Osteoprotective effects of estrogen membrane receptor GPR30 in ovariectomized rats

The detection of Gper1 as an important gene promoting jawbone regeneration in the context of estrogen deficiency

Numerous studies have demonstrated that estrogen deficiency inhibit the proliferation and differentiation of pre-osteoblasts in skeleton by affecting osteogenic signaling, lead to decreased bone mass and impaired regeneration. To explore the mechanisms maintaining bone regeneration under estrogen deficiency, we randomly selected 1102 clinical cases, in which female patients aged between 18 and 75 have underwent tooth extraction in Stomatological Hospital of Tongji University, there is little difference in the healing effect of extraction defects, suggesting that to some extent, the regeneration of jawbone is insensitive to the decreased estrogen level. To illuminate the mechanisms promoting jawbone regeneration under estrogen deficiency, a tooth extraction defect model was established in the maxilla of female rats who underwent ovariectomy (OVX) or sham surgery, and jawbone marrow stromal cells (BMSCs) were isolated for single-cell sequencing. Further quantitative PCR, RNA interference, alizarin red staining, immunohistochemistry and western blotting experiments demonstrated that in the context of ovariectomy, maxillary defects promoted G protein-coupled estrogen receptor 1 (Gper1) expression, stimulate downstream cAMP/PKA/pCREB signaling, and facilitate cell proliferation, and thus provided sufficient progenitors for osteogenesis and enhanced the regeneration capacity of the jawbone. Correspondingly, the heterozygous deletion of the Gper1 gene attenuated the phosphorylation of CREB, led to decreased cell proliferation, and impaired the restoration of maxillary defects. This study demonstrates the importance of Gper1 in maintaining jawbone regeneration, especially in the context of estrogen deficiency.

Ginsenoside Rg1 modulates PI3K/AKT pathway for enhanced osteogenesis via GPER

BACKGROUND

Osteoporosis is a systemic skeletal disorder characterized by decreased bone density and the degradation of bone tissue microarchitecture. Ginsenoside Rg1, derived from Panax ginseng, has been a part of traditional Chinese medicine in China for centuries, particularly for treating osteoporosis. However, there remains limited research on the osteogenic potential of Rg1 within the glucocorticoid-induced osteoporosis (GIOP) model and its specific mechanisms.

PURPOSE

The primary objective of this study is to investigate the osteogenic potential of Rg1 within the GIOP model and explore the signaling pathways associated with its in vivo and in vitro effects.

METHODS

Cell proliferation, differentiation and mineralization were evaluated by the Cell counting kit 8(CCK8) assay, alkaline phosphatase (ALP) test and Alizarin Red S staining, respectively. The qPCR technique was used to determine the relative expression of mRNA and the western blot was used to determine the relative expression of protein. In vivo experiments, spinal vertebrae staining in zebrafish larvae was accomplished by alizarin red S staining.

RESULTS

Zebrafish larvae's hatching, survival, malformation, and heart rate were unaffected by 50 μM of Rg1 in vivo, while the MEC3T3-E1 cell line's proliferation was unaffected by 50 μM of Rg1 in vitro. Meanwhile, Rg1 was shown to improve osteogenic differentiation or bone formation as well as the level of mRNA expression of osteogenic markers in vivo and in vitro. Treatment with Rg1 significantly increased the expression of G protein-coupled estrogen receptor (GPER) and pAKT. In addition, the GPER inhibitor G15 could significantly reduce the mRNA and protein expression levels of GPER and phosphorylated AKT, LY294002, a PI3K/AKT pathway inhibitor, markedly suppresses the expression of phosphorylated AKT, yet shows no significant impact on GPER expression. Both G15 and LY294002 can significantly blocked the Rg1-mediated enhancement of osteogenesis capacity in the GIOP model. In contrast, when both the agonists G1 of GPER and LY294002 were added, G1 increased the relative expression of mRNA and protein of GPER, but not the expression of osteogenic capacity and osteogenic markers.

