Cooperativity of Oral Microbes in Evading Neutrophil-Mediated Killing - Project Summary/Abstract
Periodontal disease is a complex inflammatory disease resulting from a dysbiotic community of oral
microbes working together to promote disease. Inflammation associated with disease is initiated by members of
the oral biofilm, but the host response to the microorganisms, including inflammatory reactions by neutrophils, is
primarily responsible for disease progression. Porphyromonas gingivalis (Pg), a keystone periodontal pathogen,
utilizes normally commensal bacteria such as Streptococcus gordonii (Sg) for recruitment and growth assistance,
with commensals, as well as keystone-pathogens, both required to promote periodontal disease development.
We have found Pg can alter the ability of macrophages to kill Sg by modifying macrophage activation phenotypes
where Sg survives in M1 macrophages at a higher rate than in M2 macrophages, likely due to differences in
reactive oxygen species (ROS) production. ROS production is a major component of neutrophils’ defense
against pathogens, where ROS species can be produced both within the phagosome as well as externally.
Neutrophils, like macrophages, are efficient phagocytes that form a powerful line of defense against periodontal
pathogens with an array of defense mechanisms including phagocytosis, neutrophil extracellular trap (NET)
production and degranulation. Neutrophils display a variety of phenotypes, including in the oral environment,
however, these phenotypes are not as well described as they are in macrophages. However, a number of
differences in neutrophil response to infections such as periodontal disease have been characterized, including
in ROS production. Therefore, the overall objective of this project is to understand how oral bacteria, both
keystone pathogens and normally commensal, affect and respond to neutrophil phenotypes. The role neutrophils
play in innate immunity is well understood throughout the scientific research community as is the importance of
phagosome development to neutrophil mediated killing. Despite these cells being the predominant phagocytes
in periodontal tissue, the influence of a changing phagosome environment on bacteria involved in periodontal
disease has yet to be fully explored in neutrophils. Our central hypothesis is that the survival of Sg and Pg
is dependent on their cooperativity in evading neutrophil defense mechanisms. To investigate this
hypothesis this project aims to (1) investigate how activation of neutrophils, including by Pg, modulates neutrophil
phagosomal maturation dynamics and (2) investigate how Pg and Sg act collaboratively to increase their survival
and inflammation. To achieve these aims a wide variety of techniques, from classical cell biology and
biochemical techniques to advanced microscopy, flow cytometry and image analysis will be used. Completion of
this project will be a valuable step in understanding how the cooperative mechanisms of commensal bacteria
with periodontal pathogens contribute to evading neutrophil-mediated killing. It will also provide the investigator
with diverse mentoring, scientific and professional training, as further outlined in the proposal, to allow a
successful transition to the next stage of an independent research career.
