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Frontiers in Cellular Neuroscience 2024Intracellular Ca-signaling in astrocytes is instrumental for their brain "housekeeping" role and astroglial control of synaptic plasticity. An important source for...
Intracellular Ca-signaling in astrocytes is instrumental for their brain "housekeeping" role and astroglial control of synaptic plasticity. An important source for elevating the cytosolic Ca level in astrocytes is a release from endoplasmic reticulum which can be triggered via two fundamental pathways: IP3 receptors and calcium-induced calcium release (CICR) mediated by Ca-sensitive ryanodine receptors (RyRs). While the physiological role for glial IP3 became a focus of intensive research and debate, ryanodine receptors received much less attention. We explored the role for ryanodine receptors in the modulation of cytosolic Ca-signaling in the cortical and hippocampal astrocytes, astrocyte-neuron communication and astroglia modulation of synaptic plasticity. Our data show that RyR-mediated Ca-induced Ca-release from ER brings substantial contribution into signaling in the functional microdomains hippocampal and neocortical astrocytes. Furthermore, RyR-mediated CICR activated the release of ATP and glutamate from hippocampal and neocortical astrocytes which, in turn, elicited transient purinergic and tonic glutamatergic currents in the neighboring pyramidal neurons. The CICR-facilitated release of ATP and glutamate was inhibited after intracellular perfusion of astrocytes with ryanodine and BAPTA and in the transgenic dnSNARE mice with impaired astroglial exocytosis. We also found out that RyR-mediated amplification of astrocytic Ca-signaling enhanced the long-term synaptic potentiation in the hippocampus and neocortex of aged mice. Combined, our data demonstrate that ryanodine receptors are essential for astrocytic Ca-signaling and efficient astrocyte-neuron communications. The RyR-mediated CICR contributes to astrocytic control of synaptic plasticity and can underlie, at least partially, neuroprotective and cognitive effects of caffein.
PubMed: 38812795
DOI: 10.3389/fncel.2024.1382010 -
Frontiers in Cellular Neuroscience 2024Multiple sclerosis (MS) is an inflammatory and demyelinating disease of the central nervous system (CNS). Current therapies primarily target the inflammatory component...
INTRODUCTION
Multiple sclerosis (MS) is an inflammatory and demyelinating disease of the central nervous system (CNS). Current therapies primarily target the inflammatory component of the disease and are highly effective in early stages of MS while limited therapies have an effect in the more chronic progressive stages of MS where resident glia have a larger role. MS lesions tend to be inflammatory even after the initial peripheral immune cell invasion has subsided and this inflammation is known to cause alternative splicing events.
METHODS
We used qPCR of normal-appearing white matter and white matter lesions from postmortem MS tissue, studies, and immunostaining in MS tissue to investigate the alternative splicing of one gene known to be important during recovery in an animal model of MS, .
RESULTS
We found a novel, intron-retained isoform which has not been annotated, upregulated specifically in MS patient white matter lesions. We found that this novel isoform activates the nonsense-mediated decay pathway in primary human astrocytes, the most populous glial cell in the CNS, and is then degraded. Overexpression of this isoform in astrocytes leads to an increased number of processing bodies , the primary site of mRNA decay. Finally, we demonstrated that MS white matter lesions have a higher burden of processing bodies compared to normal-appearing white matter, predominantly in GFAP-positive astrocytes.
DISCUSSION
The increase in alternative splicing of the gene, the stress that this alternative splicing causes, and the observation that processing bodies are increased in white matter lesions suggests that the lesion microenvironment may lead to increased alternative splicing of many genes. This alternative splicing may blunt the protective or reparative responses of resident glia in and around white matter lesions in MS patients.
PubMed: 38812791
DOI: 10.3389/fncel.2024.1379261 -
Breast cancer cell-secreted miR-199b-5p hijacks neurometabolic coupling to promote brain metastasis.Nature Communications May 2024Breast cancer metastasis to the brain is a clinical challenge rising in prevalence. However, the underlying mechanisms, especially how cancer cells adapt a distant brain...
