The Neurotropic Parasite Toxoplasma gondii Induces Astrocyte Polarization Through NFκB Pathway

Intestinal microbiota imbalance resulted by anti-Toxoplasma gondii immune responses aggravate gut and brain injury

BACKGROUND

Toxoplasma gondii infection affects a significant portion of the global population, leading to severe toxoplasmosis and, in immunocompromised patients, even death. During T. gondii infection, disruption of gut microbiota further exacerbates the damage to intestinal and brain barriers. Therefore, identifying imbalanced probiotics during infection and restoring their equilibrium can regulate the balance of gut microbiota metabolites, thereby alleviating tissue damage.

METHODS

Vimentin gene knockout (vim-/-) mice were employed as an immunocompromised model to evaluate the influence of host immune responses on gut microbiota balance during T. gondii infection. Behavioral experiments were performed to assess changes in cognitive levels and depressive tendencies between chronically infected vim-/- and wild-type (WT) mice. Fecal samples were subjected to 16S ribosomal RNA (rRNA) sequencing, and serum metabolites were analyzed to identify potential gut probiotics and their metabolites for the treatment of T. gondii infection.

RESULTS

Compared to the immunocompetent WT sv129 mice, the immunocompromised mice exhibited lower levels of neuronal apoptosis and fewer neurobehavioral abnormalities during chronic infection. 16S rRNA sequencing revealed a significant decrease in the abundance of probiotics, including several species of Lactobacillus, in WT mice. Restoring this balance through the administration of Lactobacillus murinus and Lactobacillus gasseri significantly suppressed the T. gondii burden in the intestine, liver, and brain. Moreover, transplantation of these two Lactobacillus spp. significantly improved intestinal barrier damage and alleviated inflammation and neuronal apoptosis in the central nervous system. Metabolite detection studies revealed that the levels of various Lactobacillus-related metabolites, including indole-3-lactic acid (ILA) in serum, decreased significantly after T. gondii infection. We confirmed that L. gasseri secreted much more ILA than L. murinus. Notably, ILA can activate the aromatic hydrocarbon receptor signaling pathway in intestinal epithelial cells, promoting the activation of CD8+ T cells and the secretion of interferon-gamma.

CONCLUSION

Our study revealed that host immune responses against T. gondii infection severely disrupted the balance of gut microbiota, resulting in intestinal and brain damage. Lactobacillus spp. play a crucial role in immune regulation, and the metabolite ILA is a promising therapeutic compound for efficient and safe treatment of T. gondii infection.

Anti-inflammatory and immunomodulatory effects of mesenchymal stem cell therapy on parasitic drug resistance

INTRODUCTION

The emergence of antiparasitic drug resistance poses a concerning threat to animals and humans. Mesenchymal Stem Cells (MSCs) have been widely used to treat infections in humans, pets, and livestock. Although this is an emerging field of study, the current review outlines possible mechanisms and examines potential synergism in combination therapies and the possible harmful effects of such an approach.

AREAS COVERED

The present study delved into the latest pre-clinical research on utilizing MSCs to treat parasitic infections. As per investigations, the introduction of MSCs to patients grappling with parasitic diseases like schistosomiasis, malaria, cystic echinococcosis, toxoplasmosis, leishmaniasis, and trypanosomiasis has shown a reduction in parasite prevalence. This intervention also alters the levels of both pro- and anti-inflammatory cytokines. Furthermore, the combined administration of MSCs and antiparasitic drugs has demonstrated enhanced efficacy in combating parasites and modulating the immune response.

EXPERT OPINION

Mesenchymal stem cells are a potential solution for addressing parasitic drug resistance. This is mainly because of their remarkable immunomodulatory abilities, which can potentially help combat parasites' resistance to drugs.

