Chronic Toxoplasma gondii Infection Induces Anti-N-Methyl-d-Aspartate Receptor Autoantibodies and Associated Behavioral Changes and Neuropathology

Exploring the interplay of chronic toxoplasmosis and NMDAR dysfunction: Insights into schizophrenia-like behaviors and therapeutic potential

Background

Chronic toxoplasmosis has been strongly implicated in the development of psychosis and schizophrenia. Additionally, the understanding of schizophrenia has been significantly reshaped by insights into N-methyl-D-aspartate receptor (NMDAR) hypofunction.

Aim

This study aimed to compare the behavioral, antioxidant, and NMDAR changes in mice subjected to Toxoplasma gondii infection and those treated with ketamine to induce schizophrenia-like symptoms.

Methods

Sixty male BALB/c mice were divided into six groups: toxoplasmosis (TOXO) (infected), ketamine-induced schizophrenia (KET), TOXO+KET, TOXO+sulfadiazine-trimethoprim treatment (SDT), TOXO+KET+SDT, and control (CON) (uninfected). After 10 weeks post-infection, behavioral tests were conducted, brain antioxidant status and lipid peroxidation were analyzed, and NMDA-NR1/NR2A expressions were assessed. TOXO and KET induced distinct behaviors: hyperlocomotion, anxiety, and memory impairment.

Results

Antioxidant enzyme levels decreased, and lipid peroxidation increased in TOXO and schizophrenic mice brains. NMDAR downregulation, especially NR-1 and NR2A, was evident due to T. gondii and ketamine. Sulfadiazine-trimethoprim ameliorated NMDAR downregulation, but not all of the behavioral alterations.

Conclusion

Further studies are needed to elucidate specific NMDAR subunit roles in toxoplasmosis-induced pathophysiology, offering potential therapeutic insights. This investigation highlights the intricate relationship between chronic toxoplasmosis, NMDAR dysfunction, and schizophrenia-like behaviors. Insights gained could pave the way for innovative interventions targeting both cognitive and neurological impairments associated with these conditions.

Elevated matrix Metalloproteinase-9 associated with reduced cerebellar perineuronal nets in female mice with toxoplasmosis

Brain infection by the parasite Toxoplasma gondii is thought to impair learning and memory, although the underlying mechanisms remain largely unknown. Recent studies suggest that perineuronal nets (PNNs) and their key regulator, matrix metalloproteinase-9 (MMP-9), have essential roles in synaptic plasticity associated with learning and memory. We investigated their roles in a chronic toxoplasmosis model using female mice. In mice with a high parasite burden of chronic infection, we found that MMP-9 expression was increased in the peripheral circulation and the brain. A correlation was found between the serum levels of MMP-9 and antibodies to the Toxoplasma matrix antigen MAG1, a surrogate marker for Toxoplasma tissue cysts in the brain. MMP-9 elevation was accompanied by increased expression of its endogenous regulators, TIMP-1 and NGAL. An increase in the levels of GSK-3α/β was observed, alongside a decrease in inhibitory GSK-3α/β (Ser-21/Ser-9) phosphorylation. MMP-9 expression was notably associated with the loss of PNNs but increased expression of the synaptic vesicle protein synaptophysin. There was a trend toward a negative correlation between MMP-9 and aggrecan expression, a critical PNN component. Together, these results suggest that chronic Toxoplasma infection can cause an increase in MMP-9 expression, resulting in the degradation of PNNs, which provides a possible mechanism for Toxoplasma-associated deficits in learning and memory.

Prospects and Pitfalls of Plasma Complement C4 in Schizophrenia: Building a Better Biomarker

