Abstract
Purpose :
Four lipid domains have been detected in the plasma membrane of the human eye lens fiber cells. They include the bulk, boundary, and trapped lipid, as well as the cholesterol bilayer domain (CBD). The purpose of this research was to evaluate the age-related changes in the amount of phospholipids and cholesterol in these domains. Human lenses can differ not only because of the age, but also because of the varying health history of the donor. Thus, the changes should be evaluated using samples from single donors and single lenses.
Methods :
Continuous wave (CW) electron paramagnetic resonance spin-labeling has been used to evaluate the amount of phospholipids and cholesterol in lipid domains of intact fiber-cell plasma membranes. The cortical and nuclear intact fiber-cell plasma membranes were isolated separately from the left and the right eye lenses of 15- to 70-year-old donors. The phospholipid-analog spin label and the cholesterol-analog spin label were used to evaluate the amounts of phospholipids and cholesterol, respectively. The CW approach allowed us to estimate the amount of boundary plus trapped phospholipids and trapped cholesterol.
Results :
The amount of boundary plus trapped phospholipids was greater in nuclear than in cortical membranes, and in nuclear membranes it increased with the age of the donor. The amount of cholesterol in the trapped lipid domain was greater in nuclear than in cortical membranes, and also in nuclear membranes it increased with the age of the donor. Cholesterol was, to a large degree, excluded from the trapped lipid domain in cortical membranes.
Conclusions :
The amount of phospholipids in domains induced by the presence of integral membrane proteins increases with the age at the expense of bulk phospholipids. Similarly, the amount of cholesterol in the trapped lipid domain increases with age at the expense of cholesterol in the bulk domain and CBD. These results suggest that integral membrane proteins affect phospholipid/cholesterol equilibrium in the lipid bilayer portion of the intact fiber cell plasma membranes as compared with the lens lipid membranes.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.