Déficit oligodendrocytaire et insuffisance de la remyélinisation au cours de la SEP : étude anatomoclinique et expérimentale comparative

INTRODUCTION

The mechanisms responsible for the failure of remyelination during MS are poorly understood. We have analyzed in which way oligodendrocytes (OL) could be involved.

METHODS

The number of remyelinated fiber per OL has been determined in 18 chronic MS lesions and compared to normal appearing white matter (NAWM), as well as in the center of lysophosphatidyl choline (LPC)-induced lesions in adult rats in which remyelination was accelerated by microinjection of neurotrophin-3 (NT-3).

RESULTS

In chronic MS lesions and in LPC-induced lesions the number of myelinated fibers per OL was strongly decreased compared to NAWM and to animals treated with NT-3 respectively.

CONCLUSION

Our results suggest that the capacity of OL to remyelinate axons could be impaired, due to successive relapses, during MS.

Modifications des neurofilaments et des microtubules axonaux en fonction du mécanisme lésionnel : étude pathologique et expérimentale

INTRODUCTION

The consequences of axonal or demyelinating injuries on the axonal cytoskeleton have rarely been described.

METHODS

We have compared the density of fibers labeled by anti-neurofilaments (NF) and -beta tubulin (TUB) to the density of total fibers in nine patients with axonal neuropathies of undetermined etiology (AUE), six with necrotizing angeitis with neuropathy (NAN), seven with chronic inflammatory demyelinating neuropathy (CIDP) and in five controls, as well as in six patients with chronic multiple sclerosis (MS). We also studied demyelinated rat corpus callosum after lysophosphatidyl (LPC) microinjection.

RESULTS

In AUE and NAN NF positive fibers decreased together with total fiber density, whereas TUB increased. In demyelinating lesions TUB was not altered (CIDP) or strongly decreased (MS, LPC); NF were strongly reduced in MS (where axon loss was prominent) and in LPC lesions (despite the lack of fiber degeneration) and for fiber densities<3900/mm2 in CIDP.

CONCLUSION

The initial mechanism of a disease, either axonal degeneration or demyelination, could result into a specific pattern of axonal cytoskeleton alterations.

[Necrotizing vasculitis of the peripheral nervous system: comparison of the axon cytoskeleton abnormalities with other types of neuropathies]

Morphometric and immunocytochemical data obtained from nerve biopsies in six patients with necrotizing angiopathic neuropathy were compared with the data obtained in five control patients without neurologic disease. The density of myelinated fibers were greatly decreased in all patients (more than 55 p.cent), and reached 70 p.cent in four patients. The g myelination ratio was elevated in one patient, indicating demyelination. The number of fibers immunolabeled for the neurofilament (NF) light chain (L) was also decreased from 31 to 96 p.cent. Labeling for medium (M) and heavy (H) NF subunits was less affected. On the contrary, the number of fibers expressing beta-tubulin (TUB) increased by 38 to 141 p.cent and the ratio of the number of fibers expressing TUB and NFL (TUB/NFL) was increased 3 to 33-fold (p<0.05). We have previously reported similar, though less pronounced, anomalies in axonopathies of unknown cause. These results suggest that diverse etiologies may lead to the same type of lesions of the axon cytoskeleton.

[Isolated angiitis of the central nervous system. Report of two cases and review of the literature]

Isolated angiitis of the central nervous system is a rare disease affecting mainly adults of both sex; about 210 cases have been reported. Contrary to other inflammatory arteritis, arthralgia, myalgia, weight loss and fever are exceptional and symptoms are mainly neurologic, but none is specific. The diagnosis is evoked in case of headaches and cognitive impairment, associated or not with multifocal neurologic signs. Evolution is acute, subacute or chronic. Elevated sedimentation rate and cerebrospinal fluid pleiocytosis are present in 2/3 of cases. CT scan and brain MRI generally demonstrate multifocal ischemic lesions involving cortex, white matter, basal ganglia and brainstem. Cerebral arteriography is the key investigation, showing segmental stenoses alternating with fusiform dilatations of blood vessels, which are highly suggestive but not specific. It can be normal and its repetition is then recommended. Certain diagnosis is obtained from cerebromeningeal biopsy, showing a segmental angiitis of small vessels, which is granulomatous in 88 p.100 and non granulomatous in 12 p.100 of cases. The pathogenesis is unknown. Spontaneous evolution is generally fatal. Cyclophosphamide associated with prednisone considerably improves the prognosis, especially when initiated early in the course of the disease.

