1,721,067 research outputs found
The role of gender and genetic polymorphisms in de novo choline synthesis
Get PDFCholine is an essential nutrient for humans, though some of the requirement can be met by endogenous synthesis catalyzed by phosphatidylethanolamine N-methyltransferase (PEMT). The human PEMT gene encodes three unique transcripts, A (NM_148172), B (NM_007169), and C (NM_148173) which encode two different protein isoforms. PEMT I, encoded by transcript A, localizes to the endoplasmic reticulum whereas PEMT II, synthesized from transcripts B and C, is found primarily in the mitochondrial associated membrane and is functionally distinct from PEMT I. Studies in mammals indicate a connection between estrogen and protection against choline deficiency syndrome (CDS) but the nature of this interaction is not understood. Examining the entire PEMT locus by chromatin immunoprecipitation coupled to microarray (ChIPchip), we identified several estrogen receptor-alpha (ER-α) enriched regions in the PEMT locus specifically implicating a critical regulatory region located in intron 1 of the A transcription start site, 7500 nucleotides (nt) upstream of the transcriptional start site of transcript B. We found that PEMT transcription was increased in a dose-dependent manner when primary mouse and human hepatocytes were treated with 17-β-estradiol for 24 hours and this increased message was associated with an increase in protein expression and enzyme activity. ER-α regulation of the PEMT gene is transcript specific, whereby estrogen binding results in an increase in transcripts B and C but not transcript A. We suggest that differences in dietary choline requirements occur between men and women because estrogen induces expression of the PEMT gene, allowing premenopausal women to make more choline endogenously. In humans, young women harboring a PEMT promoter SNP are 25X as likely to develop CDS as are non-carriers of this SNP. Here we demonstrate, in human hepatocytes, that a haploblock of SNPs within a key estrogen regulatory region in the PEMT gene disrupt ER-α DNA binding. Hepatocytes homozygous for the risk allele were not estrogen responsive. For the first time, we report a putative mechanism underlying the association of PEMT genetic variation and susceptibility to choline deficiency syndrome in women
Determining the Role of Choline Dehydrogenase in Sperm Cell Function
Get PDFApproximately 15% of couples suffer from infertility and male factor infertility is the suspected cause in about half of these couples. 40-60% these male factor infertility cases are idiopathic, but genetic aberrations are associated with infertility in as many as 30% of these. Although the relationship between nutrition and reproduction is established, the role of micronutrient metabolism in male fertility is understudied. Choline, an essential nutrient for humans, is important for maintaining a healthy pregnancy and normal fetal development. Choline is necessary for normal mating behavior and male fertility in D. melanogaster but the reason why remains unknown. Choline dehydrogenase (CHDH) catalyzes the conversion of choline into betaine, a methyl group donor and osmolyte. Several single nucleotide polymorphisms (SNPs)within the CHDH gene may alter the function of the CHDH. A choline dehydrogenase knockout mouse (Chdh-/-) was created to model loss-of-function mutations in humans. Mutation of Chdh reduced CHDH activity and decreased betaine concentration in all tissues that normally express this enzyme. Fetal viability, growth and one-year survival rates were not affected. Chdh-/- animals had 59% more plasma homocysteine, but hepatic AdoMet and AdoHcy were unchanged. Chdh-/- males were infertile due to poor sperm motility. Abnormal mitochondrial morphology and function were observed in Chdh-/- sperm. ATP concentration was 55% lower in Chdh-/- sperm. Dietary betaine supplementation resulted in increased Chdh-/- sperm motility, and full restoration of ATP concentration. CHDH SNP rs12676 (G233T; R→L) and IL17βR SNP rs1025689 (G126C; P→P) are associated with changes in mitochondrial function and sperm motility in men. Men who were TT for rs12676 produced sperm with dysmorphic mitochondria. Compared to GG subjects, sperm produced by GT subjects contained 40% less ATP; men who were TT for this SNP had 73% less ATP. Motility characteristics were changed in men with at least one minor allele of either rs12676 or rs1025689. CHDH protein was decreased in primary hepatocytes from individuals who were TT for rs12676, indicating this SNP marks a functional haplotype. We propose that aberrant choline metabolism stemming from decreased CHDH activity may be an underlying cause of idiopathic male factor infertility in men
The metabolic consequences of mouse betaine homocysteine S-methyltransferase deficiency
Get PDFBetaine homocysteine S-methyltransferase (BHMT, EC 2.1.1.5) catalyzes the conversion of homocysteine to methionine. Homocysteine is a potentially harmful amino acid. Its elevation is often associated with cardiovascular disease, birth defect, renal insufficiency, and age-related cognitive impairment in humans. Humans have common single nucleotide polymorphisms (SNPs) in the BHMT gene that can alter its enzyme activity and function. Elucidation of the metabolic consequences of BHMT deficiency is critical to the understanding of the relationship between BHMT mutations and diseases. To directly investigate the role of BHMT in vivo, we generated and characterized the mice with the gene encoding Bhmt deleted (Bhmt-/-). This dissertation describes two separate projects. The first project examines the roles of BHMT in one-carbon metabolism and the development of hepatic steatosis and hepatocellular carcinoma. The second project examines the role of BHMT in energy metabolism. In the first project, we generated and characterized the Bhmt-/- mouse. We found that deletion of Bhmt resulted in elevated homocysteine concentrations, in reduced methylation potential, and in profound alterations of choline metabolites in various tissues. Bhmt-/- mice developed fatty liver at five weeks of age due to reduced phosphatidylcholine concentration. Phosphatidylcholine is required for the synthesis of lipoproteins, which carry lipids from the liver to circulation. By one year of age, 64% of Bhmt-/- mice had visible hepatic tumors. Histopathological analysis revealed that Bhmt-/- mice developed hepatocellular carcinoma or carcinoma precursors. We observed that Bhmt-/- mice had reduced body weight from five to nine weeks of age. This observation led us to investigate the potential role of BHMT in energy metabolism. We found that the reduced body weight in Bhmt-/- mice was due to reduced fat mass. Bhmt-/- mice had smaller adipocytes, better glucose tolerance, and enhanced insulin sensitivity. Several factors contributed to the reduced adiposity phenotype observed in Bhmt-/- mice; these included increased energy expenditure, reduced mobilization of lipid from the liver to adipose tissue, decreased lipid synthesis within adipocytes, and enhanced whole-body glucose oxidation. This dissertation provides novel findings that BHMT plays critical roles in hepatocellular carcinoma development and energy metabolism
