bioRxiv2022
The encapsulated fungus Cryptococcus neoformans is the most common cause of fungal meningitis, with the highest rate of disease in patients with AIDS or immunosuppression. This microbe enters the human body via inhalation of infectious particles. C. neoformans capsular polysaccharide, in which the major component is glucuronoxylomannan (GXM), extensively accumulates in tissues and compromises host immune responses. C. neoformans travels from the lungs to the bloodstream and crosses to the brain via transcytosis, paracytosis, or inside of phagocytes using a "Trojan horse" mechanism. The fungus causes life-threatening meningoencephalitis with high mortality rates. Hence, we investigated the impact of intranasal exogenous GXM administration on C. neoformans infection in C57BL/6 mice. GXM enhances cryptococcal pulmonary infection and facilitates fungal systemic dissemination and brain invasion. Pre-challenge of GXM results in detection of the polysaccharide in lungs, serum, and surprisingly brain, the latter likely reached through the nasal cavity. GXM significantly alters endothelial cell tight junction protein expression in vivo, suggesting significant implications for the C. neoformans mechanisms of brain invasion. Using a microtiter transwell system, we showed that GXM disrupts the trans-endothelial electrical resistance, weakening the human brain endothelial cell monolayers co-cultured with pericytes, supportive cells of blood vessels/capillaries found in the blood-brain barrier (BBB), and promotes C. neoformans BBB penetration. Our findings should be considered in the development of therapeutics to combat the devastating complications of cryptococcosis that results in an estimated [~]200,000 deaths worldwide each year. AUTHOR SUMMARYCryptococcus neoformans infection of the central nervous system (CNS) typically begins by inhalation of fungal spores and results in devastating mortality rates worldwide. Over 200,000 deaths have been reported annually, with cryptococcal meningoencephalitis being the most severe form of the disease. This study investigates the ability of the fungus to invade, colonize, and cause damage to the host through properties of the fungal polysaccharide capsule, which allows the microbe a variety of both protective and offensive abilities. This capsule, made primarily of the polysaccharide glucuronoxylomannan (GXM), has been implicated in the progression and severity of cryptococcal infection in the CNS. We determined that GXM increases the fungal burden in the lungs of mice and enhances fungal migration to the brain. Interaction of GXM with the blood-brain barrier, which is a protective structure that regulates movement of particles into the CNS, demonstrated that GXM can disrupt the integrity of this barrier, compromising the delicate balances of fluids, immune cells, and other factors vital to the maintenance of the CNS. The findings of this study reveal the substantial role of GXM in establishing C. neoformans infection in the brain and necessitate future studies to further understand these interactions.