Cell Injury and Cell Death

1. Cell Injury and Cell Death Nirush Lertprasertsuke, M.D. Department of Pathology Faculty of Medicine, Chiang Mai University

2. Cell Injury • Normal cell: homeostasis • Sublethal injury: reversible injury • Irreversible injury • Cell death

3. Normal homeostasis • Genetic programs • metabolism • differentiation • specialization • Constraints of neighboring cells • Availability of metabotic substrates

4. Cellular Responses to Injury • Acute cell injury • Reversible cell injury • Cell death • Subcellular alterations in sublethal and chronic injury • Cellular adaptations: ~trophy/~plasia • Intracellular accumulations • Pathologic calcifications • Cell aging

5. Causes of cell injury • Oxygen Deprivation: hypoxia/ischemia • Physical agents • Chemical agents and drugs • Infectious agents • Immunologic reactions • Genetic derangements • Nutritional imbalances: self-imposed

6. Principles of cell injury • Stimulus: type, duration, severity • Cell: type, state, adaptability • Cellular targets • cell membranes: integrity • mitochondria: aerobic respiration • cytoskeleton: protein synthesis • cellular DNA: genetic apparatus • Structural and biochemical elements

7. Molecular mechanisms (1) • ATP loss causes failure of biosynthesis and ion pumps: ‘cloudy swelling’ • Cytosolic free Ca is a potent destructive agents: activates intracellular enzymes and causes cell death • protein kinases: phosphorylation of protein • phospholipases: membrane damage • proteases: cytoskeletal disassembly

11. Molecular mechanisms (2) • Reactive oxygen metabolites (free radicals) damage cells: O(-), OH(-), H2O2 • peroxidation of lipids (cell memb.) • thiol-containing protein damage (ion pump) • DNA damage (protein synthesis) • mitochondrial damage (Ca influx) • Membrane and cytoskeletal damage • immune-mediated injury

13. Morphology of Reversible cell injury • Ultrastructural damage to mitochondria • Low-amplitude swelling • (High-amplitude swelling: irreversible) • Swelling of cellular organelles: hydropic degeneration/cloudy swelling • Fatty change: sublethal impairment of metabolism: liver

19. Morphology of Cell death • Lysis: Disintegration of cellular structure followed by dissolution • Necrosis: spectrum ofmorphologic changes that follow cell death in living tissue • Apoptosis: “programmed cell death”- elimination of unwanted host cells

20. Necrosis • Concurrent processes: • Enzymic digestion: lysis • autolysis: lysosomes of the dead cells • heterolysis: immigrant leukocytes • Denaturation of proteins • Intense eosinophilia • Nonspecific DNA breakdown • Pyknosis • Karyorhexis • Karyolysis

24. Patterns of Necrosis • Coagulative necrosis • Liquefactive necrosis • Caseous necrosis • Fat necrosis • Gangrenous necrosis • Fibrinoid necrosis

25. Coagulative necrosis • Dead tissue: firm and pale • Intact c.outlines and t.architecture • Intracellular acidosis denatures enzymes • Occlusion of arterial supply • Enzymes used in Dx of tissue damage • Myocardium: CK (MB isoform), AST, LDH • Hepatocytes: ALT • Striated muscle: CK (MM isoform) • Exocrine pancreas: amylase

27. Liquefactive necrosis • Semi-liquid viscous tissue • Potent hydrolytic enzymes • Examples • Hypoxic dead in the CNS: lysosomal enzymes of the neurons and the relative lack of extracellular structural protein • Bacterial infection: pus • neutrophil hydrolases: acute inflammation

29. Caseous necrosis • Soft and white: like cream cheese • Amorphous eosinophilic mass, loss of tissue architecture • Associated with granulomatous inflammation(reaction) in Tuberculosis

31. Fat necrosis • Hard yellow-gray material: fat tissue • Examples: • Retroperitoneal fat necrosis associated with acute of the pancreas • Traumatic fat necosis: breast, buttock

32. Gangrenous necosis • Mummified darkened and shrinkage • Coagulative necrosis only or modified by liquefactive necrosis • Dry gangrene: limb (lower leg/toe) • Wet gangrene: hollow viscera (GI tract) • hemorrhage within the tissue

34. Fibrinoid necrosis • Deposits of fibrin to the wall of necrotic vessels • Causes: • Vasculitis: autoimmune disease • Hypertension

36. ApoptosisSettings • During development • Homeostatic mechanism to maintain cell populations in tissue: involution • Defense mechanism e.g. immune reaction • Injury • viral infection • low doses of injurious stimuli • Aging

37. ApoptosisMechanisms • Signaling pathways • Transmembrane signals: hormone, cytokines • Intracellular signaling: heat, viral infection • Control and integration stage: adaptor proteins, Bcl-2, p53, granzyme B • Execution phase: endonuclease activation, catabolism of cytoskeleton • Removal of dead cells

43. ApoptosisBiochemical features • Protein Cleavages:cysteine proteases • caspases: • nuclear scaffold • cytoskeletal proteins • Protein cross-linking: transglutaminase • DNA breakdown: endonucleases • 50~300 kb and then 180~200 bp • Phagocytic recognition • phosphatidylserine

44. ApoptosisMorphology • Cell shrinkage • Chromatin condensation • Formation of cytoplasmic blebs and apoptotic bodies • Phagocytosis of apoptotic cells/bodies • Single cell or small clusters with intense eosinophilic cytoplasm and dense chromatin fragments