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Objective: Cx40 (Connexin40) forms intercellular channels that coordinate the electric conduction in the heart and the vasomotor tone in large vessels. The protein was shown to regulate tumoral angiogenesis; however, whether Cx40 also contributes to physiological angiogenesis is still unknown., Approach and Results: Here, we show that Cx40 contributes to physiological angiogenesis. Genetic deletion of Cx40 leads to a reduction in vascular growth and capillary density in the neovascularization model of the mouse neonatal retina. At the angiogenic front, vessel sprouting is reduced, and the mural cells recruited along the sprouts display an altered phenotype. These alterations can be attributed to disturbed endothelial cell functions as selective reexpression of Cx40 in these cells restores normal angiogenesis. In vitro, targeting Cx40 in microvascular endothelial cells, by silencing its expression or by blocking gap junction channels, decreases their proliferation. Moreover, loss of Cx40 in these cells also increases their release of PDGF (platelet-derived growth factor) and promotes the chemoattraction of mural cells. In vivo, an intravitreal injection of a Cx40 inhibitory peptide, phenocopies the loss of Cx40 in the retinal vasculature of wild-type mice., Conclusions: Collectively, our data show that endothelial Cx40 contributes to the early stages of physiological angiogenesis in the developing retina, by regulating vessel growth and maturation. Cx40 thus represents a novel therapeutic target for treating pathological ocular angiogenesis., (© 2017 American Heart Association, Inc.)

Background: Current options for in vivo regeneration of dermal tissue remain limited. The purpose of this study was to engineer a unique scaffold capable of recruiting dermal stem cells from adjacent tissue, thus circumventing the need to seed the scaffolds with stem cells before implantation, leading to skin regeneration., Methods: A hydrogel scaffold was created through combination of type I collagen along with fractionated platelet-rich plasma. This was compared to a control hydrogel consisting of type I collagen and fetal bovine serum. Hydrogels were cultured with fresh human skin tissue and incubated with supplemental media. Gels were digested weekly for cellular content as examined by flow cytometry at the 4- and 8-week time points. The fractionated platelet-rich plasma and collagen gels were then implanted onto full-thickness skin defects on the backs of rats and compared to wounds healing by secondary intention. Wound area was evaluated for epithelialization and neovascularization., Results: Platelet-rich plasma fractionation increased platelet-derived growth factors. In contrast to collagen scaffolds, fractionated platelet-rich plasma-supplemented scaffolds recruited more dermal-derived stem cells from fresh skin tissue compared with collagen hydrogels at the 4- and 8-week time points. Furthermore, fractionated platelet-rich plasma-supplemented hydrogels accelerated wound healing, angiogenesis, and hair and sweat gland formation, ultimately regenerating a dermis-like tissue., Conclusions: Generation of hydrogels with fractionated platelet-rich plasma was able to improve cellular recruitment and growth and differentiation of dermal-derived stem cells, leading to hair growth and sweat gland formation. This provides a novel approach to regenerate skin for treating large defects.

Background: Resveratrol may provide protection against coronary artery disease. We hypothesized that supplemental resveratrol will improve cardiac perfusion in the ischemic territory of swine with hypercholesterolemia and chronic myocardial ischemia., Methods and Results: Yorkshire swine were fed either a normal diet (control, n=7), a hypercholesterolemic diet (HCC, n=7), or a hypercholesterolemic diet with supplemental resveratrol (100 mg/kg/d orally, HCRV, n=7). Four weeks later, an ameroid constrictor was placed on the left circumflex artery. Animals underwent cardiac MRI and coronary angiography 7 weeks later before euthanasia and tissue harvest. Total cholesterol was lowered about 30% in HCRV animals (P<0.001). Regional wall motion analysis demonstrated a significant decrease in inferolateral function from baseline to 7 weeks in HCC swine (P=0.04). There was no significant change in regional function in HCRV swine from baseline to 7 weeks (P=0.32). Tissue blood flow during stress was 2.8-fold greater in HCRV swine when compared with HCC swine (P=0.04). Endothelium-dependent microvascular relaxation response to Substance P was diminished in HCC swine, which was rescued by resveratrol treatment (P=0.004). Capillary density (PECAM-1 staining) demonstrated fewer capillaries in both HCC and HCRV swine versus control swine (P=0.02). Immunoblot analysis demonstrated significantly greater expression in HCRV versus HCC swine of the following markers of angiogenesis: VEGF (P=0.002), peNOS (ser1177) (P=0.04), NFkB (P=0.004), and pAkt (thr308) (P=0.001)., Conclusions: Supplemental resveratrol attenuates regional wall motion abnormalities, improves myocardial perfusion in the collateral dependent region, preserves endothelium-dependent coronary vessel function, and upregulates markers of angiogenesis associated with the VEGF signaling pathway.

