Invasion of the Central Nervous System by Cryptococcus neoformans Requires a Secreted Fungal Metalloprotease

Abstract

Cryptococcus spp. cause life-threatening fungal infection of the central nervous system (CNS), predominantly in patients with a compromised immune system. Why Cryptococcus neoformans has this remarkable tropism for the CNS is not clear. Recent research on cerebral pathogenesis of C. neoformans revealed a predominantly transcellular migration of cryptococci across the brain endothelium; however, the identities of key fungal virulence factors that function specifically to invade the CNS remain unresolved. Here we found that a novel, secreted metalloprotease (Mpr1) that we identified in the extracellular proteome of C. neoformans IMPORTANCE Cryptococcus neoformans is a medically relevant fungal pathogen causing significant morbidity and mortality, particularly in immunocompromised individuals. An intriguing feature is its strong neurotropism, and consequently the hallmark of cryptococcal disease is a brain infection, cryptococcal meningoencephalitis. For C. neoformans to penetrate the central nervous system (CNS), it first breaches the blood-brain barrier via a transcellular pathway; however, the identities of fungal factors required for this transmigration remain largely unknown. In an effort to identify extracellular fungal proteins that could mediate interactions with the brain endothelium, we undertook a proteomic analysis of the extracellular proteome and identified a secreted metalloprotease (Mpr1) belonging to the M36 class of fungalysins. Here we found that Mpr1 promotes migration of C. neoformans across the brain endothelium and into the CNS by facilitating attachment of cryptococci to the endothelium surface, thus underscoring the critical role of M36 proteases in fungal pathogenesis.

High-Resolution Genetics Identifies the Lipid Transfer Protein Sec14p as Target for Antifungal Ergolines

“…neoformans is the most common cause of fungal meningitis (reviewed in [47], and the invasion of the central nervous system by C . neoformans is strictly dependent on the secretion of proteins like phospholipase B1 (Plb1) [11], the metalloprotease Mpr1 [48], building blocks of the capsule, and enzymes involved in the assembly, maintenance and integrity of the cell wall as well as other proteins [12] [49]. Protein traffic and secretion in C .…”

Cryptococcus: from environmental saprophyte to global pathogen

“…First, the Cryptococcus cells could force their way between the tight junctions of the endothelial cells in a process known as , by using proteases such as Mpr1 to promote transendothelial migration 55 (FIG. 2).…”

Virulence-Associated Enzymes of Cryptococcus neoformans

“…Proteases play important roles in host cell penetration and virulence of C. neoformans (112). Recently, a metalloprotease was identified by proteomic analyses of the extracellular proteins from C. neoformans and found to be required for invasion of the central nervous system in murine infection of C. neoformans (113). Moreover, the metalloprotease knockout (mpr1⌬) strain was unable to cross the endothelium in an in vitro model of the human blood-brain barrier (113).…”