Estrogen receptor-related receptor-alpha (ERR-alpha) is dysregulated in inflammatory arthritis

Glutamine Metabolism Is Essential for Stemness of Bone Marrow Mesenchymal Stem Cells and Bone Homeostasis

Skeleton has emerged as an endocrine organ which is both capable of regulating energy metabolism and being a target for it. Glutamine is the most bountiful and flexible amino acid in the body which provides adenosine 5′-triphosphate (ATP) demands for cells. Emerging evidences support that glutamine which acts as the second metabolic regulator after glucose exerts crucial roles in bone homeostasis at cellular level, including the lineage allocation and proliferation of bone mesenchymal stem cells (BMSCs), the matrix mineralization of osteoblasts, and the biosynthesis in chondrocytes. The integrated mechanism consisting of WNT, mammalian target of rapamycin (mTOR), and reactive oxygen species (ROS) signaling pathway in a glutamine-dependent pattern is responsible to regulate the complex intrinsic biological process, despite more extensive molecules are deserved to be elucidated in glutamine metabolism further. Indeed, dysfunctional glutamine metabolism enhances the development of degenerative bone diseases, such as osteoporosis and osteoarthritis, and glutamine or glutamine progenitor supplementation can partially restore bone defects which may promote treatment of bone diseases, although the mechanisms are not quite clear. In this review, we will summarize and update the latest research findings and clinical trials on the crucial regulatory roles of glutamine metabolism in BMSCs and BMSC-derived bone cells, also followed with the osteoclasts which are important in bone resorption.

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.

Emerging roles of orphan nuclear receptors in regulation of innate immunity

Innate immunity constitutes the first line of defense against pathogenic and dangerous insults. However, it is a double-edged sword, as it functions in both clearance of infection and inflammatory damage. It is therefore important that innate immune responses are tightly controlled to prevent harmful excessive inflammation. Nuclear receptors (NRs) are a family of transcription factors that play critical roles in various physiological responses. Orphan NRs are a subset of NRs for which the ligands and functions are unclear. Accumulating evidence has revealed that orphan NRs play essential roles in innate immune responses to prevent pathogenic inflammatory responses and to enhance antimicrobial host defenses. In this review, we describe current knowledge on the roles and mechanisms of orphan NRs in the regulation of innate immune responses. Discovery of new functions of orphan NRs would facilitate development of novel preventive and therapeutic strategies against human inflammatory diseases.

Reduction in ERRα is associated with lichen sclerosus and vulvar squamous cell carcinoma

OBJECTIVE

ERRs (estrogen-related receptors) regulate energy metabolism, the cell cycle and inflammatory processes in both normal and cancer cells. Chronic inflammation induced by lichen sclerosus (LS) or human papilloma virus (HPV) precedes vulvar squamous cell carcinoma (vulvar SCC). We investigated the expression of ERRα, ERRβ and ERRγ in normal vulvar skin, LS as well as LS-dependent and LS-independent/HPV-related vulvar SCC.

METHODS

A total of 203 samples were analyzed for ERRα, ERRβ and ERRγ by using immunohistochemistry. These included 37 normal vulvar skin samples, 110 LS samples, 6 vulvar intraepithelial neoplasia (VIN) samples and 50 vulvar SCC samples.

RESULTS

A substantial reduction in or disappearance of ERRα was detected in all vulvar SCC samples. A total of 79% of childhood-onset LS and 51% of adulthood-onset LS lesions showed decreases in ERRα staining. A gradual reduction in ERRα cytoplasmic staining was observed from healthy vulvar skin to precursor lesions and further to SCC. Nuclear ERRα staining was observed in 8/33 (24%) LS-dependent and 10/17 (59%) LS-independent SCC samples.

CONCLUSIONS

ERRα, a key regulator of cell energy metabolism, may play a role in the pathogenesis of both LS and vulvar SCC.

