Associations between hepatic miRNA expression, liver triacylglycerols and gut microbiota during metabolic adaptation to high-fat diet in mice.

AIMS/HYPOTHESIS: Despite the current pandemic of metabolic diseases, our understanding of the diverse nature of the development of metabolic alterations in people who eat a high-fat diet (HFD) is still poor. We recently demonstrated a cardio-metabolic adaptation in mice fed an HFD, which was characterised by a specific gut and periodontal microbiota profile. Since the severity of hepatic disease is characterised by specific microRNA (miRNA) signatures and the gut microbiota is a key driver of both hepatic disease and miRNA expression, we analysed the expression of three hepatic miRNA and studied their correlation with hepatic triacylglycerol content and gut microbiota. METHODS: Two cohorts of C57BL/6 4-week-old wild-type (WT) male mice (n = 62 and n = 96) were fed an HFD for 3 months to provide a model of metabolic adaptation. Additionally 8-week-old C57BL/6 mice, either WT or of different genotypes, with diverse gut microbiota (ob/ob, Nod1, Cd14 knockout [Cd14KO] and Nod2) or without gut microbiota (axenic mice) were fed a normal chow diet. Following which, glycaemic index, body weight, blood glucose levels and hepatic triacylglycerol levels were measured. Gut (caecum) microbiota taxa were analysed by pyrosequencing. To analyse hepatic miRNA expression, real-time PCR was performed on total extracted miRNA samples. Data were analysed using two-way ANOVA followed by the Dunnett's post hoc test, or by the unpaired Student's t test. A cluster analysis and multivariate analyses were also performed. RESULTS: Our results demonstrated that the expression of miR-181a, miR-666 and miR-21 in primary murine hepatocytes is controlled by lipopolysaccharide in a dose-dependent manner. Of the gut microbiota, Firmicutes were positively correlated and Proteobacteria and Bacteroides acidifaciens were negatively correlated with liver triacylglycerol levels. Furthermore, the relative abundance of Firmicutes was negatively correlated with hepatic expression of miR-666 and miR-21. In contrast, the relative abundance of B. acidifaciens was positively correlated with miR-21. CONCLUSIONS/INTERPRETATION: We propose the involvement of hepatic miRNA, liver triacylglycerols and gut microbiota as a new triad that underlies the molecular mechanisms by which gut microbiota governs hepatic pathophysiology during metabolic adaptation to HFD.

Offspring metabolomic response to maternal protein restriction in a rat model of intrauterine growth restriction (IUGR).

Intrauterine growth restriction (IUGR), along with postnatal growth trajectory, is closely linked with metabolic diseases and obesity at adulthood. The present study reports the time-dependent metabolomic response of male offspring of rat dams exposed to maternal adequate protein diet during pregnancy and lactation (CC) or protein deprivation during pregnancy only (IUGR with rapid catch-up growth, RC) or through pregnancy and lactation (IUGR with slow postnatal growth, RR). Plasma LC-HRMS metabolomic fingerprints for 8 male rats per group, combined with multivariate statistical analysis (PLS-DA and HCA), were used to study the impact of IUGR and postnatal growth velocity on the offspring metabolism in early life (until weaning) and once they reached adulthood (8 months). Compared with CC rats, RR pups had clear-cut alterations in plasma metabolome during suckling, but none at adulthood; in contrast, in RC pups, alterations in metabolome were minimal in early life but more pronounced in the long run. In particular, our results pinpoint transient alterations in proline, arginine, and histidine in RR rats, compared to CC rats, and persistent differences in tyrosine and carnitine, compared to RC rats at adulthood. These findings suggest that the long-term deregulation in feeding behavior and fatty acid metabolism in IUGR rats depends on postnatal growth velocity.

Defective autophagy in Sf1 neurons perturbs the metabolic response to fasting and causes mitochondrial dysfunction.

