CRF receptor type 1 and 2 expression and anatomical distribution in the rat colon

Role of CRH in colitis and colitis-associated cancer: a combinative result of central and peripheral effects?

Corticotropin-releasing factor family peptides (CRF peptides) comprise corticotropin releasing hormone (CRH), urocortin (UCN1), UCN2 and UCN3. CRH is first isolated in the brain and later with UCNs found in many peripheral cells/tissues including the colon. CRH and UCNs function via the two types of receptors, CRF1 and CRF2, with CRH mainly acting on CRF1, UCN1 on both CRF1 &CRF2 and UCN2-3 on CRF2. Compiling evidence shows that CRH participates in inflammation and cancers via both indirect central effects related to stress response and direct peripheral influence. CRH, as a stress-response mediator, plays a significant central role in promoting the development of colitis involving colon motility, immunity and gut flora, while a few anti-colitis results of central CRH are also reported. Moreover, CRH is found to directly influence the motility and immune/inflammatory cells in the colon. Likewise, CRH is believed to be greatly related to tumorigenesis of many kinds of cancers including colon cancer via the central action during chronic stress while the peripheral effects on colitis-associated-colon cancer (CAC) are also proved. We and others observe that CRH/CRF1 plays a significant peripheral role in the development of colitis and CAC in that CRF1 deficiency dramatically suppresses the colon inflammation and CAC. However, up to date, there still exist not many relevant experimental data on this topic, and there seems to be no absolute clearcut between the central and direct peripheral effects of CRH in colitis and colon cancer. Taken together, CRH, as a critical factor in stress and immunity, may participate in colitis and CAC as a centrally active molecule; meanwhile, CRH has direct peripheral effects regulating the development of colitis and CAC, both of which will be summarized in this review.

Corticotropin-releasing factor receptor 1 (CRF-R1) antagonists: Promising agents to prevent visceral hypersensitivity in irritable bowel syndrome

Corticotropin-releasing factor (CRF) is a 41-amino acid polypeptide that coordinates the endocrine system, autonomic nervous system, immune system, and physiological behavior. CRF is a signaling regulator in the neuro-endocrine-immune (NEI) network that mediates visceral hypersensitivity. Rodent models to simulate changes in intestinal motility similar to those reported in the irritable bowel syndrome (IBS), demonstrate that the CRF receptor 1 (CRF-R1) mediates intestinal hypersensitivity under many conditions. However, the translation of preclinical studies into clinical trials has not been successful possibly due to the lack of sufficient understanding of the multiple variants of CRF-R1 and CRF-R1 antagonists. Investigating the sites of action of central and peripheral CRF is critical for accelerating the translation from preclinical to clinical studies.

Present and Future Therapeutic Approaches to Barrier Dysfunction

There is converging and increasing evidence, but also uncertainty, for the role of abnormal intestinal epithelial barrier function in the origin and development of a growing number of human gastrointestinal and extraintestinal inflammatory disorders, and their related complaints. Despite a vast literature addressing factors and mechanisms underlying changes in intestinal permeability in humans, and its connection to the appearance and severity of clinical symptoms, the ultimate link remains to be established in many cases. Accordingly, there are no directives or clinical guidelines related to the therapeutic management of intestinal permeability disorders that allow health professionals involved in the management of these patients to carry out a consensus treatment based on clinical evidence. Instead, there are multiple pseudoscientific approaches and commercial propaganda scattered on the internet that confuse those affected and health professionals and that often lack scientific rigor. Therefore, in this review we aim to shed light on the different therapeutic options, which include, among others, dietary management, nutraceuticals and medical devices, microbiota and drugs, and epigenetic and exosomes-manipulation, through an objective evaluation of the scientific publications in this field. Advances in the knowledge and management of intestinal permeability will sure enable better options of dealing with this group of common disorders to enhance quality of life of those affected.

Methylation Status of Corticotropin-Releasing Factor (CRF) Receptor Genes in Colorectal Cancer

The corticotropin-releasing factor (CRF) system has been strongly associated with gastrointestinal pathophysiology, including colorectal cancer (CRC). We previously showed that altered expression of CRF receptors (CRFRs) in the colon critically affects CRC progression and aggressiveness through regulation of colonic inflammation. Here, we aimed to assess the potential of CRFR methylation levels as putative biomarkers in CRC. In silico methylation analysis of CRF receptor 1 (CRFR1) and CRF receptor 2 (CRFR2) was performed using methylome data derived by CRC and Crohn's disease (CD) tissues and CRC-derived circulating cell-free DNAs (ccfDNAs). In total, 32 and 33 differentially methylated sites of CpGs (DMCs) emerged in CRFR1 and CRFR2, respectively, between healthy and diseased tissues. The methylation patterns were verified in patient-derived ccfDNA samples by qMSP and associated with clinicopathological characteristics. An automated machine learning (AutoML) technology was applied to ccfDNA samples for classification analysis. In silico analysis revealed increased methylation of both CRFRs in CRC tissue and ccfDNA-derived datasets. CRFR1 hypermethylation was also noticed in gene body DMCs of CD patients. CRFR1 hypermethylation was further validated in CRC adjuvant-derived ccfDNA samples, whereas CRFR1 hypomethylation, observed in metastasis-derived ccfDNAs, was correlated to disease aggressiveness and adverse prognostic characteristics. AutoML analysis based on CRFRs methylation status revealed a three-feature high-performing biosignature for CRC diagnosis with an estimated AUC of 0.929. Monitoring of CRFRs methylation-based signature in CRC tissues and ccfDNAs may be of high diagnostic and prognostic significance in CRC.

Impairment of CRH in the intestinal mucosal epithelial barrier of pregnant Bama miniature pig induced by restraint stress

Female, especially for pregnant female, are vulnerable to psychological stress. The morphology and metabolism of the maternal intestine are both obviously changed during pregnancy, thus making intestinal health status more fragile under psychological stress. The aim of the present study was to investigate the role of CRH and CRHR1 in the pregnant maternal intestine under psychological stress, thus exploring the mechanism of psychological stress in the pregnant maternal intestine. Bama miniature pigs were divided into the control and restraint stress groups from the first day of pregnancy. After restraint stress treatment for 18 consecutive days (D18), the plasma, duodenum, jejunum, ileum and colon were collected for study. Pregnant Bama miniature pigs subjected to restraint stress had significantly elevated CRH, adrenocorticotropic hormone (ACTH) and cortisol (COR) levels in plasma. Consistent with the increase in CRH levels, we observed enhanced oxidative stress levels in the intestine, which resulted in intestinal mucosal injury, including impaired intestinal morphology, a reduced number of goblet cells and proliferating cell nuclear antigen-positive cells, decreased expression of MUC2 and tight junctions, and elevated expression of CRHR1 and caspase-3. Moreover, exogenous CRH could directly promote IPEC-J2 cell apoptosis and influence its cell cycle (S and G2 phase) through CRHR1, and antalarmin could alleviate this phenomenon. Therefore, our results illustrated that the intestinal dysfunction of pregnant Bama miniature pigs was caused by restraint stress, and these changes were associated with the enhanced expression of CRH and CRHR1 in the intestine.

Effects of stress-related peptides on chloride secretion in the mouse proximal colon

BACKGROUND

Stress increases intestinal secretion and exacerbates symptoms of irritable bowel syndrome (IBS). Peripherally derived corticotropin-releasing factor (CRF) is known to mediate stress-induced intestinal secretion, presumably by activation of CRF₁ receptors in the gut. The present study aimed to ascertain the role of CRF₂ activation in intestinal secretion by three other members of CRF peptide family, urocortin (UCN) 1-3, in wild type (WT) and CRF₂ knockout (Crhr2^-/- ) mice.

METHODS

Mucosal/submucosal preparations from proximal colon of WT and Crhr2^-/- mice of both sexes were mounted in Ussing chambers for measurement of short-circuit current (I_sc ) as an indicator of ion secretion.

KEY RESULTS

Male mice demonstrated a significantly higher baseline I_sc than female in both WT and Crhr2^-/- genotypes. CRF and UCN1-3 (1 μM) caused greater increases in colonic I_sc (ΔI_sc ) in male than female. Colonic I_sc response to the selective CRF₁ agonist, stressin1, was similar in both sexes. In male mice, the selective CRF₂ agonists (UCN2 and UCN3) caused significantly greater ΔI_sc than CRF and stressin1. UCN2- and UCN3-evoked ΔI_SC was significantly reduced in preparations pretreated with the selective CRF₂ antagonist antisauvagine-30 and in Crhr2^-/- mice. The prosecretory effects of urocortins were due to increases in Cl^- secretion and involved enteric neurons and mast cells.

