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

Abstract

Pathogens encounter numerous antimicrobial responses during infection, including the reactive oxygen species (ROS) burst. ROS-mediated oxidation of host membrane poly-unsaturated fatty acids (PUFAs) generates the toxic alpha-beta carbonyl 4-hydroxy-2-nonenal (4-HNE). Although studied extensively in the context of sterile inflammation, research into 4-HNE's role during infection remains limited. Here, we found that 4-HNE is generated during bacterial infection, that it impacts growth and survival in a range of bacteria, and that the intracellular pathogen <i>Listeria monocytogenes</i> induces many genes in response to 4-HNE exposure. A component of the <i>L. monocytogenes</i> 4-HNE response is the expression of the genes <i>lmo0103</i> and <i>lmo0613,</i> deemed <i>rha1</i> and <i>rha2</i> (<b>r</b>eductase of <b>h</b>ost <b>a</b>lkenals), respectively, which code for two NADPH-dependent oxidoreductases that convert 4-HNE to the product 4-hydroxynonanal (4-HNA). Loss of these genes had no impact on <i>L. monocytogenes</i> bacterial burdens during murine or tissue culture infection. However, heterologous expression of <i>rha1/2</i> in <i>Bacillus subtilis</i> significantly increased bacterial resistance to 4-HNE in vitro and promoted bacterial survival following phagocytosis by murine macrophages in an ROS-dependent manner. Thus, Rha1 and Rha2 are not necessary for 4-HNE resistance in <i>L. monocytogenes</i> but are sufficient to confer resistance to an otherwise sensitive organism in vitro and in host cells. Our work demonstrates that 4-HNE is a previously unappreciated component of ROS-mediated toxicity encountered by bacteria within eukaryotic hosts.