HIF-1alpha regulates hypoxia-induced EP1 expression in osteoblastic cells

Prostaglandin Pathways: Opportunities for Cancer Prevention and Therapy

Because of profound effects observed in carcinogenesis, prostaglandins (PGs), prostaglandin-endoperoxide synthases, and PG receptors are implicated in cancer development and progression. Understanding the molecular mechanisms of PG actions has potential clinical relevance for cancer prevention and therapy. This review focuses on the current status of PG signaling pathways in modulating cancer progression and aims to provide insights into the mechanistic actions of PGs and their receptors in influencing tumor progression. We also examine several small molecules identified as having anticancer activity that target prostaglandin receptors. The literature suggests that targeting PG pathways could provide opportunities for cancer prevention and therapy.

MicroRNA-495 downregulates AQP1 and facilitates proliferation and differentiation of osteoblasts in mice with tibial fracture through activation of p38 MAPK signaling pathway

Osteoblasts are implicated in the building of the vertebrate skeleton. The current study aimed to investigate the role of microRNA-495 (miR-495) in the osteoblasts of mice with tibial fractures and the underlying mechanism involving in aquaporin-1 (AQP1) and the p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway. Initially, a microarray-based analysis was performed to screen the differentially expressed genes and miRNAs associated with tibial fracture. Following the establishment of a tibial fracture mouse model, the positive rate of the AQP1 protein in the fracture tissue was detected by immunohistochemistry (IHC). Next, to verify the binding site between miR-495 on AQP1, bioinformatics data were employed in addition to the application of a dual-luciferase reporter gene assay. The osteoblast cell line MC3T3-E1 was treated with miR-495 mimic, miR-495 inhibitor and Anisomycin to explore the potent effects of miR-495 on proliferation and differentiation of osteoblasts in mice with tibial fracture. The expression of miR-495, AQP1, p38 MAPK, PCNA, Cyclin D1, OCN, and OPN was subsequently evaluated by RT-qPCR and Western blot analysis. Cell viability, the number of calcium nodules and alkaline phosphatase (ALP) activity were detected by MTT assay, alizarin red staining, and ALP activity assay, respectively. Our results revealed that miR-495 was down-regulated while AQP1 was up-regulated in the mice with tibial fractures. AQP1 was verified as a target gene of miR-495. When the cells were treated with overexpressed miR-495 or activated p38 MAPK signaling pathway, elevated expression of PCNA, Cyclin, D1, OCN, and OPN along with an increased amount of calcium nodules, higher cell viability, and enhanced ALP activity was detected, while the expression of AQP1 was reduced. Collectively, the key findings of the present study support the notion that overexpressed miR-495 may activate the p38 MAPK signaling pathway to inhibit AQP1 and to promote the proliferation and differentiation of osteoblasts in mice with tibial fracture.

Probing the prostate tumour microenvironment II: Impact of hypoxia on a cell model of prostate cancer progression

Approximately one in six men are diagnosed with Prostate Cancer every year in the Western world. Although it can be well managed and non-life threatening in the early stages, over time many patients cease to respond to treatment and develop castrate resistant prostate cancer (CRPC). CRPC represents a clinically challenging and lethal form of prostate cancer. Progression of CRPC is, in part, driven by the ability of cancer cells to alter their metabolic profile during the course of tumourgenesis and metastasis so that they can survive in oxygen and nutrient-poor environments and even withstand treatment. This work was carried out as a continuation of a study aimed towards gaining greater mechanistic understanding of how conditions within the tumour microenvironment impact on both androgen sensitive (LNCaP) and androgen independent (LNCaP-abl and LNCaP-abl-Hof) prostate cancer cell lines. Here we have applied technically robust and reproducible label-free liquid chromatography mass spectrometry analysis for comprehensive proteomic profiling of prostate cancer cell lines under hypoxic conditions. This led to the identification of over 4,000 proteins - one of the largest protein datasets for prostate cancer cell lines established to date. The biological and clinical significance of proteins showing a significant change in expression as result of hypoxic conditions was established. Novel, intuitive workflows were subsequently implemented to enable robust, reproducible and high throughput verification of selected proteins of interest. Overall, these data suggest that this strategy supports identification of protein biomarkers of prostate cancer progression and potential therapeutic targets for CRPC.

