Extracellular Matrix Flashcards
What does ECM consist of?
Both fibrillar and non-fibrillar components - proteins and carbohydrates filling spaces between cells
What are the key functions of ECM?
- Provides physical support
- Determines the mechanical and physicochemical properties of the tissue
- Influences the growth, adhesion and differentiation status of cells
Which tissue is composed of ECM+component cells?
Connective tissue
Which collagens are components of connective tissue?
Types I, II, III (fibrillar)
Type IV (basement membrane)
Which glycoproteins are components of connective tissue?
Fibronectin
Fibrinogen
Laminins (basement membrane)
Which proteoglycans are components of connective tissue?
Aggrecan
Versican
Decorin
Perlecan (basement membrane)
What are the properties of connective tissue in the form of tendon and skin?
Tough but flexible
What are the properties of connective tissue in the form of bone?
Hard and dense
What are the properties of connective tissue in the form of cartilage?
Resilient and shock-absorbing
How do different types of connective tissue have different properties?
Different types and arrangements of oxygen
List the genetic disorders affecting ECM proteins
Osteogenesis imperfecta (OI)
Marfan’s syndrome
Alport’s syndrome
Epidermolysis bulllosa
Congenital muscular dystrophy (CMD)
What is a genetic disorder affecting ECM catabolism?
Hurler’s syndrome
Which ECM component is affected in OI?
Type I collagen
Which ECM component is affected in Marfan’s syndrome?
Fibrillin-1
Which ECM component is affected in Alport’s syndrome?
Type IV collagen (α5 chain)
Which ECM component is affected in Epidermolysis bullosa?
Laminin 5 (in all 3 chains)
Which ECM component is affected in CMD?
Laminin 2 (α2 chain)
Which genetic disorder disrupts the function of L-α-iduronidase?
Hurler’s syndrome
Identify the fibrotic disorders due to excessive ECM deposition?
Liver fibrosis - cirrhosis
Kidney fibrosis - diabetic nephropathy
Lung fibrosis - idiopathic pulmonary fibrosis (IPF)
What causes osteoarthritis?
excessive loss of ECM
What is a disorder caused by excessive loss of ECM
osteoarthritis
Which group of proteins are most abundant in mammals?
Collagens - 25% of total protein mass
How are collagen fibrils aligned in skin?
successive layers nearly at right angles to each other
How many collagen types are there in humans?
28 types
How many genes code for different types of collagens?
42 genes
How many α chains are in a collagen?
3 α chains forming a triple helix
What’s the composition of Type I collagen?
Type I
What’s the composition of Type II collagen?
Type II
What’s the composition of Type III collagen?
Type III
What is the amino acid pattern of an α chain?
x-y-glycine
(usually x=proline and y=hydroxyproline)
How long is each α chain in fibrillar collagens?
Approx 1000 amino acids
What are added to the newly synthesised collagen chains?
non-collagenous domains at N- and C-termini
When are the propeptides on N and C termini removed from the collagen?
after secretion in the case of fibrillar collagens (they remain part of the collagen in most other types)
What are some post-translational modifications of α helices?
- Hydroxylation of prolines and lysines
- Glycosylation of hydroxylysines
What happens to the α helices after modifications?
Self-assembly of three α chains
Which organelles carry out the synthesis, modification and secretion of α helices?
ER and Golgi
What type of links are made between collagens and inside collagen?
inter- and intra-molecular covalent cross-links
Which amino acids are involved in crosslinks (collagen)?
Lysine and hydroxylysine
Which molecules (cofactors) are required for hydroxylation of proline and lysine?
Iron (II) - Fe2+
Vitamin C
What type of bonding does hydroxylation aid?
(Interchain) H bonding
What is the result of Vitamin C deficiency (biochemical and tissue stability-wise)?
Under-hydroxylation of collagens
Dramatically reduced tissue stability
Scurvy - swollen bleeding gums and reopened wounds
Name the syndrome that is a spectrum of inherited connective tissue disorders
Ehlers-Danlos syndrome (EDS)
What are the common symptoms of EDS?
Stretchy skin and loose joints
What are the 3 main parts of collagen cycle affected by genetic mutations in EDS?
- Collagen production
- Collagen structure
- Collagen processing
Which types are fibril-associated collagens?
Types IX and XII
What are fibril-associated collagens?
Collagens regulating the organisation of collagen fibrils (but not forming fibrils themselves)
Wich type is a network-forming collagen and is found in all basement membranes?
Type IV
Which type of collagens doesn’t undergo cleavage and interact using N,C-terminal polypeptides?
Type IV
What is rotary shadowing?
A technique used in electron microscopy to study the three-dimensional structure of biological molecules
What is the network of collagens formed in the basement membrane (Type IV) called?
Supramolecular aggregate
What is the result of excessive production of fibrous connective tissue?
Fibrotic disorders
Why does the amino acid glycine feature so frequently in the primary sequence of a collagen chain?
Its small sidechain occupies the interior of the triple helix, allowing for tight packing
What is the diagnosis here, given that this is liver?
Fibrotic liver → cirrhosis
What causes diabetic nephropathy?
Accumulation of excessive ECM leading to a thickened glomerular basement membrane (GBM) in the glomerulus
What happens as a result of thickened GBM in diabetic nephropathy?
Restricted renal filtration potentially leading to renal failure
How to identify a fibrotic lung from normal lung?
