6B Modeling Cell Growth and Differentiation Part 2

Tissue Engineering

Overview

  • Focuses on modeling cell growth and differentiation.

  • Importance in regenerative medicine and understanding tissue development.

Stem Cell Differentiation Niche Concept

Key Points

  • A spatial relationship exists between stem cells and their differentiated progeny.

  • The stem cell niche provides cues to retain an undifferentiated state.

  • Physical migration out of the niche is linked with terminal differentiation.

    • Reference: Watt & Hogan, Science, 2000.

Example: Coupling Differentiation with Physical Migration

Epidermal Stem Cells

  • Reside in the basal layer in an undifferentiated state.

  • Require migration into outer layers to mature into epidermal cells.

  • Other examples: intestinal crypts.

    • Reference: Fuchs, J. Cell Biol., 2008.

Concepts in Stem Cell Proliferation

Definitions

  • Stem Cells: Can self-renew and differentiate into at least one unique daughter cell.

  • Transit Amplifying Cells: Intermediate phenotype, limited self-renewal, leading to at least one differentiated cell.

Types of Cell Divisions

Symmetrical and Asymmetrical Divisions

  • Symmetrical Divisions: Progeny are the same phenotype (2 stem cells or 2 differentiated cells).

  • Asymmetrical Divisions: Progeny include one stem cell and one differentiated cell.

Types of Asymmetry

  • Invariant Asymmetry: Always yields 1 stem cell and 1 daughter cell.

  • Population Asymmetry: Progeny phenotype depends on population needs.

Example: Hematopoietic Lineages

Compartmentalization in Cell Differentiation

  • Multiple transit amplifying stages leading to differentiated phenotypes.

  • Each stage is a ‘compartment’ that cells must pass through.

  • A total of 16-18 compartments allows one hematopoietic stem cell (HSC) to produce up to 10^15 mature cells.

Compartment Model for Cell Differentiation

Symmetric Divisions

  • Transition marked by cell division, linking differentiation with replication.

    • Model: dX/dt = µi * Xi (where Xi = compartment number, µi = growth rate).

  • Time to reach progeny number is influenced by residence time in compartments.

    • Equation: τdiff = Σ(1/µi).

Asymmetric Divisions in Compartment Models

Model Details

  • Probability model for cells leaving compartments and self-renewal.

  • Assumes no self-renewal in progenitor compartments:

    • (dXi/dt) = -µi * Xi + f(X0)

Self-Renewal in Progenitor Compartments

Revised Equations

  • Self-renewal affects the growth dynamics of progenitor compartments:

    • (dX/dt) incorporates self-renewal probabilities.

Including Apoptosis in Compartmental Modeling

Model Overview

  • Apoptosis alters the dynamics of cell populations within compartments:

    • Incorporate rates of division (µ), self-renewal (f), and the rate of apoptosis (α).

  • Modified equations account for these interactions.

Example: Modeling Population Dynamics

Applications

  • Development of intercellular networks.

  • Cell fate influenced by physiological needs leading to population asymmetry.

  • Kinetics modeled based on secreted molecules.

    • Reference: Kirouac et al., 2009, Molecular Systems Biology.

Additional Modeling Considerations

Adhesion-Dependent Cells

  • Distinguish between suspended cells and adhesion-dependent models,

  • Proliferation/differentiation functions must account for cell-cell contacts in adhesion-dependent settings.