Rosiglitazone improves aortic arginine transport, through inhibition of PKCα, in uremic rats

Abstract

Peroxisome proliferator-activated receptor (PPAR) agonists were shown to inhibit atherosclerosis through augmentation of endothelial nitric oxide synthase (eNOS) activity. In addition, rosiglitazone exerts a beneficial effect in chronic renal failure (CRF). Since l-arginine transport by CAT-1 (the specific arginine transporter for eNOS) is inhibited in uremia, we aimed to explore the effect of rosiglitazone on arginine transport in CRF. Arginine uptake by aortic rings was studied in control animals, rats, 6 wk following 5/6 nephrectomy (CRF) and rats with CRF treated with rosiglitazone. The decrease of arginine transport in CRF was prevented by rosiglitazone. Immunobloting revealed that CAT-1 protein was decreased in CRF but remained unchanged following rosiglitazone administration. Protein content of the membrane fraction of PKCalpha and phosphorylated CAT-1 increased significantly in CRF, effects that were prevented by rosiglitazone. PKCalpha phosphorylation was unchanged but significantly attenuated by rosiglitazone in CRF. Ex vivo administration of phorbol-12-myristate-13-acetate to rosiglitazone-treated CRF rats significantly attenuated the effect of rosiglitazone on arginine uptake. The decrease in cGMP response to carbamyl-choline (eNOS agonist) was significantly attenuated by rosiglitazone in CRF. Western blotting and immunohistochemistry analysis revealed that protein nitration was intensified in the endothelium of CRF rats and this was attenuated by rosiglitazone. In conclusion, rosiglitazone prevents the decrease in arginine uptake in CRF through both depletion and inactivation of PKCalpha. These findings are associated with restoration of eNO generation and attenuation of protein nitration and therefore may serve as a novel mechanism to explain the beneficial effects of rosiglitazone on endothelial function in uremia.

Voluntary wheel running augments aortic l-arginine transport and endothelial function in rats with chronic kidney disease

“…This suggests that exercise mediates an increase in L-arginine uptake through a posttranslational modification of CAT-1. Previous work by Ingbir et al (25) reported similar results in which treatment of uremic rats with rosiglitazone improved L-arginine uptake in aortic rings without increasing CAT-1 protein expression. Rosiglitazone treatment was associated with a decrease in aortic PKC␣ protein expression and an increase in CAT-1 phosphorylation, suggesting that PKC␣ is an important mediator of CAT-1 transport activity (25).…”

“…Previous work by Ingbir et al (25) reported similar results in which treatment of uremic rats with rosiglitazone improved L-arginine uptake in aortic rings without increasing CAT-1 protein expression. Rosiglitazone treatment was associated with a decrease in aortic PKC␣ protein expression and an increase in CAT-1 phosphorylation, suggesting that PKC␣ is an important mediator of CAT-1 transport activity (25). In the present study, we observed an increase in PKC␣ expression in the aortas of SED animals whereas levels were returned to similar levels as SHAM animals in both RUN and RUNϩARG treatment groups.…”

“…The transport of extracellular L-arginine into the endothelium occurs primarily through CAT-1 via a sodium-and pH-independent mechanism (14). L-Arginine transport has been shown to be impaired in endothelial cells cultured in uremic plasma (54) as well as in animal models of CKD (25,33,43) and is accompanied by a decline in CAT-1 protein expression in the vasculature. We confirmed these findings in the present paper as demonstrated by a significant reduction in CAT-1 protein expression and L-[ 3 H]arginine uptake in SED and ARG-treated animals.…”

“…L-Arginine transport was assessed in aortic rings using an established in vitro technique (25,33,43,44). Aortic rings were prepared into 3-mm-long ring sections, cut lengthwise into strips, and placed in HEPES buffer at 37°C.…”

Hyperuricemia Attenuates Aortic Nitric Oxide Generation, through Inhibition of Arginine Transport, in Rats

“…We hypothesize that delivery of transported arginine to membrane-bound eNOS, selectively by the cationic amino acid transporter-1 (CAT-1) rather than intra- or extra-cellular arginine concentration, is the predominant factor governing eNOS activity. Indeed, we have previously shown in several different animal models characterized by endothelial dysfunction and decreased eNOS activity that CAT-1 activity is attenuated [15,16,17,18]. The predominant mechanism resulting in diminished CAT-1 activity in all these experiments was post-translational modulation of CAT-1 by protein kinase C α (PKCα) [15,17,18].…”