Phospholipase B is critical for Cryptococcus neoformans survival in the central nervous system

Abstract

Cryptococcus neoformans (Cn) is an opportunistic, encapsulated, yeast-like fungus that causes severe meningoencephalitis, especially in countries with high HIV prevalence. In addition to its well-known polysaccharide capsule, Cn has other virulence factors such as phospholipases, a heterogeneous group of enzymes that hydrolyze ester linkages in glycerophospholipids. Phospholipase B (PLB1) has been demonstrated to play a key role in Cn pathogenicity. In this study, we used a PLB1 mutant (plb1) and its reconstituted strain (Rec1) to assess the importance of this enzyme on Cn brain infection in vivo and in vitro. Mice infected with plb1 strain survive significantly longer, have lower central nervous system (CNS) fungal load, and fewer and smaller cryptococcomas or biofilm-like brain lesions compared to H99- and Rec1-infected animals. plb1 cryptococci are significantly more phagocytosed and killed by NR-9460 microglia-like cells. plb1 cells have altered capsular polysaccharide biophysical properties that impair their ability to stimulate glia cell responses or morphological changes. We provide significant evidence demonstrating that Cn phospholipase is an important virulence factor for fungal colonization of and survival in the CNS as well as in the progression of cryptococcal meningitis. These findings may potentially help fill in a gap of knowledge in our understanding of cerebral cryptococcosis and may provide novel research avenues in Cn pathogenesis. IMPORTANCECryptococcal meningoencephalitis is a serious disease caused by infection of the neurotropic fungal pathogen Cryptococcus neoformans (Cn). Due to the increasing number of cases in HIV-infected individuals, as well as the limited therapies available, investigation into potential targets for new therapeutics has become critical. Phospholipase B (PLB1) is an enzyme synthesized by Cn that confers virulence to the fungus through capsular enlargement, immunomodulation, and intracellular replication. In this study, we examined the properties of PLB1 by comparing infection of Cn PLB1 mutant strain with both the wild-type and a PLB1 reconstituted strain. We show that PLB1 augments the survival and proliferation of the fungus in the CNS and strengthens virulence through modulation of the immune response and enhancement of specific biophysical properties of the fungus. The implications of PLB1 inhibition reveal its involvement in Cn infection and suggest that it may be a possible molecular target in the development of antifungal therapies. The results of this study support additional investigation into the mechanism of PLB1 to further understand the intricacies of Cn infection.