The role of gender and genetic polymorphisms in de novo choline synthesis

Choline 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

Calcium/Calmodulin-Dependent Protein Kinase II Alters Structural Plasticity and Cytoskeletal Dynamics in Drosophila

Drosophila dendritic arborization (da) neurons contain subclasses of neurons with distinct dendritic morphologies. We investigated calcium/calmodulin-dependent protein kinase II (CaMKII) regulation of dendritic structure and dynamics in vivo using optically transparent Drosophila larvae. CaMKII increases the dynamic nature and formation of dendritic filopodia throughout larval development but only affects neurons that normally contain dendritic filopodia. In parallel, we examined the effects of Rac1 activity on dendritic structure to explore signaling specificity. In contrast to CaMKII activity, Rac1 does not alter filopodia stability but instead causes de novo filopodia formation on all da neurons. Although both mediators increase cytoskeletal turnover, measured by fluorescence recovery after photobleaching experiments, only CaMKII increases the dynamic nature of dendritic filopodia. CaMKII signaling thus appears to use mechanisms and machinery distinct from Rac1 signaling. This study illustrates a molecular means of uncoupling cytoskeletal regulation from morphological regulation. Our results suggest that Drosophila dendritic filopodia may share some cytoskeletal regulatory mechanisms with mammalian dendritic filopodia. Furthermore, general dendrite cytoskeletal compartmentalization is conserved in multipolar neurons

Phosphatidylethanolamine N -methyltransferase ( PEMT ) gene expression is induced by estrogen in human and mouse primary hepatocytes

Choline is an essential nutrient for humans, though some of the requirement can be met by endogenous synthesis catalyzed by phosphatidylethanolamine N-methyltransferase (PEMT). Premenopausal women are relatively resistant to choline deficiency compared with postmenopausal women and men. Studies in animals suggest that estrogen treatment can increase PEMT activity. In this study we investigated whether the PEMT gene is regulated by estrogen. PEMT transcription was increased in a dose-dependent manner when primary mouse and human hepatocytes were treated with 17-β-estradiol for 24 h. This increased message was associated with an increase in protein expression and enzyme activity. In addition, we report a region that contains a perfect estrogen response element (ERE) ∼7.5 kb from the transcription start site corresponding to transcript variants {"type":"entrez-nucleotide","attrs":{"text":"NM_007169","term_id":"22538481","term_text":"NM_007169"}}NM_007169 and NM-008819 of the human and murine PEMT genes, respectively, three imperfect EREs in evolutionarily conserved regions and multiple imperfect EREs in nonconserved regions in the putative promoter regions. We predict that both the mouse and human PEMT genes have three unique transcription start sites, which are indicative of either multiple promoters and/or alternative splicing. This study is the first to explore the underlying mechanism of why dietary requirements for choline vary with estrogen status in humans.—Resseguie, M., Song, J., Niculescu, M. D., da Costa, K., Randall, T. A., Zeisel, S. H. Phosphatidylethanolamine N-methyltransferase (PEMT) gene expression is induced by estrogen in human and mouse primary hepatocytes

Aberrant Estrogen Regulation of PEMT Results in Choline Deficiency-associated Liver Dysfunction*

When dietary choline is restricted, most men and postmenopausal women develop multiorgan dysfunction marked by hepatic steatosis (choline deficiency syndrome (CDS)). However, a significant subset of premenopausal women is protected from CDS. Because hepatic PEMT (phosphatidylethanolamine N-methyltransferase) catalyzes de novo biosynthesis of choline and this gene is under estrogenic control, we hypothesized that there are SNPs in PEMT that disrupt the hormonal regulation of PEMT and thereby put women at risk for CDS. In this study, we performed transcript-specific gene expression analysis, which revealed that estrogen regulates PEMT in an isoform-specific fashion. Locus-wide SNP analysis identified a risk-associated haplotype that was selectively associated with loss of hormonal activation. Chromatin immunoprecipitation, analyzed by locus-wide microarray studies, comprehensively identified regions of estrogen receptor binding in PEMT. The polymorphism (rs12325817) most highly linked with the development of CDS (p < 0.00006) was located within 1 kb of the critical estrogen response element. The risk allele failed to bind either the estrogen receptor or the pioneer factor FOXA1. These data demonstrate that allele-specific ablation of estrogen receptor-DNA interaction in the PEMT locus prevents hormone-inducible PEMT expression, conferring risk of CDS in women