Nitric oxide, S-nitrosation, and endothelial permeability

Abstract

S-Nitrosation is rapidly emerging as a regulatory mechanism in vascular biology, with particular importance in the onset of hyperpermeability induced by pro-inflammatory agents. This review focuses on the role of endothelial nitric oxide synthase (eNOS)-derived nitric oxide (NO) in regulating S-Nitrosation of adherens junction proteins. We discuss evidence for translocation of eNOS, via caveolae, to the cytosol and analyze the significance of eNOS location for S-Nitrosation and onset of endothelial hyperpermeability to macromolecules.

Keywords: S-Nitrosation; VE-cadherin; adherens junction proteins; endothelial nitric oxide synthase; endothelial permeability; endothelium; microvascular permeability; nitric oxide; p120-catenin; regulation of inflammatory hyperpermeability.

Figure 1. Illustration of Endothelial Intercellular Junctions

PANEL A: Electron microscopy image of postcapillary venule of the hamster cheek pouch. The image was obtained after the vasculature was stimulated topically with 10^-7 M PAF. The red square identifies the insert magnified in Panel B (Durán, unpublished image). PANEL B: Insert from Panel A: Intercellular junction. A nearly constant gap separates the adjacent endothelial cells, reflecting PAF-induced hyperpermeability. PANEL C: Cartoon representing some of the known endothelial intercellular adherens junction proteins. The juxtaposition of the extracellular domains of VE-cadherin represents baseline or unstimulated state. eNOS is shown at the caveolae. Other junctional proteins are omitted due to the focus of this review.

Figure 2. eNOS-derived NO signaling pathways

The classical cGMP-dependent pathway is illustrated on the left hand side (sGC: soluble guanylyl cyclase; cGMP: cyclic guanylyl monophosphate; PKG: protein kinase G; ERK 1/2: extracellular regulated kinase 1-2). The regulatory phosphodiesterases (PDE's) and phosphatases (PPases) are also illustrated. The cGMP-indpendent S-nitrosation pathway is shown on the right side. The denitrosating agents thioredoxin (Trx), thioredoxin reductase (TrxR); glutathione (GSH) and S-Nitrosoglutathione Reductase (GSNOR) are depicted as control for the process. Both pathways are regulated through the exquisite mechanisms that control eNOS. Both pathways appear to converge at some point(s) that modulates the adherens junctional protein complex.

Figure 3. Illustration of Hypothetical Hyperpermeability Events

The cartoon represents developing concepts about how S-nitrosation of junctional proteins regulates the onset of hyperpermeability. The arrival of a pro-inflammatory agonist induces 1 and 1′, i.e., translocation of eNOS from the plasma membrane (via internalization of caveolae; refs. # 22, 25, 26) and phosphorylation of junctional proteins. Phosphorylated junctional proteins internalize to the cytosol (step 2). Cytosolic eNOS-derived NO causes S-nitrosation of junctional proteins (² -catenin and p120-catenin in our studies; ref. # ; Step 3). The combination of phosphorylation and S-nitrosation of junctional proteins is proposed as an important mechanism in the onset of pro-inflammatory agonist induced hyperpermeability, shown by a conformational change in VE-cadherin (Step 4) that would allow the passage of macromolecules.