Glucocorticoid-dependent Wnt signaling by mature osteoblasts is a key regulator of cranial skeletal development in mice

A glucocorticoid spike derails muscle repair to heterotopic ossification after spinal cord injury

Why severe injury to the central nervous system (CNS) triggers the development of large neurogenic heterotopic ossifications (NHOs) within periarticular muscles remains unknown. We report that spinal cord injury (SCI) triggers a rapid corticosterone spike in mice, which is causal for NHO development because treatments with corticosterone or the synthetic glucocorticoid (GC) receptor (GR) agonist dexamethasone are sufficient to trigger heterotopic ossification and upregulate the expression of osteoinductive and osteogenic differentiation genes in injured muscles even without SCI. The central role for GR signaling in causing NHO is further demonstrated in mice deleted for the GR gene (Nr3c1), which no longer develop NHO after SCI. Furthermore, administration of clinical GR antagonists inhibits NHO development in mice with SCI. This study identifies endogenous GC as causing pathological NHO after CNS injury and suggests that GR antagonists may be of prophylactic use to prevent NHO development in victims of severe CNS injuries.

Diagnosis and therapeutic approach to bone health in patients with hypopituitarism

The results of many studies in recent years indicate a significant impact of pituitary function on bone health. The proper function of the pituitary gland has a significant impact on the growth of the skeleton and the appearance of sexual dimorphism. It is also responsible for achieving peak bone mass, which protects against the development of osteoporosis and fractures later in life. It is also liable for the proper remodeling of the skeleton, which is a physiological mechanism managing the proper mechanical resistance of bones and the possibility of its regeneration after injuries. Pituitary diseases causing hypofunction and deficiency of tropic hormones, and thus deficiency of key hormones of effector organs, have a negative impact on the skeleton, resulting in reduced bone mass and susceptibility to pathological fractures. The early appearance of pituitary dysfunction, i.e. in the pre-pubertal period, is responsible for failure to achieve peak bone mass, and thus the risk of developing osteoporosis in later years. This argues for the need for a thorough assessment of patients with hypopituitarism, not only in terms of metabolic disorders, but also in terms of bone disorders. Early and properly performed treatment may prevent patients from developing the bone complications that are so common in this pathology. The aim of this review is to discuss the physiological, pathophysiological, and clinical insights of bone involvement in pituitary disease.

Personalized, Precision Medicine to Cure Alzheimer's Dementia: Approach #1

The goal of the treatment for Alzheimer's dementia (AD) is the cure of dementia. A literature review revealed 18 major elements causing AD and 29 separate medications that address them. For any individual with AD, one is unlikely to discern which major causal elements produced dementia. Thus, for personalized, precision medicine, all causal elements must be treated so that each individual patient will have her or his causal elements addressed. Twenty-nine drugs cannot concomitantly be administered, so triple combinations of drugs taken from that list are suggested, and each triple combination can be administered sequentially, in any order. Ten combinations given over 13 weeks require 2.5 years, or if given over 26 weeks, they require 5.0 years. Such sequential treatment addresses all 18 elements and should cure dementia. In addition, any comorbid risk factors for AD whose first presence or worsening was within ±1 year of when AD first appeared should receive appropriate, standard treatment together with the sequential combinations. The article outlines a randomized clinical trial that is necessary to assess the safety and efficacy of the proposed treatments; it includes a triple-drug Rx for equipoise. Clinical trials should have durations of both 2.5 and 5.0 years unless the data safety monitoring board (DSMB) determines earlier success or futility since it is uncertain whether three or six months of treatment will be curative in humans, although studies in animals suggest that the briefer duration of treatment might be effective and restore defective neural tracts.

Transgenic disruption of endogenous glucocorticoid signaling in osteoblasts does not alter long-term K/BxN serum transfer-induced arthritis

BACKGROUND

Disruption of glucocorticoid (GC) signaling in osteoblasts results in a marked attenuation of acute antibody-induced arthritis. The role of endogenous GCs in chronic inflammatory arthritis is however not fully understood. Here, we investigated the impact of endogenous GC signaling in osteoblasts on inflammation and bone integrity under chronic inflammatory arthritis by inactivating osteoblastic GC signaling in a long-term K/BxN serum transfer-induced induced arthritis (STIA) model.

METHODS

Intracellular GC signaling in osteoblasts was disrupted by transgenic (tg) overexpression of 11beta-hydroxysteroid dehydrogenase type 2 (11ß-HSD2). Inflammatory arthritis was induced in 5-week-old male tg mice and their wild type (WT) littermates by intraperitoneal (i.p.) injection of K/BxN serum while controls (CTRLs) received phosphate-buffered saline (PBS). In a first cohort, K/BxN STIA was allowed to abate until  the endpoint of 42 days (STIA). To mimic rheumatic flares, a second cohort was additionally injected on days 14 and 28 with K/BxN serum (STIA boost). Arthritis severity was assessed daily by clinical scoring and ankle size measurements. Ankle joints were assessed histopathologically. Systemic effects of inflammation on long bone metabolism were analyzed in proximal tibiae by micro-computed tomography (μCT) and histomorphometry.

RESULTS

Acute arthritis developed in both tg and WT mice (STIA and STIA boost) and peaked around day 8. While WT STIA and tg STIA mice showed a steady decline of inflammation until day 42, WT STIA boost and tg STIA boost mice exhibited an arthritic phenotype over a period of 42 days. Clinical arthritis severity did not differ significantly between WT and tg mice, neither in the STIA nor in the STIA boost cohorts. Correspondingly, histological indices of inflammation, cartilage damage, and bone erosion showed no significant difference between WT and tg mice on day 42. Histomorphometry revealed an increased bone turnover in tg CTRL and tg STIA boost compared to WT CTRL and WT STIA boost animals, respectively.

CONCLUSIONS

In contrast to the previously reported modulating effects of endogenous GC signaling in osteoblasts during acute K/BxN STIA, this effect seems to perish during the chronic inflammatory and resolution phase. These findings indicate that endogenous GC signaling in osteoblasts may mainly be relevant during acute and subacute inflammatory processes.

Analysis of Why Alzheimer's Dementia Never Spontaneously Reverses, Suggests the Basis for Curative Treatment

A paradox regarding Alzheimer's dementia (AD) and mild cognitive impairment (MCI) is thats spontaneous cure of AD has never been reported, whereas spontaneous cure for MCI occurs fequently. This article analyzes what accounts for this difference. It holds that it is not merely because, for any condition, a stage is reached beyond which it cannot be reversed, since even widely metastatic cancer would be curable were there effective chemotherapy and rheumatoid arthritis became controllable when immune-suppressant treatment was introduced; thus, so could AD be reversible via effective therapy. The analysis presented leads to an explanation of the paradox that is in four categories: (1) levels of transforming growth factor-β are significantly reduced after the transition from MCI to AD; (2) levels of Wnt/β-catenin are significantly reduced after the transition; (3) there is altered epidermal-mesenchymal transition (EMT) in neurons after the transition; (4) there may be risk factors that are either newly operative or pre-existing but worsened at the time of transition, that are particular to individual patients. It is suggested that addressing and ameliorating all of those four categories might cure AD. Medications to address and ameliorate each of the four categories are described.

Glucocorticoid Dose Dependency on Gene Expression in Vocal Fold Fibroblasts and Macrophages

OBJECTIVE

Glucocorticoids (GCs) modulate multiple cellular activities including inflammatory and fibrotic responses. Outcomes of GC treatment for laryngeal disease vary, affording opportunity to optimize treatment. In the current study, three clinically employed GCs were evaluated to identify optimal in vitro concentrations at which GCs mediate favorable anti-inflammatory and fibrotic effects in multiple cell types. We hypothesize a therapeutic window will emerge as a foundation for optimized therapeutic strategies for patients with laryngeal disease.

STUDY DESIGN

In vitro.

