Benzo(a)pyrene induced glycine N-methyltransferase messenger RNA expression in Fundulus heteroclitus embryos

Transgenerational effects of polycyclic aromatic hydrocarbon exposure on sheepshead minnows (Cyprinodon variegatus)

The Deepwater Horizon oil spill resulted in the release of over 640 million L of crude oil into the Gulf of Mexico, affecting over 2000 km of shoreline, including estuaries that serve as important habitats and nurseries for aquatic species. Cyprinodon variegatus (sheepshead minnow) are small-bodied fish that inhabit northern Gulf of Mexico estuaries, are easily adaptable to laboratory conditions, and are commonly used in toxicological assessment studies. The purpose of the present study was to determine the somatic, reproductive, and developmental effects of an environmentally relevant polycyclic aromatic hydrocarbon (PAH) mixture, the oil high-energy water accommodated fraction (HEWAF), on experimentally exposed sheepshead minnow (F₀ ) as well as 2 generations of offspring (F₁ and F₂ ) without additional exposure. The F₀ generation exposed to HEWAF had increased liver somatic indices, altered egg production, and decreased fertilization. Several developmental endpoints in the F₁ were altered by F₀ HEWAF exposure. As adults, low HEWAF-exposed F₁ females demonstrated decreased weight and length. Both the F₁ and F₂ generations derived from high HEWAF-exposed F₀ had deficits in prey capture compared to control F₁ and F₂ , respectively. Correlations between endpoints and tissue PAHs provide evidence that the physiological effects observed were associated with hydrocarbon exposure. These data demonstrate that PAHs were capable of causing physiological changes in exposed adult sheepshead minnow and transgenerational effects in unexposed offspring, both of which could have population-level consequences. Environ Toxicol Chem 2019;38:638-649. © 2018 SETAC.

Muscadine grape seed oil as a novel source of tocotrienols to reduce adipogenesis and adipocyte inflammation

Tocotrienols are unsaturated forms of vitamin E previously shown to reduce adipogenesis and adipose inflammation. In this study, muscadine grape seed oil (MGSO) was identified as a novel source of tocotrienols containing significant amounts of α- and γ-tocotrienol (T3) with minor seasonal changes. The aim of this study was to assess the anti-adipogenic and anti-inflammatory potential of MGSO by using primary human adipose-derived stem cells (hASCs). Differentiating hASCs were treated with MGSO and compared with rice bran and olive oil. Accumulation of triglyceride was significantly lower in MGSO-treated hASCs than rice bran and olive oils. A tocotrienol rich fraction (TRF) from MGSO was prepared by solid phase extraction and eluted with 15% 1,4-dioxane in hexane. The MGSO-derived TRF treatment significantly reduced mRNA and protein expression that are crucial to adipogenesis (e.g., PPARγ and aP2) in hASCs. Furthermore, TRF from MGSO markedly reduced LPS-induced proinflammatory gene expression in human adipocytes and cytokine secretion to the medium (IL-6 and IL-8). Collectively, our work suggests that MGSO is a stable and reliable natural source of T3 and MGSO may constitute a new dietary strategy to attenuate obesity and its associated adipose inflammation.

Expression of hypoxia-inducible factor 3α in hepatocellular carcinoma and its association with other hypoxia-inducible factors

The functional role of hypoxia-inducible factor (HIF)-3α in the development of hepatocellular carcinoma (HCC) is not yet fully understood. The aim of the present study was to elucidate the association between HIF-3α expression and the clinicopathological features as well as prognosis of HCC patients. In addition, we investigated the association between HIF-3α expression and the expression of HIF-1α and HIF-2α in tumor tissues. The protein levels of HIF-3α were determined using immunohistochemical analysis of paraffin sections of 126 paired HCC and peritumoral tissues. PLC/PRF/5 cells, a human HCC cell line, were transfected with HIF-1α and HIF-2α vectors and HIF-3α mRNA and protein expression was detected using quantitative polymerase chain reaction and western blot analysis, respectively. The expression of HIF-3α was upregulated in 46.0% (58/126) and downregulated in 42.9% (54/126) of tumor tissues, respectively, when compared to peritumoral tissues. HIF-3α protein expression was not associated with peripheral blood vessel invasion, overall survival, or disease-free survival in HCC patients (P>0.05). In HCC tissues, the levels of HIF-3α protein were positively correlated with HIF-2α, but not with HIF-1α expression in HCC tissues. HIF-3α was upregulated in PLC/PRF/5 and Hep3B cells overexpressed with HIF-1α or HIF-2α. The hypoxic microenvironment of liver cancer did not lead to elevated HIF-3α protein expression, indicating that HIF-3α is regulated differently from HIF-1α in vivo. The correlation between HIF-3α and HIF-2α expression at the cellular and tissue levels indicated that HIF-3α may be a target gene of HIF-2α. The hypoxic microenvironment did not lead to elevation of HIF-3α protein expression in liver cancer; thus, HIF-3α may be a target gene of HIF-2α.

