Aromatase expression in a human osteoblastic cell line increases in response to prostaglandin E(2) in a dexamethasone-dependent fashion

Brain-derived estrogen: a critical player in maintaining cognitive health of aged female rats, possibly involving GPR30

Brain-derived estrogen is an endogenous neuroprotective agent, whether and how might this protective function with aging, especially postmenopausal drops in circulating estrogen, remain unclear. We herein subjected 6, 14, and 18 Mon female rats to mimic natural aging, and found that estrogen synthesis is more active in the healthy aged brain, as evidenced by the highest levels of mRNA and protein expression of aromatase, the key enzyme of E2 biosynthesis, among the three groups. Aromatase knockout in forebrain neurons (FBN-Aro-/-) impaired hippocampal and cortical neurons, and cognitive function in 18 Mon rats, compared to wild-type controls. Furthermore, estrogen nuclear receptors (ERα/β) displayed opposite changes, with a significant ERα decrease and ERβ increase, while membrane receptor GPR30 expressed stably in hippocampus during aging. Intriguingly, GPR30, but not ERα and ERβ, was decreased by FBN-Aro-/-. The results indicate that GPR30 is more sensitive to brain local E2 synthesis. Our findings provide evidence of a critical role for brain-derived estrogen in maintaining healthy brain function in older individuals, possibly involving GPR30.

Chronic exposure to diclofenac induces delayed mandibular defects in medaka (Oryzias latipes) in a sex-dependent manner

Diclofenac is widely distributed in freshwater environments. To support a robust aquatic risk assessment, medaka (Oryzias latipes) were exposed to diclofenac at sublethal concentrations of 0.608, 2.15, 7.29, 26.5, and 94.8 μg/L (as mean measured concentrations) from fertilized eggs to 90-day posthatch. Except for the induction of mandibular defects, no deleterious effects were observed on hatching success and time to hatching at the embryonic stage, or on posthatch mortality, growth in hatched larvae and juveniles, and no abnormal behavior was observed. After 40-day posthatch, mandibular defects in the fish were observed at a concentration of 7.29 μg/L and above. Cumulatively, a morphological examination showed that 4% of the fish in the 7.29 μg/L treatment, 20% in the 26.5 μg/L treatment, and 38% in the 94.8 μg/L treatment exhibited mandibular defects, and the sex ratio of fish with mandibular defects was skewed toward males. These results suggest that diclofenac affects bone remodeling in the lower jaw of medaka after puberty in a sex-dependent manner. The lowest observed-effect concentration and no observed-effect concentration of diclofenac for mandibular dysmorphism through the partial life cycle exposure of the medaka were 26.5 and 7.29 μg/L, respectively.

Effect of β-agonist on the dexamethasone-induced expression of aromatase by the human monocyte cells

Emerging evidence suggests that sex steroids are important for human skin health. In particular, estrogen improves skin thickness, elasticity and moisture of older women. The major source of circulating estrogen is the ovary; however, local estrogen synthesis and secretion have important roles in, for example, bone metabolism and breast cancer development. We hypothesized that infiltrated peripheral monocytes are one of the sources of estrogen in skin tissues. We also hypothesized that, during atopic dermatitis under stress, a decline in the hypothalamus-pituitary-adrenal axis (HPA) and facilitation of the (hypothalamus)-sympathetic-adrenomedullary system (SAM) attenuates estrogen secretion from monocytes. Based on this hypothesis, we tested aromatase expression in the human peripheral monocyte-derived cell line THP-1 in response to the synthetic glucocorticoid dexamethasone (Dex), the synthetic β-agonist isoproterenol (Iso) and the β-antagonist propranolol (Pro). Dex mimics glucocorticoid secreted during excitation of the HPA, and Iso mimics catecholamine secreted during excitation of the SAM. We found that aromatase activity and the CYP19A1 gene transcript were both upregulated in THP-1 cells in the presence of Dex. Addition of Iso induced their downregulation and further addition of Pro rescued aromatase expression. These results may suggest that attenuation of estrogen secretion from peripheral monocytes could be a part of the pathology of stress-caused deterioration of atopic dermatitis. Further examination using an in vitro human skin model including THP-1 cells might be a valuable tool for investigating the therapeutic efficacy and mechanism of estrogen treatment for skin health.

