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.

Palmitoylethanolamide shows limited efficacy in controlling cerebral cryptococcosisin vivo

“…It is possible that PEA, by being a hydrophobic molecule, binds to the cell membrane ergosterol and serves as a vehicle in facilitating AmpB-mediated pore formation, killing the cell (35). These hypotheses are possible given that untreated and minocycline-treated brains showed moderate to weak glial responses and the untreated tissue exhibited ischemic necrosis, a manifestation reported in patients with CME (36,37) and in this model of infection (25).…”

“…Using a stereotaxic apparatus (Fig. 1A), we i.c.-infected 10 4 Cn strain H99 cells into the mouse striatum (n = 7 mice per group, 6-8 weeks old, female), following the brain coordinates described previously (25). The striatum is a region in the basal ganglia of the brain that coordinates multiple aspects of cognition and motor function.…”

“…Untreated brain tissue showed extensive necrosis that expanded throughout the basal ganglia (e.g., striatum, globus pallidus, and caudate nucleus; Fig. In addition, Cn invaded the tissue surrounding the cryptococcoma causing ischemic neuronal necrosis (blue arrow) and weak microglial response (red arrow), which is characteristic of GXM accumulation and the direct negative effect of minocycline in these glial cells (25). Interestingly, tissue from AmpB-treated mice evinced marked microgliosis (blue arrow) and astrocytic response (red arrow) in tissue adjacent to the cryptococcoma or encephalomalacia (middle row panels), while tissue from PEA-treated mice displayed noticeable microgliosis (red arrow) and evident swollen endothelial cells (blue arrow).…”

“…6A). Images of each group treatment were visualized under the microscope and the microglia morphology documented as previously described (25). Cn-infected brains from untreated mice presented the following microglia phenotype distribution: activated (38.52%) > ramified (31.03%) > rodshaped (15.46%) > phagocytic (11.59%) > dystrophic (3.4%) (Fig.…”

“…The craniotomy was around 1 mm in diameter and the correct brain coordinates were identified using a stereotaxic brain atlas (e.g., The Allen Mouse Brain Atlas; https://mouse.brainmap.org/static/atlas). Based on our recent study (25) and others (56,57) using the Cn H99 strain, a 1-μL suspension containing 10 4 cryptococci in sterile saline was injected into the striatum [Stereotaxic coordinates: x (medial/lateral), -2; y (anterior/posterior), 0.2; z (dorsal/ventral), -3.5)] using a 26 G Hamilton syringe connected to a pump (model: UltraMicroPump3; World Precision Instruments). We injected the fungal inoculum in a 1-μL volume to avoid tissue damage or diffusion of the cryptococci to other regions of the brain.…”