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Byline: Hayder. Al-kuraishy, Nawar. Hussien, Marwa. Al-naimi, Ali. Al-Gareeb, Claire. Lugnier Background: Acute ischemic stroke (AIS) leads to neuronal and endothelial damage that activate the release of proinflammatory mediators such [...]

Congenital heart disease is the most common type of birth defect, accounting for one-third of all congenital anomalies. Using whole-exome sequencing of 2718 patients with congenital heart disease and a search in GeneMatcher, we identified 30 patients from 21 unrelated families of different ancestries with biallelic phospholipase D1 (PLD1) variants who presented predominantly with congenital cardiac valve defects. We also associated recessive PLD1 variants with isolated neonatal cardiomyopathy. Furthermore, we established that p.I668F is a founder variant among Ashkenazi Jews (allele frequency of ~2%) and describe the phenotypic spectrum of PLDI-associated congenital heart defects. PLD1 missense variants were overrepresented in regions of the protein critical for catalytic activity, and, correspondingly, we observed a strong reduction in enzymatic activity for most of the mutant proteins in an enzymatic assay. Finally, we demonstrate that PLD1 inhibition decreased endothelial-mesenchymal transition, an established pivotal early step in valvulogenesis. In conclusion, our study provides a more detailed understanding of disease mechanisms and phenotypic expression associated with PLD1 loss of function., Introduction Congenital heart disease is the most common type of birth defect, accounting for one-third of all congenital anomalies, with a worldwide occurrence of 7 per 1000 live births (1). [...]

Abstract: Mast cells are responsible for IgE-mediated allergic responses through the secretion of various inflammatory cytokines and mediators. Therefore, the pharmacological regulation of mast cell activation is an important goal [...]

Background: Decreased expression of phospholipase C-β1 (PLC-β1) has been observed in the brains of patients with schizophrenia, but, to our knowledge, no studies have shown a possible association between this altered PLC-β1 expression and the pathogenesis of schizophrenia. Although PLC-β1-null (PLC-β[1.sup.-/-]) mice exhibit multiple endophenotypes of schizophrenia, it remains unclear how regional decreases in PLC-β1 expression in the brain contribute to specific behavioural defects. Methods: We selectively knocked down PLC-β1 in the medial prefrontal cortex (mPFC) using a small hairpin RNA strategy in mice. Results: Silencing PLC-β1 in the mPFC resulted in working memory deficits, as assayed using the delayed non-match-to-sample T-maze task. Notably, however, other schizophreniarelated behaviours observed in PLC-β[1.sup.-/-] mice, including phenotypes related to locomotor activity, sociability and sensorimotor gating, were normal in PLC-β1 knockdown mice. Limitations: Phenotypes of PLC-β1 knockdown mice, such as locomotion, anxiety and sensorimotor gating, have already been published in our previous studies. Further, the neural mechanisms underlying the working memory deficit in mice may be different from those in human schizophrenia. Conclusion: These results indicate that PLC-β1 signalling in the mPFC is required for working memory. Importantly, these results support the notion that the decrease in PLC-β1 expression in the brains of patients with schizophrenia is a pathogenically relevant molecular marker of the disorder., Introduction Understanding the pathogenic mechanism of a mental disorder in terms of molecular changes in specific neural circuitries presents one of the major challenges in neurobiological studies of psychiatric diseases. [...]

