Glucocorticoid induced osteoblast apoptosis by increasing E4BP4 expression via up-regulation of Bim

Insights and implications of sexual dimorphism in osteoporosis

Osteoporosis, a metabolic bone disease characterized by low bone mineral density and deterioration of bone microarchitecture, has led to a high risk of fatal osteoporotic fractures worldwide. Accumulating evidence has revealed that sexual dimorphism is a notable feature of osteoporosis, with sex-specific differences in epidemiology and pathogenesis. Specifically, females are more susceptible than males to osteoporosis, while males are more prone to disability or death from the disease. To date, sex chromosome abnormalities and steroid hormones have been proven to contribute greatly to sexual dimorphism in osteoporosis by regulating the functions of bone cells. Understanding the sex-specific differences in osteoporosis and its related complications is essential for improving treatment strategies tailored to women and men. This literature review focuses on the mechanisms underlying sexual dimorphism in osteoporosis, mainly in a population of aging patients, chronic glucocorticoid administration, and diabetes. Moreover, we highlight the implications of sexual dimorphism for developing therapeutics and preventive strategies and screening approaches tailored to women and men. Additionally, the challenges in translating bench research to bedside treatments and future directions to overcome these obstacles will be discussed.

NFIL3 and its immunoregulatory role in rheumatoid arthritis patients

Nuclear-factor, interleukin 3 regulated (NFIL3) is an immune regulator that plays an essential role in autoimmune diseases. However, the relationship between rheumatoid arthritis (RA) and NFIL3 remains largely unknown. In this study, we examined NFIL3 expression in RA patients and its potential molecular mechanisms in RA. Increased NFIL3 expression levels were identified in peripheral blood mononuclear cells (PBMCs) from 62 initially diagnosed RA patients and 75 healthy controls (HCs) by quantitative real-time PCR (qRT-PCR). No correlation between NFIL3 and disease activity was observed. In addition, NFIL3 expression was significantly upregulated in RA synovial tissues analyzed in the Gene Expression Omnibus (GEO) dataset (GSE89408). Then, we classified synovial tissues into NFIL3-high (≥75%) and NFIL3-low (≤25%) groups according to NFIL3 expression levels. Four hundred five differentially expressed genes (DEGs) between the NFIL3-high and NFIL3-low groups were screened out using the “limma” R package. Enrichment analysis showed that most of the enriched genes were primarily involved in the TNF signaling pathway via NFκB, IL-17 signaling pathway, and rheumatoid arthritis pathways. Then, 10 genes (IL6, IL1β, CXCL8, CCL2, PTGS2, MMP3, MMP1, FOS, SPP1, and ADIPOQ) were identified as hub genes, and most of them play a key role in RA. Positive correlations between the hub genes and NFIL3 were revealed by qRT-PCR in RA PBMCs. An NFIL3-related protein–protein interaction (PPI) network was constructed using the STRING database, and four clusters (mainly participating in the inflammatory response, lipid metabolism process, extracellular matrix organization, and circadian rhythm) were constructed with MCODE in Cytoscape. Furthermore, 29 DEGs overlapped with RA-related genes from the RADB database and were mainly enriched in IL-17 signaling pathways. Thus, our study revealed the elevated expression of NFIL3 in both RA peripheral blood and synovial tissues, and the high expression of NFIL3 correlated with the abnormal inflammatory cytokines and inflammatory responses, which potentially contributed to RA progression.

Bone remodeling stages under physiological conditions and glucocorticoid in excess: Focus on cellular and molecular mechanisms

