Annexin A1 in the brain--undiscovered roles?

Chemoproteomic profiling by bioorthogonal probes to reveal the novel targets of acrylamide in microglia

Neurotoxicity studies caused by exposure to acrylamide (AA) are of wide interest, but the methods for direct analysis of AA targets in living neuronal cells by cysteine profiling are still lacking. To address this, we developed a specific bioorthogonal probe, AAPA-P2, for chemical proteomics analysis of AA covalent binding sites. AAPA-P2 captured 754 target proteins, increasing the number of identified target proteins by 20-fold. Further screening revealed 96 proteins that are both highly sensitive and heavily modified by AAPA-P2, with validation performed on some potential key targets and binding sites. AA was found to induce neurotoxicity by binding to newly identified targets, Proteasome 26S Subunit, non ATPase 9 (PSMD9) and NADH dehydrogenase (ubiquinone) 1 alpha subcomplex 5 (NDUFA5), interfering with the ubiquitin-proteasome system, and inducing mitochondria-dependent apoptosis. The present work provides an effective bioorthogonal probe tool for identifying covalent binding targets of acrylamide and offers new insights into the molecular mechanisms underlying acrylamide-induced neurotoxicity.

A novel histone deacetylase inhibitor W2A-16 improves the barrier integrity in brain vascular endothelial cells

The maturation of brain microvascular endothelial cells leads to the formation of a tightly sealed monolayer, known as the blood-brain barrier (BBB). The BBB damage is associated with the pathogenesis of age-related neurodegenerative diseases including vascular cognitive impairment and Alzheimer's disease. Growing knowledge in the field of epigenetics can enhance the understanding of molecular profile of the BBB and has great potential for the development of novel therapeutic strategies or targets to repair a disrupted BBB. Histone deacetylases (HDACs) inhibitors are epigenetic regulators that can induce acetylation of histones and induce open chromatin conformation, promoting gene expression by enhancing the binding of DNA with transcription factors. We investigated how HDAC inhibition influences the barrier integrity using immortalized human endothelial cells (HCMEC/D3) and the human induced pluripotent stem cell (iPSC)-derived brain vascular endothelial cells. The endothelial cells were treated with or without a novel compound named W2A-16. W2A-16 not only activates Wnt/β-catenin signaling but also functions as a class I HDAC inhibitor. We demonstrated that the administration with W2A-16 sustained barrier properties of the monolayer of endothelial cells, as evidenced by increased trans-endothelial electrical resistance (TEER). The BBB-related genes and protein expression were also increased compared with non-treated controls. Analysis of transcript profiles through RNA-sequencing in hCMEC/D3 cells indicated that W2A-16 potentially enhances BBB integrity by influencing genes associated with the regulation of the extracellular microenvironment. These findings collectively propose that the HDAC inhibition by W2A-16 plays a facilitating role in the formation of the BBB. Pharmacological approaches to inhibit HDAC may be a potential therapeutic strategy to boost and/or restore BBB integrity.

The role of annexins in central nervous system development and disease

Annexins, a group of Ca2+-dependent phospholipid-binding proteins, exert diverse roles in neuronal development, normal central nervous system (CNS) functioning, neurological disorders, and CNS tumors. This paper reviews the roles of individual annexins (A1-A13) in these contexts. Annexins possess unique structural and functional features, such as Ca2+-dependent binding to phospholipids, participating in membrane organization, and modulating cell signaling. They are implicated in various CNS processes, including endocytosis, exocytosis, and stabilization of plasma membranes. Annexins exhibit dynamic roles in neuronal development, influencing differentiation, proliferation, and synaptic formation in CNS tissues. Notably, annexins such as ANXA1 and ANXA2 play roles in apoptosis and blood-brain barrier (BBB) integrity. Neurological disorders, including Alzheimer's disease, multiple sclerosis, and depression, involve annexin dysregulation, influencing neuroinflammation, blood-brain barrier integrity, and stress responses. Moreover, annexins contribute to the pathogenesis of CNS tumors, either promoting or suppressing tumor growth, angiogenesis, and invasion. Annexin expression patterns vary across different CNS tumor types, providing potential prognostic markers and therapeutic targets. This review underscores the multifaceted roles of annexins in the CNS, highlighting their importance in normal functioning, disease progression, and potential therapeutic interventions.

Laminin-Augmented Decellularized Extracellular Matrix Ameliorating Neural Differentiation and Neuroinflammation in Human Mini-Brains

Non-neural extracellular matrix (ECM) has limited application in humanized physiological neural modeling due to insufficient brain-specificity and safety concerns. Although brain-derived ECM contains enriched neural components, certain essential components are partially lost during the decellularization process, necessitating augmentation. Here, it is demonstrated that the laminin-augmented porcine brain-decellularized ECM (P-BdECM) is xenogeneic factor-depleted as well as favorable for the regulation of human neurons, astrocytes, and microglia. P-BdECM composition is comparable to human BdECM regarding brain-specificity through the matrisome and gene ontology-biological process analysis. As augmenting strategy, laminin 111 supplement promotes neural function by synergic effect with laminin 521 in P-BdECM. Annexin A1(ANXA1) and Peroxiredoxin(PRDX) in P-BdECM stabilized microglial and astrocytic behavior under normal while promoting active neuroinflammation in response to neuropathological factors. Further, supplementation of the brain-specific molecule to non-neural matrix also ameliorated glial cell inflammation as in P-BdECM. In conclusion, P-BdECM-augmentation strategy can be used to recapitulate humanized pathophysiological cerebral environments for neurological study.

Annexin A1 in the nervous and ocular systems

The therapeutic potential of Annexin A1, an important member of the Annexin superfamily, has become evident in results of experiments with multiple human systems and animal models. The anti-inflammatory and pro-resolving effects of Annexin A1 are characteristic of pathologies involving the nervous system. In this review, we initially describe the expression sites of Annexin A1, then outline the mechanisms by which Annexin A1 maintains the neurological homeostasis through either formyl peptide receptor 2 or other molecular approaches; and, finally, we discuss the neuroregenerative potential qualities of Annexin A1. The eye and the nervous system are anatomically and functionally connected, but the association between visual system pathogenesis, especially in the retina, and Annexin A1 alterations has not been well summarized. Therefore, we explain the beneficial effects of Annexin A1 for ocular diseases, especially for retinal diseases and glaucoma on the basis of published findings, and we explore present and future delivery strategies for Annexin A1 to the retina.

Regional homogeneity alterations in patients with functional constipation and their associations with gene expression profiles

Functional constipation, a highly prevalent functional gastrointestinal disorder, often accompanies by mental and psychological disorders. Previous neuroimaging studies have demonstrated brain functional and structural alterations in patients with functional constipation. However, little is known about whether and how regional homogeneity is altered in these patients. Moreover, the potential genetic mechanisms associated with these alterations remain largely unknown. The study included 73 patients with functional constipation and 68 healthy controls, and regional homogeneity comparison was conducted to identify the abnormal spontaneous brain activities in patients with functional constipation. Using Allen Human Brain Atlas, we further investigated gene expression profiles associated with regional homogeneity alterations in functional constipation patients with partial least squares regression analysis applied. Compared with healthy controls, functional constipation patients demonstrated significantly decreased regional homogeneity in both bilateral caudate nucleus, putamen, anterior insula, thalamus and right middle cingulate cortex, supplementary motor area, and increased regional homogeneity in the bilateral orbitofrontal cortex. Genes related to synaptic signaling, central nervous system development, fatty acid metabolism, and immunity were spatially correlated with abnormal regional homogeneity patterns. Our findings showed significant regional homogeneity alterations in functional constipation patients, and the changes may be caused by complex polygenetic and poly-pathway mechanisms, which provides a new perspective on functional constipation's pathophysiology.

AnnexinA6: a potential therapeutic target gene for extracellular matrix mineralization

The mineralization of the extracellular matrix (ECM) is an essential and crucial process for physiological bone formation and pathological calcification. The abnormal function of ECM mineralization contributes to the worldwide risk of developing mineralization-related diseases; for instance, vascular calcification is attributed to the hyperfunction of ECM mineralization, while osteoporosis is due to hypofunction. AnnexinA6 (AnxA6), a Ca2+-dependent phospholipid-binding protein, has been extensively reported as an essential target in mineralization-related diseases such as osteoporosis, osteoarthritis, atherosclerosis, osteosarcoma, and calcific aortic valve disease. To date, AnxA6, as the largest member of the Annexin family, has attracted much attention due to its significant contribution to matrix vesicles (MVs) production and release, MVs-ECM interaction, cytoplasmic Ca2+ influx, and maturation of hydroxyapatite, making it an essential target in ECM mineralization. In this review, we outlined the recent advancements in the role of AnxA6 in mineralization-related diseases and the potential mechanisms of AnxA6 under normal and mineralization-related pathological conditions. AnxA6 could promote ECM mineralization for bone regeneration in the manner described previously. Therefore, AnxA6 may be a potential osteogenic target for ECM mineralization.

