Clinical and pathological characterization of Central Nervous System cryptococcosis in an experimental mouse model of stereotaxic intracerebral infection

Abstract

Infection of the Central Nervous System (CNS) by the encapsulated fungus Cryptococcus neoformans can lead to high mortality meningitis, most commonly in immunocompromised patients. While the mechanisms by which the fungus crosses the blood-brain barrier to initiate infection in the CNS are well recognized, there are still substantial unanswered questions about the disease progression once the fungus is established in the brain. C. neoformans is characterized by a glucuronoxylomannan (GXM)-rich polysaccharide capsule which has been implicated in immune evasion, but its role during the host CNS infection needs further elucidation. Therefore, the present study aims to examine these key questions about the mechanisms underlying cryptococcal meningitis progression and the impact of fungal GXM release by using an intracerebral rodent infection model via stereotaxic surgery. After developing brain infection, we analyzed distinct brain regions and found that while fungal load and brain weight were comparable one-week post-infection, there were region-specific histopathological (with and without brain parenchyma involvement) and disease manifestations. Moreover, we also observed a region-specific correlation between GXM accumulation and glial cell recruitment. Further, mortality was associated with the presence of subarachnoid hemorrhaging and GXM deposition in the meningeal blood vessels and meninges in all regions infected. Our results show that using the present infection model can facilitate clinical and neuropathological observations during the progression of neurocryptococcosis. Importantly, this mouse model can be used to further investigate disease progression as it develops in humans.

Cryptococcus neoformans rapidly invades the murine brain by sequential breaching of airway and endothelial tissues barriers, followed by engulfment by microglia

“…Bloodstream dissemination of cryptococci is widely accepted, as it is consistent with a diffuse and broad distribution of C. neoformans throughout the brain, in close proximity to blood vessels, observed in in humans post-mortem brains 44,45 and that we and other characterized in murine models 29,30,46 . Additionally, murine studies can detect blood borne cryptococci after intranasal inoculation 22 .…”

“…Expression of an amoeboid morphology is commonly associated with the inflammatory activation of microglia in several pathological processes 55 . This immune activation will likely occur at all stages of infection, as was previously observed in a model of late cryptococcal meningitis, following intracerebral infection of mice 46 . Amoeboid microglia were also observed after Streptococcus pneumoniae infection 56 ; in contrast, ramified microglia are still observed in the first hours after Toxoplasma gondii infection 57 , demonstrating an interplay between neuro-immune response and invading microbe.…”

Glucuronoxylomannan intranasal challenge prior to Cryptococcus neoformans pulmonary infection enhances cerebral cryptococcosis in rodents

“…Likewise, GXM localized in blood vessels in brain parenchyma, and its deposition may have serious implications in the maintenance of the host BBB integrity. Vascular GXM accumulation and fungal occlusion have been described by others [ 52 , 53 ] and validated by us [ 32 ] as responsible of infarction and hemorrhagic dissemination in CME patients and animal models [ 46 ], respectively. Notably, the cortex and hippocampus of GXM-challenged mice were the most affected regions of the brain, suggesting that these animals may also show behavioral and cognitive impairment.…”

“…neoformans capsular GXM is released into tissues during infection where it accumulates and causes a range of adverse immunological effects [ 17 ]. Individuals with CME frequently suffer from the detrimental effects associated with increased intracranial pressure such as edema, hydrocephalus, and subarachnoid space hemorrhage, which may be related in part to GXM-mediated effects [ 32 ]. The concentration of GXM in CSF can reach 1 mg/mL [ 33 ] and post-mortem pathological examinations of brains from patients with CME indicate that this polysaccharide is extensively deposited in tissue [ 17 ].…”

Phospholipase B Is Critical for Cryptococcus neoformans Survival in the Central Nervous System

“…For all strains, we recently reported in an experimental mouse model of stereotaxic intracerebral (i.c.) infection ( 35 ) that CME-related mortality in mice is associated with the presence of subarachnoid hemorrhaging and GXM deposition in the meningeal blood vessels and meninges. These clinical manifestations have been observed and reported in human CME cases ( 36 , 37 ).…”