Cell Death Mechanisms 2024-25 PDF

Prof Wanda Lattanzi Dept Life Science and Public Health Section of Biology Room 352bis 1st Floor Istituti Biologici [email protected] Cell death mechanisms Cell death Irreversible degeneration of vital cellular functions (notably ATP production and preservation of redox homeostasis) culmin...

Prof Wanda Lattanzi Dept Life Science and Public Health Section of Biology Room 352bis 1st Floor Istituti Biologici [email protected] Cell death mechanisms Cell death Irreversible degeneration of vital cellular functions (notably ATP production and preservation of redox homeostasis) culminating in the loss of cellular integrity (permanent plasma membrane permeabilization or cellular fragmentation) [Galluzzi et al, Cell Death & Differentiation2018]. A final decision that the cell reaches to maintain tissue homeostasis. Cells can die in different ways… Types of cell death mechanisms The death can be predetermined, programmed, and cleanly executed (apoptosis) or it can be traumatic, inflammatory, and sudden (necrosis). NECROSIS APOPTOSIS Induced by damage to the cell Programmed cell death. The damaging agent can be Orderly and highly regulated physic (burns, irradiation, process, which controls tissue osmotic variations) homeostasis. chemical (acidic, toxic, lack of Upstream causes tend to nutrients or oxygen) damage DNA Types of cell death mechanisms Cell death modalities can be categorized based on their signal dependency and then classified into additional subtypes based on specific mechanisms and triggers: ✓programmed cell death ✓ apoptotic cell death ✓non-apoptotic cell death. ✓Non-programmed cell death Yan et al. WORLD ACADEMY OF SCIENCES JOURNAL 2020 Types of cell death mechanisms The Nomenclature Committee on Cell Death (NCCD) has formulated guidelines for the definition and interpretation of cell death from morphological, biochemical, and functional perspectives. The most detailed classification relies on molecularly oriented definitions of terms ADCD: autophagy-dependent cell death ICD: immunogenic cell death, LDCD: lysosome-dependent cell death MPT: mitochondrial permeability transition Galluzzi et al, Cell Death & Differentiation2018  When is a cell «dead»? Morphological criteria: the cell has lost the integrity of its plasma membrane, as defined by the incorporation of vital dyes (e.g., PI) in vitro the cell, including its nucleus, has undergone complete fragmentation into discrete bodies (‘apoptotic bodies’) its corpse (or its fragments) has been engulfed by an adjacent cell in vivo  When is a cell «dead»? Dying cells are engaged in a process that is reversible until a first irreversible phase or ‘point-of-no-return’ is trespassed RESTRICTION POINTS FOR CELL DEATH - massive activation of liasis (caspases) - complete permeabilization of the mitochondrial outer membrane - exposure of phosphatidylserine residues (‘eat me’ signals for neighboring cells) Apoptosis Programmed cell death Occurs through an orchestrated sequence of events that leads to cell death Death by apoptosis is a neat, orderly process characterized by ✓ shrinkage in volume of the cell and its nucleus ✓ loss of adhesion to neighboring cells ✓ formation of blebs at the cell surface ✓ dissection of the chromatin into small fragments* ✓ rapid engulfment of the “corpse” by phagocytosis. www.news-medical.net/whitepaper/20190225/TUNEL-Staining-an-Overview.aspx Apoptosis Can be initiated through one of two pathways: intrinsic pathway: the cell kills itself because it senses cell stress extrinsic pathway: the cell kills itself because of signals from other cells.  Induced by stressor signals outside the cell cellular stressors Initiated by endogenous  Caspase cascade Caspases: a family of cysteine proteases* that cleave a number of proteins in the cell, ultimately causing cell disassembly and death They are typically activated in cascade, by two distinct routes: one from cell surface (extrinsic pathway) and the other from mitochondria (intrinsic pathway). Initiator Caspases (8, 9, 10 and 12) are induced by pro-apototic signals** Once activated, they activate downstream effector Caspases (3, 6 and 7) * Also termed cysteine-aspartic proteases as a Cys residue in the active site nucleophilically attacks and cleaves a target protein only after an aspartic acid residue. ** Pro-apoptotic stimuli include the FasL (Fas Ligand), TNF (Tumor Necrosis Factor), Granzyme-B, GRB (Growth Factor Receptor-Bound Protein), DNA damage, Ca2+ (Calcium) channels and ER (Endoplasmic Reticulum) stress.  