Lec 9. Cell Injury - III (Overview of Apoptosis & Necrosis).pdf

Cell Injury & Cell Death – III (Apoptosis & Necrosis) Pathology Unit of BMS (UCM) Learning Objectives  Cell Path Inj.III.1. Describe the light and electronic microscopic morphologic features of reversible cell injury.  Cell Path Inj.III.2. Identify light microscopic nuclear changes that reflect DN...

Cell Injury & Cell Death – III (Apoptosis & Necrosis) Pathology Unit of BMS (UCM) Learning Objectives  Cell Path Inj.III.1. Describe the light and electronic microscopic morphologic features of reversible cell injury.  Cell Path Inj.III.2. Identify light microscopic nuclear changes that reflect DNA damage.  Cell Path Inj.III.3. Describe features of irreversible injury and name 2 functional abnormalities that characterize irreversibly injured cells.  Cell Path Inj.III.4. Identify the different morphological patterns of necrosis and relate them with their clinical significance 1. Coagulative 2.Liquefactive 3.Caseous 4. Gangrenous 5. Fat 6. Fibrinoid  Cell Path Inj.III.5. Explain the distinct pathways for initiating apoptosis  Cell Path Inj.III.6. Recognize the family of intracellular proteins that regulates rate of apoptosis & the enzyme family which executes the "death program" of apoptosis.  Cell Path Inj.III.7. Discuss the mechanisms that promote phagocytosis of apoptotic cells by macrophages. Reversible Injury & Cell Death: necrosis vs. apoptosis Fig. 2.8, PBD 9th ed, 2015 Evidence of Injury: Renal Tubular Epithelium (light microscopy) Fig. 2-9, PBD 9th ed, 2015 Normal: distinct nuclear euchromatin and heterochromatin; intact plasma membranes Reversible injury due to ischemia: Cytoplasm: blebs, swelling, and eosinophilia Evidence of Injury: Renal Tubular Epithelium (light microscopy)  Irreversible (necrosis): ruptured cytoplasmic membranes, nuclear changes (3 patterns).  The basophilia of the chromatin may fade (karyolysis).  Nuclear shrinkage and increased basophilia (pyknosis).  The pyknotic nucleus undergoes fragmentation (karyorrhexis). Cell Injury: Reversible vs. Irreversible Fig. 2-10, PBD 9th, 2015 Ultrastructural changes caused by decreased blood flow (ischemia): A: Normal proximal tubular cell: abundant microvilli & mitochondriae B. Reversible changes: loss of microvilli, membrane blebs in lumen, mildly dilated mitochrondriae C. Irreversible changes: ruptured plasma membrane, swollen mitochrondriae with dense deposits, nuclear pyknosis Reversible Cell Injury: Steatosis normal Stop EtOH; lose weight Causes: EtOH intake; obesity Steatosis (“fatty change”): clear lipid vacuoles in cytoplasm due to abnormal accumulations of triglycerides within parenchymal cells Reversible Cell Injury: swelling (hydropic change) Intracellular hydropic change: clear spaces within epidermal keratinocytes (circled) Many eosinophils in epidermis (arrow) and dermis History: A 45-year-old woman applied a new moisturizing skin cream to her face. Two weeks later, she applied the cream again, developed redness and itching within 2 minutes, followed by a papular rash 24 hours later. Her symptoms and signs result from which type of immune-mediated disorder ? Type I hypersensetivity Necrosis  The term necrosis was first used by morphologists to refer to a series of changes that accompany cell death  Necrosis is death of groups of cells results from the degradative action of enzymes on lethally injured cells (Irreversible cell injury)  Necrotic cells are unable to maintain membrane integrity, and their contents often leak out.  The leaked cellular contents often elicit a local host reaction, called inflammation, that attempts to eliminate the dead cells and start the subsequent repair process  The enzymes responsible for digestion of the cell are  either from the lysosomes of the dying cells themselves (autolysis)  or from the lysosomes of leukocytes recruited as part of the inflammatory reaction to the dead cells (heterolysis). Morphology  Results from denaturation of intracellular proteins and enzymatic digestion of the lethally injured cell  Digestion of cellular contents &the host response take hours to develop  so there would be no detectable changes in cells 11 Cytoplasmic changes  Increased eosinophilia (Pink staining from the eosin dye)  more glassy, homogeneous appearance than viable cells due to loss of glycogen particles.  