[Chronic inflammatory polyradiculoneuritis and the axonal cytoskeleton: morphometric and immunocytochemical data]

We report morphometric and immunocytochemical data obtained from nervous biopsy in 7 patients with chronic inflammatory demyelinating neuropathy (CIDP), compared to 5 controls (without neurological involvement). Fiber loss was present in all cases and reached 50 p. 100 or more in 4 cases. The g myelination ratio was elevated in 3 cases only, indicating demyelination. The number of fibers labelled for the L subunit of neurofilaments was normal in cases with moderate fiber loss and dropped down for densities < 3900/mm2 (4 cases). Labelling with anti-GAP43 antibody was considerably increased in 3 cases, but did not correlate with fiber density or disease duration. These data confirm the importance of axonal lesions in CIDP and offer the opportunity to discuss their pathophysiological mechanisms.

A single intracerebral microinjection of platelet-derived growth factor (PDGF) accelerates the rate of remyelination in vivo

We had demonstrated that platelet-derived growth factor (PDGF) enhanced the reconstruction of myelin-like membranes after their disruption by lysophosphatidylcholine (LPC) in vitro. To investigate its role in vivo, a demyelinating lesion of the corpus callosum was induced in adult Wistar rats by a stereotaxic microinjection of 1 microl LPC, then 63 pairs of rats received either 1 microg PDGF, or its vehicle buffer which were injected above LPC. The effects of PDGF were significant after 2 weeks: the number of oligodendrocytes (OL) expressing 2',3'-cyclic nucleotide 3'-phosphodiesterase in the lesion increased by 49%, mature OL labelled by in situ hybridization for myelin basic protein-mRNA increased by 27% (P<10(-2)), and the total volume of demyelination decreased by 60% compared to controls. The proliferation of cells of the OL lineage was also enhanced up to 67% by PDGF compared to LPC controls (P<2.5 x 10(-2)). Ultrastructural studies confirmed this dramatic improvement, and the ratio of remyelinated to demyelinated axons, determined at the maximal demyelination site, in the centre of the lesion, increased by 10-fold (P<2.5 x 10(-3)) in animals treated with PDGF. Remyelination was complete after 3 months for both treatments. Neither exacerbation of gliosis nor glial tumoural transformation were observed. Mechanisms through which PDGF improves remyelination could involve proliferation of OL progenitors, and/or of already differentiated surviving OLs, and a chemotactic effect, which had been identified in vitro.

[Unusual complication of rendu-osler-weber disease: paramedian bulbar syndrome]

We report a case of arteriovenous malformation of the brainstem, revealed by a progressive right pyramidal syndrome and an atrophy of the left hemi-tongue in a man presenting a Rendu-Osler-Weber disease. After embolization the clinical course was stationary.

Glutamine synthetase expression and activity are regulated by 3,5,3'-triodo-L-thyronine and hydrocortisone in rat oligodendrocyte cultures

Glutamine synthetase plays a central role in the detoxification of brain ammonia. Previously, we demonstrated that in vitro glutamine synthetase is expressed by all macroglial cell types and is developmentally regulated in oligodendrocyte lineage. Furthermore, glutamine synthetase is increased in secondary cultures of oligodendrocytes following a 72 h treatment with 30 nM 3,5,3'-triodo-L-thyronine [Baas, D., Bourbeau, D., Sarliève, L. L., Ittel, M. E., Dussault, J. H. and Puymirat, J., Oligodendrocyte maturation and progenitor cell proliferation are independently regulated by thyroid hormone. Glia, 1997, 19, 324-332]. Hydrocortisone also increases glutamine synthetase activity after 72 h [Fressinaud, C., Weinrauder, H., Delaunoy, J. P., Tholey, G., Labourdette, G. and Sarliève, L. L., Glutamine synthetase expression in rat oligodendrocytes in culture: regulation by hormones and growth factors. J. Cell. Physiol., 1991, 149, 459-468]; however, it is still unknown whether these increases in glutamine synthetase expression in oligodendrocytes after 3,5,3'-triodo-L-thyronine and hydrocortisone application are dose- and time-dependent. To further investigate this issue, we measured glutamine synthetase levels by Northern analysis, immunostaining and determination of glutamine synthetase activity after 3,5,3'-triodo-L-thyronine or hydrocortisone stimulation. We find that in rat oligodendrocyte secondary cultures, 3,5,3'-triodo-L-thyronine and hydrocortisone cause a dose- and time-dependent increase in glutamine synthetase mRNA, protein and activity. However, these hormones do not exert an additive or synergistic effect. Because purines, pyrimidines, and certain amino acids necessary for the synthesis of myelin components, are, in part, provided by the glutamine synthetase pathway, 3,5,3'-triodo-L-thyronine effect on myelination development and maturation could be mediated in part, through the glutamine synthetase gene regulation.

Oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells express glutamine synthetase: developmental and cell type-specific regulation

Glutamine synthetase (GS), the enzyme that catalyses glutamine synthesis from glutamate and ammonia, plays a central role in the detoxification of brain ammonia. In the central nervous system (CNS), GS also subserves additional important functions such as regulating glutamate, GABA and amino acid metabolism. Oligodendrocytes (OL) form the myelin sheath in the central nervous system (CNS) and are essential for efficient propagation of nerve impulses. In culture, OL arise from bipotential O-2A progenitor cells. These O-2A cells give rise to type-2 astrocytes in the presence of serum. GS is expressed in mature glial cells in vivo and in vitro, but it is unknown whether GS is present in glial progenitors. In addition, a comparison of the GS expression level among the various types of glial cells has never been done in vitro. The current study investigates in vitro GS expression levels in O-2A progenitors, astrocytes and OL. We demonstrate that the GS gene is expressed in O-2A progenitors and is expressed at different levels in each cultured glial cell type. GS also is stimulated during OL developmental maturation. Thus, the GS gene is expressed in O-2A cells and is regulated in a developmental and macroglial cell type-specific manner.

Platelet-derived growth factor partly prevents chemically induced oligodendrocyte death and improves myelin-like membranes repair in vitro

We have previously shown that pure oligodendrocyte (OL) secondary cultures derived from newborn rat brain, in which cells form myelin-like membranes, can be used as a model to investigate the putative role of growth factors in myelin repair. After disruption of these membranes by lysophosphatidylcholine (LPC), a 3 day treatment with 10 ng/ml basic fibroblast growth factor (bFGF) induced reconstruction of myelin figures, albeit less compacted than in untreated controls. Here we show that in LPC treated cultures: 1) bFGF can not prevent OL from LPC-induced cell death; 2) platelet-derived growth factor (PDGF) pretreatment although preventing some cell death does not improve recovery compared to delayed treatment; 3) PDGF is as potent as bFGF in terms of O-2A progenitor proliferation; 4) PDGF is far more effective than bFGF, inducing the reappearance of more myelin-like structures with a better compaction; 5) there is no potentiation between these growth factors; and 6) after withdrawal of bFGF the compaction of myelin figures partly increases. These results indicate that PDGF, probably by inducing O-2A progenitors to proliferate and then allowing them to differentiate into mature myelinating OL, is a better candidate than bFGF to participate in myelin repair mechanisms in the central nervous system.

Basic fibroblast growth factor down-regulates myelin basic protein gene expression and alters myelin compaction of mature oligodendrocytes in vitro

The effects of basic fibroblast growth factor (bFGF) on myelin basic protein (MBP) gene expression and myelin-like membrane formation were investigated in oligodendrocyte cultures containing mainly mature oligodendrocytes expressing MBP. These cultures were obtained by selective detachment of the cells of the oligodendrocyte lineage from 40-day-old mixed cultures derived from newborn rat brain. They were further purified by a 3-day pretreatment with cytosine arabinoside (ARA-C) in order to kill cycling cells. After withdrawal of ARA-C, daily treatment of the cells with bFGF for 3 days induced a drastic decrease in MBP mRNA level compared to control cultures treated only with ARA-C. Moreover, the percentage of oligodendrocytes labelled with anti-MBP antibodies decreased by 50%, as well as that of oligodendrocytes expressing myelin oligodendrocyte glycoprotein (MOG), whereas proteolipid protein (PLP) immunolabelled cells were less affected. At the ultrastructural level, myelin-like membranes were still abundant in the ARA-C- and bFGF-treated cultures, but they were conspicuously uncompacted compared to cultures only pretreated with ARA-C. These results bring the first evidence that bFGF is able to down-regulate myelin protein gene expression in mature oligodendrocytes and to alter myelin structure. They imply that if bFGF is secreted after a demyelinating lesion of the central nervous system (CNS), this plasticity of mature oligodendrocytes will allow final remyelination of axons to complete only after this factor has returned to low levels.

