Increased mandibular condylar growth in mice with estrogen receptor beta deficiency

Sex-dependent variation in cartilage adaptation: from degeneration to regeneration

Despite acknowledgement in the scientific community of sex-based differences in cartilage biology, the implications for study design remain unclear, with many studies continuing to arbitrarily assign demographics. Clinically, it has been well-established that males and females differ in cartilage degeneration, and accumulating evidence points to the importance of sex differences in the field of cartilage repair. However, a comprehensive review of the mechanisms behind this trend and the influence of sex on cartilage regeneration has not yet been presented. This paper aims to summarize current findings regarding sex-dependent variation in knee anatomy, sex hormones' effect on cartilage, and cartilaginous degeneration and regeneration, with a focus on stem cell therapies. Findings suggest that the stem cells themselves, as well as their surrounding microenvironment, contribute to sex-based differences. Accordingly, this paper underscores the contribution of both stem cell donor and recipient sex to sex-related differences in treatment efficacy. Cartilage regeneration is a field that needs more research to optimize strategies for better clinical results; taking sex into account could be a big factor in developing more effective and personalized treatments. The compilation of this information emphasizes the importance of investing further research in sex differences in cartilage biology.

DDIT3/CHOP mediates the inhibitory effect of ER stress on chondrocyte differentiation by AMPKα-SIRT1 pathway

Endoplasmic reticulum (ER) stress is an evolutionarily conserved cellular stress response related to multiple diseases, including temporomandibular joint (TMJ) cartilage-related diseases. Recent studies have indicated that DDIT3/CHOP (a downstream transcription factor of ER stress) is an important effector in mediating ER stress to inhibit chondrogenesis. However, the underlying mechanism by which DDIT3 regulates chondrogenesis remains unclear. In this study, tunicamycin (an ER stress agonist)-induced ER stress inhibited chondrocyte differentiation and matrix synthesis in vitro and led to an osteoarthritis-like phenotype in mouse TMJ cartilage. Meanwhile, DDIT3 expression in chondrocytes was robustly upregulated. Loss-of-function experiments validated the inhibiting effect of DDIT3 on chondrocyte differentiation and matrix synthesis. Mechanistically, the inhibiting effect was attributed to the direct and indirect regulatory effect of DDIT3 on SIRT1 (sirtuin1, silent mating type information regulation protein type 1, a member of NAD+ dependent class III histone deacetylases). On one hand, DDIT3 directly promoted the transcription of SIRT1. On the other hand, DDIT3 indirectly increased the expression of SIRT1 by promoting AMPKα phosphorylation and activation. Furthermore, activation of AMPKα or SIRT1 with the corresponding agonist AICAR or resveratrol in the DDIT3-knockdown cells partially restored the inhibiting effect of DDIT3 on chondrocyte differentiation and matrix synthesis. Collectively, these novel findings indicate that DDIT3 regulates the inhibitory effect of ER stress on chondrocyte differentiation and matrix synthesis partially via the AMPKα-SIRT1 pathway. A thorough understanding of ER stress in regulating chondrocyte homeostasis and its role in the onset of osteoarthritis may be promising to develop therapeutic targets and prevent condyle cartilage destruction.

Impact of estrogen therapy on temporomandibular joints of rats: Histological and hormone analytical study

Objectives

This research aims to evaluate the effects of estrogen deficiency and replacement on the TMJ structures of rats. The considerable similarities in the anatomical features of rats and humans make rats a suitable model for human scientific studies.

Methods

A clinical trial was conducted on 18 female Sprague-Dawley rats grouped into three categories. The GI group included 6 female rats labelled as the control group, the GII group consisted of 6 females that received ovariectomies, and the GIII group had 6 ovariectomised females that were injected with estrogen replacement therapy in a science laboratory at King Abdulaziz University. ANOVA and Tukey HSD post hoc tests were used to determine any significant differences between the levels of estrogen among the three groups.

Results

The results indicate that some TMJ structures, including the articular disc and condylar cartilaginous layer, were degraded after estrogen deficiency. However, there was a slight improvement in the cartilaginous layer thickness and proliferation of chondroid cells after estrogen replacement therapy. Estrogen level was reduced in the ovariectomized rats, and while estrogen injections increased blood hormone levels, the levels did not reach those of the control group.

Conclusion

Estrogen deficiency degraded some TMJ structures, and there is only a slight recovery after estrogen replacement therapy.

Do sex hormone imbalances contribute to idiopathic condylar resorption?

