Phosphoinositide 3-kinase c (PI3Kc) plays a fundamental role in mediating leukocyte migration to inflammation sites. However, the downstream cytoplasmic events triggered by its signaling activity are still largely obscure. To address this issue, tyrosine and serine/threonine phosphorylated proteins of chemokine-stimulated WT or PI3Kc-null macrophages were investigated. Among the proteins analyzed, the intermediate filament vimentin was found as a downstream effector of the PI3Kc signaling pathway. Specific analysis of the phosphorylation state of vimentin in macrophages showed that this protein becomes rapidly phosphorylated in both tyrosine and serine residues upon chemokine stimulation. In the absence of PI3Kc or the kinase activity of PI3Kc (PI3Kc KD/KD ), phosphorylation of vimentin was reduced. PI3Kc-null macrophages displayed impaired chemokine-driven vimentin fiber disassembly as well as reduced ability to transmigrate across endothelial cells. While WT macrophages infected with a vimentin mutant resistant to N-terminal serine phosphorylation showed a reduction in transendothelial migration, infection of PI3Kc-null macrophages with a vimentin mutant mimicking serine phosphorylation of N-terminal residues rescued the transendothelial migration defect. These results define vimentin N-terminal phosphorylation and fiber reorganization as a target of chemokine-dependent PI3Kc signaling in leukocytes.Key words: Cell migration . Intermediate filaments . Phosphoinositide 3-kinases .Signal transduction IntroductionPhosphoinositide 3-kinases (PI3K) are a family of ubiquitously expressed lipid and protein kinases. They are activated downstream transmembrane receptors [1] and are involved in several cellular responses such as metabolic regulation, survival, proliferation, cell migration and adhesion. PI3K convert PtdIns(4,5)P 2 into PtdIns(3,4,5)P 3 , a second lipid messenger product forming a docking site for various proteins harboring lipid binding modules such as the pleckstrin homology domain [2].Ã These authors contributed equally to this work. 1136Class I PI3K are heterodimeric proteins composed of a p110 catalytic subunit (a, b, g and d) and a regulatory adaptor subunit. According to their mechanism of activation, these enzymes can be further classified into two subclasses: while class IA PI3K (PI3Ka, b and d) include an adaptor protein of the p85 family and are activated by tyrosine kinase receptors, the sole known element of class IB, PI3Kg, is specifically activated by G protein-coupled receptors (GPCR) [3]. This effect is regulated by the interaction of PI3Kg with Gbg subunits of active G proteins through the involvement of either the p101 adaptor or its homologue p84/p87 [4]. Among mammalian tissues, the highest level of PI3Kg expression is found in leukocytes where this enzyme directs the chemotactic response to GPCR agonists [3]. Indeed, PI3Kg-null granulocytes show a significant reduction in chemotaxis toward chemokines and severely impaired bacteria-elicited peritoneal recruitment [5,6]. This migrati...

No abstract

Summary. Background: Thrombopoietin (TPO) is a humoral growth factor that does not induce platelet aggregation per se, but enhances platelet activation in response to several agonists. Circulating levels of TPO are increased in patients with sepsis and are mainly related to sepsis severity. Objectives: To investigate the potential contribution of elevated TPO levels in platelet activation during burn injury complicated or not by sepsis. Methods: We studied 22 burned patients, 10 without and 12 with sepsis, and 10 healthy subjects. We measured plasma levels of TPO, as well as leukocyte-platelet binding and Pselectin expression. The priming activity of plasma from burned patients or healthy subjects on platelet aggregation and leukocyte-platelet binding, and the role of TPO in these effects were also studied in vitro. Results: Burned patients without and with sepsis showed higher circulating TPO levels and increased monocyte-platelet binding compared with healthy subjects. Moreover, TPO levels, monocyte-platelet binding and Pselectin expression were significantly higher in burned patients with sepsis than in burned patients without sepsis. In vitro, plasma from burned patients without and with sepsis, but not from healthy subjects, primed platelet aggregation, monocyteplatelet binding and platelet P-selectin expression. The effect of plasma from burned patients with sepsis was significantly higher than that of plasma from burned patients without sepsis. An inhibitor of TPO prevented the priming effect of plasma from burned patients. Conclusions: Increased TPO levels may enhance platelet activation during burn injury and sepsis, potentially participating in the pathogenesis of multi-organ failure in these diseases.

