P2X receptor overexpression induced by soluble oligomers of amyloid beta peptide potentiates synaptic failure and neuronal dyshomeostasis in cellular models of Alzheimer's disease

Triggering of Major Brain Disorders by Protons and ATP: The Role of ASICs and P2X Receptors

Adenosine triphosphate (ATP) is well-known as a universal source of energy in living cells. Less known is that this molecule has a variety of important signaling functions: it activates a variety of specific metabotropic (P2Y) and ionotropic (P2X) receptors in neuronal and non-neuronal cell membranes. So, a wide variety of signaling functions well fits the ubiquitous presence of ATP in the tissues. Even more ubiquitous are protons. Apart from the unspecific interaction of protons with any protein, many physiological processes are affected by protons acting on specific ionotropic receptors-acid-sensing ion channels (ASICs). Both protons (acidification) and ATP are locally elevated in various pathological states. Using these fundamentally important molecules as agonists, ASICs and P2X receptors signal a variety of major brain pathologies. Here we briefly outline the physiological roles of ASICs and P2X receptors, focusing on the brain pathologies involving these receptors.

Neurosteroids as positive and negative allosteric modulators of ligand-gated ion channels: P2X receptor perspective

Neurosteroids are steroids synthesized de novo in the brain from cholesterol in an independent manner from peripheral steroid sources. The term "neuroactive steroid" includes all steroids independent of their origin, and newly synthesized analogs of neurosteroids that modify neuronal activities. In vivo application of neuroactive steroids induces potent anxiolytic, antidepressant, anticonvulsant, sedative, analgesic and amnesic effects, mainly through interaction with the γ-aminobutyric acid type-A receptor (GABA_AR). However, neuroactive steroids also act as positive or negative allosteric regulators on several ligand-gated channels including N-methyl-d-aspartate receptors (NMDARs), nicotinic acetylcholine receptors (nAChRs) and ATP-gated purinergic P2X receptors. Seven different P2X subunits (P2X1-7) can assemble to form homotrimeric or heterotrimeric ion channels permeable for monovalent cations and calcium. Among them, P2X2, P2X4, and P2X7 are the most abundant within the brain and can be regulated by neurosteroids. Transmembrane domains are necessary for neurosteroid binding, however, no generic motif of amino acids can accurately predict the neurosteroid binding site for any of the ligand-gated ion channels including P2X. Here, we will review what is currently known about the modulation of rat and human P2X by neuroactive steroids and the possible structural determinants underlying neurosteroid-induced potentiation and inhibition of the P2X2 and P2X4 receptors.

Aß Pathology and Neuron-Glia Interactions: A Synaptocentric View

Alzheimer's disease (AD) causes the majority of dementia cases worldwide. Early pathological hallmarks include the accumulation of amyloid-ß (Aß) and activation of both astrocytes and microglia. Neurons form the building blocks of the central nervous system, and astrocytes and microglia provide essential input for its healthy functioning. Their function integrates at the level of the synapse, which is therefore sometimes referred to as the "quad-partite synapse". Increasing evidence puts AD forward as a disease of the synapse, where pre- and postsynaptic processes, as well as astrocyte and microglia functioning progressively deteriorate. Here, we aim to review the current knowledge on how Aß accumulation functionally affects the individual components of the quad-partite synapse. We highlight a selection of processes that are essential to the healthy functioning of the neuronal synapse, including presynaptic neurotransmitter release and postsynaptic receptor functioning. We further discuss how Aß affects the astrocyte's capacity to recycle neurotransmitters, release gliotransmitters, and maintain ion homeostasis. We additionally review literature on how Aß changes the immunoprotective function of microglia during AD progression and conclude by summarizing our main findings and highlighting the challenges in current studies, as well as the need for further research.

Purinergic signaling in cognitive impairment and neuropsychiatric symptoms of Alzheimer's disease

About 10 million new cases of dementia develop worldwide each year, of which up to 70% are attributable to Alzheimer's disease (AD). In addition to the widely known symptoms of memory loss and cognitive impairment, AD patients frequently develop non-cognitive symptoms, referred to as behavioral and psychological symptoms of dementia (BPSDs). Sleep disorders are often associated with AD, but mood alterations, notably depression and apathy, comprise the most frequent class of BPSDs. BPSDs negatively affect the lives of AD patients and their caregivers, and have a significant impact on public health systems and the economy. Because treatments currently available for AD are not disease-modifying and mainly aim to ameliorate some of the cognitive symptoms, elucidating the mechanisms underlying mood alterations and other BPSDs in AD may reveal novel avenues for progress in AD therapy. Purinergic signaling is implicated in the pathophysiology of several central nervous system (CNS) disorders, such as AD, depression and sleep disorders. Here, we review recent findings indicating that purinergic receptors, mainly the A₁, A_2A, and P2X7 subtypes, are associated with the development/progression of AD. Current evidence suggests that targeting purinergic signaling may represent a promising therapeutic approach in AD and related conditions. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Neuroprotective Properties of Eudesmin on a Cellular Model of Amyloid-β Peptide Toxicity

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive impairment and memory loss. One of the hallmarks in AD is amyloid-β peptide (Aβ) accumulation, where the soluble oligomers of Aβ (AβOs) are the most toxic species, deteriorating the synaptic function, membrane integrity, and neuronal structures, which ultimately lead to apoptosis. Currently, there are no drugs to arrest AD progression, and current scientific efforts are focused on searching for novel leads to control this disease. Lignans are compounds extracted from conifers and have several medicinal properties. Eudesmin (Eu) is an extractable lignan from the wood of Araucaria araucana, a native tree from Chile. This metabolite has shown a range of biological properties, including the ability to control inflammation and antibacterial effects.

