Elevated postsynaptic [Ca2+]i and L-type calcium channel activity in aged hippocampal neurons: relationship to impaired synaptic plasticity. J Neurosci. 2001;21:9744-9756. [PMID: 11739583 DOI: 10.1523/jneurosci.21-24-09744.2001]

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.

The impact of aging on HIV-1-related neurocognitive impairment

Depending on the population studied, HIV-1-related neurocognitive impairment is estimated to impact up to half the population of people living with HIV (PLWH) despite the availability of combination antiretroviral therapy (cART). Various factors contribute to this neurocognitive impairment, which complicates our understanding of the molecular mechanisms involved. Biological aging has been implicated as one factor possibly impacting the development and progression of HIV-1-related neurocognitive impairment. This is increasingly important as the life expectancy of PLWH with virologic suppression on cART is currently projected to be similar to that of individuals not living with HIV. Based on our increasing understanding of the biological aging process on a cellular level, we aim to dissect possible interactions of aging- and HIV-1 infection-induced effects and their role in neurocognitive decline. Thus, we begin by providing a brief overview of the clinical aspects of HIV-1-related neurocognitive impairment and review the accumulating evidence implicating aging in its development (Part I). We then discuss potential interactions between aging-associated pathways and HIV-1-induced effects at the molecular level (Part II).

A biophysical minimal model to investigate age-related changes in CA1 pyramidal cell electrical activity

Aging is a physiological process that is still poorly understood, especially with respect to effects on the brain. There are open questions about aging that are difficult to answer with an experimental approach. Underlying challenges include the difficulty of recording in vivo single cell and network activity simultaneously with submillisecond resolution, and brain compensatory mechanisms triggered by genetic, pharmacologic, or behavioral manipulations. Mathematical modeling can help address some of these questions by allowing us to fix parameters that cannot be controlled experimentally and investigate neural activity under different conditions. We present a biophysical minimal model of CA1 pyramidal cells (PCs) based on general expressions for transmembrane ion transport derived from thermodynamical principles. The model allows directly varying the contribution of ion channels by changing their number. By analyzing the dynamics of the model, we find parameter ranges that reproduce the variability in electrical activity seen in PCs. In addition, increasing the L-type Ca2+ channel expression in the model reproduces age-related changes in electrical activity that are qualitatively and quantitatively similar to those observed in PCs from aged animals. We also make predictions about age-related changes in PC bursting activity that, to our knowledge, have not been reported previously. We conclude that the model's biophysical nature, flexibility, and computational simplicity make it a potentially powerful complement to experimental studies of aging.

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.

Dual Role of NMDAR Containing NR2A and NR2B Subunits in Alzheimer's Disease

Alzheimer's disease (AD) is the main cause of dementia worldwide. Given that learning and memory are impaired in this pathology, NMDA receptors (NMDARs) appear as key players in the onset and progression of the disease. NMDARs are glutamate receptors, mainly located at the post-synapse, which regulate voltage-dependent influx of calcium into the neurons. They are heterotetramers, and there are different subunits that can be part of the receptors, which are usually composed of two obligatory GluN1 subunits plus either two NR2A or two NR2B subunits. NR2A are mostly located at the synapse, and their activation is involved in the expression of pro-survival genes. Conversely, NR2B are mainly extrasynaptic, and their activation has been related to cell death and neurodegeneration. Thus, activation of NR2A and/or inactivation of NR2B-containing NMDARS has been proposed as a therapeutic strategy to treat AD. Here, we wanted to investigate the main differences between both subunits signalling in neuronal primary cultures of the cortex and hippocampus. It has been observed that Aβ induces a significant increase in calcium release and also in MAPK phosphorylation signalling in NR2B-containing NMDAR in cortical and hippocampal neurons. However, while NR2A-containing NMDAR decreases neuronal death and favours cell viability after Aβ treatment, NR2B-containing NMDAR shows higher levels of cytotoxicity and low levels of neuronal survival. Finally, it has been detected that NMDAR has no effect on pTau axonal transport. The present results demonstrate a different role between GluNA and GluNB subunits in neurodegenerative diseases such as Alzheimer's.

Hippocampal hyperphosphorylated tau-induced deficiency is rescued by L-type calcium channel blockade

Aging and Alzheimer's disease are associated with chronic elevations in neuronal calcium influx via L-type calcium channels. The hippocampus, a primary memory encoding structure in the brain, is more vulnerable to calcium dysregulation in Alzheimer's disease. Recent research has suggested a link between L-type calcium channels and tau hyperphosphorylation. However, the precise mechanism of L-type calcium channel-mediated tau toxicity is not understood. In this study, we seeded a human tau pseudophosphorylated at 14 amino acid sites in rat hippocampal cornu ammonis 1 region to mimic soluble pretangle tau. Impaired spatial learning was observed in human tau pseudophosphorylated at 14 amino acid sites-infused rats as early as 1-3 months and worsened at 9-10 months post-infusion. Rats infused with wild-type human tau exhibited milder behavioural deficiency only at 9-10 months post-infusion. No tangles or plaques were observed in all time points examined in both human tau pseudophosphorylated at 14 amino acid sites and human tau-infused brains. However, human tau pseudophosphorylated at 14 amino acid sites-infused hippocampus exhibited a higher amount of tau phosphorylation at S262 and S356 than the human tau-infused rats at 3 months post-infusion, paralleling the behavioural deficiency observed in human tau pseudophosphorylated at 14 amino acid sites-infused rats. Neuroinflammation indexed by increased Iba1 in the cornu ammonis 1 was observed in human tau pseudophosphorylated at 14 amino acid sites-infused rats at 1-3 but not 9 months post-infusion. Spatial learning deficiency in human tau pseudophosphorylated at 14 amino acid sites-infused rats at 1-3 months post-infusion was paralleled by decreased neuronal excitability, impaired NMDA receptor-dependent long-term potentiation and augmented L-type calcium channel-dependent long-term potentiation at the cornu ammonis 1 synapses. L-type calcium channel expression was elevated in the soma of the cornu ammonis 1 neurons in human tau pseudophosphorylated at 14 amino acid sites-infused rats. Chronic L-type calcium channel blockade with nimodipine injections for 6 weeks normalized neuronal excitability and synaptic plasticity and rescued spatial learning deficiency in human tau pseudophosphorylated at 14 amino acid sites-infused rats. The early onset of L-type calcium channel-mediated pretangle tau pathology and rectification by nimodipine in our model have significant implications for preclinical Alzheimer's disease prevention and intervention.

Targeting dynamin-related protein-1 as a potential therapeutic approach for mitochondrial dysfunction in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease that manifests its pathology through synaptic damage, mitochondrial abnormalities, microRNA deregulation, hormonal imbalance, increased astrocytes & microglia, accumulation of amyloid β (Aβ) and phosphorylated Tau in the brains of AD patients. Despite extensive research, the effective treatment of AD is still unknown. Tau hyperphosphorylation and mitochondrial abnormalities are involved in the loss of synapses, defective axonal transport and cognitive decline in patients with AD. Mitochondrial dysfunction is evidenced by enhanced mitochondrial fragmentation, impaired mitochondrial dynamics, mitochondrial biogenesis and defective mitophagy in AD. Hence, targeting mitochondrial proteins might be a promising therapeutic strategy in treating AD. Recently, dynamin-related protein 1 (Drp1), a mitochondrial fission protein, has gained attention due to its interactions with Aβ and hyperphosphorylated Tau, altering mitochondrial morphology, dynamics, and bioenergetics. These interactions affect ATP production in mitochondria. A reduction in Drp1 GTPase activity protects against neurodegeneration in AD models. This article provides a comprehensive overview of Drp1's involvement in oxidative damage, apoptosis, mitophagy, and axonal transport of mitochondria. We also highlighted the interaction of Drp1 with Aβ and Tau, which may contribute to AD progression. In conclusion, targeting Drp1 could be a potential therapeutic approach for preventing AD pathology.

