Characterization and regulation of corticotropin-releasing factor receptors in the central nervous, endocrine and immune systems

Corticotropin-releasing factor (CRF) plays a major role in coordinating the endocrine, autonomic, behavioural and immune responses to stress through actions in the brain and in the periphery. CRF receptors identified in brain, pituitary and spleen have comparable kinetic and pharmacological characteristics, guanine nucleotide sensitivity and adenylate cyclase-stimulating activity. Differences were observed in the molecular mass of the CRF receptor complex between brain (58,000 Da) and pituitary and spleen (75,000 Da), which appeared to be due to differential glycosylation of the receptor proteins. In autoradiographic studies, CRF receptors were localized in highest densities in anterior and intermediate lobes of the pituitary, olfactory bulb, cerebral cortex, amygdala, cerebellum and the macrophage-rich marginal zones and red pulp regions of the spleen. CRF can modulate the number of CRF receptors in both the brain and pituitary in a reciprocal manner. The demonstration of functional CRF receptors in brain, pituitary and spleen suggests the importance of this neuropeptide in integrating the responses of the CNS, endocrine and immune systems to physiological, psychological and immunological stimuli.

Effect of non-peptide corticotropin-releasing factor receptor type 1 antagonist on adrenocorticotropic hormone release and interleukin-1 receptors followed by stress

Previous studies demonstrated that ether-laparotomy significantly increased iodine-125-labeled interleukin-1alpha ([125I]IL-1alpha) binding in the mouse anterior pituitary at 2 h after the onset of stress. Corticotropin-releasing factor (CRF) receptor antagonist, D-Phe CRF (12-41), abolished ether-laparotomy-induced increase in [125I]IL-1alpha binding in the pituitary, showing that CRF plays a pivotal role in the regulation of IL-1 receptors under stress conditions. In an attempt to define the effect of CRA 1000 (2-(N-(2-methylthio-4-isopropylphenyl)-N-ethylamino-4-(4-(3-fluorophenyl)-1,2,3,6-tetrahydropyridin-1-yl)-6-methylpyrimidine), a non-peptide CRF receptor type 1 antagonist on the regulation of hypothalamic-pituitary-adrenal (HPA) axis and IL-1 receptors in the mouse, we measured plasma adrenocorticotropic hormone (ACTH) and corticosterone levels, [125I]IL-1alpha binding and the expression of transcripts for type 1 IL-1 receptor (IL-1R1 mRNA) in the pituitary at 2 h after endotoxin lipopolysaccharide (LPS) treatment or ether-laparotomy stress with or without CRA 1000 pretreatment. A single injection of LPS dramatically increased plasma ACTH and corticosterone levels compared with saline injection. In contrast, plasma ACTH levels were significantly attenuated in response to one LPS injection following oral CRA 1000 pretreatment. LPS-induced plasma corticosterone levels tended to be lower after CRA 1000 pretreatment but it did not reach statistical significance. Ether-laparotomy stress significantly increased plasma ACTH and corticosterone levels at 2 h after the onset of stress and CRA 1000 pretreatment did not affect the peak ACTH and corticosterone levels following stress. Ether-laparotomy stress resulted in a robust increase in [125I]IL-1alpha binding and IL-1R1 mRNA levels in the pituitary. CRA 1000 pretreatment significantly decreased ether-laparotomy stress-induced IL-1R1 mRNA levels but did not affect [125I]IL-1alpha binding. Pretreatment with CRA 1000 without stress significantly increased [125I]IL-1alpha binding and IL-1R1 mRNA levels compared with those in vehicle pretreatment. These data demonstrate differential effects of CRA 1000 in HPA axis following endotoxin and ether-laparotomy stress and complex interactions between CRF and IL-1 receptors during stress.

Performance-enhancing effects of CRF-BP ligand inhibitors

Intracerebroventricular (i.c.v.) administration of corticotropin-releasing factor (CRF) peptide fragments with low affinity for CRF receptors reportedly improves cognitive performance without producing anxiety. These compounds are hypothesized to act by displacing endogenous peptide from the CRF-binding protein (CRF-BP). To test this hypothesis, the present study determined whether the performance-enhancing potency of CRF fragments was related to their affinity for the CRF-BP. Rank ordering of the optimal doses of these compounds for facilitating spatial navigation corresponded to their affinity for the CRF-BP. i.c.v. pretreatment with performance-enhancing doses of r/h CRF(1-41)-OH (5 micrograms) or r/h CRF(6-33) (25 micrograms) did not increase emotionality. These findings replicate the dissociability of the cognition- and anxiety-related effects of CRF-related compounds and suggest that CRF fragments facilitate performance via the CRF-BP.

Effect of orchidectomy on the age-related modulation of IL-1beta and IL-1 receptors following lipopolysaccharide treatment in the mouse

OBJECTIVE

To compare the effect of orchidectomy (ODX) in 7- and 24-week-old C57BL/6 mice on the age-related responses of the cytokine interleukin (IL)-1beta and its receptor to intraperitoneal injection of the bacterial endotoxin, lipopolysaccharide (LPS).

METHODS

We measured IL-1beta concentrations in the plasma, hippocampus, hypothalamus and adrenal gland using ELISA and iodine-125-labeled recombinant human IL-1alpha ([(125)I]IL-1alpha) binding in the hippocampus following the intraperitoneal administration of saline or LPS.

RESULTS

There were no significant differences in the concentrations of IL-1beta and its receptors in the brain and peripheral tissues between sham-operated and ODX mice in both age groups injected with saline. LPS induced significantly higher IL-1beta production in the plasma and hippocampus in sham-operated 24-week-old mice than in 7-week-old mice. Coincident with the heightened IL-1beta response to LPS, hippocampal [(125)I]IL-1alpha binding was lower in 24-week-old mice than in 7-week-old mice after LPS injection in the sham-operated group. The age-related differences in the IL-1beta concentrations in the plasma and hippocampus and [(125)I]IL-1alpha binding in the hippocampus in response to LPS administration were abolished by ODX. Although LPS dramatically increased IL-1beta levels in the hypothalamus, no significant age-related differences in IL-1beta concentrations were seen, and ODX did not affect IL-1beta levels. In contrast, there were no significant differences between saline- and LPS-injected 7-week-old mice in relation to concentrations in the adrenal gland. Moreover, although the adrenal IL-1beta concentrations in 24-week-old mice were significantly higher than those in 7-week-old mice, ODX did not abolish these age-related differences in concentrations in the adrenal gland.

CONCLUSIONS

Our data suggest the involvement of testosterone (or gonadal product) in plasma and hippocampal IL-1beta regulation in relation to age, and demonstrate the importance of the gonadal development in mediating the effects of infectious challenge on the brain and immune function.

Corticotropin-releasing factor antagonists, binding-protein and receptors: implications for central nervous system disorders

Corticotrophin-releasing factor (CRF; interchangeable with corticotrophin-releasing hormone, CRH) is a neurohormone family of peptides which implements endocrine, physiological and behavioural responses to stressor exposure. Built-in biological diversity and selectivity of CRF system function is provided by multiple endogenous ligands and receptors which are heterogeneously distributed in both brain and peripheral tissues across species. At present, there are at least five distinct targets for CRF with unique cDNA sequences, pharmacology and localization. These fall into three distinct classes, encoded by three different genes and have been termed the CRF1 and CRF2 receptors and the CRF-binding protein. Significant gains in knowledge about the physiological role of CRF binding sites in brain have emerged recently due to the proliferation of novel, high-affinity, receptor-selective pharmacological tools as well as multiple knock-out and knock-in mutant mouse models. These results support a role for CRF binding sites in co-ordinating stress reactivity, emotionality and energy balance over the life-span of the organism.

Nephroblastoma overexpressed gene (NOV) codes for a growth factor that induces protein tyrosine phosphorylation

NOV (nephroblastoma overexpressed gene) is a member of the CCN (connective tissue growth factor [CTGF], Cyr61/Cef10, NOV) family of proteins. These proteins are cysteine-rich and are noted for having growth-regulatory functions. We have isolated the rat NOV gene, and the DNA sequence shares 90% identity with the mouse and 80% identity with the human sequences. The rat NOV gene was expressed in all rat tissues examined, including brain, lung, heart, kidney, liver, spleen, thymus and skeletal muscle. Higher levels of rat NOV mRNA were seen in the brain, lung and skeletal muscle compared to the other tissues. Examination of NOV expression in various human cell lines revealed that NOV was expressed in U87, 293, T98G, SK-N-MC and Hs683 but not in HepG2, HL60, THP1 and Jurkat. The human NOV gene was transfected into 293 cells and the expressed protein purified. When 3T3 fibroblasts were treated with this recombinant NOV protein, a dose-dependent increase in proliferation was observed. Analysis of tyrosine-phosphorylated proteins revealed that when 3T3 cells were treated with NOV, a 221 kDa protein was phosphorylated. These data suggest that NOV can act as a growth factor for some cells and binds to a specific receptor that leads to the phosphorylation of a 221 kDa protein.

