Biological Functions of Neural Stem Cells in the Adult Forebrain
The discovery of stem cells in developing and adult tissue has provided renewed hope for the development of cell replacement therapies to treat neurodegenerative disorders and their is emerging evidence that these cells play a role in psychiatric disorders. Neural stem cells (NSCs) remain active throughout the lifespan with particularly high levels of cell production during puberty and early adulthood. Currently, a number of potential stem cell-related strategies are undergoing preclinical evaluation in order to move such treatments in clinical trial. However, our understanding of the regulation and biological function of endogenous NSCs in the adult nervous system remains limited which may hamper efforts to employ NSCs therapeutically.
The present proposal will seek to shed light on the function of these cells by selectively ablating NSCs during pubertal development or adulthood and determining the consequent changes in behavior, neurochemistry and endocrine function. Converging evidence from my laboratory and others provides support for the hypothesis the ability of NSCs to generate new neurons and glia in the adult brain is related to vulnerability to psychoses. The ability of NSC ablation to mimic the behavioral symptoms of animal models of psychoses will be assessed and it is predicted that loss of NSCs will increase indices of psychoses and produce alteration in neurochemical and hormonal responsiveness that resemble those observed in schizophrenia. Further, NSCs respond to damage including neurodegeneration by increasing their proliferation to increase the available pool of progenitors, yet the consequences of this response is unknown. Although NSCs do not spontaneously exhibit the ability to repair brain damage, it is predicted that their response to damage plays an important role in preventing subsequent neuronal loss.
We have also observed that the in vivo proliferation characteristics of NSCs are altered under a variety of experimental conditions and that in some of these conditions there is reprogramming of the NSC such that the altered characteristics are maintained in vitro. We will explore the molecular bases of two reprogramming events, one which increases and the other which decreases NSC self-renewal characteristics. This novel approach to understanding the regulatory mechanisms governing NSCs is likely to lead to an increased comprehension of NSC regulation in a number of ways, including elucidating novel microRNAs and chromatin changes that modulate the properties of NSCs and these mechanisms should lead to improved application of NSCs to treating nervous system disorders.
Nervous system disorders, ranging from idiopathic neurodegeration to trauma or stroke to neuropsychiatric conditions such as schizophrenia, account for an ever increasing portion of medical costs. For most of these syndromes there are limited treatments and essentially no cures. Cell replacement therapy offers an avenue of tremendous potential for the future of regenerative medicine because restoration of lost neurons could lead to functional recovery, however, understanding the ability of neural stem cells (NSCs) to control cell turnover in the developing and adult brain is critical to harnessing their potential. Further, there are several lines of evidence implicating NSCs in a variety of neuropsychiatric disorders, however, the existing evidence is almost exclusively indirect or correlational. The present proposal is designed to solidify our understanding of the biological function of NSCs.
Characterization of adult NSCs will provide not only the potential opportunity for generating large amounts of cells for widespread grafting but also a more complete understanding of the tremendous plasticity that is central to brain function. To this end, the present proposal will conduct preclinical trials using a mouse model that allows selective ablation of the NSC population. I will investigate the functional consequences of NSC loss on a variety of indices of psychoses in a rodent models. I will also determine the importance of the burst of NSC activity during puberty to reproductive maturation. Further, I will selectively remove NSCs prior to the onset of HD symptoms in an mouse model to determine the functional consequences of damage-induced NSCs recruitment. In addition, we have observed a number of circumstances in which NSCs properties are permanently altered by environmental factors and that these changes are evident in a tissue culture environment. I will extend the analyses of this "reprogramming" and determine its molecular bases using high throughput analyses of gene expression, including microRNA and chromatin remodelling.
Accordingly, the proposed research will initiate steps towards fulfilling the hope that stem cells will be able to treat nervous system disorders by increasing our understanding of the function and molecular regulation of these cells. As such, creating new strategies to develop therapeutic avenues for the management of psychiatric and neurological disease will be of direct benefit to the citizens of California as well as reducing the associated long-term health costs. Further, the proposed research will increase the stem cell research in the state and provide training and employment to future researchers.