Gender-related differences in irritable bowel syndrome: Potential mechanisms of sex hormones

According to epidemiological studies, twice as many women as men are affected by irritable bowel syndrome (IBS) in western countries, suggesting a role for sex hormones in IBS pathophysiology. Despite growing evidence about the implications of sex hormones in IBS symptom modulation, data on mechanisms by which they influence disease development are sparse. This review aims to determine the state of knowledge about the role of sex hormones in sensorimotor dysfunctions and to address the possible interplay of sex hormones with common risk factors associated with IBS. The scientific bibliography was searched using the following keywords: irritable bowel syndrome, sex, gender, ovarian hormone, estradiol, progesterone, testosterone, symptoms, pain, sensitivity, motility, permeability, stress, immune system, brain activity, spinal, supraspinal, imaging. Ovarian hormones variations along the menstrual cycle affect sensorimotor gastrointestinal function in both healthy and IBS populations. They can modulate pain processing by interacting with neuromodulator systems and the emotional system responsible for visceral pain perception. These hormones can also modulate the susceptibility to stress, which is a pivotal factor in IBS occurrence and symptom severity. For instance, estrogen-dependent hyper-responsiveness to stress can promote immune activation or impairments of gut barrier function. In conclusion, whereas it is important to keep in mind that ovarian hormones cannot be considered as a causal factor of IBS, they arguably modulate IBS onset and symptomatology. However, our understanding of the underlying mechanisms remains limited and studies assessing the link between IBS symptoms and ovarian hormone levels are needed to improve our knowledge of the disease evolution with regard to gender. Further studies assessing the role of male hormones are also needed to understand fully the role of sex hormones in IBS. Finally, investigation of brain-gut interactions is critical to decipher how stress, ovarian hormones, and female brain processing of pain can translate into gut dysfunctions.

Estrogen-related receptor alpha confers methotrexate resistance via attenuation of reactive oxygen species production and P53 mediated apoptosis in osteosarcoma cells

Osteosarcoma (OS) is a malignant tumor mainly occurring in children and adolescents. Methotrexate (MTX), a chemotherapy agent, is widely used in treating OS. However, treatment failures are common due to acquired chemoresistance, for which the underlying molecular mechanisms are still unclear. In this study, we report that overexpression of estrogen-related receptor alpha (ERR α ), an orphan nuclear receptor, promoted cell survival and blocked MTX-induced cell death in U2OS cells. We showed that MTX induced ROS production in MTX-sensitive U2OS cells while ERR α effectively blocked the ROS production and ROS associated cell apoptosis. Our further studies demonstrated that ERR α suppressed ROS induction of tumor suppressor P53 and its target genes NOXA and XAF1 which are mediators of P53-dependent apoptosis. In conclusion, this study demonstrated that ERR α plays an important role in the development of MTX resistance through blocking MTX-induced ROS production and attenuating the activation of p53 mediated apoptosis signaling pathway, and points to ERR α as a novel target for improving osteosarcoma therapy.

Cartilage-specific overexpression of ERRγ results in Chondrodysplasia and reduced chondrocyte proliferation

While the role of estrogen receptor-related receptor alpha (ERRα) in chondrogenesis has been investigated, the involvement of ERR gamma (ERRγ) has not been determined. To assess the effect of increased ERRγ activity on cartilage development in vivo, we generated two transgenic (Tg) lines overexpressing ERRγ2 via a chondrocyte-specific promoter; the two lines exhibited ∼3 and ∼5 fold increased ERRγ2 protein expression respectively in E14.5 Tg versus wild type (WT) limbs. On postnatal day seven (P7), we observed a 4–10% reduction in the size of the craniofacial, axial and appendicular skeletons in Tg versus WT mice. The reduction in bone length was already present at birth and did not appear to involve bones that are derived via intramembranous bone formation as the bones of the calvaria, clavicle, and the mandible developed normally. Histological analysis of P7 growth plates revealed a reduction in the length of the Tg versus WT growth plate, the majority of which was attributable to a reduced proliferative zone. The reduced proliferative zone paralleled a decrease in the number of Ki67-positive proliferating cells, with no significant change in apoptosis, and was accompanied by large cell-free swaths of cartilage matrix, which extended through multiple zones of the growth plate. Using a bioinformatics approach, we identified known chondrogenesis-associated genes with at least one predicted ERR binding site in their proximal promoters, as well as cell cycle regulators known to be regulated by ERRγ. Of the genes identified, Col2al, Agg, Pth1r, and Cdkn1b (p27) were significantly upregulated, suggesting that ERRγ2 negatively regulates chondrocyte proliferation and positively regulates matrix synthesis to coordinate growth plate height and organization.

