Astroglial and oligodendroglial markers in the cuprizone animal model for de- and remyelination

Respiratory infection with influenza A virus delays remyelination and alters oligodendrocyte metabolism

Peripheral viral infection disrupts oligodendrocyte (OL) homeostasis such that endogenous remyelination may be affected. Here, we demonstrate that influenza A virus infection perpetuated a demyelination- and disease-associated OL phenotype following cuprizone-induced demyelination that resulted in delayed OL maturation and remyelination in the prefrontal cortex. Furthermore, we assessed cellular metabolism ex vivo, and found that infection altered brain OL and microglia metabolism in a manner that opposed the metabolic profile induced by remyelination. Specifically, infection increased glycolytic capacity of OLs and microglia, an effect that was recapitulated by lipopolysaccharide (LPS) stimulation of mixed glia cultures. In contrast, mitochondrial dependence was increased in OLs during remyelination, which was similarly observed in OLs of myelinating P14 mice compared to adult and aged mice. Collectively, our data indicate that respiratory viral infection is capable of suppressing remyelination, and suggest that metabolic dysfunction of OLs is implicated in remyelination impairment.

Oligodendrocyte-selective deletion of the eIF2α kinase Perk/Eif2ak3 limits functional recovery after spinal cord injury

After spinal cord injury (SCI), re-establishing cellular homeostasis is critical to optimize functional recovery. Central to that response is PERK signaling, which ultimately initiates a pro-apoptotic response if cellular homeostasis cannot be restored. Oligodendrocyte (OL) loss and white matter damage drive functional consequences and determine recovery potential after thoracic contusive SCI. We examined acute (<48 h post-SCI) and chronic (6 weeks post-SCI) effects of conditionally deleting Perk from OLs prior to SCI. While Perk transcript is expressed in many types of cells in the adult spinal cord, its levels are disproportionately high in OL lineage cells. Deletion of OL-Perk prior to SCI resulted in: (1) enhanced acute phosphorylation of eIF2α, a major PERK substrate and the critical mediator of the integrated stress response (ISR), (2) enhanced acute expression of the downstream ISR genes Atf4, Ddit3/Chop, and Tnfrsf10b/Dr5, (3) reduced acute OL lineage-specific Olig2 mRNA, but not neuronal or astrocytic mRNAs, (4) chronically decreased OL content in the spared white matter at the injury epicenter, (5) impaired hindlimb locomotor recovery, and (6) reduced chronic epicenter white matter sparing. Cultured primary OL precursor cells with reduced PERK expression and activated ER stress response showed: (1) unaffected phosphorylation of eIF2α, (2) enhanced ISR gene induction, and (3) increased cytotoxicity. Therefore, OL-Perk deficiency exacerbates ISR signaling and potentiates white matter damage after SCI. The latter effect is likely mediated by increased loss of Perk-/- OLs.

Automated analysis of gray matter damage in aged mice reveals impaired remyelination in the cuprizone model

Multiple sclerosis is a chronic autoimmune disease of the central nervous system characterized by myelin loss, axonal damage, and glial scar formation. Still, the underlying processes remain unclear, as numerous pathways and factors have been found to be involved in the development and progression of the disease. Therefore, it is of great importance to find suitable animal models as well as reliable methods for their precise and reproducible analysis. Here, we describe the impact of demyelination on clinically relevant gray matter regions of the hippocampus and cerebral cortex, using the previously established cuprizone model for aged mice. We could show that bioinformatic image analysis methods are not only suitable for quantification of cell populations, but also for the assessment of de- and remyelination processes, as numerous objective parameters can be considered for reproducible measurements. After cuprizone-induced demyelination, subsequent remyelination proceeded slowly and remained incomplete in all gray matter areas studied. There were regional differences in the number of mature oligodendrocytes during remyelination suggesting region-specific differences in the factors accounting for remyelination failure, as, even in the presence of oligodendrocytes, remyelination in the cortex was found to be impaired. Upon cuprizone administration, synaptic density and dendritic volume in the gray matter of aged mice decreased. The intensity of synaptophysin staining gradually restored during the subsequent remyelination phase, however the expression of MAP2 did not fully recover. Microgliosis persisted in the gray matter of aged animals throughout the remyelination period, whereas extensive astrogliosis was of short duration as compared to white matter structures. In conclusion, we demonstrate that the application of the cuprizone model in aged mice mimics the impaired regeneration ability seen in human pathogenesis more accurately than commonly used protocols with young mice and therefore provides an urgently needed animal model for the investigation of remyelination failure and remyelination-enhancing therapies.

