Tandem repeat of C/EBP binding sites mediates PPARgamma2 gene transcription in glucocorticoid-induced adipocyte differentiation

The effects of PPARγ inhibitor on bones and bone marrow fat in aged glucocorticoid-treated female rats

Progressive bone marrow (BM) fat accumulation is a common bone loss characteristic in older populations and glucocorticoid (GC)-induced skeletal destruction that is inversely associated with bone synthesis and directly associated with increased peroxisomal proliferator-activated receptor gamma (PPARγ) expression. PPARγ inhibition is an efficient therapeutic strategy for aged- and GC-related skeletal disorders. This study aimed to evaluate the effect of PPARγ inhibition on aged GC-treated female rats. It was hypothesised that bisphenol A diglycidyl ether (BADGE) could inhibit marrow adiposity and improve osteogenesis by inhibiting PPARγ, thereby preventing GC-induced osteoporosis (GIO). Female Sprague-Dawley rats (n = 32, age = 18 months) were randomly allocated to one of the following groups: (1) control, (2) BADGE (30 mg/kg/day, intraperitoneal), (3) methylprednisolone (MP; 30 mg/kg/day, subcutaneous), and (4) MP + BADGE. After eight weeks of treatment, bone density (BD) and trabecular bone microarchitectures were quantified by micro-computed tomography (CT), and BM adipocytes were quantified by histopathology. Additionally, mRNA and protein expression of adipogenic and osteogenic markers were quantified by reverse transcription-quantitative polymerase chain reaction. Furthermore, serum bone turnover biomarker levels were quantified by enzyme-linked immunosorbent assay. MP treatment led to marrow adipogenesis and bone deterioration. However, rats treated with MP + BADGE showed lower marrow adipogenesis, as indicated by smaller marrow adipocyte diameter, decreased density and area percentages, reduced expression of marrow adipogenic genes and proteins, improved BD and trabecular microarchitectures, increased expression of osteogenic genes and proteins, and higher levels of serum bone formation markers. These results were consistent with the differences observed between control and BADGE mono-treated rats. In conclusion, BADGE treatment attenuates BM adiposity and improves bone formation in aged GC-treated female rats by inhibiting PPARγ. Therefore, PPARγ might be a potential target for treating GIO in older populations.

Role of lncRNA LIPE-AS1 in adipogenesis

Recent studies have identified long non-coding RNAs (lncRNAs) as potential regulators of adipogenesis. In this study, we have characterized a lncRNA, LIPE-AS1, that spans genes CEACAM1 to LIPE in man with conservation of genomic organization and tissue expression between mouse and man. Tissue-specific expression of isoforms of the murine lncRNA were found in liver and adipose tissue, one of which, designated mLas-V3, overlapped the Lipe gene encoding hormone-sensitive lipase in both mouse and man suggesting that it may have a functional role in adipose tissue. Knock down of expression of mLas-V3 using anti-sense oligos (ASOs) led to a significant decrease in the differentiation of the OP9 pre-adipocyte cell line through the down regulation of the major adipogenic transcription factors Pparg and Cebpa. Knock down of mLas-V3 induced apoptosis during the differentiation of OP9 cells as shown by expression of active caspase-3, a change in the localization of LIP/LAP isoforms of C/EBPβ, and expression of the cellular stress induced factors CHOP, p53, PUMA, and NOXA. We conclude that mLas-V3 may play a role in protecting against stress associated with adipogenesis, and its absence leads to apoptosis.

Benzofuran pyran hybrid prevents glucocorticoid induced osteoporosis in mice via modulation of canonical Wnt/β-catenin signaling

Glucocorticoid induced osteoporosis (GIOP) is the second most leading cause of osteoporosis. We have identified a compound, a benzofuran pyran hybrid compound 4e that has osteogenic potential and we wanted to assess its efficacy in GIOP in male mice. We assessed the effect of dexamethasone and compound 4e on primary osteoblasts using various cell based and immunofluorescence assays. For in vivo studies we administered methylprednisolone and compound 4e as a prophylactic measure in male Balb/c mice for 28 days and then evaluated the effect on bone microarchitecture by microCT, bone formation by histology along with clinically relevant bone markers. Compound 4e preserved osteoblast differentiation as evident by higher ALP positive cells and mineralization in compound treated groups. Compound 4e also increased the expression of osteogenic genes. This compound guarded β-catenin expression both in vitro and in vivo as confirmed by western blot and immunofluorescence assays. This led to the preservation of bone microarchitecture and cortical thickness at 2.5 mg kg⁻¹ and 5 mg kg⁻¹ doses. Further compound 4e enhanced bone formation rate and regulated osteocyte death. The osteogenic potential of compound 4e was reflected by an increased level of serum marker osteocalcin and decreased levels of SOST and CTX-I. Overall, Compound 4e is able to overcome the catabolic effect of dexamethasone on bone by targeting the canonical WNT/β-catenin signaling as evidenced by both in vitro and in vivo studies.

Bad to the Bone: The Effects of Therapeutic Glucocorticoids on Osteoblasts and Osteocytes

Despite the continued development of specialized immunosuppressive therapies in the form of monoclonal antibodies, glucocorticoids remain a mainstay in the treatment of rheumatological and auto-inflammatory disorders. Therapeutic glucocorticoids are unmatched in the breadth of their immunosuppressive properties and deliver their anti-inflammatory effects at unparalleled speed. However, long-term exposure to therapeutic doses of glucocorticoids decreases bone mass and increases the risk of fractures - particularly in the spine - thus limiting their clinical use. Due to the abundant expression of glucocorticoid receptors across all skeletal cell populations and their respective progenitors, therapeutic glucocorticoids affect skeletal quality through a plethora of cellular targets and molecular mechanisms. However, recent evidence from rodent studies, supported by clinical data, highlights the considerable role of cells of the osteoblast lineage in the pathogenesis of glucocorticoid-induced osteoporosis: it is now appreciated that cells of the osteoblast lineage are key targets of therapeutic glucocorticoids and have an outsized role in mediating their undesirable skeletal effects. As part of this article, we review the molecular mechanisms underpinning the detrimental effects of supraphysiological levels of glucocorticoids on cells of the osteoblast lineage including osteocytes and highlight the clinical implications of recent discoveries in the field.

When to Start and Stop Bone-Protecting Medication for Preventing Glucocorticoid-Induced Osteoporosis

Glucocorticoid-induced osteoporosis (GIOP) leads to fractures in up to 40% of patients with chronic glucocorticoid (GC) therapy when left untreated. GCs rapidly increase fracture risk, and thus many patients with anticipated chronic GC exposures should start anti-osteoporosis pharmacotherapy to prevent fractures. In addition to low awareness of the need for anti-osteoporosis therapy among clinicians treating patients with GCs, a major barrier to prevention of fractures from GIOP is a lack of clear guideline recommendations on when to start and stop anti-osteoporosis treatment in patients with GC use. The aim of this narrative review is to summarize current evidence and provide considerations for the duration of anti-osteoporosis treatment in patients taking GCs based on pre-clinical, clinical, epidemiologic, and pharmacologic evidence. We review the pathophysiology of GIOP, outline current guideline recommendations on initiating and stopping anti-osteoporosis therapy for GIOP, and present considerations for the duration of anti-osteoporosis treatment based on existing evidence. In each section, we illustrate major points through a patient case example. Finally, we conclude with proposed areas for future research and emerging areas of interest related to GIOP clinical management.

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.