Expression of thyroid hormone receptor isoforms in rat oligodendrocyte cultures. Effect of 3,5,3'-triiodo-L-thyronine

3,5,3'-Triiodo-L-thyronine (T3) acts at the genomic level by interacting with nuclear T3 receptors (T3Rs). We have used double immunostaining to follow the expression of T3Rs and oligodendrocytes (OL) lineage markers in rat secondary cultures consisting of 85-90% OL. Using antibodies against different synthetic peptides of T3Rs (alpha common: alpha 1 + alpha 2 and beta 1) we find that alpha-T3R is expressed in both O-2A progenitors and in mature OL, while beta 1-T3R is expressed only in mature OL. In cultured OL, beta 1-T3R mRNA is upregulated the most by T3. OL exhibit more numerous and longer processes when treated by T3.

Basic fibroblast growth factor improves recovery after chemically induced breakdown of myelin-like membranes in pure oligodendrocyte cultures

The putative role of growth factors in remyelination was investigated in pure oligodendrocyte (OL) secondary cultures derived from newborn rat brain. These cells form myelin-like membranes and were used as a model system for toxic attack. A 24 hr treatment with 2.10(-5) M lysophosphatidylcholine (LPC) induced a loss of 59% of the cells in these cultures, with a 64% reduction in [125I]-iododeoxyuridine incorporation compared to untreated controls. An absence of processes and myelin-like sheaths was observed in the remaining cells. Numerous intracytoplasmic inclusions were observed on transmission electron microscopy. Immunocytochemical studies with A2B5 monoclonal antibody (mAb), which recognizes oligodendrocyte-type 2 astrocyte (O-2A) precursors, OL-1 mAb (directed against cell surface sulfatides), and anti-myelin basic protein (anti-MBP) antibody showed that the entire OL lineage was affected at all stages of maturation. A 3 day treatment with 10 ng/ml basic fibroblast growth factor (bFGF) induced reconstruction of myelin-like membranes, albeit less compacted than in untreated controls. The doubling in number of cells and the 46% increase in [125I]-iododeoxyuridine incorporation was due essentially to proliferation of O-2A progenitors. These results indicate that if bFGF release occurs during demyelination, it may participate in myelin repair mechanisms in the central nervous system.

The proliferation of mature oligodendrocytes in vitro is stimulated by basic fibroblast growth factor and inhibited by oligodendrocyte-type 2 astrocyte precursors

Basic fibroblast growth factor (bFGF) and platelet-derived growth factor (PDGF) are mitogens for bipotential oligodendrocyte-type 2 astrocyte (O-2A) progenitor cells. We investigated the mitogenic effect of these growth factors on quiescent mature oligodendrocytes (OL) expressing myelin basic protein (MBP) in OL cultures that were treated for 3 days with cytosine arabinoside (ARA-C) in order to kill O-2A precursors which divide in chemically defined medium. After treatment with ARA-C proliferation decreased and O-2A precursors identified with A2B5 monoclonal antibody were nearly undetectable. After exposure of mature OL to bFGF, cell proliferation increased markedly within 24 hr. PDGF had a much weaker effect. Cultures treated with ARA-C for 3 days and then with bFGF for the next 24 hr and incubated with BrdU for the last 2 hr before the end of the experiment were immunolabeled with anti-MBP or A2B5 and anti-bromodeoxyuridine (BrdU) antibodies. Eighty-seven percent of the cells were MBP+, 10% were both MBP+ and BrdU+, and none was A2B5+ BrdU+, showing that at least a part of the population of mature MBP+ OL retains the ability to reenter the cell cycle in vitro. Since mature OL did not proliferate in response to bFGF in the cultures not treated with ARA-C, i.e., in the presence of O-2A progenitors, we assumed that these precursors were responsible for the lack of mitogenic effect of bFGF on MBP+ OL in such conditions. Conditioned medium from O-2A precursors almost halved the bFGF-induced OL proliferation after treatment with ARA-C, suggesting that O-2A progenitors control the proliferation of a subpopulation of mature OL (possibly young mature OL) via the secretion of active molecule(s).

Adult-onset metachromatic leukodystrophy presenting as isolated peripheral neuropathy

A 38-year-old man presented with weakness of the lower limbs. Electrophysiology revealed a pronounced demyelinating neuropathy. Nerve biopsy disclosed de- and remyelinating lesions and characteristic lamellar inclusions in Schwann cells and macrophages. There was no familial history of neurologic disorder, and impairment of motor evoked potentials was the only sign of CNS involvement. Arylsulfatase A and cerebroside sulfate sulfatase activities in leukocytes and cultures of the patient's fibroblasts were low. The sulfatide loading test also revealed abnormal sulfatide accumulation. This may be the first reported case of adult metachromatic leukodystrophy presenting as peripheral neuropathy.

