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Advances in apoptotic pathways

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  • 1. ADVANCES IN APOPTOTIC PATHWAYS
    • Dr. Pooja Malhotra
    • MODERATOR
    • Dr. Nalini Gupta
  • 2. APOPTOSIS
    • Named after greek designation for “FALLING OFF”
    • Pathway of cell death induced by a tightly regulated intracellular program in which cells destined to die activate enzymes that degrade the cells own nuclear DNA and nuclear and cytoplasmic proteins.
    • Programmed cell death.
  • 3. APOPTOSIS
    • Evolutionarily conserved
    • Occurs in all animals & plants too!
    • Stages and genes conserved from nematodes
    • and flies to humans
  • 4. Physiologic or pathologic Invariably pathologic Physiologic or pathologic Intact released into apoptotic bodies Enzymatic digestion,leak out Cellular contents no frequent Adjacent inflammation Intact,altered structure disrupted Plasma membrane Fragmentation into nuleosome fragments pkynosis ,karyorhexis,karyolysis Nucleus Reduced (shrinkage) Enlarged swelling) Cell size Apoptosis Necrosis Features
  • 5.  
  • 6. MORPHOLOGY
    • Cell shrinkage.
    • Chromatin condensation- Most characteristic feature
    • .Formation of Cytoplasmic blebs and apoptotic bodies.
    • Phagocytosis of apoptotic cells or cell bodies by macrophages.
    • PLASMA MEMBRANCES REMAIN INTACT DURING APOPTOSIS UNTIL THE LAST STAGES.
    • Apoptosis doesn’t ilicit inflammation.
  • 7.  
  • 8.  
  • 9. BIOCHEMICAL FEATURES
    • Protein cleavage.
    • DNA Breakdown.
    • DNA ladders on Agarose gel electrophoresis.
    • DNA smearing on Agarose gel electrophoresis.(necrosis)
    • Phagocytic recognition - Expression of phosphatidyl serine,thrombospondin on outer layer of Plasma membranes.Facilitates recognition by AnnexinV.
  • 10.  
  • 11.  
  • 12. APOPTOSIS IN PHYSIOLOGIC SITUATIONS
    • Programmed destruction of cells during embryogenesis.
    • Hormone dependent involution in adults.
    • Cell deletion in proliferating cell population.
    • Cell Death of host cells that have outlived their usefulness.
    • Elimination of potentially harmful self reactive lymphocytes.
    • Cell death induced by cytotoxic Tcells as defence against viruses,tumours etc.
  • 13. APOPTOSIS: important in embryogenesis Morphogenesis (eliminates excess cells): Selection (eliminates non-functional cells):
  • 14. APOPTOSIS: important in embryogenesis Immunity (eliminates dangerous cells): Self antigen recognizing cell Organ size (eliminates excess cells):
  • 15. APOPTOSIS: important in adults Tissue remodeling (eliminates cells no longer needed): Virgin mammary gland Late pregnancy, lactation Involution (non-pregnant, non-lactating) Apoptosis Apoptosis - Testosterone Prostate gland
  • 16. APOPTOSIS: important in adults Tissue remodeling (eliminates cells no longer needed): Resting lymphocytes + antigen (e.g. infection) - antigen (e.g. recovery) Apoptosis Steroids, immunosuppressants: kill lymphocytes by apoptosis Lymphocytes poised to die by triggering apoptosis
  • 17. APOPTOSIS: important in adults Maintains organ size and function : Apoptosis + cell division Cells lost by apoptosis are replaced by cell division
  • 18. APOPTOSIS IN PATHOLOGIC SITUATIONS
    • Cell death by injurious stimuli-radiation,anticancer drugs,heat hypoxia
    • Cell injury in viral diseases-viral hepatitis
    • Pathologic atrophy of parenchymal organs after duct obstruction
    • Cell death in tumours
  • 19. MECHANISMS OF APOPTOSIS
    • Cascade of Molecular Events
    • Iniated by diverse ways
    • Culminate in activation of caspases
    • 2 phases: iniation phase
    • execution phase
  • 20. STAGES OF APOPTOSIS Healthy cell DEATH SIGNAL Commitment to die (reversible) EXECUTION (irreversible) Dead cell (condensed, crosslinked) ENGULFMENT DEGRADATION
  • 21. STAGES OF APOPTOSIS Genetically controlled: Caenorhabditis elegans Soil nematode (worm) Healthy cell Dead cell Committed cell ces2 ces1 ced9 ced3,4 BCL2 Caspases C. Elegans genes == mammalian genes
  • 22. CASPASES : ENEMIES WITHIN
    • Cysteine dependent aspartate specific proteases
    • CYSTEINE ASPARTYL SPECIFIC PROTEASES
    • “ CENTRAL EXECUTIONER OF CELL DEATH”
  • 23. STRUCTURE OF CASPASES
    • Present as inactive zymogens
    • 2 DOMAINS:
    • NH2 Terminal domain(20 KD),LARGE SUBUNIT
    • SMALL SUBUNIT(10 KD)
    • Activation :proteolytic processing between the domains and association of large and small subunits to form heterodimer
    • Two heterodimers associate to form hetrotetramer
  • 24.  
