Different effects of glucose starvation on expression and stability of VEGF mRNA isoforms in murine ovarian cancer cells

Application of RNA subcellular fraction estimation method to explore RNA localization regulation

RNA localization is involved in multiple biological processes. Recent advances in subcellular fractionation-based sequencing approaches uncovered localization pattern on a global scale. Most of existing methods adopt relative localization ratios (such as ratios of separately normalized transcripts per millions of different subcellular fractions without considering the difference in total RNA abundances in different fractions), however, absolute ratios may yield different results on the preference to different cellular compartment. Experimentally, adding external Spike-in RNAs to different fractionation can be used to obtain absolute ratios. In addition, a spike-in independent computational approach based on multiple linear regression model can also be used. However, currently, no custom tool is available. To solve this problem, we developed a method called subcellular fraction abundance estimator to correctly estimate relative RNA abundances of different subcellular fractionations. The ratios estimated by our method were consistent with existing reports. By applying the estimated ratios for different fractions, we explored the RNA localization pattern in cell lines and also predicted RBP motifs that were associated with different localization patterns. In addition, we showed that different isoforms of same genes could exhibit distinct localization patterns. To conclude, we believed our tool will facilitate future subcellular fractionation-related sequencing study to explore the function of RNA localization in various biological problems.

Exploring the clinical value of tumor microenvironment in platinum-resistant ovarian cancer

Platinum resistance in epithelial ovarian cancer (OvCa) is rising at an alarming rate, with recurrence of chemo-resistant high grade serous OvCa (HGSC) in roughly 75 % of all patients. Additionally, HGSC has an abysmal five-year survival rate, standing at 39 % and 17 % for FIGO stages III and IV, respectively. Herein we review the crucial cellular interactions between HGSC cells and the cellular and non-cellular components of the unique peritoneal tumor microenvironment (TME). We highlight the role of the extracellular matrix (ECM), ascitic fluid as well as the mesothelial cells, tumor associated macrophages, neutrophils, adipocytes and fibroblasts in platinum-resistance. Moreover, we underscore the importance of other immune-cell players in conferring resistance, including natural killer cells, myeloid-derived suppressive cells (MDSCs) and T-regulatory cells. We show the clinical relevance of the key platinum-resistant markers and their correlation with the major pathways perturbed in OvCa. In parallel, we discuss the effect of immunotherapies in re-sensitizing platinum-resistant patients to platinum-based drugs. Through detailed analysis of platinum-resistance in HGSC, we hope to advance the development of more effective therapy options for this aggressive disease.

Exercise as Adjunct Therapy in Cancer

Data from observational studies indicate that both physical activity as well as exercise (ie, structured physical activity) is associated with reductions in the risk of recurrence and cancer mortality after a diagnosis of certain forms of cancer. Emerging evidence from preclinical studies indicates that physical activity/exercise paradigms regulate intratumoral vascular maturity and perfusion, hypoxia, and metabolism and augments the antitumor immune response. Such responses may, in turn, enhance response to standard anticancer treatments. For instance, exercise improves efficacy of chemotherapeutic agents, and there is rationale to believe that it will also improve radiotherapy response. This review overviews the current preclinical as well as clinical evidence supporting exercise modulation of therapeutic response and postulated biological mechanisms underpinning such effects. We also examine the implications for tumor response to radiation, chemotherapy, and immunotherapy.

Endothelial Cell Metabolism

Endothelial cells (ECs) are more than inert blood vessel lining material. Instead, they are active players in the formation of new blood vessels (angiogenesis) both in health and (life-threatening) diseases. Recently, a new concept arose by which EC metabolism drives angiogenesis in parallel to well-established angiogenic growth factors (e.g., vascular endothelial growth factor). 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3-driven glycolysis generates energy to sustain competitive behavior of the ECs at the tip of a growing vessel sprout, whereas carnitine palmitoyltransferase 1a-controlled fatty acid oxidation regulates nucleotide synthesis and proliferation of ECs in the stalk of the sprout. To maintain vascular homeostasis, ECs rely on an intricate metabolic wiring characterized by intracellular compartmentalization, use metabolites for epigenetic regulation of EC subtype differentiation, crosstalk through metabolite release with other cell types, and exhibit EC subtype-specific metabolic traits. Importantly, maladaptation of EC metabolism contributes to vascular disorders, through EC dysfunction or excess angiogenesis, and presents new opportunities for anti-angiogenic strategies. Here we provide a comprehensive overview of established as well as newly uncovered aspects of EC metabolism.

Competitive binding between Seryl-tRNA synthetase/YY1 complex and NFKB1 at the distal segment results in differential regulation of human vegfa promoter activity during angiogenesis

Vascular endothelial growth factor (VEGF) plays a pivotal role in angiogenesis. Previous studies focused on transcriptional regulation modulated by proximal upstream cis-regulatory elements (CREs) of the human vegfa promoter. However, we hypothesized that distal upstream CREs may also be involved in controlling vegfa transcription. In this study, we found that the catalytic domain of Seryl-tRNA synthetase (SerRS) interacted with transcription factor Yin Yang 1 (YY1) to form a SerRS/YY1 complex that negatively controls vegfa promoter activity through binding distal CREs at -4654 to -4623 of vegfa. Particularly, we demonstrated that the -4654 to -4623 segment, which predominantly controls vegfa promoter activity, is involved in competitive binding between SerRS/YY1 complex and NFKB1. We further showed that VEGFA protein and blood vessel development were reduced by overexpression of either SerRS or YY1, but enhanced by the knockdown of either SerRS or yy1. In contrast, these same parameters were enhanced by overexpression of NFKB1, but reduced by knockdown of nfkb1. Therefore, we suggested that SerRS does not bind DNA directly but form a SerRS/YY1 complex, which functions as a negative effector to regulate vegfa transcription through binding at the distal CREs; while NFKB1 serves as a positive effector through competing with SerRS/YY1 binding at the overlapping CREs.

Neurovascular crosstalk between interneurons and capillaries is required for vision

Functional interactions between neurons, vasculature, and glia within neurovascular units are critical for maintenance of the retina and other CNS tissues. For example, the architecture of the neurosensory retina is a highly organized structure with alternating layers of neurons and blood vessels that match the metabolic demand of neuronal activity with an appropriate supply of oxygen within perfused blood. Here, using murine genetic models and cell ablation strategies, we have demonstrated that a subset of retinal interneurons, the amacrine and horizontal cells, form neurovascular units with capillaries in 2 of the 3 retinal vascular plexuses. Moreover, we determined that these cells are required for generating and maintaining the intraretinal vasculature through precise regulation of hypoxia-inducible and proangiogenic factors, and that amacrine and horizontal cell dysfunction induces alterations to the intraretinal vasculature and substantial visual deficits. These findings demonstrate that specific retinal interneurons and the intraretinal vasculature are highly interdependent, and loss of either or both elicits profound effects on photoreceptor survival and function.

VEGF189 expression is highly related to adaptation of the plateau pika (Ochotona curzoniae) inhabiting high altitudes

The plateau pika (Ochotona curzonia) has adapted to high-altitude hypoxia during evolution. Higher microvessel density in specific tissues and a blunted hypoxic pulmonary vasoconstriction response are the critical components of this adaptation. VEGF, vascular endothelial growth factor, has proved to be a key regulator of angiogenesis in response to tissue hypoxia and to play an important role in vascular vasodilation. However, the role of VEGF in adaptation to high-altitude hypoxia in the plateau pika remains unknown. In this study, we cloned cDNAs for VEGF165 and VEGF189 and examined their expression in pikas inhabiting altitudes of 3200 and 4750 m. Phylogenetic analysis reveals that pika VEGF165 and VEGF189 are evolutionarily conserved. Real-time PCR analysis demonstrates that VEGF165 and VEGF189 display tissue and altitude-specific expression patterns. Interestingly, we found that the levels of VEGF189 mRNA are significantly higher than those of VEGF165 in the brain and muscle tissues of the pika, which is different from what was previously observed in sea-level mammals. VEGF189 mRNA levels in brain, muscle, and lung of the pika increased with increased habitat altitude, whereas VEGF165 shows less change. Our study suggests an important role for VEGF189 in adaptation to hypoxia by the plateau pika in the high-altitude environment.

