The Role of P2X7 Receptor in Alzheimer's Disease

The immunomodulatory effects of psychedelics in Alzheimer's disease-related dementia

Dementia is an increasing disorder, and Alzheimer's disease (AD) is the cause of 60% of all dementia cases. Despite all efforts, there is no cure for stopping dementia progression. Recent studies reported potential effects of psychedelics on neuroinflammation during AD. Psychedelics by 5HT2AR activation can reduce proinflammatory cytokine levels (TNF-α, IL-6) and inhibit neuroinflammation. In addition to neuroinflammation suppression, psychedelics induce neuroplasticity by increasing Brain-derived neurotrophic factor (BDNF) levels through Sigma-1R stimulation. This review discussed the effects of psychedelics on AD from both neuroinflammatory and neuroplasticity standpoints.

P2X7 receptors exhibit at least three modes of allosteric antagonism

P2X receptors are trimeric ion channels activated by adenosine triphosphate (ATP) that contribute to pathophysiological processes ranging from asthma to neuropathic pain and neurodegeneration. A number of small-molecule antagonists have been identified for these important pharmaceutical targets. However, the molecular pharmacology of P2X receptors is poorly understood because of the chemically disparate nature of antagonists and their differential actions on the seven constituent subtypes. Here, we report high-resolution cryo-electron microscopy structures of the homomeric rat P2X7 receptor bound to five previously known small-molecule allosteric antagonists and a sixth antagonist that we identify. Our structural, biophysical, and electrophysiological data define the molecular determinants of allosteric antagonism in this pharmacologically relevant receptor, revealing three distinct classes of antagonists that we call shallow, deep, and starfish. Starfish binders, exemplified by the previously unidentified antagonist methyl blue, represent a unique class of inhibitors with distinct functional properties that could be exploited to develop potent P2X7 ligands with substantial clinical impact.

Unveiling the agonistic properties of Preyssler-type Polyoxotungstates on purinergic P2 receptors

The Preyssler-type polyoxotungstate ({P5W30}) belongs to the family of polyanionic metal-oxides formed by group V and VI metal ions, such as V, Mo and W, commonly known as polyoxometalates (POMs). POMs have demonstrated inhibitory effect on a significant number of ATP-binding proteins in vitro. Purinergic P2 receptors, widely expressed in eukaryotic cells, contain extracellularly oriented ATP-binding sites and play many biological roles with health implications. In this work, we use the immortalized mouse hippocampal neuronal HT-22 cells in culture to study the effects of {P5W30} on the cytosolic Ca2+ concentration. Changes in cytosolic Ca2+ concentration were monitored using fluorescence microscopy of HT-22 cells loaded with the fluorescent Ca2+ indicator Fluo3. 31P-Nuclear magnetic resonance measurements of {P5W30} indicate its stability in the medium used for cytosolic Ca2+ measurements for over 30 min. The findings reveal that addition of {P5W30} to the extracellular medium induces a sustained increase of the cytosolic Ca2+ concentration within minutes. This Ca2+ increase is triggered by extracellular Ca2+ entry into the cells and is dose-dependent, with a half-of-effect concentration of 0.25 ± 0.05 μM {P5W30}. In addition, after the {P5W30}-induced cytosolic Ca2+ increase, the transient Ca2+ peak induced by extracellular ATP is reduced up to 100% with an apparent half-of-effect concentration of 0.15 ± 0.05 μM {P5W30}. Activation of metabotropic purinergic P2 receptors affords about 80% contribution to the increase of Fluo3 fluorescence elicited by {P5W30} in HT-22 cells, whereas ionotropic receptors contribute, at most, with 20%. These results suggest that {P5W30} could serve as a novel agonist of purinergic P2 receptors.

A current review on P2X7 receptor antagonist patents in the treatment of neuroinflammatory disorders: a patent review on antagonists

Chronic inflammation is defined by an activated microglial state linked to all neurological disorders, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (a motor neuron disease that affects the brain and spinal cord). P2X7 receptors (P2X7R) are ATP-activated ion-gated channels present on microglial surfaces. Prolonged ATP release under pathological settings results in sustained P2X7R activation, which leads to inflammasome development and cytokine release. P2X7R and its enabling roles have recently been linked to neurodegenerative diseases, making it a potential research subject. This research provides an overview of current patents for chemicals, biologics, and medicinal applications. The World Intellectual Property Organization (WIPO), European Patent Office (EPO, Espacenet), and the United States Patent and Trademark Office (USPTO) databases were searched for patents using the keywords "P2X7R and Neuroinflammation." During the study period from 2015 to 2021, 103 patents were examined. The countries that protected these innovations were the United States, PCT (Patent Cooperation Treaty states), Europe, Canada, Australia, and India. Janssen Pharmaceutica NV had the most applications, followed by Acetelion Pharmaceuticals LTD., Renovis Inc., Kelly Michael G, Kincaid Jhon, Merck Patent GMBH, H Lundbeck A/S, and many more. The P2X7R is a possible diagnostic and therapeutic target for cancer, pain disorders, and inflammation. For P2X7 R, several compounds have been discovered and are presently the subject of clinical trial investigations. This study featured patents for P2X7R antagonists, which help treat conditions including neuroinflammation.

Experimental colitis in young Tg2576 mice accelerates the onset of an Alzheimer's-like clinical phenotype

Systemic inflammation and neuroinflammation affect the natural course of the sporadic form of Alzheimer's disease (AD), as supported by epidemiological and preclinical data, and several epidemiological studies indicate a higher prevalence of AD in patients with inflammatory bowel disease. In this study, we explored whether colitis induced by dextran sulfate sodium (DSS) in young, presymptomatic/preplaque mice worsens and/or anticipates age-dependent cognitive impairment in Tg2576, a widely used mouse model of AD. We demonstrated that DSS colitis induced in young Tg2576 mice anticipates the onset age of learning and memory deficit in the Morris water maze test. To explore potential mechanisms behind the acceleration of cognitive decline in Tg2576 mice by DSS colitis, we focused on gut microbiota, systemic inflammation and neuroinflammation markers. We observed a Firmicutes/Bacteroidetes ratio change in Tg2576 DSS animals comparable to that of elderly Tg2576 mice, suggesting accelerated microbiota aging in Tg2576 DSS mice, a change not observed in C57BL6 DSS mice. We also observed substantial differences between Tg2576 and WT mice in several inflammation and neuroinflammation-related parameters as early as 3 months of age, well before plaque deposition, a picture which evolved rapidly (between 3 and 5.5 months of age) in contrast to Tg2576 and WT littermates not treated with DSS. In detail, following induction of DSS colitis, WT and Tg2576 mice exhibited contrasting features in the expression level of inflammation-evoked astrocyte-associated genes in the hippocampus. No changes in microglial features occurred in the hippocampus between the experimental groups, whereas a reduced glial fibrillary acidic protein immunoreactivity was observed in Tg2576 vs. WT mice. This finding may reflect an atrophic, "loss-of-function" profile, further exacerbated by DSS where a decreased of GFAP mRNA expression level was detected. In conclusion, we suggest that as-yet unidentified peripheral mediators evoked by DSS colitis and involving the gut-brain axis emphasize an astrocyte "loss-of-function" profile present in young Tg2576 mice, leading to impaired synaptic morphological and functional integrity as a very early sign of AD.