Adenosine via an adenosine [A.sub.1] receptor ([A.sub.1]R) is a negative feedback inhibitor of adrenergic stimulation in the heart, protecting it from toxic effects of overstimulation. Stimulation of the AiR results in the activation of [G.sub.i] protein, release of free G[beta][gamma]-subunits, and activation/translocation of PKC-[epsilon] to the receptor for activated C kinase 2 protein at the Z-line of the cardiomyocyte sarcomere. Using an anti-G[beta][gamma] peptide, we investigated the role of these subunits in the AIR stimulation of phospholipase C (PLC), with the premise that the resulting diacylglycerol provides for the activation of PKC-[epsilon]. Inositol 1,4,5-triphosphate release was an index of PLC activity. Chlorocyclopentyl adenosine (CCPA), an AIR agonist, increased inositol 1,4,5-triphosphate production by 273% in mouse heart homogenates, an effect absent in [A.sub.1]R knockout hearts and inhibited by anti-G[beta][gamma] peptide. In a second study, p38 MAPK and heat shock protein 27 (HSP27), found by others to be associated with the loss of myocardial contractile function, were postulated to play a role in the actions of [A.sub.1]R. Isoproterenol, a [beta]-adrenergic receptor agonist, increased the [Ca.sup.2+] transient and sarcomere shortening magnitudes by 36 and 49%, respectively. In the rat cardiomyocyte, CCPA significantly reduced these increases, an action blocked by the p38 MAPK inhibitor SB-203580. While CCPA significantly increased the phosphorylation of HSP27, this action was inhibited by isoproterenol. These data indicate that the activation of PKC-[epsilon] by [A.sub.1]R results from the activation of PLC via free G[beta][gamma]subunits released upon [A.sub.1]R-induced dissociation of [G.sub.i][alpha][beta][gamma]. Attenuation of [beta]-adrenergic-induced contractile function by AIR may involve the activation of p38 MAPK, but not HSP27. G[beta][gamma] subunits; antiadrenergic; rodent; contractility doi: 10.1152/ajpheart.01028.2009.

The phospholipase neutral sphingomyelinase (N-SMase) has been recognized as a major mediator of processes such as inflammation, development and growth, differentiation and death of cells, as well as in diseases such as Alzheimer's, atherosclerosis, heart failure, ischemia/reperfusion damage, or combined pituitary hormone deficiency. Although activation of N-SMase by the proinflammatory cytokine TNF was described almost two decades ago, the underlying signaling pathway is unresolved. Here, we identify the Polycomb group protein EED (embryonic ectodermal development) as an interaction partner of nSMase2. In yeast, the N terminus of EED binds to the catalytic domain of nSMase2 as well as to RACK1, a protein that modulates the activation of nSMase2 by TNF in concert with the TNF receptor 1 (TNF-R1)-associated protein FAN. In mammalian cells, TNF causes endogenous EED to translocate from the nucleus and to colocalize and physically interact with both endogenous nSMase2 and RACK1. As a consequence, EED and nSMase2 are recruited to the TNF-R1*FAN*RACK1-complex in a timeframe concurrent with activation of nSMase2. After knockdown of EED by RNA interference, the TNF-dependent activation of nSMase2 is completely abrogated, identifying EED as a protein that both physically and functionally couples TNF-R1 to nSMase2, and which therefore represents the 'missing link' that completes one of the last unresolved signaling pathways of TNF-R1. embryonic ectodermal development | immune response | inflammation doi/10.1073/pnas.0908486107

Cruchaga et al. recently reported (1) evidence for genetic association between Alzheimer's disease risk and several rare DNA sequence variants in the phospholipase D3 gene (PLD3). The study's lead signal [...]

Interest in the role of rare genetic variants in the aetiology of complex diseases such as Alzheimer's disease is increasing (1, 2). Recently, Cruchaga et al. (3) provided evidence supporting [...]

Absence seizures are characterized by cortical spike-wave discharges (SWDs) on electroencephalography, often accompanied by a shift in the firing pattern of thalamocortical (TC) neurons from tonic to burst firing driven by T-type [Ca.sup.2+] currents. We recently demonstrated that the phospholipase C [beta]4 (PLC[beta]4) pathway tunes the firing mode of TC neurons via the simultaneous regulation of T- and L-type [Ca.sup.2+] currents, which prompted us to investigate the contribution of TC firing modes to absence seizures. PLC[beta]4-deficient TC neurons were readily shifted to the oscillatory burst firing mode after a slight hyperpolarization of membrane potential. TC-limited knockdown as well as whole-animal knockout of PLC[beta]4 induced spontaneous SWDs with simultaneous behavioral arrests and increased the susceptibility to drug-induced SWDs, indicating that the deletion of thalamic PLC[beta]4 leads to the genesis of absence seizures. The SWDs were effectively suppressed by thalamic infusion of a T-type, but not an L-type, [Ca.sup.2+] channel blocker. These results reveal a primary role of TC neurons in the genesis of absence seizures and provide strong evidence that an alteration of the firing property of TC neurons is sufficient to generate absence seizures. Our study presents PLC[beta]4-deficient mice as a potential animal model for absence seizures. epilepsy | gene knockdown | knockout mice | thalamus doi/10.1073/pnas.0912204106

