Dysregulation of sirtuins and key metabolic genes in skeletal muscle of pigs with spontaneous intrauterine growth restriction is associated with alterations of circulating IGF-1.

Prenatal and early postnatal life determines future health, and intrauterine growth restriction (IUGR) - associated low birth weight predisposes to metabolic syndrome in adulthood. We hypothesize here that IUGR might induce hormonal and gene expression alterations predisposing to metabolic disease. Using a porcine model of spontaneous IUGR, we determined in utero (71, 112days post-conception) and early-postnatal (2days post-birth) IGF-1, insulin and leptin levels, and in parallel we investigated, in skeletal muscle, the developmental expression patterns of sirtuins and metabolic and signaling genes IRS1, GLUT4, HK2 and GAPDH. IUGR was associated with impaired IGF-1 plasmatic levels. Gene expression of sirtuin 1, 5, 6, 7, GLUT4 and HK2 exhibited significant correlations with gestational age or body weight. SIRT1 and HK2 expression displayed an age- and weight-dependent downregulation in controls, which was lost in IUGR pigs. Conversely, SIRT2 and GLUT4 were upregulated in IUGR pigs. Within the set of genes studied, we found a significant correlation between IGF-1 levels and gene expression in control, but not IUGR samples, indicating that lower IGF-1 may be a limiting factor in IUGR. IUGR-dependent gene alterations were partly linked to epigenetic changes on histone H3 acetylation and methylation. Overall, our data indicate that several sirtuins and metabolic genes display specific gene expression trajectories during fetal and early postnatal life. Gene expression alterations observed in IUGR are correlated to IGF-1 dysregulation. Given the importance of the genes studied in metabolic control, their perinatal alterations might contribute to the predisposition to metabolic disease of adulthood.

Insulin-dependent transcriptional control in L6 rat myotubes is associated with modulation of histone acetylation and accumulation of the histone variant H2A.Z in the proximity of the transcriptional start site.

Besides its direct metabolic effects, insulin induces transcriptional alterations in its target tissues. However, whether such changes are accompanied by epigenetic changes on the chromatin template encompassing insulin responsive genes is unclear. Here, mRNA levels of insulin-responsive genes hexokinase 2 (Hk2), insulin receptor substrate (Irs2), and the PI3K subunit p85ß (Pik3r2) were compared in control versus insulin-stimulated L6 myotubes. Chromatin immunoprecipitation (ChIP) was performed with antibodies directed to histone H2A, histone variant H2A.Z, acetylated histone H3 on lysines 9/14, and acetylated H2A.Z. Insulin induced a more than 2-fold Hk2 mRNA increase, while Irs2 and Pik3r2 were downregulated. ChIP to H2A and H2A.Z showed higher H2A.Z accumulation around the transcriptional start site (TSS) of these insulin-modulated genes, while H2A.Z accumulation was lower distally to the TSS in the Hk2 promoter. H2A.Z levels and H3K9/14 acetylation correlated on several loci along the Hk2 gene, and H3K9/14 as well as H2A.Z acetylation was enhanced by insulin treatment. On the contrary, reduced H3K9/14 acetylation was observed in insulin-repressed Irs2 and Pik3r2, and recovery of acetylation by treatment with the histone deacetylase inhibitor trichostatin A reverted insulin-induced Irs2 downregulation. The chromatin regions encompassing selected insulin-responsive genes are thus featured by accumulation of H2A.Z around the TSS. H2A.Z accumulation facilitates insulin-dependent modulation of pharmacologically treatable H3K9/14 and H2A.Z acetylations. Indeed, inhibition of histone deacetylases by TSA treatment reverted insulin induced Irs2 gene downregulation. Dysregulated histone acetylation may thus be potentially targeted with histone deacetylase inhibitors.

GPR162 is a beta cell CART receptor.

Cocaine and amphetamine-regulated transcript (CART) is expressed in pancreatic islet cells and neuronal elements. We have previously established insulinotropic actions of CART in human and rodent islets. The receptor for CART in the pancreatic beta cells is unidentified. We used RNA sequencing of Cartpt knockdown (KD) INS-1 832/13 cells and identified GPR162 as the most Cartpt-regulated receptor. We therefore tested if GPR162 mediates the effects of CART in beta cells. Binding of CART to GPR162 was established using proximity ligation assay, radioactive binding, and co-immunoprecipitation, and KD of Gpr162 mRNA caused reduced binding. Gpr162 KD cells had blunted CARTp-induced exocytosis, and reduced CARTp-induced insulin secretion. Furthermore, we identified a hitherto undescribed GPR162-dependent role of CART as a regulator of cytoskeletal arrangement. Thus, our findings provide mechanistic insight into the effect of CART on insulin secretion and show that GPR162 is the CART receptor in beta cells.

Prominent action of butyrate over ß-hydroxybutyrate as histone deacetylase inhibitor, transcriptional modulator and anti-inflammatory molecule.

