Aging and alpha-synuclein affect synaptic plasticity in the dentate gyrus

Alpha-synuclein and RNA viruses: Exploring the neuronal nexus

Alpha-synuclein (α-syn), known for its pivotal role in Parkinson's disease, has recently emerged as a significant player in neurotropic RNA virus infections. Upregulation of α-syn in various viral infections has been found to impact neuroprotective functions by regulating neurotransmitter synthesis, vesicle trafficking, and synaptic vesicle recycling. This review focuses on the multifaceted role of α-syn in controlling viral replication by modulating chemoattractant properties towards microglial cells, virus-induced ER stress signaling, anti-oxidative proteins expression. Furthermore, the text underlines the α-syn-mediated regulation of interferon-stimulated genes. The review may help suggest potential therapeutic avenues for mitigating the impact of RNA viruses on the central nervous system by exploiting α-syn neuroprotective biology.

Effects of gestational inflammation on age-related cognitive decline and hippocampal Gdnf-GFRα1 levels in F1 and F2 generations of CD-1 Mice

BACKGROUND

It has been reported that age-associated cognitive decline (AACD) accelerated by maternal lipopolysaccharide (LPS) insult during late pregnancy can be transmitted to the second generation in a sex-specificity manner. In turn, recent studies indicated that glial cell line-derived neurotrophic factor (GDNF) and its cognate receptor (GFRα1) are critical for normal cognitive function. Based on this evidence, we aimed to explore whether Gdnf-GFRα1 expression contributes to cognitive decline in the F1 and F2 generations of mouse dams exposed to lipopolysaccharide (LPS) during late gestation, and to evaluate also the potential interference effect of pro-inflammatory cytokines.

METHODS

During gestational days 15-17, pregnant CD-1 mice (8-10 weeks old) received a daily intraperitoneal injection of LPS (50 μg/kg) or saline (control). In utero LPS-exposed F1 generation mice were selectively mated to produce F2 generation mice. In F1 and F2 mice aged 3 and 15 months, the Morris water maze (MWM) was used to evaluated the spatial learning and memory ability, the western blotting and RT-PCR were used for analyses of hippocampal Gdnf and GFRα1 expression, and ELISA was used to analyse IL-1β, IL-6 and TNF-α levels in serum.

RESULTS

Middle-aged F1 offspring from LPS-treated mothers exhibited longer swimming latency and distance during the learning phase, lower percentage swimming time and distance in targe quadrant during memory phase, and lower hippocampal levels of Gdnf and GFRα1 gene products compared to age-matched controls. Similarly, the middle-aged F2 offspring from the Parents-LPS group had longer swimming latency and distance in the learning phase, and lower percentage swimming time and distance in memory phase than the F2-CON group. Moreover, the 3-month-old Parents-LPS and 15-month-old Parents- and Father-LPS groups had lower GDNF and GFRα1 protein and mRNAs levels compared to the age-matched F2-CON group. Furthermore, hippocampal levels of Gdnf and GFRα1 were correlated with impaired cognitive performance in the Morris water maze after controlling for circulating pro-inflammatory cytokine levels.

CONCLUSIONS

Our findings indicate that accelerated AACD by maternal LPS exposure can be transmitted across at least two generations through declined Gdnf and GFRα1 expression, mainly via paternal linage.

Functional and Pathological Effects of α-Synuclein on Synaptic SNARE Complexes

α-Synuclein is an abundant protein at the neuronal synapse that has been implicated in Parkinson's disease for over 25 years and characterizes the hallmark pathology of a group of neurodegenerative diseases now known as the synucleinopathies. Physiologically, α-synuclein exists in an equilibrium between a synaptic vesicle membrane-bound α-helical multimer and a cytosolic largely unstructured monomer. Through its membrane-bound state, α-synuclein functions in neurotransmitter release by modulating several steps in the synaptic vesicle cycle, including synaptic vesicle clustering and docking, SNARE complex assembly, and homeostasis of synaptic vesicle pools. These functions have been ascribed to α-synuclein's interactions with the synaptic vesicle SNARE protein VAMP2/synaptobrevin-2, the synaptic vesicle-attached synapsins, and the synaptic vesicle membrane itself. How α-synuclein affects these processes, and whether disease is due to loss-of-function or gain-of-toxic-function of α-synuclein remains unclear. In this review, we provide an in-depth summary of the existing literature, discuss possible reasons for the discrepancies in the field, and propose a working model that reconciles the findings in the literature.

How Well Do Rodent Models of Parkinson's Disease Recapitulate Early Non-Motor Phenotypes? A Systematic Review

The prodromal phase of Parkinson's disease (PD) is characterised by many non-motor symptoms, and these have recently been posited to be predictive of later diagnosis. Genetic rodent models can develop non-motor phenotypes, providing tools to identify mechanisms underlying the early development of PD. However, it is not yet clear how reproducible non-motor phenotypes are amongst genetic PD rodent models, whether phenotypes are age-dependent, and the translatability of these phenotypes has yet to be explored. A systematic literature search was conducted on studies using genetic PD rodent models to investigate non-motor phenotypes; cognition, anxiety/depressive-like behaviour, gastrointestinal (GI) function, olfaction, circadian rhythm, cardiovascular and urinary function. In total, 51 genetic models of PD across 150 studies were identified. We found outcomes of most phenotypes were inconclusive due to inadequate studies, assessment at different ages, or variation in experimental and environmental factors. GI dysfunction was the most reproducible phenotype across all genetic rodent models. The mouse model harbouring mutant A53T, and the wild-type hα-syn overexpression (OE) model recapitulated the majority of phenotypes, albeit did not reliably produce concurrent motor deficits and nigral cell loss. Furthermore, animal models displayed different phenotypic profiles, reflecting the distinct genetic risk factors and heterogeneity of disease mechanisms. Currently, the inconsistent phenotypes within rodent models pose a challenge in the translatability and usefulness for further biomechanistic investigations. This review highlights opportunities to improve phenotype reproducibility with an emphasis on phenotypic assay choice and robust experimental design.

