Sepiapterin reductase: Characteristics and role in diseases

A web portal for exploring kinase-substrate interactions

Interactions between protein kinases and their substrates are critical for the modulation of complex signaling pathways. Currently, there is a large amount of information available about kinases and their substrates in disparate public databases. However, these data are difficult to interpret in the context of cellular systems, which can be facilitated by examining interactions among multiple proteins at once, such as the network of interactions that constitute a signaling pathway. We present KiNet, a user-friendly web portal that integrates and shares information about kinase-substrate interactions from multiple databases of post-translational modifications. KiNet enables the visual exploration of these interactions in systems contexts, such as pathways, domain families, and custom protein set inputs, in an interactive fashion. We expect KiNet to be useful as a knowledge discovery tool for kinase-substrate interactions, and the aggregated KiNet dataset to be useful for protein kinase studies and systems-level analyses. The portal is available at https://kinet.kinametrix.com/ .

Diurnal gene expression patterns in retina and choroid distinguish myopia progression from myopia onset

The world-wide prevalence of myopia (nearsightedness) is increasing, but its pathogenesis is incompletely understood. Among many putative mechanisms, laboratory and clinical findings have implicated circadian biology in the etiology of myopia. Consistent with a circadian hypothesis, we recently reported a marked variability in diurnal patterns of gene expression in two crucial tissues controlling post-natal refractive development - the retina and choroid-at the onset of form-deprivation myopia in chick, a widely studied and validated model. To extend these observations, we assayed gene expression by RNA-Seq in retina and choroid during the progression of established unilateral form-deprivation myopia of chick. We assayed gene expression every 4 hours during a single day from myopic and contralateral control eyes. Retinal and choroidal gene expression in myopic vs. control eyes during myopia progression differed strikingly at discrete times during the day. Very few differentially expressed genes occurred at more than one time in either tissue during progressing myopia. Similarly, Gene Set Enrichment Analysis pathways varied markedly by time during the day. Some of the differentially expressed genes in progressing myopia coincided with candidate genes for human myopia, but only partially corresponded with genes previously identified at myopia onset. Considering other laboratory findings and human genetics and epidemiology, these results further link circadian biology to the pathogenesis of myopia; but they also point to important mechanistic differences between the onset of myopia and the progression of established myopia. Future laboratory and clinical investigations should systematically incorporate circadian mechanisms in studying the etiology of myopia and in seeking more effective treatments to normalize eye growth in children.

Dopamine synthesis and transport: current and novel therapeutics for parkinsonisms

Parkinsonism is the primary type of movement disorder in adults, encompassing a set of clinical symptoms, including rigidity, tremors, dystonia, bradykinesia, and postural instability. These symptoms are primarily caused by a deficiency in dopamine (DA), an essential neurotransmitter in the brain. Currently, the DA precursor levodopa (synthetic L-DOPA) is the standard medication to treat DA deficiency, but it only addresses symptoms rather than provides a cure. In this review, we provide an overview of disorders associated with DA dysregulation and deficiency, particularly Parkinson's disease and rare inherited disorders leading predominantly to dystonia and/or parkinsonism, even in childhood. Although levodopa is relatively effective for the management of motor dysfunctions, it is less effective for severe forms of parkinsonism and is also associated with side effects and a loss of efficacy over time. We present ongoing efforts to reinforce the effect of levodopa and to develop innovative therapies that target the underlying pathogenic mechanisms affecting DA synthesis and transport, increasing neurotransmission through disease-modifying approaches, such as cell-based therapies, nucleic acid- and protein-based biologics, and small molecules.

Comprehensive Urinary Proteome Profiling Analysis Identifies Diagnosis and Relapse Surveillance Biomarkers for Bladder Cancer

Bladder cancer (BCa) is the predominant malignancy of the urinary system. Herein, a comprehensive urine proteomic feature was initially established for the noninvasive diagnosis and recurrence monitoring of bladder cancer. 279 cases (63 primary BCa, 87 nontumor controls (NT), 73 relapsed BCa (BCR), and 56 nonrelapsed BCa (BCNR)) were collected to screen urinary protein biomarkers. 4761 and 3668 proteins were qualified and quantified by DDA and sequential window acquisition of all theoretical mass spectra (SWATH-MS) analysis in two discovery sets, respectively. Upregulated proteins were validated by multiple reaction monitoring (MRM) in two independent combined sets. Using the multi-support vector machine-recursive feature elimination (mSVM-RFE) algorithm, a model comprising 13 proteins exhibited good performance between BCa and NT with an AUC of 0.821 (95% CI: 0.675-0.967), 90.9% sensitivity (95% CI: 72.7-100%), and 73.3% specificity (95% CI: 53.3-93.3%) in the diagnosis test set. Meanwhile, an 11-marker classifier significantly distinguished BCR from BCNR with 75.0% sensitivity (95% CI: 50.0-100%), 81.8% specificity (95% CI: 54.5-100%), and an AUC of 0.784 (95% CI: 0.609-0.959) in the test cohort for relapse surveillance. Notably, six proteins (SPR, AK1, CD2AP, ADGRF1, GMPS, and C8A) of 24 markers were newly reported. This paper reveals novel urinary protein biomarkers for BCa and offers new theoretical insights into the pathogenesis of bladder cancer (data identifier PXD044896).

