25. Stem Cells and Regenerative Medicine Flashcards
What are 4 defining characteristics of stem cells?
Define pluri/multi/oligo/unipotent.
What type of stem cells is a hematopoietic stem cell?
Undifferentiated, can divide indefinitely, self-renewing, give rise to progeny that differentiate into specialised cells.
Pluripotent: differentiate into cells derived from any of the 3 germ layers (except embryonic). Multipotent: give rise to several specialised cells/tissues of an organism (often tissue specific). Oligopotent: generate a few cell types within a particular tissue. Unipotent: produce only 1 cell type, still capable of self-renewal.
Multipotent.
What maintains stem cells?
What could changes in the SC niche cause?
What are the 2 different types of stem cell division?
The environment produced by surrounding differentiated SC, which may secrete specific factors into surrounding matrix or communicate with SC via gap junctions. SC may also be influenced by underlying basal lamina.
SC death, division or differentiation.
Symmetric cell division: SC + SC or differentiated cell + DC (then SC lost)
Assymetric division: SC + DC
What are the 2 main types of SC?
Briefly describe early embryonic development.
What is an embryonic SC and where does it come from? What ethical issues does this raise?
Embryonic SC - pluripotent, from 5-7d blastocysts. Adult SC - multipotent.
Fertilised egg -> blastocyst (5-6d) -> gastrula (14-16d, inner cell mass differentiates to endo/meso/ectoderm).
Seperate cells of inner cell mass from blastocyst. ESC lines derived from individual ESCs. Daughter cells alike and grow indefinitely. Ethics: destroy blastocyst to get SC, main source = IVF clinics.
How are embryonic SCs identified?
Normally there would be spontaneous embryonic SC differentiation in vitro. How do we control this? (Directed differentiation)?
What are some challenges of embryonic SC for transplantation therapies?
Immortality (grow indefinitely in culture in the primitive embryonic state), clonality (maintain normal karyotype and expression of telomerase), undifferentiated (presence of markers only found in undifferentiated cells), wide developmental potential (differentiate into wide range of cell types in vitro/vivo).
Need to understand molecules involved in mediating selection and expansion/the signals for growth and differentiaton and try and replicate in the lab.
Purity/production, cancer, immunology (rejection), ethics.
Embryonic SC can give rise to disorganised growths. Describe them.
What are some potential solutions to immune rejection in embryonic SC based therapy?
Teratomas: non-malignant tumour in animal consisting of tissues from the 3 embryonic germ layers. Usually found in ovary and testes. Produced experimentally by the growth and differentiation of injected pluripotent embryonic SCs.
Large banks of embryonic SCs, manipulation of histocompatibility genes in ESCs, replacement of hematopoietic tissue of pt with ESC-derived cells prior to graft, immunosuppressants/Abs, theraputic cloning.
Describe theraputic cloning.
What are the advantages and challenges/controversies?
Patient -> isolate cell -> remove nucleus -> put in unfertilised egg cell MINUS IT’S NUCLEUS from donor -> diploid oocyte -> initiate development -> blastocyst -> create embryo SC line -> grow in culture = pluripotent and genetically identical to donor’s cells.
Advantages: ideal tissue for regenerative medicine b/c genetically identical to pt - no tissue rejection, and can model a pt-specific disease.
Challenges: % of sucessful clones low (long time-frame to generate). Creating potential embryo (not fertilised) for research/treatment. Practical - source of occytes (should women donate for this?)/ Slippery slope to reproductive cloning.
Describe reproductive cloning.
What sort of questions are asked in ethical debates about this?
Starting mouse-> isolate cell -> remove nucleus -> put in unfertilised egg cell MINUS IT’S NUCLEUS from donor -> diploid oocyte -> implant into surrogate mum -> birth = genetically idential to starting mouse. Ethics - hard to regulate last step…
Playing God, embryo farms in future, healthcare costs increase, morally right, are embryos alive? Variability in regulations regarding human SC research. Could be used to cure age-related macular blindness..
What are adult stem cells?
What are some potential advantages of using adult SC for cell therapies?
Rare, undifferentiated cells found among differentiated cells in a tissue/organ. Can differentiate to produce major cell types of the tissue. Multipotent. 10 role: maintain + repair tissue in which it’s found. E.g. blood SC in bone marrow can become only specialised types of blood cell.
No legal/ethical concerns, using pt’s own SC = no rejection, injection of normal somatic SC hasn’t led to tumours, may learn how to repair ourselves in future. Already proven theraputically effective = skin grafts, bone marrow transplants.
What are induced pluripotent stem cells (iPS).
What are the advantages and challenges?
Best of both embryonic and adult SC: take a cell from the body and add certain genes to it (genetic reprogramming) -> iPSC cell, behaves like embryonic SC -> culture and it can differentiate to different types of specialised cells.
Advantages: no embryos or immunilogical rejection.
Challenges: cancer risk, viral integration = risk, need to demonstrate stability of re-programmed cells, improve technical efficiency.
First iPSC trial approved for age-related macula degeneration 2013. Differentiated pluripotent cell to retinal cells. But mutations in SC so halted.
Pluripotent cells have important applications in biomedical research. What are two tests that are being carried out?
Experiments to study development and gene control. E.g. making mini organs, use for reasearch, diagnostic tool, theraputic assessment.
Drug development and toxicity tests. E.g. modelling Alzheimer’s disease with iPSCs reveals different cell stress phenotypes with different drug responsiveness. Step towards personalised medicine
