Urocortins: emerging metabolic and energy homeostasis perspectives

Stress and the CRH System, Norepinephrine, Depression, and Type 2 Diabetes

Major depressive disorder (MDD) increases the risk of type 2 diabetes (T2D) by 60% in untreated patients, and hypercortisolism is common in MDD as well as in some patients with T2D. Patients with MDD, despite hypercortisolism, show inappropriately normal levels of corticotropin-releasing hormone (CRH) and plasma adrenocorticotropin (ACTH) in the cerebrospinal fluid, which might implicate impaired negative feedback. Also, a positive feedback loop of the CRH-norepinephrine (NE)-CRH system may be involved in the hypercortisolism of MDD and T2D. Dysfunctional CRH receptor 1 (CRHR1) and CRH receptor 2 (CRHR2), both of which are involved in glucose regulation, may explain hypercortisolism in MDD and T2D, at least in a subgroup of patients. CRHR1 increases glucose-stimulated insulin secretion. Dysfunctional CRHR1 variants can cause hypercortisolism, leading to serotonin dysfunction and depression, which can contribute to hyperglycemia, insulin resistance, and increased visceral fat, all of which are characteristics of T2D. CRHR2 is implicated in glucose homeostasis through the regulation of insulin secretion and gastrointestinal functions, and it stimulates insulin sensitivity at the muscular level. A few studies show a correlation of the CRHR2 gene with depressive disorders. Based on our own research, we have found a linkage and association (i.e., linkage disequilibrium [LD]) of the genes CRHR1 and CRHR2 with MDD and T2D in families with T2D. The correlation of CRHR1 and CRHR2 with MDD appears stronger than that with T2D, and per our hypothesis, MDD may precede the onset of T2D. According to the findings of our analysis, CRHR1 and CRHR2 variants could modify the response to prolonged chronic stress and contribute to high levels of cortisol, increasing the risk of developing MDD, T2D, and the comorbidity MDD-T2D. We report here the potential links of the CRH system, NE, and their roles in MDD and T2D.

Functional characterization of two DH44R genes associated with starvation and desiccation in Rhopalosiphum padi (Hemiptera: Aphididae)

CRF-like diuretic hormone receptor (CRF/DHR), also known as DH44R in insects, are G-protein coupled receptors (GPCRs) that play a role in regulating osmotic balance in various insect species. These receptors have the potential to be targeted for the development of insecticides. However, our understanding of the role of DHR genes in aphids, including Rhopalosiphum padi, a major wheat pest, is currently limited. In this study, we isolated and characterized two R. padi DHRs (RpDHR1 and RpDHR2). The expression levels of RpDHR1 increased after starvation and were restored after re-feeding. The expression levels of RpDHR1 gene decreased significantly 24 h after injection of dsRNA targeting the gene. Knockdown of RpDHR1 increased aphid mortality under starvation conditions (24, 36, 48 and 60 h). Under starvation and desiccation condition, the aphid mortality decreased after knockdown of RpDHR1. This is the first study to report the role of DHR genes in the starvation and desiccation response of aphids. The results suggest that RpDHR1 is involved in the resistance of R. padi to starvation and dehydration, making it a potential target for insecticide development. Novel insecticides could be created by utilizing DHR agonists to disrupt the physiological processes of insect pests.

Urocortin3: Local inducer of somatostatin release and bellwether of beta cell maturity

Urocortin 3 (UCN3) is a peptide hormone expressed in pancreatic islets of Langerhans of both human alpha and human beta cells and solely in murine beta cells. UCN3 signaling acts locally within the islet to activate its cognate receptor, corticotropin releasing hormone receptor 2 (CRHR2), which is expressed by delta cells, to potentiate somatostatin (SST) negative feedback to reduce islet cell hormone output. The functional importance of UCN3 signaling in the islet is to modulate the amount of SST tone allowing for finely tuned regulation of insulin and glucagon secretion. UCN3 signaling is a hallmark of functional beta cell maturation, increasing the beta cell glucose threshold for insulin secretion. In doing so, UCN3 plays a relevant functional role in accurately maintaining blood glucose homeostasis. Additionally, UCN3 acts as an indicator of beta cell maturation and health, as UCN3 is not expressed in immature beta cells and is downregulated in dedifferentiated and dysfunctional beta cell states. Here, we review the mechanistic underpinnings of UCN3 signaling, its net effect on islet cell hormone output, as well as its value as a marker for beta cell maturation and functional status.

Leptin coordinates efferent sympathetic outflow to the white adipose tissue through the midbrain centrally-projecting Edinger-Westphal nucleus in male rats

The centrally-projecting Edinger-Westphal nucleus (EWcp) hosts a large population of neurons expressing urocortin 1 (Ucn1) and about half of these neurons also express the leptin receptor (LepRb). Previously, we have shown that the peripheral adiposity hormone leptin signaling energy surfeit modulates EWcp neurons' activity. Here, we hypothesized that Ucn1/LepRb neurons in the EWcp would act as a crucial neuronal node in the brain-white adipose tissue (WAT) axis modulating efferent sympathetic outflow to the WAT. We showed that leptin bound to neurons of the EWcp stimulated STAT3 phosphorylation, and increased Ucn1-production in a time-dependent manner. Besides, retrograde transneuronal tract-tracing using pseudorabies virus (PRV) identified EWcp Ucn1 neurons connected to WAT. Interestingly, reducing EWcp Ucn1 contents by ablating EWcp LepRb-positive neurons with leptin-saporin, did not affect food intake and body weight gain, but substantially (+26%) increased WAT weight accompanied by a higher plasma leptin level and changed plasma lipid profile. We also found that ablation of EWcp Ucn1/LepRb neurons resulted in lower respiratory quotient and oxygen consumption one week after surgery, but was comparable to sham values after 3 and 5 weeks of surgery. Taken together, we report that EWcp/LepRb/Ucn1 neurons not only respond to leptin signaling but also control WAT size and fat metabolism without altering food intake. These data suggest the existence of a EWcp-WAT circuitry allowing an organism to recruit fuels without being able to eat in situations such as the fight-or-flight response.

Novel Pituitary Actions of TAC4 Gene Products in Teleost

Tachykinin 4 (TAC4) is the latest member of the tachykinin family involved in several physiological functions in mammals. However, little information is available about TAC4 in teleost. In the present study, we firstly isolated TAC4 and six neurokinin receptors (NKRs) from grass carp brain and pituitary. Sequence analysis showed that grass carp TAC4 could encode two mature peptides (namely hemokinin 1 (HK1) and hemokinin 2 (HK2)), in which HK2 retained the typical FXGLM motif in C-terminal of tachyinin, while HK1 contained a mutant VFGLM motif. The ligand-receptor selectivity showed that HK2 could activate all 6 NKRs but with the highest activity for the neurokinin receptor 2 (NK2R). Interestingly, HK1 displayed a very weak activation for each NKR isoform. In grass carp pituitary cells, HK2 could induce prolactin (PRL), somatolactin α (SLα), urotensin 1 (UTS1), neuromedin-B 1 (NMB1), cocaine- and amphetamine-regulated transcript 2 (CART2) mRNA expression mediated by NK2R and neurokinin receptor 3 (NK3R) via activation cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA), phospholipase C (PLC)/inositol 1,4,5-triphosphate (IP3)/protein kinase C (PKC) and calcium²⁺ (Ca²⁺)/calmodulin (CaM)/calmodulin kinase-II (CaMK II) cascades. However, the corresponding stimulatory effects triggered by HK1 were found to be notably weaker. Furthermore, based on the structural base for HK1, our data suggested that a phenylalanine (F) to valine (V) substitution in the signature motif of HK1 might have contributed to its weak agonistic actions on NKRs and pituitary genes regulation.

Modified UCN2 peptide treatment improves skeletal muscle mass and function in mouse models of obesity-induced insulin resistance

BACKGROUND

Type 2 diabetes and obesity are often seen concurrently with skeletal muscle wasting, leading to further derangements in function and metabolism. Muscle wasting remains an unmet need for metabolic disease, and new approaches are warranted. The neuropeptide urocortin 2 (UCN2) and its receptor corticotropin releasing factor receptor 2 (CRHR2) are highly expressed in skeletal muscle and play a role in regulating energy balance, glucose metabolism, and muscle mass. The aim of this study was to investigate the effects of modified UCN2 peptides as a pharmaceutical therapy to counteract the loss of skeletal muscle mass associated with obesity and casting immobilization.

