Littérature scientifique sur le sujet « Intravital microscopy techniques »

Microscopic imaging techniques to visualize cellular behaviors in their natural environment play a pivotal role in biomedical research. Here, we review how recent technical advances in intravital microscopy have enabled unprecedented access to cellular physiology in various organs of mice in normal and diseased states.

Leukocytes are inherently motile and interactive cells. Recent advances in intravital microscopy approaches have enabled a new vista of their behavior within intact tissues in real time. This brief review summarizes the developments enabling the tracking of immune responses in vivo.

Fluorescence microscopy has represented a crucial technique to explore the cellular and molecular mechanisms in the field of biomedicine. However, the conventional one-photon microscopy exhibits many limitations when living samples are imaged. The new technologies, including two-photon microscopy (2PM), have considerably improved the in vivo study of pathophysiological processes, allowing the investigators to overcome the limits displayed by previous techniques. 2PM enables the real-time intravital imaging of the biological functions in different organs at cellular and subcellular resolution thanks to its improved laser penetration and less phototoxicity. The development of more sensitive detectors and long-wavelength fluorescent dyes as well as the implementation of semi-automatic software for data analysis allowed to gain insights in essential physiological functions, expanding the frontiers of cellular and molecular imaging. The future applications of 2PM are promising to push the intravital microscopy beyond the existing limits. In this review, we provide an overview of the current state-of-the-art methods of intravital microscopy, focusing on the most recent applications of 2PM in kidney physiology.

Inflammation is a vital process by which the body is able to fight infection and heal wounded tissue. However inappropriate control of inflammation is responsible for a wide range of pathologies (e.g. rheumatoid arthritis, inflammatory bowel disease). One of the hallmark features of inflammation, and one of the key pathogenic mechanisms in inflammatory disorders is leukocyte recruitment. Therefore understanding the molecular mechanisms by which leukocytes travel from the bloodstream to the extravascular tissue is of great importance.Evidence suggests that there is a cascade of complex interactions between leukocytes and endothelium that to be fully understood must be studied on-line rather than using endpoint readouts such as tissue levels of leukocyte enzymes (myeloperoxidase) or histological techniques. A number of laboratories, including our own, have used a technique known as intravital microscopy to directly visualize leukocyte trafficking in individual vessels in a range of tissues, in an attempt to gain a better understanding of the mechanisms of leukocyte recruitment. Intravital microscopy entails microscopic examination of living tissues.

A system is described for in vivo noninvasive measurements of hemoglobin oxygen saturation (HbO2Sat) at the microscopic level. The spectroscopic basis for the application is resonant Raman enhancement of Hb in the violet/ultraviolet region, allowing simultaneous identification of oxy- and deoxyhemoglobin with the same excitation wavelength. The heme vibrational bands are well known, but the technique has never been used to determine microvascular HbO2Sat in vivo. A diode laser light (power: 0.3 mW) was focused onto sample areas 15–30 μm in diameter. Raman spectra were obtained in backscattering geometry by using a microscope coupled to a spectrometer and a cooled detector. Calibration was performed in vitro by using glass capillaries containing blood at several Hb concentrations, equilibrated at various oxygen tensions. HbO2Sat was estimated using the Raman band intensities at 1,360 and 1,375 cm−1. Glass capillary path length and Hb concentration had no effect on HbO2Sat estimated from Raman spectra. In vivo observations were made in blood flowing in microvessels of the rat mesentery. The Hb Raman peaks observed in oxygenated and deoxygenated blood were consistent with earlier Raman studies that used Hb solutions and isolated cells. The method allowed HbO2Sat determinations in the whole range of arterioles, venules, and capillaries. Tissue transillumination allowed diameter and erythrocyte velocity measurements in the same vessels. Raman microspectroscopy offers distinct advantages over other currently used techniques by providing noninvasive and reliable in vivo determinations of HbO2Sat in thin tissues as well as in solid organs and tissues, which are unsuitable for techniques requiring transillumination.