Functional role of P2X7 purinergic receptor in cancer and cancer-related pain

Numerous studies have revealed that the ATP-gated ion channel purinergic 2X7 receptor (P2X7R) plays an important role in tumor progression and the pathogenesis of cancer pain. P2X7R requires activation by extracellular ATP to perform its regulatory role functions. During tumor development or cancer-induced pain, ATP is released from tumor cells or other cells in the tumor microenvironment (such as tumor-associated immune cells), which activates P2X7R, opens ion channels on the cell membrane, affects intracellular molecular metabolism, and regulates the activity of tumor cells. Furthermore, peripheral organs and receptors can be damaged during tumor progression, and P2X7R expression in nerve cells (such as microglia) is significantly upregulated, enhancing sensory afferent information, sensitizing the central nervous system, and inducing or exacerbating pain. These findings reveal that the ATP-P2X7R signaling axis plays a key regulatory role in the pathogenesis of tumors and cancer pain and also has a therapeutic role. Accordingly, in this study, we explored the role of P2X7R in tumors and cancer pain, discussed the pharmacological properties of inhibiting P2X7R activity (such as the use of antagonists) or blocking its expression in the treatment of tumor and cancer pain, and provided an important evidence for the treatment of both in the future.

Understanding immune microenvironment alterations in the brain to improve the diagnosis and treatment of diverse brain diseases

Abnormal inflammatory states in the brain are associated with a variety of brain diseases. The dynamic changes in the number and function of immune cells in cerebrospinal fluid (CSF) are advantageous for the early prediction and diagnosis of immune diseases affecting the brain. The aggregated factors and cells in inflamed CSF may represent candidate targets for therapy. The physiological barriers in the brain, such as the blood‒brain barrier (BBB), establish a stable environment for the distribution of resident immune cells. However, the underlying mechanism by which peripheral immune cells migrate into the brain and their role in maintaining immune homeostasis in CSF are still unclear. To advance our understanding of the causal link between brain diseases and immune cell status, we investigated the characteristics of immune cell changes in CSF and the molecular mechanisms involved in common brain diseases. Furthermore, we summarized the diagnostic and treatment methods for brain diseases in which immune cells and related cytokines in CSF are used as targets. Further investigations of the new immune cell subtypes and their contributions to the development of brain diseases are needed to improve diagnostic specificity and therapy.

Non-invasive in vivo imaging of brain and retinal microglia in neurodegenerative diseases

Microglia play crucial roles in immune responses and contribute to fundamental biological processes within the central nervous system (CNS). In neurodegenerative diseases, microglia undergo functional changes and can have both protective and pathogenic roles. Microglia in the retina, as an extension of the CNS, have also been shown to be affected in many neurological diseases. While our understanding of how microglia contribute to pathological conditions is incomplete, non-invasive in vivo imaging of brain and retinal microglia in living subjects could provide valuable insights into their role in the neurodegenerative diseases and open new avenues for diagnostic biomarkers. This mini-review provides an overview of the current brain and retinal imaging tools for studying microglia in vivo. We focus on microglia targets, the advantages and limitations of in vivo microglia imaging approaches, and applications for evaluating the pathogenesis of neurological conditions, such as Alzheimer's disease and multiple sclerosis.

Modulation of Microglial Function by ATP-Gated P2X7 Receptors: Studies in Rat, Mice and Human

P2X receptors are a family of seven ATP-gated ion channels that trigger physiological and pathophysiological responses in a variety of cells. Five of the family members are sensitive to low concentrations of extracellular ATP, while the P2X6 receptor has an unknown affinity. The last subtype, the P2X7 receptor, is unique in requiring millimolar concentrations to fully activate in humans. This low sensitivity imparts the agonist with the ability to act as a damage-associated molecular pattern that triggers the innate immune response in response to the elevated levels of extracellular ATP that accompany inflammation and tissue damage. In this review, we focus on microglia because they are the primary immune cells of the central nervous system, and they activate in response to ATP or its synthetic analog, BzATP. We start by introducing purinergic receptors and then briefly consider the roles that microglia play in neurodevelopment and disease by referencing both original works and relevant reviews. Next, we move to the role of extracellular ATP and P2X receptors in initiating and/or modulating innate immunity in the central nervous system. While most of the data that we review involve work on mice and rats, we highlight human studies of P2X7R whenever possible.

Activity-dependent oligodendrocyte calcium dynamics and their changes in Alzheimer's disease

Oligodendrocytes (OCs) form myelin around axons, which is dependent on neuronal activity. This activity-dependent myelination plays a crucial role in training and learning. Previous studies have suggested that neuronal activity regulates proliferation and differentiation of oligodendrocyte precursor cells (OPCs) and myelination. In addition, deficient activity-dependent myelination results in impaired motor learning. However, the functional response of OC responsible for neuronal activity and their pathological changes is not fully elucidated. In this research, we aimed to understand the activity-dependent OC responses and their different properties by observing OCs using in vivo two-photon microscopy. We clarified that the Ca2+ activity in OCs is neuronal activity dependent and differentially regulated by neurotransmitters such as glutamate or adenosine triphosphate (ATP). Furthermore, in 5-month-old mice models of Alzheimer's disease, a period before the appearance of behavioral abnormalities, the elevated Ca2+ responses in OCs are ATP dependent, suggesting that OCs receive ATP from damaged tissue. We anticipate that our research will help in determining the correct therapeutic strategy for neurodegenerative diseases beyond the synapse.

Mitochondrial dysfunction and inflammasome activation in neurodegenerative diseases: Mechanisms and therapeutic implications

Impaired mitochondrial function is crucial to the pathogenesis of several neurodegenerative diseases. It causes the release of mitochondrial DNA (mtDNA), mitochondrial reactive oxygen species (mtROS), ATP, and cardiolipin, which activate the nucleotide-binding oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome. NLRP3 inflammasome is an important innate immune system element contributing to neuroinflammation and neurodegeneration. Therefore, targeting the NLRP3 inflammasome has become an interesting therapeutic approach for treating neurodegenerative diseases. This review describes the role of mitochondrial abnormalities and over-activated inflammasomes in the progression of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Multiple sclerosis (MS), Amyotrophic lateral sclerosis (ALS), and Friedrich ataxia (FRDA). We also discuss the therapeutic strategies focusing on signaling pathways associated with inflammasome activation, which potentially alleviate neurodegenerative symptoms and impede disease progression.

Purinergic receptors in cognitive disturbances

Purinergic receptors (Rs) of the ATP/ADP, UTP/UDP (P2X, P2Y) and adenosine (A1, A2A)-sensitive classes broadly interfere with cognitive processes both under quasi normal and disease conditions. During neurodegenerative illnesses, high concentrations of ATP are released from the damaged neuronal and non-neuronal cells of the brain; then, this ATP is enzymatically degraded to adenosine. Thus, the primary injury in neurodegenerative diseases appears to be caused by various protein aggregates on which a superimposed damage mediated by especially P2X7 and A2AR activation develops; this can be efficiently prevented by small molecular antagonists in animal models of the above diseases, or are mitigated in the respective knockout mice. Dementia is a leading symptom in Alzheimer's disease (AD), and accompanies Parkinson's disease (PD) and Huntington's disease (HD), especially in the advanced states of these illnesses. Animal experimentation suggests that P2X7 and A2ARs are also involved in a number of psychiatric diseases, such as major depressive disorder (MDD), obsessive compulsive behavior, and attention deficit hyperactivity disorder. In conclusion, small molecular antagonists of purinergic receptors are expected to supply us in the future with pharmaceuticals which are able to combat in a range of neurological/psychiatric diseases the accompanying cognitive deterioration.