  • 25.
    • Absolute requirement for cleavage after ASPARTIC ACID
    • Caspases recognize the Asp residues they cleave within the context of tetrapeptide motifs
    • The preferred tetrapeptide motifs differ among caspases explaining their diversity in biological functions
    • Most proximal (N- terminal)residue –P4 ,Asp-P1 ,cleavage occurs at peptidyl bond distal to targeted Asp.
  • 26. CASPASES
    • 14 CASPASES identified in humans
    • INITIATOR CASPASES/UPSTREAM CASPASES - 8,9,12;have large N terminal prodomains to enable interaction with other proteins to trigger caspase activation
    • EXECUTIONER CASPASES/ DOWNSTREAM CASPASES - 3,7; have short N terminal prodomains
    • Caspases 1,4&5 :not involved in apoptosis but in processing of pro inflammatory cytokines
  • 27. Substrates of effector caspases
    • Protein kinases
    • Signal transduction proteins
    • Cytoskeletal &nuclear matrix proteins
    • Chromatin modifying(poly ADP ribosyl polymerase)
    • DNA repair proteins
    • Inhibitory subunits of endonuclease(CIDE family proteins)
  • 28.
    • Induction of apoptosis :
    • • E xtrinsic or Cell surface death receptor mediated pathway
    • • Mitochondrial-initiated pathway (intrinsic)
    • Endoplasmic reticulum(intrinsic)
  • 29.  
  • 30. PROTEIN DOMAINS ASSOCIATED WITH APOPTOSIS REGULATION
    • CASPASE(catalytic domain)
    • DEATH DOMAINS(DD)
    • DEATH EFFECTOR DOMAINS(DED)
    • CASPASE Associated recruitement domains(CARD)
    • BIR (IAP)
    • Bcl-2 homology(BH) Domains
  • 31. CASPASE ACTIVATION MECHANISMS
  • 32. Death Domain proteins Death receptor:signalling and modulators
    • Death receptors detect the presence of extracellular death signals and in response ignite the cells intrinsic apoptosis machinery
    • Belong to TNF receptor gene super family
  • 33.
    • Structure:
    • Cysteine rich extracellular domain
    • Homologous cytoplasmic domain “DEATH DOMAIN (DD)”consisting of compact bundles of six alpha helices
  • 34. DEATH RECEPTORS
    • CD95(Fas or Apo1) - CD95L
    • TNFR1(p55 or CD 120a) – TNF,lymphotoxin
    • DR3(Apo3) - Apo3L(TWEAK)
    • DR4 - TRAIL R1
    • DR5(Apo2 ) - Apo2L(TRAILR2)
  • 35.  
  • 36.  
  • 37. APOPTOSIS: control Receptor pathway (physiological): Death receptors: (FAS, TNF-R, etc) FAS ligand TNF Death domains Adaptor proteins Pro-caspase 8 (inactive) Caspase 8 (active) Pro-execution caspase (inactive) Execution caspase (active) Death MITOCHONDRIA
  • 38. ROLE OF CD95-CD95L INTERACTION
    • Peripheral deletion of activated T cells at end of immune response
    • Killing of targets as viral infected cells or cancer cells by cytotoxic T cells&NK cells
    • Killing of inflammatory cells at immune priviliged sites
  • 39. DD NOT ALWAYS INVOLVED IN APOPTOSIS INDUCTION
    • Some non caspase activating DD proteins indirectly regulate apoptosis through effects on NFĸB
    • RIP proteins bind Tradd & activate kinases to cause degradation of IĸB releasing NFĸB to act as transcription factor
    • NFĸB inducible genes include genes for pro inflammatory cytokines ,inhibitors of apoptosis(Bcl-2,IAP members)
  • 40.
