Papers of the Month
By Ernie Hood, Mimi Huang, Prashant Rai, Nancy Urbano, and Janelle Weaver
NTP-led team finds adverse effects of PFOA and GenX in mice
In an NIEHS-funded study focusing on the placenta, scientists from the Division of the National Toxicology Program (DNTP), U.S. Environmental Protection Agency, and Duke University collaborated to compare the impact of gestational exposure to environmental contaminants perfluorooctanoic acid (PFOA) and hexafluoropropylene oxide dimer acid, known as GenX, on experimental mice.
They found that both compounds led to greater gestational weight gain, higher maternal liver weights, adverse microscopic pathological changes in the maternal liver, disproportionate placenta weights, and abnormal histopathological lesions in the mature placenta. However, the placenta lesion signatures appeared to be compound-specific, perhaps due to unique mechanisms of reproductive toxicity.
The study was the first to look at potential adverse effects on the placenta from gestational exposure to PFOA and GenX. The authors suggested that although the biological mechanism by which compounds like PFOA affect embryo growth is unknown, the placenta is now a confirmed target tissue.
GenX is a replacement compound for the commercially phased-out PFOA. The synthetic chemicals belong to the poly- and perfluoroalkyl substances class. Both have been detected in humans, with drinking water the best-understood route of exposure. GenX received intense public scrutiny in 2015 after reports that it contaminated the North Carolina Cape Fear River Basin. (EH)
Citation: Blake BE, Cope HA, Hall SM, Keys RD, Mahler BW, McCord J, Scott B, Stapleton HM, Strynar MJ, Elmore SA, Fenton SE. 2020. Evaluation of maternal, embryo, and placental effects in CD-1 mice following gestational exposure to perfluorooctanoic acid (PFOA) or hexafluoropropylene oxide dimer acid (HFPO-DA or GenX). Environ Health Perspect 128(2):27006.
Molecular details of pregnancy found using myometrial gene expression
Researchers, led by scientists at NIEHS, identified 2,890 genes from nonpregnant (NP) and term pregnant (TP) human myometrial samples that changed their expression patterns. Deficits of proper gene regulation in the myometrium, which is the muscular layer in the uterus that provides structure and contraction force during pregnancy and childbirth, could lead to difficult pregnancies or preterm birth. The research team believes that understanding the molecular events involved during pregnancy may help ease disorders associated with it.
Comparing gene expression levels from NP and TP myometrial samples showed that genes needed for structural reorganization, inflammation management, and increased carbohydrate metabolism during pregnancy underwent increased expression in support of proper pregnancy progression. Evaluation of open chromatin regions revealed that the progesterone receptor (PGR) pathway was highly active during pregnancy. When mapping where PGR was bound in the genome, the scientists were able to identify new proteins that might interact with PGR. These data confirmed that some pregnancy findings observed in animal studies were relevant to humans. The work identified new relationships that can be analyzed to better understand the molecular processes during pregnancy. (MH)
Citation: Wu SP, Anderson ML, Wang T, Zhou L, Emery OM, Li X, DeMayo FJ. 2020. Dynamic transcriptome, accessible genome, and PGR cistrome profiles in the human myometrium. FASEB J 34(2):2252–2268.
How high-fat diet may lead to liver disease
New insights into how the liver adapts to a high-fat diet may lead to novel treatments for obesity-related diseases such as nonalcoholic fatty liver disease (NAFLD), according to a study by NIEHS researchers. They found that long-term consumption of a diet high in saturated fat led to dramatic reprogramming of gene regulation in the mouse liver.
NAFLD involves the buildup of excessive fat in the liver of an individual who is not a heavy user of alcohol, increasing the risk of liver damage. When too many calories are consumed, the liver adapts by reprogramming the regulation of gene activity, but it has not been clear how the reprogramming happens.
The scientists fed mice a high-fat diet and analyzed effects on liver tissue. The mice became obese and showed other changes similar to metabolic syndrome in humans. Moreover, their livers became fatty and showed wide-ranging abnormalities at both molecular and cellular levels.
