The Extracellular Matrix in health and Disease Flashcards
1
Q
What are the four macromolecular components of the extracellular matrix?
A
- ) Structural proteins
- ) Glycosaminoglycans
- ) Proteoglycans
- ) Adhesive glycoproteins
2
Q
What are the two major structural proteins?
A
- ) Collagen (imparts strength)
2. ) Elastin (imparts resilience)
3
Q
Complex sugars that bind water and resist compression
A
Glycosaminoglycans (GAG)
4
Q
Proteins with covalently coupled GAG chain
A
Proteoglycans
5
Q
What are the major adhesive glycoproteins?
A
Fibronectin, laminin, and entactin
6
Q
These macromolecules along with water and ions are termed the
A
Ground substance
7
Q
The ground substance plus cells is termed the
A
Connective tissue
8
Q
The basal surfce of the epithelium of most tissues is underlain with
-Sheets of exctracellulr matrix (ECM) that separate cells
A
Basememnt membranes
9
Q
If the epithelium is specialized, the basement membrane is called
A
Parenchyma
10
Q
Especially abundant under epithelial cells but also surround all endothelial cells and many mesenchymal cells
A
Basement membranes
11
Q
There are three “layers” of basement membrane that can be defined at EM level that are enriched in specific ECM components. What are the three layers?
A
- ) Lamina rara
- ) Lamina densa
- ) Lamina reticularis
-in order of top to bottom
12
Q
Contains laminin, perlecan, nidogen, and type IV collagen
A
Lamina Densa
13
Q
Contains some fibronectin and specific laminin (type 5(, and type XVII collagen from the cell membrane
A
Lamina rara (lamina lucida)
14
Q
Contains types I, III, and IV collagen, several proteoglycans, and fibronectin
A
Lamina Reticularis
15
Q
Major component of adult ECM that is located outside the lamina reticularis of basement membrane that is secreted by fibroblasts and specialized mesenchymal cells
A
Stroma
16
Q
In adults, different tissues have quite different stromal
A
Matrix organization
17
Q
Has a dense extracellular compartment and is primarily made up of collagen
A
Tendon stroma
18
Q
MAde up of specific collagens (type II and IX) and the proteoglycan aggrecan
A
Cartilage stroma
19
Q
Has little matrix at all
A
Liver stroma
20
Q
Fibronectin, collagen types I, III, VII as well as elastic fibers are in the
A
Stroma (Bowman’s layer)
21
Q
The continuum between the cell surface and the extracellular matrix is mediated by
A
Syndecans and Integrins
22
Q
It is important that structures are interconnected to maintain
A
Tissue integrity
23
Q
An extracellular component in direct contact with the basal domain of epithelial cells
A
Basement membrane
24
Q
At the EM level, the basement membrane is defined by which two layers?
A
- ) Basal lamina
2. Reticular lamina
25
In some cells, specialized fibroblasts such as chondrocytes or osteoblasts secrete the
Stroma
26
Has few cells, lots of matrix, and dense irregular connective tissue
Stroma
27
A triple-helix protein that provides tensile strength
-25% of total protein
Collagen
28
Colagen is resistant to
Stretching
29
In fibril forming collagens, many triple helical structures will assemble into
Fibrils/fibers
30
There is a continuum between the cell surface and ECM mediated by
Integrins and Syndecans
31
Cell type-specific integral membrane proteins that serve as receptors for components such as fibronectin, laminin, and several collagen types and connect ECM with intracellular signaling pathways and the cytoskeleton
Integrins
32
Specific heparin-sulfate containing proteoglycans that span the cell membrane and interact with actin filaments
Syndecans
33
Triple-stranded helical molecules containing three monomer α-chains wrapped around each other that imparts strength to the molecule
Collagens
34
A unique aspect of the α-chain amino acid composition of collagen is that every third amino acid is
Glycine
35
Between the glycines in the form G-X-Y-G, we often see Proline, lysine, and hydroxylated forms of these amino acids, which contribute to
Helix stability
36
The extend of post translational modification to the collagen aminos can generate
Heterogeneity
37
Assembled extracellularly with many collagen molecules cross-linked and aligned for maximal stability and strength
Collagen fibers
38
Leads to the extensive striation pattern seen at the EM level
Collagen fiber formation
39
90% of collagens are
Fibril forming Collagen I
40
A single glycine mutation in the primary structure of a collagen helix can alter the entire
Structure
41
The number of collagen types has expanded and now totals 20, which can be classified into what 4 major categories?
