sashwati roy, phd associate professor department of surgery the extracellular matrix (ecm)
TRANSCRIPT
Sashwati Roy, PhD
Associate ProfessorDepartment of Surgery
The Extracellular Matrix (ECM)
Learning Objectives At the end of this module, you will learn to:
Describe
• the composition of the extracellular matrix and its function.
Determine
• the role and significance of insoluble and soluble components of ECM
Describe
• the clinical implication of ECM in tissue repair
• Network of proteins and carbohydrates that binds cells together
• Supports and surrounds cells• Regulates cells activities• Lattice for cell movement
Cells surrounded by spaces filled with extracellular matrix(Molecular Biology of the Cell. 4th edition.Alberts B, Johnson A, Lewis J, et al.New York: Garland Science; 2002)
Extracellular matrix (ECM)
• Mechanical support• Embryonic
development• Pathways for cellular
migration• Wound healing• Management of growth
factors
ECM key functions
Insoluble components
• (fibrous proteins: Collagen, Elastic fibers, Fibronectin, Laminin
Soluble components-
• polysaccharide chains - Proteoglycans, Hyaluronan, Adhesive glycoproteins
Class of macromolecules that form the ECM
1.Collagen2.Elastic fibers3.Fibronectin4.Laminin
INSOLUBLE COMPONENTS
Collagen
Collagen is strong,
resisting tensile forces
(in abundance in the Achilles
heel)
Major insoluble fibrous
protein of the extracellular matrix and connective
tissue
Most abundant protein in animals
Made by fibroblasts and some epithelial
cells
Crystal Structure of The Collagen Triple Helix Model Pro- Pro-Gly103 04
Crystal structure of the collagen triple helix model [(Pro-Pro-Gly)10]3. Protein Sci. 2002 February; 11(2): 262–270.
Collagen –structure
Fibrillar• Forms
structures such as tendon or cartilage
Sheet forming
Connecting• Supports and
organizes fibrous collagen
Trans-membrane
Types of collagen
Fibrillar collagen are components
of the well-known striated fibrils
The fibrillar collagen family
includes types I-III, V and XI
Fibrillar Collagen
Polymerizes into sheets
Forms basal membranes –
collagen IV
Collagen VIII – Descemet’s
membrane of cornea
Sheet forming collagen
Link fibrillar and sheet forming
collagens to into networks and
connect them to other structures
Collagen VI – short helices
interspersed with globular domains
Align collagen I into parallel structures
Connecting collagens
• Collagens serve as a structural support
• Recent evidences indicate that collagen and collagen-derived fragments control many cellular functions, including cell shape and differentiation, migration, and synthesis of proteins
Role of Collagen in Wound healing (Collagen is a key component of a healing
wound)
• are a number of different collagen dressings available.• are purified in order to render it non-antigenic. • can vary in concentration and type. • may contain ingredients, that can enhance absorbency,
flexibility, and comfort, and help maintain a moist wound environment.
• are meant to enhance the wound management aspects of the dressings.
Collagen-based Wound Dressings
By: David Brett, Wounds, 2009
Collagen-based wound
dressings
Collagen Degradation
• Proteinase resistant triple helix
• Cleaved by collagenase (MMP-1)
MMP-1
Matrix Metalloproteinases
J. Cell. Mol. Med. Vol 9, No 2, 2005 pp. 267-285
"Tissue" Proteinases
• Epidermis– collagenase (MMP-1)– stromelysin-1,2 (MMP-3,10)– plasminogen activator (urokinase type)
• Mesenchyme– collagenase (MMP-1)– stromelysin 1 (MMP-3)– 72kDa gelatinase (MMP-2)– 92kDa gelatinase (MMP-9)– plasminogen activator (uPA)
MMP Biology• MMPs secreted as zymogens• Complex activation pathways• Counteraction by Tissue Inhibitors
of Metalloproteinases (TIMPs)
Cell-associated MMPs and their target substrates that modulate cell motility.
MMP Activation in Epithelial Repair
• Injury exposes epithelia to a new ECM environment - collagen I/fibrin/fibronectin
• Migration on to these substrates requires– Regprogramming of matrix receptors (integrins)– Loss of intercellular contacts– Activation of MMP pathways
Granulocyte Proteinases
• Serine proteinases– elastase– cathepsin G– proteinase 3– azurocidin – neutrophil collagenase (MMP-8)
Macrophage proteinases– collagenase (MMP-1)– metalloelastase (MMP-12)
Modulators of Proteinase Activity
• Serpins• Maspins• TIMP's• SLPI• a-2 macroglobulin• PAI-1
1.Collagen2.Elastic fibers3.Fibronectin4.Laminin
Insoluble components
A network of elastic fibers in the extracellular matrix of the tissue gives it the required resilience so that they can recoil after transient stretch
Elastic fibers. These scanning electron micrographs show (A) a low-power view of a segment of a dog's aorta and (B) a high-power view of the dense network of longitudinally oriented elastic fibers in the outer layer of the same blood vessel.
