Chelation of hippocampal zinc enhances long-term potentiation and synaptic tagging/capture in CA1 pyramidal neurons of aged rats: implications to aging and memory

CaMKIIα-TARPγ8 signaling mediates hippocampal synaptic impairment in aging

Aging-related decline in memory and synaptic function are associated with the dysregulation of calcium homeostasis, attributed to the overexpression of voltage-gated calcium channels (VGCC). The membrane insertion of AMPAR governed by the AMPAR auxiliary proteins is essential for synaptic transmission and plasticity (LTP). In this study, we demonstrated the hippocampal expression of the transmembrane AMPAR regulatory proteins γ-8 (TARPγ8) was reduced in aged mice along with the reduced CaMKIIα activity and memory impairment. We further showed that TARPγ8 expression was dependent on CaMKIIα activity. Inhibition of CaMKIIα activity significantly reduced the hippocampal TARPγ8 expression and CA3-CA1 LTP in young mice to a similar level to that of the aged mice. Furthermore, the knockdown of hippocampal TARPγ8 impaired LTP and memory in young mice, which mimicked the aging-related changes. We confirmed the enhanced hippocampal VGCC (Cav-1.3) expression in aged mice and found that inhibition of VGCC activity largely increased both p-CaMKIIα and TARPγ8 expression in aged mice, whereas inhibition of NMDAR or Calpains had no effect. In addition, we found that the exogenous expression of human TARPγ8 in the hippocampus in aged mice restored LTP and memory function. Collectively, these results indicate that the synaptic and cognitive impairment in aging is associated with the downregulation of CaMKIIα-TARPγ8 signaling caused by VGCC activation. Our results suggest that TARPγ8 may be a key molecular biomarker for brain aging and that boosting CaMKIIα-TARPγ8 signaling may be critical for the restoration of synaptic plasticity of aging and aging-related diseases.

Neural ageing and synaptic plasticity: prioritizing brain health in healthy longevity

Ageing is characterized by a gradual decline in the efficiency of physiological functions and increased vulnerability to diseases. Ageing affects the entire body, including physical, mental, and social well-being, but its impact on the brain and cognition can have a particularly significant effect on an individual's overall quality of life. Therefore, enhancing lifespan and physical health in longevity studies will be incomplete if cognitive ageing is over looked. Promoting successful cognitive ageing encompasses the objectives of mitigating cognitive decline, as well as simultaneously enhancing brain function and cognitive reserve. Studies in both humans and animal models indicate that cognitive decline related to normal ageing and age-associated brain disorders are more likely linked to changes in synaptic connections that form the basis of learning and memory. This activity-dependent synaptic plasticity reorganises the structure and function of neurons not only to adapt to new environments, but also to remain robust and stable over time. Therefore, understanding the neural mechanisms that are responsible for age-related cognitive decline becomes increasingly important. In this review, we explore the multifaceted aspects of healthy brain ageing with emphasis on synaptic plasticity, its adaptive mechanisms and the various factors affecting the decline in cognitive functions during ageing. We will also explore the dynamic brain and neuroplasticity, and the role of lifestyle in shaping neuronal plasticity.

Synapses tagged, memories kept: synaptic tagging and capture hypothesis in brain health and disease

The synaptic tagging and capture (STC) hypothesis lays the framework on the synapse-specific mechanism of protein synthesis-dependent long-term plasticity upon synaptic induction. Activated synapses will display a transient tag that will capture plasticity-related products (PRPs). These two events, tag setting and PRP synthesis, can be teased apart and have been studied extensively-from their electrophysiological and pharmacological properties to the molecular events involved. Consequently, the hypothesis also permits interactions of synaptic populations that encode different memories within the same neuronal population-hence, it gives rise to the associativity of plasticity. In this review, the recent advances and progress since the experimental debut of the STC hypothesis will be shared. This includes the role of neuromodulation in PRP synthesis and tag integrity, behavioural correlates of the hypothesis and modelling in silico. STC, as a more sensitive assay for synaptic health, can also assess neuronal aberrations. We will also expound how synaptic plasticity and associativity are altered in ageing-related decline and pathological conditions such as juvenile stress, cancer, sleep deprivation and Alzheimer's disease. This article is part of a discussion meeting issue 'Long-term potentiation: 50 years on'.

Progressive reduction of nuclear receptor Nr4a1 mediates age-dependent cognitive decline

INTRODUCTION

Cognitive decline progresses with age, and Nr4a1 has been shown to participate in memory functions. However, the relationship between age-related Nr4a1 reduction and cognitive decline is undefined.

METHODS

Nr4a1 expressions were evaluated by quantitative PCR and immunochemical approaches. The cognition of mice was examined by multiple behavioral tests. Patch-clamp experiments were conducted to investigate the synaptic function.

RESULTS

NR4A1 in peripheral blood mononuclear cells decreased with age in humans. In the mouse brain, age-dependent Nr4a1 reduction occurred in the hippocampal CA1. Deleting Nr4a1 in CA1 pyramidal neurons (PyrNs) led to the impairment of cognition and excitatory synaptic function. Mechanistically, Nr4a1 enhanced TrkB expression via binding to its promoter. Blocking TrkB compromised the cognitive amelioration with Nr4a1-overexpression in CA1 PyrNs.

DISCUSSION

Our results elucidate the mechanism of Nr4a1-dependent TrkB regulation in cognition and synaptic function, indicating that Nr4a1 is a target for the treatment of cognitive decline.

HIGHLIGHTS

Nr4a1 is reduced in PBMCs and CA1 PyrNs with aging. Nr4a1 ablation in CA1 PyrNs impaired cognition and excitatory synaptic function. Nr4a1 overexpression in CA1 PyrNs ameliorated cognitive impairment of aged mice. Nr4a1 bound to TrkB promoter to enhance transcription. Blocking TrkB function compromised Nr4a1-induced cognitive improvement.

