Myelination and remyelination in the regenerating visual system of the goldfish

Summary The remyelination of regenerated optic axons was investigated in goldfish following either optic nerve crush or ouabain retinal intoxication. Axons grown after nerve crushing acquire thinner myelin sheaths than axons originating from reconstituted ganglion cells. If axons of reconstituted ganglion cells are crushed and allowed to regenerate, the subsequent myelination is weaker than that of control axons not interrupted by crushing, but stronger than that of axons of preexisting retinal ganglion cells.The present results suggest that a neuron is capable of inducing a normally developed myelin sheath when its axon contacts an oligodendrocyte the first time, whereas a neuron whose axon contacts an oligodendrocyte the second time is not capable of forming a normal myelin sheath in the adult animal. The present results also support the notion that the oligodendrocyte requires a neuronal signal for myelin sheath formation.Supported by the Deutsche Forschungsgemeinschaft (Wo 215/5)     

Demyelination and remyelination in anatomically distinct regions of the corpus callosum following cuprizone intoxication

Multiple sclerosis is a chronic demyelinating disease of the central nervous system. Spontaneous remyelination during early disease stages is thought to preserve and partially restore function. However, this process ceases in later stages despite the presence of pre-oligodendrocytes. Cuprizone-induced demyelination is a useful model with which to study the remyelination process. Previous studies have demonstrated heterogeneities in demyelination in individual animals. Here we investigated regional differences in demyelination and remyelination within the corpus callosum. C57BL/6 mice were fed 0.2% cuprizone for 5 weeks to induce demyelination. Remyelination was examined 2-5 weeks after cuprizone withdrawal. Immunohistochemistry and electron microscopy were used to quantify regional differences in demyelination, gliosis, and remyelination. We found that, while demyelination was limited in the rostral region of corpus callosum, nearly complete demyelination occurred in the caudal callosum, beginning at approximately −0.5 mm from bregma. Astrogliosis and microgliosis were correlated with demyelination and differed between the rostral and caudal callosal structures. Remyelination upon cessation of cuprizone ensued at different rates with splenium remyelinating faster than dorsal hippocampal commissure. Our data show anatomical differences of cuprizone-induced demyelination and remyelination in the corpus callosum and the importance of examining specific callosal regions in myelin repair studies using this model.     

Biological markers for axonal degeneration in CSF and blood of patients with the first event indicative for multiple sclerosis

Axonal degeneration is now recognized as an important pathological feature of multiple sclerosis (MS). Acute axonal damage happens early in the disease course, and therefore early changes might occur in markers in body fluids, such as cerebrospinal fluid (CSF) and blood. In our study we investigated the relevance of serum and CSF markers for axonal damage in patients with clinically isolated syndrome indicative for MS. We measured the concentration of tau, phospho-tau, S100B, Amyloid beta and neuron specific enolase (NSE) in CSF and serum. Interestingly, the NSE concentration in CSF and serum was decreased in clinically isolated syndrome (CIS)-patients in comparison to the control group indicating reduced neuronal metabolic activity in the early stage of the disease. Concerning other biomarkers, we did not observe any changes in the concentrations between groups. Moreover, we did not detect any correlation between Expanded Disability Status Scale (EDSS) and the concentration of investigated proteins.     

The neurotoxicant, cuprizone, as a model to study demyelination and remyelination in the central nervous system

Myelin of the adult CNS is vulnerable to a variety of metabolic, toxic, and autoimmune insults. That remyelination can ensue, following demyelinating insult, has been well demonstrated. Details of the process of remyelination are, however difficult to ascertain since in most experimental models of demyelination/remyelination the severity, localization of lesion site, or time course of the pathophysiology is variable from animal to animal. In contrast, an experimental model in which massive demyelination can be reproducibly induced in large areas of mouse brain is exposure to the copper chelator, cuprizone, in the diet. We review work from several laboratories over the past 3 decades, with emphasis on our own recent studies, which suggest an overall picture of cellular events involved in demyelination/remyelination. When 8 week old C57BL/6 mice are fed 0.2% cuprizone in the diet, mature olidgodendroglia are specifically insulted (cannot fulfill the metabolic demand of support of vast amounts of myelin) and go through apoptosis. This is closely followed by recruitment of microglia and phagoctytosis of myelin. Studies of myelin gene expression, coordinated with morphological studies, indicate that even in the face of continued metabolic challenge, oligodendroglial progenitor cells proliferate and invade demyelinated areas. If the cuprizone challenge is terminated, an almost complete remyelination takes place in a matter of weeks. Communication between different cell types by soluble factors may be inferred. This material is presented in the context of a model compatible with present data -- and which can be tested more rigorously with the cuprizone model. The reproducibility of the model indicates that it may allow for testing of manipulations (e.g. available knockouts or transgenics on the common genetic background, or pharmacological treatments) which may accelerate or repress the process of demyelination and or remyelination.     