OBJECTIVE: The ventromedial nucleus of the hypothalamus (VMH) is a critical component of the forebrain pathways that regulate energy homeostasis. It also plays an important role in the metabolic response to fasting. However, the mechanisms contributing to these physiological processes remain elusive. Autophagy is an evolutionarily conserved mechanism that maintains cellular homeostasis by turning over cellular components and providing nutrients to the cells during starvation. Here, we investigated the importance of the autophagy-related gene Atg7 in Sf1-expressing neurons of the VMH in control and fasted conditions. METHODS: We generated Sf1-Cre; Atg7loxP/loxP mice and examined their metabolic and cellular response to fasting. RESULTS: Fasting induces autophagy in the VMH, and mice lacking Atg7 in Sf1-expressing neurons display altered leptin sensitivity and impaired energy expenditure regulation in response to fasting. Moreover, loss of Atg7 in Sf1 neurons causes alterations in the central response to fasting. Furthermore, alterations in mitochondria morphology and activity are observed in mutant mice. CONCLUSION: Together, these data show that autophagy is nutritionally regulated in VMH neurons and that VMH autophagy participates in the control of energy homeostasis during fasting.

The endoplasmic reticulum stress-autophagy pathway controls hypothalamic development and energy balance regulation in leptin-deficient neonates.

Obesity is associated with the activation of cellular responses, such as endoplasmic reticulum (ER) stress. Here, we show that leptin-deficient ob/ob mice display elevated hypothalamic ER stress as early as postnatal day 10, i.e., prior to the development of obesity in this mouse model. Neonatal treatment of ob/ob mice with the ER stress-relieving drug tauroursodeoxycholic acid (TUDCA) causes long-term amelioration of body weight, food intake, glucose homeostasis, and pro-opiomelanocortin (POMC) projections. Cells exposed to ER stress often activate autophagy. Accordingly, we report that in vitro induction of ER stress and neonatal leptin deficiency in vivo activate hypothalamic autophagy-related genes. Furthermore, genetic deletion of autophagy in pro-opiomelanocortin neurons of ob/ob mice worsens their glucose homeostasis, adiposity, hyperphagia, and POMC neuronal projections, all of which are ameliorated with neonatal TUDCA treatment. Together, our data highlight the importance of early life ER stress-autophagy pathway in influencing hypothalamic circuits and metabolic regulation.

The timing of "catch-up growth" affects metabolism and appetite regulation in male rats born with intrauterine growth restriction.

Epidemiological studies demonstrated a relationship between low birth weight mainly caused by intrauterine growth restriction (IUGR) and adult metabolic disorders. The concept of metabolic programming centers on the idea that nutritional and hormonal status during the key period of development determines the long-term control of energy balance by programming future feeding behavior and energy expenditure. The present study examined the consequence of early or late "catch-up growth" after IUGR on feeding behavior and metabolic cues of male offspring of rat dams exposed to protein restriction during gestation and/or lactation. Our results suggest that early catch-up growth may be favorable for fasting metabolic parameters at weaning, as no differences were observed on plasma leptin, triglyceride, glucose, and insulin levels compared with controls. In contrast, if pups remained malnourished until weaning, low insulin concentration was detected and was accompanied by hyperphagia associated with a large increase in hypothalamic NPY and AgRP mRNA expression. At adult age, on a regular chow diet, only the meal structure was modified by fetal programming. The two IUGR groups demonstrated a reduced meal duration that enhanced the speed of food ingestion and consequently increased the rest period associated to the satiety state without changes in the hypothalamic expression of appetite neuropeptides. Our findings demonstrate that in IUGR, regardless of postnatal growth magnitude, metabolic programming occurred in utero and was responsible for both feeding behavior alteration and postprandial higher insulin level in adults. Additionally, catch-up growth immediately after early malnutrition could be a key point for the programming of postprandial hyperleptinemia.

Gut Dysbiosis and Adaptive Immune Response in Diet-induced Obesity vs. Systemic Inflammation.