Synthetic alkylphospholipids (APLs), such as edelfosine, miltefosine and perifosine, constitute a new class of antineoplastic compounds with various clinical applications. Here we have evaluated the antiangiogenic properties of APLs. The sensitivity of three types of vascular endothelial cells (ECs) (bovine aortic ECs, human umbilical vein ECs and human microvascular ECs) to APL-induced apoptosis was dependent on the proliferative status of these cells and correlated with the cellular drug incorporation. Although confluent, nondividing ECs failed to undergo apoptosis, proliferating ECs showed a 3-4-fold higher uptake and significant levels of apoptosis after APL treatment. These findings raised the question of whether APLs interfere with new blood vessel formation. To test the antiangiogenic properties in vitro, we studied the effect of APLs using two different experimental models. The first one tested the ability of human microvascular ECs to invade a three-dimensional human fibrin matrix and form capillary-like tubular networks. In the second model, bovine aortic ECs were grown in a collagen gel sandwich to allow tube formation. We found that all three APLs interfered with endothelial tube formation in a dose-dependent manner, with a more than 50% reduction at 25 micromol/l. Interference with the angiogenic process represents a novel mode of action of APLs and might significantly contribute to the antitumor effect of these compounds.

Background: For clinically relevant proangiogenic therapy, it would be essential that the growth of the whole vascular tree is promoted. Vascular endothelial growth factor (VEGF) is well known to induce angiogenesis, but its capability to promote growth of larger vessels is controversial. We hypothesized that blood flow remodels vascular growth during VEGF gene therapy and may contribute to the growth of large vessels., Methods and Results: Adenoviral (Ad) VEGF or LacZ control gene transfer was performed in rabbit hindlimb semimembranous muscles with or without ligation of the profound femoral artery (PFA). Contrast-enhanced ultrasound and dynamic susceptibility contrast MRI demonstrated dramatic 23- to 27-fold increases in perfusion index and a strong decrease in peripheral resistance 6 days after AdVEGF gene transfer in normal muscles. Enlargement by 20-fold, increased pericyte coverage, and decreased alkaline phosphatase and dipeptidyl peptidase IV activities suggested the transformation of capillaries toward an arterial phenotype. Increase in muscle perfusion was attenuated, and blood vessel growth was more variable, showing more sprouting angiogenesis and formation of blood lacunae after AdVEGF gene transfer in muscles with ligated PFA than in normal muscles. Three-dimensional ultrasound reconstructions and histology showed that the whole vascular tree, including large arteries and veins, was enlarged manifold by AdVEGF. Blood flow was normalized and enlarged collaterals persisted in operated limbs 14 days after AdVEGF treatment., Conclusions: This study shows that (1) blood flow modulates vessel growth during VEGF gene therapy and (2) VEGF overexpression promotes growth of arteries and veins and induces capillary arterialization leading to supraphysiological blood flow in target muscles.

Background: Neovascularization is potentially important for the treatment of ischemic heart and limb disease. We reported that reactive oxygen species (ROS) derived from gp91phox (Nox2)-containing NAD(P)H oxidase are involved in angiogenesis in mouse sponge models as well as in vascular endothelial growth factor (VEGF) signaling in cultured endothelial cells. The role of gp91phox-derived ROS in neovascularization in response to tissue ischemia is unknown, however., Methods and Results: Here, we show that neovascularization in the ischemic hindlimb is significantly impaired in gp91phox-/- mice as compared with wild-type (WT) mice as evaluated by laser Doppler flow, capillary density, and microsphere measurements. In WT mice, inflammatory cell infiltration in the ischemic hindlimb was maximal at 3 days, whereas capillary formation was prominent at 7 days when inflammatory cells were no longer detectable. Increased O2*- production and gp91phox expression were present at both time points. The dihydroethidium staining of ischemic tissues indicates that O2*- is mainly produced from inflammatory cells at 3 days and from neovasculature at 7 days after operation. Relative to WT mice, ischemia-induced ROS production in gp91phox-/- mice at both 3 and 7 days was diminished, whereas VEGF expression was enhanced and the inflammatory response was unchanged. Infusion of the antioxidant ebselen into WT mice also significantly blocked the increase in blood flow recovery and capillary density after ischemia., Conclusions: gp91phox-derived ROS play an important role in mediating neovascularization in response to tissue ischemia. NAD(P)H oxidases and their products are potential therapeutic targets for regulating angiogenesis in vivo.

Blood flow to contracting muscles is increased rapidly and is redistributed within the muscle. Recent research has highlighted that insulin causes similar changes, but these are absent in insulin resistance, resulting in impaired insulin-mediated muscle glucose uptake. Understanding the mechanisms and interactions between contraction- and insulin-mediated alterations in blood flow within muscle may reveal new approaches to overcome insulin resistance.