Elastic fibers
Elastic fibers
Elastin
• is unusually rich in proline and glycine • is not glycosylated• contains some hydroxy-proline has no
hydroxylysine.
Soluble tropoelastin (the biosynthetic precursor of elastin)
• The molecules are joined together by covalent bonds (red) to generate a cross-linked network.
• In this model, each elastin molecule in the network can expand and contract as a random coil, so that the entire assembly can stretch and recoil like a rubber band.
Elastin
Elastin
Rich in hydrophobic amino acids
Synthesized as soluble
tropoelastin
Crosslinked by lysyl oxidase
Diseases of connective TissueCutis laxa (CL), or elastolysis. is a group of rare connective tissue disorders in which the skin becomes inelastic and hangs loosely in folds.
Marfan syndrome. a genetic disorder of the connective tissue. The syndrome is carried by the gene FBN1, which encodes the connective protein fibrillin-1.
Ehlers–Danlos syndrome (EDS) is an inherited connective tissue disorder caused by a defect in the synthesis of collagen, specifically mutations in the COL5A and COL3A genes.
1.Collagen2.Elastic fibers3.Fibronectin4.Laminin
Insoluble components
Fibronectin
a dimer composed of two
very large subunits joined
by disulfide bonds at one end
Each subunit is folded into a
series of functionally
distinct domains
All forms of fibronectin are
encoded
Fibronectin binds integrins.
Molecular Biology of the Cell. 4th edition.Alberts B, Johnson A, Lewis J, et al.New York: Garland Science; 2002)
The structure of a fibronectin dimer
secreted primarily by fibroblasts
cell adhesion, growth,
migration, and differentiation
important for wound healing
cancer and fibrosis
Fibronectin
1.Collagen2.Elastic fibers3.Fibronectin4.Laminin
Insoluble components
Molecular Biology of the Cell. 4th edition.Alberts B, Johnson A, Lewis J, et al.New York: Garland Science; 2002)
Laminin
Laminin modulation during wound repair
Reduced laminin-322 levels has been associated with poor
keratinocyte migration
Hemidesmosomes bind to laminin in the
basal lamina
During wound healing, laminin-5 is
expressed by keratinocytes
The epidermal growth factor-like repeats in laminin are examples of
matrikines.
• polysaccharide chains of the class called glycosaminoglycans (GAG), which are usually found covalently linked to protein in the form of proteoglycans
Soluble components of extracellularmatrix
Figure. The repeating disaccharide sequence of a dermatan sulfate glycosaminoglycan (GAG) chain.
Molecular Biology of the Cell. 4th edition.Alberts B, Johnson A, Lewis J, et al.
New York: Garland Science; 2002)
Glycosaminoglycan (GAG)
Hyaluronan
chondroitin sulfate and dermatan
sulfate
heparan sulfate
keratan sulfate
Glycosaminoglycan (GAG)
The relative dimensions and volumes occupied by various proteins, a glycogen granule, and a single hydrated molecule of hyaluronan are shown.
Hyaluronan is a polysaccharide
Molecular Biology of the Cell. 4th edition.Alberts B, Johnson A, Lewis J, et al.
New York: Garland Science; 2002)
Proteoglycans
Molecular Biology of the Cell. 4th edition. Alberts B, Johnson A, Lewis J, et al. New York: Garland Science; 2002)
Examples of proteoglycans
• ECM are network of proteins and carbohydrates that binds cells together.
• ECM is required for mechanical support, embryonic development, pathways for cellular migration, wound healing and management of growth factors
• ECM is composed of insoluble and soluble macromolecules
• Insoluble components involve: collagen, elastic fibers, fibronectin and laminin
• The soluble components involve polysaccharide chains of the class called glycosaminoglycans (GAG), which are usually found covalently linked to protein in the form of proteoglycans
• The inheritable ECM disorders in human are Marfan syndrome, Ehlers-Danlos syndrome, venous malformation etc.
• Other ECM disorders include cancer, fibrosis, scleroderma etc,
SUMMARY
1. The Molecular and Cellular Biology of Wound Repair, edited by R.A.F. Clark, Plenum Press, NY
2. The Extracellular Matrix of Animals. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002.
Learning Resources
ECM Quiz
Questions? [email protected]
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