Activation of apoptosis by Salmonella pathogenicity island-1 effectors through both intrinsic and extrinsic pathways in Salmonella-infected macrophages

Hsin Hung Lin, Hsiu Ling Chen, Chang Ching Weng, Rajendra Prasad Janapatla, Chyi Liang Chen*, Cheng Hsun Chiu*

*Corresponding author for this work

Research output: Contribution to journalJournal Article peer-review

19 Scopus citations

Abstract

Background: Salmonella enterica serovar Typhimurium, a non-typhoidal food-borne pathogen, causes acute enterocolitis, bacteremia, extraintestinal focal infections in humans. Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2) contribute to invading into host cellular cytosol, residing in Salmonella-containing vacuoles for intracellular survival, and inducing cellular apoptosis. This study aimed to better understand the mechanism underlying apoptosis in Salmonella-infected macrophages. Methods: S. Typhimurium SL1344 was used to evaluate extrinsic and intrinsic apoptosis pathways in THP-1 monocyte-derived macrophages in response to Salmonella infection. Results: Activated caspase-3-induced apoptosis pathways, including extrinsic (caspase-8-mediated) and intrinsic (caspase-9-mediated) pathways, in Salmonella-infected macrophages were verified. THP-1 cells with dysfunction of TLR-4 and TLR-5 and Salmonella SPI-1 and SPI-2 mutants were constructed to identify the roles of the genes associated with programmed cell death in the macrophages. Caspase-3 activation in THP-1 macrophages was induced by Salmonella through TLR-4 and TLR-5 signaling pathways. We also identified that SPI-1 structure protein PrgH and effectors SipB and SipD, but not SPI-2 structure protein SsaV, could induce apoptosis via caspase-3 activation and reduce the secretion of inflammation marker TNF-α in the Salmonella-infected cells. The two effectors also reduced the translocation of the p65 subunit of NF-κB into the nucleus and the expression of TNF-α, and then inflammation was diminished. Conclusion: Non-typhoid Salmonella induced apoptosis of macrophages and thereby reduced inflammatory cytokine production through the expression of SPI-1. This mechanism in host–pathogen interaction may explain why Salmonella usually manifests as occult bacteremia with less systemic inflammatory response syndrome in the bloodstream infection of children.

Original languageEnglish
Pages (from-to)616-626
Number of pages11
JournalJournal of Microbiology, Immunology and Infection
Volume54
Issue number4
DOIs
StatePublished - 08 2021

Bibliographical note

Publisher Copyright:
© 2020

Keywords

  • Apoptosis
  • Caspase-3
  • Inflammatory cytokine
  • Macrophage
  • Salmonella pathogenicity island-1
  • Salmonella typhimurium

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