Changes in the distribution of a calcium-dependent ATPase during demyelination and remyelination in the central nervous system

Summary A calcium-adenosine triphosphatase (Ca²⁺-ATPase) activity expressed by CNS nerve fibres has been examined during demyelination and remyelination in rats, 21–26 days after an intraspinal injection of ethidium bromide. The Ca²⁺-ATPase distribution was determined cytochemically, using a technique believed primarily to reflect the presence of ecto-ATPases. We confirm that in normal nerve fibres Ca²⁺-ATPase activity was present on the external surface of the myelin sheath, and on the axolemma at the nodes of Ranvier. Labelling of the internodal axolemma was restricted to small, scattered, punctate regions. However, following demyelination the Ca²⁺-ATPase activity was expressed continuously along both the exposed, previously internodal axolemma of entirely naked axons, and it was particularly prominent at sites of contact between axons and glial-cell processes. During remyelination (which in this lesion is accomplished predominantly by Schwann cells) the proportion of the axonal surface exhibiting Ca²⁺-ATPase activity decreased in concert with the progressive thickening of the new myelin sheath. The non-myelin forming plasmalemma of Schwann cells was positive for the Ca²⁺-ATPase activity, but activity was abruptly lost at the site of compaction between the inner and outer leaflets of the forming myelin sheath. Ecto-ATPase activity is a property of some cell adhesion molecules, and it follows that the changes observed in the distribution of ATPase activity in this study may reflect changes in the axolemma which are important for the successful repair of the lesion by remyelination. The ATPase activity may, for example, reflect the changing distribution of molecules important in aiding axo-glial recognition and the establishment of axo-glial contacts.     

Deleterious role of IFNgamma in a toxic model of central nervous system demyelination

Interferon-gamma (IFNgamma) is a pleiotropic cytokine that plays an important role in many inflammatory processes, including autoimmune diseases such as multiple sclerosis (MS). Demyelination is a hallmark of MS and a prominent pathological feature of several other inflammatory diseases of the central nervous system, including experimental autoimmune encephalomyelitis, an animal model of MS. Accordingly, in this study we followed the effect of IFNgamma in the demyelination and remyelination process by using an experimental autoimmune encephalomyelitis model of demyelination/remyelination after exposure of mice to the neurotoxic agent cuprizone. We show that demyelination in response to cuprizone is delayed in mice lacking the binding chain of IFNgamma receptor. In addition, IFNgammaR(-/-) mice exhibited an accelerated remyelination process after cuprizone was removed from the diet. Our results also indicate that the levels of IFNgamma were able to modulate the microglia/macrophage recruitment to the demyelinating areas. Moreover, the accelerated regenerative response showed by the IFNgammaR(-/-) mice was associated with a more efficient recruitment of oligodendrocyte precursor cells in the demyelinated areas. In conclusion, this study suggests that IFNgamma regulates the development and resolution of the demyelinating syndrome and may be associated with toxic effects on both mature oligodendrocytes and oligodendrocyte precursor cells.     

Multicontrast MRI of remyelination in the central nervous system

Although magnetic resonance imaging (MRI) represents the most sensitive tool for the detection of white matter abnormalities in patients with multiple sclerosis (MS), the heterogeneity of MS placques severely hampers the elucidation of specific pathophysiological processes. In order to identify putative MRI markers for de- and remyelination, we employed the cuprizone mouse model which leads to a selective and reversible demyelination of the corpus callosum with little or no axonal damage. Apart from histopathology, animals were studied with high-resolution three-dimensional MRI in vivo using multiple contrasts. While individual MRI findings significantly correlated with electron microscopy, the differentiation of regions with normal, demyelinated or remyelinated white matter by one contrast alone was less specific than by histology or electron microscopy. However, an accurate MRI prediction of the in vivo myelin status was achieved by a discriminant function analysis using a combination of T1, T2 and magnetization transfer contrast. With a correct assignment of 95% of all animals examined, the procedure will allow for the survey of new therapeutic approaches aiming at improved remyelination.     

