Transnitrosylation: A Factor in Nitric Oxide–Mediated Penile Erection

Introduction Nitric oxide (NO) signaling can be mediated not only through classic 3′,5′-cyclic guanosine monophosphate but also through S-nitrosylation. However, the impact of S-nitrosylation on erectile function and in NO regulation and oxidative stress in the penis remains poorly understood. Aims To characterize the role of S-nitrosoglutathione reductase (GSNOR), a major regulator of S-nitrosylation homeostasis, on erection physiology and on endothelial NO synthase (eNOS) function and oxidative-nitrosative stress in the penis. Methods Adult GSNOR-deficient and wild-type (WT) mice were used. Erectile function was assessed in response to electrical stimulation of the cavernous nerve. Total NO in penile homogenates was measured by Griess reaction. Protein S-nitrosylation, eNOS phosphorylation on Ser-1177 (positive regulatory site), eNOS uncoupling, and markers of oxidative stress (4-hydroxy-2-nonenal, malondialdehyde, and nitrotyrosine) in the penis were measured by western blot. Main Outcome Measures Erectile function, eNOS function, and oxidative stress in the penis of GSNOR-deficient mice. Results Erectile function was intact in GSNOR-deficient mice. Total S-nitrosylated proteins were increased (P <. 05) in the GSNOR^−/− compared with WT mouse penis. Although eNOS phosphorylation on Ser-1177 did not differ between the GSNOR^−/− and WT mouse penises at baseline, electrical stimulation of the cavernous nerve increased (P <. 05) phosphorylated eNOS in the WT mouse penis but failed to increase phosphorylated eNOS in the GSNOR^−/− mouse penis. Total NO production was decreased (P <. 05), whereas eNOS uncoupling, 4-hydroxy-2-nonenal, malondialdehyde, and nitrotyrosine were increased (P <. 05) in the GSNOR-deficient mouse penis compared with the WT mouse penis. Conclusion Transnitrosylation mechanisms play an important role in regulating NO bioactivity in the penis. Deficiency of GSNOR leads to eNOS dysfunction and increased oxidative damage, suggesting that homeostatic eNOS function in the penis is governed by transnitrosylation.