Electroacupuncture modulates abnormal brain connectivity after ischemia reperfusion injury in rats: A graph theory-based approach

BACKGROUND

Electroacupuncture (EA) has been shown to facilitate brain plasticity-related functional recovery following ischemic stroke. The functional magnetic resonance imaging technique can be used to determine the range and mode of brain activation. After stroke, EA has been shown to alter brain connectivity, whereas EA's effect on brain network topology properties remains unclear. An evaluation of EA's effects on global and nodal topological properties in rats with ischemia reperfusion was conducted in this study.

METHODS AND RESULTS

There were three groups of adult male Sprague-Dawley rats: sham-operated group (sham group), middle cerebral artery occlusion/reperfusion (MCAO/R) group, and MCAO/R plus EA (MCAO/R + EA) group. The differences in global and nodal topological properties, including shortest path length, global efficiency, local efficiency, small-worldness index, betweenness centrality (BC), and degree centrality (DC) were estimated. Graphical network analyses revealed that, as compared with the sham group, the MCAO/R group demonstrated a decrease in BC value in the right ventral hippocampus and increased BC in the right substantia nigra, accompanied by increased DC in the left nucleus accumbens shell (AcbSh). The BC was increased in the right hippocampus ventral and decreased in the right substantia nigra after EA intervention, and MCAO/R + EA resulted in a decreased DC in left AcbSh compared to MCAO/R.

CONCLUSION

The results of this study provide a potential basis for EA to promote cognitive and motor function recovery after ischemic stroke.

Manganese disrupts the maturation and degradation of axonal autophagosome leading to hippocampal synaptic toxicity in mice via the activation of LRRK2 on phosphorylation of Rab10

Manganese (Mn) overexposure induces hippocampal synaptotoxicity by the accumulation of dysfunctional synaptic vesicles (SVs). Leucine-rich repeat kinase 2 (LRRK2) kinase activity is involved in regulating axonal transport (autophagosomal maturation) and lysosomal function. Nevertheless, it remains unclear whether Mn-induced synaptotoxicity is associated with the LRRK2-mediated disruption of autophagosomal maturation in axonal transport and the impairment of lysosomes in hippocampal neurons. Here, we established models of manganism in C57BL/6 mice and hippocampal neuronal HT22 cells to verify the role of LRRK2-mediated Rab10 phosphorylation in the Mn-induced dysfunction of autophagy- lysosomal fusion. Our results proved that Mn-induced the disorder of axonal transport and that lysosome impairments were associated with the increased recruitment of phospho-Rab10 at the axon and lysosomes. Next, we established Lrrk2-KD and LRRK2 kinase- specific inhibitor (GNE-0877, GNE) pre-treated HT22 cells to inhibit Lrrk2 gene expression and kinase activity, respectively. In Mn-treated Lrrk2-KD or GNE-pretreated normal neurons, our results indicated that lysosomal pH and integrity and autophagic flow were restored, indicating by decreased levels of phospho-Rab10 on lysosomes and JNK-interacting proteins (JIP4). In addition, GNE pretreatment could provide protection against Mn-induced synaptotoxicity in vivo, which was evidenced by the partial recovery in synaptic plasticity and synaptic damage. Thus, the Mn-induced abnormal activation of LRRK2 affected lysosomes and the recruitment of phospho-Rab10 by JIP4, which disrupted autophagosomal maturation in proximal axons and resulted in the hippocampal synaptic toxicity of mice.

Cognitive performance in aged rats is associated with differences in distinctive neuronal populations in the ventral tegmental area and altered synaptic plasticity in the hippocampus

Introduction

Deterioration of cognitive functions is commonly associated with aging, although there is wide variation in the onset and manifestation. Albeit heterogeneity in age-related cognitive decline has been studied at the cellular and molecular level, there is poor evidence for electrophysiological correlates. The aim of the current study was to address the electrophysiological basis of heterogeneity of cognitive functions in cognitively Inferior and Superior old (19-20 months) rats in the ventral tegmental area (VTA) and the hippocampus, having Young (12 weeks) rats as a control. The midbrain VTA operates as a hub amidst affective and cognitive facets, processing sensory inputs related to motivated behaviours and hippocampal memory. Increasing evidence shows direct dopaminergic and non-dopaminergic input from the VTA to the hippocampus.

Methods

Aged Superior and Inferior male rats were selected from a cohort of 88 animals based on their performance in a spatial learning and memory task. Using in vivo single-cell recording in the VTA, we examined the electrical activity of different neuronal populations (putative dopaminergic, glutamatergic and GABAergic neurons). In the same animals, basal synaptic transmission and synaptic plasticity were examined in hippocampal slices.

Results

Electrophysiological recordings from the VTA and hippocampus showed alterations associated with aging per se, together with differences specifically linked to the cognitive status of aged animals. In particular, the bursting activity of dopamine neurons was lower, while the firing frequency of glutamatergic neurons was higher in VTA of Inferior old rats. The response to high-frequency stimulation in hippocampal slices also discriminated between Superior and Inferior aged animals.

Discussion

This study provides new insight into electrophysiological information underlying compromised cerebral ageing. Further understanding of brain senescence, possibly related to neurocognitive decline, will help develop new strategies towards the preservation of a high quality of life.