1. ) Fibril forming
2. ) Fibril-associated
3. ) Non-fibrillar
4. ) Transmembrane
42
Most abundant in the tendons, bones, lungs, and skin (represents 90% of all collagen)
Type I (a fibril-forming) Collagen
43
Mutations in type I collagen leads to
Osteogenesis imperfecta or osteoporosis
44
Type II collagen is found in cartilage and makes up 50% of cartilage dry weight. Mutations in type II lead to
Chondrodysplasia
45
Widely distributed in the skin and aorta-"reticular" collgen
-Stained with silved
Type III collgen
46
Mutations in type III collagen cause
Type III Ehler's-Danlos-Type 3
47
Type III Ehler's-Danlos-Type 3 is characterized by
Hyperextended skin and susceptibility to anneurism
48
Types I, II, and III collagen are all
Fibril-forming
49
Type IX collagen, found in the cartilage where it decorates the outside of type II collagen fibers is an example of a
Fibril-associate collagen w/ interrupted triple helix (FACIT)
50
What are the two non-fibrillar (network forming) collagens
Type IV and Type VII
51
Located in the basal lamina of basement membranes
Type IV collagen
52
Anchors fibrils at epithelia connective tissue junctions
Type VII collagens
53
Transmembran collagen that connects basement membrane to epithelium via anchoring filaments
Type XVII collagen
54
Epidermolysis bullousa is a disease associated with
Type VII collagen
55
In collagen synthesis, the α chains are synthesized as
Pro-α-chains on RER-attached polysomes
56
In collagen biosynthesis, the signal peptide is removed. Then proline and lysine are
Hydroxylated
57
Mutations in the collagen hydroxylases alter
Collagen assembly
58
Required for helix stability at physiological temperature
Hydroxylation of Proline
59
Required for intermolecular cross-links to form
Hydroxylation of lysine
60
Required as a co-factor for the collagen hydroxylases
-deficiency causes scurvy
Vitamin C
61
If there is a vitamin C deficiency, hydroxylation does not occur and collagen α chains are
Degraded
62
Once hydroxylation has occure, the hydroxylysines are
Glycosylated
63
Next, N- and C-terminal extension containing cys-rich globular domains (non-Gly-X-Y) guide
Helix formation
64
Helix formation begins in the ER and goes in the
C- to N-terminal direction
65
Formation of hydrogen bonds between Pro and NH2 of Gly to COOH- groups on separate chains leads to formation of
Helix
66
Required for stability of the helix at 37 degrees celcius
4'OH-Pro
67
In one form of osteogenesis imperfecta, helix formation is disrupted by a single Gly to Cys substitution that alters
Hydrogen binding
68
Have low Gly, Pro, OH-Pro and do not form helix. Thus their presence prevents fibril formation within cells
Extension peptides
69
During secretion, extension peptides of fibril-forming collagen molecules (types I, II, III) are cleaved by two procollagen peptidases specific for N- and C-ends leaving a bit of globular domain which participates in
Cross-linking
70
After the extension peptides are cleaved (occurs outside of the cell), the resulting collagen molecules are termed
Tropocollagen
71
Fibril assembly from triple helical molecules can not occur if we are missing
Procollagen peptidases
72
Tropocollagen first assembles into a microfibril and then into a
Fibril
73
Microfibrils aligned with 35 nm overlap between tropocollagen molecules, which are aligned
Head to tail
74
The maximum number of possible inter-chain electrostatic and hydrophobic bonds are formed
when chains are displaced by multiples of
-leads to striated pattern seen in EM
67 nm
75
Stain silver because they have more carbohydrate and thinner fibrils, are more branched, and have fewer bundles
Type III ("Reticular") collagen
76
Covalent cross-linking of fibrils is catalyzed by
-Cu dependent
Lysyl oxidase
77
Type IX collagen, a fibril associated collagen, is less rigid and forms a
Hinge
78
The extension peptides are generally retained in
Type IX collagen
79
Functionally imortant for joint integrity
-Mutations cause epiphyseal dysplasia (leads to arthritis)
Type IX collagen
80
Major collagen of the basal lamina, more specifically the lamina densa
-has multiple regions where the triple helix is interrupted
Type IV collagen
81
Has little extracellular processing of procollagen chains. So, unlike fibrillar collagens, retains globular non-collagen-like extensions at both ends