Differential effects of one and repeated endotoxin treatment on pituitary- adrenocortical hormones in the mouse: role of interleukin-1 and tumor necrosis factor-alpha

The role of endogenous interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) in modulating the hypothalamic-pituitary-adrenal (HPA) axis response was examined in male C57BL/6 mice injected with endotoxin (lipopolysaccharide, LPS) or saline at 24-hour intervals for 4 or 8 consecutive days. The mice were divided into four groups: (1) LPS injections for 4 or 8 days and LPS injection on day 5 or 9, respectively (LPS-LPS); (2) LPS injections for 4 or 8 days and saline injection on day 5 or 9, respectively (LPS-saline); (3) saline injections for 4 or 8 days and LPS injection on day 5 or 9, respectively (saline-LPS), and (4) saline injections for 4 or 8 days and saline injection on day 5 or 9 (saline-saline). The mice were sacrificed by decapitation 2 h after the last injection and plasma levels of hormones and cytokines and tissue levels of IL-1beta were measured. Plasma adrenocorticotropin (ACTH) levels were significantly attenuated in the LPS-LPS group compared with the dramatic increases in the saline-LPS group following 4 or 8 days of endotoxin treatment. Plasma corticosterone concentrations were comparable in the LPS-LPS group after 4 days' treatment, but significantly lower following 8 days of treatment when compared with saline-LPS group. Repeated endotoxin treatment followed by a single saline injection (LPS-saline) did not alter the levels of IL-1beta in plasma or any of the tissues examined. IL-1beta levels in the hippocampus, hypothalamus, adrenal gland and plasma were elevated to comparable levels in the saline-LPS and LPS-LPS groups after 4 days of treatment. In contrast to the plasma IL-1beta response, TNFalpha levels were dramatically increased in the saline-LPS group but not in the LPS-LPS group following the 4-day treatment regimen. Increases in IL-1beta concentrations were seen in all tissues following one endotoxin challenge in the saline-LPS group following the 8-day treatment regimen, while increases were significantly attenuated in the hypothalamus, adrenal gland and plasma in LPS-LPS for 8 days. The sustained increases in tissue levels of IL-1beta following 4-day endotoxin treatment appears to have functional consequences since [125I]IL-1alpha binding was significantly decreased in the LPS-saline group compared with the saline-saline group. Furthermore, [125I]IL-1alpha binding was markedly reduced in the LPS-LPS group compared with the saline-LPS group. There was a significant positive correlation between plasma ACTH and IL-1beta after a single and repeated LPS treatment for 4 days, while a significant correlation was seen between plasma ACTH and TNFalpha following one but not repeated LPS treatment. These data demonstrate a differential regulation of IL-1beta and TNFalpha by repeated endotoxin treatment and suggest that while TNFalpha may be important modulating the attenuated pituitary adrenocortical response following the 4-day endotoxin treatment, IL-1beta appears to be the primary regulator of the response following the 8-day endotoxin treatment in the regulation of the HPA axis.

Non-peptide corticotropin-releasing hormone antagonists: syntheses and structure-activity relationships of 2-anilinopyrimidines and -triazines

Screening of our chemical library using a rat corticotropin-releasing hormone (CRH) receptor assay led to the discovery that 2-anilinopyrimidine 15-1 weakly displaced [125I]-0-Tyr-oCRH from rat frontal cortex homogenates when compared to the known peptide antagonist alpha-helical CRH(9-41) (Ki = 5700 nM vs 1 nM). Furthermore, 15-1 weakly inhibited CRH-stimulated adenylate cyclase activity in the same tissue, but it was less potent than alpha-helical CRH(9-41) (IC50 = 20 000 nM vs 250 nM). Systematic structure-activity relationship studies, using the cloned human CRH1 receptor assay, defined the pharmacophore for optimal binding to hCRH1 receptors. Several high-affinity 2-anilinopyrimidines and -triazines were discovered, some of which had superior pharmacokinetic profiles in the rat. This paper describes the structure-activity studies which improved hCRH1 receptor binding affinity and pharmacokinetic parameters in the rat. Compound 28-17 (mean hCRH1 Ki = 32 nM) had a significantly improved pharmacokinetic profile in the rat (19% oral bioavailability at 30 mg/kg) as well as in the dog (20% oral bioavailability at 5 mg/kg) relative to the early lead structures.

Characterization of [125I-Tyr0]-corticotropin releasing factor (CRF) binding to the CRF binding protein using a scintillation proximity assay

We describe the characterization of high affinity [125I-Tyr0]-human CRF binding to purified recombinant human CRF-binding protein (CRF-BP) using a scintillation proximity assay (SPA). For this stable nonseparation technique developed in 96 well microtiter plates, biotinylated CRF-BP is captured by streptavidin-coated SPA beads for the detection of bound [125I-Tyr0]-CRF. Unbound [125I-Tyr0]-CRF represented little or no signal in the assay. Total binding observed was greater than 5000 cpm with a nonspecific signal of < 100 cpm determined in the presence of excess unlabeled human CRF. A comparison of the SPA method with a charcoal precipitation method confirmed that the biotinylation procedure did not adversely affect affinity of the CRF-BP for [125I-Tyr0]-CRF. Saturation binding analysis yielded an apparent equilibrium dissociation constant (Kd) of 208 +/- 5.0 pM (+/- S.D., n = 3). An inhibition constant (Ki) for unlabeled CRF was calculated to be 0.22 +/- 0.03 nM (+/- S.D., n = 8) and a pharmacological profile for eight CRF-related neuropeptides gave a rank potency similar to previously reported results. Finally, the assay variability was assessed with intra- and inter-plate coefficients of variation which were less than 5% each.

The role of CRF2 receptors in corticotropin-releasing factor- and urocortin-induced anorexia

The experiments presented in this study were designed to assess corticotropin-releasing factor (CRF) receptor subtype mediation of CRF- and urocortin (UCN)-induced decrease in food intake. Male Sprague-Dawley rats were treated with antisense and sense oligonucleotides (ON) to CRF2 receptor mRNAs for 36 h and then received an intracerebroventricular (i.c.v.) injection of CRF, UCN (3 micrograms) or saline. Antisense treatment significantly attenuated CRF- and UCN-induced suppression in food intake and HPA activation. Administration of CRF1 receptor antagonist did not affect the decrease in food intake or activation of the HPA axis induced by i.c.v. infusion of 3 micrograms CRF. The data suggest that down-regulation of CRF2 receptors selectively attenuates CRF- and UCN-induced anorexia and hypothalamo-pituitary-adrenocortical activation in rats.

Corticotropin-releasing factor receptor blockade enhances conditioned aversive properties of cocaine in rats

The behavioral profile of corticotropin-releasing factor (CRF) in mediating anxiogenic-like and aversive responses to stressors may be particularly relevant for dependence and withdrawal in drug-experienced organisms. Moreover, stressful aspects of drug exposure in the drug naive organism may also induce CRF system activation. In the present studies, the dependence of aversive properties of cocaine on activation of endogenous CRF systems has been evaluated in rats using taste conditioning and runway self-administration paradigms. Systemic cocaine administration (20 mg/kg i.p.) produced a conditioned saccharin aversion which was dose-dependently potentiated by central administration of the CRF receptor antagonist, D-phe CRF (12 41). In addition, i.v. cocaine administration (0.75 mg/kg per injection i.v.) produced runway goal-box avoidance and conditioned place avoidance responses which were significantly accelerated by CRF antagonist treatment. In contrast, CRF receptor stimulation using CRF itself abolished cocaine-induced increases in goal latency in the runway paradigm. This generalized involvement of CRF systems in cocaine-related motivational/associative states is consistent with the comprehensive role of CRF in mediating emotional responses to non-drug stressors.

Displacement of insulin-like growth factors from their binding proteins as a potential treatment for stroke

Insulin-like growth factors I and II (IGF-I and IGF-II) play an important role in normal growth and brain development and protect brain cells from several forms of injury. The effects of IGFs are mediated by type-I and type-II receptors and modulated by potentially six specific binding proteins that form high-affinity complexes with IGFs in blood and cerebrospinal fluid (CSF) and under most circumstances inactivate them. Because brain injury is commonly associated with increases in IGFs and their associated binding proteins, we hypothesized that displacement of this large "pool" of endogenous IGF from the binding proteins would elevate "free" IGF levels to elicit neuroprotective effects comparable to those produced by administration of exogenous IGF. A human IGF-I analog [(Leu24, 59, 60, Ala31)hIGF-I] with high affinity to IGF-binding proteins (Ki = 0.3-3.9 nM) and no biological activity at the IGF receptors (Ki = >10,000 nM) increased the levels of "free, bioavailable" IGF-I in the CSF. Intracerebroventricular administration of this analog up to 1h after an ischemic insult to the rat brain had a potent neuroprotective action comparable to IGF-I. This novel strategy for increasing "free" IGF levels in the brain may be useful for the treatment of stroke and other neurodegenerative diseases.

