Cell Adhesion and the ECM Flashcards
What is the difference between the functional units of connective and epithelial tissue ?
In connective tissue, the cells make the functional components (ECM)
In epithelia, the cells are the functional components
What are the main components of the ECM ?
Fibrillar proteins + hydrated gel of glycosaminoglycans (i.e. proteoglycans)
What are examples of fibrillar proteins ? Which cell produces these ?
Collagen, elastin, fibronectin, laminin.
Fibroblasts
Which cell produces the GAGs ?
Fibroblaststs
What are GAGs ?
Charged polysaccharide sugar chains
What is the function of fibroblasts ?
Synthesizing collagen, elastin, proteoglycans
Microscopically, how does the synthesis of fibrillar proteins look?
Extensions of the fibroblasts are involved in secreting collagen filaments
What are the steps to collagen formation ?
Procollagen synthesized in RERE —-> assembled to form x3 helix —>released via secretory pathway through Golgi —> Procollagen then exoyctosed of the fibroblast and trimmed to form tropocollagen, and enzyme-catalysed cross-linked to make a fibril —> fibrils then organised into fibres
How is vitamin C relevant to the collagen synthesis ?
Vitamin C is very important for procollagen synthesis in the RER
What is a distinctive microscopic feature of fibroblasts ?
Presence of abundant RER (seen by purple stained ribosomes thanks to heamatoxylin)
How does transport of such large units occur from the RER ?
Through specialised large vesicles build in a parallel pathway.
What is the relationship between fibroblasts and tendons ?
Fibroblasts are oriented along the tendon direction (tendon is oriented collagen fibres in the same direction)
What are the structural features of Elastin ?
- Quite hydrophobic so naturally coils up
- Linked by cross-likns
Which cells produce Elastin ?
Fibroblasts, smooth muscle cells, chondroblasts
Given an example of a GAG.
Chondroitin Sulfate
What are the functions of proteoglycans ?
Provide
- Matrix support/cushioning/hydration (since GAGs highly charged)
- Glue-like function
- Links between proteins of ECM and ECM and cell surface
What are the main components of a proteoglycan aggregate ?
GAGs, core proteins, link proteins
How is the ECM linked to the cytoskeleton ?
Collagen/proteoglycans bind fibronectin which links to Integrin (transmembrane protein) which bind via Adaptor proteins to cytoskeleton (actin or other)
Which protein links the ECM components and the integrin ?
Fibronectin
What are the functions of myofibroblasts ?
- Fibroblast-like: secrete collagen (hence important in tissue healing and tissue fibrosis)
- Smooth-muscle-like (actin, myosin, desmin)
How do myofibroblasts differentiate from fibroblasts ?
They differentiate under mechanical tension.
They are then able to proliferate
What is the distinctive property of myofibroblasts ?
They are able to contract to reduce size of damaged area. They do that through focal adhesions and smooth muscle actin.
What do mast cells contain ? How do they appear in microscopy?
Granules containing hearing and histamine.
They appear filled with purple granules (purple due to matacromasia, due to negative charge of heparin)
What is the characteristic microscopic feature of plasma cells ?
Eccentric nucleus and large cytoplasm (bluish due to ribosomes).
What are the steps following phagocytosis ?
- Recycling at membrane
- Mature into lysosome
- Degradation
What are the functions of adipocytes ?
- Insulation (i.e. subcutaneous fat)
- Packing
- Energy store
How do adipocytes appear microscopically ?
Large lipid droplet with small eccentric nucleus and very little peripheral cytoplasm.
How may one preserve and stain lipids (instead of dissolving them in the processing) ?
Using frozen slice and Nile red.
What colors do Hematoxylin and eosin stain ?
Hematoxylin is dark plue/violet, stains acidic substances (DNA)
Eosin is pink/red, stains basic substances (proteins in the cytoplasm, ribosomes)
What is wrong with obob mice ?
Have mutant obob gene which results in them not making leptin (from adipocytes).
Consequently, excessive eating, obesity and Type II diabetes induced.
When injected with leptin, lost weight.
Do the conclusions of the obob mice experiment apply to humans ?
