Continuous cuprizone intoxication allows active experimental autoimmune encephalomyelitis induction in C57BL/6 mice

Titration of cuprizone induces reliable demyelination

Multiple Sclerosis (MS) is a chronic inflammatory disease of the central nervous system. Cuprizone-induced demyelination, wherein mice are fed a diet containing the copper chelator cuprizone, is a well-established model that replicates key features of demyelination and remyelination. However, the dose-response relationship of cuprizone is complex; high concentrations can induce toxicity, whereas low doses may fail to produce reliable demyelination across subjects. This study aimed to investigate whether titration of the cuprizone concentration results in reliable acute demyelination and weight stabilization. To this end, experimental animals were intoxicated with cuprizone over a period of 5 weeks to induce acute demyelination. In one group, during the first 10 days, the initial cuprizone dose was gradually reduced until the experimental animals showed stable weights. Another group was subjected to a continuous cuprizone intoxication protocol without adaptions. Histological analyses were performed to quantify the extent of demyelination and glia activation. Animals of both groups experienced significant weight loss. Histological analyses revealed, despite adopting the cuprizone concentration, substantial demyelination of various brain regions, including the corpus callosum. This pattern was consistent across multiple staining methods, including anti-proteolipid protein (PLP), anti-myelin basic protein (MBP), and luxol-fast-blue (LFB) stains. Additionally, grey matter regions, specifically the neocortex, demonstrated significant demyelination. Accompanying these changes, there was notable activation and accumulation of microglia and astrocytes in white and grey matter regions. These histopathological changes were comparably pronounced in both cuprizone-treated groups. In summary, we demonstrate that titration of cuprizone is a reliable approach to induce acute demyelination in the mouse forebrain. This work represents a significant step toward refining animal models of MS, contributing to the broader effort of understanding and treating this complex disease.

Investigation of choroid plexus variability in schizophrenia-spectrum disorders-insights from a multimodal study

Previous studies have suggested that choroid plexus (ChP) enlargement occurs in individuals with schizophrenia-spectrum disorders (SSD) and is associated with peripheral inflammation. However, it is unclear whether such an enlargement delineates a biologically defined subgroup of SSD. Moreover, it remains elusive how ChP is linked to brain regions associated with peripheral inflammation in SSD. A cross-sectional cohort of 132 individuals with SSD and 107 age-matched healthy controls (HC) underwent cerebral magnetic resonance imaging (MRI) and clinical phenotyping to investigate the ChP and associated regions. A case-control comparison of ChP volumes was conducted, and structural variance was analyzed by employing the variability ratio (VR). K-means clustering analysis was used to identify subgroups with distinct patterns of the ventricular system, and the clusters were compared in terms of demographic, clinical, and immunological measures. The relationship between ChP volumes and brain regions, previously associated with peripheral inflammation, was investigated. We did not find a significant enlargement of the ChP in SSD compared to HC but detected an increased VR of ChP and lateral ventricle volumes. Based on these regions, we identified 3 clusters with differences in cognitive measures and possibly inflammatory markers. Larger ChP volume was associated with higher volumes of hippocampus, putamen, and thalamus in SSD but not in HC. This study suggests that ChP variability, but not mean volume, is increased in individuals with SSD, compared to HC. Larger ChP volumes in SSD were associated with higher volumes of regions previously associated with peripheral inflammation.

A Novel Mouse Model for Cerebral Inflammatory Demyelination in X-Linked Adrenoleukodystrophy: Insights into Pathogenesis and Potential Therapeutic Targets

OBJECTIVE

X-linked adrenoleukodystrophy (ALD) is caused by mutations in ABCD1, a peroxisomal gene. More than half of males with an ABCD1 mutation develop inflammatory cerebral demyelination (cALD), but underlying mechanisms remain unknown and therapies are limited. We sought to develop and characterize a mouse model of cALD to facilitate study of disease mechanisms and therapy development.

METHODS

We used immunoassays and immunohistochemistry to assess novel (interleukin 18 [IL-18]) and established molecular markers in cerebrospinal fluid (CSF) and postmortem brain tissue from cALD patients. We generated a cALD phenotype in Abcd1-knockout mice using a 2-hit method that combines cuprizone and experimental autoimmune encephalomyelitis models. We then used magnetic resonance imaging (MRI) and immunohistochemistry to assess the fidelity of cALD molecular markers in the mice.

