The Adenosinergic Signaling: A Complex but Promising Therapeutic Target for Alzheimer's Disease

Adenosine deficiency facilitates CA1 synaptic hyperexcitability in the presymptomatic phase of a knockin mouse model of Alzheimer disease

The disease's trajectory of Alzheimer disease (AD) is associated with and negatively correlated to hippocampal hyperexcitability. Here, we show that during the asymptomatic stage in a knockin (KI) mouse model of Alzheimer disease (APPNL-G-F/NL-G-F; APPKI), hippocampal hyperactivity occurs at the synaptic compartment, propagates to the soma, and is manifesting at low frequencies of stimulation. We show that this aberrant excitability is associated with a deficient adenosine tone, an inhibitory neuromodulator, driven by reduced levels of CD39/73 enzymes, responsible for the extracellular ATP-to-adenosine conversion. Both pharmacologic (adenosine kinase inhibitor) and non-pharmacologic (ketogenic diet) restorations of the adenosine tone successfully normalize hippocampal neuronal activity. Our results demonstrated that neuronal hyperexcitability during the asymptomatic stage of a KI model of Alzheimer disease originated at the synaptic compartment and is associated with adenosine deficient tone. These results extend our comprehension of the hippocampal vulnerability associated with the asymptomatic stage of Alzheimer disease.

Effect of simultaneous application of adenosine A1 receptor agonist and A2A receptor antagonist on memory, inflammatory factors, and PSD-95 in lipopolysaccharide-induced memory impairment

The potential role of adenosine, a natural neuroprotective agent, and its receptors in the pathogenesis of Alzheimer's disease has been proposed. The present study aims to examine the effect of administering both an A1 receptor agonist and an A2A adenosine receptor antagonist simultaneously on memory, inflammatory factors, and PSD-95 in an LPS-induced Alzheimer's disease model in rats. Fifty-six male Wistar rats were randomly divided into seven groups: Saline, LPS, Saline + Vehicle, LPS + Vehicle, LPS + SCH58261 (A2A receptor antagonist), LPS + CPA (A1 receptor agonist), LPS + SCH58261+CPA. LPS (3 mg/kg/ip) was used to cause memory impairment. Treatment was performed by intraventricular injection of CPA at a dose of 700 μg and SCH-58261 at 40 μg for ten days. Passive avoidance and Y-maze tests were performed to examine animals' memories. IL-10, TNF-α, and PSD-95 levels were measured in the brain using ELISA and western blot, respectively. Compared to the groups receiving each medication separately, the simultaneous administration of CPA and SCH58261 improved memory (P<0.05). Additionally, compared to the single medication groups, there was a significant increase in IL-10, PSD-95, and a significant decrease in TNF-α in the brain tissue (P<0.05). These findings suggest that the activation of A1 receptors along with A2A receptor inhibition could be a potential therapeutic strategy for Alzheimer's disease. These findings suggest that A1 receptor activation combined with A2A receptor inhibition may be a promising therapeutic approach for Alzheimer's disease.

Purinergic-associated immune responses in neurodegenerative diseases

The chronic activation of immune cells can participate in the development of pathological conditions such as neurodegenerative diseases including Alzheimer's disease (AD), Multiple Sclerosis (MS), Parkinson's disease (PD), Huntington's disease (HD) and Amyotrophic Lateral Sclerosis (ALS). In recent years, compelling evidence indicates that purinergic signaling plays a key role in neuro-immune cell functions. The extracellular release of adenosine 5'-triphosphate (ATP), and its breakdown products (ADP and adenosine) provide the versatile basis for complex purinergic signaling through the activation of several families of receptors. G-protein coupled adenosine A2A receptors, ionotropic P2X and G-protein coupled P2Y receptors for ATP and other nucleotides are abundant and widely distributed in neurons, microglia, and astrocytes of the central nervous system as well as in peripheral immune cells. These receptors are strongly linked to inflammation, with a functional interplay that may influence the intricate purinergic signaling involved in inflammatory responses. In the present review, we examine the roles of the purinergic receptors in neuro-immune cell functions with particular emphasis on A2AR, P2X4 and P2X7 and their possible relevance to specific neurodegenerative disorders. Understanding the molecular mechanisms governing purinergic receptor interaction will be crucial for advancing the development of effective immunotherapies targeting neurodegenerative diseases.

Extracellular Purine Metabolism-Potential Target in Multiple Sclerosis

The purinergic signaling system comprises a complex network of extracellular purines and purine-metabolizing ectoenzymes, nucleotide and nucleoside receptors, ATP release channels, and nucleoside transporters. Because of its immunomodulatory function, this system is critically involved in the pathogenesis of multiple sclerosis (MS) and its best-characterized animal model, experimental autoimmune encephalomyelitis (EAE). MS is a chronic neuroinflammatory demyelinating and neurodegenerative disease with autoimmune etiology and great heterogeneity, mostly affecting young adults and leading to permanent disability. In MS/EAE, alterations were detected in almost all components of the purinergic signaling system in both peripheral immune cells and central nervous system (CNS) glial cells, which play an important role in the pathogenesis of the disease. A decrease in extracellular ATP levels and an increase in its downstream metabolites, particularly adenosine and inosine, were frequently observed at MS, indicating a shift in metabolism toward an anti-inflammatory environment. Accordingly, upregulation of the major ectonucleotidase tandem CD39/CD73 was detected in the blood cells and CNS of relapsing-remitting MS patients. Based on the postulated role of A2A receptors in the transition from acute to chronic neuroinflammation, the association of variants of the adenosine deaminase gene with the severity of MS, and the beneficial effects of inosine treatment in EAE, the adenosinergic system emerged as a promising target in neuroinflammation. More recently, several publications have identified ADP-dependent P2Y12 receptors and the major extracellular ADP producing enzyme nucleoside triphosphate diphosphohydrolase 2 (NTPDase2) as novel potential targets in MS.

Adenosine and adenosine receptors in metabolic imbalance-related neurological issues

Metabolic syndromes (e.g., obesity) are characterized by insulin resistance, chronic inflammation, impaired glucose metabolism, and dyslipidemia. Recently, patients with metabolic syndromes have experienced not only metabolic problems but also neuropathological issues, including cognitive impairment. Several studies have reported blood-brain barrier (BBB) disruption and insulin resistance in the brain of patients with obesity and diabetes. Adenosine, a purine nucleoside, is known to regulate various cellular responses (e.g., the neuroinflammatory response) by binding with adenosine receptors in the central nervous system (CNS). Adenosine has four known receptors: A1R, A2AR, A2BR, and A3R. These receptors play distinct roles in various physiological and pathological processes in the brain, including endothelial cell homeostasis, insulin sensitivity, microglial activation, lipid metabolism, immune cell infiltration, and synaptic plasticity. Here, we review the recent findings on the role of adenosine receptor-mediated signaling in neuropathological issues related to metabolic imbalance. We highlight the importance of adenosine signaling in the development of therapeutic solutions for neuropathological issues in patients with metabolic syndromes.

