High resolution multimode light microscopy of cell migration: long-term imaging and analysis

Long-Term Live Cell Imaging of Cell Migration: Effects of Pathogenic Fungi on Human Epithelial Cell Migration

Long-term live cell imaging was used in this study to determine the responses of human epithelial cells to pathogenic biofilms formed by Candida albicans. Epithelial cells of the skin represent the front line of defense against invasive pathogens such as C. albicans but under certain circumstances, especially when the host's immune system is compromised, the skin barrier is breached. The mechanisms by which the fungal pathogen penetrates the skin and invade the deeper layers are not fully understood. In this study we used keratinocytes grown in culture as an in vitro model system to determine changes in host cell migration and the actin cytoskeleton in response to virulence factors produced by biofilms of pathogenic C. albicans. It is clear that changes in epithelial cell migration are part of the response to virulence factors secreted by biofilms of C. albicans and the actin cytoskeleton is the downstream effector that mediates cell migration. Our goal is to understand the mechanism by which virulence factors hijack the signaling pathways of the actin cytoskeleton to alter cell migration and thereby invade host tissues. To understand the dynamic changes of the actin cytoskeleton during infection, we used long-term live cell imaging to obtain spatial and temporal information of actin filament dynamics and to identify signal transduction pathways that regulate the actin cytoskeleton and its associated proteins. Long-term live cell imaging was achieved using a high resolution, multi-mode epifluorescence microscope equipped with specialized light sources, high-speed cameras with high sensitivity detectors, and specific biocompatible fluorescent markers. In addition to the multi-mode epifluorescence microscope, a spinning disk confocal long-term live cell imaging system (Olympus CV1000) equipped with a stage incubator to create a stable in vitro environment for long-term real-time and time-lapse microscopy was used. Detailed descriptions of these two long-term live cell imaging systems are provided.

PALM and STORM: Into large fields and high-throughput microscopy with sCMOS detectors

Single Molecule Localization Microscopy (SMLM) techniques such as Photo-Activation Localization Microscopy (PALM) and Stochastic Optical Reconstruction Microscopy (STORM) enable fluorescence microscopy super-resolution: the overcoming of the resolution barrier imposed by the diffraction of light. These techniques are based on acquiring hundreds or thousands of images of single molecules, locating them and reconstructing a higher-resolution image from the high-precision localizations. These methods generally imply a considerable trade-off between imaging speed and resolution, limiting their applicability to high-throughput workflows. Recent advancements in scientific Complementary Metal-Oxide Semiconductor (sCMOS) camera sensors and localization algorithms reduce the temporal requirements for SMLM, pushing it toward high-throughput microscopy. Here we outline the decisions researchers face when considering how to adapt hardware on a new system for sCMOS sensors with high-throughput in mind.

Human oral keratinocytes: a model system to analyze host-pathogen interactions

Host-pathogen interactions are complex and dynamic processes that result in a variety of responses. The ability of the host to respond appropriately to the presence of a microbial agent defines the outcome of these interactions. Fungal infections are a problem of growing clinical importance and are responsible for serious health problems in multimorbid patients. Different model systems, including primary cells and cell lines derived from different tissues, are used to study several processes that contribute to the virulence of pathogenic fungi. In this chapter, we describe an in vitro assay to characterize the response of human oral keratinocytes (OKF6/TERT-2) to the presence of the human pathogenic fungus, Candida albicans. The dynamic cellular changes such as expression of differentiation markers can be monitored by epifluorescence deconvolution microscopy. Analyses of immunofluorescence data by linescan analysis and fluorescence intensity measurements are described to identify changes in protein expression levels. The use of this in vitro model system will also provide new information about host cell behavior and identify potential drug targets in the future.