Lecture 13 - Stem Cells & Tissue Engineering Flashcards
List the principle properties of stem cells
- Undifferentiated
- Capable of self-renewal
- Capable of differentiating into multiple cell types
- High proliferative potentiate
- Present in low numbers
- Quiescent in niche
In general, what determines stem cell behaviour?
Microenvironment (niche)
What are the roles of the ECM?
- Structural support
- Cell-cell communication
- Sequestration of GFs
- Sequestration of signalling molecules
Describe the generalised structure of the ECM
Gel-forming molecules
• Hyaluronan
• Aggrecans
• Proteoglycans
Fibrous proteins
• Collagen
• Elastin
Adhesive proteins
• Laminin
• Fibronectin
What is interesting about the behaviour of equal cells in different ECMs?
Apparently equal cells behave differently depending on the microenvironment (i.e. ECM)
What do we do when tissues or organs fail?
What are the issues with these approaches?
What is a possible future approach?
Transplantation
• Requires human donors
• Organ rejection
Prostheses
• Provides structural support, but often limited function
Making tissue from scratch?
Define tissue engineering
How does this differ from regenerative medicine?
Tissue engineering:
Process of growing new tissues and organs for the maintenance / repair / improvement / replacement of damage, diseased or poorly functioning tissues or organs
Regenerative medicine:
Application of stem cells to regrow tissues and organs
Describe some of the pioneering tissue engineering studies
Epicel:
Dermal regeneration template
Apligraf:
Carticel:
Describe the spectrum of tissue complexity in terms of tissue engineering
Increasing engineering complexity:
- Flat tissue structures:
• e.g. cornea - Hollow structures
• e.g. Trachea - Hollow, viscus structure
• e.g. Bladder - Solid organs
• e.g. Kidney
Describe how vasculature is a barrier to tissue engineering
The most successful tissue engineering attempts have been with skin and cartilage
• Cartilage is avascular
• Skin is thin enough for diffusion of nutrients
Tissues rely on vasculature for nutrients, O2, and removal of cellular waste products
Any tissue thicker than 400 μm must be vascularised
Describe what can be done to circumvent the vascularisation challenge
Provision of biochemical signals with transplant to stimulate endogenous angiogenesis and neovascularisation
( • Angiogenesis: new vessels from pre-existing
• Neovascularisation: new vessel in absence of pre-existing)
Biochemical signals:
• VEGF
• PDGF
• FGF
What are the three central components of tissue engineering?
- Soluble factors (Biomolecules)
- Scaffold (Biomaterials)
- Cells
Describe the various origins and features of cells that can be used for tissue engineering
Source:
• Autologous (from own body)
• Allogeneic (from another individual of same species)
Differentiated
or
Undifferentiated (stem cell)
How are cells selected for tissue engineering?
There is an algorithm:
Need immediately: Yes/No
Yes:
Large organs:
• Allogeneic adult SCs, ESCs
• Banked iPSCs
Small organ:
• Autologous adult SCs, allogeneic SCs
No:
Large organs:
• Autologous adult cells and iPSCs
Small organ:
• Autologous adult primary cells or SCs, iPSCs
Describe the signal molecules that are used in tissue engineering
Needed to influence tissue engineered constructs and guide differentiation
- BMPs
- FGF-2
- VEGF
- TGFB1
These factors can be incorporated into the ECM during scaffold fabrication
Describe Biomaterials used in tissue engineering
Outline the main features required of biomaterials
What functions do they carry out?
Three dimensional biomaterials
Designed to:
• Direct organisation, growth, and differentiation of cells
• Maintain space and provide structural support
• Provide biological and mechanical cues
• Support transplanted or endogenous cells to attach, survive, proliferate, and differentiate
Features:
- Must be ‘biocompatible’
- Biodegradable
• Gradual degradation / remodelling - Mimic native ECM
- Promote native ECM production
What are the various types of scaffold that can be used?
Natural:
• Polypeptides and polysaccharides
Synthetic:
• Can modify degradation rate
• Can be reproducible manufactured with mechanical properties
List some factors of biomaterials that confer different properties on engineered tissues
- Porosity
- Cell adhesion and biorecognition
- Water content
- Mechanical properties
- Resorption and degradation
- Haemostatic
Describe decellularisation of tissues
How does it occur?
What does it leave behind?
This process sees the removal of all cells from an organ
How? :
• Mechanical, enzymatic and/or chemical treatment
Leaves behind acellular, naturally occurring ECM
• Collagen rich
• Mechanical properties of tissues are retained
What are the benefits of use of decellularised tissue?
ECM is highly conserved across species and will therefore be tolerated across individuals
What are the potential approaches for the use of decellularised organs?
- Xenogeneic scaffolds
- Allogeneic scaffolds
• Only perfect organs used for transplant
• Remained could be used for scaffolds
Describe the use of Bioprinting in tissue engineering
*
How does tissue engineering relate to metabolic syndrome?
Much end-organ damage experienced in MS: • Diabetic neuropathy • Diabetic nephropathy • Diabetic retinopathy • Peripheral vascular disease • IHD • Stroke • Arthritis
These organs / tissues could potentially be engineered for transplantation
Give an operational
Maintain tissues and organ integrity by sustaining life long production of mature, functional cells in the steady state and in response to occasional stress
Compare proliferative potential and lineage restriction along the classical stem cell hierarchy
Undifferentiated stem cells at the top of the hierarchy have great proliferative potential and aren’t lineage restricted
As cells become increasingly differentiation, there is a reduction in proliferative potential and the cells become lineage restricted
List some ways that the microenvironment tells stem cells how to behave
Cues:
• Soluble factors
• Cell-cell interactions
• ECM
