Alzheimer's disease (AD), a late-onset disease manifests impairment and loss of neurons over years before the onset of clinical symptoms such as, learning and memory loss. Studies suggest that the brain attempts to replace these nerve cells throughout the course of the disease with new cells, but results are insufficient. It may be that not enough new cells are generated, or that they die due to the disease process itself, and prior to restoration of function. In AD, a major factor of the disease is production of a toxic molecule, the A-beta peptide. We plan to test if this molecule stimulates new nerve cell production, but also eventually is toxic to those cells as they develop more neuron-like functions. As these cells move into the diseased area of the brain, they must assume contact with other existing nerve cells that are essential for memory and learning functions. This step may also not occur in a normal way in AD. Because we cannot test for these activities in the AD-affected patients, and because animal or tissue culture models are inadequate, we propose to use human embryonic stem cells (hESCs) that have been treated to become neural stem cells (NSCs) and expose them to the toxic A-beta peptide and determine if they both increase in numbers and then become more fully like neurons in the brain. This latter function include migration of the new neurons moving towards normal nerve cells that have been previously damaged, for example, exposure to the toxic A-beta peptide. These studies will provide some important information on the ultimate possibility of stem cell replacement of neurons loss during the disease course.
Statement of Benefit to California:
Alzheimer's disease, a progressive neurological process leading to dementia is devastating to the patient and family. The average duration of disease is 8 years, and is both costly for families and the community, and labor intensive for the caregivers. Our preliminary studies indicate that process of new nerve cell generation is attempted by the brain itself, but insufficient. Possibility of embryonic stem cell biology offers the ultimate possibility of replacement of lost or impaired nerve cells. This proposal attempts to understanding how this replacement can occur and allow the patient to maintain normal function, especially of memory and cognition sufficient for activities of daily living.
Defining critical, several steps in neurogenesis can be best accomplished with hESCs. Exposing these cells to the toxic molecule A-beta provides a means to define if the cells become neurons and are maintained or lost due to the A-beta effect itself. If the latter is true, than drugs to block this later step could be tested on these cells. If these cells fail to replace the lost nerve cells, and connect up with remaining cells, then research targeted to promote their integration should be pursued. All of these studies lead to the ultimate goal of repairing the brain and halting the neuron loss or decreasing the rate of loss and the functional decline of the patient.
SYNOPSIS: This applicant proposes to assess several hypotheses using hESCs. First, they will determine whether soluble A-beta protein stimulates neurogenesis and not gliogenesis of hESCs. Second, they will determine whether A-beta protein is toxic to the cells. Third, they will investigate whether neural stem cells and neural progenitor cells migrate to regions of impaired or dead neurons, including those induced by A-beta, to test the hypothesis that cell death is required to stimulate neurogenesis, differentiation, and targeted migration.
INNOVATION AND SIGNIFICANCE: The preliminary data are not strong enough, rigorous enough, or motivating enough for the significance to really be assessed; unfortunately, those are the data on which the entire proposal rests. The lack of rigor and critical nature regarding those early data bode poorly for the proposed directions.
STRENGTHS: This is a very focused set of experiments intended to assess the effects of soluble A-beta on human ESCs, whether or not they induce migration of hESCs-drived neural stem cells (NSC) and neural progenitor cells (NPC), and the extent to which cell death is required to stimulate neurogenesis. Most of the studies will be done in culture, using SH-SY5Y tumor cells, and observing migration of hNSCs and hNPCs derived from hESCs, whether A-beta is toxic to these cells, and then to assess whether A-beta induced cell death is required for migration and neurogenesis. The applicant is a very experienced and productive investigator who is well-aware of the pitfalls of the experimental methods proposed.
WEAKNESSES: Data is not strong enough to support the motivating hypothesis that A-beta really leads to modifications of neurogenesis of note. The analyses shown are not critical enough or at the state-of-the-art level to avoid going down totally misleading paths. In addition, the PI has no previous experience with hESCs. However, this should not be a significant problem because the PI is working closely with other investigators such as Martin Pera and Leslie Weiner who will provide the PI with GFP-tagged hESCs.
DISCUSSION: There was no further discussion following the reviewers' comments.