Role of microglial and endothelial CD36 in post-ischemic inflammasome activation and interleukin-1β-induced endothelial activation

Role of microglia in stroke

Microglia play key roles in the post-ischemic inflammatory response and damaged tissue removal reacting rapidly to the disturbances caused by ischemia and working to restore the lost homeostasis. However, the modified environment, encompassing ionic imbalances, disruption of crucial neuron-microglia interactions, spreading depolarization, and generation of danger signals from necrotic neurons, induce morphological and phenotypic shifts in microglia. This leads them to adopt a proinflammatory profile and heighten their phagocytic activity. From day three post-ischemia, macrophages infiltrate the necrotic core while microglia amass at the periphery. Further, inflammation prompts a metabolic shift favoring glycolysis, the pentose-phosphate shunt, and lipid synthesis. These shifts, combined with phagocytic lipid intake, drive lipid droplet biogenesis, fuel anabolism, and enable microglia proliferation. Proliferating microglia release trophic factors contributing to protection and repair. However, some microglia accumulate lipids persistently and transform into dysfunctional and potentially harmful foam cells. Studies also showed microglia that either display impaired apoptotic cell clearance, or eliminate synapses, viable neurons, or endothelial cells. Yet, it will be essential to elucidate the viability of engulfed cells, the features of the local environment, the extent of tissue damage, and the temporal sequence. Ischemia provides a rich variety of region- and injury-dependent stimuli for microglia, evolving with time and generating distinct microglia phenotypes including those exhibiting proinflammatory or dysfunctional traits and others showing pro-repair features. Accurate profiling of microglia phenotypes, alongside with a more precise understanding of the associated post-ischemic tissue conditions, is a necessary step to serve as the potential foundation for focused interventions in human stroke.

Microglial Inflammatory Mechanisms in Stroke: The Jury Is Still Out

Microglia represent the main immune cell population in the CNS with unique homeostatic roles and contribution to broad neurological conditions. Stroke is associated with marked changes in microglial phenotypes and induction of inflammatory responses, which emerge as key modulators of brain injury, neurological outcome and regeneration. However, due to the limited availability of functional studies with selective targeting of microglia and microglia-related inflammatory pathways in stroke, the vast majority of observations remain correlative and controversial. Because extensive review articles discussing the role of inflammatory mechanisms in different forms of acute brain injury are available, here we focus on some specific pathways that appear to be important for stroke pathophysiology with assumed contribution by microglia. While the growing toolkit for microglia manipulation increasingly allows targeting inflammatory pathways in a cell-specific manner, reconsideration of some effects devoted to microglia may also be required. This may particularly concern the interpretation of inflammatory mechanisms that emerge in response to stroke as a form of sterile injury and change markedly in chronic inflammation and common stroke comorbidities.

Analysis of brain and blood single-cell transcriptomics in acute and subacute phases after experimental stroke

Cerebral ischemia triggers a powerful inflammatory reaction involving peripheral leukocytes and brain resident cells that contribute to both tissue injury and repair. However, their dynamics and diversity remain poorly understood. To address these limitations, we performed a single-cell transcriptomic study of brain and blood cells 2 or 14 days after ischemic stroke in mice. We observed a strong divergence of post-ischemic microglia, monocyte-derived macrophages and neutrophils over time, while endothelial cells and brain-associated macrophages showed altered transcriptomic signatures at 2 days poststroke. Trajectory inference predicted the in situ trans-differentiation of macrophages from blood monocytes into day 2 and day 14 phenotypes, while neutrophils were projected to be continuously de novo recruited from the blood. Brain single-cell transcriptomes from both female and male aged mice were similar to that of young male mice, but aged and young brains differed in their immune cell composition. Although blood leukocyte analysis also revealed altered transcriptomes after stroke, brain-infiltrating leukocytes displayed higher transcriptomic divergence than their circulating counterparts, indicating that phenotypic diversification occurs within the brain in the early and recovery phases of ischemic stroke. A portal ( https://anratherlab.shinyapps.io/strokevis/ ) is provided to allow user-friendly access to our data.

