Female hormone receptors are differentially expressed in mouse fibrocartilages

Sex diferences in serum and synovial fluid C-reactive protein concentration in healthy dogs

Differences between serum C-reactive protein (SCRP) and synovial fluid C-reactive protein (SFCRP) concentrations in healthy animals may be influenced by the sex of the individual and associated with various factors. The objective of this study was to evaluate the disparities in SCRP and SFCRP concentrations between females and males, as well as within each sex. Sixty healthy dogs (N = 60), comprising both sexes, were enrolled in the study. Peripheral blood and knee synovial fluid samples were collected for SCRP and SFCRP analysis, respectively. Serum C-reactive protein (SCRP) and SFCRP concentrations were measured, with mean of 9.61 ± 4.96 mg/L for SCRP and 1.28 ± 3.05 mg/L for SFCRP. Notably, SFCRP concentrations were consistently lower than SCRP concentrations in both sexes. Statistically significant differences were observed between sexes for both SCRP (P = 0.021) and SFCRP (P = 0.007). Further analysis within females revealed statistically significant differences between SCRP and SFCRP concentrations (P = 0.002), whereas in males, such differences were not significant (P = 0.175). Additionally, weak correlations were found between SCRP and SFCRP concentrations for both sexes (females r = 0.07; males r = 0.29). Joint capsule thickness was assessed using ultrasonography, revealing thicker joint capsules in males. A robust positive association was noted between joint capsule thickness and the SFCRP concentration in both sexes. These findings offer valuable insights into the dynamics of CRP in the context of joint health in male and female patients, elucidating the underlying pathological mechanisms of joint disease and inflammation. Overall, this underscores the importance of considering sex-specific factors in the assessment and management of joint health, as well as in the design and interpretation of studies involving SFCRP concentrations.

Assessment of Knee Menisci in Healthy Adults Using Shear Wave Elastography

OBJECTIVES

The aim of this study was to explore the application value of shear wave elastography in healthy adults with knee meniscus.

METHODS

One hundred adult subjects who underwent health checkups at our hospital from December 2022 to February 2023 were selected as research participants. Shear wave elastography was used to evaluate the periphery of the lateral and medial meniscus in both knees. To assess the mean differences in Young's modulus values between male and female groups, a one-way analysis of variance (ANOVA) and independent samples t-test were conducted. In addition, a Pearson correlation coefficient test was used to analyze the correlation between the elastic values of the meniscus and age, height, weight, and body mass index (BMI).

RESULTS

There were no significant differences in elastic values between the lateral meniscus of the left and right sides or between the medial meniscus of the left and right sides within the same gender group (P > .05). Stiffness values of the medial meniscus were higher in each gender group than those of the lateral meniscus (P < .01). Additionally, males demonstrated higher stiffness values than females (P < .01). As age increased, the Young's modulus of the meniscus increased significantly (r > .75, P < .01).

CONCLUSION

Shear wave elastography can serve as an adjunctive tool to aid in the assessment of knee meniscal elasticity.

Combination of hyperlipidemia and 17β-Estradiol induces TMJOA-like pathological changes in rats

OBJECTIVE

We explored whether hyperlipidemia or combination of hyperlipidemia and E2 could induce TMJOA.

MATERIALS AND METHODS

Four groups of female rats were treated with normal diet, normal diet with E2, high-fat diet, and high-fat diet with E2 (HFD/E2), respectively, to induce TMJOA till 8 weeks. Another three groups were then used for COX2 inhibitor celecoxib to block the induction of TMJOA. Primary condylar chondrocytes were treated with combination of E2, ox-LDL, and corresponding inhibitors for evaluating expressions of related molecules.

RESULTS

Condylar cartilage proliferation with plenty of chondrocyte apoptosis and increased staining for LOX1, nuclear NF-κB, IL-1β, and COX2 at 4 weeks and decreased condylar cartilage and increased subchondral bone density at 8 weeks were observed only in the HFD/E2 group. Celecoxib significantly alleviated the cartilage proliferation and apoptosis in the HFD/E2 group. Serum ox-LDL increased in both high-fat diet groups, while serum IL-1β increased only in the HFD/E2 group. Combination of E2 and ox-LDL synergistically induced expressions of LOX1, phosphorylated NF-κB, IL-1β, and COX2, while LOX1 inhibitor blocked the induction of phosphorylated NF-κB, and NF-κB inhibitor the induction of IL-1β, and IL-1β inhibitor the induction of COX2.

CONCLUSION

Combination of hyperlipidemia and E2-induced TMJOA-like pathological changes through LOX1/NF-κB/IL-1β/COX2-signaling pathway.

Immunohistochemical Markers of Temporomandibular Disorders: A Review of the Literature

Temporomandibular disorders (TMD) are a group of internal derangements encompassing dysfunction, displacement, degeneration of the temporomandibular joints and surroundings muscles of mastication, often accompanied by pain. Relationships between TMD and various chemical biomarkers have been examined throughout the years. This paper aims to gather evidence from the literature regarding other biomarkers and presenting them as one systematic review to investigate the potential links between TMD and different biochemical activity. To identify relevant papers, a comprehensive literature search was carried out in MEDLINE/PubMED, EMBASE, Web of Science and a manual search was performed in the International Journal of Oral and Maxillofacial Surgery, Journal of Oral and Maxillofacial surgery, and Journal of Cranio-Maxillo-Facial Surgery. The literature review produced extensive results relating to the biochemical and immunohistochemical markers of TMD. Many enzymes, inflammatory markers, proteoglycans, and hormones were identified and organized in tables, along with a brief description, study design, and conclusion of each study. Through this review, recurring evidence provides confidence in suggesting involvement of certain biomarkers that may be involved in this complex pathogenesis, in addition to pointing to differences in gender prevalence of TMD. However, more organized research on large human samples needs to be conducted to delve deeper into the understanding of how this disease develops and progresses.