Enhanced in vivo blood brain barrier transcytosis of macromolecular cargo using an engineered pH-sensitive mouse transferrin receptor binding nanobody

BACKGROUND

The blood brain barrier limits entry of macromolecular diagnostic and therapeutic cargos. Blood brain barrier transcytosis via receptor mediated transport systems, such as the transferrin receptor, can be used to carry macromolecular cargos with variable efficiency. Transcytosis involves trafficking through acidified intracellular vesicles, but it is not known whether pH-dependent unbinding of transport shuttles can be used to improve blood brain barrier transport efficiency.

METHODS

A mouse transferrin receptor binding nanobody, NIH-mTfR-M1, was engineered to confer greater unbinding at pH 5.5 vs 7.4 by introducing multiple histidine mutations. The histidine mutant nanobodies were coupled to neurotensin for in vivo functional blood brain barrier transcytosis testing via central neurotensin-mediated hypothermia in wild-type mice. Multi-nanobody constructs including the mutant M1R56H, P96H, Y102H and two copies of the P2X7 receptor-binding 13A7 nanobody were produced to test proof-of-concept macromolecular cargo transport in vivo using quantitatively verified capillary depleted brain lysates and in situ histology.

RESULTS

The most effective histidine mutant, M1R56H, P96H, Y102H-neurotensin, caused > 8 °C hypothermia after 25 nmol/kg intravenous injection. Levels of the heterotrimeric construct M1R56H, P96H, Y102H-13A7-13A7 in capillary depleted brain lysates peaked at 1 h and were 60% retained at 8 h. A control construct with no brain targets was only 15% retained at 8 h. Addition of the albumin-binding Nb80 nanobody to make M1R56H, P96H, Y102H-13A7-13A7-Nb80 extended blood half-life from 21 min to 2.6 h. At 30-60 min, biotinylated M1R56H, P96H, Y102H-13A7-13A7-Nb80 was visualized in capillaries using in situ histochemistry, whereas at 2-16 h it was detected in diffuse hippocampal and cortical cellular structures. Levels of M1R56H, P96H, Y102H-13A7-13A7-Nb80 reached more than 3.5 percent injected dose/gram of brain tissue after 30 nmol/kg intravenous injection. However, higher injected concentrations did not result in higher brain levels, compatible with saturation and an apparent substrate inhibitory effect.

CONCLUSION

The pH-sensitive mouse transferrin receptor binding nanobody M1R56H, P96H, Y102H may be a useful tool for rapid and efficient modular transport of diagnostic and therapeutic macromolecular cargos across the blood brain barrier in mouse models. Additional development will be required to determine whether this nanobody-based shuttle system will be useful for imaging and fast-acting therapeutic applications.

HYPERREFLECTIVE BAND IN THE GANGLION CELL LAYER IN RETINITIS PIGMENTOSA

PURPOSE

To describe a sign that takes the form of a continuous hyperreflective band within the thickness of the ganglion cell layer (GCL), thus dubbed the "hyperreflective ganglion cell layer band" (HGB), which the authors detected in a fraction of patients affected by retinitis pigmentosa (RP).

METHODS

Retrospective, cross-sectional, observational study. Optical coherence tomography (OCT) images of patients with RP examined between May 2015 and June 2021 were retrospectively reviewed for the presence of HGB, epiretinal membrane (ERM), macular hole, and cystoid macular edema (CME). The ellipsoid zone (EZ) width was also measured. A subgroup of patients underwent microperimetry in the central 2°, 4°, and 10°.

RESULTS

One hundred and fifty-four eyes from 77 subjects were included in the study. The HGB was present in 39 (25.3%) eyes with RP. Mean best-corrected visual acuity (BCVA) was 0.39 ± 0.05 logMAR (approximately 20/50 Snellen equivalent) and 0.18 ± 0.03 logMAR (approximately 20/32 Snellen equivalent) in eyes with and without HGB, respectively ( P < 0.001). The two groups did not differ regarding EZ width; mean 2°, 4°, and 10° retinal sensitivity; and prevalence of CME, ERM, and macular hole. The multivariable analysis showed the presence of HGB to be a predictor of poorer BCVA ( P < 0.001).

CONCLUSION

HGB is an OCT finding detectable in approximately a quarter of eyes with RP and is associated with a poorer visual function. In the discussion, the authors speculate about possible morphogenetic scenarios to explain this observation.

The P2X7 Receptor, a Multifaceted Receptor in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by impaired episodic memory and two pathological lesions: amyloid plaques and neurofibrillary tangles. In AD, damaged neurons and the accumulation of amyloid β (Aβ) peptides cause a significant release of high amounts of extracellular ATP, which acts as a danger signal. The purinergic receptor P2X7 is the main sensor of high concentrations of ATP, and P2X7 has been shown to be upregulated in the brains of AD patients, contributing to the disease's pathological processes. Further, there are many polymorphisms of the P2X7 gene that impact the risk of developing AD. P2X7 can directly modulate Aβ plaques and Tau protein lesions as well as the inflammatory response by regulating NLRP3 inflammasome and the expression of several chemokines. The significant role of microglial P2X7 in AD has been well established, although other cell types may also be important in P2X7-mediated mechanisms. In this review, we will discuss the different P2X7-dependent pathways involved in the development of AD.

TNAP and P2X7R: New Plasma Biomarkers for Alzheimer's Disease

Over the last few years, intense research efforts have been made to anticipate or improve the diagnosis of Alzheimer's disease by detecting blood biomarkers. However, the most promising blood biomarkers identified to date have some limitations, most of them related to the techniques required for their detection. Hence, new blood biomarkers should be identified to improve the diagnosis of AD, better discriminate between AD and mild cognitive impairment (MCI) and identify cognitively unimpaired (CU) older individuals at risk for progression to AD. Our previous studies demonstrated that both the purinergic receptor P2X7 and the tissue-nonspecific alkaline phosphatase ectoenzyme (TNAP) are upregulated in the brains of AD patients. Since both proteins are also present in plasma, we investigated whether plasma P2X7R and TNAP are altered in MCI and AD patients and, if so, their potential role as AD biomarkers. We found that AD but not MCI patients present increased plasma P2X7R levels. Nevertheless, TNAP plasma activity was increased in MCI patients and decreased in the AD group. ROC curve analysis indicated that measuring both parameters has a reasonable discriminating capability to diagnose MCI and AD conditions. In addition to confirming that individuals progressing to MCI have increased TNAP activity in plasma, longitudinal studies also revealed that CU individuals have lower plasma TNAP activity than stable controls. Thus, we propose that P2X7 and TNAP could serve as new plasma biomarkers for MCI and AD.

P2X7 Receptor and Extracellular Vesicle Release

Extensive evidence indicates that the activation of the P2X₇ receptor (P2X₇R), an ATP-gated ion channel highly expressed in immune and brain cells, is strictly associated with the release of extracellular vesicles. Through this process, P2X₇R-expressing cells regulate non-classical protein secretion and transfer bioactive components to other cells, including misfolded proteins, participating in inflammatory and neurodegenerative diseases. In this review, we summarize and discuss the studies addressing the impact of P2X₇R activation on extracellular vesicle release and their activities.