This review provides a rationale for the cellular and molecular mechanisms of bone remodeling stages under physiological conditions and glucocorticoids (GCs) in excess. Remodeling is a synchronous process involving bone resorption and formation, proceeding through stages of: (1) resting bone, (2) activation, (3) bone resorption, (4) reversal, (5) formation, (6) termination. Bone remodeling is strictly controlled by local and systemic regulatory signaling molecules. This review presents current data on the interaction of osteoclasts, osteoblasts and osteocytes in bone remodeling and defines the role of osteoprogenitor cells located above the resorption area in the form of canopies and populating resorption cavities. The signaling pathways of proliferation, differentiation, viability, and cell death during remodeling are presented. The study of signaling pathways is critical to understanding bone remodeling under normal and pathological conditions. The main signaling pathways that control bone resorption and formation are RANK / RANKL / OPG; M-CSF – c-FMS; canonical and non-canonical signaling pathways Wnt; Notch; MARK; TGFβ / SMAD; ephrinB1/ephrinB2 – EphB4, TNFα – TNFβ, and Bim – Bax/Bak. Cytokines, growth factors, prostaglandins, parathyroid hormone, vitamin D, calcitonin, and estrogens also act as regulators of bone remodeling. The role of non-encoding microRNAs and long RNAs in the process of bone cell differentiation has been established. MicroRNAs affect many target genes, have both a repressive effect on bone formation and activate osteoblast differentiation in different ways. Excess of glucocorticoids negatively affects all stages of bone remodeling, disrupts molecular signaling, induces apoptosis of osteocytes and osteoblasts in different ways, and increases the life cycle of osteoclasts. Glucocorticoids disrupt the reversal stage, which is critical for the subsequent stages of remodeling. Negative effects of GCs on signaling molecules of the canonical Wingless (WNT)/β-catenin pathway and other signaling pathways impair osteoblastogenesis. Under the influence of excess glucocorticoids biosynthesis of biologically active growth factors is reduced, which leads to a decrease in the expression by osteoblasts of molecules that form the osteoid. Glucocorticoids stimulate the expression of mineralization inhibitor proteins, osteoid mineralization is delayed, which is accompanied by increased local matrix demineralization. Although many signaling pathways involved in bone resorption and formation have been discovered and described, the temporal and spatial mechanisms of their sequential turn-on and turn-off in cell proliferation and differentiation require additional research.

Boron Supplementation Promotes Osteogenesis of Tibia by Regulating the Bone Morphogenetic Protein-2 Expression in African Ostrich Chicks

The present study aimed to explore the effects of supplemental boron on osteogenesis of tibia and to investigate the possible relationship between additional boron and the expression of bone morphogenetic protein-2 (BMP-2) in tibia of ostrich chicks. Therefore, forty-eight African ostrich chicks (15 days old) were supplemented with 0 mg/L, 40 mg/L, 80 mg/L, 160 mg/L, 320 mg/L, and 640 mg/L of boron in drinking water for 75 days. The paraffin sections of tibia used to measure histomorphometric parameters by hematoxylin and eosin (HE) staining, Masson's staining, and immunohistochemistry (IHC). Enzyme-linked immunosorbent assay was performed to assess the level of BMP-2, osteocalcin (BGP), glucocorticoids (GCs), osteoprotegerin (OPG), and receptor activator of nuclear factor kappa-B ligand (RANKL) in serum. TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) technique was performed to detect the cell apoptosis. The results indicated that low dose of supplemental boron (40 mg/L-160 mg/L) in drinking water promotes bone development by increasing the mature ossein. The expression of BMP2 on 45 days was higher than 90 days. Serum level of BMP-2, BGP, and GCs changed significantly in groups with low dosage of boron, and OPG/RANKL ratio was upregulated from 0 to 160 mg/L. Cell apoptosis was least in 40 mg/L and 160 mg/L groups. Taken together, low dose of boron supplemented in drinking water could promote osteogenesis and growth and development of tibia by regulating the expression and secretion of BMP-2 and providing a dynamically balanced environment for tibia growth, development, and reconstruction by regulating the concentrations of BGP, GCs, and OPG/RANKL ratio in serum.

