Role of Hypothalamic Melanocortin System in Adaptation of Food Intake to Food Protein Increase in Mice

The hypothalamic melanocortin system—the melanocortin receptor of type 4 (MC4R) and its ligands: α-melanin-stimulating hormone (α-MSH, agonist, inducing hypophagia), and agouti-related protein (AgRP, antagonist, inducing hyperphagia)—is considered to play a central role in the control of food intake. We tested its implication in the mediation of the hunger-curbing effects of protein-enriched diets (PED) in mice. Whereas there was a 20% decrease in food intake in mice fed on the PED, compared to mice fed on an isocaloric starch-enriched diet, there was a paradoxical decrease in expression of the hypothalamic proopiomelanocortin gene, precursor of α-MSH, and increase in expression of the gene encoding AgRP. The hypophagia effect of PED took place in mice with invalidation of either MC4R or POMC, and was even strengthened in mice with ablation of the AgRP-expressing neurons. These data strongly suggest that the hypothalamic melanocortin system does not mediate the hunger-curbing effects induced by changes in the macronutrient composition of food. Rather, the role of this system might be to defend the body against the variations in food intake generated by the nutritional environment

Role of Mu opioid receptors in induction of intestinal glucose production observed on high-protein diets

Une alimentation HP permet une importante diminution de la prise alimentaire, chez l’Homme et l’animal, par rapport à une alimentation STD. Les précédents travaux du laboratoire montrent que le mécanisme d’action des protéines implique une induction de la PIG chez le rat en période post-absorptive. Ce glucose, libéré et détecté dans la veine porte, permet l’activation de noyaux hypothalamiques impliqués dans la régulation des sensations de satiété. L’objectif de ce travail consistait à mettre en évidence le type de peptides pouvant induire la PIG en régime HP et d’essayer de découvrir leur mécanisme d’action. L’activité de la Glc6Pase et de l’expression des protéines Glc6Pase et PEPCK ont été quantifiées chez des rats nourris en régime STD ou HP et perfusés avec des perfusions d’acides aminés, de peptides µ-opioïdes et des solutions de di- ou tri-peptides. Les résultats montrent que le même mécanisme d’action est utilisé par les protéines et les antagonistes µ-opioïdes pour induire la PIG. Des expériences de dénervation portale et une étude immunohistochimique ont démontré la présence de récepteurs µ-opioïdes dans la veine porte probablement impliqués dans cette induction. Des perfusions de di ou tri-peptides chez le rat ont démontré que la PIG était induite par tous les di ou tri-peptides testés. L’étude phénotypique de la souris KO µ-opioïde nourrie en régime STD, HP ou ayant subi des perfusions portales de di ou tri-peptides, ont confirmé que la PIG pouvait être induite par des di ou tri-peptides et que leur mécanisme d’action nécessitait la présence de récepteurs µ-opioïdes. Cette étude suggère que tous les di- ou tri-peptides produits par la dégradation des protéines pourraient induire la PIG par un mécanisme dépendant des récepteurs µ-opioïdesProtein feeding promotes an important decrease of food intake in humans and animals, compared on chow diet. Previous data show that this mechanism implicates intestinal glucose production (IPG) induction in rat during the post-absorptive time. Glucose released and detected into the portal vein produces an activation of hypothalamic nuclei implicated in the regulation of satiety sensations. The aim of this study was to highlight peptides which could induce IPG on HP diet and try to discoverer them mechanism. Quantification of Glc6Pase and protein expression of Glc6Pase and PEPCK were assessed in rats fed on chow or HP diet and infused with amino acids, µ-opioïd peptides and di- or tri-peptides. Our results show that the same mechanism is shared by both proteins and µ-opioïd antagonists to induce IGP. Experiments of portal vein denervation and an immunochemistry study showed that µ-opioïd receptors are present in the portal vein, probably implicated in this induction. Di or tri-peptides infusions in rat exhibited that the IGP was induced by all tested di or tri-peptides. Phenotypic study of µ-opioid mice fed on chow, HP diet or having undergone portal vein infusions of di or tri-peptides, confirmed that IGP could be induced by di or tri-peptides and their mechanism takes place with µ-opioïd receptors. This study suggests that all di or tri-peptide produced by protein degradation could induce IGP by a µ-opioïd receptor-dependent mechanis

Specific activity of class II histone deacetylases in human breast cancer cells.

