Extracellular matrix Flashcards
1
Q
Who invented the first microscope?
A
Robert Hook
2
Q
What are the four major types of animal tissues?
A
Epithelial
Muscular
Nervous
Connective
3
Q
What are epithelial tissues?
A
Lining of gut or epidermal layer of skin.
4
Q
What is on the apical side of epithelial tissues?
A
Free surface
5
Q
What is on the basal side of epithelial tissues?
A
Basal lamina.
Connective tissues.
6
Q
What are cell junctions?
A
Link individual cells.
7
Q
What are the cytoskeleton filaments?
A
Mechanical forces are transmitted from cell-cell.
8
Q
What is the basal lamina?
A
Cells attached to thin layer/mat of connective tissue comprising mostly of ECM.
9
Q
What is specific about the cells in epithelial tissues?
A
Asymmetrical/polarised
10
Q
What are the 4 types of cell junctions found in epithelial tissues?
A
Adheres junctions: Cadherin
Desmosomes
Tight junctions
Gap junctions
11
Q
What is cadherin?
A
Superfamily of Ca+ dependent molecules with many distinct classical and non-classical members.
It is homophilic.
12
Q
What is the structure of adherens junctions?
A
Transmembrane spanning molecules.
Has an extracellular and transmembrane region as well as a cytoplasmic region.
They span half the distance between the cell.
13
Q
What is the function of cadherin mediated cell junctions?
A
Provide structural strength.
Organisation as cadherin can only interact with itself.
14
Q
How does cadherin mediate cell junctions?
A
In the presence of Ca2+, the vinculin attaches to the alpha-catenin causing it to go from folded to extended, as it moves the actin filament allowing the myosin II to pull on it.
15
Q
What is RAC?
A
Small gTP-binding protein involved in regulating actin cytoskeleton, the activated form of RAC seems to induce membrane ruffling.
16
Q
What is RHO?
A
A member of ATP-dependent hexameric helicases that function by wrapping nucleic acids around a single cleft extending around the entire hexamer.
17
Q
What is the function of RAC on cadherin mediate cell junctions?
A
Regulates aherens junction assembly.
18
Q
What are desmosomes?
A
Similar to adherens junctions but contain specialized cadherins that connect with intermediate filaments, allow junctions to have strength.
Considered a molecular zip.
19
Q
What are tight junctions?
A
Epithelial tissues which act as a selective permeability barrier this adds functional ability to membranes.
20
Q
How are tight junctions investigated?
A
Using tracer molecules, however tracer molecules can’t get through.
21
Q
What are gap junctions?
A
Channels made from connexins and innexins.
Allows only very tiny molecules.
22
Q
What is the function of the tight junction?
A
Seals neighbouring cells together in an epithelial sheet to prevent leakage of extracellular molecules between them; helps polarize cells.
23
Q
What is the function of adherens junctions?
A
Joins an actin bundle in one cell to a similar bundle in a neighbouring cell.
24
Q
What is the function of desmosomes?
A
Joins the intermediate filaments in one cell to those in a neighbour.
25
What is the function of a gap junctions?
Forms channel that allow small, intracellular water-soluble molecules, including inorganic ions and metabolites, to pass from cell to cell.
26
What is the ECM?
Extracellular matrix.
27
What is the extracellular matrix?
ECM is the main stress-bearing component of connective tissue and forms an indirect means of cell-cell contact.
28
What are the functions of the ECM?
Support and strength
Cellular communication
Cell migration, polarity and shape.
29
What is the basal lamina?
Very thin layer of ECM produced by cells above and below.
30
What is the function of the basal lamina?
Essential for maintaining epithelial tissues.
31
What is the basal lamina composed of?
Laminin
Type IV
XVIII collagen
Nidogen
Perlecan fibronectin
32
What are the two different types of cells found in connective tissue?
Indigenous
Immigrant
33
What kinds of indigenous connective tissues cells are there?
Primitive mesenchymal cells
Specialized cells
34
What are primitive mesenchymal cells?
Undifferentiated cells that can lead to the generation of other connective tissue cell, fat cells (adipocytes), mast cells (release histamine) and fibroblasts.
35
What are fibroblasts?
Found in many connective tissues and
synthesize most of the molecules found in the ECM.
36
What kinds of specialized cells are there in the connective tissues?
Adipocytes
Mast cells
Chondrocytes
Osteoblasts
37
What kind of immigrant cells are present in connective tissues?
Immune cells.
38
What is the composition of connective tissue EMC?
1. GAGs
2. fibrous proteins
3. glycoproteins
39
What are GAGs?
Consist of repeating sulphated disaccharide units.
Most anionic molecules produced by animals.
Often linked to form proteoglycans.
40
What are fibrous protein?
Members of collagen family.
Most abundant proteins in mammals.
41
What is the structure of fibrous proteins?