Observing astrocyte polarization in brains from mouse chronically infected with Toxoplasma gondii

Toxoplasma gondii (T. gondii) is a protozoan parasite that infects approximately one-third of the global human population, often leading to chronic infection. While acute T. gondii infection can cause neural damage in the central nervous system and result in toxoplasmic encephalitis, the consequences of T. gondii chronic infection (TCI) are generally asymptomatic. However, emerging evidence suggests that TCI may be linked to behavioral changes or mental disorders in hosts. Astrocyte polarization, particularly the A1 subtype associated with neuronal apoptosis, has been identified in various neurodegenerative diseases. Nevertheless, the role of astrocyte polarization in TCI still needs to be better understood. This study aimed to establish a mouse model of chronic TCI and examine the transcription and expression levels of glial fibrillary acidic protein (GFAP), C3, C1q, IL-1α, and TNF-α in the brain tissues of the mice. Quantitative real-time PCR (qRT-PCR), enzyme-linked immunosorbent assay, and Western blotting were employed to assess these levels. Additionally, the expression level of the A1 astrocyte-specific marker C3 was evaluated using indirect fluorescent assay (IFA). In mice with TCI, the transcriptional and expression levels of the inflammatory factors C1q, IL-1α, and TNF-α followed an up-down-up pattern, although they remained elevated compared to the control group. These findings suggest a potential association between astrocyte polarization towards the A1 subtype and synchronized changes in these three inflammatory mediators. Furthermore, immunofluorescence assay (IFA) revealed a significant increase in the A1 astrocytes (GFAP+C3+) proportion in TCI mice. This study provides evidence that TCI can induce astrocyte polarization, a biological process that may be influenced by changes in the levels of three inflammatory factors: C1q, IL-1α, and TNF-α. Additionally, the release of neurotoxic substances by A1 astrocytes may be associated with the development of TCI.

Immune system roles in pathogenesis, prognosis, control, and treatment of Toxoplasma gondii infection

Toxoplasma gondii is the protozoan causative agent of toxoplasmosis in humans and warm-blooded animals. Recent studies have illustrated that the immune system plays a pivotal role in the pathogenesis of toxoplasmosis by triggering immune cytokines like IL-12, TNF-α, and IFN-γ and immune cells like DCs, Th1, and Th17. On the other hand, some immune components can serve as prognosis markers of toxoplasmosis. In healthy people, the disease is often asymptomatic, but immunocompromised people and newborns may suffer severe symptoms and complications. Therefore, the immune prognostic markers may provide tools to measure the disease progress and help patients to avoid further complications. Immunotherapies using monoclonal antibody, cytokines, immune cells, exosomes, novel vaccines, and anti-inflammatory molecules open new horizon for toxoplasmosis treatment. In this review article, we discussed the immunopathogenesis, prognosis, and immunotherapy of Toxoplasma gondii infection.

Rapid and visual detection of Toxoplasma gondii oocyst in cat feces using loop-mediated isothermal amplification (LAMP) assay

Toxoplasma gondii is an obligate parasitic protozoon that transmits to animals and humans via ingested food. Cats that act as T. gondii's final hosts play a critical role in T. gondii transmission by shedding millions of oocysts. Timely diagnosis of infected cats is essential for preventing toxoplasmosis because oocysts are a putative T. gondii source in epidemiology. We developed a new visual LAMP assay targeting the B1 gene to analyze single oocysts in cat feces in this study. The amplification result could be visually estimated based on the color change. LAMP assay analytical sensitivity was 101 copies/µL for the B1 gene plasmid, which was tenfold better than the PCR reaction. There were no cross-reactions with other parasites. The LAMP assay can detect a single T. gondii oocyst in 200 mg of cat feces. The LAMP assay detected a single oocyst in 200 mg cat feces at a higher rate than the PCR assay (83.3% vs. 50.0%).

Dimethyl itaconate ameliorates the deficits of goal-directed behavior in Toxoplasma gondii infected mice

BACKGROUND

The neurotrophic parasite Toxoplasma gondii (T. gondii) has been implicated as a risk factor for neurodegenerative diseases. However, there is only limited information concerning its underlying mechanism and therapeutic strategy. Here, we investigated the effects of T. gondii chronic infection on the goal-directed cognitive behavior in mice. Moreover, we evaluated the preventive and therapeutic effect of dimethyl itaconate on the behavior deficits induced by the parasite.

