17β-estradiol aggravates temporomandibular joint inflammation through the NF-κB pathway in ovariectomized rats

Abstract

Objective. Women of childbearing age are more likely than men to experience temporomandibular disorders, with pain as the main symptom. Temporomandibular joint (TMJ) inflammation is believed to be a major reason for TMJ pain. Whether sex hormones are involved in the sexual dimorphism of TMJ inflammation and pain remains to be elucidated. The aim of this study was to examine whether estrogen affects TMJ inflammation and pain via the NF-B pathway.Methods. Female rats were divided into 6 groups: the control group, the sham-ovariectomized group, and 4 groups of ovariectomized rats treated with 17␤-estradiol at a dosage of 0 g/day, 20 g/day, 80 g/day, and 200 g/day, respectively, for 10 days and then injected intraarticularly with Freund's complete adjuvant to induce TMJ inflammation. The behavior-related and histologic effects of 17␤-estradiol were evaluated 24 hours after the induction of TMJ inflammation. NF-B activity in the synovial membrane was examined by electrophoretic mobility shift assay. The expression of the NF-B target genes tumor necrosis factor ␣, interleukin-1␤ (IL-1␤), IL-6, cyclooxygenase 2, and inducible nitric oxide synthase in the synovial membrane was examined by real-time polymerase chain reaction.Results. Treatment with estradiol potentiated TMJ inflammation in a dose-dependent manner and also exacerbated the inflammation-induced decrease in food intake. Correspondingly, estradiol potentiated the DNAbinding activity of NF-B and the transcription of its target genes in the synovial membrane. Furthermore, the estrogen receptor antagonist ICI 182780 or the NF-B inhibitor pyrrolidine dithiocarbamate partially blocked the effects of estradiol on TMJ inflammation and pain and the NF-B pathway.Conclusion. These results suggest that estradiol aggravates TMJ inflammation through the NF-B pathway, leading to the induction of proinflammatory cytokines.Temporomandibular disorders (TMDs) are an assorted set of clinical conditions characterized by pain in the temporomandibular joint (TMJ) and/or masticatory muscles. Joint inflammation is thought to be a major cause of pain in patients with TMDs (1-4). The prevalence, severity, and duration of pain in TMDs are greater in women than in men; such pain primarily affects women of childbearing age (5). Estrogen replacement therapy in postmenopausal women is associated with the highest prevalence of TMDs (6). In women with TMDs, serum estradiol levels during the luteal phase are higher than those in healthy control subjects (7), and synovial fluid estradiol levels in patients with TMDs are also higher than those in healthy control subjects (8). These observations suggest that sex hormones, particularly estrogen, may be involved in TMD-associated pain.Estrogen is involved in joint inflammation. The sex hormone 17␤-estradiol enhances the secretion of matrix metalloproteinases in synoviocytes (9). It also enhances interleukin-1␤ (IL-1␤)-induced secretion of IL-6 from synoviocytes in rheumatoid arthritis (10).

Estradiol Promotes M1-like Macrophage Activation through Cadherin-11 To Aggravate Temporomandibular Joint Inflammation in Rats

“…1A. The 17b-estradiol (E2) administration and histological evaluation of TMJ inflammation were performed as previously described in detail (11). In brief, rats were randomly divided into four groups with five rats in each group, namely, control, sham, 0 mg-E2, and 80 mg-E2 groups.…”

“…An estrogenreceptor-specific antagonist, ICI 182,780 (Sigma), was administrated as previously described (11). In brief, another two sham-ovariectomized groups and two 80 mg-E2 groups (n = 5 for each group) were i.p.…”

“…The embedded TMJ blocks were sectioned (5 mm) and stained with H&E, and we histologically evaluated the TMJ inflammation using previously described methods (11). Sections were subjected to Ag retrieval with 0.125% trypsin and 20 mg/ml Proteinase K solution at room temperature for 20 min.…”

“…Reverse transcription and realtime PCR were performed as previously described in detail (32). The published sequences of the commercially synthesized primers are as follows: rat b-actin sense/antisense, 59-TGACAGGATGCAGAAGGA-GA-39/59-TAGAGCCACCAATCCACACA-39; rat iNOS sense/antisense, 59-GAGTGAGGAGCAGGTTGAGG-39/59-CCAAGGTGTTGCCCTTT-TT-39; rat IL-1b, sense/antisense 59-CACCTCTCAAGCAGAGCACAG-39/59-GGGTTCCATGGTGAAGTCAAC-39; rat TNF-a sense/antisense, 59-CCAGGTTCTCTTCAAGGGACAA-39/59-CTCCTGGTATGAAATGG-CAAATC-39 (11). The following primers were designed with the Primer Premier 5.0 software and commercially synthesized: rat cadherin-11 sense/ antisense, 59-TCCAACCAGCCAATAGTTACAGT-39/59-ATCACAATGG-GCAGGAGGTAGAG-39; rat IL-10 sense/antisense, 59-CACTGCTATGT-TGCCTGCTCTTAC-39/59-GGGTCTGGCTGACTGGGAAG-39; rat arginase sense/antisense, 59-TTGATGTTGATGGACTGGAC-39/59-TCTCTGGCT-TATGATTACCTTC-39.…”

“…Sex hormones, particularly estrogens, are reported to be involved in TMD (6,(8)(9)(10). We also previously reported that estrogen aggravates TMJ inflammation through the induction of proinflammatory cytokines in the synovial membrane (11). However, the mechanism underlying estrogen-aggravated TMJ inflammation has not been fully understood.…”