cAMP induces hypertrophy and alters DNA methylation in HL-1 cardiomyocytes

cAMP is a highly regulated secondary messenger involved in many biological processes. Chronic activation of the cAMP pathway by catecholamines results in cardiac hypertrophy and fibrosis; however, the mechanism by which elevated cAMP leads to cardiomyopathy is not fully understood. To address this issue, we increased intracellular cAMP levels in HL-1 cardiomyocytes, a cell line derived from adult mouse atrium, using either the stable cAMP analog N(6),2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP) or phosphodiesterase (PDE) inhibitors caffeine and theophylline. Elevated cAMP levels increased cell size and altered expression levels of cardiac genes and micro-RNAs associated with hypertrophic cardiomyopathy (HCM), including Myh6, Myh7, Myh7b, Tnni3, Anp, Bnp, Gata4, Mef2c, Mef2d, Nfatc1, miR208a, and miR208b. In addition, DBcAMP altered the expression of DNA methyltransferases (Dnmts) and Tet methylcytosine dioxygenases (Tets), enzymes that regulate genomic DNA methylation levels. Changes in expression of DNA methylation genes induced by elevated cAMP led to increased global DNA methylation in HL-1 cells. In contrast, inhibition of DNMT activity with 5-azacytidine treatment decreased global DNA methylation levels and blocked the increased expression of several HCM genes (Myh7, Gata4, Mef2c, Nfatc1, Myh7b, Tnni3, and Bnp) observed with DBcAMP treatment. These results demonstrate that cAMP induces cardiomyocyte hypertrophy and altered HCM gene expression in vitro and that DNA methylation patterns mediate the upregulation of HCM genes induced by cAMP. These data identify a previously unknown mechanism by which elevated levels of cAMP lead to increased expression of genes associated with cardiomyocyte hypertrophy.

Transcriptomic Changes in Zebrafish Embryos and Larvae Following Benzo[a]pyrene Exposure

Benzo[a]pyrene (BaP) is an environmentally relevant carcinogenic and endocrine disrupting compound that causes immediate, long-term, and multigenerational health deficits in mammals and fish. Previously, we found that BaP alters DNA methylation patterns in developing zebrafish, which may affect gene expression. Herein, we performed a genome-wide transcriptional analysis and discovered differential gene expression and splicing in developing zebrafish. Adult zebrafish were exposed to control or 42.0 ± 1.9 µg/l BaP for 7 days. Eggs were collected and raised in control conditions or continuously exposed to BaP until 3.3 and 96 h post-fertilization (hpf). RNA sequencing (RNA-Seq) was conducted on zebrafish embryos and larvae. Data were analyzed to identify differentially expressed (DE) genes (changed at the gene or transcript variant level) and genes with differential exon usage (DEU; changed at the exon level). At 3.3 hpf, BaP exposure resulted in 8 DE genes and 51 DEU genes. At 96 hpf, BaP exposure altered expression in 1153 DE genes and 159 DEU genes. Functional ontology analysis by Ingenuity Pathway Analysis revealed that many disease pathways, including organismal death, growth failure, abnormal morphology of embryonic tissue, congenital heart disease, and adverse neuritogenesis, were significantly enriched for the DE and DEU genes, providing novel insights on the mechanisms of action of BaP-induced developmental toxicities. Collectively, we discovered substantial transcriptomic changes at the gene, transcript variant, and exon levels in developing zebrafish after early life BaP waterborne exposure, and these changes may lead to long-term adverse physiological consequences.