METHODS

High-fat-fed mice (C57Bl/6J; 26 weeks old) and ob/ob mice (11 weeks old) were injected daily with a PEGylated (Compound A) and non-PEGylated (Compound B) modified human UCN2 at 0.3 mg/kg subcutaneously for 14 days. A separate group of chow-fed C57Bl/6J mice (12 weeks old) was subjected to hindlimb cast immobilization and, after 1 week, received daily injections with Compound A. In vivo functional tests were performed to measure protein synthesis rates and skeletal muscle function. Ex vivo functional and molecular tests were performed to measure contractile force and signal transduction of catabolic and anabolic pathways in skeletal muscle.

RESULTS

Skeletal muscles (extensor digitorum longus, soleus, and tibialis anterior) from high-fat-fed mice treated with Compound A were ~14% heavier than muscles from vehicle-treated mice. Chronic treatment with modified UCN2 peptides altered the expression of structural genes and transcription factors in skeletal muscle in high-fat diet-induced obesity including down-regulation of Trim63 and up-regulation of Nr4a2 and Igf1 (P < 0.05 vs. vehicle). Signal transduction via both catabolic and anabolic pathways was increased in tibialis anterior muscle, with increased phosphorylation of ribosomal protein S6 at Ser^235/236 , FOXO1 at Ser²⁵⁶ , and ULK1 at Ser³¹⁷ , suggesting that UCN2 treatment modulates protein synthesis and degradation pathways (P < 0.05 vs. vehicle). Acutely, a single injection of Compound A in drug-naïve mice had no effect on the rate of protein synthesis in skeletal muscle, as measured via the surface sensing of translation method, while the expression of Nr4a3 and Ppargc1a4 was increased (P < 0.05 vs. vehicle). Compound A treatment prevented the loss of force production from disuse due to casting. Compound B treatment increased time to fatigue during ex vivo contractions of fast-twitch extensor digitorum longus muscle. Compound A and B treatment increased lean mass and rates of skeletal muscle protein synthesis in ob/ob mice.

CONCLUSIONS

Modified human UCN2 is a pharmacological candidate for the prevention of the loss of skeletal muscle mass associated with obesity and immobilization.

Agonist bias and agonist-dependent antagonism at corticotrophin releasing factor receptors

The corticotropin-releasing factor (CRF) receptors represent potential drug targets for the treatment of anxiety, stress, and other disorders. However, it is not known if endogenous CRF receptor agonists display biased signaling, how effective CRF receptor antagonists are at blocking different agonists and signaling pathways or how receptor activity-modifying proteins (RAMPs) effect these processes. This study aimed to address this by investigating agonist and antagonist action at CRF₁ and CRF₂ receptors. We used CRF₁ and CRF₂ receptor transfected Cos7 cells to assess the ability of CRF and urocortin (UCN) peptides to activate cAMP, inositol monophosphate (IP₁ ), and extracellular signal-regulated kinase 1/2 signaling and determined the ability of antagonists to block agonist-stimulated cAMP and IP₁ accumulation. The ability of RAMPs to interact with CRF receptors was also examined. At the CRF₁ receptor, CRF and UCN1 activated signaling in the same manner. However, at the CRF₂ receptor, UCN1 and UCN2 displayed similar signaling profiles, whereas CRF and UCN3 displayed bias away from IP₁ accumulation over cAMP. The antagonist potency was dependent on the receptor, agonist, and signaling pathway. CRF₁ and CRF₂ receptors had no effect on RAMP1 or RAMP2 surface expression. The presence of biased agonism and agonist-dependent antagonism at the CRF receptors offers new avenues for developing drugs tailored to activate a specific signaling pathway or block a specific agonist. Our findings suggest that the already complex CRF receptor pharmacology may be underappreciated and requires further investigation.

Progress in understanding the roles of Urocortin3 (UCN3) in the control of appetite from studies using animal models

Urocortin3 (UCN3), the newest member of corticotrophin releasing hormone (CRH) family polypeptides, is an anorexic factor discovered in 2001, which has a strong inhibitory effect on animal appetite regulation. UCN3 is widely distributed in various tissues of animals and has many biological functions. Based on the research progress of UCN3 on mammals and non-mammals, this paper summarized the discovery, tissue distribution, appetite regulation and mechanism of UCN3 in animals, in order to provide a reference for feeding regulation and growth in mammals and fish in further research and production.

Urocortins in the mammalian endocrine system

Urocortins (Ucns), peptides belonging to the corticotropin-releasing hormone (CRH) family, are classified into Ucn1, Ucn2, and Ucn3. They are involved in regulating several body functions by binding to two G protein-coupled receptors: receptor type 1 (CRHR1) and type 2 (CRHR2). In this review, we provide a historical overview of research on Ucns and their receptors in the mammalian endocrine system. Although the literature on the topic is limited, we focused our attention particularly on the main role of Ucns and their receptors in regulating the hypothalamic–pituitary–adrenal and thyroid axes, reproductive organs, pancreas, gastrointestinal tract, and other tissues characterized by “diffuse” endocrine cells in mammals. The prominent function of these peptides in health conditions led us to also hypothesize an action of Ucn agonists/antagonists in stress and in various diseases with its critical consequences on behavior and physiology. The potential role of the urocortinergic system is an intriguing topic that deserves further in-depth investigations to develop novel strategies for preventing stress-related conditions and treating endocrine diseases.

Modified UCN2 Peptide Acts as an Insulin Sensitizer in Skeletal Muscle of Obese Mice

The neuropeptide urocortin 2 (UCN2) and its receptor corticotropin-releasing hormone receptor 2 (CRHR2) are highly expressed in skeletal muscle and play a role in regulating energy balance and glucose metabolism. We investigated a modified UCN2 peptide as a potential therapeutic agent for the treatment of obesity and insulin resistance, with a specific focus on skeletal muscle. High-fat-fed mice (C57BL/6J) were injected daily with a PEGylated UCN2 peptide (compound A) at 0.3 mg/kg subcutaneously for 14 days. Compound A reduced body weight, food intake, whole-body fat mass, and intramuscular triglycerides compared with vehicle-treated controls. Furthermore, whole-body glucose tolerance was improved by compound A treatment, with increased insulin-stimulated Akt phosphorylation at Ser⁴⁷³ and Thr³⁰⁸ in skeletal muscle, concomitant with increased glucose transport into extensor digitorum longus and gastrocnemius muscle. Mechanistically, this is linked to a direct effect on skeletal muscle because ex vivo exposure of soleus muscle from chow-fed lean mice to compound A increased glucose transport and insulin signaling. Moreover, exposure of GLUT4-Myc-labeled L6 myoblasts to compound A increased GLUT4 trafficking. Our results demonstrate that modified UCN2 peptides may be efficacious in the treatment of type 2 diabetes by acting as an insulin sensitizer in skeletal muscle.

The CRF Family of Neuropeptides and their Receptors - Mediators of the Central Stress Response

Background:

Dysregulated stress neurocircuits, caused by genetic and/or environmental changes, underlie the development of many neuropsychiatric disorders. Corticotropin-releasing factor (CRF) is the major physiological activator of the hypothalamic-pituitary-adrenal (HPA) axis and conse-quently a primary regulator of the mammalian stress response. Together with its three family members, urocortins (UCNs) 1, 2, and 3, CRF integrates the neuroendocrine, autonomic, metabolic and behavioral responses to stress by activating its cognate receptors CRFR1 and CRFR2.

Objective:

Here we review the past and current state of the CRF/CRFR field, ranging from pharmacologi-cal studies to genetic mouse models and virus-mediated manipulations.

Results:

Although it is well established that CRF/CRFR1 signaling mediates aversive responses, includ-ing anxiety and depression-like behaviors, a number of recent studies have challenged this viewpoint by revealing anxiolytic and appetitive properties of specific CRF/CRFR1 circuits. In contrast, the UCN/CRFR2 system is less well understood and may possibly also exert divergent functions on physiol-ogy and behavior depending on the brain region, underlying circuit, and/or experienced stress conditions.

Conclusion:

A plethora of available genetic tools, including conventional and conditional mouse mutants targeting CRF system components, has greatly advanced our understanding about the endogenous mecha-nisms underlying HPA system regulation and CRF/UCN-related neuronal circuits involved in stress-related behaviors. Yet, the detailed pathways and molecular mechanisms by which the CRF/UCN-system translates negative or positive stimuli into the final, integrated biological response are not completely un-derstood. The utilization of future complementary methodologies, such as cell-type specific Cre-driver lines, viral and optogenetic tools will help to further dissect the function of genetically defined CRF/UCN neurocircuits in the context of adaptive and maladaptive stress responses.

