IGF2 and IGF1R identified as novel tip cell genes in primary microvascular endothelial cell monolayers.

Tip cells, the leading cells of angiogenic sprouts, were identified in cultures of human umbilical vein endothelial cells (HUVECs) by using CD34 as a marker. Here, we show that tip cells are also present in primary human microvascular endothelial cells (hMVECs), a more relevant endothelial cell type for angiogenesis. By means of flow cytometry, immunocytochemistry, and qPCR, it is shown that endothelial cell cultures contain a dynamic population of CD34+ cells with many hallmarks of tip cells, including filopodia-like extensions, elevated mRNA levels of known tip cell genes, and responsiveness to stimulation with VEGF and inhibition by DLL4. Furthermore, we demonstrate that our in vitro tip cell model can be exploited to investigate cellular and molecular mechanisms in tip cells and to discover novel targets for anti-angiogenesis therapy in patients. Small interfering RNA (siRNA) was used to knockdown gene expression of the known tip cell genes angiopoietin 2 (ANGPT2) and tyrosine kinase with immunoglobulin-like and EGF-like domains 1 (TIE1), which resulted in similar effects on tip cells and sprouting as compared to inhibition of tip cells in vivo. Finally, we identified two novel tip cell-specific genes in CD34+ tip cells in vitro: insulin-like growth factor 2 (IGF2) and IGF-1-receptor (IGF1R). Knockdown of these genes resulted in a significant decrease in the fraction of tip cells and in the extent of sprouting in vitro and in vivo. In conclusion, this study shows that by using our in vitro tip cell model, two novel essential tip cells genes are identified.

Identification of a novel MET mutation in high-grade glioma resulting in an auto-active intracellular protein.

MET has gained interest as a therapeutic target for a number of malignancies because of its involvement in tumorigenesis, invasion and metastasis. At present, a number of inhibitors, both antibodies against MET or its ligand hepatocyte growth factor, and small molecule MET tyrosine kinase inhibitors are in clinical trials. We here describe a novel variant of MET that is expressed in 6% of high-grade gliomas. Characterization of this mutation in a glioma cell line revealed that it consists of an intronic deletion, resulting in a splice event connecting an intact splice donor site in exon 6 with the next splice acceptor site being that of exon 9. The encoded protein lacks parts of the extracellular IPT domains 1 and 2, encoded by exons 7 and 8, resulting in a novel pseudo-IPT and is named MET(Δ7-8). MET(Δ7-8) is located predominantly in the cytosol and is constitutively active. The auto-activating nature of MET(Δ7-8), in combination with a lack of transmembrane localization, renders MET(Δ7-8) not targetable using antibodies, although the protein is efficiently deactivated by MET-specific tyrosine kinase inhibitors. Testing of MET-expressing tumors for the presence of this variant may be important for treatment decision making.

The loss of CD34+ cells in peripheral hematopoietic stem cell products cryopreserved by non-controlled rate freezing and stored at -80 °C after overnight storage.

Although peripheral blood stem cell (PBSC) products cryopreserved by non-controlled rate freezing and stored at -80 °C after overnight storage are used frequently, data regarding the rate of loss of CD34+ cells in these products are limited. In this prospective study, CD34+ cells were counted at three (fresh, post-overnight and post-thaw) points in 83 PBSC products from 41 patients by flow cytometry. Compared to fresh products, the mean losses of post-overnight and post-thaw total CD34+ cells are 16.3% and 38.4% (p = 0.02), and the mean losses of post-overnight and post-thaw viable CD34+ cells are 16.5% and 48.5%, respectively (p < 0.001). The numbers of fresh viable, post-thaw total and post-thaw viable CD34+ cells were inversely correlated with the durations of neutrophil and platelet engraftment. Our results indicate that the mean loss of post-thaw total and viable CD34+ cells is approximately 20% higher than that observed in standard cryopreservation methods. In addition, fresh viable, post-thaw total and especially post-thaw viable CD34+ cell levels are valuable predictors of both neutrophil and platelet engraftments.

New Insights in ATP Synthesis as Therapeutic Target in Cancer and Angiogenic Ocular Diseases.

Lactate and ATP formation by aerobic glycolysis, the Warburg effect, is considered a hallmark of cancer. During angiogenesis in non-cancerous tissue, proliferating stalk endothelial cells (ECs) also produce lactate and ATP by aerobic glycolysis. In fact, all proliferating cells, both non-cancer and cancer cells, need lactate for the biosynthesis of building blocks for cell growth and tissue expansion. Moreover, both non-proliferating cancer stem cells in tumors and leader tip ECs during angiogenesis rely on glycolysis for pyruvate production, which is used for ATP synthesis in mitochondria through oxidative phosphorylation (OXPHOS). Therefore, aerobic glycolysis is not a specific hallmark of cancer but rather a hallmark of proliferating cells and limits its utility in cancer therapy. However, local treatment of angiogenic eye conditions with inhibitors of glycolysis may be a safe therapeutic option that warrants experimental investigation. Most types of cells in the eye such as photoreceptors and pericytes use OXPHOS for ATP production, whereas proliferating angiogenic stalk ECs rely on glycolysis for lactate and ATP production. (J Histochem Cytochem XX.XXX-XXX, XXXX).

