3028 Paradoxical effect of IL-33 on cholesterol homeostasis in THP-1 human macrophages

Tuesday, 9 December 2014: 11:00 - 11:20
Exhibition Hall-Poster Area (Sul America)

Tania (Mucci) Elliott, MD , Allergy/Immunology, Winthrop University Hospital, Mineola, NY

Background: IL-33 in plasma of atopic patients (AP) is elevated to 10 times healthy control (HC) levels. Our group has previously demonstrated that human recombinant IL-33 or AP plasma alters cholesterol homeostasis in human macrophages. However, the role of IL-33 in cholesterol transport and accumulation is unclear. The current study assesses the specific effects of human IL-33 on cholesterol transport proteins and oxidized low density lipoprotein uptake (oxLDL) in THP-1 human macrophages.

Methods: THP-1 macrophages were incubated ± 1:500 dilution of human anti-IL-33 receptor-blocking antibody (3h), followed by 18h  incubation ± 1, 10, 20, 50 ng/ml of  human IL-33 (each condition in triplicate). Following incubation, total RNA was isolated. Expression level was determined by QRT-PCR for cholesterol efflux proteins ABCA1 and 27-hydroxylase, and for cholesterol uptake proteins CD36, LOX1, SRA1 and CXCL16. Expression was normalized to the housekeeper gene, GAPDH. (Dil)-oxLDL (Intracel, Frederick, MD) uptake was analyzed by fluorescence microscopy. Data were analyzed by one-way ANOVA with Bonferroni correction.

Results: IL-33 at 10 ng/ml augmented ABCA1 and 27-hydroxylase message to 191.1±14.9% and 227.4±28.8%, respectively (P<0.05, n=3). High concentrations of IL-33 (20 and 50ng/ml) reduced efflux protein expression to that of untreated cells while doubling expression of scavenger receptors CD36, LOX-1 and CXCL16 versus control cells (P<0.05, n=3). These changes contributed to increased oxLDL accumulation and at 50ng/ml IL-33, ox LDL reached 155.7±8.8% above control (P<0.05, n=5). Blocking of the IL-33 receptor abrogated IL-33-induced alterations in gene expression, confirming an IL-33 receptor-dependent mechanism for observed changes in cholesterol metabolism.

Conclusions: We have demonstrated a dose-dependent effect of IL-33 on the expression of ABCA1, CXCL16, CD36 and LOX1. The effect is mediated through the IL-33 receptor. High concentrations of IL-33 relevant to those observed in AP plasma resulted in a switch from an anti-atherogenic to a pro-atherogenic state. Such changes could support the development of a pro-atherogenic profile in macrophages that may be improved with treatment.