Early embryonic lethality caused by disruption of the gene for choline kinase alpha, the first enzyme in phosphatidylcholine biosynthesis

Associations of the Single Bovine Embryo Growth Media Metabolome with Successful Pregnancy

This study investigated whether metabolomic fingerprints of bovine embryo growth media improve the prediction of successful embryo implantation. In this prospective cohort study, the metabolome from in vitro-produced day 7 blastocysts with successful implantation (n = 11), blastocysts with failed implantation (n = 10), and plain culture media without embryos (n = 5) were included. Samples were analyzed using an AbsoluteIDQ® p180 Targeted Metabolomics Kit with LC-MS/MS, and a total of 189 metabolites were analyzed from each sample. Blastocysts that resulted in successful embryo implantation had significantly higher levels of methionine sulfoxide (p < 0.001), DOPA (p < 0.05), spermidine (p < 0.001), acetylcarnitine-to-free-carnitine ratio (p < 0.05), C2 + C3-to-free-carnitine ratio (p < 0.05), and lower levels of threonine (nep < 0.001) and phosphatidylcholine PC ae C30:0 (p < 0.001) compared to control media. However, when compared to embryos that failed to implant, only DOPA, spermidine, C2/C0, (C2 + C3)/C0, and PC ae C30:0 levels differentiated significantly. In summary, our study identifies a panel of differential metabolites in the culture media of bovine blastocysts that could act as potential biomarkers for the selection of viable blastocysts before embryo transfer.

The moonlighting function of glycolytic enzyme enolase-1 promotes choline phospholipid metabolism and tumor cell proliferation

Aberrantly upregulated choline phospholipid metabolism is a novel emerging hallmark of cancer, and choline kinase α (CHKα), a key enzyme for phosphatidylcholine production, is overexpressed in many types of human cancer through undefined mechanisms. Here, we demonstrate that the expression levels of the glycolytic enzyme enolase-1 (ENO1) are positively correlated with CHKα expression levels in human glioblastoma specimens and that ENO1 tightly governs CHKα expression via posttranslational regulation. Mechanistically, we reveal that both ENO1 and the ubiquitin E3 ligase TRIM25 are associated with CHKα. Highly expressed ENO1 in tumor cells binds to I199/F200 of CHKα, thereby abrogating the interaction between CHKα and TRIM25. This abrogation leads to the inhibition of TRIM25-mediated polyubiquitylation of CHKα at K195, increased stability of CHKα, enhanced choline metabolism in glioblastoma cells, and accelerated brain tumor growth. In addition, the expression levels of both ENO1 and CHKα are associated with poor prognosis in glioblastoma patients. These findings highlight a critical moonlighting function of ENO1 in choline phospholipid metabolism and provide unprecedented insight into the integrated regulation of cancer metabolism by crosstalk between glycolytic and lipidic enzymes.

Chicken or Egg? Mitochondrial Phospholipids and Oxidative Stress in Disuse-Induced Skeletal Muscle Atrophy

Significance: Accumulation of reactive oxygen species (ROS) is known to promote cellular damage in multiple cell types. In skeletal muscle, ROS has been implicated in disuse-induced muscle atrophy. However, the molecular origin and mechanism of how disuse promotes ROS and muscle dysfunction remains unclear. Recent Advances: Recently, we implicated membrane lipids of mitochondria to be a potential source of ROS to promote muscle atrophy. Critical Issues: In this review, we discuss evidence that changes in mitochondrial lipids represent a physiologically relevant process by which disuse promotes mitochondrial electron leak and oxidative stress. Future Directions: We further discuss lipid hydroperoxides as a potential downstream mediator of ROS to induce muscle atrophy. Antioxid. Redox Signal. 38, 338-351.

The role of phosphatidylcholine 34:1 in the occurrence, development and treatment of ulcerative colitis

Lipid homeostasis is considered to be related to intestinal metabolic balance, while its role in the pathogenesis and treatment of ulcerative colitis (UC) remains largely unexplored. The present study aimed to identify the target lipids related to the occurrence, development and treatment of UC by comparing the lipidomics of UC patients, mice and colonic organoids with the corresponding healthy controls. Here, multi-dimensional lipidomics based on LC-QTOF/MS, LC-MS/MS and iMScope systems were constructed and used to decipher the alteration of lipidomic profiles. The results indicated that UC patients and mice were often accompanied by dysregulation of lipid homeostasis, in which triglycerides and phosphatidylcholines were significantly reduced. Notably, phosphatidylcholine 34:1 (PC34:1) was characterized by high abundance and closely correlation with UC disease. Our results also revealed that down-regulation of PC synthase PCYT1α and Pemt caused by UC modeling was the main factor leading to the reduction of PC34:1, and exogenous PC34:1 could greatly enhance the fumarate level via inhibiting the transformation of glutamate to N-acetylglutamate, thus exerting an anti-UC effect. Collectively, our study not only supplies common technologies and strategies for exploring lipid metabolism in mammals, but also provides opportunities for the discovery of therapeutic agents and biomarkers of UC.

Cholesterol and matrisome pathways dysregulated in astrocytes and microglia

The impact of apolipoprotein E ε4 (APOE4), the strongest genetic risk factor for Alzheimer's disease (AD), on human brain cellular function remains unclear. Here, we investigated the effects of APOE4 on brain cell types derived from population and isogenic human induced pluripotent stem cells, post-mortem brain, and APOE targeted replacement mice. Population and isogenic models demonstrate that APOE4 local haplotype, rather than a single risk allele, contributes to risk. Global transcriptomic analyses reveal human-specific, APOE4-driven lipid metabolic dysregulation in astrocytes and microglia. APOE4 enhances de novo cholesterol synthesis despite elevated intracellular cholesterol due to lysosomal cholesterol sequestration in astrocytes. Further, matrisome dysregulation is associated with upregulated chemotaxis, glial activation, and lipid biosynthesis in astrocytes co-cultured with neurons, which recapitulates altered astrocyte matrisome signaling in human brain. Thus, APOE4 initiates glia-specific cell and non-cell autonomous dysregulation that may contribute to increased AD risk.

Mechanism of action and therapeutic route for a muscular dystrophy caused by a genetic defect in lipid metabolism

CHKB encodes one of two mammalian choline kinase enzymes that catalyze the first step in the synthesis of the membrane phospholipid phosphatidylcholine. In humans and mice, inactivation of the CHKB gene (Chkb in mice) causes a recessive rostral-to-caudal muscular dystrophy. Using Chkb knockout mice, we reveal that at no stage of the disease is phosphatidylcholine level significantly altered. We observe that in affected muscle a temporal change in lipid metabolism occurs with an initial inability to utilize fatty acids for energy via mitochondrial β-oxidation resulting in shunting of fatty acids into triacyglycerol as the disease progresses. There is a decrease in peroxisome proliferator-activated receptors and target gene expression specific to Chkb^−/− affected muscle. Treatment of Chkb^−/− myocytes with peroxisome proliferator-activated receptor agonists enables fatty acids to be used for β-oxidation and prevents triacyglyerol accumulation, while simultaneously increasing expression of the compensatory choline kinase alpha (Chka) isoform, preventing muscle cell injury.

Mutations in the CHKB gene cause muscular dystrophy. Here, the authors show that in mouse models of the disease changes in lipid metabolism are associated with decreased PPAR signaling, and show PPAR agonists can rescue expression of injury markers in myocytes in vitro.

Urinary metabolomics reveals the biological characteristics of early pregnancy in pigs

Background

Embryo implantation in sows is an important event during pregnancy. During this process, blastocysts undergo dramatic morphologic changes, and the endometrium becomes receptive. Studies have shown that developmental changes associated with the crosstalk between peri-implantation embryos and embryo-uterine are driven by various biomolecules secreted by the endometrium and embryos. In sows, changes in the uterus are also reflected in circulating body fluids and urine. Metabolomics reveals the metabolic state of cells, tissues, and organisms. In this study, we collected urine samples from large white sows during the peri-implantation period. The levels of urinary metabolites at different periods were analyzed using ultra-performance liquid chromatography/tandem mass spectrometry (UPLC–MS/MS) analysis techniques.

Results

A total of 32 samples were collected from 8 sows during the estrus period and at each phase of early pregnancy (9, 12, and 15 days of gestation). A total of 530 metabolites were identified with high confidence in all samples. Compared with samples collected during the estrus phase, 269 differential metabolites were found in samples obtained during early pregnancy.