SummaryIncreased vascular permeability and consequent plasma leakage from postcapillary venules is a cardinal sign of inflammation. Although the movement of plasma constituents from the vasculature to the affected tissue aids in clearing the inflammatory stimulus, excessive plasma extravasation can lead to hospitalisation or death in cases such as influenza-induced pneumonia, burns or brain injury. The use of intravital imaging has significantly contributed to the understanding of the mechanisms controlling the vascular permeability alterations that occur during inflammation. Today, intravital imaging can be performed using optical and non-optical techniques. Optical techniques, which are generally used in experimental settings, include traditional intravital fluorescence microscopy and near-infrared fluorescence imaging. Magnetic resonance (MRI) and radioisotopic imaging are used mainly in the clinical setting, but are increasingly used in experimental work, and can detect plasma leakage without optics. Although these methods are all able to visualise inflammatory plasma leakage in vivo, the spatial and temporal resolution differs between the techniques. In addition, they vary with regards to invasiveness and availability. This overview discusses the use of imaging techniques in the visualisation of inflammatory plasma leakage.

The metabolic status of the kidney is a determinant of injury susceptibility and a measure of progression for many disease processes; however, noninvasive modalities to assess kidney metabolism are lacking. In this study, we employed positron emission tomography (PET) and intravital multiphoton microscopy (MPM) to assess cortical and proximal tubule glucose tracer uptake, respectively, following experimental perturbations of kidney metabolism. Applying dynamic image acquisition PET with 2-18fluoro-2-deoxyglucose (18F-FDG) and tracer kinetic modeling, we found that an intracellular compartment in the cortex of the kidney could be distinguished from the blood and urine compartments in animals. Given emerging literature that the tumor suppressor protein p53 is an important regulator of cellular metabolism, we demonstrated that PET imaging was able to discern a threefold increase in cortical 18F-FDG uptake following the pharmacological inhibition of p53 in animals. Intravital MPM with the fluorescent glucose analog 2-[ N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG) provided increased resolution and corroborated these findings at the level of the proximal tubule. Extending our observation of p53 inhibition on proximal tubule glucose tracer uptake, we demonstrated by intravital MPM that pharmacological inhibition of p53 diminishes mitochondrial potential difference. We provide additional evidence that inhibition of p53 alters key metabolic enzymes regulating glycolysis and increases intermediates of glycolysis. In summary, we provide evidence that PET is a valuable tool for examining kidney metabolism in preclinical and clinical studies, intravital MPM is a powerful adjunct to PET in preclinical studies of metabolism, and p53 inhibition alters basal kidney metabolism.

Intravital capillary video-microscopy is a dynamic method for studying skin capillaries. The technique of direct intravital microscopy (without dyes) depends on the presence of red blood cells inside capillaries for their identification. The aim of the present study was to compare different techniques to try to establish the best method for maximizing the number of visible perfused capillaries during intravital capillary microscopy. We compared the effects of venous congestion with those of post-occlusive reactive hyperaemia (Study 1). We also investigated venous congestion followed first by post-occlusive reactive hyperaemia and then by a core heat load test (Study 2). Finally we investigated venous congestion followed by post-occlusive reactive hyperaemia combined with venous congestion (Study 3). In Study 1, capillary density increased with venous congestion from a baseline value of 74±2 (mean±S.E.M.) per field to 82±3 per field (P< 0.0001; analysis of variance). With reactive hyperaemia, there was an apparent decrease in visible capillary density to 69±2 per field. In Study 2, baseline capillary density was 69±4 per field, and this increased significantly with venous congestion to 74±4 per field (P = 0.01). With both reactive hyperaemia and core heat load, the apparent density was 62±4 per field. In Study 3 the baseline density was 70±2 per field, and this increased significantly with venous congestion to 80±3 per field (P< 0.0001). With reactive hyperaemia combined with venous congestion, the density was 81±3 per field (P = 0.328 compared with venous congestion alone). The results show that venous congestion at 60 mmHg for 2 min is the most effective method for visualization of the maximal number of perfused skin capillaries during intravital video-microscopy.

