Lecture 16 - Stem Cells - Therapies for Respiratory Diseases Flashcards
What is the gastrula?
The embryo after gastrulation has occurred; i.e. the three germ layers are present
The foetus is embedded in the endometrium
What is the germ layer derivation of the lung
Endoderm:
• Lung epithelium
Mesoderm:
• Lung mesenchyme
Ectoderm:
• Lung innervation
List some of the various cells in the lungs
The lung comprises over 50 cell types
Vasculature:
• Endothelium
Alveoli:
• Type I and II pneumocytes
Lung mesenchyme:
• Fibroblasts
• Myofibroblasts
• Smooth muscle cells
Airways:
• Ciliated cells
• Goblet cells
• Clara cells
Bronchioles: • Neuroendocrine cells • Clara cells • Ciliated cells • Basal cells
Haematopoietic cells:
• DCs
• Macrophages
• Lymphocytes
Describe the development of the lung
- Embryonic phase:
Outpouchings form from the foregut endoderm - Pseudoglandular:
Epithelial lung buds form, surrounded by loosely packed mesenchyme - Canalicular
Branching morphogenesis form the conducting and respiratory airways - Sacular
Alveolar ducts form - Alveolar
Alveolar sacs form
Where are the lung epithelial stem cells during development?
At the distal tips of the growing lung buds
What is Id2?
Describe how it has been used to investigate lung development
All lung epithelial cells are progeny of Id2(pos) stem cells
Outline the lung endodermal heirarchy
Endoderm: → Lung epithelium → Thyroid → Thymus etc.
Lung epithelium → lung embryonic stem cells
Lung embryonic stem cells:
→ Alveolar progenitor
→ Bronchiolar progenitor
Alveolar progenitor → Type II pneumocytes → Type I pneumocytes
Bronchiolar progenitor
→ Neuroendocrine cells
→ Basal cells
Basal cells → club cells
Club cells
→ Clara cells
→ Ciliated cells
What is the ‘potency’ of lung epithelial stem cells?
Multipotent
Can form all epithelial cells in the lung: • Type I and II pneumocytes • Ciliated cells • Clara cells • Basal cells • Neuroendocrine cells
What is the origin of the lung mesenchyme?
The lung mesenchymal cells (fibroblasts, smooth muscle cells) are derived from:
Splanchnic mesoderm
Where is smooth muscle present in the lungs?
In the airways
Where are the mesenchymal stem cells in the developing lungs
Distal tip of the developing lung buds
What is the importance of FGF-10?
Marker of mesenchymal stem cells present in the distal tip of the developing lung buds
What controls the proliferation and differentiation of the stem cells in the lung?
The mesenchyme releases signals that control the stem cell differentiation into the various cell types
Describe the development of innervation in the lungs
Neural crest cells (ectodermal origin) migrate down into the lungs
Describe the development of vasculature in the lungs
Endothelial progenitor cells derived from the mesoderm form the vasculature
Describe the co-development of the heart an lung
New evidence that the mesenchymal of the heart and lung develop from a shared progenitor:
Multipotent cardiopulmonary progenitor
What are the defining features of stem cells?
- Self-renewal
- Differentiation into many cell types
- Immortal
Describe how flow cytometry is used to investigate the lung
Single cell types can be isolated based on cell markers
This allows the isolation of rare stem cells (expressing certain markers)
Describe, in general, cell surface markers of stem cells
In general, stem cells express cell surface markers associated with the stem cell state, whilst having low expression of markers associated with differentiated cell lineages
Describe the importance of the lung epithelial stem cell niche
*
The factors present in the niche are specific and very important for the tissue structure
When the niche is disrupted, there are histological changes (possibly disease)
Epithelial stem cell fate and lineage is determined by this microenvironment
Describe the importance of lung mesenchymal cells for the lung epithelial cells
Lung mesenchymal cells interact directly with the epithelial cells:
• Direct their differentiation
e.g.
• Release of FGF-10
How is the lung epithelium maintained in the adult lung?
- Multi-lineage stem cells
These can differentiate into all the epithelial cell types - Lineage-restricted stem cells
Can differentiate into only alveoli or airway epithelial cells
What is the significance of EpCAM and CD24?
Lung epithelial cell progenitors are:
CD45(neg) CD31 (neg) EpCAM(pos) CD24 (lo)
This can be determined by clonogenic assay
Which techniques are useful in studying lung stem cells
Clonogenic assays
Lineage-tracing techniques
What is the stem cell implication of the tissue origin heterogeneity of the lung?
The lung is made up of cells from many different lineages:
• Endoderm, mesoderm, ectoderm
These different cell types must be maintained by different stem cells
What is the importance of lung disease?
What is the success with current therapies?
By 2020 > 1 in 6 deaths will be attributed to lung disease
COPD ranked 3rd in Global Burden of Disease
300 million people worldwide with asthma
Current therapies: • Largely palliate • Treat the symptoms • Largely unable to reverse the disease • Most diseases are dependent on lung transplant
→ This is why stem cells could be so beneficial
How could stem cells be used for therapy of lung disease?
Give some examples of the different approaches
Depends on the features of the particular disease
e.g. Acute / chronic injury, extent of damage etc.
Different stem cells would be needed for different diseases
Approaches:
• Cystic fibrosis: replacement of CFTR
• Adult RDS: regeneration of epithelia and endothelium
• Asthma: inhibition of airway remodelling, SMC hypertrophy
Describe normal endogenous stem cell responses to injury in the lung
How could this be therapeutically modulated?
What are the challenges of this approach?
Either:
1. Endogenous stem cells react to the injury too much, leading to hyperplasia, loss of architecture and cancer
- Lack of repair
Therapeutic approach:
• Switch off / on the endogenous stem cells for a better repair process
Challenges:
• In disease states, the intrinsic potential of the endogenous stem cells may be altered
• In other cases, the microenvironment may be altered
What is the benefit of stem cell transplants?
What are the challenges of this approach?
Stem cells have the intrinsic capacity to self renew, proliferate and differentiate
This is an alternative to whole tissue transplants
Challenges:
• Source of stem cells? (iPSCs, Adult SCs or ESCs?)
• The microenvironment in disease states may not be able to provide adequate signals to drive the differentiation of the stem cells
Describe the use of stem cells in gene therapy
What are the challenges of this approach?
e.g. Cystic fibrosis
Stem cells w/ a functional CFTR gene could be expanded in vitro and then transplanted back into the patient
Challenges:
• Engraftment is very difficult
• Requires depletion of the airway epithelium without harming the microenvironment
Describe how stem cells could be used in bioengineering
Decellularisation
• Lung is depleted of cells through treatment (detergents, enzymes etc.)
• Matrix scaffold is re-seeded with stem cells (matching the individual)
• This new organ can be transplanted back into the individual (without rejection)
So far this has been done with a trachea
Describe the generalised stem cell heirarchy
Stem cell → Progenitor cells → Differentiated cells
Why can’t ESCs be directly used for therapy?
They can form teratomas, as they are pluripotent
Must first direct them to differentiate into the tissue of interest
