Modulation of Lung Epithelial Function by Pseudomonas Aeruginosa

8/8/2019 Modulation of Lung Epithelial Function by Pseudomonas Aeruginosa

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Modulation of Lung Epithelial function by Pseudomonas

aeruginosa

JOURNAL :

Lau GW, Hassett DJ, Britigan BE. Modulation of Lung Epithelial function by

Pseudomonas aeruginosa. Trend in Microbiology, 2005;13(8):389-99.


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Objectives

y Introduction

y Pseudomonas aeruginosa of normal and Cystic

Fibrosis Airways

y PA product and their effects on the epithelium

y Secreted Virulence Determinants

y Benefits and limitations of experimental systems to

study PA-epithelial cell interaction

y Genetic approaches to dissect the modulation of

lung epithelia by PA

y Therapy and Prevention


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Introduction

Normal breathing gives access to mostmicroorganisms and harmful agents.Ciliary motion removes most of themicroorganisms. The bacterium thatreaches the alveolar space are depositedon the pulmonary epithelium.

Innate and acquired defense mechanismsare initiated to counter the infection.


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Pseudomonas aeruginosa of normal and Cystic

Fibrosis Airways

y Effects of PA on the epithelial cell function, includingdirect cyto-toxicity, activation of cellular signalingand pro-inflammatory response have been examined

in vivo and vitro. DNA microarray has revealed theepithelial gene expression varies with differentderived products.

y Abnormalities in the cystic fibrosis transmembrane

regulator results in cystic fibrosis which enhancessodium, chloride and water absorption,hypersecretion of mucous results, which deposits onthe epithelial cilia, either the cilia beats harder or doesnot beat.


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PA growing on the cystic fibrosis airways is

known as biofilms.

The biofilm formation requires:

y flagella,y type IV pili,

y other gene products.

PA biofilms mainly results in the high resistanceto antibiotics and phagocytic killing.


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Two models of biofilms are known:

y steps leads bacterial attachment to thesurface,

y second model is characterized by bacterialrafts.

At the chronic stage the biofilm model 2predominates. This involves

y overproduction of alginate,

y

loss of flagella,y mutation in antigenic B-band O-antigen genes

y reduces expression of the extracellularvirulence determinants.


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yMicroscopic examination of the airwayssuggests that the PA rarely colonizes in the

airways at the chronic stage. Instead of

colonizing the bacteria embeds itself in thick

mucus. Within the mucus there are low levels

of oxygen therefore creating toxic gradients.


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PA product and their effects on the

epitheliumMembrane Bound Virulence Determinants

LPS (lipopolysaccharide)ylipid A is a component of LPS and is a regulator of

epithelial function through interaction with toll like

receptor 4 signaling complex (TRL4, TRL2, CFTR)ylipid A is a hexa-acylated substances that induce

inflammatory action


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Flagella and Pili

yrequired for motility and lung infection ofP. aeruginosa

yenable attachment to cells (mucin, glycolipid, asialoGM1)

and causes release of interleukin(IL-8) through Src-Ras-ERK1/2NF-kB pathway.

yFlagellin is a globular protein component of flagella thatactivates matrilysin transcription

Alginateyis a linear co-polymeric exopolysaccharide comprisedof alpha-L-guluronate & O-acetylated beta-D-mannuronate residue and responsible for mucoidy in

P.aeruginosayits primary role is to moisten local immune responsetowards P.aeruginosa


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Secreted Virulence Determinants

y Pathogenic interaction between PA and hosts are often guided

by exoproducts secreted by the bacteria that interact with

specific host targets.

y What these exoproducts?

Quorum sensing molecules

y Communication between PA cells by small, diffusible acylated homoserine

lactones: Pseudomonas autoinducers (PAIs)y PAI have two types

y PAI-1: stimulate production of IL-8 always deactivated host

y PAI-2: does not modulate host immune function not inactivated

y Pseudomonas quinolone signal (PQS)y Intertwine with PAI-1 and PAI-2 and associated with production of

numerous virulence factors.


