The cuprizone mouse model allows the investigation of the complex molecular mechanisms behind nonautoimmune-mediated demyelination and spontaneous remyelination. While it is generally accepted that ...oligodendrocytes are specifically vulnerable to cuprizone intoxication due to their high metabolic demands, a comprehensive overview of the etiology of cuprizone-induced pathology is still missing to date. In this review we extensively describe the physico-chemical mode of action of cuprizone and discuss the molecular and enzymatic mechanisms by which cuprizone induces metabolic stress, oligodendrocyte apoptosis, myelin degeneration and eventually axonal and neuronal pathology. In addition, we describe the dual effector function of the immune system which tightly controls demyelination by effective induction of oligodendrocyte apoptosis, but in contrast also paves the way for fast and efficient remyelination by the secretion of neurotrophic factors and the clearance of cellular and myelinic debris. Finally, we discuss the many clinical symptoms that can be observed following cuprizone treatment, and how these strengthened the cuprizone model as a useful tool to study human multiple sclerosis, schizophrenia and epilepsy.
Although stroke is one of the world’s leading causes of death and disability, and more than a thousand candidate neuroprotective drugs have been proposed based on extensive in vitro and animal-based ...research, an effective neuroprotective/restorative therapy for ischaemic stroke patients is still missing. In particular, the high attrition rate of neuroprotective compounds in clinical studies should make us question the ability of in vitro models currently used for ischaemic stroke research to recapitulate human ischaemic responses with sufficient fidelity. The ischaemic stroke field would greatly benefit from the implementation of more complex in vitro models with improved physiological relevance, next to traditional in vitro and in vivo models in preclinical studies, to more accurately predict clinical outcomes. In this review, we discuss current in vitro models used in ischaemic stroke research and describe the main factors determining the predictive value of in vitro models for modelling human ischaemic stroke. In light of this, human-based 3D models consisting of multiple cell types, either with or without the use of microfluidics technology, may better recapitulate human ischaemic responses and possess the potential to bridge the translational gap between animal-based in vitro and in vivo models, and human patients in clinical trials.
Inflammatory Ly6ChiCCR2+ monocytes infiltrate the brain after stroke but their functions are not entirely clear. We report that CCR2+ monocytes and CCR2+ lymphocytes infiltrate the brain after ...permanent ischemia. To underscore the role of CCR2+ monocytes, we generated mice with selective CCR2 deletion in monocytes. One day post-ischemia, these mice showed less infiltrating monocytes and reduced expression of pro-inflammatory cytokines, markers of alternatively macrophage activation, and angiogenesis. Accordingly, Ly6Chi monocytes sorted from the brain of wild type mice 24 h post-ischemia expressed pro-inflammatory genes, M2 genes, and pro-angiogenic genes. Flow cytometry showed heterogeneous phenotypes within the infiltrating Ly6ChiCCR2+ monocytes, including a subgroup of Arginase-1+ cells. Mice with CCR2-deficient monocytes displayed a delayed inflammatory rebound 15 days post-ischemia that was not found in wild type mice. Furthermore, they showed reduced angiogenesis and worse behavioral performance. Administration of CCR2+/+ bone-marrow monocytes to mice with CCR2-deficient monocytes did not improve the behavioral performance suggesting that immature bone-marrow monocytes lack pro-reparative functions. The results show that CCR2+ monocytes contribute to acute post-ischemic inflammation and participate in functional recovery. The study unravels heterogeneity in the population of CCR2+ monocytes infiltrating the ischemic brain and suggests that pro-reparative monocyte subsets promote functional recovery after ischemic stroke.
Microglia are perhaps the most underestimated cell type of our immune system. Not only were immunologists unaware of their capabilities until recently, but also, some neuroscientists denied their ...actual existence until the late 20th century. Nowadays, their presence is confirmed extensively, as demonstrated by numerous reports describing their involvement in virtually all neuropathologies. However, despite distinct approaches, their origin remains a point of controversy. Although many agree about their myeloid‐monocytic ancestry, the precise progenitor cells and the differentiation mechanisms, which give rise to microglia in the different developmental stages of the CNS, are not unraveled yet. Mostly, this can be attributed to their versatile phenotype. Indeed, microglia show a high morphological plasticity, which is related to their functional state. This review about microglia aims to introduce the reader extensively into their ontogeny, cell biology, and involvement in different neuropathologies.
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.
Main Points
Transmembrane protein 119 (TMEM119) is not a specific microglia marker.
Under pathological conditions, TMEM119 immunoreactivity in microglia decreases.
Other cell types (i.e., follicular dendritic cells, brown adipose tissue) express TMEM119.
The spiral ligament in the cochlea has been suggested to play a significant role in the pathophysiology of different etiologies of strial hearing loss. Spiral ligament fibrocytes (SLFs), the main ...cell type in the lateral wall, are crucial in maintaining the endocochlear potential and regulating blood flow. SLF dysfunction can therefore cause cochlear dysfunction and thus hearing impairment. Recent studies have highlighted the role of SLFs in the immune response of the cochlea. In contrast to sensory cells in the inner ear, SLFs (more specifically type III fibrocytes) have also demonstrated the ability to regenerate after different types of trauma such as drug toxicity and noise. SLFs are responsible for producing proteins, such as collagen and cochlin, that create an adequate extracellular matrix to thrive in. Any dysfunction of SLFs or structural changes to the extracellular matrix can significantly impact hearing function. However, SLFs may prove useful in restoring hearing by their potential to regenerate cells in the spiral ligament.