Lipid signaling pathways are involved in cell growth, differentiation, and apoptosis, and could have a role in the progression of myelodysplastic syndromes (MDS) into acute myeloid leukemia (AML). Indeed, recent studies showed that phosphoinositide-phospholipase (PI-PL)Cbeta1 mono-allelic deletion correlates with a higher risk of AML evolution. Also, a single patient treated with azacitidine, a DNA methyltransferase inhibitor currently used in MDS, displayed a direct correlation between PI-PLCbetal1 gene expression and drug responsiveness. Consequently, we hypothesized that PI-PLCbeta1 could be a target for demethylating therapy. First, we analyzed the structure of PI-PLCbeta1 gene promoter, then quantified the degree of PI-PLCbeta1 promoter methylation and gene expression in MDS patients at baseline and during azacitidine administration. Indeed, PI-PLCbeta1 mRNA increased in responder patients, along with a reduction of PI-PLCbeta1 promoter methylation. Also, the molecular response correlated to and anticipated the clinical outcome, thus suggesting that PI-PLCbeta1 gene reactivation could predict azacitidine responsiveness. Our results demonstrate not only that PI-PLCbeta1 promoter is hypermethylated in high-risk MDS patients, but also that the amount of PI-PLCbeta1 mRNA could predict the clinical response to azacitidine, therefore indicating a promising new therapeutic approach. myelodysplastic syndromes | real-time PCR | signal transduction | inositides | epigenetic therapy

A white adipose-tissue-specific intracellular phospholipase, which releases arachidonic acid from position sn-2 of phospholipids, was recently discovered and named AdPLA. When AdPLA was induced by feeding or by insulin treatment, the arachidonic acid released from phospholipids acted as a precursor for the formation of prostaglandin [E.sub.2] ([PGE.sub.2]). Subsequent activation of the prostaglandin receptor EP3 caused decreased levels of cAMP that led to decreased lipolysis and increased adiposity. Ablation of AdPLA in knockout mice resulted in the reverse sequence of events, with a decline in arachidonic acid release and prostaglandin synthesis and an increase in levels of cAMP, leading to increased lipolysis and a decline in adiposity, even though food intake was not affected. The newly discovered AdPLA enzyme in white adipose tissue functions as a regulator of lipolysis by acting as an antilipolytic agent mediated by increased [PGE.sub.2] formation and decreased intracellular cAMP.

A study was conducted to identify target antigen in patients with idiopathic membranous nephropathy. Results indicated that a majority of patients with this ailment had a major antigen, M-type phospholipase A2 (PLA2R) present, thereby confirming the presence of the target antigen in such cases.