METHODS

Human vocal fold fibroblasts and human macrophages derived from THP-1 monocytes were treated with 0.03-1000 nM dexamethasone, 0.3-10,000 nM methylprednisolone, and 0.3-10,000 nM triamcinolone in combination with interferon-γ, tumor necrosis factor-α, or interleukin-4. Real-time polymerase chain reaction was performed to analyze inflammatory (CXCL10, CXCl11, PTGS2, TNF, IL1B) and fibrotic (CCN2, LOX, TGM2) genes, and TSC22D3, a target gene of GC signaling. EC50 and IC50 to alter inflammatory and fibrotic gene expression was calculated.

RESULTS

Interferon-γ and tumor necrosis factor-α increased inflammatory gene expression in both cell types; this response was reduced by GCs. Interleukin-4 increased LOX and TGM2 expression in macrophages; this response was also reduced by GCs. GCs induced TSC22D3 and CCN2 expression independent of cytokine treatment. EC50 for each GC to upregulate CCN2 was higher than the IC50 to downregulate other genes.

CONCLUSION

Lower concentrations of GCs repressed inflammatory gene expression and only moderately induced genes involved in fibrosis. These data warrant consideration as a foundation for optimized clinical care paradigms to reduce inflammation and mitigate fibrosis.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:1169-1175, 2023.

Update on the Role of Glucocorticoid Signaling in Osteoblasts and Bone Marrow Adipocytes During Aging

PURPOSE OF REVIEW

Bone marrow adipose tissue (BMAT) in the skeleton likely plays a variety of physiological and pathophysiological roles that are not yet fully understood. In elucidating the complex relationship between bone and BMAT, glucocorticoids (GCs) are positioned to play a key role, as they have been implicated in the differentiation of bone marrow mesenchymal stem cells (BMSCs) between osteogenic and adipogenic lineages. The purpose of this review is to illuminate aspects of both endogenous and exogenous GC signaling, including the influence of GC receptors, in mechanisms of bone aging including relationships to BMAT.

RECENT FINDINGS

Harmful effects of GCs on bone mass involve several cellular pathways and events that can include BMSC differentiation bias toward adipogenesis and the influence of mature BMAT on bone remodeling through crosstalk. Interestingly, BMAT involvement remains poorly explored in GC-induced osteoporosis and warrants further investigation. This review provides an update on the current understanding of the role of glucocorticoids in the biology of osteoblasts and bone marrow adipocytes (BMAds).

ToxCast chemical library Wnt screen identifies diethanolamine as an activator of neural progenitor proliferation

Numerous autism spectrum disorder (ASD) risk genes are associated with Wnt signaling, suggesting that brain development may be especially sensitive to genetic perturbation of this pathway. Additionally, valproic acid, which modulates Wnt signaling, increases risk for ASD when taken during pregnancy. We previously found that an autism-linked gain-of-function UBE3A T485A mutant construct hyperactivated canonical Wnt signaling, providing a genetic means to elevate Wnt signaling above baseline levels. To identify environmental use chemicals that enhance or suppress Wnt signaling, we screened the ToxCast Phase I and II libraries in cells expressing this autism-linked UBE3A T485A gain-of-function mutant construct. Using structural comparisons, we identify classes of chemicals that stimulated Wnt signaling, including ethanolamines, as well as chemicals that inhibited Wnt signaling, such as agricultural pesticides, and synthetic hormone analogs. To prioritize chemicals for follow-up, we leveraged predicted human exposure data, and identified diethanolamine (DEA) as a chemical that stimulates Wnt signaling in UBE3A T485A -transfected cells, and has a high potential for prenatal exposure in humans. DEA enhanced proliferation in primary human neural progenitor cell lines (phNPC), but did not affect expression of canonical Wnt target genes in NPCs or primary mouse neuron cultures. Instead, we found DEA increased expression of the H3K9 methylation sensitive gene CALB1, consistent with competitive inhibition of the methyl donor enzymatic pathways.

Competitive blocking of LRP4-sclerostin binding interface strongly promotes bone anabolic functions

Induction of bone formation by Wnt ligands is inhibited when sclerostin (Scl), an osteocyte-produced antagonist, binds to its receptors, the low-density lipoprotein receptor-related proteins 5 or 6 (LRP5/6). Recently, it was shown that enhanced inhibition is achieved by Scl binding to the co-receptor LRP4. However, it is not clear if the binding of Scl to LRP4 facilitates Scl binding to LRP5/6 or inhibits the Wnt pathway in an LRP5/6-independent manner. Here, using the yeast display system, we demonstrate that Scl exhibits a stronger binding affinity for LRP4 than for LRP6. Moreover, we found stronger Scl binding to LRP6 in the presence of LRP4. We further show that a Scl mutant (SclN93A), which tightly binds LRP4 but not LRP6, does not inhibit the Wnt pathway on its own. We demonstrate that SclN93A competes with Scl for a common binding site on LRP4 and antagonizes Scl inhibition of the Wnt signaling pathway in osteoblasts in vitro. Finally, we demonstrate that 2 weeks of bi-weekly subcutaneous injections of SclN93A fused to the fragment crystallizable (Fc) domain of immunoglobulin (SclN93AFc), which retains the antagonistic activity of the mutant, significantly increases bone formation rate and enhances trabecular volumetric bone fraction, trabecular number, and bone length in developing mice. Our data show that LRP4 serves as an anchor that facilitates Scl-LRP6 binding and that inhibition of the Wnt pathway by Scl depends on its prior binding to LRP4. We further provide evidence that compounds that inhibit Scl-LRP4 interactions offer a potential strategy to promote anabolic bone functions.

Wnt Pathway Extracellular Components and Their Essential Roles in Bone Homeostasis

The Wnt pathway is involved in several processes essential for bone development and homeostasis. For proper functioning, the Wnt pathway is tightly regulated by numerous extracellular elements that act by both activating and inhibiting the pathway at different moments. This review aims to describe, summarize and update the findings regarding the extracellular modulators of the Wnt pathway, including co-receptors, ligands and inhibitors, in relation to bone homeostasis, with an emphasis on the animal models generated, the diseases associated with each gene and the bone processes in which each member is involved. The precise knowledge of all these elements will help us to identify possible targets that can be used as a therapeutic target for the treatment of bone diseases such as osteoporosis.

Antitumor Effect of Sclerostin against Osteosarcoma

Simple Summary

Osteosarcoma is highly variable and heterogeneous, which is one of the reasons for its resistance to treatment. Because osteosarcoma is defined by abnormal bone formation, we hypothesize its suppression could lead to effective treatment for all types of osteosarcomas. Sclerostin is secreted by osteocytes and inhibits the canonical pathway by binding to LRP5/6, thereby suppressing bone formation. The resulting suppression of bone formation leads to bone loss and osteoporosis. Here, we investigated the antitumor effect of sclerostin against osteosarcoma and found that sclerostin suppressed the proliferative capacity and migratory ability of osteosarcoma cells.

