Ubiquitin–Synaptobrevin fusion protein causes degeneration of presynaptic motor terminals in mice

Yun Liu, Hongqiao Li, Yoshie Sugiura, Weiping Han, Gilbert Gallardo, Mikhail Khvotchev, Yinan Zhang, Ege T. Kavalali, Thomas C. Südhof, Weichun Lin

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Protein aggregates containing ubiquitin (Ub) are commonly observed in neurodegenerative disorders, implicating the involvement of the ubiquitin proteasome system (UPS) in their pathogenesis. Here, we aimed to generate a mouse model for monitoring UPS function using a green fluorescent protein (GFP)-based substrate that carries a “noncleavable” N-terminal ubiquitin moiety (Ub<sup>G76V</sup>). We engineered transgenic mice expressing a fusion protein, consisting of the following: (1) Ub<sup>G76V</sup>, GFP, and a synaptic vesicle protein synaptobrevin-2 (Ub<sup>G76V</sup>-GFP-Syb2); (2) GFP-Syb2; or (3) Ub<sup>G76V</sup>-GFP-Syntaxin1, all under the control of a neuron-specific Thy-1 promoter. As expected, Ub<sup>G76V</sup>-GFP-Syb2, GFP-Syb2, and Ub<sup>G76V</sup>-GFP-Sytaxin1 were highly expressed in neurons, such as motoneurons and motor nerve terminals of the neuromuscular junction (NMJ). Surprisingly, Ub<sup>G76V</sup>-GFP-Syb2 mice developed progressive adult-onset degeneration of motor nerve terminals, whereas GFP-Syb2 and Ub<sup>G76V</sup>-GFP-Syntaxin1 mice were normal. The degeneration of nerve terminals in Ub<sup>G76V</sup>-GFP-Syb2 mice was preceded by a progressive impairment of synaptic transmission at the NMJs. Biochemical analyses demonstrated that Ub<sup>G76V</sup>-GFP-Syb2 interacted with SNAP-25 and Syntaxin1, the SNARE partners of synaptobrevin. Ultrastructural analyses revealed a marked reduction in synaptic vesicle density, accompanying an accumulation of tubulovesicular structures at presynaptic nerve terminals. These morphological defects were largely restricted to motor nerve terminals, as the ultrastructure of motoneuron somata appeared to be normal at the stages when synaptic nerve terminals degenerated. Furthermore, synaptic vesicle endocytosis and membrane trafficking were impaired in Ub<sup>G76V</sup>-GFP-Syb2 mice. These findings indicate that Ub<sup>G76V</sup>-GFP-Syb2 may compete with endogenous synaptobrevin, acting as a gain-of-function mutation that impedes SNARE function, resulting in the depletion of synaptic vesicles and degeneration of the nerve terminals.

Original languageEnglish (US)
Pages (from-to)11514-11531
Number of pages18
JournalJournal of Neuroscience
Volume35
Issue number33
DOIs
StatePublished - Aug 19 2015

Fingerprint

Synaptic Vesicles
Presynaptic Terminals
Vesicle-Associated Membrane Protein 2
Green Fluorescent Proteins
Ubiquitin
Proteins
Nerve Degeneration
R-SNARE Proteins
SNARE Proteins
Motor Neurons
Proteasome Endopeptidase Complex
Neurons
Synaptic Membranes
Neuromuscular Junction
Carisoprodol
Endocytosis
Synaptic Transmission
Neurodegenerative Diseases
Transgenic Mice
Mutation

Keywords

  • Neurodegeneration
  • Neuromuscular junction
  • Synapse
  • Synaptic degeneration
  • Synaptic transmission
  • Transgenic mice

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Ubiquitin–Synaptobrevin fusion protein causes degeneration of presynaptic motor terminals in mice. / Liu, Yun; Li, Hongqiao; Sugiura, Yoshie; Han, Weiping; Gallardo, Gilbert; Khvotchev, Mikhail; Zhang, Yinan; Kavalali, Ege T.; Südhof, Thomas C.; Lin, Weichun.

In: Journal of Neuroscience, Vol. 35, No. 33, 19.08.2015, p. 11514-11531.

Research output: Contribution to journalArticle

Liu, Y, Li, H, Sugiura, Y, Han, W, Gallardo, G, Khvotchev, M, Zhang, Y, Kavalali, ET, Südhof, TC & Lin, W 2015, 'Ubiquitin–Synaptobrevin fusion protein causes degeneration of presynaptic motor terminals in mice', Journal of Neuroscience, vol. 35, no. 33, pp. 11514-11531. https://doi.org/10.1523/JNEUROSCI.5288-14.2015
Liu, Yun ; Li, Hongqiao ; Sugiura, Yoshie ; Han, Weiping ; Gallardo, Gilbert ; Khvotchev, Mikhail ; Zhang, Yinan ; Kavalali, Ege T. ; Südhof, Thomas C. ; Lin, Weichun. / Ubiquitin–Synaptobrevin fusion protein causes degeneration of presynaptic motor terminals in mice. In: Journal of Neuroscience. 2015 ; Vol. 35, No. 33. pp. 11514-11531.
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AU - Khvotchev, Mikhail

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