Kinetic and Spectroscopic Investigation of the Y157F and C93G/Y157F Variants of Cysteine Dioxygenase: Dissecting the Roles of the Second-Sphere Residues C93 and Y157.

In mammals, l-cysteine (Cys) homeostasis is maintained by the mononuclear nonheme iron enzyme cysteine dioxygenase (CDO), which oxidizes Cys to cysteine sulfinic acid. CDO contains a rare post-translational modification, involving the formation of a thioether cross-link between a Cys residue at position 93 (Mus musculus CDO numbering) and a nearby tyrosine at position 157 (Cys-Tyr cross-link). As-isolated CDO contains both the cross-linked and non-cross-linked isoforms, and formation of the Cys-Tyr cross-link during repeated enzyme turnover increases CDO's catalytic efficiency by ∼10-fold. Interestingly, while the C93G CDO variant lacks the Cys-Tyr cross-link, it is similarly active as cross-linked wild-type (WT) CDO. Alternatively, the Y157F CDO variant, which also lacks the cross-link but maintains the free thiolate at position 93, exhibits a drastically reduced catalytic efficiency. These observations suggest that the untethered thiolate moiety of C93 is detrimental to CDO activity and/or that Y157 is essential for catalysis. To further assess the roles of residues C93 and Y157, we performed a spectroscopic and kinetic characterization of Y157F CDO and the newly designed C93G/Y157F CDO variant. Our results provide evidence that the non-cross-linked C93 thiolate stabilizes a water at the sixth coordination site of Cys-bound Y157F Fe(II)CDO. A water is also present, though more weakly coordinated, in Cys-bound C93G/Y157F Fe(II)CDO. The presence of a water molecule, which must be displaced by cosubstrate O2, likely makes a significant contribution to the ∼15-fold and ∼7-fold reduced catalytic efficiencies of the Y157F and C93G/Y157F CDO variants, respectively, relative to cross-linked WT CDO.

TRIM47-CDO1 axis dictates hepatocellular carcinoma progression by modulating ferroptotic cell death through the ubiquitin‒proteasome system.

Hepatocellular carcinoma (HCC) is the predominant form of liver cancer, characterized by high morbidity and mortality rates, as well as unfavorable treatment outcomes. Tripartite motif-containing protein 47 (TRIM47) has been implicated in various diseases including tumor progression with the activity of E3 ubiquitin ligase. However, the precise regulatory mechanisms underlying the involvement of TRIM47 in HCC remain largely unexplored. Here, we provide evidence that TRIM47 exhibits heightened expression in tumor tissues, and its expression is in intimate association with clinical staging and patient prognosis. TRIM47 promotes HCC proliferation, migration, and invasion as an oncogene by in vitro gain- and loss-of-function experiments. TRIM47 knockdown results in HCC ferroptosis induction, primarily through CDO1 involvement to regulate GSH synthesis. Subsequent experiments confirm the interaction between TRIM47 and CDO1 dependent on B30.2 domain, wherein TRIM47 facilitates K48-linked ubiquitination, leading to a decrease in CDO1 protein abundance in HCC. Furthermore, CDO1 is able to counteract the promotional effect of TRIM47 on HCC biological functions. Overall, our research provides novel insight into the mechanism of TRIM47 in CDO1-mediated ferroptosis in HCC cells, highlighting its value as a potential target candidate for HCC therapeutic approaches.

Polymorphisms in the cysteine dioxygenase gene and their association with taurine content in the Pacific oyster Crassostrea gigas.

The Pacific oyster Crassostrea gigas is rich in taurine, which is crucial for its adaptation to the fluctuating intertidal environment and presents significant potential in improving taurine nutrition and boosting immunity in humans. Cysteine dioxygenase (CDO) is a key enzyme involved in the initial step of taurine biosynthesis and plays a crucial role in regulating taurine content in the body. In the present study, polymorphisms of CDO gene in C. gigas (CgCDO) and their association with taurine content were evaluated in 198 individuals. A total of 24 single nucleotide polymorphism (SNP) loci were identified in the exonic region of CgCDO gene by direct sequencing. Among these SNPs, c.279G>A and c.287C>A were found to be significantly associated with taurine content, with the GG and AA genotype at the two loci exhibiting enhanced taurine accumulation (p < 0.05). Haplotype analysis revealed that the 279GG/287AA haplotype had the highest taurine content of 29.24 mg/g, while the 279AA/287CC haplotype showed the lowest taurine content of 21.19 mg/g. These results indicated that the SNPs of CgCDO gene could influence the taurine content in C. gigas and have potential applications in the selective breeding of high-taurine varieties.

