Placenta growth factor is not required for exercise-induced angiogenesis

Effects of lifelong spontaneous exercise on skeletal muscle and angiogenesis in super-aged mice

There has been an increasing awareness of sarcopenia, which is characterized by a concomitant decrease in skeletal muscle mass and quality due to aging. Resistance exercise is considered more effective than aerobic exercise in terms of therapeutic exercise. To confirm the effect of long-term aerobic exercise in preventing sarcopenia, we evaluated the skeletal muscle mass, quality, and angiogenic capacity of super-aged mice that had undergone lifelong spontaneous exercise (LSE) through various experiments. Our findings show that LSE could maintain skeletal muscle mass, quality, and fitness levels in super-aged mice. In addition, ex vivo experiments showed that the angiogenic capacity was maintained at a high level. However, these results were not consistent with the related changes in the expression of genes and/or proteins involved in protein synthesis or angiogenesis. Based on the results of previous studies, it seems certain that the expression at the molecular level does not represent the phenotypes of skeletal muscle and angiogenesis. This is because aging and long-term exercise are variables that can affect both protein synthesis and the expression patterns of angiogenesis-related genes and proteins. Therefore, in aging and exercise-related research, various physical fitness and angiogenesis variables and phenotypes should be analyzed. In conclusion, LSE appears to maintain the potential of angiogenesis and slow the aging process to maintain skeletal muscle mass and quality. Aerobic exercise may thus be effective for the prevention of sarcopenia.

Effects of exercise training with weight loss on skeletal muscle expression of angiogenic factors in overweight and obese older men

Low skeletal muscle capillarization is associated with impaired glucose tolerance (IGT); however, aerobic exercise training with weight loss (AEX + WL) increases skeletal muscle capillarization and improves glucose tolerance in adults with IGT. Given that the expression of angiogenic growth factors mediates skeletal muscle capillarization, we sought to determine whether angiogenic growth factor levels are associated with low capillarization in those with IGT versus normal glucose tolerance (NGT) or to the benefits of AEX + WL in both groups. Sixteen overweight or obese men 50-75 yr of age completed 6 mo of AEX + WL with oral glucose tolerance tests and vastus lateralis muscle biopsies for measurement of muscle vascular endothelial growth factor (VEGF), placental growth factor (PlGF), soluble fms-like tyrosine kinase receptor-1 (sFlt-1), and basic fibroblast growth factor (bFGF). At baseline, all growth factor levels were numerically lower in IGT than NGT, but these did not reach statistical significance (P = 0.06-0.33). Following AEX + WL, aerobic capacity [maximal oxygen consumption (V̇o2max)] increased by 16%, whereas body weight and 120-min postprandial glucose levels decreased by 10% and 15%, respectively (P ≤ 0.001 for all). There was a main effect of AEX + WL to increase VEGF (0.095 ± 0.016 vs. 0.114 ± 0.018 ng/µg, P < 0.05), PlGF (0.004 ± 0.001 vs. 0.005 ± 0.001 ng/µg, P < 0.05), and sFlt-1 (0.216 ± 0.029 vs. 0.264 ± 0.036 ng/µg, P < 0.01), with overall increases driven by the IGT group. These results suggest that 6 mo of AEX + WL increases skeletal muscle angiogenic growth factor levels in obese older adults with IGT and NGT, which may contribute to our previous findings that AEX + WL increases capillarization to improve glucose tolerance in those with IGT.NEW & NOTEWORTHY Skeletal muscle capillarization is lower in adults with impaired glucose tolerance than normal controls. This may, in part, be attributable to differential expression of angiogenic growth factors in skeletal muscle. Using a 6-mo aerobic exercise intervention with ∼10% body weight loss (AEX + WL), we show that the expression of angiogenic growth factors tends to be lower in adults with impaired glucose tolerance compared with normal controls and that AEX + WL increased expression of angiogenic growth factors in all participants.

