Macrophages express functional receptors for calcitonin-gene-related peptide

CGRP induces myofibroblast differentiation and the production of extracellular matrix in MRC5s via autocrine and paracrine signalings

There are contradictory views on which calcitonin gene-related peptide (CGRP) causes pulmonary fibrosis. Fibrotic potency of CGRP was tested and compared to that of transforming growth factor-β (TGF-β). Myofibroblast differentiation, cell proliferation, and activations of TGF-β and Wnt pathways were examined for 24, 48, and 72 h in A549 and MRC5 cell lines stimulated with CGRP and TGF-β. CGRP-induced cell proliferation in MRC5s early on while cell proliferation in A549 occurred progressively. CGRP promoted fibroblast-myofibroblast differentiation by inducing the transcription of ACTA2, COL1A1, SMAD2/3, and SMAD4 genes, the production of collagen, fibronectin, α-smooth muscle actin, and activation of TGF-β signaling starting from 24 h. Additionally, TGF-β signaling induced by CGRP decreased the DKK1 level and activated the Wnt signaling in MRC5s. After CGRP stimulation, Wnt7a levels were increased from 24 to 72 h, while Wnt5a levels were elevated at 72 h in MRC5s. CGRP did not induce epithelial-mesenchymal transition in A549s, unlike TGF-β. A comparison of fibrotic potency of CGRP and TGF-β showed that TGF-β is a powerful profibrotic molecule and induces earlier myofibroblast differentiation. Even so, CGRP promotes myofibroblast differentiation and extracellular matrix production by inducing Smad-dependent-TGF-β and Wnt signalings via autocrine and paracrine signalings in MRC5s.

The Functional Significance of Endocrine-immune Interactions in Health and Disease

Hormones are known to influence various body systems that include skeletal, cardiac, digestive, excretory, and immune systems. Emerging investigations suggest the key role played by secretions of endocrine glands in immune cell differentiation, proliferation, activation, and memory attributes of the immune system. The link between steroid hormones such as glucocorticoids and inflammation is widely known. However, the role of peptide hormones and amino acid derivatives such as growth and thyroid hormones, prolactin, dopamine, and thymopoietin in regulating the functioning of the immune system remains unclear. Here, we reviewed the findings pertinent to the functional role of hormone-immune interactions in health and disease and proposed perspective directions for translational research in the field.

Mechanisms underlying mechanical sensitization induced by complement C5a: the roles of macrophages, TRPV1, and calcitonin gene-related peptide receptors

The complement system significantly contributes to the development of inflammatory and neuropathic pain, but the underlying mechanisms are poorly understood. Recently, we identified the signaling pathway responsible for thermal hypersensitivity induced by the complement system component C5a. Here, we examine the mechanisms of another important action of C5a, induction of mechanical hypersensitivity. We found that intraplantar injection of C5a produced a dose-dependent mechanical sensitization and that this effect was blocked by chemogenetic ablation of macrophages in both male and female mice. Knockout of TRPV1 or pretreatment with the TRPV1 antagonists, AMG9810 or 5'-iodoresiniferatoxin (5'-IRTX), significantly reduced C5a-induced mechanical sensitization. Notably, local administration of 5'-IRTX 90 minutes after C5a injection resulted in a slow, but complete, reversal of mechanical sensitization, indicating that TRPV1 activity was required for maintaining C5a-induced mechanical hypersensitivity. This slow reversal suggests that neurogenic inflammation and neuropeptide release may be involved. Indeed, pretreatment with a calcitonin gene-related peptide (CGRP) receptor antagonist (but not an antagonist of the neurokinin 1 receptor) prevented C5a-induced mechanical sensitization. Furthermore, intraplantar injection of CGRP produced significant mechanical sensitization in both wild-type and TRPV1 knockout mice. Taken together, these findings suggest that C5a produces mechanical sensitization by initiating macrophage-to-sensory-neuron signaling cascade that involves activation of TRPV1 and CGRP receptor as critical steps in this process.

Modulation of the Proliferative Response of Murine Peyer's Patch Lymphocytes by Different Peptides: CCK-8, CGRP, CCK-PZ and VIP. Preliminary Results

There is evidence of an innervation of the mucosal immune system by peptidergic fibers. The modulation of the mitogenic response of the murine Peyer's patch lymphocytes by several peptides present in the gastrointestinal tract, namely, the carboxy-terminal octapeptide of cholecystokinin (CCK-8), the entire molecule cholecystokinin-pancreozymin (CCK-PZ), the calcitonin gene-related peptide (CGRP) and the vasoactive intestinal peptide (VIP), was studied. The proliferative response of the T lymphocytes induced by 2.5 μg/ml concanavaline A (Con A) was dose dependently inhibited by CGRP and VIP, with a maximal inhibition of 40% and 55% with 10−7 M CGRP and VIP, respectively. On the contrary, CCK-PZ exerted a significant stimulatory effect, 48% increase in thymidine incorporation being observed with 62.5 mU/ml (Crick units) CCK-PZ. CCK-8 was found to have no effect on the T cell proliferation. None of the peptides tested were able to modify the mitogenic response of Peyer's patch B lymphocytes induced by 20 μg/ml lipopolysaccharide (LPS), except for CCK-PZ which induced a significant inhibition of the mitogenesis with a maximal effect of 45% inhibition at 500 mU/ml. These preliminary results show that CGRP, VIP and CCK-PZ can affect the murine Peyer's patch T and B lymphocyte response and suggest that they could be implicated in the modulation of the local immune response in the intestine.

Calcitonin gene-related peptide modulates the production of pro-inflammatory cytokines associated with periprosthetic osteolysis by THP-1 macrophage-like cells

OBJECTIVE

An anti-resorptive impact of the neuropeptide calcitonin gene-related peptide (CGRP) on periprosthetic osteolysis, the leading cause of early prosthesis loosening, has been shown previously. In this study, the impact of CGRP on pro-inflammatory cytokine production associated with periprosthetic osteolysis was analysed using THP-1 macrophage-like cells.

METHODS

Cells were stimulated with ultra-high-molecular-weight polyethylene (UHMWPE) particles (cell-to-particle ratios of 1:100 and 1:500) and lipopolysaccharides (LPS; 1 µg/ml) to establish osteolytic conditions, and simultaneously treated with CGRP (10(-8)M). Receptor activator of nuclear factor-κB (RANK), RANK ligand (RANKL) and tumour necrosis factor (TNF)-α mRNA expression were measured by quantitative RT-PCR. RANK protein was detected by Western blot. Secreted protein levels of TNF-α as well as interleukin (IL)-1β and IL-6 were quantified in cell culture supernatants by ELISA and Bio-Plex cytokine assay, respectively.

