Lesson 3.3 Regulated Cell Death PDF

LESSON 3.3 REGULATED CELL DEATH 4. 2 morphologic form of cell death? ANS: APOPTOSIS AND NECROSIS Major mechanisms of acute cell swelling are (1) hypoxia (including ischemia) and (2) 5. A part of cell death more commonly...

LESSON 3.3 REGULATED CELL DEATH 4. 2 morphologic form of cell death? ANS: APOPTOSIS AND NECROSIS Major mechanisms of acute cell swelling are (1) hypoxia (including ischemia) and (2) 5. A part of cell death more commonly as a membrane injury caused by lipid means of survival? ANS: AUTOPHAGY peroxidation or the formation of lytic pores 6. This is termed as the programmed cell through insertion of an MAC via the death,as in physiologic removal of surplus complement pathway or by bacterial cells or during injury and affects individual cytolysins. cells? ANS: APOPTOSIS The cellular response to injury depends on 7. A process of condensation and shrinkage (1) the type of cell injured and its of cells and its organelles? ANS: APOPTOSIS susceptibility and/or resistance to hypoxia and direct membrane injury and (2) the 8. The result of apoptosis? ANS: Break down nature, severity, and duration of the injury. of cell into membrane-bound fragments As examples, neurons, cardiac myocytes, 9. It involves groups or zones of cells whi h endothelium, and epithelium of the proximal implies cell death with cell swelling (oncosis)? tubule of the kidney are cells that are ANS: NECROSIS extremely susceptible to hypoxia, whereas 10. Typical result of necrosis? ANS: fibroblasts, adipocytes, and other RUPTURE OF CELL MEMBRANES mesenchymal structural cells are less susceptible.The response to injury can be 11. The release of cell contents into the degenerative, adaptive, or reversible with ECM/ interstitium resulting from necrosis restoration of normal structure and function results to? ANS: INFLAMMATORY for the affected cell; however, with more RESPONSE severe or persistent injury, acute cell swelling 12. Necrosis is accidental and unregulated? can become irreversible and progress to ANS: NO death of the cell. In recent decades, the dogma of cellular pathology has been Normal Cell and the Changes in Reversible transformed by the repeated discovery of and Irreversible Cell Injury. Reversible injury additional pathways leading to cell death. is characterized by generalized swelling of the cell, its organelles (especially 1.An essential ‘value-added’ part of mitochondria), and the cytocavitary network. embryonic development, fetal maturation Other changes include blebbing of the and homeostasis (adult somatic cells)? ANS. plasma membrane, detachment of ribosomes CELL DEATH from endoplasmic reticulum, and clumping of 2. Removal of cells during development or nuclear chromatin. Irreversible injury is remodeling of tissues as a “physiologic cell characterized by increased cell swelling, death”? ANS: PROGRAMMED CELL DEATH disruption of lysosomes, formation of amorphous densities in mitochondria, 3. As a point of no return response to membrane disruption in the cytocavitary irreversible cell injury? ANS: PATHOLOGIC network, and severe nuclear changes. CELL DEATH Irreversible nuclear changes include pyknosis (severe condensation of chromatin), followed by karyorrhexis (nuclear formation of ROS through the Fenton fragmentation) and karyolysis (nuclear reaction, and generally assuming a necrotic dissolution). Laminated structures (myelin appearance figures) derived from injured cell membranes Pyroptosis, associated with pyrexia and can appear during reversible injury, but usually initiated by inflammatory caspase 1 become more pronounced in irreversibly activation injured cells. Parthanatos, initiated by poly (ADP-ribose) The Sequential Ultrastructural Changes of polymerase 1 (PARP1)in response to severe Necrosis and Apoptosis. A, In necrosis, DNA damage, oxidative stress, hypoxia, or leakage of cell contents through the ruptured hypoglycemia plasma membrane into the extracellular matrix elicits inflammation. B, In apoptosis, Lysosome-dependent cell death, RCD with cellular fragments are extruded as plasma primary lysosomal membrane membrane-bound apoptotic bodies that are permeabilization and release of cathepsins recognized by phagocytes but do not cause Autophagy-dependent cell death inflammation (autophagy is more commonly, a means of Whereas apoptosis has long been recognized cell survival) as a programmed or regulated process, not Entosis, seen mainly in detached epithelial only responsible for physiologic removal of cells that are engulfed and subjected to surplus cells but also occurring as a reaction autophagy by neighboring epithelial or other to certain injuries, necrosis was once nonphagocytic cells considered an entirely accidental and Immunogenic cell death (a form of RCD unregulated response to injury. However, that can stimulate an adaptive immune after certain attempts to prevent apoptosis response) resulted in a regulated process of oncotic necrosis, new forms of regulated cell death 13. A vital component of various processes (RCD) have been discovered. There is including normal cell tyrnover, proper considerable interconnectivity among the development and functioning of immune different pathways to RCD, and each type of system, hormone-dependent atrophy, RCD may impart a necrotic or an apoptotic embryonic development and chemical appearance to the dead cell. Major types of induced cell death? ANS: APOPTOSIS RCD, categorized by their molecular 14. What are the morphological features of mechanisms, include the following: apoptosis? ANS: Cell shrinkage (pyknosis), Extrinsic or intrinsic apoptosis DNA fragmentation (karyorrhexis), nuclear condensation, membrane blebbing, apoptotic Necroptosis body formation Mitochondrial permeability transition 14. A type of cell death caused by loss of (MPT)–driven necrosis plasma membrane integrity following Ferroptosis, triggered by lipid peroxidation Receptor interacting kinase 3 (thus inhibited by glutathione peroxidase 4), (RIPK3)-mediated phosphorylation of the dependent on iron, which catalyzes the pseudokinase mixed lineage kinase domain 22. Detecting methods of apoptosis? ANS: like (MLKL/pMLKL)? ANS: NECROPTOSIS DNA FRAGMENTATION, CYTOCHROME C 15. Necroptosis is characterized by what RELEASE morphological features? ANS: Cell swelling, 23. Detecting methods of necroptosis? ANS: membrane rupture, retain integral nucleus, RIPK1, RIPK3, MLKL translucent cytoplasm, moderate chromatin condensation 24. Detecting methods of autophagy? ANS: Immune colloidal gold technique, GFP-LC3 16. An evolutionary ancient and highly conserved catabolic process involving the 25. Detecting methods of ferroptosis? ANS: formation of double membraned vesicles ATPG3, immunofluorescence called autophagosomes that engulf cellular 26. Detecting methods of pyroptosis? ANS: proteins and organelles for delivery to BCA, Ca2+ fluorescence, spectral analysis lysosome? ANS: AUTOPHAGY 27. These are non-lytic cell death which 17. What are the morphological features of arrest/inhibit inflammation? ANS: autophagy? ANS: Lack of chromatin OXEIPTOSIS AND APOPTOSIS condensation, massive vacuolization of the 28. These are lytic cell death whoch cytoplasm, accumulation of double induce/spread inflammation? ANS: membraned autophagic vacuoles, little or no PYROPTOSIS AND NECROPTOSIS uptake of phagocytic cells 29. Be it inrinsic or extrinsic pathway, 18. An iron-dependent form of regikated cell apoptosis may almost always entail? ANS: death caused by unrestricted lipid ACTIVATION OF CASPASES perodixation and subsequent membrane damage? ANS: FEEROPTOSIS 30. What are the initiator caspases? ANS: CASPASE 8, 10, 9, 2 19. Morphological features of ferroptosis are? ANS: Loss of plasma membrane 31. This activated by the death-inducing integrity, leakage of extracellular contents, signaling complex [DISC] of the extrinsic smaller mitochondria, mitochondria crista pathway? ANS: CASPASE 8 reduction, elevation of mitochondrial 32. This is activated with the apoptosome in densities, increase of mitochondrial the intrinsic pathway? ANS: CASPASE 9 membrane rupture 33. This activated by p53 following DNA 20. A form of lytic cell death that is triggered damage? ANS: CASPASE 2 by proinflammatory signals (cytokines) and associated with inflammation? ANS: 34. What are the other caspase of the PYROPTOSIS extrinsic pathway aside from Caspase 8? ANS: CASPASE 10 21. Morphological features of pyroptosis? ANS: Lack of cell swelling, rupture of plasma 35. What are the effector caspases? ANS: membrane, large bubbling, moderate CASPASES 3, 6, 7 chromatin condensation, membranous pore 36. What does the Initiator caspases formation, release of intracellular contents in (caspase-2, caspase-8, caspase-9, or immediate cellular millieu caspase-10) do? ANS: cleave the downstream effector (executioner) caspases 2. Internalization and recruitment of the (mainly -3, -6, and -7) intermediate membrane proteins: TNF 37. The result of cleaving of the executioner receptor–associated death domain (TRADD), caspases? ANS: execute apoptosis by Fas-associated death domain (FADD), and cleaving cell proteins after aspartate caspase-8 to form the cytoplasmic residues. death-inducing signaling complex (DISC). TRADD interacts with FADD, which in turn 38. What triggers extrinsic apoptosis? ANS: activates procaspase-8 ALTERSTION IN EXTRACELLULAR MILLIEU 3. Sufficient active caspase-8 then activates Apoptosis. In the extrinsic pathway (left), effector (executioner) caspase-3 and apoptosis is triggered by binding of a ligand caspase-7 to implement apoptosis. to a cell surface death receptor with subsequent formation of a cytoplasmic 4. Apoptosis (protein FLIP) death-inducing signaling complex that FADD-like interleukin-1 B-converting activates an initiator caspase (e.g., enzyme caspase-8). The intrinsic pathway of apoptosis is triggered by DNA damage or inhibitory protein, an antiapoptotic protein various cell stressors, especially those that blocks the extrinsic pathway result in permeabilization of the binding procaspase-8 without activating it mitochondrial outer membrane, and leads to formation of the caspase-activating complex X-linked inhibitor of apoptosis (XIAP) or apoptosome. The initiator caspase in the Blocks extrinsic pathway by inhibiting intrinsic pathway is usually caspase-9. In caspase 3 activation both the extrinsic and the intrinsic pathways, initiator caspases activate effector NOTE: Caspase-8 can also truncate Bid (BH3 (executioner) caspases, resulting in cell death interacting domain death agonist), a with the characteristic morphologic features proapoptotic Bcl-2 protein, which of apoptosis. translocates to mitochondria to trigger intrinsic apoptosis. Importantly, the protein KEY EVENTS IN EXTRINSIC APOPTOSIS FLIP blocks the extrinsic pathway by binding 1.Activation of plasma membrane receptors procaspase-8 without activating it. If either by ligand-induced trimerization of a caspase-8 activity is insufficient, death receptor (DR) and activation of DR-mediated apoptosis can be augmented dependence receptors when concentrations by mitochondria, almost always through of their ligands decline below