This announcement describes a post-doctoral fellowship opportunity to work with scientists in the Radiation Biophysics Laboratory at NASA Johnson Space Center (JSC) and at University of Houston Clear Lake.

Project Background

Space radiation is undoubtedly a major health concern for astronauts during cosmic missions especially for long-term interplanetary flights. The radiation environment in space is a complex mix of many different types of ionizing and nonionizing radiation. The space radiation environment can be resolved into three broad categories. These categories are trapped particle radiation, solar particle radiation and galactic cosmic radiation (GCR). Approximately 87% of the particles in the GCR spectrum are protons, 12% are helium nuclei and 1% are particles heavier than helium, often referred to as high-Z and high-energy (HZE) particles.  The heaviest biologically important of these HZE particles is iron because of its relatively large contribution to radiation dose and high LET. Understanding the extent and pattern of DNA damage induced by such particles in human cells is of primary importance for determining the associated biological risks and consequently successful space exploration.

Currently, the only major protection available to astronauts from space radiation is the shielding material of the space vehicle. Effective shielding of personnel and equipment from HZE particles (especially in the GCR spectrum) is a difficult task. Unlike low-LET gamma or X-rays, the presence of shielding does not always reduce the radiation risks for energetic charged particle exposure. Heavy charged particles passing through shielding material will result in an energy loss of the particles as a function of their residual range with the peak energy loss occurring as particles reach the end of their range at which point the highest dose is delivered in the traversed material. This fragmentation modifies the quality of the incident beam and results in a Bragg curve distribution consisting of a mixed radiation field including primary particles and secondary fragments. During traversal of human cells by heavy ion particles, energy deposited depends principally upon inelastic collision cross sections for the interaction of electrons with molecules, with some cells being traversed by the primary particles, others by secondary delta rays and/or no traversal at all. With regard to spaceflight, these varying track structures can arise when primary high LET particles in space interact with spacecraft-shielding material and the human body resulting in secondary radiation like neutrons and charged particles. To this effect, biophysical models are commonly used for evaluating the effectiveness of shielding in reducing biological damage and consequently designing spacecraft shielding. However, it is increasingly being acknowledged that biological measurements are urgently needed to validate the predictions resulting from these codes.

To date, studies involving the effects of shielding on radiation-induced biological outcomes have been few and far between. The US National Academy of Sciences has determined that research on shielding composition and thickness using biological measurements should be a high priority for optimizing space radiation protection during deep space missions. In order to address this issue, a large international collaboration was initiated in 1999 to study the influence shielding on the induction of chromosomal aberrations in human peripheral blood lymphocytes exposed in vitro to accelerated heavy ions.   Some experiments aimed at studying the influence of shielding on biological effectiveness of high-energy iron (Fe) ions have been reported. Dose response curves for total chromosomal exchanges in blood lymphocytes placed behind shielding material indicate that biological effects are determined by both physical beam transport through the targets and the biological effectiveness of the mixed charged-particle radiation field, following a complex pattern that cannot be described by LET alone. However, little is known about the response using other biological end-points and more importantly, the response occurring across a Bragg curve distribution of high LET radiation has been largely unclear. This may largely be due to a lack of suitable experimental designs that would allow the study of such phenomena with sufficient feasibility. Ground based studies to investigate such matters would require a Bragg curve exposure of a continuous layer of biological sample within the radiation field and furthermore would necessitate the analysis of a biological end-point directly in real-time across this distribution without compromising positional status of the cells.

We thus initiated a project to design just such an experimental scheme which would allow us to study the biological effects occurring across a Bragg curve distribution with a suitable biological end-point that would facilitate real-time analysis with sufficient resolution. Here we propose an experimental model that allows the investigation of the biological response across the Bragg curve in one consistent biological system with a resolution less then 1 mm around the Bragg peak. This system would include a biological model in which adherent cells are cultured in slide chamber flasks that allow direct on-slide biological analysis thus fixing the cellular positions with coincident localization. Using an irradiation geometry in which an iron beam is parallel to a monolayer of cells and combined polyethylene (PE) shielding we irradiated human fibroblast cells with heavy iron ions to achieve a Bragg curve distribution across an incessant layer of cells in vitro. This preliminary experimentation has already allowed us to qualitatively and quantitatively assess the genetic damage across the Bragg curve using suitable biological end-points including, ?-H2AX fluorescent distributions and micronuclei induction, respectively.

