Choline Dehydrogenase Contributes to Salt Tolerance in Dunaliella through Betaine Synthesis.

In Dunaliella tertiolecta, a microalga renowned for its extraordinary tolerance to high salinity levels up to 4.5 M NaCl, the mechanisms underlying its stress response have largely remained a mystery. In a groundbreaking discovery, this study identifies a choline dehydrogenase enzyme, termed DtCHDH, capable of converting choline to betaine aldehyde. Remarkably, this is the first identification of such an enzyme not just in D. tertiolecta but across the entire Chlorophyta. A 3D model of DtCHDH was constructed, and molecular docking with choline was performed, revealing a potential binding site for the substrate. The enzyme was heterologously expressed in E. coli Rosetta (DE3) and subsequently purified, achieving enzyme activity of 672.2 U/mg. To elucidate the role of DtCHDH in the salt tolerance of D. tertiolecta, RNAi was employed to knock down DtCHDH gene expression. The results indicated that the Ri-12 strain exhibited compromised growth under both high and low salt conditions, along with consistent levels of DtCHDH gene expression and betaine content. Additionally, fatty acid analysis indicated that DtCHDH might also be a FAPs enzyme, catalyzing reactions with decarboxylase activity. This study not only illuminates the role of choline metabolism in D. tertiolecta's adaptation to high salinity but also identifies a novel target for enhancing the NaCl tolerance of microalgae in biotechnological applications.

Choline dehydrogenase interacts with SQSTM1 to activate mitophagy and promote coelomocyte survival in Apostichopus japonicus following Vibrio splendidus infection.

Previous studies have shown that Vibrio splendidus infection causes mitochondrial damage in Apostichopus japonicus coelomocytes, leading to the production of excessive reactive oxygen species (ROS) and irreversible apoptotic cell death. Emerging evidence suggests that mitochondrial autophagy (mitophagy) is the most effective method for eliminating damaged mitochondria and ROS, with choline dehydrogenase (CHDH) identified as a novel mitophagy receptor that can recognize non-ubiquitin damage signals and microtubule-associated protein 1 light chain 3 (LC3) in vertebrates. However, the functional role of CHDH in invertebrates is largely unknown. In this study, we observed a significant increase in the mRNA and protein expression levels of A. japonicus CHDH (AjCHDH) in response to V. splendidus infection and lipopolysaccharide (LPS) challenge, consistent with changes in mitophagy under the same conditions. Notably, AjCHDH was localized to the mitochondria rather than the cytosol following V. splendidus infection. Moreover, AjCHDH knockdown using siRNA transfection significantly reduced mitophagy levels, as observed through transmission electron microscopy and confocal microscopy. Further investigation into the molecular mechanisms underlying CHDH-regulated mitophagy showed that AjCHDH lacked an LC3-interacting region (LIR) for direct binding to LC3 but possessed a FB1 structural domain that binds to SQSTM1. The interaction between AjCHDH and SQSTM1 was further confirmed by immunoprecipitation analysis. Furthermore, laser confocal microscopy indicated that SQSTM1 and LC3 were recruited by AjCHDH in coelomocytes and HEK293T cells. In contrast, AjCHDH interference hindered SQSTM1 and LC3 recruitment to the mitochondria, a critical step in damaged mitochondrial degradation. Thus, AjCHDH interference led to a significant increase in both mitochondrial and intracellular ROS, followed by increased apoptosis and decreased coelomocyte survival. Collectively, these findings indicate that AjCHDH-mediated mitophagy plays a crucial role in coelomocyte survival in A. japonicus following V. splendidus infection.

The choline dehydrogenase BetA of Acinetobacter baumannii: a flavoprotein responsible for osmotic stress protection.

Acinetobacter baumannii is outstanding for its ability to cope with low water activities which significantly contributes to its persistence in hospital environments. The vast majority of bacteria are able to prevent loss of cellular water by amassing osmoactive compatible solutes or their precursors into the cytoplasm. One such precursor of an osmoprotectant is choline that is taken up from the environment and oxidized to the compatible solute glycine betaine. Here, we report the identification of the osmotic stress operon betIBA in A. baumannii. This operon encodes the choline oxidation pathway important for the production of the solute glycine betaine. The salt-sensitive phenotype of a betA deletion strain could not be rescued by addition of choline, which is consistent with the role of BetA in choline oxidation. We found that BetA is a choline dehydrogenase but also mediates in vitro the oxidation of glycine betaine aldehyde to glycine betaine. BetA was found to be associated with the membrane and to contain a flavin, indicative for BetA donating electrons into the respiratory chain. The choline dehydrogenase activity was not salt dependent but was stimulated by the compatible solute glutamate.

