Components of the Extracellular Matrix

Slide 1 · Components of the extracellular matrix

COMPONENTS OF THE

EXTRACELLULAR MATRIX

Structure • mechanics • cell adhesion • disease

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

By the end, explain how matrix molecules shape tissue behavior.

Identify

Classify the three major ECM families

Explain mechanics

Distinguish tensile strength, recoil, compression

Explain adhesion

Connect glycoproteins, receptors and cytoskeleton

Interpret disease

Link molecular defects to clinical consequences

Slide 3 · Three major molecular families

Matrix functions arise from three complementary classes.

FIBROUS PROTEINS

Collagen: Tensile strength

Elastin: Recoil

HYDRATED GELS

Proteoglycans / hyaluronan

Compression resistance

ADHESIVE MOLECULES

Fibronectin / laminin

Cells ↔ ECM connections

Slide 4 · Each family addresses a different physical demand

A tissue must resist pulling, recover shape and withstand compression.

Tensile loads are resisted by collagen-rich structures.

Recoil depends on elastin-containing fibers.

Hydrated gel dissipates compressive forces.

Tension

Collagen network

Elastic recoil

Elastin fibers

Compression

Proteoglycan gel

Adhesion

ECM glycoproteins

Slide 5 · Interstitial matrix and basement membrane differ

ECM composition reflects its anatomical location.

Dimension

Interstitial matrix

Basement membrane

Architecture

Three-dimensional gel and fibers

Organized planar mesh

Dominant components

Collagens, elastin, fibronectin, GAGs

Type IV collagen and laminin

Relation to cells

Stromal intercellular spaces

Specialized interface with cells

Role

Support / cushioning

Adhesion / specialized surface

Slide 6 · Cells are connected to their surrounding matrix

Integrin contacts translate ECM architecture into cellular responses.

Cells engage fibronectin and laminin through integrins.

Integrins connect extracellular ligands with cytoskeletal elements.

These contacts can regulate shape, migration and growth.

ECM: Laminin / fibronectin

α

β

Cell membrane

Actin-associated signaling machinery

Slide 7 · Collagen is a three-chain triple helix

Three polypeptide chains form a rope-like structural protein.

Three separate polypeptide chains intertwine.

The triple helix provides the molecular building block.

Different collagen types have distinct tissue roles.

Three intertwined polypeptide chains

Triple-helix schematic

Slide 8 · Fibrillar collagen types

Some collagens assemble into long fibrils that bear tension.

Types I, II, III and V are examples of fibrillar collagens.

Linear fibrils constitute much of connective tissue.

Fibrillar organization differs from planar basement membrane collagen.

Type I

Fibrillar

Type II

Fibrillar

Type III

Fibrillar

Type V

Fibrillar

Slide 9 · From molecule to load-bearing fibril

Molecular alignment yields tissue-scale tensile structures.

Triple helices pack into aligned assemblies.

Lateral associations stabilize fibrillar structures.

Fibrils provide a scaffold for supportive tissue.

Triple helix

Aligned molecules

Fibril

Slide 10 · Lateral bonding creates tensile strength

Collagen fibers resist stretch because aligned helices are linked.

Interchain hydrogen bonds stabilize fibrillar assembly.

Covalent lateral cross-links contribute to high tensile strength.

This produces mechanical resistance without elastin-like recoil.

Parallel collagen molecules with lateral links

Slide 11 · Where fibrillar collagens dominate

Fibrillar networks support multiple connective tissues.

Fibrillar collagens occur in bone, tendon, cartilage and skin.

They also support blood vessels.

They accumulate in healing wounds and scars.

Bone / tendon

Load bearing

Skin / vessels

Structural integrity

Cartilage

Fibrous framework

Scar

Repair scaffold

Slide 12 · Collagen and elastin solve different load problems

High tensile resistance does not imply elastic recovery.