Synergistic effects of dimethyloxallyl glycine and recombinant human bone morphogenetic protein-2 on repair of critical-sized bone defects in rats

In bone remodeling, osteogenesis is closely coupled to angiogenesis. Bone tissue engineering using multifunctional bioactive materials is a promising technique which has the ability to simultaneously stimulate osteogenesis and angiogenesis for repair of bone defects. We developed mesoporous bioactive glass (MBG)-doped poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) composite scaffolds as delivery vehicle. Two bioactive molecules, dimethyloxalylglycine (DMOG), a small-molecule angiogenic drug, and recombinant human bone morphogenetic protein-2 (rhBMP-2), an osteoinductive growth factor, were co-incorporated into the scaffold. The synergistic effects of DMOG and rhBMP-2 released in the composite scaffolds on osteogenic and angiogenic differentiation of hBMSCs were investigated using real-time quantitative polymerase chain reaction and western blotting. Moreover, in vivo studies were conducted to observe bone regeneration and vascular formation of critical-sized bone defects in rats using micro-computed tomography, histological analyses, Microfil^® perfusion, fluorescence labeling, and immunohistochemical analysis. The results showed that DMOG and rhBMP-2 released in the MBG-PHBHHx scaffolds did exert synergistic effects on the osteogenic and angiogenic differentiation of hBMSCs. Moreover, DMOG and rhBMP-2 produced significant increases in newly-formed bone and neovascularization of calvarial bone defects in rats. It is concluded that the co-delivery strategy of both rhBMP-2 and DMOG can significantly improve the critical-sized bone regeneration.

Hypoxia inhibits mineralization ability of human dental pulp cells treated with TEGDMA but increases cell survival in accordance with the culture time

OBJECTIVE

To evaluate the cytotoxicity and mineralization effects of TEGDMA in human dental pulp cells (hDPCs) under hypoxic and normoxic culture conditions.

DESIGN

Cell viability was evaluated using XTT assay after incubation periods of 24, 48, or 72h. The expression of mineralization-related genes (osteonectin, osteopontin, dentin sialophosphoprotein, collagen type 1) and heme oxygenase 1 (HO-1) was assessed by quantitative real-time polymerase chain reaction at 24 and 72h.

RESULTS

In XTT assay, viability was higher in 0.3, 1, 2, 4, and 5mM groups in the presence of 21% O₂ after 24h (p<0.05). Additionally, while 0.3, 1, 2mM groups had higher cell viability in the presence of 21% O₂ after 48h (p<0.05), in 3mM groups cell viability was higher under 3% O₂ than 21% O₂ after both 24 and 48h (p<0.05). 1-3mM groups had higher cell viability under 3% O₂ after 72h (p<0.05). There was no difference between 4 and 5mM groups with regards to cell viability after 48 or 72h (p>0.05). In the gene expression study, TEGDMA-treated hDPCs showed lower mineralization potential in the presence of 3% than with 21% O₂ (p<0.05). hDPCs revealed higher HO 1 expression in 0.3 and 1mM groups under hypoxic than under normoxic conditions after a 72-h time period (p<0.001).

CONCLUSIONS

Hypoxic conditions increased cell survival in accordance with the culture period but inhibited the odontoblastic differentiation of hDPCs treated with TEGDMA.

Prostaglandin dependent control of an endogenous estrogen receptor agonist by osteoblasts

Estrogen receptor (ER) activation has complex effects on bone cells, and loss of circulating estradiol adversely affects skeletal status in women. Hormone replacement therapy effectively circumvents bone loss after menopause, but enhances disease risk in other tissues. Here we show that prostaglandin E2 (PGE2) augments the activity of an osteoblast-derived selective ER modulator, ObSERM. The stimulatory effect of PGE2 is replicated in part by either the PG receptor EP3 agonist 17-phenyl trinor PGE2 or by the PG receptor FP agonist PGF2α⋅ Whereas activation of the various PG receptors induces multiple downstream signals, the response to PGE2 was mimicked by activators of protein kinase C, and suppressed by inhibition of protein kinase C but not by inhibition of protein kinase A. Moreover, inhibition of nitric oxide synthesis and activation of the PTH and Wnt pathways increases ObSERM activity. Our studies therefore reveal that ObSERM activity is controlled in distinct ways and revise our understanding of ER activation within bone by agents or events associated with PG expression. They also predict ways to sustain or improve bone formation, fracture repair, and surgical healing without adding the risk of disease in other tissues where ER activation also has important biological functions.

