The Genomic Intersection of Oligodendrocyte Dynamics in Schizophrenia and Aging Unravels Novel Pathological Mechanisms and Therapeutic Potentials.

Schizophrenia is a significant worldwide health concern, affecting over 20 million individuals and contributing to a potential reduction in life expectancy by up to 14.5 years. Despite its profound impact, the precise pathological mechanisms underlying schizophrenia continue to remain enigmatic, with previous research yielding diverse and occasionally conflicting findings. Nonetheless, one consistently observed phenomenon in brain imaging studies of schizophrenia patients is the disruption of white matter, the bundles of myelinated axons that provide connectivity and rapid signalling between brain regions. Myelin is produced by specialised glial cells known as oligodendrocytes, which have been shown to be disrupted in post-mortem analyses of schizophrenia patients. Oligodendrocytes are generated throughout life by a major population of oligodendrocyte progenitor cells (OPC), which are essential for white matter health and plasticity. Notably, a decline in a specific subpopulation of OPC has been identified as a principal factor in oligodendrocyte disruption and white matter loss in the aging brain, suggesting this may also be a factor in schizophrenia. In this review, we analysed genomic databases to pinpoint intersections between aging and schizophrenia and identify shared mechanisms of white matter disruption and cognitive dysfunction.

The Phytochemical Agathisflavone Modulates miR146a and miR155 in Activated Microglia Involving STAT3 Signaling.

MicroRNAs (miRs) act as important post-transcriptional regulators of gene expression in glial cells and have been shown to be involved in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD). Here, we investigated the effects of agathisflavone, a biflavonoid purified from the leaves of Cenostigma pyramidale (Tul.), on modulating the expression of miRs and inflammatory mediators in activated microglia. C20 human microglia were exposed to oligomers of the ß-amyloid peptide (Aß, 500 nM) for 4 h or to lipopolysaccharide (LPS, 1 µg/mL) for 24 h and then treated or not with agathisflavone (1 µM) for 24 h. We observed that ß-amyloid and LPS activated microglia to an inflammatory state, with increased expression of miR-146a, miR-155, IL1-ß, IL-6, and NOS2. Treatment with agathisflavone resulted in a significant reduction in miR146a and miR-155 induced by LPS or Aß, as well as inflammatory cytokines IL1-ß, IL-6, and NOS2. In cells stimulated with Aß, there was an increase in p-STAT3 expression that was reduced by agathisflavone treatment. These data identify a role for miRs in the anti-inflammatory effect of agathisflavone on microglia in models of neuroinflammation and AD.

Astrocytes in human central nervous system diseases: a frontier for new therapies.

Astroglia are a broad class of neural parenchymal cells primarily dedicated to homoeostasis and defence of the central nervous system (CNS). Astroglia contribute to the pathophysiology of all neurological and neuropsychiatric disorders in ways that can be either beneficial or detrimental to disorder outcome. Pathophysiological changes in astroglia can be primary or secondary and can result in gain or loss of functions. Astroglia respond to external, non-cell autonomous signals associated with any form of CNS pathology by undergoing complex and variable changes in their structure, molecular expression, and function. In addition, internally driven, cell autonomous changes of astroglial innate properties can lead to CNS pathologies. Astroglial pathophysiology is complex, with different pathophysiological cell states and cell phenotypes that are context-specific and vary with disorder, disorder-stage, comorbidities, age, and sex. Here, we classify astroglial pathophysiology into (i) reactive astrogliosis, (ii) astroglial atrophy with loss of function, (iii) astroglial degeneration and death, and (iv) astrocytopathies characterised by aberrant forms that drive disease. We review astroglial pathophysiology across the spectrum of human CNS diseases and disorders, including neurotrauma, stroke, neuroinfection, autoimmune attack and epilepsy, as well as neurodevelopmental, neurodegenerative, metabolic and neuropsychiatric disorders. Characterising cellular and molecular mechanisms of astroglial pathophysiology represents a new frontier to identify novel therapeutic strategies.

Amburana cearensis seed extract stimulates astrocyte glutamate homeostatic mechanisms in hippocampal brain slices and protects oligodendrocytes against ischemia.