OBJECTIVE

In this study, the neuroprotective abilities of Eu on synaptic failure induced by AβOs were analyzed.

METHODS

Using neuronal models, PC12 cells, and in silico simulations we evaluated the neuroprotective effect of Eu (30 nM) against the toxicity induced by AβOs.

RESULTS

In primary cultures from mouse hippocampus, Eu preserved the synaptic structure against AβOs toxicity, maintaining stable levels of the presynaptic protein SV2 at the same concentration. Eu also averted synapsis failure from the AβOs toxicity by sustaining the frequencies of cytosolic Ca2+ transients. Finally, we found that Eu (30 nM) interacts with the Aβ aggregation process inducing a decrease in AβOs toxicity, suggesting an alternative mechanism to explain the neuroprotective activity of Eu.

CONCLUSION

We believe that Eu represents a novel lead that reduces the Aβ toxicity, opening new research venues for lignans as neuroprotective agents.

Alternative Pharmacological Strategies for the Treatment of Alzheimer's Disease: Focus on Neuromodulator Function

Alzheimer's disease (AD) is a neurodegenerative disorder, comprising 70% of dementia diagnoses worldwide and affecting 1 in 9 people over the age of 65. However, the majority of its treatments, which predominantly target the cholinergic system, remain insufficient at reversing pathology and act simply to slow the inevitable progression of the disease. The most recent neurotransmitter-targeting drug for AD was approved in 2003, strongly suggesting that targeting neurotransmitter systems alone is unlikely to be sufficient, and that research into alternate treatment avenues is urgently required. Neuromodulators are substances released by neurons which influence neurotransmitter release and signal transmission across synapses. Neuromodulators including neuropeptides, hormones, neurotrophins, ATP and metal ions display altered function in AD, which underlies aberrant neuronal activity and pathology. However, research into how the manipulation of neuromodulators may be useful in the treatment of AD is relatively understudied. Combining neuromodulator targeting with more novel methods of drug delivery, such as the use of multi-targeted directed ligands, combinatorial drugs and encapsulated nanoparticle delivery systems, may help to overcome limitations of conventional treatments. These include difficulty crossing the blood-brain-barrier and the exertion of effects on a single target only. This review aims to highlight the ways in which neuromodulator functions are altered in AD and investigate how future therapies targeting such substances, which act upstream to classical neurotransmitter systems, may be of potential therapeutic benefit in the sustained search for more effective treatments.

Platelets and the Role of P2X Receptors in Nociception, Pain, Neuronal Toxicity and Thromboinflammation

P2X receptors belong to a family of cation channel proteins, which respond to extracellular adenosine 5'-triphosphate (ATP). These receptors have gained increasing attention in basic and translational research, as they are central to a variety of important pathophysiological processes such as the modulation of cardiovascular physiology, mediation of nociception, platelet and macrophage activation, or neuronal-glial integration. While P2X1 receptor activation is long known to drive platelet aggregation, P2X7 receptor antagonists have recently been reported to inhibit platelet activation. Considering the role of both P2X receptors and platelet-mediated inflammation in neuronal diseases such as multiple sclerosis, Alzheimer's disease, Parkinson's disease, and stroke, targeting purinergic receptors may provide a valuable novel therapeutic approach in these diseases. Therefore, the present review illuminates the role of platelets and purinergic signaling in these neurological conditions to evaluate potential translational implications.

NLRP1 Inflammasomes: A Potential Target for the Treatment of Several Types of Brain Injury

NOD-like receptor (NLR) family pyrin domain-containing 1 (NLRP1) is a member of the NLR family. The NLRP1 inflammasome consists of the NLRP1 protein, the adaptor protein apoptosis-associated speck-like protein containing a CARD domain, and the effector molecule pro-caspase-1. When stimulated, the inflammasome initiates the cleavage of pro-caspase-1 and converts it into its active form, caspase-1; then, caspase-1 facilitates the cleavage of the proinflammatory cytokines interleukin-1β and interleukin-18 into their active and secreted forms. In addition, caspase-1 also mediates the cleavage of gasdermin D, which leads to pyroptosis, an inflammatory form of cell death. Pathological events that damage the brain and result in neuropathological conditions can generally be described as brain injury. Neuroinflammation, especially that driven by NLRP1, plays a considerable role in the pathophysiology of brain injury, such as early brain injury (EBI) of subarachnoid hemorrhage, ischemic brain injury during stroke, and traumatic brain injury (TBI). In this article, a thorough overview of NLRP1 is presented, including its structure, mechanism of activation, and role in neuroinflammation. We also present recent studies on NLRP1 as a target for the treatment of EBI, ischemic brain injury, TBI, and other types of brain injury, thus highlighting the perspective of NLRP1 as an effective mediator of catastrophic brain injury.