Glycosylation: A new signaling paradigm for the neurovascular diseases

A wide range of life-threatening conditions with complicated pathogenesis involves neurovascular disorders encompassing Neurovascular unit (NVU) damage. The pathophysiology of NVU is characterized by several features including tissue hypoxia, stimulation of inflammatory and angiogenic processes, and the initiation of intricate molecular interactions, collectively leading to an elevation in blood-brain barrier permeability, atherosclerosis and ultimately, neurovascular diseases. The presence of compelling data about the significant involvement of the glycosylation in the development of diseases has sparked a discussion on whether the abnormal glycosylation may serve as a causal factor for neurovascular disorders, rather than being just recruited as a secondary player in regulating the critical events during the development processes like embryo growth and angiogenesis. An essential tool for both developing new anti-ischemic therapies and understanding the processes of ischemic brain damage is undertaking pre-clinical studies of neurovascular disorders. Together with the post-translational modification of proteins, the modulation of glycosylation and its enzymes implicates itself in several abnormal activities which are known to accelerate neuronal vasculopathy. Despite the failure of the majority of glycosylation-based preclinical and clinical studies over the past years, there is a significant probability to provide neuroprotection utilizing modern and advanced approaches to target abnormal glycosylation activity at embryonic stages as well. This article focuses on a variety of experimental evidence to postulate the interconnection between glycosylation and vascular disorders along with possible treatment options.

Meningeal interleukin-17-producing T cells mediate cognitive impairment in a mouse model of salt-sensitive hypertension

Hypertension (HTN), a disease afflicting over one billion individuals worldwide, is a leading cause of cognitive impairment, the mechanisms of which remain poorly understood. In the present study, in a mouse model of HTN, we find that the neurovascular and cognitive dysfunction depends on interleukin (IL)-17, a cytokine elevated in individuals with HTN. However, neither circulating IL-17 nor brain angiotensin signaling can account for the dysfunction. Rather, IL-17 produced by T cells in the dura mater is the mediator released in the cerebrospinal fluid and activating IL-17 receptors on border-associated macrophages (BAMs). Accordingly, depleting BAMs, deleting IL-17 receptor A in brain macrophages or suppressing meningeal T cells rescues cognitive function without attenuating blood pressure elevation, circulating IL-17 or brain angiotensin signaling. Our data unveil a critical role of meningeal T cells and macrophage IL-17 signaling in the neurovascular and cognitive dysfunction in a mouse model of HTN.

Calcium transients in nNOS neurons underlie distinct phases of the neurovascular response to barrel cortex activation in awake mice

Neuronal nitric oxide (NO) synthase (nNOS), a Ca2+ dependent enzyme, is expressed by distinct populations of neocortical neurons. Although neuronal NO is well known to contribute to the blood flow increase evoked by neural activity, the relationships between nNOS neurons activity and vascular responses in the awake state remain unclear. We imaged the barrel cortex in awake, head-fixed mice through a chronically implanted cranial window. The Ca2+ indicator GCaMP7f was expressed selectively in nNOS neurons using adenoviral gene transfer in nNOScre mice. Air-puffs directed at the contralateral whiskers or spontaneous motion induced Ca2+ transients in 30.2 ± 2.2% or 51.6 ± 3.3% of nNOS neurons, respectively, and evoked local arteriolar dilation. The greatest dilatation (14.8 ± 1.1%) occurred when whisking and motion occurred simultaneously. Ca2+ transients in individual nNOS neurons and local arteriolar dilation showed various degrees of correlation, which was strongest when the activity of whole nNOS neuron ensemble was examined. We also found that some nNOS neurons became active immediately prior to arteriolar dilation, while others were activated gradually after arteriolar dilatation. Discrete nNOS neuron subsets may contribute either to the initiation or to the maintenance of the vascular response, suggesting a previously unappreciated temporal specificity to the role of NO in neurovascular coupling.

Endothelial cell CD36 mediates stroke-induced brain injury via BBB dysfunction and monocyte infiltration in normal and obese conditions

CD36 expressed in multiple cell types regulates inflammation, vascular function, and innate immunity. Specifically, CD36 in microvascular endothelial cells (ECs) signals to elicit inflammation and causes EC death. This study investigated roles for EC-CD36 on acute stroke pathology in normal and obese conditions. Obesity induced by a high-fat diet (HD) selectively increased CD36 expression in ECs, not in monocytes/macrophages, in the post-ischemic brain. Mice deficient CD36 in ECs (ECCD36-/-) showed reduced injury size and vascular permeability in normal conditions. While control mice fed a HD developed obesity and aggravated stroke injury, ECCD36-/- mice were resistant to develop an obesity phenotype. Subjecting ECCD36-/- mice to stroke resulted in reduced injury size and BBB disruption. Moreover, the mice had reduced MCP-1 and CCR2 gene expression, resulting in reduced monocyte trafficking with improved survival and acute motor function. Reduced MCP-1 and CCR2 expression was still evident in ECCD36-/- mice subjected to severe stroke, suggesting that monocyte trafficking is an infarct-independent metabolic effect associated with specific EC-CD36 deletion. Our findings demonstrate the importance of EC-CD36 in developing vascular comorbidities and suggest that targeting EC-CD36 is a potential preventative strategy to normalize vascular risk factors, leading to improved acute stroke outcomes.

