Search

The gyrate atrophy of the choroid and retina (GACR) is a rare genetic disease for which no definitive cure is available. GACR is due to the deficit of ornithine aminotransferase (hOAT), a pyridoxal 5′-phosphate-dependent enzyme responsible for ornithine catabolism. The hallmark of the disease is plasmatic ornithine accumulation, which damages retinal epithelium leading to progressive vision loss and blindness within the fifth decade. Here, we characterized the biochemical properties of tetrameric and dimeric hOAT and evaluated hOAT loaded in red blood cells (RBCs) as a possible enzyme replacement therapy (ERT) for GACR. Our results show that (i) hOAT has a relatively wide specificity for amino acceptors, with pyruvate being the most suitable candidate for ornithine catabolism within RBCs; (ii) both the tetrameric and dimeric enzyme can be loaded in RBC retaining their activity; and (iii) hOAT displays reduced stability in plasma, but is partly protected from inactivation upon incubation in a mixture mimicking the intracellular erythrocyte environment. Preliminary ex vivo experiments indicate that hOAT-loaded RBCs are able to metabolize extracellular ornithine at a concentration mimicking that found in patients, both in buffer and, although with lower efficiency, in plasma. Overall, our data provide a proof of concept that an RBC-mediated ERT is feasible and can be exploited as a new therapeutic approach in GACR. [ABSTRACT FROM AUTHOR]

The role of protein modifications and amino acid metabolism in the dormancy breaking of pistachio (Pistacia vera L.) kernels during moist chilling (5 ºC) and warm stratification (25 ºC) were studied. Cold-stratified kernels showed germination up to 97%, while warm-stratified ones had low germination (40%). Increased protein solubility at neutral pH was accompanied by protein carbonylation in both cotyledons and embryonic axes during cold treatment, whereas these values decreased under warm incubation. Amino acid accumulation occurred in both tissues of cold- and warm-stratified kernels. Arginase activity increased in both tissues of cold-stratified kernels but significantly declined during warm treatment. While arginine decarboxylase activity of both organs increased under cold and warm stratification of pistachio kernels, ornithine aminotransferase activity declined during these periods. These results show that increased protein solubility and its carbonylation during cold stratification may induce the protein mobilization and accumulation of amino acids for their subsequent direction to the proper metabolic pathways. In this way, protein modification and arginine metabolism by arginase can be considered germination-specific events during cold stratification of kernels. [ABSTRACT FROM AUTHOR]

The article discusses the metabolism of proline, a compound that accumulates in plants during abiotic stress to protect cellular structure and function. The difference between proline synthesis and catabolism depends on how the intermediate compound, Δ1-pyrroline-5-carboxylate (P5C), is metabolized. The study provides evidence that key enzymes involved in P5C metabolism in the mitochondria interact with each other, potentially forming enzyme complexes to facilitate metabolic channelling of P5C. This discovery has implications for understanding how proline catabolism contributes to cellular activity and reactive oxygen species production. The article also highlights the wide range of physiological responses that proline metabolism is involved in, including osmotic regulation, respiratory substrate, and programmed cell death. The authors suggest that plants have the ability to switch between different states of proline catabolism to respond to different environmental stimuli. The study also raises questions about the existence of a P5C cycle and the role of post-translational modifications and protein interactions in controlling proline metabolic enzymes. Overall, the research contributes to a better understanding of proline metabolism and its regulation in plants. [Extracted from the article]

Purpose: Gyrate atrophy of the choroid and retina (GACR) is a rare congenital disorder and mutations in the ornithine aminotransferase (OAT) gene has been specified as the underlying cause. Patients show a high level of ornithine in body fluids which may be controlled by low protein diets. Pyridoxine (vitamin B6) supplementation may also be effective, however, most patients appear to be nonresponsive to this modality of treatment. Case Report: Here, we report a characterized case of a vitamin B6-responsive GACR who had a splicing mutation in the OAT gene. The GACR diagnosis was confirmed through the clinical features, imaging, biochemical findings, and whole-exome sequencing (WES) results. WES data revealed the splicing mutation in intron 4 of the OAT gene (NM_001322967: c.425-1G>A). Conclusion: Our knowledge about the diagnosis and treatment of GACR can be improved by identifying novel mutations in the OAT gene and accurate follow-up of the patients to determine how they respond to treatment. [ABSTRACT FROM AUTHOR]

Abstract Gyrate atrophy of choroid and retina (GACR) is a chorioretinal degeneration caused by pathogenic variants in the gene encoding ornithine aminotransferase (OAT), an enzyme mainly expressed in liver. Affected patients have increased ornithine concentrations in blood and other body fluids and develop progressive constriction of vision fields leading to blindness. Current therapies are unsatisfactory and better treatments are highly needed. In two mouse models of OAT deficiency that recapitulates biochemical and retinal changes of GACR, we investigated the efficacy of an intravenously injected serotype 8 adeno‐associated (AAV8) vector expressing OAT under the control of a hepatocyte‐specific promoter. Following injections, OAT‐deficient mice showed reductions of ornithine concentrations in blood and eye cups compared with control mice injected with a vector expressing green fluorescent protein. AAV‐injected mice showed improved electroretinogram response and partial restoration of retinal structure up to one‐year post‐injection. In summary, hepatic OAT expression by AAV8 vector was effective at correction of hyperornithinemia and improved function and structure of the retina. In conclusion, this study provides proof‐of‐concept of efficacy of liver‐directed AAV‐mediated gene therapy of GACR.