CONCLUSIONS AND INFERENCE

The findings revealed sex differences in baseline colonic secretion and responses to stress-related peptides. CRF₂ receptors play a more prominent role in colonic secretion in male mice. The greater baseline secretion and responses to UCNs may contribute to the higher prevalence of diarrhea-predominant IBS in males.

Urocortin 1: A putative excitatory neurotransmitter in the enteric nervous system

BACKGROUND

Urocortin 1 (Ucn1), a stress-related peptide, is a member of the corticotropin-releasing factor (CRF) family and acts as a CRF1 receptor agonist. Ucn1 and CRF1 receptor immunoreactivity are present in the enteric nervous system (ENS), and Ucn1 elicits contraction of colonic muscle strips. Considering these findings, we have hypothesized that Ucn1 acts as an excitatory neurotransmitter in the ENS. The present study was conducted to determine whether exogenously applied Ucn1 causes contractions, whether it participates in neurally mediated contraction, and whether it is released from the ENS of the rat colon.

METHODS

Isometric tension of the rat colonic muscle strips (middle to distal colon) in a longitudinal direction was measured. The effects of Ucn1 on phasic contractions were examined in the absence and presence of antalarmin (CRF1 receptor antagonist), tetrodotoxin (TTX), and atropine. The effects of antalarmin on electrical field stimulation (EFS)-induced contractions were examined in the absence and presence of atropine. Ucn1 peptide in the bath solution was measured after EFS using an EIA kit.

KEY RESULTS

Ucn1 caused a significant and dose-dependent increase in phasic contractions. These effects were completely inhibited by antalarmin, TTX, and atropine. EFS-induced contractions were inhibited by antalarmin. Atropine markedly reduced EFS-induced contractions, and antalarmin did not decrease these contractions further. EFS elicited a significant increase in the concentration of Ucn1 in the bath solution, and this increase was completely inhibited by TTX.

CONCLUSIONS AND INFERENCES

These results suggest that Ucn1 acts as an excitatory neurotransmitter in the ENS enhancing the cholinergic neurotransmission.

Peripheral mechanisms contribute to comorbid visceral hypersensitivity induced by preexisting orofacial pain and stress in female rats

BACKGROUND

Stress exacerbates many chronic pain syndromes including irritable bowel syndrome (IBS). Among these patient populations, many suffer from comorbid or chronic overlapping pain conditions and are predominantly female. Nevertheless, basic studies investigating chronic psychological stress-induced changes in pain sensitivity have been mostly carried out in male rodents. Our laboratory developed a model of comorbid pain hypersensitivity (CPH) (stress in the presence of preexisting orofacial pain inducing chronic visceral pain hypersensitivity that significantly outlasts transient stress-induced pain hypersensitivity (SIH)) facilitating the study of pain associated with IBS. Since CPH and SIH are phenotypically similar until SIH resolves and CPH persists, it is unclear if underlying mechanisms are similar.

METHODS

In the present study, the visceromotor response (VMR) to colorectal distention was recorded in the SIH and CPH models in intact females and ovariectomized rats plus estradiol replacement (OVx + E2). Over several months, rats were determined to be susceptible or resilient to stress and the role of peripheral corticotrophin-releasing factor (CRF) underlying in the pain hypersensitivity was examined.

KEY RESULTS

Stress alone induced transient (3-4 weeks) visceral hypersensitivity, though some rats were resilient. Comorbid conditions increased susceptibility to stress prolonging hypersensitivity beyond 13 weeks. Both models had robust peripheral components; hypersensitivity was attenuated by the CRF receptor antagonist astressin and the mast cell stabilizer disodium cromoglycate (DSCG). However, DSCG was less effective in the CPH model compared to the SIH model.

CONCLUSIONS AND INFERENCES

The data indicate many similarities but some differences in mechanisms contributing to comorbid pain conditions compared to transient stress-induced pain.

Corticotropin Releasing Factor Receptors in breast cancer: Expression and activity in hormone-dependent growth in vitro

Corticotropin Releasing Factor (CRF) neuropeptides coordinate the stress response via two distinct membrane receptors (CRF-Rs). We have previously shown expression of both CRF-Rs in human breast cancer tissues. In the present study, we examined in vitro using the MCF-7 cell line model, the regulation of CRF-Rs expression and their signaling in hormone-dependent breast cancer growth. Our findings show that similarly to breast cancer biopsies, the predominant receptor type expressed in the cell line is CRF-R2α. The transcription of CRF-R1 and CRF-R2 is up and down-regulated respectively by exposure to estradiol (E2); however this effect seems not to be exerted at the level of promoter gene methylation, although in human breast cancer specimens, CRF-R1 methylation was found to be positively associated with the presence of steroid hormone receptors. Finally, we showed that specific activation of CRF-R2 increased the migration of MCF-7 cells and potentiated an estrogen-inducing effect. Our data support an involvement of CRF-R signaling in breast cancer pathophysiology via a regulatory steroid-hormone interplay.

Enteric apelin enhances the stress-induced stimulation of colonic motor functions

In response to stress, apelin and corticotropin-releasing factor (CRF) are upregulated in the gastrointestinal (GI) tract. This study was designed to investigate the effect of stress on endogenous apelin in colon and its regulatory role on colonic motor functions. Colon transit (CT) was measured in rats exposed to acute restraint stress (ARS). APJ and CRF receptor antagonists F13A and astressin were administered intraperitoneally 30 min before ARS loading. Colonic muscle contractions were evaluated by in-vivo motility recording and in-vitro organ bath studies. Detection of apelin or CRF was performed using immunohistochemistry in proximal and distal colon of non-stressed (NS) and ARS-loaded rats. Immunoreactivity of CRF1 with apelin or APJ receptor was detected with double-labeled immunofluorescence in colonic myenteric neurons. Compared with NS rats, ARS accelerated the CT which was attenuated significantly by F13A or astressin. Following ARS, the expression of CRF was increased remarkably in distal colon, while the stress-induced change was not prominent in proximal colon. Apelin-positive cells were detected in myenteric ganglia of distal colon, while no apelin immunoreactivity observed in myenteric neurons of proximal colon. Both apelin and APJ receptor are colocalized with CRF1 in myenteric neurons of distal colon. In the in-vivo colonic motility experiments, apelin-13 exhibited a rapid stimulatory effect. CRF administration increased the motility which was abolished by F13A. Apelin-induced contractions in muscle strips were no longer observed with preadministration of F13A. These results suggest that enteric apelin contributes to the action of CRF on colonic motor functions under stressed conditions.LAY SUMMARYIt has been suggested in rodents that acute stress increases the expression of apelin in gastrointestinal tissues. We have found that under stressed conditions, enteric apelin contributes to the CRF-induced alterations in colonic motor functions through APJ receptor.

Enterochromaffin cell hyperplasia in the gut: Factors, mechanism and therapeutic clues

Enterochromaffin (EC) cell is the main cell type that responsible for 5-hydroxytryptamine (5-HT) synthesis, storage and release of the gut. Intestinal 5-HT play a key role in visceral sensation, intestinal motility and permeability, EC cell hyperplasia and increased 5-HT bioavailability in the gut have been found to be involved in the symptoms generation of irritable bowel syndrome and inflammatory bowel disease. EC cells originate from intestinal stem cells, the interaction between proliferation and differentiation signals on intestinal stem cells enable EC cell number to be regulated in a normal level. This review focuses on the impact factors, pathogenesis mechanisms, and therapeutic clues for intestinal EC cells hyperplasia, and showed that EC cell hyperplasia was observed under the condition of physiological stress, intestinal infection or intestinal inflammation, the disordered proliferation and/or differentiation of intestinal stem cells as well as their progenitor cells all contribute to the pathogenesis of intestinal EC cell hyperplasia. The altered intestinal niche, i.e. increased corticotrophin releasing factor (CRF) signal, elevated nerve growth factor (NGF) signal, and Th2-dominant cytokines production, has been found to have close correlation with intestinal EC cell hyperplasia. Currently, CRF receptor antagonist, nuclear factor-κB inhibitor, and NGF receptor neutralizing antibody have been proved useful to attenuate intestinal EC cell hyperplasia, which may provide a promising clue for the therapeutic strategy in EC cell hyperplasia related diseases.