Myelin figures  large, whorled phospholipid masses  derived from damaged cell membranes  more prominent in necrotic cells than during reversible injury.  These phospholipid precipitates are then either phagocytosed by other cells  or further degraded into fatty acids; calcification of such fatty acid residues results in the generation of calcium soaps  Dead cells become calcified  When enzymes have digested cytoplasmic organelles, the cytoplasm becomes vacuolated and appears “moth-eaten.” 12  By electron microscopy  Necrotic cells are characterized by  discontinuities in plasma and organelle membranes  marked dilation of mitochondria with the appearance of large amorphous densities  disruption of lysosomes  intracytoplasmic myelin figures.  aggregates of fluffy material probably representing denatured protein 13  Nuclear changes  1. Nuclear changes assume one of three patterns. All due to breakdown of DNA and chromatin. karyolysis  The basophilia of the chromatin may fade (loss of chromatin staining)  most likely secondary to deoxyribonuclease (Dnase) activity. 2. 3. Pyknosis  nuclear shrinkage  increased basophilia  DNA condenses into a solid shrunken mass.  also seen in apoptotic cell death Karyorrhexis  The pyknotic nucleus undergoes fragmentation.  In 1 - 2 days, the nucleus in a dead cell completely disappear.  Electron microscopy  profound nuclear changes end in nuclear dissolution 14 Morphologic Patterns of Necrosis  Necrosis: cell death that results from severe damage to cell membranes, enzymatic destruction of cellular contents, and disruption of plasma membrane  Morphologic Patterns: distinctive patterns that provide clues about the underlying cause or mechanisms of necrosis  Morphologic Patterns of Necrosis:  Coagulative  Liquefactive  Caseous  Gangrenous  Fat Morphologic Pattern 1: Coagulative Necrosis Fig. 2-11, PBD 9th, 2015  Mechanism: denaturation of structural and enzymatic proteins  cell lysis  the injury denatures not only structural proteins but also enzymes.  so blocks the proteolysis of the dead cells  as a result, eosinophilic, anucleate cells may persist for days or weeks.  Most common setting: tissues irreversibly injured by ischemia  Area of necrosis caused by ischemia = infarction (AKA “infarct”)  karyolysis  fading of nuclear basophilia, followed by disappearance of nucleus  frayed, fuzzy plasma membranes  ghost outlines of dead cells Coagulative necrosis (right of line): showing preserved cellular outlines with loss of nuclei and an inflammatory infiltrate (seen as nuclei of inflammatory cells in between necrotic tubules) Kidney Infarct: wedge-shaped zone of necrosis involving area distal to occluded artery. The affected tissues exhibit a firm texture Morphologic Pattern 2: Liquefactive Necrosis  Definition: complete digestion of dead cells, transforming tissue into a gelatinous, partly solid and partly liquid mass.  Tissue may be reduced to liquid yellow purulent exudate (pus) containing neutrophils and fragments of dead cells.  Observed in bacterial infections that elaborate toxins (Staphylococcus aureus, Streptoccus pyogenes, Clostridium perfringens)  Observed in bacterial and some fungal infections that elicit an intense inflammatory response, with liquefaction due to enzymes released from leukocytes  Seen in ischemic-hypoxic death of cells in central nervous system (unique to CNS; other solid organs show coagulative necrosis) Liquefactive necrosis in CNS over time 2. RIGHT: cerebral infarction several weeks old, showing soft, partly liquefied, dissolving tissue (fig. 2-12, PBD 9th, 2015 1. ABOVE: acute ischemic infarction in middle cerebral artery territory, showing early necrosis, 1-3 days after injury (courtesy D. Agamanolis, MD) 3. RIGHT: cerebral infarction several years old, now healed as a cystic cavity with residual scar tissue formed by astrocytes (courtesy