Koshy, A. A. | Search bioRxiv

bioRxiv2021

Toxoplasma gondii injected neurons localize to the cortex and striatum and have altered firing

Toxoplasma gondii is an intracellular parasite that causes a long-term latent infection of neurons. Using a custom MATLAB-based mapping program in combination with a mouse model that allows us to permanently mark neurons injected with parasite proteins, we found that Toxoplasma-injected neurons (TINs) are heterogeneously distributed in the brain, primarily localizing to the cortex followed by the striatum. Using immunofluorescence co-localization assays, we determined that cortical TINs are commonly (>50%) excitatory neurons (FoxP2+) and that striatal TINs are often (>65%) medium spiny neurons (MSNs) (FoxP2+). As MSNs have highly characterized electrophysiology, we used ex vivo slices from infected mice to perform single neuron patch-clamping on striatal TINs and neighboring uninfected MSNs (bystander MSNs). These studies demonstrated that TINs have highly abnormal electrophysiology, while the electrophysiology of bystander MSNs was akin to that of MSNs from uninfected mice. Collectively, these data offer new neuroanatomic and electrophysiologic insights into CNS toxoplasmosis.

microbiology↗

bioRxiv2020

Transcriptional profiling reveals T cells cluster around neurons injected with Toxoplasma gondii proteins

Toxoplasma gondiis tropism for and persistence in the CNS underlies the symptomatic disease Toxoplasma causes in humans. Our recent work has shown that neurons are the primary CNS cell with which Toxoplasma interacts and infects in vivo. This predilection for neurons suggests that Toxoplasmas persistence in the CNS depends specifically upon parasite manipulation of the host neurons. Yet, most work on Toxoplasma-host cell interactions has been done in vitro and in non-neuronal cells. We address this gap by utilizing our Toxoplasma-Cre system that allows permanent marking and tracking of neurons injected with parasite effector proteins in vivo. Using laser capture microdissection (LCM) and RNA-seq, we isolated and transcriptionally profiled Toxoplasma-injected neurons (TINs), Bystander neurons (nearby non-Toxoplasma injected neurons), and neurons from uninfected mice (controls). These profiles show that TINs transcriptomes significantly differ from the transcriptomes of Bystander and control neurons and that much of this difference is driven by increased levels of transcripts from immune cells, especially CD8+ T cells and monocytes. These data suggest that when we used LCM to isolate neurons from infected mice, we also picked up fragments of CD8+ T cells and monocytes clustering in extreme proximity around TINs and, to a lesser extent, Bystander neurons. In addition, we found that Toxoplasma transcripts were primarily found in the TINs transcriptome, not in the Bystander transcriptome. Collectively, these data suggest that, contrary to common perception, neurons that directly interact with or harbor parasites can be recognized by CD8+ T cells.

bioinformatics↗