Liver kinase B1 is required for thromboxane receptor-dependent nuclear factor-κB activation and inflammatory responses

Emodin inhibits HDAC6 mediated NLRP3 signaling and relieves chronic inflammatory pain in mice

Chronic pain reduces the quality of life and ability to function of individuals suffering from it, making it a common public health problem. Neuroinflammation which is mediated by the Nod-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome activation in the spinal cord participates and modulates chronic pain. A chronic inflammatory pain mouse model was created in the current study by intraplantar injection of complete Freund's adjuvant (CFA) into C57BL/6J left foot of mice. Following CFA injection, the mice had enhanced pain sensitivities, decreased motor function, increased spinal inflammation and activated spinal astrocytes. Emodin (10 mg/kg) was administered intraperitoneally into the mice for 3 days. As a result, there were fewer spontaneous flinches, higher mechanical threshold values and greater latency to fall. Additionally, in the spinal cord, emodin administration reduced leukocyte infiltration level, downregulated protein level of IL-1β, lowered histone deacetylase (HDAC)6 and NLRP3 inflammasome activity and suppressed astrocytic activation. Emodin also binds to HDAC6 via four electrovalent bonds. In summary, emodin treatment blocked the HDAC6/NLRP3 inflammasome signaling, suppresses spinal inflammation and alleviates chronic inflammatory pain.

EphA4 regulates white matter remyelination after ischemic stroke through Ephexin-1/RhoA/ROCK signaling pathway

Ischemic stroke, which accounts for nearly 80% of all strokes, leads to white matter injury and neurobehavioral dysfunction, but relevant therapies to inhibit demyelination or promote remyelination after white matter injury are still unavailable. In this study, the middle cerebral artery occlusion/reperfusion (MCAO/R) in vivo and oxygen-glucose deprivation/reoxygenation (OGD/R) in vitro were used to establish the ischemic models. We found that Eph receptor A4 (EphA4) had no effect on the apoptosis of oligodendrocytes using TUNEL staining. In contrast, EphA4 promoted proliferation of oligodendrocyte precursor cells (OPCs), but reduced the numbers of mature oligodendrocytes and the levels of myelin-associated proteins (MAG, MOG, and MBP) in the process of remyelination in ischemic models in vivo and in vitro as determined using PDGFRα-EphA4-shRNA and LV-EphA4 treatments. Notably, conditional knockout of EphA4 in OPCs (EphA4^fl/fl  + AAV-PDGFRα-Cre) improved the levels of myelin-associated proteins and functional recovery following ischemic stroke. In addition, regulation of remyelination by EphA4 was mediated by the Ephexin-1/RhoA/ROCK signaling pathway. Therefore, EphA4 did not affect oligodendrocyte (OL) apoptosis but regulated white matter remyelination after ischemic stroke through the Ephexin-1/RhoA/ROCK signaling pathway. EphA4 may provide a novel and effective therapeutic target in clinical practice of ischemic stroke.

The Effect of Platelet-Rich Plasma on Endothelial Progenitor Cell Functionality

Platelets mediate circulating endothelial progenitor cell (EPC) recruitment and maturation, participating in vascular repair, however the underlying mechanism(s) remain unclear. We investigated the effect of platelet-rich plasma (PRP) on the functionality of CD34⁺-derived late-outgrowth endothelial cells (OECs) in culture. Confluent OECs were coincubated with PRP under platelet aggregation (with adenosine diphosphate; ADP) and nonaggregation conditions, in the presence/absence of the reversible P2Y12 platelet receptor antagonist ticagrelor. Outgrowth endothelial cell activation was evaluated by determining prostacyclin (PGI₂) and monocyte chemoattractant protein-1 (MCP-1) release and intercellular adhesion molecule-1 (ICAM-1) membrane expression. Similar experiments were performed using human umbilical vein endothelial cells (HUVECs). Platelet-rich plasma increased ICAM-1 expression and PGI₂ and MCP-1 secretion compared with autologous platelet-poor plasma, whereas ADP-aggregated platelets in PRP did not exhibit any effect. Platelet-rich plasma pretreated with ticagrelor prior to activation with ADP increased all markers to a similar extent as PRP. Similar results were obtained using HUVECs. In conclusion, PRP induces OEC activation, a phenomenon not observed when platelets are aggregated with ADP. Platelet inhibition with ticagrelor restores the PRP capability to activate OECs. Since EPC activation is important for endothelial regeneration and angiogenesis, we suggest that agents inhibiting platelet aggregation, such as ticagrelor, may promote platelet-EPC interaction and EPC function.

