Sylvain Chemtob

CHU Sainte-Justine, Montréal, Quebec, Canada

Are you Sylvain Chemtob?

Claim your profile

Publications (256)1015.19 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Purpose Pathological choroidal neovascularization (CNV) is the major cause of severe vision loss in patients with age-related macular degeneration (AMD). Inflammation is a key component in AMD, and macrophages play an important role in CNV generation. We have demonstrated that human T-lymphocyte-derived microparticles (LMPs) significantly inhibit angiogenesis in several models of ocular neovascularization. In this study, we investigated whether LMPs modulate angiogenic microenvironment by altering macrophages activitiesMethods LMPs were produced from apoptotic human T lymphocytes after treated with actinomycin D. The effects of LMPs on cell viability and cell migration were studied in apoptosis assay and migration assay respectively. Cell growth of human retinal microvascular endothelial cells was assessed after cells were co-cultured with LMPs pre-treated macrophages. A laser-induced CNV model was used to determine labelled choroidal flat-mounts.Results LMPs dose-dependently inhibited macrophages cell growth without altering cell death. In addition, LMPs dramatically abrogated VEGF-induced macrophages migration. LMPs-pretreated macrophages exhibited strong inhibitory effect on endothelial cell growth and this effect was associated with the increased expression of IL-12, CD36 and HIF-1α. In vivo, intravitreal injection of LMPs significantly suppressed laser-induced CNV and reduced macrophages infiltration at the lesion sites.Conclusion These results suggest that LMPs are potent antiangiogenic therapeutic agent. In addition to the direct effects on endothelial cells, LMPs may interfere the proangiogenic environment through modulation of macrophages function during pathophysiological conditions.
    Acta ophthalmologica 09/2014; 92(s253). · 2.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Prompt post-hypoxia-ischemia (HI) revascularization has been suggested to improve outcome in adults and newborn subjects. Other than hypoxia-inducible factor, sensors of metabolic demand remain largely unknown. During HI, anaerobic respiration is arrested resulting in accumulation of carbohydrate metabolic intermediates. As such succinate readily increases, exerting its biological effects via a specific receptor, G-protein-coupled receptor (GPR) 91. We postulate that succinate/GPR91 enhances post-HI vascularization and reduces infarct size in a model of newborn HI brain injury. The Rice-Vannucci model of neonatal HI was used. Succinate was measured by mass spectrometry, and microvascular density was evaluated by quantification of lectin-stained cryosection. Gene expression was evaluated by real-time polymerase chain reaction. Succinate levels rapidly increased in the penumbral region of brain infarcts. GPR91 was foremost localized not only in neurons but also in astrocytes. Microvascular density increased at 96 hours after injury in wild-type animals; it was diminished in GPR91-null mice leading to an increased infarct size. Stimulation with succinate led to an increase in growth factors implicated in angiogenesis only in wild-type mice. To explain the mode of action of succinate/GPR91, we investigated the role of PGE2-prostaglandin E receptor 4, previously proposed in neural angiogenesis. Succinate-induced vascular endothelial growth factor expression was abrogated by a cyclooxygenase inhibitor and a selective prostaglandin E receptor 4 antagonist. This antagonist also abolished succinate-induced neovascularization. We uncover a dominant metabolic sensor responsible for post-HI neurovascular adaptation, notably succinate/GPR91, acting via PGE2-prostaglandin E receptor 4 to govern expression of major angiogenic factors. We propose that pharmacological intervention targeting GPR91 could improve post-HI brain recovery.
