Abstract 578: Macrophage Cholesterol Levels Modulate Ion Channel Activity: Effect(s) on Ion Flux Dependent Inflammatory Events

Abstract

Accumulation of cholesterol loaded macrophage foam cells is the hallmark of atherosclerotic lesions where high cellular cholesterol content not only contributes to the plaque volume but is also responsible for the inflammatory milieu. Causal relationship exist between macrophage cholesterol content and inflammatory status involving TLR4, NFκB or cholesterol crystal mediated activation of inflammasome and IL1β secretion. Since K+ efflux is central to inflammasome activation, in this study we examined the hypothesis that cellular cholesterol content directly affects K+ channel activity as well as K+ efflux. K+ currents were monitored in mouse peritoneal macrophages (MPMs) from chow or western diet (WD) fed LDLR-/- or LDLR-/-CEHTg mice. WD feeding led to a significant increase in the K+ currents in MPMs from LDLR-/- mice (A, red). In contrast, WD feeding did not affect K+ currents in MPMs from LDLR-/-CEHTg mice; these MPMs have reduced cellular cholesterol accumulation due to increased efflux. Consistently, cholesterol loading with AcLDL led to an increase in K+ currents in THP1 macrophages (B, red) and this increase was attenuated following cholesterol efflux. The physiological effect of changes in K+ channel activity or K+ efflux on inflammasome activation in MPMs by different activators (K+ ionophore Nigericin, N or ALUM crystals) was examined. Increase in extracellular K+ (+KCl) or inhibition of K+ efflux by glyburide significantly reduced IL1β secretion (C&D). Consistently, cellular K+ levels after LPS+N or LPS+ALUM treatment were significantly reduced (E). While in MPMs only K ATP channel inhibitors reduced IL1β secretion (F), in human THP1 macrophages inhibition of K ATP as well as Na/K pump inhibitors significantly reduced IL1β secretion (G). These data demonstrate a novel mechanism for cholesterol mediated regulation of inflammatory pathways by regulation of K+ channel activity and also illustrate species specific differences in K+ channels involved