Capillary enlargement, not sprouting angiogenesis, determines beneficial therapeutic effects and side effects of angiogenic gene therapy

One Endothelium-Targeted Combined Nucleic Acid Delivery System for Myocardial Infarction Therapy

Acute myocardial infarction (MI) and ischemic heart disease are the leading causes of heart failure and mortality. Currently, research on MI treatment is focused on angiogenic and anti-inflammatory therapies. Although endothelial cells (ECs) are critical for triggering inflammation and angiogenesis, no approach has targeted them for the treatment of MI. In this study, we proposed a nonviral combined nucleic acid delivery system consisting of an EC-specific polycation (CRPPR-grafted ethanolamine-modified poly(glycidyl methacrylate), CPC) that can efficiently codeliver siR-ICAM1 and pCXCL12 for the treatment of MI. Animals treated with the combination therapy exhibited better cardiac function than those treated with each nucleic acid alone. In particular, the combination therapy of CPC/siR-ICAM1 and CPC/pCXCL12 significantly improved cardiac systolic function, anti-inflammatory responses, and angiogenesis compared to the control group. In conclusion, CPC-based combined gene delivery systems show impressive performance in the treatment of MI and provide a programmed strategy for the development of codelivery systems for various EC-related diseases.

Critical limb-threatening ischaemia and microvascular transformation: clinical implications

BACKGROUND AND AIMS

Clinical management of critical limb-threatening ischaemia (CLTI) is focused on prevention and treatment of atherosclerotic arterial occlusions. The role of microvascular pathology in disease progression is still largely unspecified and more importantly not utilized for treatment. The aim of this explorative study was to characterize the role of the microvasculature in CLTI pathology.

METHODS

Clinical high-resolution imaging of CLTI patients (n = 50) and muscle samples from amputated CLTI limbs (n = 40) were used to describe microvascular pathology of CLTI at the level of resting muscle blood flow and microvascular structure, respectively. Furthermore, a chronic, low arterial driving pressure-simulating ischaemia model in rabbits (n = 24) was used together with adenoviral vascular endothelial growth factor A gene transfers to study the effect of microvascular alterations on muscle outcome.

RESULTS

Resting microvascular blood flow was not depleted but displayed decreased capillary transit time (P < .01) in CLTI muscles. Critical limb-threatening ischaemia muscle microvasculature also exhibited capillary enlargement (P < .001) and further arterialization along worsening of myofibre atrophy and detaching of capillaries from myofibres. Furthermore, CLTI-like capillary transformation was shown to worsen calf muscle force production (P < .05) and tissue outcome (P < .01) under chronic ischaemia in rabbits and in healthy, normal rabbit muscle.

CONCLUSIONS

These findings depict a progressive, hypoxia-driven transformation of the microvasculature in CLTI muscles, which pathologically alters blood flow dynamics and aggravates tissue damage under low arterial driving pressure. Hypoxia-driven capillary enlargement can be highly important for CLTI outcomes and should therefore be considered in further development of diagnostics and treatment of CLTI.

Capillary Dynamics Regulate Post-Ischemic Muscle Damage and Regeneration in Experimental Hindlimb Ischemia

This study aimed to show the significance of capillary function in post-ischemic recovery from the perspective of physiological parameters, such as blood flow, hemoglobin oxygenation and tissue regeneration. Muscle-level microvascular alterations of blood flow and hemoglobin oxygenation, and post-ischemic myofiber and capillary responses were analyzed in aged, healthy C57Bl/6J mice (n = 48) and aged, hyperlipidemic LDLR-/-ApoB100/100 mice (n = 69) after the induction of acute hindlimb ischemia using contrast ultrasound, photoacoustic imaging and histological analyses, respectively. The capillary responses that led to successful post-ischemic muscle repair in C57Bl/6J mice included an early capillary dilation phase, preceding the return of arterial driving pressure, followed by an increase in capillary density that further supported satellite cell-induced muscle regeneration. Initial capillary enlargement was absent in the LDLR-/-ApoB100/100 mice with lifelong moderate hypercholesterolemia and led to an inability to recover arterial driving pressure, with a resulting increase in distal necrosis, chronic tissue damage and a delay in the overall recovery after ischemia. To conclude, this manuscript highlights, beyond arterial collateralization, the importance of the proper function of the capillary endothelium in post-ischemic recovery and displays how post-ischemic capillary dynamics associate beyond tissue blood flow to both hemoglobin oxygenation and tissue regeneration.

