Robbins Chapter 3 - Tissue Renewal Flashcards
What is obligatory asymmetric replication?
This is replication of stem cell in which one daughter becomes differentiated, but the other daughter remains a progenitor.
What is stochastic differentiation?
Some stem cells will produce two differentiated cells, while some will produce two stem cells.
What is transdifferentiation?
This is the change in commitment of cell lineage by a differentiated cell. The ability to perform this is developmental plasticity.
Describe how to attain embryonic stem cell and what can be done with them.
ES cells are harvested from the inner cell mass of a blastocyst. These can be maintained in culture or induced to differentiate. Useful in the production of knockout mice and therapeutic cloning.
What are induced pluriplotenet stem cells? What transcription factors are required to induce pluripotency? What is an immunologic benefit of these stem cells?
Induced pluripotent stem cells are adult cells which have been transduced in culture by the activation of genes Oct3/4, Sox-2, c-myc, and Kfl4. They are immunologically beneficial because they avoid a host immune response.
What are adult stem cells, transit amplifying cells, and progenitor cells?
Adult stem cells are multipotent cells found in various quiescent and labile tissues. They give rise to transit amplifying cells which lose the ability to self-perpetuate and give rise to progenitor cells. Progenitors are committed to a cell lineage.
What is significant about hematopoietic stem cells (HSCs) and how can they be collected (3)?
HSCs can generate any and all blood cell lineages. They can be collected directly from bone marrow, umbilical cord blood, or peripherally in patients on GM-CSF.
What is significant of mesenchymal stem cells (MSCs) in bone marrow?
MSCs do not participate in normal tissue homeostasis. They can divide into chondrocytes, osteoblasts, adipocytes, myoblasts, and endothelial precursors.
What is significant of oval cells in the liver?
Oval cells are located in the canal of herring at the periphery of the classic hepatic lobule. They serve as a reservoir of stem cells if hepatocytes are unable to regenerate the liver. Can differentiate into non-parenchymal cells of the liver as well.
What types of stem cells (3) are found in the skin? What type of regeneration do they contribute to? How are they stimulated?
Bulge stem cells - can give rise to all cells of the epidermis in instances of extreme injury
Interfollicular stem cells - scattered throughout epidermis and give rise to transit amplifying cells which proliferate the epidermis
sebaceous stem cells
Stimulated by the Wnt pathway and inhibited by bone morphogenic protein (BMP)
Describe stem cells of the intestinal epithelium.
Stem cells in the small intestine are located above the crypt cells. Within the colon they are located at the base of a crypt. Controlled by the Wnt/BMP pathway.
Describe limbal stem cells
Lie at the junction of the cornea and the conjunctiva
How is the transition through cell cycle checkpoints mediated?
Binding of cyclins to CDKs allows the phosphorylation of transcription factors required to progress the cell cycle.
Note: there are CDK inhibitors involved as well
Give an example of a CDK inhibitor
Retinoblastoma susceptibility protein (RB) binds to E2F (transcription factor). When RB is phosphorylated it will release E2F and allow transcription.
What are the sources (2) and functions (3) of EGF?
Sources = platelets and macrophages
Functions = Mitogenic for keratinocytes/fibroblasts, stimulates migration of keratinocytes, promotes granulation tissue
What are the sources (3) and functions (3) of TGF-α?
Sources = macrophages, T lymphocytes, and keratinocytes
Functions = mitogenic for epithelial cells/fibroblasts/hepatocytes, promotes granulation tissue, migration of keratinocytes
What is the source (1) and function (2) of HGF?
Source = mesenchymal cells
Function = promote proliferation of hepatocytes/epithelial cells/endothelial cells, increase migration of keratinocytes
Note: this is required for cell migration in embryonic development
What are the sources (5) and functions (5) of PDGF? How is it released? What role does it play in liver fibrosis?
Sources = platelets, macrophages, endothelial cells, keratinocytes, and smooth muscle cells.
