Novel Ratio Soluble Fms-like Tyrosine Kinase-1/Angiotensin-II (sFlt-1/ANG-II) in Pregnant Women Is Associated with Critical Illness in COVID-19.

BACKGROUND: In healthy pregnancies, components of the Renin-Angiotensin system (RAS) are present in the placental villi and contribute to invasion, migration, and angiogenesis. At the same time, soluble fms-like tyrosine kinase 1 (sFlt-1) production is induced after binding of ANG-II to its receptor (AT-1R) in response to hypoxia. As RAS plays an essential role in the pathogenesis of COVID-19, we hypothesized that angiogenic marker (sFlt-1) and RAS components (ANG-II and ACE-2) may be related to adverse outcomes in pregnant women with COVID-19; Methods: Prospective cohort study. Primary outcome was severe pneumonia. Secondary outcomes were ICU admission, intubation, sepsis, and death. Spearman's Rho test was used to analyze the correlation between sFlt-1 and ANG-II levels. The sFlt-1/ANG-II ratio was determined and the association with each adverse outcome was explored by logistic regression analysis and the prediction was assessed using receiver-operating-curve (ROC); Results: Among 80 pregnant women with COVID-19, the sFlt-1/ANG-II ratio was associated with an increased probability of severe pneumonia (odds ratio [OR]: 1.31; p = 0.003), ICU admission (OR: 1.05; p = 0.007); intubation (OR: 1.09; p = 0.008); sepsis (OR: 1.04; p = 0.008); and death (OR: 1.04; p = 0.018); Conclusion: sFlt-1/ANG-II ratio is a good predictor of adverse events such as pneumonia, ICU admission, intubation, sepsis, and death in pregnant women with COVID-19.

Circulating Maternal sFLT1 (Soluble fms-Like Tyrosine Kinase-1) Is Sufficient to Impair Spiral Arterial Remodeling in a Preeclampsia Mouse Model.

[Figure: see text].

Impairing flow-mediated endothelial remodeling reduces extravasation of tumor cells.

Tumor progression and metastatic dissemination are driven by cell-intrinsic and biomechanical cues that favor the growth of life-threatening secondary tumors. We recently identified pro-metastatic vascular regions with blood flow profiles that are permissive for the arrest of circulating tumor cells. We have further established that such flow profiles also control endothelial remodeling, which favors extravasation of arrested CTCs. Yet, how shear forces control endothelial remodeling is unknown. In the present work, we aimed at dissecting the cellular and molecular mechanisms driving blood flow-dependent endothelial remodeling. Transcriptomic analysis of endothelial cells revealed that blood flow enhanced VEGFR signaling, among others. Using a combination of in vitro microfluidics and intravital imaging in zebrafish embryos, we now demonstrate that the early flow-driven endothelial response can be prevented upon specific inhibition of VEGFR tyrosine kinase and subsequent signaling. Inhibitory targeting of VEGFRs reduced endothelial remodeling and subsequent metastatic extravasation. These results confirm the importance of VEGFR-dependent endothelial remodeling as a driving force of CTC extravasation and metastatic dissemination. Furthermore, the present work suggests that therapies targeting endothelial remodeling might be a relevant clinical strategy in order to impede metastatic progression.

The GEF Trio controls endothelial cell size and arterial remodeling downstream of Vegf signaling in both zebrafish and cell models.

Arterial networks enlarge in response to increase in tissue metabolism to facilitate flow and nutrient delivery. Typically, the transition of a growing artery with a small diameter into a large caliber artery with a sizeable diameter occurs upon the blood flow driven change in number and shape of endothelial cells lining the arterial lumen. Here, using zebrafish embryos and endothelial cell models, we describe an alternative, flow independent model, involving enlargement of arterial endothelial cells, which results in the formation of large diameter arteries. Endothelial enlargement requires the GEF1 domain of the guanine nucleotide exchange factor Trio and activation of Rho-GTPases Rac1 and RhoG in the cell periphery, inducing F-actin cytoskeleton remodeling, myosin based tension at junction regions and focal adhesions. Activation of Trio in developing arteries in vivo involves precise titration of the Vegf signaling strength in the arterial wall, which is controlled by the soluble Vegf receptor Flt1.

