Self-delivery siRNA as a versatile tool to study molecular effectors of myelin maintenance in vivo

Abstract

The myelination in Schwann cells that occurs during the fœtal life is governed by several transcription factors, including Egr2 gene. Unfortunately, mutations affecting this gene result in various human hereditary peripheral neuropathies, such as the Charcot-Marie-Tooth disease. There are few informations on myelin maintenance that is a dynamic process which is under the control of various genes. We have developed a technique to identify genes in peripheral myelin maintenance, using small interfering ribonucleic acids (siRNAs) to induce extinction of target genes in vivo. Modified self-delivery siRNAs were used to induce extinction of candidate genes without using transfection reagents. These siRNAs were injected into the sciatic nerves of adult rats. We showed that control non-targeting siRNAs did not induce significant demyelination after direct injection into sciatic nerves. The injection of anti-Egr2 siRNAs into 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 research findings involving Egr2 in active myelin maintenance. Injections of anti-Dicer siRNAs similarly induced sciatic nerve demyelination, establishing that Dicer expression in adult peripheral nerves is necessary for proper myelin maintenance. This paper also reports on an original method for the use of self-delivery siRNAs to study the molecular mechanisms of myelin maintenance in vivo.