Quercetin Alleviates Perimenopausal Depression Induced by Ovariectomy Combined with Chronic Unpredictable Mild Stress Through Regulating Serum Elements and Inhibiting Ferroptosis in Prefrontal Cortex of Rats

This study investigated the effects of quercetin on the alterations of serum elements in perimenopausal depression rat model induced by ovariectomy combined with chronic unpredictable mild stress (OVX-CUMS) and possible mechanisms. According to the results of the sucrose preference test, the rats were randomly assigned to four groups: sham, OVX-CUMS, OVX-CUMS + 17β-estradiol (17β-estradiol: 0.27 mg/kg.bw), and OVX-CUMS + Quercetin (Quercetin: 50 mg/kg.bw). At the end of experiment, serum and prefrontal cortex of rats were collected. The inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that levels of calcium (Ca), magnesium (Mg), selenium (Se), cobalt (Co) and zinc (Zn) decreased, and levels of iron (Fe) and copper (Cu) increased in serum and prefrontal cortex of OVX-CUMS rats compared with sham group (p < 0.01). Meanwhile, the levels of the above elements in prefrontal cortex had correlation with behavioral characteristics in OVX-CUMS rats (p < 0.05 or p < 0.01). The abnormal elements in serum may cross blood-brain-barrier into the brain and induce oxidative stress, leading to ferroptosis. Furtherly, the expressions of ferroptosis-related protein including GPX4 and SLC7A11 were decreased in prefrontal cortex of OVX-CUMS rats (p < 0.01), which confirmed the above results. Quercetin treatment restored the above abnormal indicators (p < 0.05 or p < 0.01) induced by OVX-CUMS in rats. Our study suggested that quercetin regulated variation of elements in serum and prefrontal cortex, further inhibiting ferroptosis in prefrontal cortex through alleviating oxidative stress in OVX-CUMS rats.

Long-term depression induction and maintenance across regions of the apical branch of CA1 dendrites

Well known as the center for learning and memory, hippocampus is the crucial brain region to study synaptic plasticity in the context of cellular fundamental mechanisms such as long-term depression (LTD) and long-term potentiation (LTP). However, despite years of extensive research, the key to our LTD queries and their induction mechanisms has not been fully understood. Previously, we reported the induction of late-LTD (L-LTD) in the distally located synapses of apical branch of hippocampal CA1 dendrites using strong low-frequency stimulation (SLFS). In contrast synapses at the proximal site could not express L-LTD. Thus, in the present study, we wanted to investigate whether or not synapses of apical dendritic branch at the proximal location could induce and maintain LTD and its related properties in in vitro rat hippocampal slices. Results indicated that the SLFS in the distal and proximal region triggered the plasticity related proteins (PRP) synthesis in both regions, as evident by the induction and maintenance of L-LTD in the distal region by virtue of synaptic and cross-tagging. In addition, the application of emetine at the time of proximal input stimulation prevented the transition of early-LTD (E-LTD) into L-LTD at the distal region, proving PRP synthesis at the proximal site. Further, it was observed that weak low-frequency stimulation (WLFS) could induce E-LTD in the proximal region along with LTD-specific tag-setting at the synapses. In conclusion, the current study suggests unique findings that the synaptic and cross-tagging mediate L-LTD expression is maintained in the proximal location of hippocampus apical CA1 dendrites.

Zinc in Cognitive Impairment and Aging

Zinc, an essential micronutrient for life, was first discovered in 1869 and later found to be indispensable for the normal development of plants and for the normal growth of rats and birds. Zinc plays an important role in many physiological and pathological processes in normal mammalian brain development, especially in the development of the central nervous system. Zinc deficiency can lead to neurodegenerative diseases, mental abnormalities, sleep disorders, tumors, vascular diseases, and other pathological conditions, which can cause cognitive impairment and premature aging. This study aimed to review the important effects of zinc and zinc-associated proteins in cognitive impairment and aging, to reveal its molecular mechanism, and to highlight potential interventions for zinc-associated aging and cognitive impairments.

LA-ICP-MS bioimaging demonstrated disturbance of metal ions in the brain of Parkinson's disease model mouse undergoing manganese-enhanced MRI

Manganese-enhanced MRI (MEMRI) is a powerful tool to study neuronal activity and microarchitecture in vivo. Yet the influence of exogenous manganese on the brain of the Parkinson's disease (PD) model mouse is poorly understood. Laser ablation connected to inductively coupled plasma mass spectrometry (LA-ICP-MS) imaging for tissue section is an ideal tool to simultaneously analyze the metabolism of endogenous metal ions. In this study, DJ-1 knockout PD model mice were subjected to an MnCl₂ saline treatment and the distribution of Mn and several other endogenous metal ions in brain regions was assessed by MEMRI and LA-ICP-MS imaging. The results demonstrated that Mn mainly deposited in subcortical regions, such as ventricles, hippocampus (HC), medial preoptic nucleus (MPO), lateral septal nucleus (LS), and ventromedial hypothalamic nucleus (VMH). The enhanced signal-to-noise ratio (S/N) determined by MEMRI for Mn is closely related to the signal in LA-ICP-MS imaging. Significantly, the treatment of MnCl₂ disturbs the homeostasis of iron, zinc, copper, and calcium in the DJ-1 mouse, which could result in more severe symptoms of PD. Therefore, the application of MEMRI in the study of neurological disease must be made with caution.

Fading memories in aging and neurodegeneration: Is p75 neurotrophin receptor a culprit?

Aging and age-related neurodegenerative diseases have become one of the major concerns in modern times as cognitive abilities tend to decline when we get older. It is well known that the main cause of this age-related cognitive deficit is due to aberrant changes in cellular, molecular circuitry and signaling pathways underlying synaptic plasticity and neuronal connections. The p75 neurotrophin receptor (p75^NTR) is one of the important mediators regulating the fate of the neurons in the nervous system. Its importance in neuronal apoptosis is well documented. However, the mechanisms involving the regulation of p75^NTR in synaptic plasticity and cognitive function remain obscure, although cognitive impairment has been associated with a higher expression of p75^NTR in neurons. In this review, we discuss the current understanding of how neurons are influenced by p75^NTR function to maintain normal neuronal synaptic strength and connectivity, particularly to support learning and memory in the hippocampus. We then discuss the age-associated alterations in neurophysiological mechanisms of synaptic plasticity and cognitive function. Furthermore, we also describe current evidence that has begun to elucidate how p75^NTR regulates synaptic changes in aging and age-related neurodegenerative diseases, focusing on the hippocampus. Elucidating the role that p75^NTR signaling plays in regulating synaptic plasticity will contribute to a better understanding of cognitive processes and pathological conditions. This will in turn provide novel approaches to improve therapies for the treatment of neurological diseases in which p75^NTR dysfunction has been demonstrated.

