Hippocampal network hyperexcitability in young transgenic mice expressing human mutant alpha-synuclein

Intracerebroventricular injection of α-synuclein preformed fibrils do not induce motor and olfactory impairment in C57BL/6 mice

INTRODUCTION

Alpha-synuclein (αSyn) is believed to play a central role in the pathogenesis of Parkinson's disease (PD). Cerebrospinal fluid (CSF) total αSyn were significantly lower in PD patients, whereas the aggregates were higher, and this phenomenon was further exacerbated with longer disease duration. However, whether CSF αSyn can be the cause and/or a consequence in PD is not fully elucidated.

METHOD

We administered 2 ng or 200 ng αSyn preformed fibrils (PFFs) by intracerebroventricular injection for consecutive 7 days in C57BL/6 mice. The olfactory function was assessed by the olfactory discrimination test and buried food-seeking test. The locomotor function was assessed by the rotarod test, pole test, open field test and CatWalk gait analysis. Phosphorylated αSyn at serine 129 was detected by the immunohistochemistry staining. Iron levels was determined by Perl's-diaminobenzidine iron staining and synchrotron-based X-ray fluorescence.

RESULTS

The mice did not exhibit any diffuse synucleinopathy in the brain for up to 30 weeks, although αSyn PFFs induced aggregation in SH-SY5Y cells and in the substantia nigra and striatum of mice with stereotactic injection. No impairment of motor behaviors or olfactory functions were observed, although there was a temporary motor enhancement at 1 week. We then demonstrated iron levels were comparable in certain brain regions, suggesting there was no iron deposition/redistribution occurred.

CONCLUSION

The intraventricular injection of αSyn PFFs does not induce synucleinopathy or behavioral symptoms. These findings have implications that CSF αSyn aggregates may not necessarily contribute to the onset or progression in PD.

The role of parvalbumin interneuron dysfunction across neurodegenerative dementias

Parvalbumin-positive (PV+) basket neurons are fast-spiking, non-adapting inhibitory interneurons whose oscillatory activity is essential for regulating cortical excitation/inhibition balance. Their dysfunction results in cortical hyperexcitability and gamma rhythm disruption, which have recently gained substantial traction as contributing factors as well as potential therapeutic targets for the treatment of Alzheimer's Disease (AD). Recent evidence indicates that PV+ cells are also impaired in Frontotemporal Dementia (FTD) and Dementia with Lewy bodies (DLB). However, no attempt has been made to integrate these findings into a coherent pathophysiological framework addressing the contribution of PV+ interneuron dysfunction to the generation of cortical hyperexcitability and gamma rhythm disruption in FTD and DLB. To fill this gap, we epitomized the most recent evidence on PV+ interneuron impairment in AD, FTD, and DLB, focusing on its contribution to the generation of cortical hyperexcitability and gamma oscillatory disruption and their interplay with misfolded protein accumulation, neuronal death, and clinical symptoms' onset. Our work deepens the current understanding concerning the role of PV+ interneuron dysfunction across neurodegenerative dementias, highlighting commonalities and differences among AD, FTD, and DLB, thus paving the way for identifying novel biomarkers and potential therapeutic targets for the treatment of these diseases.

Evidence for prodromal changes in neuronal excitability and neuroinflammation in the hippocampus in young alpha-synuclein (A30P) transgenic mice

Introduction

Neuronal hyperexcitability and neuroinflammation are thought to occur at early stages in a range of neurodegenerative diseases. Neuroinflammation, notably activation of microglia, has been identified as a potential prodromal marker of dementia with Lewy bodies (DLB). Using a transgenic mouse model of DLB that over-expresses human mutant (A30P) alpha-synuclein (hα-syn) we have investigated whether early neuroinflammation is evident in the hippocampus in young pre-symptomatic animals.

Methods

Previous studies have shown early hyperexcitability in the hippocampal CA3 region in male A30P mice at 2-4 months of age, therefore, in the current study we have immunostained this region for markers of neuronal activity (c-Fos), reactive astrocytes (glial fibrillary acidic protein, GFAP), microglia (ionizing calcium binding adapter protein 1, Iba-1) and reactive microglia (inducible nitric oxide synthase, iNOS).

