PCSK9 (Proprotein Convertase Subtilisin/Kexin 9) Enhances Platelet Activation, Thrombosis, and Myocardial Infarct Expansion by Binding to Platelet CD36.

BACKGROUND: PCSK9 (proprotein convertase subtilisin/kexin 9), mainly secreted by the liver and released into the blood, elevates plasma low-density lipoprotein cholesterol by degrading low-density lipoprotein receptor. Pleiotropic effects of PCSK9 beyond lipid metabolism have been shown. However, the direct effects of PCSK9 on platelet activation and thrombosis, and the underlying mechanisms, as well, still remain unclear. METHODS: We detected the direct effects of PCSK9 on agonist-induced platelet aggregation, dense granule ATP release, integrin αIIbß3 activation, α-granule release, spreading, and clot retraction. These studies were complemented by in vivo analysis of FeCl3-injured mouse mesenteric arteriole thrombosis. We also investigated the underlying mechanisms. Using the myocardial infarction (MI) model, we explored the effects of PCSK9 on microvascular obstruction and infarct expansion post-MI. RESULTS: PCSK9 directly enhances agonist-induced platelet aggregation, dense granule ATP release, integrin αIIbß3 activation, P-selectin release from α-granules, spreading, and clot retraction. In line, PCSK9 enhances in vivo thrombosis in a FeCl3-injured mesenteric arteriole thrombosis mouse model, whereas PCSK9 inhibitor evolocumab ameliorates its enhancing effects. Mechanism studies revealed that PCSK9 binds to platelet CD36 and thus activates Src kinase and MAPK (mitogen-activated protein kinase)-extracellular signal-regulated kinase 5 and c-Jun N-terminal kinase, increases the generation of reactive oxygen species, and activates the p38MAPK/cytosolic phospholipase A2/cyclooxygenase-1/thromboxane A2 signaling pathways downstream of CD36 to enhance platelet activation, as well. Using CD36 knockout mice, we showed that the enhancing effects of PCSK9 on platelet activation are CD36 dependent. It is important to note that aspirin consistently abolishes the enhancing effects of PCSK9 on platelet activation and in vivo thrombosis. Last, we showed that PCSK9 activating platelet CD36 aggravates microvascular obstruction and promotes MI expansion post-MI. CONCLUSIONS: PCSK9 in plasma directly enhances platelet activation and in vivo thrombosis, and MI expansion post-MI, as well, by binding to platelet CD36 and thus activating the downstream signaling pathways. PCSK9 inhibitors or aspirin abolish the enhancing effects of PCSK9, supporting the use of aspirin in patients with high plasma PCSK9 levels in addition to PCSK9 inhibitors to prevent thrombotic complications.

miR-141-3p attenuates RSL3-induced ferroptosis and intestinal epithelial-mesenchymal transition via directly inhabits ZEB1 in intestinal Behçet's syndrome.

The aims of this study were to investigate whether the ferroptosis is involved in intestinal Behçet's syndrome (IBS), and to identify if miR-141-3p could attenuate RAS-selective lethal 3 (RSL3)-induced ferroptosis and intestinal epithelial to mesenchymal transition (EMT) via directly inhabits zinc fnger E-box binding homeobox 1 (ZEB1). The expressions of ferroptosis-related proteins in the intestinal tissues of patients with IBS were investigated by immunohistochemistry and quantitative real-time PCR (qRT-PCR). Malondialdehyde (MDA) contents of the intestinal tissues and cells were detected. Serum from IBS patients and RSL3 were co-cultured with intestinal epithelial cells in vitro. In order to investigate whether RSL3-induced ferroptosis can be ameliorated by miR-141-3p, the intestinal epithelial cells were firstly stimulated with RSL3 and then incubated with miR-141-3p mimics. Western blot was used to measure the expression of EMT and ferroptosis-related proteins. Expression of GPX4 (22.51% ± 2.05%, 51.75% ± 3.47%, t = - 7.77, p = 0.000) and xCT (17.49% ± 1.57%, 28.73% ± 1.75%, t = - 4.38, p = 0.003) were significantly lower in intestinal mucosal tissues of patients with IBS compared with HC group. Compared with the HC samples, the IBS specimens had significantly higher MDA (t = 4.32, p = 0.01). Moreover, the relative mRNA levels of ferritin light chain (FTL) (t = 4.07, p = 0.02) and ferritin heavy chain (FTH) (t = 8.82, p = 0.001) in the intestinal tissues were significant higher in IBS patients than in HC group. Serum from IBS patients could induce intestinal epithelial cell ferroptosis in vitro. Moreover, miR-141-3p could attenuate intestinal epithelial cell ferroptosis-induced by RSL3 and intestinal EMT via targeting ZEB1 in vitro. Ferroptosis were induced in patients with IBS. Moreover, the serum from IBS patients could induce ferroptosis in vitro. miR-141-3p could attenuate intestinal epithelial cell ferroptosis and intestinal EMT via targeting ZEB1. Therefore, miR-141-3p may open new avenues for the treatment of IBS in the future. Key Points • Ferroptosis in IBS is first reported in this study. • In this study, we explored that the serum from IBS patients could induce ferroptosis in vitro and miR-141-3p could attenuate intestinal epithelial cell ferroptosis and intestinal EMT via targeting ZEB1.