Maternal choline supplementation alters vitamin B-12 status in human and murine pregnancy.

Despite participation in overlapping metabolic pathways, the relationship between choline and vitamin B-12 has not been well characterized especially during pregnancy. We sought to determine the effects of maternal choline supplementation on vitamin B-12 status biomarkers in human and mouse pregnancy, hypothesizing that increased choline intake would improve vitamin B-12 status. Associations between common genetic variants in choline-metabolizing genes and vitamin B-12 status biomarkers were also explored in humans. Healthy third-trimester pregnant women (n=26) consumed either 480 or 930 mg choline/day as part of a 12-week controlled feeding study. Wild-type NSA and Dlx3 heterozygous (Dlx3+/-) mice, which display placental insufficiency, consumed a 1×, 2× or 4× choline diet and were sacrificed at gestational days 15.5 and 18.5. Serum vitamin B-12, methylmalonic acid (MMA) and homocysteine were measured in all samples; holotranscobalamin (in humans) and hepatic vitamin B-12 (in mice) were also measured. The 2× choline supplementation for 12 weeks in pregnant women yielded higher serum concentrations of holotranscobalamin, the bioactive form of vitamin B-12 (~24%, P=.01). Women with genetic variants in choline dehydrogenase (CHDH) and betaine-homocysteine S-methyltransferase (BHMT) had higher serum MMA concentrations (~31%, P=.03) and lower serum holotranscobalamin concentrations (~34%, P=.03), respectively. The 4× choline dose decreased serum homocysteine concentrations in both NSA and Dlx3+/- mice (~36% and~43% respectively, P≤.015). In conclusion, differences in choline supply due to supplementation or genetic variation modulate vitamin B-12 status during pregnancy, supporting a functional relationship between these nutrients.

Investigation of betaine as a novel psychotherapeutic for schizophrenia.

BACKGROUND: Betaine is known to act against various biological stresses and its levels were reported to be decreased in schizophrenia patients. We aimed to test the role of betaine in schizophrenia pathophysiology, and to evaluate its potential as a novel psychotherapeutic. METHODS: Using Chdh (a gene for betaine synthesis)-deficient mice and betaine-supplemented inbred mice, we assessed the role of betaine in psychiatric pathophysiology, and its potential as a novel psychotherapeutic, by leveraging metabolomics, behavioral-, transcriptomics and DNA methylation analyses. FINDINGS: The Chdh-deficient mice revealed remnants of psychiatric behaviors along with schizophrenia-related molecular perturbations in the brain. Betaine supplementation elicited genetic background-dependent improvement in cognitive performance, and suppressed methamphetamine (MAP)-induced behavioral sensitization. Furthermore, betaine rectified the altered antioxidative and proinflammatory responses induced by MAP and in vitro phencyclidine (PCP) treatments. Betaine also showed a prophylactic effect on behavioral abnormality induced by PCP. Notably, betaine levels were decreased in the postmortem brains from schizophrenia, and a coexisting elevated carbonyl stress, a form of oxidative stress, demarcated a subset of schizophrenia with "betaine deficit-oxidative stress pathology". We revealed the decrease of betaine levels in glyoxylase 1 (GLO1)-deficient hiPSCs, which shows elevated carbonyl stress, and the efficacy of betaine in alleviating it, thus supporting a causal link between betaine and oxidative stress conditions. Furthermore, a CHDH variant, rs35518479, was identified as a cis-expression quantitative trait locus (QTL) for CHDH expression in postmortem brains from schizophrenia, allowing genotype-based stratification of schizophrenia patients for betaine efficacy. INTERPRETATION: The present study revealed the role of betaine in psychiatric pathophysiology and underscores the potential benefit of betaine in a subset of schizophrenia. FUND: This study was supported by the Strategic Research Program for Brain Sciences from AMED (Japan Agency for Medical Research and Development) under Grant Numbers JP18dm0107083 and JP19dm0107083 (TY), JP18dm0107129 (MM), JP18dm0107086 (YK), JP18dm0107107 (HY), JP18dm0107104 (AK) and JP19dm0107119 (KH), by the Grant-in-Aid for Scientific Research on Innovative Areas from the MEXT under Grant Numbers JP18H05435 (TY), JP18H05433 (AH.-T), JP18H05428 (AH.-T and TY), and JP16H06277 (HY), and by JSPS KAKENHI under Grant Number JP17H01574 (TY). In addition, this study was supported by the Collaborative Research Project of Brain Research Institute, Niigata University under Grant Numbers 2018-2809 (YK) and RIKEN Epigenetics Presidential Fund (100214-201801063606-340120) (TY).

