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The role of small RNAs in remyelination

Final Report Summary - SRNAS REMYELINATION (The role of small RNAs in remyelination)

Demyelination is the pathological process in which myelin sheaths are lost from around axons resulting in impairment of impulse conduction. In humans, one of the most common demyelinating diseases is multiple sclerosis (MS), an auto-immune disease targeting oligodendrocytes and the myelin sheaths that they make and maintain. Demyelinating diseases like MS involve a phase of partial recovery with remyelination, but this phenomenon is incomplete and eventually fails accompanied by axonal damage. Thus, understanding the detailed molecular mechanisms that control myelination and remyelination, the central topic of this application, is of paramount importance.

Oligodendrocytes precursors (OPC), resident in the adult CNS, are responsible for remyelination after experimental demyelinating lesions. An important event in remyelination that occurs soon after demyelination is activation of OPC. This process involves the switching on of specific sets of genes associated with oligodendrocyte differentiation, which is highly regulated spatially and temporally by a balance of the activity of transcriptional activators and repressors, but also post-transcriptionally by small RNAs including miRNAs. miRNAs are small endogenous RNA-duplex transcripts that play primordial roles in the regulation of gene expression.

In this project, we are studying the role of small RNAs, in particular of miRNAs, in myelination and remyelination following demyelination in the adult CNS. We are also exploring the role of miRNAs and other epigenetic regulators in neurodegeneration and neuroprotection. We have bred successfully the transgenic mice that we need for the project. Those mice are used to conditionally delete DGCR8 or Dicer in oligodendrocytes progenitors or in adult neurons. We have conducted preliminary demyelination studies, in which we will analyse the importance of miRNAs during the remyelination process. Furthermore, we studied important pathways that are influenced by specific miRNAs like the mammalian target of rapamycin (mTOR) and we are following up on this discovery. In parallel, neuroprotection experiments have revealed the importance of DGCR8 for proper maintenance of the adult CNS neuronal network. We found that neuron-specific depletion of DGCR8 in adult mice causes a progressive Parkinsonism-like neuropathology. We detected a likely loss of dopaminergic neurons in the substantia nigra, paralleled by the loss of neurons in the motor cortex. Furthermore, neuron-specific DGCR8-depleted mutant mice exhibited abnormal myelin deposits and severe axonal degeneration in the white matter of the spinal cord. The mutant mice showed resting tremors, bradykinesia and tail rigidity as well as a tendency to loose neuromuscular junctions. Thus, excision of DGCR8 in the adult central nervous system is a potential method to produce a Parkinsonism-like model. We are currently carrying out further experiments to extend the analysis to alternative pathways in this context including epigenetic regulation of neuroprotection.