Brain and blood single-cell transcriptomics in acute and subacute phases after experimental stroke

Cerebral ischemia triggers a powerful inflammatory reaction involving both peripheral leukocytes and brain resident cells. Recent evidence indicates that their differentiation into a variety of functional phenotypes contributes to both tissue injury and repair. However, the temporal dynamics and diversity of post-stroke immune cell subsets remain poorly understood. To address these limitations, we performed a longitudinal single-cell transcriptomic study of both brain and mouse blood to obtain a composite picture of brain-infiltrating leukocytes, circulating leukocytes, microglia and endothelium diversity over the ischemic/reperfusion time. Brain cells and blood leukocytes isolated from mice 2 or 14 days after transient middle cerebral artery occlusion or sham surgery were purified by FACS sorting and processed for droplet-based single-cell transcriptomics. The analysis revealed a strong divergence of post-ischemic microglia, macrophages, and neutrophils over time, while such diversity was less evident in dendritic cells, B, T and NK cells. Conversely, brain endothelial cells and brain associated-macrophages showed altered transcriptomic signatures at 2 days post-stroke, but low divergence from sham at day 14. Pseudotime trajectory inference predicted the in-situ longitudinal progression of monocyte-derived macrophages from their blood precursors into day 2 and day 14 phenotypes, while microglia phenotypes at these two time points were not connected. In contrast to monocyte-derived macrophages, neutrophils were predicted to be continuously de-novo recruited from the blood. Brain single-cell transcriptomics from both female and male aged mice did not show major changes in respect to young mice, but aged and young brains differed in their immune cell composition. Furthermore, blood leukocyte analysis also revealed altered transcriptomes after stroke. However, brain-infiltrating leukocytes displayed higher transcriptomic divergence than their circulating counterparts, indicating that phenotypic diversification into cellular subsets occurs within the brain in the early and the recovery phase of ischemic stroke. In addition, this resource report contains a searchable database https://anratherlab.shinyapps.io/strokevis/ to allow user-friendly access to our data. The StrokeVis tool constitutes a comprehensive gene expression atlas that can be interrogated at the gene and cell type level to explore the transcriptional changes of endothelial and immune cell subsets from mouse brain and blood after stroke.

Neuroimmune mechanisms and therapies mediating post-ischaemic brain injury and repair

The nervous and immune systems control whole-body homeostasis and respond to various types of tissue injury, including stroke, in a coordinated manner. Cerebral ischaemia and subsequent neuronal cell death activate resident or infiltrating immune cells, which trigger neuroinflammation that affects functional prognosis after stroke. Inflammatory immune cells exacerbate ischaemic neuronal injury after the onset of brain ischaemia; however, some of the immune cells thereafter change their function to neural repair. The recovery processes after ischaemic brain injury require additional and close interactions between the nervous and immune systems through various mechanisms. Thus, the brain controls its own inflammation and repair processes after injury via the immune system, which provides a promising therapeutic opportunity for stroke recovery.

Xueshuantong injection alleviates cerebral microcirculation disorder in middle cerebral artery occlusion/reperfusion rats by suppressing inflammation via JNK mediated JAK2/STAT3 and NF-κB signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

In the long history of traditional Chinese medicine, Panax notoginseng has been used as a key herb for the treatment of blood diseases. Brain microvessels support adequate blood circulation to maintain normal physiological function, therefore, brain microcirculation disorder is an important therapeutic target for various brain diseases. However, the role of Xueshuantong (XST) injection composed of saponins from P. Notoginseng (PNS) in the amelioration of cerebral microcirculation disorder is unclear.

AIMS OF THE STUDY

Cerebral microcirculation disorder and inflammation play a vital role in stroke. Capillary endothelial cells and adjacent tight junctions are fundamental to the structure and function of cerebrovascule. XST injection has been used clinically in the treatment of stroke, but no studies have reported its indication in cerebral microcirculation disorder. This study is to explore the action and mechanism of XST injection in the alleviation of cerebral microcirculation disorder in middle cerebral artery occlusion/reperfusion (MCAO/R) rats.

