Impact de Nogo-A sur les propriétés vasculogéniques des cellules endothéliales progénitrices lors de la rétinopathie induite par l’oxygène

La dégénérescence vasculaire et l’incapacité l’organisme à produire des vaisseaux sanguins de façon adéquate lors d’une condition ischémique est un fait saillant des rétinopathies ischémiques telles que la rétinopathie du prématuré (ROP). La ROP demeure la principale cause de défaillance visuelle et dans les cas extrêmes, de cécité chez les nourrissons prématurés. Elle présente deux phases distinctes soit une phase initiale clef de vasooblitération (VO) rétinienne et choroïdale qui entraînent la deuxième phase de néovascularisation (NV) rétinienne désorganisée et excessive. Au cours du développement normal, la NV oculaire a recours au phénomène d’angiogenèse qui consiste en la formation de nouveaux capillaires à partir de vaisseaux préexistants et de vasculogenèse qui consiste en la formation de nouveaux capillaires à partir de cellules endothéliales progénitrices dérivées de la moelle osseuse (BM-EPCs). Cette vasculogenèse implique la mobilisation des EPCs de la moelle osseuse vers la circulation afin d’être recrutées au site de NV pour contribuer de façon directe, soit en intégrant directement les structures vasculaires pour former des néovaisseaux, ou bien de façon indirecte par leur activité paracrine en libérant différents facteurs de croissance vasculaires. Toutefois, les mécanismes moléculaires impliqués dans la dysfonction des EPCs lors de la ROP sont encore mal compris. Au cours de mon mémoire, mes travaux ont ciblé la première phase de VO rétinienne afin de promouvoir la revascularisation par une thérapie basée sur une supplémentation d’EPCs natives ou reprogrammées. Compte tenu du rôle capital des EPCs dans la NV, mon mémoire s’est d’abord intéressé au rôle de Nogo-A (une protéine de la famille de réticulon), connue pour son action anti-angiogénique, sur l'activité fonctionnelle des EPCs en condition de ROP. Pour ce faire, nous avons utilisé un modèle de rétinopathie induite par l’oxygène (OIR) simulant la ROP. L’objectif global de ce projet consiste à évaluer l’interrelation entre l’effet de l’hyperoxie (une condition clef de la ROP) sur la voie de signalisation Nogo-A et de son récepteur NgR1 sur la fonction des EPCs. Premièrement, les résultats obtenus montrent une augmentation de l’expression de Nogo-A et NgR1 chez les BM-EPCs soumis ex vivo à l’hyperoxie, mais aussi dans les EPCs extraites des rats OIR. En addition, l’augmentation de l’expression de Nogo-A/NgR1 par l’hyperoxie corrèle avec la dysfonction angiogénique des EPCs caractérisées par une diminution de leurs capacités de migration et de tubulogenèse. De façon intéressante, l’inhibition de Nogo-A (par un peptide neutralisant) améliore la capacité migratoire et tubulogénique des EPCs, et protège leur fonction contre l’hyperoxie. Également, l’inhibition de Nogo-A induit l’expression du facteur angiogénique et mobilisateur d’EPCs, SDF-1, suggérant que NgR1 régule négativement l’expression de SDF-1. Par ailleurs, nous avions également pour objectif final d’évaluer l’efficacité protectrice d’une supplémentation d’EPCs natives ou reprogrammées (Nogo-/-) pour améliorer la revascularisation rétinienne dans un modèle de rat OIR. Les résultats montrent qu’une supplémentation intrapéritonéale d’EPCs natives diminue significativement la VO rétinienne, mais que cet effet pro-angiogénique devient plus prononcé par le traitement d’EPCs préconditionnées (reprogrammées par l’inhibition de Nogo-A) chez les rats OIR. Collectivement, nos résultats démontrent que : 1) l’hyperoxie cause une dysfonction angiogénique des BM-EPCs en induisant Nogo-A ce qui contribue à la VO rétinienne chez les rats OIR, et que 2) une supplémentation d’EPCs conditionnées (reprogrammées par l’inhibition de Nogo-A) est plus efficace qu’une