Ada2 acts upstream of Pdr802 in regulating macrophage-enhanced virulence of Cryptococcus neoformans.

Cryptococcus is the leading cause of fungal meningitis in humans and a major source of mortality in people living with HIV. Infection starts in the lungs and results in meningoencephalitis after dissemination via the bloodstream. Alveolar macrophages are the first immune cells to encounter the infection and are usually capable of clearing it. In immunocompromised hosts, Cryptococcus survives and grows inside macrophages, establishing pulmonary and ultimately central nervous system infection. The initial interaction with macrophages is a key event in pathogenesis, and we have demonstrated that macrophage exposure induces an enhanced virulence phenotype in Cryptococcus. This process can be replicated in vitro: yeast cells exposed to macrophages in culture demonstrate enhanced virulence in both zebrafish and mouse models. To understand this induction process, we investigated its effect on the cryptococcal transcriptome to determine what cryptococcal factors are required. Ada2 is a subunit of the transcription modulating Spt-Ada-Gcn5-acetyltransferase complex and is required for cryptococcal virulence. We find that a cryptococcal strain lacking Ada2 is not capable of enhanced virulence after macrophage exposure. We further show that Pdr802, a transcription factor with a significant but poorly understood role in cryptococcal pathogenesis, acts downstream of Ada2 during macrophage exposure, and loss of Pdr802 function is sufficient to block macrophage-enhanced virulence. These findings shed light on the earliest stages of cryptococcal pathogenesis and offer new clues to the functions of Pdr802.IMPORTANCECryptococcus is a fungal pathogen affecting mostly immunocompromised people, especially those with HIV. Infection starts in the lungs but ultimately disseminates to cause meningitis, leading to over 50% mortality in patients with AIDS. Cryptococcal meningitis is difficult to treat, and understanding the early stages of infection will be the first step toward preventing it. Lung macrophages are the first immune cells to encounter Cryptococcus, and while they clear the infection in some cases, in immunocompromised patients, they instead serve as a niche for cryptococcal growth. How can macrophage interaction promote infection? We have shown that in a susceptible host, cryptococcal virulence is increased after initial contact with macrophages. This effect can be replicated in vitro, as cryptococcal cells pre-exposed to cultured macrophages are more virulent in animal models. We have identified two cryptococcal genes that regulate this change in virulence, setting the stage for a better understanding of cryptococcal pathogenesis.

Duke Scholars

Author James Davis Medicine, General Internal Medicine