Astrocyte ryanodine receptors facilitate gliotransmission and astroglial modulation of synaptic plasticity

Intracellular Ca2+-signaling in astrocytes is instrumental for their brain "housekeeping" role and astroglial control of synaptic plasticity. An important source for elevating the cytosolic Ca2+ level in astrocytes is a release from endoplasmic reticulum which can be triggered via two fundamental pathways: IP3 receptors and calcium-induced calcium release (CICR) mediated by Ca2+-sensitive ryanodine receptors (RyRs). While the physiological role for glial IP3 became a focus of intensive research and debate, ryanodine receptors received much less attention. We explored the role for ryanodine receptors in the modulation of cytosolic Ca2+-signaling in the cortical and hippocampal astrocytes, astrocyte-neuron communication and astroglia modulation of synaptic plasticity. Our data show that RyR-mediated Ca2+-induced Ca2+-release from ER brings substantial contribution into signaling in the functional microdomains hippocampal and neocortical astrocytes. Furthermore, RyR-mediated CICR activated the release of ATP and glutamate from hippocampal and neocortical astrocytes which, in turn, elicited transient purinergic and tonic glutamatergic currents in the neighboring pyramidal neurons. The CICR-facilitated release of ATP and glutamate was inhibited after intracellular perfusion of astrocytes with ryanodine and BAPTA and in the transgenic dnSNARE mice with impaired astroglial exocytosis. We also found out that RyR-mediated amplification of astrocytic Ca2+-signaling enhanced the long-term synaptic potentiation in the hippocampus and neocortex of aged mice. Combined, our data demonstrate that ryanodine receptors are essential for astrocytic Ca2+-signaling and efficient astrocyte-neuron communications. The RyR-mediated CICR contributes to astrocytic control of synaptic plasticity and can underlie, at least partially, neuroprotective and cognitive effects of caffein.

Adenosine deficiency facilitates CA1 synaptic hyperexcitability in the presymptomatic phase of a knock in mouse model of Alzheimer's disease

The disease's trajectory of Alzheimer's disease (AD) is associated with and worsened by hippocampal hyperexcitability. Here we show that during the asymptomatic stage in a knock in mouse model of Alzheimer's disease (APPNL-G-F/NL-G-F; APPKI), hippocampal hyperactivity occurs at the synaptic compartment, propagates to the soma and is manifesting at low frequencies of stimulation. We show that this aberrant excitability is associated with a deficient adenosine tone, an inhibitory neuromodulator, driven by reduced levels of CD39/73 enzymes, responsible for the extracellular ATP-to-adenosine conversion. Both pharmacologic (adenosine kinase inhibitor) and non-pharmacologic (ketogenic diet) restorations of the adenosine tone successfully normalize hippocampal neuronal activity. Our results demonstrated that neuronal hyperexcitability during the asymptomatic stage of a KI model of Alzheimer's disease originated at the synaptic compartment and is associated with adenosine deficient tone. These results extend our comprehension of the hippocampal vulnerability associated with the asymptomatic stage of Alzheimer's disease.

Macrophages coordinate immune response to laser-induced injury via extracellular traps

BACKGROUND

Retinal degeneration results from disruptions in retinal homeostasis due to injury, disease, or aging and triggers peripheral leukocyte infiltration. Effective immune responses rely on coordinated actions of resident microglia and recruited macrophages, critical for tissue remodeling and repair. However, these phagocytes also contribute to chronic inflammation in degenerated retinas, yet the precise coordination of immune response to retinal damage remains elusive. Recent investigations have demonstrated that phagocytic cells can produce extracellular traps (ETs), which are a source of self-antigens that alter the immune response, which can potentially lead to tissue injury.

METHODS

Innovations in experimental systems facilitate real-time exploration of immune cell interactions and dynamic responses. We integrated in vivo imaging with ultrastructural analysis, transcriptomics, pharmacological treatments, and knockout mice to elucidate the role of phagocytes and their modulation of the local inflammatory response through extracellular traps (ETs). Deciphering these mechanisms is essential for developing novel and enhanced immunotherapeutic approaches that can redirect a specific maladaptive immune response towards favorable wound healing in the retina.

RESULTS

Our findings underscore the pivotal role of innate immune cells, especially macrophages/monocytes, in regulating retinal repair and inflammation. The absence of neutrophil and macrophage infiltration aids parenchymal integrity restoration, while their depletion, particularly macrophages/monocytes, impedes vascular recovery. We demonstrate that macrophages/monocytes, when recruited in the retina, release chromatin and granular proteins, forming ETs. Furthermore, the pharmacological inhibition of ETosis support retinal and vascular repair, surpassing the effects of blocking innate immune cell recruitment. Simultaneously, the absence of ETosis reshapes the inflammatory response, causing neutrophils, helper, and cytotoxic T-cells to be restricted primarily in the superficial capillary plexus instead of reaching the damaged photoreceptor layer.

CONCLUSIONS

Our data offer novel insights into innate immunity's role in responding to retinal damage and potentially help developing innovative immunotherapeutic approaches that can shift the immune response from maladaptive to beneficial for retinal regeneration.

Sex- and region-specific cortical and hippocampal whole genome transcriptome profiles from control and APP/PS1 Alzheimer's disease mice

A variety of Alzheimer's disease (AD) mouse models has been established and characterized within the last decades. To get an integrative view of the sophisticated etiopathogenesis of AD, whole genome transcriptome studies turned out to be indispensable. Here we carried out microarray data collection based on RNA extracted from the retrosplenial cortex and hippocampus of age-matched, eight months old male and female APP/PS1 AD mice and control animals to perform sex- and brain region specific analysis of transcriptome profiles. The results of our studies reveal novel, detailed insight into differentially expressed signature genes and related fold changes in the individual APP/PS1 subgroups. Gene ontology and Venn analysis unmasked that intersectional, upregulated genes were predominantly involved in, e.g., activation of microglial, astrocytic and neutrophilic cells, innate immune response/immune effector response, neuroinflammation, phagosome/proteasome activation, and synaptic transmission. The number of (intersectional) downregulated genes was substantially less in the different subgroups and related GO categories included, e.g., the synaptic vesicle docking/fusion machinery, synaptic transmission, rRNA processing, ubiquitination, proteasome degradation, histone modification and cellular senescence. Importantly, this is the first study to systematically unravel sex- and brain region-specific transcriptome fingerprints/signature genes in APP/PS1 mice. The latter will be of central relevance in future preclinical and clinical AD related studies, biomarker characterization and personalized medicinal approaches.