Gyrate atrophy of choroid and retina (GACR) is a chorioretinal degeneration caused by pathogenic variants in the gene encoding ornithine aminotransferase (OAT), an enzyme mainly expressed in liver. Affected patients have increased ornithine concentrations in blood and other body fluids and develop progressive constriction of vision fields leading to blindness. Current therapies are unsatisfactory and better treatments are highly needed. In two mouse models of OAT deficiency that recapitulates biochemical and retinal changes of GACR, we investigated the efficacy of an intravenously injected serotype 8 adeno‐associated (AAV8) vector expressing OAT under the control of a hepatocyte‐specific promoter. Following injections, OAT‐deficient mice showed reductions of ornithine concentrations in blood and eye cups compared with control mice injected with a vector expressing green fluorescent protein. AAV‐injected mice showed improved electroretinogram response and partial restoration of retinal structure up to one‐year post‐injection. In summary, hepatic OAT expression by AAV8 vector was effective at correction of hyperornithinemia and improved function and structure of the retina. In conclusion, this study provides proof‐of‐concept of efficacy of liver‐directed AAV‐mediated gene therapy of GACR. Synopsis: Deficiency of ornithine aminotransferase (OAT) results in increased plasma ornithine concentrations and retinal toxicity, especially in the retinal pigment epithelium (RPE). This study investigated liver‐directed gene transfer for OAT deficiency. Intravenous injections of AAV8 vector delivering OAT gene to hepatocytes reduced ornithine concentrations in plasma and eye.The treatment improved function and structure of the retina. [ABSTRACT FROM AUTHOR]

Deficit of human ornithine aminotransferase (hOAT), a mitochondrial tetrameric pyridoxal-5′-phosphate (PLP) enzyme, leads to gyrate atrophy of the choroid and retina (GA). Although 70 pathogenic mutations have been identified, only few enzymatic phenotypes are known. Here, we report biochemical and bioinformatic analyses of the G51D, G121D, R154L, Y158S, T181M, and P199Q pathogenic variants involving residues located at the monomer–monomer interface. All mutations cause a shift toward a dimeric structure, and changes in tertiary structure, thermal stability, and PLP microenvironment. The impact on these features is less pronounced for the mutations of Gly51 and Gly121 mapping to the N-terminal segment of the enzyme than those of Arg154, Tyr158, Thr181, and Pro199 belonging to the large domain. These data, together with the predicted ΔΔG values of monomer–monomer binding for the variants, suggest that the proper monomer–monomer interactions seem to be correlated with the thermal stability, the PLP binding site and the tetrameric structure of hOAT. The different impact of these mutations on the catalytic activity was also reported and discussed on the basis of the computational information. Together, these results allow the identification of the molecular defects of these variants, thus extending the knowledge of enzymatic phenotypes of GA patients. [ABSTRACT FROM AUTHOR]

AIM: To investigate the pathogenic mutations of the OAT gene in a Chinese family affected with gyrate atrophy of choroid and retina(GA)and describe their clinical manifestations.METHODS: All available family members have underwent detailed ophthalmological examinations. The sequencing results and pathogenic mutations were clarified by whole exome sequencing, bioinformatics analysis and Sanger sequencing.RESULTS: Based on the clinical manifestations and symptoms, the proband was diagnosed with GA. A missense mutation of c.722C>T(p.P241L)in exon 6 and a nonsense mutation of c.1186C>T(p.R396X)in exon 10 were identified in the OAT gene of the proband, which was a compound heterozygotic mutation. This compound heterozygous mutation showed co-segregation in the family. The heterozygous pathogenic variant of p.R396X was detected in both the proband's father and elder brother, and the heterozygous pathogenic variant of p.P241L was detected in proband's mother. Except for the proband, no other family members have abnormal clinical manifestations.CONCLUSION: The proband of this family is a compound heterozygous mutation, in which p.P241L is the first reported gene mutation type. This result expands the range of OAT gene variation and is conducive to further understanding the pathogenic factors of GA at the molecular basis level. The discovery and confirmation of the novel mutation type will also help to provide a new basis for the clinical diagnosis and gene therapy of GA.

Ornithine aminotransferase (OAT) catalyzes transfer of the delta-amino group from L-ornithine to oxo-glutarate. In plants, this reaction biochemically connects urea cycle, proline cycle, and polyamine biosynthesis pathway. OAT activity is shown to be associated with biotic and abiotic stress responses and nitrogen metabolism, but its physiological role is still unclear. In our study, we decided to investigate transcriptional regulation of the OAT gene in Arabidopsis thaliana under normal conditions and in response to various growth regulators. In the present work, the reporter gene construct containing the Escherichia coli β-glucuronidase gene (gus) under control of the A. thaliana OAT gene promoter was introduced into the genome of A. thaliana ecotype Columbia plants using the floral dip method; GUS activity was assayed in different experimental conditions including hormone treatment, low and high nitrogen and salinity. The GUS activity was analyzed histochemically. Plants were incubated with staining solution containing X-Gluc. We show that under standard growth conditions, the promoter is active during germination and in developing floral organs. OAT promoter activity specifically activates in response to different forms of auxin (IAA, NAA, and 2,4D), cytokinin (6- BAP), ethylene precursor (ACC), high nitrogen and salinity. Analysis of the OAT expression by qRT-PCR confirmed the pattern observed using the GUS reporter system. The OAT gene showed a significantly elevated expression in fourday- old seedlings and in plant roots in response to auxins and cytokinins. The analysis of the OAT promoter structure reveals cis-acting regulatory DNA elements associated with auxin regulation and abiotic stresses. The results of the study indicate that the OAT gene is involved in developmental processes and is regulated by auxin and cytokinins.