L-NAME-induced hypertension has been shown to produce concentric (eutrophic) remodeling of the heart despite an enhanced afterload. We postulated that nitric oxide synthase inhibition could limit coronary capillary growth to explain the nature of remodeling. To test our hypothesis, we aimed at determining the effect of endogenous and exogenous nitric oxide on coronary neovascularization. Aortic and coronary rings from normotensive animals were incubated in a three-dimensional type I collagen matrix in the presence of L-NAME or the nitric oxide donor SNAP. L-NAME inhibited, while SNAP stimulated, neovascularization from aortic and coronary rings after 12 days of in vitro incubation. In arterial rings harvested from rats treated with L-NAME for 14 days and in which no further in vitro treatment was added, only coronary rings showed a reduction in new capillary generation. While confirming that chronic L-NAME-treated rats develop concentric remodeling, the evaluation of capillary density did not reveal any difference as compared with the controls in 3 areas of the myocardium. In conclusion, chronic inhibition of nitric oxide synthesis in vivo produces a long-lasting reduction in the capacity of coronary arteries to generate new capillaries in vitro. Thus, our results lend support to the hypothesis that an inhibition of new capillary formation could prevent the development of compensatory ventricular hypertrophy, in favor of concentric remodeling.

The transcription factor signal transducer and activator of transcription 3 (STAT3) participates in a wide variety of physiological processes and directs seemingly contradictory responses such as proliferation and apoptosis. To elucidate its role in the heart, we generated mice harboring a cardiomyocyte-restricted knockout of STAT3 using Cre/loxP-mediated recombination. STAT3-deficient mice developed reduced myocardial capillary density and increased interstitial fibrosis within the first 4 postnatal months, followed by dilated cardiomyopathy with impaired cardiac function and premature death. Conditioned medium from STAT3-deficient cardiomyocytes inhibited endothelial cell proliferation and increased fibroblast proliferation, suggesting the presence of paracrine factors attenuating angiogenesis and promoting fibrosis in vitro. STAT3-deficient mice showed enhanced susceptibility to myocardial ischemia/reperfusion injury and infarction with increased cardiac apoptosis, increased infarct sizes, and reduced cardiac function and survival. Our study establishes a novel role for STAT3 in controlling paracrine circuits in the heart essential for postnatal capillary vasculature maintenance, interstitial matrix deposition balance, and protection from ischemic injury and heart failure.

Therapeutic angiogenesis using vascular endothelial growth factor (VEGF) is considered a promising new therapy for patients with arterial obstructive disease. Clinical improvements observed consist of improved muscle function and regression of rest pain or angina. However, direct evidence for improved vascularization, as evaluated by angiography, is weak. In this study, we report an angiogenesis-independent effect of VEGF on ischemic skeletal muscle, ie, upregulation of myoglobin after VEGF treatment. Mice received intramuscular injection with adenoviral VEGF-A or either adenoviral LacZ or PBS as control, followed by surgical induction of acute hindlimb ischemia at day 3. At day 6, capillary density was increased in calf muscle of Ad.VEGF-treated versus control mice (P<0.01). However, angiographic score of collateral arteries was unchanged between Ad.VEGF-treated and control mice. More interestingly, an increase in myoglobin was observed in Ad.VEGF-treated mice. Active myoglobin was 1.5-fold increased in calf muscle of Ad.VEGF-treated mice (P< or =0.01). In addition, the number of myoglobin-stained myofibers was 2.6-fold increased in Ad.VEGF-treated mice (P=0.001). Furthermore, in ischemic muscle of 15 limb amputation patients, VEGF and myoglobin were coexpressed. Finally, in cultured C2C12 myotubes treated with rhVEGF, myoglobin mRNA was 2.8-fold raised as compared with PBS-treated cells (P=0.02). This effect could be blocked with the VEGF receptor tyrosine kinase inhibitor SU5416. In conclusion, we show that VEGF upregulates myoglobin in ischemic muscle both in vitro and in vivo. Increased myoglobin expression in VEGF-treated muscle implies an improved muscle oxygenation, which may, at least partly, explain observed clinical improvements in VEGF-treated patients, in the absence of improved vascularization.

Background: Stromal cell-derived factor-1alpha (SDF-1alpha) is implicated as a chemokine for endothelial progenitor cells (EPCs). We therefore hypothesized that SDF-1alpha gene transfer would induce therapeutic neovascularization in vivo by functioning as a chemokine of EPC., Methods and Results: To examine SDF-1alpha-induced mobilization of EPC, we used bone marrow-transplanted mice whose blood cells ubiquitously express beta-galactosidase (LacZ). We produced unilateral hindlimb ischemia in the mice and transfected them with plasmid DNA encoding SDF-1alpha or empty plasmids into the ischemic muscles. SDF-1alpha gene transfer mobilized EPCs into the peripheral blood, augmented recovery of blood perfusion to the ischemic limb, and increased capillary density associated with partial incorporation of LacZ-positive cells into the capillaries of the ischemic limb, suggesting that SDF-1alpha induced vasculogenesis and angiogenesis. SDF-1alpha gene transfer did not affect ischemia-induced expression of vascular endothelial growth factor (VEGF) but did enhance Akt and endothelial nitric oxide synthase (eNOS) activity. Blockade of VEGF or NOS prevented all such SDF-1alpha-induced effects., Conclusions: SDF-1alpha gene transfer enhanced ischemia-induced vasculogenesis and angiogenesis in vivo through a VEGF/eNOS-related pathway. This strategy might become a novel chemokine therapy for next generation therapeutic neovascularization.

