Abstract
Purpose :
Several discoveries suggest that age-related loss in lens elasticity is a crucial factor for presbyopia. However, the basic molecular processes involved in lens hardening are unclear. Eye lens membranes contain extremely high cholesterol (Chol) content that leads to the formation of cholesterol bilayer domains (CBDs) within the lens membrane; however, the role of CBDs in lens elasticity is unclear. This study investigates the mechanical properties of the bovine lens cortical membrane (CM), nuclear membrane (NM) containing CBDs, and the whole bovine and mouse lenses.
Methods :
The total lipids (lipid plus Chol) from the cortex and nucleus of a single bovine lens were isolated using the monophasic methanol extraction method. Supported CM and NM were prepared from total lipids extracted from the cortex and nucleus using a rapid solvent exchange method, probe-tip sonication, followed by the fusion of unilamellar vesicles on the flat mica surface. The topographical images and the force curves for the CM and NM were obtained in the fluid cell using atomic force microscopy (AFM). The whole bovine and mouse lenses were affixed on custom-built glass Petri dishes using 5% agarose gel, in which the whole lens was submerged in DMEM media, and the AFM was used to obtain the force curves. Force curves were analyzed to estimate the breakthrough force, membrane area compressibility modulus (KA), and Young's modulus (E).
Results :
No significant difference between the membrane thickness of CM and NM was observed. However, the NM containing CBDs exhibited significantly lower breakthrough force, KA, and E than the CM without CBDs. The E for CM and NM are significantly higher than E for the whole lens. The E of the bovine lenses between 24 hours and 48 hours postmortem time and E of the mouse lenses between 20 hours and 68 hours postmortem time were not significantly different.
Conclusions :
The significantly higher stiffness of CM and NM compared to the stiffness of the whole lens suggests that slight modulation in CM and NM stiffness might play a crucial role in altering the overall lens stiffness. Furthermore, the NM-containing CBDs have higher membrane elasticity than CM without CBDs, suggesting that CBDs in the eye lens membrane increase lens membrane elasticity and possibly protect against lens hardening and presbyopia.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.