Programmed Cellular Necrosis Mediated by the Pore-Forming α-Toxin from Clostridium septicum

Julian I Rood,Danielle J Smith,Catherine L Kennedy,Dena Lyras,Anjana Chakravorty,Michael S Gilmore

doi:10.1371/journal.ppat.1000516

Julian I Rood, Danielle J Smith + Show 4 more

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https://doi.org/10.1371/journal.ppat.1000516

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Journal: PLoS Pathogens	Publication Date: Jul 17, 2009
Citations: 143	License type: CC BY 4.0

Affiliation: Monash University, Australian Research Council

Abstract

Programmed necrosis is a mechanism of cell death that has been described for neuronal excitotoxicity and ischemia/reperfusion injury, but has not been extensively studied in the context of exposure to bacterial exotoxins. The α-toxin of Clostridium septicum is a β-barrel pore-forming toxin and a potent cytotoxin; however, the mechanism by which it induces cell death has not been elucidated in detail. We report that α-toxin formed Ca2+-permeable pores in murine myoblast cells, leading to an increase in intracellular Ca2+ levels. This Ca2+ influx did not induce apoptosis, as has been described for other small pore-forming toxins, but a cascade of events consistent with programmed necrosis. Ca2+ influx was associated with calpain activation and release of cathepsins from lysosomes. We also observed deregulation of mitochondrial activity, leading to increased ROS levels, and dramatically reduced levels of ATP. Finally, the immunostimulatory histone binding protein HMGB1 was found to be released from the nuclei of α-toxin-treated cells. Collectively, these data show that α-toxin initiates a multifaceted necrotic cell death response that is consistent with its essential role in C. septicum-mediated myonecrosis and sepsis. We postulate that cellular intoxication with pore-forming toxins may be a major mechanism by which programmed necrosis is induced.

Highlights

Clostridium septicum is a Gram-positive anaerobic bacterium that is the primary etiological agent of atraumatic clostridial myonecrosis, a rapidly fulminating and frequently fatal necrotic disease of the human musculature [1]
We observed a-toxin-mediated programmed cellular necrosis that culminated in the release of the immunostimulatory molecule, high mobility group box 1 (HMGB1)
This mechanism of cell death induction is consistent with the extensive necrosis that is evident in C. septicum-mediated myonecrosis and with the overwhelming sepsis that frequently contributes to the high mortality rate

Summary

Introduction

Clostridium septicum is a Gram-positive anaerobic bacterium that is the primary etiological agent of atraumatic clostridial myonecrosis, a rapidly fulminating and frequently fatal necrotic disease of the human musculature [1]. The nature of aHL induced cell death in Tlymphocytes was brought into question when it was shown that while inhibition of caspases prevented DNA laddering and caspase activation in aHL-treated cells, it could not prevent cell death [18] These data raised the possibility that aHL may induce a programmed necrosis or oncosis response, as indicated by a rapid depletion of ATP and release of pro-inflammatory histone binding protein high mobility group box 1 (HMGB1) [18]. This divergence from apoptotic cell death is consistent with a growing body of evidence indicating that aside from the ‘classical’ programmed cell death pathway of apoptosis, there is a second poorly characterized ‘programmed necrosis’ or ‘oncosis’ pathway [19,20], which is ‘‘programmed in the sense that it would constitute a stereotyped, evolutionarily designed sequence of biochemical events’’ [21]

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