RESULTS

Activation of macrophage-like cells failed to enhance the production of RANK but led to a dose- and time-dependent increase of TNF-α mRNA and secreted protein levels of TNF-α, IL-1β and IL-6. Application of CGRP time-dependently suppressed TNF-α mRNA expression induced by low-particle concentrations and LPS, while both particle- and LPS-induced secretion of TNF-α was inhibited. A pronounced inhibitory effect of CGRP on LPS-induced cytokine production at 24 h of incubation was also observed with IL-1β and IL-6.

CONCLUSIONS

CGRP shows a time-dependent inhibitory effect on the secretion of osteolysis-associated pro-inflammatory cytokines, indicating an indirect anti-resorptive influence of the neuropeptide on both aseptic prosthesis loosening and bacterially induced bone resorption which might enhance the life time of total joint replacements.

Direct and indirect antimicrobial activities of neuropeptides and their therapeutic potential

As global resistance to conventional antibiotics rises we need to develop new strategies to develop future novel therapeutics. In our quest to design novel anti-infectives and antimicrobials it is of interest to investigate host-pathogen interactions and learn from the complexity of host defense strategies that have evolved over millennia. A myriad of host defense molecules are now known to play a role in protection against human infection. However, the interaction between host and pathogen is recognized to be a multifaceted one, involving countless host proteins, including several families of peptides. The regulation of infection and inflammation by multiple peptide families may represent an evolutionary failsafe in terms of functional degeneracy and emphasizes the significance of host defense in survival. One such family is the neuropeptides (NPs), which are conventionally defined as peptide neurotransmitters but have recently been shown to be pleiotropic molecules that are integral components of the nervous and immune systems. In this review we address the antimicrobial and anti-infective effects of NPs both in vitro and in vivo and discuss their potential therapeutic usefulness in overcoming infectious diseases. With improved understanding of the efficacy of NPs, these molecules could become an important part of our arsenal of weapons in the treatment of infection and inflammation. It is envisaged that targeted therapy approaches that selectively exploit the anti-infective, antimicrobial and immunomodulatory properties of NPs could become useful adjuncts to our current therapeutic modalities.

The calcitonin/calcitonin gene related peptide-alpha gene is not required for 1alpha,25-dihydroxyvitamin D3-mediated suppression of experimental autoimmune encephalomyelitis

The active form of vitamin D, 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), can suppress disease in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis. Calcium appears to be a critical component of 1,25(OH)(2)D(3)-mediated suppression of EAE, as complete disease prevention only occurs with a concomitant increase in serum calcium levels. Calcitonin (CT) is a peptide hormone released in response to acute increases in serum calcium, which led us to explore its importance in 1,25(OH)(2)D(3)-mediated suppression of EAE. Previously, we discovered that co-administration of pharmacological doses of CT enhanced the suppressive effect of 1,25(OH)(2)D(3) on EAE, suggesting CT may play a role in 1,25(OH)(2)D(3)-mediated suppression of EAE. To determine the importance of CT in EAE we have utilized a mouse strain in which the gene encoding CT and its alternative splice product, calcitonin gene related peptide-alpha (CGRP), have been deleted. Deletion of the CT/CGRP gene had no effect on EAE progression. Furthermore, treatment with 1,25(OH)(2)D(3) suppressed EAE in CT/CGRP knock-out mice equal to that in wild type mice. Therefore, we conclude that CT is not necessary for 1,25(OH)(2)D(3)-mediated suppression of EAE.

Neuronal plasticity of the “brain–skin connection”: stress-triggered up-regulation of neuropeptides in dorsal root ganglia and skin via nerve growth factor-dependent pathways

Emerging research indicates that central-nervous stress perception is translated to peripheral tissues such as the skin not only via classical stress hormones but also via neurotrophins and neuropeptides. This can result in neurogenic inflammation, which is likely to contribute to the triggering and/aggravation of immunodermatoses. Although the existence of such a "brain-skin connection" is supported by steadily increasing experimental evidence, it remains unclear to which extent perceived stress affects the sensory "hardwiring" between skin and its afferent neurons in the corresponding dorsal root ganglia (DRG). In this paper, we provide experimental evidence in a murine model of stress (exposure of C57BL/6 mice to sound stress) that stress exposure, or intracutaneous injection of recombinant nerve growth factor (NGF) to mimic the skin's response to stress, up-regulate the percentage of substance P (SP)+ or calcitonin gene-related peptide (CGRP)+ sensory neurons in skin-innervating DRG. Further, we show that the number of SP+ or CGRP+ sensory nerve fibers in the dermis of stressed C57BL/6 mice is significantly increased. Finally, we document that neutralization of NGF activity abrogates stress-induced effects on the percentage of SP+ and CGRP+ sensory neurons in skin-innervating DRG as well as on dermal sensory nerve fibers. These data suggest that high stress perception results in an intense cross talk between the skin and skin-innervating DRG, which increases the likelihood of NGF-dependent neurogenic skin inflammation by enhancing sensory skin innervation.

The neuropeptide pituitary adenylate cyclase activating protein is a physiological activator of human monocytes

Pituitary adenylate cyclase activating protein (PACAP) and its structurally related vasointestinal peptide (VIP) bind to three G-protein-coupled receptors named VPAC1 and VPAC2 for VIP/PACAP receptors and PAC1 for PACAP preferred receptors. We report that in freshly isolated human monocytes PACAP acts as a pro-inflammatory molecule. By RT-PCR, VPAC1 mRNA was the only receptor found to be expressed; VPAC1 protein was detected by Western blotting and visualized by immunohistochemistry. Signaling pathways activated by PACAP include the extracellular regulated kinase (ERK), the stress-activated MAPK p38, the focal adhesion kinase, Pyk2 and its associated cytoskeleton protein paxillin and the phosphatidylinositol 3-kinase (PI-3K). PACAP induces a transient peak in cytoplasmic calcium associated with an increase in reactive oxygen species production and upregulation in membrane expression of the integrin CD11b as well as the complement receptor 1. Control of the different pathways and functions stimulated by PACAP were evaluated using Phospholipase C (PLC), PI-3K, ERK and p38 MAPK inhibitors and led to the conclusion that PLC and to a lesser degree PI-3K activation are upstream events occurring in VPAC1 mediated PACAP stimulation of monocytes and are in contrast to ERK and p38 mandatory for the initiation of other cellular events associated with monocytes activation.