Physical activity differentially regulates VEGF, PlGF, and their receptors in the human placenta

Physical activity (PA) has beneficial effects on the function of many organs by modulating their vascular development. Regular PA during pregnancy is associated with favorable short‐ and long‐term outcomes for both mother and fetus. During pregnancy, appropriate vascularization of the placenta is crucial for adequate maternal–fetal nutrient and gas exchange. How PA modulates angiogenic factors, VEGF, and its receptors in the human placenta, is as of yet, unknown. We objectively measured the PA of women at 24–28 and 34–38 weeks of gestation. Participants were considered “active” if they had met or exceeded 150 min of moderate‐intensity PA per week during their 2nd trimester. Term placenta tissues were collected from active (n = 23) or inactive (n = 22) women immediately after delivery. We examined the expression of the angiogenic factors VEGF, PlGF, VEGFR‐1, and VEGFR‐2 in the placenta. Western blot analysis showed VEGF and its receptor, VEGFR‐1 was significantly (p < 0.05) higher both at the protein and mRNA levels in placenta from physically active compared to inactive women. No difference in VEGFR‐2 was observed. Furthermore, immunohistochemistry showed differential staining patterns of VEGF and its receptors in placental endothelial, stromal, and trophoblast cells and in the syncytial brush border. In comparison, PlGF expression did not differ either at the protein or mRNA level in the placenta from physically active or inactive women. The expression and localization pattern of VEGF and its receptors suggest that PA during pregnancy may support a pro‐angiogenic milieu to the placental vascular network.

Placenta growth factor and sFlt-1 as biomarkers in ischemic heart disease and heart failure: a review

Coronary heart disease (CHD) and heart failure (HF) produce significant morbidity/mortality but identifying new biomarkers could help in the management of each. In this article, we summarize the molecular regulation and biomarker potential of PIGF and sFlt-1 in CHD and HF. PlGF is elevated during ischemia and some studies have shown PlGF, sFlt-1 or PlGF:sFlt-1 ratio, when used in combination with standard biomarkers, strengthens predictions of outcomes. sFlt-1 and PlGF are elevated in HF with sFlt-1 as a stronger predictor of outcomes. Although promising, we discuss additional study criteria needed to confirm the clinical usefulness of PlGF or sFlt-1 in the detection and management of CHD or HF.

The Placental Growth Factor Pathway and Its Potential Role in Macular Degenerative Disease

There is growing evidence that placental growth factor (PlGF) is an important player in multiple pathologies, including tumorigenesis, inflammatory disorders and degenerative retinopathies. PlGF is a member of the vascular endothelial growth factor (VEGF) family and in the retina, binding of this growth factor to specific receptors is associated with pathological angiogenesis, vascular leakage, neurodegeneration and inflammation. Although they share some receptor signalling pathways, many of the actions of PlGF are distinct from VEGF and this has revealed the enticing prospect that it could be a useful therapeutic target for treating early and late stages of diabetic retinopathy (DR) and neovascular age-related macular degeneration (AMD). Recent research suggests that modulation of PlGF could also be important in the geographic atrophy (GA) form of late AMD by protecting the outer retina and the retinal pigment epithelium (RPE). This review discusses PlGF and its signalling pathways and highlights the potential of blocking the bioactivity of this growth factor to treat irreversible visual loss due to the two main forms of AMD.

Hypoxia activates placental growth factor expression in lymphatic endothelial cells

Placental growth factor (PlGF), a proangiogenic member of vascular endothelial growth family, is active during pathological conditions like cancer, metastasis formation and hind limb ischemia and in wound healing. Endothelial cells express PlGF and hypoxia positively modulates in vitro its expression. To verify whether hypoxia modulates PlGF expression in different cellular contexts and in vivo, we first analyzed five human and five mouse cancer cell lines showing that in eight of them hypoxia positively modulates PlGF. Next, we analyzed xenograft colorectal cancer tumors showing that human cancer cells were able to express PlGF in hypoxic area of the tumor. Surprisingly, we did not visualize mouse PlGF in CD31 positive tumor vessels, but in low CD31 positive vessels, a characteristic of lymphatic vessels. We found that hypoxia effectively activates PlGF expression in lymphatic endothelial cells as well as in LYVE1 positive tumor vessels. We also investigated two additional mouse angiogenic models, hind limb ischemia and wound healing, and we confirmed that lymphatic vessels of both ischemic muscles and skin express PlGF. These results show for the first time that hypoxia activates PlGF expression in lymphatic endothelial cells, which have to be considered an additional source for PlGF production in pathological contexts.