Idiopathic condylar resorption (ICR) is an aggressive form of temporomandibular joint disease that most frequently presents in adolescent girls during the pubertal growth spurt. Although numerous studies have indicated that the etiopathogenesis of ICR may be related to estrogen deficiency, the decisive role of estrogens remains controversial, and other sex hormone disturbances have not yet been investigated in this regard. Therefore, the aim of this study was to ascertain the role of serum estrogen levels and also the roles of other sex hormones in the pathogenesis of ICR. Ninety-four ICR patients and 324 disc displacement (DD) patients, of both sexes, were enrolled. Information on menstruation and serum levels of follicle-stimulating hormone, luteinizing hormone, prolactin, 17β-estradiol (E2), testosterone, and progesterone were recorded and analyzed. The results showed that female ICR patients had normal puberty onset, within the average age range. Use of oral contraceptives and other menstruation-regulating pharmaceuticals was similar in the two groups. Of note, neither serum E2 levels nor those of the other sex hormones differed significantly between female ICR and DD patients. However, male ICR patients had significantly increased serum testosterone levels (P=0.002) and relatively higher E2 levels (P=0.095) compared to DD patients. This study found that reduced serum E2 did not contribute to ICR; instead, systemic testosterone disturbances were found to be related to ICR.

Effect of glucosamine sulphate on the temporomandibular joint of ovariectomised rats

Glycosamine is an amino-monosaccharide present in connective and cartilage tissues that contribute to the maintenance, resistance, flexibility, and elasticity of these tissues. This study aimed to determine the in vivo effects of glucosamine sulphate (GS) on the temporomandibular joint (TMJ) of ovariectomised rats (OVX).Thirty-two rats were distributed into four groups as follows: G1, sham-OVX+saline solution; G2, sham-OVX+glucosamine sulphate (80mg/kg) - oral administration; G3, OVX+saline solution; G4, OVX+glucosamine sulphate (80mg/kg) - oral administration. Animals were treated for seven days. The TMJ was removed and stained with toluidine blue. The thickness of the cartilage layers and cytokines IL-1β, IL-6, and TNF-α levels were determined by histomorphometry and immunoassay, respectively. The administration of GS to OVX females did not change the thickness of condylar cartilage when compared with the other groups (p>0.05). There was an increase in the total cartilage thickness in sham-OVX females. IL-1β and TNF-α levels were significantly lower in sham-OVX females than in OVX females, indicating that ovariectomy acts as potent cytokine inducer. IL-6 levels were significantly higher in sham-OVX females. GS did not affect cytokine production in OVX females (p>0.05). In conclusion, the administration of GS did not affect cytokine levels, but did induce an increase in the total thickness of the TMJ condylar cartilage in sham-OVX rats.

HIF-1α Mediates Osteoclast-Induced Mandibular Condyle Growth via AMPK Signaling

During the mandibular condylar growth, the absorption of calcified cartilage matrix induced by osteoclasts is crucial for the continuous endochondral osteogenesis. Meanwhile, recent studies showed that subchondral bone resided within the low-oxygen microenvironment, and our previous study revealed that hypoxia-inducible transcription factor 1α (HIF-1α) promoted osteoclastogenesis under hypoxia. However, whether HIF-1α regulates the function of osteoclasts in the mandibular condyle cartilage remains elusive. Our study indicated that severe deformity of the mandibular condyle was displayed in 10-wk-old osteoclast-specific HIF-1α conditional knockout (CKO) mice, accompanied by shortened length of condylar process and disorganized fibrocartilage. In 1-, 2-, and 4-wk-old CKO mice, the size of the hypertrophic layer and chondrocytic layer was significantly thickened. In the chondrocytic layer, chondrocytes were atrophied, showing a form of apoptosis in 4-wk-old CKO mice. Furthermore, an increase in the thickness of the fibrous and proliferating layer was observed in 10-wk-old CKO mice, as well as a significant decrease in that of the chondrocytic and hypertrophic chondrocyte layers. Interestingly, the articular surface of the condylar process abnormally presented a horizontal concave shape, and a disk-like acellular connective tissue appeared. In addition, genetic ablation of HIF-1α blunted cartilage matrix loss by subchondral osteoclast deficiency, resulting in a high subchondral bone mass phenotype, accompanied with a decreased number of blood vessels, alkaline phosphatase staining, and vascular endothelial growth factor (VEGF) expression. Mechanistically, the number of osteoclasts in the center of the condyle in CKO mice was significantly reduced by attenuated expression of adenosine 5′-monophosphate-activated protein kinase (AMPK) signaling. These findings reveal a novel influence of HIF-1α function in osteoclasts on maintenance of osteoclast-induced resorption of calcified cartilage matrix via AMPK signaling, as well as subchondral bone formation through VEGF-dependent angiogenesis in bone marrow.

Estrogen signaling impacts temporomandibular joint and periodontal disease pathology

Women experience a higher incidence of oral diseases including periodontal diseases and temporomandibular joint disease (TMD) implicating the role of estrogen signaling in disease pathology. Fluctuating levels of estrogen during childbearing age potentiates facial pain, high estrogen levels during pregnancy promote gingivitis, and low levels of estrogen during menopause predisposes the TMJ to degeneration and increases alveolar bone loss. In this review, an overview of estrogen signaling pathways in vitro and in vivo that regulate pregnancy-related gingivitis, TMJ homeostasis, and alveolar bone remodeling is provided. Deciphering the specific estrogen signaling pathways for individual oral diseases is crucial for potential new drug therapies to promote and maintain healthy tissue.

