The molecular role of connexin 43 in human trophoblast cell fusion.

Connexin expression and gap junctional intercellular communication (GJIC) mediated by connexin 43 (Cx43)/gap junction A1 (GJA1) are required for cytotrophoblast fusion into the syncytium, the outer functional layer of the human placenta. Cx43 also impacts intracellular signaling through protein-protein interactions. The transcription factor GCM1 and its downstream target ERVW-1/SYNCYTIN-1 are key players in trophoblast fusion and exert their actions through the ERVW-1 receptor SLC1A5/ASCT-2/RDR/ATB(0). To investigate the molecular role of the Cx43 protein and its interaction with this fusogenic pathway, we utilized stable Cx43-transfected cell lines established from the choriocarcinoma cell line Jeg3: wild-type Jeg3, alphahCG/Cx43 (constitutive Cx43 expression), JpUHD/Cx43 (doxycyclin-inducible Cx43 expression), or JpUHD/trCx43 (doxycyclin-inducible Cx43 carboxyterminal deleted). We hypothesized that truncation of Cx43 at its C-terminus would inhibit trophoblast fusion and protein interaction with either ERVW-1 or SLC1A5. In the alphahCG/Cx43 and JpUHD/Cx43 lines, stimulation with cAMP caused 1) increase in GJA1 mRNA levels, 2) increase in percentage of fused cells, and 3) downregulation of SLC1A5 expression. Cell fusion was inhibited by GJIC blockade using carbenoxylone. Neither Jeg3, which express low levels of Cx43, nor the JpUHD/trCx43 cell line demonstrated cell fusion or downregulation of SLC1A5. However, GCM1 and ERVW-1 mRNAs were upregulated by cAMP treatment in both Jeg3 and all Cx43 cell lines. Silencing of GCM1 prevented the induction of GJA1 mRNA by forskolin in BeWo choriocarcinoma cells, demonstrating that GCM1 is upstream of Cx43. All cell lines and first-trimester villous explants also demonstrated coimmunoprecipitation of SLC1A5 and phosphorylated Cx43. Importantly, SLC1A5 and Cx43 gap junction plaques colocalized in situ to areas of fusing cytotrophoblast, as demonstrated by the loss of E-cadherin staining in the plasma membrane in first-trimester placenta. We conclude that Cx43-mediated GJIC and SLC1A5 interaction play important functional roles in trophoblast cell fusion.

Cholesteryl ester transfer protein gene polymorphisms increase the risk of fatty liver in females independent of adiposity.

BACKGROUND AND AIM: Environmental factors including excessive caloric intake lead to disordered lipid metabolism and fatty liver disease (FLD). However, FLD demonstrates heritability suggesting genetic factors are also important. We aimed to use a candidate gene approach to examine the association between FLD and single nucleotide polymorphisms (SNPs) in lipid metabolism genes in the adolescent population-based Western Australian Pregnancy (Raine) Cohort. METHODS: A total 951 seventeen year-olds underwent hepatic ultrasound, anthropometric and biochemical characterization, DNA extraction and genotyping for 57 SNPs in seven lipid metabolism genes (ApoB100, ATGL, ABHD5, MTTP, CETP, SREBP-1c, PPARα). Associations were adjusted for metabolic factors and Bonferroni corrected. RESULTS: The prevalence of FLD was 16.2% (11.4% male vs 21.2% female, P=0.001). Multivariate analysis of metabolic factors found suprailiac skinfold thickness (SST) to be the major predictor of FLD in females and males (odds ratio [OR] 1.11, 95% confidence interval [CI] 1.08-1.15, P=1.7×10(-10) and OR 1.17, 95%CI 1.13-1.22, P=2.4×10(-11) , respectively). In females, two SNPs in linkage disequilibrium from the CETP gene were associated with FLD: rs12447924 (OR 2.16, 95%CI 1.42-3.32, P=0.0003) and rs12597002 (OR=2.22, 95%CI 1.46-3.41 P=0.0002). In lean homozygotes, the probability of FLD was over 30%, compared with 10-15% in lean heterozygotes and 3-5% in lean wild-types. However, these associations were modified by SST, such that for obese individuals, the probability of FLD was over 30% in all genotype groups. CONCLUSIONS: Cholesteryl ester transfer protein gene polymorphisms are associated with an increased risk of FLD in adolescent females. The effect is independent of adiposity in homozygotes, thereby placing lean individuals at a significant risk of FLD.

Prostaglandins and mechanisms of preterm birth.

Increased uterine contractility at term and preterm results first from activation and then stimulation of the myometrium. Activation can be provoked by mechanical stretch of the uterus, and by an endocrine pathway resulting from increased activity of the fetal hypothalamic-pituitary-adrenal axis. In sheep fetuses, increased cortisol output during pregnancy regulates expression of prostaglandin synthase type 2 (PGHS-2) in the placenta in an oestrogen-independent manner, resulting in increased concentrations of prostaglandin E2 (PGE2) in the fetal circulation. Later increases in maternal uterine expression of PGHS-2 require increases in oestrogen and lead to increased concentrations of PGF(2alpha) in the maternal circulation. Thus, regulation of PGHS-2 at term is differentially controlled in fetal (trophoblast) and maternal (uterine epithelium) tissue. This difference may reflect expression of glucocorticoid receptor but not oestrogen receptor (ER) in placental trophoblast cells. In women, cortisol also contributes to increased prostaglandin production in fetal tissues through upregulation of PGHS-2 (amnion and chorion) and downregulation of 15-OH prostaglandin dehydrogenase (PGDH; chorion trophoblasts). The effect of cortisol on expression of PGDH in the chorion reverses a tonic stimulatory effect of progesterone, potentially through a paracrine or autocrine action. In membranes, cortisol may be derived from cortisone through activity of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 1, in addition to secretion from the maternal or fetal adrenal glands. In placenta, 11beta-HSD-2 oxidase activity predominates and expression of this enzyme is reduced with hypoxaemia and in placentae from pre-eclamptic pregnancies. In these circumstances, increased concentrations of maternal cortisol may cross into the fetal compartment, contributing to growth restriction and programming later life disease.