Endogenous hydrogen sulfide sulfhydrates IKKβ at cysteine 179 to control pulmonary artery endothelial cell inflammation

BACKGROUND

Pulmonary artery endothelial cell (PAEC) inflammation is a critical event in the development of pulmonary arterial hypertension (PAH). However, the pathogenesis of PAEC inflammation remains unclear.

METHODS

Purified recombinant human inhibitor of κB kinase subunit β (IKKβ) protein, human PAECs and monocrotaline-induced pulmonary hypertensive rats were employed in the study. Site-directed mutagenesis, gene knockdown or overexpression were conducted to manipulate the expression or activity of a target protein.

RESULTS

We showed that hydrogen sulfide (H2S) inhibited IKKβ activation in the cell model of human PAEC inflammation induced by monocrotaline pyrrole-stimulation or knockdown of cystathionine γ-lyase (CSE), an H2S generating enzyme. Mechanistically, H2S was proved to inhibit IKKβ activity directly via sulfhydrating IKKβ at cysteinyl residue 179 (C179) in purified recombinant IKKβ protein in vitro, whereas thiol reductant dithiothreitol (DTT) reversed H2S-induced IKKβ inactivation. Furthermore, to demonstrate the significance of IKKβ sulfhydration by H2S in the development of PAEC inflammation, we mutated C179 to serine (C179S) in IKKβ. In purified IKKβ protein, C179S mutation of IKKβ abolished H2S-induced IKKβ sulfhydration and the subsequent IKKβ inactivation. In human PAECs, C179S mutation of IKKβ blocked H2S-inhibited IKKβ activation and PAEC inflammatory response. In pulmonary hypertensive rats, C179S mutation of IKKβ abolished the inhibitory effect of H2S on IKKβ activation and pulmonary vascular inflammation and remodeling.

CONCLUSION

Collectively, our in vivo and in vitro findings demonstrated, for the first time, that endogenous H2S directly inactivated IKKβ via sulfhydrating IKKβ at Cys179 to inhibit nuclear factor-κB (NF-κB) pathway activation and thereby control PAEC inflammation in PAH.

Selenium and selenoproteins in prostanoid metabolism and immunity

Selenium (Se) is an essential trace element that functions in the form of the 21st amino acid, selenocysteine (Sec) in a defined set of proteins. Se deficiency is associated with pathological conditions in humans and animals, where incorporation of Sec into selenoproteins is reduced along with their expression and catalytic activity. Supplementation of Se-deficient population with Se has shown health benefits suggesting the importance of Se in physiology. An interesting paradigm to explain, in part, the health benefits of Se stems from the observations that selenoprotein-dependent modulation of inflammation and efficient resolution of inflammation relies on mechanisms involving a group of bioactive lipid mediators, prostanoids, which orchestrate a concerted action toward maintenance and restoration of homeostatic immune responses. Such an effect involves the interaction of various immune cells with these lipid mediators where cellular redox gatekeeper functions of selenoproteins further aid in not only dampening inflammation, but also initiating an effective and active resolution process. Here we have summarized the current literature on the multifaceted roles of Se/selenoproteins in the regulation of these bioactive lipid mediators and their immunomodulatory effects.

LKB1/p53/TIGAR/autophagy-dependent VEGF expression contributes to PM2.5-induced pulmonary inflammatory responses

One of the health hazards of PM2.5 exposure is to induce pulmonary inflammatory responses. In our previous study, we demonstrated that exposing both the immortalized and primary human bronchial epithelial cells to PM2.5 results in a significant upregulation of VEGF production, a typical signaling event to trigger chronic airway inflammation. Further investigations showed that PM2.5 exposure strongly induces ATR/CHK1/p53 cascade activation, leading to the induction of DRAM1-dependent autophagy to mediate VEGF expression by activating Src/STAT3 pathway. In the current study, we further revealed that TIGAR was another transcriptional target of p53 to trigger autophagy and VEGF upregulation in Beas-2B cells after PM2.5 exposure. Furthermore, LKB1, but not ATR and CHK1, played a critical role in mediating p53/TIGAR/autophagy/VEGF pathway activation also by linking to Src/STAT3 signaling cascade. Therefore, on combination of the previous report, we have identified both ATR/CHK1/p53/DRAM1- and LKB1/p53/TIGAR- dependent autophagy in mediating VEGF production in the bronchial epithelial cells under PM2.5 exposure. Moreover, the in vivo study further confirmed VEGF induction in the airway potentially contributed to the inflammatory responses in the pulmonary vascular endothelium of PM2.5-treated rats. Therefore, blocking VEGF expression or autophagy induction might be the valuable strategies to alleviating PM2.5-induced respiratory injuries.