Lipid profiles as potential mediators linking body mass index to osteoporosis among Chinese adults: the Henan Rural Cohort Study

This study is to examine the relationship between body mass index (BMI) and osteoporosis in rural areas of China, and then explore whether this association was mediated by lipid profiles. Results showed that with the increasing of BMI, the risk of osteoporosis was reduced, and lipid profiles mediate this association.

INTRODUCTION

To examine the relationship between BMI and osteoporosis, and explore whether this association was mediated by lipid profiles.

METHODS

A total of 8272 participants (18-79 years) were enrolled from the Henan Rural Cohort Study. The bone mineral density of the calcaneus was measured using an ultrasonic bone density apparatus. Logistic regression and restricted cubic splines were used to evaluate the odds ratio (OR) and 95% confidence intervals (95% CI). Mediation analysis using bootstrap was performed to examine the contribution of lipid profiles to BMI-related osteoporosis.

RESULTS

The crude and age-standardized prevalence of osteoporosis were 15.93% and 11.77%, respectively. The mean BMIs were 24.12 kg/m² for participants with osteoporosis and 25.06 kg/m² for non-osteoporosis participants (P < 0.001). After adjusting for potential confounders, subjects with obesity had a lower OR of osteoporosis (0.493 [95% CI: 0.405-0.600], P_trend < 0.001) compared with normal-weight individuals. Mediation analysis showed that lipid profile partly mediated the relationship between BMI and osteoporosis with indirect effect OR (95% CI) of 0.985 (0.978-0.992), and the proportion explained of BMI was 15.48% for lipid profile.

CONCLUSION

With the increasing of BMI, the risk of osteoporosis was reduced in the Chinese adult population, and lipid profiles may be a potential mediator linking reduced risk of osteoporosis. Elucidating the underlying mechanisms will facilitate developing feasible preventive and therapeutic measures for osteoporosis. Chinese clinical trial register: ChiCTR-OOC-15006699.

MMP-3 and MMP-8 in rat mandibular condylar cartilage associated with dietary loading, estrogen level, and aging

OBJECTIVES

The structure of the mandibular condylar cartilage (MCC) is regulated by dynamic and multifactorial processes. The aim of this study was to examine the effects of altered dietary loading, estrogen level, and aging on the structure of the condylar cartilage and the expressions of matrix metalloproteinase (MMP) -3 and MMP-8 of rat MCC.

METHODS

In this study, Crl:CD (SD) female rats were randomly divided into 3 groups according to dietary hardness: hard diet (diet board), normal diet (pellet), and soft diet (powder). In each group, the rats were further divided into 2 subgroups by ovariectomy at the age of 7 weeks. The rats were sacrificed at 5- and 14-month-old. Histomorphometric analysis of the MCC thickness was performed after toluidine blue staining. Immunochemical staining was done for MMP-3 and MMP-8. A linear mixed model was used to assess the effects of dietary loading, estrogen level, and aging.

RESULTS

Increased dietary loading was the main factor to increase the MMP-3 expression and the anterior and central thickness of the MCC. Lack of estrogen was the main factor associated with decreased MMP-8. Aging was associated with the thickness changes of the whole condylar cartilage and the reduced expression of MMP-8.

CONCLUSION

The condylar cartilage structure and metabolism of the female rats are sensitive to dietary loading changes, estrogen level as well as aging. The proper balance of these factors seems to be essential for the maintenance of the condylar cartilage.

Three-dimensional volumetric analysis of mandibular condyle changes in growing subjects: A retrospective cross-sectional study

OBJECTIVE

The purpose of this study is to analyze the mandibular condylar volumein a sample of subjects 11-26 years old.

METHODS

CBCT condylescans from 94 patients (mean age 18.2 ± 4.5 y) acquired with areconstructed layer thickness of 0.5 mm and a 512×512 matrix were examined. Data on condylar volume were compared among three groups with different age ranges: 11-16 years, 17-21years, and 22-26 years. Condylar volumetric measurements were performed with Mimics™ software.

RESULTS

A significant increase in condylar volume from puberty to young adulthood was detected (p < 0.01). Females showed a higher condylar volume in the 17-21 y group compared with the 11-16 y group. Males showed differences among all three groups.

CONCLUSION

The mandibular condyle growth seems to continue at least until 17-21 years in males but seems to stop before 17 years in females.

