Cognitive deficits in episodic Ataxia type 2 mouse models

CACNA1A haploinsufficiency leads to reduced synaptic function and increased intrinsic excitability

Haploinsufficiency of CACNA1A, encoding the pore-forming α1 subunit of P/Q-type voltage-gated calcium channels, is associated with a clinically variable phenotype ranging from cerebellar ataxia to neurodevelopmental syndromes with epilepsy and intellectual disability. To understand the pathological mechanisms of CACNA1A loss-of-function variants, we characterized a human neuronal model for CACNA1A haploinsufficiency by differentiating isogenic induced pluripotent stem cell lines into glutamatergic neurons and investigated the effect of CACNA1A haploinsufficiency on mature neuronal networks through a combination of electrophysiology, gene expression analysis and in silico modelling. We observed an altered network synchronization in CACNA1A+/- networks alongside synaptic deficits, notably marked by an augmented contribution of GluA2 subunit-lacking α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Intriguingly, these synaptic perturbations coexisted with increased non-synaptically driven activity, as characterized by inhibition of N-methyl-D-aspartate and AMPA receptors on micro-electrode arrays. Single-cell electrophysiology and gene expression analysis corroborated this increased intrinsic excitability through reduced potassium channel function and expression. Moreover, we observed partial mitigation of the CACNA1A+/- network phenotype by 4-aminopyridine, a therapeutic intervention for episodic ataxia type 2. Positive modulation of small conductance calcium-activated potassium channels could reverse the CACNA1A+/- network electrophysiological phenotype. In summary, our study pioneers the characterization of a human induced pluripotent stem cell-derived neuronal model for CACNA1A haploinsufficiency and has unveiled new mechanistic insights. Beyond showcasing synaptic deficits, this neuronal model exhibited increased intrinsic excitability mediated by diminished potassium channel function, underscoring its potential as a therapeutic discovery platform with predictive validity.

Anxiety, memory, and social impairments in the YAC128 mouse model of Huntington's disease

BACKGROUND

Huntington's disease (HD) is an autosomal dominant hereditary disorder, caused by an expansion of polyglutamine in the huntingtin protein. HD is characterized by a progressive decline in motor functions. This decline includes involuntary movements (chorea) and the worsening of controlled motions caused mainly by neuronal dysfunction in the striatum. In addition to the deterioration of motor symptoms, HD patients also suffer from cognitive changes, mood swings, apathy, depression, outbursts of anger, psychosis, and social withdrawal.

OBJECTIVE

A comprehensive examination of cognitive, affective, and social changes in the HD mouse model is required for the development of combined therapy for both motor and non-motor deficits in HD.

METHODS

The behavioral tests for anxiety, memory, and social traits were used in this study.

RESULTS

YAC128 HD transgenic mice exhibited anxiolytic behavior in the novel brightly illuminated environment of the open field and light-dark place preference tests. Moreover, YAC128 HD mice also suffered from a decline in their recognition memory during the novel object recognition test. YAC128 HD mice demonstrated reduced exploration interest during the open field with a non-social target as well as during the first day of the three-chamber social test. Social interaction was also impaired in YAC128 HD mice as it was shown in the social interaction with resident intruder test.

CONCLUSIONS

YAC128 HD mouse model may be used as a model system to test the possible treatments for both motor and non-motor symptoms including memory loss, agitation and social withdrawal.

Intellectual Disability in Episodic Ataxia Type 2: Beyond Paroxysmal Vertigo and Ataxia

BACKGROUND AND PURPOSE

Episodic ataxia type 2 (EA2) is characterized by recurrent vertigo and ataxia due to mutations in CACNA1A that encodes the α1A-subunit of the P/Q-type voltage-gated calcium channel. This study aimed to determine intellectual function in EA2.

METHODS

During 2019-2023, 13 patients (6 males, age range=10-52 years, median age=29 years) with a genetically confirmed diagnosis of EA2 had their intellectual function evaluated using the Korean versions of the Wechsler Intelligence Scales (version IV) for adults or children in 3 referral-based university hospitals in South Korea.

RESULTS

The full-scale intelligence quotients (FSIQs) among the 13 patients were below the average (90-109) in 11, low average (80-89) in 5 (38.5%), borderline (70-79) in 1 (7.7%), and indicated intellectual disability (≤69) in 5 (38.5%). These patterns of cognitive impairments were observed in all four of the following subtests: verbal comprehension, perceptual reasoning, working memory, and processing speed. The FSIQ was not correlated with the ages at onset for vertigo and ataxia (Pearson correlation: p=0.40).

