Lecture 25- Mechanobiology I

Question 1

What is mechanobiology?

Answer 1

The study of how physical forces and changes in cell or tissue mechanics contribute to development, physiology and disease

Question 2

What is mechanotransduction?

Answer 2

The conversion of a physical force to a biochemical response

Question 3

What is mechanosensing?

Answer 3

When a protein or cellular structure responds to a physical cue to initiate mechanotransduction

Question 4

What are the four key concepts in mechanotransduction?

Answer 4

1. Mechanosensing
2. Signal transduction
3. Signal integration at nucleus
4. Cellular response

Question 5

Give 2 examples of mechanotransduction?

Answer 5

1. The autoregulation of blood pressure

2. Auditory mechanotransduction and hearing

Question 6

Explain the concept of blood pressure autoregulation as an example of mechanotransduction

Answer 6

1. Normally, blood flows through the arteries and pressure of the flow increase over time until a threshold is reached
2. This threshold correlated with calcium influx into smooth muscle cells causing them to contract which reduces artery diameter
3. Therefore, increasing pressure leads to an increase artery diameter until a threshold where calcium is released and constricts the artery, decreasing diameter

Question 7

Explain the concept of hearing as an example of mechanotransduction

Answer 7

Sound pressure waves cause stereocilia to bend and regulate ion channels.

This converts the pressure wave into and electrical signal/voltage enabling us to hear

Question 8

What mechanical activity is mimicked with the lung on a chip?

Answer 8

1. Fluid flow through blood vessels
2. Air flow
3. Breathing activity

Question 9

Why is lung on chip made using PDMS?

Answer 9

Material is translucent so events can be easily monitored

Question 10

Why does the lung on chip have inlets?

Answer 10

To allow the attachment of tubing so air and liquid can be pushed in/out of the system

Question 11

Why is the lung on a chip mounted onto a microscope?

Answer 11

To view mechanisms at a cellular level

Question 12

How does the lung on a chip mimic structure and function?

Answer 12

1. Upper epithelium layer mimics alveoli
2. Lower endothelium layer mimics blood vessels
3. Upper channel allows air flow and lower channel mimics blood flow
4. Channels mimic air-liquid interference and breathing activity
5. Vacuums stretch and relax the epithelium and endothelium layers at a certain frequency to mimic breathing

Question 13

What does the lung on a chip allow the study of?

Answer 13

1. Tight junctions are formed by the stretching of cell layers
2. The stretch of epithelial layers
3. Lung inflammation
4. How the uptake of nanoparticles activates the epithelial layer and requires mechanical stretching

Question 14

What regulates mechanotransduction?

Answer 14

1. Fluid flow
2. Stretching of epithelial tissues
3. ECM stiffness

Question 15

What is the equation for stiffness?

Answer 15

Stress/strain

Measured in kPa/Pa

Question 16

Define stress

Answer 16

The force applied on a certain area (force/area) and measured in N/m (squared)

Question 17

Define strain

Answer 17

How the material responses to stress

changed in length/original length

Question 18

Define shear

Answer 18

Stress that acts parallel to area

Question 19

Define compression and tension

Answer 19

Compression = pushing force (N)

Tension = pulling force (N)

Question 20

Give examples of tissues with low, intermediate and high stiffness

Answer 20

Low: brain, embryo, breast

Intermediate: liver, kidney, fat, dermis, lung

High: muscle, cartilage, bone

Question 21

Outline the study of tight junction formation using lung on a chip

Answer 21

1. Understanding how airflow effects transepithelial resistance
2. If epithelium is loosely arranged (low electrical resistance) ions can easily travel through
3. If epithelium is arranged tightly (high electrical resistance) ions cannot travel through as easily
4. Air-liquid interface causes epithelium to form nicely and transepithelial resistance forms quicker compared to liquid interface
5. This is because cell layers stretch and form proper tight junctions

Question 22

Outline the study of epithelium leak tightness using lung on a chip

Answer 22

1. Transport efficiency is impaired using the air-liquid interface compared to the liquid interface
2. Loose epithelium allows for more leakage compared to a well formed/tight epithelium
3. Air-liquid interface is more physiological in forming tight junctions and maintaining the integrity of the epithelium and endothelium

Question 23

Outline the study of epithelium layers using lung on a chip

Answer 23

Confirms that epithelium stretches

Question 24

Outline the study of lung inflammation using lung on a chip

Answer 24

1. Under control conditions, neutrophils do not attach to endothelium because the layer is not expressing the adhesion receptor
2. But after applying with pro-inflammatory cytokine and activating with TNF the endothelium expresses adhesion receptors
3. Adhesion receptors cause neutrophils to attach and migrate to epithelium

Question 25

Outline how the uptake of nanoparticles requires mechanical stretching

Answer 25

1. Nanoparticles activates the epithelial layer
2. This leads to the activation of ICAM-1 and of the endothelium
3. An increase in stretch/strain and an increase in nanoparticles increases ICAM-1 expression
4. Also, as strain increases ROS generation increases

Question 26

How does fluid flow affect the cytoskeleton structure and how can this be visualised?

Answer 26

Fluid flow (physical cue) causes the cytoskeleton epithelial cells to rearrange and become more structured

F-actin in the cytoskeleton can be visualised using phalloidin dye