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Environmental Factor

Environmental Factor

Your Online Source for NIEHS News

January 2018

2017 Papers of the Year

From more than 2,900 NIEHS-funded studies published in 2017, leaders of the institute selected 23 for special recognition as Papers of the Year.

A new miniature 3-D model of the female reproductive tract and menstrual cycle can be used to study the effects of chemicals and drugs on the female reproductive system. NIEHS grantees developed the model, which fits in the palm of the hand and mimics a normal 28-day hormone cycle.

The new device, termed EVATAR, involves human tissue and 3-D models of the ovaries, fallopian tubes, uterus, cervix, vagina, and liver. A fluid and pumping method simulates the flow of blood between each of the organ systems. The organ models communicate with each other via secreted substances, such as hormones, replicating how organs work together in the body. According to the authors, EVATAR will also help scientists understand endometriosis, fibroids, cancer, infertility, and other hormone-related diseases of the female reproductive tract.

Research funded by grants

3-D model simulates female reproductive tract and menstrual cycle

A new miniature 3-D model of the female reproductive tract and menstrual cycle can be used to study the effects of chemicals and drugs on the female reproductive system. NIEHS grantees developed the model, which fits in the palm of the hand and mimics a normal 28-day hormone cycle.

The new device, termed EVATAR, involves human tissue and 3-D models of the ovaries, fallopian tubes, uterus, cervix, vagina, and liver. A fluid and pumping method simulates the flow of blood between each of the organ systems. The organ models communicate with each other via secreted substances, such as hormones, replicating how organs work together in the body. According to the authors, EVATAR will also help scientists understand endometriosis, fibroids, cancer, infertility, and other hormone-related diseases of the female reproductive tract.

CitationXiao S, Coppeta JR, Rogers HB, Isenberg BC, Zhu J, Olalekan SA, McKinnon KE, Dokic D, Rashedi AS, Haisenleder DJ, Malpani SS, Arnold-Murray CA, Chen K, Jiang M, Bai L, Nguyen CT, Zhang J, Laronda MM, Hope TJ, Maniar KP, Pavone ME, Avram MJ, Sefton EC, Getsios S, Burdette JE, Kim JJ, Borenstein JT, Woodruff TK. 2017. A microfluidic culture model of the human reproductive tract and 28-day menstrual cycle. Nat Commun 8:14584. (Synopsis) (Story)

Baby teeth may link autism and heavy metals

NIEHS grantees reported that baby teeth from children with autism contain more lead and lower amounts of the essential nutrients zinc and manganese compared with baby teeth from children without autism.

The researchers studied 32 pairs of twins and 12 individual twins. Each had one sibling with autism, both siblings with autism, or neither with autism. Using laser ablation-inductively coupled plasma mass spectrometry to analyze the metal uptake in the growth rings of baby teeth, the scientists revealed that the children with autism had higher lead levels in the prenatal period and in the first five months after birth compared with children without autism. The children with autism also had lower zinc levels during the third trimester and lower manganese levels both prenatally and after birth, with the highest deficiency seen four months after birth.

CitationArora M, Reichenberg A, Willfors C, Austin C, Gennings C, Berggren S, Lichtenstein P, Anckarsater H, Tammimies K, Bolte S. 2017. Fetal and postnatal metal dysregulation in autism. Nat Commun 8:15493. (Synopsis) (Story)

B vitamins may protect against epigenetic effects of air pollution

Taking B vitamins may help lessen the effects of fine particles, a common air pollutant, according to a study published by NIEHS-funded researchers. The team demonstrated that B vitamin supplements prevented epigenetic changes, which affect the function of DNA without altering the original sequence of amino acids.

Ten healthy adult volunteers were exposed to clean air and given a placebo to check baseline responses. They were then given a placebo for 4 weeks and exposed for 2 hours to air containing particulate matter less than 2.5 micrometers in diameter (PM2.5). The experiment was repeated in the same individuals, with each volunteer taking a daily B vitamin supplement for 4 weeks before another exposure to PM2.5.

Without supplementation, researchers found that PM2.5 induced epigenetic changes in genes involved in inflammation and metabolism. The authors suggested B vitamin supplementation almost completely prevented these changes.

