Abstract 90: Loss of Collectrin Augments Salt-sensitivity and Alters Nitric Oxide and Superoxide Balance.

Abstract

Collectrin, an ACE-2 homologue, plays a major role in amino acid transport in renal epithelial cells. In the rodent kidney, the expression of collectrin is upregulated after reduction of nephron mass and during salt-sensitive hypertension. These observations raise the question of how collectrin might be functionally integrated in the ACE family in the context of blood pressure (BP) regulation. We previously reported that, on a susceptible genetic background, collectrin-deficient (KO) mice have elevated baseline systolic blood pressure (SBP) and impaired endothelium-dependent relaxation (EDR) of thoracodorsal arteries (TDA). Treatment with L-NAME, a nitric oxide synthase (NOS) inhibitor, normalized their BP and EDR of TDA. Here, to determine whether collectrin plays a role in salt-sensitivity (SS), we fed mice a high salt diet (HSD) for 2 weeks. By radiotelemetry, KO mice displayed augmented salt-sensitivity (SS) (Normal salt (NS): Wild-type (WT) 133 ± 1 mm Hg, KO 141 ± 3 mm Hg; HSD: WT 141 ± 2 mm Hg, KO 155 ± 3 mm Hg; change in SBP: WT 7.8 ± 1.4 mm Hg, KO 14.4 ± 1.5 mm Hg; p ≤ 0.02), and lower urinary sodium excretion (UNa) during the first 3 days of HSD (mean UNa over 3 days: KO: 1980 ± 193 μmol/24h, WT: 2650 ± 98 μmol/24h, p = 0.006, ANOVA; n ≥ 6). The impaired pressure natriuresis in KO mice was associated with altered urinary excretion of 8-isoprostane F 2 α (WT 3.0 ± 0.67 ng/mg, KO 7.7 ± 1.5 ng/mg creatinine, p = 0.008) and nitrates/nitrites (WT 10.2 ± 1.4 nmol/day, KO 6.2 ± 0.61 nmol/day, p = 0.03, n ≥ 4 each). We previously reported that KO mice have increased state of endothelial NOS (eNOS) uncoupling. Here, by immunostaining, we found that collectrin is expressed in endothelial cells (ECs). We next queried whether collectrin affects L-arginine (L-Arg) transport in ECs. After isolation from the pulmonary artery, primary ECs from KO mice displayed impaired [ 3 H]L-Arg uptake (WT 2.00 ± 0.19, KO 0.90 ± 0.06 pmol/mg protein/min, p=0.01) To establish direct cause and effect, we over-expressed collectrin in primary human coronary ECs which resulted in increased [ 3 H]L-Arg uptake (Control 4.20 ± 0.32; Overexpression 6.60 ± 0.59 pmol/mg protein/min, p < 0.003). In conclusion, collectrin may regulate BP and SS by modulating the balance of NO and SO through its role in L-Arg transport in ECs.