Impact of calcitriol and PGD2-G-loaded lipid nanocapsules on oligodendrocyte progenitor cell differentiation and remyelination

Multiple sclerosis (MS) is a demyelinating and inflammatory disease of the central nervous system (CNS) in need of a curative treatment. MS research has recently focused on the development of pro-remyelinating treatments and neuroprotective therapies. Here, we aimed at favoring remyelination and reducing neuro-inflammation in a cuprizone mouse model of brain demyelination using nanomedicines. We have selected lipid nanocapsules (LNC) coated with the cell-penetrating peptide transactivator of translation (TAT), loaded with either a pro-remyelinating compound, calcitriol (Cal-LNC TAT), or an anti-inflammatory bioactive lipid, prostaglandin D2-glycerol ester (PGD2-G) (PGD2-G-LNC TAT). Following the characterization of these formulations, we showed that Cal-LNC TAT in combination with PGD2-G-LNC TAT increased the mRNA expression of oligodendrocyte differentiation markers both in the CG-4 cell line and in primary mixed glial cell (MGC) cultures. However, while the combination of Cal-LNC TAT and PGD2-G-LNC TAT showed promising results in vitro, no significant impact, in terms of remyelination, astrogliosis, and microgliosis, was observed in vivo in the corpus callosum of cuprizone-treated mice following intranasal administration. Thus, although calcitriol's beneficial effects have been abundantly described in the literature in the context of MS, here, we show that the different doses of calcitriol tested had a negative impact on the mice well-being and showed no beneficial effect in the cuprizone model in terms of remyelination and neuro-inflammation, alone and when combined with PGD2-G-LNC TAT.

Astrocytes: Lessons Learned from the Cuprizone Model

A diverse array of neurological and psychiatric disorders, including multiple sclerosis, Alzheimer's disease, and schizophrenia, exhibit distinct myelin abnormalities at both the molecular and histological levels. These aberrations are closely linked to dysfunction of oligodendrocytes and alterations in myelin structure, which may be pivotal factors contributing to the disconnection of brain regions and the resulting characteristic clinical impairments observed in these conditions. Astrocytes, which significantly outnumber neurons in the central nervous system by a five-to-one ratio, play indispensable roles in the development, maintenance, and overall well-being of neurons and oligodendrocytes. Consequently, they emerge as potential key players in the onset and progression of a myriad of neurological and psychiatric disorders. Furthermore, targeting astrocytes represents a promising avenue for therapeutic intervention in such disorders. To gain deeper insights into the functions of astrocytes in the context of myelin-related disorders, it is imperative to employ appropriate in vivo models that faithfully recapitulate specific aspects of complex human diseases in a reliable and reproducible manner. One such model is the cuprizone model, wherein metabolic dysfunction in oligodendrocytes initiates an early response involving microglia and astrocyte activation, culminating in multifocal demyelination. Remarkably, following the cessation of cuprizone intoxication, a spontaneous process of endogenous remyelination occurs. In this review article, we provide a historical overview of studies investigating the responses and putative functions of astrocytes in the cuprizone model. Following that, we list previously published works that illuminate various aspects of the biology and function of astrocytes in this multiple sclerosis model. Some of the studies are discussed in more detail in the context of astrocyte biology and pathology. Our objective is twofold: to provide an invaluable overview of this burgeoning field, and, more importantly, to inspire fellow researchers to embark on experimental investigations to elucidate the multifaceted functions of this pivotal glial cell subpopulation.

Dynamics of reactive astrocytes fosters tissue regeneration after cuprizone-induced demyelination

Demyelination in the central nervous system (CNS) is a hallmark of many neurodegenerative diseases such as multiple sclerosis (MS) and others. Here, we studied astrocytes during de- and remyelination in the cuprizone mouse model. To this end, we exploited the ribosomal tagging (RiboTag) technology that is based on Cre-mediated cell type-selective HA-tagging of ribosomes. Analyses were performed in the corpus callosum of GFAP-Cre+/- Rpl22HA/wt mice 5 weeks after cuprizone feeding, at the peak of demyelination, and 0.5 and 2 weeks after cuprizone withdrawal, when remyelination and tissue repair is initiated. After 5 weeks of cuprizone feeding, reactive astrocytes showed inflammatory signatures with enhanced expression of genes that modulate leukocyte migration (Tlr2, Cd86, Parp14) and they produced the chemokine CXCL10, as verified by histology. Furthermore, demyelination-induced reactive astrocytes expressed numerous ligands including Cx3cl1, Csf1, Il34, and Gas6 that act on homeostatic as well as activated microglia and thus potentially mediate activation and recruitment of microglia and enhancement of their phagocytotic activity. During early remyelination, HA-tagged cells displayed reduced inflammatory response signatures, as indicated by shutdown of CXCL10 production, and enhanced expression of osteopontin (SPP1) as well as of factors that are relevant for tissue remodeling (Timp1), regeneration and axonal repair. During late remyelination, the signatures shifted towards resolving inflammation by active suppression of lymphocyte activation and differentiation and support of glia cell differentiation. In conclusion, we detected highly dynamic astroglial transcriptomic signatures in the cuprizone model, which reflects excessive communication among glia cells and highlights different astrocyte functions during neurodegeneration and regeneration.

