Synaptic Vesicle Glycoprotein 2A Is Affected in the Central Nervous System of Mice with Huntington Disease and in the Brain of a Human with Huntington Disease Postmortem.

Synaptic dysfunction is a primary mechanism underlying Huntington disease (HD) progression. This study investigated changes in synaptic vesicle glycoprotein 2A (SV2A) density by means of C-UCB-J small-animal PET imaging in the central nervous system of mice with HD. Dynamic C-UCB-J small-animal PET imaging was performed at clinically relevant disease stages (at 3, 7, 10, and 16 mo) in the heterozygous knock-in Q175DN mouse model of HD and wild-type littermates (16-18 mice per genotype and time point). Cerebral C-UCB-J analyses were performed to assess genotypic differences during presymptomatic (3 mo) and symptomatic (7-16 mo) disease stages. C-UCB-J binding in the spinal cord was quantified at 16 mo. H-UCB-J autoradiography and SV2A immunofluorescence were performed postmortem in mouse and human brain tissues. C-UCB-J binding was lower in symptomatic heterozygous mice than in wild-type littermates in parallel with disease progression (7 and 10 mo: < 0.01; 16 mo: < 0.0001). Specific C-UCB-J binding was detectable in the spinal cord, with symptomatic heterozygous mice displaying a significant reduction ( < 0.0001). H-UCB-J autoradiography and SV2A immunofluorescence corroborated the in vivo measurements demonstrating lower SV2A in heterozygous mice ( < 0.05). Finally, preliminary analysis of SV2A in the human brain postmortem suggested lower SV2A in HD gene carriers than in controls without dementia. C-UCB-J PET detected SV2A deficits during symptomatic disease in heterozygous mice in both the brain and the spinal cord and therefore may be suitable as a novel marker of synaptic integrity widely distributed in the central nervous system. On clinical application, C-UCB-J PET imaging may have promise for SV2A measurement in patients with HD during disease progression and after disease-modifying therapeutic strategies.