Identification, structural determination, and biological activity of bovine and canine calcitonin receptor-stimulating peptides

Update on the pharmacology of calcitonin/CGRP family of peptides: IUPHAR Review 25

The calcitonin/CGRP family of peptides includes calcitonin, α and β CGRP, amylin, adrenomedullin (AM) and adrenomedullin 2/intermedin (AM2/IMD). Their receptors consist of one of two GPCRs, the calcitonin receptor (CTR) or the calcitonin receptor-like receptor (CLR). Further diversity arises from heterodimerization of these GPCRs with one of three receptor activity-modifying proteins (RAMPs). This gives the CGRP receptor (CLR/RAMP1), the AM₁ and AM₂ receptors (CLR/RAMP2 or RAMP3) and the AMY_1, AMY₂ and AMY₃ receptors (CTR/RAMPs1-3 complexes, respectively). Apart from the CGRP receptor, there are only peptide antagonists widely available for these receptors, and these have limited selectivity, thus defining the function of each receptor in vivo remains challenging. Further challenges arise from the probable co-expression of CTR with the CTR/RAMP complexes and species-dependent splice variants of the CTR (CT_(a) and CT_(b) ). Furthermore, the AMY_1(a) receptor is activated equally well by both amylin and CGRP, and the preferred receptor for AM2/IMD has been unclear. However, there are clear therapeutic rationales for developing agents against the various receptors for these peptides. For example, many agents targeting the CGRP system are in clinical trials, and pramlintide, an amylin analogue, is an approved therapy for insulin-requiring diabetes. This review provides an update on the pharmacology of the calcitonin family of peptides by members of the corresponding subcommittee of the International Union of Basic and Clinical Pharmacology and colleagues.

Receptor activity modifying proteins and their potential as drug targets

The receptor activity modifying proteins (RAMPs) are a family of membrane proteins that interact with some G protein-coupled receptors (GPCRs) to regulate their function. RAMPs can alter GPCR pharmacology and can regulate their signaling as well as trafficking to and from the cell surface. GPCRs have been successfully exploited as drug targets for many years. RAMPs therefore provide a new avenue for drug development, offering opportunities for regulating the function of therapeutically relevant RAMP-interacting GPCRs. RAMPs could be directly targeted themselves or advantage could be taken of the unique RAMP/GPCR interfaces for generating more selective drugs.

alphaCGRP and betaCGRP transcript amount in mouse tissues of various developmental stages and their tissue expression sites

The calcitonin gene-related peptides (CGRP), alphaCGRP and betaCGRP, have been implicated to play various roles in primates and rodent. However, since the expression information has been limited, in the present study, we measured the amount of gene expression in mouse brain, liver, kidney, heart, and testis at embryonic day (E) 14, E17, postnatal day (P) 1, P7, and adult using real-time PCR, and determined the precise localization of alphaCGRP and betaCGRP sense/antisense transcripts in tissues using in situ hybridization. The sense transcripts of alphaCGRP and betaCGRP were found mainly in brain, and their amount profiles were similar in the course of development: one expression peak was observed at E17 and the other at P7. The amounts of alphaCGRP transcripts were greater than those of betaCGRP transcripts in the range between 3.6 and 31 times. In the E17 and P7 brains, the localization pattern of alphaCGRP sense transcripts was similar with that of alphaCGRP antisense transcripts. Fewer transcripts were found in neuroblasts of E17 corpus callosum, and neuroblasts of P7 corpus callosum, olfactory bulb, plexus chorioideus, and ventriculus lateralis than in other brain areas. The localization pattern of betaCGRP sense and antisense transcripts was similar to that for alphaCGRP except that the betaCGRP antisense transcripts showed spot-like localizations. Additionally, the alphaCGRP sense transcript, and betaCGRP sense and antisense transcripts were found in parafollicular cells (C cells) of E17 thyroid lobe. These findings together indicate that alphaCGRP and betaCGRP have their own roles in the ontogenic process.