Functional Characterization and Evolutionary Analysis of Glycine-Betaine Biosynthesis Pathway in Red Seaweed Pyropia yezoensis.

The red seaweed Pyropia yezoensis is an ideal research model for dissecting the molecular mechanisms underlying its robust acclimation to abiotic stresses in intertidal zones. Glycine betaine (GB) was an important osmolyte in maintaining osmotic balance and stabilizing the quaternary structure of complex proteins under abiotic stresses (drought, salinity, etc.) in plants, animals, and bacteria. However, the existence and possible functions of GB in Pyropia remain elusive. In this study, we observed the rapid accumulation of GB in desiccated Pyropia blades, identifying its essential roles in protecting Pyropia cells against severe osmotic stress. Based on the available genomic and transcriptomic information of Pyropia, we computationally identified genes encoding the three key enzymes in the GB biosynthesis pathway: phosphoethanolamine N-methyltransferase (PEAMT), choline dehydrogenase (CDH), and betaine aldehyde dehydrogenase (BADH). Pyropia had an extraordinarily expanded gene copy number of CDH (up to seven) compared to other red algae. Phylogeny analysis revealed that in addition to the one conservative CDH in red algae, the other six might have originated from early gene duplication events. In dehydration stress, multiple CDH paralogs and PEAMT genes were coordinating up-regulated and shunted metabolic flux into GB biosynthesis. An elaborate molecular mechanism might be involved in the transcriptional regulation of these genes.

Comparison of Proteins Secreted into Extracellular Space of Pathogenic and Non-pathogenic Acanthamoeba castellanii

Pathogenic Acanthamoeba spp. cause granulomatous amoebic encephalitis and keratitis. Acanthamoeba keratitis (AK) is a rare but serious ocular infection that can result in permanent visual impairment or blindness. However, pathogenic factors of AK remain unclear and treatment for AK is arduous. Expression levels of proteins secreted into extracellular space were compared between A. castellanii pathogenic (ACP) and non-pathogenic strains. Two-dimensional polyacrylamide gel electrophoresis revealed 123 differentially expressed proteins, including 34 increased proteins, 7 qualitative increased proteins, 65 decreased proteins, and 17 qualitative decreased proteins in ACP strain. Twenty protein spots with greater than 5-fold increase in ACP strain were analyzed by liquid chromatography triple quadrupole mass spectrometry. These proteins showed similarity each to inosine-uridine preferring nucleoside hydrolase, carboxylesterase, oxygen-dependent choline dehydrogenase, periplasmic-binding protein proteinases and hypothetical proteins. These proteins expressed higher in ACP may provide some information to understand pathogenicity of Acanthamoeba.

Betaine is accumulated via transient choline dehydrogenase activation during mouse oocyte meiotic maturation.