GPCR19 Regulates P2X7R-Mediated NLRP3 Inflammasomal Activation of Microglia by Amyloid β in a Mouse Model of Alzheimer's Disease

Amyloid β (Aβ) and/or ATP activate the NLRP3 inflammasome (N3I) via P2X7R in microglia, which is crucial in neuroinflammation in Alzheimer’s disease (AD). Due to polymorphisms, subtypes, and ubiquitous expression of P2X7R, inhibition of P2X7R has not been effective for AD. We first report that taurodeoxycholate (TDCA), a GPCR19 ligand, inhibited the priming phase of N3I activation, suppressed P2X7R expression and P2X7R-mediated Ca⁺⁺ mobilization and N3I oligomerization, which is essential for production of IL-1β/IL-18 by microglia. Furthermore, TDCA enhanced phagocytosis of Aβ and decreased the number of Aβ plaques in the brains of 5x Familial Alzheimer’s disease (5xFAD) mice. TDCA also reduced microgliosis, prevented neuronal loss, and improved memory function in 5xFAD mice. The pleiotropic roles of GPCR19 in P2X7R-mediated N3I activation suggest that targeting GPCR19 might resolve neuroinflammation in AD patients.

Deciphering the role of PGC-1α in neurological disorders: from mitochondrial dysfunction to synaptic failure

The onset and mechanisms underlying neurodegenerative diseases remain uncertain. The main features of neurodegenerative diseases have been related with cellular and molecular events like neuronal loss, mitochondrial dysfunction and aberrant accumulation of misfolded proteins or peptides in specific areas of the brain. The most prevalent neurodegenerative diseases belonging to age-related pathologies are Alzheimer's disease, Huntington's disease, Parkinson's disease and amyotrophic lateral sclerosis. Interestingly, mitochondrial dysfunction has been observed to occur during the early onset of several neuropathological events associated to neurodegenerative diseases. The master regulator of mitochondrial quality control and energetic metabolism is the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α). Additionally, it has been observed that PGC-1α appears to be a key factor in maintaining neuronal survival and synaptic transmission. In fact, PGC-1α downregulation in different brain areas (hippocampus, substantia nigra, cortex, striatum and spinal cord) that occurs in function of neurological damage including oxidative stress, neuronal loss, and motor disorders has been seen in several animal and cellular models of neurodegenerative diseases. Current evidence indicates that PGC-1α upregulation may serve as a potent therapeutic approach against development and progression of neuronal damage. Remarkably, increasing evidence shows that PGC-1α deficient mice have neurodegenerative diseases-like features, as well as neurological abnormalities. Finally, we discuss recent studies showing novel specific PGC-1α isoforms in the central nervous system that appear to exert a key role in the age of onset of neurodegenerative diseases and have a neuroprotective function in the central nervous system, thus opening a new molecular strategy for treatment of neurodegenerative diseases. The purpose of this review is to provide an up-to-date overview of the PGC-1α role in the physiopathology of neurodegenerative diseases, as well as establish the importance of PGC-1α function in synaptic transmission and neuronal survival.

Phenolic Compounds in Calafate Berries Encapsulated by Spray Drying: Neuroprotection Potential into the Ingredient

Calafate is a berry rich in anthocyanins that presents higher content of polyphenols than other fruits. Its compounds have been described previously, however, the potential thereof in preventing and treating degenerative disorders has not yet been studied. Due to its astringency, the consumption of this berry in its natural state is limited. To profit from the aforementioned properties and reduce palatability issues, calafate berry extracts were microencapsulated by spray drying, a rapid, cost-effective and scalable process, and were then compared with freeze drying as a control. The stability of its contents and its in-vitro potential, with respect to AChE activity and neuroprotection, were measured from the obtained microcapsules, resulting from temperature treatments and different encapsulant contents. The results indicated that the spray-dried powders were stable, despite high temperatures, and their encapsulation exhibited nearly 50% efficiency. The highest quantity of polyphenols and 3-O-glycosylated anthocyanins was obtained from encapsulation with 20% maltodextrin, at 120 °C. Temperature did not affect the microcapsules’ biological action, as demonstrated by their antioxidant activities. The prevention of Aβ peptide cytotoxicity in PC12 cells (20%) revealed that encapsulated calafate can confer neuroprotection. We conclude that spray-drying is an appropriate technique for scaling-up and producing new value-added calafate formulations with anti-neurodegenerative effects and vivid colors.

