| Summary: | <p>Sarcoidosis is an enigmatic disease that has puzzled physicians for nearly a century. However many groups of sarcoidosis researchers have progressively fitted the pieces of the disease puzzle together. Today, we know that sarcoidosis is an immune-mediated disease, characterised by granuloma deposition, primarily in the lungs. There is a genetic predisposition and environmental triggers. My thesis focuses on one aspect of sarcoidosis which is almost completely unexplored – what causes progressive fibrosis in up to 30% of patients with pulmonary sarcoidosis? Fibrosis matters because it is irreversible, and the majority of progressive fibrotic sarcoidosis patients are young (40-60years of age). My project moves the focus away from traditional blood studies to the organ, using bronchoalveolar lavage samples of patients with fibrotic vs non-fibrotic sarcoidosis and lung tissue sections to ask what are the immune cells and functional pathways associated with fibrosis in pulmonary sarcoidosis. I helped develop newly available high-resolution techniques - single cell mass cytometry of lung tissue and accompanying mathematically driven spatial analysis of the data; single cell RNA sequencing of the immune cells in the broncho-alveolar lavage of the lungs and finally, single cell spatial transcriptomic of cells in the lung sections of patients with fibrotic and non-fibrotic sarcoidosis to help address this question.</p>
<p>My studies conclude that classical monocytes and macrophages with a pro-inflammatory and pro-fibrotic gene expression profile are the main immune cells associated with fibrosis in sarcoidosis. Trajectory inference analysis indicate that these lung classical monocytes differentiate into ‘monoTREM2’ macrophages and eventually the pro-fibrotic SPP1 macrophages. MonoTREM2 macrophages have highly upregulated expression of Legumain (LGMN) in fibrotic sarcoidosis compared to non-fibrotic sarcoidosis, a cysteine protease involved in the processing of auto and external peptide for MHC class II presentation in the lysosomal-endosomal systems. This gene has previously been found to drive increased synthesis of extracellular matrix proteins via TGF-β activation. This introduces the first new insight into how fibrosis could be perpetuated in sarcoidosis. The CXCL10 macrophage subset also has an IFN signature and highly expressed CHIT1 in fibrotic sarcoidosis. CHIT 1 is a prominent chitinase known to enhance TGF-β-stimulated fibroblast proliferation and myofibroblast transformation. Unbiased niche analysis using single cell spatial transcriptomics show that the two subsets of macrophages found in granuloma are the monoTREM2-SPP1 macrophages and CXCL10 macrophages, co-locating with CD4 T cells.</p>
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