PPARγ ligands decrease hydrostatic pressure-induced platelet aggregation and proinflammatory activity.

Hypertension is known to be associated with platelet overactivity, but the direct effects of hydrostatic pressure on platelet function remain unclear. The present study sought to investigate whether elevated hydrostatic pressure is responsible for platelet activation and to address the potential role of peroxisome proliferator-activated receptor-γ (PPARγ). We observed that hypertensive patients had significantly higher platelet volume and rate of ADP-induced platelets aggregation compared to the controls. In vitro, Primary human platelets were cultured under standard (0 mmHg) or increased (120, 180, 240 mmHg) hydrostatic pressure for 18 h. Exposure to elevated pressure was associated with morphological changes in platelets. Platelet aggregation and PAC-1 (the active confirmation of GPIIb/IIIa) binding were increased, CD40L was translocated from cytoplasm to the surface of platelet and soluble CD40L (sCD40L) was released into the medium in response to elevated hydrostatic pressure (180 and 240 mmHg). The PPARγ activity was up-regulated as the pressure was increased from 120 mmHg to 180 mmHg. Pressure-induced platelet aggregation, PAC-1 binding, and translocation and release of CD40L were all attenuated by the PPARγ agonist Thiazolidinediones (TZDs). These results demonstrate that platelet activation and aggregation are increased by exposure to elevated pressure and that PPARγ may modulate platelet activation induced by high hydrostatic pressure.

The involvement of the CD40-CD40L pathway in activated platelet-induced changes in HUVEC COX-2 and PPARα expression.

We aim to determine the extent of the CD40-CD40L pathway involvement in activated platelet-induced changes in human umbilical endothelial cells (HUVECs). Activated platelets were co-incubated with HUVECs in the presence or absence of CD40LmAb. HUVECs were also directly stimulated with rhCD40L. HUVEC endothelial cyclooxygenase 2 (COX-2) and peroxisome proliferator-activated receptor alpha (PPARα) expression was then assessed. To estimate COX-2 activity, PGE2 concentration was determined. PPARα activity was assessed using a nuclear factor activity kit. Co-incubation with activated platelets increased HUVEC COX-2 and PPARα mRNA expression (P < 0.01). The addition of CD40L mAb significantly attenuated these increases in mRNA and protein (both P < 0.01). Direct stimulation by rhCD40L increased HUVEC COX-2 mRNA and protein (P < 0.05) but did not significantly change the expression of PPARα mRNA and protein. CD40LmAb significantly decreased (P < 0.05) and rhCD40L significantly (P < 0.01) increased COX-2 enzymatic activity, but had almost no effects on PPARα binding activity. Activated platelets may increase HUVEC COX-2 expression and activity partly through the CD40-CD40L pathway.