PPARgamma inhibits osteogenesis via the down-regulation of the expression of COX-2 and iNOS in rats

PPARγ-SMAD6 axis-mediated inhibition of osteogenic differentiation is involved in BPS-induced osteoporosis

Bisphenol S (BPS) is extensively utilized in personal care products, foods, and paper products, raising growing concerns about its potential environmental hazards. However, few studies have reported the effects of BPS exposure on bone homeostasis. In this study, using data from the National Health and Nutrition Examination Survey, we found a negative correlation between urinary BPS and bone mineral density (BMD). To further investigate the underlying mechanisms, C57BL/6 mice were exposed to a human-equivalent dose of BPS for 6 months. Micro-CT analysis demonstrated reduced femoral BMD in the mice, indicating that osteoporosis was caused by chronic exposure. RNA-seq analysis showed that BPS activated PPARγ in human primary mesenchymal stem cells (MSCs). Additionally, 3D molecular docking confirmed a direct interaction between BPS and PPARγ. Bioinformatics analysis identified SMAD6 as a downstream target of PPARγ. Mechanistically, the BPS-PPARγ interaction activated PPARγ, promoting SMAD6 transcription, which inhibited the osteogenic differentiation of MSCs. High-throughput virtual screening further revealed that olodanrigan effectively blocked the BPS-PPARγ interaction, and in vitro assays revealed that olodanrigan blocked the inhibition of osteogenic differentiation of MSCs induced by BPS. Additionally, olodanrigan supplementation inhibited PPARγ levels, thereby reversing BPS-induced osteoporosis. In summary, this study elucidates the role of the PPARγ-SMAD6 axis in mediating BPS-induced osteoporosis and highlights olodanrigan as a promising therapeutic intervention, offering new insights into the health risks posed by BPS and potential targets for treatment.

Untargeted metabolomics revealed the mechanism of aucubin on glucocorticoid-induced osteoporosis in mice through modulating arachidonic acid metabolism

Glucocorticoid-induced osteoporosis (GIOP) represents the most prevalent form of secondary osteoporosis. Aucubin (AU), a principal active component found in traditional herbal medicines such as Eucommia ulmoides, has been demonstrated to enhance osteoblast differentiation. Nonetheless, the precise therapeutic effects of AU on GIOP and the complex underlying regulatory mechanisms warrant further investigation. We first established a GIOP model in female mice and then assessed the therapeutic effects of AU using micro-CT analysis, biomechanical testing, measurements of serum calcium (Ca) and phosphorus (P) levels, and histological analyses using Hematoxylin and Eosin (HE) and Masson staining. Subsequently, non-targeted metabolomics was employed in order to study the effects of AU on serum metabolites in GIOP mice. The levels of the factors related to these metabolites were quantified using real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) and western blot analyses. Finally, the effects of AU on osteoblastic and osteoclastic differentiation were examined. We found that AU significantly ameliorated bone microarchitecture and strength in GIOP mice. It mitigated pathological damages such as impairment of trabecular bone structure and reduction in collagen fibers, while concurrently elevating serum levels of Ca and P. Non-targeted metabolomics revealed that Arachidonic acid (AA) metabolism serves as a common pathway between the control and GIOP groups, as well as between the high-dose AU (AUH) and GIOP groups. AU notably upregulates prostaglandin-endoperoxide synthase 2 (PTGS2) and microsomal prostaglandin-E synthase 1 (PTGES) expression and downregulates prostaglandin-H2 D-isomerase (PTGDS) expression. Furthermore, AU treatment increased the expression of runt-related transcription factor 2 (Runx2) and transcription factor Sp7 (Osterix), enhanced serum alkaline phosphatase (ALP) activity, and reduced osteoclast expression. These results indicate that AU is a potential drug for treating GIOP, and its mechanism is related to regulating AA metabolism and promoting osteoblast differentiation. However, the key targets of AU in treating GIOP still need further exploration.

Effect of polystyrene nanoplastics and their degraded forms on stem cell fate

Several studies have examined the effects of micro- and nanoplastics on microbes, cells, and the environment. However, only a few studies have examined their effects-especially, those of their reduced cohesiveness-on cell viability and physiology. We synthesized surfactant-free amine-functionalized polystyrene (PS) nanoparticles (NPs) and PS-NPs with decreased crosslinking density (DPS-NPs) without changing other factors, such as size, shape, and zeta potential and examined their effects on cell viability and physiology. PS- and DPS-NPs exhibited reactive oxygen species (ROS) scavenging activity by upregulating GPX3 expression and downregulating HSP70 (ROS-related gene) and XBP1 (endoplasmic reticulum stress-related gene) expression in human bone marrow-derived mesenchymal stem cells (hBM-MSCs). Additionally, they led to upregulation of MFN2 (mitochondrial fusion related gene) expression and downregulation of FIS1 (mitochondrial fission related gene) expression, indicating enhanced mitochondrial fusion in hBM-MSCs. Cell-cycle analysis revealed that PS- and DPS-NPs increased the proportion of cells in the S phase, indicating that they promoted cell proliferation and, specifically, the adipogenic differentiation of hBM-MSCs. However, the cytotoxicity of DPS-NPs against hBM-MSCs was higher than that of PS-NPs after long-term treatment under adipogenic conditions.

The m6A demethylase FTO promotes the osteogenesis of mesenchymal stem cells by downregulating PPARG

N⁶-methyladenosine (m⁶A) is the most abundant posttranscriptional methylation modification that occurs in mRNA and modulates the fine-tuning of various biological processes in mammalian development and human diseases. In this study we investigated the role of m⁶A modification in the osteogenesis of mesenchymal stem cells (MSCs), and the possible mechanisms by which m⁶A modification regulated the processes of osteoporosis and bone necrosis. We performed systematic analysis of the differential gene signatures in patients with osteoporosis and bone necrosis and conducted m⁶A-RNA immunoprecipitation (m⁶A-RIP) sequencing to identify the potential regulatory genes involved in osteogenesis. We showed that fat mass and obesity (FTO), a primary m⁶A demethylase, was significantly downregulated in patients with osteoporosis and osteonecrosis. During the differentiation of human MSCs into osteoblasts, FTO was markedly upregulated. Both depletion of FTO and application of the FTO inhibitor FB23 or FB23-2 impaired osteogenic differentiation of human MSCs. Knockout of FTO in mice resulted in decreased bone mineral density and impaired bone formation. PPARG, a biomarker for osteoporosis, was identified as a critical downstream target of FTO. We further revealed that FTO mediated m⁶A demethylation in the 3'UTR of PPARG mRNA, and reduced PPARG mRNA stability in an YTHDF1-dependent manner. Overexpression of PPARG alleviated FTO-mediated osteogenic differentiation of MSCs, whereas knockdown of PPARG promoted FTO-induced expression of the osteoblast biomarkers ALPL and OPN during osteogenic differentiation. Taken together, this study demonstrates the functional significance of the FTO-PPARG axis in promoting the osteogenesis of human MSCs and sheds light on the role of m⁶A modification in mediating osteoporosis and osteonecrosis.

A Role for Peroxisome Proliferator-Activated Receptor Gamma Agonists in Counteracting the Degeneration of Cardiovascular Grafts

ABSTRACT

Aortic valve replacement for severe stenosis is a standard procedure in cardiovascular medicine. However, the use of biological prostheses has limitations especially in young patients because of calcifying degeneration, resulting in implant failure. Pioglitazone, a peroxisome proliferator-activated receptor gamma (PPAR-gamma) agonist, was shown to decrease the degeneration of native aortic valves. In this study, we aim to examine the impact of pioglitazone on inflammation and calcification of aortic valve conduits (AoC) in a rat model. Cryopreserved AoC (n = 40) were infrarenally implanted into Wistar rats treated with pioglitazone (75 mg/kg chow; n = 20, PIO) or untreated (n = 20, controls). After 4 or 12 weeks, AoC were explanted and analyzed by histology, immunohistology, and polymerase chain reaction. Pioglitazone significantly decreased the expression of inflammatory markers and reduced the macrophage-mediated inflammation in PIO compared with controls after 4 (P = 0.03) and 12 weeks (P = 0.012). Chondrogenic transformation was significantly decreased in PIO after 12 weeks (P = 0.001). Calcification of the intima and media was significantly reduced after 12 weeks in PIO versus controls (intima: P = 0.008; media: P = 0.025). Moreover, echocardiography revealed significantly better functional outcome of the AoC in PIO after 12 weeks compared with control. Interestingly, significantly increased intima hyperplasia could be observed in PIO compared with controls after 12 weeks (P = 0.017). Systemic PPAR-gamma activation prevents inflammation as well as intima and media calcification in AoC and seems to inhibit functional impairment of the implanted aortic valve. To further elucidate the therapeutic role of PPAR-gamma regulation for graft durability, translational studies and long-term follow-up data should be striven for.

