Microglia and border-associated macrophages (BAMs) are brain-resident self-renewing cells. Here, we examined the fate of microglia, BAMs, and recruited macrophages upon neuroinflammation and through ...resolution. Upon infection, Trypanosoma brucei parasites invaded the brain via its border regions, triggering brain barrier disruption and monocyte infiltration. Fate mapping combined with single-cell sequencing revealed microglia accumulation around the ventricles and expansion of epiplexus cells. Depletion experiments using genetic targeting revealed that resident macrophages promoted initial parasite defense and subsequently facilitated monocyte infiltration across brain barriers. These recruited monocyte-derived macrophages outnumbered resident macrophages and exhibited more transcriptional plasticity, adopting antimicrobial gene expression profiles. Recruited macrophages were rapidly removed upon disease resolution, leaving no engrafted monocyte-derived cells in the parenchyma, while resident macrophages progressively reverted toward a homeostatic state. Long-term transcriptional alterations were limited for microglia but more pronounced in BAMs. Thus, brain-resident and recruited macrophages exhibit diverging responses and dynamics during infection and resolution.
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•T. brucei parasites invade the brain via its borders and evoke macrophage expansion•Brain-resident and blood-recruited macrophages show divergent responses•Upon disease resolution, recruited macrophages rapidly disappear and do not engraft•While disease-associated microglia revert toward homeostasis, BAMs remain altered
De Vlaminck et al. examine the fate of microglia, border-associated macrophages, and recruited macrophages upon Trypanosoma brucei infection and resolution of neuroinflammation. They show how different types of brain macrophages orchestrate the immune response to invading parasites, revealing that brain-resident and recruited macrophages exhibit diverging responses and dynamics during infection and the return to homeostasis.
•CORT release pellets induce HPA-axis disruption.•Chronic CORT-exposure induces depressive-like behavior.•CORT release pellets induce a long-lasting decrease in hippocampal BDNF.
The corticosterone ...mouse model is widely used in preclinical research towards a better understanding of mechanisms of major depression. One particular administration procedure is the subcutaneous implantation of corticosterone slow-release pellets. In this report we want to provide basic evidence, regarding behavioral changes, neurotransmitter and -modulator levels and some other relevant biomolecules after hypothalamic-pituitary-adrenal-axis distortion. We show that three weeks of corticosterone pellet exposure robustly induces depressive-like but not anxiety-like behavior in mice, accompanied by a significant decrease in hippocampal brain-derived neurotrophic factor levels, at five weeks after the start of treatment. Furthermore there is an overall decrease in plasma corticosterone levels after three weeks of treatment that lasts up until the five weeks’ time point. On the other hand, no differences are observed in total monoamine, glutamate or d-serine levels, nor in glucocorticoid receptor expression, in various depression-related brain areas. Altogether this characterization delivers vital information, supplementary to existing literature, regarding the phenotyping of pellet-induced hypothalamic-pituitary-adrenal-axis disruption in mice following three weeks of continuous corticosterone exposure.
Parkinson's disease (PD) is an age-related neurodegenerative condition characterized by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). A loss of proteasome ...function participates to the pathogenesis of PD, leading to the development of rodent models in which a proteasome inhibitor is applied to the nigrostriatal pathway. We recently characterized the intranigral lactacystin (LAC) mouse model, leading to nigrostriatal degeneration, motor dysfunction and alpha-synuclein accumulation. In the present study, we compared the effect of two commonly used anesthetics for generating animal models of PD-i.e., ketamine (KET) and isoflurane (ISO)-on the vulnerability of mouse dopaminergic neurons to proteasome inhibition-induced degeneration. Both anesthetics have the potential to affect the susceptibility of the nigrostriatal pathway for toxin-induced degeneration, and are known to modulate dopamine (DA) homeostasis. Yet, their impact on nigrostriatal degeneration in the proteasome inhibition model has not been evaluated. Unilateral injection with LAC in the SNpc of mice induced motor impairment and significantly reduced the number of dopaminergic cells to ~55%, irrespective of the anesthetic used. However, LAC-induced striatal DA depletion was slightly affected by the choice of anesthetic, resulting in a significant increase in DA turnover in the ISO- but not in KET-treated mice. These results suggest that the extent of nigrostriatal dopaminergic neural loss caused by LAC is not influenced by the choice of anesthetic, and that compared to other PD models, KET is not neuroprotective in the LAC model.