Increased P2×2 receptors induced by amyloid-β peptide participates in the neurotoxicity in alzheimer's disease

Amyloid beta peptide (Aβ) is tightly associated with the physiopathology of Alzheimer's Disease (AD) as one of the most important factors in the evolution of the pathology. In this context, we previously reported that Aβ increases the expression of ionotropic purinergic receptor 2 (P2×2R). However, its role on the cellular and molecular Aβ toxicity is unknown, especially in human brain of AD patients. Using cellular and molecular approaches in hippocampal neurons, PC12 cells, and human brain samples of patients with AD, we evaluated the participation of P2×2R in the physiopathology of AD. Here, we reported that Aβ oligomers (Aβo) increased P2×2 levels in mice hippocampal neurons, and that this receptor increases at late Braak stages of AD patients. Aβo also increases the colocalization of APP with Rab5, an early endosomes marker, and decreased the nuclear/cytoplasmic ratio of Fe65 and PGC-1α immunoreactivity. The overexpression in PC12 cells of P2×2a, but not P2×2b, replicated these changes in Fe65 and PGC-1α; however, both overexpressed isoforms increased levels of Aβ. Taken together, these data suggest that P2×2 is upregulated in AD and it could be a key potentiator of the physiopathology of Aβ. Our results point to a possible participation in a toxic cycle that increases Aβ production, Ca²⁺ overload, and a decrease of PGC-1α. These novel findings put the P2×2R as a key novel pharmacological target to develop new therapeutic strategies to treat Alzheimer's Disease.

Development of Alzheimer's Disease Progressively Alters Sex-Dependent KCa and Sex-Independent KIR Channel Function in Cerebrovascular Endothelium

BACKGROUND

Development of Alzheimer's disease (AD) pathology is associated with impaired blood flow delivery of oxygen and nutrients throughout the brain. Cerebrovascular endothelium regulates vasoreactivity of blood vessel networks for optimal cerebral blood flow.

OBJECTIVE

We tested the hypothesis that cerebrovascular endothelial Gq-protein-coupled receptor (GPCR; purinergic and muscarinic) and K+ channel [Ca2+-activated (KCa2.3/SK3 and KCa3.1/IK1) and inward-rectifying (KIR2.x)] function declines during progressive AD pathology.

METHODS

We applied simultaneous measurements of intracellular Ca2+ ([Ca2+]i) and membrane potential (Vm) in freshly isolated endothelium from posterior cerebral arteries of 3×Tg-AD mice [young, no pathology (1- 2 mo), cognitive impairment (CI; 4- 5 mo), extracellular Aβ plaques (Aβ; 6- 8 mo), and Aβ plaques + neurofibrillary tangles (AβT; 12- 15 mo)].

RESULTS

The coupling of ΔVm-to-Δ[Ca2+]i during AβT pathology was lowest for both sexes but, overall, ATP-induced purinergic receptor function was stable throughout AD pathology. SKCa/IKCa channel function itself was enhanced by ∼20% during AD (Aβ+ AβT) versus pre-AD (Young + CI) in males while steady in females. Accordingly, hyperpolarization-induced [Ca2+]i increases following SKCa/IKCa channel activation and Δ[Ca2+]i-to-ΔVm coupling was enhanced by ≥two-fold during AD pathology in males but not females. Further, KIR channel function decreased by ∼50% during AD conditions versus young regardless of sex. Finally, other than a ∼40% increase in females versus males during Aβ pathology, [Ca2+]i responses to the mitochondrial uncoupler FCCP were similar among AD versus pre-AD conditions.

CONCLUSION

Altogether, AD pathology represents a condition of altered KCa and KIR channel function in cerebrovascular endothelium in a sex-dependent and sex-independent manner respectively.

Alzheimer and Purinergic Signaling: Just a Matter of Inflammation?

Alzheimer's disease (AD) is a widespread neurodegenerative pathology responsible for about 70% of all cases of dementia. Adenosine is an endogenous nucleoside that affects neurodegeneration by activating four membrane G protein-coupled receptor subtypes, namely P1 receptors. One of them, the A_2A subtype, is particularly expressed in the brain at the striatal and hippocampal levels and appears as the most promising target to counteract neurological damage and adenosine-dependent neuroinflammation. Extracellular nucleotides (ATP, ADP, UTP, UDP, etc.) are also released from the cell or are synthesized extracellularly. They activate P2X and P2Y membrane receptors, eliciting a variety of physiological but also pathological responses. Among the latter, the chronic inflammation underlying AD is mainly caused by the P2X7 receptor subtype. In this review we offer an overview of the scientific evidence linking P1 and P2 mediated purinergic signaling to AD development. We will also discuss potential strategies to exploit this knowledge for drug development.

Pathomechanism Characterization and Potential Therapeutics Identification for Parkinson's Disease Targeting Neuroinflammation

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the loss of dopaminergic (DAergic) neurons and the presence of α-synuclein-containing Lewy bodies. The unstructured α-synuclein forms insoluble fibrils and aggregates that result in increased reactive oxygen species (ROS) and cellular toxicity in PD. Neuroinflammation engaged by microglia actively contributes to the pathogenesis of PD. In this study, we showed that VB-037 (a quinoline compound), glycyrrhetic acid (a pentacyclic triterpenoid), Glycyrrhiza inflata (G. inflata, a Chinese herbal medicine), and Shaoyao Gancao Tang (SG-Tang, a formulated Chinese medicine) suppressed the nitric oxide (NO) production and interleukin (IL)-1β maturation in α-synuclein-stimulated BV-2 cells. Mouse inflammation antibody array further revealed increased IL-1α, IL-1β, tumor necrosis factor (TNF)-α, interferon (IFN)-γ, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) expression in α-synuclein-inflamed BV-2 cells and compound pretreatment effectively reduced the expression and release of these pro-inflammatory mediators. The test compounds and herbal medicines further reduced α-synuclein aggregation and associated oxidative stress, and protected cells against α-synuclein-induced neurotoxicity by downregulating NLR family pyrin domain containing 1 (NLRP1) and 3 (NLRP3), caspase 1, IL-1β, IL-6, and associated nuclear factor (NF)-κB inhibitor alpha (IκBα)/NF-κB P65 subunit (P65), c-Jun N-terminal kinase (JNK)/proto-oncogene c-Jun (JUN), mitogen-activated protein kinase 14 (P38)/signal transducer and activator of transcription 1 (STAT1) and Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) pathways in dopaminergic neurons derived from α-synuclein-expressing SH-SY5Y cells. Our findings indicate the potential of VB-037, glycyrrhetic acid, G. inflata, and SG-Tang through mitigating α-synuclein-stimulated neuroinflammation in PD, as new drug candidates for PD treatment.