Ciglitazone-a human PPARγ agonist-disrupts dorsoventral patterning in zebrafish

Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand-activated transcription factor that regulates lipid/glucose homeostasis and adipocyte differentiation. While the role of PPARγ in adipogenesis and diabetes has been extensively studied, little is known about PPARγ function during early embryonic development. Within zebrafish, maternally-loaded pparγ transcripts are present within the first 6 h post-fertilization (hpf), and de novo transcription of zygotic pparγ commences at ~48 hpf. Since maternal pparγ transcripts are elevated during a critical window of cell fate specification, the objective of this study was to test the hypothesis that PPARγ regulates gastrulation and dorsoventral patterning during zebrafish embryogenesis. To accomplish this objective, we relied on (1) ciglitazone as a potent PPARγ agonist and (2) a splice-blocking, pparγ-specific morpholino to knockdown pparγ. We found that initiation of ciglitazone-a potent human PPARγ agonist-exposure by 4 hpf resulted in concentration-dependent effects on dorsoventral patterning in the absence of epiboly defects during gastrulation, leading to ventralized embryos by 24 hpf. Interestingly, ciglitazone-induced ventralization was reversed by co-exposure with dorsomorphin, a bone morphogenetic protein signaling inhibitor that induces strong dorsalization within zebrafish embryos. Moreover, mRNA-sequencing revealed that lipid- and cholesterol-related processes were affected by exposure to ciglitazone. However, pparγ knockdown did not block ciglitazone-induced ventralization, suggesting that PPARγ is not required for dorsoventral patterning nor involved in ciglitazone-induced toxicity within zebrafish embryos. Our findings point to a novel, PPARγ-independent mechanism of action and phenotype following ciglitazone exposure during early embryonic development.

Epigenetic mechanisms are behind the regulation of the key genes associated with the osteoblastic differentiation of the mesenchymal stem cells: The role of zoledronic acid on tuning the epigenetic changes

Mesenchymal stem cells (MSCs) are multipotent stem cells and show distinct features such as capability for self-renewal and differentiation into several lineages of cells including osteoblasts, chondrocytes, and adipocytes. In this study, the methylation status of the promoter region of zinc finger and BTB domain containing 16 (ZBTB16), twist-related protein 1(Twist1), de novo DNA methyltransferases 3A (DNMT3A), SRY-box 9 (Sox9), osteocalcin (OCN), and peroxisome proliferator-activated receptor γ2 (PPARγ2) genes and their messenger RNA (mRNA) expression levels were evaluated during the osteoblastic differentiation of MSCs (ODMSCs). We planned two experimental groups including zoledronic acid (ZA)-treated and nontreated cells (negative control) which both were differentiated into the osteoblasts. Methylation level of DNA in the promoter regions was assayed by methylation-specific-quantitative polymerase chain reaction (MS-qPCR), and mRNA levels of the target inhibitory/stimulatory genes during osteoblastic differentiation of MSCs were measured using real-time PCR. During the experimental induction of ODMSCs, the mRNA expression of the OCN gene was upregulated and methylation level of its promoter region was decreased. Moreover, Sox9 and PPARγ2 mRNA levels were attenuated and their promoter regions methylation levels were significantly augmented. However, the mRNA expression of the DNMT3A was not affected during the ODMSCs though its methylation rate was increased. In addition, ZA could enhance the expression of the ZBTB16 and decrease its promoter regions methylation and on the opposite side, it diminished mRNA expression of Sox9, Twist1, and PPARγ2 genes and increased their methylation rates. Intriguingly, ZA did not show a significant impact on gene expression and methylation levels the OCN and DNMT3A. We found that methylation of the promoter regions of Sox9, OCN, and PPARγ2 genes might be one of the main mechanisms adjusting the genes expression during the ODMSCs. Furthermore, we noticed that ZA can accelerate the MSCs differentiation to the osteoblast cells via two regulatory processes; suppression of osteoblastic differentiation inhibitor genes including Sox9, Twist1, and PPARγ2, and through promotion of the ZBTB16 expression.

Interplay between microRNAs and Wnt, transforming growth factor-β, and bone morphogenic protein signaling pathways promote osteoblastic differentiation of mesenchymal stem cells

Osteoblasts are terminally differentiated cells with mesenchymal origins, known to possess pivotal roles in sustaining bone microstructure and homeostasis. These cells are implicated in the pathophysiology of various bone disorders, especially osteoporosis. Over the last few decades, strategies to impede bone resorption, principally by bisphosphonates, have been mainstay of treatment of osteoporosis; however, in recent years more attention has been drawn on bone-forming approaches for managing osteoporosis. MicroRNAs (miRNAs) are a broad category of noncoding short sequence RNA fragments that posttranscriptionally regulate the expression of diverse functional and structural genes in a negative manner. An accumulating body of evidence signifies that miRNAs direct mesenchymal stem cells toward osteoblast differentiation and bone formation through bone morphogenic protein, transforming growth factor-β, and Wnt signaling pathways. MiRNAs are regarded as excellent future therapeutic candidates because of their small size and ease of delivery into the cells. Considering their novel therapeutic significance, this review discusses the main miRNAs contributing to the anabolic aspects of bone formation and illustrates their interactions with corresponding signaling pathways involved in osteoblastic differentiation.

Individual or combination treatments with lapatinib and paclitaxel cause potential bone loss and bone marrow adiposity in rats

Cancer treatments with cytotoxic drugs have been shown to cause bone loss. However, effects on bone are less clear for ErbB-targeting tyrosine kinase inhibitors or their combination use with cytotoxic drugs. This study examined the effects of individual or combination treatments with breast cancer drugs lapatinib (a dual ErbB1/ErbB2 inhibitor) and paclitaxel (a microtubule-stabilizing cytotoxic agent) on bone and bone marrow of rats. Wistar rats received lapatinib (240 mg/kg) daily, paclitaxel (12 mg/kg) weekly, or their combination for 4 weeks, and effects on bone/bone marrow were examined at the end of week 4. Microcomputed tomographical structural analyses showed a reduction in trabecular bone volume in tibia following the lapatinib, paclitaxel or their combination treatments ( P < 0.05). Histomorphometry analyses revealed marked increases in bone marrow adipocyte contents in all treatment groups. Reverse transcription polymerase chain reaction gene expression studies with bone samples and cell culture studies with isolated bone marrow stromal cells showed that the all treatment groups displayed significantly reduced levels of osterix expression and osteogenic differentiation potential but increased expression levels of adipogenesis transcription factor peroxisome proliferator-activated receptor γ. In addition, these treatments suppressed the expression of Wnt10b and/or increased expression of Wnt antagonists (secreted frizzled-related protein 1, Dickkopf-related protein 1 and/or sclerostin). Furthermore, all treatment groups showed increased numbers of bone-resorbing osteoclasts on trabecular bone surfaces, although only the lapatinib group displayed increased levels of osteoclastogenic signal (receptor activator of nuclear factor κΒ ligand/osteoclastogenesis inhibitor osteoprotegrin expression ratio) in the bones. Thus, inhibiting ErbB1 and ErbB2 by lapatinib or blocking cell division by paclitaxel or their combination causes significant trabecular bone loss and bone marrow adiposity involving a switch in osteogenesis/adipogenesis potential, altered expression of some major molecules of the Wnt/β-catenin signalling pathway, and increased recruitment of bone-resorbing osteoclasts.

Transgenic expression of cyclooxygenase-2 (COX2) causes premature aging phenotypes in mice

Cyclooxygenase (COX) is a key enzyme in the biosynthesis of prostanoids, lipid signaling molecules that regulate various physiological processes. COX2, one of the isoforms of COX, is highly inducible in response to a wide variety of cellular and environmental stresses. Increased COX2 expression is thought to play a role in the pathogenesis of many age-related diseases. COX2 expression is also reported to be increased in the tissues of aged humans and mice, which suggests the involvement of COX2 in the aging process. However, it is not clear whether the increased COX2 expression is causal to or a result of aging. We have now addressed this question by creating an inducible COX2 transgenic mouse model. Here we show that post-natal expression of COX2 led to a panel of aging-related phenotypes. The expression of p16, p53, and phospho-H2AX was increased in the tissues of COX2 transgenic mice. Additionally, adult mouse lung fibroblasts from COX2 transgenic mice exhibited increased expression of the senescence-associated β-galactosidase. Our study reveals that the increased COX2 expression has an impact on the aging process and suggests that modulation of COX2 and its downstream signaling may be an approach for intervention of age-related disorders.

Thiazolidinedione drugs in the treatment of type 2 diabetes mellitus: past, present and future

Thiazolidinedione (TZD) drugs used in the treatment of type 2 diabetes mellitus (T2DM) have proven effective in improving insulin sensitivity, hyperglycemia, and lipid metabolism. Though well tolerated by some patients, their mechanism of action as ligands of peroxisome proliferator-activated receptors (PPARs) results in the activation of several pathways in addition to those responsible for glycemic control and lipid homeostasis. These pathways, which include those related to inflammation, bone formation, and cell proliferation, may lead to adverse health outcomes. As treatment with TZDs has been associated with adverse hepatic, cardiovascular, osteological, and carcinogenic events in some studies, the role of TZDs in the treatment of T2DM continues to be debated. At the same time, new therapeutic roles for TZDs are being investigated, with new forms and isoforms currently in the pre-clinical phase for use in the prevention and treatment of some cancers, inflammatory diseases, and other conditions. The aims of this review are to provide an overview of the mechanism(s) of action of TZDs, a review of their safety for use in the treatment of T2DM, and a perspective on their current and future therapeutic roles.

