Brain, Vol. 123, No. 1, 105-115,
January 2000
© 2000 Oxford University Press
Oligodendrocyte survival, loss and birth in lesions of chronic-stage multiple sclerosis
Graduate School Neurosciences Amsterdam, Netherlands Institute for Brain Research, Amsterdam, The Netherlands
Correspondence to:
Guus Wolswijk, Netherlands Institute for Brain Research, Meibergdreef 33, 1105 AZ Amsterdam ZO, The Netherlands E-mail: G.Wolswijk{at}nih.knaw.nl
 |
Abstract |
|---|
 Top Abstract IntroductionMaterial and methodsResultsDiscussionReferences |
|---|
One of the hallmarks of the human demyelinating disease multiple sclerosis is the inability to compensate adequately for the loss of myelin and of oligodendrocytes, the myelin-forming cells of the CNS. Oligodendrocyte precursor cells, a potential source of oligodendrocytes, have been identified in lesions of chronic multiple sclerosis, but it is not known whether they develop into new, fully differentiated oligodendrocytes, capable of remyelination. Sections of post-mortem multiple sclerosis tissue were therefore immunolabelled with antibodies to galactocerebroside (GalC), the first oligodendrocyte-specific molecule to be expressed by differentiating oligodendrocyte precursor cells, and myelin oligodendrocyte glycoprotein (MOG), a marker for mature oligodendrocytes. In total, 23 lesions from 15 subjects with chronic progressive multiple sclerosis were analysed. The immunolabelling revealed that chronic multiple sclerosis lesions contain only small numbers of immature, process-bearing, GalC-positive oligodendrocytes (0–2 cells/mm2 in 10 µm thick sections); they had a relatively large, pale nucleus (maximum diameter: 9.9 ± 0.9 µm). Although they appeared to make contact with surrounding demyelinated axons, most immature oligodendrocytes appeared not to be engaged in myelination. These findings suggest that oligodendrocyte differentiation of precursor cells is a rare event in chronic multiple sclerosis, which is consistent with the general failure of myelin repair during the later stages of this disease. The lesions in the collection, in particular those with recent demyelinating activity, contained another distinct population of oligodendrocytes. It consisted of small, round cells with a small, dense nucleus (maximum diameter: 6.8 ± 0.8 µm) that expressed both GalC and MOG but lacked processes, suggesting that these cells were mature oligodendrocytes that had survived the loss of their myelin sheaths, i.e. they were demyelinated oligodendrocytes. In the most recent lesions in the collection, the demyelinated oligodendrocytes were found in large numbers throughout the centre of the lesion (up to 700 cells/mm2), while in the older lesions they were found only at the edges. Moreover, when the borders of these older lesions still contained numerous macrophages, they tended to contain more demyelinated oligodendrocytes than those lacking macrophages. These findings suggest that mature, demyelinated oligodendrocytes gradually disappear from lesion areas with increasing age of the lesion. The present study thus suggests that the failure of myelin repair in at least some cases of chronic multiple sclerosis is due to (i) the loss of demyelinated oligodendrocytes from lesion areas and (ii) the failure of the oligodendrocyte precursor population to expand and generate new oligodendrocytes. Gaining further insight into these processes may prove crucial for the development of remyelination promoting strategies.
GalC; MOG; multiple sclerosis; oligodendrocyte precursor cell; remyelination
GalC = galactocerebroside; GFAP = glial fibrillary acidic protein; LCA = leucocyte common antigen; MBP = myelin basic protein; MOG = myelin oligodendrocyte glycoprotein; mAb = monoclonal antibody; PDGF = platelet-derived growth factor
|
Introduction |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsDiscussionReferences |
|---|
The local loss of the insulating sheath of myelin around axons in the CNS of patients with multiple sclerosis is generally not adequately compensated for during the chronic stage of the disease, resulting in the formation of confluent areas of persistent demyelination and neurological disability due, at least in part, to impaired conduction along demyelinated fibres (Prineas and McDonald, 1997
; Lassmann, 1998); recent evidence suggests that some of the disability in multiple sclerosis may result from damage to and loss of axons (Ferguson et al., 1997; Trapp et al., 1998). Spontaneous remyelination does appear to be a prominent feature in lesions that develop during the early course of multiple sclerosis (Lassmann, 1983; Prineas, 1985; Prineas et al., 1993a, b; Raine and Wu, 1993; Brück et al., 1994; Ozawa et al., 1994), although the extent to which this occurs may depend on disease subtype (Lucchinetti et al., 1996; Lassmann et al., 1997; Lassmann, 1998). The basis for this decline in regenerative potential with disease progression remains elusive, but the decline is thought to reflect the extent of loss of oligodendrocytes, the myelin-forming cells of the CNS, from lesion areas (Prineas and McDonald, 1997; Raine, 1997). Thus, lesions that develop during the chronic stages of multiple sclerosis may lack sufficient oligodendrocytes to carry out myelin repair.
The mature human CNS contains an additional potential source of new remyelinating oligodendrocytes, i.e. a population of oligodendrocyte precursor cells (Armstrong et al., 1992; Gogate et al., 1994; Scolding et al., 1995; Wolswijk, 1998a), but their fate in the demyelination process in multiple sclerosis has been revealed only recently (Wolswijk 1998b). Using a collection of appropriately fixed multiple sclerosis tissue specimens, this study showed that lesions obtained from subjects who died during the chronic stage of multiple sclerosis contained significant numbers of oligodendrocyte precursor cells, identified as cells that bound the O4 monoclonal antibody (mAb), but not antibodies to galactocerebroside (GalC) and glial fibrillary acidic protein (GFAP) (Wolswijk, 1998b). Subsequent analysis of the O4-positive oligodendrocyte precursor cells in chronic-stage multiple sclerosis lesions suggested that they were relatively quiescent, as none expressed the nuclear proliferation antigen recognized by the Ki-67 antibody (Wolswijk, 1998b). Demyelinated lesions derived from patients with chronic-stage multiple sclerosis also contain cells that bind antibodies to the 
-type receptor for platelet-derived growth factor (PDGF) (Scolding, 1998; Wolswijk, 1998b), a putative marker for oligodendrocyte precursor cells (Pringle et al., 1992; Nishiayama et al., 1996; Oumesmar et al., 1997). These cells were observed not only in the centre of the lesions, but also in the periplaque white matter and in control white matter (Scolding et al., 1998); Gogate and co-workers had shown earlier that PDGF- receptor mRNA expressing cells are present in normal-appearing temporal lobe white matter from patients with epilepsy (Gogate et al., 1994). There may be some overlap between the two populations of oligodendrocyte precursor cells in the adult human CNS, as Gogate and colleagues have shown, using in situ hybridization, that human O4-positive cells grown in tissue culture contain transcripts for the -type PDGF receptor (Gogate et al., 1994).