A mutual interplay exists between adaptive immune system and gut microbiota. Altered gut microbial ecosystems are associated with the metabolic syndrome, occurring in most obese individuals. However, it is unknown why 10-25% of obese individuals are metabolically healthy, while normal weight individuals can develop inflammation and atherosclerosis. We modeled these specific metabolic conditions in mice fed with a chow diet, an obesogenic but not inflammatory diet-mimicking healthy obesity, or Paigen diet-mimicking inflammation in the lean subjects. We analyzed a range of markers and cytokines in the aorta, heart, abdominal fat, liver and spleen, and metagenomics analyses were performed on stool samples. T lymphocytes infiltration was found in the aorta and in the liver upon both diets, however a significant increase in CD4+ and CD8+ cells was found only in the heart of Paigen-fed animals, paralleled by increased expression of IL-1, IL-4, IL-6, IL-17, and IFN-γ. Bacteroidia, Deltaproteobacteria, and Verrucomicrobia dominated in mice fed Paigen diet, while Gammaproteobacteria, Delataproteobacteria, and Erysipelotrichia were more abundant in obese mice. Mice reproducing human metabolic exceptions displayed gut microbiota phylogenetically distinct from normal diet-fed mice, and correlated with specific adaptive immune responses. Diet composition thus has a pervasive role in co-regulating adaptive immunity and the diversity of microbiota.

Neonatal ghrelin programs development of hypothalamic feeding circuits.

A complex neural network regulates body weight and energy balance, and dysfunction in the communication between the gut and this neural network is associated with metabolic diseases, such as obesity. The stomach-derived hormone ghrelin stimulates appetite through interactions with neurons in the arcuate nucleus of the hypothalamus (ARH). Here, we evaluated the physiological and neurobiological contribution of ghrelin during development by specifically blocking ghrelin action during early postnatal development in mice. Ghrelin blockade in neonatal mice resulted in enhanced ARH neural projections and long-term metabolic effects, including increased body weight, visceral fat, and blood glucose levels and decreased leptin sensitivity. In addition, chronic administration of ghrelin during postnatal life impaired the normal development of ARH projections and caused metabolic dysfunction. Consistent with these observations, direct exposure of postnatal ARH neuronal explants to ghrelin blunted axonal growth and blocked the neurotrophic effect of the adipocyte-derived hormone leptin. Moreover, chronic ghrelin exposure in neonatal mice also attenuated leptin-induced STAT3 signaling in ARH neurons. Collectively, these data reveal that ghrelin plays an inhibitory role in the development of hypothalamic neural circuits and suggest that proper expression of ghrelin during neonatal life is pivotal for lifelong metabolic regulation.

Development of the hypothalamic melanocortin system.

The melanocortin system is a critical component of the forebrain and hindbrain regulatory systems involved in energy balance. This system is composed of pro-opiomelanocortin (POMC) neurons that act, in part, through the melanocortin-4 receptor (MC4R). Although the importance of the melanocortin system in controlling feeding has been established for two decades, the understanding of the developmental substrates underlying POMC and MC4R neuron development and function has just begun to emerge. The formation of the melanocortin system involves several discrete developmental steps that include the birth and fate specification of POMC- and MC4R-containing neurons and the extension and guidance of POMC axons to their MC4R-expressing target nuclei. Each of these developmental processes appears to require specific sets of genes and developmental cues that include perinatal hormones. Recent evidence has also highlighted the importance of perinatal nutrition in controlling the ultimate architecture of the melanocortin system.

Postnatal growth after intrauterine growth restriction alters central leptin signal and energy homeostasis.