Abstract

Various risk factors and causative genes of osteosarcoma have been reported in the literature; however, its etiology remains largely unknown. Bone formation is a shared phenomenon in all types of osteosarcomas, and sclerostin is an extracellular soluble factor secreted by osteocytes that prevents bone formation by inhibiting the Wnt signaling pathway. We aimed to investigate the antitumor effect of sclerostin against osteosarcoma. Osteosarcoma model mice were prepared by transplantation into the dorsal region of C3H/He and BALB/c-nu/nu mice using osteosarcoma cell lines LM8 (murine) and 143B (human), respectively. Cell proliferations were evaluated by using alamarBlue and scratch assays. The migratory ability of the cells was evaluated using a migration assay. Sclerostin was injected intraperitoneally for 7 days to examine the suppression of tumor size and extension of survival. The administration of sclerostin to osteosarcoma cells significantly inhibited the growth and migratory ability of osteosarcoma cells. Kaplan–Meier curves and survival data demonstrated that sclerostin significantly inhibited tumor growth and improved survival. Sclerostin suppressed the proliferative capacity and migratory ability of osteosarcoma cells. Osteosarcoma model mice inhibited tumor growth and prolonged survival periods by the administration of sclerostin. The effect of existing anticancer drugs such as doxorubicin should be investigated for future clinical applications.

miR-433-3p suppresses bone formation and mRNAs critical for osteoblast function in mice

MicroRNAs (miRNAs) are key posttranscriptional regulators of osteoblastic commitment and differentiation. miR-433-3p was previously shown to target Runt-related transcription factor 2 (Runx2) and to be repressed by bone morphogenetic protein (BMP) signaling. Here, we show that miR-433-3p is progressively decreased during osteoblastic differentiation of primary mouse bone marrow stromal cells in vitro, and we confirm its negative regulation of this process. Although repressors of osteoblastic differentiation often promote adipogenesis, inhibition of miR-433-3p did not affect adipocyte differentiation in vitro. Multiple pathways regulate osteogenesis. Using luciferase-3' untranslated region (UTR) reporter assays, five novel miR-433-3p targets involved in parathyroid hormone (PTH), mitogen-activated protein kinase (MAPK), Wnt, and glucocorticoid signaling pathways were validated. We show that Creb1 is a miR-433-3p target, and this transcription factor mediates key signaling downstream of PTH receptor activation. We also show that miR-433-3p targets hydroxysteroid 11-β dehydrogenase 1 (Hsd11b1), the enzyme that locally converts inactive glucocorticoids to their active form. miR-433-3p dampens glucocorticoid signaling, and targeting of Hsd11b1 could contribute to this phenomenon. Moreover, miR-433-3p targets R-spondin 3 (Rspo3), a leucine-rich repeat-containing G-protein coupled receptor (LGR) ligand that enhances Wnt signaling. Notably, Wnt canonical signaling is also blunted by miR-433-3p activity. In vivo, expression of a miR-433-3p inhibitor or tough decoy in the osteoblastic lineage increased trabecular bone volume. Mice expressing the miR-433-3p tough decoy displayed increased bone formation without alterations in osteoblast or osteoclast numbers or surface, indicating that miR-433-3p decreases osteoblast activity. Overall, we showed that miR-433-3p is a negative regulator of bone formation in vivo, targeting key bone-anabolic pathways including those involved in PTH signaling, Wnt, and endogenous glucocorticoids. Local delivery of miR-433-3p inhibitor could present a strategy for the management of bone loss disorders and bone defect repair. © 2021 American Society for Bone and Mineral Research (ASBMR).

Glucocorticoids activate Yes-associated protein in human vocal fold fibroblasts

Fibrosis of the vocal folds poses a substantive clinical challenge potentially underlying the rapid proliferation of direct steroid injections into the upper airway. The variable clinical response to glucocorticoids (GCs) in the vocal folds is likely related to diversity inherent to GCs and patient-specific, and upstream, cell-specific responses to GCs. Broadly, we hypothesize the disparity in clinical outcomes are due to undesirable effects of GCs on resident fibroblasts. Transcriptome analysis identified significant GC-mediated modulation of Hippo signaling, a known regulator of fibrotic gene expression. Subsequent analysis confirmed GC-mediated YAP activation, a transcriptional co-factor in the Hippo signaling pathway. YAP inhibition attenuated ACTA2 expression in GC-treated human vocal fold fibroblasts. Nuclear localization and phosphorylation at Ser211, however, was not affected by YAP inhibition, suggesting nuclear translocation of YAP is indirectly driven by GR. RNA-seq analysis confirmed the influence of GCs on Wnt signaling, and canonical Wnt signaling target genes were upregulated by GCs. These data implicate YAP and its downstream targets as putative mediators of a pro-fibrotic response to GCs. Therapeutic YAP inhibition may ultimately be clinically relevant and warrants further consideration.

The rise in expression and activity of 11β-HSD1 in human mesenchymal progenitor cells induces adipogenesis through increased local cortisol synthesis

11β-Hydroxysteroid dehydrogenase 1 (11β-HSD1) plays an important role in pre-receptor glucocorticoid metabolism. This enzyme is expressed in bone, increases with age, and catalyzes the conversion of the inactive glucocorticoid cortisone into the active glucocorticoid cortisol and vice versa. Here we hypothesized that the physiological activity of 11β-HSD1 to produce cortisol in human mesenchymal progenitor cells (hMSC) is principally sufficient to shift the differentiation potential in the direction of adipogenic. We thus investigated differentiating hMSCs and the mesenchymal stem cell line SCP-1 cultured under osteogenic conditions and stimulated with supra-physiological cortisone levels. The release of active cortisol into the medium was monitored and the influence on cell differentiation analyzed. We revealed an increase in 11β-HSD1 expression followed by increased reductive activity of the enzyme, thereby inducing a more adipogenic phenotype of the cell models via cortisol with negative effects on osteogenesis. Through inhibition experiments with the specific inhibitor 10 j, we proved the enzyme specificity for cortisol synthesis and adipogenic differentiation. Increased expression of 11β-HSD1 followed by higher cortisol levels might thus explain bone marrow adiposity followed by reduced bone quality and stability in old age or in situations of supra-physiological glucocorticoid exposure.

VEGF signaling activates the matrix metalloproteinases, MmpL7 and MmpL5 at the sites of active skeletal growth and MmpL7 regulates skeletal elongation

Organisms can uptake minerals, shape them in different forms and generate teeth, skeletons or shells that support and protect them. Mineral uptake, trafficking and nucleation are tightly regulated by the biomineralizing cells through networks of specialized proteins. Specifically, matrix metalloproteases (MMPs) digest various extracellular substrates and allow for mineralization in the vertebrates' teeth and bones, but little is known about their role in invertebrates' systems. The sea urchin embryo provides an excellent invertebrate model for genetic and molecular studies of biomineralization. MMP inhibition prevents the growth of the calcite spicules of the sea urchin larval skeleton, however, the molecular mechanisms and genes that underlie this response are not well understood. Here we study the spatial expression and regulation of two membrane type MMPs that were found to be occluded in the sea urchin spicules, Pl-MmpL7 and Pl-MmpL5, and investigate the function of Pl-MmpL7 in skeletogenesis. The inhibition of MMPs does not change the volume of the calcium vesicles in the skeletogenic cells. The expression of Pl-MmpL7 and Pl-MmpL5 is regulated by the Vascular Endothelial Growth Factor (VEGF) signaling, from the time of skeleton initiation and on. The expression of these genes is localized to the subsets of skeletogenic cells where active spicule growth occurs throughout skeletogenesis. Downregulation of Pl-MmpL7 expression delays the growth of the skeletal rods and in some cases, strongly perturbs skeletal shape. The localized expression of Pl-MmpL7 and Pl-MmpL5 to the active growth zone and the effect of Pl-MmpL7 perturbations on skeletal growth, suggest that these genes are essential for normal spicule elongation in the sea urchin embryo.

Endogenous Glucocorticoid Metabolism in Bone: Friend or Foe

The role of tissue specific metabolism of endogenous glucocorticoids (GCs) in the pathogenesis of human disease has been a field of intense interest over the last 20 years, fuelling clinical trials of metabolism inhibitors in the treatment of an array of metabolic diseases. Localised pre-receptor metabolism of endogenous and therapeutic GCs by the 11β-hydroxysteroid dehydrogenase (11β-HSD) enzymes (which interconvert endogenous GCs between their inactive and active forms) are increasingly recognised as being critical in mediating both their positive and negative actions on bone homeostasis. In this review we explore the roles of endogenous and therapeutic GC metabolism by the 11β-HSD enzymes in the context of bone metabolism and bone cell function, and consider future strategies aimed at modulating this system in order to manage and treat various bone diseases.

