The implications of the response of human mesenchymal stromal cells in three-dimensional culture to electrical stimulation for tissue regeneration.

Earlier, we demonstrated that local electrical stimulation (ES) improved bone and peripheral nerve regeneration. To determine how ES induces the regeneration of different kinds of tissues, we studied the initial ES-induced regeneration process by investigating the expression of chemokines and growth factors from human mesenchymal stromal cells (hMSCs). In particular, we assessed the responses of hMSCs grown in three-dimensional (3D) culture on a collagen sponge, as 3D culture techniques induced cell behavior that was similar to in vivo cell behavior. We also compared the gene expression patterns of monolayer hMSCs with those of 3D hMSCs under the condition that cells in either culture are exposed to the same type of ES. Biphasic pulses did not affect the proliferation of hMSCs in 3D culture significantly at the magnitude applied in previous animal studies showing improved bone and peripheral nerve regeneration. However, ES enhanced the gene expression of growth factors (BMP-2, IGF-1, and VEGF), chemokines (CXCL2, interleukin (IL)-8), and chemokine receptors (CXCR4 and IL-8RB) from hMSCs grown in 3D culture. A particular difference between the 3D and monolayer cultures was found in the expression of chemokine receptors, CXCR4 and IL-8RB, which is related to the homing capabilities of mesenchymal stromal cells. These genes were expressed by cells in 3D cultures, but were not or expressed at extremely low levels by cells grown in monolayer cultures. ES led to a significant increase in the expression of CXCR4 and IL-8RB in both monolayer and 3D hMSCs, but the increase in the monolayer culture was detected at an extremely low level. These results demonstrate that ES increased the expression of a variety of growth factors and chemokine genes from 3D hMSCs, which may explain increased tissue regeneration in vivo, independent of the tissue type. A culture-dependent expression of the CXCR4 gene suggested that cell response to external stimulus in 3D systems may be more accurately reflected in in vivo findings than in monolayer cultures.