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

Lysophosphatidic Acid Receptor 1 Plays a Pathogenic Role in Permanent Brain Ischemic Stroke by Modulating Neuroinflammatory Responses

Lysophosphatidic acid receptor 1 (LPA1) plays a critical role in brain injury following a transient brain ischemic stroke. However, its role in permanent brain ischemic stroke remains unknown. To address this, we investigated whether LPA1 could contribute to brain injury of mice challenged by permanent middle cerebral artery occlusion (pMCAO). A selective LPA1 antagonist (AM152) was used as a pharmacological tool for this investigation. When AM152 was given to pMCAO-challenged mice one hour after occlusion, pMCAO-induced brain damage such as brain infarction, functional neurological deficits, apoptosis, and blood-brain barrier disruption was significantly attenuated. Histological analyses demonstrated that AM152 administration attenuated microglial activation and proliferation in injured brain after pMCAO challenge. AM152 administration also attenuated abnormal neuroinflammatory responses by decreasing expression levels of pro-inflammatory cytokines while increasing expression levels of anti-inflammatory cytokines in the injured brain. As underlying effector pathways, NF-κB, MAPKs (ERK1/2, p38, and JNKs), and PI3K/Akt were found to be involved in LPA1-dependent pathogenesis. Collectively, these results demonstrate that LPA1 can contribute to brain injury by permanent ischemic stroke, along with relevant pathogenic events in an injured brain.

Synthesis, radiosynthesis and biochemical evaluation of fluorinated analogues of sphingosine-1-phosphate receptor 3 specific antagonists using PET

Sphingosine-1-phosphate and its receptors (S1PRs) are involved in several diseases such as auto immunity, inflammation and cardiovascular disorders. The S1P analogue fingolimod (Gilenya®) is currently in use for the treatment of relapsing multiple sclerosis. S1PRs are also promising targets for clinical molecular imaging in vivo. The organ distribution of individual S1PRs can be potentially achieved by using S1PR subtype-specific (radiolabeled) chemical probes. Here, we report our efforts on synthesis and in vivo potency determination of new ligands for the S1P receptor 3 (S1P3) based on the S1P3 antagonist TY-52156 and in validation of a potential imaging tracer in vivo using Positron Emission Tomography (PET) after 18F-labelling. A p-fluorophenyl derivative exhibited excellent S1P3 antagonist activity in vitro, good serum stability, and medium lipophilicity. In vivo biodistribution experiments using 18F-PET exhibited significant uptake in the myocardium suggesting potential applications in cardiac imaging.

In vitro pharmacological characterization of standard and new lysophosphatidic acid receptor antagonists using dynamic mass redistribution assay

Lysophosphatidic acid (LPA) is a bioactive phospholipid that acts as an agonist of six G protein-coupled receptors named LPA receptors (LPA1-6). LPA elicits diverse intracellular events and modulates several biological functions, including cell proliferation, migration, and invasion. Overactivation of the LPA-LPA receptor system is reported to be involved in several pathologies, including cancer, neuropathic pain, fibrotic diseases, atherosclerosis, and type 2 diabetes. Thus, LPA receptor modulators may be clinically relevant in numerous diseases, making the identification and pharmacodynamic characterization of new LPA receptor ligands of strong interest. In the present work, label-free dynamic mass redistribution (DMR) assay has been used to evaluate the pharmacological activity of some LPA1 and LPA2 standard antagonists at the recombinant human LPA1 and LPA2 receptors. These results are compared to those obtained in parallel experiments with the calcium mobilization assay. Additionally, the same experimental protocol has been used for the pharmacological characterization of the new compound CHI. KI 16425, RO 6842262, and BMS-986020 behaved as LPA1 inverse agonists in DMR experiments and as LPA1 antagonists in calcium mobilization assays. Amgen compound 35 behaved as an LPA2 antagonist, while Merck compound 20 from WO2012028243 was detected as an LPA2 inverse agonist using the DMR test. Of note, for all the compounds, similar potency values were estimated by DMR and calcium assay. The new compound CHI was found to be an LPA1 inverse agonist, but with potency lower than that of the standard compounds. In conclusion, we have demonstrated that DMR assay can be successfully used to characterize LPA1 and LPA2 ligands. Compared to the classical calcium mobilization assay, DMR offers some advantages, in particular allowing the identification of inverse agonists. Finally, in the frame of this study, a new LPA1 inverse agonist has been identified.

