Anti-mitochondrial autoantibodies in systemic lupus erythematosus and their association with disease manifestations

Yann Becker,Renée-Claude Loignon,Éric Wagner,Tania Lévesque,Geneviève Marcoux,Imène Melki,Mélanie Dieudé,Clémence Belleannée,Marie‐Ève Tremblay ,Emmanuelle Rollet-Labelle,Lihi Eder,Nathalie Cloutier,Isabelle Allaeys,Hadrien Benk-Fortin,Paul R Fortin ,Anne‐Sophie Julien ,Joyce Rauch,Marie‐Josée Hébert ,Martin Pelletier,Hassan El Hajj,Éric Boilard

doi:10.1038/s41598-019-40900-3

Abstract

Mitochondria are organelles that govern energy supply and control cell death. Mitochondria also express bacterial features, such as the presence of inner membrane cardiolipin and a circular genome rich in hypomethylated CpG motifs. While mitochondrial extrusion by damaged organs or activated cells is thought to trigger innate immunity, it is unclear whether extracellular mitochondria also stimulate an adaptive immune response. We describe the development of novel assays to detect autoantibodies specific to two distinct components of the mitochondrion: the mitochondrial outer membrane and mitochondrial DNA. Antibodies to these two mitochondrial constituents were increased in both human and murine systemic lupus erythematosus (SLE), compared to controls, and were present at higher levels than in patients with antiphospholipid syndrome or primary biliary cirrhosis. In both bi- and multi-variate regression models, antibodies to mitochondrial DNA, but not whole mitochondria, were associated with increased anti-dsDNA antibodies and lupus nephritis. This study describes new and optimized methods for the assessment of anti-mitochondrial antibodies, and demonstrates their presence in both human and murine SLE. These findings suggest that different mitochondrial components are immunogenic in SLE, and support the concept that extracellular mitochondria may provide an important source of circulating autoantigens in SLE.

Highlights

Mitochondria are organelles that govern energy supply and control cell death
As the enzyme-linked immunosorbent assay (ELISA) is performed on intact mitochondria, these results suggest that anti-whole mitochondria antibodies (AwMA) are induced in systemic lupus erythematosus (SLE), and recognize autoantigens on the outer mitochondrial membrane that are distinct from the epitopes in antiphospholipid syndrome (APS) and primary biliary cirrhosis (PBC), both located in the mitochondrial inner membrane
Whereas increased concentrations of competing mitochondria decreased AwMA binding by up to 49.84 ± 15.01%, red blood cell microparticles (RBCMP) showed no inhibition of binding of the SLE antibodies in our assay (Fig. 3c). While these results suggest that the antibodies detected in the AwMA-ELISA might have a preferred substrate originating in mitochondrial membrane, we cannot exclude the possibility that other membrane bound microparticles or even cells may be recognized by AwMA, given the probable occurrence of numerous protein and non-protein antigens in mitochondria

Summary

Introduction

Mitochondria are organelles that govern energy supply and control cell death. Mitochondria express bacterial features, such as the presence of inner membrane cardiolipin and a circular genome rich in hypomethylated CpG motifs. Extracellular mitochondria have been described in various clinical conditions, including trauma[25,26], burn injury[27], cancer[28], rheumatoid arthritis[17,29], systemic lupus erythematosus (SLE)[15,16] and transfusion adverse reactions[17,18,30,31] Their pro-inflammatory potential is generally thought to occur through activation of Toll-like receptors (TLR), formyl peptide receptors, and cytosolic pathogen recognition receptors, all key components of the innate immune system[6,21,22,23,24]. AMA-M6 autoantibodies have been described in iatrogenic hepatitis induced by iproniazid[39], while the AMA-M7 class of antibodies targets mitochondrial epitopes, identified as sarcosine dehydrogenase and enzymes associated with flavin adenine dinucleotide, in patients with cardiomyopathy and myocarditis[40]

Methods

Results

Conclusion