Retrosplenial cortex microglia and perineuronal net densities are associated with memory impairment in aged rhesus macaques

Synapse loss and altered plasticity are significant contributors to memory loss in aged individuals. Microglia, the innate immune cells of the brain, play critical roles in maintaining synapse function, including through a recently identified role in regulating the brain extracellular matrix. This study sought to determine the relationship between age, microglia, and extracellular matrix structure densities in the macaque retrosplenial cortex. Twenty-nine macaques ranging in age from young adult to aged were behaviorally characterized on 3 distinct memory tasks. Microglia, parvalbumin (PV)-expressing interneurons and extracellular matrix structures, known as perineuronal nets (PNNs), were immuno- and histochemically labeled. Our results indicate that microglia densities increase in the retrosplenial cortex of aged monkeys, while the proportion of PV neurons surrounded by PNNs decreases. Aged monkeys with more microglia had fewer PNN-associated PV neurons and displayed slower learning and poorer performance on an object recognition task. Stepwise regression models using age and the total density of aggrecan, a chondroitin sulfate proteoglycan of PNNs, better predicted memory performance than did age alone. Together, these findings indicate that elevated microglial activity in aged brains negatively impacts cognition in part through mechanisms that alter PNN assembly in memory-associated brain regions.

Age-related deficits in neuronal physiology and cognitive function are recapitulated in young mice overexpressing the L-type calcium channel, CaV 1.3

The calcium dysregulation hypothesis of brain aging posits that an age-related increase in neuronal calcium concentration is responsible for alterations in a variety of cellular processes that ultimately result in learning and memory deficits in aged individuals. We previously generated a novel transgenic mouse line, in which expression of the L-type voltage-gated calcium, CaV 1.3, is increased by ~50% over wild-type littermates. Here, we show that, in young mice, this increase is sufficient to drive changes in neuronal physiology and cognitive function similar to those observed in aged animals. Specifically, there is an increase in the magnitude of the postburst afterhyperpolarization, a deficit in spatial learning and memory (assessed by the Morris water maze), a deficit in recognition memory (assessed in novel object recognition), and an overgeneralization of fear to novel contexts (assessed by contextual fear conditioning). While overexpression of CaV 1.3 recapitulated these key aspects of brain aging, it did not produce alterations in action potential firing rates, basal synaptic communication, or spine number/density. Taken together, these results suggest that increased expression of CaV 1.3 in the aged brain is a crucial factor that acts in concert with age-related changes in other processes to produce the full complement of structural, functional, and behavioral outcomes that are characteristic of aged animals.

Aging differentially affects LTCC function in hippocampal CA1 and piriform cortex pyramidal neurons

Aging is associated with cognitive decline and memory loss in humans. In rats, aging-associated neuronal excitability changes and impairments in learning have been extensively studied in the hippocampus. Here, we investigated the roles of L-type calcium channels (LTCCs) in the rat piriform cortex (PC), in comparison with those of the hippocampus. We employed spatial and olfactory tasks that involve the hippocampus and PC. LTCC blocker nimodipine administration impaired spontaneous location recognition in adult rats (6-9 months). However, the same blocker rescued the spatial learning deficiency in aged rats (19-23 months). In an odor-associative learning task, infusions of nimodipine into either the PC or dorsal CA1 impaired the ability of adult rats to learn a positive odor association. Again, in contrast, nimodipine rescued odor associative learning in aged rats. Aged CA1 neurons had higher somatic expression of LTCC Cav1.2 subunits, exhibited larger afterhyperpolarization (AHP) and lower excitability compared with adult neurons. In contrast, PC neurons from aged rats showed higher excitability and no difference in AHP. Cav1.2 expression was similar in adult and aged PC somata, but relatively higher in PSD95- puncta in aged dendrites. Our data suggest unique features of aging-associated changes in LTCCs in the PC and hippocampus.

Modulation of L-type calcium channels in Alzheimer's disease: A potential therapeutic target

Calcium plays a fundamental role in various signaling pathways and cellular processes in the human organism. In the nervous system, voltage-gated calcium channels such as L-type calcium channels (LTCCs) are critical elements in mediating neurotransmitter release, synaptic integration and plasticity. Dysfunction of LTCCs has been implicated in both aging and Alzheimer's Disease (AD), constituting a key component of calcium hypothesis of AD. As such, LTCCs are a promising drug target in AD. However, due to their structural and functional complexity, the mechanisms by which LTCCs contribute to AD are still unclear. In this review, we briefly summarize the structure, function, and modulation of LTCCs that are the backbone for understanding pathological processes involving LTCCs. We suggest targeting molecular pathways up-regulating LTCCs in AD may be a more promising approach, given the diverse physiological functions of LTCCs and the ineffectiveness of LTCC blockers in clinical studies.

Systemic Injection of Aged Blood Plasma in Adult C57BL/6 Mice Induces Neurophysiological Impairments in the Hippocampal CA1

BACKGROUND

Aging is characterized by systemic alterations and forms an important risk factor for Alzheimer's disease. Recently, it has been indicated that blood-borne factors present in the systemic milieu contribute to the aging process. Exposing young mice to aged blood plasma results in impaired neurogenesis and synaptic plasticity in the dentate gyrus, as well as impaired cognition. Vice versa, treating aged mice with young blood plasma rescues impairments associated with aging.

OBJECTIVE

Whether blood-borne factors are sufficient to drive impairments outside the dentate gyrus, how they impact neurophysiology, and how the functional outcome compares to impairments found in mouse models for AD is still unclear.

METHODS

Here, we treated adult mice with blood plasma from aged mice and assessed neurophysiological parameters in the hippocampal CA1.

RESULTS

Mice treated with aged blood plasma show significantly impaired levels of long-term potentiation (LTP), similar to those present in APP/PS1 mice. These impaired levels of LTP in plasma-treated mice are associated with alterations in basic properties of glutamatergic transmission and the enhanced activity of voltage-gated Ca2 + channels.

CONCLUSION

Together, the data presented in this study show that blood-borne factors are sufficient to drive neurophysiological impairments in the hippocampal CA1.

Sensitivity of the S1 neuronal calcium network to insulin and Bay-K 8644 in vivo: Relationship to gait, motivation, and aging processes

Neuronal hippocampal Ca²⁺ dysregulation is a critical component of cognitive decline in brain aging and Alzheimer's disease and is suggested to impact communication and excitability through the activation of a larger after hyperpolarization. However, few studies have tested for the presence of Ca²⁺ dysregulation in vivo, how it manifests, and whether it impacts network function across hundreds of neurons. Here, we tested for neuronal Ca²⁺ network dysregulation in vivo in the primary somatosensory cortex (S1) of anesthetized young and aged male Fisher 344 rats using single‐cell resolution techniques. Because S1 is involved in sensory discrimination and proprioception, we tested for alterations in ambulatory performance in the aged animal and investigated two potential pathways underlying these central aging‐ and Ca²⁺‐dependent changes. Compared to young, aged animals displayed increased overall activity and connectivity of the network as well as decreased ambulatory speed. In aged animals, intranasal insulin (INI) increased network synchronicity and ambulatory speed. Importantly, in young animals, delivery of the L‐type voltage‐gated Ca²⁺ channel modifier Bay‐K 8644 altered network properties, replicating some of the changes seen in the older animal. These results suggest that hippocampal Ca²⁺ dysregulation may be generalizable to other areas, such as S1, and might engage modalities that are associated with locomotor stability and motivation to ambulate. Further, given the safety profile of INI in the clinic and the evidence presented here showing that this central dysregulation is sensitive to insulin, we suggest that these processes can be targeted to potentially increase motivation and coordination while also reducing fall frequency with age.

