Choline dehydrogenase polymorphism rs12676 is a functional variation and is associated with changes in human sperm cell function

DNA methylation patterns in patients with asthenospermia and oligoasthenospermia

BACKGROUND

Spermatogenesis is a highly regulated and complex process in which DNA methylation plays a crucial role. This study aimed to explore the differential methylation profiles in sperm DNA between patients with asthenospermia (AS) and healthy controls (HCs), those with oligoasthenospermia (OAS) and HCs, and patients with AS and those with OAS.

RESULTS

Semen samples and clinical data were collected from five patients with AS, five patients with OAS, and six age-matched HCs. Reduced representation bisulfite sequencing (RRBS) was performed to identify differentially methylated regions (DMRs) in sperm cells among the different types of patients and HCs. A total of 6520, 28,019, and 16,432 DMRs were detected between AS and HC, OAS and HC, and AS and OAS groups, respectively. These DMRs were predominantly located within gene bodies and mapped to 2868, 9296, and 9090 genes in the respective groups. Of note, 12, 9, and 8 DMRs in each group were closely associated with spermatogenesis and male infertility. Furthermore, BDNF, SMARCB1, PIK3CA, and DDX27; RBMX and SPATA17; ASZ1, CDH1, and CHDH were identified as strong differentially methylated candidate genes in each group, respectively. Meanwhile, the GO analysis of DMR-associated genes in the AS vs. HC groups revealed that protein binding, cytoplasm, and transcription (DNA-templated) were the most enriched terms in the biological process (BP), cellular component (CC), and molecular function (MF), respectively. Likewise, in both the OAS vs. HC and AS vs. OAS groups, GO analysis revealed protein binding, nucleus, and transcription (DNA-templated) as the most enriched terms in BP, CC, and MF, respectively. Finally, the KEGG analysis of DMR-annotated genes and these genes at promoters suggested that metabolic pathways were the most significantly associated across all three groups.

CONCLUSIONS

The current study results revealed distinctive sperm DNA methylation patterns in the AS vs. HC and OAS vs. HC groups, particularly between patients with AS and those with OAS. The identification of key genes associated with spermatogenesis and male infertility in addition to the differentially enriched metabolic pathways may contribute to uncovering the potential pathogenesis in different types of abnormal sperm parameters.

Metabolic characterization of human sperm cells using the Seahorse metabolic flux analyzer

BACKGROUND

The concerning trend on male infertility global prevalence, together with the unexplainable causes in half of those cases, highlights that there are still aspects of this disease to be understood and solved. To address this issue, one should not only be aware of the limitations of the implemented diagnostic tools, but also understand the sperm cell in depth, structurally, biochemically, molecularly in order to develop reliable and ready-to-be new/improved diagnostic tools. In this sense, the sperm cells metabolism, highly related to its functionality, seems to be a promising aspect to explore. Though there is much information on the human sperm metabolism, there is still a lack of a quick integrated and comprehensive analysis that may be introduced with the potential to reveal innovative clinically relevant information.

OBJECTIVES

Find metabolic details on human sperm that can be accessed easily, in real time and using few cells, relying on the bivalent potential of the Seahorse flux analyzer (SFA).

RESULTS

We have obtained standard records on human sperm cells' oxygen consumption rate (OCR) and extracellular acidification rate (ECAR), that together with the metabolic metrics provided information on sperm cells' oxidative and glycolytic metabolism. Furthermore, a metabolic interindividual variation was observed.

DISCUSSION AND CONCLUSION

Although the comparison with other species or cell types is not linear and warrant further studies, the metabolic profile of human sperm cells seems to be similar to that of other species. Altogether our results corroborate the value of SFA for metabolic human sperm cell analysis, warranting new studies, and anticipating several applications in the male infertility field.

Exploring the Biomarkers and Potential Mechanisms of Botulinum Toxin Type A in the Treatment of Microglial Inflammatory Activation through P2X7 Receptors based on Transcriptome Sequencing

AIMS

This study aims to explore the potential mechanism by which Botulinum toxin type A (BoNT/ A) inhibits microglial inflammatory activation through P2X7 receptors (P2X7R).