Chronic Stress, Inflammation, and Colon Cancer: A CRH System-Driven Molecular Crosstalk

Chronic stress is thought to be involved in the occurrence and progression of multiple diseases, via mechanisms that still remain largely unknown. Interestingly, key regulators of the stress response, such as members of the corticotropin-releasing-hormone (CRH) family of neuropeptides and receptors, are now known to be implicated in the regulation of chronic inflammation, one of the predisposing factors for oncogenesis and disease progression. However, an interrelationship between stress, inflammation, and malignancy, at least at the molecular level, still remains unclear. Here, we attempt to summarize the current knowledge that supports the inseparable link between chronic stress, inflammation, and colorectal cancer (CRC), by modulation of a cascade of molecular signaling pathways, which are under the regulation of CRH-family members expressed in the brain and periphery. The understanding of the molecular basis of the link among these processes may provide a step forward towards personalized medicine in terms of CRC diagnosis, prognosis and therapeutic targeting.

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.

Toxicity of Pexacerfont, a Corticotropin-Releasing Factor Type 1 Receptor Antagonist, in Rats and Dogs

Pexacerfont is a corticotropin-releasing factor subtype 1 receptor antagonist that was developed for the treatment of anxiety- and stress-related disorders. This report describes the results of repeat-dose oral toxicity studies in rats (3 and 6 months) and dogs (3 months and 1 year). Pexacerfont was well tolerated in all of these studies at exposures equal to or greater than areas under the curve in humans (clinical dose of 100 mg). Microscopic changes in the liver (hepatocellular hypertrophy), thyroid glands (hypertrophy/hyperplasia and adenomas of follicular cells), and pituitary (hypertrophy/hyperplasia and vacuolation of thyrotrophs) were only observed in rats and were considered adaptive changes in response to hepatic enzyme induction and subsequent alterations in serum thyroid hormone levels. Evidence for hepatic enzyme induction in dogs was limited to increased liver weights and reduced thyroxine (T4) levels. Mammary gland hyperplasia and altered female estrous cycling were only observed in rats, whereas adverse testicular effects (consistent with minimal to moderate degeneration of the germinal epithelium) were only noted following chronic dosing in dogs. The testicular effects were reversible changes with exposure margins of 8× at the no observed adverse effect level. It is not clear whether the changes in mammary gland, estrous cycling, and testes represent secondary hormonal changes due to perturbation of the hypothalamic–pituitary–adrenal axis or are off-target effects. In conclusion, the results of chronic toxicity studies in rats and dogs show that pexacerfont has an acceptable safety profile to support further clinical testing.

Plasma Corticotropin-Releasing Factor Receptors and B7-2⁺ Extracellular Vesicles in Blood Correlate with Irritable Bowel Syndrome Disease Severity

Extracellular vesicles (EVs) are composed of bilayer membranes that are released by different cell types and are present in bodily fluids, such as blood, urine, and bile. EVs are thought to play a key role in intracellular communication. Based on their size and density, EVs are classified into small, medium, or large EVs. Cargo composition in EVs reflects physiological changes in health and disease. Patients with irritable bowel syndrome (IBS) exhibit visceral hypersensitivity and mood disorders. Stressful episodes often precede disease symptoms in IBS patients. Stress-induced symptoms include, but are not limited to, abdominal pain and mood swings. Perceived stress responses are mediated by two known G protein-coupled receptors (GPCRs), corticotropin-releasing factor receptor 1 and 2 (CRFRs). CRFRs belong to the Class B secretin receptor family of GPCRs. Here, we show that CRFRs were present in human and murine plasma, and in EVs purified from mouse serum. CRFRs were present in plasma from IBS patients and healthy controls. EVs secreted from immune cells influence both adaptive and innate immune responses via exchange of EVs between different immune cell types. B7-2 (CD86), a plasma membrane antigen-presenting protein, is present on EVs secreted from dendritic, B-, and mast cells, whereas CD9 is present on EVs secreted from dendritic and intestinal epithelial cells. We found that plasma CRFR levels positively correlated with B7-2+ EVs (R = 0.8597, p < 0.0001), but no association was seen with CD9+ EVs. Plasma CRFRs expression negatively correlated with IBS severity scores. Our data suggests that plasma EVs from immune cells carry CRFRs as cargos and influence cell-cell communication in health and disease.

Brain and Gut CRF Signaling: Biological Actions and Role in the Gastrointestinal Tract

BACKGROUND

Corticotropin-releasing factor (CRF) pathways coordinate behavioral, endocrine, autonomic and visceral responses to stress. Convergent anatomical, molecular, pharmacological and functional experimental evidence supports a key role of brain CRF receptor (CRF-R) signaling in stress-related alterations of gastrointestinal functions. These include the inhibition of gastric acid secretion and gastric-small intestinal transit, stimulation of colonic enteric nervous system and secretorymotor function, increase intestinal permeability, and visceral hypersensitivity. Brain sites of CRF actions to alter gut motility encompass the paraventricular nucleus of the hypothalamus, locus coeruleus complex and the dorsal motor nucleus while those modulating visceral pain are localized in the hippocampus and central amygdala. Brain CRF actions are mediated through the autonomic nervous system (decreased gastric vagal and increased sacral parasympathetic and sympathetic activities). The activation of brain CRF-R2 subtype inhibits gastric motor function while CRF-R1 stimulates colonic secretomotor function and induces visceral hypersensitivity. CRF signaling is also located within the gut where CRF-R1 activates colonic myenteric neurons, mucosal cells secreting serotonin, mucus, prostaglandin E2, induces mast cell degranulation, enhances mucosal permeability and propulsive motor functions and induces visceral hyperalgesia in animals and humans. CRF-R1 antagonists prevent CRF- and stressrelated gut alterations in rodents while not influencing basal state.

DISCUSSION

These preclinical studies contrast with the limited clinical positive outcome of CRF-R1 antagonists to alleviate stress-sensitive functional bowel diseases such as irritable bowel syndrome.

CONCLUSION

The translational potential of CRF-R1 antagonists in gut diseases will require additional studies directed to novel anti-CRF therapies and the neurobiology of brain-gut interactions under chronic stress.

Potential Mechanisms Underlying Centralized Pain and Emerging Therapeutic Interventions

Centralized pain syndromes are associated with changes within the central nervous system that amplify peripheral input and/or generate the perception of pain in the absence of a noxious stimulus. Examples of idiopathic functional disorders that are often categorized as centralized pain syndromes include fibromyalgia, chronic pelvic pain syndromes, migraine, and temporomandibular disorder. Patients often suffer from widespread pain, associated with more than one specific syndrome, and report fatigue, mood and sleep disturbances, and poor quality of life. The high degree of symptom comorbidity and a lack of definitive underlying etiology make these syndromes notoriously difficult to treat. The main purpose of this review article is to discuss potential mechanisms of centrally-driven pain amplification and how they may contribute to increased comorbidity, poorer pain outcomes, and decreased quality of life in patients diagnosed with centralized pain syndromes, as well as discuss emerging non-pharmacological therapies that improve symptomology associated with these syndromes. Abnormal regulation and output of the hypothalamic-pituitary-adrenal (HPA) axis is commonly associated with centralized pain disorders. The HPA axis is the primary stress response system and its activation results in downstream production of cortisol and a dampening of the immune response. Patients with centralized pain syndromes often present with hyper- or hypocortisolism and evidence of altered downstream signaling from the HPA axis including increased Mast cell (MC) infiltration and activation, which can lead to sensitization of nearby nociceptive afferents. Increased peripheral input via nociceptor activation can lead to “hyperalgesic priming” and/or “wind-up” and eventually to central sensitization through long term potentiation in the central nervous system. Other evidence of central modifications has been observed through brain imaging studies of functional connectivity and magnetic resonance spectroscopy and are shown to contribute to the widespreadness of pain and poor mood in patients with fibromyalgia and chronic urological pain. Non-pharmacological therapeutics, including exercise and cognitive behavioral therapy (CBT), have shown great promise in treating symptoms of centralized pain.

The Influence of Early Life Experience on Visceral Pain

Pain is the most reported and troublesome symptom of nearly all functional disorders affecting the genitourinary and gastrointestinal organs. Patients with irritable bowel syndrome (IBS), interstitial cystitis/painful bladder syndrome (IC/PBS), vulvodynia, and/or chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS; collectively termed chronic pelvic pain syndromes) report pain severe enough to impact quality of life and often suffer from symptoms of or are diagnosed with more than one of these syndromes. This increased comorbidity between chronic pelvic pain syndromes, and with pain disorders of disparate body regions, as well as with mood disorders, can be influenced by disruptions in the hypothalamic-pituitary-adrenal (HPA) axis, which regulates the response to stress and influences the perception of pain. Experiencing trauma, neglect, or abuse in early life can permanently affect the functioning of the HPA axis. As such, a significant proportion of patients suffering from comorbid chronic pelvic pain syndromes report a history of early life stress or trauma. Here we will report on how these early life experiences influence chronic pelvic pain in patients. We will also discuss various rodent models that have been developed to study this phenomenon to understand the mechanisms underlying HPA axis dysfunction, as well as potential underlying mechanisms connecting these syndromes to one another.

