Mechanisms of Disease II: Cell Damage and Cell Death

Question 1

What is the function of necrosis?

Answer 1

Removes damaged cells from an organism Failure to do so may lead to chronic inflammation Necrosis causes acute inflammation(to prevent further bigger inflammation) to clear cell debris via phagocytosis

Question 2

What are the causes of necrosis?

Answer 2

Usually lack of blood supply, e.g. injury, infection, cancer, infarction, inflammation (As the distance away from the blood vessel increases, the pH drops and partial pressure of oxygen drops significantly also- step by step explanation of the effect of this on flashcard 3 below)

Question 3

What are the steps of necrosis?

Answer 3

1. Result of an injurious agent or event.(Whole groups of cells are affected.) 2. Initial events are reversible, later ones are not. 3. Lack of oxygen prevents ATP production. 4. Cells swell due to influx of water (ATP is required for ion pumps to work).(due to osmosis here) 5. Lysosomes rupture; enzymes degrade other organelles and nuclear material hapzardly 6. Cellular debris released, triggering inflammation

Question 4

What are some nuclear changes that occur in a cell during necrosis? (from a microscope view)

Answer 4

Nuclear Changes: 1. Chromatin condensation/shrinkage. 2. Fragmentation of nucleus. 3. Dissolution of the chromatin by DNAse.

Question 5

What are some cytoplasmic changes that occur in necrosis of a cell? (microscopic view)

Answer 5

1. Opacification:(cytoplasm becomes more white instead of a see-through watery colour) protein denaturation & aggregation. 2. Complete digestion of cells by enzymes causing cell to liquify (liquefactive necrosis).

Question 6

What are some biochemical changes that occur in necrosis of a cell?

Answer 6

1. Release of enzymes such as creatine kinase or lactate dehydrogenase 2. Release of other proteins such as myoglobin These biochemical changes are useful in the clinic to measure the extent of tissue damage!

Question 7

What is apoptosis and what is it involved in?

Answer 7

Selective process for the deletion of superfluous, infected or transformed cells. Involved in:- Embryogenesis Metamorphosis Normal tissue turnover Endocrine-dependent tissue atrophy A variety of pathological conditions

Question 8

What happens in apoptosis?

Answer 8

1. Programmed cell death of one or a few cells. 2. Events are irreversible and energy (ATP) dependent. 3. Cells shrink as the cytoskeleton is disassembled. 4. Orderly packaging of organelles and nuclear fragments into membrane bound vesicles. 5. New molecules are expressed on vesicle membranes that stimulate phagocytosis without an inflammatory response (so a v clean way of disposing cellular content)

Question 9

What is a distinct feature in regards to number of cells involved in necrosis and apoptosis? What about in regards to reversibility?

Answer 9

Necrosis- multiple cells at once Apoptosis- v selective, usually one or so cells at a time Necrosis- not every part/stage is irreversible Apoptosis -ALL events are irreversible and steps require ATP

Question 10

What cytoplasmic changes can be seen when cell apoptosis happens?

Answer 10

Cytoplasmic Changes: 1. Shrinkage of cell. Organelles packaged into membrane vesicles. 2. Cell fragmentation. Membrane bound vesicles bud off. 3. Phagocytosis of cell fragments by macrophage and adjacent cell. 4. No leakage of cytosolic components.

Question 11

What nuclear changes can be seen when cell apoptosis happens?

Answer 11

Nuclear Changes: 1. Nuclear chromatin condenses on nuclear membrane. 2. DNA cleavage.

Question 12

What biochemical changes can be seen when cell apoptosis happens?

Answer 12

Biochemical changes: 1. Expression of charged sugar molecules on outer surface of cell membranes (recognised by macrophages to enhance phagocytosis) 2. Protein cleavage by proteases, caspases

Question 13

What are some examples of things that cause apoptosis?

Answer 13

1. Cell death in embryonic hand to form individual fingers. 2. Apoptosis induced by growth factor deprivation (neuronal death from lack of NGF). 3. DNA damage-mediated apoptosis. If DNA is damaged due to radiation or chemo therapeutic agents, p53 (tumour suppressor gene product) accumulates. This arrests the cell cycle enabling the cell to repair the damage. If repair process fails, p53 triggers apoptosis. 4. Cell death in tumours causing regression. 5. Cell death in viral diseases (ie viral hepatitis). 6. Cell death induced by cytotoxic T cells (ie. Cellular immune rejection or vs. host disease). 7. Death of neutrophils during an acute inflammatory response. 8. Death of immune cells( both T and B lymphocytes) after depletion of cytokines as well of death of autoreactive T cells in the developing thymus.

Question 14

What are caspases?

Answer 14

a family of proteases whose activation is central to all types of apoptosis Caspases are the point of convergence for causes of apoptosis, e.g. Extrinsic causes intrinsic causes . . . . . . Caspases………………………….> apoptosis Caspases are cysteine proteases (cysteine aspartate-specific proteases) Caspases form an activation cascade, where one cleaves and activates the next (analogous to kinase cascades) (initiator caspases and effector caspases)

Question 15

What are the 2 types of apoptosis?

Answer 15

Intrinsic: DNA damage – p53-dependent pathway Interruption of the cell cycle Inhibition of protein synthesis Viral Infection- ie once virus is in the cell Change in redox state Extrinsic: (relative to the cell not the body) Withdrawal of survival factors e.g. mitogens Extracellular signals (e.g. TNF) T cell or NK (Natural Killer) (e.g. Granzyme).

Question 16

What does caspase activation lead to?

Answer 16

Caspase activation leads to characteristic morphological changes, such as shrinkage, chromatin condensation, DNA fragmentation and plasma membrane blebbing. Initiator caspases activate themselves when in close proximity Activation, therefore, means bringing initiator caspases together

Question 17

What is extrinsic apoptosis induced by?

Answer 17

Induced by ligand binding to receptors, causing receptor dimer- (or multimer-) isation- which ultimately leads to activation of the caspase Ligand-induced multimerization: Domains shared between proteins allow them to bind together

Question 18

What is intrinsic apoptosis induced by?

Answer 18

Induced by cytochrome c released from mitochondria Note: growth factor withdrawal (extrinsic apoptosis) an exception that uses cytochrome c… Cytochrome C: Mitochondrial matrix protein Known for many years to be released in response to oxidative stress by a “permeability transition” Any inducers of the permeability transition also eventually induce apoptosis.

Question 19

How is the release of cytochrome c from the mitochondria regulated?

Answer 19

A PORE MADE OF BCL-2 FAMILY PROTEINS BCL-2 PROTEINS Can be pro- or anti-APOPTOTIC Anti-apoptotic: Repress cytochrome c release, leading cells to survive- cytochrome c therefore remains in the mitochondria pro-Apoptotic: Facilitate cytochrome c release Some are not membrane proteins All have a BH3 domain used to form dimers

Question 20

IF BCL-2 FAMILY PROTEINS REGULATE CYTOCHROME C RELEASE FROM mitochondria, WHAT regulates BCL-2 PROTEINS?

Answer 20

Transcription/ phosphorylation? BAD binds to BCL-2, displacing it from the pore, allowing the release of cytochrome C, causing cell death but eg if BAD is phosphorylated then prevents release of cytochrome C check ppt https://canvas.sgul.ac.uk/courses/2414/pages/mechanisms-of-disease-ii-cell-damage-and-cell-death-sdl?module_item_id=90324