L’objectif principal de ce travail de thèse a été de caractériser les effets de l’anti-VEGF Bevacizumab (Avastin) sur le réseau vasculaire tumoral in vivo, au cours du temps, à l’aide du modèle de la chambre dorsale chez la souris nude. Les images du réseau vasculaire tumoral acquises par microscopie intravitale ont été analysées par un algorithme de traitement d’images développé au sein de notre équipe, permettant de mettre en évidence les modifications morphologiques induites par le traitement et d’isoler des paramètres discriminants de la « normalisation » vasculaire, par comparaison à un réseau vasculaire sain. La période de « normalisation » vasculaire détectée par notre outil a été confortée par l’analyse de la fonctionnalité des vaisseaux sanguins au cours du temps, in vivo et par une analyse immunohistochimique des vaisseaux sanguins tumoraux et du tissu tumoral. A travers des essais préliminaires in vivo, en regard des résultats de ce travail concernant une fenêtre de "normalisation", nous avons cherché à vérifier l'hypothèse d'un bénéfice d'un traitement anti-VEGF préalablement à la thérapie photodynamique (PDT) sur des tumeurs de glioblastome xénogreffées en sous-cutané et en chambre dorsale. L'efficacité de la PDT est décrite comme étant dépendante d'une d'oxygénation tumorale suffisante et d'une distribution maximale de l'agent photosensibilisant au coeur des tumeurs. Parallèlement à ces travaux, nous avons cherché en équipe pluridiscilinaire à développer un modèle mathématique de la réponse au bevacizumab à partir de données biologiques réelles obtenues sur le même modèle in vivo et permettant pour l'avenir de simuler les réponses à différentes doses et différentes durées de traitement, toujours à des fins d'optimisation des protocoles thérapeutiques
The main aim of this work was to characterize the effects of the anti-VEGF Bevacizumab (Avastin) on the tumor vascular network, in vivo, over time, thanks to the skin fold chamber model on the nude mouse. Images of the vascular network obtained using intravital microscopy were analyzed par a dedicated image processing algorithm developed within our research team, allowing to highlight the morphological modifications induced by the treatment and to isolate discriminating parameters of the vascular "normalization", by comparison to healthy vascular networks. Le vascular "normalization" period detected with our tool was comforted by the analysis of the functionality of the blood vessels over time, in vivo and by an immunohistochemical analysis of the blood vessels and of the tumor tissue. In preliminary in vivo experiments, we tried to verify the hypothesis of the benefits of an anti-VEGF treatment prior to photodynamic therapy (PDT) on glioblastoma xenografts implanted subcutaneously or in the skin fold chamber. The efficacy of PDT is described as being dependent on tumor oxygenation and on the distribution of the photosensitizing agent within the tumor. In paralel to this work, we tried as a pluridisciplinary team to develop a mathematical model of the tumor response to bevacizumab using biological data obtained on the same in vivo model et that will allow in the future to simulate the response for different doses and different treatment durations, for the optimization of therapeutic protocols