BACKGROUND: Stroke is a leading cause of death and disability worldwide. A major factor in brain damage following ischemia is excitotoxicity caused by elevated levels of the neurotransmitter glutamate. In the brain, glutamate homeostasis is a primary function of astrocytes. Amburana cearensis has long been used in folk medicine and seed extract obtained with dichloromethane (EDAC) have previously been shown to exhibit cytoprotective activity in vitro. The aim of the present study was to analyse the activity of EDAC in hippocampal brain slices. METHODS: We prepared a dichloromethane extract (EDAC) from A. cearensis seeds and characterized the chemical constituents by 1H and 13C-NMR. Hippocampal slices from P6-8 or P90 Wistar rats were used for cell viability assay or glutamate uptake test. Hippocampal slices from P10-12 transgenic mice SOX10-EGFP and GFAP-EGFP and immunofluorescence for GS, GLAST and GLT1 were used to study oligodendrocytes and astrocytes. RESULTS: Astrocytes play a critical role in glutamate homeostasis and we provide immunohistochemical evidence that in excitotoxicity EDAC increased expression of glutamate transporters and glutamine synthetase, which is essential for detoxifying glutamate. Next, we directly examined astrocytes using transgenic mice in which glial fibrillary acidic protein (GFAP) drives expression of enhanced green fluorescence protein (EGFP) and show that glutamate excitotoxicity caused a decrease in GFAP-EGFP and that EDAC protected against this loss. This was examined further in the oxygen-glucose deprivation (OGD) model of ischemia, where EDAC caused an increase in astrocytic process branching, resulting in an increase in GFAP-EGFP. Using SOX10-EGFP reporter mice, we show that the acute response of oligodendrocytes to OGD in hippocampal slices is a marked loss of their processes and EDAC protected oligodendrocytes against this damage. CONCLUSION: This study provides evidence that EDAC is cytoprotective against ischemia and glutamate excitotoxicity by modulating astrocyte responses and stimulating their glutamate homeostatic mechanisms.

The Flavonoid Agathisflavone Directs Brain Microglia/Macrophages to a Neuroprotective Anti-Inflammatory and Antioxidant State via Regulation of NLRP3 Inflammasome.

Agathisflavone, purified from Cenostigma pyramidale (Tul.) has been shown to be neuroprotective in in vitro models of glutamate-induced excitotoxicity and inflammatory damage. However, the potential role of microglial regulation by agathisflavone in these neuroprotective effects is unclear. Here we investigated the effects of agathisflavone in microglia submitted to inflammatory stimulus in view of elucidating mechanisms of neuroprotection. Microglia isolated from cortices of newborn Wistar rats were exposed to Escherichia coli lipopolysaccharide (LPS, 1 µg/mL) and treated or not with agathisflavone (1 µM). Neuronal PC12 cells were exposed to a conditioned medium from microglia (MCM) treated or not with agathisflavone. We observed that LPS induced microglia to assume an activated inflammatory state (increased CD68, more rounded/amoeboid phenotype). However, most microglia exposed to LPS and agathisflavone, presented an anti-inflammatory profile (increased CD206 and branched-phenotype), associated with the reduction in NO, GSH mRNA for NRLP3 inflammasome, IL1-ß, IL-6, IL-18, TNF, CCL5, and CCL2. Molecular docking also showed that agathisflavone bound at the NLRP3 NACTH inhibitory domain. Moreover, in PC12 cell cultures exposed to the MCM previously treated with the flavonoid most cells preserved neurites and increased expression of ß-tubulin III. Thus, these data reinforce the anti-inflammatory activity and the neuroprotective effect of agathisflavone, effects associated with the control of NLRP3 inflammasome, standing out it as a promising molecule for the treatment or prevention of neurodegenerative diseases.

Early biofilm and streamer formation is mediated by wall shear stress and surface wettability: A multifactorial microfluidic study.

Biofilms are intricate communities of microorganisms encapsulated within a self-produced matrix of extra-polymeric substances (EPS), creating complex three-dimensional structures allowing for liquid and nutrient transport through them. These aggregations offer constituent microorganisms enhanced protection from environmental stimuli-like fluid flow-and are also associated with higher resistance to antimicrobial compounds, providing a persistent cause of concern in numerous sectors like the marine (biofouling and aquaculture), medical (infections and antimicrobial resistance), dentistry (plaque on teeth), food safety, as well as causing energy loss and corrosion. Recent studies have demonstrated that biofilms interact with microplastics, often influencing their pathway to higher trophic levels. Previous research has shown that initial bacterial attachment is affected by surface properties. Using a microfluidic flow cell, we have investigated the relationship between both wall shear stress (τw ) and surface properties (surface wettability) upon biofilm formation of two species (Cobetia marina and Pseudomonas aeruginosa). We investigated biofilm development on low-density polyethylene (LDPE) membranes, Permanox® slides, and glass slides, using nucleic acid staining and end-point confocal laser scanning microscopy. The results show that flow conditions affect biomass, maximum thickness, and surface area of biofilms, with higher τw (5.6 Pa) resulting in thinner biofilms than lower τw (0.2 Pa). In addition, we observed differences in biofilm development across the surfaces tested, with LDPE typically demonstrating more overall biofilm in comparison to Permanox® and glass. Moreover, we demonstrate the formation of biofilm streamers under laminar flow conditions within straight micro-channels.

