ECM

Question 1

How the ECM assists in the function of a multicellular organism?

Answer 1

1. Stabilizes the physical structure of cells
2. Molecular barrier to cell migration during infection and metastasis
3. Provides signals to the cell interior during morphogenesis
4. Wound healing
5. Maintenance of the differentiated state

Question 2

The ‘reinforcing fibers’ of the ECM?

Answer 2

Collagen

Elastin

Keratin (in hair and nails)

Question 3

What components make up the ‘hydrated gel’ in which cells and reinforcing fibers are embedded?

Answer 3

Proteoglycans (in most tissues)

Question 4

Role of…

1. Fibroblasts
2. Chondrocytes
3. Osteoblasts

Answer 4

Synthesize ECM after…

1. Wound healing
2. Formation of cartilage
3. Formation of bone

Question 5

What ‘holds’ the cells in the ECM?

Answer 5

The multi-adhesive matrix proteins

Fibronectin, laminin, thrombospondin, entactin, etc.

Question 6

Proteoglycan vs. glycosaminoglycan?

Answer 6

PGs = consist of one or more GAGs covalently attached to a core protein

Question 7

Hyaluronic acid

Answer 7

And example of the fact that not all GAGs are also PGs…

Since it does not covalently attach to a protein

Question 8

Proteoglycan aggregate in cartilage…

What happens to it during osteo-arthritis? (OA)

Answer 8

Aggrecan binds to hyaluronic acid via a link protein —> required for proper cartilage function

Proteolytic cleavage of the aggrecan core protein by matric metalliproteases (MMPs) and multidomain extracellular protease enzymes (ADAMTS) —> release the fragment carrying the GAG molecules from the PG aggregate

This loss of the GAG component —> makes the cartilage lose its self-lubricating properties —> OA

Question 9

Perlecan

Answer 9

PG important for glomerular filtration

Question 10

Decorin

Answer 10

PG used for controlling the size of collagen fibrils

Question 11

Aggrecan

Answer 11

PG found in cartilage

Mechanical support, forms large aggregates with hyaluronic acid…

Binds TGF-beta

Question 12

A multi-adhesive protein?

Answer 12

Usually large secreted protein that has binding sites for both ECM components and a receptor on the cell surface

Question 13

Fibronectin…location? And to what matrix molecule does it bind?

Answer 13

Found in loose connective tissue and provisional wound matrices

Binds to type I collagen fibrin, heparan sulfacte proteoglycan, and membrane intercolated integrins

An isoform of FN also circulates in the plasma

Question 14

Laminin-1

Location and what does it bind to?

Answer 14

Multi-adhesive matrix protein found in the basement membrane

Binding sites for type IV collagen, sulfated lipids, and carbohydrates (primarily heparan sulfate) and integrins

Question 15

Protein important for neuronal development?

Answer 15

Laminin

Question 16

Protein important in muscular distrophy?

Answer 16

Laminin

Question 17

Protein important in wound healing

Answer 17

Fibronectin

Question 18

Which cell adhesion molecules mediate interactions between the same cell types?

Answer 18

Cadherin and CAMs

Question 19

What types of cell adhesion proteins are utilized in the process of leukocyte extravasation

Answer 19

Selectins and integrins

Question 20

Why would an agonist that increases cell adhesion prevent leukocyte extravasaction and subsequent inflammation?

Answer 20

The cells bind to tightly that they cannot release to crawl between the endothelial cells

Question 21

Structure of activated vs inactivated integrin?

Answer 21

Inactive = folded up…therefore cannot bind to ECM molecules nor transduce signals

Active = ‘unfurls’ to expose a ligand binding site…cytoplasmic domains also disengage from each other and can now transduce signals

Question 22

Integrin presence and function?

Based on the fact that a cell tests postive for beta1 and alpha2 integrin chains

Answer 22

It MIGHT bind to collagen…since alpha2beta1 integrin has that specifity

HOWEVER…

Since the beta1 chain can also interact with a large number of other alpha subunits…additional experiments would be required to confirm this

Question 23

What intracellular signaling pathway can be activated by integrin ligation?

Answer 23

PI3 kinase pathways (many effects in the cell)

Rho/Rac/cdc42 pathways (primarily cytoskeletal reorganization)

ERK/MAPK pathways (primarily cell proliferation)

Question 24

Clostridium bacteria (gas gangrene)

Answer 24

Express type IV collagenases to allow invasion deeper into tissues

Cancers can do the same thing

Question 25

Function of the hydrated gel

Answer 25

Absorb and retain water for lubrication

Question 26

Charge of GAGs and what that allows them to do

Answer 26

They are negatively charged and highly polar Allows them to attract/absorb water —> useful to the body as a lubricant and shock absorber

Question 27

Duchenne vs. Becker muscular dystrophy?

Answer 27

Duchenne = absence of expression of dystrophin protein in cytosol Becker = lower expression/less functional dystrophin protein

Question 28

Dystrophin protein

Answer 28

Holds cytoskeleton plasma membraneECM Important with muscle cells b/c they expand and contract so much

Question 29

Alpha-beta-dystroglycan

Answer 29

Member of the sarcoglycan membrane complex...which helps connect the internal cytoskeleton to the ECM Specifically...connect laminin matrix proteins in the basal lamina of muscles

Question 30

Cadherin What it binds to = Location = Function =

Answer 30

1. Cadherin 2. Desmosomes 3. Mediate adhesion between cells during development (allowing tissue formation)

Question 31

NCAM What it binds to? Location? Function?

Answer 31

1. NCAM 2. Neurons and muscle 3. Neuronal development and have a similar structure to immunoglobulin molecules

Question 32

Integrin What it binds to to Location Function

Answer 32

1. Fibronectin 2. Multiple cell types 3. Allows communication across the plasma membrane...interacts with cytoskeleton

Question 33

Selectin What it binds to Location Function

Answer 33

1. Glycoprotein 2. WBCs and endothelial cells 3. Movement of WBCs (extravasation)

Question 34

Resting state in the extravasation process...

Answer 34

Resting state= selectin ligand is actively expressed Alpha-L-beta-2 integrin is inactive P-selectin molecule is within vesicles in the endothelial celsl

Question 35

After injury is detected in tissue (extravasation) —>

Answer 35

1. Platelet activating factor (PAF) released —> P-selectin released 2. When P-selectin is loosely attached to the selectin ligands —> leukocyte starts to ‘roll’ towards the affected tissue 3. Leukocyte is now activated and the released PAF goes on to activate alpha-L-beta-2 integrin molecule on the leukocyte 4. Alpha-L-beta-2 integrin molecules bind with ICAM molecules on endothelial surface...and PAF (on endothelial surfaces) binds to PAF receptor (on leukocyte) 5. Integrin/ICAM interaction allows the WBC to migrate through the endothelium into the underlying tissue to increase inflammation

Question 36

Multiple sclerosis

Answer 36

When the immune system attacks myelin within the CNS and causes hyper-inflammation within the body

Question 37

Natalizumab

Answer 37

Antagonistic drug therapy for MS Binds to alpha-L-beta2 integrin subunit Allows WBC to keep rolling through blood vessel without resulting in immune system destruction

Question 38

MS agonist drug therapy

Answer 38

ALB2 integrin agonist binds to WBC so tightly to the integrin molecule that it cannot move into the cell Biggest reduction of inflammation but can cause immune system destruction

Question 39

Role of integrin

Answer 39

Play huge role in cell cycle regulation... Obligate heterodimer (type of CAM) Binds to fibronectin