A Simplified Plasticity Model Based on Synaptic Tagging and Capture Theory: Simplified STC

The formation and consolidation of memory play a vital role for survival in an ever-changing environment. In the brain, the change and stabilization of potentiated and depressed synapses are the neural basis of memory formation and maintenance. These changes can be induced by rather short stimuli (only a few seconds or even less) but should then be stable for months or years. Recently, the neural mechanism of conversion from rapid change during the early phase of synaptic plasticity into a stable memory trace in the late phase of synaptic plasticity is more and more clear at the protein and molecular levels, among which synaptic tagging and capture (STC) theory is one of the most popular theories. According to the STC theory, the change and stabilization of synaptic efficiency mainly depend on three processes related to calcium concentration, including synaptic tagging, synthesis of plasticity-related product (PRP), and the capture of PRP by tagged synapse. Based on the STC theory, several computational models are proposed. However, these models hardly take simplicity and biological interpretability into account simultaneously. Here, we propose a simplified STC (SM-STC) model to address this issue. In the SM-STC model, the concentration of calcium ion in each neuronal compartment and synapse is first calculated, and then the tag state of synapse and PRP are updated, and the coupling effect of tagged synapse and PRP is further considered to determine the plasticity state of the synapse, either potentiation or depression. We simulated the Schaffer collaterals pathway of the hippocampus targeting a multicompartment CA1 neuron for several hours of biological time. The results show that the SM-STC model can produce a broad range of experimental phenomena known in the physiological experiments, including long-term potentiation induced by high-frequency stimuli, long-term depression induced by low-frequency stimuli, and cross-capture with two stimuli separated by a delay. Thus, the SM-STC model proposed in this study provides an effective learning rule for brain-like computation on the premise of ensuring biological plausibility and computational efficiency.

Analysis and Identification Genetic Effect of SARS-CoV-2 Infections to Alzheimer's Disease Patients by Integrated Bioinformatics

BACKGROUND

COVID-19 pandemic is a global crisis which results in millions of deaths and causes long-term neurological sequelae, such as Alzheimer's disease (AD).

OBJECTIVE

We aimed to explore the interaction between COVID-19 and AD by integrating bioinformatics to find the biomarkers which lead to AD occurrence and development with COVID-19 and provide early intervention.

METHODS

The differential expressed genes (DEGs) were found by GSE147507 and GSE132903, respectively. The common genes between COVID-19 and AD were identified. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and protein-protein interactions (PPI) network analysis were carried out. Hub genes were found by cytoscape. A multivariate logistic regression model was constructed. NetworkAnalyst was used for the analysis of TF-gene interactions, TF-miRNA coregulatory network, and Protein-chemical Interactions.

RESULTS

Forty common DEGs for AD and COVID-19 were found. GO and KEGG analysis indicated that the DEGs were enriched in the calcium signal pathway and other pathways. A PPI network was constructed, and 5 hub genes were identified (ITPR1, ITPR3, ITPKB, RAPGEF3, MFGE8). Four hub genes (ITPR1, ITPR3, ITPKB, RAPGEF3) which were considered as important factors in the development of AD that were affected by COVID-19 were shown by nomogram. Utilizing NetworkAnalyst, the interaction network of 4 hub genes and TF, miRNA, common AD risk genes, and known compounds is displayed, respectively.

CONCLUSION

COVID-19 patients are at high risk of developing AD. Vaccination is required. Four hub genes can be considered as biomarkers for prediction and treatment of AD development caused by COVID-19. Compounds with neuroprotective effects can be used as adjuvant therapy for COVID-19 patients.

Long-term plasticity in the hippocampus: maintaining within and 'tagging' between synapses

Synapses between neurons are malleable biochemical structures, strengthening and diminishing over time dependent on the type of information they receive. This phenomenon known as synaptic plasticity underlies learning and memory, and its different forms, long-term potentiation (LTP) and long-term depression (LTD), perform varied cognitive roles in reinforcement, relearning and associating memories. Moreover, both LTP and LTD can exist in an early transient form (early-LTP/LTD) or a late persistent form (late-LTP/LTD), which are triggered by different induction protocols, and also differ in their dependence on protein synthesis and the involvement of key molecular players. Beyond homosynaptic modifications, synapses can also interact with one another. This is encapsulated in the synaptic tagging and capture hypothesis (STC), where synapses expressing early-LTP/LTD present a 'tag' that can capture the protein synthesis products generated during a temporally proximal late-LTP/LTD induction. This 'tagging' phenomenon forms the framework of synaptic interactions in various conditions and accounts for the cellular basis of the time-dependent associativity of short-lasting and long-lasting memories. All these synaptic modifications take place under controlled neuronal conditions, regulated by subcellular elements such as epigenetic regulation, proteasomal degradation and neuromodulatory signals. Here, we review current understanding of the different forms of synaptic plasticity and its regulatory mechanisms in the hippocampus, a brain region critical for memory formation. We also discuss expression of plasticity in hippocampal CA2 area, a long-overlooked narrow hippocampal subfield and the behavioural correlate of STC. Lastly, we put forth perspectives for an integrated view of memory representation in synapses.