Dexras1 plays a pivotal role in maintaining the equilibrium between adipogenesis and osteogenesis

BACKGROUND

Chronic steroid treatment causes an increase in visceral adiposity and osteoporosis. It is believed that steroids may alter a balance between differentiation of mesenchymal stem cells (MSCs) into either adipocytes or osteoblasts; however, the detailed molecular mechanisms are unclear. We previously identified Dexras1 as a critical factor that potentiates adipogenesis in response to glucocorticoids. Thus, in this study, we investigated the role of Dexras1 in maintaining the balance between chronic steroid treatment-associated adipogenesis and osteoporosis.

MATERIAL AND METHODS

We treated wild type (WT) and Dexras1 knockout (KO) mice with dexamethasone for five weeks followed by 60% HFD for additional two weeks with dexamethasone. The changes of glucocorticoid-induced body weight gain and osteoporosis were analyzed. Bone marrow derived stromal cells (BMSCs) and mouse embryonic fibroblasts (MEFs) extracted from WT and Dexras1 KO mice, as well as MC3T3-E1 pre-osteoblasts and osteoclasts differentiated from RAW264.7 were analyzed to further define the role of Dexras1 in osteoblasts and osteoclasts.

RESULTS

Dual-energy X-ray absorptiometry and micro-computed tomography analyses in murine femurs revealed that Dexras1 deficiency was associated with increased osteogenesis, concurrent with reduced adipogenesis. Furthermore, Dexras1 deficiency promoted osteogenesis of BMSCs and MEFs in vitro, suggesting that Dexras1 deficiency prevents steroid-induced osteoporosis. We also observed that Dexras1 downregulated SMAD signaling pathways, which reduced the osteogenic differentiation capacity of pre-osteoblast MC3T3-E1 cells into mature osteoblasts.

CONCLUSION

We propose that Dexras1 is critical for maintaining the equilibrium between adipogenesis and osteogenesis upon steroid treatment.

Sulfated hyaluronic acid and dexamethasone possess a synergistic potential in the differentiation of osteoblasts from human bone marrow stromal cells

The development of novel bioactive biomaterials is urgently needed to meet the needs of an aging population. Both sulfated hyaluronic acid and dexamethasone are candidates for the functionalization of bone grafts, as they have been shown to enhance the differentiation of osteoblasts from bone marrow stromal cells in vitro and in vivo. However, the underlying mechanisms are not fully understood. Furthermore, studies combining different approaches to assess synergistic potentials are rare. In this study, we aim to gain insights into the mode of action of both sulfated hyaluronic acid and dexamethasone by a comprehensive analysis of the cellular fraction, released matrix vesicles, and the extracellular matrix, combining classical biochemical assays with mass spectrometry-based proteomics, supported by novel bioinformatical computations. We found elevated differentiation levels for both treatments, which were further enhanced by a combination of sulfated hyaluronic acid and dexamethasone. Single treatments revealed specific effects on osteogenic differentiation. Dexamethasone activates signalling pathways involved in the differentiation of osteoblasts, for example, CXC-motif chemokine receptor type 4 and mitogen-activated protein kinases. The effects of sulfated hyaluronic acid were predominantly linked to an alteration in the composition of the extracellular matrix, affecting the synthesis, secretion, and/or activity of fibrillary (fibronectin and thrombospondin-2) and nonfibrillary (transglutaminase-2, periostin, and lysyloxidase) extracellular matrix components, including proteases and their inhibitors (matrix metalloproteinase-2, tissue inhibitor of metalloproteinase-3). The effects were treatment specific, and less additive or contrary effects were found. Thus, we anticipate that the synergistic action of the treatment-specific effects is the key driver in elevated osteogenesis.

Peripheral blood GILZ mRNA levels in depression and following electroconvulsive therapy

Dysregulation of the hypothalamic-pituitary-adrenocortical (HPA)-axis is commonly observed in patients with depression. The delayed feedback system that mediates inhibition of HPA-axis activation is regulated by glucocorticoid receptors (GRs) found in stress-responsive areas of the brain. Glucocorticoid-induced leucine zipper (GILZ) is a key molecule in glucocorticoid biology and is thought to mediate the downstream anti-inflammatory effects of GRs. Previous reports suggest that GILZ levels are altered in the blood and brains of patients with, and animal models of, depression. However, no study has yet investigated the effects of antidepressant treatment on GILZ. Therefore, our aim was to examine peripheral blood GILZ mRNA levels in patients with depression (n = 88) compared to age- and sex-matched healthy controls (n = 63), and in patients with depression following treatment with a course of electroconvulsive therapy (ECT). We also assessed the relationship between GILZ and mood and clinical outcomes following ECT. GILZ mRNA levels were assessed using qRT-PCR. GILZ levels were found to be significantly lower in patients with depression compared to controls (p < 0.002), and ECT further decreased GILZ levels (p = 0.05). Both of these results survived adjustment for potential covariates. However, we found no association between GILZ and mood scores. Overall, these results suggest that GILZ is involved in the pathophysiology of depression and the peripheral molecular response to ECT.

Oil from Antarctic krill (Euphausia superba) facilitates bone formation in dexamethasone-treated mice

Glucocorticoids are the leading cause of secondary osteoporosis. In the current study, the in vivo effects of Antarctic krill (Euphausia superba) oil (AKO) on dexamethasone-treated mice were investigated. Results showed that AKO significantly prevents bone loss, as evidenced by improved bone mineral density, biomechanical strength, and cancellous bone microstructure. Fluorescence double-labeling of femur showed that AKO induces new bone formation. Toluidine blue staining of marrow cavity indicated that AKO increases the number of trabecula, and decreases the generation of adipose cells. Runt-related transcription factor 2 (Runx2) and Peroxisome proliferator-activated receptor γ (PPARγ) are the switches for osteogenic and adipogenic differentiation of bone marrow mesenchymal stem cells, respectively. AKO significantly promoted the expression of Runx2 protein, and reduced PPARγ expression in bone tissue. Furthermore, AKO increased the mRNA expression of osteogenesis-related genes and decreased the expression of adipogenesis-related genes. In conclusion, AKO improved glucocorticoid-induced osteoporosis via promoting bone formation.

Glucocorticoids, Inflammation and Bone

The current review on glucocorticoids (GCs), inflammation and bone is focused on three aspects: (1) the mutual effects between GCs, inflammation and bone in inflammatory rheumatic diseases, (2) current views on fracture risk assessment in patients using GCs and (3) non-pharmacological and pharmacological treatment to prevent fractures in GC-using patients with inflammatory rheumatic diseases. The use of GCs results in increased risk for fractures due to both direct and indirect negative effects of GCs on bone mass, and on bone and muscle strength. However, also the underlying inflammatory rheumatic disease is associated with the increased bone loss and fracture risk due to the chronic inflammation itself, and due to disability/immobility caused by active disease or joint destruction. The rapid and strong anti-inflammatory effect of GCs in patients with rheumatoid arthritis seems to balance the negative effects of GCs on bone in the early, active phase of the disease. Recently, an update of the American College of Rheumatology guidelines for prevention and treatment of GC-induced osteoporosis was published with renewed recommendations. To prevent fractures, general measures, including treatment of the underlying inflammatory disease adequately (even with GCs when indicated), a healthy lifestyle, including adequate calcium and vitamin D supplementation, and regular weight bearing exercises are important. In rheumatic patients with high fracture risk using GCs, especially when the cumulative dose is high and/or the underlying inflammatory disease is active, treatment with anti-osteoporotic drugs, usually an oral bisphosphonate, is indicated.

