Angiogenesis Flashcards
Describe and explain the change in oxygen flux from the arterial to the Venus end of a capillary
Oxygen flux decreases from arterial to Venus end
As blood flows through, the [O2] decreases along the capillary as it diffuses out the capillary to areas of lower [O2], therefore slowing the flow of O2
What is oxygen flux?
The flow of oxygen
Why must cancer cells be close to a blood vessel?
It has high requirements for O2, glucose, amino acids etc.
The diffusion distance of O2 is limited
What does the Krogh cylinder show?
Where cells can function based on O2 levels and closeness to blood supply
If blood flow is low, what happens to the length of Krogh cylinder?
Length of cylinder is low
If metabolic rate is high, what is the effect on the Krogh cylinder?
The diameter is small
What does oxygen tension depend on?
Closeness to capillary
Closeness to arteriole end of capillary
What are hypoxic cells?
Cells that don’t have enough oxygen to function, beyond critical oxygen tension level
What is the oxygen diffusion distances under normal metabolism rate at:
Arterial end?
Venus end?
Arterial: 70 µM
Venus: 10 µM
What is the diffusion distance in highly metabolic environments at the:
Arterial end?
Venus end?
Arterial: 150 µM
Venus end: 70 µM
What are the 6 ways cancers can stay oxygenated?
- Increase blood flow
- Cause new vessels to grow in
- Split existing blood vessels
- Metabolism anaerobically
- Grow along blood vessels
[6. Develop new vessels de novo]
What does VEGF stand for?
vascular endothelial growth factor
Describe VEGF-A’s structure
A dimer with 2 identical polypeptides
Describe how VEGF can result in the formation of new vessels
- VEGF produced and secreted into surrounding stroma
- VEGF binds to VEGF-Receptors and activates Ca2+ & other signalling pathways
- Increases permeability of blood vessels (becomes leaky)
- Enables breakdown of extracellular matrix by MMPs
- Pericytes withdraw
- Sprouts form
- Endothelial cells migrate to source of VEGF
- Cell division occurs behind migrating sprout to push it out
- Lumen formed in new endothelial
- Sprouts connect when they reach other sprouts, lumens connect, and blood can flow through
What does HIF1 protein do?
Detected change in oxygen tension
What happens in the cell when decreased oxygen tension is sensed by HIF1?
HIF1 upregulates and moves to nucleus where it can increase transcription of VEGF gene to VEGF protein
VEGF released, …
What does hypoxia upregulate?
VEGF and HIF1a
How can we tell that VEGF is upregulated by hypoxia?
VEGF is present at 5% [O2] but not 20% [O2] (normoxia)
How do we know that HIF1a induces the expression of VEGF?
When the promoter region for the VEGF gene is mutated in the areas of HIF1a binding sites, no VEGF is expressed
How does HIF1-a induce VEGF expression?
- HIF1a is ways being expressed under all conditions
- Under normoxia, HIF1a is degraded and cannot work
- Under hypoxia, HIF1a is not degraded and is able to build up
- HIF1a binds to VEGF-b, forming a stable complex which can pass through to the nucleus
- The complex can recognise and bind to the DNA sequence of the VEGF promoter region
- It helps to recruit transcription proteins, which can transcribe the VEGF gene into VEGF protein
Describe the experiment used to measure vascular permeability
Cannulate blood vessel and inject solution with few RBCS.
Perfuse vessel and record pressure driving the solution.
Use the RBCs as markers of flow and count them
Work out permeability using fluid velocity and pressure
What happens to vascular permeability if VEGF is addd but Ca2+ channels are blocked?
Vascular permeability does not change
What is oedema?
A fluid common in many cancers caused by the increase in vascular permeability
What happens to pericytes if VEGF is present?
They migrate away from. The blood vessel, allowing fluid to move out and flow through tissue easier
What is intussusseption angiogenesis?
Blood vessel splits in two
What are 2 differences between sprouting and intussuseption angiogenesis?
Sprouting requires an increase in vascular permeability
Sprouting produces a new vessel rather than splitting one into two
What is an endothelial tip cell?
The cells that have filopodia and search for other growing endothelial tissues. They migrate towards source of VEGF
What are endothelial stalk cells?
Dividing cells that push tip cells out towards source of VEGF
What happens if tip cells meet?
They change from angiogenic to quiescent
Lumen is formed
Blood is able to flow through new vessels
What is the role of Angiopoietin 1?
Stabilizes vessels
Enables epithelial cells to resist proliferation
What is the role of Angiopoietin 2?
Destabilizes vessels,
Encourages growth and proliferation
What is the role of PDGF?
Platelet derived growth factor
Recruits pericytes
Enables communication
How are antibodies used to treat cancer?
They bin to circulating VEGF to stop them from binding to VEGF-R.
What type of treatment is Avastin?
An antibody used to bind to VEGF to stop it from binding to VEGF-R
How do VEGF-R blockers work?
inhibit tyrosine kinase
Proteins aren’t released so basement membrane is not degraded
How do soluble receptors work as a treatment against VEGF?
Copies of VEGF-R modified to compete with VEGF-R by binding to VEGF
‘VEGF trap’
How does VEGF get past the extracellular matrix?
- macrophages and mast cells are recruited from stoma to release MMPs
- MMPs degrade the ECM
- VEGF binds to VEGF-R
- Permeability of membrane increases, more MMPs leak out so more ECM is degraded (positive feedback)