Linking α-synuclein-induced synaptopathy and neural network dysfunction in early Parkinson's disease

The prodromal phase of Parkinson's disease is characterized by aggregation of the misfolded pathogenic protein α-synuclein in select neural centres, co-occurring with non-motor symptoms including sensory and cognitive loss, and emotional disturbances. It is unclear whether neuronal loss is significant during the prodrome. Underlying these symptoms are synaptic impairments and aberrant neural network activity. However, the relationships between synaptic defects and network-level perturbations are not established. In experimental models, pathological α-synuclein not only impacts neurotransmission at the synaptic level, but also leads to changes in brain network-level oscillatory dynamics-both of which likely contribute to non-motor deficits observed in Parkinson's disease. Here we draw upon research from both human subjects and experimental models to propose a 'synapse to network prodrome cascade' wherein before overt cell death, pathological α-synuclein induces synaptic loss and contributes to aberrant network activity, which then gives rise to prodromal symptomology. As the disease progresses, abnormal patterns of neural activity ultimately lead to neuronal loss and clinical progression of disease. Finally, we outline goals and research needed to unravel the basis of functional impairments in Parkinson's disease and other α-synucleinopathies.

The effects of neurosteroid allopregnanolone on synaptic dysfunction in the hippocampus in experimental parkinsonism rats: An electrophysiological and molecular study

The dopaminergic system is a powerful candidate targeted for changes of synaptic plasticity in the hippocampus. Higher incidence of Parkinson's disease (PD) in men than women indicates the influence of sex hormones on the PD development. Previous studies have shown that neurodegenerative diseases such as PD are related to the decline of Allopregnanolon (Allo), a metabolite of progesterone; it is also well known that learning and memory are influenced by oscillations in steroidal hormones. Although abnormalities in hippocampal plasticity have been observed in the toxic models of PD, effects of Allo on hippocampal LTP and hippocampal synaptic protein levels, which play an important role in maintaining the integrity of neural connections, have never been analyzed thus far. Experimental groups subjected to the long-term potentiation (LTP) were studied in the CA1 area of the hippocampus. In addition, the levels of hippocampal postsynaptic density protein 95 (PSD-95), neurexin-1 (Nrxn1) and neuroligin (Nlgn) as synaptic molecular components were determined by immunoblotting. Although dopamine denervation did not alter basal synaptic transmission and pair-pulse facilitation of field excitatory postsynaptic potentials (fEPSPs), the induction and maintenance of LTP were impaired in the CA1 region. In addition, the levels of PSD-95, Nrxn1 and Nlgn were significantly decreased in the hippocampus of 6-OHDA-treated animals. Such abnormalities in synaptic electrophysiological aspects and protein levels were abolished by the treatment with Allo. These findings showed that partial dopamine depletion led to unusual synaptic plasticity in the CA1 as well as the decrease in synaptic proteins in the hippocampus. Our results demonstrated that Allo ameliorated these deficits and preserved pre- and post-synaptic proteins. Therefore, Allo may be an effective factor in maintaining synaptic integrity in the mesolimbic pathway.

HERV-W Envelope Triggers Abnormal Dopaminergic Neuron Process through DRD2/PP2A/AKT1/GSK3 for Schizophrenia Risk

An increasing number of studies have begun considering human endogenous retroviruses (HERVs) as potential pathogenic phenomena. Our previous research suggests that HERV-W Envelope (HERV-W ENV), a HERV-W family envelope protein, is elevated in schizophrenia patients and contributes to the pathophysiology of schizophrenia. The dopamine (DA) hypothesis is the cornerstone in research and clinical practice related to schizophrenia. Here, we found that the concentration of DA and the expression of DA receptor D2 (DRD2) were significantly higher in schizophrenia patients than in healthy individuals. Intriguingly, there was a positive correlation between HERV-W ENV and DA concentration. Depth analyses showed that there was a marked consistency between HERV-W ENV and DRD2 in schizophrenia. Studies in vitro indicated that HERV-W ENV could increase the DA concentration by regulating DA metabolism and induce the expression of DRD2. Co-IP assays and laser confocal scanning microscopy indicated cellular colocalization and a direct interaction between DRD2 and HERV-W ENV. Additionally, HERV-W ENV caused structural and functional abnormalities of DA neurons. Further studies showed that HERV-W ENV could trigger the PP2A/AKT1/GSK3 pathway via DRD2. A whole-cell patch-clamp analysis suggested that HERV-W ENV enhanced sodium influx through DRD2. In conclusion, we uncovered a relationship between HERV-W ENV and the dopaminergic system in the DA neurons. Considering that GNbAC1, a selective monoclonal antibody to the MSRV-specific epitope, has been promised as a therapy for treating type 1 diabetes and multiple sclerosis (MS) in clinical trials, understanding the precise function of HERV-W ENV in the dopaminergic system may provide new insights into the treatment of schizophrenia.

