GABA
                A
               Receptor Coupling Junction and Pore GABRB3 Mutations are Linked to Early-Onset Epileptic Encephalopathy

Hernández, Ciria C.; Zhang, Yujia; Hu, Ningning; Shen, Dingding; Shen, Wangzhen; Liu, Xiaoyan; Kong, Weijing; Jiang, Yuwu; Macdonald, Robert L.

doi:10.1038/s41598-017-16010-3

Cited by 28 publications

(26 citation statements)

References 62 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Accordingly, the maximal P o for GABA was estimated at 0.86 ± 0.08. This is similar to previous estimates of maximal P o for GABA in the ternary αβγ receptor 21 , 46 , 47 . The level of activity in the absence of any GABAergic drugs (P o = 0.00011 22 ) was excluded in these calculations.…”

Section: Methodssupporting

confidence: 91%

Enhanced GABAergic actions resulting from the coapplication of the steroid 3α-hydroxy-5α-pregnane-11,20-dione (alfaxalone) with propofol or diazepam

Cao

Montana

Germann

et al. 2018

Sci Rep

View full text Add to dashboard Cite

Many GABAergic drugs are in clinical use as anesthetics, sedatives, or anxiolytics. We have investigated the actions of the combinations of the neuroactive steroid 3α-hydroxy-5α-pregnane-11,20-dione (alfaxalone) with the intravenous anesthetic propofol or the benzodiazepine diazepam. The goal of the study was to determine whether coapplication of alfaxalone reduces the effective doses and concentrations of propofol and diazepam. Behavioral effects of alfaxalone, propofol, diazepam, and the combinations of the drugs were evaluated during a 30-min activity test in mice. Functional effects of the individual drugs and drug combinations were tested by measuring the decay times of spontaneous inhibitory postsynaptic currents in rat hippocampal neurons, and peak current responses from heterologously expressed concatemeric α1β2γ2L GABAA receptors. Co-administration of alfaxalone increased the sedative actions of propofol and diazepam in mice. The combination of alfaxalone with propofol or diazepam increased the decay times of sIPSCs and shifted the concentration-response relationships for GABA-activated receptors to lower transmitter concentrations. We infer that alfaxalone acts as a co-agonist to enhance the GABAergic effects of propofol and diazepam. We propose that co-administration of alfaxalone, and possibly other neuroactive steroids, can be employed to reduce dosage requirements for propofol and diazepam.

show abstract

Section: Methodssupporting

confidence: 91%

Enhanced GABAergic actions resulting from the coapplication of the steroid 3α-hydroxy-5α-pregnane-11,20-dione (alfaxalone) with propofol or diazepam

Cao

Montana

Germann

et al. 2018

Sci Rep

View full text Add to dashboard Cite

show abstract

“…The β3 T287 residue is shown in a side and overhead view of the M2 region (black sticks and spheres). Also shown is the central β3 L284 and β3 T288 residue that is also associated with DEE ( Hernandez et al , 2017 ).…”

Section: Resultsmentioning

confidence: 99%

Gain-of-function GABRB3 variants identified in vigabatrin-hypersensitive epileptic encephalopathies

Absalom

Liao

Kothur

et al. 2020

Brain Communications

View full text Add to dashboard Cite

Variants in the GABRB3 gene encoding the β3-subunit of the γ-aminobutyric acid type A (GABAA) receptor are associated with various developmental and epileptic encephalopathies. Typically, these variants cause a loss-of-function molecular phenotype whereby GABA has reduced inhibitory effectiveness leading to seizures. Drugs that potentiate inhibitory GABAergic activity, such as nitrazepam, phenobarbital or vigabatrin, are expected to compensate for this and thereby reduce seizure frequency. However, vigabatrin, a drug that inhibits GABA transaminase to increase tonic GABA currents, has mixed success in treating seizures in patients with GABRB3 variants: some patients experience seizure cessation, but there is hypersensitivity in some patients associated with hypotonia, sedation and respiratory suppression. A GABRB3 variant that responds well to vigabatrin involves a truncation variant (p.Arg194*) resulting in a clear loss-of-function. We hypothesized that patients with a hypersensitive response to vigabatrin may exhibit a different GABAA receptor phenotype. To test this hypothesis, we evaluated the phenotype of de novo variants in GABRB3 (p.Glu77Lys and p. Thr287Ile) associated with patients who are clinically hypersensitive to vigabatrin. We introduced the GABRB3 p. Glu77Lys and p. Thr287Ile variants into a concatenated synaptic and extrasynaptic GABAA receptor construct, to resemble the GABAA receptor expression by a patient heterozygous for the GABRB3 variant. The mRNA of these constructs was injected into Xenopus oocytes and activation properties of each receptor measured by two-electrode voltage clamp electrophysiology. Results showed an atypical gain-of-function molecular phenotype in the GABRB3 p. Glu77Lys and p. Thr287Ile variants characterized by increased potency of GABAA without change to the estimated maximum open channel probability, deactivation kinetics or absolute currents. Modelling of the activation properties of the receptors indicated that either variant caused increased chloride flux in response to low concentrations of GABA that mediate tonic currents. We therefore propose that the hypersensitivity reaction to vigabatrin is a result of GABRB3 variants that exacerbate GABAergic tonic currents and caution is required when prescribing vigabatrin. In contrast, drug strategies increasing tonic currents in loss-of-function variants are likely to be a safe and effective therapy. This study demonstrates that functional genomics can explain beneficial and adverse anti-epileptic drug effects, and propose that vigabatrin should be considered in patients with clear loss-of-function GABRB3 variants.

