Defining complex mechanistic interactions and responses by macrophages during Mycobacterium abscessus infection

Abstract

Phagocytosis by macrophages is critical to eradicate invading pathogens. Phagocytosis is regulated by parallel networks that control the binding and uptake of particles, subsequent lysosome delivery, and activation of downstream innate immune responses. However, whether distinct host pathways drive unique responses to targeted substrates within the lung environment remains unknown. Mycobacterium abscessus (MAB) is a rapidly growing non-tuberculous mycobacterium that infects patients with chronic lung diseases, like cystic fibrosis. While interactions between MAB and macrophages contribute to its pathogenesis, how macrophages bind, phagocytose, and control MAB remains entirely unclear. We hypothesize that understanding key MAB-macrophage interactions will identify critical host targets that can be inhibited to prevent disease. To test this hypothesis, using a genome-wide knockout library of immortalized bone marrow derived macrophages, we completed a forward genetic screen to identify host pathways that contribute to fluorescent MAB uptake. Our results show glycosaminoglycan synthesis (sGAGs) in macrophages is required to efficiently take up MAB. Both enzymatic and genetic approaches found key sGAG biosynthesis regulators, UGDH, B3GLCT, B4GALT7 and B3GAT3, influence macrophage interactions with MAB and other pathogens like Mycobacterium tuberculosis. Using a recently developed alveolar macrophage model, we are now dissecting the role of sGAGs in lung specific macrophages. Future work will determine how sGAG pathways modulate bacterial replication, cytokine responses and disease progression following MAB infection with the goal of defining key mechanisms driving host-pathogen interactions in the lungs.