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Arcuate nucleus agouti-related peptide (AgRP) neurons play a central role in feeding and are under complex regulation by both homeostatic hormonal and nutrient signals and hypothalamic neuronal pathways. Feeding may also be influenced by environmental cues, sensory inputs, and other behaviors, implying the involvement of higher brain regions. However, whether such pathways modulate feeding through direct synaptic control of AgRP neuron activity is unknown. Here, we show that nociceptin-expressing neurons in the anterior bed nuclei of the stria terminalis (aBNST) make direct GABAergic inputs onto AgRP neurons. We found that activation of these neurons inhibited AgRP neurons and feeding. The activity of these neurons increased upon food availability, and their ablation resulted in obesity. Furthermore, these neurons received afferent inputs from a range of upstream brain regions as well as hypothalamic nuclei. Therefore, aBNST GABAergic nociceptin neurons may act as a gateway to feeding behavior by connecting AgRP neurons to both homeostatic and nonhomeostatic neuronal inputs., Introduction Feeding requires the integration of multiple neuronal networks to elicit appropriate behavioral and metabolic responses (1-3). These networks are sensitive to a range of modulatory inputs including nutrients and [...]

Neuronatin (Nnat) is an imprinted gene implicated in human obesity and widely expressed in neuroendocrine and metabolic tissues in a hormone- and nutrient-sensitive manner. However, its molecular and cellular functions and precise role in organismal physiology remain only partly defined. Here we demonstrate that mice lacking Nnat globally or specifically in [beta] cells display impaired glucose-stimulated insulin secretion leading to defective glucose handling under conditions of nutrient excess. In contrast, we report no evidence for any feeding or body weight phenotypes in global Nnat-null mice. At the molecular level neuronatin augments insulin signal peptide cleavage by binding to the signal peptidase complex and facilitates translocation of the nascent preprohormone. Loss of neuronatin expression in [beta] cells therefore reduces insulin content and blunts glucose-stimulated insulin secretion. Nnat expression, in turn, is glucose- regulated. This mechanism therefore represents a novel site of nutrient-sensitive control of [beta] cell function and whole-animal glucose homeostasis. These data also suggest a potential wider role for Nnat in the regulation of metabolism through the modulation of peptide processing events., Introduction Imprinted genes display monoallelic expression according to parent of origin due to epigenetic events initiated in the germline (1). Around 150 such genes have been identified in mice, 50% [...]

Polymorphisms in the fat mass and obesity-associated gene (FTO) are associated with human obesity and obesity-prone behaviors, including increased food intake and a preference for energy-dense foods. FTO demethylates [N.sup.6]-methyladenosine, [...]

Hypothalamic AMP-activated protein kinase (AMPK) has been suggested to act as a key sensing mechanism, responding to hormones and nutrients in the regulation of energy homeostasis. However, the precise neuronal [...]

Background: Neuronatin (NNAT) is an endoplasmic reticulum proteolipid implicated in intracellular signalling. Nnat is highly-expressed in the hypothalamus, where it is acutely regulated by nutrients and leptin. Nnat pre-mRNA is differentially spliced to create Nnat-α and -β isoforms. Genetic variation of NNAT is associated with severe obesity. Currently, little is known about the long-term regulation of Nnat. Methods: Expression of Nnat isoforms were examined in the hypothalamus of mice in response to acute fast/feed, chronic caloric restriction, diet-induced obesity and modified gastric bypass surgery. Nnat expression was assessed in the central nervous system and gastrointestinal tissues. RTqPCR was used to determine isoform-specific expression of Nnat mRNA. Results: Hypothalamic expression of both Nnat isoforms was comparably decreased by overnight and 24-h fasting. Nnat expression was unaltered in diet-induced obesity, or subsequent switch to a calorie restricted diet. Nnat isoforms showed differential expression in the hypothalamus but not brainstem after bypass surgery. Hypothalamic Nnat-β expression was significantly reduced after bypass compared with sham surgery (P = 0.003), and was positively correlated with post-operative weight-loss (R2 = 0.38, P = 0.01). In contrast, Nnat-α expression was not suppressed after bypass surgery (P = 0.19), and expression did not correlate with reduction in weight after surgery (R2 = 0.06, P = 0.34). Hypothalamic expression of Nnat-β correlated weakly with circulating leptin, but neither isoform correlated with fasting gut hormone levels post- surgery. Nnat expression was detected in brainstem, brown-adipose tissue, stomach and small intestine. Conclusions: Nnat expression in hypothalamus is regulated by short-term nutrient availability, but unaltered by diet-induced obesity or calorie restriction. While Nnat isoforms in the hypothalamus are co-ordinately regulated by acute nutrient supply, after modified gastric bypass surgery Nnat isoforms show differential expression. These results raise the possibility that in the radically altered nutrient and hormonal milieu created by bypass surgery, resultant differential splicing of Nnat pre-mRNA may contribute to weight-loss. [ABSTRACT FROM AUTHOR]