Molecular Regulation of Sprouting Angiogenesis

The term angiogenesis arose in the 18th century. Several studies over the next 100 years laid the groundwork for initial studies performed by the Folkman laboratory, which were at first met with some opposition. Once overcome, the angiogenesis field has flourished due to studies on tumor angiogenesis and various developmental models that can be genetically manipulated, including mice and zebrafish. In addition, new discoveries have been aided by the ability to isolate primary endothelial cells, which has allowed dissection of various steps within angiogenesis. This review will summarize the molecular events that control angiogenesis downstream of biochemical factors such as growth factors, cytokines, chemokines, hypoxia-inducible factors (HIFs), and lipids. These and other stimuli have been linked to regulation of junctional molecules and cell surface receptors. In addition, the contribution of cytoskeletal elements and regulatory proteins has revealed an intricate role for mobilization of actin, microtubules, and intermediate filaments in response to cues that activate the endothelium. Activating stimuli also affect various focal adhesion proteins, scaffold proteins, intracellular kinases, and second messengers. Finally, metalloproteinases, which facilitate matrix degradation and the formation of new blood vessels, are discussed, along with our knowledge of crosstalk between the various subclasses of these molecules throughout the text. Compr Physiol 8:153-235, 2018.

Molecular Mechanisms for Exercise Training-Induced Changes in Vascular Structure and Function: Skeletal Muscle, Cardiac Muscle, and the Brain

Compared with resting conditions, during incremental exercise, cardiac output in humans is elevated from ~5 to 25 L min(-1). In conjunction with this increase, the proportion of cardiac output directed toward skeletal muscle increases from ~20% to 85%, while blood flow to cardiac muscle increases 500% and blood flow to specific brain structures increases nearly 200%. Based on existing evidence, researchers believe that blood flow in these tissues is matched to the increases in metabolic rate during exercise. This phenomenon, the matching of blood flow to metabolic requirement, is often referred to as functional hyperemia. This chapter summarizes mechanical and metabolic factors that regulate functional hyperemia as well as other exercise-induced signals, which are also potent stimuli for chronic adaptations in vascular biology. Repeated exposure to exercise-induced increases in shear stress and the induction of angiogenic factors alter vascular cell gene expression and mediate changes in vascular volume and blood flow control. The magnitude and regulation of this coordinated response appear to be tissue specific and coupled to other factors such as hypertrophy and hyperplasia. The cumulative effects of these adaptations contribute to increased exercise capacity, reduced relative challenge of a given submaximal exercise bout and ameliorated vascular outcomes in patient populations with pathological conditions. In the subsequent discussion, this chapter explores exercise as a regulator of vascular biology and summarizes the molecular mechanisms responsible for exercise training-induced changes in vascular structure and function in skeletal and cardiac muscle as well as the brain.

Circulating angiogenic and inflammatory cytokine responses to acute aerobic exercise in trained and sedentary young men

PURPOSE

Endurance exercise training can ameliorate many cardiovascular and metabolic disorders and attenuate responses to inflammatory stimuli. The purpose of this study was to determine whether the angiogenic and pro-inflammatory cytokine response to acute endurance exercise differs between endurance-trained and sedentary young men.

METHODS

Ten endurance-trained and ten sedentary healthy young men performed 30 min of treadmill running at 75 % VO2max with blood sampling before and after exercise. Plasma concentrations of tumor necrosis factor (TNF)-alpha, interleukin (IL)-8, IL-6, vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), placental growth factor (PlGF), and soluble VEGF receptor-1 (sFlt-1) were measured by multiplex ELISA.

