Abstract 3056: IL-19 Is A VEGFC-inducible Lymphokine That Regulates Prox1 Through RNA Stability

Introduction: During inflammatory diseases, such as atherosclerosis, malfunctional lymphangiogenesis occurs. Studies suggest that inflammation induces a zipper morphology in lymphatic junctions which limits lymphatic function, but this phenomenon has never been evaluated under atherogenic conditions. We previously reported that IL-19 is anti-inflammatory, anti-atherosclerotic, and pro-angiogenic. The purpose of this study is to test the hypothesis that IL-19 induces functional lymphangiogenesis under atherosclerotic conditions. Methods & Results: Both IL-19 and VEGFC, a vital pro-lymphangiogenic factor, induce IL-19 protein expression in lymphatic endothelial cells (LECs). Interestingly, IL-19 does not induce VEGFC protein expression. IL-19 treatment does induce expression of Prox1, the master regulator of lymphatic development. Proliferation, migration, and tube formation assays confirmed IL-19 induces lymphangiogenesis. IL-19 also promotes short- and long-term regulation of lymphatic permeability by rapidly inducing VE-cadherin phosphorylation and slowly increasing Angpt2 expression. In the presence of oxLDL, LECs have decreased permeability via electric cell-substrate impedance sensing and increased zippers via immunocytochemistry, while co-treatment with IL-19 maintains LEC barrier function. Ldlr -/- Il19 -/- double knockout (dKO) mice, known to have exacerbated atherosclerosis, have significantly worse lymphatic function compared to Ldlr -/- on a high fat diet. However, dKO and Ldlr -/- mice on chow diet have similar lymphatic function, again suggesting a role for IL-19 by maintaining lymphatic flux under pro-inflammatory conditions. Although IL-19 canonically phosphorylates STAT3 in LECs, STAT3 knockdown does not affect Prox1 expression. However, Prox1 knockdown prevents IL-19-associated lymphangiogenesis and Angpt2 upregulation. Since IL-19 is known to alter mRNA stability, we performed Actinomycin D assays and determined IL-19 increases Prox1 mRNA stability, possibly contributing to Prox1 upregulation independent of STAT3 activity. Conclusion: IL-19 is a previously un-recognized regulator of lymphangiogenesis and could potentially promote lymphatic function during inflammation.