Deletion of hepatocyte cysteine dioxygenase type 1, a bile acid repressed gene, enhances glutathione synthesis and ameliorates acetaminophen hepatotoxicity.

Liver is a major organ that metabolizes sulfur amino acids cysteine, which is the substrate for the synthesis of many essential cellular molecules including GSH, taurine, and coenzyme A. Bile acid-activated farnesoid x receptor (FXR) inhibits cysteine dioxygenase type 1 (CDO1), which mediates hepatic cysteine catabolism and taurine synthesis. To define the impact of bile acid inhibition of CDO1 on hepatic sulfur amino acid metabolism and antioxidant capacity, we developed hepatocyte-specific CDO1 knockout mice (Hep-CDO1 KO) and hepatocyte specific CDO1 transgenic mice (Hep-CDO1 Tg). Liver metabolomics revealed that genetic deletion of hepatic CDO1 reduced de novo taurine synthesis but had no impact on hepatic taurine abundance or bile acid conjugation. Consistent with reduced cysteine catabolism, Hep-CDO1 KO mice showed increased hepatic cysteine abundance but unaltered methionine cycle intermediates and coenzyme A synthesis. Upon acetaminophen overdose, Hep-CDO1 KO mice showed increased GSH synthesis capacity and alleviated liver injury. In contrast, hepatic CDO1 overexpression in Hep-CDO1 Tg mice stimulated hepatic cysteine to taurine conversion, resulting in reduced hepatic cysteine abundance. However, Hep-CDO1 Tg mice and WT showed similar susceptibility to acetaminophen-induced liver injury. Hep-CDO1 Tg mice showed similar hepatic taurine and coenzyme A compared to WT mice. In summary, these findings suggest that bile acid and FXR signaling inhibition of CDO1-mediated hepatic cysteine catabolism preferentially modulates hepatic GSH synthesis capacity and antioxidant defense, but has minimal effect on hepatic taurine and coenzyme A abundance. Repression of hepatic CDO1 may contribute to the hepatoprotective effects of FXR activation under certain pathologic conditions.

Enzyme-Catalyzed Oxidative Degradation of Ergothioneine.

Ergothioneine is a sulfur-containing metabolite that is produced by bacteria and fungi, and is absorbed by plants and animals as a micronutrient. Ergothioneine reacts with harmful oxidants, including singlet oxygen and hydrogen peroxide, and may therefore protect cells against oxidative stress. Herein we describe two enzymes from actinobacteria that cooperate in the specific oxidative degradation of ergothioneine. The first enzyme is an iron-dependent thiol dioxygenase that produces ergothioneine sulfinic acid. A crystal structure of ergothioneine dioxygenase from Thermocatellispora tengchongensis reveals many similarities with cysteine dioxygenases, suggesting that the two enzymes share a common mechanism. The second enzyme is a metal-dependent ergothioneine sulfinic acid desulfinase that produces Nα-trimethylhistidine and SO2 . The discovery that certain actinobacteria contain the enzymatic machinery for O2 -dependent biosynthesis and O2 -dependent degradation of ergothioneine indicates that these organisms may actively manage their ergothioneine content.

Identification of a novel enzyme and the regulation of key enzymes in mammalian taurine synthesis.

