Cell Injury & Cell Death Grace Denton & Stephanie Tristram G.E.Denton@warwick.ac.uk S.C.Tristram@warwick.ac.uk

What are some of the causes of cell injury and cell death? Loads of stuff can cause ‘cell injury’ – from a car crash to minute internal abnormalities such as a genetic mutation. Chemical and drugs E.g. Glucose + salt at high levels / poisons / pollutants / booze Oxygen deprivation (hypoxia) E.g. reduced blood flow (ischaemia) / cardiorespiratory failure / severe blood loss Infectious agents E.g. Bacteria / viruses / tape worms Physical agents Stuff that makes you say ouch – car crash / stab wound / burn Immune reactions Immune reactions can cause cell injury. Fact. Genetic derangements E.g. Sickle-cell anaemia (one amino acid substitution = red blood cell dies early) Nutritional imbalances Starvation / excess cholesterol = atherosclerosis / obesity = diabetes + cancer… Causes of cell injury  CHIPING: Chemical, Hypoxia, Infections, Physical, Immune, Nutrition, Genetic Sometimes the cell will be able to repair itself. If it can’t, it is lethally injured, and will die – via apoptosis or necrosis.

What are the different mechanisms of cell injury (cellular level)? Reduced ATP Mitochondrial damage leads to the leakage of pro-apoptotic proteins Entry of Ca2+ leads to increased mitochondrial permeability and activation of multiple cellular enzymes ↑ reactive oxygen species (ROS) damages lipids, proteins and DNA Membrane damage Protein misfolding, DNA damage leads to the activation of pro-apoptotic proteins

What are the different types of Cell Death? Necrosis Result of irreversible cell injury. Necrosis is the principal outcome in many commonly encountered injuries, such as those following: Ischemia Exposure to toxins Various infections Trauma Apoptosis Result of irreversible cell injury. In situations when the cell’s DNA or proteins are damaged beyond repair, the cell kills itself by apoptosis, a form of cell death that is characterized by: Nuclear dissolution Fragmentation of the cell without complete loss of membrane integrity Rapid removal of the cellular debris No inflammation

What are the comparisons of Necrosis and Apoptosis?   What are the comparisons of Necrosis and Apoptosis? Feature Necrosis Apoptosis Cell Size Enlarged (swelling) Reduced (shrinkage) Nucleus Digested Fragments Plasma membrane integrity Disrupted Intact Fate of cell contents Digested, leak out of cell Intact, packaged into apoptotic bodies Local inflammation Frequently  leaked enzymes cause local destruction No  apoptotoic bodies are neatly phagocytosed Physiological or pathological Always pathological culmination of irreversible cell injury Sometimes pathological after some forms of cell injury – e.g. DNA damage Sometimes physiological a way of eliminating unwanted cells Necrosis or Apoptosis? Physiologic or Pathologic: Either? Always pathological? Cell size: Reduced? Enlarged? Nucleus: Fragments? Digested? Plasma membrane integrity: Disrupted? Intact? Cell contents: Digested, leaked? Intact, packaged? Associated inflammation: Often? None?

Describe the process of apoptosis The nucleus and cytoplasm condense down (reduction in cell size) Plasma membrane fragments (apoptotic bodies) are phagocytosed by normal tissue phagocytes No inflammation More: Apoptosis … AKA ‘programmed cell death’ Apoptosis does not trigger an inflammatory reaction - intracellular enzymes degrade the cells’ DNA and proteins but there is no disruption to the cell membrane So, because the cell membrane is intact, there is no leakage of intracellular contents (e.g. destructive enzymes), and there is no inflammation

Give some examples of physiological and pathological apoptosis. Embryogenesis (e.g. developmental involution) Involution of hormone dependent tissue (endometrial breakdown during menstrual cycle) Cell loss in proliferating cell populations (epithelial cells in intestinal crypts) Elimination potentially harmful lymphocytes (so as to prevent autoimmune reactions) Cells no longer required Cells with DNA damage Cells with Endoplasmic Reticulum Stress (i.e. mis-folded proteins accumulation in the ER) Some infections e.g. Viruses Pathological atrophy if a duct is obstructed

The form and structure of necrosis is the result of: This is a little bit of background info on necrosis, in case you don’t want to just rote-learn the types: NECROSIS The form and structure of necrosis is the result of: denaturation of intracellular proteins enzymatic digestion of the lethally injured cell  Necrotic cells are unable to maintain membrane integrity and their contents often leak out, a process that often elicits inflammation in the surrounding tissue The enzymes that digest the necrotic cell come from within the dying cells themselves, and from the lysosomes* of leukocytes (white blood cells) that are called in as part of the inflammatory reaction When large numbers of cells die the tissue or organ is said to be necrotic So, a myocardial infarct is necrosis of a portion of the heart caused by death of many myocardial cells Necrosis of tissues has several morphologically distinct patterns, which are important to recognise because they may provide clues about the underlying cause… *Lysosome = a cell organelle (part) which has its own membrane, and contains enzymes …enlarge this pic to see one 

