Molecular cloning and characterization of the human and mouse UDP-glucose dehydrogenase genes

Changes in the amount of nucleotide sugars in aged mouse tissues

Aging affects tissue glycan profiles, which may alter cellular functions and increase the risk of age-related diseases. Glycans are biosynthesized by glycosyltransferases using the corresponding nucleotide sugar, and the availability of nucleotide sugars affects glycosylation efficiency. However, the effects of aging on nucleotide sugar profiles and contents are yet to be elucidated. Therefore, this study aimed to investigate the effects of aging on nucleotide sugars using a new LC-MS/MS method. Specifically, the new method was used to determine the nucleotide sugar contents of various tissues (brain, liver, heart, skeletal muscle, kidney, lung, and colon) of male C57BL/6NCr mice (7- or 26-month-old). Characteristic age-associated nucleotide sugar changes were observed in each tissue sample. Particularly, there was a significant decrease in UDP-glucuronic acid content in the kidney of aged mice and a decrease in the contents of several nucleotide sugars, including UDP-N-acetylgalactosamine, in the brain of aged mice. Additionally, there were variations in nucleotide sugar profiles among the tissues examined regardless of the age. The kidneys had the highest concentration of UDP-glucuronic acid among the seven tissues. In contrast, the skeletal muscle had the lowest concentration of total nucleotide sugars among the tissues; however, CMP-N-acetylneuraminic acid and CDP-ribitol were relatively enriched. Conclusively, these findings may contribute to the understanding of the roles of glycans in tissue aging.

UDP-glucose dehydrogenase supports autophagy-deficient PDAC growth via increasing hyaluronic acid biosynthesis

Autophagy is an essential degradation and recycling process that maintains cellular homeostasis during stress or nutrient deprivation. However, certain types of tumors such as pancreatic cancers can circumvent autophagy inhibition to sustain growth. The mechanism that autophagy-deficient pancreatic ductal adenocarcinoma (PDAC) uses to grow under nutrient deprivation is poorly understood. Our data show that nutrient deprivation in PDAC results in UDP-glucose dehydrogenase (UGDH) degradation, which is dependent on autophagic cargo receptor sequestosome 1 (p62). Moreover, we demonstrate that accumulated UGDH is indispensable for autophagy-deficient PDAC cells proliferation by promoting hyaluronic acid (HA) synthesis upon energy deprivation. Using an orthotopic mouse model of PDAC, we find that inhibition of HA synthesis by targeting UGDH in PDAC reduces tumor weight. Thus, the combined inhibition of HA and autophagy might be an attractive strategy for PDAC treatment.

Phenotypic and genetic characteristics of 24 cases of early infantile epileptic encephalopathy in East China, including a rare case of biallelic UGDH mutations

BACKGROUND

Early infantile epileptic encephalopathy (EIEE) is a group of highly heterogeneous diseases, both phenotypically and genetically. Usually, it starts early on and manifests as intractable epilepsy, abnormal electroencephalogram, and growth retardation/intellectual impairment. With the advent of next-generation sequencing (NGS), its genetic etiology has attracted increasing clinical attention. This study aimed to investigate the genetic characteristics and clinical phenotypes of patients with EIEE from a central hospital in Eastern China.

METHODS

This study retrospectively included the gene variants from 24 EIEE-positive patients admitted between January 2021 and January 2022 to a hospital in Anhui Province, China. The genetic diagnosis was performed in all cases by trio-based whole-exome sequencing (WES). Additionally, Video electroencephalogram (VEEG) and neuroimaging examinations were performed.

RESULTS

A total of 24 children were included. The average age at the first seizure was approximately 5 months. About 42% of children had developmental retardation of varying degrees, 43% had brain structural abnormalities, and 64% had VEEG abnormalities. In addition, other phenotypes, including endocrine metabolism and cardiac structural abnormalities, have been independently reported. In total, fifteen pathogenic gene variants were identified in 24 patients. The main pathogenic genes identified were SCN1A (25%, 6/24), KCNQ2 (8.3%, 2/24), and TBC1D24 (8.3%, 2/24). We also found an extremely rare case of EIEE84 type caused by biallelic UGDH gene variants, predicting that this variant might affect the stability of the protein structure.

CONCLUSIONS

SCN1A pathogenic variants are the main factor leading to EIEE, similar to previously published cohort reports. NGS is useful for accurate clinical diagnoses and precise treatment choices. We also reported a rare case of EIEE84 caused by variants in the UGDH gene in a Chinese patient. This study further enriches the known spectrum of pathogenic EIEE genes.

Potential roles of gut microbiota in metal mixture and bone mineral density and osteoporosis risk association: an epidemiologic study in Wuhan

Few studies have focused on the effects of multiple metal mixtures on bone health and the underlying mechanisms related to alterations in the gut microbiota. This study aimed to examine the potential roles of gut microbiota alterations in metal mixtures and their association with osteoporosis traits. Adults aged ≥ 55 years were recruited from two community healthcare centers in Wuhan City during 2016-2019. The plasma concentrations of six metals (zinc, iron, selenium, lead, cadmium, and arsenic) were measured using an inductively coupled plasma mass spectrometer. The k-means clustering method was employed to explore the exposure profiles of metal mixtures for all participants. 16S rRNA gene sequencing was used to profile the gut microbiota of participants. Combining these results with those of our previous study, we identified overlapping taxa and evaluated their potential roles. A total of 806 participants (516 females), with an average age of 67.36 years were included. The participants were grouped into three clusters using k-means clustering: Cluster 1 (n = 458), Cluster 2 (n = 199), and Cluster 3 (n = 149). The high-exposure group for iron, zinc, lead, and cadmium (Cluster 3) showed a negative association with lumbar spine 1-4 bone mineral density (BMD). A total of 201 individuals (121 females) underwent sequencing of the gut microbiota. Both alpha and beta diversities were statistically different among the three groups. Bacteroidaceae, Lachnospiraceae, Bifidobacteriaceae, Bacteroides, and Lachnospiraceae_incertae_sedis were identified as overlapping taxa associated with the metal mixtures and BMD. Interaction analysis revealed that Cluster 3 interacted with Bacteroidaceae/Bacteroides, resulting in a positive effect on LS1-4 BMD (β = 0.358 g/cm2, 95% CI: 0.047 to 0.669, P = 0.025). Our findings indicate associations between multiple metal mixtures and BMD as well as gut microbiota alterations. Exploring the interaction between metal mixtures and the gut microbiota provides new perspectives for the precise prevention and treatment of osteoporosis.

Mutual Influence of Human Cytochrome P450 Enzymes and UDP-Glucuronosyltransferases on Their Respective Activities in Recombinant Fission Yeast

Cytochromes P450 (CYPs) and UDP-glucuronosyltransferases (UGTs) are the most important human drug metabolizing enzymes, but their mutual interactions are poorly understood. In this study, we recombinantly co-expressed of each one of the 19 human members of the UGT families 1 and 2 with either CYP2C9, CYP2D6, or CYP4Z1 in fission yeast. Using these strains, we monitored a total of 72 interactions: 57 cases where we tested the influence of UGT co-expression on CYP activity and 15 cases of the opposite approach. In the majority of cases (88%), UGT co-expression had a statistically significant (p < 0.05) effect on P450 activity (58% positive and 30% negative). Strong changes were observed in nine cases, including one case with an activity increase by a factor of 23 (CYP2C9 activity in the presence of UGT2A3) but also four cases with a complete loss of activity. When monitoring the effect of CYP co-expression on the activity of five UGTs, activity changes were generally not so pronounced and, if observed, always detrimental. UGT2B7 activity was not influenced by CYP co-expression, while the other UGTs were affected to varying degrees. These data suggest the notion that mutual influence of CYPs and UGTs on each other's activity is a widespread phenomenon.

Aggrecan and Hyaluronan: The Infamous Cartilage Polyelectrolytes - Then and Now

Cartilages are unique in the family of connective tissues in that they contain a high concentration of the glycosaminoglycans, chondroitin sulfate and keratan sulfate attached to the core protein of the proteoglycan, aggrecan. Multiple aggrecan molecules are organized in the extracellular matrix via a domain-specific molecular interaction with hyaluronan and a link protein, and these high molecular weight aggregates are immobilized within the collagen and glycoprotein network. The high negative charge density of glycosaminoglycans provides hydrophilicity, high osmotic swelling pressure and conformational flexibility, which together function to absorb fluctuations in biomechanical stresses on cartilage during movement of an articular joint. We have summarized information on the history and current knowledge obtained by biochemical and genetic approaches, on cell-mediated regulation of aggrecan metabolism and its role in skeletal development, growth as well as during the development of joint disease. In addition, we describe the pathways for hyaluronan metabolism, with particular focus on the role as a "metabolic rheostat" during chondrocyte responses in cartilage remodeling in growth and disease.Future advances in effective therapeutic targeting of cartilage loss during osteoarthritic diseases of the joint as an organ as well as in cartilage tissue engineering would benefit from 'big data' approaches and bioinformatics, to uncover novel feed-forward and feed-back mechanisms for regulating transcription and translation of genes and their integration into cell-specific pathways.