    Arteriosclerosis Thrombosis and Vascular Biology 11/2013; · 6.34 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Purpose:Perinatal inflammatory stress in preterm babies is associated with increased rates of severe retinopathy of prematurity (ROP) and adverse neurological dysfunction. While sustained perinatal systemic inflammation is known to perturb and damage the cerebral neurovascular unit, the precise impact on the neurovascular retina remains ill-defined. In this study, we set out to determine the consequences of severe systemic inflammatory stress on developmental retinal vascularization and evaluate the subsequent outcome on retinal function in later life. Methods:Systemic inflammatory stress was induced in C57BL/6J mouse pups by an intraperitoneal injection of lipopolysaccharide (LPS; 1 mg/kg) at post-natal day 4. A detailed and systematic analysis of retinal microglial infiltration, retinal vascular morphology, density and growth rate was performed at key time-points throughout retinal vascularization. Retinal function in adult life was assessed with the electroretinogram at 6 weeks post-injection. Results: As early as 48 hours after intra-peritoneal administration of LPS, a significant increase in retinal vascular densities was noted throughout the retina. A pronounced increase in the number of activated microglial cell was observed in the retinal ganglion cell layer and in the outer plexiform layer just prior to their vascularization; direct physical contact between activated microglia and sprouting vessels suggested that microglia partake in promoting the aberrant retinal vascularization. With maturity, animals subjected to perinatal inflammatory stress displayed depleted retinal vascular beds and had significantly decreased retinal function as determined by electroretinograms. Conclusions: Our data reveal that early severe post-natal inflammatory stress leads to abnormal retinal vascular development, increased vessel anastomosis and ultimately, permanently compromises retinal function. The aberrant and initially exaggerated retinal vascularization observed is associated with microglial activation, providing a cellular mechanism by which perinatal sepsis predisposes to ROP.
    Investigative ophthalmology & visual science 11/2013; · 3.43 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Background: Choroidal neovascularization (CNV) is a major cause of vision loss in which choroidal vessels penetrate the retinal pigment epithelium (RPE)-an important source of growth factors, including nerve growth factor (NGF), whose activation via the p75NTR receptor promotes apoptosis and inhibits angiogenesis. We previously demonstrated that human T-lymphocyte-derived microparticles (LMPs) significantly inhibit angiogenesis in several models of ocular neovascularization. We herein investigated how LMPs modulate pro and antiangiogenic microenvironments during choroidal angiogenesis. Methods: Antiangiogenic effects of LMPs were investigated using a rat model of choroidal angiogenesis. The impact of LMPs on expression of major angiogenic factors was assessed by real-time qPCR. To determine whether p75NTR signalling was implicated in LMPs-induced activities, we used a specific antibody and shRNA targeting p75NTR. Cellular apoptosis was determined via evaluation of activated caspase-3 and annexin V binding. Results: LMPs time-dependently inhibited choroidal angiogenesis by more than 64% after 48 hours of treatment. Removal of the RPE from choroidal explants abolished the antiangiogenic effects of LMPs. mRNA levels of pigment epithelium-derived factor (PEDF) and NGF were significantly increased following LMPs treatment of intact, but not RPE-removed choroids. Downregulation of PEDF and p75NTR significantly blocked the antiangiogenic effects of LMPs. Finally, induction of choroidal endothelial cell apoptosis by LMPs was dependent on p75NTR. Conclusions: We demonstrate for the first time that LMPs markedly inhibit choroidal angiogenesis via mechanisms that are dependent on the integrity of the RPE and that are largely mediated by the PEDF and proapoptotic activities of p75NTR.
    Investigative ophthalmology & visual science 08/2013; · 3.43 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Purpose Age-related macular degeneration (AMD) represents the leading cause of vision loss in the elderly. The cumulative oxidative injury induces retinal pigment epithelium (RPE) membrane microparticles production, RPE cell death and cellular senescence. The RPE blebs are implicated in the formation of sub-retinal deposit. Nonetheless, the pathophysiological roles of RPE microparticles (RMPs) remain largely unexplored. This study was designed to investigate whether RMPs participate in the retinal cells dysfunction. Methods RMPs and fluorescent DiI-labelled RMPs were isolated from cultured ARPE-19 cells under oxidative stress. RMPs-treated RPE cells were subjected to WST-1, cellular senescent, apoptotic assay and FACS cell cycle analysis respectively. The antibody against CD36 was used in uptake experiment to determine the involvement of scavenger receptor CD36. Results Our study revealed that uptake of RMPs by RPE cells is time-dependent, and this process is partially dependent on CD36 evidenced by an approximately 50% decrease of RMPs uptake caused by CD36 antibody treatment. In addition, RMPs significantly reduced RPE cell viability in a dose-dependent manner. RMPs in a concentration of 5% µg/ml significantly induced RPE cell-cycle arrest at G0/G1 phase. RMPs-treated cells exhibited a 19% increase in G0/G1 phase, with associated increases of the senescence-associated β-galactosidase activity. Conclusion We demonstrated for the first time that RPE cells uptake microparticles derived from RPE cells under oxidative stress. These findings strongly suggest that RMPs function as mediators to exacerbate the oxidative damages to RPE cells, and indicate a pathological role of RMPs in AMD.