Inhibition of Galectins and the P2X7 Purinergic Receptor as a Therapeutic Approach in the Neurovascular Inflammation of Diabetic Retinopathy

Diabetic retinopathy (DR) is the most frequent microvascular retinal complication of diabetic patients, contributing to loss of vision. Recently, retinal neuroinflammation and neurodegeneration have emerged as key players in DR progression, and therefore, this review examines the neuroinflammatory molecular basis of DR. We focus on four important aspects of retinal neuroinflammation: (i) the exacerbation of endoplasmic reticulum (ER) stress; (ii) the activation of the NLRP3 inflammasome; (iii) the role of galectins; and (iv) the activation of purinergic 2X7 receptor (P2X7R). Moreover, this review proposes the selective inhibition of galectins and the P2X7R as a potential pharmacological approach to prevent the progression of DR.

Enhanced in Vivo Blood Brain Barrier Transcytosis of Macromolecular Cargo Using an Engineered pH-sensitive Mouse Transferrin Receptor Binding Nanobody

Background

The blood brain barrier limits entry of macromolecular diagnostic and therapeutic cargos. Blood brain barrier transcytosis via receptor mediated transport systems, such as the transferrin receptor, can be used to carry macromolecular cargos with variable efficiency. Transcytosis involves trafficking through acidified intracellular vesicles, but it is not known whether pH-dependent unbinding of transport shuttles can be used to improve blood brain barrier transport efficiency.

Methods

A mouse transferrin receptor binding nanobody, NIH-mTfR-M1, was engineered to confer greater unbinding at pH 5.5 vs 7.4 by introducing multiple histidine mutations. The histidine mutant nanobodies were coupled to neurotensin for in vivo functional blood brain barrier transcytosis testing via central neurotensin-mediated hypothermia in wild-type mice. Multi-nanobody constructs including the mutant M1 R56H, P96H, Y102H and two copies of the P2X7 receptor-binding 13A7 nanobody were produced to test proof-of-concept macromolecular cargo transport in vivo using quantitatively verified capillary depleted brain lysates and in situ histology.

Results

The most effective histidine mutant, M1 R56H, P96H, Y102H -neurotensin, caused >8°C hypothermia after 25 nmol/kg intravenous injection. Levels of the heterotrimeric construct M1 56,96,102His -13A7-13A7 in capillary depleted brain lysates peaked at 1 hour and were 60% retained at 8 hours. A control construct with no brain targets was only 15% retained at 8 hours. Addition of the albumin-binding Nb80 nanobody to make M1 R56H, P96H, Y102H -13A7-13A7-Nb80 extended blood half-life from 21 minutes to 2.6 hours. At 30-60 minutes, biotinylated M1 R56H, P96H, Y102H -13A7-13A7-Nb80 was visualized in capillaries using in situ histochemistry, whereas at 2-16 hours it was detected in diffuse hippocampal and cortical cellular structures. Levels of M1 R56H, P96H, Y102H -13A7-13A7-Nb80 reached more than 3.5 percent injected dose/gram of brain tissue after 30 nmol/kg intravenous injection. However, higher injected concentrations did not result in higher brain levels, compatible with saturation and an apparent substrate inhibitory effect.

Conclusion

The pH-sensitive mouse transferrin receptor binding nanobody M1 R56H, P96H, Y102H may be a useful tool for rapid and efficient modular transport of diagnostic and therapeutic macromolecular cargos across the blood brain barrier in mouse models. Additional development will be required to determine whether this nanobody-based shuttle system will be useful for imaging and fast-acting therapeutic applications.

Recent Development in the Understanding of Molecular and Cellular Mechanisms Underlying the Etiopathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that leads to dementia and patient death. AD is characterized by intracellular neurofibrillary tangles, extracellular amyloid beta (Aβ) plaque deposition, and neurodegeneration. Diverse alterations have been associated with AD progression, including genetic mutations, neuroinflammation, blood-brain barrier (BBB) impairment, mitochondrial dysfunction, oxidative stress, and metal ion imbalance.Additionally, recent studies have shown an association between altered heme metabolism and AD. Unfortunately, decades of research and drug development have not produced any effective treatments for AD. Therefore, understanding the cellular and molecular mechanisms underlying AD pathology and identifying potential therapeutic targets are crucial for AD drug development. This review discusses the most common alterations associated with AD and promising therapeutic targets for AD drug discovery. Furthermore, it highlights the role of heme in AD development and summarizes mathematical models of AD, including a stochastic mathematical model of AD and mathematical models of the effect of Aβ on AD. We also summarize the potential treatment strategies that these models can offer in clinical trials.

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.

The bidirectional lung brain-axis of amyloid-β pathology: ozone dysregulates the peri-plaque microenvironment

The mechanisms underlying how urban air pollution affects Alzheimer's disease (AD) are largely unknown. Ozone (O3) is a reactive gas component of air pollution linked to increased AD risk, but is confined to the respiratory tract after inhalation, implicating the peripheral immune response to air pollution in AD neuropathology. Here, we demonstrate that O3 exposure impaired the ability of microglia, the brain's parenchymal immune cells, to associate with and form a protective barrier around Aβ plaques, leading to augmented dystrophic neurites and increased Aβ plaque load. Spatial proteomic profiling analysis of peri-plaque proteins revealed a microenvironment-specific signature of dysregulated disease-associated microglia protein expression and increased pathogenic molecule levels with O3 exposure. Unexpectedly, 5xFAD mice exhibited an augmented pulmonary cell and humoral immune response to O3, supporting that ongoing neuropathology may regulate the peripheral O3 response. Circulating HMGB1 was one factor upregulated in only 5xFAD mice, and peripheral HMGB1 was separately shown to regulate brain Trem2 mRNA expression. These findings demonstrate a bidirectional lung-brain axis regulating the central and peripheral AD immune response and highlight this interaction as a potential novel therapeutic target in AD.

Aluminum induces neuroinflammation via P2X7 receptor activating NLRP3 inflammasome pathway

INTRODUCTION

Aluminum is everywhere in nature and is a recognized neurotoxicant closely associated with various neurodegenerative diseases. Neuroinflammation occurs in the early stage of neurodegenerative diseases, but the underlying mechanism by which aluminum induces neuroinflammation remains unclear.

MATERIAL AND METHODS

A 3-month subchronic aluminum exposure mouse model was established by drinking water containing aluminum chloride (AlCl₃). Microglia BV2 cells and hippocampal neuron HT22 cells were treated with AlCl₃ in vitro. BBG and YC-1 were used as intervention agents.

RESULTS

Aluminum could activate microglia and increase the level of extracellular ATP, stimulate P2X7 receptor, HIF-1α, activate NLRP3 inflammasome and CASP-1, release more cytokine IL-1β, and induce an inflammatory response in nerve cells. There was a mutual regulatory relationship between P2X7 and HIF-1α at mRNA and protein levels. The co-culture system of BV2-HT22 cells observed that conditioned medium from microglia treated with aluminum could aggravate neuronal morphological damage, inflammatory response and death. While BBG and YC-1 intervention could rescue these injuries to some extent.

CONCLUSION

The P2X7-NLRP3 pathway was involved in aluminum-induced neuroinflammation and injury. P2X7 and HIF-1α might mutually regulate and promote the progression of neuroinflammation, both BBG and YC-1 could relieve it.

