1. Human Stem Cells

2. Cells are arranged as tissues.

3. Tissue Renewal Tissues are classified as –Postmitotic-- no longer dividing; have exited cell cycle at G0. May be replaceable to a small extent by progenitor cells –Expanding--grow until adult size is attained and then stop growing, but capable of growth and repair as necessary –Renewal-- cells that are constantly being replaced; have a limited life span and rely on stem cells

4. Stem Cells Fig 13.5

5. Stem Cells Used for replacement and renewal Can divide indefinitely, appear undifferentiated Divide to produce more stem cells as well as cell to differentiate Some are pluripotent — can give rise to differentiated cells from all three germ layers.

6. Transit Amplifying Cells Produced by stem cells Can undergo some cell divisions but not indefinitely Eventually divide to produce cells that will differentiate Usually restricted potential

7. Asymmetric Division Two symmetric divisions Fig 13.6

8. Stem Cells Stem Cell Progenitor cells Differentiated cells precursor cells

9. Structure of Skin Fig 13.8

10. Structure of Skin Skin consists of the dermis (connective tissue derived from the somite and neural crest) with an overlying epidermis. The epidermis is ectodermal and consists of stratified squamous epithelium. The basement membrane of the epidermis overlies the dermis. Dermis is vascularized and provides nutrients to epidermis.

11. Structure of Skin Keratinocytes are the major differentiated cells of epidermis. Epidermal stem cells in the basal layer divide to replace themselves, to form transit amplifying cells and to form keratinocytes. In normal epidermis, the keratinocytes are replaced from basal layer cells about every two weeks. About 10% of basal layer cells are true stem cells; the rest are transit amplifying cells.

12. Layers of Epidermis Differentiation Stem cells and transit amplifying cells Terminally Differentiated

13. Layers of Epidermis Cells that leave the basal layer are no longer dividing. These keratinocytes begin expressing keratins and become progressively more differentiated. The top layer of cells is called the stratum corneum and will be sloughed off-- essentially dead cells due to programmed cell death. Gradient of Differentiation in epidermis: undifferentiated to differentiating to terminally differentiated

14. Layers of Skin

15. Skin Pigmentation Pigment in skin and hair is melanin. Melanin-- produced by melanocytes, neural crest cell deriviatives Melanocytes are found in the basal layer of the epidermis and transfer pigment (melanosomes) to keratinocytes Difference in pigmentation is not due to number of melanocytes, but to how much melanin each melanocyte produces

16. Stem Cells Fig 13.5

17. Stem Cells Embryonic and adult stem cells generally have different potentials. Embryonic stem cells are essentially inner cell mass cells that can give rise to all tissues of the embryo. Adult stem cells are usually more restricted in potential and often only give rise to one tissue type.

18. Stem Cells What are they and what do they do? Embryonic Stem (ES) Cells Adult Stem Cells –Fetal Stem Cells –Bone Marrow Mesenchymal Stem Cells (MSCs) –Hematopoietic stem cells Induced Pluripotent Stem Cells (IPS cells) Adult vs. Embryonic Stem Cells Regenerative Medicine

19. Stem Cells Unspecialized, undifferentiated cells that can reproduce themselves and give rise to specialized cells.

20. Stem Cells Stem cells are naturally used to replace many cell types in adults. Can also probably be manipulated to replace other cell types

21. Type of Stem Cells Embryonic Stem Cells Adult (Tissue-specific or somatic) Mesenchymal stem cells (MSC) Induced

22. Embryonic Stem Cells First isolated in 1981 Successfully grown in culture as cell lines in 1998

23. Fertilization combines male and female genetic information. The egg and sperm nuclei fuse to give the diploid zygotic nucleus.

24. By about 3 days after fertilization, the blastocyst stage forms with an inner cell mass and a trophectoderm.

25. Trophectoderm Inner cell mass (ICM) develops into the embryo. Trophectoderm develops into the placenta.

26. ICM

27. ESCs are pluripotent “many potentials” Pluripotent cells have the ability to form most or all of the adult cell types. They are unspecialized.

28. How do you make embryonic stem cell lines?

29. ICM Isolate ICM from in vitro fertilized egg at 4-5 days of development.

30. ICM Peel away the outer, trophectoderm layer, and grow the ICM cells.

31. Culture in the lab, subdividing as needed. Embryonic stem cellsEmbryonic germ cells

32. Stemcell project

33. Stem Cells Given the correct signals, (particularly growth factors) stem cells can differentiate into particular, specialized cell types.