The presence of oligodendrocyte precursor cells in lesions of chronic-stage multiple sclerosis suggests that they survive the demyelination process and/or repopulate lesion sites after their local destruction. The first possibility appears the most likely, as even the centre of the lesions with the most recent demyelinating activity contained significant numbers of oligodendrocyte precursor cells, as they were found throughout the demyelinated area of all lesions studied, including the very large lesions in the collection, and as they were not concentrated near lesion borders (Wolswijk, 1998a, b). If the oligodendrocyte precursor population is indeed largely unaffected by the myelin destruction process in multiple sclerosis, this suggests that the disease process specifically targets oligodendrocytes and/or their myelin sheaths, and that the limited success of myelin repair during the chronic stage of multiple sclerosis is the result of the failure of the local oligodendrocyte precursor population to expand and generate new myelin-forming cells. Oligodendrocyte precursor cells may, however, generate new oligodendrocytes in lesions that develop during the early phases of multiple sclerosis, as such lesions frequently contain oligodendrocytes that do not yet express markers for fully differentiated oligodendrocytes (Prineas et al., 1989; Brück et al., 1994; Ozawa et al., 1994).
Following the recent identification of oligodendrocyte precursor cells in chronic-stage multiple sclerosis lesions, the present study examined the potential origin of two distinct types of GalC-positive oligodendrocytes previously identified in chronic-stage multiple sclerosis lesions, i.e. a population of large, process-bearing oligodendrocytes and a population of small, round, non-myelinating oligodendrocytes (Wolswijk, 1998b). The data of the present study suggest that the first population is derived from the pool of oligodendrocyte precursor cells in the lesions, whereas the second population comprises mature oligodendrocytes that have lost their myelin-forming processes during episodes of demyelinating damage.
|
Material and methods |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsDiscussionReferences |
|---|
Preparation of sections of post-mortem CNS tissue
Blocks of post-mortem CNS tissue from subjects with a clinical diagnosis of chronic progressive multiple sclerosis containing one or more macroscopically visible lesions were fixed in 4% paraformaldehyde in PBS (phosphate-buffered saline; pH 7.4) and then processed as described in detail previously (Wolswijk, 1998b
). The clinical diagnosis of multiple sclerosis was confirmed neuropathologically by Dr W. Kamphorst, Department of Pathology, Academic Hospital of the Free Hospital, Amsterdam, The Netherlands. The average age of the multiple sclerosis subjects at death was 54 years (range 32–82 years), the average disease duration was 19 years (range 8–49 years), and the average delay between the death of the subject and the fixation of the tissue was 6 h 15 min (range from 3 h 45 min to 9 h 35 min).
Immunohistochemistry
Sections 10 µm thick were immunolabelled using indirect immunofluorescence or immunoperoxidase procedures, as described in detail in a previous paper (Wolswijk, 1998b). The primary antibodies used were: (i) a rabbit anti-human CD3 antiserum (DAKO, Denmark); (ii) a mouse IgG3 anti-GalC mAb [the Ranscht mAb; Ranscht et al., 1982)], a rabbit antiserum to cow GFAP (glial acidic fibrillary protein) (DAKO); (iii) a rabbit antiserum to human Ki-67 (DAKO); (iv) a mixture of two mouse IgG1 anti-human leucocyte common antigen (LCA) mAbs (mAbs 2B11 and PD7/26; DAKO); (v) a rabbit antiserum to myelin basic protein (MBP) (a gift of Dr H. van Noort, TNO, Leiden, The Netherlands); (vi) a mouse IgG1 anti-MOG (myelin oligodendrocyte glycoprotein) mAb [the Y10 mAb (Piddlesden et al., 1993), a gift of Dr S. Piddlesden]; (vii) a mouse IgG1 anti-neurofilament mAb (the RT97 mAb; Boehringer Mannheim, Germany); (viii) the mouse IgM O1 mAb (Sommer and Schachner, 1981; an anti-GalC mAb); (ix) the mouse IgM O4 mAb (Sommer and Schachner, 1981); and (x) a mouse IgG1 anti-vimentin mAb (Boehringer Mannheim). The binding of the primary antibodies was visualized using appropriate class- and species-specific FITC (fluorescein isothiocyanate)-, TRITC (tetramethyl rhodamine isothiocyanate)- and biotin-labelled conjugates (all from either Southern Biotechnology, Birmingham, Ala., USA or Jackson ImmunoResearch, Westgrove, Pa., USA); the binding of the biotinylated antibodies was visualized with either Cy5-conjugated (Jackson ImmunoResearch) or horseradish peroxidase-conjugated streptavidin (Vectastain ABC kit, Vector Laboratories, Burlinghame, Calif., USA); 3,3'-diaminobenzidine was used as substrate for the peroxidase. Nuclei were visualized by incubating sections in 1 mg/ml Hoechst 33258 (Sigma, St Louis, Mo., USA) (for conventional fluorescence microscopical analysis), in 1 mM TO-PRO-3 iodide (Molecular Probes) in PBS (for confocal laser scanning microscopical analysis) or in a haematoxylin solution (for bright-field microscopical analysis). Sections were examined on a Zeiss Axiophot microscope with filters optimized for distinguishing between FITC, TRITC and Hoecht 33258 emission and with bright-field and phase-contrast optics and on a Zeiss 410 confocal laser scanning microscope (CLSM) with three lasers emitting at 488, 543 and 633 nm to excite FITC, TRITC and Cy5/TO-PRO-3 iodide, respectively.