MicroRNA-22 contributes to dexamethasone-induced osteoblast differentiation inhibition and dysfunction through targeting caveolin-3 expression in osteoblastic cells

Osteoporosis is a common complication of long-term use of glucocorticoids (GCs) characterized by the loss of bone mass and damage of the microarchitecture as well as osteoblast dysfunction. Previous studies have demonstrated that microRNA-22 (miR-22) is the negative modulator of osteogenesis that may target caveolin-3 (CAV3), which has been reported to enhance bone formation and inhibit the progression of osteoporosis as well as apoptosis. The present study aimed to investigate whether miR-22 may be involved in dexamethasone (DEX)-induced inhibition of osteoblast differentiation and dysfunction by regulating CAV3 expression. Reverse transcription-quantitative PCR (RT-qPCR) was performed to measure the expression of miR-22 and western blotting was performed to determine protein levels. The results demonstrated that miR-22 expression was upregulated in DEX-treated osteoblastic cells compared with the control group. In addition, miR-22 mimic aggravated, whereas miR-22 inhibitor mitigated DEX-induced damage in osteoblastic cells compared with the control groups. Additionally, CAV3 was identified as the target of miR-22 in osteoblasts using RT-qPCR, western blotting and dual-luciferase reporter gene assay analysis. The results also demonstrated that silencing of CAV3 blocked the beneficial effects of miR-22 inhibitor against DEX-induced cell damage and apoptosis in osteoblasts, as evidenced by the increased expression levels of cleaved caspase-3, Bax and alkaline phosphatase activity as well as decreased cell viability and Bcl-2 levels. Collectively, these results indicate a novel molecular mechanism by which miR-22 contributes to DEX-induced osteoblast dysfunction and apoptosis via the miR-22/CAV3 pathway.

LncRNA NORAD promotes bone marrow stem cell differentiation and proliferation by targeting miR-26a-5p in steroid-induced osteonecrosis of the femoral head

BACKGROUND

Steroid-induced osteonecrosis of the femoral head (SONFH) is a devastating orthopedic disease, which seriously affects the quality of life of patients. The study aims to investigate the effects of LncRNA NORAD on SONFH.

METHODS

Human bone marrow-derived mesenchymal stem cells (hBMSCs) were isolated from the proximal femur of patients during routine orthopedic surgery and then cultured with dexamethasone (Dex) and transfected with NORAD overexpression vector, siRNA-NORAD and miR-26a-5p mimics. The mRNA expression of NORAD, miR-26a-5p, OPG, RANK, and RANKL was detected by RT-qPCR. Cell proliferation and apoptosis was measured by CCK-8 assay and flow cytometry, respectively. The protein expression of RUNX2, OPG, RANK, and RANKL was detected by western blot. The dual-luciferase reporter gene assay was performed to confirm the binding between NORAD and miR-26a-5p.

RESULTS

NORAD expression was downregulated in SONFH tissues, while miR-26a-5p expression was upregulated. Overexpression of NORAD improved DEX-induced inhibition of proliferation and differentiation, and promotion of apoptosis in hBMSCs, while knockdown of NORAD led to the opposite results. Moreover, NORAD improved DEX-induced inhibition of proliferation and differentiation, and promotion of apoptosis by regulation of miR-26a-5p in hBMSCs.

CONCLUSIONS

NORAD expression was downregulated in SONFH tissues, while miR-26a-5p expression was upregulated. NORAD improved DEX-induced inhibition of proliferation and differentiation, and promotion of apoptosis by regulation of miR-26a-5p in hBMSCs.

Thyroid Hormones, Glucocorticoids, Insulin, and Bone

Several endocrine systems have important effects on bone tissue. Thyroid hormones are essential for normal growth and development. Excess of these hormones will result in clinically significant changes that may require intervention. Glucocorticoids also have a marked effect on bone metabolism by several pathways. Their endogenous or exogenous excess will induce pathological processes that might elevate the risk of fractures. Insulin and the carbohydrate metabolism elicit a physiological effect on bone; however, the lack of insulin (type 1 diabetes) or insulin resistance (type 2 diabetes) have deleterious influence on bone tissue.

