Substrate Stiffness Regulates Cholesterol Efflux in Smooth Muscle Cells

Area of Science:

• Biomedical Engineering
• Cardiovascular Biology
• Cellular Mechanobiology

Background:

• Cholesterol infiltration in arterial walls drives atherosclerosis.
• Smooth muscle cells (SMCs) in the intima can become foam cells upon cholesterol exposure.
• Vascular calcification and cholesterol deposition alter the mechanical environment of SMCs.

Purpose of the Study:

• To investigate the effect of substrate stiffness on cholesterol accumulation in SMCs.
• To elucidate the role of substrate stiffness in foam cell formation.
• To understand the biophysical regulation of cholesterol metabolism in SMCs.

Main Methods:

• Culturing SMCs on substrates with varying stiffness (1-100 kPa).
• Treating SMCs with cholesterol and evaluating cholesterol content.
• Measuring expression of macrophage (CD68) and SMC contractile (ACTA2) markers.
• Analyzing the expression of cholesterol efflux gene ABCA1.
• Modulating liver X receptor (LXR) activity and performing ABCA1 gene knockdown.

Main Results:

• Cholesterol accumulation and total cholesterol content were higher on 1 kPa and 100 kPa substrates compared to 40 kPa.
• Cholesterol accumulation upregulated CD68 and downregulated ACTA2 expression.
• ABCA1 expression was significantly higher on intermediate stiffness (40 kPa) substrates.
• LXR activation increased ABCA1 and reduced cholesterol loading, with an additive effect with stiffness.
• ABCA1 knockdown increased cholesterol accumulation across all stiffness levels.

Conclusions:

• Substrate stiffness modulates cholesterol accumulation in SMCs, primarily by regulating ABCA1 expression.
• This study reveals a novel mechanism of biophysical regulation in cholesterol metabolism and SMC phenotype.
• Findings provide a basis for developing new therapies targeting atherosclerosis through mechanical cues.