Taurine has many pharmacological roles on various tissues. The maintenance of abundant taurine content in the mammalian body through endogenous synthesis, in addition to exogenous intake, is the essential factor for morphological and functional maintenances in most tissues. The synthesis of taurine from sulfur-containing amino acids is influenced by various factors. Previous literature findings indicate the influence of the intake of proteins and sulfur-containing amino acids on the activity of the rate-limiting enzymes cysteine dioxygenase and cysteine sulfinate decarboxylase. In addition, the regulation of the activity and expression of taurine-synthesis enzymes by hormones, bile acids, and inflammatory cytokines through nuclear receptors have been reported in liver and reproductive tissues. Furthermore, flavin-containing monooxygenase subtype 1 was recently identified as the taurine-synthesis enzyme that converts hypotaurine to taurine. This review introduces the novel taurine synthesis enzyme and the nuclear receptor-associated regulation of key enzymes in taurine synthesis.

Identification of novel plant cysteine oxidase inhibitors from a yeast chemical genetic screen.

Hypoxic responses in plants involve Plant Cysteine Oxidases (PCOs). They catalyze the N-terminal cysteine oxidation of Ethylene Response Factors VII (ERF-VII) in an oxygen-dependent manner, leading to their degradation via the cysteine N-degron pathway (Cys-NDP) in normoxia. In hypoxia, PCO activity drops, leading to the stabilization of ERF-VIIs and subsequent hypoxic gene upregulation. Thus far, no chemicals have been described to specifically inhibit PCO enzymes. In this work, we devised an in vivo pipeline to discover Cys-NDP effector molecules. Budding yeast expressing AtPCO4 and plant-based ERF-VII reporters was deployed to screen a library of natural-like chemical scaffolds and was further combined with an Arabidopsis Cys-NDP reporter line. This strategy allowed us to identify three PCO inhibitors, two of which were shown to affect PCO activity in vitro. Application of these molecules to Arabidopsis seedlings led to an increase in ERF-VII stability, induction of anaerobic gene expression, and improvement of tolerance to anoxia. By combining a high-throughput heterologous platform and the plant model Arabidopsis, our synthetic pipeline provides a versatile system to study how the Cys-NDP is modulated. Its first application here led to the discovery of at least two hypoxia-mimicking molecules with the potential to impact plant tolerance to low oxygen stress.

Monitoring ADO dependent proteolysis in cells using fluorescent reporter proteins.

2-Aminoethanethiol dioxygenase (ADO) is the mammalian orthologue of the plant cysteine oxidases and together these enzymes are responsible for catalysing dioxygenation of N-terminal cysteine residues of certain proteins. This modification creates an N-degron motif that permits arginylation and subsequent proteasomal degradation of such proteins via the Arg-branch of the N-degron pathway. In humans 4 proteins have been identified as substrates of ADO; regulators of G-protein signalling (RGS) 4, 5 and 16, and interleukin-32 (IL-32). Nt-cysteine dioxygenation of these proteins occurs rapidly under normoxic conditions, but ADO activity is very sensitive to O2 availability and as such the stability of substrate proteins is inversely proportional to cellular O2 levels. Much is still to understand about the biochemistry and physiology of this pathway in vitro and in vivo, and Cys N-degron targeted fluorescent proteins can provide a simple and effective tool to study this at both subcellular and high-throughput scales. This chapter describes the design, production and implementation of a fluorescent fusion protein proteolytically regulated by ADO and the N-degron pathway.

Genome-Wide Identification and Analysis of the Plant Cysteine Oxidase (PCO) Gene Family in Brassica napus and Its Role in Abiotic Stress Response.

Plant Cysteine Oxidase (PCO) is a plant O2-sensing enzyme catalyzing the oxidation of cysteine to Cys-sulfinic acid at the N-termini of target proteins. To better understand the Brassica napus PCO gene family, PCO genes in B. napus and related species were analyzed. In this study, 20, 7 and 8 PCO genes were identified in Brassica napus, Brassica rapa and Brassica oleracea, respectively. According to phylogenetic analysis, the PCOs were divided into five groups: PCO1, PCO2, PCO3, PCO4 and PCO5. Gene organization and motif distribution analysis suggested that the PCO gene family was relatively conserved during evolution. According to the public expression data, PCO genes were expressed in different tissues at different developmental stages. Moreover, qRT-PCR data showed that most of the Bna/Bra/BoPCO5 members were expressed in leaves, roots, flowers and siliques, suggesting an important role in both vegetative and reproductive development. Expression of BnaPCO was induced by various abiotic stress, especially waterlogging stress, which was consistent with the result of cis-element analysis. In this study, the PCO gene family of Brassicaceae was analyzed for the first time, which contributes to a comprehensive understanding of the origin and evolution of PCO genes in Brassicaceae and the function of BnaPCO in abiotic stress responses.