Molecular control of nitric oxide synthesis through eNOS and caveolin-1 interaction regulates osteogenic differentiation of adipose-derived stem cells by modulation of Wnt/β-catenin signaling

Background

Nitric oxide (NO) plays a role in a number of physiological processes including stem cell differentiation and osteogenesis. Endothelial nitric oxide synthase (eNOS), one of three NO-producing enzymes, is located in a close conformation with the caveolin-1 (CAV-1^WT) membrane protein which is inhibitory to NO production. Modification of this interaction through mutation of the caveolin scaffold domain can increase NO release. In this study, we genetically modified equine adipose-derived stem cells (eASCs) with eNOS, CAV-1^WT, and a CAV-1^F92A (CAV-1^WT mutant) and assessed NO-mediated osteogenic differentiation and the relationship with the Wnt signaling pathway.

Methods

NO production was enhanced by lentiviral vector co-delivery of eNOS and CAV-1^F92A to eASCs, and osteogenesis and Wnt signaling was assessed by gene expression analysis and activity of a novel Runx2-GFP reporter. Cells were also exposed to a NO donor (NONOate) and the eNOS inhibitor, l-NAME.

Results

NO production as measured by nitrite was significantly increased in eNOS and CAV-1^F92A transduced eASCs +(5.59 ± 0.22 μM) compared to eNOS alone (4.81 ± 0.59 μM) and un-transduced control cells (0.91 ± 0.23 μM) (p < 0.05). During osteogenic differentiation, higher NO correlated with increased calcium deposition, Runx2, and alkaline phosphatase (ALP) gene expression and the activity of a Runx2-eGFP reporter. Co-expression of eNOS and CAV-1^WT transgenes resulted in lower NO production. Canonical Wnt signaling pathway-associated Wnt3a and Wnt8a gene expressions were increased in eNOS-CAV-1^F92A cells undergoing osteogenesis whilst non-canonical Wnt5a was decreased and similar results were seen with NONOate treatment. Treatment of osteogenic cultures with 2 mM l-NAME resulted in reduced Runx2, ALP, and Wnt3a expressions, whilst Wnt5a expression was increased in eNOS-delivered cells. Co-transduction of eASCs with a Wnt pathway responsive lenti-TCF/LEF-dGFP reporter only showed activity in osteogenic cultures co-transduced with a doxycycline inducible eNOS. Lentiviral vector expression of canonical Wnt3a and non-canonical Wnt5a in eASCs was associated with induced and suppressed osteogenic differentiation, respectively, whilst treatment of eNOS-osteogenic cells with the Wnt inhibitor Dkk-1 significantly reduced expressions of Runx2 and ALP.

Conclusions

This study identifies NO as a regulator of canonical Wnt/β-catenin signaling to promote osteogenesis in eASCs which may contribute to novel bone regeneration strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0442-9) contains supplementary material, which is available to authorized users.

Bufei Yishen granules combined with acupoint sticking therapy suppress oxidative stress in chronic obstructive pulmonary disease rats: Via regulating peroxisome proliferator-activated receptor-gamma signaling

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine (TCM) is clinically used under the guidance of its unique theory system. Bufei Yishen (BY) granules, an oral Chinese herbal formula, is confirmed effective for treating the syndrome of lung-kidney qi deficiency in chronic obstructive pulmonary disease (COPD) patients. Shu-Fei Tie ointment is another prescription for acupoint sticking (AS) therapy based on the theory of treating an internal disease by external treatment on proper acupoints. The beneficial effects of BY granules combined with Shu-Fei Tie have been proved in previous clinical trials. However, the underlying mechanism remains unclear. The present study was initiated to explore the antioxidative mechanism of the integrated therapy of BY granules and acupoint sticking via regulating by peroxisome proliferator activated receptor-gamma (PPARγ) signaling in a cigarette-smoke/bacterial exposure induced COPD rat model.

MATERIALS AND METHODS

Rats were randomized into Control, Model, BY, AS, BY+AS and aminophylline (APL) groups. COPD rats were induced by cigarette-smoke and bacterial exposures, and were administrated with normal saline, BY granules, AS, BY+AS or aminophylline from week 9 and sacrificed at week 20. Activity of superoxide dismutase (SOD) and levels of methane dicarboxylic aldehyde (MDA) in peripheral blood and bronchoalveolar lavage fluid (BALF) were determined by hydroxylamine and thiobarbituric acid methods. The gene and protein expressions of PPARγ in the lung tissues were analyzed by quantitative polymerase chain reaction and western blot.

RESULTS

Serum and BALF SOD decreased significantly in Model group (P<0.01), while MDA increased (P<0.01). Compared to COPD rats, serum SOD was higher in all treatment groups (P<0.01), and BALF SOD was higher in BY and BY+AS groups (P<0.01); serum and BALF MDA was lower in all treatment groups (P<0.01). Serum and BALF SOD was higher in BY+AS group than in AS group, while MDA was lower (P<0.05). BALF SOD increased in BY+AS group compared with APL group, while MDA decreased (P<0.05). PPARγ mRNA and protein and the phosphorylation of PPARγ (p-PPARγ) decreased in COPD rats (P<0.01), and increased in all treatment groups (P<0.01). PPARγ mRNA was higher in BY+AS group than in AS group (P<0.05), PPARγ and p-PPARγ were higher in BY+AS group than in AS and APL groups (P<0.05, P<0.01); PPARγ protein was higher in BY group than in APL group (P<0.05).

CONCLUSION

Bufei Yishen granules, Shu-Fei Tie and their combination have beneficial effects in stable COPD, and can attenuate the oxidative stress, and the activation of PPARγ signaling might be involved in the underlying mechanisms, but there are no obvious synergistic effect of Bufei Yishen granules and Shu-Fei Tie.

Light-triggered RNA release and induction of hMSC osteogenesis via photodegradable, dual-crosslinked hydrogels

AIM

To engineer a photodegradable hydrogel system for actively controlled release of bioactive unmodified RNA at designated time points to induce hMSC osteogenesis.

MATERIALS & METHODS

RNA/polyethylenimine complexes were loaded into dual-crosslinked photodegradable hydrogels to examine the capacity of UV light application to trigger their release. The ability of released RNA to drive hMSC osteogenic differentiation was also investigated.

RESULTS & CONCLUSION

RNA release from photodegradable hydrogels was accelerated upon UV application, which was not observed in non-photodegradable hydrogels. Regardless of the presence of UV light, released siGFP exhibited high bioactivity by silencing GFP expression in HeLa cells. Importantly, siNoggin or miRNA-20a released from the hydrogels induced hMSC osteogenesis. This system provides a potentially valuable physician/patient-controlled 'on-demand' RNA delivery platform for biomedical applications.

Cysteine Dioxygenase Type 1 Inhibits Osteogenesis by Regulating Wnt Signaling in Primary Mouse Bone Marrow Stromal Cells

Mesenchymal stem cells (MSCs) are multipotent cells, which can give rise to variety of cell types, including adipocytes and osteoblasts. Previously, we have shown that cysteine dioxygenase type 1 (Cdo1) promoted adipogenesis of primary mouse bone marrow stromal cells (BMSCs) and 3T3-L1 pre-adipocytes via interaction with Pparγ. However, the role of Cdo1 in osteogenesis remains unclear. Here, we demonstrated that expression of Cdo1 was elevated during osteoblastic differentiation of BMSCs in vitro. Interestingly, knockdown of Cdo1 by siRNA led to an increased expression of osteogenic related genes, elevated alkaline phosphatase (ALP) activity, and enhanced mineralization. Overexpression of Cdo1 in BMSCs inversely suppressed the osteogenesis. Furthermore, we found that overexpression of Cdo1 impaired Wnt signaling and restricted the Wnt3a induced expression of osteogenic transcriptional factors, such as Runx2 and Dlx5. Collectively, our findings indicate Cdo1 suppresses osteogenic differentiation of BMSCs, through a potential mechanism which involves in Wnt signaling reduction concomitantly.

Rosiglitazone inhibition of calvaria-derived osteoblast differentiation is through both of PPARγ and GPR40 and GSK3β-dependent pathway

Rosiglitazone (RSG) can cause bone loss, however the mechanisms remain largely unknown. This study aims to investigate the effects of RSG on differentiation and mineralization of osteoblasts using primary cultured mouse fetal calvaria-derived osteoblasts as a model, and elucidate the receptor and signaling pathways responsible for these effects. We found that RSG suppressed the differentiation and mineralization of calvaria-derived osteoblasts. Peroxisome proliferators-activated receptor γ (PPARγ) siRNA significantly reversed the inhibitory effect of RSG on osteogenic differentiation. The expression of G protein-coupled receptor (GPR) 40 was suppressed during differentiation, but was increased by RSG treatment. GPR40 siRNA significantly reversed the inhibitory effect of RSG on osteogenesis. RSG activated glycogen synthase kinase (GSK)-3β, which in turn decreased β-catenin expression. RSG-induced GSK3β activation was mediated through both PPARγ and GPR40. These results suggest that both PPARγ and GRP40 are required for RSG-induced inhibition of mouse calvaria osteoblast differentiation, which is mediated through GSK3β-dependent pathway.

