Chapter Extracellular Matrix Flashcards
What is the extracellular matrix?
- 3D network of proteins and polysaccharides
- Most abundant in connective tissue.
- Supports sheets of epithelial cells and surrounds muscle cells, adipose cells, and peripheral nerves.
What is the basement membrane?
Thin layer of ECM and fibrous proteins that anchors and supports epithelium.
- ties epithelium to connective tissue beneath it
- acts as protective barrier and filter
Basal Lamina
- Component of the basement membrane
- Composed of ECM proteins secreted by epithelial cells
3 example - Skin
a. Outer epidermis layer-epithelial cells
b. Middle dermis layer - connective tissue.
c. Deeper subcutaneous layer
What does ECM do?
- Supports adhesion of cells
- Transmits signals through adhesion receptors.
- Binds, stores, and presents growth factors
- Shapes tissue structures.
- Guides and supports migrating cells
Collagen type 1 (fibril forming)
- form connective tissue of skin, bone, tendon, ligaments, connective tissue layers of muscle and nerves, capsules that surround internal organs, and cornea
Collagen Type 4 (network forming)
- Forms flexible sheet-like mesh due to breaks in triple helix
- important to molecular filtration, such as glomerulus which filters blood to form urine.
Collagen type 7 (anchoring fibrils)
- keeps basement membrane intact
- crucial for functional integrity of epidermis-dermis junction in skin
Osteogenesis imperfecta
- affects Type 1 collagen (fibril-forming)
- leads to weak bones that fracture easily
Alport syndrome
- Affects Type 4 collagen (network-forming)
- Causes progressive nephritis, hearing loss, and ocular lesions
Dystrophic epidermolysis bullosa (DEB)
1 epidermolysis bullosa is inherited diseases in which skin blisters in response to minor injury, hear or frictions from rubbing or scratching.
2- DEB affects type 7 collagen (anchoring fibril)
3- Important for anchoring epidermis to dermis
What allows collagen 4 to be more flexible than collagen 1
Breaks in the triple helix structure
Glycosaminoglycans
- long chain of disaccharides
- one sugar usually sulfated.
Proteoglycans
- very heterogenous in size and composition
- regulate distribution of extracellular signaling molecules
- modulate signaling events at cell surface
- serve as structural constituents of ECM
- regulate movement of molecules between intracellular and extracellular compartments
- fibroblast growth factor has to bind to PG in order to activate its cell surface receptor.
- PG help form filtering apparatus in kidney by acting as molecular sieve in glomerulus
- aggregate major PG in cartilage, enzymatic destruction one of the early signs of arthritis
- enzymes that degrade PGs are important because they allow growth factors to be released when needed.
Fibrillin
- fibrillin-1 and fibrillin-2
- forms microfibrils and associate with elastic fibers in ECM
- found in skin, lens of eye, aorta, periosteum.
- provides scaffold for tissues
- fibrillin-1 gene mutated in Marfan syndrome either has defective protein or lower amounts present in ECM
Marfan syndrome
Malformations of digits, limbs, and anterior chest wall
- myopia due to lens dislocation
- aneurysm due to large lower aorta with weak walls
Fibronectin
-two large subunits connected at their carboxyl termini by disulfide bonds
- multiple forms of protein present
- plasma forms are soluble and circulate in blood; non-adhesive
- cell/matrix forms are insoluble and found on surfaces of cells; involved in adhesion
- forms generated from one gene by alternative splicing.
Functions:
-blood clotting - plasma form attaches to fibrin in clot, which attracts fibroblasts to site.
-Wound healing, platelet adhesion and aggregation, cell adhesion, binding to bacteria, fetal fibronectin used to screen form premature delivery
Lamin
- composed of 3 chains which form cross-shaped structure
- interacts with collagen 4 and PGs
- has tissue specific isoforms
- alpha3, beta3, and gamma2 chains form laminin 5 which is in skin
a. Connects epidermis to dermis
b. Defects in any chain can cause junctional epidermolysis bullosa (JEB)
Which of the following ECM molecules is defective in Marfan syndrome
Fibrillin
Matrix degradation
- Regulated turnover of ECM is important in wound healing, bone remodeling, migration of white blood cells into tissues in response to injury and reproduction.
- excessive/inappropriate ECM degradation can cause arthritis, multiple sclerosis, tooth decay, cardiovascular disease, chronic obstructive pulmonary disease and cancer metastasis
Matrix metalloproteinases
- ECM degradative enzymes
2. Require Zn or Ca to function
Regulation of Matrix degradation
- Proteases secreted as inactive precursors that can be activated locally
- Action of proteases confined to specific areas by secreted protease inhibitors.
- a tissue inhibitors of metalloproteinases
Stages of Wound Repair
- Inflammatory
- Proliferation
- Remodeling
Role of ECM molecules and MMP’s in inflammatory stage
- fibronectin part of blood clot
- MMPs facilitate release of cells that migrate into wound
Role of ECM molecules and MMP’s in proliferative stage
- cells migrate to cover wound and form new epidermis
- provisional matrix formed
- connective tissue cells (fibroblasts) synthesize collagen, predominantly type 3
- Fibroblasts synthesize matrix form of fibronectin, which during healing is replaced by collagen
- GAGs such as hyaluronan allow cells to migrate
- PGs store and the release growth factors
- MMP expression up-regulated to degrade ECM proteins
