Host lipid metabolism is an important target for subversion by pathogenic mycobacteria such as Mycobacterium tuberculosis. The appearance of foam cells within the granuloma are well-characterised effects of chronic tuberculosis. The zebrafish-Mycobacterium marinum infection model recapitulates many aspects of human-M. tuberculosis infection and is used as a model to investigate the structural components of the mycobacterial granuloma. Here, we demonstrate that the zebrafish-M. marinum granuloma contains foam cells and that the transdifferentiation of macrophages into foam cells is driven by the mycobacterial ESX1 pathogenicity locus. This report demonstrates conservation of an important aspect of mycobacterial infection across species.

Changes to lipid metabolism are well-characterised consequences of human tuberculosis infection but their functional relevance are not clearly elucidated in these or other host-mycobacterial systems. The zebrafish-Mycobacterium marinum infection model is used extensively to model many aspects of human-M. tuberculosis pathogenesis but has not been widely used to study the role of infection-induced lipid metabolism. We find mammalian mycobacterial infection-induced alterations in host Low Density Lipoprotein metabolism are conserved in the zebrafish model of mycobacterial pathogenesis. Depletion of LDLR, a key lipid metabolism node, decreased M. marinum burden, and corrected infection-induced altered lipid metabolism resulting in decreased LDL and reduced the rate of macrophage transformation into foam cells. Our results demonstrate a conserved role for infection-induced alterations to host lipid metabolism, and specifically the LDL-LDLR axis, across host-mycobacterial species pairings.

5Host lipid metabolism is an important target for subversion by pathogenic mycobacteria such 1 6 as Mycobacterium tuberculosis. Systemic dyslipidemia and the appearance of foam cells 1 7 within the granuloma are well-characterised effects of chronic tuberculosis. The zebrafish-1 8 Mycobacterium marinum infection model recapitulates many aspects of human-M. 1 9 tuberculosis infection and serves as model to investigate the structural components of the 2 0 mycobacterial granuloma. Here, we demonstrate that the zebrafish-M. marinum granuloma 2 1 contains foam cells and that transdifferentiation of macrophages into foam cells is driven by 2 2 the mycobacterial ESX1 pathogenicity locus. Furthermore, we define a detrimental role for 2 3 infection-induced alterations host lipid metabolism in mycobacterial pathogenesis. Depletion 2 4 of LDLR, a key regulator of intracellular lipids, decreased M. marinum burden and corrected 2 5 infection-induced altered lipid metabolism. This resulted reduced macrophage transformation 2 6into foam cells within granulomas. Our results demonstrate a conserved role for host lipid 2 7 metabolism, and specifically the LDL-LDLR axis, in mycobacterial pathogenesis. 2 8 2 9 Importance 3 0 Mycobacterial infections are classically defined by the presence of granulomas at the site of 3 1 infection. Foams cells are a key component of mycobacterial granulomas and arise as a 3 2 consequence of local and systemic changes to host lipid metabolism. It is hypothesised that 3 3 foam cells provide a lipid-rich intracellular environment, promoting mycobacterial survival 3 4 within the granuloma. Here we have turned to the zebrafish-M. marinum platform to identify 3 5 the host-pathogen interactions contributing to macrophage transdifferentiation into foam cells 3 6 and the consequences of infection-induced dyslipidemia. We observe foam cells in 3 7 embryonic and adult zebrafish granulomas, and identify a role for the mycobacterial ESX1 3 8 pathogenicity locus in promoting foam cell differentiation. We show that zebrafish-M. 3 9 marinum infection results in dysregulation of host lipid metabolism, and that depletion of the 4 0 host lipid metabolism node LDLR corrects infection-induced changes to host lipid 4 1 metabolism and reduces foam cell formation. 4 2 4 3