Cell Injury and Cell Death Lecture Notes PDF

Cell injury and Cell Death Dr. Phyu Synn Oo Senior Lecturer Pathology & Pharmacology Department SOM, IMU phyusynn...

Cell injury and Cell Death Dr. Phyu Synn Oo Senior Lecturer Pathology & Pharmacology Department SOM, IMU [email protected] Inspire Empower Elevate Lecture To describe different types of outcomes cellular injury To describe the morphologic alterations in cell injury and necrosis To describe the processes of apoptosis 2  Stages of the cellular response to stress and injurious stimuli 3 PSO, 2024 Causes of cell injury 1. Hypoxia (oxygen deficiency) and ischemia (reduced blood supply). No oxygen and no nutrition. Blockage of an artery, diseases of the lung, and anaemia. 2. Toxins. Air pollutants, insecticides, carbon monoxide, asbestos, cigarette smoke, ethanol, and drugs, therapeutic drugs 3. Infectious agents. Viruses, bacteria, fungi, and parasites 4. Immunologic reactions. Autoimmune reactions against one’s own tissues, allergic reactions against environmental substances, and excessive or chronic immune responses to microbes  inflammation  damage to cells and tissues. 5. Genetic abnormalities. Chromosomal abnormalities or mutations  congenital malformations (Down syndrome, sickle cell anaemia), accumulation of damaged DNA or misfolded proteins 6. Nutritional imbalances. Protein-calorie insufficiency, vitamin deficiencies, excessive dietary intake 7. Physical agents. Trauma, extremes of temperature, radiation, electric shock, and sudden changes in atmospheric pressure 4 Mechanisms of Cell Injury and Cell Death 1. ATP depletion 2. Permeabilization of cell membranes 3. Disruption of biochemical pathways (Protein synthesis) 4. DNA damage Although certain injurious agents can cause ATP depletion, membrane damage, pathway disruption, or DNA damage in isolation, more often there is interplay among these basic mechanisms. 5  Reversible cell injury Cell injury is classified as reversible if the injured cell can regain homeostasis and return to a morphologically (and functionally) normal state. Acute cell swelling is the classic morphologic change in reversible injury. 6 PSO, 2024 Sequence of Events in Reversible Cell Injury Damaging Stimulus Failure of energy-dependent ion pumps in the plasma membrane Inability to maintain ionic and fluid homeostasis Degenerated Taken water organelles/lipid Cells and intracellular organelles swollen 7  Morphology 1. Cellular swelling Whole organ - Pallor, increased turgor, and an increase in organ weight Microscopically - small, clear vacuoles within the cytoplasm  hydropic change or vacuolar degeneration. Normal kidney tubules Early (reversible) ischemic injury Surface blebs, increased eosinophilia of cytoplasm, and swelling of occasional cells 8 PSO, 2024  Morphology 2. Fatty change Triglyceride containing lipid vacuoles in cytoplasm Organs involved in lipid metabolism (liver) 9 Ref: https://webpath.med.utah.edu/ PSO, 2024  Morphology 3. Other intracellular changes 1. Eosinophilic cytoplasm (histology) 2. Plasma membrane alterations such as blebbing, blunting, or distortion of microvilli, and loosening of intercellular attachments; Normal epithelial cell 3. Mitochondrial changes such as swelling and the appearance of phospholipid-rich amorphous densities; 4. Dilation of the ER with detachment of ribosomes and dissociation of polysomes; 5. Nuclear alterations, such as clumping of chromatin. 6. Presence of myelin figures in cytoplasm. Loss of microvilli 10 Cytoplasmic blebs PSO, 2024 Swollen mitochondria Early cell injury  Reversible Cell The cellular response to injurious stimuli Injury and Cell depends on the type of injury and its duration and severity. Death The consequences of an injurious stimulus also depend on the type of cell and its metabolic state, adaptability, and genetic makeup. Cell injury usually results from functional and biochemical abnormalities in one or more essential cellular components 11 PSO, 2024  Necrosis (Accidental cell death) Severe disturbances, such as loss of oxygen and nutrient supply and the actions of toxins, trauma Rapid and uncontrollable form of death aka “accidental” cell death. Morphologic manifestation is necrosis (greek, necros = death). Inevitable end result of severe damage beyond what a cell can repair or survive. Host reaction/inflammation (+) 12 PSO, 2024  Apoptosis (Programmed cell death) Cell death without a host reaction/inflammation A precise set of molecular pathways is activated Relies on defined genes and biochemical pathways Regulated cell death/programmed cell death Pathologic situations - DNA or proteins are damaged beyond repair Physiological cell death - to eliminate unwanted cells during development and to maintain constant cell numbers. Necrosis is always an indication of a pathologic process, apoptosis also occurs in healthy tissues and is not necessarily associated with pathologic cell injury 13 PSO, 2024  The relationship of cellular function, cell death, and the