[Show abstract][Hide abstract] ABSTRACT: The cocaine- and amphetamine-regulated transcript (CART) has been the subject of significant interest for over a decade. Work to decipher the detailed mechanism of CART function has been hampered by the lack of specific pharmacological tools like antagonists and the absence of a specific CART receptor(s). However, extensive research has been devoted to elucidate the role of the CART peptide and it is now evident that CART is a key neurotransmitter and hormone involved in the regulation of diverse biological processes, including food intake, maintenance of body weight, reward and addiction, stress response, psychostimulant effects and endocrine functions (Rogge et al., 2008; Subhedar et al., 2014). In this review, we focus on knowledge gained on CART's role in controlling appetite and energy homeostasis, and also address certain species differences between rodents and humans.
[Show abstract][Hide abstract] ABSTRACT: Neuropeptide Y (NPY) and noradrenaline are commonly co-expressed in sympathetic neurons. Both are key regulators of energy homeostasis and critical for stress-coping. However, little is known about the specific function of NPY in the catechoalminergic system in these regulations. Here we show that mice with NPY expression only in the noradrenergic and adrenergic cells of the catecholaminergic system (catNPY) exhibited exacerbated diet-induced obesity, lower body and brown adipose tissue temperatures compared to WT and NPY-/- mice under a HFD. Furthermore, chronic stress increased adiposity and serum corticosterone level in WT but not NPY-/- mice. Re-introducing NPY specifically to the catecholaninergic system in catNPY mice restored stress responsiveness associated with increased respiratory exchange ratio and decreased liver pACC to tACC ratio. These results demonstrate catecholaminergic NPY signalling is critical in mediating diet- and chronic stress-induced fat gain via effects on diet-induced thermogenesis and stress-induced increases in corticosterone levels and lipogenic capacity.
[Show abstract][Hide abstract] ABSTRACT: Objective
Orexigenic neuropeptide Y (NPY) and dynorphin (DYN) regulate energy homeostasis. Single NPY or dynorphin deletion reduces food intake or increases fat loss. Future developments of obesity therapeutics involve targeting multiple pathways. We hypothesised that NPY and dynorphin regulate energy homeostasis independently, thus double NPY and dynorphin ablation would result in greater weight and/or fat loss than the absence of NPY or dynorphin alone.
Design and Methods
We generated single and double NPY and dynorphin knockout mice (NPYΔ, DYNΔ, NPYDYNΔ) and compared body weight, adiposity, feeding behaviour, glucose homeostasis and brown adipose tissue uncoupling protein-1 (UCP-1) expression to wildtype counterparts.
Body weight and adiposity were significantly increased in NPYDYNΔ, but not in NPYΔ or DYNΔ. This was not due to increased food intake or altered UCP-1 expression, which were not significantly altered in double knockouts. NPYDYNΔ mice demonstrated increased body weight loss after a 24-hour fast, with no effect on serum glucose levels after glucose injection.
Contrary to the predicted phenotype delineated from single knockouts, double NPY and dynorphin deletion resulted in heavier mice, with increased adiposity, despite no significant changes in food intake or UCP-1 activity. This indicates that combining long-term opioid antagonism with blockade of NPY-ergic systems may not produce anti-obesity effects.
[Show abstract][Hide abstract] ABSTRACT: The potent Y1 receptor antagonist, 1229U91 has an unusual cyclic dimer structure that makes syntheses of analogue series quite challenging. We have examined three new routes to the synthesis of such peptides that has given access to novel structural variants including heterodimeric compounds, ring size variants and labelled conjugates. These compounds, including a fluorescently labelled analogue VIII show potent antagonism that can be utilised in studying Y1 receptor pharmacology.
[Show abstract][Hide abstract] ABSTRACT: Y-receptors control energy homeostasis, but the role of Npy6 receptors (Npy6r) is largely unknown. Young Npy6r-deficient (Npy6r(-/-)) mice have reduced body weight, lean mass, and adiposity, while older and high-fat-fed Npy6r(-/-) mice have low lean mass with increased adiposity. Npy6r(-/-) mice showed reduced hypothalamic growth hormone releasing hormone (Ghrh) expression and serum insulin-like growth factor-1 (IGF-1) levels relative to WT. This is likely due to impaired vasoactive intestinal peptide (VIP) signaling in the suprachiasmatic nucleus (SCN), where we found Npy6r coexpressed in VIP neurons. Peripheral administration of pancreatic polypeptide (PP) increased Fos expression in the SCN, increased energy expenditure, and reduced food intake in WT, but not Npy6r(-/-), mice. Moreover, intraperitoneal (i.p.) PP injection increased hypothalamic Ghrh mRNA expression and serum IGF-1 levels in WT, but not Npy6r(-/-), mice, an effect blocked by intracerebroventricular (i.c.v.) Vasoactive Intestinal Peptide (VPAC) receptors antagonism. Thus, PP-initiated signaling through Npy6r in VIP neurons regulates the growth hormone axis and body composition.