The coronary capillary bed and its role in blood flow and oxygen delivery: A review

The assumption that the coronary capillary blood flow is exclusively regulated by precapillary vessels is not supported by recent data. Rather, the complex coronary capillary bed has unique structural and geometric characteristics that invalidate many assumptions regarding red blood cell (RBC) transport, for example, data based on a single capillary or that increases in flow are the result of capillary recruitment. It is now recognized that all coronary capillaries are open and that their variations in flow are due to structural differences, local O₂ demand and delivery, and variations in hematocrit. Recent data reveal that local mechanisms within the capillary bed regulate flow via signaling mechanisms involving RBC signaling and endothelial-associated pericytes that contract and relax in response to humoral and neural signaling. The discovery that pericytes respond to vasoactive signals (e.g., nitric oxide, phenylephrine, and adenosine) underscores the role of these cells in regulating capillary diameter and consequently RBC flux and oxygen delivery. RBCs also affect blood flow by sensing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>P</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:msub> </mml:math> and releasing nitric oxide to facilitate relaxation of pericytes and a consequential capillary dilation. New data indicate that these signaling mechanisms allow control of blood flow in specific coronary capillaries according to their oxygen requirements. In conclusion, mechanisms in the coronary capillary bed facilitate RBC density and transit time, hematocrit, blood flow and O₂ delivery, factors that decrease capillary heterogeneity. These findings have important clinical implications for myocardial ischemia and infarction, as well as other vascular diseases.

Mapping the transcriptomic changes of endothelial compartment in human hippocampus across aging and mild cognitive impairment

Compromise of the vascular system has important consequences on cognitive abilities and neurodegeneration. The identification of the main molecular signatures present in the blood vessels of human hippocampus could provide the basis to understand and tackle these pathologies. As direct vascular experimentation in hippocampus is problematic, we achieved this information by computationally disaggregating publicly available whole microarrays data of human hippocampal homogenates. Three conditions were analyzed: ‘Young Adults’, ‘Aged’, and ‘aged with Mild Cognitive Impairment’ (MCI). The genes identified were contrasted against two independent data-sets. Here we show that the endothelial cells from the Younger Group appeared in an ‘activated stage’. In turn, in the Aged Group, the endothelial cells showed a significant loss of response to shear stress, changes in cell adhesion molecules, increased inflammation, brain-insulin resistance, lipidic alterations, and changes in the extracellular matrix. Some specific changes in the MCI group were also detected. Noticeably, in this study the features arisen from the Aged Group (high tortuosity, increased bifurcations, and smooth muscle proliferation), pose the need for further experimental verification to discern between the occurrence of arteriogenesis and/or vascular remodeling by capillary arterialization.

This article has an associated First Person interview with the first author of the paper.

Summary: An integrative picture about the mechanisms operating in the hippocampal vasculature under normal and pathological scenarios is achieved by the computational dissection of microarray data corresponding to whole tissue samples and focusing on gene splice forms.

A Pilot Optical Coherence Tomography Angiography Study on Superficial and Deep Capillary Plexus Foveal Avascular Zone in Patients With Beta-Thalassemia Major

Purpose

To investigate foveal avascular zone (FAZ) changes in the superficial (SCP) and deep (DCP) capillary plexuses in beta-thalassemia major (BTM) patients, as shown in optical coherence tomography angiography.

