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)-γ. Th1 and Th17 skewing cultures were unaltered by oxPAPC. IFN-γ is linked to T _reg instability, thus T _reg polarization experiments were repeated using Ifngr1 ^-/- CD4 ⁺ T cells. IFNγR1 (INF gamma receptor 1) deficiency did not improve cell viability in oxPAPC-treated T _regs ; however, T-bet and IFN-γ expression was not increased in surviving cells suggesting a role for IFN-γsignaling. 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-γ 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.
Competing Interests: Disclosures None.