Muriel Laffargue

Phosphoinositide 3-kinase signalling--which way to target?

Abstract Phosphoinositide 3-kinases (PI3Ks) are central to the control of cell growth, proliferation and survival, and drive the progression of tumours by activating phosphoinositide-dependent kinase, protein kinase B and the target of rapamycin. Other downstream effectors link PI3K to cell motility and the control of cardiovascular parameters. Current knowledge indicates that PI3Ks might qualify as drug targets for the treatment of cancer, chronic inflammation, allergy and cardiovascular failure. However, PI3Ks also modulate vital processes such as metabolic control and nutrient uptake. Here, mechanistic data and mouse phenotypic analyses are summarised, and the possible success of therapeutic inhibition of distinct PI3K isoforms is discussed.

Phosphoinositide 3-Kinase γ Is an Essential Amplifier of Mast Cell Function

Abstract Mast cells are key regulators in allergy and inflammation, and release histamine upon clustering of their IgE receptors. Here we demonstrate that murine mast cell responses are exacerbated in vitro and in vivo by autocrine signals through G protein-coupled receptors (GPCRs) and require functional phosphoinositide 3-kinase γ (PI3Kγ). Adenosine, acting through the A 3 adenosine receptor (A 3 AR) as well as other agonists of G αi -coupled GPCRs, transiently increased PtdIns(3,4,5) P 3 exclusively via PI3Kγ. PI3Kγ-derived PtdIns(3,4,5) P 3 was instrumental for initiating a sustained influx of external Ca 2+ and degranulation. Mice lacking PI3Kγ did not form edema after intradermal injection of adenosine and when challenged by passive systemic anaphylaxis. PI3Kγ thus relays inflammatory signals through various G i -coupled receptors and is central to mast cell function.

Resistance to thromboembolism in PI3Kγ-deficient mice

Platelet aggregation and subsequent thrombosis are the major cause of ischemic diseases such as heart attack and stroke. ADP, acting via G protein‐coupled receptors (GPCRs), is an important signal in thrombus formation and involves activation of phosphoinositide 3‐kinases (PI3K). When platelets from mice lacking the G protein‐activated PI3Kγ isoform were stimulated with ADP, aggregation was impaired. Collagen or thrombin, however, evoked a normal response. ADP stimulation of PI3Kγ‐deficient platelets resulted in decreased PKB/Akt phosphorylation and αIIbβ3 fibrinogen receptor activation. These effects did not influence bleeding time but protected PI3Kγ‐null mice from death caused by ADP‐induced platelet‐dependent thromboembolic vascular occlusion. This result demonstrates an unsuspected, well‐defined role for PI3Kγ downstream of ADP and suggests that pharmacological targeting of PI3Kγ has a potential use as antithrombotic therapy.

17Beta-estradiol promotes TLR4-triggered proinflammatory mediator production through direct estrogen receptor alpha signaling in macrophages in vivo.

17β-estradiol (E2) has been shown to promote the expression of inflammatory mediators by LPS-activated tissue resident macrophages through estrogen receptor α (ERα) signaling. However, it remained to be determined whether E2 similarly influences macrophages effector functions under inflammatory conditions in vivo, and whether this action of E2 resulted from a direct effect on macrophages. We show in this study that chronic E2 administration to ovariectomized mice significantly increased both cytokine (IL-1β, IL-6, and TNF-α) and inducible NO synthase mRNA abundance in thioglycolate (TGC)-elicited macrophages. The proinflammatory action of E2 was also evidenced at the level of released IL-1β and IL-6 by ex vivo LPS-activated macrophages. E2 concomitantly inhibited PI3K activity as well as Akt phosphorylation in TGC-elicited macrophages, suggesting that E2 promoted TLR-dependent macrophage activation by alleviating this suppressive signaling pathway. Indeed, this effect was abolished in the presence of the inhibitor wortmannin, demonstrating a key functional link between inhibition of PI3K activity and the E2 action on macrophage functions. Endogenous estrogens levels circulating in ovary-intact mice were sufficient to promote the above described actions. Finally, thanks to a CreLox strategy, targeted disruption of ERα gene in macrophages totally abolished the effect of E2 on the expression of inflammatory mediators by both resident and TGC-elicited peritoneal macrophages. In conclusion, we demonstrate that estrogens, through the activation of ERα in macrophages in vivo, enhance their ability to produce inflammatory mediators and cytokines upon subsequent TLR activation.

