1. Tissue Engineering & Drug Delivery BBI 4203
Lecture 4
Extracellular Matrix (ECM)

2. Cell-cell and cell-matrix interaction

3. Roles of extracellular matrix (ECM)
Structural support
- tensile strength, stiffness, elasticity
Cell adhesion
- many cells die in suspension - they must adhere to a surface
Cell morphology
Cell proliferation/differentiation and metabolism
- second messenger action (focal adhesion kinases)
Cell migration
- neurons trying to connect up with all the proper muscles
- embryogenesis

4. Extracellular matrix - composition
Three-dimensional array of protein fibers embedded in the
hydrogel made of glycosaminoglycans (GAGs)
Primary ECM components
Polysaccharide chains (carbohydrates)
- Glycosaminoglycans (GAGs)
- Proteoglycans
Fibrous proteins
- Collagen
- Elastin
- Fibronectin
- Laminin
Structural
Adhesive

5. Polysaccharides Condensation polymers made from sugar monomers
Primarily modified glucose
Water absorbing or water wicking
Structural polysaccharides
Cellulose, chitin
Energy storing polysaccharides
Starch and glycogen
Lubrication and viscous damping
Ground substance

6. Simple and complex carbohydrates

7. Simple sugars

8. Polysaccharides

9. Cellulose

10. Ground substance Gel-like matrix embedded with proteins and cells
Viscous aggregate of water-swollen polysaccharides linked to proteins
Acts as shock absorber and lubricant
Glycosoaminoglycans
Hylanuronic acid backbone
Proteoglycan monomers
Link proteins
Hylauronic acid gel

11. Amorphous gel matrix interspersed between cells, collagen and elastin
A=fibroblasts, B=collagen fibers, C=elastin fibers, D=reticular fibers

12. Proteoglycan aggregate: “bottle brush” structure of ground substance
Backbone
High mwt and linear GAG of HA
Proteoglycan monomer “bristles”
Low mwt linear GAG linked to core protein
Link protein links monomer to HA backbone
Higher density of bristles the more hydrated the tissue

13. Glycosoaminoglycans (GAGs)
GAG: net negatively charged and polar strands get heavily solvated, which interacts strongly w/ positive charges and H-bonds w/ water
Hyaluronic acid (HA) is main component of GAG
Linear polysaccharide of copolymer D-gluconate and N-acetyl-D-glucosamine
1000kDa
Smaller GAGs make up bristles
Chondroitin-4-sufate, chondroitin-6-sulfate, dermatan sulfate, keratin sulfate
10-35kDa

14. Glycosaminoglycans (GAGs)
Unbranched polysaccharide chains composed of repeating
disaccharide units
Relatively inflexible, water soluble, coil in random configuration
10% in weight
Occupy a large amount of space and form hydrated gels
Negatively charged since sulfated (S03-)
Main groups:
Hyaluronan (hyaluronic acid)
Dermatan sulfate
Chondroitin sulfate
Heparin sulfate
Heparin
Keratin sulfate
Typically sugars long

15. Types of GAGs

16. Hyaluronan (hyaluronic acid)
Unsulfated, not attached to protein, free of other sugar groups
Facilitates cell migration
Other GAGs attached to protein – they form
Proteoglycans (up to 95% sugar)

17. Proteoglycans
Cartilage, synovial fluid

18. Tissue hydration
Hydrated tissues: proteoglycan brushes attached per HA molecule
Connective tissue and cartilage
Low hydrated tissues: 1-2 proteoglycan brushes per HA molecule
Cornea
Nonhydrated tissues: no ground substance
Hair and nails

19. Hyaline cartilage

20. Collagen: primary structural protein in the body
12/19/2017
Collagen: primary structural protein in the body
Highly redundant, highly oriented structure -- “rope”

21. Collagen primary structure
12/19/2017
Collagen primary structure
Five types of collagen
Types I, II, III, IV, V
All with the same basic structure
[-Gly-Pro-Hyp-Gly-X-]n
~31-34% ~12-14% ~9-10%
X=Aspartic acid, Glutamic acid, Asparagine, Lysine, Arginine, Histidine (all polar ==> H bonding)

22. Secondary structure Left-handed alpha helix Pro & Hyp bulky
12/19/2017
Secondary structure
Left-handed alpha helix
Pro & Hyp bulky
Force helical structure
Nature’s polypropylene

23. Tertiary structure Right-handed triple helix Coiled-coil Tropocollagen
12/19/2017
Tertiary structure
Right-handed triple helix
Coiled-coil
Tropocollagen
Trimeric collagen molecule

24. Quaternary structure Collagen molecules pack into fibrils
12/19/2017
Quaternary structure
Collagen molecules pack into fibrils
Banded appearance due to density of fibril overlap

25. Crosslinking of tropocollagen to form collagen fibrils
12/19/2017
Crosslinking of tropocollagen to form collagen fibrils

26. Laminin
Large heterotrimeric cross-shaped protein

27. Laminin structure
Three polypeptide subunits a (5 types), b (3), and g (3)
At least 12 different types found in mammals
- Laminin 1 consists of a1, b1, g1
- Laminin 5 consists of a3A, b3, g2
Binding domains for:
- Collagen IV
- Heparin
- Heparan sulfate
- Cell binding (integrin)
- Cell specific binding (nerve, liver)

28. Laminin function

29. Basal lamina - proteins
(entactin)

30. Collagen and Elastin

32. Skin, ligament and tendon
collagen
elastin
ligament
tendon
skin
stress
strain

33. Specialized connective tissue
Un-mineralized connective tissue
Loose and dense irregular connective tissue
Tendon
Ligament
Cartilage
Blood vessels
Skin
Mineralized connective tissue
Bone
Teeth