Property

Fibrillar collagen

Elastin-rich fiber

Principal property

Resistance to tensile force

Stretch and recoil

Structural basis

Aligned, cross-linked helices

Elastic core with cross-links

Response to release

Limited recoil

Return toward baseline

Key examples

Tendon / scar

Large arteries / skin

Slide 13 · Why collagen cross-links matter

A useful fiber requires both strong molecules and strong lateral connections.

Covalently linked helices distribute force.

Loss of structural integrity compromises tissue strength.

Clinical consequences depend on the affected tissue.

Triple-helical collagen molecules

Lateral covalent bonds stabilize fibrils

Tensile strength of connective tissue

Slide 14 · Vitamin C supports collagen integrity

Hydroxylation during collagen formation depends on ascorbate.

The source highlights vitamin C–dependent lysyl hydroxylation.

Defective collagen processing weakens connective tissue.

Clinical deficiency is expressed as scurvy.

Vitamin C availability

Appropriate lysine hydroxylation

Competent collagen structure / strength

Slide 15 · Scurvy: Weakened connective tissue

Vitamin C deficiency impairs tissue strength and repair.

Poor wound healing reflects deficient collagen integrity.

Vessel wall fragility contributes to easy bleeding.

Skeletal deformities may occur during growth.

Ascorbate deficiency

Defective collagen maturation

Weak connective tissues

Poor healing / bleeding

Slide 16 · Scurvy: Tissue consequences are interconnected

The same ECM defect explains multiple manifestations.

A fragile vascular matrix predisposes to bleeding.

Inadequate collagen support undermines wound repair.

Developing skeletal tissues are vulnerable in children.

Vessels

Easy bleeding

Wounds

Delayed healing

Skeleton

Growth-related deformity

Slide 17 · Inherited defects affect collagen pathways

Disorders can arise from collagen or collagen-processing gene defects.

Mutations in collagen proteins compromise the final matrix.

Mutations in enzymes affecting processing may also weaken it.

Examples named in the source include osteogenesis imperfecta and some Ehlers–Danlos syndromes.

Structural protein / processing-gene defect

Abnormal collagen matrix

Tissue-specific inherited disorder

Slide 18 · Osteogenesis imperfecta: A collagen association

Osteogenesis imperfecta exemplifies genetic collagen dysfunction.

The source links collagen mutations to osteogenesis imperfecta.

Its inclusion illustrates how a systemic matrix defect affects skeletal integrity.

Specific genotype–phenotype relationships require the dedicated genetics section.

Molecular level

Collagen mutation

Tissue level

Altered supportive matrix

Clinical framing

Skeletal fragility

Slide 19 · Ehlers–Danlos syndromes: Matrix diversity

Some Ehlers–Danlos syndromes arise from collagen-pathway defects.

Collagen and lysyl hydroxylase mutations are named mechanisms.

The disease family is genetically and phenotypically heterogeneous.

Do not assume every Ehlers–Danlos subtype has the same defect.

Structural genes

Some syndromes

Processing enzymes

Some syndromes

Teaching caution

Subtypes differ

Slide 20 · Not every collagen forms a classical fibril

Nonfibrillar collagens organize interfaces and modulate fibrils.

Type IV collagen forms planar basement membrane networks.

Fibril-associated collagens regulate collagen interactions.

Type VII collagen provides anchoring fibrils under stratified epithelium.

Type IV

Planar network

Type IX

FACIT interaction

Type VII

Anchoring fibrils

Slide 21 · Type IV collagen: Basement membrane network

Basement membranes depend on an organized collagen IV framework.

Type IV collagen is nonfibrillar.

It contributes to a flat, lamellar ECM network.

Laminin is a key associated basement-membrane glycoprotein.

Epithelial cells

Laminin + type IV collagen network

Slide 22 · Type IX collagen: A FACIT example

Fibril-associated collagen can regulate other fibrils.

FACIT = fibril-associated collagen with interrupted triple helices.

Type IX collagen is a source example in cartilage.

These collagens influence fibril diameters and collagen interactions.