a certain Bcl-2 proteins, such as the proapoptotic Bak threshold. (Bcl-2 antagonist/killer) and Bax (Bcl-2–associated X protein). Even cells that Death Receptors: cannot initiate or propagate apoptotic FasR (Fas receptor bound by FasL) signaling can still die, but they do so via TNFR (tumor necrosis factor receptor) caspase-independent pathways of cell death. TRAILR (TNF related apoptosis inducing INTRINSIC PATHWAY ligand receptor) The intrinsic or mitochondrial pathway of apoptosis does not entail ligation of a cell Morphologic Appearance of Apoptosis. surface DR and can be triggered by a variety Morphologically, apoptosis is a process of of stressors (injury from toxins or ROS, chromatin condensation (pyknosis) and nutrient deprivation, or withdrawal of nuclear fragmentation (karyorrhexis) with growth factors or hormones) or by DNA blebbing of the plasma membrane to form damage that leads to activation of membrane-bound apoptotic bodies that p53-upregulated modulator of apoptosis contain nuclear fragments, organelles, and (PUMA). The key event of intrinsic apoptosis condensed cytosol (release factors>attract is mitochondrial outer membrane phagocytes>heterophagy). The plasma permeabilization (MOMP), which can be membrane that surrounds apoptotic bodies triggered by activation, posttranslational limits the inflammation that is common with modification, and upregulation of necrotic cell death but does express factors proapoptotic BH3-only proteins (e.g., PUMA to attract phagocytes and stimulate protein). The BH3-only proteins usually heterophagy. Not surprisingly, apoptotic and induce MOMP via oligomerization of Bax necrotic cell death can coexist in the same (Bcl-2-associated X protein, a proapoptotic tissue protein) and Bak (Bcl2-antagonist/killer)to Cell Death by Oncosis (Oncotic Necrosis) form channels in the outer mitochondrial membrane. This permeabilization of the Oncotic cell death results from irreversible outer mitochondrial membrane releases cell injury that, for example, is caused by cytochrome c from the intermembrane space hypoxia, ischemia, or direct damage to cell into the cytosol. Cytochrome c promotes the membranes. Ischemia causes particularly assembly of the caspase-activating complex extensive cell injury because the decreased or apoptosome, which consists of caspase-9 perfusion results in not only an oxygen plus apoptotic protease activating factor 1 deficit (hypoxia) but also a deficiency of (Apaf-1). MOMP also releases diablo glucose and other nutrients, plus an IAPbinding mitochondrial protein (DIABLO; accumulation of toxic metabolic diablo IAP binding mitochondrial protein, byproducts. Cell swelling, resulting from loss also known as the second mitochondrial of volume control, is the fundamental activator of caspases [SMAC]), as well as the mechanism of oncotic necrosis and catabolic hydrolases, apoptosis-inducing distinguishes it from apoptosis. Just as in factor (AIF), and endonuclease G. The reversible acute cell swelling, the initial O2 opening of the mitochondrial permeability deficit in irreversible injury causes an transition (MPT) pore is a key event in cell uncoupling of oxidative phosphorylation and death because it dissipates the proton a switch to anaerobic glycolysis with gradient needed for oxidative accumulation of lactic acid and a resulting phosphorylation. At low concentrations, decrease in pH of the cytosol. The Na+/H+ opening of the MPT pore can induce exchanger exports the excess H+ in exchange protective autophagy to remove for Na+. However, because glycolysis is less dysfunctional mitochondria. However, efficient in ATP production than oxidative MOMP is a lethal permeabilization that phosphorylation, the decreased ATP initiates intrinsic apoptosis. concentration leads to failure of ionic ATPase pumps and a loss of volume control (i.e., failure of Na+/K+-ATPase pumps with influx compartment has its own ATPase membrane of Na+, Ca2+, and water). In addition, the pumps. Ischemia opens plasma membrane normal function of enzymes, contractile calcium channels, leading to increased proteins, membrane pumps, and other cytosolic calcium concentration, which protein-based mechanisms in the cell occurs activates protein kinase C, endonucleases, in a very narrow pH range around 7.0. With phospholipases, and various proteases, glycolysis the cytosol becomes acidic, thus including calpains. Calpains abolish protein limiting or blocking these mechanisms and kinase C activity and cleave Na+/Ca2+ exacerbating cellular dysfunction. exchangers in mitochondrial and plasma membranes, leading to decreased calcium efflux and reuptake by the ER with ensuing calcium overload in the cytosol and, even worse, in the mitochondria. Although the timing of the point of no return remains elusive, if the cell fails to restore mitochondrial function, acute cell swelling becomes irreversible, leading to cell death.Paradoxically, restoration of blood flow and thus oxygen supply can exacerbate ischemic cell injury. This phenomenon is called ischemia-reperfusion injury, and it can continue for several days after reperfusion. It is attributed to “oxidative stress,” which involves the formation of ROS, calcium imbalance, opening of the mitochondrial permeability transition (MPT) pore, endothelial damage, thrombogenesis, and arrival of leukocytes in the damaged tissue. Reperfusion injury correlates with the duration of ischemia, but the susceptibility of organs (brain > heart > kidney > intestine > skeletal muscle) varies. The brain is Disruption of the intracellular calcium ion exquisitely