Coactivators enable glucocorticoid receptor recruitment to fine-tune estrogen receptor transcriptional responses

Nuclear receptors (NRs) are central regulators of pathophysiological processes; however, how their responses intertwine is still not fully understood. The aim of this study was to determine whether and how steroid NRs can influence each other’s activity under co-agonist treatment. We used a unique system consisting of a multicopy integration of an estrogen receptor responsive unit that allows direct visualization and quantification of estrogen receptor alpha (ERα) DNA binding, co-regulator recruitment and transcriptional readout. We find that ERα DNA loading is required for other type I nuclear receptors to be co-recruited after dual agonist treatment. We focused on ERα/glucocorticoid receptor interplay and demonstrated that it requires steroid receptor coactivators (SRC-2, SRC-3) and the mediator component MED14. We then validated this cooperative interplay on endogenous target genes in breast cancer cells. Taken together, this work highlights another layer of mechanistic complexity through which NRs cross-talk with each other on chromatin under multiple hormonal stimuli.

Estrogen synthesis and signaling pathways during aging: from periphery to brain

Estrogens are the primary female sex hormones and play important roles in both reproductive and non-reproductive systems. Estrogens can be synthesized in non-reproductive tissues such as liver, heart, muscle, bone and brain, and tissue-specific estrogen synthesis is consistent with a diversity of estrogen actions. In this article we review tissue and cell-specific estrogen synthesis and estrogen receptor signaling in three parts: (i) synthesis and metabolism, (ii) the distribution of estrogen receptors and signaling, and (iii) estrogen functions and related disorders, including cardiovascular diseases, osteoporosis, Alzheimer's disease (AD), and Parkinson disease (PD). This comprehensive review provides new insights into estrogens by giving a better understanding of the tissue-specific estrogen effects and their roles in various diseases.

Diverse effects of cyclic AMP variants on osteogenic and adipogenic differentiation of human mesenchymal stromal cells

Osteogenic differentiation of human mesenchymal stromal cells (hMSCs) may potentially be used in cell-based bone tissue-engineering applications to enhance the bone-forming potential of these cells. Osteogenic differentiation and adipogenic differentiation are thought to be mutually exclusive, and although several signaling pathways and cues that induce osteogenic or adipogenic differentiation, respectively, have been identified, there is no general consensus on how to optimally differentiate hMSCs into the osteogenic lineage. Some pathways have also been reported to be involved in both adipogenic and osteogenic differentiation, as for example, the protein kinase A (PKA) pathway, and the aim of this study was to investigate the role of cAMP/PKA signaling in differentiation of hMSCs in more detail. We show that activation of this pathway with dibutyryl-cAMP results in enhanced alkaline phosphatase expression, whereas another cAMP analog induces adipogenesis in long-term mineralization cultures. Adipogenic differentiation, induced by 8-bromo-cAMP, was accompanied by stronger PKA activity and higher expression of cAMP-responsive genes, suggesting that stronger activation correlates with adipogenic differentiation. In addition, a whole-genome expression analysis showed an increase in expression of adipogenic genes in 8-br-cAMP-treated cells. Furthermore, by means of quantitative polymerase chain reaction, we show differences in peroxisome proliferator-activated receptor-γ activation, either alone or in combination with dexamethasone, thus demonstrating differential effects of the PKA pathway, most likely depending on its mode of activation.

Estrogen receptor dependent gene expression by osteoblasts - direct, indirect, circumspect, and speculative effects

Hormone activated estrogen receptors (ERs) have long been appreciated as potent mediators of gene expression in female reproductive tissues. These highly targeted responses likely evolved from more elemental roles in lower organisms, in agreement with their widespread effects in the cardiovascular, immunological, central nervous, and skeletal tissue systems. Still, despite intense investigation, the multiple and often perplexing roles of ERs retain significant attention. In the skeleton, this in part derives from apparently opposing effects by ER agonists on bone growth versus bone remodeling, and in younger versus older individuals. The complexity associated with ER activation can also derive from their interactions with other hormone and growth factor systems, and their direct and indirect effects on gene expression. We propose that part of this complexity results from essential interactions between ERs and other transcription factors, each with their own biochemical and molecular intricacies. Solving some of the many questions that persist may help to achieve better, or better directed, use of agents that can drive ER activation in focused and possibly tissue restricted ways.

Timing, rather than the concentration of cyclic AMP, correlates to osteogenic differentiation of human mesenchymal stem cells

Previously, we demonstrated that protein kinase A (PKA) activation using dibutyryl-cAMP in human mesenchymal stem cells (hMSCs) induces in vitro osteogenesis and bone formation in vivo. To further investigate the physiological role of PKA in hMSC osteogenesis, we tested a selection of G-protein-coupled receptor ligands which signal via intracellular cAMP production and PKA activation. Treatment of hMSCs with parathyroid hormone, parathyroid hormone-related peptide, melatonin, epinephrine, calcitonin or calcitonin gene-related peptide did not result in accumulation of cAMP or induction of alkaline phosphatase (ALP) expression. The only ligand that did induce cAMP, prostaglandin E2, even inhibited ALP expression and mineralization, suggesting that physiological levels of cAMP may inhibit osteogenesis. Furthermore, intermittent exposure of hMSCs to dibutyryl-cAMP inhibited ALP expression, whereas we did not observe an inhibitive effect at low dibutyryl-cAMP concentrations. Taken together, our results demonstrate that cAMP can either stimulate or inhibit osteogenesis in hMSCs, depending on the duration, rather than the strength, of the signal provided.

