Assessing the Effects of Postmortem Preservation Time on Mouse Lens Properties Using Atomic Force Microscopy and Optical Coherence Tomography

Abstract

Purpose : Given that researchers use mouse lenses in various experimental studies that require ex vivo preservation, characterizing the changes that occur during preservation is critical for comparing samples taken at different time points in solution. The purpose of this study is to characterize changes in ex vivo mouse lens elasticity and internal structure induced by storage in culture media using atomic force microscopy (AFM) and optical coherence tomography (OCT).

Methods : Data was acquired on 18 young (8-11 weeks old) and 17 old (32-42 weeks old) C57BL/6J mice lenses. The mice were euthanized with CO2 prior to removal of the whole, intact lenses. In Group 1 (8 young, 5 old), the lenses were immediately submerged in Dulbecco's Modified Eagle Medium (DMEM) to preserve lens hydration, imaged using OCT, and measured with a custom atomic force microscope (AFM) to assess lens mechanical properties. The postmortem time was less than 1 hour in this group. In Group 2 (10 young, 12 old), the lenses were kept in a solution of DMEM and 1% antimycotic at 37C for 18 hours before imaging with OCT and performing AFM microindentation. To preserve the statistical independence of each sample in each group, only the OD lens of each mouse was included.

Results : For Group 1, lens elasticity was 9.3±5.2kPa and 21.4±8.6kPa for the young and old mice, respectively. For Group 2, lens elasticity was 20.1±9.0kPa and 19.6±7.3kPa for the young and old mice, respectively. There was a significant increase in stiffness of young mouse lenses kept in solution (p=0.003); lens stiffness was comparable at the two time points in old mice (p=0.352). In both young and old mice, OCT images revealed increased light scattering around the perimeter as well as surrounding the lens nucleus.

Conclusions : Even while maintaining lens hydration within an incubator, lenses from both young and old mice underwent structural changes with postmortem time. In addition, young lenses stiffened significantly so that their stiffness was comparable to that of an old mouse. Investigators should take into account the compounding variable of lens storage postmortem when conducting ex vivo experiments.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.