Targeting the Subventricular Zone to Promote Myelin Repair in the Aging Brain.

The subventricular zone (SVZ) is the largest and most active germinal zone in the adult forebrain. Neural stem cells (NSCs) of the SVZ generate olfactory interneurons throughout life and retain the intrinsic ability to generate oligodendrocytes (OLs), the myelinating cells of the central nervous system. OLs and myelin are targets in demyelinating diseases such as multiple sclerosis (MS). Remyelination is dependent on the ability of oligodendrocyte progenitor cells (OPCs) to proliferate, migrate, and terminally differentiate into myelinating OLs. During aging, there is a gradual decrease in the regenerative capacity of OPCs, and the consequent loss of OLs and myelin is a contributing factor in cognitive decline and the failure of remyelination in MS and other pathologies with aging contexts, including Alzheimer's disease (AD) and stroke. The age-related decrease in oligodendrogenesis has not been fully characterised but is known to reflect changes in intrinsic and environmental factors affecting the ability of OPCs to respond to pro-differentiation stimuli. Notably, SVZ-derived OPCs are an important source of remyelinating OLs in addition to parenchymal OPCs. In this mini-review, we briefly discuss differences between SVZ-derived and parenchymal OPCs in their responses to demyelination and highlight challenges associated with their study in vivo and how they can be targeted for regenerative therapies in the aged brain.

Epidermal Growth Factor Pathway in the Age-Related Decline of Oligodendrocyte Regeneration.

Oligodendrocytes (OLs) are specialized glial cells that myelinate CNS axons. OLs are generated throughout life from oligodendrocyte progenitor cells (OPCs) via a series of tightly controlled differentiation steps. Life-long myelination is essential for learning and to replace myelin lost in age-related pathologies such as Alzheimer's disease (AD) as well as white matter pathologies such as multiple sclerosis (MS). Notably, there is considerable myelin loss in the aging brain, which is accelerated in AD and underpins the failure of remyelination in secondary progressive MS. An important factor in age-related myelin loss is a marked decrease in the regenerative capacity of OPCs. In this review, we will contextualize recent advances in the key role of Epidermal Growth Factor (EGF) signaling in regulating multiple biological pathways in oligodendroglia that are dysregulated in aging.

Agathisflavone as a Single Therapy or in Association With Mesenchymal Stem Cells Improves Tissue Repair in a Spinal Cord Injury Model in Rats.

Agathisflavone is a flavonoid with anti-neuroinflammatory and myelinogenic properties, being also capable to induce neurogenesis. This study evaluated the therapeutic effects of agathisflavone-both as a pharmacological therapy administered in vivo and as an in vitro pre-treatment aiming to enhance rat mesenchymal stem cells (r)MSCs properties-in a rat model of acute spinal cord injury (SCI). Adult male Wistar rats (n = 6/group) underwent acute SCI with an F-2 Fogarty catheter and after 4 h were treated daily with agathisflavone (10 mg/kg ip, for 7 days), or administered with a single i.v. dose of 1 × 106 rMSCs either unstimulated cells (control) or pretreated with agathisflavone (1 µM, every 2 days, for 21 days in vitro). Control rats (n = 6/group) were treated with a single dose methylprednisolone (MP, 60 mg/kg ip). BBB scale was used to evaluate the motor functions of the animals; after 7 days of treatment, the SCI area was analyzed after H&E staining, and RT-qPCR was performed to analyze the expression of neurotrophins and arginase. Treatment with agathisflavone alone or with of 21-day agathisflavone-treated rMSCs was able to protect the injured spinal cord tissue, being associated with increased expression of NGF, GDNF and arginase, and reduced macrophage infiltrate. In addition, treatment of animals with agathisflavone alone was able to protect injured spinal cord tissue and to increase expression of neurotrophins, modulating the inflammatory response. These results support a pro-regenerative effect of agathisflavone that holds developmental potential for clinical applications in the future.

Agathisflavone Modifies Microglial Activation State and Myelination in Organotypic Cerebellar Slices Culture.

