%0 Journal Article
%T A Missense Mutation A384P Associated with Human Hyperekplexia Reveals a Desensitization Site of Glycine Receptors
%A Chen-Hung Wang
%A Ciria C. Hernandez
%A Dong Chuan Wu
%A Hsin-Yu Hsu
%A Junyi Wu
%A Mei-Lin Shen
%A Ning Zhou
%A Robert L. Macdonald
%A Yi-Ching Wang
%J The Journal of Neurosience
%D 2018
%R 10.1523/JNEUROSCI.0674-16.2018
%X Hyperekplexia, an inherited neuronal disorder characterized by exaggerated startle responses with unexpected sensory stimuli, is caused by dysfunction of glycinergic inhibitory transmission. From analysis of newly identified human hyperekplexia mutations in the glycine receptor (GlyR) ¦Á1 subunit, we found that an alanine-to-proline missense mutation (A384P) resulted in substantially higher desensitization level and lower agonist sensitivity of homomeric ¦Á1 GlyRs when expressed in HEK cells. The incorporation of the ¦Â subunit fully reversed the reduction in agonist sensitivity and partially reversed the desensitization of ¦Á1A384P. The heteromeric ¦Á1A384P¦Â GlyRs showed enhanced desensitization but unchanged agonist-induced maximum responses, surface expression, main channel conductance, and voltage dependence compared with that of the wild-type ¦Á1¦Â (¦Á1WT¦Â) GlyRs. Coexpression of the R392H and A384P mutant ¦Á1 subunits, which mimic the expression of the compound heterozygous mutation in a hyperekplexia patient, resulted in channel properties similar to those with ¦Á1A384P subunit expression alone. In comparison, another human hyperekplexia mutation ¦Á1P250T, which was previously reported to enhance desensitization, caused a strong reduction in maximum currents in addition to the altered desensitization. These results were further confirmed by overexpression of ¦Á1P250T or ¦Á1A384P subunits in cultured neurons isolated from SD rats of either sex. Moreover, the IPSC-like responses of cells expressing ¦Á1A384P¦Â induced by repeated glycine pulses showed a stronger frequency-dependent reduction than those expressing ¦Á1WT¦Â. Together, our findings demonstrate that A384 is associated with the desensitization site of the ¦Á1 subunit and its proline mutation produced enhanced desensitization of GlyRs, which contributes to the pathogenesis of human hyperekplexia.

SIGNIFICANCE STATEMENT Human startle disease is caused by impaired synaptic inhibition in the brainstem and spinal cord, which is due to either direct loss of GlyR channel function or reduced number of synaptic GlyRs. Considering that fast decay kinetics of GlyR-mediated inhibitory synaptic responses, the question was raised whether altered desensitization of GlyRs will cause dysfunction of glycine transmission and disease phenotypes. Here, we found that the ¦Á1 subunit mutation A384P, identified from startle disease patients, results in enhanced desensitization and leads to rapidly decreasing responses in the mutant GlyRs when they are activated repeatedly by the synaptic-like simulation. These observations
%U http://www.jneurosci.org/content/38/11/2818