CitationZhong J, Karlsson O, Wang G, Li J, Guo Y, Lin X, Zemplenyi M, Sanchez-Guerra M, Trevisi L, Urch B, Speck M, Liang L, Coull BA, Koutrakis P, Silverman F, Gold DR, Wu T, Baccarelli AA. 2017. B vitamins attenuate the epigenetic effects of ambient fine particles in a pilot human intervention trial. Proc Natl Acad Sci U S A 114(13):3503–3508. (Synopsis) (Story)

The mechanisms of PM2.5 influence on insulin resistance

NIEHS grantees found that short-term exposure to particulate matter less than 2.5 micrometers (PM2.5) can induce oxidative stress in the lungs. This oxidative stress may, in turn, trigger vascular insulin resistance, a critical factor in the development of diabetes. This novel link between pulmonary oxidative stress and vascular insulin resistance may explain how exposure to air pollution increases the risk of developing both cardiovascular and metabolic diseases.

The researchers studied mice fed a normal or a high-fat diet, exposing them to either air concentrated with PM2.5 or filtered air. They then measured insulin sensitivity and inflammation. Upon exposure to PM2.5, mice developed vascular insulin resistance, which is associated with development of diet-induced obesity and diabetes, even in the absence of a high-fat diet. They also found that reducing oxidative stress in the lungs prevented the PM2.5-induced vascular insulin resistance and inflammation.

CitationHaberzettl P, O'Toole TE, Bhatnagar A, Conklin DJ. 2016. Exposure to fine particulate air pollution causes vascular insulin resistance by inducing pulmonary oxidative stress. Environ Health Perspect 124(12):1830−1839. (Synopsis)

Flame retardants may impair <em>in vitro</em> fertilization

A higher concentration of some organophosphate flame retardants (PFRs) in urine was associated with negative in vitro fertilization (IVF) outcomes in women, according to an NIEHS-funded study. The findings linked exposure to PFRs in women who underwent IVF to a lower probability of embryo fertilization and implantation, as well as fewer successful pregnancies and live births.

Researchers analyzed metabolites of PFRs in urine samples from 211 women who underwent IVF at the Massachusetts General Hospital Fertility Center from 2005 to 2015. The women with the highest concentrations of PFR metabolites had lower rates of successful fertilization and implantation of the embryo compared with women with the lowest levels of metabolites. Overall, the group with the lowest levels of PFR metabolites had a 41 percent increase in clinical pregnancies and a 38 percent increase in live births compared with the group with the highest urinary metabolite concentrations.

CitationCarignan CC, Mínguez-Alarcon L, Butt CM, Williams PL, Meeker JD, Stapleton HM, Toth TL, Ford JB, Hauser R, EARTH Study Team. 2017. Urinary concentrations of organophosphate flame retardant metabolites and pregnancy outcomes among women undergoing in vitro fertilization. Environ Health Perspect 125(8):087018. (Synopsis)

Researchers remove noise from metabolomics data

NIEHS-funded researchers revealed that the actual number of unique metabolites in a typical metabolomics analysis may be close to one-tenth as large as previously thought. Using a new approach that examined the metabolites in Escherichia coli, the research team looked for signals that arose from contamination and artifacts. They also searched for degenerate features, which means that one metabolite showed up as many different signals.

They found thousands of previously unreported degenerate features, with some metabolites showing up as more than 150 signals. Removing these features reduced the number of unique analytes from approximately 25,000 to less than 2,961. After removing additional contaminants and other poorly resolved components from the data, they further reduced the number of unique analytes to less than 1,000. They created the creDBle database to provide scientists conducting metabolomics studies with access to annotated reference data sets.

CitationMahieu NG, Patti GJ. 2017. Systems-level annotation of a metabolomics data set reduces 25 000 features to fewer than 1000 unique metabolites. Anal Chem 89(19):10397−10406. (Synopsis)

Higher manganese levels associated with lower IQ in children

An NIEHS-funded study revealed that children in East Liverpool, Ohio who had higher levels of manganese (Mn) in their hair had lower IQ scores. East Liverpool, the site of a hazardous waste incinerator and a Mn processor, has exceeded U.S. Environmental Protection Agency reference levels for Mn in the air for more than a decade.

From March 2013 to June 2014, researchers analyzed blood and hair samples of 106 children, 7 to 9 years of age, from East Liverpool and surrounding communities. Participants and their caregivers received cognitive assessments and questionnaires when samples were taken.

Previous findings suggested that Mn in hair may reflect long-term exposure, whereas blood Mn levels may represent current exposure. The researchers found that increased Mn in hair samples was significantly associated with declines in IQ. They did not see the same association with blood Mn levels.

