Phagocytosis of melanized Aspergillus conidia by macrophages exerts cytoprotective effects by sustained PI3K/Akt signalling

Abstract

SummaryHost cell death is a critical component of innate immunity and often determines the progression and outcome of infections. The opportunistic human pathogen Aspergillus fumigatus can manipulate the immune system either by inducing or by inhibiting host cell apoptosis dependent on its distinct morphological form. Here, we show that conidia of Aspergillus ssp. inhibit apoptosis of macrophages induced via the intrinsic (staurosporine) and extrinsic (Fas ligand) pathway. Hence, mitochondrial cytochrome c release and caspase activation were prevented. We further found that the anti-apoptotic effect depends on both host cell de novo protein synthesis and phagocytosis of conidia by macrophages. Moreover, sustained PI3K/Akt signalling in infected cells is an important determinant to resist apoptosis. We demonstrate that pigmentless pksP mutant conidia of A. fumigatus failed to trigger protection against apoptosis and provide evidence that the sustained survival of infected macrophages depends on the presence of the grey-green conidial pigment consisting of dihydroxynaphthalene-melanin. In conclusion, we revealed a novel potential function of melanin in the pathogenesis of A. fumigatus. For the first time, we show that melanin itself is a crucial component to inhibit macrophage apoptosis which may contribute to dissemination of the fungus within the host.

Fungal Morphogenesis

“…In Aspergillus fumigatus, both hydrophobins and melanin coat the conidial surface to help the cell type evade host detection and remain protected within host phagolysosomes (Aimanianda et al 2009;Volling et al 2011;Carrion et al 2013). On germination and hyphal growth, cell wall protein CspA is unmasked, helping to mitigate hyphal damage induced by neutrophils (Levdansky et al 2010).…”

Surface Structure Characterization of Aspergillus fumigatus Conidia Mutated in the Melanin Synthesis Pathway and Their Human Cellular Immune Response

“…In airborne fungal spores, melanin helps in invasion of the host (3,4) and contributes to the virulence of fungal pathogens (5,6). Fungi produce different types of melanin: dihydroxynaphthalene (DHN)-melanin, pyomelanin, and DOPA-melanin.…”

“…Six genes have been identified in this cluster, and their functions were elucidated ( Fig. 1) (4)(5)(6)(12)(13)(14). PKSP (ALB1; AFUA_2G17600) is the first gene of the pathway and codes for a polyketide synthase, which is responsible for catalyzing the synthesis of the heptaketide naphthopyrone from acetyl coenzyme A (acetyl-CoA) and malonyl-CoA.…”

“…The role of the conidial melanin in the A. fumigatus virulence has been studied by using either melanin ghosts or the pigmentless mutant, wherein the PKSP gene, which encodes a protein involved in the first step of melanin biosynthesis, has been deleted (4,9,(16)(17)(18)(19), These reports demonstrated that melanin protects the conidia against reactive oxygen species, masks the recognition of various A. fumigatus pattern-associated molecular patterns, inhibits macrophage apoptosis and phagolysosome fusion, and attenuates the host immune response. All of these functions of melanin contribute to the increased survival of conidia in macrophages and promote the dissemination of A. fumigatus within the host.…”

Effects of LPLI on microglial phagocytosis in LPS-induced neuroinflammation model

“…23 To address whether Rac1 activation is mediated by PI3K/Akt signaling pathway, LPS-activated BV-2 cells were pre-treated with wortmannin, which covalently inactivates the PI3K catalytic site, and API-2, an Akt inhibitor. As shown in Fig.…”