Transforming growth factor-beta(1) restores antiplatelet function of endothelial cells exposed to anoxia-reoxygenation injury

Mast cell tryptase stimulates myoblast proliferation; a mechanism relying on protease-activated receptor-2 and cyclooxygenase-2

BACKGROUND

Mast cells contribute to tissue repair in fibrous tissues by stimulating proliferation of fibroblasts through the release of tryptase which activates protease-activated receptor-2 (PAR-2). The possibility that a tryptase/PAR-2 signaling pathway exists in skeletal muscle cell has never been investigated. The aim of this study was to evaluate whether tryptase can stimulate myoblast proliferation and determine the downstream cascade.

METHODS

Proliferation of L6 rat skeletal myoblasts stimulated with PAR-2 agonists (tryptase, trypsin and SLIGKV) was assessed. The specificity of the tryptase effect was evaluated with a specific inhibitor, APC-366. Western blot analyses were used to evaluate the expression and functionality of PAR-2 receptor and to assess the expression of COX-2. COX-2 activity was evaluated with a commercial activity assay kit and by measurement of PGF2α production. Proliferation assays were also performed in presence of different prostaglandins (PGs).

RESULTS

Tryptase increased L6 myoblast proliferation by 35% above control group and this effect was completely inhibited by APC-366. We confirmed the expression of PAR-2 receptor in vivo in skeletal muscle cells and in satellite cells and in vitro in L6 cells, where PAR-2 was found to be functional. Trypsin and SLIGKV increased L6 cells proliferation by 76% and 26% above control, respectively. COX-2 activity was increased following stimulation with PAR-2 agonist but its expression remained unchanged. Inhibition of COX-2 activity by NS-398 abolished the stimulation of cell proliferation induced by tryptase and trypsin. Finally, 15-deoxy-Δ-12,14-prostaglandin J2 (15Δ-PGJ2), a product of COX-2-derived prostaglandin D2, stimulated myoblast proliferation, but not PGE2 and PGF2α.

CONCLUSIONS

Taken together, our data show that tryptase can stimulate myoblast proliferation and this effect is part of a signaling cascade dependent on PAR-2 activation and on the downstream activation of COX-2.

Platelet aggregation and TGF-beta(1) plasma levels in pregnant women with preeclampsia

OBJECTIVES

Platelets and transforming growth factor-beta(1) (TGF-beta(1)) are thought to be involved in the pathogenesis of preeclampsia. Our objectives were to determine plasma concentration of TGF-beta(1) in normotensive and preeclamptic women in the third trimester of pregnancy and to evaluate the correlation of TGF-beta(1) plasma levels with platelet count and agonist-induced aggregation capacity.

METHODS

Thirty-three women with preeclampsia were compared with 36 healthy women with uncomplicated pregnancies. Peripheral venous blood samples were obtained, and TGF-beta(1) plasma levels measured by an enzyme-linked immunoassay. Platelet aggregation was induced by the agonist agents adenosine diphosphate (ADP), collagen and epinephrine, and was determined in platelet-rich plasma by aggregometry.

RESULTS

Plasma concentrations of active TGF-beta(1) were significantly higher in preeclamptic women (10.41+/-2.07ng/mL) compared with normotensive pregnant women (7.01+/-3.29ng/mL). Platelet number and platelet agonist-induced aggregation percent were significantly lower in patients with preeclampsia than in healthy pregnant women. A significant correlation was observed between TGF-beta(1) plasma levels and platelet agonist-induced aggregation percent as between plasma levels of TGF-beta(1) and platelet number in preeclamptic patients.

CONCLUSION

The association between impairment in platelet responsiveness and higher levels of TGF-beta(1) in the plasma of patients with preeclampsia suggests that this cytokine may play a role in the pathophysiological events of preeclampsia that are dependent on platelet activation.

Soluble endoglin contributes to the pathogenesis of preeclampsia

Preeclampsia is a pregnancy-specific hypertensive syndrome that causes substantial maternal and fetal morbidity and mortality. Maternal endothelial dysfunction mediated by excess placenta-derived soluble VEGF receptor 1 (sVEGFR1 or sFlt1) is emerging as a prominent component in disease pathogenesis. We report a novel placenta-derived soluble TGF-beta coreceptor, endoglin (sEng), which is elevated in the sera of preeclamptic individuals, correlates with disease severity and falls after delivery. sEng inhibits formation of capillary tubes in vitro and induces vascular permeability and hypertension in vivo. Its effects in pregnant rats are amplified by coadministration of sFlt1, leading to severe preeclampsia including the HELLP (hemolysis, elevated liver enzymes, low platelets) syndrome and restriction of fetal growth. sEng impairs binding of TGF-beta1 to its receptors and downstream signaling including effects on activation of eNOS and vasodilation, suggesting that sEng leads to dysregulated TGF-beta signaling in the vasculature. Our results suggest that sEng may act in concert with sFlt1 to induce severe preeclampsia.

Perindopril augments ecto-ATP diphosphohydrolase activity and enhances endothelial anti-platelet function in human umbilical vein endothelial cells

OBJECTIVES

Recent clinical trials have demonstrated that angiotensin-converting enzyme inhibitors (ACEIs) reduce thrombotic events by unknown mechanisms in patients with atherosclerotic cardiovascular diseases.

DESIGN

We studied the in-vitro effects of perindopril, an ACEI, on the ability of human umbilical vein endothelial cells (HUVEC) to inhibit platelet aggregation.

METHODS

Platelet aggregation in the presence of HUVEC and endothelial surface expression and activities of ecto-ATP diphosphohydrolase (ecto-ADPase), CD39, were determined. The capability of HUVEC to release prostacyclin and nitric oxide (NO) was also investigated.

RESULTS

Perindoprilat (an active metabolite of perindopril) significantly enhanced the surface expression and activities of ecto-ADPase and prostacyclin release, resulting in enhancement of ability to inhibit platelet aggregation by HUVEC. These effects of perindoprilat were also observed in HUVEC activated by tumour necrosis factor (TNF)-alpha, which increased the expression of intracellular adhesion molecule-1 (ICAM-1), CD54, and, despite up-regulation of prostacyclin release, attenuated endothelial anti-platelet properties by decreasing ecto-ADPase activity. Perindoprilat partially restored this capability, but failed to reduce enhanced expression of ICAM-1. By contrast, the role of NO as a platelet inhibitor appeared minimal in HUVEC. Candesartan, an angiotensin II receptor (AT(1)) blocker, did not affect endothelial anti-platelet property.

CONCLUSIONS

Perindoprilat was found to augment endothelial capability to inhibit platelet aggregation by increasing ecto-ADPase activity and prostacyclin release in HUVEC. This beneficial effect of perindoprilat appeared to be preserved in the activated cells exposed to TNF-alpha, although no evidence was found to support that it could reverse the inflammation process induced by cytokines.