|
Results |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsDiscussionReferences |
|---|
Identification of oligodendrocytes in chronic-stage multiple sclerosis lesions
The first oligodendrocyte-specific molecule to be expressed by differentiating oligodendrocyte precursor cells is the glycolipid GalC (Raff et al., 1978
, 1983; Curtis et al., 1988; Reynolds and Wilkin, 1988; Warrington and Pfeiffer, 1992; Pfeiffer et al., 1993; Wolswijk, 1995). These cells subsequently start synthesizing a number of other oligodendrocyte-specific molecules, including proteolipid protein and MBP (Reynolds and Wilkin, 1988; Pfeiffer et al., 1993). One of the last molecules to be expressed by maturing oligodendrocytes is MOG (Pfeiffer et al., 1993; Piddlesden et al., 1993; Ludwin, 1990). In addition to changes in antigenic phenotype and an increase in the complexity of their morphology, the nucleus of maturing oligodendrocytes changes from large and pale to small and dense (Mori and Leblond, 1970). Therefore, to distinguish between immature and fully differentiated oligodendrocytes in chronic-stage multiple sclerosis lesions, sections were labelled with antibodies to GalC and MOG and with the nuclear dyes Hoechst 33258 or TO-PRO-3 iodide. Using this labelling procedure, it was expected that immature oligodendrocytes would be GalC-positive, MOG-negative cells with a large, pale nucleus, while mature oligodendrocytes would express both GalC and MOG and possess a small, dense nucleus.
The success and the specificity of stainings involving antibodies to GalC is dependent on the fixation of the tissue and the immunolabelling procedure employed (Prineas et al., 1989; Wu and Raine, 1992; Wolswijk, 1998b). For example, no or only weak labelling with anti-GalC antibodies is observed in sections cut from unfixed, snap-frozen multiple sclerosis tissue, whereas the cytoplasm of reactive astrocytes is stained prominently in sections of formalin-fixed, paraffin-embedded material. As shown in a previous study, excellent oligodendrocyte lineage-specific labelling with anti-GalC antibodies (and the O4 mAb) is obtained in sections of 4% paraformaldehyde-fixed, 30% sucrose-treated, frozen chronic-stage multiple sclerosis tissue (Wolswijk, 1998b).
Collection of chronic-stage multiple sclerosis lesions
The expression of GalC and MOG was examined in a series of 23 appropriately fixed, macroscopically visible brain lesions (with a diameter of 
3 mm) derived from 15 subjects with chronic progressive multiple sclerosis (with a disease history of 8–49 years) (Table 1); most of the lesions in the collection were taken from white matter areas around the ventricles, a common site for lesions (Prineas and McDonald, 1997; Lassmann, 1998). As shown previously (Wolswijk, 1998b), detailed immunohistochemical analysis of the lesions with antibody markers for oligodendrocytes/myelin (antibodies to GalC, MBP and MOG), astrocytes (antibodies to GFAP), axons (anti-neurofilament antibodies) and leucocytes (anti-human LCA antibodies), i.e. (activated) microglia, macrophages and lymphocytes, indicated that the collection consisted of four distinct types of demyelinated lesions (Table 1; see also Fig. 1); these findings were based on the analysis of a minimum of 10 sections per lesion. Four of the lesions in the collection, i.e. lesions D, G, H and I, were hypercellular and contained large numbers of macrophages laden with myelin debris (>400 cells/mm2, 10 µm thick sections) and oligodendrocyte cell bodies (see later), but little myelin (type A lesions). Sixteen lesions had a centre that was hypocellular and almost free of myelin (<1% myelinated axons) and oligodendrocytes. Eleven of these had a wide border region and contained significant numbers of debris-laden macrophages in the centre [between 7 ± 6 (lesion J, subject 96-040) and 324 ± 52 (an area of lesion F, subject 96-039) cells/mm2 section (data from Wolswijk, 1998b)]; they were concentrated predominantly, but not exclusively, at the edges of the lesions, which were often hypercellular (type B lesions). The five other lesions with an oligodendrocyte- and myelin-free centre had a very sharp lesion border and were almost totally lacking in macrophages both in the centre and at the border, suggesting that they were relatively old (type C lesions); it can take several months for macrophages laden with myelin degradation products to disappear from lesion sites (Prineas et al., 1989; Brück et al., 1995; Lassmann, 1998). Finally, lesions P, R and S contained significant, but variable, numbers of myelinated axons throughout the centre (from <5% to >50%); these lesions were hypocellular and lacked macrophages and were thus also likely to be relatively old (type D lesions); with the tools available it was not possible to determine whether these three lesions were partly demyelinated or partly remyelinated. Macrophages containing debris that was still strongly immunoreactive for MBP were seen in only two of the lesions in the collection (the hypercellular lesions H and I, both from subject 96-040); their numbers were small and they were observed only in the borders of these two lesions. As MBP staining of myelin debris within macrophages is lost within 10 days of uptake by macrophages (Brück et al., 1995; Lassmann, 1998), this finding suggested that very little active myelin breakdown was occurring at the time of death of the multiple sclerosis subject in the lesions studied. Perivascular cuffs with variable numbers of LCA-positive cells (mainly lymphocytes and macrophages) were observed within and around the demyelinated area of all lesions studied (not shown).
|
|
GalC expression in chronic-stage multiple sclerosis lesions
The intensity of the labelling with antibodies to GalC was higher at the lesion border than in the white matter surrounding the demyelinated lesion and in control white matter (Fig. 1
). Individual GalC-positive cells and GalC-positive myelin segments were clearly visible in lesion areas, but not in the white matter surrounding the lesion and in control white matter (Fig. 1); however, single oligodendrocytes and myelin sheaths immunoreactive for GalC were observed in adult human cortical grey matter (not shown). In some of the chronic multiple sclerosis lesions, the anti-GalC immunoreactivity was found predominantly at the lesion borders, while in others GalC-positive cells and structures were observed throughout the demyelinated area. In addition to myelin and variable numbers of debris-laden macrophages, the anti-GalC antibodies labelled two distinct populations of oligodendrocytes in the lesion sites, i.e. large, process-bearing oligodendrocytes and small oligodendrocytes with few if any processes (Figs 1 and 2).
|
Process-bearing GalC-positive oligodendrocytes
The chronic-stage multiple sclerosis lesions in the collection contained small numbers of large, process-bearing, GalC-positive cells (Fig. 2
) scattered throughout their demyelinated areas. Their nucleus was relatively large [maximum diameter = 9.9 ± 0.9 µm (n = 13)] and often irregular in shape (Fig. 2) and thus resembled that of the O4-positive, GalC-negative, GFAP-negative oligodendrocyte precursor cells in the lesions [maximum diameter = 9.8 ± 1.5 µm (Wolswijk, 1998b)]. They also bound the O4 mAb [which recognizes an antigen(s) expressed on the surface of both oligodendrocytes and their precursor cells (Sommer and Schachner, 1981; Wolswijk and Noble, 1989)], but their cell body was not labelled with the Y10 anti-MOG mAb. Furthermore, confocal laser scanning microscope analysis showed that these cells lacked the intermediate filament GFAP and vimentin (not shown). Some of the process-bearing oligodendrocytes had a relatively simple morphology and in this respect resembled oligodendrocyte precursor cells, while others had a more complex morphology, i.e. they had many processes and they were often arranged in a more symmetrical manner than those of oligodendrocyte precursor cells (Fig. 2).
