Cryptococcus neoformanssecretes small molecules that inhibit IL-1β inflammasome-dependent secretion

Abstract

30Cryptococcus neoformans is an encapsulated yeast that causes disease mainly in 31 immunosuppressed hosts. It is considered a facultative intracellular pathogen because 32 of its capacity to survive and replicate inside phagocytes, especially macrophages. This 33 capacity is heavily dependent on various virulence factors, particularly the 34 glucuronoxylomannan (GXM) component of the polysaccharide capsule, that render the 35 non-or poorly-activated macrophage ineffective against phagocytosed yeast. Strategies 36 utilized by macrophages to prevent this scenario include pyroptosis (a rapid highly 37 inflammatory cell death) and vomocytosis (the expulsion of the pathogen from the 38 intracellular environment without lysis). Inflammasome activation in phagocytes is 39 usually protective against fungal infections, including cryptococcosis. Nevertheless, 40 recognition of C. neoformans by inflammasome receptors requires specific changes in 41 morphology or the opsonization of the yeast, impairing a proper inflammasome 42 function. In this context, we analyzed the impact of molecules secreted by C. 43 neoformans B3501 strain and its acapsular mutant Δcap67 in an inflammasome 44 activation in vitro model. Our results showed that conditioned media derived from 45 B3501 was capable of inhibiting inflammasome dependent events (i. e. IL-1β secretion 46 and LDH release via pyroptosis) more strongly than conditioned media from Δcap67, 47 57 58 59 2 60 Author's Summary 61Cryptococcus neoformans is the agent of cryptococcal meningitis, a disease that 62 can be life-threatening in immunocompromised hosts such as those infected with HIV. 63 The infection thrives in hosts that poorly activate their immune system, mainly because 64 of the yeast´s ability to survive inside macrophages and migrate towards the central 65 nervous system. Emerging data indicate that cryptococci modulate the host immune 66 response, but the underlying mechanisms remain largely uncharacterized. Here we 67 show that secreted molecules from a wild-type strain of C. neoformans impair 68 inflammatory responses driven by inflammasome activation, which in turn impact the 69 macrophage antifungal activity. We further show that this inhibition does not involve 70 GXM, the main constituent of the fungal capsule, but rather is partially dependent on 71 DL-Indole-3-lactic acid (ILA), a metabolite not previously implicated in fungal virulence. 72 73

Small molecule analysis of extracellular vesicles produced byCryptococcus gattii: identification of a tripeptide controlling cryptococcal infection in an invertebrate host model

“…The knowledge of the functions of fungal EVs has continuously increased in the recent years (7), but the biological roles of low mass structures exported in EVs are unknown. Small molecules secreted by Cryptococcus are immunologically active and affect IL-1β inflammasome-dependent secretion (24), but their association with EVs has not been established. In our study, we aimed at proving the concept that biologically active small molecules are exported in cryptococcal EVs.…”