Remodelling: an important component of asthma

Stephen T Holgate,IIR Division,

School of Medicine,University of Southampton.

sth@soton.ac.uk

Bronchial Mucosal Biopsy from a 7 year old Child with Severe Asthma Despite High Dose

Corticosteroid Treatment

Masson Trichrome stain

Desquamation

BM

EosinophilsEosinophils

Remodelling in asthma:Structural changes of the airway wall

A. Normal Lung B. Asthmatic Lung

Histopathologic Changes that EmbraceAirway Wall Remodelling in Asthma

1. Smooth muscle hypertrophy/hyperplasia2. Subepithelial collagen and glycoprotein deposition3 Extracellular matrix deposition in submucosa, muscle and adventitia4. Mucus gland hyperplasia6. Shedding and metaplasia of epithelium7. Angiogenesis8. Nerve proliferation

Scatter plot showing changes in ASM cell sizein bronchial biopsies

p < 0.001

AS

M c

ell s

ize

(µm

)

Controls

Benayoun L et al. AJRCCM 2003;167:1360-8

p < 0.001

p < 0.001

p < 0.001

p < 0.001

p = 0.003

p = 0.013 p = 0.020

Intermittent asthmatics

Mild to moderate asthmatics

Severe asthmatics

COPD

15 -

10 -

5 -

Relationship between reticular basement membrane thickness and airway smooth muscle

and inner wall area in asthma deaths

Smooth Muscle Inner Wall Area

22 -

20 -

18 -

16 -

14 -

12 -

10 -

8 -

6 -

4 -

2 -

0 2 4 6 8 10

% airway smooth muscle

% inner wall area

Reticular basement membrane thickness, µµµµm

22 -

20 -

18 -

16 -

14 -

12 -

10 -

8 -

6 -

4 -

2 -

0 2 4 6 8 10

Reticular basement membrane

thickness, µµµµm

James AL et al AJRCCM 2002; 166: 1590-5

Eosinophils

Mast cells

Eosinophil

Fibroblast

Endothelium

Epithelium

TGF-ααααFGF-7

FGF-2VEGF

TGF-ββββFGF-2

IL-6, IL-11, TGF−−−−ββββ, NGF

PDGF

ActivationECM synthesis

Mucus hypersecretion

Myofibroblast

TransdifferentiationMigration,

ECM synthesis

DifferentiationMigration

TGF−−−−ββββ,IL-13, IL-4

TNF−−−−ααααAngiogenin

AngiogenesisActivation (intergrin upregulation)

IL-4, IL-13,IL-17

ASM cells

ProliferationProtein synthesis (ECM, GFs, chemokines)

Chronic inflammation and recurrent exacerbations are associated with tissue remodelling

Activation of the epithelial mesenchymal trophic unit in chronic asthma

Th2 inflammationGENES

ENVIRONMENT

allergy

Moderate asthma

Mild allergic asthma

SevereasthmaPollution,

VirusesETS

AIRWAY

Epithelial-mesenchymaltrophic unit

allergen

viruses

Computerised tomography to “visualise”airway wall remodelling in asthma

• High-resolution computed tomography findings are correlated with disease severity in asthma. Harmanci E et al Respiration 2002; 69: 420-6

• Thoracic CT in pediatric patients with difficult-to-treat asthma. Marchac V et al Am J Roentgenol 2002; 179: 1245-52

• Nakano Y et al Quantitative assessment of airway remodelingusing high resolution CT. Chest 2002; 122: 271S-5S

• Clinical assessment of airway remodeling in asthma : utility of computed tomography. Niima A et al Clin Rev Allergy Immunol 2004; 27: 45-58

Relationship of airway wall thickness to airway sensitivity and airway reactivity in asthma

Niima A et al Am J Respir Crit Care Med 2003; 168: 983-8

• It has been assumed that airway wall thickness contributed to BHR in chronic asthma

• Helical computed tomography used to assess airway wall thickness in 55 asthmatic patients

• Airway reactivity to methacholinecorrelated negatively with airway wall thickness (r=-0.56)

Increased smooth muscle

Increased matrix deposition

Hyper-echoic band

Hypo-echoic band

Use of endobronchial ultrasound to assess airway

wall thickness in asthmaT

D

L

Airway Wall

T/D ratio = wall thickness/ total airway diameter

T/D ratio using endobronchial ultrasound

Controls Asthmaticsn = 8 n = 10

T/D

(short axis)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

Hyperechoic bands (white) occur at changes of density between air, soft tissue and cartilage.

