Estradiol via estrogen receptor beta inhibits chondrogenesis of mouse vertebral growth plate in vitro

Genistein inhibits chondrogenic differentiation and mineralization of ATDC5 cells

Isoflavones are phytoestrogens abundant in leguminous crops and are used to prevent a variety of hormonal disorders. In the present study, the effects of genistein and daidzein on the chondrogenic differentiation of ATDC5 cells were investigated. Genistein (10 μM) treatment markedly reduced production of sulfated proteoglycans and collagen fibers in the ATDC5 cells. Genistein suppressed the expression of genes involved in chondrocyte differentiation such as Sox9, Col2a1, Col10a1, Acan, and Tgfb1. Additionally, genistein significantly decreased calcium deposition in ATDC5 cells during chondrogenic differentiation; however, it increased calcification under non-chondrogenic mineralizing conditions. Daidzein exhibited a similar effect of suppressing chondrogenesis in ATDC5 cells, although its efficacy was 10-times lower than that of genistein. These findings suggest that a high concentration of genistein inhibits chondrogenesis and chondrogenic mineralization, whereas it enhances non-chondrogenic mineralization.

Estrogen Regulation of the Expression of Pain Factor NGF in Rat Chondrocytes

OBJECTIVE

Pain is the main symptom of osteoarthritis (OA). Nerve growth factor (NGF) plays a crucial role in the generation of OA pain. And estrogen-alone used resulted in a sustained joint pain reduction in postmenopausal women. So we aim to find whether estrogen alters chondrocytes' NGF level, affecting OA pain.

METHODS

Primary chondrocytes and cartilage explants isolated from Sprague Dawley rat knees were cultured with physiological concentrations of estrogen (17β-Estradiol ≥ 98%, E2), Estrogen Receptor α (ERα) inhibitor and stimulants. Then, chondrocytes NGF mRNA expression and protein release were analyzed by a quantitative real-time polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA) respectively. Additionally, cultures were pre-incubated with MEK-ERK inhibitor to identify the signaling pathway that estrogen alters NGF mRNA and protein levels.

RESULTS

We found that chondrocytes NGF expression and release were decreased by E2. E2 also reduced chondrocytes IL-1β-stimulated or TGF-β1-stimulated NGF expression. Phosphorylated extracellular signal-regulated kinasep1/2 (p-ERK1/2) signals were detected stronger than the control group by Western Blotting (WB). When we cultured chondrocytes with PD98059 (MEK-ERK inhibitor, PD), NGF mRNA expression was added to 1.41Ct (2.07±0.1 fold).

CONCLUSION

We showed that E2 reduces chondrocytes NGF expression significantly, even after stimulation by TGF-β1 or IL-1β. MEK-ERK signaling is involved in this process.

SOX9 keeps growth plates and articular cartilage healthy by inhibiting chondrocyte dedifferentiation/osteoblastic redifferentiation

Cartilage is essential throughout vertebrate life. It starts developing in embryos when osteochondroprogenitor cells commit to chondrogenesis, activate a pancartilaginous program to form cartilaginous skeletal primordia, and also embrace a growth-plate program to drive skeletal growth or an articular program to build permanent joint cartilage. Various forms of cartilage malformation and degeneration diseases afflict humans, but underlying mechanisms are still incompletely understood and treatment options suboptimal. The transcription factor SOX9 is required for embryonic chondrogenesis, but its postnatal roles remain unclear, despite evidence that it is down-regulated in osteoarthritis and heterozygously inactivated in campomelic dysplasia, a severe skeletal dysplasia characterized postnatally by small stature and kyphoscoliosis. Using conditional knockout mice and high-throughput sequencing assays, we show here that SOX9 is required postnatally to prevent growth-plate closure and preosteoarthritic deterioration of articular cartilage. Its deficiency prompts growth-plate chondrocytes at all stages to swiftly reach a terminal/dedifferentiated stage marked by expression of chondrocyte-specific (Mgp) and progenitor-specific (Nt5e and Sox4) genes. Up-regulation of osteogenic genes (Runx2, Sp7, and Postn) and overt osteoblastogenesis quickly ensue. SOX9 deficiency does not perturb the articular program, except in load-bearing regions, where it also provokes chondrocyte-to-osteoblast conversion via a progenitor stage. Pathway analyses support roles for SOX9 in controlling TGFβ and BMP signaling activities during this cell lineage transition. Altogether, these findings deepen our current understanding of the cellular and molecular mechanisms that specifically ensure lifelong growth-plate and articular cartilage vigor by identifying osteogenic plasticity of growth-plate and articular chondrocytes and a SOX9-countered chondrocyte dedifferentiation/osteoblast redifferentiation process.

