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? Sashwati.Roy@osumc.edu

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