Stem Cells and Regenerative Medicine Flashcards
What are stem cells and what do they do?
Can differentiate into many different cell types
Capable of self-renewal via cell division
Provide new cells as an organism grows and can replace cells that are damaged or lost
Several different types of stem cells: embryonic, adult, and induced pluripotent stem cells
Targeted by researchers for their therapeutic potential
What are supportive stem cell niches?
Tissue-specific stem cells are maintained in special supportive microenvironments called stem cell niches.
- Supporting ECM - neighbouring niche cells - secreted soluble signalling factors (e.g. growth factors and cytokines) - physical parameters; shear stress, tissue stiffness, and topography), - environmental signals (metabolites, hypoxia, inflammation, etc.).
Compare the different types of stem cells.
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What are the different sources of stem cells?
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How do you generate iPSC cells?
- c-Myc promotes DNA replication and relaxes chromatin structure,
- allows Oct3/4 to access its target genes.
- Sox2 and Klf4 also co-operate with Oct3/4 to activate target genes
- these encode transcription factors which establish the pluripotent transcription factor network
- result in the activation of the epigenetic processes (more open chromatin) that establish the pluripotent epigenome. The
- iPS cells have a similar global gene expression profile to that of ES cells.
How can stem cells be used for those with CV disease?
During a heart attack blood supply to heart muscle is lost. Cardiac muscle dies and is not replaced, as adult cardiomyocyte turnover is low. Instead there is often fibrosis and scarring leading to decreased cardiac function and heart failure
Research into therapies to replace lost cardiac muscle and improve blood supply to the affected region is a high priority
Also relevant for cardiomyopathies/conduction defects
What are the possible regeneration strategies for CV disease?
- Cell transplantation approaches to promote cardiac regeneration and repair, mostly aimed at replenishing lost cardiomyocytes.
- Immune rejection, manufacture/isolation of sufficient cells, mode of delivery and clinical regulation all challenges.
Neovascularisation - Improved circulation to injured area
- Paracrine effects improving CM replacement
2. Therapies based on direct stimulation of endogenous cardiomyocyte production including re-activation of developmental pathways e.g. epicardium based on models where the is no/reduced scarring and full cardiac regeneration (zebrafish, amphibians, neonatal mice).
- Immune rejection, manufacture/isolation of sufficient cells, mode of delivery and clinical regulation all challenges.
How have iPSC stem cells been used to generate hearts in primate models?
Allogenic transplantation of iPS cell-derived cardiomyocytes regenerates primate hearts
Induced pluripotent stem cells (iPSCs) are a potential source of autologous patient-specific cardiomyocytes for cardiac repair providing a major benefit over other sources of cells in terms of immune rejection.
Monkey model (Macaca fascicularis), with identical MHC structure of to humans.
Fibroblast-derived iPSCs made from a MHC haplotype (HT4) homozygous animal were differentiated into cardiomyocytes
(iPSC-CMs).
Direct intra-myocardial injection of iPSC-CMs into HT4 heterozygous monkeys after myocardial infarction.
Grafted cardiomyocytes (GFP+) survived for 12 weeks with no evidence of immune rejection.
How have human ESC-derived cardiomyocytes been studied in primate models?
Human ESC-Derived Cardiomyocytes Restore Function in Infarcted Hearts of Non-Human Primates
Transplantation of ~750 million cryopreserved human embryonic stem cell–derived cardiomyocytes (hESC-CMs) enhances cardiac function in macaque monkeys with large myocardial infarctions.
One month after hESC-CM transplantation, global left ventricular ejection fraction improved in controls, by 3 months there was an additional 12.4% improvement
Grafts formed electromechanical junctions with the host heart and by 3 months contained ~99% ventricular myocytes.
Graft-associated ventricular arrhythmias were present in some animals.
Remuscularization of the infarcted macaque heart with human myocardium provides durable improvement in left ventricular function.
How can gene reactivation be used to treat CV diseases?
Myocardial thymosin β4 is necessary for epicardial migration, coronary vasculature and cardiomyocyte survival
Importantly Tb4 addition to adult hearts can stimulate epicardial outgrowth and neovascualarisation
Re-expression of a key embryonic epicardial gene Wt1 through priming by Tb4 in vivo. Activated Wt1+ epicardial cells give rise to cardiac progenitors in the MI injured adult heart These can differentiate into de novo cardiomyocytes
How can stem cells be used for cancer?
Chemo/radiotherapy kills cancerous cells.
- Transplantation of stem cells reconstitutes healthy cells. e.g HSC transplantation for blood cells and leukocytes (lymphoma, leukemia) (ASC, iPSC)
What are the different stem cells that can treat burns?
Replace lost skin cell types, speeding up endogenous healing. Generate ECM and produce paracrine signals which aid healing.
- Foetal fibroblasts (from ESCs); improve skin repair due to the high expansion ability, low immunogenicity, and intense secretion of bioactive substances such asFGFs, VEGFs, KGFs - Epidermal stem cells; high proliferation rate and easy access and keep their potency and differentiation potential for long periods. Generate most skin cell types for repair and regeneration - Mesenchymal stem cells; They have a high differentiation potential and a certain degree of plasticity. Migrate to the injured tissues, differentiate, and regulate the tissue regeneration by the production of growth factors, cytokines, and chemokines - iPSCs; can be differentiated into dermal fibroblasts, keratinocytes, and melanocytes.
How can stem cells be used for eye injury/disease?
Stem cells at the edge of the cornea, limbal stem cells are responsible for making new corneal cells to replace damaged ones.
If these stem cells are lost due to injury or disease, the cornea can no longer be repaired. This affects the ability of light to enter the eye, resulting in a significant loss of vision.
Limbal stem cells are collected from an adequately healthy donor eye, and are expanded in the laboratory to sufficient numbers and transplanted into the damaged eye.
Repairs the cornea and permanently restores vision.
To avoid immune rejection this treatment only works if the patient has a healthy section of limbus from which to collect the limbal stem cells.
iPSC cells can be induced to make corneal epithelial cells for transplant and exposure to the right signals can transfer fibroblast cells into limbal stem cells
What is RPE and how can RPE cells be used for eye injury/disease?
Retinal pigment epithelium (RPE) is a single layer of post-mitotic cells, acting as a selective barrier to and a vegetative regulator of the overlying photoreceptor layer,
RPE has a key role in retina maintenance and parts of the retina can die without a functional RPE leading to loss of vision
RPE cells can be damaged in a variety of diseases such as: age-related macular degeneration (AMD), retinitis pigmentosa and Leber’s congenital aneurosis.
RPE cells have been made from both ESC and iPSC
Several clinical trials for diseases including age-related macular degeneration (AMD), retinitis pigmentosa and Leber’s congenital aneurosis show promise
How can NSPCs be used for spinal cord damage?
Neural stem/progenitor cell (NSPC) grafts can integrate into sites of spinal cord injury (SCI) and generate neuronal relays across lesions that can provide functional benefit.
Calcium imaging of NSPC grafts in SCI sites in vivo and in adult spinal cord slices showed NSPC grafts organize into localized and spontaneously active synaptic networks.
Optogenetic stimulation of host axons produced a neuronal response in the graft and vice versa
In vivo imaging revealed that behavioural stimulation also elicited focal synaptic responses within grafts.
Thus neural progenitor grafts can form functional synaptic subnetworks whose activity patterns resemble intact spinal cord.
