Inflammatory response and chemokine expression in the white matter corpus callosum and gray matter cortex region during cuprizone-induced demyelination

The benefits and detriments of macrophages/microglia in models of multiple sclerosis

The central nervous system (CNS) is immune privileged with access to leukocytes being limited. In several neurological diseases, however, infiltration of immune cells from the periphery into the CNS is largely observed and accounts for the increased representation of macrophages within the CNS. In addition to extensive leukocyte infiltration, the activation of microglia is frequently observed. The functions of activated macrophages/microglia within the CNS are complex. In three animal models of multiple sclerosis (MS), namely, experimental autoimmune encephalomyelitis (EAE) and cuprizone- and lysolecithin-induced demyelination, there have been many reported detrimental roles associated with the involvement of macrophages and microglia. Such detriments include toxicity to neurons and oligodendrocyte precursor cells, release of proteases, release of inflammatory cytokines and free radicals, and recruitment and reactivation of T lymphocytes in the CNS. Many studies, however, have also reported beneficial roles of macrophages/microglia, including axon regenerative roles, assistance in promoting remyelination, clearance of inhibitory myelin debris, and the release of neurotrophic factors. This review will discuss the evidence supporting the detrimental and beneficial aspects of macrophages/microglia in models of MS, provide a discussion of the mechanisms underlying the dichotomous roles, and describe a few therapies in clinical use in MS that impinge on the activity of macrophages/microglia.

Cuprizone-induced demyelination as a tool to study remyelination and axonal protection

In the brain of multiple sclerosis (MS) patients, the conduction block of axons due to demyelination and inflammation underlies early neurological symptoms, whereas axonal transection accounts for permanent deficits occurring during later disease stages. The beneficial function of myelin for the protection of the axonal compartment and network stability between neurons has been shown in numerous studies. Thus, rapid and adequate remyelination is an important factor for axonal patronage during neuroinflammatory conditions. In this review article, we discuss frequently used experimental in vivo and in vitro animal models to examine remyelination and repair in MS. The focus of the discussion is the relevance of the toxin model 'cuprizone' to study the pathology of demyelination and the physiology of remyelination. This also includes recent findings in this animal model which implicate that axonal damage is an ongoing process independent of the initiation of endogenous remyelination.

The importance of CCR4 and CCR6 in experimental autoimmune encephalomyelitis

Chemokine receptors (CCRs) play important roles in the pathogenesis of immune-mediated diseases, as well as in normal immune response. We examined the role of CCR6 and CCR4 in experimental autoimmune encephalomyelitis (EAE) by using CCR6(-/-)CCR4(-/-) double knockout (DKO) and single knockout mice. DKO mice developed less severe EAE and presented repressed recall response in the induction phase, especially in the activity of T helper 17 (Th17) cells. CCR6 expression in central nervous system (CNS)-infiltrated cells was diminished in DKO. Our results suggest that CCR6 and CCR4 were involved in a more rapid progression of EAE and that their regulation might be a therapeutic target of human inflammatory demyelinating diseases.

Astrogliosis during acute and chronic cuprizone demyelination and implications for remyelination

In multiple sclerosis, microglia/macrophage activation and astrocyte reactivity are important components of the lesion environment that can impact remyelination. The current study characterizes these glial populations relative to expression of candidate regulatory molecules in cuprizone demyelinated corpus callosum. Importantly, periods of recovery after acute or chronic cuprizone demyelination are examined to compare conditions of efficient versus limited remyelination, respectively. Microglial activation attenuates after early demyelination. In contrast, astrocyte reactivity persists throughout demyelination and a 6-week recovery period following either acute or chronic demyelination. This astrocyte reaction is characterized by (a) early proliferation, (b) increased expression of GFAP (glial fibrillary acidic protein), Vim (vimentin), Fn1 (fibronectin) and CSPGs (chondroitin sulphate proteoglycans) and (c) elaboration of a dense network of processes. Glial processes elongated in the axonal plane persist throughout lesion areas during both the robust remyelination that follows acute demyelination and the partial remyelination that follows chronic demyelination. However, prolonged astrocyte reactivity with chronic cuprizone treatment does not progress to barrier formation, i.e. dense compaction of astrocyte processes to wall off the lesion area. Multiple candidate growth factors and inflammatory signals in the lesion environment show strong correlations with GFAP across the acute cuprizone demyelination and recovery time course, yet there is more divergence across the progression of chronic cuprizone demyelination and recovery. However, differential glial scar formation does not appear to be responsible for differential remyelination during recovery in the cuprizone model. The astrocyte phenotype and lesion characteristics in this demyelination model inform studies to identify triggers of non-remyelinating sclerosis in chronic multiple sclerosis lesions.

Regional heterogeneity of cuprizone-induced demyelination: topographical aspects of the midline of the corpus callosum

The cuprizone model is a suitable animal model of de- and remyelination secondary to toxin-induced oligodendrogliopathy. From a pharmaceutical point of view, the cuprizone model is a valuable tool to study the potency of compounds which interfere with toxin-induced oligodendrocyte cell death or boost/inhibit remyelinating pathways and processes. The aim of this study was to analyze the vulnerability of neighboring white mater tracts (i.e., the fornix and cingulum) next to the midline of the corpus callosum which is the region of interest of most studies using this model. Male mice were fed cuprizone for various time periods. Different white matter areas were analyzed for myelin (anti-PLP), microglia (anti-IBA1), and astrocyte (anti-GFAP) responses by means of immunohistochemistry. Furthermore, Luxol fast blue-periodic acid Schiff stains were performed to validate loss of myelin-reactive fibers in the different regions. Cuprizone induced profound demyelination of the midline of the corpus callosum and medial parts of the cingulum that was paralleled by a significant astrocyte and microglia response. In contrast, lateral parts of the corpus callosum and the cingulum, as well as the fornix region which is just beneath the midline of the corpus callosum appeared to be resistant to cuprizone exposure. Furthermore, resistant areas displayed reduced astrogliosis and microgliosis. This study clearly demonstrates that neighboring white matter tracts display distinct vulnerability to toxin-induced demyelination. This important finding has direct relevance for evaluation strategies in this frequently used animal model for multiple sclerosis.