Myelin-mediated inhibition of oligodendrocyte precursor differentiation can be overcome by pharmacological modulation of Fyn-RhoA and protein kinase C signalling

Failure of oligodendrocyte precursor cell (OPC) differentiation contributes significantly to failed myelin sheath regeneration (remyelination) in chronic demyelinating diseases. Although the reasons for this failure are not completely understood, several lines of evidence point to factors present following demyelination that specifically inhibit differentiation of cells capable of generating remyelinating oligodendrocytes. We have previously demonstrated that myelin debris generated by demyelination inhibits remyelination by inhibiting OPC differentiation and that the inhibitory effects are associated with myelin proteins. In the present study, we narrow down the spectrum of potential protein candidates by proteomic analysis of inhibitory protein fractions prepared by CM and HighQ column chromatography followed by BN/SDS/SDS–PAGE gel separation using Nano-HPLC-ESI-Q-TOF mass spectrometry. We show that the inhibitory effects on OPC differentiation mediated by myelin are regulated by Fyn-RhoA-ROCK signalling as well as by modulation of protein kinase C (PKC) signalling. We demonstrate that pharmacological or siRNA-mediated inhibition of RhoA-ROCK-II and/or PKC signalling can induce OPC differentiation in the presence of myelin. Our results, which provide a mechanistic link between myelin, a mediator of OPC differentiation inhibition associated with demyelinating pathologies and specific signalling pathways amenable to pharmacological manipulation, are therefore of significant potential value for future strategies aimed at enhancing CNS remyelination

ABCC1: a gateway for pharmacological compounds to the ischaemic brain

By preventing access of drugs to the CNS, the blood-brain barrier hampers developments in brain pharmacotherapy. Strong efforts are currently being made to identify drugs that accumulate more efficaciously in ischaemic brain tissue. We identified an ATP-binding cassette (ABC) transporter, ABCC1, which is expressed on the abluminal surface of the brain capillary endothelium and mildly downregulated in response to focal cerebral ischaemia, induced by intraluminal middle cerebral artery occlusion. In biodistribution studies we show that ABCC1 promotes the accumulation of known neuroprotective and neurotoxic compounds in the ischaemic and non-ischaemic brain, ABCC1 deactivation reducing tissue concentrations by up to two orders of magnitude. As such, ABCC1's expression and functionality in the brain differs from the liver, spleen and testis, where ABCC1 is strongly expressed on parenchymal cells, resulting -- in case of liver and testis -- in directed transport from the tissue into the blood. After focal cerebral ischaemia, ABCC1 deactivation abolished the efficacy of both neuroprotective and neurotoxic compounds. Our data indicate that ABCC1 acts as gateway for pharmacological compounds to the stroke brain. We suggest that the tailoring of compounds binding to abluminal but not luminal ABC transporters may facilitate stroke pharmacotherapy