Amyloid Prefibrillar Oligomers: The Surprising Commonalities in Their Structure and Activity

It has been proposed that a “common core” of pathologic pathways exists for the large family of amyloid-associated neurodegenerations, including Alzheimer’s, Parkinson’s, type II diabetes and Creutzfeldt–Jacob’s Disease. Aggregates of the involved proteins, independently from their primary sequence, induced neuron membrane permeabilization able to trigger an abnormal Ca²⁺ influx leading to synaptotoxicity, resulting in reduced expression of synaptic proteins and impaired synaptic transmission. Emerging evidence is now focusing on low-molecular-weight prefibrillar oligomers (PFOs), which mimic bacterial pore-forming toxins that form well-ordered oligomeric membrane-spanning pores. At the same time, the neuron membrane composition and its chemical microenvironment seem to play a pivotal role. In fact, the brain of AD patients contains increased fractions of anionic lipids able to favor cationic influx. However, up to now the existence of a specific “common structure” of the toxic aggregate, and a “common mechanism” by which it induces neuronal damage, synaptotoxicity and impaired synaptic transmission, is still an open hypothesis. In this review, we gathered information concerning this hypothesis, focusing on the proteins linked to several amyloid diseases. We noted commonalities in their structure and membrane activity, and their ability to induce Ca²⁺ influx, neurotoxicity, synaptotoxicity and impaired synaptic transmission.

The aging mouse brain: cognition, connectivity and calcium

Aging is a complex process that differentially impacts multiple cognitive, sensory, neuronal and molecular processes. Technological innovations now allow for parallel investigation of neuronal circuit function, structure and molecular composition in the brain of awake behaving adult mice. Thus, mice have become a critical tool to better understand how aging impacts the brain. However, a more granular systems-based approach, which considers the impact of age on key features relating to neural processing, is required. Here, we review evidence probing the impact of age on the mouse brain. We focus on a range of processes relating to neuronal function, including cognitive abilities, sensory systems, synaptic plasticity and calcium regulation. Across many systems, we find evidence for prominent age-related dysregulation even before 12 months of age, suggesting that emerging age-related alterations can manifest by late adulthood. However, we also find reports suggesting that some processes are remarkably resilient to aging. The evidence suggests that aging does not drive a parallel, linear dysregulation of all systems, but instead impacts some processes earlier, and more severely, than others. We propose that capturing the more fine-scale emerging features of age-related vulnerability and resilience may provide better opportunities for the rejuvenation of the aged brain.

Differential Regional Responses in Soluble Monomeric Alpha Synuclein Abundance Following Traumatic Brain Injury

Alpha synuclein (α-synuclein) is a neuronal protein found predominately in presynaptic terminals. While the pathological effect of α-synuclein aggregates has been a topic of intense study in several neurodegenerative conditions, less attention has been placed on changes in monomeric α-synuclein and related physiological consequences on neuronal function. A growing body of evidence supports an important physiological role of α-synuclein in neurotransmission. In the context of traumatic brain injury (TBI), we hypothesized that the regional abundance of soluble monomeric α-synuclein is altered over a chronic time period post-injury. To this end, we evaluated α-synuclein in the cortex, hippocampus, and striatum of adult rats at 6 h, 1 day, 1, 2, 4, and 8 weeks after controlled cortical impact (CCI) injury. Western blot analysis demonstrated decreased levels of monomer α-synuclein protein in the ipsilateral hippocampus at 6 h, 1 day, 1, 2, and 8 weeks, as well as in the ipsilateral cortex at 1 and 2 weeks and in the ipsilateral striatum at 6 h after CCI compared with sham animals. Immunohistochemical analysis revealed lower α-synuclein and a modest reduction in synaptophysin staining in the ipsilateral hippocampus at 1 week after CCI compared with sham animals, with no evidence of intracellular or extracellular α-synuclein aggregates. Collectively, these findings demonstrate that monomeric α-synuclein protein abundance in the hippocampus is reduced over an extensive (acute-to-chronic) post-injury interval. This deficit may contribute to the chronically impaired neurotransmission known to occur after TBI.

Alpha-Synuclein RNA Expression is Increased in Major Depression

Alpha-synuclein (SNCA) is a small membrane protein that plays an important role in neuro-psychiatric diseases. It is best known for its abnormal subcellular aggregation in Lewy bodies that serves as a hallmark of Parkinson’s disease (PD). Due to the high comorbidity of PD with depression, we investigated the role of SNCA in patients suffering from major depressive disorder (MDD). SNCA mRNA expression levels were analyzed in peripheral blood cells of MDD patients and a healthy control group. SNCA mRNA expression was positively correlated with severity of depression as indicated by psychometric assessment. We found a significant increase in SNCA mRNA expression levels in severely depressed patients compared with controls. Thus, SNCA analysis could be a helpful target in the search for biomarkers of MDD.