RESULTS

Acute exercise increased IL-6 by 165 % (P < 0.05), IL-8 by 32 % (P < 0.05), PlGF by ~16 % (P < 0.05), sFlt-1 by 36 % (P < 0.001), and tended to increase bFGF by ~25 % (P = 0.06) in main effects analyses. TNF-α and VEGF did not change significantly with exercise in either group. Contrary to our hypothesis, there were no significant differences in TNF-α, IL-6, VEGF, bFGF, PlGF, or sFlt-1 between groups before or after acute exercise; however, there was a tendency for IL-8 concentrations to be higher in endurance-trained subjects compared to sedentary subjects (P = 0.06).

CONCLUSIONS

These results indicate that 30 min of treadmill running at 75 % VO2max produces a systemic angiogenic and inflammatory reaction, but endurance exercise training does not appear to significantly alter these responses in healthy young men.

Microvascular repair: post-angiogenesis vascular dynamics

Vascular compromise and the accompanying perfusion deficits cause or complicate a large array of disease conditions and treatment failures. This has prompted the exploration of therapeutic strategies to repair or regenerate vasculatures, thereby establishing more competent microcirculatory beds. Growing evidence indicates that an increase in vessel numbers within a tissue does not necessarily promote an increase in tissue perfusion. Effective regeneration of a microcirculation entails the integration of new stable microvessel segments into the network via neovascularization. Beginning with angiogenesis, neovascularization entails an integrated series of vascular activities leading to the formation of a new mature microcirculation, and includes vascular guidance and inosculation, vessel maturation, pruning, AV specification, network patterning, structural adaptation, intussusception, and microvascular stabilization. While the generation of new vessel segments is necessary to expand a network, without the concomitant neovessel remodeling and adaptation processes intrinsic to microvascular network formation, these additional vessel segments give rise to a dysfunctional microcirculation. While many of the mechanisms regulating angiogenesis have been detailed, a thorough understanding of the mechanisms driving post-angiogenesis activities specific to neovascularization has yet to be fully realized, but is necessary to develop effective therapeutic strategies for repairing compromised microcirculations as a means to treat disease.

Stimulatory effects of the flavanol (-)-epicatechin on cardiac angiogenesis: additive effects with exercise

The consumption of moderate amounts of cocoa products has been associated with reductions in the incidence of cardiovascular diseases. In animal studies, the flavanol (-)-epicatechin (Epi) yields cardioprotection. The effects may be partly due to its capacity to stimulate endothelial nitric oxide synthase (eNOS). The sustained activation of eNOS, as observed with exercise, can serve as a trigger of muscle angiogenesis via the activation of vascular endothelial growth factor (VEGF)-related events. Experiments were pursued to examine the potential of Epi to stimulate myocardial angiogenesis and determine the effects that its combined use with exercise (Ex) may trigger. Hearts obtained from a previous study were used for this purpose. Animals received 1 mg/kg of Epi or water (vehicle) via oral gavage (twice daily). Epi and/or Ex (by treadmill) was provided for 15 days. Results indicate that Ex or Epi significantly stimulate myocardial angiogenesis by ~30% above control levels. The use of Epi-Ex lead to further significant increases (to ~50%). Effects were associated with increases in protein levels and/or activation of canonical angiogenesis pathway associated events (HIF1a, VEGF, VEGFR2, PI3K, PDK, AKT, eNOS, NO, cGMP, MMP-2/-9, Src-1, and CD31). Thus, the use of Epi may represent a safe and novel means to stimulate myocardial angiogenesis.

Placental growth factor as a protective paracrine effector in the heart

In response to injury, the myocardium hypertrophies in an attempt to maintain or augment function, which is associated with ventricular remodeling and changes in capillary density. During the compensatory phase of the hypertrophic response, the myocardium maintains output and is characterized by a coordinated neo-angiogenic and fibrotic response that supports cardiomyocyte health and survival. Emerging evidence shows that paracrine-mediated cross talk between cardiac myocytes and nonmyocytes within the heart is critical for cardiac adaptation to stress, including the extent of hypertrophy and angiogenesis. This review discusses recent results indicating that placental growth factor (PGF; also called PlGF), a secreted factor within the vascular endothelial growth factor superfamily, is a pivotal mediator of adaptive cardiac hypertrophy and beneficial angiogenesis through its ability to coordinate the intercellular communication between different cell types in the heart.

