Women with reproductive capability are more likely to suffer from
temporomandibular disorders (TMD), with
orofacial pain as the most common complaint. In the past, we focused on the role of
estradiol in TMD
pain through the nervous system. In this study, we explored
estradiol's influence on synoviocyte gene expressions involved in the
allodynia of the inflamed TMJ. The influence of 17-β-estradiol on
NGF and TRPV1 expression in TMJ synovium was determined in vivo and in vitro and analyzed by Western blot and real-time PCR. Complete
Freund's adjuvant (CFA) injection into the TMJ was used to induce TMJ
arthritis.
Capsazepine served as a TRPV1 antagonist. Head withdrawal threshold was examined using a von Frey Anesthesiometer. We observed that
estradiol upregulated the expressions of TRPV1 and
NGF in a dose-dependent manner. In the primary cultured synoviocytes, TRPV1 was upregulated by
lipopolysaccharide (LPS),
estradiol, and
NGF, while
NGF antibodies fully blocked LPS and
estradiol-induced upregulation of TRPV1. Activation of TRPV1 in the primary synoviocytes with
capsaicin, a TRPV1 agonist, dose-dependently enhanced COX-2 transcription. Moreover, intra-TMJ injection of TRPV1 antagonist,
capsazepine, significantly attenuated
allodynia of the inflamed TMJ induced by intra-TMJ injection of CFA in female rats. This article presents a possible local mechanism for
estradiol that may be involved in TMJ
inflammation or
pain in the synovial membrane through the
pain-related gene TRPV1. This finding could potentially help clinicians understand the sexual dimorphism of TMD
pain.