Extracellular matrix Flashcards
Functions of the ECM
- Scaffold that stabilizes the physical structure of cells
- Molecular barrier to cell migration during infection and metastasis
- Reservoir for growth factors
- Provides signals to cell interior during morphogenesis, wound healing, and maintenance of the differentiated state
What are the “reinforcing fibers”/fibrous proteins of the ECM?
Collagen
Elastin
Keratin (in hair and nails)
What makes up the hydrated gel of the ECM?
Proteoglycans + Hyaluronic acid
(+Keratohyaline in hair and nails)
What cells are most responsible for synthesizing ECM after wound healing?
Fibroblasts
What cells are responsible for forming cartilage? Bone?
Cartilage- chondrocytes
Bone- osteoblasts
What component of the ECM holds cells in it?
Multiadhesive matrix proteins
Fibronectin, laminin, thrombospondin, tenascin, vitronectin, van williebrand factor, nidogen/entactin
What’s the difference between a proteoglycan and a glycosaminoglycan?
GAGs- carbohydrates
Proteoglycans: one or more GAGs covalently attached to a core protein
Hyaluronic acid
Hyaluronic acid is an example of a GAG that is not attached to a core protein (thus, it’s not a proteoglycan)
Name the things that self-assemble into a basement membrane/basal lamina
Perlecan (proteoglycan)
Type IV collagen
Laminin, fibronectin, nidogen/entactin
Proteoglycans: Perlecan - location and function
- Location: Basal lamina
-
Function:
- Structural function in basal lamina
- Glomerular filtration: Prevents proteins from leaving serum to enter the urine
Structure of the proteoglycan aggregate in cartilage
Aggrecan (proteoglycan) binds to hyaluronic acid via a link protein, and this complex secures high concentrations of GAGs that can hold in water
Osteoarthritis
MMT and ADMTs cleave the aggrecan core protein of cartilage, releasing the fragment carrying all the GAGs –> cartilage can’t self-lubricate
How do core proteins of proteoglycans mediate signals from outside the cell to the inside?
Binding specific ligands
How are GAGs able to hold in so much water?
GAGs are linear repeating disacharide units (usually uronic acid & amino sugar) that are very negative due to their carboxylic acid and sulfate groups –> allows them to take in water
Proteoglycans: Aggrecan - location and function
- Location: cartilage
-
Functions:
- Mechanical support by forming large aggregates w/ hyaluronic acid
- Binds TGF-B to inhibit ECM synthesis
Proteoglycans: Decorin - location and function
- Location*: Widespread in the ECM
- Function*:
- Limits the size of collagen fibrils
- Binds & sequesters TGF-B from cells
Multiadhesive matrix protein
Large secreted protein with binding sites for both ECM components and cell surface receptors
Fibronectin - where is it? what does it bind?
It’s found in loose connective tissue in wound matrices
It binds type I collagen, heparan sulfate proteoglycan, and integrins
An isoform of fibronectin also circulates in the plasma
Laminin-1 - Where is it? What does it bind?
Location: Basal lamina/basement membrane
It binds Type IV collagen, sulfated lipids, carbohydrates (primarily heparan sulfate), and integrins
What multi-adhesive matrix protein is more importnat for neuronal development and maintenance?
Laminin is the first multiadhesive matrix protein to apear during development
What multiadhesive matrix protein is importnat to wound healing?
Fibronectin laid down by fibroblasts in the early stages of wound healing
Which multiadhesive matrix protein is more importnat in muscular dystrophy?
Laminin
Fibronectin’s binding domains for cell surface receptors all have
RGD sequences; these are recognized by cell’s fibronectin receptors (like integrin)
Who synthesizes laminin?
Epithelial and endothelial cells
Laminins interact with other cells through __
LG domains that bind cabrohydrates and integrins
Which cell adhesion molecules mediate interactions between the same cell types (homophilic)?
Cadherins and NCAMs
What types of cell adhesion proteins are utilized in leukocyte extravasation?
Selectins and integrins
Which cell adhesion molecules mediate interactions between different cell types (heterophilic)?
Integrins and selectins
Integrins bind to multi-adhesion matrix proteins (like fibronectin)
Selectins bind carbohydrates, like glycoproteins on other cells
Extravasation of Leukocytes - moving WBCs from inside capillaries into the tissues
- Leukocyte expresses carbohydrates (ligands for selectins)
- PAFs in the capillaries activates the endothelial cells to exocytose P-selectins to their surface
- The WBC selectin ligand interacts with the endothelial cell P-selectin –> rolling
- The WBC PAF receptor then binds PAF on the endothelial cell surface, activating a WBC integrin
- The WBC integrin firmly adheres to the CAM on the endothelial cell surface
- Extravasation between junctions of 2 endothelial cells
- In the tissue, WBCs can now migrate along a conc gradient of PAF to the site of injury/inflammation
Whyw ould an agonist that increases cell adhesion prevent leukocyte extravasation and subsequent inflammation?
the cells bind os tightly they can’t release to actually crawl between endothelial cells
Structure of an activated vs an unactivated integrin
Unactivated- integrin is folded up so it can’tbind ECM molecules or transduce signals
Activated- unwinds to expose a ligand binding site; cytoplasmic domains also disengage and transduce signals
What could you deduce about integrin presence and funciton if a cell tested positive for B1 and a2 integrin chains?
It MIGHT bind to collagen, since the a2B1 chain has that specificity
However, the B1 chain can also itneract with many other a subunits, so we’d need additional experiements.
What intracellular signaling pathwayas can be activated by integrin ligation?
PI3 kinase pathway - many effects
Rho/Rac/Cdc42 pathways - cytoskeletal organization
ERK/MAPK - cell proliferation
An integrin antagonist vs agonist
Integrin antagonist–> reduced cell adhesion
Integrin agonist–> increased cell adhesion
Both prevent extravasation and decrease inflammation, but an integrin agonist is better.
Each _ subunit in an integrin, depending on the aB combination, will have specificity as a receptor for the RGD motif (of fibronectin), collagen, laminin, or leukocytes
B subunit
Integrins can mediate indirect interactions with teh cytoskeleton through
Talin & Vinculin
New focal adhesions lead oto synthesis of actin fibers at the leading edge to form lamellipodia; removal of old adhesions at the back lead to depolymerization of actin.
These interactions are mediated by
Integrin focal adhesion signaling
Dystrophin associated protein complex (DAPC)
Anchors contractile units of the muscle fiber to the cell membrane and adjacent muscle fibers.
