Vascular Endothelium 2 Flashcards
What is the vascular system relevant to
Every disease
What is atherosclerosis a response to
Atherosclerosis is a stereotypic arterial response to injury {756}
Exact pathology determined by nature and duration of the stimulus
Atherosclerosis as a syndrome
Describe the characteristics of atherosclerosis
Atherosclerosis is a build up of fibrous and fatty material inside the arteries and underlies CVD.
- Atherosclerosis is a chronic inflammatory disease.
- It is also a very slow disease – can take up to 4 decades to form and then rupture
List some of the chronic stimuli for the aorta
Cholesterol, smoking, high BP
Describe the stages involved in the development of atherosclerosis
Endothelial dysfunction
Fatty streak formation
Formation of an advanced complicated lesion of athersclerosis
Describe endothelial dysfunction atherosclerosis
Endothelial Dysfunction in Atherosclerosis. The earliest changes that precede the formation of lesions of atherosclerosis take place in the endothelium. These changes include increased endothelial permeability to lipoproteins and other plasma constituents, which is mediated by nitric oxide, prostacyclin, platelet-derived growth factor, angiotensin II, and endothelin; up-regulation of leukocyte adhesion molecules, including L-selectin, integrins, and platelet–endothelial-cell adhesion molecule 1, and the up-regulation of endothelial adhesion molecules, which include E-selectin, P-selectin, intercellular adhesion molecule 1, and vascular-cell adhesion molecule 1; and migration of leukocytes into the artery wall, which is mediated by oxidized low-density lipoprotein, monocyte chemotactic protein 1, interleukin-8, platelet-derived growth factor, macrophage colony-stimulating factor, and osteopontin.
Describe the formation of the advanced, complicated lesion of atherosclerosis
Formation of an Advanced, Complicated Lesion of Atherosclerosis. As fatty streaks progress to intermediate and advanced lesions, they tend to form a fibrous cap that walls off the lesion from the lumen. This represents a type of healing or fibrous response to the injury. The fibrous cap covers a mixture of leukocytes, lipid, and debris, which may form a necrotic core. These lesions expand at their shoulders by means of continued leukocyte adhesion and entry caused by the same factors as those listed in Figures 1 and 2. The principal factors associated with macrophage accumulation include macrophage colony-stimulating factor, monocyte chemotactic protein 1, and oxidized low-density lipoprotein. The necrotic core represents the results of apoptosis and necrosis, increased proteolytic activity, and lipid accumulation. The fibrous cap forms as a result of increased activity of platelet-derived growth factor, transforming growth factor ß, interleukin-1, tumor necrosis factor , and osteopontin and of decreased connective-tissue degradation.
Angiogenesis also occurs
How does a fatty streak appear
As a yellow streak
What happens in fatty streak formation
Smooth muscle migration Foam cell activation T cell activation Platelet adherence and activation Leukocyte adherence and entry
Which blood vessels consists of 3 layers
Blood vessels consist of THREE layers (except for capillaries and venules):
Describe the 3 layers of the blood vessels
- Tunica Intima – Endothelium.
- Tunica Media – Smooth Muscle Cells (VSMCs).
- Tunica Adventitia – Vasa Vasorum, Nerves.
Describe the Tunica Media
Consists of smooth muscle, then elastic membrane
Describe the Tunica Intima
Inwards- Outwards Endothelium Basement Membrane Lamina Propria (smooth muscle and connective tissue) Internal elastic membrane
Describe the Vasa Vasorum
This is a network of small blood vessels that supply the walls of larger blood vessels.
Describe the growth of endothelial cells
Single monolayer of cells, they grow in 2D and not 3D due to cellular communication (they send signals about their growth)
What is the role of the Human Cell Atlas
To sequence the transcriptome and genome of every cell in the body
What are the functions of the endothelia
- Angiogenesis.
- Thrombosis and Haemostasis.
- Inflammation.
- Angiogenesis.
