Dose-dependent response of FGF-2 for lymphangiogenesis

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.

Presence of bone marrow-derived circulating progenitor endothelial cells in the newly formed lymphatic vessels

Bone marrow (BM)-derived circulating endothelial precursor cells (CEPCs) have been reported to incorporate into newly formed blood vessels under physiologic and pathologic conditions. However, it is unknown if CEPCs contribute to lymphangiogenesis. Here we show that in a corneal lymphangiogenesis model of irradiated mice reconstituted with enhanced green fluorescent protein (EGFP)-positive donor bone marrow cells, CEPCs are present in the newly formed lymphatic vessels. Depletion of bone marrow cells by irradiation remarkably suppressed lymphangiogenesis in corneas implanted with fibroblast growth factor-2 (FGF-2). Further, transplantation of isolated EGFP-positive/vascular endothelial growth factor receptor-3-positive (EGFP+/VEGFR-3+) or EGFP+/VEGFR-2+ cell populations resulted in incorporation of EGFP+ cells into the newly formed lymphatic vessels. EGFP+/CEPCs were also present in peritumoral lymphatic vessels of a fibrosarcoma. These data suggest that BM-derived CEPCs may play a role in "lymphvasculogenesis."

Opinion: emerging mechanisms of tumour lymphangiogenesis and lymphatic metastasis

Malignant tumours can spread to lymph nodes through lymphatic vessels. Recent studies show that tumours produce a range of growth factors that directly or indirectly stimulate lymphatic vessel growth (lymphangiogenesis) and lymphatic metastasis. These findings indicate that tumour lymphangiogenesis, similar to haemangiogenesis, is a complex process that is regulated by multiple growth factors. Understanding the underlying mechanisms by which tumours induce lymphangiogenesis might provide important information for the therapeutic intervention of metastatic spread.

Angiogenesis: update 2005

Angiogenesis has critical roles in normal vascular development and in important pathologies including cancer, wound healing and inflammation. This brief article will review the angiogenic response induced by the vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) family of proteins and particularly VEGF-A, thought to be the single most important angiogenic factor. It will also review the steps and mechanisms by which VEGF-A induces the formation of new blood vessels and will provide an initial classification of the abnormal blood vessels that form in pathological angiogenesis. Finally, it will touch on the exciting relationships that are emerging between angiogenesis and the hemostatic and nervous systems.

Hepatocyte growth factor promotes lymphatic vessel formation and function

The lymphatic vascular system plays a pivotal role in mediating tissue fluid homeostasis and cancer metastasis, but the molecular mechanisms that regulate its formation and function remain poorly characterized. A comparative analysis of the gene expression of purified lymphatic endothelial cells (LEC) versus blood vascular endothelial cells (BVEC) revealed that LEC express significantly higher levels of hepatocyte growth factor receptor (HGF-R). Whereas little or no HGF-R expression was detected by lymphatic vessels of normal tissues, HGF-R was strongly expressed by regenerating lymphatic endothelium during tissue repair and by activated lymphatic vessels in inflamed skin. Treatment of cultured LEC with HGF promoted LEC proliferation, migration and tube formation. HGF-induced proliferation of LEC did not require vascular endothelial growth factor receptor-3 activation, and HGF-induced cell migration was partially mediated via integrin alpha-9. Transgenic or subcutaneous delivery of HGF promoted lymphatic vessel formation in mice, whereas systemic blockade of HGF-R inhibited lymphatic function. These results identify HGF as a novel, potent lymphangiogenesis factor, and also indicate that HGF-R might serve as a new target for inhibiting pathological lymphangiogenesis.

Fibroblast growth factor/fibroblast growth factor receptor system in angiogenesis

Fibroblast growth factors (FGFs) are a family of heparin-binding growth factors. FGFs exert their pro-angiogenic activity by interacting with various endothelial cell surface receptors, including tyrosine kinase receptors, heparan-sulfate proteoglycans, and integrins. Their activity is modulated by a variety of free and extracellular matrix-associated molecules. Also, the cross-talk among FGFs, vascular endothelial growth factors (VEGFs), and inflammatory cytokines/chemokines may play a role in the modulation of blood vessel growth in different pathological conditions, including cancer. Indeed, several experimental evidences point to a role for FGFs in tumor growth and angiogenesis. This review will focus on the relevance of the FGF/FGF receptor system in adult angiogenesis and its contribution to tumor vascularization.

Vascular endothelial growth factor promotes sensitivity to ultraviolet B-induced cutaneous photodamage

Acute ultraviolet B (UVB) irradiation of the skin results in erythema, vasodilation, edema, and angiogenesis, which is associated with the expression of vascular endothelial growth factor (VEGF) by epidermal keratinocytes. It is unclear, however, whether VEGF is required for the damage or repair process that occurs in the skin on UVB exposure. We subjected transgenic mice that overexpress VEGF, and their wild-type littermates, to graded doses of acute UVB irradiation. The skin of VEGF-overexpressing mice was highly photosensitive and became erythematic when exposed to half the UVB dose required to induce erythema in wild-type mice. Erythema was associated with proliferating dermal endothelial cells, cutaneous edema, and inflammatory cell infiltration. When subjected to 10 weeks of low-level UVB irradiation, no major changes were observed in wild-type mice, whereas VEGF transgenic mice developed skin damage associated with degradation of the dermal matrix and enhanced vascularization. Systemic treatment with an anti-VEGF blocking antibody reduced the sensitivity of wild-type mice to acute UVB irradiation without inhibiting post-UVB repair. Our results reveal that VEGF promotes the cutaneous damage that occurs after UVB exposure and that the VEGF signaling pathway might serve as a novel target for the prevention of UVB-induced photodamage.

Vascular frontiers without borders: multifaceted roles of platelet-derived growth factor (PDGF) in supporting postnatal angiogenesis and lymphangiogenesis

The platelet-derived growth factor (PDGF) family of growth factors, which primarily serves the function of stabilizing vascular networks, has now been shown to play a role in promoting tumor lymphangiogenesis. PDGF-BB, independent of VEGFR-3 signaling, induces tumor growth and metastasis in part through supporting lymphangiogenesis. These data suggest that targeting the PDGF/PDGF-receptor signaling pathway will provide a novel strategy to block tumor neoangiogenesis and lymphangiogenesis, thereby inhibiting tumor growth and metastasis.