MEPE is a novel regulator of growth plate cartilage mineralization

Matrix extracellular phosphoglycoprotein (MEPE) belongs to the SIBLING protein family which play key roles in biomineralization. Although the growth plates of MEPE-overexpressing mice display severe morphological disruption, the expression and function of MEPE in growth plate matrix mineralization remains largely undefined. Here we show MEPE and its cleavage product, the acidic serine aspartate-rich MEPE-associated motif (ASARM) peptide, to be localised to the hypertrophic zone of the growth plate. We also demonstrate that the phosphorylated (p)ASARM peptide inhibits ATDC5 chondrocyte matrix mineralization. Stable MEPE-overexpressing ATDC5 cells also had significantly reduced matrix mineralization in comparison to the control cells. Interestingly, we show that the addition of the non-phosphorylated (np)ASARM peptide promoted mineralization in the ATDC5 cells. The peptides and the overexpression of MEPE did not affect the differentiation of the ATDC5 cells. For a more physiologically relevant model, we utilized the metatarsal organ culture model. We show the pASARM peptide to inhibit mineralization at two stages of development, as shown by histological and μCT analysis. Like in the ATDC5 cells, the peptides did not affect the differentiation of the metatarsals indicating that the effects seen on mineralization are direct, as is additionally confirmed by no change in alkaline phosphatase activity or mRNA expression. In the metatarsal organ cultures, the pASARM peptide also reduced endothelial cell markers and vascular endothelial growth factor mRNA expression. Taken together these results show MEPE to be an important regulator of growth plate chondrocyte matrix mineralization through its cleavage to an ASARM peptide.

Do anti-angiogenic VEGF (VEGFxxxb) isoforms exist? A cautionary tale

Splicing of the human vascular endothelial growth factor-A (VEGF-A) gene has been reported to generate angiogenic (VEGFxxx) and anti-angiogenic (VEGFxxxb) isoforms. Corresponding VEGFxxxb isoforms have also been reported in rat and mouse. We examined VEGFxxxb expression in mouse fibrosarcoma cell lines expressing all or individual VEGF isoforms (VEGF120, 164 or 188), grown in vitro and in vivo, and compared results with those from normal mouse and human tissues. Importantly, genetic construction of VEGF164 and VEGF188 expressing fibrosarcomas, in which exon 7 is fused to the conventional exon 8, precludes VEGFxxxb splicing from occurring. Thus, these two fibrosarcoma cell lines provided endogenous negative controls. Using RT-PCR we show that primers designed to simultaneously amplify VEGFxxx and VEGFxxxb isoforms amplified only VEGFxxx variants in both species. Moreover, only VEGFxxx species were generated when mouse podocytes were treated with TGFβ-1, a reported activator of VEGFxxxb splice selection in human podocytes. A VEGF164/120 heteroduplex species was identified as a PCR artefact, specifically in mouse. VEGFxxxb isoform-specific PCR did amplify putative VEGFxxxb species in mouse and human tissues, but unexpectedly also in VEGF188 and VEGF164 fibrosarcoma cells and tumours, where splicing to produce true VEGFxxxb isoforms cannot occur. Moreover, these products were only consistently generated using reverse primers spanning more than 5 bases across the 8b/7 or 8b/5 splice junctions. Primer annealing to VEGFxxx transcripts and amplification of exon 8b primer ‘tails’ explained the artefactual generation of VEGFxxxb products, since the same products were generated when the PCR reactions were performed with cDNA from VEGF164/VEGF188 ‘knock-in’ vectors used in the generation of single VEGF isoform-expressing transgenic mice from which the fibrosarcoma lines were developed. Collectively, our results highlight important pitfalls in data interpretation associated with detecting VEGFxxxb isoforms using current methods, and demonstrate that anti-angiogenic isoforms are not commonly expressed in mouse or human tissues.

Adhesion to substrates induces dendritic cell endothelization and decreases immunological response

Dendritic cells (DCs) are antigen presenting cells capable of inducing specific immune responses against microbial infections, transplant antigens, or tumors. DCs have been shown to possess a high plasticity showing different phenotypes in response to their microenvironment. For example, tumor-associated DCs can acquire an angiogenic phenotype thus promoting tumor growth. Further, DCs cultured in vitro under different conditions are able to upregulate the expression of endothelial markers and to express angiogenic factors. Indeed, it has been shown that soluble factors such as VEGF of PGE-2, that are present in the microenvironment of several tumors, affect the biology of these cells. We hypothesize that in addition to soluble factors the adhesion to different substrates will also define the phenotype and function of DCs. Herewith we demonstrate that murine myeloid(m) DCs upregulate endothelial markers such as VE-Cadherin, and to a lesser extent TIE-2, and decrease their immune capabilities when cultured on solid surfaces as compared with the same cells cultured on ultra-low binding (ULB) surfaces. On the other hand, the expression of angiogenic molecules at the level of RNA was not different among these cultures. In order to further investigate this phenomenon we used the murine ID8 model of ovarian cancer which can generate solid tumors when cancer cells are injected subcutaneously or a malignant ascites when they are injected intraperitoneally. This model gave us the unique opportunity to investigate DCs in suspension or attached to solid surfaces under the influence of the same tumor cells. We were able to determine that DCs present in solid tumors showed higher levels of expression of endothelial markers and angiogenic molecules but were not able to respond to inflammatory stimuli at the same extent as DCs recovered from ascites. Moreover, mDCs cultured on ULB surfaces in the presence of tumor factors do not expressed endothelial markers. Taking into account all these data we consider that tumor factors might be responsible for inducing angiogenic properties in DCs, but that in some settings the expression of endothelial markers such as VE-Cadherin and TIE-2 might be a function of attachment to solid surfaces and independent of the angiogenic properties of these cells.

Angiogenesis and the tumor vasculature as antitumor immune modulators: the role of vascular endothelial growth factor and endothelin

Cancer immunotherapies have yielded promising results in recent years, but new approaches must be utilized if more patients are to experience the benefits of these therapies. Angiogenesis and the tumor endothelium confer unique immune privilege to a growing tumor, with significant effects on diverse immunological processes such as hematopoietic cell maturation, antigen presentation, effector T cell differentiation, cytokine production, adhesion, and T cell homing and extravasation. Here, we review the role of angiogenesis and the tumor endothelium on regulation of the antitumor immune response. We place particular emphasis on the role of vascular endothelial growth factor (VEGF) in the suppression of numerous immunological processes that control tumor progression. Further, we describe the unique crosstalk between the VEGF and endothelin systems, and how their interactions may shape the antitumor immune response. These insights establish new targets for combinatorial approaches to modify existing cancer immunotherapies.

The interplay between surfaces and soluble factors define the immunologic and angiogenic properties of myeloid dendritic cells

BACKGROUND

Dendritic cells (DCs) are antigen presenting cells capable of inducing specific immune responses against microbial infections, transplant antigens, or tumors. Interestingly, microenvironment conditions such as those present in tumor settings might induce a DC phenotype that is poorly immunogenic and with the capability of promoting angiogenesis. We hypothesize that this plasticity may be caused not only by the action of specific cytokines or growth factors but also by the properties of the surfaces with which they interact, such as extracellular matrix (ECM) components.

RESULTS

Herewith we studied the effect of different surfaces and soluble factors on the biology of DCs. To accomplish this, we cultured murine myeloid(m) DCs on surfaces coated with fibronectin, collagen I, gelatin, and Matrigel using poly-D-lysine and polystyrene as non-biological surfaces. Further, we cultured these cells in the presence of regular DC medium (RPMI 10% FBS) or commercially available endothelial medium (EGM-2). We determined that mDCs could be kept in culture up to 3 weeks in these conditions, but only in the presence of GM-CSF. We were able to determine that long-term DC cultures produce an array of angiogenic factors, and that some of these cultures still retain the capability to induce T cell responses.

CONCLUSIONS

Altogether these data indicate that in order to design DC-based vaccines or treatments focused on changing the phenotype of DCs associated with diseases such as cancer or atherosclerosis, it becomes necessary to fully investigate the microenvironment in which these cells are present or will be delivered.