CitationHaynes EN, Sucharew H, Hilbert TJ, Kuhnell P, Spencer A, Newman NC, Burns R, Wright R, Parsons PJ, Dietrich KN. 2017. Impact of air manganese on child neurodevelopment in East Liverpool, Ohio. Neurotoxicology; doi: 10.1016/j.neuro.2017.09.001 [Online 6 Sept. 2017]. (Synopsis)

SV2C role in dopamine release and Parkinson’s disease

Synaptic vesicle glycoprotein 2C (SV2C), a protein that helps regulate the release of neurotransmitters in the brain, may play a role in Parkinson’s disease (PD), according to NIEHS grantees. The findings suggested that SVC2 may be important for release of the neurotransmitter dopamine, and that SVC2 disruption is a feature of PD.

The researchers bred mice lacking SVC2 and found that the animals showed reduced dopamine levels in the brain and displayed decreases in motor activity. The SVC2 deletion was also associated with a reduced response to nicotine, a chemical in cigarette smoke that was previously linked to a reduced risk of PD. Because they linked SVC2 disruption to both nicotine response and dopamine release, the authors suggested that the SV2C gene may be a factor for the previously identified association between nicotine use and reduced risk of PD.

CitationDunn AR, Stout KA, Ozawa M, Lohr KM, Hoffman CA, Bernstein AI, Li Y, Wang M, Sgobio C, Sastry N, Cai H, Caudle WM, Miller GW. 2017. Synaptic vesicle glycoprotein 2C (SV2C) modulates dopamine release and is disrupted in Parkinson disease. Proc Natl Acad Sci U S A 114(11):E2253−E2262. (Synopsis)

New marker to identify aflatoxin B1 exposure

NIEHS grantees developed a way to determine whether liver cells have been exposed to the fungal product aflatoxin B1 (AFB1), a known liver carcinogen. The technique has the potential to identify mutations associated with AFB1 exposure before cancer develops.

Mice exposed to aflatoxin four days after birth eventually developed liver cancer. The researchers sequenced DNA from the mice tumors and liver cells before tumors developed. Using a new genome sequencing technique, they identified patterns in DNA mutations associated with AFB1 exposure. These mutation patterns emerged as soon as 10 weeks after exposure, before any signs of tumors.

By comparing the mutational profile of the aflatoxin-exposed mice to genetic sequences found in liver tumors in patients from around the world, the researchers found that the mouse signature closely matched the signatures of 13 patients believed to have been exposed to aflatoxin through their diet.

CitationChawanthayatham S, Valentine CC 3rd, Fedeles BI, Fox EJ, Loeb LA, Levine SS, Slocum SL, Wogan GN, Croy RG, Essigmann JM. 2017. Mutational spectra of aflatoxin B1 in vivo establish biomarkers of exposure for human hepatocellular carcinoma. Proc Natl Acad Sci U S A 114(15):E3101–E3109. (Synopsis) (Story)

In-house research

NIEHS clinical researcher helps find cause of rare congenital malformation

Working with an international team of doctors and scientists, Natalie Shaw, M.D., an NIEHS clinical investigator and pediatric endocrinologist, discovered the first genetic cause of human arhinia, or the complete absence of a nose. Mutations in this gene, called SMCHD1, were already known to cause a rare form of muscular dystrophy but had never been linked to facial development.

The authors performed DNA sequencing in 40 patients with arhinia and found that 86 percent had a missense mutation in SMCHD1. Suppressing SMCHD1 function in zebrafish embryos produced abnormalities in the facial cartilage, smaller eyes, and changes to the central nervous system. Similar knockdown studies in mice did not cause morphological abnormalities, suggesting that SMCHD1 may not be working alone. That is, arhinia might only occur when the mutant SMCHD1 protein interacts with other proteins that are encoded by humans, but not by the mouse genome.