Endogenous NGF regulates CGRP expression in human monocytes, and affects HLA-DR and CD86 expression and IL-10 production

Our recent results on autocrine nerve growth factor (NGF) synthesis in B lymphocytes, which directly regulates the expression and release of calcitonin gene-related peptide (CGRP), a neuropeptide known to down-regulate immune response, led us to propose an anti-inflammatory action of NGF. In the present work, we investigated whether the endogenous synthesis of NGF can regulate the expression of CGRP in other antigen-presenting cells, such as monocytes, and whether this may have a functional effect. Our data indicate that human monocytes synthesize basal levels of NGF and CGRP and that, following lipopolysaccharide (LPS) stimulation, NGF and CGRP expression are both up-regulated. When endogenous NGF is neutralized, the up-regulation of CGRP expression induced by LPS is inhibited. The expression of membrane molecules involved in T-cell activation such as human leukocyte antigen-DR (HLA-DR) and CD86 is affected by endogenous NGF, and similar effects were obtained using a CGRP(1) receptor antagonist. In addition, NGF deprivation in LPS-treated monocytes significantly decreases interleukin 10 (IL-10) synthesis. Our findings indicate that endogenous NGF synthesis has a functional role and may represent a physiologic mechanism to down-regulate major histocompatibility complex (MHC) class II and CD86 expression and alter the development of immune responses.

Chemokine levels in the jugular venous blood of migraine without aura patients during attacks

OBJECTIVE

To investigate changes in the levels of calcitonin gene-related peptide and its intracellular messenger cyclic adenosine monophosphate in serial samples of internal jugular blood taken from migraine patients without aura assessed during attacks, and to assess their relationship with the levels of IL-8, MCP-1, and RANTES in the same samples.

BACKGROUND

Calcitonin gene-related peptide, the marker of trigeminovascular activation, is released in both the internal and external jugular venous blood of migraine patients during attacks. Experimental evidence demonstrated that when released from C-type sensory neurons in inflammatory pain models, it differentially induced expression of neutrophil chemotactic chemokine IL-8, but not monocyte chemotactic chemokine MCP-1 or lymphocyte chemotactic chemokine RANTES. These chemokines were never investigated in migraine.

DESIGN/METHODS

Eight migraine without aura patients were admitted to the hospital during the attacks. Internal jugular venous blood samples were taken immediately after catheter insertion, at the 1st, 2nd, and 4th hours after attack onset, and within 2 hours from its cessation. The levels of the sensory neuropeptide calcitonin gene-related peptide and the messenger cyclic adenosine monophosphate were measured by RIA method, and those of IL-8, MCP-1, and RANTES were measured by ELISA method.

RESULTS

Higher calcitonin gene-related peptide levels were found in the internal jugular venous blood of migraine without aura patients compared with the time of catheter insertion (ANOVA: P<.0001) with a peak at the first hour (52.6+/-9.2 ng/mL). A transient increase in IL-8 was observed at the 2nd and 4th hours (P<.01 and P<.002, respectively), whereas no changes in the levels of MCP-1 and RANTES were found at any time of the study. The increase in IL-8 was accompanied by a parallel increase in cyclic adenosine monophosphate.

CONCLUSIONS

The present study confirms previous findings of an increase in calcitonin gene-related peptide in internal jugular venous blood of migraine without aura patients during attacks. The transient increase in the levels of IL-8 concurs with the results of recent experimental research showing a calcitonin gene-related peptide-induced activation of IL-8 gene expression, but not RANTES and MCP-1, via the transcriptional factor AP-2, which mediates transduction in response to cyclic adenosine monophosphate. Although IL-8 is transiently increased during migraine attacks, an accumulation of leukocytes secondary to neurogenic inflammation is unlikely, as it is for other inflammatory events, because they are self limiting. Other events, including nitric oxide production, may contribute to counteract meningeal transvascular leukocyte migration during migraine attacks, as suggested by the model of sterile inflammation.

Calcitonin gene-related peptide regulates gene transcription in primary afferent neurons

Although primary afferent neurons express receptors for calcitonin gene-related peptide (CGRP), understanding of the cellular effects of these receptors is limited. We determined that CGRP receptors regulate gene transcription in primary afferent neurons through a cyclic AMP (cAMP)-dependent pathway. CGRP increased cAMP in neonatal dorsal root ganglion (DRG) neurons in a concentration-dependent manner that was blocked by the receptor antagonist CGRP(8-37). The response to CGRP also occurred in adult DRG cells. In contrast, CGRP did not alter the concentration of free intracellular calcium in neonatal or adult DRG neurons. Immunohistochemical data showed that one downstream effect of the cAMP signaling pathway was phosphorylation of cAMP response element binding (CREB) protein, suggesting that CGRP regulates gene expression. This interpretation was supported by evidence that CGRP increased CRE-dependent gene transcription in neurons transiently transfected with a CRE-luciferase DNA reporter construct. The effect of CGRP on gene transcription was inhibited by H89, myristoylated-protein kinase A inhibitor(14-22)-amide and U0126, indicating that protein kinase A and mitogen-activated protein kinase/extracellular receptor kinase kinase are enzymes that mediate effects of CGRP on gene transcription. Therefore, CGRP receptors may regulate expression of proteins by primary afferent neurons during development and in response to tissue-damaging stimuli.

Calcitonin gene-related peptide partially reverses decreased production of chemokines KC and MIP-2 following murine sepsis

The secretion of calcitonin gene-related peptide (CGRP) and the chemokines KC and MIP-2 are increased in the animal models of endotoxemic and septic shock. We tested whether CGRP could modulate KC and MIP-2 secretion from different sources of macrophages after murine sepsis induced by cecal ligation and puncture (CLP). Macrophages were obtained from the peritoneal exudate and lung of female BALB/c mice 16 h after CLP and plated in culture with CGRP and/or LPS for 12 h. The results showed that peritoneal macrophage production of the chemokines (KC, MIP-2) and cytokines (TNF-alpha, IL-6) was markedly decreased in CLP mice. Alveolar macrophages did not display decreased cytokine/chemokines production after CLP. CGRP (0.1 nM-10 nM) partially reversed this decreased production of LPS-induced KC and MIP-2 from peritoneal macrophages. These results suggest that CGRP might be intimately involved in recruitment of neutrophils by promoting local production of the chemokines KC and MIP-2 in murine sepsis.

