Lecture 10 - Introduction to fibrosis Flashcards
ECM: what is it, where is it found, what are its most abundant proteins, and what is its role?
The extracellular matrix (ECM) is a three-dimensional network of extracellular macromolecules
Found in multicellular organisms
Collagen - one of the most common proteins in our bodies
The ECM defines the mechanical properties of our tissues (creates tissues along with cells)
Young’s modulus
The force/strain required to deform something by a certain amount
Used to show elasticity
ECM: how does it communicate with cells and how do cells communicate with it?
Mechanosignalling occurs, conveying mechanical pressure to communicate with cells
Then cells react to this and send out their own signals, instructing the ECM
‘Homeostatic’ systems are actively regulated to maintain a steady state within the ECM
How do cells know which cell types they should be/which genes to express?
Their environment tells them - they receive signals that tell them where they are and they express the correct genes based on this
Hydrogel: what is it, how is its stiffness controlled, and what is it composed of?
A synthetic polymer gel on which cells can be cultured
It can be made soft or stiff by varying the density of crosslinks
Often made of polyacrylamide (like a gel for SDS-PAGE)
Do cells spread more or less, are they harder or weaker, do they grow faster or slower, do they migrate towards or away from, do they promote more or less differentiation, and do they do apoptosis more or less on stiffer substrates?
Stiffer
Harder - more contractile
Faster
Towards stiffer substrates
More differentiation
Less
What cell behaviours are affected by mechanical signals?
- Cell morphology (e.g., spreading and shape)
- Contractility (how hard cells pull on their surroundings)
- Propagation rate and apoptosis
- Cell movement
- Differentiation (commitment to lineage)
Mechanobiology
An emerging field of science at the interface of biology and engineering [and physics]. It focuses on the way that physical forces and changes in cell or tissue mechanics contribute to development, physiology, and disease.
Mechanotransduction
The conversion of a mechanical input into a biochemical signal
How do cells receive mechanosignalling?
- Focal adhesions and cytoskeletal remodelling
- Ion channels
- Force-dependent matrix remodelling
- Deposition of a new matrix
- Continuous mechanical linkage to the nucleus
*Translocation of transcription factors/nuclear remodelling - Cell-cell contacts
What is the process behind cells ‘feeling’ mechanical stress - in regards to focal adhesions and cytoskeleton remodelling specifically?
1 - Force generation (actomyosin contraction)
2 - Force transmission (cytoskeleton)
3 - Mechanosensing (conversion into biochemical signals), this can be done by doing a tug-of-war type of thing
What are the key proteins in force generation and transmission?
- Integrins – membrane proteins that form focal adhesion complexes that tether the cytoskeleton to the matrix
- Actin – polymeric filaments; major component of the cytoskeleton; growth of filaments drives cell spreading.
- Myosins – ‘molecular motors’ pull against actin filaments, causing contractility.
- Talin – a protein that deforms when pulled on, activating a signalling cascade (conversion into biochemical signal).
How do cellular proteins activate downstream signalling proteins in response to mechanical stress?
Focal adhesion complex: Actin is polymerized at the edge of the cell and pulled by myosin-II (“non-muscle myosin 2A”)
This stretches Talin, causing unfolding which causes it to become more activated and allows Vinculin to bind to its activated domains, activating downstream signalling pathways
What signalling proteins are activated in response to stiff ECM and what do they do?
MAPK (“Mitogen-activated protein kinase 1”)
RhoA (“Transforming protein RhoA”)
These cause the cell to make more myosin and actin, so the cell pulls harder - retrograde flow, causes cells to move in like a tank (the wheels)
Mechanosensitive ion channels: how do they react to mechanosignalling?
The ion channels are pulled open, allowing an influx/efflux of ions, changing the internal biochemistry of the cell and causing the cell to react
Ie TRPV1 (may-b ggle)
Nuclear transmission force: how is it involved with mechanosignalling and what is it mediated by?
Environment attaches to the cytoskeleton which transmits force to the nucleus
The nucleus reacts to the force applied and
changes chromatin formation, resulting in changes in gene expression
This is mediated by the linker of the nuclear skeleton hand cytoskeleton (LINC) complex - composed of Nesprins which bind to SUN proteins which span the nuclear envelope and interact with laminins
Translocation of transcription factors: how do they react to mechanosignalling?
YAP1 (transcription factor) can be moved in and out of the nucleus
When moved into the nucleus, in a stiff environment, it drives osteogenic differentiation - bone formation
Mechanical regulation of transcription factors allows control of specific genetic programs
Fibrosis: what is it, what does it result in, and what components cause fibrosis formation?
Dysregulation of ECM - Misregulation of feedback and loss of homeostasis causing cells to deposit too much matrix
Stiffer tissues cause mechanical properties to no longer be matched to function
Fibroblasts
Fibroblasts: what do they do, what are they primarily used for, and what factors cause fibroblast activation?
Fibroblasts are cells activated at sites of injury which are responsible for synthesising extracellular matrix, such as collagen, after making myofibroblasts which are cells that secrete more ECM and make cells more contractile
They move towards wound sites and are required for wound healing
- Mechanical stimulation
- Transforming growth factor β1 (TGFB1)
Name two examples of fibrosis
Atherosclerosis - blocking of the vessels
COPD - chronic obstructive pulmonary disease
Scarring: can it be healthy?
Yes, scarring occurs after fibroblast deposits more ECM to cover the wound and prevent infection
When scarring is healthy, the scar will be replaced with healthy cells over time
If too much scar tissue is produced, this can be unhealthy and loss of function may occur
IPF: what is its name, what is it, what are its symptoms, what are its risk factors, and what is the timeline of the disease?
Idiopathic pulmonary fibrosis: idiopathic - we don’t know what mechanisms cause the disease
Causes irreversible enlargement of the bronchioles and alveoli, causing a reduction in gas exchange
Common symptoms:
* Shortness of breath
* Chronic dry cough
* Finger clubbing
Occasional symptoms:
* Fatigue
* Weaknesses
* Weight loss
Smoking, environmental exposure, chronic viral infections, abnormal acid reflux, and family history of the disease
Diagnosis after 1-2 years of symptom onset
Death after 2-3 years of suffering occurs in 50% of sufferers