Therapeutic glucocorticoids: mechanisms of actions in rheumatic diseases

Therapeutic glucocorticoids have been widely used in rheumatic diseases since they became available over 60 years ago. Despite the advent of more specific biologic therapies, a notable proportion of individuals with chronic rheumatic diseases continue to be treated with these drugs. Glucocorticoids are powerful, broad-spectrum anti-inflammatory agents, but their use is complicated by an equally broad range of adverse effects. The specific cellular mechanisms by which glucocorticoids have their therapeutic action have been difficult to identify, and attempts to develop more selective drugs on the basis of the action of glucocorticoids have proven difficult. The actions of glucocorticoids seem to be highly cell-type and context dependent. Despite emerging data on the effect of tissue-specific manipulation of glucocorticoid receptors in mouse models of inflammation, the cell types and intracellular targets of glucocorticoids in rheumatic diseases have not been fully identified. Although showing some signs of decline, the use of systemic glucocorticoids in rheumatology is likely to continue to be widespread, and careful consideration is required by rheumatologists to balance the beneficial effects and deleterious effects of these agents.

Blocking glucocorticoid signaling in osteoblasts and osteocytes prevents mechanical unloading-induced cortical bone loss

Bone loss has been supposed to be the greatest damage to the health of astronauts. It is generally believed that the mechanical unloading induced by microgravity is the main cause of bone loss. However, besides mechanical unloading, many evidences from animal models and spaceflight missions indicate that microgravity conditions can cause some stress reactions and elevated endogenous glucocorticoid (GC) levels. High levels of GCs can lead to bone loss. This study aimed to investigate whether elevated GC levels are involved in hindlimb unloading (HLU)-induced bone loss in mice. Col2.3-11β-hydroxysteroid dehydrogenase type 2 (Col2.3-11β-HSD2) transgenic mice which are characterized by specific blocking GC signaling in mature osteoblasts and osteocytes were used. Male 14-week-old Col2.3-11β-HSD2 transgenic mice and wild type littermates were tail-suspended or kept under ambulatory conditions. At the endpoint, the tibias were examined by micro-computed tomography and histomorphometry, and bone turnover was analyzed by serum biochemistry, histochemistry staining, immunohistochemistry, and real-time PCR. Mice exposed to unloading occurred a significant increase in serum GC concentrations. Compared with non-unloaded controls, HLU led to a severe damage in cortical bone microstructure and bone strength of the tibia in wild type mice but not transgenic littermates. Osteoblast activity and bone formation were inhibited, whereas osteoclast activity and bone resorption were promoted in the tibial cortical bone of wild type mice following HLU, features absented in transgenic mice. Furthermore, HLU resulted in a significant increase in the number of sclerostin-producing and receptor activator of nuclear factor-κ B ligand (RANKL)-positive osteocytes, and apoptotic osteoblasts and osteocytes in wild type mice of unloading but not in unloaded transgenic mice. In conclusion, cortical bone loss during HLU is mediated through enhancing GC signaling in osteoblasts and osteocytes and subsequently restraining bone formation and activating bone resorption. It suggests that elevated GC levels play an important role in cortical bone loss in response to mechanical unloading.

Crocin protects against dexamethasone‑induced osteoblast apoptosis by inhibiting the ROS/Ca2+‑mediated mitochondrial pathway

Osteoblast apoptosis has been identified as an important event in the development of glucocorticoid (GC)-induced osteoporosis and osteonecrosis of the femoral head. Crocin, a bioactive ingredient of saffron, has been demonstrated to induce antiapoptotic effects on numerous types of cell in vitro; however, the effects of crocin on the dexamethasone (Dex)-induced apoptosis of osteoblasts remain unclear. In the present study, the protective effects of crocin during Dex-induced apoptosis of MC3T3-E1 osteoblasts, and the underlying mechanisms, were investigated. MTT and Annexin V-FITC/PI flow cytometry assays were performed to evaluate the viability and apoptosis of cells, respectively. The mitochondrial transmembrane potential, reactive oxygen species (ROS), intracellular Ca²⁺ levels and apoptosis-associated protein expression were assessed via flow cytometry, fluorescence microscopy and western blotting. It was demonstrated that crocin pretreatment inhibited Dex-induced apoptosis of osteoblasts in a dose-dependent manner. Crocin reversed Dex-induced decreases in the mitochondrial transmembrane potential, and increases in ROS and intracellular Ca²⁺ levels. Furthermore, crocin upregulated the expression levels of B-cell lymphoma-2 (Bcl-2) and mitochondrial cytochrome c (Cyt C), and downregulated those of cleaved caspase-9, cleaved caspase-3, Bcl-2-associated X protein and cytoplasmic Cyt C. N-acetylcysteine, a ROS inhibitor, and 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid, a calcium chelator, attenuated Dex-induced osteoblast apoptosis, whereas H₂O₂ and ionomycin, a calcium ionophore that increases intracellular calcium levels, reversed the antiapoptotic effects of crocin on Dex-treated osteoblasts. These results indicated that crocin may protect osteoblasts from Dex-induced apoptosis by inhibiting the ROS/Ca²⁺-mediated mitochondrial pathway, thus suggesting that crocin has potential value as a treatment for GC-induced bone diseases.