The effect of hypoxia on the stemness and differentiation capacity of PDLC and DPC

Introduction. Stem cells are regularly cultured under normoxic conditions. However, the physiological oxygen tension in the stem cell niche is known to be as low as 1-2% oxygen, suggesting that hypoxia has a distinct impact on stem cell maintenance. Periodontal ligament cells (PDLCs) and dental pulp cells (DPCs) are attractive candidates in dental tissue regeneration. It is of great interest to know whether hypoxia plays a role in maintaining the stemness and differentiation capacity of PDLCs and DPCs. Methods. PDLCs and DPCs were cultured either in normoxia (20% O₂) or hypoxia (2% O₂). Cell viability assays were performed and the expressions of pluripotency markers (Oct-4, Sox2, and c-Myc) were detected by qRT-PCR and western blotting. Mineralization, glycosaminoglycan (GAG) deposition, and lipid droplets formation were assessed by Alizarin red S, Safranin O, and Oil red O staining, respectively. Results. Hypoxia did not show negative effects on the proliferation of PDLCs and DPCs. The pluripotency markers and differentiation potentials of PDLCs and DPCs significantly increased in response to hypoxic environment. Conclusions. Our findings suggest that hypoxia plays an important role in maintaining the stemness and differentiation capacity of PDLCs and DPCs.

Delivery of dimethyloxallyl glycine in mesoporous bioactive glass scaffolds to improve angiogenesis and osteogenesis of human bone marrow stromal cells

Development of hypoxia-mimicking bone tissue engineering scaffolds is of great importance in stimulating angiogenesis for bone regeneration. Dimethyloxallyl glycine (DMOG) is a cell-permeable, competitive inhibitor of hypoxia-inducible factor prolyl hydroxylase (HIF-PH), which can stabilize hypoxia-inducible factor 1α (HIF-1α) expression. The aim of this study was to develop hypoxia-mimicking scaffolds by delivering DMOG in mesoporous bioactive glass (MBG) scaffolds and to investigate whether the delivery of DMOG could induce a hypoxic microenvironment for human bone marrow stromal cells (hBMSC). MBG scaffolds with varied mesoporous structures (e.g. surface area and mesopore volume) were prepared by controlling the contents of mesopore-template agent. The composition, large-pore microstructure and mesoporous properties of MBG scaffolds were characterized. The effect of mesoporous properties on the loading and release of DMOG in MBG scaffolds was investigated. The effects of DMOG delivery on the cell morphology, cell viability, HIF-1α stabilization, vascular endothelial growth factor (VEGF) secretion and bone-related gene expression (alkaline phosphatase, ALP; osteocalcin, OCN; and osteopontin, OPN) of hBMSC in MBG scaffolds were systematically investigated. The results showed that the loading and release of DMOG in MBG scaffolds can be efficiently controlled by regulating their mesoporous properties via the addition of different contents of mesopore-template agent. DMOG delivery in MBG scaffolds had no cytotoxic effect on the viability of hBMSC. DMOG delivery significantly induced HIF-1α stabilization, VEGF secretion and bone-related gene expression of hBMSC in MBG scaffolds in which DMOG counteracted the effect of HIF-PH and stabilized HIF-1α expression under normoxic condition. Furthermore, it was found that MBG scaffolds with slow DMOG release significantly enhanced the expression of bone-related genes more than those with instant DMOG release. The results suggest that the controllable delivery of DMOG in MBG scaffolds can mimic a hypoxic microenvironment, which not only improves the angiogenic capacity of hBMSC, but also enhances their osteogenic differentiation.