- Vascular tone permeability
List the matrix products and growth factors of the endothelia that result in angiogenesis
Growth factors:
Insulin like growth factors
Transforming growth factors
Colony Stimulating growth factors
Matrix products: Fibronectin Collagen Laminin Proteoglycans Proteases
List the inflammatory mediators and adhesion molecules involved in inflammation
Adhesion molecules:
ICAMs
VCAMs
Selectins
Inflammatory mediators:
Interleukins 1,6,8
Leukotrienes
MHC 2
List the antithrombotic factors released by the endothelium
prostacyclin thrombomodulin antithrombin plasminogen activator heparin
List the procoagulant factors released by the endothelium
von Willebrand factor thromboxane A2 thromboplastin factor V Platelet activating factor Plasminogen activator inhibitor
List the vasodilator and vasoconstrictor factors involved in vascular tone
Vasodilator:
Nitric Oxide
Prostacyclin
Vasoconstrictor: ACE thromboxane A2 leukotrienes free radicals endothelin
At rest, what is the essential feature of the endothelium
Keeps the balances to pro and anti, essential to life.
HEALTHY STATE – Endothelia tend to maintain an anti-thrombotic, anti-inflammatory and anti-proliferative state
Describe the state of the resting endothelium at rest
- UNHEALTHY STATE – If the endothelia become damaged etc. they flip to the reverse of the above.
- In atherosclerosis, this unhealthy state is CHRONIC as it is a chronic inflammatory disease à problems.
Describe some of the stimuli that can chronically activate the endothelium and lead to atherosclerosis
Thrombosis Senescence oxLDL Glucose High BP Permeability and Leukocyte recruitment Mechanical stress Viruses Inflammation Smoking Hypercholesterolaemia (e.g. oxidatively modified lipoproteins Diabetes mellitus / metabolic syndrome Hypertension (e.g. ANG-II & ROS Sex hormonal imbalance (e.g. oestrogen deficiency & menopause ) Proinflammatory cytokines (e.g. IL-I & TNF) Oxidative stress Infectious agents (e.g. bacterial endotoxins & viruses) Environmental toxins (e.g. cigarette smoke and air pollutants) Haemodynamic forces (e.g. disturbed blood flow)
Describe the characteristics of the vascular endothelium
- Endothelia form single layers of cells and when they divide, they need to know to do this. In forming a monolayer, they undergo contact inhibition.
- Normally, once formed, the cells are stable and not a lot of new cells grow except in angiogenesis or healing
Describe Leukocyte recruitment in atherosclerosis
Recruitment of blood leukocytes into tissues takes place normally during inflammation: leukocyte adhere to the endothelium of post-capillary venules and transmigrate into tissues
In atherosclerosis, leukocytes adhere to activated endothelium of large arteries and get stuck in the subendothelial space
Newly formed post-capillary venules at the base of developing lesions provide a further portal for leukocyte entry
Monocytes migrate into the subendothelial space differentiate into macrophages
Describe leukocyte recruitment
Rolling and Activation
- At inflammation, endothelium becomes activated and expresses ligands for the leukocytes.
- Selectins on the leukocyte begin to weakly interact with the endothelium which initiates ROLLING. L-Selectins on leukocytes bind to E and P selectins on the endothelium.
Firm Adhesion
* Internal signals activate the integrins on the surface of the leukocyte, switching the integrins to a ‘high-affinity’ state.
* Integrins bind strongly to the endothelium and leukocyte adheres and transmigrates.
Integrins on the leukocyte(LFA-1, VLA-4)
bind to VCAM-1 and ICAM-1 on the endothelium.
How do the leukocytes cross the post-endothelial venule
The flatten out and move across the PEV paracellularly and transcellular
What ensures that the endothelial cells only grow in 2D
- Endothelia form single layers of cells and when they divide, they need to know to do this. In forming a monolayer, they undergo contact inhibition- when the contact reaction takes place, the cells enter quiescence.
- Normally, once formed, the cells are stable and not a lot of new cells grow except in angiogenesis or healing..
Why is it difficult to design drugs that treat problems associated with the vascular endothelium
Not all endothelia are the SAME. There are subtle differences in the glycoproteins etc.
Describe endothelial junctions
- Leukocytes transmigrate by squeezing between endothelial junctions.
- V-cadherin is present at all junctions.
- At a junction, both endothelial cells’ surface proteins bind in a homophilic way.
- This binding creates a zipper which some molecules can unzip and pass through.
Describe the differences in structures of the capillaries and post-capillary venules
Capillary: endothelial cells surrounded by basement membrane and pericapillary cells (pericytes).
Post-capillary venule: structure similar to capillaries but more pericytes
Describe the basic structure of arteries and relate this to the problem seen in atherosclerosis
Artery: three thick layers, rich in cells and extracellular matrix.
