The distinct mechanic properties of the corneal limbus revealed by Brillouin spectro-microscopy regulate the epithelial stem cell phenotype

Brillouin spectro-microscopy was used to measure differences in stiffness across live human corneas at unprecedented resolution. In parallel, epithelial stem cell and differentiation markers were assessed by confocal microscopy across the same tissues. Brillouin analysis revealed significant differences in mean frequency shift between the corneal centre and its outer edge, the limbus (with 6.66±0.04GHz and 6.24±0.09GHz, respectively). Furthermore, marker analysis showed that epithelial stem cells resided on the softer limbus, whereas the stiffer central region of the cornea supported differentiated cells. Moreover, we showed that softening the central cornea to a limbus-like compliance elicited epithelial cells to express stem cell-characteristic markers. Overall, we found a correlation between the mechanical properties of the corneal matrix and the phenotype of corneal epithelial cells. Ultimately, this work demonstrates that Brillouin spectro-microscopy has matured to a level where it can now be extensively applied to several research fields, namely in cell mechanosensing/translation studies, and in Medicine, to better diagnose disease-associated alterations in tissue compliance.