Stem cell plasticity revisited: the continuum marrow model and phenotypic changes mediated by microvesicles.

Area of Science:

• Hematology
• Stem Cell Biology
• Cellular Microenvironment

Background:

• Hematopoietic stem cells (HSCs) exhibit heterogeneity in cell-cycle state and response to microvesicles.
• Studying purified HSCs can be misleading, as they may appear dormant compared to HSCs in whole marrow.
• Stem cell plasticity is a known phenomenon, but its underlying mechanisms require further elucidation.

Purpose of the Study:

• To investigate the role of microvesicles in modulating HSC phenotype.
• To propose a dynamic stem cell population model accounting for individual cell changes and population stability.
• To reconcile discrepancies observed between whole marrow and purified HSC studies.

Main Methods:

• Analysis of HSC phenotype based on cell-cycle state.
• Investigation of microvesicle entry into HSCs.
• Comparison of HSC behavior in whole marrow versus purified populations.
• Development of a stem cell population model.

Main Results:

• HSC phenotype is influenced by both cell-cycle state and microvesicle interactions.
• Tissue-derived microvesicles, especially after injury, affect various cell types.
• Purified HSCs often appear dormant, contrasting with active cycling in whole marrow.
• Microvesicle modulation is proposed as a key driver of observed stem cell plasticity.

Conclusions:

• Stem cell plasticity is likely mediated by microvesicle modulation.
• A dynamic stem cell population model explains stable population phenotypes despite individual cell variability.
• Microenvironmental factors, including microvesicles, are critical regulators of HSC behavior.