Gyrate atrophy of the choroid and retina (GACR) is caused by pathogenic biallelic variants in the gene encoding ornithine-δ-aminotransferase (OAT), and is characterized by progressive vision loss leading to blindness. OAT is a pyridoxal-5′-phosphate (PLP) dependent enzyme that is mainly involved in ornithine catabolism, and patients with a deficiency develop profound hyperornithinemia. Therapy is aimed at lowering ornithine levels through dietary arginine restriction and, in some cases, through enhancement of OAT activity via supraphysiological dosages of pyridoxine. In this study, we aimed to extend diagnostic practices in GACR by extensively characterizing the consequences of pathogenic variants on the enzymatic function of OAT, both at the level of the enzyme itself as well as the flux through the ornithine degradative pathway. In addition, we developed an in vitro pyridoxine responsiveness assay. We identified 14 different pathogenic variants, of which one variant was present in all patients of Dutch ancestry (p.(Gly353Asp)). In most patients the enzymatic activity of OAT as well as the rate of [14C]-ornithine flux was below the limit of quantification (LOQ). Apart from our positive control, only one patient cell line showed responsiveness to pyridoxine in vitro , which is in line with the reported in vivo pyridoxine responsiveness in this patient. None of the patients harboring the p.(Gly353Asp) substitution were responsive to pyridoxine in vivo or in vitro. In silico analysis and small-scale expression experiments showed that this variant causes a folding defect, leading to increased aggregation properties that could not be rescued by PLP. Using these results, we developed a diagnostic pipeline for new patients suspected of having GACR. Adding OAT enzymatic analyses and in vitro pyridoxine responsiveness to diagnostic practices will not only increase knowledge on the consequences of pathogenic variants in OAT , but will also enable expectation management for therapeutic modalities, thus eventually improving clinical care. • We developed an in vitro pyridoxine responsiveness assay in fibroblasts of patients with GACR. • We identified a prevalent variant within the Dutch GACR cohort, p.(Gly353Asp). • We developed a new diagnostic laboratory pipeline to extend diagnostic practices in GACR. [ABSTRACT FROM AUTHOR]

The gut microbiota and diet-induced changes in microbiome composition have been linked to various liver diseases, although the specific microbes and mechanisms remain understudied. Alcohol-related liver disease (ALD) is one such disease with limited therapeutic options due to its complex pathogenesis. We demonstrate that a diet rich in soluble dietary fiber increases the abundance of Bacteroides acidifaciens (B. acidifaciens) and alleviates alcohol-induced liver injury in mice. B. acidifaciens treatment alone ameliorates liver injury through a bile salt hydrolase that generates unconjugated bile acids to activate intestinal farnesoid X receptor (FXR) and its downstream target, fibroblast growth factor-15 (FGF15). FGF15 promotes hepatocyte expression of ornithine aminotransferase (OAT), which facilitates the metabolism of accumulated ornithine in the liver into glutamate, thereby providing sufficient glutamate for ammonia detoxification via the glutamine synthesis pathway. Collectively, these findings uncover a potential therapeutic strategy for ALD involving dietary fiber supplementation and B. acidifaciens. [Display omitted] • Soluble dietary fiber improves ALD in mice by remodeling gut microbiota composition • Bacteroides acidifaciens restores the expression level of OAT after alcohol intake • OAT promotes ammonia detoxification in the liver and reduces hepatocytes damage • Bile salt hydrolase regulates OAT expression by activating intestinal FXR The effects of dietary fiber intake on ALD and the underlying mechanisms remain unclear. Shen and colleagues report that soluble dietary fiber increases Bacteroides acidifaciens in the gut of alcohol-fed mice. B. acidifaciens generates bile acids that upregulate OAT expression via the intestinal FXR, thus enhancing the ammonia detoxification of hepatocytes. [ABSTRACT FROM AUTHOR]

Ornithine δ-aminotransferase (Orn-AT) activity was detected for the enzyme annotated as a γ-aminobutyrate aminotransferase encoded by PH1423 gene from Pyrococcus horikoshii OT-3. Crystal structures of this novel archaeal ω-aminotransferase were determined for the enzyme in complex with pyridoxal 5′-phosphate (PLP), in complex with PLP and l -ornithine (l -Orn), and in complex with N -(5′-phosphopyridoxyl)- l -glutamate (PLP- l -Glu). Although the sequence identity was relatively low (28%), the main-chain coordinates of P. horikoshii Orn-AT monomer showed notable similarity to those of human Orn-AT. However, the residues recognizing the α-amino group of l -Orn differ between the two enzymes. In human Orn-AT, Tyr55 and Tyr85 recognize the α-amino group, whereas the side chains of Thr92* and Asp93*, which arise from a loop in the neighboring subunit, form hydrogen bonds with the α-amino group of the substrate in P. horikoshii enzyme. Site-directed mutagenesis suggested that Asp93* plays critical roles in maintaining high affinity for the substrate. This study provides new insight into the substrate binding of a novel type of Orn-AT. Moreover, the structure of the enzyme with the reaction-intermediate analogue PLP- l -Glu bound provides the first structural evidence for the "Glu switch" mechanism in the dual substrate specificity of Orn-AT. • The crystal structures of a novel archaeal type of ornithine δ-aminotransferase were determined. • The substrate recognition residues of this enzyme are notably different from those of human ornithine δ-aminotransferase. • This study provides the first structural evidence for the "Glu switch" mechanism of ornithine δ-aminotransferase. [ABSTRACT FROM AUTHOR]