An Atlas of the Developing Drosophila Visual System Glia and Subcellular mRNA Localization of Transcripts in Single Cells

Glial cells are essential for proper nervous system development and function. To understand glial development and function, we comprehensively annotated glial cells in a single-cell mRNA-sequencing (scRNAseq) atlas of the developing Drosophila visual system. This allowed us to study their developmental trajectories, from larval to adult stages, and to understand how specific types of glia diversify during development. For example, neuropil glia that are initially transcriptionally similar in larvae, split into ensheathing and astrocyte-like glia during pupal stages. Other glial types, such as chiasm glia change gradually during development without splitting into two cell types. The analysis of scRNA-seq allowed us to discover that the transcriptome of glial cell bodies can be distinguished from that of their broken processes. The processes contain distinct enriched mRNAs that were validated in vivo. Therefore, we have identified most glial types in the developing optic lobe and devised a computational approach to identify mRNA species that are localized to cell bodies or cellular processes.

Microglia in Alzheimer's disease: pathogenesis, mechanisms, and therapeutic potentials

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by protein aggregation in the brain. Recent studies have revealed the critical role of microglia in AD pathogenesis. This review provides a comprehensive summary of the current understanding of microglial involvement in AD, focusing on genetic determinants, phenotypic state, phagocytic capacity, neuroinflammatory response, and impact on synaptic plasticity and neuronal regulation. Furthermore, recent developments in drug discovery targeting microglia in AD are reviewed, highlighting potential avenues for therapeutic intervention. This review emphasizes the essential role of microglia in AD and provides insights into potential treatments.

ANXA1 mutation analysis in Italian patients with early onset PD

Recently, a novel pathogenic variant in Annexin A1 protein (c.4G > A, p.Ala2Thr) has been identified in an Iranian consanguineous family with autosomal recessive parkinsonism. The deficiencies of ANXA1 could lead to extracellular SNCA accumulation, defects in intracellular signaling pathways and synaptic plasticity causing parkinsonism. The aim of this study was to identify rare ANXA1 variants in 95 early-onset PD patients from South Italy. Sequencing analysis of ANXA1 gene revealed only 2 synonymous variants in PD patients (rs1050305, rs149033255). Therefore, we conclude that the recently published ANXA1 mutation is not a common cause of EOPD in Southern Italy.

Implicative role of epidermal growth factor receptor and its associated signaling partners in the pathogenesis of Alzheimer's disease

Epidermal growth factor receptor (EGFR) plays a pivotal role in early brain development, although its expression pattern declines in accordance with the maturation of the active nervous system. However, recurrence of EGFR expression in brain cells takes place during neural functioning decline and brain atrophy in order to maintain the homeostatic neuronal pool. As a consequence, neurotoxic lesions such as amyloid beta fragment (Aβ_1-42) formed during the alternative splicing of amyloid precursor protein in Alzheimer's disease (AD) elevate the expression of EGFR. This inappropriate peptide deposition on EGFR results in the sustained phosphorylation of the downstream signaling axis, leading to extensive Aβ_1-42 production and tau phosphorylation as subsequent pathogenesis. Recent reports convey that the pathophysiology of AD is correlated with EGFR and its associated membrane receptor complex molecules. One such family of molecules is the annexin superfamily, which has synergistic relationships with EGFR and is known for membrane-bound signaling that contributes to a variety of inflammatory responses. Besides, Galectin-3, tissue-type activated plasminogen activator, and many more, which lineate the secretion of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-18) result in severe neuronal loss. Altogether, we emphasized the perspectives of cellular senescence up-regulated by EGFR and its associated membrane receptor molecules in the pathogenesis of AD as a target for a therapeutical alternative to intervene in AD.

Regional heterogeneity in mitochondrial function underlies region specific vulnerability in human brain ageing: Implications for neurodegeneration

Selective neuronal vulnerability (SNV) of specific neuroanatomical regions such as frontal cortex (FC) and hippocampus (HC) is characteristic of age-associated neurodegenerative diseases (NDDs), although its pathogenetic basis remains unresolved. We hypothesized that physiological differences in mitochondrial function in neuroanatomical regions could contribute to SNV. To investigate this, we evaluated mitochondrial function in human brains (age range:1-90 y) in FC, striatum (ST), HC, cerebellum (CB) and medulla oblongata (MD), using enzyme assays and quantitative proteomics. Striking differences were noted in resistant regions- MD and CB compared to the vulnerable regions- FC, HC and ST. At younger age (25 ± 5 y), higher activity of electron transport chain enzymes and upregulation of metabolic and antioxidant proteins were noted in MD compared to FC and HC, that was sustained with increasing age (≥65 y). In contrast, the expression of synaptic proteins was higher in FC, HC and ST (vs. MD). In line with this, quantitative phospho-proteomics revealed activation of upstream regulators (ERS, PPARα) of mitochondrial metabolism and inhibition of synaptic pathways in MD. Microtubule Associated Protein Tau (MAPT) showed overexpression in FC, HC and ST both in young and older age (vs. MD). MAPT hyperphosphorylation and the activation of its kinases were noted in FC and HC with age. Our study demonstrates that regional heterogeneity in mitochondrial and other cellular functions contribute to SNV and protect regions such as MD, while rendering FC and HC vulnerable to NDDs. The findings also support the "last in, first out" hypothesis of ageing, wherein regions such as FC, that are the most recent to develop phylogenetically and ontogenetically, are the first to be affected in ageing and NDDs.

Elevation of inactive cleaved annexin A1 in the neocortex is associated with amyloid, inflammatory and apoptotic markers in neurodegenerative dementias

Inflammation is usually a tightly regulated process whose termination by mediators including Annexin A1 (AnxA1) results in the resolution of inflammatory responses. In neurodegenerative dementias, chronic neuroinflammation, along with accumulation of aggregated β-amyloid (Aβ) peptides and apoptosis, has long been recognized to be a pathological hallmark; but it is unclear whether a failure of inflammation resolution contributes to this pathophysiological process. In this study, we measured AnxA1 immunoreactivities in postmortem neocortex (Brodmann areas BA9 and BA40) of well characterized Alzheimer's disease (AD), Parkinson disease dementia (PDD) and dementia with Lewy bodies (DLB) patients as well as aged controls. Inactive cleaved AnxA1 was found to be elevated in AD and DLB in BA40. Levels of cleaved AnxA1 also positively correlated with amyloidogenic brain Aβ, anti-inflammatory markers such as IL10 and IL13, as well as with the pro-apoptotic marker cleaved caspase-3 in BA40. Our findings suggest that elevated cleaved AnxA1 in neurodegenerative dementias may reflect a failure of inflammation resolution in certain regions of the diseased brain, and also support a mechanistic link between AnxA1 and amyloid pathology, neuroinflammation and apoptosis.

Electroacupuncture promotes microglial M2 polarization in ischemic stroke via annexin A1

BACKGROUND

Neuroinflammation is the leading cause of neurological sequelae in ischemic stroke. Recently, we reported that the anti-inflammatory mediator annexin A1 (ANXA1) favored microglial M2 polarization in brain injury. The purpose of this study was to investigate electroacupuncture (EA) treatment and its potentially ANXA1-mediated anti-inflammatory effects in the middle cerebral artery occlusion/reperfusion (MCAO/R) mouse model of stroke.

METHODS

Treatment with EA consisted of dense-sparse frequencies (alternating 4 Hz sparse waves for 1.5 s and 16 Hz dense waves for 1.5 s) at CV24 and GV26. Intracerebroventricular (ICV) injection of Boc-2 (5 µM) or short hairpin RNA (sh)ANXA1 (2 µL) 3 days before EA was performed to block the effects of ANXA1.

RESULTS

EA pretreatment enhanced expression of ANXA1 and its receptor, formyl peptide receptor (FPR), when compared to MCAO/R alone. EA treatment also rescued MCAO/R-induced deficits in neurological performance, and learning and memory, and reduced infarct volume. Double immunofluorescent labeling showed that EA prevented MCAO/R-induced changes in microglial activation and morphology. EA also reduced the release of pro-inflammatory cytokines, such as interleukin (IL)-1β, inducible nitric oxide synthase (iNOS) and tumor necrosis factor (TNF)-α, while increasing the release of anti-inflammatory cytokines, such as arginase-1 (Arg-1) and brain-derived neurotrophic factor (BDNF). All EA-induced effects were either partially or completely prevented by prior administration of FPR antagonist Boc-2 or shANXA1.

CONCLUSION

The current study provides strong evidence that EA treatment has protective effects against ischemic stroke in the MCAO/R mouse model and that the mechanism likely involves the promotion of M2 polarization in microglia via ANXA1.

