Browsing by Author "Clemente, Tatiana M."

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    Coxiella burnetii Blocks Intracellular Interleukin-17 Signaling in Macrophages
    (American Society for Microbiology, 2018-09-21) Clemente, Tatiana M.; Mulye, Minal; Justis, Anna V.; Nallandhighal, Srinivas; Tran, Tuan M.; Gilk, Stacey D.; Microbiology and Immunology, School of Medicine
    Coxiella burnetii is an obligate intracellular bacterium and the etiological agent of Q fever. Successful host cell infection requires the Coxiella type IVB secretion system (T4BSS), which translocates bacterial effector proteins across the vacuole membrane into the host cytoplasm, where they manipulate a variety of cell processes. To identify host cell targets of Coxiella T4BSS effector proteins, we determined the transcriptome of murine alveolar macrophages infected with a Coxiella T4BSS effector mutant. We identified a set of inflammatory genes that are significantly upregulated in T4BSS mutant-infected cells compared to mock-infected cells or cells infected with wild-type (WT) bacteria, suggesting that Coxiella T4BSS effector proteins downregulate the expression of these genes. In addition, the interleukin-17 (IL-17) signaling pathway was identified as one of the top pathways affected by the bacteria. While previous studies demonstrated that IL-17 plays a protective role against several pathogens, the role of IL-17 during Coxiella infection is unknown. We found that IL-17 kills intracellular Coxiella in a dose-dependent manner, with the T4BSS mutant exhibiting significantly more sensitivity to IL-17 than WT bacteria. In addition, quantitative PCR confirmed the increased expression of IL-17 downstream signaling genes in T4BSS mutant-infected cells compared to WT- or mock-infected cells, including the proinflammatory cytokine genes Il1a, Il1b, and Tnfa, the chemokine genes Cxcl2 and Ccl5, and the antimicrobial protein gene Lcn2 We further confirmed that the Coxiella T4BSS downregulates macrophage CXCL2/macrophage inflammatory protein 2 and CCL5/RANTES protein levels following IL-17 stimulation. Together, these data suggest that Coxiella downregulates IL-17 signaling in a T4BSS-dependent manner in order to escape the macrophage immune response.
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    Coxiella burnetii Sterol-Modifying Protein Stmp1 Regulates Cholesterol in the Intracellular Niche
    (American Society for Microbiology, 2022) Clemente, Tatiana M.; Ratnayake, Rochelle; Samanta, Dhritiman; Augusto, Leonardo; Beare, Paul A.; Heinzen, Robert A.; Gilk, Stacey D.; Microbiology and Immunology, School of Medicine
    Coxiella burnetii replicates in a phagolysosome-like vacuole called the Coxiella-containing vacuole (CCV). While host cholesterol readily traffics to the CCV, cholesterol accumulation leads to CCV acidification and bacterial death. Thus, bacterial regulation of CCV cholesterol content is essential for Coxiella pathogenesis. Coxiella expresses a sterol-modifying protein, Stmp1, that may function to lower CCV cholesterol through enzymatic modification. Using an Stmp1 knockout (Δstmp1), we determined that Stmp1 is not essential for axenic growth. Inside host cells, however, Δstmp1 mutant bacteria form smaller CCVs which accumulate cholesterol, preferentially fuse with lysosomes, and become more acidic, correlating with a significant growth defect. However, in cholesterol-free cells, Δstmp1 mutant bacteria grow similarly to wild-type bacteria but are hypersensitive to cholesterol supplementation. To better understand the underlying mechanism behind the Δstmp1 mutant phenotype, we performed sterol profiling. Surprisingly, we found that Δstmp1 mutant-infected macrophages accumulated the potent cholesterol homeostasis regulator 25-hydroxycholesterol (25-HC). We next determined whether dysregulated 25-HC alters Coxiella infection by treating wild-type Coxiella-infected cells with 25-HC. Similar to the Δstmp1 mutant phenotype, 25-HC increased CCV proteolytic activity and inhibited bacterial growth. Collectively, these data indicate that Stmp1 alters host cholesterol metabolism and is essential to establish a mature CCV which supports Coxiella growth.