Calcitonin receptor-stimulating peptide: Its evolutionary and functional relationship with calcitonin/calcitonin gene-related peptide based on gene structure

This review focuses on the evolutionary and functional relationship of calcitonin receptor-stimulating peptide (CRSP) with calcitonin (CT)/calcitonin gene-related peptide (CGRP) in mammals. CRSP shows high sequence identity with CGRP, but distinct biological properties. CRSP genes (CRSPs) have been identified in mammals such as pigs and dogs of the Laurasiatheria, but not in primates and rodents of the Euarchontoglires or in non-placental mammals. CRSPs have genomic organizations highly similar to those of CT/CGRP genes (CT/CGRPs), which are located along with CGRPs in a locus between CYP2R1 and INSC, while the other members of the CGRP superfamily, adrenomedullin and amylin, show genomic organizations and locations distinct from CT, CGRP, and CRSP. Thus, we categorized these three peptides into the CT/CGRP/CRSP family. Non-placental mammals having one and placental mammals having multiple CT/CGRP/CRSP family genes suggests that multiplicity of CT/CGRP started at an early stage of mammalian evolution. In the placental mammals, Laurasiatheria generally possesses multiple CRSPs and only one CT/CGRP, while Euarchontoglires possesses CT/CGRP and CGRPbeta but no CRSP, indicating an increase in the diversity and multiplicity of this family of genes in mammalian evolution. Phylogenetic analysis suggests that some CRSPs have been generated very recently in mammalian evolution. Taken together, the increase in the number and complexity of the CT/CGRP/CRSP family genes may have due to evolutionary pressure to facilitate adaptation during mammalian evolution. In this regard, it is important to elucidate the physiological roles of CT, CGRP and CRSP from the viewpoint of the CT/CGRP/CRSP family even in Euarchontoglires.

Genomic and expression analysis of canine calcitonin receptor-stimulating peptides and calcitonin/calcitonin gene-related peptide

Calcitonin receptor-stimulating peptides (CRSPs) are new members of the calcitonin/calcitonin gene-related peptide (CT/CGRP) family identified in pigs, dogs and other domestic animals, and CRSP-1 is an active ligand for the CT receptor (CT-R). We recently sequenced porcine CRSP genes (Crsps) and found similarity with the CT/CGRP gene (Ct/Cgrp) in sequence and genomic organization. In this study, we identified five Crsps, Crsp-1 to Crsp-5, in dogs. Crsp-1 has five exons with an exon-intron organization identical to that of porcine Crsp-1 or Crsp-2, while Crsp-2 and Crsp-3 have additional CT-2- and CT-3-coding exons like Ct/Cgrp. Crsp-2 was renamed as Ct-2/Crsp-2 because both CRSP-2 and CT-2 mRNAs were tissue-specifically expressed. Crsp-4 and Crsp-5 are presumably generated by retrotransposition. We postulate that Crsps were generated from the gene duplication of Ct/Cgrp, and gained their diversity during mammalian evolution. Among the canine CTs and CRSPs, CRSP-1, CT-1 and CT-2 are active ligands for the CT-R, but CRSP-2 and others are inactive. Canine CRSP-1 and CT-2 are expressed in the central and peripheral systems, while CT-1 is localized in the thyroid gland. These findings indicate that dogs can be used for an experimental model as analysing the physiological roles of the CT/CGRP/CRSP family.

A 'reverse' phylogenetic approach for identification of novel osmoregulatory and cardiovascular hormones in vertebrates

Vertebrates expanded their habitats from aquatic to terrestrial environments during the course of evolution. In parallel, osmoregulatory and cardiovascular systems evolved to counter the problems of desiccation and gravity on land. In our physiological studies on body fluid and blood pressure regulation in various vertebrate species, we found that osmoregulatory and cardiovascular hormones have changed their structure and function during the transition from aquatic to terrestrial life. In fact, Na(+)-regulating and vasodepressor hormones play essential roles in fishes, while water-regulating and vasopressor hormones are dominant in tetrapods. Accordingly, Na(+)-regulating and vasodepressor hormones, such as natriuretic peptide (NP) and adrenomedullin (AM), are much diversified in teleost fishes compared with mammals. Based on this finding, new NPs and AMs were identified in mammals and other tetrapods. These hormones have only minor roles in the maintenance of normal blood volume and pressure in mammals, but their importance seems to increase when homeostasis is disrupted. Therefore, such hormones can be used for diagnosis and treatment of body fluid and cardiovascular disorders such as cardiac/renal failure and hypertension. In this review, we introduce a new approach for identification of novel Na(+)-regulating and vasodepressor hormones in mammals based on fish studies. Until recently, new hormones were first discovered in mammals, and then identified and applied in fishes. However, chances are increasing in recent years to identify new hormones first in fishes then in mammals, based on the difference in the regulatory systems between fishes and tetrapods. As the direction is opposite from the traditional phylogenetic approach, we added 'reverse' to its name. The 'reverse' phylogenetic approach offers a typical example of how comparative fish studies can contribute to the general and clinical endocrinology.