Extract and fraction of Cassia occidentalis L. (a synonym of Senna occidentalis) have osteogenic effect and prevent glucocorticoid-induced osteopenia

ETHNOPHARMACOLOGICAL RELEVANCE

Cassia occidentalis L., a synonym of Senna occidentalis (belongs to Caesalpiniaceae family) is an annual plant. Pursuing a lead from a folk practice prevalent since the late nineteenth century in Andhra Pradesh, a Southern state of India, of use of Cassia occidentalis leaf and stem for treating patients with fracture and bone diseases, we have not only confirmed its fracture healing activity but also demonstrated efficacy in preventing glucocorticoid-induced osteoporosis (GIO), the commonest form of medication-induced bone loss caused chiefly due to impairment of bone formation.

AIM OF THE STUDY

In the present work, the effects of extract and fraction of leaf and stem of Cassia occidentalis was investigated in fracture healing and GIO models of rat. The study also aimed to identify osteogenic compounds from this plant.

MATERIALS AND METHODS

Ethanolic extracts from leaf and stem of Cassia occidentalis were prepared and their efficacy tested in rat femur osteotomy (fracture healing) model. Subsequently, a butanolic fraction was prepared and osteogenic efficacy compared with the ethanolic extract, and upon finding the former to be more potent, its osteogenic effect was studied in details in GIO model. Chemical finger-printing and isolation of ten pure compounds were done to assess their osteogenic effect in rat primary osteoblast cultures.

RESULTS

Ethanolic extract of stem was more effective than the leaf extract in enhancing bone regeneration at the site of osteotomy. Further, butanolic fraction of the ethanolic extract of stem was more effective than the later in bone regeneration at the femur osteotomy site and in preventing bone loss in GIO model. The mechanism of skeletal preservation involved stimulation of new bone formation and inhibition of bone resorption. As many as six osteogenic compounds were isolated out of which apigenin-6C-glucopyranoside was most effective in vitro.

CONCLUSION

Our study found that a standardized extract of an ethanolic extract and its butanolic fraction from the stem of Cassia occidentalis has osteogenic as well as anti-resorptive effects, resulting in the protection against glucocorticoid-induced bone loss. Our results contribute towards validation of the traditional use of Cassia occidentalis in fracture healing and also suggest its beneficial use in GIO for which clinical trials are warranted.

Haem oxygenase-1 induction prevents glucocorticoid-induced osteoblast apoptosis through activation of extracellular signal-regulated kinase1/2 signalling pathway

Background

High-dose glucocorticoid (GC) therapy always causes osteoporosis partly by inducing osteoblast apoptosis. However, the underlying mechanisms of GC-induced apoptosis remain elusive. Haem oxygenase-1 (HO-1) is a cytoprotective protein that rescues cells from H₂O₂ or high glucose-induced apoptosis. In bone metabolism, HO-1 also participates in osteoclast and osteoblast differentiation.

Objective

The present study aimed to investigate the protective role of HO-1 against GC-induced osteoblast apoptosis and to elucidate the underlying mechanism.