Mitochondrial dysfunction in adult midbrain dopamine neurons triggers an early immune response

Dopamine (DA) neurons of the midbrain are at risk to become affected by mitochondrial damage over time and mitochondrial defects have been frequently reported in Parkinson’s disease (PD) patients. However, the causal contribution of adult-onset mitochondrial dysfunction to PD remains uncertain. Here, we developed a mouse model lacking Mitofusin 2 (MFN2), a key regulator of mitochondrial network homeostasis, in adult midbrain DA neurons. The knockout mice develop severe and progressive DA neuron-specific mitochondrial dysfunction resulting in neurodegeneration and parkinsonism. To gain further insights into pathophysiological events, we performed transcriptomic analyses of isolated DA neurons and found that mitochondrial dysfunction triggers an early onset immune response, which precedes mitochondrial swelling, mtDNA depletion, respiratory chain deficiency and cell death. Our experiments show that the immune response is an early pathological event when mitochondrial dysfunction is induced in adult midbrain DA neurons and that neuronal death may be promoted non-cell autonomously by the cross-talk and activation of surrounding glial cells.

Parkinson’s disease (PD) is a common neurodegenerative disorder characterized by progressive loss of dopamine (DA)-producing neurons and strongly compromised motor performance. Multiple observations suggest that DA neurons are particularly prone to acquire mitochondrial damage in adult life. This acquired mitochondrial dysfunction likely impairs DA neuron function and contributes to cell death. To study the consequences of adult-onset mitochondrial dysfunction in DA neurons, we generated a conditional activatable knockout mouse model lacking Mitofusin 2, a key regulator of mitochondrial homeostasis. This animal model allows the induction of mitochondrial dysfunction selectively in adult DA neurons and leads to motor defects and the typical pattern of neurodegeneration seen in PD. By studying gene expression in isolated DA neurons at early disease stages and by using in situ approaches on brain sections, we report an early onset of an inflammatory response. Inflammation is present already when the mutant DA neurons display the first signs of mitochondrial fragmentation and precedes the onset of respiratory chain dysfunction and neurodegeneration. The inflammatory response in DA neurons and activation of surrounding glia thus likely exacerbates or drives the neurodegenerative process in this animal model of adult-onset PD.

TRPM7 is critical for short-term synaptic depression by regulating synaptic vesicle endocytosis

Transient receptor potential melastatin 7 (TRPM7) contributes to a variety of physiological and pathological processes in many tissues and cells. With a widespread distribution in the nervous system, TRPM7 is involved in animal behaviors and neuronal death induced by ischemia. However, the physiological role of TRPM7 in central nervous system (CNS) neuron remains unclear. Here, we identify endocytic defects in neuroendocrine cells and neurons from TRPM7 knockout (KO) mice, indicating a role of TRPM7 in synaptic vesicle endocytosis. Our experiments further pinpoint the importance of TRPM7 as an ion channel in synaptic vesicle endocytosis. Ca2+ imaging detects a defect in presynaptic Ca2+ dynamics in TRPM7 KO neuron, suggesting an importance of Ca2+ influx via TRPM7 in synaptic vesicle endocytosis. Moreover, the short-term depression is enhanced in both excitatory and inhibitory synaptic transmissions from TRPM7 KO mice. Taken together, our data suggests that Ca2+ influx via TRPM7 may be critical for short-term plasticity of synaptic strength by regulating synaptic vesicle endocytosis in neurons.

The Role of Annexin A1 and Formyl Peptide Receptor 2/3 Signaling in Chronic Corticosterone-Induced Depression-Like behaviors and Impairment in Hippocampal-Dependent Memory

BACKGROUND

The activity of the Hypothalamic-Pituitary-Adrenal (HPA) axis is commonly dysregulated in stress-related psychiatric disorders. Annexin A1 (ANXA1), an endogenous ligand of Formyl Peptide Receptor (FPR) 2/3, is a member of the family of phospholipid- and calcium-binding proteins with a well-defined role in the delayed early inhibitory feedback of Glucocorticoids (GC) in the pituitary gland and implicated in the occurrence of behavioural disorders such as anxiety.

OBJECTIVE

The present study aimed to evaluate the potential role of ANXA1 and its main receptor, as a cellular mediator of behavioural disorders, in a model of Corticosterone (CORT)-induced depression and subsequently, the possible correlation between the depressive state and impairment of hippocampal memory.

METHODS

To induce the depression model, Wild-Type (WT), ANXA1 Knockout (KO), and FPR2/3 KO mice were exposed to oral administration of CORT for 28 days dissolved in drinking water. Following this, histological, biochemical and behavioural analyses were performed.

RESULTS

FPR2/3 KO and ANXA1 KO mice showed improvement in anxiety and depression-like behaviour compared with WT mice after CORT administration. In addition, FPR2/3 KO and ANXA1 KO mice showed a reduction in histological alterations and neuronal death in hippocampal sections. Moreover, CORT+ FPR2/3 KO and ANXA1 KO, exhibited a higher expression of Brain-Derived Neurotrophic Factor (BDNF), phospho-ERK, cAMP response element-binding protein (pCREB) and a decrease in Serotonin Transporter Expression (SERT) compared to WT(CORT+) mice.

CONCLUSION

In conclusion, the absence of the ANXA1 protein, even more than the absence of its main receptor (FPR 2/3), was fundamental to the inhibitory action of GC on the HPA axis; it also maintained the hippocampal homeostasis by preventing neuronal damage associated with depression.

Annexin A1 restores cerebrovascular integrity concomitant with reduced amyloid-β and tau pathology

Alzheimer's disease, characterized by brain deposits of amyloid-β plaques and neurofibrillary tangles, is also linked to neurovascular dysfunction and blood-brain barrier breakdown, affecting the passage of substances into and out of the brain. We hypothesized that treatment of neurovascular alterations could be beneficial in Alzheimer's disease. Annexin A1 (ANXA1) is a mediator of glucocorticoid anti-inflammatory action that can suppress microglial activation and reduce blood-brain barrier leakage. We have reported recently that treatment with recombinant human ANXA1 (hrANXA1) reduced amyloid-β levels by increased degradation in neuroblastoma cells and phagocytosis by microglia. Here, we show the beneficial effects of hrANXA1 in vivo by restoring efficient blood-brain barrier function and decreasing amyloid-β and tau pathology in 5xFAD mice and Tau-P301L mice. We demonstrate that young 5xFAD mice already suffer cerebrovascular damage, while acute pre-administration of hrANXA1 rescued the vascular defects. Interestingly, the ameliorated blood-brain barrier permeability in young 5xFAD mice by hrANXA1 correlated with reduced brain amyloid-β load, due to increased clearance and degradation of amyloid-β by insulin degrading enzyme (IDE). The systemic anti-inflammatory properties of hrANXA1 were also observed in 5xFAD mice, increasing IL-10 and reducing TNF-α expression. Additionally, the prolonged treatment with hrANXA1 reduced the memory deficits and increased synaptic density in young 5xFAD mice. Similarly, in Tau-P301L mice, acute hrANXA1 administration restored vascular architecture integrity, affecting the distribution of tight junctions, and reduced tau phosphorylation. The combined data support the hypothesis that blood-brain barrier breakdown early in Alzheimer's disease can be restored by hrANXA1 as a potential therapeutic approach.

The Effect of Annexin A1 as a Potential New Therapeutic Target on Neuronal Damage by Activated Microglia

Brain disease is known to cause irrevocable and fatal loss of biological function once damaged. One of various causes of its development is damage to neuron cells caused by hyperactivated microglia, which function as immune cells in brain. Among the genes expressed in microglia stimulated by various antigens, annexin A1 (ANXA1) is expressed in the early phase of the inflammatory response and plays an important role in controlling the immune response. In this study, we assessed whether ANXA1 can be a therapeutic target gene for the initial reduction of the immune response induced by microglia to minimize neuronal damage. To address this, mouse-origin microglial cells were stimulated to mimic an immune response by lipopolysaccharide (LPS) treatment. The LPS treatment caused activation of ANXA1 gene and expression of inflammatory cytokines. To assess the biological function in microglia by the downregulation of ANXA1 gene, cells were treated with short hairpin RNA-ANXA1. Downregulated ANXA1 affected the function of mitochondria in the microglia and showed reduced neuronal damage when compared to the control group in the co-culture system. Taken together, our results showed that ANXA1 could be used as a potential therapeutic target for inflammation-related neurodegenerative diseases.

Heterogeneity of glial progenitor cells during the neurogenesis-to-gliogenesis switch in the developing human cerebral cortex

The heterogeneity and molecular characteristics of progenitor cells, especially glial progenitors, in the developing human cerebral cortex remain elusive. Here, we find that EGFR expression begins to sharply increase after gestational week (GW) 20, which corresponds to the beginning stages of human gliogenesis. In addition, EGFR⁺ cells are mainly distributed in the germinal zone and frequently colocalize with the stemness marker SOX2 during this period. Then, by performing single-cell RNA sequencing on these EGFR⁺ cells, we successfully enriched and characterized various glial- and neuronal-lineage progenitor cells and validated their phenotypes in fixed slices. Notably, we identified two subgroups with molecular characteristics similar to those of astrocytes, and the immunostaining results show that these cells are mainly distributed in the outer subventricular zone and might originate from the outer radial glial cells. In short, the EGFR-sorting strategy and molecular signatures in the diverse lineages provide insights into human glial development.

