Oligodendrocyte progenitor cells (OPCs) can repair demyelinated lesions by maturing into myelin-producing oligodendrocytes. prevented Notch activation in demyelinated lesions and accelerated remyelination. These findings reveal that ET-1 is a negative regulator of OPC differentiation and remyelination and is potentially a novel therapeutic target to promote lesion repair in demyelinated tissue. INTRODUCTION Current multiple sclerosis (MS) therapies can be effective in patients with relapsing and remitting MS but have little impact in promoting remyelination in tissue leading to permanently demyelinated lesions with substantial axonal loss (Buck and Hemmer 2011 Compston and Coles 2008 Repair of demyelinated MS plaques is carried out by endogenous oligodendrocyte progenitor cells (OPCs) in a process called remyelination (Ffrench-Constant and Raff 1986 However several studies have shown that OPCs often fail to differentiate in chronic MS lesions (Chang et al. 2002 Wolswijk 1998 The molecular mechanisms that prevent OPC maturation and OL regeneration under pathological conditions are largely unknown. OPCs migrate to demyelinated lesions proliferate and eventually differentiate into mature OLs to produce myelin (Franklin and Ffrench-Constant 2008 This transition from a progenitor cell to a myelinating OL can be negatively regulated by signals which are present in the pathological lesion environment. This is created in part by a dense network of reactive astrocytes (RAs) (Compston and Coles 2008 McKhann 1982 It is still poorly understood how RAs impact OPC development and whether signals released or expressed by astrocytes limit remyelination (Moore et al. 2010 Nair et al. 2008 Interestingly recent studies have identified the Notch activator Jagged1 as a signal expressed by RAs in MS tissue that might limit OPC differentiation and remyelination (John et al. 2002 Stidworthy et al. 2004 Zhang et al. 2009 However it is still unknown how Jagged1 expression or Notch activation is regulated in demyelinated lesions and whether these pathways are beneficial or detrimental to the overall remyelination process. In a previous study we identified endothelin-1 (ET-1) as a signaling molecule synthesized in the corpus callosum (CC) following demyelinating injury (Gadea et al. 2008 ET-1 is a secreted signaling peptide which has systemic roles as a vasomodulator in the cardiovascular system (Rubanyi and Botelho 1991 Interestingly RAs produce ET-1 following various brain injuries and we found that this peptide promotes reactive astrogliosis in demyelinated tissue (Gadea et al. 2008 Jiang et al. 1993 Despite the abundance of ET-1 following injury and its essential role in inducing reactive astrogliosis the role or mechanistic action of ET-1 during remyelination have not been defined. Here we use the well-established lysolecithin model of focal demyelination to recapitulate some aspects of the focal lesions that are found in MS tissue. Specifically this model allows us to investigate the time course and cell-specificity of ET-1 signaling and how it regulates remyelination efficiency Using both genetic and pharmacological approaches we are the first to demonstrate the mechanistic action of ET-1 during remyelination. We show that astrocyte-derived ET-1 inhibits OPC differentiation and remyelination through activation of Notch signaling and that this effect can be reversed by a clinically used ET-R Benzoylpaeoniflorin pan-antagonist. Our results present a new therapeutic candidate to promote repair in demyelinated lesions where OPC differentiation is stalled Rabbit Polyclonal to MRPL12. or limited. RESULTS ET-1 is Benzoylpaeoniflorin expressed by reactive astrocytes in MS and murine demyelinated lesions We have previously demonstrated that the neuropeptide ET-1 is upregulated in the CC following lysolecithin (LPC)-induced focal demyelination and that overall ET-1 levels peak at 5 days post lesion (dpl) (Gadea et al. 2008 While we found ET-1 co-expression in GFAP+ cells in the SVZ during development (Gadea et al. 2009 expression of ET-1 in astrocytes in LPC lesions had not been analyzed. Of the three endothelin isoforms only ET-1 mRNA was found in the micro-dissected tissue from the CC and cingulum in either saline- or LPC-injected Benzoylpaeoniflorin tissue (Fig 1a b). Further ET-1 Benzoylpaeoniflorin expression analysis revealed that ET-1 was specifically upregulated in GFAP+ astrocytes within LPC lesions (Fig 1d e). The total number of ET-1+GFAP+ cells peaked between 3 and 7dpl and gradually decreased.