Stem Cells

Overview of Stem Cells

  • Main topics discussed:

    • Cell division symmetry

    • The concept of "potency"

    • Types of stem cells

    • Applications of stem cell therapy

    • Ethical considerations regarding stem cells

Definition and Characteristics of Stem Cells

  • Stem cells are defined as undifferentiated cells.

  • They have the capacity to differentiate into various specialized cell types, including:

    • Muscle cells

    • Blood cells

    • Cardiac cells

    • Nerve cells

    • Intestinal cells

    • Liver cells

Essential Properties of Stem Cells

  • Two fundamental properties of stem cells:

    • Self-renewal: The ability to divide and produce more stem cells.

    • Differentiation: The ability to differentiate into specialized cell types.

Cell Division Types

  • Cell division can occur in two main forms:

    • Symmetric Cell Division:

    • Produces two identical stem cells.

    • Can result in symmetric self-renewal or symmetric differentiation.

    • Asymmetric Cell Division:

    • Results in one stem cell and one committed cell.

Potency of Stem Cells

  • Early-stage embryonic stem cells (ES) are categorized as totipotent:

    • They can give rise to any cell type in an adult organism and can form a complete organism.

  • As development progresses, cells become more committed and lose their totipotency, resulting in pluripotent cells which can generate many, but not all, cell types.

  • Terminally differentiated cells are those that have specialized functions and are unable to replicate or differentiate further; however, “progenitor cells” exist in many adult tissues for repair and maintenance.

Sources of Stem Cells

  • Embryonic stem cells (pluripotent):

    • Sourced from the inner cell mass of the blastocyst stage of an embryo.

    • They are not totipotent because they cannot form a placenta.

  • Adult stem cells (multipotent):

    • Reside in niches within a variety of adult tissues.

    • Example: Hematopoietic Stem Cells (HSCs) found in the bone marrow.

  • Foetal stem cells:

    • In pregnant mice, these cells migrate to maternal injury sites to aid in tissue repair.

Therapeutic Applications of Stem Cells

  • Stem cells are implicated in treatments for various medical conditions, including but not limited to:

    • Stroke

    • Traumatic brain injury

    • Learning defects

    • Baldness

    • Blindness

    • Alzheimer’s disease

    • Deafness

    • Parkinson’s disease

    • Amyotrophic lateral sclerosis (ALS)

    • Missing teeth

    • Wound healing

    • Bone marrow transplantation

    • Spinal cord injury

    • Osteoarthritis

    • Rheumatoid arthritis

    • Crohn's disease

    • Certain cancers

    • Myocardial infarction

    • Muscular dystrophy

    • Diabetes

Autologous Stem Cell Therapy

  • Utilizes the patient’s own stem cells to treat disease conditions.

  • Key considerations:

    • Challenges in using donor stem cells (heterologous transplant).

    • Current medical interventions may be necessary if the patient’s own stem cells are insufficient.

  • Isolation and culture of stem cells:

    • Adult stem cells can be extracted relatively easily from tissues such as bone marrow.

    • Processes for isolating embryonic stem cells include:

    1. Sperm and egg fertilization

    2. Embryo development (5-7 days)

    3. Removal of inner cell mass (blastocyst)

    4. Growth in vitro

    5. Conditioning to stimulate differentiation into various cell types (e.g. skin, neural, skeletal muscles).

Ethical Considerations

  • Autologous embryonic stem cell therapy entails cloning human embryos, raising significant ethical and religious dilemmas.

  • Critics argue the morality of creating and destroying human embryos for stem cell harvesting.

Debates on Embryonic Stem Cell Research

  • The importance of embryonic stem cells for therapeutic and research applications leads to ethical dilemmas regarding their source and usage.

Comparison of Adult and Embryonic Stem Cell Therapy

  • Advantages of Adult Stem Cells (Multipotent):

    • Generally simpler procedure

    • No ethical concerns involved

  • Disadvantages of Adult Stem Cells:

    • Limited differentiation capabilities compared to embryonic stem cells

    • Potential absence of needed cell populations or presence of disease in harvested cells

    • Extraction process can be difficult.

  • Advantages of Embryonic Stem Cells (Pluripotent):

    • Can differentiate into any adult cell type required for therapy

    • Less invasive for patients.

  • Disadvantages of Embryonic Stem Cells:

    • More complex procedural requirements

    • Ethical concerns due to need for egg donation for procedures.

Induced Pluripotent Stem Cells (iPSCs)

  • In 2006, Prof. Shinya Yamanaka discovered the ability to reprogram adult fibroblast cells into induced pluripotent stem cells (iPSCs), resembling embryonic stem cells.

    • This involved overexpression of four key regulatory genes:

    • Oct4

    • Sox2

    • Klf4

    • c-Myc

    • In 2012, Yamanaka and Sir John Gurdon were awarded the Nobel Prize in Physiology or Medicine for this groundbreaking work.

Clinical Implications of iPSCs

  • iPSCs demonstrate potential for use in regenerative medicine, with ongoing clinical trials aimed at translating this technology from laboratory settings to actual patient treatment ("From bench to bedside").

Summary of Key Points

  • Pluripotent stem cells can become any cell type, presenting valuable therapeutic opportunities.

  • However, this plasticity may lead to complications such as the development of teratomas, which, while non-malignant, are still potentially hazardous tumors.