- In atherosclerosis, the leukocyte CANNOT pass through the whole thickness of the vessel so it gets trapped.
- Normally, transmigration occurs in the post-capillary venules where the leukocyte can pass through, meet the basement membrane and chew through it with it’s enzymes but in the arteries, it cannot pass full thickness. However in atherosclerosis, the leukocytes get stuck in the basement membrane.
What is meant by vascular permeability
The endothelium regulates the flux of fluids and molecules from blood to tissues and vice versa
What are the consequences of increased vascular permeability
- Increased permeability also results in leakage of plasma proteins from the blood, through the endothelial junctions and into the sub-endothelial space.
- In this layer, the ‘sticky’ proteoglycans can trap the plasma proteins and the leukocytes.
Can result in oedema
Describe lipoprotein trapping and oxidative modification
The activated endothelium becomes more permeable to Lipoproteins, especially LDL.
LDL moves across the endothelium and binds to proteoglycan (by oxidation) in the sub-endothelial layer, where it gets ‘stuck’.
The pro-oxidative environment is created by secretions from macrophages.
4. Macrophages phagocytose the oxLDLs forming Foam Cells- fatty streak formation.
5. Chronic inflammation begins.
Where do atherosclerotic plaques preferentially form
At bifurcations and curvatures.
Describe Laminar flow
Streamlined, outermost layer moving slowest and centre moving fastest
Describe Turbulent flow
- Turbulent flow: Interrupted with rate of flow exceeding critical velocity presenting with rough eddy currents.
Speed of fluid is continuously undergoing changes in both magnitude and direction
Describe the protective effects of laminar flow
Laminar blood flow promotes antithrombotic factors, anti-inflammatory factors, nitric oxide production, inhibition of SMC proliferation.
It protects Nitric Oxide.
Describe the effects of turbulent flow
Disturbed blood flow promotes coagulation, leukocyte adhesion, SMC proliferation, endothelial apoptosis and reduced nitric oxide production.
Atherosclerosis tends to occur at bifurcations due to turbulent flow
Describe the role of laminar flow in reducing the risk for CVD
As Laminar blood flow PROMOTES endothelial cell survival with high shear stress, risk of atherosclerosis is reduced
Describe the multiple protective effects of NO on the vascular endothelium
Reduces release of superoxide particles.
Dilates blood vessels
Inhibits monocyte adhesion
Reduces platelet activation
Reduces oxidation of LDL (major component of plaque)
Reduces proliferation of SMC in Vascular endothelium
Describe the formation of early atherosclerotic lesions
Early lesions of atherosclerosis in the human carotid artery develop in the area of a major curvature (carotid sinus) exposed to low time-average shear stress, a high oscillatory shear index, and steep temporal and spatial gradients. Endothelial cells at this site display an atheroprone phenotype, which promotes a proinflammatory milieu driven by the priming of the NF-κB signaling pathway, which is then perpetuated in response to subendothelial apoB LPs. NF-κB activation promotes the entry of blood-borne monocytes (blue cells) through the junctions of endothelial cells (orange cells) into the intima, and there, monocytes differentiate into macrophages (red cells).
Describe the epigenetic effects of laminar flow
In contrast, arterial geometries that are exposed to uniform laminar flow evoke an atheroprotective endothelial cell phenotype driven by the transcriptional integrators KLF2 and KLF4. This atheroprotective endothelial phenotype, together with a decrease in LP retention, promotes an antiinflammatory and antithrombotic environment that affords relative protection from atherosclerotic lesion development. KLF2,4 are also transcription factors for the eNOS gene.
What is meant by epigenetics
functionally relevant, inheritable changes to the genomethat do not involve a change in thenucleotide sequence, which affect gene expression
Describe the three key epigenetic mechanisms
There are three key epigenetic mechanisms that regulate gene expression (i) methylation of CpG islands, mediated by DNA methyltransferases, (ii) histone protein modifications and (iii) microRNAs. The various epigenetic modifications control gene activation and silencing affecting gene expression.
How does the genome adapt to developmental and environmental cues
The genome adapts to developmental or environmental cues through modification of DNA itself (e.g. methylation) or of proteins that associate with DNA (e.g. histones) .
