Objective To investigate the protective role of Sestrin2 overexpression in hypoxia and re-oxygenation injury (H/R) injury of hippocampal neurons and its mechanism in rats.Methods Neurons were enzymatically isolated from hippocampi of newborn Sprague-Dawley rats (less than 24 h old) and culturedinvitro. These neurons were randomly assigned into 4 groups (n=20) using a random number table: control group, H/R group, vector group and Sestrin2 overexpression group. The hippocampal neurons were seeded in 6-well plates at a density of 2×104 cells/mL; neurons in the latter two groups were transfected with lentiviruses containing empty vector andSestrin2overexpressed genes, respectively; the hippocampal neurons in the later three groups were subjected to oxygen-glucose deprivation (OGD) for 6 h followed by restoration of O2 supply for 20 h. The reactive oxygen species (ROS) content was detected by Reactive Species Assay Kit, and the ATP concentration was detected by ATP Assay Kit. Cell apoptosis rates were measured by flow cytometry. The levels of Sestrin2, dynamin-related protein 1 (Drp1), Fis1, and apoptosis-related proteins Bcl-2, Bax and cytochrome C (Cyt C) were measured by Western blotting. The ratio of Bcl-2 to Bax was calculated. The ultrastructure of mitochondria was observed by transmission electron microscopy.Results As compared with control group, H/R group had significantly lower ATP concentration, Bcl-2 protein expression and ratio of Bcl-2 to Bax ([11.15±0.42] nmol/mg proteinvs. [5.30±0.39] nmol/mg protein; 2.20±0.26vs. 0.91±0.02; 6.46± 0.41vs. 1.04±0.05), statistically higher average fluorescence intensity of ROS and cell apoptosis rate (152.41±17.38vs. 1530.00±14.69; 3.77％±0.74％vs. 56.57％±1.35％), and significantly higher protein levels of Sestrin2, Drp1, Fis1, Bax and Cyt C (0.66±0.06vs. 1.11±0.20; 0.48±0.03vs. 1.16±0.07; 1.14± 0.09vs. 2.47±0.09; 0.34±0.03vs. 0.88±0.04; 0.17±0.03vs. 0.30±0.03,P<0.05); what's more, the structure of mitochondria was obviously destroyed in I/R group. As compared with H/R group, Sestrin2 overexpression group had significantly increased ATP concentration, Sestrin2 and Bcl-2 protein expressions and ratio of Bcl-2 to Bax ([8.95±0.27] nmol/mg protein; 2.67±0.07; 1.80±0.19; 3.95±0.28), significantly lower average fluorescence intensity of ROS and cell apoptosis rate (337.27±15.32; 10.33％±2.60％), and statistically lower protein levels of Drp1, Fis1, Bax and Cyt C (0.43±0.02; 1.11±0.08; 0.45± 0.02; 0.17±0.02,P<0.05); the structure of mitochondria was relatively completed in Sestrin2 overexpression group.Conclusion Sestrin2 overexpression can inhibit mitochondrial fission, reduce accumulation of reactive oxygen species, improve mitochondrial energy metabolism and block mitochondria mediated apoptosis pathway, thereby alleviating I/R injury of rat hippocampal neurons.

Objective:To investigate the role of Sestrin2 overexpression in regulating mitochondrial fission and its mechanism in human neuroblastoma SH-SY5Y cell model of glucose and oxygen deprivation/recovery (OGD/R). Methods:(1) SH-SY5Y cells were divided into normal control group, OGD/R group, Vector group, and Sestrin2 overexpression group; Sestrin2 overexpression or empty vector stable cell lines in the Sestrin2 overexpression group and Vector group were constructed by lentivirus infection; cells in the later 3 groups were subjected to oxygen-glucose deprivation (OGD) for 4 h followed by restoration of O 2 supply for 18 h. The cell survival rate was detected by cell counting kit (CCK)-8 assay. The protein levels of Sestrin2, dynamin-related protein 1 (Drp1), mitochondrial fission protein 1 (Fis1), B-cell lymphoma-2 (Bcl-2), Bcl-2-associated X protein (Bax), Kelch-like ECH-related protein 1 (Keap1) in the cytoplasm and nuclear factor E2-related factor (Nrf2) in the nucleus were detected by Western blotting. The mitochondria ultrastructure was observed by transmission electron microscope. The Nrf2 nuclear translocation was detected by immunofluorescence staining. (2) Cell lines with Sestrin2 overexpression were divided into Sestrin2 overexpression group, Brusatol+ Sestrin2 overexpression group, and DMSO+ Sestrin2 overexpression group. Cells in the Brusatol+ Sestrin2 overexpression group were pretreated with normal medium containing Brusatol (Keap1/Nrf2 pathway inhibitor, final concentration: 100 nmol/L) for 4 h before OGD/R; cells in the DMSO+ Sestrin2 group were pretreated with normal medium containing DMSO (final volume fraction: 0.1%) for 4 h before OGD/R. Cells in these groups were then subjected to OGD for 4 h followed by restoration of O 2 supply for 18 h. The protein levels of Drp1, Fis1, Keap1 in the cytoplasm, and Nrf2 in the nucleus were measured by Western blotting. Results:(1) As compared with those in the OGD/R group, cells in the Sestrin2 overexpression group had significantly increased survival rate (61.33%±1.15% vs. 81.00%±3.00%), significantly up-regulated Bcl-2/Bax ratio (0.467±0.006 vs. 0.880±0.010), significantly decreased Drp1, Fis1 and cytoplasmic Keap1 protein levels (1.089±0.033 vs. 0.865±0.014; 0.829±0.009 vs. 0.350±0.007; 0.967±0.017 vs. 0.881±0.024), and significantly up-regulated nuclear Nrf2 protein level (0.627±0.025 vs. 0.957±0.015, P<0.05). The mitochondrial structure in the Sestrin2 overexpression group under electron microscope was more complete than that in the OGD/R group, and obvious nuclear translocation of Nrf2 was noted. (2) As compared with the Sestrin2 overexpression group, Brusatol+ Sestrin2 overexpression group had significantly decreased nuclear Nrf2 protein level (0.920±0.013 vs. 0.627±0.035), and statistically increased Drp1 and Fis1 protein levels (0.994±0.020 vs. 1.084±0.005; 0.728±0.010 vs. 0.906±0.022, P<0.05). Conclusion:Sestrin2 overexpression could suppress mitochondrial fission, reduce cell apoptosis, and attenuate OGD/R injury of SH-SY5Y cells by activating Keap1/Nrf2 pathway via down-regulating cytoplasmic Keap1 protein level and promoting Nrf2 nuclear translocation.