Estrogen-related receptor alpha interacts cooperatively with peroxisome proliferator-activated receptor-gamma coactivator-1alpha to regulate osteocalcin gene expression

Osteocalcin is one of the most abundant non-collagenous proteins in bone that is commonly used as a preliminary biomarker in bone formation. Osteocalcin also regulates energy metabolism as a hormone. Estrogen-related receptor alpha (ERRα) is primarily thought to regulate energy homeostasis through interacting with peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α). Intriguingly, ERRα may play a functional role in bone formation. We have found there are 3 ERRα response elements (ERR response element, ERRE) in the osteocalcin promoter, and ERRα interacted cooperatively with PGC-1α could improve the osteocalcin promoter activity, whereas ERRα specific antagonist, XCT-790, inhibits this enhancement. XCT-790 inhibits osteocalcin and ERRα target gene PDKs expression in osteoblast cells. Thus ERRs might have physiological roles in bone formation and energy metabolism through modulating osteocalcin gene expression.

Sex differences matter in the gut: effect on mucosal immune activation and inflammation

Background

Women and men have diverse responses to many infectious diseases. These differences are amplified following menopause. However, despite extensive information regarding the effects of sex hormones on immune cells, our knowledge is limited regarding the effects of sex and gender on the function of the mucosal immune system. Sex differences also manifest in the prevalence of gut associated inflammatory and autoimmune disorders, including Crohn’s disease, ulcerative colitis and Celiac disease. It is thus hypothesized that a baseline sex-associated difference in immune activation may predispose women to inflammation-associated disease.

Methods

Peripheral blood samples and small intestinal biopsies were obtained from 34 healthy men and women. Immunophenotypic analysis of isolated lymphocytes was performed by flow cytometry. Oligonucleotide analysis was used to study the transcriptional profile in the gut mucosal microenvironment while real-time PCR analysis was utilized to identify differential gene expression in isolated CD4+ T cells. Transcriptional analysis was confirmed by protein expression levels for genes of interest using fluorescent immunohistochemistry. Data was analyzed using the GraphPad software package.

Results

Women had higher levels of immune activation and inflammation-associated gene expression in gut mucosal samples. CD4+ and CD8+ T cells had a significantly higher level of immune activation-associated phenotype in peripheral blood as well as in gut associated lymphoid tissue along with higher levels of proliferating T cells. CD4+ T cells that showed upregulation of IL1β as well as the TH17 pathway-associated genes contributed a large part of the inflammatory profile.

Conclusion

In this study, we demonstrated an upregulation in gene expression related to immune function in the gut microenvironment of women compared to men, in the absence of disease or pathology. Upon closer investigation, CD4+ T cell activation levels were higher in the LPLs in women than in men. Sex differences in the mucosal immune system may predispose women to inflammation-associated diseases that are exacerbated following menopause. Our study highlights the need for more detailed analysis of the effects of sex differences in immune responses at mucosal effector sites.

Estrogen-related receptor α is involved in the osteogenic differentiation of mesenchymal stem cells isolated from human periodontal ligaments

Recently, it has been reported that the orphan nuclear receptor estrogen-related receptor α (ERRα) is involved in the osteogenic differentiation of mesenchymal stem cells (MSCs). Moreover, ERRα has been identified as a novel therapeutic target for treating osteoporosis and other bone diseases. Human periodontal ligament tissue-derived mesenchymal stem cells (hPDLSCs) have recently been used in stem cell-mediated therapies because of their multipotency, particularly toward osteogenic differentiation. However, it is still unclear whether ERRα can regulate the osteogenic differentiation of hPDLSCs. In the present study, we investigated the role of ERRα in the osteogenic differentiation of hPDLSCs in vitro. We isolated hPDLSCs and confirmed their capacity for multipotent differentiation. Furthermore, we examined ERRα expression in hPDLSCs by RT-PCR and immunocytochemistry. We found that the expression of ERRα mRNA was significantly increased during the late stage of osteogenic differentiation of hPDLSCs. Moreover, transfection of recombinant lentiviral-mediated miRNA targeting ERRα significantly suppressed ALP activity, mineralization capacity, and the mRNA expression of osteogenesis-related genes (ALP, OCN, RUNX2 and OPN) in hPDLSCs. Our results indicate that ERRα may promote the osteogenic differentiation of hPDLSCs in vitro.