Sepiapterin Reductase Deficiency Misdiagnosed as Neurological Sequelae of Meningitis

Introduction

Sepiapterin reductase deficiency (SRD) is an exceedingly rare neurotransmitter disease caused by an enzyme error involved in the synthesis of tetrahydrobiopterin (BH4). It has been described in nearly 60 cases so far. The clinical manifestations include motor and speech delay, axial hypotonia, dystonia, weakness, oculogyric crises, diurnal fluctuation, and improvement of symptoms during sleep. Molecular genetic analysis can demonstrate pathogenic mutations in the SPR gene, allowing for a definitive diagnosis. Levodopa/carbidopa and 5-hydroxytryptophan are used for treatment.

Case Presentation

We present a 19-year-old male patient who was evaluated for dysarthria, axial hypotonia, limb dystonia, and movement disorder. The parents described the current patient's history with febrile seizures since 9 months of age, as well as speech and neuromotor developmental retardation, which indicated that the disease began in infancy. The basal metabolic work-up was normal except for hyperprolactinemia. The definitive diagnosis of SRD was confirmed by whole exome sequencing (WES) analysis, which revealed a homozygous pathogenic mutation c.655C>T (p.Arg219*) (rs779204655) in the SPR gene. After treatment, we noted significant improvements in dystonia, axial hypotonia, and dysarthria.

Conclusion

WES analysis offers a more expeditious and dependable method for diagnosing difficult cases exhibiting neurodevelopmental problems and thus renders the possibilities of early management.

Saccharomyces cerevisiae NRE1 and IRC24 Encode Paralogous Benzil Oxidoreductases

Irc24p is a benzil oxidoreductase encoded on chromosome IX of Saccharomyces cerevisiae . We identified a putative paralog, Nre1p, encoded 284 bp downstream. Both proteins are small, cytoplasmic, and are 52% identical (70% similar). PANTHER and PFAM analysis of the amino acid sequences and rigid pairwise structure alignment predicted a conserved active site and Rossmann folds in both, implicating NADH or NADPH as likely cofactors. We purified hexahistidine-tagged Irc24p and Nre1p. Both proteins catalyze the reduction of the diketone benzil with similar kinetics and a preference for NADPH. This is the first demonstration of in vitro function for Nre1p.

Cimifugin suppresses type 2 airway inflammation by binding to SPR and regulating its protein expression in a non-enzymatic manner

BACKGROUND

Cimifugin is one of the main bioactive components of Yu-Ping-Feng-San, a well-known traditional Chinese medicine, which can effectively relieve Allergic asthma (AA) and atopic dermatitis and reduce recurrence in clinic. However, the underlying mechanism of cimifugin on AA is still unknown.

PURPOSE

In the present study, we aimed to investigate the effect and mechanism of cimifugin on AA.

STUDY DESIGN

In vivo and in vitro experimental studies were performed.

METHODS

The effect of cimifugin on AA was demonstrated in vivo and in vitro. Sepiapterin reductase (SPR) was predicted as the most potent target of cimifugin in treating AA by reverse docking. Molecular docking and microscale thermophoresis (MST) were used to analyze the direct binding between cimifugin and SPR. Overexpression and interference of SPR were performed to verify whether targeting SPR is a key step of cimifugin in the treatment of AA. QM385, an inhibitor of SPR, was administrated in vivo and in vitro to evaluate the role of SPR in AA. Further, HPLC and cell-free direct hSPR enzyme activity assay were performed to research whether cimifugin regulated SPR by influencing the enzyme activity. Simultaneously, the inhibitors of protein degradation were used in vitro to explore the mechanism of cimifugin on SPR.

