18 - ECM Remodelling and Pathology Flashcards
_______ are the contractile units of the heart
myocytes are the contractile units of the heart
Defect in myocyte contractility will lead to:
Heart dysfunction
What are the three components of the extracellular matrix?
- Fibrillar collagen network
- Basement membrane
- Proteoglycans
Label the collagen network arrangements in the myocardium
________ network surrounds a group of muscle fibres
Epimysium
________ connect epimysial and endomysial networks
Perimysium
________ surrounds individual muscle fibers
Endomysium surrounds individual muscle fibers
Label the collagen fibres
(a) Collagen fibres
(b) collagen fibrils
© Collagen Molecules (triple helices)
(d) alpha chains
Collagen is a ________ comprised of a ______
Collagen is a fibrous protein comprised of a triple helix (tropocollagen)
How is collagen assembled? (4 steps)
- Three collagen alpha chains (Pre-procollagen) are first assembled to form procollagen (within the endoplasmic reticulum)
- Procollagen is secreted from the cell, the pro peptides are cleaved by procollagen peptidases, forming a collagen molecule (or tropocollagen)
- Multiple collagen molecules form collagen fibrils (covalent cross-linking by lysyl oxidase)
- Assembly of collagen fibrils form larger collagen fibres
Ehlers-Danlos syndrome arises from a deficiency in ________
Ehlers-Danlos syndrome arises from a deficiency in procollagen peptidase
- enzyme that cleaves the ‘pro’ peptides to form a collagen molecule (tropocollagen)
Label the image
What are the cardiovascular complications associated with Ehlers Danlos syndrome?
- Systolic murmur (valve defect)
- Large vessel abnormalities: dilation of aortic root and pulmonary artery
- Congenital cardiac defects:
- Bicuspid aortic valve
- Pulmonary valvular stenosis
- Ventricular septal defect
- Atrial septal defect
Recall: EDS = deficiency of procollagen peptidase
3 major components of the basement membrane:
- collagen IV
- Laminin
- Fibronectin
Functions of the basement membrane
- Provides an interface for myocyte adhesion and continuity with the extracellular matrix
- Provides an initial barrier that will influence the exchange of macromolecules between the extracellular space and the myocyte
The basement membrane is divided into:
- Basal lamina
- lamina lucida
- lamina densa
- Lamina reticularis
The basal lamina (of the basement membrane) is comprised of:
The basal lamina (of the basement membrane) is comprised of:
- Lamina lucida (lucid layer) - laminin, entactin, integrins
- Lamina densa (dense layer) - Col IV (anchoring fibres)
Lamina reticularis (of the basement membrane) is comprised of _______
Lamina reticularis (of the basement membrane) is comprised of collagen III and fibronection
Laminin is a _______ protein (_____ chain)
Laminin is a heterotrimeric protein (alpha, beta, gamma chain)
Laminin is responsible for:
Bridging the cardiomyocyte to the ECM via binding to the cell surface receptors, integrin, and collagen type IV (basement membrane)
Fibronectin is a component of the ________ of the basement membrane
- adhesive ________ comprised of _________
Fibronectin is a component of the lamina reticularis of the basement membrane
- adhesive glycoprotein comprised of 2 almost identical polypeptide chains held together by a disulfide bond
function of fibronectin?
Connects the cell (via integrins) to the ECM (collagen)
What are integrins?
Integrins are dimeric receptor proteins consisting of an alpha and beta subunit
Serve as cell surface receptors to connect the cells (eg cardiomyocytes) to the ECM (via binding of laminin, fibronectin etc)
What is the function of integrins?
Integrins serve as cell surface receptors to connect the cells (eg cardiomyocytes) to the ECM (via binding of laminin, fibronectin etc)
What determines the ligand specificity of integrin?
The specific alpha and beta subunits in the integrin determine the ligand specificity (eg Alpha5beta1 binds to fibronectin)
What sort of cell signalling are integrins important for?
