Research Groups > Genes and Metabolism Nitric Oxide Signalling

In particular we are interested in the regulation of NO synthesis by endogenously produced competitive inhibitors (asymmetric methylarginines) of NO synthase enzymes. These molecules have been the subject of considerable interest as elevated levels have been reported in numerous disease states including hypertension, heart failure, renal failure atherosclerosis pre-eclampsia and type 2 diabetes. We have cloned a family of enzymes that degrade asymmetric methylarginine (dimethylarginine dimethylaminohydrolase, DDAH) and characterised their distribution in human tissues.

Based on the activity and distribution of these enzymes we have proposed that regulation of the metabolism of endogenously produced asymmetric methylarginines is a potential mechanism to regulate NO generation in vivo.

In order to test this hypothesis we have undertaken both genetic and pharmacological approaches. To facilitate the design of novel pharmacological tools with which to probe the role of DDAH in vivo we have solved the crystal structure of DDAH. Using this structural information we have designed novel selective inhibitors of DDAH and recently solved the crystal structure of human DDAH bound to one such molecule. Running in parallel to this pharmacological approach we have created a number of lines of genetically modified mice that mice that can conditionally delete or overexpress DDAH genes. Our initial studies of the physiological roles of DDAH and ADMA have focused on the cardiovascular system. We have demonstrated that either pharmacological or genetic inhibition of DDAH1 results in impaired vascular NO signaling leading to endothelial dysfunction, increased systemic vascular resistance and elevated systemic and pulmonary blood pressure.

In the coming years we plan to extend our analysis of DDAH/ADMA function in the cardiovascular system and study this pathway in additional organ systems in which NO signaling has been described. We will utilize novel genetically modified mice selective small molecule inhibitors of DDAH to elucidate the role of this pathway in normal physiological and pathophysiological regulation of nitric oxide signalling. We will also examine non-NO dependent effects of ADMA and non-enzymatic functions of DDAH.

The Regulation of Nitric Oxide synthesis by Methylarginines. L-arginine is the substrate for nitric oxide synthase (NOS) enzymes. Arginine residues in proteins can be methylated by protein arginine methyl transferases. Following proteolysis of arginine-methylated proteins, methylarginines (ADMA and L-NMMA) accumulate in the cytosol where inhibit NOS activity by competing with arginine at the NOS active site. Inhibitory methylarginines are metabolized by the action of dimethylarginine dimethylaminohydrolase (DDAH).