CONCLUSIONS

Patients with EA2 may have hidden intellectual disabilities even without a history of epilepsy or administration of antiepileptic drugs, and should be considered for genetic counseling and therapeutic interventions. Given the availability of medication to control episodic vertigo and ataxia, early diagnosis and management are important in preventing irreversible brain dysfunction in EA2.

A combination of chlorzoxazone and folic acid improves recognition memory, anxiety and depression in SCA3-84Q mice

Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease, is reported to be the most common type of autosomal dominant cerebellar ataxia (ADCA). SCA3 patients suffer from a progressive decline in motor coordination and other disease-associated symptoms. Moreover, recent studies have reported that SCA3 patients also exhibit symptoms of cerebellar cognitive affective syndrome (CCAS). We previously observed signs of CCAS in mouse model of SCA3. Particularly, SCA3-84Q mice suffer from anxiety, recognition memory decline, and also exhibit signs of low mood and aversion to activity. Here we studied the effect of long-term injections of SK channels activator chlorzoxazone (CHZ) together and separately with the folic acid (FA) on the cerebellar Purkinje cell (PC) firing and histology, and also on the motor and cognitive functions as well as mood alterations in SCA3-84Q hemizygous transgenic mice. We realized that both CHZ and CHZ-FA combination had similar positive effect on pure cerebellum impairments including PC firing precision, PC histology, and motor performance in SCA3-84Q mice. However, only the CHZ-FA combination, but not CHZ, had significantly ameliorated the signs of anxiety and depression, and also noticeably improved recognition memory in SCA3-84Q mice. Our results suggest that the combination therapy for both ataxia and non-motor symptoms is required for the complex treatment of ADCA.

Impairments of cerebellar structure and function in a zebrafish KO of neuropsychiatric risk gene znf536

Genetic variants in ZNF536 contribute to the risk for neuropsychiatric disorders such as schizophrenia, autism, and others. The role of this putative transcriptional repressor in brain development and function is, however, largely unknown. We generated znf536 knockout (KO) zebrafish and studied their behavior, brain anatomy, and brain function. Larval KO zebrafish showed a reduced ability to compete for food, resulting in decreased total body length and size. This phenotype can be rescued by segregating the homozygous KO larvae from their wild-type and heterozygous siblings, enabling studies of adult homozygous KO animals. In adult KO zebrafish, we observed significant reductions in anxiety-like behavior and social interaction. These znf536 KO zebrafish have decreased cerebellar volume, corresponding to decreased populations of specific neuronal cells, especially in the valvular cerebelli (Va). Finally, using a Tg[mbp:mgfp] line, we identified a previously undetected myelin structure located bilaterally within the Va, which also displayed a reduction in volume and disorganization in KO zebrafish. These findings indicate an important role for ZNF536 in brain development and implicate the cerebellum in the pathophysiology of neuropsychiatric disorders.

Memory decline, anxiety and depression in the mouse model of spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3) is an autosomal dominant hereditary disorder, caused by an expansion of polyglutamine in the ataxin-3 protein. SCA3 symptoms include progressive motor decline caused by an atrophy of the cerebellum and brainstem. However, it was recently reported that SCA3 patients also suffer from the cerebellar cognitive affective syndrome. The majority of SCA3 patients exhibit cognitive decline and approximately half of them suffer from depression and anxiety. The necessity to find a combined therapy for both motor and cognitive deficits in a SCA3 mouse model is required for the development of SCA3 treatment. Here, we demonstrated that the SCA3-84Q transgenic mice exhibited anxiety over the novel brightly illuminated environment in the open field, novelty suppressed feeding, and light-dark place preference tests. Moreover, SCA3-84Q mice also suffered from a decline in recognition memory during the novel object recognition test. SCA3-84Q mice also demonstrated floating behavior during the Morris water maze that can be interpreted as a sign of low mood and aversion to activity, i.e. depressive-like state. SCA3-84Q mice also spent more time immobile during the forced swimming and tail suspension tests which is also evidence for depressive-like behavior. Therefore, the SCA3-84Q mouse model may be used as a model system to test the possible treatments for both ataxia and non-motor symptoms including depression, anxiety, and memory loss.