Methods

Nonrandomized, comparative case series of 54 eyes of 27 BTM patients and 46 eyes of 23 healthy controls, utilizing an automated FAZ detection algorithm. Measurements included FAZ area and FAZ shape descriptors (convexity, circularity, and contour temperature). Results were compared between the two groups, and correlated to iron load and chelation therapy parameters.

Results

SCP and DCP FAZ area were not significantly different between the control and BTM groups (P = 0.778 and P = 0.408, respectively). The same was true regarding SCP FAZ convexity (P = 0.946), circularity (P = 0.838), and contour temperature (P = 0.907). In contrast, a statistically significant difference was detected between controls and BTM group regarding DCP FAZ convexity (P = 0.013), circularity (P = 0.010), and contour temperature (P = 0.014). Desferrioxamine dosage was strongly correlated to the DCP area (r = 0.650, P = 0.05) and liver magnetic resonance imaging/T2-star to DCP circularity (r = -0.492, P = 0.038). Correlations were also revealed between urine Fe excretion and DCP convexity (r = 0.531, P = 0.019), circularity (r = 0.661, P = 0.002), and contour temperature (r = -0.591, P = 0.008).

Conclusions

Retinal capillary plexuses and especially DCP seem to present unique morphologic changes in BTM patients, not in the FAZ area, but in specific shape descriptors, indicating minor but detectable FAZ changes. These changes correlate well with iron load and chelation therapy parameters. Their clinical importance and pathophysiologic implications remain to be elucidated through further studies.

Improved endothelialization of small-diameter ePTFE vascular grafts through growth factor therapy

Background

Prosthetic vascular grafts in humans characteristically lack confluent endothelialization regardless of the duration of implantation. Use of high-porosity grafts has been proposed as a way to induce endothelialization through transgraft capillarization, although early experiments failed to show increased healing in man.

Objectives

We hypothesized that transduction of tissues around the prosthetic conduit with vectors encoding VEGF receptor-2 (VEGFR2) ligands would augment transinterstitial capillarization and induce luminal endothelialization of high-porosity ePTFE grafts.

Methods

Fifty-two NZW rabbits received 87 ePTFE uni- or bilateral end-to-end interposition grafts in carotid arteries. Rabbits were randomized to local therapy with adenoviruses encoding AdVEGF-A165, AdVEGF-A109 or control AdLacZ and analyzed at 6 and 28 days after surgery by contrast-enhanced ultrasound and histology.

Results

AdVEGF-A165 and AdVEGF-A109 dramatically increased perfusion in perigraft tissues at 6 days (14.2 ± 3.6 or 16.7 ± 2.6-fold increases, P < 0.05 and P < 0.01). At 28 days, the effect was no longer significantly higher than baseline. At 6 days, no luminal endothelialization was observed in any of the groups. At 28 days, AdVEGF-A109- and AdVEGF-A165-treated animals showed enhanced ingrowth of transinterstitial capillaries (66.0 ± 13.7% and 77.4 ± 15.7% of graft thickness vs 44.7 ± 24.4% in controls, P < 0.05) and improved luminal endothelialization (11.2 ± 26.3% and 11.4 ± 22.2%, AdVEGF-A109 and AdVEGF-A165 vs 0% in controls, P < 0.05). No increased stenosis was observed in the treatment groups as compared to LacZ controls.

Conclusions

This study suggests that transient local overexpression of VEGFR2 ligands in the peri-implant tissues at the time of graft implantation is a novel strategy to increase endothelialization of high-porosity ePTFE vascular grafts and improve the patency of small-diameter vascular prostheses.

Local adventitial anti-angiogenic gene therapy reduces growth of vasa-vasorum and in-stent restenosis in WHHL rabbits

BACKGROUND

Antiproliferative drugs in drug eluting stents (DES) are associated with complications due to impaired re-endothelialization. Additionally, adventitial neovascularization has been suggested to contribute to in-stent restenosis (ISR). Since Vascular Endothelial Growth Factors (VEGFs) are the key mediators of angiogenesis, we investigated feasibility and efficacy of local gene therapy for ISR utilizing soluble decoy VEGF receptors to reduce biological activity of adventitial VEGFs.

