Deimination of arginyl residue of myelin basic protein (MBP) reduces cationicity of MBP and impedes the normal myelin membrane assembly. Less ordered structure of MBP is more susceptible to proteolytic attack that may lead to the release of highly immunogenic deiminated peptides into extracellular milieu. We have studied the association of peptides 45-89 derived from citrullinated MBP (C8 isomer) and phosphorylated MBP (C3 isomer) with the myelin lipids in a model membrane system using optical waveguide lightmode spectrometry. The analysis of association/dissociation kinetics to planar lipids under controlled hydrodynamic conditions has shown that MBP 45-89 peptide from citrullinated C8 isomer is less effectively adsorbed on the lipid membrane, than peptide from phosphorylated C3 isomer and packing densities for phosphorylated 45-89 MBP peptide is higher than for citrullinated forms. On the other hand, our results shown that continuous (24 h) exposure of mixed oligodendrocyte/microglial cells to peptides 45-89 from MBP-C8 induces apoptosis via mitochondrial pathway. In addition, peptides 45-89 stimulated the secretion of nitric oxide from microglial cells via induction of iNOS and decreased the level of the inhibitory protein IkB, indicating involvement of the transcription factor NF-kB in these processes. Our results suggest that some citrullinated peptides, initially released from oligodendrocytes, might activate microglia, which produces reactive nitrogen species and generates in turn fatal feedbacks that kill oligodendrocytes.

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Several peptide fragments of myelin basic protein (MBP) are formed in a brain during demyelinating diseases, which together with proinflammatory cytokines can influence proliferation and damage of glial cells. We studied the action of C8-isoform of MBP and its tryptic peptide fragments on viability (MTT-test) and on production of nitric oxide in rat primary glial cells. Two preparations of MBP hydrolizate were used: with-(Preparation 1) and without of encephalitogenic peptide 45-89 (Preparation 2), which was added in culture medium in a final concetration of 20 μg/ml. It was found that C8 isoform and Preparation 2 reduce viability of primary astrocytes and mixed oligodendrocyte/microglia cells, whereas Preparation 1 induces proliferation of astrocytes. After the treatment of primary culture with C8 isoform of MBP and Preparation 2 the production of nitric oxide was markedly increased in rat primary astrocytes, but decreased in oligodendrocyte/microglia cells. Addition of Preparation 1 into tissue culture medium had no effect on production of nitric oxide in both type of cells. It is supposed, that encephalitogenic fragment of MBP-C8 (45-89) has different effect on a glial cells viability and proliferation, compared with MBP-C8 and another MBP-fragments. As Preparation 1 does not change production of nitric oxide against the background of a stimulated proliferation, reduced viability of primary astrocytes under the action of C8 isoform and MBP-fragments (without 45-89) is caused by induction of nitric oxide synthase followed by increased level of nitric oxide. It is suggested that different intracellular mechanisms are responsible for actions of MBP fragments.from Infectious diseases of the nervous system: pathogenesis and worldwide impact Paris,