The soluble VEGF receptor sFlt-1 contributes to endothelial dysfunction in IgA nephropathy.

Endothelial injury is a common manifestation in IgA nephropathy (IgAN). After the previous identification of the upregulated soluble fms-like tyrosine kinase-1 (sFlt-1) correlated with endothelial injury in IgAN, in the present study, we further explored the role of sFlt-1 in endothelial injury in IgAN. We enrolled 72 patients with IgAN and detected the sFlt-1 levels. The polymeric IgA1 (pIgA1) complexes were isolated from the pooled plasma samples of another 10 patients with IgAN. Apoptosis proteins were detected in cultured human umbilical vein endothelial cells (HUVECs) with the stimulation of recombinant sFlt-1 or the caspase-9 inhibitor Z-LEHD-FMK. We identified there were positive correlations between sFlt-1 and IgA-IgG complex as well as vWF levels in patients with IgAN. The sFlt-1 levels in HUVECs were significantly upregulated by pIgA1 complex derived from IgAN patients in a concentration-dependent manner. The proliferation ability of HUVECs was damaged when stimulated with sFlt-1 protein in a time- and dose- dependent manner. And the apoptosis rate was up-regulated significantly as the stimulation concentrations of sFlt-1 increased. We found sFlt-1 challenge could significantly increase the expression of vWF. In addition, sFlt-1 increased the levels of caspase-9, caspase-3, Bax and mitochondrial membrane potential; facilitated the release of cytochrome C from mitochondria to cytoplasma. In contrast, Z-LEHD-FMK attenuated high sFlt-1-induced HUVECs apoptosis. In conclusion, our study demonstrated that sFlt-1 expression was up-regulated by the challenge of pIgA1 complex derived from patients with IgAN. Furthermore, increased sFlt-1 facilitated human umbilical vein endothelial cells apoptosis via the mitochondrial-dependent pathway.

Reconciling the distinct roles of angiogenic/anti-angiogenic factors in the placenta and maternal circulation of normal and pathological pregnancies.

A branched vascular network is crucial to placental development and is dependent on factors such as vascular endothelial growth factor (VEGF), placental growth factor (PlGF), angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), soluble fms-like tyrosine kinase-1 (sFlt-1) and soluble endoglin (sEng) to regulate blood vessel growth. Imbalances in these factors can lead to aberrant placental vascular development. Throughout pregnancy, these factors are also released into the maternal circulation to aid in adapting the maternal cardiovascular system to pregnancy. Increased secretion of anti-angiogenic factors can lead to the development of an anti-angiogenic state in the mother and contribute to the development of pregnancy pathologies such as pre-eclampsia and foetal growth restriction (FGR). Thus, what are commonly referred to as 'angiogenic factors' have distinct functions in the maternal and placental circulations making this a misnomer. Indeed, technical issues in this field such as assay methodology and lack of data considering different placental cell types mean that the physiological roles of these factors in the maternal and placental circulations are frequently muddled in the literature. This review aims to (1) unpick the distinct roles of factors that influence placental vascular development and separate these from the roles of the same factors within the maternal circulation in normal pregnancy and (2) critically assess how imbalances may contribute to the distinct pathophysiological mechanisms underlying pregnancy disorders. Together, this critical assessment of the field endeavours to improve our ability to accurately use these factors as predictive/diagnostic biomarkers in the future.

A Review of Angiogenic Imbalance in HIV-Infected Hypertensive Disorders of Pregnancy.

PURPOSE OF REVIEW: This review provides a comprehensive insight into the angiogenic profile of hypertensive and normotensive pregnancies compromised by HIV infection. Furthermore, we evaluate the economic implementation of the sFlt-1/PlGF ratio and review the reports on therapeutic apheresis in limiting sFlt-1 production. RECENT FINDINGS: In preeclampsia, an increased expression of sFlt-1 triggers angiogenic imbalance. Women of African ancestry have high levels of angiogenic factors than other racial groups. The sFlt-1/PlGF ratio shows promise in the early assessment of preeclampsia, while sFlt-1 apheresis restores angiogenic imbalance. Studies suggest antiretroviral therapy does not impact the angiogenic shift in preeclampsia development. The angiogenic profile in pregnant women of different races influences preeclampsia development. Despite the opposing immune response in HIV infection and preeclampsia, the HIV tat protein strongly mimics vascular endothelial growth factor (VEGF); hence, it is plausible to assume that HIV infection may ameliorate the angiogenic imbalance in preeclampsia.