Pearls and Pitfalls of Isolating Rat OPCs for In Vitro Culture with Different Methods

There are several in vitro models to study the biology of oligodendrocyte progenitor cells (OPCs). The use of models based on induced pluripotent stem cells or oligodendrocyte-like cell lines has many advantages but raises significant questions, such as inaccurate reproduction of neural tissue or genetic instability. Moreover, in a specific case of studying the biology of neonatal OPCs, it is particularly difficult to find good representative model, due to the unique metabolism and features of these cells, as well as neonatal brain tissue. The following study evaluates two methods of isolating OPCs from rat pups as a model for in vitro studies. The first protocol is a modification of the classical mixed glial culture with series of shakings applied to isolate the fraction of OPCs. The second protocol is based on direct cell sorting and uses magnetic microbeads that target the surface antigen of the oligodendrocyte progenitor cell-A2B5. We compared the performance of these methods and analyzed the purity of obtained cultures as well as oligodendrocyte differentiation. Although the yield of OPCs collected with these two methods is similar, both have their advantages and disadvantages. The OPCs obtained with both methods give rise to mature oligodendrocytes within a few days of culture in ITS-supplemented serum-free medium and a 5% O2 atmosphere (mimicking the endogenous oxygen conditions of the nervous tissue). Methods for isolating rat OPCs In the following study we compared methods for isolating neonatal rat oligodendrocyte progenitor cells, for the studies on the in vitro model of neonatal brain injuries. We evaluated the purity of obtained cell cultures and the ability to maturate in physiological normoxia and serum-free culture medium.

Korean Red Ginseng extract ameliorates demyelination by inhibiting infiltration and activation of immune cells in cuprizone-administrated mice

Background

Korean Red Ginseng (KRG), the steamed root of Panax ginseng, has pharmacological activities for immunological and neurodegenerative disorders. But, the role of KRGE in multiple sclerosis (MS) remains unclear.

Purpose

To determine whether KRG extract (KRGE) could inhibit demyelination in corpus callosum (CC) of cuprizone (CPZ)-induced murine model of MS.

Methods

Male adult mice were fed with a standard chow diet or a chow diet supplemented with 0.2% (w/w) CPZ ad libitum for six weeks to induce demyelination while were simultaneously administered with distilled water (DW) alone or KRGE-DW (0.004%, 0.02 and 0.1% of KRGE) by drinking.

Results

Administration with KRGE-DW alleviated demyelination and oligodendrocyte degeneration associated with inhibition of infiltration and activation of resident microglia and monocyte-derived macrophages as well as downregulation of proinflammatory mediators in the CC of CPZ-fed mice. KRGE-DW also attenuated the level of infiltration of Th1 and Th17) cells, in line with inhibited mRNA expression of IFN-γ and IL-17, respectively, in the CC. These positive effects of KRGE-DW mitigated behavioral dysfunction based on elevated plus maze and the rotarod tests.

Conclusion

The results strongly suggest that KRGE-DW may inhibit CPZ-induced demyelination due to its oligodendroglial protective and anti-inflammatory activities by inhibiting infiltration/activation of immune cells. Thus, KRGE might have potential in therapeutic intervention for MS.

