un modèle de cellules de mammifères, MAF1 réprime aussi la transcription de l'ARN polymérase 3 dans des conditions de stress, cependant il n'existe aucune donnée quant à son rôle chez un mammifère vivant. Pendant mon doctorat, j'ai utilisé une souris délétée pour le gène Maf1 afin de connaître les effets de ce gène chez un mammifère. Etonnamment, la souris Maf1-­‐/-­‐ est résistante à l'obésité même si celle-­‐ci est nourrie avec une nourriture riche en matières grasses. Des études moléculaires et de métabolomiques ont montré qu'il existe des cycles futiles de production et dégradation des lipides et des ARNt, ce qui entraîne une augmentation de la dépense énergique et favorise la résistance à l'obésité. En plus de la caractérisation de la souris Maf1-­‐/-­‐, pendant ma thèse j'ai également développé une méthode afin de normaliser les données de ChIP-­‐sequencing. Cette méthode est fondée sur l'utilisation d'un contrôle interne, représenté ici par l'ajout d'une quantité fixe de chromatine provenant d'un organisme différent de celui étudié. La méthode a amélioré considérablement la reproductibilité des valeurs entre réplicas biologiques. Elle a aussi révélé des différences entre échantillons issus de conditions différentes. Une occupation supérieure de l'ARN polymérase 3 sur les gènes Pol 3 chez les souris Maf1 KO entraîne une augmentation du niveau de précurseurs d'ARNt, ayant pour effet probable la saturation de la machinerie de maturation des ARNt. En effet, chez les souris Maf1 KO, le pourcentage d'ARNt modifiés est plus faible que chez les souris type sauvage. Ce déséquilibre entre le niveau de précurseurs et d'ARNt matures entraîne une diminution de la traduction protéique. Ces résultats ont permis d'identifier de nouvelles fonctions pour la protéine MAF1, comme étant une protéine régulatrice à la fois de la transcription mais aussi de la traduction et en étant un cible potentielle au traitement à l'obésité. -- RNA polymerase III (Pol 3) transcribes a small set of highly expressed genes involved in different molecular mechanisms. tRNAs account for almost half of the Pol 3 transcriptome and are involved in translation, bringing a new amino into the nascent polypeptide chain. In yeast, under nutrient deprivation, Maf1 acts for cell energetic economy by repressing Pol 3 transcription. In mammalian cells, MAF1 also represses Pol 3 activity under conditions of serum deprivation or DNA damages but nothing is known about its role in a mammalian organism. During my thesis studies, I used a Maf1 KO mouse model to characterize the effects of Maf1 deletion in a living animal. Surprisingly, the MAF1 KO mouse developed an unexpected phenotype, being resistant to high fat diet-­‐induced obesity and displaying an extended lifespan. Molecular and metabolomics characterizations revealed futile cycles of lipids and tRNAs, which are produced and immediately degraded, which increases energy consumption in the Maf1 KO mouse and probably explains in part the protection to obesity. Additionally to the mouse characterization, I also developed a method to normalize ChIP-­‐seq data, based on the addition of a foreign chromatin to be used as an internal control. The method improved reproducibility between replicates and revealed differences of Pol 3 occupancy between WT and Maf1 KO samples that were not seen without normalization to the internal control. I then established that increased Pol 3 occupancy in the Maf1 KO mouse liver was associated with increased levels of tRNA precursor but not of mature tRNAs, the effective molecules involved in translation. The overproduction of precursor tRNAs associated with the deletion of Maf1 apparently overwhelms the tRNA processing machinery as the Maf1 KO mice have lower levels of fully modified tRNAs. This maturation defect directly impacts on translation efficiency as polysomic fractions and newly synthetized protein levels were reduced in the liver of the Maf1 KO mouse. Altogether, these results indicate new functions for MAF1, a regulator of both transcription and translation as well as a potential target for obesity treatment.

Evidence for hypothalamic ketone body sensing: impact on food intake and peripheral metabolic responses in mice.

