Critical role of sphingosine-1-phosphate receptor-2 in the disruption of cerebrovascular integrity in experimental stroke

Plateau hypoxia-induced upregulation of reticulon 4 pathway mediates altered autophagic flux involved in blood-brain barrier disruption after traumatic brain injury

This study aimed to examine reticulon 4 (RTN4), neurite outgrowth inhibitor protein expression that changes in high-altitude traumatic brain injury (HA-TBI) and affects on blood-brain barrier's (BBB) function. C57BL/6J 6-8-week-old male mice were used for TBI model induction and randomized into the normal altitude group and the 5000-m high-altitude (HA) group, each group was divided into control (C) and 8h/12h/24h/48h-TBI according to different times post-TBI. Brain water content (BWC) and modified Neurological Severity Score were measured, RTN4 and autophagy-related indexes (Beclin1, LC3B, and SQSTM1/p62) were detected by western blot, immunofluorescence technique, and PCR in peri-injury cortical tissues. The expression of NgR1, Lingo-1, TROY, P75, PirB, S1PR2, and RhoA receptors' downstream of RTN4 was detected by PCR. HA-TBI caused increased neurological deficits including motor, sensory, balance and reflex deficits, increased BWC, earlier peak RTN4 expression and a longer duration of high expression in peri-injury cortical tissues, and enhanced levels of Beclin1, LC3B, and SQSTM1/p62 to varying degrees. Concurrently, the transcription of S1PR2 and PirB, the main signaling molecules downstream of RTN4, was significantly increased. In HA-TBI's early stages, the increased RTN4 may regulate enhanced autophagic initiation and impaired autolysosome degradation in vascular endothelial cells via S1PR2 receptor activation, thereby reducing BBB function. This suggests that autophagy could be a new target using RTN4 intervention as a clinical HA-TBI mechanism.

Overexpression of endothelial S1pr2 promotes blood-brain barrier disruption via JNK/c-Jun/MMP-9 pathway after traumatic brain injury in both in vivo and in vitro models

Objectives

The disruption of blood-brain barrier (BBB) is associated with poor outcomes of TBI patients. Sphingosine-1-phosphate receptor 2 (S1pr2), a member of the G protein-coupled receptor family, is involved in endothelial activation and the regulation of vascular integrity. We hypothesized that the inhibition of S1pr2 may alleviate BBB disruption and explored potential underlying molecular mechanisms.

Methods

Lesion volumes were assessed utilizing Nissl staining; neurological outcomes were evaluated through a battery of neurobehavioral assessments; phenotype-associated proteins were scrutinized via Western blot analysis; levels of reactive oxygen species (ROS), neuronal apoptosis, and S1pr2 expression were determined using immunofluorescence staining. The impact of S1pr2 inhibition after TBI and its underlying mechanism were elucidated using the selective S1pr2 inhibitor JTE-013, the JNK phosphorylation inhibitor SP600125, and cellular models. Chip-qPCR was employed to further elucidate the binding sites of the transcription factor c-Jun.

Results

The expression of S1pr2 significantly increased following TBI in mice. Pharmacological inhibition of S1pr2 alleviated secondary injury with reduced lesion volume, ROS generation, cerebral oedema, neurological deficits, and neuronal apoptosis; BBB disruption was also mitigated, accompanied by reduced degradation of tight junction proteins and decreased induction of matrix metalloproteinases-9 (MMP-9) post-TBI. Mechanistically, TBI induces an increase in S1pr2 specifically in endothelial cells, leading to the promotion of MMP-9 transactivation by enhancing JNK/c-Jun signaling. This results in the degradation of tight junction proteins and increased BBB permeability. Through in vitro and in vivo Chip-qPCR experiments, we verified that AP-1a and AP-1b of MMP-9 promoter function as binding sites for phosphorylated c-Jun.

Conclusion

Our findings identify a previously undisclosed role of S1pr2 in the pathophysiology of TBI. The S1pr2 inhibition presents a novel approach to alleviate BBB disruption after TBI through regulating the JNK/c-Jun/MMP-9 pathway.

Inhibition of the AP-1/TFPI2 axis contributes to alleviating cerebral ischemia/reperfusion injury by improving blood-brain barrier integrity

Reperfusion after cerebral ischemia leads to secondary damage to the nervous system, called cerebral ischemia/reperfusion injury (CIRI). The blood-brain barrier (BBB) consists of endothelial cells and tight junction (TJ) proteins, and its disruption aggravates CIRI. Two GSE datasets identified Tissue Factor Pathway Inhibitor 2 (TFPI2) as a differentially upregulated gene (Log2FC > 1, p < 0.01) in the cerebral cortex of ischemic rats, and TFPI2 affects angiogenesis of endothelial cells. Moreover, genes (c-Jun, c-Fos, FosL1) encoding subunits of Activator Protein-1 (AP-1), a transcription factor involved in IRI, were highly expressed in ischemic samples. Thus, the effects of the AP-1/TFPI2 axis on CIRI were explored. We determined increased TFPI2 expression in the cerebral cortex of rats receiving middle cerebral artery occlusion (MCAO) for 90 min and reperfusion (R) for 48 h. Then AAV2-shTFPI2 particles (5 × 1010 vg) were injected into the right lateral ventricle of rats 3 weeks before MCAO/R. TFPI2 knockdown decreased infarct size and neuronal injury in ischemic rats. It improved BBB integrity, demonstrated by reduced FITC-dextran leakage in brain tissues of MCAO/R-operated rats. Furthermore, it increased the expression of TJ proteins (Occludin, Claudin-5, TJP-1) in the cerebral cortex of rats with CIRI. Consistently, we found that TFPI2 knockdown mitigated cell damage in mouse endothelial bEND.3 cells with oxygen and glucose deprivation (ODG) for 6 h and reoxygenation (R) for 18 h (OGD/R) treatment. High co-expression of c-Jun and c-Fos significantly elevated TFPI2 promoter activity. c-Jun knockdown inhibited TFPI2 expression in OGD/R-treated bEND.3 cell. Collectively, our findings demonstrate that inhibition of the AP-1/TFPI2 axis alleviates CIRI.

Roles of Sphingosine Kinase and Sphingosine-1-Phosphate Receptor 2 in Endotoxin-Induced Acute Retinal Inflammation

PURPOSE

To investigate the roles of sphingosine kinases (SphKs) and sphingosine-1-phosphate receptors (S1PRs) in endotoxin-induced uveitis (EIU) mice.

METHODS

EIU model was induced using an intraperitoneal injection of lipopolysaccharide (LPS). The expression of SphKs and S1PRs in the retina was assessed using quantitative polymerase chain reaction (qPCR) and immunofluorescence. The effects of S1PR antagonists on the expression of inflammatory cytokines in the retina were evaluated using qPCR and western blotting. Effects of leukocyte infiltration of the retinal vessels were evaluated to determine the effects of the S1PR2 antagonist and genetic deletion of S1PR2 on retinal inflammation.

RESULTS

Retinal SphK1 expression was significantly upregulated in EIU. SphK1 was expressed in the GCL, IPL, and OPL and S1PR2 was expressed in the GCL, INL, and OPL. Positive cells in IPL and OPL of EIU retina were identified as endothelial cells. S1PR2 antagonist and genetic deletion of S1PR2 significantly suppressed the expression of IL-1α, IL-6, TNF-α, and ICAM-1, whereas S1PR1/3 antagonist did not. Use of S1PR2 antagonist and S1PR2 knockout in mice significantly ameliorated leukocyte adhesion induced by LPS.

CONCLUSION

SphK1/S1P/S1PR2 signaling was upregulated in EIU and S1PR2 inhibition suppressed inflammatory response. Targeting this signaling pathway has potential for treating retinal inflammatory diseases.

Molecular and Functional Alterations in the Cerebral Microvasculature in an Optimized Mouse Model of Sepsis-Associated Cognitive Dysfunction

Systemic inflammation has been implicated in the development and progression of neurodegenerative conditions such as cognitive impairment and dementia. Recent clinical studies indicate an association between sepsis, endothelial dysfunction, and cognitive decline. However, the investigations of the role and therapeutic potential of the cerebral microvasculature in sepsis-induced cognitive dysfunction have been limited by the lack of standardized experimental models for evaluating the alterations in the cerebral microvasculature and cognition induced by the systemic inflammatory response. Herein, we validated a mouse model of endotoxemia that recapitulates key pathophysiology related to sepsis-induced cognitive dysfunction, including the induction of an acute systemic hyperinflammatory response, blood-brain barrier (BBB) leakage, neurovascular inflammation, and memory impairment after recovery from the systemic inflammation. In the acute phase, we identified novel molecular (e.g., upregulation of plasmalemma vesicle-associated protein, PLVAP, a driver of endothelial permeability, and the procoagulant plasminogen activator inhibitor-1, PAI-1) and functional perturbations (i.e., albumin and small-molecule BBB leakage) in the cerebral microvasculature along with neuroinflammation. Remarkably, small-molecule BBB permeability, elevated levels of PAI-1, intra-/perivascular fibrin/fibrinogen deposition, and microglial activation persisted 1 month after recovery from sepsis. We also highlight molecular neuronal alterations of potential clinical relevance following systemic inflammation including changes in neurofilament phosphorylation and decreases in postsynaptic density protein 95 and brain-derived neurotrophic factor, suggesting diffuse axonal injury, synapse degeneration, and impaired neurotrophism. Our study serves as a standardized mouse model to support future mechanistic studies of sepsis-associated cognitive dysfunction and to identify novel endothelial therapeutic targets for this devastating condition.