Similarities and differences of estrogen in the regulation of temporomandibular joint osteoarthritis and knee osteoarthritis

BACKGROUND

Temporomandibular joint osteoarthritis (TMJOA) and knee osteoarthritis (knee OA) are two kinds of common osteoarthritis (OA) that are characterized by chronic degeneration of soft and hard tissues around joints. Their gender and age differences suggest that there are similarities and differences between the pathogenic mechanisms of TMJOA and knee OA.

OBJECTIVE

To review recent studies on the effect of estrogen on TMJOA and knee OA, and summarize their possible pathogenesis and molecular mechanisms.

SOURCES

Articles up to present reporting the relationship of estrogen and TMJOA or knee OA are included. An extensive electronic search was conducted of databases including PubMed, Web of science core collection.

CONCLUSION

According to epidemiological investigations, TMJOA primarily happens to females of puberty and childbearing age, while knee OA mainly affects postmenopausal women. Epidemiological investigation and experimental research suggest that estrogen may have a different effect on TMJ and on knee. Though estrogen regulates TMJOA and knee OA via estrogen-related receptors (ERR), their pathogenesis and pathway of estrogen regulation are different. To find out the accurate regulation of estrogen on TMJOA and knee OA, specific pathways and molecular mechanisms still need further exploration.

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.

WNT16 is upregulated early in mouse TMJ osteoarthritis and protects fibrochondrocytes against IL-1β induced inflammatory response by regulation of RUNX2/MMP13 cascade

WNT16 has been shown to play important roles in joint formation, bone homeostasis and knee joint osteoarthritis. However, whether WNT16 has any effect during temporomandibular joint osteoarthritis (TMJOA) is still unknown. Here, we first established a surgically induced TMJOA model by performing partial discectomy in discs of TMJ in mice. Further, we investigated the role of WNT16 during the initiation and progression of TMJOA. Our results showed that WNT16 expression is upregulated early at 4 weeks after initiation of osteoarthritis by partial discectomy in mouse TMJ cartilage, but decreased after 12 weeks post-surgery. Further cellular and molecular analyses revealed that WNT16 signals via both the canonical WNT/β-catenin and non-canonical WNT/JNK-cJUN pathways, upregulates the expression of Lubricin and SOX9, and protects against IL-1β induced inflammatory response by regulation of RUNX2/MMP13 cascade in fibrochondrocytes. In conclusion, WNT16 may play an important role in the early stage of TMJOA by regulating cartilage anabolic and catabolic factors, and may serve as novel therapeutic targets for TMJOA.

High susceptibility to collagen-induced arthritis in mice with progesterone receptors selectively inhibited in osteoprogenitor cells

Background

Progesterone receptor (PR) affects immunomodulation, and lack of PR in osteoprogenitor cells primarily affects pathways associated with immunomodulation, especially in males. In this study, we selectively deleted PR from osteoprogenitor cells using Prx1-Cre to evaluate the tissue-specific effects of PR on the pathegenesis of inflammatary arthritis (IA).

Methods

Collagen-induced arthritis (CIA) was used as an IA animal model. Both male and female PR^ΔPrx1 mice and their wild-type (WT) littermates were immunized with collagen II (CII) emulsified complete Freund’s adjuvant (CFA). Joint erosion, inflammation, and cartilage damage were assessed using a semiquantitative histologic scoring system. Bone volume and erosions in knee and ankle joints were quantitated using microCT and histology.

Results

Bone erosions developed in both paw joints in 37.5% and 41.7% of the WT and PR^ΔPrx1 female mice and in 45.4 and 83.3% of the WT and PR^ΔPrx1 male mice, respectively. Also, both joint damage and subchondral bone erosions were significantly more severe in male PRcKO-CIA mice than in male WT-CIA mice. Female PR^ΔPrx1 mice also developed higher bone loss in the knee joints than the KO-normal or WT-CIA females although with less severity compared to the male mice.

Conclusions

The presence of PR in osteoprogenitor cells decreased the development of collagen-induced arthritis and might help to explain the sex differences observed in human inflammatory arthritis.

Selective inhibition of progesterone receptor in osteochondral progenitor cells, but not in mature chondrocytes, modulated subchondral bone structures

OBJECTIVE

The presence or relative proportion of progesterone nuclear receptors (PR) in different tissues may contribute to sexual dimorphism in these tissues. PR is expressed in chondrocytes, but its function is mostly unknown. We hypothesized that the PR may regulate chondrocyte metabolism and affect subchondral bone structure.

METHODS

We utilized genetic fate mapping and immunohistochemistry to elucidate PR expression in and effect on cartilage. To define sex-dependent and chondrocyte-specific effects of the PR on subchondral bone, we selectively deleted PR in osteochondrogenic progenitor cells marked by Prx1 (Prx1; PRcKO) and Collagen 2 (Col2; PRcKO), or in matured chondrocytes marked by aggrecan (Acan; PRcKO) and evaluated subchondral bone structure at 4 months of age. Chondrocyte aging was monitored by anti-senescence marker p16INK4a, and MMP13, one of the Senescence-Associated Secretary Phenotype (SASP) components.

RESULTS

Compared to wild-type (WT) mice, the female Prx1; PRcKO and the Col2; PRcKO mice had greater total subchondral bone volume and greater subchondral cortical bone thickness, with increased estimated subchondral bone stiffness and failure load in both female and male Col2; PRcKO mice. Moreover, Col2; PRcKO mice from both sexes had greater bone formation and bone strength at the femurs. In contrast, we did not observe any subchondral bone changes in Acan; PRcKO mice other than higher work-to-failure observed in the male Acan; PRcKO mice. Despite no detected difference in articular cartilage between the WT and the PR; chondrocyte conditional deletion mice, there were greater numbers of senescent chondrocytes and increased MMP13 expression, especially in the male mutant mice.

CONCLUSION

These findings suggest that selective inhibition of PR in osteoprogenitor cells, but not in terminally differentiated chondrocytes, induced an increased subchondral bone phenotype and high estimated subchondral bone strength, which might be associated with the development of osteoarthritis in older age.