TGF-β1 Protects Trauma-injured Murine Cortical Neurons by Upregulating L-type Calcium Channel Cav1.2 via the p38 Pathway

Traumatic brain injury (TBI) is a leading cause of disability and death in adolescents, and there is a lack of effective methods of treatment. The neuroprotective effects exerted by TGF-β1 can ameliorate a range of neuronal lesions in multiple central nervous system diseases. In this study, we used an in-vitro TBI model of mechanical injury on murine primary cortical neurons and the neuro-2a cell line to investigate the neuroprotective role played by TGF-β1 in cortical neurons in TBI. Our results showed that TGF-β1 significantly increased neuronal viability and inhibited apoptosis for 24 h after trauma. The expression of Ca_v1.2, an L-type calcium channel (LTCC) isoform, decreased significantly after trauma injury, and this change was reversed by TGF-β1. Nimodipine, a classic LTCC blocker, abolished the protective effect of TGF-β1 on trauma-induced neuronal apoptosis. The knockdown of Ca_v1.2 in differentiated neuro-2a cells significantly inhibited the anti-apoptosis effect of TGF-β1 exerted on injured neuro-2a cells. Moreover, TGF-β1 rescued and enhanced the trauma-suppressed neuro-2a intracellular Ca²⁺ concentration, while the effect of TGF-β1 was partially inhibited by nimodipine. TGF-β1 significantly upregulated the expression of Ca_v1.2 by activating the p38 MAPK pathway and by inhibiting trauma-induced neuronal apoptosis. In conclusion, TGF-β1 increased trauma-injured murine cortical neuronal activity and inhibited apoptosis by upregulating Cav1.2 channels via activating the p38 MAPK pathway. Therefore, the TGF-β1/p38 MAPK/Ca_v 1.2 pathway has the potential to be used as a novel therapeutic target for TBI.

SARS-CoV-2 Morbidity in the CNS and the Aged Brain Specific Vulnerability

The infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can be the cause of a fatal disease known as coronavirus disease 2019 (COVID-19) affecting the lungs and other organs. Particular attention has been given to the effects of the infection on the brain due to recurring neurological symptoms associated with COVID-19, such as ischemic or hemorrhagic stroke, encephalitis and myelitis, which are far more severe in the elderly compared to younger patients. The specific vulnerability of the aged brain could derive from the impaired immune defenses, from any of the altered homeostatic mechanisms that contribute to the aging phenotype, and from particular changes in the aged brain involving neurons and glia. While neuronal modifications could contribute indirectly to the damage induced by SARS-CoV-2, glia alterations could play a more direct role, as they are involved in the immune response to viral infections. In aged patients, changes regarding glia include the accumulation of dystrophic forms, reduction of waste removal, activation of microglia and astrocytes, and immunosenescence. It is plausible to hypothesize that SARS-CoV-2 infection in the elderly may determine severe brain damage because of the frail phenotype concerning glial cells.

Aging-Related Alterations to Persistent Firing in the Lateral Entorhinal Cortex Contribute to Deficits in Temporal Associative Memory

With aging comes a myriad of different disorders, and cognitive decline is one of them. Studies have consistently shown a decline amongst aged subjects in their ability to acquire and maintain temporal associative memory. Defined as the memory of the association between two objects that are separated in time, temporal associative memory is dependent on neocortical structures such as the prefrontal cortex and temporal lobe structures. For this memory to be acquired, a mental trace of the first stimulus is necessary to bridge the temporal gap so the two stimuli can be properly associated. Persistent firing, the ability of the neuron to continue to fire action potentials even after the termination of a triggering stimulus, is one mechanism that is posited to support this mental trace. A recent study demonstrated a decline in persistent firing ability in pyramidal neurons of layer III of the lateral entorhinal cortex with aging, contributing to learning impairments in temporal associative memory acquisition. In this work, we explore the potential ways persistent firing in lateral entorhinal cortex (LEC) III supports temporal associative memory, and how aging may disrupt this mechanism within the temporal lobe system, resulting in impairment in this crucial behavior.

Role of Calcium Homeostasis in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease associated with senile plaques (SP) and neurofibrillary tangles (NFTs) in the brain. With aging of the population, AD has become the most common form of dementia. However, the mechanisms leading to AD are still under investigation, and there are currently no specific drugs for its treatment. Therefore, further study on the pathogenesis of AD to develop new drugs for AD treatment remains a top priority. Several studies have suggested that intracellular calcium homeostasis is dysregulated in AD, and this has been implicated in the deposition of amyloid β (Aβ), hyperphosphorylation of tau protein, abnormal synaptic plasticity, and apoptosis, all of which are involved in the occurrence and development of AD. In addition, some based on pathways linking calcium homeostasis and AD have achieved results in AD treatment. This review comprehensively explores the relationship between calcium homeostasis and the pathogenesis of AD to provide a theoretical basis for the future exploration of AD and the development of novel therapeutic drugs.

Biophysical and synaptic properties of regular spiking interneurons in hippocampal area CA3 of aged rats

Neuronal processing from the dentate gyrus to the hippocampus is critical for storage and recovery of new memory traces. In area CA3, GABAergic interneurons form a strong barrage of inhibition that modulates pyramidal cells. A well-established feature of aging is decreased GABAergic inhibition, a phenomenon that contributes to the exacerbated excitability of aged pyramidal cells. In hippocampal slices of aged rats (22-28 months old) we examined the properties of regular spiking CA3 interneurons with patch-clamp whole-cell recordings. We found enhanced firing discharge without altering the maximal firing rate of aged regular spiking interneurons. In the mossy fibers (MF) to interneurons synapse, a switch in the AMPA receptor subunit composition was found in aged interneurons. Young regular spiking interneurons predominantly express CP AMPA receptors and MF LTD. By contrast, aged regular spiking interneurons contain a higher proportion of CI AMPA receptors and respond with MF LTP. We show for the first time that the specialized MF terminals contacting interneurons, retain synaptic capabilities and provide a novel insight of the interneuron's function during aging.

Influence of Dietary Nutrient Intake on Episodic Memory Across the Adult Life Span

The aim of the study was to identify nutrients that have the ability to impact brain functioning and, as a consequence, influence episodic memory. In particular, we examined recollection, the ability to recall details of previous experiences, which is the episodic memory process most affected as age advances. A sample of 1,550 healthy participants between 21 and 80 years old participated in the study. Nutritional intake was examined through a food frequency questionnaire and software developed to determine the daily consumption of 64 nutrients based on food intake during the last year. Recollection was measured through a computerized source memory paradigm. First, we identified which nutrients influence recollection across the entire adult life span. Then, moderator analyses were conducted by dividing the sample into young (21–40 years old), middle-aged (41–60 years old) and older (61–80 years old) adults to establish in which life stage nutrients influence episodic memory. Across the adult life span, recollection accuracy was shown to benefit from the intake of sodium, heme, vitamin E, niacin, vitamin B6, cholesterol, alcohol, fat, protein, and palmitic, stearic, palmitoleic, oleic, gadoleic, alpha-linoleic and linoleic acid. The effects of energy, maltose, lactose, calcium and several saturated fatty acids on recollection were modulated by age; in older adults, the consumption of these nutrients negatively influenced episodic memory performance, and in middle-aged adults, only lactose had negative effects. Several brain mechanisms that support episodic memory were influenced by specific nutrients, demonstrating the ability of food to enhance or deteriorate episodic memory.