Aspirin blocks formation of metastatic intravascular niches by inhibiting platelet-derived COX-1/thromboxane A2

Because metastasis is associated with the majority of cancer-related deaths, its prevention is a clinical aspiration. Prostanoids are a large family of bioactive lipids derived from the activity of cyclooxygenase-1 (COX-1) and COX-2. Aspirin impairs the biosynthesis of all prostanoids through the irreversible inhibition of both COX isoforms. Long-term administration of aspirin leads to reduced distant metastases in murine models and clinical trials, but the COX isoform, downstream prostanoid, and cell compartment responsible for this effect are yet to be determined. Here, we have shown that aspirin dramatically reduced lung metastasis through inhibition of COX-1 while the cancer cells remained intravascular and that inhibition of platelet COX-1 alone was sufficient to impair metastasis. Thromboxane A2 (TXA2) was the prostanoid product of COX-1 responsible for this antimetastatic effect. Inhibition of the COX-1/TXA2 pathway in platelets decreased aggregation of platelets on tumor cells, endothelial activation, tumor cell adhesion to the endothelium, and recruitment of metastasis-promoting monocytes/macrophages, and diminished the formation of a premetastatic niche. Thus, platelet-derived TXA2 orchestrates the generation of a favorable intravascular metastatic niche that promotes tumor cell seeding and identifies COX-1/TXA2 signaling as a target for the prevention of metastasis.

Thromboxane A2 Receptor Stimulation Enhances Microglial Interleukin-1β and NO Biosynthesis Mediated by the Activation of ERK Pathway

BACKGROUND AND PURPOSE

Thromboxane A2 (TXA2) receptors (TP) interact with the ligand TXA2 to induce platelet aggregation and regulate hemostasis. Recently TP-mediated signaling has been suggested to function in multiple cell types in the brain. In this report, we aim to study the expression and physiological role of TP in microglia, in particular after brain ischemia.

METHODS

Ischemic brain sections were analyzed for TP expression. Microglial cell line and primary microglia were cultured, or neuronal cell line co-culture system was used to determine the TP mediated signaling in inflammation and microglia activation.

RESULTS

We found that the TP level was significantly increased in ipsilateral mouse brain tissue at 24 h after ischemia-reperfusion, which was also found to partly co-localize with CD11b, a marker for microglial and infiltrated monocyte/macrophage, in peri-infarct area. Immunofluorescence staining of primary microglia and microglial cell line BV2 revealed the predominant membrane distribution of TP. Conditioned culture media from TP agonist U46619-treated BV2 cells decreased neuronal SH-SY5Y cell viability and induced apoptotic morphological changes. Furthermore, U46619 enhanced IL-1β, IL-6, and iNOS mRNA expression as well as IL-1β and NO releases in BV2 cells or primary microglia. Such stimulation could be attenuated by TP antagonist SQ29548 or MEK inhibitor U0126. The dose- and time-dependent extracellular-signal-regulated kinase (ERK) phosphorylation induced by U46619 further demonstrated ERK signaling-mediated microglia activation by TP agonist.

CONCLUSION

This study has shown a novel role of TP in microglia activation via the ERK signaling pathway, which provides insights for the management of neuroinflammation in diseases like cerebral infarction.

Isolevuglandin-type lipid aldehydes induce the inflammatory response of macrophages by modifying phosphatidylethanolamines and activating the receptor for advanced glycation endproducts

AIMS

Increased lipid peroxidation occurs in many conditions associated with inflammation. Because lipid peroxidation produces lipid aldehydes that can induce inflammatory responses through unknown mechanisms, elucidating these mechanisms may lead to development of better treatments for inflammatory diseases. We recently demonstrated that exposure of cultured cells to lipid aldehydes such as isolevuglandins (IsoLG) results in the modification of phosphatidylethanolamine (PE). We therefore sought to determine (i) whether PE modification by isolevuglandins (IsoLG-PE) occurred in vivo, (ii) whether IsoLG-PE stimulated the inflammatory responses of macrophages, and (iii) the identity of receptors mediating the inflammatory effects of IsoLG-PE.