Molecular mechanisms of Alzheimer's disease: From therapeutic targets to promising drugs

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive impairment so widespread that it interferes with a person's ability to complete daily activities. AD is becoming increasingly common, and it is estimated that the number of patients will reach 152 million by 2050. Current treatment options for AD are symptomatic and have modest benefits. Therefore, considering the human, social, and economic burden of the disease, the development of drugs with the potential to alter disease progression has become a global priority. In this review, the molecular mechanisms involved in the pathology of AD were evaluated as therapeutic targets. The main aim of the review is to focus on new knowledge about mitochondrial dysfunction, oxidative stress, and neuronal transmission in AD, as well as a range of cellular signaling mechanisms and associated treatments. Important molecular interactions leading to AD were described in amyloid cascade and in tau protein function, oxidative stress, mitochondrial dysfunction, cholinergic and glutamatergic neurotransmission, cAMP-regulatory element-binding protein (CREB), the silent mating type information regulation 2 homolog 1 (SIRT-1), neuroinflammation (glial cells), and synaptic alterations. This review summarizes recent experimental and clinical research in AD pathology and analyzes the potential of therapeutic applications based on molecular disease mechanisms.

PET Imaging of P2X7 Receptor (P2X7R) for Neuroinflammation with Improved Radiosynthesis of Tracer 18 in Mice and Non-human Primates

The P2X7 receptor (P2X7R) is a key neuroinflammation target in a variety of neurodegenerative diseases. Improved radiosynthesis was developed according to the previously reported P2X7R antagonist GSK1482160. Biodistribution, radiometabolite, and dynamic positron emission tomography/computed tomography-magnetic resonance imaging (PET/CT-MRI) of the lipopolysaccharide (LPS) rat model and the transgenic mouse model of Alzheimer's disease (AD) revealed a stable, low uptake of [¹⁸F]4A in the brain of healthy rats but a higher standardized uptake value ratio (SUVR) in LPS-treated rats (1.316 ± 0.062, n = 3) than in sham (1.093 ± 0.029, n = 3). There were higher area under curves (AUCs) in the neocortex (25.12 ± 1.11 vs 18.94 ± 1.47), hippocampus (22.50 ± 3.41 vs 15.90 ± 1.59), and basal ganglia (22.26 ± 0.81 vs 15.32 ± 1.76) of AD mice (n = 3) than the controls (n = 3) (p < 0.05). Furthermore, 50 min dynamic PET in healthy nonhuman primates (NHPs) indicated [¹⁸F]4A could penetrate the blood-brain barrier (BBB). In conclusion, [¹⁸F]4A from this study is a potent P2X7R PET tracer that warrants further neuroinflammation quantification in human studies.

Continued P2X7 activation leads to mitochondrial fission and compromising microglial phagocytosis after subarachnoid haemorrhage

Subarachnoid haemorrhage (SAH) has a high rate of disability and mortality. Extremely damaging molecules, including adenosine triphosphate (ATP), are released from extravasated red blood cells and nerve cells, which activate microglia and induce sterile tissue injury and organ dysfunction. P2X purinoceptor 7 (P2X7) is one of the most important purine receptors on the microglial surface and is involved in the proinflammatory activation of microglia. While P2X7 can also affect microglial phagocytosis, the mechanism is not clear. Here, we demonstrated that microglial phagocytosis is progressively impaired under continued BzATP exposure and P2X7 activation. Furthermore, we found that P2X7 activation leads to increased intracellular Ca²⁺ levels and activates Calcineurin, which dephosphorylates dynamin-related protein 1 (DRP1) S637. The dephosphorylation of DRP1 at S637 leads to increased mitochondrial fission and decreased mitochondrial function, which may be responsible for the decreased microglial phagocytosis. Finally, we pharmacologically inhibited P2X7 activation in mice, which resulted in rescue of mitochondrial function and decreased microglial proliferation, but improved phagocytosis after SAH. Our study confirmed that P2X7 activation after SAH leads to the impairment of microglial phagocytosis through mitochondrial fission and verified that P2X7 inhibition restores microglial phagocytosis both in vitro and in vivo.

Glial Cell-Mediated Neuroinflammation in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder; it is the most common cause of dementia and has no treatment. It is characterized by two pathological hallmarks, the extracellular deposits of amyloid beta (Aβ) and the intraneuronal deposits of Neurofibrillary tangles (NFTs). Yet, those two hallmarks do not explain the full pathology seen with AD, suggesting the involvement of other mechanisms. Neuroinflammation could offer another explanation for the progression of the disease. This review provides an overview of recent advances on the role of the immune cells' microglia and astrocytes in neuroinflammation. In AD, microglia and astrocytes become reactive by several mechanisms leading to the release of proinflammatory cytokines that cause further neuronal damage. We then provide updates on neuroinflammation diagnostic markers and investigational therapeutics currently in clinical trials to target neuroinflammation.

Identification of Leukocyte Surface P2X7 as a Biomarker Associated with Alzheimer's Disease

Alzheimer's disease (AD) has shown altered immune responses in the periphery. We studied P2X7 (a proinflammatory receptor and a scavenger receptor) and two integrins, CD11b and CD11c, on the surface of circulating leukocytes and analysed their associations with Aβ-PET, brain atrophy, neuropsychological assessments, and cerebrospinal fluid (CSF) biomarkers. Total 287 age-matched, sex-balanced participants were recruited in a discovery cohort and two validation cohorts through the AIBL study and studied using tri-colour flow cytometry. Our results demonstrated reduced expressions of P2X7, CD11b, and CD11c on leukocytes, particularly monocytes, in Aβ +ve cases compared with Aβ -ve controls. P2X7 and integrin downregulation was observed at pre-clinical stage of AD and stayed low throughout disease course. We further constructed a polygenic risk score (PRS) model based on 12 P2RX7 risk alleles to assess the genetic impact on P2X7 function in AIBL and ADNI cohorts. No significant association was identified between the P2RX7 gene and AD, indicating that P2X7 downregulation in AD is likely caused by environmental changes rather than genetic factors. In conclusion, the downregulation of P2X7 and integrins at pre-clinical stage of AD indicates altered pro-inflammatory responses, phagocytic functions, and migrating capabilities of circulating monocytes in early AD pathogenesis. Our study not only improves our understanding of peripheral immune involvement in early stage of AD but also provides more insights into novel biomarker development, diagnosis, and prognosis of AD.

Evaluation of Placental Toxicity of Five Essential Oils and Their Potential Endocrine-Disrupting Effects

Pregnant women may use EOs in case of morning sickness, nausea, stress management, etc. Little is known about the potential danger that EOs represent for the placenta and therefore for the pregnancy. Our aim was to explore and compare the placental toxicity and potential endocrine disrupting effects of niaouli, orange, tea tree, wintergreen and ylang-ylang EOs, and their key compounds: 4-terpineol, 1,8-cineol, limonene, methyl salicylate and benzyl salicylate. We studied the release of four hormones and the activation of P2X7 receptor in JEG-Tox human placental cells as key biomarkers for endocrine toxicity. We observed that niaouli, orange, tea tree, wintergreen and ylang-ylang EOs and their key components disrupted at least one of the studied hormones but none of them activated the P2X7 cell death receptor. The tested EOs appear then to be more hormonal modulators rather than EDCs in human placental cells. The hormonal effects observed with the key components were very different from those observed with the EOs. EOs are very complex mixtures, and it is essential to study whole EOs rather than their components individually in safety assessment.