BACKGROUND

BoNT/A is a promising analgesic drug, and previous studies have established that it alleviates Neuropathic Pain (NP) by inhibiting microglial inflammatory activation. This study examined the biomarkers and potential mechanisms by which BoNT/A relieves neuropathic pain by mediating microglial P2X7R and analyzing transcriptome sequencing data from mouse BV-2 microglial cells.

OBJECTIVE

The P2X7R agonist Bz-ATP was used to induce microglial inflammatory activation, whilst RNAseq technology was used to explore the biomarkers and potential mechanisms through which BoNT/A suppresses microglial inflammation.

METHODS

RNA sequencing was performed on three BV-2 cell samples treated with a P2X7R specific activator (Bz-ATP) and three BV-2 cell samples pre-treated with BoNT/A. Only data that successfully passed quality control measures were included in subsequent analysis. Initially, Differentially Expressed Genes (DEGs) were identified from BoNT/A and control samples, followed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses. Biomarkers were then identified by constructing a Protein- Protein Interaction (PPI) network and utilizing the CytoHubba plug-in in Cytoscape software. Lastly, enrichment analysis and regulatory network analysis were performed to elucidate the potential mechanism of BoNT/A in the treatment of NP.

RESULTS

93 DEGs related to the "cell component size regulation" GO term and enriched in the "axon guidance" KEGG pathway were identified. Subsequently, 6 biomarkers were identified, namely PTPRF, CHDH, CKM, Ky, Sema3b, and Sema3f, which were enriched in pathways related to biosynthesis and metabolism, disease progression, signal transduction, and organelle function, including the "ribosome" and "Wnt signaling pathway." Finally, a competing endogenous RNA (ceRNAs) network was constructed from 6 mRNAs, 66 miRNAs, and 31 lncRNAs, forming a complex relationship network.

CONCLUSION

Six genes (PTPRF, Sema3b, Sema3f, CHDH, CKM, and Ky) were identified as biomarkers of microglial inflammatory activation following BoNT/A treatment. This finding may provide a valuable reference for the relief and treatment of neuropathic pain.

Impact of Z chromosome inversions on gene expression in testis and liver tissues in the zebra finch

Chromosomal inversions have been identified in many natural populations and can be responsible for novel traits and rapid adaptation. In zebra finch, a large region on the Z chromosome has been subject to multiple inversions, which have pleiotropic effects on multiple traits but especially on sperm phenotypes, such as midpiece and flagellum length. To understand the effect, the Z inversion has on these traits, we examined testis and liver transcriptomes of young males at different maturation times. We compared gene expression differences among three inversion karyotypes: AA, B*B* and AB*, where B* denotes the inverted regions on Z with respect to A. In testis, 794 differentially expressed genes were found and most of them were located on chromosome Z. They were functionally enriched for sperm-related traits. We also identified clusters of co-expressed genes that matched with the inversion-related sperm phenotypes. In liver, there were some enriched functions and some overrepresentation on chromosome Z with similar location as in testis. In both tissues, the overrepresented genes were located near the distal end of Z but also in the middle of the chromosome. For the heterokaryotype, we observed several genes with one allele being dominantly expressed, similar to expression patterns in one or the other homokaryotype. This was confirmed with SNPs for three genes, and interestingly one gene, DMGDH, had allele-specific expression originating mainly from one inversion haplotype in the testis, yet both inversion haplotypes were expressed equally in the liver. This karyotype-specific difference in tissue-specific expression suggests a pleiotropic effect of the inversion and thus suggests a mechanism for divergent phenotypic effects resulting from an inversion.