Kinetic Measurements to Investigate the Oxygen-Sensing Properties of Plant Cysteine Oxidases.

Enzymatic O2 sensors transduce the availability of O2 within the cell into a physiological, typically adaptive response. One such O2-sensing enzymatic family is the N-terminal cysteine dioxygenases in plants (plant cysteine oxidases [PCOs]). In vitro kinetic studies have determined the O2-sensing capacity of PCOs. Here we describe the rationale and experimental protocol for an assay with which the O2 sensitivity of Arabidopsis thaliana PCOs (AtPCOs) can be measured. We explain each step from the recombinant protein synthesis of AtPCOs to the steady-state kinetic assays of AtPCOs for primary substrate and O2 from which kinetic parameters can be derived. The same techniques can be applied to other N-terminal cysteine thiol dioxygenases, e.g. 2-aminoethanethiol dioxygenase (ADO), and similar principles can be applied to determine kinetic characteristics of other oxygenase enzymes towards O2.

Spectroscopic analysis of the mammalian enzyme cysteine dioxygenase.

l-Cysteine (Cys) is an essential building block for the synthesis of new proteins and serves as a precursor for several biologically important sulfur-containing molecules, such as coenzyme A, taurine, glutathione, and inorganic sulfate. However, organisms must tightly regulate the concentration of free Cys, as elevated levels of this semi-essential amino acid can be extremely harmful. The non-heme iron enzyme cysteine dioxygenase (CDO) serves to maintain the proper levels of Cys by catalyzing its oxidation to cysteine sulfinic acid. Crystal structures of resting and substrate-bound mammalian CDO revealed two surprising structural motifs in the first and second coordination spheres of the Fe center. The first is the existence of a neutral three histidine (3-His) facial triad that coordinates the Fe ion, as opposed to an anionic 2-His-1-carboxylate facial triad that is typically observed in mononuclear non-heme Fe(II) dioxygenases. The second unusual structural feature exhibited by mammalian CDO is the presence of a covalent crosslink between the sulfur of a Cys residue and an ortho-carbon of a tyrosine residue. Spectroscopic studies of CDO have provided invaluable insights into the roles that these unusual features play with regards to substrate Cys and co-substrate O2 binding and activation. In this chapter, we summarize results obtained from electronic absorption, electron paramagnetic resonance, magnetic circular dichroism, resonance Raman, and Mössbauer spectroscopic studies of mammalian CDO carried out in the last two decades. Pertinent results obtained from complementary computational studies are also briefly summarized.

Cyanide replaces substrate in obligate-ordered addition of nitric oxide to the non-heme mononuclear iron AvMDO active site.

Thiol dioxygenases are a subset of non-heme mononuclear iron oxygenases that catalyze the O2-dependent oxidation of thiol-bearing substrates to yield sulfinic acid products. Cysteine dioxygenase (CDO) and 3-mercaptopropionic acid (3MPA) dioxygenase (MDO) are the most extensively characterized members of this enzyme family. As with many non-heme mononuclear iron oxidase/oxygenases, CDO and MDO exhibit an obligate-ordered addition of organic substrate before dioxygen. As this substrate-gated O2-reactivity extends to the oxygen-surrogate, nitric oxide (NO), EPR spectroscopy has long been used to interrogate the [substrate:NO:enzyme] ternary complex. In principle, these studies can be extrapolated to provide information about transient iron-oxo intermediates produced during catalytic turnover with dioxygen. In this work, we demonstrate that cyanide mimics the native thiol-substrate in ordered-addition experiments with MDO cloned from Azotobacter vinelandii (AvMDO). Following treatment of the catalytically active Fe(II)-AvMDO with excess cyanide, addition of NO yields a low-spin (S = 1/2) (CN/NO)-Fe-complex. Continuous wave and pulsed X-band EPR characterization of this complex produced in wild-type and H157N variant AvMDO reveal multiple nuclear hyperfine features diagnostic of interactions within the first- and outer-coordination sphere of the enzymatic Fe-site. Spectroscopically validated computational models indicate simultaneous coordination of two cyanide ligands replaces the bidentate (thiol and carboxylate) coordination of 3MPA allowing for NO-binding at the catalytically relevant O2-binding site. This promiscuous substrate-gated reactivity of AvMDO with NO provides an instructive counterpoint to the high substrate-specificity exhibited by mammalian CDO for L-cysteine.