Long, stiff triple stranded helical structure.
42
What is the function of fibrous proteins?
Provides tensile (pulling) strength of tissues.
43
What is the collagen family of proteins?
Synthesized by indigenous ECM cells.
40 different types
3 polypeptides form a coil different a chain combinations lead to different types of collagen (Type I- XVIII) found in differing connective tissues.
44
What is collagen?
3 polypeptides form a coil, which can then self-aggregate into fibrils and then fibres.
45
What is the organisation of collagen strands?
1. Single collagen polypeptide chain.
2. Triple-stranded collagen molecule
3. Collagen fibril
4. Collagen fibres
46
What is procollagen?
Soluble precursor of tropocollagen formed by fibroblasts and other cells in the process of collagen synthesis.
47
What is the function of procollagen?
Procollagen prevents aggregation inside cells
48
What is the process of procollagen becoming a collagen molecule?
Procollagen is secreted from secretory vesicle.
Procollagen proteinase cleaves terminal procollagen extension.
49
What types of glycoproteins are present in the ECM?
Elastins
Fibronectins
50
What are elastins?
Provide elasticity to connective tissue (similar in structure to collagen).
Dominant component of the ECM in arteries.
51
What is fibronectins?
Bind other matrix/cell membrane proteins organize matrix and provide cell-matrix link.
52
What are integrins?
Key receptors that bind ECM components.
Alpha and beta chain large N-terminal domain.
Short intracellular domain that binds adapters similar to those seen with cadherins.
53
What ligands do a5B1 bind?
Fibronectin
54
What ligand do a6B1 bind?
Laminin
55
What ligand do a7B1 bind?
Laminin
56
What ligand do aLB2 bind?
Ig superfamily counterreceptors
57
What ligand do aHbB3 bind?
Fibrinogen
58
What ligand do a6B4?
Laminin
59
What is the distribution of a5B1 receptors?
Ubiquitous
60
What is the distribution of a6B1 receptors?
Ubiquitous
61
What is the distribution of a7B1 receptors?
Muscle
62
What is the distribution of aLB2 receptors?
White blood cells
63
What is the distribution of aHbB3 receptors?
Platelets
64
What is the distribution of a6B4 receptors?
Hemidesmosomes in epithelia
65
What is talin?
Important adapter molecule.
66
Why do integrins need an “inactive” conformation?
* many cells in connective tissue are not stationary and migrate through ECM
* use integrins to “pull” themselves through the ECM
* cell-ECM contacts therefore need to be made and broken
67
What is the ECM?
The ECM is a network of fibrous proteins and hydrated proteoglycans which surround cells in tissues.
68
What is the function of the ECM?
* provides strength and support
* guides cell migration and polarity
* permits intercellular communication
69
What does the maintenance of the ECM depend on?
Maintenance of a healthy ECM depends on a balance between synthesis and breakdown of matrix molecules.
70
How is a healthy ECM maintained?
* cells within ECM secrete the components of the ECM
* the same cells also secrete enzymes which digest/breakdown these components
* to remove damaged matrix
*matrix synthesis and breakdown must counter-balance
71
What are proteinases?
Enzymes which break down many proteins, referred to as biological scissors.
72
What is the human degradome?
A collection of 570 genes in the human genome that encode proteinases, these degrade/cleave other proteins.
73
What is the degradome divided into?
Aspartic
Threonine
Cysteine
Serine
Metallo
74
How may aspartic proteinases are there?
21
75
How may threonine proteinases are there?
28
76
How may cysteine proteinases are there?
154
77
How may serine proteinases are there?
176
78
How may metallo proteinases are there?
191
79
What are the three minimal domains for the metalloproteinase family of enzymes?
MMP (matrix metalloproteinases)
ADAM (a disintegrin-like and metalloproteinase)
ADAMTS (a ADAM with thrombospondin motifs)
80
What is the metalloproteinase domain MMP?
Key ECM modifiers.
81
What types of matrix metalloproteinases (MMP)?
* collagenases
* gelatinases
* stromelysins
* matrilsins
* membrane-type
82
What MMPs are collagenases?
1, 8, 13, 18
83
What MMPs are gelatinases?
2 and 9
84
What MMPs are stromelysins?
3, 10 and 11
85
What MMPs are matrilsins?
7 and 26
86
What MMPs are membrane type?
14, 15, 16, 17, 23, 24, 25
87
What is the ADAM domain in the metalloproteinase family?
A Disintegrin-like And Metalloproteinase.
They are mostly membrane bound.
88
What is the ADAMTS domain in the metalloproteinase family?
a ADAM with ThromboSpondin motifs.
Secreted into ECM like MMPs.
Also involved in ECM breakdown.
89
What types of ADAMTS are there?
* pro-collagenases
* aggregenases
90
Which ADAMTS are pro-collagenases?
