Aims: A hallmark of advanced atherosclerosis is inadequate immunosuppression by regulatory T (Treg) cells inside atherosclerotic lesions. Dyslipidemia has been suggested to alter Treg cell migration by affecting the expression of specific membrane proteins, thereby decreasing Treg cell migration towards atherosclerotic lesions. Besides membrane proteins, cellular metabolism has been shown to be a crucial factor in Treg cell migration. We aimed to determine whether dyslipidemia contributes to altered migration of Treg cells, in part, by affecting cellular metabolism.

Methods and results: Dyslipidemia was induced by feeding Ldlr^-/- mice a Western-type diet for 16-20 weeks and intrinsic changes in Treg cells affecting their migration and metabolism were examined. Dyslipidemia was associated with altered mTORC2 signaling in Treg cells, decreased expression of membrane proteins involved in migration, including CD62L, CCR7 and S1Pr1, and decreased Treg cell migration towards lymph nodes. Furthermore, we discovered that diet-induced dyslipidemia inhibited mTORC1 signaling, induced PPARδ activation and increased fatty acid (FA) oxidation in Treg cells. Moreover, mass-spectrometry analysis of serum from Ldlr^-/- mice with normolipidemia or dyslipidemia showed increases in multiple PPARδ ligands during dyslipidemia. Treatment with a synthetic PPARδ agonist increased the migratory capacity of Treg cells in vitro and in vivo in an FA oxidation dependent manner. Furthermore, diet-induced dyslipidemia actually enhanced Treg cell migration into the inflamed peritoneum and into atherosclerotic lesions in vitro.

Conclusions: Altogether, our findings implicate that dyslipidemia does not contribute to atherosclerosis by impairing Treg cell migration as dyslipidemia associated with an effector-like migratory phenotype in Treg cells.

Ldlr^-/- mice were fed a WTD or maintained on an NCD for 8 weeks and upon sacrifice, serum samples were collected and frozen at -80˚C until use. Polar lipids are extracted using methanol to precipitate proteins from serum samples and this method covers low abundance lipid species, including free fatty acids and lysophospholipids—lysophosphatidylcholines (LPCs) and lysophosphatidylethanolamines (LPEs). Chromatographic separation was achieved on an ACQUITY UPLC™ with a HSS T3 column (1.8 μm, 2.1 * 100 mm) coupled to a Q-TOF (Agilent 6530) high resolution mass spectrometer using reference mass correction. Lipids were detected in full scan in the negative ion mode. The leukotrienes, hydroxyl-fatty acids, epoxy-fatty acids and lipoxins were analysed using a fully targeted method as as previously described (Strassburg et al.). Oxylipid enrichment was achieved using a hydrophilic-lipophilic balance (HLB) SPE cartridge (Oasis). Oxylipid analysis used high-performance liquid chromatography (Agilent 1260) coupled to a triple-quadrupole mass spectrometer (Agilent 6460), using an Ascentis® Express column (2.7 μm, 2.1 × 150 mm). Signals from each lipid species were normalized for the response of an internal standard control, resulting in the relative response values indicated in the dataset.