Slit2 exerts anti-inflammatory actions in human placenta and is decreased with maternal obesity.

Obese pregnancies are characterised by increased inflammation. Members of the Slit/Roundabout (Robo) family are key regulators of the inflammatory response. The aim of this study was to determine the effect of (i) pre-existing maternal obesity on Slit-Robo expression in human placenta and (ii) Slit2 knockdown by siRNA in primary trophoblast cells on markers of inflammation. The expression of Slit-Robo protiens was assessed in human placenta from lean (n = 15) and obese (n = 16) patients by qRT-PCR and Western blotting. Primary trophoblast cells were used to determine the effect of pro-inflammatory mediators on Slit2 expression, and the effect of Slit2 siRNA on pro-inflammatory mediators. While there was no change in Slit3, Robo1 or Robo4 expression, Slit2 expression was significantly lower in obese placenta compared to lean placenta. Human primary trophoblast cells treated with pro-inflammatory mediators IL-1β, TNF-α and LPS significantly decreased Slit2 expression. Slit2 silencing by siRNA augmented IL-6 expression and secretion in cells stimulated with TNF-α, LPS and TNF-α; IL-8 gene expression and/or release in cells stimulated with IL-1β and LPS; TNF-α gene expression and secretion in cells stimulated with LPS; and MMP-9 gene expression and pro MMP-9 levels in cells stimulated with TNF-α. The anti-inflammatory effects of Slit2 in human placenta is a novel finding, and suggests that inflammatory mediators, which are increased with obesity, downregulates Slit2 to enhance placental inflammation. Given the central role of pro-inflammatory cytokines in placental nutrient transport, our findings suggest Slit2 may play a role in fetal growth and development.