[Potential value of placental angiogenic factors as biomarkers in preeclampsia for clinical physicians]. / Intérêts potentiels des facteurs angiogéniques placentaires comme biomarqueurs dans la pré-éclampsie pour le clinicien.

The role of angiogenic factors in the onset of clinical manifestations of preeclampsia was demonstrated in 2003 by the implication of sFlt-1, PlGF and VEGF, and in 2006 by the implication of soluble endoglin. Placental ischemia and inflammation observed in preeclampsia alter both the production and progression of angiogenic factors during pregnancy. During the first trimester, the combination of PlGF with clinical, biophysical and biological factors results in a better test than the conventional one. However, the clinical value of this method remains to be confirmed. During the second and third trimesters, the sFlt-1/PlGF ratio may be used, with or without pre-existing renal disease, for short-term prediction, diagnosis, and prognosis, and to evaluate the effectiveness of preeclampsia treatment. While a sFlt-1/PlGF ratio<38 and≤33, respectively, rules out the short-term onset and diagnosis of preeclampsia, a sFlt-1/PlGF ratio≥85 between 20 and 34 weeks of pregnancy and≥110 beyond 34 weeks of pregnancy confirms a diagnosis of preeclampsia. Angiogenic and non-angiogenic preeclampsia are identified by a sFlt-1PlGF≥85 and<85, respectively, with the risk of maternal and fetal complications at two weeks differing between the two. Similarly, a sFlt-1/PlGF ratio>665 and>205, respectively, is a good short-term predictor of adverse outcomes of early and late-onset preeclampsia. These values could be incorporated into future guidelines for better clinical management of preeclampsia.

The role of disordered angiogenesis tissue markers (sflt-1, Plgf) in present day diagnosis of preeclampsia.

Preeclampsia and conditions associated with impaired placental perfusion develop in almost 10% of all pregnancies. Patho- logic angiogenesis is one of the processes observed in preeclampsia. sFlt-1, PlGF and the sFlt-1/PlGF ratio are new and promising angiogenesis-related biomarkers. Our paper describes the present status of, and clinical practice opportunities for, these factors. According to present data, sFlt-1, PlGF and the sFlt-1/PlGF ratio are very useful tools in assessing placental angiogenesis abnormalities associated with preeclampsia and can be use in clinical practice.

VEGF receptor-1 modulates amyloid ß 1-42 oligomer-induced senescence in brain endothelial cells.

Aggregated amyloid ß (Aß) peptides in the Alzheimer's disease (AD) brain are hypothesized to trigger several downstream pathologies, including cerebrovascular dysfunction. Previous studies have shown that Aß peptides can have antiangiogenic properties, which may contribute to vascular dysfunction in the early stages of the disease process. We have generated data showing that brain endothelial cells (ECs) exposed to toxic Aß1-42 oligomers can readily enter a senescence phenotype. To determine the effect of Aß oligomers on brain ECs, we treated early passaged human brain microvascular ECs and HUVECs with high MW Aß1-42 oligomers (5 µM, for 72 h). For controls, we used no peptide treatment, 5 µM Aß1-42 monomers, and 5 µM Aß1-42 fibrils, respectively. Brain ECs treated with Aß1-42 oligomers showed increased senescence-associated ß-galactosidase staining and increased senescence-associated p21/p53 expression. Treatment with either Aß1-42 monomer or Aß1-42 fibrils did not induce senescence in this assay. We then measured vascular endothelial growth factor receptor (VEGFR) expression in the Aß1-42 oligomer-treated ECs, and these cells showed significantly increased VEGFR-1 expression and decreased VEGFR-2 levels. Overexpression of VEGFR-1 in brain ECs readily induced senescence, suggesting a direct role of VEGFR-1 signaling events in this paradigm. More importantly, small interfering RNA-mediated knockdown of VEGFR-1 expression in brain ECs was able to prevent up-regulation of p21 protein expression and significantly reduced induction of senescence following Aß1-42 oligomer treatment. Our studies show that exposure to Aß1-42 oligomers may impair vascular functions by altering VEGFR-1 expression and causing ECs to enter a senescent phenotype. Altered VEGFR expression has been documented in brains of AD patients and suggests that this pathway may play a role in AD disease pathogenesis. These studies suggest that modulating VEGFR-1 expression and signaling events could potentially prevent senescence and rejuvenate EC functions, and provides us with a novel target to pursue for prevention and treatment of cerebrovascular dysfunction in AD.-Angom, R. S., Wang, Y., Wang, E., Pal, K., Bhattacharya, S., Watzlawik, J. O., Rosenberry, T. L., Das, P., Mukhopadhyay, D. VEGF receptor-1 modulates amyloid ß 1-42 oligomer-induced senescence in brain endothelial cells.

