Endothelial Cells in Physiology and in the Pathophysiology of Vascular Disorders

Endothelial dysfunction or activation elicited by oxidatively modified low-density lipoprotein (Ox-LDL) has been implicated in the pathogenesis of atherosclerosis1–4, characterized by intimal thickening and lipid deposition in the arteries. Ox-LDL and its lipid constituents impair endothelial production of nitric oxide, and induce the endothelial expression of leukocyte adhesion molecules and smooth-muscle growth factors, which may be involved in atherogenesis5–7. Vascular endothelial cells in culture8,9 and in vivo10,11 internalize and degrade Ox-LDL through a putative receptor-mediated pathway that does not involve macrophage scavenger receptors12–15. Here we report the molecular cloning, using expression cloning strategy, of an Ox-LDL receptor from vascular endothelial cells. The cloned receptor is a membrane protein that belongs structurally to the C-type lectin family, and is expressed in vivo in vascular endothelium and vascular-rich organs.

An endothelial receptor for oxidized low-density lipoprotein

Proteinase-activated receptors are a recently described, novel family of seven-transmembrane G-protein-coupled receptors. Rather then being stimulated through ligand receptor occupancy, activation is initiated by cleavage of the N terminus of the receptor by a serine protease resulting in the generation of a new tethered ligand that interacts with the receptor within extracellular loop-2. To date, four proteinase-activated receptors (PARs) have been identified, with distinct N-terminal cleavage sites and tethered ligand pharmacology. In addition to the progress in the generation of PAR-1 antagonists, we describe the role of thrombin in such processes as wound healing and the evidence implicating PAR-1 in vascular disorders and cancer. We also identify advances in the understanding of PAR-1-mediated intracellular signaling and receptor desensitization. The cellular functions, signaling events, and desensitization processes involved in PAR-2 activation are also assessed. However, other major aspects of PAR-2 are highlighted, in particular the ability of several serine protease enzymes, in addition to trypsin, to function as activators of PAR-2. The likely physiological and pathophysiological roles for PAR-2 in skin, intestine, blood vessels, and the peripheral nervous system are considered in the context of PAR-2 activation by multiple serine proteases. The recent discovery of PAR-3 and PAR-4 as additional thrombin-sensitive PARs further highlights the complexity in assessing the effects of thrombin in several different systems, an issue that remains to be fully addressed. These discoveries have also highlighted possible PAR–PAR interactions at both functional and molecular levels. The future identification of other PARs and their modes of activation are an important future direction for this expanding field of study.

Proteinase-Activated Receptors

A stereotaxic atlas of the rat brain

Dectin-1 is a natural killer (NK)-cell-receptor-like C-type lectin that is thought to be involved in innate immune responses to fungal pathogens. This transmembrane signalling receptor mediates various cellular functions, from fungal binding, uptake and killing, to inducing the production of cytokines and chemokines. These activities could influence the resultant immune response and can, in certain circumstances, lead to autoimmunity and disease. As I discuss here, understanding the molecular mechanisms behind these functions has revealed new concepts, including collaborative signalling with the Toll-like receptors (TLRs) and the use of spleen tyrosine kinase (SYK), that have implications for the role of other non-TLR pattern-recognition receptors in immunity.

Dectin-1: a signalling non-TLR pattern-recognition receptor.

We have previously reported that intracerebroventricular administration of 6R-L-erythro-5,6,7,8-tetrahydrobiopterin (6R-BH4), a cofactor for tyrosine hydroxylase, enhances biosynthesis of 3,4-dihydroxyphenylethylamine (dopamine) in the rat brain. In the present study, we have more precisely examined the effects of 6R-BH4 on dopamine release in vivo from the rat striatum using brain microdialysis. The amount of dopamine collected in striatal dialysates was determined using HPLC with electrochemical detection after purification with an alumina batch method. When the striatum was dialyzed with Ringer solution containing various concentrations of 6R-BH4 (0.25, 0.5, and 1.0 mM), dopamine levels in striatal dialysates increased in a concentration-dependent manner. Biopterin had little effect on dopamine levels in dialysates. The 6R-BH4-induced increase in dopamine levels in dialysates was abolished after pretreatment with tetrodotoxin (50 microM) added to the perfusion fluid, but after pretreatment with nomifensine (100 mg/kg, intraperitoneal injection), an inhibitor of dopamine uptake mechanism, a larger increase was observed. After inhibition of tyrosine hydroxylase by pretreatment with alpha-methyl-p-tyrosine (250 mg/kg, intraperitoneal injection), most of the increase persisted. These results suggest that 6R-BH4 has a dopamine-releasing action, which is not dependent on biosynthesis of dopamine.

Enhancement of dopamine release in vivo from the rat striatum by dialytic perfusion of 6R-L-erythro-5,6,7,8-tetrahydrobiopterin.

Palmitoylation of Human EndothelinB ITS CRITICAL ROLE IN G PROTEIN COUPLING AND A DIFFERENTIAL REQUIREMENT FOR THE CYTOPLASMIC TAIL BY G PROTEIN SUBTYPES

Soichi Miwa

Papers

An endothelial receptor for oxidized low-density lipoprotein

Enhancement of dopamine release in vivo from the rat striatum by dialytic perfusion of 6R-L-erythro-5,6,7,8-tetrahydrobiopterin.

Palmitoylation of Human EndothelinB ITS CRITICAL ROLE IN G PROTEIN COUPLING AND A DIFFERENTIAL REQUIREMENT FOR THE CYTOPLASMIC TAIL BY G PROTEIN SUBTYPES

Structural basis of g protein specificity of human endothelin receptors : a study with endothelina/b chimeras

cDNA Cloning and Expression of Bovine Endothelin Converting Enzyme