Using Primary Fibroblasts and iPSC-Derived Neurons from Patients with AP-4-associated Hereditary Spastic Paraplegia to Support an Unbiased Autophagy-based Phenotypic Screening for Novel Therapeutic Targets

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This proposal aims to identify novel therapeutic targets for the treatment of AP-4-associated hereditary spastic paraplegia (HSP), a group of diseases associated with a autophagy dysfunction. AP-4-associated HSP is a progressive neurodegenerative disorder characterized by global developmental delay, mental retardation, epileptic seizures and progressive spasticity leading to early loss of ambulation, usually before the age of 10 years. This proposal for a two-year postdoctoral project presents a coordinated experimental approach to developing an autophagy-based phenotypic small molecule screening in patient-derived fibroblasts and iPSC-derived neurons of AP-4-associated HSP. The cellular phenotypes selected as primary, orthogonal and secondary assays are well supported by evidence from the literature and robust preliminary data. The proposed experiments describe a stepwise approach that measures AP-4 function by ATG9A translocation (primary assay), APP translocation, ATG9A-mediated autophagosome formation and transcriptome-based characterization of signaling pathways (orthogonal assays), as well as correction of neuron-specific phenotypes of AP-4 deficiency (secondary assays). This experimental design is embedded in a comprehensive research program and promises a high a high degree of translatability. AP-4-associated HSP serves as a paradigmatic disease model for a disease with defective autophagy. The proposed screens may also uncover mechanisms to treat other forms of HSP and other neurodegenerative diseases associated with defective autophagy in childhood and neurodegenerative diseases in adulthood.