Cell injury, death and adaptations Flashcards
What is Pyknosis?
Clumping and shrinking down of chromatin in cell nuclei during necrotic cell death.
What tissue/cellular changes are considered reversible stress responses?
Hypertrophy
Hyperplasia
Atrophy
Metaplasia
What is karyorrhexis?
The fragmentation chromosomes and nuclear content seen in necrosis. Nuclear membrane is lost here.
What is karyolysis?
The melting of the chromatin in the nucleus seen during necrosis. The membrane of the nucleus remains intact.
What changes are seen during cell injury in cells that store fat?
The rapid accumulation of triglycerides occurs leading to saturation with triglyceride filled vacuoles. Happens due to the failure of lipid trafficking mechanisms that usually occur in these cells when they aren’t injured. E.g. hepatocytes.
Do dying cells take on more hematoxylin dye or more eosin? Why?
Dying or injured cells appear to have more pink (eosin) cytoplasm than other cells. This is because RNA which usually binds blue hematoxylin is not as abundant in the cytoplasm of injured or dying cells. Further, denatured cytoplasmic proteins take on more eosin.
What happens to the endoplasmic reticulum during necrosis?
Becomes swollen and, when it becomes pinched off, I forms vacuoles. This is sometimes referred to vacuolar degeneration and is seen in dying cells.
Does surrounding pancreatic tissue die via necrosis or apoptosis primarily during acute pancreatitis?
Necrosis. The leaked lipases, amylases etc destroy tissues around them.
Why do necrotic cells take on a glassy appearance?
Loss of glycogen particles.
What are myelin figures?
After a cell has died by necrosis, it forms a clump of phospholipid called a myelin figure.
What are the possible degradation pathways for myelin figures?
They can either by phagocytosed by immune cells or further degraded into fatty acids that can become calcified and cause pathogenic calcification.
What is coagulative necrosis? What aetiologies are suggested by this finding?
Necrosis with preserved tissue architecture that lasts for days, presumably due to inactivation of digestive enzymes at the same time as the cells died. This finding suggests infarcted tissue everywhere except the brain. Brain infarction causes liquefactive necrosis.
What is liquefactive necrosis?
Digestion of dead cells resulting in transformation of the tissue into a viscous liquid. Seen in brain infarctions, bacterial or fungal and fungal infections.
What is gangrenous necrosis?
Refers to a limb that has had tissue undergo necrosis in multiple planes. Can involve coagulative necrosis plus liquefactive necrosis if there are bacteria involved.
What is caseous necrosis?
Cheese like necrosis derived from mycobacterial infections. Microscopically is a granuloma with central necrosis.
How does fat necrosis appear? What’s its most common cause?
Acute pancreatitis causes fat degrading enzymes to mix with peritoneal fat, causing the metabolism of triglycerides to fatty acids that calcify and turn white.
What is fibrinoid necrosis?
Vascular damage usually secondary to immune complex disease. These deposits cause leak of proteins out of vessel cells forming bright pink eosin staining amorphous structures in vessel walls.
What is dystrophic calcification?
When necrotic tissue is not completely cleared by surrounding cells or immune cells, it becomes calcified. This is dystrophic calcification.
What does cellular swelling, fatty change, plasma membrane blebbing, loss of microvilli, mitochondrial swelling, ER dilation, and eosinophilia all suggest what?
Cell injury, but not yet necrosis!
What signs indicated the point of no return to necrosis has likely taken place?
Nuclear pyknosis, karyorrhexis and karyolysis. Organellebrane destruction. Plasma membrane destruction. Myelin figures.
What situations lead to pathological apoptosis?
DNA damage from radiation or other causes.
Accumulation of misfolded proteins in th ER
Viral infections can induce apoptosis
Cytotoxic t cells can force apoptosis
Organ duct blockage
Do apoptotic cells shrink or swell?
The shrink
What cells are most likely to phagocytose apoptotic cells or cell bodies?
Macrophages
What are the key enzymes that coordinate apoptosis?
Caspases
What are the two pathways that can lead to apoptosis?
Intrinsic (triggered by mitochondria) and extrinsic (triggered by receptor binding)
Which apoptosis pathway is responsible for apoptosis in most situation?
The intrinsic mitochondrial pathway
What protein family is primarily responsible for modulating the permability of mitochondrial membranes and so intrinsic apoptosis?
The BCL2 family of proteins.
What are the most significant antiapoptotic BCL2 family proteins involved in intrinisc apoptosis?
BCL2, BCL-XL and MCL1. These proteins reside in the mitochondrial out memebrane, in the ER membranes and in the cytosolic membrane. The prevent permeability of the membrane and so prevent the leak of caspase activating proteins out of the mitochondrial intermembrane space.
