W12 Cell Death 2 Apoptosis (Yakubovskyy).pdf

Cellular Pathology 5: Cell Death Apoptosis Michael M. Yakubovskyy, MD, PhD 1 Learning Objectives 1. List the causes and explain the mechanisms of the initiation phase (including the intrinsic and extrinsic pathways) and execution phase of apoptosis 2. Describe and recognize morphologic features of...

Cellular Pathology 5: Cell Death Apoptosis Michael M. Yakubovskyy, MD, PhD 1 Learning Objectives 1. List the causes and explain the mechanisms of the initiation phase (including the intrinsic and extrinsic pathways) and execution phase of apoptosis 2. Describe and recognize morphologic features of apoptosis 3. Compare and contrast the microscopic presentation of apoptosis and necrosis 4. Outline the causes, mechanisms, and significance of necroptosis and pyroptosis 2 Apoptosis: Definition • • Genetically controlled “programmed” cell death - Greek “apoptosis” - falling off Morphologic hallmark: formation of apoptotic bodies: round-oval masses of intensely eosinophilic cytoplasm containing dense nuclear fragments 3 Apoptosis in Physiologic Conditions • • • • Removal of supernumerary cells during embryonic development, e.g., pharyngeal arches, tail, “webs” between fingers and toes Involution of hormone-dependent tissues after hormone withdrawal, e.g., endometrial breakdown in menstruation, or lactating breast after weaning Cell turnover in proliferating cell populations, e.g., epidermis or intestinal mucosa Negative selection of self-reactive T-lymphocytes in the developing thymus 4 7- and 9-Week (Fertilization Age) Embryos https://commons.wikimedia.org/wiki/File:819_Embryo_at_Seven_Weeks.jpg Ed Uthman, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons 5 https://commons.wikimedia.org/wiki/File:9-Week_Human_Embryo_from_Ectopic_Pregnancy.jpg Ed Uthman from Houston, TX, USA, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons Syndactyly • Syndactyly: webbed fingers or toes due to deficient apoptosis during embryogenesis https://commons.wikimedia.org/wiki/File:New_born_boy_showing_complete_complex_syndactyly_with_two_fingers_right_hand.JPG Dumplestilskin, uploaded by Gliu, Public domain, via Wikimedia Commons 6 https://commons.wikimedia.org/wiki/File:Celldeath.jpg User:pschemp, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons Mechanism of Apoptosis: Introduction 1. • • 2. Initiation phase Intrinsic pathway, or Extrinsic pathway Execution phase 7 Apoptosis: Pathologic Triggers • • • DNA damage induced by - High-doses of radiation (ionizing and UV light) - Cytotoxic drugs - Severe hypoxia Accumulation of misfolded proteins in neuro-degenerative diseases, e.g., Alzheimer disease Interaction of cytotoxic T-lymphocytes (CTLs) with host cells in - Viral infections - Transplant rejection 8 Mitochondrial Structure, Respiratory Chain, and Location of Cytochrome c 11 https://commons.wikimedia.org/wiki/File:Mitochondrial_respiratory_chain.svg Kelvingsong & TheBartgry, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons Intrinsic and Extrinsic Pathways: Diagram Reactome is an open source and open access resource, available to anyone. Usage of Reactome material is covered by two Creative Commons licenses: The terms of the Creative Commons Public Domain (CC0) License apply to all Reactome annotation files, e.g., identifier mapping data, specialized data files, and interaction data derived from Reactome. The terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License apply to all software and code, e.g., relating to the functionality of the reactome.org, derived websites and webservices, the Curator Tool, the Functional Interaction application, SQL and Graph Database data dumps, and Pathway Illustrations (Enhanced HighLevel Diagrams), Icon Library, Art and Branding Materials. BCL-2 Family: Control of Intrinsic Pathway Subfamily Members Function Puma and BAD Activate proapoptotic BAX and BAK Block antiapoptotic BCL-2 and BCL-XL Proapoptotic (BH1-3 proteins) BAX and BAK Form channels on the outer mitochondrial