Upregulation of proteinase-activated receptor-2 and increased response to trypsin in endothelial cells after exposure to oxidative stress in rat aortas.

Background/aims: The effects of oxidative stress on the vascular responsiveness to the agonists of proteinase-activated receptors (PARs) were investigated.

Methods: Serum-free incubation was utilized to impose oxidative stress to isolated rat aortas. Spontaneously hypertensive rats (SHR) were investigated as a model of in vivo oxidative stress.

Results: Thrombin, trypsin, PAR₁-activating peptide (PAR₁-AP), PAR₂-AP and PAR₄-AP induced little or no effect in the aortas of female Wistar-Kyoto rats (WKY). Serum-free incubation induced endothelium-dependent relaxant responses to PAR₂ agonists, but not PAR₁ or PAR₄ agonists, in a manner sensitive to diphenyleneiodonium or ascorbic acid. In male aortas, trypsin and PAR₂-AP induced a transient endothelium-dependent relaxation without serum-free incubation. The acetylcholine-induced endothelium-dependent relaxation and the sodium nitroprusside-induced endothelium-independent relaxation remained unchanged. Immunoblot analyses revealed the upregulation of PAR₂ in endothelial cells, which was abolished by either diphenyleneiodonium or ascorbic acid. Aortas of female SHR expressed a higher level of PAR₂ than WKY and responded to trypsin without serum-free incubation. Treatment with ascorbic acid attenuated the trypsin-induced relaxation and the PAR₂ expression in SHR.

Conclusion: This study provides the first evidence that oxidative stress upregulates PAR₂ in endothelial cells, thereby enhancing the endothelium-dependent relaxant response to PAR₂ agonists in rat aortas.