La Sclerosi Multipla (SM) è una patologia infiammatoria autoimmune cronica, disabilitante e demielinizzante, del sistema nervoso centrale (SNC). La migrazione di cellule T autoreattive e la loro riattivazione attraverso la presentazione antigenica effettuata dalle locali cellule presentanti l’antigene, rappresentano due eventi critici nella patogenesi della SM e nel suo modello animale, l’encefalite autoimmune sperimentale (EAE). Le risposte ai potenziali antigeni all’interno del SNC richiedono una migrazione a lungo raggio, comunicazione a corto raggio e contatti cellula-cellula diretti con le cellule presentanti l’antigene. Il principale obiettivo di questo studio è indagare il ruolo delle integrine L2 (LFA-1) e 4 (VLA-4 and 47) nella migrazione e nella motilità delle cellule autoreattive Th1 e Th17 in corso di EAE all’interno del midollo spinale utilizzando le moderne tecniche di microscopia intravitale. La microscopia intravitale permette di visualizzare questi processi dentro il midollo spinale, il quale rappresenta il principale sito di infiammazione durante l’EAE. Mediante la microscopia intravitale in epifluorescenza abbiamo prima di tutto investigato il ruolo delle integrine 4 e LFA-1 nella migrazione delle cellule autoreattive Th1 e Th17 all’interno dei vasi piali del midollo spinale durante la fase preclinica, l’esordio e la fase cronica di EAE. Abbiamo utilizzato un modello di EAE immunizzando topi C57BL/6 con il peptide MOG35-55. Le cellule Th1 e Th17 MOG-specifiche sono state prodotte in vitro da topi TCR-transgenici 2D2, marcate con label fluorescenti e iniettate in endovena nei topi immunizzati direttamente prima dell’acquisizione. I nostri risultati pongono l’accento su un ruolo selettivo per l’integrina LFA-1 nella migrazione delle cellule Th1 in particolare durante le prime fasi di malattia. Ruolo che invece non è svolto in fase cronica di malattia. Inoltre, il blocco della subunità 4, ma non dell’integrina 47 inibisce fortemente sia il rotolamento sia l’adesione stabile delle cellule Th1 all’endotelio infiammato. Questo suggerisce l’integrina VLA-4 come principale mediatrice della migrazione delle Th1 nel SNC infiammato in corso di EAE. Di notevole interesse è inoltre il selettivo ruolo per l’integrina 47 evidenziato in particolare nell’adesione stabile esclusivamente delle cellule Th17 all’esordio ed in fase cronica di malattia. Successivamente, per studiare la motilità intraparenchimale delle cellule Th1 e Th17 nel midollo spinale durante la fase preclinica della patologia, il picco di malattia e la fase cronica abbiamo utilizzato la microsocopia laser a due fotoni. I nostri risultati dimostrano una massiva infiltrazione di Th1 e Th17 nel parenchima del SNC al picco di malattia, mentre la migrazione di queste cellule durante le altre fasi della malattia è significativamente minore. In seguito, il nostro studio si è focalizzato sulla fase clinica della malattia e abbiamo osservato che le cellule Th1 e le cellule Th17 mostrano differenze significative nelle componenti direzionali, con le cellule Th1 che si muovono velocemente in direzione rettilinea, coprendo lunghe distanze nel parenchima del midollo spinale, mente le cellule Th17 girano intorno in un volume specifico del tessuto facendo stop and go. In particolare, il blocco dell’integrina LFA-1 influenza drasticamente le dinamiche delle cellule, portando ad una riduzione nella velocità e interferendo con il loro pattern di motilità rettilinea. Inoltre, in presenza di un anticorpo bloccante anti-LFA-1, le cellule Th17 mostrano una riduzione di velocità drastica. Diversamente, l’anticorpo anti-4 non ha nessun effetto sul comportamento motile delle Th1, ma riduce fortemente la velocità delle Th17 suggerendo che l’integrina VLA-4 non sia richiesta per la motilità intraparenchimale durante l’EAE. Tuttavia, alla luce dei risultati ottenuti in precedenza mediante microscopia intravitale, va preso in considerazione un selettivo ruolo esercitato dall’integrina 47 nella motilità intraparenchimale delle Th17. Complessivamente, i nostri risultati suggeriscono che l’LFA-1 sia la principale integrina che controlla la motilità delle cellule Th1 e Th17 e che 47 sia invece selettivamente coinvolta nella motilità delle cellule Th17 nel midollo spinale in condizioni infiammatorie al picco di malattia. A sostegno di questi risultati abbiamo testato un trattamento terapeutico mediante blocco locale, a livello intratecale, delle integrine LFA-1 e 47 nel nostro modello murino di EAE cronica. Entrambi i trattamenti hanno evidenziato una riduzione nello sviluppo della malattia che suggerisce l’importanza di interferire direttamente con le dinamiche delle cellule pro infiammatorie a livello del SNC. Approfondire dunque la conoscenza dei meccanismi molecolari che controllano la motilità intratissutale di cellule T attivate nel SNC potrebbe aiutarci a identificare nuove strategie terapeutiche per le patologie autoimmuni cerebrali croniche.
Multiple sclerosis (MS) is a chronic disabling autoimmune inflammatory demyelinating disease of the central nervous system (CNS). The migration of autoreactive T cells from the blood into the CNS and their reactivation through antigen presentation by local antigen presenting cells (APCs) represent critical events in the pathogenesis of MS and its animal model, the experimental autoimmune encephalomyelitis (EAE). The responses to potential antigens inside the CNS require long-range migration of cells, short-range communication and direct cell-cell contact with APCs. The main goal of this study was to investigate the role of L2 (LFA-1) and 4 (VLA-4 and 47) integrins in the migration and motility behavior of Th1 and Th17 cells, which represent key players in the induction of EAE, using intravital microscopy approaches. Intravital microscopy techniques allow the visualization of T cell migration and reactivation in the spinal cord (SC), which represents the main inflammation site during EAE. By using epifluorescence intravital microscopy (IVM) we first studied the roles of 4 and LFA-1 integrins in Th1 and Th17 cell adhesion in the pial vessels of spinal cord (SC) venules in mice immunized with MOG35-55 peptide during the preclinical phase, disease onset and chronic phase of disease. We used an EAE model by immunization of C57BL/6 mice with MOG35-55 peptide. MOG35-55-specific Th1 and Th17 cells were produced in vitro from 2D2 TCR transgenic mice, labeled with fluorescent dyes and intravenously injected in immunized mice before imaging. Our results underlined a selective role for LFA-1 integrin in Th1 cell recruitment in inflamed SC vessels during the early phases of the disease but not during the chronic phase. Moreover, blocking antibodies against the 4subunit, but not blockade of 47 integrin greatly inhibited rolling and firm adhesion of Th1 cells in the SC venules during all disease phases, suggesting that VLA-4 is the major molecule involved in Th1 cell adhesion in the SC venules during EAE. Interestingly, blockade of 47 integrin led to a significant reduction of firm adhesion in Th17 cells at the onset and chronic phase of EAE indicating a selective role of 47 integrin in the recruitment of Th17 cells in the inflamed CNS. Taking advantage of two-photon laser microscopy (TPLM) approach we next investigated the motility behavior of fluorescently labeled Th1 and Th17 cells within SC parenchyma during different disease phases. Our results showed a massive infiltration of Th1 and Th17 cells in the CNS parenchyma at disease peak, whereas the migration of these cells during other phases of disease was significantly lower. Furthermore, Th1 and Th17 cells displayed significant differences in the directional component, with Th1 cells moving faster in straight directions covering long distances deep in the SC parenchyma, whereas Th17 cells moved around in a specific volume of tissue in a stop and go mode. Notably, the blockade of LFA-1 integrin drastically affected the dynamics of Th1 cells leading to a reduction in velocity and interfering with their straight-line motility pattern. Moreover, Th17 cells displayed a drastic reduction of velocity in the presence of a blocking anti-LFA-1 antibody. The analysis of cellular morphology suggested that LFA-1 is actively involved in the cytoskeleton rearrangements necessary for T cell amoeboid migration inside the CNS, but had no role in the cytoskeleton dynamics in Th17 cells. Notably, 4integrins had no role in Th1 cells motility, but drastically reduced the dynamics of Th17 cells inside the SC parenchyma. To check the therapeutic relevance of our intravital microscopy findings, we performed intrathecal injection of anti-LFA-1 or anti-47 antibodies at disease onset and observed a significant inhibition of EAE progression in mice immunized with MOG35-55 peptide. Collectively, our data demonstrate that LFA-1 integrin differently controls intraparenchymal Th1 and Th17 cells dynamics, whereas 47 integrin is selectively involved in Th17 cell trafficking in the CNS during EAE. Furthermore, our results suggest that interfering with the molecular mechanisms controlling intraparenchymal dynamics of activated T cells may represent a new therapeutic strategy for CNS autoimmune diseases.