Localization of agonist- and antagonist-binding domains of human corticotropin-releasing factor receptors

The CRF receptors, CRFR1 and CRFR2, are members of the G protein-coupled receptor superfamily. Despite their considerable sequence similarity, CRFR1 and CRFR2 have quite different affinities for the peptide ligand rat/human CRF. Previous studies using chimeric receptors between human CRFR1 and CRFR2 have identified three potentially important regions in the second and third extracellular domains of CRF receptor for the binding of rat/human CRF. The present report further demonstrates that these same three regions also affect the binding of urocortin and sauvagine, two other members of the CRF peptide family, albeit to different extents. We also show that a fourth region in the third extracellular domain, Asp254, has been identified to be important for sauvagine but not CRF or urocortin binding. Thus, the three peptide ligands not only interact with a different set of regions on CRFR1 and CRFR2 but also differentially interact with some of the same regions. These data could, at least in part, account for the much higher affinity of CRFR2 for urocortin and sauvagine compared with rat/human CRF. We have also identified two amino acid residues, His199 in the third transmembrane domain and Met276 in the fifth transmembrane domain, that are important for binding the non-peptide high-affinity CRFR1 antagonist NBI 27914. Mutations of His199 and Met276 to the corresponding amino acids in CRFR2 each decreased the binding affinity of NBI 27914 for CRFR1 by 40- and 200-fold, respectively. This suggests that the transmembrane regions are critically important in forming the binding pocket for the nonpeptide antagonist.

Endotoxin induced increases in rat plasma pituitary-adrenocortical hormones are better reflected by alterations in tumor necrosis factor alpha than interleukin-1beta

In order to assess the relative cytokine contribution to endotoxin stimulation of pituitary-adrenocortical hormone secretion, we measured plasma levels of interleukin-1beta (IL-1beta), tumor necrosis factor (TNF alpha), adrenocorticotropin (ACTH) and corticosterone following lipopolysaccharide (LPS) challenge in rats. LPS administration induced robust increases in both plasma ACTH and corticosterone levels at 3 h after i.p. injection; while ACTH decreased towards control levels, corticosterone remained at peak concentrations at 6 h after LPS injection. Basal levels of plasma IL-1beta were below the sensitivity of the ELISA and basal levels of plasma TNF alpha were 0.25+/-0.12 pM. Small but highly variable non-significant increases in plasma IL-1beta levels were seen at 3 h and 6 h after injection of LPS. The lack of functional consequences of the small increases in IL-1beta levels was demonstrated by unchanged levels of [125I]IL-1alpha binding in liver at 3 h after LPS injection. In contrast, dramatic increases in plasma TNF alpha concentrations were observed at 3 h and decreased to non-injected control levels at 6 h after LPS injection. There was a significant positive correlation between ACTH and TNF alpha after LPS injection, while no correlation was seen between ACTH and IL-1beta. These data demonstrate differential regulation of IL-1beta and TNF alpha by endotoxin treatment and suggest that TNF alpha may be a more potent mediator of LPS-induced ACTH secretion in rat.

The CRF1 receptor mediates the excitatory actions of corticotropin releasing factor (CRF) in the developing rat brain: in vivo evidence using a novel, selective, non-peptide CRF receptor antagonist

Corticotropin releasing factor (CRF) is the key coordinator of the neuroendocrine and behavioral responses to stress. In the central nervous system, CRF excites select neuronal populations, and infusion of CRF into the cerebral ventricles of infant rats produces severe age-dependent limbic seizures. These seizures, like other CRF effects, result from activation of specific receptors. Both of the characterized members of the CRF receptor family (CRF1 and CRF2), are found in the amygdala, site of origin of CRF-induced seizures, and may therefore mediate these seizures. To determine which receptor is responsible for the excitatory effects of CRF on limbic neurons, a selective, non-peptide CRF1 antagonist was tested for its ability to abolish the seizures, in comparison to non-selective inhibitory analogues of CRF. Pretreatment with the selective CRF1 blocker (NBI 27914) increased the latency and decreased the duration of CRF-induced seizures in a dose-dependent manner. The higher doses of NBI 27914 blocked the behavioral seizures and prevented epileptic discharges in concurrent electroencephalograms recorded from the amygdala. The selective CRF1 blocker was poorly effective when given systemically, consistent with limited blood-brain barrier penetration. Urocortin, a novel peptide activating both types of CRF receptors in vitro, but with preferential affinity for CRF2 receptors in vivo, produced seizures with a lower potency than CRF. These limbic seizures, indistinguishable from those induced by CRF, were abolished by pretreatment with NBI 27914, consistent with their dependence on CRF1 activation. In summary, CRF induces limbic seizures in the immature rat, which are abolished by selective blocking of the CRF1 receptor. CRF1-messenger RNA levels are maximal in sites of seizure origin and propagation during the age when CRF is most potent as a convulsant. Taken together, these facts strongly support the role of the developmentally regulated CRF1 receptor in mediating the convulsant effects of CRF in the developing brain.

Expression and characterization of a putative high affinity human soluble leptin receptor

Leptin, a circulating 16-kDa protein secreted by adipocytes, decreases body weight by reducing food intake and enhancing energy utilization. Leptin receptors that share homology to the glycoprotein gp130 have been recently cloned. In addition, differentially spliced leptin receptor messenger RNAs have been identified. Functional mutations in either the leptin or leptin receptor gene cause obesity. In the present study, expression of the full length human leptin receptor complementary DNA encoding the long cytoplasmic domain of leptin receptor in COS7 cells resulted in high affinity membrane binding of 125I-leptin (Ki approximately 200 pM); no detectable binding was present in the medium. In addition, we expressed the extracellular domain of human leptin receptor in COS7 cells and identified a soluble leptin receptor in the conditioned medium that binds human and mouse leptin with high affinity comparable with the full length membrane receptor. Transfected COS7 cells expressing the soluble leptin receptor also demonstrated modest specific 125I-leptin binding in whole cells, presumably due to association of the soluble leptin receptor to cell membrane proteins. Data from cross-linking studies identified two specific bands in the 125I-leptin/soluble leptin receptor complex with molecular masses of approximately 130-150 kDa and 300 kDa. The 130-150 kDa molecular mass was confirmed in Western blot analysis and Coomassie staining of the purified soluble receptor and probably represents the glycosylated form of the receptor. The 300-kDa band most likely represents a homodimer of the soluble leptin receptor complex because HPLC gel filtration analysis of the 125I-leptin/soluble leptin receptor complex identified a single peak corresponding to a molecular mass of approximately 340 kDa. The soluble leptin receptor antagonized 125I-leptin binding to the membrane receptor, suggesting its potential utility as a functional tool for determining the role of endogenous leptin.

Corticotropin-releasing factor CRF1, but not CRF2, receptors mediate anxiogenic-like behavior

The recent identification and differential localization in brain of three binding sites for corticotropin-releasing factor (CRF)-like peptides (CRF1 and CRF2 receptors as well as CRF-binding protein) suggest the existence of functionally distinct neurobiological systems which mediate CRF activation. For instance, evidence from receptor knockdown and pharmacological studies suggest involvement of the CRF1 receptor in anxiogenic-like behavior and the CRF-binding protein in learning and memory processes. The present studies examined the potential functional significance of the CRF2 receptor in relation to the CRF1 receptor using two animal models of anxiety and endocrine reactivity to a stressor. CRF1 and CRF2 receptor knockdown was achieved and confirmed autoradiographically within brain regions relevant to behavioral reactivity to stressors by chronic, central administration of antisense oligonucleotides. CRF1 but not CRF2, know down produced a significant anxiolytic-like effect in the Defensive Withdrawal relative to vehicle-treated and two missense oligonucleotide negative control groups. In contrast, neither antisense treatment altered endocrine or behavioral reactivity to a swim stressor. Thus, the present data support the reported role of CRF1 receptors in the mediation of anxiogenic-like behavior and suggest a functionally distinct for role for CRF2 receptors in brain.