Piperlongumine decreases cognitive impairment and improves hippocampal function in aged mice

Piperlongumine (PL), a biologically active compound from the Piper species, has been shown to exert various pharmacological effects in a number of conditions, including tumours, diabetes, pain, psychiatric disorders and neurodegenerative disease. In this study, we evaluated the therapeutic effects of PL on hippocampal function and cognition decline in aged mice. PL (50 mg/kg/day) was intragastrically administrated to 23‑month‑old female C57BL/6J mice for 8 weeks. Novel object recognition and nest building behaviour tests were used to assess cognitive and social functions. Additionally, immunohistochemistry and western blot analysis were performed to examine the effects of PL on the hippocampus. We found that the oral administration of PL significantly improved novel object recognition and nest building behaviour in aged mice. Although neither the percentage area occupied by astrocytes and microglia nor the level of 4‑hydroxynonenal protein, a specific marker of lipid peroxidation, were altered by PL treatment, the phosphorylation levels of N‑methyl‑D‑aspartate receptor subtype 2B (NR2B), calmodulin‑dependent protein kinase II alpha (CaMKIIα) and extracellular signal‑regulated kinase 1/2 (ERK1/2) were markedly increased in the hippocampus of aged mice following the administration of PL. We also found that PL treatment resulted in a CA3‑specific increase in the phosphorylation level of cyclic AMP response element binding protein, which is recognized as a potent marker of neuronal plasticity, learning and memory. Moreover, the number of doublecortin‑positive cells, a specific marker of neurogenesis, was significantly increased following PL treatment in the dentate gyrus of the hippocampus. On the whole, these data demonstrate that PL treatment may be a potential novel approach in the treatment of age‑related cognitive impairment and hippocampal changes.

MicroRNA expressing profiles in A53T mutant alpha-synuclein transgenic mice and Parkinsonian

α-synuclein gene mutations can cause α-synuclein protein aggregation in the midbrain of Parkinson's disease (PD) patients. MicroRNAs (miRNAs) play a key role in the metabolism of α-synuclein but the mechanism involved in synucleinopathy remains unclear. In this study, we investigated the miRNA profiles in A53T-α-synuclein transgenic mice and analyzed the candidate miRNAs in the cerebrospinal fluid (CSF) of PD patients. The 12-month A53T-transgenic mouse displayed hyperactive movement and anxiolytic-like behaviors with α-synuclein aggregation in midbrain. A total of 317,759 total and 289,207 unique small RNA sequences in the midbrain of mice were identified by high-throughput deep sequencing. We found 644 miRNAs were significantly changed in the transgenic mice. Based on the conserved characteristic of miRNAs, we selected 11 candidates from the 40 remarkably expressed miRNAs and explored their expression in 44 CSF samples collected from PD patients. The results revealed that 11 microRNAs were differently expressed in CSF, emphatically as miR-144-5p, miR-200a-3p and miR-542-3p, which were dramatically up-regulated in both A53T-transgenic mice and PD patients, and had a helpful accuracy for the PD prediction. The ordered logistic regression analysis showed that the severity of PD has strong correlation with an up-expression of miR-144-5p, miR-200a-3p and miR-542-3p in CSF. Taken together, our data suggested that miRNAs in CSF, such as miR-144-5p, miR-200a-3p and miR-542-3p, may be useful to the PD diagnosis as potential biomarkers.

Cell Biology and Pathophysiology of α-Synuclein

α-Synuclein is an abundant neuronal protein that is highly enriched in presynaptic nerve terminals. Genetics and neuropathology studies link α-synuclein to Parkinson's disease (PD) and other neurodegenerative disorders. Accumulation of misfolded oligomers and larger aggregates of α-synuclein defines multiple neurodegenerative diseases called synucleinopathies, but the mechanisms by which α-synuclein acts in neurodegeneration are unknown. Moreover, the normal cellular function of α-synuclein remains debated. In this perspective, we review the structural characteristics of α-synuclein, its developmental expression pattern, its cellular and subcellular localization, and its function in neurons. We also discuss recent progress on secretion of α-synuclein, which may contribute to its interneuronal spread in a prion-like fashion, and describe the neurotoxic effects of α-synuclein that are thought to be responsible for its role in neurodegeneration.

Effect of red and black ginseng on cholinergic markers, presynaptic markers, and neurotrophins in the brain of aged mice

This study investigated the effects of chronic administration of red ginseng extract (RGE) and black ginseng extract (BGE) on memory impairment in aged (18-month-old) mice. RGE and BGE (200 mg/kg) were orally administered for 16 weeks. Aging induced DNA damage; however, RGE and BGE protected DNA from damage and allowed for DNA recovery in blood lymphocytes. Choline acetyltransferase, vesicular acetylcholine transporter, growth-associated protein 43, synaptosomal-associated protein 25, nerve growth factor, and brain-derived neurotrophic factor protein expression were significantly increased after treatment with RGE and BGE. These data suggest that chronic administration of red ginseng and black ginseng may decrease the cognitive deficits associated with normal aging.

The effects of aging in the hippocampus and cognitive decline

Aging is a natural process that is associated with cognitive decline as well as functional and social impairments. One structure of particular interest when considering aging and cognitive decline is the hippocampus, a brain region known to play an important role in learning and memory consolidation as well as in affective behaviours and mood regulation, and where both functional and structural plasticity (e.g., neurogenesis) occur well into adulthood. Neurobiological alterations seen in the aging hippocampus including increased oxidative stress and neuroinflammation, altered intracellular signalling and gene expression, as well as reduced neurogenesis and synaptic plasticity, are thought to be associated with age-related cognitive decline. Non-invasive strategies such as caloric restriction, physical exercise, and environmental enrichment have been shown to counteract many of the age-induced alterations in hippocampal signalling, structure, and function. Thus, such approaches may have therapeutic value in counteracting the deleterious effects of aging and protecting the brain against age-associated neurodegenerative processes.