Molecular Pharmacology of P2X Receptors: Exploring Druggable Domains Revealed by Structural Biology

Extracellular ATP is a critical signaling molecule that is found in a wide range of concentrations across cellular environments. The family of nonselective cation channels that sense extracellular ATP, termed P2X receptors (P2XRs), is composed of seven subtypes (P2X1-P2X7) that assemble as functional homotrimeric and heterotrimeric ion channels. Each P2XR is activated by a distinct concentration of extracellular ATP, spanning from high nanomolar to low millimolar. P2XRs are implicated in a variety of physiological and pathophysiological processes in the cardiovascular, immune, and central nervous systems, corresponding to the spatiotemporal expression, regulation, and activation of each subtype. The therapeutic potential of P2XRs is an emerging area of research in which structural biology has seemingly exceeded medicinal chemistry, as there are several published P2XR structures but currently no FDA-approved drugs targeting these ion channels. Cryogenic electron microscopy is ideally suited to facilitate structure-based drug design for P2XRs by revealing and characterizing novel ligand-binding sites. This review covers structural elements in P2XRs including the extracellular orthosteric ATP-binding site, extracellular allosteric modulator sites, channel pore, and cytoplasmic substructures, with an emphasis on potential therapeutic ligand development.

Transauricular Vagal Nerve Stimulation at 40 Hz Inhibits Hippocampal P2X7R/NLRP3/Caspase-1 Signaling and Improves Spatial Learning and Memory in 6-Month-Old APP/PS1 Mice

OBJECTIVES

Transauricular vagal nerve stimulation (taVNS) at 40 Hz attenuates hippocampal amyloid load in 6-month-old amyloid precursor protein/presenilin 1 (APP/PS1) transgenic mice, but it is unclear whether 40-Hz taVNS can improve cognition in these mice. Moreover, the underlying mechanisms are still unclear.

MATERIALS AND METHODS

6-month-old C57BL/6 (wild type [WT]) and APP/PS1 mice were subjected to 40-Hz taVNS. Novel Object Recognition and the Morris Water Maze were used to evaluate cognition. Hippocampal amyloid-β (Aβ)1-40, Aβ1-42, pro-interleukin (IL)-1β, and pro-IL-18 were measured using enzyme-linked immunosorbent assays. Hippocampal Aβ42, purinergic 2X7 receptor (P2X7R), nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (NLRP3), Caspase-1, IL-1β, and IL-18 expression were evaluated by western blotting. Histologic assessments including immunofluorescence, immunohistochemistry, Nissl staining, and Congo red staining were used to assess microglial phagocytosis, neuroprotective effects, and Aβ plaque load.

RESULTS

40-Hz taVNS improved spatial memory and learning in 6-month-old APP/PS1 mice but did not affect recognition memory. There were no effects on the cognitive behaviors of 6-month-old WT mice. taVNS at 40 Hz modulated microglia; significantly decreased levels of Aβ1-40, Aβ1-42, pro-IL-1β, and pro-IL-18; inhibited Aβ42, P2X7R, NLRP3, Caspase-1, IL-1β, and IL-18 expression; reduced Aβ deposits; and had neuroprotective effects in the hippocampus of 6-month-old APP/PS1 mice. These changes were not observed in 6-month-old WT mice.

CONCLUSION

Our results show that 40-Hz taVNS inhibits the hippocampal P2X7R/NLRP3/Caspase-1 signaling and improves spatial learning and memory in 6-month-old APP/PS1 mice.

Nicotinic Acetylcholine Receptors and Microglia as Therapeutic and Imaging Targets in Alzheimer's Disease

Amyloid-β (Aβ) accumulation and tauopathy are considered the pathological hallmarks of Alzheimer’s disease (AD), but attenuation in choline signaling, including decreased nicotinic acetylcholine receptors (nAChRs), is evident in the early phase of AD. Currently, there are no drugs that can suppress the progression of AD due to a limited understanding of AD pathophysiology. For this, diagnostic methods that can assess disease progression non-invasively before the onset of AD symptoms are essential, and it would be valuable to incorporate the concept of neurotheranostics, which simultaneously enables diagnosis and treatment. The neuroprotective pathways activated by nAChRs are attractive targets as these receptors may regulate microglial-mediated neuroinflammation. Microglia exhibit both pro- and anti-inflammatory functions that could be modulated to mitigate AD pathogenesis. Currently, single-cell analysis is identifying microglial subpopulations that may have specific functions in different stages of AD pathologies. Thus, the ability to image nAChRs and microglia in AD according to the stage of the disease in the living brain may lead to the development of new diagnostic and therapeutic methods. In this review, we summarize and discuss the recent findings on the nAChRs and microglia, as well as their methods for live imaging in the context of diagnosis, prophylaxis, and therapy for AD.

Beyond Seizure Control: Treating Comorbidities in Epilepsy via Targeting of the P2X7 Receptor

Epilepsy is one of the most common chronic diseases of the central nervous system (CNS). Treatment of epilepsy remains, however, a clinical challenge with over 30% of patients not responding to current pharmacological interventions. Complicating management of treatment, epilepsy comes with multiple comorbidities, thereby further reducing the quality of life of patients. Increasing evidence suggests purinergic signalling via extracellularly released ATP as shared pathological mechanisms across numerous brain diseases. Once released, ATP activates specific purinergic receptors, including the ionotropic P2X7 receptor (P2X7R). Among brain diseases, the P2X7R has attracted particular attention as a therapeutic target. The P2X7R is an important driver of inflammation, and its activation requires high levels of extracellular ATP to be reached under pathological conditions. Suggesting the therapeutic potential of drugs targeting the P2X7R for epilepsy, P2X7R expression increases following status epilepticus and during epilepsy, and P2X7R antagonism modulates seizure severity and epilepsy development. P2X7R antagonism has, however, also been shown to be effective in treating conditions most commonly associated with epilepsy such as psychiatric disorders and cognitive deficits, which suggests that P2X7R antagonisms may provide benefits beyond seizure control. This review summarizes the evidence suggesting drugs targeting the P2X7R as a novel treatment strategy for epilepsy with a particular focus of its potential impact on epilepsy-associated comorbidities.

Microglia in Alzheimer's Disease: An Unprecedented Opportunity as Prospective Drug Target

Alzheimer's disease (AD) is an ever more common neurodegenerative disease among the elderly, characterized by recurrent neuroinflammation and amyloid beta (Aβ) accumulation in the brain parenchyma. Recent genome-wide association studies (GWAS) have shown a distinct role for the innate immune system in AD, with microglia playing a key role. The function of microglial cells is stringently regulated by the neighboring microenvironment in the brain. Upon interruption in diseases, like AD, it demonstrates neurotoxic and neuroprotective action by M1 (neurotoxic) and M2 (neuroprotective) microglial phenotypes, respectively, in the brain. Microglial cells on activation by complement factors, toll-like receptors, and genetic variants result in Aβ' phagocytosis, synaptic pruning, and reactivation of complement pathway. Recent studies have demonstrated the presence of potential therapeutic targets in microglial cells. Immune receptors revealed on microglia as potential drug targets can be paired immunoglobulin-like type 2 receptor (PILR), CD3358, and triggering receptor expressed on myeloid cells 2 (TREM2), as they can have impact on late-onset AD occurrence and progression. Thus, targeting these receptors can accentuate the beneficial effects of microglial cells required to decelerate the progression of AD. This review emphasizes the microglial phenotypes, its function in AD brain, and potential immunological and therapeutic targets to fight this highly progressive neurodegenerative disorder.