Therapeutic implication of vascular endothelial growth factor receptor-1 (VEGFR-1) targeting in cancer cells and tumor microenvironment by competitive and non-competitive inhibitors.

The vascular endothelial growth factor receptor-1 (VEGFR-1) is a tyrosine kinase receptor for VEGF-A, VEGF-B, and placental growth factor (PlGF) ligands that is expressed in endothelial, myelomonocytic and tumor cells. VEGF-B and PlGF exclusively bind to VEGFR-1, whereas VEGF-A also binds to VEGFR-2. At variance with VEGFR-2, VEGFR-1 does not play a relevant role in physiological angiogenesis in the adult, while it is important in tumor-associated angiogenesis. VEGFR-1 and PlGF are expressed in a variety of tumors, promote invasiveness and contribute to resistance to anti-VEGF-A therapy. The currently approved antiangiogenic therapies for the treatment of a variety of solid tumors hamper VEGF-A signaling mediated by both VEGFR-2 and VEGFR-1 [i.e., the monoclonal antibody (mAb) anti-VEGF-A bevacizumab, the chimeric molecule aflibercept and several small molecule tyrosine kinase inhibitors] or exclusively by VEGFR-2 (i.e., the mAb anti-VEGFR-2 ramucirumab). However, molecules that interfere with VEGF-A/VEGFR-2 signaling determine severe adverse effects due to inhibition of physiological angiogenesis and their efficacy is hampered by tumor infiltration of protumoral myeloid cells. Blockade of VEGFR-1 may exert anti-tumor activity by multiple mechanisms: a) inhibition of tumor-associated angiogenesis; b) reduction of myeloid progenitor mobilization and tumor infiltration by VEGFR-1 expressing M2 macrophages, which contribute to tumor progression and spreading; c) inhibition of invasiveness, vasculogenic mimicry and survival of VEGFR-1 positive tumor cells. As a consequence of these properties, molecules targeting VEGFR-1 are expected to produce less adverse effects and to counteract resistance towards anti-VEGF-A therapies. More interestingly, selective VEGFR-1 inhibition might enhance the efficacy of immunotherapy with immune checkpoint inhibitors. In this review, we will examine the experimental evidence available so far that supports targeting VEGFR-1 signal transduction pathway for cancer treatment by competitive inhibitors that prevent growth factor interaction with the receptor and non-competitive inhibitors that hamper receptor activation without affecting ligand binding.

Soluble VEGFR1 signaling guides vascular patterns into dense branching morphologies.

Vascular patterning is a key process during development and disease. The diffusive decoy receptor sVEGFR1 (sFlt1) is a known regulator of endothelial cell behavior, yet the mechanism by which it controls vascular structure is little understood. We propose computational models to shed light on how vascular patterning is guided by self-organized gradients of the VEGF/sVEGFR1 factors. We demonstrate that a diffusive inhibitor can generate structures with a dense branching morphology in models where the activator elicits directed growth. Inadequate presence of the inhibitor leads to compact growth, while excessive production of the inhibitor blocks expansion and stabilizes existing structures. Model predictions were compared with time-resolved experimental data obtained from endothelial sprout kinetics in fibrin gels. In the presence of inhibitory antibodies against VEGFR1 vascular sprout density increases while the speed of sprout expansion remains unchanged. Thus, the rate of secretion and stability of extracellular sVEGFR1 can modulate vascular sprout density.