International audienceAlthough numerous studies have underlined the role of histone deacetylases (HDAC) in breast physiology and tumorigenesis, little is known on the particular contribution of the various classes of HDACs in these processes. Using estrogen receptor-alpha (ERalpha)-positive MCF-7 breast cancer cells, the effects of MC1575 and MC1568, two novel class II-specific HDAC inhibitors, were analyzed on cell proliferation, apoptosis, and estrogen signaling. The specificity of these HDAC inhibitors was validated by measuring histone and alpha-tubulin acetylation and by the specific in vitro inhibition of recombinant HDAC4 using histone and nonhistone substrates, contrasting with the lack of inhibition of class I HDACs. In addition, MC1575 did not inhibit class I HDAC gene expression, thus confirming the specific targeting of class II enzymes. Similar to trichostatin A (TSA), MC1575 displayed a dose-dependent antiproliferative effect and induced cell cycle arrest although this blockade occurred at a different level than TSA. Moreover, and in contrast to TSA, MC1575 had no effect on MCF-7 cells apoptosis. Interestingly, MC1575 was able to increase p21(waf1/CIP1) mRNA levels but did not regulate the expression of other genes such as cyclin D1, p27, p14(ARF), Bcl2, Baxalpha, Trail-R1, and Trail-R2. Finally, MC1575 strongly induced ERbeta gene expression but did not decrease ERalpha expression, nor did it switch hydroxytamoxifen to an agonist activity. Altogether, these data suggest that the class II HDAC subfamily may exert specific roles in breast cancer progression and estrogen dependence

Histone deacetylase 9 regulates breast cancer cell proliferation and the response to histone deacetylase inhibitors

International audienceHistone lysine acetylation is an epigenetic mark regulated by histone acetyltransferases and histone deacetylases (HDAC) which plays an important role in tumorigenesis. In this study, we observed a strong overexpression of class IIa HDAC9, at the mRNA and protein levels, in the most aggressive human breast cancer cell lines (i.e. in basal breast cancer cells vs luminal ones or in malignant vs begnin MCF10A breast epithelial cell lines). HDAC9 overexpression was associated with higher rates of gene transcription and increased epigenetic marks on the HDAC9 promoter. Ectopic expression of HDAC9 in MCF7 luminal breast cancer cells led to an increase in cell proliferation and to a decrease in apoptosis. These effects were associated with a deregulated expression of several genes controlled by HDAC inhibitors such as CDKN1A, BAX and TNFRSF10A. Inversely, knock-down of HDAC9 expression in MDA-MB436 basal breast cancer cells reduced cell proliferation. Moreover, high HDAC9 expression decreased the efficacy of HDAC inhibitors to reduce cell proliferation and to regulate CDKN1A gene expression. Interestingly, the gene encoding the transcription factor SOX9 was identified by a global transcriptomic approach as an HDAC9 target gene. In stably transfected MCF7 cells, SOX9 silencing significantly decreased HDAC9 mitogenic activity. Finally, in a large panel of breast cancer biopsies, HDAC9 expression was significantly increased in tumors of the basal subtype, correlated with SOX9 expression and associated with poor prognosis. Altogether, these results indicate that HDAC9 is a key factor involved in mammary carcinogenesis and in the response to HDAC inhibitors

Effect of PED on food intake and body weight in SV129 and NPY/AgRP-neurons depleted mice.

<p>Food intake (A) and body weight (B) were measured in AgRP^DTR naive mice (circles) and in AgRP^DTR mice treated as pups (squares). Mice were fed from “day 0” on the PED diet. For each point determination, n = 6 mice were studied. At day 6, because AgRP^DTR treated mice still lost weight, PED feeding was stopped and mice were switched back on the control chow diet (SED). Body weight variation (B) is expressed in % of initial body weight and food intake (A) as % of reference food intake, as described in the legend of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0019107#pone-0019107-g001" target="_blank">Fig. 1</a>. All data from day 1 are different from day 0 (Student's t test for paired data) in panel A. *, different from wild-type mice (Student's t test for unpaired data).</p

Effect of PED on food intake and body weight in C57bl6J and MC4-R KO mice.

<p>Food intake (panels A,C) and body weight (B,D) were measured in control mice (circles) and in MC4R-KO mice (squares), fed either on a starch enriched diet (SED, open forms) or on a protein enriched diet (PED, filled forms). PED was first given from “day 0”, mice being previously fed on the SED. For each point determination, n = 8 mice were studied. The data are expressed as means+/−SEM. The results have been reported to a reference value, calculated as the average of 3 prior consecutive days of SED (from days −6 to −4). The results are expressed as % of this reference. 100% represented 0.5 and 0.73 cal/d/g body weight in C57bl6J and MC4-R KO mice, respectively. All data from day 1 are different from day 0 for PED feeding (p<0.05, Student's t test for paired data), in both panel A and C.</p

Hypothalamic contents in MC4-R, POMC and AgRPmRNAs.

<p>Determinations by quantitative RT-PCR. The relative mRNA contents were measured in hypothalamus of five-weeks-old C57bl6J mice after 4 days of diet of PED compared to SED fed mice, and reported to a GAPDH mRNA as a standard. *, p<0,05 (t test for unpaired samples).</p

Effect of PED on food intake and body weight in SV129 and POMC KO mice.

<p>Food intake (A, C) and body weight (B, D) were measured in wild-type mice (circles) and in POMC-KO mice (squares), fed either on a starch enriched diet (SED, open forms) or on a protein enriched diet (PED, filled forms). Expression and presentation of data are as described in the legend of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0019107#pone-0019107-g001" target="_blank">Fig. 1</a> (n = 8 mice studied). 100% represented 0.63 and 0.69 cal/d/g body weight in 129SV and POMC KO mice, respectively. All data from day 1 are different from day 0 for PED feeding (Student's t test for paired data), in both panel A and C.</p