METHODS

The infection model was established by orally infecting the cysts of T. gondii. Dimethyl itaconate was intraperitoneally administered before or after the infection. Y-maze and temporal order memory (TOM) tests were used to evaluate the prefrontal cortex-dependent behavior performance. Golgi staining, transmission electron microscopy, indirect immunofluorescence, western blot, and RNA sequencing were utilized to determine the pathological changes in the prefrontal cortex of mice.

RESULTS

We showed that T. gondii infection impaired the prefrontal cortex-dependent goal-directed behavior. The infection significantly downregulated the expression of the genes associated with synaptic transmission, plasticity, and cognitive behavior in the prefrontal cortex of mice. On the contrary, the infection robustly upregulated the expression of activation makers of microglia and astrocytes. In addition, the metabolic phenotype of the prefrontal cortex post infection was characterized by the enhancement of glycolysis and fatty acid oxidation, the blockage of the Krebs cycle, and the disorder of aconitate decarboxylase 1 (ACOD1)-itaconate axis. Notably, the administration of dimethyl itaconate significantly prevented and treated the cognitive impairment induced by T. gondii, which was evidenced by the improvement of behavioral deficits, synaptic ultrastructure lesion and neuroinflammation.

CONCLUSION

The present study demonstrates that T. gondii infection induces the deficits of the goal-directed behavior, which is associated with neuroinflammation, the impairment of synaptic ultrastructure, and the metabolic shifts in the prefrontal cortex of mice. Moreover, we report that dimethyl itaconate has the potential to prevent and treat the behavior deficits.

The Therapeutic Potential of Salidroside for Parkinson's Disease

Parkinson's disease (PD), a neurological disorder, is characterized by the progressive loss of dopaminergic (DA) neurons in the substantia nigra. Its incidence increases with age. Salidroside, a phenolic compound extracted from Sedum roseum, reportedly has multiple biological and pharmacological activities in the nervous system. However, its effects on PD remain unclear. In this review, we summarize the effects of salidroside on PD with regard to DA metabolism, neuronal protection, and glial activation. In addition, we summarize the susceptibility genes and their underlying mechanisms related to antioxidation, inflammation, and autophagy by regulating mitochondrial function, ubiquitin, and multiple signaling pathways involving NF-κB, mTOR, and PI3K/Akt. Although recent studies were based on animal and cellular experiments, this review provides evidence for further clinical utilization of salidroside for PD.

The role of reactive astrocytes in neurotoxicity induced by ultrafine particulate matter

Epidemiological studies have shown that ambient fine particulate matter (PM) can cause various neurodegenerative diseases, including Alzheimer's disease. Reactive astrocytes are strongly induced by ambient fine PM, although their role is poorly understood. Herein, we show that A1 reactive astrocytes (A1s) were induced by neuroinflammatory microglia activated by PM with an aerodynamic diameter ≤ 0.2 μm (PM_0.2). The activated-microglia induced A1s by secreting interleukin-1α, tumor necrosis factor-α, and complement 1q, and these cytokines acting together were necessary and sufficient to induce A1s. PM_0.2-induced A1s could promote synaptic damage in neurons by secreting complement 3 (C3). SB 290157, a highly selective C3aR nonpeptide antagonist, partially ameliorated glial conditioned medium-induced synaptic injury. In vitro synaptic damage was partially prevented when A1 formation was blocked by minocycline. Finally, this study showed that N-acetyl-L-cysteine ameliorated PM_0.2-induced neural damage independent of A1 differentiation. Collectively, these findings explain why central nervous system neurons suffer synaptic damage and neuroinflammation after PM_0.2 exposure and suggest that this exposure induces A1s to contribute to synaptic damage of neurons. This study indicates a potential approach for developing improved treatment of these diseases induced by particulate exposure. SYNOPSIS: PM_0.2-activated neuroinflammatory microglia induced A1 reactive astrocytes (A1s) by secreting IL-1α, TNF-α, and C1q. PM_0.2-induced A1s could promote synaptic damage of neuron by secreting complement 3.