Nogo-A is secreted in extracellular vesicles, occurs in blood and can influence vascular permeability

Nogo-A is a transmembrane protein with multiple functions in the central nervous system (CNS), including restriction of neurite growth and synaptic plasticity. Thus far, Nogo-A has been predominantly considered a cell contact-dependent ligand signaling via cell surface receptors. Here, we show that Nogo-A can be secreted by cultured cells of neuronal and glial origin in association with extracellular vesicles (EVs). Neuron- and oligodendrocyte-derived Nogo-A containing EVs inhibited fibroblast spreading, and this effect was partially reversed by Nogo-A receptor S1PR2 blockage. EVs purified from HEK cells only inhibited fibroblast spreading upon Nogo-A over-expression. Nogo-A-containing EVs were found in vivo in the blood of healthy mice and rats, as well as in human plasma. Blood Nogo-A concentrations were elevated after acute stroke lesions in mice and rats. Nogo-A active peptides decreased barrier integrity in an in vitro blood-brain barrier model. Stroked mice showed increased dye permeability in peripheral organs when tested 2 weeks after injury. In the Miles assay, an in vivo test to assess leakage of the skin vasculature, a Nogo-A active peptide increased dye permeability. These findings suggest that blood borne, possibly EV-associated Nogo-A could exert long-range regulatory actions on vascular permeability.

Adipocyte enhancer binding protein 1 knockdown alleviates osteoarthritis through inhibiting NF-κB signaling pathway-mediated inflammation and extracellular matrix degradation

Inflammation promotes the degradation of the extracellular matrix, which contributes to the development of osteoarthritis (OA). Adipocyte enhancer binding protein 1 (AEBP1) participates in multiple pathological processes related to inflammatory diseases. However, the role of AEBP1 in OA development is unknown. We found a higher AEBP1 expression in articular cartilage of OA patients (n = 20) compared to their normal controls (n = 10). Thus, we inferred that AEBP1 might affect OA progression. Then mice with destabilization of the medial meniscus (DMM) surgery and chondrocytes with IL-1β treatment (10 ng/mL) were used to mimic OA. The increased AEBP1 expression was observed in models of OA. AEBP1 knockdown in chondrocytes reversed IL-1β-induced inflammation and extracellular matrix degradation, which was mediated by the inactivation of NF-κB signaling pathway and the increased IκBα activity. Co-immunoprecipitation assay indicated the interaction between AEBP1 and IκBα. Importantly, IκBα knockdown depleted the protective role of AEBP1 knockdown in OA. Moreover, AEBP1 knockdown in mice with OA showed similar results to those in chondrocytes. Collectively, our findings suggest that AEBP1 knockdown alleviates the development of OA, providing a novel strategy for OA treatment.

Molecular and functional alterations in the cerebral microvasculature in an optimized mouse model of sepsis-associated cognitive dysfunction

Systemic inflammation has been implicated in the development and progression of neurodegenerative conditions such as cognitive impairment and dementia. Recent clinical studies indicate an association between sepsis, endothelial dysfunction, and cognitive decline. However, the investigations of the role and therapeutic potential of the cerebral microvasculature in systemic inflammation-induced cognitive dysfunction have been limited by the lack of standardized experimental models for evaluating the alterations in the cerebral microvasculature and cognition induced by the systemic inflammatory response. Herein, we validated a mouse model of endotoxemia that recapitulates key pathophysiology related to sepsis-induced cognitive dysfunction, including the induction of an acute systemic hyperinflammatory response, blood-brain barrier (BBB) leakage, neurovascular inflammation, and memory impairment after recovery from the systemic inflammatory response. In the acute phase, we identified novel molecular (e.g. upregulation of plasmalemma vesicle associated protein, a driver of endothelial permeability, and the pro-coagulant plasminogen activator inhibitor-1, PAI-1) and functional perturbations (i.e., albumin and small molecule BBB leakage) in the cerebral microvasculature along with neuroinflammation. Remarkably, small molecule BBB permeability, elevated levels of PAI-1, intra/perivascular fibrin/fibrinogen deposition and microglial activation persisted 1 month after recovery from sepsis. We also highlight molecular neuronal alterations of potential clinical relevance following systemic inflammation including changes in neurofilament phosphorylation and decreases in postsynaptic density protein 95 and brain-derived neurotrophic factor suggesting diffuse axonal injury, synapse degeneration and impaired neurotrophism. Our study serves as a standardized model to support future mechanistic studies of sepsis-associated cognitive dysfunction and to identify novel endothelial therapeutic targets for this devastating condition.

SIGNIFICANCE

The limited knowledge of how systemic inflammation contributes to cognitive decline is a major obstacle to the development of novel therapies for dementia and other neurodegenerative diseases. Clinical evidence supports a role for the cerebral microvasculature in sepsis-induced neurocognitive dysfunction, but the investigation of the underlying mechanisms has been limited by the lack of standardized experimental models. Herein, we optimized a mouse model that recapitulates important pathophysiological aspects of systemic inflammation-induced cognitive decline and identified key alterations in the cerebral microvasculature associated with cognitive dysfunction. Our study provides a reliable experimental model for mechanistic studies and therapeutic discovery of the impact of systemic inflammation on cerebral microvascular function and the development and progression of cognitive impairment.

Microglia-neuron-vascular interactions in ischemia

Cerebral ischemia is a devastating condition that results in impaired blood flow in the brain leading to acute brain injury. As the most common form of stroke, occlusion of cerebral arteries leads to a characteristic sequence of pathophysiological changes in the brain tissue. The mechanisms involved, and comorbidities that determine outcome after an ischemic event appear to be highly heterogeneous. On their own, the processes leading to neuronal injury in the absence of sufficient blood supply to meet the metabolic demand of the cells are complex and manifest at different temporal and spatial scales. While the contribution of non-neuronal cells to stroke pathophysiology is increasingly recognized, recent data show that microglia, the main immune cells of the central nervous system parenchyma, play previously unrecognized roles in basic physiological processes beyond their inflammatory functions, which markedly change during ischemic conditions. In this review, we aim to discuss some of the known microglia-neuron-vascular interactions assumed to contribute to the acute and delayed pathologies after cerebral ischemia. Because the mechanisms of neuronal injury have been extensively discussed in several excellent previous reviews, here we focus on some recently explored pathways that may directly or indirectly shape neuronal injury through microglia-related actions. These discoveries suggest that modulating gliovascular processes in different forms of stroke and other neurological disorders might have presently unexplored therapeutic potential in combination with neuroprotective and flow restoration strategies.

1-Phosphate receptor agonists: A promising therapeutic avenue for ischemia-reperfusion injury management

Ischemia-reperfusion injury (IRI) - a complex pathological condition occurring when blood supply is abruptly restored to ischemic tissues, leading to further tissue damage - poses a significant clinical challenge. Sphingosine-1-phosphate receptors (S1PRs), a specialized set of G-protein-coupled receptors comprising five subtypes (S1PR1 to S1PR5), are prominently present in various cell membranes, including those of lymphocytes, cardiac myocytes, and endothelial cells. Increasing evidence highlights the potential of targeting S1PRs for IRI therapeutic intervention. Notably, preconditioning and postconditioning strategies involving S1PR agonists like FTY720 have demonstrated efficacy in mitigating IRI. As the synthesis of a diverse array of S1PR agonists continues, with FTY720 being a prime example, the body of experimental evidence advocating for their role in IRI treatment is expanding. Despite this progress, comprehensive reviews delineating the therapeutic landscape of S1PR agonists in IRI remain limited. This review aspires to meticulously elucidate the protective roles and mechanisms of S1PR agonists in preventing and managing IRI affecting various organs, including the heart, kidney, liver, lungs, intestines, and brain, to foster novel pharmacological approaches in clinical settings.

The peripheral corticotropin releasing factor family's role in vasculitis

Corticotropin releasing factor family peptides (CRF peptides) include 4 members, corticotropin releasing hormone (CRH), Urocortin (UCN1), UCN2 and UCN3. CRF peptides function via the two distinct receptors, CRF1 and CRF2. Among them, CRH/CRF1 has been recognized to influence immunity/inflammation peripherally. Both pro- and anti-inflammatory effects of CRH are reported. Likewise, UCNs, peripherally in cardiovascular system have been documented to have both potent protective and harmful effects, with UCN1 acting on both CRF1 & CRF2 and UCN2 & UCN3 on CRF2. We and others also observe protective and detrimental effects of CRF peptides/receptors on vasculature, with the latter of predominantly higher incidence, i.e., they play an important role in the development of vasculitis while in some cases they are found to counteract vascular inflammation. The pro-vasculitis effects of CRH & UCNs include increasing vascular endothelial permeability, interrupting endothelial adherens & tight junctions leading to hyperpermeability, stimulating immune/inflammatory cells to release inflammatory factors, and promoting angiogenesis by VEGF release while the anti-vasculitis effects may be just the opposite, depending on many factors such as different CRF receptor types, species and systemic conditions. Furthermore, CRF peptides' pro-vasculitis effects are found to be likely related to cPLA2 and S1P receptor signal pathway. This minireview will focus on summarizing the peripheral effects of CRF peptides on vasculature participating in the processes of vasculitis.

Extracellular Vesicles Maintain Blood-Brain Barrier Integrity by the Suppression of Caveolin-1/CD147/VEGFR2/MMP Pathway After Ischemic Stroke

Background

Ischemic stroke (IS) causes tragic death and disability worldwide. However, effective therapeutic interventions are finite. After IS, blood-brain barrier (BBB) integrity is disrupted, resulting in deteriorating neurological function. As a novel therapeutic, extracellular vesicles (EVs) have shown ideal restorative effects on BBB integrity post-stroke; however, the definite mechanisms remain ambiguous. In the present study, we investigated the curative effects and the mechanisms of EVs derived from bone marrow mesenchymal stem cells and brain endothelial cells (BMSC-EVs and BEC-EVs) on BBB integrity after acute IS.