RESULTS

Human and mouse cALD lesions shared histologic features of myelin phagocytosis, myelin loss, abundant microglial activation, T and B-cell infiltration, and astrogliosis. Compared to wild-type controls, Abcd1-knockout mice displayed more cerebral demyelination, blood-brain barrier disruption, and perivascular immune cell infiltration. This enhanced inflammatory response was associated with higher levels of fibrin deposition, oxidative stress, demyelination, and axonal injury. IL-18 immunoreactivity co-localized with perivascular monocytes/macrophages in both human and mouse brain tissue. In cALD patients, CSF IL-18 levels correlated with MRI lesion severity.

INTERPRETATION

Our results suggest loss of Abcd1 function in mice predisposes to more severe blood-brain barrier disruption, cerebral inflammation driven by the infiltration of peripheral immune cells, demyelination, and axonal damage, replicating human cALD features. This novel mouse model could shed light on cALD mechanisms and accelerate cALD therapy development. ANN NEUROL 2024.

Starvation in Mice Induces Liver Damage Associated with Autophagy

Anorexia nervosa (AN) induces organ dysfunction caused by malnutrition, including liver damage leading to a rise in transaminases due to hepatocyte damage. The underlying pathophysiology of starvation-induced liver damage is poorly understood. We investigate the effect of a 25% body weight reduction on murine livers in a mouse model and examine possible underlying mechanisms of starvation-induced liver damage. Female mice received a restricted amount of food with access to running wheels until a 25% weight reduction was achieved. This weight reduction was maintained for two weeks to mimic chronic starvation. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels were measured spectrophotometrically. Liver fat content was analyzed using an Oil Red O stain, and liver glycogen was determined using a Periodic acid-Schiff (PAS) stain. Immunohistochemical stains were used to investigate macrophages, proliferation, apoptosis, and autophagy. Starvation led to an elevation of AST and ALT values, a decreased amount of liver fat, and reduced glycogen deposits. The density of F4/80+ macrophage numbers as well as proliferating KI67+ cells were decreased by starvation, while apoptosis was not altered. This was paralleled by an increase in autophagy-related protein staining. Increased transaminase values suggest the presence of liver damage in the examined livers of starved mice. The observed starvation-induced liver damage may be attributed to increased autophagy. Whether other mechanisms play an additional role in starvation-induced liver damage remains to be investigated.

Glial cell changes in the corpus callosum in chronically-starved mice

Anorexia nervosa (AN) is characterized by emaciation, hyperactivity, and amenorrhea. Imaging studies in AN patients have revealed reductions in grey and white matter volume, which correlate with the severity of neuropsychological deficits. However, the cellular basis for the observed brain atrophy is poorly understood. Although distinct hypothalamic centers, including the arcuate nucleus (ARC) are critically involved in regulating feeding behavior, little is known about potential hypothalamic modifications in this disorder. Since glia e.g. astrocytes and microglia influence neuronal circuits, we investigated the glial changes underlying pathophysiology of starvation in the corpus callosum (CC) and hypothalamus. Female mice were given a limited amount of food once a day and had unlimited access to a running wheel until a 20% weight reduction was achieved (acute starvation). This weight reduction was maintained for two weeks to mimic chronic starvation. Immunohistochemistry was used to quantify the density of astrocytes, microglia, oligodendrocytes, and the staining intensity of neuropeptide Y (NPY), a potent orexigenic peptide. Chronic starvation induced a decreased density of OLIG2+ oligodendrocytes, GFAP+ astrocytes, and IBA1+ microglia in the CC. However, the densities of glial cells remained unchanged in the ARC following starvation. Additionally, the staining intensity of NPY increased after both acute and chronic starvation, indicating an increased orexigenic signaling. Chronic starvation induced glial cell changes in the CC in a mouse model of AN suggesting that glia pathophysiology may play a role in the disease.

Ryu J, Akassoglou K, Talebian S, Chu P, Pisani L, Musolino P, Steinman L, Doyle K, Robinson WH, Sharpe O, Cayrol R, Orchard P, Lund T, Vogel H, Lenail M, Han MH, Bonkowsky JL, Van Haren KP. A novel mouse model of cerebral adrenoleukodystrophy highlights NLRP3 activity in lesion pathogenesis

Objective

We sought to create and characterize a mouse model of the inflammatory, cerebral demyelinating phenotype of X-linked adrenoleukodystrophy (ALD) that would facilitate the study of disease pathogenesis and therapy development. We also sought to cross-validate potential therapeutic targets such as fibrin, oxidative stress, and the NLRP3 inflammasome, in post-mortem human and murine brain tissues.

Background

ALD is caused by mutations in the gene ABCD1 encoding a peroxisomal transporter. More than half of males with an ABCD1 mutation develop the cerebral phenotype (cALD). Incomplete penetrance and absence of a genotype-phenotype correlation imply a role for environmental triggers. Mechanistic studies have been limited by the absence of a cALD phenotype in the Abcd1-null mouse.