Betaine (N,N,N-trimethylglycine) plays key roles in mouse eggs and preimplantation embryos first in a novel mechanism of cell volume regulation and second as a major methyl donor in blastocysts, but its origin is unknown. Here, we determined that endogenous betaine was present at low levels in germinal vesicle (GV) stage mouse oocytes before ovulation and reached high levels in the mature, ovulated egg. However, no betaine transport into oocytes was detected during meiotic maturation. Because betaine can be synthesized in mammalian cells via choline dehydrogenase (CHDH; EC 1.1.99.1), we assessed whether this enzyme was expressed and active. Chdh transcripts and CHDH protein were expressed in oocytes. No CHDH enzyme activity was detected in GV oocyte lysate, but CHDH became highly active during oocyte meiotic maturation. It was again inactive after fertilization. We then determined whether oocytes synthesized betaine and whether CHDH was required. Isolated maturing oocytes autonomously synthesized betaine in vitro in the presence of choline, whereas this failed to occur in Chdh-/- oocytes, directly demonstrating a requirement for CHDH for betaine accumulation in oocytes. Overall, betaine accumulation is a previously unsuspected physiological process during mouse oocyte meiotic maturation whose underlying mechanism is the transient activation of CHDH.

Polymorphic variants of genes involved in choline pathway and the risk of intrauterine fetal death.

OBJECTIVES: Choline and folate metabolism disturbances may be involved in the occurrence of intrauterine fetal death (IUFD). The proper activity of this metabolism could be determined by genetic variants involved in choline pathway e.g. CHKA (gene encoding choline kinase α), PCYT1A (gene encoding CCTα) and CHDH (gene encoding choline dehydrogenase). Our study aimed at determining the genotype and allele frequencies of CHKA rs7928739, PCYT1A rs712012, PCYT1A rs7639752, CHDH rs893363 and CHDH rs2289205 polymorphisms in mothers with IUFD occurrence. MATERIAL AND METHODS: The study involved 76 mothers with IUFD occurrence and 215 mothers of healthy children. Genetic analysis was performed with the use of PCR/RFLP method. RESULTS: The frequency of genotypes and alleles of studied polymorphisms was similar in both groups. The study revealed no association of PCYT1A, CHKA and CHDH polymorphisms in analysed groups of women. While evaluating the co-existence of analysed polymorphisms statistically significant correlation was revealed. Co-existence of CHKA rs7928739 AC/CHDH rs2289205 AA genotypes was observed statistically more frequently in the study group than in the control group (p = 0,031). CONCLUSIONS: There is no correlation between single CHKA rs7928739, PCYT1A rs712012, PCYT1A rs7639752, CHDH rs893363 and CHDH rs2289205 polymorphisms and the incidence of intrauterine fetal death. However, revealed statistically significant difference between co-existence of CHKA rs7928739 AC/CHDH rs2289205 AA genotypes between study groups suggest the need of further analysis.

Identification of a Bipolar Disorder Vulnerable Gene CHDH at 3p21.1.

Genome-wide analysis (GWA) is an effective strategy to discover extreme effects surpassing genome-wide significant levels in studying complex disorders; however, when sample size is limited, the true effects may fail to achieve genome-wide significance. In such case, there may be authentic results among the pools of nominal candidates, and an alternative approach is to consider nominal candidates but are replicable across different samples. Here, we found that mRNA expression of the choline dehydrogenase gene (CHDH) was uniformly upregulated in the brains of bipolar disorder (BPD) patients compared with healthy controls across different studies. Follow-up genetic analyses of CHDH variants in multiple independent clinical datasets (including 11,564 cases and 17,686 controls) identified a risk SNP rs9836592 showing consistent associations with BPD (P meta = 5.72 × 10-4), and the risk allele indicated an increased CHDH expression in multiple neuronal tissues (lowest P = 6.70 × 10-16). These converging results may identify a nominal but true BPD susceptibility gene CHDH. Further exploratory analysis revealed suggestive associations of rs9836592 with childhood intelligence (P = 0.044) and educational attainment (P = 0.0039), a "proxy phenotype" of general cognitive abilities. Intriguingly, the CHDH gene is located at chromosome 3p21.1, a risk region implicated in previous BPD genome-wide association studies (GWAS), but CHDH is lying outside of the core GWAS linkage disequilibrium (LD) region, and our studied SNP rs9836592 is ∼1.2 Mb 3' downstream of the previous GWAS loci (e.g., rs2251219) with no LD between them; thus, the association observed here is unlikely a reflection of previous GWAS signals. In summary, our results imply that CHDH may play a previously unknown role in the etiology of BPD and also highlight the informative value of integrating gene expression and genetic code in advancing our understanding of its biological basis.

Choline metabolic pathway gene polymorphisms and risk for Down syndrome: An association study in a population with folate-homocysteine metabolic impairment.