Single-Cell RNA Sequencing of Calvarial and Long-Bone Endocortical Cells

Single-cell RNA sequencing (scRNA-Seq) is emerging as a powerful technology to examine transcriptomes of individual cells. We determined whether scRNA-Seq could be used to detect the effect of environmental and pharmacologic perturbations on osteoblasts. We began with a commonly used in vitro system in which freshly isolated neonatal mouse calvarial cells are expanded and induced to produce a mineralized matrix. We used scRNA-Seq to compare the relative cell type abundances and the transcriptomes of freshly isolated cells to those that had been cultured for 12 days in vitro. We observed that the percentage of macrophage-like cells increased from 6% in freshly isolated calvarial cells to 34% in cultured cells. We also found that Bglap transcripts were abundant in freshly isolated osteoblasts but nearly undetectable in the cultured calvarial cells. Thus, scRNA-Seq revealed significant differences between heterogeneity of cells in vivo and in vitro. We next performed scRNA-Seq on freshly recovered long bone endocortical cells from mice that received either vehicle or sclerostin-neutralizing antibody for 1 week. We were unable to detect significant changes in bone anabolism-associated transcripts in immature and mature osteoblasts recovered from mice treated with sclerostin-neutralizing antibody; this might be a consequence of being underpowered to detect modest changes in gene expression, because only 7% of the sequenced endocortical cells were osteoblasts and a limited portion of their transcriptomes were sampled. We conclude that scRNA-Seq can detect changes in cell abundance, identity, and gene expression in skeletally derived cells. In order to detect modest changes in osteoblast gene expression at the single-cell level in the appendicular skeleton, larger numbers of osteoblasts from endocortical bone are required. © 2020 American Society for Bone and Mineral Research.

Arthritis and the role of endogenous glucocorticoids

Rheumatoid arthritis and osteoarthritis, the most common forms of arthritis, are chronic, painful, and disabling conditions. Although both diseases differ in etiology, they manifest in progressive joint destruction characterized by pathological changes in the articular cartilage, bone, and synovium. While the potent anti-inflammatory properties of therapeutic (i.e., exogenous) glucocorticoids have been heavily researched and are widely used in clinical practice, the role of endogenous glucocorticoids in arthritis susceptibility and disease progression remains poorly understood. Current evidence from mouse models suggests that local endogenous glucocorticoid signaling is upregulated by the pro-inflammatory microenvironment in rheumatoid arthritis and by aging-related mechanisms in osteoarthritis. Furthermore, these models indicate that endogenous glucocorticoid signaling in macrophages, mast cells, and chondrocytes has anti-inflammatory effects, while signaling in fibroblast-like synoviocytes, myocytes, osteoblasts, and osteocytes has pro-inflammatory actions in rheumatoid arthritis. Conversely, in osteoarthritis, endogenous glucocorticoid signaling in both osteoblasts and chondrocytes has destructive actions. Together these studies provide insights into the role of endogenous glucocorticoids in the pathogenesis of both inflammatory and degenerative joint disease.

A Jack of All Trades: Impact of Glucocorticoids on Cellular Cross-Talk in Osteoimmunology

Glucocorticoids (GCs) are known to have a strong impact on the immune system, metabolism, and bone homeostasis. While these functions have been long investigated separately in immunology, metabolism, or bone biology, the understanding of how GCs regulate the cellular cross-talk between innate immune cells, mesenchymal cells, and other stromal cells has been garnering attention rather recently. Here we review the recent findings of GC action in osteoporosis, inflammatory bone diseases (rheumatoid and osteoarthritis), and bone regeneration during fracture healing. We focus on studies of pre-clinical animal models that enable dissecting the role of GC actions in innate immune cells, stromal cells, and bone cells using conditional and function-selective mutant mice of the GC receptor (GR), or mice with impaired GC signaling. Importantly, GCs do not only directly affect cellular functions, but also influence the cross-talk between mesenchymal and immune cells, contributing to both beneficial and adverse effects of GCs. Given the importance of endogenous GCs as stress hormones and the wide prescription of pharmaceutical GCs, an improved understanding of GC action is decisive for tackling inflammatory bone diseases, osteoporosis, and aging.

Disruption of glucocorticoid signalling in osteoblasts attenuates age-related surgically induced osteoarthritis

OBJECTIVE

Aging is a major risk factor for osteoarthritis (OA). Skeletal expression and activity of the glucocorticoid-activating enzyme 11β-hydroxysteroid-dehydrogenase type 1 increases progressively with age in humans and rodents. Here we investigated the role of endogenous osteocytic and osteoblastic glucocorticoid (GC) signalling in the development of osteoarthritic bone and cartilage damage in mice.

METHODS

We utilized transgenic (tg) mice in which glucocorticoid signalling is disrupted in osteoblasts and osteocytes via overexpression of the glucocorticoid-inactivating enzyme, 11β-hydroxysteroid-dehydrogenase type 2. Osteoarthritis was induced in 10- and 22-week-old male transgenic mice (tg-OA, n = 6/group) and their wildtype littermates (WT-OA, n = 7-8/group) by surgical destabilization of the medial meniscus (DMM). Sham-operated mice served as controls (WT- & tg-Sham, n = 3-5 and 6-8/group at 10- and 22-weeks of age, respectively).

RESULTS

Sixteen weeks after DMM surgery, mice developed features of cartilage degradation, subchondral bone sclerosis and osteophyte formation. These changes did not differ between WT and tg mice when OA was induced at 10-weeks of age. However, when OA was induced at 22-weeks of age, cartilage erosion was significantly attenuated in tg-OA mice compared to WT-OA littermates. Similarly, subchondral bone volume (-5.2%, 95% confidence intervals (CI) -9.1 to -1.2%, P = 0.014) and osteophyte size (-4.0 mm², 95% CI -7.5 to -0.5 mm², P = 0.029) were significantly reduced in tg-OA compared to WT-OA mice.

CONCLUSION

Glucocorticoid signalling in cells of the osteoblast lineage promotes the development of surgically-induced osteoarthritis in older, but not younger, male mice. These data implicate osteoblasts and osteocytes in the progression of DMM-OA, via a glucocorticoid-dependent and age-related pathway.

Osteoblast autophagy in glucocorticoid-induced osteoporosis

Administration of glucocorticoids is an effective strategy for treating many inflammatory and autoimmune diseases. However, glucocorticoid treatment can have adverse effects on bone, leading to glucocorticoid-induced osteoporosis (GIO), the most common form of secondary osteoporosis. Although the pathogenesis of GIO has been studied for decades, over the past ten years the autophagy machinery has been implicated as a novel mechanism. Autophagy in osteoblasts, osteocytes, and osteoclasts plays a critical role in the maintenance of bone homeostasis. Herein, we specifically discuss how osteoblast autophagy responds to glucocorticoids and its role in the development of GIO.

Glucocorticoids and Bone: Consequences of Endogenous and Exogenous Excess and Replacement Therapy

Osteoporosis associated with long-term glucocorticoid therapy remains a common and serious bone disease. Additionally, in recent years it has become clear that more subtle states of endogenous glucocorticoid excess may have a major impact on bone health. Adverse effects can be seen with mild systemic glucocorticoid excess, but there is also evidence of tissue-specific regulation of glucocorticoid action within bone as a mechanism of disease. This review article examines (1) the role of endogenous glucocorticoids in normal bone physiology, (2) the skeletal effects of endogenous glucocorticoid excess in the context of endocrine conditions such as Cushing disease/syndrome and autonomous cortisol secretion (subclinical Cushing syndrome), and (3) the actions of therapeutic (exogenous) glucocorticoids on bone. We review the extent to which the effect of glucocorticoids on bone is influenced by variations in tissue metabolizing enzymes and glucocorticoid receptor expression and sensitivity. We consider how the effects of therapeutic glucocorticoids on bone are complicated by the effects of the underlying inflammatory disease being treated. We also examine the impact that glucocorticoid replacement regimens have on bone in the context of primary and secondary adrenal insufficiency. We conclude that even subtle excess of endogenous or moderate doses of therapeutic glucocorticoids are detrimental to bone. However, in patients with inflammatory disorders there is a complex interplay between glucocorticoid treatment and underlying inflammation, with the underlying condition frequently representing the major component underpinning bone damage.