Indiana University-Purdue University Indianapolis (IUPUI)
Advancements in human genomics have simultaneously enhanced our basic understanding of the human body and ability to combat debilitating diseases. Historically, research has shown that there have been many hindrances to realizing this medicinal revolution. One hindrance, with particular regard to the kidney, has been our inability to effectively and routinely delivery genes to various loci, without inducing significant injury. However, we have recently developed a method using hydrodynamic fluid delivery that has shown substantial promise in addressing aforesaid issues. We optimized our approach and designed a method that utilizes retrograde renal vein injections to facilitate widespread and persistent plasmid and adenoviral based transgene expression in rat kidneys. Exogenous gene expression extended throughout the cortex and medulla, lasting over 1 month within comparable expression profiles, in various renal cell types without considerably impacting normal organ function. As a proof of its utility we by attempted to prevent ischemic acute kidney injury (AKI), which is a leading cause of morbidity and mortality across among global populations, by altering the mitochondrial proteome. Specifically, our hydrodynamic delivery process facilitated an upregulated expression of mitochondrial enzymes that have been suggested to provide mediation from renal ischemic injury. Remarkably, this protein upregulation significantly enhanced mitochondrial membrane potential activity, comparable to that observed from ischemic preconditioning, and provided protection against moderate ischemia-reperfusion injury, based on serum creatinine and histology analyses. Strikingly, we also determined that hydrodynamic delivery of isotonic fluid alone, given as long as 24 hours after AKI is induced, is similarly capable of blunting the extent of injury. Altogether, these results indicate the development of novel and exciting platform for the future study and management of renal injury.

