Brain Imaging and Registration in Larval Zebrafish

Registration of larval zebrafish brain scans to a common reference brain enables comparison of transgene and gene expression patterns, neuroanatomy, and morphometry. Here we describe methods for staining and mounting larval zebrafish to facilitate whole-brain fluorescence imaging. Following image acquisition, we provide a template for aligning brain images to a reference atlas using nonlinear registration with the ANTs software package.

In vivo Assessment of Lysosomal Stress in the Drosophila Brain Using Confocal Fluorescence Microscopy

Lysosomes play a central role in signaling, nutrient sensing, response to stress, and the degradation and recycling of cellular content. Defects in lysosomal digestive enzymes or structural components can impair lysosomal function with dire consequences to the cell, such as neurodegeneration. A number of methods exist to assess lysosomal stress in the model Drosophila, such as specific driver and reporter strains, transmission electron microscopy, and the investigation of gene expression. These methods, however, can be time consuming and, in some cases, costly. The procedure described here provides a quick, reliable, and low-cost approach to measure lysosomal stress in the Drosophila brain. Using fluorescence confocal microscopy and the LysoTracker staining, this protocol allows for the direct measurement of lysosome size and number. This method can be used to assess lysosomal stress under a number of different genetic and environmental scenarios in the Drosophila brain.

Differential LysoTracker Uptake Defines Two Populations of Distal Epithelial Cells in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal degenerative lung disease of unknown etiology. Although in its final stages it implicates, in a reactive manner, all lung cell types, the initial damage involves the alveolar epithelial compartment, in particular the alveolar epithelial type 2 cells (AEC2s). AEC2s serve dual progenitor and surfactant secreting functions, both of which are deeply impacted in IPF. Thus, we hypothesize that the size of the surfactant processing compartment, as measured by LysoTracker incorporation, allows the identification of different epithelial states in the IPF lung. Flow cytometry analysis of epithelial LysoTracker incorporation delineates two populations (Lysohigh and Lysolow) of AEC2s that behave in a compensatory manner during bleomycin injury and in the donor/IPF lung. Employing flow cytometry and transcriptomic analysis of cells isolated from donor and IPF lungs, we demonstrate that the Lysohigh population expresses all classical AEC2 markers and is drastically diminished in IPF. The Lysolow population, which is increased in proportion in IPF, co-expressed AEC2 and basal cell markers, resembling the phenotype of the previously identified intermediate AEC2 population in the IPF lung. In that regard, we provide an in-depth flow-cytometry characterization of LysoTracker uptake, HTII-280, proSP-C, mature SP-B, NGFR, KRT5, and CD24 expression in human lung epithelial cells. Combining functional analysis with extracellular and intracellular marker expression and transcriptomic analysis, we advance the current understanding of epithelial cell behavior and fate in lung fibrosis.

LysoTracker and MitoTracker Red are transport substrates of P-glycoprotein: implications for anticancer drug design evading multidrug resistance

LysoTracker and MitoTracker Red are fluorescent probes widely used for viable cell staining of lysosomes and mitochondria, respectively. They are utilized to study organelle localization and their resident proteins, assess organelle functionality and quantification of organelle numbers. The ATP‐driven efflux transporter P‐glycoprotein (P‐gp) is expressed in normal and malignant tissues and extrudes structurally distinct endogenous and exogenous cytotoxic compounds. Thus, once aromatic hydrophobic compounds such as the above‐mentioned fluorescent probes are recognized as transport substrates, efflux pumps including P‐gp may abolish their ability to reach their cellular target organelles. Herein, we show that LysoTracker and MitoTracker Red are expelled from P‐gp‐overexpressing cancer cells, thus hindering their ability to fluorescently mark target organelles. We further demonstrate that tariquidar, a potent P‐gp transport inhibitor, restores LysoTracker and MitoTracker Red cell entry. We conclude that LysoTracker and MitoTracker Red are P‐gp transport substrates, and therefore, P‐gp expression must be taken into consideration prior to cellular applications using these probes. Importantly, as MitoTracker was a superior P‐gp substrate than LysoTracker Red, we discuss the implications for the future design of chemotherapeutics evading cancer multidrug resistance. Furthermore, restoration of MitoTracker Red fluorescence in P‐gp‐overexpressing cells may facilitate the identification of potent P‐gp transport inhibitors (i.e. chemosensitizers).