Methods

We generated a cALD phenotype in 8-week-old, male Abcd1-null mice by deploying a two-hit method that combines cuprizone (CPZ) and experimental autoimmune encephalomyelitis (EAE) models. We employed in vivo MRI and post-mortem immunohistochemistry to evaluate myelin loss, astrogliosis, blood-brain barrier (BBB) disruption, immune cell infiltration, fibrin deposition, oxidative stress, and Nlrp3 inflammasome activation in mice. We used bead-based immunoassay and immunohistochemistry to evaluate IL-18 in CSF and post-mortem human cALD brain tissue.

Results

MRI studies revealed T2 hyperintensities and post-gadolinium enhancement in the medial corpus callosum of cALD mice, similar to human cALD lesions. Both human and mouse cALD lesions shared common histologic features of myelin phagocytosis, myelin loss, abundant microglial activation, T and B-cell infiltration, and astrogliosis. Compared to wild-type controls, Abcd1-null mice had more severe cerebral inflammation, demyelination, fibrin deposition, oxidative stress, and IL-18 activation. IL-18 immunoreactivity co-localized with macrophages/microglia in the perivascular region of both human and mouse brain tissue.

Interpretation

This novel mouse model of cALD suggests loss of Abcd1 function predisposes to more severe cerebral inflammation, oxidative stress, fibrin deposition, and Nlrp3 pathway activation, which parallels the findings seen in humans with cALD. We expect this model to enable long-sought investigations into cALD mechanisms and accelerate development of candidate therapies for lesion prevention, cessation, and remyelination.

Chemogenetic activation of locus coeruleus neurons ameliorates the severity of multiple sclerosis

BACKGROUND

Most current disease-modifying therapies approved for multiple sclerosis (MS) are immunomodulatory drugs that counteract the aberrant activity of the immune system. Hence, new pharmacological interventions that drive anti-inflammatory activity and neuroprotection would represent interesting alternative therapeutic approaches or complementary strategies to treat progressive forms of MS. There is evidence of reduced noradrenaline levels and alterations to locus coeruleus (LC) noradrenergic neurons in MS patients, as well as in animal models of this disease, potentially factors contributing to the pathophysiology. Drugs that enhance noradrenaline appear to have some beneficial effects in MS, suggesting their potential to dampen the underlying pathology and disease progression.

METHODS

Therefore, we explored the consequences of chronic LC noradrenergic neurons activation by chemogenetics in experimental autoimmune encephalomyelitis (EAE) mice, the most widely used experimental model of MS. LC activation from the onset or the peak of motor symptoms was explored as two different therapeutic approaches, assessing the motor and non-motor behavioral changes as EAE progresses, and studying demyelination, inflammation and glial activation in the spinal cord and cerebral cortex during the chronic phase of EAE.

RESULTS

LC activation from the onset of motor symptoms markedly alleviated the motor deficits in EAE mice, as well as their anxiety-like behavior and sickness, in conjunction with reduced demyelination and perivascular infiltration in the spinal cord and glial activation in the spinal cord and prefrontal cortex (PFC). When animals exhibited severe paralysis, LC activation produced a modest alleviation of EAE motor symptoms and it enhanced animal well-being, in association with an improvement of the EAE pathology at the spinal cord and PFC level. Interestingly, the reduced dopamine beta-hydroxylase expression associated with EAE in the spinal cord and PFC was reversed through chemogenetic LC activation.

CONCLUSION

Therefore, clear anti-inflammatory and neuroprotective effects were produced by the selective activation of LC noradrenergic neurons in EAE mice, having greater benefits when LC activation commenced earlier. Overall, these data suggest noradrenergic LC neurons may be targets to potentially alleviate some of the motor and non-motor symptoms in MS.

Low sulfated heparan sulfate mimetic differentially affects repair in immune-mediated and toxin-induced experimental models of demyelination

There is an urgent need for therapies that target the multicellular pathology of central nervous system (CNS) disease. Modified, nonanticoagulant heparins mimic the heparan sulfate glycan family and are known regulators of multiple cellular processes. In vitro studies have demonstrated that low sulfated modified heparin mimetics (LS-mHeps) drive repair after CNS demyelination. Herein, we test LS-mHep7 (an in vitro lead compound) in experimental autoimmune encephalomyelitis (EAE) and cuprizone-induced demyelination. In EAE, LS-mHep7 treatment resulted in faster recovery and rapidly reduced inflammation which was accompanied by restoration of animal weight. LS-mHep7 treatment had no effect on remyelination or on OLIG2 positive oligodendrocyte numbers within the corpus callosum in the cuprizone model. Further in vitro investigation confirmed that LS-mHep7 likely mediates its pro-repair effect in the EAE model by sequestering inflammatory cytokines, such as CCL5 which are upregulated during immune-mediated inflammatory attacks. These data support the future clinical translation of this next generation modified heparin as a treatment for CNS diseases with active immune system involvement.