Localization of ligand-binding domains of human corticotropin-releasing factor receptor: a chimeric receptor approach

Two CRF receptors, CRFR1 and CRFR2, have recently been cloned and characterized. CRFR1 shares 70% sequence identity with CRFR2, yet has much higher affinity for rat/human CRF (r/hCRF) than CRFR2. As a first step toward understanding the interactions between rat/human CRF and its receptor, the regions that are involved in receptor-ligand binding and/or receptor activation were determined by using chimeric receptor constructs of the two human CRFR subtypes, CRFR1 and CRFR2, followed by generating point mutations of the receptor. The EC50 values in stimulation of intracellular cAMP of the chimeric and mutant receptors for the peptide ligand were determined using a cAMP-dependent reporter system. Three regions of the receptor were found to be important for optimal binding of r/hCRF and/or receptor activation. The first region was mapped to the junction of the third extracellular domain and the fifth transmembrane domain; substitution of three amino acids of CRFR1 in this region (Val266, Tyr267, and Thr268) by the corresponding CRFR2 amino acids (Asp266, Leu267, and Val268) increased the EC50 value by approximately 10-fold. The other two regions were localized to the second extracellular domain of the CRFR1 involving amino acids 175-178 and His189 residue. Substitutions in these two regions each increased the EC50 value for r/hCRF by approximately 7- to 8-fold only in the presence of the amino acid 266-268 mutation involving the first region, suggesting that their roles in peptide ligand binding might be secondary.

Corticotropin-releasing factor (CRF), CRF-binding protein (CRF-BP), and CRF/CRF-BP complex in Alzheimer's disease and control postmortem human brain

In Alzheimer's disease (AD) there are dramatic reductions in human corticotropin-releasing factor (hCRF) concentration and reciprocal increases in CRF receptor density in the cortex. hCRF-binding protein (hCRF-BP), hCRF/hCRF-BP complex, and "free" hCRF were measured in 10 brain regions from control and AD postmortem human tissue. In the control brains hCRF-BP was heterogenously distributed and levels were at least 10-fold higher on a molar basis than total hCRF levels, suggesting that one major role of the binding protein is to limit the actions of hCRF at the hCRF receptors. Concordant with this hypothesis, the percentage of total hCRF that was in the bound inactive form ranged from 65 to 90% in most areas examined, with the exception of the caudate and globus pallidus where only 15 and 40% were complexed, respectively. hCRF-BP concentrations were similar in the control and AD groups except for Brodmann area (BA) 39 where there was a small but significant decrease in the AD group. Complexed hCRF levels were significantly decreased in BA 8/BA 9, BA 22, BA 39, nucleus basalis, and globus pallidus in the Alzheimer's group and free hCRF levels were significantly decreased only in three brain areas, BA 4, BA 39, and caudate; substantial (40%) but nonsignificant decreases were also noted in BA 8/BA 9 and BA 22. These data demonstrate that (1) a large proportion of the total hCRF in human brain is complexed to hCRF-BP and thus unavailable for hCRF receptor activation, (2) reductions in total hCRF alone do not necessarily predict reductions in bioactive free hCRF, and (3) total hCRF levels and hCRF-BP levels appear to be the main factors determining the quantity of bound and free hCRF in human brain.

Immunosuppressive phenotype of corticotropin-releasing factor transgenic mice is reversed by adrenalectomy

Stress elicits a wide range of physiological changes involving the nervous, endocrine, and immune systems. Corticotropin-releasing factor (CRF) plays a key role in orchestrating this response, activating both the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis, resulting in release of corticosteroids. The present study examines the immunological phenotype and responsiveness of CRF-transgenic (CRF-Tg) mice. The immune system of the CRF-Tg animals has profound changes compared to littermate controls, including a marked reduction in both cell number and immune responsiveness. There were also phenotypic changes in the lymphocytic composition of the various lymphoid organs, most notably in the spleen, where CRF-Tg mice had a greater percentage of T lymphocytes compared to littermate controls. Adrenalectomy of CRF-Tg reversed the immunological phenotype observed and restored immune responsiveness. These results demonstrate that CRF overexpression leads to profound impairment on lymphocyte development and function mediated via corticosteroids.

Brain corticotropin-releasing factor immunoreactivity and receptors in five inbred rat strains: relationship to forced swimming behaviour

In the present work we studied the relationship between behaviour in the forced swimming test (FST), a test that presumably measures depressive-like behaviour in rodents, and central corticotropin-releasing factor (CRF) concentration and binding in five strains of rats. The strains were: Brown-Norway (BN), Fisher (FIS) 344, Lewis (LEW), spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). The FST data corresponding to the pretest showed significant inter-strain differences in both struggling and immobility: BN and WKY rats displayed lower levels of struggling and longer periods of immobility, LEW and SHR rats showed intermediate levels, and FIS rats were the most active. The results of the pretest were roughly similar to those observed in the test, the activity of WKY being extremely low. The CRF binding revealed significant inter-strain differences in prefrontal cortex and hippocampus, but not in cerebellum, pons-medulla or hypothalamus: in the prefrontal cortex, BN and FIS rats showed greater CRF binding than LEW, SHR and WKY rats; in the hippocampus BN rats showed higher levels of CRF binding than the other strains. The study of CRF content in various brain areas revealed inter-strain differences in prefrontal cortex and pons-medulla, but not in parietal-temporal cortex or in hypothalamus (CRF concentrations in the hippocampus were not detectable): CRF content in the prefrontal cortex was higher in BN than in the other strains, although the differences with FIS were not statistically significant; in the pons-medulla, FIS and LEW showed significantly higher CRF content than the other strains. From the present results it appears that BN and WKY rats were more prone to adopt passive strategies in the FST, but they did not show higher brain CRF immunoreactivity or down-regulation of CRF receptors. Hence, although there were inter-strains differences in all variables studied, no evidence for a relationship between the FST behaviour and central CRF activity was found.

Corticotropin-releasing factor receptors: an overview

Corticotropin-releasing factor (CRF) is the primary physiological regulator of basal and stress-induced release of ACTH, beta-endorphin and other POMC-derived peptides from the pituitary and plays a major role in the brain and periphery in coordinating endocrine, electrophysiological, autonomic, behavioral and immune responses to stress. In addition, recent clinical data implicate CRF in the etiology and pathophysiology in a variety of endocrine, psychiatric and neurodegenerative disorders. The various effects of CRF are mediated by two distinct CRF receptors expressed at high levels in selected brain areas, but also at different levels in several other non-neuronal tissues. This chapter provides an overview of the current knowledge about CRF receptors including tissue specificity and regulatory aspects as well as molecularbiological, biochemical and pharmacological characteristics. In addition, neuroimmune, neuroendocrine and behavioral-related implications of the CRF receptor as well as its involvement in a variety of disorders are discussed. This review summarizes four decades of research beginning with the search for the factor that governs the release of ACTH and getting to the recent findings including the successful cloning of different receptor subtypes and the discovery of a new endogenous CRF-related ligand.

Enhancement of performance in multiple learning tasks by corticotropin-releasing factor-binding protein ligand inhibitors

Evidence favors a role for corticotropin-releasing factor (CRF) in learning and memory processes. A binding protein (CRF-BP) with the ability to inactivate CRF provides a novel target to modulate endogenous levels of CRF. The present studies employed three measures of information processing in rats in order to examine the impact of CRF system activation resulting from administration of CRF-BP ligand inhibitors, which increase levels of "free CRF." Acquisition of a visual discrimination paradigm and retention of a inhibitory avoidance task were dose dependently facilitated by central administration of a CRF-BP ligand inhibitor. CRF-BP ligand inhibitor treatment also improved performance in an active avoidance paradigm in aged animals. No nonspecific anorexic effects of the active dose of CRF-BP ligand inhibitor were detected in a food intake test. Moreover, the magnitude of in vivo efficacy of the CRF-BP ligand inhibitor peptide in producing a mild increase in motor activity was dissociated from that of a postsynaptic CRF receptor agonist that exerted robust and long-lasting activity increases. Thus, CRF-BP ligand inhibitors appear to elicit generalized learning enhancement effects without mimicking the robust nonspecific behavioral actions of a CRF receptor agonist.

Corticotropin-releasing factor-binding protein ligand inhibitor blunts excessive weight gain in genetically obese Zucker rats and rats during nicotine withdrawal

Elevation of the neuropeptide corticotropin-releasing factor (CRF) in the brain is associated with a reduction of food intake and body weight gain in normal and obese animals. A protein that binds CRF and the related peptide, urocortin, with high affinity, CRF-binding protein (CRF-BP), may play a role in energy homeostasis by inactivating members of this peptide family in ingestive and metabolic regulatory brain regions. Intracerebroventricular administration in rats of the high-affinity CRF-BP ligand inhibitor, rat/human CRF (6-33), which dissociates CRF or urocortin from CRF-BP and increases endogenous brain levels of "free" CRF or urocortin significantly blunted exaggerated weight gain in Zucker obese subjects and in animals withdrawn from chronic nicotine. Chronic administration of CRF suppressed weight gain nonselectively by 60% in both Zucker obese and lean control rats, whereas CRF-BP ligand inhibitor treatment significantly reduced weight gain in obese subjects, without altering weight gain in lean control subjects. Nicotine abstinent subjects, but not nicotine-naive controls, experienced a 35% appetite suppression and a 25% weight gain reduction following acute and chronic administration, respectively, of CRF-BP ligand inhibitor. In marked contrast to the effects of a CRF-receptor agonist, the CRF-BP ligand inhibitor did not stimulate adrenocorticotropic hormone secretion or elevate heart rate and blood pressure. These results provide support for the hypothesis that the CRF-BP may function within the brain to limit selected actions of CRF and/or urocortin. Furthermore, CRF-BP may represent a novel and functionally selective target for the symptomatic treatment of excessive weight gain associated with obesity of multiple etiology.