Complex brain disorders like schizophrenia may have multifactorial origins related to mis-timed heritable and environmental factors interacting during neurodevelopment. Infections, inflammation, and autoimmune diseases are over-represented in schizophrenia leading to immune system-centered hypotheses. Complement component C4 is genetically and neurobiologically associated with schizophrenia, and its dual activity peripherally and in the brain makes it an exceptional target for biomarker development. Studies to evaluate the biomarker potential of plasma or serum C4 in schizophrenia do so to understand how peripheral C4 might reflect central nervous system-derived neuroinflammation, synapse pruning, and other mechanisms. This effort, however, has produced mostly conflicting results, with peripheral C4 sometimes elevated, reduced, or unchanged between comparison groups. We undertook a pilot biomarker development study to systematically identify sociodemographic, genetic, and immune-related variables (autoimmune, infection-related, gastrointestinal, inflammatory), which may be associated with plasma C4 levels in schizophrenia (SCH; n = 335) and/or in nonpsychiatric comparison subjects (NCs; n = 233). As with previously inconclusive studies, we detected no differences in plasma C4 levels between SCH and NCs. In contrast, levels of general inflammation, C-reactive protein (CRP), were significantly elevated in SCH compared to NCs (ANOVA, F = 20.74, p < 0.0001), suggestive that plasma C4 and CRP may reflect different sources or causes of inflammation. In multivariate regressions of C4 gene copy number variants, plasma C4 levels were correlated only for C4A (not C4B, C4L, C4S) and only in NCs (R Coeff = 0.39, CI = 0.01-0.77, R2 = 0.18, p < 0.01; not SCH). Other variables associated with plasma C4 levels only in NCs included sex, double-stranded DNA IgG, tissue-transglutaminase (TTG) IgG, and cytomegalovirus IgG. Toxoplasma gondii IgG was the only variable significantly correlated with plasma C4 in SCH but not in NCs. Many variables were associated with plasma C4 in both groups (body mass index, race, CRP, N-methyl-D-aspartate receptor (NMDAR) NR2 subunit IgG, TTG IgA, lipopolysaccharide-binding protein (LBP), and soluble CD14 (sCD14). While the direction of most C4 associations was positive, autoimmune markers tended to be inverse, and associated with reduced plasma C4 levels. When NMDAR-NR2 autoantibody-positive individuals were removed, plasma C4 was elevated in SCH versus NCs (ANOVA, F = 5.16, p < 0.02). Our study was exploratory and confirmation of the many variables associated with peripheral C4 requires replication. Our preliminary results point toward autoimmune factors and exposure to the pathogen, T. gondii, as possibly significant contributors to variability of total C4 protein levels in plasma of individuals with schizophrenia.

Infection-induced extracellular vesicles evoke neuronal transcriptional and epigenetic changes

Infection with the protozoan Toxoplasma gondii induces changes in neurotransmission, neuroinflammation, and behavior, yet it remains elusive how these changes come about. In this study we investigated how norepinephrine levels are altered by infection. TINEV (Toxoplasma-induced neuronal extracellular vesicles) isolated from infected noradrenergic cells down-regulated dopamine ß-hydroxylase (DBH) gene expression in human and rodent cells. Here we report that intracerebral injection of TINEVs into the brain is sufficient to induce DBH down-regulation and distrupt catecholaminergic signalling. Further, TINEV treatment induced hypermethylation upstream of the DBH gene. An antisense lncRNA to DBH was found in purified TINEV preparations. Paracrine signalling to induce transcriptional gene silencing and DNA methylation may be a common mode to regulate neurologic function.

Association between Toxoplasma gondii Infection and Type-1 Diabetes Mellitus: A Systematic Review and Meta-Analysis

Type-1 diabetes, an autoimmune disease characterized by damage to pancreatic insulin-producing beta cells, is associated with adverse renal, retinal, cardiovascular, and cognitive outcomes, possibly including dementia. Moreover, the protozoal parasite Toxoplasma gondii has been associated with type-1 diabetes. To better characterize the association between type-1 diabetes and Toxoplasma gondii infection, we conducted a systematic review and meta-analysis of published studies that evaluated the relationship between type-1 diabetes and Toxoplasma gondii infection. A random-effects model based on nine primary studies (total number of participants = 2655) that met our inclusion criteria demonstrated a pooled odds ratio of 2.45 (95% confidence interval, 0.91-6.61). Removing one outlying study increased the pooled odds ratio to 3.38 (95% confidence interval, 2.09-5.48). These findings suggest that Toxoplasma gondii infection might be positively associated with type-1 diabetes, although more research is needed to better characterize this association. Additional research is required to determine whether changes in immune function due to type-1 diabetes increase the risk of infection with Toxoplasma gondii, infection with Toxoplasma gondii increases the risk of type-1 diabetes, or both processes occur.

Effects of diverse Types of Toxoplasma gondii on the outcome of Alzheimer's disease in the rat model

Toxoplasma gondii has lifelong persistence in the brain and its cysts can affect gene expression and change diverse biological functions of neurons. Many studies indicated T. gondii infection as a risk factor for the development of behavioral changes and neurodegenerative diseases such as Alzheimer's disease (AD), although the etiopathogenetic link between them has not been exactly elucidated. The current study aimed to examine the effects of chronic toxoplasmosis infection with Types I, II, and III strains (RH, PRU, and VEG) alone and in combination on cognitive impairments and neuronal death in the Aβ1-42-induced rat model of Alzheimer's disease. In the chronic toxoplasmosis phase, Alzheimer's induction was conducted by injecting Aβ1-42 oligomers into the rat brain hippocampus. Behavioral tests were conducted 10 days after the AD induction. Real-time PCR was performed to evaluate T. gondii parasite burden by amplification of the B1 gene. Cytokines IL-1β, TNF-α, and IL-10 were assayed in brain tissue supernatant using ELISA. Also, histopathological examinations were conducted to calculate inflammatory changes and neuronal death in the brain. Our findings showed that chronic toxoplasmosis infection with PRU reduces cognitive disorders, while the RH strain of T. gondii plays a destructive role and aggravates cognitive impairments in AD. Also, infection with a combination of PRU and VEG strains significantly improved spatial learning and memory impairments in Alzheimer's rat model. Histopathological findings also confirmed the results of behavioral tests, so that in AβPRU and AβPRU + VEG groups, neuronal death and infiltration of inflammatory cells were negligible and significantly less than in Alzheimer's and AβRH groups. Our findings indicate that chronic toxoplasmosis infection with PRU strain alone, also in combination with VEG strain can significantly improve cognitive disorders in AD rats, while RH strain plays a destructive role in AD pathogenesis.