Intrauterine growth restriction (IUGR) is closely linked with metabolic diseases, appetite disorders and obesity at adulthood. Leptin, a major adipokine secreted by adipose tissue, circulates in direct proportion to body fat stores, enters the brain and regulates food intake and energy expenditure. Deficient leptin neuronal signalling favours weight gain by affecting central homeostatic circuitry. The aim of this study was to determine if leptin resistance was programmed by perinatal nutritional environment and to decipher potential cellular mechanisms underneath.We clearly demonstrated that 5 months old IUGR rats develop a decrease of leptin sentivity, characterized by no significant reduction of food intake following an intraperitoneal injection of leptin. Apart from the resistance to leptin injection, results obtained from IUGR rats submitted to rapid catch-up growth differed from those of IUGR rats with no catch-up since we observed, for the first group only, fat accumulation, increased appetite for food rich in fat and increased leptin synthesis. Centrally, the leptin resistant state of both groups was associated with a complex and not always similar changes in leptin receptor signalling steps. Leptin resistance in IUGR rats submitted to rapid catch-up was associated with alteration in AKT and mTOR pathways. Alternatively, in IUGR rats with no catch-up, leptin resistance was associated with low hypothalamic expression of LepRa and LepRb. This study reveals leptin resistance as an early marker of metabolic disorders that appears before any evidence of body weight increase in IUGR rats but whose mechanisms could depend of nutritional environment of the perinatal period.

Loss of autophagy in pro-opiomelanocortin neurons perturbs axon growth and causes metabolic dysregulation.

The hypothalamic melanocortin system, which includes neurons that produce pro-opiomelanocortin (POMC)-derived peptides, is a major negative regulator of energy balance. POMC neurons begin to acquire their unique properties during neonatal life. The formation of functional neural systems requires massive cytoplasmic remodeling that may involve autophagy, an important intracellular mechanism for the degradation of damaged proteins and organelles. Here we investigated the functional and structural effects of the deletion of an essential autophagy gene, Atg7, in POMC neurons. Lack of Atg7 in POMC neurons caused higher postweaning body weight, increased adiposity, and glucose intolerance. These metabolic impairments were associated with an age-dependent accumulation of ubiquitin/p62-positive aggregates in the hypothalamus and a disruption in the maturation of POMC-containing axonal projections. Together, these data provide direct genetic evidence that Atg7 in POMC neurons is required for normal metabolic regulation and neural development, and they implicate hypothalamic autophagy deficiency in the pathogenesis of obesity.

Long term metabolic impact of high protein neonatal feeding: a preliminary study in male rat pups born with a low birth weight.

BACKGROUND & AIMS: Nutrition received in early life may impact adult health. The aim of the study was to determine whether high protein feeding in neonatal period would have long term metabolic effects in an animal model of low birth weight infants. METHODS: Male rat pups born from dams receiving a low protein diet during gestation were separated from their mothers, and equipped with gastrostomy tubes to receive as their sole feeding a milk formula of either adequate protein (AP; n = 14; 8.7 g protein/dL; total energy: 155 kcal/100 g), or high protein content (HP; n = 14; 13.0 g protein/dL; total energy: 171 kcal/100 g) between the 7th (D7) and 21st day (D21) of life. Rats were then weaned to standard chow until sacrificed at adulthood. RESULTS: At D18, HP feeding was associated with higher estimated rates of protein turnover (p = 0.007) and synthesis (p = 0.051), as assessed using l-[U-(13)C]valine infusion. HP milk feeding in early life was associated with an increase in weight gain from puberty through adulthood, along with an increase in food intake, serum insulin (179 ± 58 vs. 55 ± 7 pmol/L; means ± SE), pancreatic ß-cell number, plasma triglycerides (95 ± 8 vs. 73 ± 9 mg/dL), serum leptin (9.7 ± 1.0 vs. 5.5 ± 1.2 ng/mL), mesenteric fat mass, and adipocyte size. CONCLUSIONS: In an animal model of low birth weight infants, high protein neonatal feeding may have a lasting effect on fat and glucose metabolism, potentially leading to "metabolic syndrome" in adulthood.

Postnatal growth velocity modulates alterations of proteins involved in metabolism and neuronal plasticity in neonatal hypothalamus in rats born with intrauterine growth restriction.