What are the 6 different patterns of tissue necrosis? You just need to know the names, and where you’d find them, but understanding might be good too… What are the 6 different patterns of tissue necrosis? Coagulative A form of necrosis in which the architecture of dead tissues is preserved for a span of at least some days, so the affected tissue has a firm texture The cell injury denatures both the proteins but also enzymes within the cell, so stops the enzymes digesting the dead cells … ultimately the necrotic cells are removed by phagocytosis Ischemia caused by obstruction in a vessel may lead to coagulative necrosis of the supplied tissue in all organs except the brain. A localised area of coagulative necrosis is called an infarct Liquefactive Characterized by digestion of the dead cells, resulting the tissue becoming a liquid viscous mass The necrotic material is often creamy yellow because of the presence of dead leukocytes and is called pus For unknown reasons, hypoxic death of cells (i.e. due to lack of oxygen) within the central nervous system (i.e. the brain) often manifests as liquefactive necrosis Caseous Encountered most often in foci of tuberculous infection … i.e. you’ll hear about it in TB The term “caseous” (cheese-like) is derived from the crumbly white appearance of the area of necrosis 4. Fibrinoid Necrosis usually seen in immune reactions involving blood vessels

The last two aren’t ‘real’ necrosis, but the terms are used in clinical practice… 5. Fatty Refers to areas of fat destruction seen in acute pancreatitis typically resulting from release of activated pancreatic lipases into the substance of the pancreas and the peritoneal cavity These escaped pancreatic enzymes liquefy the membranes of fat cells in the peritoneum 6. Gangrenous It is usually applied to a limb, generally the lower leg, that has lost its blood supply and has undergone necrosis (typically coagulative necrosis)

Where would you see liquefactive necrosis? The brain (first answer I would give to this question) Name 3 organs where you would expect to see coagulative necrosis. Kidney, heart, adrenal glands (may occur in all organs - except the brain…!) What is the key difference between coagulative and liquefactive necrosis? Coagulative – tissue architecture is maintained (for a few days, at least) Liquefactive – tissue architecture is not maintained … it is a liquid viscous mass When do you see fatty necrosis? Fatty necrosis is really just fat destruction. Acute pancreatitis. Damaged pancreatic cells release lipases which degrade fat cells in the peritoneum When would you expect to see caseous necrosis? Tuberculosis (first answer I would give to this question)

What causes white infarction? Define infarction What causes white infarction? Infarction = an area of ischaemic necrosis in a tissue or organ Arterial occlusion in most solid tissues e.g. heart, spleen, kidney I.e. blood can’t get in… What are the two types of infarction? White Red/haemorrhagic What causes red/haemorrhagic infarction? Venous occlusion Infarction in loose tissues (e.g. lung) where blood can collect in the infarcted zone Tissues with dual blood supply (e.g. lung + small intestine) Tissues that have been previously congested by sluggish venous outflow I.e. blood can’t get out…

How are free radicals generated in cell injury? What is a free radical? A free radical is defined as “any species capable of independent existence that contains one or more unpaired electrons” (It’s a highly reactive molecule that reacts with things that it shouldn’t in order to stabilise itself) How are free radicals generated in cell injury? Chemicals/drugs reperfusion injury Inflammation Irradiation oxygen toxicity carcinogenesis How are free radicals removed? Spontaneous decay Anti-oxidants: Vit E, Vit A, Ascorbic acid (Vit C), glutathione Storage proteins: Transferrrin, ferritin Enzymes: Glutathione peroxidase What 3 things do free radicals damage? Nucleic acids Cellular proteins Cellular lipids

APPENDIX. (Some of the notes we wrote on this stuff last year…)

Cell injury / death - BACKGROUND: Once cells are stressed beyond their adaptive capacity, are exposed to inherently harmful stimuli or have an intrinsic abnormality they become damaged. This damage may lead to: Cell injury Reversible (if stimulus is removed can return to normal) Irreversible (culminating in cell death) Hallmarks - inability to reverse mitochondrial dysfunction and profound disturbance in membrane function. Cell death Apoptosis Necrosis

Mechanisms of Cell Injury Biochemical mechanisms link the injury with resultant cellular and tissue changes and associated changes in function. Principles of cell injury: The cellular response to injury depends on The type of injury The duration of injury The severity of the injurious stimulus. The consequences of the injurious stimulus depend on the following cellular characteristics: The cell type and status Adaptability of the cell Genetic make-up of the cell The injury and its associated derangements usually reflect damage to one of 5 key cellular components. Mitochondria and reduced ATP production Cell membrane Protein synthesis Cytoskeleton Genetic apparatus of the cell