Neuronal Calcium Imaging, Excitability, and Plasticity Changes in the Aldh2-/- Mouse Model of Sporadic Alzheimer's Disease

Background:

Dysregulated signaling in neurons and astrocytes participates in pathophysiological alterations seen in the Alzheimer’s disease brain, including increases in amyloid-β, hyperphosphorylated tau, inflammation, calcium dysregulation, and oxidative stress. These are often noted prior to the development of behavioral, cognitive, and non-cognitive deficits. However, the extent to which these pathological changes function together or independently is unclear.

Objective:

Little is known about the temporal relationship between calcium dysregulation and oxidative stress, as some reports suggest that dysregulated calcium promotes increased formation of reactive oxygen species, while others support the opposite. Prior work has quantified several key outcome measures associated with oxidative stress in aldehyde dehydrogenase 2 knockout (Aldh2^–/–) mice, a non-transgenic model of sporadic Alzheimer’s disease.

Methods:

Here, we tested the hypothesis that early oxidative stress can promote calcium dysregulation across aging by measuring calcium-dependent processes using electrophysiological and imaging methods and focusing on the afterhyperpolarization (AHP), synaptic activation, somatic calcium, and long-term potentiation in the Aldh2^–/– mouse.

Results:

Our results show a significant age-related decrease in the AHP along with an increase in the slow AHP amplitude in Aldh2^–/– animals. Measures of synaptic excitability were unaltered, although significant reductions in long-term potentiation maintenance were noted in the Aldh2^–/– animals compared to wild-type.

Conclusion:

With so few changes in calcium and calcium-dependent processes in an animal model that shows significant increases in HNE adducts, Aβ, p-tau, and activated caspases across age, the current findings do not support a direct link between neuronal calcium dysregulation and uncontrolled oxidative stress.

Synaptic plasticity in Alzheimer's disease and healthy aging

The strength and efficiency of synaptic connections are affected by the environment or the experience of the individual. This property, called synaptic plasticity, is directly related to memory and learning processes and has been modeled at the cellular level. These types of cellular memory and learning models include specific stimulation protocols that generate a long-term strengthening of the synapses, called long-term potentiation, or a weakening of the said long-term synapses, called long-term depression. Although, for decades, researchers have believed that the main cause of the cognitive deficit that characterizes Alzheimer's disease (AD) and aging was the loss of neurons, the hypothesis of an imbalance in the cellular and molecular mechanisms of synaptic plasticity underlying this deficit is currently widely accepted. An understanding of the molecular and cellular changes underlying the process of synaptic plasticity during the development of AD and aging will direct future studies to specific targets, resulting in the development of much more efficient and specific therapeutic strategies. In this review, we classify, discuss, and describe the main findings related to changes in the neurophysiological mechanisms of synaptic plasticity in excitatory synapses underlying AD and aging. In addition, we suggest possible mechanisms in which aging can become a high-risk factor for the development of AD and how its development could be prevented or slowed.

APPsα rescues impaired Ca2+ homeostasis in APP- and APLP2-deficient hippocampal neurons

Alterations in Ca2+ homeostasis have been reported in several in vitro and in vivo studies using mice expressing the Alzheimer's disease-associated transgenes, presenilin and the amyloid precursor protein (APP). While intense research focused on amyloid-β-mediated functions on neuronal Ca2+ handling, the physiological role of APP and its close homolog APLP2 is still not fully clarified. We now elucidate a mechanism to show how APP and its homolog APLP2 control neuronal Ca2+ handling and identify especially the ectodomain APPsα as an essential regulator of Ca2+ homeostasis. Importantly, we demonstrate that the loss of APP and APLP2, but not APLP2 alone, impairs Ca2+ handling, the refill of the endoplasmic reticulum Ca2+ stores, and synaptic plasticity due to altered function and expression of the SERCA-ATPase and expression of store-operated Ca2+ channel-associated proteins Stim1 and Stim2. Long-term AAV-mediated expression of APPsα, but not acute application of the recombinant protein, restored physiological Ca2+ homeostasis and synaptic plasticity in APP/APLP2 cDKO cultures. Overall, our analysis reveals an essential role of the APP family and especially of the ectodomain APPsα in Ca2+ homeostasis, thereby highlighting its therapeutic potential.

In Pursuit of Healthy Aging: Effects of Nutrition on Brain Function

Consuming a balanced, nutritious diet is important for maintaining health, especially as individuals age. Several studies suggest that consuming a diet rich in antioxidants and anti-inflammatory components such as those found in fruits, nuts, vegetables, and fish may reduce age-related cognitive decline and the risk of developing various neurodegenerative diseases. Numerous studies have been published over the last decade focusing on nutrition and how this impacts health. The main objective of the current article is to review the data linking the role of diet and nutrition with aging and age-related cognitive decline. Specifically, we discuss the roles of micronutrients and macronutrients and provide an overview of how the gut microbiota-gut-brain axis and nutrition impact brain function in general and cognitive processes in particular during aging. We propose that dietary interventions designed to optimize the levels of macro and micronutrients and maximize the functioning of the microbiota-gut-brain axis can be of therapeutic value for improving cognitive functioning, particularly during aging.

Dysfunction of Mitochondrial Ca2+ Regulatory Machineries in Brain Aging and Neurodegenerative Diseases

Calcium ions (Ca²⁺) play critical roles in neuronal processes, such as signaling pathway activation, transcriptional regulation, and synaptic transmission initiation. Therefore, the regulation of Ca²⁺ homeostasis is one of the most important processes underlying the basic cellular viability and function of the neuron. Multiple components, including intracellular organelles and plasma membrane Ca²⁺-ATPase, are involved in neuronal Ca²⁺ control, and recent studies have focused on investigating the roles of mitochondria in synaptic function. Numerous mitochondrial Ca²⁺ regulatory proteins have been identified in the past decade, with studies demonstrating the tissue- or cell-type-specific function of each component. The mitochondrial calcium uniporter and its binding subunits are major inner mitochondrial membrane proteins contributing to mitochondrial Ca²⁺ uptake, whereas the mitochondrial Na⁺/Ca²⁺ exchanger (NCLX) and mitochondrial permeability transition pore (mPTP) are well-studied proteins involved in Ca²⁺ extrusion. The level of cytosolic Ca²⁺ and the resulting characteristics of synaptic vesicle release properties are controlled via mitochondrial Ca²⁺ uptake and release at presynaptic sites, while in dendrites, mitochondrial Ca²⁺ regulation affects synaptic plasticity. During brain aging and the progress of neurodegenerative disease, mitochondrial Ca²⁺ mishandling has been observed using various techniques, including live imaging of Ca²⁺ dynamics. Furthermore, Ca²⁺ dysregulation not only disrupts synaptic transmission but also causes neuronal cell death. Therefore, understanding the detailed pathophysiological mechanisms affecting the recently discovered mitochondrial Ca²⁺ regulatory machineries will help to identify novel therapeutic targets. Here, we discuss current research into mitochondrial Ca²⁺ regulatory machineries and how mitochondrial Ca²⁺ dysregulation contributes to brain aging and neurodegenerative disease.

