Mechanisms of Neurodegeneration in Hereditary Prion Diseases - Prions have become the prime exemplars of self-propagating proteins that cause many devastating neurodegenerative disorders, including Alzheimer’s disease. Up to 15% of prion disease cases are inherited in an autosomal dominant fashion, and are caused by point or insertional mutations in the PRNP gene encoding PrP. The most frequent and highly penetrant mutation is E200K, which is linked to familial Creutzfeldt-Jakob disease (CJD). Inherited prion disorders pose several fascinating scientific questions: What cellular and molecular mechanisms account for the pathogenicity of the mutant PrP molecules in these diseases? Do the neurotoxic effects of the proteins depend on conversion to a self-propagating PrPSc state? Do the mutant PrPs target primarily the neurons in which they are synthesized, or is there a role for non cell-autonomous interactions with glial cells? How do astrocytes, which express as much PrP as neurons, contribute to the disease process? Almost all previous studies of familial prion disorders have utilized transgenic mice or transformed cell lines as experimental models, typically under conditions of protein over-expression. There is very little information available on the properties and toxicity of mutant PrPs expressed endogenously by human neurons or other CNS cell types derived from patients. To fill this gap, the Harris and Mostoslavsky laboratories have collaborated extensively over the past several years to apply cutting-edge iPSC approaches to human prion diseases, particularly those of genetic origin. We have been granted access to a large Israeli family of Libyan Jewish descent harboring the E200K mutation linked to CJD. We have generated of a library of iPSCs from 22 members of this family, and have used this unique collection to model and study CJD pathology in iPSC-derived neurons, astrocytes, and cerebral organoids. We have now gathered compelling preliminary evidence for the emergence in these in vitro systems of disease-relevant phenotypes related to synaptic structure and transmission. We have also begun searching for protective genetic variants that account for the markedly delayed onset of symptoms in a small number of “super-resilient” E200K carriers in Israeli and American cohorts who have lived into their 90s virtually symptom-free. To aid in this search, have amassed a unique collection of DNA samples from 102 individuals in families from four countries harboring the E200K mutation. In this application, we propose to extend these promising studies along several fronts, as summarized in the following specific aims: (1) Analyze the properties of E200K PrP in iPSC-derived neurons and astrocytes; (2) Analyze how neuronal-glial interactions contribute to the pathogenicity of E200K PrP; and (3) Use whole-exome sequence data to identify protective genetic variants present in “super-resilient” E200K carriers. Overall, this project leverages a unique collection of patient samples to elucidate fundamental pathogenic mechanisms and novel therapeutic targets likely to be shared with other neurodegenerative disorders like Alzheimer’s disease.