Differential regulation of cerebroside sulfotransferase and 2',3'-cyclic nucleotide 3'-phosphodiesterase by basic fibroblast growth factor in relation to proliferation in rat oligodendrocyte cultures

Previous results (Fressinaud, C., Sarliève, L.L., and Labourdette, G. J. J. Cell. Physiol., 141:667-674, 1989b) have shown that cerebroside sulfotransferase (CST; EC 2.8.2.11) is enriched in pure rat oligodendrocyte (OL) cultures and that its activity is increased by factors mitogenic for OL precursors and galactocerebroside (GC) expressing OL, such as basic fibroblast growth factor (bFGF), platelet-derived growth factor, and high insulin concentrations. In contrast, transforming growth factor beta or low insulin concentrations were found to be ineffective in this culture system. As bFGF mainly enhanced the proliferation of OL precursors (GC negative cells) rather than that of differentiated (GC+) cells, a relationship between OL precursor proliferation and CST increase was suggested. This hypothesis was first tested in 20-day-old OL cultures grown in chemically defined medium. The dose-response curve of [125I] Iododeoxyuridine ([125I]dUrd) incorporation toward bFGF was parallel to that of CST specific activity, and maximal stimulation was reached at 5 ng/ml bFGF for both. In contrast, 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP; EC 3.1.4.37) specific activity decreased after bFGF treatment. To determine if CST increase was linked to the proliferation of OL precursors induced by bFGF, cell proliferation was blocked by cytosine arabinoside (ARA-C). From 10(-8) to 10(-5) M ARA-C there was a dose-dependent inhibition of cell proliferation and a decrease in CST specific activity, whereas CNP specific activity was enhanced. When the cells were treated with bFGF and 10(-6) M ARA-C together, the proliferation was completely blocked and CST activity decreased by 72% below control values, whereas CNP activity was not significantly decreased. Immunocytochemical studies showed that the number of sulfatide-expressing cells and the number of cycling cells were increased after bFGF treatment, but that there was no overlapping between these two populations. Taken together these results suggest that CST activity and sulfatide expression appear shortly after the arrest of OL precursor division.

Glutamine synthetase expression in rat oligodendrocytes in culture: regulation by hormones and growth factors

Glutamine synthetase (GS, EC 6.3.1.2.) has long been considered as a protein specific for astrocytes in the brain, but recently GS immunoreactivity has been reported in oligodendrocytes both in mixed primary glial cell cultures and in vivo. We have investigated its expression and regulation in "pure" oligodendrocyte cultures. "Pure" oligodendrocyte secondary cultures were derived from newborn rat brain primary cultures enriched in oligodendrocytes as described by Besnard et al. (1987) and were grown in chemically defined medium. These cultures contain more than 90% galactocerebroside-positive oligodendrocytes and produce "myelin" membranes (Fressinaud et al., 1990) after 6-10 days in subcultures (30-35 days, total time in culture). The presence of GS in oligodendrocytes from both primary glial cell cultures and "pure" oligodendrocyte cultures was confirmed by double immunostaining with a rabbit antisheep GS and guinea pig antirat brain myelin 2', 3'-cyclic nucleotide 3'-phosphodiesterase. In "pure" oligodendrocyte cultures, about half of cells were labeled with anti-GS antibody. Furthermore, on the immunoblot performed with a rabbit antisheep GS, the GS protein in "pure" oligodendrocyte secondary cultures was visualized as a single band with an apparent molecular mass of about 43 kDa. In contrast, two protein bands for GS were observed in cultured astrocytes. On the immunoblot performed with a rabbit antichick GS, two immunopositive protein bands were observed: a major one migrating as the purified adult chick brain GS and a minor one with a lower molecular mass. Two similar immunoreactive bands were also observed in pure rat astrocyte cultures. Compared to pure rat astrocyte cultures, "pure" oligodendrocyte cultures of the same age displayed an unexpectedly high GS specific activity that could not be explained by astrocytic contamination of the cultures (less than 5%). As for cultured astrocytes, treatment of oligodendrocyte cultures with dibutyryl-adenosine 3':5'-cyclic monophosphate, triiodothyronine, or hydrocortisone increased significantly GS specific activity. Interestingly, epidermal growth factor, basic fibroblast growth factor, and platelet-derived growth factor that increase the GS activity in astrocytes do not affect this activity in oligodendrocytes. Thus we confirm the finding of Warringa et al. (1988) that GS is also expressed in oligodendrocytes. We show that its activity is regulated similarly in astrocytes and oligodendrocytes by hormones, but that it is regulated differently by growth factors in these two cell types.

