Haploinsufficiency of the GRN gene encoding Progranulin (PGRN) is the genetic cause for a common form of frontotemporal lobar degeneration (FTLD) giving rise to a distinctive frontotemporal dementia syndrome. It is the second most common form of dementia after Alzheimer's disease and currently no effective cure exists for either form of neurodegeneration. Complete lack of PGRN causes a form of neuronal ceroid lipofuscinosis (NCL), a genetically heterogeneous form of lysosomal storage disease in which the digestion of cellular membranes and glycosphingolipids is impaired, resulting in the accumulation of large misshaped lysosomes especially in neurons. This discovery has shaped our current understanding of GRN haploinsufficiency as a genetically distinct latent form of lysosomal dysfunction that accelerates the `normal' progressively diminishing lysosomal capacity during aging. Lysosomal dysfunction syndromes are thought to induce the production of inflammatory cytokines in part through the reduced generation of physiological lipid ligands for inflammation suppressing nuclear hormone receptors, which further promotes neurodegeneration by increasing microglial activation and synaptophagy. FTLD caused by GRN haploinsufficiency offers a unique therapeutic avenue by increasing gene expression from the remaining functional allele. In theory, doubling of baseline GRN expression should completely negate the risk for this form of FTLD in affected individuals. Our team has developed a comprehensive small molecule discovery strategy that has led to the identification of several chemically and mechanistically distinct classes of GRN transcriptional enhancers. The purpose of this project is to investigate the biochemical and cell biological mechanisms through which these small molecules act on the GRN gene and optimize their specificity and preclinical efficacy. This will be achieved by pursuing three major aims:
Aim 1 Prioritize and optimize PGRN enhancers for preclinical development based upon efficacy and functional signatures from integrated ex vivo and in vivo studies;
Aim 2 Determine the translational potential of PGRN enhancing compounds by evaluating their ability to normalize the cellular and brain transcriptome and lipidome;
and Aim 3 Determine the translational potential of PGRN enhancing compounds by investigating their effects on cellular membrane lipid composition and the lysosomal lipidome and proteome.
Currently no effective means of treating late-onset neurodegenerative diseases, such as FTLD caused by GRN haploinsufficiency, exists. This project will build on the drug discovery programs that are underway at the Center for Translational Neurodegeneration Research at UT Southwestern (JH) and at the Chemical Neurobiology Laboratory at Massachusetts General Hospital/Harvard Medical School (SJH), to test a subset of novel small molecules with similar or overlapping properties that was identified or independently verified in the drug screening programs at both institutions, respectively. !
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