CitationShaw ND, Brand H, Kupchinsky ZA, Bengani H, Plummer L, Jones TI, Erdin S, Williamson KA, Rainger J, Stortchevoi A, Samocha K, Currall BB, Dunican DS, Collins RL, Willer JR, Lek A, Lek M, Nassan M, Pereira S, Kammin T, Lucente D, Silva A, Seabra CM, Chiang C, An Y, Ansari M, Rainger JK, Joss S, Smith JC, Lippincott MF, Singh SS, Patel N, Jing JW, Law JR, Ferraro N, Verloes A, Rauch A, Steindl K, Zweier M, Scheer I, Sato D, Okamoto N, Jacobsen C, Tryggestad J, Chernausek S, Schimmenti LA, Brasseur B, Cesaretti C, Garcia-Ortiz JE, Beitrago TP, Silva OP, Hoffman JD, Muhlbauer W, Ruprecht KW, Loeys BL, Shino M, Kaindl AM, Cho CH, Morton CC, Meehan RR, van Heyningen V, Liao EC, Balasubramanian R, Hall JE, Seminara SB, Macarthur D, Moore SA, Yoshiura KI, Gusella JF, Marsh JA, Graham JM Jr, Lin AE, Katsanis N, Jones PL, Crowley WF Jr, Davis EE, Fitzpatrick DR, Talkowski ME. 2017. SMCHD1 mutations associated with a rare muscular dystrophy can also cause isolated arhinia and Bosma arhinia microphthalmia syndrome. Nat Genet 49:238–248. (Synopsis) (Story)

High vitamin D levels associated with decreased breast cancer risk

Researchers at NIEHS found that increased blood levels of vitamin D reduced the risk of breast cancer. Vitamin D is derived naturally from sunlight exposure, nutritional supplements, and dietary sources, and exhibits effects that could reduce the risk for cancer. The authors analyzed data from the NIEHS Sister Study, a study that examines environmental and genetic contributions to health outcomes in more than 50,000 women who each have a sister with breast cancer.

The scientists measured the vitamin D prehormone 25(OH)D in serum samples from 1,611 participants who later developed breast cancer and 1,843 randomly selected participants. They found a statistically significant association between high levels of 25(OH)D and lower breast cancer risk, with the strongest association among postmenopausal and obese women. Evidence in the larger cohort also found a reduced risk among postmenopausal women who regularly took vitamin D supplements.

CitationO’Brien KM, Sandler DP, Taylor JA, Weinberg CR. 2017. Serum vitamin D and risk of breast cancer within five years. Environ Health Perspect 125(7):077004. (Synopsis)

Las1 coordinates with Grc3 to cleave RNA

Scientists from NIEHS and the National Cancer Institute deciphered the molecular mechanisms responsible for the activity of Las1, a RNA-cutting enzyme essential for cell viability and generation of ribosomes. The findings offer new insights into the development of protein-guided gene editing tools and of neurological diseases linked to Las1 mutations.

As the factory for protein synthesis in cells, ribosomes are composed of RNAs and associated proteins. The ribosomal RNAs (rRNAs) come from the precursor rRNAs, pre-rRNAs, with spacer sequences that need to be removed by nucleases, including Las1. The sites cleaved by Las1 are phosphorylated by the polynucleotide kinase Grc3, which signals other enzymes to further process the pre-rRNAs. The researchers observed that Las1 associated with Grc3 and two Las1/Grc3 heterodimers formed a superdimer. Las1 had weak activity, but displayed efficient cleavage in the presence of Grc3.

CitationPillon MC, Sobhany M, Borgnia MJ, Williams JG, Stanley RE. 2017. Grc3 programs the essential endoribonuclease Las1 for specific RNA cleavage. Proc Natl Acad Sci U S A 114(28):E5530−E5538. (Synopsis)

Observing DNA polymerase mu repair DNA breaks

NIEHS researchers have uncovered the molecular characteristics and dynamic structural changes that enable nucleic acid synthesis by polymerase mu (pol mu) during DNA double-strand break (DSB) repair. The findings offer insight into the unique role of pol mu in repairing damaged DNA and maintaining the integrity of the genome.

The researchers tracked the structural changes of pol mu before, during, and after nucleotide insertion. They identified a new metal ion that transiently associates with the active site and stabilizes the product complex. Together with dynamic structural changes in the active site, they hypothesized that this metal ion plays a crucial role during DSBs. Consistent with previous observations, pol mu displayed only limited structure conversion during DNA synthesis, supporting its capability to accommodate more diverse damaged ends and substrates compared with other polymerases.

