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Programmed cell death, such as apoptosis, plays an essential role in embryonic development and normal homeostasis by eliminating unwanted, injured, or dangerous cells in multicellular organisms1,2,3. The loss of balance between cell death and survival can lead to fatal consequences such as cancer, heart failure, autoimmunity, and degeneration4,5,6,7,8. Activation of executioner caspases has traditionally been considered as the “point of no return” in apoptosis9,10,11, as it triggers rapid and massive cellular demolition12,13,14,15,16. Challenging this general dogma, we demonstrated that cultured dying primary cells and cancer cells can recover not only after caspase activation, but also following important cell death hallmarks including plasma membrane blebbing, cell shrinkage, mitochondrial fragmentation, release of mitochondrial cytochrome c into the cytosol, nuclear and chromatin condensation, DNA damage, nuclear fragmentation, cell surface exposure of phosphatidylserine (PS), and formation of apoptotic bodies17,18,19,20,21. We propose that anastasis is an intrinsic cell recovery phenomenon, as dying cells can recover after removal of cell death stimuli17,18,19,20,21. We coined the term “Anastasis” (Αναστάσης)18, which means “rising to life” in Greek, to describe this unexpected cell recovery phenomenon. Our observation of anastasis is further supported by recent independent studies that also reveal recovery of cells after phosphatidylserine externalization22,23,24, limited mitochondrial outer membrane permeabilization25, activation of mixed lineage kinase-like (MLKL), and cell shrinkage26.
Characterizing the mechanisms regulating anastasis will have paradigm-shifting physiological, pathological, and therapeutic implications. Anastasis could represent a previously unknown cytoprotective mechanism to rescue or preserve important postmitotic cells and tissues that are difficult to replace, and possibly account for heart failure reversal by ventricular unloading with left ventricular assist devices (LVADs)27,28, recovery of photoreceptor cells after transient exposure of excessive light29,30,31, or repair of neurons after brain injury32. If so promoting anastasis could enhance cell and tissue recovery. Conversely, anastasis could be an unexpected escape tactic used by cancer cells to survive cell-death-inducing therapy, causing cancer recurrence17,18. Therefore, suppressing anastasis in dying cancer cells during and after cancer treatment could be a novel therapeutic strategy to cure cancers by preventing their relapse.
During the process of anastasis, we have found that some recovered cells acquired permanent genetic alterations and underwent oncogenic transformation, likely due to DNA damage incurred during apoptosis18,20,21. Reversing the death process of DNA-damaged cells could be a mechanism of tumorigenesis, potentially underlying the observation that repeated tissue injury increases the risk of cancer in a variety of tissues, such as chronic thermal injury in the esophagus induced by the consumption of very hot beverages33,34,35, liver damage due to alcoholism36,37, tumor evolution after genotoxic cancer therapy38,39,40, and development of new cancers from normal tissues that arise during the intervals between cycles of anti-cancer therapy41,42,43,44. If true, targeting anastasis could prevent or arrest cancer development and progression. We have found that starvation-induced dying germ cells undergo anastasis in re-fed Drosophila19. If anastasis occurs in germ cells with DNA damage, it could be account for the observation that prolonged environmental stress promotes development of genetic diseases. For example, famines contribute to the development of transgenerational inheritable diseases such as diabetes and coronary heart diseases45. Therefore, understanding anastasis could lead to strategies for the prevention of developing inheritable diseases caused by this potential mechanism.
To harness the discovery of anastasis and direct it to develop innovative therapies, it is essential to study the cause and consequence of anastasis in live animals. However, it is technically challenging to identify and track anastatic cells in vivo, because the cells that recovered from cell death process appear morphologically indistinguishable from normal healthy cells, and there is no biomarker of anastasis identified yet17,18,21. To address these problems, we recently developed a new in vivo caspase biosensor designated “CaspaseTracker”19, to identify and track cells that survive apoptosis after caspase activation19,46, the hallmark of apoptosis10,14. Distinguishing it from the “real-time” caspase biosensors such as SCAT12,47, Apoliner48, CA-GFP49, ApoAlert18,50, C3AIs51 and iCasper52 that detect on-going caspase activity, the CaspaseTracker biosensor additionally features the ability to permanently label cells that express caspase activity even transiently. Therefore, the CaspaseTracker biosensor enables long term tracking of anastasis after reversal of caspase-mediated cell death process in vivo.