Intrauterine growth restriction (IUGR) due to maternal protein restriction is associated in rats with an alteration in hypothalamic centers involved in feeding behaviour. In order to gain insight into the mechanism of perinatal maternal undernutrition in the brain, we used proteomics approach to identify hypothalamic proteins that are altered in their expression following protein restriction in utero. We used an animal model in which restriction of the protein intake of pregnant rats (8% vs. 20%) produces IUGR pups which were randomized to a nursing regimen leading to either rapid or slow catch-up growth. We identified several proteins which allowed, by multivariate analysis, a very good discrimination of the three groups according to their perinatal nutrition. These proteins were related to energy-sensing pathways (Eno 1, E(2)PDH, Acot 1 and Fabp5), redox status (Bcs 1L, PrdX3 and 14-3-3 protein) or amino acid pathway (Acy1) as well as neurodevelopment (DRPs, MAP2, Snca). In addition, the differential expressions of several key proteins suggested possible shunts towards ketone-body metabolism and lipid oxidation, providing the energy and carbon skeletons necessary to lipogenesis. Our results show that maternal protein deprivation during pregnancy only (IUGR with rapid catch-up growth) or pregnancy and lactation (IUGR with slow postnatal growth) modulates numerous metabolic pathways resulting in alterations of hypothalamic energy supply. As several of these pathways are involved in signalling, it remains to be determined whether hypothalamic proteome adaptation of IUGR rats in response to different postnatal growth rates could also interfere with cerebral plasticity or neuronal maturation.

Hypothalamus integrity and appetite regulation in low birth weight rats reared artificially on a high-protein milk formula.

High-protein (HP) milk formulas are routinely used in infants born with a low birth weight (LBW) to enhance growth and ensure a better verbal IQ development. Indirect evidence points to a link between an HP intake during early life and the prevalence of obesity in later life. We hypothesized that HP milk supplementation to LBW pups during early postnatal life would impact hypothalamic appetite neuronal pathways development with consequences, at adulthood, on energy homeostasis regulation. Rat pups born with a LBW were equipped with gastrostomy tubes on the fifth day of life. They received a milk formula with either normal protein (NP, 8.7 g protein/dl) or high protein content (HP; 13.0 g protein/dl) and were subsequently weaned to a standard, solid diet at postnatal day 21. Rats that had been fed HP content milk gained more weight at adulthood associated with an increase of plasma insulin, leptin and triglycerides concentrations compared to NP rats. Screening performed on hypothalamus in development from the two groups of rats identified higher gene expression for cell proliferation and neurotrophin markers in HP rats. Despite these molecular differences, appetite neuronal projections emanating from the arcuate nucleus did not differ between the groups. Concerning feeding behavior at adulthood, rats that had been fed HP or NP milk exhibited differences in the satiety period, resting postprandial duration and nocturnal meal pattern. The consequences of HP milk supplementation after LBW will be discussed in regard to neural development and metabolic anomalies.

Nutritional programming affects hypothalamic organization and early response to leptin.

Nutritional programming, taking place in utero or early after birth, is closely linked with metabolic and appetite disorders in adulthood. Following the hypothesis that nutritional programming impacts hypothalamic neuronal organization, we report on discrepancies of multiple molecular and cellular early events that take place in the hypothalamus of rats submitted to intrauterine growth restriction (IUGR). Expression screening performed on hypothalami from IUGR rats at birth and at postnatal d 12 identified changes in gene expression of neurodevelopmental process (cell differentiation and cytoskeleton organization). Additionally, a slight reduction of agouti-related protein and a strong reduction of alpha-MSH-immunoreactive efferent fibers were demonstrated in the paraventricular nucleus of IUGR rats. Rapid catch-up growth of IUGR rats, 5 d after birth, had a positive effect on neurodevelopmental factors and on neuronal projections emanating from the arcuate nucleus. The molecular and cellular anomalies detected in IUGR rats can be related to the reduced and delayed plasma leptin surge from d 0-16 when compared with control and IUGR rats with catch-up growth. However, the ability of leptin to activate intracellular signaling in arcuate nucleus neurons was not reduced in IUGR rats. Other mechanism such as epigenetic regulation of the major appetite-regulating neuropeptides genes was analyzed in parallel with their mRNA expression during postnatal development. This study reveals the importance of an early catch-up growth that reduces abnormal organization of hypothalamic pathways involved in energy homeostasis, whereas protein restriction, maintained during postnatal development leads to an important immaturity of the hypothalamus.