Love/hate relationships of Achromobacter species and human macrophages
Lead Research Organisation:
Queen's University Belfast
Department Name: Sch of Medicine, Dentistry & Biomed Sci
Abstract
The success of pathogenic microbes depends on their ability to overcome immune barriers in the host including survival in host cells designed to kill pathogens (e.g., macrophages), which gobbled up microbes and trap them in membrane-bound vacuoles known as phagosomes. Engulfed pathogenic microbes, however, can disarm macrophages and counteract immune defenses by deploying proteins called effectors. When infections occur in healthy people, pathogens also elicit inflammatory responses that help the host to clear the infection.
In contrast, susceptible people, such as those with cystic fibrosis, immunosuppressive therapies, diabetes, elderly, or undergoing major surgery, cannot readily overcome pathogens. Moreover, susceptible people can be infected by opportunistic bacteria that rarely cause infection in healthy people and often display high-level multidrug antibiotic resistance, which makes treatment more difficult. For example, my research group has discovered that cystic fibrosis (CF) gene-defective macrophages cannot destroy engulfed bacteria and play a central role in maintaining the chronic inflammation state associated with infections by opportunistic bacteria.
The interplay between the host and the pathogen in these cases whereby the host is permissive to infection is not well understood, and emerging opportunistic pathogens, in general, are not well established as infection models. We think that intracellular pathogens engulfed by macrophages, combined with host underlying defects (e.g., CF mutations), induce a highly proinflammatory state that becomes deleterious to susceptible people with CF. To explore this idea, we first need to establish a relevant model system; we propose to use the emerging bacterium Achromobacter as a novel opportunistic pathogen and to compare Achromobacter's survival mechanisms in normal and CF-defective human macrophages, as non-susceptible and susceptible host cell models, respectively.
Achromobacter bacteria are increasingly becoming the dominant microbes recovered from people with cystic fibrosis (PWCF) including those with end-stage lung disease. Very little is known on the pathogenesis of Achromobacter sp. However, we have recently discovered that Achromobacter bacteria isolated from PWCF can survive and divide intracellularly in human macrophages, ultimately destroying these cells by stimulating heightened inflammation. For this, we have also found that Achromobacter deploys bacterial toxins in the host cells and represses anti-inflammatory responses.
In this research proposal we aim to define: (i) the bacterial properties associated with intracellular survival, and (ii) the macrophage cellular responses upon infection by comparing macrophages from healthy and CF people. We anticipate these studies will allow us to identify new ways to treat the infection in these people that may be applicable to other situations where the host is more susceptible due to diseases or medical treatments.
In contrast, susceptible people, such as those with cystic fibrosis, immunosuppressive therapies, diabetes, elderly, or undergoing major surgery, cannot readily overcome pathogens. Moreover, susceptible people can be infected by opportunistic bacteria that rarely cause infection in healthy people and often display high-level multidrug antibiotic resistance, which makes treatment more difficult. For example, my research group has discovered that cystic fibrosis (CF) gene-defective macrophages cannot destroy engulfed bacteria and play a central role in maintaining the chronic inflammation state associated with infections by opportunistic bacteria.
The interplay between the host and the pathogen in these cases whereby the host is permissive to infection is not well understood, and emerging opportunistic pathogens, in general, are not well established as infection models. We think that intracellular pathogens engulfed by macrophages, combined with host underlying defects (e.g., CF mutations), induce a highly proinflammatory state that becomes deleterious to susceptible people with CF. To explore this idea, we first need to establish a relevant model system; we propose to use the emerging bacterium Achromobacter as a novel opportunistic pathogen and to compare Achromobacter's survival mechanisms in normal and CF-defective human macrophages, as non-susceptible and susceptible host cell models, respectively.
Achromobacter bacteria are increasingly becoming the dominant microbes recovered from people with cystic fibrosis (PWCF) including those with end-stage lung disease. Very little is known on the pathogenesis of Achromobacter sp. However, we have recently discovered that Achromobacter bacteria isolated from PWCF can survive and divide intracellularly in human macrophages, ultimately destroying these cells by stimulating heightened inflammation. For this, we have also found that Achromobacter deploys bacterial toxins in the host cells and represses anti-inflammatory responses.
In this research proposal we aim to define: (i) the bacterial properties associated with intracellular survival, and (ii) the macrophage cellular responses upon infection by comparing macrophages from healthy and CF people. We anticipate these studies will allow us to identify new ways to treat the infection in these people that may be applicable to other situations where the host is more susceptible due to diseases or medical treatments.
Technical Summary
The biology of host pathogen-interaction dynamics in infection-permissive hosts is not well understood, and in general, we lack well-established infection models for emerging, highly antibiotic resistant opportunistic pathogens. One of these examples are bacterial species of the genus Achromobacter, which are becoming emerging pathogens in people with cystic fibrosis (CF) and people with other immunocompromised conditions. We hypothesize that intracellular pathogens engulfed by macrophages, combined with host underlying defects (e.g., CFTR mutations), induce a highly proinflammatory state that becomes deleterious to the host.
Based on our pilot data showing that the Achromobacter Type 3 secretion system drives pyroptosis and immunopathology via independent activation of NLRC4 and NLRP3 inflammasomes, this proposal will tackle 2 aims:
Aim 1. To Characterise the intracellular survival of Achromobacter species in human macrophages by undertaking by (i) defining the properties of the Achromobacter-containing vacuole (ACV), (ii) identifying Achromobacter genes required for intracellular survival, and (iii) defining the role of Achromobacter's Type 3 secretion system in macrophage cytotoxicity and pyroptosis.
Aim 2. To determine how macrophages respond to Achromobacter infection by (i) defining the mechanism of T3SS-dependent specific activation of the NLRP3 inflammasome, and (ii) Examining the proinflammatory potential of Achromobacter infection in CF-defective macrophages based on gene editing (to create clinically relevant CFTR mutations) of immunocompetent pluripotent stem cells from which macrophages will be derived.
This proposal will unravel the molecular dialogue between Achromobacter and monocytic macrophages in both healthy and disease-susceptible conditions and will provide knowhow and tools for the potential discovery of novel anti-inflammatory therapies.
Based on our pilot data showing that the Achromobacter Type 3 secretion system drives pyroptosis and immunopathology via independent activation of NLRC4 and NLRP3 inflammasomes, this proposal will tackle 2 aims:
Aim 1. To Characterise the intracellular survival of Achromobacter species in human macrophages by undertaking by (i) defining the properties of the Achromobacter-containing vacuole (ACV), (ii) identifying Achromobacter genes required for intracellular survival, and (iii) defining the role of Achromobacter's Type 3 secretion system in macrophage cytotoxicity and pyroptosis.
Aim 2. To determine how macrophages respond to Achromobacter infection by (i) defining the mechanism of T3SS-dependent specific activation of the NLRP3 inflammasome, and (ii) Examining the proinflammatory potential of Achromobacter infection in CF-defective macrophages based on gene editing (to create clinically relevant CFTR mutations) of immunocompetent pluripotent stem cells from which macrophages will be derived.
This proposal will unravel the molecular dialogue between Achromobacter and monocytic macrophages in both healthy and disease-susceptible conditions and will provide knowhow and tools for the potential discovery of novel anti-inflammatory therapies.