Immunoregulatory and neutrophil-like monocyte subsets with distinct single-cell transcriptomic signatures emerge following brain injury

Monocytes represent key cellular elements that contribute to the neurological sequela following brain injury. The current study reveals that trauma induces the augmented release of a transcriptionally distinct CD115+/Ly6Chi monocyte population into the circulation of mice pre-exposed to clodronate depletion conditions. This phenomenon correlates with tissue protection, blood-brain barrier stability, and cerebral blood flow improvement. Uniquely, this shifted the innate immune cell profile in the cortical milieu and reduced the expression of pro-inflammatory Il6, IL1r1, MCP-1, Cxcl1, and Ccl3 cytokines. Monocytes that emerged under these conditions displayed a morphological and gene profile consistent with a subset commonly seen during emergency monopoiesis. Single-cell RNA sequencing delineated distinct clusters of monocytes and revealed a key transcriptional signature of Ly6Chi monocytes enriched for Apoe and chitinase-like protein 3 (Chil3/Ym1), commonly expressed in pro-resolving immunoregulatory monocytes, as well as granule genes Elane, Prtn3, MPO, and Ctsg unique to neutrophil-like monocytes. The predominate shift in cell clusters included subsets with low expression of transcription factors involved in monocyte conversion, Pou2f2, Na4a1, and a robust enrichment of genes in the oxidative phosphorylation pathway which favors an anti-inflammatory phenotype. Transfer of this monocyte assemblage into brain-injured recipient mice demonstrated their direct role in neuroprotection. These findings reveal a multifaceted innate immune response to brain injury and suggest targeting surrogate monocyte subsets may foster tissue protection in the brain.

Anti-inflammatory potency of novel ecto-5'-nucleotidase/CD73 inhibitors in astrocyte culture model of neuroinflammation

Three novel cytosine-derived α,β-methylene diphosphonates designated MRS4598, MRS4552, and MRS4602 were tested in the range of 1 × 10-9 to 1 × 10-3 M for their efficacy and potency in inhibiting membrane-bound ecto-5'-nucleotidase/CD73 activity in primary astrocytes in vitro. The compounds were also tested for their ability to attenuate the reactive astrocyte phenotype induced by proinflammatory cytokines. The main findings are as follows: A) The tested compounds induced concentration-dependent inhibition of CD73 activity, with maximal inhibition achieved at ∼1 × 10-3M; B) All compounds showed high inhibitory potency, as reflected by IC50 values in the submicromolar range; C) All compounds showed high binding capacity, as reflected by Ki values in the low nanomolar range; D) Among the tested compounds, MRS4598 showed the highest inhibitory efficacy and potency, as reflected by IC50 and Ki values of 0.11 μM and 18.2 nM; E) Neither compound affected astrocyte proliferation and cell metabolic activity at concentrations near to IC50; E) MRS4598 was able to inhibit CD73 activity in reactive astrocytes stimulated with TNF-α and to induce concentration-dependent inhibition of CD73 in reactive astrocytes stimulated with IL-1β, with an order of magnitude higher IC50 value; F) MRS4598 was the only compound tested that was able to induce shedding of the CD73 from astrocyte membranes and to enhance astrocyte migration in the scratch wound migration assay, albeit at concentration well above its IC50 value. Given the role of CD73 in neurodegenerative diseases, MRS4598, MRS4552, and MRS4602 are promising pharmacological tools for the treatment of neurodegeneration and neuroinflammation.

Assessing the role of T cells in response to retinal injury to uncover new therapeutic targets for the treatment of retinal degeneration

BACKGROUND

Retinal degeneration is a disease affecting the eye, which is an immune-privileged site because of its anatomical and physiological properties. Alterations in retinal homeostasis-because of injury, disease, or aging-initiate inflammatory cascades, where peripheral leukocytes (PL) infiltrate the parenchyma, leading to retinal degeneration. So far, research on PL's role in retinal degeneration was limited to observing a few cell types at specific times or sectioning the tissue. This restricted our understanding of immune cell interactions and response duration.

METHODS

In vivo microscopy in preclinical mouse models can overcome these limitations enabling the spatio-temporal characterization of PL dynamics. Through in vivo imaging, we assessed structural and fluorescence changes in response to a focal injury at a defined location over time. We also utilized minimally invasive techniques, pharmacological interventions, and knockout (KO) mice to determine the role of PL in local inflammation. Furthermore, we investigated PL abundance and localization during retinal degeneration in human eyes by histological analysis to assess to which extent our preclinical study translates to human retinal degeneration.

RESULTS

We demonstrate that PL, especially T cells, play a detrimental role during retinal injury response. In mice, we observed the recruitment of helper and cytotoxic T cells in the parenchyma post-injury, and T cells also resided in the macula and peripheral retina in pathological conditions in humans. Additionally, we found that the pharmacological PL reduction and genetic depletion of T-cells reduced injured areas in murine retinas and rescued the blood-retina barrier (BRB) integrity. Both conditions promoted morphological changes of Cx3cr1+ cells, including microglial cells, toward an amoeboid phenotype during injury response. Interestingly, selective depletion of CD8+ T cells accelerated recovery of the BRB compared to broader depletions. After anti-CD8 treatment, the retinal function improved, concomitant to a beneficial immune response.

CONCLUSIONS

Our data provide novel insights into the adaptive immune response to retinal injury in mice and human retinal degeneration. Such information is fundamental to understanding retinal disorders and developing therapeutics to modulate immune responses to retinal degeneration safely.

Characteristics of activation of monocyte-derived macrophages versus microglia after mouse experimental intracerebral hemorrhage

Both monocyte-derived macrophages (MDMs) and brain resident microglia participate in hematoma resolution after intracerebral hemorrhage (ICH). Here, we utilized a transgenic mouse line with enhanced green fluorescent protein (EGFP) labeled microglia (Tmem119-EGFP mice) combined with a F4/80 immunohistochemistry (a pan-macrophage marker) to visualize changes in MDMs and microglia after ICH. A murine model of ICH was used in which autologous blood was stereotactically injected into the right basal ganglia. The autologous blood was co-injected with CD47 blocking antibodies to enhance phagocytosis or clodronate liposomes for phagocyte depletion. In addition, Tmem119-EGFP mice were injected with the blood components peroxiredoxin 2 (Prx2) or thrombin. MDMs entered the brain and formed a peri-hematoma cell layer by day 3 after ICH and giant phagocytes engulfed red blood cells were found. CD47 blocking antibody increased the number of MDMs around and inside the hematoma and extended MDM phagocytic activity to day 7. Both MDMs and microglia could be diminished by clodronate liposomes. Intracerebral injection of Prx2 but not thrombin attracted MDMs into brain parenchyma. In conclusion, MDMs play an important role in phagocytosis after ICH which can be enhanced by CD47 blocking antibody, suggesting the modulation of MDMs after ICH could be a future therapeutic target.