Behavioral Changes Induced by Latent Toxoplasmosis Could Arise from CNS Inflammation and Neuropathogenesis

Chronic infection with Toxoplasma gondii, a neurotropic parasite, has been linked to multiple behavioral changes in rodents and humans. The pathogenic mechanisms underlying these correlations are not known. I discuss here from animal studies the distribution of tissue cysts, the constant immune surveillance, the critical role of cyst burden, and the time-dependent consequences, which I believe are crucial to explaining the behavioral changes. In line with the brain-wide distribution of tissue cysts and chronic neuroinflammation, infected mice displayed a broad range of behavioral phenotypes. Many studies suggest that behavioral changes in mice are directly associated with tissue cyst presence or cyst burden and the host immune response. Cyst burden may not exert direct effects; however, the mechanisms causing behavioral and neuropathological changes are potentially the consequence of cyst burden over time, such as the neuroinflammation required to control the reactivation of tissue cysts. The reduction of neuroinflammation has proven that neuropathogenesis and behavioral abnormalities can be reversed, at least partially, in infected mice. Overall, Toxoplasma-induced behavioral changes are likely to be an indirect consequence of the host immune response in a parasite burden-dependent manner.

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.

Impact of Plant-Based Foods and Nutraceuticals on Toxoplasma gondii Cysts: Nutritional Therapy as a Viable Approach for Managing Chronic Brain Toxoplasmosis

Toxoplasma gondii is an obligate intracellular parasite that mainly infects warm-blooded animals including humans. T. gondii can encyst and persist chronically in the brain, leading to a broad spectrum of neurological sequelae. Despite the associated health threats, no clinical drug is currently available to eliminate T. gondii cysts. In a continuous effort to uncover novel therapeutic agents for these cysts, the potential of nutritional products has been explored. Herein, we describe findings from in vitro and in vivo studies that support the efficacy of plant-based foods and nutraceuticals against brain cyst burden and cerebral pathologies associated with chronic toxoplasmosis. Finally, we discuss strategies to increase the translatability of preclinical studies and nutritional products to address whether nutritional therapy can be beneficial for coping with chronic T. gondii infections in humans.

Social preference is maintained in mice with impaired startle reflex and glutamate/D-serine imbalance induced by chronic cerebral toxoplasmosis

Toxoplasma gondii is an opportunistic protozoan pathogen with a wide geographic distribution. The chronic phase of toxoplasmosis is often asymptomatic in humans and is characterized by tissue cysts throughout the central nervous system and muscle cells. T. gondii and other pathogens with tropism for the central nervous system are considered risk factors in the etiology of several neuropsychiatric disorders, such as schizophrenia and bipolar disorder, besides neurological diseases. Currently, it is known that cerebral toxoplasmosis increases dopamine levels in the brain and it is related to behavioral changes in animals and humans. Here we evaluate whether chronic T. gondii infection, using the cystogenic ME-49 strain, could induce behavioral alterations associated with neuropsychiatric disorders and glutamatergic neurotransmission dysfunction. We observed that the startle amplitude is reduced in the infected animals as well as glutamate and D-serine levels in prefrontal cortical and hippocampal tissue homogenates. Moreover, we did not detect alterations in social preference and spontaneous alternation despite severe motor impairment. Thus, we conclude that behavioral and cognitive aspects are maintained even though severe neural damage is observed by chronic infection of C57Bl/6 mice with the ME-49 strain.