BACKGROUND/OBJECTIVES: Choline is an essential nutrient involved in one-carbon metabolism, but its role in mechanisms underlying meiotic non-disjunction is poorly known. The relationship between folate-homocysteine metabolic pathway gene polymorphism and Down syndrome (DS) risk has been widely analyzed, but there are limited reports on its correlation with choline metabolism. In the present case-control association study, we investigated the relationship of three single-nucleotide polymorphisms (SNPs) (phosphatidylethanolamine N-methyltransferase (PEMT) rs12325817, choline dehydrogenase (CHDH) rs12676 and homocysteine methyltransferase (BHMT) rs3733890) of choline metabolism with risk for DS. SUBJECT/METHODS: Genotyping of 228 mothers of a down syndrome child (DSM) and 200 control mothers (CMs) for all SNPs was performed by PCR coupled with restriction fragment length polymorphism method. RESULTS: A significantly increased risk for BHMT +742AA genotype with an odds ratio of 4.96 (95% confidence interval (CI): 1.66-14.88, P=0.0036) was observed. For PEMT rs12325817 and CHDH rs12676, no significant difference in allelic and genotypic frequencies was observed. In genotypic combination analysis considering PEMT -744GG/CHDH +432GG/BHMT +742GG as the reference combination, PEMT -744GC/CHDH +432GG/BHMT +742GG genotypic combination was significantly higher in DSM compared with that in CMs with an odds ratio of 2.061 (95% CI: 1.10-3.86, P=0.0342). We also observed an epistatic interaction between methylenetetrahydrofolate reductase (MTHFR) rs1801133 and choline metabolic pathway gene variants. CONCLUSIONS: Our findings indicate impaired choline metabolism showing a greater risk for DS, especially in a population associated with homocysteine-folate impairment. Further studies are required to confirm our findings.

Osmotic stress response in Acinetobacter baylyi: identification of a glycine-betaine biosynthesis pathway and regulation of osmoadaptive choline uptake and glycine-betaine synthesis through a choline-responsive BetI repressor.

Acinetobacter baylyi, a ubiquitous soil bacterium, can cope with high salinity by uptake of choline as precursor of the compatible solute glycine betaine. Here, we report on the identification of a choline dehydrogenase (BetA) and a glycine betaine aldehyde dehydrogenase (BetB) mediating the oxidation of choline to glycine betaine. The betAB genes were found to form an operon together with the potential transcriptional regulator betI. The transcription of the betIBA operon and the two recently identified choline transporters was upregulated in response to choline and choline plus salt. The finding that the osmo-independent transporter BetT1 undergoes a higher upregulation in response to choline alone than betT2 suggests that BetT1 does not primarily function in osmoadaptation. Electrophoretic mobility shift assays led to the conclusion that BetI mediates transcriptional regulation of both, the betIBA gene operon and the choline transporters. BetI was released from the DNA in response to choline which together with the transcriptional upregulation of the bet genes in the presence of choline suggests that BetI is a choline sensing transcriptional repressor.

A vascular lesion mimicking a primitive brain tumour in a patient examined by 18F-choline PET/CT and MRI / Una lesión vascular imitando un tumor cerebral primitivo en un paciente examinado con PET 18F-colina/TAC y RM

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Comparative genomics and mutagenesis analyses of choline metabolism in the marine Roseobacter clade.

Choline is ubiquitous in marine eukaryotes and appears to be widely distributed in surface marine waters; however, its metabolism by marine bacteria is poorly understood. Here, using comparative genomics and molecular genetic approaches, we reveal that the capacity for choline catabolism is widespread in marine heterotrophs of the marine Roseobacter clade (MRC). Using the model bacterium Ruegeria pomeroyi, we confirm that the betA, betB and betC genes, encoding choline dehydrogenase, betaine aldehyde dehydrogenase and choline sulfatase, respectively, are involved in choline metabolism. The betT gene, encoding an organic solute transporter, was essential for the rapid uptake of choline but not glycine betaine (GBT). Growth of choline and GBT as a sole carbon source resulted in the re-mineralization of these nitrogen-rich compounds into ammonium. Oxidation of the methyl groups from choline requires formyltetrahydrofolate synthetase encoded by fhs in R. pomeroyi, deletion of which resulted in incomplete degradation of GBT. We demonstrate that this was due to an imbalance in the supply of reducing equivalents required for choline catabolism, which can be alleviated by the addition of formate. Together, our results demonstrate that choline metabolism is ubiquitous in the MRC and reveal the role of Fhs in methyl group oxidation in R. pomeroyi.