Emerging Potential of Exosomes in Regenerative Medicine for Temporomandibular Joint Osteoarthritis

Exosomes are nanosized vesicles (30–140 nm) of endocytic origin that play important roles in regenerative medicine. They are derived from cell membranes during endocytic internalization and stabilize in biological fluids such as blood and synovia. Temporomandibular joint osteoarthritis (TMJ OA) is a degenerative disease, which, in addition to chronic pain, is characterized by progressive cartilage breakdown, condylar bone remodeling, and synovitis. However, traditional clinical treatments have limited symptom- and structure-modifying effects to restore damaged cartilage and other TMJ tissues. This is due to the limited self-healing capacity of condylar cartilage. Recently, stem-cell-derived exosomes have been studied as an alternative therapeutic approach to tissue repair and regeneration. It is known that trophic regulation of mesenchymal stem cells (MSCs) has anti-inflammatory and immunomodulatory effects under pathological conditions, and research on MSC-derived exosomes is rapidly accumulating. MSC-derived exosomes mimic the major therapeutic effects of MSCs. They affect the activity of immune effector cells and possess multilineage differentiation potential, including chondrogenic and osteogenic differentiation. Furthermore, exosomes are capable of regenerating cartilage or osseous compartments and restoring injured tissues and can treat dysfunction and pain caused by TMJ OA. In this review, we looked at the uniqueness of TMJ, the pathogenesis of TMJ OA, and the potential role of MSC-derived exosomes for TMJ cartilage and bone regeneration.

Estrogen Selectively Enhances TMJ Disc but Not Knee Meniscus Matrix Loss

The preponderance of temporomandibular joint (TMJ) degenerative disorders in women and their early onset during reproductive years have implicated female sex hormones, particularly 17-β estradiol (E2), in the pathogenesis of these disorders. Nevertheless, the mechanisms by which E2 contributes to TMJ degenerative disorders and the reasons for its targeted effects on the TMJ but not other joints remain poorly understood. Here, we developed an ovariectomized mouse model in which systemic E2 concentrations mimicked those in cycling women, and we determined the effect of E2 on the targeted turnover of TMJ fibrocartilage matrix via E2-induced matrix metalloproteinases MMP9 and MMP13. Infusion of E2 and progesterone (P4; hormone control) over 7 d resulted in 5- and 8-fold greater serum E2 and P4 levels relative to controls, respectively, achieving systemic hormone levels similar to high baseline levels in cycling women. Administration of E2 but not P4 caused a significant loss of TMJ collagen and glycosaminoglycans, which was accompanied by amplification of ERα and specific increases in MMP9 and MMP13 expression. This dose of E2 had no effect on knee meniscus fibrocartilage, demonstrating the specificity of the degradative effect of E2. Dose-response experiments showed a greater sensitivity and a higher peak induction of MMP9 and MMP13 in TMJ fibrocartilaginous cells than knee meniscus cells to E2, providing an explanation for the differential responses of these tissues to E2. Using MMP9- and MMP13-null mice, we observed no discernible effects of each proteinase individually to E2-mediated TMJ matrix loss but noted a significant compensatory reciprocal induction of each MMP by E2 in the absence of the other. The redundancy in E2's induction of MMP9 and MMP13 suggests that the proteinases may together contribute to E2-mediated TMJ fibrocartilage loss. These results advance our understanding of E2-mediated upregulation of MMP9 and MMP13 on fibrocartilage matrix turnover targeted to the TMJ.

Relaxin inhibits patellar tendon healing in rats: a histological and biochemical evaluation

BACKGROUND

Female patients are more likely to have tendon injuries than males, especially those who has a higher concentration of relaxin. Previous studies have demonstrated that relaxin attenuates extracellular matrix (ECM) formation. However, the mechanism of relaxin on tendon repair remains unclear. We hypothesize that relaxin inhibits tendon healing by disrupting collagen synthesis.

METHODS

A patellar tendon window defect model was established using Sprague-Dawley rats. The center of the patellar tendon was removed from the patella distal apex and inserted to the tibia tuberosity in width of 1 mm. Then, the rats were injected with saline (0.2 μg/kg/day) or relaxin (0.2 μg/kg/day) for two and four weeks, which was followed by biomechanical analysis and histological and histochemical examination.

RESULTS

Mechanical results indicated that relaxin induces a significant decrease in tear resistance, stiffness, and Young's modulus compared to those rats without relaxin treatment. In addition, it was shown that relaxin activates relaxin family peptide receptor 1(RXFP1), disturbs the balance between matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteases (TIMPs), and reduces the deposition of collagen in injury areas.

CONCLUSIONS

Relaxin impairs tendon healing in rats. Also, relaxin might lead to tendon injury more commonly for females than males.

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.

Prevalence of chondrocalcinosis in a Mexican tertiary care institution of musculoskeletal disorders

INTRODUCTION/OBJECTIVES

The prevalence of chondrocalcinosis (CC) was reported as variable according to the geographic populations. However, there are no data regarding its prevalence in Mexico. Thus, we decided to investigate the Mexican prevalence of CC in a cohort of patients from a tertiary health care institution.

METHODS

A retrospective analysis of radiographs of knees and wrists from our institution was performed. Inclusion criteria included patients > 50 years old having radiographs of knees and wrists. Radiographic presence of CC was classified according to a dichotomous evaluation assayed by two rheumatologists experts on the area.

RESULTS

A total of 3.350 radiographs from 1.602 patients were evaluated. Forty-seven patients showed calcifications in at least one knee or wrist for an overall prevalence of 3%, of which 23.4% were men and 76.6% women. The knee was more commonly affected than the wrist (85.1% and 14.9% respectively). The prevalence according to gender was 2.9% in women, whereas, it was 3.2% in men. Only two patients (4.3%) showed a contemporaneous presence of CC in both hands and both knees. At knee level, the prevalence was 2.7%, whereas at the wrist, we reported a prevalence of 4.9%.