Multi-Omics Analysis Revealed a Significant Alteration of Critical Metabolic Pathways Due to Sorafenib-Resistance in Hep3B Cell Lines

Hepatocellular carcinoma (HCC) is the second prominent cause of cancer-associated death worldwide. Usually, HCC is diagnosed in advanced stages, wherein sorafenib, a multiple target tyrosine kinase inhibitor, is used as the first line of treatment. Unfortunately, resistance to sorafenib is usually encountered within six months of treatment. Therefore, there is a critical need to identify the underlying reasons for drug resistance. In the present study, we investigated the proteomic and metabolomics alterations accompanying sorafenib resistance in hepatocellular carcinoma Hep3B cells by employing ultra-high-performance liquid chromatography quadrupole time of flight mass spectrometry (UHPLC-QTOF-MS). The Bruker Human Metabolome Database (HMDB) library was used to identify the differentially abundant metabolites through MetaboScape 4.0 software (Bruker). For protein annotation and identification, the Uniprot proteome for Homo sapiens (Human) database was utilized through MaxQuant. The results revealed that 27 metabolites and 18 proteins were significantly dysregulated due to sorafenib resistance in Hep3B cells compared to the parental phenotype. D-alanine, L-proline, o-tyrosine, succinic acid and phosphatidylcholine (PC, 16:0/16:0) were among the significantly altered metabolites. Ubiquitin carboxyl-terminal hydrolase isozyme L1, mitochondrial superoxide dismutase, UDP-glucose-6-dehydrogenase, sorbitol dehydrogenase and calpain small subunit 1 were among the significantly altered proteins. The findings revealed that resistant Hep3B cells demonstrated significant alterations in amino acid and nucleotide metabolic pathways, energy production pathways and other pathways related to cancer aggressiveness, such as migration, proliferation and drug-resistance. Joint pathway enrichment analysis unveiled unique pathways, including the antifolate resistance pathway and other important pathways that maintain cancer cells' survival, growth, and proliferation. Collectively, the results identified potential biomarkers for sorafenib-resistant HCC and gave insights into their role in chemotherapeutic drug resistance, cancer initiation, progression and aggressiveness, which may contribute to better prognosis and chemotherapeutic outcomes.

Teprotumumab Divergently Alters Fibrocyte Gene Expression: Implications for Thyroid-associated Ophthalmopathy

CONTEXT

Teprotumumab, an IGF-I receptor (IGF-IR) inhibitor, is effective in thyroid-associated ophthalmopathy (TAO). The drug can modulate induction by TSH of IL-6 and IL-8 in CD34+ fibrocytes and their putative derivatives, CD34+ orbital fibroblasts (CD34+ OF). Fibrocytes express multiple thyroid autoantigens and cytokines implicated in TAO, which are downregulated by Slit2. Inflammation and disordered hyaluronan (HA) accumulation occur in TAO. Whether teprotumumab alters these processes directly in fibrocytes/CD34+ OF remains uncertain.

OBJECTIVE

Determine teprotumumab effects on expression/synthesis of several TAO-relevant molecules in fibrocytes and GD-OF.

DESIGN/SETTING/PARTICIPANTS

Patients with TAO and healthy donors were recruited from an academic endocrine and oculoplastic practice.

MAIN OUTCOME MEASURES

Real-time PCR, specific immunoassays.

RESULTS

Teprotumumab attenuates basal and TSH-inducible autoimmune regulator protein, thyroglobulin, sodium iodide symporter, thyroperoxidase, IL-10, and B-cell activating factor levels in fibrocytes. It downregulates IL-23p19 expression/induction while enhancing IL-12p35, intracellular and secreted IL-1 receptor antagonists, and Slit2. These effects are mirrored by linsitinib. HA production is marginally enhanced by teprotumumab, the consequence of enhanced HAS2 expression.

CONCLUSION

Teprotumumab affects specific gene expression in fibrocytes and GD-OF in a target-specific, nonmonolithic manner, whereas IGF-IR control of these cells appears complex. The current results suggest that the drug may act on cytokine expression and HA production systemically and locally, within the TAO orbit. These findings extend our insights into the mechanisms through which IGF-IR inhibition might elicit clinical responses in TAO, including a potential role of Slit2 in attenuating inflammation and tissue remodeling.

UDP-glucose 6-dehydrogenase lessens sorafenib sensitivity via modulating unfolded protein response

As the first-generation targeted therapy, sorafenib remains an effective single-drug treatment for advanced hepatocellular carcinoma (HCC). Unfortunately, the existence of resistance restricts the long-term benefit of patients. UDP-glucose 6-dehydrogenase (UGDH) is the key enzyme of glucuronic acid metabolism which was largely reported in mediating drug systemic elimination. In this study, we explore its critical role in regulating sorafenib sensitivity. Here we find sorafenib exposure could activate glucuronic acid metabolism, accompanied with the elevated expression of UGDH. Interference with the route by silencing UGDH could boost HCC cells sensitivity to sorafenib. Meanwhile, the analysis of HCC patients with sorafenib treatment displayed that low UGDH expression predicted superior prognosis. Further screening assay suggested that unfolded protein response (UPR) involves in UGDH silencing-mediated apoptosis. Xenograft model confirmed that combined UGDH intervention could significantly improve sorafenib efficacy. Our results reveal the impact of sorafenib exposure on glucuronic acid metabolism reprogramming and provide UGDH as a promising target to improve sorafenib efficacy.

Long non-coding RNAs in <i>Sus scrofa</i> ileum under starvation stress

Objective

In this study, we aimed to identify long non-coding RNAs (lncRNAs) that play important roles in starvation stress, analyze their functions, and discover potential molecular targets to alleviate starvation stress to provide a theoretical reference for subsequent in-depth research.

Methods

We generated a piglet starvation stress animal model. Nine Yorkshire weaned piglets were randomly divided into a long-term starvation stress group (starved for 72 h), short-term starvation stress group (starved for 48 h), and the control group. LncRNA libraries were constructed using high-throughput sequencing of piglet ileums.

Results

We obtained 11,792 lncRNAs, among which, 2,500 lncRNAs were novel. In total, 509 differentially expressed (DE)lncRNAs were identified in this study. Target genes of DElncRNAs were predicted via cis and trans interactions, and functional and pathway analyses were performed. Gene ontology functions and Kyoto encyclopedia of genes and genomes analysis revealed that lncRNA-targeted genes mainly participated in metabolic pathways, cellular processes, immune system processes, digestive systems, and transport activities. To reveal the mechanism underlying starvation stress, the interaction network between lncRNAs and their targets was constructed based on 26 DElncRNAs and 72 DEmRNAs. We performed an interaction network analysis of 121 DElncRNA–DEmRNA pairs with a Pearson correlation coefficient greater than 0.99.

Conclusion

We found that MSTRG.19894.13, MSTRG.16726.3, and MSTRG.12176.1 might play important roles in starvation stress. This study not only generated a library of enriched lncRNAs in piglets, but its outcomes also provide a strong foundation to screen key lncRNAs involved in starvation stress and a reference for subsequent in-depth research.

An Overview of in vivo Functions of Chondroitin Sulfate and Dermatan Sulfate Revealed by Their Deficient Mice

Chondroitin sulfate (CS), dermatan sulfate (DS) and heparan sulfate (HS) are covalently attached to specific core proteins to form proteoglycans in their biosynthetic pathways. They are constructed through the stepwise addition of respective monosaccharides by various glycosyltransferases and maturated by epimerases as well as sulfotransferases. Structural diversities of CS/DS and HS are essential for their various biological activities including cell signaling, cell proliferation, tissue morphogenesis, and interactions with a variety of growth factors as well as cytokines. Studies using mice deficient in enzymes responsible for the biosynthesis of the CS/DS and HS chains of proteoglycans have demonstrated their essential functions. Chondroitin synthase 1-deficient mice are viable, but exhibit chondrodysplasia, progression of the bifurcation of digits, delayed endochondral ossification, and reduced bone density. DS-epimerase 1-deficient mice show thicker collagen fibrils in the dermis and hypodermis, and spina bifida. These observations suggest that CS/DS are essential for skeletal development as well as the assembly of collagen fibrils in the skin, and that their respective knockout mice can be utilized as models for human genetic disorders with mutations in chondroitin synthase 1 and DS-epimerase 1. This review provides a comprehensive overview of mice deficient in CS/DS biosyntheses.