CHDH, a key mitochondrial enzyme, plays a diagnostic role in metabolic disorders diseases and tumor progression

Human choline dehydrogenase (CHDH) is a transmembrane protein located in mitochondria. CHDH has been shown to be one of the important catalytic enzymes that catalyze the oxidation of choline to betaine and is involved in mitochondrial autophagy after mitochondrial damage. In recent years, an increasing number of studies have focused on CHDH and found a close association with the pathogenesis of various diseases, including tumor prognosis. Here we summarized the genomic localization, protein structure and basic functions of CHDH and discuss the progress of CHDH research in metabolic disorders and other diseases. Moreover, we described the regulatory role of CHDH on the progression of different types of malignant tumors. In addition, major pathogenic mechanisms of CHDH in multiple diseases may be associated with single nucleotide polymorphism (SNP). We look forward to providing new strategies and basis for clinical diagnosis and prognosis prediction of diseases by diagnosing SNP loci of CHDH genes. Our work evaluates the feasibility of CHDH as a molecular marker relevant to the diagnosis of some metabolic disorders diseases and tumors, which may provide new targets for the treatment of related diseases and tumors.

Metabonomic analysis of seminal plasma in necrozoospermia patients based on liquid chromatography-mass spectrometry

BACKGROUND

In the pathological study of necrozoospermia-a form of sperm mortality-the underlying metabolic mechanism remains unclear. Thus, the aim of this study was to characterize metabolic alterations in the seminal plasma of necrozoospermic patients and to provide insights into the etiology of the disease.

METHODS

Seminal plasma samples were collected from patients diagnosed with necrozoospermia (n=28) as well as normozoospermia (n=37). The samples were analyzed using nontargeted metabolomics based on liquid chromatography-mass spectrometry (LC-MS). The raw data were subjected to multivariate analysis to identify metabolites correlated with necrozoospermia. Differential metabolites were subjected to pathway analysis using MetaboAnalyst.

RESULTS

The results of the metabolomic analysis showed that there were 194 differential metabolites between the two groups; 129 metabolites were upregulated and 65 metabolites were downregulated. Among the differential metabolites, the top ten differential metabolites were choline, benzaldehyde, pyrazinamide, 5-aminoimidazole-4-carboxamide, and dihydrothymine. The following differential metabolite pathways were identified, and the top five metabolite pathways were arachidonic acid metabolism, steroid hormone biosynthesis, alanine aspartate and glutamate metabolism, bile secretion, and prostate cancer.

CONCLUSIONS

The elevation of choline and 2-hydroxyglutarate levels in seminal plasma was an important finding, and the results also indicate that abnormalities in arachidonic acid metabolism and glutamate metabolism were an underlying pathological mechanism of necrozoospermia.

Ldha-Dependent Metabolic Programs in Sertoli Cells Regulate Spermiogenesis in Mouse Testis

Sertoli cells play indispensable roles in spermatogenesis by providing the advanced germ cells with structural, nutritional, and regulatory support. Lactate is regarded as an essential Sertoli-cell-derived energy metabolite that nurses various types of spermatogenic cells; however, this assumption has not been tested using genetic approaches. Here, we have reported that the depletion of lactate production in Sertoli cells by conditionally deleting lactate dehydrogenase A (Ldha) greatly affected spermatogenesis. Ldha deletion in Sertoli cells significantly reduced the lactate production and resulted in severe defects in spermatogenesis. Spermatogonia and spermatocytes did not show even mild impairments, but the spermiogenesis of Ldha conditional knockout males was severely disrupted. Further analysis revealed that 2456 metabolites were altered in the sperm of the knockout animals, and specifically, lipid metabolism was dysregulated, including choline, oleic acid, and myristic acid. Surprisingly, choline supplementation completely rescued the spermiogenesis disorder that was caused by the loss of Ldha activities. Collectively, these data have demonstrated that the interruption of Sertoli-cell-derived lactate impacted sperm development through a choline-mediated mechanism. The outcomes of these findings have revealed a novel function of lactate in spermatogenesis and have therapeutic applications in treating human infertility.

Nutrition, genetic variation and male fertility

Infertility affects nearly 50 million couples worldwide, with 40-50% of cases having a male factor component. It is well established that nutritional status impacts reproductive development, health and function, although the exact mechanisms have not been fully elucidated. Genetic variation that affects nutrient metabolism may impact fertility through nutrigenetic mechanisms. This review summarizes current knowledge on the role of several dietary components (vitamins A, B₁₂, C, D, E, folate, betaine, choline, calcium, iron, caffeine, fiber, sugar, dietary fat, and gluten) in male reproductive health. Evidence of gene-nutrient interactions and their potential effect on fertility is also examined. Understanding the relationship between genetic variation, nutrition and male fertility is key to developing personalized, DNA-based dietary recommendations to enhance the fertility of men who have difficulty conceiving.