Experimental models of spontaneous autoimmune disease in the central nervous system

Animal models have become essential tools for studying the human autoimmune disease. They are of vital importance in explorations of disease aspects, where, for diverse reasons, human material is unavailable. This is especially true for disease processes preceding clinical diagnosis and for tissues, which are inaccessible to routine biopsy. Early developing multiple sclerosis (MS) makes an excellent point in case for these limitations. Useful disease models should be developing spontaneously, without a need of artificial, adjuvant-supported induction protocols, and they should reflect credibly at least some of the complex features of human disease. The aim of this review is to compile models that exhibit spontaneous organ-specific autoimmunity and explore their use for studying MS. We first evaluate a few naturally occurring models of organ-specific autoimmune diseases and then screen autoimmunity in animals with compromised immune regulation (neonatal thymectomy, transgenesis, etc.). While most of these models affect organs other than the nervous tissues, central nervous system (CNS)-specific autoimmune disease is readily noted either after transgenic overexpression of cytokines or chemokines within the CNS or by introducing CNS-specific immune receptors into the lymphocyte repertoire. Most recently, spontaneous autoimmunity resembling MS was obtained by transgenic expression of self-reactive T cell receptors and B cell receptors. These transgenic models are not only of promise for studying directly disease processes during the entire course of the disease but may also be helpful in drug discovery.     

Schwann cell remyelination and recurrent demyelination in the central nervous system of mice infected with attenuated Theiler's virus.

Theiler's murine encephalomyelitis virus (TMEV) infection produces a chronic demyelinating disease in mice, and myelin breakdown appears to be immune-mediated. By using an attenuated TMEC strain, WW virus, to infect mice, the course of the disease was slowed and the severity of the inflammatory and glial responses were reduced. In this circumstance, most of the demyelinating lesions showed extensive remyelination, predominantly by Schwann cells. In addition, it was demonstrated that there was recurrent demyelinating activity in the central nervous system (CNS) of infected animals. It is suggested that the rapidity and intensity of demyelinating lesions may influence the potential for remyelination and that Schwann cell participation may be a more important mechanism of myelin repair than it is now thought to be. The fact that there is a recurrent demyelination in TMEV infection increases its relevance as an experimental animal model for multiple sclerosis.     

Distinct pathological patterns in relapsing-remitting and chronic models of experimental autoimmune enchephalomyelitis and the neuroprotective effect of glatiramer acetate

The respective roles of inflammatory and neurodegenerative processes in the pathology of multiple sclerosis (MS) and in its animal model experimental autoimmune encephalomyelitis (EAE) are controversial. Novel treatment strategies aim to operate within the CNS to induce neuroprotection and repair processes in addition to their anti-inflammatory properties. In this study we analyzed and compared the in situ pathological manifestations of EAE utilizing two different models, namely the relapsing-remitting PLP-induced and the chronic MOG-induced diseases. To characterize pathological changes, both transmission electron microscopy (TEM) and immunohistochemistry were employed. The effect of the approved MS drug glatiramer acetate (GA, Copaxone) on myelin damage/repair and on motor neuron loss/preservation was studied in both EAE models. Ultrastructural spinal cord analysis revealed multiple white matter damage foci, with different patterns in the two EAE models. Thus, the relapsing-remitting model was characterized mainly by widespread myelin damage and by remyelinating fibers, whereas in the chronic model axonal degeneration was more prevalent. Loss of lower motor neurons was manifested only in mice with chronic MOG-induced disease. In the GA-treated mice, smaller lesions, increased axonal density and higher prevalence of normal appearing axons were observed, as well as decreased demyelination and degeneration. Furthermore, quantitative analysis of the relative remyelination versus demyelination, provides for the first time evidence of significant augmentation of remyelination after GA treatment. The loss of motor neurons in GA-treated mice was also reduced in comparison to that of EAE untreated mice. These effects were obtained even when GA treatment was applied in a therapeutic schedule, namely after the appearance of clinical symptoms. Hence, the remyelination and neuronal preservation induced by GA are in support of the neuroprotective consequences of this treatment.     

