SCD Gene Therapy, iPSCs & Stem Cell Differentiation Notes

CRISPR-Cas9 gene therapy for Sickle-Cell Disease (SCD)

  • CRISPR-Cas9 gene editing is helping to tackle SCD in two ways.

    • Using a guide RNA, the Cas9 enzyme can target and repair the faulty β-globin\beta\text{-globin} gene.

    • Cas9 promotes the production of fetal haemoglobin by breaking a gene that encodes a repressor such as BCL11A.

  • Key components and targets:

    • Cas9 enzyme

    • Guide RNA (to direct Cas9 to the target site)

    • β-globin\beta\text{-globin} gene (beta-globin gene)

    • BCL11A (repressor of HbF)

    • Fetal haemoglobin (HbF)

  • Two mechanisms described:

    • Direct repair of the faulty β-globin\beta\text{-globin} gene to restore normal adult haemoglobin production and red blood cell (RBC) function.

    • Upregulation of HbF by disrupting BCL11A (a repressor), thereby allowing HbF production to resume.

  • Diagrammatic/process details mentioned in the transcript:

    • "Incorrect base" in the ẞ-globin gene can be replaced (e.g., T replaced with A) to yield a corrected base.

    • DNA damage occurs and there may be error-prone repair after Cas9 cleavage.

    • Gene repaired and normal red blood cells produced.

    • Corrected base leads to normal RBCs.

    • Fetal haemoglobin production is no longer blocked, and sickling of red blood cells is prevented.

  • Notation and terminology:

    • ẞ-globin gene is denoted as the β-globin\beta\text{-globin} gene.

    • HbF = fetal haemoglobin; HbF production can compensate for defective adult haemoglobin.

    • BCL11A is a repressor of HbF; disrupting it lifts repression on HbF.

    • The figure captions emphasize a link between DNA repair outcomes and restored RBC function.

  • Significance and implications:

    • Two complementary strategies address SCD: correcting the β-globin gene and enabling HbF to prevent RBC sickling.

    • Conceptual bridge between gene repair and transcriptional regulation of HbF to mitigate disease symptoms.

Medical Applications of iPSCs

  • Process flow for patient-specific tissue repair using induced pluripotent stem cells (iPSCs):

    • 1) Remove skin cells from the patient.

    • 2) Reprogram skin cells so they become induced pluripotent stem (iPS) cells.

    • 3) Treat iPS cells so that they differentiate into a specific cell type.

    • 4) Return cells to the patient, where they can repair damaged tissue.

  • Example context mentioned:

    • Treated iPS-derived cells could repair damaged heart tissue or address other diseases.

  • Source note:

    • 2011 Pearson Education, Inc.

Cultured stem cells: Potency and differentiation

  • Core concept:

    • Cultured stem cells can be subjected to different culture conditions to direct differentiation into various cell types.

  • Embryonic stem cells (ESCs):

    • Derived from an early human embryo at the blastocyst stage (the mammalian equivalent of the blastula).

    • Pluripotent: capable of generating all embryonic cell types.
      -Caption in the diagram: "Cells generating all embryonic cell types".

  • Adult stem cells (ASCs):

    • From bone marrow in this example.

    • Multipotent: capable of generating multiple, but not all, cell types.
      -Caption in the diagram: "Cells generating some cell types".

  • Differentiation outcomes (examples shown):

    • Liver cells

    • Nerve cells

    • Blood cells

  • Key definitions:

    • Pluripotent: ability to give rise to nearly all cell types of the body (all embryonic cell types).

    • Multipotent: ability to give rise to multiple, but limited, cell types.

  • Relationship between culture conditions and lineage outcomes:

    • Different culture conditions steer stem cells toward specific lineages.

  • Visual concepts from the page:

    • ESCs have the potential to generate all embryonic cell types.

    • ASCs have a more restricted differentiation potential.