    • TNFR1,DR3,DR6 :capable of activating both NFĸB &apoptosis through FADD and Tradd
    • DR4 &DR5: contain only Fadd but not Tradd,hence no activation of NFĸB,no pro inflammatory response& function as effective inducers of apoptosis
    • TRAIL ligand (binds to DR4) is under consideration for clinical use in treatment of cancer
  • 41.  
  • 42. ROLE OF MITOCHONDRIA IN APOPTOSIS
    • Mechanisms for release of mitochondrial factor:
    • Damage to mitochondrial membrane
    • Change in membrane potential
    • Altered p53
  • 43. ROLE OF MITOCHONDRIA IN APOPTOSIS
    • CASPASE DEPENDENT PATHWAYS:
    • Smac/Diablo
    • Cytochrome c
    • CASPASE INDEPENDENT PATHWAYS:
    • Apoptosis inducing factor
    • Endonuclease G
  • 44.  
  • 45.  
  • 46. ENDOPLASMIC RETICULUM AND APOPTOSIS
    • ER stress:
    • Misfolded proteins,Ca 2+ imbalance,loss of oxidizing environment,hypoxia/ischemia
    • Apoptosis
    • (Ca 2+ release,trancription regulated,caspase activation)
    • Caspase 12 knockout mice shown to be resistant to apoptosis induced by amyloid Aß peptide (alzheimers disease)
  • 47.  
  • 48. Inhibitors of apoptosis
    • Bcl-2 family of proteins
    • Inhibitors of apoptosis(IAP)
  • 49. Cells are balanced between life and death DAMAGE Physiological death signals DEATH SIGNAL PROAPOPTOTIC PROTEINS ANTIAPOPTOTIC PROTEINS
  • 50. Bcl-2 Family proteins
    • Mitochondrial pathway of apoptosis governed by Bcl-2 family proteins
    • Mediate cross talk between intrinsic and extrinsic pathways
    • Bcl-2 family proteins conserved throughout metazoan evolution
    • Both pro and anti apoptotic proteins are present
    • 20 members of Bcl-2 family gene have been described till date
  • 51. APOPTOSIS: control Intrinsic pathway (damage): Mitochondria Cytochrome c release Pro-caspase 9 cleavage Pro-execution caspase (3) cleavage Caspase (3) cleavage of cellular proteins, Nuclease activation, Etc. Death BAX BAK BOK BCL-Xs BAD BID B IK BIM NIP3 BNIP3 BCL-2 BCL-XL BCL-W MCL1 BFL1 DIVA NR-13 Several viral proteins Pro apoptotic Anti apoptotic
  • 52. Bcl-2 Family proteins
    • Bcl-2 Family proteins divided into 2 groups
    • α helical pore/channel like proteins(Bcl-2, Bcl-XL,Mcl-1,Boo,Bax, Bak, Bid)
    • Have conserved stretches of amino acid sequence homology-BH1,BH2,BH3
    • Form ion conducting channels in synthetic membranes in vitro
  • 53.
    • Second subset have only BH3 domain in common
    • Include Bad, Bim,Bik, Hrk, APR
    • All are proapoptotic
    • Induce cell death by dimerizing with antiapoptotic Bcl-2 family members and functioning as dominant negative inhibitors of Bcl-2,Bcl- XL
    • Mutations in BH3 domains abolishes their ability to bind Bcl-2 & hence abrogates their ability to induce apoptosis,
  • 54.  
  • 55.  
  • 56.  
  • 57. Cross talk between apoptotic pathways
  • 58.  
  • 59.
    • Bcl-2 regulate release of cytochrome c from mitochondria
    • Control release of some caspases(2,3,9)sequestred in some of the cells
    • Release of apoptosis inducing factor(AIF)
    • Release of Smac/Diablo(inhibitor of IAP family proteins)
  • 60.  
  • 61. Role of Bcl-2 proteins in disease
    • Bax is increased in apoptosing neurons in alzheimers disease
    • Bax expression is induced in neurons after ischemia reperfusion injury
    • Loss of function mutations noted in human tumors
    • Bcl-2Translocations noted in lymphomas(follicular,HD,etc); overexpression is noted in solid tumoursleading to resistance to chemotherapy and radiation therapy induced apoptosis
  • 62. IAP FAMILY PROTEINS
    • Family of evolutionary conserved apoptotic supressors
    • All members have at least one copy of so called Bir (baculo virus iap repeat)domain required for their antiapoptotic activity
    • 7 members identified so far
    • NAIP,c-IAP1,c-IAP2,Survivin,livin,apollon,XIAP
    • Bind to and inhibit caspase 3,7( BIR domains BIR1&BIR2)&9(BIR 3)
    • XIAP, c-IAP1,c-IAP2 are inhibitors of iniator caspase9 as well as effector caspases 3 &7
  • 63.  