In particular, the liver’s adaptation to the fat-rich diet was mediated by a protein called hepatocyte nuclear factor 4 alpha (Hnf4-alpha). This finding suggested that Hnf4-alpha may play a central role in orchestrating changes in gene regulation in response to metabolic cues. Further research on Hnf4-alpha could lead to potential therapies for patients with metabolic disease. (JW)
Citation: Qin Y, Grimm SA, Roberts JD, Chrysovergis K, Wade PA. 2020. Alterations in promoter interaction landscape and transcriptional network underlying metabolic adaptation to diet. Nat Commun 11(1):962. [Story.]
InsP8 regulates XPR1 transport of inorganic phosphate
Researchers at NIEHS uncovered how the important cellular protein xenotropic and polytropic retrovirus receptor 1 (XPR1) is regulated by 1,5-bis-diphosphoinositolpolyphosphate (InsP8), an energetic cell-signaling molecule. Mutations in genes that regulate InsP8 could contribute to skeletal diseases, such as rickets and the bone-softening condition known as osteomalacia.
Previous studies largely neglected this member of the inositol pyrophosphate (PP-InsP) signaling family. However, NIEHS researchers found InsP8 to be the dominant molecule in regulating XPR1, which controls the flow of inorganic phosphate (Pi) through cells. Thus, cellular Pi homeostasis is dependent on InsP8. Before this study, the biological mechanisms of human Pi homeostasis were largely unknown.
The scientists used three novel approaches to describe the human Pi balance. CRISPR-Cas9 was used to identify and create cell lines to show that InsP8 is responsible for the regulation of XPRI. Complementary genetic and pharmacological tools were used to distinguish between InsP8 and InsP7. Finally, the researchers delivered metabolically resistant PP-InsP analogs into the cells using liposomes. These findings could expand the understanding of genetic factors that contribute to bone-related disease. It could also help researchers understand bone maintenance and treat certain genetic disorders, such as ectopic brain calcification. (NU)
Citation: Li X, Gu C, Hostachy S, Sahu S, Wittwer C, Jessen HJ, Fiedler D, Wang H, Shears SB. 2020. Control of XPR1-dependent cellular phosphate efflux by InsP8 is an exemplar for functionally-exclusive inositol pyrophosphate signaling. Proc Natl Acad Sci U S A 117(7):3568–3574.
Toll-like receptor cooperation promotes lung injury
NIEHS scientists discovered that two different receptors, called toll-like receptor 4 and 5 (TLR4 and TLR5), directly interact with each other to worsen lung inflammation during exposure to environmental pollutants.
Immune cells from the lungs and blood of participants in the NIEHS Environmental Polymorphism Registry were stimulated with pollutants, such as ozone and endotoxin, found in house dust. These pollutants activate the TLR4 receptor, and through TLR4, the immune system. Although cells of normal participants, which carried functional TLR4 and TLR5, showed increased inflammatory response against these pollutants, participants with nonfunctional TLR5 exhibited reduced inflammatory signatures in their cells. Similar results were observed when animal models that lacked functional TLR5 were tested with environmental pollutants.
The researchers also showed that TLR5 directly binds with TLR4 inside cellular compartments and helps magnify the inflammatory signals being relayed by TLR4. This previously unidentified synergy between two independent signaling pathways during lung inflammation could help scientists understand the mechanism behind diseases like asthma and help develop rational therapeutic approaches. (PR)
Citation: Hussain S, Johnson CG, Sciurba J, Meng X, Stober VP, Liu C, Cyphert-Daily JM, Bulek K, Qian W, Solis A, Sakamachi Y, Trempus CS, Aloor JJ, Gowdy KM, Foster WM, Hollingsworth JW, Tighe RM, Li X, Fessler MB, Garantziotis S. 2020. TLR5 participates in the TLR4 receptor complex and promotes MyD88-dependent signaling in environmental lung injury. eLife 2020 (9):e50458. (Story)
(Ernie Hood is a contract writer for the NIEHS Office of Communications and Public Liaison. Mimi Huang, Ph.D., is an Intramural Research Training Award [IRTA] fellow in the DNTP Systems Toxicology Group. Prashant Rai, Ph.D., is a visiting fellow in the NIEHS Clinical Investigation of Host Defense Group. Nancy Urbano is an IRTA postbaccalaureate fellow in the DNTP Predictive Toxicology and Screening Group. Janelle Weaver, Ph.D., is a contract writer for the NIEHS Office of Communications and Public Liaison.)