Localization of functional calcitonin gene-related peptide binding sites in a subpopulation of cultured dorsal root ganglion neurons

In this study we investigated whether cultured dorsal root ganglion (DRG) neurons from the adult rat express binding sites for calcitonin gene-related peptide (CGRP). These were identified on fixed cells by using CGRP labeled at the N-terminal site with 1.4-nm gold particles. After 1 day in culture, about 20% of small to medium-sized DRG neurons showed CGRP-gold binding. Binding of CGRP-gold was dose-dependently reduced by coadministration of CGRP. The calcium imaging technique in living cells revealed that the bath administration of CGRP evoked an increase of the intracellular calcium in up to 30% of the DRG neurons tested. Both depletion of intracellular calcium stores by thapsigargin or using a calcium-free medium blocked the CGRP-mediated increase of cytosolic calcium in most neurons. Thus intracellular and extracellular sources of calcium are relevant for the CGRP response. Using the whole-cell patch-clamp technique, about 30% of the neurons were found to exhibit an inward current and a depolarization upon administration of CGRP close to the neurons. Immunocytochemical double-labeling techniques showed that most of the CGRP-gold binding sites were expressed in unmyelinated (neurofilament 200-negative) DRG neurons. Most of the neurons with CGRP-gold binding sites also expressed the tyrosine kinase A receptor, and all of them showed CGRP-like immunoreactivity. This study shows, therefore, that a subpopulation of unmyelinated, peptidergic primary afferent neurons express CGRP binding sites that can be activated by CGRP in an excitatory direction. The binding sites may serve as autoreceptors because all of these neurons also synthesize CGRP. The activation of CGRP binding sites may sensitize primary afferent neurons and influence the release of mediators.

Molecular cloning and characterization of mouse calcitonin gene-related peptide receptor

The calcitonin gene-related peptide (CGRP) plays important roles as a neurotransmitter/neuromodulator in the central nervous system, and as a potent vasodilator when secreted from peripheral, perivascular nerves through its specific receptors. In this study, we cloned mouse cDNA counterparts of the human CGRP receptor composed of calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein 1 (RAMP1) and examined the signal transduction mechanism through the CGRP receptor. Mouse CRLR (mCRLR) is a 462-amino acid G protein-coupled heptahelical receptor, and mouse RAMP1 (mRAMP1) is a 148-amino acid single membrane-spanning protein with a short cytoplasmic portion. Specific binding of (125)I-CGRP was detected only when both mCRLR and mRAMP1 cDNAs were cotransfected to COS-7 cells, and the Kd value of the receptor was 2.2 x 10(-10) M. CGRP induced a marked elevation of the intracellular cAMP levels in COS-7 cells cotransfected with mCRLR and mRAMP1. CGRP signaling through the mCRLR/mRAMP1 receptor complex was found to increase the promoter activities of cyclic AMP responsive element and serum responsive element in the co-transfected HeLa cells. These results indicate that mCRLR and mRAMP1 constitute a functional mouse CGRP receptor for the transduction of CGRP signaling by PKA and extracellular signal-regulated kinase signal transduction pathways.

NGF modulates CGRP synthesis in human B-lymphocytes: a possible anti-inflammatory action of NGF?

We investigated whether the sensory neuropeptide, calcitonin gene-related peptide (CGRP), could be synthesised by human lymphocytes. Our results indicate that in activated B-cells, there is a strong expression of CGRP gene transcripts, which is almost absent in resting cells. Since B-cells autocrinally produce NGF, the neutralisation of endogenous NGF by anti-NGF antibodies resulted in a marked reduction in CGRP expression in both resting and activated B-cells. Thus, NGF appears to directly affect the synthesis of CGRP in B-cells as in sensory neurons. By regulating CGRP synthesis in lymphocytes and neuronal cells, NGF can influence the intensity and duration of the immune response.

Bone marrow-derived macrophages express functional CGRP receptors and respond to CGRP by increasing transcription of c-fos and IL-6 mRNA

Calcitonin gene-related peptide (CGRP) is a sensory neuropeptide with inflammatory and immunoregulatory properties. CGRP inhibits IL-7 responses by B cell precursors by direct and indirect mechanisms. We recently found that CGRP induces IL-6 and TNF-alpha in long-term bone marrow cultures and that IL-6 and TNF-alpha also inhibit IL-7 responses. Because these are heterogeneous cultures, it was not clear which cells produced IL-6 and TNF-alpha. To determine whether bone marrow-derived macrophages (BMDM) were the source, we did studies to determine whether BMDMs express mRNAs for CGRP receptors and whether CGRP induces c-fos, IL-6, and TNF-alpha mRNA. We found that BMDMs express mRNAs for CRLR and RAMP1, the minimal components for CGRP receptors. CGRP also stimulated dose- and time-dependent increases in c-fos and IL-6. In contrast, CGRP did not induce TNF-alpha in BMDMs. These results suggest that BMDMs are a source of CGRP-induced IL-6 in bone marrow.

Osteoclasts and giant cells: macrophage-macrophage fusion mechanism

Membrane fusion is a ubiquitous event that occurs in a wide range of biological processes. While intracellular membrane fusion mediating organelle trafficking is well understood, much less is known about cell-cell fusion mediating sperm cell-oocyte, myoblast-myoblast and macrophage-macrophage fusion. In the case of mononuclear phagocytes, their fusion is not only associated with the differentiation of osteoclasts, cells which play a key role in the pathogenesis of osteoporosis, but also of giant cells that are present in chronic inflammatory reactions and in tumours. Despite the biological and pathophysiological importance of intercellular fusion events, the actual molecular mechanism of macrophage fusion is still unclear. One of the main research themes in my laboratory has been to investigate the molecular mechanism of mononuclear phagocyte fusion. Our hypothesis has been that macrophage-macrophage fusion, similar to virus-cell fusion, is mediated by specific cell surface proteins. But, in contrast with myoblasts and sperm cells, macrophage fusion is a rare event that occurs in specific instances. To test our hypothesis, we established an in vitro cell-cell fusion assay as a model system which uses alveolar macrophages. Upon multinucleation, these macrophages acquire the osteoclast phenotype. This indicates that multinucleation of macrophages leads to a specific and novel functional phenotype in macrophages. To identify the components of the fusion machinery, we generated four monoclonal antibodies (mAbs) which block the fusion of alveolar macrophages and purified the unique antigen recognized by these mAbs. This led us to the cloning of MFR (Macrophage Fusion Receptor). MFR was cloned simultaneously as P84/SHPS-1/SIRPalpha/BIT by other laboratories. We subsequently showed that the recombinant extracellular domain of MFR blocks fusion. Most recently, we identified a lower molecular weight form of MFR that is missing two extracellular immunoglobulin (Ig) C domains. Shortly after we cloned MFR, CD47 was reported to be a ligand for P84/SIRPalpha. We have since generated preliminary results which suggest that CD47 interacts with MFR during adhesion/fusion and is a member of the fusion machinery. We also identified CD44 as a plasma membrane protein which, like MFR, is highly expressed at the onset of fusion. The recombinant soluble extracellular domain of CD44 blocks fusion by interacting with a cell-surface binding site. We now propose a model in which both forms of MFR, CD44, and CD47 mediate macrophage adhesion/fusion and therefore the differentiation of osteoclasts and giant cells.