The role of adenosine A2A receptors in Alzheimer's disease and tauopathies

Adenosine signals through four distinct G protein-coupled receptors that are located at various synapses, cell types and brain areas. Through them, adenosine regulates neuromodulation, neuronal signaling, learning and cognition as well as the sleep-wake cycle, all strongly impacted in neurogenerative disorders, among which Alzheimer's Disease (AD). AD is a complex form of cognitive deficits characterized by two pathological hallmarks: extracellular deposits of aggregated β-amyloid peptides and intraneuronal fibrillar aggregates of hyper- and abnormally phosphorylated Tau proteins. Both lesions contribute to the early dysfunction and loss of synapses which are strongly associated to the development of cognitive decline in AD patients. The present review focuses on the pathophysiological impact of the A_2ARs dysregulation observed in cognitive area from AD patients. We are reviewing not only evidence of the cellular changes in A_2AR levels in pathological conditions but also describe what is currently known about their consequences in term of synaptic plasticity, neuro-glial miscommunication and memory abilities. We finally summarize the proof-of-concept studies that support A_2AR as credible targets and the clinical interest to repurpose adenosine drugs for the treatment of AD and related disorders. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Macrophages and microglia in glioblastoma: heterogeneity, plasticity, and therapy

Glioblastoma (GBM) is the most aggressive tumor in the central nervous system and contains a highly immunosuppressive tumor microenvironment (TME). Tumor-associated macrophages and microglia (TAMs) are a dominant population of immune cells in the GBM TME that contribute to most GBM hallmarks, including immunosuppression. The understanding of TAMs in GBM has been limited by the lack of powerful tools to characterize them. However, recent progress on single-cell technologies offers an opportunity to precisely characterize TAMs at the single-cell level and identify new TAM subpopulations with specific tumor-modulatory functions in GBM. In this Review, we discuss TAM heterogeneity and plasticity in the TME and summarize current TAM-targeted therapeutic potential in GBM. We anticipate that the use of single-cell technologies followed by functional studies will accelerate the development of novel and effective TAM-targeted therapeutics for GBM patients.

Lysine-40 succinylation of TAGLN2 induces glioma angiogenesis and tumor growth through regulating TMSB4X

Protein lysine succinylation (K_succ) represents an important regulatory mechanism of tumor development. In this work, the difference of protein K_succ between HCMEC/D3 co-cultured with U87 (glioma endothelia cells, GEC) and without U87 (normal endothelia cells, NEC) was investigated using TMT labeling and affinity enrichment followed by high-resolution LC-MS/MS analysis. Interestingly, TAGLN2 was highly succinylated at K40 in GEC (15.36 folds vs. NEC). Compared to the Vector group, TAGLN2^WT and a succinylation-mimetic TAGLN2^K40E greatly promoted the angiogenesis of glioma in vitro and in vivo. Furthermore, the adhesion and metastasis of U87 co-cultured with GEC in the TAGLN2^WT or TAGLN2^K40E group were also significantly promoted. This was consistent with the increased expression of VE-cadherin and actin cytoskeleton remodeling induced by TAGLN2 K40succ in GEC. In addition, high K40succ of TAGLN2 was associated with poor prognosis in patients with glioma. Overexpression of TAGLN2^K40E also markedly promoted the proliferation and migration of glioma cells, further analysis of in vivo xenograft tumors showed that there was a significant decrease in tumor size and angiogenesis in the TAGLN2^K40R group. Notably, the co-localization of TMSB4X and TAGLN2 mainly in the nucleus and cytoplasm of glioma cells was detected by immunofluorescence staining. We identified TMSB4X as a potential target of TAGLN2, which was proved to interact with TAGLN2^WT rather than TAGLN2^K40A. And the inhibition of TMSB4X could markedly attenuate the proliferation and migration of glioma cells induced by TAGLN2 K40succ. The results revealed K40_succ of TAGLN2 could be a novelty diagnosis and therapeutic target for gliomas.

The adenosinergic signaling in the pathogenesis and treatment of multiple sclerosis

Multiple sclerosis (MS) is a highly disabling, progressive neurodegenerative disease with no curative treatment available. Although significant progress has been made in understanding how MS develops, there remain aspects of disease pathogenesis that are yet to be fully elucidated. In this regard, studies have shown that dysfunctional adenosinergic signaling plays a pivotal role, as patients with MS have altered levels adenosine (ADO), adenosine receptors and proteins involved in the generation and termination of ADO signaling, such as CD39 and adenosine deaminase (ADA). We have therefore performed a literature review regarding the involvement of the adenosinergic system in the development of MS and propose mechanisms by which the modulation of this system can support drug development and repurposing.

Adenosine A2A receptor antagonists: from caffeine to selective non-xanthines

A long evolution of knowledge of the psychostimulant caffeine led in the 1960s to another purine natural product, adenosine and its A2A receptor. Adenosine is a short-lived autocrine/paracrine mediator that acts pharmacologically at four different adenosine receptors in a manner opposite to the pan-antagonist caffeine and serves as an endogenous allostatic regulator. Although detrimental in the developing brain, caffeine appears to be cerebroprotective in aging. Moderate caffeine consumption in adults, except in pregnancy, may also provide benefit in pain, diabetes, and kidney and liver disorders. Inhibition of A2A receptors is one of caffeine's principal effects and we now understand this interaction at the atomic level. The A2A receptor has become a prototypical example of utilizing high-resolution structures of GPCRs for the rational design of chemically diverse drug molecules. The previous focus on discovery of selective A2A receptor antagonists for neurodegenerative diseases has expanded to include immunotherapy for cancer, and clinical trials have ensued. LINKED ARTICLES: This article is part of a themed issue on Structure Guided Pharmacology of Membrane Proteins (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.14/issuetoc.

Caffeine intake exerts dual genome-wide effects on hippocampal metabolism and learning-dependent transcription

Caffeine is the most widely consumed psychoactive substance in the world. Strikingly, the molecular pathways engaged by its regular consumption remain unclear. We herein addressed the mechanisms associated with habitual (chronic) caffeine consumption in the mouse hippocampus using untargeted orthogonal omics techniques. Our results revealed that chronic caffeine exerts concerted pleiotropic effects in the hippocampus at the epigenomic, proteomic, and metabolomic levels. Caffeine lowered metabolism-related processes (e.g., at the level of metabolomics and gene expression) in bulk tissue, while it induced neuron-specific epigenetic changes at synaptic transmission/plasticity-related genes and increased experience-driven transcriptional activity. Altogether, these findings suggest that regular caffeine intake improves the signal-to-noise ratio during information encoding, in part through fine-tuning of metabolic genes, while boosting the salience of information processing during learning in neuronal circuits.

