Calcitonin gene-related peptide (CGRP) has been implicated in craniofacial pain and headache by virtue of its expression in the trigeminal ganglion and roles in neurogenic inflammation and nociception. In particular, CGRP levels are elevated in migraine, then returned to normal coincident with headache relief. However, despite the prevalence of migraine and other trigeminal pain syndromes, the mechanisms that regulate trigeminal CGRP expression remain mostly unknown. The sustained pain of migraine suggests the existence of feedback mechanisms that maintain elevated CGRP levels. One of the biological activities of CGRP is to trigger the release of cytokines. We propose to test the hypothesis that cytokines create a positive feedback loop onto presynaptic receptors to stimulate CGRP gene expression in the trigeminal ganglion. We have introduced reporter genes into primary cultures of rat trigeminal ganglia neurons and have begun studies monitoring promoter activity in vivo. In preliminary data we have shown that two cytokines, TNF-a and activin, can stimulate the CGRP promoter. In the case of TNF-a, the stimulation may be mediated by MAP kinase activation of the neuron-specific 18-bp enhancer that binds the bHLH-Zip protein USF. We propose to study the role of USF in CGRP gene activation by cytokines. As a strategy to attenuate this activation, we will use gene transfer of MAP kinase phosphatase-1. The approach will be to complement culture studies with retrograde delivery of viral vectors to the ganglia from the mouse whisker pad. Regulation of the CGRP promoter will be monitored by bioluminescence assays following acute and chronic elevation of cytokines. In this manner, viral gene transfer will be used as a tool for studying feedback control of CGRP gene expression and for targeting regulatory genes to neurons. The significance of this proposal is that it will restablish a molecular mechanism linking cytokines and neuropeptides and potentially reveal new therapeutic (strategies to attenuate neuropeptide synthesis.
Showing the most recent 10 out of 20 publications