Urocortins and their unfolding role in mammalian social behavior

The corticotropin-releasing factor (CRF) system is well known for its major role in coordinating the endocrine, autonomic and behavioral responses to stress. These functions have been shown to be mediated mainly by the binding of the CRF neuropeptide to its specific receptor CRFR1. Yet, the CRF system comprises several more neuropeptides, including the three urocortins, UCN1, UCN2 and UCN3, of which the latter two bind specifically to a distinct receptor-CRFR2. Unlike the brain-wide abundant expression of CRF and CRFR1, the brain expression of the urocortins and CRFR2 is rather restricted and seems to be focused in limbic areas associated with social behavior. Here, we will review accumulating evidence from recent studies that unfold the role of UCN2 and UCN3 in regulating mammalian social behavior, via activation of CRFR2.

The Corticotropin-Releasing Factor Family: Physiology of the Stress Response

The physiological stress response is responsible for the maintenance of homeostasis in the presence of real or perceived challenges. In this function, the brain activates adaptive responses that involve numerous neural circuits and effector molecules to adapt to the current and future demands. A maladaptive stress response has been linked to the etiology of a variety of disorders, such as anxiety and mood disorders, eating disorders, and the metabolic syndrome. The neuropeptide corticotropin-releasing factor (CRF) and its relatives, the urocortins 1–3, in concert with their receptors (CRFR1, CRFR2), have emerged as central components of the physiological stress response. This central peptidergic system impinges on a broad spectrum of physiological processes that are the basis for successful adaptation and concomitantly integrate autonomic, neuroendocrine, and behavioral stress responses. This review focuses on the physiology of CRF-related peptides and their cognate receptors with the aim of providing a comprehensive up-to-date overview of the field. We describe the major molecular features covering aspects of gene expression and regulation, structural properties, and molecular interactions, as well as mechanisms of signal transduction and their surveillance. In addition, we discuss the large body of published experimental studies focusing on state-of-the-art genetic approaches with high temporal and spatial precision, which collectively aimed to dissect the contribution of CRF-related ligands and receptors to different levels of the stress response. We discuss the controversies in the field and unravel knowledge gaps that might pave the way for future research directions and open up novel opportunities for therapeutic intervention.

Stress-induced suppression of neuropeptide Y-induced hunger in anorexic chicks involves corticotrophin-releasing factor signalling and the paraventricular nucleus of the hypothalamus

The Virginia lines of chickens have been selected for low (LWS) or high (HWS) juvenile body weight and have different severities of anorexia and obesity, respectively. The LWS that are exposed to stressors at hatch are refractory to neuropeptide Y (NPY)-induced food intake and the objective of the present study was to determine the underlying mechanisms. Chicks were exposed to a stressor (-20°C for 6 minutes and 22°C and delayed access to food for 24 hours) after hatching and the hypothalamic nuclei, including the lateral hypothalamus (LH), paraventricular nucleus (PVN), ventromedial hypothalamus (VMH) and arcuate nucleus (ARC), were collected 5 days later. In LWS but not HWS, stress exposure up-regulated corticotrophin-releasing factor (CRF), CRF receptor subtypes 1 and 2 (CRFR1 and CRFR2, respectively), melanocortin receptor 4 and urocortin 3 in the PVN, as well as CRFR2 mRNA in the VMH and ARC. In LWS, stress exposure was also associated with greater NPY and NPY receptor subtype 5 mRNA in the ARC and PVN, respectively, as well as decreased agouti-related peptide mRNA in the ARC. In HWS, stress exposure was associated with increased CRFR1 and decreased cocaine- and amphetamine-regulated transcript in the ARC and PVN, respectively. Refractoriness of the food intake response to NPY in LWS may thus result from the over-riding anorexigenic tone in the PVN associated with CRF signalling. Indeed, the orexigenic effect of NPY was restored when LWS were injected with a CRF receptor antagonist, astressin, before stress exposure. The results of the present study provide insights into the molecular basis of eating disorders and suggest that CRF signalling in the PVN may exacerbate the anorexic phenotype in the presence of environmental stressors.

All mixed up: defining roles for β-cell subtypes in mature islets

Following differentiation during fetal development, β cells further adapt to their postnatal role through functional maturation. While adult islets are thought to contain functionally mature β cells, recent analyses of transgenic rodent and human pancreata reveal a number of novel heterogeneity markers in mammalian β cells. The marked heterogeneity long after maturation raises the prospect that diverse populations harbor distinct roles aside from glucose-stimulated insulin secretion. In this review, we outline our current understanding of the β-cell maturation process, emphasize recent literature on novel heterogeneity markers, and offer perspectives on reconciling the findings from these two areas.

Anatomical Organization of Urocortin 3-Synthesizing Neurons and Immunoreactive Terminals in the Central Nervous System of Non-Human Primates [Sapajus spp.]

Urocortin 3 (UCN3) is a neuropeptide member of the corticotropin-releasing factor (CRF) peptide family that acts as a selective endogenous ligand for the CRF, subtype 2 (CRF₂) receptor. Immunohistochemistry and in situ hybridization data from rodents revealed UCN3-containing neurons in discrete regions of the central nervous system (CNS), such as the medial preoptic nucleus, the rostral perifornical area (PFA), the medial nucleus of the amygdala and the superior paraolivary nucleus. UCN3-immunoreactive (UCN3-ir) terminals are distributed throughout regions that mostly overlap with regions of CRF₂ messenger RNA (mRNA) expression. Currently, no similar mapping exists for non-human primates. To better understand the role of this neuropeptide, we aimed to study the UCN3 distribution in the brains of New World monkeys of the Sapajus genus. To this end, we analyzed the gene and peptide sequences in these animals and performed immunohistochemistry and in situ hybridization to identify UCN3 synthesis sites and to determine the distribution of UCN3-ir terminals. The sequencing of the Sapajus spp. UCN3-coding gene revealed 88% and 65% identity to the human and rat counterparts, respectively. Additionally, using a probe generated from monkey cDNA and an antiserum raised against human UCN3, we found that labeled cells are mainly located in the hypothalamic and limbic regions. UCN3-ir axons and terminals are primarily distributed in the ventromedial hypothalamic nucleus (VMH) and the lateral septal nucleus (LS). Our results demonstrate that UCN3-producing neurons in the CNS of monkeys are phylogenetically conserved compared to those of the rodent brain, that the distribution of fibers agrees with the distribution of CRF₂ in other primates and that there is anatomical evidence for the participation of UCN3 in neuroendocrine control in primates.

The relationship of urocortin-2 with insulin resistance patients having PCOS

In this study, we aimed to compare the serum urocortin-2 (UCN2) levels in women with polycystic ovary syndrome (PCOS) and healthy women. Thirty-eight patients with PCOS and 41 healthy women were included in the study whose age and BMI matched. The fasting serum glucose, insulin, free testosterone, hs-CRP and UCN2 levels of the all participants were examined. HOMA-IR formula was used in order to calculate the insulin resistance. Circulating UCN2 levels were significantly elevated in women with PCOS compared with controls (142.93 ± 59.48 versus 98.56 ± 65.01 pg/ml, p = 0.002). FBG, serum insulin, hs-CRP and HOMA-IR levels were found to be increased in women with PCOS. There was a positive correlation between UCN2 and free-testosterone in only PCOS group (r = 0.235, p = 0.027). Multivariate logistic regression analyses revealed that the odds ratio for PCOS was 2.31 for patients in the highest quartile of UCN2 compared with those in the lowest quartile (OR = 2.31, 95% CI = 1.88-2.83, p=0.021). Multiple linear regression analysis revealed that HOMA-IR, hs-CRP and free-testosterone independently predicted UCN2 levels (p < 0.05). UCN2 levels were significantly higher in PCOS cases when compared to control group. UCN2 is thought to be effective on pathophysiology of PCOS by paracrine and autocrine pathways.

High-Sensitivity Sandwich ELISA for Plasma NT-proUcn2: Plasma Concentrations and Relationship to Mortality in Heart Failure

BACKGROUND

Urocortin 2 (Ucn2) has powerful hemodynamic, renal, and neurohormonal actions and likely participates in normal circulatory homeostasis and the compensatory response to heart failure (HF). A validated assay for endogenous circulating Ucn2 would facilitate investigations into Ucn2 physiology and elucidate its derangement and potential as a biomarker in heart disease.

