Maintenance de la myéline périphérique : physiologie et physiopathologie

Abstract : The synthesis of the myelin sheath by Schwann cells in the peripheral nervous system is under the control of several transcription factors including Egr2, which was shown to be also involved in the maintenance of peripheral myelin. We set up a new method to study the involvement of various genes in peripheral myelin maintenance, using small interfering RNAs (siRNAs) to silence target genes in vitro and in vivo. We used modified self-delivery siRNAs to silence candidate genes without using transfection reagents. These siRNAs were first used on organotypic co-cultures of dorsal root ganglia from embryonic rat and then injected into the sciatic nerves of adult rats. We showed that control non-targeting siRNAs did not induce significant demyelination either in co-cultures or in vivo, after direct injection in sciatic nerves. We then showed that anti-Egr2 siRNAs down-regulated in vitro their target gene expression by ~60%. In addition, treatment with anti-Egr2 siRNAs resulted in abnormalities of the myelin sheaths in co-cultures. The injection of anti-Egr2 siRNAs in the sciatic nerves of adult rats induced a significant and rapid demyelination, as shown by the loss of Myelin Protein Zero expression in the injected area on immunohistochemistry experiments (optic microscopy) and by direct evidence of demyelination on epon-embedded transversal sections of sciatic nerves (optic and electron microscopy). These results confirm previous data involving Egr2 in active myelin maintenance, which were obtained using conditional knockout experiments in mice. Injections of anti-Dicer siRNAs similarly induced sciatic nerve demyelination, establishing that Dicer expression in adult peripheral nerves is necessary for proper myelin maintenance. Our results constitute a proof of concept for the use of self-delivery siRNAs to investigate the molecular mechanisms of myelin maintenance in vivo and also to induce a gene-driven demyelination “on demand” in peripheral nerves.
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Adama Ouedraogo. Maintenance de la myéline périphérique : physiologie et physiopathologie. Physiologie [q-bio.TO]. Université de Limoges, 2014. Français. ⟨NNT : 2014LIMO0043⟩. ⟨tel-01166028⟩

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