Homocystinuria due to 5,10-methylenetetrahydrofolate reductase deficiency revealed by stroke in adult siblings

Three patients from a single family of six siblings had homocystinemia and homocystinuria due to 5,10-methylenetetrahydrofolate reductase deficiency and had severe recurrent strokes in adult life. Two of the patients died 1 year after clinical onset.

[Multiple sclerosis: review of main experimental data and pathogenic hypotheses]

The pathogenesis of multiple sclerosis (MS) is considered from three different viewpoints: genetic, viral and immunological. A genetic predisposition intervenes, as testified by the familial forms of MS and by the frequency of HLA A3B7 and DR2 groups in MS patients. The hypothesis of an inherited enzyme deficiency in oligodendrocytes is discussed. Many viruses are known to induce demyelination in animals, and the intrathecal production of antibodies to measles virus as well as the in vitro discovery of DNA transcripts of this virus in patients are suggestive of a viral factor. Experimental allergic encephalomyelitis (EAE) and chronic EAE have made it possible to study the immune and other mechanisms which might be involved in MS. While the myelin basic protein and the M2 antigen appear to be the first antigen targets, the demyelinating agents in this model are antibodies to galactocerebroside. The factors responsible for demyelination in MS have not yet been elucidated, but the antibodies present in the cerebrospinal fluid do not seem to be demyelinating in vitro. Descriptions of the cells which constitute the lesions and of the antigen markers they express suggest that endothelial cells and astrocytes (possibly presenting antigens to lymphocytes) might play a part in the genesis of the lesions. Experiments concerning the modulation and suppression of EAE allow new therapeutic approaches to be envisaged.

Normal composition of the major lipids and the distribution of their fatty acids in central nervous system myelin further discriminate mld from shiverer mice

The primary defect in myelin deficiency (mld), an autosomal recessive mutation in mice with severe hypomyelination of the central nervous system (CNS), is a reduction in the synthesis of myelin basic protein (MBP) due to reduced amounts of MBP-specific mRNA. The present study was performed to determine whether alterations of myelin lipid composition might be associated with this defect. Although a 20-fold reduction of myelin was found in mld brain, the lipid/protein and the phospholipid/sulfatide ratios of purified myelin were unchanged. The analysis of polar lipids demonstrated no striking difference. However, phosphatidylethanolamine (including plasmalogens of the ethanolamine type) was decreased by 7.7% in mld. Fatty acids of total and polar lipids (phospholipids + glycolipids) exhibited a slight decrease in 20:1(n-11) and 20:1(n-9). In conclusion, these results further differentiate mld from its allele shiverer, which shares with mld a dramatic reduction of MBP and absence of major dense line but, in contrast, presents other important biochemical differences in CNS myelin.

Comparison of the mechanisms of action of insulin and triiodothyronine on the synthesis of cerebroside sulfotransferase in cultures of cells dissociated from brains of embryonic mice

The effect of low (physiological) concentrations of insulin (2 and 20 ng/ml) and L-triiodothyronine (T3) were studied on two myelin-related enzymes: (1) the 3'-phosphoadenosine-5'-phosphosulfate:cerebroside sulfotransferase (CST, EC 2.8.2.11) catalyzing the production of sulfatide, and (2) the myelin enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP, EC 3.1.4.3.7) in myelinogenic cultures of cells dissociated from embryonic mouse brain. Insulin treatment (20 ng/ml) of the cells in the presence of serum increased CST activity at 18 and 25 days in vitro (DIV) by 86 and 211%, respectively. At 18 DIV and under the same conditions, CNP was significantly stimulated (95%) by high doses of insulin (2,000 ng/ml) only, while arylsulfatase A (EC 3.1.6.1) or cerebroside sulfatase activities, both of which are involved in sulfatide degradation, were unchanged. Thus, it can be assumed that the observed increase of the incorporation of [35S]O4 into sulfatide after insulin treatment of mixed cell cultures is the result of CST induction rather than a decreased catabolism. The level of CST activity in insulin-treated cells (20 ng/ml) in serum-free medium was also increased at 18 and 25 DIV by about 50 and 70%, respectively. Conversely, none of the insulin concentrations used in the absence of serum (even at high doses) had any effect, either at 18 or 25 DIV on CNP and ASA activities. The involvement of insulin in the regulation of sulfatide synthesis was further confirmed by dose-response curves relating the activity of CST to hormone concentration in the medium. The increase in the activity of CST in insulin-treated cells was due only to the increase in the Vmax of this enzyme, suggesting that it may be attributed to enzyme induction. A study of kinetic parameters of CST indicated that there were no differences in pH optimum and Km values between control and induced enzyme. Further experiments using cycloheximide point to a direct effect of insulin on oligodendrocyte CST induction. Data similar to those described above for insulin were also obtained with T3. As for insulin, T3 stimulated the induction of CST but in serum-free medium only. This effect was prevented by cycloheximide. In addition, the induction of CST by T3 was blocked by actinomycin D. This was not the case for insulin. These results suggest that T3 and insulin act on CST by different mechanisms, i.e. at transcriptional and post-translational levels, respectively. Apart from this, the insulin effect on CST activity was additive to that of T3.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of cerebroside sulfotransferase activity in cultured oligodendrocytes: effect of growth factors and insulin

