Pathophysiology of adaptor protein 5 complex related hereditary spastic paraplegia

• Applicant: Professor Dr. Christian Andreas Hübner
• Subject Area: Molecular and Cellular Neurology and Neuropathology ; Human Genetics ; Molecular Biology and Physiology of Neurons and Glial Cells
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 263893404

Axonopathies are characterized by the degeneration of neuronal projection fibers. In hereditary spastic paraplegia (HSP) fibers of the corticospinal tract are primarily affected, which results in a progressive spastic gait disorder. HSP is characterized by a broad genetic heterogeneity with more than 50 different loci (SPGs) identified to date. Here we propose to characterize the cellular defects in three different HSP subtypes, namely SPG11, SPG15, and SPG48, which are closely connected to the recently identified adaptor protein complex 5 (AP5). Both Zfyve26 mutated in SPG15 and Spatacsin mutated in SPG11 can be coimmunoprecipitated with the AP5 complex, while AP5Z1 associated with SPG48 is a subunit of the AP5 complex itself. Based on knockdown experiments in cell lines it has been speculated that the AP5 complex is involved in protein transport to the lysosome. SPG15-knockout-mice generated by us show a progressive gait disorder with ataxia, which is associated with cortical neuron loss and loss of Purkinje cells in the cerebellum. As a hint for an endolysosomal defect in SPG15 knockout mice we observed a shift of Lamp1-positive brain fractions towards higher densities, alterations of lysosomal enzyme activities in brain extracts and the accumulation of intracellular autofluorescent material in Lamp1-positive vesicular structures. We know propose to narrow down the underlying defect by comparing endolysosomal proteins in SPG15-control and -knockout cells. As accumulation of autofluorescent material is also evident in SPG11-knockout-mice generated in our lab, these mice will be included in our analyses. To better delineate possible AP5-dependent and -independent defects, we propose to generate SPG48-knockout-mice in addition. By comparing the different mouse models and analysis of the endolysosomal system of SPG15-, SPG11- and SPG48-deficient cells we hope to get insights into the pathogenesis of AP5 associated HSP and AP5 functions.

• DFG Programme: Research Grants