Reducing Aspergillus fumigatus Virulence through Targeted Dysregulation of the Conidiation Pathway

Abstract

Inhalation of conidia of the opportunistic mold <i>Aspergillus fumigatus</i> by immunocompromised hosts can lead to invasive pulmonary disease. Inhaled conidia that escape immune defenses germinate to form filamentous hyphae that invade lung tissues. Conidiation rarely occurs during invasive infection of the human host, allowing the bulk of fungal energy to be directed toward vegetative growth. We hypothesized that forced induction of conidiation during infection can suppress <i>A. fumigatus</i> vegetative growth, impairing the ability of this organism to cause disease. To study the effects of conidiation pathway dysregulation on <i>A. fumigatus</i> virulence, a key transcriptional regulator of conidiation (<i>brlA</i>) was expressed under the control of a doxycycline-inducible promoter. Time- and dose-dependent <i>brlA</i> overexpression was observed in response to doxycycline both <i>in vitro</i> and <i>in vivo.</i> Exposure of the inducible <i>brlA</i> overexpression strain to low doses of doxycycline under vegetative growth conditions <i>in vitro</i> induced conidiation, whereas high doses arrested growth. Overexpression of <i>brlA</i> attenuated <i>A. fumigatus</i> virulence in both an invertebrate and mouse model of invasive aspergillosis. RNA sequencing studies and phenotypic analysis revealed that <i>brlA</i> overexpression results in altered cell signaling, amino acid, and carbohydrate metabolism, including a marked upregulation of trehalose biosynthesis and a downregulation in the biosynthesis of the polysaccharide virulence factor galactosaminogalactan. This proof of concept study demonstrates that activation of the conidiation pathway in <i>A. fumigatus</i> can reduce virulence and suggests that <i>brlA</i>-inducing small molecules may hold promise as a new class of therapeutics for <i>A. fumigatus</i> infection.<b>IMPORTANCE</b> The mold <i>Aspergillus fumigatus</i> reproduces by the production of airborne spores (conidia), a process termed conidiation. In immunocompromised individuals, inhaled <i>A. fumigatus</i> conidia can germinate and form filaments that penetrate and damage lung tissues; however, conidiation does not occur during invasive infection. In this study, we demonstrate that forced activation of conidiation in filaments of <i>A. fumigatus</i> can arrest their growth and impair the ability of this fungus to cause disease in both an insect and a mouse model of invasive infection. Activation of conidiation was linked to profound changes in <i>A. fumigatus</i> metabolism, including a shift away from the synthesis of polysaccharides required for cell wall structure and virulence in favor of carbohydrates used for energy storage and stress resistance. Collectively, these findings suggest that activation of the conidiation pathway may be a promising approach for the development of new agents to prevent or treat <i>A. fumigatus</i> infection.