An enzyme that selectively S-nitrosylates proteins to regulate insulin signaling

Nitric oxide production and protein S-nitrosation in algae

Key roles for nitric oxide in signalling processes and plant physiological processes are now well established. In particular, the identification and functional characterisation of proteins regulated by S-nitrosation, a NO-dependent post-translational modification, provided remarkable insights into the subtle mechanisms by which NO mediates its effects. Nevertheless, and despite the considerable progress in understanding NO signalling, the question of how plant cells produce NO is not yet fully resolved. Interestingly, there is now compelling evidence that algae constitute promising biological models to investigate NO production and functions in plants. This article reviews recent highlights of research on NO production in algae and provides an overview of S-nitrosation in these organisms at the proteome level.

The Ever-Expanding Influence of the Endothelial Nitric Oxide Synthase

Nitric oxide (NO) generated by the endothelial NO synthase (eNOS) plays an essential role in the maintenance of vascular homeostasis and the prevention of vascular inflammation. There are a myriad of mechanisms that regulate the activity of the enzyme that may prove to represent interesting therapeutic opportunities. In this regard, the kinases that phosphorylate the enzyme and regulate its activity in situations linked to vascular disease seem to be particularly promising. Although the actions of NO were initially linked mainly to the activation of the guanylyl cyclase and the generation of cyclic GMP in vascular smooth muscle cells and platelets, it is now clear that NO elicits the majority of its actions via its ability to modify redox-activated cysteine residues in a process referred to as S-nitrosylation. The more wide spread use of mass spectrometry to detect S-nitrosylated proteins has helped to identify just how large the NO sphere of influence is and just how many cellular processes are affected. It may be an old target, but the sheer impact of eNOS on vascular health really justifies a revaluation of therapeutic options to maintain and protect its activity in situations associated with a high risk of developing cardiovascular disease.

Small molecule BLVRB redox inhibitor promotes megakaryocytopoiesis and stress thrombopoiesis in vivo

Biliverdin IXβ reductase (BLVRB) is an NADPH-dependent enzyme previously implicated in a redox-regulated mechanism of thrombopoiesis distinct from the thrombopoietin (TPO)/c-MPL axis. Here, we apply computational modeling to inform molecule design, followed by de novo syntheses and screening of unique small molecules retaining the capacity for selective BLVRB inhibition as a novel platelet-enhancing strategy. Two distinct classes of molecules are identified, and NMR spectroscopy and co-crystallization studies confirm binding modes within the BLVRB active site and ring stacking between the nicotinamide moiety of the NADP+ cofactor. A diazabicyclo derivative displaying minimal off-target promiscuity and excellent bioavailability characteristics promotes megakaryocyte speciation in biphenotypic (erythro/megakaryocyte) cellular models and synergizes with TPO-dependent megakaryocyte formation in hematopoietic stem cells. Upon oral delivery into mice, this inhibitor expands platelet recovery in stress thrombopoietic models with no adverse effects. In this work, we identify and validate a cellular redox inhibitor retaining the potential to selectively promote megakaryocytopoiesis and enhance stress-associated platelet formation in vivo distinct from TPO receptor agonists.

Mitochondrial hyperactivity and reactive oxygen species drive innate immunity to the yellow fever virus-17D live-attenuated vaccine

