Signaling pathways that mediate nerve growth factor-induced increase in expression and release of calcitonin gene-related peptide from sensory neurons

Abstract

Nerve growth factor (NGF) can augment transmitter release in sensory neurons by acutely sensitizing sensory neurons and by increasing the expression of calcitonin gene-related peptide (CGRP) over time. The current study examined the intracellular signaling pathways that mediate these two temporally distinct effects of NGF to augment CGRP release from sensory neurons. Growing sensory neurons in 30 or 100 ng/ml of NGF for 7 days increases CGRP content and this increase augments the amount of CGRP that is released by high extracellular potassium. Overexpressing a dominant negative Ras, Ras(17N) or treatment with a farnesyltransferase inhibitor attenuates the NGF-induced increase in CGRP content. Conversely, overexpressing a constitutively active Ras augments the NGF-induced increase in content of CGRP. Inhibiting MEK activity also blocks the ability of NGF to increase CGRP expression. In contrast to the ability of chronic NGF to increase peptide content, acute exposure of sensory neurons to 100 ng/ ml NGF augments capsaicin-evoked release of CGRP without affecting the content of CGRP. This sensitizing action of NGF is not affected by inhibiting Ras, MEK, or PI3 kinases. In contrast, the NGF-induced increase in capsaicin-evoked release of CGRP is blocked by the PKC inhibitor, BIM and the Src family kinases inhibitor, PP2. These data demonstrate that different signaling pathways mediate the alterations in expression of CGRP by chronic NGF and the acute actions of the neurotrophin to augment capsaicin-evoked release of CGRP in the absence of a change in the content of the peptide. KeywordsRas; sensitization; inflammatory pain; ERK; PKC; Src Corresponding Author: Dr. Michael Vasko Indiana University School of Medicine, 635 Barnhill Dr., A401, Indianapolis, IN 46202, Fax: (317) 274-7714, vaskom@iupui.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptNeuroscience. Author manuscript; available in PMC 2011 December 15. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptIn adult animals, the neurotrophin, nerve growth factor (NGF) is an inflammatory mediator that contributes to hypersensitivity by acting directly on small-diameter sensory neurons (Shu and Mendell, 1999). During tissue injury or inflammation, NGF levels are elevated in peripheral tissues (Woolf et al., 1994, Safieh-Garabedian et al., 1995. In animal models of inflammation, treatment with antibodies that block the actions of NGF or with the fusion protein TrkA-IgG, which sequesters NGF, attenuates hypersensitivity to noxious thermal and mechanical s...

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