Date on Master's Thesis/Doctoral Dissertation

5-2018

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Microbiology and Immunology

Degree Program

Microbiology and Immunology, PhD

Committee Chair

Bodduluri, Haribabu

Committee Co-Chair (if applicable)

Jala, Venkatakrishna Rao

Committee Member

Jala, Venkatakrishna Rao

Committee Member

Lawrenz, Matthew

Committee Member

Yan, Jun

Committee Member

Zhang, Huang-Ge

Author's Keywords

crystalline silica; LTB4; inflammasome; lipidosome; sterile inflammation

Abstract

Silicosis is an irreversible lung inflammatory disease caused by chronic exposure to crystalline silica (CS) and is one of the most prevalent occupational diseases worldwide. Lipid chemoattractant Leukotriene B4 (LTB4) plays an important role in neutrophilic inflammation that drives silicosis and promotes lung cancer. Previous studies in our laboratory have demonstrated that CS-induced neutrophilic inflammation and lung tumor burden in K-rasLA1 mice is abrogated in the LTB4-receptor deficient mice. Another pathway whose importance is well studied in the progression of silicosis is the Nalp3 inflammasome pathway. Studies have shown inflammasome- dependent IL-1b to be important for the development of CS-induced pulmonary fibrosis. In this study, we examined the cellular mechanisms involved in CS-induced inflammatory pathways. We demonstrate that phagocytosis of CS particles is essential for the production of LTB4 and IL-1b in macrophages, mast cells and neutrophils. CS uptake induced rapid formation of lipid bodies in the cytoplasm independent of inflammasome activation. The appearance of these lipid bodies correlated with LTB4 production in mouse bone marrow-derived macrophages. LTB4 synthesis enzymes 5-LO, FLAP and LTA4H, co-localized within the lipid bodies suggesting that they are not merely storage vesicles but the sites of CS-induced LTB4 production. We coined the term “lipidosome” to define the functional unit of LTB4 synthesis in these lipid bodies. Our studies with bafilomycin-A1 and NLRP3 deficient mice, confirmed that LTB4 synthesis in the lipidosome is independent of inflammasome activation. siRNA knockdown and confocal microscopy studies revealed that lipidosome is closely associated with phagosome and their formation appeared to be seamlessly linked to the phagosome maturation pathway. GTPases Rab5c, Rab40c along with JNK1 are essential for lipidosome formation and LTB4 production. Additionally, activation of JNK pathway is necessary for both LTB4 and IL-1b production. BI-78D3, a JNK inhibitor, completely abrogated CS-induced neutrophilic inflammation in an in-vivo air pouch model. In conclusion, these results highlight an inflammasome independent and JNK activation dependent lipidosome pathway as a major regulator of LTB4 synthesis and CS-induced sterile inflammation.

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