Actin-mediated Microglial Chemotaxis via G-Protein Coupled Purinergic Receptor in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease mainly associated with aging, oxidative stress and genetic mutations. There are two pathological proteins involved in AD; Amyloid-β peptide and microtubule-associated protein Tau (MAPT). The β- and γ-secretase enzyme cleaves the Amyloid precursor protein, which results in the formation of extracellular plaques in brain. While, Tau undergoes hyperphosphorylation and other post-translational modifications (PTMs), which eventually generates Tau oligomers, and intracellular neurofibrillary tangles (NFTs) in neurons. Moreover, the brain-resident glia and infiltrated macrophages elevate the level of CNS inflammation, which trigger the oxidative damage of neuronal circuits by reactive oxygen species (ROS) and Nitric oxide (NO). Microglia is the primary immune cell in the CNS, which is continuously surveilling the neuronal synapses and pathogen invasion. Microglia in the resting state is called 'Ramified', which possess long surveilling extensions with a small cell body. But, upon activation, microglia retracts the cellular extensions and transform into round migratory cells, called as 'Amoeboid' state. Activated microglia undergoes actin remodeling by forming lamellipodia and filopodia, which directs the migratory axis while podosomes formed are involved in extracellular matrix degradation for invasion. Protein-aggregates in malfunctioning synapses and in CNS milieu can be detected by microglia, which results in its activation and migration. Subsequently, the phagocytosis of synapses leads to the inflammatory burst and memory loss. The extracellular nucleotides released from damaged neurons and the cytokine-chemokine gradients allow the neighboring microglia and macrophages to migrate-infiltrate at the site of neuronal-damage. The ionotropic (P2XR) and metabotropic (P2YR) purinergic receptor recognize extracellular ATP/ADP, which propagates through the intracellular calcium signaling, chemotaxis, phagocytosis and inflammation. The P2Y receptors give 'find me' or 'eat me' signals to microglia to either migrate or phagocytose cellular debris. Further, the actin cytoskeleton helps microglia to mediate directed chemotaxis and neuronal repair during neurodegeneration. Hence, we aim to emphasize the connection between purinergic signaling and actin-driven mechanical movements of microglia for migration and inflammation in AD.

Lithocholic acid inhibits P2X2 and potentiates P2X4 receptor channel gating

The family of ATP-gated purinergic P2X receptors comprises seven bunits (P2X1-7) that are unevenly distributed in the central and peripheral nervous systems as well as other organs. Endogenous modulators of P2X receptors are phospholipids, steroids and neurosteroids. Here, we analyzed whether bile acids, which are natural products derived from cholesterol, affect P2X receptor activity. We examined the effects of primary and secondary bile acids and newly synthesized derivatives of lithocholic acid on agonist-induced responses in HEK293T cells expressing rat P2X2, P2X4 and P2X7 receptors. Electrophysiology revealed that low micromolar concentrations of lithocholic acid and its structural analog 4-dafachronic acid strongly inhibit ATP-stimulated P2X2 but potentiate P2X4 responses, whereas primary bile acids and other secondary bile acids exhibit no or reduced effects only at higher concentrations. Agonist-stimulated P2X7 responses are significantly potentiated by lithocholic acid at moderate concentrations. Structural modifications of lithocholic acid at positions C-3, C-5 or C-17 abolish both inhibitory and potentiation effects to varying degrees, and the 3α-hydroxy group contributes to the ability of the molecule to switch between potentiation and inhibition. Lithocholic acid allosterically modulates P2X2 and P2X4 receptor sensitivity to ATP, reduces the rate of P2X4 receptor desensitization and antagonizes the effect of ivermectin on P2X4 receptor deactivation. Alanine-scanning mutagenesis of the upper halve of P2X4 transmembrane domain-1 revealed that residues Phe48, Val43 and Tyr42 are important for potentiating effect of lithocholic acid, indicating that modulatory sites for lithocholic acid and ivermectin partly overlap. Lithocholic acid also inhibits ATP-evoked currents in pituitary gonadotrophs expressing native P2X2, and potentiates ATP currents in nonidentified pituitary cells expressing P2X4 receptors. These results indicate that lithocholic acid is a bioactive steroid that may help to further unveil the importance of the P2X2, and P2X4 receptors in many physiological processes.