Clock represses preadipocytes adipogenesis via GILZ

Adiposity is a worldwide health threat that needs to be prevented. Circadian gene Clock (circadian locomotor output cycles kaput) is closely correlated to adiposity; for example, weight gain, adipocytes size expansion, and serum lipid level rise in Clock^Δ19 mice compared to C57BL/6J mice. However, the precise role of Clock during adipogenic differentiation is unknown. Herein, the circadian gene Clock is shown to regulate adipogenesis mediated by GILZ. Clock-mediated attenuation and upregulation influenced lipid synthesis and affected the levels of adipogenic transcriptional factors, C/EBP-β, C/EBP-α, PPAR-γ, and FABP4, both in vivo and in vitro (primary adipose-derived stromal cells and 3T3-L1 cells). Chromatin immunoprecipitation (ChIP) assay, reporter gene assay, and serum shock assay found that Clock transcriptionally regulated the glucocorticoid-induced leucine zipper (GILZ). Furthermore, GILZ attenuation could relieve the inhibitory effect of Clock on lipid synthesis and GILZ overexpression also reduced the promotion role of Clock attenuation in adipogenesis suggesting that Clock inhibits adipogenic differentiation of preadipocytes via GILZ. The current results demonstrate how circadian genes are likely to regulate adiposity, affecting the adipogenic differentiation process, as well as, increasing the fat cells number. Therefore, this study may provide novel insights into the underlying mechanism explaining the correlation between Clock mutation and adiposity.

Mechanism of triptolide in treating ankylosing spondylitis through the anti‑ossification effect of the BMP/Smad signaling pathway

The present study aimed to examine the mechanism of triptolide in the treatment of ankylosing spondylitis (AS) through the anti‑ossification effect of bone morphogenetic protein (BMP)/small mothers against decapentaplegic (Smad) pathway. Male rats were randomly divided into five groups: Normal rat group; model group; triptolide low dose group (10 mg/kg); triptolide middle dose group (20 mg/kg); triptolide high dose group (40 mg/kg). The spinal joint capsules of each group of rats were collected to perform primary cell culture to determine the levels of cell proliferation. Western blot and reverse transcription‑polymerase chain reaction analyses, and ELISA were used to detect the mRNA and protein expression levels of core‑binding factor α1 (Cbfal), BMP receptor type II (BMPRII), Smad1, Smad4, Smad5 and Smad6, the protein expression of phosphorylation indicators, including phosphorylated (p)Smad1 and pSmad5, the mRNA expression of tumor necrosis factor‑α (TNF‑α), interleukin (IL)‑1β and IL‑6 in rat plasma, and the mRNA expression of BMP/Smads in fibroblasts induced by recombinant human (rh)BMP‑2. The effects on AS in the rats were also examined. The results revealed that, following intervention with triptolide, inflammation was suppressed, and the mRNA expression levels of TNF‑α, IL‑1β and IL‑6 were reduced. The expression levels of Cbfal, BMPRII, Smad1, Smad4 and Smad5 were also reduced, whereas the expression of Smad6 was increased. Following induction by rhBMP‑2, the effects of triptolide weakened, with the most marked effects observed at the highest concentration, suggesting that triptolide functions through the BMP/Smad signaling pathway. Taken together, the results suggested that triptolide may be used to treat AS, the mechanism of which may be through the BMP/Smad pathway.

Sclerostin activity plays a key role in the negative effect of glucocorticoid signaling on osteoblast function in mice

Stress during prenatal development is correlated with detrimental cognitive and behavioral outcomes in offspring. However, the long-term impact of prenatal stress (PS) and disrupted glucocorticoid signaling on bone mass and strength is not understood. In contrast, the detrimental effect of lead (Pb) on skeletal health is well documented. As stress and Pb act on common biological targets via glucocorticoid signaling pathways and co-occur in the environment, this study first sought to assess the combined effect of stress and Pb on bone quality in association with alterations in glucocorticoid signaling. Bone parameters were evaluated using microCT, histomorphometry, and strength determination in 8-month-old male mouse offspring subjected to PS on gestational days 16 and 17, lifetime Pb exposure (100 p.p.m. Pb in drinking water), or to both. Pb reduced trabecular bone mass and, when combined with PS, Pb unmasked an exaggerated decrement in bone mass and tensile strength. Next, to characterize a mechanism of glucocorticoid effect on bone, prednisolone was implanted subcutaneously (controlled-release pellet, 5 mg·kg-1 per day) in 5-month-old mice that decreased osteoblastic activity and increased sclerostin and leptin levels. Furthermore, the synthetic glucocorticoid dexamethasone alters the anabolic Wnt signaling pathway. The Wnt pathway inhibitor sclerostin has several glucocorticoid response elements, and dexamethasone administration to osteoblastic cells induces sclerostin expression. Dexamethasone treatment of isolated bone marrow cells decreased bone nodule formation, whereas removal of sclerostin protected against this decrement in mineralization. Collectively, these findings suggest that bone loss associated with steroid-induced osteoporosis is a consequence of sclerostin-mediated restriction of Wnt signaling, which may mechanistically facilitate glucocorticoid toxicity in bone.

Interleukin-1β (IL-1β) transcriptionally activates hepcidin by inducing CCAAT enhancer-binding protein δ (C/EBPδ) expression in hepatocytes

Hepcidin is a liver-derived hormone that negatively regulates serum iron levels and is mainly regulated at the transcriptional level. Previous studies have clarified that in addition to hepatic iron levels, inflammation also efficiently increases hepatic hepcidin expression. The principle regions responsible for efficient hepcidin transcription are bone morphogenetic protein-responsive elements (BMP-REs) 1 and 2 as well as the signal transducer and activator of transcription 3-binding site (STAT-BS). Here, we show that the proinflammatory cytokine interleukin-1β (IL-1β) efficiently increases hepcidin expression in human HepG2 liver-derived cells and primary mouse hepatocytes. The primary region responsible for IL-1β-mediated hepcidin transcription was the putative CCAAT enhancer-binding protein (C/EBP)-binding site (C/EBP-BS) at the hepcidin promoter spanning nucleotides -329 to -320. IL-1β induces the expression of C/EBPδ but neither C/EBPα nor C/EBPβ in hepatocytes, and C/EBPδ bound to the C/EBP-BS in an IL-1β-dependent manner. Lipopolysaccharide (LPS) induced the expression of IL-1β in Kupffer cells and hepatocytes in the mouse liver; furthermore, the culture supernatants from the macrophage-like cell line RAW264.7 treated with LPS potentiated the stimulation of hepcidin expression in hepatocytes. The present study reveals that: 1) inflammation induces IL-1β production in Kupffer cells and hepatocytes; 2) IL-1β increases C/EBPδ expression in hepatocytes; and 3) induction of C/EBPδ activates hepcidin transcription via the C/EBP-BS that has been uncharacterized yet. In cooperation with the other pathways activated by inflammation, IL-1β pathway stimulation leads to excess production of hepcidin, which could be causative to anemia of inflammation.

Glucocorticoid-Induced Leucine Zipper in Central Nervous System Health and Disease

The central nervous system (CNS) is a large network of intercommunicating cells that function to maintain tissue health and homeostasis. Considerable evidence suggests that glucocorticoids exert both neuroprotective and neurodegenerative effects on the CNS. Glucocorticoids act by binding two related receptors in the cytoplasm, the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR). The glucocorticoid receptor complex mediates cellular responses by transactivating target genes and by protein: protein interactions. The paradoxical effects of glucocorticoids on neuronal survival and death have been attributed to the concentration and the ratio of mineralocorticoid to glucocorticoid receptor activation. Glucocorticoid-induced leucine zipper (GILZ) is a recently identified protein transcriptionally upregulated by glucocorticoids. Constitutively, expressed in many tissues including brain, GILZ mediates many of the actions of glucocorticoids. It mimics the anti-inflammatory and anti-proliferative effects of glucocorticoids but exerts differential effects on stem cell differentiation and lineage development. Recent experimental data on the effects of GILZ following induced stress or trauma suggest potential roles in CNS diseases. Here, we provide a short overview of the role of GILZ in CNS health and discuss three potential rationales for the role of GILZ in Alzheimer's disease pathogenesis.