    Acta ophthalmologica 08/2013; 91(s252). · 2.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Age-related macular degeneration (AMD) is a prominent cause of blindness in the Western world. To date, its molecular pathogenesis as well as the sequence of events leading to retinal degeneration remain largely ill-defined. While the invasion of choroidal neovessels in the retina is the primary mechanism that precipitates loss of sight, an earlier dry form precedes it. Here we provide the first evidence for the protective role of the Retinal Pigment Epithelium (RPE)-resident metabolite receptor, succinate receptor 1 (SUCNR1; G-Protein coupled Receptor-91 (GPR91), in preventing dry AMD-like lesions of the outer retina. Genetic analysis of 925 patients with geographic atrophy and 1199 AMD-free peers revealed an increased risk of developing geographic atrophy associated with intronic variants in theSUCNR1 gene. In mice, outer retinal expression of SUCNR1 is observed in the RPE as well as microglial cells and decreases progressively with age. Accordingly, Sucnr1-/- mice show signs of premature sub-retinal dystrophy with accumulation of oxidized-LDL, abnormal thickening of Bruch's membrane and a buildup of subretinal microglia. The accumulation of microglia in Sucnr1-deficient mice is likely triggered by the inefficient clearance of oxidized lipids by the RPE as bone marrow transfer of wild-type microglia into Sucnr1-/- mice did not salvage the patho-phenotype and systemic lipolysis was equivalent between wild-type and control mice. Our findings suggest that deficiency in SUCNR1 is a possible contributing factor to the pathogenesis of dry AMD and thus broaden our understanding of this clinically unmet need.
    Aging 06/2013; · 4.70 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: OBJECTIVE: Proinflammatory cytokines contribute to the development of retinal vasculopathies. However, the role of these factors and the mechanisms by which they elicit their effects in retina are not known. We investigated whether activated microglia during early stages of ischemic retinopathy produces excessive interleukin-1β (IL-1β), which elicits retinal microvascular degeneration not directly but rather by triggering the release of the proapoptotic/repulsive factor semaphorin-3A (Sema3A) from neurons. APPROACH AND RESULTS: Sprague Dawley rats subjected to retinopathy induced by hyperoxia (80% O2; O2-induced retinopathy) exhibited retinal vaso-obliteration associated with microglial activation, NLRP3 upregulation, and IL-1β and Sema3A release; IL-1β was mostly generated by microglia. Intraperitoneal administration of IL-1 receptor antagonists (Kineret, or rytvela [101.10]) decreased these effects and enhanced retinal revascularization; knockdown of Sema3A resulted in microvessel preservation and, conversely, administration of IL-1β caused vaso-obliteration. In vitro, IL-1β derived from activated primary microglial cells, cultured under hyperoxia, stimulated the release of Sema3A in retinal ganglion cells-5, which in turn induced apoptosis of microvascular endothelium; antagonism of IL-1 receptor decreased microglial activation and on retinal ganglion cells-5 abolished the release of Sema3A inhibiting ensuing endothelial cell apoptosis. IL-1β was not directly cytotoxic to endothelial cells. CONCLUSIONS: Our findings suggest that in the early stages of O2-induced retinopathy, retinal microglia are activated to produce IL-1β, which sustains the activation of microglia and induces microvascular injury through the release of Sema3A from adjacent neurons. Interference with IL-1 receptor or Sema3A actions preserves the microvascular bed in ischemic retinopathies and, consequently, decreases ensued pathological preretinal neovascularization.