To determine whether the processes of these antigenically and morphologically immature oligodendrocytes were connected to myelin sheaths, sections were double-labelled with anti-GalC antibodies and antibodies to either MOG or MBP. These experiments showed that only a few (<10%) of these cells were engaged in myelination (Fig. 2). Confocal laser scanning microscopy of sections triple-immunolabelled with antibodies to GalC, MBP and neurofilament revealed that even the processes of the non-myelin-forming, antigenically immature oligodendrocytes appeared to be in close contact with surrounding, demyelinated axons (Fig. 2).
The density of the immature oligodendrocyte population in the lesions studied was much lower than that of the oligodendrocyte precursor population. While between 2 and 34 cells/mm2 in the chronic-stage multiple sclerosis lesions in the collection were oligodendrocyte precursor cells (Wolswijk, 1998b), the density of the immature oligodendrocyte population was much less than 1 cell/mm2 in most lesions (Wolswijk, 1998b). For example, the demyelinated area present in three sections of a region of lesion B from subject 95-095 (in total 24 mm2) contained 333 O4-positive, GalC-negative oligodendrocyte precursor cells (an average density of 13.9 cells/mm2 section), but only two process-bearing GalC-positive oligodendrocytes (a density of <0.1 cells/mm2 section). The highest density of immature oligodendrocytes was found in lesion Q (2 ± 1 cells/mm2 section).
Rounded GalC-positive oligodendrocytes
The vast majority of the GalC-positive cells in the chronic-stage multiple sclerosis lesions studied were small, round cells with little cytoplasm and few, if any, processes; they were observed not only in the 23 lesions in the collection but also in much smaller lesions (with a diameter of <3 mm) (not shown). The nucleus was small [maximum diameter = 6.8 ± 0.8 m (n = 64)] and generally round or oval; the nucleochromatin often appeared clumped or condensed. Double-labellings of sections with anti-GalC antibodies and the Y10 anti-MOG mAb revealed that the GalC-positive cell bodies were MOG-positive (Fig. 2), and thus appeared to belong to fully matured oligodendrocytes. As illustrated in Fig. 2, these cells expressed much lower levels of MOG than myelin. Moreover, in contrast to previous reports (e.g. Brück et al., 1994; Ozawa et al., 1994), the perikarya of mature oligodendrocytes in periplaque white matter and also in control white matter appeared not to be labelled with antibodies to MOG, even when sections were examined using a confocal laser scanning microscope (not shown). Additional immunolabellings involving the O4 mAb and the O1 mAb [which is another anti-GalC mAb (Sommer and Schachner, 1981)] showed that the rounded oligodendrocytes were both O4-positive (Fig. 2) and O1-positive. As expected, they did not bind antibodies to LCA (a marker for leucocytes), CD3 (a marker for T lymphocytes, which are also small round cells), GFAP or vimentin (not shown).
Confocal laser scanning microscope analysis of sections labelled with antibodies to GalC and either MOG or MBP suggested that most of the rounded oligodendrocytes were not connected to myelin segments, even though they were often found in areas of the lesions that still contained some myelin, such as the lesion edges (Figs 1 and 2). This notion was supported by the observation that the rounded oligodendrocytes were frequently present in areas completely devoid of myelin. Immunolabelling of sections with both anti-GalC and anti-NF antibodies showed that the rounded oligodendrocytes also did not extend processes to surrounding, demyelinated axons (Fig. 2).
The number and distribution of the rounded oligodendocytes in the 23 lesions studied varied considerably. For example, in the hypercellular lesions D, G, H and I they were present in large numbers throughout the lesion area [up to ~700 cells/mm2 (lesion I)], while in the type B and C lesions the rounded cells were present almost exclusively at the lesion borders (Figs 1 and 2); their centres contained in most cases <5 rounded oligodendrocytes per mm2 section. As illustrated in Fig. 1 and Table 2, the margins of the type B lesions, i.e. lesions with many debris-laden macrophages at their border, tended to contain more rounded oligodendrocytes in the border than type C lesions, i.e. lesions with few, if any, phase-bright macrophages at the border (Table 2; Fig. 1). For example, only a single row of rounded oligodendrocytes was observed at the edges of lesion B (subject 95-095) (Fig. 1D), whereas several rows of rounded oligodendrocytes were present in the border of an area of lesion W (subject 97-160) (Fig. 1C). Only a very occasional rounded oligodendrocyte was encountered in the centre of lesions with reduced numbers of myelin sheaths (not shown).