Testosterone enhances taurine synthesis by upregulating androgen receptor and cysteine sulfinic acid decarboxylase expressions in male mouse liver.

Taurine is an end-product of cysteine metabolism, whereas cysteine dioxygenase (CDO) and cysteine sulfinate decarboxylase (CSAD) are key enzymes regulating taurine synthesis. Sex steroids, including estrogens and androgens, are associated with liver physiopathological processes; however, we still do not know whether taurine and sex steroids interact in regulating liver physiology and hepatic diseases, and whether there are sex differences, although our recent study shows that the estrogen is involved in regulating taurine synthesis in mouse liver. The present study was thus proposed to identify whether 17-ß-estradiol and testosterone (T) play their roles by regulating CDO and CSAD expression and taurine synthesis in male mouse liver. Our results demonstrated that testosterone did not have a significant influence on CDO expression but significantly enhanced CSAD, androgen receptor (AR) expressions, and taurine levels in mouse liver, cultured hepatocytes, and HepG2 cells, whereas these effects were abrogated by AR antagonist flutamide. Furthermore, our results showed that testosterone increased CSAD-promoter-luciferase activity through the direct interaction of the AR DNA binding domain with the CSAD promoter. These findings first demonstrate that testosterone acts as an important factor to regulate sulfur amino acid metabolism and taurine synthesis through AR/CSAD signaling pathway. In addition, the in vivo and in vitro experiments showed that 17-ß-estradiol has no significant effects on liver CSAD expression and taurine synthesis in male mice and suggest that the effects of sex steroids on the taurine synthesis in mouse liver have sex differences. These results are crucial for understanding the physiological functions of taurine/androgen and their interacting mechanisms in the liver.NEW & NOTEWORTHY This study demonstrates that testosterone functions to enhance taurine synthesis by interacting with androgen receptor and binding to cysteine sulfinate decarboxylase (CSAD) promoter zone. Whereas estrogen has no significant effects either on liver CSAD expression or taurine synthesis in male mice and suggests that the effects of sex steroids on taurine synthesis in the liver have gender differences. These new findings are the potential for establishing effective protective and therapeutic strategies for liver diseases.

Target of rapamycin signaling couples energy to oxygen sensing to modulate hypoxic gene expression in Arabidopsis.

Plants respond to oxygen deprivation by activating the expression of a set of hypoxia-responsive genes (HRGs). The master regulator of this process is a small group of transcription factors belonging to group VII of the ethylene response factors (ERF-VIIs). ERF-VIIs are highly unstable under aerobic conditions due to the continuous oxidation of their characteristic Cys residue at the N terminus by plant cysteine oxidases (PCOs). Under hypoxia, PCOs are inactive and the ERF-VIIs activate transcription of the HRGs required for surviving hypoxia. However, if the plant exposed to hypoxia has limited sugar reserves, the activity of ERF-VIIs is severely dampened. This suggests that oxygen sensing by PCO/ERF-VII is fine-tuned by another sensing pathway, related to sugar or energy availability. Here, we show that oxygen sensing by PCO/ERF-VII is controlled by the energy sensor target of rapamycin (TOR). Inhibition of TOR by genetic or pharmacological approaches leads to a much lower induction of HRGs. We show that two serine residues at the C terminus of RAP2.12, a major ERF-VII, are phosphorylated by TOR and are needed for TOR-dependent activation of transcriptional activity of RAP2.12. Our results demonstrate that oxygen and energy sensing converge in plants to ensure an appropriate transcription of genes, which is essential for surviving hypoxia. When carbohydrate metabolism is inefficient in producing ATP because of hypoxia, the lower ATP content reduces TOR activity, thus attenuating the efficiency of induction of HRGs by the ERF-VIIs. This homeostatic control of the hypoxia-response is required for the plant to survive submergence.

