Growth factor expanded-glial restricted precursor cells: support of neurons by derived astrocytes

Growth factor expanded precursor cells may be useful for therapeutic strategies in central nervous system tissue repair and regeneration. The ability to maintain precursor cells in a state of self-renewal allows for the production of large numbers of cells. The use of glial-restricted precursor cells (GRP) is therefore of great interest in the use of derived astrocytes for reparative strategies, such as on synthetic devices for guiding nerve growth. GRP cells could be a critical improvement because of the decrease in neuron supporting properties that differentiated astrocytes display with time in culture. In accordance to what has been observed for differentiated cells, precursor cells may also continue to measure elapsed time despite their state of self-renewal. It has not been addressed whether these internal timing mechanisms results in altered properties of the derived cells. This study investigated the changes in neurite outgrowth and cell adhesive properties of astrocytes derived from growth factor expanded GRP cells over various periods of time in culture. Astrocytes differentiation was induced after GRP cells were expanded in culture for up to seven weeks. Cerebella granule neuron adhesion and neurite outgrowth were measured on monolayers of GRP-derived astrocytes at weekly intervals. Extended self-renewal of GRP cells in culture did not pause the functional changes associated with astrocytes maturation and astrocytes derived from expanded progenitors increased their surface area in correspondence with the length of time culture. In addition to the flattened morphologies, prolonged proliferation also resulted in decreased chondroitin sulfate proteoglycan expression. These changes in astrocytes morphology and proteoglycan expression correlated with decreased neurite out-growth and cell adhesion, and may correspond to the capability of GRP cell to intrinsically time the progress of development despite their state of self-renewal. An important implication of these findings is the insight that growth factor expansion of precursor cells in culture resulted in cells with a progressive degrease in neuron supporting properties.