Selective packaging of mitochondrial proteins into extracellular vesicles prevents the release of mitochondrial DAMPs

Kiran Todkar,Firas El-Mortada,Marc Germain,Véronique Desjardins,Lilia Chikhi,Geneviève Pépin

doi:10.1038/s41467-021-21984-w

Abstract

Most cells constitutively secrete mitochondrial DNA and proteins in extracellular vesicles (EVs). While EVs are small vesicles that transfer material between cells, Mitochondria-Derived Vesicles (MDVs) carry material specifically between mitochondria and other organelles. Mitochondrial content can enhance inflammation under pro-inflammatory conditions, though its role in the absence of inflammation remains elusive. Here, we demonstrate that cells actively prevent the packaging of pro-inflammatory, oxidized mitochondrial proteins that would act as damage-associated molecular patterns (DAMPs) into EVs. Importantly, we find that the distinction between material to be included into EVs and damaged mitochondrial content to be excluded is dependent on selective targeting to one of two distinct MDV pathways. We show that Optic Atrophy 1 (OPA1) and sorting nexin 9 (Snx9)-dependent MDVs are required to target mitochondrial proteins to EVs, while the Parkinson’s disease-related protein Parkin blocks this process by directing damaged mitochondrial content to lysosomes. Our results provide insight into the interplay between mitochondrial quality control mechanisms and mitochondria-driven immune responses.

Highlights

Most cells constitutively secrete mitochondrial DNA and proteins in extracellular vesicles (EVs)
Mitochondrial content, especially oxidized components, can act as damage-associated molecular patterns (DAMPs) that activate an inflammatory response when present in the cytosol or released from cells[16,17,18,19,20,21,22]. This can be demonstrated by exposing immune cells, such as the RAW264.7 macrophage cell line, to mitochondria isolated from other cells (here mouse embryonic fibroblasts (MEFs), Supplementary Fig. 1a) and monitoring two different inflammatory pathways (Interferon using IP10, and NF-κB using IL6)
Mitochondrial content could readily be found in EVs isolated from different cell lines under conditions where cell death was kept below 5% to avoid the presence of apoptotic bodies (Protein yield in Supplementary Fig. 1B; Cell death in Supplementary Fig. 1C; Mitochondrial content in Fig. 1c), but was absent from non-conditioned media (Supplementary Fig. 1D)

Summary

Introduction

Most cells constitutively secrete mitochondrial DNA and proteins in extracellular vesicles (EVs). We demonstrate that cells actively prevent the packaging of pro-inflammatory, oxidized mitochondrial proteins that would act as damage-associated molecular patterns (DAMPs) into EVs. Importantly, we find that the distinction between material to be included into EVs and damaged mitochondrial content to be excluded is dependent on selective targeting to one of two distinct MDV pathways. This process is dependent on mitochondria-derived vesicles (MDVs), small vesicles that carry mitochondrial proteins to other organelles This accurate sorting of mitochondrial components requires two distinct MDV pathways.

Methods

Results

Conclusion