Oxidized Phospholipid oxPAPC Alters Regulatory T-Cell Differentiation and Decreases Their Protective Function in Atherosclerosis in Mice

BACKGROUND: Regulatory T cells (T-regs) are protective in atherosclerosis but reduced during disease progression due to cell death and loss of stability. However, the mechanisms of T-reg dysfunction remain unknown. Oxidized phospholipids are abundant in atherosclerosis and can activate innate immune cells, but little is known regarding their impact on T cells. Given T-reg loss during atherosclerosis progression and oxidized phospholipid levels in the plaque microenvironment, we investigated whether oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (oxPAPC), an oxidized phospholipid associated with atherosclerotic plaques, alters T-reg differentiation and function.METHODS: CD4(+) T cells were polarized to T-reg, T helper (Th) 1, and Th17 cells with or without oxPAPC and assessed by flow cytometry. Gene expression in oxPAPC-treated T-regs was analyzed by bulk RNA sequencing. Functional studies of oxPAPC-induced T-regs were performed by coculturing T-regs with CellTrace Violet-labeled cells in vitro, and by adoptively transferring T-regs to hyperlipidemic Ldlr(-/-) mice to measure atherosclerosis progression.RESULTS: Compared with controls, oxPAPC-treated T-regs were less viable, but surviving cells expressed higher levels of the Th1-associated markers T-bet, CXCR3, and IFN (interferon)-gamma. Th1 and Th17 skewing cultures were unaltered by oxPAPC. IFN-gamma is linked to T-reg instability, thus T-reg polarization experiments were repeated using Ifngr1(-/-) CD4(+) T cells. IFN gamma R1 (INF gamma receptor 1) deficiency did not improve cell viability in oxPAPC-treated T-regs; however, T-bet and IFN-gamma expression was not increased in surviving cells suggesting a role for IFN-gamma signaling. OxPAPC-treated T-regs were less suppressive in vitro, and adoptive transfer studies in hyperlipidemic Ldlr(-/-) mice showed that oxPAPC-induced T-regs possessed altered tissue homing and were insufficient to inhibit atherosclerosis progression.CONCLUSIONS: OxPAPC elicits T-reg-specific changes altering T-reg differentiation and inducing a Th1-like phenotype in surviving cells partially through IFN-gamma signaling. This is biologically relevant as oxPAPC-treated T-regs do not reduce atherosclerosis progression in Ldlr(-/-) mice. This study supports the role of oxidized phospholipids in negatively impacting T-reg differentiation and atheroprotective function.

Automated summary

This study investigates the impact of oxidized phospholipid on regulatory T cells (T-regs) in atherosclerosis. The results demonstrate that oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (oxPAPC) treatment alters T-reg differentiation and induces a Th1-like phenotype in surviving cells. Furthermore, oxPAPC-treated T-regs exhibit reduced suppressive function and are insufficient to inhibit atherosclerosis progression in mice. This study highlights the negative effect of oxidized phospholipids on T-reg differentiation and atheroprotective function.