Improving Proteostasis of Trafficking-Deficient GABA(A) Receptor Variants by Activating IRE1.

Gamma-aminobutyric acid type A receptors (GABA(A)Rs) are essential for maintaining the excitation-inhibition balance in the central nervous system. Genetic variations of GABA(A)Rs result in a variety of neurological disorders, such as epilepsy. A key pathogenic mechanism involves protein misfolding and defective assembly of GABA(A)Rs in the endoplasmic reticulum (ER), resulting in impaired surface expression and loss of function. Here, we investigated three trafficking-deficient variants of the GABA(A)R α1 subunit (GABRA1), including D219N (ClinVar Variation ID: 127232), G251D (Variation ID: 419523), and P260L. We demonstrated that selective pharmacological activation of the IRE1/XBP1s signaling arm of the unfolded protein response using IXA62, IXA554, and IXA105 increases total and surface protein levels of all three α1 variants without affecting wild-type receptor protein levels in HEK293T cells. Patch-clamping recordings further showed that treatment with IXA62, IXA554, and IXA105 increases the peak GABA-evoked current amplitudes in HEK293T cells expressing α1(D219N) and α1(G251D). Mechanistic analyses revealed that IXA62 and IXA554 remodel the GABA(A)R-associated proteostasis network by promoting folding and anterograde trafficking while inhibiting degradation in HEK293T cells expressing α1(D219N) variant and human iPSC-derived neurons carrying α1(G251D) variant. These results suggest that selective IRE1/XBP1s activation pharmacologically can be further developed to provide a potential therapeutic avenue for genetic epilepsies caused by GABA(A)R trafficking defects.