Abstract T P246: Phenotypic Characterization of Cerebral Microvasculature in Transgenic Mice With Endothelium Targeted Over-expression of GTP Cyclohydrolase I
Background: Optimal availability of tetrahydrobiopterin (BH4) is a critical determinant of nitric oxide (NO) production by endothelial nitric oxide synthase (eNOS) in the vascular endothelium. Biosynthesis of BH4 is regulated by the enzymatic activation of GTP cyclohydrolase I (GTPCH-I). While the physiological role of GTPCH-I and BH4 have been extensively characterized in peripheral vasculature, their role in regulation of cerebral vascular function has not been investigated.
Methods: The role of GTPCH-I in regulation of cerebral vascular function was studied in cerebral microvessels isolated from wild-type (WT) mice and from mice with endothelium-targeted overexpression of GTPCH-I (eGTPCH-I Tg) mice. Vascular protein expression, intracellular levels of biopterin and cGMP (second messenger of NO) as well as production of NO and superoxide anions were determined.
Results: Endothelium targeted over-expression of GTPCH-I resulted in significant increase in levels of BH4, as well as its oxidized product, 7,8-dihydrobiopterin (7,8-BH2). Importantly, ratio of BH4 to 7,8-BH2, indicative of BH4 available for eNOS activation, was significantly increased in cerebral microvessels of eGTPCH-I Tg mice. However, protein expression of eNOS, levels of nitrate/nitrite - indicative of NO production remained unchanged between cerebral microvessels of WT mice and eGTPCH-I Tg mice. Furthermore, increased BH4 biosynthesis did not affect production of superoxide anions or expression of antioxidant enzymes. Moreover, intracellular levels of cGMP, reflective of NO signaling and activation of soluble guanylate cyclase, were not affected in eGTPCH-I Tg mice.
Conclusion: Our results suggest that, despite a significant increase in BH4 bioavailability, generation of endothelial NO in cerebral microvessels remained unchanged in eGTPCH-I Tg mice. We conclude that under physiological conditions the levels of BH4 are optimal for activation of eNOS and NO/cGMP signaling in wild-type mice.
Author Disclosures: A.R. Santhanam: None. L.V. d'Uscio: None. Z.S. Katusic: None.
- © 2015 by American Heart Association, Inc.