The effects of mechanical strain on mouse eye lens capsule and cellular microstructure

Abstract

The understanding of multiscale load transfer within complex soft tissues is incomplete. The eye lens is ideal for multiscale tissue mechanics studies as its principal function is to fine focus light at different distances onto the retina via mechanical shape changes. The biomechanical function, resiliency, and intricate microstructure of the lens make it an excellent non-connective soft tissue model. We hypothesized that compressive strain applied onto whole lens tissue leads to deformation of specific microstructures and that this deformation is reversible following removal of load. For this examination, mouse lenses were compressed by sequential application of increasing load. Using confocal microscopy and quantitative image analysis, we determined that axial strain ≥10% reduces capsule thickness, expands epithelial cell area, and separates fiber cell tips at the anterior region of the lenses. At the equatorial region, strain ≥6% increases fiber cell widths. The effects of strain on lens epithelial cell area, capsule thickness, and equatorial fiber cell widths are reversible following the release of lenses from strain. However, although fiber cell tip separation following the removal of low loads is reversible, the separation becomes irreversible with application of higher loads. This irreversible separation between fiber cell tips leads to incomplete bulk lens resiliency. The lens is an accessible biomechanical model system that provides new insights on multiscale transfer of loads in soft tissues.

Age-related changes in eye lens biomechanics, morphology, refractive index and transparency

“…The B6-albino mice were a generous gift from Dr. William E. Balch (The Scripps Research Institute).The tdTomato-positive (tdTomato+) mice, used for live imaging, express a tdTomato tandem dimer protein fused in frame to connexin 43 [117] (rendering it an inactive channel). Based on our previous study, tdTomato+ lenses are comparable in shape, size and stiffness to C57BL6/J wild-type lenses [53]. The tdTomato+ mice were maintained with a single copy of the transgene, and tdTomato-negative (tdTomato-) wild-type lenses were also used for experiments.…”

“…This may be due in part to the abnormally large nucleus in 30-month-old lenses that resists compression, similar to increased stiffness and size of the human lens nucleus with age. Our previous data suggests that resilience in mouse lenses depends on the recovery of the anterior Ysuture that opens up under coverslip compression [53].…”

“…We conducted a detailed study of the lens capsule and cell size in lenses from 2-12 months old mice. Utilizing WGA staining for the lens capsule and tdTomato+labelled epithelial cell [53], we were able to measure capsule thickness in live lenses ( Figure 5A). The lens capsule increased in thickness between 2 to 4 months of age but did not change in thickness beyond 4 months of age.…”

Lens Stretching Modulates Lens Epithelial Cell Proliferation via YAP Regulation

“…10,[16][17][18] Axial strains acting upon the lens, similar to those experienced during disaccommodation, have been observed to lead to a reversible increase in LEC area indicating that mechanical loading of the lens is transduced onto its cells. 19 This change in LEC area provides strong evidence that a lifetime of accommodation and disaccommodation and the resulting changes in LEC area would play a part in driving strain-responsive behaviors in LECs.…”

TPM3.1 association with actin stress fibers is required for lens epithelial to mesenchymal transition

“…Following euthanasia, eyes were enucleated and lenses were dissected as previously described 14 . Lenses were immediately placed in medium 199 supplemented with 1% penicillin-streptomycin.…”