S1P/S1PR signaling pathway advancements in autoimmune diseases

Sphingosine-1-phosphate (S1P) is a versatile sphingolipid that is generated through the phosphorylation of sphingosine by sphingosine kinase (SPHK). S1P exerts its functional effects by binding to the G protein-coupled S1P receptor (S1PR). This lipid mediator plays a pivotal role in various cellular activities. The S1P/S1PR signaling pathway is implicated in the pathogenesis of immune-mediated diseases, significantly contributing to the functioning of the immune system. It plays a crucial role in diverse physiological and pathophysiological processes, including cell survival, proliferation, migration, immune cell recruitment, synthesis of inflammatory mediators, and the formation of lymphatic and blood vessels. However, the full extent of the involvement of this signaling pathway in the development of autoimmune diseases remains to be fully elucidated. Therefore, this study aims to comprehensively review recent research on the S1P/S1PR axis in diseases related to autoimmunity.

MiRNA-338-3p Inhibits Neuroinflammation in the Corpus Callosum of LCV-LPS Rats Via STAT1 Signal Pathway

Neuroinflammation is a common characteristic of intracranial infection (ICI), which is associated with the activation of astrocytes and microglia. MiRNAs are involved in the process of neuroinflammation. This study aimed to investigate the potential mechanism by which miR-338-3p negatively modulate the occurrence of neuroinflammation. We here reported that the decreased levels of miR-338-3p were detected using qRT-PCR and the upregulated expression of TNF-α and IL-1β was measured by ELISA in the cerebrospinal fluid (CSF) in patients with ICI. A negative association between miR-338-3p and TNF-α or IL-1β was revealed by Pearson correlation analysis. Sprague-Dawley (SD) rats were injected with LPS (50 μg) into left cerebral ventricule (LCV), following which the increased expression of TNF-α and IL-1β and the reduction of miR-338-3p expression were observed in the corpus callosum (CC). Moreover, the expression of TNF-α and IL-1β in the astrocytes and microglia in the CC of LCV-LPS rats were saliently inhibited by the overexpression of miR-338-3p. In vitro, cultured astrocytes and BV2 cells transfected with mimic-miR-338-3p produced less TNF-α and IL-1β after LPS administration. Direct interaction between miR-338-3p and STAT1 mRNA was validated by biological information analysis and dual luciferase assay. Furthermore, STAT1 pathway was found to be implicated in inhibition of neuroinflammation induced by mimic miR-338-3p in the astrocytes and BV2 cells. Taken together, our results suggest that miR-338-3p suppress the generation of proinflammatory mediators in astrocyte and BV2 cells induced by LPS exposure through the STAT1 signal pathway. MiR-338-3p could act as a potential therapeutic strategy to reduce the neuroinflammatory response. Diagram describing the cellular and molecular mechanisms associated with LPS-induced neuroinflammation via the miR-338-3p/STAT1 pathway. LPS binds to TLRs on astrocytes or microglia to activate the STAT1 pathway and upregulate the production of pro-inflammatory cytokines. However, miR-338-3p inhibits the expression of STAT1 and reduces the production of inflammatory mediators.

Immune System and Brain/Intestinal Barrier Functions in Psychiatric Diseases: Is Sphingosine-1-Phosphate at the Helm?

Over the past few decades, extensive research has shed light on immune alterations and the significance of dysfunctional biological barriers in psychiatric disorders. The leaky gut phenomenon, intimately linked to the integrity of both brain and intestinal barriers, may play a crucial role in the origin of peripheral and central inflammation in these pathologies. Sphingosine-1-phosphate (S1P) is a bioactive lipid that regulates both the immune response and the permeability of biological barriers. Notably, S1P-based drugs, such as fingolimod and ozanimod, have received approval for treating multiple sclerosis, an autoimmune disease of the central nervous system (CNS), and ulcerative colitis, an inflammatory condition of the colon, respectively. Although the precise mechanisms of action are still under investigation, the effectiveness of S1P-based drugs in treating these pathologies sparks a debate on extending their use in psychiatry. This comprehensive review aims to delve into the molecular mechanisms through which S1P modulates the immune system and brain/intestinal barrier functions. Furthermore, it will specifically focus on psychiatric diseases, with the primary objective of uncovering the potential of innovative therapies based on S1P signaling.

Artemisinin exerts a protective effect in the MPTP mouse model of Parkinson's disease by inhibiting microglial activation via the TLR4/Myd88/NF-KB pathway

AIMS

We performed cell and animal experiments to explore the therapeutic effect of artemisinin on Parkinson's disease (PD) and the TLR4/Myd88 signaling pathway.

METHODS

C57 mice were randomly divided into the blank, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced and artemisinin-treated groups. Clinical symptoms, the number of dopaminergic (DAergic) neurons in the substantia nigra, and microglial cell activation were compared among the three groups. Subsequently, BV-2 cell activation and TLR4/Myd88 pathway component expression were compared among the blank, MPP⁺ -treated, artemisinin-treated, and TLR4 activator-treated groups.

