Estrogen modulates iodoacetate-induced gene expression in bovine cartilage explants

Physiological levels of estradiol limit murine osteoarthritis progression

Among patients with knee osteoarthritis (OA), postmenopausal women are over-represented. The purpose of this study was to determine whether deficiency of female sex steroids affects OA progression and to evaluate the protective effect of treatment with a physiological dose of 17β-estradiol (E2) on OA progression using a murine model. Ovariectomy (OVX) of female mice was used to mimic a postmenopausal state. OVX or sham-operated mice underwent surgery for destabilization of the medial meniscus (DMM) to induce OA. E2 was administered in a pulsed manner for 2 and 8 weeks. OVX of OA mice did not influence the cartilage phenotype or synovial thickness, while both cortical and trabecular subchondral bone mineral density (BMD) decreased after OVX compared with sham-operated mice at 8 weeks post-DMM surgery. Additionally, OVX mice displayed decreased motor activity, reduced threshold of pain sensitivity, and increased number of T cells in the inguinal lymph nodes compared to sham-operated mice 2 weeks after OA induction. Eight weeks of treatment with E2 prevented cartilage damage and thickening of the synovium in OVX OA mice. The motor activity was improved after E2 replacement at the 2 weeks time point, which was also associated with lower pain sensitivity in the OA paw. E2 treatment protected against OVX-induced loss of subchondral trabecular bone. The number of T cells in the inguinal lymph nodes was reduced by E2 treatment after 8 weeks. This study demonstrates that treatment with a physiological dose of E2 exerts a protective role by reducing OA symptoms.

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.

Estrogen reduces mechanical injury-related cell death and proteoglycan degradation in mature articular cartilage independent of the presence of the superficial zone tissue

OBJECTIVE

To study the effect of 17β-estradiol (E2) and the superficial zone (SFZ) on cell death and proteoglycan degradation in articular cartilage after a single injurious compression in vitro.

METHOD

Cartilage explants from the femoropatellar groove of 2 year old cows with or without the SFZ were cultured serum-free with physiological concentrations of E2 and injured by an unconfined single load compression (strain 50%, velocity 2 mm/s). After 96 h cell death was measured histomorphometrically (nuclear blebbing (NB) and TUNEL staining) and release of glycosaminoglycans (GAG) by DMMB assay.

RESULTS

Injurious compression increased significantly the number of cells with NB and TUNEL staining and release of GAG. Physiological concentrations of E2 prevented the injury-related cell death and reduced the GAG release significantly in a receptor-mediated manner (shown by co-stimulation with the antiestrogen fulvestrant/faslodex/ICI-182,780). The presence of the SFZ did not alter the NB response to either the mechanical injury or E2, but reduced the overall release of GAG significantly.

CONCLUSION

E2 prevents injury-related cell death and GAG release, and might be useful for the development of treatment options for either cartilage-related sports injuries or osteoarthritis (OA). The SFZ does not seem to play an important role in (1) the E2-related tissue response and (2) the mechanically-induced cell death in deeper regions of the explants and GAG release. The latter might be related to the unconfined nature of the injury model.

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.

Estrogen receptor-related receptor α regulation by interleukin-1β in prostaglandin E(2)- and cAMP-dependent pathways in osteoarthritic chondrocytes

OBJECTIVE

We reported previously that the orphan nuclear receptor, estrogen receptor-related receptor α (ERRα), is expressed in articular chondrocytes and is dysregulated in a mouse model of inflammatory arthritis. The aim of this study, therefore, was to determine whether ERRα is also dysregulated in patients with osteoarthritis (OA).

METHODS

ERRα messenger RNA (mRNA) and protein were quantified in normal and OA cartilage samples and in OA chondrocytes in vitro, with and without short-term treatment with a variety of OA-associated factors and signaling pathway agonists and inhibitors.

RESULTS

ERRα expression was lower in OA than in normal articular cartilage. Interleukin-1β (IL-1β) markedly up-regulated ERRα expression in OA chondrocytes in vitro, and agonist or inhibitor treatment indicated that the up-regulation was dependent on cyclooxygenase 2 (COX-2; NS398), prostaglandin E(2), cAMP (8-bromo-cAMP), and protein kinase A (PKA; KT5720). Treatment with the ERRα inverse agonist XCT790 decreased the expression of SOX9 and the up-regulation of ERRα by IL-1β, suggesting autoregulation of ERRα in the IL-1β pathway. Matrix metalloproteinase 13 (MMP-13) expression was also decreased by treatment with XCT790 plus IL-1β versus IL-1β alone, and the down-regulation of MMP-13 mRNA and protein observed with XCT790 alone suggests that the up-regulation of MMP-13 by IL-1β is ERRα-dependent.

CONCLUSION

We report the first evidence that ERRα expression is regulated by IL-1β in COX-2-, cAMP-, and PKA-dependent pathways in OA chondrocytes. We confirmed that SOX9 is an ERRα target gene in human, as in rodent, chondrocytes and identified MMP-13 as a potential new target gene, which suggests that ERRα may both respond to the healing signal and contribute to extracellular degradation in OA cartilage.

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.