Low Annexin A1 level in HTLV-1 infected patients is a potential biomarker for the clinical progression and diagnosis of HAM/TSP

BACKGROUND

Human T-lymphotropic virus 1 (HTLV-1) is etiologically associated with the chronic inflammatory neurodegenerative disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) Annexin A1 (AnxA1) is an anti-inflammatory protein with proposed neuroprotective and anti-neuroinflammatory functions. We hypothesized that ANXA1 gene expression may be dysregulated in HTLV-1-infected HAM/TSP patients.

METHODS

This study involved 37 individuals infected with HTLV-1, including 21 asymptomatic (AS) carriers and 16 with HAM/TSP, and a control group of 30 individuals negative for HTLV-1 and HTLV-2. For AS HTLV-1-positive and HAM/TSP patients, ANXA1 and formyl peptide receptor (FPR1, FPR2 and FPR3) expression and HTLV-1 proviral load (PVL) in peripheral blood cells were evaluated by real-time quantitative PCR (qPCR), and plasma AnxA1 levels were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

ANXA1 gene expression was increased in the AS group compared with the HAM/TSP and control groups, but the differences were not statistically significant. FPR1 gene expression was higher in patients with HTLV-1 than in controls (AS, p = 0.0032; HAM/TSP, p < 0.0001). Plasma AnxA1 levels were higher in the AS group than in the HAM/TSP group (p = 0.0045), and PVL was higher in patients with HAM/TSP than in AS individuals (p = 0.0162). The use of a combined ROC curve using Annexin 1 levels and proviral load significantly increased the sensitivity and specificity to predict progression to HAM/TSP (AUC = 0.851 and AUC = 0.937, respectively, to AUC = 1000).

CONCLUSIONS

Our results suggest that AnxA1 may be dysregulated in HAM/TSP patients. Serological detection of AnxA1 in association with proviral load may provide a prognostic biomarker for HTLV-1-associated neurodegenerative disease.

Annexin A1 Attenuates Neutrophil Migration and IL-6 Expression through Fpr2 in a Mouse Model of Streptococcus suis-Induced Meningitis

Streptococcus suis serotype 2 is a crucial pathogenic cause of bacterial meningitis, a life-threatening disease with neurological sequelae and high rates of mortality. Inflammation triggered by S. suis infection must be precisely regulated to prevent further tissue damage.

Streptococcus suis serotype 2 is a crucial pathogenic cause of bacterial meningitis, a life-threatening disease with neurological sequelae and high rates of mortality. Inflammation triggered by S. suis infection must be precisely regulated to prevent further tissue damage. As a glucocorticoid anti-inflammatory mediator, annexin A1 (AnxA1) mainly acts through formyl peptide receptor 2 (Fpr2) to alleviate inflammation in the peripheral system. In this study, we evaluated the roles of AnxA1 and Fpr2 in a mouse model of S. suis meningitis created via intracisternal infection in Fpr2-deficient (Fpr2^−/−) and wild-type (WT) mice. We revealed that Fpr2^−/− mice were highly susceptible to S. suis meningitis, displaying increased inflammatory cytokine levels, bacterial dissemination, and neutrophil migration compared with WT mice. Additionally, AnxA1 exerted anti-inflammatory effects through Fpr2, such as attenuation of leukocyte infiltration, inflammatory mediator production, and astrocyte or microglial activation in the brain. Importantly, we found that the antimigratory function of AnxA1 decreases neutrophil adherence to the endothelium through Fpr2. Finally, an in vitro study revealed that AnxA1 potentially suppresses interleukin-6 (IL-6) expression through the Fpr2/p38/COX-2 pathway. These data demonstrated that Fpr2 is an anti-inflammatory receptor that regulates neutrophil migration in mice with S. suis meningitis and identified AnxA1 as a potential therapeutic option.

Apoptotic neurons and amyloid-beta clearance by phagocytosis in Alzheimer's disease: Pathological mechanisms and therapeutic outlooks

Neuronal survival and axonal renewal following central nervous system damage and in neurodegenerative illnesses, such as Alzheimer's disease (AD), can be enhanced by fast clearance of neuronal apoptotic debris, as well as the removal of amyloid beta (Aβ) by phagocytic cells through the process of efferocytosis. This process quickly inhibits the release of proinflammatory and antigenic autoimmune constituents, enhancing the formation of a microenvironment vital for neuronal survival and axonal regeneration. Therefore, the detrimental features associated with microglial phagocytosis uncoupling, such as the accumulation of apoptotic cells, inflammation and phagoptosis, could exacerbate the pathology in brain disease. Some mechanisms of efferocytosis could be targeted by several promising agents, such as curcumin, URMC-099 and Y-P30, which have emerged as potential treatments for AD. This review aims to investigate and update the current research regarding the signaling molecules and pathways involved in efferocytosis and how these could be targeted as a potential therapy in AD.

The Contribution of Formyl Peptide Receptor Dysfunction to the Course of Neuroinflammation: A Potential Role in the Brain Pathology

Chronic inflammatory processes within the central nervous system (CNS) are in part responsible for the development of neurodegenerative and psychiatric diseases. These processes are associated with, among other things, the increased and disturbed activation of microglia and the elevated production of proinflammatory factors. Recent studies indicated that the disruption of the process of resolution of inflammation (RoI) may be the cause of CNS disorders. It is shown that the RoI is regulated by endogenous molecules called specialized pro-resolving mediators (SPMs), which interact with specific membrane receptors. Some SPMs activate formyl peptide receptors (FPRs), which belong to the family of seven-transmembrane G protein-coupled receptors. These receptors take part not only in the proinflammatory response but also in the resolution of the inflammation process. Therefore, the activation of FPRs might have complex consequences.

This review discusses the potential role of FPRs, and in particular the role of FPR2 subtype, in the brain under physiological and pathological conditions and their involvement in processes underlying neurodegenerative and psychiatric disorders as well as ischemia, the pathogenesis of which involves the dysfunction of inflammatory processes.

Ac2-26 Alleviates Brain Injury after Cardiac Arrest and Cardiopulmonary Resuscitation in Rats via the eNOS Pathway

Background

Brain injury is the leading cause of death following cardiac arrest (CA) and cardiopulmonary resuscitation (CPR). Ac2-26 and endothelial nitric oxide synthase (eNOS) have been shown to reduce neuroinflammation. This study is aimed at determining the mechanism by which Ac2-26 protects against inflammation during brain injury following CA and CPR.

Methods

Sixty-four rats were randomized into sham, saline, Ac2-26, and Ac2-26+L-NIO (endothelial nitric oxide synthase (eNOS) inhibitor) groups. Rats received Ac2-26, Ac2-26+L-NIO, or saline after CPR. Neurologic function was assessed at baseline, 24, and 72 hours after CPR. At 72 hours after resuscitation, serum and brain tissues were collected.

Results

Blood-brain barrier (BBB) permeability increased, and the number of surviving neurons and neurological function decreased in the saline group compared to the sham group. Anti-inflammatory and proinflammatory factors, neuron-specific enolase (NSE) levels, and the expression of eNOS, phosphorylated (p)-eNOS, inducible nitric oxide synthase (iNOS), and oxidative stress-related factors in the three CA groups significantly increased (P < 0.05). BBB permeability decreased, and the number of surviving neurons and neurological function increased in the Ac2-26 group compared to the saline group (P < 0.05). Ac2-26 increased anti-inflammatory and reduced proinflammatory markers, raised NSE levels, increased the expression of eNOS and p-eNOS, and reduced the expression of iNOS and oxidative stress-related factors compared to the saline group (P < 0.05). The effect of Ac2-26 on brain injury was reversed by L-NIO (P < 0.05).

Conclusions

Ac2-26 reduced brain injury after CPR by inhibiting oxidative stress and neuroinflammation and protecting the BBB. The therapeutic effect of Ac2-26 on brain injury was largely dependent on the eNOS pathway.

Cellular and molecular characterization of multiplex autism in human induced pluripotent stem cell-derived neurons

Background

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with pronounced heritability in the general population. This is largely attributable to the effects of polygenic susceptibility, with inherited liability exhibiting distinct sex differences in phenotypic expression. Attempts to model ASD in human cellular systems have principally involved rare de novo mutations associated with ASD phenocopies. However, by definition, these models are not representative of polygenic liability, which accounts for the vast share of population-attributable risk.