Roles of neuropathology-associated reactive astrocytes: a systematic review

In the contexts of aging, injury, or neuroinflammation, activated microglia signaling with TNF-α, IL-1α, and C1q induces a neurotoxic astrocytic phenotype, classified as A1, A1-like, or neuroinflammatory reactive astrocytes. In contrast to typical astrocytes, which promote neuronal survival, support synapses, and maintain blood-brain barrier integrity, these reactive astrocytes downregulate supportive functions and begin to secrete neurotoxic factors, complement components like C3, and chemokines like CXCL10, which may facilitate recruitment of immune cells across the BBB into the CNS. The proportion of pro-inflammatory reactive astrocytes increases with age through associated microglia activation, and these pro-inflammatory reactive astrocytes are particularly abundant in neurodegenerative disorders. As the identification of astrocyte phenotypes progress, their molecular and cellular effects are characterized in a growing array of neuropathologies.

The Defensive Interactions of Prominent Infectious Protozoan Parasites: The Host's Complement System

The complement system exerts crucial functions both in innate immune responses and adaptive humoral immunity. This pivotal system plays a major role dealing with pathogen invasions including protozoan parasites. Different pathogens including parasites have developed sophisticated strategies to defend themselves against complement killing. Some of these strategies include the employment, mimicking or inhibition of host's complement regulatory proteins, leading to complement evasion. Therefore, parasites are proven to use the manipulation of the complement system to assist them during infection and persistence. Herein, we attempt to study the interaction´s mechanisms of some prominent infectious protozoan parasites including Plasmodium, Toxoplasma, Trypanosoma, and Leishmania dealing with the complement system. Moreover, several crucial proteins that are expressed, recruited or hijacked by parasites and are involved in the modulation of the host´s complement system are selected and their role for efficient complement killing or lysis evasion is discussed. In addition, parasite's complement regulatory proteins appear as plausible therapeutic and vaccine targets in protozoan parasitic infections. Accordingly, we also suggest some perspectives and insights useful in guiding future investigations.

Microglia and astrocyte responses to neuropathogenic protozoan parasites

Cerebral toxoplasmosis and cerebral malaria are two important neurological diseases caused by protozoan parasites. In this review, we discuss recent findings regarding the innate immune responses of microglia and astrocytes to Toxoplasma and Plasmodium infection. In both infections, these tissue-resident glial cells perform a sentinel function mediated by alarmin crosstalk that licenses adaptive type 1 immunity in the central nervous system. Divergent protective or pathogenic effects of type 1 activation of these astrocytes and microglia are revealed depending on the inherent lytic potential of the protozoan parasite.

A1/A2 astrocytes in central nervous system injuries and diseases: Angels or devils?

Astrocytes play a pivotal role in maintaining the central nervous system (CNS) homeostasis and function. In response to CNS injuries and diseases, reactive astrocytes are triggered. By purifying and genetically profiling reactive astrocytes, it has been now found that astrocytes can be activated into two polarization states: the neurotoxic or pro-inflammatory phenotype (A1) and the neuroprotective or anti-inflammatory phenotype (A2). Although the simple dichotomy of the A1/A2 phenotypes does not reflect the wide range of astrocytic phenotypes, it facilitates our understanding of the reactive state of astrocytes in various CNS disorders. This article reviews the recent evidences regarding A1/A2 astrocytes, including (a) the specific markers and morphological characteristics, (b) the effects of A1/A2 astrocytes on the neurovascular unit, and (c) the molecular mechanisms involved in the phenotypic switch of astrocytes. Although many questions remain, a deeper understanding of different phenotypic astrocytes will eventually help us to explore effective strategies for neurological disorders by targeting astrocytes.