Building Blood Vessels

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Building Blood Vessels

• Dll4 signalling through Notch1 regulates
  formation of tip cells during angiogenesis

Mats Hellström, Li-Kun Phng, Jennifer J. Hofmann,
Elisabet Wallgard, Leigh Coultas, Per Lindblom,
Jackelyn Alva, Ann-Katrin Nilsson, Linda
Karlsson, Nicholas Gaiano, Keejung Yoon, Janet
Rossant, M. Luisa Iruela-Arispe, Mattias Kalén,
Holger Gerhardt and Christer Betsholtz
Isis Trenchard April 13, 2007
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Why grow blood vessels?

• Therapeutic Targets
• Tissue Engineering

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A Primer on Blood Vessel Growth

• 3 ways to grow new blood vessels
• Angiogenesis
• Arteriogenesis
• Vasculogenesis
• VEGF-A Vascular Endothelial Growth Factor

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Motivation

• Knew VEGF-A gradient is need to make tip cells,
  but not known how these tip cells are selected.
• Goal Figure out how tip cells are selected.

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What is a tip cell?

• Cell that leads or guides the direction of growth
  of blood vessel.
• Have filopodia.
• Whats a filopodium? a spike-like actin
  protrusion at the leading edge of migrating
  cells, functions as a sensor of the local
  environment and has a mechanical role in
  protrusionhttp//www.biophysj.org/cgi/reprint/89/
  2/782.pdf

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So how did they study tip cell development?

• Knew that Notch signaling had a role in vascular
  development.
• Studied retinal angiogenesis in one week old mice.

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What is a notch protein?

• The Notch protein sits like a trigger penetrating
  the cell membrane, with part of it inside and
  part outside. Proteins when binding to the
  exterior part cause the release of a portion of
  the interior part, which typically then makes its
  way to the cell nucleus to alter gene
  expression.
• In this study Notch1 and Dll4

http//en.wikipedia.org/wiki/Notch_signaling
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Experiment 1

• Inhibit Notch1 and see what happens.
• How?
• Gamma secretase inhibitors (GSI)
• DAPT
• Compound X
• Secretases are enzymes that "snip" pieces off a
  longer protein that is embedded in the cell
  membrane.

http//en.wikipedia.org/wiki/Secretase
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Experiment 1 Results
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Experiment 2

• So what is Notch1 doing exactly?
• Control the expression of Notch1s ligand Dll4
• Used transgenic mice (Dll4/-) and in separate
  experiment used Notch1 knock-out mice.

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Experiment 2 Results
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Experiment 3

• What happens when you turn up Notch1?
• Used Jag1 which increases Notch1 expression
• Direct gain of function experiment

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Experiment 3 Results

• Decreased filopodia.
• Decreased vessel density.

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Experimental Conclusions
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Significance

• GSIs as therapeutics
• Blood vessel conduits

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References