Methods

Here, we performed what is, to our knowledge, the first attempt to model multiplex autism using patient-derived induced pluripotent stem cells (iPSCs) in a family manifesting incremental degrees of phenotypic expression of inherited liability (absent, intermediate, severe). The family members share an inherited variant of uncertain significance (VUS) in GPD2, a gene that was previously associated with developmental disability but here is insufficient by itself to cause ASD. iPSCs from three first-degree relatives and an unrelated control were differentiated into both cortical excitatory (cExN) and cortical inhibitory (cIN) neurons, and cellular phenotyping and transcriptomic analysis were conducted.

Results

cExN neurospheres from the two affected individuals were reduced in size, compared to those derived from unaffected related and unrelated individuals. This reduction was, at least in part, due to increased apoptosis of cells from affected individuals upon initiation of cExN neural induction. Likewise, cIN neural progenitor cells from affected individuals exhibited increased apoptosis, compared to both unaffected individuals. Transcriptomic analysis of both cExN and cIN neural progenitor cells revealed distinct molecular signatures associated with affectation, including the misregulation of suites of genes associated with neural development, neuronal function, and behavior, as well as altered expression of ASD risk-associated genes.

Conclusions

We have provided evidence of morphological, physiological, and transcriptomic signatures of polygenic liability to ASD from an analysis of cellular models derived from a multiplex autism family. ASD is commonly inherited on the basis of additive genetic liability. Therefore, identifying convergent cellular and molecular phenotypes resulting from polygenic and monogenic susceptibility may provide a critical bridge for determining which of the disparate effects of rare highly deleterious mutations might also apply to common autistic syndromes.

Inflammatory and Pro-resolving Mediators in Frontotemporal Dementia and Alzheimer's Disease

Chronic inflammation contributes to neuronal death in Alzheimer's disease (AD) and frontotemporal dementia (FTD). Here we evaluated inflammatory and pro-resolving mediators in AD and behavioural variant of FTD (bvFTD) patients compared with controls, since neuroinflamamtion is a common feature in both diseases. Ninety-eight subjects were included in this study, divided into AD (n = 32), bvFTD (n = 30), and control (n = 36) groups. The levels of hsCRP, IL-1β, IL-6, TNF, and TGF-β1, as well as annexin A1 (AnxA1) and lipoxin A4 (LXA4) were measured in blood and cerebrospinal fluid (CSF). The expression profile of AnxA1 was evaluated in peripheral blood mononuclear cells (PBMCs) as well the distribution of ANXA1 rs2611228 polymorphism. We found reduced peripheral levels of hsCRP and TNF in AD compared with bvFTD patients and controls, and increased levels of TGF-β1 in AD compared to controls. Moreover, reduced plasma levels of AnxA1 were observed in bvFTD compared to AD and controls. There was a significant cleavage of AnxA1 in PBMCs in both dementia groups. The results suggest differential regulation of inflammatory and pro-resolving mediators in bvFTD and AD, while AnxA1 cleavage may impair pro-resolving mechanisms in both groups.

Novel Role for the AnxA1-Fpr2/ALX Signaling Axis as a Key Regulator of Platelet Function to Promote Resolution of Inflammation

Supplemental Digital Content is available in the text.

Background:

Ischemia reperfusion injury (I/RI) is a common complication of cardiovascular diseases. Resolution of detrimental I/RI-generated prothrombotic and proinflammatory responses is essential to restore homeostasis. Platelets play a crucial part in the integration of thrombosis and inflammation. Their role as participants in the resolution of thromboinflammation is underappreciated; therefore we used pharmacological and genetic approaches, coupled with murine and clinical samples, to uncover key concepts underlying this role.

Methods:

Middle cerebral artery occlusion with reperfusion was performed in wild-type or annexin A1 (AnxA1) knockout (AnxA1^−/−) mice. Fluorescence intravital microscopy was used to visualize cellular trafficking and to monitor light/dye–induced thrombosis. The mice were treated with vehicle, AnxA1 (3.3 mg/kg), WRW4 (1.8 mg/kg), or all 3, and the effect of AnxA1 was determined in vivo and in vitro.

Results:

Intravital microscopy revealed heightened platelet adherence and aggregate formation post I/RI, which were further exacerbated in AnxA1^−/− mice. AnxA1 administration regulated platelet function directly (eg, via reducing thromboxane B₂ and modulating phosphatidylserine expression) to promote cerebral protection post-I/RI and act as an effective preventative strategy for stroke by reducing platelet activation, aggregate formation, and cerebral thrombosis, a prerequisite for ischemic stroke. To translate these findings into a clinical setting, we show that AnxA1 plasma levels are reduced in human and murine stroke and that AnxA1 is able to act on human platelets, suppressing classic thrombin-induced inside-out signaling events (eg, Akt activation, intracellular calcium release, and Ras-associated protein 1 [Rap1] expression) to decrease α_IIbβ₃ activation without altering its surface expression. AnxA1 also selectively modifies cell surface determinants (eg, phosphatidylserine) to promote platelet phagocytosis by neutrophils, thereby driving active resolution. (n=5–13 mice/group or 7–10 humans/group.)

Conclusions:

AnxA1 affords protection by altering the platelet phenotype in cerebral I/RI from propathogenic to regulatory and reducing the propensity for platelets to aggregate and cause thrombosis by affecting integrin (α_IIbβ₃) activation, a previously unknown phenomenon. Thus, our data reveal a novel multifaceted role for AnxA1 to act both as a therapeutic and a prophylactic drug via its ability to promote endogenous proresolving, antithromboinflammatory circuits in cerebral I/RI. Collectively, these results further advance our knowledge and understanding in the field of platelet and resolution biology.

Neurotoxic effects of MPTP on mouse cerebral cortex: Modulation of neuroinflammation as a neuroprotective strategy

Parkinson's disease (PD) is a progressive neurological disorder, mainly characterized by the progressive loss of dopaminergic neurons in the Substantia nigra pars compacta (SNpc) and by the presence of intracellular inclusions, known as Lewy bodies. Despite SNpc being considered the primary affected region in PD, the neuropathological features are confined solely to the nigro-striatal axis. With disease progression other brain regions are also affected, namely the cerebral cortex, although the spreading of the neurologic damage to this region is still not completely unraveled. Tauroursodeoxycholic acid (TUDCA) is an endogenous bile acid that has been shown to have antioxidant properties and to exhibit a neuroprotective effect in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mice model of PD. Moreover, TUDCA anti-inflammatory properties have been reported in glial cells, making it a prominent therapeutic agent in PD. Here, we used C57BL/6 mice injected with MPTP in a sub-acute paradigm aiming to investigate if the neurotoxic effects of MPTP could be extended to the cerebral cortex. In parallel, we evaluated the anti-oxidant, neuroprotective and anti-inflammatory effects of TUDCA. The anti-inflammatory mechanisms elicited by TUDCA were further dissected in microglia cells. Our results show that MPTP leads to a decrease of ATP and activated AMP-activated protein kinase levels in mice cortex, and to a transient increase in the expression of antioxidant downstream targets of nuclear factor erythroid 2 related factor 2 (Nrf-2), and parkin. Notably, MPTP increases pro-inflammatory markers, while down-regulating the expression of the anti-inflammatory protein Annexin-A1 (ANXA1). Importantly, we show that TUDCA treatment prevents the deleterious effects of MPTP, sustains increased levels of antioxidant enzymes and parkin, and most of all negatively modulates neuroinflammation and up-regulates ANXA1 expression. Additionally, results from cellular models using microglia corroborate TUDCA modulation of ANXA1 synthesis, linking inhibition of neuroinflammation and neuroprotection by TUDCA.

Annexin A1-derived peptide Ac2-26 in a pilocarpine-induced status epilepticus model: anti-inflammatory and neuroprotective effects

Background

The inflammatory process has been described as a crucial mechanism in the pathophysiology of temporal lobe epilepsy. The anti-inflammatory protein annexin A1 (ANXA1) represents an interesting target in the regulation of neuroinflammation through the inhibition of leukocyte transmigration and the release of proinflammatory mediators. In this study, the role of the ANXA1-derived peptide Ac_2-26 in an experimental model of status epilepticus (SE) was evaluated.

Methods

Male Wistar rats were divided into Naive, Sham, SE and SE+Ac_2-26 groups, and SE was induced by intrahippocampal injection of pilocarpine. In Sham animals, saline was applied into the hippocampus, and Naive rats were only handled. Three doses of Ac_2-26 (1 mg/kg) were administered intraperitoneally (i.p.) after 2, 8 and 14 h of SE induction. Finally, 24 h after the experiment-onset, rats were euthanized for analyses of neuronal lesion and inflammation.