Ca2+ Dyshomeostasis Disrupts Neuronal and Synaptic Function in Alzheimer's Disease

Ca²⁺ homeostasis is essential for multiple neuronal functions and thus, Ca²⁺ dyshomeostasis can lead to widespread impairment of cellular and synaptic signaling, subsequently contributing to dementia and Alzheimer's disease (AD). While numerous studies implicate Ca²⁺ mishandling in AD, the cellular basis for loss of cognitive function remains under investigation. The process of synaptic degradation and degeneration in AD is slow, and constitutes a series of maladaptive processes each contributing to a further destabilization of the Ca²⁺ homeostatic machinery. Ca²⁺ homeostasis involves precise maintenance of cytosolic Ca²⁺ levels, despite extracellular influx via multiple synaptic Ca²⁺ channels, and intracellular release via organelles such as the endoplasmic reticulum (ER) via ryanodine receptor (RyRs) and IP₃R, lysosomes via transient receptor potential mucolipin channel (TRPML) and two pore channel (TPC), and mitochondria via the permeability transition pore (PTP). Furthermore, functioning of these organelles relies upon regulated inter-organelle Ca²⁺ handling, with aberrant signaling resulting in synaptic dysfunction, protein mishandling, oxidative stress and defective bioenergetics, among other consequences consistent with AD. With few effective treatments currently available to mitigate AD, the past few years have seen a significant increase in the study of synaptic and cellular mechanisms as drivers of AD, including Ca²⁺ dyshomeostasis. Here, we detail some key findings and discuss implications for future AD treatments.

Effect of ladostigil treatment of aging rats on gene expression in four brain areas associated with regulation of memory

Episodic and spatial memory decline in aging and are controlled by the hippocampus, perirhinal, frontal and parietal cortices and the connections between them. Ladostigil, a drug with antioxidant and anti-inflammatory activity, was shown to prevent the loss of episodic and spatial memory in aging rats. To better understand the molecular effects of aging and ladostigil on these brain regions we characterized the changes in gene expression using RNA-sequencing technology in rats aged 6 and 22 months. We found that the changes induced by aging and chronic ladostigil treatment were brain region specific. In the hippocampus, frontal and perirhinal cortex, ladostigil decreased the overexpression of genes regulating calcium homeostasis, ion channels and those adversely affecting synaptic function. In the parietal cortex, ladostigil increased the expression of several genes that provide neurotrophic support, while reducing that of pro-apoptotic genes and those encoding pro-inflammatory cytokines and their receptors. Ladostigil also decreased the expression of axonal growth inhibitors and those impairing mitochondrial function. Together, these actions could explain the protection by ladostigil against age-related memory decline.

Brain Aging and Anesthesia

Herein, the authors review the neuroanatomical and the neurophysiological aspects of the normal aging evolution based on the recent literature and briefly describe the difference between physiological and pathological brain aging, with consideration of the currently recommended anesthesia management of older patients. The population of elderly patients is growing drastically with advances in medicine that have prolonged the life span. One of the direct consequence has been a significant increase in the request for anesthesia care for older patients despite the type of surgery (cardiac vs noncardiac and mainly orthopedic). Because the brain of this category of patients undergoes a specific triple influence (immune, metabolic, and inflammatory), some particular physiological, anatomical, and structural modifications must be taken into account because they expose these patients more specifically to postoperative cognitive disturbances. To prevent type of adverse outcome, a better knowledge and understanding of these neurosciences must be promoted. The strategies developed to prevent such adverse outcomes include the determination and detection of significant at-risk patients and improvement in the titration of anesthesia to reduce exposure of anesthesia to these patients through an adapted anesthesia-induced unconsciousness that avoids, as much as possible, the risk of toxic overdose with an overly deep brain depression. To accomplish this, the unprocessed electroencephalogram (EEG) and its spectrogram may represent a significant improvement in monitoring, first by allowing for the rapid recognition of repetitive or persistent EEG suppression by the on-line reading of the raw EEG trace and second by allowing for the accurate determination of the adequate anesthetic-induced state, obtained in general in this category of patients by substantially lowered doses of anesthetic agents. This represents a new methodology for anesthesia titration that is adjusted on a more case-by-case basis and is related to the physiology of individual patients. A better understanding of aging-induced brain transformations remains the key regarding the improvement of the anesthetic management of the always growing population of elderly patients. The promotion of the unprocessed EEG may represent the best method of preventing the risk of anesthetic toxicity, including postoperative cognitive dysfunctions.

Age-related shift in LTD is dependent on neuronal adenosine A2A receptors interplay with mGluR5 and NMDA receptors

Synaptic dysfunction plays a central role in Alzheimer's disease (AD), since it drives the cognitive decline. An association between a polymorphism of the adenosine A2A receptor (A2AR) encoding gene-ADORA2A, and hippocampal volume in AD patients was recently described. In this study, we explore the synaptic function of A2AR in age-related conditions. We report, for the first time, a significant overexpression of A2AR in hippocampal neurons of aged humans, which is aggravated in AD patients. A similar profile of A2AR overexpression in rats was sufficient to drive age-like memory impairments in young animals and to uncover a hippocampal LTD-to-LTP shift. This was accompanied by increased NMDA receptor gating, dependent on mGluR5 and linked to enhanced Ca2+ influx. We confirmed the same plasticity shift in memory-impaired aged rats and APP/PS1 mice modeling AD, which was rescued upon A2AR blockade. This A2AR/mGluR5/NMDAR interaction might prove a suitable alternative for regulating aberrant mGluR5/NMDAR signaling in AD without disrupting their constitutive activity.

Memory and Learning Deficits Are Associated With Ca2+ Dyshomeostasis in Normal Aging

Neuronal intracellular Ca2+ homeostasis is critical to the normal physiological functions of neurons and neuronal Ca2+ dyshomeostasis has been associated with the age-related decline of cognitive functions. Accumulated evidence indicates that the underlying mechanism for this is that abnormal intracellular Ca2+ levels stimulate the dysregulation of intracellular signaling, which subsequently induces neuronal cell death. We examined intracellular Ca2+ homeostasis in cortical (in vivo) and hippocampal (in vitro) neurons from young (3-months), middle-age (12-months), and aged (24-months) wild type C57BL6J mice. We found a progressive age-related elevation of intracellular resting calcium ([Ca2+]r) in cortical (in vivo) and hippocampal (in vitro) neurons associated with increased hippocampal neuronal calpain activity and reduced cell viability. In vitro, removal of extracellular Ca2+ or treatment with SAR7334 or dantrolene reduced [Ca2+]r in all age groups and dantrolene treatment lowered calpain activity and increased cell viability. In vivo, both middle-aged and aged mice showed cognitive deficits compared to young mice, which improved after dantrolene treatment. These findings support the hypothesis that intracellular Ca2+ dyshomeostasis is a major mechanism underlying the cognitive deficits seen in both normal aging and degenerative neurologic diseases.

Normal ageing of the brain: Histological and biological aspects

All the hallmarks of ageing are observed in the brain, and its cells, especially neurons, are characterized by their remarkably long lifetime. Like any organ or system, the brain is exposed to ageing processes which affect molecules, cells, blood vessels, gross morphology and, uniquely for this organ, cognition. The preponderant cerebral structures are characterized by the cellular processes of neurons and glial cells and while the quantity of cerebral interstitial fluid is limited, it is now recognized as playing a crucial role in maintaining cerebral homeostasis. Most of our current knowledge of the ageing brain derives from studies of neurodegenerative disorders. It is interesting to note that common features of these disorders, like Tau, phosphoTau and amyloid peptide accumulation, can begin relatively early in life as a result of physiological ageing and are present in subclinical cases while also being used as early-stage markers of neurodegenerative diseases in progression. In this article, we review tissue and cellular modifications in the ageing brain. Commonly described macroscopic, microscopic and vascular changes that in the ageing brain are contrasted with those seen in neurodegenerative contexts. We also review the molecular changes that occur with age in the brain, such as modifications in gene expression, insulin/insulin-like growth factor 1 signalling dysfunction, post-translational protein modifications, mitochondrial dysfunction, autophagy and calcium conductance changes.

