Plasma membrane perforation by GSDME during apoptosis-driven secondary necrosis

Secondary necrosis has long been perceived as an uncontrolled process resulting in total lysis of the apoptotic cell. Recently, it was shown that progression of apoptosis to secondary necrosis is regulated by Gasdermin E (GSDME), which requires activation by caspase-3. Although the contribution of GSDME in this context has been attributed to its pore-forming capacity, little is known about the kinetics and size characteristics of this. Here we report on the membrane permeabilizing features of GSDME by monitoring the influx and efflux of dextrans of different sizes into/from anti-Fas-treated L929sAhFas cells undergoing apoptosis-driven secondary necrosis. We found that GSDME accelerates cell lysis measured by SYTOX Blue staining but does not affect the exposure of phosphatidylserine on the plasma membrane. Furthermore, loss of GSDME expression clearly hampered the influx of fluorescently labeled dextrans while the efflux happened independently of the presence or absence of GSDME expression. Importantly, both in- and efflux of dextrans were dependent on their molecular weight. Altogether, our results demonstrate that GSDME regulates the passage of compounds together with other plasma membrane destabilizing subroutines.

Efferocytosis in the Central Nervous System

The effective clearance of apoptotic cells is essential for maintaining central nervous system (CNS) homeostasis and restoring homeostasis after injury. In most cases of physiological apoptotic cell death, efferocytosis prevents inflammation and other pathological conditions. When apoptotic cells are not effectively cleared, destruction of the integrity of the apoptotic cell membrane integrity, leakage of intracellular contents, and secondary necrosis may occur. Efferocytosis is the mechanism by which efferocytes quickly remove apoptotic cells from tissues before they undergo secondary necrosis. Cells with efferocytosis functions, mainly microglia, help to eliminate apoptotic cells from the CNS. Here, we discuss the impacts of efferocytosis on homeostasis, the mechanism of efferocytosis, the associations of efferocytosis failure and CNS diseases, and the current clinical applications of efferocytosis. We also identify efferocytosis as a novel potential target for exploring the causes and treatments of CNS diseases.

Defective efferocytosis as a predictor of COVID-19 mortality

COVID-19 is a generally benign coronavirus disease that can spread rapidly, except for those with a group of risk factors. Since the pathogenesis responsible for the severity of the disease has not been clearly revealed, effective treatment alternatives has not been developed. The hallmark of the SARS-CoV-2-infected cells is apoptosis. Apoptotic cells are cleared through a sterile process defined as efferocytosis by professional and nonprofessional phagocytic cells. The disease would be rapidly brought under control in the organism that can achieve effective efferocytosis, which is also a kind of innate immune response. In the risk group, the efferocytic process is defective. By the addition of the apoptotic cell load associated with SARS-COV-2 infection, failure to achieve efferocytosis of dying cells can initiate secondary necrosis that is a highly destructive process. Uncontrolled inflammation and coagulation abnormalities caused by secondary necrosis reason in various organ failures, lung in particular, which are responsible for the poor prognosis. Following the short and simplified information, this opinion paper aims to present possible treatment options that can control the severity of COVID-19 by detailing the mechanisms that can cause defective efferocytosis.

Having an Old Friend for Dinner: The Interplay between Apoptotic Cells and Efferocytes

Apoptosis, the programmed and intentional death of senescent, damaged, or otherwise superfluous cells, is the natural end-point for most cells within multicellular organisms. Apoptotic cells are not inherently damaging, but if left unattended, they can lyse through secondary necrosis. The resulting release of intracellular contents drives inflammation in the surrounding tissue and can lead to autoimmunity. These negative consequences of secondary necrosis are avoided by efferocytosis—the phagocytic clearance of apoptotic cells. Efferocytosis is a product of both apoptotic cells and efferocyte mechanisms, which cooperate to ensure the rapid and complete removal of apoptotic cells. Herein, we review the processes used by apoptotic cells to ensure their timely removal, and the receptors, signaling, and cellular processes used by efferocytes for efferocytosis, with a focus on the receptors and signaling driving this process.

