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2016 ; 7
(2
): e02242
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Gliotoxin Suppresses Macrophage Immune Function by Subverting
Phosphatidylinositol 3,4,5-Trisphosphate Homeostasis
#MMPMID27048806
Schlam D
; Canton J
; Carreņo M
; Kopinski H
; Freeman SA
; Grinstein S
; Fairn GD
mBio
2016[Apr]; 7
(2
): e02242
PMID27048806
show ga
Aspergillus fumigatus, an opportunistic fungal pathogen, spreads in the
environment by releasing numerous conidia that are capable of reaching the small
alveolar airways of mammalian hosts. In otherwise healthy individuals,
macrophages are responsible for rapidly phagocytosing and eliminating these
conidia, effectively curbing their germination and consequent invasion of
pulmonary tissue. However, under some circumstances, the fungus evades
phagocyte-mediated immunity and persists in the respiratory tree. Here, we report
thatA. fumigatusescapes macrophage recognition by strategically targeting
phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3] metabolism through
gliotoxin, a potent immunosuppressive mycotoxin. Time-lapse microscopy revealed
that, in response to the toxin, macrophages cease to ruffle, undergo abrupt
membrane retraction, and fail to phagocytose large targets effectively. Gliotoxin
was found to prevent integrin activation and interfere with actin dynamics, both
of which are instrumental for phagocytosis; similar effects were noted in
immortalized and primary phagocytes. Detailed studies of the underlying molecular
mechanisms of toxicity revealed that inhibition of phagocytosis is attributable
to impaired accumulation of PtdIns(3,4,5)P3and the associated dysregulation of
downstream effectors, including Rac and/or Cdc42. Strikingly, in response to the
diacylglycerol mimetic phorbol 12-myristate 13-acetate, gliotoxin-treated
macrophages reactivate beta integrins, reestablish actin dynamics, and regain
phagocytic capacity, despite the overt absence of plasmalemmal PtdIns(3,4,5)P3
Together, our findings identify phosphoinositide metabolism as a critical
upstream target of gliotoxin and also indicate that increased diacylglycerol
levels can bypass the requirement for PtdIns(3,4,5)P3signaling during membrane
ruffling and phagocytosis. IMPORTANCE: Aspergillus fumigatusis the most frequent
cause of human infections in theAspergillusgenus. In immunocompromised
populations, invasive aspergillosis (IA) is associated with a mortality rate of
up to 90%, and current antifungal therapies have failed to prevent or reverse the
infection. Therefore, a deeper understanding of the interactions betweenA.
fumigatusand its host is required. In healthy humans, alveolar macrophages can
ingest and eliminate fungal spores, thus limiting their germination into
mycotoxin-producing hyphae. Our studies reveal that gliotoxin-the most
abundantAspergillusmycotoxin-undermines the ability of phagocytes to carry out
their protective functions. By targeting PtdIns(3,4,5)P3signaling and
downregulating phagocytic immune defenses, the toxin could also exacerbate
polymicrobial infections. Notably, we were able to reverse gliotoxin toxicity by
addition of diacylglycerol analogues, which may provide the basis for therapeutic
interventions.