Dextrans, which is a generic term used to describe a family of glucans, are branched polysaccharide molecules derived from lactic acid bacteria in the presence of sucrose. These complex branched glucans have various uses in the medical industry, including plasma expanders and anticoagulants, and have also been investigated for their utility in targeted and sustained delivery of drugs, proteins, enzymes, and imaging agents for renal applications. Simultaneous advances in renal intravital microscopy have brought several advantages over in vitro and ex vivo models by providing real-time assessments of dynamic processes at the cellular and subcellular levels. Such advances have been used to support regenerative medicine strategies. Consequently, this chapter aims to provide an overview of how fluorescent dextrans have supported renal gene and cell therapies and evolving tissue engineering techniques.

The knowledge gained through imaging platelets has formed the backbone of our understanding of their biology in health and disease. Early investigators relied on conventional light microscopy with limited resolution and were primarily able to identify the presence and basic morphology of platelets. The advent of high resolution technologies, in particular, electron microscopy, accelerated our understanding of the dynamics of platelet ultrastructure dramatically. Further refinements and improvements in our ability to localize and reliably identify platelet structures have included the use of immune-labeling techniques, correlative-fluorescence light and electron microscopy, and super-resolution microscopies. More recently, the expanded development and application of intravital microscopy in animal models has enhanced our knowledge of platelet functions and thrombus formation in vivo, as these experimental systems most closely replicate native biological environments. Emerging improvements in our ability to characterize platelets at the ultrastructural and organelle levels include the use of platelet cryogenic electron tomography with quantitative, unbiased imaging analysis, and the ability to genetically label platelet features with electron dense markers for analysis by electron microscopy.