Interaction of dietary fat types and gut microbiome on modulation of whole body energy balance
Get PDFDietary fats and gut microbes are regarded as environmental factors for the onset of obesity. However, whether there is a direct association between dietary fat type and gut microbiome that promotes obesity remains unclear. In this study, we tested the effect of modulation of the gut microbiome by antibiotics on energy balance in Sprague Dawley rats fed a 45% high fat diet containing primarily saturated fatty acids (SFA) vs. polyunsaturated fatty acids (PUFA). Antibiotic treatment successfully decreased the gut microbiome as evidenced by decreased microbiome α-diversity and β-diversity. We found that food intake was decreased by antibiotic treatment irrespective diet. PUFA-fed rats gained less weight and consumed less food than those fed SFA independent of microbiome composition. No differences were seen in energy expenditure among the 4 groups. Gut hormone and adipokine gene and protein expression was measured in ileum, colon, white adipose tissue (WAT) and blood serum. Compared with SFA, PUFA fed rats had less ileum peptide YY , colon glucagon-like peptide-1, WAT sterol regulatory element binding transcription factor 1 and more ileum β-defensins, WAT adiponectin gene expression. However, no differences were seen in serum protein expression among the 4 groups. In conclusion, SFA are more obesogenic and promote food intake as compared to PUFA and this positive energy balance is independent of the gut microbiome. The mechanisms by which SFA modulate body weight and food intake warrant further investigation.Master of Scienc
Deletion of Chdh (Choline dehydrogenase) in Mice Does Not Alter Brain Mitosis and Apoptosis
Get PDFCholine is an essential nutrient. Large amounts of choline are delivered across the placenta to the developing fetus, contributing to brain development and, consequently, affecting memory performance during adulthood. Rodent studies have described specific epigenetic mechanisms, whereby choline deprivation altered the neurobiology of progenitor cells, modifying their proliferation and survival. Choline, via oxidation to betaine, provides one-carbon units to the methionine cycle and further, to all methylation processes part of the epigenetic control. We found that the choline dehydrogenase (Chdh) gene, responsible for this conversion, is expressed in the brain of adult and fetal mice. By deleting the Chdh gene, we investigated the effects of low betaine synthesis on fetal brain development. We assessed cell proliferation in Chdh+/+ and Chdh-/- fetuses at embryonic day 17 (E17) by immunohistochemistry. Mitosis and apoptosis were not significantly altered by fetal genotype. Further studies will be needed to establish if gene-specific methylation is altered between Chdh wildtype and knockout mice fetuses.Master of Scienc
The Mechanism of Lipopolysaccharide Inhibition of Glucose Production and Its Significance to Cancer
Get PDFNuclear factor kappa B (NFκB) induces insulin resistance in mammals, possibly representing a counter-regulatory response by which the host escapes NFκB-induced hypoglycemia. However, the underlying mechanism remains unclear. To identify the mechanism of NFκB-induced hypoglycemia, we measured hepatocyte glucose production and whole-body glucose utilization in mice. Inhibition of glucose production and utilization by lipopolysaccharide depended on toll-like receptor 4, myeloid differentiation factor 88 and NFκB, while tumor necrosis factor alpha and the insulin signaling intermediate phosphatidylinositol 3-kinase were unnecessary. Taxol, a widely-used cancer drug, also activates toll-like receptor 4 and several of its downstream intermediates, but its mechanism is unclear. To determine whether Taxol destroys tumors by decreasing glucose availability, we measured glucose utilization in vitro. Taxol decreased glucose utilization in MCF7 cells. Additionally, Taxol increased plasma adiponectin, a biomarker of low fasting glucose utilization, in treatment-responsive breast cancer patients. This biomarker could predict the effectiveness of Taxol in individuals.Master of Scienc
Ethnic- and Gender-Specific Effects of Sugar Sweetened Beverages on Serum Uric Acid Concentrations and Inflammation
Get PDFElevated serum uric acid (hyperuricemia) increases the risk for gout, renal and cardiovascular disease. Hyperuricemia also induces inflammation in human smooth muscle and endothelial cells, reflected in the upregulation of C-reactive protein (CRP), an acute-phase reactant. Sugar-sweetened beverages (SSBs) increase SUA and CRP concentrations. However, it is not clear if SUA and/or CRP response to SSB is dependent on gender, ethnicity and genotype. Our project’s main aim was to determine the ethnic-, gender- and genotype-specific effects of SSBs on SUA and CRP in Caucasian, African-American or Hispanic adults. Our study in 62 subjects showed that following SSB consumption, SUA increased by 0.66 mg/dL within 30 minutes and then gradually restored to baseline concentration. Throughout the intervention, SUA was significantly different between Caucasians and African-Americans (p<0.05) and men and women (p<0.01). The present data demonstrates that SUA response is mainly dependent on an individual’s gender and ethnicity.Master of Scienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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