Thrombopoietin (TPO) is a humoral growth factor that has been shown to increase platelet activation in response to several agonists. Patients with sepsis have increased circulating TPO levels, which may enhance platelet activation, potentially participating to the pathogenesis of multi-organ failure. Aim of this study was to investigate whether TPO affects myocardial contractility and participates to depress cardiac function during sepsis. We showed the expression of the TPO receptor c-Mpl on myocardial cells and tissue by RT-PCR, immunofluorescence and western blotting. We then evaluated the effect of TPO on the contractile function of rat papillary muscle and isolated heart. TPO did not change myocardial contractility in basal conditions, but, when followed by epinephrine (EPI) stimulation, it blunted the enhancement of contractile force induced by EPI both in papillary muscle and isolated heart. An inhibitor of TPO prevented TPO effect on cardiac inotropy. Treatment of papillary muscle with pharmacological inhibitors of phosphatidylinositol 3-kinase, NO synthase, and guanilyl cyclase abolished TPO effect, indicating NO as the final mediator. We finally studied the role of TPO in the negative inotropic effect exerted by human septic shock (HSS) serum and TPO cooperation with TNF-alpha and IL-1beta. Pre-treatment with the TPO inhibitor prevented the decrease in contractile force induced by HSS serum. Moreover, TPO significantly amplified the negative inotropic effect induced by TNF-alpha and IL-1beta in papillary muscle. In conclusion, TPO negatively modulates cardiac inotropy in vitro and contributes to the myocardial depressing activity of septic shock serum.

Background and PurposeThrombopoietin (TPO), a growth factor primarily involved in thrombopoiesis may also have a role in the pathophysiology of sepsis. In patients with sepsis, indeed, TPO levels are markedly increased, with disease severity being the major independent determinant of TPO concentrations. Moreover, TPO increases and correlates with ex vivo indices of platelet activation in patients with burn injury upon sepsis development, and may contribute to depress cardiac contractility in septic shock. Still, the role of TPO in sepsis pathophysiology remains controversial, given the protective role of TPO in other experimental disease models, for instance in doxorubicin-induced cardiotoxicity and myocardial ischemia/reperfusion injury. The aim of our study was to define the contribution of TPO in the development of organ damage induced by endotoxemia or sepsis, and to investigate the effects of inhibiting TPO in these conditions.MethodsWe synthesized a chimeric protein able to inhibit TPO, mTPOR-MBP, and studied its effect in two murine experimental models, acute endotoxemia and cecal ligation and puncture (CLP) model.ResultsIn both models, TPO levels markedly increased, from 289.80±27.87 pg/mL to 465.60±45.92 pg/mL at 3 hours in the LPS model (P<0.01), and from 265.00±26.02 pg/mL to 373.70±26.20 pg/mL in the CLP model (P<0.05), respectively. Paralleling TPO levels, also platelet-monocyte aggregates increased, from 32.86±2.48% to 46.13±1.39% at 3 hours in the LPS model (P<0.01), and from 43.68±1.69% to 56.52±4.66% in the CLP model (P<0.05). Blockade of TPO by mTPOR-MBP administration reduced histological damage in target organs, namely lung, liver, and gut. In particular, neutrophil infiltration and lung septal thickening were reduced from a score of 1.86±0.34 to 0.60±0.27 (P<0.01) and from 1.43±0.37 to 0.40±0.16 (P<0.05), respectively, in the LPS model at 3 hours, and from a score of 1.75±0.37 to 0.38±0.18 (P<0.01) and from 1.25±0.31 to 0.13±0.13 (P<0.001), respectively, in the CLP model. Similarly, the number of hepatic microabscesses was decreased from 14.14±1.41 to 3.64±0.56 in the LPS model at 3 hours (P<0.001), and from 1.71±0.29 to 0.13±0.13 in the CLP model (P<0.001). Finally, the diameter of intestinal villi decreased from 90.69±3.95 μm to 70.74±3.60 μm in the LPS model at 3 hours (P<0.01), and from 74.29±4.29 μm to 57.50±1.89 μm in the CLP model (P<0.01). This protective effect was associated with the blunting of the increase in platelet-monocyte adhesion, and, on the contrary, with increased platelet-neutrophil aggregates in the circulation, which may be related to decreased neutrophil sequestration into the inflamed tissues. Conversely, circulating cytokine levels were not significantly changed, in both models, by mTPOR-MBP administration.ConclusionOur results demonstrate that TPO participates in the development of organ damage induced by experimental endotoxemia or polymicrobial sepsis via a mechanism involving increased platelet-leukocyte adhesion, but not cytokine release, and suggest that block...