Cognitive Decline and Mood Alterations in the Mouse Model of Spinocerebellar Ataxia Type 2

Spinocerebellar ataxia type 2 (SCA2) is a hereditary disorder, caused by an expansion of polyglutamine in the ataxin-2 protein. Although the mutant protein is expressed throughout all the cell and organ types, the cerebellum is primarily affected. The disease progression is mainly accompanied by a decline in motor functions. However, the disturbances in cognitive abilities and low mental state have also been reported in patients. Recent evidence suggests that the cerebellar functionality expands beyond the motor control. Thus, the cerebellum turned out to be involved into the language, verbal working, and spatial memory; executive functions such as working memory, planning, organizing, and strategy formation; and emotional processing. Here, we used the transgenic SCA2-58Q mice to evaluate their anxiety, cognitive functions, and mood alterations. The expression of the mutant ataxin-2 specifically in the cerebellar Purkinje cells (PCs) in SCA2-58Q mice allowed us to study the direct involvement of the cerebellum into the cognitive and affective control. We determined that SCA2-58Q mice exhibit anxiolytic behavior, decline in spatial memory, and a depressive-like state. Our results support the idea of cerebellar involvement in cognitive control and the handling of emotions.

A chlorzoxazone-folic acid combination improves cognitive affective decline in SCA2-58Q mice

Spinocerebellar ataxia type 2 (SCA2) is a polyglutamine disorder caused by a pathological expansion of CAG repeats in ATXN2 gene. SCA2 is accompanied by cerebellar degeneration and progressive motor decline. Cerebellar Purkinje cells (PCs) seem to be primarily affected in this disorder. The majority of the ataxia research is focused on the motor decline observed in ataxic patients and animal models of the disease. However, recent evidence from patients and ataxic mice suggests that SCA2 can also share the symptoms of the cerebellar cognitive affective syndrome. We previously reported that SCA2-58Q PC-specific transgenic mice exhibit anxiolytic behavior, decline in spatial memory, and a depressive-like state. Here we studied the effect of the activation of the small conductance calcium-activated potassium channels (SK channels) by chlorzoxazone (CHZ) combined with the folic acid (FA) on the PC firing and also motor, cognitive and affective symptoms in SCA2-58Q mice. We realized that CHZ-FA combination improved motor and cognitive decline as well as ameliorated mood alterations in SCA2-58Q mice without affecting the firing rate of their cerebellar PCs. Our results support the idea of the combination therapy for both ataxia and non-motor symptoms in ataxic mice without affecting the firing frequency of PCs.

Experimental Treatment with Edaravone in a Mouse Model of Spinocerebellar Ataxia 1

Edaravone is a mitochondrially targeted drug with a suggested capability to modify the course of diverse neurological diseases. Nevertheless, edaravone has not been tested yet in the context of spinocerebellar ataxia 1 (SCA1), an incurable neurodegenerative disease characterized mainly by cerebellar disorder, with a strong contribution of inflammation and mitochondrial dysfunction. This study aimed to address this gap, exploring the potential of edaravone to slow down SCA1 progression in a mouse knock-in SCA1 model. SCA1^154Q/2Q and healthy SCA1^2Q/2Q mice were administered either edaravone or saline daily for more than 13 weeks. The functional impairments were assessed via a wide spectrum of behavioral assays reflecting motor and cognitive deficits and behavioral abnormalities. Moreover, we used high-resolution respirometry to explore mitochondrial function, and immunohistochemical and biochemical tools to assess the magnitude of neurodegeneration, inflammation, and neuroplasticity. Data were analyzed using (hierarchical) Bayesian regression models, combined with the methods of multivariate statistics. Our analysis pointed out various previously documented neurological and behavioral deficits of SCA1 mice. However, we did not detect any plausible therapeutic effect of edaravone on either behavioral dysfunctions or other disease hallmarks in SCA1 mice. Thus, our results did not provide support for the therapeutic potential of edaravone in SCA1.

