Mitochondrial inner membrane permeabilisation enables mtDNA release during apoptosis.

Joel S Riley,Stephen Wg Tait,Jonathan Lopez,Matthew Pearson,James Chapman,Andrew Oberst,Catherine Cloix,João F Passos,Ann P Wheeler,Jim O'Prey,Hiromi Sesaki,Giovanni Quarato,Kevin M Ryan,Leo M Carlin

doi:10.15252/embj.201899238

Abstract

During apoptosis, pro‐apoptotic BAX and BAK are activated, causing mitochondrial outer membrane permeabilisation (MOMP), caspase activation and cell death. However, even in the absence of caspase activity, cells usually die following MOMP. Such caspase‐independent cell death is accompanied by inflammation that requires mitochondrial DNA (mtDNA) activation of cGAS‐STING signalling. Because the mitochondrial inner membrane is thought to remain intact during apoptosis, we sought to address how matrix mtDNA could activate the cytosolic cGAS‐STING signalling pathway. Using super‐resolution imaging, we show that mtDNA is efficiently released from mitochondria following MOMP. In a temporal manner, we find that following MOMP, BAX/BAK‐mediated mitochondrial outer membrane pores gradually widen. This allows extrusion of the mitochondrial inner membrane into the cytosol whereupon it permeablises allowing mtDNA release. Our data demonstrate that mitochondrial inner membrane permeabilisation (MIMP) can occur during cell death following BAX/BAK‐dependent MOMP. Importantly, by enabling the cytosolic release of mtDNA, inner membrane permeabilisation underpins the immunogenic effects of caspase‐independent cell death.

Highlights

To initiate cell death, apoptosis often requires mitochondrial outer membrane permeabilisation, or MOMP (Tait & Green, 2013)
In healthy U2OS cells, dual immuno-staining of the mitochondria outer membrane protein TOM20 and DNA revealed that mitochondrial DNA (mtDNA) nucleoids are contained within mitochondria surrounded by a continuous outer membrane (Figure 1A)
We find that under caspaseinhibited conditions, BAX/BAK-mediated MOMP allows extrusion of the mitochondrial inner membrane into the cytoplasm

Summary

Introduction

Apoptosis often requires mitochondrial outer membrane permeabilisation, or MOMP (Tait & Green, 2013). Irrespective of caspase activity, cells typically do not survive following widespread MOMP, defining it as a point-of-no-return (Ekert, Read et al, 2004, Haraguchi, Torii et al, 2000, Tait, Ichim et al, 2014, Tait, Parsons et al, 2010). Because of this central role in dictating cell fate, MOMP is tightly controlled, primarily via pro- and anti-apoptotic members of the BCL-2 protein family (Lopez & Tait, 2015). BAX and BAK are activated, leading to their oligomerization in the mitochondrial outer membrane and MOMP (Cosentino & Garcia-Saez, 2017)

Methods

Results

Conclusion