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    Coxiella burnetii Type 4B Secretion System-dependent manipulation of endolysosomal maturation is required for bacterial growth
    (Public Library of Science, 2019-12-23) Samanta, Dhritiman; Clemente, Tatiana M.; Schuler, Baleigh E.; Gilk, Stacey D.; Microbiology and Immunology, School of Medicine
    Upon host cell infection, the obligate intracellular bacterium Coxiella burnetii resides and multiplies within the Coxiella–Containing Vacuole (CCV). The nascent CCV progresses through the endosomal maturation pathway into a phagolysosome, acquiring endosomal and lysosomal markers, as well as acidic pH and active proteases and hydrolases. Approximately 24–48 hours post infection, heterotypic fusion between the CCV and host endosomes/lysosomes leads to CCV expansion and bacterial replication in the mature CCV. Initial CCV acidification is required to activate C. burnetii metabolism and the Type 4B Secretion System (T4BSS), which secretes effector proteins required for CCV maturation. However, we found that the mature CCV is less acidic (pH~5.2) than lysosomes (pH~4.8). Further, inducing CCV acidification to pH~4.8 causes C. burnetii lysis, suggesting C. burnetii actively regulates pH of the mature CCV. Because heterotypic fusion with host endosomes/lysosomes may influence CCV pH, we investigated endosomal maturation in cells infected with wildtype (WT) or T4BSS mutant (ΔdotA) C. burnetii. In WT-infected cells, we observed a significant decrease in proteolytically active, LAMP1-positive endolysosomal vesicles, compared to mock or ΔdotA-infected cells. Using a ratiometric assay to measure endosomal pH, we determined that the average pH of terminal endosomes in WT-infected cells was pH~5.8, compared to pH~4.75 in mock and ΔdotA-infected cells. While endosomes progressively acidified from the periphery (pH~5.5) to the perinuclear area (pH~4.7) in both mock and ΔdotA-infected cells, endosomes did not acidify beyond pH~5.2 in WT-infected cells. Finally, increasing lysosomal biogenesis by overexpressing the transcription factor EB resulted in smaller, more proteolytically active CCVs and a significant decrease in C. burnetii growth, indicating host lysosomes are detrimental to C. burnetii. Overall, our data suggest that C. burnetii inhibits endosomal maturation to reduce the number of proteolytically active lysosomes available for heterotypic fusion with the CCV, possibly as a mechanism to regulate CCV pH.
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    Manipulation of Host Cholesterol by Obligate Intracellular Bacteria
    (Frontiers, 2017-05-05) Samanta, Dhritiman; Mulye, Minal; Clemente, Tatiana M.; Justis, Anna V.; Gilk, Stacey D.; Microbiology and Immunology, School of Medicine
    Cholesterol is a multifunctional lipid that plays important metabolic and structural roles in the eukaryotic cell. Despite having diverse lifestyles, the obligate intracellular bacterial pathogens Chlamydia, Coxiella, Anaplasma, Ehrlichia, and Rickettsia all target cholesterol during host cell colonization as a potential source of membrane, as well as a means to manipulate host cell signaling and trafficking. To promote host cell entry, these pathogens utilize cholesterol-rich microdomains known as lipid rafts, which serve as organizational and functional platforms for host signaling pathways involved in phagocytosis. Once a pathogen gains entrance to the intracellular space, it can manipulate host cholesterol trafficking pathways to access nutrient-rich vesicles or acquire membrane components for the bacteria or bacteria-containing vacuole. To acquire cholesterol, these pathogens specifically target host cholesterol metabolism, uptake, efflux, and storage. In this review, we examine the strategies obligate intracellular bacterial pathogens employ to manipulate cholesterol during host cell colonization. Understanding how obligate intracellular pathogens target and use host cholesterol provides critical insight into the host-pathogen relationship.
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    A Treatment to Eliminate SARS-CoV-2 Replication in Human Airway Epithelial Cells Is Safe for Inhalation as an Aerosol in Healthy Human Subjects
    (American Association for Respiratory Care (AARC), 2020-09-21) Davis, Michael D.; Clemente, Tatiana M.; Giddings, Olivia K.; Ross, Kristie; Cunningham, Rebekah S.; Smith, Laura; Simpson, Edward; Liu, Yunlong; Kloepfer, Kirsten; Ramsey, I. Scott; Zhao, Yi; Robinson, Christopher M.; Gilk, Stacey D.; Gaston, Benjamin; Pediatrics, School of Medicine
    Background: Low airway surface pH is associated with many airway diseases, impairs antimicrobial host defense and worsens airway inflammation. Inhaled Optate is designed to safely to raise airway surface pH and is well-tolerated in humans. Raising intracellular pH partially prevents activation of SARS-CoV-2 in primary normal human airway epithelial (NHAE) cells, decreasing viral replication by several mechanisms. Methods: Here, we grew primary normal human airway epithelial (NHAE) cells from healthy subjects, infected them with SARS-CoV-2 (isolate USA-WA1/2020), and used clinical Optate at concentrations used in humans in vivo to determine whether it would prevent viral infection and replication. Cells were pre-treated with Optate or placebo prior to infection (MOI of 0.1) and viral replication was determined by plaque assay and nucleocapsid (N) protein levels. Healthy human subjects also inhaled Optate as part of a Phase 2a safety trial. Results: Optate almost completely prevented viral replication at each time point between 24 and 120 hours, relative to placebo, both by plaque assay and by N protein expression (p < 0.001). Mechanistically, Optate inhibited expression of major endosomal trafficking genes and raised NHAE intracellular pH. Optate had no effect on NHAE cell viability at any time point. Inhaled Optate was well tolerated in 10 normal subjects, with no change in lung function, vital signs or oxygenation. Conclusions: Inhaled Optate may be well-suited for a clinical trial in patients with a pulmonary SARS-CoV-2 infection. However, it is vitally important for patient safety that formulations designed for inhalation with regards to pH, isotonicity and osmolality be used. An inhalational treatment that safely prevents SARS-CoV-2 viral replication could be helpful for treating patients with pulmonary SARS-CoV-2 infection.