Experimental Models of Irritable Bowel Syndrome and the Role of the Enteric Neurotransmission

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal diseases in humans. It is characterized by visceral pain and/or discomfort, hypersensitivity and abnormal motor responses along with change in gut habits. Although the etio-pathogenesis of IBS is only partially understood, a main role has been attributed to psychosocial stress of different origin. Animal models such as neonatal maternal separation, water avoidance stress and wrap restraint stress have been developed as psychosocial stressors in the attempt to reproduce the IBS symptomatology and identify the cellular mechanisms responsible for the disease. The study of these models has led to the production of drugs potentially useful for IBS treatment. This review intends to give an overview on the results obtained with the animal models; to emphasize the role of the enteric nervous system in IBS appearance and evolution and as a possible target of drug therapies.

Involvement of Corticotropin-Releasing Factor and Receptors in Immune Cells in Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder defined by ROME IV criteria as pain in the lower abdominal region, which is associated with altered bowel habit or defecation. The underlying mechanism of IBS is not completely understood. IBS seems to be a product of interactions between various factors with genetics, dietary/intestinal microbiota, low-grade inflammation, and stress playing a key role in the pathogenesis of this disease. The crosstalk between the immune system and stress in IBS mechanism is increasingly recognized. Corticotropin-releasing factor (CRF), a major mediator in the stress response, is involved in altered function in GI, including inflammatory processes, colonic transit time, contractile activity, defecation pattern, pain threshold, mucosal secretory function, and barrier functions. This mini review focuses on the recently establish local GI-CRF system, its involvement in modulating the immune response in IBS, and summarizes current IBS animal models and mapping of CRF, CRFR1, and CRFR2 expression in colon tissues. CRF and receptors might be a key molecule involving the immune and movement function via brain-gut axis in IBS.

Involvement of CRF2 signaling in enterocyte differentiation

AIM

To determine the role of corticotropin releasing factor receptor (CRF2) in epithelial permeability and enterocyte cell differentiation.

METHODS

For this purpose, we used rat Sprague Dawley and various colon carcinoma cell lines (SW620, HCT8R, HT-29 and Caco-2 cell lines). Expression of CRF2 protein was analyzed by fluorescent immunolabeling in normal rat colon and then by western blot in dissociated colonic epithelial cells and in the lysates of colon carcinoma cell lines or during the early differentiation of HT-29 cells (ten first days). To assess the impact of CRF2 signaling on colonic cell differentiation, HT-29 and Caco-2 cells were exposed to Urocortin 3 recombinant proteins (Ucn3, 100 nmol/L). In some experiments, cells were pre-exposed to the astressin 2b (A2b) a CRF2 antagonist in order to inhibit the action of Ucn3. Intestinal cell differentiation was first analyzed by functional assays: the trans-cellular permeability and the para-cellular permeability were determined by Dextran-FITC intake and measure of the transepithelial electrical resistance respectively. Morphological modifications associated to epithelial dysfunction were analyzed by confocal microscopy after fluorescent labeling of actin (phaloidin-TRITC) and intercellular adhesion proteins such as E-cadherin, p120ctn, occludin and ZO-1. The establishment of mature adherens junctions (AJ) was monitored by following the distribution of AJ proteins in lipid raft fractions, after separation of cell lysates on sucrose gradients. Finally, the mRNA and the protein expression levels of characteristic markers of intestinal epithelial cell (IEC) differentiation such as the transcriptional factor krüppel-like factor 4 (KLF4) or the dipeptidyl peptidase IV (DPPIV) were performed by RT-PCR and western blot respectively. The specific activities of DPPIV and alkaline phosphatase (AP) enzymes were determined by a colorimetric method.

RESULTS

CRF2 protein is preferentially expressed in undifferentiated epithelial cells from the crypts of colon and in human colon carcinoma cell lines. Furthermore, CRF2 expression is down regulated according to the kinetic of HT-29 cell differentiation. By performing functional assays, we found that Ucn3-induced CRF2 signaling alters both para- and trans-cellular permeability of differentiated HT-29 and Caco-2 cells. These effects are partly mediated by Ucn3-induced morphological changes associated with the disruption of mature AJ in HT-29 cells and tight junctions (TJ) in Caco-2 cells. Ucn3-mediated activation of CRF2 decreases mRNA and protein expression levels of KLF4 a transcription factor involved in IEC differentiation. This signaling is correlated to a down-regulation of key IEC markers such as DPPIV and AP, at both transcriptional and post-transcriptional levels.

CONCLUSION

Our findings suggest that CRF2 signaling could modulate IEC differentiation. These mechanisms could be relevant to the stress induced epithelial alterations found in inflammatory bowel diseases.

The Effect of Peripheral CRF Peptide and Water Avoidance Stress on Colonic and Gastric Transit in Guinea Pigs

Functional dyspepsia (FD) and irritable bowel syndrome (IBS) are common gastrointestinal (GI) diseases; however, there is frequent overlap between FD and IBS patients. Emerging evidence links the activation of corticotropin releasing factor (CRF) receptors with stress-related alterations of gastric and colonic motor function. Therefore, we investigated the effect of peripheral CRF peptide and water avoidance stress (WAS) on upper and lower GI transit in guinea pigs. Dosages 1, 3, and 10 μg/kg of CRF were injected intraperitoneally (IP) in fasted guinea pigs 30 minutes prior to the intragastric administration of charcoal mix to measure upper GI transit. Colonic transits in non-fasted guinea pigs were assessed by fecal pellet output assay after above IP CRF doses. Blockade of CRF receptors by Astressin, and its effect on GI transit was also analyzed. Guinea pigs were subjected to WAS to measure gastrocolonic transit in different sets of experiments. Dose 10 μg/kg of CRF significantly inhibited upper GI transit. In contrast, there was dose dependent acceleration of the colonic transit. Remarkably, pretreatment of astressin significantly reverses the effect of CRF peptide on GI transit. WAS significantly increase colonic transit, but failed to accelerate upper GI transit. Peripheral CRF peptide significantly suppressed upper GI transit and accelerated colon transit, while central CRF involved WAS stimulated only colonic transit. Therefore, peripheral CRF could be utilized to establish the animal model of overlap syndrome.

Corticotropin-releasing factor stimulates colonic motility via muscarinic receptors in the rat

AIM

To measure exogenous corticotropin-releasing factor (CRF)-induced motility of the isolated rat colon and to demonstrate the effect of pharmacologic inhibition on CRF-induced motility.

METHODS

The isolated vascularly-perfused rat colon was used. Luminal pressure was monitored via microtip catheter pressure transducers in the proximal and distal colon. At first, exogenous CRF was administered in a stepwise manner and the concentration of CRF yielding maximal colonic motility was selected. After recording basal colonic motility, hexamethonium, phentolamine, propranolol, atropine and tetrodotoxin were infused into the isolated colon. Initially, only the test drug was infused; then, CRF was added. The motility index was expressed as percentage change over basal level.

RESULTS

Administration of 1.4, 14.4, 144 and 288 pmol/L CRF progressively increased colonic motility in the proximal and distal colon. Infusion of atropine or tetrodotoxin reduced CRF-induced motility of both the proximal and distal colon, whereas hexamethonium, phentolamine and propranolol had no effect.

CONCLUSION

CRF-induced colonic motility appears to be mediated by local cholinergic signaling via muscarinic receptors. Muscarinic receptors are potential targets for counteracting CRF-induced colonic hypermotility.

Pharmacotherapy in smoking cessation: Corticotropin Releasing Factor receptors as emerging intervention targets

Smoking represents perhaps the single most important health risk factor and a global contributor to mortality that can unquestionably be prevented. Smoking is responsible for many diseases, including various types of cancer, chronic obstructive pulmonary disease, coronary heart disease, peripheral vascular disease and peptic ulcer, while it adversely affects fetal formation and development. Since smoking habit duration is a critical factor for mortality, the goal of treatment should be its timely cessation and relapse prevention. Drug intervention therapy is an important ally in smoking cessation. Significant positive steps have been achieved in the last few years in the development of supportive compounds. In the present review, we analyze reports studying the role of Corticotropin Releasing Factor (CRF), the principle neuroendocrine mediator of the stress response and its two receptors (CRF1 and CRF2) in the withdrawal phase as well as in the abstinence from nicotine use. Although still in pre-clinical evaluation, therapeutic implications of these data were investigated in order to highlight potential pharmaceutical interventions.