Schizophrenia-associated SLC39A8 polymorphism is a loss-of-function allele altering glutamate receptor and innate immune signaling

Schizophrenia is a complex and heterogenous disease that presents with abnormalities in glutamate signaling and altered immune and inflammatory signals. Genome-wide association studies have indicated specific genes and pathways that may contribute to schizophrenia. We assessed the impact of the functional missense variant SLC39A8 (ZIP8)-A391T (ZIP8^A391T) on zinc transport, glutamate signaling, and the neuroinflammatory response. The ZIP8^A391T mutation resulted in reduced zinc transport into the cell, suggesting a loss in the tight control of zinc in the synaptic cleft. Electrophysiological recordings from perturbed neurons revealed a significant reduction in NMDA- and AMPA-mediated spontaneous EPSCs (sEPSCs) and a reduction in GluN2A and GluA1/2/3 receptor surface expression. All phenotypes were rescued by re-expression of wild-type ZIP8 (ZIP8^WT) or application of the membrane-impermeable zinc chelator ZX1. ZIP8 reduction also resulted in decreased BBB integrity, increased IL-6/IL-1β protein expression, and increased NFκB following TNFα stimulation, indicating that ZIP8 loss-of-function may exacerbate immune and inflammatory signals. Together, our findings demonstrate that the A391T missense mutation results in alterations in glutamate and immune function and provide novel therapeutic targets relevant to schizophrenia.

Age-related changes in hippocampal-dependent synaptic plasticity and memory mediated by p75 neurotrophin receptor

The plasticity mechanisms in the nervous system that are important for learning and memory are greatly impacted during aging. Notably, hippocampal-dependent long-term plasticity and its associative plasticity, such as synaptic tagging and capture (STC), show considerable age-related decline. The p75 neurotrophin receptor (p75NTR ) is a negative regulator of structural and functional plasticity in the brain and thus represents a potential candidate to mediate age-related alterations. However, the mechanisms by which p75NTR affects synaptic plasticity of aged neuronal networks and ultimately contribute to deficits in cognitive function have not been well characterized. Here, we report that mutant mice lacking the p75NTR were resistant to age-associated changes in long-term plasticity, associative plasticity, and associative memory. Our study shows that p75NTR is responsible for age-dependent disruption of hippocampal homeostatic plasticity by modulating several signaling pathways, including BDNF, MAPK, Arc, and RhoA-ROCK2-LIMK1-cofilin. p75NTR may thus represent an important therapeutic target for limiting the age-related memory and cognitive function deficits.

Designing neuroreparative strategies using aged regenerating animal models

In our ever-aging world population, the risk of age-related neuropathies has been increasing, representing both a social and economic burden to society. Since the ability to regenerate in the adult mammalian central nervous system is very limited, brain trauma and neurodegeneration are often permanent. As a consequence, novel scientific challenges have emerged and many research efforts currently focus on triggering repair in the damaged or diseased brain. Nevertheless, stimulating neuroregeneration remains ambitious. Even though important discoveries have been made over the past decades, they did not translate into a therapy yet. Actually, this is not surprising; while these disorders mainly manifest in aged individuals, most of the research is being performed in young animal models. Aging of neurons and their environment, however, greatly affects the central nervous system and its capacity to repair. This review provides a detailed overview of the impact of aging on central nervous system functioning and regeneration potential, both in non-regenerating and spontaneously regenerating animal models. Additionally, we highlight the need for aging animal models with regenerative capacities in the search for neuroreparative strategies.

Carnosine research in relation to aging brain and neurodegeneration: A blessing for geriatrics and their neuronal disorders

Carnosine, an endogenous dipeptide (β-Ala-l-His), is enriched in prefrontal cortex and olfactory bulb of the brain, blood and also in muscle. It has mainly antioxidant and antiglycating properties which makes this molecule unique. Its content reduces during aging and aging-induced neurodegenerative diseases. Aging is a progressive biological process that leads to develop the risk factors of diseases and death. During aging the morphological, biochemical, cellular and molecular changes occur in brain and blood including other tissues. The objective of this review is to combine the updated information from the existing literature about the aging-induced neurodegeneration and carnosine research to meet the lacuna of mechanism of carnosine. The grey matter and white matter loses its normal ratio in aging, and hence the brain volume and weight. Different aging related neurodegenerative disorders arise due to loss of neurons, and synapses as a result of proteinopathies in some cases. Carnosine, being an endogenous biomolecule and having antioxidant, antiglycating properties has shown its potency to counteract erroneous protein biosynthesis, stress, activated microglial and astrocyte activity, and different neurodegenerative disorders. It (carnosine) can also inhibit the metal ion-induced degeneration by acting as a metal chelator. In this review the trends in carnosine research in relation to aging brain and neurodegeneration have been discussed with a view to its (carnosine) eligibility (including its mechanism of action) to be used as a promising neurotherapeutic for the betterment of elderly populations of our society at the national and international levels in near future.

Sleep, brain vascular health and ageing

Sleep maintains the function of the entire body through homeostasis. Chronic sleep deprivation (CSD) is a prime health concern in the modern world. Previous reports have shown that CSD has profound negative effects on brain vasculature at both the cellular and molecular levels, and that this is a major cause of cognitive dysfunction and early vascular ageing. However, correlations among sleep deprivation (SD), brain vascular changes and ageing have barely been looked into. This review attempts to correlate the alterations in the levels of major neurotransmitters (acetylcholine, adrenaline, GABA and glutamate) and signalling molecules (Sirt1, PGC1α, FOXO, P66^shc, PARP1) in SD and changes in brain vasculature, cognitive dysfunction and early ageing. It also aims to connect SD-induced loss in the number of dendritic spines and their effects on alterations in synaptic plasticity, cognitive disabilities and early vascular ageing based on data available in scientific literature. To the best of our knowledge, this is the first article providing a pathophysiological basis to link SD to brain vascular ageing.

CircGRIA1 shows an age-related increase in male macaque brain and regulates synaptic plasticity and synaptogenesis

Circular RNAs (circRNAs) are abundant in mammalian brain and some show age-dependent expression patterns. Here, we report that circGRIA1, a conserved circRNA isoform derived from the genomic loci of α-mino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor subunit Gria1, shows an age-related and male-specific increase in expression in the rhesus macaque prefrontal cortex and hippocampus. We show circGRIA1 is predominantly localized to the nucleus, and find an age-related increase in its association with the promoter region of Gria1 gene, suggesting it has a regulatory role in Gria1 transcription. In vitro and in vivo manipulation of circGRIA1 negatively regulates Gria1 mRNA and protein levels. Knockdown of circGRIA1 results in an age-related improvement of synaptogenesis, and GluR1 activity-dependent synaptic plasticity in the hippocampal neurons in males. Our findings underscore the importance of circRNA regulation and offer an insight into the biology of brain aging.

