Mechanism of endoplasmic reticulum stress-induced vascular endothelial dysfunction

Background

We recently reported that ER stress plays a key role in vascular endothelial dysfunction during hypertension. In this study we aimed to elucidate the mechanisms by which ER stress induction and oxidative stress impair vascular endothelial function.

Methodology/principal findings

We conducted in vitro studies with primary endothelial cells from coronary arteries stimulated with tunicamycin, 1 μg/mL, in the presence or absence of two ER stress inhibitors: tauroursodeoxycholic acid (Tudca), 500 μg/mL, and 4-phenylbutyric acid (PBA), 5 mM. ER stress induction was assessed by enhanced phosphorylation of PERK and eIF2α, and increased expression of CHOP, ATF6 and Grp78/Bip. The ER stress induction increased p38 MAPK phosphorylation, Nox2/4 mRNA levels and NADPH oxidase activity, and decreased eNOS promoter activity, eNOS expression and phosphorylation, and nitrite levels. Interestingly, the inhibition of p38 MAPK pathway reduced CHOP and Bip expressions enhanced by tunicamycin and restored eNOS promoter activation as well as phosphorylation. To study the effects of ER stress induction in vivo, we used C57BL/6J mice and p47phox^−/− mice injected with tunicamycin or saline. The ER stress induction in mice significantly impaired vascular endothelium-dependent and independent relaxation in C57BL/6J mice compared with p47phox^−/− mice indicating NADPH oxidase activity as an intermediate for ER stress in vascular endothelial dysfunction.

Conclusion/significance

We conclude that chemically induced ER stress leads to a downstream enhancement of p38 MAPK and oxidative stress causing vascular endothelial dysfunction. Our results indicate that inhibition of ER stress could be a novel therapeutic strategy to attenuate vascular dysfunction during cardiovascular diseases.     

Identification of chemerin receptor (ChemR23) in human endothelial cells: Chemerin-induced endothelial angiogenesis

Chemerin acting via its distinct G protein-coupled receptor CMKLR1 (ChemR23), is a novel adipokine, circulating levels of which are raised in inflammatory states. Chemerin shows strong correlation with various facets of the metabolic syndrome; these states are associated with an increased incidence of cardiovascular disease (CVD) and dysregulated angiogenesis. We therefore, investigated the regulation of ChemR23 by pro-inflammatory cytokines and assessed the angiogenic potential of chemerin in human endothelial cells (EC). We have demonstrated the novel presence of ChemR23 in human ECs and its significant up-regulation (P < 0.001) by pro-inflammatory cytokines, TNF-α, IL-1β and IL-6. More importantly, chemerin was potently angiogenic, as assessed by conducting functional in-vitro angiogenic assays; chemerin also dose-dependently induced gelatinolytic (MMP-2 & MMP-9) activity of ECs (P < 0.001). Furthermore, chemerin dose-dependently activated PI3K/Akt and MAPKs pathways (P < 0.01), key angiogenic and cell survival cascades. Our data provide the first evidence of chemerin-induced endothelial angiogenesis and MMP production and activity.     

ERK-regulated differential expression of the Mitf 6a/b splicing isoforms in melanoma

The master regulator of the melanocyte lineage Mitf is intimately involved in development as well as melanoma, controlling cell survival, differentiation, proliferation and metastasis/migration. Consistent with its central role, Mitf expression and Mitf post-translational modifications are tightly regulated. An additional potential level of regulation is afforded by differential splicing of Mitf exon-6 leading to the generation of two isoforms that differ by the presence of six amino-acids in the Mitf (+) isoform and which have differential effects on cell cycle progression. However, whether the ratio of the two isoforms is regulated and whether their expression correlates with melanoma progression is not known. Here, we show that the differential expression of the Mitf 6a/b isoforms is dependent on the MAPKinase signalling, being linked to the activation of MEK1-ERK2, but not to N-RAS/B-RAF mutation status. In addition, quantification of Mitf 6a/b splicing forms in 86 melanoma samples revealed substantially increased levels of the Mitf (−) form in a subset of metastatic melanomas. The results suggest that differential expression of the Mitf 6a/b isoforms may represent an additional mechanism for regulating Mitf function and melanoma biology.     

The macrophage-derived neutrophil chemotactic factor, MNCF: a lectin with TNF-alpha-like activities on neutrophils

The macrophage-derived neutrophil chemotactic factor (MNCF) is an α-galactoside-binding lectin, known to induce dexamethasone-insensitive neutrophil recruitment. We further characterized MNCF effects on neutrophils and showed that it shares with TNF-α the ability to delay apoptosis and to trigger degranulation. MNCF and TNF-α effects show similar kinetics and involve Src kinases and MAPKinases dependent pathways. They were, however, clearly distinguished, since the soluble TNF-receptor etanercept prevented TNF but not MNCF effects, while melibiose disaccharide inhibited MNCF but not TNF effects. Absorption of MNCF on detoxi-gel did not alter its properties, precluding an LPS contamination effect. By contrast, galectin-3 required LPS to activate neutrophils. Specific antibodies allowed to further demonstrate that MNCF and galectin-3 are two distinct molecules. Finally, MNCF- and IL-8-induced neutrophil activation differed by their kinetic and sensitivity to pertussis toxin. In conclusion, MNCF is a distinct neutrophil agonist, with pro-inflammatory activities involving its carbohydrate recognition domain.