Apolipoprotein A-1 regulates osteoblast and lipoblast precursor cells in mice

Imbalances in lipid metabolism affect bone homeostasis, altering bone mass and quality. A link between bone mass and high-density lipoprotein (HDL) has been proposed. Indeed, it has been recently shown that absence of the HDL receptor scavenger receptor class B type I (SR-B1) causes dense bone mediated by increased adrenocorticotropic hormone (ACTH). In the present study we aimed at further expanding the current knowledge as regards the fascinating bone-HDL connection studying bone turnover in apoA-1-deficient mice. Interestingly, we found that bone mass was greatly reduced in the apoA-1-deficient mice compared with their wild-type counterparts. More specifically, static and dynamic histomorphometry showed that the reduced bone mass in apoA-1(-/-) mice reflect decreased bone formation. Biochemical composition and biomechanical properties of ApoA-1(-/-) femora were significantly impaired. Mesenchymal stem cell (MSC) differentiation from the apoA-1(-/-) mice showed reduced osteoblasts, and increased adipocytes, relative to wild type, in identical differentiation conditions. This suggests a shift in MSC subtypes toward adipocyte precursors, a result that is in line with our finding of increased bone marrow adiposity in apoA-1(-/-) mouse femora. Notably, osteoclast differentiation in vitro and osteoclast surface in vivo were unaffected in the knock-out mice. In whole bone marrow, PPARγ was greatly increased, consistent with increased adipocytes and committed precursors. Further, in the apoA-1(-/-) mice marrow, CXCL12 and ANXA2 levels were significantly decreased, whereas CXCR4 were increased, consistent with reduced signaling in a pathway that supports MSC homing and osteoblast generation. In keeping, in the apoA-1(-/-) animals the osteoblast-related factors Runx2, osterix, and Col1a1 were also decreased. The apoA-1(-/-) phenotype also included augmented CEPBa levels, suggesting complex changes in growth and differentiation that deserve further investigation. We conclude that the apoA-1 deficiency generates changes in the bone cell precursor population that increase adipoblast, and decrease osteoblast production resulting in reduced bone mass and impaired bone quality in mice.

Preclinical Study of Cell Therapy for Osteonecrosis of the Femoral Head with Allogenic Peripheral Blood-Derived Mesenchymal Stem Cells

PURPOSE

To explore the value of transplanting peripheral blood-derived mesenchymal stem cells from allogenic rabbits (rPBMSCs) to treat osteonecrosis of the femoral head (ONFH).

MATERIALS AND METHODS

rPBMSCs were separated/cultured from peripheral blood after granulocyte colony-stimulating factor mobilization. Afterwards, mobilized rPBMSCs from a second passage labeled with PKH26 were transplanted into rabbit ONFH models, which were established by liquid nitrogen freezing, to observe the effect of rPBMSCs on ONFH repair. Then, the mRNA expressions of BMP-2 and PPAR-γ in the femoral head were assessed by RT-PCR.

RESULTS

After mobilization, the cultured rPBMSCs expressed mesenchymal markers of CD90, CD44, CD29, and CD105, but failed to express CD45, CD14, and CD34. The colony forming efficiency of mobilized rPBMSCs ranged from 2.8 to 10.8 per million peripheral mononuclear cells. After local transplantation, survival of the engrafted cells reached at least 8 weeks. Therein, BMP-2 was up-regulated, while PPAR-γ mRNA was down-regulated. Additionally, bone density and bone trabeculae tended to increase gradually.

CONCLUSION

We confirmed that local transplantation of rPBMSCs benefits ONFH treatment and that the beneficial effects are related to the up-regulation of BMP-2 expression and the down-regulation of PPAR-γ expression.

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.

Analysis of Genomic Sequence Motifs for Deciphering Transcription Factor Binding and Transcriptional Regulation in Eukaryotic Cells

Eukaryotic genomes contain a variety of structured patterns: repetitive elements, binding sites of DNA and RNA associated proteins, splice sites, and so on. Often, these structured patterns can be formalized as motifs and described using a proper mathematical model such as position weight matrix and IUPAC consensus. Two key tasks are typically carried out for motifs in the context of the analysis of genomic sequences. These are: identification in a set of DNA regions of over-represented motifs from a particular motif database, and de novo discovery of over-represented motifs. Here we describe existing methodology to perform these two tasks for motifs characterizing transcription factor binding. When applied to the output of ChIP-seq and ChIP-exo experiments, or to promoter regions of co-modulated genes, motif analysis techniques allow for the prediction of transcription factor binding events and enable identification of transcriptional regulators and co-regulators. The usefulness of motif analysis is further exemplified in this review by how motif discovery improves peak calling in ChIP-seq and ChIP-exo experiments and, when coupled with information on gene expression, allows insights into physical mechanisms of transcriptional modulation.

Non-classical Transcriptional Activity of Retinoic Acid

It has long been established that the transcriptional activity of retinoic acid (RA) is mediated by members of the nuclear receptor family of ligand-activated transcription factors termed RA receptors (RARs). More recent observations have established that RA also activates an additional nuclear receptor, PPARβ/δ. Partitioning RA between RARs and PPARβ/δ is governed by different intracellular lipid-binding proteins: cellular RA binding protein 2 (CRABP2) delivers RA to nuclear RARs and a fatty acid binding protein (FABP5) delivers the hormone from the cytosol to nuclear PPARβ/δ. Consequently, RA signals through RARs in CRABP2-expressing cells, but activates PPARβ/δ in cells that express a high level of FABP5. RA elicits different and sometimes opposing responses in cells that express different FABP5/CRABP2 ratios because PPARβ/δ and RARs regulate the expression of distinct sets of genes. An overview of the observations that led to the discovery of this non-classical activity of RA are presented here, along with a discussion of evidence demonstrating the involvement of the dual transcriptional activities of RA in regulating energy homeostasis, insulin responses, and adipocyte and neuron differentiation.

Optimized osteogenic differentiation protocol from R1 mouse embryonic stem cells in vitro

Embryonic stem cells (ESCs) are a unique model that allows the study of molecular pathways underlying commitment and differentiation. One such lineage is osteoblasts, which are responsible for forming bone tissue in the body. There are many osteogenic differentiation protocols in the literature utilizing different soluble factors. The goal of the present study was to increase the efficacy of our osteogenic differentiation protocol from R1 cells. We have studied the effects of the addition of the following factors: dexamethasone, retinoic acid, and peroxisome-proliferator-activated receptor-gamma inhibitor, which have been reported to enhance osteogenesis. We found that among the 6 different protocols that were tested, the addition of retinoic acid with later addition of dexamethasone gives the most enrichment of osteogenic lineage cells. Thus, our findings provide valuable guidelines for culture condition to differentiate mouse R1 ESCs to osteoblastic cells in vitro.

Heterogeneity in mechanisms influencing glucocorticoid sensitivity: the need for a systems biology approach to treatment of glucocorticoid-resistant inflammation

Glucocorticoids (GCs) have impressive anti-inflammatory and immunosuppressive effects and show a diversity of actions across a variety of cell phenotypes. Implicit in efforts to optimize GCs as anti-inflammatory agents for any or all indications is the notion that the relevant mechanism(s) of action of GCs are fully elucidated. However, recent advances in understanding GC signalling mechanisms have revealed remarkable complexity and contextual dependence, calling into question whether the mechanisms of action are sufficiently well-described to embark on optimization. In the current review, we address evidence for differences in the mechanism of action in different cell types and contexts, and discuss contrasts in mechanisms of glucocorticoid insensitivity, with a focus on asthma and Chronic Obstructive Pulmonary Disease (COPD). Given this complexity, we consider the potential breadth of impact and selectivity of strategies directed to reversing the glucocorticoid insensitivity.