Different Methods for Evaluating Microglial Activation Using Anti-Ionized Calcium-Binding Adaptor Protein-1 Immunohistochemistry in the Cuprizone Model

Microglia play an important role in the pathology of various central nervous system disorders, including multiple sclerosis (MS). While different methods exist to evaluate the extent of microglia activation, comparative studies investigating the sensitivity of these methods are missing for most models. In this study, we systematically evaluated which of the three commonly used histological methods (id est, quantification of microglia density, densitometrically evaluated staining intensity, or cellular morphology based on the determination of a ramification index, all measured in anti-ionized calcium-binding adaptor protein-1 (IBA1) immunohistochemical stains) is the most sensitive method to detect subtle changes in the microglia activation status in the context of MS. To this end, we used the toxin-induced cuprizone model which allows the experimental induction of a highly reproducible demyelination in several central nervous system regions, paralleled by early microglia activation. In this study, we showed that after 3 weeks of cuprizone intoxication, all methods reveal a significant microglia activation in the white matter corpus callosum. In contrast, in the affected neocortical grey matter, the evaluation of anti-IBA1 cell morphologies was the most sensitive method to detect subtle changes of microglial activation. The results of this study provide a useful guide for future immunohistochemical evaluations in the cuprizone and other neurodegenerative models.

Transmembrane protein 119 is neither a specific nor a reliable marker for microglia

Microglia are the resident innate immune cells of the central nervous system (CNS) parenchyma. To determine the impact of microglia on disease development and progression in neurodegenerative and neuroinflammatory diseases, it is essential to distinguish microglia from peripheral macrophages/monocytes, which are eventually equally recruited. It has been suggested that transmembrane protein 119 (TMEM119) serves as a reliable microglia marker that discriminates resident microglia from blood-derived macrophages in the human and murine brain. Here, we investigated the validity of TMEM119 as a microglia marker in four in vivo models (cuprizone intoxication, experimental autoimmune encephalomyelitis (EAE), permanent filament middle cerebral artery occlusion (fMCAo), and intracerebral 6-hydroxydopamine (6-OHDA) injections) as well as post mortem multiple sclerosis (MS) brain tissues. In all applied animal models and post mortem MS tissues, we found increased densities of ionized calcium-binding adapter molecule 1⁺ (IBA1⁺ ) cells, paralleled by a significant decrease in TMEM119 expression. In addition, other cell types in peripheral tissues (i.e., follicular dendritic cells and brown adipose tissue) were also found to express TMEM119. In summary, this study demonstrates that TMEM119 is not exclusively expressed by microglia nor does it label all microglia, especially under cellular stress conditions. Since novel transgenic lines have been developed to label microglia using the TMEM119 promotor, downregulation of TMEM119 expression might interfere with the results and should, thus, be considered when working with these transgenic mouse models.

Neurological Benefits, Clinical Challenges, and Neuropathologic Promise of Medical Marijuana: A Systematic Review of Cannabinoid Effects in Multiple Sclerosis and Experimental Models of Demyelination

Despite current therapeutic strategies for immunomodulation and relief of symptoms in multiple sclerosis (MS), remyelination falls short due to dynamic neuropathologic deterioration and relapses, leading to accrual of disability and associated patient dissatisfaction. The potential of cannabinoids includes add-on immunosuppressive, analgesic, neuroprotective, and remyelinative effects. This study evaluates the efficacy of medical marijuana in MS and its experimental animal models. A systematic review was conducted by a literature search through PubMed, ProQuest, and EBSCO electronic databases for studies reported since 2007 on the use of cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC) in MS and in experimental autoimmune encephalomyelitis (EAE), Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), and toxin-induced demyelination models. Study selection and data extraction were performed by 3 reviewers, and 28 studies were selected for inclusion. The certainty of evidence was appraised using the Cochrane GRADE approach. In clinical studies, there was low- and moderate-quality evidence that treatment with ~1:1 CBD/THC mixtures as a nabiximols (Sativex®) oromucosal spray reduced numerical rating scale (NRS) scores for spasticity, pain, and sleep disturbance, diminished bladder overactivity, and decreased proinflammatory cytokine and transcription factor expression levels. Preclinical studies demonstrated decreases in disease severity, hindlimb stiffness, motor function, neuroinflammation, and demyelination. Other experimental systems showed the capacity of cannabinoids to promote remyelination in vitro and by electron microscopy. Modest short-term benefits were realized in MS responders to adjunctive therapy with CBD/THC mixtures. Future studies are recommended to investigate the cellular and molecular mechanisms of cannabinoid effects on MS lesions and to evaluate whether medical marijuana can accelerate remyelination and retard the accrual of disability over the long term.