Methods

EVs were isolated from BMSCs and BECs, and we investigated the therapeutic effect in vitro oxygen-glucose deprivation (OGD) insulted BECs model and in vivo rat middle cerebral artery occlusion (MCAo) model. The cell monolayer leakage, tight junction expression, and metalloproteinase (MMP) activity were evaluated, and rat brain infarct volume and neurological function were also analyzed.

Results

The administration of two kinds of EVs not only enhanced ZO-1 and Occludin expressions but also reduced the permeability and the activity of MMP-2/9 in OGD-insulted BECs. The amelioration of the cerebral infarction, BBB leakage, neurological function deficits, and the increasing ZO-1 and Occludin levels, as well as MMP activity inhibition was observed in MCAo rats. Additionally, the increased levels of Caveolin-1, CD147, vascular endothelial growth factor receptor 2 (VEGFR2), and vascular endothelial growth factor A (VEGFA) in isolated brain microvessels were downregulated after EVs treatment. In vitro, the employment of Caveolin-1 and CD147 siRNA partly suppressed the expressions of VEGFR2, VEGFA and MMP-2/9 activity and reduced the leakage of OGD insulted BECs and enhanced ZO-1 and Occludin expressions.

Conclusion

Our study firstly demonstrates that BEC and BMSC-EVs administrations maintain BBB integrity via the suppression of Caveolin-1/CD147/VEGFR2/MMP pathway after IS, and the efficacy of BMSC-EVs is superior to that of BEC-EVs.

Immune-Neurovascular Interactions in Experimental Perinatal and Childhood Arterial Ischemic Stroke

Emerging clinical and preclinical data have demonstrated that the pathophysiology of arterial ischemic stroke in the adult, neonates, and children share similar mechanisms that regulate brain damage but also have distinct molecular signatures and involved cellular pathways due to the maturational stage of the central nervous system and the immune system at the time of the insult. In this review, we discuss similarities and differences identified thus far in rodent models of 2 different diseases-neonatal (perinatal) and childhood arterial ischemic stroke. In particular, we review acquired knowledge of the role of resident and peripheral immune populations in modulating outcomes in models of perinatal and childhood arterial ischemic stroke and the most recent and relevant findings in relation to the immune-neurovascular crosstalk, and how the influence of inflammatory mediators is dependent on specific brain maturation stages. Finally, we discuss the current state of treatments geared toward age-appropriate therapies that signal via the immune-neurovascular interaction and consider sex differences to achieve successful translation.

Evidence Implicating Blood-Brain Barrier Impairment in the Pathogenesis of Acquired Epilepsy following Acute Organophosphate Intoxication

Organophosphate (OP) poisoning can trigger cholinergic crisis, a life-threatening toxidrome that includes seizures and status epilepticus. These acute toxic responses are associated with persistent neuroinflammation and spontaneous recurrent seizures (SRS), also known as acquired epilepsy. Blood-brain barrier (BBB) impairment has recently been proposed as a pathogenic mechanism linking acute OP intoxication to chronic adverse neurologic outcomes. In this review, we briefly describe the cellular and molecular components of the BBB, review evidence of altered BBB integrity following acute OP intoxication, and discuss potential mechanisms by which acute OP intoxication may promote BBB dysfunction. We highlight the complex interplay between neuroinflammation and BBB dysfunction that suggests a positive feedforward interaction. Lastly, we examine research from diverse models and disease states that suggest mechanisms by which loss of BBB integrity may contribute to epileptogenic processes. Collectively, the literature identifies BBB impairment as a convergent mechanism of neurologic disease and justifies further mechanistic research into how acute OP intoxication causes BBB impairment and its role in the pathogenesis of SRS and potentially other long-term neurologic sequelae. Such research is critical for evaluating BBB stabilization as a neuroprotective strategy for mitigating OP-induced epilepsy and possibly seizure disorders of other etiologies. SIGNIFICANCE STATEMENT: Clinical and preclinical studies support a link between blood-brain barrier (BBB) dysfunction and epileptogenesis; however, a causal relationship has been difficult to prove. Mechanistic studies to delineate relationships between BBB dysfunction and epilepsy may provide novel insights into BBB stabilization as a neuroprotective strategy for mitigating epilepsy resulting from acute organophosphate (OP) intoxication and non-OP causes and potentially other adverse neurological conditions associated with acute OP intoxication, such as cognitive impairment.

Immune pathway activation in neurons triggers neural damage after stroke

Ischemic brain injury is a severe medical condition with high incidences in elderly people without effective treatment for the resulting neural damages. Using a unilateral mouse stroke model, we analyze single-cell transcriptomes of ipsilateral and contralateral cortical penumbra regions to objectively reveal molecular events with single-cell resolution at 4 h and 1, 3, and 7 days post-injury. Here, we report that neurons are among the first cells that sense the lack of blood supplies by elevated expression of CCAAT/enhancer-binding protein β (C/EBPβ). To our surprise, the canonical inflammatory cytokine gene targets for C/EBPβ, including interleukin-1β (IL-1β) and tumor necrosis factor α (TNF-α), are subsequently induced also in neuronal cells. Neuronal-specific silencing of C/EBPβ or IL-1β and TNF-α substantially alleviates downstream inflammatory injury responses and is profoundly neural protective. Taken together, our findings reveal a neuronal inflammatory mechanism underlying early pathological triggers of ischemic brain injury.

Ozanimod differentially preserves human cerebrovascular endothelial barrier proteins and attenuates matrix metalloproteinase-9 activity following in vitro acute ischemic injury

Endothelial integrity is critical in mitigating a vicious cascade of secondary injuries following acute ischemic stroke (AIS). Matrix metalloproteinase-9 (MMP-9), a contributor to endothelial integrity loss, is elevated during stroke and is associated with worsened stroke outcome. We investigated the FDA-approved selective sphingosine-1-phosphate receptor 1 (S1PR1) ligand, ozanimod, on the regulation/activity of MMP-9 as well as endothelial barrier components [platelet endothelial cell adhesion molecule 1 (PECAM-1), claudin-5, and zonula occludens 1 (ZO-1)] in human brain microvascular endothelial cells (HBMECs) following hypoxia plus glucose deprivation (HGD). We previously reported that S1PR1 activation improves HBMEC integrity; however, mechanisms underlying S1PR1 involvement in endothelial cell barrier integrity have not been clearly elucidated. We hypothesized that ozanimod would attenuate an HGD-induced increase in MMP-9 activity that would concomitantly attenuate the loss of integral barrier components. Male HBMECs were treated with ozanimod or vehicle and exposed to 3 h of normoxia (21% O2) or HGD (1% O2). Immunoblotting, zymography, qRT-PCR, and immunocytochemical labeling techniques assessed processes related to MMP-9 and barrier markers. We observed that HGD acutely increased MMP-9 activity and reduced claudin-5 and PECAM-1 levels, and ozanimod attenuated these responses. In situ analysis, via PROSPER, suggested that attenuation of MMP-9 activity may be a primary factor in maintaining these integral barrier proteins. We also observed that HGD increased intracellular mechanisms associated with augmented MMP-9 activation; however, ozanimod had no effect on these select factors. Thus, we conclude that ozanimod has the potential to attenuate HGD-mediated decreases in HBMEC integrity in part by decreasing MMP-9 activity as well as preserving barrier properties.NEW & NOTEWORTHY We have identified a potential novel mechanism by which ozanimod, a selective sphingosine-1-phosphate receptor 1 (S1PR1) agonist, attenuates hypoxia plus glucose deprivation (HGD)-induced matrix metalloproteinase-9 (MMP-9) activity and disruptions in integral human brain endothelial cell barrier proteins. Our results suggest that ischemic-like injury elicits increased MMP-9 activity and alterations of barrier integrity proteins in human brain microvascular endothelial cells (HBMECs) and that ozanimod via S1PR1 attenuates these HGD-induced responses, adding to its therapeutic potential in cerebrovascular protection during the acute phase of ischemic stroke.

Blood-spinal cord barrier disruption in degenerative cervical myelopathy

Degenerative cervical myelopathy (DCM) is the most prevalent cause of spinal cord dysfunction in the aging population. Significant neurological deficits may result from a delayed diagnosis as well as inadequate neurological recovery following surgical decompression. Here, we review the pathophysiology of DCM with an emphasis on how blood-spinal cord barrier (BSCB) disruption is a critical yet neglected pathological feature affecting prognosis. In patients suffering from DCM, compromise of the BSCB is evidenced by elevated cerebrospinal fluid (CSF) to serum protein ratios and abnormal contrast-enhancement upon magnetic resonance imaging (MRI). In animal model correlates, there is histological evidence of increased extravasation of tissue dyes and serum contents, and pathological changes to the neurovascular unit. BSCB dysfunction is the likely culprit for ischemia-reperfusion injury following surgical decompression, which can result in devastating neurological sequelae. As there are currently no therapeutic approaches specifically targeting BSCB reconstitution, we conclude the review by discussing potential interventions harnessed for this purpose.