Congenital Disorders of Deficiency in Glycosaminoglycan Biosynthesis

Glycosaminoglycans (GAGs) including chondroitin sulfate, dermatan sulfate, and heparan sulfate are covalently attached to specific core proteins to form proteoglycans, which are distributed at the cell surface as well as in the extracellular matrix. Proteoglycans and GAGs have been demonstrated to exhibit a variety of physiological functions such as construction of the extracellular matrix, tissue development, and cell signaling through interactions with extracellular matrix components, morphogens, cytokines, and growth factors. Not only connective tissue disorders including skeletal dysplasia, chondrodysplasia, multiple exostoses, and Ehlers-Danlos syndrome, but also heart and kidney defects, immune deficiencies, and neurological abnormalities have been shown to be caused by defects in GAGs as well as core proteins of proteoglycans. These findings indicate that GAGs and proteoglycans are essential for human development in major organs. The glycobiological aspects of congenital disorders caused by defects in GAG-biosynthetic enzymes including specific glysocyltransferases, epimerases, and sulfotransferases, in addition to core proteins of proteoglycans will be comprehensively discussed based on the literature to date.

Targeting UDP-α-d-glucose 6-dehydrogenase alters the CNS tumor immune microenvironment and inhibits glioblastoma growth

Glioblastoma (GBM, WHO grade IV glioma) is the most common and lethal malignant brain tumor in adults with a dismal prognosis. The extracellular matrix (ECM) supports GBM progression by promoting tumor cell proliferation, migration, and immune escape. Uridine diphosphate (UDP)-glucose 6-dehydrogenase (UGDH) is the rate-limiting enzyme that catalyzes the biosynthesis of glycosaminoglycans that are the principal component of the CNS ECM. We investigated how targeting UGDH in GBM influences the GBM immune microenvironment, including tumor-associated microglia/macrophages (TAMs) and T cells. TAMs are the main immune effector cells in GBM and can directly target tumor cells if properly activated. In co-cultures of GBM cells and human primary macrophages, UGDH knockdown in GBM cells promoted macrophage phagocytosis and M1-like polarization. In orthotropic human GBM xenografts and syngeneic mouse glioma models, targeting UGDH decreased ECM deposition, increased TAM phagocytosis marker expression, reduced M2-like TAMs and inhibited tumor growth. UGDH knockdown in GBM cells also promoted cytotoxic T cell infiltration and activation in orthotopic syngeneic mouse glioma models. The potent and in-human-use small molecule GAG synthesis inhibitor 4-methylumbelliferone (4-MU) was found to inhibit GBM cell proliferation and migration in vitro, mimic the macrophage and T-cell responses to UGDH knockdown in vitro and in vivo and inhibit growth of orthotopic murine GBM. Our study shows that UGDH supports GBM growth through multiple mechanisms and supports the development of ECM-based therapeutic strategies to simultaneously target tumor cells and their microenvironment.

Systematic exploration of Astragalus membranaceus and Panax ginseng as immune regulators: Insights from the comparative biological and computational analysis

BACKGROUND

Immune system plays a decisive role for defending various pathogenic microorganisms. Astragalus membranaceus (AM) and Panax ginseng (PG) are two tonic herbs used in traditional Chinese medicine (TCM) as immune booster and help to control diseases with their healthy synergistic effect on immune system.

PURPOSE

This study was aimed to investigate the promote effect and molecular mechanisms of AM and PG on immune system as booster and to control the target diseases using animal and computational systematic study.

METHODS

Computational models including absorption, distribution, metabolism, and elimination (ADME) with weighted ensemble similarity (WES) algorithm-based models and ClueGo network analysis were used to find the potential bioactive compounds targets and pathways, which were responsible for immune regulation. Viscera index analysis, proliferation activity of splenic lymphocytes and cytotoxic activity of NK cells assays were performed to validate the effect of AM and PG on immune system of long-term administrated mice. Metabonomic study of mice plasma was conducted to investigate effect of AM and PG on the endogenous metabolic perturbations, together with correlation analysis.

RESULTS

AM and PG simultaneously showed the ability to strengthen the immune system function including enhancement of spleen and thymus index, proliferation of splenic lymphocytes and cytotoxic activity of NK cells. Besides, the different molecular mechanisms of AM and PG on immune regulation were also investigated by analyzing the potential bioactive compounds, enzymes actions and pathways. Quercetin, formononetin and kaempferol were the main immune-related compounds in AM, while ginsenoside Ra1, ginsenoside Rh1 and kaempferol in PG. About 10 target proteins were found close to immune regulation, including acetylcholinesterase (ACHE, common target in AM and PG), sphingosine kinase 1(SPHK1), cytidine deaminase (CDA), and Choline O-acetyltransferase (CHAT). Glycerophospholipid metabolism was regulated in both AM and PG groups. Pyrimidine metabolism and sphingolipid metabolism were considered as the special pathway in AM groups. Energy metabolism and glycerolipid metabolism were the special pathways in PG groups.

CONCLUSION

A novel comprehensive molecular mechanism analysis method was established and applied to clarify the scientific connotation of AM and PG as immune regulation, with similar herbal tonic effect provided in clinical practice of TCM, which can provide a new line of research for drug development (immune booster) using AM and PG.

Genome-wide analysis of UGDH genes in Populus trichocarpa and responsiveness to nitrogen treatment

Plant UDP-glucose 6-dehydrogenase (UGDH) is an important enzyme for the formation of hemicellulose and pectin. Previous studies on UGDH have primarily focused on the biosynthesis of cell wall polysaccharides, while few studies have focused on their regulation by exogenous nitrogen. In the present study, four genes encoding PtUGDH proteins were analyzed by bioinformatics methods. And, the expression profiles of PtUGDH genes under different nitrogen treatments were evaluated with qRT-PCR. The results showed that PtUGDHs have conserved NAD coenzyme binding motif GAGYVGG and the catalytic motif GFGGSCFQKDIL. According to the phylogenetic analysis, PtUGDHs were divided into two subgroups. PtUGDH3 and PtUGDH4 were closely related to AtUGDH1 (important for normal development of Arabidopsis cell wall structure). Chromosomal distribution and genome synteny analysis revealed four segmental-duplicated gene pairs on chr4, 8, 10 and 17. Tissue-specific data from PlantGenIE showed that PtUGDH3 and PtUGDH4 were highly expressed in stems. The qRT-PCR detection showed that the expression of PtUGDH3 in the lower stem and PtUGDH2 of upper leaves were significantly increased induced by low ammonium or nitrate condition. This comprehensive analysis of the UGDH family in poplar provides new insights into their regulation by nitrogen, and would increase our understanding of the roles of UGDHs in hemicellulose and pectin biosynthesis in the cell wall and during poplar development.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02697-9.

Slit2 Regulates Hyaluronan & Cytokine Synthesis in Fibrocytes: Potential Relevance to Thyroid-Associated Ophthalmopathy

CONTEXT

CD34+ fibrocytes have been implicated in development of thyroid-associated ophthalmopathy (TAO), a consequential autoimmune manifestation of Graves disease (GD). In TAO, CD34+ fibrocytes appear to masquerade as CD34+ orbital fibroblasts mixed with CD34- OF (collectively, GD-OF). Slit2, an axon guidance glycoprotein, is expressed by CD34- OF and attenuates GD-OF gene expression. Cardinal features of TAO include hyaluronan (HA) accumulation and cytokine-driven inflammation.

OBJECTIVE

Compare expression of HA synthase isoenzymes (HAS1-3), UDP-glucose dehydrogenase (UGDH), synthesis of HA, interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in fibrocytes and GD-OF. Determine whether Slit2 alters gene expression patterns.

DESIGN/SETTING/PARTICIPANTS

Patients with TAO and healthy donors were recruited from an academic practice.

MAIN OUTCOME MEASURES

Real-time polymerase chain reaction, HA, IL-6, and TNF-α immunoassays.

RESULTS

HA synthesis and release from fibrocytes is substantially lower than in GD-OF. HAS1 expression dominates in fibrocytes while HAS2 in GD-OF. In contrast, HAS2 and UGDH expression dominate GD-OF and localize to CD34- OF. Recombinant human Slit2 (rhSlit2) substantially upregulates HA synthesis and HAS2 expression in fibrocytes but attenuates IL-6 and TNF-α production in these cells. In contrast, knocking down Slit2 in GD-OF reduces HA synthesis and HAS2 and UGDH expression while upregulating IL-6 and TNF-α.

CONCLUSION

The dramatic differences in HA, IL-6, and TNF-α production, and HAS and UGDH expression found in fibrocytes and GD-OF appear, at least in part, to be attributable to Slit2. These findings provide novel insight into the differences in gene expression exhibited by CD34+ fibrocytes and CD34+ OF and therefore reveal important aspects of disease pathogenesis.