Molecular mechanisms of glucocorticoids on skeleton and bone regeneration after fracture

Glucocorticoid hormones (GCs) have profound effects on bone metabolism. Via their nuclear hormone receptor - the GR - they act locally within bone cells and modulate their proliferation, differentiation, and cell death. Consequently, high glucocorticoid levels - as present during steroid therapy or stress - impair bone growth and integrity, leading to retarded growth and glucocorticoid-induced osteoporosis, respectively. Because of their profound impact on the immune system and bone cell differentiation, GCs also affect bone regeneration and fracture healing. The use of conditional-mutant mouse strains in recent research provided insights into the cell-type-specific actions of the GR. However, despite recent advances in system biology approaches addressing GR genomics in general, little is still known about the molecular mechanisms of GCs and GR in bone cells. Here, we review the most recent findings on the molecular mechanisms of the GR in general and the known cell-type-specific actions of the GR in mesenchymal cells and their derivatives as well as in osteoclasts during bone homeostasis, GC excess, bone regeneration and fracture healing.

Anti-osteogenic function of a LIM-homeodomain transcription factor LMX1B is essential to early patterning of the calvaria

The calvaria (upper part of the skull) is made of plates of bone and fibrous joints (sutures and fontanelles), and the proper balance and organization of these components are crucial to normal development of the calvaria. In a mouse embryo, the calvaria develops from a layer of head mesenchyme that surrounds the brain from shortly after mid-gestation. The mesenchyme just above the eye (supra-orbital mesenchyme, SOM) generates ossification centers for the bones, which then grow toward the apex gradually. In contrast, the mesenchyme apical to SOM (early migrating mesenchyme, EMM), including the area at the vertex, does not generate an ossification center. As a result, the dorsal midline of the head is occupied by sutures and fontanelles at birth. To date, the molecular basis for this regional difference in developmental programs is unknown. The current study provides vital insights into the genetic regulation of calvarial patterning. First, we showed that osteogenic signals were active in both EMM and SOM during normal development, which suggested the presence of an anti-osteogenic factor in EMM to counter the effect of these signals. Subsequently, we identified Lmx1b as an anti-osteogenic gene that was expressed in EMM but not in SOM. Furthermore, head mesenchyme-specific deletion of Lmx1b resulted in heterotopic ossification from EMM at the vertex, and craniosynostosis affecting multiple sutures. Conversely, forced expression of Lmx1b in SOM was sufficient to inhibit osteogenic specification. Therefore, we conclude that Lmx1b plays a key role as an anti-osteogenic factor in patterning the head mesenchyme into areas with different osteogenic competence. In turn, this patterning event is crucial to generating the proper organization of the bones and soft tissue joints of the calvaria.

Low-dose dexamethasone affects osteoblast viability by inducing autophagy via intracellular ROS

Glucocorticoids (GCs) are closely associated with the progression of GC-induced osteoporosis (GIOP) by inhibiting osteoblast viability. However, endogenous GCs are important for bone development. In addition, previous studies have demonstrated that GCs could induce autophagy, a cytoprotective process that is protective against various stressors. In the present study, the aim is to explore whether osteoblasts exhibited dose-dependent viability in the presence of GCs due to autophagy. hFOB 1.19 osteoblasts were treated with various doses of dexamethasone (DEX; 10⁻⁸-10⁻⁴ M) for 0, 24, 48 and 72 h. The results revealed a biphasic effect of DEX on the viability of hFOB 1.19 cells; a high dose of DEX (≥10⁻⁶ M) accelerated cell apoptosis, while a low dose of DEX (10⁻⁸ M) increased cell viability. Furthermore, significantly increased autophagy was observed in the low dose DEX treatment group, as indicated by the expression of the autophagy-associated proteins beclin 1 and microtubule-associated protein light chain 3, and the detection of autophagosomes. Another finding was that DEX upregulated intracellular reactive oxygen species (ROS), which was decreased by the autophagy agonist rapamycin. The increase in autophagy and cell viability associated with low-dose DEX (10⁻⁸ M) was suppressed by the ROS scavenger catalase and the autophagy inhibitor 3-methyladenine. In conclusion, the results revealed that GCs affected osteoblast viability in a dose-dependent manner. A low dose of GCs increased osteoblast viability by inducing autophagy via intracellular ROS. The results indicate that autophagy may be a novel mechanism by which osteoblasts survive GC exposure and provide a potential therapeutic target for treating GIOP.

Induced global deletion of glucocorticoid receptor impairs fracture healing

Although endogenous glucocorticoids (GCs) are important regulators of bone integrity and the immune system, their role in bone repair after fracture-a process highly dependent on inflammation and bone formation-is unclear. Because most effects of GCs are mediated by the glucocorticoid receptor (GR), we used an inducible global GR knockout (GR^{gtROSACreERT2}) mouse model to eliminate endogenous GC action in all cells contributing to bone repair. The healing process was analyzed by cytokine/chemokine multiplex analysis, flow cytometry, histology, gene-expression analysis, microcomputed tomography, and biomechanical analysis. We observed increased early systemic and local inflammatory responses, as well as a significantly higher number of T cells infiltrating the fracture callus. Later in the healing process, we found impaired endochondral ossification in the absence of the GR, leading to persistent cartilage in the calli of the GR^{gtROSACreERT2} mice, decreased bending stiffness, and a significantly lower proportion of healed bones. Collectively, our data show that the absence of the GR significantly impairs fracture healing associated with a defective cartilage-to-bone transition, underscoring an important role of GCs during fracture healing.-Rapp, A. E., Hachemi, Y., Kemmler, J., Koenen, M., Tuckermann, J., Ignatius, A. Induced global deletion of glucocorticoid receptor impairs fracture healing.

Stress, Glucocorticoids and Bone: A Review From Mammals and Fish

Glucocorticoids (GCs) are the final effector products of a neuroendocrine HPA/HPI axis governing energy balance and stress response in vertebrates. From a physiological point of view, basal GC levels are essential for intermediary metabolism and participate in the development and homeostasis of a wide range of body tissues, including the skeleton. Numerous mammalian studies have demonstrated that GC hormones exert a positive role during bone modeling and remodeling as they promote osteoblastogenesis to maintain the bone architecture. Although the pharmacological effect of the so-called stress hormones has been widely reported, the role of endogenous GCs on bone mineral metabolism as result of the endocrine stress response has been largely overlooked across vertebrates. In addition, stress responses are variable depending on the stressor (e.g., starvation, predation, and environmental change), life cycle events (e.g., migration and aging), and differ among vertebrate lineages, which react differently according to their biological, social and cognitive complexity (e.g., mineral demands, physical, and psychological stress). This review intends to summarize the endogenous GCs action on bone metabolism of mammals and fish under a variety of challenging circumstances. Particular emphasis will be given to the regulatory loop between GCs and the parathyroid hormone (PTH) family peptides, and other key regulators of mineral homeostasis and bone remodeling in vertebrates.