Functions
- Chemotactic for PMNs, macrophages, fibroblasts, and smooth muscle cells
- Activates PMNs, macrophages, and fibroblasts
- Mitogenic for fibroblasts, endothelial cells, and smooth muscle cells
- Production of MMP, hyaluronic acid, and fibronectin
- stimulates angiogenesis and wound contraction
Released from platelet granules upon platelet activation
Activates hepatic stellate cells in liver fibrosis
What is the function (3) of VEGF and the two clinically significant receptors?
Function = angiogenesis, increase vascular permeability, and promote proliferation of endothelial cells
VEGFR-2 is the main receptor involved with vasculo- and angiogenesis
VEGFR-3 is the main receptor in lymphangiogenesis
What are sources (5) and functions (5) of FGF-1 and -2?
Sources = macrophages, mast cells, T lymphocytes, endothelial cells, and fibroblasts
Functions
1. Chemotactic for keratinocytes and fibroblasts
2. Stimulates the proliferation of keratinocytes and fibroblasts
3-5. Stimulates angiogenesis, wound contraction, and matrix deposition
Note: FGF-2 is important in wound re-epithelialization
What is the source (1) and function (4) of KGF?
Source = fibroblasts
Functions
1-3. Stimulate migration, proliferation, and differentiation of keratincytes
4. Promotes re-epithelialization
What is significant about the interaction of heparin sulfate and FGF?
Heparin sulfate is a component the ECM that binds FGF creating a reservoir
What are the sources (7) and functions (4) of TGF-β?
Sources = PMNs, macrophages, platelets, smooth muscle cells, lymphocytes, fibroblasts, and endothelial cells
Functions
- Chemotactic for PMNs, macrophages, lymphocytes, fibroblasys, and smooth muscle cells
- Stimulates angiogenesis and fibroplasia
- Inhibits production of MMP
- Inhibits proliferation of keratinocytes
Discuss how RTKs transduce signals and relevant ligands for these receptors (7)?
RTK’s transduce signals through the activation of effector molecules - GRB-2, phospholipase C, and PI3K
Ligands - EGF, VEGF, TGF-alpha, HGF, FGF, PDGF, and insulin
What is the mechanism of action of GRB-2?
Mediates the production of RAS-GTP which can activate the MAPK pathway
What is the mechanism of action of PLC?
Forms IP3 from phospholipids. IP3 causes release of stored calcium and activation of DAG. Both have the effect of increasing Protein kinase C funciton
What is the mechanism of action of PI3K?
Phosphorylates membrane phospholipids which will result in the activation of protein kinase B (Akt)
What second messengers do tyrosine kinase associated receptors activate?
Jak/STAT
In liver regeneration what signals (2) are responsible for priming of hepatocytes and what signals (2) are responsible for initiating DNA replication?
Il-6 and HGF
IL-6 and TGF-alpha
What color is collagen in a trichrome stain?
Blue, everything else is red or clear
What is the three amino acid repeat of collagen?
Gly-X-Y
X and Y = any amino acid other than cysteine or tryptophan
Note: Hydroxyproline stabilizes the triple helix
Describe the synthesis of collagen
Translated into a pre-pro-alpha chain which is hydroxylated and glycosylated during translation. Secreted as a pro-chain which is cleaved by proteases. Cross-linking of collagen fibrils occurs through the oxidation of lysine to hydroxylysine by lysyl oxidase.
What explains poor wound healing in scurvy?
Vitamin C is required for hydroxylation of collagen
Where are Collagen Types I, II, III, IV, and VII found?
Type I - hard and soft tissues, replaces type III in wound healing
Type II - cartilage and tendons
Type III - preliminary matrix in wound repair, replaced by Type I
Type IV - major component of the basement membrane along with laminins
Type VII - anchors epithelia to mesenchymal structures
Describe the interaction of elastin and fibrillin in producing elastic fibers. How do elastic fibers relate to TGF-β?
Elastic fibers are a core of elastin proteins surrounded by fibrillin. Fibrillin serves to create a scaffold for the deposition of elastin.
Elastic fibers influence the availability of TGF-β
What are the two types of fibronectin and their functions?
Plasma fibronectin binds to fibrin to reinforce clots and provide a substratum for ECM
Tissue fibrin can bind collagen, integrins, proteoglycans, and cell receptors allowing for cell-matrix and cell-cell interactions.