Results

Pilocarpine induced generalised SE in all animals, causing neuronal damage, and systemic treatment with Ac_2-26 decreased neuronal degeneration and albumin levels in the hippocampus. Also, both SE groups showed an intense influx of microglia, which was corroborated by high levels of ionised calcium binding adaptor molecule 1(Iba-1) and monocyte chemoattractant protein-1 (MCP-1) in the hippocampus. Ac_2-26 reduced the astrocyte marker (glial fibrillary acidic protein; GFAP) levels, as well as interleukin-1β (IL-1β), interleukin-6 (IL-6) and growth-regulated alpha protein (GRO/KC). These effects of the peptide were associated with the modulation of the levels of formyl peptide receptor 2, a G-protein-coupled receptor that binds to Ac_2-26, and the phosphorylated extracellular signal-regulated kinase (ERK) in the hippocampal neurons.

Conclusions

The data suggest a neuroprotective effect of Ac_2-26 in the epileptogenic processes through downregulation of inflammatory mediators and neuronal loss.

Annexin A1 as Neuroprotective Determinant for Blood-Brain Barrier Integrity in Neonatal Hypoxic-Ischemic Encephalopathy

Blood-brain barrier (BBB) disruption is associated with hypoxia-ischemia (HI) induced brain injury and life-long neurological pathologies. Treatment options are limited. Recently, we found that mesenchymal stem/stromal cell derived extracellular vesicles (MSC-EVs) protected the brain in ovine fetuses exposed to HI. We hypothesized that Annexin A1 (ANXA1), present in MSC-EVs, contributed to their therapeutic potential by targeting the ANXA1/Formyl peptide receptor (FPR), thereby preventing loss of the BBB integrity. Cerebral ANXA1 expression and leakage of albumin into the fetal ovine brain parenchyma after HI were analyzed by immunohistochemistry. For mechanistic insights, barrier integrity of primary fetal endothelial cells was assessed after oxygen-glucose deprivation (OGD) followed by treatment with MSC-EVs or human recombinant ANXA1 in the presence or absence of FPR inhibitors. Our study revealed that BBB integrity was compromised after HI which was improved by MSC-EVs containing ANXA1. Treatment with these MSC-EVs or ANXA1 improved BBB integrity after OGD, an effect abolished by FPR inhibitors. Furthermore, endogenous ANXA1 was depleted within 24 h after induction of HI in cerebovasculature and ependyma and upregulated 72 h after HI in microglia. Targeting ANXA1/FPR with ANXA1 in the immature brain has great potential in preventing BBB loss and concomitant brain injury following HI.

Estrogen Promotes Pro-resolving Microglial Behavior and Phagocytic Cell Clearance Through the Actions of Annexin A1

Local production of estrogen rapidly follows brain tissue injury, but the role this hormone plays in regulating the response to neural damage or in the modulation of mediators regulating inflammation is in many ways unclear. Using the murine BV2 microglia model as well as primary microglia from wild-type and annexin A1 (AnxA1) null mice, we have identified two related mechanisms whereby estradiol can modulate microglial behavior in a receptor specific fashion. Firstly, estradiol, via estrogen receptor β (ERβ), enhanced the phagocytic clearance of apoptotic cells, acting through increased production and release of the protein AnxA1. Secondly, stimulation of either ERβ or the G protein coupled estrogen receptor GPER promoted the adoption of an anti-inflammatory/pro-resolving phenotype, an action similarly mediated through AnxA1. Together, these data suggest the hypothesis that locally produced estrogen acts through AnxA1 to exert powerful pro-resolving actions, controlling and limiting brain inflammation and ultimately protecting this highly vulnerable organ. Given the high degree of receptor selectivity in evoking these responses, we suggest that the use of selective estrogen receptor ligands may hold therapeutic promise in the treatment of neuroinflammation, avoiding unwanted generalized effects.

Inflammatory molecules might become both biomarkers and therapeutic targets for stroke management

Stroke is the fifth leading cause of death and the most frequent cause of disability worldwide. Currently, stroke diagnosis is based on neuroimaging; therefore, the lack of a rapid tool to diagnose stroke is still a major concern. In addition, therapeutic approaches to combat ischemic stroke are still scarce, since the only approved therapies are directed toward restoring blood flow to the affected brain area. However, due to the reduced time window during which these therapies are effective, few patients benefit from them; therefore, alternative treatments are urgently needed to reduce stroke brain damage in order to improve patients' outcome. The inflammatory response triggered after the ischemic event plays an important role in the progression of stroke; consequently, the study of inflammatory molecules in the acute phase of stroke has attracted increasing interest in recent decades. Here, we provide an overview of the inflammatory processes occurring during ischemic stroke, as well as the potential for these inflammatory molecules to become stroke biomarkers and the possibility that these candidates will become interesting neuroprotective therapeutic targets to be blocked or stimulated in order to modulate inflammation after stroke.

Annexins in Translational Research: Hidden Treasures to Be Found

The vertebrate annexin superfamily (AnxA) consists of 12 members of a calcium (Ca²⁺) and phospholipid binding protein family which share a high structural homology. In keeping with this hallmark feature, annexins have been implicated in the Ca²⁺-controlled regulation of a broad range of membrane events. In this review, we identify and discuss several themes of annexin actions that hold a potential therapeutic value, namely, the regulation of the immune response and the control of tissue homeostasis, and that repeatedly surface in the annexin activity profile. Our aim is to identify and discuss those annexin properties which might be exploited from a translational science and specifically, a clinical point of view.

S100A11 protects against neuronal cell apoptosis induced by cerebral ischemia via inhibiting the nuclear translocation of annexin A1

The subcellular location of annexin A1 (ANXA1) determines the ultimate fate of neurons after ischemic stroke. ANXA1 nuclear translocation is involved in neuronal apoptosis after cerebral ischemia, and extracellular ANXA1 is also associated with regulation of inflammatory responses. As the factors and mechanism that influence ANXA1 subcellular translocation remain unclear, studies aiming to determine and clarify the role of ANXA1 as a cell fate ‘regulator’ within cells are critically needed. In this study, we found that intracerebroventricular injection of the recombinant adenovirus vector Ad-S100A11 (carrying S100A11) strongly improved cognitive function and induced robust neuroprotective effects after ischemic stroke in vivo. Furthermore, upregulation of S100A11 protected against neuronal apoptosis induced by oxygen-glucose deprivation and reoxygenation (OGD/R) in vitro. Surprisingly, S100A11 overexpression markedly decreased ANXA1 nuclear translocation and subsequently alleviated OGD/R-induced neuronal apoptosis. Notably, S100A11 exerted its neuroprotective effect by directly binding ANXA1. Importantly, S100A11 directly interacted with ANXA1 through the nuclear translocation signal (NTS) of ANXA1, which is essential for ANXA1 to import into the nucleus. Consistent with our previous studies, ANXA1 nuclear translocation after OGD/R promoted p53 transcriptional activity, induced mRNA expression of the pro-apoptotic Bid gene, and activated the caspase-3 apoptotic pathway, which was almost completely reversed by S100A11 overexpression. Thus, S100A11 protects against cell apoptosis by inhibiting OGD/R-induced ANXA1 nuclear translocation. This study provides a novel mechanism whereby S100A11 protects against neuronal cells apoptosis, suggesting the potential for a previously unidentified treatment strategy in minimizing apoptosis after ischemic stroke.

A novel cell-penetrating peptide protects against neuron apoptosis after cerebral ischemia by inhibiting the nuclear translocation of annexin A1

Nuclear translocation of annexin A1 (ANXA1) has recently been reported to participate in neuronal apoptosis after cerebral ischemia. Prevention of the nuclear translocation of ANXA1 should therefore inhibit neuronal apoptosis and protect against cerebral stroke. Here, we found that, in the repeat III domain of ANXA1, the amino-acid residues from R228 to F237 function as a unique nuclear translocation signal (NTS) and are required for nuclear translocation of ANXA1. Intriguingly, we synthesized a cell-penetrating peptide derived by conjugating the trans-activator of transcription (Tat) domain to the NTS sequence. This Tat-NTS peptide specifically blocked the interaction of ANXA1 with importin β and, consequently, the nuclear translocation of ANXA1 without affecting the nucleocytoplasmic shuttling of other proteins. The Tat-NTS peptide inhibited the transcriptional activity of p53, decreased Bid expression, suppressed activation of the caspase-3 apoptosis pathway and improved the survival of hippocampal neurons subjected to oxygen-glucose deprivation and reperfusion in vitro. Moreover, using a focal brain ischemia animal model, we showed that the Tat-NTS peptide could be efficiently infused into the ischemic hippocampus and cortex by unilateral intracerebroventricular injection. Injection of the Tat-NTS peptide alleviated neuronal apoptosis in the ischemic zone. Importantly, further work revealed that administration of the Tat-NTS peptide resulted in a dramatic reduction in infarct volume and that this was correlated with a parallel improvement in neurological function after reperfusion. Interestingly, the effects of Tat-NTS were injury specific, with little impact on neuronal apoptosis or cognitive function in sham-treated nonischemic animals. In conclusion, based on its profound neuroprotective and cognitive-preserving effects, it is suggested that the Tat-NTS peptide represents a novel and potentially promising new therapeutic candidate for the treatment of ischemic stroke.