Integration of Sugar Metabolism and Proteoglycan Synthesis by UDP-glucose Dehydrogenase

Regulation of proteoglycan and glycosaminoglycan synthesis is critical throughout development, and to maintain normal adult functions in wound healing and the immune system, among others. It has become increasingly clear that these processes are also under tight metabolic control and that availability of carbohydrate and amino acid metabolite precursors has a role in the control of proteoglycan and glycosaminoglycan turnover. The enzyme uridine diphosphate (UDP)-glucose dehydrogenase (UGDH) produces UDP-glucuronate, an essential precursor for new glycosaminoglycan synthesis that is tightly controlled at multiple levels. Here, we review the cellular mechanisms that regulate UGDH expression, discuss the structural features of the enzyme, and use the structures to provide a context for recent studies that link post-translational modifications and allosteric modulators of UGDH to its function in downstream pathways.

SLC35B1 significantly contributes to the uptake of UDPGA into the endoplasmic reticulum for glucuronidation catalyzed by UDP-glucuronosyltransferases

The transport of UDP-glucuronic acid (UDPGA), a co-substrate of UDP-glucuronosyltransferase (UGT), to the intraluminal side of the endoplasmic reticulum (ER) is an essential step in the glucuronidation of exogenous and endogenous compounds. According to a previous study, the expression of recombinant SLC35B1, SLC35B4, or SLC35D1, nucleotide sugar transporters, in V79 cells has the potential to transport UDPGA into the lumen of microsomes. The purpose of this study is to examine whether the transport of UDPGA by these transporters substantially affects UGT activity. Since the knockdown of UDP-glucose 6-dehydrogenase, a synthetase of UDPGA, in HEK293 cells stably expressing UGT1A1 (HEK/UGT1A1 cells) resulted in a significant decrease in 4-methylumbelliferone (4-MU) glucuronosyltransferase activity, supplementation of a sufficient amount of UDPGA is required for UGT activity. By performing qRT-PCR using cDNA samples from 21 human liver samples, we observed levels of the SLC35B1 and SLC35D1 mRNAs that were 15- and 14-fold higher, respectively, than the levels of the SLC35B4 mRNA, and SLC35B1 showed the largest (37-fold) interindividual variability. Interestingly, 4-MU glucuronosyltransferase activity was significantly decreased upon the knockdown of SLC35B1 in HEK/UGT1A1 cells, and this phenomenon was also observed in HepaRG cells. Using siRNAs targeting 23 different SLC35 subfamilies, the knockdown of SLC35B1 and SLC35E3 decreased 4-MU glucuronosyltransferase activity in HEK/UGT1A1 cells. However, the 4-MU glucuronosyltransferase activity was not altered by SLC35E3 knockdown in HepaRG cells, suggesting that SLC35B1 was the main transporter of UDPGA into the ER in the human liver. In conclusion, SLC35B1 is a key modulator of UGT activity by transporting UDPGA to the intraluminal side of the ER.

Loss-of-function mutations in UDP-Glucose 6-Dehydrogenase cause recessive developmental epileptic encephalopathy

Developmental epileptic encephalopathies are devastating disorders characterized by intractable epileptic seizures and developmental delay. Here, we report an allelic series of germline recessive mutations in UGDH in 36 cases from 25 families presenting with epileptic encephalopathy with developmental delay and hypotonia. UGDH encodes an oxidoreductase that converts UDP-glucose to UDP-glucuronic acid, a key component of specific proteoglycans and glycolipids. Consistent with being loss-of-function alleles, we show using patients' primary fibroblasts and biochemical assays, that these mutations either impair UGDH stability, oligomerization, or enzymatic activity. In vitro, patient-derived cerebral organoids are smaller with a reduced number of proliferating neuronal progenitors while mutant ugdh zebrafish do not phenocopy the human disease. Our study defines UGDH as a key player for the production of extracellular matrix components that are essential for human brain development. Based on the incidence of variants observed, UGDH mutations are likely to be a frequent cause of recessive epileptic encephalopathy.

A Missense Mutation in the UGDH Gene Is Associated With Developmental Delay and Axial Hypotonia

UDP-glucose dehydrogenase (UGDH) encodes an oxidoreductase that converts two successive oxidations of UDP-glucose to produce UDP-glucuronic acid, a key component in the synthesis of several polysaccharides such as glycosaminoglycan and the disaccharide hyaluronic acid. UGDH is critical to the production of extracellular matrix components which are essential to the migration and connectivity of neurons early in human brain development. In this report, we describe one child of a consanguineous family who presented with distinct clinical features including global developmental delay, axial hypotonia, bilateral undescended testis, and subtle dysmorphic features. Whole genome sequencing and a segregation was performed to identify the genetic cause of the disease within the family. Though mutations in the UGDH protein have been described as causing developmental delay in various model organisms, to our knowledge, this is the first identification of the novel homozygous missense variant in exon8 of UGDH NM_003359.3: c.950 G>A (p.Arg317Gln) and most likely the cause of the patient's phenotype. This variant falls in an active region and replaces the highly conserved Arginine 317 residues across mammals.

Thyroid-associated ophthalmopathy: Emergence of teprotumumab as a promising medical therapy

Thyroid-associated ophthalmopathy (TAO) remains a vexing autoimmune component of Graves' disease that can diminish the quality of life as a consequence of its impact on visual function, physical appearance and emotional well-being. Because of its relative rarity and variable presentation, the development of highly effective and well-tolerated medical therapies for TAO has been slow relative to other autoimmune diseases. Contributing to the barriers of greater insight into TAO has been the historical absence of high-fidelity preclinical animal models. Despite these challenges, several agents, most developed for treatment of other diseases, have found their way into consideration for use in active TAO through repurposing. Among these, teprotumumab is a fully human inhibitory monoclonal antibody against the insulin-like growth factor I receptor. It has shown remarkable effectiveness in moderate to severe, active TAO in two completed multicenter, double masked, and placebo controlled clinical trials. The drug exhibits a favorable safety profile. Teprotumumab has recently been approved by the U.S. F.D.A, and may rapidly become the first line therapy for this disfiguring and potentially blinding condition.

The role of cell mediated immunopathogenesis in thyroid-associated ophthalmopathy

Currently, thyroid-associated ophthalmopathy (TAO) lacks effective treatment due to our lack of clarity in its immunopathogenesis. Orbital fibroblasts play a key role in altering inflammation and immune response in TAO, and are considered as the key target and effector cells in its pathogenesis. The orbit infiltrating CD34+ fibrocytes add on to the process by expressing high levels of autoantigens and inflammatory cytokines, while also differentiating into myofibroblasts or adipocytes. This review focuses on the role of orbital fibroblasts and CD34+ fibrocytes in the pathogenesis of TAO, highlighting the basis of emerging treatments.

A Genome-Wide Haploid Genetic Screen Identifies Heparan Sulfate-Associated Genes and the Macropinocytosis Modulator TMED10 as Factors Supporting Vaccinia Virus Infection

Vaccinia virus is a promising viral vaccine and gene delivery candidate and has historically been used as a model to study poxvirus-host cell interactions. We employed a genome-wide insertional mutagenesis approach in human haploid cells to identify host factors crucial for vaccinia virus infection. A library of mutagenized HAP1 cells was exposed to modified vaccinia virus Ankara (MVA). Deep-sequencing analysis of virus-resistant cells identified host factors involved in heparan sulfate synthesis, Golgi organization, and vesicular protein trafficking. We validated EXT1, TM9SF2, and TMED10 (TMP21/p23/p24δ) as important host factors for vaccinia virus infection. The critical roles of EXT1 in heparan sulfate synthesis and vaccinia virus infection were confirmed. TM9SF2 was validated as a player mediating heparan sulfate expression, explaining its contribution to vaccinia virus infection. In addition, TMED10 was found to be crucial for virus-induced plasma membrane blebbing and phosphatidylserine-induced macropinocytosis, presumably by regulating the cell surface expression of the TAM receptor Axl.IMPORTANCE Poxviruses are large DNA viruses that can infect a wide range of host species. A number of these viruses are clinically important to humans, including variola virus (smallpox) and vaccinia virus. Since the eradication of smallpox, zoonotic infections with monkeypox virus and cowpox virus are emerging. Additionally, poxviruses can be engineered to specifically target cancer cells and are used as a vaccine vector against tuberculosis, influenza, and coronaviruses. Poxviruses rely on host factors for most stages of their life cycle, including attachment to the cell and entry. These host factors are crucial for virus infectivity and host cell tropism. We used a genome-wide knockout library of host cells to identify host factors necessary for vaccinia virus infection. We confirm a dominant role for heparin sulfate in mediating virus attachment. Additionally, we show that TMED10, previously not implicated in virus infections, facilitates virus uptake by modulating the cellular response to phosphatidylserine.

