B10 vascular wall biochem Flashcards
what are the diff types of capillaries
- continuous (basal membrane intact + tight junctions between endothelium) - BBB and muscle
- fenestrated (pores but continuous basement membrane) - glomerulus and endocrine glands
- sinusoids (pores AND discontinuous basement membrane) - spleen, liver, bone marrow
where do the components of a vascular wall originate and differentiate from?
- endothelial layer –> epithelial progenitor cells
- smooth muscle of T intima –> vascular progenitor cells (and slight transdifferentiation from endothelial progenitors)
- blood - hematopoietic stem cells
what determines if a vessel will determine into an artery or vein
-depending on the TFs expressed during differentiation
VEINS: express COUP-TF2
ARTERIES: express VEGF
(both silence the TF coding for the opposite vessel)
when does angiogenesis stop?
IT DOESNT - we still need it as adults + for remodelling and differentiation
!! this can be comromised by certain pathologies: diabetes disrupts it (decreasing flow to some areas) and tumours take advantage of it to create new blood vessels for selfnutrition
describe the general structure of endothelial cells ()
-simple squamous epithelium
-central nucleus and few organelles in perinuclear zone
-highly number of caveole (vesicles)
-receptors, transporters and junctions between their basolateral membranes
-high plasticity and paracrine/ endocrine properties
!! SOSS: weibel-palade bodies in cytoplasm: contain von willebrand factor and p-selectin which play a role in inflammation and homeostasis
functions of endothelial cells (4)
-inflammation response
-blood homeostasis
-vessel remodelling
-barrier, paracrine and endocrine functions
endothelial glycocalyx definition, structure + function
DEF: gel like layer coating luminal side of enodthelial cells, and regulator of endothelial functions
STRUCTURE: proteins, hyaluronic acid, GAGs, reservoir for molecules (SOD) -> NOT covalently bonded bcos this would take energy
!! SOS !! FUNCTION:
-endothelial gatekeeper determining vascular permeability
-repulse RBC
-decrease platelet interaction
-mechanotransducer of biochemical signals
what are the ways in which substances can pass through endothelial cells? (2)
- PARACELLULAR: passage through junctions (lateral domain), ATP independent
- TRANSCELLULAR: transport through the cell either via membrane transporters or via caveolae vesicles (uses ATP)
describe the vesicular transcellular pathway (6 STEPS)
- albumin (carrying target substance) binds to g60 receptor
- SRE kinase phosphorylates caveolin 1 (otherwise this cant happen)
- Activation of molecules that form vesicle (dynamin and intersectin)
- Interaction of RAS with the above molecules allows membrane to reorganise into activated vesicle
- vesicle docking via T/V-snares
- vesicle transport via microtubules from apical to basal membrane
types of junctions involved in basolateral endothelial membrane + main components
- TIGHT: occludins, claudins, ZO1/2/3, JAMs
- ADHERENS: VE cadherin complexes linked to actin via catenins
- FOCAL ADHESION: basolateral domain, integrins (a/b) interacting with cytoskeleton and proteins (fibrinogen / laminin / collagen)
Describe the mechanism by which endothelial cells can influence their permeability
-endocellular gap size (permeability) is controlled by actomyosin through the ratio of MLCK: MLCP, and mediated by diff factors
- inactivated: RAC/ cAMP/ sphingosine - active MLCP - dephosphorylation - less contractile force - barrier enhancement
- activated (eg inflammation) - RHO/ histamine/VEGF factors - active MLCK - phosphorylation - more contractile force - increased permeability
describe the role of platelets in endothelial barrier control
ROLE ON ADHERENS J:
- release endothelial trophogens(EGF/VEGF-A) which maintain AJ integrity
- Trophogens bind to respective receptors on endothelial membrane to induce a VEGF A response
- VEGF A paracrine response –> induces phosphorylation of VEGF receptor and increases stability of the junctions and cytoskeletal binding
!! HENCE: lack of platelets causes increased permeability and can cause hemmorage where RBC pass through endothelium
what are the 2 metabolic states of endothelial cells
- BASAL STATE: non adhesive and non thrombotic surface (VEGF - depending on its isoform)
- ACTIVATED STATE: increased expression of procoagulants and proinflammatory factors (cytokines and GFs)
!! transition between the two occurs under conditions of high stress (hypertension, turbulent flow, cytokines, pathogens, smoking and hypoxia)