Exploring the potential impact of nutritionally actionable genetic polymorphisms on idiopathic male infertility: a review of current evidence

Infertility affects about 15% of the world's population. In 40%–50% of infertile couples, a male factor underlies the problem, but in about 50% of these cases, the etiology of male infertility remains unexplained. Some clinical data show that lifestyle interventions may contribute to male reproductive health. Cessation of unhealthy habits is suggested for preserving male fertility; there is growing evidence that most preexisting comorbidities, such as obesity and metabolic syndrome, are highly likely to have an impact on male fertility. The analysis of genetic polymorphisms implicated in metabolic activity represents one of the most exciting areas in the study of genetic causes of male infertility. Although these polymorphisms are not directly connected with male infertility, they may have a role in specific conditions associated with it, that is, metabolic disorders and oxidative stress pathway genes that are potentially associated with an increased risk of male infertility due to DNA and cell membrane damage. Some studies have examined the impact of individual genetic differences and gene-diet interactions on male infertility, but their results have not been synthesized. We review the current research to identify genetic variants that could be tested to improve the chances of conceiving spontaneously through personalized diet and/or oral vitamin and mineral supplementation, by examining the science of genetic modifiers of dietary factors that affect nutritional status and male fertility.

Antiretroviral treatment leading to secondary trimethylaminuria: Genetic associations and successful management with riboflavin

WHAT IS KNOWN AND OBJECTIVE

Trimethylaminuria is a metabolic disorder characterized by excessive excretion of trimethylamine in body fluids following FMO3 gene mutations. Secondary forms of the disease may be due to consumption of trimethylamine precursor-rich foods or metabolism of some xenobiotics.

CASE SUMMARY

A HIV patient developed secondary trimethylaminuria following antiretroviral treatment. Riboflavin supplementation ameliorated his phenotype. ¹ H-NMR confirmed increased urine level of TMA. Several genes involved in choline catabolism harboured missense mutations. Riboflavin supplement improved enzymatic activity of mutated enzymes promoting TMA clearance.

WHAT IS NEW AND CONCLUSION

Antiretrovirals may increase the concentration of TMA precursors. The present study reports antiretroviral treatment as risk factor for such secondary trimethylaminuria. Riboflavin is an effective treatment.

Precision (Personalized) Nutrition: Understanding Metabolic Heterogeneity

People differ in their requirements for and responses to nutrients and bioactive molecules in the diet. Many inputs contribute to metabolic heterogeneity (including variations in genetics, epigenetics, microbiome, lifestyle, diet intake, and environmental exposure). Precision nutrition is not about developing unique prescriptions for individual people but rather about stratifying people into different subgroups of the population on the basis of biomarkers of the above-listed sources of metabolic variation and then using this stratification to better estimate the different subgroups’ dietary requirements, thereby enabling better dietary recommendations and interventions. The hope is that we will be able to subcategorize people into ever-smaller groups that can be targeted in terms of recommendations, but we will never achieve this at the individual level, thus, the choice of precision nutrition rather than personalized nutrition to designate this new field. This review focuses mainly on genetically related sources of metabolic heterogeneity and identifies challenges that need to be overcome to achieve a full understanding of the complex interactions between the many sources of metabolic heterogeneity that make people differ from one another in their requirements for and responses to foods. It also discusses the commercial applications of precision nutrition.

A Conceptual Framework for Studying and Investing in Precision Nutrition

Nutrients and food-derived bioactive molecules must transit complex metabolic pathways, and these pathways vary between people. Metabolic heterogeneity is caused by genetic variation, epigenetic variation, differences in microbiome composition and function, lifestyle differences and by variation in environmental exposures. This review discusses a number of these sources of metabolic heterogeneity and presents some of the research investments that will be needed to make applications of precision nutrition practical.

