Regulation Of S-nitrosylation Research Articles

Regulation of S-Nitrosylation in Aging and Senescence.

Nitric oxide signals through several distinct mechanisms, including interaction with the heme group of guanylyl cyclase enzymes resulting in modulation of cGMP levels in the vascular endothelium. Alternatively, reactive nitrogen oxide species can bind cysteine residues in target proteins forming S-nitrosothiols. S-nitrosylation is recognized as an important post-translational modification of dozens of proteins, which plays a key role in cellular homeostasis, metabolism, and various disease states. By denitrosylating target proteins, S-nitrosoglutathione reductase (GSNOR/ADH5) plays a pivotal role in the regulation of protein S-nitrosylation. GSNOR expression is reduced in primary senescent cells that accumulate during aging in rodents and humans. Reduced GSNOR activity is accompanied by mitochondrial nitrosative stress, characterized by elevated S-nitrosylation of Drp1 and Parkin with the downstream effect of impaired mitophagy. The mechanism involves epigenetic downregulation of GSNOR by the ten-eleven translocation 1 protein. Conflicting recent reports show that GSNOR levels change with age in mice and humans. One report found that GSNOR levels decreased in peripheral blood mononuclear cell and brains of young to middle-aged mice. However, another report more convincingly showed that there was a significant increase in the hippocampal expression of GSNOR in both old humans and mice. Increased GSNOR in old mice resulted in loss of synaptic plasticity and reduced long-term potentiation memory, in part, by reducing calmodulin kinase IIa activation, which is known to increase the number of AMPA glutamate receptors near synapses. GSNOR levels may be a key biochemical hallmark of aging, but subject to the Goldilocks principle such that its levels need to be maintained in a narrow range according to context, making it a problematic therapeutic target in aging as opposing changes in expression or activity would be needed to stimulate mitophagy in senescence and synaptic plasticity in aging brains.

Lymphocyte Development RequiresS-nitrosoglutathione Reductase

NO is critical to immunity, but its role in the development of the immune system is unknown. In this study, we show that S-nitrosoglutathione reductase (GSNOR), a protein key to the control of protein S-nitrosylation, is important for the development of lymphocytes. Genetic deletion of GSNOR in mice results in significant decrease in both T and B lymphocytes in the periphery. In thymus, GSNOR deficiency causes excessive protein S-nitrosylation, increases apoptosis, and reduces the number of CD4 single-positive thymocytes. Lymphopenia and increase in S-nitrosylation and apoptosis in GSNOR-deficient mice are largely abolished by genetic deletion of inducible NO synthase. Furthermore, the protection of lymphocyte development by GSNOR is apparently intrinsic to hematopoietic cells. Thus, GSNOR, likely through regulation of S-nitrosylation and apoptosis, physiologically plays a protective role in the development of the immune system.

High Glucose Attenuates Protein S-Nitrosylation in Endothelial Cells

Hyperglycemia-induced endothelial dysfunction, via a defect of nitric oxide (NO) bioactivity and overproduction of superoxide, is regarded as one of the most significant events contributing to the vascular lesions associated with diabetes. However, the mechanisms underlying such hyperglycemic injury remain undefined. We hypothesized that alterations in cellular protein S-nitrosylation may contribute to hyperglycemia-induced endothelial dysfunction. We exposed endothelial cells to high glucose in the presence and absence of reactive oxygen species inhibitors and used the biotin switch assay to analyze the alteration in the global pattern of protein S-nitrosylation compared with cells cultured under normal glucose conditions. We identified endogenous S-nitrosylated proteins by mass spectrometry and/or immunoblotting with specific antibodies. High-glucose treatment induced a significant reduction of endogenous S-nitrosylated proteins that include endothelial NO synthase, beta-actin, vinculin, diacylglycerol kinase-alpha, GRP78, extracellular signal-regulated kinase 1, and transcription factor nuclear factor-kappaB (NF-kappaB). Interestingly, these changes were completely reversed by inhibition of superoxide production, suggesting a key role for oxidative stress in the regulation of S-nitrosylation under hyperglycemic conditions. In addition, we found that in parallel with the restoration of decreased S-nitrosylation of NF-kappaB, high glucose-induced NF-kappaB activation was blocked by the superoxide inhibitors. The alterations in protein S-nitrosylation may underlie the adverse effect of hyperglycemia on the vasculature, such as endothelial dysfunction and the development of diabetic vascular complications.