Saturation of acyl chains converts cardiolipin from an antagonist to an activator of Toll-like receptor-4

Malvina Pizzuto,Clare E Bryant,Caroline Lonez,Monique Gangloff,Pablo Pelegrin,Helios Martínez-Banaclocha,Panagiotis Tourlomousis,Jean-Marie Ruysschaert,Nicholas J Gay,Alberto Baroja-Mazo

doi:10.1007/s00018-019-03113-5

Abstract

Cardiolipins (CLs) are tetra-acylated diphosphatidylglycerols found in bacteria, yeast, plants, and animals. In healthy mammals, CLs are unsaturated, whereas saturated CLs are found in blood cells from Barth syndrome patients and in some Gram-positive bacteria. Here, we show that unsaturated but not saturated CLs block LPS-induced NF-κB activation, TNF-α and IP-10 secretion in human and murine macrophages, as well as LPS-induced TNF-α and IL-1β release in human blood mononuclear cells. Using HEK293 cells transfected with Toll-like receptor 4 (TLR4) and its co-receptor Myeloid Differentiation 2 (MD2), we demonstrate that unsaturated CLs compete with LPS for binding TLR4/MD2 preventing its activation, whereas saturated CLs are TLR4/MD2 agonists. As a consequence, saturated CLs induce a pro-inflammatory response in macrophages characterized by TNF-α and IP-10 secretion, and activate the alternative NLRP3 inflammasome pathway in human blood-derived monocytes. Thus, we identify that double bonds discriminate between anti- and pro-inflammatory properties of tetra-acylated molecules, providing a rationale for the development of TLR4 activators and inhibitors for use as vaccine adjuvants or in the treatment of TLR4-related diseases.Graphical abstract

Highlights

Cardiolipin (CL) is a tetra-acylated diphosphatidylglycerol found in yeast, bacteria, plants, and animals
After 5 h, supernatants were collected and TNF-α quantified in the supernatants as a measure of Toll-like receptor 4 (TLR4)/NF-κB activation, while cell viability was evaluated by MTT test (Fig. S7b)
They highlighted the anti-inflammatory properties of extracellular CL and showed that CL competes with LPS for binding recombinant immobilized Myeloid Differentiation 2 (MD2), these studies did not investigate the ability of CL to interfere with the binding of LPS to TLR4/MD2 complex or with the TLR4 dimerization

Summary

Introduction

Cardiolipin (CL) is a tetra-acylated diphosphatidylglycerol found in yeast, bacteria, plants, and animals. Acyl chain length and degree of unsaturation vary depending on species, tissue, and pathological conditions [1,2,3]. Thanks to the enzyme tafazzin that remodels CL after synthesis, saturated CLs are almost absent in mammals [2, 4]. In Barth syndrome (BTHS), genetic mutations of tafazzin induce a loss of selectivity leading to a decrease in unsaturated CL and an increase in CL with saturated chains, especially C16:0 [2]. Saturation of CL leads to defective mitochondrial bioenergetics and explains why BTHS patients have cardiac and skeletal myopathy

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