Endogenous glucocorticoid signalling in osteoblasts is necessary to maintain normal bone structure in mice

The role of endogenous glucocorticosteroids (GC) in bone development is ill-defined. Using the Col2.3-11betaHSD2 transgenic (tg) mouse model, we examined the effect of osteoblast-targeted disruption of intracellular GC signalling on bone growth and strength, and its modulation by factors such as age, gender and skeletal site. Tibiae and L3 vertebrae of 3 and 7-week-old, male and female wild type (WT) mice and their tg, age and sex matched littermates were analysed by micro-CT and mechanical testing. Data were analysed separately for 3 and 7-week-old mice by 2-way ANOVA using genotype (WT, tg), gender and their interactions as factors. Transgenic mice were characterised by lower bone volume, lower trabecular number and higher trabecular separation in tibial trabecular bone, as well as lower tibial cortical bone area and periosteal and endosteal perimeters. These changes resulted in a marked decrease in mechanical bone strength and stiffness in sexually mature, 7-week-old mice. In the tibia, the observed transgene effect was present in 3 and 7-week-old animals, indicating that the biological effect of disrupted GC signalling was independent of sexual maturity. This was not the case for the vertebral bones, where significant differences between tg and WT mice were seen in 7 but not in 3-week-old animals, suggesting that the effects of the transgene at this site may be modulated by age and/or changes in circulating sex hormone levels. Taken together, our results demonstrate that endogenous glucocorticoids may be required for normal bone growth but that their effect on bone structure and strength varies according to the skeletal site and sexual maturity of the animals.

Differential modulation of RANKL isoforms by human osteoarthritic subchondral bone osteoblasts: influence of osteotropic factors

BACKGROUND

Osteoarthritis (OA) is the most common human joint disease. Recent studies suggest that an abnormal subchondral bone metabolism is intimately involved in the genesis of this disease. Bone remodelling is tightly regulated by a molecular triad composed of OPG/RANK/RANKL. RANKL exists as 3 isoforms: RANKL1, 2, and 3. RANKL1 and 2 enhance osteoclastogenesis whereas RANKL3 inhibits this phenomenon. We previously reported that human OA subchondral bone osteoblasts can be discriminated into two subgroups according to their level of PGE2 [low (L) or high (H)]. Moreover, we also showed that L-OA osteoblasts express higher levels of total RANKL compared to H-OA osteoblasts. In this study, we investigated the level of membranous RANKL, comparing L- and H-OA subchondral bone osteoblasts, as well as its modulation by osteotropic factors. The impact of the modulation of RANKL1 and 3 on the membranous RANKL level was also studied.

METHODS

Gene expression was determined using real-time PCR for RANKL1 and semi-quantitative PCR for RANKL3. Membranous RANKL was measured by flow cytometry. The modulation of membranous RANKL and RANKL isoforms was monitored on the L- and H-OA osteoblasts and also following treatment with osteotropic factors, including vitamin D3 (50 nM), IL-1beta (100 pg/ml), TNF-alpha (5 ng/ml), PGE2 (500 nM), PTH (100 nM), IL-6 (10 ng/ml) and IL-17 (10 ng/ml).

RESULTS

Membranous RANKL levels were significantly increased in L-OA osteoblasts compared to normal (p<0.01) and H-OA (p<0.05). The gene expression level of the RANKL1 profile was reminiscent of the membranous RANKL level. Although RANKL3 gene expression was lower on the H-OA osteoblasts than on normal and L-OA osteoblasts (p<0.03), the overall outcome favoured RANKL1. Treatment with the tested factors showed a significant increase in membranous RANKL on the L-OA osteoblasts, with the exception of PTH and IL-17. Interestingly in this subpopulation, the RANKL3 gene expression level was significantly increased upon PTH and IL-17 treatment. No effect of the tested osteotropic factors was found on the H-OA.

CONCLUSION

Our findings showed that the normal, L- and H-OA subchondral bone osteoblasts differentially express membranous RANKL and RANKL isoforms, and that treatment with osteotropic factors generally favours increased membranous localization of RANKL on L-OA compared to H-OA osteoblasts. This phenomenon appears to take place through differential modulation of each RANKL isoform.