A novel member of the calcitonin gene-related peptide family, calcitonin receptor-stimulating peptide, inhibits the formation and activity of osteoclasts

We isolated a novel peptide, calcitonin receptor-stimulating peptide-1 (CRSP-1), from porcine brain and found that the administration of this peptide into rats induced a transient decrease in plasma calcium concentration. Therefore, we investigated the effects of CRSP-1 on osteoclastogenesis. Osteoclast-like cells were formed from spleen cells or bone marrow cells by a combination of the receptor activator of nuclear factor-kappaB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF). CRSP-1 dose-dependently inhibited the formation of multinucleated osteoclast-like cells, and a calcitonin receptor inhibitor antagonized in part the inhibition of osteoclast formation by CRSP-1. Furthermore, CRSP-1 destroyed the actin ring that is a typical index of osteoclast resorption activity; it contributed to this action via the signaling pathway of protein kinase A. Our findings indicate that CRSP-1 inhibits osteoclastogenesis by inhibiting the formation and activity of multinucleated osteoclasts. The inhibitory effects of CRSP-1 on osteoclast metabolism were similar in degree to those of porcine calcitonin. CRSP-1 might provide a clue to the development of tools useful in the prevention and treatment of osteoporosis.

Evolutionary history of the calcitonin gene-related peptide family in vertebrates revealed by comparative genomic analyses

The calcitonin gene-related peptide (CGRP) family is composed of CGRP, amylin and adrenomedullin (AM) in mammals. In teleost fish, AM forms an independent subfamily of five members (AM1-5), which inspired us to trace the evolutionary history of the CGRP family throughout vertebrates by comparative genomic approach. Linkage mapping and synteny analyses of the CGRP family genes in medaka, Oryzias latipes, revealed that AM1/CGRP, AM2/amylin, and AM5 genes were located on respective proto-chromosomes before the divergence of teleost lineage. In teleost fish, additional whole genome duplication generated AM1/4, CGRP1/2, AM2/3, but one of the duplicated amylin and AM5 genes was silenced. In mammals, the amylin or AM2 gene was translocated to different chromosomes, while the CGRP gene was multiplied in tandem to generate CGRP-alpha,beta, and recently identified calcitonin receptor-stimulating peptide genes. Based on these data, we identified a novel AM5 gene in several mammalian species as we previously did for AM2.

Isolation and characterization of a glycine-extended form of calcitonin receptor-stimulating peptide-1: another biologically active form of calcitonin receptor-stimulating peptide-1

In this study, we isolated a peptide eliciting a potent stimulatory effect on cAMP production in LLC-PK(1) cells from acid extracts of porcine brain. By structural analysis, this peptide was determined to be a C-terminal glycine-extended form of calcitonin receptor-stimulating peptide-1 (CRSP-1-Gly). Synthetic CRSP-1-Gly enhanced the cAMP production in COS-7 cells expressing calcitonin (CT) receptor as strongly as CRSP-1. Measurement of immunoreactive (IR) CRSP-1-Gly by radioimmunoassay using the specific antisera against CRSP-1-Gly showed that a relatively high level (>1pmol/g wet weight) of IR-CRSP-1-Gly was detected in the midbrain, hypothalamus, anterior and posterior lobes of pituitary, and thyroid gland, and the ratio of IR-CRSP-1-Gly to total IR-CRSP-1 varies from 0.02 to 0.35 in each tissue. These results suggest that CRSP-1-Gly is actually present in the tissues as one of major endogenous molecular forms of CRSP-1, and can regulate the cells expressing the CT receptor both in the central nervous system and peripheral tissues in a manner similar to that of CRSP-1. IR-CRSP-2 and IR-CRSP-3 are also present in the brain and other tissues, but their tissue concentrations are 33% on average and less than 3% that of total IR-CRSP-1, respectively.

