New strategy predicts polycyclic aromatics toxicity

Researchers in the Division of the National Toxicology Program (NTP) at NIEHS have successfully compiled a rich resource to explore data on polycyclic aromatic compound (PACs) toxicity. This data-driven approach to contextualizing PAC hazard characterization allows researchers to predict eight different toxicity profiles of various PACs and other classes of compounds.

PACs are a structurally diverse class of human-made toxicants found widely in the environment. Unfortunately, information about human exposure and health effects of PACs is limited. To facilitate greater understanding of PAC toxicity in a cost-effective manner, NTP researchers created an automated approach to identify PAC structures using computer workflows, algorithms, and clusters. Using existing data on similar compounds, the scientists categorized PACs based on structure and hazard characterization. The analysis results are available and searchable through an interactive web application(https://ntp.niehs.nih.gov/go/pacs_tableau).

Data compiled from this effort can be used to prioritize individual PACs for in-depth, resource intensive studies to quickly expand understanding of mechanisms involved in PAC toxicity. Additionally, the approach can be used for other classes of compounds that require hazard characterization. (SR)

Citation: Hsieh JH, Sedykh A, Mutlu E, Germolec DR, Auerbach SS, Rider CV. 2020. Harnessing in silico, in vitro, and in vivo data to understand the toxicity landscape of polycyclic aromatic compounds (PACs). Chem Res Toxicol; doi:10.1021/acs.chemrestox.0c00213 [Online 16 October 2020].

Novel pathway shows WNK1 is involved in embryo implantation

Researchers at NIEHS have discovered a novel pathway regulating embryo implantation. Errors in that process can lead to pregnancy complications and miscarriages. A key player appears to be WNK1, a kinase protein found in both mice and humans that is typically studied in the renal and nervous systems.

Combining transcriptomics and proteomics, as well as in vitro studies with human cell lines and in vivo studies with mouse models, the researchers identified the role of WNK1 in uterine function. Specifically, they found that WNK1 regulates cell-proliferation, estrogen responsiveness, and the serine-threonine kinase AKT signaling, through interactions with the phosphatase PP2A. Loss of WNK1 led to AKT hypersignaling, which disrupted the expression of genes needed for embryo implantation. In an unexpected discovery, the authors observed that the morphology of the uterus in the WNK1 knockout mice (KO) parallels that of adenomyosis in humans. Adenomyosis occurs when the endometrial lining penetrates the muscle wall of the uterus, sometimes causing severe cramping and heavy menstrual periods. The finding demonstrates that WNK1 may protect the uterus from endocrine disruptors and that the WNK1 KO mice are a potential model for adenomyosis. (MH)

Citation: Chi RPA, Wang T, Huang CL, Wu SP, Young SL, Lydon JP, DeMayo FJ. 2020. WNK1 regulates homeostasis and its ability to support pregnancy. JCI Insight 5(22):141832.

Uterine fibroids in young African Americans

NIEHS researchers and collaborators conducted the first large study to measure age-specific uterine fibroid incidence and growth. They enrolled 1,693 young African Americans — the U.S. ethnic group with the highest burden of this condition.

Standardized ultrasound examinations at baseline and after 18 months identified any fibroids greater than 0.5 centimeters (cm) in diameter. Overall, nearly 10% of women who were fibroid-free at baseline had fibroids by follow-up. Incidence increased with age, with 6% for those ages 23-25 to 13% for those ages 32-35. New fibroid development was even higher for women who had fibroids at baseline. Fibroid growth (N = 344 fibroids) varied dramatically by fibroid size at baseline. Small fibroids, less than 1 cm diameter, exhibited a high average growth rate, with a nearly 200% increase in volume over 18 months. At the same time, 23% of these small fibroids were no longer detectable at follow-up. The larger fibroids grew more slowly, and all of those 4 cm in diameter or greater at baseline remained at follow-up.

These findings are useful for estimating fibroid growth over time and for developing future life-course strategies to alleviate the major health burden caused by these tumors. (SM)

Citation: Baird DD, Patchel SA, Saldana TM, Umbach DM, Cooper T, Wegienka G, Harmon QE. 2020. Uterine fibroid incidence and growth in an ultrasound-based, prospective study of young African Americans. Am J Obstet Gynecol 223(3):402.e1–402.e18.

Polymerase mu provides scaffold for single- and double-strand breaks

NIEHS researchers, in collaboration with scientists at the University of North Carolina at Chapel Hill, have shown for the first time how the human DNA polymerase mu (Pol-mu) engages double-strand breaks (DSB). The results suggest that Pol-mu addresses DSBs that contain single-nucleotide homology at the break site by using a mechanism similar to how it handles single-strand breaks (SSBs).

The scientists used X-ray crystallography to capture snapshots of three different human Pol-mu structures interacting with DSBs. These structures revealed few differences in how Pol-mu bound double and single strand breaks. Using biochemical assays, the researchers showed that human Pol-mu can help process multiple types of DSBs. The authors noted that some amino acids appear to be critical for engaging more complex DSBs. The findings provide a clearer understanding of how human Pol-mu participates in repairing different DNA strand breaks as part of an established repair pathway. (CH)

Citation: Kaminski AM, Pryor JM, Ramsden DA, Kunkel TA, Pedersen LC, Bebenek K. 2020. Structural snapshots of human DNA polymerase mu engaged on a DNA double-strand break. Nat Commun 11(1):4784.

Scientists create sensors for measuring brain dopamine levels

NIEHS researchers and collaborators at New York University and Peking University created a series of genetically encoded fluorescent sensors for imaging and quantifying levels of dopamine (DA) in the brain. The neurotransmitter dopamine is involved in motor control, learning and memory, and emotion control. Errors in DA signaling have been linked to a host of psychiatric and neurological disorders, including schizophrenia and Parkinson’s disease. The newly developed sensors will help scientists better understand these conditions.

The authors previously developed DA sensors using a green fluorescent protein (GFP) in naturally occurring DA receptors. Upon binding with DA molecules, a ligand-stabilized conformational change in the receptor prompted the sensors to emit more photons and appear brighter.

In the present work, they improved the GFP to obtain 2-3 times greater detection range and superior in vivo performance, compared with the first-generation sensors. Additionally, they generated red fluorescent sensors using the red fluorescent protein (RFP) known as cpmApple. These sensors have the benefit of exhibiting spectra specific to the RFP and separate from those observed with GFP-based sensors. As a result, the team was able to accurately record distinct neurochemical phenomena in relation to dopamine levels. (NA)

Citation: Sun F, Zhou J, Dai B, Qian T, Zeng J, Li X, Zhuo Y, Zhang Y, Wang Y, Qian C, Tan K, Feng J, Dong H, Lin D, Cui G, Li Y. 2020. Next-generation GRAB sensors for monitoring dopaminergic activity in vivo. Nat Methods 17(11):1156–1166.