Cell density-dependent modulation of perlecan synthesis by dichloro(2,9-dimethyl-1,10-phenanthroline)zinc(II) in vascular endothelial cells

Sb-Phenyl-N-methyl-5,6,7,12-tetrahydrodibenz[c,f][1,5]azastibocine Induces Perlecan Core Protein Synthesis in Cultured Vascular Endothelial Cells

Vascular endothelial cells synthesize and secrete perlecan, a large heparan sulfate proteoglycan that increases the anticoagulant activity of vascular endothelium by inducing antithrombin III and intensifying fibroblast growth factor (FGF)-2 activity to promote migration and proliferation in the repair process of damaged endothelium during the progression of atherosclerosis. However, the exact regulatory mechanisms of endothelial perlecan expression remain unclear. Since organic-inorganic hybrid molecules are being developed rapidly as tools to analyze biological systems, we searched for a molecular probe to analyze these mechanisms using a library of organoantimony compounds and found that the Sb-phenyl-N-methyl-5,6,7,12-tetrahydrodibenz[c,f][1,5]azastibocine (PMTAS) molecule promotes the expression of perlecan core protein gene without exhibiting cytotoxicity in vascular endothelial cells. In the present study, we characterized proteoglycans synthesized by cultured bovine aortic endothelial cells using biochemical techniques. The results indicated that PMTAS selectively induced perlecan core protein synthesis, without affecting the formation of its heparan sulfate chain, in vascular endothelial cells. The results also implied that this process is independent of the endothelial cell density, whereas in vascular smooth muscle cells, it occurred only at high cell density. Thus, PMTAS would be a useful tool for further studies on the mechanisms underlying perlecan core protein synthesis in vascular cells, which is critical in the progression of vascular lesions, such as those during atherosclerosis.

Syndecan-1 downregulates syndecan-4 expression by suppressing the ERK1/2 and p38 MAPK signaling pathways in cultured vascular endothelial cells

Syndecan-1 and syndecan-4 are members of the syndecan family of transmembrane heparan sulfate proteoglycans. Vascular endothelial cells synthesize both species of proteoglycans and use them to regulate the blood coagulation-fibrinolytic system and their proliferation via their heparin-like activity and FGF-2 binding activity, respectively. However, little is known about the crosstalk between the expressions of the proteoglycan species. Previously, we reported that biglycan, a small leucine-rich dermatan sulfate proteoglycan, intensifies ALK5-Smad2/3 signaling by TGF-β₁ and downregulates syndecan-4 expression in vascular endothelial cells. In the present study, we investigated the crosstalk between the expressions of syndecan-1 and other proteoglycan species (syndecan-4, perlecan, glypican-1, and biglycan) in bovine aortic endothelial cells in a culture system. These data suggested that syndecan-1 downregulated syndecan-4 expression by suppressing the endogenous FGF-2-dependent ERK1/2 pathway and FGF-2-independent p38 MAPK pathway in the cells. Moreover, this crosstalk was a one-way communication from syndecan-1 to syndecan-4, suggesting that syndecan-4 compensated for the reduced activity in the regulation of vascular endothelial cell functions caused by the decreased expression of syndecan-1 under certain conditions.

Cell density-dependent accumulation of low polarity gold nanocluster in cultured vascular endothelial cells

We have previously reported the cytotoxicity and various biological responses of organic-inorganic hybrid molecules. However, because all the molecules used were electrophilic, the effect of the hybrid molecule without electrophilicity remains unclear. The glutathione-protected gold nanocluster, Au₂₅(SG)₁₈, is an organic-inorganic hybrid molecule that shows a low intramolecular polarity and high stability. In this study, we examined the cytotoxicity and intracellular accumulation of Au₂₅(SG)₁₈ in cultured vascular endothelial cells and compared these characteristics with those of negatively charged gold nanoparticles (AuNPs). Both Au₂₅(SG)₁₈ and AuNPs accumulated in vascular endothelial cells in a dose-dependent manner without cytotoxicity and more accumulation was observed at low cell densities. However, Au₂₅(SG)₁₈ accumulated significantly less than AuNPs in the cells. These results suggest that the intramolecular polarity of organic-inorganic hybrid molecules could regulate intracellular accumulation.

Transcriptional Induction of Cystathionine γ-Lyase, a Reactive Sulfur-Producing Enzyme, by Copper Diethyldithiocarbamate in Cultured Vascular Endothelial Cells

As toxic substances can enter the circulating blood and cross endothelial monolayers to reach parenchymal cells in organs, vascular endothelial cells are an important target compartment for such substances. Reactive sulfur species protect cells against oxidative stress and toxic substances, including heavy metals. Reactive sulfur species are produced by enzymes, such as cystathionine γ-lyase (CSE), cystathionine β-synthase, 3-mercaptopyruvate sulfurtransferase, and cysteinyl-tRNA synthetase. However, little is known about the regulatory mechanisms underlying the expression of these enzymes in vascular endothelial cells. Bio-organometallics is a research field that analyzes biological systems using organic-inorganic hybrid molecules (organometallic compounds and metal coordinating compounds) as molecular probes. In the present study, we analyzed intracellular signaling pathways that mediate the expression of reactive sulfur species-producing enzymes in cultured bovine aortic endothelial cells, using copper diethyldithiocarbamate (Cu10). Cu10 selectively upregulated CSE gene expression in vascular endothelial cells independent of cell density. This transcriptional induction of endothelial CSE required both the diethyldithiocarbamate scaffold and the coordinated copper ion. Additionally, the present study revealed that ERK1/2, p38 MAPK, and hypoxia-inducible factor (HIF)-1α/HIF-1β pathways mediate transcriptional induction of endothelial CSE by Cu10. The transcription factors NF-κB, Sp1, and ATF4 were suggested to act in constitutive CSE expression, although the possibility that they are involved in the CSE induction by Cu10 cannot be excluded. The present study used a copper complex as a molecular probe to reveal that the transcription of CSE is regulated by multiple pathways in vascular endothelial cells, including ERK1/2, p38 MAPK, and HIF-1α/HIF-1β. Bio-organometallics appears to be an effective strategy for analyzing the functions of intracellular signaling pathways in vascular endothelial cells.