Byline: Daniele Luca (1), Angelo Minucci (2), Enrico Zecca (3), Marco Piastra (1), Domenico Pietrini (1), Virgilio P. Carnielli (4,5), Cecilia Zuppi (2), Ascanio Tridente (6), Giorgio Conti (1), Ettore D. Capoluongo (2) Keywords: Bile acids; Phospholipase A2; Surfactant; Lung injury; Neonate; Infant Abstract: Background and purposes Bile acids have been implicated in some forms of acute lung injury, including meconium aspiration and bile acid pneumonia in neonates, or aspiration related ARDS in adults. Secretory phospholipase A2 (sPLA2) is now known as a key enzyme in the lung injury pathways and is supposed to be responsible for surfactant dysfunction. Our aim was to investigate the interaction between bile acids and sPLA2 in an extracellular environment representing an in vitro model of aspiration. Methods In vitro study using broncho-alveolar lavage (BAL) of 23 neonates/infants ( Results High concentrations of BA (5 umol/l) significantly increased (P = 0.012) sPLA2 activity, leading to increased surfactant catabolism. This finding was not observed with lower BA concentration and this is consistent with available literature data and may indicate an anionic activation of the enzyme by bile acids. Increased activity was significantly reverted by the addition of exogenous surfactant (P = 0.004) which was able to reduce sPLA2 activity almost to the baseline level. Conclusions BA are likely to contribute to lung injury, causing surfactant inactivation through the increased sPLA2 activity. Other mechanisms cannot be excluded and require further studies to be clarified. Author Affiliation: (1) Pediatric Intensive Care Unit, Department of Anaesthesiology and Intensive Care, University Hospital 'A.Gemelli', Catholic University of the Sacred Heart, L.go A. Gemelli 8, 00168, Rome, Italy (2) Laboratory of Clinical Molecular Biology, Institute of Biochemistry and Clinical Biochemistry, University Hospital 'A.Gemelli', Catholic University of the Sacred Heart, Rome, Italy (3) Division of Neonatology, Department of Pediatrics, University Hospital 'A.Gemelli', Catholic University of the Sacred Heart, Rome, Italy (4) Division of Neonatology, Institute of Mother and Child Health 'G. Salesi', Polytechnical University of Marche, Ancona, Italy (5) Nutrition Unit, Institute of Child Health and Great Ormond Street Hospital, London, UK (6) Prince Charles Hospital, Merthyr, UK Article History: Registration Date: 02/10/2008 Received Date: 17/06/2008 Accepted Date: 21/09/2008 Online Date: 14/10/2008

Byline: Daniele Luca (1), Silvia Baroni (2), Giovanni Vento (1), Marco Piastra (3), Domenico Pietrini (3), Federica Romitelli (2), Ettore Capoluongo (2), Costantino Romagnoli (1), Giorgio Conti (3), Enrico Zecca (1) Keywords: Phospholipase A2; Lung injury; Newborn infants; Neonatal respiratory distress syndrome Abstract: Purposes Secretory phospholipase A2 hydrolyzes phosphoglycerides and it has been shown to be involved in alveolar inflammation and surfactant degradation. It plays an important role in acute lung injury but it has never been studied in newborn infants. We were aimed to investigate the phospholipase A2 activity in neonatal lung injury and its relationship with ventilatory findings. Setting Third level university hospital NICU. Methods We measured phospholipase activity in broncho-alveolar lavage fluid of 21 neonates with hyaline membrane disease, 10 with pneumonia or sepsis and 10 controls, ventilated for extrapulmonary reasons. Fluid was obtained before surfactant administration on the first day of life and phospholipase activity was measured using an ultrasensitive enzymatic method. Before lavage, lung mechanics in pressure controlled synchronized intermittent mandatory ventilation was analyzed. Results Phospholipase A2 was higher in babies ventilated for sepsis/pneumonia compared to hyaline membrane disease and to control babies. Phospholipase correlated negatively with dynamic compliance, positively with inspired oxygen fraction, mean airway pressure and oxygenation index. These correlations still remained significant after multivariate analysis, adjusting for possible confounding factors. Phospholipase was not correlated with blood and alveolar pH, gestational age, birth weight, blood gases, Apgar score, tidal volume, surfactant need and ventilation time. Conclusions These are the first data about phospholipase A2 in neonates. The enzyme plays a role in neonatal lung injury, especially in infection related respiratory failure. It is associated with lung stiffness, higher mean airway pressure and need for oxygen. Author Affiliation: (1) Neonatal Intensive Care Unit, Department of Pediatrics, University Hospital 'A. Gemelli', Catholic University of the Sacred Heart, L.go A. Gemelli 8, 00168, Rome, Italy (2) Institute of Clinical Biochemistry, University Hospital 'A. Gemelli', Catholic University of the Sacred Heart, Rome, Italy (3) Pediatric Intensive Care Unit, Department of Anaesthesiology and Intensive Care, University Hospital 'A. Gemelli', Catholic University of the Sacred Heart, Rome, Italy Article History: Registration Date: 11/07/2008 Received Date: 17/03/2008 Accepted Date: 10/07/2008 Online Date: 22/07/2008 Article note: This study has been partially presented to 48th Meeting of the European Society for Pediatric Research, selected for the Final Young Investigators Award Plenary Session (Prague, Czech Rep., October 6--8, 2007).