Abstract Background Ornithine aminotransferase (OAT, EC:2.6.1.13), alternatively known as ornithine delta aminotransferase (δOAT), is a pyridoxal phosphate (PLP)-dependent enzyme involved in the conversion of ornithine into glutamyl-5-semi-aldehyde (GSA) and vice versa. Up till now, there has been no study on OAT in wheat despite the success of its isolation from rice, maize, and sorghum. This study focuses on identification and molecular characterization of OAT in wheat. Results In total, three homeologous OAT genes in wheat genome were found on chromosome group 5, named as TaOAT-5AL, TaOAT-5BL, and TaOAT-5DL. Sequence alignment between gDNA and its corresponding cDNA obtained a total of ten exons and nine introns. A phylogenetic tree was constructed and results indicated that OATs shared highly conserved domains between monocots and eudicots, which was further illustrated by using WebLogo to generate a sequence logo. Further subcellular localization analysis indicated that they functioned in mitochondria. Protein-protein interactions supported their role in proline biosynthesis through interactions with genes, such as delta 1-pyrroline-5-carboxylate synthetase (P5CS) and pyrroline-5-carboxylate reductase (P5CR), involved in the proline metabolic pathway. Promoter analysis exposed the presence of several stress responsive elements, implying their involvement in stress regulation. Expression profiling illustrated that TaOAT was highly induced in the wheat plants exposed to drought or salt stress condition. Upregulated expression of TaOATs was observed in stamens and at the heading stage. A potential role of TaOAT genes during floret development was also revealed. Furthermore, the transgenic plants overexpressing TaOAT showed enhanced tolerance to drought stress by increasing proline accumulation. In addition, salt tolerance of the transgenic plants was also enhanced. Conclusion TaOATs genes were involved in proline synthesis and nitrogen remobilization because they interacted with genes related to proline biosynthesis enzymes and arginine catabolism. In addition, TaOAT genes had a role in abiotic stress tolerance and a potential role in floret development. The results of this study may propose future research in the improvement of wheat resistance to abiotic stresses.

Gyrate atrophy of the choroid and retina (GACR) is a rare inborn error of amino acid metabolism caused by bi-allelic variations in OAT. GACR is characterised by vision decline in early life eventually leading to complete blindness, and high plasma ornithine levels. There is no curative treatment for GACR, although several therapeutic modalities aim to slow progression of the disease by targeting different steps within the ornithine pathway. No international treatment protocol is available. We systematically collected all international literature on therapeutic interventions in GACR to provide an overview of published treatment effects. Following the PRISMA guidelines, we conducted a systematic review of the English literature until December 22nd 2020. PubMed and Embase databases were searched for studies related to therapeutic interventions in patients with GACR. A total of 33 studies (n = 107 patients) met the inclusion criteria. Most studies were designed as case reports (n = 27) or case series (n = 4). No randomised controlled trials or large cohort studies were found. Treatments applied were protein-restricted diets, pyridoxine supplementation, creatine or creatine precursor supplementation, l -lysine supplementation, and proline supplementation. Protein-restricted diets lowered ornithine levels ranging from 16.0–91.2%. Pyridoxine responsiveness was reported in 30% of included mutations. Lysine supplementation decreased ornithine levels with 21–34%. Quality assessment showed low to moderate quality of the articles. Based primarily on case reports ornithine levels can be reduced by using a protein restricted diet, pyridoxine supplementation (variation-dependent) and/or lysine supplementation. The lack of pre-defined clinical outcome measures and structural follow-up in all included studies impeded conclusions on clinical effectiveness. Future research should be aimed at 1) Unravelling the OAT biochemical pathway to identify other possible pathologic metabolites besides ornithine, 2) Pre-defining GACR specific clinical outcome measures, and 3) Establishing an international historical cohort. [ABSTRACT FROM AUTHOR]

To investigate the effect of herbicide Trifluralin and the role of magnetized water on enzymatic activities and content of proline and growth substances including gibberellin (GA3) and cytokinin (6- benzyl amino purine), an experiment was conducted using squash (Cucurbita pepo L. var. Shiraz Hybrid F1) seedlings. Four levels of trifluralin (0, 5, 15 and 25 ppm) and irrigation by distilled and magnetized water were applied in a completely randomized design in 3 replicates at Urmia University in 2016. Different levels of trifluralin were added to pots 2 days after planting. Seedlings were treated by modified Hoagland solution with diurnal temperature 30:18 °C, relative humidity of 70-80 percent and light period of 16:8 hr, during a 5-week growing period in growth chamber. The effect of magnetized water and trifluralin on ornithine amino-transferase (OAT), proline dehydrogenase (PDH) and content of proline in both shoots and roots as well as GA3 and cytokinin was significant (p>0.01) according to ANOVA. The content of proline and OAT in roots and shoots as well as GA3 and cytokinin increased significantly, although the PDH of roots and shoots decreased under the influence of magnetized water. The content of proline and OAT increased and GA3, cytokinin and the activity of PDH declined by the increase of the levels of trifluralin. Overall, it can be concluded that the growth and biochemical indices of squash plants were improved by magnetized water under toxicity of herbicide trifluralin.

The deficit of human ornithine aminotransferase (hOAT) is responsible for gyrate atrophy (GA), a rare recessive inherited disorder. Although more than 60 disease-associated mutations have been identified to date, the molecular mechanisms explaining how each mutation leads to the deficit of OAT are mostly unknown. To fill this gap, we considered six representative missense mutations present in homozygous patients concerning residues spread over the hOAT structure. E. coli expression, spectroscopic, kinetic and bioinformatic analyses, reveal that the R154L and G237D mutations induce a catalytic more than a folding defect, the Q90E and R271K mutations mainly impact folding efficiency, while the E318K and C394Y mutations give rise to both folding and catalytic defects. In a human cellular model of disease folding-defective variants, although at a different extent, display reduced protein levels and/or specific activity, due to increased aggregation and/or degradation propensity. The supplementation with Vitamin B6, to mimic a treatment strategy available for GA patients, does not significantly improve the expression/activity of folding-defective variants, in contrast with the clinical responsiveness of patients bearing the E318K mutation. Thus, we speculate that the action of vitamin B6 could be also independent of hOAT. Overall, these data represent a further effort toward a comprehensive analysis of GA pathogenesis at molecular and cellular level, with important relapses for the improvement of genotype/phenotype correlations and the development of novel treatments.