Oligodendrocytes produce the myelin that is critical for rapid neuronal transmission in the central nervous system (CNS). Disruption of myelin has devastating effects on CNS function, as in the demyelinating disease multiple sclerosis (MS). Microglia are the endogenous immune cells of the CNS and play a central role in demyelination and repair. There is a need for new potential therapies that regulate myelination and microglia to promote repair. Agathisflavone (FAB) is a non-toxic flavonoid that is known for its anti-inflammatory and neuroprotective properties. Here, we examined the effects of FAB (5-50 µM) on myelination and microglia in organotypic cerebellar slices prepared from P10-P12 Sox10-EGFP and Plp1-DsRed transgenic mice. Immunofluorescence labeling for myelin basic protein (MBP) and neurofilament (NF) demonstrates that FAB significantly increased the proportion of MBP + /NF + axons but did not affect the overall number of oligodendroglia or axons, or the expression of oligodendroglial proteins CNPase and MBP. FAB is known to be a phytoestrogen, but blockade of α- or ß- estrogen receptors (ER) indicated the myelination promoting effects of FAB were not mediated by ER. Examination of microglial responses by Iba1 immunohistochemistry demonstrated that FAB markedly altered microglial morphology, characterized by smaller somata and reduced branching of their processes, consistent with a decreased state of activation, and increased Iba1 protein expression. The results provide evidence that FAB increases the extent of axonal coverage by MBP immunopositive oligodendroglial processes and has a modulatory effect upon microglial cells, which are important therapeutic strategies in multiple neuropathologies.

Astrocytes in Bipolar Disorder.

Bipolar disorder (BD) is a complex group of neuropsychiatric disorders, typically comprising both manic and depressive episodes. The underlying neuropathology of BD is not established, but a consistent feature is progressive thinning of cortical grey matter (GM) and white matter (WM) in specific pathways, due to loss of subpopulations of neurons and astrocytes, with accompanying disturbance of connectivity. Dysregulation of astrocyte homeostatic functions are implicated in BD, notably regulation of glutamate, calcium signalling, circadian rhythms and metabolism. Furthermore, the beneficial therapeutic effects of the frontline treatments for BD are due at least in part to their positive actions on astrocytes, notably lithium, valproic acid (VPA) and carbamazepine (CBZ), as well as antidepressants and antipsychotics that are used in the management of this disorder. Treatments for BD are ineffective in a large proportion of cases, and astrocytes represent new therapeutic targets that can also serve as biomarkers of illness progression and treatment responsiveness in BD.

The synaptic blocker botulinum toxin A decreases the density and complexity of oligodendrocyte precursor cells in the adult mouse hippocampus.

Oligodendrocyte progenitor cells (OPCs) are responsible for generating oligodendrocytes, the myelinating cells of the CNS. Life-long myelination is promoted by neuronal activity and is essential for neural network plasticity and learning. OPCs are known to contact synapses and it is proposed that neuronal synaptic activity in turn regulates their behavior. To examine this in the adult, we performed unilateral injection of the synaptic blocker botulinum neurotoxin A (BoNT/A) into the hippocampus of adult mice. We confirm BoNT/A cleaves SNAP-25 in the CA1 are of the hippocampus, which has been proven to block neurotransmission. Notably, BoNT/A significantly decreased OPC density and caused their shrinkage, as determined by immunolabeling for the OPC marker NG2. Furthermore, BoNT/A resulted in an overall decrease in the number of OPC processes, as well as a decrease in their lengths and branching frequency. These data indicate that synaptic activity is important for maintaining adult OPC numbers and cellular integrity, which is relevant to pathophysiological scenarios characterized by dysregulation of synaptic activity, such as age-related cognitive decline, Multiple Sclerosis and Alzheimer's disease.

Functional genomic analyses highlight a shift in Gpr17-regulated cellular processes in oligodendrocyte progenitor cells and underlying myelin dysregulation in the aged mouse cerebrum.

Brain ageing is characterised by a decline in neuronal function and associated cognitive deficits. There is increasing evidence that myelin disruption is an important factor that contributes to the age-related loss of brain plasticity and repair responses. In the brain, myelin is produced by oligodendrocytes, which are generated throughout life by oligodendrocyte progenitor cells (OPCs). Currently, a leading hypothesis points to ageing as a major reason for the ultimate breakdown of remyelination in Multiple Sclerosis (MS). However, an incomplete understanding of the cellular and molecular processes underlying brain ageing hinders the development of regenerative strategies. Here, our combined systems biology and neurobiological approach demonstrate that oligodendroglial and myelin genes are amongst the most altered in the ageing mouse cerebrum. This was underscored by the identification of causal links between signalling pathways and their downstream transcriptional networks that define oligodendroglial disruption in ageing. The results highlighted that the G-protein coupled receptor Gpr17 is central to the disruption of OPCs in ageing and this was confirmed by genetic fate-mapping and cellular analyses. Finally, we used systems biology strategies to identify therapeutic agents that rejuvenate OPCs and restore myelination in age-related neuropathological contexts.

