Hypercholesterolemia Alters the Gene Expression of Novel Components of the Extracellular Matrix in Experimental Vein Grafts

Abstract

The success rate of vascular bypass procedures is limited by the development of intimal hyperplasia (IH). Hypercholesterolemia has been shown to accelerate IH in both arteries and experimental vein grafts; however the mechanism remains uncertain. Hyaluronic acid synthase (HAS-1) is a transmembrane enzyme responsible for the formation of hyaluronan; an important constituent of extracellular matrix (ECM). The integrin receptor for hyaluronan is CD-44. Both CD-44 and HAS-1 have been studied in the development of ECM of wounds but have yet to be examined in the ECM of IH within vein grafts. The purpose of this study was to determine if the expression of CD-44 and HAS-1 is increased during the early stages of IH and how cholesterol supplementation affects these genes. Forty white male New Zealand rabbits were divided into two groups: cholesterol supplemented (1% cholesterol chow) and noncholesterol supplemented. Each set of 20 rabbits was then divided into four additional groups (n = 5); a nonoperative group (control) and three operative groups that underwent a right interposition carotid bypass using jugular vein. Grafts were harvested at 3, 7, and 21 days after surgery for molecular studies and histology. Ribonuclease protection assays were performed using ³²P-labeled riboprobes for HAS-1, CD-44, and 18s rRNA. Densitometric analysis is expressed as a ratio (riboprobe/rRNA). Cholesterol levels differed significantly between cholesterol supplemented and nonsupplemented groups (1419 ± 130 mg/dl and 48 ± 12 mg/dl) (p < 0.01). There was a significant increase in the expression of HAS-1 and CD-44 in the vein grafts compared to normal jugular vein. Cholesterol supplementation caused a further increase in CD-44 gene expression versus nonsupplemented vein grafts. These data demonstrate a role for CD-44 and HAS-1 transcription in vein graft intimal hyperplasia, which is further altered by cholesterol supplementation. Lastly, these results could explain differences seen in the development of IH with hypercholesterolemia and ultimately provide for improved therapies in alleviating this process.