Mouse Vasculature

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Mouse Vasculature Embryonic Day 11
Arteries
Veins
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The main component of the vasculature are the
endothelial cells (ECs) which form the inner
wall of all blood vessels
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The adult vascular system is quiescent except
during a) the female reproductive cycle and b)
wound healing following injury
Endothelial cells rarely form tumors, e.g.,
hemangiomas, usually in children
However, formation of new blood vessels is a
critical component in the growth of solid tumors
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Blood vessel formation

• Adult Vascular System
• Endothelium is a stable structure except
• 1. reproductive cycle
• 2. following injury

• Embryonic Vascular System
• Very dynamic
• 1. Vasculogenesis
• 2. Angiogenesis
• 3. Remodeling Perivascular cell
  interactions
• 4. Organogenesis

• Pathological Angiogenesis
• Reactivation of embryonic mechanisms
• of vascular development

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Development of the vascular system
1. Morphogenesis
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Cell migration during gastrulation
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Vasculogenesis Mouse day 7.5
1st Aortic Arch
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Vascular Remodeling Chicken embryo
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Marking of early angioblasts TMLacZ Knock-in
mice Day 7.5
Pre-endocardial Tubes
Proximal lateral mesoderm
Weiler et al., 1997
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Early Vasculature Day 8.5
Endocardium
Vitelline Vein
Dorsal Aortae
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Vascular Network Day 9.5
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Development of the vascular system
2. The molecules
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Genes important for vascular development



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Genetic regulation of blood vessel formation
Conway et al., Cardiovascular Research, 2001
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Development of the vascular system
3. The cells
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Embryonic Endothelial Progenitor Cells (EPCs)
Hematopoietic Cells Flk-1-/Tal1
Hemangioblast (Blood Islands) Flk-1 / Tal1
Extraembryonic-Yolk Sac
Mesodermal Cells
Endothelial Cells Flk-1 / Tal1- / CD31
Angioblast Flk-1 / CD31 or CD31-
Blood Cells CD45
Endothelial Cells Flk-1 /CD31
Hemogenic Endothelium
Circulating ECs / EPCs QH1
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Cellular progenitors of vascular structures
Conway et al., Cardiovascular Research, 2001
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Embryonic Assembly of Blood Vessels Angiogenesis
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ALM1 KO mice lack hematopoietic Stem cells (HSCs)
and have defects in angiogenesis
WT /
AML1 -/-
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Rescue of angiogenesis with wt HSCs
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HSCs guide sprouting by secreting Ang-1
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Properties of vascular progenitor cells
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E7.5
eEPCs
Vascular stem cells
Host vessels green Donor
endothelial stem cells red
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eEPCs express genes important for vascular
development
c-Kit, Sca-1, Tie-2, Flk-1low, CD34low
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Hanging-drop differentiation protocol of ES
cells
ES Stem Cells
Blood vessels
Cardiomyocytes
Neurons
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Expression of endothelial-specific markers
during Embryonic Stem (ES) cell differentiation
Photograps from A. Sachinidis J. Hescheler,
UKOE
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Bmp 2
Cerberus
Brachyury
Vegfr-2 (Flk-1)
Ang 2
VE-cadherin
vWF
CD31 (Pecam-1)
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Expression of cardiomyocyte-specific markers
during Embryonic Stem (ES) cell differentiation
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Bmp 2
Cerberus
Brachyury
Gata-4/6
Nkx2.5
MLC-2a
MLC-2v
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Flk-1 ES-derived EPCs are bi-potent
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Flk-1 ES-derived EPCs give rise to ECs SMCs
after transplantation
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Brachyury/Flk-1 cells acquire cardiomyocyte
characteristics
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Brachyury/Flk-1 cells give rise to
cardiovascular and hematopoietic lineages
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(No Transcript)
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Isl1 cells give rise to Cardiomyocytes,
Endothelial and Smooth Muscle Cells
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Model of cardiovascular progenitor differentiation
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Nkx2.5 cells give rise to myocardial and smooth
muscle cells
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Summary I Endothelial cells, cardiomyocytes,
smooth muscle cells and blood cells share common
progenitors
Understanding the genetic pathways that link and
separate these cell lineages might help us
differentiate adult stem cells, for example bone
marrow stem cells, to cardiovascular tissues for
regeneration after ischemic injury
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Bone marrow stem cells could transdifferentiate
into different cell types
HSC
neurons
hepatocytes
endothelial cells
skeletal muscle cells
blood cells
cardiomyocytes
Smooth muscle cells
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Growth of blood vessels in the brain following
middle cerebral artery occlusion
Newly formed vessels 3 months later
Infarct area 24h after MCAO
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Tumor angiogenesis
Liver
Newly-formed blood vessels
Tumor
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Summary II
The molecular and cellular mechanisms of
embryonic blood vessel formation are
recapitulated to various degree in pathological
neovascularization, e.g., tumor-induced
angiogenesis
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Cellular mechanisms of blood vessel growth in the
adult organism
1. Angiogenesis
Angiogenic factors activate local quiescent
endothelial cells to grow
Folkman, 1971
2. Neovasculogenesis
Bone-marrow derived endothelial progenitor cells
(EPCs) home to angiogenic sites and enhance
vessel growth
Asahara Isner, 1997
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Post-natal Endothelial Progenitor Cells
Peripheral Blood
Bone Marrow
Culture
HSCs
EPCs
Early Outgrowth EPCs / ECs
Myeloid Precursors
EPCs
Late Outgrowth EPCs / ECs
MSCs
Endothelial cells
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Adult bone marrow-derived cells take part in
angiogenesis
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eEPCs contribute to new blood vessels at low
frequency 2-5
Host blood vessels
Donor eEPCs
Merge
Wei,Hatzopoulos, Beltinger, Cancer Cell 2004
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Summary III
HSC-derived cells are mobilized and take part
directly and indirectly in formation of new blood
vessels
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eEPCs home to lung tumor metastases LM8
osteosarcoma
Lung tissue
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eEPC Recruitment depends on a tumors degree of
vascularization
Met2
Met1
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Target tumor metastases with eEPCs armed with a
suicide gene
eEPCs-CD
5-fluorocytosine (5-FC)
5-fluorouracil (5-FU)
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eEPC-based suicide gene approach treatment
eEPCs i.v.
5-FC (or PBS) i.p. b.i.d
Survival ()
Survival time (days)
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eEPC suicide gene approach results in fewer
metastases
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Summary IV
Vascular stem cells can be used for therapy to
stimulate blood vessel formation or to target
tumor growth