METHOD

We developed a chemiluminescence-based sandwich ELISA to measure plasma N-terminal (NT)-proUcn2 in non-HF patients (control; n = 160) and HF patients with reduced (HFREF; n = 134) and preserved (HFPEF; n = 121) left ventricular ejection fraction (LVEF).

RESULTS

The ELISA had a limit of detection of 8.47 ng/L (1.52 pmol/L) and working range of 23.8–572 ng/L. Intra- and interassay CV and total error were 4.8, 16.2, and 17.7%, respectively. The median (interquartile range) plasma NT-proUcn2 concentration in controls was 112 (86–132) ng/L. HFREF, HFPEF, and all HF plasma concentrations were significantly increased [117 (98–141) ng/L, P = 0.0007; 119 (93–136) ng/L, P = 0.0376, and 119 (97–140) ng/L, P = 0.001] compared with controls but did not differ significantly between HFREF and HFPEF. NT-proUcn2 was modestly related to age (r = 0.264, P = 0.001) and cardiac troponin T (r = 0.258, P = 0.001) but not N-terminal pro-B-type natriuretic peptide, body mass index, LVEF, or estimated glomerular filtration rate. On multivariate analysis, plasma NT-proUcn2 was independently and inversely related to 2-year mortality in HF.

CONCLUSIONS

The validated ELISA measured human NT-proUcn2 in plasma and showed modest but significant increases in HF patients compared with controls. In HF, the unusual inverse relationship between plasma NT-proUcn2 and 2-year mortality portends potential prognostic value but requires further corroboration.

Adrenal and Ovarian Phenotype of a Tissue-Specific Urocortin 2-Overexpressing Mouse Model

Urocortin 2 (UCN2) is a neuropeptide of the CRH family, involved in homeostatic mechanisms, the stress response, and control of anxiety. To elucidate the effects of UCN2 on steroidogenesis, we developed a mouse model that allows a Cre recombinase-determined conditional overexpression of UCN2 (UCN2-COE). In these mice SF1-Cre-driven overexpression of UCN2 was restricted to the adrenal glands, gonads, and parts of the hypothalamus. UCN2-COE animals of both sexes revealed significantly higher plasma UCN2 levels and significantly higher UCN2 expression levels in the adrenals and ovaries. In contrast, the baseline expression of UCN2 was already high in the testes of control mice with no further increase achievable in UCN2-COE animals. Adrenal steroidogenesis of UCN2-COE animals was investigated under baseline conditions, upon an ACTH stimulation test, and following a restraint stress test. A tendency toward lower expression of steroidogenic enzymes was detectable in UCN2-COE animals of both sexes with slight differences between males and females. A similar reduction in the expression levels of the final steps of ovarian steroidogenesis, accompanied by reduced plasma estradiol levels, was observed in female UCN2-COE animals. Thus, adrenal UCN2 overexpression resulted in down-regulation of adrenal steroidogenesis, suggesting a reduction in the stress response in the mouse (stress coping behavior). Similarly, UCN2 overexpression in the ovaries caused a decrease in steroidogenesis and reduction of follicles that had undergone ovulation. Nevertheless, this finding was not associated with reduced fertility.

Regulation of the hypothalamic-pituitary-adrenal axis by neuropeptides

The major endocrine response to stress occurs via activation of the hypothalamic-pituitary-adrenal (HPA) axis, leading ultimately to increases in circulating glucocorticoids, which are essential for the metabolic adaptation to stress. The major players in the HPA axis are the hypothalamic neuropeptide, corticotropin releasing hormone (CRH), the pituitary hormone adrenocorticotropic hormone, and the negative feedback effects of adrenal glucocorticoids. In addition, a number of other neuropeptides, including vasopressin (VP), angiotensin II, oxytocin, pituitary adenylate cyclase activating peptide, orexin and cholecystokinin, and nesfatin can affect HPA axis activity by influencing the expression and secretion of CRH, and also by modulating pituitary corticotroph function or adrenal steroidogenesis. Of these peptides, VP co-secreted with CRH from axonal terminals in the external zone of the median eminence plays a prominent role by potentiating the stimulatory effect of CRH and by increasing the number of pituitary corticotrophs during chronic challenge. Although the precise role and significance of many of these neuropeptides in regulating HPA axis activity requires further investigation, it is likely that they are part of a multifactorial system mediating the fine tuning of HPA axis activity during adaptation to a variety of physiological and stressful conditions.

Involvement of mTOR in Type 2 CRF Receptor Inhibition of Insulin Signaling in Muscle Cells

Type 2 corticotropin-releasing factor receptor (CRFR2) is expressed in skeletal muscle and stimulation of the receptor has been shown to inhibit the effect of insulin on glucose uptake in muscle cells. Currently, little is known about the mechanisms underlying this process. In this study, we first showed that both in vivo and in vitro CRFR2 expression in muscle was closely correlated with insulin sensitivity, with elevated receptor levels observed in insulin resistant muscle cells. Stimulation of CRFR2 by urocortin 2 (Ucn 2), a CRFR2-selective ligand, in C2C12 myotubes greatly attenuated insulin-induced glucose uptake. The inhibitory effect of CRFR2 signaling required cAMP production and is involved the mammalian target of rapamycine pathway, as rapamycin reversed the inhibitory effect of CRFR2 stimulation on insulin-induced glucose uptake. Moreover, stimulation of CRFR2 failed to inhibit glucose uptake in muscle cells induced by platelet-derived growth factor, which, similar to insulin, signals through Akt-mediated pathway but is independently of insulin receptor substrate (IRS) proteins to promote glucose uptake. This result argues that CRFR2 signaling modulates insulin's action likely at the levels of IRS. Consistent with this notion, Ucn 2 reduced insulin-induced tyrosine phosphorylation of IRS-1, and treatment with rapamycin reversed the inhibitory effect of Ucn 2 on IRS-1 and Akt phosphorylation. In conclusion, the inhibitory effect of CRFR2 signaling on insulin action is mediated by cAMP in a mammalian target of rapamycine-dependent manner, and IRS-1 is a key nodal point where CRFR2 signaling modulates insulin-stimulated glucose uptake in muscle cells.

New insights into the evolution of vertebrate CRH (corticotropin-releasing hormone) and invertebrate DH44 (diuretic hormone 44) receptors in metazoans

The corticotropin releasing hormone receptors (CRHR) and the arthropod diuretic hormone 44 receptors (DH44R) are structurally and functionally related members of the G protein-coupled receptors (GPCR) of the secretin-like receptor superfamily. We show here that they derive from a bilaterian predecessor. In protostomes, the receptor became DH44R that has been identified and functionally characterised in several arthropods but the gene seems to be absent from nematode genomes. Duplicate DH44R genes (DH44 R1 and DH44R2) have been described in some arthropods resulting from lineage-specific duplications. Recently, CRHR-DH44R-like receptors have been identified in the genomes of some lophotrochozoans (molluscs, which have a lineage-specific gene duplication, and annelids) as well as representatives of early diverging deuterostomes. Vertebrates have previously been reported to have two CRHR receptors that were named CRHR1 and CRHR2. To resolve their origin we have analysed recently assembled genomes from representatives of early vertebrate divergencies including elephant shark, spotted gar and coelacanth. We show here by analysis of synteny conservation that the two CRHR genes arose from a common ancestral gene in the early vertebrate tetraploidizations (2R) approximately 500 million years ago. Subsequently, the teleost-specific tetraploidization (3R) resulted in a duplicate of CRHR1 that has been lost in some teleost lineages. These results help distinguish orthology and paralogy relationships and will allow studies of functional conservation and changes during evolution of the individual members of the receptor family and their multiple native peptide agonists.

CRFR1 activation protects against cytokine-induced β-cell death

During the development of diabetes β-cells are exposed to elevated concentrations of proinflammatory cytokines, TNFα and IL1β, which in vitro induce β-cell death. The class B G-protein-coupled receptors (GPCRs): corticotropin-releasing factor receptor 1 (CRFR1) and CRFR2 are expressed in pancreatic islets. As downstream signaling by other class B GPCRs can protect against cytokine-induced β-cell apoptosis, we evaluated the protective potential of CRFR activation in β-cells in a pro-inflammatory setting. CRFR1/CRFR2 ligands activated AKT and CRFR1 signaling and reduced apoptosis in human islets. In rat and mouse insulin-secreting cell lines (INS-1 and MIN6), CRFR1 agonists upregulated insulin receptor substrate 2 (IRS2) expression, increased AKT activation, counteracted the cytokine-mediated decrease in BAD phosphorylation, and inhibited apoptosis. The anti-apoptotic signaling was dependent on prolonged exposure to corticotropin-releasing factor family peptides and followed PKA-mediated IRS2 upregulation. This indicates that CRFR signaling counteracts proinflammatory cytokine-mediated apoptotic pathways through upregulation of survival signaling in β-cells. Interestingly, CRFR signaling also counteracted basal apoptosis in both cultured INS-1 cells and intact human islets.

