Abstract
Purpose :
Eph-ephrin bidirectional signaling is essential for lens transparency. Our studies in mouse lenses demonstrate that the ephrin-A5 ligand and the EphA2 receptor are needed for normal lens epithelial cells. We determined whether EphA2 and ephrin-A5 are important for lens biomechanical properties and refractive index.
Methods :
We used tissue mechanical testing, scanning electron microscopy (SEM) and interferometric measurements using an X-ray synchrotron beam source to determine the gradient of refractive index (GRIN) to compare mouse lenses with genetic disruption of EphA2 or ephrin-A5.
Results :
Biomechanical testing revealed no change in the stiffness of EphA2(-/-) and ephrin-A5(-/-) lenses compared to littermate controls. However, knockout lenses were more resilient and recovered almost completely after load removal. Morphometric analysis revealed that while there is no change in the overall lens volume, there is a decrease in lens aspect ratio (equatorial/axial diameter) in both knockout lenses. Surprisingly, the EphA2(-/-) lens had a small, soft and disc-shaped lens nucleus different from the control, spherical and hard lens nucleus. SEM images revealed changes in the cell morphology of EphA2(-/-) fiber cells close to the center of the lens. Inner EphA2(-/-) lens fibers had more pronounced tongue-and-groove interdigitations and formed square arrays only in the deepest layers of the lens nucleus. We did not observe nucleus and fiber cell defects in ephrin-A5(-/-) lenses. GRIN measurements demonstrated an overall decrease in refractive index magnitude across EphA2(-/-) lenses, which is most pronounced at the center of the knockout lenses.
Conclusions :
In summary, disruption of Eph-ephrin signaling in the lens leads to changes in resilience and lens shape. Loss of EphA2 disrupts the nuclear compaction resulting in a small and soft lens nucleus. These results suggest that lens nuclear size and stiffness do not contribute significantly to overall mechanical properties of mouse lenses under compression. Little is known about the mechanisms the drive nuclear compaction, and our data suggests that Eph-ephrin signaling may be required for fiber cell membrane reorganization and compaction and for establishing a normal GRIN. This work reveals that Eph-ephrin signaling is not only required for normal lens epithelial cells, but also for fiber cell maturation and compaction, lens shape and resilience.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.