Both outside in (focus of this course) and inside out signalling
Paxillin and Rac lead to:
Cytoskeleton organization
Akt is important for:
survival
ERK½ is important for:
Hypertrophy
What is the structure of proteoglycans?
- very large molecules
- Consist of a protein core and glycosaminoglycan (GAG - long unbranched polysaccharides)
- Form large complexes, both to other proteoglycans and to fibrous matrix proteins (collagens)
Four functions of proteoglycans?
- Because of negatively charged GAGs, attract small cations and water, forming a porous, hydrated gel
- Can affect the activity and stability of proteins and signaling molecules within the matrix
- Serve as the “filler” substance between cells in an organism
- Resistant to compression, return to original shape. Hence very important in areas of compression eg Joints
ECM accumulation =
fibrosis
how is the ECM remodelled after pressure overload?
Pressure overloaded hypertrophy (POH) → Aortic stenosis
- Thickening of collagen fibres
- Increased ECM content between the myocytes
How does volume overload hypertrophy (VOH) affect ECM remodelling?
- Loss of normal ECM architecture between the myocytes
- Poorly organized ECM
How is ecm remodeling affected by dilated cardiomyopathy (DCM)
- Dense but poorly organized ECM
Four functions of the ECM in the myocardium?
- Alignment of myocytes during systole and diastole
- Translating single myocyte contractility into whole heart pumping function
- A reservoir for a number of matrix-bound growth factors and cytokines
- Essential for maintaining alignment of myofibrils within the myocyte through a collagen-basement membrane-integrin-cytoskeletal-myofibril relation
Which two molecules are critical for regulating and maintaining the ECM integrity?
MMPs and TIMPs
MMPs = Matrix Metalloproteinases
TIMPs = Tissue inhibitor of metalloproteinases
Transcription of MMP:
Induced by bioactive molecules, cytokines, growth factors, oxidative stress and mechanical stimuli
What activates MMP?
Proteolytic activation, or by ROS (reactive oxygen species)
Inhibition of MMP:
Inhibited by physiological (tissue inhibitor of metalloproteinases, TIMPs) or pharmacological inhibitors
TIMPs bind to catalytic domain of MMPs to inhibit them with a stoich of 1:1
Where do TIMPs bind in order to inhibit MMPs?
N-terminus of TIMPs bind to the catalytic domain of MMPs to inhibit them
What is the general structure of TIMP molecule?
Disulfide bonds at 12 strictly conserved Cystein residues maintain the six loop structure
Label the table
Family of Tissue Inhibitor of Metalloproteinases (TIMPs)
label the arterial network
A. Facial artery
B. Subclavian a. and v.
C. Portal V
D. Aorta
E. Descending Aorta
F. Internal Iliac a.
G. Saphenous v
H. Popiteal a
I. Common carotid a
J. Brachial a
K. Superior mesenteric a
L. Ulnar a
M. Radial a
N. External iliac a
O. Femoral a
P. Profunda femoris a
The aorta plays important roles in:
- LV performance
- Myocardial perfusion
- Central hemodynamics
- Arterial function
Label the vascular wall structure
A. Internal basement membrane
B. Intima
C. Adventitia
D. Media
E. External basement membrane
The intima includes (2)
Endothelial cells and the internal basement membrane
The media contains (3)
- Smooth muscle cells
- Elastin
- Collagen
The adventitia contains (3)
- Fibroblasts
- Connective tissue containing elastic fibres
- The external basement membrane
Label the vessel
a. endothelium
b. internal elastic intima
c. fibrocollagenous tissue
d. Tunica intima
e. smooth muscle
f. tunica media
g. fibrocollagenous tissue with external elastic lamina
h. fibrocollagenous tissue
i. Tinica adventitia
Difference between arteries and veins
Arteries:
Thicker media
Collagen-rich ECM in adventitia (prevents vascular rupture at extremely high pressure)
High elastin content
What defines the mechanical properties of the vessel?
