title: Pigment epithelial cells isolated from human peripheral iridectomies have limited properties of retinal stem cells.
abstract: OBJECTIVE
  The identification of cells with properties of retinal progenitor cells (RPCs) in the adult human ciliary margin (CM) prompted a number of studies of their proliferative and differentiation potential. One of the remaining challenges is to find a feasible method of isolating RPCs from the patient's eye. In the human CM, only the iris pigment epithelium (IPE) is easily obtained by a minimally invasive procedure. In the light of recent studies questioning the existence of RPCs in the adult mammalian CM, we wanted to assess the potential of the adult human IPE as source of RPCs.
  
  
  METHODS
  The IPE were isolated from peripheral iridectomies during glaucoma surgery, and IPE and ciliary body (CB) epithelium were also isolated from post-mortem tissue. Cells were cultivated in sphere-promoting conditions or as monolayers. Whole-tissue samples, undifferentiated and differentiated cells were studied by immunocytochemistry, RT-PCR and transmission electron microscopy.
  
  
  RESULTS
  The adult human IPE, like the CB, expressed markers of RPCs such as Pax6, Sox2 and Nestin in vivo. Both sphere-promoting and monolayer cultures preserved this phenotype. However, both IPE/CB cultures expressed markers of differentiated epithelial cells such as Claudin, microphtalmia-associated transcription factor (MITF) and Cytokeratin-19. Ultrastructurally, IPE spheres displayed epithelial-like junctions and contained mature melanosomes. After induced differentiation, IPE-derived cells showed only partial neuronal differentiation expressing β-III-tubulin, Map-2 and Rhodopsin, whereas no mature glial markers were found.
  
  
  CONCLUSIONS
  Proliferative cells with some properties of RPCs can be isolated from the adult human IPE by peripheral iridectomies. Yet, many cells retain properties of differentiated epithelial cells and lack central properties of somatic stem cells.
authors.affiliation: Department of Ophthalmology, Oslo University Hospital, Center for Eye Research, University of Oslo, Oslo, Norway.
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Frøen
authors.forename: Erik O
authors.initials: EO
authors.lastname: Johnsen
authors.forename: Goran
authors.initials: G
authors.lastname: Petrovski
authors.forename: Erika
authors.initials: E
authors.lastname: Berényi
authors.forename: Andrea
authors.initials: A
authors.lastname: Facskó
authors.forename: András
authors.initials: A
authors.lastname: Berta
authors.forename: Bjørn
authors.initials: B
authors.lastname: Nicolaissen
authors.forename: Morten C
authors.initials: MC
authors.lastname: Moe
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000378:metabolism; D049109:Cell Proliferation; D002469:Cell Separation; D002478:Cells, Cultured; D002924:Ciliary Body / Q000166:cytology / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D019084:Fluorescent Antibody Technique, Indirect; D005901:Glaucoma / Q000601:surgery; D006801:Humans; D032801:Iridectomy; D007498:Iris / Q000166:cytology* / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D008875:Middle Aged; D010857:Pigment Epithelium of Eye / Q000166:cytology* / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000166:cytology* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013234:Stem Cells / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D015415:Biomarkers; D017931:DNA Primers