Breast cancer metastasis to the brain is a clinical challenge rising in prevalence. However, the underlying mechanisms, especially how cancer cells adapt a distant brain niche to facilitate colonization, remain poorly understood. A unique metabolic feature of the brain is the coupling between neurons and astrocytes through glutamate, glutamine, and lactate. Here we show that extracellular vesicles from breast cancer cells with a high potential to develop brain metastases carry high levels of miR-199b-5p, which shows higher levels in the blood of breast cancer patients with brain metastases comparing to those with metastatic cancer in other organs. miR-199b-5p targets solute carrier transporters (SLC1A2/EAAT2 in astrocytes and SLC38A2/SNAT2 and SLC16A7/MCT2 in neurons) to hijack the neuron-astrocyte metabolic coupling, leading to extracellular retention of these metabolites and promoting cancer cell growth. Our findings reveal a mechanism through which cancer cells of a non-brain origin reprogram neural metabolism to fuel brain metastases.
Topics: Humans; MicroRNAs; Breast Neoplasms; Brain Neoplasms; Female; Animals; Cell Line, Tumor; Astrocytes; Neurons; Mice; Excitatory Amino Acid Transporter 2; Extracellular Vesicles; Monocarboxylic Acid Transporters; Gene Expression Regulation, Neoplastic; Glutamic Acid; Glutamine; Brain; Lactic Acid; Cell Proliferation
PubMed: 38811525
DOI: 10.1038/s41467-024-48740-0 -
Neurology(R) Neuroimmunology &... Jul 2024New-onset refractory status epilepticus (NORSE) occurs in previously healthy children or adults, often followed by refractory epilepsy and poor outcomes. The mechanisms...
BACKGROUND AND OBJECTIVES
New-onset refractory status epilepticus (NORSE) occurs in previously healthy children or adults, often followed by refractory epilepsy and poor outcomes. The mechanisms that transform a normal brain into an epileptic one capable of seizing for prolonged periods despite treatment remain unclear. Nonetheless, several pieces of evidence suggest that immune dysregulation could contribute to hyperexcitability and modulate NORSE sequelae.
METHODS
We used single-nucleus RNA sequencing to delineate the composition and phenotypic states of the CNS of 4 patients with NORSE, to better understand the relationship between hyperexcitability and immune disturbances. We compared them with 4 patients with chronic temporal lobe epilepsy (TLE) and 2 controls with no known neurologic disorder.
RESULTS
Patients with NORSE and TLE exhibited a significantly higher proportion of excitatory neurons compared with controls, with no discernible difference in inhibitory GABAergic neurons. When examining the ratio between excitatory neurons and GABAergic neurons for each patient individually, we observed a higher ratio in patients with acute NORSE or TLE compared with controls. Furthermore, a negative correlation was found between the ratio of excitatory to GABAergic neurons and the proportion of GABAergic neurons. The ratio between excitatory neurons and GABAergic neurons correlated with the proportion of resident or infiltrating macrophages, suggesting the influence of microglial reactivity on neuronal excitability. Both patients with NORSE and TLE exhibited increased expression of genes associated with microglia activation, phagocytic activity, and NLRP3 inflammasome activation. However, patients with NORSE had decreased expression of genes related to the downregulation of the inflammatory response, potentially explaining the severity of their presentation. Microglial activation in patients with NORSE also correlated with astrocyte reactivity, possibly leading to higher degrees of demyelination.
DISCUSSION
Our study sheds light on the complex cellular dynamics in NORSE, revealing the potential roles of microglia, infiltrating macrophages, and astrocytes in hyperexcitability and demyelination, offering potential avenues for future research targeting the identified pathways.
Topics: Humans; Status Epilepticus; Male; Female; Adult; Drug Resistant Epilepsy; Single-Cell Analysis; Brain; Transcriptome; Epilepsy, Temporal Lobe; Young Adult; Child; Middle Aged; Adolescent; GABAergic Neurons; Gene Expression Profiling; Microglia
PubMed: 38810181
DOI: 10.1212/NXI.0000000000200259 -
Neural Regeneration Research Dec 2024
PubMed: 38808980
DOI: 10.4103/NRR.NRR-D-23-01705 -
Journal of Biomedical Research Feb 2024Intracranial hemorrhage (ICH) causes numerous neurological deficits and deaths worldwide each year, leaving a significant health burden on the public. The...