P<0.004

Direct measurements of the airway wallby endobronchial radial ultrasound identifies

thickening of the large airways in asthma,consistent with structural remodelling

Shaw TJ. et al. Eur Respir J 2004; 23: 813-7

Wall thickness/diameter ratio (T/D)vs Hyperresponsiveness

PC20 Histamine (mg/ml)

0.1 1 10

T/D

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

0.30

r = 0.708p < 0.01

Percentage wall area (%WA)vs Hyperresponsiveness

PC20 Histamine (mg/ml)

0.1 1 10

%W

A

54

56

58

60

62

64

66

68

70

72

r = 0.560p < 0.05

Relationship between airway wall thickness and airway hyperresponsiveness

? Remodelling starts as a protective response to repeated bronchoconstriction by creating a stiffer airway

Per

cent

age

Wal

l Are

a

Wal

l thi

ckne

ss/d

iam

eter

rat

io

EBUS to assess airway wall thickness in reversible and “fixed” asthma compared to normal controls

Normal Reversible “Fixed”

Inne

r w

all a

rea

(mm

2

P=0.002P=0.03

Helium ion microscopy and atomic force microscopy of asthmatic airway collagen fibrils

HeIM image of collagen (top) and AFM height image of an asthmatic biopsy section showing interstitial collagen type I fibrils in inner airway wall (right). The line section in the inset shows the typical D-banding of

Immuno-reactive soluble matrix components in BALfrom normal & asthmatic subjects

0

0.05

0.1

0.15

0.2

0.25

0.3

Co

llag

enV

I (n

g/m

l)

p = 0.004

p = 0.008

p = 0.003

normal atopy mild/mod asthma

severe

0

1

2

3

4

5

6

7

normal atopy Mildasthma

severe

Lam

inin

(ng

/ml)

p = 0.120

p = 0.123

p = 0.113

Collagen VILaminin

0

1

2

3

4

5

6

7

Ten

asci

n(n

g/m

l)

p = 0.013

p = 0.016

p = 0.056

normal atopy mild/mod asthma

severe

Tenascin C

Healthy Controlsn=10

Mild Asthman=9

Severe Asthman=10

Inte

rstit

ial

imm

unor

eact

ivity

(% a

rea

of b

iops

y)

10

20

30

40

50

60

70

p=0.004

p=0.05

p<0.0001

Collagen III

Inte

rstia

lIm

mun

orea

ctiv

ity(%

area

of b

iops

ies)

Healthy controls Mild asthma Severe asthman=10 n=9 n=10

Immuno-reactive matrix components in bronchial biopsies from normal & asthmatic subjects

Risk factors for airway remodelling in asthma manifested by post-bronchodilator FEV1/FVC ratio: a longitudinal population

study from childhood to adulthood.Rasmussen F et al. Am J Respir Crit Care Med 2002; 165:1480-8

• At age 18 & 26 yrs: low FEV1/FVC ratio in 7.4 & 6.4%.

• From age 9-26 yrs those with consistently low ratios showed 2x greater decline in lung function over time.

• Asthma, BHR, low lung function in childhood & male sex independently associated with low ratio & accelerated decline in lung function.

• Airway remodelling begins in childhood continues into adult life.

Do corticosteroids prevent or reverse remodelling in asthma ?

• Corticosteroids have been shown to reduce the thickness of the reticular basement membrane & number of microvessels but have no effect on smooth muscle mass.

(Chetta A et al. Am J Respir Crit Care Med. 2003; 167: 751-7).

• Long term intervention studies of inhaled corticosteroids in childhood asthma (CAMP & START) showed little or no effects on post bronchodilator FEV1.

