Definition
Calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide with potent receptor mediated vasodilatory and cardioexcitatory properties1.
Discovery
It was discovered when alternative processing of RNA transcripts from the calcitonin gene were shown to result in the production of distinct mRNAs encoding CGRP2. A human form of CGRP was isolated from thyroid tissue of patients with medullary thyroid carcinoma3.
Classification
CGRP belongs to the regulatory-peptide family that also includes adrenomedullin and amylin4.
Structural Characteristics
CGRP consists of an amino-terminal disulphide bridge linked loop between amino acids 2 and 7 followed by alpha helix between amino acids 8 and 18 and a poorly defined turn between residues 19 and 215. The carboxy and amino terminals of CGRP can interact independently with its receptors5.
Mode of action
CGRP exerts its function by binding to two G-protein coupled receptors, CGRP1 and CGRP2. One of the major functions of CGRP is vasodilation of cardiac muscles5. In order to achieve this, CGRP first binds to CGRP1 receptor which results in the production of cAMP which in turn activates Protein Kinase A (PKA)6. PKA phosphorylates and opens potassium channels that cause relaxation of muscles6.
Functions
CGRP is widely distributed in the central and peripheral nervous systems5. It produces vascular relaxation via binding to CGRP1 receptor5. Studies in mice have shown that CGRP may play a role in controlling blood pressure5. CGRP also protects tissue injury through its vasodilatory functions. Through its activity as a vasodilator, CGRP influence the activity of inflammatory cells by recruiting more cells at the site of inflammation7. CGRP plays a role in migraine as it is found that its levels raise during painful phases of the disease8. CGRP plays a protective role in cardiac tissue. The infusion of CGRP is beneficial in increasing cardiac output and lowering blood pressure in patients with congestive heart failure5.
References
1. Tortorella C, Macchi C, Forneris M and Nussdorfer GG (2001). Calcitonin gene-related peptide (CGRP), acting via CGRP type 1 receptors, inhibits potassium-stimulated aldosterone secretion and enhances basal catecholamine secretion from rat adrenal gland. Int. J Mol. Med., 8(3), 261-4.
2. Amara SG, Jonas V, Rosenfeld MG, Ong ES and Evans RM (1982). Alternative RNA processing in calcitonin gene expression generates mRNAs encoding different polypeptide products. Nature, 298, 240–244.
3. Aiyar N, Rand K, Elshourbagy NA, Zeng Z, Adamou JE, Bergsma DJ, and Li Y (1996). A cDNA encoding the Calcitonin Generelated peptide type 1 receptor. J Biol Chem., 271, 11325–11329.
4. Bell D and McDermott BJ (1996). Calcitonin gene-related peptide in the cardiovascular system: characterization of receptor populations and their (patho)physiological significance. Pharmacol Rev., 48, 253–288.
5. Susan DB and Andrew DG (2004). Vascular Actions of Calcitonin Gene-Related Peptide and Adrenomedullin. Physiol Rev., 84, 903-934.
6. Hirata Y, Takagi Y, Takata S, Fukuda Y, Yoshimi H, and Fujita T (1988). Calcitonin gene-related peptide receptor in cultured vascular smooth muscle and endothelial cells. Biochem Biophys Res Commun., 151, 1113–1121.
7. Lambrecht BN (2001). Immunologists getting nervous: neuropeptides, dendritic cells and T cell activation. Respir Res., 2, 133–138.
8. Durham, P (2006). Calcitonin gene-related peptide (CGRP) and migraine. Headache, 48: S3–8.