Calcitonin gene-related peptide inhibits lipopolysaccharide-induced interleukin-12 release from mouse peritoneal macrophages, mediated by the cAMP pathway

Previously we showed that calcitonin gene-related peptide (CGRP), a neuropeptide, inhibited lipopolysaccharide (LPS)-induced tumour necrosis factor-alpha (TNF-alpha) production and increased interleukin (IL)-6 release at low concentrations via activation of the cAMP pathway in mouse peritoneal macrophages (Mphi). In this study we examined whether CGRP could modulate IL-12 release from mouse peritoneal Mphi, and if so, what signal transduction pathway was involved. Mphi were obtained from the peritoneal exudate of male BALB/c mice. The cells were plated on culture dishes at a density of 5 x 105 cells per well and allowed to adhere for 2 hr. After incubation for 24 hr, the Mphi were cultured with 0.1 microg/ml of LPS, alone or together with CGRP (1-1000 nM) for 24 hr. The amount of IL-12 in the cell medium was measured by enzyme-linked immunosorbent assay (ELISA). The results showed that CGRP attenuated LPS-induced IL-12 release in a concentration-dependent manner. Production of IL-12 was decreased from 95.9+/-4.6 to 73.4+/-5.7 pg/ml by 100 nM CGRP. The two cAMP phosphodiesterase (PDE) inhibitors, 3-isobutyl-1-methyl-xanthine (IBMX) and rolipram, significantly potentiated the CGRP response, and the level of IL-12 was further decreased by 28% and 47%, respectively. However, CGRP had no effect on IL-12 production from unstimulated Mphi. The LPS-induced IL-12 release from Mphi could also be reduced by forskolin, an activator of adenylate cyclase, and 8-Br-cAMP, an analogue of cAMP. Using the reverse transcription-polymerase chain reaction (RT-PCR), we found that CGRP also decreased the LPS-induced IL-12 p40 mRNA levels. Furthermore, pretreatment with H89 (0.1 microM or 1 microM), an inhibitor of cAMP-dependent protein kinase, diminished CGRP effects, IL-12 production and gene expression. These data suggest that LPS-induced IL-12 release and gene expression were attenuated by CGRP via an activated cAMP-protein kinase A (PKA) pathway in mouse peritoneal Mphi.

Calcitonin gene-related peptide induces IL-8 synthesis in human corneal epithelial cells

Calcitonin gene-related peptide (CGRP), a neuropeptide with proinflammatory activities, is released from termini of corneal sensory neurons in response to pain stimuli. Because neutrophil infiltration of the clear corneal surface is a hallmark of corneal inflammation in the human eye, we determined whether CGRP can bind to human corneal epithelial cells (HCEC) and induce expression of the neutrophil chemotactic protein IL-8. It was found that HCEC specifically bound CGRP in a saturable manner with a Kd of 2.0 x 10-9 M. Exposure of HCEC to CGRP induced a significant increase in intracellular cAMP levels and enhanced IL-8 synthesis nearly 4-fold. The capacity of CGRP to stimulate cAMP and IL-8 synthesis was abrogated in the presence of the CGRP receptor antagonist CGRP8-37. CGRP stimulation had no effect on the half-life of IL-8 mRNA while increasing IL-8 pre-mRNA synthesis >2-fold. In contrast to IL-8, CGRP did not induce monocyte chemotactic protein-1 or RANTES synthesis, nor did the neuropeptide enhance detectable increases in steady state levels of mRNA specific for these two beta-chemokines. The results suggest that HCEC possess CGRP receptors capable of initiating a signal transduction cascade that differentially activates expression of the IL-8 gene but not the genes for monocyte chemotactic protein-1 or RANTES. The capacity of CGRP to stimulate IL-8 synthesis in HCEC suggests that sensory neurons are involved in induction of acute inflammation at the eye surface.

Calcitonin gene-related peptide potentiates LPS-induced IL-6 release from mouse peritoneal macrophages

The secretion of IL-6 after stimulation of macrophages has been found to play a central role in the regulation of defense mechanism, haematopoiesis, and acute phase reaction. It was reported that cAMP is involved in the regulation of IL-6 production. Since calcitonin gene-related peptide (CGRP) is known to increase cAMP accumulation in mouse macrophages, we examined whether CGRP would induce IL-6 release in macrophages. Macrophages were obtained from the peritoneal exudate of male Balb/c mouse. The cells were plated on culture dishes at a density of 2.5 x 10(5) cells per well and allowed to adhere for 2 h. After incubation for 48 h with two changes of PRMI-1640, the macrophages were cultured with CGRP and LPS 1 microg/ml for 12 h. The IL-6 level in medium was measured by ELISA kits. The results showed that CGRP had no direct effects on IL-6 production, but it potentiated LPS-induced IL-6 production in a concentration-dependent manner. When CGRP was at a concentration of 10(-10) M, the LPS-induced IL-6 production was increased from 5.16 +/- 0.48 to 8.88 +/- 0.48 ng/ml. The effect of CGRP 10(-10) M was reversed by hCGRP(8-37) 10(-8) M, an antagonist of CGRP1 receptor. The LPS-induced IL-6 production from macrophages was also potentiated by forskolin 5 microM, an activator of adenylate cyclase. Furthermore, pretreatment with H-89 1 microM or Rp-cAMPS 100 microM, the inhibitors of cAMP-dependent protein kinase, inhibited the effect of CGRP by 31% and 98%, respectively. These results demonstrate that the LPS-induced IL-6 release is potentiated by CGRP via the activation of cAMP pathway in mouse resident peritoneal macrophages.