Assessing In Vivo Oxygen Dynamics Using Plant N-Terminal Degrons in Saccharomyces cerevisiae.

The expression of plant cysteine oxidase (PCO) enzyme in Saccharomyces cerevisiae enables the Arg/Cys N-degron pathway (Cys-NDP) for selective protein degradation that, in plants, functions as direct oxygen perception mechanism. A synthetic construct based on the plant Cys-NDP substrate related to apetala 2.12 (RAP2.12), the dual luciferase oxygen reporter (DLOR), exploits the N-terminal Cys of RAP2.12, and its oxygen-dependent degradation through the Cys-NDP. The luminescent output of DLOR can be used as a proxy for intracellular oxygen dynamics in budding yeast. Replacement of the luciferase reporter of the DLOR with fluorescent proteins would furthermore facilitate the imaging of reporter dynamics in living cells. In this chapter, we describe the methods for delivering the DLOR synthetic construct to yeast and calibrating its output by means of oxygen quantification in the culture with a physical oxygen sensor. We explain the setup needed to carry out hypoxic treatments with several colonies as replicates. We also describe the method to measure oxygen concentration in the culture, the closest indication of intracellular oxygen levels, as a way that would serve to calibrate the DLOR output. Finally, we propose a strategy to replace the luminescent reporters in the DLOR with fluorescent proteins to visualize oxygen dynamics in vivo.

DFT insights into the mechanism of O2 activation catalyzed by a structural and functional model of cysteine dioxygenase with tris(2-pyridyl)methane-based ligand architecture.

Cysteine dioxygenation is an important step in the metabolism of toxic L-cysteine (Cys) in the human body, carried out by cysteine dioxygenase enzyme (CDO). The disruption of this process is found to elicit neurological health issues. This work reports a computational investigation of mechanistic aspects of this reaction, using a recently reported tris(2-pyridyl)methane-based biomimetic model complex of CDO. The computed results indicate that, the initial SO2 bond formation process is the slowest step in the S-dioxygenation process, possessing an activation barrier of 12.7 kcal/mol. The remaining steps were found to be downhill requiring very small activation energies. The transition states were found to undergo spin crossover between triplet and quintet states, while the singlet surface remained unstable throughout the entire reaction. In essence, the mechanistic scheme and multistate reactivity pattern together with the relatively small computed rate-limiting activation barrier as well as the exothermic formation energy demonstrate that the model complex is an efficient biomimetic CDO model. In addition, the study also substantiates the involvement of Fe(IV)oxido intermediates in the mechanism of S-dioxygenation by the chosen model complex. The insights derived from the O2 activation process might pave way for development of more accurate CDO model catalysts that might be capable of even more efficiently mimicking the geometric, spectroscopic and functional features of the CDO enzyme.

Cdo1 promotes PPARγ-mediated adipose tissue lipolysis in male mice.

Cysteine dioxygenase 1 (Cdo1) is a key enzyme in taurine synthesis. Here we show that Cdo1 promotes lipolysis in adipose tissue. Adipose-specific knockout of Cdo1 in mice impairs energy expenditure, cold tolerance and lipolysis, exacerbates diet-induced obesity (DIO) and decreases adipose expression of the key lipolytic genes encoding ATGL and HSL, with little effect on adipose taurine levels. White-adipose-specific overexpression of ATGL and HSL blunts the role of adipose Cdo1 deficiency in promoting DIO. Mechanistically, Cdo1 interacts with PPARγ and facilitates the recruitment of Med24, the core subunit of mediator complex, to ATGL and HSL gene promoters, thereby transactivating their expression. Further, mice with transgenic overexpression of Cdo1 show better cold tolerance, ameliorated DIO and higher lipolysis capacity. Thus, we uncover an unexpected and important role of Cdo1 in regulating adipose lipolysis.