RESULTS

Behavioral symptoms were improved, the number of DAergic neurons in the substantia nigra of the midbrain was increased, and microglial cell activation was decreased in artemisinin-treated MPTP-induced PD model mice compared with control-treated MPTP-induced PD model mice (p < 0.05). The cell experiments revealed that artemisinin treatment reduced MPP⁺ -induced BV-2 cell activation and inhibited the TLR4/Myd88 signaling pathway. Moreover, the effect of artemisinin on the BV-2 cell model was inhibited by the TLR4 activator LPS (p < 0.05).

CONCLUSION

Artemisinin may reduce damage to DAergic neurons in a PD mouse model by decreasing microglial activation through the TLR4-mediated MyD88-dependent signaling pathway. However, this finding cannot explain the relationship between microglia and DAergic neurons.

Metabolic and Transcriptomic Signatures of the Acute Psychological Stress Response in the Mouse Brain

Acute stress response triggers various physiological responses such as energy mobilization to meet metabolic demands. However, the underlying molecular changes in the brain remain largely obscure. Here, we used a brief water avoidance stress (WAS) to elicit an acute stress response in mice. By employing RNA-sequencing and metabolomics profiling, we investigated the acute stress-induced molecular changes in the mouse whole brain. The aberrant expression of 60 genes was detected in the brain tissues of WAS-exposed mice. Functional analyses showed that the aberrantly expressed genes were enriched in various processes such as superoxide metabolism. In our global metabolomic profiling, a total of 43 brain metabolites were significantly altered by acute WAS. Metabolic pathways upregulated from WAS-exposed brain tissues relative to control samples included lipolysis, eicosanoid biosynthesis, and endocannabinoid synthesis. Acute WAS also elevated the levels of branched-chain amino acids, 5-aminovalerates, 4-hydroxy-nonenal-glutathione as well as mannose, suggesting complex metabolic changes in the brain. The observed molecular events in the present study provide a valuable resource that can help us better understand how acute psychological stress impacts neural functions.

Outcomes of the 2019 hydrocephalus association workshop, "Driving common pathways: extending insights from posthemorrhagic hydrocephalus"

The Hydrocephalus Association (HA) workshop, Driving Common Pathways: Extending Insights from Posthemorrhagic Hydrocephalus, was held on November 4 and 5, 2019 at Washington University in St. Louis. The workshop brought together a diverse group of basic, translational, and clinical scientists conducting research on multiple hydrocephalus etiologies with select outside researchers. The main goals of the workshop were to explore areas of potential overlap between hydrocephalus etiologies and identify drug targets that could positively impact various forms of hydrocephalus. This report details the major themes of the workshop and the research presented on three cell types that are targets for new hydrocephalus interventions: choroid plexus epithelial cells, ventricular ependymal cells, and immune cells (macrophages and microglia).

Biological functions of bacterial lysophospholipids

Lysophospholipids (LPLs) are lipid-derived metabolic intermediates in the cell membrane. The biological functions of LPLs are distinct from their corresponding phospholipids. In eukaryotic cells LPLs are important bioactive signaling molecules that regulate many important biological processes, but in bacteria the function of LPLs is still not fully defined. Bacterial LPLs are usually present in cells in very small amounts, but can strongly increase under certain environmental conditions. In addition to their basic function as precursors in membrane lipid metabolism, the formation of distinct LPLs contributes to the proliferation of bacteria under harsh circumstances or may act as signaling molecules in bacterial pathogenesis. This review provides an overview of the current knowledge of the biological functions of bacterial LPLs including lysoPE, lysoPA, lysoPC, lysoPG, lysoPS and lysoPI in bacterial adaptation, survival, and host-microbe interactions.

Reactive microglia and mitochondrial unfolded protein response following ventriculomegaly and behavior defects in kaolin-induced hydrocephalus

Ventriculomegaly induced by the abnormal accumulation of cerebrospinal fluid (CSF) leads to hydrocephalus, which is accompanied by neuroinflammation and mitochondrial oxidative stress. The mitochondrial stress activates mitochondrial unfolded protein response (UPRmt), which is essential for mitochondrial protein homeostasis. However, the association of inflammatory response and UPRmt in the pathogenesis of hydrocephalus is still unclear. To assess their relevance in the pathogenesis of hydrocephalus, we established a kaolin-induced hydrocephalus model in 8-week-old male C57BL/6J mice and evaluated it over time. We found that kaolin-injected mice showed prominent ventricular dilation, motor behavior defects at the 3-day, followed by the activation of microglia and UPRmt in the motor cortex at the 5-day. In addition, PARP-1/NF-κB signaling and apoptotic cell death appeared at the 5-day. Taken together, our findings demonstrate that activation of microglia and UPRmt occurs after hydrocephalic ventricular expansion and behavioral abnormal-ities which could be lead to apoptotic neuronal cell death, providing a new perspective on the pathogenic mechanism of hydrocephalus.

