Location
Philadelphia, PA
Start Date
1-5-2024 1:00 PM
End Date
1-5-2024 4:00 PM
Description
Introduction
The obligate intracellular bacterium, Coxiella burnetii is transmitted to humans via inhalation of contaminated aerosols and subsequently causes Q fever. Coxiella persists in modified phagolysosomes termed Coxiella-containing vacuoles (CCV) within the alveolar macrophages it infects. Acutely, Q fever presents as a flu-like illness; however, chronic infection is often characterized by non-curable endocarditis. Q fever endocarditis can develop years after the initial infection, indicating the bacterium's ability to survive long-term. While the specific host cell pathways Coxiella targets to achieve this long-term survival remain unknown, our lab has demonstrated that Coxiella actively manipulates host lipid storage organelles known as lipid droplets (LDs) in alveolar macrophages. LD breakdown is essential for bacterial intracellular growth and releases precursors for prostaglandin E2 (PGE2). PGE2 suppresses the host immune response during Coxiella infection and may help provide a hospitable intracellular niche for Coxiella to persist. However, the host transcription factors responsible for LD manipulation and PGE2 production in Coxiella-infected cells are unknown. Peroxisome proliferator-activated receptors (PPAR) are lipid-activated transcription factors that regulate LD metabolism and immune responses in macrophages. The three PPAR subtypes—PPARα, PPARβ/δ, and PPARγ—contribute to the pathogenesis of many intracellular pathogens. Hence, we hypothesize that PPARs are important for Coxiella burnetii survival in alveolar macrophages.
Methods
To assess Coxiella’s impact on host PPAR protein production, we measured PPARα, β/δ, and γ concentrations in infected and uninfected mouse alveolar macrophages using ELISAs. To assess the effect of PPAR modulation on Coxiella growth, we performed confocal microscopy and measured Coxiella CCV size in macrophages treated with PPAR subtype-specific agonists and antagonists.
Results
While PPARα protein levels remain unchanged, ELISA results suggest decreased PPARγ protein production in Coxiella-infected cells compared to uninfected cells. Further investigations will explore PPARβ/δ protein production. Intriguingly, treatment with PPARα and PPARβ/δ agonists and antagonists decreases bacterial growth, whereas PPARγ agonist or antagonist treatment does not affect Coxiella intracellular growth.
Discussion
Our studies demonstrate that while PPARγ protein levels are decreased during infection, PPARγ activity is not essential for Coxiella intracellular growth. Alternatively, altering PPARα and PPARβ/δ activity reduces bacterial intracellular growth, demonstrating their importance in Coxiella infection. Since PPARα and PPARβ/δ are involved in LD breakdown, which is essential for Coxiella growth, our data suggest a direct link between these PPAR subtypes and LD metabolism in supporting Coxiella intracellular survival. Future studies will identify if Coxiella directly manipulates PPAR subtype activity and investigate the relationship between PPAR subtypes and LD metabolism during Coxiella infection. Our studies suggest the potential of PPARs as therapeutic targets to inhibit Coxiella’s long-term intracellular survival.
Embargo Period
12-17-2024
The role of PPARs during Coxiella burnetii infection
Philadelphia, PA
Introduction
The obligate intracellular bacterium, Coxiella burnetii is transmitted to humans via inhalation of contaminated aerosols and subsequently causes Q fever. Coxiella persists in modified phagolysosomes termed Coxiella-containing vacuoles (CCV) within the alveolar macrophages it infects. Acutely, Q fever presents as a flu-like illness; however, chronic infection is often characterized by non-curable endocarditis. Q fever endocarditis can develop years after the initial infection, indicating the bacterium's ability to survive long-term. While the specific host cell pathways Coxiella targets to achieve this long-term survival remain unknown, our lab has demonstrated that Coxiella actively manipulates host lipid storage organelles known as lipid droplets (LDs) in alveolar macrophages. LD breakdown is essential for bacterial intracellular growth and releases precursors for prostaglandin E2 (PGE2). PGE2 suppresses the host immune response during Coxiella infection and may help provide a hospitable intracellular niche for Coxiella to persist. However, the host transcription factors responsible for LD manipulation and PGE2 production in Coxiella-infected cells are unknown. Peroxisome proliferator-activated receptors (PPAR) are lipid-activated transcription factors that regulate LD metabolism and immune responses in macrophages. The three PPAR subtypes—PPARα, PPARβ/δ, and PPARγ—contribute to the pathogenesis of many intracellular pathogens. Hence, we hypothesize that PPARs are important for Coxiella burnetii survival in alveolar macrophages.
Methods
To assess Coxiella’s impact on host PPAR protein production, we measured PPARα, β/δ, and γ concentrations in infected and uninfected mouse alveolar macrophages using ELISAs. To assess the effect of PPAR modulation on Coxiella growth, we performed confocal microscopy and measured Coxiella CCV size in macrophages treated with PPAR subtype-specific agonists and antagonists.
Results
While PPARα protein levels remain unchanged, ELISA results suggest decreased PPARγ protein production in Coxiella-infected cells compared to uninfected cells. Further investigations will explore PPARβ/δ protein production. Intriguingly, treatment with PPARα and PPARβ/δ agonists and antagonists decreases bacterial growth, whereas PPARγ agonist or antagonist treatment does not affect Coxiella intracellular growth.
Discussion
Our studies demonstrate that while PPARγ protein levels are decreased during infection, PPARγ activity is not essential for Coxiella intracellular growth. Alternatively, altering PPARα and PPARβ/δ activity reduces bacterial intracellular growth, demonstrating their importance in Coxiella infection. Since PPARα and PPARβ/δ are involved in LD breakdown, which is essential for Coxiella growth, our data suggest a direct link between these PPAR subtypes and LD metabolism in supporting Coxiella intracellular survival. Future studies will identify if Coxiella directly manipulates PPAR subtype activity and investigate the relationship between PPAR subtypes and LD metabolism during Coxiella infection. Our studies suggest the potential of PPARs as therapeutic targets to inhibit Coxiella’s long-term intracellular survival.
Comments
Winner of 2024 PCOM David Miller, DO ’60 Endowed Memorial Research Day Masters in Biomedical Science Award