Alleviating early demyelination in ischaemia/reperfusion by inhibiting sphingosine-1-phosphate receptor 2 could protect visual function from impairment

Retinal ischaemia/reperfusion (I/R) injury is a common cause of retinal ganglion cell (RGC) apoptosis and axonal degeneration, resulting in irreversible visual impairment. However, there are no available neuroprotective and neurorestorative therapies for retinal I/R injury, and more effective therapeutic approaches are needed. The role of the myelin sheath of the optic nerve after retinal I/R remains unknown. Here, we report that demyelination of the optic nerve is an early pathological feature of retinal I/R and identify sphingosine-1-phosphate receptor 2 (S1PR2) as a therapeutic target for alleviating demyelination in a model of retinal I/R caused by rapid changes in intraocular pressure. Targeting the myelin sheath via S1PR2 protected RGCs and visual function. In our experiment, we observed early damage to the myelin sheath and persistent demyelination accompanied by S1PR2 overexpression after injury. Blockade of S1PR2 by the pharmacological inhibitor JTE-013 reversed demyelination, increased the number of oligodendrocytes, and inhibited microglial activation, contributing to the survival of RGCs and alleviating axonal damage. Finally, we evaluated the postoperative recovery of visual function by recording visual evoked potentials and assessing the quantitative optomotor response. In conclusion, this study is the first to reveal that alleviating demyelination by inhibiting S1PR2 overexpression may be a therapeutic strategy for retinal I/R-related visual impairment.

The therapeutic potential of sphingolipids for cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide and Inflammation plays a critical role in the development of CVD. Despite considerable progress in understanding the underlying mechanisms and various treatment options available, significant gaps in therapy necessitate the identification of novel therapeutic targets. Sphingolipids are a family of lipids that have gained attention in recent years as important players in CVDs and the inflammatory processes that underlie their development. As preclinical studies have shown that targeting sphingolipids can modulate inflammation and ameliorate CVDs, targeting sphingolipids has emerged as a promising therapeutic strategy. This review discusses the current understanding of sphingolipids' involvement in inflammation and cardiovascular diseases, the existing therapeutic approaches and gaps in therapy, and explores the potential of sphingolipids-based drugs as a future avenue for CVD treatment.

Blood neurofilament light chain in Parkinson's disease

Blood neurofilament light chain (NfL) is an easily accessible, highly sensitive and reliable biomarker for neuroaxonal damage. Currently, its role in Parkinson's disease (PD) remains unclear. Here, we demonstrate that blood NfL can distinguish idiopathic PD from atypical parkinsonian syndromes (APS) with high sensitivity and specificity. In cross-sectional studies, some found significant correlations between blood NfL with motor and cognitive function, whereas others did not. In contrast, prospective studies reported very consistent associations between baseline blood NfL with motor progression and cognitive worsening. Amongst PD subtypes, especially postural instability and gait disorder (PIGD) subtype, symptoms and scores are reliably linked with blood NfL. Different non-motor PD comorbidities have also been associated with high blood NfL levels suggesting that the neuroaxonal damage of the autonomic nervous system as well as serotonergic, cholinergic and noradrenergic neurons is quantifiable. Numerous absolute NfL cutoff levels have been suggested in different cohort studies; however, validation across cohorts remains weak. However, age-adjusted percentiles and intra-individual blood NfL changes might represent more valid and consistent parameters compared with absolute NfL concentrations. In summary, blood NfL has the potential as biomarker in PD patients to be used in clinical practice for prediction of disease severity and especially progression.

Global sphingosine-1-phosphate receptor 2 deficiency attenuates neuroinflammation and ischemic-reperfusion injury after neonatal stroke

Arterial ischemic stroke is common in neonates-1 per 2,300-5,000 births-and therapeutic targets remain insufficiently defined. Sphingosine-1-phosphate receptor 2 (S1PR2), a major regulator of the CNS and immune systems, is injurious in adult stroke. Here, we assessed whether S1PR2 contributes to stroke induced by 3 h transient middle cerebral artery occlusion (tMCAO) in S1PR2 heterozygous (HET), knockout (KO), and wild type (WT) postnatal day 9 pups. HET and WT of both sexes displayed functional deficits in Open Field test whereas injured KO at 24 h reperfusion performed similarly to naives. S1PR2 deficiency protected neurons, attenuated infiltration of inflammatory monocytes, and altered vessel-microglia interactions without reducing increased cytokine levels in injured regions at 72 h. Pharmacologic inhibition of S1PR2 after tMCAO by JTE-013 attenuated injury 72 h after tMCAO. Importantly, the lack of S1PR2 alleviated anxiety and brain atrophy during chronic injury. Altogether, we identify S1PR2 as a potential new target for mitigating neonatal stroke.

Molecular profiling of the stroke-induced alterations in the cerebral microvasculature reveals promising therapeutic candidates

Stroke-induced cerebral microvascular dysfunction contributes to aggravation of neuronal injury and compromises the efficacy of current reperfusion therapies. Understanding the molecular alterations in cerebral microvessels in stroke will provide original opportunities for scientific investigation of novel therapeutic strategies. Toward this goal, using a recently optimized method which minimizes cell activation and preserves endothelial cell interactions and RNA integrity, we conducted a genome-wide transcriptomic analysis of cerebral microvessels in a mouse model of stroke and compared these transcriptomic alterations with the ones observed in human, nonfatal, brain stroke lesions. Results from these unbiased comparative analyses have revealed the common alterations in mouse stroke microvessels and human stroke lesions and identified shared molecular features associated with vascular disease (e.g., Serpine1/Plasminogen Activator Inhibitor-1, Hemoxygenase-1), endothelial activation (e.g., Angiopoietin-2), and alterations in sphingolipid metabolism and signaling (e.g., Sphigosine-1-Phosphate Receptor 2). Sphingolipid profiling of mouse cerebral microvessels validated the transcript data and revealed the enrichment of sphingomyelin and sphingoid species in the cerebral microvasculature compared to brain and the stroke-induced increase in ceramide species. In summary, our study has identified novel molecular alterations in several microvessel-enriched, translationally relevant, and druggable targets, which are potent modulators of endothelial function. Our comparative analyses have revealed the presence of molecular features associated with cerebral microvascular dysfunction in human chronic stroke lesions. The results shared here provide a detailed resource for therapeutic discovery of candidates for neurovascular protection in stroke and potentially, other pathologies exhibiting cerebral microvascular dysfunction.

The role of sphingosine 1-phosphate metabolism in brain health and disease

Lipids are essential structural and functional components of the central nervous system (CNS). Sphingolipids are ubiquitous membrane components which were discovered in the brain in the late 19^th century. In mammals, the brain contains the highest concentration of sphingolipids in the body. Sphingosine 1-phosphate (S1P) derived from membrane sphingolipids evokes multiple cellular responses which, depending on its concentration and localization, make S1P a double-edged sword in the brain. In the present review we highlight the role of S1P in brain development and focus on the often contrasting findings regarding its contributions to the initiation, progression and potential recovery of different brain pathologies, including neurodegeneration, multiple sclerosis (MS), brain cancers, and psychiatric illnesses. A detailed understanding of the critical implications of S1P in brain health and disease may open the door for new therapeutic options. Thus, targeting S1P-metabolizing enzymes and/or signaling pathways might help overcome, or at least ameliorate, several brain illnesses.

Imaging of microglia in post-stroke inflammation

Microglia constantly survey the central nervous system microenvironment and maintain brain homeostasis. Microglia activation, polarization and inflammatory response are of great importance in the pathophysiology of ischemic stroke. For exploring biochemical processes in vivo, positron emission tomography (PET) is a superior imaging tool. Translocator protein 18 kDa (TSPO), is a validated neuroinflammatory biomarker which is widely used to evaluate various central nervous system (CNS) pathologies in both preclinical and clinical studies. TSPO level can be elevated due to peripheral inflammatory cells infiltration and glial cells activation. Therefore, a clear understanding of the dynamic changes between microglia and TSPO is critical for interpreting PET studies and understanding the pathophysiology after ischemic stroke. Our review discusses alternative biological targets that have attracted considerable interest for the imaging of microglia activation in recent years, and the potential value of imaging of microglia in the assessment of stroke therapies.

Radiomics Analysis of Diffusion-Weighted Imaging and Long-Term Unfavorable Outcomes Risk for Acute Stroke

BACKGROUND

Diffusion-weighted imaging radiomics could be used as prognostic biomarkers in acute ischemic stroke. We aimed to identify a clinical and diffusion-weighted imaging radiomics model for individual unfavorable outcomes risk assessment in acute ischemic stroke.

METHODS

A total of 1716 patients with acute ischemic stroke from 2 centers were divided into a training cohort and a validation cohort. Patient outcomes were measured with the modified Rankin Scale score. An unfavorable outcome was defined as a modified Rankin Scale score greater than 2. The primary end point was all-cause mortality or outcomes 1 year after stroke. The MRI-DRAGON score was calculated based on previous publications. We extracted and selected the infarct features on diffusion-weighted imaging to construct a radiomic signature. The clinic-radiomics signature was built by measuring the Cox proportional risk regression score (CrrScore) and compared with the MRI-DRAGON score and the ClinicScore. CrrScore model performance was estimated by 1-year unfavorable outcomes prediction.

RESULTS

A high radiomic signature predicted a higher probability of unfavorable outcomes than a low radiomic signature in the training (hazard ratio, 3.19 [95% CI, 2.51-4.05]; P<0.0001) and validation (hazard ratio, 3.25 [95% CI, 2.20-4.80]; P<0.0001) cohorts. The diffusion-weighted imaging Alberta Stroke Program Early CT Score, age, glucose level before therapy, National Institutes of Health Stroke Scale score on admission, glycated hemoglobin' radiomic signature, hemorrhagic infarction, and malignant cerebral edema were associated with an unfavorable outcomes risk after multivariable adjustment. A CrrScore nomogram was developed to predict outcomes and had the best performance in the training (area under the curve, 0.862) and validation cohorts (area under the curve, 0.858). The CrrScore model time-dependent areas under the curve of the probability of unfavorable outcomes at 1 year in the training and validation cohorts were 0.811 and 0.801, respectively.