The purinergic P2X7 receptor as a potential drug target to combat neuroinflammation in neurodegenerative diseases

Neurodegenerative diseases (NDDs) represent a huge social burden, particularly in Alzheimer's disease (AD) in which all proposed treatments investigated in murine models have failed during clinical trials (CTs). Thus, novel therapeutic strategies remain crucial. Neuroinflammation is a common pathogenic feature of NDDs. As purinergic P2X7 receptors (P2X7Rs) are gatekeepers of inflammation, they could be developed as drug targets for NDDs. Herein, we review this challenging hypothesis and comment on the numerous studies that have investigated P2X7Rs, emphasizing their molecular structure and functions, as well as their role in inflammation. Then, we elaborate on research undertaken in the field of medicinal chemistry to determine potential P2X7R antagonists. Subsequently, we review the state of neuroinflammation and P2X7R expression in the brain, in animal models and patients suffering from AD, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, multiple sclerosis, and retinal degeneration. Next, we summarize the in vivo studies testing the hypothesis that by mitigating neuroinflammation, P2X7R blockers afford neuroprotection, increasing neuroplasticity and neuronal repair in animal models of NDDs. Finally, we reviewed previous and ongoing CTs investigating compounds directed toward targets associated with NDDs; we propose that CTs with P2X7R antagonists should be initiated. Despite the high expectations for putative P2X7Rs antagonists in various central nervous system diseases, the field is moving forward at a relatively slow pace, presumably due to the complexity of P2X7Rs. A better pharmacological approach to combat NDDs would be a dual strategy, combining P2X7R antagonism with drugs targeting a selective pathway in a given NDD.

Ginkgo biloba Alleviates Cisplatin-Mediated Neurotoxicity in Rats via Modulating APP/Aβ/P2X7R/P2Y12R and XIAP/BDNF-Dependent Caspase-3 Apoptotic Pathway

Neurotoxicity is an obvious adverse effect in Patients encountering a complete course of chemotherapy. The present work is conducted to evaluate the neuroprotective effect of Ginkgo biloba (Ginkgo) against the neurotoxicity induced by Cisplatin (Cis) in rats. Forty male Wistar albino rats were arranged into four groups: (1) Control group, rats were given saline; (2) Cis group, rats were injected by Cis 2 mg/kg body weight i.p., twice a week starting on the fifth day for thirty days; (3) Ginkgo group, rats were administered Ginkgo (50 mg/kg orally) daily for thirty days; and (4) Ginkgo+Cis group, rats received Ginkgo (50 mg/kg orally) daily and on the fifth day, rats were injected with Cis (2 mg/Kg body weight i.p.) twice a week for thirty days. Cis significantly increased Gamma glutamyltransferase (GGT) and Acetyl Cholinesterase (CHE) as compared to the control group and also disturbed cerebral oxidative/antioxidant redox. Co-administration of Ginkgo and Cis reversed the adverse effect of Cis on the brain tissue. Moreover, co-administration of Ginkgo and Cis ameliorated Cis induced brain damage by reducing Amyloid precursor protein (APP), amyloid β (Aβ), P2Y12R and P2X7R mRNA expressions and proteins. Furthermore, Ginkgo regulated XIAP/BDNF expressions with a consequent decrease of caspase-3 and DNA fragmentation%. The current results concluded that concurrent treatment with Ginkgo can mitigate neurotoxicity mediated by Cis in experimental animals through exhibiting antioxidant effect by restoring cerebral oxidative/antioxidant redox and anti-apoptotic effect via regulating cerebral APP/Aβ/P2Y12R/P2X7R and XIAP/BDNF signaling pathways.

The Role of P2X7 Receptor in Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease characterized by a progressive cognitive decline associated with global brain damage. Initially, intracellular paired helical filaments composed by hyperphosphorylated tau and extracellular deposits of amyloid-β (Aβ) were postulated as the causing factors of the synaptic dysfunction, neuroinflammation, oxidative stress, and neuronal death, detected in AD patients. Therefore, the vast majority of clinical trials were focused on targeting Aβ and tau directly, but no effective treatment has been reported so far. Consequently, only palliative treatments are currently available for AD patients. Over recent years, several studies have suggested the involvement of the purinergic receptor P2X7 (P2X7R), a plasma membrane ionotropic ATP-gated receptor, in the AD brain pathology. In this line, altered expression levels and function of P2X7R were found both in AD patients and AD mouse models. Consequently, genetic depletion or pharmacological inhibition of P2X7R ameliorated the hallmarks and symptoms of different AD mouse models. In this review, we provide an overview of the current knowledge about the role of the P2X7R in AD.