morphologic changes of cell injury 14 PSO, 2024  Morphological Cytoplasmic changes changes in Increased eosinophilia Glassy, homogeneous appearance Necrosis Vacuolated cytoplasm - “moth-eaten.” Nuclear changes by breakdown of DNA and chromatin. Nuclear Nuclear Nuclear complete Shrinkage Fragmentation dissolution Fates of necrotic cells Digested by enzymes and disappear 15 Dystrophic calcification PSO, 2024  Ultrastructural features of reversible and irreversible cell injury (necrosis) Normal epithelial cell of the Early cell injury Late cell injury proximal kidney tubule Loss of microvilli Markedly swollen mitochondria Cytoplasmic blebs containing electron-dense deposits, Swollen mitochondria Disrupted plasma membrane Swelling and fragmentation of 16 organelles. PSO, 2024  Morphologic Patterns of 1. Coagulative necrosis Tissue Necrosis 2. Liquefactive necrosis 3. Gangrenous necrosis 4. Caseous necrosis 5. Fat necrosis 6. Fibrinoid necrosis 17 PSO, 2024  (1) Coagulative necrosis Causes – hypoxia, ischemia (except brain) or toxic injury Pathophysiology - the injury denatures both structural proteins and enzymes  limiting the proteolysis of the dead cells Most easily recognized in the liver, kidney, myocardium, or skeletal muscle, in which the temporary preservation of cell outlines and tissue architecture Morphology Underlying tissue architecture is preserved Affected tissues  a firm texture Eosinophilic, anucleate cells may persist for days or weeks Infarcts (areas of necrosis caused by ischemia) in all solid organs except the brain. 18 PSO, 2024  Coagulative necrosis. (A) A wedge-shaped kidney infarct (yellow) with distinct margins. (B) Microscopic view of the edge of the infarct, with normal kidney (N) and necrotic cells in the infarct (I). The necrotic cells show preserved outlines with loss of nuclei, and an inflammatory infiltrate is present (difficult to discern at this magnification). 19 PSO, 2024  Myocardial Infarction: Cardiac muscle fibers lost their nuclei & cytoplasmic organelles and wavy contraction bands across the fibers. 20 PSO, 2024  (2) Liquefactive necrosis Characterized by Liquefaction/softening of affected tissues Pathophysiology – microbes stimulate the accumulation of inflammatory cells and the enzymes of leukocytes digest (“liquefy”) the tissue Hypoxic death of cells within the central nervous system often causes liquefactive necrosis Morphology Dead cells are completely digested  transforming the tissue into a viscous liquid (eventually removed by phagocytes) Process is initiated by acute inflammation, as in a bacterial infection, the material is frequently creamy yellow and is called pus. A localized collection of pus is called an abscess 21 PSO, 2024  Liquefactive necrosis of brain following cerebral infarction Liver abscess 22  (3) Gangrenous Term used in clinical practice necrosis A form of coagulative necrosis used for specific sites Sites - lower limbs, appendix, gall bladder, intestines Combination of loss of blood supply and undergone coagulative necrosis involving multiple tissue layers  dry gangrene Superimposed bacterial infection  wet gangrene 23 PSO, 2024  Gangrenous necrosis of small intestine Wet Gangrene of the lower extremity Dry gangrene of toes 24 (4) Caseous necrosis Foci of tuberculous infection  hypersensitivity reaction to lipopolysaccharide in the cell wall of TB bacilli Caseous means “cheese-like,”  friable yellow-white appearance of the area of necrosis on gross examination Microscopically  a collection of fragmented or lysed cells with an amorphous granular pink appearance (often surrounded by a collection of macrophages and other inflammatory cells  called a granuloma) 25 Tuberculosis of the lung, with a large area of caseous necrosis containing yellow-white and cheesy debris. Multiple caseating granuloma 26 (5) Fat necrosis Focal areas of fat destruction Abdominal trauma or acute pancreatitis  enzymes leak out of damaged pancreatic acinar cells and ducts  digest peritoneal fat cells, including stored triglycerides  released fatty acids+ calcium  produce grossly identifiable chalky white lesions On histologic examination, shadowy outlines of necrotic fat cells surrounded by granular basophilic calcium deposits and an inflammatory reaction. 27  Fat necrosis in acute pancreatitis. The areas of white chalky deposits represent foci of fat necrosis with calcium soap formation (saponification) at sites of lipid breakdown in the mesentery. 28 PSO, 2024 (6) Fibrinoid necrosis Visible by light microscopy Immune reaction  complexes of antigens and antibodies deposited in the walls of blood vessels and in severe hypertension Deposited immune complexes and plasma proteins  leaked into the walls of injured vessels  produce a bright pink, amorphous appearance on H&E preparations called fibrinoid (fibrin-like) Morphology - thick walls with fragments of embedded cellular debris, serum, and fibrin E.g., Rheumatoid arthritis, Peptic ulcer disease, Immune vasculitis (e.g., polyarteritis nodosa), Vascular reactions, Preeclampsia, Hypertensive emergency, vasculitis and in transplanted organs undergoing rejection 29 Fibrinoid necrosis The vascular wall exhibits annular deposition of amorphous and proteinaceous material, and inflammatory infiltrates. These are the typical features of fibrinoid necrosis. 