Pharmacological activation of ATF6 remodels the proteostasis network to rescue pathogenic GABAA receptors

Abstract

Background

Genetic variants in the subunits of the gamma-aminobutyric acid type A (GABA_A) receptors are implicated in the onset of multiple pathologic conditions including genetic epilepsy. Previous work showed that pathogenic GABA_A subunits promote misfolding and inefficient assembly of the GABA_A receptors, limiting receptor expression and activity at the plasma membrane. However, GABA_A receptors containing variant subunits can retain activity, indicating that enhancing the folding, assembly, and trafficking of these variant receptors offers a potential opportunity to mitigate pathology associated with genetic epilepsy.

Results

Here, we demonstrate that pharmacologically enhancing endoplasmic reticulum (ER) proteostasis using small molecule activators of the ATF6 (Activating Transcription Factor 6) signaling arm of the unfolded protein response (UPR) increases the assembly, trafficking, and surface expression of variant GABA_A receptors. These improvements are attributed to ATF6-dependent remodeling of the ER proteostasis environment, which increases protein levels of pro-folding ER proteostasis factors including the ER chaperone BiP (Immunoglobulin Binding Protein) and trafficking receptors, such as LMAN1 (Lectin Mannose-Binding 1) and enhances their interactions with GABA_A receptors. Importantly, we further show that pharmacologic ATF6 activators increase the activity of GABA_A receptors at the cell surface, revealing the potential for this strategy to restore receptor activity to levels that could mitigate disease pathogenesis.

Conclusions

These results indicate that pharmacologic ATF6 activators offer an opportunity to restore GABA_A receptor activity in diseases including genetic epilepsy and point to the potential for similar pharmacologic enhancement of ER proteostasis to improve trafficking of other disease-associated variant ion channels implicated in etiologically-diverse diseases.