Methods

Mouse osteoblastic MC3T3-E1 cells were treated with dexamethasone (Dex) for 24 h in the presence or absence of cobalt (III) protoporphyrin IX chloride (CoPP, an inducer of HO-1). In some experiments, U0126 was added to the culture 1 h before CoPP treatment. The induction of apoptosis was determined by flow cytometry. Cell viability was evaluated using a cell counting kit-8 (CCK-8) assay. The expression levels of Bax and bcl-2 were measured by real-time polymerase chain reaction and Western blot. HO-1, extracellular signal-regulated kinase (ERK)-1/2 and pERK1/2 protein levels were measured by Western blot analysis.

Results

Dex promoted apoptosis and inhibited cell viability in MC3T3-E1 cells. In addition, Dex significantly increased Bax expression and reduced Bcl-2 expression. The expression of HO-1 was also reduced after Dex treatment. HO-1 induction by CoPP significantly attenuated Dex-induced apoptosis as evidenced by Annexin V/PI staining. The mRNA expression level of antiapoptotic gene Bcl-2 was also increased after CoPP treatment. Moreover, CoPP treatment increased the phosphorylation of ERK1/2. U0126, an inhibitor of ERK activation, significantly abrogated the protective effects of CoPP.

Conclusion

Our results demonstrate that HO-1 induction by CoPP can attenuate Dex-induced apoptosis of mouse osteoblastic MC3T3-E1 cells. The antiapoptotic effect of HO-1 induction may be correlated with the activation of ERK1/2 signalling pathway. The translational potential of this article: HO-1 induction by CoPP can prevent GC-induced osteoblast apoptosis. Our findings will highlight the therapeutic potential of HO-1 induction in GC-induced osteoporosis.

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.

E4BP4 facilitates glucocorticoid sensitivity of human bronchial epithelial cells via down-regulation of glucocorticoid receptor-beta

It has recently been recognized that a subset of asthma patients suffer from glucocorticoid (GC) insensitivity, and glucocorticoid receptor-β (GR-β) is associated with corticosteroid resistance, but the underlying mechanisms remain unknown. Here we demonstrated that Interleukin-17A induced glucocorticoid sensitivity in human bronchial epithelial cells (16HBE) is enhanced, which is depend on E4 promoter-binding protein 4 (E4BP4) mediated GR-β expression. Our data show that the expression of E4BP4 is significantly up-regulated in 16HBE cells, and the depletion of E4BP4 dramatically decreased glucocorticoid sensitivity in IL-17A induced 16HBE cells. Mechanistic studies revealed that E4BP4 plays a crucial role in Interleukin-17A induced glucocorticoid sensitivity in 16HBE cells via down-regulating GR-β, which is probably mediated by PI3K/Akt activation. Collectively, we can draw the conclusion that E4BP4 contribute to enhance the GCs sensitivity, which may offer a new strategy for therapeutic intervention for GC-insensitive asthma.

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.

Regulation of Clock Genes by Adrenergic Receptor Signaling in Osteoblasts

The clock system has been identified as one of the major mechanisms controlling cellular functions. Circadian clock gene oscillations also actively participate in the functions of various cell types including bone-related cells. Previous studies demonstrated that clock genes were expressed in bone tissue and also that their expression exhibited circadian rhythmicity. Recent findings have shown that sympathetic tone plays a central role in biological oscillations in bone. Adrenergic receptor (AR) signaling regulates the expression of clock genes in cancellous bone. Furthermore, α₁-AR signaling in osteoblasts is known to negatively regulate the expression of bone morphogenetic protein-4 (Bmp4) by up-regulating nuclear factor IL-3 (Nfil3)/e4 promoter-binding protein 4 (E4BP4). The ablation of α_1B-AR signaling also increases the expression of the Bmp4 gene in bone. The findings of transient overexpression and siRNA experiments have supported the involvement of the transcription factor CCAAT/enhancer-binding protein delta (C/EBPδ, Cebpd) in Nfil3 and Bmp4 expression in MC3T3-E1 cells. These findings suggest that the effects of Cebpd are due to the circadian regulation of Bmp4 expression, at least in part, by the up-regulated expression of the clock gene Nfil3 in response to α_1B-AR signaling in osteoblasts. Therefore, AR signaling appears to modulate cellular functionality through the expression of clock genes that are circadian rhythm regulators in osteoblasts. The expression of clock genes regulated by the sympathetic nervous system and clock-controlled genes that affect bone metabolism are described herein.