Cloning of a cDNA encoding a novel interleukin-1 receptor related protein (IL 1R-rp2)

We have identified and isolated both the rat and human cDNAs for a novel putative receptor related to the interleukin-1 type 1 receptor. We have named this protein interleukin 1 receptor related protein two (IL 1R-rp2). The rat cDNA for IL1R-rp2 was first identified using oligonucleotides of degenerate sequence in a polymerase chain reaction (PCR) paradigm with rat brain mRNA as the template. The protein encoded by both of these cDNAs are 561 amino acids long and exhibit 42% and 26% overall identity with the interleukin-1 type 1 and type 2 receptors, respectively. RNase protection assays from rat tissues revealed a predominant expression for IL 1R-rp2 in the lung and epididymis with lower levels detected in the testis and cerebral cortex. By in situ hybridization we were able to determine that the expression in rat brain appeared to be non-neuronal and associated with the cerebral vasculature. When expressed transiently in COS-7 cells the receptor was incapable of high affinity binding to either [125I]-recombinant human IL 1 alpha or [125I]-recombinant human IL 1 beta. Together, these data demonstrate the existence of a novel protein that is related to the interleukin-1 receptor but does not bind IL-1 by itself.

Neurobiology of corticotropin releasing factor (CRF) receptors and CRF-binding protein: implications for the treatment of CNS disorders

The actions of CRF in the brain and in the periphery are mediated through multiple binding sites. There are three receptors, CRF1, CRF2 alpha and CRF2 beta, which encode 411, 415 and 431 amino acid proteins and transduce signals via the stimulation of intracellular cAMP production. The recent identification of high-affinity non-peptide CRF receptor antagonists should allow for rapid progress in drug development of CRF receptor antagonists. In addition to the receptors, the actions of CRF in brain and in the periphery can also be modulated by a binding protein of 322 amino acids. Ligands of CRF-BP, such as CRF (6-33) can elevate brain levels of 'free' CRF and improve learning and memory without stress-like side effects of CRF receptor agonists. Urocortin, a mammalian CRF-related peptide with close sequence homology to fish urotensin, interacts with CRF1, CRF2 receptors and with CRF-BP. These data indicate that CRF receptor antagonists may be useful for the treatment of the disease states where CRF is elevated such as anxiety and depression, anorexia nervosa and stroke and that ligand inhibitors of CRF-BP may be used to elevate brain levels of 'free' urocortin and other CRF-related peptides.

125I-Tyro-sauvagine: a novel high affinity radioligand for the pharmacological and biochemical study of human corticotropin-releasing factor 2 alpha receptors

Corticotropin-releasing factor (CRF) receptors encoded by two distinct genes have recently been identified and termed CRF1 and CRF2. CRF and the non-mammalian-related peptide sauvagine bind to and activate CRF1 receptors with high affinity and equal potency. Although CRF is significantly weaker at the CRF2 receptor, sauvagine retains its high affinity interactions with this receptor subtype. We expressed the human CRF1 and CRF2 receptor subtypes in stable cell lines and characterized 125I-Tyr0-sauvagine, a high affinity radiolabel suitable for the pharmacological and functional profiles of these proteins. 125I-Tyr0-sauvagine has high affinity (200-400 PM) for CRF1 receptors and demonstrates a pharmacological profile identical to that of 125I-Tyr0-ovine CRF-labeled CRF1 receptors. 125I-Tyr0-sauvagine binding to human CRF2 alpha receptors is saturable and of high affinity (KD = 100-300 PM) and demonstrates guanine nucleotide sensitivity typical of agonist binding to receptors. The pharmacological profile of 125I-Tyr0-sauvagine binding to CRF2 alpha receptors with respect to inhibition by CRF-related analogs is similar to the agonist profile of potencies obtained by measurements of cAMP production stimulated by these analogs in CRF2 alpha expressing cell lines and distinct from the profile of the CRF1 receptor subtype. Thus, the related nonmammalian peptides sauvagine and urotensin have high affinity and rat/ human CRF and ovine CRF have lower affinity for CRF2 receptors labeled with 125I-Tyr0-sauvagine. Because the distribution of CRF1 and CRF2 alpha receptors has been demonstrated to be distinct, suggesting selective functional roles for each receptor subtype, the ability to label CRF2 alpha receptors with 125I-Tyr0-sauvagine in vitro represents a unique opportunity for the discovery of subtype-selective nonpeptide ligands, which would presumably target different aspects of CRF-mediated disorders. We have thus identified and characterized a novel high affinity radioligand for the labeling of CRF2 receptors.

Cloning and characterization of an alternatively processed human type II interleukin-1 receptor mRNA

Two types of interleukin (IL)-1 receptors with three extracellular immunoglobulin-like domains, limited homology (28%), and different pharmacological characteristics termed type I and type II have been cloned from mouse and human cell lines. Both receptors exist in transmembrane and soluble forms; the soluble IL-1 receptor is thought to be post-translationally derived from cleavage of the extracellular portion of the membrane receptors. In preliminary cross-linking studies with radiolabeled IL-1, we found that monkey kidney COS1 cells express a soluble receptor with molecular mass of approximately 55-60 kDa, which is different from previously reported soluble IL-1 receptors. This soluble IL-1 receptor protein from COS1 cells was purified to homogeneity by affinity chromatography using recombinant IL-1beta as the ligand and shown to have an affinity for human 125I-IL-1beta (KD approximately 2-3 nM) comparable to the human type II IL-1 receptor (IL-1RII). The purified protein was microsequenced, and the sequence information was used to design primers to clone the COS1 IL-1RII using reverse transcription-coupled polymerase chain reaction; the DNA comparison with monkey COS1 and human IL-1RII indicate that they are 95% identical at the nucleic acid and amino acid levels. In addition, another cDNA, which represents an alternatively processed mRNA of the IL-1RII gene, was also cloned both from monkey COS1 and human Raji cells and was shown to have approximately 95% sequence identity between these species. While the cDNA of the novel alternatively processed gene has a 5' end identical to the IL-1RII, the 200 base pairs at the 3' end are different and the sequence predicts a soluble IL-1 receptor protein of 296 amino acids. Radioligand binding studies of the alternatively processed IL-1RII mRNA demonstrated kinetic and pharmacological characteristics similar to the known type II IL-1 receptor. COS7 cells (which lack IL-1 receptor) transfected with the transmembrane form of the human IL-1RII cDNA showed 125I-IL-1beta binding in both the membrane fractions and supernatant. In contrast, COS7 cells transfected with the alternatively processed human IL-1RII cDNA showed high affinity 125I-IL-1beta binding (Ki approximately 1.2 nM) predominantly in the supernatant; a very small amount of detectable membrane IL-1 binding activity was also observed presumably due to association of the soluble IL-1 receptor and membrane-integrated proteins. In cross-linking and ligand blot studies, the alternatively processed human IL-1RII cDNA-transfected COS7 cells expressed a soluble IL-1 receptor with molecular masses ranging from 60 to 160 kDa, further indicating the association between this soluble IL-1 receptor and other soluble proteins. In summary, we report the purification and characterization of a soluble IL-1 receptor expressed by COS1 cells and the cloning of an alternatively processed type II IL-1 receptor mRNA from both human and COS1 cells. The alternative splicing of a primary transcript leading to a secreted protein provides a potentially important mechanism by which soluble IL-1RII can be produced.

Regulation of corticotropin-releasing factor-binding protein expression in cultured rat astrocytes

The regulation of brain corticotropin-releasing factor (CRF)-binding protein (BP), an endogenous modulator of the CRF family of neuropeptides, has been difficult to pursue due to a lack of basal expression in a known cell line or primary cells in vitro. In light of the ability of intracellular factors to modulate neuronal and glial function, we examined the effects of a variety of signal transduction modulators on CRF-BP expression in cultured astrocytes. In particular, the effect of agents that stimulate protein kinase A and protein kinase C pathways was evaluated. CRF-BP was measured using a ligand immunoradiometric assay. Forskolin, dibutyryl cyclic AMP and 3-isobutyl-1-methylxanthine treatment resulted in a dose-dependent increase in CRF-BP levels detected in the medium from astrocytes and neurons. The increase in CRF-BP expression was not due to increased cell proliferation as measured by [3H]thymidine incorporation. In addition, treatment of the astrocytes with phorbol myristate acetate, a protein kinase C activator, caused a robust increase in CRF-BP levels in the medium. Steroids such as dexamethasone, corticosterone, hydrocortisone and, to a lesser extent, dehydroepiandosterone inhibited the stimulated release of CRF-BP from astrocytes. These data define a primary role for intracellular messengers in regulating CRF-BP expression in neurons and astrocytes.