Increased lipoprotein-associated phospholipase [A.sub.2] (Lp-[PLA.sub.2]) activity is associated with increased risk of cardiac events, but it is not known whether Lp-[PLA.sub.2] is a causative agent. Here we show that selective inhibition of Lp-[PLA.sub.2] with darapladib reduced development of advanced coronary atherosclerosis in diabetic and hypercholesterolemic swine. Darapladib markedly inhibited plasma and lesion Lp-[PLA.sub.2] activity and reduced lesion lysophosphatidylcholine content. Analysis of coronary gene expression showed that darapladib exerted a general anti-inflammatory action, substantially reducing the expression of 24 genes associated with macrophage and T lymphocyte functioning. Darapladib treatment resulted in a considerable decrease in plaque area and, notably, a markedly reduced necrotic core area and reduced medial destruction, resulting in fewer lesions with an unstable phenotype. These data show that selective inhibition of Lp-[PLA.sub.2] inhibits progression to advanced coronary atherosclerotic lesions and confirms a crucial role of vascular inflammation independent from hypercholesterolemia in the development of lesions implicated in the pathogenesis of myocardial infarction and stroke., Atherosclerosis, the most common cause of myocardial infarction, stroke and cardiovascular death, is an inflammatory-immunomodulatory disease (1,2). A key early step in its development is the accumulation and subsequent oxidation [...]

The mammalian target of rapamycin (mTOR) assembles a signaling network essential for the regulation of cell growth, which has emerged as a major target of anticancer therapies. The tuberous sclerosis complex I and 2 (TSC1/2) proteins and their target, the small GTPase Rheb, constitute a key regulatory pathway upstream of mTOR. Phospholipase D (PLD) and its product phosphatidic acid are also upstream regulators of the mitogenic mTOR signaling. However, how the TSC/Rheb and PLD pathways interact or integrate in the rapamycin-sensitive signaling network has not been examined before. Here, we find that PLD1, but not PLD2, is required for Rheb activation of the mTOR pathway, as demonstrated by the effects of RNAi. The overexpression of Rheb activates PLD1 in cells in the absence of mitogenic stimulation, and the knockdown of Rheb impairs serum stimulation of PLD activation. Furthermore, the overexpression of TSC2 suppresses PLD1 activation, whereas the knockdown or deletion of TSC2 leads to elevated basal activity of PLD. Consistent with a TSC-Rheb-PLD signaling cascade, AMPK and PI3K, both established regulators of TSC2, appear to lie upstream of PLD as revealed by the effects of pharmacological inhibitors, and serum activation of PLD is also dependent on amino acid sufficiency. Finally, Rheb binds and activates PLD1 in vitro in a GTP-dependent manner, strongly suggesting that PLD1 is a bona fide effector for Rheb. Hence, our findings reveal an unexpected interaction between two cascades in the mTOR signaling pathways and open up additional possibilities for targeting this important growth-regulating network for the development of anticancer drugs. rapamycin | tuberous sclerosis complex | phosphatidic acid