Small molecule compounds promote the proliferation of chondrocytes and chondrogenic differentiation of stem cells in cartilage tissue engineering

The application of tissue engineering to generate cartilage is limited because of low proliferative ability and unstable phenotype of chondrocytes. The sources of cartilage seed cells are mainly chondrocytes and stem cells. A variety of methods have been used to obtain large numbers of chondrocytes, including increasing chondrocyte proliferation and stem cell chondrogenic differentiation via cytokines, genes, and proteins. Natural or synthetic small molecule compounds can provide a simple and effective method to promote chondrocyte proliferation, maintain a stable chondrocyte phenotype, and promote stem cell chondrogenic differentiation. Therefore, the study of small molecule compounds is of great importance for cartilage tissue engineering. Herein, we review a series of small molecule compounds and their mechanisms that can promote chondrocyte proliferation, maintain chondrocyte phenotype, or induce stem cell chondrogenesis. The studies in this field represent significant contributions to the research in cartilage tissue engineering and regenerative medicine.

Estrogen enhances mismatch repair by induction of MLH1 expression via estrogen receptor-β

Epidemiological data demonstrated that hormone replace treatment has protective effect against colorectal cancer (CRC). Our previous studies showed that this effect may be associated with DNA mismatch repair. This study aims to investigate the mechanism of estrogen induction of MLH1, and whether colorectal tumor proliferation can be inhibited through induction of MLH1 by estrogen signal pathway. Human CRC cell lines were used to examine the regulation of MLH1 expression by over-expression and depletion of estrogen receptor-α (ERα) and estrogen receptor-β (ERβ), under the treatment with 17β-estradiol or β-Estradiol 6-(O-carboxy-methyl)oxime:BSA, followed by a real-time Q-PCR and Western blotting analysis. Luciferase reporter and chromatin immunoprecipitation assays were used to identify the estrogen response elements in the proximal promoter of MLH1 gene. Then, the influence of estrogen-induced MLH1 on CRC tumor growth were determined in vitro and in vivo. We found that mismatch repair ability and microsatellite stability of cells were enhanced by estrogen via induction of MLH1 expression, which was mediated by ERβ, through a transcriptional activation process. Furthermore, we identified that ERβ exerted an inhibitory effect on CRC tumor proliferation in vitro and in vivo, combined with 5-FU, through up-regulation of MLH1 expression. Finally, we concluded that estrogen enhances mismatch repair ability and tumor inhibition effect in vitro and in vivo, via induction of MLH1 expression mediated by ERβ.

Regulation of bone growth via ligand-specific activation of estrogen receptor alpha

Estrogens are well known for their capacity to promote bone maturation and at high doses to induce growth plate closure and thereby stop further growth. High-dose estrogen treatment has therefore been used to limit growth in extremely tall girls. However, recent data suggest that this treatment may have severe side effects, including increased risk of cancer and reduced fertility. We hypothesized that estrogenic effects in bone are mediated via ERα signaling. Twelve-week-old ovariectomized female C57BL/6 mice were subcutaneously injected for 4 weeks with E2 or selective ERα (PPT) or ERβ (DPN) agonists. After killing, tibia and femur lengths were measured, and growth plate morphology was analyzed. E2- and PPT-treated mice had shorter tibiae and femur bones when compared to vehicle-treated controls, whereas animals treated with DPN had similar bone lengths compared to controls. Growth plate height and hypertrophic zone height were reduced in animals treated with E2 or PPT but not in those treated with DPN, supporting that the effect was mediated via ERα. Moreover, PCNA staining revealed suppressed proliferation of chondrocytes in the tibia growth plate in PPT- or E2-treated mice compared to controls. Our data show that estrogenic effects on bone growth and growth plate maturation are mainly mediated via ERα. Our findings may have direct implications for the development of new and more selective treatment modalities of extreme tall stature using selective estrogen receptor modulators that may have low side effects than high-dose E2 treatment.

Estradiol Synthesis in Gut-Associated Lymphoid Tissue: Leukocyte Regulation by a Sexually Monomorphic System

17β-estradiol is a potent sex hormone synthesized primarily by gonads in females and males that regulates development and function of the reproductive system. Recent studies show that 17β-estradiol is locally synthesized in nonreproductive tissues and regulates a myriad of events, including local inflammatory responses. In this study, we report that mesenteric lymph nodes (mLNs) and Peyer's patches (Pps) are novel sites of de novo synthesis of 17β-estradiol. These secondary lymphoid organs are located within or close to the gastrointestinal tract, contain leukocytes, and function at the forefront of immune surveillance. 17β-estradiol synthesis was initially identified using a transgenic mouse with red fluorescent protein coexpressed in cells that express aromatase, the enzyme responsible for 17β-estradiol synthesis. Subsequent immunohistochemistry and tissue culture experiments revealed that aromatase expression was localized to high endothelial venules of these lymphoid organs, and these high endothelial venule cells synthesized 17β-estradiol when isolated and cultured in vitro. Both mLNs and Pps contained 17β-estradiol with concentrations that were significantly higher than those of peripheral blood. Furthermore, the total amount of 17β-estradiol in these organs exceeded that of the gonads. Mice lacking either aromatase or estrogen receptor-β had hypertrophic Pps and mLNs with more leukocytes than their wild-type littermates, demonstrating a role for 17β-estradiol in leukocyte regulation. Importantly, we did not observe any sex-dependent differences in aromatase expression, 17β-estradiol content, or steroidogenic capacity in these lymphoid organs.