RESULTS

We found cimifugin effectively alleviated AA by reducing airway hyperresponsiveness, inhibiting type 2 cytokines-mediated airway inflammation, and restoring the expression of epithelial barrier proteins. Molecular docking predicted the direct binding ability of cimifugin to SPR, which was further verified by MST. Notably, the therapeutic effect of cimifugin on AA was dampened with SPR interfering, in contrast, the phenotypic features of AA were significantly alleviated with QM385 application both in vivo and in vitro. Interestingly, cimifugin showed no effect on the enzyme activity of SPR, as the level of its substrate sepiapterin was not affected with cimifugin treatment by cell-free enzyme activity assay. Furthermore, we found cimifugin could reduce SPR protein expression without affecting its mRNA expression probably through autophagosome pathway.

CONCLUSIONS

To our knowledge, we're reporting for the first time that cimifugin can suppresses type 2 airway inflammation to alleviate AA by directly binding to SPR and regulating its protein expression in a non-enzymatic manner.

Insights into Molecular Structure of Pterins Suitable for Biomedical Applications

Pterins are an inseparable part of living organisms. Pterins participate in metabolic reactions mostly as tetrahydropterins. Dihydropterins are usually intermediates of these reactions, whereas oxidized pterins can be biomarkers of diseases. In this review, we analyze the available data on the quantum chemistry of unconjugated pterins as well as their photonics. This gives a comprehensive overview about the electronic structure of pterins and offers some benefits for biomedicine applications: (1) one can affect the enzymatic reactions of aromatic amino acid hydroxylases, NO synthases, and alkylglycerol monooxygenase through UV irradiation of H₄pterins since UV provokes electron donor reactions of H₄pterins; (2) the emission properties of H₂pterins and oxidized pterins can be used in fluorescence diagnostics; (3) two-photon absorption (TPA) should be used in such pterin-related infrared therapy because single-photon absorption in the UV range is inefficient and scatters in vivo; (4) one can affect pathogen organisms through TPA excitation of H₄pterin cofactors, such as the molybdenum cofactor, leading to its detachment from proteins and subsequent oxidation; (5) metal nanostructures can be used for the UV-vis, fluorescence, and Raman spectroscopy detection of pterin biomarkers. Therefore, we investigated both the biochemistry and physical chemistry of pterins and suggested some potential prospects for pterin-related biomedicine.

WSV056 Inhibits Shrimp Nitric Oxide Synthase Activity by Downregulating Litopenaeus vannamei Sepiapterin Reductase to Promote White Spot Syndrome Virus Replication

Sepiapterin reductase (Spr) plays an essential role in the biosynthesis of tetrahydrobiopterin (BH4), a key cofactor of multiple enzymes involved in various physiological and immune processes. Suppression of Spr could result in BH4 deficiency-caused diseases in human and murine models. However, information on the biological function of Spr in invertebrates is limited. In this study, two Sprs (CG12116 and Sptr) from Drosophila melanogaster were found to be downregulated in transgenic flies overexpressing white spot syndrome virus (WSSV) immediate-early protein WSV056. CG12116 and Sptr exerted an inhibitory effect on the replication of the Drosophila C virus. A Litopenaeus vannamei Spr (LvSpr) exhibiting similarity of 64.1–67.5% and 57.3–62.2% to that of invertebrate and vertebrate Sprs, respectively, were cloned. L. vannamei challenged with WSSV revealed a significant decrease in LvSpr transcription and Spr activity in hemocytes. In addition, the BH4 co-factored nitric oxide synthase (Nos) activity in shrimp hemocytes was reduced in WSSV-infected and LvSpr knockdown shrimp, suggesting WSSV probably inhibits the LvNos activity through LvSpr downregulation to limit the production of nitric oxide (NO). Knockdown of LvSpr and LvNos caused the reduction in NO level in hemocytes and the increase of viral copy numbers in WSSV-infected shrimp. Supplementation of NO donor DETA/NO or double gene knockdown of WSV056 + LvSpr and WSV056 + LvNos recovered the NO production, whereas the WSSV copy numbers were decreased. Altogether, the findings demonstrated that LvSpr and LvNos could potentially inhibit WSSV. In turn, the virus has evolved to attenuate NO production via LvSpr suppression by WSV056, allowing evasion of host antiviral response to ensure efficient replication.