Reversal of β cell de-differentiation by a small molecule inhibitor of the TGFβ pathway

Dysfunction or death of pancreatic β cells underlies both types of diabetes. This functional decline begins with β cell stress and de-differentiation. Current drugs for type 2 diabetes (T2D) lower blood glucose levels but they do not directly alleviate β cell stress nor prevent, let alone reverse, β cell de-differentiation. We show here that Urocortin 3 (Ucn3), a marker for mature β cells, is down-regulated in the early stages of T2D in mice and when β cells are stressed in vitro. Using an insulin expression-coupled lineage tracer, with Ucn3 as a reporter for the mature β cell state, we screen for factors that reverse β cell de-differentiation. We find that a small molecule inhibitor of TGFβ receptor I (Alk5) protects cells from the loss of key β cell transcription factors and restores a mature β cell identity even after exposure to prolonged and severe diabetes.

DOI:http://dx.doi.org/10.7554/eLife.02809.001

Diabetes is a condition that develops when the body does not produce or use a hormone called insulin effectively. Insulin helps fat and muscle cells absorb glucose from the blood, and so diabetes can result in high levels of blood glucose, which can cause strokes, blindness, and heart disease.

In healthy individuals, beta cells in the pancreas (a large gland located behind the stomach) produce insulin. The beta cells develop from endocrine progenitor cells, which are unspecialised cells that can either duplicate themselves or ‘differentiate’ to form one of the specialised cell types found in the pancreas.

In diabetic patients, however, certain stresses (such as an immune attack in type-1 diabetics or insulin-resistance due to obesity, pregnancy, or ageing in type-2 diabetics) can cause mature beta cells to lose their identity in a process known as ‘de-differentiation’. This means that beta cells either revert back to an earlier stage in their development or adopt a new dysfunctional identity. When this occurs, the body loses beta cells and is unable to produce insulin.

It was not known whether de-differentiated beta cells in diabetic patients can recover to form mature beta cells that are capable of producing insulin. Additionally, the drugs currently used to treat diabetes are able to lower blood glucose levels, but these drugs do not replace the lost beta cells.

Blum et al. now show that mice stop expressing a gene called Urocortin 3 when beta cells first start to de-differentiate. Only functional beta cells express Urocortin 3, so this gene is a useful ‘marker’ that can be used to tell if a cell is a mature, functional beta cell or not. Using this system, Blum et al. found that if de-differentiated cells are transplanted into a non-diabetic mouse, they are able to revert back into mature beta cells that can produce insulin. This happens even if the cells have been de-differentiated for a long time.

Blum et al. then used this system to investigate ways of protecting against or reversing beta cell de-differentiation. Using small molecules to block the activity of a protein called TGF beta receptor 1 was found to protect against beta cell de-differentiation and to restore the identity of mature beta cells. The findings of Blum et al. represent a first step towards the possible development of new drugs to prevent or even restore the loss of healthy, mature beta cells in diabetic patients.

DOI:http://dx.doi.org/10.7554/eLife.02809.002

Molecular evolution of GPCRs: CRH/CRH receptors

Corticotrophin-releasing hormone (CRH) is the pivotal neuroendocrine peptide hormone associated with the regulation of the stress response in vertebrates. However, CRH-like peptides are also found in a number of invertebrate species. The origin of this peptide can be traced to a common ancestor of lineages leading to chordates and to arthropods, postulated to occur some 500 million years ago. Evidence indicates the presence of a single CRH-like receptor and a soluble binding protein system that acted to transduce and regulate the actions of the early CRH peptide. In vertebrates, genome duplications led to the divergence of CRH receptors into CRH1 and CRH2 forms in tandem with the development of four paralogous ligand lineages that included CRH; urotensin I/urocortin (Ucn), Ucn2 and Ucn3. In addition, taxon-specific genome duplications led to further local divergences in CRH ligands and receptors. Functionally, the CRH ligand-receptor system evolved initially as a molecular system to integrate early diuresis and nutrient acquisition. As multicellular organisms evolved into more complex forms, this ligand-receptor system became integrated with the organismal stress response to coordinate homoeostatic challenges with internal energy usage. In vertebrates, CRH and the CRH1 receptor became associated with the hypothalamo-pituitary-adrenal/interrenal axis and the initial stress response, whereas the CRH2 receptor was selected to play a greater role in diuresis, nutrient acquisition and the latter aspects of the stress response.

CRF and urocortin peptides as modulators of energy balance and feeding behavior during stress

Early on, corticotropin-releasing factor (CRF), a hallmark brain peptide mediating many components of the stress response, was shown to affect food intake inducing a robust anorexigenic response when injected into the rodent brain. Subsequently, other members of the CRF signaling family have been identified, namely urocortin (Ucn) 1, Ucn 2, and Ucn 3 which were also shown to decrease food intake upon central or peripheral injection. However, the kinetics of feeding suppression was different with an early decrease following intracerebroventricular injection of CRF and a delayed action of Ucns contrasting with the early onset after systemic injection. CRF and Ucns bind to two distinct G-protein coupled membrane receptors, the CRF1 and CRF2. New pharmacological tools such as highly selective peptide CRF1 or CRF2 agonists or antagonists along with genetic knock-in or knock-out models have allowed delineating the primary role of CRF2 involved in the anorexic response to exogenous administration of CRF and Ucns. Several stressors trigger behavioral changes including suppression of feeding behavior which are mediated by brain CRF receptor activation. The present review will highlight the state-of-knowledge on the effects and mechanisms of action of CRF/Ucns-CRF1/2 signaling under basal conditions and the role in the alterations of food intake in response to stress.

Roles for corticotropin-releasing factor receptor type 1 in energy homeostasis in mice

OBJECTIVE

Expression of corticotropin-releasing factor type 1 receptor (CRFR1) has been shown on pancreatic β cells, and its activation potentiates glucose-stimulated insulin secretion (GSIS). However, the roles of CRFR1 in energy metabolism beyond insulin release remain elusive.

MATERIALS/METHODS

We characterized the metabolic phenotypes of mice lacking CRFR1 (CRFR1KO mice) under conditions of energy excess.

RESULTS

When fed a normal diet, the glucose profile of CRFR1KO mice in response to a glucose tolerance test was similar to that of wild-type (WT) mice, while serum insulin levels were significantly lower in CRFR1KO mice, reflecting high insulin sensitivity in part due to very low glucocorticoid levels. Histology of the pancreas revealed islet hypoplasia in CRFR1KO mice, suggesting a role of CRFR1 in maintaining the β cell mass in a manner similar to incretins. In response to a high-fat diet, CRFR1KO mice showed insulin resistance, but serum insulin levels during glucose challenge remained at a low level, indicating defective GSIS. In addition, CRFR1KO mice showed resistance to diet-induced obesity and hepatic steatosis. Although total food intake was not different between CRFR1KO and WT mice, oxygen consumption was significantly increased in CRFR1KO mice. The increased energy expenditure may explain the lean phenotype of CRFR1KO mice under conditions of energy excess.

CONCLUSIONS

Our results suggest that CRFR1 plays important roles in whole body energy homeostasis, providing compelling evidence of the close relationship between energy homeostasis and the function of the hypothalamic-pituitary-adrenal axis.