Intracranial hemorrhage (ICH) causes numerous neurological deficits and deaths worldwide each year, leaving a significant health burden on the public. The pathophysiology of ICH is complicated, and involves both primary and secondary injury. Hematoma, as the prime pathology of ICH, undergoes metabolism and triggers biochemical and biomechanical alterations in the brain, leading to secondary injury. Past endeavors mainly aimed at biochemical-initiated mechanisms for causing secondary injury have made limited progress in recent years, although ICH itself is also highly biomechanics-related. The discovery of the mechanical-activated cation channel Piezo1 provides a new avenue to further explore underlying mechanisms of secondary injury. The current article reviews the structure and gating mechanisms of Piezo1, its roles in the physiology/pathophysiology of neurons, astrocytes, microglia, and bone-marrow-derived macrophages, and especially its roles in erythrocytic turnover and iron metabolism, revealing a potential interplay between the biomechanics and biochemistry of hematoma in ICH. Collectively, these advances provide deeper insights into the secondary injury of ICH and lay the foundations for future research.
PubMed: 38808569
DOI: 10.7555/JBR.37.20230241 -
Frontiers in Cellular and Infection... 2024While astrocytes participate in the CNS innate immunity against herpes simplex virus type 1 (HSV-1) infection, they are the major target for the virus. Therefore, it is...
INTRODUCTION
While astrocytes participate in the CNS innate immunity against herpes simplex virus type 1 (HSV-1) infection, they are the major target for the virus. Therefore, it is of importance to understand the interplay between the astrocyte-mediated immunity and HSV-1 infection.
METHODS
Both primary human astrocytes and the astrocyte line (U373) were used in this study. RT-qPCR and Western blot assay were used to measure IFNs, the antiviral IFN-stimulated genes (ISGs), IFN regulatory factors (IRFs) and HSV-1 DNA. IRF1 knockout or knockdown was performed with CRISPR/Cas9 and siRNA transfection techniques.
RESULTS
Poly(dA:dT) could inhibit HSV-1 replication and induce IFN-β/IFN-λs production in human astrocytes. Poly(dA:dT) treatment of astrocytes also induced the expression of the antiviral ISGs (Viperin, ISG56 and MxA). Among IRFs members examined, poly(dA:dT) selectively unregulated IRF1 and IRF9, particularly IRF1 in human astrocytes. The inductive effects of poly(dA:dT) on IFNs and ISGs were diminished in the IRF1 knockout cells. In addition, IRF1 knockout attenuated poly(dA:dT)-mediated HSV-1 inhibition in the cells.
CONCLUSION
The DNA sensors activation induces astrocyte intracellular innate immunity against HSV-1. Therefore, targeting the DNA sensors has potential for immune activation-based HSV-1 therapy.
Topics: Humans; Astrocytes; Interferon Regulatory Factor-1; Herpesvirus 1, Human; Virus Replication; Immunity, Innate; Poly dA-dT; Herpes Simplex; Cytosol; Cell Line; Cells, Cultured; DNA, Viral; Gene Knockout Techniques
PubMed: 38808062
DOI: 10.3389/fcimb.2024.1383811 -
Journal of Neuroinflammation May 2024Intrauterine inflammation is considered a major cause of brain injury in preterm infants, leading to long-term neurodevelopmental deficits. A potential contributor to...
BACKGROUND
Intrauterine inflammation is considered a major cause of brain injury in preterm infants, leading to long-term neurodevelopmental deficits. A potential contributor to this brain injury is dysregulation of neurovascular coupling. We have shown that intrauterine inflammation induced by intra-amniotic lipopolysaccharide (LPS) in preterm lambs, and postnatal dopamine administration, disrupts neurovascular coupling and the functional cerebral haemodynamic responses, potentially leading to impaired brain development. In this study, we aimed to characterise the structural changes of the neurovascular unit following intrauterine LPS exposure and postnatal dopamine administration in the brain of preterm lambs using cellular and molecular analyses.
METHODS
At 119-120 days of gestation (term = 147 days), LPS was administered into the amniotic sac in pregnant ewes. At 126-7 days of gestation, the LPS-exposed lambs were delivered, ventilated and given either a continuous intravenous infusion of dopamine at 10 µg/kg/min or isovolumetric vehicle solution for 90 min (LPS, n = 6; LPS, n = 6). Control preterm lambs not exposed to LPS were also administered vehicle or dopamine (CTL, n = 9; CTL, n = 7). Post-mortem brain tissue was collected 3-4 h after birth for immunohistochemistry and RT-qPCR analysis of components of the neurovascular unit.
