Trehalose-6-phosphate is required for metabolism and virulence in the human fungal pathogen Aspergillus fumigatus
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High mortality rates associated with Invasive Pulmonary Aspergillosis (IPA), commonly caused by the mold Aspergillus fumigatus, have dramatically increased in immunocompromised patients during the past 30 years. With limited antifungal drugs available and inconsistent outcomes associated with current antifungal drug treatment, much effort is being focused on new antifungal drug development. A. fumigatus has evolved multifactorial mechanisms to survive various stress conditions encountered in environment and in vivo during infection. Targeting the biochemical pathways utilized by the fungus to adapt to stress conditions is one proposed approach for development of new antifungal drugs. Biosynthesis of the disaccharide trehalose is one such target that is not found in mammals. This dissertation aimed to characterize the role of the trehalose biosynthesis pathway in the biology and virulence of A. fumigatus. My objectives were to identify the function of putative enzyme encoding genes involved in the TPS1/TPS2 pathway and establish the contribution of each protein to the virulence of A. fumigatus in clinically relevant IPA murine models. My data suggests that the Trehalose-6-phosphate intermediate of the TPS1/TPS2 pathway plays a critical role in regulating fungal metabolic homeostasis and integrity of fungal cell wall. A mutant deficient in the TPS2 ortholog, OrlA, displayed increased sensitivity to cell wall perturbing drugs and importantly was attenuated in virulence in two murine models of IPA. My data further suggests that the attenuated virulence phenotype is directly linked to these changes in the fungal cell wall that alter the innate immune response to this fungal strain. In contrast, trehalose itself while having a general role in stress protection does not have a role in virulence in IPA models. Finally, my data suggest intricate links between the mobilization of trehalose and accumulation of T6P that also affect fungal metabolism and cell wall homeostasis via the activity of trehalose phosphorylase enzymes. In conclusion, my data supports the hypothesis that the trehalose biosynthesis pathway is a potential target for antifungal drug development in A. fumigatus particularly at the level of TPS2 activity. However, the underlying host immune status must also be taken into account when targeting this key fungal metabolic pathway.