The histone demethylase PHF2 promotes fat cell differentiation as an epigenetic activator of both C/EBPα and C/EBPδ

Histone modifications on major transcription factor target genes are one of the major regulatory mechanisms controlling adipogenesis. Plant homeodomain finger 2 (PHF2) is a Jumonji domain-containing protein and is known to demethylate the histone H3K9, a repressive gene marker. To better understand the function of PHF2 in adipocyte differentiation, we constructed stable PHF2 knock-down cells by using the mouse pre-adipocyte cell line 3T3-L1. When induced with adipogenic media, PHF2 knock-down cells showed reduced lipid accumulation compared to control cells. Differential expression using a cDNA microarray revealed significant reduction of metabolic pathway genes in the PHF2 knock-down cell line after differentiation. The reduced expression of major transcription factors and adipokines was confirmed with reverse transcription- quantitative polymerase chain reaction and Western blotting. We further performed co-immunoprecipitation analysis of PHF2 with four major adipogenic transcription factors, and we found that CCATT/enhancer binding protein (C/EBP)α and C/EBPδ physically interact with PHF2. In addition, PHF2 binding to target gene promoters was confirmed with a chromatin immunoprecipitation experiment. Finally, histone H3K9 methylation markers on the PHF2-binding sequences were increased in PHF2 knock-down cells after differentiation. Together, these results demonstrate that PHF2 histone demethylase controls adipogenic gene expression during differentiation.

Development of novel treatment strategies for inflammatory diseases-similarities and divergence between glucocorticoids and GILZ

Glucocorticoids (GC) are the most commonly prescribed medications for patients with inflammatory diseases, despite their well-known adverse metabolic effects. Previously, it was understood that the anti-inflammatory effects of the GC/GC receptor (GR) complex were mediated via transrepression, whilst the adverse metabolic effects were mediated via transactivation. It has recently become clear that this “divergent actions” paradigm of GC actions is likely insufficient. It has been reported that the GC/GR-mediated transactivation also contributes to the anti-inflammatory actions of GC, via up-regulation of key anti-inflammatory proteins. One of these is glucocorticoid-induced leucine zipper (GILZ), which inhibits inflammatory responses in a number of important immune cell lineages in vitro, as well as in animal models of inflammatory diseases in vivo. This review aims to compare the GILZ and GC effects on specific cell lineages and animal models of inflammatory diseases. The fact that the actions of GILZ permit a GILZ-based gene therapy to lack GC-like adverse effects presents the potential for development of new strategies to treat patients with inflammatory diseases.

Role of glucocorticoid-induced leucine zipper (GILZ) in bone acquisition

Glucocorticoids (GCs) have both anabolic and catabolic effects on bone. However, no GC anabolic effect mediator has been identified to date. Here we show that targeted expression of glucocorticoid-induced leucine zipper (GILZ), a GC anti-inflammatory effect mediator, enhances bone acquisition in mice. Transgenic mice, in which the expression of GILZ is under the control of a 3.6-kb rat type I collagen promoter, exhibited a high bone mass phenotype with significantly increased bone formation rate and osteoblast numbers. The increased osteoblast activity correlates with enhanced osteogenic differentiation and decreased adipogenic differentiation of bone marrow stromal cell cultures in vitro. In line with these changes, the mRNA levels of key osteogenic regulators (Runx2 and Osx) increased, and the level of adipogenic regulator peroxisome proliferator-activated receptor (PPAR) γ2 decreased significantly. We also found that GILZ physically interacts with C/EBPs and disrupts C/EBP-mediated PPARγ gene transcription. In conclusion, our results showed that GILZ is capable of increasing bone acquisition in vivo, and this action is mediated via a mechanism involving the inhibition of PPARγ gene transcription and shifting of bone marrow MSC/progenitor cell lineage commitment in favor of the osteoblast pathway.

Transcription factor Snail is a novel regulator of adipocyte differentiation via inhibiting the expression of peroxisome proliferator-activated receptor γ

Snail belongs to the superfamily of zinc-finger transcription factors and plays a crucial role in processes regulating cell fate, such as the formation of mesoderm and initiation of epithelial-mesenchymal transition. We have previously discovered that Snail modulates adiponectin expression in 3T3-L1 cells during adipogenesis. In the present study, we elucidated the functional role of Snail in adipocyte differentiation and its underlying molecular mechanism. Snail expression was dramatically decreased during adipogenesis in 3T3-L1 cells. Overexpression of Snail blocked adipocyte differentiation by suppressing the expression of peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT-enhancer-binding protein alpha, while knockdown of Snail expression stimulated adipogenesis in 3T3-L1 cells. Chromatin immunoprecipitation assay and luciferase assay showed that Snail inhibits the transcriptional activity of the PPARγ gene by directly binding to the E-box motifs in the PPARγ promoter. Wnt10b induced phosphorylation of glycogen synthase kinase 3 beta (GSK3β), leading to inhibition of adipogenesis in 3T3-L1 cells in accordance with increased expression of Snail, whereas adipogenic capacity was restored in Snail siRNA-transfected preadipocytes. LiCl (a GSK3β inhibitor)-treated cells also showed increased expression of Snail, with a reduced adipogenic potential. Snail-overexpressing 3T3-F442A cells did not differentiate into mature adipocytes in immunodeficient nude mice. Taken together, Snail is a novel regulator of adipocyte differentiation, which acts by direct suppression of PPARγ expression. Our data also indicate that the expression of Snail is mediated by the Wnt-GSK3β signaling pathway.

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.

Glucocorticoid-induced osteoporosis: an update on current pharmacotherapy and future directions

INTRODUCTION

Glucocorticoid-induced osteoporosis (GIOP) is one of the most devastating side-effects of glucocorticoid (GC) use, as it is associated with an increased fracture risk. The importance of GIOP as a health problem is underlined by the frequent use of GC treatment in patients with various chronic diseases and by the high rates of osteoporosis found in these patient groups.

AREAS COVERED

Recent studies on bone metabolism and the influence of GCs have contributed to a better understanding of the pathogenesis of GIOP. Furthermore, new intervention trials have reported beneficial effects of antiresorptive and anabolic agents on GIOP. This article reviews the epidemiology and pathophysiology of osteoporosis and fractures in GC-treated patients and discusses current pharmacotherapy and possible future treatment options.

EXPERT OPINION

Several guidelines for the management of GIOP have been published, using different criteria for bone mineral density (BMD) thresholds and for GC dosages above which anti-osteoporotic therapy should be started. Although alendronate and risedronate are currently first choice, the anabolic agent teriparatide seems to be superior and might be considered as a potential first-line therapy for patients with low BMD on long-term GC treatment. Adherence to anti-osteoporotic drugs is limited, particularly in GIOP patients, due to several factors.

