Jiou Wang, Ph.D. - US grants

Neurodegeneration is a poorly understood biological phenomenon and an increasing public health challenge for our aging society. Discoveries of causal genetic mLitations have accelerated understanding the molecular mechanisms of these diseases. Mutations in Cu/Zn superoxide dismutase (SODI) have been linked to a subset of amyotrophic lateral sclerosis (ALS), a devastating motor neuron degenerative disease that leads to progressive paralysis. Understanding how a large number of S0D1 mutations, mostly single amino acid changes, cause the specific motor neuron degeneration may provide important insight into more prevalent sporadic ALS. To this end, we have developed novel SODI transgenic C. elegans and mice that exhibit neuronal dysfunction and locomotor defects. Protein;misfolding and aggregation, an increasingly common association with major neurodegenerative diseases, lare a main feature of both the invertebrate and the mammalian animal models. Initial characterization ofthe models traced the behavioral defects to synaptic dysfunctions. Here we propose to combine the use of the genetically tractable C. elegans and the mouse models to dissect the disease mechanism, including the role of protein aggregation. The elucidation may contribute to a better understanding of ALS as well as neurodegenerative diseases in general.

DESCRIPTION (provided by applicant): Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by the degeneration of motor neurons. In some forms of ALS, protein misfolding and aggregation of specific proteins, including Cu/Zn superoxide dismutase (SOD1), have been implicated in motor neuron degeneration. Considerable advances in the understanding of neurodegenerative diseases, including ALS, have been made through studies involving genetically engineered mouse models. However, the complexity, time, and resources required for analyzing age-dependent neurodegeneration in mice limit the usefulness of mouse systems for large-scale genetic and chemical screens. To overcome these limitations, this laboratory has developed and validated a simpler invertebrate model of ALS in Caenorhabditis elegans, a fast- growing, transparent nematode that is amenable to molecular genetic analysis. This C. elegans model recapitulates the major features of human ALS, including a pronounced locomotor defect and the protein aggregation pathology in neurons. This model has made it possible to dissect the mechanism of SOD1-induced neurodegeneration in an efficient manner, using unbiased and large-scale genetic screens. These studies have led to the identification of genes that influence and modulate the neurodegeneration and protein aggregation in ALS disease models. The goal of the proposed project is to identify and elucidate the mechanisms through which ALS pathogenesis is influenced by these novel modifiers. The specific aims are to identify and characterize key genes that influence and modulate the disease, to delineate the pathways through which the pathogenesis is influenced, and to extend the findings to related mammalian systems. The proposed studies, which combine mammalian systems with innovative and promising approaches using C. elegans, are expected to provide insight into fundamental mechanisms of neurodegeneration that may lead to novel approaches for treating ALS and related neurodegenerative diseases.

? DESCRIPTION (provided by applicant): Nucleotide repeat elements, including microsatellites or short tandem repeats, are common in eukaryotic genomes. Expansions of short nucleotide repeats have been linked to nearly 40 different types of genetic disorders, primarily neurological and neuromuscular disorders. Our understanding of how these repeat elements in the human genome cause diseases is still at its infancy. Recently, a hexanucleotide repeat expansion in a noncoding region of C9orf72 was linked to the neurodegenerative disease amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). ALS is characterized by loss of motor neurons, and the C9orf72 repeat expansion represents the most common genetic cause of both familial and sporadic ALS. FTD is characterized by degeneration of the frontal and temporal lobes of the brain and is the second most common type of dementia for people older than 65; the C9orf72 repeat expansion is also one of the most common genetic causes for FTD. The C9orf72 repeat expansion is also found to contribute to Alzheimer's disease and Huntington's disease. To help relieve the public health burden associated with these diseases, it is important to understand the mechanisms underlying the pathogenesis. We have recently discovered that the C9orf72 nucleotide repeat structures initiate molecular cascades of disease. The goal of the proposed project is to elucidate the mechanisms through which nucleotide repeat expansions, such as that in C9orf72, lead to molecular defects and neuronal toxicity. The specific aims are to identify and characterize key biochemical features of the repeat expansion, to delineate the pathways through which the pathogenesis is generated, and to identify potential intervention strategies. The proposed studies, which combine biochemical, molecular, and genetic approaches, are expected to provide insight into fundamental mechanisms of neurodegeneration associated with nucleotide repeats that may ultimately leads to novel approaches for treating relevant neurodegenerative diseases.

Neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are increasing public health challenges, for which effective treatment is still lacking. At least two major themes have emerged from the studies of ALS/FTD, concerning etiology related to both RNA metabolism and protein homeostasis. However, the RNA- and protein-based pathogenesis are likely to be interdependent. Here we propose to unravel the key molecular pathways in the common pathogenic processes at the intersection of RNA and protein homeostasis. FUS is one of the RNA-binding proteins that have linked to ALS/FTD. Recently, we discovered a new role for RNA-binding proteins, as exemplified by FUS, in the direct regulation of the activities of microRNAs, which are small RNAs functioning as critical regulators of gene expression. Moreover, considering the notion that FUS protein is capable of undergoing phase separation, assembling into stress granules, and forming protein aggregates, and building on our preliminary evidence, we propose to elucidate the previously unrecognized mechanisms through which aberrant formation of stress granules and protein aggregates disrupt the RNA homeostasis maintained by ALS/FTD associated proteins. Furthermore, our studies will be directed at uncovering the cellular quality control systems that are built in to maintain the RNA/protein homeostasis and understanding how these systems go awry in diseases. Our unique potential to contribute to this field is both conceptual and technical: We have developed a unique combination of biochemical/C. elegans/mammalian systems to study the mechanisms of neurodegeneration, and our recent success bodes well for future plans. The findings will not only provide novel understandings of the molecular causes of disease for key ALS genes but also suggest new strategies for harnessing the cellular defense system to prevent and treat the relevant forms of ALS and other related neurodegenerative diseases. We predict that the advances gained through our research efforts will eventually lead to new therapeutic interventions to address these devastating diseases.

Neurodegeneration is an increasing public health issue and remains an unsolved biomedical challenge. Genetic discoveries have provided news avenues for investigating the molecular mechanisms of several neurodegenerative diseases. Recently, a hexanucleotide repeat expansion in a noncoding region of the C9orf72 gene was linked to the neurodegenerative disease amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). ALS is characterized by loss of motor neurons, and the C9orf72 mutation represents the most common genetic cause of both familial and sporadic ALS. FTD is characterized by degeneration of the frontal and temporal lobes of the brain and is the second most common type of dementia for people older than 65; the C9orf72 mutation is also the most common genetic causes for FTD. The C9orf72 mutation is also found to contribute to Alzheimer?s disease and Huntington?s disease. Despite intense efforts and rapid advances, our understanding of the disease mechanisms and treatment strategies for C9orf72-linked ALS/FTD are still at the early stages. To help relieve the public health burden associated with these diseases, it is important to understand the mechanisms underlying the pathogenesis. We have recently discovered that C9orf72 plays an important role in the regulation of autophagy and related metabolic processes, suggesting that further studies of C9orf72 functions could shed light on the mechanism of ALS/FTD pathogenesis. The goal of the proposed project is to elucidate the mechanisms through which dysregulation of C9orf72 functions leads to molecular defects and neuronal toxicity. The specific aims are to identify the central mechanisms through which C9orf72 regulates autophagy and related metabolism, to delineate the pathways through which the pathogenesis is generated, and to identify potential intervention strategies. The proposed studies, which combine biochemical, molecular, and genetic approaches, are expected to provide insight into fundamental mechanisms of neurodegeneration in ALS/FTD that may ultimately leads to novel approaches for treating these devastating neurodegenerative diseases.

Project Summary Neurodegeneration is an increasing public health challenge and remains an unsolved biomedical problem. Protein misfolding and aggregation are a central feature of neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). The complexity of neurodegeneration calls for large-scale unbiased screening studies. Over the past few years, we have made breakthrough observations with significant implications for understanding the cellular defense systems against proteotoxicity underlying pathogenesis in ALS/FTD. Using a unique blend of genetic, biochemical, and cell biological approaches, we have uncovered novel pathways that enable reprogramming of protein quality control to counter proteotoxicity. The newly proposed work in this project is aimed at elucidating mechanisms underlying newly identified regulators and master switches in protein quality control. The studies on the previously unrecognized higher-order regulators could expand our understanding of proteotoxic-stress-responsive quality control systems in the cell, beyond the well-established heat shock response or unfolded protein response. Our unique abilities to contribute to this field are at both conceptual and technical levels: In additional to novel pathways, we have developed unique C. elegans/mammalian reporter systems to study proteotoxicity-associated neurodegeneration, and our recent success bodes well for future plans. Furthermore, our expanding repertoire of tools will allow us to extend the findings to diverse models and patient cells. The specific aims are to elucidate the mechanisms through which a novel conserved pathway, involving a previously unknown transcriptional master switch, in the regulation of protein quality control, to delineate the pathways through which a novel target and its signaling pathway regulate proteotoxicity, and to develop new tools for more advanced search for key regulators of proteotoxicity and quality control. The findings will not only provide novel entry points for understanding the toxicities of key ALS/FTD proteins, such as SOD1, TDP-43, and C9orf72 DPRs, but also reveal molecular targets for harnessing the cellular defense system to prevent and treat the relevant neurodegenerative diseases. We predict that the advances gained through our research efforts will eventually lead to new therapeutic interventions to address these diseases in the world?s rapidly aging population.