Calcitonin gene-related peptide-containing pathways in the rat forebrain

The present study focuses on the topographical distribution of calcitonin gene-related peptide (CGRP)-containing cell bodies and fibers and their connections and pathways in the rat forebrain. We confirm previously reported CGRP projections from the perifornical area of the hypothalamus to the lateral septum, from the posterior thalamus to the caudate putamen and cerebral cortex, and from the parabrachial nuclei to the central extended amygdala, lateral hypothalamus, and ventromedial thalamus. Despite previous descriptions of CGRP in the central nervous system, important neuroanatomical aspects of the forebrain CGRP system remained obscure, which we addressed by using brain lesion techniques combined with modern immunohistology. We first report CGRP terminal fields in the olfactory-anterior septal region and also CGRP projections from the parabrachial nuclei to the olfactory-anterior septal region, the medial prefrontal cortex, the interstitial nucleus of the anterior commissure, the nucleus of the lateral olfactory tract, the anterior amygdaloid area, the posterolateral cortical amygdaloid nucleus, and the dorsolateral part of the lateral amygdaloid nucleus. In addition, we identified a CGRP cell group in the premamillary nuclei and showed that it projects to the medial CGRP layer of the lateral septum. CGRP fibers usually join other pathways rather than forming bundles. They run along the fornix from the hypothalamus, along the supraoptic decussations or the inferior thalamic peduncle-stria terminalis pathway from the posterior thalamus, and along the superior cerebellar peduncle, thalamic fasciculus, and ansa peduncularis from the parabrachial nuclei. This description of the forebrain CGRP system will facilitate investigation of its role in higher brain functions.

Structure and biological properties of three calcitonin receptor-stimulating peptides, novel members of the calcitonin gene-related peptide family

In this review, we describe the structure and biological properties of calcitonin receptor-stimulating peptide-1 (CRSP-1), CRSP-2 and CRSP-3, the novel members of the CGRP family. CRSP-1, which has been identified in the pig, cow, dog, and horse, is a specific ligand for the calcitonin (CT) receptor, and porcine CRSP-1 elicits a 100-fold greater effect on a recombinant porcine CT receptor than porcine CT, although this peptide has high structural similarity with CGRP. CRSP-1 is expressed and synthesized mainly in the central nervous system (CNS), pituitary and thyroid gland. In an in vivo experiment, bolus administration of CRSP-1 into rats reduced the plasma calcium concentration, but did not alter blood pressure, indicating its action as a CT receptor agonist in the peripheral circulation. In the CNS, CRSP-1 is also deduced to be an endogenous agonist for the CT receptor. CRSP-2 has been identified in the pig and dog, and CRSP-3 has been identified only in the pig. They are expressed and synthesized mainly in the CNS and thyroid gland. However, their endogenous molecular forms, receptors, and biological activity remain unidentified.

Biological importance of the peptides of the calcitonin family as revealed by disruption and transfer of corresponding genes

The hormone calcitonin (CT) of thyroid C-cell origin, the neuropeptides alpha- and beta-calcitonin gene-related peptide (CGRP), the widely expressed hormone and tissue factor adrenomedullin (AM), and amylin (AMY) that is co-produced with insulin in pancreatic beta-cells, are structurally related peptides. They have in common six or seven amino acid ring structures, linked by disulfide bridges between cysteine residues, and amidated carboxyl termini that are both required for biological activity. The actions of the peptides in vivo have traditionally been studied after intravenous and intracerebroventricular administration. As a result, CT lowers serum calcium and reduces pain perception. alpha- and beta CGRP and AM are highly potent vasodilatory peptides. AMY inhibits food intake through its action in the area postrema of the brain. Physiological actions of the peptides summarized in the present review have been defined through gene knockout and overexpression strategies.