scRNA-seq analysis of skin CD45+ cells mice where Tsc2 is deleted in CD11c-expressing cells
Rationale: Chronic sarcoidosis is a complex granulomatous disease with limited treatment options that can progress over time. Understanding the molecular pathways contributing to disease would aid in new therapeutic development.  Objectives: To understand if macrophages from non-resolving chronic sarcoidosis patients are predisposed to macrophage aggregation and granuloma formation, and if modulation of the underlying molecular pathways influence sarcoidosis granuloma formation.  Methods: Macrophages were cultivated in vitro from isolated peripheral blood CD14+ monocytes and evaluated for spontaneous aggregation. Transcriptomics analyses, phenotypic and drug inhibitory experiments were performed on these monocyte-derived macrophages. Human skin biopsies from sarcoidosis patients and a myeloid Tsc2-specific sarcoidosis mouse model were analyzed for validatory experiments. Measurements and Main Results: Monocyte-derived macrophages from chronic sarcoidosis patients spontaneously formed extensive granulomas in vitro compared to healthy controls. Transcriptomic analyses separated healthy and sarcoidosis macrophages and identified an enrichment in lipid metabolic processes. In vitro patient granulomas, sarcoidosis mouse model granulomas, and those directly analyzed from lesional patient skin expressed an aberrant lipid metabolism profile and contained increased neutral lipids. Conversely, a combination of statins and cholesterol-reducing agents reduced granuloma formation both in vitro and in vivo in a sarcoidosis mouse model.  Conclusions: Together, our findings show that altered lipid metabolism in sarcoidosis macrophages is associated with its predisposition to granuloma formation and suggest cholesterol-reducing therapies as a treatment option in patients. Overall design: Skin CD45+ immune cells