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Induced pluripotent stem cells - summary extra class Aline Verstraeten
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this is a summary for the extra (cancelled) lesson on iPSCs given by Aline Verstraeten (recorded powerpoint).
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Induced pluripotent stem cells (iPSCs)Defini&ons and general principles
Defini&on: Stem cells
• Can divide and create an iden&cal copy of themselves, a process called self-renewal
• Can differen&ate/mature into cells that make up every type or several types of &ssue(s) and
organ(s) in the body, a process called pluripotency/to&potency/mul&potency
— depending in how many cell types it can differen&ate in to, we call them pluripotent,
to&potent or mul&potent
o mul&potent = restricted number of cells
o pluripotent = they can differen&ate into any cell type in the embryo
o to&potent = they can differen&ate into any cell type of the fetus + surrounding
&ssues (e.g. placenta)
Defini&on: pluripotent
• Different types
— Early embryonic cells – to&potency
o can differen&ate into any cell type of the human body as well as the placental
cells
— Embryonic stem cells (ESCs) – pluripotency
o if you are not interested in the placenta, you can use embryonic stem cells as
an alterna&ve
— Adult stem cells: e.g., hematopoie&c stem cell – mul&potency
o immature cells
o they can only differen&ate into a certain lineage of cells
§ hematopoie&c stem cells in the bone marrow or in the blood à these
cells can only differen&ate to the different cell types present in blood
— Induced pluripotent stem cells (iPSCs) – pluripotency
o same characteris&cs as the embryonic stem cells
o why is this interes&ng? these stem cells are created from soma&c &ssue (e.g.
skin, blood from a person) ßà embryonic stem cells are harvested form
human embryo’s = ethical concerns surrounding the use of embryonic stem
cells, because you are neutralizing liNle babies/fetuses (it’s s&ll before the feel
pain, but it is ethically not that straight forward)
Ques&on 1: you aim to create cor&cal neurons from an Alzheimer’s disease pa&ent. Hematopoie&c
stem cells can be used for this purpose?
à False, because hematopoie&c stem cells can only differen&ate into the blood lineage; they can not
create neurons
To create these cor&cal neurons from stem cells, you can either use pluripotent stem cells or you can
use embryonic stem cells. If you want to start from pluripotent stem cells, you should use neuron stem
cells
Defini&on: induced
• you start from a soma&c cell à this will be differen&ated
you bring back/induce the stem cell capaci&es in this cell type
• So for example, you start from fibroblasts = skin cells, or kera&nocytes, or blood cells à you
will reprogram this cell into an embryonic cell. You do this by using different transcrip&on
factors, e.g. Yamanaka factors
, IPSC discovery
• this technique was discovered by Yamanaka in 2006 à 2012: Nobel prize
• they only use 4 transcrip&on factors à deliver these to terminally differen&ated cells (works
in every cell type) à cells go back toward a stem cell profile = they get the proper&es of these
stem cells, the express stem cell marker genes, they get the morphology of these stem cells,
and they can differen&ate into the cells of all the 3 germ layers (ecto-, endo- and mesoderm)
Ques&on 2: ESCs and iPSCs are both pluripotent. ESCs are more commonly used in biomedical research,
because they are less “ar&ficial” (not “created” in the lab).
à it is true that ESCs are not created in the lab = these cells come from the embryo = are not ar&ficially
made
à BUT !! the ESCs are associated with some ethical concerns, so in prac&ce iPSCs are more oeen used
à you have provide for example legal offices with a very good reason why you want to use ESCs
Differen&a&on: 2D cultures
• you can create different cell types out of 1 stem cell
• most typically we differen&ate these cells into 2D cultures à make monolayers of whatever
cell type you are interested in
• if you want a &ssue type that consists of mul&ple cell types, you can start from 1 iPSC line and
create the different cell types of interest from this 1 iPSC
• Based on embryological knowledge à you can only make a soma&c cell out of the stem cell if
you know which transcrip&on or growth factors are needed to bring a stem cell towards for
example a neuron. You need to know the normal development, otherwise you are not able to
do these differen&a&ons
• Many protocols available based on the informa&on gained in the last years
— Addi&on of growth & transcrip&on factors
— Lacking for some cell types, knowledge gaps
— Not uniformly good, compara&ve tes&ng needed (you need to test mul&ple ones to
know which performs best)
— It’s all in the details
— Con&nuous op&miza&on à it can be that you worked with a certain protocol, but a
few years later, a newer protocol becomes available because of the fact that addi&onal
knowledge have been gained, and then you start over to improve the cultures
Applica&ons
Disease modelling & drug development
• disease modelling = you want to replicate what is happening in the human body of a pa&ent as
compared to a control à you can do it in an animal model, or in cells
— you will compare the cells in the disease condi&on with the normal condi&on
• Useful for &ssue types with limited access in pa&ents and controls
— e.g. brain: can only be harvested aeer death, but here you are looking at the late state
(not the begin condi&ons) à not interes&ng for drug development
o iPSCs from e.g. Alzheimer’s pa&ent à differen&ated into neurons à these are
immature = look at early stage of the disease à when the person dies: you
have the complete brain
o control persons = more difficult to obtain
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