CitationJamsen JA, Beard WA, Pedersen LC, Shock DD, Moon AF, Krahn JM, Bebenek K, Kunkel TA, Wilson SH. 2017. Time-lapse crystallography snapshots of a double-strand break repair polymerase in action. Nat Commun 8(1):253. (Synopsis)

Mouse embryos are not female by default

NIEHS researchers and their colleagues at Baylor College of Medicine discovered that COUP-TFII, a nuclear receptor present in developing organs of embryos, is responsible for sexual differentiation. Their findings challenge the prevailing theory that the lack of androgen determines which reproductive tract is maintained in the embryo.

Using a mouse model, the researchers found that female embryos deficient in COUP-TFII retained both the male and female reproductive tracts. When the mouse embryos were exposed to an androgen antagonist, the knockout embryos still exhibited both reproductive tracts, indicating that a lack of androgen is not responsible for the regression of the male duct. Using reverse transcription polymerase chain reaction, the researchers found higher expression of fibroblast growth factor in the mesonephroi of the knockout embryos compared with the controls. The mesonephros is the embryo’s excretory organ where COUP-TFII is housed.

CitationZhao F, Franco HL, Rodriguez KF, Brown PR, Tsai MJ, Tsai SY, Yao HH. 2017. Elimination of the male reproductive tract in the female embryo is promoted by COUP-TFII in mice. Science 357(6352):717−720. (Synopsis) (Story)

SIRT1 regulates intestinal inflammation through microbiome

SIRT1, a key repressor of inflammation, regulates inflammation in the intestines by altering intestinal microbiota. SIRT1 modulates epithelial homeostasis in the intestines, and disruption of this homeostasis leads to disorders, such as inflammatory bowel disease (IBD).

After developing mice with a deletion of SIRT1 in the intestinal epithelium, the scientists found that intestinal SIRT1 knockout mice exhibited more spontaneous inflammation in the intestine than control mice. Furthermore, SIRT1 knockout mice also had altered fecal microbiota, and less species richness and diversity in their gut bacteria. The gut microbiome affects nutrient metabolism and the immune system, so disrupting the gut microbiome can lead to disease.

IBD patients have reduced Lactobacillus in their gut, and the SIRT1 knockout mice also had reduced Lactobacillus. The scientists theorized that SIRT1 is critical for preventing intestinal inflammation by mediating host-microbiome interactions, especially Lactobacillus.

CitationWellman AS, Metukuri MR, Kazgan N, Xu X, Xu Q, Ren NSX, Czopik A, Shanahan MT, Kang A, Chen W, Azcarate-Peril MA, Gulati AS, Fargo DC, Guarente L, Li X. 2017. Intestinal epithelial Sirtuin 1 regulates intestinal inflammation during aging in mice by altering the intestinal microbiota. Gastroenterology 153(3):772–786. (Synopsis)

TNF needed for one type of allergic airway inflammation

New findings from NIEHS scientists suggest that toll-like receptor (TLR) ligands and proteases in the environment act through different molecular pathways to promote airway inflammation. The work may help explain why some asthma patients benefit from drugs that inhibit tumor necrosis factor (TNF), a protein secreted during inflammatory responses.

Asthma, a chronic inflammatory disease of the airways, is associated with exposure to a variety of adjuvants, or substances, that promote allergic inflammatory responses. Using two types of adjuvants, TLR ligands and proteases, the researchers found they promoted distinct forms of airway inflammation, and that only TLR ligands increased the level of TNF.

The scientists further identified mechanisms through which TNF induced airway inflammation, and confirmed that TNF is an indispensable component in the TLR ligand-mediated, but not protease-mediated, form of asthma.

CitationWhitehead GS, Thomas SY, Shalaby KH, Nakano K, Moran TP, Ward JM, Flake GP, Nakano H, Cook DN. 2017. TNF is required for TLR ligand-mediated but not protease-mediated allergic airway inflammation. J Clin Invest 127(9):3313–3326. (Synopsis)

ZATT reverses DNA-protein crosslinks during chemotherapy

NIEHS researchers and their collaborators identified a newly discovered protein named ZATT that works together with another protein called TDP2 to remove DNA protein crosslinks (DPCs). This research is important, because a class of front-line chemotherapeutic drugs hijacks a cellular enzyme and causes it to trap a DNA break inside of a DPC. This type of DNA damage is challenging for cancer cells to repair and is responsible for the potent cell-killing effects of these drugs.

The human genome becomes entangled when compacted into a cell nucleus, and an enzyme called topoisomerase 2 (TOP2) is needed to untangle DNA, especially in rapidly growing tumor cells. Environmental toxins, antibiotics, and commonly used chemotherapy agents prevent TOP2 from completing its reaction cycle. The scientists showed that TDP2 and ZATT first remove the DPC, allowing cellular DNA repair machinery to re-seal the DNA break.

