CELL INJURY.pptx 1 year registar oncology

cell injury, death and adaptation summary

1. CELL INJURY, CELL DEATH AND ADAPTATIONS MRO 1

2. additions differences between intrinsic n extrincic how its stimulated receptors involved caspaces involved specific for wch one examples of physiologic apoptosis i.e classify things comparison of necrosis n apoptosis

3. Discussion Reversible Cell Injury - Hydropic swelling - intracellular accumulations Irreversible cell injury - necrosis - apoptosis Cellular Adapation - atrophy -hypertrophy -metaplasia -hyperplasia -dysplasia

4. Cell injury cell injury results from a disruption of one or more of the cellular components that maintain cell viability injury at one point induces a cascade of effects cell injury maybe reversible, results in cell adaptation or lead to cell death there are 2 types of cell injury 1) reversible cell injury 2) irreversible cell injury

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6. causes of cell injury hypoxia physical chemical infectious immunologic reactions genetic defects nutritional imbalances radiation aging

7. Reversible cell injury This occurs in the early stages of injury or in mild forms of injury. functional and morphologic changes occur in cells. no membrane damage or nuclear dissolution. When the damaging stimulus is removed the functional and morphologic changes are reversible.

8. MORPHOLOGY OF CELL AND TISSUE INJURY All stresses and noxious influences exert their effects first at the molecular or biochemical level. Cellular function is lost first followed by cell death. morphologic changes appear much later after cell death. eg ischaemic heart disease Function is lost in 1-2mins Death occurs 20-30mins Morphologic changes seen after 2-3 hrs

9. . REVERSIBLE INJURY Is characterised by cellular swelling and fatty change. CELLULAR SWELLING Is the first manifestation of almost all forms of injury to cells It is due to failure of energy dependant ion pumps in the plasma membrane. There is loss of ability to maintain ionic and fluid homeostasis. When it affects many cells in an organ it causes pallor (compression of capillaries), increased tugor and an increase in the weight of an organ. There are clear vacuoles in the cytoplasm. (pinched off segments from the ER

10. Reversible- hydropic swelling

11. FATTY CHANGE Seen in cells participating in fat metabolism eg liver myocardium Lipid vacuoles appear in the cytoplasm It is reversible

12. phenomena of cell injury irreversibility inability to restore mitochondrial function loss of structure and function of plasma membrane and intracellular membranes loss of DNA and chromatin integrity

13. Irreversible cell injury- Cell death Occurs with continuing damage to cells. The injury becomes irreversible The cell cannot recover and dies two types of cell death 1)necrosis 2)apoptosis

14. Necrosis -cell death characterised by a breakdown of cell membranes and unregulated digestion of cell components and cellular enzymes leak out and ultimately digest the cell. - release of cellular components often triggers an inflammatory response and further tissue damage. - enzymes for digestion come from lysosomes of dying cells themselves or from leucocytes recruited as part of inflammatory reactions -commonly encounted injuries include ischaemia, infections, trauma, toxins.

15. . Morphology of necrotic cells Necrosis is characterised by changes in the cytoplasm and nuclei of injured cells. Cytoplasmic changes Increased eosinophilia compared with normal cells Cells have glassy homogenous appearance due to loss of glycogen particles Myelin figures more prominent in necrotic cells than during reversible injury. Cytoplasm vacuolated or moth eaten due to digestion of cytoplasmic organelles Discontinuities in plasma and organelle membranes Dilatation of mitochondria. Disruption of lysosomes

16. . Nuclear changes Nuclear changes assume one of three patterns all due to breakdown of DNA and chromatin. karyolysis - basophilia of the chromatin fades due to deoxyribonuclease activity. Pyknosis - nuclear shrinkage and basophilia Karryorrhexis - fragmentation of pyknotic nucleus . In 1 or 2 days the nucleus in a dead cell may completely disappear. FATE OF NECROTIC CELLS May persist for some time. May be digested by enzymes and disappear. Dead cells may be replaced by myelin figures . Myelin figures are phagocytosed or degraded to fatty acids Fatty acids bind calcium resulting in calcification of dead cells.