    Arteriosclerosis Thrombosis and Vascular Biology 06/2013; · 6.34 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: OBJECTIVE: Nitro-oxidative stress exerts a significant role in the genesis of hypoxic-ischemic (HI) brain injury. We previously reported that the ω-6 long chain fatty acids, transarachidonic acids (TAAs), which are nitrative stress-induced nonenzymatically generated arachidonic acid derivatives, trigger selective microvascular endothelial cell death in neonatal neural tissue. The primary molecular target of TAAs remains unidentified. GPR40 is a G protein-coupled receptor activated by long chain fatty acids, including ω-6; it is highly expressed in brain, but its functions in this tissue are largely unknown. We hypothesized that TAAs play a significant role in neonatal HI-induced cerebral microvascular degeneration through GPR40 activation.Approach and Results-Within 24 hours of a HI insult to postnatal day 7 rat pups, a cerebral infarct and a 40% decrease in cerebrovascular density was observed. These effects were associated with an increase in nitrative stress markers (3-nitrotyrosine immunoreactivity and TAA levels) and were reduced by treatment with nitric oxide synthase inhibitor. GPR40 was expressed in rat pup brain microvasculature. In vitro, in GPR40-expressing human embryonic kidney (HEK)-293 cells, [(14)C]-14E-AA (radiolabeled TAA) bound specifically, and TAA induced calcium transients, extracellular signal-regulated kinase 1/2 phosphorylation, and proapoptotic thrombospondin-1 expression. In vivo, intracerebroventricular injection of TAAs triggered thrombospondin-1 expression and cerebral microvascular degeneration in wild-type mice, but not in GPR40-null congeners. Additionally, HI-induced neurovascular degeneration and cerebral infarct were decreased in GPR40-null mice. CONCLUSIONS: GPR40 emerges as the first identified G protein-coupled receptor conveying actions of nonenzymatically generated nitro-oxidative products, specifically TAAs, and is involved in (neonatal) HI encephalopathy.
    Arteriosclerosis Thrombosis and Vascular Biology 03/2013; · 6.34 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Angiogenesis of the microvasculature is central to the etiology of many diseases including proliferative retinopathy, age-related macular degeneration and cancer. A mouse model of microvascular angiogenesis would be very valuable and enable access to a wide range of genetically manipulated tissues that closely approximate small blood vessel growth in vivo. Vascular endothelial cells cultured in vitro are widely used, however, isolating pure vascular murine endothelial cells is technically challenging. A microvascular mouse explant model that is robust, quantitative and can be reproduced without difficulty would overcome these limitations. Here we characterized and optimized for reproducibility an organotypic microvascular angiogenesis mouse and rat model from the choroid, a microvascular bed in the posterior of eye. The choroidal tissues from C57BL/6J and 129S6/SvEvTac mice and Sprague Dawley rats were isolated and incubated in Matrigel. Vascular sprouting was comparable between choroid samples obtained from different animals of the same genetic background. The sprouting area, normalized to controls, was highly reproducible between independent experiments. We developed a semi-automated macro in ImageJ software to allow for more efficient quantification of sprouting area. Isolated choroid explants responded to manipulation of the external environment while maintaining the local interactions of endothelial cells with neighboring cells, including pericytes and macrophages as evidenced by immunohistochemistry and fluorescence-activated cell sorting (FACS) analysis. This reproducible ex vivo angiogenesis assay can be used to evaluate angiogenic potential of pharmacologic compounds on microvessels and can take advantage of genetically manipulated mouse tissue for microvascular disease research.
    PLoS ONE 01/2013; 8(7):e69552. · 3.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Acute renal failure (ARF) is a serious medical complication characterized by an abrupt and sustained decline in renal function. Despite significant advances in supportive care there is currently no effective treatment to restore renal function. Prostaglandin E(2) (PGE(2)) is a lipid hormone mediator abundantly produced in the kidney where it acts locally to regulate renal function; several studies suggest that modulating EP(4) receptor activity could improve renal function following kidney injury. An optimized peptidomimetic ligand of EP(4) receptor, THG213.29, was tested for its efficacy to improve renal function (glomerular filtration rate, renal plasma flow and urine output) and histological changes in a model of ARF induced by either cisplatin or renal artery occlusion in Sprague-Dawley rats. THG213.29 modulated PGE(2) binding dissociation kinetics, indicative of an allosteric binding mode. Consistently, THG213.29 antagonized EP(4)-mediated relaxation of piglet saphenous vein rings, partially inhibited EP(4)-mediated cAMP production, but did not affect Gαi activation or ß-arrestin recruitment. In vivo, THG213.29 significantly improved renal function and histological changes in cisplatin- and renal artery occlusion-induced ARF models. THG213.29 increased mRNA expression of heme-oxygenase 1, Bcl2 and fibroblast growth factor 2 (FGF-2) in renal cortex; correspondingly in EP(4)-transfected HEK293 cells, THG213.29 augmented FGF-2, and abrogated EP(4)-dependent overexpression of inflammatory IL-6 and of apoptotic DAXX and BAD. Our results demonstrate that THG213.29 represents a novel class of diuretic agent with noncompetitive allosteric modulator effects on EP(4) receptor resulting in improved renal function and integrity following acute renal failure.