Long-term safety, efficacy, and patient acceptability of teriparatide in the management of glucocorticoid-induced osteoporosis

Glucocorticoids are commonly prescribed medications to treat multiple diseases across many medical specialties. One of the most common yet largely unappreciated side effect of glucocorticoid use is increased risk of fracture. Many different therapies are indicated to prevent and treat this condition; many guidelines exist that suggest appropriate use of both glucocorticoids and the medications approved to prevent this common side effect of glucocorticoid therapy. Nevertheless, 30%-50% of patients on long-term glucocorticoid therapy sustain a fracture. Teriparatide, recombinant human parathyroid hormone (1-34), is a daily self-injectable therapy for 24 months approved for use in patients taking long-term glucocorticoids. Teriparatide has been shown to increase bone mineral density and reduce vertebral fracture risk in glucocorticoid-treated patients. Glucocorticoids have many adverse effects on bone that teriparatide has been shown to prevent or negate. Given the fact that preventive therapy for glucocorticoid-induced osteoporosis is often not prescribed, one wonders whether a daily self-injectable therapy for this condition would be prescribed by physicians and accepted by patients. This article reviews the epidemiology, pathophysiology, treatment, guidelines, and persistence data (when available) for patients with glucocorticoid-induced osteoporosis treated with teriparatide.

The effect of core decompression on local expression of BMP-2, PPAR-γ and bone regeneration in the steroid-induced femoral head osteonecrosis

Background

To investigate the efficacy of the sole core decompression surgery for the treatment of steroid-induced femoral head osteonecrosis.

Methods

The model was established by administration of steroids in combination with horse serum. The rabbits with bilateral femoral head osteonecrosis were randomly selected to do the one side of core decompression. The other side was used as the sham. Quantitative RT-PCR and western blot techniques were used to measure the local expression of BMP-2 and PPAR-γ. Bone tissues from control and operation groups were histologically analyzed by H&E staining. The comparisons of the local expression of BMP-2 and PPAR-γ and the bone regeneration were further analyzed between different groups at each time point.

Results

The expression of BMP-2 in the osteonecrosis femoral head with or without decompression was significantly lower than that in normal animals. BMP-2 expression both showed the decreasing trend with the increased post-operation time. No significant difference of BMP-2 expression occurred between femoral head osteonecrosis with and without decompression. The PPAR-γ expression in the femoral head osteonecrosis with and without core decompression both was significantly higher than that in control. Its expression pattern showed a significantly increased trend with increased the post-operation time. However, there was no significant difference of PPAR-γ expression between the femoral head osteonecrosis with and without decompression at each time point. Histopathological analysis revealed that new trabecular bone and a large number of osteoblasts were observed in the steroid-induced femoral head osteonecrosis with lateral decompression at 8 weeks after surgery, but there still existed trabecular bone fractures and bone necrosis.

Conclusions

Although decompression takes partial effect in promoting bone regeneration in the early treatment of femoral head osteonecrosis, such an effect does not significantly improve or reverse the pathological changes of femoral head necrosis. Thus, the long-term effect of core decompression in the treatment of steroid-induced femoral head osteonecrosis is not satisfactory.

Secreted factors from adipose tissue increase adipogenic differentiation of mesenchymal stem cells

OBJECTIVES

Adipose tissue engineering is one of the hottest topics in the field of regenerative medicine. Fat tissue has been considered as an abundant and accessible source of adult stem cells by tissue engineers, since it gives rise to adipose stem cells. However, recent reports have pointed out that adipose tissue, as a secretory and endocrine organ, might secrete cytokines that regulate body functions such as metabolism, infammation and more. In this study, we aim to investigate the adipogenic-inducing factors secreted by fat tissue.

MATERIALS AND METHODS

Conditioned medium were collected by culturing fat tissue fragments in plastic flasks. Mesenchymal stem cells (MSCs) cultured in conditioned medium (CM) to test the adipogenic-inducing factors. Oil red O staining, reverse transcription/polymerase chain reaction and immunocytofluorescent staining were performed to examine the differentiation of MSCs in CM.

RESULTS

MSCs cultured in CM of adipose tissue spontaneously differentiated into adipocytes. Furthermore, supplementation of insulin or dexamethasone to CM accelerated the process of lipid accumulation of differentiated MSCs.

DISCUSSION

Results from this study demonstrated that fat tissues secrete small molecules, which induce adipogenic differentiation of MSCs.

CONCLUSIONS

Our study provides clues for improving adipose tissue engineering by using fragmented adipose tissue as sources of fat-inducing factors.

Myxoid liposarcoma-associated EWSR1-DDIT3 selectively represses osteoblastic and chondrocytic transcription in multipotent mesenchymal cells

Background

Liposarcomas are the most common class of soft tissue sarcomas, and myxoid liposarcoma is the second most common liposarcoma. EWSR1-DDIT3 is a chimeric fusion protein generated by the myxoid liposarcoma-specific chromosomal translocation t(12;22)(q13;q12). Current studies indicate that multipotent mesenchymal cells are the origin of sarcomas. The mechanism whereby EWSR1-DDIT3 contributes to the phenotypic selection of target cells during oncogenic transformation remains to be elucidated.

Methodology/Principal Findings

Reporter assays showed that the EWSR1-DDIT3 myxoid liposarcoma fusion protein, but not its wild-type counterparts EWSR1 and DDIT3, selectively repressed the transcriptional activity of cell lineage-specific marker genes in multipotent mesenchymal C3H10T1/2 cells. Specifically, the osteoblastic marker Opn promoter and chondrocytic marker Col11a2 promoter were repressed, while the adipocytic marker Ppar-γ2 promoter was not affected. Mutation analyses, transient ChIP assays, and treatment of cells with trichostatin A (a potent inhibitor of histone deacetylases) or 5-Aza-2′-deoxycytidine (a methylation-resistant cytosine homolog) revealed the possible molecular mechanisms underlying the above-mentioned selective transcriptional repression. The first is a genetic action of the EWSR1-DDIT3 fusion protein, which results in binding to the functional C/EBP site within Opn and Col11a2 promoters through interaction of its DNA-binding domain and subsequent interference with endogenous C/EBPβ function. Another possible mechanism is an epigenetic action of EWSR1-DDIT3, which enhances histone deacetylation, DNA methylation, and histone H3K9 trimethylation at the transcriptional repression site. We hypothesize that EWSR1-DDIT3-mediated transcriptional regulation may modulate the target cell lineage through target gene-specific genetic and epigenetic conversions.

Conclusions/Significance

This study elucidates the molecular mechanisms underlying EWSR1-DDIT3 fusion protein-mediated phenotypic selection of putative target multipotent mesenchymal cells during myxoid liposarcoma development. A better understanding of this process is fundamental to the elucidation of possible direct lineage reprogramming in oncogenic sarcoma transformation mediated by fusion proteins.

[Mechanisms and therapeutics of glucocorticoid-induced osteoporosis]

Mechanisms of glucocorticoid-induced osteoporosis (GIOP) are categorized into local and systemic effects. In the local mechanisms, direct inhibitory effect of glucocorticoid on bone formation is thought to be one of the important mechanisms of GIOP. In contrast, secondary hyperparathyroidism induced by negative balance of calcium due to inhibition of absorption and increase of excretion is an important systemic mechanism of GIOP. Other mechanisms of GIOP are also shown in this review. From clinical points of view, serum markers for evaluation of GIOP have been discussed. Osteocalcin, procollagen type I N-terminal peptide, and bone-specific alkaline phosphatase as markers of bone formation are decreased in GIOP. Collagen I N-terminal telopeptide and tartrate resistent acid phosphatase isoform 5b as markers of bone resorption are increased in GIOP. Clinical guidelines have recommended that bisphosphonate is the first choice for the treatment of GIOP. Teriparatide is recombinant human parathyroid hormone 1-34, which should be considered as a therapeutic option for those at high risk of bone fracture. Denosumab, an anti receptor activator of nuclear factor-β ligand approved as a drug for postmenopausal osteoporosis was also effective for GIOP in clinical trials.

