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Abstract:

Different types of dementias such as frontotemporal lobar degeneration (FLTD) affect 44.4 millions of people worldwide and no effective therapyexists. Understanding the basic underlying neurodegeneration mechanismsand neural development is required in order to find a cure for these brain disorders. Hence, it is necessary to find simple and valid methods to study these pathologies. However the complexity of the central nervoussystem (CNS) challenges the development of human model systems. Using human embryonic stem cells hESC as a cellular model for human disorders enables the examination of molecular and biochemical genetic defects during development to a given cell lineage as well as defects arising in mature cell types. However, for most genetic disorders, no hESC lines are available. Induced pluripotent stem cells (iPSC) are similar to ESC linesand can be used to model several human disorders, such as Parkinson’s and Huntington’s disease amongothers. The goal of this project was tostudy neural development and neurodegeneration in a human cell culture model from FTD-patients’ iPSC.FTLD refers to a group of neurodegenerative conditions that affect the frontal and temporal regions of the brain. FTLD patients are clinically characterized by personality changes and uninhibited behavior, often combined with a gradual and progressive language dysfunction. Seven genes have been identified in familial FTLD patients in which different mutations were identified: MAPT, GRN, C9OF72, VCP, normal">TARDBP, FUS and CHMP2b. We focused on progranulin (PGRN), a neurotrophic factor, shown tobe a major cause of frontotemporal dementia (FTD), even though the exact role of the loss of this protein in FTD development is still unknown. As defects in cortical neurons are responsible for the development of the disease, cortical neuronal differentiations from hESC/hiPSC lines wereperformed and the cortical differentiation of patient-derived FTD-iPSC lines as a human cell culture model for progranulin-deficiency were evaluated.We found that iPSCs generated from FTD patients associatedwith GRN mutation poorly differentiate to cortical neurons, while differentiation to motor neurons appears normal. Restoration of PGRN expression could rescue the phenotype observed. Loss of PGRN caused aberrant activation of the WNT signaling pathway during neuronal differentiation, and inhibition of WNT signaling partially rescued the FTD-iPSC corticogenesis defect.We also created a unique model of PGRN haploinsufficiency in hESC by seamless insertion of the pathogenic IVS1+5G>C mutation,using TALENs and PiggyBac transposase. We demonstrated thesufficiency of IVS1+5G>C mutation to cause GRN haploinsufficiency, however introduction of this mutation in hESC was not sufficient for recapitulating the functional deficits seen in iPSC derived from patients with FTD due toGRN mutations, suggesting that additional patient-specific factors are required. normal">