Mycobacterial-induced lipid droplets function as an immunoinflammatory platform in DCs through mechanisms dependent of DGAT-1 and PGE2 production

Tuberculosis (TB) represents a major challenge to public health. In the lungs, Mycobacterium tuberculosis (Mtb) infects macrophages and dendritic cells (DCs), which initiate the immune response. Mtb manipulates host lipid metabolism to survive and has triacylglycerol as a carbon source to persist in a latent state in the host. Thus, herein, we evaluated the functions of lipid droplets (LD) in DC activation and bacterial burden during mycobacterial infection. The involvement of diacylglycerol acyltransferase 1 (DGAT-1), a triacylglycerol synthesis enzyme, and the eicosanoid prostaglandin (PG) E2 were also investigated. DCs were differentiated from C57BL/6 bone marrow with GM-CSF and infected with BCG (MOI 5). BCG-infected DCs presented an increase in lipid droplets (LD), triacylglycerol (TAG), cholesterol ester (CE); and lipid-related and proinflammatory gene expression. To evaluate the role of TAG synthesis, BCG-infected DCs were treated with DGAT-1 inhibitor (A922550). DGAT1 inhibition reduced LDs accumulation, MHCII surface expression, the proinflammatory gene inos expression, and the secretion of IL-1beta, IL-10 and TNF-alpha in DCs infected by BCG. Interestingly, PGE₂ secretion was also reduced by DGAT-1 inhibition on infected DCs. PGE₂ is important to inflammatory response of TB and to T cells differentiation. Then, PGE₂ was added to DCs and promoted an increased BCG burden, cytokines release and LDs accumulation in BCG infected-DCs. PGE₂ treatment reverted DGAT1 inhibition effects in cytokines secretion, but failed to modulate LDs accumulation in DGAT1 inhibitor treated-DCs. Together, TAG synthesis by DGAT1 and the lipid mediator PGE₂ are important to LDs formation and functions in the inflammatory response of DCs infected by mycobacteria. We intend to further investigate the role of lipid metabolism pathways in antigen presentation by Mtb-infected DCs, which may contribute to the comprehension of immune response of TB and the development of new therapies.