The role of L-type calcium channels in neuronal excitability and aging

Over the last two decades there has been significant progress towards understanding the neural substrates that underlie age-related cognitive decline. Although many of the exact molecular and cellular mechanisms have yet to be fully understood, there is consensus that alterations in neuronal calcium homeostasis contribute to age-related deficits in learning and memory. Furthermore, it is thought that the age-related changes in calcium homeostasis are driven, at least in part, by changes in calcium channel expression. In this review, we focus on the role of a specific class of calcium channels: L-type voltage-gated calcium channels (LVGCCs). We provide the reader with a general introduction to voltage-gated calcium channels, followed by a more detailed description of LVGCCs and how they serve to regulate neuronal excitability via the post burst afterhyperpolarization (AHP). We conclude by reviewing studies that link the slow component of the AHP to learning and memory, and discuss how age-related increases in LVGCC expression may underlie cognitive decline by mediating a decrease in neuronal excitability.

L-type Ca2+ channel-mediated Ca2+ influx adjusts neuronal mitochondrial function to physiological and pathophysiological conditions

L-type voltage-gated Ca2+ channels (LTCCs) are implicated in neurodegenerative processes and cell death. Accordingly, LTCC antagonists have been proposed to be neuroprotective, although this view is disputed, because intentional LTCC activation can also have beneficial effects. LTCC-mediated Ca2+ influx influences mitochondrial function, which plays a crucial role in the regulation of cell viability. Hence, we investigated the effect of modulating LTCC-mediated Ca2+ influx on mitochondrial function in cultured hippocampal neurons. To activate LTCCs, neuronal activity was stimulated by increasing extracellular K+ or by application of the GABAA receptor antagonist bicuculline. The activity of LTCCs was altered by application of an agonistic (Bay K8644) or an antagonistic (isradipine) dihydropyridine. Our results demonstrated that activation of LTCC-mediated Ca2+ influx affected mitochondrial function in a bimodal manner. At moderate stimulation strength, ATP synthase activity was enhanced, an effect that involved Ca2+-induced Ca2+ release from intracellular stores. In contrast, high LTCC-mediated Ca2+ loads led to a switch in ATP synthase activity to reverse-mode operation. This effect, which required nitric oxide, helped to prevent mitochondrial depolarization and sustained increases in mitochondrial Ca2+ Our findings indicate a complex role of LTCC-mediated Ca2+ influx in the tuning and maintenance of mitochondrial function. Therefore, the use of LTCC inhibitors to protect neurons from neurodegeneration should be reconsidered carefully.

Experiments in macaque monkeys provide critical insights into age-associated changes in cognitive and sensory function

The use of animal models in brain aging research has led to numerous fundamental insights into the neurobiological processes that underlie changes in brain function associated with normative aging. Macaque monkeys have become the predominant nonhuman primate model system in brain aging research due to their striking similarities to humans in their behavioral capacities, sensory processing abilities, and brain architecture. Recent public concern about nonhuman primate research has made it imperative to attempt to clearly articulate the potential benefits to human health that this model enables. The present review will highlight how nonhuman primates provide a critical bridge between experiments conducted in rodents and development of therapeutics for humans. Several studies discussed here exemplify how nonhuman primate research has enriched our understanding of cognitive and sensory decline in the aging brain, as well as how this work has been important for translating mechanistic implications derived from experiments conducted in rodents to human brain aging research.

The Puzzling Role of Neuron-Specific PMCA Isoforms in the Aging Process

The aging process is a physiological phenomenon associated with progressive changes in metabolism, genes expression, and cellular resistance to stress. In neurons, one of the hallmarks of senescence is a disturbance of calcium homeostasis that may have far-reaching detrimental consequences on neuronal physiology and function. Among several proteins involved in calcium handling, plasma membrane Ca²⁺-ATPase (PMCA) is the most sensitive calcium detector controlling calcium homeostasis. PMCA exists in four main isoforms and PMCA2 and PMCA3 are highly expressed in the brain. The overall effects of impaired calcium extrusion due to age-dependent decline of PMCA function seem to accumulate with age, increasing the susceptibility to neurotoxic insults. To analyze the PMCA role in neuronal cells, we have developed stable transfected differentiated PC12 lines with down-regulated PMCA2 or PMCA3 isoforms to mimic age-related changes. The resting Ca²⁺ increased in both PMCA-deficient lines affecting the expression of several Ca²⁺-associated proteins, i.e., sarco/endoplasmic Ca²⁺-ATPase (SERCA), calmodulin, calcineurin, GAP43, CCR5, IP₃Rs, and certain types of voltage-gated Ca²⁺ channels (VGCCs). Functional studies also demonstrated profound changes in intracellular pH regulation and mitochondrial metabolism. Moreover, modification of PMCAs membrane composition triggered some adaptive processes to counterbalance calcium overload, but the reduction of PMCA2 appeared to be more detrimental to the cells than PMCA3.

Learning and aging affect neuronal excitability and learning

The first study that demonstrated a change in intrinsic neuronal excitability after learning in ex vivo brain tissue slices from a mammal was published over thirty years ago. Numerous other manuscripts describing similar learning-related changes have followed over the years since the original paper demonstrating the postburst afterhyperpolarization (AHP) reduction in CA1 pyramidal neurons from rabbits that learned delay eyeblink conditioning was published. In addition to the learning-related changes, aging-related enlargement of the postburst AHP in CA1 pyramidal neurons have been reported. Extensive work has been done relating slow afterhyperpolarization enhancement in CA1 hippocampus to slowed learning in some aging animals. These reproducible findings strongly implicate modulation of the postburst AHP as an essential cellular mechanism necessary for successful learning, at least in learning tasks that engage CA1 hippocampal pyramidal neurons.

Changes in presynaptic calcium signalling accompany age-related deficits in hippocampal LTP and cognitive impairment

The loss of cognitive function accompanying healthy aging is not associated with extensive or characteristic patterns of cell death, suggesting it is caused by more subtle changes in synaptic properties. In the hippocampal CA1 region, long‐term potentiation requires stronger stimulation for induction in aged rats and mice and long‐term depression becomes more prevalent. An age‐dependent impairment of postsynaptic calcium homeostasis may underpin these effects. We have examined changes in presynaptic calcium signalling in aged mice using a transgenic mouse line (SyG37) that expresses a genetically encoded calcium sensor in presynaptic terminals. SyG37 mice showed an age‐dependent decline in cognitive abilities in behavioural tasks that require hippocampal processing including the Barnes maze, T‐maze and object location but not recognition tests. The incidence of LTP was significantly impaired in animals over 18 months of age. These effects of aging were accompanied by a persistent increase in resting presynaptic calcium, an increase in the presynaptic calcium signal following Schaffer collateral fibre stimulation, an increase in postsynaptic fEPSP slope and a reduction in paired‐pulse facilitation. These effects were not caused by synapse proliferation and were of presynaptic origin since they were evident in single presynaptic boutons. Aged synapses behaved like younger ones when the extracellular calcium concentration was reduced. Raising extracellular calcium had little effect on aged synapses but altered the properties of young synapses into those of their aged counterparts. These effects can be readily explained by an age‐dependent change in the properties or numbers of presynaptic calcium channels.

