The Epilepsy-Related Protein PCDH19 Regulates Tonic Inhibition, GABA A R Kinetics, and the Intrinsic Excitability of Hip
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The Epilepsy-Related Protein PCDH19 Regulates Tonic Inhibition, GABAAR Kinetics, and the Intrinsic Excitability of Hippocampal Neurons Giulia M. Serratto 1 & Erika Pizzi 2 & Luca Murru 1,3 & Sara Mazzoleni 1,4 & Silvia Pelucchi 5 & Elena Marcello 5 & Michele Mazzanti 2 & Maria Passafaro 1,3 & Silvia Bassani 1,3 Received: 21 April 2020 / Accepted: 25 August 2020 # The Author(s) 2020
Abstract PCDH19 encodes for protocadherin-19 (PCDH19), a cell-adhesion molecule of the cadherin superfamily preferentially expressed in the brain. PCDH19 mutations cause a neurodevelopmental syndrome named epileptic encephalopathy, early infantile, 9 (EIEE9) characterized by seizures associated with cognitive and behavioral deficits. We recently reported that PCDH19 binds the alpha subunits of GABAA receptors (GABAARs), modulating their surface availability and miniature inhibitory postsynaptic currents (mIPSCs). Here, we investigated whether PCDH19 regulatory function on GABAARs extends to the extrasynaptic receptor pool that mediates tonic current. In fact, the latter shapes neuronal excitability and network properties at the base of information processing. By combining patch-clamp recordings in whole-cell and cell-attached configurations, we provided a functional characterization of primary hippocampal neurons from embryonic rats of either sex expressing a specific PCDH19 short hairpin (sh)RNA. We first demonstrated that PCDH19 downregulation reduces GABAAR-mediated tonic current, evaluated by current shift and baseline noise analysis. Next, by single-channel recordings, we showed that PCDH19 regulates GABAARs kinetics without altering their conductance. In particular, GABAARs of shRNA-expressing neurons preferentially exhibit brief openings at the expense of long ones, thus displaying a flickering behavior. Finally, we showed that PCDH19 downregulation reduces the rheobase and increases the frequency of action potential firing, thus indicating neuronal hyperexcitability. These findings establish PCDH19 as a critical determinant of GABAAR-mediated tonic transmission and GABAARs gating, and provide the first mechanistic insights into PCDH19-related hyperexcitability and comorbidities. Keywords PCDH19 . GABAAR . Hyperexcitability . Intellectual disability . ASD
Introduction Giulia M. Serratto and Erika Pizzi contributed equally to this work. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12035-020-02099-7) contains supplementary material, which is available to authorized users. * Silvia Bassani [email protected] 1
Institute of Neuroscience, CNR, 20129 Milan, Italy
2
Department of Bioscience, University of Milan, 20133 Milan, Italy
3
NeuroMI Milan Center for Neuroscience, University of Milano-Bicocca, 20126 Milan, Italy
4
Department of Medical Biotechnology and Translational Medicine, University of Milan, 20129 Milan, Italy
5
Department of Pharmacological and Biomolecular Sciences, University of Milan, 20133 Milan, Italy
Mutations in the human gene PCDH19 result in an epi
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