Hypoxia disrupts the expression levels of circadian rhythm genes in hepatocellular carcinoma

Disturbance in the expression of circadian rhythm genes is a common feature in certain types of cancer, however the mechanisms mediating this disturbance remain to be elucidated. The present study aimed to investigate the effect of hypoxia on the expression of circadian rhythm genes in liver cancer cells and to identify the mechanisms underlying this effect in hepatocellular carcinoma (HCC). The HCC cell line, PLC/PRF/5. was treated with either a vehicle control or CoCl2 at 50, 100 or 200 µΜ for 24 h. Following treatment, the protein expression levels of hypoxia‑inducible factor (HIF)‑1α and HIF‑2α were detected by western blotting and the mRNA expression levels of circadian rhythm genes, including circadian locomotor output cycles kaput (Clock), brain and muscle Arnt‑like 1 (Bmal1), period (Per)1, Per2, Per3, cryptochrome (Cry)1, Cry2 and casein kinase Iε (CKIε), were detected by reverse transcription quantitative polymerase chain reaction (RT‑qPCR). Expression plasmids containing HIF‑1α or HIF‑2α were transfected into the PLC/PRF/5 cells using liposomes and RT‑qPCR was used to determine the effects of the transfections on the expression levels of circadian rhythm genes. Following treatment with CoCl2, the protein expression levels of HIF‑1α and HIF‑2α were upregulated in a CoCl2 concentration‑dependent manner. The mRNA expression levels of Clock, Bmal1 and Cry2 were increased, and the mRNA expression levels of Per1, Per2, Per3, Cry1 and CKIε were decreased following CoCl2 treatment (P<0.05). In the PLC/PRF/5 cells transfected with the plasmid containing HIF‑1α, the mRNA expression levels of Clock, Bmal1 and Cry2 were increased, and the mRNA expression levels of Per1, Per2, Per3, Cry1 and CKIε were decreased. In the PLC/PRF/5 cells transfected with the plasmid containing HIF‑2α, the mRNA expression levels of Clock, Bmal1, Per1, Cry1, Cry2 and CKIε were upregulated, and the mRNA expression levels of Per2 and Per3 were downregulated (P<0.05). A hypoxic microenvironment may contribute to the disturbance in the expression of circadian genes in HCC. HIF‑1α and HIF‑2α are involved in this process and have redundant, but not identical effects.

Caffeine exposure alters cardiac gene expression in embryonic cardiomyocytes

Previous studies demonstrated that in utero caffeine treatment at embryonic day (E) 8.5 alters DNA methylation patterns, gene expression, and cardiac function in adult mice. To provide insight into the mechanisms, we examined cardiac gene and microRNA (miRNA) expression in cardiomyocytes shortly after exposure to physiologically relevant doses of caffeine. In HL-1 and primary embryonic cardiomyocytes, caffeine treatment for 48 h significantly altered the expression of cardiac structural genes (Myh6, Myh7, Myh7b, Tnni3), hormonal genes (Anp and BnP), cardiac transcription factors (Gata4, Mef2c, Mef2d, Nfatc1), and microRNAs (miRNAs; miR208a, miR208b, miR499). In addition, expressions of these genes were significantly altered in embryonic hearts exposed to in utero caffeine. For in utero experiments, pregnant CD-1 dams were treated with 20-60 mg/kg of caffeine, which resulted in maternal circulation levels of 37.3-65.3 μM 2 h after treatment. RNA sequencing was performed on embryonic ventricles treated with vehicle or 20 mg/kg of caffeine daily from E6.5-9.5. Differential expression (DE) analysis revealed that 124 genes and 849 transcripts were significantly altered, and differential exon usage (DEU) analysis identified 597 exons that were changed in response to prenatal caffeine exposure. Among the DE genes identified by RNA sequencing were several cardiac structural genes and genes that control DNA methylation and histone modification. Pathway analysis revealed that pathways related to cardiovascular development and diseases were significantly affected by caffeine. In addition, global cardiac DNA methylation was reduced in caffeine-treated cardiomyocytes. Collectively, these data demonstrate that caffeine exposure alters gene expression and DNA methylation in embryonic cardiomyocytes.

