JournalofNeuroscienceResearch69:466–476(2002) DifferentialLineageRestrictionofRat RetinalProgenitorCellsinVitroandinVivo PengYang,1 MagdaleneJ.Seiler,1,2* RobertB.Aramant,1,2 and ScottR.Whittemore2–4 1DepartmentofOphthalmologyandVisualSciences,UniversityofLouisville,Louisville,Kentucky 2DepartmentofAnatomicalSciencesandNeurobiology,UniversityofLouisville,Louisville,Kentucky 3DepartmentofNeurologicalSurgery,UniversityofLouisville,Louisville,Kentucky 4KentuckySpinalCordInjuryResearchCenter,UniversityofLouisville,Louisville,Kentucky Toidentifyandcharacterizethelineagepotentialofrat horizontal,bipolar,amacrine,andganglioncells;andMu¨l- neuralretinaprogenitorcells(NRPCs)invitroanden- lerglialcellsandastrocytes.Retinalneuronaldifferentia- graftedintoratswithretinaldegeneration,NRPCswere tionoccursinlateembryonicdevelopmentandearly isolatedfromneuralretinasofembryonicday17Long postnatallifeintherat(Cepkoetal.,1996).Similarlyto Evansratsandculturedinserum-freeorserum- neuronsinotherCNSandPNSlocations,retinalneurons containingmediawithfibroblastgrowthfactor2and retainnointrinsiccapabilityofself-regenerationinre- neurotrophin3.Afterexpansion,cellulardifferentiation sponsetoinheritedoracquireddamage.Therefore,ex- wasinitiatedbythewithdrawalofthesegrowthfactors. trinsiccellsandtissueswithvaryingdegreesofdifferenti- Despiteformingprimaryneurospheres,NRPCscultured ation,suchasretinalpieces(TurnerandBlair,1986), inserum-freemediumsurvivedpoorlyafterpassage.In photoreceptorcells(SilvermanandHughes,1989;Kaplan contrast,NRPCsculturedinserum-containingmedium etal.,1997),andtissuesheets(SeilerandAramant,1998; couldbeexpandedforupto12passagesanddifferen- tiatedintoglialfibrillaryacidicprotein-positiveglialcells Aramantetal.,1999;Wochetal.,2001),introduced andretina-specificneuronsexpressingrhodopsin, throughsurgicaltransplantationarethenecessarysources S-antigen,calbindin,recoverin,andcalretinin.Forinvivo forreplacingdamagedretinalneurons. analysis,passage1(P1)undifferentiatedNRPCswere Anotherapproachtoreplacingdegeneratedneurons labeledwithbromodeoxyuridine(BrdU),implantedinto istouseneuralstemandprogenitorcells,whichare thesubretinalspaceofRoyalCollegeofSurgeons(RCS) intrinsictothehippocampus(AltmanandDas,1965; rats,andanalyzedimmunohistochemically4weeks KaplanandHinds,1977;Bayeretal.,1982;Kuhnetal., postgrafting.ThegraftedNRPCsshowedextensiveglial 1996),subventricularzone(Lewis,1968;Reynoldsand differentiation,irrespectiveoftheirtopographiclocaliza- Weiss,1992;LoisandAlvarez-Buylla,1993;Morsheadet tion.AfewBrdU-labeledgraftedNRPCsexpressedpro- al.,1994),spinalcord(Weissetal.,1996;Kalyanietal., teinkinaseC,amarkerforbipolarandamacrine 1997),retinalpigmentedciliarymargin(Ahmadetal., interneuron-specificdifferentiation.Otherretina-specific 2000;Tropepeetal.,2000),andneuralretina(Ahmadet oroligodendrocyticdifferentiationwasnotdetectedin al.,1999)oftheCNS.CNSneuralstemandprogenitor thegraftedcells.AlthoughNRPCsarecapableofself- cellsareundifferentiated,expressingtheneuralprecursor renewalandmultilineagedifferentiationinvitro,theyde- intermediatefilamentnestin(HockfieldandMcKay,1985; velopedmostlyintoglialcellsfollowingengraftmentinto CattaneoandMcKay,1990).Afterdifferentiationinvitro theadultretina.Thesedatasuggestthattheadultretina orinvivo,neuralstemandprogenitorcellscandevelop retainsepigeneticsignalsthatareeitherrestrictivefor alongneuronal,astrocytic,andoligodendrocyticpathways neuronaldifferentiationorinstructiveforglialdifferentia- (WhittemoreandSnyder,1996;McKay,1997;Gage, tion.Inductionoflineage-specificcelldifferentiationof 2000).Moreover,stemcellscantransdifferentiatewhen engraftedNRPCstofacilitateretinalrepairwilllikelyre- graftedtoectopicsites(Bjornsonetal.,1999;Clarkeetal., quireinitiationofspecificdifferentiationinvitropriorto 2000). graftingand/ormodificationofthehostenvironmentcon- comitantlywithNRPCgrafting.©2002Wiley-Liss,Inc. *Correspondenceto:MagdaleneJ.Seiler,PhD,DepartmentofOphthal- Keywords:retinalprogenitorcell;photoreceptor;bipo- mologyandVisualSciences,UniversityofLouisvilleSchoolofMedicine, larcell;transplantation 301EastMuhammadAliBoulevard,Louisville,KY40202. E-mail:[email protected] Received9January2002;Revised30April2002;Accepted7May2002 Themammalianneuralretinaiscomposedofsix Publishedonline27June2002inWileyInterScience(www. classesofdistinctneurons:coneandrodphotoreceptors; interscience.wiley.com).DOI:10.1002/jnr.10320 ©2002Wiley-Liss,Inc. Retinal Progenitor Cell Differentiation In Vitro and In Vivo 467 Differentiation of in vitro expanded neural stem and and efficiency with which the sphere-forming cells retained the progenitor cells into cells expressing retinal cell pheno- ability to form secondary (P1) spheres, the numbers of P0 and P1 types either has not been investigated or has been found spheres