Large areas of honeycombing
What is obesrved in stained slices of fibrotic lung?
Excessive blue staining due to increased collagen production
What happens on a moleculer level in Alport syndrome?
Mutations in collagen IV → abnormally split and laminated GBM → progressive loss of kidney function
What are the observations from pathological slides for Alport syndrome?
Basement membrane not intact/abnormally split
What is the basal lamina made up of (collagen and glycoprotein components)?
Collagen IV and Laminin
What are laminins made up of?
Heterotrimeric protein:
α, β, γ chains in cross shaped arrangement
How many laminin variant are there?
genome codes for 5α, 3β, 3γ chains
giving rise to 16 variants
What do the N-termini of laminin associate with?
Self-assemnly
Integrins
Nidogens
Collagen IV
How many N-termini are present in a laminin?
3 N-termini
What does the C terminus of laminin associate with?
Cell surface receptors (i.e. integrins)
Dystroglycan
Perlecan
What is regulated via the C-terminus associations of laminin?
Cell adhesion
What is the gene coding for laminin-α2 chain?
LAMA2
Which laminin variant forms a trimer with laminin-α2 chain?
laminin-211
α2, β1, γ1
What does laminin-211 associate with?
α7β1 integrin and α-dystroglycan
for adhesion and basal membrane assembly (in muscles)
What is deficient in CMD?
LAMA2
What is the result of LAMA2 deficiency?
no laminin-α2 → no laminin-211 → no integrin or dystroglycan association → basal lamina disrupted → progressive muscle weakness and degeneration
What is the role of elastic fibers?
Provide elasticity to tissues
Where are elastic fibres found?
Found in skin, blood vessels, and lungs
What are elastic fibres composed of?
An elastin core and surrounding microfibrils rich in the protein fibrillin
What is a small protein of around 2 kDa arranged in a random coil?
Elastin
What are the domains of elastin?
Alternating hydrophilic and hydrophobic domains
What happens during the formation of mature elastin?
Lysine residues in hydrophilic domain are crosslinked
Which parts of the body are manifested in Marfan’s syndrome?
Skeletal, ocular and cardiovascular
Which genetic disorder is related with abnormal thickening of the aorta?
Marfan’s syndrome
What is the major physiological finding in people with Marfan’s syndrome?
Abnormal thickening of the aorta
What causes the abnormal thickening of the aorta in Marfan’s syndrome?
Fibrillin-1 mutations → Fragmentation and disarray of elastic fibres → thickening of the aorta
What is the anticipated fatal risk of Marfan’s syndrome?
Individuals can be predisposed to aortic ruptures
Which ECM protein is a 500kD dimer which is disulphide linked?
Fibronectin
What interactions does fibronectin have?
Cell surface receptors:
- integrins
- heparins
Collagen binding
What are the roles of fibronectin?
Regulate cell adhesion
Migration in embryogenesis
Tissue repair
Promoting coagulation
What is the association between actin and fibronectin?
Fibronectins link
ECM and actin cytoskeleton (through integrins)
What are proteoglycans made up of?
Glycosamineglycans (GAG) attached to a core protein
What are GAG chains made up of?
Repeating disaccharides
(one of two sugars includes amine groups)
What is observed in microscopic slide of aortic tissue in Marfan’s syndrome?
larger diameter - thickening
disaarray of elastic fibers
What are the two forms of fibronectins?
Insoluble in ECM
Soluble plasma proteins
How are the charge of GAG chains modified?
Through sulfation or carboxylation to increase the (negativity of) charge
Why is the negative charge of GAG chains important?
It attracts cations such as Na+ which draws a significant aamount of water into the ECM
What are the 4 main varieties of GAG chains?
- Hyaluronan
- Chondroitin/Dermatan sulfate
- Heparan sulfate
- Keratan sulfate
Which GAG chain is found in decorin?
Dermatan sulfate (DS)
Which GAG chain is found in snydecan?
Hepaaran sulfate (HS)
Which GAG chains are found in aggrecan?
Keratan sulfate (KS) and Chondroitin sulfate (CS)
Which GAG chain is different than others in terms of its components as a proteoglycan?
Hyaluronan - it is not attached to a core protein and it is unsulfated
Where is hyaluronan found in the body?
Highly viscous tissues - vitreous humour of the eye and synovial fluid of joints
What is the role of hyaluronan?
Protecting the cartilaginous surface from damage
Which proteoglycan is a major constituent of cartilage?
Aggrecan
Where is aggrecan located and what does it do there?
Located in the cartilage matrix being perfectly suited to resist compressive forces
What are the 2 proteoglycans protecting cartilage from damage?
Aggrecan and Hyaluronan
Which property of aggrecan allows it to resist compressions?
Highly sulfated GAG chains increasing the negative charge → Osmatically active cations are attracted → Drawing water to the site → Water is given up under compressive load to increase tensile strength
Which disorder is the leading leading cause of lower extremity disability in older adults?
Osteoarthritis (OA)
What is lost in OA?
ECM is lost via degradation - cartilage damage
What happens to the proteoglycans in OA?
Aggrecan cleavage by aggrecanases and metalloproteinases
Which property of cartilage is lost?
Cushioning properties of cartilage over the end of bones are lost
What are integrins?
Cell surface receptors that bind to ECM molecules
