Development of osteoarthritic features in estrogen receptor knockout mice

Proteomic and genomic profiling of plasma exosomes from patients with ankylosing spondylitis

INTRODUCTION

Recent advances in understanding the biology of ankylosing spondylitis (AS) using innovative genomic and proteomic approaches offer the opportunity to address current challenges in AS diagnosis and management. Altered expression of genes, microRNAs (miRNAs) or proteins may contribute to immune dysregulation and may play a significant role in the onset and persistence of inflammation in AS. The ability of exosomes to transport miRNAs across cells and alter the phenotype of recipient cells has implicated exosomes in perpetuating inflammation in AS. This study reports the first proteomic and miRNA profiling of plasma-derived exosomes in AS using comprehensive computational biology analysis.

METHODS

Plasma samples from patients with AS and healthy controls (HC) were isolated via ultracentrifugation and subjected to extracellular vesicle flow cytometry analysis to characterise exosome surface markers by a multiplex immunocapture assay. Cytokine profiling of plasma-derived exosomes and cell culture supernatants was performed. Next-generation sequencing was used to identify miRNA populations in exosomes enriched from plasma fractions. CD4+ T cells were sorted, and the frequency and proliferation of CD4+ T-cell subsets were analysed after treatment with AS-exosomes using flow cytometry.

RESULTS

The expression of exosome marker proteins CD63 and CD81 was elevated in the patients with AS compared with HC (q<0.05). Cytokine profiling in plasma-derived AS-exosomes demonstrated downregulation of interleukin (IL)-8 and IL-10 (q<0.05). AS-exosomes cocultured with HC CD4+ T cells induced significant upregulation of IFNα2 and IL-33 (q<0.05). Exosomes from patients with AS inhibited the proliferation of regulatory T cells (Treg), suggesting a mechanism for chronically activated T cells in this disease. Culture of CD4+ T cells from healthy individuals in the presence of AS-exosomes reduced the proliferation of FOXP3+ Treg cells and decreased the frequency of FOXP3+IRF4+ Treg cells. miRNA sequencing identified 24 differentially expressed miRNAs found in circulating exosomes of patients with AS compared with HC; 22 of which were upregulated and 2 were downregulated.

CONCLUSIONS

Individuals with AS have different immunological and genetic profiles, as determined by evaluating the exosomes of these patients. The inhibitory effect of exosomes on Treg in AS suggests a mechanism contributing to chronically activated T cells in this disease.

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.

Uncovering the "riddle of femininity" in osteoarthritis: a systematic review and meta-analysis of menopausal animal models and mathematical modeling of estrogen treatment

OBJECTIVE

Post-menopausal women are disproportionately affected by osteoarthritis (OA). As such, the purpose of this study was to (1) summarize the state-of-the-science aimed at understanding the effects of menopause on OA in animal models and (2) investigate how dosage and timing of initiation of estrogen treatment affect cartilage degeneration.

DESIGN

A systematic review identified articles studying menopausal effects on cartilage in preclinical models. A meta-analysis was performed using overlapping cartilage outcomes in conjunction with a rigor and reproducibility analysis. Ordinary differential equation models were used to determine if a relationship exists between cartilage degeneration and the timing of initiation or dosage of estrogen treatment.

RESULTS

Thirty-eight manuscripts were eligible for inclusion. The most common menopause model used was ovariectomy (92%), and most animals were young at the time of menopause induction (86%). Most studies did not report inclusion criteria, animal monitoring, protocol registration, or data accessibility. Cartilage outcomes were worse in post-menopausal animals compared to age-matched, non-menopausal animals, as evidenced by cartilage histological scoring [0.75, 1.72], cartilage thickness [-4.96, -0.96], type II collagen [-4.87, -0.56], and c-terminal cross-linked telopeptide of type II collagen (CTX-II) [2.43, 5.79] (95% CI of Effect Size (+greater in menopause, -greater in non-menopause)). Moreover, modeling suggests that cartilage health may be improved with early initiation and higher doses of estrogen treatment.

CONCLUSIONS

To improve translatability, animal models that consider aging and natural menopause should be utilized, and more attention to rigor and reproducibility is needed. Timing of initiation and dosage may be important factors modulating therapeutic effects of estrogen on cartilage.

Mechanotransduction pathways in articular chondrocytes and the emerging role of estrogen receptor-α

In the synovial joint, mechanical force creates an important signal that influences chondrocyte behavior. The conversion of mechanical signals into biochemical cues relies on different elements in mechanotransduction pathways and culminates in changes in chondrocyte phenotype and extracellular matrix composition/structure. Recently, several mechanosensors, the first responders to mechanical force, have been discovered. However, we still have limited knowledge about the downstream molecules that enact alterations in the gene expression profile during mechanotransduction signaling. Recently, estrogen receptor α (ERα) has been shown to modulate the chondrocyte response to mechanical loading through a ligand-independent mechanism, in line with previous research showing that ERα exerts important mechanotransduction effects on other cell types, such as osteoblasts. In consideration of these recent discoveries, the goal of this review is to position ERα into the mechanotransduction pathways known to date. Specifically, we first summarize our most recent understanding of the mechanotransduction pathways in chondrocytes on the basis of three categories of actors, namely mechanosensors, mechanotransducers, and mechanoimpactors. Then, the specific roles played by ERα in mediating the chondrocyte response to mechanical loading are discussed, and the potential interactions of ERα with other molecules in mechanotransduction pathways are explored. Finally, we propose several future research directions that may advance our understanding of the roles played by ERα in mediating biomechanical cues under physiological and pathological conditions.

