Semaphorin 5A (Sema5A), a member of the semaphorin family of proteins is a bifunctional molecule involved in attractive or repulsive cues in neurite outgrowth, cellular migration and metastasis. One of the characteristic features of Sema5A is the presence of a known regulator of angiogenesis - type I thrombospondin specific repeat (TSP-1) domains. A recent study in mice has shown that a homozygous null mutation in Sema5A is lethal due to a specific defect in regional patterning of cranial blood vessels. However, not much is known about the functional role of Sema5A in mediating angiogenesis. We hypothesize that Sema5A directly and indirectly regulates angiogenesis. We examined the expression of Sema5A and its receptor, Plexin B3, on endothelial cells. A direct role for Sema5A in modulating angiogenic phenotypes such as endothelial cell proliferation, chemotaxis, migration and survival, increased production of matrix metalloproteinases (MMPs) and the growth of new blood vessels from existing vessels was evaluated. An indirect role for Sema5A was examined by analyzing expression of known angiogenic regulators in endothelial cells following Sema5A treatment. Our data demonstrate that human dermal microvascular endothelial cells (HMEC) constitutively express Plexin B3 mRNA and protein, but not Sema5A. However, HMEC cells stimulated with recombinant Sema5A protein displayed significantly (p < 0.05) enhanced cell proliferation, survival, chemotaxis and capillary tube formation with a reduction in apoptosis compared to unstimulated cells. Vascular endothelial growth factor (VEGF) was used as a positive control. There was an increase in the expression of active MMP-2 and MMP-9 as well as known angiogenic regulators, VEGF, IL-8 and FGF-2 in endothelial cells treated with Sema5A. Furthermore, in the in vivo chorioallantoic membrane assay numerous newly formed capillaries were observed growing toward the Sema5A protein source. In summary, our data demonstrates the novel role of Sema5A as a proangiogenicmolecule that directly regulates the angiogenic phenotype and increases the expression of known angiogenic regulators in endothelial cells.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA