Stimulatory Autoantibodies to the PDGF Receptor in SSc Silvia Svegliati Baroni et al. A Gabrielli, E

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Stimulatory Autoantibodies to the PDGF Receptor
in SScSilvia Svegliati Baroni et al.(A
Gabrielli, EV Avvedimento)Ancona, Turino and
Napoli, Italia

• NEJM 20063542667-76

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Rationale

• Systemic sclerosis (scleroderma) is characterized
  by immunologic abnormalities, injury of
  endothelial cells, and tissue fibrosis.
• Abnormal oxidative stress has been documented in
  scleroderma and linked to fibroblast activation.

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PDGF
PDGF
PDGF
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Rationale

• Systemic sclerosis (scleroderma) is characterized
  by immunologic abnormalities, injury of
  endothelial cells, and tissue fibrosis.
• Abnormal oxidative stress has been documented in
  scleroderma and linked to fibroblast activation.
• Since platelet-derived growth factor (PDGF)
  stimulates the production of reactive oxygen
  species (ROS) and since IgG from patients with
  scleroderma reacts with human fibroblasts,
• The authors tested the hypothesis that patients
  with scleroderma have serum autoantibodies that
  stimulate the PDGF receptor (PDGFR), activating
  collagen-gene expression.

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Methods

• Sera from 46 patients with PSS and 75 controls,
  including patients with other autoimmune
  diseases.

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(No Transcript)
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Methods

• Sera from 46 patients with PSS and 75 controls,
  including patients with other autoimmune
  diseases.
• Measuring the production of ROS produced by the
  incubation of purified IgG with mouse-embryo
  fibroblasts carrying inactive copies of PDGFR a
  or ß chains orthe same cells expressing PDGFR a
  or ß.
• Generation of ROS was assayed with andwithout
  specific PDGFR inhibitors.
• Antibodies were characterized by IP, WB and
  absorption experiments.

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Fig 1A Stimulation of Reactive Oxygen Species.
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Fig 1B Immunoprecipitation
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Fig 1C Absorption
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Fig1D. Absorption
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Results

• Stimulatory Abs to the PDGFR are found in all
  patients with PSS.
• They recognize native PDGFR inducing
• tyrosine phosphorylation
• ROS accumulation.
• Their activity is abolished by preincubation
• with cells expressing the PDGFR a chain,
• with recombinant PDGFR
• by PDGFR tyrosine kinase inhibitors.

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Effect of PSS autoAb on fibroblast
No effect of the EPGF inhibitor AG1478
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Results

• Stimulatory IgG Abs to the PDGFR are found in all
  patients with PSS.
• They recognize native PDGFR inducing
• tyrosine phosphorylation (not shown)
• ROS accumulation.
• Their activity is abolished by preincubation
• with cells expressing the PDGFR a chain,
• with recombinant PDGFR
• by PDGFR tyrosine kinase inhibitors.
• They selectively induce
• The Ha-Ras-ERK1/2 cascade
• The ROS cascade

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Fig 4A Induction of actin in normal human
fibroblast ?myofibroblast
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Fig 4B. Induction of Type I Collagen in normal
human fibroblasts
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Results

• Stimulatory Abs to the PDGFR are found in all
  patients with PSS.
• They recognize native PDGFR inducing
• tyrosine phosphorylation
• ROS accumulation.
• Their activity is abolished by preincubation
• with cells expressing the PDGFR a chain,
• with recombinant PDGFR
• by PDGFR tyrosine kinase inhibitors.
• They selectively induce
• The Ha-Ras-ERK1/2 cascade
• The ROS cascade
• They stimulate
• type I collagengene expression

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Conclusions Stimulatory autoAbs against PDGFR

• Exist.
• Appear to be a specific (only in) hallmark (all)
  PSS.
• Are at a higher level in early (lt5y) than late
  (gt10y) PSS.
• Exist also in PSS-like disease GVH (10/10).
• Have many features of pathogenic autoantibodies
• IgG (Ag driven process)
• Target a Cell Surface Ag (accessible in vivo)
• Target a Functional Ag (a receptor
  physiopathologically relevant)
• Target the Native Ag (conformational epitopes).
• Are in vitro, long acting stimulators like LATS.

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Perspectives

• The study needs to be confirmed and extended to
  endothelial and smooth muscle cells who may not
  always have PDGFRs or the same ROS
  microenvironment. Indeed, PSS patients with PHT
  all have those Abs but all Ab-positive PSS do not
  have clinical PHT.
• New treatment strategies can be suggested
  combining
• Inhibition of tyrosine kinase imatinib mesylate.
• Anti-oxidants for ROS
• Inhibitors of Ha-Ras statins
• B cell depletion rituximab
• Decoy receptor.