Arginine uptake is attenuated, through post-translational regulation of cationic amino acid transporter-1, in hyperlipidemic rats

Abstract

Endothelial cell dysfunction (ECD) is a common feature of hypercholesterolemia. Defective nitric oxide (NO) generation due to decreased endothelial nitric oxide synthase (eNOS) activity is a crucial parameter characterizing ECD. l-arginine is the sole precursor for NO biosynthesis. Among several transporters that mediate l-arginine uptake, cationic amino acid transporter-1 (CAT-1) acts as a specific arginine transporter for eNOS. Our hypothesis implies that CAT-1 is a major determinant of eNOS activity in hypercholesterolemia. We studied aortic arginine uptake, CAT-1 and CAT-2 mRNA expression, and CAT-1, and PKCα protein in: (a) control, untreated animals (CTL), (b) rats fed with 4% cholesterol + 1% cholate and 2% corn oil for 6 weeks (CHOL) and (c) rats with hypercholesterolemia treated orally with either atorvastatin (CHOL + ATORVA, 20 mg/kg BW/day) or arginine 1% (CHOL + ARG) in the drinking water (modalities which have been shown to enhance CAT-1 activity and improve endothelial function). Serum cholesterol levels significantly increased in cholesterol fed animals, an increase which was blocked by atorvastatin (CTL: 66.8 ± 15, CHOL: 133.9 ± 22, CHOL + ARG: 128.2 ± 20, CHOL + ATORVA: 77 ± 15 mg/dl). Arginine transport was significantly decreased in CHOL. Treatment with neither arginine nor atorvastatin had an effect. Using RT-PCR, we found no change in aortic CAT-1 and CAT-2 mRNA expression in CHOL as well as following arginine or atorvastatin administration. The abundance of CAT-1 protein was significantly augmented in cholesterol fed rats and was not affected by arginine or atorvastatin. PKCα protein content, which was previously shown to regulate CAT-1 activity, increased significantly in CHOL and was neither affected by atorvastatin nor arginine. In conclusion, aortic arginine uptake is attenuated in hypercholesterolemia, through post-translational modulation of CAT-1 protein, possibly via upregulation of PKCα.