supplémentation d’EPCs natives pour améliorer la réparation vasculaire rétinienne. Pour conclure, nous mettons donc en évidence une cible potentielle qui est la protéine Nogo-A afin de préserver l’activité biologique des EPCs et ultimement, l’intégrité vasculaire chez les rats OIR.Vascular degeneration and the inability of the body to produce adequate blood vessels during an ischemic condition is a salient feature of ischemic retinopathies such as retinopathy of prematurity (ROP). ROP remains the leading cause of visual impairment and in extreme cases, blindness in premature infants. It presents two distinct phases: a key initial phase of retinal and choroidal vasoobliteration (VO) which leads to the second phase of disorganized and excessive retinal neovascularization (NV). During normal development, ocular NV uses the phenomenon of angiogenesis which consists of the formation of new capillaries from pre-existing vessels and vasculogenesis which consists of the formation of new capillaries from progenitor endothelial cells derived from the marrow bone (BM-EPCs). This vasculogenesis involves the mobilization of EPCs from the bone marrow to the circulation in order to be recruited at the NV site to contribute directly, either by directly integrating the vascular structures to form new vessels, or indirectly by their paracrine activity by releasing different vascular growth factors. However, the molecular mechanisms involved in the dysfunction of EPCs during ROP are still poorly understood. During my thesis, my work targeted the first phase of retinal VO in order to promote revascularization by therapy based on supplementation of native or reprogrammed EPCs. Given the capital role of EPCs in NV, my thesis was first interested in the role of Nogo-A (a protein of the reticulon family), known for its anti-angiogenic action, on the functional activity of EPCs in ROP condition. To do this, we used an oxygen-induced retinopathy (OIR) model simulating ROP. The overall objective of this project is to assess the interrelationship between the effect of hyperoxia (a key condition of ROP) on the Nogo-A signaling pathway and its NgR1 receptor on the function of EPCs. First, the results obtained show an increase in the expression of Nogo-A and NgR1 in BM-EPCs subjected to hyperoxia ex vivo, but also in EPCs extracted from OIR rats. In addition, the increase in the expression of Nogo-A / NgR1 by hyperoxia correlates with the angiogenic dysfunction of EPCs characterized by a decrease in their capacity for migration and tubulogenesis. Interestingly, inhibition of Nogo-A (by a neutralizing peptide) improves the migratory and tubulogenic capacity of EPCs, and protects their function against hyperoxia. Also, inhibition of Nogo-A induces expression of the angiogenic and mobilizing factor of EPCs, SDF-1, suggesting that NgR1 negatively regulates the expression of SDF-1. In addition, our final objective was also to evaluate the protective efficacy of supplementation of native or reprogrammed EPCs (Nogo - / -) to improve retinal revascularization in an OIR rat model. The results show that intraperitoneal supplementation of native EPCs significantly decreases retinal VO, but that this pro-angiogenic effect becomes more pronounced by treatment of preconditioned EPCs (reprogrammed by inhibition of Nogo-A) in OIR rats. Collectively, our results demonstrate that: 1) hyperoxia causes angiogenic dysfunction of BM-EPCs by inducing Nogo-A which contributes to retinal VO in OIR rats, and that 2) supplementation of conditioned (reprogrammed by inhibition of Nogo-A) is more effective than supplementation of native EPCs in improving retinal vascular repairs. To conclude, we therefore highlight a potential target which is the Nogo-A protein in order to preserve the biological activity of EPCs and ultimately, vascular integrity in OIR rats