The clearance time of infused hematopoietic stem cell from the blood circulation.

There is no detailed information about the clearance time of infused hematopoietic stem cell (HSC) from the blood circulation in humans. In this prospective study, peripheral blood CD34+ cell counts were detected during the 4days period following autologous HSC transplantation in 20 patients by means of flow cytometry. The median CD34+ cells were at the highest level in the first hour and decreased below pre-infusion values on the first day after HSC infusion. By nonparametric analysis, positive correlation was found between CD34+ cell levels at the first hour and the post-thaw CD34+ cell dose (r=0.57, p=0.01). An inverse correlation was determined between CD34+ cell levels at the first hour and neutrophil engraftment (r=-0.54, p=0.01). Compared with the patients having CD34+ cell count of ⩾2µL(-1) in the first hour following HSC infusion, the patients having CD34+ cell count of <2µL(-1) had delayed both neutrophil (20 vs. 12, p=0.008) and platelet (47 vs. 11, p=0.01) engraftments. Our results indicated that infused HSCs were removed from the blood circulation within 1day. In addition, CD34+ cell levels at the first hour may be used as an important indicator to predict the delay of neutrophil and platelet engraftments.

CD31 expression on peripheral blood stem cells predicts both early neutrophil and platelet engraftments.

No detailed information currently exists about the immune phenotypic profiles of peripheral blood stem cells (PBSCs) obtained by different mobilization regimens. The effects of these profiles on the outcome of transplantation are largely unknown. In this prospective study, the surface immune phenotypic features (CD11a, CD18, CD31, CD38, CD44, CD62e, CD62L, CD90, CD117, CD135 and CD184 expression) of sorted PBSCs that had been mobilized by growth factor with (group I and group II) or without (group III) disease-specific chemotherapies were investigated. The immune phenotypic features on mobilized PBSCs in groups I, II and III were not significantly different. The CD31 (platelet endothelial cell adhesion molecule-1) positivity ratio on PBSCs inversely correlated with both the duration of neutrophil (r=-0.32, p=0.03) and platelet (r=-0.36, p=0.02) engraftment. No relationship was found between the engraftment (neutrophil and platelet) durations and CD184 (chemokine receptor CXC motif receptor 4 [CXCR4]) expression on PBSCs. We demonstrated that the surface immune phenotypic profiles on PBSCs obtained by several mobilization regimens were not different. To our knowledge, this is the first study to demonstrate that CD31 expression on human PBSCs may positively affect both neutrophil and platelet engraftment. Contrary to our expectations, CD184 (CXCR4) expression on PBSCs has no effect on neutrophil or platelet engraftment. Considered together, our results suggest that additional surface antigens (such as CD31) may be more effective in the homing process.

Risk factors for microbial contamination of peripheral blood stem cell products.

BACKGROUND: Despite the well-known contamination rates and presence of microbial agents in stem cell products, the risk factors affecting microbial contamination have not been well described. STUDY DESIGN AND METHODS: In a 12-year period, we retrospectively reviewed culture results of peripheral blood stem cell products with the intent of identifying risk factors for microbial contamination. RESULTS: Microbial contamination was detected in 28 (5.7%) products of the postprocessing period and in 18 (3.66%) products of the postthawing period. Large-volume leukapheresis (LVL; odds ratio [OR], 5.85; 95% confidence interval [CI], 1.52-22.49; p = 0.01) and high numbers of stem cell culture sampling (OR, 1.4; 95% CI, 1.03-1.91; p = 0.03) were found to be risk factors for postprocessing bacterial contamination. The presence of postprocessing bacterial contamination was a risk factor for postthawing (OR, 28.89; 95% CI, 6.67-125.15; p < 0.001) and posttransplant (OR, 3.25; 95% CI, 1.24-8.50; p = 0.01) microbial growth. In transplants that were performed using contaminated products, the same pathogen was detected in 20% of patients and different pathogens were found in 35% of patients. CONCLUSION: Cultures should be carefully monitored in LVL products and in samples with high numbers of cultures performed. Growth of different bacterial pathogens must be considered in transplants that are performed with contaminated products.

The effect of cholesterol levels on hematopoietic stem cell mobilization.

Data regarding effects of cholesterol levels on hematopoietic stem cell mobilization are limited. We retrospectively reviewed the relationship between serum total cholesterol levels and peripheral blood CD34 (PBCD34) cell counts in 52 granulocyte colony stimulating factor (G-CSF) induced mobilization cycles with or without chemotherapy. The cholesterol levels between the poor and good mobilization groups (median 172mg/dl vs. 183.5mg/dl, respectively, p=0.18) were not different. No significant correlation was obtained between the cholesterol levels and PBCD34 counts (r=0.02, p=0.85). No significant correlation was obtained between cholesterol levels and PBCD34 counts in patients neither mobilized with G-CSF alone (r=-0.02, p=0.9) nor G-CSF plus chemotherapy (r=0.04, p=0.8). The results of the study indicate that there was no effect of cholesterol on hematopoietic stem cell mobilization. Prospective cohort studies are needed to demonstrate the effect of cholesterol on mobilization and its extent in humans.

