The role of cell-to-cell communication in rickettsial pathogenesis: an approach to unravel new virulence factors

Overview

Project Summary

Approximately 1 billion people are estimated to be at risk of infection with obligate intracellular bacteria (1). Among these pathogens are different species of
Rickettsia, causing globally emerging communicable diseases known as rickettsioses, which are expected to increase the burden to public health (2, 7). The
absence of diagnostic tests for early detection, which often leads to high numbers of undiagnosed and untreated cases, together with the lack of a protective
vaccine, life-threatening nature of some forms of the disease, and the potential use of Rickettsia as bioterrorism weapons strengthen the need to better understand
the pathogenesis of the disease (2). Moreover, advances in the identification of critical virulence factors, and their subsequent mechanisms of action to evade the
host immune system, have been primarily hampered by the genetic intractability of Rickettsia species, thus limiting the development of novel and alternative
diagnostics and/or therapeutics (1). Our laboratory found that macrophage permissiveness to rickettsial infection acts as a critical virulence factor and a strategy
employed by pathogenic Rickettsia species to escape host immune defenses likely through a “Trojan horse” mechanism (3). We have then been focused on the use
of high-throughput methodologies (transcriptomics and proteomics) to understand how rickettsial species hijack host cellular pathways during infection (4-6). We
have already demonstrated that a profound remodeling of several host signaling pathways (e.g., apoptosis, metabolic, and inflammatory) by pathogenic Rickettsia
species underlies the sophisticated ability of these bacteria to replicate within these cells, typically equipped to destroy pathogens (4-6). Our results also
demonstrated that the drastic reprogramming of the intracellular environment of Rickettsia-infected cells is accompanied by significant alterations on the
secretome of those cells (e.g., IL-1β, IFN-γ, HMGB1) (4). Consequently, and in line with what has been described for other successful intracellular pathogens, we now
hypothesize that alterations on the secretome of Rickettsia-infected cells may impact cell-to-cell communication mechanisms, as a means to impair effective host
immune responses and/or promote infection in bystander cells. Therefore, we herein propose to start unraveling the role of cellular cross-talk for the development
of rickettsial pathogenesis in two Work Packages (WPs) (attached scheme):
WPA- Define how Rickettsia-induced bystander activation affects the course of infection.In this WP, we propose to characterize the molecular alterations on
the host secretome of Rickettsia-infected cells and evaluate how these alterations impact Rickettsia’s survival and proliferation in bystander cells. Rationale:Upon
infection, pathogenic Rickettsia species reprogram several host signaling pathways, thus anticipating substantial alterations on the secretome of those cells. We
now hypothesize that the alterations on the secretome of Rickettsia-infected cells contain the molecular cues necessary to reprogram signaling pathways in
bystander macrophages towards molecular/metabolic profiles more prone to rickettsial infection.
Work plan
Abstract
8/26
WPB- Evaluate the impact of Rickettsia infection on EVs/exosomes released by host cells. Herein, we propose to quantitatively resolve alterations in the
molecular cargo of EVs/exosomes resulting from Rickettsia infection and to identify the Rickettsia- and/or host-derived molecules responsible for bystander
reprogramming. Rationale:EVs/exosomes carry a variety of immunostimulatory and/or immunosuppressive molecules that affect the activation profiles of
bystander cells, thus impacting immune responses and/or infection in said cells.
Significance:This proposal aims to decipher the strategies evolved by pathogenic Rickettsia species to subvert innate and adaptive immunity leading to new
diagnostic and/or therapeutic approaches.
Innovation:This project will unveil the molecular details of cell-to-cell communication mechanisms undertaken in rickettsial infection through the use of highly
complementary approaches that will illuminate both the host and bacterial players shaping this interface. This will lead to the identification of a plethora of new
molecular factors that will be critical to understanding differences in rickettsial pathogenesis.

Project Details