2, 3, and 14
91
Which ADAMTS are aggregenases?
1, 4, 5, 8, 9, 15
92
What is catabolism?
Breakdown.
93
What is the metalloproteinase family?
Are key ECM modifiers.
Principally mediating breakdown (catabolism) of ECM components.
Release/activation of growth factors, hormones, cytokines anchored in ECM.
94
What is the metalloproteinase family characterized by?
*Zn2+ binding catalytic domain
*Secretion into ECM as inactive pro-enzymes
*Activated by removal of pro “bait” region by other proteinases.
95
What is the metalloproteinase family inhibited by?
*a2 macroglobulin (in blood, ubiquitous proteinase inhibitor)
*Tissue inhibitors of metalloproteinases (TIMPs)
96
What are tissue inhibitors of metalloproteinases (TIMPs)?
A family of small secreted proteins which “slot” into active sites of metallo’s catalytic domains.
97
Where do neo-epitopes come from?
Cleavage of ECM components generates specific catabolic fragments and the formation of neo-epitopes.
98
What are neo-epitopes
Neoepitopes are a class of major histocompatibility complex (MHC) bounded peptides.
99
What is the function of neo-epitopes?
Neoepitopes are recognized by the immune system as targets for T cells and can elicit immune response to cancer.
100
What leads to increased ECM synthesis?
Loading stress also produces fragments of ECM
componentsthese fragments stimulate increased ECM synthesis.
101
What are the main things the Control of ECM synthesis/breakdown (re-modelling) is crucial for?
1. embryonic development
2. wound healing
3. prevention of tumour development
102
Which inflammatory cytokines increase synthesis of the ECM?
TGF beta
IGF-1
bFGF
103
Which inflammatory cytokines decrease synthesis of the ECM?
IL-1
TNF-alpha
104
Which inflammatory cytokines increase catabolism of the ECM?
IL-1
TNF-alpha
105
Which inflammatory cytokines decrease catabolism of the ECM?
TGF beta
IGF-1
IL-6
106
What are connective tissue?
Have reduced cellular content, (cell-cell contact is rare) with increased extracellular matrix (ECM) content, compared to epithelial, muscle and nervous tissue.
107
What are the main types of cartilage?
* hyaline
* fibro
* elastic
108
Where is the hyaline type of cartilage?
Ribs
Nose
Larynx
Trachea
Articular joints
109
Where is the fibro type of cartilage?
Joint capsules
Ligaments
110
Where is the elastic type of cartilage?
Ear
Epiglottis
Larynx
111
What is hyaline type of cartilage defined by?
Defined by the presence of the indigenous chondrocyte.
112
What is a chondrocyte?
A cell which has secreted the matrix of cartilage and become embedded in it.
113
What is Ehlers Danlos syndrome?
Defective deposition of collagen - hyperextensible joints.
114
What is the structure of the aggrecan complex?
115
Why is it important that the aggrecan complex is highly charged?
They attract water and form a hydrated gel.
116
What is the function of the hydrated gel that the highly charged aggrecan complex?
* provides resistance to compression
* results in swelling pressure (turgor)
* provides strength and support
117
Why is the aggrecan complex highly charged?
Due to GAG content.
118
What are ECM chondrocytes?
*They are large and mature.
* in groups of 2-8 cells
* rich in RER and Golgi
* secrete high amounts of type II collagen and aggrecan
119
What does chondrocyte proliferation and ECM synthesis require?
*TGF-b, fibroblast growth factor (FGF),
*Insulin-like growth factor (IGF-1)
*Parathyroid hormone-related protein
(PTHrP)
120
What is sox-9?
SOX-9 recognizes the sequence CCTTGAG along with other members of the HMG-box class DNA-binding proteins.
121
What is the function of sox-9?
Sox9 turns out to be a master regulator of cartilage development. It has essential roles in the specification and differentiation of mesenchymal cells toward the chondrogenic lineage in all developing skeletal elements.
122
What is ossification?
Bone formation
123
What is Endochondrial Ossification?
“Cartilage model” is replaced by bone during fetal development. e.g. long bones
124
What are morphogens?
Secreted signalling molecules which determine the location (spatial patterning) via inductive signalling.
125
What is inductive signalling?
Requires morphogens passing between cells and through the developing ECM.
Involves members of the hedgehog family.
126
What are the stages of bone formation?
Stem cells receive from sox-9 turns on PTHrp which allows cartilage to develop into bone.
127
What members of the hedgehog family are involved in inductive signalling?
Sonic (SHH)
Desert (DHH)
Indian (IHH)
128
What does the hedgehog family do during bone formation?
Controls the production of the key skeletal morphogen PTHrP.
129
What is the role of PTHrP?
IHH and PTHrP interact via positive feedback loops that maintain spatial chondrocyte proliferation.
130
What is hedgehog signalling?