TET2 Loss Dysregulates the Behavior of Bone Marrow Mesenchymal Stromal Cells and Accelerates Tet2-/--Driven Myeloid Malignancy Progression

TET2 is a methylcytosine dioxygenase that regulates cytosine hydroxymethylation. Although there are extensive data implicating a pivotal role of TET2 in hematopoietic stem/progenitor cells (HSPCs), the importance of TET2 in bone marrow mesenchymal stromal cells (BMSCs) remains unknown. In this study, we show that loss of TET2 in BMSCs increases cell proliferation and self-renewal and enhances osteoblast differentiation potential of BMSCs, which may in turn alter their behavior in supporting HSPC proliferation and differentiation. In addition, Tet2 loss alters BMSCs in promoting Tet2-deficiency-mediated myeloid malignancy progression. Tet2 loss in BMSCs also dysregulates hydroxylation of 5-methylcytosine (5mC) and the expression of genes that are key for BMSC proliferation and osteoblast differentiation, leading to alteration of biological characteristics in vivo. These results highlight the critical role of TET2 in the maintenance of BMSC functions and osteoblast differentiation and provide evidence that dysregulation of epigenetic modifiers in BMSCs contributes to the progression of myeloid malignancies.

Wnt co-receptors Lrp5 and Lrp6 differentially mediate Wnt3a signaling in osteoblasts

Wnt3a is a major regulator of bone metabolism however, very few of its target genes are known in bone. Wnt3a preferentially signals through transmembrane receptors Frizzled and co-receptors Lrp5/6 to activate the canonical signaling pathway. Previous studies have shown that the canonical Wnt co-receptors Lrp5 and Lrp6 also play an essential role in normal postnatal bone homeostasis, yet, very little is known about specific contributions by these co-receptors in Wnt3a-dependent signaling. We used high-throughput sequencing technology to identify target genes regulated by Wnt3a in osteoblasts and to elucidate the role of Lrp5 and Lrp6 in mediating Wnt3a signaling. Our study identified 782 genes regulated by Wnt3a in primary calvarial osteoblasts. Wnt3a up-regulated the expression of several key regulators of osteoblast proliferation/ early stages of differentiation while inhibiting genes expressed in later stages of osteoblastogenesis. We also found that Lrp6 is the key mediator of Wnt3a signaling in osteoblasts and Lrp5 played a less significant role in mediating Wnt3a signaling.

Revisiting asthma therapeutics: focus on WNT signal transduction

Asthma is a complex disease of the airways that develops as a consequence of both genetic and environmental factors. This interaction has highlighted genes important in early life, particularly those that control lung development, such as the Wingless/Integrase-1 (WNT) signalling pathway. Although aberrant WNT signalling is involved with an array of human conditions, it has received little attention within the context of asthma. Yet it is highly relevant, driving events involved with inflammation, airway remodelling, and airway hyper-responsiveness (AHR). In this review, we revisit asthma therapeutics by examining whether WNT signalling is a valid therapeutic target for asthma.

Strain dependent differences in glucocorticoid-induced bone loss between C57BL/6J and CD-1 mice

We have investigated the effect of long-term glucocorticoid (GC) administration on bone turnover in two frequently used mouse strains; C57BL/6J and CD1, in order to assess the influence of their genetic background on GC-induced osteoporosis (GIO). GIO was induced in 12 weeks old female C57BL/6J and CD1 mice by subcutaneous insertion of long-term release prednisolone or placebo pellets. Biomechanical properties as assessed by three point bent testing revealed that femoral elasticity and strength significantly decreased in CD1 mice receiving GC, whereas C57BL/6J mice showed no differences between placebo and prednisolone treatment. Bone turnover assessed by microcomputer tomography revealed that contrary to C57BL/6J mice, prednisolone treated CD1 mice developed osteoporosis. In vitro experiments have underlined that, at a cellular level, C57BL/6J mice osteoclasts and osteoblasts were less responsive to GC treatment and tolerated higher doses than CD1 cells. Whilst administration of long-term release prednisolone pellets provided a robust GIO animal model in 12 weeks old CD1 mice, age matched C57BL/6J mice were not susceptible to the bone changes associated with GIO. This study indicates that for the induction of experimental GIO, the mouse strain choice together with other factors such as age should be carefully evaluated.

Signalling pathways in trophic skeletal development and morphogenesis: Insights from studies on teleost fish

During the development of the vertebrate feeding apparatus, a variety of complicated cellular and molecular processes participate in the formation and integration of individual skeletal elements. The molecular mechanisms regulating the formation of skeletal primordia and their development into specific morphological structures are tightly controlled by a set of interconnected signalling pathways. Some of these pathways, such as Bmp, Hedgehog, Notch and Wnt, are long known for their pivotal roles in craniofacial skeletogenesis. Studies addressing the functional details of their components and downstream targets, the mechanisms of their interactions with other signals as well as their potential roles in adaptive morphological divergence, are currently attracting considerable attention. An increasing number of signalling pathways that had previously been described in different biological contexts have been shown to be important in the regulation of jaw skeletal development and morphogenesis. In this review, I provide an overview of signalling pathways involved in trophic skeletogenesis emphasizing studies of the most species-rich group of vertebrates, the teleost fish, which through their evolutionary history have undergone repeated episodes of spectacular trophic diversification.

Molecular Actions of Glucocorticoids in Cartilage and Bone During Health, Disease, and Steroid Therapy

Cartilage and bone are severely affected by glucocorticoids (GCs), steroid hormones that are frequently used to treat inflammatory diseases. Major complications associated with long-term steroid therapy include impairment of cartilaginous bone growth and GC-induced osteoporosis. Particularly in arthritis, GC application can increase joint and bone damage. Contrarily, endogenous GC release supports cartilage and bone integrity. In the last decade, substantial progress in the understanding of the molecular mechanisms of GC action has been gained through genome-wide binding studies of the GC receptor. These genomic approaches have revolutionized our understanding of gene regulation by ligand-induced transcription factors in general. Furthermore, specific inactivation of GC signaling and the GC receptor in bone and cartilage cells of rodent models has enabled the cell-specific effects of GCs in normal tissue homeostasis, inflammatory bone diseases, and GC-induced osteoporosis to be dissected. In this review, we summarize the current view of GC action in cartilage and bone. We further discuss future research directions in the context of new concepts for optimized steroid therapies with less detrimental effects on bone.

Partial 1q Duplications and Associated Phenotype

Duplications of the long arm of chromosome 1 are rare. Distal duplications are the most common and have been reported as either pure trisomy or unbalanced translocations. The paucity of cases with pure distal 1q duplications has made it difficult to delineate a partial distal trisomy 1q syndrome. Here, we report 2 patients with overlapping 1q duplications detected by G-banding. Array CGH and FISH were performed to characterize the duplicated segments, exclude the involvement of other chromosomes and determine the orientation of the duplication. Patient 1 presents with a mild phenotype and carries a 22.5-Mb 1q41q43 duplication. Patient 2 presents with a pure 1q42.13qter inverted duplication of 21.5 Mb, one of the smallest distal 1q duplications ever described and one of the few cases characterized by array CGH, thus contributing to a better characterization of distal 1q duplication syndrome.

Disruption of glucocorticoid signaling in chondrocytes delays metaphyseal fracture healing but does not affect normal cartilage and bone development

States of glucocorticoid excess are associated with defects in chondrocyte function. Most prominently there is a reduction in linear growth but delayed healing of fractures that require endochondral ossification to also occur. In contrast, little is known about the role of endogenous glucocorticoids in chondrocyte function. As glucocorticoids exert their cellular actions through the glucocorticoid receptor (GR), we aimed to elucidate the role of endogenous glucocorticoids in chondrocyte function in vivo through characterization of tamoxifen-inducible chondrocyte-specific GR knockout (chGRKO) mice in which the GR was deleted at various post-natal ages. Knee joint architecture, cartilage structure, growth plates, intervertebral discs, long bone length and bone micro-architecture were similar in chGRKO and control mice at all ages. Analysis of fracture healing in chGRKO and control mice demonstrated that in metaphyseal fractures, chGRKO mice formed a larger cartilaginous callus at 1 and 2 week post-surgery, as well as a smaller amount of well-mineralized bony callus at the fracture site 4 week post-surgery, when compared to control mice. In contrast, chondrocyte-specific GR knockout did not affect diaphyseal fracture healing. We conclude that endogenous GC signaling in chondrocytes plays an important role during metaphyseal fracture healing but is not essential for normal long bone growth.

