Steroid Receptors as targets for myelin regeneration by endogenous adult neural stem cells

The nerve fibres of the brain and spinal cord (the CNS) are surround by an insulating material called myelin that protects the fibres and allows them to carry electrical impulses very rapidly. Myelin is made by a cell called an oligodendrocyte. This cell is the primary target in several neurological diseases most notably multiple sclerosis (MS). Early in the disease the brains own stem cells are able to replace the lost oligodendrocytes and hence myelin can be restored (a regenerative process called remyelination). However, as the disease progresses and the patient ages remyelination becomes less efficient and the fibres are left without their myelin: in this state they are very vulnerable to irreversible degeneration. Therapies that enhance remyelination will have a major impact on the treatment of MS - however, none currently exist. In this project UK and Chinese laboratories will strengthen an existing collaboration to test the ability of a naturally-derived plant compound called diosgenin, which is already in clinical use, to enhance remyelination in laboratory models of MS and will continue studies to understand the mechanisms of action of diosgenin in remyelination.

In this project the UK and China research groups with complementary expertise in remyelination biology will continue to further explore the remyelination enhancing properties of a plant steroid diosgenin. Using a combination of in vivo (toxin and immune-mediated rodent [transgenic] models of demyelination) and in vitro (primary OPC culture and myelinating co-cultures) approaches we will: 1) test whether diosgenin accelerates remyelination via oestrogen receptors, 2) explore the downstream processes mediating the pro-remyelination effects, and 3) test the affects of diosgenin on experimental autoimmune encephalomyelitis (EAE). The in vivo models we will use are 1) focal injection of lysolecithin into spinal cord white matter of adult mice, using conditional and genomic knockouts of oestrogen receptors and downstream mediating factors identified, 2) focal injection of ethidium bromide into the rat cerebellum peduncle, and 3) EAE, induced in C57BL/6J mice by immunizing with MOG35-55 peptide in complete Freund's adjuvant followed by i.p. injection of pertussis toxin. Animals with be treated with diosgenin at 20mg/kg, or corn oil as control. To compare the effect of knockout and/or treatment, the extent of OPC recruitment, oligodendrocyte differentiation and remyelination will be analysed with controls at 5, 10 and 21 days after lesion induction. In vitro/ex vivo approaches include: 1) primary isolated OPCs to test functions of identified mediating factors of diosgenin with small interference RNA knockdown techniques or lentivirus mediated overexpression (OPC proliferation, viability, differentiation will be examined using specific stage markers of oligodendrocyte lineage), 2) co-culture of OPC with dorsal root ganglion neurons to test the myelinating efficacy of OPCs subjected to various treatments, and 3) cerebellar slice cultures for remyelination studies.

Both the UK and China applicants are engaged in programmes of research that aim to see fundamental aspects of remyelination biology translated into new regenerative therapies that will have substantial impact on the lives of individuals with demyelinating disease. The work described in this application is positioned towards the front end of the pipeline that leads from scientific discovery to clinical implementation, involving laboratory based studied to address pre-clinical questions. If the hypotheses addressed in this application are upheld it will not only lead to a further series of laboratory based studies on the role of sex steroid receptor mediated signalling in CNS remyelination but will also strengthen the case for 1) preliminary clinical trials with diosgenin for remyelination enhancement in MS patients (similar to the one currently been formulated by the Cambridge laboratory in collaboration with clinical colleagues in Cambridge, Edinburgh and UCL using the RXR agonist bexarotene), and 2) diosgenin as a chemical start point for a drug discovery programme towards more effective oestrogen receptor based drugs (for which the MRC Developmental Pathway Funding Scheme and/or Wellcome Trust Seeding Drug Discovery Scheme would provide suitable opportunities for advancing this work towards a clinical outcome). The pathway to impact will benefit from the extensive interactions that the Cambridge group have established with the pharmaceutical industry, which include collaborations and consultative agreements with Amgen, Biogen Idec, Merck-Serono and Aventis and current collaborations with GSK and Medimmune.