Yanhong Shi, PhD - US grants

[unreadable] DESCRIPTION (provided by applicant): Orphan nuclear receptor TLX is expressed in adult mammalian brains and critical in maintaining the proliferative state of neural stem cells. TLX knockout mice display impaired cell proliferation and reduced neural progenitors in neurogenic areas of adult brains. The objective of this study is to identify endogenous TLX ligands in the central nervous system using novel affinity/GC-MS technology and identify synthetic TLX ligands by chemical library screening using cell-based assays. These ligands will be used as tools to study neural stem cell self-renewal and to provide insights into the molecular mechanisms that control neural stem cell proliferation and differentiation. We will also perform preliminary experiments to test the effects of these small molecules on stem cell propagation and neuronal regeneration in neurodegenerative animal models to determine if they are potential pharmacological tools for the improvement of neurodegenerative diseases. Ultimately, these small molecules will be tested as potential therapeutical ligands for the treatment of neurodegenerative diseases such as Alzheimer's disease. These studies will integrate a variety of interdisciplinary approaches and engage full collaborations between two independent groups. Each group will contribute unique yet complementary expertise and resources to the project. Results from these studies will provide unique insights into the nature of TLX ligands and how their functions are related to neural stem cell self-renewal and neurogenesis. Thus, these studies are directly responsive to the NINDS Collaborative Research in Stem Cell Biology. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Stem cell technology holds great promise for the treatment of a variety of human diseases that currently lack effective therapies. Identifying factors that control stem cell self-renewal is an important step in moving stem cell technology from the laboratory to the clinics. One factor that plays an important role in regulating this process is orphan nuclear receptor TLX. TLX is specifically expressed in mammalian brains and is essential to maintain adult neural stem cells in the undifferentiated and self-renewable state. The objective of this study is to uncover the regulatory cascade of TLX by identifying its downstream target genes and upstream regulators. This study will be critical to the implementation of neural stem cell-based cell replacement therapy for the treatment of neurodegenerative diseases such as Alzheimer's and Parkinson's diseases and brain injuries. The results of this study will provide new insights into TLX signaling pathway and define novel elements that control neural stem cell maintenance and self-renewal. Each component of the TLX signaling network, either downstream target genes or upstream regulators, will be novel molecular targets for intervening neurodegenerative diseases.

DESCRIPTION (provided by applicant): This application addresses broad Challenge Area (14: Stem Cells) and specific Challenge Topic (14-NS-101: Reverse Engineering Human Neurological Disease). Viral or plasmid introduction of a transcription factor quartet is proven a powerful strategy to trigger reprogramming somatic cells into induced pluripotent stem (iPS) cells without the need of embryos or eggs. However, genetic manipulation using transgenes represents a serious hurdle to the use of these iPS cells for therapeutic application. While reactivation of trangenes could lead to tumorigenesis, leaky expression of transgenes may inhibit iPS cell differentiation, increasing the risk of immature teratoma formation. One way to solve this problem is to identify small molecules that induce endogenous pluripotent regulators without gene transfer. Furthermore, generation of iPS cells using existing technology by viral transduction or plasmid transfection of the reprogramming factors is a process with very low efficiency. The main goal of this research is to derive transgene-free human iPS cells using small molecules and to identify compounds that enhance reprogramming efficiency. This study will lead to the development of new methods for the derivation ofpluripotent human stem cell lines with high efficiency and open a new avenue to generate patient- and disease-specific pluripotent stem cells. These chemically derived iPS cells will become valuable tools for developmental biology, drug discovery, and regenerative medicine. PUBLIC HEALTH RELEVANCE: Chemical derivation of human iPS cells in virus-free and transgene-free means will open a new avenue to generate patient- and disease-specific pluripotent stem cells with high efficiency. These genetically unmodified iPS cells will be applicable in stem cell-based cell replacement therapies for the treatment of neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases, and brain injuries.