|
As the density of the rounded oligodendrocytes in the centre and/or borders of the chronic-stage multiple sclerosis lesions studied was often relatively high and as these cells sometimes appeared to be clumped together (Figs 1 and 2
), it was checked whether any of the cells expressed a nuclear proliferation-associated protein recognized by the Ki-67 antibody; this molecule is expressed during the late G1, S, G2 and M phases but not in the G0 phase of the cell cycle (Gerdes et al., 1984; Brown and Gatter, 1990). Although all GalC-positive (or O4-positive), rounded cells present in four to six sections were examined (in many cases, >100 cells/section), none had a Ki-67-immunoreactive nucleus; also, none of the immature oligodendrocytes in the lesions was found to contain a Ki-67-positive nucleus. As shown previously (Wolswijk, 1998b), some of the 23 lesions did contain some Ki-67-positive nuclei in the demyelinated centre, but their numbers were small [highest density = 2 ± 1 positive nuclei/mm2 section (lesion N, subject 96-074)]. |
Discussion |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsDiscussionReferences |
|---|
The present study provides evidence that chronic-stage multiple sclerosis lesions contain only small numbers of immature oligodendrocytes. The morphology of those that were examined ranged from precursor-like cells to cells that were engaged in myelinating small numbers of axons. Although these cells could have been derived from dedifferentiated mature oligodendrocytes (Wood and Bunge, 1991
; Canoll et al., 1999), it is more likely that the immature oligodendrocytes in the lesions had been recruited from the local pool of oligodendrocyte precursor cells. If this is indeed the case, then this suggests that oligodendrocytic differentiation of precursor cells is generally a rare event in chronic multiple sclerosis lesions or that the newly generated oligodendrocytes die as soon as they reach a certain developmental stage. These findings complement previous studies showing that myelinating oligodendrocytes tend to be present in only very small numbers in the centre of chronic multiple sclerosis lesions (Prineas and McDonald, 1997; Lassmann, 1998; Mews et al., 1998; Wolswijk, 1998b) and are consistent with the limited success of myelin repair during the chronic stage of the disease (Prineas and McDonald, 1997; Lassmann, 1998). Whether oligodendrocyte differentiation of precursor cells is inhibited by factor(s) present in the lesion area or whether intrinsic factor(s) play a role remains unclear. These factor(s) may possibly not play a role early on in the disease, as antigenically immature oligodendrocytes are frequently present in early multiple sclerosis lesions (Prineas et al., 1989; Brück et al., 1994; Ozawa et al., 1994). Further insight into this and into the failure of the oligodendrocyte precursor population to expand may provide clues as to how the repair of demyelinated lesions in multiple sclerosis may be promoted therapeutically, e.g. by supplying lesions sites with putative mitogenic factors for these cells, such as PDGF, basic fibroblast growth factor (FGF-2) and glial growth factor-2 (GGF2) (Wolswijk and Noble, 1989, 1992; Wolswijk et al., 1991; Engel and Wolswijk, 1996; Shi et al., 1998), and/or by reducing the local production of remyelination inhibitory factors.
Ozawa and colleagues examined the generation of new oligodendrocytes in lesions of chronic-stage multiple sclerosis in a different way (Ozawa et al., 1994). By comparing in separate sections the number of oligodendrocytes expressing mRNAs for proteolipid protein, a marker for oligodendrocytes engaged in the synthesis and maintenance of myelin, with the number of MOG-positive, fully matured cells, they found that oligodendrocytes containing proteolipid protein mRNA outnumbered those that expressed MOG. These findings thus suggest that such lesions contained cells that were engaged in myelination, but were not fully differentiated, which is consistent with the possibility that small numbers of new oligodendrocytes are generated in chronic-stage multiple sclerosis lesions, either from the pool of precursor cells or from dedifferentiated, mature oligodendrocytes. It is important to note, however, that the immature oligodendrocytes in the study of Ozawa and colleagues were at a much later developmental stage than those identified in the present study, as the majority of these were non-myelinating.
The vast majority of the GalC-positive oligodendrocytes in the demyelinated area of the chronic-stage multiple sclerosis lesions studied were rounded cells that appeared not to be engaged in myelination. Although such rounded oligodendrocytes or oligodendrocyte-like cells have been observed previously in both early and chronic lesions (e.g. Raine et al., 1981; Prineas et al., 1989; Brück et al., 1994; Ozawa et al., 1994), their origin has remained unclear. The data presented here, together with earlier observations by other investigators, suggest that these cells are probably demyelinated oligodendrocytes, i.e. mature oligodendrocytes that have survived the loss of the myelin sheath during bouts of disease activity, rather than newly generated, non-myelinating oligodendrocytes. First, like mature oligodendrocytes, the rounded cells expressed MOG, a marker for terminally differentiated oligodendrocytes (Ludwin, 1990; Pfeiffer et al., 1993; Piddlesden et al., 1993), and had a small, spherical nucleus (Brück et al., 1994; Ozawa et al., 1994; this study). Secondly, the highest number of rounded oligodendrocytes was found in areas of the lesions with the most recent demyelinating activity, as evidenced by the presence of large numbers of debris-laden macrophages (this study). Thirdly, the lesion environment did not prevent the expression of a process-bearing morphology, as the small numbers of immature oligodendrocytes in the lesion areas did extend processes and, moreover, were sometimes found in the same area of the lesion as the rounded oligodendrocytes (this study). In other words, if these cells had been generated by oligodendrocyte precursor cells, it seems most likely that they would have displayed a process-bearing morphology. If the rounded oligodendrocytes in both acute/early and chronic lesions are indeed demyelinated, mature oligodendrocytes, then this suggests that in at least some cases of multiple sclerosis the myelin sheath and not the oligodendrocyte cell body is the primary and specific target of the disease process.
The distribution and density of the demyelinated oligodendrocytes in the various types of chronic-stage lesions in the collection suggests the following scenario for lesion development in at least some cases of multiple sclerosis. During episodes of demyelinating damage, mature, myelinating oligodendrocytes lose their myelin sheath. These demyelinated oligodendrocytes may perhaps re-form new processes and remyelinate denuded axons during early stages of multiple sclerosis, while during the later stages of the disease factor(s) present in the lesion area may prevent this; it is not yet clear whether demyelinated oligodendrocytes are able to generate new myelin sheaths. Without perhaps the trophic support from axons, or because of the absence of diffusible oligodendrocyte survival factor(s), the demyelinated oligodendrocytes gradually disappear starting from the centre, so that at later stages of lesion formation the rounded oligodendrocytes are found only at the lesion edges. This loss of oligodendrocytes from lesion areas is probably a very slow process, taking weeks or months, as very few oligodendrocytes appear to be undergoing degeneration in chronic-stage multiple sclerosis lesions (Raine, 1997; G. Wolswijk, unpublished observations) and as the demyelinated oligodendrocytes are often found in areas completely devoid of macrophages. This view of lesion development is supported by the results obtained from the analysis of seven lesions derived from multiple sclerosis subject 96-040 (lesions G–M). Lesions H and I, which were the most recent lesions of the seven, as evidenced by the presence of small numbers of MBP-positive macrophages, were packed with large numbers of demyelinated oligodendrocytes and macrophages laden with myelin debris. Lesion G lacked MBP-positive macrophages and had a centre that contained fewer rounded oligodendrocytes and debris-laden macrophages than lesions H and I, while the remaining four lesions had a hypocellular centre lacking myelin and oligodendrocytes. In these lesions, the rounded oligodendrocytes were present only at their (macrophage-containing) borders. If this scenario of lesion development for some types of multiple sclerosis is correct, then myelin repair in multiple sclerosis may be promoted therapeutically by increasing the local concentrations of factors that increase the survival of demyelinated oligodendrocytes and promote the regeneration of their myelin-forming processes.