Key message: The drought and salt tolerances of wheat were enhanced by ectopic expression of the Arabidopsis ornithine aminotransferase (AtOAT) encoded gene. The OAT was confirmed to play a role in proline biosynthesis in wheat. Proline (Pro) accumulation is a common response to both abiotic and biotic stresses in plants. Ornithine aminotransferase (OAT) is pyridoxal-5-phosphate dependent enzyme involved in plant proline biosynthesis. During stress condition, proline is synthesized via glutamate and ornithine pathways. The OAT is the key enzyme in ornithine pathway. In this study, an OAT gene AtOAT from Arabidopsis was expressed in wheat for its functional characterization under drought, salinity, and heat stress conditions. We found that the expression of AtOAT enhanced the drought and salt stress tolerances of wheat by increasing the proline content and peroxidase activity. In addition, it was confirmed that the expression of AtOAT also played a partial tolerance to heat stress in the transgenic wheat plants. Moreover, quantitative real-time PCR (qRT-PCR) analysis showed that the transformation of AtOAT up-regulated the expression of the proline biosynthesis associated genes TaOAT, TaP5CS, and TaP5CR, and down-regulated that of the proline catabolism related gene TaP5CDH in the transgenic plants under stress conditions. Moreover, the genes involved in ornithine pathway (Orn-OAT-P5C/GSA-P5CR-Pro) were up-regulated along with the up-regulation of those genes involved in glutamate pathway (Glu-P5CS-P5C/GSA-P5CR-Pro). Therefore, we concluded that the expression of AtOAT enhanced wheat abiotic tolerance via modifying the proline biosynthesis by up-regulating the expression of the proline biosynthesis-associated genes and down-regulating that of the proline catabolic gene under stresses condition. [ABSTRACT FROM AUTHOR]

Copyright of Current Retina Journal / Güncel Retina Dergisi is the property of Anadolu Kitabevi Basim Yayim Medikal Turizm Kirtasiye Tic. Ltd. Sti. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: Gyrate atrophy of the choroid and retina (GA) is a rare autosomal recessive disorder characterized by nyctalopia, myopia, sharply demarcated expanding peripheral chorioretinal atrophic lesions, early cataract, progressive visual loss and hyperornithinemia. Only three cases of GA associated with rhegmatogenous retinal detachments (RRD) have been reported. The genotype-phenotype correlation of RRD in GA is limited by lack of genetic information in the previously reported cases. Here we report two young sisters with a characteristic GA phenotype associated with a novel variant in the ornithine aminotransferase gene (OAT), in whom one developed unilateral RRD at the age of 9 years. Materials and Methods: Retrospective report of two cases including genetic analysis and multimodal retinal imaging. Results: A 9-year-old Saudi girl presented with a funnel-shaped RRD, extensive proliferative vitreoretinopathy, peripheral choroidal detachment and neovascular glaucoma in her right eye. Fundus examination of her left eye showed an attached retina with sharply-demarcated peripheral chorioretinal atrophic patches suggestive of GA. Whole exome sequencing confirmed GA by revealing a homozygous c.980 C > G (p. Pro327Arg) variant in exon 8 of OAT. The RRD was inoperable. The chorioretinal lesions in the left eye enlarged slowly over 3 years of follow up. Examination of the proband's older sister revealed a similar but more advanced GA phenotype in both eyes. Conclusions: A characteristic GA phenotype associated with a novel variant in OAT is reported. This variant might be associated with childhood-onset RRD in the proband. [ABSTRACT FROM AUTHOR]

Background: Ornithine aminotransferase (OAT, EC:2.6.1.13), alternatively known as ornithine delta aminotransferase (δOAT), is a pyridoxal phosphate (PLP)-dependent enzyme involved in the conversion of ornithine into glutamyl-5-semi-aldehyde (GSA) and vice versa. Up till now, there has been no study on OAT in wheat despite the success of its isolation from rice, maize, and sorghum. This study focuses on identification and molecular characterization of OAT in wheat. Results: In total, three homeologous OAT genes in wheat genome were found on chromosome group 5, named as TaOAT-5AL, TaOAT-5BL, and TaOAT-5DL. Sequence alignment between gDNA and its corresponding cDNA obtained a total of ten exons and nine introns. A phylogenetic tree was constructed and results indicated that OATs shared highly conserved domains between monocots and eudicots, which was further illustrated by using WebLogo to generate a sequence logo. Further subcellular localization analysis indicated that they functioned in mitochondria. Protein-protein interactions supported their role in proline biosynthesis through interactions with genes, such as delta 1-pyrroline-5-carboxylate synthetase (P5CS) and pyrroline-5-carboxylate reductase (P5CR), involved in the proline metabolic pathway. Promoter analysis exposed the presence of several stress responsive elements, implying their involvement in stress regulation. Expression profiling illustrated that TaOAT was highly induced in the wheat plants exposed to drought or salt stress condition. Upregulated expression of TaOATs was observed in stamens and at the heading stage. A potential role of TaOAT genes during floret development was also revealed. Furthermore, the transgenic plants overexpressing TaOAT showed enhanced tolerance to drought stress by increasing proline accumulation. In addition, salt tolerance of the transgenic plants was also enhanced. Conclusion: TaOATs genes were involved in proline synthesis and nitrogen remobilization because they interacted with genes related to proline biosynthesis enzymes and arginine catabolism. In addition, TaOAT genes had a role in abiotic stress tolerance and a potential role in floret development. The results of this study may propose future research in the improvement of wheat resistance to abiotic stresses. [ABSTRACT FROM AUTHOR]