Facilitation of human osteoblast apoptosis by sulindac and indomethacin under hypoxic injury

Hypoxic-ischemia injury occurs after trauma causes consequential bone necrosis. Non-steroid anti-inflammatory drugs (NSAIDs) are frequently used in orthopedic clinics for pain relief. However, the underlying mechanism and outcome for usage of NSAIDs is poorly understood. To investigate the damage and loss of osteoblast function in hypoxia, two hypoxia mimetics, cobalt chloride (CoCl(2)) and desferrioxamine (DFO), were used to create an in vitro hypoxic microenvironment. The cell damage was observed by decreases of cell viability and increases in cyclooxygenase-2 and cleaved poly(ADP-ribose) polymerase (PARP). Cell apoptosis was confirmed by WST-1 cytotoxic assays and flow cytometry. The functional expression of osteoblast in alkaline phosphatase (ALP) activity was significantly decreased by CoCl(2) and inhibited when treated with DFO. To simulate the use of NSAID after hypoxic injury, four types of anti-inflammatory drugs, sulindac sulfide (SUL), indomethacin (IND), aspirin (Asp), and sodium salicylate (NaS), were applied to osteoblasts after 1 h of hypoxia mimetic treatment. SUL and IND further enhanced cell death after hypoxia. ALP activity was totally abolished in hypoxic osteoblasts under IND treatment. Facilitation of osteoblast apoptosis occurred regardless of IND dosage under hypoxic conditions. To investigate osteoblast in vivo, local hypoxia was created by fracture of tibia and then treated the injured mice with IND by oral feeding. IND-induced osteoblast apoptosis was confirmed by positive staining of TUNEL assay in fractured mice. Significant delay of fracture healing in bone tissue was also observed with the treatment of IND. These results provide information pertaining to choosing appropriate anti-inflammatory drugs for orthopedic patients.

ANGPTL4 induction by prostaglandin E2 under hypoxic conditions promotes colorectal cancer progression

Prostaglandin E(2) (PGE(2)), the most abundant COX-2-derived prostaglandin found in colorectal cancer, promotes tumor cell proliferation and survival via multiple signaling pathways. However, the role of PGE(2) in tumor hypoxia is not well understood. Here, we show a synergistic effect of PGE(2) and hypoxia on enhancing angiopoietin-like protein 4 (ANGPTL4) expression and that elevation of ANGPTL4 promotes colorectal cancer growth. PGE(2) induces ANGPTL4 expression at both the mRNA and protein levels under hypoxic conditions. Moreover, hypoxia induces one of the PGE(2) receptors, namely EP1. Activation of EP1 enhances ANGPTL4 expression, whereas blockage of EP1 by an antagonist inhibits PGE(2) induction of ANGPTL4 under hypoxic conditions. Importantly, overexpression of ANGPTL4 promotes cell proliferation and tumor growth in vitro and in vivo. In addition, treatment with ANGPTL4 recombinant protein increases colorectal carcinoma cell proliferation through effects on STAT1 signaling. The MAP kinase and Src pathways mediate ANGPTL4-induced STAT1 expression and activation. These results are relevant to human disease because we found that the expression of ANGPTL4 and STAT1 are elevated in 50% of human colorectal cancers tested and there is a positive correlation between COX-2 and ANGPTL4 as well STAT1 expression in colorectal carcinomas. Collectively, these findings suggest that PGE(2) plays an important role in promoting cancer cell proliferation via ANGPTL4 under hypoxic conditions.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Hypoxia increases Annexin A2 expression in osteoblastic cells via VEGF and ERK

Vascular endothelial growth factor (VEGF)-stimulated angiogenesis is critical for endochondral ossification that occurs during bone development and bone repair. Under these circumstances, VEGF production appears to be driven by low oxygen tension, under the control of the hypoxia-inducible factor-α family of transcription factors (HIF-α). Annexin 2 (AnxA2) a calcium-dependent phospholipid binding protein has been implicated in VEGF-mediated retinal neovascularization and is upregulated by VEGF in choroid retinal endothelial cells. AnxA2 is also expressed in cells of the osteoblast lineage and chondrocytes and may play a role in matrix mineralization. In this paper, we examined the effects of hypoxia (1% O(2)) and VEGF on the expression of AnxA2 in osteoblastic MC3T3-E1 cells. Hypoxia, desferrioxamine (hypoxia mimetic), and recombinant VEGF all increased AnxA2 mRNA and protein levels in osteoblastic cells. The hypoxia-induced increase in AnxA2 was inhibited by a blocking antibody to VEGF-R1; however, VEGF(120), a VEGF-R1 agonist, demonstrated no influence upon Anxa2 expression. This suggests that VEGF induction of Annexin A2 is not mediated via VEGF-R1 agonism alone but by VEGF-R1 and Neuropilin-1 or Neuropilin-2 heterodimers. In addition, we demonstrated that VEGF-stimulated changes in AnxA2 expression via a pathway involving Src and MEK kinase. These data demonstrate that AnxA2 expression in osteoblasts is under the control of VEGF, which may have implications for both angiogenesis and bone mineralization under low oxygen conditions.

