Angiogenesis is an important process in maintaining normal physiology as well as in the pathology of many diseases. Angiogenesis based therapies have the potential to have a phenomenal impact on a diseases affecting more than one billion people worldwide, including all cancers, cardiovascular disease, blindness, arthritis, complications of AIDS, diabetes, Alzheimer’s disease, and more than 70 other major health conditions affecting children and adults, in developed and developing nations. In this study, we investigate the role of Interleukin-19 (IL-19) and Allograft inflammatory factor-1 (AIF-1) in endothelial cells (EC) proliferation, migration, activation and angiogenic potential.

IL-19 is a recently described member of the IL-10 family of anti-inflammatory cytokines. Nothing has been reported on the expression or mechanism(s) of IL-19 effects in endothelial cells. We have found that IL-19 is expressed in aortic endothelium, and can be induced in cultured EC by serum and inflammatory cytokine challenge. IL-19 is chemotactic for EC, and promotes cell spreading, migration, and wound healing. IL-19 pretreatment also enhances the migration of EC to Vascular endothelial growth factor (VEGF). IL-19 activates the signaling proteins STAT3, p44/42 MAPK, and Rac1, and induces expression of Matrix Metalloproteinase-2, which is obligate for EC migration. IL-19 promotes tube-like structure formation on Matrigel by Human Umbilical Vein EC (HUVEC), and promotes microvessel formation in mouse aortic ring assay. Taken together, these data suggest that IL-19 is a chemotactic cytokine for, and promotes the proliferation, migration, activation and angiogenic potential of endothelial cells. AIF-1 is a cytoplasmic, calcium-binding, inflammation-responsive scaffold protein that has been implicated in the regulation of inflammation. The expression and function of AIF-1 in EC is uncharacterized. AIF-1 expression co-localized with CD31-positive endothelial cells in neointima of inflamed human arteries, but not normal arteries. AIF-1 is detected at low levels in unstimulated EC, but expression can be increased in response to serum and soluble factors. Stable transfection of AIF-1 siRNA in EC reduced AIF-1 protein expression by 73%, and significantly reduced EC proliferation and migration. Rescue of AIF-1 expression restored both proliferation and migration of siRNA expressing ECs, and AIF-1 over expression enhanced both of these activities, suggesting a strong association between AIF-1 expression and EC activation. Activation of MAPK p44/42 and PAK1 was significantly reduced in siRNA ECs challenged with inflammatory stimuli. Reduction of AIF-1 expression did not decrease EC tube-like structure or microvessel formation from aortic rings, but over-expression of AIF-1 did significantly increase the number and complexity of these structures. These data indicate that AIF-1 expression plays an important role in proliferation, migration, signal transduction, and may have a role in angiogenesis.