Estrogen receptor alpha mediates mandibular condylar cartilage growth in male mice

OBJECTIVES

In the appendicular skeleton, estrogen via ERα signalling has been shown to mediate endochondral growth plate fusion in both males and females. However, the role of ERα in mediating growth of the mandibular condylar cartilage is unknown. Thus, this study focuses on the characterization of the mandibular condylar cartilage phenotype in young and adult male ERαKO mice.

SETTING

Columbia University Medical Center.

MATERIAL AND METHODS

WT and ERαKO C57BL/6 male mice were sacrificed at 49 days or 9 months for phenotypic analysis. Changes to MCC thickness, cell number and cell density were measured using histomorphometric methods. Cartilage-specific gene expression and OARSI scores were investigated for 49-day and 9-month-old male ERαKO and WT mice.

RESULTS

In young mice, a significant increase in the number of mandibular condylar cartilage cells and a significant decrease in the expression of Col10, Runx2 and DMP1 were observed in the male ERαKO mice compared to WT. In 9-month-old mice, we found a similar increase in the number of cells but no change in osteoarthritic histological scoring in ERαKO mice compared to WT mice.

CONCLUSION

In summary, estrogen plays a role in mediating mandibular condylar maturation in young male mice. However, according to this study, it does not play a role in mediating long-term growth or age-related mandibular condylar cartilage degeneration in males.

Estrogen Promotes Mandibular Condylar Fibrocartilage Chondrogenesis and Inhibits Degeneration via Estrogen Receptor Alpha in Female Mice

Temporomandibular joint degenerative disease (TMJ-DD) is a chronic form of TMJ disorder that specifically afflicts people over the age of 40 and targets women at a higher rate than men. Prevalence of TMJ-DD in this population suggests that estrogen loss plays a role in the disease pathogenesis. Thus, the goal of the present study was to determine the role of estrogen on chondrogenesis and homeostasis via estrogen receptor alpha (ERα) during growth and maturity of the joint. Young and mature WT and ERαKO female mice were subjected to ovariectomy procedures and then given placebo or estradiol treatment. The effect of estrogen via ERα on fibrocartilage morphology, matrix production, and protease activity was assessed. In the young mice, estrogen via ERα promoted mandibular condylar fibrocartilage chondrogenesis partly by inhibiting the canonical Wnt signaling pathway through upregulation of sclerostin (Sost). In the mature mice, protease activity was partly inhibited with estrogen treatment via the upregulation and activity of protease inhibitor 15 (Pi15) and alpha-2-macroglobulin (A2m). The results from this work provide a mechanistic understanding of estradiol on TMJ growth and homeostasis and can be utilized for development of therapeutic targets to promote regeneration and inhibit degeneration of the mandibular condylar fibrocartilage.

Quercetin Stimulates Bone Marrow Mesenchymal Stem Cell Differentiation through an Estrogen Receptor-Mediated Pathway

Objectives

The present study aimed to investigate the overall effect of quercetin on mouse bone marrow mesenchymal stem cell (BMSC) proliferation and osteogenic differentiation in vitro.

Materials and Methods

BMSCs were treated with different concentrations of quercetin for 6 days. The effects of quercetin on cell proliferation were assessed at predetermined times using Cell Counting Kit-8 (CCK-8) assay. The cells were then treated with quercetin, estrogen, or an estrogen receptor (ER) antagonist (which was also administered in the presence of quercetin or estrogen) for 7 or 21 days. The effects of quercetin on BMSC osteogenic differentiation were analyzed by an alkaline phosphatase (ALP) assay kit, Alizarin Red S staining (ARS), quantitative real-time PCR (qPCR), and western blotting.

Results

The CCK-8 and ALP assays and ARS staining showed that quercetin significantly enhanced BMSC proliferation, ALP activity, and extracellular matrix production and mineralization, respectively. The qPCR results indicated that quercetin promoted osterix (OSX), runt-related transcription factor 2 (RUNX2), and osteopontin (OPN) transcription in the presence of osteoinduction medium, and the western blotting results indicated that quercetin enhanced bone morphogenetic protein 2 (BMP2), Smad1, Smad4, RUNX2, OSX, and OPN expression and Smad1 phosphorylation. Treatment with the ER inhibitor ICI182780 blocked the effects of quercetin.

Conclusions

Our data demonstrated that quercetin promotes BMSC proliferation and osteogenic differentiation. Quercetin enhances BMP signaling pathway activation and upregulates the expression of downstream genes, such as OSX, RUNX2, and OPN, via the ER.

Association of Condylar Bone Quality with TMJ Osteoarthritis

The etiology and treatment of temporomandibular joint (TMJ) osteoarthritis (TMJOA) remain complex and unclear. Based on clinical observations, we hypothesized that low condylar bone quality is significantly correlated with TMJOA and explored this association in a cross-sectional study with human patients. A total of 254 postmenopausal female participants were included in this study. Radiographic findings from cone beam computed tomography (CBCT) and clinical symptoms were used to classify each TMJ data sample as healthy control ( n = 124) or TMJOA ( n = 130). Condylar bone mineral density (BMD) (computed tomography Hounsfield unit [CT HU]) and bone volume fraction (BV/TV) were measured and modeled as predictors of healthy control versus TMJOA status in multilevel logistic regression analyses. Both CT HU (adjusted odds ratio [AOR] = 0.9989, interquartile odds ratio [IOR] = 0.4206) and BV/TV (AOR= 0.8096, IOR = 0.1769) were negatively associated with TMJOA ( P = 0.049, 0.011, respectively). To assess the diagnostic performance of CT HU and BV/TV for identification of TMJOA, receiver operating characteristic (ROC) curves were plotted. The estimated areas under the curve (AUC) were 0.6622 for BV/TV alone, 0.6074 for CT HU alone, and 0.7136 for CT HU and BV/TV together. The model incorporating CT HU and BV/TV together had a significantly higher AUC than the models using BV/TV alone ( P = 0.038) or HU alone ( P = 0.021). In conclusion, we found that low condylar bone quality was significantly correlated with TMJOA development and that condylar CT HU and BV/TV can be used together as a potential diagnostic tool for TMJOA. Careful clinical evaluation of the condyle coupled with appropriate radiographic interpretation would thus be critical for the early detection of TMJOA.

Sex differences in the estrogen-dependent regulation of temporomandibular joint remodeling in altered loading

OBJECTIVE

Temporomandibular joint (TMJ) diseases predominantly afflict women, suggesting a role of estrogen in the disease etiology. Previously, we determined that decreased occlusal loading (DOL) inhibited collagen type II (Col2) expression in the mandibular condylar cartilage (MCC) of female wild-type (WT) mice whereas no change was observed in males. This decrease in chondrogenesis was abolished by estrogen receptor beta (ERβ) deficiency in females. Therefore, the goal of this study was to examine the role of estradiol - ERβ signaling in mediating DOL effects in male mice to further decipher sex differences.

METHODS

Male 21 day-old WT and ERβKO male mice were treated with either placebo or estradiol and exposed to normal or DOL for 4 weeks. Cartilage thickness and cell proliferation, gene expression and immunohistochemistry of chondrogenic markers and estrogen receptor alpha (ERα), and analysis of bone histomorphometry via microCT were completed to ascertain the effect of estradiol on DOL effects to the TMJ.

RESULTS

ERβKO male mice lack a MCC phenotype. In both genotypes, estradiol treatment increased Col2 gene expression and trabecular thickness. DOL in combination with estradiol treatment caused a significant increase in Col2 gene expression in both genotypes.

CONCLUSIONS

The sex differences in DOL-induced inhibition of Col2 expression do not appear to be mediated by differences in estradiol levels between male and female mice. Greater understanding on the role of estrogen and altered loading are critical in order to decipher the sex dimorphism of TMJ disorders.

Signs and symptoms of temporomandibular disorders in women and men

INTRODUCTION

Women are more likely to present temporomandibular disorders (TMD); however, studies comparing genders in Brazilian samples are rare.

PURPOSE

To analyze the proportion of men and women, as well as the association between gender and age, problem duration, and TMD symptoms in patients admitted to an university clinic for treatment.

METHODS

Interview and assessment data of protocols from 1,000 patients diagnosed with TMD were collected and analyzed and then divided into two groups, male (n = 177) and female (n = 823). The exploratory analysis was based on contingency tables and χ2 test was carried out. Subsequently, the logistic regression model was used and the odds ratios (OR) concerning the evaluated comparisons were calculated.

RESULTS

Females were more prevalent in the sample, and mean ages and TMD duration were similar between the groups, with higher occurrence in young adults (19 to 40 years old). The OR values showed an association between the female gender and the signs/symptoms of pain in the temporomandibular joint, pain in the facial muscles, neck and shoulders, headache, fatigue in the muscles of mastication, otologic symptoms, and dysphonia. Women had two times higher chances of presenting these symptoms than men.

CONCLUSION

In the sample of Brazilian patients with TMD, the number of women who presented a higher prevalence of painful symptoms was greater, followed by otologic symptoms and complaints of dysphonia. The prevalence of joint noise was similar in both studied groups.

Effects of bisphosphonates on mandibular condyle of ovariectomized osteoporotic rats using micro-ct and histomorphometric analysis

OBJECTIVE

To evaluate microarchitectural changes in condylar cartilage and associated subchondral bone after bisphosphonates treatment using an ovariectomized (OVX) osteoporosis rat model.

