Papers of the Month
By Kathleen Foley, Virginia Guidry, Stephani Kim, Payel Sil, and Andrew Trexler
NTP finds high exposure to RFR linked to cancer in male rats
The National Toxicology Program (NTP) has released its final reports from studies of rats and mice exposed to high levels of radio frequency radiation (RFR) like that used in 2G and 3G cell phones. NTP found clear evidence that exposed male rats developed cancerous heart tumors and some evidence that exposed male rats developed tumors in the brain and adrenal glands.
For female rats, and male and female mice, the researchers saw equivocal, or uncertain, evidence of associations between exposure to RFR and cancer. The final reports represent the consensus of NTP and an external expert panel who reviewed the studies in March.
The researchers said the results cannot be directly extrapolated to humans, but still provide important information about RFR, previously assumed by many to be safe. The animals received RFR across their whole bodies at levels and durations greater than what people typically experience. They were housed in chambers specifically built for these studies and were exposed intermittently, 10 minutes on and 10 minutes off, for a total of about nine hours a day for most of their natural lifetime. Additional studies are being planned. (VG)
Citation: National Toxicology Program. 2018. Toxicology and carcinogenesis studies in Hsd:Sprague Dawley SD rats exposed to whole-body radio frequency radiation at a frequency (900 MHz) and modulations (GSM and CDMA) used by cell phones. TR 595. Research Triangle Park, NC: National Toxicology Program.NTP. 2018. Toxicology and carcinogenesis studies in B6C3F1/N mice exposed to whole-body radio frequency radiation at a frequency (1,900 MHz) and modulations (GSM and CDMA) used by cell phones. TR 596. Research Triangle Park, NC: National Toxicology Program.
Researchers identify protein necessary for pregnancy
A team led by NIEHS researchers found that SOX17 protein may be necessary for successful pregnancy. SOX17 mediates the activity of progesterone, the hormone responsible for regulating embryo implantation in the uterus. It was also shown to effect leukemia inhibitory factor (LIF) and Indian hedgehog homolog (IHH) signaling, two proteins implicated in establishing pregnancy. This new understanding of the genetic regulation of embryo implantation may help those who struggle with infertility.
The scientists used two infertile mice models for the first experiment. One model lacked SOX17 in cells that contained progesterone receptors, whereas the other lacked SOX17 in the uterine epithelium, the part of the uterus that first encounters a fertilized egg. Expression of LIF was significantly reduced in both models, which suggests SOX17 regulates LIF expression. For the second experiment, the team used CRISPR-Cas9 to remove the SOX17 binding region of IHH. Doing so resulted in significantly lower IHH expression in mice that lacked the SOX17 binding region compared with those with the binding region. The finding indicated that SOX17 has a significant role in regulating IHH expression. Because many pregnancy failures are due to embryo implantation failure, the research suggests some miscarriages may occur because of a SOX17 defect. (KF)
Citation: Wang X, Li X, Wang T, Wu S-P, Jeong J-W, Kim TH, Young SL, Lessey BA, Lanz RB, Lydon JP, DeMayo FJ. 2018. SOX17 regulates uterine epithelial-stromal cross-talk acting via a distal enhancer upstream of Ihh. Nat Commun 9(1):4421. (Story)
A novel biomarker for acute respiratory distress syndrome
NIEHS researchers and their collaborators have identified cholestenoic acid (CA) as a novel biomarker for acute respiratory distress syndrome (ARDS), a life-threatening respiratory condition characterized by tissue damage and fluid buildup in the lungs. ARDS has a high mortality rate of 30-40 percent, and only a few lung biomarkers, or measurable substances in the body that indicate disease, have been validated. None of these biomarkers are routinely used in clinical practice.
CA is produced in the lungs by alveolar macrophages, and previous studies determined that plasma CA levels decrease after surgical removal of the lung. The researchers hypothesized that plasma CA levels would decrease as the severity of ARDS increased in patients. Team members measured plasma CA levels in ARDS patients participating in a trial conducted by the National Heart, Lung, and Blood Institute. They found that patients with lower CA levels experienced increased 90-day mortality, decreased ventilator-free days, and decreased days without organ failure.