Wnts produced by Osterix-expressing osteolineage cells regulate their proliferation and differentiation

Wnt signaling is a critical regulator of bone development, but the identity and role of the Wnt-producing cells are still unclear. We addressed these questions through in situ hybridization, lineage tracing, and genetic experiments. First, we surveyed the expression of all 19 Wnt genes and Wnt target gene Axin2 in the neonatal mouse bone by in situ hybridization, and demonstrated--to our knowledge for the first time--that Osterix-expressing cells coexpress Wnt and Axin2. To track the behavior and cell fate of Axin2-expressing osteolineage cells, we performed lineage tracing and showed that they sustain bone formation over the long term. Finally, to examine the role of Wnts produced by Osterix-expressing cells, we inhibited Wnt secretion in vivo, and observed inappropriate differentiation, impaired proliferation, and diminished Wnt signaling response. Therefore, Osterix-expressing cells produce their own Wnts that in turn induce Wnt signaling response, thereby regulating their proliferation and differentiation.

Transcriptional dynamics of a conserved gene expression network associated with craniofacial divergence in Arctic charr

Background

Understanding the molecular basis of craniofacial variation can provide insights into key developmental mechanisms of adaptive changes and their role in trophic divergence and speciation. Arctic charr (Salvelinus alpinus) is a polymorphic fish species, and, in Lake Thingvallavatn in Iceland, four sympatric morphs have evolved distinct craniofacial structures. We conducted a gene expression study on candidates from a conserved gene coexpression network, focusing on the development of craniofacial elements in embryos of two contrasting Arctic charr morphotypes (benthic and limnetic).

Results

Four Arctic charr morphs were studied: one limnetic and two benthic morphs from Lake Thingvallavatn and a limnetic reference aquaculture morph. The presence of morphological differences at developmental stages before the onset of feeding was verified by morphometric analysis. Following up on our previous findings that Mmp2 and Sparc were differentially expressed between morphotypes, we identified a network of genes with conserved coexpression across diverse vertebrate species. A comparative expression study of candidates from this network in developing heads of the four Arctic charr morphs verified the coexpression relationship of these genes and revealed distinct transcriptional dynamics strongly correlated with contrasting craniofacial morphologies (benthic versus limnetic). A literature review and Gene Ontology analysis indicated that a significant proportion of the network genes play a role in extracellular matrix organization and skeletogenesis, and motif enrichment analysis of conserved noncoding regions of network candidates predicted a handful of transcription factors, including Ap1 and Ets2, as potential regulators of the gene network. The expression of Ets2 itself was also found to associate with network gene expression. Genes linked to glucocorticoid signalling were also studied, as both Mmp2 and Sparc are responsive to this pathway. Among those, several transcriptional targets and upstream regulators showed differential expression between the contrasting morphotypes. Interestingly, although selected network genes showed overlapping expression patterns in situ and no morph differences, Timp2 expression patterns differed between morphs.

Conclusion

Our comparative study of transcriptional dynamics in divergent craniofacial morphologies of Arctic charr revealed a conserved network of coexpressed genes sharing functional roles in structural morphogenesis. We also implicate transcriptional regulators of the network as targets for future functional studies.

Electronic supplementary material

The online version of this article (doi:10.1186/2041-9139-5-40) contains supplementary material, which is available to authorized users.

A living biosensor model to dynamically trace glucocorticoid transcriptional activity during development and adult life in zebrafish

Glucocorticoids (GCs) modulate many cellular processes through the binding of the glucocorticoid receptor (GR) to specific responsive elements located upstream of the transcription starting site or within an intron of GC target genes. Here we describe a transgenic fish line harboring a construct with nine GC-responsive elements (GREs) upstream of a reporter (EGFP) coding sequence. Transgenic fish exhibit strong fluorescence in many known GC-responsive organs. Moreover, its enhanced sensitivity allowed the discovery of novel GC-responsive tissue compartments, such as fin, eyes, and otic vesicles. Long-term persistence of transgene expression is seen during adult stages in several organs. Pharmacological and genetic analysis demonstrates that the transgenic line is highly responsive to drug administration and molecular manipulation. Moreover, reporter expression is sensitively and dynamically modulated by the photoperiod, thus proving that these fish are an in vivo valuable platform to explore GC responsiveness to both endogenous and exogenous stimuli.

Metyrapone alleviates deleterious effects of maternal food restriction on lung development and growth of rat offspring

Maternal food restriction (MFR) causes intrauterine growth restriction, a known risk factor for developing chronic lung disease. However, it is unknown whether this negative outcome is gender specific or preventable by blocking the MFR-induced hyperglucocorticoidism. Using a well-established rat model, we used metyrapone (MTP), an inhibitor of glucocorticoid synthesis, to study the MFR-induced lung changes on postnatal day (p) 21 in a gender-specific manner. From embryonic day 10 until delivery, pregnant dams were fed either an ad libitum diet or a 50% caloric restricted diet with or without MTP supplementation. Postnatally, the offspring were fed ad libitum from healthy dams until p21. Morphometric, Western blot, and immunohistochemical analysis of the lungs demonstrated that MTP mitigated the MFR-mediated decrease in alveolar count, decrease in adipogenic protein peroxisome proliferator-activated receptor γ, increase in myogenic proteins (fibronectin, α-smooth muscle actin, and calponin), increase in Wnt signaling intermediates (lymphoid enhancer-binding factor 1 and β-catenin), and increase in glucocorticoid receptor (GR) levels. The MFR-induced lung phenotype and the effects of MTP were similar in both genders. To elucidate the mechanism of MFR-induced shift of the adipogenic-to-myogenic phenotype, lung fibroblasts were used to independently study the effects of (1) nutrient restriction and (2) excess steroid exposure. Nutrient deprivation increased myogenic proteins, Wnt signaling intermediates, and GR, all changes blocked by protein supplementation. MTP also blocked, likely by normalizing nicotinamide adenine dinucleotide phosphate levels, the corticosterone-induced increase in myogenic proteins, but had no effect on GR levels. In summary, protein restriction and increased glucocorticoid levels appear to be the key players in MFR-induced lung disease, affecting both genders.

Glucocorticoids and bone: local effects and systemic implications

Glucocorticoids (GCs) are highly effective in the treatment of inflammatory and autoimmune conditions but their therapeutic use is limited by numerous adverse effects. Recent insights into the mechanisms of action of both endogenous and exogenous GCs on bone cells have unlocked new approaches to the development of effective strategies for the prevention and treatment of GC-induced osteoporosis. Furthermore, topical studies in rodents indicate that the osteoblast-derived peptide, osteocalcin, plays a central role in the pathogenesis of GC-induced diabetes and obesity. These exciting findings mechanistically link the detrimental effects of GCs on bone and energy metabolism. In this article we review the physiology and pathophysiology of GC action on bone cells, and discuss current and emerging concepts regarding the molecular mechanisms underlying adverse effects of GCs such as osteoporosis and diabetes.

Acute murine antigen-induced arthritis is not affected by disruption of osteoblastic glucocorticoid signalling

Background

The role of endogenous glucocorticoids (GC) in the initiation and maintenance of rheumatoid arthritis (RA) remains unclear. We demonstrated previously that disruption of GC signalling in osteoblasts results in a profound attenuation of K/BxN serum-induced arthritis, a mouse model of RA. To determine whether or not the modulation of the inflammatory response by osteoblasts involves T cells, we studied the effects of disrupted osteoblastic GC-signalling in the T cell-dependent model of antigen-induced arthritis (AIA).

