|
POSTDOCTORAL FELLOWSHIP.
Multipotent stem cells exist throughout the body and maintain the health of a given tissue by replenishing cells lost or damaged throughout life. These unique cells retain the capability to proliferate, migrate and differentiate to return functionality to a tissue compromised by age, disease or a variety of genotoxic/cytotoxic stressors such as ionizing radiation.
Our laboratory has accumulated a wealth of data showing that relatively low doses of radiation found in space, such as protons and heavy ions, can compromise the function of specific tissues and organs through a variety of biochemical mechanisms that involve oxidative stress. While the details vary, oxidative stress that persists after irradiation has been shown to reduce bone density, impair muscle regrowth and inhibit neurogenesis. These acute, functional decrements could severely compromise the capability of astronauts to complete mission-critical tasks, where accelerated muscle fatigue and confusion caused by muscle and neural stem cell loss could result from relatively mild exposures to the space radiation environment. Each of these debilitating conditions can, in part, be caused by radiation-induced oxidative stress, a condition we have shown to adversely impact the function of tissue-specific stem cell populations. Our data reinforces the importance of these multipotent cells and suggests they represent critical targets for countermeasures aimed at ameliorating radiation and spaceflight-related sequelae.
To expand on our past space-related research, we propose in vitro and in vivo experiments to determine if/how relatively low doses of protons can initiate radioadaptive changes in stem cells found in the brain and skeletal muscle. Our proposal will evaluate how low dose proton exposure will impact stem cell proliferation, differentiation and survival and whether such endpoints can be altered by prior exposure. We hypothesize that stem cells incurring particle traversals during spaceflight can undergo adaptive changes that attenuate their response to subsequent larger exposures (e.g. from a solar flare). We will also investigate whether the mechanistic basis of adaptation involves changes in the redox environment such as oxidative stress.
Specific Aims:
To determine if/how low dose proton irradiation elicits radioadaptive changes in neural precursor cells from the central nervous system that depend on oxidative stress.
To determine the acute dose response of satellite cells to proton irradiation with respect to survival, phenotypic fate and oxidative stress.
Elucidate how low dose irradiation impacts neurogenesis in mice expressing human catalase targeted to the mitochondria.
In aims 1 and 2, a range of biochemical, oxidative and immunohistochemical approaches will be used that involve the quantification of reactive oxygen and nitrogen species and the detection of oxidative damage in neural precursor and satellite cells. Fluorogenic dyes will be used in conjunction with fluorescent activated cell cytometer/sorter analysis, and damage-specific antibodies will be used for immunostaining of irradiated cells to detect and measure oxidative stress. Similar approaches will be used to determine the role of the mitochondria in oxidative processes and how such stress impacts differentiation of these multipotent cells. Lastly, we will utilize mice genetically modified to minimize mitochondrial hydrogen peroxide to determine how reducing intracellular oxidants impacts neurogenesis. Dual staining immunohistochemistry will be used to quantify the numbers of differentiated cell types in tissue sections derived from irradiated animals labeled with bromodeoxyuridine as a marker for proliferation. Completion of these studies will help establish whether adaptation occurs after low dose proton irradiation, and whether stem cells and oxidative stress represent logical targets for countermeasure strategies. |
Developed and operated by: NASA Research and Education Support Services
