Our research focus is on two ion channel groups with a prominent role in the regulation of excitability, the neuronal Kv7 channels and the GABA(A) receptors. A number of genetic alterations detected in recent years in the corresponding KCNQ2/3 and GABRx genes has been linked to epilepsy phenotypes, ranging from milder forms to severe epileptic encephalopathies. We use heterologous expression, murine primary neuronal cultures and human induced pluripotent stem (hiPS) cells to study the impact of the disease-causing mutations on the molecular, cellular and neuronal network level and are interested to employ these findings to better understand the biological processes these channels are involved in. Our mission is to establish in vitro models that can be used in the precision medicine approaches and enable individualized treatment of the severely affected patients.
Pathophysiology of neuronal KCNQ channels
Mutations in the KCNQ2 and KCNQ3 genes encoding voltage-gated potassium channels Kv7.2 and Kv7.3 have been associated with a rare benign form of neonatal epilepsy (BFNS), but more complex phenotypes, including peripheral nerve hyperexcitability and myokymia or Rolandic epilepsy with centrotemporal spikes emerged over time. Recently, several studies in cohorts of severely affected children with refractory epilepsy and mental retardation linked de novo mutations in KCNQ2 to an epileptic encephalopathy (EE) phenotype.
Kv7.2 and Kv7.3 are found expressed throughout different brain regions and can form homo- and hetero- tetrameric channels, which conduct slow potassium current activated at subthreshold membrane potentials, the so called M-current (Wang et al. 1998). Functional analysis of mutations in these channels revealed a loss-of-function as a major pathomechanism, suggesting happloinsufficiency as a cause of neonatal seizures and a dominant-negative effect underlining the epileptic encephalopathy (Fig. 1).
We are interested to further explore the function of neuronal KCNQ channels using a combination of in vitro approaches, from recordings in Xenopus laevis oocytes, expression of mutant channels in mammalian cell lines and primary neuronal cultures to generation of patient specific induced pluripotents stem cells. In addition, we use a Kcnq2 knock-out mouse to examine effects of a moderate and complete reduction of the M-current on the activity of neuronal networks.
Research staff: Filip Rosa, Sabina Vejzovic, Heidi Löffler
Figure 1. Pathophysiological mechanisms underlying KCNQ2 channelopathies (Maljevic & Lerche, 2014). Majority of mutations associated with neonatal seizures cause loss-of-function by haploinsufficiency mechanism, whereas dominant-negative effect seems to be a common mechanism underlining KCNQ2 epileptic encephalopathy.
Role of GABA(A) Receptors in epilepsy
GABA(A) receptors, which present the major inhibitory receptors of the central nervous system, are composed of five different subunits encoded by seventeen genes classified into eight classes (α to ρ). The most abundant form in mammalian brain consists of two α1-, two β2- and a γ2 subunit. Several mutations affecting γ2, α1-, α6- and δ-subunit encoding genes have been linked to genetic generalized epilepsy. As expected, all mutations described so far, cause a significant loss of function in heterologous expression systems. The molecular mechanisms of the GABA(A) receptor mutations include defects of the gating behavior, a reduced affinity for GABA and a reduced surface expression by protein degradation or defective trafficking.
We are interested in examining newly detected mutations in Xenopus laevis oocytes and mammalian cell lines. Moreover, we have generated a knock-in mouse model carrying a GABA(A) receptor mutation associated with absence seizures, which is currently being analyzed using video-EEG monitoring and behavioral tests.
Research staff: Merle Bock, Cristina Niturad, Siona Pfeffer
Figure 2: A truncating mutation found in the GABRA1 gene has been associated with genetic generalized epilepsy. Functional analysis revealed that the mutant channel yielded no currents in response to GABA application because it was not expressed in the surface membrane (after Maljevic et al., 2006).
Selected original articles
Muona M, Berkovic SF, Dibbens LM, Oliver KL, Maljevic S, Bayly MA, Joensuu T, Canafoglia L, Franceschetti S, Michelucci R, Markkinen S, Heron SE, Hildebrand MS, Andermann E, Andermann F, Gambardella A, Tinuper P, Licchetta L, Scheffer IE, Criscuolo C, Filla A, Ferlazzo E, Ahmad J, Ahmad A, Baykan B, Said E, Topcu M, Riguzzi P, King MD, Ozkara C, Andrade DM, Engelsen BA, Crespel A, Lindenau M, Lohmann E, Saletti V, Massano J, Privitera M, Espay AJ, Kauffmann B, Duchowny M, Møller RS, Straussberg R, Afawi Z, Ben-Zeev B, Samocha KE, Daly MJ, Petrou S, Lerche H, Palotie A, Lehesjoki AE.
A recurrent de novo mutation in KCNC1 causes progressive myoclonus epilepsy.
Nat Genet 2015;47:39-46.
Orhan G, Bock M, Schepers D, Ilina EI, Reichel SN, Löffler H, Jezutkovic N, Weckhuysen S, Mandelstam S, Suls A, Danker T, Guenther E, Scheffer IE, De Jonghe P, Lerche H, Maljevic S. Dominant-negative effects of KCNQ2 mutations are associated with epileptic encephalopathy.
Ann Neurol 2014;75:382-94.
Füll Y, Seebohm G, Lerche H, Maljevic S.
A conserved threonine in the S1-S2 loop of Kv7.2 and K v7.3 channels regulates voltage-dependent activation. Pflugers Arch. 2013;465:797-804.
Maljevic S, Naros G, Yalçin Ö, Blazevic D, Loeffler H, Cağlayan H, Steinlein OK, Lerche H.
Temperature and pharmacological rescue of a folding-defective, dominant-negative Kv7.2 mutation associated with neonatal seizures.
Hum Mutat 2011;32:E2283-93.
Liao Y, Deprez L, Maljevic S, Pitsch J, Claes L, Hristova D, Jordanova A, Ala-Mello S, Bellan-Koch A, Blazevic D, Schubert S, Thomas EA, Petrou S, Becker AJ, De Jonghe P, Lerche H.
Molecular correlates of age-dependent seizures in an inherited neonatal-infantile epilepsy.
Hunter J, Maljevic S, Shankar A, Siegel A, Weissman B, Holt P, Olson L, Lerche H, Escayg A.
Subthreshold changes of voltage-dependent activation of the Kv7.2channel in neonatal epilepsy.
Neurobiol Dis 2006;24:194-201.
Maljevic S, Krampfl K, Cobilanschi J, Tilgen N, Beyer S, Weber YG, Schlesinger F, Ursu D, Melzer W, Cossette P, Bufler J, Lerche H, Heils A.
A mutation in the GABA(A) receptor alpha(1)-subunit is associated with absence epilepsy.
Ann Neurol 2006;59:983-7.
Maljevic S, Lerche H.
Potassium channel genes and benign familial neonatal epilepsy. Prog Brain Res 2014;213:17-53.
Maljevic S, Lerche H.
Potassium channels: a review of broadening therapeutic possibilities for neurological diseases. J Neurol 2013;260:2201-11.
Maljevic S, Wuttke TV, Seebohm G, Lerche H.
Pflugers Arch 2010;460:277-88.
Maljevic S, Wuttke TV, Lerche H.
Nervous system Kv7 disorders: breakdown of a subthreshold brake.
J Physiol 2008;586:1791-801.
Zentrum für Neurologie
Hertie-Institut für klinische Hirnforschung
Abteilung Neurologie mit Schwerpunkt Epileptologie
Tel.: +49 (0)7071 29-81922