The Transcriptional Response of Cryptococcus neoformans to Ingestion by Acanthamoeba castellanii and Macrophages Provides Insights into the Evolutionary Adaptation to the Mammalian Host

Abstract

Virulence of Cryptococcus neoformans for mammals, and in particular its intracellular style, was proposed to emerge from evolutionary pressures on its natural environment by protozoan predation, which promoted the selection of strategies that allow intracellular survival in macrophages. In fact, Acanthamoeba castellanii ingests yeast cells, which then can replicate intracellularly. In addition, most fungal factors needed to establish infection in the mammalian host are also important for survival within the amoeba. To better understand the origin of C. neoformans virulence, we compared the transcriptional profile of yeast cells internalized by amoebae and murine macrophages after 6 h of infection. Our results showed 656 and 293 genes whose expression changed at least 2-fold in response to the intracellular environments of amoebae and macrophages, respectively. Among the genes that were found in both groups, we focused on open reading frame (ORF) CNAG_05662, which was potentially related to sugar transport but had no determined biological function. To characterize its function, we constructed a mutant strain and evaluated its ability to grow on various carbon sources. The results showed that this gene, named PTP1 (polyol transporter protein 1), is involved in the transport of 5-and 6-carbon polyols such as mannitol and sorbitol, but its presence or absence had no effect on cryptococcal virulence for mice or moth larvae. Overall, these results are consistent with the hypothesis that the capacity for mammalian virulence originated from fungus-protozoan interactions in the environment and provide a better understanding of how C. neoformans adapts to the mammalian host.

The Intracellular Life ofCryptococcus neoformans

“…These challenges are counteracted by equally powerful mechanisms on the yeast side. Upon ingestion, the yeast upregulates gene expression of oxidative stress enzymes (80), starvation responses, and the autophagic machinery (81). These collaborate with the antioxidant properties of fungal melanin and the capsule to efficiently protect the fungus from host attack.…”

Fungal Pathogens: Survival and Replication within Macrophages

“…The natural environment for Cryptococcus species is soil, which is often rich in predatory amoebae that use phagocytosis to engulf cryptococcal spores as a food source. Thus, a compelling hypothesis is that cryptococci have evolved mechanisms to avoid amoebal predation and that these survival attributes are therefore transferable when spores find their way into a vertebrate host (Steenbergen et al 2001;Derengowski et al 2013). The bacterial organism that causes legionnaires disease, Legionella pneumophilia, is thought to have evolved in a similar way (Smith and May 2013).…”

Macrophage–Cryptococcus Interactions: An Update

“…Indeed, C. neoformans gene expression following ingestion by amoeba and macrophages reveals similar patterns of gene expression (39). In fact, multiple stress gene response elements are linked to Cryptococcus -specific environmental sensors and function through common kinase signaling pathways.…”