Enhanced Hippocampal Spare Capacity in Q175DN Mice Despite Elevated mHTT Aggregation.

Background: Huntington's disease (HD) is a neurodegenerative disease resulting in devastating motor, cognitive, and psychiatric deficits. The striatum is a brain region that controls movement and some forms of cognition and is most significantly impacted in HD. However, despite well-documented deficits in learning and memory in HD, knowledge of the potential implication of other brain regions such as the hippocampus remains limited. Objective: Here, we study the comparative impact of enhanced mHTT aggregation and neuropathology in the striatum and hippocampus of two HD mouse models. Methods: We utilized the zQ175 as a control HD mouse model and the Q175DN mice lacking the PGK-Neomycin cassette generated in house. We performed a comparative characterization of the neuropathology between zQ175 and Q175DN mice in the striatum and the hippocampus by assessing HTT aggregation, neuronal and glial pathology, chaperone expression, and synaptic density. Results: We showed that Q175DN mice presented enhanced mHTT aggregation in both striatum and hippocampus compared to zQ175. Striatal neurons showed a greater susceptibility to enhanced accumulation of mHTT than hippocampal neurons in Q175DN despite high levels of mHTT in both regions. Contrary to the pathology seen in the striatum, Q175DN hippocampus presented enhanced spare capacity showing increased synaptic density, decreased Iba1+ microglia density and enhanced HSF1 levels in specific subregions of the hippocampus compared to zQ175. Conclusions: Q175DN mice are a valuable tool to understand the fundamental susceptibility differences to mHTT toxicity between striatal neurons and other neuronal subtypes. Furthermore, our findings also suggest that cognitive deficits observed in HD animals might arise from either striatum dysfunction or other regions involved in cognitive processes but not from hippocampal degeneration.

Identification of CK2α' selective inhibitors by the screening of an allosteric-kinase-inhibitor-like compound library.

Protein Kinase CK2 is a holoenzyme composed of two regulatory subunits (CK2ß) and two catalytic subunits (CK2α and CK2α'). CK2 controls several cellular processes including proliferation, inflammation, and cell death. However, CK2α and CK2α' possess different expression patterns and substrates and therefore impact each of these processes differently. Elevated CK2α participates in the development of cancer, while increased CK2α' has been associated with neurodegeneration, especially Huntington's disease (HD). HD is a fatal disease for which no effective therapies are available. Genetic deletion of CK2α' in HD mouse models has ameliorated neurodegeneration. Therefore, pharmacological inhibition of CK2α' presents a promising therapeutic strategy for treating HD. However, current CK2 inhibitors are unable to discriminate between CK2α and CK2α' due to their high structural homology, especially in the targeted ATP binding site. Using computational analyses, we found a potential Type IV ("D" pocket) allosteric site on CK2α' that contained different residues than CK2α and was distal from the ATP binding pocket featured in both kinases. With this potential allosteric site in mind, we screened a commercial library containing ~29,000 allosteric-kinase-inhibitor-like compounds using a CK2α' activity-dependent ADP-Glo™ Kinase assay. Obtained hits were counter-screened against CK2α revealing two CK2α' selective compounds. These two compounds might serve as the basis for further medicinal chemistry optimization for the potential treatment of HD.

Discovery of a CK2α'-Biased ATP-Competitive Inhibitor from a High-Throughput Screen of an Allosteric-Inhibitor-Like Compound Library.

Protein kinase CK2 is a holoenzyme composed of two regulatory subunits (CK2ß) and two catalytic subunits (CK2α and CK2α'). CK2 controls several cellular processes, including proliferation, inflammation, and cell death. However, CK2α and CK2α' possess different expression patterns and substrates and therefore impact each of these processes differently. Elevated CK2α participates in the development of cancer, while increased CK2α' has been associated with neurodegeneration, especially Huntington's disease (HD). HD is a fatal disease for which no effective therapies are available. Genetic deletion of CK2α' in HD mouse models has ameliorated neurodegeneration. Therefore, pharmacological inhibition of CK2α' presents a promising therapeutic strategy for treating HD. However, current CK2 inhibitors are unable to discriminate between CK2α and CK2α' due to their high structural homology, especially in the targeted ATP-binding site. Using computational analyses, we found a potential type IV ("D" pocket) allosteric site that contained different residues between CK2α and CK2α' and was distal from the ATP-binding pocket featured in both kinases. We decided to look for allosteric modulators that might interact in a biased fashion with the type IV pocket on both CK2α and CK2α'. We screened a commercial library containing ∼29,000 allosteric-kinase-inhibitor-like compounds using a CK2α' activity-dependent ADP-Glo Kinase assay. Obtained hits were counter-screened against CK2α using the ADP-Glo Kinase assay, revealing two CK2α'-biased compounds. These two compounds might serve as the basis for further medicinal chemistry optimization for the potential treatment of HD.

Tumor suppressor p53 regulates heat shock factor 1 protein degradation in Huntington's disease.

p53 and HSF1 are two major transcription factors involved in cell proliferation and apoptosis, whose dysregulation contributes to cancer and neurodegeneration. Contrary to most cancers, p53 is increased in Huntington's disease (HD) and other neurodegenerative diseases, while HSF1 is decreased. p53 and HSF1 reciprocal regulation has been shown in different contexts, but their connection in neurodegeneration remains understudied. Using cellular and animal models of HD, we show that mutant HTT stabilized p53 by abrogating the interaction between p53 and E3 ligase MDM2. Stabilized p53 promotes protein kinase CK2 alpha prime and E3 ligase FBXW7 transcription, both of which are responsible for HSF1 degradation. Consequently, p53 deletion in striatal neurons of zQ175 HD mice restores HSF1 abundance and decrease HTT aggregation and striatal pathology. Our work shows the mechanism connecting p53 stabilization with HSF1 degradation and pathophysiology in HD and sheds light on the broader molecular differences and commonalities between cancer and neurodegeneration.

CK2 alpha prime and alpha-synuclein pathogenic functional interaction mediates synaptic dysregulation in huntington's disease.

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.