Appetite-suppressing effects and interactions of centrally administered corticotropin-releasing factor, urotensin I and serotonin in rainbow trout (Oncorhynchus mykiss)

Corticotropin-releasing factor (CRF), urotensin I (UI) and serotonin (5-HT) are generally recognized as key regulators of the anorexigenic stress response in vertebrates, yet the proximal effects and potential interactions of these central messengers on food intake in salmonids are not known. Moreover, no study to date in fishes has compared the appetite-suppressing effects of CRF and UI using species-specific peptides. Therefore, the objectives of this study were to (1) assess the individual effects of synthesized rainbow trout CRF (rtCRF), rtUI as well as 5-HT on food intake in rainbow trout, and (2) determine whether the CRF and serotonergic systems interact in the regulation of food intake in this species. Intracerebroventricular (icv) injections of rtCRF and rtUI both suppressed food intake in a dose-related manner but rtUI [ED₅₀ = 17.4 ng/g body weight (BW)] was significantly more potent than rtCRF (ED₅₀ = 105.9 ng/g BW). Co-injection of either rtCRF or rtUI with the CRF receptor antagonist α-hCRF_(9–41) blocked the reduction in food intake induced by CRF-related peptides. Icv injections of 5-HT also inhibited feeding in a dose-related manner (ED₅₀ = 14.7 ng/g BW) and these effects were blocked by the serotonergic receptor antagonist methysergide. While the anorexigenic effects of 5-HT were reversed by α-hCRF_(9–41) co-injection, the appetite-suppressing effects of either rtCRF or rtUI were not affected by methysergide co-injection. These results identify CRF, UI and 5-HT as anorexigenic agents in rainbow trout, and suggest that 5-HT-induced anorexia may be at least partially mediated by CRF- and/or UI-secreting neurons.

Evolution and phylogeny of the corticotropin-releasing factor (CRF) family of peptides: expansion and specialization in the vertebrates

New sequence data on CRF family members from a number of genomes has led to the modification of our understanding of CRF evolution in the Metazoa. The corticotropin-releasing factor (CRF) family of peptides include four paralogous lineages in jawed vertebrates; CRF, urotensin-I/urocortin/sauvagine, urocortin 2 (Ucn2) and urocortin 3 (Ucn3). CRF and the urotensin-I/urocortin/sauvagine group represent a gene duplication from one lineage, whereas Ucns 2 and 3 are the result of a gene duplication in the other paralogous lineage. Both paralogous lineages are the result of a gene duplication from a single ancestral peptide that occurred after the divergence of the tunicates from the ancestor that led to the evolution of chordates and vertebrates. The presence of a single CRF-like peptide in tunicates and insects suggests that a single CRF-like ancestor was present before the separation of deuterostomes and protostomes. Currently there is no strong evidence that indicates that CRF-like peptides were present in metazoan taxa that evolved before this time although the structural similarity between some CRF peptides in insects, tunicates and vertebrates with the calcitonin family of peptides hints that prior to the formation of deuterostomes and protostomes the ancestral peptide possessed both CRF and calcitonin-like structural attributes. Here, we show evidences of conservation of CRF-like function dating back to early prokaryotes. This ancestral CRF-calcitonin-like peptide may have initially resulted from a horizontal gene transfer event from prokaryotes to a protistan species that later gave rise to the metazoans.

Differential Changes in Expression of Stress- and Metabolic-Related Neuropeptides in the Rat Hypothalamus during Morphine Dependence and Withdrawal

Chronic morphine treatment and naloxone precipitated morphine withdrawal activates stress-related brain circuit and results in significant changes in food intake, body weight gain and energy metabolism. The present study aimed to reveal hypothalamic mechanisms underlying these effects. Adult male rats were made dependent on morphine by subcutaneous implantation of constant release drug pellets. Pair feeding revealed significantly smaller weight loss of morphine treated rats compared to placebo implanted animals whose food consumption was limited to that eaten by morphine implanted pairs. These results suggest reduced energy expenditure of morphine-treated animals. Chronic morphine exposure or pair feeding did not significantly affect hypothalamic expression of selected stress- and metabolic related neuropeptides - corticotropin-releasing hormone (CRH), urocortin 2 (UCN2) and proopiomelanocortin (POMC) compared to placebo implanted and pair fed animals. Naloxone precipitated morphine withdrawal resulted in a dramatic weight loss starting as early as 15–30 min after naloxone injection and increased adrenocorticotrophic hormone, prolactin and corticosterone plasma levels in morphine dependent rats. Using real-time quantitative PCR to monitor the time course of relative expression of neuropeptide mRNAs in the hypothalamus we found elevated CRH and UCN2 mRNA and dramatically reduced POMC expression. Neuropeptide Y (NPY) and arginine vasopressin (AVP) mRNA levels were transiently increased during opiate withdrawal. These data highlight that morphine withdrawal differentially affects expression of stress- and metabolic-related neuropeptides in the rat hypothalamus, while relative mRNA levels of these neuropeptides remain unchanged either in rats chronically treated with morphine or in their pair-fed controls.

The cytokine ciliary neurotrophic factor (CNTF) activates hypothalamic urocortin-expressing neurons both in vitro and in vivo

Ciliary neurotrophic factor (CNTF) induces neurogenesis, reduces feeding, and induces weight loss. However, the central mechanisms by which CNTF acts are vague. We employed the mHypoE-20/2 line that endogenously expresses the CNTF receptor to examine the direct effects of CNTF on mRNA levels of urocortin-1, urocortin-2, agouti-related peptide, brain-derived neurotrophic factor, and neurotensin. We found that treatment of 10 ng/ml CNTF significantly increased only urocortin-1 mRNA by 1.84-fold at 48 h. We then performed intracerebroventricular injections of 0.5 mg/mL CNTF into mice, and examined its effects on urocortin-1 neurons post-exposure. Through double-label immunohistochemistry using specific antibodies against c-Fos and urocortin-1, we showed that central CNTF administration significantly activated urocortin-1 neurons in specific areas of the hypothalamus. Taken together, our studies point to a potential role for CNTF in regulating hypothalamic urocortin-1-expressing neurons to mediate its recognized effects on energy homeostasis, neuronal proliferaton/survival, and/or neurogenesis.

Effects of contact dermatitis on hepatic gene expression in broilers

1. Severe foot and hock dermatitis in broiler chickens can reduce growth rate and increase susceptibility to bacterial infection, affecting both profitability and welfare. However, little is known about the underlying physiological changes associated with foot and hock lesions. 2. This study compared global hepatic gene expression in control birds and those with ammonia-induced foot and hock lesions using Agilent 44 K chicken oligonucleotide microarrays (8 birds per group). 3. In total, 417 genes were differentially expressed of which 174 could be mapped onto the genome. Genes associated with energy metabolism, thyroid hormone activity and cellular control were affected, while there was also evidence of an up-regulation of genes linked to a pro-inflammatory response. 4. It is conceivable that pain is the underlying cause for the observed changes in energy metabolism genes. 5. Changes in hepatic gene expression provide new information on how a chicken's physiological mechanisms alter to cope with foot and hock lesions. The findings support other data indicating that birds with increased severity of lesions are likely to be in pain and that growth will be compromised. Reduction of the incidence of dermatitis by improved husbandry should therefore benefit both welfare and commercial performance.

Food-intake regulation during stress by the hypothalamo-pituitary-adrenal axis

The prevalence of obesity is increasing worldwide with serious consequences such as diabetes mellitus type 2 and cardiovascular diseases. Emotional stress is considered to be one of the main reasons of obesity development in humans. However, there are some contradictory results, which should be addressed. First of all stress induces anorexia, but not overeating in laboratory animals. Glucocorticoids, the effector molecules of the hypothalamo-pituitary-adrenocortical (HPA) axis stimulate and stress inhibits food intake. It is also not clear if stress is diabetogenic or an antidiabetogenic factor. The review will discusses these issues and the involvement of the whole HPA axis and its separate molecules (glucocorticoids, adrenocorticotropin, corticotropin-releasing hormone) in food intake regulation under stress.

Cellular insulin resistance disrupts leptin-mediated control of neuronal signaling and transcription

Central resistance to the actions of insulin and leptin is associated with the onset of obesity and type 2 diabetes mellitus, whereas leptin and insulin signaling is essential for both glucose and energy homeostasis. Although it is known that leptin resistance can lead to attenuated insulin signaling, whether insulin resistance can lead to or exacerbate leptin resistance is unknown. To investigate the molecular events underlying crosstalk between these signaling pathways, immortalized hypothalamic neuronal models, rHypoE-19 and mHypoA-2/10, were used. Prolonged insulin exposure was used to induce cellular insulin resistance, and thereafter leptin-mediated regulation of signal transduction and gene expression was assessed. Leptin directly repressed agouti-related peptide mRNA levels but induced urocortin-2, insulin receptor substrate (IRS)-1, IRS2, and IR transcription, through leptin-mediated phosphatidylinositol 3-kinase/Akt activation. Neuronal insulin resistance, as assessed by attenuated Akt phosphorylation, blocked leptin-mediated signal transduction and agouti-related peptide, urocortin-2, IRS1, IRS2, and insulin receptor synthesis. Insulin resistance caused a substantial decrease in insulin receptor protein levels, forkhead box protein 1 phosphorylation, and an increase in suppressor of cytokine signaling 3 protein levels. Cellular insulin resistance may cause or exacerbate neuronal leptin resistance and, by extension, obesity. It is essential to unravel the effects of neuronal insulin resistance given that both peripheral, as well as the less widely studied central insulin resistance, may contribute to the development of metabolic, reproductive, and cardiovascular disorders. This study provides improved understanding of the complex cellular crosstalk between insulin-leptin signal transduction that is disrupted during neuronal insulin resistance.