17. . As a result of cell death tissues or organs display certain macroscopic changes 1) coagulative necrosis solid organs except brain, affected tissue takes a firm texture and is preserved for several days due to protein denaturation mainly due to hypoxia 2) Liquifactive necrosis digestion of dead cells to a viscous liquid mass due to bacterial, fungal infections Inflammatory cells and enzymes digest or liquify the tissue forming a liquid viscous mass. hypoxic infarcts in brain present as this type of necrosis 3) Caseous necrosis combination of coagulative and liquefactive necrosis caused by TB, fungi necrotic tissue is like clumped cheese Cellular outlines cannot be discerned. The area of caseous necrosis is often enclosed within a distinctive inflammatory border

18. . 4) fat necrosis fat tissue result from action of activated lipases on fatty tissues e.g pancrease, breast calcium, sodium- may bind to these to produce a chalky white substance 5) gangrenous necrosis coagulative necrosis from multiple layers, due to ishaemia of lower limbs and GIT wet - when there is bacterial infection superimposed on coagulative necrosis. 6) fribrinoid caused by immune mediated vascular damage complexes of antigen and antibodies- immune complexes within aterial wall together with fibrin Immune complexes together with fibrin produce a bright pink and armorphous complex called fibrinoid .

19. Apoptosis Apoptosis or p rogrammed c ell d eath ( PCD ) is a mode of cell death that occurs under normal physiological conditions and the cell is an active participant in its own demise (“cellular suicide ”). It is important for the development of multicellular organism (embryonic development ) and homeostasis of their tissues (adult ).

20. importance of apoptosis Apoptosis is a beneficial and important phenomenon: Normal cell turn over Tissue homeostasis Induction and maintenance of immune tolerance Development of the nervous system Endocrine-dependent tissue atrophy Elimination of activated, damaged and abnormal cells Embryogenisis

21. Excess apoptosis Neurodegenerative diseases Deficient apoptosis Cancer Autoimmun e diseases

22. Major inducers of apoptosis irreparable DNA damage cell cycle perturbation aberrations in cell metabolism growth factor withdrawal death ligands activation calcium influx free radicals infections radiation chemotherapy

23. Mechanism of apoptosis Extrinsic pathway (d eath receptor- mediated events) Intrinsic pathway (mitochondria- mediated events)

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25. Caspases Caspases stands for c ysteine asp artate -specific prote ase . so named because the cleave proteins after aspartic acid residue Synthesized in the cell as precursors named procaspase which are inactive proenzymes (zymogen) with 32-56 kDa Caspases are the major executioners in apoptosis and activity is irreversible, once activated commits cell to death At least 14 different members of caspases in mammalian cells have been identified

26. Caspase structure

27. Caspase subgroups To date, ten major caspases have been identified and broadly categorized into:  Signaling or Initiator caspases ( 2, 8, 9, 10)  Effector or Executioner caspases ( 3, 6, 7 )  Inflammatory caspases ( 1, 4, 5) The other caspases that have been identified include: Caspases 11 , 12, 13, 14 Central role in cascade of apoptotic events is played by caspase 3 (CPP32

28. Caspase role in apoptosis Cut off contact with surrounding cells Reorganize cytoskeleton inhibit DNA replication and repair Interrupt splicing activate degrading enzymes DN ases- cleave DNA in nucleus Disrupt nuclear structure Induce cell to display signals marking it for phagocytosis (translocation of phosphatidyl serine from inside the cell to outer surface) Disintegrate cells into apoptotic bodies

29. Intrinsic pathway i nduced by intracellular signals such as oxidative stress, radiation (DNA damage), absence of certain growth factors, hypoxia, viral infections this will cause increase mitochondrial outer membrane permeabili ty Release of pro-apoptotic proteins such as cytochrome c, Smac /DIABLO, AIF, endonuclease G and CAD from the inter-membrane space into the cyt oplasm Cytochrome c binds and activates Apaf-1 forming apoptosome apoptosome activates procaspase 9 to caspase 9 Caspase-9 activation - subsequent caspase-3 activation and cell death. Smac/DIABLO promote caspase activation by binding to inhibitors of apoptosis protein (IAP) which subsequently lead to disruption in the interaction of IAPs with caspase 3 or 9