Conclusions

The identified metabolites included lipids and lipid-like molecules, organic acids and their derivatives, organic oxygen compounds, organoheterocyclic compounds, benzenoids, among others. Metabolites, such as choline and pregnanediol-3-glucuronide, play important roles in pregnancy in sows and other animals. These results reveal the metabolic changes in urine of sows during early pregnancy phase. The differential urinary metabolites can be used for assessing peri-implantation status in sows. Understanding these metabolic changes may promote the management of pregnant sows through various interventions such as provision of proper nutrition.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40813-022-00256-z.

Bi-allelic variants in CHKA cause a neurodevelopmental disorder with epilepsy and microcephaly

The Kennedy pathways catalyze the de novo synthesis of phosphatidylcholine and phosphatidylethanolamine, the most abundant components of eukaryotic cell membranes. In recent years, these pathways have moved into clinical focus since four out of ten genes involved have been associated with a range of autosomal recessive rare diseases such as a neurodevelopmental disorder with muscular dystrophy (CHKB), bone abnormalities and cone-rod dystrophy (PCYT1A), and spastic paraplegia (PCYT2, SELENOI). We identified six individuals from five families with bi-allelic variants in CHKA presenting with severe global developmental delay, epilepsy, movement disorders, and microcephaly. Using structural molecular modeling and functional testing of the variants in a in a cell-based S. cerevisiae model, we determined that these variants reduce the enzymatic activity of CHKA and confer a significant impairment of the first enzymatic step of the Kennedy pathway. In summary, we present CHKA as a novel autosomal recessive gene for a neurodevelopmental disorder with epilepsy and microcephaly.

Mild Choline Deficiency and MTHFD1 Synthetase Deficiency Interact to Increase Incidence of Developmental Delays and Defects in Mice

Folate and choline are interconnected metabolically. The MTHFD1 R653Q SNP is a risk factor for birth defects and there are concerns that choline deficiency may interact with this SNP and exacerbate health risks. 80–90% of women do not meet the Adequate Intake (AI) for choline. The objective of this study was to assess the effects of choline deficiency on maternal one-carbon metabolism and reproductive outcomes in the MTHFD1-synthetase deficient mouse (Mthfd1S), a model for MTHFD1 R653Q. Mthfd1S^+/+ and Mthfd1S^+/− females were fed control (CD) or choline-deficient diets (ChDD; 1/3 the amount of choline) before mating and during pregnancy. Embryos were evaluated for delays and defects at 10.5 days gestation. Choline metabolites were measured in the maternal liver, and total folate measured in maternal plasma and liver. ChDD significantly decreased choline, betaine, phosphocholine, and dimethylglycine in maternal liver (p < 0.05, ANOVA), and altered phosphatidylcholine metabolism. Maternal and embryonic genotype, and diet-genotype interactions had significant effects on defect incidence. Mild choline deficiency and Mthfd1S^+/− genotype alter maternal one-carbon metabolism and increase incidence of developmental defects. Further study is required to determine if low choline intakes contribute to developmental defects in humans, particularly in 653QQ women.

Identification of unprecedented ATP-competitive choline kinase inhibitors

In this article we describe the identification of unprecedented ATP-competitive ChoKα inhibitors starting from initial hit NMS-P830 that binds to ChoKα in an ATP concentration-dependent manner. This result is confirmed by the co-crystal structure of NMS-P830 in complex with Δ75-ChoKα. NMS-P830 is able to inhibit ChoKα in cells resulting in the reduction of intracellular phosphocholine formation. A structure-based medicinal chemistry program resulted in the identification of selective compounds that have good biochemical activity, solubility and metabolic stability and are suitable for further optimization. The ChoKα inhibitors disclosed in this article demonstrate for the first time the possibility to inhibit ChoKα with ATP-competitive compounds.

Choline Kinase Alpha Is a Novel Transcriptional Target of the Brg1 in Hepatocyte: Implication in Liver Regeneration

Liver regeneration is a key compensatory process in response to liver injury serving to contain damages and to rescue liver functions. Hepatocytes, having temporarily exited the cell cycle after embryogenesis, resume proliferation to regenerate the injured liver parenchyma. In the present study we investigated the transcriptional regulation of choline kinase alpha (Chka) in hepatocytes in the context of liver regeneration. We report that Chka expression was significantly up-regulated in the regenerating livers in the partial hepatectomy (PHx) model and the acetaminophen (APAP) injection model. In addition, treatment with hepatocyte growth factor (HGF), a strong pro-proliferative cue, stimulated Chka expression in primary hepatocytes. Chka depletion attenuated HGF-induced proliferation of hepatocytes as evidenced by quantitative PCR and Western blotting measurements of pro-proliferative genes as well as EdU incorporation into replicating DNA. Of interest, deletion of Brahma-related gene 1 (Brg1), a chromatin remodeling protein, attenuated Chka induction in the regenerating livers in mice and in cultured hepatocytes. Further analysis revealed that Brg1 interacted with hypoxia-inducible factor 1 alpha (HIF-1α) to directly bind to the Chka promoter and activate Chka transcription. Finally, examination of human acute liver failure (ALF) specimens identified a positive correlation between Chka expression and Brg1 expression. In conclusion, our data suggest that Brg1-dependent trans-activation of Chka expression may contribute to liver regeneration.

DNA Methylation of Human Choline Kinase Alpha Promoter-Associated CpG Islands in MCF-7 Cells

Choline kinase (CK) is the enzyme catalyzing the first reaction in CDP-choline pathway for the biosynthesis of phosphatidylcholine. Higher expression of the α isozyme of CK has been implicated in carcinogenesis, and inhibition or downregulation of CKα (CHKA) is a promising anticancer approach. This study aimed to investigate the regulation of CKα expression by DNA methylation of the CpG islands found on the promoter of this gene in MCF-7 cells. Four CpG islands have been predicted in the 2000 bp promoter region of ckα (chka) gene. Six CpG island deletion mutants were constructed using PCR site-directed mutagenesis method and cloned into pGL4.10 vectors for promoter activity assays. Deletion of CpG4C region located between -225 and -56 significantly increased the promoter activity by 4-fold, indicating the presence of important repressive transcription factor binding site. The promoter activity of methylated full-length promoter was significantly lower than the methylated CpG4C deletion mutant by 16-fold. The results show that DNA methylation of CpG4C promotes the binding of the transcription factor that suppresses the promoter activity. Electrophoretic mobility shift assay analysis showed that cytosine methylation at MZF1 binding site in CpG4C increased the binding of putative MZF1 in nuclear extract. In conclusion, the results suggest that DNA methylation decreased the promoter activity by promoting the binding of putative MZF1 transcription factor at CpG4C region of the ckα gene promoter.

Choline Kinase: An Unexpected Journey for a Precision Medicine Strategy in Human Diseases

Choline kinase (ChoK) is a cytosolic enzyme that catalyzes the phosphorylation of choline to form phosphorylcholine (PCho) in the presence of ATP and magnesium. ChoK is required for the synthesis of key membrane phospholipids and is involved in malignant transformation in a large variety of human tumours. Active compounds against ChoK have been identified and proposed as antitumor agents. The ChoK inhibitory and antiproliferative activities of symmetrical bispyridinium and bisquinolinium compounds have been defined using quantitative structure-activity relationships (QSARs) and structural parameters. The design strategy followed in the development of the most active molecules is presented. The selective anticancer activity of these structures is also described. One promising anticancer compound has even entered clinical trials. Recently, ChoKα inhibitors have also been proposed as a novel therapeutic approach against parasites, rheumatoid arthritis, inflammatory processes, and pathogenic bacteria. The evidence for ChoKα as a novel drug target for approaches in precision medicine is discussed.