Dexamethasone pre-treatment protects brain against hypoxic-ischemic injury partially through up-regulation of vascular endothelial growth factor A in neonatal rats

Dexamethasone (Dex) provides neuroprotection against subsequent hypoxia ischemia (HI) in newborn rats, but the mechanism of this neuroprotection is not well understood. It is known that vascular endothelial growth factor A (VEGF) has neuroprotective effects. The objective of this study was to evaluate the role of the VEGF signaling pathway in the Dex-induced neuroprotection in newborn rats. Seven-day-old rat pups had the right carotid artery permanently ligated followed by 140 or 160 min of hypoxia (8% oxygen). Rat pups received two i.p. injections of either saline or Dex (0.25 mg/kg) at 24 and 4 h before HI exposure. To quantify the effects of a glucocorticoid receptor (GR) blocker, on postnatal day (PD) 6 and 15 min prior to Dex treatment rat pups received s.c. vehicle or RU486 (GR blocker, 60 mg/kg). After 24 h at PD 7, all rat pups had HI as described earlier. To quantify the effects of a VEGFR 2 blocker, at 24 h after Dex/Veh treatment (PD7), SU5416, a VEGFR 2 inhibitor or vehicle was injected intracerebroventricularly in the right hemisphere at 30 min before and 2 h after HI. Dex pre-treatment reduced brain injury and enhanced the HI-induced brain VEGF protein while a GR blocker inhibited these effects. Treatment with VEGFR 2 blocker decreased Dex-induced neuroprotection also. Dex pre-treatment enhanced the HI-induced increase in mRNA expression of VEGF splice variants and decreased the HI-induced reduction of Akt phosphorylation. Additionally, it also decreased HI-induced increase of caspase-3 activity and DNA fragments in neonatal rat brain. We conclude that Dex provides robust neuroprotection against subsequent HI in newborn rats via GR likely with the partial involvement of VEGF signaling pathway.

Vascular endothelial growth factor-A isoform and (co)receptor expression are differentially regulated by 17β-oestradiol in the ovariectomised mouse uterus

The angiogenic effects of 17β-oestradiol (E2) in the mouse endometrium are mediated by vascular endothelial growth factor-A (VEGFA). We analysed the temporal and spatial changes in VEGFA isoform and (co)receptor expression in ovariectomised mouse uteri following E2 treatment. VEGFA isoform and receptor mRNA were quantified in whole uterine tissue collected 2, 6, 12 and 24 h after E2 or vehicle treatment. Laser capture microdissection was used to investigate mRNA expression in epithelial, stromal and myometrial tissues separately. Endothelial cell proliferation, VEGFA and VEGF receptor-2 (VEGFR2) protein were visualised using immunohistochemistry. Endometrial endothelial cell proliferation was only observed 24 h after E2 treatment. In whole uterine tissue, total Vegfa, Vegfa164 and Vegfa120 mRNA expression increased 2 h post E2 treatment, and then decreased by 24 h. Vegfa188 expression was lower in E2-treated animals at all time points relative to control animals. Vegfr2 and neuropilin-1 (Nrp1) mRNA expression did not change following E2 treatment; Nrp2 expression decreased by 24 h. When uterine compartments were considered separately at 24 h post E2 or vehicle, stromal Vegfa120, Vegfa188 and Vegfr2 mRNA expression and myometrial Vegfa120 and Vegfa188 mRNA expression were reduced in E2-treated mice relative to controls, whereas epithelial Vegfa188 mRNA expression increased. The highest VEGFA immunoexpression was observed in luminal epithelium; expression increased at 24 h relative to other time points. No changes were noted in VEGFR2 immunoexpression among treatment groups. We have provided the first evidence that VEGFA isoform and receptor mRNA expression are differentially regulated by E2 in different uterine cell compartments.

Astrocyte-derived vascular endothelial growth factor stabilizes vessels in the developing retinal vasculature

Vascular endothelial growth factor (VEGF) plays a critical role in normal development as well as retinal vasculature disease. During retinal vascularization, VEGF is most strongly expressed by not yet vascularized retinal astrocytes, but also by retinal astrocytes within the developing vascular plexus, suggesting a role for retinal astrocyte-derived VEGF in angiogenesis and vessel network maturation. To test the role of astrocyte-derived VEGF, we used Cre-lox technology in mice to delete VEGF in retinal astrocytes during development. Surprisingly, this only had a minor impact on retinal vasculature development, with only small decreases in plexus spreading, endothelial cell proliferation and survival observed. In contrast, astrocyte VEGF deletion had more pronounced effects on hyperoxia-induced vaso-obliteration and led to the regression of smooth muscle cell-coated radial arteries and veins, which are usually resistant to the vessel-collapsing effects of hyperoxia. These results suggest that VEGF production from retinal astrocytes is relatively dispensable during development, but performs vessel stabilizing functions in the retinal vasculature and might be relevant for retinopathy of prematurity in humans.

Differential expression of vascular endothelial growth factor-A isoforms in the mouse uterus during early pregnancy

While vascular endothelial growth factor (VEGF)-A mediates endometrial vascular remodelling during early pregnancy in mice, individual VEGF-A isoforms have not been investigated, despite their different biological properties. Using mice as a model, the expression of VEGF-A isoforms and receptors in the mouse uterus during early pregnancy was quantified. It was postulated that selected isoform expression would increase concurrent with increased endometrial endothelial cell proliferation at this time. Uteri were collected on days 1-5 of pregnancy and mRNA expression was quantified by quantitative reverse-transcription polymerase chain reaction, VEGF-A protein by Western blot and VEGF receptor (VEGFR)-2 by immunohistochemistry. The lowest expression of isomers Vegf(120) and Vegf(164) was observed on day 2 of pregnancy, increasing thereafter. Vegfr-2 mRNA expression was significantly higher on days 3-5 of pregnancy relative to days 1-2 (P<0.05). No significant changes were noted in Vegf(188), Nrp1 or Nrp2 mRNA. VEGF(188) protein expression was consistently higher than other isoforms. These data demonstrate differential regulation of VEGF-A isoforms in mouse uterus during early pregnancy.

Molecular blockade of VEGFR2 in human epithelial ovarian carcinoma cells

Human epithelial ovarian cancer (EOC) is the most lethal neoplasm affecting the female genital tract, and is characterized by overexpression of vascular endothelial growth factor (VEGF) and growth as ascites. Anti-VEGF strategies are currently used in EOC therapy with promising results; however, molecular targeting of specific VEGF receptors on the cancer cells themselves has not been explored to date. We previously showed that activation of a VEGF/VEGFR2 signaling loop in EOC cells supports their survival in suspension, and short-term pharmacological inhibition of this loop increased EOC cell apoptosis in vitro. In this study, we stably knocked down VEGFR2 in OVCAR-3 and SKOV-3 EOC cells using short hairpin RNA (shRNA), an RNA interference strategy that could potentially overcome chemoresistance arising with angiogenic inhibitors. Unexpectedly, we observed an induction of more aggressive cellular behavior in transfected cells, leading to increased growth in mouse xenografts, enhanced accumulation of ascites, increased VEGF and neuropilin-1 (NRP-1) expression, and decreased expression of adhesion proteins, notably cadherins and integrins. Sonic hedgehog (SHH) pathways do not seem to be involved in the upregulation of NRP-1 message in VEGFR2 knockdown cells. Supporting our mouse model, we also found a significant increase in the ratio between NRP-1 and VEGFR2 with increasing tumor grade in 80 cases of human EOC. The change in EOC behavior that we report in this study occurred independent of the angiogenic response and shows the direct effect of VEGF blockade on the cancer cells themselves. Our findings highlight the possible confounding events that may affect the usefulness of RNAi in a therapeutic setting for disrupting EOC cell survival in ascites.