Aging-related 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurochemial and behavioral deficits and redox dysfunction: improvement by AK-7

Aging is a prominent risk factor for the occurrence and progression of Parkinson disease (PD). Aging animals are more significant for PD research than young ones. It is promising to develop effective treatments for PD through modulation of aging-related molecules. Sirtuin 2 (SIRT2), a strong deacetylase highly expressed in the brain, has been implicated in the aging process. In our present study, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 12mg/kg once daily) was observed to bring about significant behavioral deficits and striatal dopamine depletion in aging male and female mice, while it did not do so in young animals. MPTP did not cause significant reduction in striatal 5-hydroxytryptamine content in aging male and female mice. Furthermore, we observed that MPTP treatment resulted in significant reduction in GSH content and significant increase in MDA content and SIRT2 expression in the substantia nigra (SN) of aging mice, while it did not do so in young animals. Importantly, we observed that AK-7 (a selective SIRT2 inhibitor) significantly improved behavior abnormality and neurochemical deficits in aging male and female mice treated with MPTP. Significant increase in GSH content and significant decrease in MDA content were also observed in the SN of aging male and female mice co-treated with MPTP and AK-7 compared with the MPTP-treated animals. Our results indicated that MPTP induce aging-related neurochemical and behavioural deficits and dysfunction of redox network in male and female mice and AK-7 may be neuroprotective in PD through modulating redox network.

Behavioral and Neurochemical Deficits in Aging Rats with Increased Neonatal Iron Intake: Silibinin's Neuroprotection by Maintaining Redox Balance

Aging is a critical risk factor for Parkinson's disease. Silibinin, a major flavonoid in Silybum marianum, has been suggested to display neuroprotective properties against various neurodegenerative diseases. In the present study, we observed that neonatal iron (120 μg/g body weight) supplementation resulted in significant abnormality of behavior and depletion of striatal dopamine (DA) in the aging male and female rats while it did not do so in the young male and female rats. No significant change in striatal serotonin content was observed in the aging male and female rats with neonatal supplementation of the same dose of iron. Furthermore, we found that the neonatal iron supplementation resulted in significant increase in malondialdehyde (MDA) and decrease in glutathione (GSH) in the substantia nigra (SN) of the aging male and female rats. No significant change in content of MDA and GSH was observed in the cerebellum of the aging male and female rats with the neonatal iron supplementation. Interestingly, silibinin (25 and 50 mg/kg body weight) treatment significantly and dose-dependently attenuated depletion of striatal DA and improved abnormality of behavior in the aging male and female rats with the neonatal iron supplementation. Moreover, silibinin significantly reduced MDA content and increased GSH content in the SN of the aging male and female rats. Taken together, our results indicate that elevated neonatal iron supplementation may result in neurochemical and behavioral deficits in the male and female rats with aging and silibinin may exert dopaminergic neuroprotection by maintaining redox balance.

The Benefits of Exercise on Structural and Functional Plasticity in the Rodent Hippocampus of Different Disease Models

In this review, the benefits of physical exercise on structural and functional plasticity in the hippocampus are discussed. The evidence is clear that voluntary exercise in rats and mice can lead to increases in hippocampal neurogenesis and enhanced synaptic plasticity which ultimately result in improved performance in hippocampal-dependent tasks. Furthermore, in models of neurological disorders, including fetal alcohol spectrum disorders, traumatic brain injury, stroke, and neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's disease exercise can also elicit beneficial effects on hippocampal function. Ultimately this review highlights the multiple benefits of exercise on hippocampal function in both the healthy and the diseased brain.

Aging-related rotenone-induced neurochemical and behavioral deficits: role of SIRT2 and redox imbalance, and neuroprotection by AK-7

Aging is one of the strongest risk factors for Parkinson’s disease (PD). SIRT2 has been implicated in the aging process. It is pertinent to investigate the role of SIRT2 in aging-related dopaminergic neurotoxicity and to develop effective therapeutic strategies for PD through the use of aging animals. In this study, we observed that rotenone induced significant behavior abnormality and striatal dopamine depletion in aging rats, while it did not do so in young rats. No significant change in striatal serotonin level was observed in the aging rats after rotenone administration. There was also aging-related rotenone-induced increase in substantia nigra (SN) SIRT2 expression in the rats. In addition, there was aging-related rotenone-induced SN malondialdehyde (MDA) increase and glutathione (GSH) decrease in the rats. No significant changes in cerebellar SIRT2, MDA, or GSH levels were observed in the aging rats after rotenone administration. Striatal dopamine content was significantly inversely correlated with SN SIRT2 expression in the rats. AK-7 significantly diminished striatal dopamine depletion and improved behavior abnormality in the rotenone-treated aging rats. Furthermore, AK-7 significantly decreased MDA content and increased GSH content in the SN of rotenone-treated aging rats. Finally, the effect of AK-7 on dopaminergic neurons and redox imbalance was supported by the results from primary mesencephalic cultures. Our study helps to elucidate the mechanism for the participation of aging in PD and suggests that SN SIRT2 may be involved in PD neurodegeneration, that AK-7 may be neuroprotective in PD, and that maintaining redox balance may be one of the mechanisms underlying neuroprotection by AK-7.