CONCLUSIONS

The prevalence of CC for Mexican population had not been reported so far. This a starting point to break the silence and encourage the knowledge of how this disease is associated with possible risk factors in Mexican population. Key Points •The prevalence of chondrocalcinosis in Mexico was 3%. •The prevalence of knee chondrocalcinosis increases according to the age in women's. •The nixtamalized meals could be a protective factor for CC in Mexican population.

Sexual dimorphism of estrogen-sensitized synoviocytes contributes to gender difference in temporomandibular joint osteoarthritis

OBJECTIVES

Temporomandibular joint osteoarthritis (TMJOA) is approximately twice as prevalent in women than in men. Synoviocytes are believed to play a critical role in joint inflammation. However, it is unknown whether synoviocytes from different genders possess sexual dimorphisms that contribute to female-predominant TMJOA.

MATERIALS AND METHODS

Freund's complete adjuvant combined with monosodium iodoacetate was used to induce TMJOA in female and male rats. Histologic and radiographic features were used to evaluate TMJOA. The expression of CD68, MCP-1, iNOS, and IL-1β was detected by immunohistochemistry and real-time PCR. Primary fibroblast-like synoviocytes (FLSs) isolated from the synovial membrane of female and male rats were used for in vitro experiments.

RESULTS

Female rats showed aggravated TMJOA features as compared to male rats. Increased expression of iNOS and IL-1β was detected in synovial membrane from female TMJOA rats as compared to male rats. Furthermore, greater amounts of CD68-positive macrophage infiltration and increased MCP-1 expression around the synovial membrane were detected in female TMJOA rats compared to males. Primary cultured FLSs from female rats showed higher sensitivity to TNF-α treatment and recruited increased macrophage migration than male FLSs. More important, ovariectomy (OVX) by ablation in female rats repressed the sensitivity of female FLSs to TNF-α treatment due to the loss of estrogen production. Blockage of the estrogen receptor repressed estrogen-potentiated TNF-α-induced pro-inflammatory cytokine expression in OVX-FLSs. Moreover, the injection of estrogen receptor antagonists relieved the cartilage destruction and bone deterioration of TMJOA in female rats.

CONCLUSION

Estrogen-sensitized synoviocytes in female rats may contribute to gender differences in the incidence and progression of TMJOA.

Time-dependent regulation of morphological changes and cartilage differentiation markers in the mouse pubic symphysis during pregnancy and postpartum recovery

Animal models commonly serve as a bridge between in vitro experiments and clinical applications; however, few physiological processes in adult animals are sufficient to serve as proof-of-concept models for cartilage regeneration. Intriguingly, some rodents, such as young adult mice, undergo physiological connective tissue modifications to birth canal elements such as the pubic symphysis during pregnancy; therefore, we investigated whether the differential expression of cartilage differentiation markers is associated with cartilaginous tissue morphological modifications during these changes. Our results showed that osteochondral progenitor cells expressing Runx2, Sox9, Col2a1 and Dcx at the non-pregnant pubic symphysis proliferated and differentiated throughout pregnancy, giving rise to a complex osteoligamentous junction that attached the interpubic ligament to the pubic bones until labour occurred. After delivery, the recovery of pubic symphysis cartilaginous tissues was improved by the time-dependent expression of these chondrocytic lineage markers at the osteoligamentous junction. This process potentially recapitulates embryologic chondrocytic differentiation to successfully recover hyaline cartilaginous pads at 10 days postpartum. Therefore, we propose that this physiological phenomenon represents a proof-of-concept model for investigating the mechanisms involved in cartilage restoration in adult animals.

17β-estradiol Induces MMP-9 and MMP-13 in TMJ Fibrochondrocytes via Estrogen Receptor α

Temporomandibular joint (TMJ) disorders, including degenerative TMJ disease, occur primarily in women of reproductive age. Previous studies showed elevated estrogen levels in subjects with TMJ disorders relative to controls and the presence of estrogen receptors α and β (ERα and ERβ) in TMJ fibrocartilage. Additionally, estrogen-induced overexpression of specific matrix metalloproteinases (MMPs), including MMP-9 and MMP-13, in TMJ fibrocartilage is accompanied by loss of extracellular matrices. However, the contribution of ERα and ERβ in estrogen-mediated induction of MMP-9 and MMP-13 and the signaling cascade leading to the upregulation of these MMPs have not been elucidated. Here, we show that specific siRNAs and selective ER antagonists effectively block ERα or ERβ expression in primary mouse TMJ fibrochondrocytes, but that only blockage of ERα suppresses MMP-9 and MMP-13 levels induced by 17β-estradiol (E2). Overexpression of ERα but not ERβ enhances E2-induced MMP-9. Using the same loss-of-function and gain-of-function approaches, we demonstrate that E2 stimulates ERK activation through ERα and that inhibition of ERK phosphorylation reduces E2-induced MMP-9. Furthermore, we reveal that E2 promotes NF-κB and ELK-1 activation through ERα/ERK signaling and that knockdown of either one decreases the respective activity of these signaling mediators and MMP-9 expression induced by E2, indicating that both contribute to E2/ERα/ERK-mediated MMP-9 upregulation. This is supported by findings in which mutated binding sites of either NF-κB or ELK-1 in the MMP-9 promoter lead to a significant reduction of E2-stimulated promoter activity. Our findings provide novel molecular mechanisms for the understanding of E2-mediated upregulation of MMPs, having implications to pathophysiologic TMJ cartilage matrix turnover that may yield therapeutic intervention targets for TMJ disorders.