Hypoxic preconditioning provides neuroprotection and increases vascular endothelial growth factor A, preserves the phosphorylation of Akt-Ser-473 and diminishes the increase in caspase-3 activity in neonatal rat hypoxic-ischemic model

Vascular endothelial growth factor A (VEGF) likely plays a role in the hypoxic preconditioning (PC) induced tolerance to subsequent hypoxic-ischemic (HI) injury to the brain. However, limited data is available concerning VEGF in the developing brain after HI following PC. Neuroprotection by VEGF involves activation of Akt which inhibits apoptotic processes that contribute significantly to the brain injury in neonatal HI. We evaluated whether PC provides neuroprotection and affects VEGF, Akt and caspase-3 following HI in the developing rat brain. Newborn rats (6 days) were subjected to normoxia (21% O(2)) or PC (8% O(2)) for 3h followed by 24h of reoxygenation. The rats then had the right carotid artery permanently ligated followed by 140 min of hypoxia (8% O(2)) (HI or PC+HI). Brains from rats at the corresponding age without any exposure to PC or HI were examined for comparison (Sham). PC significantly reduced brain damage as measured by weight loss of the right hemisphere at 22 days after HI and by gross and microscopic morphology. PC amplified and prolonged the induction of mRNA of VEGF splice variants measured by real-time RT-PCR and enhanced the increase in VEGF protein measured by ELISA in brain following HI. PC preserved the phosphorylation of Akt-Ser-473 and diminished the increase in caspase-3 activity in brain following HI. We conclude that PC provides neuroprotection and augments and preserves the increase in VEGF following HI in the newborn rat brain which may play an important role in neuroprotection.

Sonic hedgehog is required for vascular outgrowth in the hindbrain choroid plexus

Critical to the exchange and metabolic functions served by tissues like brain choroid plexi and lung is the coherent development of an epithelial sheet of large surface area in tight apposition to an extensive vascular bed. Here, we present functional experiments in the mouse demonstrating that Sonic hedgehog (Shh) produced by hindbrain choroid plexus epithelium induces the extensive vascular outgrowths and vascular surface area fundamental to choroid plexus functions, but does not induce the more specialized endothelial cell features of fenestrations and bore size. Our findings indicate that these Shh-dependent vascular elaborations occur even in the presence of Vegf and other established angiogenic factors, suggesting either that the levels of these factors are inadequate in the absence of Shh or that a different set of factors may be more essential to choroid plexus outgrowth. Transducing the Shh signal is a perivascular cell-the pericyte-rather than the more integral vascular endothelial cell itself. Moreover, our findings suggest that hindbrain choroid plexus endothelial cells, as compared to other vascular endothelial cells, are more dependent upon pericytes for instruction. Thus, in addition to Shh acting on the progenitor pool for choroid plexus epithelial cells, as previously shown, it also acts on choroid plexus pericytes, and together serves the important role of coordinating the development of two disparate yet functionally dependent structures-the choroid plexus vasculature and its ensheathing epithelium.

Glucose is a key regulator of VEGFR2/KDR in human epithelial ovarian carcinoma cells

Epithelial ovarian cancer (EOC) is a serious gynecological cancer and there may be an increased risk of developing EOC in women with metabolic disruptions such as diabetes-related hyperglycemia, obesity or high glycemic load. Upregulation of vascular endothelial growth factor (VEGF) in ischemic conditions (e.g. hypoxia, hypoglycemia) induces tumor angiogenesis. We previously showed that EOC cells employ an autocrine VEGF/VEGFR2 signaling loop. Here we demonstrate the influence of glucose levels on VEGF and its receptors in the human EOC lines OVCAR-3 and CAOV-3. Glucose (but not pyruvate) deprivation induced significant increase in VEGF transcription and secretion, but a rapid reduction in VEGFR2 protein synthesis and glycosylation, combined with a reduction in co-receptor neuropilin-1 (NRP-1) protein levels. In contrast, mRNA for KDR and NRP-1 was increased upon glucose depletion suggesting a mechanism of feed back upon protein reduction. The addition of the proteosome inhibitor epoxomycin restored VEGFR2 under glucose free conditions, suggesting degradation as the main mechanism of VEGFR2 reduction and transcriptional activation through the unfolded protein response (UPR) which was activated in glucose-starved cells through the upregulation of the Endoplasmic reticulum chaperon GRP-78. Our finding that glucose can regulate VEGF/VEGFR2 levels suggests that initiation and/or progression of ovarian surface epithelial cells towards a neoplastic phenotype might be modulated by dietary conditions, and that a patient's metabolic status may alter the effectiveness of the known anti-angiogenic therapies. This information provides opportunities to explore the biology of EOC progression and improve our understanding of the mechanistic insight of this interesting regulatory effect.

Sirolimus inhibits the growth and metastatic progression of hepatocellular carcinoma

PURPOSE

Immunosuppressive therapy after liver transplantation for hepatocellular carcinoma (HCC) is one of the major contributory factors for HCC recurrence and metastasis. Sirolimus, a potent immunosuppressant, has been reported to be an effective inhibitor in a variety of tumors. The present study is designed to explore whether sirolimus could block the growth and metastatic progression of HCC.

METHODS

MHCC97H cells were used as targets to explore the effect of sirolimus on cell cycle progression, apoptosis, proliferation, and its antiangiogenic mechanism. LCI-D20, a highly metastatic model of human HCC in nude mice, was also used as the model tumor to explore the effect of sirolimus on tumor growth and metastatic progression.

RESULTS

In vitro, sirolimus induced cell cycle arrest at the G1 checkpoint and blocked proliferation of MHCC97H cells but did not induce apoptosis. In vivo, sirolimus prevented tumor growth and metastatic progression in LCI-D20. Intratumoral microvessel density and circulating levels of VEGF in tumor-bearing mice were also significantly reduced in sirolimus treatment group. Quantitative RT-PCR showed that sirolimus down-regulated the mRNA expression of VEGF and HIF-1a, but not of bFGF, and TGF-b in MHCC97H cells. Furthermore, western blot analysis confirmed that sirolimus also decreased expression of HIF-1a at protein level, in parallel with the down-regulation of the levels of VEGF protein excretion in a time-dependent manner as compared to untreated control cells following anoxia.

CONCLUSIONS

The immunosuppressive macrolide sirolimus prevents the growth and metastatic progression of HCC, and suppresses VEGF synthesis and secretion by downregulating HIF-1a expression. Sirolimus may be useful for clinical application in patients who received a liver transplant for HCC.

Dexamethasone induces neurodegeneration but also up-regulates vascular endothelial growth factor A in neonatal rat brains

The use of dexamethasone (Dex) in premature infants to prevent and/or treat bronchopulmonary dysplasia can adversely affect early neurodevelopment and probably result in loss of cerebral volume. Vascular endothelial growth factor A (VEGF), specifically VEGF(164) isoform has neurotrophic, neuroprotective and neurogenesis enhancing effects. Previous studies have demonstrated that Dex usually down-regulates VEGF. In the present study we investigated the effect of Dex on brain growth and VEGF in the neonatal rat brain. The pups in each litter were divided into the vehicle (n=84) or Dex-treated (n=98) groups. Rat pups in the Dex group received one of three different regimens of i.p. Dex which included tapering doses on postnatal days 3-6 (0.5, 0.25, 0.125 and 0.06 mg/kg, respectively), or repeated doses of 0.5 or 1 mg/kg/day on postnatal days 4-6 or single dose of 0.031, 0.06, 0.125, 0.25 or 0.5 mg/kg on postnatal day 6. The total VEGF protein and mRNA expression of the three main VEGF splice variants (VEGF(120), VEGF(164), and VEGF(188)) were measured in the rat pup brain using enzyme-linked immunosorbent assay and real-time reverse transcription polymerase chain reaction, respectively. Treatment with Dex significantly decreased the gain of body and brain weight. The tapering and repeated doses of Dex significantly increased caspase-3 activity, VEGF protein and the expression of mRNA of VEGF(164) and VEGF(188) splice variants but the single dose did not. We conclude that Dex is neurodegenerative in the developing brain but also increases VEGF which may play a neurotrophic and neuroprotective role.