Angiogenesis, an essential component of a variety of physiological and pathological processes, offers attractive opportunities for therapeutic regulation. We hypothesized that matrix metalloproteinase-9 genetic deficiency (MMP-9-/-) will impair angiogenesis triggered by tissue ischemia, induced experimentally by femoral artery ligation in mice. To investigate the role of MMP-9, we performed a series of biochemical and histological analyses, including zymography, simultaneous detection of perfused capillaries, MMP-9 promoter activity, MMP-9 protein, and macrophages in MMP-9-/- and wild-type (WT) mice. We found that ischemia resulted in doubling of capillary density in WT and no change in the MMP-9-/- ischemic tissues, which translated into increased (39%) perfusion capacity only in the WT at 14 days after ligation. We also confirmed that capillaries in the MMP-9-/- presented significantly (P<0.05) less points of capillary intersections, interpreted by us as decreased branching. The combined conclusions from simultaneous localizations of MMP-9 expression, capillaries, and macrophages suggested that macrophage MMP-9 participates in capillary branching. Transplantation of WT bone marrow into the MMP-9-/-, restored capillary branching, further supporting the contribution of bone marrow-derived macrophages in supplying the necessary MMP-9. Our study indicates that angiogenesis triggered by tissue ischemia requires MMP-9, which may be involved in capillary branching, a potential novel role for this MMP that could be exploited to control angiogenesis.

Background: Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) induces both angiogenesis and vascular permeability. Although its angiogenic activity has been well characterized, the signaling pathways of VEGF-induced permeability remain poorly understood., Methods and Results: Using the mouse corneal micropocket assay, Miles assay, and a combination of cytochemical, electron microscopic, and biochemical assays, we demonstrate that VEGF-induced vascular leakage partly can be separated from its angiogenic activity. VEGF but not FGF-2 induced capillaries with a highly fenestrated endothelium, a feature linked with increased vascular permeability. A cell-permeable Rac antagonist (TAT-RacN17) converted VEGF-induced, leaky vascular plexuses into well-defined vascular networks. In addition, this Rac mutant blocked formation of VEGF-induced endothelial fenestrations and vascular permeability but only partially inhibited angiogenesis. Studies on endothelial cell cultures further revealed that VEGF stimulated phosphorylation of VEGF receptor-2 (VEGFR-2), leading to activation of Rac as well as increased phosphorylation of phospholipase Cgamma (PLCgamma), protein kinase B (Akt), endothelial nitric oxide synthase (eNOS), and extracellular regulated kinase (Erk1/2). We further found that phosphatidylinositol-3-OH kinase (PI3K) acted upstream of Rac and Akt-eNOS in VEGF/VEGFR-2 signaling., Conclusions: Our findings indicate that the small GTP-binding protein Rac is a key component in mediation of VEGF-induced vascular permeability but less so in neovascularization. This may have conceptual implications for applying Rac antagonists in treatment and prevention of VEGF-induced vascular leakage and edema in connection with ischemic disorders.

Background: Stromal cell-derived factor-1 (SDF-1) is a chemokine considered to play an important role in the trafficking of hematopoietic stem cells. Given the close relationship between hematopoietic stem cells and endothelial progenitor cells (EPCs), we investigated the effect of SDF-1 on EPC-mediated vasculogenesis., Methods and Results: Flow cytometric analysis demonstrated expression of CXCR4, the receptor of SDF-1, by 66+/-3% of EPCs after 7 days in culture. In vitro modified Boyden chamber assay showed a dose-dependent EPC migration toward SDF-1 (control versus 10 ng/mL SDF-1 versus 100 ng/mL SDF-1, 24+/-2 versus 71+/-3 versus 140+/-6 cells/mm2; P<0.0001). SDF-1 attenuated EPC apoptosis (control versus SDF-1, 27+/-1 versus 7+/-1%; P<0.0001). To investigate the effect of SDF-1 in vivo, we locally injected SDF-1 into athymic ischemic hindlimb muscle of nude mice combined with human EPC transplantation to determine whether SDF-1 augmented EPC-induced vasculogenesis. Fluorescence microscopic examination disclosed increased local accumulation of fluorescence-labeled EPCs in ischemic muscle in the SDF-1 treatment group (control versus SDF-1=241+/-25 versus 445+/-24 cells/mm2, P<0.0001). At day 28 after treatment, ischemic tissue perfusion was improved in the SDF-1 group and capillary density was also increased. (control versus SDF-1, 355+/-26 versus 551+/-30 cells/mm2; P<0.0001)., Conclusion: These findings indicate that locally delivered SDF-1 augments vasculogenesis and subsequently contributes to ischemic neovascularization in vivo by augmenting EPC recruitment in ischemic tissues.