In vitro study to identify ligand-independent function of estrogen receptor-α in suppressing DNA damage-induced chondrocyte senescence

In osteoarthritis (OA), chondrocytes undergo many pathological alternations that are linked with cellular senescence. However, the exact pathways that lead to the generation of a senescence-like phenotype in OA chondrocytes are not clear. Previously, we found that loss of estrogen receptor-α (ERα) was associated with an increased senescence level in human chondrocytes. Since DNA damage is a common cause of cellular senescence, we aimed to study the relationship among ERα levels, DNA damage, and senescence in chondrocytes. We first examined the levels of ERα, representative markers of DNA damage and senescence in normal and OA cartilage harvested from male and female human donors, as well as from male mice. The influence of DNA damage on ERα levels was studied by treating human chondrocytes with doxorubicin (DOX), which is an often-used DNA-damaging agent. Next, we tested the potential of overexpressing ERα in reducing DNA damage and senescence levels. Lastly, we explored the interaction between ERα and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway. Results indicated that the OA chondrocytes contained DNA damage and displayed senescence features, which were accompanied by significantly reduced ERα levels. Overexpression of ERα reduced the levels of DNA damage and senescence in DOX-treated normal chondrocytes and OA chondrocytes. Moreover, DOX-induced the activation of NF-κB pathway, which was partially reversed by overexpressing ERα. Taken together, our results demonstrated the critical role of ERα in maintaining the health of chondrocytes by inhibiting DNA damage and senescence. This study also suggests that maintaining the ERα level may represent a new avenue to prevent and treat OA.

Effect of cell receptors in the pathogenesis of osteoarthritis: Current insights

Osteoarthritis (OA) is a chronic arthritic disease characterized by cartilage degradation, synovial inflammation, and subchondral bone lesions. The studies on the pathogenesis of OA are complex and diverse. The roles of receptors signaling in chondrocyte anabolism, inflammatory factors expression of synovial fibroblast, and angiogenesis in subchondral bone are particularly important for exploring the pathological mechanism of OA and clinical diagnosis and treatment. By reviewing the relevant literature, this article elaborates on the abnormal expression of receptors and the signaling transduction pathways from different pathological changes of OA anatomical components, aiming to provide new research ideas and clinical therapeutic value for OA pathogenesis.

Novel role of estrogen receptor-α on regulating chondrocyte phenotype and response to mechanical loading

OBJECTIVE

In knee cartilage from patients with osteoarthritis (OA), both preserved cartilage and damaged cartilage are observed. In this study, we aim to compare preserved with damaged cartilage to identify the molecule(s) that may be responsible for the mechanical loading-induced differences within cartilage degradation.

METHODS

Preserved and damaged cartilage were harvested from the same OA knee joint. RNA Sequencing was performed to examine the transcriptomic differences between preserved and damaged cartilage cells. Estrogen receptor-α (ERα) was identified, and its function of was tested through gene knockin and knockout. The role of ERα in mediating chondrocyte response to mechanical loading was examined via compression of chondrocyte-laded hydrogel in a strain-controlled manner. Findings from the studies on human samples were verified in animal models.

RESULTS

Level of estrogen receptor α (ERα) was significantly reduced in damaged cartilage compared to preserved cartilage, which were observed in both human and mice samples. Knockdown of ESR1, the gene encoding ERα, resulted in an upregulation of senescence- and OA-relevant markers in chondrocytes. Conversely, knockin of ESR1 partially reversed the osteoarthritic and senescent phenotype of OA chondrocytes. Using a three-dimensional (3D) culture model, we demonstrated that mechanical overload significantly suppressed ERα level in chondrocytes with concomitant upregulation of osteoarthritic phenotype. When ESR1 expression was suppressed, mechanical loading enhanced hypertrophic and osteogenic transition.

CONCLUSION

Our study demonstrates a new estrogen-independent role of ERα in mediating chondrocyte phenotype and its response to mechanical loading, and suggests that enhancing ERα level may represent a new method to treat osteoarthritis.

Ex Vivo Systems to Study Chondrogenic Differentiation and Cartilage Integration

Articular cartilage injury and repair is an issue of growing importance. Although common, defects of articular cartilage present a unique clinical challenge due to its poor self-healing capacity, which is largely due to its avascular nature. There is a critical need to better study and understand cellular healing mechanisms to achieve more effective therapies for cartilage regeneration. This article aims to describe the key features of cartilage which is being modelled using tissue engineered cartilage constructs and ex vivo systems. These models have been used to investigate chondrogenic differentiation and to study the mechanisms of cartilage integration into the surrounding tissue. The review highlights the key regeneration principles of articular cartilage repair in healthy and diseased joints. Using co-culture models and novel bioreactor designs, the basis of regeneration is aligned with recent efforts for optimal therapeutic interventions.

