Maintenance of the self-renewal properties of neural progenitor cells cultured in three-dimensional collagen scaffolds by the REDD1-mTOR signal pathway

Three-dimensional (3-D) culture, compared with traditional two-dimensional (2-D) cell culture, can provide physical signals and 3-D matrix close to the in vivo microenvironments. Here, sponge-like collagen scaffolds were used to assess how 3-D culture would affect the differentiation and self-renewal of neural progenitor cells (NPCs). Cultured in differentiation medium without growth factors, cells in 3-D collagen scaffolds yielded much higher clone formation efficiency and expressed less neuron marker, TUJ1, compared with cells cultured on 2-D plates. mTOR inactivation was identified and showed to supported the self-renewal of NPCs in 3-D culture. At the same time, REDD1 was highly expressed in cells cultured in 3-D conditions, which blocks the activity of mTOR. Moreover, knocking-down REDD1 induced the differentiation of NPCs in 3-D collagen scaffolds. These results indicated that mTOR inactivation by REDD1 mediated the self-renewal regulation of NPCs in 3-D cultures. Thus, 3-D collagen scaffolds maintained self-renewal properties of NPCs, and the inhibitory regulator of mTOR (such as REDD1) played an important role in the regulation of self-renewal and differentiation of NPCs.