Inhibition of LPS-induced TNF-alpha production by calcitonin gene-related peptide (CGRP) in cultured mouse peritoneal macrophages

The purpose of this study was to examine whether rCGRP has effects on TNF-alpha produced by mouse resident peritoneal macrophages. Macrophages were obtained from the peritoneal exudate of male Balb/c mouse. The cells were plated on culture dishes at a density of 2.5x10(5) cells per well and allowed to adhere for 2 hr. Pretreatment with rCGRP (10 nM-1 microM) for 24 hr, the macrophages were cultured with LPS 1 microg/ml for another 24 h. The medium was harvested for measuring TNF-alpha by ELISA kits. The results showed that rCGRP had no direct effects on TNF-alpha production, but it inhibited LPS-induced TNF-alpha production in a concentration-dependent manner. When rCGRP was at a concentration of 1 microM, the LPS-induced TNF-alpha production was inhibited by 39%. The effect of rCGRP was reversed by hCGRP(8-37) (10 microM), an antagonist of CGRP1 receptor. The LPS-induced TNF-alpha production from macrophages was also inhibited by forskolin 3 microM, an activator of adenylate cyclase. Furthermore, pretreatment with H-89 1 microM or Rp-cAMPS 100 microM, the inhibitors of cAMP-dependent protein kinase, the effect of rCGRP was abolished. These data suggest that the LPS-induced TNF-alpha production is inhibited by rCGRP via activation of cAMP responses in mouse resident peritoneal macrophages.

Neuroanatomical localization, pharmacological characterization and functions of CGRP, related peptides and their receptors

Calcitonin generelated peptide (CGRP) is a neuropeptide discovered by a molecular approach over 10 years ago. More recently, islet amyloid polypeptide or amylin, and adrenomedullin were isolated from human insulinoma and pheochromocytoma respectively, and revealed between 25 and 50% sequence homology with CGRP. This review discusses findings on the anatomical distributions of CGRP mRNA, CGRP-like immunoreactivity and receptors in the central nervous system, as well as the potential physiological roles for CGRP. The anatomical distribution and biological activities of amylin and adrenomedullin are also presented. Based upon the differential biological activity of various CGRP analogs, the CGRP receptors have been classified in two major classes, namely the CGRP1 and CGRP2 subtypes. A third subtype has also been proposed (e.g. in the nucleus accumbens) as it does not share the pharmacological properties of the other two classes. The anatomical distribution and the pharmacological characteristics of amylin binding sites in the rat brain are different from those reported for CGRP but share several similarities with the salmon calcitonin receptors. The receptors identified thus far for CGRP and related peptides belong to the G protein-coupled receptor superfamily. Indeed, modulation of adenylate cyclase activity following receptor activation has been reported for CGRP, amylin and adrenomedullin. Furthermore, the binding affinity of CGRP and related peptides is modulated by nucleotides such as GTP. The cloning of various calcitonin and most recently of CGRP1 and adrenomedullin receptors was reported and revealed structural similarities but also significant differences to other members of the G protein-coupled receptors. They may thus form a new subfamily. The cloning of the amylin receptor(s) as well as of the other putative CGRP receptor subtype(s) are still awaited. Finally, a broad variety of biological activities has been described for CGRP-like peptides. These include vasodilation, nociception, glucose uptake and the stimulation of glycolysis in skeletal muscles. These effects may thus suggest their potential role and therapeutic applications in migraine, subarachnoid haemorrhage, diabetes and pain-related mechanisms, among other disorders.

Lack of effect of calcitonin gene-related peptide and amylin on major markers of glucose metabolism in hepatocytes

Effects of amylin and calcitonin gene-related peptide on several processes involved in carbohydrate metabolism were investigated in rat hepatocytes, non-parenchymal cells (Kupffer, Ito and endothelial cells) and alveolar macrophages. In hepatocytes, cAMP levels were increased 25-fold by glucagon (10 nM), less than 2-fold by calcitonin gene-related peptide (100 nM) and not at all by amylin (100 nM). In non-parenchymal cells and cultured alveolar macrophages, calcitonin gene-related peptide potently, and amylin weakly, stimulated cAMP levels. In hepatocytes neither amylin nor calcitonin gene-related peptide affected glycogen phosphorylase activity, glucose output, lactate uptake, glycogen synthesis, glycogen mass or tyrosine aminotransferase activity. The density of calcitonin gene-related peptide specific binding sites in parenchymal cells was 10-fold less then seen in non-parenchymal cells. We found no significant evidence of specific amylin binding sites. These results are consistent with the notion that amylin does not exert a direct effect in hepatocytes. However, we do not rule out that amylin may affect hepatic glucose output indirectly through Cori cycling of lactate derived from skeletal muscle or from interactions through non-parenchymal cells.

Calcitonin gene-related peptide inhibits proliferation and antigen presentation by human peripheral blood mononuclear cells: effects on B7, interleukin 10, and interleukin 12

CGRP is a neuropeptide that has previously been described to possess immunosuppressive activities. CGRP is released from peripheral nerves that, in the skin, are in close physical association with dendritic APC. We sought to investigate the mechanisms by which CGRP can inhibit immune responses by studying its effects on human peripheral blood mononuclear cells (PBMC). Using allogeneic monocytes as stimulator cells, CGRP could inhibit the proliferation of PBMC by 47% when CGRP was present for the duration of culture. Interestingly, when the stimulator monocytes were incubated with CGRP for 2 h prior to irradiation then washed, the observed inhibition increased to 85%, suggesting that CGRP was exerting a direct effect on the monocyte stimulator population. Finally, the recall response to tetanus toxoid (TT) by PBMC from individuals vaccinated with TT 14 d prior was inhibited by 25-50% in the presence of CGRP. Also, CGRP decreased the levels of B7.2 but not B7.1 on treated monocytes, and this inhibition could be abrogated by the addition of anti-IL-10 antibody, suggesting that the inhibition was mediated by an increase in IL-10 production. Moreover, increased IL-10 production was confirmed by ELISA. Both IL-12 p40 and IFN-gamma levels in CGRP-treated cultures were found to be decreased by approximately 30%. The decrease in IL-12 p40 levels could be reversed by addition of anti-IL-10. These data suggest that CGRP inhibits PBMC proliferation, in part, through the release of IL-10, which in turn can downregulate important co-stimulatory molecules and the cytokines IL-12 and IFN-gamma.

