Flow cytometric detection of hyper-polarized mitochondria in regulated and accidental cell death processes.

Shikonin induced necroptosis in Jurkat cells were identified flow cytometrically by the up-regulation of RIP3 in live cells and that a proportion of these cells underwent other forms of regulated cell death (RCD) which included parthanatos (< 10%), or cleaved PARP (< 10%) and DNA Damage (> 30%). Live necroptotic cells also possessed functioning mitochondria with hyper-polarized mitochondria membrane potential and generated a fivefold increase in cellular reactive oxygen species (ROS) which was resistant to inhibition by zVAD and necrostatin-1 (Nec-1). After loss of plasma membrane integrity these dead necroptotic cells then showed a higher incidence of parthanatos (> 40%), or cleaved PARP (> 15%) but less DNA Damage (< 15%). Inhibition of shikonin induced apoptosis and necroptosis by zVAD and Nec-1 respectively resulted in live necroptotic cells with an increased incidence of cleaved PARP and reduced levels of DNA Damage respectively. Dead necroptotic cells then showed a reduced incidence of parthanatos and DNA Damage after inhibition by zVAD and Nec-1 respectively. A high proportion of these dead necroptotic cells (30%) which lacked plasma membrane integrity also displayed functioning hyper-polarized mitochondria with high levels of cellular ROS and thus had the capacity to influence the outcome of RCD processes rather than just been the end product of cell death, the necrotic cell. Flow cytometry can thus measure multiple forms of RCD and the level of cellular ROS and MMP which highlights the inter-connection between cell death processes and that a single cell may simultaneously display multiple forms of RCD.