MATERIALS AND METHODS

MCAO/R rats and LPS-induced bEnd.3 cells were employed for the investigation of effect and mechanism of XST injection. Brain damages were evaluated by neurobehavioral assessment, 2, 3, 5-triphenyltetrazolium chloride (TTC) staining, hematoxylin and eosin staining (H&E), and Nissl staining. Morphology and density changes of cerebral microvessels were monitored by immunohistochemistry. Cell permeability was detected by measurement of trans-endothelial electrical resistance (TEER) and sodium fluorescein (NaF) leakage. The mRNA and protein expressions of inflammatory cytokines, tight junction proteins, adhesion molecules, Janus kinase 2 (JAK2), signal transducer and activator of transcription-3 (STAT3), inhibitor of NF-κB (IκB), nuclear factor-κB (NF-κB) and c-jun N-terminal kinase (JNK) in brain microvessels and lipopolysaccharide (LPS)-induced bEnd.3 cells were measured by real-time PCR and Western blot, respectively.

RESULTS

XST injection at 48 mg/kg significantly improved the neurological damage, inflammatory infiltration, and microvessel morphology, and increased microvessel density in brain of MCAO/R rats. The endothelial permeability was significantly mitigated by XST injection in LPS-induced bEnd.3 cells. Meanwhile, the tight junction proteins such as zona occludens 1 (ZO-1) and occludin were elevated remarkably in brain microvessel of MCAO/R rats and LPS-induced bEnd.3 cells. Moreover, the expression of inflammatory mediators including interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, inducible nitric oxide synthase (iNOS), cycloocygenases 2 (COX-2), vascular cellular adhesion molecule-1 (VCAM-1), matrix metalloproteinase (MMP)-2, and MMP-9 were inhibited by XST injection. In addition, XST injection suppressed the phosphorylation of JAK2, STAT3, IκB, NF-κB and JNK, which could be abolished by anisomycin, the JNK agonist.

CONCLUSION

XST injection improved cerebral microvescular structure damage and dysfunction in MCAO/R rats through inhibiting inflammation activated by JNK mediated JAK2/STAT3 and NF-κB signaling pathways. The novel findings may provide theoretical basis for the clinical application in the treatment of cerebral microcirculation disorder.

All-in-One Theranostic Platform Based on Hollow Microcapsules for Intragastric-Targeting Antiulcer Drug Delivery, CT Imaging, and Synergistically Healing Gastric Ulcer

Bismuth-containing therapies are suggested as first-line and rescue alternatives for gastric ulcer (GU) treatment and Helicobacter pylori eradication. The current treatment strategy is called quadruple therapy and includes proton pump inhibitors, bismuth, and two broad-band antibiotics. This fact may affect medication compliance, leading to a resistance rate of more than 25% to clarithromycin or metronidazole. To counter this, from the perspective of natural products, an intragastric-targeting all-in-one theranostic platform is established: a drug carrier microcapsule composed of multiple synergistic antiulcer drugs, including bismuth, gallotannin, and antibiotics is obtained (BiG@MCs), and the therapeutic effects of BiG@MCs in rodent models are further evaluated. The results show that the BiG@MCs are spherical with homogeneous particle size (3 ± 0.5 µm) and can be response-released to the acidic environment of the stomach (pH 2.0-3.0), preventing the premature release of the BiG@MCs in physiological conditions. It is worth noting that the bismuth component can be easily identified by computed tomography and other detection instruments, which provide the possibility for drug tracing. In summary, these results indicate that BiG@MCs provide a versatile intragastric-targeting drug delivery platform for GU therapeutics.

Scavenger receptor CD36 governs recruitment of myeloid cells to the blood-CSF barrier after stroke in neonatal mice

Background

Ischemic stroke induces the activation and recruitment of peripheral leukocytes to the injured brain. These cells can infiltrate the brain through multiple routes, either by penetrating blood–brain barrier or via blood–CSF barriers at the meninges or the choroid plexus (CP). We previously showed that myeloid cell trafficking via the CP occurs early after neonatal arterial stroke and modulates injury. CD36 is a receptor that mediates function of endothelial cells and cells of the monocyte lineage under various neurodegenerative conditions and can influence brain injury after neonatal stroke. Here we asked whether CD36 impacts injury by altering leukocyte trafficking through the CP in neonatal mice subjected to transient middle cerebral artery occlusion (tMCAO).

