Hippocampal levels and activity of the sodium/potassium transporting ATPase subunit α-3 (AT1A3) are paralleling memory training in the multiple T-maze in the C57BL/6J mouse

Subjective cognitive decline in conjunction with cerebrospinal fluid anti-ATP1A3 autoantibodies and a low amyloid β 1-42/1-40 ratio: Report and literature review

BACKGROUND

Animal studies reveal the role of the sodium/potassium transporting ATPase α-3 subunit (ATP1A3) in maintaining the resting membrane potential and thus in synaptic information processing and potentially cognitive disorders. However, autoantibodies against AT1A3 have not previously been reported in patients with subjective cognitive decline.

CASE PRESENTATION

We report the case of a 57-year-old female who underwent neuropsychological testing, magnetic resonance imaging (MRI) and 18 F fluorodesoxyglucose positron emission tomography (FDG-PET) imaging, and cerebrospinal fluid (CSF) analysis. Neural autoantibodies were assessed in serum and CSF. We found a normal cognitive profile together with a self-reported cognitive decline, and such consistent with subjective cognitive decline (SCD). Analysis of the cerebrospinal fluid revealed anti-ATP1A3 autoantibodies. ATP1A3 autoantibodies were also detected in serum. Analysis of amyloid pathology markers in the CSF showed a slightly reduced amyloid β1-42/ amyloid β1-40 ratio. In view of the possible paraneoplastic autoantibodies, whole-body FDG-PET was performed, which did not reveal a malignancy-specific lesion. FDG-PET of the brain also showed no hypometabolism. We diagnosed SCD based on CSF-affirmed possible Alzheimer´s pathologic change with ATP1A3 autoantibodies in CSF and serum.

CONCLUSIONS

To our knowledge, this is the first report of CSF and serum ATP1A3 autoantibodies associated with SCD although an incidental finding cannot be fully excluded. In addition, amyloid pathology was detected via CSF biomarkers, suggesting that ATP1A3 autoantibodies are a potentially promising biomarker in SCD with an Alzheimer´s pathologic change if confirmed in large-scale studies.

Novel E815K knock-in mouse model of alternating hemiplegia of childhood

De novo mutations causing dysfunction of the ATP1A3 gene, which encodes the α3 subunit of Na⁺/K⁺-ATPase pump expressed in neurons, result in alternating hemiplegia of childhood (AHC). AHC manifests as paroxysmal episodes of hemiplegia, dystonia, behavioral abnormalities, and seizures. The first aim of this study was to characterize a novel knock-in mouse model (Atp1a3^E815K+/-, Matoub, Matb^+/-) containing the E815K mutation of the Atp1a3 gene recognized as causing the most severe and second most common phenotype of AHC with increased morbidity and mortality as compared to other mutations. The second aim was to investigate the effects of flunarizine, currently the most effective drug used in AHC, to further validate our model and to help address a question with significant clinical implications that has not been addressed in prior studies. Specifically, many E815K patients have clinical decompensation and catastrophic regression after discontinuing flunarizine therapy; however, it is not known whether this is congruent with the natural course of the disease and is a result of withdrawal from an acute beneficial effect, withdrawal from a long-term protective effect or from a detrimental effect of prior flunarizine exposure. Our behavioral and neurophysiological testing demonstrated that Matb^+/- mice express a phenotype that bears a strong resemblance to the E815K phenotype in AHC. In addition, these mice developed spontaneous seizures with high incidence of mortality and required fewer electrical stimulations to reach the kindled state as compared to wild-type littermates. Matb^+/- mice treated acutely with flunarizine had reduction in hemiplegic attacks as compared with vehicle-treated mice. After withdrawal of flunarizine, Matb^+/- mice that had received flunarizine did neither better nor worse, on behavioral tests, than those who had received vehicle. We conclude that: 1) Our mouse model containing the E815K mutation manifests clinical and neurophysiological features of the most severe form of AHC, 2) Flunarizine demonstrated acute anti-hemiplegic effects but not long-term beneficial or detrimental behavioral effects after it was stopped, and 3) The Matb^+/- mouse model can be used to investigate the underlying pathophysiology of ATP1A3 dysfunction and the efficacy of potential treatments for AHC.