CONCLUSIONS

This study investigates the mineralization effects and mechanisms of Ginsenoside Rg1 both in vitro and in vivo. For the first time, we propose that Rg1 might regulate osteogenesis by modulating AKT phosphorylation through mediating GPER expression within the PI3K/AKT pathway in the GIOP model. This discovery introduces novel targets and avenues for osteoporosis treatment.

Comorbidity of osteoporosis and Alzheimer's disease: Is `AKT `-ing on cellular glucose uptake the missing link?

Osteoporosis and Alzheimer's disease (AD) are both degenerative diseases. Osteoporosis often proceeds cognitive deficits, and multiple studies have revealed common triggers that lead to energy deficits in brain and bone. Risk factors for osteoporosis and AD, such as obesity, type 2 diabetes, aging, chemotherapy, vitamin deficiency, alcohol abuse, and apolipoprotein Eε4 and/or Il-6 gene variants, reduce cellular glucose uptake, and protective factors, such as estrogen, insulin, exercise, mammalian target of rapamycin inhibitors, hydrogen sulfide, and most phytochemicals, increase uptake. Glucose uptake is a fine-tuned process that depends on an abundance of glucose transporters (Gluts) on the cell surface. Gluts are stored in vesicles under the plasma membrane, and protective factors cause these vesicles to fuse with the membrane, resulting in presentation of Gluts on the cell surface. This translocation depends mainly on AKT kinase signaling and can be affected by a range of factors. Reduced AKT kinase signaling results in intracellular glucose deprivation, which causes endoplasmic reticulum stress and iron depletion, leading to activation of HIF-1α, the transcription factor necessary for higher Glut expression. The link between diseases and aging is a topic of growing interest. Here, we show that diseases that affect the same biochemical pathways tend to co-occur, which may explain why osteoporosis and/or diabetes are often associated with AD.

Role of estrogen receptors in health and disease

Estrogen receptors (ERs) regulate multiple complex physiological processes in humans. Abnormal ER signaling may result in various disorders, including reproductive system-related disorders (endometriosis, and breast, ovarian, and prostate cancer), bone-related abnormalities, lung cancer, cardiovascular disease, gastrointestinal disease, urogenital tract disease, neurodegenerative disorders, and cutaneous melanoma. ER alpha (ERα), ER beta (ERβ), and novel G-protein-coupled estrogen receptor 1 (GPER1) have been identified as the most prominent ERs. This review provides an overview of ERα, ERβ, and GPER1, as well as their functions in health and disease. Furthermore, the potential clinical applications and challenges are discussed.

Estrogen deficiency during puberty affects the expression of microRNA30a and microRNA503 in the mandibular condyle

BACKGROUND

The aim of this study was investigated if estrogen deficiency during puberty affects the expression of miRNA30a and miRNA503 in maxillary and mandibular growth centers, and also evaluated if ERα and ERβ are correlated with miRNA30a and miRNA503 expressions.

METHODS

Samples from 12 female Wistar rats randomized into experimental group (OVX) and control group (SHAM). At an age of 45 days animals were euthanized for miRNA expression analyses. RT-qPCR was performed to determine miRNA30a and miRNA503 expression in growth sites: midpalatal suture, condyle, mandibular angle, symphysis/parasymphysis and coronoid process. The data was carried out using the parametric tests at 5% of significance level.

RESULTS

miRNA 30a and miRNA503 presented higher levels in the condylar site in SHAM group when compared with OVX (p = 0.002 and p = 0.020, respectively). In the growth centers, a statistical significant difference was observed only for miRNA30a (p = 0.004), when compared mandibular angle with condyle the in OVX group (p = 0.001). A strong positive correlation between miRNA503 and ERα in the condyle of OVX group was observed (r = 0.90; p = 0.039 and it also between miRNA503 and ERβ in the coronoid process of the OVX group (r = 0.88; p = 0.05).

CONCLUSION

The results suggested that estrogen regulates specific miRNAs in maxillary and mandibular growth centers, which may participate in posttranscriptional regulation of estrogen-regulated genes.