Fibrillar collagen framework

Type IX FACIT association

Regulated fibril interactions / dimensions

Slide 23 · Type VII collagen: Epithelial anchorage

Anchoring fibrils help retain stratified squamous epithelium.

Type VII collagen forms anchoring fibrils.

These fibrils preserve epithelial structural attachment.

Defects can lead to inherited blistering skin disorders.

Basement membrane

Type VII anchoring fibrils

Slide 24 · A blistering phenotype can reflect failed anchorage

Epithelial separation follows loss of structural attachment.

Type VII collagen normally contributes to anchoring fibrils.

Mutations weaken the epithelial attachment system.

The source links these defects to blistering diseases.

Type VII collagen mutation

Abnormal anchoring fibrils

Epithelial attachment failure

Skin blistering

Slide 25 · Compare structural collagen roles

Collagen nomenclature encodes distinct assembly functions.

Example

Architecture

Functional role

Types I / II / III / V

Fibrillar

Tensile support

Type IV

Nonfibrillar network

Basement membrane

Type IX

FACIT

Fibril interactions

Type VII

Anchoring fibrils

Epithelial anchorage

Slide 26 · Elastin permits recovery after stretch

Elasticity means return toward baseline after deformation.

Elastin fibers deform with mechanical stress.

After force release, fibers recoil toward their resting state.

This is functionally different from collagen tensile resistance.

REST

STRETCH

Cross-linked elastin recoils after release

Slide 27 · Elastic fibers contain elastin and fibrillin

An elastic fiber has a mechanically active core and associated scaffold.

An elastin-rich central core supports recoil.

Fibrillin glycoprotein forms an associated meshlike network.

The composite supports both mechanics and tissue organization.

Fibrillin microfibrillar network

Central elastin-rich core

Slide 28 · Stretch and recoil: A reversible cycle

Hydrophobic elastin domains can deform yet recover.

Cross-links help preserve elastic fiber integrity.

Stretch extends the structure while cross-links hold it together.

Release of tension restores the relaxed configuration.

REST

STRETCH

Cross-linked elastin recoils after release

Slide 29 · Large arteries require repeated recoil

Arterial walls undergo recurrent pulsatile deformation.

Large blood vessels repeatedly expand under pulsatile flow.

Elastic ECM allows return toward baseline configuration.

Loss of wall integrity may have serious mechanical consequences.

Pulsatile flow

Arterial wall distension

Elastic fiber recoil

Slide 30 · Other elastin-rich mechanical settings

Elasticity also supports valves, skin, ligaments and uterus.

Cardiac valves must accommodate cyclical motion.

Skin and ligaments encounter repeated stretch.

The uterus experiences substantial mechanical deformation.

Valves

Cyclic deformation

Skin

Repeated stretch

Ligaments

Elastic response

Uterus

Tissue distensibility

Slide 31 · Fibrillin has mechanical and regulatory roles

Fibrillin is more than passive elastic-fiber support.

It contributes to the network associated with elastin.

It influences availability of free transforming growth factor β (TGF-β).

Both functions are implicated in Marfan syndrome.

Structural role

Elastic-fiber scaffold

Regulatory role

TGF-β bioavailability

Slide 32 · Marfan syndrome: Compromised elastic support

Fibrillin synthesis defects weaken susceptible tissues.

The source links fibrillin defects with skeletal abnormalities.

It also highlights weakened aortic walls.

Altered regulation of free TGF-β contributes to pathogenesis.

Fibrillin synthesis defect

Altered elastic-fiber integrity

Weakened aortic wall / skeletal changes

Slide 33 · Fibrillin influences TGF-β bioavailability

Matrix proteins can control extracellular signaling cues.

Fibrillin normally influences availability of free TGF-β.

Perturbation changes matrix-associated signaling regulation.

This complements the mechanical explanation of Marfan syndrome.

Fibrillin-containing extracellular network

Control of free TGF-β availability

Cellular / tissue responses

Slide 34 · Collagen and elastin: Choose the mechanism

Two fibrous proteins have distinct structural tasks.