Measurement of corticotropin-releasing factor (CRF), CRF-binding protein (CRF-BP), and CRF/CRF-BP complex in human plasma by two-site enzyme-linked immunoabsorbant assay

The actions of human corticotropin-releasing factor (hCRF) in brain, pituitary, and plasma are modulated by a 37-kDa protein [CRF-binding protein (CRF-BP)] that binds to hCRF and neutralizes the peptide's biological activity, suggesting that only the free unbound peptide is biologically active. To accurately predict the biological consequences resulting from changes in total hCRF levels, we have developed two-site enzyme-linked immunosorbent assays (ELISAs) for hCRF-BP, free hCRF, and the hCRF-BP/hCRF complex. The assays were validated by measuring each factor in 1) maternal plasma at times when CRF and hCRF-BP levels are altered, and 2) plasma from normal elderly human subjects who have undergone a hCRF stimulation test. The hCRF-BP ELISA has a sensitivity of 2.7 fmol and a range of detection from 2.7-8000 fmol. Both the hCRF and hCRF-BP/ hCRF assays have a sensitivity of 0.4 fmol, with a useful range of detection from 0.4-40 fmol. Maternal plasma hCRF-BP levels remained unaltered between the 16-21 and 34-39 month gestational age groups. However, levels rose from 0.88 +/- 0.069 nmol/L in the 16-21 month gestational age group to 1.01 +/- 0.09 nmol/L in the 28-33 month gestational age group. Bound hCRF levels dramatically rose from undetectable at 16-21 months of gestation to 200 +/- 69 and 442 +/- 106 pmol/L in the 28-33 and 34-39 month gestational age groups, respectively. In comparison, free hCRF levels remained low throughout gestation, but dramatically rose to 318 +/- 120 pmol/L from 34-39 months of gestation. Binding site occupancy on the hCRF-BP decreased when bound and free hCRF levels were elevated. After treating the third trimester plasma sample with the high affinity hCRF-BP ligand, alpha-helical CRF-(9-41), all of the bound hCRF was displaced from the binding protein, and free hCRF levels rose from 87 to 284 pmol/L. The plasma hCRF-BP level was 0.9 +/- 0.08 nmol/L in normal human volunteers (10 men and 9 women; mean +/- SD age, 74.2 +/- 7.7 yr), decreased to 60% of basal levels 15 min after a bolus injection of 1 microgram/kg synthetic hCRF, and gradually returned to preinjection levels after 120 min. Conversely, bound and free hCRF levels increased from undetectable levels before hCRF injection to 0.58 +/- 0.03 nmol/L at 15 min and then rapidly decreased to undetectable levels at 120 min. These data validate the ELISAs in combination with high affinity hCRF-BP ligands for measuring bound and free hCRF in human plasma and suggest the utility of these assays for further determining alterations in peripheral CRF in conditions such as pregnancy.

Urocortin interaction with corticotropin-releasing factor (CRF) binding protein (CRF-BP): a novel mechanism for elevating "free' CRF levels in human brain

Here we demonstrate that urocortin, a new mammalian member of the corticotropin-releasing factor (CRF) neuropeptide family has high affinity for both the recombinant human CRF binding protein (CRF-BP) and for a membrane-associated form of the protein solubilized from postmortem human cerebrocortical brain tissue. The rank order of binding potency for both the human recombinant CRF-BP and for the solubilized human brain CRF-BP is: urotensin > hCRF > urocortin > sauvagine. The bound hCRF/hCRF-BP complex was detected in the postmortem human brain tissue using an ELISA assay specific for the hCRF/hCRF-BP complex. A large proportion (65%) of the endogenous hCRF was found to be complexed to the CRF-BP and thus unavailable for CRF receptor activation. Incubation of human brain postmortem tissue extracts with urocortin and urotensin resulted in a dramatic decrease in hCRF/hCRF-BP levels and a concomitant increase in "free' hCRF levels. Thus, urocortin and other putative CRF-related peptides may elevate endogenous levels of "free' hCRF in brain by displacing hCRF from the binding protein. These data define an indirect endogenous mechanism for activation of CRF receptors by new mammalian members of the CRF family of neuropeptides.

Age-related reciprocal modulation of interleukin-1beta and interleukin-1 receptors in the mouse brain-endocrine-immune axis

The cytokine interleukin-1 (IL-1) alters a variety of immune, central nervous system and neuroendocrine activities characteristic of an integrator of the brain-endocrine-immune response to stress. In an attempt to define the regulation of IL-1 and IL-1 receptors in the mouse brain-endocrine-immune axis during maturation, we measured tissue levels of IL-1beta using an ELISA and iodine-125-labeled recombinant human interleukin-1alpha ([125I]IL-1alpha) binding in hippocampus, pituitary, testis and spleen following intraperitoneal injection of saline or the bacterial endotoxin, lipopolysaccharide (LPS) in 3- and 24-week-old C57BL/6 mice. Basal IL-1beta levels were detectable in all the tissues examined. Basal levels of IL-1beta in the hippocampus, spleen and testis in 24-week-old mice were significantly higher than those in 3-week-old mice. [125I]IL-1alpha binding was detectable in all the mouse tissues examined and [125I]IL-1alpha binding levels in the pituitary, spleen and testis in 3-week-old mice were significantly higher than those in 24-week-old mice. To further evaluate the modulation of IL-1 receptors in aging, we measured [125I]IL-1alpha binding in 2-, 5-, 10-, 18-, and 24-month-old mice. [125I]IL-1alpha binding in testis in 24-month-old mice was higher than the other groups; [125I]IL-1alpha binding in the hippocampus and spleen was unchanged during these periods. Dramatic increases in IL-1beta concentrations were observed at 2 h after LPS injection in the pituitary, spleen, testis and plasma in both 3- and 24-week-old mice groups. In contrast, IL-1beta levels in the hippocampus increased in response to LPS injection only in 24-week-old mice. [125I]IL-1alpha binding in hippocampus was significantly decreased in 24- but not in 3-week-old mice after LPS injection. [125I]IL-1alpha binding in the spleen and testis were significantly decreased in both age groups following LPS administration. These data demonstrate differential regulation of IL-1 and its receptors in the brain-endocrine-immune axis during maturation and in response to endotoxin challenge.

Rat homolog of mouse interleukin-1 receptor accessory protein: cloning, localization and modulation studies

A protein which facilitates the binding between interleukin-1 (IL-1) and the type I IL-1 receptor (designated as interleukin-1 receptor accessory protein, IL-1RAcP) has recently been cloned in mouse cells. In the present study, a rat homolog of the mouse IL-1RAcP was isolated from a rat superior cervical ganglion library. The deduced 570 amino acid sequences between rat and mouse IL-1RAcP have > 95% sequence identity to each other with similar predicted signal peptide sequence (20 amino acids), extracellular domain (339 amino acids), a single transmembrane domain (24 amino acids) and a long intracellular domain (187 amino acids). The rat IL-1RAcP has approximately 25% sequence identity to the rat type I IL-1 receptor and a predicted extracellular domain with three immunoglobulin-like loops. RNase protection assays demonstrated that rat IL-1RAcP is expressed in both brain and peripheral tissues with the highest densities present in liver and brain areas such as hypothalamus, cerebral cortex, hippocampus and cerebellum; significantly lower densities were present in lung and in immune tissues such as thymus and spleen. The presence of IL-1RAcP in brain was confirmed by in situ hybridization histochemical studies with a discrete localization present in the dentate gyrus of the hippocampus. The IL-1RAcp was down-regulated in parallel with the type I IL-1 receptor in the liver following endotoxin treatment in rats. These data demonstrating the presence and modulation of a rat homolog of a mouse IL-1RAcP, which is highly expressed in brain and peripheral tissues containing type I rat IL-1 receptor, further suggest the importance of the interaction between the two proteins in rat in modulating the actions of IL-1. On the other hand, the presence of the IL-1RAcP in brain areas which show an absence of type I IL-1 receptors suggests additional functions for this protein in the rat.

Corticotrophin-releasing factor receptors: from molecular biology to drug design

Corticotrophin-releasing factor (CRF) acts within both the brain and the periphery to coordinate the overall response of the body to stress. The involvement of the CRF systems in a variety of both CNS and peripheral disease states has stimulated great interest in this peptide as a potential site of therapeutic intervention. The recent cloning of multiple CRF receptor subtypes has precipitated a new era in CRF research that has allowed precise molecular, pharmacological and anatomical examination of mammalian CRF receptors. In this article, Derek Chalmers and colleagues highlight the major differences between the two classes of CRF receptors, CRF1 and CRF2, and a functionally related CRF-binding protein, and discuss the relevance of these sites to the ongoing development of CRF-based therapeutics.

