Renhai Cao

Angiogenic synergism, vascular stability and improvement of hind-limb ischemia by a combination of PDGF-BB and FGF-2

The establishment of functional and stable vascular networks is essential for angiogenic therapy. Here we report that a combination of two angiogenic factors, platelet-derived growth factor (PDGF)-BB and fibroblast growth factor (FGF)-2, synergistically induces vascular networks, which remain stable for more than a year even after depletion of angiogenic factors. In both rat and rabbit ischemic hind limb models, PDGF-BB and FGF-2 together markedly stimulated collateral arteriogenesis after ligation of the femoral artery, with a significant increase in vascularization and improvement in paw blood flow. A possible mechanism of angiogenic synergism between PDGF-BB and FGF-2 involves upregulation of the expression of PDGF receptor (PDGFR)-α and PDGFR-β by FGF-2 in newly formed blood vessels. Our data show that a specific combination of angiogenic factors establishes functional and stable vascular networks, and provides guidance for the ongoing clinical trials of angiogenic factors for the treatment of ischemic diseases.

Leptin induces vascular permeability and synergistically stimulates angiogenesis with FGF-2 and VEGF

Most endocrine hormones are produced in tissues and organs with permeable microvessels that may provide an excess of hormones to be transported by the blood circulation to the distal target organ. Here, we investigate whether leptin, an endocrine hormone, induces the formation of vascular fenestrations and permeability, and we characterize its angiogenic property in the presence of other angiogenic factors. We provide evidence that leptin-induced new blood vessels are fenestrated. Under physiological conditions, capillary fenestrations are found in the leptin-producing adipose tissue in lean mice. In contrast, no vascular fenestrations were detected in the adipose tissue of leptin-deficient ob/ob mice. Thus, leptin plays a critical role in the maintenance and regulation of vascular fenestrations in the adipose tissue. Leptin induces a rapid vascular permeability response when administrated intradermally. Further, leptin synergistically stimulates angiogenesis with fibroblast growth factor (FGF)-2 and vascular endothelial growth factor (VEGF), the two most potent and commonly expressed angiogenic factors. These findings demonstrate that leptin has another new function—the increase of vascular permeability.

Blockade of vascular endothelial growth factor receptor-3 signaling inhibits fibroblast growth factor-2-induced lymphangiogenesis in mouse cornea

Vascular endothelial growth factor receptor-3 (VEGFR-3) is a major mediator of lymphangiogenesis. Recently, VEGFR-3 ligands, VEGF-C, and VEGF-D were reported to promote tumor lymphangiogenesis and lymphatic metastasis, and these processes were inhibited by blocking of the VEGFR-3-signaling pathway. Here, we have adapted the mouse corneal angiogenesis assay to study potential lymphangiogenic factors and inhibitors. Immunohistochemical analysis with lymphatic endothelial markers showed that VEGF-C induces lymphatic as well as blood vessel growth in the cornea. By contrast, VEGF induced angiogenesis but not lymphangiogenesis. Fibroblast growth factor-2 (FGF-2) stimulated both lymphangiogenesis and angiogenesis. FGF-2 up-regulated VEGF-C expression in vascular endothelial and perivascular cells. Furthermore, administration of blocking anti-VEGFR-3 antibodies inhibited the FGF-2-induced lymphangiogenesis. These findings show that VEGFR-3 can mediate lymphangiogenesis induced by other growth factors. Because increased expression of FGF-2 and VEGF-C has been associated with lymphatic metastasis, our results provide a potential strategy for the inhibition of lymphatic metastasis in cancer therapy.

