Extracellular matrix

Question 1

Functions of the ECM

Answer 1

• 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

Question 2

What are the “reinforcing fibers”/fibrous proteins of the ECM?

Answer 2

Collagen

Elastin

Keratin (in hair and nails)

Question 3

What makes up the hydrated gel of the ECM?

Answer 3

Proteoglycans + Hyaluronic acid

(+Keratohyaline in hair and nails)

Question 4

What cells are most responsible for synthesizing ECM after wound healing?

Answer 4

Fibroblasts

Question 5

What cells are responsible for forming cartilage? Bone?

Answer 5

Cartilage- chondrocytes

Bone- osteoblasts

Question 6

What component of the ECM holds cells in it?

Answer 6

Multiadhesive matrix proteins

Fibronectin, laminin, thrombospondin, tenascin, vitronectin, van williebrand factor, nidogen/entactin

Question 7

What’s the difference between a proteoglycan and a glycosaminoglycan?

Answer 7

GAGs- carbohydrates

Proteoglycans: one or more GAGs covalently attached to a core protein

Question 8

Hyaluronic acid

Answer 8

Hyaluronic acid is an example of a GAG that is not attached to a core protein (thus, it’s not a proteoglycan)

Question 9

Name the things that self-assemble into a basement membrane/basal lamina

Answer 9

Perlecan (proteoglycan)

Type IV collagen

Laminin, fibronectin, nidogen/entactin

Question 10

Proteoglycans: Perlecan - location and function

Answer 10

• Location: Basal lamina
• Function:
  
  • Structural function in basal lamina
  • Glomerular filtration: Prevents proteins from leaving serum to enter the urine

Question 11

Structure of the proteoglycan aggregate in cartilage

Answer 11

Aggrecan (proteoglycan) binds to hyaluronic acid via a link protein, and this complex secures high concentrations of GAGs that can hold in water

Question 12

Osteoarthritis

Answer 12

MMT and ADMTs cleave the aggrecan core protein of cartilage, releasing the fragment carrying all the GAGs –> cartilage can’t self-lubricate

Question 13

How do core proteins of proteoglycans mediate signals from outside the cell to the inside?

Answer 13

Binding specific ligands

Question 14

How are GAGs able to hold in so much water?

Answer 14

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

Question 15

Proteoglycans: Aggrecan - location and function

Answer 15

• Location: cartilage
• Functions:
  
  • Mechanical support by forming large aggregates w/ hyaluronic acid
  • Binds TGF-B to inhibit ECM synthesis

Question 16

Proteoglycans: Decorin - location and function

Answer 16

• Location*: Widespread in the ECM
• Function*:
• Limits the size of collagen fibrils
• Binds & sequesters TGF-B from cells

Question 17

Multiadhesive matrix protein

Answer 17

Large secreted protein with binding sites for both ECM components and cell surface receptors

Question 18

Fibronectin - where is it? what does it bind?

Answer 18

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

Question 19

Laminin-1 - Where is it? What does it bind?

Answer 19

Location: Basal lamina/basement membrane

It binds Type IV collagen, sulfated lipids, carbohydrates (primarily heparan sulfate), and integrins

Question 20

What multi-adhesive matrix protein is more importnat for neuronal development and maintenance?

Answer 20

Laminin is the first multiadhesive matrix protein to apear during development

Question 21

What multiadhesive matrix protein is importnat to wound healing?

Answer 21

Fibronectin laid down by fibroblasts in the early stages of wound healing

Question 22

Which multiadhesive matrix protein is more importnat in muscular dystrophy?

Answer 22

Laminin

Question 23

Fibronectin’s binding domains for cell surface receptors all have

Answer 23

RGD sequences; these are recognized by cell’s fibronectin receptors (like integrin)

Question 24

Who synthesizes laminin?

Answer 24

Epithelial and endothelial cells

Question 25

Laminins interact with other cells through \_\_

Answer 25

LG domains that bind cabrohydrates and integrins

Question 26

Which cell adhesion molecules mediate interactions between the same cell types (**homophilic**)?

Answer 26

Cadherins and NCAMs

Question 27

What types of cell adhesion proteins are utilized in leukocyte extravasation?

Answer 27

Selectins and integrins

Question 28

Which cell adhesion molecules mediate interactions between different cell types (heterophilic)?

Answer 28

Integrins and selectins ## Footnote **Integrins** bind to multi-adhesion matrix proteins (like fibronectin) **Selectins** bind carbohydrates, like glycoproteins on other cells

Question 29

Extravasation of Leukocytes - moving WBCs from inside capillaries into the tissues

Answer 29

1. Leukocyte expresses carbohydrates (**ligands for selectins**) 2. **PAFs** in the capillaries activates the endothelial cells to exocytose **P-selectins** to their surface 3. The WBC selectin ligand interacts with the endothelial cell **P-selectin --\>** rolling 4. The WBC PAF receptor then binds PAF on the endothelial cell surface, activating a **WBC integrin** 5. The WBC integrin firmly adheres to the **CAM** on the endothelial cell surface 6. Extravasation between junctions of 2 endothelial cells 7. In the tissue, WBCs can now migrate along a conc gradient of PAF to the site of injury/inflammation

Question 30

Whyw ould an agonist that increases cell adhesion prevent leukocyte extravasation and subsequent inflammation?

Answer 30

the cells bind os tightly they can't release to actually crawl between endothelial cells

Question 31

Structure of an activated vs an unactivated integrin

Answer 31

**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

Question 32

What could you deduce about integrin presence and funciton if a cell tested positive for B₁ and a₂ integrin chains?

Answer 32

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.

Question 33

What intracellular signaling pathwayas can be activated by integrin ligation?

Answer 33

**PI3 kinase** pathway - many effects **Rho/Rac/Cdc42** pathways - cytoskeletal organization **ERK/MAPK** - cell proliferation

Question 34

An integrin **antagonist** vs **agonist**

Answer 34

**Integrin antagonist--\>** reduced cell adhesion **Integrin agonist--\>** increased cell adhesion Both prevent extravasation and decrease inflammation, but an integrin agonist is better.

Question 35

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

Answer 35

B subunit

Question 36

Integrins can mediate indirect interactions with teh cytoskeleton through

Answer 36

Talin & Vinculin

Question 37

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

Answer 37

Integrin focal adhesion signaling

Question 38

**Dystrophin associated protein complex (DAPC)**

Answer 38

Anchors contractile units of the muscle fiber to the cell membrane and adjacent muscle fibers.