Proteostasis Regulators Restore Function of Epilepsy-Associated GABAA Receptors

Quantitative interactome proteomics identifies proteostasis network for GABAA receptors

“…Previously, we reported that a number of proteostasis network components regulate the folding, degradation and trafficking of GABA A receptors (34,43,(60)(61)(62), and most of them, such as BiP (HspA5), calnexin (CANX), Grp94 (Hsp90B1), VCP, and SEL1L, were identified from this quantitative SILAC-based IP-MS/MS analysis, indicating the effectiveness of this proteomics approach. For example, we showed that BiP and calnexin interacted with both WT α1 and α1(A322D) subunits; further, overexpression of BiP or calnexin was sufficient to enhance the ER-to-Golgi trafficking efficiency of WT α1 and α1(A322D) subunits (34).…”

“…Here, we verified that HspA8, a Hsp70 family chaperone in the cytosol, and its co-chaperones, DNAJA1 and DNAJA2, interact with WT α1 and α1(A322D) subunits ( Figure 4A ), suggesting that Hsp70s and their Hsp40 co-chaperones coordinate the folding of GABA A receptors both in the ER and in the cytosol. Previously, we showed that calnexin (CANX) interacts with WT α1 and α1(A322D) subunits in a glycosylation-dependent manner (34,43,44). Here, we verified that UGGT1, a reglucosylation enzyme that rescues glycoproteins with minor folding defects, interacts with α1 subunits ( Figure 4A ), suggesting its potential role in folding glycosylated GABA A receptors.…”

GABAA Receptor Variants in Epilepsy

“…Since many of the pathogenic variants in GABAA receptors lead to impaired protein biogenesis in the ER, reduced receptor surface trafficking, and thus loss of function due to protein conformational defects, correcting proteostasis deficiency is a promising therapeutic strategy to treat such genetic epilepsies (12,101). Indeed, a number of investigations demonstrated that enhancing the protein folding and surface trafficking of pathogenic GABAA receptors containing various subunit variants is sufficient to restore their functions (38,40,49,102,103), suggesting a therapeutic potential of the proteostasis maintenance strategy.…”

“…The predominately composed 122 receptors contribute around 43-60% of all GABAARs in the adult brain (37). It has been well characterized that many epilepsy-related variants in GABAARs affect protein folding, assembly, and trafficking of the subunits, leading to impaired channel function, such as altered kinetics and conductance (12,38).…”

The Endoplasmic Reticulum Membrane Complex Promotes Proteostasis of GABAA Receptors

“…Therefore, there is an urgent need to develop new therapeutic strategy to treat epilepsy, especially drug-resistant epilepsy. Since one major disease-causing mechanism for loss of function of GABA A receptors is their reduced trafficking to the plasma membrane, one promising approach is to adapt the proteostasis network to restore their surface trafficking and thus function (Di et al , 2013; Di et al, 2021; Fu et al , 2018; Han et al , 2015a; Han et al , 2015b). Here, we demonstrated that overexpression of EMC3 and EMC5/6 enhances the functional surface expression of a number of pathogenic GABA A receptor variants (Figure 5) , highlighting the potential of the EMC as a therapeutic target to treat genetic epilepsy resulting from loss of function of GABA A receptors.…”