The neuropeptide calcitonin gene-related peptide stimulates insulin-like growth factor I production by primary fetal rat osteoblasts

Calcitonin gene-related peptide (CGRP)-immunoreactive sensory nerve terminals infiltrate all tissues including bone, in which CGRP may play a local regulatory role. To initiate studies on the role of this neuropeptide in bone, osteoblasts were isolated from fetal rat calvariae, treated with CGRP, and analyzed for cAMP and insulin-like growth factor I (IGF-I) production. CGRP alpha and -beta induced a cAMP accumulation in osteoblastic cells, suggesting that they express functional receptors for CGRP. CGRP induced an increase in both IGF-I transcripts and immunoreactive polypeptide. In contrast to prostaglandin E2 (PGE2) treatment, this increase was not accompanied by an augmentation in IGF binding proteins. Although PGE2 induced a more significant increase in IGF-I transcripts than did CGRP, the concentration of IGF-I polypeptide produced by osteoblasts was similar in response to both treatments. It is concluded from this study that CGRP has potent anabolic effects on osteoblasts, an observation which opens possibilities to study the potential therapeutic role of CGRP in osteoporosis.

Enhancement of phagocytosis by calcitonin gene-related peptide (CGRP) in cultured mouse peritoneal macrophages

Calcitonin gene-related peptide (CGRP) is widely distributed in sensory neurons and nerve fibers. To clarify the function of CGRP on the immune system, the effect of CGRP on phagocytosis by peritoneal macrophages was examined by means of flow cytofluorometry. CGRP enhanced phagocytosis of latex beads in a dose-dependent manner. Because the phosphodiesterase inhibitor 3-isobutyl, 1-methylxanthine (IBMX) enhanced the CGRP-induced enhancement of phagocytosis, the enhancement might be mediated by cAMP. In the presence of mannan, the phagocytosis was suppressed and the CGRP-induced enhancement was also blocked, suggesting that mannose receptors on macrophages were involved in mediating the phagocytosis of latex beads, and CGRP enhanced the mannose receptor-mediated phagocytosis. The present results indicate that CGRP can modulate the function of macrophages in nerve terminals of sensory neurons during the development and maintenance of inflammation.

Calcitonin gene-related peptide and ATP induce immediate early gene expression in cultured rat microglial cells

Factors affecting gene expression in microglial cells were investigated using the induction of immediate early genes in cultured microglia as a model. In particular, the actions of calcitonin gene-related peptide (CGRP) and ATP, both of which have been proposed as signalling molecules in the activation of glial cells, were evaluated using Northern blotting and in situ hybridization methods. In the presence of CGRP, c-fos and junB mRNAs accumulated in microglial cultures, whereas no significant change in c-jun and TIS11 mRNAs occurred. A similar pattern of immediate early gene activation was obtained when adenylate cyclase was stimulated with forskolin. CGRP also stimulated cyclic AMP accumulation with a half-maximal effect in the range 2-5 nM, suggesting a possible role for cyclic AMP as a mediator of the effects of CGRP on gene expression. In contrast to the selective induction of c-fos and junB by CGRP and forskolin, ATP led to the accumulation of all four immediate early genes studied, i.e., c-fos, junB, c-jun, and TIS11. Similar results were obtained when protein kinase C was stimulated with phorbol ester indicating that the induction of immediate early gene expression by ATP and CGRP involves different intracellular mechanisms. The action of ATP was mimicked by ADP and the poorly hydrolyzable analogues, ADP beta S and 2-methylthio ATP, but not by beta, gamma-methylene ATP, AMP, or adenosine, indicating that the receptor mediating the actions of ATP on microglial gene expression is probably of the P2Y-purinoreceptor type. The results suggest roles for CGRP and ATP as transcriptional activators in microglial cells.

Specific induction of cAMP in Langerhans cells by calcitonin gene-related peptide: relevance to functional effects

Epidermal Langerhans cells (LC) are associated anatomically with epidermal nerves, and a product of these nerves, calcitonin gene-related peptide (CGRP), inhibits the antigen-presenting capacity of LC and macrophages. As the CGRP receptor appears to be coupled to Gs alpha protein, which in turn activates adenylate cyclase, the ability of CGRP to induce cAMP in LC was examined and correlated with functional effects. LC were isolated from murine epidermal cells using antibodies on magnetic microspheres. Exposure to CGRP induced a significant increase in cAMP content, which could be inhibited by coculture with a truncated form of CGRP [CGRP-(8-37)] that is a specific competitive inhibitor of CGRP. Substance P and calcitonin failed to induce cAMP in LC. Although culture in CGRP reduced the ability of murine epidermal cells enriched for LC content to present pigeon cytochrome c to a responsive clone or to present antigen for elicitation of delayed-type hypersensitivity in immune mice, culture in forskolin had little or no effect on antigen presentation despite increased cAMP content of LC as much or more than that induced by CGRP. The effect of CGRP on antigen presentation in these systems could be blocked with CGRP-(8-37). CGRP inhibited the induction of B7-2 by lipopolysaccharide on peritoneal macrophages and a LC line, whereas calcitonin did not. CGRP induces specific accumulation of cAMP in LC and inhibits LC antigen-presenting function by a receptor-mediated event. However, the induction of cAMP by itself does not account for inhibition of antigen presentation. Suppression of the expression of B7-2 may be one mechanism by which CGRP inhibits antigen presentation.

A role for calcitonin gene related peptide (CGRP) in the regulation of early B lymphocyte differentiation

In previous studies we identified high affinity adenylyl cyclase linked receptors for calcitonin gene related peptide (CGRP) on rat T and B cells, on lymphocyte cell lines including the mouse pre-B cell line 70Z/3, and on cells in mouse bone marrow. The effect of CGRP on early B cell differentiation has been examined using the 70Z/3, and on cells in mouse bone marrow. The effect of CGRP on early B cell differentiation has been examined using the 70Z/3 cell line. CGRP inhibits the lipopolysaccharide (LPS) induction of surface immunoglobulin (sIg) protein expression in 70Z/3 cells, an effect that is associated with a decrease in the steady-state levels of Ig heavy (mu) and light (kappa) chain mRNA. In this report, experiments are described that provide further information on the mechanism by which CGRP inhibits sIg expression. The kinetics of CGRP inhibition of LPS-induced sIg expression was examined in 70Z/3 cells. An optimal window for the inhibitory effect of CGRP on SIg induction occurs at least 24 h after the cells are treated with LPS. To determine whether the inhibitory effects of CGRP on sIg expression are mediated by an inhibition of NF kappa-B translocation to the nucleus, electrophoretic mobility shift assays were performed using nuclear proteins from 70Z/3 cells. There was no difference in NF kappa-B binding activity in cells that had been treated with LPS or LPS + CGRP, suggesting that the inhibitory effect of CGRP is not mediated by an inhibition of NF kappa-B activity. These studies provide further evidence that CGRP plays an inhibitory role in early B cell differentiation. Finally, a model is proposed that describes an integrated role for CGRP in the homeostatic regulation of early B cell differentiation.