Inhibition of Sirtuin 2 exerts neuroprotection in aging rats with increased neonatal iron intake

Impaired iron homeostasis may cause damage to dopaminergic neurons and is critically involved in the pathogenesis of Parkinson's disease. At present, very little is understood about the effect of neonatal iron intake on behavior in aging animals. Therefore, we hypothesized that increased neonatal iron intake would result in significant behavior abnormalities and striatal dopamine depletion during aging, and Sirtuin 2 contributes to the age-related neurotoxicity. In the present study, we observed that neonatal iron intake (120 μg/g per day) during postnatal days 10–17 resulted in significant behavior abnormalities and striatal dopamine depletion in aging rats. Furthermore, after AK-7 (a selective Sirtuin 2 inhibitor) was injected into the substantia nigra at postnatal 540 days and 570 days (5 μg/side per day), striatal dopamine depletion was significantly diminished and behavior abnormality was improved in aging rats with neonatal iron intake. Experimental findings suggest that increased neonatal iron intake may result in Parkinson's disease-like neurochemical and behavioral deficits with aging, and inhibition of Sirtuin 2 expression may be a neuroprotective measure in Parkinson's disease.

The Synaptic Function of α-Synuclein

α-Synuclein is an abundant neuronal protein which localizes predominantly to presynaptic terminals, and is strongly linked genetically and pathologically to Parkinson's disease and other neurodegenerative diseases. While the accumulation of α-synuclein in the form of misfolded oligomers and large aggregates defines multiple neurodegenerative diseases called "synucleinopathies", its cellular function has remained largely unclear, and is the subject of intense investigation. In this review, I focus on the structural characteristics of α-synuclein, its cellular and subcellular localization, and discuss how this relates to its function in neurons, in particular at the neuronal synapse.

Role of α-synuclein in neurodegeneration: implications for the pathogenesis of Parkinson's disease

α-Syn (α-synuclein) is a small soluble acidic protein that is extensively expressed in the nervous system. Genetic, clinical and experimental studies demonstrate that α-syn is strongly implicated in the pathogenesis of PD (Parkinson's disease). However, the pathogenic mechanism remains elusive. In the present chapter, we first describe the normal expression and potential physiological functions of α-syn. Then, we introduce recent research progress related to the pathogenic role of α-syn in PD, with special emphasis on how α-syn oligomers cause the preferential degeneration of dopaminergic neurons in the substantia nigra and the spreading of α-syn pathology in the brain of PD patients.

Behavioral characterization of A53T mice reveals early and late stage deficits related to Parkinson's disease

Parkinson's disease (PD) pathology is characterized by the formation of intra-neuronal inclusions called Lewy bodies, which are comprised of alpha-synuclein (α-syn). Duplication, triplication or genetic mutations in α-syn (A53T, A30P and E46K) are linked to autosomal dominant PD; thus implicating its role in the pathogenesis of PD. In both PD patients and mouse models, there is increasing evidence that neuronal dysfunction occurs before the accumulation of protein aggregates (i.e., α-syn) and neurodegeneration. Characterization of the timing and nature of symptomatic dysfunction is important for understanding the impact of α-syn on disease progression. Furthermore, this knowledge is essential for identifying pathways and molecular targets for therapeutic intervention. To this end, we examined various functional and morphological endpoints in the transgenic mouse model expressing the human A53T α-syn variant directed by the mouse prion promoter at specific ages relating to disease progression (2, 6 and 12 months of age). Our findings indicate A53T mice develop fine, sensorimotor, and synaptic deficits before the onset of age-related gross motor and cognitive dysfunction. Results from open field and rotarod tests show A53T mice develop age-dependent changes in locomotor activity and reduced anxiety-like behavior. Additionally, digigait analysis shows these mice develop an abnormal gait by 12 months of age. A53T mice also exhibit spatial memory deficits at 6 and 12 months, as demonstrated by Y-maze performance. In contrast to gross motor and cognitive changes, A53T mice display significant impairments in fine- and sensorimotor tasks such as grooming, nest building and acoustic startle as early as 1-2 months of age. These mice also show significant abnormalities in basal synaptic transmission, paired-pulse facilitation and long-term depression (LTD). Combined, these data indicate the A53T model exhibits early- and late-onset behavioral and synaptic impairments similar to PD patients and may provide useful endpoints for assessing novel therapeutic interventions for PD.

Improved spatial learning and memory by perilla diet is correlated with immunoreactivities to neurofilament and α-synuclein in hilus of dentate gyrus

BACKGROUND

Perilla (Perilla frutescens) oil is very rich in α-linolenic acid, an omega-3 fatty acid. As it is widely reported that omega-3 fatty acid supplementation improves cognitive function in children and adults, feeding rats with perilla diets followed by analysis of proteomic changes in the hippocampus can provide valuable information on the mechanism of learning and memory at the molecular level. To identify proteins playing roles in learning and memory, differentially expressed proteins in the hippocampus of the 5 week old rats fed perilla diets for 3 weeks or 3 months were identified by proteomic analysis and validated by immunological assays.

RESULTS

The perilla diet groups showed improved spatial learning and memory performances in a T-maze test. They also displayed elevated level of 22:6n-3 fatty acid, an omega-3 fatty acid (p<0.05), in the brain compared to the control diet group. Quantitative proteomic analysis using 2-D gels as well as functional annotation grouping with the differentially expressed proteins in the hippocampus showed that those proteins involved in cytoskeleton and transport were the major differentially expressed proteins in the 3-week group, whereas those involved in energy metabolism, neuron projection and apoptosis in addition to cytoskeleton and transport were the major ones in the 3 month group. Differential protein expression in the hippocampus was validated by Western blotting using four selected proteins, known to be involved in synaptic plasticity; AMPA receptor, neurofilament, α-synuclein, and β-soluble NSF attachment protein. Brain sections from the perilla-diet groups showed enhanced immunoreactivities to α-synuclein and neurofilament. Especially, neurofilament immunoreactive cells manifested longer neurite projections in the hilus of dentate gyrus of the perilla-diet groups.