Biochanin A Regulates Key Steps of Inflammation Resolution in a Model of Antigen-Induced Arthritis via GPR30/PKA-Dependent Mechanism

Biochanin A (BCA) is a natural organic compound of the class of phytochemicals known as flavonoids and isoflavone subclass predominantly found in red clover (Trifolium pratense). It has anti-inflammatory activity and some pro-resolving actions, such as neutrophil apoptosis. However, the effect of BCA in the resolution of inflammation is still poorly understood. In this study, we investigated the effects of BCA on the neutrophilic inflammatory response and its resolution in a model of antigen-induced arthritis. Male wild-type BALB/c mice were treated with BCA at the peak of the inflammatory process (12 h). BCA decreased the accumulation of migrated neutrophils, and this effect was associated with reduction of myeloperoxidase activity, IL-1β and CXCL1 levels, and the histological score in periarticular tissues. Joint dysfunction, as seen by mechanical hypernociception, was improved by treatment with BCA. The resolution interval (Ri) was also quantified, defining profiles of acute inflammatory parameters that include the amplitude and duration of the inflammatory response monitored by the neutrophil infiltration. BCA treatment shortened Ri from ∼23 h observed in vehicle-treated mice to ∼5.5 h, associated with an increase in apoptotic events and efferocytosis, both key steps for the resolution of inflammation. These effects of BCA were prevented by H89, an inhibitor of protein kinase A (PKA) and G15, a selective G protein–coupled receptor 30 (GPR30) antagonist. In line with the in vivo data, BCA also increased the efferocytic ability of murine bone marrow–derived macrophages. Collectively, these data indicate for the first time that BCA resolves neutrophilic inflammation acting in key steps of the resolution of inflammation, requiring activation of GPR30 and via stimulation of cAMP-dependent signaling.

Neuropeptides are associated with pain threshold and bone microstructure in ovariectomized rats

OBJECTIVES

Postmenopausal osteoporosis (PMO) is a metabolic skeletal disorder with impaired bone density and bone quality in postmenopausal women. The aim of the present study was to investigate the correlation between neuropeptides, bone microstructure and pain threshold in ovariectomized (OVX) rats.

METHODS

Female rats were randomly divided into the ovariectomized (OVX) group and the sham surgery (SHAM) group. Bone microstructure and immunocytochemistry for substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) in tibial and DRG were performed. Pain threshold was assessed at post-operative 11 weeks. Pearson correlation coefficients were calculated between neuropeptides, bone microstructure and pain threshold.

RESULTS

Significant decreases in bone volume fraction (BV/TV) and trabecular number (Tb. N) but significant increases in trabecular spacing (Tb.Sp) were showed in OVX group. Mechanical pain threshold (MPT) in OVX group was significantly decreased. The MOD values for SP, CGRP and VIP of tibial in OVX group were significantly lower, whereas NPY, NPY1R and NPY2R were significantly higher. And SP, CGRP, VIP, NPY and NPY2R of DRG were significantly increased in OVX group, while NPY1R was significantly decreased. Correlation analysis showed that NPY, Y1R and Y2R in bone were negatively correlated with BV/TV. MPT was negatively correlated with NPY and Y2R in DRG, and positively correlated with Y1R in DRG.

CONCLUSIONS

Our results suggested that SP, CGRP, VIP and NPY were involved in the osteoporotic bone microstructure and mechanical hypersensitivity in OVX rats, indicating the potential to utilize neuropeptides as novel therapeutic targets for PMO.

Sweroside promotes osteoblastic differentiation and mineralization via interaction of membrane estrogen receptor-α and GPR30 mediated p38 signalling pathway on MC3T3-E1 cells

BACKGROUND

Dipsaci Radix has been clinically used for thousands of years in China for strengthening muscles and bones. Sweroside is the major active iridoid glycoside isolated from Dipsaci Radix. It has been reported that sweroside can promote alkaline phosphatase (ALP) activity in both the human osteosarcoma cell line MG-63 and rat osteoblasts. However, the underlying mechanism involved in these osteoblastic processes is poorly understood.

PURPOSE

This study aimed to characterize the bone protective effects of sweroside and to investigate the signaling pathway that is involved in its actions in MC3T3-E1 cells.

