Transcript Molecular Medicine SF

Molecular signalling in
inflammation
2 lectures
2nd Med Molecular Medicine
Andrew Bowie, School of Biochemistry and
Immunology
Definition of Inflammation
• A normally beneficial host response to
foreign challenge or tissue injury that leads
ultimately to the restoration of tissue
structure and function.
• Normally is self-limiting while prolonged
inflammation can lead to disease
The molecular basis?
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The key stages:
Initiation…
Signal transduction…
Altered gene expression…
Resolution
Initiation of inflammation
1. Infection-induced inflammation now well
characterised
2. ‘Sterile Inflammation’ is not
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Rheumatoid Arthritis
Atherosclerosis
IBD
Psoriasis
Initiation of inflammation by infection
• Quasi-infectious stimuli (e.g. LPS) used for decades to
model inflammation and sepsis
• Inflammatory mediators involved, and their effects wellcharacterised
• Only recently have the initiating events been described.
• Involves PRRs recognising PAMPs
• Three key families of PRRs:
– Toll-like receptors (TLRs)
– Nucleotide-binding oligomerisation domain proteins
(NODs)
– RIG-I-like receptors (RLRs)
TLRs are PRRs for PAMPs
Medzhitov (2001) Nature Rev. Immunol. 1, 135
2. Toll-Like
T1/ST2
IL-1RAPL
TIGIRR-1
SIGIRR
hTLR1
hTLR2
hTLR3
hTLR4
hTLR5
hTLR6
hTLR7
hTLR8
hTLR9
hTLR10
mTLR11
mTLR12
mTLR13
3. TIR Adaptors
MyD88, Mal, TRIF, TRAM
SARM
Plants
N
L6
RPPs
Mammals
IL-1RI
1L-1RAcP
IL-18R
IL-18RAcP
IL-1Rrp2
dToll 1-8
Insects
Mammals
1. IL-1RI-Like
TLRs have a role in both the innate and
adaptive immune responses
NO
TNF, IL-6
Adapted from Medzhitov (2001) Nature Rev. Immunol. 1, 135
NODs
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Implicated in inflammatory diseases
Intracellular proteins
Some are PRRs
NOD domain
LRR domain
Effector domains (e.g. CARD)
RLRs (and TLRs) recognise viral RNA
Taken from Akira et al., Cell 124, 783-801, 2006
Sterile inflammation Vs infection-induced
• Little known about sterile inflammation but
probably involves many of the same pathways
• Similar end-points, e.g. TNF production
• Therapeutic opportunity: upsteam blockade of
signalling rather than targetting individual
downstream cytokines
• Endogenous ligands of TLRs initiate it?
• ‘Danger signals’
Detection of PAMPs and DAMPs by TLRs
Karin et al., (2006) Cell 124, 823
Overview of gene induction
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Signalling pathways affect gene induction
DNA  mRNA  Protein
Transcription
Regulation of RNA (stabilisation, splicing)
Translation
Post-translational modification
Signalling by TLRs, NODs &RLS
• Leads to changes in gene induction
• These genes encode many inflammatory
mediators (N.B. IL-1 and TNF)
• Transcription factors activated (e.g. NFkB)
• MAP kinases activated (e.g. p38 MAPK)
• The inflammasome & caspases activated
NFkB
•Central mediator of immune and inflammatory responses.
•Activated by diverse stimuli.
•Role in many physiological and pathological processes.
Activator
P
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p50
IkBa
P
Degradation
p65
IkBa
p50
p65
Gene Induction
Phosphorylation of IKKs
IKK
complex g
a b
p50
p65
IkBa
Cyto
Nuc
p50
p50
p65P
IkBa
p65
P
Ubiquitination
by E3 Ligase
Degradation
Gene Indn
RIP
IRAK?
NIK TAK1
PKCz
MEKK1
S6 KINASE
TPL-2
MEKK 2 + 3
Phosphorylation of IKKs
p105 Phosp
and degrad
IKK
complex g
Cyto
a b
p50
p65
IkBa
Nuc
p50
p50
p65P
IkBa
p65
P
Y42 Phosp
p65 Phosp
PI3K
Ubiquitination
by E3 Ligase
PKA
Degradation
Gene Indn
Basic signalling paradigm for TLRs
leading to NFkB activation
TLR
MyD88
IRAK
TRAF6
IKK
NFkB
LPS
TRAM
How LPS (via TLR4) causes
NFkB activation
Mal
MyD88
TRIF
TRAF6
Uq
RIP1
TAB2/3
TAK1
NEMO
IKKa IKKb
P
P
I-kB NF-kB
P
NF-kB
nucleus
TLR2/1 or 2/6
TLR3
TLR4
TLR5
TLR7/8/9
MD2
Mal
MyD88
TRIF
Mal
MyD88
TRIF
MyD88
MyD88
TRAM
IRAKs
IRAKs
RIP1
TBK1
TRAF6
NFkB
NFkB
TNFa
IL6
IL8
TNFa
IL6
IL8
IRF3
IFNb
RANTES
TRAF6
NFkB
TNFa
IL6
IL8
TBK1
IRF3
IFNb
RANTES
IRAKs
IRAKs
TRAF6
TRAF6
NFkB
NFkB
TNFa
IL6
IL8
TNFa
IL6
IL8
IRF5/7
IFNa
P38 MAP kinase
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Activated by TLR pathways
TRAF6  TAK1  MKK  MAP kinase
P38 phosphorylates some Txn Factors
P38 has a role in stabilising cytokine
mRNA
Caspase 1
Caspase 1 is activated by the inflammasome
…but what activates the inflammasome??
How NODs signal changes in gene expression
Aberrant NOD signalling in disease
IL-1
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Gene upregulated in inflammation
Pro-IL-1 cleaved by ICE (Caspase 1)
Secreted
IL1R1, IL-1R2, IL1ra
IL-1 signalling cascade
Gene induction (IL-8, CAMs, COX, iNOS)
TNF
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Proinflammatory and apoptotic
Key role in RA
How it signals
How its regulated
Regulation of TNF production and
function
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TNF gene expression – NFkB and p38
Membrane bound initially (cleaved by TACE)
Receptor shedding
Receptor endocytosis
SODD (silencer of death domains)
TRIP (TRAF interacting protein), A20.
NFkB/IkB autoregulation
Normally,
initiation of
inflammation
(e.g. by TLR4) is
tightly regulated
Resolution of inflammation
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Further gene products and lipid mediators
Suppress pro-inflammatory gene expression
Inhibit cell trafficking
Induce apoptosis of inflammatory cells
Injurious stimulus cleared
Normal tissue structure and function
restored.
Reading list
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Akira & Takeda (2004) Toll-like receptor signalling. Nature
Reviews Immunology 4: 499-511
Inohara & Nunez (2003) NODs: Intracellular proteins involved
in inflammation and apoptosis. Nature Reviews Immunology 3:
371-382
Meylan, Tschopp & Karin (2006) Intracellular pattern
recognition receptors in the host response. Nature 442: 39-44
Kanneganti, Lamkanfi & Nunez (2007) Intracellular NOD-like
Receptors in Host Defense and Disease. Immunity 27: 549-559