Question

Collagen

Elastin

Strong against pulling?

Major role

Not primary explanation

Returns after stretching?

Limited recoil

Major role

Molecular basis

Triple helix + lateral links

Cross-linked hydrophobic domains

Associated disorders

OI / some EDS / scurvy

Fibrillin defects / Marfan

Slide 35 · Proteoglycans are core proteins with GAG chains

A core protein carries long carbohydrate side chains.

Glycosaminoglycans (GAGs) attach to a core protein.

This highly charged assembly attracts water.

Proteoglycans form space-filling compressible gels.

Core protein

GAG side chains

Brush-like, highly hydrated macromolecule

Slide 36 · Chondroitin and keratan sulfate are GAGs

These long polysaccharides form proteoglycan side chains.

Chondroitin sulfate is a named GAG example.

Keratan sulfate is another named GAG example.

Their sulfated groups contribute to fixed negative charge.

Chondroitin sulfate

GAG side chain

Keratan sulfate

GAG side chain

Slide 37 · Hyaluronan organizes large aggregates

Many proteoglycans attach along a long hyaluronan polymer.

Hyaluronan provides a long assembly backbone.

Linked proteoglycans give an extended brush-like architecture.

The aggregate occupies hydrated extracellular space.

Proteoglycan monomers bearing GAG side chains

Hyaluronan backbone

Large aggregate assembled along a continuous polymer

Slide 38 · Negative charge creates a water-rich gel

Fixed negative charges recruit ions and osmotically retained water.

Densely packed sulfated sugars carry negative charge.

Cations—especially sodium—are attracted to the matrix.

Water follows osmotically, generating a viscous gel.

Core protein

GAG side chains

Negative charge attracts Na⁺ and water

Slide 39 · A hydrated gel resists compression

Compressive loads are buffered by fluid-rich matrix.

The hydrated matrix behaves as a compressible gel.

Water content helps oppose local compression.

The resultant cushioning is distinct from collagen tensile strength.

Negatively charged GAGs

Cation + water accumulation

Highly hydrated ECM gel

Compression resistance

Slide 40 · Cartilage couples cushioning and lubrication

Proteoglycans protect articular surfaces in more than one way.

Hydrated gels resist compressive loading.

Proteoglycans also supply lubrication between adjacent bony surfaces.

This complements the collagen framework of cartilage.

Fibrous framework

Collagen

Hydrated phase

Proteoglycans

Mechanical result

Cushion + lubrication

Slide 41 · Proteoglycans also store signals

The ECM binds factors as well as mechanical loads.

Proteoglycans bind growth factors secreted into the ECM.

Examples include FGF and HGF.

Matrix association can influence local availability of signals.

Growth factor secreted

Binding to matrix proteoglycan

Localized growth-factor reservoir

Slide 42 · Heparan sulfate can bind FGF-2

Growth-factor presentation is a matrix-dependent process.

Heparan sulfate proteoglycans bind basic FGF (FGF-2).

Matrix binding retains factor near responsive cells.

Released factors may later interact with cell receptors.

FGF-2 present in ECM

Binding by heparan sulfate

Availability near FGF receptor

Slide 43 · Syndecan is a cell-surface proteoglycan

Not all proteoglycans are embedded only within interstitial matrix.

Syndecan contains a transmembrane core protein.

Extracellular GAG side chains interact with growth factors.

Its intracellular tail associates with actin cytoskeleton.

FGF-2 binding to GAG chains

Syndecan core protein

Cell membrane

Cytoplasmic actin association

Slide 44 · Syndecan can facilitate FGF-2 signaling

Growth factors released from damaged ECM may be captured at the surface.

Injury can liberate matrix-associated FGF-2.

Syndecan side chains bind FGF-2 near the cell surface.

This facilitates engagement with FGF receptors.

Damaged ECM releases FGF-2

Syndecan GAG chains bind FGF-2

FGF receptor engagement facilitated

Slide 45 · Adhesive molecules build molecular bridges

Cell–ECM, ECM–ECM and cell–cell contacts involve distinct proteins.

