Visible fibrinolysis by endothelial cells: effect of vitamins and sterols

Deficiency of growth factor midkine exacerbates necrotizing glomerular injuries in progressive glomerulonephritis

Inflammatory cell infiltration and fibrin deposition play important roles in the development of crescentic glomerulonephritis (GN). In particular, activation of coagulation is an indispensable factor in crescent formation. However, the mechanisms underlying the pathogenesis of crescent formation have not been completely elucidated. We identified the growth factor midkine (MK) as a novel key molecule in the progression of crescentic GN induced by anti-glomerular basement membrane antibody. Despite the lack of significant differences in autologous and heterologous reactions, MK-deficient (Mdk(-/-)) mice unexpectedly showed a greater number of necrotizing glomerular injuries than wild-type (Mdk(+/+)) mice. Likewise, more tubulointerstitial damage was observed in Mdk(-/-) mice, and this damage positively correlated with glomerular injury. Plasminogen activator inhibitor (PAI)-1 was strongly induced in the injured glomerulus of Mdk(-/-) mice, particularly in crescents and endothelial cells. This enhanced PAI-1 production was associated with an increase in inflammatory cell infiltration and matrix deposition in the glomerulus and the interstitium of Mdk(-/-) mice. In line with these in vivo data, primary cultured endothelial cells derived from Mdk(-/-) mice exhibited higher PAI-1 mRNA expression on fibrin challenge and less fibrinolysis than Mdk(+/+) mice. In contrast, the expression of plasminogen activators was not affected. Our combined data suggest that MK leads to a blockade of PAI-1, which is closely associated with the suppression of crescentic GN.

Midkine enhances fibrinolytic activity of bovine endothelial cells

A hitherto unknown function of midkine (MK) was found in the regulation of fibrinolytic activity of vascular endothelial cells. Recombinant murine MK enhanced plasminogen activator (PA)/plasmin levels in bovine aortic endothelial cells (BAECs) in a dose- and time-dependent manner. After incubation with 10 ng/ml MK for 18 h, PA and plasmin levels increased 6- and 4-fold, respectively. This effect was attributed to a moderate upregulation of urokinase-type PA expression as well as to a significant down-regulation of PA inhibitor-1 (PAI-1) expression. BAECs constitutively synthesized and secreted MK and its production was enhanced 2-fold with 1 microM retinoic acid or 10 microM retinol. It was found that MK served as a substrate for tissue transglutaminase. In the culture medium, MK existed as a transglutaminase-mediated complex of 36 kDa. Addition of anti-MK antibody to BAEC cultures resulted in a decrease of basal PA activity and an increase of basal PAI-1 levels and attenuated the ability of retinol to enhance PA activity 50% and potentiated the ability to increase PAI-1 levels 4-fold. Furthermore, MK and basic fibroblast growth factor (bFGF) acted more than additively in enhancing PA levels. We conclude that in BAECs MK is a novel autocrine factor sustaining the fibrinolytic property. MK functions as a mediator of retinoid and cooperates with bFGF to enhance fibrinolytic activity of BAECs.

Mechanism of retinoid-induced activation of latent transforming growth factor-beta in bovine endothelial cells

Cell-associated plasmin is a putative physiological activator of latent transforming growth factor-beta (LTGF-beta). Since retinoids enhance the production of plasminogen activator (PA) and thereby increase cell-associated plasmin activity, we tested the possibility that retinoids might induce the activation of LTGF-beta using bovine endothelial cells (ECs) as a model system. ECs treated with physiological concentrations of retinol or retinoic acid formed active TGF-beta in the culture media in a dose- and time-dependent fashion. Cells were treated with 2 microM retinol for 24 h, and the amount of TGF-beta produced during a subsequent 12-h incubation period was measured. Out of a total of 14 pM LTGF-beta secreted, 0.7 pM was converted to active TGF-beta. Northern blot analyses showed that mRNA levels for TGF-beta 2 but not for TGF-beta 1 increased in cells treated with retinol. Inclusion of either inhibitors of PA or of plasmin or antibody against PA in the culture medium as well as depletion of plasminogen from the serum blocked the formation of TGF-beta, suggesting that PA, plasminogen, and the resulting plasmin are essential for activation of LTGF-beta in retinoid-stimulated cells. Antibody against the LTGF-beta binding protein blocked activation implying that localization of LTGF-beta through its binding protein may be important. However, inhibition of binding of LTGF-beta to the cell surface mannose 6-phosphate receptor did not prevent activation. These data indicate that retinoids up-regulate the production of LTGF-beta in ECs and induce activation of LTGF-beta, perhaps, by increasing PA and plasmin levels. Thus, TGF-beta might be a local mediator of some of the biological activities of retinoids both in vivo and in vitro.

Toxicity of sitosterol to human umbilical vein endothelial cells in vitro

The pathogenesis of the early development of atherosclerosis in sitosterolaemia is unknown. The effect of sitosterol on vascular endothelial cells in vitro was investigated by culturing human umbilical vein endothelial cells in the presence of up to 0.7 mmol l-1 of sitosterol. Liposomes were used to supply the high sterol concentrations. Exposure to 0.7 mmol l-1 of sitosterol for 72 h caused contraction of the endothelial cells and increased release of intracellular lactate dehydrogenase. After 96 h incubation the cells were partly detached from the substrate. At this time-point 0.35 mmol l-1 of sitosterol also caused perturbation of the endothelial cells. However, we could not confirm previous reports that tissue plasminogen activator production was enhanced by sitosterol.

Enhancement of plasminogen activator activity in cultured endothelial cells by granulocyte colony-stimulating factor

A hitherto unknown function of granulocyte colony-stimulating factor (G-CSF) was found using cultured endothelial cells. G-CSF stimulated activity of plasminogen activator (PA) in both extracellular and intracellular milieus of endothelial cells obtained from bovine carotid and aortic artery. This effect was dependent on the concentration of G-CSF added to the culture medium and on the treatment time. The extracellular activity was enhanced approximately 5-fold at a concentration of 5,000 colony-forming unit (CFU)/ml (2.6 nM) and in about a 15-hr treatment period. Analyses by fibrin and reverse fibrin autography revealed that activity of PA was much more increased than that of PA inhibitor in endothelial cells treated with G-CSF.