Biology subjects

Shirasaki, Y.

Publications and source records attributed to Shirasaki, Y..

3 recordsLinked to original sources

bioRxiv2026

Hmgb1 release kinetics shape its extracellular functions during regulated cell death

Danger-associated molecular patterns (DAMPs), such as high mobility group protein B1 (HMGB1), are released from dying cells, yet the kinetics and functional consequences of their release remain unclear. Using Hmgb1-mCherry transgenic mice and live-cell imaging, we visualize Hmgb1 and interleukin-1{beta} (IL-1{beta}) secretion at single-cell resolution. Hmgb1 exhibits two distinct release kinetics: short-duration completed within 1 min and long duration spanning several minutes. Mathematical modeling demonstrates that short-duration release generates substantially higher local Hmgb1 concentrations and steeper gradients near the dying cell than long-duration release. Such rapid release may enable one or a few dying cells to produce sufficient Hmgb1 to stimulate neighboring cells, consistent with its role as an alarmin. In vivo imaging of cisplatin-induced kidney injury reveals an inverse correlation between intracellular Hmgb1 levels and monocyte infiltration. Together, these findings suggest that Hmgb1 release kinetics shape its extracellular functions during regulated cell death.

cell biology↗

bioRxiv2025

Early-peaking caspase-7 activity at the plasma membrane drives apoptotic phosphatidylserine exposure

Apoptosis is an immunologically silent form of regulated cell death executed by caspase1. Caspase cleaves hundreds of substrates throughout the cell to regulate apoptotic processes2, including phosphatidylserine (PS) externalization3-5. However, spatio-temporal regulation of caspase activity in dying cells remains unclear. Here, we show that caspase activity peaks earlier at the plasma membrane (PM) during apoptosis by establishing a Dual Forster resonance energy transfer (Dual FRET) imaging system that combines subcellularly targeted FRET-based caspase biosensors with a cytosolic reference counterpart6,7. Genetic analysis identified caspase-7, an executioner caspase considered an inefficient backup for caspase-3, the major executioner caspase8,9, as a caspase responsible for the Early-Peaking Caspase Activity at the PM (EP-CAP). Mechanistically, EP-CAP is mediated via electrostatic interactions between PS in the inner leaflet of the PM and polybasic residues in the N-terminal intrinsically disordered region (IDR) of caspase-7, which are liberated by the caspase-mediated removal of polyacidic residues. Physiologically, EP-CAP facilitates the efficient cleavage of phospholipid scramblases for the rapid externalization of PS and subsequent efferocytosis. Accordingly, we propose that caspase-7, but not caspase-3, is a bona fide immunologically silent death caspase reinforcing the non-inflammatory nature of apoptosis via EP-CAP.

cell biology↗

bioRxiv2022

Quantitative live-cell imaging of secretion activity reveals dynamic immune responses

The measurement of cytokine secretions has contributed to the development of immunology; however, new methods that enable highly sensitive and efficient analysis are required for the precise characterisation of dynamic secretion activity when using rare cells or limited human specimens. Here, we report a new technology for quantitative live-cell imaging of secretion activity (qLCI-S), that enables high-throughput and dual-colour detection of prolonged secretion activity at the single-cell level, followed by transcriptome analysis for individual cells based on their phenotype. The power of the qLCI-S was demonstrated by visualising the individual and longitudinal cytokine secretion patterns of group 2 innate lymphoid cells, which comprised <0.01% human peripheral blood mononuclear cells, and identifying their minor subpopulations. This new technology will provide new insights into the spatiotemporal dynamic nature of various secretory functions and the development of fundamental tools for phenotypic drug discovery and regenerative and precision medicine.

biophysics↗