METHODS

Thirty six-month-old female Sprague-Dawley rats were randomly divided into sham, OVX, and risedronate (RIS)-treated groups. Both OVX and RIS groups received bilateral ovariectomy. OVX group was treated subcutaneously with saline, whereas RIS group received risedronate treatment (2.4 μg/kg) subcutaneously for 3 months. At the end of 3 months, animals were sacrificed and the entire condyles were harvested for micro-CT and histological analyses. Immunohistochemistry (IHC) was performed to assess the expression of type I/II collagen protein by semiquantitative imaging analysis.

RESULTS

Micro-CT analysis showed OVX group had significant condylar subchondral bone loss compared to sham as shown by significant decrease in bone volume fraction (P = 0.028), trabecular thickness (P = 0.041), and significant increase in trabecular spacing (P = 0.003). In RIS group, partial inhibition of OVX-induced bone loss was detected. HE staining showed proliferative layer of condylar cartilage reduced, while hypertrophic chondrocyte layer increased significantly in RIS group compared to sham and OVX groups. IHC showed reduced expression of Col I in both the OVX and RIS groups, whereas expression of Col II was reduced in the OVX group but increased in the RIS group.

CONCLUSION

Our findings suggest that systemic bisphosphonate treatment influences the structure and ossification of condylar cartilage and it has a dual action on condyle in a postmenopausal osteoporosis rat model which raises the concerns for the potential side effects of BPs on condyle to elder patients.

The obesity of bone

During the last decades, obesity and osteoporosis have become important global health problems, and the belief that obesity is protective against osteoporosis has recently come into question. In fact, some recent epidemiologic and clinical studies have shown that a high level of fat mass might be a risk factor for osteoporosis and fragility fractures. Several potential mechanisms have been proposed to explain the complex relationship between adipose tissue and bone. Indeed, adipose tissue secretes various molecules, named adipokines, which are thought to have effects on metabolic, skeletal and cardiovascular systems. Moreover, fat tissue is one of the major sources of aromatase, an enzyme that synthesizes estrogens from androgen precursors, hormones that play a pivotal role in the maintenance of skeletal homeostasis, protecting against osteoporosis. Moreover, bone cells express several specific hormone receptors and recent observations have shown that bone-derived factors, such as osteocalcin and osteopontin, affect body weight control and glucose homeostasis. Thus, the skeleton is considered an endocrine target organ and an endocrine organ itself, likely influencing other organs as well. Finally, adipocytes and osteoblasts originate from a common progenitor, a pluripotential mesenchymal stem cell, which has an equal propensity for differentiation into adipocytes or osteoblasts (or other lines) under the influence of several cell-derived transcription factors. This review will highlight recent insights into the relationship between fat and bone, evaluating both potential positive and negative influences between adipose and bone tissue. It will also focus on the hypothesis that osteoporosis might be considered the obesity of bone.

Dependence of cytokine levels on the sex of experimental animals: a pilot study on the effect of oestrogen in the temporomandibular joint synovial tissues

The aim of this study was to evaluate the effects of 17β-oestradiol (E2) on cartilage thickness and cytokine levels in the temporomandibular joint (TMJ). Thirty rats (15 female, 15 male) were orchidectomized (ORX), ovariectomized (OVX), or sham-operated. After 21 days, animals were assigned to six groups: (1) sham-ORX; (2) ORX; (3) ORX+E2; (4) sham-OVX; (5) OVX; and (6) OVX+E2. Treatments were administered daily for 21 days. The thickness of cartilage layers (fibrous, proliferative, maturation, and hypertrophic) and cytokine levels (interleukins IL-1α, IL-1β, IL-6, and tumour necrosis factor alpha (TNF-α)) were measured by histomorphometry and ELISA, respectively. Kruskal-Wallis/Dunn's tests were used (alpha=5%). Sham-ORX showed thicker layers than ORX+E2, but not thicker than ORX. All layers, except the hypertrophic layer, were thicker in sham-OVX than OVX or OVX+E2. Although IL-1β levels were higher in castrated animals, E2 did not affect the level of this cytokine. IL-1α levels were higher in both ORX (P=0.0010) and ORX+E2 (P=0.0053) than in sham-ORX. However, E2 decreased IL-1α levels in OVX (P=0.0129). When compared to sham-ORX/OVX, IL-6 levels were not affected by E2 in males but were reduced in OVX (P=0.0079) and increased in OVX+E2 (P=0.0434). Levels of TNF-α were reduced by E2 in both ORX+E2 and OVX+E2. E2 treatment caused gender- and layer-dependent changes in the cartilage. Castration increased all cytokine levels, except for IL-6, without respect to gender.

Oestrogen receptor beta mediates decreased occlusal loading induced inhibition of chondrocyte maturation in female mice

OBJECTIVE

Temporomandibular joint (TMJ) disorders predominantly afflict women, suggesting that estrogen may play a role in the disease process. Defects in mechanical loading-induced TMJ remodelling are believed to be a major etiological factor in TMJ degenerative disease. Previously, we found that, decreased occlusal loading caused a significant decrease in early chondrocyte maturation markers (Sox9 and Col 2) in female, but not male, C57BL/6 wild type mice (1). The goal of this study was to examine the role of Estrogen Receptor (ER) beta in mediating these effects.