METHODS

Cell proliferation, differentiation and mineralization were evaluated by the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay, ALP test and Alizarin Red S staining, respectively. The concentration of sweroside in intracellular and extracellular fluids was determined by ultra-performance liquid chromatography coupled to triple quadrupole xevo-mass spectrometry (UPLC/TQ-XS-MS). Proteins associated with the osteoblastic signaling pathway were analysed by western blot and immunofluorescence methods.

RESULTS

Sweroside did not obviously affect the proliferation but significantly promoted the ALP activity and mineralization of MC3T3-E1 cells. The maximal absorption amount 0.465 ng/ml (1.3 × 10^-9 M) of sweroside was extremely lower than the tested concentration of 358.340 ng/ml (10^-6 M), indicating an extremely low absorption rate by MC3T3-E1 cells. Moreover, the ALP activity, the protein expression of ER-α and G protein-coupled receptor 30 (GPR30) induced by sweroside were markedly blocked by both the ER antagonist ICI 182780 and the GPR30 antagonist G15. In addition, sweroside also activated the phosphorylation of p38 kinase (p-p38), while the phosphorylation effects together with ALP and mineralization activities were completely blocked by a p38 antagonist, SB203580. Additionally, the phosphorylation of p38 induced by sweroside were markedly blocked by both the ER antagonist ICI 182780 and the GPR30 antagonist G15.

CONCLUSIONS

The present study indicated that sweroside, as a potential agent in treatment of osteoporosis, might exert beneficial effects on MC3T3-E1 cells by interaction with the membrane estrogen receptor-α and GPR30 that then activates the p38 signaling pathway. This is the first study to report the specific mechanism of the effects of sweroside on osteoblastic differentiation and mineralization of MC3T3-E1 cells.

Role of estrone on the regulation of osteoblastogenesis

Although estradiol bone contribution has been deeply studied, little is known about the action of estrone. We investigated the direct action of estrone on osteoblasts growth and differentiation, with focus on the biochemical mechanism displayed by the estrogen. Murine calvarial osteoblast cultures in vitro exposed to 10 nM estrone were employed. Estrone enhanced gene expression of the osteogenic differentiation marker, Runx2 mRNA (150% above control). The hormone significantly increased cell proliferation (38% above control), nitric oxide production (108% above control), alkaline phosphatase activity (50% above control), in addition to stimulation of extracellular matrix mineralization. Using specific antagonists, we found that the mechanism of action of estrone involves estrogen receptor, nitric oxide synthase and MAPK signalling pathways participation. The hormone acts by its own and probably not via conversion to estradiol, since 17 B HSD inhibition did not affect the hormonal action. This work shows a novel action of estrone on bone cells promoting osteoblastogenesis.

Role of estrogen and its receptors mediated-autophagy in cell fate and human diseases

Studies have shown that morbidity of several diseases varies between males and females. This difference likely arises due to sex-related hormones. Estrogen, a primary female sex steroid hormone, plays a critical role in mediating many of the physiological functions like growth, differentiation, metabolism, and cell death. Recently, it has been demonstrated that estrogen mediates autophagy through its receptors (ERs) namely ERα, ERβ, and G-protein coupled estrogen receptor (GPER). However, the specific role of estrogen and its receptors mediated-autophagy in cell fate and human diseases such as cancers, cardiovascular disease and nervous system disease remains unclear. In this review, we comprehensively summarize the complex role of estrogen and its receptors-mediated autophagy in different cell lines and human diseases. In addition, we further discuss the key signaling molecules governing the role of ERs in autophagy. This review will serve as the basis for a proposed model of autophagy constituting a new frontier in estrogen-related human diseases. Here, we discuss the dual role of ERα in classical and non-classical autophagy through B-cell lymphoma 2 (BCL2)-associated athanogene 3 (BAG3). Next, we review the role of ERβ in pro-survival pathways through the promotion of autophagy under stress conditions. We further discuss activation of GPER via estrogen often mediates autophagy or mitophagy suppression, respectively. In summary, we believe that understanding the relationship between estrogen and its receptors mediated-autophagy on cell fate and human diseases will provide insightful knowledge for future therapeutic implications.