Keeping the ageing brain wired: a role for purine signalling in regulating cellular metabolism in oligodendrocyte progenitors.

White matter (WM) is a highly prominent feature in the human cerebrum and is comprised of bundles of myelinated axons that form the connectome of the brain. Myelin is formed by oligodendrocytes and is essential for rapid neuronal electrical communication that underlies the massive computing power of the human brain. Oligodendrocytes are generated throughout life by oligodendrocyte precursor cells (OPCs), which are identified by expression of the chondroitin sulphate proteoglycan NG2 (Cspg4), and are often termed NG2-glia. Adult NG2+ OPCs are slowly proliferating cells that have the stem cell-like property of self-renewal and differentiation into a pool of 'late OPCs' or 'differentiation committed' OPCs(COPs) identified by specific expression of the G-protein-coupled receptor GPR17, which are capable of differentiation into myelinating oligodendrocytes. In the adult brain, these reservoirs of OPCs and COPs ensure rapid myelination of new neuronal connections formed in response to neuronal signalling, which underpins learning and cognitive function. However, there is an age-related decline in myelination that is associated with a loss of neuronal function and cognitive decline. The underlying causes of myelin loss in ageing are manifold, but a key factor is the decay in OPC 'stemness' and a decline in their replenishment of COPs, which results in the ultimate failure of myelin regeneration. These changes in ageing OPCs are underpinned by dysregulation of neuronal signalling and OPC metabolic function. Here, we highlight the role of purine signalling in regulating OPC self-renewal and the potential importance of GPR17 and the P2X7 receptor subtype in age-related changes in OPC metabolism. Moreover, age is the main factor in the failure of myelination in chronic multiple sclerosis and myelin loss in Alzheimer's disease, hence understanding the importance of purine signalling in OPC regeneration and myelination is critical for developing new strategies for promoting repair in age-dependent neuropathology.

Reactive astrocyte nomenclature, definitions, and future directions.

Reactive astrocytes are astrocytes undergoing morphological, molecular, and functional remodeling in response to injury, disease, or infection of the CNS. Although this remodeling was first described over a century ago, uncertainties and controversies remain regarding the contribution of reactive astrocytes to CNS diseases, repair, and aging. It is also unclear whether fixed categories of reactive astrocytes exist and, if so, how to identify them. We point out the shortcomings of binary divisions of reactive astrocytes into good-vs-bad, neurotoxic-vs-neuroprotective or A1-vs-A2. We advocate, instead, that research on reactive astrocytes include assessment of multiple molecular and functional parameters-preferably in vivo-plus multivariate statistics and determination of impact on pathological hallmarks in relevant models. These guidelines may spur the discovery of astrocyte-based biomarkers as well as astrocyte-targeting therapies that abrogate detrimental actions of reactive astrocytes, potentiate their neuro- and glioprotective actions, and restore or augment their homeostatic, modulatory, and defensive functions.

Accelerated Dystrophy and Decay of Oligodendrocyte Precursor Cells in the APP/PS1 Model of Alzheimer's-Like Pathology.

Myelin disruption is a feature of natural aging and Alzheimer's disease (AD). In the CNS, myelin is produced by oligodendrocytes, which are generated throughout life by oligodendrocyte progenitor cells (OPCs). Here, we examined age-related changes in OPCs in APP/PS1 mice, a model for AD-like pathology, compared with non-transgenic (Tg) age-matched controls. The analysis was performed in the CA1 area of the hippocampus following immunolabeling for NG2 with the nuclear dye Hoescht, to identify OPC and OPC sister cells, a measure of OPC replication. The results indicate a significant decrease in the number of OPCs at 9 months in APP/PS1 mice, compared to age-matched controls, without further decline at 14 months. Also, the number of OPC sister cells declined significantly at 14 months in APP/PS1 mice, which was not observed in age-matched controls. Notably, OPCs also displayed marked morphological changes at 14 months in APP/PS1 mice, characterized by an overall shrinkage of OPC process domains and increased process branching. The results indicate that OPC disruption is a pathological sign in the APP/PS1 mouse model of AD.