    AJP Regulatory Integrative and Comparative Physiology 11/2012; · 3.28 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The synthetic hexapeptide growth hormone releasing peptide-6 (GHRP-6) exhibits dual affinity for the growth hormone secretagogue receptor 1a (GHS-R1a) and the cluster of differentiation 36 (CD36) receptor. Azapeptide GHRP-6 analogues have been synthesized, exhibiting micromolar affinity to the CD36 receptor with reduced affinity toward the GHS-R1a. A combinatorial split-and-mix approach furnished aza-GHRP-6 leads, which were further examined by alanine scanning. Incorporation of an aza-amino acid residue respectively at the D-Trp(2), Ala(3), or Trp(4) position gave aza-GHRP-6 analogues with reduced affinity toward the GHS-R1a by at least a factor of 100 and in certain cases retained affinity for the CD36 receptor. In the latter cases, the D-Trp(2) residue proved important for CD36 receptor affinity; however, His(1) could be replaced by Ala(1) without considerable loss of binding. In a microvascular sprouting assay using a choroid explant, [azaTyr(4)]-GHRP-6 (15), [Ala(1), azaPhe(2)]-GHRP-6 (16), and [azaLeu(3), Ala(6)]-GHRP-6 (33) all exhibited antiangiogenic activity.
    Journal of Medicinal Chemistry 06/2012; 55(14):6502-11. · 5.61 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Retinopathy of prematurity (ROP) is a major cause of severe visual deficits in children. This review focuses on the role of newly identified factors from retinal neurons, which through their opposing actions on vascular development contribute to ROP. These hypoxia-generated mediators include the Krebs cycle intermediate, succinate acting via GPR91, and the neuronal guidance molecule Semaphorin 3A. CONCLUSION: Neuron-derived factors guide retinal vascularization and are major contributors to the pathogenesis of ROP.
    Acta Paediatrica 04/2012; 101(8):819-26. · 1.97 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Microparticles possess therapeutic potential regarding angiogenesis. We have demonstrated the contribution of apoptotic human CEM T lymphocyte-derived microparticles (LMPs) as inhibitors of angiogenic responses in animal models of inflammation and tumor growth. In the present study, we characterized the antivascular endothelial growth factor (VEGF) effects of LMPs on pathological angiogenesis in an animal model of oxygen-induced retinopathy and explored the role of receptor-mediated endocytosis in the effects of LMPs on human retinal endothelial cells (HRECs). LMPs dramatically inhibited cell growth of HRECs, suppressed VEGF-induced cell migration in vitro experiments, and attenuated VEGF-induced retinal vascular leakage in vivo. Intravitreal injections of fluorescently labeled LMPs revealed accumulation of LMPs in retinal tissue, with more than 60% reductions of the vascular density in retinas of rats with oxygen-induced neovascularization. LMP uptake experiments demonstrated that the interaction between LMPs and HRECs is dependent on temperature. In addition, endocytosis is partially dependent on extracellular calcium. RNAi-mediated knockdown of low-density lipoprotein receptor (LDLR) reduced the uptake of LMPs and attenuated the inhibitory effects of LMPs on VEGF-A protein expression and HRECs cell growth. Intravitreal injection of lentivirus-mediated RNA interference reduced LDLR protein expression in retina by 53% and significantly blocked the antiangiogenic effects of LMPs on pathological vascularization. In summary, the potent antiangiogenic LMPs lead to a significant reduction of pathological retinal angiogenesis through modulation of VEGF signaling, whereas LDLR-mediated endocytosis plays a partial, but pivotal, role in the uptake of LMPs in HRECs.