Hormonal modulation of connective tissue homeostasis and sex differences in risk for osteoarthritis of the knee

Young female athletes experience a higher incidence of ligament injuries than their male counterparts, females experience a higher incidence of joint hypermobility syndrome (a risk factor for osteoarthritis development), and post-menopausal females experience a higher prevalence of osteoarthritis than age-matched males. These observations indicate that fluctuating sex hormone levels in young females and loss of ovarian sex hormone production due to menopause likely contribute to observed sex differences in knee joint function and risk for loss of function. In studies of osteoarthritis, however, there is a general lack of appreciation for the heterogeneity of hormonal control in both women and men. Progress in this field is limited by the relatively few preclinical osteoarthritis models, and that most of the work with established models uses only male animals. To elucidate sex differences in osteoarthritis, it is important to examine sex hormone mechanisms in cells from knee tissues and the sexual dimorphism in the role of inflammation at the cell, tissue, and organ levels. There is a need to determine if the risk for loss of knee function and integrity in females is restricted to only the knee or if sex-specific changes in other tissues play a role. This paper discusses these gaps in knowledge and suggests remedies.

An energetic orphan in an endocrine tissue: a revised perspective of the function of estrogen receptor-related receptor alpha in bone and cartilage

Estrogen receptor-related receptor alpha (ERRα) is an orphan nuclear receptor with sequence homology to the estrogen receptors, ERα/β, but it does not bind estrogen. ERRα not only plays a functional role in osteoblasts but also in osteoclasts and chondrocytes. In addition, the ERRs, including ERRα, can be activated by coactivators such as peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC1α and β) and are implicated in adipogenesis, fatty acid oxidation, and oxidative stress defense, suggesting that ERRα-through its activity in bone resorption and adipogenesis--may regulate the insulin and leptin pathways and contribute to aging-related changes in bone and cartilage. In this review, we discuss data on ERRα and its cellular and molecular modes of action, which have broad implications for considering the potential role of this orphan receptor in cartilage and bone endocrine function, on whole-organism physiology, and in the bone aging process.

TRPM2 Ca2+ channel regulates energy balance and glucose metabolism

TRPM2 Ca(2+)-permeable cation channel is widely expressed and activated by markers of cellular stress. Since inflammation and stress play a major role in insulin resistance, we examined the role of TRPM2 Ca(2+) channel in glucose metabolism. A 2-h hyperinsulinemic euglycemic clamp was performed in TRPM2-deficient (KO) and wild-type mice to assess insulin sensitivity. To examine the effects of diet-induced obesity, mice were fed a high-fat diet for 4-10 mo, and metabolic cage and clamp studies were conducted in conscious mice. TRPM2-KO mice were more insulin sensitive partly because of increased glucose metabolism in peripheral organs. After 4 mo of high-fat feeding, TRPM2-KO mice were resistant to diet-induced obesity, and this was associated with increased energy expenditure and elevated expressions of PGC-1α, PGC-1β, PPARα, ERRα, TFAM, and MCAD in white adipose tissue. Hyperinsulinemic euglycemic clamps showed that TRPM2-KO mice were more insulin sensitive, with increased Akt and GSK-3β phosphorylation in heart. Obesity-mediated inflammation in adipose tissue and liver was attenuated in TRPM2-KO mice. Overall, TRPM2 deletion protected mice from developing diet-induced obesity and insulin resistance. Our findings identify a novel role of TRPM2 Ca(2+) channel in the regulation of energy expenditure, inflammation, and insulin resistance.

