Huntington’s disease (HD) is a neurodegenerative disorder caused by a CAG trinucleotide repeat expansion in the HTT gene for which no therapies are available. HTT mutation causes protein misfolding and aggregation, preferentially affecting medium spiny neurons (MSNs) of the basal ganglia. Transcriptional perturbations in synaptic genes and neuroinflammation are key processes that precede MSN dysfunction and motor symptom onset. Understanding the interplay between these processes is crucial to develop effective therapeutic strategies to treat HD. We investigated the role of protein kinase CK2α’, a kinase upregulated in MSNs in HD and previously associated with Parkinson’s disease (PD), in the regulation of neuroinflammation and synaptic function in HD. We used the heterozygous knock-in zQ175 HD mouse model and compared that to zQ175 mice lacking one allele of CK2α’ (zQ175:CK2α’(±)). CK2α’ haploinsufficiency in zQ175 mice resulted in decreased levels of pro-inflammatory cytokines, HTT aggregation, astrogliosis and transcriptional alterations of synaptic genes related to glutamatergic signaling. zQ175:CK2α’(±) mice also presented increased frequency of striatal miniature excitatory postsynaptic currents (mEPSCs), an indicator of synaptic activity, and improved motor coordination compared to zQ175 mice. Neuropathological and phenotypic changes mediated by CK2α’ were connected to alpha-synuclein (α-syn) dysregulation and correlated with differences in α-syn serine 129 phosphorylation (pS129-α-syn), a post-translational modification involved in α-synucleinopathy and shown to be regulated by CK2 in PD. pS129-α-syn was increased in the nuclei of MSNs in zQ175 mice and in the striatum of patients with HD, and it decreased in zQ175:CK2α’(±) mice. Collectively, our data established a novel connection between CK2α’, neuroinflammation and synaptic gene dysregulation with synucleinopathy in HD and suggested common molecular mechanisms of neurodegeneration between HD and PD. Our results also support CK2α’ inhibition as a potential therapeutic strategy to modulate neuronal function and neuroprotection in HD.

ObjectiveSpinocerebellar ataxia type 3 (SCA3) is the most common dominantly inherited ataxia, and biomarkers are needed to noninvasively monitor disease progression and treatment response. Anti‐ATXN3 antisense oligonucleotide (ASO) treatment has been shown to mitigate neuropathology and rescue motor phenotypes in SCA3 mice. Here, we investigated whether repeated ASO administration reverses brainstem and cerebellar neurochemical abnormalities by magnetic resonance spectroscopy (MRS).MethodsSymptomatic SCA3 mice received intracerebroventricular treatment of ASO or vehicle and were compared to wild‐type vehicle‐treated littermates. To quantify neurochemical changes in treated mice, longitudinal 9.4T MRS of cerebellum and brainstem was performed. Acquired magnetic resonance (MR) group means were analyzed by 2‐way analysis of variance mixed‐effects sex‐adjusted analysis with post hoc Sidak correlation for multiple comparisons. Pearson correlations were used to relate SCA3 pathology and behavior.ResultsMR spectra yielded 15 to 16 neurochemical concentrations in the cerebellum and brainstem. ASO treatment in SCA3 mice resulted in significant total choline rescue and partial reversals of taurine, glutamine, and total N‐acetylaspartate across both regions. Some ASO‐rescued neurochemicals correlated with reduction in diseased protein and nuclear ATXN3 accumulation. ASO‐corrected motor activity correlated with total choline and total N‐acetylaspartate levels early in disease.InterpretationSCA3 mouse cerebellar and brainstem neurochemical trends parallel those in patients with SCA3. Decreased total choline may reflect oligodendrocyte abnormalities, decreased total N‐acetylaspartate highlights neuronal health disturbances, and high glutamine may indicate gliosis. ASO treatment fully or partially reversed select neurochemical abnormalities in SCA3 mice, indicating the potential for these measures to serve as noninvasive treatment biomarkers in future SCA3 gene silencing trials. ANN NEUROL 2023

Striatal medium spiny neurons are highly susceptible in Huntington's disease (HD), resulting in progressive synaptic perturbations that lead to neuronal dysfunction and death. Non-invasive imaging techniques, such as proton magnetic resonance spectroscopy ( 1 H-MRS), are used in HD mouse models and patients with HD to monitor neurochemical changes associated with neuronal health. However, the association between brain neurochemical alterations and synaptic dysregulation remains unknown, limiting our ability to monitor potential treatments that may affect synapse function. We conducted in vivo longitudinal 1 H-MRS in the striatum followed by ex vivo analyses of excitatory synapse density of two synaptic circuits disrupted in HD, thalamo-striatal (T-S), and cortico-striatal (C-S) pathways, to assess the relationship between neurochemical alterations and changes in synapse density. We used the zQ175 (Tg/0) HD mouse model as well as zQ175 mice lacking one allele of CK2α'(zQ175 (Tg/0 ) :CK2α' (+/−) ), a kinase previously shown to regulate synapse function in HD. Longitudinal analyses of excitatory synapse density showed early and sustained reduction in T-S synapses in zQ175 mice, preceding C-S synapse depletion, which was rescued in zQ175:CK2α' (+/−) . Changes in T-S and C-S synapses were accompanied by progressive alterations in numerous neurochemicals between WT and HD mice. Linear regression analyses showed C-S synapse number positively correlated with 1 H-MRS-measured levels of GABA, while T-S synapse number positively correlated with levels of phosphoethanolamine and negatively correlated with total creatine levels. These associations suggest that these neurochemical concentrations measured by 1 H-MRS may facilitate monitoring circuit-specific synaptic dysfunction in the zQ175 mouse model and in other HD pre-clinical studies.