CitationSchellenberg MJ, Lieberman JA, Herrero-Ruiz A, Butler LR, Williams JG, Munoz-Cabello AM, Mueller GA, London RE, Cortes-Ledesma F, Williams RS. 2017. ZATT (ZNF451)-mediated resolution of topoisomerase 2 DNA-protein cross-links. Science 357(6358):1412−1416. (Synopsis) (Story)

Enhancers within genes dampen protein production

NIEHS researchers and their colleagues reported that the presence of an intragenic enhancer, or an enhancer region located inside of a gene, can reduce host gene transcription, which means less production of the encoded protein. Enhancers are small regions of DNA known to help activate gene transcription.

Scientists previously thought that enhancers mainly served as activators of transcription, but this research showed that the location of the enhancer is important in determining whether it promotes or slows transcription. The underlying mechanism is likely interference from RNA polymerase II, which is involved in transcribing the enhancer. The interference might be protective in cases in which the host gene codes for an oncoprotein, because loss of enhancer transcription means loss of interference and gain of host gene expression, leading to cancer.

CitationCinghu S, Yang P, Kosak JP, Conway AE, Kumar D, Oldfield AJ, Adelman K, Jothi R. 2017. Intragenic enhancers attenuate host gene expression. Mol Cell 68(1):104−117.e6. (Synopsis) (Story)

Biomarkers of ovarian reserve do not predict fertility

NIEHS epidemiologist Donna Baird, Ph.D., collaborated with fertility specialist, Anne Steiner, M.D., at the University of North Carolina at Chapel Hill and found that biomarkers of low ovarian reserve, which refer to the number of eggs a woman has left, did not predict fertility in older women. The discovery changed the current understanding of fertility.

The study followed 750 women who had been trying to conceive for three months or less. Participants provided urine and blood samples at enrollment, and were given home urine pregnancy tests. Blood samples were analyzed for indicators of low ovarian reserve, such as follicle-stimulating hormone, anti-Mullerian hormone, and inhibin B.

After following participants for 12 months or to the time of conception, the team discovered that indicators of low ovarian reserve were not associated with reduced fertility compared with signs of normal ovarian reserve.

CitationSteiner AZ, Pritchard D, Stanczyk FZ, Kesner JS, Meadows JW, Herring AH, Baird DD. 2017. Association between biomarkers of ovarian reserve and infertility among older women of reproductive age. JAMA 318(14):1367−1376. (Synopsis) (Story)

Rif1 is a novel regulator of ERVs

Rif1 is a novel regulator of endogenous retroviruses (ERVs), according to NIEHS scientists and their collaborators. The discovery is important, because it provides insights for the proper control of retrotransposons in the mammalian genome.

Retrotransposons are mobile genetic elements that jump around the genome and spread by copying and pasting themselves. ERVs are long terminal repeat retrotransposons that can increase the complexity of the genome and regulate the activity of genes in development and disease. If ERVs are not kept under control, they can lead to genome instability and unwanted expression of genes. For this reason, cells have developed mechanisms to inhibit or limit the activity of ERVs. The team demonstrated that Rif1 directly occupies genomic loci near ERVs. It silences ERVs and nearby genes by promoting the recruitment of epigenetic regulators to maintain a repressive chromatin state.

CitationLi P, Wang L, Bennett BD, Wang J, Li J, Qin Y, Takaku M, Wade PA, Wong J, Hu G. 2017. Rif1 promotes a repressive chromatin state to safeguard against endogenous retrovirus activation. Nucleic Acids Res 45(22)12723−12738. (Synopsis)

GLIS3 is essential for biosynthesis of thyroid hormones

NIEHS researchers have revealed that transcriptional factor GLI-similar 3 (GLIS3) is required for biosynthesis of thyroid hormones (THs) and proliferation of thyroid follicular cells that generate THs. The findings offer new insight into the development and treatment of thyroid disorders, including hypothyroidism and goiter, which is an enlarged thyroid.

Using a mouse model with a GLIS3 deficiency, the scientists found that loss of GLIS3 caused a major reduction in TH levels and proliferation of follicular cells, and prevented goiter development. GLIS3 directly bound to the promoters of several genes responsible for TH biosynthesis. GLIS3 knockout mice exhibited suppressed expression of these genes and impaired activation of the TSH-mediated mTORC1 pathway that promotes cell proliferation. The data indicate that GLIS3 acts downstream of TSH/TSHR and is a key regulator of TH biosynthesis.