E4BP4 mediates glucocorticoid-regulated adipogenesis through COX2

Adipogenesis is mediated by glucocorticoids via transcriptional regulation of glucocorticoid receptor (GR) target genes. However, the mechanism by which GR participates in adipogenesis has hitherto been poorly characterized. In this study, E4 promoter-binding protein 4 (E4BP4) was found to have a critical role in adipogenic differentiation of preadipocytes. Gain-of-function and loss-of-function studies revealed that E4BP4 acts as a positive regulator of adipogenesis in 3T3-L1 cells. E4BP4 was markedly induced by glucocorticoid (dexamethasone) via GR and cAMP response element-binding protein (CREB) during adipogenesis. Knockdown of E4BP4 abolished dexamethasone-induced adipogenesis, and overexpression of E4BP4 partially accounted for the actions of dexamethasone in adipogenic differentiation. Promoter deletion analysis confirmed that E4BP4 transcriptionally represses COX2 promoter activity, whereas COX2 overexpression reversed the acceleration of E4BP4 in adipogenesis. Thus, E4BP4 acts as a key pro-adipogenic transcription factor by trans-repressing COX2 in glucocorticoid-associated adipocyte differentiation.

4-Phenyl butyric acid prevents glucocorticoid-induced osteoblast apoptosis by attenuating endoplasmic reticulum stress

Apoptosis of osteoblasts triggered by high-dose glucocorticoids (GCs) has been identified as a major cause of osteoporosis. However, the molecular mechanisms underlying GC-induced osteoporosis remain elusive. This study was conducted to make clear the mechanism of GC-induced osteoblast apoptosis and to examine whether reduction of ER stress by 4-PBA inhibited osteoblast apoptosis. After treatment with dexamethasone (Dex) or hydrocortisone, cell viability was assessed using an MTT assay. Flow cytometry was performed to assess the apoptosis of MC3T3-E1 cells. The expression levels of ER stress-related proteins (CHOP, GRP78, eIF2α, and phospho-eIF2α) and apoptosis-related proteins (cleaved Caspase-3, Bcl-2, and Bax) in MC3T3-E1 cells were measured by Western blot analysis. We found that both Dex and hydrocortisone reduced cell proliferation and promoted apoptosis in MC3T3-E1 cells. In addition, the protein expression levels of cleaved Caspase-3 and Bax increased and the protein expression level of Bcl-2 decreased in MC3T3-E1 cells exposed to Dex. In addition, the Dex exposure also resulted in a release of cytochrome c (Cyt C) from mitochondria. The cellular ATP content was decreased following prolonged treatment with Dex. 4-PBA attenuated ER stress and mitochondrial dysfunction induced by Dex in MC3T3-E1 cells. Dex-mediated apoptosis of MC3T3-E1 cells is aggravated by ER stress. Moreover, Dex-induced apoptosis in MC3T3-E1 cells was inhibited by 4-PBA, suggesting that ER stress involved in Dex-induced apoptosis. In conclusion, inhibition of ER stress by 4-PBA could reduce GC-induced apoptosis in MC3T3-E1 cells.

Pigment Epithelium-Derived Factor (PEDF) Protects Osteoblastic Cell Line from Glucocorticoid-Induced Apoptosis via PEDF-R

Pigment epithelial-derived factor (PEDF) is known as a widely expressed multifunctional secreted glycoprotein whose biological actions are cell-type dependent. Recent studies demonstrated that PEDF displays cytoprotective activity in several cell types. However, it remains unknown whether PEDF is involved in glucocorticoid-induced osteoblast death. The aim of this study was to examine the role of PEDF in osteoblast survival in response to dexamethasone, an active glucocorticoid analogue, and explore the underlying mechanism. In the present study, dexamethasone (DEX) was used to induce MC3T3-E1 pre-osteoblast apoptosis. PEDF mRNA and protein levels and cell apoptosis were determined respectively. Then PEDF receptor (PEDF-R)- and lysophosphatidic acid (LPA)-related signal transductions were assessed. Here we show that DEX down-regulates PEDF expression, which contributes to osteoblast apoptosis. As a result, exogenous recombinant PEDF (rPEDF) inhibited DEX-induced cell apoptosis. We confirmed that PEDF-R was expressed on MC3T3-E1 pre-osteoblast membrane and could bind to PEDF which increased the level of LPA and activated the phosphorylation of Akt. Our results suggest that PEDF attenuated DEX-induced apoptosis in MC3T3-E1 pre-osteoblasts through LPA-dependent Akt activation via PEDF-R.