Suppression of angiogenesis, tumor growth, and wound healing by resveratrol, a natural compound in red wine and grapes

Resveratrol (3,5,4′‐trihydroxystilbene) is a natural compound found in several plants, including grapes, peanuts, and pines, and in their related products. Red wine is probably the most frequently consumed drink that is enriched in resveratrol. We investigated whether drinking resveratrol could suppress angiogenesis, a process of blood vessel growth involved in initiation, development, and progression of many diseases, including cancer, metastasis, and diabetic retinopathy. We found that resveratrol suppresses the growth of new blood vessels in animals. It directly inhibits capillary endothelial cell growth. It blocks both VEGF‐ and FGF‐receptor‐mediated angiogenic responses. In addition, resveratrol inhibits the phosphorylation of mitogen‐activated kinase isoforms (MAPKp44/MAPKp42) induced by fibroblast growth factor‐2 in proliferating endothelial cells in a dose‐dependent manner. Oral administration of resveratrol significantly inhibits the growth of a murine fibrosarcoma in mice, and it significantly delays angiogenesis‐dependent wound healing in mice. Our findings suggest that ingestion of resveratrol‐enriched food could be beneficial for the prevention of cancer. However, its antiangiogenic effect could delay wound healing and possibly other angiogenesis‐dependent processes under physiological conditions.

Angiogenesis Inhibitor, TNP-470, Prevents Diet-Induced and Genetic Obesity in Mice

Adipose tissue growth has been proposed to involve recruitment of new blood vessels. Here, we test the hypothesis that delivery of an angiogenesis inhibitor in mice may prevent diet-induced obesity, the most common type of obesity in humans. We show that systemic administration of a selective angiogenesis inhibitor, TNP-470 (AGM-1470), prevents obesity in high caloric diet-fed wt mice as well as in genetically leptin-deficient ob/ob mice. Inhibition of obesity in mice by TNP-470 involves a reduction of vascularity in the adipose tissue. This therapeutic strategy appears to selectively affect the growth of adipose tissue as measured by the ratio between total fat and lean body mass. Interestingly, the treatment with TNP-470 results in decreased serum levels of low-density lipoprotein cholesterol. Furthermore, insulin levels are reduced, which indicates increased insulin sensitivity, suggesting that angiogenesis inhibitors may prevent the development of type II diabetes. Our findings suggest that similarly to growth and organogenesis in other tissues, adipose tissue growth is dependent on angiogenesis. Our observations may have conceptual implications for the prevention of obesity and related disorders.

Deletion of the Laminin α4 Chain Leads to Impaired Microvessel Maturation

ABSTRACT The laminin α4 chain, a component of laminin-8 and -9, is expressed in basement membranes, such as those beneath endothelia, the perineurium of peripheral nerves, and around developing muscle fibers. Laminin α4-null mice presented with hemorrhages during the embryonic and neonatal period and had extensive bleeding and deterioration of microvessel growth in experimental angiogenesis, as well as mild locomotion defects. Histological examination of newborn mice revealed delayed deposition of type IV collagen and nidogen into capillary basement membranes, and electron microscopy showed discontinuities in the lamina densa. The results demonstrate a central role for the laminin α4 chain in microvessel growth and, in the absence of other laminin α chains, in the composition of endothelial basement membranes.

Comparative Evaluation of FGF-2–, VEGF-A–, and VEGF-C–Induced Angiogenesis, Lymphangiogenesis, Vascular Fenestrations, and Permeability

Abstract— Several endothelial growth factors induce both blood and lymphatic angiogenesis. However, a systematic comparative study of the impact of these factors on vascular morphology and function has been lacking. In this study, we report a quantitative analysis of the structure and macromolecular permeability of FGF-2–, VEGF-A–, and VEGF-C–induced blood and lymphatic vessels. Our results show that VEGF-A stimulated formation of disorganized, nascent vasculatures as a result of fusion of blood capillaries into premature plexuses with only a few lymphatic vessels. Ultrastructural analysis revealed that VEGF-A–induced blood vessels contained high numbers of endothelial fenestrations that mediated high permeability to ferritin, whereas the FGF-2–induced blood vessels lacked vascular fenestrations and showed only little leakage of ferritin. VEGF-C induced approximately equal amounts of blood and lymphatic capillaries with endothelial fenestrations present only on blood capillaries, mediating a medium level of ferritin leakage into the perivascular space. No endothelial fenestrations were found in FGF-2–, VEGF-A–, or VEGF-C–induced lymphatic vessels. These findings highlight the structural and functional differences between blood and lymphatic vessels induced by FGF-2, VEGF-A, and VEGF-C. Such information is important to consider in development of novel therapeutic strategies using these angiogenic factors.