For this project, our goal is to use the induction of micronuclei as our biomarker of choice for generating the intended biological Bragg curves, resulting in data analyses that will facilitate a highly desirable resolution of 1 mm across the Bragg distribution. The micronucleus assay is one of the most commonly used methods for measuring DNA damage rates in human populations and has been successfully applied in many ground-based space radiation studies. It is a reliable measure of chromosomal deletions occurring at the genomic level in cells exposed to radiation and is of suitable relevance to health risks especially since numerous malignant growths, such as bladder adenocarcinoma and glioma, have been attributed to various chromosomal deletions. The segregation of such genetic material can be detected in vitro by quantitative assessment of micronuclei frequency in binucleated cells. Some associations, to a certain degree, have already been established for increased micronuclei frequencies in the blood lymphocytes of cancer patients and occupational exposure of workers to radiation and other genotoxic agents. In ground-based studies, a significantly increased induction of micronuclei has been observed in the tracheal and the deep lung epithelial cells of HZE irradiated wistar rats than those exposed to low LET gamma irradiation. Additionally, structured energy deposition from the tracks of primary protons and the associated high-LET secondary particles produced in targets has been attributed to the DNA damage differences (as measured by micronuclei) in epithelial cells.   It is well known that HZE-irradiation induces bystander effects in non-hit cells, and micronucleus formation has been observed in bystander cells from cultures of human cells exposed to low fluences of alpha-particles. Together, these findings validate the reliability of the MN assay in measuring HZE irradiation-induced biological damage, and substantiates its use as a biological end-point in our proposed project.

Post-Doctoral Fellow’s Role

The fellow is expected to conduct experiments that address the objectives of the proposed study. S/he will participate in all aspects of the project, including experimental design, data analysis and manuscript preparation. Limited travel to Brookhaven National Laboratory is expected to expose the samples to energetic charged particles at the NASA Space Radiation Laboratory.

JSC Resources to be made available

The post-doctoral fellow will be able to routinely work at Johnson Space Center. S/he will have access to the tissue culture facility and microscopes in the Radiation Biophysics Laboratory and facilities in other JSC laboratories.

Desired Background of Fellowship Applicants

A Ph.D. in biology or nuclear engineering/physics is desired. The positions will suit individuals with a background in mammalian cell culture, and with skills in fluorescence microscopy. Prior experience in radiation exposure is also desired.

Point of Contact

Dr. Larry Rohde
Division of Natural Science
University of Houston-Clear Lake
2700 Bay Area Blvd.
Houston, TX 77058
Phone: 281-283-3743
E-mail: rohde@uhcl.edu 9.5pt;color:fuchsia">

Dr. Honglu Wu
Human Adaptation and Countermeasures Division
NASA Johnson Space Center
Houston, TX  77058
Phone: 281-483-6470
E-mail: honglu.wu-1@nasa.gov

PI Biographies

Larry Rohde, Ph.D.

Education

1984            Biology, Tarleton State University, Texas A&M System

1986             M.S. in Teaching, Biology, Tarleton State University, Texas A&M System

1995             Ph.D., Biomedical Research, University of Texas Health Science Center, Houston

1995-1999   Postdoctoral Study, Stanford University School of Medicine

Current position

Associate Professor of Biology      University of Houston-Clear Lake, Division of Natural Sciences, School of Natural and Applied Sciences