A crosstalk between muscarinic and CRF2 receptors regulates cellular adhesion properties of human colon cancer cells

Patients with inflammatory bowel disease often suffer from chronic and relapsing intestinal inflammation that favor the development of colitis associated cancer. An alteration of the epithelial intestinal barrier function observed in IBD is supposed to be a consequence of stress. It has been proposed that corticotrophin-releasing factor receptor (CRF2), one of the two receptors of CRF, the principal neuromediator of stress, acts on cholinergic nerves to induce stress-mediated epithelial barrier dysfunction. Non-neuronal acetylcholine (Ach) and muscarinic receptors (mAchR) also contribute to alterations of epithelial cell functions. In this study, we investigated the mechanisms through which stress and Ach modulate epithelial cell adhesive properties. We show that Ach-induced activation of mAchR in HT-29 cells results in cell dissociation together with changes in cell-matrix contacts, which correlates with the acquisition of invasive potential consistent with a matrix metalloproteinase (MMP) mode of invasion. These processes result from mAchR subsequent stimulation of the cascade of src/Erk and FAK activation. Ach-induced secretion of laminin 332 leads to α3β1 integrin activation and RhoA-dependent reorganization of the actin cytoskeleton. We show that Ach-mediated effects on cell adhesion are blocked by astressin 2b, a CRF2 antagonist, suggesting that Ach action depends partly on CRF2 signaling. This is reinforced by the fact that Ach-mediated activation of mAchR stimulates both the synthesis and the release of CRF2 ligands in HT-29 cells (effects blocked by atropine). In summary, our data provides evidence for a novel intracellular circuit involving mAchR acting on CRF2-signaling that could mediate colonic mucosal barrier dysfunction and exacerbate mucosal inflammation.

Repeated otilonium bromide administration prevents neurotransmitter changes in colon of rats underwent to wrap restraint stress

Otilonium bromide (OB) is a spasmolytic drug successfully used for the treatment of irritable bowel syndrome (IBS). Its efficacy has been attributed to the block of L- and T-type Ca²⁺ channels and muscarinic and tachykinin receptors in the smooth muscle. Furthermore, in healthy rats, repeated OB administration modified neurotransmitter expression and function suggesting other mechanisms of action. On this basis, we investigated whether repeated OB treatment prevented the functional and neurochemical changes observed in the colon of rats underwent to wrap restrain stress (WRS) a psychosocial stressor considered suitable to reproduce the main IBS signs and symptoms. In control, WRS and OB/WRS rats functional parameters were measured in vivo and morphological investigations were done ex vivo in the colon. The results showed that OB counteracts most of the neurotransmitters changes caused by WRS. In particular, the drug prevents the decrease in SP-, NK1r-, nNOS-, VIP-, and S100β-immunoreactivity (IR) and the increase in CGRP-, and CRF1r-IR. On the contrary, OB does not affect the increase in CRF2r-IR neurons observed in WRS rats and does not interfere with the mild mucosal inflammation due to WRS. Finally, OB per se increases the Mr2 expression in the muscle wall and decreases the number of the myenteric ChAT-IR neurons. Functional findings show a significantly reduction in the number of spontaneous abdominal contraction in OB treated rats. The ability of OB to block L-type Ca²⁺ channels, also expressed by enteric neurons, might represent a possible mechanism through which OB exerts its actions.

Mechanisms of Stress-Induced Visceral Pain: Implications in Irritable Bowel Syndrome

Visceral pain is a term describing pain originating from the internal organs of the body and is a common feature of many disorders, including irritable bowel syndrome (IBS). Stress is implicated in the development and exacerbation of many visceral pain disorders. Recent evidence suggests that stress and the gut microbiota can interact through complementary or opposing factors to influence visceral nociceptive behaviours. The Young Investigator Forum at the International Society of Psychoneuroendocrinology (ISPNE) annual meeting reported experimental evidence suggesting the gut microbiota can affect the stress response to affect visceral pain. Building upon human imaging data showing abnormalities in the central processing of visceral stimuli in patients with IBS and knowledge that the amygdala plays a pivotal role in facilitating the stress axis, the latest experimental evidence supporting amygdala-mediated mechanisms in stress-induced visceral pain was reviewed. The final part of the session at ISPNE reviewed experimental evidence suggesting that visceral pain in IBS may be a result, at least in part, of afferent nerve sensitisation following increases in epithelial permeability and mucosal immune activation.

Sex- and corticotropin-releasing factor receptor 2- dependent actions of urocortin 1 during inflammation

We investigated whether corticotropin-releasing factor receptor 2 (CRF2) and its high-affinity agonist urocortin 1 (Ucn1) mediate sex-specific signaling and immune responses. Intrarectal trinitrobenzene sulfonic acid was used to induce experimental colitis in wild-type, CRF2 knockout (CRF2KO), and heterozygous (CRF2Ht) mice of both sexes. Changes in plasma extravasation, organ weight, survival, immune cell numbers, inflammatory cytokines, and the MAPK signaling pathway were assessed. Stored intestinal biopsies from patients with Crohn's disease (CD) and age- and sex-matched individuals without inflammatory bowel disease (IBD) were examined by immunofluorescence and confocal microscopy to characterize Ucn1 and CRF receptor expression. CRF2Ht mice of both sexes showed decreased survival during colitis compared with other genotypes. Ucn1 improved survival in male mice alone. Ucn1 restored colon length and spleen and adrenal weight and decreased colonic TNF-α, IL-6, and IL-1β levels in male CRF2Ht mice alone. CRF2Ht mice of both sexes showed decreased phosphorylation of MAPK p38 and heat shock protein 27 (Hsp27) levels. Ucn1 restored p-Hsp27 levels in male CRF2Ht mice alone. Expression of the chaperone protein Hsp90 decreased during colitis, except in male CRF2Ht mice. Taken together, our data indicate that sex shows significant interaction with genotype and Ucn1 during colitis. Human duodenal and colonic biopsies revealed that sex-specific differences exist in levels of CRF receptors and Ucn1 expression in patients with CD compared with the matched non-IBD subjects. To conclude, Ucn1 mediates sex-specific immune and cellular signaling responses via CRF2, emphasizing the need for inclusion of females in preclinical studies.

Endogenous CRF in rat large intestine mediates motor and secretory responses to stress

BACKGROUND

Corticotropin-releasing factor (CRF) mediates our body's overall responses to stress. The role of central CRF in stress-stimulated colonic motility is well characterized. We hypothesized that transient perturbation in expression of enteric CRF is sufficient to change stress-induced colonic motor and secretory responses.

METHODS

Sprague-Dawley rats (adult, male) were subjected to 1-h partial restraint stress (PRS) and euthanized at 0, 4, 8, and 24 h. CRF mRNA and peptide levels in the colon were quantified by real-time RT-PCR, enzyme immuno-assay and immunohistochemistry. Double-stranded RNA (dsRNA) designed to target CRF (dsCRF) was injected into the colonic wall to attain RNA interference-mediated inhibition of CRF mRNA expression. DsRNA for β-globin was used as a control (dsControl). Four days after dsRNA injection, rats were subjected to 1-h PRS. Fecal output was measured. Ussing chamber techniques were used to assess colonic mucosal ion secretion and transepithelial tissue conductance.

KEY RESULTS

Exposure to PRS elevated CRF expression and increased CRF release in the rat colon. Injection of dsCRF inhibited basal CRF expression and prevented the PRS-induced increase in CRF expression, whereas CRF expression in dsControl-injected colons remained high after PRS. In rats treated with dsControl, PRS caused a significant increase in fecal pellet output, colonic baseline ion secretion, and transepithelial tissue conductance. Inhibition of CRF expression in the colon prevented PRS-induced increase in fecal output, baseline ion secretion, and transepithelial tissue conductance.

CONCLUSIONS & INFERENCES

These results provide direct evidence that transient perturbation in peripherally expressed CRF prevents colonic responses to stress.

Corticotropin-releasing factor (CRF) system localization in human fetal heart

OBJECTIVE

The corticotropin-releasing factor (CRF) family consists of the neuropeptides CRF, Ucn I, II and III and the binding sites CRFR1, CRFR2 and CRF-BP. It regulates stress response and the homeostasis of an organism. In this study, we examined the presence of the CRF system in the human hearts of normal and pathological fetuses.