3-O-Acetyloleanolic acid inhibits VEGF-A-induced lymphangiogenesis and lymph node metastasis in an oral cancer sentinel lymph node animal model.

BACKGROUND: Sentinel lymph node metastasis is a common and early event in the metastatic process of head and neck squamous cell carcinoma (HNSCC) and is the most powerful prognostic factor for survival of HNSCC patients. 3-O-acetyloleanolic acid (3AOA), a pentacyclic triterpenoid compound isolated from seeds of Vigna sinensis K., has been reported to have potent anti-angiogenesis and anti-tumor activities. However, its effects on tumor-related lymphangiogenesis and lymph node metastasis are not yet understood. METHODS: The in vitro inhibitory effects of 3AOA on VEGF-A-induced lymphangiogenesis were investigated via in vitro experiments using mouse oral squamous cell carcinoma (SCCVII) cells and human lymphatic microvascular endothelial cells (HLMECs). The in vivo inhibitory effects of 3AOA on VEGF-A-induced lymphangiogenesis and sentinel lymph node metastasis were investigated in an oral cancer sentinel lymph node (OCSLN) animal model. RESULTS: 3AOA inhibited tumor-induced lymphangiogenesis and sentinel lymph node metastasis in an OCSLN animal model, and reduced expression of VEGF-A, a lymphangiogenic factor in hypoxia mimetic agent CoCl2-treated SCCVII cells. 3AOA inhibited proliferation, tube formation, and migration of VEGF-A-treated HLMECs. The lymphatic vessel formation that was stimulated in vivo in a by VEGF-A Matrigel plug was reduced by 3AOA. 3AOA suppressed phosphorylation of vascular endothelial growth factor (VEGFR) -1 and - 2 receptors that was stimulated by VEGF-A. In addition, 3AOA suppressed phosphorylation of the lymphangiogenesis-related downstream signaling factors PI3K, FAK, AKT, and ERK1/2. 3AOA inhibited tumor growth, tumor-induced lymphangiogenesis, and sentinel lymph node metastasis in a VEGF-A-induced OCSLN animal model that was established using VEGF-A overexpressing SCCVII cells. CONCLUSION: 3AOA inhibits VEGF-A-induced lymphangiogenesis and sentinel lymph node metastasis both in vitro and in vivo. The anti-lymphangiogenic effects of 3AOA are probably mediated via suppression of VEGF-A/VEGFR-1 and VEGFR-2 signaling in HLMECs, and can be a useful anti-tumor agent to restrict the metastatic spread of oral cancer.

Vascular endothelial growth factor receptor 1 (VEGFR1) tyrosine kinase signaling facilitates granulation tissue formation with recruitment of VEGFR1+ cells from bone marrow.

Vascular endothelial growth factor (VEGF)-A facilitates wound healing. VEGF-A binds to VEGF receptor 1 (VEGFR1) and VEGFR2 and induces wound healing through the receptor's tyrosine kinase (TK) domain. During blood flow recovery and lung regeneration, expression of VEGFR1 is elevated. However, the precise mechanism of wound healing, especially granulation formation on VEGFR1, is not well understood. We hypothesized that VEGFR1-TK signaling induces wound healing by promoting granulation tissue formation. A surgical sponge implantation model was made by implanting a sponge disk into dorsal subcutaneous tissue of mice. Granulation formation was estimated from the weight of the sponge and the granulation area from the immunohistochemical analysis of collagen I. The expression of fibroblast markers was estimated from the expression of transforming growth factor-beta (TGF-ß) and cellular fibroblast growth factor-2 (FGF-2) using real-time PCR (polymerase chain reaction) and from the immunohistochemical analysis of S100A4. VEGFR1 TK knockout (TK-/-) mice exhibited suppressed granulation tissue formation compared to that in wild-type (WT) mice. Expression of FGF-2, TGF-ß, and VEGF-A was significantly suppressed in VEGFR1 TK-/- mice, and the accumulation of VEGFR1+ cells in granulation tissue was reduced in VEGFR1 TK-/- mice compared to that in WT mice. The numbers of VEGFR1+ cells and S100A4+ cells derived from bone marrow (BM) were higher in WT mice transplanted with green fluorescent protein (GFP) transgenic WT BM than in VEGFR1 TK-/- mice transplanted with GFP transgenic VEGFR1 TK-/- BM. These results indicated that VEGFR1-TK signaling induced the accumulation of BM-derived VEGFR1+ cells expressing F4/80 and S100A4 and contributed to granulation formation around the surgically implanted sponge area in a mouse model.

