Interleukin-6 changes tight junction permeability and intracellular phospholipid content in a human enterocyte cell culture model

Abstract

Proinflammatory cytokines and secretory phospholipase A 2 (sPLA 2 ) are elevated in patients with inflammatory bowel disease (IBD). We previously reported that the proinflammatory cytokine IL-6 increased the expression of sPLA 2 (a hydrolyzer of phosphatidylcholine) and decreased membrane integrity in an intestinal epithelial cell culture model. To determine the physiological effects of the IL-6 mediated increase in sPLA 2 on decreased epithelial layer integrity, we investigated alterations of intracellular/secretory phospholipid (PL) composition in a cell culture model. In addition, since other PLs may also mediate epithelial membrane activity, we investigated the effect of IL-6 on PL activity in a Caco-2 enterocyte culture model. Caco-2 cells were incubated for 72 h with IL-6 or media alone (control). Both media and cell lysate were analyzed for PL composition using thin-layer chromatography. The PL composition in the media did not show any differences between the two groups ( p >0.1). Total intracellular PL contents were also unchanged; however, IL-6 led to significant changes in PL composition including an increase in phosphatidylethanolamine (PE) and sphingomyelin (SM) and a decrease in phosphatidylcholine (PC) and lysophosphatidylcholine (LPC) ( p <0.05). Both PE and SM are known as inflammatory signaling factors involved in human IBD. Our study suggests that the decreased membrane integrity seen with IL-6 application may occur via intracellular PL alterations, rather than through the direct effects of sPLA 2 .