Hydroxylase inhibition attenuates colonic epithelial secretory function and ameliorates experimental diarrhea

Hydroxylases are oxygen-sensing enzymes that regulate cellular responses to hypoxia. Transepithelial Cl(-) secretion, the driving force for fluid secretion, is dependent on O(2) availability for generation of cellular energy. Here, we investigated the role of hydroxylases in regulating epithelial secretion and the potential for targeting these enzymes in treatment of diarrheal disorders. Ion transport was measured as short-circuit current changes across voltage-clamped monolayers of T(84) cells and mouse colon. The antidiarrheal efficacy of dimethyloxallyl glycine (DMOG) was tested in a mouse model of allergic disease. Hydroxylase inhibition with DMOG attenuated Ca(2+)- and cAMP-dependent secretory responses in voltage-clamped T(84) cells to 20.2 ± 2.6 and 38.8 ± 6.7% (n=16; P≤0.001) of those in control cells, respectively. Antisecretory actions of DMOG were time and concentration dependent, being maximal after 18 h of DMOG (1 mM) treatment. DMOG specifically inhibited Na(+)/K(+)-ATPase pump activity without altering its expression or membrane localization. In mice, DMOG inhibited agonist-induced secretory responses ex vivo and prevented allergic diarrhea in vivo. In conclusion, hydroxylases are important regulators of epithelial Cl(-) and fluid secretion and present a promising target for development of new drugs to treat transport disorders.

Betacellulin inhibits osteogenic differentiation and stimulates proliferation through HIF-1alpha

Cellular signaling via epidermal growth factor (EGF) and EGF-like ligands can determine cell fate and behavior. Osteoblasts, which are responsible for forming and mineralizing osteoid, express EGF receptors and alter rates of proliferation and differentiation in response to EGF receptor activation. Transgenic mice over-expressing the EGF-like ligand betacellulin (BTC) exhibit increased cortical bone deposition; however, because the transgene is ubiquitously expressed in these mice, the identity of cells affected by BTC and responsible for increased cortical bone thickness remains unknown. We have therefore examined the influence of BTC upon mesenchymal stem cell (MSC) and pre-osteoblast differentiation and proliferation. BTC decreases the expression of osteogenic markers in both MSCs and pre-osteoblasts; interestingly, increases in proliferation require hypoxia-inducible factor-alpha (HIF-alpha), as an HIF antagonist prevents BTC-driven proliferation. Both MSCs and pre-osteoblasts express EGF receptors ErbB1, ErbB2, and ErbB3, with no change in expression under osteogenic differentiation. These are the first data that demonstrate an influence of BTC upon MSCs and the first to implicate HIF-alpha in BTC-mediated proliferation.

Betacellulin inhibits osteogenic differentiation and stimulates proliferation through HIF-1alpha

Cellular signaling via epidermal growth factor (EGF) and EGF-like ligands can determine cell fate and behavior. Osteoblasts, which are responsible for forming and mineralizing osteoid, express EGF receptors and alter rates of proliferation and differentiation in response to EGF receptor activation. Transgenic mice over-expressing the EGF-like ligand betacellulin (BTC) exhibit increased cortical bone deposition; however, because the transgene is ubiquitously expressed in these mice, the identity of cells affected by BTC and responsible for increased cortical bone thickness remains unknown. We have therefore examined the influence of BTC upon mesenchymal stem cell (MSC) and pre-osteoblast differentiation and proliferation. BTC decreases the expression of osteogenic markers in both MSCs and pre-osteoblasts; interestingly, increases in proliferation require hypoxia-inducible factor-alpha (HIF-α), as an HIF antagonist prevents BTC-driven proliferation. Both MSCs and pre-osteoblasts express EGF receptors ErbB1, ErbB2, and ErbB3, with no change in expression under osteogenic differentiation. These are the first data that demonstrate an influence of BTC upon MSCs and the first to implicate HIF-α in BTC-mediated proliferation.