Abstract
The plasma membranes of the human lens fiber cell are overloaded with cholesterol that not only saturates the phospholipid bilayer of these membranes but also leads to the formation of pure cholesterol bilayer domains. Cholesterol level increases with age, and for older persons, it exceeds the cholesterol solubility threshold, leading to the formation of cholesterol crystals. All these changes occur in the normal lens without too much compromise to lens transparency. If the cholesterol content in the cell membranes of other organs increases to extent where cholesterol crystals forma, a pathological condition begins. In arterial cells, minute cholesterol crystals activate inflammasomes, induce inflammation, and cause atherosclerosis development. In this review, we will indicate possible factors that distinguish between beneficial and negative cholesterol action, limiting cholesterol actions to those performed through cholesterol in cell membranes and by cholesterol crystals.
Highlights
The plasma membrane of the human eye lens fiber cell is unique in its enormous cholesterol content, which increases, over time, to a level that is incomparable with other tissue/organ cells [1,2]
The major difference between cholesterol action in the lens versus in other tissues and organs is that the eye lens is avascular, and other human body tissues and organs are exposed to blood and its related components, including cholesterol transported in low-density lipoproteins (LDL) and high-density lipoprotein (HDL), oxygen transported by red blood cells, and all cells of the immune system
Since the organelle-free zone in the lens consists of only the plasma membranes and cytosol, the high cholesterol content seems to be important and beneficial
Summary
The plasma membrane of the human eye lens fiber cell is unique in its enormous cholesterol content, which increases, over time, to a level that is incomparable with other tissue/organ cells [1,2]. At this high content, cholesterol saturates the lipid bilayer portion of fiber cell membranes and induces formation of pure cholesterol bilayer domains (CBDs) within this bilayer. In addition to the increased cholesterol content that occurrs with age, the phospholipid composition of fiber cells changes drastically [3,4,5]. Is a sign of a pathological condition [13,14] but is not harmful to the eye lens [2]
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