membrane, through which cytochrome c leaks into the cytosol Antiapoptotic (BH1-4 proteins) BCL2 and BCL-XL Block BAX and BAK channels Sensors (BH3-only proteins) 15 Apoptosis: Structural Changes 1. Shrinkage of cell/cytoplasm with preservation of organelles (mitochondria, ER) 2. Chromatin condensation (pyknosis) under the preserved nuclear envelope with following fragmentation of the nucleus 3. Formation of cytoplasmic blebs 4. Formation of apoptotic bodies: round-oval densely eosinophilic masses with dark-blue nuclear fragments (round or crescentic) 5. Rapid phagocytosis (efferocytosis) by macrophages and adjacent cells 16 Apoptosis, gif Long-term live cell imaging (12h) of multinucleated mouse pre-adipocyte trying to undergo mitosis. Due to the excess of genetic material the cell fails to replicate and dies by apoptosis. 17 https://en.wikipedia.org/wiki/Apoptosis#/media/File :Apoptosis_in_mouse_pre-adipocytes.gif Apoptosis, Nucleus Fragmentation (EM, Left; LM, Right) https://commons.wikimedia.org/wiki/File:Apoptosis.jpg Ltumanovskaya V. Nagibin, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons — EM, UA https://commons.wikimedia.org/wiki/File:Apoptosis_multi_mouseliver.jpg Laboratory of Experimental Pathology, Division of Intramural Research, NIEHS (NIH), Public domain, via Wikimedia Commons 18 Apoptosis in Pathologic Conditions: Defective Apoptosis • Defective apoptosis —> increased cell survival - Defective apoptosis in physiologic conditions • Webbed fingers and toes • Supernumerary nipples - Defective apoptosis in pathologic conditions • Cells with neoplastic transformation —> cancer (breast, prostate, ovarian, etc.) • Reduced elimination of autoreactive lymphocytes —> autoimmune disorders 19 Apoptosis in Pathologic Conditions: Increased Apoptosis • Increased apoptosis —> excessive cell death - DNA damage after exposure to ionizing radiation of after treatment with cytotoxic drugs —> intrinsic pathway —> death of neoplastic and labile cells - Accumulation of misfolded proteins in neurons —> intrinsic pathway —> loss of neurons —> neurogenerative diseases (Alzheimer, Huntington, Parkinson, etc.) - CTL-initiated extrinsic pathway —> cell death in viral infection, e.g., acute viral hepatitis - Pathologic atrophy after duct obstruction, e.g., pancreas or kidney 20 Necrosis vs Apoptosis Feature Necrosis Apoptosis Cell size Enlarged (swelling) due to preceding cell injury Reduced (shrinkage) Nucleus Karyolysis Pyknosis —> karyorrhexis Pyknosis with preserved nuclear envelope —> nuclear fragmentation Plasma membrane Disrupted Intact Cellular contents Enzymatic digestion; may leak out of cell Intact; may be released in apoptotic bodies Inflammatory response Present Absent Invariably pathologic Physiologic or Physiologic with elimination of unwanted cells (culmination of irreversible cell pathologic role Pathologic, induced by DNA damage, etc. injury) 21 Other Types of Cell Death LO4. Explain mechanisms and significance of necroptosis and pyroptosis Necroptosis Necroptosis: “programmed necrosis” • Described in variety of pathologies including ischemia-reperfusion injury, acute pancreatitis, neurodegenerative diseases, etc. • Mechanism: begins as apoptosis and finishes as necrosis 1. TNF-TNFR1 interaction (as extrinsic pathway of apoptosis) 2. Activation of a specific signaling cascade 3. Cell injury and death: ATP depletion, ROS generation, plasma membrane rupture (as necrosis) • Caspases are not involved • 23 Pyroptosis Pyroptosis: a lytic “programmed” death of cells involved in inflammatory response • Mechanism - Recognition of pathogens by macrophages and dendritic cells - Formation of a special structure named “inflammasome” - Activation of caspase 1 (with following activation of IL-1ß and initiation of inflammatory response) • Caspases 3/6/7/8/9 are not involved - Activation of gasdermin D protein - Formation of gasdermin D pores in the cytomembrane - Cellular swelling and lysis/death to prevent intracellular proliferation of microorganisms • 24 The End 25