Chronic Estradiol Administration In Vivo Promotes the Proinflammatory Response of Macrophages to TLR4 Activation: Involvement of the Phosphatidylinositol 3-Kinase Pathway

Short-term exposure to 17β-estradiol (E2) in vitro has been reported to decrease the production of proinflammatory cytokines by LPS-activated macrophages through estrogen receptor α (ERα)-dependent activation of the PI3K pathway. In the present study, we confirm that in vitro exposure of mouse peritoneal macrophages to E2 enhanced Akt phosphorylation and slightly decreased LPS-induced cytokine production. In striking contrast, we show that chronic administration of E2 to ovariectomized mice markedly increases the expression of IL-1β, IL-6, IL-12p40, and inducible NO synthase by resident peritoneal macrophages in response to LPS ex vivo. These results clearly indicate that short-term E2 treatment in vitro does not predict the long-term effect of estrogens in vivo on peritoneal macrophage functions. We show that this in vivo proinflammatory effect of E2 was mediated through ERα. Although the expression of components of the LPS-recognition complex remained unchanged, we provided evidences for alterations of the TLR4 signaling pathway in macrophages from E2-treated mice. Indeed, E2 treatment resulted in the inhibition of PI3K activity and Akt phosphorylation in LPS-activated macrophages, whereas NF-κB p65 transcriptional activity was concomitantly increased. Incubation of macrophages with the PI3K inhibitor wortmanin enhanced proinflammatory cytokine gene expression in response to TLR4 activation, and abolishes the difference between cells from placebo- or E2-treated mice, demonstrating the pivotal role of the PI3K/Akt pathway. We conclude that the macrophage activation status is enhanced in vivo by E2 through ERα and, at least in part, by the down-modulation of the PI3K/Akt pathway, thereby alleviating this negative regulator of TLR4-signaling.

Genetic and pharmacological targeting of phosphoinositide 3-kinase-gamma reduces atherosclerosis and favors plaque stability by modulating inflammatory processes.

Background— The role of inflammation at all stages of the atherosclerotic process has become an active area of investigation, and there is a notable quest for novel and innovative drugs for the treatment of atherosclerosis. The lipid kinase phosphoinositide 3-kinase-&ggr; (PI3K&ggr;) is thought to be a key player in various inflammatory, autoimmune, and allergic processes. These properties and the expression of PI3K&ggr; in the cardiovascular system suggest that PI3K&ggr; plays a role in atherosclerosis. Methods and Results— Here, we demonstrate that a specific PI3K&ggr; inhibitor (AS605240) is effective in murine models of established atherosclerosis. Intraperitoneal administration of AS605240 (10 mg/kg daily) significantly decreased early atherosclerotic lesions in apolipoprotein E–deficient mice and attenuated advanced atherosclerosis in low-density lipoprotein receptor–deficient mice. Furthermore, PI3K&ggr; levels were elevated in both human and murine atherosclerotic lesions. Comparison of low-density lipoprotein receptor–deficient mice transplanted with wild-type or PI3K&ggr;-deficient bone marrow demonstrated that functional PI3K&ggr; in the hematopoietic lineage is required for atherosclerotic progression. Alleviation of atherosclerosis by targeting of PI3K&ggr; activity was accompanied by decreased macrophage and T-cell infiltration, as well as increased plaque stabilization. Conclusions— These data identify PI3K&ggr; as a new target in atherosclerosis with the potential to modulate multiple stages of atherosclerotic lesion formation, such as fatty streak constitution, cellular composition, and final fibrous cap establishment.

