·Bilateral sciatic nerves of SD rats were placed in DMEM medium and pretreated with heat stress in vitro at 37 ℃, 42 ℃ and 45 ℃ for 1 h (37 ℃ group, 42 ℃ group and 45 ℃ group, respectively). A fresh nerve group was set up as the control (Con) group. The number of nerves in each group was 36. The expression of HSP70 in sciatic nerve was detected by Western blotting. The previously described nerves were stored in a cryopreservation solution with liquid nitrogen for 4 weeks. The expressions of major histocompatibility complex class Ⅰ (MHC-Ⅰ), MHC-Ⅱ, caspase-3 and caspase-9 were determined by Western blotting. The survival of sciatic nerve cells was detected by flow cytometry. The cryopreserved sciatic nerves were cultured at 37 ℃ with 5% CO₂ for 7 d. The expressions of brain-derived neurotrophic factors (BDNF) and glial cell line-derived neurotrophic factors (GDNF) were detected by Western blotting. The cryopreserved sciatic nerves and the fresh sciatic nerves of SD rats were employed to repair the 10-mm-defect of sciatic nerve in the corresponding Wistar rats in the 37 ℃-Allo group, 42 ℃-Allo group, 45 ℃-Allo group, Con-Allo group and Fresh-Allo group. Meanwhile, an isograft group was also established (Fresh-Iso group). Each group had six Wistar rats. After 20 weeks of transplantation, the compound muscle action potential (CMAP) and nerve conduction velocity (NCV) were detected using electrophysiology. Toluidine blue staining was performed to observe the number of regenerated myelinated nerve fibers. The ultrastructure of the regenerated nerves was visualized through a transmission electron microscope.

·HSP70 expression level was higher in the 42 °C group than that in the 37 °C group, 45 °C group and Con group, respectively (all P<0.05). After 4 weeks of cryopreservation, the expressions of MHC-Ⅰ and MHC-Ⅱ in the 42 ℃ group were not statistically different from those in the 37 ℃ group, 45 ℃ group and Con group, respectively. The expression levels of caspase-3 and caspase-9 in the 42 °C group were lower than those in the 37 °C group , 45 °C group and Con group, respectively, and the survival rate of sciatic nerve cells was increased (all P<0.05). After 7 d of culture, the expressions of BDNF and GDNF in the 42 ℃ group were higher than those in the 37 ℃ group, 45 ℃ group and Con group (all P=0.000), respectively. After 20 weeks of the transplantation, CMAP, NCV, the number of myelinated nerve fibers and myelin sheath thickness in the 42 °C-Allo group were superior to those in the Cont-Allo group and Fresh-Allo group (all P=0.000).

·Highly expressed HSP70 can minimize cryopreservation injury in sciatic nerves of rats, improve nerve cell viability after preservation, and promote nerve regeneration after allotransplantation.