Advances in glucocorticoid-induced osteoporosis

Glucocorticoid-induced osteoporosis (GIOP) is one of the most important side effects of glucocorticoid use, as it leads to an increased risk of fractures. Recently, many published studies have focused on the cellular and molecular mechanisms of bone metabolism, the pathophysiology of GIOP, and the intervention options to prevent GIOP. In this review, recent advances in GIOP are summarized, particularly recent progress in our understanding of the mechanisms of GIOP resulting in improved insight that might result in the development of new treatment options in the near future.

Retinoic acid-induced Smad3 expression is required for the induction of osteoblastogenesis of mesenchymal stem cells

Mesenchymal stem cells are pluripotent precursor cells that can differentiate into osteoblasts, adipocytes, chondrocytes and myocytes. Despite their important therapeutic potential little is known about the transcriptional cascades that govern lineage decisions in these cells. Treatment of C3H10T1/2 mouse mesenchymal stem cells with retinoic acid (RA) inhibits adipogenesis and enhances osteoblastogenesis. In particular, RA treatment stimulates the expression of the osteoblast master regulator, runt-related transcription factor 2 (Runx2), whose expression is necessary for the formation of bone. We have shown previously in mesenchymal stem cells that RA acts to stimulate osteoblastogenesis by interfering with the actions of the bzip transcription factor CCAAT/Enhancer Binding Protein beta (C/EBPβ), where it binds to a negative regulatory element within the Runx2 promoter and inhibits its expression. Herein we show that Smad3, whose expression is stimulated by RA, relays the effects of RA on differentiation by initiating the displacement of C/EBPβ from the Runx2 promoter. In addition to stimulating Smad3 expression, RA also stimulated the nuclear localization of this factor, such that in the absence of RA, ectopic Smad3 was unable to drive osteoblastogenesis. While not sufficient to promote osteoblastogenesis, knockdown of Smad3 using a specific shRNA prevented the RA-mediated stimulation of differentiation and displacement of C/EBPβ from the Runx2 P1 promoter. Taken together, these data indicate that Smad3 is an important mediator of RA activity during mesenchymal stem cell differentiation and is necessary for the stimulation of osteoblastogenesis.

Peroxisome proliferator-activated receptor-γ stimulates 11β-hydroxysteroid dehydrogenase type 1 in rat vascular smooth muscle cells

Glucocorticoids are metabolized in vascular tissue by two types of 11β-hydroxysteroid dehydrogenases (11HSD1, 11HSD2) and thus these enzymes are considered to be important factors that modulate the diverse and complex effects of glucocorticoids on cardiovascular function. The present study evaluated the effect of peroxisome proliferator-activated receptor-γ (PPARγ) agonist pioglitazone on 11HSD1 vascular smooth muscle cells (VSMC) and compared the effect with that of corticosterone. Using primary cultures of VSMC derived from rat aorta, we showed that pioglitazone significantly increases 11HSD1 activity and mRNA expression in a dose-dependent manner with EC(50) 243 nM and that this effect is not blocked by RU 486, an antagonist of the glucocorticoid receptor. In contrast, corticosterone had no effect on 11HSD1. Pioglitazone positively regulated transcription of two CCAAT/enhancer-binding proteins (C/EBPs), specifically C/EBPα a potent activator of 11HSD1 gene transcription in some cells types, and C/EBPζ, whereas C/EBPβ and C/EBPδ were not changed. In contrast, corticosterone stimulated the expression of C/EBPβ and C/EBPδ, but the levels of C/EBPα and C/EBPζ were not changed. In conclusion, activation of PPARγ in VSMC up-regulates vascular 11HSD1 and thus reactivates 11-oxo metabolites to biologically active glucocorticoids through a mechanism that seems to involve C/EBPα and C/EBPζ. Our data provide one of the possible explanations for PPARγ agonists' effects on the cardiovascular system.

Dexamethasone modulates osteogenesis and adipogenesis with regulation of osterix expression in rat calvaria-derived cells

Osteoblasts and adipocytes originate from common mesenchymal progenitor cells and although a number of compounds can induce osteoblastic and adipogenic differentiation from progenitor cells, the underlying mechanisms have not been elucidated. The present study examined the synergistic effects of dexamethasone (Dex) and bone morphogenetic protein (BMP)-2 on the differentiation of clonal mesenchymal progenitor cells isolated from rat calvaria into osteoblasts and adipocytes, as well as the effects of the timing of treatment. Cells were cultured for various periods of time in the presence of Dex and/or BMP-2. When cells were treated with Dex+BMP-2 during the early phase of differentiation, they differentiated into adipocytes. However, when cells were treated with Dex+BMP-2 during the late phase of differentiation, a synergistic effect on in vitro matrix mineralization was observed. To examine differences between the early and late phases of differentiation, ALP activity was measured in the presence of BMP-2. ALP activity increased markedly on Day 9, corresponding to the onset of the synergistic effect of Dex. Dex treatment inhibited osterix (OSX) expression in cells committed to adipogenic differentiation, but not in cells committed to osteogenic differentiation following BMP-2 treatment. The isoform2 OSX promoter region was found to be involved in the effects of Dex on cells during the early phase of differentiation. Furthermore, cells stably expressing OSX (isoform2) formed mineralized nodules even though they had been treated with Dex+BMP-2 during the early phase of differentiation. It appears that Dex modulates osteogenesis and adipogenesis in mesenchymal stem cells by regulating OSX expression.

Constitutively active Stat5A and Stat5B promote adipogenesis

OBJECTIVE

The metabolic syndrome is an important social problem affecting many people in developed countries. Obesity is a leading cause of this syndrome, hence understanding molecular mechanisms underlying obesity is of prime importance for preventive medicine to develop novel methods to alleviate the corresponding social cost as well as for pharmaceutical companies to develop antimetabolic drugs.

METHODS

Since adipocytes play an important role in obesity, we explored the signaling pathways leading to differentiation of adipocytes. We used a preadipocyte cell line to monitor the differentiation of adipocytes, and virus-mediated gene transfer to assess the role of the transcription factor Stat5 in adipogenesis. Adipocyte differentiation was assessed by Northern blot and Western blot analyses as well as accumulation of fat droplets in cells. Promoter activity of the proadipogenic transcription factor peroxisome proliferator-activated receptor-gamma (PPARγ) was evaluated by luciferase assay.

RESULTS

Virus-mediated gene transfer of the constitutively active form of both Stat5A and Stat5B resulted in enhanced adipocyte differentiation in the absence of fetal bovine serum (FBS) as judged by expression of proadipogenic factors as well as accumulation of fat droplets in cells. Such a proadipogenic effect of Stat5 is, in part, mediated by its ability to enhance transcription of PPARγ, a master transcriptional regulator in adipogenesis.

CONCLUSION

The constitutively active form of Stat5A and Stat5B promoted adipocyte differentiation in the absence of FBS via induction of PPARγ.

Maf promotes osteoblast differentiation in mice by mediating the age-related switch in mesenchymal cell differentiation

Aging leads to the disruption of the homeostatic balance of multiple biological systems. In bone marrow multipotent mesenchymal cells undergo differentiation into various anchorage-dependent cell types, including osteoblasts and adipocytes. With age as well as with treatment of antidiabetic drugs such as thiazolidinediones, mesenchymal cells favor differentiation into adipocytes, resulting in an increased number of adipocytes and a decreased number of osteoblasts, causing osteoporosis. The mechanism behind this differentiation switch is unknown. Here we show an age-related decrease in the expression of Maf in mouse mesenchymal cells, which regulated mesenchymal cell bifurcation into osteoblasts and adipocytes by cooperating with the osteogenic transcription factor Runx2 and inhibiting the expression of the adipogenic transcription factor Pparg. The crucial role of Maf in both osteogenesis and adipogenesis was underscored by in vivo observations of delayed bone formation in perinatal Maf(-/-) mice and an accelerated formation of fatty marrow associated with bone loss in aged Maf(+/-) mice. This study identifies a transcriptional mechanism for an age-related switch in cell fate determination and may provide a molecular basis for novel therapeutic strategies against age-related bone diseases.