Native DIGE proteomic analysis of mitochondria from substantia nigra and striatum during neuronal degeneration and its compensation in an animal model of early Parkinson's disease

Cause of Parkinson's disease (PD) is still not understood. Motor symptoms are not observed at early stages of disease due to compensatory processes. Dysfunction of mitochondria was indicated already at preclinical PD. Selective toxin 6-OHDA was applied to kill dopaminergic neurons in substantia nigra and disturb neuronal transmission in striatum. Early phase of active degeneration and later stage, when surviving cells adapted to function normally, were analysed. 2D BN/SDS difference gel electrophoresis (DIGE) of mitochondrial proteome enabled to point out crucial processes involved at both time-points in dopaminergic structures. Marker proteins such as DPYSL2, HSP60, ATP1A3, EAAT2 indicated structural remodelling, cytoskeleton rearrangement, organelle trafficking, axon outgrowth and regeneration. Adaptations in dopaminergic and glutamatergic neurotransmission, recycling of synaptic vesicles, along with enlargement of mitochondria mass were proposed as causative for compensation. Changed expression of carbohydrates metabolism and oxidative phosphorylation proteins were described, including their protein-protein interactions and supercomplex assembly.

Apolipoprotein D Internalization Is a Basigin-dependent Mechanism

Apolipoprotein D (apoD), a member of the lipocalin family, is a 29-kDa secreted glycoprotein that binds and transports small lipophilic molecules. Expressed in several tissues, apoD is up-regulated under different stress stimuli and in a variety of pathologies. Numerous studies have revealed that overexpression of apoD led to neuroprotection in various mouse models of acute stress and neurodegeneration. This multifunctional protein is internalized in several cells types, but the specific internalization mechanism remains unknown. In this study, we demonstrate that the internalization of apoD involves a specific cell surface receptor in 293T cells, identified as the transmembrane glycoprotein basigin (BSG, CD147); more particularly, its low glycosylated form. Our results show that internalized apoD colocalizes with BSG into vesicular compartments. Down-regulation of BSG disrupted the internalization of apoD in cells. In contrast, overexpression of basigin in SH-5YSY cells, which poorly express BSG, restored the uptake of apoD. Cyclophilin A, a known ligand of BSG, competitively reduced apoD internalization, confirming that BSG is a key player in the apoD internalization process. In summary, our results demonstrate that basigin is very likely the apoD receptor and provide additional clues on the mechanisms involved in apoD-mediated functions, including neuroprotection.

Environmental stimulation improves performance in the ox-maze task and recovers Na+,K+-ATPase activity in the hippocampus of hypoxic-ischemic rats

In animal models, environmental enrichment (EE) has been found to be an efficient treatment for alleviating the consequences of neonatal hypoxia-ischemia (HI). However the potential for this therapeutic strategy and the mechanisms involved are not yet clear. The aim of present study is to investigate behavioral performance in the ox-maze test and Na+,K+-ATPase, catalase (CAT) and glutathione peroxidase (GPx) activities in the hippocampus of rats that suffered neonatal HI and were stimulated in an enriched environment. Seven-day-old rats were submitted to the HI procedure and divided into four groups: control maintained in standard environment (CTSE), control submitted to EE (CTEE), HI in standard environment (HISE) and HI in EE (HIEE). Animals were stimulated with EE for 9 weeks (1 h/day for 6 days/week) and then behavioral and biochemical parameters were evaluated. Present results indicate learning and memory in the ox-maze task were impaired in HI rats and this effect was recovered after EE. Hypoxic-ischemic event did not alter the Na+,K+-ATPase activity in the right hippocampus (ipsilateral to arterial occlusion). However, on the contralateral hemisphere, HI caused a decrease in this enzyme activity that was recovered by EE. The activities of GPx and CAT were not changed by HI in any group evaluated. In conclusion, EE was effective in recovering learning and memory impairment in the ox-maze task and Na+,K+-ATPase activity in the hippocampus caused by HI. The present data provide further support for the therapeutic potential of environmental stimulation after neonatal HI in rats.

The expanding spectrum of neurological phenotypes in children with ATP1A3 mutations, Alternating Hemiplegia of Childhood, Rapid-onset Dystonia-Parkinsonism, CAPOS and beyond

BACKGROUND

ATP1A3 mutations have now been recognized in infants and children presenting with a diverse group of neurological phenotypes, including Rapid-onset Dystonia-Parkinsonism (RDP), Alternating Hemiplegia of Childhood (AHC), and most recently, Cerebellar ataxia, Areflexia, Pes cavus, Optic atrophy, and Sensorineural hearing loss (CAPOS) syndrome.