Several studies have shown that type IV fibrocytes, located in the spiral ligament, degenerate first after noise exposure. Interestingly, this is the region where
expression is most abundant. As it ...is suggested that cochlin plays a role in our innate immune system, our goal is to investigate hearing thresholds and inner ear inflammation after noise exposure in
knockout (
) mice compared to
wildtype (
) mice. Animals were randomly allocated to a noise exposure group and a control group. Vestibular and auditory testing was performed at 48 h and one week after noise exposure. Whole mount staining and cryosectioning of the cochlea was performed in order to investigate hair cells, spiral ganglion neurons, inner ear inflammation,
expression and fibrocyte degeneration. Hearing assessment revealed that
mice had significantly larger threshold shifts than
mice after noise exposure. We were unable to identify any differences in hair cells, neurons, fibrocytes and influx of macrophages in the inner ear between both groups. Interestingly,
expression was significantly lower in the group exposed to noise. Our results indicate that the absence of
has a protective influence on hearing thresholds after noise exposure, but this is not related to reduced inner ear inflammation in the knockout.
Subtle adjustment of the activation status of CNS resident microglia and peripheral macrophages, to promote their neuroprotective and neuroregenerative functions, may facilitate research towards ...curing neurodegenerative disorders. In the present study, we investigated whether targeted intracerebral delivery of the anti-inflammatory cytokine interleukin (IL)13, by means of transplanting IL13-expressing mesenchymal stem cells (IL13-MSCs), can promote a phenotypic switch in both microglia and macrophages during the pro-inflammatory phase in a mouse model of ischemic stroke.
We used the CX
CR1
CCR2
transgenic mouse model to separately recognize brain-resident microglia from infiltrated macrophages. Quantitative immunohistochemical analyses were applied to characterize polarization phenotypes of both cell types.
Distinct behaviors of both cell populations were noted dependent on the anatomical site of the lesion. Immunohistochemistry revealed that mice grafted with IL13-MSCs, in contrast to non-grafted and MSC-grafted control mice, were able to drive recruited microglia and macrophages into an alternative activation state, as visualized by a significant increase of Arg-1 and a noticeable decrease of MHC-II expression at day 14 after ischemic stroke. Interestingly, both Arg-1 and MHC-II were expressed more abundantly in macrophages than in microglia, further confirming the distinct behavior of both cell populations.
The current data highlight the importance of controlled and localized delivery of the anti-inflammatory cytokine IL13 for modulation of both microglia and macrophage responses after ischemic stroke, thereby providing pre-clinical rationale for the application of L13-MSCs in future investigations of neurodegenerative disorders.
Abstract
Quorum sensing peptides (QSPs) are bacterial peptides produced by Gram-positive bacteria to communicate with their peers in a cell-density dependent manner. These peptides do not only act as ...interbacterial communication signals, but can also have effects on the host. Compelling evidence demonstrates the presence of a gut-brain axis and more specifically, the role of the gut microbiota in microglial functioning. The aim of this study is to investigate microglial activating properties of a selected QSP (PapRIV) which is produced by
Bacillus cereus
species. PapRIV showed in vitro activating properties of BV-2 microglia cells and was able to cross the in vitro Caco-2 cell model and reach the brain. In vivo peptide presence was also demonstrated in mouse plasma. The peptide caused induction of IL-6, TNFα and ROS expression and increased the fraction of ameboid BV-2 microglia cells in an NF-κB dependent manner. Different metabolites were identified in serum, of which the main metabolite still remained active. PapRIV is thus able to cross the gastro-intestinal tract and the blood–brain barrier and shows in vitro activating properties in BV-2 microglia cells, hereby indicating a potential role of this quorum sensing peptide in gut-brain interaction.
Hearing impairment is the most frequent sensory deficit, affecting 466 million people worldwide and has been listed by the World Health Organization (WHO) as one of the priority diseases for research ...into therapeutic interventions to address public health needs. Inner ear gene therapy is a promising approach to restore sensorineural hearing loss, for which several gene therapy applications have been studied and reported in preclinical animal studies.
To perform a systematic review on preclinical studies reporting cochlear gene therapy, with a specific focus on transduction efficiency.
An initial PubMed search was performed on April 1st 2021 using the PRISMA methodology. Preclinical
studies reporting primary data regarding transduction efficiency of gene therapy targeting the inner ear were included in this report.
Thirty-six studies were included in this review. Transduction of various cell types in the inner ear can be achieved, according to the viral vector used. However, there is significant variability in the applied vector delivery systems, including promoter, viral vector titer, etc.
Although gene therapy presents a promising approach to treat sensorineural hearing loss in preclinical studies, the heterogeneity of methodologies impedes the identification of the most promising tools for future use in inner ear therapies.
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