The effects of diabetes medications on post-operative long bone fracture healing

PURPOSE

Diabetes has long been known to have an impact on bone repair. More recently, however, most diabetic patients receive medications to normalise this hyperglycaemic environment. To date, no studies have investigated the effects of diabetic medications on fracture healing in humans.

METHOD

Patients were identified from two tertiary trauma centres. Inclusion criteria were adult patients having sustained a closed diaphyseal femoral or tibial fracture, treated surgically. Exclusion criteria were open, pathological or peri-prosthetic fractures, and patients having sustained polytrauma. Matched non-diabetic controls were identified, matched for age, sex, fracture classification and osteosynthesis. Output measures were: time to callus first appearance, bridging of involved cortices and time to union, along with the eventual outcome: union/non-union.

RESULTS

A total of 36 (25 males) eligible patients were identified with a control group of 166 patients (138 males). ANOVA demonstrated class of medication to have a significant effect at two of the three time points and on the eventual outcome. Multiple regression analysis also demonstrated significant impact (p = 0.02).

CONCLUSION

All classes of medication demonstrated anti-osteogenic effects compared to the control cohort. Biguanides demonstrated this in contrast to the in vitro evidence to date. Sulphonylureas demonstrated this to a greater extent; however, no in vitro evidence is available for comparison within this class. Clinicians should be aware of these delays in bone healing when treating diabetic patients and aim for optimal blood glucose control until such time as further research can be undertaken.

Surface topography enhances differentiation of mesenchymal stem cells towards osteogenic and adipogenic lineages

Surface topography impacts on cell growth and differentiation, but it is not trivial to generate defined surface structures and to assess the relevance of specific topographic parameters. In this study, we have systematically compared in vitro differentiation of mesenchymal stem cells (MSCs) on a variety of groove/ridge structures. Micro- and nano-patterns were generated in polyimide using reactive ion etching or multi beam laser interference, respectively. These structures affected cell spreading and orientation of human MSCs, which was also reflected in focal adhesions morphology and size. Time-lapse demonstrated directed migration parallel to the nano-patterns. Overall, surface patterns clearly enhanced differentiation of MSCs towards specific lineages: 15 μm ridges increased adipogenic differentiation whereas 2 μm ridges enhanced osteogenic differentiation. Notably, nano-patterns with a periodicity of 650 nm increased differentiation towards both osteogenic and adipogenic lineages. However, in absence of differentiation media surface structures did neither induce differentiation, nor lineage-specific gene expression changes. Furthermore, nanostructures did not affect the YAP/TAZ complex, which is activated by substrate stiffness. Our results provide further insight into how structuring of tailored biomaterials and implant interfaces - e.g. by multi beam laser interference in sub-micrometer scale - do not induce differentiation of MSCs per se, but support their directed differentiation.

Cysteine dioxygenase type 1 promotes adipogenesis via interaction with peroxisome proliferator-activated receptor gamma

Mammalian cysteine dioxygenase type 1 (CDO1) is an essential enzyme for taurine biosynthesis and the biodegradation of toxic cysteine. As previously suggested, Cdo1 may be a marker of liposarcoma progression and adipogenic differentiation, but the role of Cdo1 in adipogenesis has yet been reported. In this study, we found that the expression of Cdo1 is dramatically elevated during adipogenic differentiation of 3T3-L1 pre-adipocytes and mouse bone marrow-derived mesenchymal stem cells (mBMSCs). Conversely, knockdown of Cdo1 inhibited expression of adipogenic specific genes and lipid droplet formation in 3T3-L1 cells and mBMSCs. Mechanistically, we found Cdo1 interacted with Pparγ in response to adipogenic stimulus. Further, depletion of Cdo1 reduced the recruitment of Pparγ to the promoters of C/EBPα and Fabp4. Collectively, our finding indicates that Cdo1 may be a co-activator of Pparγ in adipogenesis, and may contribute to the development of disease associated with excessive adipose tissue.

Sustained localized presentation of RNA interfering molecules from in situ forming hydrogels to guide stem cell osteogenic differentiation

To date, RNA interfering molecules have been used to differentiate stem cells on two-dimensional (2D) substrates that do not mimic three-dimensional (3D) microenvironments in the body. Here, in situ forming poly(ethylene glycol) (PEG) hydrogels were engineered for controlled, localized and sustained delivery of RNA interfering molecules to differentiate stem cells encapsulated within the 3D polymer network. RNA interfering molecules were released from the hydrogels in a sustained and controlled manner over the course of 3-6 weeks, and exhibited high bioactivity. Importantly, it was demonstrated that the delivery of siRNA and/or miRNA from the hydrogel constructs enhanced the osteogenic differentiation of encapsulated stem cells. Prolonged delivery of siRNA and/or miRNA from this polymeric scaffold permitted extended regulation of cell behavior, unlike traditional siRNA experiments performed in vitro. This approach presents a powerful new methodology for controlling cell fate, and is promising for multiple applications in tissue engineering and regenerative medicine.

Ethanol Extracts of Fresh Davallia formosana (WL1101) Inhibit Osteoclast Differentiation by Suppressing RANKL-Induced Nuclear Factor- κ B Activation

The rhizome of Davallia formosana is commonly used to treat bone disease including bone fracture, arthritis, and osteoporosis in Chinese herbal medicine. Here, we report the effects of WL1101, the ethanol extracts of fresh rhizomes of Davallia formosana on ovariectomy-induced osteoporosis. In addition, excess activated bone-resorbing osteoclasts play crucial roles in inflammation-induced bone loss diseases, including rheumatoid arthritis and osteoporosis. In this study, we examined the effects of WL1101 on receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis. Treatment with WL1101 significantly inhibited RANKL-stimulated osteoclastogenesis. Two isolated active compounds, ((−)-epicatechin) or WL14 (4-hydroxy-3-aminobenzoic acid) could also inhibit RANKL-induced osteoclastogenesis. WL1101 suppressed the RANKL-induced nuclear factor-κB (NF-κB) activation and nuclear translocation, which is the key process during osteoclastogenesis, by inhibiting the activation of IκB kinase (IKK) and IκBα. In animal model, oral administration of WL1101 (50 or 200 mg/kg/day) effectively decreased the excess bone resorption and significantly antagonized the trabecular bone loss in ovariectomized rats. Our results demonstrate that the ethanol extracts of fresh rhizomes of Davallia formosana inhibit osteoclast differentiation via the inhibition of NF-κB activation and effectively ameliorate ovariectomy-induced osteoporosis. WL1101 may thus have therapeutic potential for the treatment of diseases associated with excessive osteoclastic activity.

Dextromethorphan inhibits osteoclast differentiation by suppressing RANKL-induced nuclear factor-κB activation

Dextromethorphan (DXM), a commonly used antitussive, is a dextrorotatory morphinan. Here, we report that DXM inhibits the receptor activator of nuclear factor kappa B ligand (RANKL)-induced osteoclastogenesis and bone resorption by abrogating the activation of NF-κB signalling in vitro. Oral administration of DXM ameliorates ovariectomy (OVX)-induced osteoporosis in vivo.

INTRODUCTION

DXM was reported to possess anti-inflammatory properties through inhibition of the release of pro-inflammatory factors. However, the potential role and action mechanism of DXM on osteoclasts and osteoblasts remain unclear. In this study, in vitro and in vivo studies were performed to investigate the potential effects of DXM on osteoclastogenesis and OVX-induced bone loss.

METHODS

Osteoclastogenesis was examined by the TRAP staining, pit resorption, TNF-α release, and CCR2 and CALCR gene expression. Osteoblast differentiation was analyzed by calcium deposition. Osteogenic and adipogenic genes were measured by real-time PCR. Signaling pathways were explored using Western blot. ICR mice were used in an OVX-induced osteoporosis model. Tibiae were measured by µCT and serum markers were examined with ELISA kits.

RESULTS

DXM inhibited RANKL-induced osteoclastogenesis. DXM mainly inhibited osteoclastogenesis via abrogation of IKK-IκBα-NF-κB pathways. However, a higher dosage of DXM antagonized the differentiation of osteoblasts via the inhibition of osteogenic signals and increase of adipogenic signals. Oral administration of DXM (20 mg/kg/day) partially reduced trabecular bone loss in ovariectomized mice.

CONCLUSION

DXM inhibits osteoclast differentiation and activity by affecting NF-κB signaling. Therefore, DXM at suitable doses may have new therapeutic applications for the treatment of diseases associated with excessive osteoclastic activity.