Exercise training and peripheral arterial disease

Peripheral arterial disease (PAD) is a common vascular disease that reduces blood flow capacity to the legs of patients. PAD leads to exercise intolerance that can progress in severity to greatly limit mobility, and in advanced cases leads to frank ischemia with pain at rest. It is estimated that 12 to 15 million people in the United States are diagnosed with PAD, with a much larger population that is undiagnosed. The presence of PAD predicts a 50% to 1500% increase in morbidity and mortality, depending on severity. Treatment of patients with PAD is limited to modification of cardiovascular disease risk factors, pharmacological intervention, surgery, and exercise therapy. Extended exercise programs that involve walking approximately five times per week, at a significant intensity that requires frequent rest periods, are most significant. Preclinical studies and virtually all clinical trials demonstrate the benefits of exercise therapy, including improved walking tolerance, modified inflammatory/hemostatic markers, enhanced vasoresponsiveness, adaptations within the limb (angiogenesis, arteriogenesis, and mitochondrial synthesis) that enhance oxygen delivery and metabolic responses, potentially delayed progression of the disease, enhanced quality of life indices, and extended longevity. A synthesis is provided as to how these adaptations can develop in the context of our current state of knowledge and events known to be orchestrated by exercise. The benefits are so compelling that exercise prescription should be an essential option presented to patients with PAD in the absence of contraindications. Obviously, selecting for a lifestyle pattern that includes enhanced physical activity prior to the advance of PAD limitations is the most desirable and beneficial.

PlGF: a multitasking cytokine with disease-restricted activity

Placental growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family that also comprises VEGF-A (VEGF), VEGF-B, VEGF-C, and VEGF-D. Unlike VEGF, PlGF is dispensable for development and health but has diverse nonredundant roles in tissue ischemia, malignancy, inflammation, and multiple other diseases. Genetic and pharmacological gain-of-function and loss-of-function studies have identified molecular mechanisms of this multitasking cytokine and characterized the therapeutic potential of delivering or blocking PlGF for various disorders.

The discovery of placenta growth factor and its biological activity

Angiogenesis is a complex biological phenomenon crucial for a correct embryonic development and for post-natal growth. In adult life, it is a tightly regulated process confined to the uterus and ovary during the different phases of the menstrual cycle and to the heart and skeletal muscles after prolonged and sustained physical exercise. Conversly, angiogenesis is one of the major pathological changes associated with several complex diseases like cancer, atherosclerosis, arthritis, diabetic retinopathy and age-related macular degeneration. Among the several molecular players involved in angiogenesis, some members of VEGF family, VEGF-A, VEGF-B and placenta growth factor (PlGF), and the related receptors VEGF receptor 1 (VEGFR-1, also known as Flt-1) and VEGF receptor 2 (VEGFR-2, also known as Flk-1 in mice and KDR in human) have a decisive role. In this review, we describe the discovery and molecular characteristics of PlGF, and discuss the biological role of this growth factor in physiological and pathological conditions.

Venous thromboembolism in patients with cancer and its relationship to the coagulation cascade and vascular endothelial growth factor

Venous thromboembolism (VTE) is a well-recognized problem in malignancy. Patients with cancer who have VTE have a worse prognosis than other patients with cancer. Hypercoagulability in patients with cancer is related to malignancy itself and its treatment. These patients have multiple risk factors for thromboembolism, such as being immobilized, having central venous catheters, and receiving chemoradiation therapy. Cancer procoagulant, tissue factor, factor VIII, and thrombin have important roles in causing cancer-associated thromboembolism. Tumors require neovascularization for delivering oxygen and other nutrients. Therefore, angiogenesis facilitates tumor growth, invasion, and metastasis. New blood vessels formed by angiogenesis are thrombogenic. Hypercoagulability and tumor growth are closely related. Vascular endothelial growth factor (VEGF) is a proangiogenic factor that may also cause VTE in patients with cancer. The relationship between cancer, angiogenesis, VEGF, and thrombosis is reviewed herein. Studies are ongoing to enhance our understanding of this complex interaction.