Translational value of choroid plexus imaging for tracking neuroinflammation in mice and humans

Neuroinflammation is a pathophysiological hallmark of multiple sclerosis and has a close mechanistic link to neurodegeneration. Although this link is potentially targetable, robust translatable models to reliably quantify and track neuroinflammation in both mice and humans are lacking. The choroid plexus (ChP) plays a pivotal role in regulating the trafficking of immune cells from the brain parenchyma into the cerebrospinal fluid (CSF) and has recently attracted attention as a key structure in the initiation of inflammatory brain responses. In a translational framework, we here address the integrity and multidimensional characteristics of the ChP under inflammatory conditions and question whether ChP volumes could act as an interspecies marker of neuroinflammation that closely interrelates with functional impairment. Therefore, we explore ChP characteristics in neuroinflammation in patients with multiple sclerosis and in two experimental mouse models, cuprizone diet-related demyelination and experimental autoimmune encephalomyelitis. We demonstrate that ChP enlargement-reconstructed from MRI-is highly associated with acute disease activity, both in the studied mouse models and in humans. A close dependency of ChP integrity and molecular signatures of neuroinflammation is shown in the performed transcriptomic analyses. Moreover, pharmacological modulation of the blood-CSF barrier with natalizumab prevents an increase of the ChP volume. ChP enlargement is strongly linked to emerging functional impairment as depicted in the mouse models and in multiple sclerosis patients. Our findings identify ChP characteristics as robust and translatable hallmarks of acute and ongoing neuroinflammatory activity in mice and humans that could serve as a promising interspecies marker for translational and reverse-translational approaches.

Cuprizone-induced demyelination triggers a CD8-pronounced T cell recruitment

The loss of myelinating oligodendrocytes is a key characteristic of many neurological diseases, including Multiple Sclerosis (MS). In progressive MS, where effective treatment options are limited, peripheral immune cells can be found at the site of demyelination and are suggested to play a functional role during disease progression. In this study, we hypothesize that metabolic oligodendrocyte injury, caused by feeding the copper chelator cuprizone, is a potent trigger for peripheral immune cell recruitment into the central nervous system (CNS). We used immunohistochemistry and flow cytometry to evaluate the composition, density, and activation status of infiltrating T lymphocytes in cuprizone-intoxicated mice and post-mortem progressive MS tissues. Our results demonstrate a predominance of CD8⁺ T cells along with high proliferation rates and cytotoxic granule expression, indicating an antigenic and pro-inflammatory milieu in the CNS of cuprizone-intoxicated mice. Numbers of recruited T cells and the composition of lymphocytic infiltrates in cuprizone-intoxicated mice were found to be comparable to those found in progressive MS lesions. Finally, amelioration of the cuprizone-induced pathology by treating mice with laquinimod significantly reduces the number of recruited T cells. Overall, this study provides strong evidence that toxic demyelination is a sufficient trigger for T cells to infiltrate the demyelinated CNS. Further investigation of the mode of action and functional consequence of T cell recruitment might offer promising new therapeutic approaches for progressive MS.

Revisiting the Pathoetiology of Multiple Sclerosis: Has the Tail Been Wagging the Mouse?

Multiple Sclerosis (MS) is traditionally considered an autoimmune-mediated demyelinating disease, the pathoetiology of which is unknown. However, the key question remains whether autoimmunity is the initiator of the disease (outside-in) or the consequence of a slow and as yet uncharacterized cytodegeneration (oligodendrocytosis), which leads to a subsequent immune response (inside-out). Experimental autoimmune encephalomyelitis has been used to model the later stages of MS during which the autoimmune involvement predominates. In contrast, the cuprizone (CPZ) model is used to model early stages of the disease during which oligodendrocytosis and demyelination predominate and are hypothesized to precede subsequent immune involvement in MS. Recent studies combining a boost, or protection, to the immune system with disruption of the blood brain barrier have shown CPZ-induced oligodendrocytosis with a subsequent immune response. In this Perspective, we review these recent advances and discuss the likelihood of an inside-out vs. an outside-in pathoetiology of MS.