Gabaergic Rescue of Associative Motor Learning in Spinocerebellar Ataxia Type 6 Mice

• Applicant: Professorin Dr. Melanie D. Mark
• Subject Area: Experimental Models for the Understanding of Nervous System Diseases
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 511099028

Spinocerebellar ataxia type 6 (SCA6) is a progressive, degenerative neurological disorder characterized by its late onset and almost pure cerebellar ataxia, which is caused by an expanded CAG repeat in exon 47 of the P/Q type calcium channel gene. The carboxy terminus (CT) of the alpha subunit of the P/Q type calcium channel (a1ACT) contains the CAG repeats and is translated from an IRES (intragenic internal ribosome entry site) within the CACNA1A, leading to a more stable diseased CT (a1ACTSCA6) peptide fragment which specifically accumulates in cytosolic and to a lesser extent in nuclear Purkinje cells (PC) protein aggregates from SCA6 patients. These diseased CT fragments may potentially be acting as a dominant negative mutant to interfere with the normal interactions between P/Q type calcium channels and its substrates (binding partners) which eventually leads to the SCA6 disease state. Past work showed that GABAergic drug treatment (ie gabapentin, pregabalin or baclofen) of cortical cerebellar atrophy patients and SCA1 mice improved their ataxic symptoms. Together these studies implicate a misfunction of GABABR in ataxia. In this study we would like to identify the specific protein targets and second messenger pathways which a1ACTSCA6 is impairing, so we can develop GPCR specific optogenetic tools to rescue associative motor learning from the cerebellar cortex. Our preliminary eye blink conditioning (EBC) data where we demonstrate a partial recovery of EBC responses with light activation of GABABR optogenetic tool in SCA6 mice suggests that a1ACTSCA6 interferes with the Gi/o-pathway of the GABABR or its downstream effectors. To demonstrate that a1ACTSCA6 is disrupting normal GABABR function, we will measure Gi/o-induced GIRK activity in the presence of a1ACTSCA6 compared to control a1ACT following GABABR stimulation. Secondly, we would like to show a direct interaction between the a1ACTSCA6 and GABABR by immunoprecipitation (IP) assays from cerebellar lysates of a1ACTSCA6 expressing mice. Then we would like to investigate whether the light-activated GABABR can recover impaired LTD in a1ACTSCA6 expressing PCs by measuring LTD induction at the PF-PC synapses in the presence of the light-activated GABABR. Lastly, we would relieve SCA6-like symptoms for associative motor learning with our light-activated GABABR in SCA6 mice. These studies will potentially provide a beneficial therapeutic tool for SCA6 patients.

• DFG Programme: Research Grants