Myocyte vascular endothelial growth factor is required for exercise-induced skeletal muscle angiogenesis

We have previously shown, using a Cre-LoxP strategy, that vascular endothelial growth factor (VEGF) is required for the development and maintenance of skeletal muscle capillarity in sedentary adult mice. To determine whether VEGF expression is required for skeletal muscle capillary adaptation to exercise training, gastrocnemius muscle capillarity was measured in myocyte-specific VEGF gene-deleted (mVEGF(-/-)) and wild-type (WT) littermate mice following 6 wk of treadmill running (1 h/day, 5 days/wk) at the same running speed. The effect of training on metabolic enzyme activity levels and whole body running performance was also evaluated in mVEGF(-/-) and WT mice. Posttraining capillary density was significantly increased by 59% (P < 0.05) in the deep muscle region of the gastrocnemius in WT mice but did not change in mVEGF(-/-) mice. Maximal running speed and time to exhaustion during submaximal running increased by 20 and 13% (P < 0.05), respectively, in WT mice after training but were unchanged in mVEGF(-/-) mice. Training led to increases in skeletal muscle citrate synthase (CS) and phosphofructokinase (PFK) activities in both WT and mVEGF(-/-) mice (P < 0.05), whereas β-hydroxyacyl-CoA dehydrogenase (β-HAD) activity was increased only in WT mice. These data demonstrate that skeletal muscle capillary adaptation to physical training does not occur in the absence of myocyte-expressed VEGF. However, skeletal muscle metabolic adaptation to exercise training takes place independent of myocyte VEGF expression.

Hypoxia increases placenta growth factor expression in human myocardium and cultured neonatal rat cardiomyocytes

BACKGROUND

Placenta growth factor (PlGF) plays an important role in pathologic angiogenesis and is believed to be an independent biomarker in patients with coronary artery disease. However, little is known regarding the regulation of PlGF expression in heart tissue.

METHODS

We determined expression changes in PlGF and its receptor, VEGFR1, in normal and abnormal biopsies from human cardiac allografts and in cardiomyocytes cultured under hypoxia or cyclical stretch conditions.

RESULTS

Human donor myocardium and biopsies from allografts without fibrin deposits expressed PlGF and VEGFR1 mRNA. Biopsies (n = 7) with myocardial fibrin, elevated serum cardiac troponin I titers (p < 0.03) and cellular infiltrates (p < 0.05) expressed 1.6-fold more PlGF mRNA than biopsies from allografts without fibrin (n = 11; p < 0.05). PlGF protein was localized in cardiomyocytes, extracellular matrix and some microvessels in areas with fibrin deposition. VEGFR1 mRNA expression was not different between groups. Cultured neonatal rat cardiomyocytes constitutively expressed PlGF/VEGFR1 under normoxia. PlGF expression was increased 3.88 +/- 0.62-fold after 12 hours (n = 6; p </= 0.05) and 3.64 +/- 0.41-fold after 24 hours of hypoxia (n = 6; p <or= 0.05). Shorter periods of hypoxia, conditioned media from hypoxic cells and cyclical stretch did not significantly alter PlGF or VEGFR1 expression.

CONCLUSIONS

Cardiomyocyte PIGF expression is upregulated by hypoxia in vitro and its expression increases significantly in allografts with myocardial damage. Collectively, these results provide important temporal and spatial evidence that endogenous PlGF may facilitate cardiac healing after myocardial hypoxia/ischemia.

FLT1 and its ligands VEGFB and PlGF: drug targets for anti-angiogenic therapy?