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Type 3 secretion system (T3SS)y allows P. aeruginosa to translocate or to deliver protein toxins

(effectors) directly into the cytoplasm of targeted host cells.

y Secretion is triggered by cell contact.

y Only seen in early stage of infection

yPseudomonas produce four T3SS proteins.

y ExoU

y a phospholipase that inhibit survival pathway and activatedproapoptotic pathway

y ExoS and ExoT

y The N-terminal ofExoS & ExoT encode for GTPase activating proteinactivity

y The C-terminal domains ADP-ribosyltaranferase activity

y ExoY

y Increase lung epithelial intracellular cAMP

y Cell rounding and detachment.

y Inhibit phagocytosis

y Disrupts pulmonary endothelial barrier function


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Phenazines

ysecondary metabolites which function as microbialcompetitiveness and virulence

yPhenazines: pyocyanin-1-hydroxyphenazine and

phenazine-1-carboxylic acid

yPseudomonas aeruginosa secretes phenazine into theCF airways copiuos amounts. These secretions

penetrates biological membranes and cause damage to

lung epithelia, alters epithelial cytokine production, and

modulate cellular signaling pathway.


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Exoproteases

y

Secretes elastases (LasA and LasB), alkaline protease,and protease IV.

yElastases activates the mitogen-activated protein phase

(MAPK) pathway which increases IL-8 expression and

augument respiratory epithelium permiability


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Phopholipases

yPseudomonas aeruginosa elaborates several

phospholipase: hemolytic PlcH and non-hemolytic PlcN,

PlcB and PldA.

yAnti-PLC antibody can be detected in CF patients, and

the isolation of PA strains is capable of secreting PLCs

which is usually associated with poor clinical status


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Exotoxin-A (ETA)yMost PA isolates secretes ETA as a potent inhibitor ofprotein synthesis via ADP-ribosylation of elongation

factor 2.

yETA can be expressed by the availability of iron which is

chelated by two siderophores pyochelin and pyoverdin.yETA can bind to 2-macroglobulin receptor

yETA can kill airway epithelia non-apoptotically via

mitochondrial dysfunction , superoxide production and

DNA degradation


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Rhamnolipid

yRhamnolipid contains: rhanose and glycolipid biosulfactant

Nitrate reductase (NirS)yLysed bacteria can release NirS which directly stimulates theexpression of IL-8 and monocyte chemoreactant protein-1(MCP-1) but not tumor necrosis factor- (TNF-) or IL-1

y

However, NirS can stimulate alveolar macrophageproduction of TNF- or IL-1


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Benefits and limitations of experimental systems to study

PA-epithelial cell interaction

y The agar or alginate bead model should not be constructedas one that represents CF airway disease because it is simplya chronic lung infection.

y The acute pneumonia model probably serve well as areasonable representation of infection in non-CF airways andperhaps early stages of CF airway colonization byenvironmental isolates

y The model host systems represent a convinient method to

screen for conserved PA virulence determinants that arerequired to infect evolutionarily diverged hosts, but anyfindings require confirmation in mammalian system


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Genetic approaches to dissect the modulation of

lung epithelia by PA

y Genomic sequence PA01 and PA14 , available and

most widely used.

y Genomic approach : Microarrays and Proteomics


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Therapy and Prevention

y PA highly resistant to antibiotic, due to anti-PA

coumpounds that block QS.y Furanones marine macro alga Delisea pulchra :

y Inhibit QS in PA

y Suprress virulence factors expression and biofilm formation

yAccelerat bacterial clearance

y Render PA within preformed biofilm susceptible toPolymorhonuclear leukocyte killing.

y Combination of PMNs,QS inhibitors, and antibiotics couldeliminate PA before chronic infections.

y The PAI-1 could be remove by human acyl-homoserinelactone acylase.


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y Antioxidants such as gluthathione aerosol, thioredoxin,

and anti-oxidant supplement.y Vaccination : Mucoid exopolysaccharide commony -

found in sera of older CF patients. Only for reducing the

opsonic antibodies.

y LPS O-antigen have been encouraging but not clinicalefficacious.

y Polysaccharide protein conjugates and passive

immunization with immune sera offer additional

immunotherapeutic reagents .


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Modulation of Lung Epithelial Function by Pseudomonas Aeruginosa

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