Monocarboxylates have been implicated in the control of energy homeostasis. Among them, the putative role of ketone bodies produced notably during high-fat diet (HFD) has not been thoroughly explored. In this study, we aimed to determine the impact of a specific rise in cerebral ketone bodies on food intake and energy homeostasis regulation. A carotid infusion of ketone bodies was performed on mice to stimulate sensitive brain areas for 6 or 12 h. At each time point, food intake and different markers of energy homeostasis were analyzed to reveal the consequences of cerebral increase in ketone body level detection. First, an increase in food intake appeared over a 12-h period of brain ketone body perfusion. This stimulated food intake was associated with an increased expression of the hypothalamic neuropeptides NPY and AgRP as well as phosphorylated AMPK and is due to ketone bodies sensed by the brain, as blood ketone body levels did not change at that time. In parallel, gluconeogenesis and insulin sensitivity were transiently altered. Indeed, a dysregulation of glucose production and insulin secretion was observed after 6 h of ketone body perfusion, which reversed to normal at 12 h of perfusion. Altogether, these results suggest that an increase in brain ketone body concentration leads to hyperphagia and a transient perturbation of peripheral metabolic homeostasis.

Sorcin links pancreatic β cell lipotoxicity to ER Ca2+ stores.

NlmCategory="UNASSIGNED">Preserving β cell function during the development of obesity and insulin resistance would limit the worldwide epidemic of type 2 diabetes (T2DM). Endoplasmic reticulum (ER) calcium (Ca(2+)) depletion induced by saturated free fatty acids and cytokines causes β cell ER stress and apoptosis, but the molecular mechanisms behind these phenomena are still poorly understood. Here, we demonstrate that palmitate-induced sorcin (SRI) down-regulation, and subsequent increases in glucose-6-phosphatase catalytic subunit-2 (G6PC2) levels contribute to lipotoxicity. SRI is a calcium sensor protein involved in maintaining ER Ca(2+) by inhibiting ryanodine receptor activity and playing a role in terminating Ca(2+)-induced Ca(2+) release. G6PC2, a GWAS gene associated with fasting blood glucose, is a negative regulator of glucose-stimulated insulin secretion (GSIS). High fat feeding in mice and chronic exposure of human islets to palmitate decreases endogenous SRI expression while levels of G6PC2 mRNA increase. Sorcin null mice are glucose intolerant, with markedly impaired GSIS and increased expression of G6pc2. Under high fat diet, mice overexpressing SRI in the β cell display improved glucose tolerance, fasting blood glucose and GSIS, whereas G6PC2 levels are decreased and cytosolic and ER Ca(2+) are increased in transgenic islets. SRI may thus provide a target for intervention in T2DM.

Increased male offspring's risk of metabolic-neuroendocrine dysfunction and overweight after fructose-rich diet intake by the lactating mother.

An adverse endogenous environment during early life predisposes the organism to develop metabolic disorders. We evaluated the impact of intake of an iso-caloric fructose rich diet (FRD) by lactating mothers (LM) on several metabolic functions of their male offspring. On postnatal d 1, ad libitum eating, lactating Sprague-Dawley rats received either 10% F (wt/vol; FRD-LM) or tap water (controls, CTR-LM) to drink throughout lactation. Weaned male offspring were fed ad libitum a normal diet, and body weight (BW) and food intake were registered until experimentation (60 d of age). Basal circulating levels of metabolic markers were evaluated. Both iv glucose tolerance and hypothalamic leptin sensitivity tests were performed. The hypothalamus was dissected for isolation of total RNA and Western blot analysis. Retroperitoneal (RP) adipose tissue was dissected and either kept frozen for gene analysis or digested to isolate adipocytes or for histological studies. FRD rats showed increased BW and decreased hypothalamic sensitivity to exogenous leptin, enhanced food intake (between 49-60 d), and decreased hypothalamic expression of several anorexigenic signals. FRD rats developed increased insulin and leptin peripheral levels and decreased adiponectinemia; although FRD rats normally tolerated glucose excess, it was associated with enhanced insulin secretion. FRD RP adipocytes were enlarged and spontaneously released high leptin, although they were less sensitive to insulin-induced leptin release. Accordingly, RP fat leptin gene expression was high in FRD rats. Excessive fructose consumption by lactating mothers resulted in deep neuroendocrine-metabolic disorders of their male offspring, probably enhancing the susceptibility to develop overweight/obesity during adult life.

Morphologic and electroretinographic phenotype of SR-BI knockout mice after a long-term atherogenic diet.