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.

Chondrocyte-Specific RUNX2 Overexpression Accelerates Post-traumatic Osteoarthritis Progression in Adult Mice

RUNX2 is a transcription factor critical for chondrocyte maturation and normal endochondral bone formation. It promotes the expression of factors catabolic to the cartilage extracellular matrix and is upregulated in human osteoarthritic cartilage and in murine articular cartilage following joint injury. To date, in vivo studies of RUNX2 overexpression in cartilage have been limited to forced expression in osteochondroprogenitor cells preventing investigation into the effects of chondrocyte-specific RUNX2 overexpression in postnatal articular cartilage. Here, we used the Rosa26^Runx2 allele in combination with the inducible Col2a1^CreERT2 transgene or the inducible Acan^CreERT2 knock-in allele to achieve chondrocyte-specific RUNX2 overexpression (OE) during embryonic development or in the articular cartilage of adult mice, respectively. RUNX2 OE was induced at embryonic day 13.5 (E13.5) for all developmental studies. Histology and in situ hybridization analyses suggest an early onset of chondrocyte hypertrophy and accelerated terminal maturation in the limbs of the RUNX2 OE embryos compared to control embryos. For all postnatal studies, RUNX2 OE was induced at 2 months of age. Surprisingly, no histopathological signs of cartilage degeneration were observed even 6 months following induction of RUNX2 OE. Using the meniscal/ligamentous injury (MLI), a surgical model of knee joint destabilization and meniscal injury, however, we found that RUNX2 OE accelerates the progression of cartilage degeneration following joint trauma. One month following MLI, the numbers of MMP13-positive and TUNEL-positive chondrocytes were significantly greater in the articular cartilage of the RUNX2 OE joints compared to control joints and 2 months following MLI, histomorphometry and Osteoarthritis Research Society International (OARSI) scoring revealed decreased cartilage area in the RUNX2 OE joints. Collectively, these results suggest that although RUNX2 overexpression alone may not be sufficient to initiate the OA degenerative process, it may predetermine the rate of OA onset and/or progression following traumatic joint injury. © 2019 American Society for Bone and Mineral Research.

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-related receptor γ causes osteoarthritis by upregulating extracellular matrix-degrading enzymes

The estrogen-related receptor (ERR) family of orphan nuclear receptor is composed of ERRα, ERRβ, and ERRγ, which are known to regulate various isoform-specific functions under normal and pathophysiological conditions. Here, we investigate the involvement of ERRs in the pathogenesis of osteoarthritis (OA) in mice. Among ERR family members, ERRγ is markedly upregulated in cartilage from human OA patients and various mouse models of OA. Adenovirus-mediated overexpression of ERRγ in mouse knee joint or transgenic expression of ERRγ in cartilage leads to OA. ERRγ overexpression in chondrocytes directly upregulates matrix metalloproteinase (MMP)-3 and MMP13, which are known to play crucial roles in cartilage destruction in OA. In contrast, genetic ablation of Esrrg or shRNA-mediated downregulation of Esrrg in joint tissues abrogates experimental OA in mice. Our results collectively indicate that ERRγ is a novel catabolic regulator of OA pathogenesis.

The pathogenesis of osteoarthritis is unclear. The authors show that estrogen-related receptor gamma is upregulated in cartilage from patients and mouse models, where it drives production of matrix-degrading MMPs in chondrocytes, and that its downregulation ameliorates pathology in mice.

Estradiol and proinflammatory cytokines stimulate ISG20 expression in synovial fibroblasts of patients with osteoarthritis

Interferon stimulated gene 20-kDa (ISG20) has been implicated in the pathology of osteoarthritis (OA) and it has been separately found to be responsive to estrogen stimulation. OA disproportionately affects women, and especially older women, suggesting some role of reproductive hormones in its pathology. The current study characterized the expression of ISG20 following stimulation with estradiol (E2) and proinflammatory cytokines in OA synovial fibroblasts (OASFs). E2 and the proinflammatory cytokines interleukin-6 (IL-6), lipopolysaccharide (LPS), and tumor necrosis factor α (TNF-α) were used to stimulate OASFs in vitro. The expression of ISG20 before and after stimulation was detected using quantitative real-time polymerase chain reaction (RT-qPCR) and Western blotting. E2 and proinflammatory cytokine (IL-6, LPS and TNF-α) stimulation significantly induced the expression of ISG20 both at the messenger RNA (mRNA) and protein level. Moreover, the induction was time- and dose-dependent. Small interfering RNA (siRNA) was transfected into OASFs, and expression of the inflammatory factors interleukin-1α (IL-1α), IL-6, and interleukin-10 (IL-10) was detected using RT-qPCR. Silencing ISG20 with siRNA inhibited the expression of IL-1α, IL-6, and IL-10. Thus, expression of ISG20 was regulated by estradiol and proinflammatory factors, while ISG20 in turn regulated the expression of other inflammatory factors. These data support the contention that ISG20 plays a role in the inflammatory process of OA.

