Angiogenisis Flashcards
What are the 2 processes reprising or got the formation of new blood vessels
Vasculogenesis -
Angiogenesis -
Vasculogensis
Differentiation of angioblasts into endotheialcells and the new formation of vascular network.
Occurs during embryogenesis
Angiogenesis
The formation of vascular spouts from pre exsisting vessels
Results in a highly branched vascular network.
Occurs during development and post natal life.
When does angiogenesis occur
During development
Post natal -
Blood vessel in placenta
Thickening of endometrium
ReSponse to stimulus
What are the main on switches of angiogenesis known as
Angiogenesis stimulating growth factors
What are the main off switches of angiogenesis known as
Angiogenesis inhibitors
How is angiogenesis tirner off
The production of more inhibitors than stimuiators
What eye conditions could unregauktion of angiogenesis lead to
Age related macular degeneration
Wet- presecence if immature vascularisation in retina which leak - occulusiom of retina - blindness
Diabetic retinopathy
How does angiogenesis contribute to atherosclerotic plaque
When blood vessels become thickened from atherosclerotic plaque , hypoxemia is stimulated in the local area. This is a stimulus to switch in angiogenesis process .
Thickened bv starts to make fragile micro vessels in order to supply oxygen to the area , this can lead to leakage of these immature vessels - formation of blood clotting , leading to cycle of plaques IN CVD.
Endometriosis
Lining of the womb, which normally thickens during menstral cycle, starts to grow outside of the womb. In bad cases , these lesions can cause tubular and ovarian adhesions, which needs removed by surgury.
Elevation in VEGF A and soluble vascular endothelial growth factor receptor 1 and 2 (sVEGFR 1+2)
Crohns disease
SVEGFR has been shown to be increased in patients. , increased angiogenesis is also leading to underlying o pathology.
Cancer
Cancer is a angiogenesis dependant process . A bowing tumour needs vat vascular network to provide nutrients and oxygen . In addition , new tumour blood vessels provide a way for tumour cells to enter the circulation and metastazie to sdistabt organs.
How does tumour stimulate angiogenesis
After about 2mm inner cells of tumour become starved of oxygen. This is a signal to the cells that they need oxygen
The repsponse is to stimulate angiogenesis
Secretion of gf to stimulate angiogenesis act on endothelial cells of capillary network.
Pridtcuon of new BV , supply oxygen and nutrients ti growing tumour , gets bugger , can develop beyond orginal place of growing cells
Travels through body - metastatic spread
Multi step process Of angiogenesis
Key proangiogenic factors
Vascular endothelial growth factor (VEGF)
angiopoietin 1
Basic fibroblast growth factor (FGF-2)
Platelet derived growth factor (PDGF)
Main tissues vegf is expressed in
Brain
Kidney
Liver
Spleen
What does vegf regulate in the Body
Vascular permeability after binding to endothelial cells , important for the initiation of angiogenesis.
How do you know VEGf plays important role in development of vascular system
If you delete even one allele of VEGf the embryo will not survive
What growth factors and cytokines indice transcription of VEGf
PDGF
epidermal growth factor
TNF a and b
Interleukin b
How is vegf regulated
By tissue oxygen tension - levels of vegf sensitive to oxygen levels of environment
Vegf receptors,
Vegfr 1+2
Regyaktuon o PEF vegfr regulated by oxygen levels
Angiopoeitins
Family of proteins . Four types agp 1234
Bund ti tyrosine receptor kinase. 2 molecules of meditator bind together. Causing receptor to dimerise , leading to tyrosine kinase function of this receptor and ibtraceukkar signal transduction downstream of receptor activator.
These receptors - tie 1 and 2 are preferentially expressed on endothelial cells.
Basic fgf
Basic fibroblast growth factor.
Secreted by
Stem cells
Vascular endothelial cells
Binding to receptor shown to trigger intracellular signalling cascade leading to
Proliferation and migration of endothelial cell
Angiogenesis
Production of proteases
Differentiation
FGF2 again binds ro tyrosi;kinase receptor
Platelet derived growth fvactorsn
Comproswd of four different polypeptide chains which are inactive in their monomeric form
4 diff Types a b c d
After the polypeptides have been translated they exhibit their effects by dimerising and binding to tyrosine kinase receptor.
Associated with various steps in angiogenesis
Maturation of newly formed vascular network
Proliferation and migration of endothelial cells
Stimulation and activation of endotheialcells and release of proangiogenic factors.
What enzymes are required to break down basement men,brand
Urokinase plasminogen activator uPA
Matrix metalloproteimase
Role of stromal cells
Tumour cells can release many soluble factors such as those that switch on angiogenesis.
Other solubke factors recruit stromal cells to tissue micro environment.
Recruitment of these tissue stromal cells are also a source of expression of proangiogenic factors.