Recent advances on the inhibition of human solute carriers: Therapeutic implications and mechanistic insights

Solute carriers (SLCs) are membrane transport proteins tasked with mediating passage of hydrophilic molecules across lipid bilayers. Despite the extensive roles played in all aspects of human biology, SLCs remain vastly under-explored as therapeutic targets. In this brief review, we first discuss a few successful cases of drugs that exert their mechanisms of action through inhibition of human SLCs, and introduce select examples of human SLCs that have untapped therapeutic potential. We then highlight two recent structural studies which uncovered detailed structural mechanisms of inhibition exhibited against two different human major facilitator superfamily (MFS) transporters of clinical relevance.

A2A Adenosine Receptor Antagonists in Neurodegenerative Diseases

BACKGROUND

Alzheimer's disease (AD) is the most common form of dementia worldwide, with approximately 6 million cases reported in America in 2020. The clinical signs of AD include cognitive dysfunction, apathy, anxiety and neuropsychiatric signs, and pathogenetic mechanisms that involve amyloid peptide-β extracellular accumulation and tau hyperphosphorylation. Unfortunately, current drugs to treat AD can provide only symptomatic relief but are not disease-modifying molecules able to revert AD progression. The endogenous modulator adenosine, through A_2A receptor activation, plays a role in synaptic loss and neuroinflammation, which are crucial for cognitive impairment and memory damage.

OBJECTIVE

In this review, recent advances covering A_2A adenosine receptor antagonists will be extensively reviewed, providing a basis for the rational design of future A_2A inhibitors.

METHODS

Herein, the literature on A_2A adenosine receptors and their role in synaptic plasticity and neuroinflammation, as well as the effects of A_2A antagonism in animal models of AD and in humans, are reviewed. Furthermore, current chemical and structure-based strategies are presented.

RESULTS

Caffeine, the most widely consumed natural product stimulant and an A_2A antagonist, improves human memory. Similarly, synthetic A_2A receptor antagonists, as described in this review, may provide a means to fight AD.

CONCLUSION

This review highlights the clinical potential of A_2A adenosine receptor antagonists as a novel approach to treat patients with AD.

Sleep, Sirtuin 1 and Alzheimer's disease: A review

Sleep plays a major role in brain health, and cognition. Disrupted sleep is a well-described symptom of Alzheimer's disease (AD). However, accumulating evidence suggests suboptimal sleep also increases AD risk. The deacetylase Sirtuin 1 (Sirt 1), encoded by the SIRT1 gene, impacts sleep via its relationship to wake-sleep neurotransmitters and somnogens. Evidence from animal and human studies supports a significant and complex relationship between sleep, Sirt 1/ SIRT1 and AD. Numerous hypotheses attempt to explain the critical impact of Sirt 1/ SIRT1 on wake- and sleep- promoting neurons, their related mechanisms and neurotransmitters. However, there is a paucity of studies assessing the interaction between sleep and Sirt 1/ SIRT1, as a principal component of sleep regulation, on AD pathology. In this review, we explore the potential association between Sirt 1/ SIRT1, sleep, and AD aetiology. Given sleep is a likely modifiable risk factor for AD, and recent studies suggest Sirt 1/ SIRT1 activation can be modulated by lifestyle or dietary approaches, further research in this area is required to explore its potential as a target for AD prevention and treatment.

Emerging roles of dysregulated adenosine homeostasis in brain disorders with a specific focus on neurodegenerative diseases

In modern societies, with an increase in the older population, age-related neurodegenerative diseases have progressively become greater socioeconomic burdens. To date, despite the tremendous effort devoted to understanding neurodegenerative diseases in recent decades, treatment to delay disease progression is largely ineffective and is in urgent demand. The development of new strategies targeting these pathological features is a timely topic. It is important to note that most degenerative diseases are associated with the accumulation of specific misfolded proteins, which is facilitated by several common features of neurodegenerative diseases (including poor energy homeostasis and mitochondrial dysfunction). Adenosine is a purine nucleoside and neuromodulator in the brain. It is also an essential component of energy production pathways, cellular metabolism, and gene regulation in brain cells. The levels of intracellular and extracellular adenosine are thus tightly controlled by a handful of proteins (including adenosine metabolic enzymes and transporters) to maintain proper adenosine homeostasis. Notably, disruption of adenosine homeostasis in the brain under various pathophysiological conditions has been documented. In the past two decades, adenosine receptors (particularly A₁ and A_2A adenosine receptors) have been actively investigated as important drug targets in major degenerative diseases. Unfortunately, except for an A_2A antagonist (istradefylline) administered as an adjuvant treatment with levodopa for Parkinson's disease, no effective drug based on adenosine receptors has been developed for neurodegenerative diseases. In this review, we summarize the emerging findings on proteins involved in the control of adenosine homeostasis in the brain and discuss the challenges and future prospects for the development of new therapeutic treatments for neurodegenerative diseases and their associated disorders based on the understanding of adenosine homeostasis.

The Medicinal Chemistry of Caffeine

The purine alkaloid caffeine is the most widely consumed psychostimulant drug in the world and has multiple beneficial pharmacological activities, for example, in neurodegenerative diseases. However, despite being an extensively studied bioactive natural product, the mechanistic understanding of caffeine's pharmacological effects is incomplete. While several molecular targets of caffeine such as adenosine receptors and phosphodiesterases have been known for decades and inspired numerous medicinal chemistry programs, new protein interactions of the xanthine are continuously discovered providing potentially improved pharmacological understanding and a molecular basis for future medicinal chemistry. In this Perspective, we gather knowledge on the confirmed protein interactions, structure activity relationship, and chemical biology of caffeine on well-known and upcoming targets. The diversity of caffeine's molecular activities on receptors and enzymes, many of which are abundant in the CNS, indicates a complex interplay of several mechanisms contributing to neuroprotective effects and highlights new targets as attractive subjects for drug discovery.

Metabolic Aspects of Adenosine Functions in the Brain

Adenosine, acting both through G-protein coupled adenosine receptors and intracellularly, plays a complex role in multiple physiological and pathophysiological processes by modulating neuronal plasticity, astrocytic activity, learning and memory, motor function, feeding, control of sleep and aging. Adenosine is involved in stroke, epilepsy and neurodegenerative pathologies. Extracellular concentration of adenosine in the brain is tightly regulated. Adenosine may be generated intracellularly in the central nervous system from degradation of AMP or from the hydrolysis of S-adenosyl homocysteine, and then exit via bi-directional nucleoside transporters, or extracellularly by the metabolism of released nucleotides. Inactivation of extracellular adenosine occurs by transport into neurons or neighboring cells, followed by either phosphorylation to AMP by adenosine kinase or deamination to inosine by adenosine deaminase. Modulation of the nucleoside transporters or of the enzymatic activities involved in the metabolism of adenosine, by affecting the levels of this nucleoside and the activity of adenosine receptors, could have a role in the onset or the development of central nervous system disorders, and can also be target of drugs for their treatment. In this review, we focus on the contribution of 5'-nucleotidases, adenosine kinase, adenosine deaminase, AMP deaminase, AMP-activated protein kinase and nucleoside transporters in epilepsy, cognition, and neurodegenerative diseases with a particular attention on amyotrophic lateral sclerosis and Huntington's disease. We include several examples of the involvement of components of the adenosine metabolism in learning and of the possible use of modulators of enzymes involved in adenosine metabolism or nucleoside transporters in the amelioration of cognition deficits.