    AJP Regulatory Integrative and Comparative Physiology 02/2012; 302(8):R941-9. · 3.28 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Aganirsen, an antisense oligonucleotide inhibiting insulin receptor substrate (IRS)-1 expression, has been shown to promote the regression of pathologic corneal neovascularization in patients. In this study, the authors aimed to demonstrate the antiangiogenic activity of aganirsen in animal models of retinal neovascularization. Eyedrops of aganirsen were applied daily in nonhuman primates after laser-induced choroidal neovascularization (CNV; model of wet age-related macular degeneration [AMD]) and in newborn rats after oxygen-induced retinopathy (OIR; model of ischemic retinopathy). Retinal aganirsen concentrations were assessed in rabbits and monkeys after topical delivery (21.5, 43, or 86 μg). Clinical significance was further evaluated by determination of IRS-1 expression in monkey and human retinal biopsy specimens. Topical corneal application of aganirsen attenuated neovascular lesion development dose dependently in African green monkeys. The incidence of high-grade CNV lesions (grade IV) decreased from 20.5% in vehicle-treated animals to 1.7% (P < 0.05) at the 86-μg dose. Topical aganirsen inhibited retinal neovascularization after OIR in rats (P < 0.05); furthermore, a single intravitreal injection of aganirsen reduced OIR as effectively as ranibizumab, and their effects were additive. Significantly, topical applications of aganirsen did not interfere with physiological retinal vessel development in newborn rats. Retinal delivery after topical administration was confirmed, and retinal expression of IRS-1 was demonstrated to be elevated in patients with subretinal neovascularization and AMD. Topical application of aganirsen offers a safe and effective therapy for both choroidal and retinal neovascularization without preventing its normal vascularization. Together, these findings support the clinical testing of aganirsen for human retinal neovascular diseases.
    Investigative ophthalmology & visual science 02/2012; 53(3):1195-203. · 3.43 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The prostaglandin-F2α (PGF2α) receptor (FP) was targeted to develop tocolytic agents for inhibiting preterm labor. Azabicycloalkane and azapeptide mimics 2-10 were synthesized based on the (3S,6S,9S)-indolizidin-2-one amino acid analogue PDC113.824 (1), which was shown to modulate FP by a biased allosteric mechanism, involving both Gαq- and Gα12-mediated signaling pathways, and exhibited significant tocolytic activity delaying preterm labor in a mouse model ( Goupil ; et al. J. Biol. Chem. 2010 , 285 , 25624 - 25636 ). Although changes in azabicycloalkane stereochemistry and ring size caused loss of activity, replacement of the indolizidin-2-one amino acid with azaGly-Pro and azaPhe-Pro gave azapeptides 6 and 8, which reduced PGF2α-induced myometrial contractions, potentiated the effect of PGF2α on Gαq-mediated ERK1/2 activation, and inhibited FP modulation of cell ruffling, a response dependent on the Gα12/RhoA/ROCK signaling pathway. Revealing complementarities of azabicycloalkane and azapeptide mimics, novel probes, and efficient tocolytic agents were made to study allosteric modulation of the FP receptor.
    Journal of Medicinal Chemistry 08/2011; 54(17):6085-97. · 5.61 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Retinopathy of prematurity (ROP) is a major cause of visual impairment in premature infants. It is characterized by an arrest in normal retinal vascular development associated with microvascular degeneration, followed by an abnormal hypoxiainduced neovascularization. Recent studies point out that ROP is a multifactorial disease, implicating both oxygen-dependent and oxygen-independent mechanisms. Oxygen-dependent factors leading to microvascular degeneration include generation of reactive oxygen species and suppression of specific oxygen-regulated vascular survival factors, such as vascular endothelial growth factor (VEGF) and erythropoietin. The other major mechanism for the initial capillary loss is oxygen-independent and implicates a deficit in growth factor IGF-1/IGFBP3. The proliferative, second phase of ROP is triggered by increases in vascular growth factors concentrations, in an attempt to compensate for the hypoxic retina. Novel signaling pathways for vascular repair, implicating both metabolite signaling and inflammatory lipids signaling, represent new therapeutic avenues for ROP.