at day 6 after plating were counted. only in cells isolated from the eye (Ahmad et al., 1999; For the adherent cultures, the media included 1% fetal Tropepe et al., 2000; Yang et al., 2002), suggesting that bovine serum (FBS; Invitrogen) in addition to the components there are intrinsic and/or extrinsic limitations affecting in the serum-free medium. In pilot studies (data not shown), retinal cell differential fate. The present data show that rat many different variations of serum-free medium were tried. neural retina progenitor cells (NRPCs) develop into ret- However, the cells did not grow well and could not be passaged. inal neurons in vitro, expressing the retinal cell-specific Therefore, 1% FBS was included in all experiments described in antigens rhodopsin and S-antigen, whereas the undiffer- this paper. In addition, FGF-2 was tested in combination with entiated NRPCs transplanted into the subretinal space of platelet-derived growth factor (PDGF; 10 ng/ml; Caldwell et rats with retinal degeneration did not show corresponding al., 2001). No difference in cell proliferation and cell phenotypes differentiation. Engrafted NRPCs adopted mostly a glial after differentiation was observed (data not shown). Therefore, fate and occasionally a bipolar/amacrine cell phenotype. PDGF was not included in the experiments in this study. Half the culture medium was changed every 2 days and FGF-2 added MATERIALS AND METHODS every other day. Cells grew to 70–80% confluence in 7–14 days NRPC Isolation and were harvested with a cell lifter (Fisher Scientific, Fair Lawn, NJ). P1 and later passages of cells were plated at the same ϭ Embryonic day (E) 17 fetuses (n 17) were harvested density as the P0 cells in the PO/FN-coated dishes. from timed-pregnant, outbred Long Evans rats (Harlan Sprague For immunocytochemical identification of dividing cells Dawley, Indianapolis, IN). All animals were treated according to from proliferating cultures, 10 ␮M bromodeoxyuridine (BrdU; the Guidelines for the Use of Animals in Neuroscience Research and Sigma, St. Louis, MO) was added either overnight or 5 days the National Institutes of Health Guide for the Care and Use of immediately before the day when induction of differentiation Laboratory Animals, with the approval of the University of Lou- began or termination of the cultures. The cells used for trans- isville Institutional Animal Care and Use Committee. The fetal plantation were expanded in expansion cultures and pulsed with eyes were collected in Hank’s balanced salt solution (HBSS; 10 ␮M BrdU for 5 days immediately before the day of trans- Invitrogen, Carlsbad, CA) and transferred to fresh HBSS in a plantation. Before each transplantation experiment, the percent- 35-mm petri dish on ice. Neural retinas were separated free of ages of nestin-positive (undifferentiated) and GFAP-positive vitreous, lens, retinal pigmented epithelium (RPE), and cornea. (differentiated) immunophenotypes of the cells to be used were Special care was taken to exclude the optic disk and the ciliary examined to ensure that the cells were mostly undifferentiated. margin by cutting off a circular 1.5-mm zone from the center of the optic nerve and the margin of the ciliary bodies. Neural In Vitro Differentiation retinas were digested in 0.05% trypsin (Invitrogen) in artificial Expanded cells were harvested and replated on PO/FN- cerebral spinal fluid [ACSF; 124 mM NaCl, 5 mM KCl, coated 12-well dishes (Costar Corning Inc, Corning, NY) at a 5 2 1.3 mM MgCl2, 2 mM CaCl2, 26 mM NaHCO3, and 10 mM density of 10 cells/cm . Cells were induced to differentiate by D-glucose, pH 7.35, aerated with 95% O2/5% CO2 (Reynolds replacing the FGF-2 and NT3 with 10% FBS for 5–21 days, and Weiss, 1992)] for 10 min at room temperature and triturated with one or two medium changes. No attempt was made to gently with a fire-polished, siliconized Pasteur glass pipette to differentiate the cells under serum-free conditions. To test the release single cells. The cell suspension was centrifuged at 150g effect of Matrigel on the cells, cells were grown on Matrigel- for 5 min, and the resulting pellets were resuspended in fresh coated dishes (growth factor-reduced and laminin- and collagen culture medium. Cell viability was evaluated with trypan blue, IV-based Matrigel matrix; 1:20; Becton Dickinson Labware, and the cell concentration was adjusted for plating. Bedford, MA). After differentiation, no difference in phenotypes was observed in P1 and P2 cells (data not shown). Expansion and Passage Isolated cells were cultured at 5 ϫ 104 cells/cm2 under Transplantation two conditions: as a cell suspension in uncoated flasks (Ahmad et Five inbred albino Royal College of Surgeons (RCS) rats al., 1999) or as a monolayer on dishes precoated with 10 ␮g/ml