Neuronal Cells Rearrangement During Aging and Neurodegenerative Disease: Metabolism, Oxidative Stress and Organelles Dynamic

Brain cells normally respond adaptively to oxidative stress or bioenergetic challenges, resulting from ongoing activity in neuronal circuits. During aging and in neurodegenerative disorders, these mechanisms are compromised. In fact, neurons show unique age-related changes in functions and metabolism, resulting in greater susceptibility to insults and disease. Aging affects the nervous system as well as other organs. More precisely, as the nervous system ages, neuron metabolism may change, inducing glucose hypometabolism, impaired transport of critical substrates underlying metabolism, alterations in calcium signaling, and mitochondrial dysfunction. Moreover, in neuronal aging, an accumulation of impaired and aggregated proteins in the cytoplasm and in mitochondria is observed, as the result of oxidative stress: reduced antioxidant defenses and/or increase of reactive oxygen species (ROS). These changes lead to greater vulnerability of neurons in various regions of the brain and increased susceptibility to several diseases. Specifically, the first part of the review article will focus on the major neuronal cells’ rearrangements during aging in response to changes in metabolism and oxidative stress, while the second part will cover the neurodegenerative disease areas in detail.

Effects of sustained cognitive activity on white matter microstructure and cognitive outcomes in healthy middle-aged adults: A systematic review

Adults who remain cognitively active may be protected from age-associated changes in white matter (WM) and cognitive decline. To determine if cognitive activity is a precursor for WM plasticity, the available literature was systematically searched for Region of Interest (ROI) and whole-brain studies assessing the efficacy of cognitive training (CT) on WM microstructure using Diffusion Tensor Imaging (DTI) in healthy adults (> 40 years). Seven studies were identified and included in this review. Results suggest there are beneficial effects to WM microstructure after CT in frontal and medial brain regions, with some studies showing improved performance in cognitive outcomes. Benefits of CT were shown to be protective against age-related WM microstructure decline by either maintaining or improving WM after training. These results have implications for determining the capacity for training-dependent WM plasticity in older adults and whether CT can be utilised to prevent age-associated cognitive decline. Additional studies with standardised training and imaging protocols are needed to confirm these outcomes.

The plasma membrane calcium pumps-The old and the new

The plasma membrane Ca²⁺-ATPase (PMCA) pumps play a critical role in the maintenance of calcium (Ca²⁺) homeostasis, crucial for optimal neuronal function and cell survival. Loss of Ca²⁺ homeostasis is a key precursor in neuronal dysfunction associated with brain aging and in the pathogenesis of neurodegenerative disorders. In this article, we review evidence showing age-related changes in the PMCAs in synaptic plasma membranes (SPMs) and lipid raft microdomains isolated from rat brain. Both PMCA activity and protein levels decline progressively with increasing age. However, the loss of activity is disproportionate to the reduction of protein levels suggesting the presence of dysfunctional PMCA molecules in aged brain. PMCA activity is also diminished in post-mortem human brain samples from Alzheimer's disease and Parkinson's disease patients and in cell models of these neurodegenerative disorders. Experimental reduction of the PMCAs not only alter Ca²⁺ homeostasis but also have diverse effects on neurons such as reduced neuritic network, impaired release of neurotransmitter and increased susceptibility to stressful stimuli, particularly to agents that elevate intracellular Ca²⁺ [Ca²⁺]_i. Loss of PMCA is likely to contribute to neuronal dysfunction observed in the aging brain and in the development of age-dependent neurodegenerative disorders. Therapeutic (pharmacological and/or non-pharmacological) approaches that can enhance PMCA activity and stabilize [Ca²⁺]_i homeostasis may be capable of preventing, slowing, and/or reversing neuronal degeneration.

Role of STIM1 in neurodegeneration

STIM1 is an endoplasmic reticulum (ER) protein with a key role in Ca2+ mobilization. Due to its ability to act as an ER-intraluminal Ca2+ sensor, it regulates store-operated Ca2+ entry (SOCE), which is a Ca2+ influx pathway involved in a wide variety of signalling pathways in eukaryotic cells. Despite its important role in Ca2+ transport, current knowledge about the role of STIM1 in neurons is much more limited. Growing evidence supports a role for STIM1 and SOCE in the preservation of dendritic spines required for long-term potentiation and the formation of memory. In this regard, recent studies have demonstrated that the loss of STIM1, which impairs Ca2+ mobilization in neurons, risks cell viability and could be the cause of neurodegenerative diseases. The role of STIM1 in neurodegeneration and the molecular basis of cell death triggered by low levels of STIM1 are discussed in this review.

Fighting the Cause of Alzheimer's and GNE Myopathy

Age is the common risk factor for both neurodegenerative and neuromuscular diseases. Alzheimer disease (AD), a neurodegenerative disorder, causes dementia with age progression while GNE myopathy (GNEM), a neuromuscular disorder, causes muscle degeneration and loss of muscle motor movement with age. Individuals with mutations in presenilin or amyloid precursor protein (APP) gene develop AD while mutations in GNE (UDP N-acetylglucosamine 2 epimerase/N-acetyl Mannosamine kinase), key sialic acid biosynthesis enzyme, cause GNEM. Although GNEM is characterized with degeneration of muscle cells, it is shown to have similar disease hallmarks like aggregation of Aβ and accumulation of phosphorylated tau and other misfolded proteins in muscle cell similar to AD. Similar impairment in cellular functions have been reported in both disorders such as disruption of cytoskeletal network, changes in glycosylation pattern, mitochondrial dysfunction, oxidative stress, upregulation of chaperones, unfolded protein response in ER, autophagic vacuoles, cell death, and apoptosis. Interestingly, AD and GNEM are the two diseases with similar phenotypic condition affecting neuron and muscle, respectively, resulting in entirely different pathology. This review represents a comparative outlook of AD and GNEM that could lead to target common mechanism to find a plausible therapeutic for both the diseases.

Fucosterol from an Edible Brown Alga Ecklonia stolonifera Prevents Soluble Amyloid Beta-Induced Cognitive Dysfunction in Aging Rats

Fucosterol from edible brown seaweeds has various biological activities, including anti-inflammatory, anti-adipogenic, antiphotoaging, anti-acetylcholinesterase, and anti-beta-secretase 1 activities. However, little is known about its effects on soluble amyloid beta peptide (sAβ)-induced endoplasmic reticulum (ER) stress and cognitive impairment. Fucosterol was isolated from the edible brown seaweed Ecklonia stolonifera, and its neuroprotective effects were analyzed in primary hippocampal neurons and in aging rats. Fucosterol attenuated sAβ1-42-induced decrease in the viability of hippocampal neurons and downregulated sAβ1-42-induced increase in glucose-regulated protein 78 (GRP78) expression in hippocampal neurons via activation of tyrosine receptor kinase B-mediated ERK1/2 signaling. Fucosterol co-infusion attenuated sAβ1-42-induced cognitive impairment in aging rats via downregulation of GRP78 expression and upregulation of mature brain-derived neurotrophic factor expression in the dentate gyrus. Fucosterol might be beneficial for the management of cognitive dysfunction via suppression of aging-induced ER stress.

