Spastin depletion increases tubulin polyglutamylation and impairs kinesin-mediated neuronal transport, leading to working and associative memory deficits.

André T Lopes,Matthias Kneussel,Christian Lohr,Franco L Lombino,Irm Hermans-Borgmeyer,Frank F Heisler,Jürgen R Schwarz,Edda Thies,Petra Breiden,Kira V Gromova,Laura Ruschkies,Michaela Schweizer,Torben J Hausrat,Timo Fischer,Peter Scheiffele

doi:10.1371/journal.pbio.3000820

André T Lopes, Matthias Kneussel + Show 13 more

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https://doi.org/10.1371/journal.pbio.3000820

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Abstract

Mutations in the gene encoding the microtubule-severing protein spastin (spastic paraplegia 4 [SPG4]) cause hereditary spastic paraplegia (HSP), associated with neurodegeneration, spasticity, and motor impairment. Complicated forms (complicated HSP [cHSP]) further include cognitive deficits and dementia; however, the etiology and dysfunctional mechanisms of cHSP have remained unknown. Here, we report specific working and associative memory deficits upon spastin depletion in mice. Loss of spastin-mediated severing leads to reduced synapse numbers, accompanied by lower miniature excitatory postsynaptic current (mEPSC) frequencies. At the subcellular level, mutant neurons are characterized by longer microtubules with increased tubulin polyglutamylation levels. Notably, these conditions reduce kinesin-microtubule binding, impair the processivity of kinesin family protein (KIF) 5, and reduce the delivery of presynaptic vesicles and postsynaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Rescue experiments confirm the specificity of these results by showing that wild-type spastin, but not the severing-deficient and disease-associated K388R mutant, normalizes the effects at the synaptic, microtubule, and transport levels. In addition, short hairpin RNA (shRNA)-mediated reduction of tubulin polyglutamylation on spastin knockout background normalizes KIF5 transport deficits and attenuates the loss of excitatory synapses. Our data provide a mechanism that connects spastin dysfunction with the regulation of kinesin-mediated cargo transport, synapse integrity, and cognition.

Highlights

Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogenous group of neurodegenerative disorders characterized by spasticity and weakness of the lower extremities
Individual genotypes were identified by PCR analysis (Fig 1B), and the loss of spastin protein was confirmed by western blotting from hippocampal lysate (Fig 1C)
Data are represented as means ± SEM

Summary

Introduction

Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogenous group of neurodegenerative disorders characterized by spasticity and weakness of the lower extremities. More than 70 genetic loci of HSP (spastic paraplegia 1 [SPG1] to SPG79) have been identified, and the pathogenic mechanisms encompass a wide range of cellular dysfunctions, from endoplasmic reticulum (ER) morphogenesis to transport, metabolism, and myelination [1]. Mutations in the spastin gene (SPG4) cause the majority of all HSP cases described [2]. Together with mutations in the gene encoding the kinesin family protein (KIF) 5 (SPG10) [1, 3], this suggests a contribution of transport processes in disease etiology. SPG4-linked HSP had been considered as a “pure” or “uncomplicated” form, with the main clinical feature of slowly progressive spasticity of the legs

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