Asa 5505 Activation Key Generator
To assess whether the effect of ST on TGF-1 activation is mediated by D1-like vs. D2-like receptors, we stimulated platelets with phorbol ester PDBu, a D1-like receptor agonist, in the presence of D2-like receptor agonist quinpirole. We found that PDBu- and quinpirole-induced active TGF-1 production was significantly suppressed by D2-like receptor blockade (p=0.009) (Fig. 4A,B ).
Asa 5505 Activation Key Generator
To test the activation of cells by platelet releasates under shear stress or in stirring we transfected HEK293 cells with either human or chicken β-actin promoter-driven luciferase reporter vector. Cells were stimulated by platelet releasates under shear stress or in stirring, and luciferase activity was measured. Platelet releasates under shear stress induced more luciferase activity than releasates in stirring, whereas active TGF-1 levels from the cells stimulated by platelet releasates under stirring were comparable to or even higher than those induced by platelet releasates under shear stress (Fig. 5A,B ). In addition, both platelet releasates under stirring and shear stress promoted expression of the Col1a1 gene in HUVEC, but only platelet releasates under stirring induced expression of the pro-fibrotic gene periostin and EndoMT marker -SMA (data not shown). These results suggest that D1-like and D2-like receptors are differently activated by platelet-released microvesicles during SS or OSS, respectively. This differential pattern of signaling activation appeared to be the result of a receptor-ligand interaction between platelets and ECs mediated by microvesicles.
We also addressed the molecular mechanism by which D1-like receptor stimulation elevates fluid flow-induced active TGF-1 levels and found that A431 cells subjected to fluid shear stress in the presence of D1-like receptor agonist, SKF 38393, were significantly less responsive to fluid shear stress (as indicated by their smaller increase in SMA and vimentin expression) (Fig. 6A,B ). This observation suggested that the increase in active TGF-1 levels in response to D1-like receptor stimulation may involve activation of SMAD2/3 proteins by the TGF-1 receptor-mediated signaling pathway. The finding that stimulation of D1-like receptor alone induced EndoMT markers and increased active TGF-1 by in vitro flow suggests a possible contribution of this receptor in in vivo mechanisms of endothelial injury and repair, including fibrosis.