In contrast to the rounded oligodendrocytes examined in the present study, Schönrock and colleagues found that some early multiple sclerosis lesions (biopsy material) contained small numbers of MOG-positive cells with apparently no processes that expressed the proliferation antigen recognized by the Ki-67 antibody (Schönrock et al., 1998). This observation suggests that mature, demyelinated oligodendrocytes may be proliferatively active in lesions that develop during the early course of multiple sclerosis; however, no mitotic figures were observed in these oligodendrocytes [In fact, mitotic oligodendrocytes have never been observed in multiple sclerosis lesions (Raine, 1997).] The proliferation of oligodendrocyte precursor cells was not analysed in this study, but a proportion of the Ki-67-positive cells were not labelled with markers for oligodendrocytes, astrocytes or microglia/macrophages. It is thus possible that some of the Ki-67-positive nuclei belonged to oligodendrocyte precursor cells in the lesion areas.
It is becoming clear that significant numbers of oligodendrocyte precursor cells may remain in many chronically demyelinated multiple sclerosis lesions and that mature oligodendrocytes may initially survive the loss of their myelin-forming processes. Together with the observation that spontaneous myelin repair is often a prominent feature of lesions that develop during the early course of multiple sclerosis, these findings indicate that the potential for repair of demyelinated multiple sclerosis lesions is more pronounced than previously thought. It remains to be determined whether the oligodendrocyte precursor population can be stimulated therapeutically to expand and generate remyelinating oligodendrocytes and whether demyelinated oligodendrocytes can be stimulated to form new myelin sheaths.
|
Acknowledgments |
|---|
The author wishes to thank the team of the NBB (Anke de Boer, Hans Daniëls, Bart Fisser, Mariann Fodor, André Goessen, Stephan Guldenaar, Anne Holtrop, Marina Kahlmann, Wouter Kamphorst, Michiel Kooreman, Elly de Nijs, Sylvia Pindak, Rixt Riemersma, Ahmad Salehi, Dick Swaab, Unga Unmehopa, Paul van der Valk, Michiel Vermaak, Richard Vos, Rob de Vries, Harry Winters and José Wouda) for collecting the multiple sclerosis tissue and for advice, Sara Piddlesden and Hans van Noort for their generous gift of antibodies, Gerben van der Meulen for assistance with the preparation of the figures and Mark Noble, Dick Swaab and Paul Dijkhuizen for critical reading of the manuscript. Financial support for this study came from the Netherlands Foundation `Friends MS Research', the Multiple Sclerosis Society of Great Britain and Northern Ireland, and BIOGEN Inc. (Cambridge, Mass., USA). Human brain tissue was obtained from the Netherlands Brain Bank (NBB) in Amsterdam (Coordinator Dr R. Ravid).
|
References |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsDiscussionReferences |
|---|
Armstrong RG, Dorn HH, Kufta CV, Friedman E, Dubois-Dalcq ME. Pre-oligodendrocytes from adult human CNS. J Neurosci 1992; 12: 1538–47.[Abstract]
Brown D, Gatter KC. Monoclonal antibody Ki-67: its use in histopathology. [Review]. Histopathology 1990; 17: 489–503.[Web of Science][Medline]
Brück W, Schmied M, Suchanek G, Brück Y, Breitschopf H, Poser S, et al. Oligodendrocytes in the early course of multiple sclerosis. Ann Neurol 1994; 35: 65–73.[Web of Science][Medline]
Brück W, Porada P, Poser S, Rieckmann P, Hanefeld F, Kretzschmar HA, et al. Monocyte/macrophage differentiation in early multiple sclerosis lesions. Ann Neurol 1995; 38: 788–96.[Web of Science][Medline]
Canoll PD, Kraemer R, Teng KK, Marchionni MA, Salzer JL. GGF/neuregulin induces a phenotypic reversion of oligodendrocytes. Mol Cell Neurosci 1999; 13: 79–94.[Web of Science][Medline]
Curtis R, Cohen J, Fok-Seang J, Hanley MR, Gregson NA, Reynolds R, et al. Development of macroglial cells in rat cerebellum. I. Use of antibodies to follow early in vivo development and migration of oligodendrocytes. J. Neurocytol 1988; 17: 43–54
Engel U, Wolswijk G. Oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells derived from adult rat spinal cord: in vitro characteristics and response to PDGF, bFGF and NT-3. Glia 1996; 16: 16–26.[Web of Science][Medline]
Ferguson B, Matyszak MK, Esiri MM, Perry VH. Axonal damage in acute multiple sclerosis lesions. Brain 1997; 120: 393–9.
Gerdes J, Lemke H, Baisch H, Wacker HH, Schwab U, Stein H. Cell cycle analysis of a cell proliferation-associated human nuclear antigen defined by the monoclonal antibody Ki-67. J Immunol 1984; 133: 1710–5.[Abstract]
Gogate N, Verma L, Zhou JM, Milward E, Rusten R, O'Conner M, et al. Plasticity in the adult human oligodendrocyte lineage. J Neurosci 1994; 14: 4571–87.[Abstract]
Lassmann H. Comparative neuropathology of chronic experimental allergic encephalomyelitis and multiple sclerosis. [Review]. Schriftenr Neurol 1983; 25: 1–135
Lassmann H. Pathology of multiple sclerosis. [Review]. In: Compston A, Ebers G, Lassmann H, McDonald I, Matthews B, Wekerle H, editors. McAlpine's multiple sclerosis. 3rd ed. London: Churchill Livingstone; 1998. p. 323–58.
Lassmann H, Brück W, Lucchinetti C, Rodriguez M. Remyelination in multiple sclerosis. [Review]. Mult Scler 1997; 3: 133–6.
