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The oxidized phospholipid oxPAPC protects from septic shock by targeting the non-canonical inflammasome in macrophages.

ABSTRACT: Lipopolysaccharide (LPS) of Gram-negative bacteria can elicit a strong immune response. Although extracellular LPS is sensed by TLR4 at the cell surface and triggers a transcriptional response, cytosolic LPS binds and activates non-canonical inflammasome caspases, resulting in pyroptotic cell death, as well as canonical NLRP3 inflammasome-dependent cytokine release. Contrary to the highly regulated multiprotein platform required for caspase-1 activation in the canonical inflammasomes, the non-canonical mouse caspase-11 and the orthologous human caspase-4 function simultaneously as innate sensors and effectors, and their regulation is unclear. Here we show that the oxidized phospholipid 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (oxPAPC) inhibits the non-canonical inflammasome in macrophages, but not in dendritic cells. Aside from a TLR4 antagonistic role, oxPAPC binds directly to caspase-4 and caspase-11, competes with LPS binding, and consequently inhibits LPS-induced pyroptosis, IL-1? release and septic shock. Therefore, oxPAPC and its derivatives might provide a basis for therapies that target non-canonical inflammasomes during Gram-negative bacterial sepsis.

SUBMITTER: Chu LH

PROVIDER: S-EPMC5843631 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature

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The oxidized phospholipid oxPAPC protects from septic shock by targeting the non-canonical inflammasome in macrophages.

Chu Lan H LH Indramohan Mohanalaxmi M Ratsimandresy Rojo A RA Gangopadhyay Anu A Morris Emily P EP Monack Denise M DM Dorfleutner Andrea A Stehlik Christian C

Nature communications 20180308 1

Lipopolysaccharide (LPS) of Gram-negative bacteria can elicit a strong immune response. Although extracellular LPS is sensed by TLR4 at the cell surface and triggers a transcriptional response, cytosolic LPS binds and activates non-canonical inflammasome caspases, resulting in pyroptotic cell death, as well as canonical NLRP3 inflammasome-dependent cytokine release. Contrary to the highly regulated multiprotein platform required for caspase-1 activation in the canonical inflammasomes, the non-ca ...[more]

PMID: 29520027

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

Dataset Information

The oxidized phospholipid oxPAPC protects from septic shock by targeting the non-canonical inflammasome in macrophages.

Publications

The oxidized phospholipid oxPAPC protects from septic shock by targeting the non-canonical inflammasome in macrophages.

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