In Drosophila, secreted Hedgehog, via interaction with Patched and Smoothened, keeps proteolytic processing of Cubitus interruptus (Ci) turned off, so it can move to nucleus and activate gene expression.
131
How does the formation of long bones begin?
Formation of long bones initiates at primary ossification centres.
Cartilage is catabolized and osteoid ECM becomes calcified, trapping osteoblasts.
132
What is the process of IHH/PTHrP feedback in long bone formation?
1. PTHrP maintains chondrocyte proliferation and cartilage production this prevents their terminal differentiation.
2. As the proliferating cells move further way from the central cells these start to receive less PTHrP.
3. This reduces IHH
4. They make less PTHrP
5. Become more osteoblast-like and contribute to the ossification process.
133
What are the key feature of articular cartilage?
*Connective tissue ECM that directs bone development during embryogenesis
*Essential for permitting mechanical load and
movement of articulated bones
*Contains a single cell type – chondrocyte
134
What is hyaline?
A pre-cursor for bone.
135
What are the features of fibro cartilage?
Least flexible
Fewest cells
Highest collagen
136
What are the features of elastic cartilage?
Most flexible due to increased elastin.
Most cells.
137
What is osteoarthritis?
Usually slow but progressive loss of ECM and the “chondrogenic phenotype” in articular cartilage due to mechanical or degradative damage without obvious cause (primary OA).
138
What are the symptoms of osteoarthritis?
*Results in (severe) limitation in joint movement
*Joint deformity
*Inflammation
*Severe pain that substantially reduces quality of life.
139
What are the key ECM breakdown events in OA?
1. Aggrecan
2. Collagen
140
What genetics are suspected to be responsible for OA?
GDF5
RUNX2
PTHLH
SMAD3
141
What is GDF5?
Growth factor member of TGF-b family important in ECM homeostasis.
142
What is RUNX2?
Master transcription factor responsible for driving endochondrial ossification including MMP-13 expression.
143
What is PTHLH?
Encodes PTHrP chondrocyte growth factor driven by IHH secretion.
144
What is SMAD3?
Intracellular signalling protein involved in TGF-b production.
145
What is the current cure for OA?
There is no cure.
146
What are the current therapies for OA?
1. surgery
2. non-steroidal anti-inflammatories
3. identify and target key proteinases
4. Genetic screening may allow susceptible patients to have physiotherapy prior to disease onset
147
What is Rheumatoid arthritis (RA, inflammatory)?
Progressive loss of ECM and chondrogenic phenotype in articular cartilage due to immune cell-mediated damage.
148
What are the symptoms of RA?
*Results in (severe) limitation in joint movement
*Joint deformity
*Inflammation
*Severe pain that substantially reduces quality of life
149
What is RF?
“Rheumatoid factor”(RF) discovered in blood of many RA patients.
RF defined as an “autoantibody’.
However it was later found there is no direct link.
150
What was the speculated action of RF in RA?
* Many RA patients also have auto-antibodies reactive with a number of nuclear structural antigens.
* Many of these ant-nuclear antigen antibodies have also been shown to react with epitopes that contain citrullinated amino acids.
151
What are citrullinated amino acids ?
Citrullination or deimination is the conversion of the amino acid arginine in a protein into the amino acid citrulline.
152
What is citrulline?
Citrulline is not one of the 20 standard amino acids encoded by DNA in the genetic code. Instead, it is the result of a post-translational modification
153
What are anti-citrullinated peptide antibodies; ACPA?
60% of RA patients have antibodies that are specific for eptiopes from self-antigens that contain citrullinated amino acids.
154
Do all RA victims have ACPAs?
Yes, however they are found in 2% of healthy people disproving a direct link.
155
What is RA characterized by?
Characterized by inflammation of the synovium due to the presence of specific B and CD4 TH cell mediated autoimmunity.
156
What is the process of autoimmunity in RA?
Unknown triggers inflammation in synovial membrane, attracting leukocytes into the tissue.
Autoreactive CD4-T cells activate macrophage, resulting in production of pro-inflammatory cytokines and sustained inflammation.
Cytokines induce production of MMP and RANK ligand by fibroblasts.
MMPs attack tissues.
Activation of bone-destroying osteoclast, resulting in joint destruction.
157
What is CIA?
Collagen induced arthritis
158
What is PGIA?
Proteoglycan induced arthritis
159
What is the cure for RA?
There is no cure.
160
What are the current therapies for RA?
1. non-steroidal anti-inflammatory drugs NSAID
2. late 1980s, identification of TNF-a as a key target for therapy.
3. Introduction of Infliximab (monoclonal antibody that binds TNF-a and blocks its action).
4.Monoclonal antibody Rituximab (specific for CD20) kills B cells
5. Better genetic/ACPA screening may allow susceptible patients to be identified earlier.