Anti-Inflammatory and Antiatherogenic Effects of the NLRP3 Inflammasome Inhibitor Arglabin in ApoE2.Ki Mice Fed a High-Fat Diet

Background— This study was designed to evaluate the effect of arglabin on the NLRP3 inflammasome inhibition and atherosclerotic lesion in ApoE2Ki mice fed a high-fat Western-type diet. Methods and Results— Arglabin was purified, and its chemical identity was confirmed by mass spectrometry. It inhibited, in a concentration-dependent manner, interleukin (IL)-1&bgr; and IL-18, but not IL-6 and IL-12, production in lipopolysaccharide and cholesterol crystal–activated cultured mouse peritoneal macrophages, with a maximum effect at ≈50 nmol/L and EC50 values for both cytokines of ≈ 10 nmol/L. Lipopolysaccharide and cholesterol crystals did not induce IL-1&bgr; and IL-18 production in Nlrp3−/− macrophages. In addition, arglabin activated autophagy as evidenced by the increase in LC3-II protein. Intraperitoneal injection of arglabin (2.5 ng/g body weight twice daily for 13 weeks) into female ApoE2.Ki mice fed a high-fat diet resulted in a decreased IL-1&bgr; plasma level compared with vehicle-treated mice (5.2±1.0 versus 11.7±1.1 pg/mL). Surprisingly, arglabin also reduced plasma levels of total cholesterol and triglycerides to 41% and 42%, respectively. Moreover, arglabin oriented the proinflammatory M1 macrophages into the anti-inflammatory M2 phenotype in spleen and arterial lesions. Finally, arglabin treatment markedly reduced the median lesion areas in the sinus and whole aorta to 54% (P=0.02) and 41% (P=0.02), respectively. Conclusions— Arglabin reduces inflammation and plasma lipids, increases autophagy, and orients tissue macrophages into an anti-inflammatory phenotype in ApoE2.Ki mice fed a high-fat diet. Consequently, a marked reduction in atherosclerotic lesions was observed. Thus, arglabin may represent a promising new drug to treat inflammation and atherosclerosis.

PKCβ Phosphorylates PI3Kγ to Activate It and Release It from GPCR Control

The GPCR-activated PI3Kγ is also a key enzyme downstream of the IgE high affinity receptor FcεRI. PKCβ-dependent phosphorylation of PI3Kγ on Ser582 is the ‘missing link’ that functions as a molecular switch to divert PI3Kγ from GPCR inputs.

Elastin fragmentation and atherosclerosis progression: The elastokine concept

Atherosclerosis is a progressive multifaceted inflammatory disease affecting large- and medium-sized arteries. Typical feature of this disease is the formation and build-up of atherosclerotic plaques characterized by vascular extracellular matrix degradation and remodeling. Many studies have documented degradation of native elastin, the main extracellular matrix protein responsible for resilience and elasticity of arteries, by local release of elastases, leading to the production of elastin-derived peptides (EDP). These peptides have been proposed to actively participate in the progression of the disease by accelerating different biological processes, such as LDL oxidation and calcification of the vascular wall. These pathophysiological effects are mediated by the binding of EDP on a peculiar heterotrimeric receptor named elastin receptor complex (ERC). In this article, we review the contribution of elastin in biological processes involved in atherosclerosis progression from its initial elastase-driven degradation to its ultimate cellular effects. Finally, we discuss the ERC and its derived signaling pathways as promising therapeutic targets.

PI3K-C2γ is a Rab5 effector selectively controlling endosomal Akt2 activation downstream of insulin signalling

In the liver, insulin-mediated activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway is at the core of metabolic control. Multiple PI3K and Akt isoenzymes are found in hepatocytes and whether isoform-selective interplays exist is currently unclear. Here we report that insulin signalling triggers the association of the liver-specific class II PI3K isoform γ (PI3K-C2γ) with Rab5-GTP, and its recruitment to Rab5-positive early endosomes. In these vesicles, PI3K-C2γ produces a phosphatidylinositol-3,4-bisphosphate pool specifically required for delayed and sustained endosomal Akt2 stimulation. Accordingly, loss of PI3K-C2γ does not affect insulin-dependent Akt1 activation as well as S6K and FoxO1-3 phosphorylation, but selectively reduces Akt2 activation, which specifically inhibits glycogen synthase activity. As a consequence, PI3K-C2γ-deficient mice display severely reduced liver accumulation of glycogen and develop hyperlipidemia, adiposity as well as insulin resistance with age or after consumption of a high-fat diet. Our data indicate PI3K-C2γ supports an isoenzyme-specific forking of insulin-mediated signal transduction to an endosomal pool of Akt2, required for glucose homeostasis.