Having an Old Friend For Dinner: The Interplay between Apoptotic Cells and Efferocytes

Apoptosis, the programmed and intentional death of senescent, damaged, or otherwise superfluous cells, is the natural end-point for most cells within multicellular organisms. Apoptotic cells are not inherently damaging, but if left unattended they can lyse through secondary necrosis. The resulting release of intracellular contents drives inflammation in the surrounding tissue and can lead to autoimmunity. These negative consequences of secondary necrosis are avoided by efferocytosis—the phagocytic clearance of apoptotic cells. Efferocytosis is a product of both apoptotic cell and efferocyte mechanisms, which cooperate to ensure the rapid and complete removal of apoptotic cells. Herein, the processes used by apoptotic cells to ensure their timely removal, and the receptors, signaling, and cellular processes used by efferocytes to identify, remove, and process the apoptotic cells, are reviewed.

Osthole Induces Apoptosis, Secondary Necrosis and Mitophagy Via NQO1-Mediated ROS Overproduction in HeLa Cells

Background: Osthole is a natural coumarin which has been proved to inhibit growth of cancer cells by inducing cancer cells death, while its mechanism of anticancer remains unclearly. In our study, we found that osthole activated multiple forms of cell death including apoptosis, secondary necrosis and mitophagy in receptor interacting protein kinase (RIP) 3-deficient cervical cancer HeLa cells. Methods: Cell viability was detected by MTT assay. Cell membrane integrity was detected by LDH release assay and PI staining. Cell apoptosis and necrosis were detected by flow cytometry assay. Reactive oxygen species (ROS) was detected by DCFH-DA staining and mitochondrial membrane potential (MMP) was detected by JC-1 staining using flow cytometry. The expression of proteins was detected by western blotting assay and proteomics. Xenograft tumor model was used to evaluate the effect of osthole in vivo.Results: Our study showed osthole caused HeLa cells apoptosis and secondary necrosis, which is a phenomenon of the apoptotic cells’ plasma membrane breakdown. And when Hela cells pretreatment with Z-DEVD-FMK, an irreversible caspase-3 inhibitor, not only inhibited osthole-induced apoptosis but also necrosis. Moreover, we found that Z-DEVD-FMK reversed the effect of osthole on the induction of cleaved the N-terminal fragment of GSDME in Hela cells. Furthermore, inhibition of NAD (P) H: quinone oxidoreductase 1 (NQO1) by osthole induced the overproduction of reactive oxygen species (ROS). ROS inhibitor N-Acetyl-L-cysteine (NAC) not only reduced osthole-induced apoptosis, but also reversed its effect on the necrotic induction and the GSDME N-terminal generation. It was shown that osthole decreased mitochondrial membrane potential (MMP) and increased the expression of PTEN-induced putative kinase 1 (PINK1) and Parkin, which indicated that the activation of mitophagy induced by osthole. Meanwhile, as well as apoptosis and secondary necrosis, mitophagy was also restrained by NAC. Conclusions: In conclusion, all these data suggested that osthole induced apoptosis, secondary necrosis and mitophagy via NQO1-mediated ROS overproduction.

Caspase-1 cleaves Bid to release mitochondrial SMAC and drive secondary necrosis in the absence of GSDMD

Caspase-1 drives a lytic inflammatory cell death named pyroptosis by cleaving the pore-forming cell death executor gasdermin-D (GSDMD). Gsdmd deficiency, however, only delays cell lysis, indicating that caspase-1 controls alternative cell death pathways. Here, we show that in the absence of GSDMD, caspase-1 activates apoptotic initiator and executioner caspases and triggers a rapid progression into secondary necrosis. GSDMD-independent cell death required direct caspase-1–driven truncation of Bid and generation of caspase-3 p19/p12 by either caspase-8 or caspase-9. tBid-induced mitochondrial outer membrane permeabilization was also required to drive SMAC release and relieve inhibitor of apoptosis protein inhibition of caspase-3, thereby allowing caspase-3 auto-processing to the fully active p17/p12 form. Our data reveal that cell lysis in inflammasome-activated Gsdmd-deficient cells is caused by a synergistic effect of rapid caspase-1–driven activation of initiator caspases-8/-9 and Bid cleavage, resulting in an unusually fast activation of caspase-3 and immediate transition into secondary necrosis. This pathway might be advantageous for the host in counteracting pathogen-induced inhibition of GSDMD but also has implications for the use of GSDMD inhibitors in immune therapies for caspase-1–dependent inflammatory disease.