Bone marrow stromal cells stimulate neurite outgrowth over neural proteoglycans (CSPG), myelin associated glycoprotein and Nogo-A Karina T. Wright a,d , Wagih El Masri b , Aheed Osman b , Sally Roberts a,d , Giselle Chamberlain c,d , Brian A. Ashton c,d , William E.B. Johnson a,d, * a Centre for Spinal Studies, Robert Jones & Agnes Hunt Orthopaedic Hospital, Oswestry, Shropshire SY10 7AG, UK b Midlands Centre for Spinal Injuries, Robert Jones & Agnes Hunt Orthopaedic Hospital, Oswestry, Shropshire SY10 7AG, UK c Leopold Muller Arthritis Research Centre, Robert Jones & Agnes Hunt Orthopaedic Hospital, Oswestry, Shropshire SY10 7AG, UK d Institute for Science and Technology in Medicine, Keele University, Keele, Staffordshire ST5 5BG, UK Received 24 December 2006 Available online 10 January 2007 Abstract In animal models, transplantation of bone marrow stromal cells (MSC) into the spinal cord following injury enhances axonal regen- eration and promotes functional recovery. How these improvements come about is currently unclear. We have examined the interaction of MSC with neurons, using an established in vitro model of nerve growth, in the presence of substrate-bound extracellular molecules that are thought to inhibit axonal regeneration, i.e., neural proteoglycans (CSPG), myelin associated glycoprotein (MAG) and Nogo-A. Each of these molecules repelled neurite outgrowth from dorsal root ganglia (DRG) in a concentration-dependent manner. However, these nerve-inhibitory effects were much reduced in MSC/DRG co-cultures. Video microscopy demonstrated that MSC acted as ‘‘cellular bridges’’ and also ‘‘towed’’ neurites over the nerve-inhibitory substrates. Whereas conditioned medium from MSC cultures stimulated DRG neurite outgrowth over type I collagen, it did not promote outgrowth over CSPG, MAG or Nogo-A. These findings suggest that MSC transplantation may promote axonal regeneration both by stimulating nerve growth via secreted factors and also by reducing the nerve-inhibitory effects of the extracellular molecules present. Ó 2007 Elsevier Inc. All rights reserved. Keywords: Bone marrow stromal cells; Spinal cord injury; Cell transplantation; CSPG; Myelin inhibitors; Neurite outgrowth In recent years, there has been extensive interest in the development of cell transplantation therapies for lesions to the central nervous system (CNS), such as spinal cord injury (SCI). Potential donor cell types include embryonic [1] and adult neural stem or precursor cells [2,3] Schwann cells [4,5] olfactory ensheathing cells [6–8] and bone mar- row-derived cells [9–12]. For clinical transplantation, bone marrow-derived stromal cells (MSC), in particular, repre- sent an attractive cell source as they can be easily and reproducibly isolated from bone marrow aspirates, expand- ed efficiently in culture, and re-introduced into patients as autografts [13]. In animal models of SCI, their transplanta- tion after injury has consistently promoted functional recovery [9,10,12,14,15]. The mechanisms responsible for this improvement, however, are largely unclear. It has been suggested that bone marrow-derived cells may differentiate to form neurons and glial cells and thereby replace neural tissue [16–21], but the evidence for this is somewhat contro- versial [22–25]. Alternatively, MSC are known to synthe- sise growth factors and cytokines that promote neuronal survival and axonal growth [12,15] and that may reduce inflammatory responses and hence cavity formation in the injured spinal cord [14]. Their alignment with regener- ating axons has also been taken as evidence that MSC may act as ‘‘guiding strands’’ for the axons along spinal cord tracts [10]. A major feature of SCI is the inhibition of axonal regeneration by extracellular molecules [26], including neural proteoglycans (CSPG) synthesised by reactive 0006-291X/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2007.01.013 * Corresponding author. Fax: +44 1691 404054. E-mail address: Eustace.Johnson@rjah.nhs.uk (W.E.B. Johnson). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 354 (2007) 559–566