Age-related loss of progenitor cell function
Loss of progenitor cell function is a significant part of all chronic aging in vivo. For example the proliferation rate and number of divisions of aged epidermal progenitor cells in vivo have been found to decrease by up to 50% (Charruyer et al, JID 129, 2009).
2D Colony Formation
In vitro, progenitor cells provide the characteristic colony formation that is required for extended culture longevity. Changes in function can be quantitatively documented by changes in colony number and size.
In addition, colony formation tests also give important additional insights into progenitor cell function, as the morphology and density of the colonies also give important insights into the exact phenotype of the progenitor cells (stem cells, early-stage transient amplifying cells, late-stage transient amplifying cells).
3D Structure Formation
A powerful visualization of progenitor cell function can also be obtained using 3D cultures. Only fully functional progenitor cells are able to form a thick and well stratified epidermis in vitro. Loss of function following aging challenge is easily visible in subsequently established 3D cultures.