Immunohistochemical Characterization of TRPV1 Staining in Human Dental Pulp

The TRPV1 ion channel plays a critical role in inflammatory pain and heat hyperalgesia. Various different commercially-available antibodies have been used to characterize the normal localization and changes in expression of TRPV1 in different pain conditions. We are using the human dental pulp as a model system to study peripheral pain mechanisms and have noted certain staining patterns with TRPV1 antibodies that may have important implications to the results of other studies. Objectives: Critical characterization of TRPV1 staining patterns obtained with two different antibodies used previously to describe TRPV1 staining in primate/human tissues (Chemicon rat-specific/Affinity BioReagents human-specific) within N52 or PGP9.5-identified human pulp axons that are characterized as to: 1) state of myelination with myelin basic protein (MBP), and 2) as peptidergic or nonpeptidergic as based on CGRP content. Non-neural expressions in S-100-identified Schwann cells and in CD-31-identified blood vessels were also evaluated. Methods: Pulp from normal fully-erupted third molars was fixed, sectioned and stained with multiple antibodies with the indirect immunofluorescence method and staining patterns evaluated with four-laser confocal microscopy. Results: Both TRPV1 antibodies showed expression within the myelin sheath of myelinated fibers and the cytoplasm of some S-100-identified Schwann cells. The human-specific antibody shows selective expression in a subset of unmyelinated fibers that are most common in the subodontoblastic plexus and that are mostly N52+ and CGRP+ in character. Furthermore, the human-specific antibody also reveals TRPV1 expression in some CD31+ blood vessels. Conclusions: Use of human-specific TRPV1 antibody shows expression within a subset of small axons that also express other markers of nociceptors, whereas the prominent expression seen within Schwann cells, myelin and vessels identifies the need for co-labeling studies to identify expression within specific elements. These non-neural expressions may play a potential role in TRPV1-mediated pain mechanisms.

Support: NIDCR #DE015576/M.Henry and UTHSCSA Department of Endodontics