Abstract Depression and anxiety are disabling and highly prevalent psychiatric disorders. To better understand the neurobiological basis of mood and anxiety disorders, relevant animal models are ...needed. The corticosterone mouse model is frequently used to study depression. Chronic stress and accompanying glucocorticoid elevation causes pathological changes in the central nervous system, which are related to psychiatric symptoms. Exogenous administration of corticosterone is therefore often used to induce depressive-like behavior in mice and in some cases also features of anxiety-like behavior are shown. However, a thorough characterization of this model has never been conducted and housing conditions of the used subjects often differ between the implemented protocols. We chronically administered a subcutaneous corticosterone bolus injection to single- and group-housed mice, and we subsequently evaluated the face validity of this model by performing a battery of behavioral tests (forced swim test, mouse-tail suspension test, saccharin intake test, novelty-suppressed feeding test, elevated plus maze, light/dark paradigm and open field test). Our results show that corticosterone treatment has a substantial overall effect on depressive-like behavior. Increases in anxiety-like behavior on the other hand are mainly seen in single housed animals, independent of treatment. The current study therefore does not only show a detailed behavioral characterization of the corticosterone mouse model, but furthermore also elucidates the critical influence of housing conditions on the behavioral outcome in this model.
The astrocytic cystine/glutamate antiporter system x
(with xCT as the specific subunit) imports cystine in exchange for glutamate and has been shown to interact with multiple pathways in the brain ...that are dysregulated in age-related neurological disorders, including glutamate homeostasis, redox balance, and neuroinflammation. In the current study, we investigated the effect of genetic xCT deletion on lactacystin (LAC)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced degeneration of the nigrostriatal pathway, as models for Parkinson's disease (PD). Dopaminergic neurons of adult xCT knock-out mice (xCT
) demonstrated an equal susceptibility to intranigral injection of the proteasome inhibitor LAC, as their wild-type (xCT
) littermates. Contrary to adult mice, aged xCT
mice showed a significant decrease in LAC-induced degeneration of nigral dopaminergic neurons, depletion of striatal dopamine (DA) and neuroinflammatory reaction, compared to age-matched xCT
littermates. Given this age-related protection, we further investigated the sensitivity of aged xCT
mice to chronic and progressive MPTP treatment. However, in accordance with our previous observations in adult mice (Bentea et al., 2015a), xCT deletion did not confer protection against MPTP-induced nigrostriatal degeneration in aged mice. We observed an increased loss of nigral dopaminergic neurons, but equal striatal DA denervation, in MPTP-treated aged xCT
mice when compared to age-matched xCT
littermates. To conclude, we reveal age-related protection against proteasome inhibition-induced nigrostriatal degeneration in xCT
mice, while xCT deletion failed to protect nigral dopaminergic neurons of aged mice against MPTP-induced toxicity. Our findings thereby provide new insights into the role of system x
in mechanisms of dopaminergic cell loss and its interaction with aging.