Objective: Diabetes mellitus is associated with cognitive deficits and an increased risk of dementia, particularly in the elderly. These deficits and the corresponding neurophysiological structural and functional alterations are linked to both metabolic and vascular changes, related to chronic hyperglycaemia, but probably also defects in insulin action in the brain. To elucidate the specific role of brain insulin signalling in neuronal functions that are relevant for cognitive processes we have investigated the behaviour of neurons and synaptic plasticity in the hippocampus of mice lacking the insulin receptor substrate protein 2 (IRS-2). Research Design and Methods: To study neuronal function and synaptic plasticity in the absence of confounding factors such as hyperglycaemia, we used a mouse model with a central nervous system- (CNS)-restricted deletion of IRS-2 (NesCreIrs2KO). Results: We report a deficit in NMDA receptor-dependent synaptic plasticity in the hippocampus of NesCreIrs2KO mice, with a concomitant loss of metaplasticity, the modulation of synaptic plasticity by the previous activity of a synapse. These plasticity changes are associated with reduced basal phosphorylation of the NMDA receptor subunit NR1 and of downstream targets of the PI3K pathway, the protein kinases Akt and GSK-3β. Conclusions: These findings reveal molecular and cellular mechanisms that might underlie cognitive deficits linked to specific defects of neuronal insulin signalling. [ABSTRACT FROM AUTHOR]

Recent evidence suggests that alterations in insulin/insulin-like growth factor 1 (IGF1) signaling (IIS) can increase mammalian life span. For example, in several mouse mutants, impairment of the growth hormone (GH)/IGF1 axis increases life span and also insulin sensitivity. However, the intracellular signaling route to altered mammalian aging remains unclear. We therefore measured the life span of mice lacking either insulin receptor substrate (IRS) 1 or 2, the major intracellular effectors of the IIS receptors. Our provisional results indicate that female Irs1-/- mice are long-lived. Furthermore, they displayed resistance to a range of age-sensitive markers of aging including skin, bone, immune, and motor dysfunction. These improvements in health were seen despite mild, lifelong insulin resistance. Thus, enhanced insulin sensitivity is not a prerequisite for IIS mutant longevity. Irs1-/- female mice also displayed normal anterior pituitary function, distinguishing them from long-lived somatotrophic axis mutants. In contrast, Irs2-/- mice were short-lived, whereas Irs1+/- and Irs2+/- mice of both sexes showed normal life spans. Our results therefore suggest that IRS1 signaling is an evolutionarily conserved pathway regulating mammalian life span and may be a point of intervention for therapies with the potential to delay age-related processes. [ABSTRACT FROM AUTHOR]

Insulin receptor substrate 2 (Irs2) plays complex roles in energy homeostasis. We generated mice lacking Irs2 in beta cells and a population of hypothalamic neurons (RIPCreIrs2KO), in all neurons (NesCreIrs2KO), and in proopiomelanocortin neurons (POMCCreIrs2KO) to determine the role of Irs2 in the CNS and beta cell. RIPCreIrs2KO mice displayed impaired glucose tolerance and reduced beta cell mass. Overt diabetes did not ensue, because beta cells escaping Cre-mediated recombination progressively populated islets. RIPCreIrs2KO and NesCreIrs2KO mice displayed hyperphagia, obesity, and increased body length, which suggests altered melanocortin action. POMCCreIrs2KO mice did not display this phenotype. RIPCreIrs2KO and NesCreIrs2KO mice retained leptin sensitivity, which suggests that CNS Irs2 pathways are not required for leptin action. NesCreIrs2KO and POMCCreIrs2KO mice did not display reduced beta cell mass, but NesCreIrs2KO mice displayed mild abnormalities of glucose homeostasis. RIPCre neurons did not express POMC or neuropeptide Y. Insulin and a melanocortin agonist depolarized RIPCre neurons, whereas leptin was ineffective. Insulin hyperpolarized and leptin depolarized POMC neurons. Our findings demonstrate a critical role for IRS2 in beta cell and hypothalamic function and provide insights into the role of RIPCre neurons, a distinct hypothalamic neuronal population, in growth and energy homeostasis. [ABSTRACT FROM AUTHOR]

Insulin has been shown to impact on learning and memory in both humans and animals, but the downstream signaling mechanisms involved are poorly characterized. Insulin receptor substrate-2 (Irs2) is an adaptor protein that couples activation of insulin- and insulin-like growth factor-1 receptors to downstream signaling pathways. Here, we have deleted Irs2, either in the whole brain or selectively in the forebrain, using the nestin Cre- or D6 Cre-deleter mouse lines, respectively. We show that brain- and forebrain-specific Irs2 knockout mice have enhanced hippocampal spatial reference memory. Furthermore, NesCreIrs2KO mice have enhanced spatial working memory and contextual- and cued-fear memory. Deletion of Irs2 in the brain also increases PSD-95 expression and the density of dendritic spines in hippocampal area CA1, possibly reflecting an increase in the number of excitatory synapses per neuron in the hippocampus that can become activated during memory formation. This increase in activated excitatory synapses might underlie the improved hippocampal memory formation observed in NesCreIrs2KO mice. Overall, these results suggest that Irs2 acts as a negative regulator on memory formation by restricting dendritic spine generation.