!!! these two states are in physiological balance –> an issue occurs when there is HYPERPERMEABILITY: this can cause chronic inflammation, cancer, sepsis, etc
Describe the smooth muscle of vascular wall (VSM)
-not striated, no sarcomeres
-NO TROPONIN
-contain myosin and actin bundles
-found in vessels as sheets of SM strands
FUNCTION: vasodilation and constriction due to their contraction
!! action relies on presence of factors (hormones, nerve impulses) + environmental conditions bcos they do not contract voluntarily
Describe the contraction of VSM cells
-SLOW SUSTAINED AND TONIC CONTRACTIONS
-contractions (stretched state) reduce vessel lumen diameter, and relaxation (unstretched state) increase vessel lumen diameter
- Ca2+ entrance
- bind to calmodulin
- activation of MLCK
- phosphorylation of MLC2 which allows myosin actin cross bridge formation
- MLCP activated for relaxation which dephosphorylats myosin chain and allows breakage of cross bridges
!! ca2+ conc increase depends on extracellular transport (via voltage gated chanells) and intracellular stores in SER
what is redundacy
having more than 1 mechanism/ regulatory process that achieves the same result
–> needed in VSM for example bcos diff receptors for regulation are found in different locations in the body (which receive diff stimuli)
what receptors are present on the VSM cells + function towards contraction (3)
- Gs-R (stimulatory): increase cAMP and induce relaxation (beta2)
- Gq-R (stimulatory): increase IP3 & Rho-kinase and induce contraction (alpha1)
- Gi-R (inhibitory): decrase cAMP and induce contraction (alpha2)
!! diff receptors for the same result needed for VSM in diff locations in the body
role of cAMP in VSM contraction
-cAMP inactivates MLCK and hence inhibits the phosphorylation of the myosin chain
-hence increase cAMP decreases contraction and induces relaxation (and vice versa)
what is the role of Rho kinase in VSM contraction
-inhibits MLCP and so there is less dephosphorylation of the myosin chain
-increased RhoK increases contraction
role of IP3 in VSM contraction
IP3 induces the release of Ca2+ from intracellular SER stores
-hence increased IP3 increases contraction (and inhibits relaxation) - and vice versa
Role of NO in VSM contraction
- produced by NOS (nitric oxide synthase enzyme)
-activates cGMP which activates MLCP which increases dephosphorylation of myosin chain
-increased NO induces relaxation
how is NO synthesised + released
ENZYME: 4 diff isoforms of NOS: NOS1/2/3 and nNOS (neuronal - also has neurotransmitter role) - active as DIMER
SYNTHESIS: from L-Arginine using NADPH and oxygen –> forms nitric oxide + citrulline
RELEASE: Ach stimulates it by releasing Ca2+ that stimulates NOS to form more NO –> NO is released into SM and
detailed mechanism of NOS function (4)
!! uses 5 redox cofactors (NADPH, FAD, FMN, heme and BH4)
- NOS transfers e- from NADPH to FAD and FMN
- in heme presence, NOS forms FUNCTIONAL DIMER (Activated)
- with sufficient arginine and BH4 present, NOS dimer couples heme and O2 reduction to the synthesis of NO
- Citrulline formed as a byproduct
how is NOS regulated?
SERINE1177: usually unphosphorylated, can be phosphorylated with certain factors (PKA / CAMK)
these factors are stimulated by secondary factors: oestrogens, VEGF, insulin, shear stress
!! PLUS: Ca2+ activates eNOS
structure and role of Endothelin 1 on VSM contraction
-short aa peptide produced by vascular epithelium.
-production is activated by angiotensin 2/ADH, and is decreased by NO/ANP
EFFECT: POTENT VASOCONSTRICTION (coupled with the Gq protein)
Describe the main metabolic features of endothelial cells (4)
- circulating factors, some having vasoactive properties
- enzyme expression:
-MAO inactivating serotonin and epinephrine
-extracellular SOD
-ECE (endothelin production)
-NEP (inactivates ANP which affects ET-1) - maintaining the ECM via production of collagen 4 and laminin
- modulation of VSM contraction (NO / endothelin)
what are the possible pathologies related to faulty endothelial metabolism
TRIGGER: high stress (hypertension, smoking, obesity, aging)
!! diabetes is also a big cause bcos it produces AGEs that cause oxidative stress, and that can cause edothelial dysfunction
CONSEQUENCE: systemic endothelial dysfunction which manifests all around the body: retinopathies, cognitive decline, cardiomyopathies, nephropathies
what is the role of bradykinin and where is it released from
POTENT VASODILATION (hence mediates inflammation and slightly lowers BP)
-released by mast cells under inflammatory conditions
