Cell Migration Flashcards
What are 2 ways cell migration is relevant to tissue engineering?
- host immune cell response
- migration of stem cells for repopulating a space where tissue has been lost
Describe some host responses that may occur at the site of implant
-injury/wound healing response
- acute inflammation
-formation of granulation tissue
- foreign body reaction
- fibrosis/encapsulation
What are the 4 stages of normal wound healing?
- haemostasis
- inflammation
- proliferation
- remodelling
Define haemostasis
blood clot forms & bleeding is halted
Define inflammation
infiltration by macrophages to the wound site to fight off infection
Define proliferation
fibroblasts proliferate & epithelial cells start to cover the wound
Define Remodelling
cells of the dermis & epidermis reoragnise to reduce scarring
Describe injury response
- injury occurs
- vasodilation response
- increase in vascualr permeability
- clots formed through coagulation cascade
- chemo-attractants in matrix stimulate recruitment of other cells
Describe neutrophil migration/activation
- 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
What events are involved in foreign body response?
- macrophage infiltration
- giant cell formation (macrophages join together to form multi-nucleated foreign body)
- fibroblast activation
- collagen matrix production & deposition
Detail giant cell formation
- 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
Describe Fibroblast activation
- matrix producing cells
- signalling provided by the macrophages attracts fibroblasts
- migrate & proliferate at site of biomaterial implant
- produce extracellular matrix around biomaterial
What can occur when the newly formed ECM surrounds the biomaterial?
- integrates with biomaterial & facilitates tissue repair/regeneration
- develops pathological +ive feedback loops where more & more ECM is made = leads to encapsulation
Describe Encapsulation
- occurs when biomaterial is isolated by formation of thick collagen rich tissue capsule
- problematic as it can render tissue engineered scaffold non-functional
Where can encapsulation cause particular problems?
- breast & other soft tissue implants
- causes leakage, damage & severe health concerns for patients requiring removal of implant
How do we stop encapsulation?
- increase biocompatibility of material used
- some surface coatings that mimic natural tissue can increase this
What can be used in coatings?
- whole proteins that are components of extracellular matrix, such as fibronectin, osteocalcin
- peptides
- synthetic chemistries that mimic active portions of certian peptides
Describe the use of Mesenchymal stem cell migration
- 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
What are 2 theories on how cells move their front edge ?
- cytoskeletal model
- membrane flow model
Describe the Cytoskeletal Model
- 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
Describe the Membrane Flow model
- 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
What biological factors regulate BMSC migration ?
- stormal derived factor 1 increases BMSC recruitment
- Osteopontin increases BMSC migration
- Vascular endothelial growth factor increases migration & proliferation
What does BMSC stand for?
Bone Marrow derived Stem Cells
What are some properties of scaffolds that promote stem cell migration?
- interconnected pores of suitable size
- correct stiffness
- correct surface chemsitry
- material has got to have the correct hydrophilic/hydrophobic properties
Describe how stem cells are tracked in the body? (Hoehn et al)
- 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
Describe how stem cells are tracked in the body? (GFP)
- 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
What is a con of GFP tracking?
- 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
Define Metastasis
- spreading/movements of cells from the primary tumor to a distant organ
How do tumor cells migrate?
- 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
Describe migration from a primary tumor
- 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
Describe Invadapodia
- 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
Describe Invadapodia Initiation
- 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
Describe Invadapodia Stabilisation
- 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
Describe Invadapodia Maturation
- proteins with proteolytic activity are recruited to invadopodia making them able to promote focal ECM degradation
What can induce Invadopodia formation?
- exposure to acidic pH
- matric rigidity
- hypoxia
- Reactive oxygen species
