A Pathogen and a Non-pathogen Spotted Fever Group Rickettsia Trigger Differential Proteome Signatures in Macrophages

Abstract

We have previously reported that Rickettsia conorii and Rickettsia montanensis have distinct intracellular fates within THP-1 macrophages, suggesting that the ability to proliferate within macrophages may be a distinguishable factor between pathogenic and non-pathogenic Spotted fever group (SFG) members. To start unraveling the molecular mechanisms underlying the capacity (or not) of SFG Rickettsia to establish their replicative niche in macrophages, we have herein used quantitative proteomics by SWATH-MS to profile the alterations resulted by the challenge of THP-1 macrophages with R. conorii and R. montanensis. We show that the pathogenic, R. conorii, and the non-pathogenic, R. montanensis, member of SFG Rickettsia trigger differential proteomic signatures in macrophage-like cells upon infection. R. conorii specifically induced the accumulation of several enzymes of the tricarboxylic acid cycle, oxidative phosphorylation, fatty acid β-oxidation, and glutaminolysis, as well as of several inner and outer membrane mitochondrial transporters. These results suggest a profound metabolic rewriting of macrophages by R. conorii toward a metabolic signature of an M2-like, anti-inflammatory activation program. Moreover, several subunits forming the proteasome and immunoproteasome are found in lower abundance upon infection with both rickettsial species, which may help bacteria to escape immune surveillance. R. conorii-infection specifically induced the accumulation of several host proteins implicated in protein processing and quality control in ER, suggesting that this pathogenic Rickettsia may be able to increase the ER protein folding capacity. This work reveals novel aspects of macrophage-Rickettsia interactions, expanding our knowledge of how pathogenic rickettsiae explore host cells to their advantage.

Host Epigenetics in Intracellular Pathogen Infections

“…Rickettsia spp. are obligate intracellular Gram-negative bacteria that require a vector for host transmission [ 65 , 66 ]. Rickettsiae are transmitted to humans by the bite of infected ticks and mites as well as by the feces of infected lice and fleas.…”

“…As a result of the bacterial influence on host chromatin modifications and defense gene transcription, intracellular pathogens cause dysregulation of host cell function leading to disease [ 37 , 77 ]. The cellular mechanisms responsible for epigenetic regulation includereversible post-translational histone modifications (acetylation, methylation and phosphorylation) and methylation of CpG dinucleotides in chromosomal DNA and noncoding RNA-mediated gene regulation [ 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 ].…”

“…The rickettsial species can also modulate immunometabolism, although this process is still not well understood. Recent proteomic studies have revealed that rickettsiae modify the activity of host proteins involved in various metabolic processes [ 66 ]. Significant alterations were observed in glycolysis, pentose phosphate pathway (PPP), tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS), fatty acid metabolism and amino acid metabolism.…”

“…Rickettsial infection has been found to reduce the activity of enzymes involved in glycolysis and PPP, including glucose-6 phosphate isomerase, fructosebiphosphatase A, phosphoglycerate kinase 1, enolase 1, pyruvate kinase M1/2 and lactate dehydrogenase B [ 66 ]. These processes generate nicotinamide adenine dinucleotide phosphate (NADPH) and finally determine the synthesis of pentose sugars.…”

Targeted Proteomics for Studying Pathogenic Bacteria

“…Despite the non‐targeted way of collecting data, the analysis of DIA data can be performed in both a targeted manner as well as non‐targeted (see below). Recently, DIA/SWATH‐MS was employed to assess differential proteome signatures between pathogenic and nonpathogenic Rickettsia inside macrophages and unraveled the ligands of Streptococcus pneumonia interacting with human brain endothelial cells …”