DESIGN

21-day-old male (n = 24) and female (n = 25) ER beta KO mice were exposed to decreased occlusal loading (soft diet administration and incisor trimming) for 4 weeks. At 49 days of age the mice were sacrificed. Proliferation, gene expression, Col 2 immunohistochemistry and micro-CT analysis were performed on the mandibular condyles.

RESULTS

Decreased occlusal loading triggered similar effects in male and female ER beta KO mice; specifically, significant decreases in Col 10 expression, subchondral total volume, bone volume, and trabecular number.

CONCLUSION

Decreased occlusal loading induced inhibition of chondrocyte maturation markers (Sox9 and Col 2) did not occur in female ER beta deficient mice.

Sex steroid actions in male bone

Sex steroids are chief regulators of gender differences in the skeleton, and male gender is one of the strongest protective factors against osteoporotic fractures. This advantage in bone strength relies mainly on greater cortical bone expansion during pubertal peak bone mass acquisition and superior skeletal maintenance during aging. During both these phases, estrogens acting via estrogen receptor-α in osteoblast lineage cells are crucial for male cortical and trabecular bone, as evident from conditional genetic mouse models, epidemiological studies, rare genetic conditions, genome-wide meta-analyses, and recent interventional trials. Genetic mouse models have also demonstrated a direct role for androgens independent of aromatization on trabecular bone via the androgen receptor in osteoblasts and osteocytes, although the target cell for their key effects on periosteal bone formation remains elusive. Low serum estradiol predicts incident fractures, but the highest risk occurs in men with additionally low T and high SHBG. Still, the possible clinical utility of serum sex steroids for fracture prediction is unknown. It is likely that sex steroid actions on male bone metabolism rely also on extraskeletal mechanisms and cross talk with other signaling pathways. We propose that estrogens influence fracture risk in aging men via direct effects on bone, whereas androgens exert an additional antifracture effect mainly via extraskeletal parameters such as muscle mass and propensity to fall. Given the demographic trends of increased longevity and consequent rise of osteoporosis, an increased understanding of how sex steroids influence male bone health remains a high research priority.

Estrogen via estrogen receptor beta partially inhibits mandibular condylar cartilage growth

OBJECTIVE

Temporomandibular joint (TMJ) diseases predominantly afflict women, suggesting a role for female hormones in the disease process. However, little is known about the role of estrogen receptor (ER) signaling in regulating mandibular condylar cartilage growth. Therefore, the goal of this study was to examine the effects of altered estrogen levels on the mandibular condylar cartilage in wild type (WT) and ER beta Knockout (KO) mice.

MATERIALS AND METHODS

21-day-old female WT (n = 37) and ER beta KO mice (n = 36) were either sham operated or ovariectomized, and treated with either placebo or estradiol. The mandibular condylar cartilage was evaluated by histomorphometry, proliferation was analyzed by double ethynyl-2'-deoxyuridine/bromodeoxyuridine (EdU/BrdU) labeling, and assays on gene and protein expression of chondrocyte maturation markers were performed.

RESULTS

In WT mice, ovariectomy caused a significant increase in mandibular condylar cartilage cell numbers, a significant increase in Sox9 expression and a significant increase in proliferation compared with sham operated WT mice. In contrast, ovariectomy did not cause any of these effects in the ER beta KO mice. Estrogen replacement treatment in ovariectomized WT mice caused a significant decrease in ER alpha expression and a significant increase in Sost expression compared with ovariectomized mice treated with placebo. Estrogen replacement treatment in ovariectomized ER beta KO mice caused a significant increase in Col2 expression, no change in ER alpha expression, and a significant increase in Sost expression.

CONCLUSION

Estrogen via ER beta inhibits proliferation and ER alpha expression while estrogen independent of ER beta induces Col2 and Sost expression.

Urethral dysfunction in female mice with estrogen receptor β deficiency

Estrogen has various regulatory functions in the growth, development, and differentiation of the female urogenital system. This study investigated the roles of ERβ in stress urinary incontinence (SUI). Wild-type (ERβ^+/+) and knockout (ERβ^−/−) female mice were generated (aged 6–8 weeks, n = 6) and urethral function and protein expression were measured. Leak point pressures (LPP) and maximum urethral closure pressure (MUCP) were assessed in mice under urethane anesthesia. After the measurements, the urethras were removed for proteomic analysis using label-free quantitative proteomics by nano-liquid chromatography–mass spectrometry (LC-MS/MS) analysis. The interaction between these proteins was further analysed using MetaCore. Lastly, Western blot was used to confirm the candidate proteins. Compared with the ERβ^+/+ group, the LPP and MUCP values of the ERβ^−/− group were significantly decreased. Additionally, we identified 85 differentially expressed proteins in the urethra of ERβ^−/− female mice; 57 proteins were up-regulated and 28 were down-regulated. The majority of the ERβ knockout-modified proteins were involved in cell-matrix adhesion, metabolism, immune response, signal transduction, nuclear receptor translational regelation, and muscle contraction and development. Western blot confirmed the up-regulation of myosin and collagen in urethra. By contrast, elastin was down-regulated in the ERβ^−/− mice. This study is the first study to estimate protein expression changes in urethras from ERβ^−/− female mice. These changes could be related to the molecular mechanism of ERβ in SUI.