    Archives de Pédiatrie 07/2011; 18 Suppl 2:S79-85. · 0.36 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Vascular degeneration and the ensuing abnormal vascular proliferation are central to proliferative retinopathies. Given the metabolic discordance associated with these diseases, the authors explored the role of ghrelin and its growth hormone secretagogue receptor 1a (GHSR-1a) in proliferative retinopathy. In a rat model of oxygen-induced retinopathy (OIR), the contribution of ghrelin and GHSR-1a was investigated using the stable ghrelin analogs [Dap3]-ghrelin and GHRP6 and the GSHR-1a antagonists JMV-2959 and [D-Lys3]-GHRP-6. Plasma and retinal levels of ghrelin were analyzed by ELISA, whereas retinal expression and localization of GHSR-1a were examined by immunohistochemistry and Western blot analysis. The angiogenic and vasoprotective properties of ghrelin and its receptor were further confirmed in aortic explants and in models of vaso-obliteration. Ghrelin is produced locally in the retina, whereas GHSR-1a is abundantly expressed in retinal endothelial cells. Ghrelin levels decrease during the vaso-obliterative phase and rise during the proliferative phase of OIR. Intravitreal delivery of [Dap3]-ghrelin during OIR significantly reduces retinal vessel loss when administered during the hyperoxic phase. Conversely, during the neovascular phase, ghrelin promotes pathologic angiogenesis through the activation of GHSR-1a. These angiogenic effects were confirmed ex vivo in aortic explants. New roles were disclosed for the ghrelin-GHSR-1a pathway in the preservation of retinal vasculature during the vaso-obliterative phase of OIR and during the angiogenic phase of OIR. These findings suggest that the ghrelin-GHSR-1a pathway can exert opposing effects on retinal vasculature, depending on the phase of retinopathy, and thus holds therapeutic potential for proliferative retinopathies.
    Investigative ophthalmology & visual science 06/2011; 52(8):5376-86. · 3.43 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Retinopathy of prematurity (ROP) is a major cause of visual handicap in the pediatric population. To date, this disorder is thought to stem from deficient retinal vascularization. Intriguingly, functional electrophysiological studies in patients with mild or moderate ROP and in the oxygen-induced retinopathy (OIR) model in rats reveal central photoreceptor disruption that overlies modest retinal vessel loss; a paucity of retinal vasculature occurs predominantly at the periphery. Given that choroidal circulation is the major source of oxygen and nutrients to the photoreceptors, the authors set out to investigate whether the choroidal vasculature system may be affected in OIR. Rat models of OIR treating newborn animals with 80% or 50/10% alternated oxygen level for the first two postnatal weeks were used to mimic ROP in humans. Immunohistology staining and vascular corrosion casts were used to investigate the vessel layout of the eye. To investigate the effect of 15-deoxy-Δ12,14-PGJ(2) (15d-PGJ(2); a nonenzymatic product of prostaglandin D(2)) on endothelial cells, in vitro cell culture and ex vivo choroid explants were employed and intravitreal injections were performed in animals. The authors herein demonstrate that deficient vascularity occurs not only in the retinal plexus but also in the choroid. This sustained, marked choroidal degeneration is specifically confined to central regions of the retina that present persistent photoreceptor loss and corresponding functional deficits. Moreover, the authors show that 15d-PGJ(2) is a prominent contributor to this choroidal decay. The authors demonstrate for the first time pronounced, sustained choroidal vascular involution during the development of ROP. Findings also suggest that effective therapeutic strategies to counter ROP should consider choroidal preservation.
    Investigative ophthalmology & visual science 05/2011; 52(9):6238-48. · 3.43 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The pro-inflammatory cytokine IL-1β has been shown to promote angiogenesis. It can have a neurotoxic or neuroprotective effect. Here, we have studied the expression of IL-1β in vivo and the effect of the IL-1 receptor antagonist on choroidal neovascularization (CNV) and retinal degeneration (RD). IL-1β expression significantly increased after laser injury (real time PCR) in C57BL/6 mice, in the C57BL/6 Cx3cr1(-/-) model of age-related macular degeneration (enzyme-linked immunoabsorbent assay), and in albino Wistar rats and albino BALB Cx3cr1(+/+) and Cx3cr1(-/-) mice (enzyme-linked immunoabsorbent assay) after light injury. IL-1β was localized to Ly6G-positive, Iba1-negative infiltrating neutrophils in laser-induced CNV as determined by IHC. IL-1 receptor antagonist treatment significantly inhibited CNV but did not affect Iba1-positive macrophage recruitment to the injury site. IL-1β significantly increased endothelial cell outgrowth in aortic ring assay independently of vascular endothelial growth factor, suggesting a direct effect of IL-1β on choroidal endothelial cell proliferation. Inhibition of IL-1β in light- and laser-induced RD models did not alter photoreceptor degeneration in Wistar rats, C57BL/6 mice, or RD-prone Cx3cr1(-/-) mice. Our results suggest that IL-1β inhibition might represent a valuable and safe alternative to inhibition of vascular endothelial growth factor in the control of CNV in the context of concomitant photoreceptor degeneration as observed in age-related macular degeneration.
