Role of environmental iron in Candida albicans cell wall remodeling and its effect on host-pathogen interaction during oropharyngeal candidiasis

Candida albicans exists as a commensal yeast in healthy people while it can cause mucosal and systemic fungal infections including oropharyngeal candidiasis (OPC) in immunocompromised individuals and diabetics. C. albicans has the ability to sense environmental iron as a signal with the help of its signaling pathways, such as Mitogen Activated Protein Kinase (MAPK) Cek1, to modulate gene expression in response to extrinsic iron levels. Recent evidence has shed light on the role of different iron levels between free iron rich gut and free iron deplete blood, allowing C. albicans to choose between a commensal or virulent lifestyle in these respective niches. Nothing is known about how variations in iron levels within the oral cavity will influence virulence during OPC. Our preliminary data shows that iron chelation in murine OPC causes significant reduction in virulence, while iron supplementation leads to greater fungal load in the tongue tissue of the infected mice. We also show how iron communicated with various signaling pathways including C. albicans MAPK Cek1 to modulate the fungal cell wall (CW), thereby affecting response to antifungals (by changing CW component levels) and host immune attack (by affecting exposure of immunogenic β-glucan in the CW). The main goal of this project is to understand the mechanisms behind iron-mediated changes in C. albicans CW that in turn effect the outcome of infection during OPC. Besides, in vitro experiments to address this goal, we will use our murine OPC model and mice will be repleted or depleted in systemic iron levels with iron supplementation (with iron dextran) and iron chelation (with iron chelator Deferasirox), respectively. We will also study mucosal colonization by C. albicans in Caenorhabditis elegans worms with human-like iron disorders, to evaluate fitness of fungal virulence traits directly in host with varying iron levels. Our overall hypothesis is that iron communicates with various signaling pathways to modulate fungal CW, in turn affecting hyphal morphogenesis, drug sensitivity, and susceptibility to host immune response, in OPC. We will test our hypothesis using three specific aims: 1) Define iron-induced signaling mechanisms that modulate C. albicans β-glucan exposure, levels of CW components, and hyphal morphogenesis, 2) Determine how iron affects C. albicans CW remodeling and hyphal morphogenesis during murine OPC to impact antifungal drug susceptibility, and 3) Evaluate how changes in host iron levels modulate innate immune defense mechanisms against C. albicans in vitro, during murine OPC, and in C. elegans. This work will provide insights into how varying iron levels in susceptible populations will affect the outcome of C. albicans infection during OPC.