Lecture 19

BM210: Stem Cells Lecture Notes

Ben Pickard, University of Strathclyde

Learning Outcomes

  • By the end of the lecture, you should:

    • Understand the properties of stem cells.

    • Understand the balance between proliferation and differentiation of stem cells.

    • Appreciate the therapeutic potential of stem cells in ‘regenerative medicine’.

    • Be familiar with their research uses, particularly in mouse transgenics and modeling patient diseases.

What Are Stem Cells?

  • Stem cells are:

    • Immortal, unspecialized cells.

    • They have the potential to choose between:

    • Prolonged self-renewal of identical copies.

    • Differentiation into all tissue types.

The Stem Cell Balancing Act

  • The balance between the processes of:

    • Self-renewal

    • Differentiation

  • Fates of stem cells include:

    • Endoderm

    • Ectoderm

    • Mesoderm

Terminology in Stem Cell Differentiation

  • Terminology used to describe the capability of stem cells includes:

    • Totipotent: Can generate any cell type including the placenta.

    • Pluripotent: Can give rise to almost all cell types.

    • Multipotent: Can give rise to a limited range of cell types.

    • Unipotent: Can only produce one cell type.

Totipotency

  • Defined as the ability to generate all cell types of the adult organism plus the placenta.

  • The initial zygote is totipotent. As development proceeds, cells become committed to specific fates, which restricts their potentials.

Pluripotent Stem Cells

  • These cells theoretically can give rise to every cell type in the animal body.

  • They can proliferate indefinitely.

  • First recognized in teratocarcinomas, which can cause abnormal tumors when injected into immunocompromised mice.

Adult Stem Cells

  • Present in various tissues of adult animals.

  • Important for tissue repair and homeostasis.

  • Examples include:

    • Spermatogonial Stem Cells: Unipotent stem cells producing spermatozoa.

    • Haematopoietic Stem Cells: Multipotent stem cells that give rise to all types of blood cells (erythrocytes and leukocytes).

Types of Mammalian Pluripotent Stem Cell Lines

  • Types include:

    • Embryonic Stem Cells (ES)

    • Embryonic Carcinoma Cells (EC)

    • Embryonic Germ Cells (EG)

    • Epiblast Stem Cells

    • Induced Pluripotent Stem Cells (iPS)

Stages in Early Development

  • Totipotent Stage (Fertilization, day 1):

    • Includes the 2-cell, 4-cell, and Morula stages, culminating in a blastocyst.

  • Pluripotent Stage:

    • Embryo reaches 128-cell stage (blastocyst) allowing for implantation and formation of placenta by day 7.

Cleavage Stage

  • Process of division where the zygote undergoes rapid divisions without significant growth.

  • Results in clusters of cells maintaining size relative to the original zygote.

The Blastocyst Structure

  • A structure consisting of 128 cells composed of:

    • Inner Cell Mass (embryoblast): Develops into embryonic stem cells.

    • Outer Cell Mass (trophoblast): Forms the placenta.

Markers of Pluripotency

  • Signature proteins indicative of pluripotency include:

    • CD31

    • CD34

    • Nanog

    • Oct3/4

    • Sox2

    • CD44

    • Numerous other markers specific to stem cells.

Maintaining Pluripotency in the Laboratory

  • Growth in culture requires ‘feeder layers’ which provide factors that suppress differentiation and promote self-renewal.

  • An identified factor in mouse ES cells is the Leukaemia Inhibitory Factor (LIF).

Differentiation of ES Cells

  • ES cells can be differentiated into various cell types such as:

    • Cardiomyocytes

    • Hematopoietic progenitors

    • Neurons

    • Pancreatic islet cells

    • And many others, offering hope for cell-replacement therapies.

Applications in Transgenic Mouse Models

  • Mouse ES cells can be genetically modified to create models of human genetic disorders by manipulating gene expression.

Regenerative Medicine

  • Application of stem cells for tissue/organs repair from damage due to disease or injury, with examples including:

    • Stroke (brain)

    • Spinal cord injury

    • Liver cirrhosis

    • Chronic kidney disease

    • Cystic fibrosis in the lungs

Challenges in Stem Cell Transplantation

  • Major concerns include:

    • Need for large quantities of stem cells, which is hard to achieve.

    • Risks of differentiation control, potential for teratomas (tumors).

    • Issues of histocompatibility leading to rejection, necessary for anti-rejection treatments.

Storage of Stem Cells

  • Engaging in umbilical blood storage for future therapies is noted as an emerging practice.

Human Stem Cell Therapy Concepts

  • Different methodologies can involve:

    • Direct injection into injured tissues to promote integration and healing.

    • Differentiation in vitro followed by transplantation.

    • Evaluation of organoid structures post-transplantation for functional efficacy.

Role of Stem Cells in Brain Injury Recovery

  • Considers Yavagal's findings where stem cells act as drug factories post-stroke, facilitating repair and acting as neuroprotectors.

Innovations in Tissue Engineering

  • 3D printing technology applied to develop functional organs using bioink for living cell structures.

Clinical Applications of Stem Cell-Derived Organoids

  • Potential applications include:

    • Understanding and modeling disease processes.

    • Testing drugs during the drug development process tailored to patient-specific needs.

Research on Induced Pluripotent Stem Cells (iPS)

  • Development facilitated through somatic cell nuclear transfer and reprogramming of adult cells into pluripotent states.

  • Advantages include ease of creation, but concerns remain over safety and completeness of reprogramming.

Research Contributors

  • Significant contributions from:

    • John Gurdon for somatic cell nuclear transfer.

    • Shinya Yamanaka for induction of pluripotent stem cells.

Conclusion

  1. Stem cell biology is grounded in our knowledge of early mammalian development.

  2. Understanding signals governing self-renewal versus differentiation is critical.

  3. Technical achievement in the development of embryonic stem cells has opened avenues for research and therapies.

  4. Stem cells serve dual roles in direct therapies and research tools for illness investigation.