A Kinase Anchor Protein 150 (AKAP150)-associated Protein Kinase A Limits Dendritic Spine Density

Abstract

The A kinase anchor protein AKAP150 recruits the cAMPdependent protein kinase (PKA) to dendritic spines. Here we show that in AKAP150 (AKAP5) knock-out (KO) mice frequency of miniature excitatory post-synaptic currents (mEPSC) and inhibitory post-synaptic currents (mIPSC) are elevated at 2 weeks and, more modestly, 4 weeks of age in the hippocampal CA1 area versus litter mate WT mice. Linear spine density and ratio of AMPAR to NMDAR EPSC amplitudes were also increased. Amplitude and decay time of mEPSCs, decay time of mIPSCs, and spine size were unaltered. Mice in which the PKA anchoring C-terminal 36 residues of AKAP150 are deleted (D36) showed similar changes. Furthermore, whereas acute stimulation of PKA (2-4 h) increases spine density, prolonged PKA stimulation (48 h) reduces spine density in apical dendrites of CA1 pyramidal neurons in organotypic slice cultures. The data from the AKAP150 mutant mice show that AKAP150-anchored PKA chronically limits the number of spines with functional AMPARs at 2-4 weeks of age. However, synaptic transmission and spine density was normal at 8 weeks in KO and D36 mice. Thus AKAP150-independent mechanisms correct the aberrantly high number of active spines in juvenile AKAP150 KO and D36 mice during development.Dendritic spines receive most of the excitatory input in mammalian neurons (1, 2) and compartmentalize signaling that regulates the synaptic response (3, 4). Several protein kinases and phosphatases, including CaMKII, cAMP-dependent protein kinase (PKA), 3 PKC, and protein phosphatase PP2A and PP2B (calcineurin) (5) play prominent roles in synaptic plasticity. Synaptic activity translates into their activation, thereby affecting spine stability, morphology, and postsynaptic responses (6 -13). Spines are dynamically gained and lost during synaptogenesis (9, 14 -16) and in response to neuronal activity (17-19).AKAP150 is a product of the Akap5 gene in mice and is the main AKAP that recruits PKA to postsynaptic sites (20 -25). It binds with its very C terminus to the N-terminal dimerization domain of the regulatory RII subunits of PKA (26,27). It also binds PKC (28), PP2B (29,30), and the SH3-GK region of the postsynaptic scaffolding proteins SAP97 and PSD-95 (31, 32). PSD-95 binds with its PDZ domains to the C-terminal ((S/ T)X(I/V)) motif of NMDA-type glutamate receptor (NMDAR) NR2 subunits (33). PSD-95 also binds to the C terminus of stargazin (␥2) and its homologues ␥3, ␥4, and ␥8, which associate with AMPAR-type glutamate receptor (AMPAR) for postsynaptic localization in conjunction with . SAP97 directly binds to the AMPAR GluR1 subunit via a PDZ-C-terminal interaction (37) to link AKAP150 and thereby PKA, PKC,. Phosphorylation of GluR1 on Ser-845 by PKA can increase channel activity (42) and accumulation of GluR1-containing AMPAR at the postsynaptic site during hippocampal LTP (43, 44) (see also Refs. 45,46). The N terminus of AKAP150 also binds F-actin, cadherin, adenylyl cyclases, and PIP 2 and targets AKAP150 to dendritic spines and the central region binds PSD-...

An Autism-Linked Mutation Disables Phosphorylation Control of UBE3A

“…A previous study found that chronic pharmacological inhibition of PKA led to increased dendritic spine densities along with supernumerary synapses (Lu et al, 2011). To determine if this effect was mediated by UBE3A, we chronically treated E15.5 neurons from WT and Ube3a m−/p+ mice with the small molecule inhibitor KT5720 (on DIV 19), then processed cells for the excitatory postsynaptic marker PSD-95 and the excitatory presynaptic marker vGLUT1 (Figure 7A and 7B).…”

NMDA Receptor-Dependent LTD Requires Transient Synaptic Incorporation of Ca 2+ -Permeable AMPARs Mediated by AKAP150-Anchored PKA and Calcineurin

“…These increases in spine density were accompanied by sizeable increases in the frequency, but not amplitudes, of spontaneous miniature excitatory postsynaptic currents (mEPSC), indicating increases in the number, but not strength, of excitatory synapses on CA1 neurons (Lu et al, 2011). However, imaging of Golgi-stained CA1 neurons from 150ΔPKA mice showed only a very slight increase in spine density relative to WT (Figure 1E,F: WT 1.85±0.07, ΔPKA 2.06±0.07 spines/μm dendrite, n=29–39 dendrite segments, *p=0.042 by unpaired t-test).…”

Adenylyl Cyclase Anchoring by a Kinase Anchor Protein AKAP5 (AKAP79/150) Is Important for Postsynaptic β-Adrenergic Signaling

“…PPT-LTP Requires Activity of GluA2-lacking AMPA Receptors-Despite the fact that Ser-845 phosphorylation was dramatically reduced in our KO versus WT mice, basal synaptic transmission was normal in 8 -12-week-old KO and also D36 mice (47). Although Ser-845 phosphorylation up-regulates GluA1 surface expression upon stimulation of PKA (19 -23), Ser-845 phosphorylation does not seem to be an important determinant for postsynaptic responses under basal conditions because phosphorylation-deficient S845A KI mice have normal basal synaptic transmission (30).…”

“…This interaction is important for long term depression (LTD) and for curbing long term potentiation (LTP) (41,42). AKAP5 is the main postsynaptic AKAP (43)(44)(45)(46)(47). Functionally, AKAP5 links PKA, PKC, and the antagonistic phosphatase PP2B via SAP97 and perhaps also PSD-95 to GluA1 for dynamic phosphorylation and dephosphorylation (17, 37, 48 -50).…”

“…We systematically compared ␤-adrenergic regulation of Ser-845 phosphorylation and of postsynaptic glutamate receptor responses in AKAP150 KO mice (59) and mice in which the last 36 residues of AKAP150 had been deleted (D36 mice) (43,(45)(46)(47) to test the functional roles of AKAP150 with respect to PKA versus AC targeting. We found that basal Ser-845 phosphorylation and its up-regulation by ␤-adrenergic stimulation is much more drastically impaired in AKAP5 KO than in D36 mice.…”