Selective translocation of Ca ²⁺ /calmodulin protein kinase IIα (CaMKIIα) to inhibitory synapses

Abstract

Ca 2+ /Calmodulin protein kinase IIα (CaMKIIα) has a central role in regulating neuronal excitability. It is well established that CaMKIIα translocates to excitatory synapses following strong glutamatergic stimuli that induce NMDA-receptor (NMDAR)-dependent longterm potentiation in CA1 hippocampal neurons. We now show that CaMKIIα translocates to inhibitory but not excitatory synapses in response to more moderate NMDAR-activating stimuli that trigger GABA A -receptor (GABA A R) insertion and enhance inhibitory transmission. Such moderate NMDAR activation causes Thr286 autophosphorylation of CaMKIIα, which our results demonstrate is necessary and sufficient, under basal conditions, to localize CaMKIIα at inhibitory synapses and enhance surface GABA A R expression. Although stronger glutamatergic stimulation coupled to AMPA receptor insertion also elicits Thr286 autophosphorylation, accumulation of CaMKIIα at inhibitory synapses is prevented under these conditions by the phosphatase calcineurin. This preferential targeting of CaMKIIα to glutamatergic or GABAergic synapses provides neurons with a mechanism whereby activity can selectively potentiate excitation or inhibition through a single kinase mediator.C a 2+ /Calmodulin protein kinase IIα (CaMKIIα) is essential for NMDA receptor (NMDAR)-dependent potentiation of many excitatory synapses (1, 2). However, CaMKIIα also directly phosphorylates the inhibitory GABA A receptor (GABA A R) α1, β2, β3, and γ2 subunits (3-5). CaMKIIα activation increases GABA A Rs in synaptosomal preparations (6), and potentiates GABA A R-mediated currents in neurons of the spinal cord dorsal horn (7), cortex (8), cerebellum (9, 10), and hippocampus (7, 11). We recently reported that hippocampal inhibitory synapses are potentiated upon activation of NMDARs through a CaMKIIα-dependent insertion of GABA A Rs into the membrane (12). The similar role of CaMKIIα in NMDAR-dependent excitatory and inhibitory potentiation raises the question of how specificity in the modulation of excitatory or inhibitory synapses is maintained.CaMKIIα translocates to excitatory synapses on dendritic spines following long-term potentiation (LTP) induction (13,14), glutamate receptor activation (15-17), or sensory stimulation in vivo (18). However, it is not known whether CaMKIIα must similarly translocate to inhibitory synapses on dendritic shafts to modulate GABAergic transmission. If so, an understanding of the differential regulation of CaMKIIα targeting to inhibitory and excitatory synapses would provide important insight into the control of neuronal excitability.Here we show that although strong activation of NMDARs induces translocation of CaMKIIα to excitatory synapses and enhances surface AMPAR levels, a weaker activation of NMDARs localizes CaMKIIα to inhibitory synapses. This differential translocation of CaMKIIα is dependent on the activation of calcineurin (CaN), which prevents CaMKIIα targeting to inhibitory synapses in response to strong stimuli. Analysis of CaMKIIα mutants further reveals that whe...

Activity-dependent inhibitory synapse remodeling through gephyrin phosphorylation

“…Slice cultures (16)(17)(18)(19)(20) were rapidly stored at −80°C until homogenization. Tissue was lysed in lysis buffer (50 mM Tris pH 7.4-8, 120 mM NaCl, 0.5% Nonidet P-40) containing Complete miniprotease inhibitor (Roche Diagnostics) and phosphatase inhibitors (Sigma-Aldrich).…”

“…To investigate the underlying molecular mechanisms, we first examined a possible implication of multifunctional Ca 2+ /calmodulin-dependent protein kinase II (CaMKII), recently shown to accumulate at inhibitory synapses following glutamate stimulation (19). Treatment of slice cultures with the CaMKII inhibitor KN-93 (10 μM) during TBS fully prevented the activity-dependent increase in gephyrin cluster formation and size ( Fig.…”

Enzymatic Activity of CaMKII Is Not Required for Its Interaction with the Glutamate Receptor Subunit GluN2B

“…Primary hippocampal cultures were transfected with GFP-CaMKII at 12 DIV and, after 24 hours of expression, live images were captured during induction of a Ca 21 -stimulus with glutamate/glycine (100/10 mM, in the presence of 1 mM Mg 21 ). Under these conditions, costimulation of AMPARs helps to alleviate the Mg 21 block of NMDARs to trigger a sufficiently strong NMDAR-mediated Ca 21 -stimulus (Bayer et al, 2006;Marsden et al, 2010). CaMKII is known to translocate to synaptic sites under this stimulation protocol (Shen and Meyer, 1999), a process that is dependent on GluN2B (She et al, 2012).…”

Translocation of CaMKII to dendritic microtubules supports the plasticity of local synapses

“…They likely depend on the localization of this binding, such as the soma, dendrites, the axon, or even the growth cone, and on the activity pattern that leads to this interaction. to excitatory synapses (Bayer et al, 2001(Bayer et al, , 2006Hudmon et al, 2005) and is required for translocation to inhibitory synapses (Marsden et al, 2010). To date, of all the active mutants tested, only the mutation E96K did not exhibit dendritic translocation, while it did to synapses.…”