METHOD

Sixty-nine adult WHHL rabbit aortas were subjected to endothelial denudation. Six weeks later catheter-mediated local intramural infusion of 1.5x10e10 pfu adenoviruses encoding soluble VEGF Receptor-1 (sVEGFR1), sVEGFR2, sVEGFR3 or control LacZ and bare metal stent implantation were performed in the same aortic segment. Marker protein expression was assessed at 6d in LacZ cohort. Immunohistochemistry, morphometrical analyses and angiography were performed at d14, d42 and d90.

RESULTS

Transgene expression was localized to adventitia. All decoy receptors reduced the size of vasa-vasorum at 14d, AdsVEGFR2 animals also had reduced density of adventitial vasa-vasorum, whereas AdsVEGFR3 increased the density of vasa-vasorum. At d42, AdsVEGFR1 and AdsVEGFR2 reduced ISR (15.7 ± 6.9% stenosis, P < 0.01 and 16.5 ± 2.7%, P < 0.05, respectively) vs. controls (28.3 ± 7.6%). Moreover, AdsVEGFR-3 treatment led to a non-significant trend in the reduction of adventitial lymphatics at all time points and these animals had significantly more advanced neointimal atherosclerosis at 14d and 42d vs. control animals.

CONCLUSIONS

Targeting adventitial neovascularization using sVEGFR1 and sVEGFR2 is a novel strategy to reduce ISR. The therapeutic effects dissipate at late follow up following short expression profile of adenoviral vectors. However, inhibition of VEGFR3 signaling accelerates neoatherosclerosis.

Snake venom VEGF Vammin induces a highly efficient angiogenic response in skeletal muscle via VEGFR-2/NRP specific signaling

Vascular Endothelial Growth Factors (VEGFs) are promising molecules for the treatment of ischemic diseases by pro-angiogenic therapy. Snake venom VEGFs are a novel subgroup with unique receptor binding profiles and as such are potential new therapeutic agents. We determined the ligand-receptor interactions, gene regulation and angiogenic properties of Vipera ammodytes venom VEGF, Vammin, and compared it to the canonical angiogenic factor VEGF-A to evaluate the use of Vammin for therapeutic angiogenesis. Vammin efficiently induced VEGFR-2 mediated proliferation and expression of genes associated with proliferation, migration and angiogenesis. VEGF-A₁₆₅ and especially VEGF-A₁₀₉ induced less pronounced effects. Vammin regulates a number of signaling pathways by inducing the expression of NR4A family nuclear receptors and regulators of calcium signaling and MAP kinase pathways. Interestingly, MARC1, which encodes an enzyme discovered to catalyze reduction of nitrate to NO, was identified as a novel VEGFR-2 regulated gene. In rabbit skeletal muscle adenoviral delivery of Vammin induced prominent angiogenic responses. Both the vector dose and the co-receptor binding of the ligand were critical parameters controlling the type of angiogenic response from sprouting angiogenesis to vessel enlargement. Vammin induced VEGFR-2/NRP-1 mediated signaling more effectively than VEGF-A, consequently it is a promising candidate for development of pro-angiogenic therapies.

Cardiovascular Gene Therapy: Past, Present, and Future

Cardiovascular diseases remain a large global health problem. Although several conventional small-molecule treatments are available for common cardiovascular problems, gene therapy is a potential treatment option for acquired and inherited cardiovascular diseases that remain with unmet clinical needs. Among potential targets for gene therapy are severe cardiac and peripheral ischemia, heart failure, vein graft failure, and some forms of dyslipidemias. The first approved gene therapy in the Western world was indicated for lipoprotein lipase deficiency, which causes high plasma triglyceride levels. With improved gene delivery methods and more efficient vectors, together with interventional transgene strategies aligned for a better understanding of the pathophysiology of these diseases, new approaches are currently tested for safety and efficacy in clinical trials. In this article, we integrate a historical perspective with recent advances that will likely affect clinical development in this research area.