Macrophages in synovial inflammation

Synovial macrophages are one of the resident cell types in synovial tissue and while they remain relatively quiescent in the healthy joint, they become activated in the inflamed joint and, along with infiltrating monocytes/macrophages, regulate secretion of pro-inflammatory cytokines and enzymes involved in driving the inflammatory response and joint destruction. Synovial macrophages are positioned throughout the sub-lining layer and lining layer at the cartilage–pannus junction and mediate articular destruction. Sub-lining macrophages are now also considered as the most reliable biomarker for disease severity and response to therapy in rheumatoid arthritis (RA). There is a growing understanding of the molecular drivers of inflammation and an appreciation that the resolution of inflammation is an active process rather than a passive return to homeostasis, and this has implications for our understanding of the role of macrophages in inflammation. Macrophage phenotype determines the cytokine secretion profile and tissue destruction capabilities of these cells. Whereas inflammatory synovial macrophages have not yet been classified into one phenotype or another it is widely known that TNFα and IL-l, characteristically released by M1 macrophages, are abundant in RA while IL-10 activity, characteristic of M2 macrophages, is somewhat diminished. Here we will briefly review our current understanding of macrophages and macrophage polarization in RA as well as the elements implicated in controlling polarization, such as cytokines and transcription factors like NFκB, IRFs and NR4A, and pro-resolving factors, such as LXA4 and other lipid mediators which may promote a non-inflammatory, pro-resolving phenotype, and may represent a novel therapeutic paradigm.

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.

Involvement of the orphan nuclear estrogen receptor-related receptor α in osteoclast adhesion and transmigration

The orphan nuclear receptor, estrogen receptor-related receptor α (ERRα) is expressed in osteoblasts and osteoclasts (OCs) and has been proposed to be a modulator of estrogen signaling. To determine the role of ERRα in OC biology, we knocked down ERRα activity by transient transfection of an siRNA directed against ERRα in the RAW264.7 monocyte-macrophage cell line that differentiates into OCs in the presence of receptor activator of nuclear factor κB-ligands and macrophage colony-stimulating factor. In parallel, stable RAW cell lines expressing a dominant-negative form of ERRα and green fluorescent protein (RAW-GFP-ERRαΔAF2) were used. Expression of OC markers was assessed by real-time PCR, and adhesion and transmigration tests were performed. Actin cytoskeletal organization was visualized using confocal microscopy. We found that RAW264.7 cells expressing siRNA directed against ERRα and RAW-GFP-ERRαΔAF2 OCs displayed abnormal spreading, and decreased osteopontin and β3 integrin subunit expression compared with the corresponding control cells. Decreased adhesion and the absence of podosome belts concomitant with abnormal localization of c-src were also observed in RAW-GFP-ERRαΔAF2-derived OCs. In addition, RAW-GFP-ERRαΔAF2-derived OCs failed to transmigrate through osteoblast cell layers. Our data show that the impairment of ERRα function does not alter OC precursor proliferation and differentiation but does alter the adhesion/spreading and migration capacities of mature OCs.

ERRalpha regulates osteoblastic and adipogenic differentiation of mouse bone marrow mesenchymal stem cells

The orphan nuclear receptor estrogen-related receptor-alpha (ERRalpha) has been reported to have both a positive and a negative regulatory role in osteoblastic and adipocytic differentiation. We have studied the role of ERRalpha in osteoblastic and adipogenic differentiation of mesenchymal stem cells. Bone marrow mesenchymal stem cells were isolated from ERRalpha deficient mice and their differentiation capacities were compared to that of the wild-type cells. ERRalpha deficient cultures displayed reduced cellular proliferation, osteoblastic differentiation, and mineralization. In the complementary experiment, overexpression of ERRalpha in MC3T3-E1 cells increased the expression of osteoblastic markers and mineralization. Alterations in the expression of bone sialoprotein (BSP) may at least partially explain the effects on mineralization as BSP expression was reduced in ERRalpha deficient MSCs and enhanced upon ERRalpha overexpression in MC3T3-E1 cells. Furthermore, a luciferase reporter construct driven by the BSP promoter was efficiently transactivated by ERRalpha. Under adipogenic conditions, ERRalpha deficient cultures displayed reduced adipocytic differentiation. Our data thus propose a positive role for ERRalpha in osteoblastic and adipocytic differentiation. The variability in the results yielded in the different studies implies that ERRalpha may play different roles in bone under different physiological conditions.

