The role of organelle contact sites in macrophage antifungal responses

/ ABSTRACT Cellular organelles interact at membrane contact sites, enabling inter-organelle communication and coordination of basic cellular processes through lipid transfer, calcium signaling, and membrane dynamics. Membrane contact sites have also been shown to regulate cellular responses to infection, including scaffolding innate immune signaling complexes, generation of antimicrobial effectors, degrading pathogens, and resolving inflammation. However, the role of membrane contact sites in antifungal innate immunity are underexplored. Fungal pathogens can cause invasive and life-threatening disease, and the incidence of invasive fungal disease and antifungal resistance has increased in recent decades. In particular, Candida albicans is a commensal colonizer of human mucosal epithelia and opportunistic pathogen that can cause bloodstream infections with a high mortality rate. C. albicans infections were recently estimated to cause nearly a million deaths per year. As phagocytic cells are crucial to protect against systemic C. albicans infection, understanding regulators of the antifungal functions of phagocytes will be crucial for development of host-targeted therapeutic strategies to treat fungal disease. This proposal aims to address the regulation of membrane contact sites in macrophages and their roles in antifungal innate immunity. Preliminary data providing rationale for this proposal include that the ER stress sensor IRE1α coordinates membrane contact sites between the ER and endocytic vesicles to promote phagosomal calcium flux shortly after phagocytosis of C. albicans. This phagosomal calcium flux supports phagosome maturation, fungal killing, and the degradative capacity of macrophages. Additionally, IRE1α coordinates mitochondrial stress responses during C. albicans infection. Mitochondrial stress responses are known regulators of host responses to viral and bacterial infection but are poorly understood in antifungal innate immunity. These findings suggest crucial roles for membrane contact sites in antifungal innate immunity, although there is a fundamental gap in our understanding of the regulators of organelle dynamics and how they coordinate antifungal responses. Therefore, Aim 1 will characterize regulators of phagosomal calcium flux and its roles in fungal infection and the degradative capacity of phagolysosomes. Aim 2 will investigate the role of ER-mitochondria contact sites and mitochondrial stress responses in fungal infection. The mentored phase of this award is supported by a comprehensive training plan that will provide necessary training in quantitative and super-resolution imaging and bioinformatics. The candidate’s background in innate immunology, molecular biology, and host-pathogen interactions will be unified by mentors with expertise in cell biology, fungal genetics and pathogenesis, and bioinformatics. The overall outcome of the proposed research will be to uncover new roles for organellar interactions in antifungal innate immunity, revealing key molecular regulators of macrophage antifungal responses and potential targets for therapeutic intervention. This research will also yield fundamental understanding of the cellular processes of phagocytic cells and their ability to contain rapidly growing pathogens. Project Number: 1K99AI184677-01A1 | Fiscal Year: 2026 | NIH Institute/Center: National Institute of Allergy and Infectious Diseases (NIAID) | Principal Investigator: Michael McFadden | Institution: UNIVERSITY OF MICHIGAN AT ANN ARBOR, ANN ARBOR, MI | Award Amount: $194,400 | Activity Code: K99 | Study Section: Special Emphasis Panel[ZRG1 IIDA-N (82)] View on NIH RePORTER: https://reporter.nih.gov/project-details/1K99AI18467701A1