Dangguijihwang-tang and Dangguijakyak-san Prevent Menopausal Symptoms and Dangguijihwang-tang Prevents Articular Cartilage Deterioration in Ovariectomized Obese Rats with Monoiodoacetate-Induced Osteoarthritis

We investigated whether dangguijakyak-san (DJY) and dangguijihwang-tang (DJH), oriental medicines traditionally used for inflammatory diseases, could prevent and/or delay the progression of postmenopausal symptoms and osteoarthritis in osteoarthritis-induced estrogen-deficient rats. Treated ovariectomized (OVX) rats consumed either 1% DJY or 1% DJH in the diets. Positive-control rats were given 30 μg/kg bw 17β-estradiol and control rats were given 1% fat as were the normal-control rats. All rats received high-fat diets for 8 weeks. At the 9th week, OVX rats received articular injections of monoiodoacetate (MIA) or saline (normal control) into the right knee. At 3 weeks after MIA injection, DJY reduced visceral-fat mass and improved glucose metabolism by reducing insulin resistance, whereas DJH increased BMD and decreased insulin resistance. DJH improved weight distribution in the right knee and maximum running velocity on a treadmill at days 14 and 21 as much as those of the positive control. TNF-α, IL-1β, and IL-6 levels in articular cartilage were much higher in the control than the positive control, whereas both DJY and DJH reduced the levels to those of the positive control. The histological analysis assessed articular cartilage damage near the tidemark and proteoglycan loss in the control versus the positive control; DJY and DJH prevented this damage and proteoglycan loss. In conclusion, DJY may provide an effective treatment for improving glucose tolerance, and DJH may be appropriate for preventing osteoarthritis.

ERβ compensates for the absence of ERα function to promote osteoblast viability by inhibition of SOST signaling

Estrogen receptors α and β (ERα and ERβ) serve key functions in bone development and maintenance, and in the metabolism of bone mineral. ERβ and ERα form heterodimers, and ERβ negatively regulates the transactivation of ERα. ERβ also inhibits recruitment of ERα to the estrogen-responsive promoters. However, the relationship of ERα and ERβ in the regulation of osteoblast viability and differentiation remains unclear. The present study aimed to investigate whether ERβ plays a role in balancing ERα activity in osteoblast cells. Downregulation of ERα by short hairpin RNA (shRNA) was found to significantly increase cell cycle arrest at G1 phase (P<0.01). In addition, this effect was found to be significantly enhanced by downregulation of ERβ (P<0.05). Inversely, ERα-knocked down osteoblasts were treated with ERβ agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) to activate ERβ. It was found that activation of ERβ significantly rescued the arrest of cell cycle induced by the downregulation of ERα (P<0.05). Furthermore, downregulation of ERα was found to significantly inhibit cell viability (P<0.01), and knockdown of ERβ was found to have a significant synergic effect with ERα downregulation on the inhibition of cell viability (P<0.01). Treatment with ERβ agonist DPN significantly rescued the effects of downregulation of ERα on cell viability (P<0.01). It was also demonstrated that the synergic effects of ERα and ERβ deletion was via upregulation of SOST gene expression, and the subsequent inhibition of OPG and Runx2 gene expression. Thus, ERβ may serve a function in balancing osteoblast viability and differentiation induced by ERα.

Gender-specific differential expression of exosomal miRNA in synovial fluid of patients with osteoarthritis

The pathogenesis of osteoarthritis (OA) is poorly understood, and therapeutic approaches are limited to preventing progression of the disease. Recent studies have shown that exosomes play a vital role in cell-to-cell communication, and pathogenesis of many age-related diseases. Molecular profiling of synovial fluid derived exosomal miRNAs may increase our understanding of OA progression and may lead to the discovery of novel biomarkers and therapeutic targets. In this article we report the first characterization of exosomes miRNAs from human synovial fluid. The synovial fluid exosomes share similar characteristics (size, surface marker, miRNA content) with previously described exosomes in other body fluids. MiRNA microarray analysis showed OA specific exosomal miRNA of male and female OA. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis identified gender-specific target genes/signaling pathways. These pathway analyses showed that female OA specific miRNAs are estrogen responsive and target TLR (toll-like receptor) signaling pathways. Furthermore, articular chondrocytes treated with OA derived extracellular vesicles had decreased expression of anabolic genes and elevated expression of catabolic and inflammatory genes. In conclusion, synovial fluid exosomal miRNA content is altered in patients with OA and these changes are gender specific.

Relationship between soy milk intake and radiographic knee joint space narrowing and osteophytes

The purpose of this study was to examine the cross-sectional association between dietary soy milk intake and the prevalence of radiographic knee joint space narrowing (JSN) and osteophytes (OST). Soy milk intake was assessed using a validated semiquantitative food frequency questionnaire and classified into three categories: never, <once a day, and ≥once a day. JSN and OST were assessed individually based on the Osteoarthritis Research Society International atlas. Multivariable logistic models were used after adjusting for potentially confounding factors. A total of 5764 subjects were included. Both the models suggested a significant inverse association between soy milk intake and OST. In model 1 (adjusted for age, body mass index, and sex), the prevalence of OST decreased in "≥once a day" category (OR 0.52, 95 % CI 0.28-0.98, P = 0.042) and "<once a day" category (OR 0.78, 95 % CI 0.66-0.93, P = 0.005) comparing to "never" category of soy milk intake, and the P for trend was 0.001. The outcomes were similar in model 2 (adjusted based on model 1, with additional factors of total energy intake, activity level, smoking status, alcohol-drinking status, educational background, diabetes, hypertension, and other dairy product intake) ("≥once a day" category: OR 0.49, 95 % CI 0.26-0.92, P = 0.026; "<once a day" category: OR 0.79, 95 % CI 0.67-0.94, P = 0.009), and the P for trend was 0.001. However, the significant associations between soy milk intake and JSN in both the models were not observed. Dietary soy milk intake was found to be negatively associated with OST, but not JSN, independent of some major confounding factors.