CONCLUSIONS

The CrrScore model allows the accurate prediction of patients with acute ischemic stroke outcomes and can potentially guide rehabilitation therapies for patients with different risks of unfavorable outcomes.

The Dark Side of Sphingolipids: Searching for Potential Cardiovascular Biomarkers

Cardiovascular diseases (CVDs) are the leading cause of death and illness in Europe and worldwide, responsible for a staggering 47% of deaths in Europe. Over the past few years, there has been increasing evidence pointing to bioactive sphingolipids as drivers of CVDs. Among them, most studies place emphasis on the cardiovascular effect of ceramides and sphingosine-1-phosphate (S1P), reporting correlation between their aberrant expression and CVD risk factors. In experimental in vivo models, pharmacological inhibition of de novo ceramide synthesis averts the development of diabetes, atherosclerosis, hypertension and heart failure. In humans, levels of circulating sphingolipids have been suggested as prognostic indicators for a broad spectrum of diseases. This article provides a comprehensive review of sphingolipids' contribution to cardiovascular, cerebrovascular and metabolic diseases, focusing on the latest experimental and clinical findings. Cumulatively, these studies indicate that monitoring sphingolipid level alterations could allow for better assessment of cardiovascular disease progression and/or severity, and also suggest them as a potential target for future therapeutic intervention. Some approaches may include the down-regulation of specific sphingolipid species levels in the circulation, by inhibiting critical enzymes that catalyze ceramide metabolism, such as ceramidases, sphingomyelinases and sphingosine kinases. Therefore, manipulation of the sphingolipid pathway may be a promising strategy for the treatment of cardio- and cerebrovascular diseases.

Signal Transduction and Gene Regulation in the Endothelium

Extracellular signals act on G-protein-coupled receptors (GPCRs) to regulate homeostasis and adapt to stress. This involves rapid intracellular post-translational responses and long-lasting gene-expression changes that ultimately determine cellular phenotype and fate changes. The lipid mediator sphingosine 1-phosphate (S1P) and its receptors (S1PRs) are examples of well-studied GPCR signaling axis essential for vascular development, homeostasis, and diseases. The biochemical cascades involved in rapid S1P signaling are well understood. However, gene-expression regulation by S1PRs are less understood. In this review, we focus our attention to how S1PRs regulate nuclear chromatin changes and gene transcription to modulate vascular and lymphatic endothelial phenotypic changes during embryonic development and adult homeostasis. Because S1PR-targeted drugs approved for use in the treatment of autoimmune diseases cause substantial vascular-related adverse events, these findings are critical not only for general understanding of stimulus-evoked gene regulation in the vascular endothelium, but also for therapeutic development of drugs for autoimmune and perhaps vascular diseases.

RTN4/Nogo-A-S1PR2 negatively regulates angiogenesis and secondary neural repair through enhancing vascular autophagy in the thalamus after cerebral cortical infarction

Cerebral infarction induces angiogenesis in the thalamus and influences functional recovery. The mechanisms underlying angiogenesis remain unclear. This study aimed to investigate the role of RTN4/Nogo-A in mediating macroautophagy/autophagy and angiogenesis in the thalamus following middle cerebral artery occlusion (MCAO). We assessed secondary neuronal damage, angiogenesis, vascular autophagy, RTN4 and S1PR2 signaling in the thalamus. The effects of RTN4-S1PR2 on vascular autophagy and angiogenesis were evaluated using lentiviral and pharmacological approaches. The results showed that RTN4 and S1PR2 signaling molecules were upregulated in parallel with angiogenesis in the ipsilateral thalamus after MCAO. Knockdown of Rtn4 by siRNA markedly reduced MAP1LC3B-II conversion and levels of BECN1 and SQSTM1 in vessels, coinciding with enhanced angiogenesis in the ipsilateral thalamus. This effect coincided with rescued neuronal loss of the thalamus and improved cognitive function. Conversely, activating S1PR2 augmented vascular autophagy, along with suppressed angiogenesis and aggravated neuronal damage of the thalamus. Further inhibition of autophagic initiation with 3-methyladenine or spautin-1 enhanced angiogenesis while blockade of lysosomal degradation by bafilomycin A₁ suppressed angiogenesis in the ipsilateral thalamus. The control of autophagic flux by RTN4-S1PR2 was verified in vitro. Additionally, ROCK1-BECN1 interaction along with phosphorylation of BECN1 (Thr119) was identified in the thalamic vessels after MCAO. Knockdown of Rtn4 markedly reduced BECN1 phosphorylation whereas activating S1PR2 increased its phosphorylation in vessels. These results suggest that blockade of RTN4-S1PR2 interaction promotes angiogenesis and secondary neural repair in the thalamus by suppressing autophagic activation and alleviating dysfunction of lysosomal degradation in vessels after cerebral infarction.Abbreviations: 3-MA: 3-methyladenine; ACTA2/ɑ-SMA: actin alpha 2, smooth muscle, aorta; AIF1/Iba1: allograft inflammatory factor 1; BafA1: bafilomycin A₁; BMVECs: brain microvascular endothelial cells; BrdU: 5-bromo-2'-deoxyuridine; CLDN11/OSP: claudin 11; GFAP: glial fibrillary acidic protein; HUVECs: human umbilical vein endothelial cells; LAMA1: laminin, alpha 1; MAP2: microtubule-associated protein 2; MBP2: myelin basic protein 2; MCAO: middle cerebral artery occlusion; PDGFRB/PDGFRβ: platelet derived growth factor receptor, beta polypeptide; RECA-1: rat endothelial cell antigen-1; RHOA: ras homolog family member A; RHRSP: stroke-prone renovascular hypertensive rats; ROCK1: Rho-associated coiled-coil containing protein kinase 1; RTN4/Nogo-A: reticulon 4; RTN4R/NgR1: reticulon 4 receptor; S1PR2: sphingosine-1-phosphate receptor 2; SQSTM1: sequestosome 1.

Sphingolipid metabolism and signaling in cardiovascular diseases

Sphingolipids are a structural component of the cell membrane, derived from sphingosine, an amino alcohol. Its sphingoid base undergoes various types of enzymatic transformations that lead to the formation of biologically active compounds, which play a crucial role in the essential pathways of cellular signaling, proliferation, maturation, and death. The constantly growing number of experimental and clinical studies emphasizes the pivotal role of sphingolipids in the pathophysiology of cardiovascular diseases, including, in particular, ischemic heart disease, hypertension, heart failure, and stroke. It has also been proven that altering the sphingolipid metabolism has cardioprotective properties in cardiac pathologies, including myocardial infarction. Recent studies suggest that selected sphingolipids may serve as valuable biomarkers useful in the prognosis of cardiovascular disorders in clinical practice. This review aims to provide an overview of the current knowledge of sphingolipid metabolism and signaling in cardiovascular diseases.

Sphingosine-1-phosphate receptor modulators in stroke treatment

Sphingosine-1-phosphate (S1P) is a bioactive lysophospholipid that can influence a broad range of biological processes through its binding to five distinct G protein-coupled receptors. S1P receptor modulators are a new group of immunosuppressive agents currently used in the immunotherapy of multiple sclerosis. Inflammation following stroke may exacerbate injury. Given that S1P signaling is linked to multiple immune processes, therapies targeting the S1P axis may be suitable for treating stroke. In this review, we outline S1P metabolism and S1P receptors, discuss the mechanisms of action of S1P receptor modulators in lymphocyte migration and their direct action on cells of the central nervous system, and provide a concise summary of the efficacy of S1P receptor modulators in animal studies and clinical trials on treatments for stroke.

Storax Inhibits Caveolae-Mediated Transcytosis at Blood-Brain Barrier After Ischemic Stroke in Rats

Background and Purpose: Blood-brain barrier (BBB) disruption following ischemic stroke (IS) contributes to hemorrhagic transformation, brain edema, increased neural dysfunction, secondary injury, and mortality. The prevailing view attributes the destruction of tight junction proteins (TJs) to the resulting BBB damage following IS. However, recent studies define a stepwise impairment of the transcellular barrier followed by the paracellular barrier which accounts for the BBB leakage in IS. The increased endothelial transcytosis that has been proven to be caveolae-mediated, preceding and independent of TJs disintegration. Emerging experimental investigations suggested Storax attenuates BBB damage after stroke. This study aimed to test our hypothesis that Storax inhibits caveolae-mediated transcytosis at BBB after ischemic stroke in rats. Methods: Male Wistar rats (250-300 g) were subjected to transient middle cerebral artery occlusion (t-MCAO). Brain water content and the cerebral infarction size were assessed by brain tissue drying-wet method and 2,3,5-triphenyltetrazolium chloride (TTC) staining. BBB permeability was detected by the leakage of Evans blue and Albumin-Alexa594. The ultrastructure of BBB was examined by transmission electron microscopy (TEM). Cav-1 and Mfsd2a were quantified by western blotting and immunofluorescence staining, AQP4, PDGFR-β, ZO-1 and Occludin were quantified by western blotting. Results: Storax treatment of 0.1 g/kg had no significant effects on brain lesions. Storax treatment of 0.2, 0.4, and 0.8 g/kg led to a significant decrease in infarction size, and the Storax 0.4, 0.8 g/kg groups displayed a significant reduction in brain water content. Storax treatment of 0.8 g/kg showed mild toxic reactions. Thus, 0.4 g/kg Storax was selected as the optimal dose for subsequent studies. Storax significantly inhibited the fluorescent albumin intensity in the brain parenchyma and the number of caveolae in ECs, alongside attenuating the ultrastructural disruption of BBB at 6 h after stroke. Meanwhile, Storax significantly increased the expression of Mfsd2a and PDGFR-β, and decrease the expression of Cav-1 and AQP4, corresponding to the significantly decreased Cav-1 positive cells and increased Mfsd2a positive cells. However, Storax has no significant effects on Evan blue leakage or the expression ZO-1, Occludin. Conclusion: Our experimental findings demonstrate Storax treatment inhibits caveolae-mediated transcytosis at BBB in the focal stroke model of rats. We also speculate that regulation of Cav-1, Mfsd2a, AQP4, and PDGFR-β expressions might be associated with its beneficial pharmacological effect, but remain to define and elucidate in future investigation.