Results

We found an interesting biphasic change in the expression of c-Fos in A30P mice with high expression at 1 month, consistent with early onset of hyperexcitability, but lower expression from 2-4 months in male A30P mice compared to wild-type (WT) controls, possibly indicating chronic hyperexcitability. Neuroinflammation was indicated by significant increases in the % area of GFAP and the number of Iba-1+ cells that expressed iNOS immunoreactivity in the CA3 region in 2-4 months A30P male mice compared to WT controls. A similar increase in % area of GFAP was observed in female A30P mice, however, the Iba-1 count was not different between female WT and A30P mice. In WT mice aged 2-4 months only 4.6% of Iba-1+ cells co-expressed iNOS. In contrast, in age matched A30P mice 87% of cells co-expressed Iba-1 and iNOS. Although there was no difference in GFAP immunoreactivity at 1 month, Iba-1/iNOS co-expression was also increased in a cohort of 1 month old A30P mice.

Discussion

Abnormal hα-syn expression in A30P mice caused early changes in network excitability, as indicated by c-Fos expression, and neuroinflammation which might contribute to disease progression.

Delineating mechanisms underlying parvalbumin neuron impairment in different neurological and neurodegenerative disorders: the emerging role of mitochondrial dysfunction

Given the current paucity of effective treatments in many neurological disorders, delineating pathophysiological mechanisms among the major psychiatric and neurodegenerative diseases may fuel the development of novel, potent treatments that target shared pathways. Recent evidence suggests that various pathological processes, including bioenergetic failure in mitochondria, can perturb the function of fast-spiking, parvalbumin-positive neurons (PV+). These inhibitory neurons critically influence local circuit regulation, the generation of neuronal network oscillations and complex brain functioning. Here, we survey PV+ cell vulnerability in the major neuropsychiatric, and neurodegenerative diseases and review associated cellular and molecular pathophysiological alterations purported to underlie disease aetiology.

Exploring the correlation between serum α-synuclein and abnormal electroencephalography patterns in children with epilepsy, as well as electroencephalographic discharge index

BACKGROUND

This study investigates the correlation between serum α-synuclein and abnormal electroencephalography patterns as well as the electroencephalographic discharge index in children with epilepsy.

METHODS

Fasting venous blood of 4 ml were collected from the participants, centrifuged at 3000 rpm with a centrifuge radius of 15 cm for 20 min, and stored in a -70 °C freezer for serum α-synuclein examination. Normal EEG: Exhibits symmetrical α or β rhythm primarily in the occipital region.

RESULTS

The electroencephalogram (EEG) examination results showed that out of the 110 children with epilepsy, 9 had normal EEGs, 35 had mild EEG abnormalities, 46 had moderate EEG abnormalities, and 20 had severe EEG abnormalities. It is noteworthy that the control group did not exhibit any abnormalities in EEG. In the epilepsy group, serum α-synuclein levels were higher than those in the normal group, while α-wave power and θ-wave power were lower than in the normal group (p < 0.05). Among children with epilepsy, those with mild EEG abnormalities, moderate EEG abnormalities, and severe EEG abnormalities had higher serum α-synuclein levels and electroencephalographic discharge indices compared to children with normal EEGs (p < 0.05). Additionally, among children with EEG abnormalities, those with mild, moderate, and severe EEG abnormalities had progressively increasing serum α-synuclein levels and electroencephalographic discharge indices (p < 0.05).

CONCLUSIONS

Children with epilepsy exhibit elevated serum α-synuclein levels, and there is a positive correlation between α-synuclein levels and the grading of EEG abnormalities as well as the electroencephalographic discharge index.

