Palmitoylation controls the stability of 190 kDa Ankyrin-G in dendritic spines and is regulated by ZDHHC8 and lithium

Abstract

The ANK3 gene, which encodes ankyrin-G (AnkG), is associated with a variety of neuropsychiatric and cognitive disorders including bipolar disorder, autism spectrum disorder, and schizophrenia. These diseases are characterized by abnormal dendritic and synaptic architecture. AnkG is a multifunctional scaffold protein with several isoforms: The 480 kDa and 270 kDa isoforms have roles at the axon initial segment and node of Ranvier, but the function of the 190 kDa isoform (AnkG-190) is less well understood. Moreover, AnkG isoforms are regulated by palmitoylation, but palmitoylation of AnkG-190 has not been investigated in neurons. Here we show that AnkG is required for normal dendrite and spine architecture in vivo and that stabilizes pyramidal neuron dendrites. We found that palmitoylation at Cys70 stabilizes in spine heads and at dendritic plasma membrane nanodomains. Finally, we found that lithium, a commonly used mood stabilizer, reduces AnkG-190 palmitoylation and increases its mobility in spines by inhibiting ZDHHC8 action. Taken together, our data reveal a novel mechanism regulating dendritic architecture and mood stabilizer action on palmitoylation of an important psychiatric disorder risk factor. SignificanceThe ANK3 gene has been associated with bipolar disorder and schizophrenia although the mechanisms of disease are not known. The AnkG 190 kDa isoform, AnkG-190, was previously described for its role in dendritic spines. Here, we show it is required to stabilize dendritic arborization and show that palmitoylation, a post-translation modification which allows proteins to stabilize at the membrane, is critical for its localization. Moreover, we show that lithium, a mood stabilizer commonly used in bipolar disorder, modifies AnkG-190 palmitoylation and its dendritic spine localization by inhibiting ZDHHC8 activity, another protein encoded by a psychiatric disorder risk gene. We describe a new novel function for Ank-190 and the early mechanistic actions of lithium in neurons.

Roles of palmitoylation in structural long-term synaptic plasticity

“…In unpolarized MDCK cells, a C70A mutation abolishes the association of Ankyrin-G-190 with lateral membrane, suggesting palmitoylation at Cys70 is required for cellular localization of Ankyrin-G-190 [ 106 ]. Of particular interest, a very recent study carried out in cultured rat primary cortical neurons showed that palmitoylation at Cys70 stabilizes Ankyrin-G-190 in spine heads and at dendritic plasma membrane nanodomains to maintain the dendrite and spine architecture (Preprint [ 290 ]). Mutated ankyrin-G-190 C70A displayed a diffuse distribution with decreased nanodomains in spine and dendrites (Preprint [ 290 ]).…”

“…Of particular interest, a very recent study carried out in cultured rat primary cortical neurons showed that palmitoylation at Cys70 stabilizes Ankyrin-G-190 in spine heads and at dendritic plasma membrane nanodomains to maintain the dendrite and spine architecture (Preprint [ 290 ]). Mutated ankyrin-G-190 C70A displayed a diffuse distribution with decreased nanodomains in spine and dendrites (Preprint [ 290 ]). Differing from the Ankyrin-G-190 palmitoylation in MDCK and HEK293 cells [ 107 ], only ZDHHC8, but not ZDHHC5, catalyzes the palmitoylation of Ankyrin-G-190 in dendritic spines (Preprint [ 290 ]).…”

“…Mutated ankyrin-G-190 C70A displayed a diffuse distribution with decreased nanodomains in spine and dendrites (Preprint [ 290 ]). Differing from the Ankyrin-G-190 palmitoylation in MDCK and HEK293 cells [ 107 ], only ZDHHC8, but not ZDHHC5, catalyzes the palmitoylation of Ankyrin-G-190 in dendritic spines (Preprint [ 290 ]). Moreover, treatment with lithium, a commonly used mood stabilizer for treating bipolar disorder, selectively decreased the level of AnkG-190 palmitoylation and subsequently increased its mobility in dendritic spines by inhibiting ZDHHC8 action (Preprint [ 290 ]), indicating palmitoylation of AnkG-190 may also be involved in psychiatric disease.…”

“…Encoded by the ANK3 gene, Ankyrin-G contains diverse isoforms including small isoforms (100-120 kDa) and large isoforms, in which the larger isoforms (190,270 and 480 kDa) are highly expressed in neurons [281][282][283][284]. Compared with the extensively studied roles of 270 and 480 kDa isoforms in axon initial segment (AIS), nodes of Ranvier (NoR) and inhibitory GABAergic synapses [109,[285][286][287][288][289], the Ankyrin-G 190 kDa isoform (Ankyrin-G-190) was shown to function in regulating the dendritic spine structure and glutamatergic neurotransmission ( [244], Preprint [290]). At synapses, Ankyrin-G-190 forms subsynaptic nanodomains in the spine head surrounding PSDs and within the spine neck to stabilize dendrite and spine architecture both in vitro and in vivo ( [244], Preprint [290]).…”

“…Compared with the extensively studied roles of 270 and 480 kDa isoforms in axon initial segment (AIS), nodes of Ranvier (NoR) and inhibitory GABAergic synapses [109,[285][286][287][288][289], the Ankyrin-G 190 kDa isoform (Ankyrin-G-190) was shown to function in regulating the dendritic spine structure and glutamatergic neurotransmission ( [244], Preprint [290]). At synapses, Ankyrin-G-190 forms subsynaptic nanodomains in the spine head surrounding PSDs and within the spine neck to stabilize dendrite and spine architecture both in vitro and in vivo ( [244], Preprint [290]). Ankyrin-G-190 most likely serves as a perisynaptic scaffold associated with β-spectrin-actin cytoskeleton to support and stabilize the anchoring of perisynaptic AMPAR since Ankyrin-G-190 knockdown leads to a reduction of AMPAR GluA1 levels in spines and consequently reduces mEPSC amplitude [244].…”