Adenoviral-mediated expression of antisense RNA to fibroblast growth factors disrupts murine vascular development

Endoglin deficiency impairs VEGFR2 but not FGFR1 or TIE2 activation and alters VEGF-mediated cellular responses in human primary endothelial cells

Hereditary hemorrhagic telangiectasia (HHT) is a genetic disease characterized by vascular dysplasia. Mutations of the endoglin (ENG) gene that encodes a co-receptor of the transforming growth factor β1 signaling pathway cause type I HHT. ENG is primarily expressed in endothelial cells (ECs), but its interaction with other key angiogenic pathways to control angiogenesis has not been well addressed. The aim of this study is to investigate ENG interplay with VEGFR2, FGFR1 and TIE2 in primary human ECs. ENG was knocked-down with siRNA in human umbilical vein ECs (HUVECs) and human lung microvascular ECs (HMVEC-L). Gene expression was measured by RT-qPCR and Western blotting. Cell signaling pathway activation was analyzed by detecting phosphor-ERK and phosphor-AKT levels. Cell migration and apoptosis were assessed using the Boyden chamber assay and the CCK-8 Kit, respectively. Loss of ENG in HUVECs led to significantly reduced expression of VEGFR2 but not TIE2 or FGFR1, which was also confirmed in HMVEC-L. HUVECs lacking ENG had significantly lower levels of active Rac1 and a substantial reduction of the transcription factor Sp1, an activator of VEGFR2 transcription, in nuclei. Furthermore, VEGF- but not bFGF- or angiopoietin-1-induced phosphor-ERK and phosphor-AKT were suppressed in ENG deficient HUVECs. Functional analysis revealed that ENG knockdown inhibited cell migratory but enhanced anti-apoptotic activity induced by VEGF. In contrast, bFGF, angiopoietin-1 and -2 induced HUVEC migration and anti-apoptotic activities were not affected by ENG knockdown. In conclusion, ENG deficiency alters the VEGF/VEGFR2 pathway, which may play a role in HHT pathogenesis.

Heparan sulfate in angiogenesis: a target for therapy

Heparan sulfate (HS), a long linear polysaccharide of alternating disaccharide residues, interacts with a wide variety of proteins, including many angiogenic factors. The involvement of HS in signaling of pro-angiogenic factors (e.g. vascular endothelial growth factor and fibroblast growth factor 2), as well as interaction with anti-angiogenic factors (e.g. endostatin), warrants its role as an important modifier of (tumor) angiogenesis. This review summarizes our current understanding of the role of HS in angiogenic growth factor signaling, and discusses therapeutic strategies to target HS and modulate angiogenesis.

Vascular precursor cells

Understanding the mechanisms that regulate the proliferation and differentiation of human stem and progenitor cells is critically important for the development and optimization of regenerative medicine strategies. For vascular regeneration studies, specifically, a true "vascular stem cell" population has not yet been identified. However, a number of cell types that exist endogenously, or can be generated or propagated ex vivo, function as vascular precursor cells and can participate in and/or promote vascular regeneration. Herein, we provide an overview of what is known about the regulation of their differentiation specifically toward a vascular endothelial cell phenotype.

Stem cell-derived vascular endothelial cells and their potential application in regenerative medicine

Although a 'vascular stem cell' population has not been identified or generated, vascular endothelial and mural cells (smooth muscle cells and pericytes) can be derived from currently known pluripotent stem cell sources including human embryonic stem cells and induced pluripotent stem cells. We review the vascular potential of these human pluripotent stem cells, the mechanisms by which they are induced to differentiate toward a vascular endothelial cell fate, and their applications in regenerative medicine.

