4-Hydroxy-2-nonenal antimicrobial toxicity is neutralized by an intracellular pathogen

Area of Science:

• Microbiology
• Immunology
• Biochemistry

Background:

• Pathogens face antimicrobial responses like reactive oxygen species (ROS) during infection.
• ROS oxidize host lipids, producing toxic 4-hydroxy-2-nonenal (4-HNE), but its role in infection is understudied.
• 4-HNE is a key mediator of sterile inflammation, but its impact on bacterial pathogens requires further investigation.

Purpose of the Study:

• To investigate the generation and impact of 4-HNE during bacterial infection.
• To identify bacterial mechanisms for counteracting 4-HNE toxicity.
• To explore the role of specific enzymes in bacterial resistance to host-derived aldehydes.

Main Methods:

• Exposure of various bacteria, including *Listeria monocytogenes*, to 4-HNE.
• Gene expression analysis of *L. monocytogenes* in response to 4-HNE.
• Genetic manipulation of *L. monocytogenes* (deletion of *rha1/2* genes).
• Heterologous expression of *rha1/2* in *Bacillus subtilis*.
• In vitro and in vivo assays measuring bacterial survival and resistance to 4-HNE and phagocytosis.

Main Results:

• 4-HNE is generated during bacterial infection and affects bacterial growth and survival.
• *L. monocytogenes* induces genes, including *rha1* and *rha2*, in response to 4-HNE.
• Rha1 and Rha2 are NADPH-dependent oxidoreductases converting 4-HNE to 4-HNA.
• Loss of *rha1/2* in *L. monocytogenes* did not affect bacterial burden in vivo.
• Heterologous expression of *rha1/2* in *B. subtilis* conferred significant 4-HNE resistance in vitro and enhanced survival during macrophage phagocytosis.

Conclusions:

• 4-HNE is a significant toxic component of ROS-mediated host defense against bacteria.
• Rha1 and Rha2 are sufficient to confer resistance to 4-HNE in bacteria.
• These findings highlight a previously unappreciated mechanism of bacterial defense against host-derived oxidative stress.