Remyelination in the central nervous system

Abstract

Multiple Sclerosis (MS) is an inflammatory disease which causes areas of demyelination in the Central Nervous System (CNS) and affects only humans. Current therapies for MS are focused on anti-inflammatory treatment, which reduce the occurrence and clinical relapses of the disease. However, progressive disability of the disease is related to axonal degeneration. After demyelination, remyelination occurs, which helps repair the demyelinated lesions and protects axons from degeneration. However, this endogenous remyelination is inefficient, and currently there are no therapies available to enhance remyelination. The aim of this thesis was to first characterize a fast and reliable model to study CNS remyelination in vitro, and second to investigate the role of semaphorin 3a (Sema3A) and semaphorin 3f (Sema3F) signaling in CNS remyelination. Various in vivo models have been developed to investigate the pathology of multiple sclerosis, and can be used to test remyelination therapies. However, in vivo models are expensive, animal- and time- consuming. Until now, there has been no well-characterized and robust in vitro model for remyelination study. In this thesis, an ex vivo slice culture system with mouse brain and spinal cord was developed, and characterized by immunofluorescent microscopy and transmission electron microscopy, for CNS remyelination study. Automated (re)myelinating quantification by image pro plus software was developed and validated to provide a fast and reliable way for testing factors that change remyelination efficiency. Two such factors are Sema3A and 3F, which were initially identified as axon guidance cues during development. Sema3A (repulsive) and 3F (attractive) were proved to play a role in oligodendrocyte precursor cell (OPC) migration during development, and hypothesized to be important in remyelination. In this thesis, I investigated the effects and mechanisms for this by adding recombinant SEMA3A or SEMA3F or by knockdown their obligatory receptors Neuropilin (Nrp) 1 and 2, using lentivirus induced miRNAi. Slice culture and primary OPC culture were used to determine the effect on OPC survival, migration, proliferation, differentiation and myelination.