MECHANISTIC STUDY OF ALZHEIMER’S DISEASE AND NEUROD1-MEDIATED IN VIVO CELL CONVERSION

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Author:
Wang, Yue
Graduate Program:
Molecular, Cellular and Integrative Biosciences
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 27, 2018
Committee Members:
  • Gong Chen, Dissertation Advisor
  • Douglas Cavener, Committee Chair
  • Bernhard Luscher, Committee Member
  • Kevin Douglas Alloway, Committee Member
  • Yingwei Mao, Outside Member
Keywords:
  • Alzheimer's disease
  • NeuroD1
  • Cell conversion
  • Beneficial effect
  • GAD67
  • Haploinsufficiency
  • Small molecule cocktail
  • Therapy
  • In vivo
Abstract:
Nerve injury often results in the disruption of neuronal circuits and loss of neurological functions [1]. However, adult mammalian brains lack self-repair capability [2]. While a small subset of neural stem cells have been discovered in the adult brains, they are not sufficient to repair damaged brains. [3]. Besides injuries of the CNS, neurodegenerative disease can also damage the brain functions and severely impact the quality of life of patients. Particularly, the Alzheimer’s disease (AD) is a neurodegenerative disorder that is now the 6th leading cause of death in the United States [4]. AD is typically characterized by abnormal molecular and cellular changes such as accumulated extracellular amyloid plaques, intracellular neurofibrillary tangles, neurodegeneration, activated astrocytes and microglia, and enhanced immune responses. In addition, behavioral changes involving learning and memory deficits are also observed in AD patients. The lack of effective therapies places a heavy burden on society, with increasing urgency to find a solution due to an extended life span in modern society [5, 6]. Current explorations of potential therapeutic methods cover multiple directions: (1) Amyloid-β or tau antibodies; (2) in vivo cell conversion; (3) cell transplantations; (4) small molecule cocktail intervention; (5) deep brain stimulation; (6) innate inflammatory regulation. However, Amyloid-β or tau antibodies faced a series of failures in clinical trials that has shaken the foundations of the “amyloid theory” and “tau theory”. Therefore, great efforts need to take place on the investigation of the other potential strategies for an effective AD treatment. Recent studies [7], including our own, demonstrated that astrocytes can be directly converted into functional mature neurons in vitro [8, 9] and in vivo [8]. Ectopic over-expression of the cell fate determinant transcriptional factors and small molecule cocktail application, therefore, serve as promising strategies for possible in vivo interventions for AD. Here we report the short-term and long-term beneficial effects of NeuroD1-mediated astrocyte-to-neuron conversion in the brain of an AD mouse model 5xFAD. The reactive astrocytes can be effectively converted into morphological and functional mature neurons within one month. The short-term beneficial effects of NeuroD1-mediated cell conversion include the amelioration of abnormal hypertrophic reactive astrocytes, reversal of neuronal loss by regeneration of new neurons, together with reduced intracellular amyloid-β peptides. Long-term beneficial effects include an increased neurites such as axons and dendrites and augmented synaptic density, well-preserved myelination, and better integrity of blood vessels in the AD mouse brains. To achieve a more comprehensive therapy for AD, we also tested the effectiveness of a small-molecules cocktail to promote adult neurogenesis in AD brains. Our observation revealed a novel chemical drug recipe as a potential candidate for treating AD. Besides the development of the two potential therapeutic strategies, our mechanistic research on the AD mouse model revealed that GAD67 may be involved in the modulation of the pathological procession of Aβ. Therefore, GAD67 may serve as a new drug target for future clinical study. In summary, our work has investigated the beneficial effects induced by a novel technique of ectopic over-expression of NeuroD1 in focal region of the AD mouse brain for in vivo reprogramming of reactive astrocytes into functional neurons. Besides, we examined the effectiveness of a new chemical drug recipe for inducing adult neurogenesis in AD mouse brain. Furthermore, GAD67 was also identified as a novel target for AD treatment in our study. Our mechanistic study of AD and the discovery of a comprehensive therapeutic strategy pave the way for a better understanding and treatment for AD patients.