NOD2-mediated P2Y12 upregulation increases platelet activation and thrombosis in sepsis.

BACKGROUND: Platelets from septic patients exhibit increased reactivity. However, the underlying mechanism of sepsis-induced platelet hyperactivity is still not completely understood. OBJECTIVE: P2Y12 is a central receptor for platelet activation. In this study, we investigated the role of platelet P2Y12 in platelet hyperactivity during sepsis. METHODS: We measured platelet P2Y12 expression and aggregation in response to ADP in septic patients and cecal ligation and puncture (CLP)-treated mice. We also detected the downstream signaling of P2Y12 in resting platelets from patients and mice with sepsis. The role of nucleotide-binding oligomerization domain 2 (NOD2)/RIP2/NF-κB/P65 pathway in sepsis-induced platelet P2Y12 high expression was also investigated. Finally, we compared the antiplatelet and antithrombotic effects of clopidogrel, prasugrel, and ticagrelor in experimental sepsis in mice and rats. RESULTS: Compared to healthy subjects, platelets from septic patients exhibit P2Y12 hyperactivity and higher P2Y12 expression. pAkt is enhanced and pVASP is impaired in resting platelets from the patients, indicating the constitutive activation of platelet P2Y12 receptor. Mouse sepsis model recapitulates the findings in septic patients. NOD2 deficiency attenuates sepsis-induced platelet P2Y12 high expression, hyperactivity, and thrombosis. Prasugrel and ticagrelor are potent P2Y12 inverse agonists, and exhibit superior antiplatelet and antithrombotic efficacy over clopidogrel in mice and rats with sepsis. CONCLUSIONS: NOD2 activation upregulates platelet P2Y12 expression, which is constitutively activated and contributes to platelet hyperactivity in septic status. Compared to clopidogrel, prasugrel and ticagrelor are potent P2Y12 inverse agonists with superior antiplatelet and antithrombotic efficacy in experimental sepsis.

GSK669, a NOD2 receptor antagonist, inhibits thrombosis and oxidative stress via targeting platelet GPVI.

