apoptotic cell clearance and the resolution of inflammation
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Apoptotic Cell Clearance and the Resolution of Inflammation. Jeremy Hughes MD PhD Wellcome Trust Senior Research Fellow in Clinical Science MRC Centre for Inflammation Research, University of Edinburgh. Talk Outline: Apoptosis in inflammation Current apoptotic cell recognition mechanisms - PowerPoint PPT PresentationTRANSCRIPT
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Apoptotic Cell Clearance and the Resolution of Inflammation
Jeremy Hughes MD PhD
Wellcome Trust Senior Research Fellow in Clinical Science
MRC Centre for Inflammation Research, University of Edinburgh.
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Talk Outline:
•Apoptosis in inflammation
•Current apoptotic cell recognition mechanisms
•Regulation of macrophage phenotype by apoptotic cell ingestion
•Efficient apoptotic cell clearance limits autoimmune responses
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Apoptosis in Inflammation
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Physiological apoptosis •Embryological development•Tissue homeostasis•Regulation of leukocyte populations e.g. neutrophils• Deletion of autoreactive T cells in thymus
Pathological apoptosis•Inflammation•Infection •Cancer•Autoimmunity
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Proximal tubule Interstitial cell
Renal Cell Apoptosis - TUNEL staining
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Elevated levels of apoptosis documented in disease states/experimental models e.g.
•Obstructive nephropathy Gobe ands Axelsen demonstrated that excess apoptosis resulted in tubular atrophy (Lab Invest. 1987 56:273)
•Mesangial proliferative glomerulonephritis Baker et al demonstrated that mesangial cell apoptosis is critically important in resolving Thy 1 GN (JCI 1994 94:2105)
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Large scale renal cell apoptosis is pro-inflammatory
•Ischaemia reperfusion injury (kidney/cardiac)(Daemen et al, University of Maastricht)
APOPTOSISMIP-2 and KC levels
Neutrophil infiltrate
Renal Dysfunction
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Anti-apoptosis treatments are protective
APOPTOSISMIP-2 and KC levels
Neutrophil infiltrate
Renal Dysfunction
•ZVAD•IGF-1•Acute phase proteins
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Apoptosis May Be Pro-inflammatory
Apoptosis
Rapid efficientphagocytosis
Excess death orDefectivePhagocytosis
Anti-inflammatory Pro-inflammatory (MCP-1, IL-8 from apoptotic cell)
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APOPTOSIS = double edged sword
•Pro-inflammatory•Tissue atrophy
•Resolution of hypercellularity•Modulation of Mø function
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Recognition and clearance of apoptotic cells
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Apoptotic cells are readily phagocytosed
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An Intraperitoneal Competition Assay
Apoptotic cells
Live cells
•Injected IP
•30 min incubation
•Mø rich greater omental lymphoid organ excised
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Preferential and rapid clearance of apoptotic cells
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Current recognition mechanisms
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Recognition of apoptotic cells is complicated!