Regulation of aberrant proteasome activity re-establishes plasticity and long-term memory in an animal model of Alzheimer's disease

Reduced retrograde memory performance at the cognitive level and aggregation/deposition of amyloid beta (Aβ) in the brain at the cellular level are some of the hallmarks of Alzheimer's Disease (AD). A molecular system that participates in the removal of proteins with an altered conformation is the Ubiquitin-Proteasome System (UPS). Impairments of the UPS in wild-type (WT) mice lead to defective clearance of Aβ and prevent long-term plasticity of synaptic transmission. Here we show data whereby in contrast to WT mice, the inhibition of proteasome-mediated protein degradation in an animal model of AD by MG132 or lactacystin restores impaired activity-dependent synaptic plasticity and its associative interaction, synaptic tagging and capture (STC) in vitro, as well as associative long-term memory in vivo. This augmentation of synaptic plasticity and memory is mediated by the mTOR pathway and protein synthesis. Our data offer novel insights into the rebalancing of proteins relevant for synaptic plasticity which are regulated by UPS in AD-like animal models. In addition, the data provide evidence that proteasome inhibitors might be effective in reinstating synaptic plasticity and memory performance in AD, and therefore offer a new potential therapeutic option for AD treatment.

Zinc-mediated Neurotransmission in Alzheimer's Disease: A Potential Role of the GPR39 in Dementia

With more people reaching an advanced age in modern society, there is a growing need for strategies to slow down age-related neuropathology and loss of cognitive functions, which are a hallmark of Alzheimer's disease. Neuroprotective drugs and candidate drug compounds target one or more processes involved in the neurodegenerative cascade, such as excitotoxicity, oxidative stress, misfolded protein aggregation and/or ion dyshomeostasis. A growing body of research shows that a G-protein coupled zinc (Zn²⁺) receptor (GPR39) can modulate the abovementioned processes.

Zn²⁺ itself has a diverse activity profile at the synapse, and by binding to numerous receptors, it plays an important role in neurotransmission. However, Zn²⁺ is also necessary for the formation of toxic oligomeric forms of amyloid beta, which underlie the pathology of Alzheimer’s disease. Furthermore, the binding of Zn²⁺ by amyloid beta causes a disruption of zincergic signaling, and recent studies point to GPR39 and its intracellular targets being affected by amyloid pathology.

In this review, we present neurobiological findings related to Zn²⁺ and GPR39, focusing on its signaling pathways, neural plasticity, interactions with other neurotransmission systems, as well as on the effects of pathophysiological changes observed in Alzheimer's disease on GPR39 function.

Direct targeting of the GPR39 might be a promising strategy for the pharmacotherapy of zincergic dyshomeostasis observed in Alzheimer’s disease. The information presented in this article will hopefully fuel further research into the role of GPR39 in neurodegeneration and help in identifying novel therapeutic targets for dementia.

Aging and the clock: Perspective from flies to humans

Endogenous circadian oscillators regulate molecular, cellular and physiological rhythms, synchronizing tissues and organ function to coordinate activity and metabolism with environmental cycles. The technological nature of modern society with round-the-clock work schedules and heavy reliance on personal electronics has precipitated a striking increase in the incidence of circadian and sleep disorders. Circadian dysfunction contributes to an increased risk for many diseases and appears to have adverse effects on aging and longevity in animal models. From invertebrate organisms to humans, the function and synchronization of the circadian system weakens with age aggravating the age-related disorders and pathologies. In this review, we highlight the impacts of circadian dysfunction on aging and longevity and the reciprocal effects of aging on circadian function with examples from Drosophila to humans underscoring the highly conserved nature of these interactions. Additionally, we review the potential for using reinforcement of the circadian system to promote healthy aging and mitigate age-related pathologies. Advancements in medicine and public health have significantly increased human life span in the past century. With the demographics of countries worldwide shifting to an older population, there is a critical need to understand the factors that shape healthy aging. Drosophila melanogaster, as a model for aging and circadian interactions, has the capacity to facilitate the rapid advancement of research in this area and provide mechanistic insights for targeted investigations in mammals.

Regional Distributions of Iron, Copper and Zinc and Their Relationships With Glia in a Normal Aging Mouse Model

Microglia and astrocytes can quench metal toxicity to maintain tissue homeostasis, but with age, increasing glial dystrophy alongside metal dyshomeostasis may predispose the aged brain to acquire neurodegenerative diseases. The aim of the present study was to investigate age-related changes in brain metal deposition along with glial distribution in normal C57Bl/6J mice aged 2-, 6-, 19- and 27-months (n = 4/age). Using synchrotron-based X-ray fluorescence elemental mapping, we demonstrated age-related increases in iron, copper, and zinc in the basal ganglia (p < 0.05). Qualitative assessments revealed age-associated increases in iron, particularly in the basal ganglia and zinc in the white matter tracts, while copper showed overt enrichment in the choroid plexus/ventricles. Immunohistochemical staining showed augmented numbers of microglia and astrocytes, as a function of aging, in the basal ganglia (p < 0.05). Moreover, qualitative analysis of the glial immunostaining at the level of the fimbria and ventral commissure, revealed increments in the number of microglia but decrements in astroglia, in older aged mice. Upon morphological evaluation, aged microglia and astroglia displayed enlarged soma and thickened processes, reminiscent of dystrophy. Since glial cells have major roles in metal metabolism, we performed linear regression analysis and found a positive association between iron (R² = 0.57, p = 0.0008), copper (R² = 0.43, p = 0.0057), and zinc (R² = 0.37, p = 0.0132) with microglia in the basal ganglia. Also, higher levels of iron (R² = 0.49, p = 0.0025) and zinc (R² = 0.27, p = 0.040) were correlated to higher astroglia numbers. Aging was accompanied by a dissociation between metal and glial levels, as we found through the formulation of metal to glia ratios, with regions of basal ganglia being differentially affected. For example, iron to astroglia ratio showed age-related increases in the substantia nigra and globus pallidus, while the ratio was decreased in the striatum. Meanwhile, copper and zinc to astroglia ratios showed a similar regional decline. Our findings suggest that inflammation at the choroid plexus, part of the blood-cerebrospinal-fluid barrier, prompts accumulation of, particularly, copper and iron in the ventricles, implying a compromised barrier system. Moreover, age-related glial dystrophy/senescence appears to disrupt metal homeostasis, likely due to induced oxidative stress, and hence increase the risk of neurodegenerative diseases.