Latest advances in mechanisms of epileptic activity in Alzheimer's disease and dementia with Lewy Bodies

Alzheimer's disease (AD) and dementia with Lewy bodies (DLB) stand as the prevailing sources of neurodegenerative dementia, impacting over 55 million individuals across the globe. Patients with AD and DLB exhibit a higher prevalence of epileptic activity compared to those with other forms of dementia. Seizures can accompany AD and DLB in early stages, and the associated epileptic activity can contribute to cognitive symptoms and exacerbate cognitive decline. Aberrant neuronal activity in AD and DLB may be caused by several mechanisms that are not yet understood. Hyperexcitability could be a biomarker for early detection of AD or DLB before the onset of dementia. In this review, we compare and contrast mechanisms of network hyperexcitability in AD and DLB. We examine the contributions of genetic risk factors, Ca2+ dysregulation, glutamate, AMPA and NMDA receptors, mTOR, pathological amyloid beta, tau and α-synuclein, altered microglial and astrocytic activity, and impaired inhibitory interneuron function. By gaining a deeper understanding of the molecular mechanisms that cause neuronal hyperexcitability, we might uncover therapeutic approaches to effectively ease symptoms and slow down the advancement of AD and DLB.

Hippocampal synaptic failure is an early event in experimental parkinsonism with subtle cognitive deficit

Learning and memory mainly rely on correct synaptic function in the hippocampus and other brain regions. In Parkinson's disease, subtle cognitive deficits may even precede motor signs early in the disease. Hence, we set out to unravel the earliest hippocampal synaptic alterations associated with human α-synuclein overexpression prior to and soon after the appearance of cognitive deficits in a parkinsonism model. We bilaterally injected adeno-associated viral vectors encoding A53T-mutated human α-synuclein into the substantia nigra of rats, and evaluated them 1, 2, 4 and 16 weeks post-inoculation by immunohistochemistry and immunofluorescence to study degeneration and distribution of α-synuclein in the midbrain and hippocampus. The object location test was used to evaluate hippocampal-dependent memory. Sequential window acquisition of all theoretical mass spectrometry-based proteomics and fluorescence analysis of single-synapse long-term potentiation were used to study alterations to protein composition and plasticity in isolated hippocampal synapses. The effect of L-DOPA and pramipexole on long-term potentiation was also tested. Human α-synuclein was found within dopaminergic and glutamatergic neurons of the ventral tegmental area, and in dopaminergic, glutamatergic and GABAergic axon terminals in the hippocampus from 1 week post-inoculation, concomitant with mild dopaminergic degeneration in the ventral tegmental area. In the hippocampus, differential expression of proteins involved in synaptic vesicle cycling, neurotransmitter release and receptor trafficking, together with impaired long-term potentiation were the first events observed (1 week post-inoculation), preceding cognitive deficits (4 weeks post-inoculation). Later on, at 16 weeks post-inoculation, there was a deregulation of proteins involved in synaptic function, particularly those involved in the regulation of membrane potential, ion balance and receptor signalling. Hippocampal long-term potentiation was impaired before and soon after the onset of cognitive deficits, at 1 and 4 weeks post-inoculation, respectively. L-DOPA recovered hippocampal long-term potentiation more efficiently at 4 weeks post-inoculation than pramipexole, which partially rescued it at both time points. Overall, we found impaired synaptic plasticity and proteome dysregulation at hippocampal terminals to be the first events that contribute to the development of cognitive deficits in experimental parkinsonism. Our results not only point to dopaminergic but also to glutamatergic and GABAergic dysfunction, highlighting the relevance of the three neurotransmitter systems in the ventral tegmental area-hippocampus interaction from the earliest stages of parkinsonism. The proteins identified in the current work may constitute potential biomarkers of early synaptic damage in the hippocampus and hence, therapies targeting these could potentially restore early synaptic malfunction and consequently, cognitive deficits in Parkinson's disease.

Subclinical Epileptiform Activity in Dementia with Lewy Bodies

BACKGROUND

Patients with dementia with Lewy bodies (DLB) have a higher probability of seizures than in normal aging and in other types of neurodegenerative disorders. Depositions of α-synuclein, a pathological hallmark of DLB, can induce network excitability, which can escalate into seizure activity. Indicator of seizures are epileptiform discharges as observed using electroencephalography (EEG). However, no studies have so far investigated the occurrence of interictal epileptiform discharges (IED) in patients with DLB.