Close pathological correlations between chronic kidney disease and reproductive organ-associated abnormalities in female cotton rats

Cotton rat ( Sigmodon hispidus) is a useful experimental rodent for the study of human infectious diseases. We previously clarified that cotton rats, particularly females, developed chronic kidney disease characterized by cystic lesions, inflammation, and fibrosis. The present study investigated female-associated factors for chronic kidney disease development in cotton rats. Notably, female cotton rats developed separation of the pelvic symphysis and hypertrophy in the vaginal parts of the cervix with age, which strongly associated with pyometra. The development of pyometra closely associated with the deterioration of renal dysfunction or immunological abnormalities was indicated by blood urea nitrogen and serum creatinine or spleen weight and serum albumin/globulin ratio, respectively. These parameters for renal dysfunction and immunological abnormalities were statistically correlated. These phenotypes found in the female reproductive organs were completely inhibited by ovariectomy. Further, the female cotton rats with pyometra tended to show more severe chronic kidney disease phenotypes and immunological abnormalities than those without pyometra; these changes were inhibited in ovariectomized cotton rats. With regard to renal histopathology, cystic lesions, inflammation, and fibrosis were ameliorated by ovariectomy. Notably, the immunostaining intensity of estrogen receptor α and estrogen receptor β were weak in the healthy kidneys, but both estrogen receptors were strongly induced in the renal tubules showing cystic changes. In conclusion, the close correlations among female reproductive organ-associated abnormalities, immunological abnormalities, and renal dysfunction characterize the chronic kidney disease features of female cotton rats. Thus, the cotton rat is a unique rodent model to elucidate the pathological crosstalk between chronic kidney disease and sex-related factors. Impact statement The increasing number of elderly individuals in the overall population has led to a concomitant age-related increase in chronic kidney disease. Moreover, the global prevalence of patients with chronic kidney disease is gradually increasing, which poses a serious public health problem. The limited number of spontaneous chronic kidney disease animal models, which resemble chronic kidney disease pathogenesis in elderly individuals, is a major limitation in the development of experimental and curative medicines for chronic kidney disease. This pathological study clarified that sex-related factors, including hormones, and abnormalities of the female reproductive system, such as pyometra, are closely associated with chronic kidney disease development by using cotton rats ( Sigmodon hispidus). Further, ovariectomy inhibited the phenotypes of the female reproductive system, immunological abnormalities, and chronic kidney disease. Thus, this laboratory rodent serves as a novel and useful spontaneous chronic kidney disease model to elucidate the candidate disease factors and the pathogenesis of chronic kidney disease both in human and experimental medicine.

Immortalization and characterization of mouse temporomandibular joint disc cell clones with capacity for multi-lineage differentiation

OBJECTIVE

Despite the importance of temporomandibular joint (TMJ) disc in normal function and disease, studying the responses of its cells has been complicated by the lack of adequate characterization of the cell subtypes. The purpose of our investigation was to immortalize, clone, characterize and determine the multi-lineage potential of mouse TMJ disc cells.

DESIGN

Cells from 12-week-old female mice were cultured and immortalized by stable transfection with human telomerase reverse transcriptase (hTERT). The immortalized cell clones were phenotyped for fibroblast- or chondrocyte-like characteristics and ability to undergo adipocytic, osteoblastic and chondrocytic differentiation.

RESULTS

Of 36 isolated clones, four demonstrated successful immortalization and maintenance of stable protein expression for up to 50 passages. Two clones each were initially characterized as fibroblast-like and chondrocyte-like on the basis of cell morphology and growth rate. Further the chondrocyte-like clones had higher mRNA expression levels of cartilage oligomeric matrix protein (COMP) (>3.5-fold), collagen X (>11-fold), collagen II expression (2-fold) and collagen II:I ratio than the fibroblast-like clones. In contrast, the fibroblast-like clones had higher mRNA expression level of vimentin (>1.5-fold), and fibroblastic specific protein 1 (>2.5-fold) than the chondrocyte-like clones. Both cell types retained multi-lineage potential as demonstrated by their capacity to undergo robust adipogenic, osteogenic and chondrogenic differentiation.

CONCLUSIONS

These studies are the first to immortalize TMJ disc cells and characterize chondrocyte-like and fibroblast-like clones with retained multi-differentiation potential that would be a valuable resource in studies to dissect the behavior of specific cell types in health and disease and for tissue engineering.

Sex-steroid regulation of relaxin receptor isoforms (RXFP1 & RXFP2) expression in the patellar tendon and lateral collateral ligament of female WKY rats

The incidence of non-contact knee injury was found higher in female than in male and is related to the phases of the menstrual cycle. This raised the possibility that female sex-steroids are involved in the mechanism underlying this injury via affecting the expression of the receptors for relaxin, a peptide hormone known to modulate ligament laxity. Therefore, this study aims to investigate the effect of sex-steroids on relaxin receptor isoforms (RXFP1 & RXFP2) expression in the ligaments and tendons of the knee.

METHODS

Ovariectomized adult female WKY rats were treated with different doses of estrogen (0.2, 2, 20 μg/kg), progesterone (4mg) and testosterone (125 & 250μg/kg) for three consecutive days. At the end of the treatment, the animals were sacrificed and the patellar tendon and lateral collateral ligament were harvested for mRNA and protein expression analyses by Real Time PCR and Western blotting respectively.

RESULTS

RXFP1, the main isoform expressed in these knee structures and RXFP2 showed a dose-dependent increase in expression with estrogen. Progesterone treatment resulted in an increase while testosterone caused a dose-dependent decrease in the mRNA and protein expression of both relaxin receptor isoforms.

DISCUSSION

Progesterone and high dose estrogen up-regulate while testosterone down-regulates RXFP1 and RXFP2 expression in the patellar tendon and lateral collateral ligament of rat's knee.

CONCLUSION

Relaxin receptor isoforms up-regulation by progesterone and high dose estrogen could provide the basis for the reported increase in knee laxity while down-regulation of these receptor isoforms by testosterone could explain low incidence of non-contact knee injury in male.

The effect of relaxin on the musculoskeletal system

Relaxin is a hormone structurally related to insulin and insulin-like growth factor, which exerts its regulatory effect on the musculoskeletal and other systems through binding to its receptor in various tissues, mediated by different signaling pathways. Relaxin alters the properties of cartilage and tendon by activating collagenase. This hormone is also involved in bone remodeling and healing of injured ligaments and skeletal muscle. In this review, we have summarized the literature on the effect of relaxin in musculoskeletal system to provide a broad perspective for future studies in this field.