Methods

In neonatal mice with intact or globally disrupted CD36 signalling (CD36 KO), we characterized the phenotypes of myeloid cells by flow cytometry and the underlying gene expression signatures in the CPs contralateral and ipsilateral to tMCAO by RNA sequencing analyses, focussing on early post-reperfusion time window.

Results

Flow cytometry in the isolated CPs revealed that CD36 mediates stepwise recruitment of myeloid cells to the CP ipsilateral to tMCAO early after reperfusion, with a predominant increase first in inflammatory monocyte subsets and neutrophils followed by patrolling monocytes. RNA sequencing analyses demonstrated marked changes in gene expression in the CP ipsilateral compared to the CP contralateral to tMCAO in wild type mice. Changes were further modified by lack of CD36, including distinction in several clusters of genes involved in inflammatory, metabolic and extracellular matrix signalling in the CP ipsilateral to tMCAO.

Conclusion

Altogether, our data suggest cooperation between blood–CSF–brain interface via the CP through CD36-mediated signalling following neonatal stroke with a key role for inflammatory monocytes and neutrophils.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02388-z.

Knockdown of hsa_circ_0000729 Inhibits the Tumorigenesis of Non-Small Cell Lung Cancer Through Mediation of miR-1281/FOXO3 Axis

Background

Non-small cell lung cancer (NSCLC) is a subtype of lung cancer which seriously threatens the health of people. Circular RNAs (CircRNAs) are endogenous RNAs which have stable closed structure; they are known to be involved in tumorigenesis of NSCLC. Meanwhile, hsa_circ_0000729 was reported to be upregulated in NSCLC. Nevertheless, the function of hsa_circ_0000729 in NSCLC remains unclear.

Methods

Western blot and RT-qPCR were performed to investigate protein and mRNA levels, respectively. CCK-8 assay was performed to test the cell viability and cell death was investigated by flow cytometry. NSCLC cell pyroptosis was observed by electron microscope. In addition, the migration and invasion of NSCLC cells were detected by wound healing and transwell assay. The relation among hsa_circ_0000729, miR-1281 and FOXO3 was explored by dual luciferase reporter assay and RNA pull-down.

Results

Hsa_circ_0000729 was found to be upregulated in NSCLC cells, and hsa_circ_0000729 knockdown obviously suppressed the proliferation of NSCLC cells through inducing pyroptosis. In addition, silencing of hsa_circ_0000729 notably inhibited the invasion and migration of NSCLC cells. Meanwhile, hsa_circ_0000729 could bind with miR-1281, and FOXO3 was directly targeted by miR-1281. Moreover, the anti-tumor effect of hsa_circ_0000729 siRNAs on NSCLC was markedly reversed by miR-1281 antagomir. Furthermore, silencing of hsa_circ_0000729 inhibited the tumor growth of NSCLC in vivo.

Conclusion

Knockdown of hsa_circ_0000729 inhibits the tumorigenesis of NSCLC through mediation of miR-1281/FOXO3 axis. Thus, hsa_circ_0000729 might be served as a crucial mediator in NSCLC.

Dissecting the Crosstalk between Endothelial Mitochondrial Damage, Vascular Inflammation, and Neurodegeneration in Cerebral Amyloid Angiopathy and Alzheimer's Disease

Alzheimer’s disease (AD) is the most prevalent cause of dementia and is pathologically characterized by the presence of parenchymal senile plaques composed of amyloid β (Aβ) and intraneuronal neurofibrillary tangles of hyperphosphorylated tau protein. The accumulation of Aβ also occurs within the cerebral vasculature in over 80% of AD patients and in non-demented individuals, a condition called cerebral amyloid angiopathy (CAA). The development of CAA is associated with neurovascular dysfunction, blood–brain barrier (BBB) leakage, and persistent vascular- and neuro-inflammation, eventually leading to neurodegeneration. Although pathologically AD and CAA are well characterized diseases, the chronology of molecular changes that lead to their development is still unclear. Substantial evidence demonstrates defects in mitochondrial function in various cells of the neurovascular unit as well as in the brain parenchyma during the early stages of AD and CAA. Dysfunctional mitochondria release danger-associated molecular patterns (DAMPs) that activate a wide range of inflammatory pathways. In this review, we gather evidence to postulate a crucial role of the mitochondria, specifically of cerebral endothelial cells, as sensors and initiators of Aβ-induced vascular inflammation. The activated vasculature recruits circulating immune cells into the brain parenchyma, leading to the development of neuroinflammation and neurodegeneration in AD and CAA.