Recent Publications

1. Rohde LH, Ao Y and Naumovski L. p53-Interacting Protein 53BP2 Inhibits Clonogenic Survival and Sensitizes Cells to Doxorubicin but not Paclitaxel-induced Apoptosis. Oncogene (2001) 20:2720-2725.
2. Lopez C, Ao Y, Rohde LH, Perez T., O’Conner D., Lu X., Ford J.M. and Naumovski L. Proapoptotic p53-Interacting Protein 53BP2 Is Induced by UV Irradiation but Suppressed by p53. Molecular and Cellular Biology, 2000; 20:8018-8025.
3. Rohde LH, Janatpour MJ, McMaster MT, Fisher SJ, Zhou Y, Lim K-H, French M, Hoke D. Julian J and Carson DD.  Complimentary Expression of Heparin/Heparan Sulfate Interacting Protein and Perlecan at the Human Fetal-Maternal Interface.  Biol.  Reproduction 1998;   58:1075-1083.
4. Rohde LH, Julian J, Babaknia A and Carson DD.  Cell surface expression of HIP, a novel heparin/heparan sulfate binding protein, of human uterine epithelial cells and cell lines.  J. Biol. Chem. 1996;  271:11824-11830.

Honglu Wu, Ph.D.

Education

1982     Physics, Peking University

1986     M.S. Physics, Michigan State University

1990     Ph.D. Physics, University of New Mexico

Current positions

Radiobiologist and Laboratory Manager, Radiation Biophysics Laboratory, Human Adaptation and Countermeasures Office, NASA Johnson Space Center, Houston, Texas

Recent publications

1. H. Wu, M. Hada, J. Meador, X. Hu, A. Rusek and F. A. Cucinotta, Induction of micronuclei across the Bragg curve of energetic heavy ions. Radiation Research (2006) To be published.
2. N. Desai, E. Davis, P. O’Neill, M. Durante, F. A. Cucinotta and H. Wu, Immunofluorescent Detection of DNA Double Strand Breaks Induced by High-LET irradiation. Radiat. Res. 164, 518-522 (2005).
3. N. Desai, M. Durante, Z. W. Lin, F. Cucinotta and H. Wu, High LET-induced H2AX phosphorylation around the Bragg curve, Adv. Space Res. 35, 236-242 (2005).
4. N. Desai, H. Wu, K. George, S. Gonda and F. A. Cucinotta, Developmental assays for simultaneous measurement of multiple radiation induced protein expression profiles using the Luminex system. Adv. Space Res. 34, 1362-1367 (2004).
5. H. Wu, M. Durante, Y. Furusawa, K. George, T. Kawata and F. A. Cucinotta, Truly incomplete and complex chromosomal exchanges in human fibroblasts exposed to energetic heavy ions in vitro. Radiat. Res. 160, 418-424 (2003).
6. H. Wu, M. Durante, Y. Furusawa, K. George, T. Kawata and F. A. Cucinotta, mFISH analysis of chromosome aberrations in human fibroblasts exposed to energetic iron ions in vitro. Adv. Space Res. 31, 1537-1542 (2003).
7. H. Wu, Y. Furusawa, K. George, T. Kawata and F. A. Cucinotta, Analysis of Unrejoined chromosomal breakage in human fibroblast cells exposed to low- and high-LET radiation. J. Radiat. Res. 43, S181-185 (2002).
8. M. Durante, K. George, H. Wu and F. A. Cucinotta, Karyotypes of human lymphocytes exposed to high-energy iron ions. Radiat. Res. 158, 581-590 (2002).
9. H. Wu, Radiation-induced inter/intra-chromosomal exchange probabilities and their dependence on DNA content of the chromosome. Radiat. Res. 156, 603-606 (2001).
10. S. R. Gonda, H. Wu, P. L. Pingerelli and B. W. Glickman, Three-dimensional transgenic cell model to quantify genotoxic effects of space environment. Adv. Space Res. 27, 421-430 (2001).
11. H. Wu, M. Durante and J. N. Lucas, Relationship between radiation-induced aberrations in individual chromosomes and their DNA content: Effects of interaction distance. Int. J. Radiat. Biol. 77, 781-786 (2001).
12. H. Wu and M. Durante, A biophysical model for estimating the frequency of radiation-induced mutations resulting from chromosomal translocations, Adv.  Space Res. 27, 361-367 (2001).
13. K. George, H. Wu, V. Willingham, Y. Furusawa, T. Kawata and F. A. Cucinotta, High- and low-LET induced chromosome damage in human lymphocytes: a time-course of aberrations in metaphase and interphase. Int. J. Radiat. Biol. 77, 175-183 (2001).

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