Not all endothelium is equal: regional and sex-dependent roles of DDAH1 in regulating endothelial function

Asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthases (NOS), is primarily metabolized by dimethylarginine dimethylaminohydrolases (DDAH1 and 2). This study used endothelial-specific DDAH1 knockout (DDAH1 En-/- ) mice to test whether reduced endothelial DDAH1 activity impairs cerebral endothelial function and worsens outcomes after cerebral ischaemia-reperfusion. Using male and female, DDAH1 En-/- and control (DDAH1 fl/fl ) mice, we assessed vasoreactivity of middle cerebral (MCA), common carotid (CCA), and systemic arteries (thoracic aortae and first-order mesenteric arteries) ex vivo; and quantified CCA expression of genes associated with vascular smooth muscle (VSM) contractility. ADMA concentrations, and mRNA expression of protein arginine methyltransferases ( PRMT), and DDAH were quantified in human cerebral (hCMEC/D3) and aortic (HAEC) endothelial cells. Outcomes following transient MCA occlusion (tMCAo) were also evaluated in male mice. In male DDAH1 En-/- mice, NO-dependent vasodilator responses in MCA and CCA were significantly impaired compared to controls, while responses in systemic arteries were unaffected. Vasoconstrictor responses were paradoxically reduced in CCA from male DDAH1 En-/- mice in association with altered expression of genes involved in VSM contractility. In contrast to males, vasoreactivity was unaltered in MCA and CCA from female DDAH1 En-/- mice. Both PRMT1 and DDAH mRNA expression were higher in hCMEC/D3 compared with HAEC cells, in association with no change in ADMA concentrations. Lastly, in male DDAH1 En-/- mice, infarct volumes and functional outcomes post-tMCAo were comparable with controls. These findings underscore a role for endothelial DDAH1 in maintaining endothelial function in cerebral arteries from male but not female mice. However, endothelial DDAH1 does not influence stroke outcomes.