The yellow fever virus 17D (YFV-17D) live attenuated vaccine is considered one of the most successful vaccines ever generated associated with high antiviral immunity, yet the signaling mechanisms that drive the response in infected cells are not understood. Here, we provide a molecular understanding of how metabolic stress and innate immune responses are linked to drive type I IFN expression in response to YFV-17D infection. Comparison of YFV-17D replication with its parental virus, YFV-Asibi, and a related dengue virus revealed that IFN expression requires RIG-I-Like Receptor signaling through MAVS, as expected. However, YFV-17D uniquely induces mitochondrial respiration and major metabolic perturbations, including hyperactivation of electron transport to fuel ATP synthase. Mitochondrial hyperactivity generates reactive oxygen species (ROS) including peroxynitrite, blocking of which abrogated MAVS oligomerization and IFN expression in non-immune cells without reducing YFV-17D replication. Scavenging ROS in YFV-17D-infected human dendritic cells increased cell viability yet globally prevented expression of IFN signaling pathways. Thus, adaptation of YFV-17D for high growth imparts mitochondrial hyperactivity to meet energy demands, resulting in generation of ROS as the critical messengers that convert a blunted IFN response into maximal activation of innate immunity essential for vaccine effectiveness.

Endogenous production of nitric oxide by iNOS in human cells restricts inflammatory activation and cholesterol/fatty acid biosynthesis

Nitric oxide (NO) is a bioactive gas that is known to control many physiological processes. In human parenchymal cells, the function of iNOS-derived NO is incompletely understood. Here, we used RNA-seq to examine the role of iNOS-derived NO in the control of gene expression in a human lung epithelial cell line treated with inflammatory cytokines. iNOS-derived NO restricted the expression of genes involved in immune signaling, including the immune-related genes CXCL9 and E-selectin that were not previously known to be inhibited by iNOS. We also determined that iNOS-derived NO inhibits the expression of genes needed for cholesterol/fatty acid biosynthesis in response to cytokine stimulation, a process not previously known to be affected by NO. These findings establish the regulation of immune activation and cholesterol/fatty acid biosynthesis as main functions of iNOS in human parenchymal cells.

The denitrosylase SCoR2 controls cardioprotective metabolic reprogramming

Acute myocardial infarction (MI) is a leading cause of morbidity and mortality, and therapeutic options remain limited. Endogenously generated nitric oxide (NO) is highly cardioprotective, but protection is not replicated by nitroso-vasodilators (e.g., nitrates, nitroprusside) used in clinical practice, highlighting specificity in NO-based signaling and untapped therapeutic potential. Signaling by NO is mediated largely by S-nitrosylation, entailing specific enzymes that form and degrade S-nitrosothiols in proteins (SNO-proteins), termed nitrosylases and denitrosylases, respectively. SNO-CoA Reductase 2 (SCoR2; product of the Akr1a1 gene) is a recently discovered protein denitrosylase. Genetic variants in SCoR2 have been associated with cardiovascular disease, but its function is unknown. Here we show that mice lacking SCoR2 exhibit robust protection in an animal model of MI. SCoR2 regulates ketolytic energy availability, antioxidant levels and polyol homeostasis via S-nitrosylation of key metabolic effectors. Human cardiomyopathy shows reduced SCoR2 expression and an S-nitrosylation signature of metabolic reprogramming, mirroring SCoR2-/- mice. Deletion of SCoR2 thus coordinately reprograms multiple metabolic pathways-ketone body utilization, glycolysis, pentose phosphate shunt and polyol metabolism-to limit infarct size, establishing SCoR2 as a novel regulator in the injured myocardium and a potential drug target.

Impact statement

Mice lacking the denitrosylase enzyme SCoR2/AKR1A1 demonstrate robust cardioprotection resulting from reprogramming of multiple metabolic pathways, revealing widespread, coordinated metabolic regulation by SCoR2.

Regulation and function of insulin and insulin-like growth factor receptor signalling

Receptors of insulin and insulin-like growth factors (IGFs) are receptor tyrosine kinases whose signalling controls multiple aspects of animal physiology throughout life. In addition to regulating metabolism and growth, insulin-IGF receptor signalling has recently been linked to a variety of new, cell type-specific functions. In the last century, key questions have focused on how structural differences of insulin and IGFs affect receptor activation, and how insulin-IGF receptor signalling translates into pleiotropic biological functions. Technological advances such as cryo-electron microscopy have provided a detailed understanding of how native and engineered ligands activate insulin-IGF receptors. In this Review, we highlight recent structural and functional insights into the activation of insulin-IGF receptors, and summarize new agonists and antagonists developed for intervening in the activation of insulin-IGF receptor signalling. Furthermore, we discuss recently identified regulatory mechanisms beyond ligand-receptor interactions and functions of insulin-IGF receptor signalling in diseases.