30 Apoptosis Pathway of cell death in which cells activate enzymes that degrade the cells’ own nuclear DNA and nuclear and cytoplasmic proteins “falling off”  fragments of the apoptotic cells Plasma membrane remains intact but is altered in such a way that the fragments, called apoptotic bodies  , are recognised and rapidly phagocytosed by macrophages Not elicit an inflammatory reaction in the host 31 Causes of Physiologic apoptosis. Apoptosis During the normal development of an organism Adult - to eliminate unwanted cells - highly proliferative and hormone-responsive tissues, immune system Apoptosis in pathologic conditions. Severe DNA damage, e.g., after exposure to radiation and cytotoxic drugs. Accumulation of misfolded proteins Infectious agents, particularly some viruses 32  Causes of apoptosis Condition Mechanism of Apoptosis During embryogenesis Loss of growth factor signaling Turnover of proliferative tissues (e.g., Loss of growth factor signaling intestinal epithelium, lymphocytes in bone marrow, and thymus) Physiologic Involution of hormone-dependent tissues Decreased hormone levels lead to reduced survival (e.g., endometrium) signals Decline of leukocyte numbers at the end of Loss of survival signals as stimulus for leukocyte activation immune and inflammatory responses is eliminated Elimination of potentially harmful self- Strong recognition of self-antigens induces apoptosis by reactive lymphocytes both the mitochondrial and death receptor pathways DNA damage Activation of proapoptotic proteins by BH3-only sensors Pathologic Accumulation of misfolded proteins Activation of proapoptotic proteins by BH3-only sensors, possibly direct activation of caspases Infections, especially certain viral Activation of the mitochondrial pathway by viral proteins infections Killing of infected cells by cytotoxic T lymphocytes, which PSO, 2024 activate caspases Mechanisms of apoptosis Anti-apoptotic: BCL2 Pro-apoptotic: BAX 34 Morphology of apoptotic cell Microscopically, Nuclei - chromatin condensation, aggregation, and karyorrhexis Cells shrink, cytoplasmic buds, and fragment into apoptotic bodies Apoptosis may be histologically undetectable. Round or oval mass of intensely eosinophilic cytoplasm with fragments of dense nuclear chromatin Fragmented nuclei with condensed chromatin and the shrunken cell bodies 35  Electron Micrograph of Cultured Cells Undergoing Apoptosis Some nuclei have peripheral crescents of compacted chromatin, and others are uniformly dense or fragmented. 36 PSO, 2024 The Sequential Ultrastructural Changes of Necrosis and Apoptosis A, In necrosis, leakage of cell contents through the ruptured plasma membrane into the extracellular matrix elicits inflammation. B, In apoptosis, cellular fragments are extruded as plasma membrane- bound apoptotic bodies that are recognized by phagocytes but do not cause inflammation. 3 7 A 56-year-old man dies 24 hours after the onset of substernal chest pain radiating down his left arm to ulnar aspect of his fingertips. Which morphologic findings is an indicator of irreversible injury? ⓘ Start presenting to display the poll results on this slide. PSO, 2024 Features of Necrosis and Apoptosis Feature Necrosis Apoptosis Cell size Enlarged (swelling) Reduced (shrinkage) Nucleus Pyknosis → karyorrhexis → Fragmentation into nucleosome-sized karyolysis fragments Plasma membrane Disrupted Intact; altered structure, especially orientation of lipids Cellular contents Enzymatic digestion; may leak Intact; may be released in apoptotic out of cell bodies Adjacent inflammation Frequent Absent Physiologic or Invariably pathologic Often physiologic; means of eliminating pathologic role (culmination of irreversible cell unnecessary cells; may be pathologic injury) after some forms of cell injury, especially DNA and protein damage 39 References Kumar V, Abbas AK, Aster JC, Deyrup AT, Das A (2023). ‘Chapter 1: Cell Injury, Cell Death and Adaptations,’ in Robbins & Kumar Basic Pathology, 11th ed. Philadelphia, Pennsylvania: Elsevier. Kumar V, Abbas AK, Aster JC. (2018). ‘Chapter 2: Cell Injury, Cell Death, and Adaptations,’ in Robbins Basic Pathology, 10th ed., Philadelphia, Pennsylvania: Elsevier. Pp.31-56. https://next.amboss.com/us/article/VP0GdT?q=cell%20death#Zb3483fa4a700b90a3cd8ccb27fb6b899 Miller MA, Zachary JF. Mechanisms and Morphology of Cellular Injury, Adaptation, and Death. Pathologic Basis of Veterinary Disease. 2017:2–43.e19. PSO, 2024 Thank you. [email protected] IMU Education Sdn Bhd No. 126, Jalan Jalil Perkasa 19 199201005893 (237397-W) Bukit Jalil, 57000 Kuala Lumpur, Malaysia 603 8656 7228 Formerly known as International Medical University. imu.edu.my