Neuroretinal-Derived Caveolin-1 Promotes Endotoxin-Induced Inflammation in the Murine Retina

Purpose

The immune-privileged environment and complex organization of retinal tissue support the retina's essential role in visual function, yet confound inquiries into cell-specific inflammatory effects that lead to dysfunction and degeneration. Caveolin-1 (Cav1) is an integral membrane protein expressed in several retinal cell types and is implicated in immune regulation. However, whether Cav1 promotes or inhibits inflammatory processes in the retina (as well as in other tissues) remains unclear. Previously, we showed that global-Cav1 depletion resulted in reduced retinal inflammatory cytokine production but paradoxically elevated retinal immune cell infiltration. We hypothesized that these disparate responses are the result of differential cell-specific Cav1 functions in the retina.

Methods

We used Cre/lox technology to deplete Cav1 specifically in the neural retinal (NR) compartment to clarify the role NR-specific Cav1 (NR-Cav1) in the retinal immune response to intravitreal inflammatory challenge induced by activation of Toll-like receptor-4 (TLR4). We used multiplex protein suspension array and flow cytometry to evaluate innate immune activation. Additionally, we used bioinformatics assessment of differentially expressed membrane-associated proteins to infer relationships between NR-Cav1 and immune response pathways.

Results

NR-Cav1 depletion, which primarily affects Müller glia Cav1 expression, significantly altered immune response pathway regulators, decreased retinal inflammatory cytokine production, and reduced retinal immune cell infiltration in response to LPS-stimulated inflammatory induction.

Conclusions

Cav1 expression in the NR compartment promotes the innate TLR4-mediated retinal tissue immune response. Additionally, we have identified novel potential immune modulators differentially expressed with NR-Cav1 depletion. This study further clarifies the role of NR-Cav1 in retinal inflammation.

Can quantifying morphology and TMEM119 expression distinguish between microglia and infiltrating macrophages after ischemic stroke and reperfusion in male and female mice?

Background

Ischemic stroke is an acquired brain injury with gender-dependent outcomes. A persistent obstacle in understanding the sex-specific neuroinflammatory contributions to ischemic brain injury is distinguishing between resident microglia and infiltrating macrophages—both phagocytes—and determining cell population-specific contributions to injury evolution and recovery processes. Our purpose was to identify microglial and macrophage populations regulated by ischemic stroke using morphology analysis and the presence of microglia transmembrane protein 119 (TMEM119). Second, we examined sex and menopause differences in microglia/macrophage cell populations after an ischemic stroke.

Methods

Male and female, premenopausal and postmenopausal, mice underwent either 60 min of middle cerebral artery occlusion and 24 h of reperfusion or sham surgery. The accelerated ovarian failure model was used to model postmenopause. Brain tissue was collected to quantify the infarct area and for immunohistochemistry and western blot methods. Ionized calcium-binding adapter molecule, TMEM119, and confocal microscopy were used to analyze the microglia morphology and TMEM119 area in the ipsilateral brain regions. Western blot was used to quantify protein quantity.

Results

Post-stroke injury is increased in male and postmenopause female mice vs. premenopause female mice (p < 0.05) with differences primarily occurring in the caudal sections. After stroke, the microglia underwent a region, but not sex group, dependent transformation into less ramified cells (p < 0.0001). However, the number of phagocytic microglia was increased in distal ipsilateral regions of postmenopausal mice vs. the other sex groups (p < 0.05). The number of TMEM119-positive cells was decreased in proximity to the infarct (p < 0.0001) but without a sex group effect. Two key findings prevented distinguishing microglia from systemic macrophages. First, morphological data were not congruent with TMEM119 immunofluorescence data. Cells with severely decreased TMEM119 immunofluorescence were ramified, a distinguishing microglia characteristic. Second, whereas the TMEM119 immunofluorescence area decreased in proximity to the infarcted area, the TMEM119 protein quantity was unchanged in the ipsilateral hemisphere regions using western blot methods.

Conclusions

Our findings suggest that TMEM119 is not a stable microglia marker in male and female mice in the context of ischemic stroke. Until TMEM119 function in the brain is elucidated, its use to distinguish between cell populations following brain injury with cell infiltration is cautioned.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02105-2.

Potential of Caffeine in Alzheimer's Disease-A Review of Experimental Studies

Alzheimer's disease (AD) is the most common type of dementia leading to progressive memory loss and cognitive impairment. Considering that pharmacological treatment options for AD are few and not satisfactory, increasing attention is being paid to dietary components that may affect the development of the disease. Such a dietary component may be caffeine contained in coffee, tea or energy drinks. Although epidemiological data suggest that caffeine intake may counteract the development of cognitive impairment, results of those studies are not conclusive. The aim of the present study is to review the existing experimental studies on the efficacy of caffeine against AD and AD-related cognitive impairment, focusing on the proposed protective mechanisms of action. In conclusion, the reports of studies on experimental AD models generally supported the notion that caffeine may exert some beneficial effects in AD. However, further studies are necessary to elucidate the role of caffeine in the effects of its sources on cognition and possibly AD risk.

Challenges of BDNF-based therapies: From common to rare diseases

Neurotrophins are a well-known family of neurotrophic factors that play an important role both in the central and peripheral nervous systems, where they modulate neuronal survival, development, function and plasticity. Brain-derived neurotrophic factor (BDNF) possesses diverse biological functions which are mediated by the activation of two main classes of receptors, the tropomyosin-related kinase (Trk) B and the p75 neurotrophin receptor (p75^NTR). The therapeutic potential of BDNF has drawn attention since dysregulation of its signalling cascades has been suggested to underlie the pathogenesis of both common and rare diseases. Multiple strategies targeting this neurotrophin have been tested; most have found obstacles that ultimately hampered their effectiveness. This review focuses on the involvement of BDNF and its receptors in the pathophysiology of Alzheimer's disease (AD), Amyotrophic Lateral Sclerosis (ALS) and Rett Syndrome (RTT). We describe the known mechanisms leading to the impairment of BDNF/TrkB signalling in these disorders. Such mechanistic insight highlights how BDNF signalling compromise can take various shapes, nearly disease-specific. Therefore, BDNF-based therapeutic strategies must be specifically tailored and are more likely to succeed if a combination of resources is employed.

