The Cryptococcal Enzyme Inositol Phosphosphingolipid-Phospholipase C Confers Resistance to the Antifungal Effects of Macrophages and Promotes Fungal Dissemination to the Central Nervous System

Abstract

In recent years, sphingolipids have emerged as critical molecules in the regulation of microbial pathogenesis. In fungi, the synthesis of complex sphingolipids is important for the regulation of pathogenicity, but the role of sphingolipid degradation in fungal virulence is not known. Here, we isolated and characterized the inositol phosphosphingolipid-phospholipase C1 (ISC1) gene from the fungal pathogen Cryptococcus neoformans and showed that it encodes an enzyme that metabolizes fungal inositol sphingolipids. Isc1 protects C. neoformans from acidic, oxidative, and nitrosative stresses, which are encountered by the fungus in the phagolysosomes of activated macrophages, through a Pma1-dependent mechanism(s). In an immunocompetent mouse model, the C. neoformans ⌬isc1 mutant strain is almost exclusively found extracellularly and in a hyperencapsulated form, and its dissemination to the brain is remarkably reduced compared to that of control strains. Interestingly, the dissemination of the C. neoformans ⌬isc1 strain to the brain is promptly restored in these mice when alveolar macrophages are pharmacologically depleted or when infecting an immunodeficient mouse in which macrophages are not efficiently activated. These studies suggest that Isc1 plays a key role in protecting C. neoformans from the intracellular environment of macrophages, whose activation is important for preventing fungal dissemination of the ⌬isc1 strain to the central nervous system and the development of meningoencephalitis.

Isc1p Plays a Key Role in Hydrogen Peroxide Resistance and Chronological Lifespan through Modulation of Iron Levels and Apoptosis

“…Isc1p deficiency increased H 2 O 2 -and aginginduced intracellular oxidation, protein carbonylation, and lipid peroxidation. In agreement, Isc1p protects the fungus Cryptococcus neoformans from the oxidative stress environment of macrophages (Shea et al, 2006). Interestingly, isc1⌬ cells accumulate IPC and M(IP) 2 C (Sawai et al, 2000), and other yeast mutants showed an inverse correlation between oxidative stress resistance or chronological lifespan and M(IP) 2 C levels (Aerts et al, 2006).…”

Chemokine Receptor 2-Mediated Accumulation of Fungicidal Exudate Macrophages in Mice That Clear Cryptococcal Lung Infection

“…21 The intracellular sequestra-tion of viable cryptococci within AMs contributes to propagation of infection during the pre-effector phase of the host response [approximately 0 -14 days post-infection (dpi)]. [25][26][27][28][29] Yet, AMs also protect against deleterious and ineffective inflammation before the onset of adaptive immunity. 30 Previous studies 31,32 identified macrophage accumulation in the lungs of cryptococcal-infected mice during the effector phase (approximately 14 -28 dpi) of the host response.…”

Sphingolipids from the human fungal pathogen Aspergillus fumigatus

“…In contrast, the deletion of ISC1, coding for an inositol phosphosphingolipid-phospholipase C, enhances the sensitivity of yeast to oxidative stresses and to acidic environments. In a mouse model of cryoptococcosis in immunocompetent mice, ΔISC1 mutant are less virulent and more sensitive to phagolysosome stress inside the macrophage, showing the importance of IPC structures in fungal pathobiology [80]. These data show that both fungal types of SPL, GlcCer and IPC, are required for the resistance to host environment.…”