The Effect Of Cyclic Tensile Strain On Schwann Cells Growth And Alteration Of Gene Expression Patterns

Introduction:The aim of this study is to investigate the effects of different cyclic tensile strain (CTS) on the proliferation and the mRNA expression of the Schwann cells divided from the sciatic nerve of newborn rats, and to explain the potential relationship of the mechanics stimulation and the lengthening of peripheral nerve.Methods:1. The model for applying CTS to the SCs in vivo:The silicon rubber was made into a membrane with the thickness of0.1cm. Based on elastic modulus and Poisson’s ratio of the silicone rubber membrane,3D FEM was adopted to simulate the stretch stress-induced deformation of the membrane. MTT method was used to compare the growing situation of cells cultured on silicone membranes and standard plastic plates, respectively. Embedding experiment was taken to found if the material has biological toxicity. Results With the strain of0.5%～20%, the area with effective strain was in the center of the membrane, accounting for90%of the total area. At the same time, there were some differences in biocompatibility between the silicon rubber membrane and the standard plastic plate, but the material itself did not have any toxicity.2. SCs purifying:SCs were obtained from the sciatic nerves of6-day-old Wista neonatal rats with the method of double enzyme digestion. Immunocytochemistry was used to identifed the SCs. The cells were divided into3groups and3different methods (could jet, improved could jet and differential enzyme digestion) were used to purify separately. After that, we calculated the purity by morphology method, and used flow cytometry to examine the proliferation of the cells.3.CTS applying to SCs:SCs were isolated from the sciatic nerve of206-day-old rats, expanded in monolayer, and cyclically strained for6hours, applying0and5%strains at a frequency of0.25Hz with the use of the ElectroForce3200test instrument and the BioDynamic chamber (BOSE). The change of morphology of SCs before and after CTS was compared. The flow cytometry method was used to examine the Schwann cells proliferation and cell cycle distribution in vivo at24hours following the application of CTS. To get more insight into the mechanism of CTS, we performed genome-wide expression profiling of CTS-treated cells using cDNA microarrays (Agilent Rattus norvegicus12×135K Array) that contain26419genes.Results:1. With the strain of0.5%～20%, the area with effective strain was in the center of the membrane, accounting for90%of the total area. At the same time, there were some differences in biocompatibility between the silicon rubber membrane and the standard plastic plate, but the material itself did not have any toxicity.2. For the purification and the activity, there were no statistical significance between the improved could jet method group and the could jet method group (p>0.05), but both of them are higher than the differential enzyme digestion group (p<0.05); furthermore, using the improved could jet method we collected more SCs than the other2groups.3. The proliferative index (PI) and the proportion of cells in the period of DNA synthesis increased with the magnitude value of CTS in the5%group, and decreased in the10%group. Gene expression profile analysis revealed that894genes were up-regulated and1570genes were down-regulated by5%CTS.Discussion and Conclusions:The proliferation of Schwann cells and the amount of CTS were dose-related; an appropriate amount of CTS could act on Schwann cells by a mechanism. promoting their proliferation and changing the gene expressions, to promote axonal regeneration and the extension of nerves. The gene may be relate to the restoration of axon in peripheral nerve.