Bacillus anthracis induces NLRP3 inflammasome activation and caspase-8-mediated apoptosis of macrophages to promote lethal anthrax.

Abstract

Lethal toxin (LeTx)-mediated killing of myeloid cells is essential for Bacillus anthracis, the causative agent of anthrax, to establish systemic infection and induce lethal anthrax. The "LeTx-sensitive" NLRP1b inflammasome of BALB/c and 129S macrophages swiftly responds to LeTx intoxication with pyroptosis and secretion of interleukin (IL)-1β. However, human NLRP1 is nonresponsive to LeTx, prompting us to investigate B. anthracis host-pathogen interactions in C57BL/6J (B6) macrophages and mice that also lack a LeTx-sensitive Nlrp1b allele. Unexpectedly, we found that LeTx intoxication and live B. anthracis infection of B6 macrophages elicited robust secretion of IL-1β, which critically relied on the NLRP3 inflammasome. TNF signaling through both TNF receptor 1 (TNF-R1) and TNF-R2 were required for B. anthracis-induced NLRP3 inflammasome activation, which was further controlled by RIPK1 kinase activity and LeTx-mediated proteolytic inactivation of MAP kinase signaling. In addition to activating the NLRP3 inflammasome, LeTx-induced MAPKK inactivation and TNF production sensitized B. anthracis-infected macrophages to robust RIPK1- and caspase-8-dependent apoptosis. In agreement, purified LeTx triggered RIPK1 kinase activity- and caspase-8-dependent apoptosis only in macrophages primed with TNF or following engagement of TRIF-dependent Toll-like receptors. Consistently, genetic and pharmacological inhibition of RIPK1 inhibited NLRP3 inflammasome activation and apoptosis of LeTx-intoxicated and B. anthracis-infected macrophages. Caspase-8/RIPK3-deficient mice were significantly protected from B. anthracis-induced lethality, demonstrating the in vivo pathophysiological relevance of this cytotoxic mechanism. Collectively, these results establish TNF- and RIPK1 kinase activity-dependent NLRP3 inflammasome activation and macrophage apoptosis as key host-pathogen mechanisms in lethal anthrax.

• Authors: Filip Van Hauwermeiren, Nina Van Opdenbosch, Hanne Van Gorp, Nathalia de Vasconcelos, Geert van Loo, Peter Vandenabeele, Thirumala-Devi Kanneganti, Mohamed Lamkanfi
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 119 Issue 2 (01 11 2022) ISSN: 1091-6490 [Electronic] United States
• PMID: 34996874 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2022 the Author(s). Published by PNAS.

Chemical References

• Inflammasomes
• Interleukin-1beta
• NLR Family, Pyrin Domain-Containing 3 Protein
• Nlrp3 protein, mouse
• Receptor-Interacting Protein Serine-Threonine Kinases
• Ripk1 protein, mouse
• Casp8 protein, mouse
• Caspase 8

Topics

• Animals
• Anthrax
• Apoptosis
• Bacillus anthracis (metabolism)
• Caspase 8 (genetics, metabolism)
• Host-Pathogen Interactions (physiology)
• Inflammasomes (genetics, metabolism)
• Interleukin-1beta (metabolism)
• Macrophages (metabolism)
• Mice
• Mice, Inbred BALB C
• Mice, Inbred C57BL
• NLR Family, Pyrin Domain-Containing 3 Protein (genetics, metabolism)
• Pyroptosis
• Receptor-Interacting Protein Serine-Threonine Kinases
• Signal Transduction