Atherosclerosis is an inflammatory disease that is associated with monocyte recruitment and subsequent differentiation into lipid-laden macrophages at sites of arterial lesions, leading to the development of atherosclerotic plaques. PLC is a key member of signaling pathways initiated by G protein--coupled ligands in macrophages. However, the role of this enzyme in the regulation of macrophage function is not known. Here, we studied macrophages from mice lacking PLC [beta]2, PLC [beta]3, or both PLC isoforms and found that PLC [beta]3 is the major functional PLC [beta] isoform in murine macrophages. Although PLC [beta]3 deficiency did not affect macrophage migration, adhesion, or phagocytosis, it resulted in macrophage hypersensitivity to multiple inducers of apoptosis. PLC [beta]3 appeared to regulate this sensitivity via PKC-dependent upregulation of Bcl-XL. The significance of PLC [beta] signaling in vivo was examined using the apoE-deficient mouse model of atherosclerosis. Mice lacking both PLC [beta]3 and apoE exhibited fewer total macrophages and increased macrophage apoptosis in atherosclerotic lesions, as well as reduced atherosclerotic lesion size when compared with mice lacking only apoE. These results demonstrate what we believe to be a novel role for PLC activity in promoting macrophage survival in atherosclerotic plaques and identify PLC [beta]3 as a potential target for treatment of atherosclerosis., Introduction PLC hydrolyzes phosphatidylinositol 4,5-bisphosphate to generate 2 second messengers, inositol 1,3,4-triphosphate and diacylgl-ycerol. While inositol 1,3,4-triphosphate regulates [Ca.sup.2+] efflux, it and diacylglycerol activate PKC (1). The [beta] family of [...]

Oxidant-induced lipid peroxidation and cell death mediate pathologies associated with ischemia-reperfusion and inflammation. Our previous work in rabbit renal proximal tubular cells (RPTC) demonstrated that inhibition of [Ca.sup.2+]-independent phospholipase [A.sub.2] (iPL[A.sub.2]) potentiates oxidant-induced lipid peroxidation and necrosis, implicating iPL[A.sub.2] in phospholipid repair. This study was conducted to identify a RPTC mitochondrial PL[A.sub.2] and determine the role of PL[A.sub.2] in oxidant-induced mitochondrial dysfunction, iPL[A.sub.2] activity was detected in Percoll-purified rabbit renal cortex mitochondria (RCM) and in isolated mitochondrial inner membrane fractions from rabbit and human RCM. Immunoblot analysis and inhibitor sensitivity profiles revealed that iPL[A.sub.2[gamma]] is the RCM iPL[A.sub.2] activity. RCM iPL[A.sub.2] activity was enhanced in the presence of ATP and was blocked by the PKC[member of] V1-2 inhibitor. Oxidant-induced mitochondrial lipid peroxidation and swelling were accelerated by pretreatment with R-BEL, but not S-BEL. Furthermore, oxidant treatment of isolated RCM resulted in decreased iPL[A.sub.2[gamma]] activity. These results reveal that RCM iPL[A.sub.2] is iPL[A.sub.2[gamma]], RCM iPL[A.sub.2[gamma]] is regulated by phosphorylation by PKC[member of], iPL[A.sub.2[gamma]] protects RCM from oxidant-induced lipid peroxidation and dysfunction, and that a strategy to preserve or enhance iPL[A.sub.2[gamma]] activity may be of therapeutic benefit. group VIB PL[A.sub.2]; lipid peroxidation

ACh stimulates arachidonic acid (AA) release from membrane phospholipids of vascular endothelial cells (ECs). In rabbit aorta, AA is metabolized through the 15-lipoxygenase pathway to form vasodilatory eicosanoids 15-hydroxy-11,12-epoxyeicosatrienoic acid (HEETA) and 11,12,15-trihydroxyeicosatrienoic acid (THETA). AA is released from phosphatidylcholine (PC) and phosphatidylethanolamine (PE) by phospholipase [A.sub.2] ([PLA.sub.2]), or from phosphatidylinositol (PI) by phospholipase C (PLC) pathway. The diacylglycerol (DAG) lipase can convert DAG into 2-arachidonoylglycerol from which free AA can be released by monoacylglycerol (MAG) lipase or fatty acid amidohydrolase (FAAH). We used specific inhibitors to determine the involvement of the PLC pathway in ACh-induced AA release. In rabbit aortic rings precontracted by phenylephrine, ACh induced relaxation in the presence of indomethacin and N[omega]-nitro-L-arginine (L-NNA). These relaxations were blocked by the PLC inhibitor U-73122, DAG lipase inhibitor RHC-80267, and MAG lipase/FAAH inhibitor URB-532. Cultured rabbit aortic ECs were labeled with [[sup.14]C]AA and stimulated with methacholine ([10.sup.-5] M). Free [[sup.14]C]AA was released by methacholine. Methacholine decreased the [[sup.14]C]AA content of PI, DAG, and MAG fractions but not PC or PE fractions. Methacholine-induced release of [[sup.14]C]AA was blocked by U-73122, RHC-80267, and URB-532 but not by U-73343, an inactive analog of U-73122. The data suggested that ACh activates PLC, DAG lipase, and MAG lipase pathway to release AA from membrane lipids. This pathway is important in regulating vasodilatory eicosanoid synthesis and vascular relaxation in rabbit aorta. endothelium-dependent hyperpolarizing factor; phospholipid; monoacylglycerol lipase; trihydroxyeicosatrienoic acid; hydroxyepoxyeicosatrienoic acid