Microenvironment changes (in pH) affect VEGF alternative splicing

Vascular endothelial growth factor-A (VEGF-A) has several isoforms, which differ in their capacity to bind extracellular matrix proteins and also in their affinity for VEGF receptors. Although the relative contribution of the VEGF isoforms has been studied in tumor angiogenesis, little is known about the mechanisms that regulate the alternative splicing process. Here, we tested microenvironment cues that might regulate VEGF alternative splicing. To test this, we used endometrial cancer cells that produce all VEGF isoforms as a model, and exposed them to varying pH levels, hormones, glucose and CoCl₂ (to mimic hypoxia). Low pH had the most consistent effects in inducing variations in VEGF splicing pattern (VEGF121 increased significantly, p < 0.001, when compared to VEGF145, 165 or 189). This was accompanied by activation of the p38 stress pathway and SR proteins (splicing factors) expression and phosphorylation. SF2/ASF, SRp20 and SRp40 down-regulation by siRNA impaired the effects of pH stimulation, blocking the shift in VEGF isoforms production. Taken together, we show for the first time that acidosis (low pH) regulates VEGF-A alternative splicing, may be through p38 activation and suggest the possible SR proteins involved in this process.

Mechanical signals modulated vascular endothelial growth factor-A (VEGF-A) alternative splicing in osteoblastic cells through actin polymerisation

Since VEGF-A is involved in mechanically induced bone gain and because vegf exists under 6 isoforms exerting various biological effects, we studied vegf isoform expression and VEGF protein production in osteoblastic cells (rat Ros17/2.8 and human osteoblasts) submitted to 4 mechanical regimens. Mechanical regimens (1% stretch deformation) were designed with a fixed number of cycles (450) delivered at various frequencies (0.05 to 5 Hz). We found a negative correlation (R(2)=0.76, p<0.0001) between production of soluble VEGF and mechanical stretch frequency and a positive correlation (R(2)=0.99, p<0.0001) between production of matrix-bound VEGF and mechanical stretch frequency. mRNA expressions of soluble VEGF isoforms (121, 165) were specifically expressed under low frequency while matrix-bound VEGF isoforms (206, 189, 165, 145) were specifically expressed under high frequency in human osteoblasts. As f-actin stress fiber formation was significantly increased selectively in high frequency conditions, we disrupted actin fibers in Ros17/2.8 and found that immobilisation of VEGF was abolished. Conversely, Jasplakinolide treatment which increases stress fiber formation was able to mimic high frequency stretch-induced immobilisation of VEGF. Thus, we speculate that the stretch-induced increase in cell tension is responsible for matrix-bound vegf isoform production. Mechanically induced selection of soluble or matrix-bound VEGF production may modify osteoblast and endothelial cell crosstalk crucial during osteogenesis and fracture healing.

Increased distension stimulates distal capillary growth as well as expression of specific angiogenesis genes in fetal mouse lungs

Tracheal occlusion (TO) performed surgically in utero near the end of gestation causes a rapid increase in the distension of future airspaces, resulting in accelerated lung development. The authors hypothesize that TO stimulates microvascular growth concomitant with a rapid increase in the expression of genes implicated in angiogenesis. Mouse fetuses underwent in utero surgery (TO or sham-TO surgery) at 16.5 days of gestation, whereupon development was allowed to continue for a further 1 or 24 hours. Microvascular changes were assessed by immunohistochemical staining of fetal lung sections for platelet endothelial cell adhesion molecule-1. Levels of vascular endothelial growth factor-A (VEGF-A; isoforms 120, 164 and 188), VEGF receptors 1 and 2 (VEGFR-1 and -2), angiopoietins 1 and 2, and Tie2 mRNAs were determined by quantitative real-time polymerase chain reaction (PCR). The authors observed more intercapillary interconnection, less isolated capillaries, and a more extended capillary network inside septa of lungs that underwent 24 h of TO versus sham-TO. Moreover, the authors observed a significant increase in mRNA levels of VEGF 188 and VEGFR-1 as early as 1 hour following TO and of VEGFR-1 and angiopoietin 1 after 24 hours. Together, these results suggest that surgically applied stretching quickly enhances the expression of specific angiogenesis and vessel maintenance genes, which seems to result in the maturation and organization of a more extensive and complex capillary network.

Sequence- and target-independent angiogenesis suppression by siRNA via TLR3

Clinical trials of small interfering RNA (siRNA) targeting vascular endothelial growth factor-A (VEGFA) or its receptor VEGFR1 (also called FLT1), in patients with blinding choroidal neovascularization (CNV) from age-related macular degeneration, are premised on gene silencing by means of intracellular RNA interference (RNAi). We show instead that CNV inhibition is a siRNA-class effect: 21-nucleotide or longer siRNAs targeting non-mammalian genes, non-expressed genes, non-genomic sequences, pro- and anti-angiogenic genes, and RNAi-incompetent siRNAs all suppressed CNV in mice comparably to siRNAs targeting Vegfa or Vegfr1 without off-target RNAi or interferon-alpha/beta activation. Non-targeted (against non-mammalian genes) and targeted (against Vegfa or Vegfr1) siRNA suppressed CNV via cell-surface toll-like receptor 3 (TLR3), its adaptor TRIF, and induction of interferon-gamma and interleukin-12. Non-targeted siRNA suppressed dermal neovascularization in mice as effectively as Vegfa siRNA. siRNA-induced inhibition of neovascularization required a minimum length of 21 nucleotides, a bridging necessity in a modelled 2:1 TLR3-RNA complex. Choroidal endothelial cells from people expressing the TLR3 coding variant 412FF were refractory to extracellular siRNA-induced cytotoxicity, facilitating individualized pharmacogenetic therapy. Multiple human endothelial cell types expressed surface TLR3, indicating that generic siRNAs might treat angiogenic disorders that affect 8% of the world's population, and that siRNAs might induce unanticipated vascular or immune effects.

Should tumor VEGF expression influence decisions on combining low-dose chemotherapy with antiangiogenic therapy? Preclinical modeling in ovarian cancer

Because of its low toxicity, low-dose (LD) chemotherapy is ideally suited for combination with antiangiogenic drugs. We investigated the impact of tumor vascular endothelial growth factor A (VEGF-A) expression on the efficacy of LD paclitaxel chemotherapy and its interactions with the tyrosine kinase inhibitor SU5416 in the ID8 and ID8-Vegf models of ovarian cancer. Functional linear models using weighted penalized least squares were utilized to identify interactions between Vegf, LD paclitaxel and antiangiogenic therapy. LD paclitaxel yielded additive effects with antiangiogenic therapy against tumors with low Vegf expression, while it exhibited antagonism to antiangiogenic therapy in tumors with high Vegf expression. This is the first preclinical study that models interactions of LD paclitaxel chemotherapy with antiangiogenic therapy and tumor VEGF expression and offers important lessons for the rational design of clinical trials.

Coordinated vascular endothelial growth factor expression and signaling during skeletal myogenic differentiation

Angiogenesis is largely controlled by hypoxia-driven transcriptional up-regulation and secretion of vascular endothelial growth factor (VEGF) and its binding to the endothelial cell tyrosine receptor kinases, VEGFR1 and VEGFR2. Recent expression analysis suggests that VEGF is expressed in a cell-specific manner in normoxic adult tissue; however, the transcriptional regulation and role of VEGF in these tissues remains fundamentally unknown. In this report we demonstrate that VEGF is coordinately up-regulated during terminal skeletal muscle differentiation. We reveal that this regulation is mediated in part by MyoD homo- and hetero-dimeric transcriptional mechanisms. Serial deletions of the VEGF promoter elucidated a region containing three tandem CANNTG consensus MyoD sites serving as essential sites of direct interaction for MyoD-mediated up-regulation of VEGF transcription. VEGF-null embryonic stem (ES) cells exhibited reduced myogenic differentiation compared with wild-type ES cells, suggesting that VEGF may serve a role in skeletal muscle differentiation. We demonstrate that VEGFR1 and VEGFR2 are expressed at low levels in myogenic precursor cells and are robustly activated upon VEGF stimulation and that their expression is coordinately regulated during skeletal muscle differentiation. VEGF stimulation of differentiating C2C12 cells promoted myotube hypertrophy and increased myogenic differentiation, whereas addition of sFlt1, a VEGF inhibitor, resulted in myotube hypotrophy and inhibited myogenic differentiation. We further provide evidence indicating VEGF-mediated myogenic marker expression, mitogenic activity, migration, and prosurvival functions may contribute to increased myogenesis. These data suggest a novel mechanism whereby VEGF is coordinately regulated as part of the myogenic differentiation program and serves an autocrine function regulating skeletal myogenesis.