• “The effects of corticosteroids on remodelling seems to vary a great deal: some aspects are responsive while others are not or less so ….It is likely that when used optimally corticosteroids will have limited efficacy overall”. (Ward C , Walters H. Curr Opin Clin Immunol 2005; 5: 43-8).

Contrast between normal and asthmatic airways

NormalNormal Severe AsthmaSevere Asthma

Allergy InflammationStructural

changes

SYMPTOMS

While inhaled steroids suppress inflammation they do not influence the underlying natural history of asthma (the

PEAK study; Prevention of Early Asthma in Kids)

Fluticosone, 88µµµµg bd

Placebo

Guilbert TW et al N Eng J Med 2006; 354: 1985-7

N=285, aged2-3 yrs

Remodelling results from injury to airway from repeated cycles of inflammation and repair

Environmental trigger

Intact epithelium Impaired repairDamaged epithelium

Growth factors and cytokines

Chronic inflammation

Fibroblastproliferation

Myofibroblastactivation

TGF-ββββEGF

Remodelling

Asthma Eotaxin

Mast cell

ET-1 andVEGF

Adapted from Boxhall C, et al. Eur Respir J 2006

Growthfactors

Growthfactors

Is chronic asthma the consequence of altered epithelial repair leading to a chronic wound scenario, chronic

inflammation and remodelling?

Impaired Epithelial Repair Augments TGFβ2 Release

Scrape wounded+ EGF + AG1478

Scrape wounded+ EGF

Unwounded + EGF+AG1478

SFM

EGF

EGF + AG1478

Puddicombe et al FASEB J 2000

Epithelial cell repair in vitro is impaired in paediatric asthma Kicic A. et al. Am J Respir Crit Care Med. 2010; 181: 889-98.

Airway plugging in fatal asthmaHypersecretion of mucus: A response to epithelialinjury and a major therapeutic target in asthma

Growthfactors

Fibroblasts

Smooth muscle

Microbial

components

Epithelium

Air

Pollutants

Allergens and

Chemicals

Growthfactors

Dendriticcells

Th-2 cells

Eosinophils

mast cells

SPDEF↑ STAT6↑FoxA2↓

Goblet cell metaplasia

IL-4/13

Bronchial epithelium can be programmed to orchestrate both Th2 inflammation and remodelling

X X XX

Th2IL33, TARC, IL13, eotaxin

Epithelial Damage- Barrier loss- Macromolecular permeability

Damaging Agents

Proliferation and Differentiation- Ciliagenesis- Secretory function

Interim Repair- Barrier restored- Secretory cell function

Immediate Response- Formation of temporary barrier

Leaky

TGFβ

MMPs, collagen,Junctional proteins

Fibroblast proliferation, Myofibroblast activation

Resolution: healing by primary intention

Incomplete repair:

healing by secondary intention

Chronic inflammationRemodelling

Leaky

EMTUInjury, repair, remodelling

inflammation

Immunological Development

PERSISTENT ASTHMA

Virus-related wheeze

Atopy

Viruses, Tobacco smoke, Allergens,Air pollution

allergens, exercise,

cold airirritants

External Environment, tobacco smoke, viruses, allergen

(Th1, Th2)

epitheliumVulnerable

airway structure Innate immunity

BHR

Birth

Adulthood

Age 3-5

Puberty

inflammation

BHR

ASTHMA

Mechanical strain

epithelium

Lung Morphogenesis

Immunological DevelopmentPrenatal

External Environment

In utero

EMTUInjury, repair, remodelling

inflammation

Immunological Development

PERSISTENT ASTHMA

Virus-related wheeze

Atopy

Viruses, Tobacco smoke, Allergens,Air pollution

allergens, exercise,

cold airirritants

External Environment, tobacco smoke, viruses, allergen

(Th1, Th2)

epitheliumVulnerable

airway structure Innate immunity

BHR

Birth

Adulthood

Age 3-5

Puberty

inflammation

BHR

ASTHMA

Mechanical strain

epithelium

Lung Morphogenesis

Immunological DevelopmentPrenatal

External Environment

In utero