Less than 5 years ago, it was still not clear whether anti-angiogenic drugs would prove successful in the clinic. After numerous patients with cancer or age-related macular degeneration have been treated with these drugs, they have now become part of the standard range of therapeutic tools. Despite this milestone, anti-angiogenic therapy still faces a number of clinical hurdles, such as improving efficacy, avoiding escape and resistance, and minimizing toxicity. Hopefully, other agents with complementary mechanisms, such as those that target placental growth factor, will offer novel opportunities for improved treatment.

Redox regulation of the VEGF signaling path and tissue vascularization: Hydrogen peroxide, the common link between physical exercise and cutaneous wound healing

Vascularization, under physiological or pathophysiological conditions, typically takes place by one or more of the following processes: angiogenesis, vasculogenesis, arteriogenesis, and lymphangiogenesis. Although all of these mechanisms of vascularization have sufficient contrasting features to warrant consideration under separate cover, one common feature shared by all is their sensitivity to the VEGF signaling pathway. Conditions such as wound healing and physical exercise result in increased production of reactive oxygen species such as H(2)O(2), and both are associated with increased tissue vascularization. Understanding these two scenarios of adult tissue vascularization in tandem offers the potential to unlock the significance of redox regulation of the VEGF signaling pathway. Does H(2)O(2) support tissue vascularization? H(2)O(2) induces the expression of the most angiogenic form of VEGF, VEGF-A, by a HIF-independent and Sp1-dependent mechanism. Ligation of VEGF-A to VEGFR2 results in signal transduction leading to tissue vascularization. Such ligation generates H(2)O(2) via an NADPH oxidase-dependent mechanism. Disruption of VEGF-VEGFR2 ligation-dependent H(2)O(2) production or decomposition of such H(2)O(2) stalls VEGFR2 signaling. Numerous antioxidants exhibit antiangiogenic properties. Current evidence lends firm credence to the hypothesis that low-level endogenous H(2)O(2) supports vascular growth.

Plgf−/−eNos−/−mice show defective angiogenesis associated with increased oxidative stress in response to tissue ischemia

Neo-angiogenesis is a complex phenomenon modulated by the concerted action of several molecular factors. We have generated a congenic line of knockout mice carrying null mutations of both placental growth factor (PlGF) and endothelial nitric oxide synthase (eNOS), two genes that play a pivotal role in the regulation of pathological angiogenesis. In the present study, we describe the phenotype of this new experimental animal model after surgically induced hind-limb ischemia. Plgf-/-, eNos-/-, Plgf-/- eNos-/-, and wild-type C57BL/6J mice were studied. Plgf-/- eNos-/- mice showed the most severe phenotype: self-amputation, and death occurred in up to 47% of the animals studied; in ischemic legs, capillary density was severely reduced; macrophage infiltration and oxidative stress increased as compared to the other groups of animals. These changes were associated with an up-regulation of both inducible NOS (iNOS) expression and vascular endothelial growth factor (VEGF) protein levels in ischemic limbs, and to an increased extent of protein nitration. Our results demonstrate that the deletion of these two genes, Plgf, which acts in synergism with VEGF, and eNos, a downstream mediator of VEGF, determines a significant change in the vascular response to an ischemic stimulus and that oxidative stress within the ischemic tissue represents a crucial factor to maintain tissue homeostasis.

Angiogenesis during exercise and training

In this review the factors involved in angiogenesis are discussed in their various roles in initiating angiogenesis and inducing changes in the extracellular matrix to facilitate sprouting angiogenesis which is a major part of the angiogenesis seen in exercise and exercise training. A key role in angiogenesis is played by vascular endothelial growth factor (VEGF). The regulation of blood vessel growth to match the needs of the tissue depends on the control of VEGF production through changes in the stability of its mRNA and in its rate of transcription. The detailed studies describing its characteristics and its upregulation in acute exercise are presented along with a brief overview of the changes in the extracellular matrix that facilitate sprouting angiogenesis that occurs in response to exercise and training. Although the mechanisms involved in the growth and remodeling of arterioles and larger vessels are less detailed some recent studies have provided new insights. These are presented here to show a relationship between capillary development and arteriolar growth or remodeling in exercise training that raises questions to be addressed in future studies.