RESULTS
LPS exposure increased vascular leakage in the presence of increased vascular density and remodelling with increased astrocyte "end feet" vessel coverage, together with downregulated mRNA levels of the tight junction proteins Claudin-1 and Occludin. Dopamine administration decreased vessel density and size, decreased endothelial glucose transporter, reduced neuronal dendritic coverage, increased cell proliferation within vessel walls, and increased pericyte vascular coverage particularly within the cortical and deep grey matter. Dopamine also downregulated VEGFA and Occludin tight junction mRNA, and upregulated dopamine receptor DRD1 and oxidative protein (NOX1, SOD3) mRNA levels. Dopamine administration following LPS exposure did not exacerbate any effects induced by LPS.
CONCLUSION
LPS exposure and dopamine administration independently alters the neurovascular unit in the preterm brain. Alterations to the neurovascular unit may predispose the developing brain to further injury.
Topics: Animals; Dopamine; Sheep; Female; Animals, Newborn; Lipopolysaccharides; Pregnancy; Brain; Inflammation; Blood-Brain Barrier; Premature Birth
PubMed: 38807204
DOI: 10.1186/s12974-024-03137-0 -
Neurology International May 2024It is well known that the brain is quite vulnerable to oxidative stress, initiating neuronal loss after ischemia-reperfusion (IR) injury. A potent protective mechanism...
It is well known that the brain is quite vulnerable to oxidative stress, initiating neuronal loss after ischemia-reperfusion (IR) injury. A potent protective mechanism is ischemic preconditioning (IPC), where proteins are among the primary targets. This study explores redox-active proteins' role in preserving energy supply. Adult rats were divided into the control, IR, and IPC groups. Protein profiling was conducted to identify modified proteins and then verified through activity assays, immunoblot, and immunohistochemical analyses. IPC protected cortex mitochondria, as evidenced by a 2.26-fold increase in superoxide dismutase (SOD) activity. Additionally, stable core subunits of respiratory chain complexes ensured sufficient energy production, supported by a 16.6% increase in ATP synthase activity. In hippocampal cells, IPC led to the downregulation of energy-related dehydrogenases, while a significantly higher level of peroxiredoxin 6 (PRX6) was observed. Notably, IPC significantly enhanced glutathione reductase activity to provide sufficient glutathione to maintain PRX6 function. Astrocytes may mobilize PRX6 to protect neurons during initial ischemic events, by decreased PRX6 positivity in astrocytes, accompanied by an increase in neurons following both IR injury and IPC. Maintained redox signaling via astrocyte-neuron communication triggers IPC's protective state. The partnership among PRX6, SOD, and glutathione reductase appears essential in safeguarding and stabilizing the hippocampus.
PubMed: 38804479
DOI: 10.3390/neurolint16030040 -
Neurology International Apr 2024The development of the optic nerve and its surrounding tissues during the early fetal period is a convoluted period because it spans both the organogenesis period and...
The development of the optic nerve and its surrounding tissues during the early fetal period is a convoluted period because it spans both the organogenesis period and the fetal period. This study details the microscopic anatomy and histoembryology of the optic nerve in embryos during the early fetal period, including the second half of the first trimester of pregnancy. Serial sections through the orbit of variously aged embryos allowed us to analyze the nerve in both longitudinal and transverse aspects. A histological assessment and description of the structures surrounding and inside the nerve were performed, highlighting the cellular subtypes involved. By employing immunohistochemical techniques, we could characterize the presence and distribution of astrocytes within the optic nerve. Our findings suggest that by the 8th gestational week (WG) the structures are homologs to all the adult ones but with an early appearance so that maturation processes take place afterward. By this age, the axons forming the nerve are definitive adult axons. The glial cells do not yet exhibit adult phenotype, but their aspect becomes adult toward the 13th week. During its development the optic nerve increases in size then, at 14 weeks, it shrinks considerably, possibly through its neural maturation process. The morphological primordium of the blood-nerve barrier can be first noted at 10 WG and at 13 WG the morphological blood-nerve barrier is definitive. The meningeal primordium can be first noted as a layer of agglomerated fibroblasts, later toward 13 WG splitting in pachymeninx and leptomeninges and leaving space for intrinsic blood vessels.
PubMed: 38804475
DOI: 10.3390/neurolint16030035