The effect and mechanism of 19S proteasome PSMD11/Rpn6 subunit in D-Galactose induced mimetic aging models

Regulating proteasome activity is a potent therapeutic aspect of age-related hearing loss, which has been proven to protect neurons from age-related damaging. PSMD11, subunit of the 19S proteasome regulatory particle, is known to mainly up-regulate proteasome activity and prolong aging. However, the mechanism of PSMD11 in age-related hearing loss has not been deeply explored. In the present study, we explore the function and mechanism of PSMD11 protecting neurons in d-Galactose (D-Gal) mimetic aging models. Age-related pathologies were detected by Taq-PCR, ABR, Transmission electron microscopy, toluidine blue and β-galactosidase staining. The relative expressions of the proteins were explored by Western blotting, oxyblot, immunoprecipitation and immunofluorescence. Flow cytometry was used to manifest the oxidative state. We discovered that proteasome activity was impaired with aging, and that ROS and toxic protein accumulated in D-Gal induced aging models. PSMD11 changed with aging, and was associated with the metabolism of proteasome activity in the D-Gal treated models. Moreover, the knockdown or overexpression of PSMD11 was sufficient to change the oxidative state caused by D-Gal. Our results also demonstrated that PSMD11 could bond to AMPKα1/2 in the auditory cortex and PC12 cells, and AMPKα2 but not AMPKα1 was efficient to regulate the function of PSMD11. Deeper insights into the mechanisms of regulating PSMD11 for the anti-aging process are needed, and may offer novel therapeutic methods for central presbycusis.

Changes in PGC-1α/SIRT1 Signaling Impact on Mitochondrial Homeostasis in Amyloid-Beta Peptide Toxicity Model

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive impairment that increasingly afflicts the elderly population. Soluble oligomers (AβOs) has been implicated in AD pathogenesis: however, the molecular events underlying a role for Aβ are not well understood. We studied the effects of AβOs on mitochondrial function and on key proteins that regulate mitochondrial dynamics and biogenesis in hippocampal neurons and PC-12 cells. We find that AβOs treatment caused a reduction in total Mfn1 after a 2 h exposure (42 ± 11%); while DRP1 increased at 1 and 2 h (205 ± 22% and 198 ± 27%, respectively), correlating to changes in mitochondrial morphology. We also observed that SIRT1 levels were reduced after acute and chronic AβOs treatment (68 ± 7% and 77 ± 6%, respectively); while PGC-1α levels were reduced with the same time treatments (68 ± 8% and 67 ± 7%, respectively). Interestingly, we found that chronic treatment with AβOs increased the levels of pSIRT1 (24 h: 157 ± 18%), and we observed changes in the PGC-1α and p-SIRT1 nucleus/cytosol ratio and SIRT1-PGC-1α interaction pattern after chronic exposure to AβOs. Our data suggest that AβOs induce important changes in the level and localization of mitochondrial proteins related with the loss of mitochondrial function that are mediated by a fast and sustained SIRT1/PGC-1α complex disruption promoting a “non-return point” to an irreversible synaptic failure and neuronal network disconnection.

Characterization of a new molecule capable of inhibiting several steps of the amyloid cascade in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder in elderly people. Existent therapies are directed at alleviating some symptoms, but are not effective in altering the course of the disease.

METHODS

Based on our previous study that showed that an Aβ-interacting small peptide protected against the toxic effects of amyloid-beta peptide (Aβ), we carried out an array of in silico, in vitro, and in vivo assays to identify a molecule having neuroprotective properties.

RESULTS

In silico studies showed that the molecule, referred to as M30 (2-Octahydroisoquinolin-2(1H)-ylethanamine), was able to interact with the Aβ peptide. Additionally, in vitro assays showed that M30 blocked Aβ aggregation, association to the plasma membrane, synaptotoxicity, intracellular calcium, and cellular toxicity, while in vivo experiments demonstrated that M30 induced a neuroprotective effect by decreasing the toxicity of Aβ in the dentate gyrus of the hippocampus and improving the alteration in spatial memory in behavior assays.

DISCUSSION

Therefore, we propose that this new small molecule could be a useful candidate for the additional development of a treatment against AD since it appears to block multiple steps in the amyloid cascade. Overall, since there are no drugs that effectively block the progression of AD, this approach represents an innovative strategy.

SIGNIFICANCE

Currently, there is no effective treatment for AD and the expectations to develop an effective therapy are low. Using in silico, in vitro, and in vivo experiments, we identified a new compound that is able to inhibit Aβ-induced neurotoxicity, specifically aggregation, association to neurons, synaptic toxicity, calcium dyshomeostasis and memory impairment induced by Aβ. Because Aβ toxicity is central to AD progression, the inhibition mediated by this new molecule might be useful as a therapeutic tool.

Exploring the Role of P2X Receptors in Alzheimer's Disease

Several studies have pointed to soluble oligomers of beta amyloid peptide (SOAβ) as the principal neurotoxic agents responsible for the generation of synaptotoxic events that can explain the main symptoms of Alzheimer’s disease (AD). Among the toxic features associated with SOAβ, one of the most notorious is the formation of a non-selective pore-like structure in the plasma membrane, which may partly explain the overload of intracellular Ca²⁺. There is evidence that the pore causes leakage of key intracellular compounds, such as adenosine triphosphate (ATP), to the extracellular milieu. Extracellular ATP activates P2X receptors (P2XR), which are ligand-gated ion channels (LGICs) widely expressed in both neuron and glial cells and act as neuromodulators of synaptic activity by promoting Ca²⁺ entry and facilitating neurotransmitter release. There is abundant evidence correlating the overexpression of these receptors to neurodegenerative diseases, including AD, thus opening the possibility that P2XR could potentiate the toxic mechanisms induced by SOAβ and contribute to intracellular Ca²⁺ overload in neurons and other mechanisms related to glial activation and inflammation. In this review, we correlate scientific evidence related to the main toxic effects induced by SOAβ and those that are mediated by purinergic P2XR. The data suggest that these purinergic receptors participate in the deleterious cellular and molecular effects of SOAβ that lead to the pathogenesis of AD. This information sheds light on the participation of new components in SOAβ toxicity that could be interesting as pharmacological targets for the development of molecular or chemical compounds able to modulate them.

