Chondroitin Sulphate Proteoglycans and Microglia Prevent Migration and Integration of Grafted Müller Stem Cells Into Degenerating Retina

¹ Institute of Ophthalmology and Moorfields Eye Hospital, London, EC1V 9EL, UK
² Centre for Brain repair, University of Cambridge, UK
³ Department of Ophthalmology, Lund University, Sweden

^* To whom correspondence should be addressed. E-mail: g.limb{at}ucl.ac.uk.

	Abstract

At present there are severe limitations to the successful migration and integration of stem cells transplanted into the degenerated retina to restore visual function. This study investigated the potential role of chondroitin sulphate proteoglycans (CSPGs) and microglia in the migration of human Müller glia with neural stem cell characteristics following subretinal injection into the Lister hooded (LH) and Royal College of Surgeons (RCS) rat retinae. Neonate LH rat retina showed minimal baseline microglial accumulation (CD68 positive cells) which increased significantly 2 weeks after transplantation (p<0.001), particularly in the ganglion cell (GCL) and inner plexiform (IPL) layers. In contrast, non-transplanted 5 week old RCS rat retina showed considerable baseline microglial accumulation in the outer nuclear layer (ONL) and photoreceptor outer segment debris zone (DZ) which further increased (p< 0.05) throughout the retina 2 weeks after transplantation. Marked deposition of the N-terminal fragment of CSPGs, as well as neurocan and versican was observed in the DZ of 5 week old RCS rat retinae which contrasted with the limited expression of these proteins in the GCL of the adult and neonate LH rat retinae. Staining for CSPGs and CD68 revealed co-localization of these two molecules in cells infiltrating the ONL and DZ of the degenerating RCS rat retina. Enhanced immune suppression with oral prednisolone and intraperitoneal injections of indomethacin caused a reduction in the number of microglia, but did not facilitate Müller stem cell migration. However, injection of cells with Chondroitinase ABC (ChABC) combined with enhanced immune suppression caused a dramatic increase in the migration of Müller stem cells into all the retinal cell layers. These observations suggest that both microglia and CSPG constitute a barrier for stem cell migration following transplantation into experimental models of retinal degeneration, and that control of matrix deposition and the innate microglial response to neural retina degeneration may need to be addressed when translating cell based therapies to treat human retinal disease.