Type IV collagen
82
The extension peptides of type IV collagen are not
Cleaved
83
Both the C- and N-termini of type IV collagen react to form dimers and tetramers respectively. This results in a
"Chicken-wire" array
84
Contain dimers that form networks of anchoring fibrils that connect lamina densa with matrix components in reticularis or stroma
Type VII collagen
85
In type IV collagen, the C-termini of monomers interact with eachother via disulfide bonds to form dimers, while the N-termini attach to the
Lamina densa and anchoring plaque of stroma
86
Absence of type IV collagen leads to
-stroma peels from basement membrane
Blistering
87
Attaches basement membrane to epithelial surface via anchoring filaments
-mutation leads to blistering
Type XVII collagen
88
If either type VII or type XVII are mutated, the result is
Blistering
89
If VII is mutated, the blistering occurs
Below lamina densa
90
If type XVII is mutated, the blistering occurs
Above lamina densa
91
Mutants with shortened C-termini cannot associate, which results is
Blistering
92
Structural component of ECM that allow stretching and recoil of connective tissues
Elastin
93
One tissue with high elastic fiber (elastin) content is the
Aorta
94
Like collagen, elastin is assembled
Extracellularly
95
Elastin monomers are highly cross-linked via
Unique amino acids
96
What are the two major molecular components in elastic fibers?
Cross-linked elastin monomers and fibrillin
97
Participates in the cross-linking of elastin
Fibrilin
98
The importance of fibrillin has been seen in
-results from missense mutations in the structural gene encoding fibrillin 1
Marfan syndrom
99
Marfan syndrome results from missense mutations in the structural gene encoding fibrillin 1 and leads to elongated extremities and enhanced rupture of the
Aorta
100
At the histological level, elastin can be visualized by the orcein stain, while at EM level, mature elastin molecules are generally surrounded by
Fibrillin
101
Long, unbranched polysaccharide chains consisting of repeating disaccharides that are distinct in different classes but contain alternating amino sugar and uronic acid
Glycosaminoglycans
102
The most important glycosaminoglycans (GAGs) are
Hyaluronic acid, chondroitin sulfate, and heparan
| sulfate
103
All classes of GAGs are sulfated on an amino sugar except
Hyaluronic acid
104
Are inflexible with a negative charge that binds water and osmotically active cations
GAG chains
105
GAG chains have a highly extended
Random coil
106
As a result GAG occupy huge space; ECM with high GAG content has the consistency of a hydrated gel and can resist compression and participate in
"Sieving"
107
There are major clinical deficits if normal catabolism of GAG is not maintained. This is seen clearly in
Lysosomal storage diseases
108
Lethal conditions result from accumulation in lysosome
| of iduronic acid from dermatan sulfate and heparan sulfate in
Hurler's syndrome
109
Most GAG classes are covalently coupled to "core" protein and thus termed
-again, hyaluronic acid is an acception
Proteoglycans
110
Epithelium and Basement Membrane
peeled away and type VII anchoring
fibrils are disrupted in
Epidermolys Bullosa
111
The prototype proteoglycan is the proteoglycan from cartilage that is 90-95% carbohydrate and is now termed
Aggrecan
112
Membrane associated proteoglycans
Heparin Sulfate (HS) proteoglycans
113
Some heparan sulfate-containing-PGs are integral
membrane proteins with membrane spanning domains in addition to extracellular attachment sites for HS chains. These include members of the
Syndecan family
114
These heparan sulfate
PGs can bind a wide array of molecules including both other matrix components and growth
factors.
Syndecans
115
The binding of one specific growth factor, fibroblast growth factor (FGF) to syndecan is required to maximize
Mitogenic activity
116
There are also additional heparin sulfate proteoglycans that are completely extracellular, such as
Perlecan
117
Located in the lamina densa of basement membranes
Perlecan
118
The interaction of syndecan w/ the cytoskeleton illustrates one connection between ECM and
Internal signaling pathways
119
What are three matrix glycoproteins?
