SK Channel Openers as Therapeutics for Cerebellar Ataxia

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Cerebellar ataxia is a lethal neurological disease, which afflicts about 150,000 people in the US. There are currently no known preventive, neuroprotective or symptomatic treatments for this devastating disease. Using a transgenic mouse model we recently identified a novel mechanism of initiation of cerebellar ataxia through hyperexcitability of the deep cerebellar neurons (DCN), the sole output pathway of the cerebellum. Small conductance Ca -activated K+ (SK) channels, key regulators of firing frequency in the DCN, were silenced in DCN neurons of Tg mice with a naturally occurring dominant-inhibitory SK isoform (SK3-1B) that suppresses the entire SK channel family. Tg mice developed severe cerebellar ataxia by the 12th day of life characterized by motor incoordination, intention tremor and gait abnormalities in the absence of neurodegeneration. This model, together with findings from other animal models for cerebellar ataxia, strongly suggests that increased DCN excitability may be an important step in the causation of this disorder. Pharmacological reduction of DCN excitability may provide a novel therapeutic approach for cerebellar ataxia. Since SK channels are critical in regulating the firing frequency of DCN neurons and their blockade causes enhanced firing, an opener of SK channels should slow down DCN firing and ameliorate the symptoms of cerebellar ataxia. Riluzole, a FDA approved drug for the therapy of amyotrophic lateral sclerosis, has been reported to be a potent SK channel opener. In a preliminary study in a Tg mouse model for human spinocerebellar ataxia type 2 (SCA2), we found that riluzole produced a dramatic improvement in motor performance after only 4 days of treatment. We plan to extend these exciting preliminary findings by pursuing three specific aims: Aim 1: Evaluation of riluzole in two animal models of ataxia; Aim 2: Design of a more potent and selective SK opener that unlike riluzole does not block slowly- inactivating sodium channels; Aim 3: Evaluation of our new SK opener in two animal models of ataxia. Taken together these important proof-of-concept studies will help to determine whether SK channel openers constitute a new therapeutic approach to improve motor performance in dominant cerebellar ataxias.