To explore the effect of SS31 peptide on autophagy after spinal cord injury (SCI) and possible mechanism.

Allen method was used to construct the spinal cord injury model in rats. Sprague-Dawley rats were randomly divided into sham surgery group (sham group), SCI group and SS31 peptide group, with 30 rats in each group. The sham group only received laminectomy. The rats in SCI group were sustained SCI and were given no intervention. The rats in SS31 group received SS31 peptide injection after SCI. Scores of Basso Beattie Bresnahan (BBB) motor functions were assessed at 6 h, 1, 3, 7 and 14 d after the injury. The changes in related proteins of Beclin-1 and LC3-II were also detected.

Scores of BBB scale at 6 h and at days 1, 3, 7 and 14 after injury in SCI group (0, 1.7±0.4, 3.5±0.6, 6.1±0.7, 10.1±0.6) and SS31 peptide group (0, 2.5±0.7, 4.1±0.7, 9.3±0.6, 13.4±0.6) were lower than that in sham group (21 at all time points) (P<0.05). Scores of BBB scale at days 7 and 14 after injury in SS31 peptide group (9.3±0.6, 13.4±0.6) was higher than that in SCI group (6.1±0.7, 10.1±0.6) (P<0.05). There was no significant difference upon scores of BBB scale of SS31 peptide group at 6 h and at days 1 and 3 after injury (0, 2.5±0.7, 4.1±0.7), compared with SCI group (0, 1.7±0.4, 3.5±0.6) (P>0.05). Compared with sham group, the expression of Beclin-1 in SCI group and SS31 peptide group was increased, reached a peak at day 3 (1.478±0.030, 1.841±0.051), remained high level at day 7 (1.302±0.049, 1.551±0.032) and showed high expression at day 14 (1.252±0.048, 1.471±0.062) (P<0.05). Compared with sham group, the expression of LC3-II in SCI group and SS31 peptide group also increased, reached a peak at day 3 (0.348±0.028, 0.655±0.052), remained high level at day 7 (0.301±0.053, 0.432±0.052) and also showed high expression at day 14 (0.268±0.049, 0.371±0.052) (P<0.05). The expressions of Beclin-1 and LC3-II in SS31 peptide group at day 3 after injury were 1.841±0.051 and 0.455±0.052, higher than that in SCI group (1.478±0.030, 0.348±0.028) (P<0.05). In SS31 peptide group at 6 h and days 1, 7 and 14 after injury, the expressions of Beclin-1 (0.582±0.028, 0.723±0.049, 1.551±0.032, 1.471±0.062) and LC3-II (0.172±0.031, 0.256±0.051, 0.432±0.052, 0.371±0.052) had no significant difference in comparison with corresponding expressions of Beclin-1 (0.584±0.021, 0.642±0.051, 1.302±0.049, 1.252±0.048) and LC3-II (0.156±0.019, 0.184±0.050, 0.301±0.053, 0.268±0.049) in SCI group (P>0.05).

SS31 peptide can improve motor function and enhance the autophagy of nerve cells after SCI in rats, which may be one of the mechanisms for SS31 peptide treating spinal cord injury.

Spinal cord injuries; Autophagy; Beclin-1