Calcitonin gene-related peptide promotes Schwann cell proliferation

Schwann cells in culture divide in response to defined mitogens such as PDGF and glial growth factor (GGF), but proliferation is greatly enhanced if agents such as forskolin, which increases Schwann cell intracellular cAMP, are added at the same time as PDGF or GGF (Davis, J. B., and P. Stroobant. 1990. J. Cell Biol. 110:1353-1360). The effect of forskolin is probably due to an increase in numbers of PDGF receptors (Weinmaster, G., and G. Lemke. 1990. EMBO (Eur. Mol. Biol. Organ.) J. 9:915-920. Neuropeptides and beta-adrenergic agonists have been reported to have no effect on potentiating the mitogenic response of either PDGF or GGF. We show that the neuropeptide calcitonin gene-related peptide (CGRP) increases Schwann cell cAMP levels, but the cells rapidly desensitize. We therefore stimulated the cells in pulsatile fashion to partly overcome the effects of desensitization and show that CGRP can synergize with PDGF to stimulate Schwann cell proliferation, and that CGRP is as effective as forskolin in the pulsatile regime. CGRP is a good substrate for the neutral endopeptidase 24.11. Schwann cells in vivo have this protease on their surface, so the action of CGRP could be terminated by this enzyme and desensitization prevented. We therefore suggest that CGRP may play an important role in stimulating Schwann cell proliferation by regulating the response of mitogenic factors such as PDGF.

Effects of CGRP, forskolin, PMA, and ionomycin on pHi dependence of Na-H exchange in UMR-106 cells

We examined the effects of calcitonin gene-related peptide (CGRP), forskolin, phorbol 12-myristate 13-acetate (PMA), and ionomycin on the intracellular pH (pHi) dependence of Na-H exchange in UMR-106 cells. In the nominal absence of CO2-HCO3-, each agent increased pHi, measured with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). From the rate of pHi recovery (dpHi/dt) from an acid load, and intracellular buffering power, we computed the pHi dependence of the total acid-extruding flux (JTotal). All four agents increased JTotal. From dpHi/dt data obtained in the presence of ethylisopropyl amiloride (EIPA, a blocker of Na-H exchange), we determined the EIPA-resistant component of JTotal (JEIPA/R). We estimated the Na-H exchange flux (JNa-H) as the difference JTotal-JEIPA/R-CGRP, forskolin, and PMA produced similar increases in the slope of the JNa-H vs. pHi-relationship. The net effect of these agents, as well as ionomycin, was to increase JNa-H over a broad pHi range. Ionomycin alkaline shifted the JEIPA/R vs. pHi relationship; the other agents had no effect. Our results indicate that CGRP increased JTotal by stimulating Na-H exchange, with little effect on EIPA-resistant processes. A signaling pathway involving only adenosine 3',5'-cyclic monophosphate, only protein kinase C, or only Ca2+ cannot account for the effects of CGRP on both pHi and pHi dependence of JNa-H. Thus, CGRP probably affects UMR-106 pHi physiology via more than one pathway.

The role of calcitonin gene-related peptide (CGRP) in macrophages: the presence of functional receptors and effects on proliferation and differentiation into osteoclast-like cells

It has been shown that both calcitonin gene-related peptide (CGRP) and amylin bind weakly to calcitonin (CT) receptors in osteoclast-like cells formed in vitro and inhibit bone resorption by a cAMP-dependent mechanism. Osteoclasts are thought to be derived from cells of the monocyte macrophage lineage, in which CGRP, but not CT, induces cAMP production. In this study, we determined the presence of functional receptors for CGRP in mouse alveolar macrophages and the effects of this peptide on proliferation and osteoclastic differentiation in mouse alveolar and bone marrow-derived macrophages. Human CT did not stimulate cAMP production in macrophages. Human CGRP stimulated cAMP production in mouse alveolar macrophages and bone marrow-derived macrophages dose-dependently. Human amylin, which has 43% homology with human CGRP, also stimulated these macrophages to produce cAMP, but only at a 100-fold higher concentration. The increment in cAMP production induced by human CGRP and amylin was abolished by the addition of human CGRP(8-37), a selective antagonist for CGRP receptors. Specific binding of [125I]human CGRP to alveolar macrophages was detected (dissociation constant, 2.5 x 10(-8) M; binding sites, 1.4 x 10(4)/cell). Amylin, but not CT, displaced the bound [125I]human CGRP from alveolar macrophages, but at a 100-fold higher concentration. No specific binding of [125I]human CT and [125I]human amylin to alveolar macrophages could be detected. Pretreatment with human CGRP for 24 h dose-dependently suppressed DNA synthesis in alveolar macrophages induced by granulocyte-macrophage colony-stimulating factor (GM-CSF). CGRP also suppressed the number of macrophage colonies formed from bone marrow cells induced by macrophage colony-stimulating factor (M-CSF).(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of a calcitonin gene-related peptide (CGRP) receptor on mouse bone marrow cells

Calcitonin gene-related peptide, (CGRP), a vasoactive neuropeptide, is found throughout the peripheral nervous system, and CGRP receptors are present on mature lymphocytes. The current studies describe a CGRP receptor on isolated mouse bone marrow cells. The affinity, distribution and specificity of CGRP receptors were analyzed using radioligand binding assays. [125I]CGRP binding in mouse bone marrow cells was dependent on cell concentration and was stable from 5 to 60 min at room temperature. The average Kd is 3.29 +/- 1.24 nM and the average receptor density is 2796 +/- 365 sites/cell. Competition binding analysis found rat alpha and beta CGRP to be the most inhibitory, (Ki values 0.899 and 0.711 nM, respectively), followed by human alpha CGRP and the antagonist human CGRP8-37. The neuropeptides human and salmon calcitonin did not inhibit [125I]CGRP binding to bone marrow cells. The presence of CGRP receptors on mouse bone marrow cells provides further evidence for a direct role for CGRP in modulating the function and differentiation of cellular components of the immune and inflammatory systems.

Calcitonin gene-related peptide: multiple actions, multiple receptors

Calcitonin gene-related peptide (CGRP) shows diversity both in its effects and its receptors. It is likely to have roles as a neurotransmitter, neuromodulator, local hormone and trophic factor. Its effects include rapid changes in neuronal activity, relaxation of many types of smooth muscle, actions on metabolism and changes in gene expression. Receptor heterogeneity has been revealed from experiments comparing agonist potency ratios and antagonist affinities. The evidence from these approaches is reviewed in this article and a speculative receptor classification scheme is proposed. Some of the likely future directions for CGRP research are discussed.