The UniProt Consortium, Bateman A, Martin MJ, Orchard S, Magrane M, Adesina A, Ahmad S, Bowler-Barnett EH, Bye-A-Jee H, Carpentier D, Denny P, Fan J, Garmiri P, Gonzales LJDC, Hussein A, Ignatchenko A, Insana G, Ishtiaq R, Joshi V, Jyothi D, Kandasaamy S, Lock A, Luciani A, Luo J, Lussi Y, Marin JSM, Raposo P, Rice DL, Santos R, Speretta E, Stephenson J, Totoo P, Tyagi N, Urakova N, Vasudev P, Warner K, Wijerathne S, Yu CWH, Zaru R, Bridge AJ, Aimo L, Argoud-Puy G, Auchincloss AH, Axelsen KB, Bansal P, Baratin D, Batista Neto TM, Blatter MC, Bolleman JT, Boutet E, Breuza L, Gil BC, Casals-Casas C, Echioukh KC, Coudert E, Cuche B, de Castro E, Estreicher A, Famiglietti ML, Feuermann M, Gasteiger E, Gaudet P, Gehant S, Gerritsen V, Gos A, Gruaz N, Hulo C, Hyka-Nouspikel N, Jungo F, Kerhornou A, Mercier PL, Lieberherr D, Masson P, Morgat A, Paesano S, Pedruzzi I, Pilbout S, Pourcel L, Poux S, Pozzato M, Pruess M, Redaschi N, Rivoire C, Sigrist CJA, Sonesson K, Sundaram S, Sveshnikova A, Wu CH, Arighi CN, Chen C, Chen Y, Huang H, Laiho K, Lehvaslaiho M, McGarvey P, Natale DA, Ross K, Vinayaka CR, Wang Y, Zhang J. UniProt: the Universal Protein Knowledgebase in 2025

The aim of the UniProt Knowledgebase (UniProtKB; https://www.uniprot.org/) is to provide users with a comprehensive, high-quality and freely accessible set of protein sequences annotated with functional information. In this publication, we describe ongoing changes to our production pipeline to limit the sequences available in UniProtKB to high-quality, non-redundant reference proteomes. We continue to manually curate the scientific literature to add the latest functional data and use machine learning techniques. We also encourage community curation to ensure key publications are not missed. We provide an update on the automatic annotation methods used by UniProtKB to predict information for unreviewed entries describing unstudied proteins. Finally, updates to the UniProt website are described, including a new tab linking protein to genomic information. In recognition of its value to the scientific community, the UniProt database has been awarded Global Core Biodata Resource status.

Redox regulation, protein S-nitrosylation, and synapse loss in Alzheimer's and related dementias

Redox-mediated posttranslational modification, as exemplified by protein S-nitrosylation, modulates protein activity and function in both health and disease. Here, we review recent findings that show how normal aging, infection/inflammation, trauma, environmental toxins, and diseases associated with protein aggregation can each trigger excessive nitrosative stress, resulting in aberrant protein S-nitrosylation and hence dysfunctional protein networks. These redox reactions contribute to the etiology of multiple neurodegenerative disorders as well as systemic diseases. In the CNS, aberrant S-nitrosylation reactions of single proteins or, in many cases, interconnected networks of proteins lead to dysfunctional pathways affecting endoplasmic reticulum (ER) stress, inflammatory signaling, autophagy/mitophagy, the ubiquitin-proteasome system, transcriptional and enzymatic machinery, and mitochondrial metabolism. Aberrant protein S-nitrosylation and transnitrosylation (transfer of nitric oxide [NO]-related species from one protein to another) trigger protein aggregation, neuronal bioenergetic compromise, and microglial phagocytosis, all of which contribute to the synapse loss that underlies cognitive decline in Alzheimer's disease and related dementias.