Localized Increased Permeability of Blood-Brain Barrier for Antibody Conjugates in the Cuprizone Model of Demyelination

The development of new neurotherapeutics depends on appropriate animal models being chosen in preclinical studies. The cuprizone model is an effective tool for studying demyelination and remyelination processes in the brain, but blood-brain barrier (BBB) integrity in the cuprizone model is still a topic for debate. Several publications claim that the BBB remains intact during cuprizone-induced demyelination; others demonstrate results that could explain the increased BBB permeability. In this study, we aim to analyze the permeability of the BBB for different macromolecules, particularly antibody conjugates, in a cuprizone-induced model of demyelination. We compared the traditional approach using Evans blue injection with subsequent dye extraction and detection of antibody conjugates using magnetic resonance imaging (MRI) and confocal microscopy to analyze BBB permeability in the cuprizone model. First, we validated our model of demyelination by performing T2-weighted MRI, diffusion tensor imaging, quantitative rt-PCR to detect changes in mRNA expression of myelin basic protein and proteolipid protein, and Luxol fast blue histological staining of myelin. Intraperitoneal injection of Evans blue did not result in any differences between the fluorescent signal in the brain of healthy and cuprizone-treated mice (IVIS analysis with subsequent dye extraction). In contrast, intravenous injection of antibody conjugates (anti-GFAP or non-specific IgG) after 4 weeks of a cuprizone diet demonstrated accumulation in the corpus callosum of cuprizone-treated mice both by contrast-enhanced MRI (for gadolinium-labeled antibodies) and by fluorescence microscopy (for Alexa488-labeled antibodies). Our results suggest that the methods with better sensitivity could detect the accumulation of macromolecules (such as fluorescent-labeled or gadolinium-labeled antibody conjugates) in the brain, suggesting a local BBB disruption in the demyelinating area. These findings support previous investigations that questioned BBB integrity in the cuprizone model and demonstrate the possibility of delivering antibody conjugates to the corpus callosum of cuprizone-treated mice.

Role of lipocalin 2 in stroke

Stroke is the second leading cause of death worldwide; however, the treatment choices available to neurologists are limited in clinical practice. Lipocalin 2 (LCN2) is a secreted protein, belonging to the lipocalin superfamily, with multiple biological functions in mediating innate immune response, inflammatory response, iron-homeostasis, cell migration and differentiation, energy metabolism, and other processes in the body. LCN2 is expressed at low levels in the brain under normal physiological conditions, but its expression is significantly up-regulated in multiple acute stimulations and chronic pathologies. An up-regulation of LCN2 has been found in the blood/cerebrospinal fluid of patients with ischemic/hemorrhagic stroke, and could serve as a potential biomarker for the prediction of the severity of acute stroke. LCN2 activates reactive astrocytes and microglia, promotes neutrophil infiltration, amplifies post-stroke inflammation, promotes blood-brain barrier disruption, white matter injury, and neuronal death. Moreover, LCN2 is involved in brain injury induced by thrombin and erythrocyte lysates, as well as microvascular thrombosis after hemorrhage. In this paper, we review the role of LCN2 in the pathological processes of ischemic stroke; intracerebral hemorrhage; subarachnoid hemorrhage; and stroke-related brain diseases, such as vascular dementia and post-stroke depression, and their underlying mechanisms. We hope that this review will help elucidate the value of LCN2 as a therapeutic target in stroke.

Remyelination in Multiple Sclerosis: Findings in the Cuprizone Model

Remyelination therapies, which are currently under development, have a great potential to delay, prevent or even reverse disability in multiple sclerosis patients. Several models are available to study the effectiveness of novel compounds in vivo, among which is the cuprizone model. This model is characterized by toxin-induced demyelination, followed by endogenous remyelination after cessation of the intoxication. Due to its high reproducibility and ease of use, this model enjoys high popularity among various research and industrial groups. In this review article, we will summarize recent findings using this model and discuss the potential of some of the identified compounds to promote remyelination in multiple sclerosis patients.

Cuprizone feeding induces swollen astrocyte endfeet

The cuprizone model is a widely used model to study the pathogenesis of multiple sclerosis (MS). Due to the selective loss of mature oligodendrocytes and myelin, it is mainly being used to study demyelination and the mechanisms of remyelination, as well as the efficiency of compounds or therapeutics aiming at remyelination. Although early investigations using high dosages of cuprizone reported the occurrence of hydrocephalus, it has long been assumed that cuprizone feeding at lower dosages does not induce changes at the blood-brain barrier (BBB). Here, by analyzing BBB ultrastructure with high-resolution electron microscopy, we report changes at astrocytic endfeet surrounding vessels in the brain parenchyma. Particularly, edema formation around blood vessels and swollen astrocytic endfeet already occurred after feeding low dosages of cuprizone. These findings indicate changes in BBB function that will have an impact on the milieu of the central nervous system (CNS) in the cuprizone model and need to be considered when studying the mechanisms of de- and remyelination.