CONCLUSION

Improved cognitive function upon administration of n-3 fatty acid-rich perilla diet is associated with the differential expression of hippocampal proteins related to cytoskeleton, energy metabolism, transport, neuro-projection, and apoptosis. Particularly, the enhanced immunoreactivities to α-synuclein and neurofilament in the hilus of dentate gyrus suggest that perilla diet supplementation promotes neuronal signaling and alters synaptic plasticity for improved learning and memory.

Impaired c-Fos and polo-like kinase 2 induction in the limbic system of fear-conditioned α-synuclein transgenic mice

α-Synuclein (αSYN) is genetically and neuropathologically linked to a spectrum of neurodegenerative diseases including Parkinson's disease, dementia with Lewy bodies, and related disorders. Cognitive impairment is recapitulated in several αSYN transgenic mouse lines. However, the mechanisms of dysfunction in affected neurons are largely unknown. Here we measured neuronal activity induced gene products in the limbic system of αSYN transgenic mice upon fear conditioning (FC). Induction of the synaptic plasticity marker c-Fos was significantly reduced in the amygdala and hippocampus of (Thy1)-h[A30P]αSYN transgenic mice in an age-dependent manner. Similarly, the neuronal activity inducible polo-like kinase 2 (Plk2) that can phosphorylate αSYN at the pathological site serine-129 was up-regulated in both brain regions upon FC. Plk2 inductions were also significantly impaired in aged (Thy1)-h[A30P]αSYN transgenic mice, both in the amygdala and hippocampus. Plk2 inductions in the amygdala after FC were paralleled by a small but significant increase in the number of neuronal cell bodies immunopositive for serine-129 phosphorylated αSYN in young but not aged (Thy1)-h[A30P]αSYN transgenic mice. In addition, we observed in the aged hippocampus a distinct type of apparently unmodified transgenic αSYN profiles resembling synaptic accumulations of αSYN. Thus, the cognitive decline observed in aged αSYN transgenic mice might be due to impairment of neurotransmission and synaptic plasticity in the limbic system by distinct αSYN species.

Aberrant striatal synaptic plasticity in monogenic parkinsonisms

In the recent past, the pathogenesis of Parkinson's disease (PD) has evolved from a neurodegenerative disorder considered entirely sporadic to a disease with an unequivocal genetic component. Indeed, different inherited forms of PD have been discovered and characterized, although the functional roles of the gene products identified are still under intense investigation. To gain a better understanding of the cellular and molecular pathogenic mechanisms of hereditary forms of PD, different animal models have been generated. Although most of the rodent models display neither obvious behavioral impairment nor evidence for neurodegeneration, remarkable abnormalities of dopamine-mediated neurotransmission and corticostriatal synaptic plasticity have been described, indicative of a fundamental distortion of network function within the basal ganglia. The picture emerging from a critical review of recent data on monogenic parkinsonisms suggests that mutations in PD genes might cause developmental rearrangements in the corticobasal ganglia circuitry, compensating the dopaminergic dysfunction observed both in mice and humans, in order to maintain proper motor function.

Blue native/SDS-PAGE combined with iTRAQ analysis reveals advanced glycation end-product-induced changes of synaptosome proteins in C57 BL/6 mice

Evidence shows that administration of high-level D-galactose induces the production of advanced glycation end-products (AGEs) that have been implicated in the development of diabetic complications such as neuropathy. The deterioration of learning and memory during neuropathy might be associated with the altered expression of proteins in synapse. To evaluate AGE-induced protein network alterations in synapse, blue native/SDS-PAGE and iTRAQ proteomic methods were used to screen for differentially expressed synaptic proteins of cerebral cortex in D-galactose-induced C57 BL/6 mice. In total, the expression level of 84 proteins is changed during AGE accumulation. The significantly differentially expressed proteins mainly participate in neurotransmission, energy metabolism and signal transduction pathway, suggesting that energy metabolism is damaged and neurotransmission is attenuated in synapse. The results of in vivo activities of malondialdehyde and superoxide dismutase suggested that AGE accumulation in the brain leads to the generation of reactive oxygen species. Therefore, elucidating the differentially expressed proteins underlying the AGE accumulation will open a new window to the mechanism of learning and memory impairments in neuropathy.

The hippocampal neuroproteome with aging and cognitive decline: past progress and future directions

Although steady progress on understanding brain aging has been made over recent decades through standard anatomical, immunohistochemical, and biochemical techniques, the biological basis of non-neurodegenerative cognitive decline with aging remains to be determined. This is due in part to technical limitations of traditional approaches, in which only a small fraction of neurobiologically relevant proteins, mRNAs or metabolites can be assessed at a time. With the development and refinement of proteomic technologies that enable simultaneous quantitative assessment of hundreds to thousands of proteins, neuroproteomic studies of brain aging and cognitive decline are becoming more widespread. This review focuses on the contributions of neuroproteomic investigations to advances in our understanding of age-related deficits of hippocampus-dependent spatial learning and memory. Accumulating neuroproteomic data demonstrate that hippocampal aging involves common themes of dysregulated metabolism, increased oxidative stress, altered protein processing, and decreased synaptic function. Additionally, growing evidence suggests that cognitive decline does not represent a "more aged" phenotype, but rather is associated with specific neuroproteomic changes that occur in addition to age-related alterations. Understanding if and how age-related changes in the hippocampal neuroproteome contribute to cognitive decline and elucidating the pathways and processes that lead to cognitive decline are critical objectives that remain to be achieved. Progress in the field and challenges that remain to be addressed with regard to animal models, behavioral testing, and proteomic reporting are also discussed.