Aromatase expression in human chondrocytes: An induction due to culture

OBJECTIVES

Despite the high prevalence of osteoarthritis (OA) in postmenopausal women, a relationship between circulating estrogen levels and the development of OA has not been found. Therefore, the purpose of this study was to evaluate the expression and activity of aromatase, a key enzyme in local production of estrogens, in human OA cultured articular chondrocytes, and to determine the physiological relevance of this enzyme in cartilage.

METHODS

Human OA articular chondrocytes were isolated and cultured. Local production of estradiol was measured after incubation with 100 ng/ml testosterone for 8 and 24h. Furthermore, chondrocytes were culture for 2h, 48 h, 7 days or 15 days, or in alginate beads for 10 days. Aromatase, type II and X collagen, aggrecan, alkaline phosphatase, and Runx2 expression were evaluated in cartilage, freshly isolated chondrocytes and cultured chondrocytes.

RESULTS

Aromatase was expressed and active in cultured human chondrocytes. Human cartilage, freshly isolated chondrocytes, and chondrocytes cultured for 2h expressed an insignificant amount of aromatase; however, expression arose after 48 h of culture and remained increased thereafter. Aromatase expression was not related to estrogen deprivation and was inversely correlated with differentiation. Re-differentiation did not reduce its expression.

CONCLUSIONS

Aromatase presents an almost undetectable expression in human cartilage but is induced in cultured chondrocytes. Therefore, human cartilage might act as a mere target for estrogens rather than a producer, and researchers using cell expansion in culture for latter therapies should consider these changes in estrogen metabolism which may not be reverted after re-differentiation.

Changes in Membrane Receptors and Ion Channels as Potential Biomarkers for Osteoarthritis

Osteoarthritis (OA), a degenerative joint condition, is currently difficult to detect early enough for any of the current treatment options to be completely successful. Early diagnosis of this disease could increase the numbers of patients who are able to slow its progression. There are now several diseases where membrane protein biomarkers are used for early diagnosis. The numbers of proteins in the membrane is vast and so it is a rich source of potential biomarkers for OA but we need more knowledge of these before they can be considered practical biomarkers. How are they best measured and are they selective to OA or even certain types of OA? The first step in this process is to identify membrane proteins that change in OA. Here, we summarize several ion channels and receptors that change in OA models and/or OA patients, and may thus be considered candidates as novel membrane biomarkers of OA.

Postmenopausal Chinese women show accelerated lumbar disc degeneration compared with Chinese men

Background/Objective

Postmenopausal women may have accelerated disc degeneration due to relative oestrogen deficiency. Two new studies supporting this concept were carried out.

Methods

Study I: The data were from the Osteoporotic Fractures in Men (Hong Kong) and Women (Hong Kong) studies. Both were population-based studies on bone health for elderly Chinese men and women (age ≥ 65 years, n = 2000 for men and n = 2000 for women). Based on lumbar spine radiographs, changes in L1/2-L4/5 disc space height were classified into four categories: 0 = normal; 1 = mild narrowing (< 30% reduction in disc height); 2 = moderate narrowing (30-60% reduction in disc height); and 3 = severe narrowing (> 60% reduction in disc height). Sums of the disc space narrowing scores of each participant were plotted against their age. Study II: 12 healthy individuals and 53 persons who had mild nonspecific low back pain (30 males and 35 females; mean age, 53.4 years; age range, 23-76 years) were recruited. Magnetic resonance imaging was performed on a 3-T system. A multiecho turbo spin echo pulse sequence was used for lumbar disc T2 mapping. Regions of interest were manually drawn over nucleus pulposus on the T2 map of the discs. The means of T2 relaxation times of discs L1/2-L4/5 of the participants were plotted against their age.

Results

Study I: Elderly women had a higher disc space narrowing score than elderly men, and the slope of the plot was steeper for females than for males. When the plots were extrapolated to younger age, they intersected at 59.67 years. Study II: An age-related reduction of T2 value in the nucleus pulposus was demonstrated, which was faster in females than in males. Although females tended to have initial higher T2 value before 50 years, this trend was reversed in elderly persons, with an intersection at 52.4 years.

Conclusion

Postmenopausal Chinese women show accelerated lumbar disc degeneration compared with Chinese men.