UDP-glucose accelerates SNAI1 mRNA decay and impairs lung cancer metastasis

Cancer metastasis is the primary cause of morbidity and mortality, and accounts for up to 95% of cancer-related deaths¹. Cancer cells often reprogram their metabolism to efficiently support cell proliferation and survival^2,3. However, whether and how those metabolic alterations contribute to the migration of tumour cells remain largely unknown. UDP-glucose 6-dehydrogenase (UGDH) is a key enzyme in the uronic acid pathway, and converts UDP-glucose to UDP-glucuronic acid⁴. Here we show that, after activation of EGFR, UGDH is phosphorylated at tyrosine 473 in human lung cancer cells. Phosphorylated UGDH interacts with Hu antigen R (HuR) and converts UDP-glucose to UDP-glucuronic acid, which attenuates the UDP-glucose-mediated inhibition of the association of HuR with SNAI1 mRNA and therefore enhances the stability of SNAI1 mRNA. Increased production of SNAIL initiates the epithelial-mesenchymal transition, thus promoting the migration of tumour cells and lung cancer metastasis. In addition, phosphorylation of UGDH at tyrosine 473 correlates with metastatic recurrence and poor prognosis of patients with lung cancer. Our findings reveal a tumour-suppressive role of UDP-glucose in lung cancer metastasis and uncover a mechanism by which UGDH promotes tumour metastasis by increasing the stability of SNAI1 mRNA.

Potential Roles of CD34+ Fibrocytes Masquerading as Orbital Fibroblasts in Thyroid-Associated Ophthalmopathy

CONTEXT

Orbital tissues in thyroid-associated ophthalmopathy exhibit particular reactivity and undergo characteristic remodeling. Mechanisms underlying these changes have remained largely unexplained. Studies have characterized orbital connective tissues and derivative fibroblasts to gain insights into local manifestations of a systemic autoimmune syndrome.

EVIDENCE ACQUISITION

A systematic search of PubMed was undertaken for studies related to thyroid-associated ophthalmopathy (TAO), orbital fibroblasts, and fibrocytes involved in pathogenesis.

EVIDENCE SYNTHESIS

Orbital tissues display marked cellular heterogeneity. Fibroblast subsets, putatively derived from multiple precursors, inhabit the orbit in TAO. Among them are cells displaying the CD34+CXC chemokine receptor 4+collagen I+ phenotype, identifying them as fibrocytes, derived from the monocyte lineage. Their unique presence in the TAO orbit helps explain the tissue reactivity and characteristic remodeling that occurs in the disease. Their unanticipated expression of several proteins traditionally thought to be thyroid gland specific, including the TSH receptor and thyroglobulin, may underlie orbital involvement in Graves disease. Although no currently available information unambiguously establishes that CD34+ orbital fibroblasts originate from circulating fibrocytes, inferences from animal models of lung disease suggest that they derive from bone marrow. Further studies are necessary to determine whether fibrocyte abundance and activity in the orbit determine the clinical behavior of TAO.

CONCLUSION

Evidence supports a role for fibrocytes in the pathogenesis of TAO. Recognition of their presence in the orbit now allows development of therapies specifically targeting these cells that ultimately could allow the restoration of immune tolerance within the orbit and perhaps systemically.

Insulin-like Growth Factor-I Receptor and Thyroid-Associated Ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is a complex disease process presumed to emerge from autoimmunity occurring in the thyroid gland, most frequently in Graves disease (GD). It is disfiguring and potentially blinding, culminating in orbital tissue remodeling and disruption of function of structures adjacent to the eye. There are currently no medical therapies proven capable of altering the clinical outcome of TAO in randomized, placebo-controlled multicenter trials. The orbital fibroblast represents the central target for immune reactivity. Recent identification of fibroblasts that putatively originate in the bone marrow as monocyte progenitors provides a plausible explanation for why antigens, the expressions of which were once considered restricted to the thyroid, are detected in the TAO orbit. These cells, known as fibrocytes, express relatively high levels of functional TSH receptor (TSHR) through which they can be activated by TSH and the GD-specific pathogenic antibodies that underpin thyroid overactivity. Fibrocytes also express insulin-like growth factor I receptor (IGF-IR) with which TSHR forms a physical and functional signaling complex. Notably, inhibition of IGF-IR activity results in the attenuation of signaling initiated at either receptor. Some studies suggest that IGF-IR-activating antibodies are generated in GD, whereas others refute this concept. These observations served as the rationale for implementing a recently completed therapeutic trial of teprotumumab, a monoclonal inhibitory antibody targeting IGF-IR in TAO. Results of that trial in active, moderate to severe disease revealed dramatic and rapid reductions in disease activity and severity. The targeting of IGF-IR with specific biologic agents may represent a paradigm shift in the therapy of TAO.

The deubiquitinating enzymes USP4 and USP17 target hyaluronan synthase 2 and differentially affect its function

The levels of hyaluronan, a ubiquitous glycosaminoglycan prominent in the extracellular matrix, is balanced through the actions of hyaluronan-synthesizing enzymes (HAS1, 2 and 3) and degrading hyaluronidases (Hyal 1, 2, 3 and PH20). Hyaluronan accumulates in rapidly remodeling tissues, such as breast cancer, due to deregulated expression of the HAS2 gene and/or alterations of HAS2 activity. The activity of HAS2 is regulated by post-translational modifications, including ubiquitination. In order to identify deubiquitinating enzymes (DUBs) that are involved in de-ubiquitination of HAS2, a complementary (cDNA) library of 69 Flag-HA-tagged human DUBs cloned into retroviral vectors was screened in human embryonic kidney (HEK) 293T cells for their ability to de-ubiquitinate myc-tagged HAS2. Several DUBs were found to decrease the ubiquitination of 6myc-HAS2, among which, the most effective were USP17 and USP4. USP17 efficiently removed polyubiquitination, whereas USP4 preferentially removed monoubiquitination of 6myc-HAS2. Co-immunoprecipitation studies revealed interactions between HAS2 and USP17, as well as between HAS2 and USP4, in membrane preparations of HEK293T cells. USP17 significantly stabilized 6myc-HAS2 protein levels, whereas USP4 did not. The silencing of USP17 led to decreased hyaluronan production, whereas the suppression of USP4 increased hyaluronan synthesis. Importantly, high levels of USP17 and HAS2 were detected in a panel of cancer cell lines compared to normal cells, and immunohistochemical stainings revealed higher expression of USP17 and HAS2 in tissues of lung cancer patients compared to normal tissue. In conclusion, USP17 and USP4 differently affect HAS2 ubiquitination, and the stability and function of HAS2.

Loss of exogenous androgen dependence by prostate tumor cells is associated with elevated glucuronidation potential

Prostate epithelial cells control the potency and availability of androgen hormones in part by inactivation and elimination. UDP-glucose dehydrogenase (UGDH) catalyzes the NAD(+)-dependent oxidation of UDP-glucose to UDP-glucuronate, an essential precursor for androgen inactivation by the prostate glucuronidation enzymes UGT2B15 and UGT2B17. UGDH expression is androgen stimulated, which increases the production of UDP-glucuronate and fuels UGT-catalyzed glucuronidation. In this study, we compared the glucuronidation potential and its impact on androgen-mediated gene expression in an isogenic LNCaP model for androgen-dependent versus castration-resistant prostate cancer. Despite significantly lower androgen-glucuronide output, LNCaP 81 castration-resistant tumor cells expressed higher levels of UGDH, UGT2B15, and UGT2B17. However, the magnitude of androgen-activated UGDH and prostate-specific antigen (PSA) expression, as well as the androgen receptor (AR)-dependent repression of UGT2B15 and UGT2B17, was blunted several-fold in these cells. Consistent with these results, the ligand-activated binding of AR to the PSA promoter and subsequent transcriptional activation were also significantly reduced in castration-resistant cells. Analysis of the UDP-sugar pools and flux through pathways downstream of UDP-glucuronate production revealed that these glucuronidation precursor metabolites were channeled through proteoglycan and glycosaminoglycan biosynthetic pathways, leading to increased surface expression of Notch1. Knockdown of UGDH diminished Notch1 and increased glucuronide output. Overall, these results support a model in which the aberrant partitioning of UDP-glucuronate and other UDP-sugars into alternative pathways during androgen deprivation contributes to the loss of prostate tumor cell androgen sensitivity by promoting altered cell surface proteoglycan expression.

