Argininosuccinate lyase is an essential regulator of nictric oxide homeostatis

Nitric Oxide (NO) is an essential signaling molecule for diverse physiological and disease processes. The regulation of NO flux has focused on the study of the three NO synthases (NOS), but their respective genetic deficiencies exhibit only modest phenotypes. In humans, the urea cycle disorder argininosuccinic aciduria (ASA) caused by deficiency of argininosuccinic acid lyase (ASL) shows systemic features that may reflect global dysregulation of NO homeostasis due to deficiency of intracellular arginine synthesis and/or inability to utilize extracellular arginine. A hypomorphic mouse model of Asl deficiency shows multi-system dysregulation of NO synthesis that is manifest at physiological, histological, and biochemical levels. Endothelial nitric oxide synthase (eNos) and Asl epistasis further supports the specificity of NO dysregulation in this model. Importantly, ASA patients have decreased biochemical markers and dynamic measures of NO production, while ASA fibroblasts cannot utilize extracellular arginine for NO synthesis. NO synthesis from arginine requires formation of a protein complex that includes HSP90, ASL, ASS, and NOS that is decreased in hypomorphic Asl mice. Together, these data show that channeling of both intracellular and extracellular arginine by ASL regulates systemic NO production within a novel metabolomic compartment that explains the arginine paradox