Risk factors for adverse events during collection of peripheral blood stem cells.

We retrospectively reviewed peripheral blood stem cell (PBSCs) collections following 528 mobilization cycles over a 10-year period. A total of 206 (13.1%) AEs occurred in association with the 1572 procedures. One hundred and ninety-one (12.15%) of the AEs were classified as clinical AEs and 15 (0.95%) were classified as apheresis instrument related AEs. The most common clinical AE was numbness of the lips, tongue, or extremities (161 procedures, 10.2%) related to the infusion of acid citrate dextrose-A (ACD). Multivariate analysis revealed high amounts of ACD/weight (odds ratio [OR]=1.11, p=0.009), high numbers of procedures (OR=1.33, p<0.001) and female gender (OR=2.83, p<0.001) as being significantly associated with clinical AEs. Female gender was shown to be the most important risk factor for clinical AEs. Females who have a significantly increased risk of AEs would benefit from prophylactic calcium before and/or during PBSC collection.

Angiogenesis in gynecological cancers and the options for anti-angiogenesis therapy.

Angiogenesis is required in cancer, including gynecological cancers, for the growth of primary tumors and secondary metastases. Development of anti-angiogenesis therapy in gynecological cancers and improvement of its efficacy have been a major focus of fundamental and clinical research. However, survival benefits of current anti-angiogenic agents, such as bevacizumab, in patients with gynecological cancer, are modest. Therefore, a better understanding of angiogenesis and the tumor microenvironment in gynecological cancers is urgently needed to develop more effective anti-angiogenic therapies, either or not in combination with other therapeutic approaches. We describe the molecular aspects of (tumor) blood vessel formation and the tumor microenvironment and provide an extensive clinical overview of current anti-angiogenic therapies for gynecological cancers. We discuss the different phenotypes of angiogenic endothelial cells as potential therapeutic targets, strategies aimed at intervention in their metabolism, and approaches targeting their (inflammatory) tumor microenvironment.

The role of glycolysis and mitochondrial respiration in the formation and functioning of endothelial tip cells during angiogenesis.

During sprouting angiogenesis, an individual endothelial tip cell grows out from a pre-existing vascular network and guides following and proliferating stalk cells to form a new vessel. Metabolic pathways such as glycolysis and mitochondrial respiration as the major sources of adenosine 5'-triphosphate (ATP) for energy production are differentially activated in these types of endothelial cells (ECs) during angiogenesis. Therefore, we studied energy metabolism during angiogenesis in more detail in tip cell and non-tip cell human umbilical vein ECs. Small interfering RNA was used to inhibit transcription of glycolytic enzymes PFKFB3 or LDHA and mitochondrial enzyme PDHA1 to test whether inhibition of these specific pathways affects tip cell differentiation and sprouting angiogenesis in vitro and in vivo. We show that glycolysis is essential for tip cell differentiation, whereas both glycolysis and mitochondrial respiration occur during proliferation of non-tip cells and in sprouting angiogenesis in vitro and in vivo. Finally, we demonstrate that inhibition of mitochondrial respiration causes adaptation of EC metabolism by increasing glycolysis and vice versa. In conclusion, our studies show a complex but flexible role of the different metabolic pathways to produce ATP in the regulation of tip cell and non-tip cell differentiation and functioning during sprouting angiogenesis.

CD34 Promotes Pathological Epi-Retinal Neovascularization in a Mouse Model of Oxygen-Induced Retinopathy.

The sialomucins CD34 and podocalyxin (PODXL) are anti-adhesive molecules expressed at the luminal membrane of endothelial cells of small blood vessels and facilitate vascular lumen formation in the developing mouse aorta. CD34 transcript and protein levels are increased during human angiogenesis, its expression is particularly enriched on endothelial tip cell filopodia and CD34 is a marker for tip cells in vitro. Here, we investigated whether CD34 merely marks endothelial tip cells or has a functional role in tip cells and angiogenesis. We assessed that silencing CD34 in human microvascular endothelial cells has little effect on endothelial cell migration or invasion, but has a significant effect on vascular-endothelial growth factor-induced angiogenic sprouting activity in vitro. In vivo, the absence of CD34 reduced the density of filopodia on retinal endothelial tip cells in neonatal mice, but did not influence the overall architecture of the retinal vascular network. In oxygen-induced retinopathy, Cd34-/- mice showed normal intra-retinal regenerative angiogenesis but the number of pathological epi-retinal neovascular tufts were reduced. We conclude that CD34 is not essential for developmental vascularization in the retina, but its expression promotes the formation of pathological, invasive vessels during neovascularization.

Correction: CD34 Promotes Pathological Epi-Retinal Neovascularization in a Mouse Model of Oxygen-Induced Retinopathy.

[This corrects the article DOI: 10.1371/journal.pone.0157902.].