Effect and clinical implications of the low-energy diode laser on bone cell proliferation

Laser is a simple, noninvasive technique that has proven useful for treating damaged tissue. However, its effects on bone regeneration and the mechanisms involved are poorly understood. The objective of this study was to evaluate the effects on MG-63 cell proliferation of application of a pulsed diode laser (Ezlase) of 940 nm at low energy levels. After 24 hr of culture, osteoblasts underwent pulsed laser radiation at 0.5, 1, 1.5, and 2 W and fluences of 1-5 J. A control group was not irradiated. After the treatment, cells were incubated for 24 hr, and cell proliferation was analyzed using a spectrophotometric measure of cell respiration (MTT assay). Results were expressed as percentage proliferation versus controls. At 24-hr culture, cell proliferation was increased in laser-treated cells at intensities of 0.5, 1, and 1.5 W/cm(2) versus controls; the energy density was positively correlated with cell growth, which reached a peak at 3 J and decreased at higher fluences. The use of pulsed low-level laser with low-energy density range thus appears to exert a biostimulatory effect on bone tissue. Although the data on cell proliferation are robust, in-depth investigation is required into the effect of these irradiation doses on other cell parameters. The present findings demonstrate that laser therapy could be highly useful in tissue regeneration in different clinical settings, including nursing, physical therapy, dentistry, and traumatology.

Epimedium-derived flavonoids modulate the balance between osteogenic differentiation and adipogenic differentiation in bone marrow stromal cells of ovariectomized rats via Wnt/β-catenin signal pathway activation

OBJECTIVE

To observe the function of wnt/β-catenin signal pathway on the process that epimedium-derived flavonoids (EFs) regulate the balance between osteogenic differentiation and adipogenic differentiation in bone marrow stromal cells of ovariectomized rats, and to provide an experimental evidence for the mechanism of EFs on treating postmenopausal osteoporosis.

METHODS

Bone marrow stromal cells from ovariectomized rats were separated and cultivated in the condition of osteoinductive medium or liquid medium for 15 days. Low- (1 μg/mL), medium- (10 μg/mL) and high- (100 μg/mL) dose EFs were administrated correspondingly. Alkaline phosphatase (ALP) staining, ALP activity determination, oil red O staining and realtime polymerese chain reaction (RT-PCR) were used to determine the effect of EFs on osteogenic differentiation and adipogenic differentiation in bone marrow stromal cells of ovariectomized rats. Moreover, in order to explore the mechanism of EFs on osteogenic differentiation and adipogenic differentiation in bone marrow stromal cells of ovariectomized rats, Dickkopf-related protein 1 (DKK1) was used in the medium group. Enzymelinked immunosorbent assay (ELISA) and RT-PCR were used to determine mRNA levels of β-catenin, low density lipoprotein receptor-related protein 5 (LRP5) and T cell factor (TCF) protein, known as wnt/β-catenin signal pathway related factors.

RESULTS

EFs increased mRNA expression levels of ALP and early osteoblast differentiation factors, such as runt-related transcription factor 2 (Runx2), osteocalcin and collagen I, and decreased mRNA expression levels of fat generation factors, such as peroxisome proliferator activated receptor gamma 2 (PPARγ-2) and CCAAT enhancer-binding protein-α (C/EBPα) in a dose-dependent manner. While osteoblast differentiation factors were down-regulated, fat generation factors were up-regulated when DKK1 was applied. Also EFs up-regulated mRNA expression levels of β-catenin, LRP5 and TCF protein which could be blocked by DKK1.

CONCLUSION

EFs regulate the balance between osteogenic differentiation and adipogenic differentiation in bone marrow stromal cells of ovariectomized rats by activating wnt/β-catenin signal pathway, which may be an important molecular mechanism of EFs on treating postmenopausal osteoporosis.

Mineralization content alters osteogenic responses of bone marrow stromal cells on hydroxyapatite/polycaprolactone composite nanofiber scaffolds

Synthetic tissue scaffolds have a high potential impact for patients experiencing osteogenesis imperfecta. Using electrospinning, tissue scaffolds composed of hydroxyapatite/polycaprolactone (HAp/PCL) composite nanofibers were fabricated with two different HAp concentrations—1% and 10% of the solid scaffold weight. After physico-chemical scaffold characterization, rat bone marrow stromal cells were cultured on the composite scaffolds in maintenance medium and then in osteogenic medium. Quantitative PCR, colorimetric assays, immunofluorescent labeling, and electron microscopy measured osteogenic cell responses to the HAp/PCL scaffolds. In maintenance conditions, both Hap/PCL scaffolds and control scaffolds supported cell colonization through seven days with minor differences. In osteogenic conditions, the 10% HAp scaffolds exhibited significantly increased ALP assay levels at week 3, consistent with previous reports. However, qPCR analysis demonstrated an overall decrease in bone matrix-associated genes on Hap/PCL scaffolds. Osteopontin and osteocalcin immunofluorescent microscopy revealed a trend that both mineralized scaffolds had greater amounts of both proteins, though qPCR results indicated the opposite trend for osteopontin. Additionally, type I collagen expression decreased on HAp scaffolds. These results indicate that cells are sensitive to minor changes in mineral content within nanofibers, even at just 1% w/w, and elucidating the sensing mechanism may lead to optimized osteogenic scaffold designs.

Effects of brucine on bone metabolism in multiple myeloma

The aim of this study was to explore the effects of brucine on bone metabolism in multiple myeloma (MM) and to compare brucine and bortezomib regarding the effects on MM in vitro. The half maximal inhibitory concentration (IC50) values of brucine and bortezomib in the MM cell line U266 were detected by MTT assay. In addition, the expression of alkaline phosphatase (ALP), osteocalcin (OC), osteoprotegerin (OPG) and osteoprotegerin ligand (also termed receptor activator of nuclear factor κB ligand) (RANKL) at mRNA levels were measured by RT-PCR. IC50 of bortezomib in the U266 cell line at 48 h was 22.4 nmol/l, and that of brucine was 0.16 nmol/l. Compared with osteoblasts incubated with MM cell supernatant alone, the mRNA levels of ALP, OC and OPG in osteoblasts co-treated with brucine and MM cell supernatant were higher (p<0.05), while the mRNA expression of RANKL was lower, and the ranges of the changes were all larger than those of the group treated with bortezomib (P<0.05). Brucine exerts effects on bone metabolism in multiple myeloma through the regulation of osteoclasts by osteoblasts.

The effects of rosiglitazone on osteoblastic differentiation, osteoclast formation and bone resorption

Rosiglitazone has the potential to activate peroxisome proliferator-activated receptor-γ (PPARγ), which in turn can affect bone formation and resorption. However, the mechanisms by which rosiglitazone regulates osteoclastic orosteoblastic differentiation are not fully understood. This study examines how rosiglitazone affects osteoclast formation, bone resorption and osteoblast differentiation from mouse bone marrow. Rosiglitazone treatment not only inhibited the formation of tartrate-resistant acid phosphatase-positive cells, but also prevented pit formation by bone marrow cells in a dose- and time-dependent manner. Rosiglitazone also suppressed the receptor activator of nuclear factor (NF)-κB ligand (RANKL) receptor(RANK) expression but increased PPARγ2 expression in the cells. In addition, rosiglitazone diminished RANKL induced activation of NF-κB-DNA binding by blocking IκBαphosphorylation. Furthermore, it reduced collagen and osteocalcin levels to nearly zero and prevented mRNA expression of osteoblast-specific proteins including runtrelated transcription factor-2, osteocalcin, and type I collagen.However, mRNA levels of adipocyte-specific marker, aP2, were markedly increased in the cells co-incubated with rosiglitazone. These results suggest that PPARγ activation by rosiglitazone inhibits osteoblast differentiation with increased adipogenesis in bone marrow cells and also may prevent osteoclast formation and bone resorptionin the cells.

Diabetes and fracture healing: the skeletal effects of diabetic drugs

INTRODUCTION

Over 39,000 diabetic patients are surgically treated for trauma and orthopaedic injuries annually in the UK, yet the effects of diabetic medications on the skeletal system is an under researched and under acknowledged field.

AREAS COVERED

This review covers all English language novel experimental data reports investigating the effects of the main classes of diabetic drugs on the skeletal system, specifically their effects on fracture healing, located through the literature search engines Medline and Web of Science.

EXPERT OPINION

Post-surgical gylcaemic control is paramount in insulin-controlled type 1 diabetic patients. Data on pharmacological control compounds used in type 2 diabetes are limited. Reports to date indicate thiazolidinediones to exert anti-osteogenic effects, in contrast to the observed osteogenic effects of biguanides. Ongoing research is desirable to guide future clinical recommendations.

Effect of rosiglitazone on bone quality in a rat model of insulin resistance and osteoporosis

OBJECTIVE

Rosiglitazone (RSG) is an insulin-sensitizing drug used to treat type 2 diabetes mellitus. The A Diabetes Outcome Progression Trial (ADOPT) shows that women taking RSG experienced more fractures than patients taking other type 2 diabetes drugs. These were not osteoporotic vertebral fractures but, rather, occurred in the limbs. The purpose of this study was to investigate how RSG treatment alters bone quality, which leads to fracture risk, using the Zucker fatty rat as a model.