Homologous desensitization of human corticotropin-releasing factor1 receptor in stable transfected mouse fibroblast cells

Previous radioligand binding and second messenger studies have shown that corticotropin-releasing factor (CRF) modulates its receptor following both in vivo and in vitro treatment. In the present study, we determined the sequence of events leading to CRF-induced downregulation and desensitization of cloned CRF receptors in murine fibroblast cells (Ltk-) stably transfected with CRF1 DNA (from human pituitary). Treatment of cells with rat/human CRF produced a dose- and time-dependent decrease in [125I]Tyr degrees-ovine CRF ([125I]oCRF) binding and a concomitant decrease in CRF-stimulated adenylate cyclase activity. Significant decreases in [125I]oCRF binding and agonist-stimulated cAMP production were evident minutes after CRF treatment with maximal (60-80%) reductions seen following 1 h of CRF treatment. Scatchard analysis revealed that the decrease in [125I]oCRF binding was due to the downregulation of the receptor with no significant alteration seen in the affinity of the ligand. Since the transfected cell line is engineered using an artificial promoter, we did not detect any significant changes in CRF1 receptor mRNA levels following CRF treatment for up to 24 h.

Interleukin-1 receptors in the brain-endocrine-immune axis. Modulation by stress and infection

In the present study, we examined the in vitro and in vivo modulation of IL-1 receptors by stress and endotoxin treatment. The treatment of AtT-20 mouse pituitary adenoma cells for 24 h with neuroendocrine mediators of stress such as CRF and catecholamines produced dose-dependent increases in cAMP production and [125I]IL-1 alpha binding. In contrast, somatostatin and dexamethasone significantly inhibited CRF-stimulated cAMP production and decreased both basal and CRF-mediated increases in [125I]IL-1 alpha binding. Furthermore, in keeping with the effects of stress mediators to up-regulate IL-1 receptors in AtT-20 cells, ether-laparotomy stress in mice resulted in a significant increase in [125I]IL-1 alpha binding in the pituitary with no significant alterations observed in the brain; in contrast, [125I]oCRF binding in the pituitary was significantly decreased after the ether-laparotomy stress. Next, we investigated the modulation of IL-1 beta levels and [125I]IL-1 alpha binding following endotoxin treatment. IL-1 beta levels were dramatically increased in the peripheral tissues (pituitary, testis, and spleen) at 2-6 h after a single LPS injection (30 micrograms LPS/mouse); however, no significant changes were observed in brain (hippocampus and hypothalamus). [125I]IL-1 alpha binding in the pituitary gland, liver, spleen, and testis was significantly decreased at 2 h following a single administration of both low (30 micrograms LPS/mouse) and high (300 micrograms LPS/mouse) doses of endotoxin. [125I]IL-1 alpha binding in the hippocampus was not significantly altered at 2 h by low dose of LPS and was significantly decreased by high-dose administration of LPS (300 micrograms/mouse). Following two LPS injections (at 0 and 12 h), dramatic increases in IL-1 beta concentrations in the hypothalamus, hippocampus, spleen, and testis were observed at 2 h after the second LPS injection; a small but statistically nonsignificant change was evident in the pituitary. Moreover, dramatic decreases in [125I]IL-1 alpha binding were seen after two injections of 30 micrograms LPS/mouse in both central and peripheral tissues. These data provide further support for a role for IL-1 in coordinating brain-endocrine-immune responses to stress and infection.

Modulation of interleukin-1 receptors in the brain-endocrine-immune axis by stress and infection

We summarize data from some of our recent studies on in vitro and in vivo modulation of interleukin-1 (IL-1) receptors in the mouse brain-endocrine-immune axis by stress and infection. Ether-laparotomy stress in mice resulted in a selective increase in pituitary IL-1 receptors and a significant decrease in pituitary receptors for corticotropin-releasing factor (CRF), a major regulator of the endocrine response to stress. Intraperitoneal injection of rat/human CRF mimicked the effects of stress and resulted in a dramatic increase in [125I]IL-1alpha binding in the pituitary; [125I]IL-1alpha binding in the hippocampus, spleen, and testis was unaffected by stress or CRF treatment. Glucocorticoid treatment with dexamethasone alone did not alter [125I]IL-1alpha binding but significantly inhibited CRF-induced upregulation of IL-1 receptors in the pituitary. The intracellular mechanism(s) involved in stress and CRF-induced upregulation of IL-1 receptors in the pituitary gland were examined by evaluating the effects of treatment of AtT-20 mouse pituitary corticotroph cells with a variety of neuroendocrine mediators of stress. CRF, forskolin, and isoproterenol (beta2 adrenergic receptor agonist) produced dose-dependent increases in cAMP production and [125I]IL-1alpha binding. In contrast, somatostatin and dexamethasone significantly inhibited CRF-stimulated increase of cAMP production and [125I]IL-1alpha binding, suggesting a primary role for cAMP in the regulation of pituitary IL-1 receptors. Next, we investigated the modulation of IL-1beta levels and IL-1 receptors following infection of mice with the endotoxin, lipopolysaccharide (LPS). Acute administration of low doses of endotoxin (30 mu g LPS/mouse) dramatically increased IL-1beta levels and reciprocally decreased [125I]IL-1alpha binding in peripheral tissues (pituitary, testis, liver, and spleen) but not in brain (hippocampus). This effect appeared to be dose related since higher doses of endotoxin (300 mu g LPS/mouse) significantly decreased [125I]IL-1alpha binding in both peripheral tissues and brain. Endotoxin induced modulation of the IL-1 system was also dependent on the treatment regimen since two low-dose LPS injections (at 0 and 12 h) increased IL-1beta concentrations and decreased [125I]IL-1alpha binding in both central and peripheral tissues. These data provide further support for a role for IL-1 in coordinating brain-endocrine-immune responses to stress and infection.

Displacement of corticotropin releasing factor from its binding protein as a possible treatment for Alzheimer's disease

In Alzheimer's disease (AD) there are dramatic reductions in the content of corticotropin releasing factor (CRF), reciprocal increases in CRF receptors, and morphological abnormalities in CRF neurons in affected brain areas. Cognitive impairment in AD patients is associated with a lower cerebrospinal fluid concentration of CRF, which is known to induce increases in learning and memory in rodents. This suggests that CRF deficits contribute to cognitive impairment. The identification in post-mortem brain of CRF-binding protein (CRF-BP), a high-affinity binding protein that inactivates CRF, and the differential distribution of CRF-BP and CRF receptors, provides the potential for improving learning and memory without stress effects of CRF receptor agonists. Here we show that ligands that dissociate CRF from CRF-BP increase brain levels of 'free CRF' in AD to control levels and show cognition-enhancing properties in models of learning and memory in animals without the characteristic stress effects of CRF receptor agonists.

Corticotropin releasing factor binding protein (CRF-BP) is expressed in neuronal and astrocytic cells

Corticotropin releasing factor (CRF) binding protein (CRF-BP) was measured in media and cell lysates of primary rat astrocytes, microglia and neurons with the use of a ligand immunoradiometric assay (LIRMA). A low basal level of CRF-BP was detected in the media and cell lysates from primary neuronal and astrocyte cells after 48 h in culture. No basal expression of CRF-BP was detected in cell lysates or media from primary microglial cultures. The CRF-BP expressed in cultured astrocytes and neurons had the same pharmacological characteristics as the human recombinant molecule. After forskolin, IBMX or forskolin/IBMX treatment, a robust increase in secreted CRF-BP levels in the media from astrocytes and neurons, but not microglia, was observed. An increase in CRF-BP-like immunoreactivity in cell lysates was also observed after IBMX/forskolin treatment. In situ hybridization analysis revealed that CRF-BP mRNA was increased in primary cultured astrocytes after IBMX/forskolin stimulation suggesting that regulation was at the level of gene transcription. 'Axon sparing' lesions produced with 0.12 M quinolinic acid in PBS injected intracerebrally (unilaterally into dorsal hippocampus) resulted in loss of CRF-BP expression in neurons. These data provide evidence for the differential localization and regulation of CRF-BP in different cell types in brain and suggest that CRF-BP expression may be locally increased in disease states associated with astrocytosis and gliosis.

