Chronic Toxoplasma gondii infection contributes to decreasing of perineuronal nets surrounding neurons in the Corpus striatum of mice

Chronic infection by atypical Toxoplasma gondii strain induces disturbance in microglia population and altered behaviour in mice

Toxoplasma gondii chronic infection is characterized by the establishment of tissue cysts in the brain and increased levels of IFN-γ, which can lead to brain circuitry interference and consequently abnormal behaviour in mice. In this sense, the study presented here sought to investigate the impact of chronic infection by two T. gondii strains in the brain of infection-resistant mice, as a model for studying the involvement of chronic neuroinflammation with the development of behavioural alterations. For that, male BALB/c mice were divided into three groups: non-infected (Ni), infected with T. gondii ME49 clonal strain (ME49), and infected with TgCkBrRN2 atypical strain (CK2). Mice were monitored for 60 days to establish the chronic infection and then submitted to behavioural assessment. The enzyme-linked immunosorbent assay was used for measurement of specific IgG in the blood and levels of inflammatory cytokines and neurotrophic factors in the brain, and the cell's immunophenotype was determined by multiparametric flow cytometry. Mice infected with ME49 clonal strain displayed hyperlocomotor activity and memory deficit, although no signs of depressive- and/or anxiety-like behaviour were detected; on the other hand, chronic infection with CK2 atypical strain induced anxiety- and depressive-like behaviour. During chronic infection by CK2 atypical strain, mice displayed a higher number of T. gondii brain tissue cysts and inflammatory infiltrate, composed mainly of CD3⁺ T lymphocytes and Ly6C^hi inflammatory monocytes, compared to mice infected with the ME49 clonal strain. Infected mice presented a marked decrease of microglia population compared to non-infected group. Chronic infection with CK2 strain produced elevated levels of IFN-γ and TNF-ɑ in the brain, decreased NGF levels in the prefrontal cortex and striatum, and altered levels of fractalkine (CX3CL1) in the prefrontal cortex and hippocampus. The persistent inflammation and the disturbance in the cerebral homeostasis may contribute to altered behaviour in mice, as the levels of IFN-γ were shown to be correlated with the behavioural parameters assessed here. Considering the high incidence and life-long persistence of T. gondii infection, this approach can be considered a suitable model for studying the impact of chronic infections in the brain and how it impacts in behavioural responses.

Chronic Toxoplasma gondii infection contributes to perineuronal nets impairment in the primary somatosensory cortex

Toxoplasma gondii is able to manipulate the host immune system to establish a persistent and efficient infection, contributing to the development of brain abnormalities with behavioral repercussions. In this context, this work aimed to evaluate the effects of T. gondii infection on the systemic inflammatory response and structure of the primary somatosensory cortex (PSC). C57BL/6 and BALB/c mice were infected with T. gondii ME49 strain tissue cysts and accompanied for 30 days. After this period, levels of cytokines IFN-γ, IL-12, TNF-α and TGF-β were measured. After blood collection, mice were perfused and the brains were submitted to immunohistochemistry for perineuronal net (PNN) evaluation and cyst quantification. The results showed that C57BL/6 mice presented higher levels of TNF-α and IL-12, while the levels of TGF-β were similar between the two mouse lineages, associated with the elevated number of tissue cysts, with a higher occurrence of cysts in the posterior area of the PSC when compared to BALB/c mice, which presented a more homogeneous cyst distribution. Immunohistochemistry analysis revealed a greater loss of PNN labeling in C57BL/6 animals compared to BALB/c. These data raised a discussion about the ability of T. gondii to stimulate a systemic inflammatory response capable of indirectly interfering in the brain structure and function.

Upregulation of lncRNA147410.3 in the Brain of Mice With Chronic Toxoplasma Infection Promoted Microglia Apoptosis by Regulating Hoxb3

Toxoplasma gondii is neurotropic and affects the function of nerve cells, while the mechanism is unclear. LncRNAs are abundantly enriched in the brain and participated in the delicate regulation of the central nervous system (CNS) development. However, whether these lncRNAs are involved in the regulation of microglia activation during the process of T. gondii infection is largely unknown. In this study, the upregulation of a novel lncRNA147410.3 (ENSMUST00000147410.3) was identified as a key factor to influence this process. The target gene of lncRNA147410.3 was predicted and identified as Hoxb3. The localization of lncRNA147410.3 in the brain and cells was proved in the nucleus of neuroglia through FISH assay. Furthermore, the function of lncRNA147410.3 on neuronal cell was confirmed that lncRNA147410.3 could affect proliferation, differentiation, and apoptosis of mouse microglia by positively regulating Hoxb3. Thus, our study explored the modulatory action of lncRNA147410.3 in T. gondii infected mouse brain, providing a scientific basis for using lncRNA147410.3 as a therapeutic target to treat neurological disorder induced by T. gondii.

Toxoplasma gondii infection damages the perineuronal nets in a murine model

BACKGROUND

Behavioral and neurochemical alterations associated with toxoplasmosis may be influenced by the persistence of tissue cysts and activation of an immune response in the brain of Toxoplasma gondii-infected hosts. The cerebral extracellular matrix is organised as perineuronal nets (PNNs) that are both released and ensheath by some neurons and glial cells. There is evidences to suggest that PNNs impairment is a pathophysiological mechanism associated with neuropsychiatric conditions. However, there is a lack of information regarding the impact of parasitic infections on the PNNs integrity and how this could affect the host’s behavior.

OBJECTIVES

In this context, we aimed to analyse the impact of T. gondii infection on cyst burden, PNNs integrity, and possible effects in the locomotor activity of chronically infected mice.

METHODS

We infected mice with T. gondii ME-49 strain. After thirty days, we assessed locomotor performance of animals using the open field test, followed by evaluation of cysts burden and PNNs integrity in four brain regions (primary and secondary motor cortices, prefrontal and somesthetic cortex) to assess the PNNs integrity using Wisteria floribunda agglutinin (WFA) labeling by immunohistochemical analyses.

FINDINGS AND MAIN CONCLUSIONS

Our findings revealed a random distribution of cysts in the brain, the disruption of PNNs surrounding neurons in four areas of the cerebral cortex and hyperlocomotor behavior in T. gondii-infected mice. These results can contribute to elucidate the link toxoplasmosis with the establishment of neuroinflammatory response in neuropsychiatric disorders and to raise a discussion about the mechanisms related to changes in brain connectivity, with possible behavioral repercussions during chronic T. gondii infection.