Estrogen and inflammation modulate estrogen receptor alpha expression in specific tissues of the temporomandibular joint

Reproductive Biology and Endocrinology BioMed Central Open Access Research Estrogen and inflammation modulate estrogen receptor alpha expression in specific tissues of the temporomandibular joint Jyoti Puri, Bob Hutchins, Larry L Bellinger and Phillip R Kramer* Address: Department of Biomedical Sciences, Texas A&M Health Science Center, Baylor College of Dentistry, Dallas, Texas, USA Email: Jyoti Puri - ; Bob Hutchins - ; Larry L Bellinger - ; Phillip R Kramer* - * Corresponding author Published: 31 December 2009 Reproductive Biology and Endocrinology 2009, 7:155 doi:10.1186/1477-7827-7-155 Received: 6 October 2009 Accepted: 31 December 2009 This article is available from: http://www.rbej.com/content/7/1/155 © 2009 Puri et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background: Estrogen is known to play role in temporomandibular joint (TMJ) disorders and estrogen effects can be mediated by estrogen receptor (ER) alpha present in the TMJ. Cells expressing the estrogen receptor ERalpha are present in the temporomandibular joint (TMJ) but changes in expression due to estrogen and inflammation have not been characterized. In this study, ERalpha protein content and the number of cells expressing ERalpha was measured in 17 betaestradiol-treated rats after inflammation was induced in the TMJ. Methods: Sixteen ovariectomized female rats were divided into two groups such that one group received 17 beta estradiol (E2) and the other was given vehicle (VEH). Groups were then subdivided further, one received injections of saline and the other received Complete Freund's adjuvant (CFA) within the superior joint space of the TMJ. Thus the four groups include no E2/ saline, E2/saline, no E2/CFA and E2/CFA. After treatment, the rats were sacrificed, and the TMJ anterior, disc, retrodiscal and synovial tissues were analyzed by western blot and immunocytochemistry. Positive stained cells were counted using a Nikon epifluorescent microscope. Results: The western blot showed that ERalpha protein significantly decreased with inflammation. The number of ERalpha-positive cells in the TMJ was not affected by inflammation or 17 betaestradiol with exception of the retrodiscal tissue. In the retrodiscal tissue 17 beta-estradiol significantly decreased the number of ERalpha-positive cells but only in a non-inflamed joint. Conclusions: In conclusion, inflammation and 17 beta-estradiol can modulate ERalpha expression in the TMJ but the effects are tissue specific. Background Epidemiological studies have shown that during their reproductive years, women experience a higher frequency of temporomandibular joint disorders than males with a ratio of = 1.5- 2 [1]. It has been postulated that estrogen could be the primary molecule leading to the higher fre- quency of TMJ disorders in women. Endogenous estrogen affects the remodeling processes within the TMJ [2,3] possibly by changing the extracellular matrix in the joint [4] or by changing bone volume [2]. Such changes can result in internal derangement of the TMJ. Estrogen modulation of matrix metalloproteinase (MMP) expression has also Page 1 of 8 (page number not for citation purposes) Reproductive Biology and Endocrinology 2009, 7:155 been observed in the cartilage of the TMJ [5,6]; high levels of MMP have been reported to play a role in TMJ osteoarthritis [7,8]. Moreover, the level of estrogen in the synovial fluid has been correlated to the severity of arthritis in postmenopausal women [9], and in animal models estrogen has been shown to modulate inflammation in the TMJ [10,11]. 17 β-estradiol is the most potent and dominant form of estrogen in the human female, having biological effects through binding the estrogen receptor alpha (ERα) and beta (ERβ) [12]. ERα and ERβ acts via binding to the DNA [13] or by having biological effects through interacting with various kinases, such as mitogen-activated protein kinase, phosphatidylinositol-3 kinase or tyrosine kinase [12]. Also both receptors can interact with membraneassociated molecules such as ion channels and G proteincoupled receptors to alter the physiology of the cell [12]. The wide distribution of the estrogen receptors ERα and ERβ in the thymus [14,15], bone marrow [16] and spleen [17] suggests that it plays a modulatory role in the immune system, such as modulating differentiation, activation, proliferation and antibody production from lymphoid cells [18]. Immune responses are important in joint disorders and an alteration in ERα and ERβ expression would have an impact on how estrogen affects the immune response in the TMJ. In particular, ERα was found in the articular cartilage and subchondral bone of TMJ which implies that estrogen directly acted on the cells in the TMJ tissue to alter the gene expression and cellular physiology [19]. In contrast to the ERα expression in the rat, ERα nuclear staining was not detected in the bone, cartilaginous or connective tissues of the human or baboon TMJ, but it was present in the immune cells such as macrophage and lymphocytes [20,21]. In addition ER knockout studies have shown a major role for ERα in immune modulation [22,23]. Because ERα is present in the immune cells in the human TMJ [20,21], a likely target of 17 β-estradiol in the human TMJ is ERαpositive immune cells. Furthermore ER-α gene polymorphisms is associated with a predisposition to TMJ disorders [24]. Such data from both animal and clinical studies support a significant role of ERα in the increased incidence of TMJ inflammation [24,25]. In an intact rat 17 β-estradiol and progesterone concentrations change during the estrus cycle [26]. Multiple fluctuating hormones could complicate our understanding of how 17 β-estradiol modulates estrogen receptor expression. Hormone administration in overiectomized animals allows us to study the effect of 17 β-estradiol, avoiding http://www.rbej.com/content/7/1/155 fluctuating levels. Thus, our study was focused on the effect of a single, physiological concentration of 17 βestradiol. This concentration of 17 β-estradiol was equal to that observed during the estrus cycle [26]. The level of receptor will determine the cellular sensitivity to 17 β-estradiol, because this hormone acts primarily through the estrogen receptor(s) [27]. This paper particularly focuses on ERα expression in response to17β-estradiol and inflammation. The aim of the present study is to first quantify the tissue content of ERα in the female rat TMJ, and second, to determine whether changes in the ERα expression in the TMJ result from alterations in inflammation or the concentration of 17β-estradiol. Methods Animals and tissue preparation The Baylor College of Dentistry Institutional Animal Care and (...truncated)