Endogenous estrogen regulation of inflammatory arthritis and cytokine expression in male mice, predominantly via estrogen receptor alpha

OBJECTIVE

A number of experimental observations have associated elevated estrogen levels with amelioration of inflammation. The involvement of estrogen and estrogen receptor (ER) isotypes in the regulation of inflammation in males is not well understood. In this study, we used specific ERalpha and ERbeta agonists in male mice deficient in estrogen because of a deletion of aromatase (aromatase-knockout [ArKO] mice) to investigate ER isotype utilization in estrogen regulation of inflammation.

METHODS

Lipopolysaccharide (LPS)-induced cytokine expression and antigen-induced arthritis (AIA) were investigated in male ArKO and WT littermate mice, as well as in response to selective agonists of ERalpha (16alpha-LE2) and ERbeta (8beta-VE2). The therapeutic effect of selective ER agonists was also examined in mice with collagen-induced arthritis (CIA).

RESULTS

Estrogen deficiency in ArKO mice was associated with significant increases in LPS-induced serum interleukin-6 (IL-6), tumor necrosis factor, monocyte chemotactic protein 1, and interferon-gamma levels, which were significantly abrogated by administration of 16alpha-LE2, but not 8beta-VE2. In contrast, both 16alpha-LE2 and 8beta-VE2 significantly increased LPS-induced IL-10 levels. Estrogen deficiency was also associated with significant exacerbation of AIA and antigen-specific T cell proliferation, which was reversed by administration of either 16alpha-LE2 or 8beta-VE2. ArKO mice showed increased antigen-specific T cell proliferation in response to immunization with type II collagen (CII). Administration of 16alpha-LE2, but not 8beta-VE2, significantly reduced the severity of CIA, which was associated with inhibition of anti-CII-specific IgG.

CONCLUSION

These data indicate that endogenous estrogen plays an essential inhibitory role in inflammation in male mice and that ERalpha is the dominant receptor that mediates these effects.

The effects of hormone replacement therapy on autoimmune disease: rheumatoid arthritis and systemic lupus erythematosus

Autoimmune diseases are generally more common in women than men; however, there is no simple explanation for this. Sex hormones, especially estrogen (but also prolactin and testosterone), play important roles in these diseases. Estrogens are generally considered to enhance autoimmunity and have multiple effects on the immune system through various cell types and molecular pathways. There is much evidence supporting the role of estrogen in the pathogenesis of systemic lupus erythematosus (SLE): the disease occurs much more frequently in women, especially during the years of child-bearing potential, and commonly flares during pregnancy. The relationship between estrogen and the development of SLE is complex, however. Exogenous estrogens have been historically avoided in women with SLE due to the widely held view that they could activate disease and their use remains controversial. Current evidence from prospective trials suggests that there may be a small increased risk of mild/moderate flares in women with SLE taking hormone replacement therapy (HRT), but the risk of major flare does not appear to be increased. In rheumatoid arthritis, HRT does not appear to be associated with an increased risk of disease flare and may actually improve disease activity. In all individuals with autoimmune disease, the risk of venous thrombosis associated with oral HRT is an important factor that should also be considered.

Distinct roles for AF-1 and -2 of ER-alpha in regulation of MMP-13 promoter activity

Previous studies have indicated that ER-alpha can influence the activity of the MMP-13 promoter. ER-alpha activity is mediated by two separate transcriptional activation domains (AF-1 and AF-2). The present study focused on analyzing the roles of these domains on the activation of the MMP-13 promoter. Transfection of synoviocytes with an ER-alpha construct lacking the C-terminus AF-2 domain led to significant elevation in MMP-13 promoter activity compared to wild type ER-alpha. Progressive deletions in the N-terminal AF-1 domain led to significant losses in MMP-13 promoter activity. MMP-13 promoter mutagenesis indicated that an AP-1 regulatory site was essential for ER-alpha mutant activity. Thus, both AF-1 and AF-2 domains of ER-alpha are required for regulation of MMP-13 promoter activity. As ER variants and ER related proteins have been implicated in bone and joint disorders, these findings provide understanding of the possible role of ER variants in the development of such conditions.