Great advances have been made in the identification of the soluble angiogenic factors, insoluble extracellular matrix (ECM) molecules, and receptor signaling pathways that mediate control of angiogenesis--the growth of blood capillaries. This review focuses on work that explores how endothelial cells integrate these chemical signals with mechanical cues from their local tissue microenvironment so as to produce functional capillary networks that exhibit specialized form as well as function. These studies have revealed that ECM governs whether an endothelial cell will switch between growth, differentiation, motility, or apoptosis programs in response to a soluble stimulus based on its ability to mechanically resist cell tractional forces and thereby produce cell and cytoskeletal distortion. Transmembrane integrin receptors play a key role in this mechanochemical transduction process because they both organize a cytoskeletal signaling complex within the focal adhesion and preferentially focus mechanical forces on this site. Molecular filaments within the internal cytoskeleton--microfilaments, microtubules, and intermediate filaments--also contribute to the cell's structural and functional response to mechanical stress through their role as discrete support elements within a tensegrity-stabilized cytoskeletal array. Importantly, a similar form of mechanical control also has been shown to be involved in the regulation of contractility in vascular smooth muscle cells and cardiac myocytes. Thus, the mechanism by which cells perform mechanochemical transduction and the implications of these findings for morphogenetic control are discussed in the wider context of vascular development and cardiovascular physiology.

Background: The neurotrophin nerve growth factor (NGF) regulates neuron survival and differentiation. Implication in neovascularization is supported by statement of NGF and its high-affinity receptor at vascular level and by NGF property of stimulating vascular endothelial cell proliferation. The present study investigated the involvement of endogenous NGF in spontaneous reparative response to ischemia. Mechanisms and therapeutic potential of NGF-induced neovascularization were examined., Methods and Results: Unilateral limb ischemia was produced in CD1 mice by femoral artery resection. By ELISA and immunohistochemistry, we documented that statement of NGF and its high-affinity receptor is upregulated in ischemic muscles. The functional relevance of this phenomenon was assessed by means of NGF-neutralizing antibody. Chronic NGF blockade abrogated the spontaneous capillarization response to ischemia and augmented myocyte apoptosis. Then we tested whether NGF administration may exert curative effects. Repeated NGF injection into ischemic adductors increased capillary and arteriole density, reduced endothelial cell and myofiber apoptosis, and accelerated perfusion recovery, without altering systemic hemodynamics. In normoperfused muscles, NFG-induced capillarization was blocked by vascular endothelial growth factor-neutralizing antibodies, dominant-negative Akt, or NO synthase inhibition., Conclusions: These results indicate that NGF plays a functional role in reparative neovascularization. Furthermore, supplementation of the growth factor promotes angiogenesis through a vascular endothelial growth factor-Akt-NO-mediated mechanism. In the setting of ischemia, potentiation of NGF pathway stimulates angiogenesis and arteriogenesis, thereby accelerating hemodynamic recovery. NGF might be envisaged as a utilitarian target for the treatment of ischemic vascular disease.

Background: Recent studies have demonstrated that gene transfer with hepatocyte growth factor (HGF) induces angiogenesis for coronary and peripheral artery diseases. We investigated the ability of gene transfer with human HGF to induce angiogenesis in the rat lung., Methods and Results: The left lung was selectively transfected with a cDNA encoding human HGF via the left pulmonary artery, using the HVJ-liposome method (H group); rats transfected with the same vector lacking the HGF gene served as controls (C group). HGF gene transfer significantly increased the capillary density in the left lung compared with the C group 7 days after transfection (15.0+/-1.3 versus 8.0+/-1.7 mm(2), P<0.01). The left to right average blood perfusion ratio detected by laser Doppler imaging increased significantly in the H group 14 days after transfection (1.12+/-0.09 versus 0.91+/-0.11, P<0.01). A right pulmonary artery clamp test, in which only the left lung received all the pulmonary blood flow from the right ventricle, revealed that the increase in right ventricular pressure was significantly attenuated in the H group compared with the C group 7 days after transfection (8.6+/-3.5 versus 15.3+/-2.8 mm Hg, P<0.01)., Conclusions: Trans-pulmonary arterial transfer of the human HGF gene into the left lung increased capillary density and blood perfusion, and decreased vascular resistance when blood flow increased. These results suggest therapeutic angiogenesis induced by HGF gene expression in the lung may be found suitable in treating subjects with decreased pulmonary vasculature or increased pulmonary vascular resistance.

This study examined the potential role of angiotensin type 2 (AT(2)) receptor on angiogenesis in a model of surgically induced hindlimb ischemia. Ischemia was produced by femoral artery ligature in both wild-type and AT(2) gene-deleted mice (Agtr2(-)/Y). After 28 days, angiogenesis was quantitated by microangiography, capillary density measurement, and laser Doppler perfusion imaging. Protein levels of vascular endothelial growth factor (VEGF), endothelial nitric oxide synthase (eNOS), Bax, and Bcl-2 were determined by Western blot analysis in hindlimbs. The AT(2) mRNA level (assessed by semiquantitative RT-PCR) was increased in the ischemic hindlimb of wild-type mice. Angiographic vessel density and laser Doppler perfusion data showed significant improvement in ischemic/nonischemic leg ratio, 1.9- and 1.7-fold, respectively, in Agtr2(-)/Y mice compared with controls. In ischemic leg of Agtr2(-)/Y mice, revascularization was associated with an increase in the antiapoptotic protein content, Bcl-2 (211% of basal), and a decrease (60% of basal) in the number of cell death, determined by TUNEL method. Angiotensin II treatment (0.3 mg/kg per day) raised angiogenic score, blood perfusion, and both VEGF and eNOS protein content in ischemic leg of wild-type control but did not modulate the enhanced angiogenic response observed in untreated Agtr2(-)/Y mice. Finally, immunohistochemistry analysis revealed that VEGF was mainly localized to myocyte, whereas eNOS-positive staining was mainly observed in the capillary of ischemic leg of both wild-type and AT(2)-deficient mice. This study demonstrates for the first time that the AT(2) receptor subtype may negatively modulate ischemia-induced angiogenesis through an activation of the apoptotic process.