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The ‘phagocytic synapse’
Savill et al Nature Rev 2002 2:965
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Multiple receptor families involved
Phagocyte surface receptors:
•Integrins (1, 2, 3, 5) - Adhesion molecules and ECM•Scavenger receptors (SRA, CD36) - Lipids•Complement receptors - Pathogens•CD14 - bacterial lipopolysaccharide (LPS)•Phosphatidylserine receptor (PSR)•Lectins
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Multiple receptor families involved
Bridging molecules:•Thrombospondin•C1q
Apoptotic surface:•Phosphatidylserine (PS)•ICAM-3•Sugars•‘Apoptotic cell associated molecular patterns’
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CD14 + LPS
NFB activation
TNF secretion
Phagocyte receptors involved are multifunctional
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CD14 + LPS
NFB activation
TNF secretion
Phagocyte receptors involved are multifunctional
CD14 + Apoptotic cell
Increased TGF decreased NFB
No TNF secretion
‘Turn off’ signal
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Apoptotic cell clearance regulates macrophage phenotype and promotes
the resolution of inflammation
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Classically vs Alternatively Activated Macrophages
Classical Activation:•Pathogens (LPS, DNA)•IFN and TNF, IL-1
Alternative Activation:•IL-4, IL-10, IL-13•TGF•Glucorticoids
‘Angry’ macrophage•TNF& cytokines•Nitric oxide (NO)•ROS
‘Healing’ macrophage•IGF1•PDGF•bFGF•VEGF•TGF
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Activated macrophages may be cytotoxic (NO,TNF)
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Macrophages in Inflammation and Tissue Healing
Acute Inflammation
Classical Activation predominates:
•Pro-inflammatory mediators•Cell killing•Pathogen killing•ECM degradation
Resolving Inflammation
Alternative Activation predominates:
•Anti-inflammatory mediators•Pro-cell survival•Pro-angiogenesis•ECM stabilisation
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Interaction with apoptotic cells exerts critical effects upon macrophages
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Macrophage Response to Apoptotic Cell Ingestion
Macrophage release of autocrine and paracrine mediators:•TGF•PGE2•PAF
Downregulated expression of ‘killer molecules’: •iNOS •TNF
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Macrophage Response to Apoptotic Cell Ingestion
Net effect is: •‘deactivation’ of macrophages and •‘re-programming’ to reparative phenotype
AC ingestion also: •increases macrophage survival and •reduces macrophage proliferation (Reddy et al. J Immunol 2002 169:702)
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TNF/NO
2. Susceptiblemesangial cell
1. Activated Mø
4. MC inducedinto apoptosis
3. killing
5. Phagocytosisinhibits furtherkilling
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Phagocytosis adds ‘new meaning’ to cell death
Savill et al Nature Rev 2002 2:965
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Can we harness the potential power of the interaction of macrophages with
apoptotic cells?
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AC Administration Ameliorates Lung Injury
PBS Apoptotic Cells
d1
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Huynh et al JCI 2002 109(1):41
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Corticosteroids:•Induce lymphocyte apoptosis•Sensitise mesangial cells to apoptosis•Significantly increase macrophage capacity to ingest apoptotic cells
AC clearance upregulated by:•Cytokines•Lipoxins
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Efficient apoptotic cell clearance prevents the generation of
autoimmune responses
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Apoptotic cells contain potential autoantigens
Normal Cell Apoptotic Cell
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Apoptosis and Autoimmunity
Apoptosis
InadequateMø/resident cellPhagocytosis
Excessive level of apoptosis
Apoptotic cell ingested by dendriticcell and potential antigen presentation
Autoimmune response
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C1q and apoptotic cells recognition
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C1q and Apoptotic Cell Clearance
Apoptotic Cells + C1q WT serum
Apoptotic Cells + C1q KO serum
•Injected IP into C1q KO mouse
•30 min incubation
•Greater omental lymphoid organ excised
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Clq and autoimmunity
•Clq deficient patients have high incidence of developing SLE
•Clq KO mice spontaneously develop autoimmune glomerulonephritis with excess apoptotic cells in the kidney
•Clq KO mice develop more severe NTN
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Organ and Cell Specific Subtleties in Apoptotic Cell Clearance
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PMNs - specific upregulation of apoptotic PMN clearance by Ab ligation of macrophage CD44
Lungs - surfactants involved in apoptotic cell clearance
Clq KO mice - •excess apoptotic cells evident in kidney•defective clearance of AC in the peritoneum •normal AC clearance in UV irradiated skin
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Modulation of apoptotic cell clearance may provide novel treatments for diseases characterised by:
•Acute inflammation and marked cell death
•Macrophage dependent tissue injury
•Autoimmune responses
Clinical Implications
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Acknowledgements
Edinburgh FundingTiina Kipari Wellcome TrustSimon Watson Medical Research Jean Francois Cailhier CouncilClaire TaylorMichael ClayKris Houlberg