Injection with Toxoplasma gondii protein affects neuron health and survival

Sustained rhoptry docking and discharge requires Toxoplasma gondii intraconoidal microtubule-associated proteins

In Apicomplexa, rhoptry discharge is essential for invasion and involves an apical vesicle (AV) docking one or two rhoptries to a macromolecular secretory apparatus. Toxoplasma gondii is armed with 10-12 rhoptries and 5-6 microtubule-associated vesicles (MVs) presumably for iterative rhoptry discharge. Here, we have addressed the localization and functional significance of two intraconoidal microtubule (ICMT)-associated proteins instrumental for invasion. Mechanistically, depletion of ICMAP2 leads to a dissociation of the ICMTs, their detachment from the conoid and dispersion of MVs and rhoptries. ICMAP3 exists in two isoforms that contribute to the control of the ICMTs length and the docking of the two rhoptries at the AV, respectively. This study illuminates the central role ICMTs play in scaffolding the discharge of multiple rhoptries. This process is instrumental for virulence in the mouse model of infection and in addition promotes sterile protection against T. gondii via the release of key effectors inducing immunity.

Culture of vibrating microtome tissue slices as a 3D model in biomedical research

The basic idea behind the use of 3-dimensional (3D) tools in biomedical research is the assumption that the structures under study will perform at the best in vitro if cultivated in an environment that is as similar as possible to their natural in vivo embedding. Tissue slicing fulfills this premise optimally: it is an accessible, unexpensive, imaging-friendly, and technically rather simple procedure which largely preserves the extracellular matrix and includes all or at least most supportive cell types in the correct tissue architecture with little cellular damage. Vibrating microtomes (vibratomes) can further improve the quality of the generated slices because of the lateral, saw-like movement of the blade, which significantly reduces tissue pulling or tearing compared to a straight cut. In spite of its obvious advantages, vibrating microtome slices are rather underrepresented in the current discussion on 3D tools, which is dominated by methods as organoids, organ-on-chip and bioprinting. Here, we review the development of vibrating microtome tissue slices, the major technical features underlying its application, as well as its current use and potential advances, such as a combination with novel microfluidic culture chambers. Once fully integrated into the 3D toolbox, tissue slices may significantly contribute to decrease the use of laboratory animals and is likely to have a strong impact on basic and translational research as well as drug screening.

Complement-dependent loss of inhibitory synapses on pyramidal neurons following Toxoplasma gondii infection

The apicomplexan parasite Toxoplasma gondii has developed mechanisms to establish a central nervous system infection in virtually all warm-blooded animals. Acute T. gondii infection can cause neuroinflammation, encephalitis, and seizures. Meanwhile, studies in humans, nonhuman primates, and rodents have linked chronic T. gondii infection with altered behavior and increased risk for neuropsychiatric disorders, including schizophrenia. These observations and associations raise questions about how this parasitic infection may alter neural circuits. We previously demonstrated that T. gondii infection triggers the loss of inhibitory perisomatic synapses, a type of synapse whose dysfunction or loss has been linked to neurological and neuropsychiatric disorders. We showed that phagocytic cells (including microglia and infiltrating monocytes) contribute to the loss of these inhibitory synapses. Here, we show that these phagocytic cells specifically ensheath excitatory pyramidal neurons, leading to the preferential loss of perisomatic synapses on these neurons and not those on cortical interneurons. Moreover, we show that infection induces an increased expression of the complement C3 gene, including by populations of these excitatory neurons. Infecting C3-deficient mice with T. gondii revealed that C3 is required for the loss of perisomatic inhibitory synapses. Interestingly, loss of C1q did not prevent the loss of perisomatic synapses following infection. Together, these findings provide evidence that T. gondii induces changes in excitatory pyramidal neurons that trigger the selective removal of inhibitory perisomatic synapses and provide a role for a nonclassical complement pathway in the remodeling of inhibitory circuits in the infected brain.

Understanding neuroinflammation through central nervous system infections

Neuroinflammation is now recognized to compound many central nervous system (CNS) pathologies, from stroke to dementia. As immune responses evolved to handle infections, studying CNS infections can offer unique insights into the CNS immune response and address questions such as: What defenses and strategies do CNS parenchymal cells deploy in response to a dangerous pathogen? How do CNS cells interact with each other and infiltrating immune cells to control microbes? What pathways are beneficial for the host or for the pathogen? Here, we review recent studies that use CNS-tropic infections in combination with cutting-edge techniques to delve into the complex relationships between microbes, immune cells, and cells of the CNS.

Pierre J, Xiong X, Howland JG, Josselyn SA, Frankland PW, Parkinson J. Toxoplasma infection in male mice alters dopamine-sensitive behaviors and host gene expression patterns associated with neuropsychiatric disease

During chronic infection, the single celled parasite, Toxoplasma gondii, can migrate to the brain where it has been associated with altered dopamine function and the capacity to modulate host behavior, increasing risk of neurocognitive disorders. Here we explore alterations in dopamine-related behavior in a new mouse model based on stimulant (cocaine)-induced hyperactivity. In combination with cocaine, infection resulted in heightened sensorimotor deficits and impairment in prepulse inhibition response, which are commonly disrupted in neuropsychiatric conditions. To identify molecular pathways in the brain affected by chronic T. gondii infection, we investigated patterns of gene expression. As expected, infection was associated with an enrichment of genes associated with general immune response pathways, that otherwise limits statistical power to identify more informative pathways. To overcome this limitation and focus on pathways of neurological relevance, we developed a novel context enrichment approach that relies on a customized ontology. Applying this approach, we identified genes that exhibited unexpected patterns of expression arising from the combination of cocaine exposure and infection. These include sets of genes which exhibited dampened response to cocaine in infected mice, suggesting a possible mechanism for some observed behaviors and a neuroprotective effect that may be advantageous to parasite persistence. This model offers a powerful new approach to dissect the molecular pathways by which T. gondii infection contributes to neurocognitive disorders.

Host cell proteins modulated upon Toxoplasma infection identified using proteomic approaches: a molecular rationale

Toxoplasma gondii is a pathogenic protozoan parasite belonging to the apicomplexan phylum that infects the nucleated cells of warm-blooded hosts leading to an infectious disease known as toxoplasmosis. Apicomplexan parasites such as T. gondii can display different mechanisms to control or manipulate host cells signaling at different levels altering the host subcellular genome and proteome. Indeed, Toxoplasma is able to modulate host cell responses (especially immune responses) during infection to its advantage through both structural and functional changes in the proteome of different infected cells. Consequently, parasites can transform the invaded cells into a suitable environment for its own replication and the induction of infection. Proteomics as an applicable tool can identify such critical proteins involved in pathogen (Toxoplasma)-host cell interactions and consequently clarify the cellular mechanisms that facilitate the entry of pathogens into host cells, and their replication and transmission, as well as the central mechanisms of host defense against pathogens. Accordingly, the current paper reviews several proteins (identified using proteomic approaches) differentially expressed in the proteome of Toxoplasma-infected host cells (macrophages and human foreskin fibroblasts) and tissues (brain and liver) and highlights their plausible functions in the cellular biology of the infected cells. The identification of such modulated proteins and their related cell impact (cell responses/signaling) can provide further information regarding parasite pathogenesis and biology that might lead to a better understanding of therapeutic strategies and novel drug targets.