RESEARCH DESIGN AND METHODS

A total of 61 female 4-month-old rats were divided into six groups. One Sham group was a control and another was administered oral RSG 10 mg/kg/day. Four ovariectomized (OVX) groups were dosed as follows: controls, RSG 10 mg/kg, alendronate (ALN, injected at 0.7 mg/kg/week), and RSG 10 mg/kg plus ALN. After 12 weeks of treatment, bone quality was evaluated by mechanical testing. Microarchitecture, bone mineral density (BMD), cortical bone porosity, and bone remodeling were also measured.

RESULTS

OVX RSG 10 mg/kg rats had lower vertebral BMD and compromised trabecular architecture versus OVX controls. Increased cortical bone porosity and decreased mechanical properties occurred in these rats. ALN treatment prevented decreased BMD and architectural and mechanical properties in the OVX model. Reduced bone formation, increased marrow adiposity, and excess bone resorption were observed in RSG-treated rats.

CONCLUSIONS

RSG decreases bone quality. An unusual finding was an increase in cortical bone porosity induced by RSG, consistent with its effect on long bones of women. ALN, an inhibitor of bone resorption, enhanced mechanical strength and may provide an approach to partially counter the deleterious skeletal effects of RSG.

15-deoxy-Δ(12,14) -prostaglandin-J2 and ciglitazone inhibit TNF-α-induced matrix metalloproteinase 13 production via the antagonism of NF-κB activation in human synovial fibroblasts

Collagenase-3 (matrix metalloproteinase, MMP-13) plays an important role in the degradation of cartilage in pathologic conditions. MMP-13 is elevated in joint tissues in both rheumatoid arthritis (RA) and osteoarthritis (OA). In addition, inflammation-stimulated synovial fibroblasts are able to release MMP-13 and other cytokines in these diseases. The peroxisome proliferator-activated receptor-γ (PPARγ) ligands are recently considered as new anti-inflammatory compounds and these ligands were reported to ameliorate inflammatory arthritis. The aim of this study is to evaluate the mechanisms how PPARγ ligands inhibit the inflammatory response in synovial fibroblasts. Two PPARγ ligands, cyclopentenone prostaglandin 15-deoxy-Δ(12,14) -prostaglandin-J2 (15d-PGJ2) and synthetic thiazolidinedione compound ciglitazone were examined in this study. Here we found that 15d-PGJ2 and ciglitazone markedly inhibited TNF-α-induced MMP-13 production in human synovial fibroblasts. In addition, activation of nuclear factor κB (NF-κB) is strongly associated with MMP-13 induction by TNF-α and the activation of NF-κB was determined by Western blot, reporter assay, and immunofluorescence. It was found that 15d-PGJ2 markedly attenuated the translocation of NF-κB by direct inhibition of the activation of IKK via a PPARγ-independent manner. Ciglitazone also inhibits TNF-α-induced MMP-13 expression by suppressing NF-κB activation mainly via the modulation of p38-MAPK. Collectively, our data demonstrate that 15d-PGJ2 and ciglitazone attenuated TNF-α-induced MMP-13 expression in synovial fibroblasts primarily through the modulation of NF-κB signaling pathways. These compounds may have therapeutic application in inflammatory arthritis.

Osteoblast-targeted overexpression of PPARγ inhibited bone mass gain in male mice and accelerated ovariectomy-induced bone loss in female mice

PPARγ has critical role in the differentiation of mesenchymal stem cells into adipocytes while suppressing osteoblastic differentiation. We generated transgenic mice that overexpress PPARγ specifically in osteoblasts under the control of a 2.3-kb procollagen type 1 promoter (Col.1-PPARγ). Bone mineral density (BMD) of 6- to 14-week-old Col.1 - PPARγ male mice was 8% to 10% lower than that of their wild-type littermates, whereas no difference was noticed in Col.1-PPARγ female mice. Col.1-PPARγ male mice exhibited decreased bone volume (45%), trabecular thickness (23%), and trabecular number (27%), with a reciprocal increase in trabecular spacing (51%). Dynamic histomorphometric analysis also revealed that bone-formation rate (42%) and mineral apposition rate (32%) were suppressed significantly in Col.1-PPARγ male mice compared with their wild-type littermates. Interestingly, osteoclast number and surface also were decreased by 40% and 58%, respectively, in Col.1-PPARγ male mice. In vitro whole-marrow culture for osteoclastogenesis also showed a significant decrease in osteoclast formation (approximately 35%) with the cells from Col.1-PPARγ male mice, and OPG/RANKL ratio was reduced in stromal cells from Col.1-PPARγ male mice. Although there was no significant difference in BMD in Col.1-PPARγ female mice up to 30 weeks, bone loss was accelerated after ovariectomy compared with wild-type female mice (-3.9% versus -6.8% at 12 weeks after ovariectomy, p < .01), indicating that the effects of PPARγ overexpression becomes more evident in an estrogen-deprived state in female mice. In conclusion, in vivo osteoblast-specific overexpression of PPARγ negatively regulates bone mass in male mice and accelerates estrogen-deficiency-related bone loss in female mice.

PPARgamma2 expression in growth plate chondrocytes is regulated by p38 and GSK-3

Although peroxisome proliferator activated receptor (PPAR)γ remains a critical regulator of preadipocyte differentiation, new roles have been discovered in inflammation, bone morphogenesis, endothelial function, cancer, longevity and atherosclerosis. Despite the demonstration of PPARγ expression in chondrocytes, its role and the pathways affecting its expression and activity in chondrocytes remain largely unknown. We investigated the effects of PPARγ activation on chondrocyte differentiation and its participation in chondrocyte lipid metabolism. PPARγ2 expression is highly regulated during chondrocyte differentiation in vivo and in vitro PPARγ activation with troglitazone resulted in increased Indian hedgehog expression and reduced collagen X expression, confirming previously described roles in the inhibition of differentiation. However, the major effect of PPARγ2 in chondrocytes appears to be on lipid metabolism. During differentiation chondrocytes increase expression of the lipid-associated metabolizing protein, Lpl, which is accompanied by increased gene expression of PPARγ. PPARγ expression is suppressed by p38 activity, but requires GSK-3 activity. Furthermore, Lpl expression is regulated by p38 and GSK-3 signalling. This is the first study demonstrating a relationship between PPARγ2 expression and chondrocyte lipid metabolism and its regulation by p38 and GSK-3 signalling.

Dynamic expression of DKK1 protein in the process whereby Epimedium-derived flavonoids up-regulate osteogenic and down-regulate adipogenic differentiation of bone marrow stromal cells in ovariectomized rats

OBJECTIVE

To observe the dynamic expression of DKK1 protein in the process whereby Epimedium-derived flavonoids (EFs) regulate the balance between osteogenic and adipogenic differentiation of bone marrow stromal cells in ovariectomized rats, and to provide experimental evidence for the mechanism of EFs in the treatment of postmenopausal osteoporosis.

METHODS

  Bone marrow stromal cells from ovariectomized rats were separated and cultivated in osteoinductive or liquid medium for 15 days in vitro. EFs (10 µg/mL) were applied to both cultures. Alkaline phosphatase (ALP) staining, ALP activity determination, Oil Red O staining and fluorescence quantitative polymerase chain reaction were used to determine the influence of EFs on osteogenic and adipogenic differentiation of bone marrow stromal cells in ovariectomized rats. Moreover, in order to explore the exact mechanism of EFs on osteogenic and adipogenic differentiation of bone marrow stromal cells in ovariectomized rats, enzyme linked immunosorbent assay was used to determine the dynamic expression of DKK1 protein in this process.

RESULTS

EFs increased activity of ALP and mRNA expression of Runx2 (early osteoblast differentiation factor) and decreased mRNA expression of PPARγ-2 (key factor of fat generation). Importantly, EFs down-regulated expression of DKK1 protein in an osteogenic induction medium and inhibited up-regulation of DKK1 protein in an adipogenic induction medium.

CONCLUSION

  EFs regulate the balance between osteogenic and adipogenic differentiation of bone marrow stromal cells in ovariectomized rats by down-regulating expression of DKK1 protein. This may be an important molecular mechanism of EFs in the context of treatment of postmenopausal osteoporosis.

Sonic Hedgehog influences the balance of osteogenesis and adipogenesis in mouse adipose-derived stromal cells

Adipose-derived stromal cells (ASCs) present a great potential for tissue engineering, as they are capable of differentiating into osteogenic and adipogenic cell types, among others. In this study, we examined the role of Hedgehog signaling in the balance of osteogenic and adipogenic differentiation in mouse ASCs. Results showed that Hedgehog signaling increased during early osteogenic differentiation (Shh, Ptc1, and Gli1), but decreased during adipogenic differentiation. N-terminal Sonic Hedgehog (Shh-N) significantly increased in vitro osteogenic differentiation in mouse ASCs, by all markers examined (*p < 0.01). Concomitantly, Shh-N abrogated adipogenic differentiation, by all markers examined (*p < 0.01). Conversely, blockade of endogenous Hedgehog signaling, with the Hedgehog antagonist cyclopamine, enhanced adipogenesis at the expense of osteogenesis. We next translated these results to a mouse model of appendicular skeletal regeneration. Using quantitative real-time polymerase chain reaction and in situ hybridization, we found that skeletal injury (a monocortical 1 mm defect in the tibia) results in a localized increase in Hedgehog signaling. Moreover, grafting of ASCs treated with Shh-N resulted in significantly increased bone regeneration within the defect site. In conclusion, Hedgehog signaling enhances the osteogenic differentiation of mouse ASCs, at the expense of adipogenesis. These data suggest that Hedgehog signaling directs the lineage differentiation of mesodermal stem cells and represents a promising strategy for skeletal tissue regeneration.