Hormonal contraception and pelvic girdle pain during pregnancy: a population study of 91,721 pregnancies in the Norwegian Mother and Child Cohort

STUDY QUESTION

Is pre-pregnancy hormonal contraception use associated with the development of pelvic girdle pain during pregnancy?

SUMMARY ANSWER

In contrast to combined oral contraceptive pills, long lifetime exposure to progestin-only contraceptive pills or the use of a progestin intrauterine device during the final year before pregnancy were associated with pelvic girdle pain.

WHAT IS ALREADY KNOWN

Pelvic girdle pain severely affects many women during pregnancy. Smaller studies have suggested that hormonal contraceptive use is involved in the underlying mechanisms, but evidence is inconclusive.

STUDY DESIGN, SIZE, DURATION

A population study during the years 1999-2008.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A total of 91,721 pregnancies included in the Norwegian Mother and Child Cohort Study. Data were obtained by two self-administered questionnaires during pregnancy weeks 17 and 30.

MAIN RESULTS AND THE ROLE OF CHANCE

Pelvic girdle pain was present in 12.9% of women who had used combined oral contraceptive pills during the last pre-pregnancy year, 16.4% of women who had used progestin-only contraceptive pills, 16.7% of women who had progestin injections and 20.7% of women who had used progestin intrauterine devices, compared with 15.3% of women who did not report use of hormonal contraceptives. After adjustment for other study factors, the use of a progestin intrauterine device was the only factor based on the preceding year associated with pelvic girdle pain [adjusted odds ratios (OR) 1.20; 95% confidence interval (CI): 1.11-1.31]. Long lifetime exposure to progestin-only contraceptive pills was also associated with pelvic girdle pain (adjusted OR 1.49; 95% CI: 1.01-2.20).

LIMITATIONS, REASONS FOR CAUTION

The participation rate was 38.5%. However, a recent study on the potential biases of skewed selection in the Norwegian Mother and Child Cohort Study found the prevalence estimates but not the exposure-outcome associations to be influenced by the selection.

WIDER IMPLICATIONS OF THE FINDINGS

The results suggest that combined oral contraceptives can be used without fear of developing pelvic girdle pain during pregnancy. However, the influence of progestin intrauterine devices and long-term exposure to progestin-only contraceptive pills requires further study.

STUDY FUNDING/COMPETING INTEREST(S)

The present study was supported by the Norwegian Research Council. None of the authors has a conflict of interest.

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.

Relaxin induces matrix-metalloproteinases-9 and -13 via RXFP1: induction of MMP-9 involves the PI3K, ERK, Akt and PKC-ζ pathways

We determined the precise role of relaxin family peptide (RXFP) receptors-1 and -2 in the regulation of MMP-9 and -13 by relaxin, and delineated the signaling cascade that contributes to relaxin's modulation of MMP-9 in fibrocartilaginous cells. Relaxin treatment of cells in which RXFP1 was silenced resulted in diminished induction of MMP-9 and -13 by relaxin, whereas overexpression of RXFP1 potentiated the relaxin-induced expression of these proteinases. Suppression or overexpression of RXFP2 resulted in no changes in the relaxin-induced MMP-9 and -13. Studies using chemical inhibitors and siRNAs to signaling molecules showed that PI3K, Akt, ERK and PKC-ζ and the transcription factors Elk-1, c-fos and, to a lesser extent, NF-κB are involved in relaxin's induction of MMP-9. Our findings provide the first characterization of signaling cascade involved in the regulation of any MMP by relaxin and offer mechanistic insights on how relaxin likely mediates extracellular matrix turnover.

Temporal changes in matrix metalloproteinases, their inhibitors, and cathepsins in mouse pubic symphysis during pregnancy and postpartum

Remodeling and relaxation of the mouse pubic symphysis (PS) are central events in parturition. The involvement of endogenous proteins such as matrix metalloproteinases (MMPs), tissue inhibitors of matrix metalloproteinases (TIMPs), and cathepsins in these phenomena remains unclear. In this work, we used a combination of immunolocalization, protein expression/activity, and relative messenger RNA (mRNA) expression to examine the changes in selected MMPs (-2, -9, and -8), TIMPs (-1 and -2), and cathepsins (B and K) during pregnancy and postpartum in mice. Immunohistochemistry revealed the presence of all of these proteins in the cytoplasm of chondrocytes, fibrochondrocytes, and fibroblast-like cells in the interpubic tissues. Zymography showed increases in the active forms of MMP-2 and -9 primarily on days 15 to 19 of pregnancy. Western blotting showed enhanced expression of MMP-8 on days 12 to 15 of pregnancy, with no changes in cathepsins B and K. Matrix metalloproteinases 2, TIMP-1 and -2, and cathepsin B had significant relative gene expression throughout pregnancy. These findings indicate that during pregnancy and postpartum there are variations in the expression and activity of proteins that may have an important role in remodeling the pubic symphysis during these events.

High iNOS mRNA and protein localization during late pregnancy suggest a role for nitric oxide in mouse pubic symphysis relaxation

Remodeling and relaxation of the mouse pubic symphysis (PS) are central events in parturition. The mouse PS remodels in a hormone-controlled process that involves the modification of the fibrocartilage into an interpubic ligament (IpL), followed by its relaxation prior to parturition. It is recognized that nitric oxide synthase (NOS) and consequently nitric oxide (NO) generation play important roles in extracellular matrix modification, and may promote cytoskeleton changes that contribute to the remodeling of connective tissue, which precedes the onset of labor. To our knowledge, no studies thus far have investigated inducible nitric oxide synthase (iNOS) expression, protein localization, and NO generation in the mouse PS during pregnancy. In this work, we used a combination of the immunolocalization of iNOS, its relative mRNA expression, and NO production to examine the possible involvement of iNOS in remodeling and relaxation of the mouse IpL during late pregnancy. The presence of iNOS was observed in chondrocytes and fibroblast-like cells in the interpubic tissues. In addition, iNOS mRNA and NO production were higher during preterm labor on Day 19 of pregnancy (D19) than NO production on D18 or in virgin groups. The significant increase in iNOS mRNA expression and NO generation from the partially relaxed IpL at D18 to the completely relaxed IpL at D19 may indicate that NO plays an important role in late pregnancy during relaxation of the mouse IpL.