CitationKang HS, Kumar D, Liao G, Lichti-Kaiser K, Gerrish K, Liao XH, Refetoff S, Jothi R, Jetten AM. 2017. GLIS3 is indispensable for TSH/TSHR-dependent thyroid hormone biosynthesis and follicular cell proliferation. J Clin Invest; doi: 10.1172/JCI94417 [Online 30 October 2017]. (Synopsis)

National Toxicology Program (NTP) research

NTP screens for genotoxicity with high-throughput techniques

NTP researchers and collaborators evaluated the usefulness of quantitative high-throughput approaches to assess the genotoxicity, or the ability to cause DNA damage, of compounds in the Tox21 library of 10,000 compounds. The Tox21 high-throughput screening program is part of a collaborative effort to institute new methods for toxicity testing.

The scientists assessed p53 activity in human colon cancer cells (HCT-116). p53 is a transcription factor that is activated in response to cellular stress, particularly DNA damage. Results showed that 4.7 percent of compounds activated p53. Additional data mining revealed significant associations between these compounds and elevated expression of p53 downstream genes. Further analysis revealed specific associations between p53 activation and specific chemical substructures. The authors concluded that assessment of p53 activation was useful for characterization of genotoxic potential.

CitationWitt KL, Hsieh JH, Smith-Roe SL, Xia M, Huang R, Zhao J, Auerbach SS, Hur J, Tice RR. 2017. Assessment of the DNA damaging potential of environmental chemicals using a quantitative high-throughput screening approach to measure p53 activation. Environ Mol Mutagen 58(7):494–507. (Synopsis)

NTP optimizes liver model for improved toxicity screening

NTP scientists developed a novel way of culturing liver cells to vastly improve modeling of the human liver. In this new process, 3-D HepaRG liver cells were grown in spheroid structures that more closely resemble the architecture of the human liver. This approach allows for more effective screening of chemicals with the potential to cause liver toxicity.

The researchers determined that the 3-D HepaRG spheroid model was a cost-effective and user-friendly way to maintain cultured cells for toxicity screening and to achieve consistency. The model also maintained drug metabolizing activity, which is key for predicting metabolism-dependent toxicities, and accurately reflected the liver toxicity of several chemicals known to cause liver toxicity in humans. For example, it distinguished liver toxic troglitazone and trovafloxacin from the safer analogues rosiglitazone and levofloxacin, respectively.

CitationRamaiahgari SC, Waidyanatha S, Dixon D, DeVito MJ, Paules RS, Ferguson SS. 2017. From the Cover: Three-dimensional (3D) HepRG spheroid model with physiologically relevant xenobiotic metabolism competence and hepatocyte functionality for liver toxicity screening. Toxicol Sci 159(1):124–136. (Synopsis)

NTP develops new method of predicting human health risk

Scientists from the NTP and the U.S. Environmental Protection Agency published analyses of high-throughput screening (HTS) data generated in Tox21 using in vitro to in vivo extrapolation (IVIVE). The analyses used all of the Tox21 chemical screening data to quantitatively address the likelihood of human in vivo hazards with Tox21 compounds. The authors suggest that IVIVE provides a framework that rapidly and quantitatively relates in vitro toxicology data to estimates of oral equivalent exposures using either in vitro or in silico-derived toxicokinetic parameters.

The researchers predicted the equivalent maximum blood concentration to in vitro responses in a manner that is analogous to decision-making methods for clinical drug-drug interactions. Of 3,925 unique chemicals, 36 HTS compounds gave possible in vivo interaction likelihoods lower than median human exposures as predicted by the EPA’s Tox21-ToxCast dose-likelihood predictions. IVIVE can prioritize compounds and can be tailored for fit-for-purpose applications. See a publicly available version of IVIVE at https://sandbox.ntp.niehs.nih.gov/ivive.

CitationSipes NS, Wambaugh JF, Pearce R, Auerbach SS, Wetmore BA, Hsieh JH, Shapiro AJ, Svoboda D, DeVito MJ, Ferguson SS. 2017. An intuitive approach for predicting potential human health risk with the Tox21 10k library. Environ Sci Technol 51(18):10786−10796.

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