Increased expression of VEGF121/VEGF165-189 ratio results in a significant enhancement of human prostate tumor angiogenesis

Vascular endothelial growth factor (VEGF) is a proangiogenic factor upregulated in many tumors. The alternative splicing of VEGF mRNA renders 3 major isoforms of 121, 165 and 189 amino-acids in humans (1 less amino-acid for each mouse VEGF isoform). We have designed isoform specific real time QRT-PCR assays to quantitate VEGF transcripts in mouse and human normal and malignant prostates. In the human normal prostate, VEGF(165) was the predominant isoform (62.8% +/- 5.2%), followed by VEGF(121) (22.5% +/- 6.3%) and VEGF(189) (p < 0.001) (14.6% +/- 2.1%). Prostate tumors showed a significant increase in the percentage of VEGF(121) and decreases in VEGF(165) (p < 0.01) and VEGF(189) (p < 0.05). However, the amount of total VEGF mRNA was similar between normal and malignant prostates. VEGF(164) was the transcript with the highest expression in the mouse normal prostate. Unlike human prostate cancer, tumors from TRAMP mice demonstrated a significant increase in total VEGF mRNA levels and in each of the VEGF isoforms, without changes in the relative isoform ratios. Morpholino phosphorodiamide antisense oligonucleotide technology was used to increase the relative amount of VEGF(121) while proportionally decreasing VEGF(165) and VEGF(189) levels in human prostate cell lines, through the modification of alternative splicing, without changing transcription levels and total amount of VEGF. The increase in the VEGF(121)/VEGF(165-189) ratio in PC3 cells resulted in a dramatic increase in prostate tumor angiogenesis in vivo. Our results underscore the importance of VEGF(121) in human prostate carcinoma and demonstrate that the relative expression of the different VEGF isoforms has an impact on prostate carcinogenesis.

Age-dependent expression of VEGF isoforms and receptors in the rabbit anterior cruciate ligament

Vascular endothelial growth factor (VEGF) gene gives rise to several distinct isoforms of VEGF. Those isoforms differ in biochemical and biological properties, and it has been reported that their expression patterns are tissue and age specific as well. We investigated the expression levels of VEGF isoforms (VEGF121, VEGF165, VEGF183, VEGF189) and its receptors (VEGFR-1, flt-1 and VEGFR-2, flk-1/KDR) in the anterior cruciate ligament (ACL) of 2- to 3-week-, 2-month-, and 18-month-old New Zealand White rabbits using Sybr green Real-Time RT-PCR. VEGF isoforms and both receptors were expressed in the ACL at all investigated ages. VEGF121 was found to be the most abundant isoform at the ages under investigation, followed by VEGF165, VEGF189 and VEGF183. All isoforms showed decreased expression levels with age, however the larger membrane bound isoforms, VEGF183 and VEGF189, showed the most striking age-associated decrease in expression level. VEGFR-1 expression levels increased with age, while the expression level of VEGFR-2 expression was highest at 2-3 weeks and was significantly lower at 2 and 18 months of age. Distinct age-associated differences in the expression level of VEGF isoforms as well as their receptors suggest differential physiological functions during development, maturation and ageing of the ACL.

Characterization and differential expression of vascular endothelial growth factor isoforms and receptors in swine corpus luteum throughout estrous cycle

Corpus luteum (CL) undergoes growth and regression during each estrous cycle; these processes are accompanied by growth and regression of the luteal vascular bed. Vascular endothelial growth factor (VEGF) is the main regulator of angiogenesis, inducing endothelial cell proliferation, migration, vascular permeability, and vessel lumen formation. VEGF presents several isoforms that are produced by alternative splicing of the same mRNA transcript. We determined by real time RT-PCR the expression patterns of VEGF isoform and receptor mRNAs, as well as the VEGF protein levels in pig CL throughout a whole estrous cycle. Four novel VEGF isoforms (VEGF144, VEGF147, VEGF182, and VEGF164b) were found for the first time in swine and the seven identified isoforms can be grouped in four different patterns of expression. The most expressed splice variants were VEGF120 and VEGF164. All isoforms showed their highest mRNA levels in newly formed CLs (day 1), followed by a decrease during mid-late luteal phase (days 10-17), except for VEGF182, VEGF188 and VEGF144 that showed a differential regulation during late luteal phase (day 14) or at luteolysis (day 17). VEGF protein levels paralleled the most expressed and secreted VEGF120 and VEGF164 isoforms. The VEGF receptors mRNAs showed a different pattern of expression in relation to their ligands, increasing between day 1 and 3 and gradually decreasing during the mid-late luteal phase. The differential regulation of VEGF isoforms may suggest specific physiological roles for some of them, particularly in angioregression occurring during the apoptotic structural luteolysis.

Quantification of vascular endothelial growth factor and neuropilins mRNAs during rat brain maturation by real-time PCR

1. Vascular endothelial growth factor (VEGF) has been related with several brain functions such as angiogenesis, neuroprotection, and neurogenesis. 2. We studied the mRNA expression of the two most important isoforms of VEGF (VEGF120 and VEGF164) as well as one type of VEGF receptors, neuropilins (NRP), during maturation in the rat brain using real-time PCR. 3. Today, real-time PCR is the method of choice for rapid and reliable quantification of mRNA transcription. 4. VEGF120 has little changes in its expression between P5 and P30. 5. However, VEGF164 increased its expression 2-folds at P15 in comparison to P5, remaining at this level in the adult brain (P30). 6. Both types of NRP, NRP-1 and NRP-2, which only bind VEGF164, increased their expression about 2-folds only at P30, at levels similar to those observed for VEGF164.

Alteration of splicing signals in a genomic/cDNA hybrid VEGF gene to modify the ratio of expressed VEGF isoforms enhances safety of angiogenic gene therapy

Vascular endothelial growth factor (VEGF)-mediated physiological angiogenesis results from the concerted action of three major VEGF isoforms (VEGF121, 165, 189), which arise from alternate splicing. We have previously shown that expression of a mixture of VEGF isoforms via gene transfer is considerably more potent than expression of a single VEGF isoform. To test the hypothesis that different mixtures of VEGF isoforms may offer the same therapeutic benefit with a better safety profile, we compared the efficacy and safety of an adenovirus gene transfer vector expressing the three major VEGF isoforms (AdVEGF-All) in the normal ratio to those of AdVEGF-All6A+, in which the splicing sequences for exon 6A were altered to promote expression of VEGF189 at the expense of VEGF121. Both vectors were equally potent in mediating recovery of hind-limb blood flow following experimental ischemia. By contrast, intravenous administration of AdVEGF-All6A+ yielded enhanced survival and a lower capacity to support tumor growth compared to AdVEGF-All, and intratracheal administration of AdVEGF-All6A+ resulted in less pulmonary edema than that of AdVEGF-All. We conclude that AdVEGF-All and AdVEGF-All6A+ are similar in potency but that AdVEGF-All6A+ is safer. This suggests that AdVEGF-All6A+ may be the preferred candidate for clinical development.

ErbB2 overexpression in mammary cells upregulates VEGF through the core promoter

The angiogenic molecule, vascular endothelial growth factor (VEGF), is a critical regulator of normal and pathologic angiogenesis. ErbB2, an epidermal growth factor receptor family member whose overexpression in mammary tumors is correlated with poor patient prognosis, has been implicated as a positive modulator of VEGF expression. Mammary tumor cells overexpressing ErbB2 (NAFA cells) and a normal mouse mammary cell line (HC11) transfected with ErbB2 expression vectors were used to study the effects of ErbB2 overexpression on VEGF regulation. We found that ErbB2 overexpression led to an increase in endogenous VEGF mRNA as well as ErbB3 protein levels in HC11 cells. Additionally, we determined that ErbB2 overexpression-mediated upregulation of VEGF involves at least two distinct promoter elements, one previously identified as the hypoxia responsive element and the other the core promoter region (-161 to -51bp), which is specifically controlled via two adjacent SP1 binding sites (-80 to -60bp).

