Critical role of interleukin-1β for transcriptional regulation of endothelial 6-pyruvoyltetrahydropterin synthase

Objective - Synthesis of tetrahydrobiopterin ( BH4), an essential cofactor for nitric oxide synthases, is strongly induced on immunostimulation in vascular endothelial cells ( VECs). Expression of GTP cyclohydrolase I ( GTPCH), the first enzyme in BH4 biosynthesis, is regulated by cytokines and considered rate- limiting. Herein we investigated the molecular mechanism and relevance of cytokine- dependent regulation of 6- pyruvoyltetrahydropterin synthase ( PTPS), the second enzyme in BH4 synthesis, in human coronary artery endothelial cells ( HCAECs). Methods and Results - Real- time polymerase chain reaction revealed a 4- fold induction of PTPS and a 300- fold induction of GTPCH expression by interleukin (IL)- 1 beta/ tumor necrosis factor-alpha/ interferon-gamma, mainly through de novo transcription. On immunostimulation, PTPS became rate- limiting. Importantly, IL- 1beta induced PTPS rather than GTPCH. As a result, IL- 1beta contributed significantly to the amount of BH4 produced ( + 40%) but concomitantly reduced the accumulation of the GTPCH intermediate, 7,8- dihydroneopterin triphosphate ( - 50%). Conclusion - Our data show that PTPS induction is necessary for optimized BH4 synthesis in cytokine- stimulated HCAECs and point to IL- 1 beta as a leading cytokine in this process.