CEPT1-Mediated Phospholipogenesis Regulates Endothelial Cell Function and Ischemia-Induced Angiogenesis Through PPARα

De novo phospholipogenesis, mediated by choline-ethanolamine phosphotransferase 1 (CEPT1), is essential for phospholipid activation of transcription factors such as peroxisome proliferator-activated receptor α (PPARα) in the liver. Fenofibrate, a PPARα agonist and lipid-lowering agent, decreases amputation incidence in patients with diabetes. Because we previously observed that CEPT1 is elevated in carotid plaque of patients with diabetes, we evaluated the role of CEPT1 in peripheral arteries and PPARα phosphorylation (Ser12). CEPT1 was found to be elevated in diseased lower-extremity arterial intima of individuals with peripheral arterial disease and diabetes. To evaluate the role of Cept1 in the endothelium, we engineered a conditional endothelial cell (EC)-specific deletion of Cept1 via induced VE-cadherin-CreERT2-mediated recombination (Cept1Lp/LpCre ⁺). Cept1Lp/LpCre ⁺ ECs demonstrated decreased proliferation, migration, and tubule formation, and Cept1Lp/LpCre ⁺ mice had reduced perfusion and angiogenesis in ischemic hind limbs. Peripheral ischemic recovery and PPARα signaling were further compromised by streptozotocin-induced diabetes and ameliorated by feeding fenofibrate. Cept1 endoribonuclease-prepared siRNA decreased PPARα phosphorylation in ECs, which was rescued with fenofibrate but not PC16:0/18:1. Unlike Cept1Lp/LpCre ⁺ mice, Cept1Lp/LpCre ⁺ Ppara ^-/- mice did not demonstrate hind-paw perfusion recovery after feeding fenofibrate. Therefore, we demonstrate that CEPT1 is essential for EC function and tissue recovery after ischemia and that fenofibrate rescues CEPT1-mediated activation of PPARα.

Choline kinase alpha impairment overcomes TRAIL resistance in ovarian cancer cells

Background

Choline kinase-α (ChoKα/CHKA) overexpression and hyper-activation sustain altered choline metabolism conferring the cholinic phenotype to epithelial ovarian cancer (OC), the most lethal gynecological tumor. We previously proved that CHKA down-modulation reduced OC cell aggressiveness and increased sensitivity to in vitro chemotherapeutics’ treatment also affecting intracellular content of one-carbon metabolites. In tumor types other than ovary, methionine decrease was shown to increase sensitivity to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-receptor 2 triggering. These effects were suggestive of a potential role for ChoKα in regulating susceptibility to TRAIL cytokine.

Methods

The relationship between ChoKα/CHKA and TRAIL-receptor 2 (TRAIL-R2) expression was investigated in silico in OC patients’ GEO datasets and in vitro in a panel of OC cell lines upon transient CHKA silencing (siCHKA). The effect of siCHKA on metabolites content was assessed by LC-MS. The triggered apoptotic signalling was studied following soluble-TRAIL or anti-TRAIL-R2 agonist antibody treatment. Lipid rafts were isolated by Triton X-100 fractionation. Preclinical ex vivo studies were performed in OC cells derived from patients’ ascites using autologous PBLs as effectors and a bispecific anti-TRAIL-R2/anti-CD3 antibody as triggering agent.

Results

Here we demonstrate that siCHKA specifically overcomes resistance to TRAIL-mediated apoptosis in OC cells. Upon siCHKA we detected: a significant sensitization to caspase-dependent apoptosis triggered by both soluble TRAIL and anti-TRAIL-R2 agonist antibody, a specific increase of TRAIL-R2 expression and TRAIL-R2 relocation into lipid rafts. In siCHKA-OC cells the acquired TRAIL sensitivity was completely reverted upon recovery of ChoKα expression but, at variance of other tumor cell types, TRAIL sensitivity was not efficiently phenocopied by methionine deprivation. Of note, we were also able to show that siCHKA sensitized tumor cells derived ex vivo from OC patients’ ascites to the cytotoxic activity of autologous lymphocytes redirected by a bispecific anti-TRAIL-R2/anti-CD3 antibody.

Conclusions

Our findings suggest that ChoKα/CHKA impairment, by restoring drug-induced or receptor-mediated cell death, could be a suitable therapeutic strategy to be used in combination with chemotherapeutics or immunomodulators to improve OC patients’ outcome.

Effects of choline on the phenotype of the cultured bovine preimplantation embryo

Choline is a precursor of acetylcholine, phosphatidylcholine, and the methyl-donor betaine. Reports indicate that supplementation with rumen-protected choline improves postpartum reproductive function of dairy cows. The objective was to determine whether addition of choline to culture medium of in vitro-produced embryos alters the phenotype of the resultant blastocysts. Treatments were choline chloride (ChCl; 0.004, 1.3, 1.8, and 6.37 mM) and phosphatidylcholine (1.3 mM). Treatment with 0.004 mM ChCl improved development to the blastocyst stage, increased blastocyst cell number, and increased the percentage of blastocysts that were hatching or hatched. Development was not affected by higher concentrations of ChCl but was reduced by 1.3 mM phosphatidylcholine. Treatment of embryos with 1.3 mM ChCl (but not other concentrations) increased expression in blastocysts of 11 of 165 genes examined (AMOT, NANOG, HDAC8, HNF4A, STAT1, MBNL3, SOX2, STAT3, KDM2B, SAV1, and GPAM) and decreased expression of one gene (ASS1). Treatment with 1.3 mM ChCl decreased global DNA methylation at d 3.5 of development and increased DNA methylation at d 7.5 in blastocysts. Treatment with 1.8 mM ChCl also increased methylation in blastocysts. In conclusion, addition of choline to the culture medium alters the phenotype of preimplantation bovine embryos produced in vitro. Choline chloride can act in a concentration-dependent manner to alter development, expression of specific genes, and DNA methylation.

Hepatic Choline Transport Is Inhibited During Fatty Acid-Induced Lipotoxicity and Obesity

Choline is an essential nutrient and a critical component of the membrane phospholipid phosphatidylcholine (PC), the neurotransmitter acetylcholine, while also contributing to the methylation pathway. In the liver specifically, PC is the major membrane constituent and can be synthesized by the cytidine diphosphate-choline or the phosphatidylethanolamine N-methyltransferase pathway. With the continuing global rise in the rates of obesity and nonalcoholic fatty liver disease, we sought to explore how excess fatty acids on primary hepatocytes and diet-induced obesity affect choline uptake and metabolism. Our results demonstrate that hepatocytes chronically treated with palmitate, but not oleate or a mixture, had decreased choline uptake, which was associated with lower choline incorporation into PC and lower expression of choline transport proteins. Interestingly, a reduction in the rate of degradation spared PC levels in response to palmitate when compared with control. The effects of palmitate treatment were independent of endoplasmic reticulum stress, which counterintuitively augmented choline transport and transporter expression. In a model of obesity-induced hepatic steatosis, male mice fed a 60% high-fat diet for 10 weeks had significantly diminished hepatic choline uptake compared with lean mice fed a control diet. Although the transcript and protein expression of various choline metabolic enzymes fluctuated slightly, we observed reduced protein expression of choline transporter-like 1 (CTL1) in the liver of mice fed a high-fat diet. Polysome profile analyses revealed that in livers of obese mice, the CTL1 transcript, despite being more abundant, was translated to a lesser extent compared with lean controls. Finally, human liver cells demonstrated a similar response to palmitate treatment. Conclusion: Our results suggest that the altered fatty acid milieu seen in obesity-induced fatty liver disease progression may adversely affect choline metabolism, potentially through CTL1, but that compensatory mechanisms work to maintain phospholipid homeostasis.

The Four Arabidopsis Choline/Ethanolamine Kinase Isozymes Play Distinct Roles in Metabolism and Development

Phosphatidylcholine and phosphatidylethanolamine are two major phospholipid classes in eukaryotes. Each biosynthesis pathway starts with the phosphorylation of choline (Cho) or ethanolamine (Etn) catalyzed by either choline or ethanolamine kinase (CEK). Arabidopsis contains four CEK isoforms, but their isozyme-specific roles in metabolism and development are poorly described. Here, we showed that these four CEKs have distinct substrate specificities in vitro. While CEK1 and CEK2 showed substrate preference for Cho over Etn, CEK3 and CEK4 had clear substrate specificity for Cho and Etn, respectively. In vivo, CEK1, CEK2, and CEK3 exhibited kinase activity for Cho but not Etn, although the latter two isoforms showed rather minor contributions to total Cho kinase activity in both shoots and roots. The knockout mutants of CEK2 and CEK3 both affected root growth, and these isoforms had nonoverlapping cell-type-specific expression patterns in the root meristematic zone. In-depth phenotype analysis, as well as chemical and genetic complementation, revealed that CEK3, a Cho-specific kinase, is involved in cell elongation during root development. Phylogenetic analysis of CEK orthologs in Brassicaceae species showed evolutionary divergence between Etn kinases and Cho kinases. Collectively, our results demonstrate the distinct roles of the four CEK isoforms in Cho/Etn metabolism and plant development.