Metal Ions in Alzheimer's Disease: A Key Role or Not?

Despite tremendous research efforts in universities and pharmaceutical companies, effective drugs are still lacking for the treatment of Alzheimer's disease (AD). The biochemical mechanisms of this devastating neurodegenerative disease have not yet been clearly understood. Besides a small percentage of cases with early onset disease having a genetic origin (<5%, familial AD), most cases develop in the elderly as a sporadic form due to multiple and complex parameters of aging. Consequently, AD is spreading in all countries with a long life expectancy. AD is characterized by deposition of senile plaques made of β-amyloid proteins (Aβ) and by hyperphosphorylation of tau proteins, which have been considered as the main drug targets up to now. However, antibodies targeting amyloid aggregates, as well as enzyme inhibitors aiming to modify the amyloid precursor protein processing, have failed to improve cognition in clinical trials. Thus, to set up effective drugs, it is urgent to enlarge the panel of drug targets. Evidence of the link between AD and redox metal dysregulation has also been supported by post-mortem analyses of amyloid plaques, which revealed accumulation of copper, iron, and zinc by 5.7, 2.8, and 3.1 times, respectively, the levels observed in normal brains. Copper-amyloid complexes, in the presence of endogenous reductants, are able to catalyze the reduction of dioxygen and to produce reduced, reactive oxygen species (ROS), leading to neuron death. The possibility of using metal chelators to regenerate normal trafficking of metal ions has been considered as a promising strategy in order to reduce the redox stress lethal for neurons. However, most attempts to use metal chelators as therapeutic agents have been limited to existing molecules available from the shelves. Very few chelators have resulted from a rational design aiming to create drugs with a safety profile and able to cross the blood-brain barrier after an oral administration. In the human body, metals are handled by a sophisticated protein network to strictly control their transport and reactivity. Abnormal concentrations of certain metals may lead to pathological events due to misaccumulation and irregular reactivity. Consequently, therapeutic attempts to restore metal homeostasis should carefully take into account the coordination chemistry specificities of the concerned redox-active metal ions. This Account is focused on the role of the main biologically redox-active transition metals, iron and copper. For iron, the recent debate on the possible role of magnetite in AD pathogenesis is presented. The section devoted to copper is focused on the design of specific copper chelators as drug candidates able to regulate copper homeostasis and to reduce the oxidative damage responsible for the neuron death observed in AD brains. A short survey on non-redox-active metal ions is also included at the beginning, such as aluminum and its controversial role in AD and zinc which is a key metal ion in the brain.

The DRD2 Taq1A A1 Allele May Magnify the Risk of Alzheimer's in Aging African-Americans

Alzheimer's disease is an irreversible, progressive brain disorder that slowly destroys cognitive skills and the ability to perform the simplest tasks. More than 5 million Americans are afflicted with Alzheimer's; a disorder which ranks third, just behind heart disease and cancer, as a cause of death for older people. With no real cure and in spite of enormous efforts worldwide, the disease remains a mystery in terms of treatment. Importantly, African-Americans are two times as likely as Whites to develop late-onset Alzheimer's disease and less likely to receive timely diagnosis and treatment. Dopamine function is linked to normal cognition and memory and carriers of the DRD2 Taq1A A1 allele have significant loss of D2 receptor density in the brain. Recent research has shown that A1 carriers have worse memory performance during long-term memory (LTM) updating, compared to non-carriers or A2-carriers. A1carriers also show less blood oxygen level-dependent (BOLD) activation in the left caudate nucleus which is important for LTM updating. This latter effect was only seen in older adults, suggesting magnification of genetic effects on brain functioning in the elderly. Moreover, the frequency of the A1 allele is 0.40 in African-Americans, with an approximate prevalence of the DRD2 A1 allele in 50% of an African-American subset of individuals. This is higher than what is found in a non-screened American population (≤ 28%) for reward deficiency syndrome (RDS) behaviors. Based on DRD2 known genetic polymorphisms, we hypothesize that the DRD2 Taq1A A1 allele magnifies the risk of Alzheimer's in aging African-Americans. Research linking this high risk for Alzheimer's in the African-American population, with DRD2/ANKK1-TaqIA polymorphism and neurocognitive deficits related to LTM, could pave the way for novel, targeted pro-dopamine homeostatic treatment.

N4 -Tetradentate Chelators Efficiently Regulate Copper Homeostasis and Prevent ROS Production Induced by Copper-Amyloid-β1-16

The disruption of copper homeostasis and the oxidative stress induced by Cu-amyloids are crucial features of Alzheimer's disease pathology. The copper specific N₄ -tetradendate ligands TDMQ20 and 1 are able to fully inhibit in vitro the aerobic oxidation of ascorbate induced by Cu-Aβ_1-16 , even in the presence of 100 molar equivalents of Zn^II with respect to Cu^II , whereas other ligands with N₂ O₂ or N₃ O₂ coordination spheres failed to do so. This essential result indicates that, in addition to metal selectivity, the coordination sphere of copper chelators should exhibit a N₄ -tetradendate motif to be able to reduce an oxidative stress in the zinc-rich physiological environment of brain. The N₄ -scaffolds of these two aminoquinoline-based ligands, TDMQ20 or 1, suitable for a square-planar coordination of copper(II), allowed them to enhance both the selectivity for copper and the ability to reduce the oxidative stress induced by copper-amyloid in a zinc-rich environment.