Localization of novel corticotropin-releasing factor receptor (CRF2) mRNA expression to specific subcortical nuclei in rat brain: comparison with CRF1 receptor mRNA expression

Corticotropin-releasing factor (CRF) is the primary factor involved in controlling the release of ACTH from the anterior pituitary and also acts as a neurotransmitter in a variety of brain systems. The actions of CRF are mediated by G-protein coupled membrane bound receptors and a high affinity CRF receptor, CRF1, has been previously cloned and functionally characterized. We have recently isolated a cDNA encoding a second member of the CRF receptor family, designated CRF2, which displays approximately 70% homology at the nucleotide level to the CRF1 receptor and exhibits a distinctive pharmacological profile. The present study utilized in situ hybridization histochemistry to localize the distribution of CRF2 receptor mRNA in rat brain and pituitary gland and compared this with the distribution of CRF1, receptor expression. While CRF1 receptor expression was very high in neocortical, cerebellar, and sensory relay structures, CRF2 receptor expression was generally confined to subcortical structures. The highest levels of CRF2 receptor mRNA in brain were evident within the lateral septal nucleus, the ventromedial hypothalamic nucleus and the choroid plexus. Moderate levels of CRF2 receptor expression were evident in the olfactory bulb, amygdaloid nuclei, the paraventricular and suraoptic nuclei of the hypothalamus, the inferior colliculus and 5-HT-associated raphe nuclei of the midbrain. CRF2-expressing cells were also evident in the bed nucleus of the stria terminalis, the hippocampal formation and anterior and lateral hypothalmic areas. In addition, CRF2 receptor mRNA was also found in cerebral arterioles throughout the brain. Within the pituitary gland, CRF2 receptor mRNA was detectable only at very low levels in scattered cells while CRF1 receptor mRNA was readily detectable in anterior and intermediate lobes. This heterogeneous distribution of CRF1 and CRF2 receptor mRNA suggests distinctive functional roles for each receptor in CRF-related systems. The CRF1 receptor may be regarded as the primary neuroendocrine pituitary CRF receptor and important in cortical, cerebellar and sensory roles of CRF. The anatomical distribution of CRF2 receptor mRNA indicates a role for this novel receptor in hypothalamic neuroendocrine, autonomic and general behavioral actions of central CRF.

Corticotropin releasing factor (CRF) binding protein: a novel regulator of CRF and related peptides

A 37-kDa corticotropin releasing factor (CRF) binding protein (CRF-BP) was purified from human plasma by repeated affinity purification and subsequently sequenced and cloned. The human and rat CRF-BP cDNAs encode proteins of 322 amino acids with one putative signal sequence, one N-glycosylation site, and 10 conserved cysteines. Human CRF-BP binds human CRF with high affinity but has low affinity for the ovine peptide. In contrast, sheep CRF-BP binds human and ovine CRF with high affinity. The CRF-BP gene consists of seven exons and six introns and is located on chromosome 13 and loci 5q of the mouse and human genomes, respectively. CRF-BP inhibits the adrenocorticotrophic hormone (ACTH) releasing properties of CRF in vitro. CRF-BP dimerizes after binding CRF and clears the peptide from blood. This clearance mechanism protects the maternal pituitary gland from elevated plasma CRF levels found during the third trimester of human pregnancy. CRF-BP is expressed in the brains of all species so far tested but is uniquely expressed in human liver and placenta. In brain, CRF-BP is membrane associated and is predominantly expressed in the cerebral cortex and subcortical limbic structures. In some brain areas CRF-BP colocalizes with CRF and CRF receptors. The protein is also present in pituitary corticotropes, where it is under positive glucocorticoid control, and is likely to locally modulate CRF-induced ACTH secretion. The ligand requirements of the CRF receptor and the CRF-BP can be distinguished in that central human CRF fragments, such as CRF (6-33) and CRF (9-33), have high affinity for CRF-BP but low affinity for the CRF receptor. The binding protein's ability to inhibit CRF-induced ACTH secretion can be reversed by CRF (6-33) and CRF (9-33), suggesting that ligand inhibitors may have utility in elevating free CRF levels in disease states associated with decreased CRF. Thus, by controlling the amount of free CRF which activates CRF receptors, it is likely that the CRF-BP is an important modulator of CRF both in the CNS and in the periphery.

CRF2 alpha and CRF2 beta receptor mRNAs are differentially distributed between the rat central nervous system and peripheral tissues

We have recently described the cloning and characterization of a novel corticotropin-releasing factor receptor subtype (CRF2) from rat brain that exists in two alternatively spliced forms, CRF2 alpha and CRF2 beta. These forms differ in their N-terminal coding sequence which results in the production of two distinct receptors of 411 and 431 amino acids, respectively. To assess whether these two forms might represent distinct targets for CRF action, RNase protection and in situ hybridization studies were performed using specific N-terminal cRNA probes. The results showed a differential distribution of the mRNAs for these two receptor forms in the rat. The mRNA for CRF2 alpha is found almost exclusively in the brain, particularly in the hypothalamus, lateral septum, and olfactory bulb, whereas the mRNA for CRF2 beta appears to be both in the brain and in the periphery, with the greatest abundance in the heart and skeletal muscle. Thus, the data suggest that these alternatively spliced forms of the CRF2 receptor may represent functionally distinct CRF receptors. In addition, it highlights the importance of probe specificity for in situ hybridization studies.

Corticotropin-releasing factor treatment upregulates interleukin-1 receptors in the mouse pituitary: reversal by dexamethasone

Intraperitoneal injection of rat/human corticotropin-releasing factor (CRF) (40 micrograms/kg/0.2 ml of saline) resulted in a dramatic increase in specific iodine-125-labeled human interleukin-1 alpha ([125I]IL-1 alpha) binding in the male C57BL/6 mouse pituitary at 2 and 6 h after the injection although it did not affect [125I]IL-1 alpha binding in the mouse hippocampus, spleen and testis at any time after the injection. [125I]IL-1 alpha binding was unchanged at 2 h following dexamethasone (DEX) treatment (1 mg/kg/0.2 ml of 4% ethanol-saline) in the mouse pituitary and the hippocampus. In contrast, DEX inhibited CRF-induced upregulation of IL-1 receptors in the pituitary at 2 h after the injection. These data demonstrate complex interactions between CRF and DEX on IL-1 receptors during stress.

Modulation of interleukin-1 receptors in the neuro-endocrine-immune axis

Interleukin-1 (IL-1) receptors with kinetics, pharmacological and biochemical characteristics of type I IL-1 receptors have been identified in the mouse neuro-endocrine-immune axis. In the present study, we examined the in-vitro and in-vivo modulation of IL-1 receptors by stress and endotoxin treatment. The treatment of AtT-20 mouse pituitary adenoma cells for 24 hr with neuro-endocrine mediators of stress such as corticotropin releasing factor (CRF) and catecholamine (beta 2 adrenergic) receptor agonists produced a dose-dependent increase in cAMP and [125I]IL-1 alpha binding. In contrast, somatostatin and dexamethasone significantly inhibited CRF-stimulated cAMP production and decreased both basal and CRF-mediated increase of [125I]IL-1 alpha binding. Furthermore, in keeping with the effects of stress mediators to upregulate IL-1 receptors in AtT-20 cells, ether-laparotomy stress in mice resulted in a significant increase in [125I]IL-1 alpha binding in the pituitary with no significant alterations observed in the brain; in contrast, [125I]oCRF binding in the pituitary was significantly decreased after the ether-laparotomy stress. Next, we investigated the modulation of IL-1 beta levels and [125I]IL-1 alpha binding following endotoxin lipopolysaccharide (LPS) treatment. IL-1 beta levels were dramatically increased in the peripheral tissues (pituitary, testis and spleen) at 2-6 hr after a single LPS injection (30 micrograms LPS/mouse). However, no significant changes were observed in brain (hippocampus and hypothalamus). [125I]IL-1 alpha binding in the pituitary gland, liver, spleen and testis was significantly decreased at 2 hr following a single administration of both low (30 micrograms LPS/mouse) and high (300 micrograms LPS/mouse) doses of endotoxin. [125I]IL-1 alpha binding in the hippocampus was not significantly altered at 2 hr by a low dose of LPS and was significantly decreased by high dose administration of LPS (300 micrograms/mouse). Following two LPS injections (at 0 and 12 hr), dramatic increases in IL-1 beta concentrations in the hypothalamus, hippocampus, spleen and testis were observed at 2 hr after the second LPS injection; a small but statistically nonsignificant change was evident in the pituitary. Moreover, dramatic decreases in [125I]IL-1 alpha binding were seen after two injections of 30 micrograms LPS/mouse in both central and peripheral tissues. These data provide further support for a role for IL-1 in co-ordinating neuro-endocrine-immune responses to stress and infection.

Relative affinities of dopaminergic drugs at dopamine D2 and D3 receptors

Quantitative autoradiography was used to evaluate the pharmacological profile of dopamine D2-like receptors labeled by [125I]iodosulpiride. Caudate/putamen, a brain region associated primarily with dopamine D2 receptor mRNA, was used as a prototypical D2 tissue; cerebellar lobule X (D3 mRNA associated), as a D3 tissue. 7-OH-DPAT ((+/-)-2-dipropylamino-7-hydroxy-1,2,3,4- tetrahydronaphthalene) exhibited selectively for cerebellar receptors (24-fold), followed by quinpirole (6-fold). Haloperidol and domperidone were 4- and 18-fold more potent at striatal receptors, respectively. These data are in close agreement with that derived from dopamine D2 and D3 receptor-expressing cell lines.