Despite ample evidence for the therapeutic potential of inhibition of the cystine/glutamate antiporter system x
c
−
in neurological disorders and in cancer, none of the proposed inhibitors is ...selective. In this context, a lot of research has been performed using the EMA- and FDA-approved drug sulfasalazine (SAS). Even though this molecule is already on the market for decades as an anti-inflammatory drug, serious side effects due to its use have been reported. Whereas for the treatment of the main indications, SAS needs to be cleaved in the intestine into the anti-inflammatory compound mesalazine, it needs to reach the systemic circulation in its intact form to allow inhibition of system x
c
−
. The higher plasma levels of intact SAS (or its metabolites) might induce adverse effects, independent of its action on system x
c
−
. Some of these effects have however been attributed to system x
c
−
inhibition, calling into question the safety of targeting system x
c
−
. In this study we chronically treated system x
c
−
- deficient mice and their wildtype littermates with two different doses of SAS (160 mg/kg twice daily or 320 mg/kg once daily, i.p.) and studied some of the adverse effects that were previously reported. SAS had a negative impact on the survival rate, the body weight, the thermoregulation and/or stress reaction of mice of both genotypes, and thus independent of its inhibitory action on system x
c
−
. While SAS decreased the total distance travelled in the open-field test the first time the mice encountered the test, it did not influence this parameter on the long-term and it did not induce other behavioral changes such as anxiety- or depressive-like behavior. Finally, no major histological abnormalities were observed in the spinal cord. To conclude, we were unable to identify any undesirable system x
c
−
-dependent effect of chronic administration of SAS.
Zonisamide (ZNS), an anticonvulsant drug exhibiting symptomatic effects in Parkinson's disease (PD), was recently reported to exert neuroprotection in rodent models. One of the proposed ...neuroprotective mechanisms involves increased protein expression of xCT, the specific subunit of the cystine/glutamate antiporter system xc−, inducing glutathione (GSH) synthesis. Here, we investigated the outcome of ZNS treatment in a mouse model of PD based on intranigral proteasome inhibition, and whether the observed effects would be mediated by system xc−. The proteasome inhibitor lactacystin (LAC) was administered intranigrally to male C57BL/6J mice receiving repeated intraperitoneal injections of either ZNS 30mgkg−1 or vehicle. Drug administration was initiated three days prior to stereotaxic LAC injection and was maintained until six days post-surgery. One week after lesion, mice were behaviorally assessed and investigated in terms of nigrostriatal neurodegeneration and molecular changes at the level of the basal ganglia, including expression levels of xCT. ZNS reduced the loss of nigral dopaminergic neurons following LAC injection and the degree of sensorimotor impairment. ZNS failed, however, to modulate xCT expression in basal ganglia of lesioned mice. In a separate set of experiments, the impact of ZNS treatment on system xc− was investigated in control conditions in vivo as well as in vitro. Similarly, ZNS did not influence xCT or glutathione levels in naive male C57BL/6J mice, nor did it alter system xc− activity or glutathione content in vitro. Taken together, these results demonstrate that ZNS treatment provides neuroprotection and behavioral improvement in a PD mouse model based on proteasome inhibition via system xc− independent mechanisms.
•ZNS decreases LAC-induced nigral DA-ergic neurodegeneration.•ZNS reduces the degree of LAC-induced sensorimotor dysfunction.•ZNS does not influence the expression or activity of system xc−.
There is considerable preclinical and clinical evidence indicating that abnormal changes in glutamatergic signaling underlie the development of mood disorders. Astrocytic glutamate dysfunction, in ...particular, has been recently linked with the pathogenesis and treatment of mood disorders, including anxiety and depression. System xc- is a glial cystine/glutamate antiporter that is responsible for nonvesicular glutamate release in various regions of the brain. Although system xc- is involved in glutamate signal transduction, its possible role in mediating anxiety or depressive-like behaviors is currently unknown. In the present study, we phenotyped adult and aged system xc- deficient mice in a battery of tests for anxiety and depressive-like behavior (open field, light/dark test, elevated plus maze, novelty suppressed feeding, forced swim test, tail suspension test). Concomitantly, we evaluated the sensorimotor function of system xc- deficient mice, using motor and sensorimotor based tests (rotarod, adhesive removal test, nest building test). Finally, due to the presence and potential functional relevance of system xc- in the eye, we investigated the visual acuity of system xc- deficient mice (optomotor test). Our results indicate that loss of system xc- does not affect motor or sensorimotor function, in either adult or aged mice, in any of the paradigms investigated. Similarly, loss of system xc- does not affect basic visual acuity, in either adult or aged mice. On the other hand, in the open field and light/dark tests, and forced swim and tail suspension tests respectively, we could observe significant anxiolytic and antidepressive-like effects in system xc- deficient mice that in certain cases (light/dark, forced swim) were age-dependent. These findings indicate that, under physiological conditions, nonvesicular glutamate release via system xc- mediates aspects of higher brain function related to anxiety and depression, but does not influence sensorimotor function or spatial vision. As such, modulation of system xc- might constitute the basis of innovative interventions in mood disorders.
