Mutations in AKAP5 Disrupt Dendritic Signaling Complexes and Lead to Electrophysiological and Behavioral Phenotypes in Mice

Abstract

AKAP5 (also referred to as AKAP150 in rodents and AKAP79 in humans) is a scaffolding protein that is highly expressed in neurons and targets a variety of signaling molecules to dendritic membranes. AKAP5 interacts with PKA holoenzymes containing RIIα or RIIβ as well as calcineurin (PP2B), PKC, calmodulin, adenylyl cyclase type V/VI, L-type calcium channels, and β-adrenergic receptors. AKAP5 has also been shown to interact with members of the MAGUK family of PSD-scaffolding proteins including PSD95 and SAP97 and target signaling molecules to receptors and ion channels in the postsynaptic density (PSD). We created two lines of AKAP5 mutant mice: a knockout of AKAP5 (KO) and a mutant that lacks the PKA binding domain of AKAP5 (D36). We find that PKA is delocalized in both the hippocampus and striatum of KO and D36 mice indicating that other neural AKAPs cannot compensate for the loss of PKA binding to AKAP5. In AKAP5 mutant mice, a significant fraction of PKA becomes localized to dendritic shafts and this correlates with increased binding to microtubule associated protein-2 (MAP2). Electrophysiological and behavioral analysis demonstrated more severe deficits in both synaptic plasticity and operant learning in the D36 mice compared with the complete KO animals. Our results indicate that the targeting of calcineurin or other binding partners of AKAP5 in the absence of the balancing kinase, PKA, leads to a disruption of synaptic plasticity and results in learning and memory defects.

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

“…The increase in mEPSCs frequency and spine density is more dramatic in AKAP150 D36 than KO mice, possibly because other AKAPs substitute for AKAP150 in KO mice. However, protein levels of other AKAPs are not up-regulated in the KO mice (25). Truncation of the PKA binding site of AKAP150 in D36 mice does not disrupt its overall expression nor its localization to postsynaptic densities (22,23).…”

“…It leaves intact the identified binding sites for other binding partners including F-actin, calmodulin, PIP 2 , cadherin, adenylyl cyclase, PKC, PSD-95, and PP2B (20,28,30,(47)(48)(49)(50)(51). As the C-terminally deleted AKAP150 still binds PP2B, the phosphorylation status of postsynaptic proteins might be shifted more toward dephosphorylation in D36 than KO mice upon Ca 2ϩ influx, which activates PP2B, with KO but not D36 having lost AKAP150 as a PP2B adaptor (25).…”

“…We found later that PKA activity and anchoring is required during LTD induction (23). Because LTP and LTD are both impaired in D36 mice rather than affected in an opposite manner, PKA must act via different molecular pathways in LTP and LTD. More recently we found that LTP is actually not impaired in AKAP150 KO mice in contrast to D36 mice (see "Discussion") and that D36 but not KO mice have impaired reversal learning of operant conditioning (25). Despite these different phenotypes we now report that both mouse strains show an increase in mEPSC frequency and linear spine density at 2-4 but not 8 weeks of age, suggesting that PKA anchoring is the most critical function of AKAP150 in controlling spine formation or maintenance.…”

“…AKAP150 KO and D36 mouse strains were generated as previously described (22,25,52). Briefly, the entire coding sequence of the AKAP150 (Akap5) gene (GenBank TM locus XM138063 position 2126 -2131) was replaced with a neomycin phosphotransferase cassette in AKAP150 KO mice by homologous recombination in embryonic stem cells in a 129S1/SvImJ background (Jackson Laboratories, Bar Harbor, ME).…”

“…We previously generated AKAP150 KO mice and mice that lack the PKA binding site at the C terminus of AKAP150 (D36 mice) (22,25,52). We showed earlier that PKA and its anchoring by AKAP150 plays an important role in LTP at an age of 2-3 weeks and again from 8 weeks on but not during 3-6 weeks (22).…”