17β-estradiol Attenuates Neural Cell Apoptosis Through Inhibition of JNK Phosphorylation in SCI Rats and Excitotoxicity Induced by Glutamate in Vitro

We investigated whether 17β-estradiol (E2) treatment could prevent the apoptosis of neural cells after spinal cord injury (SCI) and cultured cortical cells through inhibition of JNK (c-Jun N-terminal kinase) phosphorylation. SCI-induced rats were randomly divided into three groups: control, E2-treated, and sham-treated. Five rats from each group were sacrificed at 2, 4, 6, 12, or 24 h postinjury. Apoptotic neural cells were assessed using the TUNEL method. JNK phosphorylation was detected with immunohistochemistry. Cultured cortical cells were pretreated with E2 and the specific JNK inhibitor SP600125 and then treated with glutamate-induced cytotoxicity in vitro. Neuron viability was determined with an methyl thiazolyl tetrazolium (MTT) assay, morphology of apoptotic cells was observed with 4',6-diamidino-2-phenylindole (DAPI) staining, and JNK phosphorylation was detected using Western blot analysis. Treatment with E2 reduced neuron apoptosis and inhibited JNK phosphorylation. Moreover, the number of apoptotic cells was correlated with JNK phosphorylation 24 h after the rats suffered the SCI. Pretreatment with E2 significantly maintained neural cell viability, attenuated apoptosis, and inhibited JNK phosphorylation induced by glutamate in vitro. These neuroprotective effects of E2 on neural cells were blocked by the co-administration of SP600125. Our results suggest that neuroprotection from E2 is partially mediated by the inhibition of JNK phosphorylation.