Lysosomal Acidification in Cultured Astrocytes Using Nanoparticles

Following cellular engulfment, nanoparticles end up in the lysosomes, making them an ideal tool for modifying the lysosomal environment. Here, we describe how acidic nanoparticles can be used to lower the pH of lysosomes in cultured, primary astrocytes and thereby increase their degradation capacity. To guarantee that the cell culture is completely devoid of professional phagocytes, we isolate, expand, and differentiate neural stem cells from embryonic mouse cortex to achieve astrocytes for these experiments. Immunostainings with LAMP2-specific antibodies can be performed to verify the lysosomal localization of the nanoparticles, and the effect on lysosomal acidification can easily be followed with LysoTracker dye.

Cresyl violet: a superior fluorescent lysosomal marker

We have characterized cresyl violet as a membrane-permeant fluorophore that localizes to lysosomes and acidic vacuoles of budding yeast, Drosophila, human, murine and canine cells. An acidotropic weak base, cresyl violet is shown to be virtually insensitive to physiological alkali and divalent cations. Because of its unique spectral properties, it can be used in combination with green, red and far-red fluorophores, is less susceptible to photobleaching than alternative acidotropic probes, and does not undergo photoconversion. At concentrations that yield bright labeling of acidic compartments, cresyl violet does not alter the organellar pH nor does it affect the buffering capacity. Its affordability, together with its chemical and spectral properties, make cresyl violet a superior lysosomal marker devoid of many of the negative characteristics associated with other lysosomal probes.

Live Imaging of LysoTracker-Labelled Phagolysosomes Tracks Diurnal Phagocytosis of Photoreceptor Outer Segment Fragments in Rat RPE Tissue Ex Vivo

Renewal of rod photoreceptor outer segments in the mammalian eye involves synchronized diurnal shedding after light onset of spent distal outer segment fragments (POS) linked to swift clearance of shed POS from the subretinal space by the adjacent retinal pigment epithelium (RPE). Engulfed POS phagosomes in RPE cells mature to acidified phagolysosomes, which accomplish enzymatic degradation of POS macromolecules. Here, we used an acidophilic fluorophore LysoTracker to label acidic organelles in freshly dissected, live rat RPE tissue flat mounts. We observed that all RPE cells imaged contained numerous acidified POS phagolysosomes whose abundance per cell was dramatically increased 2 h after light onset as compared to either 1 h before or 4 h after light onset. Lack of organelles of similar diameter (of 1-2 μm) in phagocytosis-defective mutant RCS rat RPE confirmed that LysoTracker live imaging detected POS phagolysosomes. Lack of increase in lysosomal membrane protein LAMP-1 in RPE/choroid during the diurnal phagocytic burst suggests that formation of POS phagolysosomes in RPE in situ may not involve extra lysosome membrane biogenesis. Taken together, we report a new imaging approach that directly detects POS phagosome acidification and allows rapid tracking and quantification of POS phagocytosis by live RPE -tissue ex situ.

Phagocyte interactions with Mycobacterium tuberculosis--Simultaneous analysis of phagocytosis, phagosome maturation and intracellular replication by imaging flow cytometry

Utilization of compounds that enhance the innate immune response against Mycobacterium tuberculosis is an attractive strategy for combating tuberculosis in the post-antibiotic era. Thus, it is crucial to develop methods that can be used to screen for such compounds and to investigate their mechanisms of action. Here, we used imaging flow cytometry (ImageStreamX Mk II),which enables rapid quantification of microscopic images in flow, to study the interaction between phagocytes and M. tuberculosis. Macrophage-differentiated THP-1 cells were infected with GFP-expressing M. tuberculosis H37Ra, and methods for rapidly assessing phagocytosis, phagosome maturation, and bacterial replication inside the cells were developed and evaluated. These aspects of innate immunity are essential in determining the outcome of mycobacterial infection of phagocytes. The technique was found effective for monitoring phagocytosis of mycobacteria, phagosomal acidification and phagolysosomal fusion, as well as for measuring mycobacterial replication inside the cells. Several of these aspects could be analyzed simultaneously in the same sample, providing a great deal of information about the phagocyte–mycobacterial interaction at once. Thus, this method has great potential to be useful both for basic research questions and for evaluating compounds that enhance the innate immune response against M. tuberculosis.