Evidence for negative selection of gene variants that increase dependence on dietary choline in a Gambian cohort.

Choline is an essential nutrient, and the amount needed in the diet is modulated by several factors. Given geographical differences in dietary choline intake and disparate frequencies of single-nucleotide polymorphisms (SNPs) in choline metabolism genes between ethnic groups, we tested the hypothesis that 3 SNPs that increase dependence on dietary choline would be under negative selection pressure in settings where choline intake is low: choline dehydrogenase (CHDH) rs12676, methylenetetrahydrofolate reductase 1 (MTHFD1) rs2236225, and phosphatidylethanolamine-N-methyltransferase (PEMT) rs12325817. Evidence of negative selection was assessed in 2 populations: one in The Gambia, West Africa, where there is historic evidence of a choline-poor diet, and the other in the United States, with a comparatively choline-rich diet. We used 2 independent methods, and confirmation of our hypothesis was sought via a comparison with SNP data from the Maasai, an East African population with a genetic background similar to that of Gambians but with a traditional diet that is higher in choline. Our results show that frequencies of SNPs known to increase dependence on dietary choline are significantly reduced in the low-choline setting of The Gambia. Our findings suggest that adequate intake levels of choline may have to be reevaluated in different ethnic groups and highlight a possible approach for identifying novel functional SNPs under the influence of dietary selective pressure.

Choline dehydrogenase interacts with SQSTM1/p62 to recruit LC3 and stimulate mitophagy.

CHDH (choline dehydrogenase) is an enzyme catalyzing the dehydrogenation of choline to betaine aldehyde in mitochondria. Apart from this well-known activity, we report here a pivotal role of CHDH in mitophagy. Knockdown of CHDH expression impairs CCCP-induced mitophagy and PARK2/parkin-mediated clearance of mitochondria in mammalian cells, including HeLa cells and SN4741 dopaminergic neuronal cells. Conversely, overexpression of CHDH accelerates PARK2-mediated mitophagy. CHDH is found on both the outer and inner membranes of mitochondria in resting cells. Interestingly, upon induction of mitophagy, CHDH accumulates on the outer membrane in a mitochondrial potential-dependent manner. We found that CHDH is not a substrate of PARK2 but interacts with SQSTM1 independently of PARK2 to recruit SQSTM1 into depolarized mitochondria. The FB1 domain of CHDH is exposed to the cytosol and is required for the interaction with SQSTM1, and overexpression of the FB1 domain only in cytosol reduces CCCP-induced mitochondrial degradation via competitive interaction with SQSTM1. In addition, CHDH, but not the CHDH FB1 deletion mutant, forms a ternary protein complex with SQSTM1 and MAP1LC3 (LC3), leading to loading of LC3 onto the damaged mitochondria via SQSTM1. Further, CHDH is crucial to the mitophagy induced by MPP+ in SN4741 cells. Overall, our results suggest that CHDH is required for PARK2-mediated mitophagy for the recruitment of SQSTM1 and LC3 onto the mitochondria for cargo recognition.

A GMC oxidoreductase homologue is required for acetylation of glycopeptidolipid in Mycobacterium smegmatis.

The Mycobacterium tuberculosis Rv3409c gene is required for modulation of the Toll-like receptor 2 (TLR-2) signaling response in infected macrophages. Although each is annotated as encoding a cholesterol oxidase, neither Rv3409c nor its ortholog MSMEG1604 is required for the metabolism of cholesterol in mycobacteria. Here we report that a unique lipid, L1334, accumulates in a MSMEG1604 transposon mutant in the Mycobacterium smegmatis cell envelope. L1334 is a polar glycopeptidolipid that is hyperrhamnosylated and in which the 6-deoxytalose moiety is not acetylated. The alteration of L1334 acetylation is consistent with a reduced level of interference with TLR-2 signaling in mutant infected macrophages.

