NTP collaboration enhances multiwalled carbon nanotubes research

Inhalation of multiwalled carbon nanotubes (MWCNTs) alters the immune response to dust mite allergens and leaves mice susceptible to airway inflammation and fibrosis, according to a team of NIEHS-funded researchers that included scientists at the National Toxicology Program (NTP), North Carolina State University, and Battelle Biomedical Research Centre. The findings provide new insights into the effects of inhaled MWCNTs on susceptibility to allergic lung disease.

MWCNTs are tiny hollow nanoscale fibers used in a range of industrial and consumer products. As the number of products containing these nanomaterials rises, so do concerns over their potential toxicity. In this study, researchers exposed mice by inhalation to varying concentrations of MWCNTs particles in the air for five days a week over a 30-day period, before exposing them to a dose of house dust mite (HDM) allergens.

The researchers were surprised to find that exposure to MWCNTs dampened several aspects of the immune response to HDM. However, exposure to both substances led to significant lung damage, including lesions around the airways and blood vessels, as well as scarring of lung tissue, which was not seen with either exposure alone. The study highlights the impacts of dose, exposure route, and timing of exposure on the toxicity of carbon nanotubes. (MB)

Citation: Ihrie MD, Taylor-Just AJ, Walker NJ, Stout MD, Gupta A, Richey JS, Hayden BK, Baker GL, Sparrow BR, Duke KS, Bonner JC. 2019. Inhalation exposure to multi-walled carbon nanotubes alters the pulmonary allergic response of mice to house dust mite allergen. Inhal Toxicol 31(5):192–202.

Protein curvature can dictate target specificity

Researchers at NIEHS and the University of Texas at Dallas identified a new mechanism by which proteins conform to select specific RNA targets. All aspects of RNA, including its localization and expression, are tightly regulated for proper cellular functions, such as development. These features are often dysregulated during disease. One mechanism of regulation is through the interactions between RNA-binding proteins and their target RNA. Thus, it is important to understand how RNA-binding proteins select and recognize their targets.

NIEHS researchers identified a stretch of amino acid residues in Lateral Signaling Target 1 (LST-1) that interacts with the PUF protein FBF-2, both of which are required for germline stem cell maintenance. Using crystallography to study the interaction between FBF-2, LST-1, and RNA, the researchers observed that FBF-2 could recognize a shorter RNA motif and that the FBF-2 protein structure was more curved. A high-throughput sequencing strategy, called SEQRS, provided data on RNA-protein interactions. The researchers determined from these data that target selectivity of FBF-2 was altered after binding with LST-1. LST-1 binding decreased the affinity between FBF-2 and RNA, and the identified mRNA targets of FBF-2 were enriched for specific pathways. Together, these data demonstrated a mechanism through which a protein complex can increase the selectivity of an RNA-binding protein to regulate specific regulatory networks. (ML)

Citation: Qiu C, Bhat VD, Rajeev S, Zhang C, Lasley AE, Wine RN, Campbell ZT, Hall TMT. 2019. A crystal structure of a collaborative RNA regulatory complex reveals mechanisms to refine target specificity. eLife; doi: 10.7554/eLife.48968 [Online 9 August 2019].

Pesticide exposure during pregnancy associated with poor fetal growth

In the Generation R Study, a prospective birth cohort in Rotterdam, the Netherlands, NIEHS researchers determined that urinary biomarkers of organophosphate pesticides were associated with decreased fetal weight and length measured during mid-pregnancy, but not at delivery. This study revealed associations between organophosphate pesticides and pregnancy that were not previously examined and helped researchers understand how the environment affects fetal development.

Individuals may be exposed to organophosphate pesticides, which are insecticides with neurotoxic capabilities, through occupational use, proximity to agricultural uses, and diet. The team performed a longitudinal study on more than 700 pregnant women in the Netherlands. The scientists used multiple urine samples to measure markers of exposure to organophosphate pesticides and ultrasound scans to measure fetal growth during early, middle, and late periods of pregnancy.

After finding that organophosphate pesticide exposure led to decreased fetal weight and length, the authors determined that early and mid-pregnancy periods may be the window of vulnerability. These results build upon previous work and suggest that organophosphate pesticide exposure in pregnant women could affect the developing fetus. (SR)

Citation: Ferguson KK, van den Dries MA, Gaillard R, Pronk A, Spaan S, Tiemeier H, Jaddoe VWV. 2019. Organophosphate pesticide exposure in pregnancy in association with ultrasound and delivery measures of fetal growth. Environ Health Perspect 127(8):87005.

Small particles in air pollution associated with epigenetic age

NIEHS researchers and their collaborators found a link between airborne particulate matter (PM) smaller than 2.5 micrometers (PM2.5) and epigenetic age in a nationwide cohort of women. Epigenetic age is the estimated biologic age of a person, as determined by the pattern of methyl groups, a type of chemical tag attached to DNA. Epigenetic age has been associated with a higher risk of chronic disease and mortality. This new research suggests that air pollution may influence epigenetic aging, providing further evidence for a connection between air pollution and chronic disease.

Using the geographical location of each participant’s residence, the scientists estimated exposure to PM2.5 and PM10, or particles less than 10 micrometers, and nitrogen dioxide (NO2). DNA methylation was measured in participants’ blood, and three different epigenetic clocks were used to calculate the epigenetic ages of the women. PM is a complex mixture of different types of particles, with patterns that vary geographically. Although the team found little association with PM10 or NO2, they found that women exposed to PM2.5 containing elements characteristic of soil in the Western U.S. had the greatest increase in biologic age. This research provides additional evidence supporting previously observed associations between air pollution and chronic diseases like breast cancer. (MH)

Citation: White AJ, Kresovich JK, Keller JP, Xu Z, Kaufman JD, Weinberg CR, Taylor JA, Sandler DP. 2019. Air pollution, particulate matter composition and methylation-based biologic age. Environ Int 132:105071.

Pol Mu allows insertion of mutagenic damage during repair

Using X-ray crystallography, NIEHS researchers and their collaborators have determined how polymerase Mu (Pol Mu) interacts with DNA damage caused by ultraviolet (UV) and ionizing radiation. The damage examined in this study is called 8-oxo-7,8-dihydro-2’-guanosine (8OG) and its insertion causes a specific change in DNA structure. The work provides more insight into how DNA damage caused by radiation leads to disease.

Exposure to UV and ionizing radiation causes DNA breaks, and repair of these breaks involves a collection of proteins performing nonhomologous end-joining (NHEJ). Gap-filling polymerases, including Pol Mu, aid in NHEJ. The research team found that Pol Mu accommodates 8OG in its active site, which is different from other gap-filling polymerases. Pol Mu binds 8OG in a specific orientation that encourages placement of an incorrect nucleotide.

To confirm that Pol Mu frequently uses incorrect DNA, the scientists developed a cell-based assay. This assay examined how often a correct nucleotide versus incorrect nucleotide was inserted. When the correct nucleotide was inserted, the DNA was cut by one protein, whereas the incorrect nucleotide was cut by a different protein. The assay determined that Pol Mu often incorporates the incorrect nucleotide, making it likely to play a significant role in diseases caused by exposure to UV and ionizing radiation. (KH)

Citation: Kaminski AM, Chiruvella KK, Ramsden DA, Kunkel TA, Bebenek K, Pedersen LC. 2019. Unexpected behavior of DNA polymerase Mu opposite template 8-oxo-7,8-dihydro-2'-guanosine. Nucleic Acids Res 47(17):9410−9422.