Autoantibodies Against Ubiquitous and Confined Antigens in Patients With Ocular, Neuro-Ophthalmic and Congenital Cerebral Toxoplasmosis

Toxoplasma gondii infection can trigger autoreactivity by different mechanisms. In the case of ocular toxoplasmosis, disruption of the blood-retinal barrier may cause exposure of confined retinal antigens such as recoverin. Besides, cross-reactivity can be induced by molecular mimicry of parasite antigens like HSP70, which shares 76% identity with the human ortholog. Autoreactivity can be a determining factor of clinical manifestations in the eye and in the central nervous system. We performed a prospective observational study to determine the presence of autoantibodies against recoverin and HSP70 by indirect ELISA in the serum of 65 patients with ocular, neuro-ophthalmic and congenital cerebral toxoplasmosis. We found systemic autoantibodies against recoverin and HSP70 in 33.8% and 15.6% of individuals, respectively. The presence of autoantibodies in cases of OT may be related to the severity of clinical manifestations, while in cases with CNS involvement they may have a protective role. Unexpectedly, anti-recoverin antibodies were found in patients with cerebral involvement, without ocular toxoplasmosis; therefore, we analyzed and proved cross-reactivity between recoverin and a brain antigen, hippocalcin, so the immunological phenomenon occurring in one immune-privileged organ (e.g. the central nervous system) could affect the environment of another (egg. the eye).

Behavioral Manipulation by Toxoplasma gondii: Does Brain Residence Matter?

The protozoan parasite Toxoplasma gondii infects a wide range of intermediate hosts. The parasite produces brain cysts during the latent phase of its infection, in parallel to causing a loss of innate aversion in the rat host towards cat odors. Host behavioral change presumably reflects a parasitic manipulation to increase predation by definitive felid hosts, although evidence for increased predation is not yet available. In this opinion piece, we propose a neuroendocrine loop to explain the role of gonadal steroids in the parasitized hosts in mediating the behavioral manipulation. We argue that the presence of tissue cysts within the host brain is merely incidental to the behavioral change, without a necessary or sufficient role.

Persistent Toxoplasma Infection of the Brain Induced Neurodegeneration Associated with Activation of Complement and Microglia

Toxoplasma gondii, a common neurotropic parasite, is increasingly being linked to neuropsychiatric disorders, including schizophrenia, Alzheimer's disease, and Parkinson's disease. However, the pathogenic mechanisms underlying these associations are not clear. Toxoplasma can reside in the brain for extensive periods in the form of tissue cysts, and this process requires a continuous immune response to prevent the parasite's reactivation. Because neuroinflammation may promote the onset and progression of neurodegenerative diseases, we investigated neurodegeneration-associated pathological changes in a mouse model of chronic Toxoplasma infection. Under conditions of high-grade chronic infection, we documented the presence of neurodegeneration in specific regions of the prefrontal cortex, namely, the anterior cingulate cortex (ACC) and somatomotor cortex (SC). Neurodegeneration occurred in both glutamatergic and GABAergic neurons. Neurons that showed signs of degeneration expressed high levels of CX3CL1, were marked by profoundly upregulated complement proteins (e.g., C1q and C3), and were surrounded by activated microglia. Our findings suggest that chronic Toxoplasma infection leads to cortical neurodegeneration and results in CX3CL1, complement, and microglial interactions, which are known to mediate the phagocytic clearance of degenerating neurons. Our study provides a mechanistic explanation for the link between Toxoplasma infection and psychiatric disorders.

NanI Sialidase Is an Important Contributor to Clostridium perfringens Type F Strain F4969 Intestinal Colonization in Mice

Clostridium perfringens type F (formerly enterotoxigenic C. perfringens type A) strains produce an enterotoxin (CPE) to cause acute cases of food poisoning and chronic nonfoodborne human gastrointestinal diseases (NFD), e.g., antibiotic-associated diarrhea (AAD). NFD strains also produce NanI sialidase, an extracellular enzyme that releases sialic acids from sialyated host macromolecules. Recent in vitro studies suggested that NanI may contribute to NFD strain intestinal colonization by enhancing the adherence of such strains to intestinal cells and promoting their bacterial growth using generated sialic acid as an energy source. The current study tested this hypothesis by developing a mouse intestinal colonization model involving clindamycin pretreatment to produce conditions mimicking those during AAD. In this model, the type F NFD strain F4969 persisted for at least 4 days in the small intestine, cecum, and colon. When clindamycin-pretreated mice were challenged by oral gavage with equivalent numbers of F4969 bacteria or its isogenic nanI null mutant, significantly lower numbers of the nanI mutant were recovered from all intestinal segments, and it was completely cleared from the small intestine by day 4. Complementation of the mutant to restore NanI production also promoted colonization. When the same nanI null mutant strain was coinoculated into the mouse model together with a nanI-producing strain, the numbers of this mutant were restored to wild-type F4969 levels in all intestinal segments. This result suggests that sialidases produced by other bacteria might also provide some support for C. perfringens intestinal colonization. Collectively, these in vivo findings identify NanI to be the first known significant contributor to chronic intestinal colonization by NFD strains.