S-Nitrosylation of NOTCH1 Regulates Mesenchymal Stem Cells Differentiation Into Hepatocyte-Like Cells by Inhibiting Notch Signalling Pathway

The differentiation of mesenchymal stem cells (MSCs) into hepatocyte-like cells (HLCs) is considered one of the most promising strategies for alternative hepatocyte transplantation to treat end-stage liver disease. To advance this method, it is crucial to gain a deeper understanding of the mechanisms governing hepatogenic differentiation. The study demonstrated that suppression of the intracellular domain release of the Notch pathway receptor via the γ-secretase inhibitor N-[(3, 5-difluorophenyl)acetyl]-L-alanyl-2-phenylglycine-1, 1-dimethylethyl ester (DAPT) significantly promotes the expression of hepatocyte-related genes and proteins in HLCs. Increased expression of intracellular inducible NO synthase (iNOS) during differentiation led to elevated endogenous NO production. Biotin switch assays revealed a gradual increase in S-nitrosylation (SNO)-NOTCH1 and a decrease in overall NOTCH1 expression during hepatogenic differentiation. The addition of the exogenous NO donor S-nitrosoglutathione (GSNO) and the SNO inhibitor dithiothreitol (DTT) further demonstrated that the elevated expression of SNO-NOTCH1 promotes the differentiation of MSCs into mature hepatocytes. Briefly, our results fully demonstrated that the modification of the extracellular domain of NOTCH1 by NO, leading to the formation of SNO-NOTCH1, significantly promotes hepatogenic differentiation by inhibiting the Notch signalling pathway. Our study highlights the critical role of SNO-NOTCH1 in regulating the Notch signalling pathway and offers new insights into the mechanisms driving this differentiation process.

The hunt for transnitrosylase

The biochemical interplay between antioxidants and pro-oxidants maintains the redox homeostatic balance of the cell, which, when perturbed to moderate or high extents, has been implicated in the onset and/or progression of chronic diseases such as diabetes mellitus, cancer, and neurodegenerative diseases. Thioredoxin, glutaredoxin, and lipoic acid-like thiol oxidoreductase systems constitute a unique ensemble of robust cellular antioxidant defenses, owing to their indispensable roles as S-denitrosylases, S-deglutathionylases, and disulfide reductants in maintaining a reduced free thiol state with biological relevance. Thus, in cells subjected to nitrosative stress, cellular antioxidants will S-denitrosylate their cognate S-nitrosoprotein substrates, rather than participate in trans-S-nitrosylation via protein-protein interactions. Researchers have been at the forefront of vaguely establishing the concept of 'transnitrosylation' and its influence on pathophysiology with experimental evidence from in vitro studies that lack proper biochemical logic. The suggestive and reiterative use of antioxidants as transnitrosylases in the scientific literature leaves us on a cliffhanger with several open-ended questions that prompted us to 'hunt' for scientific logic behind the trans-S-nitrosylation chemistry. Given the gravity of the situation and to look at the bigger picture of 'trans-S-nitrosylation', we aim to present a novel attempt at justifying the hesitance in accepting antioxidants as capable of transnitrosylating their cognate protein partners and reflecting on the need to resolve the controversy that would be crucial from the perspective of understanding therapeutic outcomes involving such cellular antioxidants in disease pathogenesis. Further characterization is required to identify the regulatory mechanisms or conditions where an antioxidant like Trx, Grx, or DJ-1 can act as a cellular transnitrosylase.

