Osteoporosis in experimental postmenopausal polyarthritis: the relative contributions of estrogen deficiency and inflammation

Generalized osteoporosis in postmenopausal rheumatoid arthritis (RA) is caused both by estrogen deficiency and by the inflammatory disease. The relative importance of each of these factors is unknown. The aim of this study was to establish a murine model of osteoporosis in postmenopausal RA, and to evaluate the relative importance and mechanisms of menopause and arthritis-related osteoporosis. To mimic postmenopausal RA, DBA/1 mice were ovariectomized, followed by the induction of type II collagen-induced arthritis. After the mice had been killed, paws were collected for histology, one femur for bone mineral density (BMD) and sera for analyses of markers of bone resorption (RatLaps; type I collagen cross-links, bone formation (osteocalcin) and cartilage destruction (cartilage oligomeric matrix protein), and for the evaluation of antigen-specific and innate immune responsiveness. Ovariectomized mice displayed more severe arthritis than sham-operated controls. At termination of the experiment, arthritic control mice and non-arthritic ovariectomized mice displayed trabecular bone losses of 26% and 22%, respectively. Ovariectomized mice with arthritis had as much as 58% decrease in trabecular BMD. Interestingly, cortical BMD was decreased by arthritis but was not affected by hormonal status. In addition, markers of bone resorption and cartilage destruction were increased in arthritic mice, whereas markers of bone formation were increased in ovariectomized mice. This study demonstrates that the loss of endogenous estrogen and inflammation contribute additively and equally to osteoporosis in experimental postmenopausal polyarthritis. Markers of bone remodeling and bone marrow lymphocyte phenotypes indicate different mechanisms for the development of osteoporosis caused by ovariectomy and arthritis in this model

Hormone replacement therapy in rheumatoid arthritis is associated with lower serum levels of soluble IL-6 receptor and higher insulin-like growth factor 1

Hormone replacement therapy (HRT) modulates the imbalance in bone remodeling, thereby decreasing bone loss. Sex hormones are known to influence rheumatic diseases. The aim of this study was to investigate the effects of HRT on the serum levels of hormones and cytokines regulating bone turnover in 88 postmenopausal women with active rheumatoid arthritis (RA) randomly allocated to receive HRT plus calcium and vitamin D(3 )or calcium and vitamin D(3 )alone for 2 years. An increase in estradiol (E(2)) correlated strongly with improvement of bone mineral density in the hip (P < 0.001) and lumbar spine (P < 0.001). Both baseline levels and changes during the study of IL-6 and erythrocyte sedimentation rate were correlated positively (P < 0.001). HRT for 2 years resulted in an increase of the bone anabolic factor, insulin-like growth factor 1 (IGF-1) (P < 0.05) and a decrease of serum levels of soluble IL-6 receptor (sIL-6R) (P < 0.05), which is known to enhance the biological activity of IL-6, an osteoclast-stimulating and proinflammatory cytokine. Baseline levels of IL-6 and IGF-1 were inversely associated (P < 0.05), and elevation of IGF-1 was connected with decrease in erythrocyte sedimentation rate (P < 0.05) after 2 years. Interestingly, increase in serum levels of E(2 )was associated with reduction of sIL-6R (P < 0.05) and reduction of sIL-6R was correlated with improved bone mineral density in the lumbar spine (P < 0.05). The latter association was however not significant after adjusting for the effect of E(2 )(P = 0.075). The influences of IGF-1 and the IL-6/sIL-6R pathways suggest possible mechanisms whereby HRT may exert beneficial effects in RA. However, to confirm this hypothesis future and larger studies are needed

Estren promotes androgen phenotypes in primary lymphoid organs and submandibular glands

BACKGROUND: Estrogens and androgens have extensive effects on the immune system, for example they suppress both T and B lymphopoiesis in thymus and bone marrow. Submandibular glands are sexually dimorphic in rodents, resulting in larger granular convoluted tubules in males compared to females. The aim of the present experiments was to investigate the estrogenic and androgenic effects of 4-estren-3α,17β-diol (estren) on thymus, bone marrow and submandibular glands, and compare the effects to those of 17β-estradiol (E2) and 5α-dihydrotestosterone (DHT), respectively. Estrogen receptors (ERs) were blocked by treatment of mice with the ER-antagonist ICI 182,780; also, knock-out mice lacking one or both ERs were used. RESULTS: As expected, the presence of functional ERs was mandatory for all the effects of E2. Similar to DHT-treatment, estren-treatment resulted in decreased thymus weight, as well as decreased frequency of bone marrow B cells. Treatment with estren or DHT also resulted in a shift in submandibular glands towards an androgen phenotype. All the effects of estren and DHT were independent of ERs. CONCLUSION: Our study is the first to show that estren has similar effects as the androgen DHT on lymphopoiesis in thymus and bone marrow, and on submandibular glands, and that these effects are independent of estrogen receptors. This supports the hypothesis of estren being able to signal through the androgen receptor