RESULTS

IsoLG-PE levels were elevated in plasma of patients with familial hypercholesterolemia and in the livers of mice fed a high-fat diet to induce obesity and hepatosteatosis. IsoLG-PE potently stimulated nuclear factor kappa B (NFκB) activation and expression of inflammatory cytokines in macrophages. The effects of IsoLG-PE were blocked by the soluble form of the receptor for advanced glycation endproducts (sRAGE) and by RAGE antagonists. Furthermore, macrophages derived from the bone marrow of Ager null mice failed to express inflammatory cytokines in response to IsoLG-PE to the same extent as macrophages from wild-type mice.

INNOVATION

These studies are the first to identify IsoLG-PE as a mediator of macrophage activation and a specific receptor, RAGE, which mediates its biological effects.

CONCLUSION

PE modification by IsoLG forms RAGE ligands that activate macrophages, so that the increased IsoLG-PE generated by high circulating cholesterol levels or high-fat diet may play a role in the inflammation associated with these conditions.

20-Hydroxyeicosatetraenoic acid involved in endothelial activation and thrombosis

Endothelial cells play an important role in the process of coagulation and the function of platelets. We have previously reported that 20-hydroxyeicosatetraenoic acid (20-HETE), a metabolite of arachidonic acid, increased platelet aggregation and induced hemostasis. The purpose of the present study is to investigate whether 20-HETE-mediated endothelial activation has effect on the coagulation and platelet aggregation. C57Bl/6 mice were treated with PBS or 20-HETE (20 μg/kg) for 2 h, and then we performed a carotid artery or femoral artery thrombosis model by FeCl3. Detection of blood flow indicated that 20-HETE pretreatment accelerated formation of thrombus in both common carotid artery and femoral artery. In vitro, the secretion and expression of von Willebrand factor (vWF) in cultured human umbilical vein endothelial cells (HUVECs) with 20-HETE stimulation were increased, subsequently. The protein level of vWF in HUVECs was decreased at 1 h but increased with prolonged treatment with 20-HETE (>4 h). In contrast, vWF in the culture medium was increased under administration of 20-HETE at 1 h. As a result, adhesion of platelets on HUVECs was significantly increased by 20-HETE. In HUVECs, the extracellular signal-regulated kinase (ERK) pathway was activated by 20-HETE in a dose-dependent manner, and the inhibitors of ERK and L-type Ca2+channel blocked the release of vWF mediated by 20-HETE. In conclusion, 20-HETE instigates endothelial activation and induces the expression and secretion of vWF via the activation of ERK and calcium channel and therefore triggers thrombosis.

Liver kinase B1 suppresses lipopolysaccharide-induced nuclear factor κB (NF-κB) activation in macrophages

Liver kinase B1 (LKB1), a serine/threonine kinase, is a tumor suppressor and metabolic regulator. Recent data suggest that LKB1 is essential in regulating homeostasis of hematopoietic cells and immune responses. However, its role in macrophages and innate immune system remains unclear. Here we report that macrophage LKB1 inhibits pro-inflammatory signaling in response to LPS. LPS-induced pro-inflammatory cytokines and pro-inflammatory enzymes were monitored in bone marrow-derived macrophages isolated from myeloid cell-specific LKB1 knock out mice and their wild type littermate control mice. LPS induced higher levels of pro-inflammatory cytokines and pro-inflammatory enzymes in bone marrow-derived macrophages from LKB1 KO than those from wild type mice. Consistently, LPS induced higher levels of NF-κB activation in LKB1-deficient macrophages than those in wild type. Further, LPS stimulation significantly increased LKB1 phosphorylation at serine 428, which promoted its binding to IκB kinaseβ (IKKβ), resulting in the inhibition of NF-κB. Finally, LPS injection caused higher levels of cytokine release and more severe tissue injury in the lung tissues of LKB1 KO mice than in those of control mice. We conclude that LKB1 inhibits LPS-induced NF-κB activation in macrophages.