Kendall P. Dean

Bipolar disorder (BD) is a debilitating neuropsychiatric disorder characterized by recurrent mood perturbations, cognitive and functional impairment, and increased risk of suicide. Genome-wide association studies (GWAS) have repeatedly identified the gene ANK3 , which encodes the neuronal scaffolding protein ankyrin-G, as a risk locus for BD. Ankyrin-G interacts directly with the GABA _A receptor-associated protein (GABARAP) to stabilize inhibitory synapses, providing a potential mechanistic link between ANK3 variation and GABAergic dysfunction observed in BD. Previously, we identified an ANK3 p.W1989R variant in a family with BD and demonstrated that this variant abolishes the ankyrin-G/GABARAP interaction, resulting in inhibitory signaling deficits in mice. Here, we investigated the effects of this variant in human induced pluripotent stem cell (hiPSC)-derived neurons generated from an affected individual heterozygous for the ANK3 p.W1989R variant. CRISPR correction of the variant increased inhibitory synapse density on both glutamatergic and GABAergic patient-derived neurons. Integrated spatial transcriptomics and calcium imaging identified cell-type-dependent changes in gene expression and calcium dynamics. ANK3 p.W1989R somatostatin (SST) positive interneurons displayed altered calcium dynamics and reduced SST expression. To determine whether the variant impacts SST interneuron-mediated inhibition of cortical circuits, we selectively stimulated prefrontal cortical SST interneurons in heterozygous Ank3 p.W1989R mice and recorded optically evoked inhibitory postsynaptic currents (oIPSCs) from cortical pyramidal neurons. SST interneuron-mediated oIPSC peak amplitude, charge transfer, and decay times were reduced in variant mice, without a significant change in the paired-pulse ratio. These findings, using complementary human and mouse models, identify novel roles for ankyrin-G in SST interneuron-mediated inhibitory signaling and demonstrate that altered inhibitory connectivity and SST interneuron function are associated with ANK3 p.W1989R. This work provides mechanistic insight into how disrupted ankyrin-G-dependent synaptic function may contribute to inhibitory signaling deficits relevant to BD.

Bipolar disorder (BD) is a prevalent psychiatric condition characterized by mood dysregulation, psychosocial impairment, and an increased risk of suicide. The gene ANK3 has been identified as a risk locus for BD through multiple genome-wide association studies (GWAS). However, the mechanisms by which ANK3 variants influence BD pathophysiology and treatment response remain unclear. ANK3 encodes ankyrin-G, a protein that organizes the axon initial segment (AIS) and nodes of Ranvier by scaffolding ion channels and cell adhesion molecules to the cytoskeleton. Recent studies show that ankyrin-G interacts with the GABA _A receptor-associated protein (GABARAP) to stabilize inhibitory synapses, potentially linking ANK3 variants to inhibitory (GABAergic) signaling deficits associated with BD. We previously demonstrated that the BD-associated variant, ANK3 p.W1989R, disrupts the ankyrin-G/ GABARAP interaction, resulting in inhibitory deficits and cortical pyramidal neuron hyperexcitability in mice. In this study, we investigate how lithium, a common BD therapeutic, modulates neuronal excitability in this model. Our findings show that chronic lithium treatment selectively enhances presynaptic GABAergic neurotransmission, reduces neuronal hyperexcitability, and partially rescues AIS length, without altering the density of GABAergic synapses. We also show that the selective glycogen synthase kinase-3 beta (GSK-3β) inhibitor Tideglusib recapitulates the enhancement of presynaptic GABAergic signaling. These findings shed new light on how ANK3 variants may contribute to inhibitory deficits in BD and demonstrate that lithium treatment is able to restore these deficits, likely through GSK-3β inhibition. Furthermore, these findings highlight GSK-3β inhibition as a promising therapeutic strategy for treating BD and other neurological disorders affected by GABAergic dysfunction.

Dysfunction in sodium channels and their ankyrin scaffolding partners have both been implicated in neurodevelopmental disorders, including autism spectrum disorder (ASD). In particular, the genes SCN2A, which encodes the sodium channel Na_V1.2, and ANK2, which encodes ankyrin-B, have strong ASD association. Recent studies indicate that ASD-associated haploinsufficiency in Scn2a impairs dendritic excitability and synaptic function in neocortical pyramidal cells, but how Na_V1.2 is anchored within dendritic regions is unknown. Here, we show that ankyrin-B is essential for scaffolding Na_V1.2 to the dendritic membrane of mouse neocortical neurons, and that haploinsufficiency of Ank2 phenocopies intrinsic dendritic excitability and synaptic deficits observed in Scn2a^+/- conditions. Thus, these results establish a direct, convergent link between two major ASD risk genes and reinforce an emerging framework suggesting that neocortical pyramidal cell dendritic dysfunction can be etiological to neurodevelopmental disorder pathophysiology.