sensitive to ischemia because of balance is integral to the transition from its high metabolic activity, absolute potentially reversible acute cell swelling to requirement for glucose, high concentration irreversible injury and cell death. The of polyunsaturated fatty acids, and release of intracellular concentration of calcium is excitatory neurotransmitters. A less generally one-fourth that of extracellular susceptible tissue (e.g., adipose tissue, calcium. In a normally functioning cell, fibrous tissue) can, to an extent, undergo calcium is sequestered into three major atrophy or enter a quiescent state in compartments: the cytosol (low response to decreased perfusion, using concentration), ER (midrange concentration), autophagy and apoptosis as means to and mitochondria (high concentration). Each remove effete organelles or dead cells, (PRR, e.g., Toll-like receptors [TLR3 and respectively. TLR4]). Depending on the ubiquitination status of RIPK1, a cell can respond to ligation Necrosis and Apoptosis, Mouse Hepatitis of TNFR1 in at least three different ways: (1) Virus Infection, Liver, Mouse. The virus survival via activation of nuclear factor causes hepatocellular death, typically by kappa B (NFκB), (2) extrinsic apoptosis oncotic necrosis, but sometimes by through association of RIPK1’s N-terminal apoptosis. Note coagulative necrosis (lower death domain (DD) with adaptor proteins left) with lytic necrosis (center left) and such as TRADD or FADD, or (3) necroptosis individual cells with features of apoptosis through association of RIPK1 with the (arrows). Hematoxylin and eosin (H&E) stain trimerized DR and activation of RIPK3. Apoptosis, Cytologic Features. A, Pancreas, Interestingly, it was the realization that rat. Individual acinar cells are shrunken, caspase inhibition, rather than protecting the condensed, and fragmented (arrows). cell from death by apoptosis could redirect it Apoptotic bodies are in adjacent cells, but to regulated necrotic cell death, that led to inflammation is absent. Hematoxylin and the discovery of necroptosis. Inhibition of eosin (H&E) stain. B, Hippocampus, brain, caspase-8, in particular, is important in mouse. Individual neurons are shrunken, redirecting the cell from apoptosis toward condensed, and fragmented (arrows). H&E necroptosis with assembly of the so-called stain. necrosome, composed of RIPK1, RIPK3, and Regulated Cell Death (RCD) with MLKL. Although the requirement for RIPK1 Morphologic Features of Necrosis. With the may not be absolute, MLKL, activated by discovery that inhibition of caspases did not RIPK3, is considered the major mediator of rescue cells from apoptotic death but instead cell death through plasma membrane redirected them to a regulated process of permeabilization through as yet poorly oncotic necrosis, the idea arose that necrosis understood mechanisms. could, at least in certain situations, be Regulated Cell Death by Mitochondrial regulated by signaling pathways. In fact, with Permeability Transition (MPT)–Driven the exception of the immediate death of cells Necrosis. Another form of RCD, in response to extreme physical or chemical mitochondrial permeability transition injury, RCD through a variety of signaling (MPT)–driven necrosis is commonly pathways seems to be the norm. A couple of triggered by oxidative stress or excess examples of RCD with a necrotic intracellular Ca2+ and depends on morphologic appearance follow. cyclophilin D to form the permeability Necroptosis. Necroptosis is a form of RCD transition pore complex between inner and that depends on the sequential activation of outer mitochondrial membranes. This leads RIPK3 and MLKL. The myriad triggers of to mitochondrial swelling, production of necroptosis (e.g., TNF, FasL [Fas ligand], DNA ROS, and depletion of oxidized nicotinamide damage, lipopolysaccharide, and interferon adenine dinucleotide (NAD+). Mitochondrial γ) are detected by plasma membrane death production of ROS, mainly through reduced receptors (DR, e.g., FasR [Fas receptor] or forms of nicotinamide adenine dinucleotide TNFR1) or pathogen recognition receptors phosphate (NADPH) oxidases, is considered requisite to TNF-α–induced necrosis. ROS, reperfusion. Free radicals damage cell lipids along with Ca2+ dysregulation and depletion (especially the phospholipids of cell of NAD+ and ATP, propagates the signal in membranes), proteins, and nucleic acids. regulated necrosis. Finally, the execution Endogenous free radicals, such as reactive phase, with its catastrophic ATP depletion, oxygen or nitrogen species, serve physiologic cell swelling, lipid peroxidation, and functions in cell signaling and in defense lysosomal membrane permeability with against microbes but also can harm cells, release of cathepsins, leads to irreversible especially in the setting of ischemia cell injury and death. /reperfusion injury. Free radicals, with their unpaired electron, are prone to extract a H+ Cell Membrane Injury Leading to Cell Death. from the polyunsaturated fatty acids in cell The failure to restore mitochondrial function membranes. The fatty acid that loses a H+ and repair cell membrane damage is a critical becomes, itself, a free radical that can then be component of irreversible cell injury. In oxidized to an even more reactive radical particular, uncoupled oxidative that will extract a H+ from the neighboring phosphorylation and impaired mitochondrial fatty acid, propagating a chain reaction that calcium sequestration significantly increase leads to membrane disintegration. the risk for cell death. Injured cell