The Role of Neuronal NLRP1 Inflammasome in Alzheimer's Disease: Bringing Neurons into the Neuroinflammation Game

The innate immune system and inflammatory response in the brain have critical impacts on the pathogenesis of many neurodegenerative diseases including Alzheimer's disease (AD). In the central nervous system (CNS), the innate immune response is primarily mediated by microglia. However, non-glial cells such as neurons could also partake in inflammatory response independently through inflammasome signalling. The NLR family pyrin domain-containing 1 (NLRP1) inflammasome in the CNS is primarily expressed by pyramidal neurons and oligodendrocytes. NLRP1 is activated in response to amyloid-β (Aβ) aggregates, and its activation subsequently cleaves caspase-1 into its active subunits. The activated caspase-1 proteolytically processes interleukin-1β (IL-1β) and interleukin-18 (IL-18) into maturation whilst co-ordinately triggers caspase-6 which is responsible for apoptosis and axonal degeneration. In addition, caspase-1 activation induces pyroptosis, an inflammatory form of programmed cell death. Studies in murine AD models indicate that the Nlrp1 inflammasome is indeed upregulated in AD and neuronal death is observed leading to cognitive decline. However, the mechanism of NLRP1 inflammasome activation in AD is particularly elusive, given its structural and functional complexities. In this review, we examine the implications of the human NLRP1 inflammasome and its signalling pathways in driving neuroinflammation in AD.

Age-associated decline in Nrf2 signaling and associated mtDNA damage may be involved in the degeneration of the auditory cortex: Implications for central presbycusis

Central presbycusis is the most common sensory disorder in the elderly population, however, the underlying molecular mechanism remains unclear. NF‑E2‑related factor 2 (Nrf2) is a key transcription factor in the cellular response to oxidative stress, however, the role of Nrf2 in central presbycusis remains to be elucidated. The aim of the present study was to investigate the pathogenesis of central presbycusis using a mimetic aging model induced by D‑galactose (D‑gal) in vivo and in vitro. The degeneration of the cell was determined with transmission electron microscopy, terminal deoxynucleotidyl transferase‑mediated deoxyuridine 5'‑triphosphate nick‑end labeling staining, and senescence‑associated β‑galactosidase staining. The expression of protein was detected by western blotting and immunofluorescence. The quantification of the mitochondrial DNA (mtDNA) 4,834‑base pair (bp) deletion and mRNA was detected by TaqMan quantitative polymerase chain reaction (qPCR) and reverse transcription‑qPCR respectively. Cell apoptosis and intracellular ROS in vitro were determined with flow cytometry. The levels of nuclear Nrf2, and the mRNA levels of Nrf2‑regulated antioxidant genes, were downregulated in the auditory cortex of aging rats, which was accompanied by an increase in 8‑hydroxy‑2'‑deoxyguanosine formation, an accumulation of mtDNA 4,834‑bp deletion, and neuron degeneration. In addition, oltipraz, a typical Nrf2 activator, was found to protect cells against D‑gal‑induced mtDNA damage and mitochondrial dysfunction by activating Nrf2 target genes in vitro. It was also observed that activating Nrf2 with oltipraz inhibited cell apoptosis and delayed senescence. Taken together, the data of the present study suggested that the age‑associated decline in Nrf2 signaling activity and the associated mtDNA damage in the auditory cortex may be implicated in the degeneration of the auditory cortex. Therefore, the restoration of Nrf2 signaling activity may represent a potential therapeutic strategy for central presbycusis.

Small molecule inducers of ABCA1 and apoE that act through indirect activation of the LXR pathway

apoE is the primary lipid carrier within the CNS and the strongest genetic risk factor for late onset Alzheimer's disease (AD). apoE is primarily lipidated via ABCA1, and both are under transcriptional regulation by the nuclear liver X receptor (LXR). Considerable evidence from genetic (using ABCA1 overexpression) and pharmacological (using synthetic LXR agonists) studies in AD mouse models suggests that increased levels of lipidated apoE can improve cognitive performance and, in some strains, can reduce amyloid burden. However, direct synthetic LXR ligands have hepatotoxic side effects that limit their clinical use. Here, we describe a set of small molecules, previously annotated as antagonists of the purinergic receptor, P2X7, which enhance ABCA1 expression and activity as well as apoE secretion, and are not direct LXR ligands. Furthermore, P2X7 is not required for these molecules to induce ABCA1 upregulation and apoE secretion, demonstrating that the ABCA1 and apoE effects are mechanistically independent of P2X7 inhibition. Hence, we have identified novel dual activity compounds that upregulate ABCA1 across multiple CNS cell types, including human astrocytes, pericytes, and microglia, through an indirect LXR mechanism and that also independently inhibit P2X7 receptor activity.