30. The control & regulation of apoptotic mitochondrial events occurs through members of the Bcl-2 family of proteins  Anti-apoptotic proteins include Bcl-2, Bcl -x, Bcl -XL, Bcl -w  P ro-apoptotic proteins include Bax , Bak , Bid, Bad, Bim , Bik T he main mechanism of action of the Bcl-2 family of proteins is to release apoptotic signaling factors from mitochondria through mitondria outer membrane permeabilization

31. Regulation of intrinsic pathway in healthy cells the Bcl-2 protein maintain integrity of cell membrane in response to growth factors and other stimuli by holding the proapoptotic members of the family, Bak and Bax in check. when cells are deprived of growth factor signals or exposed to agents that damage DNA, sensors called BH3 are activated and shift balance in favour of proapoptotic Bak and Bax Bak and Bax dimerise and insert into the mitochondrial membrane and form channels through which cytochrome C enters cytoplasm.

32. when balance of proapoptotic and antiapoptotic members of the Bcl2 family is desrupted it results in deregulated apoptosis in resulting cells can be due to an overexpression of antiapoptotic proteins or an underexpression of proapoptotic proteins or both e.g in chronic lymphocytic leukaemia BCL-2 is overexpressed preventing cells from undergoing apoptosis, allowing them to survive and accumulate.

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34. Extrinsic pathway many cells express death receptors that trigger apoptosis extrinsic pathway is activated by etracellular ligands binding to cell surface death receptors “Death receptors” that are members of the tumor necrosis factor (TNF) receptor superfamily. Death receptors have a cytoplasmic domain of about 80 amino acids called the “death domain ”. This death domain plays a critical role in transmitting the death signal from the cell surface to the intracellular signaling pathways.

35. . prototypic death receptors are TNF receptor 1 and Fas (CD95) their respective ligands are TNF and Fas ligand death receptors have an intracellular domain that recruits adaptor proteins such as TNF associated death domain (TRADD) or Fas associated death domain (FADD) binding of death ligand to death receptor results in formation of an adaptor protein and the whole ligand receptor- adaptor protein complex forms the DISC (death inducing signalling complex) DISC initiates assembly and activates procaspase-8 active caspase 8 then processes downstream effector caspases which subsequently cleaves specific substrates resulting in cell death

36. known associated receptors & ligands corresponding death include: Receptor Ligand FasR (CD95/APO1 ) FasL DR3 Apo3L DR4 (TRAIL-R1 ) Apo2L DR5 ( TRAIL-R2 ) Apo2L TNFR1 TNF- α TNFR2 TNF-ß

37. - Binding of trimeric FasL to Fas - Trimerization and clustering of Fas - Recruitment of Fas-associated death domain (FADD) to Fas - Formation of Death-Inducing Signaling Complex (DISC ) - Activation of caspase-8 (autoactivation ) - Activation of effector caspases - Apoptosis

38. e.g T lymphocytes express Fas ligand (Fas L) when these T cells recognise Fas expressing targets, Fas molecules are crosslinked by FasL and bind adaptor proteins via death domain the leads to recruitment and activation of caspase 8 which in turn activates downstream caspases involved in elimination of self reactive lymphocytes and in killing of target cells by some cytotoxic T lymphocyte that express FasL

39. Intrinsic endoplasm reticular pathway ER is for synthesis and folding of different types of proteins its an important sensor of cellular stress that can withold protein synthesis and metabolism to restore cellular homeostasis When cells are in rest, the pro-apoptotic Bax and Bak (Bax/Bak) remain inactive by interaction with BCL2 both on the mitochondrial as well as endoplasmic reticulum (ER) membranes, whereas Bim (BH3) is inhibited by binding to cytoskeleta l dynein of microtubules. Severe ER stress leads to activation of c-Jun N-terminal kinase (JNK) and induction of C/EBP homologous protein (CHOP) in the initiation phase Anti-apoptotic effect of BCL2 is eliminated by both JNK and CHOP Bim is phosphorylated by JNK and is released from the cytoskeleton and become s activated . Together, all these changes allow activation of Bax and Bak, transmission of the signal from the ER to the mitochondria leading to death. It has been proposed that Caspase 12 is a key mediator of ER stress-induced apoptosis

