Approaches to repair the injured brain or even prevent age-related neurodegeneration are in their infancy but there is growing interest in the role of neural stem cells in these conditions. Indeed, there is hope that some day stem cells can be used for the treatment of spinal cord injury, stroke, or Parkinson’s disease and stem cells are even mentioned in the public with respect to Alzheimer’s disease. To utilize stem cells for these conditions and, equally important to avoid potential adverse events in premature clinical trials, we need to understand the environment that supports and controls neural stem cell survival, proliferation, and functional integration into the brain. This “neurogenic” environment is controlled by local cues in the neurogenic niche, by cell-intrinsic factors, and by soluble factors which can act as mitogens or inhibitory factors potentially over longer distances. While some of these factors are starting to be identified very little is known why neurogenesis decreases so dramatically with age and what factors might mediate these changes. Because exercise or diet can increase stem cell activity even in old animals and lead to the formation of new neurons there is hope that neurogenesis in the aged brain could be restored to that seen in younger brains and that stem cell transplants could survive in an old brain given the right “young” environmental factors. Indeed, our preliminary data demonstrate that systemic factors circulating in the blood are potent regulators of neurogenesis. By studying how the most promising of these factors influence key aspects of the neurogenic niche in vitro and in vivo we hope to gain an understanding about the molecular interactions that support stem cell activity and the generation of new neurons in the brain. The experiments supported under this grant will help us to identify and understand the minimal signals required to regulate adult neurogenesis. These findings could be highly significant for human health and biomedical applications if they ultimately allow us to stimulate neurogenesis in a controlled way to repair, augment, or replace neural networks that are damaged or lost due to injury and degeneration.
Statement of Benefit to California:
In California there are hundreds of thousands of elderly individuals with age-related debilitating brain injuries, ranging from stroke to Alzheimer’s and Parkinson’s disease. Approaches to repair the injured brain or even prevent age-related neurodegeneration are in their infancy but there is growing interest in the role of neural stem cells in these conditions. However, to potentially utilize such stem cells we need to understand the basic mechanisms that control their activity in the aging brain. The proposed research will start to address this problem using a novel and innovative approach and characterize protein factors in blood that regulate stem cell activity in the old brain. Such factors could be used in the future to support stem cell transplants into the brain or to increase the activity of the brain’s own stem cells.
Year 1We are interested in identifying soluble protein factors in blood which can either promote or inhibit stem cell activity in the brain. Through a previous aging study and the transfer of blood from young to old mice and vice versa we had identified several proteins which correlated with reduced stem cell function and neurogenesis in young mice exposed to old blood. Over the past year we studied two factors, CCL11/eotaxin and beta2-microglobulin in more detail in tissue culture and in mice. We could demonstrate that both factors administered into the systemic environment of mice reduce neurogenesis in a brain region involved in learning and memory. We have also begun to test the effect of these factors on human neural stem cells and we started experiments to try to identify protein factors which can enhance neurogenesis.
Year 2While age-related cognitive dysfunction and dementia in humans are clearly distinct entities and affect different brain regions, the aging brain shows the telltale molecular and cellular changes that characterize most neurodegenerative diseases. Remarkably, the aging brain remains plastic and exercise or dietary changes can increase cognitive function in humans and animals, with animal brains showing a reversal of some of the aforementioned biological changes associated with aging. We showed recently that blood-borne factors coming outside the brain can inhibit or promote adult neurogenesis in an age-dependent fashion in mice. Accordingly, exposing an old mouse to a young systemic environment or to plasma from young mice increased neurogenesis, synaptic plasticity, and improved contextual fear conditioning and spatial learning and memory. Preliminary proteomic studies show several proteins with stem cell activity increase in old “rejuvenated” mice supporting the notion that young blood may contain increased levels of beneficial factors with regenerative capacity. We believe we have identified some of these factors now and tested them on cultured mouse and human neural stem cell derived cells. Preliminary data suggest that these factors have beneficial effects and we will test whether these effects hold true in living mice.
Year 3Cognitive function in humans declines in essentially all domains starting around age 50-60 and neurodegeneration and Alzheimer’s disease seems to be inevitable in all but a few who survive to very old age. Mice with a fraction of the human lifespan show similar cognitive deterioration indicating that specific biological processes rather than time alone are responsible for brain aging. While age-related cognitive dysfunction and dementia in humans are clearly distinct entities the aging brain shows the telltale molecular and cellular changes that characterize most neurodegenerative diseases including synaptic loss, dysfunctional autophagy, increased inflammation, and protein aggregation. Remarkably, the aging brain remains plastic and exercise or dietary changes can increase cognitive function in humans and animals. Using heterochronic parabiosis or systemic application of plasma we showed recently that blood-borne factors present in the systemic milieu can rejuvenate brains of old mice. Accordingly, exposing an old mouse to a young systemic environment or to plasma from young mice increased neurogenesis, synaptic plasticity, and improved contextual fear conditioning and spatial learning and memory. Unbiased genome-wide transcriptome studies from our lab show that hippocampi from old “rejuvenated” mice display increased expression of a synaptic plasticity network which includes increases in c-fos, egr-1, and several ion channels. In our most recent studies, plasma from young but not old humans reduced neuroinflammation in brains of immunodeficient mice (these mice allow us to avoid an immune response against human plasma). Together, these studies lend strong support to the existence of factors with beneficial, “rejuvenating” activity in young plasma and they offer the opportunity to try to identify such factors.