Vascular potential of human pluripotent stem cells

Cardiovascular disease is the number one cause of death and disability in the US. Understanding the biological activity of stem and progenitor cells, and their ability to contribute to the repair, regeneration and remodeling of the heart and blood vessels affected by pathological processes is an essential part of the paradigm in enabling us to achieve a reduction in related deaths. Both human embryonic stem (ES) cells and induced pluripotent stem (iPS) cells are promising sources of cells for clinical cardiovascular therapies. Additional in vitro studies are needed, however, to understand their relative phenotypes and molecular regulation toward cardiovascular cell fates. Further studies in translational animal models are also needed to gain insights into the potential and function of both human ES- and iPS-derived cardiovascular cells, and enable translation from experimental and preclinical studies to human trials.

The role of quaking in mammalian embryonic development

Functional studies of the mouse quaking gene (Qk) have focused on its role in the postnatal central nervous system during myelination. However, the death of the majority of homozygous mouse quaking alleles revealed that quaking has a critical role in embryonic development prior to the start of myelination. Surprisingly, the lethal alleles revealed that quaking has a function in embryonic blood vessel formation and remodeling. Further studies ofthe extraembryonic yolk sac showed that Qk regulates visceral endoderm differentiated function at the cellular level, including the local synthesis of retinoic acid (RA), which then exerts paracrine control of endothelial cells within adjacent mesoderm. Endoderm-derived RA regulates proliferation of endothelial cells and extracellular matrix (ECM) production, which in a reciprocal manner, modulates visceral endoderm survival and function. Although exogenous RA can rescue endothelial cell growth control and ECM production in mutants carrying a lethal mutation, which lack functional Qk, neither visceral endoderm function nor vascular remodeling is restored. Thus, Qk also regulates cell autonomous functions of visceral endoderm that are critical for vascular remodeling. Interestingly, quaking is highly expressed during normal cardiac development, particularly in the outflow tract, suggesting potentially unique functions in the developing heart. Together, the work on Qk in mammalian embryos reveals an essential, yet under appreciated, role in cardiovascular development. This suggests that certain functions may remain conserved in the early embryo throughout the evolution of nonvertebrate and vertebrate organisms and that additional roles for quaking remain to be discovered.

Signaling hierarchy regulating human endothelial cell development

OBJECTIVE

Our present knowledge of the regulation of mammalian endothelial cell differentiation has been largely derived from studies of mouse embryonic development. However, unique mechanisms and hierarchy of signals that govern human endothelial cell development are unknown and, thus, explored in these studies.

METHODS AND RESULTS

Using human embryonic stem cells as a model system, we were able to reproducibly and robustly generate differentiated endothelial cells via coculture on OP9 marrow stromal cells. We found that, in contrast to studies in the mouse, bFGF and VEGF had no specific effects on the initiation of human vasculogenesis. However, exogenous Ihh promoted endothelial cell differentiation, as evidenced by increased production of cells with cobblestone morphology that coexpress multiple endothelial-specific genes and proteins, form lumens, and exhibit DiI-AcLDL uptake. Inhibition of BMP signaling using Noggin or BMP4, specifically, using neutralizing antibodies suppressed endothelial cell formation; whereas, addition of rhBMP4 to cells treated with the hedgehog inhibitor cyclopamine rescued endothelial cell development.

CONCLUSIONS

Our studies revealed that Ihh promoted human endothelial cell differentiation from pluripotent hES cells via BMP signaling, providing novel insights applicable to modulating human endothelial cell formation and vascular regeneration for human clinical therapies.

Visceral endoderm function is regulated byquaking and required for vascular development