OBJECTIVES

To investigate if IED as measured with ear-EEG occurs with a higher frequency in patients with DLB compared to healthy controls (HC).

METHODS

In this longitudinal observational exploratory study, 10 patients with DLB and 15 HC were included in the analysis. Patients with DLB underwent up to three ear-EEG recordings, each lasting up to 2 days, over a period of 6 months.

RESULTS

At baseline, IED were detected in 80% of patients with DLB and in 46.7% of HC. The spike frequency (spikes or sharp waves/24 hours) was significantly higher in patients with DLB as compared to HC with a risk ratio of 2.52 (CI, 1.42-4.61; P-value = 0.001). Most IED occurred at night.

CONCLUSIONS

Long-term outpatient ear-EEG monitoring detects IED in most patients with DLB with an increased spike frequency compared to HC. This study extends the spectrum of neurodegenerative disorders in which epileptiform discharges occurs at an elevated frequency. It is possible that epileptiform discharges are, therefore, a consequence of neurodegeneration. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

A cytoskeleton-membrane interaction conserved in fast-spiking neurons controls movement, emotion, and memory

The pathogenesis of schizophrenia is believed to involve combined dysfunctions of many proteins including microtubule-associated protein 6 (MAP6) and Kv3.1 voltage-gated K+ (Kv) channel, but their relationship and functions in behavioral regulation are often not known. Here we report that MAP6 stabilizes Kv3.1 channels in parvalbumin-positive (PV+ ) fast-spiking GABAergic interneurons, regulating behavior. MAP6-/- and Kv3.1-/- mice display similar hyperactivity and avoidance reduction. Their proteins colocalize in PV+ interneurons and MAP6 deletion markedly reduces Kv3.1 protein level. We further show that two microtubule-binding modules of MAP6 bind the Kv3.1 tetramerization domain with high affinity, maintaining the channel level in both neuronal soma and axons. MAP6 knockdown by AAV-shRNA in the amygdala or the hippocampus reduces avoidance or causes hyperactivity and recognition memory deficit, respectively, through elevating projection neuron activity. Finally, knocking down Kv3.1 or disrupting the MAP6-Kv3.1 binding in these brain regions causes avoidance reduction and hyperactivity, consistent with the effects of MAP6 knockdown. Thus, disrupting this conserved cytoskeleton-membrane interaction in fast-spiking neurons causes different degrees of functional vulnerability in various neural circuits.

Traditional and Innovative Anti-seizure Medications Targeting Key Physiopathological Mechanisms: Focus on Neurodevelopment and Neurodegeneration

Despite the wide range of compounds currently available to treat epilepsy, there is still no drug that directly tackles the physiopathological mechanisms underlying its development. Indeed, antiseizure medications attempt to prevent seizures but are inefficacious in counteracting or rescuing the physiopathological phenomena that underlie their onset and recurrence, and hence do not cure epilepsy. Classically, the altered excitation/inhibition balance is postulated as the mechanism underlying epileptogenesis and seizure generation. This oversimplification, however, does not account for deficits in homeostatic plasticity resulting from either insufficient or excessive compensatory mechanisms in response to a change in network activity. In this respect, both neurodevelopmental epilepsies and those associated with neurodegeneration may share common underlying mechanisms that still need to be fully elucidated. The understanding of these molecular mechanisms shed light on the identification of new classes of drugs able not only to suppress seizures, but also to present potential antiepileptogenic effects or "disease-modifying" properties.

Epilepsy and Alzheimer's Disease: Current Concepts and Treatment Perspective on Two Closely Related Pathologies

