A comparison of epithelial and neural properties in progenitor cells derived from the adult human ciliary body and brain

Cells isolated from the ciliary body (CB) of the adult human eye possess properties of retinal stem/progenitor cells and can be propagated as spheres in culture. As these cells are isolated from a non-neural epithelium which has neuroepithelial origin, they may have both epithelial and neural lineages. Since it is the properties of neural progenitor cells that are sought after in a future scenario of autotransplantation, we wanted to directly compare human CB spheres with neurospheres derived from the human subventricular zone (SVZ), which is the best characterized neural stem cell niche in the CNS of adults. The CB epithelium was dissected from donor eyes (n = 8). Biopsies from the ventricular wall were harvested during neurosurgery due to epilepsy (n = 7). CB and SVZ tissue were also isolated from Brown Norwegian rats. Dissociated single cells were cultivated in a sphere-promoting medium and passaged every 10–30 days. Fixed spheres were studied by immunohistochemistry, quantitative RT-PCR and scanning/transmission electron microscopy. We found that both CB and SVZ spheres contained a mixed population of cells embedded in extracellular matrix. CB spheres, in contrast to SVZ neurospheres, contained pigmented cells with epithelial morphology that stained for cytokeratins (3/12 +  19), were connected through desmosomes and tight-junctions and produced PEDF. Markers of neural progenitors (nestin, Sox-2, GFAP) were significantly lower expressed in human CB compared to SVZ spheres, and nestin positive cells in the CB spheres also contained pigment. There was higher expression of EGF and TGF-β receptors in human CB spheres, and a comparative greater activation of the canonical Wnt pathway. These results indicate that adult human CB spheres contain progenitor cells with epithelial properties and limited expression of neural progenitor markers compared to CNS neurospheres. Further studies mapping the regulation between epithelial and neural properties in the adult human CB spheres are vital to fully utilize them as a clinical source of retinal progenitor cells in the future.