The Critical Role of Tetrahydrobiopterin (BH4) Metabolism in Modulating Radiosensitivity: BH4/NOS Axis as an Angel or a Devil

Ionizing radiation and radioactive materials have been widely used in industry, medicine, science and military. The efficacy of radiotherapy and adverse effects of normal tissues are closed related to cellular radiosensitivity. Molecular mechanisms underlying radiosensitivity are of significance to tumor cell radiosensitization as well as normal tissue radioprotection. 5,6,7,8-Tetrahydrobiopterin (BH4) is an essential cofactor for nitric oxide synthases (NOS) and aromatic amino acid hydroxylases, and its biosynthesis involves de novo biosynthesis and a pterin salvage pathway. In this review we overview the role of BH4 metabolism in modulating radiosensitivity. BH4 homeostasis determines the role of NOS, affecting the production of nitric oxide (NO) and oxygen free radicals. Under conditions of oxidative stress, such as UV-radiation and ionizing radiation, BH4 availability is diminished due to its oxidation, which subsequently leads to NOS uncoupling and generation of highly oxidative free radicals. On the other hand, BH4/NOS axis facilitates vascular normalization, a process by which antiangiogenic therapy corrects structural and functional flaws of tumor blood vessels, which enhances radiotherapy efficacy. Therefore, BH4/NOS axis may serve as an angel or a devil in regulating cellular radiosensitivity. Finally, we will address future perspectives, not only from the standpoint of perceived advances in treatment, but also from the potential mechanisms. These advances have demonstrated that it is possible to modulate cellular radiosensitivity through BH4 metabolism.

Metastatic Melanoma Progression Is Associated with Endothelial Nitric Oxide Synthase Uncoupling Induced by Loss of eNOS:BH4 Stoichiometry

Melanoma is the most aggressive type of skin cancer due to its high capability of developing metastasis and acquiring chemoresistance. Altered redox homeostasis induced by increased reactive oxygen species is associated with melanomagenesis through modulation of redox signaling pathways. Dysfunctional endothelial nitric oxide synthase (eNOS) produces superoxide anion (O2-•) and contributes to the establishment of a pro-oxidant environment in melanoma. Although decreased tetrahydrobiopterin (BH4) bioavailability is associated with eNOS uncoupling in endothelial and human melanoma cells, in the present work we show that eNOS uncoupling in metastatic melanoma cells expressing the genes from de novo biopterin synthesis pathway Gch1, Pts, and Spr, and high BH4 concentration and BH4:BH2 ratio. Western blot analysis showed increased expression of Nos3, altering the stoichiometry balance between eNOS and BH4, contributing to NOS uncoupling. Both treatment with L-sepiapterin and eNOS downregulation induced increased nitric oxide (NO) and decreased O2• levels, triggering NOS coupling and reducing cell growth and resistance to anoikis and dacarbazine chemotherapy. Moreover, restoration of eNOS activity impaired tumor growth in vivo. Finally, NOS3 expression was found to be increased in human metastatic melanoma samples compared with the primary site. eNOS dysfunction may be an important mechanism supporting metastatic melanoma growth and hence a potential target for therapy.

Novel Approaches, Drug Candidates, and Targets in Pain Drug Discovery

Because of the problems associated with opioids, drug discovery efforts have been employed to develop opioids with reduced side effects using approaches such as biased opioid agonism, multifunctional opioids, and allosteric modulation of opioid receptors. Receptor targets such as adrenergic, cannabinoid, P2X3 and P2X7, NMDA, serotonin, and sigma, as well as ion channels like the voltage-gated sodium channels Nav1.7 and Nav1.8 have been targeted to develop novel analgesics. Several enzymes, such as soluble epoxide hydrolase, sepiapterin reductase, and MAGL/FAAH, have also been targeted to develop novel analgesics. In this review, old and recent targets involved in pain signaling and compounds acting at these targets are summarized. In addition, strategies employed to reduce side effects, increase potency, and efficacy of opioids are also elaborated. This review should aid in propelling drug discovery efforts to discover novel analgesics.

Sepiapterin reductase: Characteristics and role in diseases

Sepiapterin reductase, a homodimer composed of two subunits, plays an important role in the biosynthesis of tetrahydrobiopterin. Furthermore, sepiapterin reductase exhibits a wide distribution in different tissues and is associated with many diseases, including brain dysfunction, chronic pain, cardiovascular disease and cancer. With regard to drugs targeting sepiapterin reductase, many compounds have been identified and provide potential methods to treat various diseases. However, the underlying mechanism of sepiapterin reductase in many biological processes is unclear. Therefore, this article summarized the structure, distribution and function of sepiapterin reductase, as well as the relationship between sepiapterin reductase and different diseases, with the aim of finding evidence to guide further studies on the molecular mechanisms and the potential clinical value of sepiapterin reductase. In particular, the different effects induced by the depletion of sepiapterin reductase or the inhibition of the enzyme suggest that the non-enzymatic activity of sepiapterin reductase could function in certain biological processes, which also provides a possible direction for sepiapterin reductase research.