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Lipoprotein-like particles and cholesteryl esters in human Bruch's membrane: initial characterization
Chuan-Ming Li1, Byung Hong Chung, J Brett Presley
1Department of Ophthalmology, University of Alabama School of Medicine, Birmingham, AL 35294-009, USA.
Investigative Ophthalmology & Visual Science
|June 28, 2005
Summary
Researchers isolated lipoprotein-like particles (LLPs) from aged human eye tissues. These LLPs differ from plasma lipoproteins and may be novel particles assembled by the retinal pigment epithelium.
Area of Science:
- Ophthalmology
- Lipid Metabolism
- Molecular Biology
Background:
- Bruch's membrane (BrM) and choroid (Ch) accumulate lipids with age.
- The composition and origin of these lipids, particularly cholesteryl esters, are not fully understood.
- Lipoprotein-like particles (LLPs) are implicated in lipid transport.
Purpose of the Study:
- To isolate and characterize cholesteryl ester-containing LLPs from normal aged human BrM/Ch.
- To compare these LLPs to plasma lipoproteins.
- To investigate the expression of apolipoproteins within the ocular tissues.
Main Methods:
- LLPs were isolated from aged human BrM/Ch using high-salt buffer and density gradient ultracentrifugation.
- Particle composition (cholesterol, triglycerides, phospholipids, cholesteryl esters) and morphology were analyzed.
- Apolipoprotein gene expression was assessed using RT-PCR, Western blot, and immunofluorescence.
Main Results:
- Two LLP peaks were identified; Peak 2, enriched in esterified cholesterol, contained ~100 nm particles resembling in situ BrM particles.
- Both peaks contained apolipoprotein B (apoB) and apolipoprotein A-I (apoA-I).
- Cholesteryl ester composition differed between fresh and preserved tissues, and from other ocular tissues.
Conclusions:
- BrM/Ch LLPs exhibit distinct density, cholesterol distribution, and morphology compared to plasma lipoproteins.
- Peak 2 LLPs are esterified cholesterol-rich and resemble BrM particles.
- Intraocular apoB and apoA-I expression suggests the retinal pigment epithelium may assemble novel lipoprotein particles.