Chết tế bào có chương trình TS.BS. Đoàn Thị Kim Phượng phuongdk75@gmail.com Chết tế bào do tổn thương - Tổn thương cơ học - Phơi nhiễm với chất độc hại Chết tế bào tự nguyện - Các tín hiệu nội sinh - Các tín hiệu ngoại sinh Chết tb có chương trình liên quan chặt chẽ tới sự phân hủy protein, đứt gẫy ADN của tế bào. Sau đó các sản phẩm này đc các tế bào khác nhanh chóng thực bào. Là một phần cần thiết trong cuộc sống của mọi sinh vật đa bào Đóng vai trò chính từ khi phát triển phôi cho đến khi chết. Apoptosis cần cho sự phát triển phôi thai – Đứt đuôi nòng nọc – Sự hình thành cấu tạo các ngón chân, ngón tay của thai nhi Apoptosis cần để phá hủy tế bào Examples: – Tế bào bị nhiễm vius – Tế bào của hệ thống miễn dịch – Tế bào có ADN tổn thương – Tế bào ung thư Chết TB có chương trình vs. Chết TB tổn thương Chết TB tổn thương • • • • TB sưng to Vỡ màng ATP bị suy yếu TB ly giải, đáp ứng với phản Ứng viêm • DNA đứt gẫy ngẫu nhiên hoặc nhòe • Trong cơ thể, toàn bộ vùng mô bị ảnh hưởng Chết Tb có chương trình • • • • TB kết đặc Màng còn nguyên vẹn Yêu cầu ATP Tb bị thực bào, không có phản ứng mô • DNA đứt gẫy từng vạch • Trong cơ thể, các tb đơn lẻ bị ảnh hưởng NECROSIS Vs APOPTOSIS Wilde, 1999 STAGES OF APOPTOSIS Induction of apoptosis related genes, signal transduction Sherman et al., 1997 APOPTOSIS: Morphology organelle membrane blebbing & changes reduction cell mitochondrial leakage shrinkage nuclear fragmentation chromatin condensation Hacker., 2000 APOPTOSIS: Morphological events cell shrinkage organelle reduction mitochondrial leakage chromatin condensation nuclear fragmentation membrane blebbing & changes Blebbing & Apoptotic bodies Bleb The control retained over the cell membrane & cytoskeleton allows intact pieces of the cell to separate for recognition & phagocytosis by MFs Apoptotic body MF MF What makes a cell decide to commit suicide? Withdrawal of positive signals examples : – growth factors for neurons – Interleukin-2 (IL-2) Receipt of negative signals examples : – increased levels of oxidants within the cell – damage to DNA by oxidants – death activators : • Tumor necrosis factor alpha (TNF-) • Lymphotoxin (TNF-β) • Fas ligand (FasL) Caenorhabditis elegans 1090 cells decision to die 131 cells execution ced-3 ced-4 egl-1 ced-9 ces-2 ces-1 engulfment ced-1 ced-2 ced-5 ced-6 ced-7 ced-10 apoptosis degradation nuc-1 Apoptosis: Pathways “Extrinsic Pathway” Death Ligands Death Receptors “Intrinsic Pathway” DNA damage & p53 Mitochondria/ Cytochrome C Initiator Caspase 8 Effector Caspase 3 Initiator Caspase 9 PCD MAJOR PLAYERS IN APOPTOSIS • • • • Caspases Adaptor proteins TNF & TNFR family Bcl-2 family Ligand-induced cell death Ligand FasL TNF TRAIL Receptor Fas (CD95) TNF-R DR4 (Trail-R) Ligand-induced cell death “The death receptors” FasL Ligand-induced trimerization Trail TNF Death Domains Death Effectors Induced proximity of Caspase 8 Activation of Caspase 8 APOPTOSIS: Signaling & Control pathways I Externally driven Apoptotic signals p53 Internally Cytochrome C driven Externally driven Activators of initiator enzymes Initiator caspases mitochondrion 6, 8, 9,12 Execution caspases 2, 3, 7 Apoptosis events Activation APOPTOSIS: Signaling & Control pathways II Externally driven Apoptotic signals p53 Internally Cytochrome C Bcl2 driven Externally driven Inhibitors Activators of initiator enzymes Initiator caspases 6, 8, 9,12 External Survival Internal factors Execution caspases 2, 3, 7 Apoptosis events Inhibitors of apoptosis Inhibition The mitochondrial pathway DNA Fas damage Casp8 p53 Growth factor receptors PI3K Bid Bid Bax Bid Bax Akt casp3 BAD Bcl2 casp9 Apaf1 ATP Cyt.C IAPs casp3 Smac/ DIABLO H2O2 AIF Pollack etal., 2001 REGULATION OF APOPTOSIS Stimuli apoptosis selection of targets (Rich et al., 2000) Apoptosis by conflicting signals that scramble the normal status of cell (Canlon & Raff, 1999) Apoptotic stimulicytokines, death factors (FasL) (Tabibzadeh et al., 1999) DNA breaks p53 is activated arrest cell cycle or activate self destruction (Blaint & Vousden, 2001) Importance of Apoptosis • Important in normal physiology / development – Development: Immune systems maturation, Morphogenesis, Neural development – Adult: Immune privilege, DNA Damage and wound repair. • Excess apoptosis – Neurodegenerative diseases • Deficient apoptosis – Cancer – Autoimmunity FUTURE PERSPECTIVES The biological roles of newly identified death receptors and ligands need to be studied Need to know whether defects in these ligands and receptors contribute to disease CONCLUSION an important process of cell death can be initiated extrinsically through death ligands (e.g. TRAIL, FasL) activating initiator caspase 8 through induced proximity. can be initiated intrinsically through DNA damage (via cytochrome c) activating initiator caspase 9 through oligomerization. Initiator caspases 8 and 9 cleave and activate effector caspase 3, which leads to cell death. DNA DAMAGE p53 The bcl-2 family N BH4 BH3 BH1 Receptor domain Ligand Pore domain formation phosphorylation Raf-1 calcineurin BH2 TM C Membrane anchor Group I Bcl-2 Group II bax Group III Bad bid bik Back P53 & Apoptosis p53 first arrests cell growth between G1 S This allows for DNA repair during delay If the damage is too extensive then p53 induces gene activation leading to apoptosis (programmed cell death) BACK 3 mechanisms of caspase activation a. Proteolytic cleavage e.g. pro-caspase 3 b. Induced proximity, e.g. pro-caspase 8 c. Oligomerization, e.g. cyt c, Apaf-1 & caspase 9 Back Apoptosis signal to kill infected cells Cytolytic lymphocyte/CTL (& natural killer lymphocyte) presents Fas ligand/CD178 on its surface to tell the infected cell to die Fas ligand Externally driven Apoptotic signals Cytochrome c Initiator caspases The immunological synapse holds the cells much tighter together than shown here Fas/ CD95 is the ‘death receptor’ Execution caspases Apoptosis events