  • 64. IAP PROTEINS AND DISEASE
    • Inactivating mutations of NAIP described in Spinal muscular atrophy (a motor neuron degenerative disorder)
    • Overexpression of Survivin seen in many cancers
  • 65. Smac/Diablo and IAP
    • Smac/Diablo binds IAP members- XIAP,Ciap1,Ciap2,survivin and allows apoptosis to occur
    • Smac/Diablo encoded by nuclear genome ,transported into mitochondria and stored in the space between inner & outer membranes
    • Disruption of mitochondrial membrane barrier function leads to activation of these proteins
  • 66.  
  • 67. FLIP PROTEINS
    • Belongs to family of proteins containg DED
    • In contrast to other members(FLASH)which enhance apoptosis it supresses caspase 8 activation by Fas & other death receptors
    • FLIP shares sequence homology with procaspase 8 & 10,has a pseudocaspase domain lacking critical regions for protease activity
    • Associates with pro caspase 8 as well as competes with it for binding to Fadd ;thus downregulating apoptosis
    • Decreased expression of FLIP noted in MI
  • 68.  
  • 69. NITRIC OXIDE IN APOPTOSIS
    • Possesses both pro &anti apoptotic activity
    • Proapoptotic activity:caspase activation,ability to induce oxidative stress
    • Antiapoptotic activity: FLIP regulation
    • NO negatively regulates Fas CD95 induced apoptosis through inhibition of Ubiquitin Proteasome mediated degradation of FLICE inhibitory protein
  • 70. APOPTOSIS: Role in Disease Neurodegeneration PARKINSON'S DISEASE ALZHEIMER'S DISEASE HUNTINGTON'S DISEASE STROKE
  • 71. STROKE DAMAGED NEURONS MAY COMMIT CELLULAR SUICIDE
    • Recent evidence suggests that neurons die from apoptosis and not necrosis in oxygen deprived brains as occurring during stroke,during perinatal period
    • CASPASE INHIBITORS may be the potential new drugs for stroke
  • 72. G CSF POTENTIAL NEW DRUG FOR STROKE AND NEURODEGENERATIVE DISORDERS
    • Potent hematopietic factor
    • Shows strong antiapoptotic activity in mature neurons
    • G- CSF and its receptor expression increased in ischemia
    • Activates multiple cell survival pathways
  • 73. IS APOPTOSIS THE KEY IN ALZHEIMERS DISEASE?
    • Neurons display characteristic signs of apoptosis such as DNA breaks
    • Apoptosis in alzheimers is induced by Aß protein
    • MUTANT PRESENILINS CONTRIBUTE TO DISEASE BY FURTHER RAISING Aß LEVELS
    • Presenilin mutatins increase neuronal vulnerability to apoptosis
  • 74.  
  • 75.  
  • 76. APOPTOSIS: Role in Disease Cancer Apoptosis eliminates damaged cells (damage => mutations => cancer Tumor suppressor p53 controls senescence and apoptosis responses to damage Most cancer cells defective in apoptotic response High levels of anti-apoptotic proteins or Low levels of pro-apoptotic proteins ===> CANCER
  • 77. APOPTOSIS AND HIV
  • 78. APOPTOSIS AND HIV
    • All T cells express Fas
    • Expression of a HIV gene(nef) causes infected T Cells to express high levels of FasL
    • When infected T cells encounter uninfected one, interaction of FasL with Fas on uninfected cells leads to death by apoptosis
  • 79.  
  • 80. DETECTION OF APOPTOSIS IN TUMOUR PARAFFIN SECTIONS
    • Based on morphology
    • Detection of DNA Fragmentation:TUNEL (terminal deoxynucleotidyl transferase mediated dUTP nick end labelling)method
    • IHC:Detection of cleaved caspase 3:
    • Highly specific marker for apoptosis
    • Can be used as a discriminating criterion to distinguish apoptosis from necrosis
  • 81.
    • IHC DETERMINATION OF CASPASE CLEAVED TARGET PROTEINS
    • Detection of cleaved cytokeratin 18:M30 antibody,precedes TUNEL positivity,represents early event,lost in late stages of c
    • caspase mediatedcleavage of actin fragments recog by FRACTIN
    • FRACTIN stains apoptotic bodies indicating late event
    • PARP(poly ADP ribose polymerase) :one of the earliest nuclear protein cleaved by caspasesinto 89 &24kD fragments ,detects early apoptosis
  • 82. Thank you!