The expression and functionality of transient receptor potential vanilloid 1 in ovarian endometriomas

Pains of various kinds--dysmenorrhea, chronic pelvic pain, and dyspareunia--are the major complaints from women with endometriosis, representing the most debilitating nature of the disease. Despite extensive research, our understanding as how endometriosis causes pain is still fragmentary. In this study, we examined transient receptor potential vanilloid 1 (TRPV1)-positive nerve fibers in ectopic endometrium from women with ovarian endometriomas and in endometrium from women without endometriosis and correlated the density with the severity of dysmenorrhea in cases. We also performed an immunohistochemistry analysis of TRPV1 in ectopic and control endometrium. After finding TRPV1 immunoreactivity in ectopic endometrial cells, we further examined whether TRPV1 is functional in ectopic endometrial stromal cells (EESCs). We found that the density of TRPV1-positive nerve fibers in ectopic endometrial implants is higher than that in control endometrium and correlates positively with the severity of dysmenorrhea in women with endometriosis. In addition, TRPV1 expression was also found to be elevated significantly in EESCs when stimulated with inflammatory mediators such as prostaglandin E2 (PGE(2) ) and tumor necrosis factor-α (TNF-α). Finally, we found that TRPV1 activation can induce the release of nitric oxide (NO) and interleukin 1β (IL-1β) in EESCs. The latter finding appears to be consistent with the reports of increased TRPV1 protein expression following peripheral inflammation. Our results suggest that the increased TRPV1-positive nerve fibers may integrate various stimuli on peripheral terminals or primary sensory neurons and generate hyperalgesia in endometriosis. The expression and functionality of TRPV1 in EESCs also suggest that TRPV1 may have neurosecretory functions that are yet to be elucidated.