Glucose deprivation increases mRNA stability of vascular endothelial growth factor through activation of AMP-activated protein kinase in DU145 prostate carcinoma

The induction of proangiogenic cytokines such as vascular endothelial growth factor (VEGF) is a critical feature of tumor angiogenesis. In the present study, we examined the mechanisms of VEGF gene expression induced by glucose deprivation in cancer cells, a role of AMP-activated protein kinase (AMPK) in the process, and the signal transduction pathway. AMPK functions as an energy sensor to provide metabolic adaptation under ATP-depleting conditions such as hypoxia and nutritional deprivation. Here, we show that glucose deprivation leads to a significant increase in the mRNA level of VEGF, GLUT1, and PFKFB3 genes in several cancer cells via a hypoxia-inducible factor-1-independent mechanism, and we demonstrate an essential role of AMPK in these gene expressions. Our data suggest that VEGF mRNA induction by glucose deprivation is due to an increase in mRNA stability, and the AMPK activity is necessary and sufficient to confer the stability to VEGF mRNA. We further show that reactive oxygen species is involved in glucose deprivation-induced AMPK activity in DU145 human prostate carcinomas, and c-Jun amino-terminal kinase acts as an upstream component in AMPK activation cascades under these conditions. LKB1, which was recently identified as a direct upstream kinase of AMPK, was not detected in DU145 cells. In conclusion, our results demonstrate a novel and major role of AMPK in the post-transcriptional regulation of VEGF, further implying its potential role in tumor angiogenesis.

Acceleration of Follicular Development by Administration of Vascular Endothelial Growth Factor in Cycling Female Rats

To address the role of follicular angiogenesis in the determination of ovulatory follicles and the effects of different vascular endothelial growth factor (VEGF) isoforms on follicular angiogenesis and development, mature female rats were treated with an angiogenic inhibitor (TNP-470), and also with VEGF 120 or 164 at different dosages (0.4, 0.8, 4.0 or 8.0 microg/kg body weight) for 3 days during the estrous cycle. Ovarian follicular angiogenesis, the population of large follicles and ovulation were examined. VEGF 120 (0.8 microg/kg) and 164 (8.0 microg/kg) treatments stimulated follicular angiogenesis in the theca interna layer, while TNP-470 treatment showed severe depression of follicular angiogenesis, and completely inhibited ovulation. After administration of VEGF 120 or 164, the number of healthy preovulatory follicles and ovulated oocytes increased significantly, concomitantly with a decrease in the number of atretic preovulatory follicles. The oocytes ovulated had normal fertilizability and developed to term with the same litter size as in the control rats. Our findings suggest that follicular angiogenesis may be a determinant of follicular development during the periovulatory phase, and that VEGF isoforms may play different important roles in regulating follicular angiogenesis.

Differential expression of VEGF isoforms and receptors in knee joint menisci under systemic hypoxia

Vascular endothelial growth factor (VEGF) gene gives rise to several distinct isoforms of VEGF, which differ in their expression patterns as well as their biochemical and biological properties. We examined the expression levels of VEGF isoforms and their receptors in the medial and lateral meniscus of rabbits under normal physiologic conditions as well their expression levels after 8 and 24 h of systemic normobaric hypoxia (13%). VEGF121 is the most abundant VEGF isoform in the medial and lateral meniscus, followed by VEGF165, VEGF189, and VEGF183. While the soluble VEGF121 and VEGF165 are only upregulated at 8 h of hypoxia, the membrane-bound VEGF183 and VEGF189 are further increased at 24 h. VEGFR-2 is expressed at a much higher level than VEGFR-1 under normal conditions, and both receptors are upregulated under hypoxia. Differential expression levels under normoxia as well as a differential response to hypoxia may indicate different functions of VEGF isoforms in the meniscus.

Interferon alpha 2a down-regulates VEGF expression through PI3 kinase and MAP kinase signaling pathways

An earlier report demonstrated that interferon alpha (IFN-alpha) inhibited tumor growth and recurrence in an MHCC97 xenograft model in nude mice by suppressing tumor angiogenesis rather than by inhibiting tumor cell proliferation. However, the underlying molecular mechanism was not fully elucidated. In this study, we demonstrated that IFN-alpha 2a could down-regulate VEGF expression both in mRNA and in protein levels, as well as down-regulating HIF-1 alpha mRNA expression in MHCC97 cells in vitro. A cDNA micro array analysis followed by Northern and Western blot analysis revealed that PI3 kinase and MAP kinase signaling pathways might be inhibited by IFN-alpha 2a. Blocking the function of IFN-alpha receptor with a specific peptide could eliminate the inhibitory effects of IFN-alpha 2a on VEGF expression. In addition, wortmannin and PD098059, respective inhibitors of the PI3 kinase and the MAP kinase signaling pathways, when used independently or in combination, could also down-regulate the VEGF synthesis and secretion in a similar pattern of IFN-alpha 2a. These observations may lead to the conclusion that IFN-alpha 2a could suppress VEGF synthesis and secretion by down-regulating HIF-1 alpha expression, via inhibition of the PI3 kinase and/or the MAP kinase signaling pathways.

Adenovirus-mediated transfer of a minigene expressing multiple isoforms of VEGF is more effective at inducing angiogenesis than comparable vectors expressing individual VEGF cDNAs

To assess the hypothesis that angiogenic gene therapy with the genomic form of vascular endothelial growth factor (VEGF) expressing the three major isoforms could be more potent than a vector expressing a single isoform, we designed an adenovirus vector (AdVEGF-All) expressing a VEGF cDNA/genomic hybrid gene. AdVEGF-All expressed all three major isoforms (121, 165, 189) in a 2:2:1 ratio. AdVEGF-All was 100-fold more potent than cDNA vectors expressing VEGF 121, 165, or 189 in restoring blood flow to the ischemic mouse hind limb. Interestingly, a mixture of Ad vectors individually expressing the VEGF 121, 165, and 189 cDNAs was equipotent to an equivalent dose of AdVEGF-All. Thus, a mixture of VEGF isoforms provides a more potent angiogenic response than a single isoform, suggesting that the individual isoforms function synergistically, an observation with important implications for gene and recombinant protein therapy.

Increase of both angiogenesis and bone mass in response to exercise depends on VEGF

Physiological angiogenesis during bone remodeling is undefined. Treadmill-running rats displayed bone marrow angiogenesis concomitant with bone formation increase and resorption decrease and upregulation of VEGF and its R1 receptor mRNA in proximal tibia. VEGF blockade over 5 weeks of training fully prevented the exercise-induced bone mass gain.

INTRODUCTION

We investigated the role of vascular endothelial growth factor (VEGF) and angiogenesis in the osteogenic response to exercise.

MATERIALS AND METHODS

Nine-week-old male Wistar rats were treadmill-trained at 60% Vo(2max) for various periods. Bone and vascular histomorphometry was performed after 2- and 5-week experiments. On-line RT PCR for VEGF and its receptors R1 and R2 was done after a 10-day experiment. In the 5-week experiment, running rats received either a VEGF inhibitory antibody or a placebo.

RESULTS

After 2 weeks, tibial BMD did not change; however, vessel number in the proximal metaphysis increased by 20% in running versus sedentary rats. In running rats, vessel number correlated positively (r = 0.88) with bone formation rate and negatively (r = -0.85) with active resorption surfaces. After 10 days of training, upregulation of VEGF and VEGF receptor R1 mRNA was detected in periosteum and metaphyseal bone. VEGF blockade in 5-week trained rats fully prevented the exercise-induced increase in metaphyseal BMD (9%) and cancellous bone volume (BV/TV; 25%), as well as the increased vessel number (25%). In 5-week placebo-treated running rats, bone formation rate returned to initial values, whereas osteoclastic surfaces continued to decline compared with both sedentary and anti-VEGF-treated running rats.

CONCLUSION

VEGF signaling-mediated bone angiogenesis is tightly related to exercise-induced bone cellular uncoupling and is indispensable for bone gain induced by exercise.

Expression of VEGF isoforms by epiphyseal chondrocytes during low-oxygen tension is HIF-1 alpha dependent

OBJECTIVE

To establish the role of hypoxia and HIF-1 alpha for VEGF expression of murine epiphyseal chondrocytes. To analyze the effect of hypoxia on VEGF isoform expression.