Project Summary Alzheimer's disease (AD) is the most common neurodegenerative disorder and a leading cause of disability and death. However, the precise mechanisms underlying AD pathogenesis remains to be elucidated. Although many transgenic mouse models have been generated for AD research and these models are important for our understanding of the pathological basis of the disease, none has captured the entire spectrum of the disease pathology, including considerable neuronal loss. This is likely due to significant species differences between mouse and human neural cells. Therefore, there is an urgent need to establish human disease modeling platforms to complement studies in animal models for AD research and drug development. Since the advent of induced pluripotent stem cell (iPSC) technology a decade ago, human iPSCs (hiPSCs) have been widely used for disease modeling and drug discovery. However, given the relative immaturity of cells differentiated from hiPSC, it is challenging to use them to model late-onset diseases, for which cellular aging is important in disease pathology. Direct reprogramming is an alternative cellular reprogramming technology, which allows direct conversion of one type of somatic cells, such as fibroblasts, into another type of somatic cells, such as neurons. It has been shown that direct reprogramming enables generation of human neurons that possess key elements of cellular aging, because this reprogramming process does not go through the rejuvenating iPSC stage. The objective of this proposal is to develop aging-relevant cellular models of late-onset AD (LOAD), using direct reprogramming technology in combination with CRISPR/Cas9-mediated gene editing and 3D neural culture, in order to recapitulate the age-associated phenotypes and uncover novel pathological mechanisms of LOAD. We propose to establish cellular models of LOAD using both neurons and astrocytes directly reprogrammed from patient fibroblasts or differentiated from induced neural stem cells (iNSCs) obtained through direct reprogramming. While the strongest risk factor for AD is aging, the strongest genetic risk factor of AD is apolipoprotein (apo) E4. We hypothesize that cellular aging and apoE genotype interact with each other to initiate and/or modulate LOAD pathologies. Accordingly, we propose three complementary aims to test this hypothesis. Aim 1: To generate isogenic human fibroblast lines with different apoE genotypes as cell sources for direct reprogramming. Aim 2: To model LOAD using directly reprogrammed human neurons and astrocytes. Aim 3: To model LOAD using directly reprogrammed NSC-derived neurons and astrocytes. The outcomes of the proposed studies will likely help to further define the roles of apoE4 in the development of age-associated AD pathological features, to uncover novel mechanisms for age and apoE4-related AD pathogenesis, and to design novel therapeutic strategies for AD.

Project Summary Alzheimer?s disease (AD) is the most common form of dementia in the elderly and there is no cure for this disease to date. The molecular and cellular mechanisms underlying AD pathogenesis remains to be elucidated, in order to develop effective therapies for this disease. Many transgenic mouse models have been generated for AD research and these models provide important insights to aid our understanding of the pathological basis of the disease. However, there are significant species differences between mouse and human neural cells, which may explain the observation that none of the animal models has captured the entire spectrum of the disease pathology, including considerable neuronal loss. Therefore, establishing human disease modeling platforms is needed to complement studies in animal models to better understand AD. Human induced pluripotent stem cells (hiPSCs) have been widely used for disease modeling and drug discovery since the development of the iPSC technology. However, the fetal-like properties of hiPSCs present a challenge to model late-onset diseases, for which cellular aging is important in disease pathology. Direct reprogramming converts one type of somatic cells into another without going through the iPSC stage that involves extensive epigenetic modifications, enabling generation of human neurons that possess key elements of cellular aging. Therefore, directly reprogrammed cells derived from patient somatic cells would allow us to model age-related, late-onset diseases, such as late-onset AD, in a human cellular platform. The objective of this proposal is to uncover molecular and cellular mechanisms underlying AD using aging- relevant cellular models derived from direct reprogramming in combination with CRISPR/Cas9 gene editing. We propose to establish cellular models for AD using astrocyte-neuron co-cultures derived from directly reprogrammed cells. While the apolipoprotein (Apo) E4 has been identified as the strongest genetic risk for late-onset AD, the C allele risk variant rs11136000 in the clusterin (CLU) gene represents the third strongest known genetic risk factor for late-onset AD. The mechanism as to how the CLU risk variant contributes to AD pathologies remains largely unknown. We hypothesize that CLU modulates late-onset AD pathologies in an ApoE isoform- and age-dependent manner. Accordingly, we propose three complementary aims to test this hypothesis. Aim 1: To derive isogenic neural cells with different APOE and CLU genotypes via CRISPR/Cas9 gene editing and direct reprogramming. Aim 2: To generate isogenic NSCs with different APOE and CLU genotypes by CRISPR/Cas9 editing. Aim 3: To define the individual and combined effects of APOE and CLU variants on AD pathogenesis using astrocyte-neuron co-cultures. The proposed studies will likely help to define the roles of the CLU risk variant in the development of age-associated AD pathological features, to uncover novel mechanisms underlying AD pathogenesis, and to design novel therapeutic strategies for AD.

