Review
Experimental in vivo and in vitro models of multiple sclerosis: EAE and beyond

https://doi.org/10.1016/j.msard.2011.09.002Get rights and content

Abstract

Although the primary cause of multiple sclerosis (MS) is unknown, the widely accepted view is that aberrant (auto)immune responses possibly arising following infection(s) are responsible for the destructive inflammatory demyelination and neurodegeneration in the central nervous system (CNS). This notion, and the limited access of human brain tissue early in the course of MS, has led to the development of autoimmune, viral and toxin-induced demyelination animal models as well as the development of human CNS cell and organotypic brain slice cultures in an attempt to understand events in MS. The autoimmune models, collectively known as experimental autoimmune encephalomyelitis (EAE), and viral models have shaped ideas of how environmental factors may trigger inflammation, demyelination and neurodegeneration in the CNS. Understandably, these models have also heavily influenced the development of therapies targeting the inflammatory aspect of MS. Demyelination and remyelination in the absence of overt inflammation are better studied in toxin-induced demyelination models using cuprizone and lysolecithin. The paradigm shift of MS as an autoimmune disease of myelin to a neurodegenerative disease has required more appropriate models reflecting the axonal and neuronal damage. Thus, secondary progressive EAE and spastic models have been crucial to develop neuroprotective approaches.

In this review the current in vivo and in vitro experimental models to examine pathological mechanisms involved in inflammation, demyelination and neuronal degeneration, as well as remyelination and repair in MS are discussed. Since this knowledge is the basis for the development of new therapeutic approaches for MS, we particularly address whether the currently available models truly reflect the human disease, and discuss perspectives to further optimise and develop more suitable experimental models to study MS.

Introduction

Multiple sclerosis (MS), a common demyelinating disease of young adults can be classified in the group of inflammatory, demyelinating disease. That many inflammatory, demyelinating disorders in humans and animals, where the aetiological agent is known, are due to viral infection has lead to the development of several viral models to study MS. The autoimmune view of MS is strongly supported by the animal model experimental autoimmune encephalomyelitis (EAE), a group of disorders characterised by inflammation, myelin damage and neurodegeneration induced following immunisation with brain antigens. Remyelination, however, is better studied in toxin models such as the cuprizone model, where adaptive immune responses are not involved. Despite the extensive use of these models, the clinical course, immunology and neuropathology reflect only part of the pathological spectrum of MS, indicating that responses to therapies in animal models often cannot predict efficacy in humans. Thus, to understand the interactions between the human immune system and the human CNS, in vitro cultures of microglia, oligodendrocytes, astrocytes and neurons have been established. To study complex interactions of the blood–brain barrier (BBB) and cellular interactions, mouse brain spheroid cultures have been used to examine e.g. myelin damage. Of more relevance are human brain organotypic brain slice cultures in which the cells as well as the extracellular matrix are intact. While the latter models require further refinements to model demyelination and neurodegeneration, these new approaches highlight the importance and availability of novel yet relevant models to study the complexity of MS.

Several important issues surrounding the use of experimental animal models to study MS, or indeed other disorders, have recently been addressed (Baker et al., 2011, Vesterinen et al., 2010). Here, we also draw attention to the ‘Animals in Research: Reporting In Vivo Experiments’ (ARRIVE) guidelines recently released with the aim of improving the quality of research using animals (Kilkenny et al., 2010). Given the currently available 8400 papers on EAE it is appropriate to highlight and bring to attention this report. Examining and, where appropriate, adopting the ARRIVE guidelines will clearly improve experimental findings in MS research using experimental systems to model the disease.

Section snippets

Viral models

The similarities between MS pathology and viral demyelinating disorders of the CNS (Table 1) as well as epidemiological observations have made the infectious aetiology of MS an attractive hypothesis. Electron microscopical and virological studies have supported this by revealing the presence of viruses in MS brain tissues. In animals natural infections e.g. canine distemper virus in dogs, visna virus in sheep, and mink encephalitis, induce myelin damage in the CNS, and several of these were

Experimental autoimmune encephalomyelitis

Immunisation of susceptible animals with CNS antigens gives rise to a spectrum of inflammatory disorders collectively named EAE (Table 2). Although the experimental disease in animals was originally termed experimental disseminated encephalomyelitis, the idea that the ‘disease’ was allergic gave rise to the name experimental allergic encephalomyelitis. More recently, allergic has been replaced by autoimmune. Despite differences in disease course and pathology, EAE is still the most intensely

Transgenic mouse models

The generation of transgenic (tg) mice has greatly aided our understanding of the pathogenic mechanisms operating in EAE. Here we briefly review the major approaches using tg mice to examine the role of autoimmune responses to myelin, chemokines, cytokines and mechanisms of neuronal or oligodendrocyte damage. Transgenic mice expressing HLA haplotypes linked to susceptibility to MS have allowed dissection of human elements involved in EAE. While these animals offer unique approaches to

Toxin models

In principal, toxin demyelination can be induced by either focal application or systemic administration of the toxin. Agents for focal demyelination used so far are lysolecithin, also called lysophosphatidylcholine (LPC), ethidium bromide (EB) (Franklin et al., 1993, Mothe and Tator, 2008, Talbott et al., 2006), 6-aminonicotinamide (Blakemore, 1978), antibodies to oligodendrocyte-related proteins (Rosenbluth et al., 2003, Rosenbluth and Schiff, 2009), bacterial endotoxin (Felts et al., 2005)

In vitro models

Although animal studies have significantly contributed to the understanding of MS they only partially mimic the underlying pathogenic processes. In vitro approaches are thus crucial to study the role of CNS cells, allowing manipulations that cannot easily be performed in vivo. Many of the CNS culture systems commonly used are of animal origin. We would like to stress at this point that several essential differences exist between the rodent and human brain. Thus human in vitro models, such as

Perspectives and conclusions

The choice of the experimental model ultimately depends on the research question and the availability of technical equipment for e.g. stereotactic injections. The clinical episodes of neurological disease in EAE models provide excellent opportunities to uncover immune mechanisms leading to both myelin damage and neuronal and axonal degeneration and dysfunction. For therapeutic studies, the chronic-relapsing models better reflect the human situation in MS, allowing strategies to inhibit

Acknowledgments

The authors thank MS Research; the multiple sclerosis society of the Netherlands, the multiple sclerosis of Great Britain and Northern Ireland, the Deutsche Forschungsgemeinschaft (DFG), Hertie foundation and the DANA foundation for financial support for studies involved in this review. Dr. Hans van Noort is gratefully acknowledged for his critical and constructive views on this manuscript.

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