Rickettsia massiliae and Rickettsia conorii Israeli Spotted Fever Strain Differentially Regulate Endothelial Cell Responses

• Published in: PloS one 2015-09, Vol.10 (9), p.e0138830-e0138830
• Main Authors: Bechelli, Jeremy, Smalley, Claire, Milhano, Natacha, Walker, David H, Fang, Rong
• Format: Article
• Language: English
• Subjects: Animals; Annexin V; Apoptosis; Boutonneuse Fever - genetics; Boutonneuse Fever - metabolism; Boutonneuse Fever - microbiology; Capillary Permeability; Caspase; Caspase 1 - metabolism; Caspase-1; Cell culture; Cell death; Cell Line; Cell Membrane Permeability; Cell Survival; Cercopithecus aethiops; Chemokines; Cytokines; Cytokines - genetics; Cytokines - metabolism; Dehydrogenase; Dehydrogenases; DNA, Bacterial - genetics; Endothelial cells; Endothelial Cells - metabolism; Endothelial Cells - microbiology; Endothelium; Enzyme-Linked Immunosorbent Assay; Fatalities; Fever; Gene expression; Gene Expression Regulation; Health aspects; Homology; Host-Pathogen Interactions; Humans; Infection; Infections; Inflammation; Interleukin 6; Interleukin 8; L-Lactate dehydrogenase; Lactate dehydrogenase; Lactic acid; Medical research; Microvasculature; Monocyte chemoattractant protein 1; Monolayers; Mortality; Next-generation sequencing; Pathogenesis; Pathology; Permeability; Pharmacology; Protein biosynthesis; Protein synthesis; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; Rickettsia; Rickettsia - genetics; Rickettsia - physiology; Rickettsia conorii - genetics; Rickettsia conorii - physiology; Rickettsia Infections - genetics; Rickettsia Infections - metabolism; Rickettsia Infections - microbiology; Rickettsia massiliae; Rickettsia rickettsii; Rickettsiosis; Species Specificity; Staining; Statistical analysis; Statistical significance; Transcription; Vero Cells; Virulence
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0138830

Rickettsiae primarily target microvascular endothelial cells. However, it remains elusive how endothelial cell responses to rickettsiae play a role in the pathogenesis of rickettsial diseases. In the present study, we employed two rickettsial species with high sequence homology but differing virulence to investigate the pathological endothelial cell responses. Rickettsia massiliae is a newly documented human pathogen that causes a mild spotted fever rickettsiosis. The "Israeli spotted fever" strain of R. conorii (ISF) causes severe disease with a mortality rate up to 30% in hospitalized patients. At 48 hours post infection (HPI), R. conorii (ISF) induced a significant elevation of IL-8 and IL-6 while R. massiliae induced a statistically significant elevated amount of MCP-1 at both transcriptional and protein synthesis levels. Strikingly, R. conorii (ISF), but not R. massiliae, caused a significant level of cell death or injury in HMEC-1 cells at 72 HPI, demonstrated by live-dead cell staining, annexin V staining and lactate dehydrogenase release. Monolayers of endothelial cells infected with R. conorii (ISF) showed a statistically significant decrease in electrical resistance across the monolayer compared to both R. massiliae-infected and uninfected cells at 72 HPI, suggesting increased endothelial permeability. Interestingly, pharmacological inhibitors of caspase-1 significantly reduced the release of lactate dehydrogenase by R. conorii (ISF)-infected HMEC-1 cells, which suggests the role of caspase-1 in mediating the death of endothelial cells. Taken together, our data illustrated that a distinct proinflammatory cytokine profile and endothelial dysfunction, as evidenced by endothelial cell death/injury and increased permeability, are associated with the severity of rickettsial diseases.