Fibronectin is prominent in interstitial ECM.

Laminin is prominent in basement membranes.

Integrins are transmembrane adhesion receptors.

Fibronectin

Interstitial ECM

Laminin

Basement membrane

Integrins

Cell-surface receptors

Slide 46 · Fibronectin is a modular heterodimer

Fibronectin uses distinct binding domains to join matrix elements.

Fibronectin is a large disulfide-linked heterodimer.

Tissue and plasma forms exist.

Multiple domains recognize different matrix ligands.

Two disulfide-linked subunits

Modular binding domains: Collagen, fibrin, heparin, integrins

Slide 47 · Fibronectin binds several partner molecules

Its modular domains permit diverse extracellular connections.

Fibronectin can bind collagen and fibrin.

It also binds heparin and proteoglycans.

Cell binding occurs through integrin receptors.

Collagen

Matrix fiber

Fibrin

Provisional matrix

Heparin / GAGs

Carbohydrate-rich matrix

Integrins

Cell attachment

Slide 48 · Fibronectin has tissue and plasma sources

Fibronectin is supplied by multiple cell populations.

Fibroblasts, monocytes and endothelial cells synthesize it.

The protein exists in tissue and plasma forms.

Both forms contribute during wound repair.

Fibroblasts

Matrix-producing cells

Monocytes

Inflammatory lineage

Endothelium

Vascular interface

Slide 49 · Fibronectin scaffolds wound repair

The wound matrix provides a platform for sequential repair events.

Tissue and plasma fibronectin form a wound scaffold.

This supports subsequent ECM deposition.

The scaffold also supports angiogenesis and reepithelialization.

Fibronectin-containing scaffold

Subsequent ECM deposition

Angiogenesis + reepithelialization

Slide 50 · Laminin is a cross-shaped heterotrimer

Its structure creates multiple basement membrane interactions.

Laminin has three distinct subunits.

The source describes a cross-shaped architecture.

It is the most abundant basement membrane glycoprotein.

Three-chain cross-shaped heterotrimer

Slide 51 · Laminin connects cells with the basement membrane

A laminin network connects cellular adhesion with matrix constituents.

Laminin interacts with underlying type IV collagen.

Heparan sulfate is another binding partner.

It supports cell attachment to the basement membrane.

Epithelial cells

Laminin + type IV collagen network

Slide 52 · Laminin also regulates cell behavior

Basement membrane engagement can convey information to cells.

Laminin has structural adhesion functions.

It can modulate cell proliferation and differentiation.

It also influences cell motility.

Laminin–cell contact

Adhesion-associated signaling

Proliferation / differentiation / motility

Slide 53 · Integrins are α/β heterodimers

Two different subunits form a transmembrane adhesion receptor.

An α-subunit pairs with a β-subunit.

Together they bind extracellular ligands.

They connect cell architecture with the external matrix.

ECM: Laminin / fibronectin

α

β

Cell membrane

Actin-associated signaling machinery

Slide 54 · Integrins link ECM to the actin cytoskeleton

The connection is structural and also signaling-active.

Extracellular fibronectin or laminin engages integrins.

Intracellular complexes connect to actin.

Ligand engagement can initiate signaling cascades.

ECM: Laminin / fibronectin

α

β

Cell membrane

Actin-associated signaling machinery

Slide 55 · The RGD motif is a recognition sequence

Arginine–glycine–aspartic acid is abbreviated RGD.

RGD is a ligand motif recognized by several integrins.

RGD-mediated interactions enable focal substrate attachment.

Integrin binding specificity varies among family members.

ECM ligand containing RGD

Recognition by compatible integrin

Attachment + downstream responses

Slide 56 · Integrins coordinate cellular responses

Matrix adhesion can modify behavior rather than merely tether cells.

Locomotion requires regulated adhesion and detachment.

Signaling helps control cell shape and differentiation.

Matrix inputs can influence proliferation.