Cerebroside sulfotransferase (EC 2.8.2.11, CST) specific activity has been determined in oligodendrocyte (OL)-enriched glial cell cultures from newborn rat brain grown in serum supplemented medium. This activity is detectable at 5 days in vitro (DIV) and reaches its maximum value at 12 DIV. This period corresponds to that of oligodendrocyte precursor proliferation in these cultures. The activity decreases thereafter and remains nearly constant after 24 DIV. The developmental curve of CST activity is parallel in pure oligodendrocyte subcultures but twice higher than in primary cultures. These data confirm that CST is highly enriched in OL. Basic fibroblast growth factor (bFGF) (15 ng/ml) and platelet derived growth factor (PDGF) (0.75 U/ml) both enhance CST activity by 90% and 72%, respectively. This increase is in the same range than that of DNA content in treated cultures, whereas protein increase is smaller (50% and 22%, respectively). In contrast, transforming growth factor beta 1 (TGF beta 1, 0.5 and 5 ng/ml) does not significantly enhance CST activity nor DNA content of OL cultures. Insulin at high concentrations (5 micrograms/ml) also enhances CST activity but has no effect at physiological concentrations (20 ng/ml). These results show that CST activity can be controlled by growth factors. They suggest that CST activity is more closely related to OL and OL precursor proliferation than to myelination itself since its maximal activity preceeds myelination in vitro.

[Autoimmune hypoglycemia: the fault of pyritinol?]

Initially reported in Japan, autoimmune hypoglycemia is related to the presence of insulin-binding antibodies, even in patients who have never been treated with insulin. The authors report a case of spontaneous autoimmune hypoglycemia in a French woman receiving pyritinol. The difference between insulin and C peptide radioimmunoassay levels prompted a search for insulin antibodies. In vitro studies confirmed their presence and showed that they were immunoglobulins G with two binding sites without species specificity. The outcome of autoimmune hypoglycemia is usually favourable, with a rapid decrease of insulin antibodies but steroid therapy is needed when serious clinical manifestations are present. The differential diagnosis with factitious hypoglycemia may be difficult. The reasons for the appearance of the insulin antibodies and the exact mechanisms of hypoglycemia remain hypothetical. However, drugs with a sulfhydril group, such as pyritinol, could play a causative role in this syndrome.

[Developmental adrenal tuberculosis. Value of x-ray computed tomography]

Two cases of Addison's disease secondary to active adrenal tuberculosis are reported. Computed tomography showed hypertrophy of the adrenal gland, which was bilateral in one case and unilateral in the other. Repeat computed tomography scans during antituberculous chemotherapy demonstrated a progressive change of the adrenals toward atrophy and calcification, while the adrenal function remained impaired. The authors recall that adrenal tuberculosis may be unilateral first, then bilateral, and that the gland is initially hypertrophic before hormonal deficiency appears; later on, adrenal atrophy and calcification develop. Computed tomography seems to be useful in the aetiological diagnosis of Addison's disease. Moreover, it helps in determining whether or not antituberculous therapy is indicated, which is not always easy to decide in the absence of "active" focus. The finding, with or without positive tuberculin skin tests, of an adrenal hypertrophy unexplainable by any other pathology (e.g. metastasis, histoplasmosis) should call for antituberculous treatment, especially since it sometimes results in recovery of adrenal function.

Bronchial leiomyoma: report of a case successfully treated by endoscopic neodymium-yttrium aluminum garnet laser

A 40-year-old woman was admitted with dyspnea and episodes of bronchial infection. Leiomyoma of the right lateral basal bronchus was diagnosed and partially removed by a biopsy forceps, and neodymium-yttrium aluminum garnet laser therapy successfully destroyed the rest of this mass.