Shenqi Xingnao Granules ameliorates cognitive impairments and Alzheimer’s disease-like pathologies in APP/PS1 mouse model

Objective

Alzheimer's disease (AD) is along with cognitive decline due to amyloid-β (Aβ) plaques, tau hyperphosphorylation, and neuron loss. Shenqi Xingnao Granules (SQXN), a traditional Chinese medicine, significantly ameliorated the cognitive function and daily living abilities of patients with AD. However, till date, no study has investigated the mechanism of action of SQXN on AD. The present study aimed to verify the effects of SQXN treatment on cognitive impairments and AD-like pathologies in APP/PS1 mice.

Methods

Four-month-old APP/PS1 transgenic (Tg) mice were randomly divided into a model group and SQXN-treated (3.5, 7, 14 g/kg per day) groups. Learning-memory abilities were determined by Morris water maze and object recognition test. All mice were sacrificed and the brain samples were collected after 75 d. The soluble Aβ contents were detected by Elisa kit; The levels of expression of NeuN, APP, phosphorylated tau and related protein were measured by Western blotting; The inflammation factors were detected by the proinflammatory panel kit.

Results

Four-month-old APP/PS1 mice were administered SQXN by oral gavage for 2.5 months. Using the Morris water maze tests and Novel object recognition, we found that SQXN restored behavioral deficits in the experimental group of Tg mice when compared with the controls. SQXN also inhibited neuronal loss (NeuN marker). SQXN treatment decreased soluble Aβ42 through inhibiting the expression of sAPPβ and BACE-1 without regulating full-length amyloid precursor protein (FL APP). Insulin degrading enzyme (IDE), the Aβ degrading enzyme, were increased by SQXN. In addition, SQXN reduced hyperphosphorylated tau protein levels and prevented excessive activation of p-GSK-3β in the brain of APP/PS1 mice. Compared with APP/PS1 transgenic negative mice, IFN-γ, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-12p70, KC/GRO and TNF-α were not obviously changed in the brain of 6.5-month-old APP/PS1 transgenic (Tg) mice. However, SQXN could inhibited the expression of IL-2.

Conclusion

These results demonstrate that SQXN ameliorates the cognitive impairments in APP/PS1 mice. The possible mechanisms involve its inhibition of neuronal loss, soluble Aβ deposition, tau hyperphosphorylation and inflammation.

Potential therapeutic targets for intracerebral hemorrhage-associated inflammation: An update

Intracerebral hemorrhage (ICH) is a subtype of stroke with high mortality and disability but no specific or effective treatment. In the last two decades, much has been learned about the pathologic mechanisms of ICH. It is now known that after ICH onset, immune and inflammatory responses contribute to blood-brain barrier disruption, edema development, and cell death processes, jointly resulting in secondary brain injury. However, the translation of potential therapies from preclinical to clinical success has been disappointing. With the development of new laboratory technology, recent progress has been made in the understanding of ICH pathomechanisms, and promising therapeutic targets have been identified. This review provides an update of recent progress on ICH and describes the prospects for further preclinical studies in this field. Our goal is to discuss new therapeutic targets and directions for the treatment of ICH and promote the effective transformation from preclinical to clinical trials.

Plant-Derived Antioxidants Protect the Nervous System From Aging by Inhibiting Oxidative Stress

Alzheimer's disease (AD) has become a major disease contributing to human death and is thought to be closely related to the aging process. The rich antioxidant substances in plants have been shown to play a role in delaying aging, and in recent years, significant research has focused on also examining their potential role in AD onset and progression. Many plant-derived antioxidant research studies have provided insights for the future treatment and prevention of AD. This article reviews various types of plant-derived antioxidants with anti-aging effects on neurons. Also it distinguishes the different types of active substances that exhibit different degrees of protection for the nervous system and summarizes the mechanism thereof. Plant-derived antioxidants with neuroprotective functions can protect various components of the nervous system in a variety of ways and can have a positive impact on interventions to prevent and alleviate AD. Furthermore, when considering neuroprotective agents, glial cells also contribute to the defense of the nervous system and should not be ignored.

Amyloid beta (1-42) downregulates adenosine-2b receptors in addition to mitochondrial impairment and cholinergic dysfunction in memory-sensitive mouse brain regions

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by memory impairment. Adenosinergic receptors are considered as a potential alternative in the management of several neurodegenerative disorders. However, there is no information available on the role of A2b receptor in the pathophysiology of AD. Therefore, the effect of Aβ on the level of expression of A2b receptor was investigated in discrete memory-sensitive mouse brain regions. Aβ (1-42) was injected intracerebroventricularly to healthy male mouse to induce AD-like behavioral manifestations on Day-1 (D-1) of the experimental protocol. The animals were subjected to the Morris water maze (MWM) test on D-14 to D-18. On D-18, the animals were subjected to the Y-maze test after 30 min lag to the MWM paradigm. Aβ significantly attenuated the spatial working memory in MWM and Y-maze tests. In addition, Aβ significantly increased cholinergic dysfunction in terms of decrease in the activity of ChAT and ACh level and increase in the AChE activity in the hippocampus, pre-frontal cortex and amygdala of AD-like animals. Further, there was a significant increase in the extent of apoptosis in the selected mouse brain regions. Moreover, Aβ caused a substantial reduction in the mitochondrial function, integrity and bioenergetics in all the mouse brain regions. Furthermore, there was a significant decrease in the level of expression of A2b receptors in the selected brain regions of the rodents. Hence, it can be assumed that A2b receptor downregulation could be another therapeutic target in the management of AD.

Therapeutic Potential of Agonists and Antagonists of A1, A2a, A2b and A3 Adenosine Receptors

Adenosine is a naturally occurring nucleoside and an essential component of the energy production and utilization systems of the body. Adenosine is formed by the degradation of adenosine-triphosphate (ATP) during energy-consuming processes. Adenosine regulates numerous physiological processes through activation of four subtypes of G-protein coupled membrane receptors viz. A1, A2A, A2B and A3. Its physiological importance depends on the affinity of these receptors and the extracellular concentrations reached. ATP acts as a neurotransmitter in both peripheral and central nervous systems. In the peripheral nervous system, ATP is involved in chemical transmission in sensory and autonomic ganglia, whereas in central nervous system, ATP, released from synaptic terminals, induces fast excitatory postsynaptic currents. ATP provides the energetics for all muscle movements, heart beats, nerve signals and chemical reactions inside the body. Adenosine has been traditionally considered an inhibitor of neuronal activity and a regulator of cerebral blood flow. Since adenosine is neuroprotective against excitotoxic and metabolic dysfunctions observed in neurological and ocular diseases, the search for adenosinerelated drugs regulating adenosine transporters and receptors can be important for advancement of therapeutic strategies against these diseases. This review will summarize the therapeutic potential and recent SAR and pharmacology of adenosine and its receptor agonists and antagonists.

