The Role of Testosterone and Gibberellic Acid in the Melanization of Cryptococcus neoformans

Jamila S Tucker,Erin E Mcclelland,Tiffany E Guess

doi:10.3389/fmicb.2020.01921

Abstract

Cryptococcus neoformans, a spore-producing pathogenic yeast, affects immunocompromised individuals causing meningoencephalitis. Once C. neoformans is introduced via the respiratory tract, it is engulfed by macrophages and other phagocytes. One of C. neoformans’s primary virulence factors is the pigment melanin, which is formed in the cell wall and protects the yeast against UV radiation and oxidizing agents produced by macrophages during phagocytosis. To better understand the observed sex bias (3:1; male:female) in C. neoformans infections, the phenotype of various virulence factors was determined in the presence of exogenous sex hormones. C. neoformans melanized faster in the presence of testosterone than it did in the presence of estradiol. Using a combination of RNA sequencing analysis and ELISA results, we identified a growth hormone, gibberellic acid (GA), produced in C. neoformans that was highly upregulated in the presence of testosterone. A variety of knockout strains of genes involved in the GA biosynthesis pathway showed significantly reduced melanization in the presence of testosterone. Additionally, inhibitors of GA also reduced melanization in the presence of testosterone. Thus, these data suggest that the gibberellic biosynthesis pathway is involved in melanization in C. neoformans, and the melanization difference observed in the presence of testosterone may be due to increased production of GA, which may partly explain the sex bias observed in C. neoformans infections.

Highlights

Decades of epidemiological data indicate an approximately 3 male:1 female sex bias in C. neoformans infections (Campbell, 1966; Edwards et al, 1970); the reasons for these differences remain controversial (Emmons, 1955)
To determine if testosterone was perhaps a substrate for melanization, cells were grown on plates containing testosterone or estrogen without L-DOPA; the cells did not melanize in the presence of either hormone
To derive quantitative data of this difference, the wild-type H99S C. neoformans strain was grown in liquid L-DOPA medium supplemented with steroid hormones or ethanol as a vehicle control for 5 days

Summary

Introduction

Decades of epidemiological data indicate an approximately 3 male: female sex bias in C. neoformans infections (Campbell, 1966; Edwards et al, 1970); the reasons for these differences remain controversial (Emmons, 1955). Males are more susceptible to primary cutaneous cryptococcosis than females (Du et al, 2015); while a study completed in Australia indicated that immunocompetent males have an increased risk of C. neoformans infections, due to unknown reasons (Chen et al, 2000). This could be due to a T cell deficit in immunocompetent males, as healthy males have lower ex vivo T cell percentages during a C. neoformans infection than females (Guess et al, 2019). To determine if steroid hormones were contributing to this sex difference, we measured virulence factor expression in the presence of these hormones and assayed the phenotype of various virulence factors

Methods

Results

Discussion

Conclusion