Alzheimer?s disease (AD) is the leading cause of neurodegenerative disorders with over 5 million cases in the U.S. This represents one of the most compelling health-related burdens facing our society in the near future. Current approved therapies for AD include cholinesterase inhibitors to prevent the degradation of the neurotransmitter acetylcholine, although they have modest benefit and are effective only during the early stages of the disease process. The progressive dysfunction of the limbic system and loss of neurons in these regions of the brain are responsible for the dramatic cognitive decline seen in this disease. Loss of cholinergic neurons in the medial septal nucleus (MSN) and the nucleus basalis are observed in AD, in addition to the loss of glutamatergic pyramidal neurons in the hippocampal formation. Transplantation of cholinergic neurons and glutamatergic pyramidal neurons in rodents results in restoration of spatial learning and memory function. Dysfunctional GABAergic interneurons within the hippocampal formation have been shown to cause hyperactivity of neural circuits within the limbic system. Transplants of GABAergic interneurons into the hippocampus of rodent models of AD demonstrate normalization of this hyperactivity and restoration of learning and memory. In AD subjects with the APOE4 genotype, astrocytes derived from patients? iPSCs exhibit abnormal morphology. Transplants of astrocytes in other rodent models of neurodegenerative diseases restore neurological function. The translation of cell replacement therapy to the clinic for treating AD requires a source of authentic human progenitor cells. Recent studies utilizing blastocyst complementation in gene- edited animals have resulted in the generation of authentic cells and organs such as islet cells and pancreas, renal cells and kidney, and pulmonary cells and lung. We propose to use this approach to generate authentic hippocampal GABAergic interneurons and astrocytes in mice for cell therapy in the APOE4 knock-in (KI) mouse model of AD. A single Specific Aim is designed to characterize GABAergic neurons and astrocytes in the brains of HHEX KO mouse fetuses following complementation with pluripotent murine stem cells. Two Sub-Aims will (i) compare fetal GABAergic hippocampal interneurons and hippocampal astrocytes derived from intra-species murine chimeras vs. wild-type fetuses; and (ii) transplant exogenic hippocampal GABAergic interneurons and astrocytes derived from intra-species HHEX KO mouse chimeras into the brains of APOE4 KI mice to determine efficacy of using exogenic neural cells as a source for transplantation. The results from these studies will provide proof-of-principle that blastocyst complementation in gene edited animals may serve as a platform for generating exogenic neural cells for transplantation in AD, and as a potential future human therapeutic modality.
The cognitive deficits observed in Alzheimer?s disease (AD) are due to dysfunctional cells within the brain?s limbic system. Neural transplantation of limbic system cells has demonstrated recovery of learning and memory in animal models of AD. In our grant application, we propose to develop a platform system that generates authentic neural cells in multiple areas of the brain that employs the technologies of gene editing and blastocyst complementation. This technology may one day allow us to generate human neural cells for transplantation in AD.