Developmental maturation of innate immune cell function correlates with susceptibility to central nervous system autoimmunity

MS is an inflammatory CNS disorder, which typically occurs in early adulthood and rarely in children. Here we tested whether functional maturation of innate immune cells may determine susceptibility to CNS autoimmune disease in EAE. Two‐week‐old mice were resistant to active EAE, which causes fulminant paralysis in adult mice; this resistance was associated with an impaired development of Th1 and Th17 cells. Resistant, young mice had higher frequencies of myeloid‐derived suppressor cells and plasma‐cytoid DCs. Furthermore, myeloid APCs and B cells from young mice expressed lower levels of MHC class II and CD40, produced decreased amounts of proinflammatory cytokines, and released enhanced levels of anti‐inflammatory IL‐10. When used as APCs, splenocytes from 2‐week‐old mice failed to differentiate naive T cells into Th1 and Th17 cells irrespective of the T‐cell donor's age, and promoted development of Treg cells and Th2 cells instead. Adoptive transfer of adult APCs restored the ability of 2‐week‐old mice to generate encephalitogenic T cells and develop EAE. Collectively, these findings indicate that the innate immune compartment functionally matures during development, which may be a prerequisite for development of T‐cell‐mediated CNS autoimmune disease.     

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) in central nervous system inflammation

In a wide variety of acute and chronic central nervous system (CNS) disorders, inflammatory processes contribute to the damage of brain cells and progression of the disease. Along with other regulatory cytokines, tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is involved in the pathology of multiple sclerosis (MS) and murine experimental autoimmune encephalomyelitis (EAE), bacterial meningitis (BM), HIV encephalitis (HIVE), stroke and Alzheimer's disease (AD). In these conditions, TRAIL is released within the brain mainly by activated microglia and leukocytes infiltrating from the blood stream. TRAIL promotes apoptosis of parenchymal cells in MS/EAE, HIVE, AD and stroke through interaction with TRAIL death receptors expressed on these cells. Frequently, cells in the diseased brain display increased susceptibility to apoptosis induction by TRAIL due to upregulation of death receptors and downregulation of decoy receptors. On the other hand, TRAIL inhibits the proliferation of encephalitogenic T cells in EAE, and it is involved in the clearance of infected brain macrophages in HIVE and of activated neutrophils in BM by interaction with their death receptors. Especially in BM, the ability of TRAIL to limit an acute granulocyte-driven inflammation carries significant neuroprotective potential. Given the diversity of beneficial and harmful effects in the immune and nervous system, TRAIL is a double-edged sword in diseases involving CNS inflammation.     

Class differentiation of immunoglobulin-containing cerebrospinal fluid cells in inflammatory diseases of the central nervous system

Summary An immunocytochemical technique allowing repeated use of antisera is applied to identify immunoglobulin-containing cells (ICC) of the IgG, IgA, and IgM class in the cerebrospinal fluid (CSF) of 298 patients with various neurological disorders. The demonstration of ICC in the CSF is highly indicative of an inflammatory disease (p<0.0001; Chi-square test). In the group of noninflammatory disorders ICC are only found in three cases of lymphomas, two dysgerminomas, and one glioblastoma. ICC of all classes are seen in acute viral and bacterial infections of the CNS including tick-borne meningopolyneuritis Bannwarth. IgG-positive ICC predominate in chronic inflammatory disorders like multiple sclerosis and HIV encephalitis. In HIV-positive patients IgA-or IgM-positive cells are strongly indicative of an opportunistic infection of the brain. Persistent high levels of ICC in three patients with bacterial meningitis are associated with a fatal outcome.Abbreviations ICC Immunoglobulin-containing cells - CNS central nervous system - CSF cerebrospinal fluid - Ig immunoglobulin     

Demyelination and remyelination in the rat central nervous system following ethidium bromide injection

Intracisternal injection of ethidium bromide induced status spongiosus with prominent degenerative changes in oligodendroglia in the subpial regions of the central nervous system of the rat. Chronologic investigation of the lesions has revealed that status spongiosus resulted in myelin degeneration, and by the 6th day postinjection many axons were demyelinated. At this time, numerous debris-filled phagocytic cells were observed among the totally naked axons. Vesicular transformation of myelin was the common degenerative change. Features suggestive of separation of myelin lamellae by phagocytic cells were also observed. In the demyelinated areas, oligodendroglial cells disappeared completely. By the 12th day postinjection, remyelination was apparent and numerous active oligodendroglia appeared in association with thinly myelinated axons. Some central nervous system axons were myelinated by Schwann cells. These patterns of demyelination and remyelination observed in ethidium bromide-treated rats were compared with those observed in other demyelinating conditions of varied etiology such as experimental allergic encephalomyelitis, diphtheria toxin, or lysolecithin injection and cuprizone intoxication.     

