Flow Cytometry Analysis of Anastasis using CellTrace Far Red (CTFR) cell tracker in Cultured Mammalian T Lymphocytes

Abstract

Anastasis is a cellular recovery process that rescues apoptotic cells from the brink of death. Our lab has developed a model for studying anastasis using cultured mouse HT2 lymphocytes dependent on the cytokine interleukin 2 (IL2). Within 24 hours of IL2 deprivation, HT2 cells display characteristic changes underlying apoptosis, including cellular condensation, membrane blebbing and fragmentation into apoptotic bodies, phosphatidylserine externalization, caspase 3 activation as well as G1 cell cycle arrest. HT2 cells can subsequently be rescued by adding IL2 back into the culture medium. In this study, we have used quantitative flow cytometry in conjunction with CellTrace Far Red (CTFR) and SYTOX Green (live/dead indicator) to track the kinetics of anastasis and re‐entry of viable apoptotic cells into the cell cycle. HT2 lymphocytes continuously maintained in IL2 comprised a homogeneous, viable population of CTFR+ cells which decreased in fluorescence intensity with each subsequent cell cycle for up to 96 hours post‐CTFR labelling. To investigate apoptosis reversal, HT2 cells were labeled with CTFR, deprived of IL2 for 24 hours and then rescued with IL2 re‐addition for periods of 24, 48, and 72 hours. Our findings indicate that viable, CTFR+ HT2 cells gradually resumed cell cycle entry over the 72‐hour rescue period. As caspase activation represents a cellular marker of early‐mid stage apoptotic cells, we also investigated caspase 3/7 activity in viable CTFR+ cells using the Nucview‐488 fluorescent caspase 3 substrate. Three distinct populations of caspase‐high, medium and low, viable CTFR+ HT2 cells were observed at 24 hours following IL2 deprivation. IL2‐rescued cells subsequently segregated into caspase‐high and low populations, ultimately merging into a single, caspase‐low population by 72 hours post‐rescue. Collectively, our findings suggest that CTFR tracking can be used successfully as a tool to follow the kinetics of apoptosis reversal in IL2‐dependent mouse HT2 lymphocytes, and is a promising model for the study of the mechanistic basis of anastasis.Support or Funding InformationUnion College Faculty and Student Research Grants