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Atherosclerosis alters the composition, structure and function of arterial smooth muscle cell plasma membranes
M Chen1, R P Mason, T N Tulenko
1Department of Physiology, Medical College of Pennsylvania, Philadelphia 19129, USA.
Abstract:
The object of this study was to examine changes in plasma membranes of arterial smooth muscle (ASM) during atherogenesis obtained from cholesterol-fed (2%) rabbits. A microsomal fraction highly enriched with plasma membrane markers was prepared by subcellular organelle fractionation from ASM freshly isolated from the thoracic aorta. The membranes were analyzed for unesterified (free) cholesterol (FC) content, membrane bilayer structural parameters (X-ray diffraction), phospholipid (PL) composition, and Na+/K(+)-ATPase activity and kinetics. Following 8 weeks on diet, membrane FC content increased 67.1%. Small angle X-ray diffraction demonstrated an increase in membrane hydrocarbon core electron density and an increase in overall lipid bilayer width (56-62 A). This increase in bilayer width was highly correlated with the membrane FC content (r = 0.992). Both membrane FC content And bilayer width independently correlated with time on cholesterol diet. The phospholipid profile of the membrane revealed a 16.4% increase in phosphatidylcholine (PC), 19.3% decrease in phosphatidylethanolamine (PE) and 62.8% increase in sphingomyelin (SM) content with no change in total PL content. Na+/K(+)-ATPase activity was decreased 52.2% (P < 0.005), and [3H]ouabain binding kinetics demonstrated a 27.6% decrease in maximum binding sites (Bmax) (P < 0.01) while the dissociation constant (Kd) remained unaltered. Membranes obtained from control ASM cells enriched with FC in culture demonstrated changes similar to those in atherosclerotic ASM membranes including an increase in membrane FC content, an increase in bilayer width, and a decrease in Na+/K(+)-ATPase activity with decreased ouabain Bmax. These data demonstrate marked compositional, structural and functional changes in ASM cell membrane characteristics in dietary atherosclerosis. These changes were highly correlated with cholesterol accumulation in the plasma membrane bilayer and were observed before the appearance of visible lesions. We suggest that these membrane defects may be linked with early atherogenesis.
Insights
Diet-induced atherosclerosis in rabbits alters arterial smooth muscle plasma membranes. Increased free cholesterol and altered phospholipids change membrane structure and reduce Na+/K+-ATPase activity, indicating early atherogenesis defects.
Area of Science:
- Cardiovascular Research
- Cell Biology
- Biochemistry
Background:
- Atherosclerosis involves arterial smooth muscle cells (ASM).
- Plasma membrane changes are implicated in early disease development.
- Dietary cholesterol is a known risk factor for atherosclerosis.
Purpose of the Study:
- To investigate plasma membrane alterations in ASM during early atherogenesis.
- To correlate changes in membrane composition and structure with cholesterol feeding.
- To assess functional consequences on membrane-bound enzymes.
Main Methods:
- Subcellular fractionation to isolate ASM plasma membranes from cholesterol-fed rabbits.
- Analysis of free cholesterol (FC) content, phospholipid (PL) composition.
- X-ray diffraction for membrane bilayer structure, Na+/K+-ATPase activity assays.
Main Results:
- Cholesterol feeding significantly increased membrane FC content and lipid bilayer width.
- Significant alterations in phospholipid profile (increased PC, SM; decreased PE).
- Reduced Na+/K+-ATPase activity and decreased ouabain binding sites (Bmax).
Conclusions:
- Dietary cholesterol induces significant compositional and structural changes in ASM plasma membranes.
- These alterations correlate with increased free cholesterol and precede visible atherosclerotic lesions.
- Plasma membrane defects may play a crucial role in the early stages of atherogenesis.