Inflammation as death or life signal in diabetic fracture healing

Increased apoptosis of chondrocytes and osteoblasts and prolonged survival of osteoclasts lead to early destruction of callus tissue and impair bone remodeling in fracture healing of diabetic patients. Diabetes is accompanied by an increased inflammatory state, reactive oxygen species (ROS) generation and accumulation of advanced glycation end products (AGEs), a heterogenous group of toxic metabolites that can induce inflammation. Prolonged hyperglycemia and insulin resistance correlate with increased apoptosis rate and, accordingly, the proapoptotic role of several inflammatory mediators, ROS and AGEs has been also documented. In this review we summarize the most recent reports supporting the idea that inflammatory signaling increases chondrocyte and osteoblast death and prolongs osteoclast survival, resulting in impaired bone regeneration in diabetes. Antagonising inflammatory signal pathways and solution of inflammation may deserve greater attention in the management of diabetic fracture healing.

Osteogenic differentiation of bone marrow stromal cells on poly(epsilon-caprolactone) nanofiber scaffolds

Nanofiber poly(epsilon-caprolactone) (PCL) scaffolds were fabricated by electrospinning, and their ability to enhance the osteoblastic behavior of marrow stromal cells (MSCs) in osteogenic media was investigated. MSCs were isolated from Wistar rats and cultured on nanofiber scaffolds to assess short-term cytocompatibility and long-term phenotypic behavior. Smooth PCL substrates were used as control surfaces. The short-term cytocompatibility results indicated that nanofiber scaffolds supported greater cell adhesion and viability compared with control surfaces. In osteogenic conditions, MSCs cultured on nanofiber scaffolds also displayed increased levels of alkaline phosphatase activity for 3 weeks of culture. Calcium phosphate mineralization was substantially accelerated on nanofiber scaffolds compared to control surfaces as indicated through von Kossa and calcium staining, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Increased levels of intra- and extracellular levels of osteocalcin and osteopontin were observed on nanofiber scaffolds using immunofluorescence techniques after 3 weeks of culture. These results demonstrate the enhanced tissue regeneration property of nanofiber scaffolds, which may be of potential use for engineering osteogenic scaffolds for orthopedic applications.

Upregulation of heme oxygenase-1 inhibits the maturation and mineralization of osteoblasts

Heme-oxygenase-1 (HO-1), an important enzyme involved in vascular disease, transplantation, and inflammation, catalyzes the degradation of heme into carbon monoxide and biliverdin. It has been reported that overexpression of HO-1 inhibits osteoclastogenesis. However, the effect of HO-1 on osteoblast differentiation is still not clear. We here used adenoviral vector expressing recombinant human HO-1 and HO-1 inducer hemin to study the effects of HO-1 in primary cultured osteoblasts. The results showed that induction of HO-1 inhibited the maturation of osteoblasts including mineralized bone nodule formation, alkaline phosphatase activity and decreased mRNA expression of several differentiation markers such as alkaline phosphatase, osteocalcin, and RUNX2. Furthermore, downstream products of HO-1, bilirubin, carbon monoxide, and iron, are involved in the inhibitory action of HO-1. HO-1 can be induced by H(2)O(2), lipopolysaccharide and inflammatory cytokines such as TNF-alpha and IL-1beta in osteoblasts and also in STZ-induced diabetic mice. In addition, endogenous PPARgamma ligand, 15-deoxy-Delta(12,14)-prostaglandin-J2 (15d-PGJ2) markedly increased both mRNA and protein levels of HO-1 in osteoblasts via PI3K-Akt and MAPK pathways. Blockade of HO activity by ZnPP IX antagonized the inhibitory action on osteocalcin expression by hemin and 15d-PGJ2. Our results indicate that upregulation of HO-1 inhibits the maturation of osteoblasts and HO-1 may be involved in oxidative- or inflammation-induced bone loss.

Gene expression profiles in Atlantic salmon adipose-derived stromo-vascular fraction during differentiation into adipocytes

BACKGROUND

Excessive fat deposition is one of the largest problems faced by salmon aquaculture industries, leading to production losses due to high volume of adipose tissue offal. In addition, increased lipid accumulation may impose considerable stress on adipocytes leading to adipocyte activation and production and secretion of inflammatory mediators, as observed in mammals.

RESULTS

Microarray and qPCR analyses were performed to follow transcriptome changes during adipogenesis in the primary culture of adipose stromo-vascular fraction (aSVF) of Atlantic salmon. Cellular heterogeneity decreased by confluence as evidenced by the down-regulation of markers of osteo/chondrogenic, myogenic, immune and vasculature lineages. Transgelin (TAGLN), a marker of the multipotent pericyte, was prominently expressed around confluence while adipogenic PPARgamma was up-regulated already in subconfluent cells. Proliferative activity and subsequent cell cycle arrest were reflected in the fluctuations of pro- and anti-mitotic regulators. Marked regulation of genes involved in lipid and glucose metabolism and pathways producing NADPH and glycerol-3-phosphate (G3P) was seen during the terminal differentiation, also characterised by diverse stress responses. Activation of the glutathione and thioredoxin antioxidant systems and changes in the iron metabolism suggested the need for protection against oxidative stress. Signs of endoplasmic reticulum (ER) stress and unfolded protein response (UPR) occured in parallel with the increased lipid droplet (LD) formation and production of secretory proteins (adipsin, visfatin). The UPR markers XBP1 and ATF6 were induced together with genes involved in ubiquitin-proteasome and lysosomal proteolysis. Concurrently, translation was suppressed as evidenced by the down-regulation of genes encoding elongation factors and components of the ribosomal machinery. Notably, expression changes of a panel of genes that belong to different immune pathways were seen throughout adipogenesis. The induction of AP1 (Jun, Fos), which is a master regulator of stress responses, culminated by the end of adipogenesis, concurrent with the maximal observed lipid deposition.

CONCLUSIONS

Our data point to an intimate relationship between metabolic regulation and immune responses in white adipocytes of a cold-blooded vertebrate. Stress imposed on adipocytes by LD formation and expansion is prominently reflected in the ER compartment and the activated UPR response could have an important role at visceral obesity in fish.

Regulation of oligodendrocyte progenitor cell maturation by PPARδ: effects on bone morphogenetic proteins

In EAE (experimental autoimmune encephalomyelitis), agonists of PPARs (peroxisome proliferator-activated receptors) provide clinical benefit and reduce damage. In contrast with PPARγ, agonists of PPARδ are more effective when given at later stages of EAE and increase myelin gene expression, suggesting effects on OL (oligodendrocyte) maturation. In the present study we examined effects of the PPARδ agonist GW0742 on OPCs (OL progenitor cells), and tested whether the effects involve modulation of BMPs (bone morphogenetic proteins). We show that effects of GW0742 are mediated through PPARδ since no amelioration of EAE clinical scores was observed in PPARδ-null mice. In OPCs derived from E13 mice (where E is embryonic day), GW0742, but not the PPARγ agonist pioglitazone, increased the number of myelin-producing OLs. This was due to activation of PPARδ since process formation was reduced in PPARδ-null compared with wild-type OPCs. In both OPCs and enriched astrocyte cultures, GW0742 increased noggin protein expression; however, noggin mRNA was only increased in astrocytes. In contrast, GW0742 reduced BMP2 and BMP4 mRNA levels in OPCs, with lesser effects in astrocytes. These findings demonstrate that PPARδ plays a role in OPC maturation, mediated, in part, by regulation of BMP and BMP antagonists.

Mechanical loading regulates NFATc1 and beta-catenin signaling through a GSK3beta control node

Mechanical stimulation can prevent adipogenic and improve osteogenic lineage allocation of mesenchymal stem cells (MSC), an effect associated with the preservation of beta-catenin levels. We asked whether mechanical up-regulation of beta-catenin was critical to reduction in adipogenesis as well as other mechanical events inducing alternate MSC lineage selection. In MSC cultured under strong adipogenic conditions, mechanical load (3600 cycles/day, 2% strain) inactivated GSK3beta in a Wnt-independent fashion. Small interfering RNA targeting GSK3beta prevented both strain-induced induction of beta-catenin and an increase in COX2, a factor associated with increased osteoprogenitor phenotype. Small interfering RNA knockdown of beta-catenin blocked mechanical reduction of peroxisome proliferator-activated receptor gamma and adiponectin, implicating beta-catenin in strain inhibition of adipogenesis. In contrast, the effect of both mechanical and pharmacologic inhibition of GSK3beta on the putative beta-catenin target, COX2, was unaffected by beta-catenin knockdown. GSK3beta inhibition caused accumulation of nuclear NFATc1; mechanical strain increased nuclear NFATc1, independent of beta-catenin. NFATc1 knockdown prevented mechanical stimulation of COX2, implicating NFATc1 signaling. Finally, inhibition of GSK3beta caused association of RNA polymerase II with the COX2 gene, suggesting transcription initiation. These results demonstrate that mechanical inhibition of GSK3beta induces activation of both beta-catenin and NFATc1 signaling, limiting adipogenesis via the former and promoting osteoblastic differentiation via NFATc1/COX2. Our novel findings suggest that mechanical loading regulates mesenchymal stem cell differentiation through inhibition of GSK3beta, which in turn regulates multiple downstream effectors.

