Motor neuropathy‐associated mutation impairs Seipin functions in neurotransmission

Gain‐of‐toxic‐function mutations in Seipin (Asparagine 88 to Serine (N88S) and Serine 90 to Leucine (S90L) mutations, both of which disrupt the N‐glycosylation) cause autosomal dominant motor neuron diseases. However, the mechanism of how these missense mutations lead to motor neuropathy is unclear. Here, we analyze the impact of disruption of N‐glycosylation of Seipin on synaptic transmission by over‐expressing mutant Seipin in cultured cortical neurons via lentiviral infection. Immunostaining shows that over‐expressed Seipin is partly colocalized with synaptic vesicle marker synaptophysin. Electrophysiological recordings reveal that the Seipin mutation significantly decreases the frequency, but not the amplitudes of miniature excitatory post‐synaptic currents and miniature inhibitory post‐synaptic currents. The amplitude of both evoked excitatory post‐synaptic currents and inhibitory post‐synaptic current is also compromised by mutant Seipin over‐expression. The readily releasable pool and vesicular release probability of synaptic vesicles are both altered in neurons over‐expressing Seipin‐N88S, whereas neither γ‐amino butyric acid (GABA) nor α‐Amino‐3‐hydroxy‐5‐methyl‐4‐ isoxazolepropionic acid (AMPA) induced whole cell currents are affected. Moreover, electron microscopy analysis reveals decreased number of morphologically docked synaptic vesicles in Seipin‐N88S‐expressing neurons. These data demonstrate that Seipin‐N88S mutation impairs synaptic neurotransmission, possibly by regulating the priming and docking of synaptic vesicles at the synapse. Motoneuropathy‐associated endoplasmic reticulum (ER) protein Seipin‐N88S mutation disrupts N‐glycosylation and decreased the frequency of miniature excitatory and inhibitory post‐synaptic currents (PSCs), and the amplitude of evoked excitatory and inhibitory PSCs. The readily releasable pool and synaptic vesicle (SV) release probability were reduced in neurons over‐expressing Seipin‐N88S, along with decreased number of docked vesicles. We propose that Seipin‐N88S mutation impairs synaptic neurotransmission by regulating the docking of synaptic vesicles. Motoneuropathy‐associated endoplasmic reticulum (ER) protein Seipin‐N88S mutation disrupts N‐glycosylation and decreased the frequency of miniature excitatory and inhibitory post‐synaptic currents (PSCs), and the amplitude of evoked excitatory and inhibitory PSCs. The readily releasable pool and synaptic vesicle (SV) release probability were reduced in neurons