Endothelial S1pr2 regulates post-ischemic angiogenesis via AKT/eNOS signaling pathway

Aims: It is important to understand the mechanism that regulates post-ischemic angiogenesis and to explore a new therapeutic target for an effective improvement of revascularization in peripheral artery disease (PAD) patients. Post-ischemic angiogenesis is a highly orchestrated process, which involves vascular endothelial cells (ECs) proliferation, migration and assembly into capillaries. We found a significant reduction of S1pr2 (sphingosine 1-phosphate receptor 2) in endothelial cells after hindlimb ischemia (HLI). We thus hypothesized that EC-S1pr2 might be involved in the regulation of post-ischemic angiogenesis and blood flow recovery during peripheral arterial disease (PAD). Methods and Results: We generated both EC-specific S1pr2 loss-of-function and S1pr2 gain-of-function mice. Our study showed that EC-specific S1pr2 loss-of-function significantly enhanced post-ischemic angiogenesis and improved blood flow recovery upon femoral artery ligation, whereas the EC-specific S1pr2 gain-of-function severely hindered post-ischemic angiogenesis and reduced blood flow recovery in ischemic limbs. We next identified that S1pr2 inhibited AKT/eNOS signaling pathway, and thus inhibited EC proliferation/migration and angiogenic activity. As expected, pharmacological inhibition of S1pr2 by JTE013 improved post-ischemic angiogenesis and improved blood flow perfusion after femoral artery ligation. Moreover, we developed RGD-peptide magnetic nanoparticles packaging S1pr2-siRNA which specifically targeted ECs and achieved an efficient silencing of S1pr2 expression in ECs in vivo. This EC-targeted strategy to dampen S1pr2 significantly enhanced post-ischemic angiogenesis and boosted blood perfusion after HLI, supplying a novel therapy target for patients with peripheral arterial disease. Conclusions: This present study demonstrates that EC-expressing S1pr2 tightly controls post-ischemic angiogenesis and blood flow perfusion recovery. This research provides a novel strategy for EC-target knockdown of S1pr2 as a new therapeutic intervention for patients with peripheral artery disease.

Sphingosine-1-phosphate and Sphingosine-1-phosphate receptors in the cardiovascular system: pharmacology and clinical implications

Sphingosine-1-phosphate (S1P) is a lipid that binds and activates five distinct receptor subtypes, S1P₁, S1P₂, S1P₃, S1P₄, S1P₅, widely expressed in different cells, tissues and organs. In the cardiovascular system these receptors have been extensively studied, but no drug acting on them has been approved so far for treating cardiovascular diseases. In contrast, a number of S1P receptor agonists are approved as immunomodulators, mainly for multiple sclerosis, because of their action on lymphocyte trafficking. This chapter summarizes the available information on S1P receptors in the cardiovascular system and discusses their potential for treating cardiovascular conditions and/or their role on the clinical pharmacology of drugs so far approved for non-cardiovascular conditions. Basic research has recently produced data useful to understand the molecular pharmacology of S1P and S1P receptors, regarding biased agonism, S1P storage, release and vehiculation and chaperoning by lipoproteins, paracrine actions, intracellular non-receptorial S1P actions. On the other hand, the approval of fingolimod and newer generation S1P receptor ligands as immunomodulators, provides information on a number of clinical observations on the impact of these drugs on cardiovascular system which need to be integrated with preclinical data. S1P receptors are potential targets for prevention and treatment of major cardiovascular conditions, including hypertension, myocardial infarction, heart failure and stroke.

The S1PR2‐CCL2‐BDNF‐TrkB pathway mediates neuroinflammation and motor incoordination in hyperammonaemia

Aims

Chronic hyperammonaemia and inflammation synergistically induce neurological impairment, including motor incoordination, in hepatic encephalopathy. Hyperammonaemic rats show neuroinflammation in the cerebellum which enhances GABAergic neurotransmission leading to motor incoordination. We aimed to identify underlying mechanisms. The aims were (1) to assess if S1PR2 is involved in microglial and astrocytic activation in the cerebellum of hyperammonaemic rats; (2) to identify pathways by which enhanced S1PR2 activation induces neuroinflammation and alters neurotransmission; (3) to assess if blocking S1PR2 reduces neuroinflammation and restores motor coordination in hyperammonaemic rats.

Methods

We performed ex vivo studies in cerebellar slices from control or hyperammonaemic rats to identify pathways by which neuroinflammation enhances GABAergic neurotransmission in hyperammonaemia. Neuroinflammation and neurotransmission were assessed by immunochemistry/immunofluorescence and western blot. S1PR2 was blocked by intracerebral treatment with JTE‐013 using osmotic mini‐pumps. Motor coordination was assessed by beam walking.

Results

Chronic hyperammonaemia enhances S1PR2 activation in the cerebellum by increasing its membrane expression. This increases CCL2, especially in Purkinje neurons. CCL2 activates CCR2 in microglia, leading to microglial activation, increased P2X4 membrane expression and BDNF in microglia. BDNF enhances TrkB activation in neurons, increasing KCC2 membrane expression. This enhances GABAergic neurotransmission, leading to motor incoordination in hyperammonaemic rats. Blocking S1PR2 in hyperammonaemic rats by intracerebral administration of JTE‐013 normalises the S1PR2‐CCL2‐CCR2‐BDNF‐TrkB‐KCC2 pathway, reduces glial activation and restores motor coordination in hyperammonaemic rats.

Conclusions

Enhanced S1PR2‐CCL2‐BDNF‐TrkB pathway activation mediates neuroinflammation and incoordination in hyperammonaemia. The data raise a promising therapy for patients with hepatic encephalopathy using compounds targeting this pathway.

Lipids in Liver Failure Syndromes: A Focus on Eicosanoids, Specialized Pro-Resolving Lipid Mediators and Lysophospholipids

Lipids are organic compounds insoluble in water with a variety of metabolic and non-metabolic functions. They not only represent an efficient energy substrate but can also act as key inflammatory and anti-inflammatory molecules as part of a network of soluble mediators at the interface of metabolism and the immune system. The role of endogenous bioactive lipid mediators has been demonstrated in several inflammatory diseases (rheumatoid arthritis, inflammatory bowel disease, atherosclerosis, cancer). The liver is unique in providing balanced immunotolerance to the exposure of bacterial components from the gut transiting through the portal vein and the lymphatic system. This balance is abruptly deranged in liver failure syndromes such as acute liver failure and acute-on-chronic liver failure. In these syndromes, researchers have recently focused on bioactive lipid mediators by global metabonomic profiling and uncovered the pivotal role of these mediators in the immune dysfunction observed in liver failure syndromes explaining the high occurrence of sepsis and subsequent organ failure. Among endogenous bioactive lipids, the mechanistic actions of three classes (eicosanoids, pro-resolving lipid mediators and lysophospholipids) in the pathophysiological modulation of liver failure syndromes will be the topic of this narrative review. Furthermore, the therapeutic potential of lipid-immune pathways will be described.

Sphingosine-1-Phosphate Signaling in Ischemic Stroke: From Bench to Bedside and Beyond

Sphingosine-1-phosphate (S1P) signaling is being increasingly recognized as a strong modulator of immune cell migration and endothelial function. Fingolimod and other S1P modulators in ischemic stroke treatment have shown promise in emerging experimental models and small-scale clinical trials. In this article, we will review the current knowledge of the role of S1P signaling in brain ischemia from the aspects of inflammation and immune interventions, sustaining endothelial functions, regulation of blood-brain barrier integrity, and functional recovery. We will then discuss the current and future therapeutic perspectives of targeting S1P for the treatment of ischemic stroke. Mechanism studies would help to bridge the gap between preclinical studies and clinical practice. Future success of bench-to-bedside translation shall be based on in depth understanding of S1P signaling during stroke and on the ability to have a fine temporal and spatial regulation of the signal pathway.

Inhibition of Sphingosine-1-Phosphate Receptor 2 Prevents Thoracic Aortic Dissection and Rupture

Background: Numerous pieces of evidence have indicated that thoracic aortic dissection (TAD) is an inflammatory disease. Sphingosine-1-phosphate receptor 2 (S1PR2) signaling is a driver in multiple inflammatory diseases. Here, we examined the S1PR2 expression in TAD lesions and explored the effect of interfering with S1PR2 on TAD formation and progression.

Methods: Aorta specimens and blood samples were collected from patients with TAD and matched controls. The expression of S1PR1, S1PR2, and S1PR3 was examined. The effect of inhibiting S1PR2 on TAD was evaluated in a TAD mouse model induced by β-aminopropionitrile fumarate (BAPN) and AngII. The presence of sphingosine kinase 1 (SPHK1), S1P, and neutrophil extracellular traps (NETs) was investigated. Further, the possible association between S1PR2 signaling and NETs in TAD was analyzed.

