Preeclampsia is Associated With Reduced ISG15 Levels Impairing Extravillous Trophoblast Invasion

Abstract

Among several interleukin (IL)-6 family members, only IL-6 and IL-11 require a gp130 protein homodimer for intracellular signaling due to lack of intracellular signaling domain in the IL-6 receptor (IL-6R) and IL-11R. We previously reported enhanced decidual IL-6 and IL-11 levels at the maternal-fetal interface with significantly higher peri-membranous IL-6 immunostaining in adjacent interstitial trophoblasts in preeclampsia (PE) vs. gestational age (GA)-matched controls. This led us to hypothesize that competitive binding of these cytokines to the gp130 impairs extravillous trophoblast (EVT) differentiation, proliferation and/or invasion. Using global microarray analysis, the current study identified inhibition of interferon-stimulated gene 15 (<i>ISG15</i>) as the only gene affected by both IL-6 plus IL-11 vs. control or IL-6 or IL-11 treatment of primary human cytotrophoblast cultures. <i>ISG15</i> immunostaining was specific to EVTs among other trophoblast types in the first and third trimester placental specimens, and significantly lower <i>ISG15</i> levels were observed in EVT from PE vs. GA-matched control placentae (<i>p</i> = 0.006). Induction of primary trophoblastic stem cell cultures toward EVT linage increased <i>ISG15</i> mRNA levels by 7.8-fold (<i>p</i> = 0.004). <i>ISG15</i> silencing in HTR8/SVneo cultures, a first trimester EVT cell line, inhibited invasion, proliferation, expression of <i>ITGB1</i> (a cell migration receptor) and filamentous actin while increasing expression of <i>ITGB4</i> (a receptor for hemi-desmosomal adhesion). Moreover, <i>ISG15</i> silencing further enhanced levels of IL-1β-induced pro-inflammatory cytokines (<i>CXCL8</i>, <i>IL-6</i> and <i>CCL2</i>) in HTR8/SVneo cells. Collectively, these results indicate that <i>ISG15</i> acts as a critical regulator of EVT morphology and function and that diminished <i>ISG15</i> expression is associated with PE, potentially mediating reduced interstitial trophoblast invasion and enhancing local inflammation at the maternal-fetal interface. Thus, agents inducing <i>ISG15</i> expression may provide a novel therapeutic approach in PE.