Motility

Locomotion

Cell architecture

Shape

Cell fate

Differentiation

Growth

Proliferation

Slide 57 · Leukocyte adhesion needs integrins

Firm adhesion enables migration at inflammatory sites.

Leukocyte integrins mediate firm attachment to endothelium.

They also participate in passage across tissue barriers.

The source connects this to inflammation and leukocyte migration.

Activated leukocyte adhesion

Firm endothelial interaction

Transendothelial migration

Slide 58 · Platelet aggregation also uses integrins

Adhesion receptors participate in hemostatic interactions.

Integrins are essential in platelet aggregation.

Thus, the same receptor family participates beyond classical ECM adhesion.

The detailed platelet pathway is addressed in hemostasis teaching.

Platelet integrin engagement

Cell–cell adhesive bridging

Platelet aggregation

Slide 59 · The basement membrane is a coordinated matrix

Type IV collagen, laminin and adhesion receptors work together.

Type IV collagen creates the network framework.

Laminin provides cell-associated adhesive linkages.

Integrins connect these interactions to cells.

Epithelial cells

Laminin + type IV collagen network

Slide 60 · Why ECM integrity matters for regeneration

A preserved scaffold guides organized tissue repair.

Matrix and basement membrane provide a regenerative scaffold.

Loss of scaffold integrity disrupts organized repair.

These principles extend the parent ECM section.

Preserved ECM / basement membrane

Cell adhesion and tissue organization

Effective architecture during repair

Slide 61 · Application: Impaired wound healing and bleeding

A patient with poor healing and easy bleeding has a nutritional deficiency. Which ECM process is most directly implicated?

A. Vitamin C–dependent collagen maturation

B. Hyaluronan-mediated hydration

C. Laminin basement binding

D. Fibrillin-associated recoil

Discuss the molecular component before revealing the answer.

Slide 62 · Application: Nutritional collagen deficiency

Molecular failure produces mechanically fragile tissues.

Vitamin C–dependent collagen maturation

Scurvy causes impaired collagen integrity.

Poor tissue support explains bleeding and delayed wound healing.

Distinguish this from elastin recoil and GAG-based compression.

Slide 63 · Application: Aortic wall weakness

An inherited disorder affects elastic-fiber microfibrils and weakens the aortic wall. Which protein is implicated?

A. Fibronectin

B. Fibrillin

C. Type IV collagen

D. Hyaluronan

Discuss the molecular component before revealing the answer.

Slide 64 · Application: Elastic-fiber disease

The extracellular defect has mechanical and signaling effects.

Fibrillin

Fibrillin contributes to elastic-fiber architecture.

The source links its defect to Marfan syndrome and aortic weakness.

Fibrillin additionally regulates free TGF-β availability.

Slide 65 · Application: Epithelial anchoring failure

An inherited skin disorder causes blistering through failed anchoring fibrils. Which collagen is the relevant example?

A. Type II

B. Type IV

C. Type VII

D. Type IX

Discuss the molecular component before revealing the answer.

Slide 66 · Application: Collagen VII anchoring fibrils

The level of matrix organization determines clinical phenotype.

Type VII collagen

Type VII collagen forms anchoring fibrils.

These preserve stratified squamous epithelial attachments.

Its disruption can cause inherited blistering skin disease.

Slide 67 · Integrated map: Molecule to function

Identify each molecule by the mechanical or biological task it performs.

Collagen

Triple helix → tensile framework / specialized anchors

Elastin–fibrillin

Recoil and elastic-fiber integrity

Proteoglycans

Hydration, compression resistance, growth-factor depot

Fibronectin / laminin / integrins

Matrix bridges, cell adhesion and signaling

Slide 68 · Reference and source boundaries

Primary content drawn from the supplied Robbins chapter extract.

Primary source

Robbins, Cotran & Kumar, 11th ed. (2026), chapter 1

Source location

Components of the ECM, printed pp. 21–23

Additional context

Extracellular Matrix, printed pp. 20–21

Figure policy

Original editable schematics; no textbook image reproduced