What are the most signficiant pro-apoptotic BCL2 family proteins involved in intrinsic apoptosis?
BAX and BAK. On activation BAX and/Bak oligomerise and increase the mitochondrial out membrane permeability by forming a channel. They may even form a channel. They also inhibit BCL2 itself which has antiaptotic function.
What are the regulated apoptosis inititors (pro-apoptotic) from the BCL2 family linked to cellular stress sensors? What’s the other name for these?
Sometimes called the BH3- only proteins. This is because they only have the BH3 domain (other BCL-2 families have BH1-4)
-BAD
-BIM
-BID
-Puma
-Noxa
What proteins do growth factors influence in order to reduce the risk of apoptosis?
Growth factors usually leady to increased production of BCL2 +/- BCL-XL +/ - MCL-1 which all contribute to mitochondrial membrane stability and impermeability, this preventing apoptosis and promoting longevity.
What do extracellular survival signals do to BCL2 exert anti-apoptotic effects on the cell?
Extracellular signals usually bind to their receptors and exert their effects on apoptosis by increasing the concentration of BCL2 inctracellularly.
What does cytochrome C bind to once released from the cytosol to continue the intrinsic apoptosis cascade of events? The complex of this structure and cyctochrome see creates a new organelle called what?
It binds to APAF-1 (apoptosis activating factor 1). This complex is called the apoptosome!
What does the apoptososome bind to to continue the apoptosis pathway?
APAF-1 coupled with cytochrome C from the intermembrane space of mitochonria (the apoptosome) binds to an activated caspase-9. Caspase-9 is then catalytically active.
After Caspase-9 is made catalytically active by the apoptosome (cyctochrome C and APAF-1), what does it do?
Caspase-9 triggers a caspase cascade - caspase-3 and others, that trigger the controlled distruction o f the cell.
What are Smac/DIABLO? (hint: to do with apoptosis)
Smac (second mitochondrial activatory of caspases) AKA DIABLO (direct IAP (inhibitor of apoptosis) binding protein with low pI) - are proteins other than cytochrome C that are released from the mitochondria as part of intrinsic apoptosis. They bind do inhibitors of apoptosis, neutralise them, and thus drive the cell towards apoptosis.
What’s the family of receptors generally associated with extrinsic apoptosis? What are its 2 key members?
Tumor necrosis factor receptor - specifically, the members of this family that have the intracellular ‘death’ domain. Note that some of the receptors in this family are associated with inflammation and proliferation, but they critically lack the death domain. Key members of this TNF death receptor family is Fas (CD95) and TNFR1.
What extrinsic apoptosis receptor is involved in the death of self-reactive T cells during maturation?
Fas-FasL
What extrinsic apoptosis initiating protein is used by cytotoxic T-cells to intitiate apoptosis on cells infected with virus or tumour cells?
Fas ligand
When Fas becomes bound to Fas-ligand, it complexes with other Fas (>3). Their death domains now complexed are able to bind to an adaptor protein called what?
Fas-associated death domain (FADD).
FADD, the Fas-associated death domain adaptor protein that binds to Fas-Fas ligand intracellularly, binds to and activates what key enzyme to continue the extrinisc apoptosis pathway?
Caspase 8 OR Caspase 10
Caspase 8, once activated by FADD (the result of Fas-Fas ligand binding), does what as part of the extrinsic apoptosis pathway?
Once active, it is the linking stage of the extrinsic with the intrinsic apoptosis pathway. Caspase 8 cleaves other caspases in th executioner pathway like Caspase 3 and caspase 6. It has the same enzymatic activity as Caspase 9 from the intrinsic apoptosis family.
What is the role of FLIP (FLICE (Fas-associated death domain–like interleukin 1β–converting enzyme) Inhibitory Protein) AKA CFLAR (Capase 8 and FADD-Like Apoptosis Regulator)? What pathogens take advantage of this?
FLIP aka CFLAR inhibtis the binding of FADD (Fas-associated death domain, generated by the binding of Fas L- Fas as part of the extrinisc apoptosis pathway) to Caspase 8. FLIP/CFLAR therefore blocks the progression of extrinisic apoptosis. v-FLIP is a viral version of this protein that is used to prevent its host cells from undergoing apoptosis at the hand of T-cell initiated Fas L.
What are the best studied ‘executioner caspases’?
Caspase 3 and 6. Both can be activated by Caspase 8 or 10 (extrinsic pathway) or caspase 9 (intrinsic pathway).
