Adhesion and proliferation are enhanced in vitro in Schwann cells from nerve undergoing Wallerian degeneration

Proliferation of Schwann cells during nerve degeneration or regeneration is well documented in vivo. We investigated whether the proliferative response of Schwann cells to injury is retained in vitro. Using 5-month-old male C57BL mice, Schwann cells were isolated from sciatic nerves under 3 experimental conditions: (1) uninjured, (2) after permanent nerve-transection, or (3) after nerve-crush, which permits axonal regeneration. Schwann cells rarely attached to polylysine-coated coverslips when isolated from uninjured or 1 day posttransection/crush nerves. The number of adherent cells increased when Schwann cells were isolated 3 days after nerve-transection or -crush. When cells were isolated from transected nerves, cell adhesion reached a peak 2 weeks after the injury and then declined. Maximal attachment of Schwann cells occurred when the cells were isolated 2-4 weeks after nerve-crush. The percentage of Schwann cells with spreading processes corresponded closely with the number of thymidine-labeled cells at 1 day in vitro. The in vitro capacity of cells to spread and incorporate thymidine reached maximal levels at 5 days posttransection/crush. Capacity of cells to spread and incorporate thymidine subsequently decreased with time following transection. However, a biphasic elevation in cell spreading and thymidine incorporation was observed in Schwann cells isolated from crushed nerves. Maximal growth of Schwann cells in vitro occurred at 1-2 weeks posttransection and at 1-4 weeks postcrush. Adhesion and spreading of Schwann cells were promoted by coating coverslips with laminin or fibronectin. Preincubation of Schwann cells with soluble laminin or fibronectin prevented the initial cell attachment induced by the corresponding protein. Our results suggest that Schwann cells from injured nerves possess binding sites for laminin and fibronectin, which are, in part, responsible for the enhanced adhesion of Schwann cells in vitro. This study provides a new method for preparation of Schwann cells from peripheral nerves of adult mice.