No, because:
- Leptin is increased in obese patient (correlates with obesity and BMI)
- Resistance to leptin (due to problem with leptin receptor) triggers more leptin production
- Injection of leptin produced modest reduction in weight so very high levels of leptin only partially effective
What is the function of cell adhesion ?
Link cells and their cytoskeleton to other cells and to the ECM.
What is the function of tight junctions (=sealing strands) ?
Controlling the passage of substances between cells Defining polarity (by fencing off membrane lipids and proteins) Linking to actin cytoskeleton
Describe the structure of tight junctions.
Zipper-like
Made of claudins and occludins
May be tight or leaky
How do claudins and occludins vary ?
- They have tissue-specific types.
- Especially claudins, 24 different types
- Depending on the function of the tissue, they allow for different permeability of epithelium through paracellular pathway.
What is the function of adherens junctions ?
Anchoring ACTIN filaments to the membrane
What are structural specifities of adherens junctions ?
Not as dense as desmosomes BUT still got adaptor proteins, cadherins (which can link to other cadherins) instead of integrins.
What are the main types of cadherins and which tissues do they belong in ?
VE-cadherins (endothelial cells)
N-cadherins (neurons, heart muscle)
E-cadherins (epithelia)
P-cadherins (placenta, epidermis)
What is the function of desmosomes ?
Linking between strong intermediate filaments in adjacent cells.
What are structural specifities of desmosomes ?
Thicker than adherens junctions.
Intermediate filaments anchored to cytoplasmic dense plaque with adaptor proteins. Adaptor proteins interact with cadherins (instead of integrin). Cadherin goes through membrane and links with cadherins on other side (hence intermediate filaments link)
What are the functions of gap junction ?
- Communication
- Hydrophilic channel + small molecules pass (ATP, ions)
- Coordination of function
What are the structural specificities of gap junctions ?
2 Connexons (=hemichannels= assembly of 6 connexin proteins with central pore) which can open and close
List specialised links between cell and the ECM.
Focal adhesions=half junctions
Hemidesmosomes
Integrins
What is the function of focal adhesions ?
Linking outside of cell (ECM) with actin filaments
Signalling platforms
What are the structural specificities of focal adhesions ?
Integrins linking actin (through an adaptor protein) to fibronectin or laminin in the ECM
Membrane protein is integrin.
What is the function of hemidesmosomes ?
Linking outside of cell (ECM) with intermediate filaments
What are the structural specificities of hemidesmosomes ?
Integrins linking keratin intermediate filament (through an adaptor protein) to laminin in the ECM.
Membrane protein is integrin.
What is the major difference between hemidesmosomes and focal adhesion (not structurally) ? What is a consequence of this ?
Hemidesmosomes are more stable (more permanent, less dynamic). As a result they link epithelial cells to BM.
What is Duchenne’s muscular dystrophy ?
Gene mutation leading to absence of dystrophin adaptor due to the premature termination of translation. Results in damage to muscle fibre due to muscle tearing.
What are the symptoms of Duchenne’s muscular dystrophy ?
Muscle tearing
Muscle weakness
Unable to walk by 12 years
What treatment has been suggested to for Duchenne’s muscular dystrophy ? How was it been approved ?
PTC 124 (ataluren), thought to override premature STOP signal mutation (through ataluren-facilitated translation of premature stop signal) to produce normal dystrophin.
An experiment:
-Human muscle biopsies from DMD patient grown in cultures. Increasing doses of ataluren increased retention of dystrophin.
Hence, NICE approved of the treatment.
What happens when carcinoma is in situ ?
- Tumour cells accumulate due to mutations disregulating cell cycle
- Cells have not breached BM yet
What happens in micro-invasion (cancer stage) ?
- Expression of cadherins reduced, cells converts from epithelial cells to mesenchymal cells
- Microinvasion begins aided by secretion of metalloproteases (MPPs) which can chop BM
- BM breached
- In invading tumour, leading cells express integrins which promote interaction with ECM and non-epithelial cells during movement
What happens during progression to metastasis ?
- Autocrine motility factors from tumour (increase their motility).
- Angiogenesis factors (e.g. VEGFs) promote vascularisation
- Entry into lymphatics and blood circulation
- Dissemination-metastasis