What apoptotic cells do their plasma membranes to make them more apetising to phagocytes?
They pressent more phosphatidylserine on the outer leaflet of the plasma membrane phospholipid bilayer (the inverse of the health cell state).
What is efferocytosis?
It refers to the extremely rapid clearance of cells that have died via apoptosis.
Necroptosis is what?
Hybrid cell death - part necrosis part apoptosis.
What occurs during necroptosis?
The cell dies in a necrotic way but it is triggered by an internal signalling cascade. In this way, it apperas to be hybrid of necrosis and apoptosis.
Are caspases involved in necroptosis?
No. Although the process of necroptosis starts in a similar way, with binding of an TNF family receptor (the best studied is TNFR1), the intracellular signalling leading to cell death is by different proteins.
In TNFR1 necroptosis, what are the intracellular signalling molecules involved?
Receptor-interactin protein kinase 1 and 3 form a multiprotein complex with TNF ligated TNFR1 intracellular domains (RIPK3). This phosphosphorylates MLKL (Mixed lineage kinase domain-like protein), These MLKL molecules polymerise into oligomers and disrupt the plasma membrane leading to necrosis.
Do cells that die via necroptosis appear necrotic or apoptotic under light microscopy?
Necrotic. The apoptosis like feature of necroptosis is that the necrosis is initiated with intracellular signalling.
In TNFR1 necroptosis, what protein is eventually responsible for plasma membrane rupture?
MLKL (mixed lineage kinase domain-like protein)
What is pyroptosis?
Apoptosis accompanied by the release of the pyrogen IL-1. This is mediated by recognition of microbial products by intracellular toll like receptors leading to inflammasome activation, which casuses Caspase 1 activation, which cleaves an IL-1 precursor leading to its release. Caspase 4 and 5 are later actived and cause the controlled death of the cell.
Which caspase is responsible for IL-1 precursor activation?
Caspase 1
How does pyroptosis compare with apoptosis?
Apoptosis is purely non-inflammatory and non-necrotic process driven by caspases. Like apoptosis, pyroptosis is also non-necrotic. It is unlike apoptosis however in that it is a purposfully proinflammatory process that is driven by caspases that do this acitvely - caspase 1,4,5.
What is ferroptosis?
Death caused by excessive intracellular levels of iron or reactive oxygen species. Resembles necrosis under light microscopy.
How do increased iron or reactive oxygen species cause cell death in ferroptosis?
The excess iron or reactive oxygen species overwhelm the glutathion-dependent atioxiant defences in the cell, and unchecked membrane lipid peroxidation. This disrupts the plsama membrane, interfering with its fluidity, lipid-protein interactions, ion permeability, and transmembrane signalling pathways. The process is however regulated by specific intracellular signalling pathways and can be everted if the causeative agents are reduced - thus the distinction from necrosis.
Does ferroptosis look more like necrosis or apoptosis under light microscopy?
Necrosis. The process is however regulated by specific intracellular signalling pathways and can be everted if the causeative agents are reduced - thus the distinction from necrosis in name.
Autophagy describes what?
A cell eating its own contents. It’s the way in which intracellular contents are recycled.
What are the steps involved in autophagy?
‘Initiation’ and ‘nucleation’ complexes combine and trigger the engulfment of no longer needed intracellular components in membrane derived from the ER to be begin forming the autophagosome. A key protein (microtubule-associated protein light chain 3) is involved in ensuring the elongation of the membrane around th autophagmosome until it becomes fully enclosed. The autophagosome then fuses with lysosomes which destroy its contents for reuse.
What is the effect of uncontrolled calcium concentration rise intracellularly?
Phopholipase, endonuclease, ATPase, and protease activity all increases in an uncontrolled manner, leading to the destruction of the cell inside out.
How do cell sdie from ischaemia?
ATP production reduced to glycolysis -> sodium/K pump failure -> water influx and cell oedema -> pH rise due to lactate production leads to DNA damage -> ribosomal detachment -> necrotic death
What is the most common type of metaplasia seen?
Change from columner to squamous metaplasia. Seen in smokers in their bronchial epithelium.
What is cholesterolosis?
The accumulation of cholesterol laden macrophages in the lamina propria of the gallbadder
In nephrotic disease, what is likely to be seen in the cells of the proximal renal tubules?
Reabsportion droplets - reabsorption of some of the protein that is being lost in the glomerulus is seen as small vacuoles of protein in the proximal renal tubular cells, taken up by pinocytosis. The protein appears pink (eosinophilic). The ER of these cells becomes hughely distended and forms ‘Russell bodies’ (dense homogenous eosinophillic inclusions).