The quaking (qkI) gene produces three major alternatively spliced variants (qkI-5,-6,-7) that encode for proteins that share the RNA binding, KH domain. Previous studies utilizing the qk(k2) allele, which contains an N-ethyl-N-nitrosourea (ENU)-induced point mutation in the KH domain, demonstrate that this functional region of qkI is required for embryonic vascular development. In the current studies we demonstrate that qk(l-1)/qk(l-1) mutants, which lack the QKI-5 splice variant, also died at midgestation due to vascular remodeling defects. In addition, although all three QKI isoforms were expressed in the visceral endoderm of wildtype yolk sacs, qkI-6 and qkI-7 transcript and protein expression were suppressed in qk(k2)/qk(k2) and qk(l-1)/qk(l-1) mutant yolk sacs, suggesting that the KH-domain of QKI-5 was required for qkI-6 and qkI-7 expression. Further studies revealed that the cellular role of qkI is to regulate visceral endoderm function, including the local synthesis of retinoic acid (RA) and the subsequent control of endothelial cell proliferation, matrix production, and visceral endoderm survival. Although these defects were rescued by exogenous RA, visceral endoderm function or vascular remodeling were not restored. Thus, we conclude that qkI regulates visceral endoderm function, which is critical for vascular remodeling.

Beyond angiogenesis: the cardioprotective potential of fibroblast growth factor-2

In the field of cardiovascular research, a number of independent approaches have been explored to protect the heart from acute and chronic ischemic damage. Fibroblast growth factor-2 (FGF-2) recently has received considerable attention with respect to its angiogenic potential. While therapeutic angiogenesis may serve to salvage chronically ischemic myocardium, more acute treatments are in demand to increase cardiac resistance to injury (preconditioning) and to guard against secondary injury after an acute ischemic insult. Here, we look beyond the angiogenic potential of FGF-2 and examine its acute cardioprotective activity as demonstrated under experimental conditions, both as an agent of a preconditioning-like response and for secondary injury prevention at the time of reperfusion. Factors to consider in moving to the clinical setting will be discussed, including issues of dosage, treatment duration, and routes of administration. Finally, issues of safety and clinical trial design will be considered. The prospect of such a multipotent growth factor having clinical usefulness opens the door to effective treatment of both acute and chronic ischemic heart disease, something well worth the attention of the cardiovascular community.

Generation of a Specific Immunological Response to FGF‐2 Does Not Affect Wound Healing or Reproduction

Angiogenesis, the process of new capillary formation from pre-existing vessels, has been established as an important mechanism involved in pathologic processes, such as cancer, as well as in normal physiology (Ribatti, D.; Vacca, A.; Roncali, L.; Dammacco, F. Angiogenesis under normal and pathological conditions. Haematologica 1991, 76 (4), 311-320). Basic fibroblast growth factor (FGF-2) is a critical mediator of angiogenesis that is important for normal reproduction and wound healing. FGF-2 mediates its pro-angiogenic effects by binding to heparin sulfate proteoglycan in addition to a tyrosine kinase receptor (Baird, A.; Schubert, D.; Ling, N.; Guillemin, R. Receptor and heparin-binding domain of basic fibroblast growth factor. Proc. Natl. Acad. Sci. U. S. A. 1998, 5 (7), 2324-2328; Richard, C.; Roghani, M.; Moscatelli, D. Fibroblast growth factor (FGF)-2 mediates cell attachment through interactions with two FGF receptor-1 isoforms and extracellular matrix or cell-associated heparin sulfate proteoglycans. Biochem. Biophys. Res. Commun. 2000, 276 (2), 399-405; Casu, B.; Guerrini, M.; Naggi, A.; Perez, M.; Torri, G.; Ribatti, D.; Carminati, P.; Giannini, G.; Penco, S.; Pisano, C.; Belleri, M.; Rusnati, M.; Presta, M. Short heparin sequences spaced by glycol-split urinate residues are antagonists of fibroblast growth factor 2 and angiogenesis inhibitors. Biochemistry 2002, 41 (33), 10519-10528; Murphy, P.V.; Pitt, N.; O'Brien, A.; Enright, P.M.; Dunne, A.; Wilson, S.J.; Duane, R.M.; O'Boyle, K.M. Identification of novel inhibitors of fibroblast growth factor (FGF-2) binding to heparin and endothelial cell survival from a structurally diverse carbohybrid library. Bioorg. Med. Chem. Lett. 2002, 12 (22), 3287-3290). We developed a liposomal-based peptide vaccine, L(HBD) that targets the heparin binding domain of the FGF-2 molecule. This vaccine, when inoculated into mice, inhibits angiogenesis in response to FGF-2 in a hepatic sponge model as well as tumor progression in two models of pulmonary metastatic disease. In the present studies, we further characterize the immunological and physiological responses to this vaccine. Vaccinated animals generated a specific anti-FGF-2 antibody (titer of 1:5000) that was able to inhibit FGF-2 binding to heparin sulfate in a dose dependent fashion. Cell mediated immunity was evidenced by a delayed type hypersensitivity response following challenge with the heparin binding domain peptide. Despite an immune response toward FGF-2, vaccination with L(HBD) did not result in alterations in mean time to wound healing when compared to unvaccinated animals or those treated with a liposome control. In reproductive studies, vaccinated females were not impaired in their ability to: 1) become pregnant, 2) support the growth and development of their embryos, and 3) deliver viable offspring. Furthermore, when assessed histologically, these offspring did not demonstrate any alterations in organogenesis when compared to pups born to untreated or liposome control treated females. Thus, while vaccination against FGF-2 induces a specific FGF-2 antibody response, and inhibits angiogenesis and tumor development in a pathological setting, it does not adversely alter normal physiological events dependent on FGF-2.