The role of the folate pathway in pancreatic cancer risk

BACKGROUND

Pancreatic cancer is the third leading cause of cancer related deaths in the United States. Several dietary factors have been identified that modify pancreatic cancer risk, including low folate levels. In addition to nutrition and lifestyle determinants, folate status may be influenced by genetic factors such as single nucleotide polymorphisms (SNPs). In the present study, we investigated the association between folate levels, genetic polymorphisms in genes of the folate pathway, and pancreatic cancer.

METHODS

Serum and red blood cell (RBC) folate levels were measured in pancreatic cancer and control subjects. Genotypes were determined utilizing Taqman probes and SNP frequencies between cases and controls were assessed using Fisher's exact test. Logistic regression was used to estimate the odds ratio (OR) and corresponding 95% confidence intervals (CIs) to measure the association between genotypes and pancreatic cancer risk. The association between folate levels and SNP expression was calculated using one-way ANOVA.

RESULTS

Mean RBC folate levels were significantly lower in pancreatic cancer cases compared to unrelated controls (508.4 ± 215.9 ng/mL vs 588.3 ± 229.2 ng/mL, respectively) whereas serum folate levels were similar. Irrespective of cancer status, several SNPs were found to be associated with altered serum folate concentrations, including the D919G SNP in methionine synthase (MTR), the L474F SNP in serine hydroxymethyl transferase 1 (SHMT1) and the V175M SNP in phosphatidyl ethanolamine methyltransferase (PEMT). Further, the V allele of the A222V SNP and the E allele of the E429A SNP in methylene tetrahydrofolate reductase (MTHFR) were associated with low RBC folate levels. Pancreatic cancer risk was found to be significantly lower for the LL allele of the L78R SNP in choline dehydrogenase (CHDH; OR = 0.29; 95% CI 0.12-0.76); however, it was not associated with altered serum or RBC folate levels.

Substitutions of S101 decrease proton and hydride transfers in the oxidation of betaine aldehyde by choline oxidase

Choline oxidase oxidizes choline to glycine betaine, with two flavin-mediated reactions to convert the alcohol substrate to the carbon acid product. Proton abstraction from choline or hydrated betaine aldehyde in the wild-type enzyme occurs in the mixing time of the stopped-flow spectrophotometer, thereby precluding a mechanistic investigation. Mutagenesis of S101 rendered the proton transfer reaction amenable to study. Here, we have investigated the aldehyde oxidation reaction catalyzed by the mutant enzymes using steady-state and rapid kinetics with betaine aldehyde. Stopped-flow traces for the reductive half-reaction of the S101T/V/C variants were biphasic, corresponding to the reactions of proton abstraction and hydride transfer. In contrast, the S101A enzyme yielded monophasic traces like wild-type choline oxidase. The rate constants for proton transfer in the S101T/C/V variants decreased logarithmically with increasing hydrophobicity of residue 101, indicating a behavior different from that seen previously with choline for which no correlation was determined. The rate constants for hydride transfer also showed a logarithmic decrease with increasing hydrophobicity at position 101, which was similar to previous results with choline as a substrate for the enzyme. Thus, the hydrophilic character of S101 is necessary not only for efficient hydride transfer but also for the proton abstraction reaction.

Genetic Variation in Choline-Metabolizing Enzymes Alters Choline Metabolism in Young Women Consuming Choline Intakes Meeting Current Recommendations