Ageing reduces the reproductive performance of male white shrimp Litopenaeus vannamei by altering sperm intracellular Ca2+ concentrations and interfering with sperm apoptosis

Although the effects of age on the reproductive performance of various invertebrates, including white shrimp Litopenaeus vannamei are increasingly well documented, the mechanisms manifesting these impacts remain poorly understood. To ascertain the mechanisms of age on reproductive performance, the sperm quality, intracellular contents of Ca²⁺, insemination and hatching rates, and status of sperm apoptosis in terms of the expression of key regulatory genes were investigated in 11 and 16 month old male L. vannamei. The aged male individuals (16 months) had lesser reproductive performance in terms of fertilization and hatching rates. In addition, fewer and less viable sperm were detected in aged shrimp, which may be due to the altered expression of apoptosis-related genes. Furthermore, the aged males had lesser intracellular contents of Ca²⁺ in the sperm which may decrease the capacity of these gametes to undergo a complete acrosome reaction. In general, due to the decrease in intracellular contents of Ca²⁺ and alterations in the process of apoptosis, aged L. vannamei have relatively lesser quality sperm and may, therefore, have lesser reproductive performance.

STIM1 deficiency is linked to Alzheimer's disease and triggers cell death in SH-SY5Y cells by upregulation of L-type voltage-operated Ca2+ entry

Abstract

STIM1 is an endoplasmic reticulum protein with a role in Ca²⁺ mobilization and signaling. As a sensor of intraluminal Ca²⁺ levels, STIM1 modulates plasma membrane Ca²⁺ channels to regulate Ca²⁺ entry. In neuroblastoma SH-SY5Y cells and in familial Alzheimer’s disease patient skin fibroblasts, STIM1 is cleaved at the transmembrane domain by the presenilin-1-associated γ-secretase, leading to dysregulation of Ca²⁺ homeostasis. In this report, we investigated expression levels of STIM1 in brain tissues (medium frontal gyrus) of pathologically confirmed Alzheimer’s disease patients, and observed that STIM1 protein expression level decreased with the progression of neurodegeneration. To study the role of STIM1 in neurodegeneration, a strategy was designed to knock-out the expression of STIM1 gene in the SH-SY5Y neuroblastoma cell line by CRISPR/Cas9-mediated genome editing, as an in vitro model to examine the phenotype of STIM1-deficient neuronal cells. It was proved that, while STIM1 is not required for the differentiation of SH-SY5Y cells, it is absolutely essential for cell survival in differentiating cells. Differentiated STIM1-KO cells showed a significant decrease of mitochondrial respiratory chain complex I activity, mitochondrial inner membrane depolarization, reduced mitochondrial free Ca²⁺ concentration, and higher levels of senescence as compared with wild-type cells. In parallel, STIM1-KO cells showed a potentiated Ca²⁺ entry in response to depolarization, which was sensitive to nifedipine, pointing to L-type voltage-operated Ca²⁺ channels as mediators of the upregulated Ca²⁺ entry. The stable knocking-down of CACNA1C transcripts restored mitochondrial function, increased mitochondrial Ca²⁺ levels, and dropped senescence to basal levels, demonstrating the essential role of the upregulation of voltage-operated Ca²⁺ entry through Ca_v1.2 channels in STIM1-deficient SH-SY5Y cell death.

Key messages

STIM1 protein expression decreases with the progression of neurodegeneration in Alzheimer’s disease.

STIM1 is essential for cell viability in differentiated SH-SY5Y cells.

STIM1 deficiency triggers voltage-regulated Ca²⁺ entry-dependent cell death.

Mitochondrial dysfunction and senescence are features of STIM1-deficient differentiated cells.

Electronic supplementary material

The online version of this article (10.1007/s00109-018-1677-y) contains supplementary material, which is available to authorized users.

A mathematical and computational model of the calcium dynamics in Caenorhabditis elegans ASH sensory neuron

We propose a mathematical and computational model that captures the stimulus-generated Ca²⁺ transients in the C. elegans ASH sensory neuron. The rationale is to develop a tool that will enable a cross-talk between modeling and experiments, using modeling results to guide targeted experimental efforts. The model is built based on biophysical events and molecular cascades known to unfold as part of neurons' Ca²⁺ homeostasis mechanism, as well as on Ca²⁺ signaling events. The state of ion channels is described by their probability of being activated or inactivated, and the remaining molecular states are based on biochemically defined kinetic equations or known biochemical motifs. We estimate the parameters of the model using experimental data of hyperosmotic stimulus-evoked Ca²⁺ transients detected with a FRET sensor in young and aged worms, unstressed and exposed to oxidative stress. We use a hybrid optimization method composed of a multi-objective genetic algorithm and nonlinear least-squares to estimate the model parameters. We first obtain the model parameters for young unstressed worms. Next, we use these values of the parameters as a starting point to identify the model parameters for stressed and aged worms. We show that the model, in combination with experimental data, corroborates literature results. In addition, we demonstrate that our model can be used to predict ASH response to complex combinations of stimulation pulses. The proposed model includes for the first time the ASH Ca²⁺ dynamics observed during both "on" and "off" responses. This mathematical and computational effort is the first to propose a dynamic model of the Ca²⁺ transients' mechanism in C. elegans neurons, based on biochemical pathways of the cell's Ca²⁺ homeostasis machinery. We believe that the proposed model can be used to further elucidate the Ca²⁺ dynamics of a key C. elegans neuron, to guide future experiments on C. elegans neurobiology, and to pave the way for the development of more mathematical models for neuronal Ca²⁺ dynamics.

Hallmarks of Brain Aging: Adaptive and Pathological Modification by Metabolic States

During aging, the cellular milieu of the brain exhibits tell-tale signs of compromised bioenergetics, impaired adaptive neuroplasticity and resilience, aberrant neuronal network activity, dysregulation of neuronal Ca2+ homeostasis, the accrual of oxidatively modified molecules and organelles, and inflammation. These alterations render the aging brain vulnerable to Alzheimer's and Parkinson's diseases and stroke. Emerging findings are revealing mechanisms by which sedentary overindulgent lifestyles accelerate brain aging, whereas lifestyles that include intermittent bioenergetic challenges (exercise, fasting, and intellectual challenges) foster healthy brain aging. Here we provide an overview of the cellular and molecular biology of brain aging, how those processes interface with disease-specific neurodegenerative pathways, and how metabolic states influence brain health.

Expression of a Constitutively Active Human Insulin Receptor in Hippocampal Neurons Does Not Alter VGCC Currents

Memory and cognitive decline are the product of numerous physiological changes within the aging brain. Multiple theories have focused on the oxidative, calcium, cholinergic, vascular, and inflammation hypotheses of brain aging, with recent evidence suggesting that reductions in insulin signaling may also contribute. Specifically, a reduction in insulin receptor density and mRNA levels has been implicated, however, overcoming these changes remains a challenge. While increasing insulin receptor occupation has been successful in offsetting cognitive decline, alternative molecular approaches should be considered as they could bypass the need for brain insulin delivery. Moreover, this approach may be favorable to test the impact of continued insulin receptor signaling on neuronal function. Here we used hippocampal cultures infected with lentivirus with or without IRβ, a constitutively active, truncated form of the human insulin receptor, to characterize the impact continued insulin receptor signaling on voltage-gated calcium channels. Infected cultures were harvested between DIV 13 and 17 (48 h after infection) for Western blot analysis on pAKT and AKT. These results were complemented with whole-cell patch-clamp recordings of individual pyramidal neurons starting 96 h post-infection. Results indicate that while a significant increase in neuronal pAKT/AKT ratio was seen at the time point tested, effects on voltage-gated calcium channels were not detected. These results suggest that there is a significant difference between constitutively active insulin receptors and the actions of insulin on an intact receptor, highlighting potential alternate mechanisms of neuronal insulin resistance and mode of activation.