Antisense basic fibroblast growth factor alters the time course of mitogen-activated protein kinase in arterialized vein graft remodeling

PURPOSE

Neointimal hyperplasia (NIH) is complete by 3 weeks in rabbit vein grafts implanted into the arterial circulation. Activation of the mitogen-activated protein kinase (MAPK) family of protein kinases is thought to be critical in remodeling events such as cellular proliferation, differentiation, and migration, as found in NIH. We previously demonstrated that antisense basic fibroblast growth factor (ASbFGF) inhibited the synthesis of basic fibroblast growth factor (bFGF) in the balloon injury model of NIH. We examined the effect of ASbFGF on NIH and the time course of MAPK, extracellular signal-regulated kinase (ERK) 1/2, c-Jun N-terminal protein kinase (JNK), and p38 kinase activation in arterialized vein grafts.

METHODS

Carotid interposition of a vein bypass graft was performed in 75 New Zealand White rabbits. Segments of the external jugular vein were transfected with a replication-deficient adenovirus containing the messenger RNA sequence for rat ASbFGF at 1 x 10(10) plaque-forming units per milliliter; control animals were given phosphate-buffered saline solution (PBS) alone. Rabbits were killed at 30 minutes, 4 days, 7 days, and 21 days (n = 8). Four grafts in each group were fixed with formalin and embedded in paraffin, then processed with elastin-collagen and hematoxylin-eosin stains. The other four grafts were individually frozen, and total protein was extracted. Phosphorylation of MAPK, ERK1/2, JNK, and p38, was determined with Western blot analysis and immunohistochemistry. Groups were compared with analysis of variance.

RESULTS

The thickness of neointima in the PBS group and the ASbFGF group at 21 days was 60.2 +/- 2.1 and 39.4 +/- 2.1 microm, respectively (P <.01). In both the control and ASbFGF groups, all 3 MAPKs demonstrated activation compared with preimplantation levels. However, when compared with the PBS group the ASbFGF group showed greater than 33% inhibition of all three MAPKs by day 4 and day 7 (P <.05), but no significant difference in any MAPK activation by day 21 (P >.05, all groups). Cells staining positive for activated MAPK were found in the neointima and adventitia of vein grafts in both the PBS and ASbFGF groups.

CONCLUSION

MAPKs are activated during the first week after vein graft implantation. Grafts treated with ASbFGF demonstrated reduced MAPK activation and less neointimal thickening. These results suggest that the process of vein graft adaptation to the arterial circulation, and subsequent NIH, may depend on basic fibroblast growth factor activity, which is mediated, at least in part, by a MAPK-dependent mechanism.