Pregnant Women and Endocrine Disruptors: Role of P2X7 Receptor and Mitochondrial Alterations in Placental Cell Disorders

In pregnant women, the lungs, skin and placenta are exposed daily to endocrine-disrupting chemicals (EDCs). EDCs induce multiple adverse effects, not only on endocrine organs, but also on non-endocrine organs, with the P2X7 cell death receptor being potentially the common key element. Our objective was first to investigate mechanisms of EDCs toxicity in both endocrine and non-endocrine cells through P2X7 receptor activation, and second, to compare the level of activation in lung, skin and placental cells. In addition, apoptosis in placental cells was studied because the placenta is the most exposed organ to EDCs and has essential endocrine functions. A total of nine EDCs were evaluated on three human cell models. We observed that the P2X7 receptor was not activated by EDCs in lung non-endocrine cells but was activated in skin and placenta cells, with the highest activation in placenta cells. P2X7 receptor activation and apoptosis are pathways shared by all tested EDCs in endocrine placental cells. P2X7 receptor activation along with apoptosis induction could be key elements in understanding endocrine placental and skin disorders induced by EDCs.

Detection and Functional Evaluation of the P2X7 Receptor in hiPSC Derived Neurons and Microglia-Like Cells

A large body of evidence suggests the involvement of the ATP-gated purinergic receptor P2X7 (P2X7R) in neurodegenerative diseases, including Alzheimer's disease. While it is well-described to be present and functional on microglia cells contributing to inflammatory responses, some reports suggest a neuronal expression of the receptor as well. Here, we present experimental results showing P2X7 receptors to be expressed on human hiPSC-derived microglia-like cells, hiPSC-derived neuronal progenitors and hiPSC-derived matured neuronal cells. By applying cell surface protein detection assays, we show that P2X7R is not localized on the cell membrane, despite being detected in neuronal cells and thus may not be available for directly mediating neurotoxicity. On hiPSC-derived microglia-like cells, a clear membranous expression was detected. Additionally, we have not observed differences in P2X7R functions between control and familial Alzheimer's disease patient-derived neuronal cells. Functional assays employing a P2X7R antagonist JNJ 47965567 confirm these findings by showing P2X7R-dependent modulation of microglia-like cells viability upon treatment with P2X7R agonists ATP and BzATP, while the same effect was absent from neuronal cells. Since the majority of P2X7R research was done on rodent models, our work on human hiPSC-derived cells presents a valuable contribution to the field, extending the work on animal models to the human cellular system and toward clinical translation.

Inherent P2X7 Receptors Regulate Macrophage Functions during Inflammatory Diseases

Macrophages are mononuclear phagocytes which derive either from blood-borne monocytes or reside as resident macrophages in peripheral (Kupffer cells of the liver, marginal zone macrophages of the spleen, alveolar macrophages of the lung) and central tissue (microglia). They occur as M1 (pro-inflammatory; classic) or M2 (anti-inflammatory; alternatively activated) phenotypes. Macrophages possess P2X7 receptors (Rs) which respond to high concentrations of extracellular ATP under pathological conditions by allowing the non-selective fluxes of cations (Na⁺, Ca²⁺, K⁺). Activation of P2X7Rs by still higher concentrations of ATP, especially after repetitive agonist application, leads to the opening of membrane pores permeable to ~900 Da molecules. For this effect an interaction of the P2X7R with a range of other membrane channels (e.g., P2X4R, transient receptor potential A1 [TRPA1], pannexin-1 hemichannel, ANO6 chloride channel) is required. Macrophage-localized P2X7Rs have to be co-activated with the lipopolysaccharide-sensitive toll-like receptor 4 (TLR4) in order to induce the formation of the inflammasome 3 (NLRP3), which then activates the pro-interleukin-1β (pro-IL-1β)-degrading caspase-1 to lead to IL-1β release. Moreover, inflammatory diseases (e.g., rheumatoid arthritis, Crohn’s disease, sepsis, etc.) are generated downstream of the P2X7R-induced upregulation of intracellular second messengers (e.g., phospholipase A2, p38 mitogen-activated kinase, and rho G proteins). In conclusion, P2X7Rs at macrophages appear to be important targets to preserve immune homeostasis with possible therapeutic consequences.

Psychological Stress as a Risk Factor for Accelerated Cellular Aging and Cognitive Decline: The Involvement of Microglia-Neuron Crosstalk

The relationship between the central nervous system (CNS) and microglia is lifelong. Microglia originate in the embryonic yolk sac during development and populate the CNS before the blood-brain barrier forms. In the CNS, they constitute a self-renewing population. Although they represent up to 10% of all brain cells, we are only beginning to understand how much brain homeostasis relies on their physiological functions. Often compared to a double-edged sword, microglia hold the potential to exert neuroprotective roles that can also exacerbate neurodegeneration once compromised. Microglia can promote synaptic growth in addition to eliminating synapses that are less active. Synaptic loss, which is considered one of the best pathological correlates of cognitive decline, is a distinctive feature of major depressive disorder (MDD) and cognitive aging. Long-term psychological stress accelerates cellular aging and predisposes to various diseases, including MDD, and cognitive decline. Among the underlying mechanisms, stress-induced neuroinflammation alters microglial interactions with the surrounding parenchymal cells and exacerbates oxidative burden and cellular damage, hence inducing changes in microglia and neurons typical of cognitive aging. Focusing on microglial interactions with neurons and their synapses, this review discusses the disrupted communication between these cells, notably involving fractalkine signaling and the triggering receptor expressed on myeloid cells (TREM). Overall, chronic stress emerges as a key player in cellular aging by altering the microglial sensome, notably via fractalkine signaling deficiency. To study cellular aging, novel positron emission tomography radiotracers for TREM and the purinergic family of receptors show interest for human study.

Inflamed brain: Targeting immune changes and inflammation for treatment of depression

Although there are a number of clinically effective treatments for depression, many patients exhibit treatment resistance. Recent clinical and preclinical studies reveal that peripheral and brain immune changes and inflammation are involved in the pathophysiology of depression. This 'Inflamed Brain' research provides critical clues for understanding of disease pathophysiology and many candidate molecules that are potentially useful for identifying novel drug targets for the treatment of depression. In this review, we will present clinical evidence on the role of inflammation in the pathophysiology of depression. We will also summarize current clinical trials which test drugs targeting inflammation for the treatment of patients with depression. Furthermore, we will briefly provide preclinical evidence demonstrating altered immune system function and inflammation in stress-induced animal models and will discuss the future potential of inflammation-related drug targets. Collectively, inflammatory signatures identified in clinical and preclinical studies may allow us to stratify depressive patients based on biotypes, contributing to the development of novel mechanism-based interventions that target specific patient populations.

Bispecific Tau Antibodies with Additional Binding to C1q or Alpha-Synuclein

BACKGROUND

Alzheimer's disease (AD) and other tauopathies are neurodegenerative disorders characterized by cellular accumulation of aggregated tau protein. Tau pathology within these disorders is accompanied by chronic neuroinflammation, such as activation of the classical complement pathway by complement initiation factor C1q. Additionally, about half of the AD cases present with inclusions composed of aggregated alpha-synuclein called Lewy bodies. Lewy bodies in disorders such as Parkinson's disease and Lewy body dementia also frequently occur together with tau pathology.