Background: The in vivo mechanism by which inhibition of NO synthase impairs ischemia-induced coronary vascular growth is unknown. We hypothesized that production of the growth inhibitor angiostatin increases during decreased NO production, blunting angiogenesis and collateral growth., Methods and Results: Measurements were made in myocardial tissue or interstitial fluid (MIF) from dogs undergoing repetitive coronary occlusions under control conditions or during antagonism of NO synthase (N(G)-nitro-L-arginine methyl ester [L-NAME]) for 7, 14, or 21 days. A sham group was instrumented identically but received no occlusions. In controls, capillary density in the ischemic zone increased initially but returned to baseline at the later times. In the L-NAME group, capillary density was lower at 7 days compared with that of controls. MIF from control dogs induced in vitro endothelial tube formation and cell proliferation, significantly greater than that from the L-NAME group. MIF from shams did not stimulate tube formation. In controls or shams, tube formation or cell proliferation did not change after administration of antiangiostatin, but this antibody restored the responses to control levels in the L-NAME group. Angiostatin expression in MIF was increased in the L-NAME group compared with controls and shams. The activities of tissue matrix metalloproteinases (MMPs) MMP-2 and MMP-9, which generate angiostatin, were increased in the L-NAME group., Conclusions: Inhibition of NO synthase increased expression of angiostatin and activities of MMP-2 and MMP-9. Our findings indicate that angiostatin inhibits coronary angiogenesis during compromised NO production and may underscore the impairment of coronary angiogenesis during endothelial dysfunction.

The authors investigated the multi-step mechanism of healing after cardiomyoplasty, focusing on the process of angiogenesis. The authors contend that enhancement of angiogenesis and prevention of ischemia-reperfusion injuries immediately after muscle mobilization will be effective in improving cardiomyoplasty results. After cardiomyoplasty, autologous biologic glue (ABG) was administered between the latissimus dorsi muscle (LDM) and myocardium. By 2 months, a new pseudo interlayer was present that bridged the gap between the LDM and myocardium. Neovascularization was visible in the form of numerous small capillaries. Marked degeneration of the LDM was noted, possibly caused by muscle ischemia-reperfusion damage after mobilization. Pockets were created of ischemic and nonischemic LDM to test for angiogenesis. One was left free of ABG (control); one received ABG only; one received ABG and pyrrolostatin. Some of the capillaries were large and had erythrocytes inside. biopsy samples showed 9.4 +/- 1.9% of the sample was occupied by blood vessels (compared with 3.6 +/- 0.7% in control muscle). These preliminary studies prove the feasibility of the authors' concept and provide evidence that angiogenesis can accelerate the healing process and provide an organic bridge between the LDM and myocardium after cardiomyoplasty.

Numerous studies have examined the effects of exercise training on coronary angiogenesis. Although the conclusions drawn from these studies are sometimes conflicting, variabilities in training (magnitude, type and intensity), age and other factors need to be closely examined. Most studies on young animals indicate that capillary growth occurs providing that the training intensity is appropriate. Furthermore, there is evidence that growth of arteries and resistance vessels can occur as indicated by 1) direct measurements of vessels and 2) calculation of minimal coronary vascular resistance during pharmacologically induced vasodilation. Although the mechanism(s) underlying exercise-induced angiogenesis is unknown, mechanical events associated with increased flow and/or increased venous return, as well as resting bradycardia may serve to trigger growth factors involved in mitogenic, migratory, and tube formation of endothelial cells. In contrast, exercise training per se does not appear to enhance collateral vessel growth. However, there is evidence that collateral growth is accelerated with training in animals with coronary artery occlusion.

To test whether angiotensin-converting enzyme (ACE) inhibition may prevent myocardial damage and may affect coronary microvasculature in spontaneously hypertensive rats (SHR), young 5-week-old SHR were treated for 3 months with spirapril and changes in blood pressure (BP) were monitored. Untreated SHR were used as controls. The rats were killed; left ventricular (LV) shape, weight, and wall thickness were examined and the ventricular myocardium was analyzed morphometrically to determine the effect of the drug on the relative amount, number per unit area of myocardium, and average dimension of foci of myocardial scarring. Moreover, volume fraction, surface, numerical density, and diffusion distance for oxygen of the coronary capillaries were analyzed. BP remained 20-30% lower in treated SHR with respect to controls, and LV weight and thickness decreased 20 and 21%, respectively. The number and dimension of the foci of fibrosis were reduced, resulting in an overall 68% decrement in the amount of myocardial damage. Finally, a 28% increment in numerical density of capillary profiles associated with a 13% reduction in their cross-sectional area decreased the diffusion distance for oxygen from the capillary wall to the myocytes by 14% in treated SHR. Spirapril decreases BP and LV weight and thickness in the SHR model of hypertension and substantially improves coronary capillary microvasculature, decreasing hypertensive myocardial damage. These results may be attributed to inhibition of the systemic effects of angiotensin II (AII) as well as to a local protective action of the drug against possible intramyocardial AII production.