•Phenotypic screen of adult and aged system xc- deficient mice.•Loss of system xc- decreases anxiety-like behavior.•Loss of system xc- decreases depressive-like behavior.•Age-dependent changes in emotional behavior.•System xc- deficient mice demonstrate intact sensorimotor function and spatial vision.
Background Multiple sclerosis (MS) is an autoimmune demyelinating disease that affects the central nervous system (CNS), leading to neurodegeneration and chronic disability. Accumulating evidence ...points to a key role for neuroinflammation, oxidative stress, and excitotoxicity in this degenerative process. System xc - or the cystine/glutamate antiporter could tie these pathological mechanisms together: its activity is enhanced by reactive oxygen species and inflammatory stimuli, and its enhancement might lead to the release of toxic amounts of glutamate, thereby triggering excitotoxicity and neurodegeneration. Methods Semi-quantitative Western blotting served to study protein expression of xCT, the specific subunit of system xc -, as well as of regulators of xCT transcription, in the normal appearing white matter (NAWM) of MS patients and in the CNS and spleen of mice exposed to experimental autoimmune encephalomyelitis (EAE), an accepted mouse model of MS. We next compared the clinical course of the EAE disease, the extent of demyelination, the infiltration of immune cells and microglial activation in xCT-knockout (xCT-/-) mice and irradiated mice reconstituted in xCT-/- bone marrow (BM), to their proper wild type (xCT+/+) controls. Results xCT protein expression levels were upregulated in the NAWM of MS patients and in the brain, spinal cord, and spleen of EAE mice. The pathways involved in this upregulation in NAWM of MS patients remain unresolved. Compared to xCT+/+ mice, xCT-/- mice were equally susceptible to EAE, whereas mice transplanted with xCT-/- BM, and as such only exhibiting loss of xCT in their immune cells, were less susceptible to EAE. In none of the above-described conditions, demyelination, microglial activation, or infiltration of immune cells were affected. Conclusions Our findings demonstrate enhancement of xCT protein expression in MS pathology and suggest that system xc - on immune cells invading the CNS participates to EAE. Since a total loss of system xc - had no net beneficial effects, these results have important implications for targeting system xc - for treatment of MS.
•Unaffected xCT protein levels in RAW264.7 macrophages after TMEV infection.•Activity of system xc− unchanged in RAW264.7 macrophages after TMEV infection.•Neither early nor chronic TMEV-induced ...disease alters xCT protein levels in CNS.
Changes in the expression of xCT, the specific subunit of system xc− or the cystine/glutamate antiporter, have been associated with several neurological disorders and system xc− was recently proposed as a potential target for the development of new treatment strategies for multiple sclerosis (MS). In this study we used Theiler's murine encephalomyelitis virus (TMEV) infection, both in vitro and in vivo, as a model to further evaluate the involvement of system xc− in MS. Protein levels of xCT, as well as activity of system xc− were unaffected in RAW264.7 macrophages after infection with the demyelinating DA strain of TMEV. Also, protein expression of xCT remained stable in spinal cord and brain of FVB mice 1–2 and 6 weeks after intracranial injection of the DA strain of TMEV. These results demonstrate that TMEV infection of macrophages or FVB mice has no effect on system xc− and as such cannot be used as a model to study the involvement of system xc− in MS.
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