While great strides have been made in understanding the genetics and pathophysiology of AD, mechanisms leading to AD are not fully understood. From our genome wide association studies, and those of others, it is clear that common forms of AD have complex genetic underpinnings with many different genes involved, each likely to have a small effect size. One critical barrier to the study of AD, as in many human disorders, has been the lack of appropriate tissues to study. Brain tissue is available from autopsy cases;however, since it is tissue from end-stage disease, it is not clear if these samples are representative of the processes which lead to AD. Confounding factors in the study of brain autopsy material include the presence of many different cell types, secondary effects due to the presence of AD, presence of co-morbid disease, effects of drugs used to treat AD, and factors related to obtaining fresh material. Because of the large number of genes implicated in AD and their small effect size, a second critical barrier to the murine (or other organism) model systems is the inability to simultaneously introduce all of the relevant genetic factors into a single model system. With these facts in mind, there is a clear need for the development of novel, autologous sources of mature human brain cells/neurons in which the genetic risk factors for AD can be studied. The goal of this proposal is to harness the directed differentiation of induced pluripotent stem (iPS) cells to produce an unlimited supply of neuronal-lineage cells to fulfill this role. Since these cells are from an AD subject, they inherently possess the appropriate genetic risk factors. Ultimately, these cell lines can be used as models of AD in which treatment therapies can be evaluated.
Our aims i nclude the derivation of a novel, in vitro system for the production of an unlimited supply of neuronal-lineage cells from the directed differentiation of clinical grade transgene-free induced pluripotent stem (iPS) cells generated from fibrobasts of AD subjects.
In aim 2, (A) we will test the hypothesis that APP/A2 processing is abnormal in iPS derived neurons and (B) utilize the iPS model system as a discovery tool to identify new pathways relevant to AD by examining the relationship between genetic variation and gene expression patterns. We are uniquely positioned to perform these studies given: a) our published expertise in developing reagents for reprogramming;b) our prior experience in developing protocols for the directed differentiation of embryonic stem (ES) cells;c) our extensive clinical registry of AD subjects seen at the Boston University Alzheimer Disease Center and d) or extensive experience in understanding the genetic underpinnings of AD.
In this study, starting with skin tissue from AD subjects, we will develop an induced pluripotent stem cell - neuron model that accurately represents the genetic complexity that predisposes individuals to AD. We will then use this model to identify novel biochemical pathways important in early stages of AD. In the future, these models can be used in the discovery of new therapeutics that may be used to modulate disease severity or may also lead to the development of regenerative medicine approaches to the treatment of AD.