Background: In adults, acquired pressure-overload left ventricular hypertrophy can result in myocardial ischemia, which may be due in part to insufficient capillary growth during development of hypertrophy. The coronary microvascular response to congenital pressure-overload hypertrophy in children has not been previously characterized., Methods and Results: Average capillary density and heterogeneity of capillary spacing were measured in 63 postmortem human hearts with left ventricular hypertrophy and control hearts without heart disease. Pathology specimens were chosen that had left ventricular hypertrophy caused by 1) congenital isolated aortic valve stenosis in infants less than 1 year old at death, children 9-14 years old, and adults 15-30 years old; 2) congenital isolated coarctation of the aorta in adults 15-39 years old; and 3) acquired aortic stenosis in adults 51-86 years old. Major findings of the study were: 1) Human left ventricular capillary density and heterogeneity of capillary spacing are similar to other mammalian species. 2) Capillary density is higher in infants (3,315 +/- 85 capillaries per square millimeter), decreases with increasing heart weight during normal growth in early childhood (children, 2,388 +/- 75 capillaries per square millimeter, p less than 0.05), and thereafter remains relatively constant. 3) Capillary density with left ventricular hypertrophy is dependent on the age of onset. Congenital aortic stenosis and coarctation are characterized by an increase in capillary supply proportional to myocyte volume, maintaining capillary density similar to control hearts. Adults with acquired aortic stenosis have decreased capillary density (1,671 +/- 66 capillaries per square millimeter, p less than 0.01 versus control)., Conclusions: Pressure-overload left ventricular hypertrophy in children demonstrates proportional capillary angiogenesis, whereas in adults, hypertrophy appears to be associated with failure of compensatory angiogenesis.

We compared six young (1 year) and six senescent (11 years) purebred beagles to determine the effects of aging on the coronary microvasculature. The hearts were perfusion-fixed in vitro, and myocardial specimens were subjected to microscopic image analysis. Absolute left ventricular mass increased by 55% with age, while cardiocyte cross-sectional area increased by 10% and 30% in the midmyocardium and endomyocardium, respectively. Although capillary numerical density was lower in the senescent dogs (16% in midmyocardium and 19% in endomyocardium), volume density was similar in the two groups because capillary diameter increased significantly with age in both regions. Capillary length density was reduced by 27% with age in the endomyocardium of the old beagles. Wall/lumen ratios of arterioles of three size classes (less than or equal to 15, 16-25, and 26-50 microns) were found to be nearly identical for the two age groups. Mean arteriolar diameter increased within the smallest size class in both ventricular regions. In contrast, a twofold or greater increase in wall thickness with age occurred in the left anterior descending coronary artery and its first branch, which was mainly due to expansion of the medial interstitium. The connective tissue fraction of the myocardium was significantly higher in the senescent than in the young in the epimyocardium and midmyocardium but not in the endomyocardium. These data provide evidence for three conclusions regarding aging of coronary vessels in beagles. First, a decline in capillary length density is limited to the endomyocardium.(ABSTRACT TRUNCATED AT 250 WORDS)

This paper describes the qualitative and quantitative composition of dog myocardium over the first 5 months of life. The quantitative composition of dog right and left ventricle over this period does not vary. A stereological analysis of electron micrographs representing 32,000 micron2 of tissue surface revealed that 79% of the heart is made up of myofibers, whereas 21% is extracellular space. Twenty-eight percent of the extracellular compartment by volume is vasculature (tissue was preserved by immersion rather than vascular perfusion); 72% is occupied by nonvascular elements and "empty" space. In contrast to the remarkable constancy of quantitative composition of the whole myocardium, myocyte shape and dimensions and the arrangement of intercellular connections vary dramatically over the age period studied. In early postnatal life, the morphology of blood vessels, many of which have completely partitioned lumina, also changes significantly.

