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

PLoS Biol. 2020 Aug 31;18(8):e3000820. doi: 10.1371/journal.pbio.3000820. eCollection 2020 Aug.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials
  • Animals
  • Cell Membrane / metabolism
  • Dendritic Spines / metabolism
  • Dendritic Spines / ultrastructure
  • Excitatory Postsynaptic Potentials
  • Glutamic Acid / metabolism*
  • Hippocampus / pathology
  • Hippocampus / physiopathology
  • Kinesins / metabolism*
  • Memory Disorders / metabolism*
  • Memory Disorders / physiopathology*
  • Memory, Short-Term*
  • Mice, Knockout
  • Microtubules / metabolism
  • Microtubules / ultrastructure
  • Motor Activity
  • Neurons / metabolism*
  • Neurons / pathology
  • Neurons / ultrastructure
  • Protein Transport
  • Spastin / deficiency*
  • Spastin / metabolism
  • Synapses / metabolism
  • Synapses / ultrastructure
  • Synaptic Vesicles / metabolism
  • Tubulin / metabolism*

Substances

  • Tubulin
  • Glutamic Acid
  • Spastin
  • Kinesins

Grant support

This work was supported by Deutsche Forschungsgemeinschaft (DFG) grants GRK1459 and FOR2419-KN556/11-1, FOR2419-KN556/11-2, and KN556/12-1 to MK, and a Research Promotion Fund of the University of Hamburg Faculty of Medicine to ATL (https://www.dfg.de/en/; https://www.uke.de/english/organizational-structure/faculty-of-medicine/index.html). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.