The Vascular ECM
Vascular ECM defines the mechanical properties of the vessel:
In a major artery (such as aorta) these properties include:
- A highly resilient wall
- Low energy loss during an inflation-deflation (expansion-recoil)
- Nonlinear elasticity
Three major structural proteins in vascular ECM
-
Elastin
- Elastic fibres (elastin + microfibrils)
- fibrillins
- Elastic fibres (elastin + microfibrils)
-
Collagens
- Type I and Type III - fibrillar - impart strength on vessel wall
- Type IV - non fibrillar - associated wtih fibrillin-1
- connect elastic fibres to the basement membrane
-
Proteoglycans
- Large proteoglycans (eg versican, aggrecan)
- Form an extensive, interconnected polymeric network in the extracellular space
- Small proteoglycans - eg decorin, biglycan, fibromodulin, osteoglycin and lumican
- secreted and bind to ECM molecules such as collagen, elastin, fibronectin
- Large proteoglycans (eg versican, aggrecan)
Major structural proteins in the vascular ECM:
-
Elastin
- Elastic fibres (elastin + microfibrils)
- fibrillins
- Elastic fibres (elastin + microfibrils)
-
Collagens
- Type I and Type III - _____ - impart ________
- Type IV - ______ - associated with ______
- connect ______ to the _______
-
Proteoglycans
- Large proteoglycans (eg ______, _______)
- Form an ________
- Small proteoglycans - eg ______, _____, ______, ______ and _____
- secreted and bind to _________
- Large proteoglycans (eg ______, _______)
-
Elastin
- Elastic fibres (elastin + microfibrils)
- fibrillins
- Elastic fibres (elastin + microfibrils)
-
Collagens
- Type I and Type III - fibrillar - impart strength on vessel wall
- Type IV - non fibrillar - associated wtih fibrillin-1
- connect elastic fibres to the basement membrane
-
Proteoglycans
- Large proteoglycans (eg versican, aggrecan)
- Form an extensive, interconnected polymeric network in the extracellular space
- Small proteoglycans - eg decorin, biglycan, fibromodulin, osteoglycin and lumican
- secreted and bind to ECM molecules such as collagen, elastin, fibronectin
- Large proteoglycans (eg versican, aggrecan)
What is an elastic fibre?
- An extracellular fibrous protein, predominant in the vascular ECM
- Gives the vessel their ‘elastic property’
- unlike collagen (dense fibres), elastic fibres are made up of relax strands
What give vessels their elastic property?
elastic fibres
Elastic fibres are made up of _____ strands
relax strands
Elastin is formed on a scaffold of _______
Elastin is formed on a scaffold of microfibrils
The largest component of the elastic fibre is _____
The largest component of the elastic fibre is elastin
Precursor protein of elastin is:
tropoelastin
Elastin is assembled along a scaffold of parallel _______
Elastin is assembled along a scaffold of parallel microfibrils
What are tropoelastins?
- soluble monomers which are secreted and deposited into the microfibril bundles, and cross-linked by lysyl oxidase to form insoluble elastin core
Microfibrils are composed of numerous ___________ such as:
Microfibrils are composed of numerous heterogeneous glycoproteins, such as fibrillin-1 , fibrillin-2 and microfibril-associated glycoproteins (MAGP1, MAGP2)
Fibrillin is a _______ secreted by ______ that incorporates into ______ to provide ________
Fibrillin is a glycoprotein secreted by fibroblasts that incorporates into microfibrils to provide a scaffold for deposition of elastin
_______ is essential for formation of elastic fiber
fibrillin is essential for formation of elastic fiber
Fibrillin-1 deficiency leads to _______
Fibrillin-1 deficiency leads to marfan syndrome
_______ deficiency leads to marfan syndrome
Fibrillin-1 deficiency leads to marfan syndrome
What are the life-threatening complications of Marfan Syndrome?
Marfan syndrome: deficiency in Fibrillin-1
- Vascular fragility
- aneurysms
- The most common cause of death = aortic rupture