Antioxidants, such as superoxide dismutase membranes have increased permeability, so (SOD), catalase, glutathione peroxidase, and when membrane ATPase ion pumps fail, vitamins A, C, and E, are protective because extracellular calcium enters the cell. The they scavenge free radicals and can break the calcium imbalance exacerbates the damage chain reaction of lipid peroxidation. to mitochondria and to the cytoskeleton and activates endonucleases, proteases, and Reactive Oxygen Species (ROS). Reactive phospholipases. Phospholipase A oxygen species (ROS), such as superoxide catalytically hydrolyzes the phospholipids of anion (O2−), hydrogen peroxide (H2O2), and the cell membranes, further exacerbating cell the hydroxyl radical (HO ), are commonly and mitochondrial membrane damage and formed duringoxidative phosphorylation and the progression to irreversible cell injury. function as signaling molecules that affect cell proliferation and survival. ROS are also Free Radical Injury. A free radical is any generated in cell membranes of the nucleus, molecule with an unpaired electron, mitochondria, peroxisomes, ER, and other including ROS and reactive nitrogen species organelles in response to injury by ionizing (e.g., NO). Such highly reactive molecules are radiation, xenobiotics,c ultraviolet light, heat, short-lived products of oxidative metabolism inflammatory cytokines, and specific and occur in membranes of mitochondria and microbial components, as examples. In other organelles. NADPH oxidase, an cellular homeostasis, imbalances resulting enzyme complex found in membranes of a from excessive ROS or other oxidants are variety of cell types, especially phagocytes, counteracted by catalase and superoxide such as neutrophils and macrophages, dismutases (SOD), groups of enzymes that functions in the production of ROS. Free catalyze the conversion of superoxide radicals contribute to mitochondrial injury molecules into oxygen and hydrogen and to cell death by oncotic necrosis, peroxide. When ROS accumulation exceeds especially when ischemia is followed by the counteractive antioxidant capacity, the segments of the cerebral cortex are resultant oxidative stress damages DNA and discolored or changed in texture or RNA, cell membranes (lipid peroxidation), structure. An infarct, which is necrosis proteins in general (oxidation of amino acids), resulting from regional loss of blood supply, and specific enzymes (oxidative is recognized because it assumes the shape deactivation). Oxidative stress has been of the vascular field—rhomboidal in many implicated in aging, diminished resistance to tissues (e.g., lung or skin) or in end-artery infection, diabetes mellitus, neuronal organs (organs with a single blood supply), degeneration, cancer, and other disease conical (wedge shaped in two dimensions) processes. with its base at the edge of the spleen or cortical surface of the kidney. Morphologic Appearance of Necrotic Cells and Tissues Cytoarchitecture of Cellular Necrosis. A, Schematic representation of nuclear and (Oncotic Necrosis). The appearance of cytoplasmic changes in the stages of necrotic cells depends on the type of necrosis. rER, Rough endoplasmic reticulum. necrosis, the tissue involved, the cause of B, Pyknosis and karyolysis, renal cortex, cell death, and the time elapsed. In this chloroform toxicosis, mouse. Some tubular chapter, necrosis (or necrotic) generally epithelial cells have undergone hydropic implies oncotic cell death. degeneration; others are necrotic with Gross Appearance of Necrotic Tissue. Soon pyknosis (arrow) or karyolysis (arrowhead). after death of the cell, necrotic tissue may Hematoxylin and eosin (H&E) stain. C, have the same macroscopic features (gross Karyorrhexis, lymphocytes, spleen, dog. appearance) as those of potentially Necrotic lymphocytes have fragmented reversible acute cell swelling, namely, nuclei (arrow) because of parvovirus swelling and pallor. With time, necrosis infection. H&E stain. becomes more obvious with a loss of Histologic Changes in Necrosis (Oncotic structural detail and demarcation from Necrosis). The light microscopic changes of adjacent viable tissue. Zonal necrosis, such as necrosis were described in the 19th century centrilobular hepatic necrosis or renal by Rudolf Virchow. The hallmarks are proximal tubular necrosis, particularly if pyknosis (nuclear condensation with diffuse rather than segmental or focal, can be shrinkage and intense basophilia), indistinguishable in its early stages from karyorrhexis (nuclear fragmentation), or reversible degeneration. In contrast, unifocal karyolysis (nuclear dissolution or loss). Dead or multifocal (randomly distributed) necrosis cells also tend to have intense cytoplasmic or segmental zonal necrosis is more easily eosinophilia because of the denatured seen precisely because it differs from protein and loss of ribosomes, hence loss of adjacent viable tissue. Multifocal hepatic basophilia. Later the dead cell may have necrosis, for example, is recognizable in part cytoplasmic pallor and become swollen, because the necrotic foci differ from rounded, and detached from the basement surrounding viable tissue, and every hepatic membrane or from neighboring cells. lobule is not affected in the same manner. Likewise, segmental laminar cerebrocortical Ultrastructure of Necrotic Cells (Oncotic necrosis is recognized because only Necrosis). Initially the necrotic cell is swollen, rounded, and detached from delayed. However, the degradation of nucleic adjacent cells and from the basal lamina, in acids is not hindered. Thus, a