1. ) Fibronectin
2. ) Laminin
3. ) Nidogen (enactin)
120
A glycoprotein formed by two identical chains joined by disulfide linkages close to the C-termini
Fibronectin
121
Fibronectin can exist in a soluble dimeric form that circulates in serum and is involved in
Wound healing
122
Fibronectin can exist as oligamers attached to the
Cell surface
123
Fibronectin can exist as fibronectin fibrils that form an insoluble matrix in the
Stroma
124
Synthesized, secreted and bound to fibroblasts and other cell types
-Initially inversely correlated with tumor formation and altered growth
Insoluble form of fibronectin
125
Cells lacking fibronectin would lose adhesiveness, round up, and
divide
126
An important feature of fibronectin is its
-allows interconnection between series of cell-matrix components at the surface and in the matrix
Modular organization
127
Fibronectin has two binding sites for
Integrins, collagen, heparin, and fibrin
128
Produced by hepatocytes and secreted into the bloodstream
Plasma fibronectin
129
Produced by fibroblasts and forms part of the extracellular matrix
Cellular fibronectin
130
Can bind to both collagen and laminin
Integrins
131
Made up of three major subunits (α, β1, β2) arranged in pattern containing one long arm and three short arms; multiple additional forms have been identified
Laminins
132
Laminins generally promote
Adhesion
133
Located in high abundance in the lamina densa and mediates interactions between cell surface and basement membrane
-has a high affinity for type IV collagen and the HSPG perlecan
Laminin 1
134
Fibronectin and laminin bind to integrins through
RGD
135
Dumbbell shaped structure that binds to laminin 1 and type IV collagen and mediates their interaction with the lamina densa
Nidogen (enactin)
136
What are two major membrane-spanning molecules that serve as receptors for ECM components
1. ) Syndecans
| 2. ) Integrins
137
Integrins are dimers composed of
α subunits (18 different types isolated so far) and β
| subunits (8 different types)
138
Extracellular laminin, fibronectin, collagen and numerous other cell adhesion molecules all bind
Integrin
139
Important amino acid sequence for many integrin binding interactions
RGD
140
Found on epithelial and mesenchymal cell surfaces and also found on some circulating blood cells
Integrins
141
Once binding to the matrix or other cells has occurred, integrins regulate the activity of kinases such as the
-allows several intracellulr signaling pathways to assemble
Focal adhesion kinase (FAK)
142
Also bind cytoskeletal-associated proteins and thus serve to link
the ECM and cytoskeleton
Integrins
143
Links fibronectin to actin filaments probably through talin
Integrin α5/β1
144
Integrin α5/β1 is a co-receptor with other receptors that lead to phosphorylation of
Paxilin and FAK
145
Major receptor for laminin and may be altered in some forms of muscular dystrophy
Integrin α6/β1
146
Part of hemidesmosome and anchors intermediate (keratin), not actin filaments
Integrin α6/β4
147
Both integrin subunits are involved in binding substrate via
RGD sequence
148
Binds cytoskeleton (often actin) that can initiate formation of signaling complexes
β-subuint of integrin
149
Bind the actin cytoskeleton and organize signaling molecules
Integrins
150
After binding substrate, integrins
Cluster
151
A focal adhesion forms at the site of actin bound integrin via
Rho GTPase
152
One subfamily of integrin receptors (β3), is found on platelets and binds fibrinogen during clotting. Mutations in β3 result in
Glanzmann's disease
153
Another subfamily (β2) is found on white blood cells. Deficiency of β2 results in
-prevents binding of white cells to endothelium
Leukocyte adhesion deficiency
154
Cell membrane proteins that both interact with ECM components
Integrins and Syndecans
155
Changes β2 integrin conformation to allow its binding to endothelial surface receptors
Lymphocyte binding to endothelium via selectin
156
Initial interaction with endothelium is through a different low affinity receptor (selectin). Intracelluar signaling alters integrin conformation which then allows specific, high affinity binding to endothelium and ultimately leukocyte infiltration from blood into the tissue. This describes
Leukocyte adhesion to endothelium
157
Regulation of platelet activation is critical because if platelets aggregated randomly, this would lead to
Erroneous clotting
158
Ensures that binding to integrin occurs only in appropriate environment when clotting is needed
Regulation of integrin affinity
159
Regulation of integrin activation is especially important for
lymphocyte binding to endothelium (β2) and platelet binding to fibrinogen (β3)
160
What do the following integrins bind and where are they found?
1. ) Integrin α6/β4
2. ) Integrin α2/β3
1. ) Laminin, Hemidesmosomes
| 2. ) Fibrinogen, Platelets
161
Found on white blood cells and help mediate attachment to epithelial cells and subsequent movement of WBC into tissue
Integrin αL/β2