40. Inhibitors of apoptosis Apoptosis, cytokinesis and signal transduction are regulated by a group of structurally and functionally similar proteins which are the inhibitors of apoptosis IAPs are endogenous inhibitors of caspases and by binding their conserved BIR domains to the active sites of caspases, they can inhibit caspase activity by promoting degradation of active caspases or by keeping the caspases away from their substrates. To date eight IAPs have been identified, named as, NAIP (BIRC1), c-IAP1 (BIRC2), c-IAP2 (BIRC3), X-linked IAP (XIAP, BIRC4), Survivin (BIRC5), Apollon (BRUCE, BIRC6), Livin/ML-IAP (BIRC7) and IAP-like protein 2 (BIRC8)

41. other pathways of cell death necroptosis- features of apoptosis and necrosis - initiated by engagement of TNF receptos - receptor interacting protein kinases are activated - results in dissolution of the cell like in necrosis - said to be associated in inflammatory reactions where TNF is produced pyroptosis- activation of cytosolic danger sensing protein complex called inflammasome -results in activation of caspases, so of which cause production of cytokines which result in inflammation and others trigger apoptosis -

42. Autophagy self eating in nutrient deprivation starved cell can survive by eating its own contents and recycling to provide nutrients and energy intracellular organelles and cytosol are sequestered within an ER-derived autophagic vacuole, vacuole fuses with lysosome to form autophagolysosome and the lysosomal enzymes digest cellular components. form of adaptation that helps cells survive lean times if cell is starved for longer , autophagy may eventually lead to apoptotic cell death

43. Mechanism of cell injury- oxidative stress induced by ROS- free radicals free radical mediated cell injury is seen in radiation injury, hypoxia, chemical injury cell death maybe due to necrosis, apoptosis or necroptosis Free radicals are chemical species with a single unpaired electron in an outer orbit. Such chemical states are extremely unstable, and free radicals readily react with inorganic and organic molecules when generated in cells, they avidly attack nucleic acids as well as a variety of cellular proteins and lipids

44. . L ipids - Double bonds in membrane polyunsaturated lipids are vulnerable to attack by oxygen-derived free radicals. - The lipid–radical interactions yield peroxides, which are themselves unstable and reactive, and an autocatalytic chain reaction ensues. - Damage to plasma membranes as well as mitochondrialand lysosomal membranes DNA damage - ROS react with thiamine in DNA –single strand breaks. Protein crosslinking - sulfhydryl-mediated protein crosslinking resulting in enhanced degradation or loss of enzymatic activity. - Free radical reactions also may directly cause polypeptide fragmentation. - Damaged proteins may fail to fold properly and trigger apoptosis

45. mechanism of cell injury- DNA damage exposure of cells to radiation, chemotherapy agents and intracellular ROS may induce DNA damage ATM is activated in response to DNA damage which leads to accumulation of p53 protein. p53 will arrest cell cycle at G1 phase to allow DNA repair by causing transcription of p21 which will inhibit cycline/CDK complex and prevent phosphorylation of Rb protein it also induces expression of DNA damage repair genesif DNA damage is too great to be repaired successfully, p53 will trigger apoptosis mainly by stimulating BH3 only sensor protein and ultimately activate Bax,Bak proapoptotic memebers of Bcl2 family

46. Cellular adaptation reversible changes in number, size, phenotype, metabolic activity or function of cells in response to change in environment physiologic- response of cells to normal stimulation by hormones or endogenous chemical mediators e.g breastenlargement during pregnancy pathological- response to stress and allow cells to modulate their structure and function and thus escape injury

47. . hypertrophy- an increase in size of cells resulting in an increase in size of organ (e.g uterus, heart-htn) hyperplasia- increase in the number of cells from increased proliferation of differentiated cells or less differentiated progenitor cells (breast, prostate) Atrophy- shrinkage in size of cell by loss of cell substance, results in diminished function of cell but not death. Metaplasia-one adult cell type is replaced by by another adult cell type e.g cilliated columnar cells of trachea and bronchi replaced by stratified squamous epithelial cells. dysplasia- abnormal cell growth, development, or maturation in a tissue or organ

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