Defects in Conidiophore Development and Conidium-Macrophage Interactions in a Dioxygenase Mutant of Aspergillus fumigatus

Abstract

Oxygenated fatty acids, or oxylipins, play an essential role in physiological signaling and developmental processes in animals, plants, and fungi. Previous characterization of three Aspergillus fumigatus dioxygenases (PpoA, PpoB, and PpoC), similar in sequence to mammalian cyclooxygenases, showed that PpoA is responsible for the production of the oxylipins 8R-hydroperoxyoctadecadienoic acid and 5S,8R-dihydroxy-9Z,12Z-octadecadienoic acid and that PpoC is responsible for 10R-hydroxy-8E,12Z-hydroperoxyoctadecadienoic acid. Here, ⌬ppo mutants were characterized to elucidate the role of fungal dioxygenases in A. fumigatus development and host interactions. The ⌬ppoC strain displayed distinct phenotypes compared to those of other ⌬ppo mutants and the wild type, including altered conidium size, germination, and tolerance to oxidative stress as well as increased uptake and killing by primary alveolar macrophages. These experiments implicate oxylipins in pathogen development and suggest that ⌬ppoC represents a useful model for studying the A. fumigatus-host interaction.Aspergillus species are soil-dwelling, saprophytic fungi and opportunistic pathogens that cause a variety of diseases in plants and animals. One of the most devastating pulmonary diseases caused by Aspergillus fumigatus is invasive aspergillosis, cases of which have steadily increased over the past several decades due in part to the increased number of immunocompromised people, the use of immunosuppressive agents, and surveillance; associated mortality rates from IA range from 40% to 90% (8,9,10,15). In addition to difficulties associated with diagnosis and treatment, the pathogenesis and development of A. fumigatus remain poorly understood.Several recent studies implicated a role for oxylipins, oxygenated fatty acid derivatives, in host interactions and fungal development (19,23). Oxylipins are generated by various oxygenases, including linoleate dioxygenases, the related prostaglandin synthases or cyclooxygenases, and lipoxygenases (4). These metabolites are often associated with sporulation processes for a number of fungal genera including Aspergillus (2, 26), Alternaria (6), Sclerotinia (7), and Neurospora (14, 17). For example, the deletion of all three Aspergillus nidulans ppo genes resulted in alterations in sporulation patterns, primarily in altering the ratio of asexual spore development to sexual spore development in this species. Exogenous exposure to purified oxylipins also engenders similar developmental processes in A. nidulans, thus supporting a direct role for oxylipins as sporulation signals (2). In addition, there is strong support for oxylipin-mediated cross-kingdom signaling between interacting organisms (1, 2, 5).In fungi, the oxylipin biosynthetic pathway is best understood in A. nidulans, where three dioxygenases (PpoA, PpoB, and PpoC) with amino acid sequence homology to mammalian cyclooxygenases have been genetically and biochemically defined (22,24,25,26). Biochemical analyses of A. nidulans and A. fumigatus ppo mutants revealed ...

Pathogenesis ofAspergillus fumigatusin Invasive Aspergillosis

“…An unrelated mutant of oxylipin biosynthesis, in which the three cyclooxygenase genes in A. fumigatus were silenced by RNA interference, also demonstrated increased virulence correlating with increased resistance to H 2 O 2 (208). The individual deletion of the cyclooxygenase genes did not yield an increase in virulence, although a loss of one gene, ppoC, resulted in greater resistance to H 2 O 2 as well as aberrant conidium morphology and increased phagocytosis by macrophages (49). Finally, the deletion of the glycosylphosphatidylinositol-anchored protein ECM33 resulted in a hypervirulent strain with increased germination and resistance to cell wall-destabilizing agents (174).…”

Distinct Roles for VeA and LaeA in Development and Pathogenesis ofAspergillus flavus

“…LaeA is a key determinant in aspergillosis caused by A. fumigatus and seed rot by A. flavus (3,21), and Ppo loss impacts virulence attributes of A. fumigatus (11,40), A. nidulans (39), and A. flavus (19). Considering the interdependence of oxylipin function with VeA coupled with the VeA-LaeA interaction, we postulated that VeA mutants would also be impaired in seed pathogenesis in a manner similar to that of LaeA mutants and, furthermore, that both mutants could be affected in density-dependent development.…”

Leucine/Valine Residues Direct Oxygenation of Linoleic Acid by (10R)- and (8R)-Dioxygenases

“…Recent gene deletion studies suggest that 10R-DOX of A. fumigatus can affect germination, the size of conidia, and influence the pathogenicity in cellular models of aspergillosis (4,6,39). Oxygenation of 20:4n-6 by 10R-DOX is of interest in this context.…”