Caspase cascade Caspases are synthesized as inactive zymogens (pro-caspases) that are activated post-translationally after the appropriate stimulus → dimerization/oligomerization of pro-caspases → cleavage into a small subunit and large subunit → the subunits associate with each other to form an active heterodimer caspase. Apoptosis extrinsic pathway Initiated by stressor that damage intracellular mechanisms, inducing DNA damage, hypoxia or oxidative stress (e.g. chemotherapy, radiotherapy). It plays an important function in development and in the elimination of damaged cells. Pro-apoptotic signaling induces loss of outer mitochondrial membrane integrity, release of cytochrome c in the cytoplasm, citC binds the apoptotic protease activating factor 1 (APAF1) and inactive caspase 9 to form the apoptosome The apoptosome cleaves and activate caspase-9 The initiator caspase-9 then cleaves and activates the executioner caspases-3/6/7  Apoptosis intrinsic pathway Stimulated by external events mediated by the death receptors: Fas receptors tumor necrosis factor (TNF) receptors TNF-related apoptosis-inducing ligand (TRAIL) receptors. As a surface receptor interacts with its ligand it induces the recruitment of adaptor proteins such as Fas-associated protein with death domain (FADD) and Tumor necrosis factor receptor type 1-associated DEATH domain protein (TRADD) These recruit a series of downstream factors, including Caspase-8/10. Caspase 8/10 is the initiator caspase in the extrinsic pathway and will in turn activate effector caspases 3/6/7. Apoptotic cell disruption Membrane contraction: The plasma membrane forms introflexions on its surface (process mediated by rho associated coiled-coil-containing protein kinase 1, ROCK1). Formation of membrane protrusions: the cell emanates elongated membrane protrusions of different types and morphology (microtubular spikes, apoptopods, beaded apoptopods). Process mediated by Pannexin 1, component of membrane channels. Fragmentation: the cell fragments into multiple vesicles (apoptotic bodies) that are phagocytosed. Membrane protrusions make it possible to bring cell bodies closer to phagocytes. Apoptotic debris removal After cell death, phagocytes intervene to eliminate the debris of the dead cell. The dying/dead cell emits signals that attract phagocytes: "find-me signals" And signals that signal phagocytes that they must be eliminated: "eat- me signals" Necrosis Unprogrammed form of cell death that occurs in response to overwhelming chemical or physical insult, representing external forces: extreme physical temperature pressure, chemical stress osmotic shock Swelling of both the cell and its internal membranous organelle Membrane breakdown with leakage of cell contents Induction of inflammation Necrosis Cell rupture causes the release of Damage-associated molecular patterns (DAMPs), recognized by immune cells → trigger inflammatory response Gong et al. Nat Rev Immunol 2020 Necrosis – versus - apoptosis Necrosis – versus - apoptosis Necrosis – versus - apoptosis Necroptosis A form of programmed necrosis, it occurs due to extracellular signals (death receptor-ligand binding) or intracellular cues (foreign microbial nucleic acids) A regulated form of necrosis, a process of cellular self-destruction that is activated when apoptosis is otherwise prevented It progresses independently of caspase activity. https://blog.cellsignal.com/mechanisms-of-cell-death-necrosis-necroptosis  Necroptosis RIPK3-dependent phosphorylation of MLKL (key executioner of necroptosis) → generate a pore complex in the plasma membrane leading to the secretion of DAMPs, cell swelling, and membrane rupture. One can observe different stages of cell breakdown during necroptosis, including the swelling of organelles, breakage of the cell membrane, and eventually, the disintegration of the cytoplasm and nucleus. Receptor-interacting protein kinase-3 (RIPK3) Mixed lineage kinase domain-like protein (MLKL) DeRoo et al, Int. J. Mol. Sci. 2020, 21(21), 8174; https://doi.org/10.3390/ijms21218174  Autophagic cell death Occurs in the absence of chromatin condensation but accompanied by massive autophagic vacuolization of the cytoplasm. Autophagic cells are not enfulfed in phagocytes, but rather self-digest their components fusion between autophagosomes and lysosomes generates autolysosomes both the autophagosome inner membrane and its luminal content are degraded by acidic lysosomal hydrolases This catabolic process marks the completion of the autophagic pathway  Autophagic cell death Linder and Kögel. Biology 2019, 8(4), 82; https://doi.org/10.3390/biology8040082 https://www.nejm.org/doi/full/10.1056/nejmra0901217 Other cell death modalities Other cell death modalities Cell type-specific cell death modalities ‘Mitotic catastrophe’ (cell death preceded by multinucleation’) Occurs either during or shortly after a dysregulated/failed mitosis accompanied by morphological alterations including micronucleation (which often results from chromosomes and/or chromosome fragments that have not been distributed evenly between daughter nuclei multinucleation (the presence of two or more nuclei with similar or heterogeneous sizes, deriving from a deficient separation during cytokinesis). ‘Anoikis’ (death following detachment) Apoptosis induced by the loss of the attachment to the substrate or to other cells ‘Excitotoxicity’ Occurring in neurons challenged with excitatory amino acids, such as glutamate Leads to the opening of Ca2+-permeable channels leading to cytosolic Ca2+ overload and activation of lethal signaling pathways Excitotoxicity seemingly overlaps with other types of death such as apoptosis and necrosis ‘Corneification’ the last stage of epidermal cell differentiation -> formation of corneocytes in the epidermis.