VEGFR2 alteration in Alzheimer's disease.

Alzheimer's disease (AD) is a common disorder of progressive cognitive decline among elderly subjects. Angiogenesis-related factors including vascular endothelial growth factor (VEGF) might be involved in the pathogenesis of AD. Soluble form of the VEGF receptor is likely to be an intrinsic negative counterpart of VEGF. We measured the plasma levels of VEGF and its two soluble receptors (sVEGFR1 and sVEGFR2) in 120 control subjects, 75 patients with mild cognitive impairment, and 76 patients with AD using ELISA. Plasma levels of VEGF in patients with AD were higher than those in healthy control subjects. However, plasma levels of sVEGFR1 and sVEGFR2 were lower in patients with AD than in healthy control subjects. Levels of VEGFR2 mRNA were significantly decreased in human umbilical vein endothelial cells after amyloid-beta treatment. Further, protein levels of VEGFR2 were also decreased in the brains of AD model mice. In addition, we show that the expression of sVEGFR2 and VEGFR2 was also decreased by the transfection with the Notch intracellular domain. These results indicate that the alterations of VEGF and its two receptors levels might be associated with those at risk for Alzheimer's disease.

Inflammatory and Angiogenic Factors Linked to Longitudinal Microvascular Changes in Hemodialysis Patients Irrespective of Treatment Dose Intensity.

BACKGROUND: Cardiovascular disease is a major contributor to the poor outcomes observed in hemodialysis. We investigated the relationship between hemodialysis intensity and vascular parameters in high-dose (HDHD; >12hrs/week) and Conventional (CHD; ≤12hrs/week) hemodialysis intensity over a 6-month period. METHODS: We present the 6-month longitudinal analysis of a 2-year multicenter study investigating the effects of HDHD on cardiovascular parameters. We used pulse wave velocity, 24hr ambulatory blood pressure and sublingual dark field capillaroscopy measurements to assess macro- and microcirculation on 6-monthly basis. Pro-inflammatory and endothelial biomarkers were also measured at 6-monthly intervals. RESULTS: 47 participants (21 HDHD, 26 CHD) were studied. CHD were older (63.5±14.2 vs 53.7±12.6 yr; p=0.018), with shorter dialysis vintage (median 23 vs 61 months; p=0.001). There was considerable variability in the degree and direction of change of circulatory measurements over a 6-month period. Hemodialysis intensity (hrs/week) did not correlate to these changes, when adjusted for age, dialysis vintage and comorbidity. Higher levels of Interleukin (IL)-8 measured at baseline independently predicted an increase in the Perfused Boundary Region (5-25µm) of the endothelial glycocalyx (p=0.010) whilst higher levels of soluble Flt-1 had a significant inverse effect (p=0.002) in an adjusted linear model. CONCLUSION: Hemodialysis intensity did not predict changes in either macro- or microvascular parameters. Inflammation mediated through the IL-8 pathway predicted microvascular injury while Flt-1, a potential marker of angiogenesis and endothelial repair, might have a significant protective role. Further understanding of these pathways will be necessary to improve dialysis outcomes.

Vegfd modulates both angiogenesis and lymphangiogenesis during zebrafish embryonic development.

