PPARgamma agonists inhibit angiogenesis by suppressing PKCalpha- and CREB-mediated COX-2 expression in the human...

Area of Science:

• Endocrinology
• Molecular Biology
• Vascular Biology

Background:

• Peroxisome proliferator-activated receptor (PPAR)gamma activation is known to inhibit angiogenesis.
• The pro-angiogenic enzyme cyclooxygenase (COX)-2 plays a role in endothelial cell function.

Purpose of the Study:

• To investigate the effects of PPARgamma agonists on COX-2 expression in human endothelium.
• To elucidate the molecular mechanisms underlying PPARgamma-mediated inhibition of angiogenesis.

Main Methods:

• Human endothelial cells were treated with PPARgamma agonists (rosiglitazone, GW1929) and stimulated with vascular endothelial growth factor (VEGF) or phorbol myristate acetate (PMA).
• COX-2 activity, protein, and mRNA expression were measured.
• PPARgamma antagonists and small-interfering RNAs (siRNAs) were used to confirm specificity.
• Reporter assays and siRNA targeting CRE-binding protein (CREB) were employed to study transcriptional regulation.
• Protein kinase C (PKC)alpha and beta activation and membrane translocation were assessed.

Main Results:

• PPARgamma agonists significantly attenuated VEGF- and PMA-stimulated COX-2 activity, protein, and mRNA expression.
• This inhibitory effect was reversed by PPARgamma antagonists and siRNAs.
• PPARgamma agonists inhibited COX-2 promoter activity via interference with the cAMP response element (CRE) site.
• Downregulation of CREB confirmed its role in COX-2 transcription.
• PPARgamma agonists reduced CREB activation and specifically inhibited VEGF- and PMA-stimulated PKCalpha membrane translocation.

Conclusions:

• Vascular endothelial growth factor (VEGF) induces CREB-mediated COX-2 expression through a PKCalpha-dependent pathway in human endothelium.
• PPARgamma agonists exert anti-angiogenic effects, at least partly, by interfering with VEGF-stimulated PKCalpha-mediated activation of CREB and subsequent COX-2 expression.