Multiplexed Capillary Electrophoresis as Analytical Tool for Fast Optimization of Multi-Enzyme Cascade Reactions - Synthesis of Nucleotide Sugars: Dedicated to Prof. Dr. Vladimir Křen on the occasion of his 60th birthday

Nucleotide sugars are considered as bottleneck and expensive substrates for enzymatic glycan synthesis using Leloir-glycosyltransferases. Synthesis from cheap substrates such as monosaccharides is accomplished by multi-enzyme cascade reactions. Optimization of product yields in such enzyme modules is dependent on the interplay of multiple parameters of the individual enzymes and governed by a considerable time effort when convential analytic methods like capillary electrophoresis (CE) or HPLC are applied. We here demonstrate for the first time multiplexed CE (MP-CE) as fast analytical tool for the optimization of nucleotide sugar synthesis with multi-enzyme cascade reactions. We introduce a universal separation method for nucleotides and nucleotide sugars enabling us to analyze the composition of six different enzyme modules in a high-throughput format. Optimization of parameters (T, pH, inhibitors, kinetics, cofactors and enzyme amount) employing MP-CE analysis is demonstrated for enzyme modules for the synthesis of UDP-α-D-glucuronic acid (UDP-GlcA) and UDP-α-D-galactose (UDP-Gal). In this way we achieve high space-time-yields: 1.8 g/L⋆h for UDP-GlcA and 17 g/L⋆h for UDP-Gal. The presented MP-CE methodology has the impact to be used as general analytical tool for fast optimization of multi-enzyme cascade reactions.

Inhibiting Hexamer Disassembly of Human UDP-Glucose Dehydrogenase by Photoactivated Amino Acid Cross-Linking

The enzyme UDP-glucose dehydrogenase (UGDH) catalyzes the reaction of UDP-glucose to UDP-glucuronate through two successive NAD(+)-dependent oxidation steps. Human UGDH apoprotein is purified as a mixture of dimeric and hexameric species. Addition of substrate and cofactor stabilizes the oligomeric state to primarily the hexameric form. To determine if the dynamic conformations of hUGDH are required for catalytic activity, we used site-specific unnatural amino acid incorporation to facilitate cross-linking of monomeric subunits into predominantly obligate oligomeric species. Optimal cross-linking was achieved by encoding p-benzoyl-l-phenylalanine at position 458, normally a glutamine located within the dimer-dimer interface, and exposing the enzyme to long wavelength ultraviolet (UV) radiation in the presence of substrate and cofactor. Hexameric complexes were purified by gel filtration chromatography and found to contain significant fractions of dimer and trimer (approximately 50%) along with another 10% higher-molecular mass species. The activity of the cross-linked enzyme was reduced by almost 60% relative to that of the un-cross-linked UGDH mutant, and UV exposure had no effect on the activity of the wild-type enzyme. These results support a model for catalysis in which the ability to dissociate the dimer-dimer interface is as important for maximal enzyme function as has been previously shown for the formation of the hexamer.

Hyaluronan Is Crucial for Stem Cell Differentiation into Smooth Muscle Lineage

Deciphering the extracellular signals that regulate SMC differentiation from stem cells is vital to further our understanding of the pathogenesis of vascular disease and for development of cell-based therapies and tissue engineering. Hyaluronan (HA) has emerged as an important component of the stem cell niche, however its role during stem cell differentiation is a complicated and inadequately defined process. This study aimed to investigate the role of HA in embryonic stem cell (ESC) differentiation toward a SMC lineage. ESCs were seeded on collagen-IV in differentiation medium to generate ESC-derived SMCs (esSMCs). Differentiation coincided with increased HA synthase (HAS) 2 expression, accumulation of extracellular HA and its assembly into pericellular matrices. Inhibition of HA synthesis by 4-methylumbelliferone (4MU), removal of the HA coat by hyaluronidase (HYAL) or HAS2 knockdown led to abrogation of SMC gene expression. HA activates ERK1/2 and suppresses EGFR signaling pathways via its principle receptor, CD44. EGFR inactivation coincided with increased binding to CD44, which was further augmented by addition of high molecular weight (HMW)-HA either exogenously or via HAS2 overexpression through adenoviral gene transfer. HMW-HA-stimulated esSMCs displayed a functional role in vascular tissue engineering ex vivo, vasculogenesis in a matrigel plug model and SMC accumulation in neointimal lesions of vein grafts in mice. These findings demonstrate that HAS2-induced HA synthesis and organization drives ESC-SMC differentiation. Thus, remodeling of the HA microenvironment is a critical step in directing stem cell differentiation toward a vascular lineage, highlighting HA as a potential target for treatment of vascular diseases. Stem Cells 2016;34:1225-1238.

A Haploid Genetic Screen Identifies Heparan Sulfate Proteoglycans Supporting Rift Valley Fever Virus Infection

Rift Valley fever virus (RVFV) causes recurrent insect-borne epizootics throughout the African continent, and infection of humans can lead to a lethal hemorrhagic fever syndrome. Deep mutagenesis of haploid human cells was used to identify host factors required for RVFV infection. This screen identified a suite of enzymes involved in glycosaminoglycan (GAG) biogenesis and transport, including several components of the cis-oligomeric Golgi (COG) complex, one of the central components of Golgi complex trafficking. In addition, disruption of PTAR1 led to RVFV resistance as well as reduced heparan sulfate surface levels, consistent with recent observations that PTAR1-deficient cells exhibit altered Golgi complex morphology and glycosylation defects. A variety of biochemical and genetic approaches were utilized to show that both pathogenic and attenuated RVFV strains require GAGs for efficient infection on some, but not all, cell types, with the block to infection being at the level of virion attachment. Examination of other members of the Bunyaviridae family for GAG-dependent infection suggested that the interaction with GAGs is not universal among bunyaviruses, indicating that these viruses, as well as RVFV on certain cell types, employ additional unidentified virion attachment factors and/or receptors.

IMPORTANCE

Rift Valley fever virus (RVFV) is an emerging pathogen that can cause severe disease in humans and animals. Epizootics among livestock populations lead to high mortality rates and can be economically devastating. Human epidemics of Rift Valley fever, often initiated by contact with infected animals, are characterized by a febrile disease that sometimes leads to encephalitis or hemorrhagic fever. The global burden of the pathogen is increasing because it has recently disseminated beyond Africa, which is of particular concern because the virus can be transmitted by widely distributed mosquito species. There are no FDA-licensed vaccines or antiviral agents with activity against RVFV, and details of its life cycle and interaction with host cells are not well characterized. We used the power of genetic screening in human cells and found that RVFV utilizes glycosaminoglycans to attach to host cells. This furthers our understanding of the virus and informs the development of antiviral therapeutics.

TSH-receptor-expressing fibrocytes and thyroid-associated ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is a vexing and undertreated ocular component of Graves disease in which orbital tissues undergo extensive remodelling. My colleagues and I have introduced the concept that fibrocytes expressing the haematopoietic cell antigen CD34 (CD34(+) fibrocytes), which are precursor cells of bone-marrow-derived monocyte lineage, express the TSH receptor (TSHR). These cells also produce several other proteins whose expression was traditionally thought to be restricted to the thyroid gland. TSHR-expressing fibrocytes in which the receptor is activated by its ligand generate extremely high levels of several inflammatory cytokines. Acting in concert with TSHR, the insulin-like growth factor 1 receptor (IGF-1R) expressed by orbital fibroblasts and fibrocytes seems to be necessary for TSHR-dependent cytokine production, as anti-IGF-1R blocking antibodies attenuate these proinflammatory actions of TSH. Furthermore, circulating fibrocytes are highly abundant in patients with TAO and seem to infiltrate orbital connective tissues, where they might transition to CD34(+) fibroblasts. My research group has postulated that the infiltration of fibrocytes into the orbit, their unique biosynthetic repertoire and their proinflammatory and profibrotic phenotype account for the characteristic properties exhibited by orbital connective tissues that underlie susceptibility to TAO. These insights, which have emerged in the past few years, might be of use in therapeutically targeting pathogenic orbit-infiltrating fibrocytes selectively by utilizing novel biologic agents that interfere with TSHR and IGF-1R signalling.

The pathophysiology of thyroid eye disease

The pathophysiology of thyroid eye disease (TED) is complex and incompletely understood. Orbital fibroblasts (OFs) seem to be the key effector cells that are responsible for the characteristic soft tissue enlargement seen in TED. They express potentially pathogenic autoantigens, such as thyrotropin receptor and insulin-like growth factor-1 receptor. An intricate interplay between these autoantigens and the autoantibodies found in Graves disease may lead to the activation of OFs, which then leads to increased hyaluronan production, proinflammatory cytokine synthesis, and enhanced differentiation into either myofibroblasts or adipocytes. Some of the OFs in TED patients seem to be derived from infiltrating fibrocytes. These cells originate from the bone marrow and exhibit both fibroblast and myeloid phenotype. In the TED orbit, they may mediate the orbital expansion and inflammatory infiltration. Last, lymphocytes and cytokines are intimately involved in the initiation, amplification, and maintenance of the autoimmune process in TED.