Angiogenesis is become uncontrollably activated and not regulated in a normal fashion
How is vascular stabilised in angiogenesis
At leading end , there is continuous cycles or endothelial cells proliferation and remodelling of t(e basement membrane .
Part of this process is both release of basement membrane proteins from the endothelial cells and also the release of factors that digest basement membrane.
This continues to vascular reaches tissue that stimulates the angiogenesis process
At the trailing edge the vascular is matured , one of the most important process here is the recruitment of pericytes and smooth muscle cells ,. Cknrollled by PDGF from new capillaries
Once their is sufficient maturation proangiogenic factors down regulated. Endotheialcells go back into resting state.
What happens in pathological angiogenis vascular maturation
Angiogenis not switched of.
Vascular not properly insulated by Pericytes and smooth muscle cells
Leads to leaky irregular sized vessels.
5 classes of angiogenic antagonist
Inhibition of proteases (inhinit synthesis of MMP)
Inhibitors of endothelial cell migration and proliferation
Inhibitors of angiogenic growth factors
Inhibitors of matrix proteins on endothelial cell surface
Inhibitors with a unique mechanism
Types of anti veg f drugs
MONOCLONAL ANTIBODIES
DIrected against specific proganiogenic growth factors like VEGf
SMALL MOLECULE TYROSINE KINASE INHIBITORS
Where do anti VEGf drugs inhinit at
At the level of the growth factor
At the level of the growth factor binding to the receptor
Level of the receptor transduction pathway once receptor has been activated
How do antibody mediated VEGF inhibition work a
Anyubidy has a high affinity for its antigen ( VEGF or VEGFR) this will either neutralise the growth factor or or binds to receotor and inhibits down stream signalling of that receptor
Also leads to cytotoxic response in the cell via antibody dependant cell mediated toxicity or complement dependant cytotoxicity
Examples of monoclonal antibodies
Ramucirumab
Anti VEGf 2 inhibitor
Alfibercept
Hugh binding affinity
Made of extra cellular domains of VEGfr 1 and 2
Fused to constant region of human 1gG1
Binds ti vegf and neutarlisesbut and orecents it from binding to down stream receptor
What are protein kinases
Enzymes found in cells that catalyse the transfer of gonna phosphate from atp onto the hydroxyl group on amino acid residue on target protein .
Resukts in conformational change in target protein that can reveal a catalytic active domain in target protein and stimulate activation of the target protein.
Wheee are RTK relatively conserved and where do they differ
Conserved - tyrosine kinase domain
Variability found in the extra cellular domain
How does activation of tyrosine kinase domain happen
Ligand binds to RTK
receptor dimerise
Dimerisation resukts in auto phosphorylation in intracellukar domain of RTK
Confirmation change revealing ATP and substrate binding domains of tyrosine kinase domain of RTK
How many sub families of NRTKS are there and how are they defined
Nine and defined according to sequins similarities
How does activation NRTKs occur
Various interactions with other signalling proteins and confirmation hcnsges like In RTI occur revealing ATP And substrate binding domain of the protein
Types of kinase
Serine / threonine kinase
Receptor tyrosine kinssses
Non receptor tyrosine kinases
What do serine / threonine kinases do
Catalyse the phosphorylation of serine / threonine
Example of serine threonine kinase and it structure
RAF
Enclosed format where the catylytic site is nit accessible to substrate or ATP
What happen upon activation of raf
Conformational change that opens up the catyltic domain revealing the ATP and substrate binding domain on the protein
Tyrosine kinase inhibitorsn
Description
These are membrane permeable organic mole files that diffuse through the membrane bilayer and target the ATP binding site of various kinases causing their inhibition
These inhibitors may target various different tk domains suggesting structural similarity and decreased drug specificity
Example of two multi kinase inhibitors
Sorafanib
Thalidomide
Sorafanib
Inhibits ATP binding site of RAF and receptor tk domain of a number of RTK. - multi kinase inhibitors
Sorafanib competes with ATP for hydrophobic binding pocket of kinase.
Thalidomide
Thalidomide marketed over 400 years ago as mild sensitive and help with morning sickness
Limbs didn’t form in baby
One thought of this cause is that thilomide inhibits angiogenis
Now used as anti angiogenesis therapy
Family of drug known as IMid - immunomodulatory drugs with an imide drugs
Binds to cereblon protein - substrates come in contact with cereblon and become ibiquitinated and causes degradation of that protein
Therefore it has an inhibitory effect on pro ag factors
Limitation of anti angiogenic treatments
Prolonged administration of anti angiogenic drugs reduce the micro vascular density within tumour and the and may compromise the delivery of chemo to the tumour cells
Macugen
VEGf antagonist
Binds to VEGf prevents it from binding to receptor
Aptamer - short strand of DNA