cell that has the case of epithelium, or from the ECM, in undergone coagulative necrosis has the the case of mesenchymal cells. Chromatin is expected nuclear features of cell death (i.e., clumped. The cytosol is electron lucent. pyknosis, karyorrhexis, or karyolysis), but Mitochondria are swollen and develop the cell outlines are still visible histologically. flocculent densities. The ER and the rest of Coagulative necrosis is most easily the cytocavitary network swell and fragment recognized in the liver, kidney, myocardium, into vesicles. Ultimately, cell swelling or skeletal muscle, in which the temporary disrupts membranes, including the plasma preservation of cell outlines also preserves membrane, at which point the dead cell tissue architecture so that the outlines of bursts, then collapses. hepatic plates, renal tubules, or muscle bundles are visible at the light microscopic Types of Oncotic Necrosis. It can be level. Neurons also undergo coagulative diagnostically useful, although somewhat necrosis before disappearing by lytic arbitrary, to classify necrosis by its necrosis. Grossly, coagulative necrosis morphologic features. This classification appears pale tan to pale gray, often sharply depends on the tissue involved, the nature of demarcated from the normal color of the injurious agent, and the time elapsed adjacent viable tissue, and solid (without after cell death. Necrosis has been classified apparent crumbling, sloughing, liquefaction, traditionally as coagulative, caseous, or other obvious loss of structure).Infarction liquefactive or lytic, and gangrenous. The typically begins as coagulative necrosis, student should remember that the especially in tissues such as kidney, where morphologic appearance of necrotic cells and scaffolding provided by tubular basement tissues changes with time. For example, the membranes and interstitial fibrous tissue morphologic features of coagulative necrosis maintains the tissue structure. Initially the can progress to those of lytic necrosis with tissue with loss of its blood supply is liquefaction, particularly in certain tissues or blanched, but within minutes blood enters in the presence of numerous leukocytes. the infarcted tissue because blood flow Coagulative Necrosis. The term coagulative either was restored in the obstructed vessel necrosis refers to the denaturation of or arrives from collateral circulation cytoplasmic proteins, which at the histologic (therefore infarcts in organs with a dual level imparts an opaque and intense blood supply, such as the lung, are typically cytoplasmic eosinophilia to necrotic cells. hemorrhagic) or leaks from veins in adjacent Coagulative necrosis is a typical early unaffected tissue. In an end-artery organ, response to hypoxia, ischemia, or toxic such as the kidney, macrophages remove the injury. It appears that the initial injury or the blood from acute hemorrhagic infarcts over subsequent cellular acidosis denatures not the course of a few days, and the infarct only structural proteins but also lysosomal becomes pale and sharply demarcated by a enzymes in the affected cell. Normally, red rim, attributable to hyperemia, lysosomal enzymes would cause proteolytic hemorrhage, and acute inflammation, from disintegration of the entire cell, but as a adjacent renal parenchyma. result of this denaturation, proteolysis is Coagulative Necrosis, Infarct, Cut Surface, Corynebacterium pseudotuberculosis, the Kidney, Single Lobe, Ox. A, A pale tan wedge cause of caseous lymphadenitis in sheep and of coagulative necrosis extends from the goats, is another bacterium that can replicate medulla to the capsular surface of the kidney. in phagosomes of macrophages without The apical (medullary) portion of this renal being destroyed by lysosomal enzymes. The infarct has a dark red border of reactive chronic stage of infection results in caseous hyperemia and inflammation (arrows). B, abscesses in peripheral or internal lymph Coagulative necrosis of renal tubular nodes or other organs, such as the lungs. epithelial cells. Necrotic cells (lower half of Caseous Lymphadenitis (Caseous Necrosis), figure) have homogeneous eosinophilic Caudal Mediastinal Lymph Node, cytoplasm and pyknosis or karyolysis, but Transverse Section, Sheep. A, The lymph faint cell outlines and tubular architecture node contains a caseated abscess. In caseous are retained. Hematoxylin and eosin (H&E) lymphadenitis, caseous necrosis appears as stain. inspissated, yellow-white, and concentrically Caseous Necrosis. Caseous, from the Latin laminated exudate. B,Degenerated or lysed word for cheese, refers to the curdled or leukocytes, including many neutrophils, are cheeselike gross appearance of this form of at the center (lower left) of an abscessed necrosis. In comparison to coagulative lymph node. Note a band of intact necrosis, caseous necrosis is an older lesion neutrophils between the caseous necrosis with complete loss of cellular or tissue (lower left) and epithelioid macrophages architecture. Macroscopically, caseation (upper right). Hematoxylin and eosin (H&E) may appear as crumbled, granular, or stain. laminated yellow-white exudate in the Coagulation Necrosis, Infarcts, Kidney, Cow. center of a granuloma or a chronic abscess. Note the yellow-white areas of acute Histologically, the lysis of leukocytes and coagulation necrosis surrounded by a red rim parenchymal cells converts the necrotic of hyperemia and inflammation. tissue into a granular to amorphous—cell outlines are not visible—eosinophilic Tuberculosis (Caseous Necrosis), Lymph