Functions of Hematopoietic Stem Cells

‭Functions of Hematopoietic Stem Cells‬ ‭✪Plan:We see the actors who are around the stem cell, that is to say the fibroblasts, endothelial‬ ‭cells, macrophages (all of which are in the stroma of the MOH). Fibroblasts and endothelial cells‬ ‭can secrete TGF beta which will inhibit stem cells, maintaining them in a quiescent form while‬ ‭endothelial cells which have been stimulated can secrete growth factors which will induce stem cell‬ ‭differentiation. Fibroblasts can secrete Stem Cell factor which will stimulate stem cells. The‬ ‭activated stem cell is very sensitive to interleukins 3 (Il3) which is a multi CSF interleukin, i.e.‬ ‭which acts on progenitors undifferentiated and then we have growth factors which are a little more‬ ‭specific. For example GM CSF (GM for granulocyte monocyte. CSF for colony stimulating factor)‬ ‭which will promote the commitment of progenitors towards differentiation into neutrophils and‬ ‭monocytes.‬ ‭✪We can have synthetic GM CSF available which is used during very aggressive‬ ‭chemotherapy.ssive because there are often neutropenias and therefore defenses weakened immune‬ ‭systems because chemotherapy does not differentiate between tumor cells or good cells like‬ ‭hematopoietic cells which are very sensitive because they have a very rapid renewal rate.‬ ‭Chemotherapy will destroy these cells and to prevent these patients from remaining too long‬ ‭without immune defense we can give GM CSF so that they rebuild their neut number as quickly as‬ ‭possible, rophile and monocytes sufficient to defend against bacterial attacks.‬ ‭‬ ● ‭●‬ ‭●‬ ‭ or the red lineage we have erythropoietin which is a specific factor.‬ F ‭For the monocytic line we have MCSF for monocyte colony stimulating factor.‬ ‭We have G CSF which is more specific than GM because it only acts on the neutrophil line.‬ ‭ Important: Cytokines can have very variable actions depending on the target cells and for‬ ✪ ‭example here we will see TGF beta which has an inhibitory action at the level of stem cells‬ ‭therefore which keeps them in a quiescent manner also has an inhibitory action at the level of‬ ‭certain erythroblastic progenitors. On the other hand, it has a stimulatory action for erythroblastic‬ ‭progenitors but which are further along the differentiation pathway. because they have acquired‬ ‭other characteristics. TGF beta which has an inhibitory role in stem cell level also has a stimulating‬ ‭action on the granular lineage.‬ ‭ Hematopoietic stem cells have potential:the reconstruction of a hematopoiesis in a subject who‬ ✪ ‭has been irradiated. This is important in 2 circumstances: 1-In allografts: patients who have had‬ ‭leukemia, heavy chemotherapy, irradiation, they can be referred if they have a compatible donor‬ ‭and at that time the Donor stem cells will reconstitute the patient's hematopoiesis.‬ ‭ When a soldier was irradiated. To save it, we must recover the stem cells, expand them and‬ ✪ ‭therefore make them proliferate ex vivo and then re-inject them into the patient and it is always this‬ ‭potential for reconstitution of the MOH which is exploited.‬ ‭ Interleukin 5 is a factor acting mainly on the eosinophil lineage.Item discussed:Can‬ ✪ ‭hematopoietic stem cells function in culture conditions yielding blood cells but also other muscle‬ ‭cells or epithelial cells?Nothing is decided yet and it is the same for stem cells in muscle level.‬