Methods

Acute arthritis was induced in pre-immunised 11-week-old male 11β-hydroxysteroid dehydrogenase type 2 transgenic (tg) mice and their wild-type (WT) littermates by intra-articular injection of methylated bovine serum albumine (mBSA) into one knee joint. Knee diameter was measured every 1–2 days until euthanasia on day 14 post injection. In a separate experiment, arthritis was maintained for 28 days by weekly reinjections of mBSA. Tissues were analysed by histology, histomorphometry and microfocal-computed tomography. Serum cytokines levels were determined by multiplex suspension array.

Results

In both short and long term experiments, arthritis developed in tg and WT mice with no significant difference between both groups. Histological indices of inflammation, cartilage damage and bone erosion were similar in tg and WT mice. Bone volume and turnover at the contralateral tibia and systemic cytokine levels were not different.

Conclusions

Acute murine AIA is not affected by a disruption in osteoblastic GC signalling. These data indicate that osteoblasts do not modulate the T cell-mediated inflammatory response via a GC-dependent pathway.

Prx1 and 3.2kb Col1a1 promoters target distinct bone cell populations in transgenic mice

Bones consist of a number of cell types including osteoblasts and their precursor cells at various stages of differentiation. To analyze cellular organization within the bone, we generated Col1a1CreER-DsRed transgenic mice that express, in osteoblasts, CreER and DsRed under the control of a mouse 3.2kb Col1a1 promoter. We further crossed Col1a1CreER-DsRed mice with Prx1CreER-GFP mice that express CreER and GFP in osteochondro progenitor cells under the control of a 2.4kb Prx1 promoter. Since the 3.2kb Col1a1 promoter becomes active in osteoblasts at early stages of differentiation, and Prx1CreER-GFP-expressing periosteal cells show endogenous Col1a1 expression, we expected to find a cell population in which both the 2.4kb Prx1 promoter and the 3.2kb Col1a1 promoter are active. However, our histological and flow cytometric analyses demonstrated that these transgenes are expressed in distinct cell populations. In the periosteum of long bones, Col1a1CreER-DsRed is expressed in the innermost layer directly lining the bone surface, while Prx1CreER-GFP-expressing cells are localized immediately outside of the Col1a1CreER-DsRed-expressing osteoblasts. In the calvaria, Prx1CreER-GFP-expressing cells are also localized in the cranial suture mesenchyme. Our experiments further showed that Col1a1CreER-DsRed-expressing cells lack chondrogenic potential, while the Prx1CreER-GFP-expressing cells show both chondrogenic and osteogenic potential. Our results indicate that Col1a1CreER-DsRed-expressing cells are committed osteoblasts, while Prx1CreER-GFP-expressing cells are osteochondro progenitor cells. The Prx1CreER-GFP and Col1a1CreER-DsRed transgenes will offer novel approaches for analyzing lineage commitment and early stages of osteoblast differentiation under physiologic and pathologic conditions.

Molecular determinants of glucocorticoid actions in inflammatory joint diseases

Since their discovery in 1948, glucocorticoids have been widely used clinically to treat inflammatory disorders like rheumatoid arthritis. However, their usefulness, especially in rheumatoid arthritis therapy, is hampered by severe side effects on bone leading to glucocorticoid-induced osteoporosis. The molecular and cellular mechanisms mediating the beneficial and adverse effects remain poorly understood. Nevertheless, advanced molecular biological analyses and in vivo approaches using conditional mutant mice have helped to unravel in part the underlying mechanisms of immunosuppression and side effects of glucocorticoid therapy in arthritis, thereby contributing to an improved understanding of these therapeutically important hormones.

Determinants of bone marrow adiposity: the modulation of peroxisome proliferator-activated receptor-γ2 activity as a central mechanism

Although the presence of adipocytes in the bone marrow is a normal physiological phenomenon, the role of these cells in bone homeostasis and during pathological states has not yet been fully delineated. As osteoblasts and adipocytes originate from a common progenitor, with an inverse relationship existing between osteoblastogenesis and adipogenesis, bone marrow adiposity often negatively correlates with osteoblast number and bone mineral density. Bone adiposity can be affected by several physiological and pathophysiological factors, with abnormal, elevated marrow fat resulting in a pathological state. This review focuses on the regulation of bone adiposity by physiological factors, including aging, mechanical loading and growth factor expression, as well as the pathophysiological factors, including diseases such as anorexia nervosa and dyslipidemia, and pharmacological agents such as thiazolidinediones and statins. Although these factors regulate bone marrow adiposity via a plethora of different intracellular signaling pathways, these diverse pathways often converge on the modulation of the expression and/or activity of the pro-adipogenic transcription factor peroxisome proliferator-activated receptor (PPAR)-γ2, suggesting that any factor that affects PPAR-γ2 may have an impact on the fat content of bone.

Glucocorticoid-induced osteoporosis: mechanisms, management, and future perspectives

Glucocorticoids are widely used for their unsurpassed anti-inflammatory and immunomodulatory effects. However, the therapeutic use of glucocorticoids is almost always limited by substantial adverse outcomes such as osteoporosis, diabetes, and obesity. These unwanted outcomes are a major dilemma for clinicians because improvements in the primary disorder seem to be achievable only by accepting substantial adverse effects that are often difficult to prevent or treat. To understand the pathogenesis of glucocorticoid-induced osteoporosis, it is necessary to consider that the actions of glucocorticoids on bone and mineral metabolism are strongly dose and time dependent. At physiological concentrations, endogenous glucocorticoids are key regulators of mesenchymal cell differentiation and bone development, with additional regulatory roles in renal and intestinal calcium handling. However, at supraphysiological concentrations, glucocorticoids affect the same systems in different and often unfavourable ways. For many years, these anabolic and catabolic actions of glucocorticoids on bone were deemed paradoxical. In this Review, we highlight recent advances in our understanding of the mechanisms underlying the physiology and pathophysiology of glucocorticoid action on the skeleton and discuss present and future management strategies for glucocorticoid-induced osteoporosis.

The interrelationship between bone and fat: from cellular see-saw to endocrine reciprocity

The number of mature osteoblasts and marrow adipocytes in bone is influenced by the differentiation of the common mesenchymal progenitor cell towards one phenotype and away from the other. Consequently, factors which promote adipogenesis not only lead to fatty marrow but also inhibit osteoblastogenesis, resulting in decreased osteoblast numbers, diminished bone formation and, potentially, inadequate bone mass and osteoporosis. In addition to osteoblast and bone adipocyte numbers being influenced by this skewing of progenitor cell differentiation towards one phenotype, mature osteoblasts and adipocytes secrete factors which may evoke changes in the cell fate and function of each other. This review examines the endogenous factors, such as PPAR-γ2, Wnt, IGF-1, GH, FGF-2, oestrogen, the GP130 signalling cytokines, vitamin D and glucocorticoids, which regulate the selection between osteoblastogenesis and adipogenesis and the interrelationship between fat and bone. The role of adipokines on bone, such as adiponectin and leptin, as well as adipose-derived oestrogen, is reviewed and the role of bone as an energy regulating endocrine organ is discussed.

Endogenous Glucocorticoids and Bone

While the adverse effects of glucocorticoids on bone are well described, positive effects of glucocorticoids on the differentiation of osteoblasts are also observed. These paradoxical effects of glucocorticoids are dose dependent. At both physiologicaland supraphysiological levels of glucocorticoids, osteoblasts and osteocytes are the major glucocorticoid target cells. However, the response of the osteoblasts to each of these is quite distinct. At physiology levels, glucocorticoids direct mesenchymal progenitor cells to differentiate towards osteoblasts and thus increase bone formation in a positive way. In contrast with ageing, the excess production of glucocorticoids, at both systemic and intracellular levels, appear to impact on osteoblast and osteocytes in a negative way in a similar fashion to that seen with therapeutic glucocorticoids. This review will focus on therole of glucocorticoids in normal bone physiology, with particular emphasis on the mechanism by which endogenous glucocorticoids impact on bone and its constituent cells.