Cerebellar soluble lectin is responsible for cell adhesion and participates in myelin compaction in cultured rat oligodendrocytes

Cultures of rat oligodendrocytes were used to test the possible role of the cerebellar soluble lectin (CSL) in myelin formation. Immunocytochemistry at the ultrastructural level showed that the lectin is present in the cytoplasm of the perikaryon of cultured oligodendrocytes and also on the plasma membrane of the cell body and processes. It is present in compact myelin and in the zones of contacts between different myelin sheaths or oligodendrocyte membranes. Staining of blots of the cultures with iodinated CSL indicated that endogenous glycoprotein ligands for CSL are present in the culture, rendering probable the hypothesis that cell contacts between different oligodendrocytes or between adjacent lamellae in myelin are mediated by lectin-glycoprotein interactions. This hypothesis was demonstrated by two effects of anti-CSL Fab fragments (4 micrograms/ml) on oligodendrocyte cultures: (1) the almost complete detachment of the cell layer from the culture substratum, and (2) the loss of myelin compaction by a separation of lamellae at the intraperiod line. The present findings could explain the complexity of the contacts between cultured oligodendrocyte processes by the formation of CSL bridges between glycoproteins of the membranes of these cells. CSL seems to be a key molecule in adhesion both for intercellular contacts and fixation of cells to the substratum. The small number of glycoprotein subunits found in oligodendrocytes that interact with CSL suggests that CSL-mediated cell adhesion involves a special class of glycoprotein glycans.

Analysis of unsaturated fatty acids of endoneurium and perineurium from normal and degenerating rat sciatic nerve. Morphological correlations

The major portion of the endoneurial lipids is found in myelin. Since perineurial cells differ morphologically from endoneurial cell components, we attempted to determine whether these morphological differences also extended to a difference in fatty acid (FA) composition. Under normal circumstances, unsaturated FAs are more abundant than saturated ones (55-60% of total FAs) in endoneurium and perineurium. A characteristic biochemical difference between these two structures lies in the distribution of linoleic acid (C18:2(n-6)) which represents 20% of total FAs in perineurium and only 2% in endoneurium. Wallerian degeneration takes place after injection of pure glycerol into the endoneurium. This is followed by regeneration characterized by a proliferation of perineurial cells infiltrating the center of the nerve fascicule forming microcompartments. The changes in linoleic acid content reflect these morphological changes. A marked increase in linoleic acid is detected in the endoneurial fraction in parallel with the observed infiltration of perineurial cells into the nerve fascicule.

Changes in composition of endoneurial and perineurial fatty acids during glycerol-induced Wallerian degeneration and regeneration in the sciatic nerve of the adult rat

Intraneural injection of pure glycerol induces Wallerian degeneration with subsequent regeneration. In agreement with other reports, we observed an increase in endoneurial polyunsaturated fatty acids 8 days after the glycerol injection. Levels then fell until day 30. After a period of 5 months, there was an increase in C18:2(n-6) in the intrafascicular tissue, concomitant with a marked fall in this fatty acid in the remaining extrafascicular perineurium. The rise in C18:2(n-6) in endoneurium correlated with infiltration of this tissue by perineurial cells. Interactions between perineurium and endoneurium during nerve regeneration are discussed.

Acute pure sensory paraneoplastic neuropathy with perivascular endoneurial inflammation: ultrastructural study of capillary walls

We studied a patient with epidermoid carcinoma of the lung (treated surgically 1 year earlier) and an acute symmetric pure sensory neuropathy that regressed almost completely within 1 month. Superficial peroneal nerve biopsy 15 days after onset showed evidence of demyelination with perivascular endoneurial inflammation. On ultrastructural examination, lymphocytes were seen passing through endothelial cells of endoneurial capillaries.

Fatty acid composition of endoneurium and perineurium from adult rat sciatic nerve

Reports on lipid composition of peripheral nervous system have generally been restricted to the saturated fatty acids of the endoneurium. In this work we attempt to determine the fatty acid composition of the different lipid classes in both endo- and perineurium from sciatic nerve microdissection on adult rats. Unsaturated fatty acids were found to make up around 60% of total fatty acids in samples of endoneurium and perineurium, with monounsaturated fatty acids forming 40-50% of total unsaturated fatty acid content. Although the same fatty acids were present in both tissues there was a striking difference in C 18:1 (n-9) and C 18:2 (n-6) ratio between endoneurium and perineurium, which is particularly rich in linoleic acid. The nonpolar perineurial lipids were found to be richest in linoleic acid. Phospholipids were present in the perineurium, and they contained high proportions of saturated and medium-chain monounsaturated fatty acids.