IL4Ralpha signaling delays foam cell formation in atherosclerotic lesions

Background

Lipid uptake by macrophages is a central process in atherosclerotic plaque development. Especially oxidized LDL (oxLDL) shifts macrophages towards foam cell development. We speculate that the cytokines interleukin (IL)4 and IL13 signaling via IL4 receptor alpha (IL4RA) can counteract oxLDL induced macrophage differentiation and reduce atherosclerotic plaque progression.

Purpose

Here, we aim to clarify the impact of IL4 and IL13 on foam cell formation and atherosclerotic development.

Methods

Human monocyte-derived macrophages were treated with oxidized low-density lipoprotein (oxLDL) in the presence or absence of IL4 and IL13 and foam cell development was examined using RNA sequencing, mass spectrometry and flow cytometry. To identify in vivo consequences wild-type and IL-4RA knockout mice on an LDL receptor (LDLR)- deficient background were fed high-fat diet (HFD) with 21 % fat and 0.20 % cholesterol for 4 weeks or 14 weeks.

Results

Both oxLDL and IL4/IL13 challenge each induced a distinct profile of genes when analyzing a time course set at 2h, 6h, and 24h post stimulation using bulk RNA sequencing. Characteristic for oxLDL was a predominant downregulation of genes whereas IL4/IL13 showed strong induction and downregulation capacity. When combining both stimuli, the induction capability of IL4/IL13 was diminished through the presence of oxLDL. When combining both challenges, we found retaining of oxidative phosphorylation dependent pathway genes and a reduction in genes associated with cholesterol homeostasis. We were able to confirm these RNA observations on altered lipid metabolism using metabolomics demonstrating failing of OXPHOS in oxLDL-treated macrophages but an increased capability when treated with IL4/IL13 while challenged with oxLDL. In addition, we observed reduced oxLDL uptake and CD36 expression in macrophages treated with oxLDL and IL4/IL13.

Mice deficient for IL4RA showed overall increased atherosclerotic plaque formation together with elevated numbers of GPNMB and TREM2 positive foam cells in established atherosclerotic lesions after 14 weeks of HFD. In addition, we also found an increased proinflammatory phenotype in IL4RA deficient mice with enhanced plasma levels of MCP1, and enhanced accumulation of CD4 T cells within the lesion.

Conclusions

Our data emphasize an atheroprotective function of IL-4/IL-13 signaling by combating oxLDL-induced proinflammatory protein induction and delaying formation of metabolically inept foam cells. We propose that this mechanism needs to be considered when patients receive treatment for diseases linked to increased IL4/IL13 production as allergies and asthma as chronic inhibition of those cytokines might in turn increase cardiovascular risk.