Adaptor protein complex 4 deficiency: a paradigm of childhood-onset hereditary spastic paraplegia caused by defective protein trafficking: Human molecular genetics

R. Behne, J. Teinert, M. Wimmer, A. D'Amore, A.K. Davies, J.M. Scarrott, K. Eberhardt, B. Brechmann, I.P.-F. Chen, E.D. Buttermore, L. Barrett, S. Dwyer, T. Chen, J. Hirst, A. Wiesener, D. Segal, A. Martinuzzi, S.T. Duarte, J.T. Bennett, T. BourinarisH. Houlden, A. Roubertie, F.M. Santorelli, M. Robinson, M. Azzouz, J.O. Lipton, G.H.H. Borner, M. Sahin, D. Ebrahimi-Fakhari

Research output: Contribution to journalArticle

Abstract

Deficiency of the adaptor protein complex 4 (AP-4) leads to childhood-onset hereditary spastic paraplegia (AP-4-HSP): SPG47 (AP4B1), SPG50 (AP4M1), SPG51 (AP4E1) and SPG52 (AP4S1). This study aims to evaluate the impact of loss-of-function variants in AP-4 subunits on intracellular protein trafficking using patient-derived cells. We investigated 15 patient-derived fibroblast lines and generated six lines of induced pluripotent stem cell (iPSC)-derived neurons covering a wide range of AP-4 variants. All patient-derived fibroblasts showed reduced levels of the AP4E1 subunit, a surrogate for levels of the AP-4 complex. The autophagy protein ATG9A accumulated in the trans-Golgi network and was depleted from peripheral compartments. Western blot analysis demonstrated a 3-5-fold increase in ATG9A expression in patient lines. ATG9A was redistributed upon re-expression of AP4B1 arguing that mistrafficking of ATG9A is AP-4-dependent. Examining the downstream effects of ATG9A mislocalization, we found that autophagic flux was intact in patient-derived fibroblasts both under nutrient-rich conditions and when autophagy is stimulated. Mitochondrial metabolism and intracellular iron content remained unchanged. In iPSC-derived cortical neurons from patients with AP4B1-associated SPG47, AP-4 subunit levels were reduced while ATG9A accumulated in the trans-Golgi network. Levels of the autophagy marker LC3-II were reduced, suggesting a neuron-specific alteration in autophagosome turnover. Neurite outgrowth and branching were reduced in AP-4-HSP neurons pointing to a role of AP-4-mediated protein trafficking in neuronal development. Collectively, our results establish ATG9A mislocalization as a key marker of AP-4 deficiency in patient-derived cells, including the first human neuron model of AP-4-HSP, which will aid diagnostic and therapeutic studies. © The Author(s) 2020. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Original languageEnglish
Pages (from-to)320-334
Number of pages15
JournalHum. Mol. Genet.
Volume29
Issue number2
DOIs
Publication statusPublished - 2020

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    Behne, R., Teinert, J., Wimmer, M., D'Amore, A., Davies, A. K., Scarrott, J. M., Eberhardt, K., Brechmann, B., Chen, IP-F., Buttermore, E. D., Barrett, L., Dwyer, S., Chen, T., Hirst, J., Wiesener, A., Segal, D., Martinuzzi, A., Duarte, S. T., Bennett, J. T., ... Ebrahimi-Fakhari, D. (2020). Adaptor protein complex 4 deficiency: a paradigm of childhood-onset hereditary spastic paraplegia caused by defective protein trafficking: Human molecular genetics. Hum. Mol. Genet., 29(2), 320-334. https://doi.org/10.1093/hmg/ddz310