Environmental Factor

Environmental Factor

Your Online Source for NIEHS News

July 2018

Papers of the Month

NTP chemists show body treats BPS similar to other bisphenols

National Toxicology Program (NTP) chemists have conducted a full evaluation of the absorption, distribution, metabolism, and excretion of bisphenol S (BPS) in rats and mice. BPS and its derivatives are being used increasingly in consumer products as an alternative to bisphenol A (BPA). The impact that the large-scale replacement of BPA by other analogues, such as BPS, has on public health is of ongoing interest to the NTP. As part of this effort, how BPS is processed in both humans and rodent models following exposure is necessary for putting toxicological findings into the greater context of human exposure.

This evaluation provided a comparison of clearance of BPS and derivatives in human, rat, and mouse liver cells. Generally, clearance in rodent hepatocytes was faster than in human hepatocytes in vitro. Following oral exposure of radiolabeled BPS in rats and mice, main excretion was found to be via the kidneys. Excretion via the kidneys became saturated with an increasing dose, indicated by the higher dose excreted in feces. Retention of BPS-derived species in tissues was low. The data also indicated that BPS is metabolized mainly via glucuronidation and sulfonation. These observations are consistent with previous reports on other members of the bisphenol class. (AD)

CitationWaidyanatha S, Black SR, Snyder RW, Yueh YL, Sutherland V, Patel PR, Watson SL, Fennell TR. 2018. Disposition and metabolism of the bisphenol analogue, bisphenol S, in Harlan Sprague Dawley rats and B6C3F1/N mice and in vitro in hepatocytes from rats, mice, and humans. Toxicol Appl Pharmacol 351:32–45.

Recently discovered protein modification regulates glucose metabolism

Scientists at NIEHS and their collaborators showed that the enzyme p300 mediates lysine 2-hydroxyisobutyrylation (Khib), a recently discovered type of post-translational modification (PTM). The authors discovered that this PTM targets enzymes involved in glycolysis, a pathway that produces cellular energy from the breakdown of glucose. These findings reveal an important role of p300-mediated Khib in regulating cellular glucose metabolism.

The authors showed that, in addition to functioning as a writer for lysine acetylation (Kac), p300 can also act as a writer for Khib. Using a quantitative proteomics approach, the authors identified 149 potential p300-targeted Khib sites in HCT116 human cells. Interestingly, only 6 of these sites overlapped with p300-targeted Kac sites. The finding suggested that p300 exhibits a differential sequence preference between the two PTMs.

PTMs, such as Khib and Kac, are known to regulate enzyme activity. Using bioinformatics tools, the authors discovered that p300-mediated Khib primarily targets glycolytic enzymes. They demonstrated that specific glycolytic enzymes lacking p300-mediated Khib were sufficient to impair glycolysis and decrease cell survival under glucose-depleted conditions. The work provides the foundation for future studies aimed at further understanding Khib’s influence on metabolism and metabolic diseases. (KG)

CitationHuang H, Tang S, Ji M, Tang Z, Shimada M, Liu X, Qi S, Locasale JW, Roeder RG, Zhao Y, Li X. 2018. EP300-mediated lysine 2-hyroxyisobutyrylation regulates glycolysis. Mol Cell 70(4):663–678.e6

DNA strands are copied differently during replication

NIEHS researchers and collaborators found that when double-stranded DNA in a cell is duplicated, one strand is copied more accurately than the other. DNA contains leading and lagging strands, and DNA duplication is facilitated by an enzyme called DNA polymerase. This study examined whether these strands are copied at different rates, which sheds light on the relevance of mutational signatures observed in many cancers.

