Heterozygosity for missense mutations in Seipin, namely N88S and S90L, leads to a broad spectrum of motor neuropathy, while a number of loss-of-function mutations in Seipin are associated with the Berardinelli-Seip congenital generalized lipodystrophy type 2 (CGL2, BSCL2), a condition that is characterized by severe lipoatrophy, insulin resistance, and intellectual impairment. The mechanisms by which Seipin mutations lead to motor neuropathy, lipodystrophy, and insulin resistance, and the role Seipin plays in central nervous system (CNS) remain unknown. The goal of this study is to understand the functions of Seipin in the CNS using a loss-of-function approach, i.e. by knockdown (KD) of Seipin gene expression. Excitatory post-synaptic currents (EPSCs) were impaired in Seipin-KD neurons, while the inhibitory post-synaptic currents (IPSCs) remained unaffected. Expression of a shRNA-resistant human Seipin rescued the impairment of EPSC produced by Seipin KD. Furthermore, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-induced whole-cell currents were significantly reduced in Seipin KD neurons, which could be rescued by expression of a shRNA-resistant human Seipin. Fluorescent imaging and biochemical studies revealed reduced level of surface AMPA receptors, while no obvious ultrastructural changes in the pre-synapse were found. These data suggest that Seipin regulates excitatory synaptic function through a post-synaptic mechanism.
Cerebral Cortex/cytology , Heterotrimeric GTP-Binding Proteins/metabolism , Mutation, Missense/genetics , Neurons/physiology , Synaptic Transmission/genetics , 6-Cyano-7-nitroquinoxaline-2,3-dione/pharmacology , Animals , Biotinylation , Brain/cytology , Brain/metabolism , Cells, Cultured , Dose-Response Relationship, Drug , Enzyme-Linked Immunosorbent Assay , Excitatory Amino Acid Agents/pharmacology , Excitatory Postsynaptic Potentials/drug effects , Excitatory Postsynaptic Potentials/genetics , GTP-Binding Protein gamma Subunits , Gene Expression Regulation/drug effects , Gene Expression Regulation/genetics , Heterotrimeric GTP-Binding Proteins/genetics , Immunoprecipitation , Lipodystrophy, Congenital Generalized , Mice , Microscopy, Electron, Transmission , Neurons/drug effects , Neurons/ultrastructure , Patch-Clamp Techniques , RNA, Small Interfering/metabolism , RNA, Small Interfering/pharmacology , Receptors, AMPA/metabolism , Synapses/metabolism , Synapses/ultrastructure , Synaptic Transmission/drug effects , Synaptophysin/metabolism , Synaptosomes/drug effects , Synaptosomes/metabolism , Synaptosomes/ultrastructure , alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid/pharmacology