Vascular endothelial growth factor and basic fibroblast growth factor differentially modulate early postnatal coronary angiogenesis

The roles of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF [FGF-2]) in early postnatal regulation of coronary angiogenesis were investigated by administering neutralizing antibodies to these growth factors between postnatal days 5 and 12. Immunohistochemistry and Western blotting both revealed decreases in VEGF protein in the hearts of rats treated with either antibody. In contrast, bFGF mRNA increased in both treated groups, whereas VEGF mRNA was unchanged. Using stereological assessment of perfusion-fixed hearts, we found that both anti-VEGF and anti-bFGF inhibited the rapid and marked capillary growth that occurs during this time period and that the effects of the two neutralizing antibodies are not additive. Arteriolar growth, as indicated by a lower length density, was inhibited by anti-bFGF, but not anti-VEGF. When both anti-VEGF and anti-bFGF were administered, arteriolar length density was not significantly lower, but the population of small arterioles (<15 microm) was markedly reduced, whereas the percentage of large arterioles (26 to 50 microm) more than doubled. Thus, inhibition of both growth factors negated or limited the formation of small arterioles and facilitated an expansion of the largest arterioles. These in vivo data are the first to document that during the early neonatal period, (1) both VEGF and bFGF modulate capillary growth, (2) bFGF facilitates arteriolar growth, and (3) the two growth factors interact to establish the normal hierarchy of the arteriolar tree.

Overexpression of FGF-2 increases cardiac myocyte viability after injury in isolated mouse hearts

We generated transgenic (TG) mice overexpressing fibroblast growth factor (FGF)-2 protein (22- to 34-fold) in the heart. Chronic FGF-2 overexpression revealed no significant effect on heart weight-to-body weight ratio or expression of cardiac differentiation markers. There was, however, a significant 20% increase in capillary density. Although there was no change in FGF receptor-1 expression, relative levels of phosphorylated c-Jun NH(2)-terminal kinase and p38 kinase as well as of membrane-associated protein kinase C (PKC)-alpha and total PKC-epsilon were increased in FGF-2-TG mouse hearts. An isolated mouse heart model of ischemia-reperfusion injury was used to assess the potential of increased endogenous FGF-2 for cardioprotection. A significant 34-45% increase in myocyte viability, reflected in a decrease in lactate dehydrogenase released into the perfusate, was observed in FGF-2 overexpressing mice and non-TG mice treated exogenously with FGF-2. In conclusion, FGF-2 overexpression causes augmentation of signal transduction pathways and increased resistance to ischemic injury. Thus, stimulation of endogenous FGF-2 expression offers a potential mechanism to enhance cardioprotection.

Transient modulation of gene expression in the neurulation staged mouse embryo

Transient modulation of gene expression in the embryo during early organogenesis will allow studies to be conducted that determine tissue- and stage-specific function(s) of genes. To achieve this goal, viral vectors and antisense oligodeoxynucleotides have been used to produce gain-of-function and loss-of-function models. Adenoviral transduction of whole embryos, embryonic heart and vasculature, and primary neural crest cell culture has been reported. The morphological consequences of overexpression or decreasing expression of selected genes have been evaluated using these tools. Gene-teratogen interaction studies have also been performed. The viral vectors appear to be important tools for modulating gene expression and hold great promise for future research.