Association of lipid-related genes implicated in conceptus elongation with female fertility traits in dairy cattle

Elongation of the preimplantation conceptus is a requirement for pregnancy success in ruminants, and failures in this process are highly associated with subfertility in dairy cattle. Identifying genetic markers that are related to early conceptus development and survival and utilizing these markers in selective breeding can improve the reproductive efficiency of dairy herds. Here, we evaluated the association of 1,679 SNP markers within or close to 183 candidate genes involved in lipid metabolism of the elongating conceptus with different fertility traits in US Holstein cattle. A total of 27,371 bulls with predicted transmitting ability records for daughter pregnancy rate, cow conception rate, and heifer conception rate were used as the discovery population. The associations found in the discovery population were validated using 2 female populations (1,122 heifers and 2,138 lactating cows) each with 4 fertility traits, including success to first insemination, number of services per conception, age at first conception for heifers, or days open for cows. Marker effects were estimated using a linear mixed model with SNP genotype as a linear covariate and a random polygenic effect. After multiple testing correction, 39 SNP flagging 27 candidate genes were associated with at least one fertility trait in the discovery population. Of these 39 markers, 3 SNP were validated in the heifer population and 4 SNP were validated in the cow population. The 3 SNP validated in heifers are located within or near genes CAT, MYOF, and RBP4, and the 4 SNP validated in lactating cows are located within or close to genes CHKA, GNAI1, and HMOX2. These validated genes seem to be relevant for reducing pregnancy losses, and the SNP within these genes are excellent candidates for inclusion in genomic tests to improve reproductive performance in dairy cattle.

Mitofusins regulate lipid metabolism to mediate the development of lung fibrosis

Accumulating evidence illustrates a fundamental role for mitochondria in lung alveolar type 2 epithelial cell (AEC2) dysfunction in the pathogenesis of idiopathic pulmonary fibrosis. However, the role of mitochondrial fusion in AEC2 function and lung fibrosis development remains unknown. Here we report that the absence of the mitochondrial fusion proteins mitofusin1 (MFN1) and mitofusin2 (MFN2) in murine AEC2 cells leads to morbidity and mortality associated with spontaneous lung fibrosis. We uncover a crucial role for MFN1 and MFN2 in the production of surfactant lipids with MFN1 and MFN2 regulating the synthesis of phospholipids and cholesterol in AEC2 cells. Loss of MFN1, MFN2 or inhibiting lipid synthesis via fatty acid synthase deficiency in AEC2 cells exacerbates bleomycin-induced lung fibrosis. We propose a tenet that mitochondrial fusion and lipid metabolism are tightly linked to regulate AEC2 cell injury and subsequent fibrotic remodeling in the lung.

How To Build a Bone: PHOSPHO1, Biomineralization, and Beyond

Since its characterization two decades ago, the phosphatase PHOSPHO1 has been the subject of an increasing focus of research. This work has elucidated PHOSPHO1's central role in the biomineralization of bone and other hard tissues, but has also implicated the enzyme in other biological processes in health and disease. During mineralization PHOSPHO1 liberates inorganic phosphate (P_i) to be incorporated into the mineral phase through hydrolysis of its substrates phosphocholine (PCho) and phosphoethanolamine (PEA). Localization of PHOSPHO1 within matrix vesicles allows accumulation of P_i within a protected environment where mineral crystals may nucleate and subsequently invade the organic collagenous scaffold. Here, we examine the evidence for this process, first discussing the discovery and characterization of PHOSPHO1, before considering experimental evidence for its canonical role in matrix vesicle–mediated biomineralization. We also contemplate roles for PHOSPHO1 in disorders of dysregulated mineralization such as vascular calcification, along with emerging evidence of its activity in other systems including choline synthesis and homeostasis, and energy metabolism. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Metabolites and Lipids Associated with Fetal Swine Anatomy via Desorption Electrospray Ionization - Mass Spectrometry Imaging

Chemical imaging by mass spectrometry (MS) has been largely used to study diseases in animals and humans, especially cancer; however, this technology has been minimally explored to study the complex chemical changes associated with fetal development. In this work, we report the histologically-compatible chemical imaging of small molecules by desorption electrospray ionization (DESI) - MS of a complete swine fetus at 50 days of gestation. Tissue morphology was unperturbed by morphologically-friendly DESI-MS analysis while allowing detection of a wide range of small molecules. We observed organ-dependent localization of lipids, e.g. a large diversity of phosphatidylserine lipids in brain compared to other organs, as well as metabolites such as N-acetyl-aspartic acid in the developing nervous system and N-acetyl-L-glutamine in the heart. Some lipids abundant in the lungs, such as PC(32:0) and PS(40:6), were  similar to surfactant composition reported previously. Sulfatides were highly concentrated in the fetus liver, while hexoses were barely detected at this organ but were abundant in lung and heart. The chemical information on small molecules recorded via DESI-MS imaging coupled with traditional anatomical evaluation is a powerful source of bioanalytical information which reveals the chemical changes associated with embryonic and fetal development that, when disturbed, causes congenital diseases such as spina bifida and cleft palate.

Lipidomics reveal aryl hydrocarbon receptor (Ahr)-regulated lipid metabolic pathway in alpha-naphthyl isothiocyanate (ANIT)-induced intrahepatic cholestasis

1. Ultra-performance liquid chromatography coupled with electrospray ionization quadrupole mass spectrometry (UPLC-ESI-QTOF MS)-based lipidomics was employed to elucidate new mechanism of alpha-naphthyl isothiocyanate (ANIT)-induced intrahepatic cholestasis in mice. 2. Multiple lipid components significantly increased in ANIT-induced intrahepatic cholestasis, including PC 16:0, 20:4, PC 16:0, 22:6, PC 16:0, 18:2, LPC 18:2, PC 18:2, LPC 18:1, PC 18:1, 14:0, SM 18:1, 16:0, oleoylcarnitine and palmitoylcarnitine. This alteration of lipid profile was induced by the changed expression of genes choline kinase (Chk) a, sphingomyelin phosphodiesterase (SMPD) and stearoyl-coenzyme A desaturase 1 (SCD1). 3. Knockout of aryl hydrocarbon receptor (Ahr) in mice can significantly reverse ANIT-induced intrahepatic cholestasis, as indicated by lowered ALT, AST and ALP activity, and liver histology. Aryl hydrocarbon receptor knockout significantly reversed ANIT-induced lipid metabolism alteration through regulating the expression of Chka. 4. In conclusion, this study demonstrated ANIT-induced lipid metabolism disruption might be the potential pathogenesis of ANIT-induced intrahepatic cholestasis in mice.

Molecular causes of elevated phosphoethanolamine in breast and pancreatic cancer cells

Elevated phosphoethanolamine (PE) is frequently observed in MRS studies of human cancers and xenografts. The role of PE in cell survival and the molecular causes underlying this increase are, however, relatively underexplored. In this study, we investigated the roles of ethanolamine kinases (Etnk-1 and 2) and choline kinases (Chk-α and β) in contributing to increased PE in human breast and pancreatic cancer cells. We investigated the effect of silencing Etnk-1 and Etnk-2 on cell viability as a potential therapeutic strategy. Both breast and pancreatic cancer cells showed higher PE compared with their nonmalignant counterparts. We identified Etnk-1 as a major cause of the elevated PE levels in these cancer cells, with little or no contribution from Chk-α, Chk-β, or Etnk-2. The increase of PE observed in pancreatic cancer cells in culture was replicated in the corresponding tumor xenografts. Downregulation of Etnk-1 with siRNA resulted in cell cytotoxicity that correlated with PE levels in breast and pancreatic cancer cells. Etnk-1 may provide a potential therapeutic target in breast and pancreatic cancers.