Adipose tissue cysteine dioxygenase type 1 is associated with an anti-inflammatory profile, impacting on systemic metabolic traits.

BACKGROUND: Adipose tissue is a source of multiple factors that modulate systemic insulin sensitivity and cardiovascular risk. Taurine is obtained from the diet but it is less known that it is endogenously synthesized by cysteine dioxygenase type 1 (CDO1). CDO1 exerts a role in adipose tissue from rodent models, but the potential translational value in humans is not available in the literature. METHODS: CDO1 gene expression was analysed in visceral and subcutaneous adipose tissue samples in association with metabolic traits in participants with different degrees of obesity in four independent cohorts. CDO1 was also evaluated in isolated human adipocytes in vitro. Mechanistically, CDO1gene knockdown (KD) of human preadipocytes and adipose-derived mesenchymal stem cells (ASC52telo) (using lentiviral particles) was also evaluated. Mitochondrial respiratory function of adipocytes was evaluated using Seahorse. FINDINGS: Both visceral (VAT) and subcutaneous adipose tissue (SAT) CDO1 mRNA was associated with gene expression markers of adipose tissue function in the four cohorts. Higher CDO1 expression was linked to decreased fasting triglycerides and blood HbA1c even after adjusting by age, BMI and sex. In addition, CDO1 mRNA positively correlated with the expression of genes involved in adipogenesis and negatively with different inflammatory markers. Both VAT and SAT CDO1 mRNA was mainly expressed in adipocytes and significantly increased during adipocyte differentiation, but attenuated under inflammatory conditions. Mechanistically, CDO1 gene KD reduced taurine biosynthesis, evidencing lower CDO1 activity. In both human preadipocytes and ASC52telo cells, CDO1 gene KD resulted in decreased gene expression markers of adipogenesis (ADIPOQ, FABP4, FASN, SLC2A4, CEBPA) and increased inflammatory genes (TNF and IL6) during adipocyte differentiation. Of note, CDO1 gene KD led to decreased mitochondrial respiratory function in parallel to decreased expression of mitochondrial function-, but not biogenesis-related genes. INTERPRETATION: Current findings show the relevance of CDO1 in adipose tissue physiology, suggesting its contribution to an improved systemic metabolic profile. FUNDING: This work was partially supported by research grants PI16/01173, PI19/01712, PI20/01090 and PI21/01361 from the Instituto de Salud Carlos III from Spain, Fondo Europeo de Desarrollo Regional (FEDER) funds, and VII Spanish Diabetes Association grants to Basic Diabetes Research Projects led by young researchers.

CCl4 inhibits the expressions of hepatic taurine biosynthetic enzymes and taurine synthesis in the progression of mouse liver fibrosis.

Carbon tetrachloride (CCl4) is a widely used hepatotoxin for the studies of liver fibrosis and cirrhosis, and taurine has function to abate liver fibrosis induced by CCl4. But the interacting mechanisms between taurine and CCl4 in liver are still largely unknown. These made us to hypothesize that CCl4 may induce liver fibrosis by affecting the expressions of taurine biosynthetic enzymes and taurine synthesis. We thus assayed the expressions of hepatic cysteine dioxygenase (CDO), cysteine sulfonate acid decarboxylase (CSAD) and taurine transporter (TauT) in the progression of mouse liver fibrosis induced by CCl4. The results demonstrated that CCl4 treatment markedly decreased hepatic CSAD, CDO expressions, and taurine levels in hepatic tissue, although TauT expression did not exhibit significant decline. It was contrasting that hepatic α-SMA, serum AST, ALT, ALP kept increasing, which were accompanied by the pathological characters of liver, whereas taurine supplement attenuated the progression of liver fibrosis induced by CCl4. These results demonstrate that CCl4 may induce liver fibrosis by inhibiting hepatic CSAD and CDO expressions and taurine synthesis, which are crucial for our understanding the mechanisms of liver fibrosis induced by CCl4, and also potential for establishing therapeutic strategies of liver fibrosis and related diseases.