Inhibition of angiogenesis by a mouse sprouty protein

Sprouty negatively modulates branching morphogenesis in the Drosophila tracheal system. To address the role of mammalian Sprouty homologues in angiogenesis, another form of branching morphogenesis, a recombinant adenovirus engineered to express murine Sprouty-4 selectively in endothelial cells, was injected into the sinus venosus of embryonic day 9.0 cultured mouse embryos. Sprouty-4 expression inhibited branching and sprouting of small vessels, resulting in abnormal embryonic development. In vitro, Sprouty-4 inhibited fibroblast growth factor and vascular endothelial cell growth factor-mediated cell proliferation and migration and prevented basic fibroblast growth factor and vascular endothelial cell growth factor-induced MAPK phosphorylation in endothelial cells, indicating inhibition of tyrosine kinase-mediated signaling pathways. The ability of constitutively activated mutant Ras(L61) to rescue Sprouty-4 inhibition of MAPK phosphorylation suggests that Sprouty inhibits receptor tyrosine kinase signaling upstream of Ras. Thus, Sprouty may regulate angiogenesis in normal and disease processes by modulating signaling by endothelial tyrosine kinases.

LIF transduces contradictory signals on capillary outgrowth through induction of stat3 and (P41/43)MAP kinase

The signaling pathways regulating blood vessel growth and development are not well understood. In the present report, an in vitro model was used to identify signaling pathways regulating capillary formation in embryonic endothelial cells. Basic fibroblast growth factor (bFGF) plus leukemia inhibitory factor (LIF) optimally stimulate the formation of capillary-like structures of the embryonic endothelial cell line IEM. LIF stimulation of IEM cells leads to activation of the Stat3 as well as the (P41/43)mitogen-activated protein kinase ((P41/43)MAPK) cascade, while bFGF does not activate Stat3 but does induce the (P41/43)MAPK cascade. Inhibition of Stat3 DNA-binding activity by expression of a dominant inhibitory Stat3 mutant increases the capillary outgrowth of the IEM cells induced by LIF. Increased Stat3 activity by overexpression of the wild-type Stat3 greatly reduced capillary outgrowth. In contrast, inhibition of the (P41/43)MAPK cascade using a MEK-1 inhibitor dramatically inhibits the LIF-induced capillary outgrowth. Moreover, the increased formation of capillary-like structures of the IEM cells mediated by Stat3 inhibition does not overcome the requirement for activation of the (P41/43)MAPK pathway for capillary outgrowth. Stat3 activity correlates with the LIF-induced expression of the negative feedback regulators of the Janus (JAK) family of tyrosine kinases, SOCS-1 and SOCS-3. These results provide evidence that Stat3 acts as a negative regulator of capillary outgrowth, possibly by increasing SOCS-1 or SOCS-3 expression. The contradictory signals stimulated by LIF could be necessary to control the intensity of the response leading to capillary outgrowth in vivo.

Maintenance of vascular integrity in the embryo requires signaling through the fibroblast growth factor receptor

Basic fibroblast growth factor (FGF)-2 is important for vessel formation and/or maintenance of vascular integrity in the embryo. FGF signaling may be mediated through transmembrane tyrosine kinase receptors or directly through intracellular pathways that do not involve receptor activation. To determine the role of receptor-mediated signaling in endothelial cells, an adenovirus encoding truncated FGF receptor (FGFR)-1, under the control of the cytomegalovirus promoter, was expressed in endothelial cells. FGF signaling was impaired, as indicated by inhibition of MAPK phosphorylation. Functional consequences included inhibition of endothelial cell migration and induction of apoptosis. To address the role of endothelial FGFR signaling in vascular development, recombinant adenovirus encoding a dominant-negative FGFR was injected into the sinus venosus of embryonic day 9.0 cultured mouse embryos. Previous studies demonstrated that transgenes delivered via adenovirus, under the control of the cytomegalovirus promoter, are expressed selectively in the developing vasculature. Embryos expressing a control adenovirus developed normally, whereas those expressing the FGFR-1 mutant exhibited abnormal embryonic and extra-embryonic vascular development. These data demonstrate that FGF, by signaling through the FGFR, plays a pivotal role in the development and maintenance of a mature vascular network in the embryo.

Adenoviral-mediated expression of antisense RNA to basic fibroblast growth factor reduces tangential stress in arterialized vein grafts

PURPOSE

The purpose of this study was to test whether basic fibroblast growth factor (bFGF) participates in arterialized vein graft remodeling.

