Nitric Oxide Directly Promotes Vascular Endothelial Insulin Transport

Abstract

Insulin resistance strongly associates with decreased nitric oxide (NO) bioavailability and endothelial dysfunction. In the vasculature, NO mediates multiple processes that affect insulin delivery, including dilating both resistance and terminal arterioles in skeletal muscle in vivo. However, whether NO directly regulates vascular endothelial cell (EC) insulin uptake and its transendothelial transport (TET) is unknown. We report in this article that l-NG-nitro-l-arginine methyl ester (l-NAME) pretreatment blocked, whereas l-arginine and sodium nitroprusside (SNP) each enhanced, EC uptake of fluorescein isothiocyanate (FITC)-labeled insulin. SNP also partly or fully reversed the inhibition of EC insulin uptake caused by l-NAME, wortmannin, the Src inhibitor PP1, and tumor necrosis factor-α. In addition, SNP promoted [125I]TyrA14insulin TET by ∼40%. Treatment with insulin with and without SNP did not affect EC cyclic guanosine monophosphate (cGMP) levels, and the cGMP analog 8-bromo-cGMP did not affect FITC-insulin uptake. In contrast, treatment with insulin and SNP significantly increased EC protein S-nitrosylation, the colocalization of S-nitrosothiol (S-NO) and protein-tyrosine phosphatase 1B (PTP1B), and Akt phosphorylation at Ser473 and inhibited PTP1B activity. Moreover, a high-fat diet significantly inhibited EC insulin-stimulated Akt phosphorylation and FITC-insulin uptake that was partially reversed by SNP in rats. Finally, inhibition of S-nitrosylation by knockdown of thioredoxin-interacting protein completely eliminated SNP-enhanced FITC-insulin uptake. We conclude that NO directly promotes EC insulin transport by enhancing protein S-nitrosylation. NO also inhibits PTP1B activity, thereby enhancing insulin signaling.

Pharmacologic manipulation of lysosomal enzyme transport across the blood–brain barrier

“…Nitric oxide (NO) can influence vesicle activity and re-location processes, and NO directly stimulates insulin transport in vascular endothelial cells. 39 One of our prior studies showed that LPS affects insulin transport across the BBB by modulating NOS isozyme activity. 23 NO released by endothelial NOS and inducible NOS acts to stimulate insulin transport.…”

Pull the Trigger, it Fires: The Critical Role of Insulin-Stimulated Caveolin-1 Tyrosine 14 Phosphorylation in Regulation of Insulin Trans-Endothelial Transport

“…We have demonstrated that insulin, through its signaling pathways in the endothelium, facilitates its own movement across the endothelial cells [15]. Very recently, we reported that eNOS and its activity play a critical role in regulation of insulin uptake and TET as inhibition of eNOS activity completely eliminates endothelial insulin uptake and TET [16]. Next critical question we would ask is how insulin intracellular signaling stimulates and coordinates the assembling of the molecular machinery for insulin trans-endothelial transport?…”

“…This process is significantly impaired in insulin resistance states such as obesity and type 2 diabetes [2,[7][8][9]. Current evidence obtained by us and others indicate that insulin TET is transcellular process and mediated by transporting caveolae that contain or associate with multiple structural and signaling molecules including the insulin receptor (IR), IGF-1receptor, caveolin-1, dynamin-2, actin filaments and eNOS [10][11][12][13][14][15][16][17][18]. Among these components, caveolae and its key structural protein caveolin-1 have been shown to serve as the center to organize the molecular transcytotic machinery mediating insulin TET [13].…”

Nitric oxide vs insulin secretion, action and clearance

“…Shaked et al [11] demonstrated that the NO-dependent TXNIP inhibition contributed to the protective effect of insulin against glucose-induced beta cell apoptosis. Finally, Wang et al [12] recently reported the ability of NO to stimulate transendothelial insulin transport by enhancing protein S-nitrosylation, which could be abolished by knockout of TXNIP.…”