Microglial autophagy is impaired by prolonged exposure to β-amyloid peptides: evidence from experimental models and Alzheimer's disease patients

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the presence of misfolded proteins, amyloid-β (Aβ) aggregates, and neuroinflammation in the brain. Microglial cells are key players in the context of AD, being capable of releasing cytokines in response to Aβ and degrading aggregated proteins by mechanisms involving the ubiquitin-proteasome system and autophagy. Here, we present in vivo and in vitro evidence showing that microglial autophagy is affected during AD progression. PDAPPJ20 mice-murine model of AD-exhibited an accumulation of the autophagy receptor p62 and ubiquitin+ aggregates in Iba1+ microglial cells close to amyloid deposits in the hippocampus. Moreover, cultured microglial BV-2 cells showed an enhanced autophagic flux during a 2-h exposure to fibrillar Aβ, which was decreased if the exposure was prolonged to 24 h, a condition analogous to the chronic exposure to Aβ in the human pathology. The autophagic impairment was also associated with lysosomal damage, depicted by membrane permeabilization as shown by the presence of the acid hydrolase cathepsin-D in cytoplasm and altered LysoTracker staining. These results are compatible with microglial exhaustion caused by pro-inflammatory conditions and persistent exposure to aggregated Aβ peptides. In addition, we found LC3-positive autophagic vesicles accumulated in phagocytic CD68+ microglia in human AD brain samples, suggesting defective autophagy in microglia of AD brain. Our results indicate that the capacity of microglia to degrade Aβ and potentially other proteins through autophagy may be negatively affected as the disease progresses. Preserving autophagy in microglia thus emerges as a promising approach for treating AD. Graphical abstract.

The antioxidant resveratrol acts as a non-selective adenosine receptor agonist

Resveratrol (RSV) is a natural polyphenolic antioxidant with a proven protective role in several human diseases involving oxidative stress, although the molecular mechanism underlying this effect remains unclear. The present work tried to elucidate the molecular mechanism of RSV's role on signal transduction modulation. Our biochemical analysis, including radioligand binding, real time PCR, western blotting and adenylyl cyclase activity, and computational studies provide insights into the RSV binding pathway, kinetics and the most favored binding pose involving adenosine receptors, mainly A_2A subtype. In this study, we show that RSV target adenosine receptors (AdoRs), affecting gene expression, receptor levels, and the downstream adenylyl cyclase (AC)/PKA pathway. Our data demonstrate that RSV activates AdoRs. Moreover, RSV activate A_2A receptors by directly binding to the classical orthosteric binding site. Intriguingly, RSV-induced receptor activation can stimulate or inhibit AC activity depending on concentration and exposure time. Such subtle and multifaceted regulation of the AdoRs/AC/PKA pathway might contribute to the protective role of RSV. Our findings suggest that RSV molecular action is mediated, at least in part, by activation of adenosine receptors and create the opportunity to interrogate the therapeutic use of RSV in pathological conditions involving AdoRs, such as Alzheimer.

Complex regulation of ecto-5'-nucleotidase/CD73 and A2AR-mediated adenosine signaling at neurovascular unit: A link between acute and chronic neuroinflammation

The review summarizes available data regarding the complex regulation of CD73 at the neurovascular unit (NVU) during neuroinflammation. Based on available data we propose the biphasic pattern of CD73 regulation at NVU, with an early attenuation and a postponed up-regulation of CD73 activity. Transient attenuation of CD73 activity on leukocyte/vascular endothelium and leukocyte/astrocyte surface, required for the initiation of a neuroinflammatory response, may be effectuated either by catalytic inhibition of CD73 and/or by shedding of the CD73 molecule from the cell surface, while postponed induction of CD73 is effectuated by transcriptional up-regulation of Nt5e and posttranslational modifications. Neuroinflammatory conditions are also associated with significant enhancement and gain-of-function of A_2AR-mediated adenosine signaling. However, in contrast to the temporary prevalence of A_2AR over A₁R signaling during an acute inflammatory response, prolonged induction of A_2AR and resulting perpetual CD73/A_2AR coupling may be a contributing factors in the transition between acute and chronic neuroinflammation. Thus, pharmacological targeting of the CD73/A_2AR axis may attenuate inflammatory response and ameliorate neurological deficits in chronic neuroinflammatory conditions.

Autism genes and the leukocyte transcriptome in autistic toddlers relate to pathogen interactomes, infection and the immune system. A role for excess neurotrophic sAPPα and reduced antimicrobial Aβ

Prenatal and early childhood infections have been implicated in autism. Many autism susceptibility genes (206 Autworks genes) are localised in the immune system and are related to immune/infection pathways. They are enriched in the host/pathogen interactomes of 18 separate microbes (bacteria/viruses and fungi) and to the genes regulated by bacterial toxins, mycotoxins and Toll-like receptor ligands. This enrichment was also observed for misregulated genes from a microarray study of leukocytes from autistic toddlers. The upregulated genes from this leukocyte study also matched the expression profiles in response to numerous infectious agents from the Broad Institute molecular signatures database. They also matched genes related to sudden infant death syndrome and autism comorbid conditions (autoimmune disease, systemic lupus erythematosus, diabetes, epilepsy and cardiomyopathy) as well as to estrogen and thyrotropin responses and to those upregulated by different types of stressors including oxidative stress, hypoxia, endoplasmic reticulum stress, ultraviolet radiation or 2,4-dinitrofluorobenzene, a hapten used to develop allergic skin reactions in animal models. The oxidative/integrated stress response is also upregulated in the autism brain and may contribute to myelination problems. There was also a marked similarity between the expression signatures of autism and Alzheimer's disease, and 44 shared autism/Alzheimer's disease genes are almost exclusively expressed in the blood-brain barrier. However, in contrast to Alzheimer's disease, levels of the antimicrobial peptide beta-amyloid are decreased and the levels of the neurotrophic/myelinotrophic soluble APP alpha are increased in autism, together with an increased activity of α-secretase. sAPPα induces an increase in glutamatergic and a decrease in GABA-ergic synapses creating and excitatory/inhibitory imbalance that has also been observed in autism. A literature survey showed that multiple autism genes converge on APP processing and that many are able to increase sAPPalpha at the expense of beta-amyloid production. A genetically programmed tilt of this axis towards an overproduction of neurotrophic/gliotrophic sAPPalpha and underproduction of antimicrobial beta-amyloid may explain the brain overgrowth and myelination dysfunction, as well as the involvement of pathogens in autism.