Single nucleotide polymorphisms (SNPs) in choline metabolizing genes are associated with disease risk and greater susceptibility to organ dysfunction under conditions of dietary choline restriction. However, the underlying metabolic signatures of these variants are not well characterized and it is unknown whether genotypic differences persist at recommended choline intakes. Thus, we sought to determine if common genetic risk factors alter choline dynamics in pregnant, lactating, and non-pregnant women consuming choline intakes meeting and exceeding current recommendations. Women (n = 75) consumed 480 or 930 mg choline/day (22% as a metabolic tracer, choline-d9) for 10–12 weeks in a controlled feeding study. Genotyping was performed for eight variant SNPs and genetic differences in metabolic flux and partitioning of plasma choline metabolites were evaluated using stable isotope methodology. CHKA rs10791957, CHDH rs9001, CHDH rs12676, PEMT rs4646343, PEMT rs7946, FMO3 rs2266782, SLC44A1 rs7873937, and SLC44A1 rs3199966 altered the use of choline as a methyl donor; CHDH rs9001 and BHMT rs3733890 altered the partitioning of dietary choline between betaine and phosphatidylcholine synthesis via the cytidine diphosphate (CDP)-choline pathway; and CHKA rs10791957, CHDH rs12676, PEMT rs4646343, PEMT rs7946 and SLC44A1 rs7873937 altered the distribution of dietary choline between the CDP-choline and phosphatidylethanolamine N-methyltransferase (PEMT) denovo pathway. Such metabolic differences may contribute to disease pathogenesis and prognosis over the long-term.

The Female Post-Mating Response Requires Genes Expressed in the Secondary Cells of the Male Accessory Gland in Drosophila melanogaster

Seminal proteins from the Drosophila male accessory gland induce post-mating responses (PMR) in females. The PMR comprise behavioral and physiological changes that include increased egg laying, decreased receptivity to courting males, and changes in the storage and use of sperm. Many of these changes are induced by a "sex peptide" (SP) and are maintained by SP's binding to, and slow release from, sperm. The accessory gland contains two secretory cell types with distinct morphological and developmental characteristics. Products of these "main" and "secondary" cells work interdependently to induce and maintain the PMR. To identify individual genes needed for the morphology and function of secondary cells, we studied iab-6(cocu) males, whose secondary cells have abnormal morphology and fail to provide products to maintain the PMR. By RNA-seq, we identified 77 genes that are downregulated by a factor of >5× in iab-6(cocu) males. By functional assays and microscopy, we tested 20 candidate genes and found that at least 9 are required for normal storage and release of SP in mated females. Knockdown of each of these 9 genes consequently leads to a reduction in egg laying and an increase in receptivity over time, confirming a role for the secondary cells in maintaining the long-term PMR. Interestingly, only 1 of the 9 genes, CG3349, encodes a previously reported seminal fluid protein (Sfp), suggesting that secondary cells may perform essential functions beyond the production and modification of known Sfps. At least 3 of the 9 genes also regulate the size and/or abundance of secondary cell vacuoles, suggesting that the vacuoles' contents may be important for the machinery used to maintain the PMR.

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.—Silver, M. J., Corbin, K. D., Hellenthal, G., da Costa, K.-A., Dominguez-Salas, P., Moore, S. E., Owen, J., Prentice, A. M., Hennig, B. J., Zeisel, S. H. Evidence for negative selection of gene variants that increase dependence on dietary choline in a Gambian cohort.

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.

Adaptive divergence of a transcriptional enhancer between populations of Drosophila melanogaster

As species colonize new habitats they must adapt to the local environment. Much of this adaptation is thought to occur at the regulatory level; however, the relationships among genetic polymorphism, expression variation and adaptation are poorly understood. Drosophila melanogaster, which expanded from an ancestral range in sub-Saharan Africa around 15 000 years ago, represents an excellent model system for studying regulatory evolution. Here, we focus on the gene CG9509, which differs in expression between an African and a European population of D. melanogaster. The expression difference is caused by variation within a transcriptional enhancer adjacent to the CG9509 coding sequence. Patterns of sequence variation indicate that this enhancer was the target of recent positive selection, suggesting that the expression difference is adaptive. Analysis of the CG9509 enhancer in new population samples from Europe, Asia, northern Africa and sub-Saharan Africa revealed that sequence polymorphism is greatly reduced outside the ancestral range. A derived haplotype absent in sub-Saharan Africa is at high frequency in all other populations. These observations are consistent with a selective sweep accompanying the range expansion of the species. The new data help identify the sequence changes responsible for the difference in enhancer activity.

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.