A novel role of the tumor suppressor GNMT in cellular defense against DNA damage

Glycine N-methyltransferase (GNMT) is a folate binding protein commonly diminished in human hepatoma yet its role in tumor development remains to be established. GNMT binds to methylfolate but is also inhibited by it; how such interactions affect human carcinogenesis is unclear. We postulated that GNMT plays a role in folate-dependent methyl group homeostasis and helps maintain genome integrity by promoting nucleotide biosynthesis and DNA repair. To test the hypothesis, GNMT was over-expressed in GNMT-null cell lines cultured in conditions of folate abundance or restriction. The partitioning of folate dependent 1-carbon groups was investigated using stable isotopic tracers and GC/MS. DNA damage was assessed as uracil content in cell models, as well as in Gnmt wildtype (Gnmt(+/+)), heterozygote (Gnmt(+/-)) and knockout (Gnmt(-/-)) mice under folate deplete, replete, or supplementation conditions. Our study demonstrated that GMMT 1) supports methylene-folate dependent pyrimidine synthesis; 2) supports formylfolate dependent purine syntheses; 3) minimizes uracil incorporation into DNA when cells and animals were exposed to folate depletion; 4) translocates into nuclei during prolonged folate depletion. In conclusion, loss of GNMT impairs nucleotide biosynthesis. Over-expression of GNMT enhances nucleotide biosynthesis and improves DNA integrity by reducing uracil misincorporation in DNA both in vitro and in vivo. To our best knowledge, the role of GNMT in folate dependent 1-carbon transfer in nucleotide biosynthesis has never been investigated. The present study gives new insights into the underlying mechanism by which GNMT can participate in tumor prevention/suppression in humans.

The multi-functional roles of GNMT in toxicology and cancer

Although glycine N-methyltransferase (GNMT) has been discovered for five decades, its function was not elucidated until recently. In this review, we discuss the multiple roles of GNMT in toxicology and cancer. Besides catalyzing the production of methylglycine (sarcosine) in one carbon metabolism pathway, GNMT was found to be able to bind a number of polycyclic aromatic hydrocarbons and inhibit DNA adducts formation. Moreover, GNMT exerts protective effects against the cytotoxicity and carcinogenicity of benzo(a)pyrene and aflatoxin B(1) in vitro and in vivo. Occupational study showed that workers who had genotypes with higher GNMT promoter activity may have lower content of oxidative damaged DNA products in their urine. In terms of cancer, recent studies using GNMT knockout mouse models demonstrated that GNMT deficiency has high penetrance in inducing the development of steatohepatitis and hepatocellular carcinoma. In terms of the mechanism, besides dysregulation of epigenetic modification, insights have been provided by recent identification of two novel proteins interacting with GNMT-DEPTOR and NPC2. These studies suggest that GNMT not only is involved in mTOR signaling pathway, but also plays an important role in the intracellular trafficking of cholesterol. The implication of these findings to the preventive medicine and translational research will be discussed.

Benzo[a]pyrene effects on glycine N-methyltransferase mRNA expression and enzyme activity in Fundulus heteroclitus embryos

Benzo[a]pyrene (BaP) is a ubiquitous environmental polycyclic aromatic hydrocarbon (PAH) contaminant that is both a carcinogen and a developmental toxicant. We hypothesize that some of BaP's developmental toxicity may be mediated by effects on glycine N-methyltransferase (GNMT). GNMT is a mediator in the methionine and folate cycles, and the homotetrameric form enzymatically transfers a methyl group from S-adenosylmethionine (SAM) to glycine forming S-adenosylhomocysteine (SAH) and sarcosine. SAM homeostasis, as regulated by GNMT, is critically involved in regulation of DNA methylation, and altered GNMT expression is associated with liver pathologies. The homodimeric form of GNMT has been suggested as the 4S PAH-binding protein. To further study BaP-GNMT interactions, Fundulus heteroclitus embryos were exposed to waterborne BaP at 10 and 100mug/L and both GNMT mRNA expression and enzyme activity were determined. Whole mount in situ hybridization showed GNMT mRNA expression was increased by BaP in the liver region of 7, 10 and 14dpf F. heteroclitus embryos. In contrast to mRNA induction, in vivo BaP exposure decreased GNMT enzyme activity in 4, 10 and 14dpf embryos. However, in vitro incubations of adult F. heteroclitus liver cytosol with BaP did not cause decreased enzyme activity. In conclusion, BaP exposure altered GNMT expression, which may represent a new target pathway for BaP-mediated embryonic toxicities and DNA methylation changes.