[Show abstract][Hide abstract] ABSTRACT: Hormone peptide tyrosine-tyrosine (PYY) is secreted into circulation from the gut L-endocrine cells in response to food intake, thus inducing satiation during interaction with its preferred receptor, Y2R. Clinical applications of systemically administered PYY for the purpose of reducing body weight were compromised as a result of the common side effect of visceral sickness. We describe here a novel approach of elevating PYY in saliva in mice, which, although reliably inducing strong anorexic responses, does not cause aversive reactions. The augmentation of salivary PYY activated forebrain areas known to mediate feeding, hunger, and satiation while minimally affecting brainstem chemoreceptor zones triggering nausea. By comparing neuronal pathways activated by systemic versus salivary PYY, we identified a metabolic circuit associated with Y2R-positive cells in the oral cavity and extending through brainstem nuclei into hypothalamic satiety centers. The discovery of this alternative circuit that regulates ingestive behavior without inducing taste aversion may open the possibility of a therapeutic application of PYY for the treatment of obesity via direct oral application.
Journal of Neuroscience 11/2013; 33(47):18368-18380. · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It has been hypothesized that the peripheral taste system may be modulated in the context of an animal's metabolic state. One purported mechanism for this phenomenon is that circulating gastrointestinal peptides modulate the functioning of the peripheral gustatory system. Recent evidence suggests endocrine signaling in the oral cavity can influence food intake (FI) and satiety. We hypothesized that these hormones may be affecting FI by influencing taste perception. We used immunohistochemistry along with genetic knockout models and the specific reconstitution of peptide YY (PYY) in saliva using gene therapy protocols to identify a role for PYY signaling in taste. We show that PYY is expressed in subsets of taste cells in murine taste buds. We also show, using brief-access testing with PYY knockouts, that PYY signaling modulates responsiveness to bitter-tasting stimuli, as well as to lipid emulsions. We show that salivary PYY augmentation, via viral vector therapy, rescues behavioral responsiveness to a lipid emulsion but not to bitter stimuli and that this response is likely mediated via activation of Y2 receptors localized apically in taste cells. Our findings suggest distinct functions for PYY produced locally in taste cells vs. that circulating systemically.-La Sala, M. S., Hurtado, M. D., Brown, A. R., Bohórquez, D. V., Liddle, R. A., Herzog, H., Zolotukhin, S., Dotson, C. D. Modulation of taste responsiveness by the satiation hormone peptide YY.
[Show abstract][Hide abstract] ABSTRACT: Immune challenge of mice with Bacille Calmette-Guérin (BCG) has been reported to cause transient weight loss and a behavioural sickness response. While BCG-induced depression involves the kynurenine pathway, weight loss occurs independently of this factor. Since neuropeptide Y (NPY) and peptide YY (PYY) are involved in the regulation of food intake, we hypothesized that they play a role in the BCG-induced weight loss.
Male wild-type (WT), PYY knockout (PYY-/-), NPY knockout (NPY-/-) and NPY-/-;PYY-/- double knockout mice were injected with vehicle or BCG (approximately 10(8) CFU per mouse), and their weight, locomotion, exploration and ingestion were recorded for 2 weeks post-treatment.
Deletion of PYY and NPY aggravated the BCG-induced loss of body weight, which was most pronounced in NPY-/-;PYY-/- mice (maximum loss: 15 %). The weight loss in NPY-/-;PYY-/- mice did not normalize during the 2 week observation period. BCG suppressed the circadian pattern of locomotion, exploration and food intake. However, these changes took a different time course than the prolonged weight loss caused by BCG in NPY-/-;PYY-/- mice. The effect of BCG to increase circulating interleukin-6 (measured 16 days post-treatment) remained unaltered by knockout of PYY, NPY or NPY plus PYY.