substance with basophilic nuclear debris. Node, Transverse Section, Ox. A, The lymph Calcification of the necrotic tissue can node contains numerous coalescing caseated contribute to the basophilic granular granulomas. Caseous necrosis is appearance.Caseous necrosis is prominent in characterized by off-white, crumbly exudate. the granulomas of bovine tuberculosis, B, Granulomatous inflammation in caseous caused by Mycobacterium bovis. M. bovis necrosis. Cell walls are disrupted, and tissue replicates within macrophages, protected by architecture is lost. Degenerated or lysed components of its cell wall from destruction leukocytes, including many neutrophils, are by lysosomal enzymes until, with the at the center (right) of a granuloma; note development of cell-mediated (type IV) epithelioid macrophages at left. hypersensitivity, cytotoxic T lymphocytes Liquefactive Necrosis. In liquefactive destroy the infected macrophages, as well as necrosis, cells are lysed, parenchymal cells of the infected organ.  necrosis, cerebrum, dog. The pale zone in and the necrotic tissue is converted to a fluid deep laminae of the cerebral cortex is an area phase. This manifestation is typically the final of liquefactive necrosis with loss of stage of necrosis in parenchyma of the brain parenchyma. All that remains is the or spinal cord because of the lack of a vasculature with gitter cells in intervening fibrous interstitium (X scaffolding) to uphold spaces. tissue structure and because cells of the CNS tend to be rich in lipids and lytic enzymes. Gangrenous Necrosis. Gangrene denotes a The term for the macroscopic (gross) type of necrosis that tends to develop at the appearance of necrosis in the brain and distal aspect of extremities, such as the spinal cord is malacia. Neurons are generally limbs, tail, or pinnae, or in dependent the cells most susceptible to necrosis, portions of organs, such as the mammary especially from hypoxia or ischemia, and glands or lung lobes. Gangrene can be develop (early in the process of cell death) designated as wet or dry; these forms are the morphologic features of coagulative unrelated. If the dependent necrotic tissue is necrosis. With time, however, the glial cells infected by certain bacteria, wet gangrene also undergo necrosis and parenchymal ensues. If those bacteria are gas forming liquefaction begins. Initially, malacia may (e.g., Clostridium spp.), then wet gangrene merely result in a translucency of affected becomes gas gangrene. In the lung, wet tissue, but within a few days necrotic tissue gangrene is often a sequel to the lytic undergoes yellowing, softening, or swelling. necrosis of aspiration pneumonia. The Liquefaction progresses with arrival of aspirated material could be foreign material macrophages (gitter cells) to phagocytize the (food or medicament) or gastric content (a myelin debris and other components of the mixture of ingesta and gastric secretions). necrotic tissue. Eventually the parenchymal Such foreign materials can be caustic in their cells are completely lysed or phagocytized, own right and are likely to deliver bacteria and all that remains is the vasculature with from the environment or oropharynx into the partial filling of the intervening spaces by lung. Staphylococcal infection of the lipid- and debris-laden gitter cells. In organs ruminant mammary gland can result in or tissues outside the CNS, liquefactive gangrenous mastitis, a form of wet necrosis is most commonly encountered as gangrene. Grossly, tissues with wet gangrene part of pyogenic (pus-forming) Bacterial are red-black and wet. Histologically, the infection with suppurative (neutrophil-rich) lesion of wet gangrene resembles that of inflammation and is observed at the centers liquefactive necrosis but is usually of abscesses or other collections of accompanied by more numerous leukocytes, neutrophils. especially neutrophils.Dry gangrene is the result of decreased vascular perfusion Liquefactive Necrosis. A, Acute and/or loss of blood supply. It is a form of polioencephalomalacia, brain, goat. A infarction resulting in coagulative necrosis thiamine deficiency has resulted in that imparts a dry, leathery texture to the cerebrocortical malacia, which necrotic tissue, providing that it remains free microscopically is liquefactive necrosis with of putrefactive bacteria. Arterial thrombosis focal tissue separation (arrows). Note yellow (e.g., “saddle thrombus” formation at the iliac discoloration of affected cortex. B, Cortical bifurcation of the aorta in cats) and frostbite usually the result of feeding a diet high in are causes of dry gangrene of extremities. polyunsaturated fatty acids and low in Dry gangrene is also the lesion of “fescue vitamin E or other antioxidants, setting the foot” in cattle, effect of the ergot alkaloids stage for ROS production and lipid produced by endophyte-infected fescue peroxidation. Yellow fat disease is often seen grass. in carnivores, such as cats or mink, on a fish-based diet. Affected adipose tissue is Gangrenous Necrosis. A, Wet gangrene, firm, nodular, and yellow-brown.Enzymatic mammary gland (longitudinal section necrosis of fat occurs mainly in through the teat), sheep. Staphylococcal peripancreatic adipose tissue, where it is infection caused the gangrenous mastitis in attributed to release of lipases from necrotic this ewe. Note wet and hemorrhagic necrosis pancreatic acinar cells. Grossly, necrotic of mammary tissue and overlying skin, adipose tissue becomes firm and nodular especially at the distal (ventral) aspect of the with off-white chalky