Expression of estrogen receptors α and β in the trigeminal mesencephalic nucleus of adult women and men

Temporomandibular disorders are more prevalent in women than in men and phases of pain relate to the estrous cycle. Several studies described the location of estrogen receptors (ER) in the temporomandibular joint (TMJ), the masseteric muscles and cartilage, but it was unknown whether they are also expressed within the pseudounipolar neurons of the trigeminal mesencephalic nucleus, which receives direct sensory inputs from these structures. Therefore, we studied expression of ERα and ERβ protein in the trigeminal mesencephalic nucleus of ten human brains (five female/five male). Both receptors were uniformly expressed on neurons, but not other cell types within the target structure. Thus, sensory inputs from the TMJ and adjacent structures are likely to be modulated by estrogen at the level of the first sensory neuron which may underlie the well-known correlation of pain incidence and phases of the estrous cycle.

Dose-dependent effect of estrogen suppresses the osteo-adipogenic transdifferentiation of osteoblasts via canonical Wnt signaling pathway

Fat infiltration within marrow cavity is one of multitudinous features of estrogen deficiency, which leads to a decline in bone formation functionality. The origin of this fat is unclear, but one possibility is that it is derived from osteoblasts, which transdifferentiate into adipocytes that produce bone marrow fat. We examined the dose-dependent effect of 17β-estradiol on the ability of MC3T3-E1 cells and murine bone marrow-derived mesenchymal stem cell (BMMSC)-derived osteoblasts to undergo osteo-adipogenic transdifferentiation. We found that 17β-estradiol significantly increased alkaline phosphatase activity (P<0.05); calcium deposition; and Alp, Col1a1, Runx2, and Ocn expression levels dose-dependently. By contrast, 17β-estradiol significantly decreased the number and size of lipid droplets, and Fabp4 and PPARγ expression levels during osteo-adipogenic transdifferentiation (P<0.05). Moreover, the expression levels of brown adipocyte markers (Myf5, Elovl3, and Cidea) and undifferentiated adipocyte markers (Dlk1, Gata2, and Wnt10b) were also affected by 17β-estradiol during osteo-adipogenic transdifferentiation. Western blotting and immunostaining further showed that canonical Wnt signaling can be activated by estrogen to exert its inhibitory effect of osteo-adipogenesis. This is the first study to demonstrate the dose-dependent effect of 17β-estradiol on the osteo-adipogenic transdifferentiation of MC3T3-E1 cells and BMMSCs likely via canonical Wnt signaling. In summary, our results indicate that osteo-adipogenic transdifferentiation modulated by canonical Wnt signaling pathway in bone metabolism may be a new explanation for the gradually increased bone marrow fat in estrogen-inefficient condition.

Estrogen aggravates iodoacetate-induced temporomandibular joint osteoarthritis

Temporomandibular joint osteoarthritis (TMJOA) is clinically characterized by female preponderance, with a female-to-male ratio of more than 2:1; however, the underlying mechanism remains obscure. We examined the effects of estrogen on TMJOA induced by monosodium iodoacetate. Female rats were randomly and equally divided into 5 groups: control, sham-ovariectomized, and ovariectomized rats treated, respectively, with 17β-estradiol (E2) at doses of 0 µg, 20 µg, and 80 µg/day until the end of the experiment. After induction of TMJOA, TMJs were evaluated by histopathology and microCT, and the expression of Fas, FasL, caspase 3, and caspase 8 was evaluated by real-time polymerase chain-reaction or immunohistochemistry. Another 5 groups of female rats were used to evaluate the effect of estrogen receptor antagonist ICI 182780 on E2 effects on TMJOA, when injected intraperitoneally into the control, sham-ovariectomized, and 80-µg-E2-treated groups. We found that E2 potentiated cartilage degradation and subchondral bone erosion in iodoacetate-induced TMJOA. E2 also potentiated mRNA expression of Fas, FasL, caspase 3, and caspase 8 in the condylar cartilage. Moreover, the estrogen receptor antagonist partially blocked E2 effects on TMJOA. These findings suggest that E2 could aggravate TMJOA, which may be an important mechanism underlying the sexual dimorphism of TMJOA.