Apoptosis: Lect 23 Flashcards
Necrosis:
- pathological
- energy indep. (passive)
- acute cell injury
- unable to maintain homeostasis
- loss of membrane integrity
- cell contents released
- surrounding tissue damage
- inflammation
Apoptosis
- physiological
- energy dep. (active)
- genetic
- programmed CD
- maintains integrity
- cell/nuclear condensation
- no surround tissue damage
- no inflammation
Morphological progression of apoptosis
-cell shrinkage > chromatin condensation of nuclear envelope “pyknosis” > nuclear envelope discontinues and DNA is fragmented “karyorrhexis” > cell memb. shows irreg. buds “blebs” > cell into vesicles “apoptotic bodies” > phagocytised by neighboring cells.
Normal roles of apoptosis:
- tissue remodeling in development “digits”
- elimination of transitory organs/tissues “nephrons”
- nervous system formation.
- menstruation: sloughing of inner uterus lining.
- cell elimination of T-cells
3 Main Component to Apop. pathway:
- Regulators: either inhibit apop (Bcl-2 & Bcl-xL) or initiate the apop. (Bak and Bax).
- Adapters: act by binding to procaspases; facilitating procas -> casp directly or self activation of procasp by aggregation (ApaF-1)
- Effectors: “caspases” proteases that serve to excute apop by targeting enzymes.
The Intrinsic Pathway:
- used to eliminate cells in response to genotoxic damage, mito damage, absence of GFs, loss of substrate adhesion.
- involves the release of cytochrome C from mitoch. forming the apoptosome.
- uses Apaf-1 and caspase 9&2 for initiation of apoptosis.
Intrinsic pathway steps:
- cell/DNA damage -> knases activated > phosphorylate/activate p53.
- p53 binds to DNA > transcription of Bax and cell cycle inhib p21.
- Bax into mitoch > release of cyto C from mito.
- cyto C binds to adapter protein, Apaf-1 > aggregates & binds to procasp. (apoptosome)
- procasp cleaved to form active casp.
Extrinsic Death Pathway – Fas
- elimination of unwanted cells during development & termination of immune response.
- initiated by activation TNF “cell death recp” – Fas receptor
- uses caspase 8/10 for apop initiation.
Extrinsic pathway steps:
- killer lymphocytes express Fas ligand on their cell surface.
- killer lym. binds to target cell via Fas death rcp.
- Fas L + Fas rcp binding recruits adapter mx.
- procasp aggregate by binding to “death effector domain” of adaptor forming death-inducing signaling complex DISC.
- procasp cleaved = apop.
Extrinsic pathway
- can also act through mitoch. due to action of BID protein which is activated by casp 8. facilitating cyto C release
- BID, BAX and BAK = proapoptotic Bcl-2 fam members.
Perforin/Granzyme Pathway:
- in response to viral infected cells.
1. cytotoxic T-cell secrete perforin and granzymes.
2. perforin forms pore in target cell
3. granzyme B enters cell and activates casp 10 = inactivation of apop inhibitors.
4. also activates casp 3 = execution of apoptosis
Targets of Caspases:
- Apoptosis regulators
- Bcl-2, Bax
- procaspases - Cell Adhesion mx.
- catenins, cadherins - Cytoskeletal proteins
- actins, keratins, tubulin - Nuclear structural proteins
- laminins
Extracellular survival factors:
-can inhibit apoptosis by binding to surface rcp > activate/produce apop inhib; Bcl-2 and inactivation of proapoptotic proteins; Bad.
p53 induces apoptosis by increasing expression of:
- pro-apoptotic Bcl-2 family members
- Fas receptors (CD95)
- IGFBP-3 (secreted out and binds to IGF1/2 (survival proteins).
Marker for apoptosis:
- DNA fragmentation in apoptotic cells facilitated by a caspase activated Dnase enzyme; cleaves DNA internucleosomal linker sites. = ladder effect in gel electrophoresis.
- Annexin 5 binds to phos.serine and presents it to outer cell surface
- Caspase assay: enzymatic assays used to detect active caspase.