The literature on epileptic seizures in Alzheimer's disease has significantly increased over the past decades. Remarkably, several studies suggest a bi-directional link between these two common neurological diseases, with either condition carrying a nearly 2-fold risk of contracting the other in comparison to healthy subjects. In this respect, evidence from both clinical and preclinical studies indicates that epileptogenesis and neurodegeneration possibly share common underlying mechanisms. However, the precise association between epileptogenesis and neurodegeneration still needs to be fully elucidated. Targeted intervention to reduce abnormal network hyperexcitability might constitute a therapeutic strategy to postpone the onset of later neurodegenerative changes and consequent cognitive decline by many years in patients. By virtue of this, an early diagnosis and treatment of seizures in patients with Alzheimer's disease should be pursued. To date, no guidelines are available for treating epileptic activity in this context, largely due to the paucity of studies sufficient to answer the related questions. Accordingly, clinical trials are mandatory, not only to inform clinicians about symptomatic management of seizures in Alzheimer's disease patients but also to detect if treatment with antiseizure medications could have disease-modifying effects. Moreover, it will be fundamental to expand the application of animal models of Alzheimer's disease to comorbid conditions, such as epilepsy both to reveal the mechanisms underlying seizure onset and to better define their role in cognitive decline. Such models could also be useful to identify pharmacological compounds having therapeutically effectiveness as well as reliable early biomarkers for seizures in Alzheimer's disease.

Relationships between Inflammation and Age-Related Neurocognitive Changes

The relationship between inflammation and age-related neurocognitive changes is significant, which may relate to the age-related immune dysfunctions characterized by the senescence of immune cells and elevated inflammatory markers in the peripheral circulation and the central nervous system. In this review, we discuss the potential mechanisms, including the development of vascular inflammation, neuroinflammation, organelle dysfunctions, abnormal cholesterol metabolism, and glymphatic dysfunctions as well as the role that the key molecules play in the immune-cognition interplay. We propose potential therapeutic pharmacological and behavioral strategies for ameliorating age-related neurocognitive changes associated with inflammation. Further research to decipher the multidimensional roles of chronic inflammation in normal and pathological aging processes will help unfold the pathophysiological mechanisms underpinning neurocognitive disorders. The insight gained will lay the path for developing cost-effective preventative measures and the buffering or delaying of age-related neurocognitive decline.

Estrogen-related receptor gamma regulates mitochondrial and synaptic genes and modulates vulnerability to synucleinopathy

Many studies implicate mitochondrial dysfunction as a key contributor to cell loss in Parkinson disease (PD). Previous analyses of dopaminergic (DAergic) neurons from patients with Lewy-body pathology revealed a deficiency in nuclear-encoded genes for mitochondrial respiration, many of which are targets for the transcription factor estrogen-related receptor gamma (Esrrg/ERRγ). We demonstrate that deletion of ERRγ from DAergic neurons in adult mice was sufficient to cause a levodopa-responsive PD-like phenotype with reductions in mitochondrial gene expression and number, that partial deficiency of ERRγ hastens synuclein-mediated toxicity, and that ERRγ overexpression reduces inclusion load and delays synuclein-mediated cell loss. While ERRγ deletion did not fully recapitulate the transcriptional alterations observed in postmortem tissue, it caused reductions in genes involved in synaptic and mitochondrial function and autophagy. Altogether, these experiments suggest that ERRγ-deficient mice could provide a model for understanding the regulation of transcription in DAergic neurons and that amplifying ERRγ-mediated transcriptional programs should be considered as a strategy to promote DAergic maintenance in PD.

Glutamate and GABA in Microglia-Neuron Cross-Talk in Alzheimer's Disease

The physiological balance between excitation and inhibition in the brain is significantly affected in Alzheimer’s disease (AD). Several neuroactive compounds and their signaling pathways through various types of receptors are crucial in brain homeostasis, among them glutamate and γ-aminobutyric acid (GABA). Activation of microglial receptors regulates the immunological response of these cells, which in AD could be neuroprotective or neurotoxic. The novel research approaches revealed the complexity of microglial function, including the interplay with other cells during neuroinflammation and in the AD brain. The purpose of this review is to describe the role of several proteins and multiple receptors on microglia and neurons, and their involvement in a communication network between cells that could lead to different metabolic loops and cell death/survival. Our review is focused on the role of glutamatergic, GABAergic signaling in microglia–neuronal cross-talk in AD and neuroinflammation. Moreover, the significance of AD-related neurotoxic proteins in glutamate/GABA-mediated dialogue between microglia and neurons was analyzed in search of novel targets in neuroprotection, and advanced pharmacological approaches.