34. Differentiation The process of cells becoming specialized into the many different cell types of an adult. Controlling differentiation is one of the most difficult aspects of stem cell technology. Often ESCs spontaneously differentiate

35. Smooth muscle lymphocyte neurons erythrocytes

36. Stem Cells Different combinations of growth factors have led to: vascular smooth muscle fat cells cardiac muscle cells macrophages neurons astrocytes oligodendocytes blood cells.

37. Uses of embryonic stem cells To further basic science –Culturing with different growth factors and other treatments can lead to different patterns of differentiation. –Studying such differentiation in the lab can help scientists understand normal differentiation in the embryo.

38. Uses of embryonic stem cells As a potential therapy for many different types of diseases or other conditions –Treatments for over 70 conditions are in progress in animal models –Two human trials in progress Macular degeneration Macular dystrophy

39. Problems with embryonic stem cells Original lines were grown with mouse “feeder cells”. Could lead to cells taking up mouse viruses. Difficulty in obtaining pure cultures of a particular type of differentiated cell-- this is improving Embryonic stem cells that do not differentiate correctly can lead to the formation of tumors-- undifferentiated, replicating cells. Uses embryos?

40. Adult Stem Cells Muscle Bone Brain Liver Blood Pancreas Skin

41. Adult Stem Cells Somatic or Tissue-specific Found in many different tissues May reside in specific areas called “stem cell niches” Used for replacement of worn or injured cells In some tissues, they remain without dividing until needed for tissue repair “Expanding”

42. Adult Stem Cells Often of restricted potential –Stem cells in the brain make different nervous system cells—neurons, astrocytes and oligodendrocytes –Hematopoietic stem cells make blood cells –Skin stem cells replace epidermal layer –Mesenchymal stem cells (MSCs) make bone cells, adipocytes, chondrocytes and other connective tissue

43. Hematopoietic Stem Cells Fig 13.17

44. Hematopoietic Stem Cells Found in the bone marrow of adults Found in various sites during embryogenesis including: –Yolk sac –AGM (aorta-gonad-mesonephros) mesoderm –Liver –Spleen and Lymph nodes –Finally bone marrow

45. Hematopoietic Stem Cells Constant state of renewal of cells HSCs can renew themselves and lead to a variety of different cell types: –Erythrocytes (RBCs) –Granulocytes (neutrophils, eosinophils, basophils –Monocytes (similar to macrophages) –Megakaryocytes--fragment to form platelets –Lymphocytes (B cells and T cells)

46. Hematopoietic Stem Cells Bone marrow grafts were the first stem cell therapy (1950s) Bone marrow is easily killed by irradiation, and can be replaced through bone marrow transplants Donor transplant into bloodstream will populate the bones and begin dividing to produce the different types of blood cells

47. Fetal Stem Cells Taken from fetuses More similar to adult stem cells, only younger and “fresher” Generally not pluripotent, though some amniotic fluid cells may be.

48. Mesenchymal Stem Cells (Stromal Cells) First isolated from bone marrow and recently found to be pluripotent Found in stroma– connective tissue Similar to ES-- can be cultured for long periods of time Can be induced to differentiate into many, though not all, cell types

49. Mesencyhmal Stem Cells MSCs have also been isolated from extracted teeth. Can easily be stored and frozen for later use

50. http://stemcells.nih.gov/

51. Adult vs. Embryonic Stem Cells Adult stem cells may be multipotent, but they are rarely pluripotent although MSCs are. Many adult stem cells are rare and generally difficult to isolate Most adult stem cells have not been established as cell lines that can be grown indefinitely although there is progress in this regard.

52. Adult vs Embryonic Stem Cells Adult stem cells have been successfully used to treat a number of conditions- bone marrow transplants first done over 50 years ago Adult stem cells seem less likely to result in tumors, though a recent report has shown transformation in one case. Ethical issues?

53. Induced Pluripotent Stem Cells Reprogram somatic cells into stem cells by forced expression of some stem cell genes First worked out in mice in 2006 Human iPSCs were made in 2007

54. Induced Pluripotent Stem Cells Uses viral vectors to add the genes in– potential problem as virus may cause cancer Made from patient’s own cells so little chance for immune rejection Once induced, they would work just like ESCs.

55. Induced Pluripotent Stem Cells iPSCs are being used –To study development and differentiation –for drug testing in culture –Eventual goal is for gene therapy, but not there yet! A trial has occurred in Japan using iPSCs to treat macular degeneration– results not yet available.

57. Regenerative Medicine In mice, stem cells have been used to treat: Type 1 Diabetes Parkinson’s Disease Spinal cord injuries Heart muscle damage Rheumatoid arthritis And many other conditions

59. Current Stem Cell Trials Due in class on Wednesday Pick one of the types of stem cells and find information about uses, current trials (whether human or otherwise), successes, etc. –Embryonic –IPSC –MSC –Adult (Tissue-specific)