Up-regulation of type II collagen gene by 17β-estradiol in articular chondrocytes involves Sp1/3, Sox-9, and estrogen receptor α

The existence of a link between estrogen deprivation and osteoarthritis (OA) in postmenopausal women suggests that 17β-estradiol (17β-E2) may be a modulator of cartilage homeostasis. Here, we demonstrate that 17β-E2 stimulates, via its receptor human estrogen receptor α 66 (hERα66), type II collagen expression in differentiated and dedifferentiated (reflecting the OA phenotype) articular chondrocytes. Transactivation of type II collagen gene (COL2A1) by ligand-independent transactivation domain (AF-1) of hERα66 was mediated by "GC" binding sites of the -266/-63-bp promoter, through physical interactions between ERα, Sp1/Sp3, Sox9, and p300, as demonstrated in chromatin immunoprecipitation (ChIP) and Re-Chromatin Immuno-Precipitation (Re-ChIP) assays in primary and dedifferentiated cells. 17β-E2 and hERα66 increased the DNA-binding activities of Sp1/Sp3 and Sox-9 to both COL2A1 promoter and enhancer regions. Besides, Sp1, Sp3, and Sox-9 small interfering RNAs (siRNAs) prevented hERα66-induced transactivation of COL2A1, suggesting that these factors and their respective cis-regions are required for hERα66-mediated COL2A1 up-regulation. Our results highlight the genomic pathway by which 17β-E2 and hERα66 modulate Sp1/Sp3 heteromer binding activity and simultaneously participate in the recruitment of the essential factors Sox-9 and p300 involved respectively in the chondrocyte-differentiated status and COL2A1 transcriptional activation. These novel findings could therefore be attractive for tissue engineering of cartilage in OA, by the fact that 17β-E2 could promote chondrocyte redifferentiation.

KEY MESSAGES

17β-E2 up-regulates type II collagen gene expression in articular chondrocytes. An ERα66/Sp1/Sp3/Sox-9/p300 protein complex mediates this stimulatory effect. This heteromeric complex interacts and binds to Col2a1 promoter and enhancer in vivo. Our findings highlight a new regulatory mechanism for 17β-E2 action in chondrocytes. 17β-E2 might be an attractive candidate for cartilage engineering applications.

Age dependent changes in cartilage matrix, subchondral bone mass, and estradiol levels in blood serum, in naturally occurring osteoarthritis in Guinea pigs

The Dunkin Hartley (DH) guinea pig is a widely used naturally occurring osteoarthritis model. The aim of this study was to provide detailed evidence of age-related changes in articular cartilage, subchondral bone mineral density, and estradiol levels. We studied the female Dunkin Hartley guinea pigs at 1, 3, 6, 9, and 12 months of age (eight animals in each group). Histological analysis were used to identify degenerative cartilage and electron microscopy was performed to further observe the ultrastructure. Estradiol expression levels in serum were assessed, and matrix metalloproteinase 3 and glycosaminoglycan expression in cartilage was performed by immunohistochemistry. Bone mineral density of the tibia subchondral bone was measured using dual X-ray absorptiometry. Histological analysis showed that the degeneration of articular cartilage grew more severe with increasing age starting at 3 months, coupled with the loss of normal cells and an increase in degenerated cells. Serum estradiol levels increased with age from 1 to 6 months and thereafter remained stable from 6 to 12 months. Matrix metalloproteinase 3 expression in cartilage increased with age, but no significant difference was found in glycosaminoglycan expression between 1- and 3-month old animals. The bone mineral density of the tibia subchondral bone increased with age before reaching a stable value at 9 months of age. Age-related articular cartilage degeneration occurred in Dunkin Hartley guinea pigs beginning at 3 months of age, while no directly positive or negative correlation between osteoarthritis progression and estradiol serum level or subchondral bone mineral density was discovered.

Association of single nucleotide polymorphisms in estrogen receptor alpha gene with susceptibility to knee osteoarthritis: a case-control study in a Chinese Han population

Osteoarthritis (OA) is the most prevalent form of arthritis and its multifactorial nature has been increasingly recognized. Genetic factors play an important role in OA etiology and estrogen receptor alpha (ESR1) gene polymorphisms may be involved. This study tried to explore whether the ESR1 gene single nucleotide polymorphisms (SNPs) were associated with primary knee OA in the Chinese Han population. Two SNPs, rs2234693 and rs9340799, were genotyped in 469 cases and 522 controls. Rs2234693 was associated with knee OA in the dominant genetic model (TT + TC versus CC) (P = 0.025) and a higher T allele frequency existed (P = 0.047) among females. The combined genotype (TT + TC) (P = 0.025) and T allele (P = 0.016) were related with mild knee OA only. For rs9340799, A allele was associated with knee OA in all subjects (P = 0.031) and females (P = 0.046). Statistical differences were detected in the dominant genetic model (AA + AG versus GG) among females (P = 0.030). The combined genotype (AA + AG) (P = 0.036) and A allele (P = 0.039) were merely correlated with mild knee OA. ESR1 gene is considerably associated with knee OA etiology in the Chinese Han population.