Intramyocardial Injection of Recombinant Adeno-Associated Viral Vector Coexpressing PR39/Adrenomedullin Enhances Angiogenesis and Reduces Apoptosis in a Rat Myocardial Infarction Model

Cotransfer of angiogenic and antiapoptotic genes could be the basis of new gene therapy strategies for myocardial infarction. In this study, rAAV-PR39-ADM, coexpressing antimicrobial peptide (PR39) and adrenomedullin (ADM), was designed with the mediation of recombinant adeno-associated virus. In vitro, CRL-1730 cells were divided into four groups, namely, the sham group, the AAV-null group, the NS (normal saline) group, and the PR39-ADM group. Immunocytochemistry analysis, CCK-8 assays, Matrigel assays, and apoptotic analysis were performed; in vivo, myocardial infarction model was established through ligation of the left coronary artery on rats, and treatment groups corresponded to those used in vitro. Myocardial injury, cardiac performance, and the extent of myocardial apoptosis were assessed. Results suggested that rAAV-PR39-ADM administration after myocardial infarction improved cell viability and cardiac function, attenuated apoptosis and myocardial injury, and promoted angiogenesis. Subsequently, levels of 6×His, HIF-1α, VEGF, p-Akt, Akt, ADM, Bcl-2, and Bax were measured by western blot. rAAV-PR39-ADM increased p-Akt, HIF-1α, and VEGF levels and induced higher Bcl-2 expression and lower Bax expression. In conclusion, our results demonstrate that rAAV-PR39-ADM mitigates myocardial injury by promoting angiogenesis and reducing apoptosis. This study suggests a potential novel gene therapy-based method that could be used clinically for myocardial infarction.

Self-assembly of c-myc DNA promoted by a single enantiomer ruthenium complex as a potential nuclear targeting gene carrier

Gene therapy has long been limited in the clinic, due in part to the lack of safety and efficacy of the gene carrier. Herein, a single enantiomer ruthenium(II) complex, Λ-[Ru(bpy)2(p-BEPIP)](ClO4)2 (Λ-RM0627, bpy = 4,4'-bipyridine, p-BEPIP = 2-(4-phenylacetylenephenyl)imidazole [4,5f][1, 10] phenanthroline), has been synthesized and investigated as a potential gene carrier that targets the nucleus. In this report, it is shown that Λ-RM0627 promotes self-assembly of c-myc DNA to form a nanowire structure. Further studies showed that the nano-assembly of c-myc DNA that induced Λ-RM0627 could be efficiently taken up and enriched in the nuclei of HepG2 cells. After treatment of the nano-assembly of c-myc DNA with Λ-RM0627, over-expression of c-myc in HepG2 cells was observed. In summary, Λ-RM0627 played a key role in the transfer and release of c-myc into cells, which strongly indicates Λ-RM0627 as a potent carrier of c-myc DNA that targets the nucleus of tumor cells.

Split for the cure: VEGF, PDGF-BB and intussusception in therapeutic angiogenesis

Therapeutic angiogenesis is an attractive strategy to treat patients suffering from ischaemic conditions and vascular endothelial growth factor-A (VEGF) is the master regulator of blood vessel growth. However, VEGF can induce either normal or aberrant angiogenesis depending on its dose localized in the microenvironment around each producing cell in vivo and on the balanced stimulation of platelet-derived growth factor-BB (PDGF-BB) signalling, responsible for pericyte recruitment. At the doses required to induce therapeutic benefit, VEGF causes new vascular growth essentially without sprouting, but rather through the alternative process of intussusception, or vascular splitting. In the present article, we briefly review the therapeutic implications of controlling VEGF dose on one hand and pericyte recruitment on the other, as well as the key features of intussusceptive angiogenesis and its regulation.

