Biology subjects

Voss, O. H.

Publications and source records attributed to Voss, O. H..

3 recordsLinked to original sources

bioRxiv2024

Rickettsia rickettsii encodes a secretory lipase that facilitates intracytosolic colonization in host cells.

The key cellular processes required for rickettsial obligate intracellular lifestyle, include internalization by phagocytosis, regulation of intracellular trafficking, and evasion of lysosomal destruction to establish an intracytosolic replication niche, remain poorly defined. Recent reports showed that rickettsial phospholipases play an important role in vacuolar escape, but their functions are dispensable depending on the host cell-type. Here, we report the identification of a highly conserved putative lipase containing a Serine hydrolase motif (GXSXG), named RLip (Rickettsia Lipase). Our work reveals that RLip expression is cytotoxic to yeast cells, a genetically tractable heterologous model system. We demonstrate that RLip possesses lipase enzymatic activity and show a lipid specificity towards phosphoinositide (PI)(3), PI(3,4,5)P3, and PI(3,4)P2, and to a lesser extent PI(4,5)P2. Further, we found that RLip expression is induced during infection of pathogenic R. rickettsii, while its expression is low or undetectable for R. parkeri (mild-pathogenic) and R. montanensis (non-pathogenic), respectively, during host invasion. Intriguingly, RLip is highly enriched in the cytoplasmic fraction of host cells, however, minimally retained by the rickettsiae themselves, suggesting RLip is synthesized during infection and then secreted into the host cell cytoplasm. Neutralization of RLip activity, by antibody-blocking, significantly abrogated R. rickettsii escape from bactericidal phagolysosomal fusion, suggesting RLip plays a critical role in facilitating the intracytosolic colonization of pathogenic R. rickettsii. ImportanceArthropod-borne rickettsial diseases are on the rise globally, presenting a perilous threat to humans and livestock. However, our inadequate understanding on how Rickettsia manipulates cellular processes, including the evasion of lysosomal destruction, has impaired the development of effective therapeutic interventions. Here, we identify of a conserved putative lipase containing a Serine hydrolase motif, named RLip (Rickettsia Lipase). Our work demonstrates that RLip possesses lipase enzymatic activity and is enriched in the cytoplasm of host cells, while minimally retained by the bacteria itself. Neutralization of RLip activity abrogated R. rickettsii escape from bactericidal phagolysosomal fusion. In sum, our data support a mechanism by which pathogenic R. rickettsii employs RLip to escape from bactericidal phagolysosomal fusion in order to colonize the host.

microbiology↗

bioRxiv2024

Pathogenic rickettsiae utilize the phosphatidylserine binding receptor CD300f on macrophages for host invasion and pathogenesis.

Some arthropod-borne obligate intracellular rickettsiae are among the most virulent human pathogens. Rickettsia species modulate immune (e.g., macrophages; M{Phi}) and non-immune cell (e.g., endothelial cells) responses to create a habitable environment for host colonization. In particular, M{Phi} play a crucial role in either terminating an infection at an early stage or succumbing to bacterial replication and colonization. However, our understanding on how Rickettsia species invade host cells, including M{Phi}, remain poorly defined. In this study, we describe a mechanism of host invasion by Rickettsia species, involving rickettsial phosphatidylserine (PS), as a ligand, and the CD300f receptor on M{Phi}. Using bone marrow-derived macrophages (BMDM{Phi}) from wild-type (WT) and CD300f-/- mice, we demonstrated that engulfment of both pathogenic R. typhi (the etiologic agent of murine typhus) and R. rickettsii (the etiologic agent of Rocky Mountain spotted fever) species as well as the non-pathogenic R. montanensis was significantly reduced in CD300f-/- BMDM{Phi} as compared to that of WT BMDM{Phi}. Furthermore, our mechanistic analysis suggests bacterial PS as the potential source for the CD300f-mediated rickettsiae engulfment by M{Phi}. In vivo infection studies using WT and CD300f-/- C57BL/6J mice showed that CD300f-/- animals were protected against R. typhi-or R. rickettsii-induced fatal rickettsiosis, which correlated with levels of bacterial burden detected in the spleens of mice. Adoptive transfer studies further revealed that CD300f-expressing M{Phi} are important mediators to control rickettsiosis in vivo. Collectively, our findings describe a previously unappreciated role for the efferocytic receptor, CD300f, to facilitate engulfment of rickettsiae within the host.

microbiology↗

bioRxiv2021

Pathogenic, but not non-pathogenic, Rickettsia manipulate inflammasome-dependent IL-1 responses to facilitate their replication and host dissemination.

Rickettsia species (spp.) are strict obligate intracellular bacteria, with some being pathogenic in their mammalian host, including humans. One critical feature of these stealthy group of pathogens is their ability to manipulate hostile cytosolic environments to their benefits. Although our understanding of Rickettsia cell biology and pathogenesis are evolving, the mechanisms by which pathogenic Rickettsia spp. evade host innate immune detection remains elusive. Here, we showed that disease severity in wild-type (WT) C57BL/6J mice infected with R. typhi (etiologic agent of murine typhus) and R. rickettsii (etiologic agent of Rocky Mountain Spotted Fever), but not with non-pathogenic R. montanensis, correlated with levels of bacterial burden as detected in the spleens, as well as the serum concentrations of pro-inflammatory cytokine IL-1 and to a lesser extent IL- 1{beta}. Antibody-mediated neutralization of IL-1 confirmed a key role in controlling mortality rates and bacterial burdens of rickettsiae-infected WT mice. As macrophages are a primary source of both IL-1 and IL-1{beta} cytokines, we determined the mechanism of the anti-rickettsial activities using bone-marrow-derived macrophages. We found that pathogenic R. typhi and R. rickettsii, but not non-pathogenic R. montanensis, eluded pro- IL-1 induction and benefited pre-dominantly from the reduced IL-1 secretion, via a Caspase-11-Gsdmd-dependent pathway, to facilitate intracytosolic replication. Adoptative transfer experiments identified that IL-1 secretion by macrophages was critical for controlling rickettsiosis in WT mice. In sum, we identified a previously unappreciated pathway by which pathogenic, unlike non-pathogenic, rickettsiae preferentially target the Caspase-11-Gsdmd-IL-1 signaling axis in macrophages thus supporting their replication within the host. IMPORTANCECurrently, no vaccines are available to prevent rickettsioses, while vector-borne rickettsial infections in humans are on the rise globally. In fact, the insufficient understanding of how pathogenic Rickettsia species circumvent host immune defense mechanisms has significantly hindered the development of more effective therapeutics. Here, we identified a previously unappreciated role for the Caspase-11-Gsdmd-IL-1 signaling axis, to limiting the replication of pathogenic R. rickettsia and R. typhi species in murine macrophages and wild-type (WT) C57BL/6J mice. Adoptative transfer studies further identified IL-1-secreting macrophages as critical mediators in controlling rickettsial infection in WT mice. Collectively, these findings provide insight into the potential mechanism of how pathogenic, but not non-pathogenic Rickettsia spp., benefit from a reduction in the Caspase-11-Gsdmd-mediated release of IL-1 to support host colonization.

microbiology↗