De-differentiation Response of Cultured Astrocytes to Injury Induced by Scratch or Conditioned Culture Medium of Scratch-Insulted Astrocytes

Our previous reports indicated that astrocytes (ASTs) in injured adult rat spinal cord underwent a process of de-differentiation, and may acquire the potential of neural stem cells (NSCs). However, the AST de-differentiation and transitional rejuvenation process following injury is still largely unclear. The aim of the present study was to determine whether injured in vitro ASTs can re-enter the multipotential-like stem cell pool and regain NSC characteristics, and to further understand the mechanism of AST de-differentiation. We used an in vitro scratch-wound model to evoke astrocytic response to mechanical injury. GFAP and nestin double-labeled indirect immunofluorescence were carried out to characterize these scratched cells at various periods. Western-blot analysis was used to determine the changes of GFAP and nestin expression following injury. Furthermore, the rate of proliferation was determined by immunocytochemical detection of BrdU incorporating cells. These scratch-wound ASTs were cultured with stem cells medium to explore their ability to generate neurospheres and examine the self-renewal and multi-potency of such neurospheres. Moreover, scratched AST culture supernatant as conditioned cultured medium (ACM) was used to investigate if some diffusible factors derived from injured ASTs could induce de-differentiation of AST. The results showed: (1) the nestin positivity first appeared in GFAP-positive cells at the edge of the scratch, subsequently, disseminated into un-insulted zone. The expression of nestin in AST was increased with longer culture, while that of GFAP was decreased. Furthermore, these nestin-immunoreactive ASTs could generate neurospheres, which showed self-renewal and could be differentiated into neurons, ASTs and oligodendrocytes. (2) Scratched ASTs culture supernatant can induce astrocytic proliferation and de-differentiation. These results reveal that the in vitro injured ASTs can de-differentiate into nestin-positive stem/precursor cells, the process of de-differentiation may arise from direct injury or some diffusible factors released from injured ASTs.