The incidence and mortality of lung cancer ranked the first among all types of cancer in China, and non‐small cell lung cancer (NSCLC) is the most common type of lung cancer accounting for 85% of all lung cancers. Given that the survival rate of patients with advanced NSCLC is still poor nowadays, identification of novel therapeutic targets and the development of effective therapies are desired for the treatment of NSCLC in clinics. In this study, we reported the upregulation of ornithine aminotransferase (OAT) in NSCLC cells and clinical tumor samples as well as its association with the advanced TNM stage, metastasis, and poor tumor differentiation of lung cancer. Using different NSCLC cell lines, we demonstrated that OAT promoted the proliferation, invasion, and migration, inhibited the apoptosis, and altered cell cycle of NSCLC cells; besides, the involvement of OAT‐miR‐21‐glycogen synthase kinase‐3β signaling in the functional role of OAT in NSCLC was also revealed. Importantly, in the absence of OAT, the growth and metastasis of tumor lung cancer xenograft was significantly suppressed in the nude mice. Based on our findings, OAT may be a potential novel biomarker for the diagnosis and therapeutic outcome monitoring of NSCLC. Inhibition of OAT may also represent a new therapeutic strategy of NSCLC. [ABSTRACT FROM AUTHOR]

Among the over 50 gyrate atrophy‐causing mutations of ornithine δ‐aminotransferase (OAT), the R180T involves an active site residue located at the dimer interface, which in the crystal structure of OAT complexed with 5‐fluoromethylornithine engages a salt bridge with the α‐carboxylate of the substrate analogue. Starting from the previous finding that no transaminase activity was detected in CHO‐K1 cells expressing the R180T variant, here we try to shed light at the protein level on the structural and/or functional defects of the R180T variant. To this aim, the variant has been cloned, expressed, purified and characterized by a combination of biochemical and structural studies. Although the R180T variant shares a similar overall conformation with the wild‐type, its crystal structure solved at 1.8 Ǻ reveals slight structural alterations at the active site and at the dimeric interface. These changes are consistent with the spectroscopic and kinetic results, indicating that the variant, as compared with the wild‐type OAT, shows (a) an increased Km value for l‐ornithine (l‐Orn), (b) an altered pyridoxal 5′‐phosphate binding mode and affinity and (c) an increased thermostability. In addition, the R180T mutant exhibits a remarkable loss of catalytic activity and is endowed with the ability to catalyse not only the δ‐transamination but also, albeit to a lesser extent, the α‐transamination of l‐Orn. Overall, these data indicate that the slight structural changes caused by the R180T mutation, preventing a proper collocation of l‐Orn at the active site of OAT, are responsible for the notable reduction of the catalytic efficiency. Enzymes: Ornithine aminotransferase EC 2.6.1.13. Databases: 6HX7.pdb. [ABSTRACT FROM AUTHOR]

Aim: The aim is to present the clinical course, diagnostics and treatment of six-year-old girl with gyrate atrophy and bilateral cystoid macular edema. Case report: Four-year old girl was found with low vision and convergent strabismus in a systematic medical examination. After two years of the amblyopia treatment bilateral macular edema was detected and the child was refered to The Department of Ophthalmology. She presented with the both eyes best corrected visual acuity 0.15, bilateral cystoid macular edema and peripheral, oval zones of chorioretinal atrophy. Antiedematous therapy was administered. Clinical work-up revealed extremely high plasma concentrations of ornithine and the diagnosis of gyrate atrophy (GA) of the chorioretina due to the lack of mitochondrial enzyme ornithine aminotransferase was established. The therapy with pyridoxine (vitamin B6) was started. This treatment led to slight reduction of serum ornithin concentrations; hence, low-protein diet was introduced, but decrease of ornithine concentrations was still insufficient. Therefore, the treatment with amino acid L-lysine was introduced in the therapy. Plasma ornithine concentrations successfully decreased to almost one third of the initial concentration. There was a transient decrease of cystoid macular edema, but atrophic lesions of the peripheral fundus progressed. Conclusion: Cystoid macular edema in patients with gyrate atrophy was followed by impaired visual acuity. Despite the intensive treatment macular edema persisted and further progression of atrophic lesion on the fundus periphery was detected. The maintenance of low plasma ornithine levels is an essential prerequisite for slowing the development of the disease and postponing the permanent loss of visual function. [ABSTRACT FROM AUTHOR]

Gyrus atrophy is a rare autosomal recessive hereditary disease secondary to a mutation of the OAT gene on chromosome 10 which results in a deficiency of the mitochondrial enzyme ornithine aminotransferase that causes a 20-fold increase in serum concentrations of the amino acid ornithine. The disease is characterized by atrophic choroid and retinal patches that begin in the peripheral retina in the first decade and later spread centrally to the macular area, causing cystic changes and posterior subcapsular cataracts. The clinical picture is characterized by night blindness, constriction of the visual field and finally decreased central vision and blindness. In this article, we present the case of a 53-year-old woman with no significant hereditary antecedents who presented a decrease in visual acuity after several months of evolution. [ABSTRACT FROM AUTHOR]