Using Escherichia coli as a model organism, the researchers used a system looking at mutations in the lacI gene. In the presence of mutations, the lacI gene is turned off, and mutants can be seen as colonies on selective media. The researchers sequenced more than 1,000 mutants and found that lagging strand replication was more accurate. They suggested that during DNA replication, the polymerase interacts with the leading and lagging strands differently, and its increased proficiency to dissociate from the lagging strand contributes to its accuracy. (SS)

CitationMaslowska KH, Makiela-Dzbenska K, Mo JY, Fijalkowska IJ, Schaaper RM. 2018. High-accuracy lagging-strand DNA replication mediated by DNA polymerase dissociation. Proc Natl Acad Sci U S A 115(16):4212–4217.

NIEHS researchers develop new method to study brain diseases

NIEHS researchers developed a new tool called spectrally resolved fiber photometry that simultaneously measures the activities of two distinct neuronal populations that control movement in an animal model. These findings might help address questions related to Parkinson`s disease, a neurological disorder mainly characterized by tremors, slowness of movement, and impaired balance.

In general, an animal’s ability to move is controlled by two groups of neurons in the brain’s basal ganglia, the direct pathway (D1) and the indirect pathway (D2). Scientists used a Cre-Lox vector-based strategy to target these striatal direct and indirect pathway neurons. They found that when neural activity in D1 neurons is stronger than activity in D2 neurons, the animal does a start and go, which means it starts and moves to another location. However, when the activity of D2 neurons is stronger than that of D1 neurons, the mouse does a start and stop, meaning it initiates a movement, but stops immediately. They suggest that this novel technique could help study other brain conditions, such as Alzheimer’s disease, stroke, multiple sclerosis, and addiction. (RV)

CitationMeng C, Zhou J, Papaneri A, Peddada T, Xu K, Cui G. 2018. Spectrally resolved fiber photometry for multi-component analysis of brain circuits. Neuron 98(4):707–717.e4. (Article)

Effects of synthetic estrogen on male mice exposed neonatally

NIEHS researchers have shown that exposure to endocrine-disrupting chemicals (EDCs) at birth and during development adversely affects fertility of male mice through changes in their reproductive tracts. They identified a set of estrogen-responsive uterine genes, usually expressed in female mice, that become expressed in the exposed male mice. The finding, which suggests the male reproductive tract undergoes feminization after early exposure to EDCs, helps to increase the understanding of EDC exposure on human health and reproductive diseases.

Researchers exposed wild-type and estrogen receptor alpha knockout (alphaERKO) mice to diethylstilbestrol (DES), a synthetic estrogen, after birth. They analyzed gene expression and DNA methylation profiles at various time points as the mice aged. This method allowed identification of a large collection of differentially expressed genes, including identification of 155 estrogen-responsive uterine genes not normally expressed in male tissues.

DNA methylation patterns are known to indicate if a gene is turned on or off. Estrogen receptor alpha (ERalpha) regulates genes in response to estrogen hormone or estrogen-like compounds, such as EDCs. By comparing DNA methylation patterns observed in wild-type versus alphaERKO mice, with or without DES exposure, the scientists determined that the differentially expressed estrogen-responsive uterine genes were partially a result of ERalpha’s gene regulation activities. (KH)

CitationLi Y, Hamilton KJ, Wang T, Coons LA, Jefferson WN, Li R, Wang Y, Grimm SA, Ramsey JT, Liu L, Gerrish KE, Williams CJ, Wade PA, Korach KS. 2018. DNA methylation and transcriptome aberrations mediated by ER alpha in mouse seminal vesicles following developmental DES exposure. Proc Natl Acad Sci U S A 115(18):E4189–E4198.

(Anika Dzierlenga, Ph.D., is an Intramural Research Training Award (IRTA) fellow in the NIEHS Developmental and Reproductive Toxicology Group. Katie Glenn, Ph.D., is an IRTA fellow in the NIEHS Mechanisms of Mutation Group. Kiri Hoff, Ph.D., is an IRTA fellow in the NIEHS Mitochondrial DNA Replication Group. Salahuddin Syed, Ph.D., is an IRTA fellow in the NIEHS DNA Replication Fidelity Group. Ravikanth Velagapudi, Ph.D., is a visiting fellow in the NIEHS Neuropharmacology Group.)

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