Cellular and molecular mechanisms of autoimmune demyelination in the central nervous system

Experimental autoimmune encephalomyelitis (EAE), particularly in its chronic form, shares features with the major human demyelinating disease multiple sclerosis (MS). The roles of lymphocytes and antigen-presenting cells in EAE are increasingly clear. However, little information has been collated on the molecular events involving myelin components in the initiation and perpetuation of the autoimmune condition and in demyelination itself. To draw together relevant data, this review first outlines the molecular structure of the myelin sheath. Evidence implicating individual myelin molecules, as autoimmunogens, as targets for autoimmune attack, or as participants in the demyelinating processes in EAE, is then discussed. Finally, the extent to which the experimental findings are mirrored in MS, and the natural genesis of myelin-directed autoimmunity are considered.     

Role of axonal signals in myelination of the central nervous system

The myelination of the axons of the central nervous system (CNS) is assumed by the oligodendrocytes, which depend at least in part on signals of axonal origin. The axonal influence on myelination seems to consist of the sum of positive and negative factors, which can either act on the axon or on the oligodendrocyte, allowing the neuron to decide when and where myelinization is initiated. The induction factors appear to be mediated, in some cases, by electrical activity. Among the negative factors, certain factors such as the adhesion molecule PSA-NCAM seem to act by inhibiting the adhesion between the axon and the oligodendrocytic extension. Others, such as the inhibitory signalling pathway, jagged1/Notch1, appear to trigger an inhibitory oligodendroglial signalling, therapy preventing maturation and myelination. The recent determination of the role of these axonal signals has provided a new approach to the mechanisms of normal myelination. These results could be extrapolated to the process of remyelination in human demyelinating pathologies such as multiple sclerosis, and open up new therapeutic research possibilities aimed at neuronal protection.     

T cells specific for the myelin oligodendrocyte glycoprotein mediate an unusual autoimmune inflammatory response in the central nervous system

Myelin oligodendrocyte glycoprotein (MOG)-specific T cells mediate an autoimmune inflammatory response in the central nervous system (CNS) that differs radically from conventional models of T cell-mediated experimental allergic encephalomyelitis (EAE). Using synthetic peptides an encephalitogenic T cell epitope of MOG for the Lewis rat was identified within the extracellular IgG V-like domain of the protein, amino acids 44-53 (FSRVVHLYRN).The adoptive transfer of CD4⁺ T cells specific for this epitope induce an intense, dose-dependent inflammatory response in the CNS of naive syngeneic recipients. However, unlike the inflammatory response induced by myelin basic protein (MBP)-specific T cell lines, inflammation mediated by the MOG peptide-specific T cells failed to induce a gross neurological deficit. This unexpected observation was not due to a reduction in the overall inflammatory response in the CNS, but was specifically associated with a decrease in the extent of parenchymal (as opposed to perivascular) inflammation, a selective decrease in the number of ED1⁺ macrophages infiltrating the CNS, and a total lack of peripheral nerve inflammation. The decreased recruitment of macrophages into the CNS could not be ascribed to deficiences in the synthesis of interferon-γ, tumor necrosis factor-a, interleukin (IL)-6 or IL-2 by the T cell line. Moreover, this sub-clinical inflammatory response induced severe blood-brain barrier dysfunction as demonstrated by the induction of severe clinical disease following intravenous injection of a demyelinating MOG-specific monoclonal antibody. The neurological deficit in EAE thus exhibits an unexpected dependence on the identity of the target autoantigen, which determines the extent and nature of the local inflammatory response and ultimately the extent of the neurological deficit.     

An autoradiographic study of cellular proliferation in remyelination of the central nervous system.

The proliferation and origin remyelinating oligodendrocytes was studied by light and electron miscrosopic autoradiography in the superior cerebellar peduncles of mice demyelinated by Cuprizone. In the early phases of demyelination, the cells undergoing mitotic activity were macrophages and astrocytes. In the later phases of demyelination, immature proliferating oligodendrocytes appeared; these differentiated into mature (dark) oligodendrocytes which were responsible for the remyelination of axons seen when animals were again placed on normal diets. The pattern of differentiation recapitulated that seen in developing oligodendrocytes in normal animals. Dark oligodendrocytes did not show mitotic activity. There was no mitotic activity in the subependymal cells around the fourth ventricle adjacent to the superior cerebellar peduncles. This study demonstrates the regenerative capacity of oligodendrocytes and their ability to carry out remeylination in the central nervous system.