Ligustilide, a major bioactive component of Angelica sinensis, promotes bone formation via the GPR30/EGFR pathway

Angelica sinensis (Oliv.) Diels is a widely-used traditional Chinese herbal medicine in treating osteoporosis. Ligustilide (LIG) is the main component of A. sinensis and is considered to be the most effective biologically active ingredient in this plant. LIG has been found to have multiple pharmacological activities, such as anti-atherosclerosis, neuroprotection, anticancer, anti-inflammatory and analgesic. However, little is known regarding its anti-osteoporotic effects. The aims of this study were to investigate any protective effect of LIG on bone formation. The results showed that LIG significantly ameliorated inhibition of bone formation in zebrafish caused by prednisolone. LIG promoted osteoblast differentiation, including that of the pre-osteoblastic cell line MC3T3-E1 and bone marrow mesenchymal stem cells. LIG greatly improved the viability of MC3T3-E1 cells exposed to H₂O₂, attenuated H₂O₂-induced apoptosis and increased the expression of Bcl-2. Furthermore, LIG treatment lead to marked activation of phosphorylated EGFR and ERK1/2. These effects could be obviously inhibited by blocking GPR30 signaling with the specific inhibitor G15. Collectively, the results reveal that GPR30 is a positive switch for LIG to increase bone formation via regulation of EGFR, and these results provide evidence for the potential of LIG to treat osteoporosis.

Pyk2 deficiency potentiates osteoblast differentiation and mineralizing activity in response to estrogen or raloxifene

Bone remodeling is controlled by the actions of bone-degrading osteoclasts and bone-forming osteoblasts (OBs). Aging and loss of estrogen after menopause affects bone mass and quality. Estrogen therapy, including selective estrogen receptor modulators (SERMs), can prevent bone loss and increase bone mineral density in post-menopausal women. Although investigations of the effects of estrogen on osteoclast activity are well advanced, the mechanism of action of estrogen on OBs is still unclear. The proline-rich tyrosine kinase 2 (Pyk2) is important for bone formation and female mice lacking Pyk2 (Pyk2-KO) exhibit elevated bone mass, increased bone formation rate and reduced osteoclast activity. Therefore, in the current study, we examined the role of estrogen signaling on the mechanism of action of Pyk2 in OBs. As expected, Pyk2-KO OBs showed significantly higher proliferation, matrix formation, and mineralization than WT OBs. In addition we found that Pyk2-KO OBs cultured in the presence of either 17β-estradiol (E2) or raloxifene, a SERM used for the treatment of post-menopausal osteoporosis, showed a further robust increase in alkaline phosphatase (ALP) activity and mineralization. We examined the possible mechanism of action and found that Pyk2 deletion promotes the proteasome-mediated degradation of estrogen receptor α (ERα), but not estrogen receptor β (ERβ). As a consequence, E2 signaling via ERβ was enhanced in Pyk2-KO OBs. In addition, we found that Pyk2 deletion and E2 stimulation had an additive effect on ERK phosphorylation, which is known to stimulate cell differentiation and survival. Our findings suggest that in the absence of Pyk2, estrogen exerts an osteogenic effect on OBs through altered ERα and ERβ signaling. Thus, targeting Pyk2, in combination with estrogen or raloxifene, may be a novel strategy for the prevention and/or treatment of bone loss diseases.

Respective role of membrane and nuclear estrogen receptor (ER) α in the mandible of growing mice: Implications for ERα modulation