Current Status of Research on Osteoporosis after Solid Organ Transplantation: Pathogenesis and Management

Improved survival following organ transplantation has brought to the forefront some long-term complications, among which osteoporosis and associated fractures are the major ones that adversely affect the quality of life in recipients. The pathogenesis of osteoporosis in transplant recipients is complex and multifactorial which may be related to increased bone resorption, decreased bone formation, or both. Studies have shown that the preexisting underlying metabolic bone disorders and the use of immunosuppressive agents are the major risk factors for osteoporosis and fractures after organ transplantation. And rapid bone loss usually occurs in the first 6–12 months with a significant increase in fracture risk. This paper will provide an updated review on the possible pathogenesis of posttransplant osteoporosis and fractures, the natural history, and the current prevention and treatment strategies concerning different types of organ transplantation.

Congenital adrenal hyperplasia with localized aggressive periodontitis and amelogenesis imperfecta

Congenital adrenal hyperplasia (CAH) is an inherited medical condition that implies defects in steroid biosynthesis. The dental findings of a female patient with CAH are reported. The patient suffered from severe periodontal tissue destruction, obvious enamel defects, as well as some occlusal problems. The management approach is presented and the possibility of interrelation of her dental findings with her medical condition is discussed.

Regulation of Bim in Health and Disease

The BH3-only Bim protein is a major determinant for initiating the intrinsic apoptotic pathway under both physiological and pathophysiological conditions. Tight regulation of its expression and activity at the transcriptional, translational and post-translational levels together with the induction of alternatively spliced isoforms with different pro-apoptotic potential, ensure timely activation of Bim. Under physiological conditions, Bim is essential for shaping immune responses where its absence promotes autoimmunity, while too early Bim induction eliminates cytotoxic T cells prematurely, resulting in chronic inflammation and tumor progression. Enhanced Bim induction in neurons causes neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's diseases. Moreover, type I diabetes is promoted by genetically predisposed elevation of Bim in β-cells. On the contrary, cancer cells have developed mechanisms that suppress Bim expression necessary for tumor progression and metastasis. This review focuses on the intricate network regulating Bim activity and its involvement in physiological and pathophysiological processes.

Glucocorticoid-mediated co-regulation of RCAN1-1, E4BP4 and BIM in human leukemia cells susceptible to apoptosis

Glucocorticoids (GCs) are known to induce apoptosis of leukemia cells via gene regulatory changes affecting key pro-and anti-apoptotic genes. Three genes previously implicated in GC-evoked apoptosis in the CEM human T-cell leukemia model, RCAN1, E4BP4 and BIM, were studied in a panel of human lymphoid and myeloid leukemia cell lines. Of the two RCAN1 transcripts, the synthetic GC Dexamethasone (Dex) selectively upregulates RCAN1-1, but not RCAN1-4, in GC-susceptible Sup-B15, RS4;11, Kasumi-1 cells but not in GC-resistant Sup T1 and Loucy cells. E4BP4 and BIM regulation correlated with that of RCAN1-1. A putative GRE and four EBPREs were identified within 1500bp upstream from the transcription start site of RCAN1-1. GC-refractory CEM C1-15 cells sensitized to GC-evoked apoptosis by ectopic E4BP4 expression, CEM C1-15mE#3, showed restored RCAN1-1 upregulation, suggesting that RCAN1-1 is a downstream target of E4BP4. A model for coordinated regulation of RCAN1-1, E4BP4 and BIM, and their role in GC-evoked apoptosis is proposed.