Psychiatric-Like Impairments in Mouse Models of Spinocerebellar Ataxias

Many patients with spinocerebellar ataxia (SCA) suffer from diverse neuropsychiatric issues, including memory impairments, apathy, depression, or anxiety. These neuropsychiatric aspects contribute per se to the reduced quality of life and worse prognosis. However, the extent to which SCA-related neuropathology directly contributes to these issues remains largely unclear. Behavioral profiling of various SCA mouse models can bring new insight into this question. This paper aims to synthesize recent findings from behavioral studies of SCA patients and mouse models. The role of SCA neuropathology for shaping psychiatric-like impairments may be exemplified in mouse models of SCA1. These mice evince robust cognitive impairments which are shaped by both the cerebellar as well as out-of-cerebellar pathology. Although emotional-related alternations are also present, they seem to be less robust and more affected by the specific distribution and character of the neuropathology. For example, cerebellar-specific pathology seems to provoke behavioral disinhibition, leading to seemingly decreased anxiety, whereas complex SCA1 neuropathology induces anxiety-like phenotype. In SCA1 mice with complex neuropathology, some of the psychiatric-like impairments are present even before marked cerebellar degeneration and ataxia and correlate with hippocampal atrophy. Similarly, complete or partial deletion of the implicated gene (Atxn1) leads to cognitive dysfunction and anxiety-like behavior, respectively, without apparent ataxia and cerebellar degeneration. Altogether, these findings collectively suggest that the neuropsychiatric issues have a biological basis partially independent of the cerebellum. As some neuropsychiatric issues may stem from weakening the function of the implicated gene, therapeutic reduction of its expression by molecular approaches may not necessarily mitigate the neuropsychiatric issues.

Cerebellar contribution to threat probability in a SCA6 mouse model

Fear and anxiety have proven to be essential during the evolutionary process. However, the mechanisms involved in recognizing and categorizing threat probability (i.e. low to high) to elicit the appropriate defensive behavior are yet to be determined. In this study, we investigated the cerebellar contribution in evoking appropriate defensive escape behavior using a purely cerebellar, neurodegenerative mouse model for spinocerebellar ataxia type 6 which is caused by an expanded CAG repeat in exon 47 of the P/Q type calcium channel α1A subunit. These mice overexpress the carboxy terminus (CT) of the P/Q type calcium channel containing an expanded 27 CAG repeat specifically in cerebellar Purkinje cells (CT-longQ27PC). We found that our CT-longQ27PC mice exhibit anxiolytic behavior in the open field, elevated plus maze and light/dark place preference tests, which could be recovered with more threatening conditions such as brighter lighting, meowing sounds and an ultrasound repellent. Their innate fear to find safety in the Barnes maze and visual cliff tests was also diminished with subsequent trials, which could be partially recovered with an ultrasound repellent in the Barnes maze. However, under higher threat conditions such as in the light/dark place preference with ultrasound repellent and in the looming tests, CT-longQ27PC mice responded with higher defensive escape behaviors as controls. Moreover, CT-longQ27PC mice displayed increased levels of CT-labeled aggregates compared with controls. Together these data suggest that cerebellar degeneration by overexpression of CT-longQ27PC is sufficient to impair defensive escape responses in those mice.

Deletion of the P/Q-Type Calcium Channel from Serotonergic Neurons Drives Male Aggression in Mice

Aggressive behavior is one of the most conserved social interactions in nature and serves as a crucial evolutionary trait. Serotonin (5-HT) plays a key role in the regulation of our emotions, such as anxiety and aggression, but which molecules and mechanisms in the serotonergic system are involved in violent behavior are still unknown. In this study, we show that deletion of the P/Q-type calcium channel selectively from serotonergic neurons in the dorsal raphe nuclei (DRN) augments aggressive behavior in male mice, while anxiety is not affected. These mice demonstrated increased induction of the immediate early gene c-fos and in vivo serotonergic firing activity in the DRN. The ventrolateral part of the ventromedial hypothalamus is also a prominent region of the brain mediating aggression. We confirmed a monosynaptic projection from the DRN to the ventrolateral part of the ventromedial hypothalamus, and silencing these projections with an inhibitory designer receptor exclusively activated by a designer drug effectively reduced aggressive behavior. Overall, our findings show that deletion of the P/Q-type calcium channel from DRN neurons is sufficient to induce male aggression in mice and regulating its activity may serve as a therapeutic approach to treat violent behavior.SIGNIFICANCE STATEMENT In this study, we show that P/Q-type calcium channel is mediating aggression in serotonergic neurons from the dorsal raphe nucleus via monosynaptic projections to the ventrolateral part of the ventromedial hypothalamus. More importantly, silencing these projections reduced aggressive behavior in mice and may serve as a therapeutic approach for treating aggression in humans.