Current concepts in the molecular pathogenesis of thyroid-associated ophthalmopathy

Graves' disease (GD) is a common autoimmune condition. At its core, stimulatory autoantibodies are directed at the thyroid-stimulating hormone receptor (TSHR), resulting in dysregulated thyroid gland activity and growth. Closely associated with GD is the ocular condition known as thyroid-associated ophthalmopathy (TAO). The pathogenesis of TAO remains enigmatic as do the connections between the thyroid and orbit. This review highlights the putative molecular mechanisms involved in TAO and suggests how these insights provide future directions for identifying therapeutic targets. Genetic, epigenetic, and environmental factors have been suggested as contributory to the development of GD and TAO. Thyroid-stimulating hormone receptor and insulin-like growth factor receptor (IGF-1R) are expressed at higher levels in the orbital connective tissue from individuals with TAO than in healthy tissues. Together, they form a functional complex and appear to promote signaling relevant to GD and TAO. Orbital fibroblasts display an array of cell surface receptors and generate a host of inflammatory molecules that may participate in T and B cell infiltration. Recently, a population of orbital fibroblasts has been putatively traced to bone marrow-derived progenitor cells, known as fibrocytes, as they express CD45, CD34, CXCR4, collagen I, functional TSHR, and thyroglobulin (Tg). Fibrocytes become more numerous in GD and we believe traffic to the orbit in TAO. Numerous attempts at developing complete animal models of GD have been largely unsuccessful, because they lack fidelity with the ocular manifestations seen in TAO. Better understanding of the pathogenesis of TAO and development of improved animal models should greatly accelerate the identification of medical therapy for this vexing medical problem.

UDP-glucose dehydrogenase activity and optimal downstream cellular function require dynamic reorganization at the dimer-dimer subunit interfaces

UDP-glucose dehydrogenase (UGDH) provides precursors for steroid elimination, hyaluronan production, and glycosaminoglycan synthesis. The wild-type UGDH enzyme purifies in a hexamer-dimer equilibrium and transiently undergoes dynamic motion that exposes the dimer-dimer interface during catalysis. In the current study we created and characterized point mutations that yielded exclusively dimeric species (obligate dimer, T325D), dimeric species that could be induced to form hexamers in the ternary complex with substrate and cofactor (T325A), and a previously described exclusively hexameric species (UGDHΔ132) to investigate the role of quaternary structure in regulation of the enzyme. Characterization of the purified enzymes revealed a significant decrease in the enzymatic activity of the obligate dimer and hexamer mutants. Kinetic analysis of wild-type UGDH and the inducible hexamer, T325A, showed that upon increasing enzyme concentration, which favors the hexameric species, activity was modestly decreased and exhibited cooperativity. In contrast, cooperative kinetic behavior was not observed in the obligate dimer, T325D. These observations suggest that the regulation of the quaternary assembly of the enzyme is essential for optimal activity and allosteric regulation. Comparison of kinetic and thermal stability parameters revealed structurally dependent properties consistent with a role for controlled assembly and disassembly of the hexamer in the regulation of UGDH. Finally, both T325A and T325D mutants were significantly less efficient in promoting downstream hyaluronan production by HEK293 cells. These data support a model that requires an operational dimer-hexamer equilibrium to function efficiently and preserve regulated activity in the cell.

UDP-glucose dehydrogenase polymorphisms from patients with congenital heart valve defects disrupt enzyme stability and quaternary assembly

Cardiac valve defects are a common congenital heart malformation and a significant clinical problem. Defining molecular factors in cardiac valve development has facilitated identification of underlying causes of valve malformation. Gene disruption in zebrafish revealed a critical role for UDP-glucose dehydrogenase (UGDH) in valve development, so this gene was screened for polymorphisms in a patient population suffering from cardiac valve defects. Two genetic substitutions were identified and predicted to encode missense mutations of arginine 141 to cysteine and glutamate 416 to aspartate, respectively. Using a zebrafish model of defective heart valve formation caused by morpholino oligonucleotide knockdown of UGDH, transcripts encoding the UGDH R141C or E416D mutant enzymes were unable to restore cardiac valve formation and could only partially rescue cardiac edema. Characterization of the mutant recombinant enzymes purified from Escherichia coli revealed modest alterations in the enzymatic activity of the mutants and a significant reduction in the half-life of enzyme activity at 37 °C. This reduction in activity could be propagated to the wild-type enzyme in a 1:1 mixed reaction. Furthermore, the quaternary structure of both mutants, normally hexameric, was destabilized to favor the dimeric species, and the intrinsic thermal stability of the R141C mutant was highly compromised. The results are consistent with the reduced function of both missense mutations significantly reducing the ability of UGDH to provide precursors for cardiac cushion formation, which is essential to subsequent valve formation. The identification of these polymorphisms in patient populations will help identify families genetically at risk for valve defects.

Role of insulin-like growth factor-1 (IGF-1) pathway in the pathogenesis of Graves' orbitopathy

The etiology of Graves' orbitopathy (GO) remains enigmatic and thus controversy surrounds its pathogenesis. The role of the thyroid stimulating hormone receptor (TSHR) and activating antibodies directed against it in the hyperthyroidism of Graves' disease (GD) is firmly established. Less well elucidated is what part the TSHR pathway might play in the development of GO. Also uncertain is the participation of other cell surface receptors in the disease. Elevated levels of insulin-like growth factor-1 receptor (IGF-1R) have been found in orbital fibroblasts as well as B and T cells from patients with GD. These abnormal patterns of IGF-1R display are also found in rheumatoid arthritis and carry functional consequences. In addition, activating IgGs capable of displacing IGF-1 from IGF-1R have also been detected in patients with these diseases. IGF-1R forms a complex with TSHR which is necessary for at least some of the non-canonical signaling observed following TSHR activation. Functional TSHR and IGF-1R have also been found on fibrocytes, CD34⁺ bone marrow-derived cells from the monocyte lineage. Levels of TSHR on fibrocytes greatly exceed those found on orbital fibroblasts. When ligated by TSH or M22, a TSHR-activating monoclonal antibody, fibrocytes produce extremely high levels of several cytokines and chemokines. Moreover, fibrocytes infiltrate both the orbit and thyroid in GD. In sum, based on current evidence, IGF-1R and TSHR can be thought of as "partners in crime". Involvement of the former probably transcends disease boundaries, while TSHR may not.

Proteomics analyses of human optic nerve head astrocytes following biomechanical strain

We investigate the role of glial cell activation in the human optic nerve caused by raised intraocular pressure, and their potential role in the development of glaucomatous optic neuropathy. To do this we present a proteomics study of the response of cultured, optic nerve head astrocytes to biomechanical strain, the magnitude and mode of strain based on previously published quantitative models. In this case, astrocytes were subjected to 3 and 12% stretches for either 2 h or 24 h. Proteomic methods included nano-liquid chromatography, tandem mass spectrometry, and iTRAQ labeling. Using controls for both stretch and time, a six-plex iTRAQ liquid chromatography- tandem MS (LC/MS/MS) experiment yielded 573 proteins discovered at a 95% confidence limit. The pathways included transforming growth factor β1, tumor necrosis factor, caspase 3, and tumor protein p53, which have all been implicated in the activation of astrocytes and are believed to play a role in the development of glaucomatous optic neuropathy. Confirmation of the iTRAQ analysis was performed by Western blotting of various proteins of interest including ANXA 4, GOLGA2, and αB-Crystallin.

Structural basis of cooperativity in human UDP-glucose dehydrogenase

BACKGROUND

UDP-glucose dehydrogenase (UGDH) is the sole enzyme that catalyzes the conversion of UDP-glucose to UDP-glucuronic acid. The product is used in xenobiotic glucuronidation in hepatocytes and in the production of proteoglycans that are involved in promoting normal cellular growth and migration. Overproduction of proteoglycans has been implicated in the progression of certain epithelial cancers, while inhibition of UGDH diminished tumor angiogenesis in vivo. A better understanding of the conformational changes occurring during the UGDH reaction cycle will pave the way for inhibitor design and potential cancer therapeutics.

METHODOLOGY

Previously, the substrate-bound of UGDH was determined to be a symmetrical hexamer and this regular symmetry is disrupted on binding the inhibitor, UDP-α-D-xylose. Here, we have solved an alternate crystal structure of human UGDH (hUGDH) in complex with UDP-glucose at 2.8 Å resolution. Surprisingly, the quaternary structure of this substrate-bound protein complex consists of the open homohexamer that was previously observed for inhibitor-bound hUGDH, indicating that this conformation is relevant for deciphering elements of the normal reaction cycle.