The researchers suggest CA could be a novel biomarker for ARDS and be applicable to patients with a range of lung diseases, but more studies are needed. (SK)
Citation: Madenspacher JH, Stapleton RD, Suratt BT, Dixon AE, Lih FB, Lowe JM, Mould KJ, Janssen WJ, Morrell ED, Wurfel MM, Garantziotis S, Tomer KB, Fessler MB. 2018. Cholestenoic acid is a prognostic biomarker in acute respiratory distress syndrome. J Allergy Clin Immunol; doi: 10.1016/j.jaci.2018.09.017 [Online 5 October 2018].
Two calcium channels support development of fertilized eggs
The TRPM7 and CaV3.2 ion channels play an essential role in egg activation during fertilization, according to NIEHS researchers and their collaborators. Because calcium (Ca2plus) uptake is required for successful embryo development, the findings have important implications for in vitro fertilization (IVF).
Before fertilization, eggs from all animal species, including humans, accumulate Ca2plus using several different ion channels. Once sperm-egg fusion occurs, Ca2plus oscillations begin to activate embryo development. These oscillations cause Ca2plus to leave the egg by crossing the egg membrane, but it also re-enters the egg. Ca2plus re-entry is needed so that the oscillations can continue and is made possible by CaV3.2 and TRPM7. TRPM7 transports both Ca2plus and magnesium ions (Mg2plus), but is inhibited by high levels of Mg2plus.
Using CaV3.2 and TRPM7 knockout mice, the researchers found that missing TRPM7 alters Ca2plus oscillations and leads to abnormal development, whereas the loss of both TRPM7 and CaV3.2 leads to premature stoppage of Ca2plus oscillations and impaired fertility.
These findings show that TRPM7 and CaV3.2 Ca2plus uptake is required for Ca2plus signaling and successful embryo development. The study also suggests that the wide range of Mg2plus/Ca2plus ratios in IVF media could inhibit TRPM7 and decrease the success of fertility treatments. (AT)
Citation: Bernhardt ML, Stein P, Carvacho I, Krapp C, Ardestani G, Mehregan A, Umbach DM, Bartolomei MS, Fissore RA, Williams CJ. 2018. TRPM7 and CaV3.2 channels mediate Ca2plus influx required for egg activation at fertilization. Proc Natl Acad Sci U S A 115(44):E10370−E10378.
Imaging reveals DNA wrapping around mitochondrial protein
A collaboration between scientists at NIEHS and North Carolina State University demonstrated that mitochondrial single-stranded DNA binding proteins (mtSSBs) may not always protect single-stranded replication intermediates, which results in improper maintenance of mitochondrial DNA (mtDNA) and metabolic diseases.
During DNA replication, DNA strands are separated and become more vulnerable to nuclease attack, chemical modifications, and the binding of inappropriate proteins. Single-stranded DNA binding proteins (SSBs) are believed to safeguard the integrity of mtDNA, protecting it from degradation. The researchers used a recently developed atomic force microscopy (AFM) imaging technique, called Dual-Resonance-frequency-Enhanced Electrostatic force Microscopy (DREEM), to measure surface electric potential differences across mtSSB-DNA complexes. Their results showed that the non-cooperative wrapping of ssDNA around SSBs during replication could leave the mitochondrial genome vulnerable.
Human mtSSB and Escherichia coli-SSB share significant sequence and structural homology, with the key difference that the former lacks a C-terminal tail. Both form SSB-ssDNA complexes. However, DREEM imaging has revealed that the E. coli-SSB-ssDNA complexes adopt a more compact DNA binding mode than human mtSSB-DNA complexes.
DREEM shows promise as a powerful tool to study the interaction between DNA and replication proteins, which could aid in intercepting defective mtDNA replication as identified in patients. (PS)
Citation: Kaur P, Longley MJ, Pan H, Wang H, Copeland WC. 2018. Single-molecule DREEM imaging reveals DNA wrapping around human mitochondrial single-stranded DNA binding protein. Nucleic Acids Res 46(21):11287–11302.
(Kathleen Foley is an Intramural Research Training Award (IRTA) postbaccalaureate fellow in the NIEHS Receptor Biology Group. Virginia Guidry, Ph.D., is a technical writer and public information specialist in the NIEHS Office of Communications and Public Liaison, and a regular contributor to the Environmental Factor. Stephani Kim, Ph.D., is an IRTA fellow in the NIEHS Perinatal and Early Life Epidemiology Group. Payel Sil, Ph.D., is an IRTA fellow in the NIEHS Inflammation and Autoimmunity Group. Andrew Trexler is a postbaccalaureate research fellow in the National Cancer Institute Center for Cancer Research Laboratory of Toxicology and Toxicokinetics, housed at NIEHS.)