Lassmann H, Raine CS, Antel J, Prineas JW. Immunopathology of multiple sclerosis: report on an international meeting held at the Institute of Neurology of the University of Vienna. J Neuroimmunol 1998; 86: 213–7.[Web of Science][Medline]
Lucchinetti CF, Brück W, Rodriguez M, Lassmann H. Distinct patterns of multiple sclerosis pathology indicates heterogeneity on pathogenesis. [Review]. Brain Pathol 1996; 6: 259–74.[Web of Science][Medline]
Ludwin SK. Oligodendrocyte survival in Wallerian degeneration. Acta Neuropathol (Berl) 1990; 80: 184–91.[Medline]
Mews I, Bergmann M, Bunkowski S, Gullotta F, Brück W. Oligodendrocyte and axon pathology in clinically silent multiple sclerosis lesions. Mult Scler 1998; 4: 55–62.
Mori C, Leblond CP. Electron microscopic identification of three classes of oligodendrocytes and a preliminary study of their proliferative activity in the corpus callosum of young rats. J Comp Neurol 1970; 139: 1–28.[Web of Science][Medline]
Ozawa K, Suchanek G, Breitschopf H, Brück W, Budka H, Jellinger K, et al. Patterns of oligodendroglia pathology in multiple sclerosis. Brain 1994; 117: 1311–22.
Pfeiffer SE, Warrington AE, Bansal R. The oligodendrocyte and its many cellular processes. [Review]. Trends Cell Biol 1993; 3: 191–7.[Medline]
Piddlesden SJ, Lassmann H, Zimprich F, Morgan BP, Linington C. The demyelinating potential of antibodies to myelin oligodendrocyte glycoprotein is related to their ability to fix complement. Am J Pathol 1993; 143: 555–64.[Abstract]
Prineas JW. The neuropathology of multiple sclerosis. [Review]. In: Vinken PJ, Bruyn GW, Klawans HL, editors. Handbook of clinical neurology, Vol. 47. Amsterdam: Elsevier Science; 1985. p. 213–57.
Prineas JW, McDonald WI. Demyelinating diseases. [Review]. In: Graham DI, Lantos PL, editors. Greenfield's neuropathology. 6th ed. London: Arnold; 1997. p. 813–96.
Prineas JW, Kwon EE, Goldenberg PZ, Ilyas AA, Quarles RH, Benjamins JA, et al. Multiple sclerosis: oligodendrocyte proliferation and differentiation in fresh lesions. Lab Invest 1989; 61: 489–503.[Web of Science][Medline]
Prineas JW, Barnard RO, Revesz T, Kwon EE, Sharer L, Cho ES. Multiple sclerosis. Pathology of recurrent lesions. Brain 1993a; 116: 681–93.
Prineas JW, Barnard RO, Kwon EE, Sharer LR, Cho ES. Multiple sclerosis: remyelination of nascent lesions. Ann Neurol 1993b; 33: 137–51.[Web of Science][Medline]
Raff MC, Mirsky R, Fields KL, Lisak RP, Dorfman SH, Silberberg DH, et al. Galactocerebroside is a specific cell-surface antigenic marker for oligodendrocytes in culture. Nature 1978; 274: 813–6.[Medline]
Raff MC, Miller RH, Noble M. A glial progenitor cell that develops in vitro into an astrocyte or an oligodendrocyte depending on culture medium. Nature 1983; 303: 390–6.[Medline]
Raine CS. The Norton Lecture: a review of the oligodendrocyte in the multiple sclerosis lesion. [Review]. J Neuroimmunol 1997; 77: 135–52.[Web of Science][Medline]
Raine CS, Wu E. Multiple sclerosis: remyelination in acute lesions. J Neuropathol Exp Neurol 1993; 52: 199–204.[Web of Science][Medline]
Raine CS, Scheinberg L, Waltz JM. Multiple sclerosis: oligodendrocyte survival and proliferation in an active established lesion. Lab Invest 1981; 45: 534–46.[Web of Science][Medline]
Ranscht B, Clapshaw PA, Price J, Noble M, Seifert W. Development of oligodendrocytes and Schwann cells studied with a monoclonal antibody against galactocerebroside. Proc Natl Acad Sci USA 1982; 79: 2709–13.
Reynolds R, Wilkin GP. Development of macroglial cells in rat cerebellum. II. An in situ immunohistochemical study of oligodendroglial lineage from precursor to mature myelinating cell. Development 1988; 102: 409–25.[Abstract]
Schönrock LM, Kuhlmann T, Adler S, Bitsch A, Brück W. Identification of glial cell proliferation in early multiple sclerosis lesions. Neuropathol Appl Neurobiol 1998; 24: 320–30.[Web of Science][Medline]
Scolding NJ, Rayner PJ, Sussman J, Shaw C, Compston DS. A proliferative adult human oligodendrocyte progenitor. Neuroreport 1995; 6: 441–5.[Web of Science][Medline]
Scolding N, Franklin R, Stevens S, Heldin C-H, Compston A, Newcombe J. Oligodendrocyte progenitors are present in the normal adult human CNS and in the lesions of multiple sclerosis. Brain 1998; 121: 2221–8.
Shi J, Marinovich A, Barres BA. Purification and characterization of adult oligodendrocyte precursor cells from the rat optic nerve. J Neurosci 1998; 18: 4627–36.
Sommer I, Schachner M. Monoclonal antibodies (O1 to O4) to oligodendrocyte cells surfaces: an immunocytological study in the central nervous system. Dev Biol 1981; 83: 311–27.[Web of Science][Medline]
Trapp BD, Peterson J, Ransohoff RM, Rudick R, Mörk S, Bö L. Axonal transection in the lesions of multiple sclerosis. N Engl J Med 1998; 338: 278–85.
Warrington AE, Pfeiffer SE. Proliferation and differentiation of O4+ oligodendrocytes in postnatal rat cerebellum: analysis in unfixed tissue slices using anti-glycolipid antibodies. J Neurosci Res 1992; 33: 338–53.[Web of Science][Medline]
Wolswijk G. Strongly GD3+ cells in the developing and adult rat cerebellum belong to the microglial lineage rather than to the oligodendrocyte lineage. Glia 1995; 13: 13–26.[Web of Science][Medline]
Wolswijk G. Oligodendrocyte regeneration in the adult rodent CNS and the failure of this process in multiple sclerosis. [Review]. Prog Brain Res 1998a; 117: 233–47.[Web of Science][Medline]
Wolswijk G. Chronic stage multiple sclerosis lesions contain a relatively quiescent population of oligodendrocyte precursor cells. J Neurosci 1998b; 18: 601–9.
