Single-Cell Imaging of Caspase-1 Dynamics Reveals an All-or-None Inflammasome Signaling Response

• Published in: Cell reports (Cambridge) 2014-08, Vol.8 (4), p.974-982
• Main Authors: Liu, Ting, Yamaguchi, Yoshifumi, Shirasaki, Yoshitaka, Shikada, Koichi, Yamagishi, Mai, Hoshino, Katsuaki, Kaisho, Tsuneyasu, Takemoto, Kiwamu, Suzuki, Toshihiko, Kuranaga, Erina, Ohara, Osamu, Miura, Masayuki
• Format: Article
• Language: English
• Subjects: Animals; Caspase 1 - physiology; Cells, Cultured; Enzyme Activation; Humans; Inflammasomes - metabolism; Interleukin-1beta - physiology; Kinetics; Lipopolysaccharides - pharmacology; Macrophages, Peritoneal - enzymology; Macrophages, Peritoneal - immunology; Mice, Transgenic; Signal Transduction; Single-Cell Analysis
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2014.07.012

Inflammasome-mediated caspase-1 activation is involved in cell death and the secretion of the proinflammatory cytokine interleukin-1β (IL-1β). Although the dynamics of caspase-1 activation, IL-1β secretion, and cell death have been examined with bulk assays in population-level studies, they remain poorly understood at the single-cell level. In this study, we conducted single-cell imaging using a genetic fluorescence resonance energy transfer sensor that detects caspase-1 activation. We determined that caspase-1 exhibits all-or-none (digital) activation at the single-cell level, with similar activation kinetics irrespective of the type of inflammasome or the intensity of the stimulus. Real-time concurrent detection of caspase-1 activation and IL-1β release demonstrated that dead macrophages containing activated caspase-1 release a local burst of IL-1β in a digital manner, which identified these macrophages as the main source of IL-1β within cell populations. Our results highlight the value of single-cell analysis in enhancing understanding of the inflammasome system and chronic inflammatory diseases. [Display omitted] •Single-cell analysis shows macrophage caspase-1 activation is an all-or-none response•All cells in which caspase-1 is activated undergo cell death•The kinetics of caspase-1 activation is independent of stimulus type and intensity•Only cells with caspase-1 activation exhibit an IL-1β burst. Inflammasomes are key regulators of innate immunity through caspase-1 activation that induces proinflammatory cytokine production and cell death. How inflammasomes and caspase-1 activation occurs at the single-cell level is largely unknown. Using a genetically encoded FRET sensor to monitor caspase-1 activity in a single macrophage, Liu et al. find that caspase-1 is activated in an all-or-none manner, irrespective of the type or strength of stimuli. This activation induces the digital secretion of a proinflammatory cytokine independent of cell death.