Relaxin and gonadal steroid receptors in uterosacral ligaments of women with and without pelvic organ prolapse

INTRODUCTION AND HYPOTHESIS

This study evaluates the expression of estrogen receptor isoforms alpha (ERα) and beta (ERβ), progesterone receptor (PR), and relaxin receptor isoforms 1 and 2 (LGR7, LGR8) in uterosacral ligament (USL) tissue of women with pelvic organ prolapse and controls.

METHODS

Tissue samples of USL from women with and without pelvic organ prolapse (POP) were subjected to immunohistochemistry against ERα, ERβ, PR, and LGR7 proteins. The respective mRNA expression as well as of LGR8 was assessed by quantitative real-time polymerase chain reaction.

RESULTS

The cellular distribution of the receptor proteins was different due to cell types, independent of POP: ERα and PR were found in smooth muscle cells, but not in endothelial cells, whereas ERβ was found in endothelial cells, but not in connective tissue. ERα, ERβ, PR, and LGR7 mRNAs could be detected in all patients of both groups. ERα mRNA expression was significantly and ERβ mRNA borderline significantly higher in USL of patients with POP: ERα: p < 0.001, ERβ: p = 0.057.

CONCLUSIONS

Enhanced effects of estrogen via altered mRNA expression patterns of ERα and ERβ--but not those of progesterone--may exist in USL of patients affected by POP. A local effect of relaxin needs to be further clarified because of this first report of prevalent ligamental expression of LGR7.

Sex differences in chondrocyte maturation in the mandibular condyle from a decreased occlusal loading model

Temporomandibular joint disorders (TMDs) predominantly afflict women of childbearing age. Defects in mechanical loading-induced temporomandibular joint (TMJ) remodeling are believed to be a major etiological factor in the development of TMD. The goal of this study was to determine if there are sex differences in CD-1 and C57BL/6 mice exposed to a decreased occlusal loading TMJ remodeling model. Male and female CD-1 and C57BL/6 mice, 21 days old, were each divided into two groups. They were fed either a normal pellet diet (normal loading) or a soft diet and had their incisors trimmed out of occlusion (decreased occlusal loading) for 4 weeks. The mandibular condylar cartilage was evaluated by histology, and the subchondral bone was evaluated by micro-CT analysis. Gene expression from both was evaluated by real-time PCR analysis. In both strains and sexes of mice, decreased occlusal loading caused similar effects in the subchondral bone, decreases in bone volume and total volume compared with their normal loading controls. However, in both strains, decreased occlusal loading caused a significant decrease in the expression of collagen type II (Col2) and Sox9 only in female mice, but not in male mice, compared with their normal loading controls. Decreased occlusal loading causes decreased bone volume in both sexes and a decrease in early chondrocyte maturation exclusively in female mice.

Impaired bone healing pattern in mice with ovariectomy-induced osteoporosis: A drill-hole defect model

OBJECTIVE

To establish a drill-hole defect model in osteoporotic mouse femur by comparing temporal cortical bone healing pattern between OVX-induced osteoporotic bone and sham-operated bone.

METHODS

3-month-old female C57BL/6 mice were randomly divided into an ovariectomy group (OVX) and a sham-operated group (Sham). At 6 weeks post-surgery, 7 mice from each group were sacrificed to examine the distal femur and femoral shaft by both micro-CT and mechanical testing for confirming established osteoporosis induced by OVX. In the remaining mice, a cortical bone defect 0.8mm in diameter was created on the mid-diaphysis of the right femur. The local repair process at days 0, 3, 7, 10, 14 and 21 after creation of the drill-hole was in vivo monitored by high-resolution micro-CT scanning. At each time point, each animal was scanned four times and was removed from the scanner between scans to determine reproducibility. Mice were sacrificed at each time point (n=12 at days 0, 3, 7, 10 and 14; n=20 at day 21). Before sacrifice, sera were collected to examine expression of bone formation marker P1NP (procollagen type I N-terminal propeptide) and bone resorption marker CTX (C-terminal telopeptide of type I collagen). After sacrifice, callus samples were collected and subjected to the following analyses: micro-CT-based angiography; histological examination; immunohistochemical staining to determine estrogen receptor expression; quantitative real-time PCR analysis of collagen type I, collagen type II, collagen type X, osteocalcin, tartrate-resistant acid phosphatase, estrogen receptor alpha (ER alpha) and estrogen receptor beta (ER beta) gene expression; and three-point mechanical testing.

RESULTS

At 6 weeks post-surgery, OVX mice had significantly lower bone mass, impaired bone micro architecture and compromised mechanical properties compared to the Sham mice. In vivo micro-CT analysis revealed that the bone volume fraction in the defect region was significantly lower in the OVX group from day 10 to day 21 post-injury as compared to the Sham group, and was significantly lower in the intra-medulla region in the OVX group from day 7 to day 14 as compared to the Sham group, consistent with the histological data. Analysis of bone biochemical markers indicated that circulating P1NP levels normalized by baseline in the OVX mice were significantly lower than in the Sham mice from day 7 to day 10, and that temporal expression of circulating CTX levels normalized by baseline was also lower in the OVX mice as compared to the Sham mice. These results were consistent with quantitative real-time PCR analysis. ER alpha mRNA expression was significantly lower in the OVX mice, whereas ER beta mRNA expression was significantly higher in the OVX mice as compared to the Sham mice at all time points examined, consistent with immunohistochemical staining. The restoration of femoral mechanical property, determined based on ultimate load and energy-to-failure, was significantly lower in the OVX mice than in the Sham mice. In addition, in vivo micro-CT scanning for quantifying new bone formation in the defect site was highly reproducible in this model.

