TARPs gamma-2 and gamma-7 are essential for AMPA receptor expression in the cerebellum.
The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors require auxiliary subunits termed transmembrane AMPA receptor regulatory proteins (TARPs), which promote receptor trafficking to the cell surface and synapses and modulate channel pharmacology and gating. Of six TARPs, gamma-2 and gamma-7 are the two major TARPs expressed in the cerebellum. In the present study, we pursued their roles in synaptic expression of cerebellar AMPA receptors. In the cerebellar cortex, gamma-2 and gamma-7 were preferentially localized at various asymmetrical synapses. Using quantitative Western blot and immunofluorescence, we found severe reductions in GluA2 and GluA3 and mild reduction in GluA4 in gamma-2-knockout (KO) cerebellum, whereas GluA1 and GluA4 were moderately reduced in gamma-7-KO cerebellum. GluA2, GluA3 and GluA4 were further reduced in gamma-2/gamma-7 double-KO (DKO) cerebellum. The large losses of GluA2 and GluA3 in gamma-2-KO mice and further reductions in DKO mice were confirmed at all asymmetrical synapses examined with postembedding immunogold. Most notably, the GluA2 level in the postsynaptic density fraction, GluA2 labeling density at parallel fiber-Purkinje cell synapses, and AMPA receptor-mediated currents at climbing fiber-Purkinje cell synapses were all reduced to approximately 10% of the wild-type levels in DKO mice. On the other hand, the reduction in GluA4 in gamma-7-KO granular layer reflected its loss at mossy fiber-granule cell synapses, whereas that of GluA1 and GluA4 in gamma-7-KO molecular layer was caused, at least partly, by their loss in Bergmann glia. Therefore, gamma-2 and gamma-7 cooperatively promote synaptic expression of cerebellar AMPA receptors, and the latter also promotes glial expression.
Yamazaki
Maya
M
Department of Cellular Neurobiology, Brain Research Institute, Niigata University, Niigata 951-8585, Japan.
Fukaya
Masahiro
M
Hashimoto
Kouichi
K
Yamasaki
Miwako
M
Tsujita
Mika
M
Itakura
Makoto
M
Abe
Manabu
M
Natsume
Rie
R
Takahashi
Masami
M
Kano
Masanobu
M
Sakimura
Kenji
K
Watanabe
Masahiko
M
D000818:Animals; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009457:Neuroglia / Q000378:metabolism / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D057907:Post-Synaptic Density / Q000378:metabolism / Q000648:ultrastructure; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D018091:Receptors, AMPA / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism / Q000648:ultrastructure
C113940:Cacng2 protein, mouse; D015220:Calcium Channels; D008565:Membrane Proteins; D021122:Protein Subunits; D018091:Receptors, AMPA; C519955:TARP gamma-7 protein, mouse