How does mechanical stimulus from the ECM alter cell actions?
The ECM is linked to the cell cytoskeleton through integrin and focal adhesion complexes. Focal adhesion complexes include vincullin, talin, and paxillin. These proteins will transduce signals through the cytoplasm to the nucleus.
What are two examples of cadherins?
Zonula adherens - tight junctions near the apical surface of the cell
Desmosomes - stronger and more extensive junction
How are cadherins linked to the cell cytoskeleton?
Cadherins are linked to beta-catenins which are connected to the cytoskeleton through a-catenin
Note: This interaction allows for contact inhibition
Which cadherin is implicated in breast and gastric cancers?
E-cadherin dysfunction has been linked to these cancers
How do Wnt and Beta-catenin relate to one another? How does this relate to liver and GI cancers?
Wnt is a receptor which leads to the accumulation of free cytoplasmic beta-catenin when activated. Accumulation of beta-catenin can result in increased cell migration.
How dose hyaluronan stimulate leukocyte recruitment?
Hyaluronidases will for low molecular weight HA (LMW HA) which act as a chemotactic factor for leukocytes by binding CD44 in the ECM and activating the production of cytokines.
What are the steps (6) of angiogenesis?
- vasodilation and increased permeability in resopnse to VEGF and NO
- Degradation of basement membrane by MMP
- migration of endothelial cells
- proliferation of endothelial cells
- maturation of endothelial cells
- recruitment of periendothelial cells
How does VEGF specifically participate in angiogenesis?
Allows the recruitment of endothelial precursor cells. Stimualtes the migration, proliferation, and differentiation of endothelial cells.
Note: Endothelial cells also respond to FGF-2
Describe notch/delta interaction in angiogenesis
Notch is expressed by stalk cells of proliferating vessels. Deltal-like ligand (Dll4) is expressed by tip cells of proliferating vessels. Dll4 expression is promoted by VEGF. As Notch is activated it induces the maturation of stalk cells leading to organization of capillaries and prevention of excessive angiogenesis by decreasing the responsiveness to VEGF.
Describe the roles of Ang1, Ang2, PDGF, and TGF-β in stabilizing new vessels.
Ang1 binds to Tie2 to cause the recruitment of periendothelial cells
Ang2 increases the responsiveness of endothelial cells to VEGF. Unless there is an absence of VEGF, in which case angiogenesis is inhibited.
PDGF - recruits smooth muscle cells
TGF-β - stabilizes new vessels by inducing the deposition of ECM
What is the role of integrin αVβ3 in angiogenesis?
critical for the maintenance and formation of new blood vessels
How do matricellular proteins like thrombospondin, SPARC, and etc. participate in angiogenesis?
They destabilize cell-matrix interactions allowing angiogenesis
What is endostatin?
This is a fragment of collagen liberated by proteases in angiogenesis. It serves to inhibit angiogenesis.
Describe the steps (7) in cutaneous wound healing?
Formation of blood clot, formation of granulation tissue, cell proliferation and collagen deposition, scar formation, wound contraction, connective tissue remodeling, and recovery of tensile strength
Describe the process of cell proliferation and collagen deposition in cutaneous wound healing.
Collagen fibrils will appear vertically at the edges of the wound. Epithelial cells will proliferate along the edges of the wound at the dermis and fuse at midline. Subsequent proliferation leads to thickening of the epidermis. Concurrent with re-epithelialization collagen fibrils begin to bridge the wound. Preliminary matrix is made of Type III collagen, fibronectin, and fibrin. this will eventually be replaced with type I collagen.
Under what influence do myofibroblasts form and what is their function?
Influences to differentiate from fibroblasts by PDGF, TGF-beta, and FGF-2
What is a keloid?
This occurs when a scar overgrows the boundaries of the original wound
Note: African-americans are prone to this
What is an exuberant granulation?
This is excessive proliferation of granulation tissue leading to the blockage of re-epithelialization and the production of proud flesh.
Note: must be removed by cautery or surgically
What is a desmoid/aggressive fibromatoses?
recurrence of exuberant fibroblast proliferation after excision
Note: fall in the grey area between benign proliferation and malignancy