MATERIALS AND METHODS

VEGF mRNA and VEGF isoform expression was investigated in epiphyses of murine newborns by in situ hybridization and real-time PCR. Further, epiphyseal chondrocytes were isolated from newborn mice with homozygous flanking of the HIF-1 alpha gene with lox-P sites. HIF-1 alpha was deleted by infection with adenovirus containing cre-recombinase. After chondrocytes reached confluency they were exposed to 0.5% or 20% oxygen, respectively. Total VEGF and VEGF isoform mRNA expression levels were measured by real-time PCR. Secreted VEGF protein was determined by ELISA.

RESULTS

VEGF mRNA signals were detected in the hypertrophic zone and in the center of the proliferative zone of the murine epiphysis, which is considered to be hypoxic. Real-time PCR revealed that VEGF(120)is the dominant isoform in vivo. In cultured epiphyseal chondrocytes strongly increased VEGF gene expression levels were detected after exposure to hypoxia. Furthermore, secretion of VEGF protein was significantly enhanced under 0.5% oxygen. Remarkably, functional inactivation of HIF-1 alpha abolished the hypoxic increase of VEGF expression in chondrocytes completely. Furthermore, the soluble isoforms VEGF(120)and VEGF(164)are the most abundantly expressed splice variants in chondrocytes exposed to low oxygen levels.

CONCLUSIONS

The data presented here clearly indicate that hypoxia is able to induce the synthesis of soluble VEGF isoforms by epiphyseal chondrocytes, most likely through stabilization of HIF-1 alpha. Thus it can be speculated that HIF-1 alpha is an essential prerequisite for hypoxic VEGF synthesis in the epiphysis, thereby contributing to the formation and invasion of blood vessels in long bone development.

Specific roles for the PI3K and the MEK-ERK pathway in IGF-1-stimulated chemotaxis, VEGF secretion and proliferation of multiple myeloma cells: study in the 5T33MM model

Insulin-like growth factor-1 (IGF-1) has been described as an important factor in proliferation, cell survival and migration of multiple myeloma (MM) cells. Angiogenesis correlates with development and prognosis of the MM disease. Vascular endothelial growth factor (VEGF) is one of the prominent factors involved in this process. The different functions of IGF-1 were investigated in the 5TMM mouse model with emphasis on proliferation, migration and VEGF secretion, and the signalling pathways involved. Western Blot analysis revealed that ERK1/2 and Akt (PKB) were activated after IGF-1 stimulation. The activation of ERK1/2 was reduced by the PI3K inhibitor Wortmannin, implying that the PI3K pathway is involved in its activation. Insulin-like growth factor-1 induced an increase in DNA synthesis in MM cells, which was mediated by a PI3K/Akt-MEK/ERK pathway. Insulin-like growth factor-1 enhanced F-actin assembly and this process was only PI3K mediated. Stimulation by IGF-1 of VEGF production was reduced by PD98059, indicating that only the MEK–ERK pathway is involved in IGF-1-stimulated VEGF production. In conclusion, IGF-1 mediates its multiple effects on MM cells through different signal transduction pathways. In the future, we can study the potential in vivo effects of IGF-1 inhibition on tumour growth and angiogenesis in MM.

Induction of protein growth factor systems in the ovaries of transgenic mice overexpressing human type 2 lysophosphatidic acid G protein-coupled receptor (LPA2)

The lipid growth factor lysophosphatidic acid (LPA) is produced by ovarian cancer cells in quantities sufficient to attain concentrations of up to 10 microM. An autocrine circuit was demonstrated when ovarian cancer cells, but not normal ovarian surface epithelial cells, were proven to express LPA(2) (Edg-4) and LPA(3) (Edg-7) G protein-coupled receptors for LPA. Human LPA(2) now has been expressed transgenically in C57BL/6 mouse ovaries under direction of the alpha-inhibin large promoter. Human LPA(2) mRNA and protein were detected in all transgenic (TG) mouse ovaries at levels far higher than in other tissues and at least fivefold higher than in cultured lines of human ovarian cancer cells, with the expected sex cord-stromal distribution. Most LPA(2) TG ovaries produced significantly higher levels than non-TG ovaries of type A, but not type B, vascular endothelial growth factor (VEGF), isomers of VEGF-A, and urokinase-type plasminogen activator (uPA). Many LPA(2) TG ovaries had elevated expression of VEGF receptors 1 and 2, and a depressed level of type 2 PA inhibitor. Thus, the LPA-LPA(2) circuit regulates ovarian cells both directly and through increases in protein growth factor systems.

Angiogenic switch during 5T2MM murine myeloma tumorigenesis: role of CD45 heterogeneity

The active role of angiogenesis during disease progression is well recognized in solid tumors. In hematologic malignancies such as multiple myeloma (MM), it is not known whether tumor neovascularization is an epiphenomenon or whether it is actively involved in disease progression. At clinical presentation, myeloma disease and the associated angiogenesis are both well established. Here the 5T2MM murine model was used to analyze angiogenesis during preclinical myeloma stages. Bone marrow (BM) of 5T2MM-inoculated mice was analyzed at weekly intervals until the end stage of the disease. Histologic analysis and assessment of microvessel density (MVD) by CD31 staining demonstrated a preangiogenic stage of small tumor aggregates followed by an angiogenic switch and subsequently an angiogenic stage of progressive tumor growth and large, confluent tumor nodules. Flow cytometric analysis that indicated an increase in percentage CD45- MM cells preceded the angiogenic switch. Real-time polymerase chain reaction (RT-PCR) of sorted CD45+ and CD45- MM cells indicated higher vascular endothelial growth factor 120 (VEGF120) and VEGF164 transcripts in CD45- MM cells. VEGF enzyme-linked immunosorbent assay (ELISA) revealed high secretion by CD45- MM cells but no protein secretion by CD45+ MM cells, indicating angiogenic heterogeneity among the MM cells. These data suggest that, like in solid tumors, angiogenic switch and angiogenic heterogeneity exist in MM.

Vector-based RNAi, a novel tool for isoform-specific knock-down of VEGF and anti-angiogenesis gene therapy of cancer

Vascular endothelial growth factor (VEGF) carries out multifaceted functions in tumor development, and it exists as at least five isoforms with distinct biologic activities and clinical implications. Several strategies have been developed to block VEGF for cancer therapy; however, the approach to target-specific VEGF isoform(s) has not been explored to date. In the present study, we show that DNA vector-based RNA interference (RNAi), in which RNAi sequences targeting murine VEGF isoforms are inserted downstream of an RNA polymerase III promoter, has potential applications in isoform-specific "knock-down" of VEGF. Large molecular weight VEGF isoforms were specifically reduced in vitro in the presence of isoform-specific RNAi constructs. Additionally, H1 promoter may be superior to U6 promoter when used for vector-based RNAi of VEGF isoforms. This strategy provides a novel tool to study the function of various VEGF isoforms and may contribute to VEGF isoform-specific treatment in cancer.

Generation of a syngeneic mouse model to study the effects of vascular endothelial growth factor in ovarian carcinoma

Vascular endothelial growth factor (VEGF) performs multifaceted functions in the tumor microenvironment promoting angiogenesis, suppressing anti-tumor immune response, and possibly exerting autocrine functions on tumor cells. However, appropriate syngeneic animal models for in vivo studies are lacking. Using retroviral transfection and fluorescence-activated cell sorting, we generated a C57BL6 murine ovarian carcinoma cell line that stably overexpresses the murine VEGF164 isoform and the enhanced green fluorescent protein. VEGF164 overexpression dramatically accelerated tumor growth and ascites formation, significantly enhanced tumor angiogenesis, and substantially promoted the survival of tumor cells in vivo. In vitro, VEGF164 overexpression significantly enhanced cell survival after growth factor withdrawal and conferred resistance to apoptosis induced by cis-platin through an autocrine mechanism. VEGF/green fluorescent protein-expressing tumors were not recognized by the adaptive immune system. After vaccination, a specific anti-tumor T-cell response was detected, but tumor growth was not inhibited. This engineered murine carcinoma model should prove useful in the investigation of the role of VEGF in modulating the tumor microenvironment and affecting the complex interactions among angiogenesis mechanisms, anti-tumor immune mechanisms, and tumor cell behavior at the natural state or during therapy in ovarian carcinoma.