DESIGN

Heart tissues from 40 archival human fetuses were divided into Group A (without pathology, 'normal'), Group B (with chromosomal abnormalities) and Group C (with congenital disorders). Immunohistochemistry was used to localize the CRF system. Results correlated to gestational trimester and pathology.

RESULTS

Immunoreactivity for all antigens was found in cardiac myocytes of all groups, in almost all samples, except Ucn III which was present in almost half of the fetuses of Groups B and C and was not detected at all in Group A. Ucn III was more often present during the earlier stage of development (<21 weeks) and in fetuses with congenital disorders. In a fetus diagnosed with heart pathology, all but Ucn III antigens were also present.

CONCLUSIONS

We localized a complete CRF system in the human fetal heart and correlated the presence of Ucn III to development and pathology. More studies are needed to verify and clarify the exact role of the CRF system in the human fetal heart.

Corticotropin-releasing Factor Changes the Phenotype and Function of Dendritic Cells in Mouse Mesenteric Lymph Nodes

Background/Aims

Dendritic cells (DCs) are a significant contributor to the pathology of numerous chronic inflammatory autoimmune disorders; however, the effects of Corticotropin-releasing factor (CRF) on intestinal DCs are poorly understood. In this study, we investigated the role of CRF in alterations of intestinal dendritic cell phenotype and function.

Methods

Mouse mesenteric lymph node dendritic cells (MLNDCs) were obtained using magnetic bead sorting. Surface expression of CRF receptor type 1 (CRF-R1) and CRF-R2 was determined by double-labeling immunofluorescence and quantitative polymerase chain reaction (qPCR) and MLNDCs were subsequently exposed to CRF in the presence or absence of CRF-R1 and CRF-R2 antagonists. Expression of surface molecules (MHC-I and MHC-II) and co-stimulatory molecules (CD80 and CD86) was determined by flow cytometric and western blot analyses, and the T cell stimulatory capacity of MLNDCs was evaluated by mixed lymphocyte reaction.

Results

Immunofluorescent staining and quatitative polymerase chain reaction indicated that both the CRF receptors (CRF-R1 and CRF-2) are expressed on the surface of MLNDCs. Exposure to CRF increased the expression of MHC-II on MLNDCs as well as their capacity to stimulate T cell proliferation. MLNDCs treated with CRF-R1 antagonist exhibited a phenotype characterized by a less activated state and reduced surface expression of MHC-II, and consequently showed reduced capacity to stimulate T cells. In contrast, treatment of MLNDCs with CRF-R2 antagonist yielded an opposite result.

Conclusions

CRF can alter the phenotype and function of intestinal DCs through direct action on CRF-R1 and CRF-R2, and activation of the CRF-R1 and CRF-R2 pathways yields opposing outcomes.

Corticotropin-releasing factor receptor type 1 and type 2 interaction in irritable bowel syndrome

Irritable bowel syndrome (IBS) displays chronic abdominal pain or discomfort with altered defecation, and stress-induced altered gut motility and visceral sensation play an important role in the pathophysiology. Corticotropin-releasing factor (CRF) is a main mediator of stress responses and mediates these gastrointestinal functional changes. CRF in brain and periphery acts through two subtype receptors such as CRF receptor type 1 (CRF1) and type 2 (CRF2), and activating CRF1 exclusively stimulates colonic motor function and induces visceral hypersensitivity. Meanwhile, several recent studies have demonstrated that CRF2 has a counter regulatory action against CRF1, which may imply that CRF2 inhibits stress response induced by CRF1 in order to prevent it from going into an overdrive state. Colonic contractility and sensation may be explained by the state of the intensity of CRF1 signaling. CRF2 signaling may play a role in CRF1-triggered enhanced colonic functions through modulation of CRF1 activity. Blocking CRF2 further enhances CRF-induced stimulation of colonic contractility and activating CRF2 inhibits stress-induced visceral sensitization. Therefore, we proposed the hypothesis, i.e., balance theory of CRF1 and CRF2 signaling as follows. Both CRF receptors may be activated simultaneously and the signaling balance of CRF1 and CRF2 may determine the functional changes of gastrointestinal tract induced by stress. CRF signaling balance might be abnormally shifted toward CRF1, leading to enhanced colonic motility and visceral sensitization in IBS. This theory may lead to understanding the pathophysiology and provide the novel therapeutic options targeting altered signaling balance of CRF1 and CRF2 in IBS.

Peripheral corticotropin-releasing factor receptor type 2 activation increases colonic blood flow through nitric oxide pathway in rats

BACKGROUND

Corticotropin-releasing factor (CRF) peptides exert profound effects on the secretomotor function of the gastrointestinal tract. Nevertheless, despite the presence of CRF peptides and receptors in colonic tissue, their influence on colonic blood flow (CBF) is unknown.

AIM

To determine the effect and mechanism of members of the CRF peptide family on CBF in isoflurane-anesthetized rats.

METHODS

Proximal CBF was measured with laser-Doppler flowmetry simultaneously with mean arterial blood pressure (MABP) measurement. Rats were injected with intravenous human/rat CRF (CRF1 > CRF2 affinity), mouse urocortin 2 (mUcn2, selective CRF2 agonist), or sauvagine (SVG, CRF2 > CRF1 affinity) at 1-30 µg/kg. The nitric oxide (NO) synthase inhibitor, L-NAME (3 mg/kg, iv), the cyclooxygenase inhibitor, indomethacin (Indo, 5 mg/kg, ip), or selective CRF2 antagonist, astressin2-B (Ast2B, 50 µg/kg, iv) was given before SVG injection (10 µg/kg, iv).

RESULTS

SVG and mUcn2 dose-dependently increased CBF while decreasing MABP and colonic vascular resistance (CVR). CRF had no effect on CBF, but increased CVR. The hyperemic effect of SVG was inhibited by L-NAME but not by Indo, whereas hypotension was partially reduced by L-NAME. Sensory denervation had no effect on SVG-induced changes. Ast2B inhibited SVG-induced hyperemia and decreased CVR, and partially reduced the hypotension.

CONCLUSIONS

Peripheral CRF2 activation induces colonic hyperemia through NO synthesis, without involving prostaglandin synthesis or sensory nerve activation, suggesting a direct action on the endothelium and myenteric neurons. Members of the CRF peptide family may protect the colonic mucosa via the activation of the CRF2 receptor.

Role of Corticotropin-releasing Factor Signaling in Stress-related Alterations of Colonic Motility and Hyperalgesia

The corticotropin-releasing factor (CRF) signaling systems encompass CRF and the structurally related peptide urocortin (Ucn) 1, 2, and 3 along with 2 G-protein coupled receptors, CRF₁ and CRF₂. CRF binds with high and moderate affinity to CRF₁ and CRF₂ receptors, respectively while Ucn1 is a high-affinity agonist at both receptors, and Ucn2 and Ucn3 are selective CRF₂ agonists. The CRF systems are expressed in both the brain and the colon at the gene and protein levels. Experimental studies established that the activation of CRF₁ pathway in the brain or the colon recaptures cardinal features of diarrhea predominant irritable bowel syndrome (IBS) (stimulation of colonic motility, activation of mast cells and serotonin, defecation/watery diarrhea, and visceral hyperalgesia). Conversely, selective CRF₁ antagonists or CRF₁/CRF₂ antagonists, abolished or reduced exogenous CRF and stress-induced stimulation of colonic motility, defecation, diarrhea and colonic mast cell activation and visceral hyperalgesia to colorectal distention. By contrast, the CRF₂ signaling in the colon dampened the CRF₁ mediated stimulation of colonic motor function and visceral hyperalgesia. These data provide a conceptual framework that sustained activation of the CRF₁ system at central and/or peripheral sites may be one of the underlying basis of IBS-diarrhea symptoms. While targeting these mechanisms by CRF₁ antagonists provided a relevant novel therapeutic venue, so far these promising preclinical data have not translated into therapeutic use of CRF₁ antagonists. Whether the existing or newly developed CRF₁ antagonists will progress to therapeutic benefits for stress-sensitive diseases including IBS for a subset of patients is still a work in progress.

