Faster Cryptococcus Melanization Increases Virulence in Experimental and Human Cryptococcosis

Abstract

Cryptococcus spp. are human pathogens that cause 181,000 deaths per year. In this work, we systematically investigated the virulence attributes of Cryptococcus spp. clinical isolates and correlated them with patient data to better understand cryptococcosis. We collected 66 C. neoformans and 19 C. gattii clinical isolates and analyzed multiple virulence phenotypes and host–pathogen interaction outcomes. C. neoformans isolates tended to melanize faster and more intensely and produce thinner capsules in comparison with C. gattii. We also observed correlations that match previous studies, such as that between secreted laccase and disease outcome in patients. We measured Cryptococcus colony melanization kinetics, which followed a sigmoidal curve for most isolates, and showed that faster melanization correlated positively with LC3-associated phagocytosis evasion, virulence in Galleria mellonella and worse prognosis in humans. These results suggest that the speed of melanization, more than the total amount of melanin Cryptococcus spp. produces, is crucial for virulence.

What’s New in Cryptococcus gattii: From Bench to Bedside and Beyond

“…Capsule size correlates with virulence, although not case-fatalit [ 61 ]. Notably, C. gattii seems to have a greater propensity to form titan cells [ 62 ].…”

“…C. gattii melanise more slowly than C. neoformans [ 61 ]. Melanin modulates susceptibility to amphotericin and fluconazole [ 61 ], and the speed of melanisation may correlate with virulence and subsequent morbidity and mortality, making this another important avenue of investigation into differences in disease phenotype between the species. It is important to note that there is no evidence showing a relationship between susceptibility and treatment outcome.…”

“We've got to get out”—Strategies of human pathogenic fungi to escape from phagocytes

“…In general, it stops the LC3‐associated phagocytosis (LAP) pathway by blocking the assembly of the NADPH oxidase, and inhibits the progression of phagolysosome formation. This has so far been shown for A. fumigatus (Akoumianaki et al, 2016), Rhizopus oryzae (Andrianaki et al, 2018), and C. neoformans (de Sousa et al, 2022), but is proposed to be true for all melanized fungi (Chamilos et al, 2016). At least in part, this is attributed to its ability to sequester the signaling molecule, calcium (Kyrmizi et al, 2018).…”

The emerging role of extracellular vesicles in fungi: a double-edged sword

“…These EVs could also induce an immune response on macrophages, to escape intracellular restriction ( Zhang et al, 2021 ). Cryptococcus gattii promoted intracellular multiplication in macrophages, by secreting EVs and disseminating virulence factors (such as melanin, laccase, and podoconjugates) into the host ( Goulart et al, 2010 ; De Sousa et al, 2022 ). Malassezia released EVs that induced IL-4 and TNF-α reactions in peripheral blood mononuclear cells (PBMCs; Gehrmann et al, 2011 ).…”

“…Likewise, it can multiply within macrophages, in a process associated with intracellular replication and cytoplasmic accumulation of polysaccharide-containing vesicles ( Goulart et al, 2010 ). Cryptococcus EVs have multiple biological roles related to the transport of various important virulence molecules, such as melanin, laccase, podoconjugates, and others ( De Sousa et al, 2022 ). Genes coding for proteins involved in vesicle formation and transport may be associated with virulence.…”