Inducible VEGF expression by human embryonic stem cell-derived mesenchymal stromal cells reduces the minimal islet mass required to reverse diabetes

Islet transplantation has been hampered by loss of function due to poor revascularization. We hypothesize that co-transplantation of islets with human embryonic stem cell-derived mesenchymal stromal cells that conditionally overexpress VEGF (hESC-MSC:VEGF) may augment islet revascularization and reduce the minimal islet mass required to reverse diabetes in mice. HESC-MSCs were transduced by recombinant lentiviruses that allowed conditional (Dox-regulated) overexpression of VEGF.

HESC-MSC

VEGF were characterized by tube formation assay. After co-transplantation of hESC-MSC:VEGF with murine islets in collagen-fibrin hydrogel in the omental pouch of diabetic nude mice, we measured blood glucose, body weight, glucose tolerance and serum C-peptide. As control, islets were transplanted alone or with non-transduced hESC-MSCs. Next, we compared functional parameters of 400 islets alone versus 200 islets co-transplanted with hESC-MSC:VEGF. As control, 200 islets were transplanted alone. Metabolic function of islets transplanted with hESC-MSC:VEGF significantly improved, accompanied by superior graft revascularization, compared with control groups. Transplantation of 200 islets with hESC-MSC:VEGF showed superior function over 400 islets alone. We conclude that co-transplantation of islets with VEGF-expressing hESC-MSCs allowed for at least a 50% reduction in minimal islet mass required to reverse diabetes in mice. This approach may contribute to alleviate the need for multiple donor organs per patient.

Long-lasting fibrin matrices ensure stable and functional angiogenesis by highly tunable, sustained delivery of recombinant VEGF164

Clinical trials of therapeutic angiogenesis by vascular endothelial growth factor (VEGF) gene delivery failed to show efficacy. Major challenges include the need to precisely control in vivo distribution of growth factor dose and duration of expression. Recombinant VEGF protein delivery could overcome these issues, but rapid in vivo clearance prevents the stabilization of induced angiogenesis. Here, we developed an optimized fibrin platform for controlled delivery of recombinant VEGF, to robustly induce normal, stable, and functional angiogenesis. Murine VEGF164 was fused to a sequence derived from α2-plasmin inhibitor (α2-PI1-8) that is a substrate for the coagulation factor fXIIIa, to allow its covalent cross-linking into fibrin hydrogels and release only by enzymatic cleavage. An α2-PI1-8-fused variant of the fibrinolysis inhibitor aprotinin was used to control the hydrogel degradation rate, which determines both the duration and effective dose of factor release. An optimized aprotinin-α2-PI1-8 concentration ensured ideal degradation over 4 wk. Under these conditions, fibrin-α2-PI1-8-VEGF164 allowed exquisitely dose-dependent angiogenesis: concentrations ≥25 μg/mL caused widespread aberrant vascular structures, but a 500-fold concentration range (0.01-5.0 μg/mL) induced exclusively normal, mature, nonleaky, and perfused capillaries, which were stable after 3 mo. Optimized delivery of fibrin-α2-PI1-8-VEGF164 was therapeutically effective both in ischemic hind limb and wound-healing models, significantly improving angiogenesis, tissue perfusion, and healing rate. In conclusion, this optimized platform ensured (i) controlled and highly tunable delivery of VEGF protein in ischemic tissue and (ii) stable and functional angiogenesis without introducing genetic material and with a limited and controllable duration of treatment. These findings suggest a strategy to improve safety and efficacy of therapeutic angiogenesis.

The impact of the receptor binding profiles of the vascular endothelial growth factors on their angiogenic features

BACKGROUND

Vascular endothelial growth factors (VEGFs) are potential therapeutic agents for treatment of ischemic diseases. Their angiogenic effects are mainly mediated through VEGF receptor 2 (VEGFR2).

