Chunk #36 — DISCUSSION — CNIH-2/-3 selectively interact with GluA1 subunits and are required for synaptic expression of GluA1-containing AMPARs in CA1 pyramidal neurons
of CNIH-2/-3 match those seen with the selective deletion of GluA1 (Lu et al., 2009). Because neurons lacking CNIH proteins look physiologically similar to neurons lacking GluA1, we hypothesized that removal of CNIH-2/-3 might have different effects in various AMPAR KO mice and therefore used these tools to probe CNIH-2 function. Knocking down CNIH-2 in hippocampal slices from GluA2 KO mice causes a profound reduction of AMPAR-eEPSCs, whereas knocking down CNIH-2 in slices from GluA1 KO mice has no effect, either on the amplitude or kinetics of AMPAR EPSCs. These physiological results support a selective action of CNIH-2/-3 on GluA1-containing receptors. We also found that CNIH-2 and GluA1 co-IP with GluA2 when using wild-type hippocampal homogenates. However, in striking contrast, when using homogenates from GluA1 KO mice, CNIH-2 does not co-IP with GluA2. Furthermore, GluA2A3/γ-8 receptors, the most likely composition of the receptors remaining in neurons lacking GluA1 or CNIH-2/-3, are twice as fast as GluA1A2/γ-8 receptors. Thus, the 50% reduction in mEPSC decay observed in neurons lacking GluA1 and CNIH-2/-3 can be explained by the selective loss of synaptic GluA1-containing AMPARs.