Metabolic crosstalk between choline/1-carbon metabolism and energy homeostasis

There are multiple identified mechanisms involved in energy metabolism, insulin resistance and adiposity, but there are here-to-fore unsuspected metabolic factors that also influence these processes. Studies in animal models suggest important links between choline/1-carbon metabolism and energy homeostasis. Rodents fed choline deficient diets become hypermetabolic. Mice with deletions in one of several different genes of choline metabolism have phenotypes that include increased metabolic rate, decreased body fat/lean mass ratio, increased insulin sensitivity, decreased ATP production by mitochondria, or decreased weight gain on a high fat diet. In addition, farmers have recognized that the addition of a metabolite of choline (betaine) to cattle and swine feed reduces body fat/lean mass ratio. Choline dietary intake in humans varies over a > three-fold range, and genetic variation exists that modifies individual requirements for this nutrient. Although there are some epidemiologic studies in humans suggesting a link between choline/1-carbon metabolism and energy metabolism, there have been no controlled studies in humans that were specifically designed to examine this relationship.

Conceptual shifts needed to understand the dynamic interactions of genes, environment, epigenetics, social processes, and behavioral choices

Social and behavioral research in public health is often intimately tied to profound, but frequently neglected, biological influences from underlying genetic, environmental, and epigenetic events. The dynamic interplay between the life, social, and behavioral sciences often remains underappreciated and underutilized in addressing complex diseases and disorders and in developing effective remediation strategies. Using a case-study format, we present examples as to how the inclusion of genetic, environmental, and epigenetic data can augment social and behavioral health research by expanding the parameters of such studies, adding specificity to phenotypic assessments, and providing additional internal control in comparative studies. We highlight the important roles of gene-environment interactions and epigenetics as sources of phenotypic change and as a bridge between the life and social and behavioral sciences in the development of robust interdisciplinary analyses.

The human flavoproteome

Vitamin B2 (riboflavin) is an essential dietary compound used for the enzymatic biosynthesis of FMN and FAD. The human genome contains 90 genes encoding for flavin-dependent proteins, six for riboflavin uptake and transformation into the active coenzymes FMN and FAD as well as two for the reduction to the dihydroflavin form. Flavoproteins utilize either FMN (16%) or FAD (84%) while five human flavoenzymes have a requirement for both FMN and FAD. The majority of flavin-dependent enzymes catalyze oxidation-reduction processes in primary metabolic pathways such as the citric acid cycle, β-oxidation and degradation of amino acids. Ten flavoproteins occur as isozymes and assume special functions in the human organism. Two thirds of flavin-dependent proteins are associated with disorders caused by allelic variants affecting protein function. Flavin-dependent proteins also play an important role in the biosynthesis of other essential cofactors and hormones such as coenzyme A, coenzyme Q, heme, pyridoxal 5'-phosphate, steroids and thyroxine. Moreover, they are important for the regulation of folate metabolites by using tetrahydrofolate as cosubstrate in choline degradation, reduction of N-5.10-methylenetetrahydrofolate to N-5-methyltetrahydrofolate and maintenance of the catalytically competent form of methionine synthase. These flavoenzymes are discussed in detail to highlight their role in health and disease.

A brief history of choline

In 1850, Theodore Gobley, working in Paris, described a substance, 'lecithine', which he named after the Greek 'lekithos' for egg yolk. Adolph Strecker noted in 1862 that when lecithin from bile was heated, it generated a new nitrogenous chemical that he named 'choline'. Three years later, Oscar Liebreich identified a new substance, 'neurine', in the brain. After a period of confusion, neurine and choline were found to be the same molecule, and the name choline was adapted. Lecithin was eventually characterized chemically as being phosphatidylcholine. In 1954, Eugene Kennedy described the cytidine 5-dihphosphocholine pathway by which choline is incorporated into phosphatidylcholine. A second route, the phosphatidylethanolamine-N-methyltransferase pathway, was identified by Jon Bremer and David Greenberg in 1960. The role of choline as part of the neurotransmitter acetylcholine was established by Otto Loewi and Henry Dale. Working in the 1930s at the University of Toronto, Charles Best showed that choline prevented fatty liver in dogs and rats. The importance of choline as an essential nutrient for human health was determined in the 1990s through controlled feeding studies in humans. Recently, an understanding of the role of genetic variation in setting the dietary requirement for choline in people is being unraveled.