Role of Corticotropin-releasing Factor in Gastrointestinal Permeability

The interface between the intestinal lumen and the mucosa is the location where the majority of ingested immunogenic particles face the scrutiny of the vast gastrointestinal immune system. Upon regular physiological conditions, the intestinal micro-flora and the epithelial barrier are well prepared to process daily a huge amount of food-derived antigens and non-immunogenic particles. Similarly, they are ready to prevent environmental toxins and microbial antigens to penetrate further and interact with the mucosal-associated immune system. These functions promote the development of proper immune responses and oral tolerance and prevent disease and inflammation. Brain-gut axis structures participate in the processing and execution of response signals to external and internal stimuli. The brain-gut axis integrates local and distant regulatory networks and super-systems that serve key housekeeping physiological functions including the balanced functioning of the intestinal barrier. Disturbance of the brain-gut axis may induce intestinal barrier dysfunction, increasing the risk of uncontrolled immunological reactions, which may indeed trigger transient mucosal inflammation and gut disease. There is a large body of evidence indicating that stress, through the brain-gut axis, may cause intestinal barrier dysfunction, mainly via the systemic and peripheral release of corticotropin-releasing factor. In this review, we describe the role of stress and corticotropin-releasing factor in the regulation of gastrointestinal permeability, and discuss the link to both health and pathological conditions.

A complete corticotropin releasing factor system localized in human fetal lung

OBJECTIVE

The Corticotropin Releasing Factor (CRF) system (neuropeptides CRF, Ucn I, II, III and binding sites CRFR1, CRFR2, CRF-BP) is responsible for stress regulation and the homeostasis of an organism. Herein we study the CRF system in human normal and pathological fetal lungs.

DESIGN

Lung tissues from 46 archival human fetuses were divided into Group A (normal), Group B (chromosomal abnormalities) and Group C (congenital disorders). Presence of elements of the CRF system was evaluated using immunohistochemistry and was correlated to pathology, lung developmental stage and clinicopathological characteristics.

RESULTS

Immunoreactivity for all antigens was found in both epithelial and mesenchymal lung cells of the bronchi and alveoli. Ucn I and CRFR1 were more frequently present in Group A. Ucns were more frequently localized at the pseudoglandular stage. There was a positive correlation between the presence of the CRF neuropeptides and between CRFR1 and CRF. Two fetuses with lung malformations showed low or no detectable presence of the CRF system.

CONCLUSIONS

We report the presence of a complete CRF system in human fetal lungs correlating its developmental stage and several pathologies. Our results are in agreement with findings in experimental animal models, implicating the CRF system in fetal lung development, its action being more significant in the early stages.

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.

Crosstalk between interleukin-6 and corticotropin-releasing factor modulate submucosal plexus activity and colonic secretion

BACKGROUND

Irritable bowel syndrome (IBS) is a common disorder of the gut with symptoms such as diarrhoea, constipation, abdominal pain and bloating, that are frequently exacerbated by stress. Circulating levels of the pro-inflammatory cytokine, interleukin-6 (IL-6), which can activate colonic enteric neurons, are elevated in IBS patients. These studies aim to explore the relationship between IL-6 and the stress peptide, corticotropin-releasing factor (CRF) in colonic submucosal neurons.

METHODS

Calcium imaging, Ussing chamber electrophysiology and immunohistochemistry were conducted on rat distal colons to investigate potential crosstalk between IL-6 and CRF.

KEY RESULTS

Colonic secretions from the maternal separation rat model of IBS stimulated increases in intracellular calcium in naïve submucosal neurons via CRF1 receptors (n=15, p<0.05). Moreover, IL-6 (n=50, p<0.01) but not IL-1β (n=46, p>0.05) or TNFα (n=46, p>0.05) potentiated the CRF-evoked calcium response. CRF (1μM, 1h, n=5) stimulation also induced colonic secretion of IL-6 and inhibited the pro-secretory effects of IL-6 on colonic ion transfer (n=12).

CONCLUSIONS AND INFERENCES

These studies demonstrate the modulatory effects of CRF on colonic IL-6 secretion, neuronal activation and secretory function. These findings may provide an insight into the molecular mechanisms underlying symptom flares in IBS during periods of high stress.

Corticotropin-releasing factor receptor subtype 2 in human colonic mucosa: Down-regulation in ulcerative colitis

AIM: To assess corticotropin-releasing factor receptor 2 (CRF₂) expression in the colon of healthy subjects and patients with ulcerative colitis (UC).

METHODS: We examined CRF₂ gene and protein expression in the distal/sigmoid colonic mucosal biopsies from healthy subjects and patients with UC (active or disease in remission), human immunodeficiency virus (HIV) and functional bowel disease (FBD) by reverse transcription-polymerase chain reaction and immunofluorescence.

RESULTS: Gene expression of CRF₂ was demonstrated in the normal human colonic biopsies, but not in the human colorectal adenocarcinoma cell line Caco2. Receptor protein localization showed immunoreactive CRF₂ receptors in the lamina propria and in the epithelial cells of the distal/sigmoid biopsy samples. Interestingly, CRF₂ immunoreactivity was no longer observed in epithelial cells of patients with mild-moderately active UC and disease in remission, while receptor protein expression did not change in the lamina propria. No differences in CRF₂ expression profile were observed in distal/sigmoid intestinal biopsies from HIV infection and FBD patients, showing no signs of inflammation.

CONCLUSION: The down-regulation of the CRF₂ receptor in the distal/sigmoid biopsies of UC patients is indicative of change in CRF₂ signalling associated with the process of inflammation.

Peripheral corticotropin-releasing factor (CRF) induces stimulation of gastric contractions in freely moving conscious rats: role of CRF receptor types 1 and 2

BACKGROUND

Peripheral corticotrophin-releasing factor (CRF) plays an important role in stress-induced alterations of gastrointestinal motility. CRF injected peripherally inhibits gastric emptying, but its effect on gastric contractions has not been clarified in freely moving conscious rats.

METHODS

Intraluminal gastric pressure waves were measured in freely moving conscious non-fasted rats using the perfused manometric method. We assessed the area under the manometric trace as the motor index (MI), and compared this result with those obtained 1 h before and after drug administration.

KEY RESULTS

Subcutaneous injection (sc) of CRF (15 μg kg(-1)) increased the MI significantly. Pretreatment with intravenous astressin (100 μg kg(-1)), a non-selective CRF antagonist, blocked the sc CRF (15 μg kg(-1))-induced response, but astressin(2)-B (200 μg kg(-1), sc), a selective CRF receptor type 2 (CRF(2)) antagonist, enhanced the CRF-induced increase in MI significantly. Meanwhile urocortin 2 (15 μg kg(-1), sc), a selective CRF(2) agonist, did not alter the basal MI, but it inhibited the sc CRF (15 μg kg(-1))-induced stimulation of gastric contractions. The intraperitoneal injection of cortagine (30 μg kg(-1)), a selective CRF receptor type 1 (CRF(1)) agonist, mimicked the response induced by sc CRF.

CONCLUSIONS & INFERENCES

Peripheral CRF stimulates gastric contractions through CRF(1). CRF(2) activation inhibits the response induced by CRF, suggesting that CRF(2) may have a modulatory action to CRF(1) signaling in gastric motor activity.

Early life stress triggers persistent colonic barrier dysfunction and exacerbates colitis in adult IL-10-/- mice

BACKGROUND

It has become increasingly evident that disease flares in the human inflammatory bowel diseases are influenced by life stress. It is known that life stress can trigger disturbances in intestinal barrier function and activate proinflammatory signaling pathways, which are important contributors to intestinal inflammation and clinical disease; however, the exact mechanisms of stress-induced inflammatory bowel disease exacerbations remain to be elucidated. Here, we presented a model of early life stress-induced exacerbation of colitis in interleukin (IL)-10 mice.

METHODS

C57Bl/6 wild-type and IL-10 mice were exposed to neonatal maternal separation (NMS) stress on postnatal days 1 to 18 and reared under normal conditions until 10 to 12 weeks of age. At this time, histopathology, colitis scores, intestinal barrier function, proinflammatory cytokine expression, and mast cell activity were evaluated.

RESULTS

NMS increased the severity of colitis IL-10 mice indicated by greater colitis scores and colonic proinflammatory cytokine concentrations. NMS and IL-10 increased colonic permeability; however, NMS alone did not induce colitis. Increased mast cell activation and colonic tryptase release were observed in IL-10 mice exposed to NMS, indicating mast cell activation.

CONCLUSIONS

This study demonstrates that colitis in IL-10 mice can be exacerbated by NMS stress. The precise mechanisms of enhanced colitis severity in NMS IL10 mice are unclear but persistent defects in intestinal barrier function likely play a contributing role. NMS serves as a novel model to investigate the mechanisms by which early life stress influences the development and course of inflammatory bowel disease in adulthood.

