Quantitative Proteomics of the Endothelial Secretome Identifies RC0497 as Diagnostic of Acute Rickettsial Spotted Fever Infections

Am J Pathol. 2020 Feb;190(2):306-322. doi: 10.1016/j.ajpath.2019.10.007. Epub 2020 Jan 16.

Abstract

Mediterranean spotted fever is a reemerging acute tick-borne infection produced by the α-proteobacterium, Rickettsia conorii. Rickettsia conorii infects vascular endothelial cells producing disseminated plasma leakage, manifesting as nonspecific fever, headache, and maculopapular rash. Because there are no available tests of early infection, Mediterranean spotted fever is often undiagnosed and untreated, resulting in significant mortality. To address this critical need, we have applied a quantitative proteomics pipeline for analyzing the secretome of primary human umbilical vein endothelial cells. Of the 104 proteins whose abundance changed significantly in the R. conorii-infected human umbilical vein endothelial cells' secretome, 46 proteins were up-regulated: 45 were host secreted proteins (including cytokines), and 1 was a rickettsial protein, the putative N-acetylmuramoyl-l-alanine amidase RC0497. Proteins with sequence highly homologous to RC0497 were found to be shared by many species of the spotted fever group rickettsiae, but not typhus group rickettsiae. Quantitative targeted proteomics studies of plasma from a mouse model of sublethal and lethal R. conorii identified RC0497 in the blood, and its circulating levels were proportionally associated with infection outcome. Finally, the presence of RC0497 in the serum samples from a cohort of humans presenting with acute rickettsioses was confirmed. The detection of RC0497 has the potential to be a sensitive and specific marker for acute rickettsial spotted rickettsioses.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biomarkers / blood*
  • Boutonneuse Fever / diagnosis*
  • Boutonneuse Fever / epidemiology
  • Boutonneuse Fever / microbiology
  • Cohort Studies
  • Female
  • Host-Pathogen Interactions
  • Human Umbilical Vein Endothelial Cells / metabolism*
  • Human Umbilical Vein Endothelial Cells / microbiology
  • Humans
  • Male
  • Mice
  • Mice, Inbred C3H
  • N-Acetylmuramoyl-L-alanine Amidase / blood*
  • Proteome / analysis*
  • Proteomics
  • Rickettsia / isolation & purification
  • Rickettsia / pathogenicity*
  • Rickettsia Infections / complications*
  • Rickettsia Infections / microbiology
  • Rickettsia Infections / transmission
  • Texas / epidemiology

Substances

  • Biomarkers
  • Proteome
  • N-Acetylmuramoyl-L-alanine Amidase