Isbrandt, Dirk | Merseburg, Andrea - C 09

The mouse lines studied here model often catastrophic and therapy-refractory early epileptic encephalopathies (EEEs) with neurodevelopmental comorbidities such as autism, ADHD, and cognitive impairment.

Our project will lead to a better understanding of the molecular pathogenesis of these disorders and help identify novel treatment strategies for HCN1 or KCNT1-associated epileptic encephalopathies.

Mutations in neuronal ion channel genes are a frequent cause of early epileptic encephalopathies (EEEs). Our previous work suggests that, in neuronal channelopathies, interventions timed to specific vulnerable windows of brain development may be able to prevent or arrest disease progression. As the molecular pathophysiology and mechanisms underlying neuronal network dysfunction are incompletely understood and are difficult to study in patients, we will investigate molecular mechanisms of epileptogenesis during brain development using knock-in EEE mouse models based on human HCN1 or KCNT1 channelopathies.

These models will be characterized with respect to the temporal dynamics of in vivo hippocampal and cortical network activity during brain maturation, the consequences for neuronal structure, region- and cell population-specific transcriptomic changes during epileptogenesis, and behavioral outcome. By combining CRISPR interference precision (CRISPRi) gene regulation technology with the Tet-off system-mediated temporal control of gene expression, we will identify critical developmental time windows and important cell populations for disease progression and characterize the underlying molecular mechanisms at cellular resolution.

The results gained from these analyses will guide genetic or pharmacological treatment strategies in our mouse lines, which are ultimately aimed at improving therapeutic strategies for epilepsy that are not restricted to HCN1 or KCNT1 EEEs.

1.   When and in which brain regions do seizures start?

2.   In which neuron types do mutant HCN1 or KCNT1 subunits drive epileptogenesis?

3. Do developmental time windows exist that are critical for epileptogenesis and disease progression?

4.  What are the molecular mechanisms linking the biophysical changes of mutant HCN1 or KCNT1 subunits to persistent cellular and network hyperexcitability and neurodegeneration?

In a translational approach, we investigated whether normalizing neonatal network activity during sensitive windows of early brain development ameliorated the behavioral and network phenotypes of Kv7/M current-deficient mice.²

Our results suggested that a potential treatment window may be restricted to the early postnatal period, because restoring Kv7-channel function after weaning did not prevent the phenotype.¹ In addition, we discovered abnormal in vivo network activity in the hippocampus and cortex during the vulnerable time window for Kv7 deficiency.² Targeting GABA signaling by transient NKCC1 blockade with bumetanide during this period prevented chronic structural, physiological, and behavioral changes from developing.² In control littermates, neonatal bumetanide application did not have adverse effects.

Our study linked altered cortical network and hippocampal unit activity in the neonatal mouse brain to structural and functional outcome in adulthood. The beneficial effects of targeting GABA signaling by NKCC1 or GABA_A receptor blockade in a critical newborn period implicates early GABA_A receptor-mediated activity in the pathophysiology of the Kv7 epileptic encephalopathy model.