Expression of familial Alzheimer disease presenilin 1 gene attenuates vesicle traffic and reduces peptide secretion in cultured astrocytes devoid of pathologic tissue environment

In the brain, astrocytes provide metabolic and trophic support to neurones. Failure in executing astroglial homeostatic functions may contribute to the initiation and propagation of diseases, including Alzheimer disease (AD), characterized by a progressive loss of neurones over years. Here, we examined whether astrocytes from a mice model of AD isolated in the presymptomatic phase of the disease exhibit alterations in vesicle traffic, vesicular peptide release and purinergic calcium signaling. In cultured astrocytes isolated from a newborn wild-type (wt) and 3xTg-AD mouse, secretory vesicles and acidic endosomes/lysosomes were labeled by transfection with plasmid encoding atrial natriuretic peptide tagged with mutant green fluorescent protein (ANP.emd) and by LysoTracker, respectively. The intracellular Ca(2+) concentration ([Ca(2+)]i) was monitored with Fluo-2 and visualized by confocal microscopy. In comparison with controls, spontaneous mobility of ANP- and LysoTracker-labeled vesicles was diminished in 3xTg-AD astrocytes; the track length (TL), maximal displacement (MD) and directionality index (DI) were all reduced in peptidergic vesicles and in endosomes/lysosomes (P < 0.001), as was the ATP-evoked attenuation of vesicle mobility. Similar impairment of peptidergic vesicle trafficking was observed in wt rat astrocytes transfected to express mutated presenilin 1 (PS1M146V). The ATP-evoked ANP discharge from single vesicles was less efficient in 3xTg-AD and PS1M146V-expressing astrocytes than in respective wt controls (P < 0.05). Purinergic stimulation evoked biphasic and oscillatory [Ca(2+)]i responses; the latter were less frequent (P < 0.001) in 3xTg-AD astrocytes. Expression of PS1M146V in astrocytes impairs vesicle dynamics and reduces evoked secretion of the signaling molecule ANP; both may contribute to the development of AD.

Intra-Vacuolar Proliferation of F. Novicida within H. Vermiformis

Francisella tularensis is a gram negative facultative intracellular bacterium that causes the zoonotic disease tularemia. Free-living amebae, such as Acanthamoeba and Hartmannella, are environmental hosts of several intracellular pathogens. Epidemiology of F. tularensis in various parts of the world is associated with water-borne transmission, which includes mosquitoes and amebae as the potential host reservoirs of the bacteria in water resources. In vitro studies showed intracellular replication of F. tularensis within A. castellanii cells. Whether ameba is a biological reservoir for Francisella in the environment is not known. We used Hartmannella vermiformis as an amebal model system to study the intracellular life of F. novicida. For the first time we show that F. novicida survives and replicates within H. vermiformis. The iglC mutant strain of F. novicida is defective for survival and replication not only within A. castellanii but also in H. vermiformis cells. In contrast to mammalian cells, where bacteria replicate in the cytosol, F. novicida resides and replicates within membrane-bound vacuoles within the trophozoites of H. vermiformis. In contrast to the transient residence of F. novicida within acidic vacuoles prior to escaping to the cytosol of mammalian cells, F. novicida does not reside transiently or permanently in an acidic compartment within H. vermiformis when examined 30 min after initiation of the infection. We conclude that F. tularensis does not replicate within acidified vacuoles and does not escape into the cytosol of H. vermiformis. The Francisella pathogenicity island locus iglC is essential for intra-vacuolar proliferation of F. novicida within H. vermiformis. Our data show a distinct intracellular lifestyle for F. novicida within H. vermiformis compared to mammalian cells.