INTERLEUKIN-19 IS A NOVEL IMMUNO-MODULATORY AND PRO-ANGIOGENIC ADIPOKINE

Abstract

Uncontrolled, systemic inflammation coupled to obesity is associated with increased morbidity and mortality of cardiovascular disease. As a consequence of adipose tissue expansion, hypoxia ensues resulting in inflammation, and the release of various factors to restore sufficient blood flow to the tissue. However, this is often inadequate and does not result in proper tissue oxygenation. Currently little is known about the potential for endogenously expressed immuno-modulatory cytokines to attenuate inflammation and also provide pro-angiogenic effects. Interleukin-19 is uniquely immuno-modulatory, pro-angiogenic and is expressed in adipose tissue. There is no known mechanism to explain the role of IL-19 in adipose tissue expansion. We hypothesize that IL-19 acts as a novel adipokine whose expression in inflamed adipose tissue promotes a compensatory, immuno-modulatory effect and is a counter-regulatory response to inflammatory stimuli. We report that IL-19 is expressed in adipose tissue at both the transcript and protein level and its expression is increased in inflamed visceral adipose tissue but not subcutaneous adipose tissue. Utilizing Il19-/- knockout mice, we found the loss of IL-19 leads to a metabolic phenotype characterized by reduced glucose and insulin tolerance, a reduction in protective gene expression with increased pro-inflammatory factors, increased adipose tissue hypoxia and fibrosis, decreased adipose tissue vessel density and increased adipocyte hypertrophy both in response to standard chow diet and chronic high fat diet. In cultured adipocytes the addition of IL-19 leads to increased metabolically protective factors while also increasing glucose uptake. Acute treatment with IL-19 reduced glucose and insulin intolerance in obese wild-type mice. These data suggest that IL-19 presents a novel therapeutic opportunity in that IL-19 can effectively allow adipose tissue expansion without concomitant inflammation and insulin insensitivity. Interleukin Enhancer-binding Factor 3 (ILF3), an RNA-binding protein, is best known for its role in innate immunity by participation in cellular anti-viral responses. A role for ILF3 in angiogenesis is unreported. Our working hypothesis is that ILF3 promotes angiogenesis through cytokine-inducible mRNA stabilization of pro-angiogenic transcripts. ILF3 expression in CD31+ capillaries of hypoxic cardiac tissue was detected by immunohistochemistry. Pro-angiogenic stimuli induce ILF3 mRNA and protein expression in cultured human coronary artery endothelial cells (hEC). Angiogenic indices including proliferation, migration and tube formation are all significantly reduced in hEC when ILF3 is knocked down using siRNA, but are significantly increased when ILF3 is overexpressed using adenovirus. Protein and mRNA abundance of several angiogenic factors including CXCL1, VEGF, and IL-8 are decreased when ILF3 is knocked down by siRNA. These factors are increased when ILF3 is overexpressed by adenovirus. ILF3 is phosphorylated and translocates from the nucleus to the cytoplasm in response to angiogenic stimuli. Pro-angiogenic transcripts containing adenine and uridine-rich (AU-rich) elements (AREs) were bound to ILF3 determined using RNA immunoprecipitation. ILF3 stabilizes pro-angiogenic transcripts including VEGF, CXCL1, and IL-8 in hEC. Together these data suggest that in endothelial cells, the RNA stability protein, ILF3, plays a novel and central role in angiogenesis.