Ankyrin-G regulates forebrain connectivity and network synchronization via interaction with GABARAP

Abstract

GABAergic circuits are critical for the synchronization and higher order function of brain networks. Defects in this circuitry are linked to neuropsychiatric diseases, including bipolar disorder, schizophrenia, and autism. Work in cultured neurons has shown that ankyrin-G plays a key role in the regulation of GABAergic synapses on the axon initial segment and somatodendritic domain of pyramidal neurons where it interacts directly with the GABA A receptor associated protein (GABARAP) to stabilize cell surface GABA A receptors. Here, we generated a knock-in mouse model expressing a mutation that abolishes the ankyrin-G/GABARAP interaction ( Ank3 W1989R) to understand how ankyrin-G and GABARAP regulate GABAergic circuitry in vivo. We found that Ank3 W1989R mice exhibit a striking reduction in forebrain GABAergic synapses resulting in pyramidal cell hyperexcitability and disruptions in network synchronization. In addition, we identified changes in pyramidal cell dendritic spines and axon initial segments consistent with compensation for hyperexcitability. Finally, we identified the ANK3 W1989R variant in a family with bipolar disorder, suggesting a potential role of this variant in disease. Our results highlight the importance of ankyrin-G in regulating forebrain circuitry and provide novel insights into how ANK3 loss-of-function variants may contribute to human disease.

Atg8-Family Proteins—Structural Features and Molecular Interactions in Autophagy and Beyond

“…For example, α-helically extended LIR in ankyrins AnkB shows an affinity to GABARAPs in sub-nanomolar ranges (K D values 0.21–0.29 nM) [ 100 ]. The physiological importance of the GABARAP:AnkG interaction is underscored by the study in which a LIR-deficient form of AnkG (W1989R), which fails to bind to GABARAP, leads to a massive reduction in forebrain GABAergic synapses associated with hyperexcitability of pyramidal cell and disruptions in the synchronization of neuronal networks [ 111 ]. Interestingly, LC3 proteins display a lower affinity for this LIR (K D 3.2–10.5 nM), highlighting the functional specialization within the LC3/GABARAP family.…”

Cargo hold and delivery: Ankyrins, spectrins, and their functional patterning of neurons

“…Similarly, 480 kDa ankyrin‐G interacts with GABARAP, a MAP member of the ubiquitin‐like LC3 family at extrasynaptic somatodendritic plasma membranes of pyramidal neurons (Tseng et al, ). 480 kDa ankyrin‐G binds GABARAP through a tryptophan residue (W1989) within a LC3‐interacting (LIR) motif in the inserted region (Alemu et al, ; Nelson et al, ; Tseng et al, ). 480 kDa ankyrin‐G localization at extrasynaptic GABAergic microdomains is promoted by protein–protein interactions via the inserted region and by its direct insertion into the plasma membrane through C70‐dependent palmitoylation, which are both required for stabilizing GABA A receptor synapses (Tseng et al, ).…”

“…480 kDa ankyrin-G binds GABARAP through a tryptophan residue (W1989) within a LC3-interacting (LIR) motif in the inserted region (Alemu et al, 2012;Nelson et al, 2018;Tseng et al, 2015). 480 kDa ankyrin-G localization at extrasynaptic GABAergic microdomains is promoted by protein-protein interactions via the inserted region and by its direct insertion into the plasma membrane through C70-dependent palmitoylation, which are both required for stabilizing GABA A receptor synapses .…”

Neurodevelopmental mutation of giant ankyrin-G disrupts a core mechanism for axon initial segment assembly

“…The neurospecific domain interacts with multiple protein partners at the AIS, including GABARAP (35, 36), Nude1/NudeL1 (37), and microtubule end-binding (EB) proteins (23). Humans bearing a R1989W mutation of gAnkG that reduces the affinity for GABARAP by over a 1,000-fold have bipolar symptoms, while mice bearing the same mutation exhibit reduction in GABAergic synapses and hyperexcitability (38).…”