Human choline dehydrogenase: medical promises and biochemical challenges.

Human choline dehydrogenase (CHD) is located in the inner membrane of mitochondria primarily in liver and kidney and catalyzes the oxidation of choline to glycine betaine. Its physiological role is to regulate the concentrations of choline and glycine betaine in the blood and cells. Choline is important for regulation of gene expression, the biosynthesis of lipoproteins and membrane phospholipids and for the biosynthesis of the neurotransmitter acetylcholine; glycine betaine plays important roles as a primary intracellular osmoprotectant and as methyl donor for the biosynthesis of methionine from homocysteine, a required step for the synthesis of the ubiquitous methyl donor S-adenosyl methionine. Recently, CHD has generated considerable medical attention due to its association with various human pathologies, including male infertility, homocysteinuria, breast cancer and metabolic syndrome. Despite the renewed interest, the biochemical characterization of the enzyme has lagged behind due to difficulties in the obtainment of purified, active and stable enzyme. This review article summarizes the medical relevance and the physiological roles of human CHD, highlights the biochemical knowledge on the enzyme, and provides an analysis based on the comparison of the protein sequence with that of bacterial choline oxidase, for which structural and biochemical information is available.

Dietary and genetic manipulations of folate metabolism differentially affect neocortical functions in mice.

Converging evidence suggests that folate-mediated one-carbon metabolism may modulate cognitive functioning throughout the lifespan, but few studies have directly tested this hypothesis. This study examined the separate and combined effects of dietary and genetic manipulations of folate metabolism on neocortical functions in mice, modeling a common genetic variant in the MTHFD1 gene in humans. Mutant (Mthfd1(gt/+)) and wildtype (WT) male mice were assigned to a folate sufficient or deficient diet at weaning and continued on these diets throughout testing on a series of visual attention tasks adapted from the 5-choice serial reaction time task. WT mice on a deficient diet exhibited impulsive responding immediately following a change in task parameters that increased demands on attention and impulse control, and on trials following an error. This pattern of findings indicates a heightened affective response to stress and/or an inability to regulate negative emotions. In contrast, Mthfd1(gt/+) mice (regardless of diet) exhibited attentional dysfunction and a blunted affective response to committing an error. The Mthfd1(gt/+) mice also showed significantly decreased expression levels for genes encoding choline dehydrogenase and the alpha 7 nicotinic cholinergic receptor. The effects of the MTHFD1 mutation were less pronounced when combined with a deficient diet, suggesting a compensatory mechanism to the combined genetic and dietary perturbation of folate metabolism. These data demonstrate that common alterations in folate metabolism can produce functionally distinct cognitive and affective changes, and highlight the importance of considering genotype when making dietary folate recommendations.

Serratia entomophila bet gene induction and the impact of glycine betaine accumulation on desiccation tolerance.

AIMS: The genes involved in choline transport and oxidation to glycine betaine in the biopesticidal bacterium Serratia entomophila were characterized, and the potential of osmoprotectants, coupled with increased NaCl concentrations, to improve the desiccation tolerance of this species was investigated. METHODS AND RESULTS: Serratia entomophila carries sequences similar to the Escherichia coli betTIBA genes encoding a choline transporter and dehydrogenase, a betaine aldehyde dehydrogenase and a regulatory protein. Disruption of betA abolished the ability of Ser. entomophila to utilize choline as a carbon source. Quantitative reverse-transcriptase PCR analysis revealed that betA transcription was reduced compared to that of the upstream genes in the operon, and that NaCl and choline induced bet gene expression. Glycine betaine and choline increased the NaCl tolerance of Ser. entomophila, and osmotically preconditioned cultures survived better than control cultures following desiccation and immediately after application to agricultural soil. CONCLUSIONS: Addition of glycine betaine and NaCl to growth medium can greatly enhance the desiccation survival of Ser. entomophila, and its initial survival in soil. SIGNIFICANCE AND IMPACT OF THE STUDY: Serratia entomophila is sensitive to desiccation and does not persist under low soil moisture conditions. Techniques described here for enhancing the desiccation survival of Ser. entomophila can be used to improve formulations of this bacterium, and allow its application under a wider range of environmental conditions.