Angiogenic factors FGF2 and PDGF-BB synergistically promote murine tumor neovascularization and metastasis

Tumors produce multiple growth factors, but little is known about the interplay between various angiogenic factors in promoting tumor angiogenesis, growth, and metastasis. Here we show that 2 angiogenic factors frequently upregulated in tumors, PDGF-BB and FGF2, synergistically promote tumor angiogenesis and pulmonary metastasis. Simultaneous overexpression of PDGF-BB and FGF2 in murine fibrosarcomas led to the formation of high-density primitive vascular plexuses, which were poorly coated with pericytes and VSMCs. Surprisingly, overexpression of PDGF-BB alone in tumor cells resulted in dissociation of VSMCs from tumor vessels and decreased recruitment of pericytes. In the absence of FGF2, capillary ECs lacked response to PDGF-BB. However, FGF2 triggers PDGFR-alpha and -beta expression at the transcriptional level in ECs, which acquire hyperresponsiveness to PDGF-BB. Similarly, PDGF-BB-treated VSMCs become responsive to FGF2 stimulation via upregulation of FGF receptor 1 (FGFR1) promoter activity. These findings demonstrate that PDGF-BB and FGF2 reciprocally increase their EC and mural cell responses, leading to disorganized neovascularization and metastasis. Our data suggest that intervention of this non-VEGF reciprocal interaction loop for the tumor vasculature could be an important therapeutic target for the treatment of cancer and metastasis.

Hypoxia-Independent Angiogenesis in Adipose Tissues during Cold Acclimation

The molecular mechanisms of angiogenesis in relation to adipose tissue metabolism remain poorly understood. Here, we show that exposure of mice to cold led to activation of angiogenesis in both white and brown adipose tissues. In the inguinal depot, cold exposure resulted in elevated expression levels of brown-fat-associated proteins, including uncoupling protein-1 (UCP1) and PGC-1alpha. Proangiogenic factors such as VEGF were upregulated, and endogenous angiogenesis inhibitors, including thrombospondin, were downregulated. In wild-type mice, the adipose tissues became hypoxic during cold exposure; in UCP1(-/-) mice, hypoxia did not occur, but, remarkably, the augmented angiogenesis was unaltered and was thus hypoxia independent. Intriguingly, VEGFR2 blockage abolished the cold-induced angiogenesis and significantly impaired nonshivering thermogenesis capacity. Unexpectedly, VEGFR1 blockage resulted in the opposite effects: increased adipose vascularity and nonshivering thermogenesis capacity. Our findings have conceptual implications concerning application of angiogenesis modulators for treatment of obesity and metabolic disorders.

Insulin-like growth factors 1 and 2 induce lymphangiogenesis in vivo

Lymphangiogenesis is an important process that contributes to the spread of cancer. Here we show that insulin-like growth factors 1 (IGF-1) and 2 (IGF-2) induce lymphangiogenesis in vivo. In a mouse cornea assay, IGF-1 and IGF-2 induce lymphangiogenesis as detected with LYVE-1, a specific marker for lymphatic endothelium. Interestingly, IGF-1-induced lymphangiogenesis could not be blocked by a soluble vascular endothelial growth factor receptor 3, suggesting that the vascular endothelial growth factor receptor 3-signaling pathway is not required for IGF-induced lymphangiogenesis. In vitro, IGF-1 and IGF-2 significantly stimulated proliferation and migration of primary lymphatic endothelial cells. IGF-1 and IGF-2 induced phosphorylation of intracellular signaling components, such as Akt, Src, and extracellular signal-regulated kinase in lymphatic endothelial cells. Immunohistochemistry, RT-PCR, and Affymetrix GeneChip microarray analysis showed that the receptors for IGFs are present in lymphatic endothelium. Together, our findings suggest that IGFs might act as direct lymphangiogenic factors, although any indirect roles in the induction of lymphangiogenesis cannot be excluded. Because members of the IGF ligand and receptor families are widely expressed in various types of solid tumors, our findings suggest that these factors are likely to contribute to lymphatic metastasis.