Parkinson's disease mouse models in translational research

Animal models with high predictive power are a prerequisite for translational research. The closer the similarity of a model to Parkinson’s disease (PD), the higher is the predictive value for clinical trials. An ideal PD model should present behavioral signs and pathology that resemble the human disease. The increasing understanding of PD stratification and etiology, however, complicates the choice of adequate animal models for preclinical studies. An ultimate mouse model, relevant to address all PD-related questions, is yet to be developed. However, many of the existing models are useful in answering specific questions. An appropriate model should be chosen after considering both the context of the research and the model properties. This review addresses the validity, strengths, and limitations of current PD mouse models for translational research.

AMPA-receptor-mediated excitatory synaptic transmission is enhanced by iron-induced α-synuclein oligomers

Aggregated α-synuclein (α-syn) is a characteristic pathological finding in Parkinson's disease and related disorders, such as dementia with Lewy bodies. Recent evidence suggests that α-syn oligomers represent the principal neurotoxic species; however, the pathophysiological mechanisms are still not well understood. Here, we studied the neurophysiological effects of various biophysically-characterized preparations of α-syn aggregates on excitatory synaptic transmission in autaptic neuronal cultures. Nanomolar concentrations of large α-syn oligomers, generated by incubation with organic solvent and Fe(3+) ions, were found to selectivity enhance evoked α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)-receptor, but not NMDA-receptor, mediated synaptic transmission within minutes. Moreover, the analysis of spontaneous AMPA-receptor-mediated miniature synaptic currents revealed an augmented frequency. These results collectively indicate that large α-syn oligomers alter both pre- and post-synaptic mechanisms of AMPA-receptor-mediated synaptic transmission. The augmented excitatory synaptic transmission may directly contribute to nerve cell death in synucleinopathies. Indeed, already low micromolar glutamate concentrations were found to be toxic in primary cultured neurons incubated with large α-syn oligomers. In conclusion, large α-syn oligomers enhance both pre- and post-synaptic AMPA-receptor-mediated synaptic transmission, thereby aggravating intracellular calcium dyshomeostasis and contributing to excitotoxic nerve cell death in synucleinopathies.

The role of α-synuclein in neurotransmission and synaptic plasticity

Alpha-synuclein (α-syn), a synaptic protein richly expressed in the central nervous system, has been implicated in several neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, multiple system atrophy, and dementia with Lewy bodies, which are collectively known as synucleinopathies. By contrast to the clear evidence for the involvement of α-syn in synucleinopathies, its physiological functions remain elusive, which becomes an impediment for revelation of its pathological mechanism. Since α-syn is richly expressed in presynaptic terminals and associated with synaptic vesicles, a large number of studies have been focused on revealing the potential functions of this protein in neurotransmission and synaptic plasticity. In this review article, we summarized recent advances for the role of α-syn in synaptic vesicle recycling, neurotransmitter synthesis and release, and synaptic plasticity. We discussed the possible relevance between the loss of normal α-syn functions in disease conditions and the onset of some neurodegenerative diseases.

Aging alters the expression of neurotransmission-regulating proteins in the hippocampal synaptoproteome

Decreased cognitive performance reduces independence and quality of life for aging individuals. Healthy brain aging does not involve significant neuronal loss, but little is known about the effects of aging at synaptic terminals. Age-related cognitive decline likely reflects the manifestation of dysregulated synaptic function and ineffective neurotransmission. In this study, hippocampal synaptosomes were enriched from young-adult (3 months), adult (12 months), and aged (26 months) Fischer 344 x Brown Norway rats, and quantitative alterations in the synaptoproteome were examined by 2-DIGE and MS/MS. Bioinformatic analysis of differentially expressed proteins identified a significant effect of aging on a network of neurotransmission-regulating proteins. Specifically, altered expression of DNM1, HPCA, PSD95, SNAP25, STX1, SYN1, SYN2, SYP, and VAMP2 was confirmed by immunoblotting. 14-3-3 isoforms identified in the proteomic analysis were also confirmed as a result of their implication in the regulation of the synaptic vesicle cycle and neurotransmission modulation. The findings of this study demonstrate a coordinated down-regulation of neurotransmission-regulating proteins that suggests an age-based deterioration of hippocampal neurotransmission occurring between adulthood and advanced age. Altered synaptic protein expression may decrease stimulus-induced neurotransmission and vesicle replenishment during prolonged or intense stimulation, which are necessary for learning and the formation and perseverance of memory.

Genetic mouse models of Parkinson's disease The state of the art

The identification of several mutations causing familial forms of Parkinson's disease (PD) has led to the creation of multiple lines of mice expressing similar genetic alterations. These models present a unique opportunity for understanding pathophysiological mechanisms leading to PD in a mammalian brain and provide models that are suitable for the preclinical testing of new therapies. Different lines of mice recapitulate the symptoms and pathological features of PD to various extents. This chapter examines their respective advantages and highlights some of the key findings that have already emerged from the analysis of these new models of PD.