SB-QTVW: An alternate index to differentiate between healthy and acute ischemic/infarcted patients using vector magnitude derived QT variability

Myocardial ischemia alters ventricular repolarization through a variety of mechanisms. Studies show that QTVI, an index of QT variability, is elevated during acute ischemia and cardiomyopathy. This indicates an increased QT variability in ischemic patients. Preliminary studies from our laboratory showed that the length of vector magnitude derived QT interval varies by less than 16 ms in healthy controls, and frequently varies more than 16 ms in ischemic patients. With this study, we introduced an alternative index - QT Variability Window (QTVW), and tested the hypothesis that ischemia causes the length of resting QT intervals in vector magnitude to vary more than a QTVW of 16 ms. Results from our study support our hypothesis. Furthermore, in certain cases, our algorithm was able to differentiate between the healthy controls and acute ischemic patients using as few as 20 consecutive beats. These findings provide an alternative index, QTVW, to assess ventricular repolarization following ischemia

Surface properties of glass micropipettes and their effect on biological studies

In this paper, an investigation on surface properties of glass micropipettes and their effect on biological applications is reported. Pipettes were pulled under different pulling conditions and the effect of each pulling parameter was analyzed. SEM stereoscopic technique was used to reveal the surface roughness properties of pipette tip and pipette inner wall in 3D. More than 20 pipettes were reconstructed. Pipette heads were split open using focused ion beam (FIB) milling for access to the inner walls. It is found that surface roughness parameters are strongly related on the tip size. Bigger pipettes have higher average surface roughness and lower developed interfacial area ratio. Furthermore, the autocorrelation of roughness model of the inner surface shows that the inner surface does not have any tendency of orientation and is not affected by pulling direction. To investigate the effect of surface roughness properties on biological applications, patch-clamping tests were carried out by conventional and FIB-polished pipettes. The results of the experiments show that polished pipettes make significantly better seals. The results of this work are of important reference value for achieving pipettes with desired surface properties and can be used to explain biological phenomenon such as giga-seal formation

Fractional Ca2+ Currents through TRP and TRPL Channels in Drosophila Photoreceptors

AbstractLight responses in Drosophila photoreceptors are mediated by two Ca2+ permeable cation channels, transient receptor potential (TRP) and TRP-like (TRPL). Although Ca2+ influx via these channels is critical for amplification, inactivation, and light adaptation, the fractional contribution of Ca2+ to the currents (Pf) has not been measured. We describe a slow (τ ∼ 350 ms) tail current in voltage-clamped light responses and show that it is mediated by electrogenic Na+/Ca2+ exchange. Assuming a 3Na:1Ca stoichiometry, we derive empirical estimates of Pf by comparing the charge integrals of the exchanger and light-induced currents. For TRPL channels, Pf was ∼17% as predicted by Goldman-Hodgkin-Katz (GHK) theory. Pf for TRP (29%) and wild-type flies (26%) was higher, but lower than the GHK prediction (45% and 42%). As predicted by GHK theory, Pf for both channels increased with extracellular [Ca2+], and was largely independent of voltage between –100 and –30 mV. A model incorporating intra- and extracellular geometry, ion permeation, diffusion, extrusion, and buffering suggested that the deviation from GHK predictions was largely accounted for by extracellular ionic depletion during the light-induced currents, and the time course of the Na+/Ca2+ exchange current could be used to obtain estimates of cellular Ca2+ buffering capacities

Ca2+ Extrusion by NCX Is Compromised in Olfactory Sensory Neurons of OMP−/− Mice

The role of olfactory marker protein (OMP), a hallmark of mature olfactory sensory neurons (OSNs), has been poorly understood since its discovery. The electrophysiological and behavioral phenotypes of OMP knockout mice indicated that OMP influences olfactory signal transduction. However, the mechanism by which this occurs remained unknown.We used intact olfactory epithelium obtained from WT and OMP(-/-) mice to monitor the Ca(2+) dynamics induced by the activation of cyclic nucleotide-gated channels, voltage-operated Ca(2+) channels, or Ca(2+) stores in single dendritic knobs of OSNs. Our data suggested that OMP could act to modulate the Ca(2+)-homeostasis in these neurons by influencing the activity of the plasma membrane Na(+)/Ca(2+)-exchanger (NCX). Immunohistochemistry verifies colocalization of NCX1 and OMP in the cilia and knobs of OSNs. To test the role of NCX activity, we compared the kinetics of Ca(2+) elevation by stimulating the reverse mode of NCX in both WT and OMP(-/-) mice. The resulting Ca(2+) responses indicate that OMP facilitates NCX activity and allows rapid Ca(2+) extrusion from OSN knobs. To address the mechanism by which OMP influences NCX activity in OSNs we studied protein-peptide interactions in real-time using surface plasmon resonance technology. We demonstrate the direct interaction of the XIP regulatory-peptide of NCX with calmodulin (CaM).Since CaM also binds to the Bex protein, an interacting protein partner of OMP, these observations strongly suggest that OMP can influence CaM efficacy and thus alters NCX activity by a series of protein-protein interactions

Mechanics rules cell biology

Cells in the musculoskeletal system are subjected to various mechanical forces in vivo. Years of research have shown that these mechanical forces, including tension and compression, greatly influence various cellular functions such as gene expression, cell proliferation and differentiation, and secretion of matrix proteins. Cells also use mechanotransduction mechanisms to convert mechanical signals into a cascade of cellular and molecular events. This mini-review provides an overview of cell mechanobiology to highlight the notion that mechanics, mainly in the form of mechanical forces, dictates cell behaviors in terms of both cellular mechanobiological responses and mechanotransduction