Effects of gold thioglucose treatment on central corticotrophin-releasing hormone systems in mice

Systemic administration of gold thioglucose (GTG) causes a hypothalamic lesion that extends from the ventral part of the ventromedial hypothalamus (VMH) to the dorsal part of the arcuate nucleus (ARC), resulting in hyperphagia and obesity in mice. In the present study, we used in situ hybridisation histochemistry to explore the effects of GTG on the central corticotrophin-releasing hormone (CRH) system, which regulates feeding and energy homeostasis. Type 2 CRH receptor (CRHR-2) mRNA expression decreased by 40% at 8 weeks in the VMH and by 40-60% at 2 and 8 weeks in the ARC after GTG injection. By contrast, CRHR-2 mRNA expression in the hypothalamic paraventricular nucleus (PVN) and lateral septum was unchanged. Urocortin (Ucn) 3 mRNA expression in the perifornical area and medial amygdala decreased, whereas CRH mRNA expression in the PVN increased at 2 and 8 weeks after GTG injection. Ucn 1 mRNA expression in the Edingher-Westphal nucleus and Ucn 2 mRNA expression in the PVN were unchanged. Because Ucn 3 is an anorexigenic and a possible endogenous ligand for VMH CRHR-2, our results suggest that decreased Ucn 3 expression and decreased VMH CRHR-2 expression contribute, in part, to GTG-induced hyperphagia and obesity. To determine whether VMH CRHR-2 mediates the anorexigenic effects of Ucn 3, Ucn 3 was administered i.c.v. and food intake was measured 8 weeks after GTG treatment. Ucn 3 decreased cumulative food intake on days 4-7 after surgery compared to i.c.v. administration of vehicle in control mice. By contrast, the anorexigenic effects of i.c.v. Ucn 3 were abolished in GTG-treated mice. Taken together, our results indicate that the Ucn 3 pathway, which innervates the VMH, is involved in appetite regulation via CRHR-2. It remains to be determined whether CRHR-2 in the ARC has additional roles in appetite regulation by Ucn 3.

Posttranslational processing of human and mouse urocortin 2: characterization and bioactivity of gene products

Mouse (m) and human (h) urocortin 2 (Ucn 2) were identified by molecular cloning strategies and the primary sequence of their mature forms postulated by analogy to closely related members of the corticotropin-releasing factor (CRF) neuropeptide family. Because of the paucity of Ucn 2 proteins in native tissues, skin, muscle, and pancreatic cell lines were transduced with lentiviral constructs and secretion media were used to isolate and characterize Ucn 2 products and study processing. Primary structures were assigned using a combination of Edman degradation sequencing and mass spectrometry. For mUcn 2, transduced cells secreted a 39 amino acid peptide and the glycosylated prohormone lacking signal peptide; both forms were C-terminally amidated and highly potent to activate the type 2 CRF receptor. Chromatographic profiles of murine tissue extracts were consistent with cleavage of mUcn 2 prohormone to a peptidic form. By contrast to mUcn 2, mammalian cell lines transduced with hUcn 2 constructs secreted significant amounts of an 88 amino acid glycosylated hUcn 2 prohormone but were unable to further process this molecule. Similarly, WM-266-4 melanoma cells that express endogenous hUcn 2 secreted only the glycosylated prohormone lacking the signal peptide and unmodified at the C terminus. Although not amidated, hUcn 2 prohormone purified from overexpressing lines activated CRF receptor 2. Hypoxia and glycosylation, paradigms that might influence secretion or processing of gene products, did not significantly impact hUcn 2 prohormone cleavage. Our findings identify probable Ucn 2 processing products and should expedite the characterization of these proteins in mammalian tissues.

Intravenous injection of urocortin 1 induces a CRF2 mediated increase in circulating ghrelin and glucose levels through distinct mechanisms in rats

Urocortins (Ucns) injected peripherally decrease food intake and gastric emptying through peripheral CRF(2) receptors in rodents. However, whether Ucns influence circulating levels of the orexigenic and prokinetic hormone, ghrelin has been little investigated. We examined plasma levels of ghrelin and blood glucose after intravenous (iv) injection of Ucn 1, the CRF receptor subtype involved and underlying mechanisms in ad libitum fed rats equipped with a chronic iv cannula. Ucn 1 (10 μg/kg, iv) induced a rapid onset and long lasting increase in ghrelin levels reaching 68% and 219% at 0.5 and 3h post injection respectively and a 5-h hyperglycemic response. The selective CRF(2) agonist, Ucn 2 (3 μg/kg, iv) increased fasting acyl (3h: 49%) and des-acyl ghrelin levels (3h: 30%) compared to vehicle while the preferential CRF(1) agonist, CRF (3 μg/kg, iv) had no effect. Ucn 1's stimulatory actions were blocked by the selective CRF(2) antagonist, astressin(2)-B (100 μg/kg, iv). Hexamethonium (10 mg/kg, sc) prevented Ucn 1-induced rise in total ghrelin levels while not altering the hyperglycemic response. These data indicate that systemic injection of Ucns induces a CRF(2)-mediated increase in circulating ghrelin levels likely via indirect actions on gastric ghrelin cells that involves a nicotinic pathway independently from the hyperglycemic response.

Urocortin 3 marks mature human primary and embryonic stem cell-derived pancreatic alpha and beta cells

The peptide hormone Urocortin 3 (Ucn 3) is abundantly and exclusively expressed in mouse pancreatic beta cells where it regulates insulin secretion. Here we demonstrate that Ucn 3 first appears at embryonic day (E) 17.5 and, from approximately postnatal day (p) 7 and onwards throughout adult life, becomes a unifying and exclusive feature of mouse beta cells. These observations identify Ucn 3 as a potential beta cell maturation marker. To determine whether Ucn 3 is similarly restricted to beta cells in humans, we conducted comprehensive immunohistochemistry and gene expression experiments on macaque and human pancreas and sorted primary human islet cells. This revealed that Ucn 3 is not restricted to the beta cell lineage in primates, but is also expressed in alpha cells. To substantiate these findings, we analyzed human embryonic stem cell (hESC)-derived pancreatic endoderm that differentiates into mature endocrine cells upon engraftment in mice. Ucn 3 expression in hESC-derived grafts increased robustly upon differentiation into mature endocrine cells and localized to both alpha and beta cells. Collectively, these observations confirm that Ucn 3 is expressed in adult beta cells in both mouse and human and appears late in beta cell differentiation. Expression of Pdx1, Nkx6.1 and PC1/3 in hESC-derived Ucn 3⁺ beta cells supports this. However, the expression of Ucn 3 in primary and hESC-derived alpha cells demonstrates that human Ucn 3 is not exclusive to the beta cell lineage but is a general marker for both the alpha and beta cell lineages. Ucn 3⁺ hESC-derived alpha cells do not express Nkx6.1, Pdx1 or PC1/3 in agreement with the presence of a separate population of Ucn 3⁺ alpha cells. Our study highlights important species differences in Ucn 3 expression, which have implications for its utility as a marker to identify mature beta cells in (re)programming strategies.

Urocortins: CRF's siblings and their potential role in anxiety, depression and alcohol drinking behavior

It is widely accepted that stress, anxiety, depression and alcohol abuse-related disorders are in large part controlled by corticotropin-releasing factor (CRF) receptors. However, evidence is accumulating that some of the actions on these receptors are mediated not by CRF, but by a family of related Urocortin (Ucn) peptides Ucn1, Ucn2 and Ucn3. The initial narrow focus on CRF as the potential main player acting on CRF receptors appears outdated. Instead it is suggested that CRF and the individual Ucns act in a complementary and brain region-specific fashion to regulate anxiety-related behaviors and alcohol consumption. This review, based on a symposium held in 2011 at the research meeting on "Alcoholism and Stress" in Volterra, Italy, highlights recent evidence for regulation of these behaviors by Ucns. In studies on stress and anxiety, the roles of Ucns, and in particular Ucn1, appear more visible in experiments analyzing adaptation to stressors rather than testing basal anxiety states. Based on these studies, we propose that the contribution of Ucn1 to regulating mood follows a U-like pattern with both high and low activity of Ucn1 contributing to high anxiety states. In studies on alcohol use disorders, the CRF system appears to regulate not only dependence-induced drinking, but also binge drinking and even basal consumption of alcohol. While dependence-induced and binge drinking rely on the actions of CRF on CRFR1 receptors, alcohol consumption in models of these behaviors is inhibited by actions of Ucns on CRFR2. In contrast, alcohol preference is positively influenced by actions of Ucn1, which is capable of acting on both CRFR1 and CRFR2. Because of complex distribution of Ucns in the nervous system, advances in this field will critically depend on development of new tools allowing site-specific analyses of the roles of Ucns and CRF.