One-Carbon Metabolism: Biological Players in Epithelial Ovarian Cancer

Metabolism is deeply involved in cell behavior and homeostasis maintenance, with metabolites acting as molecular intermediates to modulate cellular functions. In particular, one-carbon metabolism is a key biochemical pathway necessary to provide carbon units required for critical processes, including nucleotide biosynthesis, epigenetic methylation, and cell redox-status regulation. It is, therefore, not surprising that alterations in this pathway may acquire fundamental importance in cancer onset and progression. Two of the major actors in one-carbon metabolism, folate and choline, play a key role in the pathobiology of epithelial ovarian cancer (EOC), the deadliest gynecological malignancy. EOC is characterized by a cholinic phenotype sustained via increased activity of choline kinase alpha, and via membrane overexpression of the alpha isoform of the folate receptor (FRα), both of which are known to contribute to generating regulatory signals that support EOC cell aggressiveness and proliferation. Here, we describe in detail the main biological processes associated with one-carbon metabolism, and the current knowledge about its role in EOC. Moreover, since the cholinic phenotype and FRα overexpression are unique properties of tumor cells, but not of normal cells, they can be considered attractive targets for the development of therapeutic approaches.

The critical role of phosphatidylcholine and phosphatidylethanolamine metabolism in health and disease

Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are the most abundant phospholipids in all mammalian cell membranes. In the 1950s, Eugene Kennedy and co-workers performed groundbreaking research that established the general outline of many of the pathways of phospholipid biosynthesis. In recent years, the importance of phospholipid metabolism in regulating lipid, lipoprotein and whole-body energy metabolism has been demonstrated in numerous dietary studies and knockout animal models. The purpose of this review is to highlight the unappreciated impact of phospholipid metabolism on health and disease. Abnormally high, and abnormally low, cellular PC/PE molar ratios in various tissues can influence energy metabolism and have been linked to disease progression. For example, inhibition of hepatic PC synthesis impairs very low density lipoprotein secretion and changes in hepatic phospholipid composition have been linked to fatty liver disease and impaired liver regeneration after surgery. The relative abundance of PC and PE regulates the size and dynamics of lipid droplets. In mitochondria, changes in the PC/PE molar ratio affect energy production. We highlight data showing that changes in the PC and/or PE content of various tissues are implicated in metabolic disorders such as atherosclerosis, insulin resistance and obesity. This article is part of a Special Issue entitled: Membrane Lipid Therapy: Drugs Targeting Biomembranes edited by Pablo V. Escribá.

Stella modulates transcriptional and endogenous retrovirus programs during maternal-to-zygotic transition

The maternal-to-zygotic transition (MZT) marks the period when the embryonic genome is activated and acquires control of development. Maternally inherited factors play a key role in this critical developmental process, which occurs at the 2-cell stage in mice. We investigated the function of the maternally inherited factor Stella (encoded by Dppa3) using single-cell/embryo approaches. We show that loss of maternal Stella results in widespread transcriptional mis-regulation and a partial failure of MZT. Strikingly, activation of endogenous retroviruses (ERVs) is significantly impaired in Stella maternal/zygotic knockout embryos, which in turn leads to a failure to upregulate chimeric transcripts. Amongst ERVs, MuERV-L activation is particularly affected by the absence of Stella, and direct in vivo knockdown of MuERV-L impacts the developmental potential of the embryo. We propose that Stella is involved in ensuring activation of ERVs, which themselves play a potentially key role during early development, either directly or through influencing embryonic gene expression.

Impaired embryonic development in glucose-6-phosphate dehydrogenase-deficient Caenorhabditis elegans due to abnormal redox homeostasis induced activation of calcium-independent phospholipase and alteration of glycerophospholipid metabolism

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a commonly pervasive inherited disease in many parts of the world. The complete lack of G6PD activity in a mouse model causes embryonic lethality. The G6PD-deficient Caenorhabditis elegans model also shows embryonic death as indicated by a severe hatching defect. Although increased oxidative stress has been implicated in both cases as the underlying cause, the exact mechanism has not been clearly delineated. In this study with C. elegans, membrane-associated defects, including enhanced permeability, defective polarity and cytokinesis, were found in G6PD-deficient embryos. The membrane-associated abnormalities were accompanied by impaired eggshell structure as evidenced by a transmission electron microscopic study. Such loss of membrane structural integrity was associated with abnormal lipid composition as lipidomic analysis revealed that lysoglycerophospholipids were significantly increased in G6PD-deficient embryos. Abnormal glycerophospholipid metabolism leading to defective embryonic development could be attributed to the increased activity of calcium-independent phospholipase A₂ (iPLA) in G6PD-deficient embryos. This notion is further supported by the fact that the suppression of multiple iPLAs by genetic manipulation partially rescued the embryonic defects in G6PD-deficient embryos. In addition, G6PD deficiency induced disruption of redox balance as manifested by diminished NADPH and elevated lipid peroxidation in embryos. Taken together, disrupted lipid metabolism due to abnormal redox homeostasis is a major factor contributing to abnormal embryonic development in G6PD-deficient C. elegans.

Targeting Phospholipid Metabolism in Cancer

All cancers tested so far display abnormal choline and ethanolamine phospholipid metabolism, which has been detected with numerous magnetic resonance spectroscopy (MRS) approaches in cells, animal models of cancer, as well as the tumors of cancer patients. Since the discovery of this metabolic hallmark of cancer, many studies have been performed to elucidate the molecular origins of deregulated choline metabolism, to identify targets for cancer treatment, and to develop MRS approaches that detect choline and ethanolamine compounds for clinical use in diagnosis and treatment monitoring. Several enzymes in choline, and recently also ethanolamine, phospholipid metabolism have been identified, and their evaluation has shown that they are involved in carcinogenesis and tumor progression. Several already established enzymes as well as a number of emerging enzymes in phospholipid metabolism can be used as treatment targets for anticancer therapy, either alone or in combination with other chemotherapeutic approaches. This review summarizes the current knowledge of established and relatively novel targets in phospholipid metabolism of cancer, covering choline kinase α, phosphatidylcholine-specific phospholipase D1, phosphatidylcholine-specific phospholipase C, sphingomyelinases, choline transporters, glycerophosphodiesterases, phosphatidylethanolamine N-methyltransferase, and ethanolamine kinase. These enzymes are discussed in terms of their roles in oncogenic transformation, tumor progression, and crucial cancer cell properties such as fast proliferation, migration, and invasion. Their potential as treatment targets are evaluated based on the current literature.

An essential developmental function for murine phosphoglycolate phosphatase in safeguarding cell proliferation

Mammalian phosphoglycolate phosphatase (PGP) is thought to target phosphoglycolate, a 2-deoxyribose fragment derived from the repair of oxidative DNA lesions. However, the physiological role of this activity and the biological function of the DNA damage product phosphoglycolate is unknown. We now show that knockin replacement of murine Pgp with its phosphatase-inactive Pgp^D34N mutant is embryonically lethal due to intrauterine growth arrest and developmental delay in midgestation. PGP inactivation attenuated triosephosphate isomerase activity, increased triglyceride levels at the expense of the cellular phosphatidylcholine content, and inhibited cell proliferation. These effects were prevented under hypoxic conditions or by blocking phosphoglycolate release from damaged DNA. Thus, PGP is essential to sustain cell proliferation in the presence of oxygen. Collectively, our findings reveal a previously unknown mechanism coupling a DNA damage repair product to the control of intermediary metabolism and cell proliferation.

Molecular structure and differential function of choline kinases CHKα and CHKβ in musculoskeletal system and cancer

Choline, a hydrophilic cation, has versatile physiological roles throughout the body, including cholinergic neurotransmission, memory consolidation and membrane biosynthesis and metabolism. Choline kinases possess enzyme activity that catalyses the conversion of choline to phosphocholine, which is further converted to cytidine diphosphate-coline (CDP-choline) in the biosynthesis of phosphatidylcholine (PC). PC is a major constituent of the phospholipid bilayer which constitutes the eukaryotic cell membrane, and regulates cell signal transduction. Choline Kinase consists of three isoforms, CHKα1, CHKα2 and CHKβ, encoded by two separate genes (CHKA(Human)/Chka(Mouse) and CHKB(Human)/Chkb(Mouse)). Both isoforms have similar structures and enzyme activity, but display some distinct molecular structural domains and differential tissue expression patterns. Whilst Choline Kinase was discovered in early 1950, its pivotal role in the development of muscular dystrophy, bone deformities, and cancer has only recently been identified. CHKα has been proposed as a cancer biomarker and its inhibition as an anti-cancer therapy. In contrast, restoration of CHKβ deficiency through CDP-choline supplements like citicoline may be beneficial for the treatment of muscular dystrophy, bone metabolic diseases, and cognitive conditions. The molecular structure and expression pattern of Choline Kinase, the differential roles of Choline Kinase isoforms and their potential as novel therapeutic targets for muscular dystrophy, bone deformities, cognitive conditions and cancer are discussed.