CONCLUSION

In all subunits of the present open structure, Thr131 has translocated into the active site occupying the volume vacated by the absent active water and partially disordered NAD+ molecule. This conformation suggests a mechanism by which the enzyme may exchange NADH for NAD+ and repolarize the catalytic water bound to Asp280 while protecting the reaction intermediates. The structure also indicates how the subunits may communicate with each other through two reaction state sensors in this highly cooperative enzyme.

Divergent Sp1 protein levels may underlie differential expression of UDP-glucose dehydrogenase by fibroblasts: role in susceptibility to orbital Graves disease

UDP-glucose dehydrogenase (UGDH) catalyzes the formation of UDP-glucuronate. Glucuronate represents an integral component of the glycosaminoglycan, hyaluronan, which accumulates in orbital Graves disease. Here we report that orbital fibroblasts express higher levels of UGDH than do those from skin. This is a consequence of greater UGDH gene promoter activity and more abundant steady-state UGDH mRNA. Six Sp1 sites located in the proximal 550 bp of the UGDH gene promoter appear to determine basal promoter activity, as does a previously unrecognized 49-bp sequence spanning -1436 nucleotides (nt) and -1388 nt that negatively affects activity. Nuclear Sp1 protein is more abundant in orbital fibroblasts, and its binding to specific sites on DNA is greater than that in dermal fibroblasts. Mutating each of these Sp1 sites in a UGDH gene promoter fragment, extending from -1387 to +71 nt and fused to a luciferase reporter, results in divergent activities when transfected in orbital and dermal fibroblasts. Reducing Sp1 attenuated UGDH gene promoter activity, lowered steady-state UGDH mRNA levels, and reduced UGDH enzyme activity. Targeting Sp1 and UGDH with specific siRNAs also lowered hyaluronan synthase-1 (HAS-1) and HAS-2 levels and reduced hyaluronan accumulation in orbital fibroblasts. These findings suggest that orbital fibroblasts express high levels of UGDH in an anatomic-specific manner, apparently the result of greater constitutive Sp1. These high UGDH levels may underlie susceptibility of the orbit to localized overproduction of hyaluronan in Graves disease.

UDP-glucose dehydrogenase: structure and function of a potential drug target

Biosynthesis of the glycosaminoglycan precursor UDP-α-D-glucuronic acid occurs through a 2-fold oxidation of UDP-α-D-glucose that is catalysed by UGDH (UDP-α-D-glucose 6-dehydrogenase). Structure-function relationships for UGDH and proposals for the enzymatic reaction mechanism are reviewed in the present paper, and structure-based sequence comparison is used for subclassification of UGDH family members. The eukaryotic group of enzymes (UGDH-II) utilize an extended C-terminal domain for the formation of complex homohexameric assemblies. The comparably simpler oligomerization behaviour of the prokaryotic group of enzymes (UGDH-I), in which dimeric forms prevail, is traced back to the lack of relevant intersubunit contacts and trimmings within the C-terminal region. The active site of UGDH contains a highly conserved cysteine residue, which plays a key role in covalent catalysis. Elevated glycosaminoglycan formation is implicated in a variety of human diseases, including the progression of tumours. The inhibition of synthesis of UDP-α-D-glucuronic acid using UGDH antagonists might therefore be a useful strategy for therapy.

The novel UDP glycosyltransferase 3A2: cloning, catalytic properties, and tissue distribution

The human UDP glycosyltransferase (UGT) 3A family is one of three families involved in the metabolism of small lipophilic compounds. Members of these families catalyze the addition of sugar residues to chemicals, which enhances their excretion from the body. The UGT1 and UGT2 family members primarily use UDP glucuronic acid to glucuronidate numerous compounds, such as steroids, bile acids, and therapeutic drugs. We showed recently that UGT3A1, the first member of the UGT3 family to be characterized, is unusual in using UDP N-acetylglucosamine as sugar donor, rather than UDP glucuronic acid or other UDP sugar nucleotides (J Biol Chem 283:36205-36210, 2008). Here, we report the cloning, expression, and characterization of UGT3A2, the second member of the UGT3 family. Like UGT3A1, UGT3A2 is inactive with UDP glucuronic acid as sugar donor. However, in contrast to UGT3A1, UGT3A2 uses both UDP glucose and UDP xylose but not UDP N-acetylglucosamine to glycosidate a broad range of substrates including 4-methylumbelliferone, 1-hydroxypyrene, bioflavones, and estrogens. It has low activity toward bile acids and androgens. UGT3A2 transcripts are found in the thymus, testis, and kidney but are barely detectable in the liver and gastrointestinal tract. The low expression of UGT3A2 in the latter, which are the main organs of drug metabolism, suggests that UGT3A2 has a more selective role in protecting the organs in which it is expressed against toxic insult rather than a more generalized role in drug metabolism. The broad substrate and novel UDP sugar specificity of UGT3A2 would be advantageous for such a function.

Thyroid eye disease

Thyroid eye disease (TED) is the most common cause of proptosis in adults, and should always be a consideration in patients with unexplained diplopia, pain, or optic nerve dysfunction. At least 80% of TED is associated with Graves disease (GD), and at least 50% of patients with GD develop clinically evident symptomatic TED. The most confusing patients for doctors of all subspecialties are the patients with eye symptoms and signs that precede serum evidence of a thyroid imbalance. Management of TED may include immunosuppressive medications, radiation, or surgery. Although the prognosis for optic nerve function is excellent, the restrictive dysmotility can result in permanent disability. Orbit and eyelid reconstruction are reserved for stable, inactive patients and are the final steps in minimizing facial alterations and enhancing the patient's daily functioning.

Potential role for bone marrow-derived fibrocytes in the orbital fibroblast heterogeneity associated with thyroid-associated ophthalmopathy

Fibroblast heterogeneity has been recognized for decades, but the basis for multiple phenotypes among these cells has been investigated only recently. More than 15 years ago, Bucalla and his colleagues described for the first time a population of fibroblast-like cells among circulating mononuclear blood cells. Subsequently these mesenchymal cells, termed fibrocytes, have been characterized and found to participate in normal and pathological tissue remodelling. In this review, I have attempted to present the evidence generated thus far suggesting that fibrocytes are participants in autoimmune diseases where tissues are injured and undergo remodelling. Aspects of their phenotype suggest that they are well suited to help orchestrate immune responses through mononuclear cell recruitment and their ability to produce inflammatory mediators and extracellular matrix molecules. These attributes also raise the possibility that they might be useful targets against which therapeutic agents might be aimed.

The activity of hyaluronan synthase 2 is regulated by dimerization and ubiquitination

Hyaluronan is a component of the extracellular matrix, which affects tissue homeostasis. In this study, we investigated the regulatory mechanisms of one of the hyaluronan-synthesizing enzymes, HAS2. Ectopic expression of Flag- and 6myc-HAS2 in COS-1 cells followed by immunoprecipitation and immunoblotting revealed homodimers; after co-transfection with Flag-HAS3, also heterodimers were seen. Furthermore, the expressed HAS2 was ubiquitinated. We identified one acceptor site for ubiquitin on lysine residue 190. Mutation of this residue led to inactivation of the enzymatic activity of HAS2. Interestingly, K190R-mutated HAS2 formed dimers with wt HAS2 and quenched the activity of wt HAS2, thus demonstrating a functional role of the dimeric configuration.

Immunopathogenesis of thyroid eye disease: emerging paradigms

Graves disease represents a systemic autoimmune process targeting the thyroid, orbit, and pretibial skin. The thyroid dysfunction is treatable, but no consistently effective medical therapy has yet been described for the orbital manifestations of Graves disease, also known as thyroid-associated ophthalmopathy or thyroid eye disease. Several autoantigens are potentially relevant to the pathogenesis of thyroid eye disease. Activating antibodies generated against the thyrotropin receptor can be detected in a majority of patients, and these drive hyperthyroidism. However, stimulating antibodies against the insulin-like growth factor-1 receptor (IGF-1R) may also play a role in the extra-thyroid manifestations of Graves disease. IGF-1R is overexpressed by orbital fibroblasts derived from patients with thyroid eye disease, whereas IGF-1R(+) T and IGF-1R(+) B cells are considerably more frequent in Graves disease. Actions of several cytokines and the molecular interplay peculiar to the orbit appear to provoke the inflammation, fat expansion, and deposition of excessive extracellular matrix molecules in thyroid eye disease. Based upon these new insights, several therapeutic strategies can now be proposed that, for the first time, might specifically interrupt its pathogenesis.