Urocortin is a novel regulator of osteoclast differentiation and function through inhibition of a canonical transient receptor potential 1-like cation channel

This study investigated the role of urocortin (UCN), a member of the corticotrophin-releasing factor (CRF) family of peptides, in osteoclast maturation and function. We found that 10(-7) M UCN significantly (P<0.05) suppressed osteoclast differentiation from bone marrow precursor cells in culture and reduced the expression of several osteoclastic markers. Furthermore, UCN potently suppressed osteoclast bone resorption, by significantly inhibiting both the plan area of bone resorbed by osteoclasts and actin ring formation within osteoclasts at 10(-9) M (P<0.05), with complete inhibition at 10(-7) M (P<0.001). UCN also inhibited osteoclast motility (10(-7) M) but had no effect on osteoclast survival. Osteoclasts expressed mRNA encoding both UCN and the CRF receptor 2β subtype. Pre-osteoclasts however, expressed CRF receptor 2β alone. Unstimulated osteoclasts contained constitutively active cation channel currents with a unitary conductance of 3-4 pS, which were inhibited by over 70% with UCN (10(-7) M). Compounds that regulate calcium signalling and energy status of the cell, both crucial for osteoclast activity were investigated. The non-selective cation channel blockers, lanthanum (La(3)(+)) and gadolinium (Gd(3)(+)), inhibited actin ring formation in osteoclasts, whereas modulators of voltage-dependent Ca(2)(+) channels and K(ATP) channels had no effect. These findings show for the first time that UCN is a novel anti-resorptive molecule that acts through a direct effect on osteoclasts and their precursor cells.

Mapping the CRF-urocortins system in human osteoarthritic and rheumatoid synovial fibroblasts: effect of vasoactive intestinal peptide

In addition to the brain and pituitary gland, the corticotrophin-releasing factor (CRF) system is expressed in peripheral tissues. In this study we characterize the expression of CRF, urocortins (UCN1, UCN2, and UCN3), and their receptors (CRFR1 and CRFR2) in osteoarthritis (OA) and rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS). Moreover, we analyze the vasoactive intestinal peptide (VIP) effect on the CRF system, as well as its physiological consequences on mediators of inflammatory/destructive processes. CRF and UCNs exhibit differential pattern in OA and RA-FLS. By real-time PCR we detected more expression of CRF and UCN1 in RA, and UCN2 and UCN3 in OA, while the CRFR2 expression was similar. In RA-FLS VIP treatment resulted in a significant decrease of the proinflammatory peptides, CRF and UCN1, and a significant increase of the potential anti-inflammatory agents, UCN3 and CRFR2. Using Western blot assays, we showed that the ratio between phospho-CREB (p-CREB) and c-AMP response element-binding (CREB) is higher in OA and significantly lower in RA-FLS after VIP treatment, with consequences upon cAMP response element in CRF and UCN1 genes. Real-time PCR and EIA proved that VIP significantly inhibits cycloxygenase-2 (COX-2) and prostaglandin E2 (PGE2) in RA-FLS. In all cases, we consider significant data when P < 0.05. These data indicate a role of endogenous CRF, UCNs, and CRFR2 in the OA and RA joint microenvironment. We confirm the anti-inflammatory function of VIP, through the modulation of the expression of CRF system that impacts in a reduction of mediators with inflammatory/destructive functions, supporting its therapeutic potential in rheumatic diseases.

Involvement of CRF2 receptor in the brain regions in restraint-induced anorexia

We have reported that corticotropin-releasing factor (CRF) receptor subtypes, CRF1 and CRF2, are involved in stress-induced anorexia. To clarify in which brain regions the CRF receptor is involved in mediating stress-induced anorexia, we examined the effect of microinjecting CRF1-selective or CRF2-selective antagonist into the lateral septum or the bed nucleus of the stria terminalis (BNST), which are implicated in regulating stress response. The results demonstrated that injecting antisauvagine-30 into the lateral septum or the BNST significantly attenuated restraint-induced anorexia, whereas injecting antalarmin into these regions did not affect anorexia. These results suggest that the CRF2 receptor in the lateral septum and the BNST is involved in the stress-induced inhibitory mechanism of feeding behavior.

Molecular determinants and feedback circuits regulating type 2 CRH receptor signal integration

In most target tissues, the adenylyl cyclase/cAMP/PKA, the extracellular signal regulated kinase and the protein kinase B/Akt are the main pathways employed by the type 2 corticotropin-releasing hormone receptor to mediate the biological actions of urocortins (Ucns) and CRH. To decipher the molecular determinants of CRH-R2 signaling, we studied the signaling pathways in HEK293 cells overexpressing recombinant human CRH-R2β receptors. Use of specific kinase inhibitors showed that the CRH-R2β cognate agonist, Ucn 2, activated extracellular signal regulated kinase in a phosphoinositide 3-kinase and cyclic adenosine monophosphate/PKA-dependent manner with contribution from Epac activation. Ucn 2 also induced PKA-dependent association between AKAP250 and CRH-R2β that appeared to be necessary for extracellular signal regulated kinase activation. PKB/Akt activation was also mediated via pertussis toxin-sensitive G-proteins and PI3-K activation but did not require cAMP/PKA, Epac or protein kinase C for optimal activation. Potential feedback mechanisms that target the CRH-R2β itself and modulate receptor trafficking and endocytosis were also investigated. Indeed, our results suggested that inhibition of either PKA or extracellular signal regulated kinase pathway accelerates CRH-R2β endocytosis. Furthermore, Ucn 2-activated extracellular signal regulated kinase appeared to target β-arrestin1 and modulate, through phosphorylation at Ser412, β-arrestin1 translocation to the plasma membrane and CRH-R2β internalization kinetics. Loss of this "negative feedback" mechanism through inhibition of the extracellular signal regulated kinase activity resulted in significant attenuation of Ucn 2-induced cAMP response, whereas Akt phosphorylation was not affected by altered receptor endocytosis. These findings reveal a complex interplay between the signaling molecules that allow "fine-tuning" of CRH-R2β functional responses and regulate signal integration. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

Stress controversies: post-traumatic stress disorder, hippocampal volume, gastroduodenal ulceration*

Stress in mammals triggers a neuroendocrine response mediated by the hypothalamic-pituitary-adrenal axis and the autonomic nervous system. Increased activity of these two systems induces behavioural, cardiovascular, endocrine and metabolic cascades that enable the individual to fight or flee and cope with the stress. Our understanding of stress and stress-response mechanisms is generally robust. Here, however, we review three themes that remain controversial and perhaps deserve further scrutiny and investigation before they achieve canonical status. The themes are, first, hypocortisolaemia in post-traumatic stress disorder (PTSD). A reduction rather than a stress-induced increase in adrenal glucocorticoid levels, as seen in major depressive disorder (MDD), is puzzling and furthermore is not a consistent feature of PTSD. Overall, studies on PTSD show that glucocorticoid levels may be normal or higher or lower than normal. The second theme concerns the reduction in volume of the hippocampus in MDD attributed to the neurotoxicity of hypercortisolaemia. Again, as for hypocortisolaemia in PTSD, reduced hippocampal volume in MDD has been found in some but not all studies. Third, the discovery of a causal association between Helicobacter pylori and peptic ulcers apparently brought to an end the long-held view that peptic ulceration was caused predominantly by stress. However, recent studies suggest that stress can cause peptic ulceration in the absence of H. pylori. Predictably, the aetiological pendulum of gastric and duodenal ulceration has swung from 'all stress' to 'all bacteria' followed by a sober realisation that both factors may play a role. This raises the question as to whether stress and H. pylori interact, and if so how? All three controversies are of clinical significance, pose fundamental questions about stress mechanisms and offer important areas for future research.