Looking Beyond Structure: Membrane Phospholipids of Skeletal Muscle Mitochondria

Skeletal muscle mitochondria are highly dynamic and are capable of tremendous expansion to meet cellular energetic demands. Such proliferation in mitochondrial mass requires a synchronized supply of enzymes and structural phospholipids. While transcriptional regulation of mitochondrial enzymes has been extensively studied, there is limited information on how mitochondrial membrane lipids are generated in skeletal muscle. Herein we describe how each class of phospholipids that constitute mitochondrial membranes are synthesized and/or imported, and summarize genetic evidence indicating that membrane phospholipid composition represents a significant modulator of skeletal muscle mitochondrial respiratory function. We also discuss how skeletal muscle mitochondrial phospholipids may mediate the effect of diet and exercise on oxidative metabolism.

Choline kinase alpha-Putting the ChoK-hold on tumor metabolism

It is well established that lipid metabolism is drastically altered during tumor development and response to therapy. Choline kinase alpha (ChoKα) is a key mediator of these changes, as it represents the first committed step in the Kennedy pathway of phosphatidylcholine biosynthesis and ChoKα expression is upregulated in many human cancers. ChoKα activity is associated with drug resistant, metastatic, and malignant phenotypes, and represents a robust biomarker and therapeutic target in cancer. Effective ChoKα inhibitors have been developed and have recently entered clinical trials. ChoKα's clinical relevance was, until recently, attributed solely to its production of second messenger intermediates of phospholipid synthesis. The recent discovery of a non-catalytic scaffolding function of ChoKα may link growth receptor signaling to lipid biogenesis and requires a reinterpretation of the design and validation of ChoKα inhibitors. Advances in positron emission tomography, magnetic resonance spectroscopy, and optical imaging methods now allow for a comprehensive understanding of ChoKα expression and activity in vivo. We will review the current understanding of ChoKα metabolism, its role in tumor biology and the development and validation of targeted therapies and companion diagnostics for this important regulatory enzyme. This comes at a critical time as ChoKα-targeting programs receive more clinical interest.

Choline Metabolism Alteration: A Focus on Ovarian Cancer

Compared with normal differentiated cells, cancer cells require a metabolic reprograming to support their high proliferation rates and survival. Aberrant choline metabolism is a fairly new metabolic hallmark reflecting the complex reciprocal interactions between oncogenic signaling and cellular metabolism. Alterations of the involved metabolic network may be sustained by changes in activity of several choline transporters as well as of enzymes such as choline kinase-alpha (ChoK-α) and phosphatidylcholine-specific phospholipases C and D. Of note, the net outcome of these enzymatic alterations is an increase of phosphocholine and total choline-containing compounds, a "cholinic phenotype" that can be monitored in cancer by magnetic resonance spectroscopy. This review will highlight the molecular basis for targeting this pathway in epithelial ovarian cancer (EOC), a highly heterogeneous and lethal malignancy characterized by late diagnosis, frequent relapse, and development of chemoresistance. Modulation of ChoK-α expression impairs only EOC but not normal ovarian cells, thus supporting the hypothesis that "cholinic phenotype" is a peculiar feature of transformed cells and indicating ChoK-α targeting as a novel approach to improve efficacy of standard EOC chemotherapeutic treatments.

Phosphorylation of Human Choline Kinase Beta by Protein Kinase A: Its Impact on Activity and Inhibition

Choline kinase beta (CKβ) is one of the CK isozymes involved in the biosynthesis of phosphatidylcholine. CKβ is important for normal mitochondrial function and muscle development as the lack of the ckβ gene in human and mice results in the development of muscular dystrophy. In contrast, CKα is implicated in tumorigenesis and has been extensively studied as an anticancer target. Phosphorylation of human CKα was found to regulate the enzyme’s activity and its subcellular location. This study provides evidence for CKβ phosphorylation by protein kinase A (PKA). In vitro phosphorylation of CKβ by PKA was first detected by phosphoprotein staining, as well as by in-gel kinase assays. The phosphorylating kinase was identified as PKA by Western blotting. CKβ phosphorylation by MCF-7 cell lysate was inhibited by a PKA-specific inhibitor peptide, and the intracellular phosphorylation of CKβ was shown to be regulated by the level of cyclic adenosine monophosphate (cAMP), a PKA activator. Phosphorylation sites were located on CKβ residues serine-39 and serine-40 as determined by mass spectrometry and site-directed mutagenesis. Phosphorylation increased the catalytic efficiencies for the substrates choline and ATP about 2-fold, without affecting ethanolamine phosphorylation, and the S39D/S40D CKβ phosphorylation mimic behaved kinetically very similar. Remarkably, phosphorylation drastically increased the sensitivity of CKβ to hemicholinium-3 (HC-3) inhibition by about 30-fold. These findings suggest that CKβ, in concert with CKα, and depending on its phosphorylation status, might play a critical role as a druggable target in carcinogenesis.

New more polar symmetrical bipyridinic compounds: new strategy for the inhibition of choline kinase α1

AIM

Research of the antitumor properties of biscationic compounds has received significant attention over the last few years.

RESULTS

A novel family of 1,1'-([2,2'-bipyridine]-5,5'-diylbis(methylene))bis-substituted bromide (9a-k), containing two nitrogen atoms in the linker, considered as hypothetical hydrogen bond acceptors, were synthesized and evaluated as ChoK inhibitors and their antiproliferative activity against six cancer cell lines.

CONCLUSION

The most promising compounds in this series are 1,1'-([2,2'-bipyridine]-5,5'-diylbis(methylene))bis(4-(methyl(phenyl)amino)-quinolinium bromide derivatives 9g-i (analogs to RSM932A), that significantly inhibit cancer cell growth at even submicromolar concentrations, especially against leukemia cells. Compounds 9g-i also inhibit the ChoKα1 with good or moderate values, as predicted by initial docking studies. In addition, the most active compound 9h remarkably induces apoptosis in two cell lines following the mitochondrial pathway.

Choline kinase-α protein and phosphatidylcholine but not phosphocholine are required for breast cancer cell survival

High levels of total choline and phosphocholine (PC) are consistently observed in aggressive cancers. Choline kinase (Chk) catalyzes choline phosphorylation to produce PC in phosphatidylcholine (PtdCho) biosynthesis. PtdCho is the most abundant phospholipid in eukaryotic cell membranes and plays a dual role as the structural component of membranes and as a substrate to produce lipid second messengers such as phosphatidic acid and diacylglycerol. Chk-α, but not Chk-β, is overexpressed in various cancers, and is closely associated with tumor progression and invasiveness. We have previously shown that downregulation of mRNA using small interfering RNA (siRNA) against Chk-α (siRNA-Chk) or Chk short hairpin RNA, and the resultant decrease of Chk-α protein levels, significantly reduced proliferation in breast cancer cells and tumors. A novel potent and selective small-molecule Chk-α inhibitor, V-11-0711, that inhibits the catalytic activity of Chk has recently been developed. Here, we used triple negative MDA-MB-231 and SUM149 breast cancer cells to further investigate the role of Chk-α in cancer, by examining Chk-α protein levels, cell viability/proliferation, choline phospholipid and lipid metabolism, lipid droplet formation, and apoptosis, following treatment with V-11-0711. Under the conditions used in this study, treatment with V-11-0711 significantly decreased PC levels but did not reduce cell viability as long as Chk-α protein and PtdCho levels were not reduced, suggesting that Chk-α protein and PtdCho, but not PC, may be crucial for breast cancer cell survival. These data also support the approach of antitumor strategies that destabilize Chk-α protein or downregulate PtdCho in breast cancer treatment.