Estrogens, osteoarthritis and inflammation

Estrogens participate in several biological processes through different molecular mechanisms. Their final actions consist of a combination of both direct and indirect effects on different organ and tissues. Estrogen may have pro- and anti-inflammatory properties depending on the situation and the involved tissue. In general, acute loss of estrogens increases the levels of reactive oxygen species and activates nuclear factor-κB and pro-inflammatory cytokine production, indicating their predominant anti-inflammatory properties. Furthermore, pro-inflammatory cytokine expression has been shown to be attenuated by estrogen replacement. Osteoarthritis and cardiovascular disease are two of the more prevalent diseases once menopause is established, which has suggested the link between estrogens and both processes. In addition, deletion of estrogen receptors in female mice results in cartilage damage, osteophytosis and changes in the subchondral bone of the joints suggesting that estrogens have a protective role on the maintenance of joint homeostasis. Furthermore, in spite of the negative effect of estrogen replacement reported in 2002 by the Women's Health Initiative study, several works published afterwards have explored the potential protective effect of estrogen supplementation in animal models and have postulated that these actions may justify a beneficial role of estrogens in different diseases where inflammation is the major feature. In this review, we will analyze the effects of estrogens on certain pathological situations such as osteoarthritis, some autoimmune diseases and coronary heart disease, especially in postmenopausal women.

Targeting bone alleviates osteoarthritis in osteopenic mice and modulates cartilage catabolism

OBJECTIVE

Subchondral bone modifications occur early in the development of osteoarthritis (OA). The level of bone resorption might impact cartilage remodeling. We therefore assessed the in vivo and in vitro effects of targeting bone resorption in OA and cartilage metabolism.

METHODS

OA was induced by meniscectomy (MNX) in ovariectomized osteopenic mice (OP) treated with estradiol (E2), pamidronate (PAM), or phosphate buffered saline (PBS) for 6 weeks. We assessed the subchondral bone and cartilage structure and the expression of cartilage matrix proteases. To assess the involvement of bone soluble factors in cartilage metabolism, supernatant of human bone explants pre-treated with E2 or PAM were transferred to cartilage explants to assess proteoglycan release and aggrecan cleavage. OPG/RANKL mRNA expression was assessed in bone explants by real-time quantitative PCR. The role of osteoprotegerin (OPG) in the bone-cartilage crosstalk was tested using an OPG neutralizing antibody.

RESULTS

Bone mineral density of OP mice and osteoclast number were restored by E2 and PAM (p<0.05). In OP mice, E2 and PAM decreased ADAMTS-4 and -5 expression, while only PAM markedly reduced OA compared to PBS (2.0±0.63 vs 5.2±0.95; p<0.05). OPG/RANKL mRNA was increased in human bone explants treated with both drugs (2.2-3.7-fold). Moreover, supernatants from bone explants cultured with E2 or PAM reduced aggrecan cleavage and cartilage proteoglycan release (73±8.0% and 80±22% of control, respectively, p<0.05). This effect was reversed with osteoprotegerin blockade.

CONCLUSION

The inhibition of bone resorption by pamidronate in osteopenic mice alleviates the histological OA score with a reduction in the expression of aggrecanases. Bone soluble factors, such as osteoprotegerin, impact the cartilage response to catabolic factors. This study further highlights the importance of subchondral bone in the regulation of joint cartilage damage in OA.

An osteochondral culture model to study mechanisms involved in articular cartilage repair

Although several treatments for cartilage repair have been developed and used in clinical practice the last 20 years, little is known about the mechanisms that are involved in the formation of repair tissue after these treatments. Often, these treatments result in the formation of fibrocartilaginous tissue rather than normal articular cartilage. Because the repair tissue is inferior to articular cartilage in terms of mechanical properties and zonal organization of the extracellular matrix, complaints of the patient may return. The biological and functional outcome of these treatments should thus be improved. For this purpose, an in vitro model allowing investigation of the involved repair mechanisms can be of great value. We present the development of such a model. We used bovine osteochondral biopsies and created a system in which cartilage defects of different depths can be studied. First, our biopsy model was characterized extensively: we studied the viability by means of lactate dehydrogenase (LDH) excretion over time and we investigated expression of cartilage-related genes in osteochondral biopsies and compared it with conventional cartilage-only explants. After 28 days of culture, LDH was detected at low levels and mRNA could be retrieved. The expression of cartilage-related genes decreased over time. This was more evident in cartilage-only explants, indicating that the biopsy model provided a more stable environment. We also characterized the subchondral bone: osteoclasts and osteoblasts were active after 28 days of culture, which was indicated by tartrate acid phosphatase staining and alkaline phosphatase measurements, respectively, and matrix deposition during culture was visualized using calcein labeling. Second, the applicability of the model was further studied by testing two distinct settings: (1) implantation of chondrocytes in defects of different depths; (2) two different seeding strategies of chondrocytes. Differences were observed in terms of volume and integration of newly formed tissue in both settings, suggesting that our model can be used to model distinct conditions or even to mimic clinical treatments. After extensive characterization and testing of our model, we present a representative and reproducible in vitro model that can be used to evaluate new cartilage repair treatments and study mechanisms in a controlled and standardized environment.