Epigenetic processes are essential for development and differentiation, and can also arise under the influence of the environment
Can epigenetic pathways be targeted by drugs
yes
Describe how stable flow can regulate endothelial epigenetic pathways
Stable flow (s-flow) downregulates expression of DNA methyltransferases (DNMTs), which allows the promoter of antiatherogenic genes, such as Klf4 and HoxA5, to remain demethylated, enabling their expression.
Describe how disturbed flow can regulate endothelial epigenetic pathways
Disturbed flow (d-flow) upregulates DNMT expression, leading to hypermethylation of the promoter of antiatherogenic genes, such as Klf4 and HoxA5, repressing their expression.
What is meant by angiogenesis
Angiogenesis is the sprouting of new vessels from the endothelial lining of preexisting vessels. Angiogenesis has long been thought to represent the principal paradigm for neovascularization to maintain homeostasis and for co-optation via the angiogenic switch for tumor growth
Describe the Janus paradox
The Janus Paradox The idea that angiogenesis plays a beneficial but also detrimental role for the cardiovascular system.
- Good – People who suffer from acute MI obtain fibrotic heart tissue that develops into heard failure BUT using therapeutic angiogenesis, we can prevent tissue damage by forming new vessels to supply these areas.
- Bad – angiogenesis promotes atherosclerotic plaque formation as degraded products in the necrotic core simulate hypoxia which stimulates proliferation of the vaso Vasorum (little vessels) which are thin. These thin vessels are then more likely to break.
Describe the characteristics of angiogenesis
- Angiogenesis is totally controlled by endothelial cells and has a role in atherosclerosis.
- Importantly, angiogenesis has a negative role in maintaining cancer growth.
- Hypoxic tissues release chemicals that activate ECs and triggers them to differentiate to ‘tip’ cells which control formation of the blood vessel. Pericytes then aid growth.
- Vascular Endothelium Growth Factor (VEGF) plays an important role in angiogenesis.
How can angiogenesis promote the formation of the atherosclerotic plaque
Angiogenesis at the base of the plaque- growth of plaque, abnormal- leukocytes enter- plaque growth.
What do blood vessels form before
Tissues
Describe therapeutic angiogenesis
Another path for blood to travel, overcoming the block.
What is meant by senescence
Cellular senescence: growth arrest that halts the proliferation of ageing and/or damaged cells.
Senescence is a response to stress and damage.
Senescent cells have distinctive morphology and acquire specific markers (e.g. b-gal)
What is good about senescence
Prevents the transmission of damage to daughter cells.
Replicative senescence: the limited proliferative capacity of human cells in culture.
What are the consequences of senescence
Senescent cells are pro-inflammatory and contribute to many diseases.
Describe how senescence can contribute to atherosclerotic plaque progression
- This is a way of making sure damaged cells don’t take over and is considered the body’s defence against cancer.
- However, senescent cells (growth arrested cells) can develop a pro-inflammatory response.
- Endothelial senescence can be induced by CV risk factors such as oxidative stress (this means it DOES NOT CAUSE atherosclerotic plaque formation) and as the cells are pro-inflammatory and pro-thrombotic therefore, they can contribute to atherosclerotic plaque progression.
Describe the telomeric-dependent mechanisms of senescence
Senescence was initially considered to reflect the finite capacity for division that normal diploid cells exhibit when propagated in culture, hence the term “replicative senescence.”
At the molecular level senescence resulting from successive rounds of cell division has been linked to the progressive shortening and eventual dysfunction of telomeres, the physical ends of chromosomes. In mammalian cells telomeres consist of a repeated DNA sequence (TTAGGG) that extends over a length of several thousand base pairs and associates to an array of specialized telomere binding proteins. Synthesis of telomeric DNA requires the presence of telomerase, a ribonucleoprotein complex that catalyses the addition of TTAGGG repeats to the 3’-end of the DNA chain. The majority of human adult somatic cells either lack or have very low levels of telomerase (25). Under these conditions, and due to the inability of conventional DNA polymerases to replicate the end of the lagging strand, DNA synthesis during cell division results in a gradual loss of telomeric DNA (68). In addition, due to its high GGG content, telomeric DNA is particularly susceptible to oxidative damage and the generation of single strand breaks. Accordingly, the rate of telomere erosion is also greatly affected by the oxidative burden of the cell (91). Telomere erosion eventually compromises its functional integrity and leads to the induction of a DNA damage checkpoint response that halts the cell-cycle permanently (15).