Results: In the aortic tissues of patients with TAD and a mouse model, the S1PR2 expression was significantly up-regulated. In the TAD mouse model, JTE013, a specific S1PR2 antagonist, not only blunted the TAD formation and aortic rupture, but also preserved the elastic fiber architecture, reduced the smooth muscle cells apoptosis level, and mitigated the aortic wall inflammation. Augmented tissue protein expression of SPHK1, citrullinated histone H3 (CitH3, a specific marker of NETs), and serum S1P, CitH3 were detected in TAD patients. Surgical repair normalized the serum S1P and CitH3 levels. Immunofluorescence staining revealed that S1PR2 colocalized with NETs. The protein expression levels of SPHK1 and serum S1P levels positively correlated with the protein expression and serum levels of CitH3, separately. Furthermore, JTE013 treatment reduced NETs accumulation.

Conclusion: Inhibiting S1PR2 attenuates TAD formation and prevents aortic rupture. Targeting S1PR2 may provide a promising treatment strategy against TAD.

CRH/CRHR1 modulates cerebrovascular endothelial cell permeability in association with S1PR2 and S1PR3 under oxidative stress

Corticotrophin-releasing hormone (CRH) has been demonstrated to participate in vascular inflammation and permeability. Our previous studies have shown that blockade of S1PR2 or CRHR1 inhibited H₂O₂-induced brain endothelial hyperpermeability via inhibiting cPLA₂ phosphorylation. However, little is known about the linkage between S1PRs and CRHR1 in oxidative stress-induced cerebrovascular endothelial hyperpermeability. Here we observed the opposite effects of S1PR2 to those of S1PR3 on the monolayer permeability of bEnd3 cells in response to H₂O₂. Interestingly, activation of CRHR1 was found to reverse the effects resulting from blockade/silencing of both S1PR2 and S1PR3. In bEnd3 monolayer, blockade/knockdown of S1PR2 reduced the endothelial hyperpermeability and suppressed the tight junction protein ZO-1 redistribution caused by H₂O₂, along with the inhibition of p38, ERK and cPLA₂ phosphorylation. On the contrary, suppression/silencing of S1PR3 further promoted H₂O₂-induced endothelial hyperpermeability and ZO-1 redistribution, accompanied by the increased phosphorylation of p38, ERK and cPLA₂. In the presence of CRH, the effects resulting from the suppression of both S1PR2 and S1PR3 were abolished. Our results elucidate a possible linkage between CRHR1 and S1PR2/S1PR3 involving in the regulation of endothelial monolayer permeability under oxidative stress condition.

Blood-Brain Barrier Dysfunction Amplifies the Development of Neuroinflammation: Understanding of Cellular Events in Brain Microvascular Endothelial Cells for Prevention and Treatment of BBB Dysfunction

Neuroinflammation is involved in the onset or progression of various neurodegenerative diseases. Initiation of neuroinflammation is triggered by endogenous substances (damage-associated molecular patterns) and/or exogenous pathogens. Activation of glial cells (microglia and astrocytes) is widely recognized as a hallmark of neuroinflammation and triggers the release of proinflammatory cytokines, leading to neurotoxicity and neuronal dysfunction. Another feature associated with neuroinflammatory diseases is impairment of the blood-brain barrier (BBB). The BBB, which is composed of brain endothelial cells connected by tight junctions, maintains brain homeostasis and protects neurons. Impairment of this barrier allows trafficking of immune cells or plasma proteins into the brain parenchyma and subsequent inflammatory processes in the brain. Besides neurons, activated glial cells also affect BBB integrity. Therefore, BBB dysfunction can amplify neuroinflammation and act as a key process in the development of neuroinflammation. BBB integrity is determined by the integration of multiple signaling pathways within brain endothelial cells through intercellular communication between brain endothelial cells and brain perivascular cells (pericytes, astrocytes, microglia, and oligodendrocytes). For prevention of BBB disruption, both cellular components, such as signaling molecules in brain endothelial cells, and non-cellular components, such as inflammatory mediators released by perivascular cells, should be considered. Thus, understanding of intracellular signaling pathways that disrupt the BBB can provide novel treatments for neurological diseases associated with neuroinflammation. In this review, we discuss current knowledge regarding the underlying mechanisms involved in BBB impairment by inflammatory mediators released by perivascular cells.

Serum Sphingosine-1-Phosphate Levels Are Associated With Severity and Outcome in Patients With Cerebral Ischemia

BACKGROUND AND PURPOSE

The aim of this study was to examine whether sphingosine-1-phosphate (S1P) levels in patients with acute stroke are associated with stroke severity and outcome.

METHODS

In a prospective stroke cohort (MARK-STROKE), 374 patients with acute ischemic stroke or transient ischemic attack were enrolled (mean age: 67.9±13.0 years, sex: 64.7% male), and serum-S1P at admission was analyzed with tandem mass spectrometry. In addition to cross-sectional analyses, 79 adverse events (death, stroke, myocardial infarction, rehospitalization) were recorded in 270 patients during follow-up. Regression analyses were adjusted for age, sex, low-density lipoprotein cholesterol, and vascular risk factors. Results were validated in an independent stroke cohort with 219 patients with acute ischemic stroke (CIRCULAS).

RESULTS

Low serum-S1P was associated with higher National Institutes of Health Stroke Scale score at admission and with anterior circulation nonlacunar infarcts determined by multivariate regression analyses. During a follow-up of 294±170 days, patients with S1P in the lowest tertile (<1.33 µmol/L) had more adverse events (Kaplan-Meier analysis, P=0.048 for trend). In adjusted Cox regression analysis, the lowest S1P tertile was associated with a worse outcome after stroke (hazard ratio, HR 0.51 [95% confidence interval 0.28-0.92]). Results were confirmed in an independent cohort, ie, low S1P levels were associated with higher National Institutes of Health Stroke Scale, larger infarct volumes and worse outcome after 90 days (β-coefficient: -0.03, P=0.026; β-coefficient: -0.099, P=0.009 and odds ratio 0.52 [0.28-0.96], respectively).

CONCLUSIONS

Our findings imply a detrimental role of low S1P levels in acute stroke and therefore underpin the therapeutic potential of S1P-mimics.

Critical Roles of Lysophospholipid Receptors in Activation of Neuroglia and Their Neuroinflammatory Responses

Activation of microglia and/or astrocytes often releases proinflammatory molecules as critical pathogenic mediators that can promote neuroinflammation and secondary brain damages in diverse diseases of the central nervous system (CNS). Therefore, controlling the activation of glial cells and their neuroinflammatory responses has been considered as a potential therapeutic strategy for treating neuroinflammatory diseases. Recently, receptor-mediated lysophospholipid signaling, sphingosine 1-phosphate (S1P) receptor- and lysophosphatidic acid (LPA) receptor-mediated signaling in particular, has drawn scientific interest because of its critical roles in pathogenies of diverse neurological diseases such as neuropathic pain, systemic sclerosis, spinal cord injury, multiple sclerosis, cerebral ischemia, traumatic brain injury, hypoxia, hydrocephalus, and neuropsychiatric disorders. Activation of microglia and/or astrocytes is a common pathogenic event shared by most of these CNS disorders, indicating that lysophospholipid receptors could influence glial activation. In fact, many studies have reported that several S1P and LPA receptors can influence glial activation during the pathogenesis of cerebral ischemia and multiple sclerosis. This review aims to provide a comprehensive framework about the roles of S1P and LPA receptors in the activation of microglia and/or astrocytes and their neuroinflammatory responses in CNS diseases.

Sphingosine 1-phosphate and its receptors in ischemia

Sphingosine 1-phosphate (S1P), a metabolite of sphingolipids, is mainly derived from red blood cells (RBCs), platelets and endothelial cells (ECs). It plays important roles in regulating cell survival, vascular integrity and inflammatory responses through its receptors. S1P receptors (S1PRs), including 5 subtypes (S1PR1-5), are G protein-coupled receptors and have been proved to mediate various and complex roles of S1P in atherosclerosis, myocardial infarction (MI) and ischemic stroke by regulating endothelial function and inflammatory response as well as immune cell behavior. This review emphasizes the functions of S1PRs in atherosclerosis and ischemic diseases such as MI and ischemic stroke, enabling mechanistic studies and new S1PRs targeted therapies in atherosclerosis and ischemia in the future.

Protective Effects of Complement Component 8 Gamma Against Blood-Brain Barrier Breakdown

The blood-brain barrier (BBB) regulates the traffic of micromolecules and macromolecules between the peripheral blood and the central nervous system, to maintain brain homeostasis. BBB disruption and dysfunction accompany a variety of neurological disorders and are closely related with the neuroinflammatory cascades that are triggered by leukocyte infiltration and glial activation. Here, we explored the role of complement component 8 gamma (C8G) in the maintenance of BBB integrity. Previously, C8G was shown to inhibit neuroinflammation by interfering with the sphingosine-1-phosphate (S1P)-S1PR2 interaction. The results of the present study revealed that C8G is localized in perivascular astrocytes, whereas S1PR2 is expressed in endothelial cells (ECs). In the lipopolysaccharide (LPS)-induced neuroinflammation model, the intracerebroventricular administration of the recombinant C8G protein protected the integrity of the BBB, whereas shRNA-mediated C8G knockdown enhanced BBB permeability and neutrophil infiltration. Using pharmacological agonists and antagonists of S1PR2, we demonstrated that C8G inhibited the inflammatory activation of ECs in culture by antagonizing S1PR2. In the in vitro BBB model, the addition of the recombinant C8G protein preserved endothelial integrity, whereas the knockdown of C8G exacerbated endothelial leakage under inflammatory conditions. Together, our findings indicate an important role for astrocytic C8G in protecting the BBB in the inflamed brain, suggesting a novel mechanism of cross talk between astrocytes and ECs in terms of BBB maintenance.