Synaptic aging disrupts synaptic morphology and function in cerebellar Purkinje cells

Synapses are key structures in neural networks, and are involved in learning and memory in the central nervous system. Investigating synaptogenesis and synaptic aging is important in understanding neural development and neural degeneration in diseases such as Alzheimer disease and Parkinson's disease. Our previous study found that synaptogenesis and synaptic maturation were harmonized with brain development and maturation. However, synaptic damage and loss in the aging cerebellum are not well understood. This study was designed to investigate the occurrence of synaptic aging in the cerebellum by observing the ultrastructural changes of dendritic spines and synapses in cerebellar Purkinje cells of aging mice. Immunocytochemistry, DiI diolistic assays, and transmission electron microscopy were used to visualize the morphological characteristics of synaptic buttons, dendritic spines and synapses of Purkinje cells in mice at various ages. With synaptic aging in the cerebellum, dendritic spines and synaptic buttons were lost, and the synaptic ultrastructure was altered, including a reduction in the number of synaptic vesicles and mitochondria in presynaptic termini and smaller thin specialized zones in pre- and post-synaptic membranes. These findings confirm that synaptic morphology and function is disrupted in aging synapses, which may be an important pathological cause of neurodegenerative diseases.

Cognitive Decline in Neuronal Aging and Alzheimer's Disease: Role of NMDA Receptors and Associated Proteins

Molecular changes associated with neuronal aging lead to a decrease in cognitive capacity. Here we discuss these alterations at the level of brain regions, brain cells, and brain membrane and cytoskeletal proteins with an special focus in NMDA molecular changes through aging and its effect in cognitive decline and Alzheimer disease. Here, we propose that some neurodegenerative disorders, like Alzheimer's disease (AD), are characterized by an increase and acceleration of some of these changes.

CA1 pyramidal cells have diverse biophysical properties, affected by development, experience, and aging

Neuron types (e.g., pyramidal cells) within one area of the brain are often considered homogeneous, despite variability in their biophysical properties. Here we review literature demonstrating variability in the electrical activity of CA1 hippocampal pyramidal cells (PCs), including responses to somatic current injection, synaptic stimulation, and spontaneous network-related activity. In addition, we describe how responses of CA1 PCs vary with development, experience, and aging, and some of the underlying ionic currents responsible. Finally, we suggest directions that may be the most impactful in expanding this knowledge, including the use of text and data mining to systematically study cellular heterogeneity in more depth; dynamical systems theory to understand and potentially classify neuron firing patterns; and mathematical modeling to study the interaction between cellular properties and network output. Our goals are to provide a synthesis of the literature for experimentalists studying CA1 PCs, to give theorists an idea of the rich diversity of behaviors models may need to reproduce to accurately represent these cells, and to provide suggestions for future research.

Improvement of long-term memory access with a pro-dopamine regulator in an elderly male: Are we targeting dopamine tone?

With aging, there is decline in both short-term and long-term memory. This effect is magnified by epigenetic insults on specific, dopamine- related genes (e.g., DRD2, DAT1) as well as by impaired or reduced mRNA transcription. In addition, long-term memory ability is positively correlated with dopamine function and there is evidence that aging is associated with a reduction in brain dopamine D2 receptors, with an acceleration seen in aging-induced dementia. As a result, the authors tested the acute effect of a Pro-Dopamine Regulator (KB220Z, liquid Nano variant) on an aspect of long-term memory performance in a 77-year-old, highly functional male, using the Animal Naming Test (ANT). An improvement in long-term memory retrieval had initially been noted during the subject’s follow-up neurology exam, after he had been, for other reasons, taking KB220z. The patient had been given a number of ANTs by his primary and, later, another neurologist, from 2013 to 2016. Because the number of ANT observations was small (N = 7 with two groups) and the data uncorrelated, a non-parametric Wilcoxon-Mann-Whitney test was performed to test mean differences. After KB220z, the patient had much higher scores (p = 0.04762) on the ANT vs. when not taking it. His scores increased from the 30^th percentile (pre-test) to the 76^th percentile, after the first administration of KB220z and, later, to the 98^th percentile, after a second administration of KB220z, six months later. The results indicate that KB220z, given acutely, increased a form of long-term memory retrieval in a highly functional, elderly male. Larger, double-blind, randomized controlled studies are encouraged.

Characteristic of Extracellular Zn2+ Influx in the Middle-Aged Dentate Gyrus and Its Involvement in Attenuation of LTP

An increased influx of extracellular Zn²⁺ into neurons is a cause of cognitive decline. The influx of extracellular Zn²⁺ into dentate granule cells was compared between young and middle-aged rats because of vulnerability of the dentate gyrus to aging. The influx of extracellular Zn²⁺ into dentate granule cells was increased in middle-aged rats after injection of AMPA and high K⁺ into the dentate gyrus, but not in young rats. Simultaneously, high K⁺-induced attenuation of LTP was observed in middle-aged rats, but not in young rats. The attenuation was rescued by co-injection of CaEDTA, an extracellular Zn²⁺ chelator. Intracellular Zn²⁺ in dentate granule cells was also increased in middle-aged slices with high K⁺, in which the increase in extracellular Zn²⁺ was the same as young slices with high K⁺, suggesting that ability of extracellular Zn²⁺ influx into dentate granule cells is greater in middle-aged rats. Furthermore, extracellular zinc concentration in the hippocampus was increased age-dependently. The present study suggests that the influx of extracellular Zn²⁺ into dentate granule cells is more readily increased in middle-aged rats and that its increase is a cause of age-related attenuation of LTP in the dentate gyrus.