show abstract

“…Additionally, some evidence supports the idea that rapid activity‐induced elevation of [Cl − ] i via the GABA A receptor contributes to disease (e.g., epileptic activity and neuropathic pain) [43–45], depending on locally produced glycolytic ATP [46]. Recently, mice with mutations in the β3 subunit or removal of this subunit have been shown to have epilepsy [47]. Previous data demonstrating that the ATPase plays an important role in maintaining [Cl − ] i levels showed that enzymatic activity is increased during seizures [13] and returns to baseline levels when the seizures are eliminated.…”

Section: Discussionmentioning

confidence: 99%

Ectopic GABA_A receptor β3 subunit determines Cl⁻/‐ATPase and chloride transport in HEK 293FT cells

et al. 2020

View full text Add to dashboard Cite

Neuronal intracellular chloride concentration ([Cl À ] i) is a crucial determinant of transmission mediated by the c-aminobutyric acid type A receptor (GABA A R), which subserves synaptic and extrasynaptic inhibition as well as excitation. The Cl À ion is the main carrier of charge through the GABA A R; however, bicarbonate ions (HCO À 3) flowing in the opposite direction can also contribute to the net current. The direction of Cl À and HCO À 3 fluxes is determined by the underlying electrochemical gradient, which is controlled by Cl À transporters and channels. Accumulating evidence suggests that active mechanisms of chloride transport across the GABA A R pore can underlie the regulation of [Cl À ] i. Measurement of Cl À / HCO À 3-ATPase activity and Cl À transport in HEK 293FT cells expressing homomeric or heteromeric GABA A R ensembles (a2, b3, or c2) with fluorescent dye for chloride demonstrated that receptor subtypes containing the b3 subunit show enzymatic activity and participate in GABA-mediated or ATP-dependent Cl À transport. GABA-mediated flow of Cl À ions into and out of the cells occurred for a short time period but then rapidly declined. However, Cl À ion flux was stabilized for a long time period in the presence of HCO À 3 ions. The reconstituted b3 subunit isoform, purified as a fusion protein, confirmed that b3 is critical for ATPase; however, only the triplet variant showed the full receptor function. The high sensitivity of the enzyme to c-phosphate inhibitors led us to postulate that the b3 subunit is catalytic. Our discovery of a GABA A R type that requires ATP consumption for chloride movement provides new insight into the molecular mechanisms of inhibitory signaling.

show abstract

GABA A Receptor Coupling Junction and Pore GABRB3 Mutations are Linked to Early-Onset Epileptic Encephalopathy

Cited by 28 publications

References 62 publications

Enhanced GABAergic actions resulting from the coapplication of the steroid 3α-hydroxy-5α-pregnane-11,20-dione (alfaxalone) with propofol or diazepam

Enhanced GABAergic actions resulting from the coapplication of the steroid 3α-hydroxy-5α-pregnane-11,20-dione (alfaxalone) with propofol or diazepam

Gain-of-function GABRB3 variants identified in vigabatrin-hypersensitive epileptic encephalopathies

Ectopic GABA_A receptor β3 subunit determines Cl⁻/‐ATPase and chloride transport in HEK 293FT cells

Contact Info

Product

Resources

About

GABA A Receptor Coupling Junction and Pore GABRB3 Mutations are Linked to Early-Onset Epileptic Encephalopathy

Cited by 28 publications

References 62 publications

Enhanced GABAergic actions resulting from the coapplication of the steroid 3α-hydroxy-5α-pregnane-11,20-dione (alfaxalone) with propofol or diazepam

Enhanced GABAergic actions resulting from the coapplication of the steroid 3α-hydroxy-5α-pregnane-11,20-dione (alfaxalone) with propofol or diazepam

Gain-of-function GABRB3 variants identified in vigabatrin-hypersensitive epileptic encephalopathies

Ectopic GABAA receptor β3 subunit determines Cl−/‐ATPase and chloride transport in HEK 293FT cells

Contact Info

Product

Resources

About

Ectopic GABA_A receptor β3 subunit determines Cl⁻/‐ATPase and chloride transport in HEK 293FT cells