METHODS

Existing literature on ATP1A3-related disorders in the pediatric population were reviewed, with attention to clinical features and associated genotypes among those with RDP, AHC, or CAPOS syndrome phenotypes.

RESULTS

While classically defined phenotypes associated with AHC, RDP, and CAPOS syndromes are distinct, common elements among ATP1A3-related neurological disorders include characteristic episodic neurological symptoms and signs that vary in severity, duration, and frequency of occurrence. Affected children typically present in the context of an acute onset of paroxysmal, episodic neurological symptoms ranging from oculomotor abnormalities, hypotonia, paralysis, dystonia, ataxia, seizure-like episodes, or encephalopathy. Neurodevelopmental delays or persistence of dystonia, chorea, or ataxia after resolution of an initial episode are common, providing important clues for diagnosis.

CONCLUSIONS

The phenotypic spectrum of ATP1A3-related neurological disorders continues to expand beyond the distinct yet overlapping phenotypes in patients with AHC, RDP, and CAPOS syndromes. ATP1A3 mutation analysis is appropriate to consider in the diagnostic algorithm for any child presenting with episodic or fluctuating ataxia, weakness or dystonia whether they manifest persistence of neurological symptoms between episodes. Additional work is needed to better identify and classify affected patients and develop targeted treatment approaches.

Centella asiatica Attenuates Diabetes Induced Hippocampal Changes in Experimental Diabetic Rats

Diabetes mellitus has been reported to affect functions of the hippocampus. We hypothesized that Centella asiatica, a herb traditionally being used to improve memory, prevents diabetes-related hippocampal dysfunction. Therefore, the aim of this study was to investigate the protective role of C. asiatica on the hippocampus in diabetes. Methods. Streptozotocin- (STZ-) induced adult male diabetic rats received 100 and 200 mg/kg/day body weight (b.w) C. asiatica leaf aqueous extract for four consecutive weeks. Following sacrifice, hippocampus was removed and hippocampal tissue homogenates were analyzed for Na(+)/K(+)-, Ca(2+)- and Mg(2+)-ATPases activity levels. Levels of the markers of inflammation (tumor necrosis factor, TNF-α; interleukin, IL-6; and interleukin, IL-1β) and oxidative stress (lipid peroxidation product: LPO, superoxide dismutase: SOD, catalase: CAT, and glutathione peroxidase: GPx) were determined. The hippocampal sections were visualized for histopathological changes. Results. Administration of C. asiatica leaf aqueous extract to diabetic rats maintained near normal ATPases activity levels and prevents the increase in the levels of inflammatory and oxidative stress markers in the hippocampus. Lesser signs of histopathological changes were observed in the hippocampus of C. asiatica leaf aqueous extract treated diabetic rats. Conclusions. C. asiatica leaf protects the hippocampus against diabetes-induced dysfunction which could help to preserve memory in this condition.

Alternating hemiplegia of childhood-related neural and behavioural phenotypes in Na+,K+-ATPase α3 missense mutant mice

Missense mutations in ATP1A3 encoding Na⁺,K⁺-ATPase α3 have been identified as the primary cause of alternating hemiplegia of childhood (AHC), a motor disorder with onset typically before the age of 6 months. Affected children tend to be of short stature and can also have epilepsy, ataxia and learning disability. The Na⁺,K⁺-ATPase has a well-known role in maintaining electrochemical gradients across cell membranes, but our understanding of how the mutations cause AHC is limited. Myshkin mutant mice carry an amino acid change (I810N) that affects the same position in Na⁺,K⁺-ATPase α3 as I810S found in AHC. Using molecular modelling, we show that the Myshkin and AHC mutations display similarly severe structural impacts on Na⁺,K⁺-ATPase α3, including upon the K⁺ pore and predicted K⁺ binding sites. Behavioural analysis of Myshkin mice revealed phenotypic abnormalities similar to symptoms of AHC, including motor dysfunction and cognitive impairment. 2-DG imaging of Myshkin mice identified compromised thalamocortical functioning that includes a deficit in frontal cortex functioning (hypofrontality), directly mirroring that reported in AHC, along with reduced thalamocortical functional connectivity. Our results thus provide validation for missense mutations in Na⁺,K⁺-ATPase α3 as a cause of AHC, and highlight Myshkin mice as a starting point for the exploration of disease mechanisms and novel treatments in AHC.