Abstract 1669: Study Of Endothelial Specific DDAH1 Gene Deficient Mice Revels That Vascular Endothelium Is The Primary Site To Remove Toxic Asymmetric Methylarginines
Asymmetric methylarginines are produced by type I Protein Arginine Methyltransferases which are broadly distributed in many cell types. Asymmetric methylarginines inhibit nitric oxide synthase (NOS) activity to decrease NO production. Asymmetric methylarginines are metabolized by Dimethylarginine Dimethylaminohydrolase (DDAH). Thus, we found that specific gene silencing of DDAH1 in HUVEC led to a doubling of ADMA concentration with an 80% decrease in NO generation. This was associated with decreased tube formation and inhibition of HUVEC proliferation. Since a previous study showed that global DDAH1 deficiency was embryonic lethal, and we previously demonstrated that in heart DDAH1 is predominantly expressed in vascular endothelial cells, we speculated that selective vascular endothelial DDAH1 deficiency would largely abolish DDAH1 expression in many tissues and might be embryonic lethal as well. Using the Cre-LoxP approach, we generated endothelial specific DDAH1 KO mice (endo-DDAH1 KO). Endo-DDAH1 KO had no apparent effect on growth or development as compared with wild type littermates, indicating that expression of DDAH1 is not indispensable. Interestingly, DDAH1 expression was totally abolished in kidney, lung, brain, spleen and liver in some endo-DDAH1 KO mice. Endo-DDAH1 KO mice had significantly increased plasma ADMA concentrations (1.27μM in the endo-DDAH KO vs. 0.69μM in control mice), and hypertension (systolic blood pressure132 vs. 113 mmHg), which was associated with decreased acetylcholine-induced NO production and number of vessels sprouting from isolated aortic rings. Furthermore, endothelial repair after vascular injury was impaired in the endo-DDAH1 KO. Although asymmetric methylarginines are produced by many cell types, the nearly exclusive DDAH1 expression in endothelium indicates that vascular endothelial cells are the primary site to remove asymmetric methylarginines. This study demonstrates for the first time that vascular endothelium can be a primary site to actively dispose of toxic molecules produced by other type of cells. The data also suggest that DDAH1 can play a regulatory role in endothelial cell proliferation.