BACKGROUND AND PURPOSE: Previously, we discovered that the activation of nucleotide-binding oligomerization domain 2 (NOD2) enhances platelet activation. We here investigated the antiplatelet and antithrombotic potential of GSK669, a NOD2 antagonist. EXPERIMENTAL APPROACH: Effects of GSK669 on platelet functions, reactive oxygen species (ROS) and proinflammatory cytokine generation were detected. NOD2-/- platelets were used to confirm GSK669 target. The interaction between GSK669 and glycoprotein VI (GPVI) was detected using surface plasmon resonance (SPR) spectroscopy. GPVI downstream signaling was examined by Western blot. The antithrombotic and antioxidative effects were investigated using mouse mesenteric arteriole thrombosis model and pulmonary embolism model. KEY RESULTS: GSK669 significantly inhibits platelet proinflammatory cytokine release induced by muramyl dipeptide, platelet aggregation, ATP release, and ROS generation induced by collagen and collagen related peptide (CRP). Platelet spreading and clot retraction are also inhibited. GSK669 also decreases collagen-induced phosphorylation of Src, Syk, PLCγ2, and Akt. The antiplatelet effect of GSK669 is NOD2-independent and mediated by GPVI antagonism. Consistent with its antiplatelet activity as a GPVI antagonist, GSK669 inhibits platelet adhesion on collagen in flow condition. Notably, GSK669 inhibits mouse mesenteric arteriole thrombosis similarly to aspirin without bleeding. The antithrombotic effect of GSK669 is further confirmed in the pulmonary embolism model; decreased malonaldehyde (MDA) and increased superoxide dismutase (SOD) levels in mouse plasma reveal a significant antioxidant effect of GSK669. CONCLUSION AND IMPLICATIONS: Beyond its anti-inflammatory effect as a NOD2 antagonist, GSK669 is also an efficient and safe antiplatelet agent combined with antioxidant effect by targeting GPVI. An antiplatelet agent bearing antioxidative and anti-inflammatory activities without bleeding risk may have therapeutic advantage over current antiplatelet drugs for atherothrombosis.

PAK Membrane Translocation and Phosphorylation Regulate Platelet Aggregation Downstream of Gi and G12/13 Pathways.

Platelet activation plays a pivotal role in physiological hemostasis and pathological thrombosis causing heart attack and stroke. Previous studies conclude that simultaneous activation of Gi and G12/13 signaling pathways is sufficient to cause platelet aggregation. However, using Gq knockout mice and Gq-specific inhibitors, we here demonstrated that platelet aggregation downstream of coactivation of Gi and G12/13 depends on agonist concentrations; coactivation of Gi and G12/13 pathways only induces platelet aggregation under higher agonist concentrations. We confirmed Gi and G12/13 pathway activation by showing cAMP (cyclic adenosine monophosphate) decrease and RhoA activation in platelets stimulated at both low and high agonist concentrations. Interestingly, we found that though Akt and PAK (p21-activated kinase) translocate to the platelet membrane upon both low and high agonist stimulation, membrane-translocated Akt and PAK only phosphorylate at high agonist concentrations, correlating well with platelet aggregation downstream of concomitant Gi and G12/13 pathway activation. PAK inhibitor abolishes Akt phosphorylation, inhibits platelet aggregation in vitro and arterial thrombus formation in vivo. We propose that the PAK-PI3K/Akt pathway mediates platelet aggregation downstream of Gi and G12/13, and PAK may represent a potential antiplatelet and antithrombotic target.

Discovery, cocrystallization and biological evaluation of novel piperidine derivatives as high affinity Ls-AChBP ligands possessing α7 nAChR activities.

A series of novel pyridine-substituted piperidine derivatives were discovered as low nanomolar Ls-AChBP ligands with α7 nAChR partial agonism or antagonism activities. A high-resolution antagonist-bound Ls-AChBP complex was successfully resolved with a classic Loop C opening phenomenon and unique sulfur-π interactions which deviated from our previous docking mode to a large extent. With the knowledge of the co-complex, 27 novel piperidine derivatives were designed and synthesized. The structure-activity relationships (SARs) of the aromatic and pyridine regions were well established and binding modes were illustrated with the help of molecular docking which indicated that interactions with Trp 143 and the "water bridge" are essential for the high binding affinities. Halogen bonding as well as the space around 5'- or 6'- position of the pyridine ring was also proposed to influence the binding conformation of the compounds. Notably, two enantiomers of compound 2 showed opposite functions toward α7 nAChR and compound (S)-2 showed sub-nanomolar affinity (Ki = 0.86 nM) on Ls-AChBP and partial agonism (pEC50 = 4.69 ±â€¯0.11,Emax = 36.1%) on α7 nAChR with reasonable pharmacokinetics (PK) properties and fine ability of blood-brain-barrier (BBB) penetration. This study provided promising hits to develop candidates targeting nAChR-related CNS diseases.