Role of CACHD1 in the development of temporal lobe epilepsy and absence epilepsy

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Epilepsy is a major economic and personal burden for the American public, affecting over 3 million Americans (1-2% of the population) with over 200,000 new cases diagnosed each year. There is no cure for epilepsy. Seizures can only be suppressed using antiepileptic drugs. Unfortunately, these drugs are ineffective in approximately 30% of patients and are often associated with adverse side effects. T-type calcium channels (T-channels) play an important role in controlling neuronal excitability. T- channels open near the resting membrane potential of many neurons, allowing them to act as pacemaker currents that trigger sodium dependent action potential. Increases in T-channel expression and activity have been reported in animal models of temporal lobe epilepsy (TLE), contributing to neuronal hyperexcitability. In absence epilepsy, T-channel activity has been linked to thalamocortical network oscillations that give rise to spike wave discharges (SWD). Despite growing evidence for a role of T-channels in both TLE and absence epilepsy, little is known about the mechanisms by which T-channel activity and expression levels are increased, facilitating increases in neuronal excitability and seizure susceptibility. We recently discovered a novel T-channel modulator, the Ca2+ channel and chemotaxis receptor domain containing 1 (CACHD1) protein. CACHD1 is structurally similar to 2 subunits, the major target of gabapentinoids. CACHD1 is highly expressed in both human and rodent hippocampal and thalamic brain regions with overlapping expression patterns to all three T- channel subtypes. CACHD1 promotes cell surface expression levels of T-channels and increases peak current densities, leading to an increase in neuronal excitability and increased seizure susceptibility. Knockout of CACHD1 prevents γ-butyrolactone (GBL) induced absence seizures and delays the onset of kindled seizures and reduces seizure durations. In view of these findings, CACHD1 could facilitate increases in neuronal excitability associated with TLE and absence epilepsy, making it a novel target for therapy. In this proposal we will test our central hypothesis that CACHD1 increases neuronal excitability via increases in T-channel function, facilitating the onset and severity of both absence epilepsy and TLE. On completion of these studies we will have advanced our current understanding for the role of CACHD1 in the development of absence epilepsy and TLE, providing a novel target for therapy development.