Pilotto, FedericaFedericaPilottoDouthwaite, ChristopherChristopherDouthwaiteDiab, RimRimDiabYe, XiaoQianXiaoQianYeAl Qassab, Zahraa Ahmed MohammedZahraa Ahmed MohammedAl QassabTietje, ChristophChristophTietjeMounassir, MeriemMeriemMounassirOdriozola Quesada, AdolfoAdolfoOdriozola QuesadaThapa, AishwaryaAishwaryaThapaBuijsen, Ronald A MRonald A MBuijsenLagache, SophieSophieLagacheUldry, Anne-ChristineAnne-ChristineUldryHeller, ManfredManfredHeller0000-0002-6364-7325Müller, Stefan JürgStefan JürgMüllervan Roon-Mom, Willeke M CWilleke M Cvan Roon-MomZuber, BenoîtBenoîtZuber0000-0001-7725-5579Liebscher, SabineSabineLiebscherSaxena, SmitaSmitaSaxena0000-0003-4574-45912024-10-252024-10-252023-08-16https://boris-portal.unibe.ch/handle/20.500.12422/167885Toxic proteinaceous deposits and alterations in excitability and activity levels characterize vulnerable neuronal populations in neurodegenerative diseases. Using in vivo two-photon imaging in behaving spinocerebellar ataxia type 1 (Sca1) mice, wherein Purkinje neurons (PNs) degenerate, we identify an inhibitory circuit element (molecular layer interneurons [MLINs]) that becomes prematurely hyperexcitable, compromising sensorimotor signals in the cerebellum at early stages. Mutant MLINs express abnormally elevated parvalbumin, harbor high excitatory-to-inhibitory synaptic density, and display more numerous synaptic connections on PNs, indicating an excitation/inhibition imbalance. Chemogenetic inhibition of hyperexcitable MLINs normalizes parvalbumin expression and restores calcium signaling in Sca1 PNs. Chronic inhibition of mutant MLINs delayed PN degeneration, reduced pathology, and ameliorated motor deficits in Sca1 mice. Conserved proteomic signature of Sca1 MLINs, shared with human SCA1 interneurons, involved the higher expression of FRRS1L, implicated in AMPA receptor trafficking. We thus propose that circuit-level deficits upstream of PNs are one of the main disease triggers in SCA1.enGABAergic neurons Purkinje neurons cerebellar circuit chemogenetics circuit modulation excitation/inhibition iPSCs in vivo imaging molecular layer interneuronsspinocerebellar ataxia type 1 mouse models neurodegenerative disease600 - Technology::610 - Medicine & health500 - Science::570 - Life sciences; biologyarticle10.48350/1834673732122210.1016/j.neuron.2023.05.016