The purinergic system cooperates with the algogenic factors bradykinin and CGRP in modulating neuron/glia communication in mouse trigeminal ganglia from wild type and R192Q Cav2.1 knock-in mice: implications for basic mechanisms of migraine pain

According to the WHO, migraine is a rather common disorder affecting 15% of adults in the Western World. It has been included in the list of the 20 more disabling pathologies, due to the dramatic reduction of the patient’s quality of life, and also to massive personal and social costs, in terms of both medical expenses and lost workdays. Although new drugs have been introduced on the market in recent years (e.g., tryptans), a significant number of migraineurs are still insensitive to the currently available pharmacological approaches and experience recurrent headache attacks, that can become increasingly frequent with additional associated health risks (for example, a twofold increased probability of undergoing an ischemic stroke). The high number of non-responder patients suggests that there still are yet-to-be identified molecular players at the basis of the disease, which are not targeted by currently utilized drugs. The trigeminal (TG)-brainstem sensory system has recently emerged as a key player in the development and maintenance of migraine pain. Moreover, data from the literature and from our laboratories clearly indicate that, to promote and maintain migraine-associated pain, TG neurons act in strict synergy with non-neuronal cells, in particular “satellite” glial cells (SGCs), which envelop neuronal bodies within the ganglion. The crosstalk between neurons and SGCs is at least partly mediated by the activation of purinergic receptors responding to endogenously released adenine and uracil nucleotides, like ATP and UTP. We previously showed that the algogenic mediator bradykinin (BK) potentiates G protein-coupled purinergic P2Y-receptors on SGCs in primary trigeminal cultures (Ceruti et al., 2008). Our present study investigated the molecular basis of this effect in wild type (WT) mice and CaV2.1 a1 R192Q mutant knock-in (KI) mice expressing a human mutation causing familial hemiplegic migraine type 1. Single-cell calcium imaging of WT cultures revealed functional BK receptors in neurons only, suggesting a paracrine action by BK to release a soluble mediator responsible for its effects on SGCs. We identified this mediator as the neuropeptide CGRP, whose levels were markedly increased by BK, while the CGRP antagonist CGRP8-37 and the anti-migraine drug sumatriptan inhibited BK actions. Unlike CGRP, BK was ineffective in neuron-free SGCs cultures, confirming the neuronal source of CGRP. P2Y receptor potentiation induced by CGRP in SGCs was mediated via activation of the ERK1/2 pathways, and following exposure to CGRP significant release of several cytokines was also detected, which could further contribute to cell-to-cell communication within the TG. Interestingly, both basal and BK-stimulated CGRP release was higher in KI mouse cultures. Indeed, BK significantly up-regulated the number of SGCs showing functional P2Y receptors, particularly the UTP-sensitive subtypes, only in cultures from KI and not from WT mice. Our findings suggest, for the first time, that P2Y receptors on glial cells act as novel players in the cellular processes underlying migraine pathophysiology and might represent new targets for the development of innovative therapeutic agents against migraine pain (Ceruti et al., 2011). References - Ceruti S, Fumagalli M, Villa G, Verderio C, Abbracchio MP 2008. Purinoceptor-mediated calcium signaling in primary neuron-glia trigeminal cultures. Cell Calcium. 43(6):576-90. - Ceruti S, Villa G, Fumagalli M, Colombo L, Magni G, Zanardelli M, Fabbretti E, Verderio C, van den Maagdenberg AM, Nistri A, Abbracchio MP 2011. Calcitonin Gene-Related Peptide-Mediated Enhancement of Purinergic Neuron/Glia Communication by the Algogenic Factor Bradykinin in Mouse Trigeminal Ganglia from Wild-Type and R192Q Cav2.1 Knock-In Mice: Implications for Basic Mechanisms of Migraine Pain. J Neurosci. 31(10):3638-3649.