Novel Regulation of Renal Function by S-Nitrosylation

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PROJECT SUMMARY/ABSTRACT Nitric oxide (NO), generated in the kidney by renal tubular NO synthase (eNOS), can exert renoprotective effects. However, the mechanisms by which NO does so remain poorly understood. Nitric oxide bioactivity is principally conveyed by S-nitrosylation of proteins, the oxidative modification of protein thiols by NO to form S-nitrosothiols (SNOs). Protein S-nitrosylation is reversibly regulated by enzymatic mechanisms including S-nitrosylases and denitrosylases and accumulating evidence implicates dysregulated S- nitrosylation in disease. Here, we identify a novel enzymatic machinery subserving protein S-nitrosylation in the kidney, including a novel metabolic intermediate S-nitroso-coenzyme A (SNO-CoA) that conveys NO bioactivity and its cognate reductase, SNO-CoA reductase (SCoAR), an enzyme of previously unknown function that is highly expressed in kidney proximal tubules. SCoAR mediates the breakdown of SNO-CoA thereby lowering steady-state levels of SNO-proteins (in equilibrium with SNO-CoA). Knockout of SCoAR in mice (SCoAR-/-) is shown to increase S-nitrosylation within the kidney and to protect against ischemia/reperfusion (I/R) injury, whereas deletion of eNOS (SCoAR-/-/eNOS-/-) abrogates this protection. Thus classic renoprotection by eNOS is identified with the SNO-CoA/SCoAR system. Using metabolic profiling and mass spec (MS)-based SNO-protein identification, we have found that renoprotection by the SNO-CoA/SCoAR system is likely mediated by metabolic reprogramming within the kidney. Mechanistically, our data suggest that pyruvate kinase (PKM2) is a major locus of regulation by the SNO-CoA/SCoAR system during acute kidney injury (AKI). Our grant thus explores the idea that S-nitrosylation of PKM2 is renoprotective through metabolic reprogramming that entails SCoAR-regulated coordination of fuel utilization and antioxidant/regenerative defenses. To lay the groundwork for new therapies, we have also screened for SCoAR inhibitors and successfully developed a new class of drug candidate with nanomolar potency, which will be studied herein. Thus, our discovery not only reveals the first physiological function of the SNO-CoA/SCoAR system in mammals, but promises to open a new chapter in our understanding of AKI with immediate therapeutic implications. !