Vascular endothelial growth factors (VEGFs) control angiogenesis and lymphangiogenesis during development and in pathological conditions. In the zebrafish trunk, Vegfa controls the formation of intersegmental arteries by primary angiogenesis and Vegfc is essential for secondary angiogenesis, giving rise to veins and lymphatics. Vegfd has been largely thought of as dispensable for vascular development in vertebrates. Here, we generated a zebrafish vegfd mutant by genome editing. vegfd mutants display significant defects in facial lymphangiogenesis independent of vegfc function. Strikingly, we find that vegfc and vegfd cooperatively control lymphangiogenesis throughout the embryo, including during the formation of the trunk lymphatic vasculature. Interestingly, we find that vegfd and vegfc also redundantly drive artery hyperbranching phenotypes observed upon depletion of Flt1 or Dll4. Epistasis and biochemical binding assays suggest that, during primary angiogenesis, Vegfd influences these phenotypes through Kdr (Vegfr2) rather than Flt4 (Vegfr3). These data demonstrate that, rather than being dispensable during development, Vegfd plays context-specific indispensable and also compensatory roles during both blood vessel angiogenesis and lymphangiogenesis.

Differential regulation of blood flow-induced neovascularization and mural cell recruitment by vascular endothelial growth factor and angiopoietin signalling.

KEY POINTS: Combining nitric oxide (NO)-mediated increased blood flow with angiopoietin-1-Tie2 receptor signalling induces arteriolargenesis - the formation of arterioles from capillaries - in a model of physiological angiogenesis. This NO-Tie-mediated arteriolargenesis requires endogenous vascular endothelial growth factor (VEGF) signalling. Inhibition of VEGF signalling increases pericyte coverage in microvessels. Together these findings indicate that generation of functional neovasculature requires close titration of NO-Tie2 signalling and localized VEGF induction, suggesting that the use of exogenous VEGF expression as a therapeutic for neovascularization may not be successful. ABSTRACT: Signalling through vascular endothelial growth factor (VEGF) receptors and the tyrosine kinase with IgG and EGF domains-2 (Tie2) receptor by angiopoietins is required in combination with blood flow for the formation of a functional vascular network. We tested the hypothesis that VEGF and angiopoietin-1 (Ang1) contribute differentially to neovascularization induced by nitric oxide (NO)-mediated vasodilatation, by comparing the phenotype of new microvessels in the mesentery during induction of vascular remodelling by over-expression of endothelial nitric oxide synthase in the fat pad of the adult rat mesentery during inhibition of angiopoietin signalling with soluble Tie2 (sTie2) and VEGF signalling with soluble Fms-like tyrosine kinase receptor-1 (sFlt1). We found that NO-mediated angiogenesis was blocked by inhibition of VEGF with sFlt1 (from 881 ± 98% increase in functional vessel area to 279 ± 72%) and by inhibition of angiopoietin with sTie2 (to 337 ± 67%). Exogenous angiopoietin-1 was required to induce arteriolargenesis (8.6 ± 1.3% of vessels with recruitment of vascular smooth muscle cells; VSMCs) in the presence of enhanced flow. sTie2 and sFlt1 both inhibited VSMC recruitment (both 0%), and VEGF inhibition increased pericyte recruitment to newly formed vessels (from 27 ± 2 to 54 ± 3% pericyte ensheathment). We demonstrate that a fine balance of VEGF and angiopoietin signalling is required for the formation of a functional vascular network. Endogenous VEGF signalling prevents excess neovessel pericyte coverage, and is required for VSMC recruitment during increased nitric oxide-mediated vasodilatation and angiopoietin signalling (NO-Tie-mediated arteriogenesis). Therapeutic vascular remodelling paradigms may therefore require treatments that modulate blood flow to utilize endogenous VEGF, in combination with exogenous Ang1, for effective neovascularization.

Placental growth factor (PlGF) and sFlt-1 during pregnancy: physiology, assay and interest in preeclampsia.

The placental growth factor (PlGF) and its soluble receptor (sFlt-1) are circulating angiogenic factors. During pregnancy these factors are released by the placenta into the maternal circulation. Preeclampsia affects 2-7% of pregnant women according to their risk factors and is characterized by high blood pressure and the onset of de novo proteinuria in the second half of pregnancy. Alterations of the sFlt-1/PlGF ratio in preeclampsia correlate with the diagnosis and adverse outcomes, particularly when the disease presents prematurely (<34 weeks). These factors can be assayed in maternal blood and measuring the sFlt-1/PlGF ratio is now available. We propose in this work to update the knowledge of these two molecules, describe their roles and evolution during normal pregnancy and preeclampsia, and finally to focus on the available assays.