细胞生物学

Autophagy plays a crucial role in cellular homeostasis and is responsible for removing and degrading damaged cytoplasmic cargo. This lysosome-mediated catabolic process removes defective organelles and misfolded proteins, and impaired autophagy has been directly linked to ageing and numerous diseases. This emphasises the importance of developing intervention methods to counteract this dysregulation. One promising intervention is thermal therapy, specifically hyperthermia, which is described in this protocol. In order to investigate this form of treatment, a rapid and reliable detection method is required to allow comparison of autophagy status under different conditions. While methods such as transmission electron microscopy (TEM) or western blotting can provide valuable structural analysis, they are often time-consuming and expensive, and are not suitable for small, round cells such as peripheral blood mononuclear cells (PBMCs). The method described in this protocol enables absolute quantification of PBMCs using the Guava^® Autophagy Detection kit after heat treatment with water-filtered infrared-A radiation (wIRA), compared with an untreated control. This method is based on antibody labelling, and subsequent flow cytometric analysis enables the number of autophagosomes to be determined by measuring the FITC intensity. This protocol provides rapid, reliable results and can be adapted to investigate not only heat therapy, but also other interventions, such as caloric restriction.

Autophagy is a conserved homeostatic mechanism involved in cellular homeostasis and many disease processes. Although it was first described in yeast cells undergoing starvation, we have learned over the years that autophagy gets activated in many stress conditions and during development and aging in mammalian cells. Understanding the fundamental mechanisms underlying autophagy effects can bring us closer to better insights into the pathogenesis of many disease conditions (e.g., cardiac muscle necrosis, Alzheimer’s disease, and chronic lung injury). Due to the complex and dynamic nature of the autophagic processes, many different techniques (e.g., western blotting, fluorescent labeling, and genetic modifications of key autophagy proteins) have been developed to delineate autophagy effects. Although these methods are valid, they are not well suited for the assessment of time-dependent autophagy kinetics. Here, we describe a novel approach: the use of DAPRed for autophagic flux measurement via live cell imaging, utilizing A549 cells, that can visualize and quantify autophagic flux in real time in single live cells. This approach is relatively straightforward in comparison to other experimental procedures and should be applicable to any in vitro cell/tissue models.

Key features

• Allows real-time qualitative imaging of autophagic flux at single-cell level.

• Primary cells and cell lines can also be utilized with this technique.

• Use of confocal microscopy allows visualization of autophagy without disturbing cellular functions.

Autophagy is a key player in the maintenance of cellular homeostasis in eukaryotes, and numerous diseases, including cancer and neurodegenerative disorders, are associated with alterations in autophagy. The interest for studying autophagy has grown intensely in the last two decades, and so has the arsenal of methods utilised to study this highly dynamic and complex process. Changes in the expression and/or localisation of autophagy-related proteins are frequently assessed by Western blot and various microscopy techniques. Such analyses may be indicative of alterations in autophagy-related processes and informative about the specific marker being investigated. However, since these proteins are part of the autophagic machinery, and not autophagic cargo, they cannot be used to draw conclusions regarding autophagic cargo flux. Here, we provide a protocol to quantitatively assess bulk autophagic flux by employing the long-lived protein degradation assay. Our procedure, which traces the degradation of ¹⁴C valine-labelled proteins, is simple and quick, allows for processing of a relatively large number of samples in parallel, and can in principle be used with any adherent cell line. Most importantly, it enables quantitative measurements of endogenous cargo flux through the autophagic pathway. As such, it is one of the gold standards for studying autophagic activity.