D. Agamanolis, MD) Morphologic Pattern 3: Caseous Necrosis  Definition: a distinctive form of coagulation necrosis, associated with granulomatous inflammation  Gross appearance of necrosis is “cheesy” (yellow, friable)  Seen in tuberculosis and a subset of fungal infections  Distinctive histopathologic lesion is Granuloma Central acellular necrosis Rim of macrophages with multinucleated giant cells and lymphocytes Fig. 2-13, PBD 9th, 2015 Morphologic Pattern 3: Caseous Necrosis Caseating granuloma: a central zone of necrosis, surrounded by macrophages (histiocytes) multinucleated giant cells, and lymphocytes Central acellular necrosis (circle) Multinucleated giant cells (fusion of macrophages) Peripheral zone of lymphocytes and macrophages (rectangle) Which organism is most likely to be detected by performing an acid-fast stain of this lesion? ________TB____________________ Morphologic Pattern 4: Gangrenous Necrosis  Definition: grossly distinctive type of necrosis of a body part, usually the leg, that has undergone coagulation necrosis due to ischemia.  Necrosis typically involves epidermis, dermis, subcutis, and deeper tissues  Without superimposed infection: dry gangrene  With superimposed infection: wet gangrene (liquefactive necrosis due to leukocytes & bacteria)  Gangrenous necrosis is not to be confused with “gas gangrene”, a result of acute necrotizing infection with Clostridium perfringens that produces gas in soft tissues. Morphologic Pattern 4: Gangrenous Necrosis Dry gangrene: pink-red areas correspond to early ischemic necrosis; blue-black areas indicate more advanced necrosis Wet gangrene: long-standing ischemic necrosis with bacterial superinfection, causing liquefactive changes (central yellow-green area) Morphologic Pattern 5: Fat Necrosis White foci of dead fat cells in retroperitoneum Mechanism: lipase from inflamed pancreas destroys membranes of adipocytes, converts TGs to fatty acids that combine with calcium  chalky white deposits in fat Necrotic adipocytes without peripheral nuclei; phagocytosis of dead cells by macrophages and multinucleated giant cells (arrow) Fat Necrosis  Focal areas of fat destruction  Occurs in adipose tissue of pancreas, breast tissue, abdomen, subcutaneous fat  Release of activated pancreatic lipases into the substance of the pancreas and the peritoneal cavity.  Occurs in the abdominal emergency as acute pancreatitis  Pancreatic enzymes leak out of acinar cells and liquefy the membranes of fat cells in the peritoneum.  The released lipases split the triglyceride esters contained within fat cells.  The fatty acids, combine with calcium to produce grossly visible chalky-white areas (fat saponification)  enable the surgeon and the pathologist to identify the lesions  Microscopic examination:  The necrosis takes the form of foci of shadowy (unclear) outlines of necrotic fat cells  with basophilic calcium deposits  surrounded by an inflammatory reaction 24 Morphologic Pattern 6: Fibrinoid Necrosis  Definition: special form of necrosis usually seen in immune reactions involving blood vessels.  This pattern of necrosis typically occurs when complexes of antigens and antibodies are deposited in the walls of arteries.  Deposits of these “immune complexes,” together with fibrin that has leaked out of vessels, result in a bright pink and amorphous appearance in H&E stains, called “fibrinoid” (fibrin-like) by pathologists  Examples:  immunologically mediated syndromes (e.g. polyarteritis nodosa, Rheumatic fever, SLE,..) & malignant hypertension Fibrinoid necrosis in an artery The wall of the artery shows a circumferential bright pink area of necrosis with protein deposition & inflammation (neutrophils with dark nuclei) References (textbooks only)  Kumar, Abbas, Aster: Pathologic Basis of Disease, 9th edition, Elsevier, 2015.  Rubin, Strayer: Rubin’s Pathology: Clinicopathologic Foundations of Medicine, 6th ed., Lippincott, Williams, and Wilkins, 2011.  McGee, Isaacson, Wright: Oxford Textbook of Pathology, Oxford University Press, 1992.  Majno, Norris: Cell, Tissues, and Disease, 2nd edition, Oxford University Press, 2004