Glucocorticoid-induced differentiation of primary cultured bone marrow mesenchymal cells into adipocytes is antagonized by exogenous Runx2

Long-term clinical use of glucocorticoids often causes the serious side effect of non-traumatic avascular osteonecrosis. The aim of this study was to examine the effects and mechanisms of a glucocorticoid, dexamethasone (Dex), on differentiation of primary cultured rat bone marrow mesenchymal cells (BMCs). We also tried to block the inhibitory effects of Dex on osteoblast differentiation. Adipocyte markers (peroxisome proliferator-activated receptorgamma-2 and aP2) were increased in response to Dex treatment in a dose- and time-dependent manner, while osteoblastic markers [Runx2, COL 1, osterix, alkaline phosphatase (ALP) and OC] were down-regulated, consistent with ALP and osteocalcin promoter activity. To validate the effects of Runx2 on the expression of osteogenesis and adipocyte genes, pCMV/Flag-Runx2 was transfected into BMCs, and relevant markers were detected after 10(-7) M Dex treatment for 48 h. The results indicated that Dex treatment induced adipogenic differentiation and suppressed proliferation. No significant difference was detected in expressions of these genes between Runx2-transfected cells and Dex-treated BMCs. These data suggest that Dex primarily induced adipocyte differentiation of BMCs. Exogenous Runx2 can antagonize the effect of Dex on osteoblast differentiation.

Repression of cellular retinoic acid-binding protein II during adipocyte differentiation

In preadipocytes, retinoic acid (RA) regulates gene expression by activating the nuclear RA receptor (RAR) and its cognate intracellular lipid-binding protein CRABP-II. It was previously reported that RA inhibits adipocyte differentiation but only when administered early during the differentiation program. The data presented here indicate that the diminished ability of RA to activate RAR following induction of differentiation stems from down-regulation of CRABP-II. The observations show that expression of CRABP-II in preadipocytes is repressed by all three components of the classical hormonal mixture that induces adipocyte differentiation, i.e. isobutylmethylxanthine, insulin, and dexamethasone. Isobutylmethylxanthine-dependent activation of protein kinase A triggered the phosphorylation of the transcription factor cAMP-response element-binding protein, which induced the expression of the cAMP-response element-binding protein family repressor cAMP-response element modulator. In turn, cAMP-response element modulator was found to associate with a cognate response element in the CRABP-II promoter and to repress CRABP-II expression. The data further show that CRABP-II is a direct target gene for the glucocorticoid receptor and that it is subjected to dexamethasone-induced glucocorticoid receptor-mediated repression during adipogenesis. Finally, the observations demonstrate that permanent repression of CRABP-II in mature adipocytes is exerted by the master regulator of adipocyte differentiation CCAAT/enhancer-binding protein alpha and is directly mediated through CCAAT/enhancer-binding protein alpha-response elements in the CRABP-II promoter. Taken together, the observations emphasize the important role of CRABP-II in regulating the transcriptional activity of RA through RAR, and they demonstrate that repression of this gene is critical for allowing adipogenesis to proceed.

Gravity, a regulation factor in the differentiation of rat bone marrow mesenchymal stem cells

Background

Stem cell therapy has emerged as a potential therapeutic option for tissue engineering and regenerative medicine, but many issues remain to be resolved, such as the amount of seed cells, committed differentiation and the efficiency. Several previous studies have focused on the study of chemical inducement microenvironments. In the present study, we investigated the effects of gravity on the differentiation of bone marrow mesenchymal stem cells (BMSCs) into force-sensitive or force-insensitive cells.

Methods and results

Rat BMSCs (rBMSCs) were cultured under hypergravity or simulated microgravity (SMG) conditions with or without inducement medium. The expression levels of the characteristic proteins were measured and analyzed using immunocytochemical, RT-PCR and Western-blot analyses. After treatment with 5-azacytidine and hypergravity, rBMSCs expressed more characteristic proteins of cardiomyocytes such as cTnT, GATA4 and β-MHC; however, fewer such proteins were seen with SMG. After treating rBMSCs with osteogenic inducer and hypergravity, there were marked increases in the expression levels of ColIA1, Cbfa1 and ALP. Reverse results were obtained with SMG. rBMSCs treated with adipogenic inducer and SMG expressed greater levels of PPARgamma. Greater levels of Cbfa1- or cTnT-positive cells were observed under hypergravity without inducer, as shown by FACS analysis. These results indicate that hypergravity induces differentiation of rBMSCs into force-sensitive cells (cardiomyocytes and osteoblasts), whereas SMG induces force-insensitive cells (adipocytes).

Conclusion

Taken together, we conclude that gravity is an important factor affecting the differentiation of rBMSCs; this provides a new avenue for mechanistic studies of stem cell differentiation and a new approach to obtain more committed differentiated or undifferentiated cells.

Minireview: live and let die: molecular effects of glucocorticoids on bone cells

Glucocorticoids (GCs) are efficient drugs that are used to treat various immune-mediated diseases, but their long-term administration is associated with multiple metabolic side effects, including osteoporosis. Molecular analyses of the mechanisms exerted by the GC receptor have resulted in the development of GC receptor agonists that selectively repress or activate GC target genes. This review summarizes the cellular and molecular effects of GCs on bone cells and highlights the critical signaling pathways that may evolve into future therapeutic strategies.

Stress fracture and military medical readiness: bridging basic and applied research

PURPOSE

Military recruits and distance runners share a special risk of stress fracture injury. Recent efforts by US and Israeli military-sponsored researchers have uncovered important mechanisms and practical low-cost interventions. This article summarizes key findings relevant to prevention of stress fracture, including simple strategies to identify and to mitigate risk.

METHODS

Published research supported through the Bone Health and Military Medical Readiness research program and related military bone research was analyzed for contributions to preventing stress fracture in military recruits and optimizing bone health.

RESULTS

Thousands of military recruits helped test hypotheses about predictors of risk, safer exercise regimens, and rest, nutrition, gait training, and technology interventions to reduce stress fracture risk. Concurrent cellular, animal, and human laboratory studies were used to systematically investigate mechanisms of mechanical forces acting on bone and interactions through muscle, hormonal and genetic influences, and metabolism. The iterative and sometimes simultaneous process of basic discovery and field testing produced new knowledge that will provide safer science-based physical training.

DISCUSSION

Human training studies evaluating effects on bone require special commitment from investigators and funders due to volunteer compliance and attrition challenges. The findings from multiple studies indicate that measures of bone elasticity, fragility, and geometry are as important as bone mineral density in predicting fracture risk, with applications for new measurement technologies. Risk may be reduced by high intakes of calcium, vitamin D, and possibly protein (e.g., milk products). Prostaglandin E2, insulin-like growth factor 1, and estrogens are important mediators of osteogenesis, indicating reasons to limit the use of certain drugs (e.g., ibuprofen), to avoid excessive food restriction, and to treat hypogonadism. Abnormal gait may be a correctable risk factor. Brief daily vibration may stimulate bone mineral accretion similar to weight-bearing exercise. Genetic factors contribute importantly to bone quality, affecting fracture susceptibility and providing new insights into fracture healing and tissue reengineering.