Wolswijk G, Noble M. Identification of an adult-specific glial progenitor cell. Development 1989; 105: 387–400.[Abstract]
Wolswijk G, Noble M. Cooperation between PDGF and FGF converts slowly dividing O-2Aadult progenitor cells to rapidly dividing cells with characteristics of O-2Aperinatal progenitor cells. J Cell Biol 1992; 118: 889–900.
Wolswijk G, Riddle PN, Noble M. Platelet-derived growth factor is mitogenic for O-2Aadult progenitor cells. Glia 1991; 4: 495–503.[Web of Science][Medline]
Wood PM, Bunge RP. The origin of remyelinating cells in the adult central nervous system: the role of the mature oligodendrocyte. [Review]. Glia 1991; 4: 225–32.[Web of Science][Medline]
Wu E, Raine CS. Multiple sclerosis: interactions between oligodendrocytes and hypertrophic astrocytes and their occurrence in other, nondemyelinating conditions. Lab Invest 1992; 67: 88–99.[Web of Science][Medline]
Received March 24, 1999. Revised June 16, 1999. Second revision on July 30, 1999. Accepted July 30, 1999.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  T. Kuhlmann, V. Miron, Q. Cuo, C. Wegner, J. Antel, and W. Bruck Differentiation block of oligodendroglial progenitor cells as a cause for remyelination failure in chronic multiple sclerosis Brain, July 1, 2008; 131(7): 1749 - 1758. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. S. Paintlia, M. K. Paintlia, A. K. Singh, and I. Singh Inhibition of Rho Family Functions by Lovastatin Promotes Myelin Repair in Ameliorating Experimental Autoimmune Encephalomyelitis Mol. Pharmacol., May 1, 2008; 73(5): 1381 - 1393. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Patrikios, C. Stadelmann, A. Kutzelnigg, H. Rauschka, M. Schmidbauer, H. Laursen, P. S. Sorensen, W. Bruck, C. Lucchinetti, and H. Lassmann Remyelination is extensive in a subset of multiple sclerosis patients Brain, December 1, 2006; 129(12): 3165 - 3172. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Wegner, M. M. Esiri, S. A. Chance, J. Palace, and P. M. Matthews Neocortical neuronal, synaptic, and glial loss in multiple sclerosis. Neurology, September 26, 2006; 67(6): 960 - 967. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Sohn, J. Natale, L.-J. Chew, S. Belachew, Y. Cheng, A. Aguirre, J. Lytle, B. Nait-Oumesmar, C. Kerninon, M. Kanai-Azuma, et al. Identification of Sox17 as a transcription factor that regulates oligodendrocyte development. J. Neurosci., September 20, 2006; 26(38): 9722 - 9735. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. M. Frohman, M. K. Racke, and C. S. Raine Multiple sclerosis--the plaque and its pathogenesis. N. Engl. J. Med., March 2, 2006; 354(9): 942 - 955. [Full Text] [PDF]
|
|
|
|
 |
|
 C. Beeton and K. G. Chandy Potassium Channels, Memory T Cells, and Multiple Sclerosis Neuroscientist, December 1, 2005; 11(6): 550 - 562. [Abstract] [PDF]
|
|
|
|
 |
|
 T. Niculescu, S. Weerth, F. Niculescu, C. Cudrici, V. Rus, C. S. Raine, M. L. Shin, and H. Rus Effects of Complement C5 on Apoptosis in Experimental Autoimmune Encephalomyelitis J. Immunol., May 1, 2004; 172(9): 5702 - 5706. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Imitola, E. Y. Snyder, and S. J. Khoury Genetic programs and responses of neural stem/progenitor cells during demyelination: potential insights into repair mechanisms in multiple sclerosis Physiol Genomics, August 15, 2003; 14(3): 171 - 197. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F. Barkhof, W. Bruck, C. J. A. De Groot, E. Bergers, S. Hulshof, J. Geurts, C. H. Polman, and P. van der Valk Remyelinated Lesions in Multiple Sclerosis: Magnetic Resonance Image Appearance Arch Neurol, August 1, 2003; 60(8): 1073 - 1081. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Wolswijk and R. Balesar Changes in the expression and localization of the paranodal protein Caspr on axons in chronic multiple sclerosis Brain, July 1, 2003; 126(7): 1638 - 1649. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D M Chari and W F Blakemore New insights into remyelination failure in multiple sclerosis: implications for glial cell transplantation Multiple Sclerosis, August 1, 2002; 8(4): 271 - 277. [Abstract] [PDF]
|
|
|
|
|
|
M A Moscarello, B Mak, T A Nguyen, D D Wood, F Mastronardi, and S K Ludwin Paclitaxel (Taxol) attenuates clinical disease in a spontaneously demyelinating transgenic mouse and induces remyelination Multiple Sclerosis, April 1, 2002; 8(2): 130 - 138. [Abstract] [PDF]
|
|
|
|
 |
|
 L. Calza, M. Fernandez, A. Giuliani, L. Aloe, and L. Giardino Thyroid hormone activates oligodendrocyte precursors and increases a myelin-forming protein and NGF content in the spinal cord during experimental allergic encephalomyelitis PNAS, February 20, 2002; (2002) 52704499. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Wolswijk Oligodendrocyte precursor cells in the demyelinated multiple sclerosis spinal cord Brain, February 1, 2002; 125(2): 338 - 349. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Chang, W. W. Tourtellotte, R. Rudick, and B. D. Trapp Premyelinating Oligodendrocytes in Chronic Lesions of Multiple Sclerosis N. Engl. J. Med., January 17, 2002; 346(3): 165 - 173. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. Mader, U. Seeger, R. Weissert, U. Klose, T. Naegele, A. Melms, and W. Grodd Proton MR spectroscopy with metabolite-nulling reveals elevated macromolecules in acute multiple sclerosis Brain, May 1, 2001; 124(5): 953 - 961. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. Calza, M. Fernandez, A. Giuliani, L. Aloe, and L. Giardino Thyroid hormone activates oligodendrocyte precursors and increases a myelin-forming protein and NGF content in the spinal cord during experimental allergic encephalomyelitis PNAS, March 5, 2002; 99(5): 3258 - 3263. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||