Platelets as drivers of ischemia/reperfusion injury after stroke

Ischemic stroke is a leading cause of morbidity and mortality worldwide and, despite reperfusion either via thrombolysis or thrombectomy, stroke patients often suffer from lifelong disabilities. These persistent neurological deficits may be improved by treating the ischemia/reperfusion (I/R) injury that occurs following ischemic stroke. There are currently no approved therapies to treat I/R injury, and thus it is imperative to find new targets to decrease the burden of ischemic stroke and related diseases. Platelets, cell fragments from megakaryocytes, are primarily known for their role in hemostasis. More recently, investigators have studied the nonhemostatic role of platelets in inflammatory pathologies, such as I/R injury after ischemic stroke. In this review, we seek to provide an overview of how I/R can lead to platelet activation and how activated platelets, in turn, can exacerbate I/R injury after stroke. We will also discuss potential mechanisms by which platelets may ameliorate I/R injury.

Sphingosine-1-Phosphate, Motor Severity, and Progression in Parkinson's Disease (MARK-PD)

BACKGROUND

Treatment with sphingosine-1-phosphate (S1P) agonists confers neuroprotective effects in animal models of Parkinson's disease (PD).

OBJECTIVES

We assessed the association of serum S1P levels with motor and cognitive symptoms in patients with PD.

METHODS

S1P concentrations were analyzed with liquid chromatography-tandem mass spectrometry (LC-MS/MS) in serum of 196 PD patients and in 196 age- and sex-matched controls. Motor (Unified Parkinson's disease rating scale III [UPDRS III], Hoehn and Yahr) and cognitive (Montreal Cognitive Assessment [MoCA]) function were assessed at baseline. Follow-up data was available from 64 patients (median [interquartile range], 513 [381-677] days).

RESULTS

S1P levels were lower in PD patients compared with controls, that is 1.75 (1.38-2.07) and 1.90 (1.59-2.18) μmol/L, respectively (P = 0.001). In PD patients, lower S1P concentrations were associated with higher UPDRS III scores and Hoehn and Yahr stage. In the follow-up cohort, S1P concentrations below the median were associated with faster motor decline (hazard ratio: 4.78 [95% CI, 1.98, 11.50]), but not with cognitive worsening.

CONCLUSIONS

Our observations reveal an association of S1P with PD. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The S1P2 receptor regulates blood-brain barrier integrity and leukocyte extravasation with implications for neurodegenerative disease

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid which modulates vascular integrity through its receptors, S1P₁-S1P₅. Notably, S1P₂ has been shown to mediate the disruption of cerebrovascular integrity in vitro and in vivo. However, the mechanism underlying this process has not been fully elucidated. We evaluated the role of S1P₂ in blood-brain barrier (BBB) disruption induced by lipopolysaccharide (LPS)-mediated systemic inflammation and found that BBB disruption and neutrophil infiltration were significantly attenuated in S1pr2^-/- mice relative to S1pr2^+/- littermates. This is concomitant with attenuation of LPS-induced transcriptional activation of IL-6 and downregulation of occludin. Furthermore, S1pr2^-/- mice had significantly reduced expression of genes essential for neutrophil infiltration: Sele, Cxcl1, and Cxcl2. Conversely, pharmacological agonism of S1P₂ induced transcriptional activation of E-selectin in vitro and in vivo. Although S1P₂ does not appear to be required for activation of microglia, stimulation of microglial cells with the S1P₂ potentiated the response of endothelial cells to LPS. These results demonstrate that S1P₂ promotes LPS-induced neutrophil extravasation by inducing expression of endothelial adhesion molecule gene, Sele, and potentiating microglial inflammation of endothelial cells. It is likely that S1P₂ is a mediator of cerebrovascular inflammation and represents a potential therapeutic target for neurodegenerative disease such as vascular cognitive impairment.

Gamma subunit of complement component 8 is a neuroinflammation inhibitor

The complement system is part of the innate immune system that comprises several small proteins activated by sequential cleavages. The majority of these complement components, such as components 3a (C3a) and C5a, are chemotactic and pro-inflammatory. However, in this study, we revealed an inhibitory role of complement component 8 gamma (C8G) in neuroinflammation. In patients with Alzheimer's disease, who exhibit strong neuroinflammation, we found higher C8G levels in brain tissue, CSF, and plasma. Our novel findings also showed that the expression level of C8G increases in the inflamed mouse brain, and that C8G is mainly localized to brain astrocytes. Experiments using recombinant C8G protein and shRNA-mediated knockdown showed that C8G inhibits glial hyperactivation, neuroinflammation, and cognitive decline in acute and chronic animal models of Alzheimer's disease. Additionally, we identified sphingosine-1-phosphate receptor 2 (S1PR2) as a novel interaction protein of C8G and demonstrated that astrocyte-derived C8G interacts with S1PR2 to antagonize the pro-inflammatory action of S1P in microglia. Taken together, our results reveal the previously unrecognized role of C8G as a neuroinflammation inhibitor. Our findings pave the way towards therapeutic containment of neuroinflammation in Alzheimer's disease and related neurological diseases.

The bile acid TUDCA and neurodegenerative disorders: An overview

Bear bile has been used in Traditional Chinese Medicine for thousands of years due to its therapeutic potential and clinical applications. The tauroursodeoxycholic acid (TUDCA), one of the acids found in bear bile, is a hydrophilic bile acid and naturally produced in the liver by conjugation of taurine to ursodeoxycholic acid (UDCA). Several studies have shown that TUDCA has neuroprotective action in several models of neurodegenerative disorders (ND), including Alzheimer's disease, Parkinson's disease, and Huntington's disease, based on its potent ability to inhibit apoptosis, attenuate oxidative stress, and reduce endoplasmic reticulum stress in different experimental models of these illnesses. Our research extends the knowledge of the bile acid TUDCA actions in ND and the mechanisms and pathways involved in its cytoprotective effects on the brain, providing a novel perspective and opportunities for treatment of these diseases.

Endothelial S1P1 Signaling Counteracts Infarct Expansion in Ischemic Stroke

RATIONALE

Cerebrovascular function is critical for brain health, and endogenous vascular protective pathways may provide therapeutic targets for neurological disorders. S1P (Sphingosine 1-phosphate) signaling coordinates vascular functions in other organs, and S1P1 (S1P receptor-1) modulators including fingolimod show promise for the treatment of ischemic and hemorrhagic stroke. However, S1P1 also coordinates lymphocyte trafficking, and lymphocytes are currently viewed as the principal therapeutic target for S1P1 modulation in stroke.

OBJECTIVE

To address roles and mechanisms of engagement of endothelial cell S1P1 in the naive and ischemic brain and its potential as a target for cerebrovascular therapy.

METHODS AND RESULTS

Using spatial modulation of S1P provision and signaling, we demonstrate a critical vascular protective role for endothelial S1P1 in the mouse brain. With an S1P1 signaling reporter, we reveal that abluminal polarization shields S1P1 from circulating endogenous and synthetic ligands after maturation of the blood-neural barrier, restricting homeostatic signaling to a subset of arteriolar endothelial cells. S1P1 signaling sustains hallmark endothelial functions in the naive brain and expands during ischemia by engagement of cell-autonomous S1P provision. Disrupting this pathway by endothelial cell-selective deficiency in S1P production, export, or the S1P1 receptor substantially exacerbates brain injury in permanent and transient models of ischemic stroke. By contrast, profound lymphopenia induced by loss of lymphocyte S1P1 provides modest protection only in the context of reperfusion. In the ischemic brain, endothelial cell S1P1 supports blood-brain barrier function, microvascular patency, and the rerouting of blood to hypoperfused brain tissue through collateral anastomoses. Boosting these functions by supplemental pharmacological engagement of the endothelial receptor pool with a blood-brain barrier penetrating S1P1-selective agonist can further reduce cortical infarct expansion in a therapeutically relevant time frame and independent of reperfusion.

CONCLUSIONS

This study provides genetic evidence to support a pivotal role for the endothelium in maintaining perfusion and microvascular patency in the ischemic penumbra that is coordinated by S1P signaling and can be harnessed for neuroprotection with blood-brain barrier-penetrating S1P1 agonists.

Cellular stress signaling activates type-I IFN response through FOXO3-regulated lamin posttranslational modification

Neural stem/progenitor cells (NSPCs) persist over the lifespan while encountering constant challenges from age or injury related brain environmental changes like elevated oxidative stress. But how oxidative stress regulates NSPC and its neurogenic differentiation is less clear. Here we report that acutely elevated cellular oxidative stress in NSPCs modulates neurogenic differentiation through induction of Forkhead box protein O3 (FOXO3)-mediated cGAS/STING and type I interferon (IFN-I) responses. We show that oxidative stress activates FOXO3 and its transcriptional target glycine-N-methyltransferase (GNMT) whose upregulation triggers depletion of s-adenosylmethionine (SAM), a key co-substrate involved in methyl group transfer reactions. Mechanistically, we demonstrate that reduced intracellular SAM availability disrupts carboxymethylation and maturation of nuclear lamin, which induce cytosolic release of chromatin fragments and subsequent activation of the cGAS/STING-IFN-I cascade to suppress neurogenic differentiation. Together, our findings suggest the FOXO3-GNMT/SAM-lamin-cGAS/STING-IFN-I signaling cascade as a critical stress response program that regulates long-term regenerative potential.

Neural stem and progenitor cells (NSPCs) encounter constant stresses during aging, such as elevated oxidative stress. Here the authors show that oxidative stress induced reduction in NSPC neural differentiation is mediated by a FOXO3-GNMT/SAM-lamin-cGAS/STING-IFN-I signalling cascade initiated by FOXO3 oxidation.