Oestrogen receptors are involved in the osteogenic differentiation of periodontal ligament stem cells

The existence of PDLSCs [PDL (periodontal ligament) stem cells] in PDL has been identified and such cells may function in periodontal reconstruction, including bone formation. Oestrogens/ERs (oestrogen receptors; ERα and ERβ) exert important effects in bone formation, however, the relationship between ERs and PDLSCs has not been established. In the present study, PDLSCs were isolated and assays for detecting stem-cell biomarkers and multipotential differentiation potential confirmed the validity of human PDLSCs. The results of RT–PCR (reverse transcription–PCR) and Western blotting showed that ERα and ERβ were expressed at higher levels in PDLSCs as compared with PDLCs (PDL cells), and 17β-oestradiol obviously induced the osteogenic differentiation of PDLSCs in vitro. Furthermore, a pan-ER inhibitor or lentivirus-mediated siRNA (small interfering RNA) targeting ERα or ERβ blocked the oestrogen-induced osteogenic differentiation of PDLSCs. The results indicate that both ERα and ERβ were involved in the process of osteogenic differentiation of PDLSCs.

GRIP1 enhances estrogen receptor alpha-dependent extracellular matrix gene expression in chondrogenic cells

OBJECTIVE

The role of postmenopause on the pathogenesis of cartilage degeneration has been an open question. We assessed cartilage degeneration in estrogen receptor (ER)alpha null mice and examined the role of glucocorticoid receptor-interacting protein 1 (GRIP1) in the ERalpha-dependent transcription of a type II collagen gene (col2a1) with special reference to a crosstalk with the transforming growth factor (TGF)-beta signaling pathway.

METHODS

The vertebral cartilaginous endplate from female ERalpha null mice was subjected to histological analyses. Col2a1 expression of primary chondrocytes (PCs) obtained from ERalpha null mice after 17beta-estradiol (E(2)) and TGF-beta1 stimulation was examined by reverse transcription polymerase chain reaction (RT-PCR). Estrogen response element (ERE) or col2a1 promoter-enhancer luciferase reporter system was used to investigate the crosstalk among ERalpha, GRIP1, and MKK6. Col2a1 expression and glycosaminoglycan (GAG) content were measured in ATDC5 cells treated with GRIP1 small interfering RNA (siRNA).

RESULTS

ERalpha deficiency clearly accelerated impairment of the vertebral cartilaginous endplate. E(2) and TGF-beta1 stimulation increased col2a1 expression in PC from wild-type mice, but not that from ERalpha null mice. The same stimulation increased the col2a1 promoter-enhancer reporter activity, and the elevated activity was decreased by dominant-negative ERalpha and p38 mitogen-activated protein kinase (MAPK) inhibitor. GRIP1 increased the E(2)-dependent ERE activation in the presence of ERalpha and constitutive-active MKK6. GRIP1 siRNA repressed col2a1 expression and GAG production in ATDC5 cells.

CONCLUSIONS

Crosstalks between ERalpha/GRIP1 and TGF-beta/MKK6/p38 MAPK pathway have protective roles on cartilage metabolism via regulating the extracellular matrices expression. The finding may lead to the development of a novel therapeutic approach for cartilage degeneration.

Common variations in estrogen-related genes are associated with severe large-joint osteoarthritis: a multicenter genetic and functional study

OBJECTIVE

Several lines of evidence suggest that estrogens influence the development of osteoarthritis (OA). The aim of this study was to explore the association of two common polymorphisms within the aromatase (CYP19A1) and estrogen receptor (ER) alpha (ESR1) genes with severe OA of the lower limbs.

METHODS

The rs1062033 (CYP19A1) and rs2234693 (ESR1) single nucleotide polymorphisms were genotyped in 5528 individuals (3147 patients with severe hip or knee OA, and 2381 controls) from four centres in Spain and the United Kingdom. Gene expression was measured in femoral bone samples from a group of patients.

RESULTS

In the global analysis, both polymorphisms were associated with OA, but there was a significant sex interaction. The GG genotype at rs1062033 was associated with an increased risk of knee OA in women [odds ratio (OR) 1.23; P=0.04]. The CC genotype at rs2234693 tended to be associated with reduced OA risk in women (OR 0.76, P=0.028, for knee OA; OR=0.84, P=0.076 for hip OA), but with increased risk of hip OA in men (OR 1.28; P=0.029). Women with unfavourable genotypes at both loci had an OR of 1.61 for knee OA (P=0.006). The rs1062033 genotype associated with higher OA risk was also associated with reduced expression of the aromatase gene in bone.

CONCLUSIONS

Common genetic variations of the aromatase and ER genes are associated with the risk of severe OA of the large joints of the lower limb in a sex-specific manner. These results are consistent with the hypothesis that estrogen activity may influence the development of large-joint OA.

Osteoarthritis associated with estrogen deficiency

Osteoarthritis (OA) affects all articular tissues and finally leads to joint failure. Although articular tissues have long been considered unresponsive to estrogens or their deficiency, there is now increasing evidence that estrogens influence the activity of joint tissues through complex molecular pathways that act at multiple levels. Indeed, we are only just beginning to understand the effects of estrogen deficiency on articular tissues during OA development and progression, as well as on the association between OA and osteoporosis. Estrogen replacement therapy and current selective estrogen receptor modulators have mixed effectiveness in preserving and/or restoring joint tissue in OA. Thus, a better understanding of how estrogen acts on joints and other tissues in OA will aid the development of specific and safe estrogen ligands as novel therapeutic agents targeting the OA joint as a whole organ.