Brain-gut interactions in inflammatory bowel disease

Psycho-neuro-endocrine-immune modulation through the brain-gut axis likely has a key role in the pathogenesis of inflammatory bowel disease (IBD). The brain-gut axis involves interactions among the neural components, including (1) the autonomic nervous system, (2) the central nervous system, (3) the stress system (hypothalamic-pituitary-adrenal axis), (4) the (gastrointestinal) corticotropin-releasing factor system, and (5) the intestinal response (including the intestinal barrier, the luminal microbiota, and the intestinal immune response). Animal models suggest that the cholinergic anti-inflammatory pathway through an anti-tumor necrosis factor effect of the efferent vagus nerve could be a therapeutic target in IBD through a pharmacologic, nutritional, or neurostimulation approach. In addition, the psychophysiological vulnerability of patients with IBD, secondary to the potential presence of any mood disorders, distress, increased perceived stress, or maladaptive coping strategies, underscores the psychological needs of patients with IBD. Clinicians need to address these issues with patients because there is emerging evidence that stress or other negative psychological attributes may have an effect on the disease course. Future research may include exploration of markers of brain-gut interactions, including serum/salivary cortisol (as a marker of the hypothalamic-pituitary-adrenal axis), heart rate variability (as a marker of the sympathovagal balance), or brain imaging studies. The widespread use and potential impact of complementary and alternative medicine and the positive response to placebo (in clinical trials) is further evidence that exploring other psycho-interventions may be important therapeutic adjuncts to the conventional therapeutic approach in IBD.

Expression of corticotropin releasing factor receptor type 1 (CRF1) in the human gastrointestinal tract and upregulation in the colonic mucosa in patients with ulcerative colitis

Brain corticotropin-releasing factor (CRF) acting on CRF receptor type 1 (CRF(1)) is a main signaling pathway in the stress response. CRF is also produced in a variety of peripheral sites and acts locally as a proinflammatory mediator. We investigated CRF(1) mRNA expression in the human gastrointestinal tract, and localized CRF(1) immunoreactive cells in the colonic mucosa of healthy subjects and patients with ulcerative colitis (UC). In 4 male healthy subjects (24-29 years), CRF(1) transcript was detected by RT-PCR throughout the gastrointestinal tract with the highest levels in the ileum and rectum and the lowest level in the colon. Immunohistochemistry on whole thickness sigmoid colon sections showed that CRF(1) was localized in the lamina propria and epithelial cells and enteric neurons. In sigmoid colonic biopsies, immunohistochemically double-labeled cells with CRF(1) and CD163, a marker for macrophages, represent 79% of total CRF(1) immunoreactive (IR) cells in healthy subjects. In 10 UC patients, the total number of CRF(1) IR cells and CRF(1)/CD163 double-labeled macrophages was increased by 4.2 and 4.0 folds respectively compared to healthy subjects. These findings indicate that CRF(1) is distributed throughout the GI tract of healthy human subjects. The increase of CRF(1) IR cells prominently in macrophages of the sigmoid colonic mucosa of UC patients provides anatomical support for a role of CRF(1) signaling in modulating the immune-inflammatory process of UC.

Repeated exposure to water immersion stress reduces the Muc2 gene level in the rat colon via two distinct mechanisms

The mucin family plays a number of important roles in intestinal homeostasis. Among its members, the gel-forming Muc2, produced in goblet cells, is a major component of mucus and contributes to intestinal barrier integrity. Whereas psychological stress is known to impair intestinal barrier, the effects of chronic or repeated stress on mucin expression and goblet cell differentiation have not been well documented. The present study first examined the effects of different levels of exposure (3 days, 1 and 2 weeks) to water immersion stress on intestinal mucin gene expression in rats, and then explored the mechanisms underlying the stress-induced decrease in the colonic Muc2 level. Repeated water immersion stress for 1 and 2 weeks decreased colonic Muc2 gene levels to 40% of that of non-stressed animals, while exposure to stress for 3 days induced only a 25% decrease. The goblet cell numbers counts in the colons of the 1- and 2-week stress groups, but not the 3-day stress group, were decreased to 85% of that in non-stressed animals. Cdx2 expression, a transcriptional factor related to Muc2 synthesis in the goblet cells, was decreased in all stress groups, whereas Rath1 and Klf4 expressions, transcriptional factors related to goblet cell differentiation in Notch signaling were decreased in the 1-week stress group. Collectively, the repeated exposure to water immersion stress decreases Muc2 synthesis in the goblet cells via decreased Cdx2 expression and subsequently reduces the goblet cell number via Notch signaling suppression.

Importance of stress receptor-mediated mechanisms in the amygdala on visceral pain perception in an intrinsically anxious rat

BACKGROUND

Stress worsens abdominal pain experienced by patients with irritable bowel syndrome (IBS), a chronic disorder of unknown origin with comorbid anxiety. Previously, we have demonstrated colonic hypersensitivity in Wistar-Kyoto rats (WKYs), a high-anxiety strain, which models abdominal pain in IBS. In low-anxiety rats, we have demonstrated that the central nucleus of the amygdala (CeA) regulates colonic hypersensitivity and anxiety induced by selective activation of either glucocorticoid receptors (GR) or mineralocorticoid receptors (MR), which is also mediated by the corticotropin releasing factor (CRF) Type-1 receptor. The goal of the present study was to test the hypothesis that the CeA through GR, MR, and/or CRF-1R regulates colonic hypersensitivity in WKYs.

METHODS

One series of WKYs had micropellets of a GR antagonist, an MR antagonist or cholesterol (control) stereotaxically implanted onto the CeA. Another series were infused in the CeA with CRF-1R antagonist, or vehicle. Colonic sensitivity was measured as a visceromotor response (VMR) to graded colorectal distension (CRD).

KEY RESULTS

The exaggerated VMR to graded CRD in WKYs was unaffected by GR or MR antagonism in the CeA. In contrast, direct CeA infusion of CRF-1R antagonist significantly inhibited the VMR to CRD at noxious distension pressures.

CONCLUSIONS & INFERENCES

Stress hormones in the CeA regulate colonic hypersensitivity in the rat through strain-dependent parallel pathways. The colonic hypersensitivity in WKYs is mediated by a CRF-1R mechanism in the CeA, independent of GR and MR. These complementary pathways suggest multiple etiologies whereby stress hormones in the CeA may regulate abdominal pain in IBS patients.

Systemic urocortin 2, but not urocortin 1 or stressin 1-A, suppresses feeding via CRF2 receptors without malaise and stress

BACKGROUND AND PURPOSE

Infusion of corticotropin-releasing factor (CRF)/urocortin (Ucn) family peptides suppresses feeding in mice. We examined whether rats show peripheral CRF/Ucn-induced anorexia and determined its behavioural and pharmacological bases.

EXPERIMENTAL APPROACH

Male Wistar rats (n= 5-12 per group) were administered (i.p.) CRF receptor agonists with different subtype affinities. Food intake, formation of conditioned taste aversion and corticosterone levels were assessed. In addition, Ucn 1- and Ucn 2-induced anorexia was studied in fasted CRF(2) knockout (n= 11) and wild-type (n= 13) mice.

KEY RESULTS

Ucn 1, non-selective CRF receptor agonist, reduced food intake most potently (~0.32 nmol·kg(-1) ) and efficaciously (up to 70% reduction) in fasted and fed rats. The peptides' rank-order of anorexic potency was Ucn 1 ≥ Ucn 2 > >stressin(1) -A > Ucn 3, and efficacy, Ucn 1 > stressin(1) -A > Ucn 2 = Ucn 3. Ucn 1 reduced meal frequency and size, facilitated feeding bout termination and slowed eating rate. Stressin(1) -A (CRF(1) agonist) reduced meal size; Ucn 2 (CRF(2) agonist) reduced meal frequency. Stressin(1) -A and Ucn 1, but not Ucn 2, produced a conditioned taste aversion, reduced feeding efficiency and weight regain and elicited diarrhoea. Ucn 1, but not Ucn 2, also increased corticosterone levels. Ucn 1 and Ucn 2 reduced feeding in wild-type, but not CRF(2) knockout, mice.

CONCLUSIONS AND IMPLICATIONS

CRF(1) agonists, Ucn 1 and stressin(1) -A, reduced feeding and induced interoceptive stress, whereas Ucn 2 potently suppressed feeding via a CRF(2) -dependent mechanism without eliciting malaise. Consistent with their pharmacological differences, peripheral urocortins have diverse effects on appetite.