The aging heart in focus: The advanced understanding of heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) accounts for 50 % of heart failure (HF) cases, making it the most common type of HF, and its prevalence continues to increase in the aging society. HFpEF is a systemic syndrome resulting from many risk factors, such as aging, metabolic syndrome, and hypertension, and its clinical features are highly heterogeneous in different populations. HFpEF syndrome involves the dysfunction of multiple organs, including the heart, lung, muscle, and vascular system. The heart shows dysfunction of various cells, including cardiomyocytes, endothelial cells, fibroblasts, adipocytes, and immune cells. The complex etiology and pathobiology limit experimental research on HFpEF in animal models, delaying a comprehensive understanding of the mechanisms and making treatment difficult. Recently, many scientists and cardiologists have attempted to improve the clinical outcomes of HFpEF. Recent advances in clinically related animal models and systemic pathology studies have improved our understanding of HFpEF, and clinical trials involving sodium-glucose cotransporter 2 inhibitors have significantly enhanced our confidence in treating HFpEF. This review provides an updated comprehensive discussion of the etiology and pathobiology, molecular and cellular mechanisms, preclinical animal models, and therapeutic trials in animals and patients to enhance our understanding of HFpEF and improve clinical outcomes.

Nitric Oxide Signaling and Regulation in the Cardiovascular System: Recent Advances

Nitric oxide (NO) from endothelial NO synthase importantly contributes to vascular homeostasis. Reduced NO production or increased scavenging during disease conditions with oxidative stress contribute to endothelial dysfunction and NO deficiency. In addition to the classical enzymatic NO synthases (NOS) system, NO can also be generated via the nitrate-nitrite-NO pathway. Dietary and pharmacological approaches aimed at increasing NO bioactivity, especially in the cardiovascular system, have been the focus of much research since the discovery of this small gaseous signaling molecule. Despite wide appreciation of the biological role of NOS/NO signaling, questions still remain about the chemical nature of NOS-derived bioactivity. Recent studies show that NO-like bioactivity can be efficiently transduced by mobile NO-ferroheme species, which can transfer between proteins, partition into a hydrophobic phase, and directly activate the soluble guanylyl cyclase-cGMP-protein kinase G pathway without intermediacy of free NO. Moreover, interaction between red blood cells and the endothelium in the regulation of vascular NO homeostasis have gained much attention, especially in conditions with cardiometabolic disease. In this review we discuss both classical and nonclassical pathways for NO generation in the cardiovascular system and how these can be modulated for therapeutic purposes. SIGNIFICANCE STATEMENT: After four decades of intensive research, questions persist about the transduction and control of nitric oxide (NO) synthase bioactivity. Here we discuss NO signaling in cardiovascular health and disease, highlighting new findings, such as the important role of red blood cells in cardiovascular NO homeostasis. Nonclassical signaling modes, like the nitrate-nitrite-NO pathway, and therapeutic opportunities related to the NO system are discussed. Existing and potential pharmacological treatments/strategies, as well as dietary components influencing NO generation and signaling are covered.

Impact of different hormones on the regulation of nitric oxide in diabetes

Polymetabolic syndrome achieved pandemic proportions and dramatically influenced public health systems functioning worldwide. Chronic vascular complications are the major contributors to increased morbidity, disability, and mortality rates in diabetes patients. Nitric oxide (NO) is among the most important vascular bed function regulators. However, NO homeostasis is significantly deranged in pathological conditions. Additionally, different hormones directly or indirectly affect NO production and activity and subsequently act on vascular physiology. In this paper, we summarize the recent literature data related to the effects of insulin, estradiol, insulin-like growth factor-1, ghrelin, angiotensin II and irisin on the NO regulation in physiological and diabetes circumstances.