Superpulsed laser irradiation increases osteoblast activity via modulation of bone morphogenetic factors

BACKGROUND AND OBJECTIVE

Laser therapy is a new approach applicable in different medical fields when bone loss occurs, including orthopedics and dentistry. It has also been used to induce soft-tissue healing, for pain relief, bone, and nerve regeneration. With regard to bone synthesis, laser exposure has been shown to increase osteoblast activity and decrease osteoclast number, by inducing alkaline phosphatase (ALP), osteopontin, and bone sialoprotein expression. Studies have investigated the effects of continuous or pulsed laser irradiation, but no data are yet available on the properties of superpulsed laser irradiation. This study thus aimed to investigate the effect of superpulsed laser irradiation on osteogenic activity of human osteoblast-like cells, paying particular attention to investigating the molecular mechanisms underlying the effects of this type of laser radiation.

STUDY DESIGN/MATERIALS AND METHODS

Human osteoblast-like MG-63 cells were exposed to 3, 7, or 10 superpulsed laser irradiation (pulse width 200 nanoseconds, minimum peak power 45 W, frequency 30 kHz, total energy 60 J, exposure time 5 minutes). The following parameters were evaluated: cell growth and viability (light microscopy, lactate dehydrogenase release), calcium deposits (Alizarin Red S staining), expression of bone morphogenetic factors (real-time PCR).

RESULTS

Superpulsed laser irradiation decreases cell growth, induces expression of TGF-beta2, BMP-4, and BMP-7, type I collagen, ALP, and osteocalcin, and increases the size and the number of calcium deposits. The stimulatory effect is maximum on day 10, that is, after seven applications.

CONCLUSIONS

Reported results show that superpulsed laser irradiation, like the continuous and pulsed counterparts, possesses osteogenic properties, inducing the expression of molecules known to be important mediators of bone formation and, as a consequence, increasing calcium deposits in human MG-63 cells. Moreover, the data suggest a new potential role for PPARgamma as a regulator of osteoblast proliferation.

Thiazolidinedione-induced skeletal fragility--mechanisms and implications

Recent evidence suggests that the risk of several types of fracture is increased in type 2 diabetes mellitus (T2DM). Thiazolidinediones (TZDs) are now widely used in the management of T2DM, and their use may increase in other diseases characterized by insulin resistance. The PPAR-gamma, the molecular target of the TZDs currently in clinical use, is expressed in skeletal tissue. Evidence from preclinical studies has demonstrated that activation of PPAR-gamma (i) inhibits bone formation by diverting mesenchymal stem cells from the osteogenic to the adipocytic lineage and (ii) may increase bone resorption by stimulating the development of osteoclasts. There is also potential for indirect adverse skeletal effects of PPAR-gamma activation by modulation of circulating levels of hormones and cytokines known to influence bone metabolism. Recent studies in humans have demonstrated that TZDs decrease markers of bone formation decrease bone mass, and increase fracture rates, at least in women. The implication of these findings is that fracture risk should be considered in patients with T2DM for whom TZD therapy is being considered, and appropriate therapy instigated to prevent fractures in individuals ascertained to be at high risk.

Identification and expansion of human osteosarcoma-cancer-stem cells by long-term 3-aminobenzamide treatment

A novel cancer stem-like cell line (3AB-OS), expressing a number of pluripotent stem cell markers, was irreversibly selected from human osteosarcoma MG-63 cells by long-term treatment (100 days) with 3-aminobenzamide (3AB). 3AB-OS cells are a heterogeneous and stable cell population composed by three types of fibroblastoid cells, spindle-shaped, polygonal-shaped, and rounded-shaped. With respect to MG-63 cells, 3AB-OS cells are extremely smaller, possess a much greater capacity to form spheres, a stronger self-renewal ability and much higher levels of cell cycle markers which account for G1-S/G2-M phases progression. Differently from MG-63 cells, 3AB-OS cells can be reseeded unlimitedly without losing their proliferative potential. They show an ATP-binding cassette transporter ABCG2-dependent phenotype with high drug efflux capacity, and a strong positivity for CD133, marker for pluripotent stem cells, which are almost unmeasurable in MG-63 cells. 3AB-OS cells are much less committed to osteogenic and adipogenic differentiation than MG-63 cells and highly express genes required for maintaining stem cell state (Oct3/4, hTERT, nucleostemin, Nanog) and for inhibiting apoptosis (HIF-1alpha, FLIP-L, Bcl-2, XIAP, IAPs, and survivin). 3AB-OS may be a novel tumor cell line useful for investigating the mechanisms by which stem cells enrichment may be induced in a tumor cell line. The identification of a subpopulation of cancer stem cells that drives tumorigenesis and chemoresistance in osteosarcoma may lead to prognosis and optimal therapy determination. Expression patterns of stem cell markers, especially CD133 and ABCG2, may indicate the undifferentiated state of osteosarcoma tumors, and may correlate with unfavorable prognosis in the clinical setting.

Stimulation of osteogenic differentiation and inhibition of adipogenic differentiation in bone marrow stromal cells by alendronate via ERK and JNK activation

To elucidate the mechanism of the effect of bisphosphonates on bone metabolism, we investigated the effect of alendronate, a widely used bisphosphonate, on osteogenic and adipogenic differentiation in bone marrow stromal cells (BMSCs) derived from ovariectomized SD rats. Alendronate treatment not only increased the mRNA level of bone morphogenetic protein-2, runt-related transcription factor 2, osteopontin, bone sialoprotein, and alkaline phosphatase activity after osteogenic induction, but also decreased the mRNA level of peroxisome proliferator activated receptor gamma 2 and total droplet number indicated by Oil Red O staining after adipogenic induction. The effect of alendronate treatment was dose-dependent, and the difference of the osteogenic or the adipogenic potential between the treated group and the non-treated group was statistically significant (p<0.001). The MAPK-specific inhibitors, PD98059 and SP600125, but not the p38-specific inhibitor, blocked the alendronate-induced regulation of BMSC differentiation. Analysis of BMSCs induced in the presence of alendronate revealed an immediate increase in ERK and JNK phosphorylation. Taken together, these data suggest that alendronate acts on BMSCs to stimulate osteogenic differentiation and inhibit adipogenic differentiation in a dose-dependent manner; this effect is mediated via activating ERK and JNK.

The bone-adipose axis in obesity and weight loss

Body fat and lean mass are correlated with bone mineral density, with obesity apparently exerting protection against osteoporosis. The pathophysiological relevance of adipose tissue in bone integrity resides in the participation of adipokines in bone remodeling through effects on deposition and resorption. On the other hand, the skeleton has recently emerged as an endocrine organ with effects on body weight control and glucose homeostasis through the actions of bone-derived factors such as osteocalcin and osteopontin. The cross-talk between adipose tissue and the skeleton constitutes a homeostatic feedback system with adipokines and molecules secreted by osteoblasts and osteoclasts representing the links of an active bone-adipose axis. Given the impact of bariatric surgery on absorption and the adipokine secretory pattern, to focus on the changes taking place following surgical-induced weight loss on this dynamic system merits detailed consideration.

Regulation of the maturation of osteoblasts and osteoclastogenesis by glutamate

Glutamate, an important central excitatory neurotransmitter, is also secreted by osteoblasts and may be involved in the regulation of bone metabolism. Glutamate receptors for N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) are demonstrated in bone cells. Here we investigated the in vivo effects of glutamate by local injection of AMPA, NMDA, and their antagonists into tibia as well as their in vitro effects on the maturation of osteoblasts and formation of osteoclasts. AMPA receptor antagonist CNQX and NMDA receptor antagonist MK-801 significantly inhibited the maturation and mineralization of osteoblasts in high-glutamate alpha-MEM. On the other hand, AMPA and NMDA up-regulated the mineralized deposition and osteocalcin mRNA expression of primary osteoblasts cultured in glutamate-free DMEM. AMPA and NMDA induced the phosphorylation of extracellular signal-related kinases (ERK) in osteoblasts within 15 min. In addition, NMDA but not AMPA up-regulated the number of osteoclasts while MK801 antagonized this potentiating effect. To explore the action of glutamate agonists on bone formation in animal model, AMPA was locally injected into tibia and it was found that the bone volume in secondary spongiosa significantly increased and co-treatment of CNQX antagonized the enhancing effect of AMPA. These results suggest that glutamate may play a physiological role in regulating the maturation of osteoblasts and osteoclastogenesis. Activation of both AMPA and NMDA receptors regulates the maturation of osteoblasts. NMDA but not AMPA affects receptor for activation of NF-kappaB ligand (RANKL)-induced osteoclastogenesis.