Apoptosis Mechanisms and Pathways

Cell Death & Apoptosis

• Cell death is a vital process in maintaining a constant number of cells within the body.
• Two major forms of cell death include apoptosis (programmed cell death) and necrosis (killing, decay, and destruction).
• Apoptosis is a tightly regulated, controlled process that eliminates unwanted or damaged cells without causing inflammation to surrounding cells.

Apoptosis in Development & Diseases

• Embryonic development heavily relies on apoptosis.
• During development, apoptosis eliminates cells to sculpt tissues and organs into their proper shapes.
• Apoptosis is crucial for proper immune function, removing immune cells that don't pass regulatory tests.

Objectives

• Understanding various cell death pathways.
• Assessing cell death mechanisms.
• Delving into the physiological process of apoptosis.
• Exploring the association between apoptotic pathway defects and diseases.

Cell Death

• The body maintains a stable cell count by eliminating cells when necessary.
• Apoptosis is cell suicide, a programmed cell death.
• Necrosis is cell death characterized by cell killing, decay, and destruction.

Embryonic Development

• Embryonic development involves programmed cell death.
• Apoptosis sculpts an embryo into its final form.
• Examples include processes such as the absorption of the tadpole's tail.

Adult Cell Death

• Billions of healthy cells are lost via apoptosis every hour in adults.
• Regulation of cells removed.
• Controls during development prevent damaged cells from proliferating.

Apoptosis Publications/Year

• The number of publications regarding apoptosis increased significantly over time, with a notable rise towards the late 1990s.

Apoptotic Pathways

• Illustrates apoptotic signalling, pathways, and details.
  • C. elegans apoptosis
  • Drosophila apoptosis
  • Mammalian apoptosis

Nobel Prize in Physiology/Medicine 2002

• Sydney Brenner, H. Robert Horvitz, and John Sulston shared the 2002 Nobel Prize for their genetic regulation of organ development and programmed cell death.

Apoptotic Changes

• Morphological changes in apoptosis include cellular shrinkage, nuclear fragmentation, and formation of apoptotic bodies.
• Biochemical changes during apoptosis involve caspase activation and endonuclease activation.

Apoptosis Results

• Apoptosis produces a swift, clean death of cells without harming nearby cells or triggering an immune response.
• DNA fragmentation is a hallmark of the process.
• Key features include cell shrinkage, mitochondrial cytochrome c release, and altered plasma membrane.

Death by Injury vs. Death by Suicide (Necrosis vs. Apoptosis)

• Key visual representations compare apoptosis (a controlled and distinct process with preserved membrane integrity) versus necrosis (a disordered and destructive process with compromised membrane integrity).
• Apoptosis's morphological features and biochemical pathways are compared and contrasted with necrosis.

What is Apoptosis?

• Apoptosis is programmed cell death.
• It involves cellular condensation and no tissue reaction.
• Membranes remain intact in apoptosis.
• In apoptosis, DNA fragments create a ladder-like pattern.
• In vivo, apoptosis involves individual cells.
• Necrosis involves cellular swelling and broken membranes.
• In necrosis, ATP is depleted and there's an inflammatory reaction.
• DNA fragmentation is random or smeared in necrosis.
• Whole areas of tissue are affected in necrosis.

Morphological Differences in Apoptosis and Necrosis

• Necrosis involves chromatin clumping, swollen organelles, and flocculent mitochondria.
• Apoptosis involves mild convolution, chromatin and cytoplasmic condensation, nuclear fragmentation, apoptotic bodies, phagocytosis, and no inflammation.

Necrosis

• Necrosis is the process of irreversible cell damage and occurs due to harmful factors.
• Progressive changes from normal cells include disaggregation of polysomes, focal chromatin margination, and mild mitochondrial swelling.
• Irreversible changes lead to high amplitude mitochondrial swelling, mitochondrial matrix intensification, and progressive endoplasmic reticulum dilation.
• The process involves lysosomal rupture and impairment of plasma membrane integrity.
• Eventually, recognizable cellular organelles are lost.

What Makes a Cell Commit Suicide?

• Cells commit suicide due to signals like loss of positive signals (e.g., growth factors, TNF-α), presence of negative signals (e.g., DNA damage), and other stimuli.

Steps in Apoptosis

• Decisions to initiate apoptosis, the actual cell death process, engulfment of remaining parts by immune cells, and final degradation of the cell are part of the process.
• This involves condensing the nucleus, fragmenting the cytoplasm, and creating apoptotic bodies.
• DNA fragments into nucleosomes.

Apoptotic Signaling

• Illustrates various stimuli, signals, regulators, and effectors involved in apoptotic signaling pathways.
• Key proteins and processes, including those that promote life or death in cellular contexts, are highlighted.

Apoptosis: Morphology

• Depicts the steps of apoptosis, including membrane blebbing, mitochondrial leakage, nuclear fragmentation, and chromatin condensation.

Biochemical Changes in Apoptosis

• Initiates via caspase activation and continues with the activation of endonucleases..
• Caspases, cysteine proteases, are essential for apoptosis as inactive precursors activated by other proteins following the appropriate signal.

Caspases

• Caspases are proteases involved in apoptosis.
• These proteases are crucial for degradation of cellular components.
• Often present as inactive procaspases, which require other proteins to be activated.