PURPOSE: To evaluate functional and ultrastructural changes in the retina of scavenger receptor B1 (SR-BI) knockout (KO) mice consuming a high fat cholate (HFC) diet. METHODS: Three-month-old male KO and wild-type (WT) mice were fed an HFC diet for 30 weeks. After diet supplementation, plasma cholesterol levels and electroretinograms were analyzed. Neutral lipids were detected with oil red O, and immunohistochemistry was performed on cryostat ocular tissue sections. The retina, Bruch's membrane (BM), retinal pigment epithelium (RPE), and choriocapillaris (CC) were analyzed by transmission electron microscopy. RESULTS: Using the WT for reference, ultrastructural changes were recorded in HFC-fed SR-BI KO mice, including lipid inclusions, a patchy disorganization of the photoreceptor outer segment (POS) and the outer nuclear layer (ONL), and BM thickening with sparse sub-RPE deposits. Within the CC, there was abnormal disorganization of collagen fibers localized in ectopic sites with sparse and large vacuolization associated with infiltration of macrophages in the subretinal space, reflecting local inflammation. These lesions were associated with electroretinographic abnormalities, particularly increasing implicit time in a- and b-wave scotopic responses. Abnormal vascular endothelial growth factor (VEGF) staining was detected in the outer nuclear layer. CONCLUSIONS: HFC-fed SR-BI KO mice thus presented sub-RPE lipid-rich deposits and functional and morphologic alterations similar to some features observed in dry AMD. The findings lend further support to the hypothesis that atherosclerosis causes retinal and subretinal damage that increases susceptibility to some forms of AMD.

Meal-induced thermogenesis and obesity: is a fat meal a risk factor for fat gain in children?

Diet composition, in particular fat intake, has been suggested to be a risk factor for obesity in humans. Several mechanisms may contribute to explain the impact of fat intake on fat gain. One factor may be the low thermogenesis induced by a mixed meal rich in fat. In a group of 11 girls (10.1 +/- 0.3 yr), 6 obese (body mass index, 25.6 +/- 0.6 kg/m(2)), and 5 nonobese (body mass index, 19 +/- 1.6 kg/m(2)), we tested the hypothesis that a mixed meal rich in fat can elicit energy saving compared with an isocaloric and isoproteic meal rich in carbohydrate. The postabsorptive resting energy expenditure and the thermic effect of a meal (TEM) after a low fat (LF; 20% fat, 68% carbohydrate, and 12% protein) or an isocaloric (2500 kJ or 600 Cal) and isoproteic high fat (HF; 48% fat, 40% carbohydrate, and 12% protein) meal were measured by indirect calorimetry. Each girl repeated the test with a different, randomly assigned menu (HF or LF) 1 week after the first test. TEM, expressed as a percentage of energy intake was significantly higher after a LF meal than after a HF meal (6.5 +/- 0.7% vs. 4.3 +/- 0.4%; P < 0.01). The postprandial respiratory quotient (RQ) was significantly higher after a LF meal than after a HF meal (0.86 +/- 0.013 vs. 0.83 +/- 0.014; P < 0.001). The HF low carbohydrate meal induced a significantly lower increase in carbohydrate oxidation than the LF meal (20.3 +/- 6.2 vs. 61.3 +/- 7.8 mg/min; P < 0.001). On the contrary, fat oxidation was significantly higher after a HF meal than after a LF meal (-1.3 +/- 2.4 vs. -15.1 +/- 3.6 mg/min; P < 0.01). However, the postprandial fat storage was 8-fold higher after a HF meal than after a LF meal (17.2 +/- 1.7 vs. 1.9 +/- 1.8 g; P < 0.001). These results suggest that a high fat meal is able to induce lower thermogenesis and a higher positive fat balance than an isocaloric and isoproteic low fat meal. Therefore, diet composition per se must be taken into account among the various risk factors that induce obesity in children.

PI3Kγ within a nonhematopoietic cell type negatively regulates diet-induced thermogenesis and promotes obesity and insulin resistance.

Obesity is associated with a chronic low-grade inflammation, and specific antiinflammatory interventions may be beneficial for the treatment of type 2 diabetes and other obesity-related diseases. The lipid kinase PI3Kγ is a central proinflammatory signal transducer that plays a major role in leukocyte chemotaxis, mast cell degranulation, and endothelial cell activation. It was also reported that PI3Kγ activity within hematopoietic cells plays an important role in obesity-induced inflammation and insulin resistance. Here, we show that protection from insulin resistance, metabolic inflammation, and fatty liver in mice lacking functional PI3Kγ is largely consequent to their leaner phenotype. We also show that this phenotype is largely based on decreased fat gain, despite normal caloric intake, consequent to increased energy expenditure. Furthermore, our data show that PI3Kγ action on diet-induced obesity depends on PI3Kγ activity within a nonhematopoietic compartment, where it promotes energetic efficiency for fat mass gain. We also show that metabolic modulation by PI3Kγ depends on its lipid kinase activity and might involve kinase-independent signaling. Thus, PI3Kγ is an unexpected but promising drug target for the treatment of obesity and its complications.