OBJECTIVE

Immunotherapy is currently the most promising treatment strategy for tauopathies. However, the presence of multiple pathological processes within tauopathies makes it desirable to simultaneously target more than one disease pathway.

METHODS

Herein, we have developed three bispecific antibodies based on published antibody binding region sequences. One bispecific antibody binds to tau plus alpha-synuclein and two bispecific antibodies bind to tau plus C1q.

RESULTS

Affinity of the bispecific antibodies to their targets compared to their monospecific counterparts ranged from nearly identical to one order of magnitude lower. All bispecific antibodies retained binding to aggregated protein in patient-derived brain sections. The bispecific antibodies also retained their ability to inhibit aggregation of recombinant tau, regardless of whether the tau binding sites were in IgG or scFv format. Mono- and bispecific antibodies inhibited cellular seeding induced by AD-derived pathological tau with similar efficacy. Finally, both Tau-C1q bispecific antibodies completely inhibited the classical complement pathway.

CONCLUSION

Bispecific antibodies that bind to multiple pathological targets may therefore present a promising approach to treat tauopathies and other neurodegenerative disorders.

Functional Role of Non-Muscle Myosin II in Microglia: An Updated Review

Myosins are a remarkable superfamily of actin-based motor proteins that use the energy derived from ATP hydrolysis to translocate actin filaments and to produce force. Myosins are abundant in different types of tissues and involved in a large variety of cellular functions. Several classes of the myosin superfamily are expressed in the nervous system; among them, non-muscle myosin II (NM II) is expressed in both neurons and non-neuronal brain cells, such as astrocytes, oligodendrocytes, endothelial cells, and microglia. In the nervous system, NM II modulates a variety of functions, such as vesicle transport, phagocytosis, cell migration, cell adhesion and morphology, secretion, transcription, and cytokinesis, as well as playing key roles during brain development, inflammation, repair, and myelination functions. In this review, we will provide a brief overview of recent emerging roles of NM II in resting and activated microglia cells, the principal regulators of immune processes in the central nervous system (CNS) in both physiological and pathological conditions. When stimulated, microglial cells react and produce a number of mediators, such as pro-inflammatory cytokines, free radicals, and nitric oxide, that enhance inflammation and contribute to neurodegenerative diseases. Inhibition of NM II could be a new therapeutic target to treat or to prevent CNS diseases.

Structural basis for the functional properties of the P2X7 receptor for extracellular ATP

The P2X7 receptor, originally known as the P2Z receptor due to its distinctive functional properties, has a structure characteristic of the ATP-gated ion channel P2X receptor family. The P2X7 receptor is an important mediator of ATP-induced purinergic signalling and is involved the pathogenesis of numerous conditions as well as in the regulation of diverse physiological functions. Functional characterisations, in conjunction with site-directed mutagenesis, molecular modelling, and, recently, structural determination, have provided significant insights into the structure–function relationships of the P2X7 receptor. This review discusses the current understanding of the structural basis for the functional properties of the P2X7 receptor.

Purinergic signaling in nervous system health and disease: Focus on pannexin 1

Purinergic signaling encompasses the cycle of adenosine 5' triphosphate (ATP) release and its metabolism into nucleotide and nucleoside derivatives, the direct release of nucleosides, and subsequent receptor-triggered downstream intracellular pathways. Since the discovery of nerve terminal and glial ATP release into the neuropil, purinergic signaling has been implicated in the modulation of nervous system development, function, and disease. In this review, we detail our current understanding of the roles of the pannexin 1 (PANX1) ATP-release channel in neuronal development and plasticity, glial signaling, and neuron-glial-immune interactions. We additionally provide an overview of PANX1 structure, activation, and permeability to orientate readers and highlight recent research developments. We identify areas of convergence between PANX1 and purinergic receptor actions. Additional highlights include data on PANX1's participation in the pathophysiology of nervous system developmental, degenerative, and inflammatory disorders. Our aim in combining this knowledge is to facilitate the movement of our current understanding of PANX1 in the context of other nervous system purinergic signaling mechanisms one step closer to clinical translation.

P2X7 Receptor Agonist 2'(3')-O-(4-Benzoylbenzoyl)ATP Differently Modulates Cell Viability and Corticostriatal Synaptic Transmission in Experimental Models of Huntington's Disease

Huntington’s disease (HD) is a life-threatening neurodegenerative disorder. Altered levels and functions of the purinergic ionotropic P2X7 receptors (P2X7Rs) have been found in animal and cellular models of HD, suggesting their possible role in the pathogenesis of the disease; accordingly, the therapeutic potential of P2X7R antagonists in HD has been proposed. Here we further investigated the effects of P2X7R ligands in in vitro and ex vivo HD experimental models. In ST14A/Q120 rat striatal cells, we found a reduction of P2X7R expression; however, the P2X7R agonist 2′(3′)-O-(4-benzoylbenzoyl)adenosine-5′-triphosphate (BzATP) induced cellular death, and this effect was fully reversed by the antagonist periodate-oxidized adenosine 5′-triphosphate (OxATP). Moreover, in corticostriatal slices from symptomatic R6/2 mice, BzATP reduced the synaptic transmission to a larger extent than in wild-type (WT) mice. Such an effect was accompanied by a concomitant increase of the paired-pulse ratio, suggesting a presynaptic inhibitory action. This was confirmed to be the case, since while the effects of BzATP were unaffected by the P2X7R antagonist OxATP, they were blocked by the adenosine A₁ receptor (A₁R) antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), suggesting possible BzATP hydrolysis to 2′(3′)-O-(4-benzoylbenzoyl)adenosine (Bz-adenosine) and consequent activation of A₁Rs as a mechanism. Taken together, these data point out that 1) P2X7R expression and activity are confirmed to be altered in the presence of HD mutation; 2) in some experimental settings, such an abnormal functioning can be ascribed to presynaptic A₁Rs activation.

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.

Conventional and Non-Conventional Roles of Non-Muscle Myosin II-Actin in Neuronal Development and Degeneration

Myosins are motor proteins that use chemical energy to produce mechanical forces driving actin cytoskeletal dynamics. In the brain, the conventional non-muscle myosin II (NMII) regulates actin filament cytoskeletal assembly and contractile forces during structural remodeling of axons and dendrites, contributing to morphology, polarization, and migration of neurons during brain development. NMII isoforms also participate in neurotransmission and synaptic plasticity by driving actin cytoskeletal dynamics during synaptic vesicle release and retrieval, and formation, maturation, and remodeling of dendritic spines. NMIIs are expressed differentially in cerebral non-neuronal cells, such as microglia, astrocytes, and endothelial cells, wherein they play key functions in inflammation, myelination, and repair. Besides major efforts to understand the physiological functions and regulatory mechanisms of NMIIs in the nervous system, their contributions to brain pathologies are still largely unclear. Nonetheless, genetic mutations or deregulation of NMII and its regulatory effectors are linked to autism, schizophrenia, intellectual disability, and neurodegeneration, indicating non-conventional roles of NMIIs in cellular mechanisms underlying neurodevelopmental and neurodegenerative disorders. Here, we summarize the emerging biological roles of NMIIs in the brain, and discuss how actomyosin signaling contributes to dysfunction of neurons and glial cells in the context of neurological disorders. This knowledge is relevant for a deep understanding of NMIIs on the pathogenesis and therapeutics of neuropsychiatric and neurodegenerative diseases.