Abstract Gyrate atrophy (GA) is a rare recessive disorder characterized by progressive blindness, chorioretinal degeneration and systemic hyperornithinemia. GA is caused by point mutations in the gene encoding ornithine δ-aminotransferase (OAT), a tetrameric pyridoxal 5′-phosphate-dependent enzyme catalysing the transamination of l -ornithine and α-ketoglutarate to glutamic–γ-semialdehyde and l -glutamate in mitochondria. More than 50 OAT variants have been identified, but their molecular and cellular properties are mostly unknown. A subset of patients is responsive to pyridoxine administration, although the mechanisms underlying responsiveness have not been clarified. Herein, we studied the effects of the V332M mutation identified in pyridoxine-responsive patients. The Val332-to-Met substitution does not significantly affect the spectroscopic and kinetic properties of OAT, but during catalysis it makes the protein prone to convert into the apo-form, which undergoes unfolding and aggregation under physiological conditions. By using the CRISPR/Cas9 technology we generated a new cellular model of GA based on HEK293 cells knock-out for the OAT gene (HEK-OAT_KO). When overexpressed in HEK-OAT_KO cells, the V332M variant is present in an inactive apodimeric form, but partly shifts to the catalytically-competent holotetrameric form in the presence of exogenous PLP, thus explaining the responsiveness of these patients to pyridoxine administration. Overall, our data represent the first integrated molecular and cellular analysis of the effects of a pathogenic mutation in OAT. In addition, we validated a novel cellular model for the disease that could prove instrumental to define the molecular defect of other GA-causing variants, as well as their responsiveness to pyridoxine and other putative drugs. Graphical abstract Unlabelled Image Highlights • The molecular and cellular effects of most mutations in OAT leading to GA are unknown. • We found that the purified recombinant V332M variant shows a folding defect • The V332M variant converts into the apo-form during catalysis. • We generated a cellular model of GA, where the V332M variant is present in an inactive apoform. • PLP promotes holoenzyme formation, thus explaining pyridoxine responsiveness of the patients. [ABSTRACT FROM AUTHOR]

Background: Small cell lung cancer (SCLC) is highly aggressive and is associated with a dismal prognosis. However, there are no clinically recognized biomarkers for early diagnosis. In this study, we used quantitative proteomics to build differential mitochondrial protein profiles that may be used for early diagnosis and investigated the pathogenesis of lung cancer. Methods: We cultured SCLC cells (NCI‐H446) and normal human bronchial epithelial cells (16‐HBE); mitochondria were extracted and purified using differential and Percoll density gradient centrifugation. Subsequently, we used Western blot analysis to validate mitochondrial purity and labeled proteins/peptides from NCI‐H446 and 16‐HBE cells using relative and absolute quantification of ectopic tags. We then analyzed mixed samples and identified proteins using two‐dimensional liquid chromatography‐tandem mass spectrometry. Additionally, we performed subsequent bioinformatic proteome analyses using the programs ExPASy, GOA, and STRING. Finally, the relationship between ornithine aminotransferase expression and clinicopathological features in lung cancer patients was evaluated using immunohistochemistry. Results: One hundred and fifty‐three mitochondrial proteins were differentially expressed between 16‐HBE and NCI‐H446 cells. The expression of 30 proteins between 16‐HBE and NCI‐H446 cells increased more than 1.3‐fold. The upregulation of ornithine aminotransferase was associated with pathological grade and clinical tumor node metastasis stage. Conclusion: Our experiment represented a promising method for building differential mitochondrial protein profiles between NCI‐H446 and 16‐HBE cells. Such analysis may also help to identify novel biomarkers of lung cancer. [ABSTRACT FROM AUTHOR]

Toxoplasma gondii , an Apicomplexan parasite, causes significant morbidity and mortality, including severe disease in immunocompromised hosts and devastating congenital disease, with no effective treatment for the bradyzoite stage. To address this, we used the Tropical Disease Research database, crystallography, molecular modeling, and antisense to identify and characterize a range of potential therapeutic targets for toxoplasmosis. Phosphoglycerate mutase II (PGMII), nucleoside diphosphate kinase (NDK), ribulose phosphate 3-epimerase (RPE), ribose-5-phosphate isomerase (RPI), and ornithine aminotransferase (OAT) were structurally characterized. Crystallography revealed insights into the overall structure, protein oligomeric states and molecular details of active sites important for ligand recognition. Literature and molecular modeling suggested potential inhibitors and druggability. The targets were further studied with vivoPMO to interrupt enzyme synthesis, identifying the targets as potentially important to parasitic replication and, therefore, of therapeutic interest. Targeted vivoPMO resulted in statistically significant perturbation of parasite replication without concomitant host cell toxicity, consistent with a previous CRISPR/Cas9 screen showing PGM, RPE, and RPI contribute to parasite fitness. PGM, RPE, and RPI have the greatest promise for affecting replication in tachyzoites. These targets are shared between other medically important parasites and may have wider therapeutic potential. [ABSTRACT FROM AUTHOR]

Hyperammonemia is the common biochemical hallmark of urea cycle disorders, activating neurotoxic pathways. If untreated, affected individuals have a high risk of irreversible brain damage and mortality. Here we show that acute hyperammonemia strongly enhances transamination-dependent formation of osmolytic glutamine and excitatory glutamate, thereby inducing neurotoxicity and death in ammoniotelic zebrafish larvae via synergistically acting overactivation of NMDA receptors and bioenergetic impairment induced by depletion of 2-oxoglutarate. Intriguingly, specific and irreversible inhibition of ornithine aminotransferase (OAT) by 5-fluoromethylornithine rescues zebrafish from lethal concentrations of ammonium acetate and corrects hyperammonemia-induced biochemical alterations. Thus, OAT inhibition is a promising and effective therapeutic approach for preventing neurotoxicity and mortality in acute hyperammonemia. [ABSTRACT FROM AUTHOR]