METHODS

Rabbits underwent in vivo gene transfer and carotid interposition vein grafting. Segments of external jugular vein were infected with an adenovirus that expressed antisense bFGF RNA (Ad.ASbFGF) at 1 x 10(10) PFU/mL to inhibit new synthesis of bFGF by cells in the vein graft wall. Control rabbits were treated with either adenovirus that encoded beta-galactosidase (Ad.lacZ) at 1 x 10(10) PFU/mL or vehicle (phosphate-buffered saline solution [PBS]). At 3 days, 3 grafts per treatment group were harvested for the determination of gene expression of ASbFGF RNA by reverse transcriptase-polymerase chain reaction. Rabbits were killed, and perfusion was fixed 2 months after the grafting. Total wall thickness and lumen circumference of vein grafts and normal arteries were measured in cross sections. Calculated mean tangential stress (+/-SD) for the ASbFGF-treated group and controls was compared for significance. Grafts were immunohistochemically stained to assess bFGF protein production.

RESULTS

Only the grafts infected with the Ad.ASbFGF gene expressed ASbFGF RNA. Grafts that were treated with Ad.ASbFGF displayed lower tangential stress (10.9 +/- 2.3 dynes/cm(2)) than PBS alone (22 +/- 2.8 dynes/cm(2)) or Ad. lacZ-treated controls (20.6 +/- 5.4 dynes/cm(2); P <.001). Tangential stress in the Ad.ASbFGF group was comparable to a normal carotid artery (13.9 +/- 2.1 dynes/cm(2)). The difference in mean total wall thickness was significant among the 3 treatment groups: Ad.ASbFGF, 164 +/- 3.4 microm); Ad.lacZ, 100 +/- 3.3 microm; and PBS, 96 +/- 3.6 microm; P <.01). Luminal circumference was not different among the groups. The Ad.ASbFGF-treated vein graft wall was composed of thick layers of concentric smooth muscle cells and elastin fibers in contrast to the sponge-like appearance observed in control arterialized vein grafts. Reduction in bFGF protein was noted only in the Ad.ASbFGF-treated group.

CONCLUSION

Inhibition of bFGF synthesis in vivo with the use of adenoviral gene transfer of antisense RNA to bFGF promotes a vein graft with decreased tangential stress while maintaining the luminal area. The vein graft wall is remodeled and qualitatively resembles an artery so that wall tangential stress in Ad.ASbFGF and normal artery are not significantly different. The lack of significant difference in lumen circumference among groups suggests that wall thickening in the Ad. ASbFGF grafts is not at the expense of luminal narrowing. Our results suggest that ASbFGF RNA expression may represent an effective strategy in limiting the failure of arterialized venous conduits.

Fibroblast growth factor-2

Fibroblast growth factor-2 (FGF-2) is a heparin-binding growth factor which occurs in several isoforms resulting from alternative initiations of translation: an 18 kD cytoplasmic isoform and four larger molecular weight nuclear isoforms (22, 22.5, 24 and 34 kD). FGF-2 has pleiotropic roles in many cell types and tissues; it is a motogenic, angiogenic and survival factor which is involved in cell migration, cell differentiation and in a variety of developmental processes. Although devoid of signal peptide, it could be secreted. It acts mainly through a paracrine/autocrine mechanism involving high affinity transmembrane receptors and heparan sulfate proteoglycan low affinity receptors, but also through still unknown intracrine process(es) on intracellular targets. FGF-2 has many biological functions which are probably isoform-specific. Nevertheless, FGF-2 is not essential for embryonic development as knock-out mice for the growth factor are viable and fertile although they exhibit abnormalities in neuronal differentiation. Use of FGF-2 as therapeutic agent for the treatment of ischemic cardiovascular disease is promising and clinical trials are in progress.