Using Gene Essentiality and Synthetic Lethality Information to Correct Yeast and CHO Cell Genome-Scale Models

Essentiality (ES) and Synthetic Lethality (SL) information identify combination of genes whose deletion inhibits cell growth. This information is important for both identifying drug targets for tumor and pathogenic bacteria suppression and for flagging and avoiding gene deletions that are non-viable in biotechnology. In this study, we performed a comprehensive ES and SL analysis of two important eukaryotic models (S. cerevisiae and CHO cells) using a bilevel optimization approach introduced earlier. Information gleaned from this study is used to propose specific model changes to remedy inconsistent with data model predictions. Even for the highly curated Yeast 7.11 model we identified 50 changes (metabolic and GPR) leading to the correct prediction of an additional 28% of essential genes and 36% of synthetic lethals along with a 53% reduction in the erroneous identification of essential genes. Due to the paucity of mutant growth phenotype data only 12 changes were made for the CHO 1.2 model leading to an additional correctly predicted 11 essential and eight non-essential genes. Overall, we find that CHO 1.2 was 76% less accurate than the Yeast 7.11 metabolic model in predicting essential genes. Based on this analysis, 14 (single and double deletion) maximally informative experiments are suggested to improve the CHO cell model by using information from a mouse metabolic model. This analysis demonstrates the importance of single and multiple knockout phenotypes in assessing and improving model reconstructions. The advent of techniques such as CRISPR opens the door for the global assessment of eukaryotic models.

Choline kinase β mutant mice exhibit reduced phosphocholine, elevated osteoclast activity, and low bone mass

The maintenance of bone homeostasis requires tight coupling between bone-forming osteoblasts and bone-resorbing osteoclasts. However, the precise molecular mechanism(s) underlying the differentiation and activities of these specialized cells are still largely unknown. Here, we identify choline kinase β (CHKB), a kinase involved in the biosynthesis of phosphatidylcholine, as a novel regulator of bone homeostasis. Choline kinase β mutant mice (flp/flp) exhibit a systemic low bone mass phenotype. Consistently, osteoclast numbers and activity are elevated in flp/flp mice. Interestingly, osteoclasts derived from flp/flp mice exhibit reduced sensitivity to excessive levels of extracellular calcium, which could account for the increased bone resorption. Conversely, supplementation of cytidine 5'-diphosphocholine in vivo and in vitro, a regimen that bypasses CHKB deficiency, restores osteoclast numbers to physiological levels. Finally, we demonstrate that, in addition to modulating osteoclast formation and function, loss of CHKB corresponds with a reduction in bone formation by osteoblasts. Taken together, these data posit CHKB as a new modulator of bone homeostasis.

The E2F2 transcription factor sustains hepatic glycerophospholipid homeostasis in mice

Increasing evidence links metabolic signals to cell proliferation, but the molecular wiring that connects the two core machineries remains largely unknown. E2Fs are master regulators of cellular proliferation. We have recently shown that E2F2 activity facilitates the completion of liver regeneration after partial hepatectomy (PH) by regulating the expression of genes required for S-phase entry. Our study also revealed that E2F2 determines the duration of hepatectomy-induced hepatic steatosis. A transcriptomic analysis of normal adult liver identified “lipid metabolism regulation” as a major E2F2 functional target, suggesting that E2F2 has a role in lipid homeostasis. Here we use wild-type (E2F2^+/+) and E2F2 deficient (E2F2^−/−) mice to investigate the in vivo role of E2F2 in the composition of liver lipids and fatty acids in two metabolically different contexts: quiescence and 48-h post-PH, when cellular proliferation and anabolic demands are maximal. We show that liver regeneration is accompanied by large triglyceride and protein increases without changes in total phospholipids both in E2F2^+/+ and E2F2^−/− mice. Remarkably, we found that the phenotype of quiescent liver tissue from E2F2^−/− mice resembles the phenotype of proliferating E2F2^+/+ liver tissue, characterized by a decreased phosphatidylcholine to phosphatidylethanolamine ratio and a reprogramming of genes involved in generation of choline and ethanolamine derivatives. The diversity of fatty acids in total lipid, triglycerides and phospholipids was essentially preserved on E2F2 loss both in proliferating and non-proliferating liver tissue, although notable exceptions in inflammation-related fatty acids of defined phospholipid classes were detected. Overall, our results indicate that E2F2 activity sustains the hepatic homeostasis of major membrane glycerolipid components while it is dispensable for storage glycerolipid balance.

Choline kinase beta is required for normal endochondral bone formation

BACKGROUND

Choline kinase has three isoforms encoded by the genes Chka and Chkb. Inactivation of Chka in mice results in embryonic lethality, whereas Chkb(-/-) mice display neonatal forelimb bone deformations.

METHODS

To understand the mechanisms underlying the bone deformations, we compared the biology and biochemistry of bone formation from embryonic to young adult wild-type (WT) and Chkb(-/-) mice.

RESULTS

The deformations are specific to the radius and ulna during the late embryonic stage. The radius and ulna of Chkb(-/-) mice display expanded hypertrophic zones, unorganized proliferative columns in their growth plates, and delayed formation of primary ossification centers. The differentiation of chondrocytes of Chkb(-/-) mice was impaired, as was chondrocyte proliferation and expression of matrix metalloproteinases 9 and 13. In chondrocytes from Chkb(-/-) mice, phosphatidylcholine was slightly lower than in WT mice whereas the amount of phosphocholine was decreased by approximately 75%. In addition, the radius and ulna from Chkb(-/-) mice contained fewer osteoclasts along the cartilage/bone interface.

CONCLUSIONS

Chkb has a critical role in the normal embryogenic formation of the radius and ulna in mice.

GENERAL SIGNIFICANCE

Our data indicate that choline kinase beta plays an important role in endochondral bone formation by modulating growth plate physiology.

Phosphatidylcholine metabolism and choline kinase in human osteoblasts

There is a paucity of information about phosphatidylcholine (PC) biosynthesis in bone formation. Thus, we characterized PC metabolism in both primary human osteoblasts (HOB) and human osteosarcoma MG-63 cells. Our results show that the CDP-choline pathway is the only de novo route for PC biosynthesis in both HOB and MG-63 cells. Both CK activity and CKα expression in MG-63 cells were significantly higher than those in HOB cells. Silencing of CKα in MG-63 cells had no significant effect on PC concentration but decreased the amount of phosphocholine by approximately 80%. The silencing of CKα also reduced cell proliferation. Moreover, pharmacological inhibition of CK activity impaired the mineralization capacity of MG-63 cells. Our data suggest that CK and its product phosphocholine are required for the normal growth and mineralization of MG-63 cells.

Choline kinase-alpha by regulating cell aggressiveness and drug sensitivity is a potential druggable target for ovarian cancer

Background:

Aberrant choline metabolism has been proposed as a novel cancer hallmark. We recently showed that epithelial ovarian cancer (EOC) possesses an altered MRS-choline profile, characterised by increased phosphocholine (PCho) content to which mainly contribute over-expression and activation of choline kinase-alpha (ChoK-alpha).

Methods:

To assess its biological relevance, ChoK-alpha expression was downmodulated by transient RNA interference in EOC in vitro models. Gene expression profiling by microarray analysis and functional analysis was performed to identify the pathway/functions perturbed in ChoK-alpha-silenced cells, then validated by in vitro experiments.

Results:

In silenced cells, compared with control, we observed: (I) a significant reduction of both CHKA transcript and ChoK-alpha protein expression; (II) a dramatic, proportional drop in PCho content ranging from 60 to 71%, as revealed by ¹H-magnetic spectroscopy analysis; (III) a 35–36% of cell growth inhibition, with no evidences of apoptosis or modification of the main cellular survival signalling pathways; (IV) 476 differentially expressed genes, including genes related to lipid metabolism. Ingenuity pathway analysis identified cellular functions related to cell death and cellular proliferation and movement as the most perturbed. Accordingly, CHKA-silenced cells displayed a significant delay in wound repair, a reduced migration and invasion capability were also observed. Furthermore, although CHKA silencing did not directly induce cell death, a significant increase of sensitivity to platinum, paclitaxel and doxorubicin was observed even in a drug-resistant context.

Conclusion:

We showed for the first time in EOC that CHKA downregulation significantly decreased the aggressive EOC cell behaviour also affecting cells' sensitivity to drug treatment. These observations open the way to further analysis for ChoK-alpha validation as a new EOC therapeutic target to be used alone or in combination with conventional drugs.