deposits, the result of udder. B, Dry gangrene, digits, ox. saponification (soap formation). Vasoconstriction from ergot alkaloids Microscopically, fat necrosis elicits produced by endophyte-infected fescue inflammation that consists mainly of grass caused this ischemic necrosis of the lipid-laden macrophages and variable distal aspects of the hind limbs. Note that number of neutrophils. Lipids are removed by one of the claws (left) has been lost as a solvents during histologic processing, so the result of the process. cytoplasm of normal adipocytes is not Gangrenous Necrosis. Wet gangrene, udder, stained, whereas necrotic adipocytes tend to ewe. Skin is darkened and reddened over the have pale eosinophilic to amphophilic necrotic mammary tissue. Note sharp line of cytoplasm with scattered basophilic soap demarcation of ventral necrotic tissue from deposits.Traumatic fat necrosis is typically adjacent viable tissue. the result of blunt trauma or chronic Necrosis of Epithelium. Necrosis that pressure on adipose tissue against bony develops in epithelial surfaces (e.g., prominences, such as the subcutaneous epidermis or corneal epithelium) or epithelial adipose tissue compressed against the linings (e.g., mucosal epithelium of the sternum in recumbent cattle. Ischemia is respiratory, digestive, or reproductive tracts) believed to be the ultimate cause of cell causes exfoliation or sloughing of dead cells, death. Inflammation and saponification are resulting in erosion of the epithelium, or, with inconspicuous in this form of fat full-thickness necrosis, in ulceration. Trauma, necrosis.Necrosis of abdominal fat in cattle certain microbes (e.g., herpesviruses), and is an example of idiopathic fat necrosis. This loss of blood supply are among the many lesion tends to develop in the abundant causes of epithelial necrosis. mesenteric and retroperitoneal adipose tissue of overconditioned cows. Some have Necrosis of Adipose Tissue (Fat Necrosis). attributed retroperitoneal fat necrosis to Fat necrosis can be classified etiologically as ischemia associated with consumption of nutritional, enzymatic, traumatic, and endophyte-infected tall fescue grass. idiopathic. Nutritional fat necrosis, also Idiopathic fat necrosis is also encountered in known as steatitis or yellow fat disease, is the ventral parietal peritoneum (e.g., can be repaired by hyperplasia of adjacent falciform ligament) of horses and ponies. normal epithelial cells without scarring if Fat Necrosis. A, Enzymatic necrosis of fat in the defect is small or shallow and if basal or the mesentery. Note numerous irregularly other progenitor cells remain nearby to fill shaped white areas of fat necrosis. k, kidney; the gap (i.e., healing in coronavirus or gb, gallbladder. B, Enzymatic necrosis of fat; parvovirus infection of the small intestine). peripancreatic adipose tissue, dog. Recurrent Adipose tissue, in contrast, is ill equipped to bouts of pancreatitis with leakage of lipases replace necrotic fat lobules because of the and other enzymes cause saponification of low regenerative capacity of adipocytes. necrotic adipose tissue, giving it a chalky, Regulated Cell Death with Morphologic off-white appearance. C, Peripancreatic Features of Necrosis adipose tissue, dog. Note the necrotic adipose tissue (bottom half of the figure) Mitochondrial Permeability Transition with saponification (basophilic areas) and the (MPT)- driven Necrosis border of neutrophils and macrophages (top Triggers: oxidative stress, excess half of the figure). intracellular Ca2+ Sequelae to Oncotic Necrosis. Oncotic Formation of permeability transition necrosis elicits an inflammatory reaction in pore complex between inner and most tissues. In the CNS, the inflammatory outer mitochondrial membranes – reaction is slow to develop and consists depends on cyclophilin D. mainly of an influx of macrophages that Result: mitochondrial swelling, become gitter cells. In most other tissues a production of ROS, depletion of band of reactive hyperemia encircles the oxidized nicotinamide adenine necrotic tissue and brings leukocytes to the dinucleotide (NAD+). site. The neutrophils and macrophages ROS, Ca2+ dysregulation and NAD+ phagocytize and lyse the necrotic tissue, and ATP depletion - propagates the converting coagulative to liquefactive signal in regulated necrosis necrosis and hastening (in many cases) the Execution phase>irreversible cell removal of damaged tissue. In other cases, injury>death foreign material or bone fragments resist - Catastrophic ATP depletion digestion and form a sequestrum. Smaller - Cell swelling cavitations left by liquefactive necrosis may - Lipid peroxidation heal without scarring, depending on the - Lysosomal membrane regenerative capacity of the affected tissue. permeability with release of The liver is an organ with high regenerative cathepsins capacity and, because of its dual blood Injured cell membrane supply, is not prone to infarction. In contrast, - Increased permeability the injured nephrons in renal infarcts are - Failure of ATPase ionic seldom restored to full function and are pump>Ca enters usually replaced by a fibrous scar.Focal - 1. Exacerbate mitochondrial epithelial necrosis that results in ulceration damage  - 2. Activates endonucleases, proteases, and phospholipases - 3. Phospholipase A: catalytically hydrolyzes the phospholipids of cell membranes Uncoupled oxidative phosphorylation Impaired mitochondrial calcium sequestration Irreversible cell injury - Failure to restore mitochondrial function - Failure to repair cell membrane damage