Estrogens play an important role in bone growth and maturation as well as in the regulation of bone turnover in adults. Although the effects of 17β-estradiol (E2) are well documented in long bones and vertebrae, little is known regarding its action in the mandible. E2 actions could be mediated by estrogen receptor (ER) α or β. ERs act primarily as transcriptional factors through two activation functions (AFs), AF1 and AF2, but they can also elicit membrane-initiated steroid signaling (MISS). The aim of the present study was to define ER pathways involved in E2 effects on mandibular bone. Using mice models targeting ERβ or ERα, we first show that E2 effects on mandibular bone are mediated by ERα and do not require ERβ. Second, we show that nuclear ERαAF2 is absolutely required for all the actions of E2 on mandibular bone. Third, inactivation of ERαMISS partially reduced the E2 response on bone thickness and volume, whereas there was no significant impact on bone mineral density. Altogether, these results show that both nuclear and membrane ERα are requested to mediate full estrogen effects in the mandible of growing mice. Finally, selective activation of ERαMISS is able to exert an effect on alveolar bone but not on the cortical compartment, contrary to its protective action on femoral cortical bone. To conclude, these results highlight similarities but also specificities between effects of estrogen in long bones and in the mandible that could be of interest in therapeutic approaches to treat bone mass reduction. © 2018 American Society for Bone and Mineral Research.

Extra-nuclear effects of estrogen on cortical bone in males require ERαAF-1

Estradiol (E2) signaling via estrogen receptor alpha (ERα) is important for the male skeleton as demonstrated by ERα inactivation in both mice and man. ERα mediates estrogenic effects not only by translocating to the nucleus and affecting gene transcription but also by extra-nuclear actions e.g., triggering cytoplasmic signaling cascades. ERα contains various domains, and the role of activation function 1 (ERαAF-1) is known to be tissue specific. The aim of this study was to determine the importance of extra-nuclear estrogen effects for the skeleton in males and to determine the role of ERαAF-1 for mediating these effects. Five-month-old male wild-type (WT) and ERαAF-1-inactivated (ERαAF-1⁰) mice were orchidectomized and treated with equimolar doses of 17β-estradiol (E2) or an estrogen dendrimer conjugate (EDC), which is incapable of entering the nucleus and thereby only initiates extra-nuclear ER actions or their corresponding vehicles for 3.5 weeks. As expected, E2 treatment increased cortical thickness and trabecular bone volume per total volume (BV/TV) in WT males. EDC treatment increased cortical thickness in WT males, whereas no effect was detected in trabecular bone. In ERαAF-1⁰ males, E2 treatment increased cortical thickness, but did not affect trabecular bone. Interestingly, the effect of EDC on cortical bone was abolished in ERαAF-1⁰ mice. In conclusion, extra-nuclear estrogen signaling affects cortical bone mass in males, and this effect is dependent on a functional ERαAF-1. Increased knowledge regarding estrogen signaling mechanisms in the regulation of the male skeleton may aid the development of new treatment options for male osteoporosis.

G-1 exerts neuroprotective effects through G protein-coupled estrogen receptor 1 following spinal cord injury in mice

Spinal cord injury (SCI) always occurs accidently and leads to motor dysfunction because of biochemical and pathological events. Estrogen has been shown to be neuroprotective against SCI through estrogen receptors (ERs), but the underlying mechanisms have not been fully elucidated. In the present study, we investigated the role of a newly found membrane ER, G protein-coupled estrogen receptor 1 (GPR30 or GPER1), and discussed the feasibility of a GPR30 agonist as an estrogen replacement. Forty adult female C57BL/6J mice (10-12 weeks old) were divided randomly into vehicle, G-1, E2, G-1 + G-15 and E2 + G-15 groups. All mice were subjected to SCI using a crushing injury approach. The specific GPR30 agonist, G-1, mimicked the effects of E2 treatment by preventing SCI-induced apoptotic cell death and enhancing motor functional recovery after injury. GPR30 activation regulated phosphatidylinositol 3-kinase (PI3K)/Akt and MAPK/extracellular signal-regulated kinase (ERK) signalling pathways, increased GPR30 and anti-apoptosis proteins Bcl-2 and brain derived neurotrophic factor (BDNF), but decreased the pro-apoptosis factor Bax and cleaved caspase-3. However, the neuroprotective effects of G-1 and E2 were blocked by the specific GPR30 antagonist, G-15. Thus, GPR30 rather than classic ERs is required to induce estrogenic neuroprotective effects. Given that estrogen replacement therapy may cause unexpected side effects, especially on the reproductive system, GPR30 agonists may represent a potential therapeutic approach for treating SCI.