Mitochondrial Hyperactivity and Reactive Oxygen Species Drive Innate Immunity to the Yellow Fever Virus-17D Live-Attenuated Vaccine

The yellow fever virus 17D (YFV-17D) live attenuated vaccine is considered one of the successful vaccines ever generated associated with high antiviral immunity, yet the signaling mechanisms that drive the response in infected cells are not understood. Here, we provide a molecular understanding of how metabolic stress and innate immune responses are linked to drive type I IFN expression in response to YFV-17D infection. Comparison of YFV-17D replication with its parental virus, YFV-Asibi, and a related dengue virus revealed that IFN expression requires RIG-I-like Receptor signaling through MAVS, as expected. However, YFV-17D uniquely induces mitochondrial respiration and major metabolic perturbations, including hyperactivation of electron transport to fuel ATP synthase. Mitochondrial hyperactivity generates reactive oxygen species (mROS) and peroxynitrite, blocking of which abrogated IFN expression in non-immune cells without reducing YFV-17D replication. Scavenging ROS in YFV-17D-infected human dendritic cells increased cell viability yet globally prevented expression of IFN signaling pathways. Thus, adaptation of YFV-17D for high growth uniquely imparts mitochondrial hyperactivity generating mROS and peroxynitrite as the critical messengers that convert a blunted IFN response into maximal activation of innate immunity essential for vaccine effectiveness.

Pathophysiological Relationship between Type 2 Diabetes Mellitus and Metabolic Dysfunction-Associated Steatotic Liver Disease: Novel Therapeutic Approaches

Type 2 diabetes mellitus (T2DM), often featuring hyperglycemia or insulin resistance, is a global health concern that is increasing in prevalence in the United States and worldwide. A common complication is metabolic dysfunction-associated steatotic liver disease (MASLD), the hepatic manifestation of metabolic syndrome that is also rapidly increasing in prevalence. The majority of patients with T2DM will experience MASLD, and likewise, individuals with MASLD are at an increased risk for developing T2DM. These two disorders may act synergistically, in part due to increased lipotoxicity and inflammation within the liver, among other causes. However, the pathophysiological mechanisms by which this occurs are unclear, as is how the improvement of one disorder can ameliorate the other. This review aims to discuss the pathogenic interactions between T2D and MASLD, and will highlight novel therapeutic targets and ongoing clinical trials for the treatment of these diseases.

Activation of hepatic acetyl-CoA carboxylase by S-nitrosylation in response to diet

Nitric oxide (NO), produced primarily by nitric oxide synthase enzymes, is known to influence energy metabolism by stimulating fat uptake and oxidation. The effects of NO on de novo lipogenesis (DNL), however, are less clear. Here we demonstrate that hepatic expression of endothelial nitric oxide synthase is reduced following prolonged administration of a hypercaloric high-fat diet. This results in marked reduction in the amount of S-nitrosylation of liver proteins including notably acetyl-CoA carboxylase (ACC), the rate-limiting enzyme in DNL. We further show that ACC S-nitrosylation markedly increases enzymatic activity. Diminished endothelial nitric oxide synthase expression and ACC S-nitrosylation may thus represent a physiological adaptation to caloric excess by constraining lipogenesis. Our findings demonstrate that S-nitrosylation of liver proteins is subject to dietary control and suggest that DNL is coupled to dietary and metabolic conditions through ACC S-nitrosylation.

'NO-how' enzymatic S-nitrosylation controls insulin pathophysiology

Whether S-nitrosylation is the result of an unselective chemical process or enzymatically driven has been debated for years. A recent study by Zhou et al. identifies and characterizes the first S-nitroso-CoA (SNO-CoA)-assisted nitrosylase (SCAN) that catalyzes protein S-nitrosylation in mammals, including insulin receptor (INSR)/insulin receptor substrate 1 (IRS1), with implications for human metabolism.

Enzymatic and non-enzymatic transnitrosylation: "SCAN"ning the SNO-proteome

In a recent study in Cell, Zhou et al.1 propose enzymatic transfer of nitric-oxide (NO)-related species from SNO-CoA to target proteins involved in insulin signaling; this function comprises an SNO-CoA-Assisted Nitrosylase (SCAN).