Stem cells and regenerative medicine Flashcards
What are stem cells?
What the stem cells do:
→ Can differentiate into many different cell types
→ Capable of self-renewal via cell division (both symmetric and asymmetric cell division)
Purpose of stem cells:
→ Provide new cells (depending on the signals that the stem cell receives) as an organism grows and can replace cells that are damaged or lost
Types of stem cells:
→ Several different types of stem cells: embryonic, adult and induced pluripotent stem cells
→ Targeted by researchers for their therapeutic potential
What do each of the 3 germ layers give rise to, as examples?
→ Ectoderm - produces nervous, epithelial and sensory tissue
→ Mesoderm - skeletal and cardiac muscle, blood and connective tissues
→ Endoderm - organs e.g lungs, pancreas, stomach, liver germ cells etc
What are stem cell niches and what are they for?
→ Tissue-specific stem cells are maintained in special supportive micro-environments
→ Found at specific anatomical locations
→ Niches interact with stem cells to regulate cell fate
→ Protect stem cells from depletion and host from excessive stem cell proliferation
- Supporting ECM molecules such as fibrinogen, collagen
- 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 stem cells
ESC
→ Pluripotent - almost unlimited growth potential and may differentiate into any kind of cell
→ Higher risk of tumour creation - unregulated stem cell proliferation rate is higher in ESCs
→ Risk of being genetically different from recipients cells - higher risk of rejection
→ Unlimited numbers of cells due to high cell potency
→ Very low probability of mutation-induced damage in the DNA
ASC
→ Oligopotent - unipotent - limited cell potency
→ Less risk of tumour creation
→ Compatible with recipients cells - low risk of rejection
→ Limited numbers may be obtained
→ Higher probability of mutation-induced damage in the DNA - risk of diseases
iPSC
→ Less growth potential than embryonic stem cells
→ Less risk of tumour formation
→ Compatible with recipients cells - low risk of rejection
→ Rather limited numbers may be obtained
→ Higher probability of mutation-induced damage in the DNA - risk of diseases
What are the pluriopotency factors involved with generating iPSCs (induced pluripotent stem cells)?
→ c-Myc promotes DNA replication and relaxes chromatin structure
→ Which 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
→ iPS cells have a similar global gene expression profile to that of ES cells
Summary of lecture part 1
→ Stem cells are essential for replacing lost/damaged tissue due to their ability to self-renew via cell division and the ability to differentiate into many different cell types
→ There are three main stem cell sources: adult (tissue specific stem cells), embryonic stem cells and induced pluripotent stem cells
→ Scientists and doctors can harness the power of stem cells and genetic engineering to provide therapies to replace lost/damaged tissue
What are 2 regeneration strategies looking at cardiovascular complications?
1) 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 are some challenges.
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)
What is Myocardial thymosin β4 (Tb4) and what is it necessary for?
→ Produced by cardiacmyocytes
→ It 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
Summary of lecture part 2
→ The adult heart has a low level of endogenous regenerative ability.
→ In the event of an injury such as myocardial infarction scar tissue forms instead of healthy cardiac muscle leading to heart failure
→ Preclinical and initial clinical studies suggest stem cell therapy maybe therapeutic, possibly via direct integration of grafted cells to the myocardium/coronary vessels or by re-expression of developmental gene programmes and paracrine signals which help the host tissue to regenerate
How is stem cell therapy relevant in terms of cancer treatment?
→ 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)
→ Clinical trials for other tumour types; brain and breast cancer, neuroblastoma, sarcoma
→ Effector immune cells from iPSC/ESCs e.g. engineered T and NK cells targeted for immunotherapy.
→ Production of anti-cancer vaccines
→ MSCs/NSCs deliver genes, nanoparticles, and oncolytic viruses to tumour niche due to intrinsic tumour tropism
→ Exosomes extracted from the culture of drug-priming MSCs/NSCs can target the drugs to tumour sites
→ Mutation correction in vitro, drug testing in vitro before replacement in vivo
Summarise some various types of stem cells that have been identified for use in burns therapy and what they do
→ Fetal 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.
generally (?)
→ Replace lost skin cell types, speeding up endogenous healing.
→ Generate ECM and produce paracrine signals which aid healing
What therapy/information towards therapies has been investigated regarding eye injuries?
→ 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 transfor fibroblast cells into limbal stem cells
→ 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 promising results
What is Retinal pigment epithelium (RPE)?
→ 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 promising results
What has been discovered about Neural stem/progenitor cell grafts? (in relation to spinal cord injury)
→ 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
What are some conclusions from the last part of this lecture that can be made?
→ Preclinical and clinical trials are on-going for a wide variety of stem-cell based therapeutic approaches
→ In cancer, stem cells can be used repopulate the body with healthy non-malignant cells and genetic engineering of stem cells can produce cells with anti-cancer properties
→ Transplantation approaches are providing positive results for eye diseases, burn wound healing and spinal cord injuries
→ Many other stem-cell based therapies are currently being developed for different tissues and diseases