The L-arginine/NO pathway is an important regulator of pulmonary hypertension, the leading cause of mortality in patients with the chronic lung disease of prematurity, bronchopulmonary dysplasia. L-arginine can be metabolized by NO synthase (NOS) to form L-citrulline and NO, a potent vasodilator. Alternatively, L-arginine can be metabolized by arginase to form urea and L-ornithine, a precursor to collagen and proline formation important in vascular remodelling. In the current study, we hypothesized that C3H/HeN mice exposed to prolonged hyperoxia would have increased arginase expression and pulmonary vascular wall cell proliferation. C3H/HeN mice were exposed to 14 days of 85% O2 or room air and lung homogenates analyzed by western blot for protein levels of arginase I, arginase II, endothelial NOS (eNOS), ornithine decarboxylase (ODC), ornithine aminotransferase (OAT), and α-smooth muscle actin (a-SMA). Hyperoxia did not change arginase I or eNOS protein levels. However, arginase II protein levels were 15-fold greater after hyperoxia exposure than in lungs exposed to room air. Greater protein levels of ODC and OAT were found in lungs following hyperoxic exposure than in room air animals. α-SMA protein levels were found to be 7-fold greater in the hyperoxia exposed lungs than in room air lungs. In the hyperoxia exposed lungs there was evidence of greater pulmonary vascular wall cell proliferation by α-SMA immunohistochemistry than in room air lungs. Taken together, these data are consistent with a more proliferative vascular phenotype, and may explain the propensity of patients with bronchopulmonary dysplasia to develop pulmonary hypertension. [ABSTRACT FROM AUTHOR]

Accounting for aroma production in different aromatic indica rice varieties based on variations in the levels of concerned metabolites and enzymes is poorly explored. The present investigation was, therefore, focused on unraveling the differential levels of metabolites and activities of enzymes related to aroma formation in eleven indigenous aromatic rice varieties, as compared with four non-aromatic varieties. The levels of metabolites such as proline (Pro) and Δ-pyrroline-5-carboxylate (P5C), and the activity of related enzymes such as proline dehydrogenase (PDH), Δ-pyrroline-5-carboxylate synthetase (P5CS), and ornithine aminotransferase (OAT) were comparatively higher in the aromatic varieties, with Kalonunia and Tulaipanji registering the highest Pro, Kalonunia the highest P5C content, Gobindobhog with the highest PDH activity, Gobindobhog and Tulaipanji with the highest P5CS, and Pusa Basmati-1 with the highest OAT activity. The levels of putrescine (Put) and γ-aminobutyric acid (GABA) were comparatively lower in aromatic varieties, with concomitant higher diamine oxidase (DAO) activity, especially in the varieties Gobindobhog and Tulaipanji. The betaine-aldehyde dehydrogenase 2 (BADH2) enzyme activity was remarkably lesser in aromatic varieties, especially Radhunipagal and Gobindobhog. Though the metabolites such as glycine-betaine and higher polyamines such as spermidine and spermine showed no specific trend with respect to their quantitative level in either aromatic or non-aromatic varieties, they were notably lower in the aromatic varieties such as Gobindobhog, Kalonunia, and Tulaipanji, indicating a possibility of their involvement in aroma formation. Therefore, the levels of metabolites such as Pro, P5C and methylglyoxal (MG), and the activity of enzymes such as PDH, P5CS, OAT, and DAO were comparatively higher in the aromatic rice varieties than the non-aromatic ones, whereas the levels of Put, GABA, and BADH2 were lower. Overall, the present study showed that there exist variations in the accumulations of such metabolites as well as differential activity of enzymes controlling their production, which altogether regulate generation of aroma in aromatic varieties. [ABSTRACT FROM AUTHOR]

Ornithine δ-aminotransferase (OAT, E.C. 2.6.1.13) catalyzes the transfer of the δ-amino group from ornithine (Orn) to α-ketoglutarate (aKG), yielding glutamate-5-semialdehyde and glutamate (Glu), and vice versa. In mammals, OAT is a mitochondrial enzyme, mainly located in the liver, intestine, brain, and kidney. In general, OAT serves to form glutamate from ornithine, with the notable exception of the intestine, where citrulline (Cit) or arginine (Arg) are end products. Its main function is to control the production of signaling molecules and mediators, such as Glu itself, Cit, GABA, and aliphatic polyamines. It is also involved in proline (Pro) synthesis. Deficiency in OAT causes gyrate atrophy, a rare but serious inherited disease, a further measure of the importance of this enzyme. [ABSTRACT FROM AUTHOR]

Ornithine is a non-essential amino acid produced as an intermediate molecule in urea cycle. It is a key substrate for the synthesis of proline, polyamines and citrulline. Ornithine also plays an important role in the regulation of several metabolic processes leading to diseases like hyperorithinemia, hyperammonemia, gyrate atrophy and cancer in humans. However, the mechanism of action behind the multi-faceted roles of ornithine is yet to be unraveled completely. Several types of cancers are also characterized by excessive polyamine synthesis from ornithine by different rate limiting enzymes. Hence, in this review we aim to provide extensive insights on potential roles of ornithine in many of the disease related cellular processes and also on the structural features of ornithine interacting proteins, enabling development of therapeutic modalities. [ABSTRACT FROM AUTHOR]