DRP1/DMNL-1-mediated mitochondrial fission augments Rickettsia parkeri replication in macrophages

Pathogenic Spotted Fever Group (SFG) Rickettsia species, including Rickettsia parkeri, replicate in endothelial cells and macrophages in vitro and during infections in murine models of disease. We demonstrated that infection of human macrophage-like cells with a related SFG Rickettsia, R. conorii, resulted in a significant increase in mitochondria-associated proteins. However, the role of mitochondrial functions in Rickettsia pathogenesis is unknown. Here, we found that R. parkeri exploits mitochondrial dynamics to promote intracellular replication in mouse and human macrophages by activating the mitochondrial fission regulator, the dynamin-related protein 1 (DRP1). R. parkeri proliferated in macrophages, which coincided with a significant increase in mitochondria fission, mitochondria content, and host cell ATP production, primarily due to mitochondrial respiration compared to uninfected cells. In addition, R. parkeri infection also led to a temporal increase in DRP1 serine phosphorylation that was dependent on rickettsial de novo protein synthesis. Importantly, R. parkeri growth was significantly impacted in DRP1-deficient macrophages. These results suggest that the modulation of mitochondrial fission, content, and function is important for replication and survival of pathogenic SFG Rickettsia species in macrophages. Our data highlight that hijacking mitochondrial dynamics and function is essential for intracellular replication of Rickettsia species and may be a shared mechanism utilized by related obligate intracellular pathogens for growth.