Elevated blood levels of lipoprotein-associated phospholipase A(sub 2) may predict which men will have a heart attack or die from coronary artery disease. This enzyme may modify low-density lipoproteins inside coronary arteries.

Uninterrupted oxygeneration or hypoxic injury, with or without exogenous phospholipase A2 (PLA2) addition, was applied to isolated rat proximal tubules to examine the assumption that PLA2 activity is a crucial mediator of hypoxic renal tubular injury, and consequently of ischemic acute renal failure. Lactic dehydrogenase secretion was used to measure cell death. The advantageous and harmful effects on O2-deprived renal tubules could result from PLA2 activity.

Background Chronic lymphocytic leukemia (CLL), the most common adulthood leukemia, is characterized by the accumulation of abnormal [CD5.sup.+] B lymphocytes, which results in a progressive failure of the immune system. Despite intense research efforts, drug resistance remains a major cause of treatment failure in CLL, particularly in patients with dysfunctional TP53. The objective of our work was to identify potential approaches that might overcome CLL drug refractoriness by examining the pro-apoptotic potential of targeting the cell surface receptor CD47 with serum-stable agonist peptides. Methods and Findings In peripheral blood samples collected from 80 patients with CLL with positive and adverse prognostic features, we performed in vitro genetic and molecular analyses that demonstrate that the targeting of CD47 with peptides derived from the C-terminal domain of thrombospondin-1 efficiently kills the malignant CLL B cells, including those from high-risk individuals with a dysfunctional TP53 gene, while sparing the normal T and B lymphocytes from the CLL patients. Further studies reveal that the differential response of normal B lymphocytes, collected from 20 healthy donors, and leukemic B cells to CD47 peptide targeting results from the sustained activation in CLL B cells of phospholipase C gamma-1 (PLC[gamma]1), a protein that is significantly over-expressed in CLL. Once phosphorylated at tyrosine 783, PLC[gamma]1 enables a [Ca.sup.2+]-mediated, caspase-independent programmed cell death (PCD) pathway that is not down-modulated by the lymphocyte microenvironment. Accordingly, down-regulation of PLC[gamma]1 or pharmacological inhibition of PLC[gamma]1 phosphorylation abolishes CD47-mediated killing. Additionally, in a CLL-xenograft model developed in NOD/scid gamma mice, we demonstrate that the injection of CD47 agonist peptides reduces tumor burden without inducing anemia or toxicity in blood, liver, or kidney. The limitations of our study are mainly linked to the affinity of the peptides targeting CD47, which might be improved to reach the standard requirements in drug development, and the lack of a CLL animal model that fully mimics the human disease. Conclusions Our work provides substantial progress in (i) the development of serum-stable CD47 agonist peptides that are highly effective at inducing PCD in CLL, (ii) the understanding of the molecular events regulating a novel PCD pathway that overcomes CLL apoptotic avoidance, (iii) the identification of PLC[gamma]1 as an over-expressed protein in CLL B cells, and (iv) the description of a novel peptide-based strategy against CLL., Introduction Chronic lymphocytic leukemia (CLL), a human malignancy caused by an imbalance between proliferation and programmed cell death (PCD) [1], is the most common form of leukemia in adults. CLL [...]