Butyrate and R-ß-hydroxybutyrate are two related short chain fatty acids naturally found in mammals. Butyrate, produced by enteric butyric bacteria, is present at millimolar concentrations in the gastrointestinal tract and at lower levels in blood; R-ß-hydroxybutyrate, the main ketone body, produced by the liver during fasting can reach millimolar concentrations in the circulation. Both molecules have been shown to be histone deacetylase (HDAC) inhibitors, and their administration has been associated to an improved metabolic profile and better cellular oxidative status, with butyrate inducing PGC1α and fatty acid oxidation and R-ß-hydroxybutyrate upregulating oxidative stress resistance factors FOXO3A and MT2 in mouse kidney. Because of the chemical and functional similarity between the two molecules, we compared here their impact on multiple cell types, evaluating i) histone acetylation and hydroxybutyrylation levels by immunoblotting, ii) transcriptional regulation of metabolic and inflammatory genes by quantitative PCR and iii) cytokine secretion profiles using proteome profiling array analysis. We confirm that butyrate is a strong HDAC inhibitor, a characteristic we could not identify in R-ß-hydroxybutyrate in vivo nor in vitro. Butyrate had an extensive impact on gene transcription in rat myotubes, upregulating PGC1α, CPT1b, mitochondrial sirtuins (SIRT3-5), and the mitochondrial anti-oxidative genes SOD2 and catalase. In endothelial cells, butyrate suppressed gene expression and LPS-induced secretion of several pro-inflammatory genes, while R-ß-hydroxybutyrate acted as a slightly pro-inflammatory molecule. Our observations indicate that butyrate induces transcriptional changes to a higher extent than R-ß-hydroxybutyrate in rat myotubes and endothelial cells, in keep with its HDAC inhibitory activity. Also, in contrast with previous reports, R-ß-hydroxybutyrate, while inducing histone ß-hydroxybutyrylation, did not display a readily detectable HDAC inhibitor activity and exerted a slight pro-inflammatory action on endothelial cells.

The histone deacetylase inhibitor sodium butyrate improves insulin signalling in palmitate-induced insulin resistance in L6 rat muscle cells through epigenetically-mediated up-regulation of Irs1.

Dietary administration of the histone deacetylase (HDAC) inhibitor butyric acid - a short chain fatty acid present in milk products and also bacterially produced in the intestine - has been shown to increase energy expenditure and favour insulin sensitivity in mice through induction of PGC1α (peroxisome proliferator-activated receptor gamma co-activator 1α) and AMPK (AMP-activated protein kinase) in skeletal muscle, and a consequential increase of mitochondrial fatty acid oxidation. Here, we investigate whether such physiological improvements are associated to epigenetic effects dependent on increased histone acetylation and whether butyrate exerts a direct action on skeletal muscle insulin signalling. We show that sodium butyrate (NaBut) ameliorates the insulin-resistant phenotype, induced in L6 myotubes by prolonged exposure to palmitate, by i) increasing the insulin-induced phosphorylation of both PKB (protein kinase B) and MAPK (mitogen activated protein kinase), the two branches of insulin signalling and ii) increasing histone H3 acetylation - even in the presence of palmitate - on chromatin in proximity of the Irs1 (insulin receptor substrate 1) transcriptional start site. Consequently, NaBut induced Irs1 mRNA and protein overexpression, which in turn relayed higher insulin-stimulated IRS1 tyrosine phosphorylation and PI 3-kinase (phosphoinositide 3-kinase) association, suggesting that the increased IRS1 expression may mediate the insulin-sensitizing effects of NaBut. Furthermore, downstream of PKB, NaBut induced GSK3ß gene upregulation. Our observations indicate that NaBut - through its action as HDAC inhibitor - can promote insulin responsiveness in L6 myotubes under conditions of lipid-induced insulin resistance.

[Epigenetics in transgenerational responses to environmental impacts: from facts and gaps]. / Épigénétique et réponses transgénérationnelles aux impacts de l'environnement--Des faits aux lacunes.

The existence of non-genetic and non-cultural mechanisms that transfer information on the memory of parental exposures to various environments, determining the reactivity of the following generations to their environments during their life, are of growing interest. Yet fundamental questions remain about the nature, the roles and relative importance of epigenetic marks and processes, non-coding RNAs, or other mechanisms, and their persistence over generations. A model incorporating the various transmission systems, their cross-talks and windows of susceptibility to the environment as a function of sex/gender of parent and offspring, has yet to be built.

Essential roles of four-carbon backbone chemicals in the control of metabolism.

The increasing incidence of obesity worldwide and its related cardiometabolic complications is an urgent public health problem. While weight gain results from a negative balance between the energy expenditure and calorie intake, recent research has demonstrated that several small organic molecules containing a four-carbon backbone can modulate this balance by favoring energy expenditure, and alleviating endoplasmic reticulum stress and oxidative stress. Such small molecules include the bacterially produced short chain fatty acid butyric acid, its chemically produced derivative 4-phenylbutyric acid, the main ketone body D-ß-hydroxybutyrate - synthesized by the liver - and the recently discovered myokine ß-aminoisobutyric acid. Conversely, another butyrate-related molecule, α-hydroxybutyrate, has been found to be an early predictor of insulin resistance and glucose intolerance. In this minireview, we summarize recent advances in the understanding of the mechanism of action of these molecules, and discuss their use as therapeutics to improve metabolic homeostasis or their detection as early biomarkers of incipient insulin resistance.