Caspases (proteases)

• A crucial role is taken by caspase proteases.
• Caspase activation requires proteolytic cleavage.
• Key steps include removal of prodomains and linker regions, assembly into complexes of large and small subunits, and the subsequent formation of a tetramer.
• Caspase family members number over 14.

Caspase Functions and Structure

• Shows different caspase groups involved in apoptosis.
• Key caspases (initiator/effector) are detailed in diagrams.

Apoptotic: Pathways - Extrinsic Pathway - Death Receptor Mediated

• Visual description of the extrinsic pathway (death receptor mediated).
• Presents steps of caspase activation using FADD, Fas receptor, and ligand interaction.

Apoptotic: Pathways - Intrinsic Pathway - Mitochondrial Mediated

• Demonstrates the intrinsic pathway or mitochondrial pathway.
• Steps of cytochrome c release, Apaf-1 activation, apoptosome assembly, and the resulting caspase cascade are explained.

Ligand/Death-Induced Cell Death

• Presents a tabular format of the ligands and the receptors involved in cell death.
• Explains the various pathways involved.

Ligand-Induced Cell Death

• Death ligands (e.g., FasL, TRAIL) trigger cell death through interaction with death receptors.
• Ligand binding leads to receptor trimerization.
• Death domains and the activation of caspase 8 are key components of this process.

The Mitochondrial Pathway / Extrinsic Linking Intrinsic

• Illustrates the intricacies of the mitochondrial pathway, encompassing connections to extrinsic pathways and growth factor receptors.
• Shows the roles of p53, Bax, Bid, BAD, Bcl2, Apaf1, and cytochrome c in cell death regulation.

Assessing and Imaging Apoptosis

• Explains methods for visually detecting or assessing apoptosis.
• Illustrates microscopy and flow cytometry techniques as examples.

Detection of Apoptotic Changes in DNA

• Discusses methods employed to detect apoptotic changes in DNA, including nucleic acid staining for morphological analysis, TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) assay to identify DNA fragmentation, and single-cell electrophoresis techniques or comet assays.

Importance of Apoptosis

• Essential for physiological functions, development, and repair.
• Defects in apoptosis can contribute to neurodegenerative diseases, cancer, and autoimmunity.

Other Forms of Cell Death

• Presents several cell death methods besides apoptosis and necrosis.
  • Autophagic cell death.
  • Necroptosis .

Autophagic Cell Death

• Autophagy (self-eating) as a survival or destructive mechanism in healthy or stressed cells.
• Different steps in autophagy that lead to cell death or survival.

Necroptosis

• Necroptosis as a programmed form of necrotic cell death.
• Necroptosis is distinct in cell death mechanisms.
  • rapid membrane permeabilization
    • release of cell contents.
    • exposure of damage-associated molecular patterns.

Apoptosis Excess

• Discusses instances of apoptosis excess in ischemia-reperfusion injury, noting that initiator caspases and apoptosis of endothelial cells are central to this process.

Cancer and Apoptosis

• Evasion of apoptosis can initiate cancer.
• Activating apoptosis in cancer cells is a therapeutic strategy to eliminate cancer cells and combat uncontrolled proliferation.

Genes Playing Role in Cancer Development

• Discusses the central role played by oncogenes, tumor suppressor genes, and DNA repair genes within the development of cancerous cells.

Functions of Cellular Proto-Oncogenes

• Discusses specific proto-oncogenes and their signaling pathways, explaining how growth factors, receptors, and cytoplasmic signal transduction are involved.

Oncogenes

• Proto-oncogenes mutate to form oncogenes, causing constitutive activation of signaling pathways, thus resulting in uncontrolled cell proliferation.
• The mutated form (oncogene) of the ras proto-oncogene is a key example.

Tumor Suppressor Genes

• Normally, tumor suppressor genes inhibit cellular proliferation, and loss-of-function mutations in these genes contribute towards cancer development.

p53 Tumor Suppressor Genes

• p53 is a critical transcription factor that regulates cellular responses to DNA damage.
• Its activation leads to cellular responses such as cell cycle arrest to repair DNA damage, and apoptosis if damage cannot be repaired.
• p53 gene mutation or disruption affects its activation potential and contributes to unchecked cell proliferation—a primary characteristic of cancers.

Cancer Treatment/Therapies

• Illustrates a complex network of cellular signaling pathways involved in cellular processes and cancer therapy.
• Explains that numerous factors regulate the interactions in the network.

Promising Cancer Targets

• Emphasizes key proteins or targets that are crucial to understanding and potentially treating specific cancers more effectively.
• Illustrates interaction networks amongst several proteins to show the complex organization.

Apoptosis - Programmed Cell Death

• Defines apoptosis as a process of programmed cell death where the cell destroys itself.
• Differentiates apoptosis from necrosis, highlighting the distinct mechanisms through which cells die.
• Introduces the concept of cellular signals that could trigger apoptosis.
• Presents apoptosis-related components and the differences and similarities between mitogens, growth factors, and survival factors.
• Examines specific cell cycle stages related to apoptosis.
• Discusses how telomeres and telomerase affect aging and the possibility of using telomerase to prevent aging.
• Highlights the existence or nonexistence of various human cell types and their functions.

This quiz explores the intrinsic and extrinsic pathways of apoptosis, focusing on the biochemical and morphological changes that occur during programmed cell death. Test your understanding of the role of caspases, cytochrome c, and the differences between apoptosis and necrosis, alongside their implications in health and disease.