Androgen Receptors in Epithelial Cells Regulate Thymopoiesis and Recent Thymic Emigrants in Male Mice

Androgens have profound effects on T cell homeostasis, including regulation of thymic T lymphopoiesis (thymopoiesis) and production of recent thymic emigrants (RTEs), i. e., immature T cells that derive from the thymus and continue their maturation to mature naive T cells in secondary lymphoid organs. Here we investigated the androgen target cell for effects on thymopoiesis and RTEs in spleen and lymph nodes. Male mice with a general androgen receptor knockout (G-ARKO), T cell-specific (T-ARKO), or epithelial cell-specific (E-ARKO) knockout were examined. G-ARKO mice showed increased thymus weight and increased numbers of thymic T cell progenitors. These effects were not T cell-intrinsic, since T-ARKO mice displayed unaltered thymus weight and thymopoiesis. In line with a role for thymic epithelial cells (TECs), E-ARKO mice showed increased thymus weight and numbers of thymic T cell progenitors. Further, E-ARKO mice had more CD4(+)and CD8(+)T cells in spleen and an increased frequency of RTEs among T cells in spleen and lymph nodes. Depletion of the androgen receptor in epithelial cells was also associated with a small shift in the relative number of cortical (reduced) and medullary (increased) TECs and increased CCL25 staining in the thymic medulla, similar to previous observations in castrated mice. In conclusion, we demonstrate that the thymic epithelium is a target compartment for androgen-mediated regulation of thymopoiesis and consequently the generation of RTEs

Impact of estrogen on IgG glycosylation and serum protein glycosylation in a murine model of healthy postmenopause

IntroductionThe glycosylation of immunoglobulin (Ig) G regulates IgG interaction capability with Fc gamma receptors found in all immune cells. In pathogenic conditions, estrogen can impact IgG levels and glycosylation. Following menopause, when estrogen levels decline affecting the immune system and potentially leading to a heightened susceptibility of immune activation.PurposeIn this study, we aim to determine if estrogen levels can regulate IgG glycosylation in postmenopausal healthy situations.MethodsMice were ovariectomized to simulate an estrogen-deficient postmenopausal status and then treated with 17-beta-estradiol (E2) at different doses and different administration strategies.ResultsUsing a highly sensitive liquid chromatography-tandem mass spectrometry (MS/MS) glycoproteomic method, we demonstrated that E2 treatment increased the degree of glycosylation on IgG-Fc with both galactosylation and sialylation in the position required for interaction with Fc gamma receptors. We also observed that only long-term estrogen deficiency reduces IgG levels and that estrogen status had no impact on total IgG sialylation on both Fab and Fc domains or general glycoprotein sialylation evaluated by ELISA. Furthermore, E2 status did not affect the total sialic acid content of total cells in lymphoid organs and neither B cells nor plasma cells.ConclusionThe study concluded that E2 treatment does not affect total serum glycoprotein sialylation but alters IgG glycosylation, including IgG sialylation, implying that estrogen functions as an intrinsic modulator of IgG sialylation and could thereby be one pathway by which estrogen modulates immunity

SERMs have substance specific effects on bone and these effects are mediated via ERαAF-1 in female mice

The bone-sparing effect of estrogens is mediated primarily via estrogen receptor (ER)α, which stimulates gene transcription through activation function (AF)-1 and AF-2. The role of ERαAF-1 for the estradiol (E(2)) effects is tissue specific. The selective ER modulators (SERMs) raloxifene (Ral), lasofoxifene (Las), and bazedoxifene (Bza) can be used to treat postmenopausal osteoporosis. They all reduce the risk for vertebral fractures, whereas Las and partly Bza, but not Ral, reduce the risk for nonvertebral fractures. Here, we have compared the tissue specificity of Ral, Las, and Bza and evaluated the role of ERαAF-1 for the effects of these SERMs, with an emphasis on bone parameters. We treated ovariectomized (OVX) wild-type (WT) mice and OVX mice lacking ERαAF-1 (ERαAF-1(0)) with E(2), Ral, Las, or Bza. All three SERMs increased trabecular bone mass in the axial skeleton. In the appendicular skeleton, only Las increased the trabecular bone volume/tissue volume and trabecular number, whereas both Ral and Las increased the cortical bone thickness and strength. However, Ral also increased cortical porosity. The three SERMs had only a minor effect on uterine weight. Notably, all evaluated effects of these SERMs were absent in ovx ERαAF-1(0) mice. In conclusion, all SERMs had similar effects on axial bone mass. However, the SERMs had slightly different effects on the appendicular skeleton since only Las increased the trabecular bone mass and only Ral increased the cortical porosity. Importantly, all SERM effects require a functional ERαAF-1 in female mice. These results could lead to development of more specific treatments for osteoporosis