    American Journal Of Pathology 05/2011; 178(5):2416-23. · 4.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cellular migration is a complex process that requires the polymerization of actin filaments to drive cellular extension. Smooth muscle and cancer cell migration has been shown to be affected by coagulation factors, notably the factor VII (FVIIa) and tissue factor (TF) complex. The present studies delineated mediators involved with the process of FVIIa/TF-induced cell migration and utilized a simple, precise, and reproducible, migration assay. Both FVIIa and protease-activated receptor-2 (PAR2)-activating peptide, SLIGRL, increased the migration rate of porcine cerebral microvascular endothelial cells (pCMVECs) overexpressing human TF. Ras homolog gene family member A (RhoA) and cortactin were upregulated during the process; expression of HIF, actin polymerization nuclear diaphanous-related formin-1 and -2 (Dia1, and Dia2) were unaffected. Gene silencing by shRNA to PAR2, RhoA, and cortactin attenuated this gene upregulation and migration induced by FVIIa/TF. Utilizing immunocellular localization, we demonstrate that during FVIIa/TF and PAR2 activation, cortactin molecules translocate from the cytoplasm to the cell periphery and assist in lamellipodia formation of pCMVECs. Overall, we demonstrate a novel regulation and role for cortactin in FVIIa/TF-mediated endothelial cell migration that occurs through a PAR2 and RhoA dependent mechanism.
    AJP Regulatory Integrative and Comparative Physiology 03/2011; 300(3):R577-85. · 3.28 Impact Factor

Publication Stats

4k Citations
1,015.19 Total Impact Points

Institutions

  • 1996–2013
    • CHU Sainte-Justine
      Montréal, Quebec, Canada
  • 1989–2013
    • Université du Québec à Montréal
      Montréal, Quebec, Canada
  • 2010–2012
    • Centre jeunesse de Montréal-Institut universitaire
      Montréal, Quebec, Canada
  • 1993–2012
    • Université de Montréal
      • • Department of Pediatrics
      • • Department of Chemistry
      • • Department of Pathology and Cell Biology
      • • Department of Biological Sciences
      • • Department of Pharmacology
      • • Center for Mathematical Research
      Montréal, Quebec, Canada
  • 2011
    • Assistance Publique – Hôpitaux de Paris
      Lutetia Parisorum, Île-de-France, France
    • Unité Inserm U1077
      Caen, Lower Normandy, France
    • McGill University Health Centre
      Montréal, Quebec, Canada
  • 2009–2010
    • Boston Children's Hospital
      • Department of Ophthalmology
      Boston, MA, United States
    • Université René Descartes - Paris 5
      Lutetia Parisorum, Île-de-France, France
  • 1988–2010
    • McGill University
      • • Department of Pharmacology and Therapeutics
      • • Department of Neurology and Neurosurgery
      • • Division of Ophthalmology
      • • Department of Pediatrics
      Montréal, Quebec, Canada
  • 2008
    • Centre Hospitalier Universitaire de Québec (CHUQ)
      Québec, Quebec, Canada
    • French Institute of Health and Medical Research
      Lutetia Parisorum, Île-de-France, France
    • New York Medical College
      • Department of Pharmacology
      New York City, NY, United States
  • 2005
    • University of Antwerp
      Antwerpen, Flanders, Belgium
  • 2003
    • Université de Sherbrooke
      Sherbrooke, Quebec, Canada
  • 1999–2001
    • University of California, San Francisco
      • Cardiovascular Research Institute
      San Francisco, CA, United States
  • 1997
    • California State University, Long Beach
      Long Beach, California, United States
  • 1992–1993
    • University of Iowa
      • Department of Pediatrics
      Iowa City, IA, United States