Expression of phosphatidylcholine biosynthetic enzymes during early embryogenesis in the amphibian Bufo arenarum

In the principal route of phosphatidylcholine (PC) synthesis the regulatory steps are catalysed by CTP:phosphocholine cytidylyltransferase (CCT) and choline kinase (CK). Knock-out mice in Pcyt1a (CCT gene) and Chka1 (CK gene) resulted in preimplantation embryonic lethality, demonstrating the essential role of this pathway. However, there is still a lack of detailed CCT and CK expression analysis during development. The aim of the current work was to study the expression during early development of both enzymes in the external-fertilization vertebrate Bufo arenarum. Reverse transcription polymerase chain reaction (RT-PCR) and western blot confirmed their presence in unfertilized eggs. Analysis performed in total extracts from staged embryos showed constant protein levels of both enzymes until the 32-cell stage: then they decreased, reaching a minimum in the gastrula before starting to recover. CTP:phosphocholine cytidylyltransferase is an amphitropic enzyme that inter-converts between cytosolic inactive and membrane-bound active forms. Immunoblot analysis demonstrated that the cytosolic:total CCT protein ratio does not change throughout embryogenesis, suggesting a progressive decline of CCT activity in early development. However, PC (and phosphatidylethanolamine) content per egg/embryo remained constant throughout the stages analysed. In conclusion, the current data for B. arenarum suggest that net synthesis of PC mediated by CCT and CK is not required in early development and that supplies for membrane biosynthesis are fulfilled by lipids already present in the egg/embryo reservoirs.

Characterization of choline kinase in human endothelial cells

High choline kinase-α (Chk-α) expression is frequently observed in cancer cells, making it a novel target for pharmacological and molecular inhibition. As inhibiting agents are delivered systemically, it is important to determine Chk-α expression levels in endothelial cells that line both normal and tumor vasculature, and the effect of Chk-α downregulation on these cells. Here, we characterized Chk-α expression and the effect of its downregulation in human umbilical vein endothelial cells (HUVECs) relative to MDA-MB-231 human breast cancer cells. We used small interfering RNA (siRNA) to downregulate Chk-α expression. Basal mRNA levels of Chk-α were approximately three-fold lower in HUVECs relative to MDA-MB-231 breast cancer cells. Consistent with the differences in Chk-α protein levels, phosphocholine levels were approximately 10-fold lower in HUVECs relative to MDA-MB-231 cells. Transient transfection with siRNA-Chk resulted in comparable levels of mRNA and protein in MDA-MB-231 breast cancer cells and HUVECs. However, there was a significant reduction in proliferation in MDA-MB-231 cells, but not in HUVECs. No significant difference in CD31 immunostaining was observed in tumor sections obtained from mice injected with control luciferase-short hairpin (sh)RNA or Chk-shRNA lentivirus. These data suggest that systemically delivered agents that downregulate Chk-α in tumors will not affect endothelial cell proliferation during delivery, and further support the development of Chk-α downregulation as a cancer-specific treatment.

A functional siRNA screen identifies genes modulating angiotensin II-mediated EGFR transactivation

The angiotensin type 1 receptor (AT1R) transactivates the epidermal growth factor receptor (EGFR) to mediate cellular growth, however, the molecular mechanisms involved have not yet been resolved. To address this, we performed a functional siRNA screen of the human kinome in human mammary epithelial cells that demonstrate a robust AT1R-EGFR transactivation. We identified a suite of genes encoding proteins that both positively and negatively regulate AT1R-EGFR transactivation. Many candidates are components of EGFR signalling networks, whereas others, including TRIO, BMX and CHKA, have not been previously linked to EGFR transactivation. Individual knockdown of TRIO, BMX or CHKA attenuated tyrosine phosphorylation of the EGFR by angiotensin II stimulation, but this did not occur following direct stimulation of the EGFR with EGF, indicating that these proteins function between the activated AT1R and the EGFR. Further investigation of TRIO and CHKA revealed that their activity is likely to be required for AT1R-EGFR transactivation. CHKA also mediated EGFR transactivation in response to another G protein-coupled receptor (GPCR) ligand, thrombin, indicating a pervasive role for CHKA in GPCR-EGFR crosstalk. Our study reveals the power of unbiased, functional genomic screens to identify new signalling mediators important for tissue remodelling in cardiovascular disease and cancer.

The metabolic burden of methyl donor deficiency with focus on the betaine homocysteine methyltransferase pathway

Methyl groups are important for numerous cellular functions such as DNA methylation, phosphatidylcholine synthesis, and protein synthesis. The methyl group can directly be delivered by dietary methyl donors, including methionine, folate, betaine, and choline. The liver and the muscles appear to be the major organs for methyl group metabolism. Choline can be synthesized from phosphatidylcholine via the cytidine-diphosphate (CDP) pathway. Low dietary choline loweres methionine formation and causes a marked increase in S-adenosylmethionine utilization in the liver. The link between choline, betaine, and energy metabolism in humans indicates novel functions for these nutrients. This function appears to goes beyond the role of the nutrients in gene methylation and epigenetic control. Studies that simulated methyl-deficient diets reported disturbances in energy metabolism and protein synthesis in the liver, fatty liver, or muscle disorders. Changes in plasma concentrations of total homocysteine (tHcy) reflect one aspect of the metabolic consequences of methyl group deficiency or nutrient supplementations. Folic acid supplementation spares betaine as a methyl donor. Betaine is a significant determinant of plasma tHcy, particularly in case of folate deficiency, methionine load, or alcohol consumption. Betaine supplementation has a lowering effect on post-methionine load tHcy. Hypomethylation and tHcy elevation can be attenuated when choline or betaine is available.

Elevated dimethylglycine in blood of children with congenital heart defects and their mothers

OBJECTIVE

Congenital Heart Defects (CHD) may be related to nutritional deficiencies affecting the methylation cycle. We aimed to study the metabolic markers of the betaine homocysteine methyl transferase (BHMT) pathway in children with CHD and their mothers compared to children without CHD and their mothers.

MATERIALS AND METHODS

Children with CHD (n=105, age < 3 years) and mothers of 80 of the affected children were studied. The controls were non-CHDs children of comparable age as the CHD group (n=52) and their mothers (n=50). We measured serum or plasma concentrations of the metabolites of the methylation cycle homocysteine (HCY), methylmalonic acid (MMA), cystathionine, S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), betaine, choline, and dimethylglycine (DMG).

RESULTS

Children with CHD had higher plasma SAM (131 vs. 100 nmol/L) and DMG (8.7 vs. 6.0 μmol/L) and lower betaine/DMG ratio (7.5 vs. 10.2) compared to the controls. Mothers of CHD children showed also higher DMG (6.1 vs. 4.1 µmol/L) and lower betaine/DMG ratio compared with the mothers of the controls. Higher SAM levels were related to higher cystathionine, MMA, betaine, choline, and DMG. MMA elevation in the patients was related to higher HCY, SAM, betaine and DMG.

CONCLUSIONS

Elevated DMG in CHD children and their mothers compared to the controls can indicate upregulation of the BHMT pathway in this disease group. Nutritional factors are related to metabolic imbalance during pregnancy that may be related to worse birth outcome.

The role of phosphatidylcholine and choline metabolites to cell proliferation and survival

The reorganization of metabolic pathways in cancer facilitates the flux of carbon and reducing equivalents into anabolic pathways at the expense of oxidative phosphorylation. This provides rapidly dividing cells with the necessary precursors for membrane, protein and nucleic acid synthesis. A fundamental metabolic perturbation in cancer is the enhanced synthesis of fatty acids by channeling glucose and/or glutamine into cytosolic acetyl-CoA and upregulation of key biosynthetic genes. This lipogenic phenotype also extends to the production of complex lipids involved in membrane synthesis and lipid-based signaling. Cancer cells display sensitivity to ablation of fatty acid synthesis possibly as a result of diminished capacity to synthesize complex lipids involved in signaling or growth pathways. Evidence has accrued that phosphatidylcholine, the major phospholipid component of eukaryotic membranes, as well as choline metabolites derived from its synthesis and catabolism, contribute to both proliferative growth and programmed cell death. This review will detail our current understanding of how coordinated changes in substrate availability, gene expression and enzyme activity lead to altered phosphatidylcholine synthesis in cancer, and how these changes contribute directly or indirectly to malignant growth. Conversely, apoptosis targets key steps in phosphatidylcholine synthesis and degradation that are linked to disruption of cell cycle regulation, reinforcing the central role that phosphatidylcholine and its metabolites in determining cell fate.