Ac2-26 Induces IKKβ Degradation Through Chaperone-Mediated Autophagy Via HSPB1 in NCM-Treated Microglia

Annexin A1 (ANXA1) is an endogenous protein with potent anti-inflammatory properties in the brain. Although ANXA1 has been predominantly studied for its binding to formyl peptide receptors (FPRs) on plasma membranes, little is known regarding whether this protein has an anti-inflammatory effect in the cytosol. Here, we investigated the mechanism by which the ANXA1 peptide Ac2-26 decreases high TNF-α production and IKKβ activity, which was caused by oxygen glucose deprivation/reperfusion (OGD/R)-induced neuronal conditioned medium (NCM) in microglia. We found that exogenous Ac2-26 crosses into the cytoplasm of microglia and inhibits both gene expression and protein secretion of TNF-α. Ac2-26 also causes a decrease in IKKβ protein but not IKKβ mRNA, and this effect is inverted by lysosome inhibitor NH₄CL. Furthermore, we demonstrate that Ac2-26 induces IKKβ accumulation in lysosomes and that lysosomal-associated membrane protein 2A (LAMP-2A), not LC-3, is enhanced in microglia exposed to Ac2-26. We hypothesize that Ac2-26 mediates IKKβ degradation in lysosomes through chaperone-mediated autophagy (CMA). Interestingly, ANXA1 in the cytoplasm does not interact with IKKβ but with HSPB1, and Ac2-26 promotes HSPB1 binding to IKKβ. Furthermore, both ANXA1 and HSPB1 can interact with Hsc70 and LAMP-2A, but IKKβ only associates with LAMP-2A. Downregulation of HSPB1 or LAMP-2A reverses the degradation of IKKβ induced by Ac2-26. Taken together, these findings define an essential role of exogenous Ac2-26 in microglia and demonstrate that Ac2-26 is associated with HSPB1 and promotes HSPB1 binding to IKKβ, which is degraded by CMA, thereby reducing TNF-α expression.

Augmenting Endogenous Levels of Retinal Annexin A1 Suppresses Uveitis in Mice

PURPOSE

The purpose of this study was to examine the expression of the anti-inflammatory protein Annexin A1 (AnxA1) in mice and human retinae during uveitis and to determine whether local administration of human recombinant AnxA1 (hrAnxA1) can suppress uveitis in mice.

METHODS

Retinal sections from mice (healthy normal and uveitis) and postmortem human (no history of eye disease (n = 5) and uveitis (n = 7)) were stained for AnxA1 expression and imaged by immunofluorescence microscopy. AnxA1 cellular expression was determined by colabeling with CD45, glial fibrillary acidic protein (GFAP), and Iba-1 cells, with additional staining of AnxA1 receptors formyl peptide receptor 1 (FPR1) and FPRL1/FPR2. Mice with acute endotoxin-induced uveitis and chronic experimental autoimmune uveitis were treated locally by intravitreal injection with hrAnxA1, and disease was assessed by clinical scoring and quantification of leukocyte infiltrate via flow cytometry.

RESULTS

Constitutive expression of AnxA1 was observed in both healthy mouse and human retinae, and its expression increased during uveitis compared to healthy controls. AnxA1 colocalizes predominantly with CD45⁺ cells, GFAP⁺ macroglia, and to a lesser extent, Iba-1⁺ myeloid cells. We also demonstrate that local treatment with hrAnxA1 attenuates the severity of uveitis in mice.

CONCLUSIONS

These data indicate that locally expressed AnxA1 is elevated in the retina during intraocular inflammation. We demonstrate that local administration of hrAnxA1 to augment levels results in suppression of uveitis in mice.

TRANSLATIONAL RELEVANCE

Our data suggest that elevated expression of retinal AnxA1 in human uveitis may be immunoregulatory and that local supplementation with hrAnxA1 may provide a potential novel treatment for inflammatory eye diseases such as noninfectious uveitis.

Neuroprotective Effects of Annexin A1 Tripeptide after Deep Hypothermic Circulatory Arrest in Rats

Resolution agonists, including lipid mediators and peptides such as annexin A1 (ANXA1), are providing novel approaches to treat inflammatory conditions. Surgical trauma exerts a significant burden on the immune system that can affect and impair multiple organs. Perioperative cerebral injury after cardiac surgery is associated with significant adverse neurological outcomes such as delirium and postoperative cognitive dysfunction. Using a clinically relevant rat model of cardiopulmonary bypass (CPB) with deep hypothermic circulatory arrest (DHCA), we tested the pro-resolving effects of a novel bioactive ANXA1 tripeptide (ANXA1sp) on neuroinflammation and cognition. Male rats underwent 2 h CPB with 1 h DHCA at 18°C, and received vehicle or ANXA1sp followed by timed reperfusion up to postoperative day 7. Immortalized murine microglial cell line BV2 were treated with vehicle or ANXA1sp and subjected to 2 h oxygen-glucose deprivation followed by timed reoxygenation. Microglial activation, cell death, neuroinflammation, and NF-κB activation were assessed in tissue samples and cell cultures. Rats exposed to CPB and DHCA had evident neuroinflammation in various brain areas. However, in ANXA1sp-treated rats, microglial activation and cell death (apoptosis and necrosis) were reduced at 24 h and 7 days after surgery. This was associated with a reduction in key pro-inflammatory cytokines due to inhibition of NF-κB activation in the brain and systemically. Treated rats also had improved neurologic scores and shorter latency in the Morris water maze. In BV2 cells treated with ANXA1sp, similar protective effects were observed including decreased pro-inflammatory cytokines and cell death. Notably, we also found increased expression of ANXA1, which binds to NF-κB p65 and thereby inhibits its transcriptional activity. Our findings provide evidence that treatment with a novel pro-resolving ANXA1 tripeptide is neuroprotective after cardiac surgery in rats by attenuating neuroinflammation and may prevent postoperative neurologic complications.

Inhibition of Phosphodiesterase-4 during Pneumococcal Pneumonia Reduces Inflammation and Lung Injury in Mice

Pneumococcal pneumonia is a leading cause of mortality worldwide. The inflammatory response to bacteria is necessary to control infection, but it may also contribute to tissue damage. Phosphodiesterase-4 inhibitors, such as rolipram (ROL), effectively reduce inflammation. Here, we examined the impact of ROL in a pneumococcal pneumonia murine model. Mice were infected intranasally with 10(5)-10(6) CFU of Streptococcus pneumoniae, treated with ROL in a prophylactic or therapeutic schedule in combination, or not, with the antibiotic ceftriaxone. Inflammation and bacteria counts were assessed, and ex vivo phagocytosis assays were performed. ROL treatment during S. pneumoniae infection decreased neutrophil recruitment into lungs and airways and reduced lung injury. Prophylactic ROL treatment also decreased cytokine levels in the airways. Although modulation of inflammation by ROL ameliorated pneumonia, bacteria burden was not reduced. On the other hand, antibiotic therapy reduced bacteria without reducing neutrophil infiltration, cytokine level, or lung injury. Combined ROL and ceftriaxone treatment decreased lethality rates and was more efficient in reducing inflammation, by increasing proresolving protein annexin A1 (AnxA1) expression, and bacterial burden by enhancing phagocytosis. Lack of AnxA1 increased inflammation and lethality induced by pneumococcal infection. These data show that immunomodulatory effects of phosphodiesterase-4 inhibitors are useful during severe pneumococcal pneumonia and suggest their potential benefit as adjunctive therapy during infectious diseases.

Annexin A1 restores Aβ1-42 -induced blood-brain barrier disruption through the inhibition of RhoA-ROCK signaling pathway

The blood–brain barrier (BBB) is composed of brain capillary endothelial cells and has an important role in maintaining homeostasis of the brain separating the blood from the parenchyma of the central nervous system (CNS). It is widely known that disruption of the BBB occurs in various neurodegenerative diseases, including Alzheimer's disease (AD). Annexin A1 (ANXA1), an anti‐inflammatory messenger, is expressed in brain endothelial cells and regulates the BBB integrity. However, its role and mechanism for protecting BBB in AD have not been identified. We found that β‐Amyloid 1‐42 (Aβ42)‐induced BBB disruption was rescued by human recombinant ANXA1 (hrANXA1) in the murine brain endothelial cell line bEnd.3. Also, ANXA1 was decreased in the bEnd.3 cells, the capillaries of 5XFAD mice, and the human serum of patients with AD. To find out the mechanism by which ANXA1 recovers the BBB integrity in AD, the RhoA‐ROCK signaling pathway was examined in both Aβ42‐treated bEnd.3 cells and the capillaries of 5XFAD mice as RhoA was activated in both cases. RhoA inhibitors alleviated Aβ42‐induced BBB disruption and constitutively overexpressed RhoA‐GTP (active form of RhoA) attenuated the protective effect of ANXA1. When pericytes were cocultured with bEnd.3 cells, Aβ42‐induced RhoA activation of bEnd.3 cells was inhibited by the secretion of ANXA1 from pericytes. Taken together, our results suggest that ANXA1 restores Aβ42‐induced BBB disruption through inhibition of RhoA‐ROCK signaling pathway and we propose ANXA1 as a therapeutic reagent, protecting against the breakdown of the BBB in AD.