Project Summary Canavan disease (CD) is a rare, autosomal recessive neurodevelopmental disorder that affects children from infancy. Most children with infantile-onset CD, the most prevalent form of the disease, will die within the first decade of life. There is neither a cure nor a standard treatment for this disease. CD is caused by genetic mutations in the aspartoacylase (ASPA) gene, which encodes a metabolic enzyme synthesized by oligodendrocytes in the brain. ASPA breaks down N-acetyl-aspartate (NAA), an amino acid derivative in the brain. The cycle of production and breakdown of NAA appears to be critical for maintaining the white matter of the brain, which consists of nerve fibers covered by myelin. Indications of CD include lack of ASPA activity, accumulation of NAA, myelination defect, and spongy degeneration (vacuolation) in the brain. The clinical symptoms include impaired motor function and mental retardation. There is currently no approved therapy for this condition. Therefore, there is a clear, unmet medical need for an effective therapy for CD. The development of human induced pluripotent stem cell (hiPSC) technology has opened exciting avenues for cell therapy. In our preliminary studies, we have used hiPSC technology to generate CD patient iPSCs and differentiated these iPSCs into neural progenitor cells (CD iNPCs). We then introduced a functional ASPA gene into CD iNPCs through lentiviral transduction to generate genetically engineered functional ASPA-containing iNPCs, termed ASPA iNPCs. In order to move the ASPA iNPC cell product to the clinic, we developed current Good Manufacturing Practice (cGMP)-compatible process to manufacture the ASPA iNPCs. The resultant ASPA iNPCs generated from three different CD patients were tested in a CD mouse model for efficacy and safety. After being transplanted into brains of CD mice, the ASPA iNPCs provided sustained ASPA activity, led to significantly lower NAA level, considerable rescue of spongy degeneration and myelination defect in the brain, and substantially improved motor function in the transplanted CD mice. Importantly, no tumorigenesis or other adverse effect was observed in the transplanted mice. These robust preclinical data provide strong rationale for the proposed study. The object of the proposed research is to establish a hiPSC-based cell therapy for CD. The cell products have proven in preclinical studies to be long lasting and efficacious with a favorable safety profile. We propose the following Specific Aims: Aim 1: To conduct IND-enabling qualification runs and perform final manufacturing of the ASPA iNPC cell products. Aim 2: To perform definitive preclinical efficacy and safety/tumorigenicity studies of the ASPA iNPC cell products. Aim 3: To obtain IND approval. Aim 4: To conduct a phase I clinical trial to establish the safety and feasibility of administering the ASPA iNPC cell products to CD patients. This study could lead to the development of a novel cell therapy for CD and demonstrate the feasibility of using hiPSC-based cell products for the treatment of similar diseases.

Project Summary Brain aging is characterized by reduced cognitive capacities, learning and memory. The exact mechanisms of brain aging remain elusive. Because aging is the greatest risk factor for major debilitating neurodegenerative disorders, including Alzheimer's disease (AD), it is important to uncover mechanisms underlying brain aging in order to develop effective therapies for age-related neurodegenerative diseases. AD is the most common neurodegenerative disorder and a leading cause of disability and death. However, the precise mechanisms underlying AD pathogenesis remains to be elucidated. Although many transgenic mouse models have been generated for AD research and these models are important for our understanding of the pathological basis of the disease, it is increasingly recognized that there are significant species differences between mouse and human neural cells. Therefore, there is an urgent need to establish human disease modeling platforms to complement studies in animal models for AD research. Direct reprogramming is a cellular reprogramming technology, which allows direct conversion of one type of somatic cells, such as fibroblasts, into another type of somatic cells, such as neurons. It has been shown that direct reprogramming enables generation of human neurons that possess key elements of cellular aging. Therefore, directly reprogrammed cells could provide a human cellular platform for us to model brain aging and age-related late-onset diseases, such as late-onset AD (LOAD). The objective of this proposal is to develop human age-relevant glial cellular models using direct reprogramming technology, in order to recapitulate age-associated phenotypes in brain aging and neurodegeneration and uncover novel underlying mechanisms. Increasing evidence suggests that astrocytes play important roles in brain health and pathogenesis of neurodegenerative diseases. Therefore, we propose to establish cellular models for brain aging and AD using astrocytes directly reprogrammed from fibroblasts of aged subjects and LOAD patients and co-cultures of astrocytes with other brain cell types, including microglia, oligodendrocytes, and neurons. We hypothesize that cellular aging regulates astrocyte function and cell-cell interactions to modulate brain aging phenotypes and LOAD pathologies. Accordingly, we propose the following Specific Aims:Aim 1: To generate age-associated astrocytes through direct reprogramming and evaluate how cellular aging regulates astrocytic functions. Aim 2: To determine whether and how astrocytic cellular aging modulates neuroinflammation and neuronal phenotypes. Aim 3: To determine whether and how astrocytic cellular aging regulates OPC properties and myelination. The proposed studies will likely help to define roles of glial cellular aging in brain functional deterioration during aging and uncover the underlying mechanisms, which could lead to the development of novel strategies to maintain brain health and reduce risk for AD. The knowledge gained from this study could help us to design novel therapeutic strategies for AD.