The impact of age on the physical and cellular properties of the human limbal stem cell niche

The limbal niche in the corneoscleral junction of the eye, habitat of the limbal epithelial stem cells (LESC), facilitates corneal epithelial regeneration by providing physical support and chemical signalling. Anatomical structures within the limbus, namely, limbal epithelial crypts and focal stromal projections, are believed to function as a putative niche for LESCs. In this study, the impact of age on the topography of this niche was investigated. Also, the relationship between niche topography and limbal epithelial cell phenotype was assessed. Ex vivo imaging of the limbus in cadaveric tissue of donors aged from infancy to 90 years was carried out using electron and confocal microscopy. The data suggested that the area occupied by the crypts was sharply reduced after the age of 60 years. The niche microstructures also became smoother with donor age. The phenotypic assessment of cultured limbal epithelial cells harvested from donors of different ages showed that the levels of putative stem cell markers as well as telomerase activity and telomere length remained unchanged, regardless of niche topography. However, the colony forming efficiency of the cultures was significantly reduced with age (p < 0.05). This is the first comprehensive study of the effect of age on the structural and phenotypic characteristics of the human limbal niche. The results have a significant biological value as they suggest a correlation of limbal architecture with decline of re-epithelialisation rate in older patients. Overall, the data also suggest that LESCs harvested from younger donors may be more suitable for cultured LESC therapy production.