The restorative role of annexin A1 at the blood-brain barrier

Annexin A1 is a potent anti-inflammatory molecule that has been extensively studied in the peripheral immune system, but has not as yet been exploited as a therapeutic target/agent. In the last decade, we have undertaken the study of this molecule in the central nervous system (CNS), focusing particularly on the primary interface between the peripheral body and CNS: the blood-brain barrier. In this review, we provide an overview of the role of this molecule in the brain, with a particular emphasis on its functions in the endothelium of the blood-brain barrier, and the protective actions the molecule may exert in neuroinflammatory, neurovascular and metabolic disease. We focus on the possible new therapeutic avenues opened up by an increased understanding of the role of annexin A1 in the CNS vasculature, and its potential for repairing blood-brain barrier damage in disease and aging.

The anti-inflammatory Annexin A1 induces the clearance and degradation of the amyloid-β peptide

Background

The toxicity of amyloid-β (Aβ) peptide present in the brain of Alzheimer’s disease (AD) patients is thought to be mediated via the increased secretion of pro-inflammatory mediators, which can lead to neuronal dysfunction and cell death. In addition, we have previously shown that inflammation can affect Aβ generation. More recently, we have reported that in vitro administration of the anti-inflammatory mediator Annexin A1 (ANXA1) following an inflammatory challenge suppressed microglial activation and this effect was mediated through formyl peptide receptor-like 1 (FPRL1/FPR2) signalling. The aim of this study was to determine the potential role of ANXA1 in the generation and clearance of Aβ.

Methods

We first compared ANXA1 protein expression in the brains of AD patients and healthy controls as well as in the 5XFAD model of AD. To determine the role of ANXA1 in the processing of amyloid precursor protein (APP) and the degradation of Aβ, N2a neuroblastoma cells were treated with human recombinant ANXA1 or transfected with ANXA1 siRNA. We also investigated the effect of ANXA1 on Aβ phagocytosis and microglial activation in BV2 cells treated with synthetic Aβ.

Results

Our data show that ANXA1 is increased in the brains of AD patients and animal models of AD at early stages. ANXA1 was able to reduce the levels of Aβ by increasing its enzymatic degradation by neprilysin in N2a cells and to stimulate Aβ phagocytosis by microglia. These effects were mediated through FPRL1 receptors. In addition, ANXA1 inhibited the Aβ-stimulated secretion of inflammatory mediators by microglia.

Conclusions

These data suggest that ANXA1 plays a pivotal role in Aβ clearance and supports the use of ANXA1 as potential pharmacological tool for AD therapeutics.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0692-6) contains supplementary material, which is available to authorized users.

Nuclear translocation of annexin 1 following oxygen-glucose deprivation-reperfusion induces apoptosis by regulating Bid expression via p53 binding

Previous data have suggested that the nuclear translocation of annexin 1 (ANXA1) is involved in neuronal apoptosis after ischemic stroke. As the mechanism and function of ANXA1 nuclear migration remain unclear, it is important to clarify how ANXA1 performs its role as an apoptosis 'regulator' in the nucleus. Here we report that importazole (IPZ), an importin β (Impβ)-specific inhibitor, decreased ANXA1 nuclear accumulation and reduced the rate of neuronal death induced by nuclear ANXA1 migration after oxygen-glucose deprivation-reoxygenation (OGD/R). Notably, ANXA1 interacted with the Bid (BH3-interacting-domain death agonist) promoter directly; however; this interaction could be partially blocked by the p53 inhibitor pifithrin-α (PFT-α). Accordingly, ANXA1 was shown to interact with p53 in the nucleus and this interaction was enhanced following OGD/R. A luciferase reporter assay revealed that ANXA1 was involved in the regulation of p53-mediated transcriptional activation after OGD/R. Consistent with this finding, the nuclear translocation of ANXA1 after OGD/R upregulated the expression of Bid, which was impeded by IPZ, ANXA1 shRNA, or PFT-α. Finally, cell-survival testing demonstrated that silencing ANXA1 could improve the rate of cell survival and decrease the expression of both cleaved caspase-3 and cleaved poly(ADP-ribose) polymerase. These data suggested that Impβ-dependent nuclear ANXA1 migration participates in the OGD/R-dependent induction of neuronal apoptosis. ANXA1 interacts with p53 and promotes p53 transcriptional activity, which in turn regulates Bid expression. Silencing ANXA1 decreases the expression of Bid and suppresses caspase-3 pathway activation, thus improving cell survival after OGD/R. This study provides a novel mechanism whereby ANXA1 regulates apoptosis, suggesting the potential for a previously unidentified treatment strategy in minimizing apoptosis after OGD/R.

Factors controlling permeability of the blood-brain barrier

As the primary protective barrier for neurons in the brain, the blood-brain barrier (BBB) exists between the blood microcirculation system and the brain parenchyma. The normal BBB integrity is essential in protecting the brain from systemic toxins and maintaining the necessary level of nutrients and ions for neuronal function. This integrity is mediated by structural BBB components, such as tight junction proteins, integrins, annexins, and agrin, of a multicellular system including endothelial cells, astrocytes, pericytes, etc. BBB dysfunction is a significant contributor to the pathogeneses of a variety of brain disorders. Many signaling factors have been identified to be able to control BBB permeability through regulating the structural components. Among those signaling factors are inflammatory mediators, free radicals, vascular endothelial growth factor, matrix metalloproteinases, microRNAs, etc. In this review, we provide a summary of recent progress regarding these structural components and signaling factors, relating to their roles in various brain disorders. Attention is also devoted to recent research regarding impact of pharmacological agents such as isoflurane on BBB permeability and how iron ion passes across BBB. Hopefully, a better understanding of the factors controlling BBB permeability helps develop novel pharmacological interventions of BBB hyperpermeability under pathological conditions.

The Role and Effects of ANXA1 in Temporal Lobe Epilepsy: A Protection Mechanism?

Background

The endogenous protein annexin A1 (ANXA1) is an anti-inflammatory mediator in the brain that is thought to contribute to the progression of many neurological conditions. However, its exact role in temporal lobe epilepsy (TLE) remains unclear. We hypothesized that ANXA1 exerts negative actions on TLE by alleviating inflammatory damage in neurons. To identify the potential mechanism of TLE by assessing ANXA1 expression in TLE rats.

Material/Methods

TLE was induced in rats (n=70) via an intraperitoneal injection of lithium chloride (LiCl) and pilocarpine (PILO). The control group (n=10) received an injection of the equivalent amount of saline. ANXA1 expression was detected via immunohistochemistry and Western blotting.

Results

Successful establishment of the TLE model in rats resulted in epileptic seizures. ANXA1 was immunohistochemically detected as brownish yellow particles in the dentate gyrus and the CA1 region of the door zone; this expression was predominantly localized to the cytoplasm of glia rather than neurons. ANXA1 expression was stronger in TLE rats compared with the control group. ANXA1 expression in TLE was also assessed via Western blotting, and compared between groups at various time points. ANXA1 expression was significantly increased in the acute (the first 24 h) and chronic (after 1 month) phases (P<0.001) but significantly decreased during the recovery phase (72 h, 1 week, and 2 weeks) (P<0.001). These findings suggest that ANXA1 expression is correlated with TLE activity.

Conclusions

Our data suggest that ANXA1 plays an important role in TLE by alleviating inflammatory damage and protecting neurons.

Neuroinflammatory biomarkers: From stroke diagnosis and prognosis to therapy

Stroke is the third leading cause of death in industrialized countries and one of the largest causes of permanent disability worldwide. Therapeutic options to fight stroke are still limited and the only approved drug is tissue-plasminogen activator (tPA) and/or mechanical thrombectomy. Post-stroke inflammation is well known to contribute to the expansion of the ischemic lesion, whereas its resolution stimulates tissue repair and neuroregeneration processes. As inflammation highly influences susceptibility of stroke patients to overcome the disease, there is an increasing need to develop new diagnostic, prognostic and therapeutic strategies for post-stroke inflammation. This review provides a brief overview of the contribution of the inflammatory mechanisms to the pathophysiology of stroke. It specially focuses on the role of inflammatory biomarkers to help predicting stroke patients' outcome since some of those biomarkers might turn out to be targets to be therapeutically altered overcoming the urgent need for the identification of potent drugs to modulate stroke-associated inflammation. This article is part of a Special Issue entitled: Neuro Inflammation edited by Helga E. de Vries and Markus Schwaninger.