These data show that NPY and PYY are both required to protect from the action of BCG-evoked immune challenge to cause prolonged weight loss and disturb energy balance. The findings attest to an important role of NPY and PYY in orchestrating homeostatic reactions to infection and immune stimulation.
British Journal of Pharmacology 08/2013; · 5.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Expression of dynorphin, an endogenous opioid peptide, increases with age and has been associated with memory impairments in rats. In human, prodynorphin (Pdyn) gene polymorphisms might be linked to cognitive function in the elderly. Moreover, elevated dynorphin levels have been reported in postmortem samples from Alzheimer's disease patients. However, the cellular and molecular processes affected by higher dynorphin levels during aging remain unknown. Using Pdyn(-/-) mice, we observed significant changes in the function and expression of Group 1 metabotropic glutamate receptor (mGluR). Compared with age-matched wild-type (WT) littermates, we found increased expression of mGluR1α and mGluR5 in the hippocampus and cortex of old, but not young, Pdyn(-/-) mice. Increased Group 1 mGluR expression in aged Pdyn(-/-) mice was associated with enhanced mGluR-mediated long-term depression, a form of synaptic plasticity. Notably, whereas aged WT mice developed spatial and recognition memory deficits, aged Pdyn(-/-) mice performed similarly as young mice. Pharmacological treatments with 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide, a positive modulator of mGlu5 receptors, or norbinaltorphimine, an antagonist for dynorphin-targeted κ-opioid receptor, rescued memory in old WT mice. Conversely, mGlu5 receptor antagonist 2-methyl-6-(phenylethynyl)pyridine hydrochloride impaired spatial memory of old Pdyn(-/-) mice. Intact cognition in aged Pdyn(-/-) mice paralleled with increased expression of Group 1 mGluR-related genes Homer 1a and Arc. Finally, aged Pdyn(-/-) mice displayed less anxiety-related behaviors than age-matched WT mice. Together, our results suggest that elevated Pdyn expression during normal aging reduces mGluR expression and signaling, which in turn impairs cognitive functions and increases anxiety.
Journal of Neuroscience 07/2013; 33(31):12792-804. · 6.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Objective: PYY3-36 and PP potently inhibit food intake in rodents and humans, however, it is unclear whether they have any synergistic/additive interaction in decreasing food intake. Design and Methods: Fasted WT, Y2(-/-) , Y4(-/-) or Y2Y4(-/-) mice were i.p. administrated with saline, PYY3-36 and/or PP. Results: We demonstrate that combined injection of PYY3-36 and PP reduces food intake in an additive manner. This effect is mediated via Y2 and Y4 receptors, respectively. We demonstrate that PYY3-36 and PP activate distinct neuronal pathways in the hypothalamus, as demonstrated by immunostaining for c-fos, which shows distinct patterns in response to either hormone. After PYY3-36 injection, neurons in the dorsal aspect of the Arc, PVN and DMH are activated with minimal responses seen in the VMH and LHA of WT mice. These effects are absent in Y2(-/-) mice. PP activates preferably the lateral aspect of the Arc, the DMH, VMH and LHA in a Y4 receptor-dependent manner. Importantly, the expression pattern of c-fos immunoreactive neurons induced by combined treatment appears to be the sum of the effects of single treatments rather than a result of synergistic interaction. Conclusions: These findings demonstrate that PYY3-36 and PP activate distinct pathways in the hypothalamus to reduce food intake in an additive manner.
[Show abstract][Hide abstract] ABSTRACT: The opioid system is well recognized as an important regulator of appetite and energy balance. We now hypothesized that the hypothalamic opioid system might modulate the orexigenic effect of ghrelin. Using pharmacological and gene silencing approaches we demonstrate that ghrelin utilizes a hypothalamic kappa opioid receptor (KOR) pathway to increase food intake in rats. Pharmacological blockade of KOR decreases the acute orexigenic effect of ghrelin. Inhibition of KOR expression in the hypothalamic arcuate nucleus is sufficient to blunt ghrelin-induced food intake. By contrast, the specific inhibition of KOR expression in the ventral tegmental area does not affect central ghrelin-induced feeding. This new pathway is independent of ghrelin-induced AMPK activation, but modulates the levels of the transcription factors and orexigenic neuropeptides triggered by ghrelin to finally stimulate feeding. Our novel data implicate hypothalamic KOR signaling in the orexigenic action of ghrelin.Neuropsychopharmacology accepted article preview online, 24 January 2013; doi:10.1038/npp.2013.28.