CONCLUSION

The bone healing of the drill-hole defect was impaired in mice with OVX-induced osteoporosis. The present study provides a model to investigate the functional role of specific gene in osteoporotic bone healing and may facilitate development of novel therapeutic strategies for promoting osteoporotic bone healing.

Effects of relaxin and estrogens on bone remodeling markers, receptor activator of NF-kB ligand (RANKL) and osteoprotegerin (OPG), in rat adjuvant-induced arthritis

Rheumatoid arthritis (RA) is characterized by joint inflammation and bone destruction. The receptor activator of nuclear factor-kappa B ligand (RANKL)-osteoprotegerin (OPG) system is important for maintaining the balance between bone resorption and formation. Both serum RANKL/OPG protein and synovial tissue RANKL/OPG mRNA ratios are elevated in patients with RA. Studies indicate that hormones of pregnancy, estrogens and relaxin, administered in combination, reduce circulating (TNF)-α and joint inflammation in a rat adjuvant-induced arthritis (AIA) model of RA. The purpose of this study was to investigate whether relaxin (RLX), alone or in combination with estrogens, regulates the bone remodeling markers RANKL and OPG in vivo and in vitro. Results show that in AIA rats, treatment with relaxin, estradiol valerate (EV) or EV in combination with relaxin had no effect on circulating RANKL. However, EV increased systemic OPG and combined treatment with EV and relaxin further increased circulating OPG in comparison to EV alone. Importantly, the RANKL/OPG protein ratio was lower in rats treated with EV or EV+RLX when compared to arthritic controls. Relaxin in combination with EV decreased local RANKL transcripts, increased OPG mRNA and decreased the RANKL/OPG mRNA ratio in joints of arthritic rats when compared to controls. RLX family peptide receptor 1 (RXFP1) gene expression in joints of AIA rats increased in response to EV and EV+RLX. In parathyroid hormone-pretreated murine UMR 106-01 osteoblast cells, 17-β-estradiol (E) and E+RLX increased RXFP1 transcripts, while RLX reduced RANKL mRNA and protein expression. However, in vitamin D-treated primary rat osteoblast cells E+RLX increased OPG protein and reduced the RANKL/OPG protein ratio. These results suggest that modulation of the RANKL-OPG system by estrogens and RLX may contribute to their antiarthritic effects on bone during pregnancy.

Neurobiology of estrogen status in deep craniofacial pain

Pain in the temporomandibular joint (TMJ) region often occurs with no overt signs of injury or inflammation. Although the etiology of TMJ-related pain may involve multiple factors, one likely risk factor is female gender or estrogen status. Evidence is reviewed from human and animal studies, supporting the proposition that estrogen status acts peripherally or centrally to influence TMJ nociceptive processing. A new model termed the "TMJ pain matrix" is proposed as critical for the initial integration of TMJ-related sensory signals in the lower brainstem that is both modified by estrogen status, and closely linked to endogenous pain and autonomic control pathways.

The adult human pubic symphysis: a systematic review

The pubic symphysis is a unique joint consisting of a fibrocartilaginous disc sandwiched between the articular surfaces of the pubic bones. It resists tensile, shearing and compressive forces and is capable of a small amount of movement under physiological conditions in most adults (up to 2 mm shift and 1° rotation). During pregnancy, circulating hormones such as relaxin induce resorption of the symphyseal margins and structural changes in the fibrocartilaginous disc, increasing symphyseal width and mobility. This systematic review of the English, German and French literature focuses on the normal anatomy of the adult human pubic symphysis. Although scientific studies of the joint have yielded useful descriptive data, comparison of results is hampered by imprecise methodology and/or poorly controlled studies. Several aspects of the anatomy of the pubic symphysis remain unknown or unclear: the precise attachments of surrounding ligaments and muscles; the arrangement of connective tissue fibres within the interpubic disc and the origin, structure and function of its associated interpubic cleft; the biomechanical consequences of sexual dimorphism; potential ethnic variations in morphology; and its precise innervation and blood supply. These deficiencies hinder our understanding of the normal form and function of the joint, which is particularly relevant when attempting to understand the mechanisms underlying pregnancy-related pubic symphyseal pain, a neglected and relatively common cause of pubic pain. A better understanding of the normal anatomy of the human pubic symphysis should improve our understanding of such problems and contribute to better treatments for patients suffering from symphyseal pain and dysfunction.

Matrix metalloproteinase induction by relaxin causes cartilage matrix degradation in target synovial joints

Our long-term goal is to understand the mechanisms by which relaxin and estrogen potentially contribute to joint diseases, particularly those afflicting the fibrocartilaginous temporomandibular joint (TMJ). Previously, we showed that relaxin produces a dose-dependent induction of tissue-degrading enzymes of the matrix metalloproteinase (MMP) family, specifically MMP-1 (collagenase-1), MMP-3 (stromelysin-1), MMP-9 (92-kDa gelatinase), and MMP-13 (collagenase-3) in cell isolates and tissue explants from TMJ fibrocartilage. The induction of these MMPs is accompanied by loss of collagen and glycosaminoglycans (GAGs), which was blocked by a pan-MMP inhibitor. We also found the targeted in vivo loss of collagen and GAGs in TMJ discs of ovariectomized rabbits treated with beta-estradiol, relaxin, or both hormones together. Progesterone attenuated the induction of MMPs and matrix loss by relaxin and estrogen. The modulation of matrix composition in TMJ fibrocartilage by these hormones was similar to that observed in the pubic symphysis and differed from that of the knee meniscus. The two target tissues showing the greatest modulation of MMPs and matrix loss, namely, the TMJ disc and pubic symphysis, had similar expression profiles of the estrogen receptors alpha and beta, relaxin-1 receptor (RXFP1, LGR7), and insulin-like peptide 3 receptor (RXFP2, LGR8) and these profiles differed from those in cells from the knee meniscus. These findings suggest a novel model for targeted tissue turnover of cartilage of specific joints through hormone-mediated induction of select MMPs.