Effect of TLR4/MyD88/NF-kB axis in paraventricular nucleus on ventricular arrhythmias induced by sympathetic hyperexcitation in post-myocardial infarction rats

Sympathetic activation after myocardial infarction (MI) leads to ventricular arrhythmias (VAs), which can result in sudden cardiac death (SCD). The toll-like receptor 4 (TLR4)/myeloid differentiation primary response 88 (MyD88)/nuclear factor-kappa B (NF-kB) axis within the hypothalamic paraventricular nucleus (PVN), a cardiac-neural sympathetic nerve centre, plays an important role in causing VAs. An MI rat model and a PVN-TLR4 knockdown model were constructed. The levels of protein were detected by Western blotting and immunofluorescence, and localizations were visualized by multiple immunofluorescence staining. Central and peripheral sympathetic activation was visualized by immunohistochemistry for c-fos protein, renal sympathetic nerve activity (RSNA) measurement, heart rate variability (HRV) analysis and norepinephrine (NE) level detection in serum and myocardial tissue measured by ELISA. The arrhythmia scores were measured by programmed electrical stimulation (PES), and cardiac function was detected by the pressure-volume loop (P-V loop). The levels of TLR4 and MyD88 and the nuclear translocation of NF-kB within the PVN were increased after MI, while sympathetic activation and arrhythmia scores were increased and cardiac function was decreased. However, inhibition of TLR4 significantly reversed these conditions. PVN-mediated sympathetic activation via the TLR4/MyD88/NF-kB axis ultimately leads to the development of VAs after MI.

Resveratrol Alleviates Ischemic Brain Injury by Inhibiting the Activation of Pro-Inflammatory Microglia Via the CD147/MMP-9 Pathway

OBJECTIVE

Ischemic stroke is one of the most common diseases with high mortality and disability. This study was intended to investigate the mechanism of resveratrol (RES) regulating microglia activation through the CD147/matrix metalloproteinase-9 (MMP-9) pathway on ischemic stroke.

METHODS

The middle cerebral artery occlusion (MCAO) mouse model and oxygen and glucose deprivation (OGD) cell model were established. The behavioral defects, neuronal damage, cerebral infarction volume, and histopathological changes were assessed in MCAO mice. The activation of pro-inflammatory microglia CD86⁺/Iba-1⁺ and anti-inflammatory microglia CD206⁺/Iba-1⁺ was detected. The expressions of pro-inflammatory microglia markers (CD11b, CD16) and cytokines (TNF-α, IL-1β, and IL-6) were measured. The activation of the CD147/MMP-9 pathway was detected and its effect on microglia activation was assessed.

RESULTS

After RES administration, the neuronal dysfunction, infarct volume, and morphological changes of neurons were improved in MCAO mice. Meanwhile, the motivation of pro-inflammatory microglia and the release of inflammatory factors were repressed. RES suppressed the stimulation of OGD/R microglia and the release of inflammatory factors. The expression of CD147 and MMP-9 in primary microglia was up-regulated. Inhibition of CD147 can reduce pro-inflammatory microglia activation by inhibiting MMP-9 expression. RES inhibited the CD147/MMP-9 axis in OGD/R microglia, and overexpression of CD147 partially reversed the inhibitory effect of RES on the activation and release of inflammatory factors in OGD/R microglia.

CONCLUSION

RES restrained the stimulation of pro-inflammatory microglia by down-regulating the CD147/MMP-9 axis, and thus protected against ischemic brain injury.

Microglia as the Critical Regulators of Neuroprotection and Functional Recovery in Cerebral Ischemia

Microglial activation is considered as the critical pathogenic event in diverse central nervous system disorders including cerebral ischemia. Proinflammatory responses of activated microglia have been well reported in the ischemic brain and neuroinflammatory responses of activated microglia have been believed to be the potential therapeutic strategy. However, despite having proinflammatory roles, microglia can have significant anti-inflammatory roles and they are associated with the production of growth factors which are responsible for neuroprotection and recovery after ischemic injury. Microglia can directly promote neuroprotection by preventing ischemic infarct expansion and promoting functional outcomes. Indirectly, microglia are involved in promoting anti-inflammatory responses, neurogenesis, and angiogenesis in the ischemic brain which are crucial pathophysiological events for ischemic recovery. In fact, anti-inflammatory cytokines and growth factors produced by microglia can promote neuroprotection and attenuate neurobehavioral deficits. In addition, microglia regulate phagocytosis, axonal regeneration, blood-brain barrier protection, white matter integrity, and synaptic remodeling, which are essential for ischemic recovery. Microglia can also regulate crosstalk with neurons and other cell types to promote neuroprotection and ischemic recovery. This review mainly focuses on the roles of microglia in neuroprotection and recovery following ischemic injury. Furthermore, this review also sheds the light on the therapeutic potential of microglia in stroke patients.