Cell Migration

Question 1

What are 2 ways cell migration is relevant to tissue engineering?

Answer 1

1. host immune cell response
2. migration of stem cells for repopulating a space where tissue has been lost

Question 2

Describe some host responses that may occur at the site of implant

Answer 2

-injury/wound healing response
- acute inflammation
-formation of granulation tissue
- foreign body reaction
- fibrosis/encapsulation

Question 3

What are the 4 stages of normal wound healing?

Answer 3

1. haemostasis
2. inflammation
3. proliferation
4. remodelling

Question 4

Define haemostasis

Answer 4

blood clot forms & bleeding is halted

Question 5

Define inflammation

Answer 5

infiltration by macrophages to the wound site to fight off infection

Question 6

Define proliferation

Answer 6

fibroblasts proliferate & epithelial cells start to cover the wound

Question 7

Define Remodelling

Answer 7

cells of the dermis & epidermis reoragnise to reduce scarring

Question 8

Describe injury response

Answer 8

• injury occurs
• vasodilation response
• increase in vascualr permeability
• clots formed through coagulation cascade
• chemo-attractants in matrix stimulate recruitment of other cells

Question 9

Describe neutrophil migration/activation

Answer 9

• signalling to monocytes/macrophages
• key to phagocytosis & cell recruitment
• release of granules
• generation of oxidative bursts
• present at injury site for up to 3 days post
• formation of neutrophil exxtracellular traps

Question 10

What events are involved in foreign body response?

Answer 10

• macrophage infiltration
• giant cell formation (macrophages join together to form multi-nucleated foreign body)
• fibroblast activation
• collagen matrix production & deposition

Question 11

Detail giant cell formation

Answer 11

• macrophages fuse together to form giant multi-nucleated cells
• they aim to phagocytose foreign material
• their size & membrane ruffling make them better equipped to clear up larger particles than normal macrophages
• responsible for debris clearing which is necessary for tissue remodelling

Question 12

Describe Fibroblast activation

Answer 12

• matrix producing cells
• signalling provided by the macrophages attracts fibroblasts
• migrate & proliferate at site of biomaterial implant
• produce extracellular matrix around biomaterial

Question 13

What can occur when the newly formed ECM surrounds the biomaterial?

Answer 13

• integrates with biomaterial & facilitates tissue repair/regeneration
• develops pathological +ive feedback loops where more & more ECM is made = leads to encapsulation

Question 14

Describe Encapsulation

Answer 14

• occurs when biomaterial is isolated by formation of thick collagen rich tissue capsule
• problematic as it can render tissue engineered scaffold non-functional

Question 15

Where can encapsulation cause particular problems?

Answer 15

• breast & other soft tissue implants
• causes leakage, damage & severe health concerns for patients requiring removal of implant

Question 16

How do we stop encapsulation?

Answer 16

• increase biocompatibility of material used
• some surface coatings that mimic natural tissue can increase this

Question 17

What can be used in coatings?

Answer 17

• whole proteins that are components of extracellular matrix, such as fibronectin, osteocalcin
• peptides
• synthetic chemistries that mimic active portions of certian peptides

Question 18

Describe the use of Mesenchymal stem cell migration

Answer 18

• Bone marrow derived mesenchymal stem cells (BMSC) good source of cells for regenerative purposes
• can migrate to injured tissues & site of biomaterial implantation
• can differentiate into useful cell types
• secrete chemokines, cytokines & growth factors

Question 19

What are 2 theories on how cells move their front edge ?

Answer 19

1. cytoskeletal model
2. membrane flow model

Question 20

Describe the Cytoskeletal Model

Answer 20

• moves using its leading edge
• fast actin polymerisation occurs at the cell’s front edge
• actin filaments ‘push’ the leading edge forward
• cytoskeletal elements can interact plasma membrane

Question 21

Describe the Membrane Flow model

Answer 21

• some studies found that the front end of the migrating cell to have extra portions of membrane added from internal membrane pools
• extension of leading edge occurs by addition of membrane at front of the cell
• actin filaments might stabilise the added membrane - a structured extension/lamella is formed

Question 22

What biological factors regulate BMSC migration ?

Answer 22

• stormal derived factor 1 increases BMSC recruitment
• Osteopontin increases BMSC migration
• Vascular endothelial growth factor increases migration & proliferation

Question 23

What does BMSC stand for?

Answer 23

Bone Marrow derived Stem Cells

Question 24

What are some properties of scaffolds that promote stem cell migration?

Answer 24

• interconnected pores of suitable size
• correct stiffness
• correct surface chemsitry
• material has got to have the correct hydrophilic/hydrophobic properties

Question 25

Describe how stem cells are tracked in the body? (Hoehn et al)

Answer 25

- Hoehn et al 2002 - used ultrasmall superparamagnetic iron-oxide particles put into cultured cells prior to implantation using lipofection - these particles are then detectable using a novel in vivo magnetic resonance imaging & could be trakced to site of ischemic stroke damage in rats

Question 26

Describe how stem cells are tracked in the body? (GFP)

Answer 26

- commonly used cell tracker - cells grow green under a fluorescent microscope - can be instigated to glow when engineered cells express certian genes but is also used for tracking stem cells after implantation

Question 27

What is a con of GFP tracking?

Answer 27

- Ansari et al 2016 showed that GFP causes too much damage to the cell to give an accurate account of where the cell might go

Question 28

Define Metastasis

Answer 28

- spreading/movements of cells from the primary tumor to a distant organ

Question 29

How do tumor cells migrate?

Answer 29

- cells appear to migrate down extracellular matrix fibres, which enables them to enter blood vessels & then spread to remote organs - signals such as epidermal growth factors act as chemoattractant - allowing chemotactic migration to occur

Question 30

Describe migration from a primary tumor

Answer 30

- invadopodia degrade basement membrane - carcinoma cells breack the confines of tumor - cross the basement membrane & uses fibres of ECM to travel to blood vessels - similar mechanisms (invadopidia) to breach wall of the blood vessels

Question 31

Describe Invadapodia

Answer 31

- F-actin based with lipids - that from membrane protrusions - specialised adhesive structures that are able to touch ECM & focuse activity of proteolytic enzymes that breakthrough dense encapsulation to break micro-environment of tumour

Question 32

Describe Invadapodia Initiation

Answer 32

- assembly of actin-based precursors complexes & actin polymerisation that extentds plasma membrane - drives elongation of cellular finger like protrusions - critical step = activation of actin-related protein complex that initiates actin nucleation & necessary to start actin filament branching

Question 33

Describe Invadapodia Stabilisation

Answer 33

- newly formed actin filaments are crosslinked into tightly packed bundles - anchored to plasma membrane to form a stable 3D functional structure - this is done by; fimbrin, VASP, myosinX

Question 34

Describe Invadapodia Maturation

Answer 34

- proteins with proteolytic activity are recruited to invadopodia making them able to promote focal ECM degradation

Question 35

What can induce Invadopodia formation?

Answer 35

- exposure to acidic pH - matric rigidity - hypoxia - Reactive oxygen species