METHODS

Receptor binding, signaling, and biological efficacy of several VEGFR2 ligands were compared to determine their characteristics regarding angiogenic activity and vascular permeability.

RESULTS

Tested VEGFR2 ligands induced receptor tyrosine phosphorylation with different efficacy depending on their binding affinities. However, the tyrosine phosphorylation pattern and the activation of the major downstream signaling pathways were comparable. The maximal angiogenic effect stimulated by different VEGFR2 ligands was dependent on their ability to bind to co-receptor Neuropilin (Nrp), which was shown to form complexes with VEGFR2. The ability of these VEGFR2 ligands to induce vascular permeability was dependent on their concentration and VEGFR2 affinity, but not on Nrp binding.

CONCLUSIONS

VEGFR2 activation alone is sufficient for inducing endothelial cell proliferation, formation of tube-like structures and vascular permeability. The level of VEGFR2 activation is dependent on the binding properties of the ligand used. However, closely similar activation pattern of the receptor kinase domain is seen with all VEGFR2 ligands. Nrp binding strengthens the angiogenic potency without increasing vascular permeability.

GENERAL SIGNIFICANCE

This study sheds light on how different structurally closely related VEGFR2 ligands bind to and signal via VEGFR2/Nrp complex to induce angiogenesis and vascular permeability. The knowledge of this study could be used for designing VEGFR2/Nrp ligands with improved therapeutic properties.

Induction of aberrant vascular growth, but not of normal angiogenesis, by cell-based expression of different doses of human and mouse VEGF is species-dependent

Therapeutic angiogenesis by vascular endothelial growth factor (VEGF) gene delivery is an attractive approach to treat ischemia. VEGF remains localized around each producing cell in vivo, and overexpression of mouse VEGF(164) (mVEGF(164)) induces normal or aberrant angiogenesis, depending strictly on its dose in the microenvironment in vivo. However, the dose-dependent effects of the clinically relevant factor, human VEGF(165) (hVEGF(165)), are unknown. Here we exploited a highly controlled gene delivery platform, based on clonal populations of transduced myoblasts overexpressing specific VEGF levels, to rigorously compare the in vivo dose-dependent effects of hVEGF(165) and mVEGF(164) in skeletal muscle of severe combined immune deficient (SCID) mice. While low levels of both factors efficiently induced similar amounts of normal angiogenesis, only high levels of mVEGF(164) caused widespread angioma-like structures, whereas equivalent or even higher levels of hVEGF(165) induced exclusively normal and mature capillaries. Expression levels were confirmed both in vitro and in vivo by enzyme-linked immunosorbent assay (ELISA) and quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). However, in vitro experiments showed that hVEGF(165) was significantly more effective in activating VEGF receptor signaling in human endothelial cells than mVEGF(164), while the opposite was true in murine endothelial cells. In conclusion, we found that, even though hVEGF is similarly efficient to the syngenic mVEGF in inducing angiogenesis at lower doses in a widely adopted and convenient mouse preclinical model, species-dependent differences in the relative activation of the respective receptors may specifically mask the toxic effects of high doses of the human factor.

Restoring the renal microvasculature to treat chronic kidney disease

Chronic kidney disease is characterized by progressive loss of the renal microvasculature, which leads to local areas of hypoxia and induction of profibrotic responses, scarring and deterioration of renal function. Revascularization alone might be sufficient to restore kidney function and regenerate the structure of the diseased kidney. For revascularization to be successful, however, the underlying disease process needs to be halted or alleviated and there must remain a sufficient number of surviving nephron units that can serve as a scaffold for kidney regeneration. This Perspectives article describes how revascularization might be achieved using vascular growth factors or adoptive transfer of endothelial progenitor cells and provides a brief outline of the studies performed to date. An overview of how therapeutic strategies targeting the microvasculature could be enhanced in the future is also presented.