To determine whether anemia-induced cardiac hypertrophy affects ventricular size and shape and the component structures of the capillary network of the left and right ventricles, young male rats were fed an iron- and copper-deficient diet for 7 weeks. By that time, blood hemoglobin content fell to 5 +/- 1 g/dl, and packed cell volume fell to 18 +/- 3%. To further characterize the implications of anemia, red blood cell number, hemoglobin corpuscular content, systemic arterial pressure, heart rate, and blood viscosity were measured. Moreover, the changes in ventricular weights were analyzed in terms of the alterations in ventricular wall area and ventricular wall thickness to establish the impact of the elevation in load associated with a high cardiac output state on ventricular remodeling. The quantitative properties of the capillary circulation were also examined biventricularly by low power electron microscopic morphometry to evaluate the adaptive growth potential of the coronary microcirculation in this form of cardiac hypertrophy. Anemia was found to interfere with the production of red blood cells and their mean corpuscular hemoglobin content and resulted in a 40% reduction in blood viscosity and a 12% and 27% decrease in systolic and diastolic blood pressure, respectively. The changes in heart rate were not statistically significant. In comparison with control animals, heart weight increased by 50%, but the enlargement in right ventricular mass (65%) was greater than that of the left ventricle (47%). Ventricular hypertrophy occurred with increases in wall area and wall thickness although the former increased consistently more than the latter in either ventricle. Tissue growth was accompanied by a 60% lengthening of the capillary network, which in combination with an increase in capillary diameter resulted in a 65% and 34% expansion in capillary luminal volume and 56% and 20% larger luminal surface density in the left and right sides of the heart, respectively. In conclusion, hypochromic microcytic anemia leads to eccentric ventricular hypertrophy with a significant amount of capillary proliferation that may tend to protect the myocardium from the increased potential for ischemic injury.

This study was undertaken to determine what changes occur in the intestinal microvasculature during the rapid growth associated with juvenile maturation. A technique was developed that permitted the comparison of the same microvessels in exactly the same intestinal region at two time periods of an animal's life. A region of the terminal ileum of 5-week-old rats was exposed and marked, and photographs and video recordings were made of the microvessels. Four weeks later, the marked intestinal region was located, and photography and videography of the microvessels were repeated. Comparison of indexes for body, intestinal, and microvascular growth for the treated rats and age- and colony-matched controls revealed no significant differences. The number and branching pattern of arterioles observed in the marked region remained remarkably constant during the 4 weeks between observation periods, even though body and bowel mass of the treated animals increased approximately 2.5 times. The lengths of the arterioles were increased (18%) by almost the same proportion as the axis of bowel (22%) in which they were oriented. The average distance between capillaries in the radial intestinal muscle layer was also increased by about the same percentage (24%) as that of tissue elongation (22%). The overall data are consistent with the hypothesis that during the growth spurt of juvenile life, the arterioles present at the weanling stage are elongated and new branches do not develop. The net effect of tissue growth with a minimal change in numbers of arterioles is a decreased ratio of number of arterioles to tissue mass as a normal consequence of maturation.

We have previously reported that chronic bradycardial pacing increases both capillary density/mm2 (CD) and maximal work output in normal rabbit hearts. This technique has now been applied to rabbits with volume-overload hypertrophy due to lesion of the aortic valve. Four groups of animals were studied: controls (C), paced (P), valve-lesioned (VL), and paced valve-lesioned (PVL). The aortic valve was lesioned 8 weeks before the acute experiments; pacing was started 4 weeks before the acute experiments, and thus, the PVL group had developed hypertrophy before pacing was started. The degree of hypertrophy was similar in VL hearts whether paced or not: heart wt/body wt ratio increased by 33.5 +/- 8.9% (mean +/- SEM) in VL and 25.2 +/- 8.2% in PVL versus control animals of similar body weight (p less than 0.001). The hearts of the PVL animals showed a higher CD (2,277 +/- 107) than VL hearts (1,383 +/- 43), CD in C hearts of similar weights being 1,595 +/- 103, and in P hearts 2,350 +/- 194. Thus, CD was lower by 14% in VL and higher by 43% in PVL than in C hearts. Valve-lesioning had a significant effect in reducing maximal cardiac minute work (p less than 0.001), whereas pacing significantly improved maximal cardiac minute work (p less than 0.001) to 2.467 +/- 0.206 J/g x 10(-4) in the P group versus 1.609 +/- 0.105 in the C group.(ABSTRACT TRUNCATED AT 250 WORDS)

Various indices of capillary supply to the rat heart were studied in neonatal rats injected for 2 or 4 weeks with protamine sulfate in saline (subcutaneously, 60 mg/kg body weight, 2 times/day). Cardiac capillarization was evaluated not only by traditional indices for the capillary supply, such as mean capillary density and myocyte-to-capillary ratio, but also by a more advanced morphometric method of capillary domains. This method allows the estimation of both the average radius of the Krogh tissue cylinder and its variability, which reflects the heterogeneity of capillary spacing found to be an independent morphological determinant of oxygen diffusion in the tissue. The results were evaluated with respect to regional differences (subendocardial vs. middle section), age differences, and the effect of protamine. No regional differences in capillary supply were found in this experimental situation. Hearts from older rats had significantly decreased capillary supply, expressed as lower capillary density, larger capillary domains, and greater radius of the tissue cylinder. On the other hand, the heterogeneity of capillary spacing decreased significantly with age. Protamine-injected animals, when compared to their control littermates, had a significantly higher cell-to-capillary ratio, lower capillary density, larger capillary domains, greater radius of the tissue cylinder, and larger variability in capillary spacing. Thus, protamine was effective in impeding rapid capillary growth in the hearts from rats in the early postnatal period. Close to half of all the existing capillaries in the adult rat hearts are formed during the first 3-4 postnatal weeks.